Experimental comparisons between SAODV and AODV routing protocols There have been various secure routing protocols proposed for mobile ad hoc networks. Most of these protocols are analyzed by two standard techniques: simulation and security analysis. There has been a lack of work related to the performance of secure routing protocols in real network testbed. In this paper, we present quantitative results for the performance comparisons between AODV and SAODV routing protocols by using a small-scale experimental testbed, which consists of 10 laptops within a 250 m by 100 m rugby field. Apart from outdoor testing, we also compare the results with those obtained via simulation and indoor emulation. The workload includes both UDP and TCP traffic. Results show that SAODV is effective in preventing routing message tampering and data dropping attacks. For outdoor experiments, we also estimate the average distance within a communication gray zone under different bit rates. A Mobile Ad-hoc NETwork (MANET) consists of a set of wireless mobile nodes communicating with each other without any centralized control or fixed network infrastructure. Over the past decade, many routing protocols have been proposed in the literature (e.g., [1] - [4] ). Examples include AODV (Ad hoc Ondemand Distance Vector) [1] and DSR (Dynamic Source Routing) [2] protocols. These protocols have been studied extensively. There have been various testbed experiments for ad hoc networks (e.g., DSR [17] , ABR [18] , link-level measurements [19] ). Each one differs by the routing protocol being tested, the number of nodes, and the implementation details.. For the implementation study of the AODV routing protocol, two of them which are RFC-compliant and have passed the interoperability testing include AODV-UU [20] and Kernel-AODV [22] . Others include AODV-UIUC [23] and AODVWindows from UCSB [24] and UoBWinAODV [25] . In [29] , Chin et al. compared AODV and DSDV (Destination-Sequenced Distance Vector) in a testbed with 5 nodes. In [30] , Gray et al. compared the packet delivery ratio between AODV, APRL (Any Path Routing without Loops), ODMRP (On-Demand Multicast Routing Protocol), and STARA (Traffic-dependent Adaptive Routing Algorithm) in both outdoor and indoor environments. The outdoor experiments consisted of 33 nodes moving within an athletic field. Some of the recent work on ad-hoc network testbed included the study of directional antennas [32] as well as multichannel wireless mesh networks [33] [34] .. Most of these ad-hoc routing protocols assume that there is an implicit trust-your-neighbor relationship in which all the neighboring nodes behave properly. However, real MANETs are subject to attacks by malicious users, who try to paralyze the network by manipulating the messages (e.g., dropping all data or control packets, sending incorrect route advertisement messages). This problem is further complicated by the lack of centralized management control, error-prone wireless channels, and the dynamic changes in network topology due to node mobility.. A number of secure ad-hoc routing protocols have been proposed [5] - [11] with the aim of preventing different types of attacks (e.g., message tampering, message dropping, message replay). Most of these protocols are analyzed by using two techniques: simulation and security analysis (e.g., [13] [14] [16] ). The implementation of ARAN [8] is described in [31] . Although there is some work on security in wireless sensor networks, the authors are not able to find other experimental works on secure routing in mobile ad hoc networks in the literature.. Our work is motivated by the following questions: 1) Do user mobility and physical layer's impairments (e.g., multipath fading, interference) affect the effectiveness of secure routing protocols?. 2) Does the extra control overhead and processing incurred by the security mechanisms affect the performance in the upper layer (e.g., TCP, UDP)?. To answer the above questions, we set up an experimental testbed and evaluate the performance between AODV [1] and SAODV (Secure AODV) [5] routing protocols under different environments. The outdoor testbed consists of ten 802.11-enabled laptops within a 250 m by 100 m rugby field. Although this is a small testbed, we did learn some lessons from the outdoor test experiments. In addition, we compare the results with those obtained via simulation and mobility emulation in indoor environments. We chose AODV in our study because it is one of the ad hoc routing protocols standardized within the IETF (Internet Engineering Task Force).. The main contributions of this paper are as follows: (1) By extending the AODV-UU module [20] , we successfully implemented the security features (i.e., digital signature, hash chains) necessary for SAODV in linux environment.. (2) Three sets of results (simulation, indoor emulation, outdoor) under TCP or UDP traffic confirm that SAODV is effective in preventing the control message tampering and data dropping attacks.. (3) Measurements from outdoor experimental testing show that the width of the communication gray zone is about 9 m and 18 m under the transmission rate of 2 Mb/s and 11 Mb/s, respectively.. This paper is organized as follows. Section 2 provides an overview of AODV and SAODV. In Section 3, we describe the settings for the simulation, indoor, and outdoor experiments. Results and discussions are presented in Section 4. Conclusions are given in Section 5. In this paper, we presented the quantitative performance comparisons between AODV and SAODV routing protocols under different environments (simulation, indoor emulation, and outdoor). We successfully implemented SAODV functionalities by modifying AODV-UU module. For outdoor testing, we built an experimental testbed with ten laptops under a 250 m by 100 m rugby field. Results under UDP and TCP traffic showed that SAODV is effective in preventing control message tampering and data dropping attacks. In addition, we also measured the communication gray zone area under different transmission bit rates. Results show that SAODV is effective in preventing control message tampering and data dropping attacks under UDP traffic.. For future work, we plan to compare the performance between other secure routing protocols (e.g., [8] ). The number of nodes in our outdoor testbed will be increased (incrementally) over time. We also plan to study the performance improvement of cross-layer optimization between different layers (e.g., physical, MAC, network) in mobile ad-hoc networks under our outdoor testbed. In this section, we first describe the hardware platform and the approach we used to implement SAODV. We then describe the setup for simulation, indoor emulation, and outdoor experiments.

