Variations and Commonalities in Processes of Collaboration: The Need for Multi-Site Workplace Studies Abstract. Workplace studies have made a major contribution to the field of CSCW, drawing attention to subtle practices that enable effective collaboration. However, workplace studies typically focus on a single setting, making it difficult to assess the generalisability of the findings. Through a multi-site workplace study, we explore a specific collaborative process, that of the handover which occurs when a patient is transferred from one hospital or ward to another. The study demonstrates that the term 'handover' captures a variety of collaborative practices that vary in both their form and content, reflecting aspects of the setting in which they occur. Multi-site workplace studies are shown to be essential for CSCW, not only generating findings that have relevance beyond a single setting but also focusing attention on aspects of work practice that may otherwise go unnoticed. Workplace studies are concerned with the practical accomplishment of workplace activities and the ways in which tools and technologies feature in work and interaction within organisational environments . While workplace studies have emerged from within various disciplines, such as sociology, anthropology and cognitive science, predominantly they are naturalistic, ethnographic studies . Similarly, while a number of analytic orientations, such as Distributed Cognition and Activity Theory, have informed such studies, ethnomethodology has arguably had the greatest influence on workplace studies.. One of the initial motivations behind the use of workplace studies within Computer Supported Cooperative Work (CSCW) came from recognition that rejection of systems by their intended users typically results from lack of attention to the social context of work practice (Forsythe 1999) . Thus, workplace studies have typically focused on a single setting, gaining an understanding of the detail of work practice as an essential precursor to design. Despite this acceptance within CSCW of the importance of such studies for design, the exact relationship between workplace studies and design has been much debated (Plowman et al. 1995; Schmidt 2000; Dourish 2006) .. In this paper, we contribute to these debates by considering what multi-site workplace studies can offer to the CSCW community and how they might inform design, using a study of clinical handover as an example. Such studies would mean a move away from focusing on a single setting, in order to understand the commonalities and variations across a range of settings, thus increasing the generalisability of the findings. In the following section, we explore the generalisability of workplace studies, reviewing arguments about generalisability within CSCW and considering workplace studies that have taken a multi-site approach. We then introduce the topic of patient transfer, the collaborative process that our study was concerned with. We then describe the study we conducted and, for each setting, we describe the process of handover for the transfer of patients into the setting. In the Discussion section, we then reflect on how the handovers vary across the settings and the aspects of the setting that this variation could be related to, as well as considering the ways in which the handover process is consistent across the settings. We conclude by discussing the implications of this research for both technological support of handover and the study of collaborative work. To conclude, this paper has presented the findings from a study of patient transfer conducted across a range of clinical settings. Through this analysis we have demonstrated the potential for multi-site workplace studies to contribute to CSCW, enabling designers to anticipate the needs of a particular setting by highlighting features of a setting that impact the collaborative process of interest. Following each period of observation, fieldnotes were written up and audio recordings transcribed. These were entered in to Atlas.ti. Initially, data from each setting was analysed individually, so as to allow themes that were unique to a particular setting to emerge. All handovers were carefully read and annotated by hand, asking questions of the data and paying attention to what was occurring and in what order, what was being accomplished and what strategies were used to achieve this on the basis that handover is a practical accomplishment (Emerson et al. 1995) .. From this, a series of codes were developed, capturing different aspects of the handovers, such as who was involved, the location, the content and the ordering of the content, the nature of the communication, and the artefacts that were used. These codes were then applied to the data within Atlas.ti. Indexing the data was treated as a way of engaging with the data on a line by line basis, using the constant comparative method to enable similarities and differences within settings to become apparent (Glaser and Strauss 1967) . From this, for each setting, we produced a rich description of the different processes of handover that were observed. Our analysis can be described as ethnomethodologically-informed (Crabtree et al. 2000) , maintaining a commitment to the preservation of the detail of work practices within each setting.. Having undertaken this initial analysis, we returned to the data, again using the constant comparative method but this time identifying similarities and differences between settings.. The analysis presented in this paper focuses specifically on patient transfers. Elsewhere, we have reported findings from our study relating to shift handover (Randell et al. 2008; Randell et al. 2010 ). We observed transfers of patients both into and out of the four settings but in the following analysis we focus on those handovers that were received by staff when a patient was transferred into the setting. This focus is due to the fact that we have more information on such handovers; being based within the setting where the handover was being received, we were able to gather data on the subsequent patient care as well as the perspective of those who would provide that subsequent patient care on the handover process. Patients principally come to the ward from the emergency assessment unit (EAU), although on occasion a patient may be moved to the ward from another ward, be admitted directly from an outpatient clinic, or be transferred from a different