O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O B O O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


All-or-Nothing Transforms as a countermeasure to differential side-channel analysis Abstract Side-channel attacks on hardware implementations of cryptographic algorithms have recently been the focus of much attention in the research community. Differential power analysis (DPA) has been shown to be particularly effective at retrieving secret information stored within an implementation. The design of DPA-resistant systems that are efficient in terms of speed and area poses a significant challenge. All-or-Nothing Transforms are cryptographic transforms, which are currently employed in numerous applications. We examine All-or-Nothing Encryption systems from the DPA perspective. This paper shows that All-or-Nothing cryptosystems, whilst not preventing sidechannel leakage, do fundamentally inhibit DPA attacks. Furthermore, we develop extensions to the All-or-Nothing protocol to strengthen the DPA resistance of the cryptosystem, Electronic devices naturally leak information about the data they are processing. For example, such leakage can manifest itself in the execution time of a cryptographic algorithm on the device [25] , via its power consumption [26] , or through electromagnetic emanations from the device [16, 38] . Side-channel attacks encompass the class of implementation attacks, which passively monitor these unavoidable physical manifestations, and then manipulate them to compromise the system's integrity. This field has been a popular research topic since its introduction to the cryptographic community in 1996 [25] . Inevitably, along with the development of an array of powerful attacks, there has also been active research to find appropriate, effective, and efficient countermeasures [7, 17, 20, 28, 37, 40, 41, 43] .. All-or-Nothing Transforms (AONTs) are unkeyed probabilistic transforms, with numerous applications in cryptography, that were originally proposed by Rivest [39] , as a means of complicating brute force key searches on block ciphers with short key lengths. Essentially, All-or-Nothing Encryption (AONE) consists of two stages. By applying an AONT to a plaintext message, a 'pseudo-message' is formed. The transform is highly diffusive, such that retrieval of the plaintext depends on all the bits of the pseudo-message. This preprocessing stage is not considered encryption, however, as the AONT does not use a secret key. An All-or-Nothing Encryption mode is formed when the pseudo-message is encrypted using a symmetric or asymmetric cipher.. In this paper, we consider All-or-Nothing cryptosystems from the point of view of side-channel attacks. We demonstrate how AONE systems are inherently resistant to DPA attacks. In addition, we demonstrate how the normal AONE mode can be extended, to further strengthen such encryption systems against DPA. We use hardware implementations as a running example, but our arguments should apply to embedded software implementations with straightforward modifications.. The paper is organized as follows. Sections 2 and 3 provide the necessary background on DPA and AONTs, respectively. We concentrate on the properties of AONTs which make them interesting in the context of DPA in Sect. 4 . In Sect. 5, we propose an extension to the existing AONE protocol, aimed at completing the DPA resistance of AONE systems. Finally, we examine example constructions of the new protocol in Sect. 6 and conclude in Sect. 7. Boolean and affine masking are among the most popular DPA countermeasures in the literature [8, 43] . If masking schemes are applied at the algorithm level, they must be designed specifically for a given encryption algorithm. This extra design effort typically provides first-order DPA security, at the cost of efficiency [36] . Masking at the gate level can be performed independently of the encryption algorithm, but such schemes also typically impact the area and speed of the cryptosystem [19] . In our analysis, we use hardware implementations as a running example, but our arguments should apply to embedded software implementations with straightforward modifications. The Extended All-or-Nothing Encryption protocol provides DPA resistance that is not specific to a particular encryption algorithm. Clearly, extra area and time are required in order to perform the pre-and post-encryption transforms. As an example, consider the OAEP transform, which is based on a hash function. Whilst a hash function cannot achieve the same throughput as a block cipher [21] , we have shown that it is not necessary to encrypt the entire AONT output, because of the All-or-Nothing property, since it is sufficient to encrypt just some of the pseudo-message blocks. Therefore, the impact of using an AONT can be minimized. However, a thorough comparison between AONTs and masking schemes is beyond the scope of this paper.. It has also been shown that even masked implementations are susceptible to higher-order DPA attacks [35] . These higher-order attacks circumvent the masking countermeasure by considering multiple samples within a power trace. These samples correspond to places in the algorithm where the same mask is used with different (but predictable) data. However, all of these higher-order attacks include a hypothesis phase based on known data. All-or-Nothing encryption removes the ability of an attacker to form hypotheses and, therefore, provides protection against higher-order attacks as well as first-order attacks. In Sects. 5.2 and 5.3, we describe how All-or-Nothing encryption schemes can be augmented to bring DPA resistance to implementations of the encryption and decryption operations. This can be regarded as a DPA countermeasure at the protocol level for block ciphers. Below, we compare this new solution with previous related work.. Relation to Masking All-or-Nothing encryption can be viewed as a type of masking countermeasure at the algorithm level. For each message packet m j to be encrypted, the AONT uses a new random 'mask' r j . The AONT expands the randomness in r j and uses it to mask all of the bits of the message m j . Therefore, the masked message m j is unpredictable to a DPA attacker. Similarly, the output of the encryption operation c j is unpredictable to an attacker, since it is concealed using r j−1 .. This DPA countermeasure differs from previously proposed masking schemes in the literature, because mask correction is not applied. Mask correction ensures that a ciphertext c that is transmitted is the same string that would have been generated by encrypting the message using an unprotected implementation of the encryption algorithm. On the other hand, in Extended All-or-Nothing Encryption, the ciphertext c that is transmitted is not the same string that would have been generated by an unprotected implementation of the encryption algorithm. In a sense, the 'mask correction' required to retrieve the message m is applied at the receiver side by the decryption protocol, when the inverse AONT is calculated. All-or-Nothing Transforms (AONTs) were proposed by Rivest [39] in 1997, for the purpose of deterring exhaustive ('brute force') key searches on block ciphers. An All-orNothing Transform uses a random string r to map a plaintext message m (of variable length) to a pseudo-message m . The pseudo-message is subsequently encrypted with an encryption function E and key k; for example, using a symmetric block cipher such as AES [32] .. All-or-Nothing decryption allows the receiver to recover the message m from the transmitted ciphertext c . The receiver applies the decryption function D with key k to recover m . Subsequently, the inverse AONT is applied, to recover r and m. The All-or-Nothing encryption and decryption protocols are illustrated in Fig. 1 .. The resulting cryptosystem has the property that a brute force attacker must decrypt all of the ciphertext blocks when testing each key. Hence, the average execution time of a brute force attack on an AONE mode is increased in proportion to the number of blocks in the ciphertext. In Sects. 4 and 5 of this paper, we propose the use of All-or-Nothing Encryption to protect against DPA attacks. The focus of the discussion is on block cipher-based symmetric-key cryptosystems. However, we note that the technique can also be applied to protect asymmetric encryption schemes against DPA.. An equivalent construction exists for asymmetric ciphers, where this process blinds a message such that an attacker cannot manipulate messages, for example Optimal Asymmetric Encryption Padding (OAEP) [2, 4] .

B I O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Cross-validation and bootstrapping are unreliable in small sample classification The interest in statistical classification for critical applications such as diagnoses of patient samples based on supervised learning is rapidly growing. To gain acceptance in applications where the subsequent decisions have serious consequences, e.g. choice of cancer therapy, any such decision support system must come with a reliable performance estimate. Tailored for small sample problems, cross-validation (CV) and bootstrapping (BTS) have been the most commonly used methods to determine such estimates in virtually all branches of science for the last 20 years. Here, we address the often overlooked fact that the uncertainty in a point estimate obtained with CV and BTS is unknown and quite large for small sample classification problems encountered in biomedical applications and elsewhere. To avoid this fundamental problem of employing CV and BTS, until improved alternatives have been established, we suggest that the final classification performance always should be reported in the form of a Bayesian confidence interval obtained from a simple holdout test or using some other method that yields conservative measures of the uncertainty. Currently there is a rapidly growing interest to use supervised statistical learning techniques (Michell, 1997; Hastie et al., 2001; Webb, 2002) to design classifiers for different forms of decision support in performance sensitive applications found e.g. in biomedicine. Important examples are predictions of tumour subtype and clinical outcome based on mRNA levels in tumour samples measured using modern large-scale microarray technologies (Rosenwald et al., 2002; van't Veer et al., 2002; Yeoh et al., 2002) . In these examples the classification of a new tumour sample is intended to guide the choice of treatment. Misclassification would lead to sub-standard treatment that may have serious consequences for the patient. Therefore, reliable information about the classifier performance is critical for the acceptance of classification guided therapy.. Since the 1980s, cross-validation (CV) (Lachenbrusch and Mickey, 1968; Stone, 1974) and bootstrapping (BTS) (Efron, 1979 (Efron, , 1983 Efron and Tibshirani, 1993) have been the dominating methods for estimation of the unknown performance of a classifier designed for discrimination. CV and BTS are acknowledged for making efficient use of the samples available, a feature which makes them especially suitable for use in situations where only a limited number of examples are available. To the present date, CV and BTS still are the most commonly used methods, even though many theoretical contributions and practical alternatives have been reported (Hand, 1986 (Hand, , 1997 Vapnik, 1995; Schiavo and Hand, 2000) . The importance of reliable performance estimation when using small data sets must not be underestimated. No matter how sophisticated and powerful algorithms for classification are developed and applied, if no reliable performance estimates are obtained, no reliable decisions can be made based on classification results.. There are several ways to interpret the quantity estimated by CV and BTS. In this work, we choose the most common approach which is to consider CV and BTS as estimators of the true error rate e true , i.e. the error rate of a designed classifier when applied to a very large independent test set. In other words, the true error rate is the probability of misclassification when applying the classifier to an unknown future test example, which is the quantity of interest for a decision maker. Here, we ignore the additional complexity that the size of the training sets in CV are slightly smaller than the total number of training examples available, a fact that introduces a bias in the performance estimates. CV and BTS are methods designed to estimate the classifier performance using the samples available via partitioning (CV) or resampling with replacement (BTS). An almost trivial, but often overlooked, fact is that a single point estimate, e est , of a true performance, e true , is not useful unless it is known to be close to e true . For simulated data sets describing the same problem, a good estimator is reflected by a narrow joint distribution (probability density function, pdf) p(e true , e est ) of the estimate and the corresponding true value. For real problems there is only a single data set available, and the true performance is not known. Thus, p(e true , e est ) cannot be estimated in a real application but it is important to understand its properties based on simulated data.. A given combination of classification problem, classification and learning algorithm, performance estimator, and data set size, defines an unknown joint distribution of estimated and true performance, p(e true , e est ). In Fig. 1a one example of such a joint distribution is shown. For a given e est the uncertainty about e true is described by the conditional distribution p(e true je est ) which is illustrated in Fig. 1b . Notably, in a real application we would only have access to a single error rate point estimate e est and we would not know the associated conditional distribution p(e true je est ) of interest. In this work, we address this fact by first illustrating the uncertainty in the CV and BTS estimates for realistic situations and then by suggesting the use of Bayesian confidence intervals or other conservative alternatives to assess and report classification performance. In conclusion, for classification problems we would like to point out that, (1) For a single data set, there is no way of knowing how reliable a particular CV or BTS performance estimate is. (2) Simulations show that CV and BTS estimates are unreliable for sample sizes commonly encountered in real world applications. (3) Calculating a Bayesian confidence interval (or some alternative conservative confidence interval) based on a holdout test still seem to be the only rigorous yet practically useful alternative for assessing and reporting classifier performance.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O B I O O O O O O O O O O O O O O O O O O O O O O


Fingerprint Verification by Fusion of Optical and Capacitive Sensors Abstract. A few works have been presented so far on information fusion for fingerprint verification. None, however, have explicitly investigated the use of multi-sensor fusion, in other words, the integration of the information provided by multiple devices to capture fingerprint images. In this paper, a multi-sensor fingerprint verification system based on the fusion of optical and capacitive sensors is presented. Reported results show that such a multi-sensor system can perform better than traditional fingerprint matchers based on a single sensor. Personal authentication through biometrics is aimed at granting or denying access to restricted resources (e.g., computer, ATM, or a restricted area in a building). The person accessing a certain resource submits her/his identity and biometrics to the automatic verification system. The system matches the given biometric with the one stored in its database associated with the claimed identity. 1 Corresponding author A degree of similarity, named "score", is computed. If the score is higher than a certain acceptance threshold, the person is classified as "genuine" (i.e., the claimed identity is accepted), if not, he/she is classified as an "impostor", and access to the required resource is denied.. Fingerprints are one of the most widely used biometrics in personal authentication. Their widespread use in both civil and forensic applications has been largely due to the fact that fingerprints are very difficult to steal and reproduce, and cannot be left behind. So far, many algorithms (Jain et al., 1997; Jain et al., 2000; Prabhakar and Jain, 2002) have been proposed to match two fingerprints. However, it is very difficult to design a matching algorithm capable of satisfying the stringent requirements of many real applications in terms of verification errors, especially when very low false acceptance (FAR) and false rejection (FRR) rates are required.. Therefore, recent works have argued in favour of information fusion to improve current performances of fingerprint verification systems. So far, fusion of multiple matching algorithms, different fingerprints, and multiple impressions of the same fingerprint have been investigated experimentally (Jain et al., 1999; Prabhakar and Jain, 2002; Marcialis and Roli, 2003a; Marcialis and Roli, 2003b; .. However, to the best of our knowledge, no work has investigated fusion of different imaging sensors. We believe this topic deserves attention, as multi sensor fusion offers some important potentialities for fingerprint verification. First, information fusion theory and the results achieved in other application fields support the hypothesis that by combining information from different physical sensors the performance of fingerprint verification can be improved substantially . Secondly, fusion of different sensors can improve population coverage by reducing enrolment and verification failures . Persons with fingerprints that are poorly captured by one sensor could be enrolled satisfactorily by another. Finally, multi-sensor fusion may discourage fraudulent attempts to deceive personal identity verification systems. Deceiving a multisensor system by submitting fake fingers would require different kinds of fake fingers for each sensor.. On the other hand, increases in system cost and user co-operation in the enrolment and verification phases are the main drawbacks of multi sensor fusion. It should be noted, however, that similar drawbacks are observed in "multi-modal" verification systems combining multiple biometrics (e.g., fingerprint and face) . In the case of fingerprint verification, the ultimate choice will depend on the performance improvements that can be achieved by the fusion of different sensors, whose analysis is precisely the aim of this work, and on the related trade-off with increases in system cost and the required user co-operation.. In this paper, a multi-sensor fingerprint matcher based on optical and capacitive sensors is presented. A specific matching algorithm is used for fingerprint images captured by each sensor.. Verification scores provided by each matcher are fused by score transformation. Reported results show that with this multi-sensor fusion, it is possible to outperform verification performances of the best matcher based on a single sensor. Moreover, analysis of the "complementarity" between optical and capacitive sensors clearly supports the potentialities of their fusion.. Section 