hospital. The majority of patients on this ward are elderly and many require palliative care. The accounts of handover presented above demonstrate that the term 'patient transfer' describes a range of practices that vary in their form and content and therefore how misleading analysis of only one setting could be. While all the handovers are concerned with the transfer of responsibility for, and information about, a patient and involve both written and verbal communication, we see variation in the types of information transferred, the amount of information, how that information is organised (a standard structure versus the chronological presentation of information), who participates and where the participants are located, access to and use of artefacts, and the nature of the communication such as the extent to which questions are asked. How the handover takes place appears to be influenced by a range of factors, such as the workload, staffing levels, the roles and responsibilities of those participating in the handover, the patient history and state, the artefacts that are available at the time of the verbal handover report, and the goals of those participating in the handover.. One could argue that, rather than undertaking multi-site workplace studies, what is needed is to look for commonalities across studies undertaken separately (Schmidt et al. 2007 ). However, it is not only that multi-site workplace studies can enable us to identify commonalities, but seeing the differences across settings focuses our attention on aspects of work practice that we otherwise may not notice. For example, it was in comparing handovers across settings that our attention was drawn to the differing goals across the settings of those participating in the handovers. In the EAU, the A&E nurses are concerned with keeping the flow of patients moving, while the EAU nurses appear as gatekeepers, often questioning the need for the patient to be admitted to hospital. Where those collaborating have not done so before or do not collaborate frequently, particular goals can become important which are not visible in other contexts, so that in handovers from the DGH to the paediatric acute retrieval service, members of the retrieval team use the handover to build a relationship with the staff at the DGH.. Below we consider a particular aspect of the settings, that of the level of heterogeneity between those giving and receiving the handover, and the implications that this has for the handover process. We then make suggestions for the conduct of multi-site workplace studies and how they can feed into design.

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


A new class of sequential circuits with combinational test generation complexity AbstractÐWe introduce a new class of sequential circuits with combinational test generation complexity which we call internally balanced structures. It is shown that sequential circuits can be classified by their structure as follows: {sequential circuits of acyclic structure} ' {sequential circuits of internally balanced structure} ' {sequential circuits of balanced structure} and that internally balanced structures allow test generation with combinational test generation complexity. On the other hand, if finite state machines (FSMs) are classified by their realization possibility, it can be shown that {FSMs which can be realized as a sequential circuit of acyclic structure} = {FSMs which can be realized as a sequential circuit of internally balanced structure} ' {FSMs which can be realized as a sequential circuit of balanced structure}. Hence, any FSM realizable with acyclic structure can be also realized with internally balanced structure which allows test generation with combinational test generation complexity. In addition, we discuss the definition of test generation possibility with combinational test generation complexity and introduce a new definition which covers the previous narrow definition. Finally, we study applications to design for testability based on the partial scan and to test generation time reduction for sequential circuits in general, using characteristics of the internally balanced structures. The experimental results shows the effectiveness of this approach. T EST generation for a sequential circuit is, in general, a difficult and intractable task which may be unsolvable within a reasonable time for a large-scale circuit [1] , [2] . Methods of solution include design for testability, like the scan design method, in which some or all of the flip-flops are replaced with scan flip-flops so that they are chained into a shift register during test mode and, hence, they can be directly controlled and observed [1] , [2] . When all the flipflops of a circuit are replaced with scan flip-flops (full scan design), all the scan flip-flops are treated as equivalents to external I/O terminals and, hence, the test generation can be performed for the remaining circuit (called the ªkernel circuitº) with the exclusion of all flip-flops, i.e., for the combinational part of the sequential circuit. Therefore, the full scan design method can reduce the test generation problem for a sequential circuit to the problem of test generation for a combinational circuit.. If the test generation problem for a sequential circuit can be reduced to the problem of test generation for a combinational circuit where all the flip-flops of the sequential circuit can be replaced by wires, then such a sequential circuit is called a sequential circuit allowing test generation with combinational test generation complexity or, simply, a sequential circuit with combinational test generation complexity, and this transformation is called combinational transformation (C-transformation). For example, balanced structures [3] are one class of circuit structures with this feature. A sequential circuit is a balanced structure if, for any pair of primary input and primary output, all paths between them have the same number of flip-flops. In [4] , a subclass of balanced structure, called strongly balanced structures, is introduced.. In this paper, we shall first introduce an extended combinational transformation (C*-transformation) and a wider class of sequential circuits with combinational test generation complexity which we call internally balanced structures. It is shown that sequential circuits can be classified by their structure as follows: {sequential circuits of acyclic structure} ' {sequential circuits of internally balanced structure} ' {sequential circuits of balanced structure}. Sequential circuits of acyclic structure do not necessarily allow test generation with combinational test generation complexity. However, it can be shown that sequential circuits of internally balanced structure allow test generation with combinational test generation complexity as well as balanced structure. On the other hand, if finite state machines (FSMs) are classified by their realization possibility, it can be shown that {FSMs which can be realized as a sequential circuit of acyclic structure} = {FSMs which can be realized as a sequential circuit of internally balanced structure} ' {FSMs which can be realized as a sequential circuit of balanced structure}. From this result, we can see that any FSM realizable with acyclic structure can be also realized with internally balanced structure which is capable of test generation with combinational test generation complexity. In addition, in this paper, we shall discuss the definition of test generation possibility with combinational test generation complexity and introduce a new definition which covers the narrow definition by [3] . Finally, we shall study applications to design for testability based on the partial scan and to test generation time reduction for sequential circuits in general, using characteristics of the internally balanced structures. The experimental results shows the effectiveness of this approach. We have defined classes for sequential circuits allowing test generation with combinational test generation complexity and have identified their characteristics. The acyclic structures do not exhibit these characteristics. We introduced a new class of internally balanced structures as a class that exhibits these characteristics. The FSMs that can be realized with acyclic structures can be also realized with internally balanced structures. Further, we introduced a new definition of test generation possibility with combinational test generation complexity. In this paper, we additionally studied applications to design for testability based on the partial scan and to test generation time reduction for sequential circuits in general, using characteristics of the internally balanced structures. The experimental results showed the effectiveness of this approach.

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HoloTrap: Interactive hologram design for multiple dynamic optical trapping This work presents an application that generates just-in-time holograms to be displayed in a holographic optical tweezers setup, a technique which allows the manipulation of particles in the range from micrometers to nanometers. The software is written in Java, and implements the random binary masks method to generate the holograms. It allows customization of the parameters adapted to the experimental setup and the used hologram display, taking into account the specific characteristics of the device, such as the modulation or the presence of aberrations. The performance of the software is evaluated, achieving 12 fps at full display resolution when run on a Pentium IV HT, 3.2 GHz computer, which allows real time interaction with the sample. Experimental results of the manipulation of microspheres using this program are provided. In this paper we describe an application to generate multiple dynamic holographic optical tweezers interactively. This program allows a user to calculate holograms to be displayed in an optical tweezers setup, resulting in trap patterns reconfigurable in real time. Moreover, the application leaves experimental setup factors as parameters to make the program completely customizable. In addition to this, considers the possibility of inclusion of aberration correction of the wavefront.. Optical tweezers are generated by strongly focusing a laser beam, thus creating an optical gradient trap for dielectric particles from micrometric samples to nanometric scale [1] due to the transfer of light momentum to the trapped particle. This technique has many applications in the manipulation of biological samples [2] because of its harmlessness and the possibility of measurement of the forces involved in molecular and biological processes, which are in the same range than the forces applied by optical tweezers (about pN).. Holography allows the design of the light wavefront by spatially modifying the amplitude and phase of the beam [3] . Knowing how light propagates in the setup, the relationship between the plane where the hologram is introduced and elsewhere is determined. In this way, one can calculate the hologram that reconstructs a desired light distribution in another plane. The use of digital holography in optical tweezers represents a lot of flexibility in the design of trap patterns. This technique has resulted in the introduction of large arrays of optical traps and three-dimensional control [4] , [5] . Moreover, the shape of the beam can be modified to generate non Gaussian beams such as vortex, which transfer angular momentum to the trapped particle [6] or non-diffracting beams [7] .. The kind of devices used to display digital holograms is Spatial Light Modulators (SLMs), which allow the modification of its complex transmittance/ reflectance dynamically by computer control. The relationship between the sample plane and the hologram plane is an inverse Fourier transform, so the hologram is in general complex valued. These devices are unable to modulate the whole complex plane, and in general one is constrained to certain values due to the SLM modulation constraints that we should have to be taken into account while the hologram generation process. Algorithms have to be designed to find an optimal solution constraining the hologram values to the discrete complex values available because of the modulator. These algorithms are based in iterative methods [8] , [9] or in extensive search procedures [10] . These two approaches are time-consuming and do not allow real-time interaction with the sample given that they cannot be calculated and displayed just-in-time. We have recently proposed a method to calculate holograms for the generation of optical tweezers based on the random mask encoding method for multiplexing phase-only filters [11] . This method is, to our knowledge, the fastest with control of the trap in 3D, because it is not iterative and the number of operations implied is lower than the required using other direct