2 describes the proposed system in detail. Section 3 reports experimental results. Section 4 draws some preliminary conclusions. Figure 1 shows the architecture of our multi-sensor verification system. The first stage of the system is made up of two fingerprint capture devices, namely, an optical and a capacitive sensor. In the second stage features from the fingerprint images provided by each sensor are processed and extracted. The third stage is made up of the matching algorithm applied separately to the two sets of features. This stage produces two matching scores, which are combined to obtain a "fused" matching score. Finally, an acceptance threshold is applied to make the final decision (the claimed identity is accepted or rejected). Although some information fusion approaches have already been investigated to improve current performances of fingerprint verification systems (Jain et al., 1999; Prabhakar and Jain, 2002; Marcialis and Roli, 2003a; Marcialis and Roli, 2003b; , no previous work has explicitly studied the possibility of fusing the information provided by different imaging sensors. As discussed in the introduction, the integration of multiple fingerprint sensors offers some potential advantages that deserve to be investigated.. In this paper, a multi-sensor fingerprint verification system, based on the fusion of optical and capacitive sensors, has been presented. The reported results show that this multi-sensor system can improve the performances of the best individual sensor (the optical sensor). In particular, improvements in terms of 1%FAR and 1%FRR could justify the increase in system cost and user cooperation required by multi sensor fusion, especially for high security applications. The analysis of sensor complementarity reported in Section 3.4 points out the potentialities of this kind of multisensor fusion for fingerprint verification. Most verification errors made by individual sensors can be corrected by fusion (Table 3) , and there is still room for further improvement (Table 2) To sum up, we believe that this first work on multi-sensor fusion has shown the potentialities of this approach to fingerprint verification. Further theoretical work and experiments with other data bases are obviously necessary to investigate the conditions under which performance improvements provided by this kind of fusion can justify the increase in system cost and user cooperation. The first two rows of Table 1 show the performances of matchers based on optical and capacitive sensors in terms of EER, 1%FAR, and 1%FRR. As can be expected, the optical sensor strongly outperformed the capacitive sensor. For the considered data set, this result is probably due to the fact that the acquisition area of the capacitive sensor is small, and it was not possible to characterise each fingerprint with a sufficient number of minutiae. For fusion purposes, such a large difference in performances among sensors is known to be an issue, as complex trainable fusion rules are usually required to obtain similar or higher performances than those of the best single sensor . Simple fusion rules, such as mean and product, suffer from differences in sensor accuracy, and usually provide worse results than the best single sensor, except for the case of sensors that are so "complementary" that errors in individual sensors can easily be compensated by fusion . It is worth noting that fusion with mean and product rules therefore provided similar or slightly higher performances than those of the optical sensor (Table 1 ). This result suggests that optical and capacitive sensors are strongly complementary, and, remarkably, their complementarity can be exploited by simple fusion rules. In Section 3.4, we will analyse further the complementarity of the two sensors for decision fusion purposes. Improvements in EER over the optical sensor, of around 1%, were obtained with the two trainable fusion rules, Logistic-CE and Logistic-FD (Table 1) . 1%FAR was decreased by 2% over the optical sensor by trainable fusion rules. Relevant improvements were obtained in terms of 1%FRR (more than 20% using the Logistic-FD fusion rule). It should be noted that these improvements in terms of 1%FAR and 1%FRR are particularly important for high security applications, and can justify the increases in cost and user cooperation required by multi sensor fusion. Figure 2 shows the ROC curves of the matcher based on the optical sensor (Optical), the best fixed fusion rule (Mean), and the best trainable fusion rule (Logistic-FD). The ROC curves of combined matchers are always better than those of the matcher based on an optical sensor. In particular, the ROC curve of the combined matcher based on the Logistic-FD fusion rule is significantly lower than those of the other matchers.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Rivals for the crown: Reply to Opthof and Leydesdorff We reply to the criticism of Opthof and Leydesdorff on the way in which our institute applies journal and field normalizations to citation counts. We point out why we believe most of the criticism is unjustified, but we also indicate where we think Opthof and Leydesdorff raise a valid point. Opthof and Leydesdorff (in press; henceforth O&L) criticize the way in which our institute, the Centre for Science and Technology Studies (CWTS) of Leiden University, applies journal and field normalizations to citation counts. The criticism of O&L focuses on two of our citation-based indicators of research performance. These indicators are our so-called crown indicator, which normalizes for differences among fields, and a related indicator that normalizes for differences among journals. To illustrate their criticism, O&L use a research performance evaluation of the Academic Medical Center (AMC) of the University of Amsterdam. In this reply, we will comment on the various issues raised by O&L. We will point out why we believe most of their criticism is unjustified. We will also indicate where we think O&L raise a valid point. An open scientific debate on the advantages and disadvantages of different citation-based indicators of research performance is crucial for bibliometric performance assessment to be conducted in the most proper way. At CWTS, we therefore very much welcome constructive criticism on our approach to research performance assessment. As we have pointed out, the criticism of O&L is inaccurate in various respects, in particular in the way in which it treats the AMC report (AMC, 2008) . In addition, some of the main arguments of O&L are seriously flawed. Rather than providing new insights, these arguments create unnecessary confusion. Having said this, we acknowledge that O&L also raise a valid and important point. The normalization method of the CWTS crown indicator has the unsatisfactory property that it gives more weight to publications from fields with a high expected number of citations than to publications from fields with a low expected number of citations. This point was also made by Lundberg (2007) , and the issue is studied in detail in a paper that we have just finished (Waltman et al., 2010) . At CWTS, we are currently revising our crown indicator in such a way that publications from different fields are weighed equally.. We very much agree with O&L that citation-based performance indicators should be used carefully, especially at lower levels of aggregation, such as at the level of individual researchers or small research groups. At CWTS, we always communicate this in a clear and open manner to our customers. In the case of the research performance evaluation of the AMC, the data provided by CWTS indeed seem to have been interpreted with great care (e.g., AMC, 2008, p. 88) . O&L also argue that -the transparency and traceability of (bibliometric) indicators should be one of the primary objectives‖. This point is fully shared by CWTS. Contrary to what O&L suggest, customers of CWTS can always get access to the raw data based on which CWTS has calculated its performance indicators. We consider this essential for proper bibliometric performance assessment.

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


TRANSIENT RESPONSE OF A DISTRIBUTED RLC INTERCONNECT BASED ON DIRECT POLE Extraction With higher operating frequencies, transmission lines are required to model global onchip interconnects. In this paper, an accurate and efficient solution for the transient response at the far end of a transmission line based on a direct pole extraction of the system is proposed. Closed form expressions of the poles are developed for two special interconnect systems: an RC interconnect and an RLC interconnect with zero driver resistance. By performing a system conversion, the poles of an interconnect system with general circuit parameters are solved. The Newton-Raphson method is used to further improve the accuracy of the poles. Based on these poles, closed form expressions for the step and ramp response are determined. Higher accuracy can be obtained with additional pairs of poles. The computational complexity of the model is proportional to the number of pole pairs. With two pairs of poles, the average error of the 50% delay is 1% as compared with Spectre simulations. With ten pairs of poles, the average error of the 10%-to-90% rise time and the overshoots is 2% and 1.9%, respectively. Frequency dependent effects are also successfully included in the proposed method and excellent match is observed between the proposed model and Spectre simulations. With increasing on-chip signal frequencies, the effect of interconnect inductance has become more significant, particularly in global interconnects. Furthermore, the clock period is continuously decreasing. The timing characteristics of on-chip signals therefore need to be determined and controlled more precisely. Accurate interconnect models, such as RLC transmission lines, and efficient solutions to analyze on-chip interconnects are required in the integrated circuit design process. By extracting the exact poles, an efficient method has been proposed in this paper for determining the transient output response of a distributed RLC interconnect. As demonstrated in the paper, two pairs of poles can provide an accurate delay estimate exhibiting an average error of 1% as compared with Spectre simulations. For high frequency related waveform properties, such as the rise time and overshoot, an average error of less than 2% can be obtained with ten pairs of poles. The computational complexity of the proposed method is proportional to the number of pole pairs. By using a ladder structure, frequency dependent effects can also be included in the method. Excellent agreement is observed between the proposed model and Spectre simulations.