methods, such as the gratings and lenses one [12] . Other advantage of this algorithm is that it does not produces ghosts traps or replicas reported in other methods [13] .. Other methods such as the generalized phase contrast approach [14] or time sharing of the laser beam allow real-time interaction with the sample because they do not require of hologram codification, but are constrained to 2 dimensional trap patterns and do not permit the generation of non Gaussian beams. Some authors use the phase and gratings method to calculate the desired trap pattern. The method could be the bottleneck in the response performance of the programs, because it includes computation of trigonometric functions, as explained in section 3. For example, another application implements this method achieving 3-5 fps [15] . Alternatively it has been proposed to use GPU programming procedures to improve video-rate [16] . This kind of programming is rather uncommon, but it may provide a solution to implement an iterative algorithm in real time. Other applications, such as BioRyx R [17] , are intended to be used with their commercial setup and do not allow customization, as the software we present.. We present the software developed to interact with the trapped particles in real time. This application calculates and displays the holograms that generate the trap pattern as a reaction of the user commands. First we will make an outline of the experimental setup (section 2) emphasizing the aspects that have to be taken into account in the software design and the algorithm that is implemented in the application (section 3). This application, written in Java T M 2 Platform Standard Edition 5.0, will be detailed in section 4. The sample plane can be visualized in another monitor, using the camera software. We will show how we incorporated our camera image into the application, although as the camera is controlled with its own drivers and we cannot distribute this second version. Nevertheless, the distributed version is fully operative. We will explain how to control your own camera in section 4.3. The performance of the software and an example of the program's use will be shown in section 5. We have presented a software to calculate and display holograms in real time to generate multiple dynamic optical tweezers. The application allows the user to generate, delete or modify traps interactively. The random binary masks method has been implemented, because this method is the fastest to generate multiple trap patterns. This software takes into account different parameters given by the setup and modulator used, and so it is not limited to a single configuration. The different options have been detailed, including the adaptation to the modulation and the correction of possible aberrations. The scale factor and the hologram size can be also modified. Some strategies to accelerate the calculation and displaying time of the hologram have been explained. A second version of the program takes advantage of the property libraries of the camera used in order to embed the image provided by the camera and the program. We explain how to the camera image can be incorporated to improve the software. The performance of the software is comparable to other applications using hardware-oriented programming languages. We have shown an example of manipulation of microspheres using this program. As future work we would like to control a IICAM compliant FireWire camera with the software to make it fully compatible.

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 B I 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 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 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 B I 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 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 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 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


Distributed Beamforming in Wireless Multiuser Relay-Interference Networks With Quantized Feedback We study fixed data rate communication schemes for wireless relay-interference networks with any number of transmitters, relays, and receivers. The transmitters and the relays have individual short-term power constraints. We analyze both amplifyand-forward (AF) and decode-and-forward (DF) relaying strategies with a two channel use quantized network beamforming protocol. We design the quantizer of the channel state information to minimize the probability that at least one receiver incorrectly decodes its desired symbol(s). Correspondingly, we introduce a generalized diversity measure that encapsulates the conventional one as the first-order diversity. Additionally, it incorporates the secondorder diversity, which is concerned with the transmitter power dependent logarithmic terms that appear in the error rate expression. We first show that for AF relays, the maximal achievable diversity in the presence of interference is strictly less than the transmit diversity bound in terms of the second-order diversity. We then prove that it is possible to achieve the transmit diversity bound using DF relays as if there is no interference and as if coding over an arbitrary number of channel uses is allowed. Relay selection provides the best possible diversity gain for both relaying strategies. Finally, we show that all the aforementioned diversity gains can be achieved using distributed decision making with asymptotically zero feedback rate per receiver. Such a performance is made possible by a special distributed quantizer design method we have called localization.Index Terms-Beamforming, distributed vector quantization, diversity gain, interference, wireless relay network. One way of achieving high diversity gains through cooperation is network (relay) beamforming [14] - [22] , in which the relays adaptively adjust their transmit powers and phases according to the channel information that they have. Indeed, for networks with a single-user networks with and no interference, network beamforming using amplify-and-forward (AF) relays has shown to achieve the full diversity gain, [14] , [18] . On the other hand, the optimal beamforming policy requires one or two CSI-dependent real numbers to be made available at the relays. For single-user networks, the only node in the network that can obtain the entire CSI is the receiver. Therefore, the real numbers should be broadcasted from the receiver to the relays as feedback