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Analyzing Image Structure by Multidimensional Frequency Modulation Abstract-We develop a mathematical framework for quantifying and understanding multidimensional frequency modulations in digital images. We begin with the widely accepted definition of the instantaneous frequency vector (IF) as the gradient of the phase and define the instantaneous frequency gradient tensor (IFGT) as the tensor of component derivatives of the IF vector. Frequency modulation bounds are derived and interpreted in terms of the eigendecomposition of the IFGT. Using the IFGT, we derive the ordinary differential equations (ODEs) that describe image flowlines. We study the diagonalization of the ODEs of multidimensional frequency modulation on the IFGT eigenvector coordinate system and suggest that separable transforms can be computed along these coordinates. We illustrate these new methods of image pattern analysis on textured and fingerprint images. We envision that this work will find value in applications involving the analysis of image textures that are nonstationary yet exhibit local regularity. Examples of such textures abound in nature.Index Terms-Theory and models, image processing and computer vision, image models. N ONSTATIONARY texture analysis remains an important and unresolved research problem in image analysis. One of the most challenging aspects is the development of numerical measures that can capture and quantify both the texture patterns as well as information-bearing spatial variations in the patterns. An important tool that has been developed for this purpose is the Image Modulation model, also termed the Amplitude-Modulation Frequency-Modulation (AM-FM) image model, which models nonstationary image content using an AM-FM expansion.. By way of example, consider the two images in Fig. 1 . The Fig. 1a shows a piece of a fingerprint, while Fig. 1b shows a woodgrain. Both images are excellent examples of emergent AM-FM patterns.. Nonstationarity in the fingerprint image manifests as variations in both the ridge orientations and in the ridge spacings. In the core region of the fingerprint-the uppermiddle region of Fig. 1a -the ridges are closely packed. Away from the core region, the spacing between the ridges increases. There is also significant variation in the ridge orientation throughout the image.. The nonstationarities present in the woodgrain image of Fig. 1b are significantly more variable than those in the fingerprint. There are clear breaks and discontinuities in the grain. There is considerable variation in the grain spacing, grain orientation, and grain width.. To reveal the underlying image structure, we propose a simple image model, where the textured pattern can be thought of as a harmonic image that is coordinate transformed into the observed texture. We consider the following approximation:. IðxÞ % aðxÞ cos 'ðxÞ:. In (1), an image IðxÞ is approximated by an AM-FM image aðxÞ cos 'ðxÞ. The AM function aðxÞ is assumed to be nonnegative, slowly varying functions which correspond to the component texture envelopes or contrasts. The phase 'ðxÞ of the FM function cos 'ðxÞ captures the pattern variation, which is more intuitively expressed by the instantaneous frequency vector (IF). r'ðxÞ ¼ @' @x 1 ðxÞ; @' @x 2 ðxÞ. where r is the gradient operator. In order to utilize the model (1) to analyze an image IðxÞ, it is first necessary to compute the AM-FM component images. Previous papers have detailed methods for achieving relevant AM-FM demodulation, namely, computation of the amplitude function, the phase function, and/or the instantaneous frequency vector function.. More complicated textured images may also be analyzed through the model in (1), but the relationship of the single dominating component to the underlying image structure will be much more complicated. Furthermore, for more complex images, continuity, and differentiability conditions will need to be enforced for the instantaneous frequency vector estimates.. In this paper, we explore how the spatial variations of the instantaneous frequency vector can be used to characterize the underlying patterns in textured images. We develop a number of new texture feature measures and show how complex patterns reveal themselves through the new measures. Geometric interpretations are given of how the proposed methods can be used to analyze complex patterns. Our primary focus is on developing the underlying theory while exploring some basic applications. We will also review several existing applications of the underlying theory and review how they can benefit from the work that we present here.. For developing the underlying theory, we note that the local variations in the instantaneous frequency vectors form flowlines that are revealed by the ordinary differential equations (ODEs) of the frequency modulation. The collection of image flowlines provides an intuitive global picture of how the underlying image patterns vary continuously through an image. We also show how a significant simplification of the ODEs can be obtained by diagonalizing them along the directions of maximum and minimum FM.. It is important to note that our local flowline approach cannot be extended at a global level. As shown by Penrose in [1, p. 438], for ridge-rich images such as fingerprints and palm-prints, there is no hope of developing global topological models assuming continuous ridge orientations. Similarly, there is no hope of imposing a globally continuous instantaneous frequency vector field on fingerprints since ridge directions are not directed [1] . In addition, in general, there is no hope of defining ridge lines globally, as constant image intensity lines [1, p. 439] . Several difficulties associated with defining ridges for general problems in image processing and computer vision are described in [2] .. Early work on the importance of phase in both 1D and multidimensional signal processing was explored in [3] . In [3] , Oppenheim and Lim derived conditions that allow approximate and exact reconstructions of a signal using only phase information. In [4] , Fleet and Jepson developed phase-based methods for motion estimation. The authors used velocity tuned Gabor filters to show that phase-based methods can provide robust velocity estimates at a betterresolution, with subpixel accuracy.. Significant work has been done on 1D AM-FM signal analysis, particularly for application to speech signal analysis [5] , [6] , [7] , [8] , [9] . Multidimensional AM-FM demodulation methods have been studied in [10] , [11] , [12] , [13] , [14] , [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] . Other related research includes bounds on demodulation accuracy for discrete modulated signals [29] , and Cramer-Rao bounds on AM-FM estimates [30] .. AM-FM models have been used in many image pattern analysis applications, including shape from shading [31] , image interpolation [32] , fingerprint classification [33] , image retrieval in digital libraries [34] , image segmentation [35] , [36] , [37] , and video segmentation [38] .. The paper is organized as follows: Section 2 summarizes methods for 2D AM-FM demodulation. Section 3 provides a framework for understanding and interpreting multidimensional frequency modulation in images in terms of the instantaneous frequency gradient tensor (the Hessian of the phase). Section 4 derives ordinary differential equations (ODEs) that describe image flowlines, which result from solving the ODEs associated with the instantaneous frequency vectors. Expressions are also derived for the phase and the instantaneous frequency vectors. Section 5 presents geometric conditions for diagonalizing the ODEs along the eigenvector directions of the instantaneous frequency gradient tensor. Results on real patterned images are presented in Section 6, and concluding remarks are given in Section 7. We have developed a theory and have shown some applications of multidimensional frequency modulation models for image analysis. We believe that a wide variety of future image and video processing applications can be built on the theory presented here. A number of new local texture measures were proposed for characterizing and understanding local spatial frequency content. At a more global level, the ODEs suggest themselves in the computation of coordinate systems that can be used to transform complex textured patterns to simple harmonics.. There is a wide range of applications, ranging from new image segmentation methods to image and video coding, that can benefit from the use of these new spatial frequency content measures and the ODES of frequency modulation. We have shown promising results on image segmentation (ridge extraction) and on the computation of curvilinear coordinate systems. In future work, it will be quite natural to explore global coordinate systems for developing image and video processing methods over well-suited, curvilinear coordinate systems defined in terms of multidimensional frequency modulation. We are currently investigating the use of spatial frequency content for scalable image and video coding applications, where we use the local spatial frequency content to control the number of nodes in globally defined, image-adaptive mesh systems. (13), it follows immediately that the flowline is given by (14) . For the instantaneous frequency vector along the flowline, we begin by differentiating the instantaneous frequency vector OðxðtÞÞ with respect to time:

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I I B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Can a personal website be useful as an information source to assess individual scientists? The case of European highly cited researchers Abstract The web is not only the main scholarly communication tool but also an important source of additional information about the individual researchers, their scientific and academic activities and their formally and informally published results. The aim of this study is to investigate whether successful scientists use their personal websites to disseminate their work and career details and to know which specific contents are provided on those sites, in order to check if they could be used in research evaluation. The presence of the highly cited researchers working at European institutions were analysed, a group clearly biased towards senior male researchers working in large countries (United Kingdom and Germany). Results show that about two thirds of them have a personal website, specially the scientists from Denmark, Israel and the United Kingdom. The most frequent disciplines in those websites are economics, mathematics, computer sciences and space sciences, which probably reflect the success of open access subject repositories like RepEc, Arxiv or CiteSeerX. Other pieces of information analysed from the websites include personal and contact data, past experience and description of expertise, current activities and lists of the author's scientific papers. Indicators derived from most of these items can be used for developing a portfolio with evaluation purposes, but the overall availability of them in the population analysed is not representative enough by now for achieving that objective. Reasons for that insufficient coverage and suggestions for improvement are discussed. The web has become an outstanding tool for the collection and dissemination of scholarly information (Pitzek 2002; Chen et al. 2009a, b) . Indeed, professors and researchers are increasingly reliant on electronic resources (Herring 2002) and it is practically mandatory for them to maintain some sort of online presence (Hyland 2011) . However, the completeness of this presence, defined as the necessary and essential information for a specific academic topic on the Internet, is unsatisfactory (Chen et al. 2009b) .. The web has also clearly changed the communication system of academics (Barjak 2006) , and as Lawrence (2001b) underlines, the ability to locate relevant research quickly enhances communication and scientific progress. Moreover, the web is one of the popular sources for open access (OA) publishing. According to Kousha (2009) , the ''knowledge of characteristics shaping the OA citation networks can give a better understanding about their potential uses for open access scholarly research''. Open access initiatives (OAI), defending free access to scientific production, are growing stronger. The association of All European Academies has recently described (ALLEA 2012) the optimal panorama for Open Science in the 21st century for Europe, listing the requirements to be fulfilled to achieve this goal.. Although OA academic information contributes to scientific progress and many researchers are making their work available (Swan 2007) , measuring the online impact of web publishing is a highly problematic task (Thelwall and Harries 2004) . Nevertheless, there are several studies that have examined the value of different web sources for scholarly impact assessment (Kousha and Thelwall 2007, 2008; Kousha, Thelwall, and Rezaie 2010; Thelwall, Kousha, Kayvan, et al. 2008 ). The fact that scientific impact is now related to online impact is commonly accepted by scientific journals, universities and departments of all countries; but some doubts exist about the relevance of web links for individual scientists (Barjak, Li and Thelwall 2007) . Moreover, ''the impact of scientists on the web may be influenced by the country in which they work'', and the ''national size of a discipline might imply greater impact in one country than in another'' (Barjak, Li and Thelwall 2007) .. For scientists, one of the ways to provide free access to their scholarly publications is the personal website. In fact, many scientists publish information about research online through personal websites and research group websites (Barjak, Li and Thelwall 2007; Dumont and Frindte 2005) . Antelman (2004) showed that most freely available articles are found on personal websites, not in repositories or OA journals. It would be interesting to analyze whether this trend has continued in recent years or if this have changed. Along these lines, Chen et al. (2009a) report that OA repositories, while an important source of academic information, generally show a low proportion of citation. Barjak (2006) stresses that personal websites are a useful platform for publications already reviewed and publicized, but he expresses doubts about the effectiveness of this type of self-publishing, what type of scientist it appeals to, and how the work posted on the web might be characterized.. The personal website as a reflection of the scientist's activity A personal website can have different social uses (Petric 2006 ) and the reasons behind creating it are different: a need to socialize (Papacharissi 2002b; Zinkhan et al. 1999 ), a desire to control or influence others (Schmitt, Dayanim, and Matthias 2008; Zinkhan et al. 1999) , self-presentation (Döring 2002; Dumont and Frindte 2005; Papacharissi 2002a; Weibel, Wissmath and Groner 2010) , entertainment (Papacharissi 2002b; Weibel, Wissmath and Groner 2010) or identity expression (Döring 2002; Marcus, Machilek, and Schütz 2006; Schmitt, Dayanim, and Matthias 2008) . At any rate, they generally reflect the identity of the author (Hyland 2011; Parks and Archley-Landas 2003; Thoms and Thelwall 2005; Vazire and Gosling 2004) . Flanagin and Metzger (2003) advocate that personal websites be evaluated in terms of perceived credibility, depending on matters such as gender.. Besides these reasons, the scientist' personal website can be created to disseminate the different activities that they carry out, such as teaching, research, etc. Traditionally researchers disseminated their research results mainly through scientific journals and conferences; now, however, there are additional ways of divulgation such as OA journals and the self-archive of a copy of publications in OA repositories, personal websites, departmental websites, departmental digital archives or disciplinary archives (Bailey 2010) . A self-archived copy of their research may be made available, either in its final form or in a previous version (post-print or pre-print). In this regard, some studies have showed that the more widely available a publication is, the more likely it is to be linked or cited (Aguillo, Ortega, and Fernández 2008; Antelman 2004; Kousha and Thelwall 2006; Kurtz 2004; Lawrence 2001a, b; Shin 2003; Swan 2007; Vaughan and Thelwall 2003) , whereas other studies (Davis et al. 2008; Frandsen 2009a, b) do not find this correlation. Swan (2010) provides a compilation of these studies and other ones on the OA citation advantages.. The present study is focused on scientists' personal websites hosted on institutional domains (university, faculty, department, laboratory, hospital, etc.) . There are others channels in addition to institutional personal websites for having a web presence, like a noninstitutional personal website; however, it may be more difficult to find on the Web. Furthermore, the personal website's credibility is perhaps stronger when it is presented within the institutional realm to which it belongs. Other channels for having a web presence are: research group websites, institutional repositories, thematic repositories (ArXiv, SAO/ NASA Astrophysics Data System, RePEc), scholarly databases (Google Scholar, Microsoft Academic Search, Mendeley, CiteULike) or social websites (Facebook, Linkedln), although they mainly provide information related to scholarly publications. An institutional personal website is perhaps a more appropriate means for providing other researcher's information that often is difficult to find, such as contact details, experience and expertise (education, past mobility, former and current positions, awards and honors), research interest, research project, the complete CV, learning materials or conference presentations.. So, a scientist's personal website can be the most complete channel for disseminating his/her work and career as well as for increasing his/her visibility. This leads us to think that one scientist's personal website, so long reflects the different activities undertaken by the researcher (teaching, research, popularization, internationalization, etc.) might be used as a complementary information source to evaluate that scientist. Thus, this study explores whether successful scientists use their personal websites to disseminate their work and career information and whether the contents provided on these sites reflect properly the different