information. In practice, the feedback links have a limited bandwidth which results in a limited number of bits that can be utilized for feedback. One way of capturing such a limited feedback is to model it as a source coding problem (see e.g., [23] , [24] and the references therein). Then, one is concerned with the question of how to design the quantizers and the corresponding quantized beamforming codebooks to maximize the reliability of the system. Such a formulation proves to be very effective: It has been shown in [8] , [25] that for AF networks with that it is possible to obtain both maximal diversity, as well as high array gain with only a few feedback bits from the receiver.. A special case of quantized feedback for cooperative networks is the relay selection scheme [8] , [26] - [38] . In this scheme, only one relay is allowed to transmit given a constant fading block. This requires bits of feedback per channel state. It has been analytically shown in [8] that, for single-user AF networks, the relay selection scheme provides full diversity. For single-user networks with DF relays, [39] proves that relay selection achieves full diversity as well. Selection cooperation with DF relays in an interference-free multi-source network with orthogonal channel allocation has been discussed in [40] .. There are several other works in the context of cooperative networking with limited feedback apart from the ones we have already mentioned. An iterative phase adjustment scheme for distributed beamforming has been proposed in [41] . In [42] , the authors study the optimal outage exponents for DF relay channels with quantized CSI. Cooperative relaying with partial rate and/or power control have been studied in [6] , [43] . The idea of Grassmannian beamforming [44] , which was originally proposed for point-to-point multiple-input multiple-output (MIMO) channels, has been extended to MIMO relay networks in [45] .. A comprehensive overview of the vast literature on MIMO systems with feedback can be found in [23] , [24] . In particular, beamforming [44] , [46] - [50] and precoded space-time coding [51] - [58] schemes that incorporate limited feedback have been extensively studied. Diversity-multiplexing tradeoffs in MIMO channels with quantized CSI have been determined in [59] , [60] . Other works that study the interplay between rate and outage in fading channels with partial CSI include [61]- [64] . An interfer-ence cancellation scheme for a two-user MIMO multiple access channel with quantized feedback has been introduced in [65] .. Quantized feedback schemes have also been studied for non-cooperative multiuser interference networks with several receivers. In [66] , the author considers zero-forcing beamforming with finite rate feedback in multiple-input multiple-output (MIMO) broadcast channels. Interference alignment for multiuser interference networks with limited feedback has been studied in [67] . Unlike what we shall study in this work, where we seek to optimize the reliability of the system in terms of the diversity gain, the goal of the above two papers was to optimize the data transmission rate in terms of the multiplexing gain. A common conclusion that we can infer from both studies is that, in order to achieve the same multiplexing gain as a system with perfect CSI, the feedback rate per receiver should be increased at least logarithmically with the transmitter power; any constant feedback rate results in a complete loss of multiplexing gain. This is unlike point-to-point systems where feedback is not even necessary to achieve the maximal multiplexing gain [66] , and a few feedback bits is usually sufficient to transmit with rates that are close to the one with perfect CSI [48] . The feedback requirements of interference networks thus appear to be considerably higher than that of interference-free networks. A relevant question in this context is to determine the feedback requirements if instead we would like to ensure maximal reliability in the presence of interference.

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


Constraint preserving boundary conditions for the Ideal Newtonian MHD equations We study and develop constraint preserving boundary conditions for the Newtonian magnetohydrodynamic equations and analyze the behavior of the numerical solution upon considering different possible options. Magnetic fields play an important role in the behavior of plasmas and are thought mediate important effects like dynamos in the core of planets and the formation of jets in active galactic nuclei and gamma ray bursts; induce a variety of magnetic instabilities; realize solar flares, etc. (see e.g. [1, 2] ). Understanding the role of magnetic fields in these and other phenomena have spurred through the years many efforts to obtain solutions of the magnetohydrodynamic equations. The non-linear nature of these equations limits the understanding that can be gained in a particular problem via analytical techniques. This implies that solutions for complex systems must be obtained by numerical means and a suitable numerical implementation must be constructed for this purpose. Such implementation must be able to evolve the solution to the future of some initial configuration and guarantee its quality. A delicate, subsidiary quantity, can be monitored in part to estimate this. This quantity is the "monopole constraint" ∂ i B i which must be zero at the analytical level for a consistent solution. This quantity is not a part of the main variables, rather it is a derived quantity which should be satisfied by a true physical solution. In practice, unless a numerical implementation of the MHD equations is carefully designed this constraint can be severely violated. This, in turn, signals (and is sometimes the cause) of a degrading numerical solution. For these reasons, several approaches have been investigated and developed for guaranteeing a controlled behavior of this quantity. One such approach is known as the constraint transport technique [3, 4] which adopts a particular algorithm that staggers the variables appropriately to ensure the satisfaction of the constraint at round-off level within Finite Difference and Finite Elements techniques. This approach has been quite successful in a number of applications across different disciplines and particularly relevant in astrophysics applications [5, 6, 7, 8, 9, 10, 11, 12] . However, by design it imposes limits on the algorithmic options available to an implementation. This fact can be at odds, or introduce complications, with applications where adaptive mesh refinement is required and/or advanced numerical techniques (that exploit useful properties of the equations) are adopted. An alternative approach, which controls the constraint at truncation-error level maintains complete freedom in the numerical techniques to be adopted. This approach, referred to as divergence cleaning puts the burden to control the constraint not on the algorithm to be employed but rather on the system of equations to be solved itself [13, 14] . This is achieved by considering an additional variable suitably coupled to the system through another equation so that, through the evolution, the constraint behavior is kept under control. While this method has, to date, received less attention than the constraint transport one, successful applications in diverse scenarios have already illustrated its usefulness (e.g. [14, 15, 4, 16, 17] ).. Regardless of the technique employed, boundary conditions can play a significant role and may spoil all efforts towards a correct implementation in the absence of boundaries. Clearly, even when a stable option is adopted, it need not be consistent with the goal of preserving the constraint (be it at round-off or truncation levels) and so carefully designed boundary conditions must be formulated. Commonly employed options include straightforward outflowtype conditions -which do not enforce the constraint-or "absorbing" boundary conditions which aim to reduce the influence of spurious effects induced at the boundary in the numerical solution [18] .. In the present work we concentrate on formulating constraint preserving boundary conditions for the Newtonian ideal MHD equations (for systems with and without divergence cleaning). Such a task is intimately related to the hyperbolic properties of the equations and so we re-analyze the system of equations and discuss alternatives for controlling the constraints through the divergence cleaning technique.. We therefore organize our presentation along the following lines. In section II we analyze the system of equations and the formulation of boundary conditions beginning with a simplified model from which we draw the strategy to apply in the complete MHD system. Section III presents a series of tests that highlight the benefits gained by our construction. We conclude in section IV with some final comments. We have investigated the numerical solution to the (ideal) Newtonian magnetohydrodynamics equations and developed boundary conditions which at the continuum level are constraint preserving and so would not introduce further violations in the computational domain. At the numerical level these conditions do introduce some truncation-error level violations which converge away with resolution. These boundary conditions developed are consistent with maximally dissipative ones and so the discrete energy of the system remains bounded. We also examined the constraint's behavior when enlarging the system so as to couple an extra field. The addition of such field, together with a suitable modification of the equations induces a non-zero speed in the propagation of the constraint and allows for driving its value to zero. We have studied, in particular, two of the many equivalent systems. One which is fully conservative -which is only weakly hyperbolic without the addition of the extra field which renders it symmetric hyperbolic-and a Galilean invariant one which is symmetric hyperbolic -even without adding the extra field-but is not expressible in conservative form.. In order to examine the solution's behavior we implemented the equations in Cartesian coordinates and with a spatial discretization that preserves the initial constraint error. This allows us to separate bulk from boundary effects and observe that the main violations do indeed occur at boundaries. To examine the boundary condition effects on the evolution we adopt three types of boundary conditions: -The most direct one, and crudest, sets to zero all right hand sides in a buffer boundary region.. This might lead to inconsistencies for one might be prescribing conditions to outgoing modes. This condition is essentially equivalent the most commonly employed one of flux-copying near boundary points. -The second one is the "no-incoming" boundary condition where one projects out all incoming modes in the evolution equations leaving the rest (tangential and outgoing modes) intact. The implementation of this condition is slightly delicate as modes can change directions over time, and so may turn from being incoming to being outgoing and vice-versa.. -The third condition preserves the constraint in the sense that is deduced by setting to zero the incoming mode related to the constraint propagation. This condition is a modification to the previous one where now instead of projecting out all incoming modes, one incoming mode is fixed so that the incoming constraint mode is zero as a result. Not surprisingly the first option displays the worst behavior for the constraint as not only nothing is done to minimize the constraint violations introduced through the boundaries but further inconsistencies in the solution are induced there. As a result, in the best case the constraint mode bounces back from the boundary into the integration region. The second option performed substantially better displaying a gain of an order of magnitude in constraint preservation. This is a result of the boundary condition allowing for one of the φ modescarrying constraint violations-to leave the integration region. With the third alternative an additional order of magnitude (at least) is gained with respect to the non-incoming condition. This condition not only allows for constraint violations to leave the computational domain but does not introduce significant violations at the boundary.. Thus we see that appropriately handling the boundary conditions the problem of constraint behavior can be significantly controlled. It should be mentioned that we still do not have a mathematically rigorous proof that the constraint preserving boundary conditions is well posed. However, in simpler systems -like the toy model we discussed at the beginning of the paper-a proof could be devised at least for the case where the eigenvalues do not change sign. Further work in this direction is needed to put the analysis and results obtained in stronger grounds.