activities undertaken by those scientists, with the belief that if that happens, the personal website could be used as a complementary information source for evaluation.. Scientists could be evaluated, at least part of their activities, on the basis of their personal websites; for example, bibliometric methods could be used to evaluate the formal publications, webometric methods for the impact of teaching supporting resources and altmetric methods to evaluate the informal activities and the social impact. However, the assessment would be meaningless if the contents are not exhaustive enough. For this reason this preliminary study focuses on the contents provided on scientists' personal websites and it not intend to address how to evaluate them, that is reserved for a further paper. Today a researcher can have a diverse and rich web presence through various channels such as research group websites, institutional repositories, disciplinary repositories, scholarly databases or social websites; however they mainly provide information related to scholarly publications. A researcher's personal website is an excellent tool to provide, in addition to his/her list of publications, other information that is often difficult to find, such as experience and expertise, research projects performed, teaching commitment (materials for onsite or distance learning), conference presentations, events involvement, etc. So, a scientist's personal website can become one of the most complete channel for disseminating his/her work and career and perhaps the preferred one given a stronger control the authors themselves have on its contents. Keeping this in mind, the present study attempts to know which contents are provided by a recognized group of scientists on their personal websites, exploring the possibility that some of them could be used in research evaluation.. However, we do not analyze in the current paper not what information is important for the evaluation purposes or how website contents should be used in evaluation.. We limited the scope of study to institutional websites, that is, those hosted on the domain of the institution to which the scientists belonged. However, it should be noted that some scientists create their personal websites outside the domain of the institutions to which they belong to, maybe due to these institutions do not have a policy of personal websites or they do not offer the necessary means. To solve this problem, these academic institutions should be aware of the benefits of creating a space within its domain for researchers' personal websites, and so to improve the visibility of both faculty members and the institution per se. Other solutions to try that scientists do not create their personal websites outside the domain of academic institutions might be to develop a friendly CMS environment, a supportive publication policy and some guidelines for creating personal websites, as well as to recognize and to compensate the effort and time required for its maintenance, which as Hess (2002) states, in some cases takes place during researchers' free time.. Other consideration could be to give freedom to researchers with regard to design and contents. We strongly feel that the scientist must be the unique responsible for the contents of his/her personal website, and the institution merely should provide the necessary infrastructure and support, so that researchers were not limited by the institutional webmaster decisions or fancy useless designs. This freedom is important because, as Thoms and Thelwall (2005) indicate, the term ''personal website'' loses its meaning when truly personal content, and therefore identity, is sacrificed.. The study focused on highly cited scientists who work at European institutions. Their identification of them was based on ''ISIHighlyCited'' database created by ISI/Thomson Reuters. The biases of the ISI/Thomson databases are well known and have been addressed in bibliometrics literature since the 1960s. Because these shortcomings also affect the highly cited researcher database, they should be taken into account in any discussion involving citation. The database used has a language-biased coverage toward English speaking countries, especially toward the United States. It also has a disciplinary-biased coverage, and in this case the number of social sciences researchers and the absence of any authors specializing in Humanities. It also should be noted the difficulty to find the correct researcher's personal website due to the problems with author name homonymy and synonymy.. The EHC group was clearly biased towards senior male researchers working in large countries, especially in United Kingdom and Germany. The low presence of women among the EHC researchers seems to support previous studies (see Sect. Introduction) which have shown that female researchers tend to be less cited than men as well as the higher the academic position, the lower the presence of women. However, the increase of women in academia should change this trend over time.. Results showed that 64 % of this population had a personal website. One explanation for this relatively low percentage may be the fact that most researchers were more than 60 years old. Although they are researchers with established careers and a lot of knowledge to share, the reasons why they do not use the web to share that knowledge could be different: (1) they do not know to use these technologies; (2) they do not consider it appropriate, either because they disagree with OAI or because they do not need promote their work, since they have already achieved an international recognition; (3) they do not have enough time to create a personal webpage and/or maintain it updated; (4) they use other web-based ways to disseminate their research, for instance through thematic or institutional repositories, blogs, social networks, etc. In fact, results in this study showed that EHC researchers that belonged to life sciences and health sciences, especially molecular biology and genetics, preferred to use the group research website rather than personal website to divulge their academic and research activities.. Many of the EHC researchers with personal website worked in Denmark, Israel and United Kingdom. Broken down by disciplines, economist scientists were the best represented in personal web space, followed by mathematics, computer science and space sciences researchers, which probably reflects the success of subject OA repositories in these disciplines like ArXiv, RepEc or CiteSeerX. The reason for the high web presence for economists and computer scientists might be the need to increase their visibility due to their concerns about the tendency to use publication databases that do not adequately cover these disciplines, such as Thomson/ISI web of science. This result supports the Barjak's study (Barjak 2006) in which he indicated that economists and computer scientists are more reliant than scientists from other disciplines on the web for obtaining and disseminating information, and that computer scientists depend predominantly on personal websites when searching for information.. In terms of gender, most highly cited men with personal websites worked in hard sciences, while most of the highly cited women were dedicated to life sciences. There were also differences between countries: in United Kingdom the researchers with the highest web presence pertained to health sciences; in Germany, Switzerland and Italy they pertained to hard sciences; and in France and Israel they worked in engineering.. We checked other information topics provided on personal websites and results suggested that those related to personal information was usually comprehensive, past experience and expertise should be improved and current activity was short of the information needed for the evaluation purposes. Although the topics included in most of the websites are appropriated, unfortunately the contents provided are insufficient for a proper evaluation exercise for now. It should be interesting to examine other populations to see if they show the same behavior. Based on ISI/Thomson Reuters data of year 2011, we located 1,498 highly cited researchers working at European institutions, distributed in 22 different countries. These researchers represented 22.4 % of total of the highly cited researchers identified by ISI/ Thomson Reuters.. European highly cited researchers' characteristics As shown in Fig. 2 , the distribution of EHC researchers was skewed, with a few countries (United Kingdom, Germany, France, Switzerland and Netherlands) accounting for most of these researchers. Almost half these scientists were in United Kingdom and Germany, especially in the first one. This can be due to role played by the language in the high citation levels of authors with bias toward English speaking countries. In ''Others'' were included the countries with less than 10 highly cited researchers: Ireland (9), Hungary (7), Russia (7), Greece (5), Poland (2), Romania (2), Cyprus (1) and Portugal (1).. We compared these data with Batty and Basu' studies (Batty 2003a, b; Basu 2006 ), based on data from December 2002 and April 2004 respectively, and we found that the number of EHC researchers had increased proportionally and therefore these researchers