O O B I 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 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 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 B I 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 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 B 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 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 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 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 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


An extension of vose's markov chain model for genetic algorithms The paper presents an extension of Vose's Markov chain model for genetic algorithm (GA). The model contains not only standard genetic operators such as mutation and crossover but also two new operators -translation to the left/right and permutation of bits. The presented model can be used for finding the transition matrices and for the investigation of asymptotic properties by using Markov transition functions. The ergodity of the Markov chain describing the GA with new operators, translation to the left/right and permutation, is shown. The model is specialized for a case of Bentley's GA. For this GA the ergodity of the Markov chains and the asymptotic correctness in the probabilistic sense are shown. To model other aspects of the Bentley's GA (effective fitness, total transmission probability) the microscopic Exact Poli GP Schema Theory for Subtree-Swapping Crossover is used. There are many works based on Schema Theory [3] explaining how the GAs work. The other approach to the formalization of GA is based on the microscopic Markov chain models, such as Vose's model of SGA [5] . The Markov chain model enables the investigation of asymptotic properties and transition matrices. The only one known Markov chain model for more complicated evolutionary algorithm -GP with homologous crossover, without mutation -is presented in [4] by Poli. The paper presents an extension of Vose's Markov chain model for SGA to GA with new operators -translation to the left/right and permutation of bits. The model is specialized for the case of Bentley's GA [1] which is used to generate 3D-solids designs in a CAD system. Next, the microscopic Exact Poli GP Schema Theory for SubtreeSwapping Crossovers is applied to the Bentley's GA to calculate the effective fitness and the total transmission probability for a fixed-size-and-shape schema under hierarchical crossover. The paper has presented the extension of Vose's Markov chain model for GA with mutation, crossover, translation to the left/right, and permutation of bits. The ergodity of the Markov chain describing the GA has been shown. The presented theory has been applied to the Bentley's GA. The ergodity of the Markov chain and the asymptotic correctness in the probabilistic sense for the Bentley's GA has been shown. Also the microscopic Exact Poli GP Schema Theory for Subtree-Swapping Crossovers has been applied to the Bentley's GA to calculate the effective fitness and the total transmission probability for a fixed-size-and-shape schema under hierarchical crossover.

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


Predicting linear B-cell epitopes using amino acid anchoring pair composition Background: Accurate identification of linear B-cell epitopes plays an important role in peptide vaccine designs, immunodiagnosis, and antibody productions. Although several prediction methods have been reported, unsatisfied accuracy has limited the broad usages in linear B-cell epitope prediction. Therefore, developing a reliable model with significant improvement on prediction accuracy is highly desirable. Results: In this study, we developed a novel model for prediction of linear B-cell epitopes, APCpred, which was derived from the combination of amino acid anchoring pair composition (APC) and Support Vector Machine (SVM) methods. Systematic comparisons with the existing prediction models demonstrated that APCpred method significantly improved the prediction accuracy both in fivefold cross-validation of training datasets and in independent blind datasets. In the fivefold cross-validation test with Chen872 dataset at window size of 20, APCpred achieved AUC of 0.809 and accuracy of 72.94%, which was much more accurate than the existing models, e.g., Bayesb, Chen's AAP methods and the enhanced combination method of AAP with five AP scales. For the fivefold cross-validation test with ABC16 dataset, APCpred achieved an improved AUC of 0.794 and A CC of 73.00% at window size of 16, and attained an AUC of 0.748 and A CC of 67.96% on Blind387 dataset after being trained with ABC16 dataset. Trained with Lbtope_Confirm dataset, APCpred achieved an increased Acc of 55.09% on FBC934 dataset. Within sequence window sizes from 12 to 20, APCpred final model on homology-reduced dataset achieved an optimal AUC of 0.748 and A CC of 68.43% in fivefold cross-validation at the window size of 20. Conclusion: APCpred model demonstrated a significant improvement in predicting linear B-cell epitopes using the features of amino acid anchoring pair composition (APC). Based on our study, a webserver has been developed for on-line prediction of linear B-cell epitopes, which is a free access at: http:/ccb.bmi.ac.cn/APCpred/.Background B-cell epitope is a part of an antigen recognized region that is bound to immunoglobulin molecules to stimulate B-cell response [1] . Based on structural characteristics, Bcell epitopes can be categorized into two types: linear (continuous) epitopes