were distributed in the same countries. As an exception, Poland and Portugal had not increased the number of their highly cited scientists.. The findings regarding gender were noteworthy: 1,425 of this population (95 %) were males, while just 73 (5 %) were females. However, this pattern did not hold true in all the countries as for example the percentage of women was 14 % in Sweden and 12 % in Italy. This low presence of women among the highly cited scientists was not surprising, since previous studies had shown that female researchers tended to be less cited than men (Aksnes et al. 2011b; Kretschmer et al. 2012; Pudovkin et al. 2012) and that the higher the academic position, the lower the presence of women (Bordons et al. 2003; Mauleón and Bordons 2006; Prpic 2002; Torres-Salinas, Muñoz-Muñoz, and Jiménez-Contreras 2011) . However, a study by Sánchez Peñas and Willett (2006) of five LIS departments showed that although men published significantly more than women, no significant differences existed in the number of citations. A substantial proportion of EHC researchers (117) were assigned to only one discipline, 77 to two disciplines, eight to three disciplines, and one researcher to four disciplines. Table 1 shows the distribution by discipline and country of these researchers. Disciplines are grouped under five larger areas: life sciences, health sciences, hard sciences, engineering and social sciences. The largest group (9 %) within Europe's highly cited researchers was that of pharmacologists, followed by botany & zoology (6.8 %), physics (6.6 %) and microbiology (6.3 %). The very low number of highly cited researchers in the social sciences (economics/ business, psychology/psychiatry and general social sciences) reflects the bias in the coverage of the database used.. Concerning gender, male researchers were concentrated mainly in the health sciences (29 %) and life sciences (26 %), with a lesser presence in hard sciences (23 %) and engineering (17 %), and scarcely found in social sciences (3 %). Female researches were also mainly concentrated in life sciences (37 %) and health sciences (37 %), having a limited presence in hard sciences (15 %) and social sciences (8 %) and scarcely present in engineering (3 %). These data correlated with those of other studies (Aksnes et al. 2011b; Bordons et al. 2003; Mauleón and Bordons 2006; Pudovkin, Kretschmer, and Stegmann 2012) , reporting that women were particularly concentrated in the medical sciences, and hardly appeared in engineering, for example.. The scientists' age was an item collected for just 771 (51 %) researchers of the population analysed, for reasons explained in the Methods section. We found that 4 % of these researchers were between 40 and 49 years in age; 25 % between 50 and 59; 42 % between 60 and 69; and 29 % over 70 years old. So, almost three quarters of the EHC researchers were over 60. This might suggest that most of them are people who have an established research career. However, two studies about Norwegian researchers (Aksnes et al. 2011a, b) found that the over 60 cohort were significantly less cited than their younger colleagues.

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O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O B I I O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Disjunction property and complexity of substructural logics We systematically identify a large class of substructural logics that satisfy the disjunction property (DP), and show that every consistent substructural logic with the DP is PSPACE-hard. Our results are obtained by using algebraic techniques. PSPACE-completeness for many of these logics is furthermore established by proof theoretic arguments. Logics that may lack some of the structural rules (exchange, weakening and contraction) are generally called substructural logics [22, 10] . They include various nonclassical logics (such as relevance, superintuitionistic and fuzzy logics [8, 4, 14] ), and arise from various algebraic structures (such as ordered groups, relation algebras, and ideal lattices of rings). Remarkably, some logics popular in computer science can also be thought of as extensions of substructural logics (such as linear logic [12] , the logic of bunched implications [20] , and separation logic [23] ). Since substructural logics are abundant in various fields, it is important to establish basic logical properties and complexity results not just for each logic independently, but also for a wide class of logics uniformly. In fact, such a systematic study was undertaken in 90's, and the field has been rapidly growing since then. See [10] for the current state of the art.. In the spirit of the latter systematic approach, this paper aims to establish a uniform complexity result on the decision problem for a wide class of substructural logics. It is well known that there are several substructural logics which are PSPACE-complete, for instance intuitionistic logic [25] and the multiplicative, additive fragment of linear logic MALL [19] . The same holds for full Lambek calculus FL (the multiplicative-additive fragment of intuitionistic noncommutative linear logic) [17] and some of its extensions. See [18, 15] for surveys.. Such results often rely on proof theoretic methods, and presuppose that the logic under consideration possesses a good sequent calculus for which the cut elimination theorem holds. In contrast, we consider arbitrary extensions of the base logic FL by axioms and inference rules. Instead of relying on the existence of cut-free sequent calculi, we extensively use algebraic techniques, as is common in the study of substructural logics (cf. [8, 10] ).. More specifically, we focus on the disjunction property (DP), which provides a sufficient condition for PSPACE-hardness. We define the class of -monoidal inference rules, which basically consists of rules in the language of lattice conjunction, disjunction and monoid multiplication. We also define the class of M 2 axioms, which naturally correspond to the -monoidal inference rules. These classes are sufficiently large and contain many rules and axioms that often appear in the literature (see Figure 4 in Section 3.3). We then prove:. (i) Every extension of FL by -monoidal inference rules and M 2 axioms satisfies the DP (Section 3).. (ii) Every consistent extension of FL with the DP is PSPACE-hard (Section 4).. These two results together establish that a wide range of substructural logics are PSPACEhard.. In proving (i), we develop a way of constructing suitable well-connected algebras, which substantially generalizes the construction of [24] . Our algebraic methodology turns out to be far more applicable than the usual proof theoretic one based on cut-free proof analysis.. The statement (ii) is a generalization of the same result for superintuitionistic logics [4, Theorem 18.30] . To prove this, we modify the coding of quantified Boolean formulas by [15] along the idea of [26] . In passing, we also note that every consistent substructural logic is coNP-hard.. Finally in Section 5, we turn to the problem of membership in PSPACE. By a standard proof theoretic argument, we show that substructural logics defined by analytic and shrinking structural rules are PSPACE-complete. We have shown that a wide class of substructural logics above FL satisfies the disjunction property, and thus the decision problems for them are PSPACE-hard. Our methodology is mainly algebraic, in contrast to the existing works that are largely proof theoretic. We hope that our algebraic method will bring new insight into the complexity issue of substructural logics.. We have also shown that some of the PSPACE-hard logics are indeed PSPACE-complete. While the current argument is a standard proof theoretic one, it would be interesting to find an algebraic method that works for membership in PSPACE.. Concerning future research directions, recall that the DP is not a necessary condition for PSPACE-hardness, a counterexample being LQ, intuitionistic logic with weak excluded middle. Hence it is natural to look for a weaker form of the DP which is sufficient for PSPACE-hardness and captures a wider class of substructural logics, including LQ.. Refining our result in this direction is of particular interest because of the apparent dichotomy phenomenon. By the result of this paper, we now know that a great number of substructural logics are PSPACE-hard. We also know that many others are coNP-complete (recall that all consistent substructural logics are at least coNP-hard). This class includes classical logic and most of major many-valued logics such as (finite-or infinite-valued) Gödel logics, Lukasiewicz logics, product logic and Hájek's basic logic [1] ; see [4] for some coNP-complete superintuitionistic logics. On the other hand, we do not know any substructural logic that is neither coNP-complete nor PSPACE-hard.. 1 Hence a natural question arises:. Dichotomy problem: Is there a substructural logic which is neither coNP-complete nor PSPACE-hard?. This is a fundamentally important problem, which is reminiscent of the famous dichotomy conjecture in constraint satisfaction problems [9] . For this problem, even a partial solution would be very interesting.

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