and conformational (discontinuous) epitopes. Linear epitopes are made up of short contiguous amino acids, whereas, conformational epitopes are composed of amino acids that are not contiguous in primary sequence but are brought together by the folded BioData Mining B-cell linear epitopes are short sequences on the antigenic proteins, which contain structure characters to exposure themselves to antibodies, and easily bind to the antibodies, even if they are disengaged from the source proteins. In order to have antigenic functions, epitope sequences must be different from the random sequences generated from Swissprot database. We believe that B-cell linear epitopes sequences must fold into a stable structure to show the sequences' information for being bound to antibodies. We propose that the amino acid anchoring pairs play important roles in stabilizing folding of epitopes structure by producing the force for folding in three-dimensional spaces. Thus, in this paper, we studied the roles of amino acid pairs in prediction of B-cell linear epitopes. Since it has been reported that 86.7% epitopes' length was at most 20 amino acids in Bcipep database [12] , during dealing with the large variability in the length of the epitopes, we chose to fix length of epitopes with lengths ranging from 12 to 20 peptides in the method of El-Manzalawy [12] and Saha [10] , instead of windows of five or seven amino acids at the center of a linear epitope as Parker [5] and Karplus [6] did. The existing B-cell linearepitope finding methods are far less than optimal or may only find part of epitope sequences, which may indicate that the prediction methods based on composition of The four classifiers were trained using ABC16 dataset and evaluated using the third dataset of Blind287. "*" denotes the information was obtained on online prediction of ABCpred with the third dataset though an automatic program script. The bold denotes the largest A CC value of the prediction. Both models were trained on Lbtope_Confirm dataset. The bold denotes the largest Acc value of the prediction.

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


Stability and fairness of explicit congestion control with small buffers T.D.Voice.99@cantab.netRate control protocols that utilise explicit feedback from routers are able to achieve fast convergence to an equilibrium which approximates processor-sharing on a single bottleneck link, and hence such protocols allow short flows to complete quickly. For a network, however, processor-sharing is not uniquely defined but corresponds with a choice of fairness criteria, and proportional fairness has a reasonable claim to be the network generalization of processor-sharing.In this paper, we develop a variant of RCP (rate control protocol) that achieves α-fairness when buffers are small, including proportional fairness as the case α = 1. At the level of theoretical abstraction treated, our model incorporates a general network topology, and heterogeneous propagation delays. For our variant of the RCP algorithm, we establish a simple decentralized sufficient condition for local stability.An outstanding question for explicit congestion control is whether the presence of feedback based on queue size is helpful or not, given the presence of feedback based on rate mismatch. We show that, for the variant of RCP considered here, feedback based on queue size may cause the queue to be less accurately controlled.A further outstanding question for explicit congestion control is the scale of the step-change in rate that is necessary at a resource to accommodate a new flow. We show that, for the variant of RCP considered here, this can be estimated from the aggregate flow through the resource, without knowledge of individual flow rates. There is currently considerable interest in explicit congestion control protocols, which use a field in each packet to convey relatively precise information on congestion from resources to endpoints. These protocols contrast with TCP and its various enhancements, where endpoints implicitly estimate congestion from noisy information, essentially the single bit of feedback provided by a dropped or marked packet. Examples of explicit congestion control protocols include XCP [10] and RCP [6] .. We shall discuss in detail the rate control protocol RCP, which uses explicit feedback from routers to allow fast convergence to an equilibrium where a bottleneck link is shared equally over flows [6] . RCP approximates the processorsharing queueing discipline when there is a single bottleneck link, and hence allows short flows to complete quickly [4, 5] . For the processor-sharing discipline at a single bottleneck link, the mean time to transfer a file is proportional to the size of the file, and is insensitive to the distribution of file sizes [2, 5] .. For a network with multiple constrained resources there exist several possible generalizations of the processor-sharing discipline. A conveniently parameterized family, that of the α-fair rate allocations, was introduced in [15] . The parameter α lies in the range (0, ∞), and the cases α → 0, α = 1 and α → ∞ correspond respectively to an allocation which achieves maximum throughput, is proportionally fair or is max-min fair [15, 21] .. Max-min is the fairness criterion commonly envisaged in connection with RCP, but it is not the only possibility. Proportional fairness, in particular, has a claim to be the natural network generalization of processor-sharing, with a growing literature showing that it has exact or approximate insensitivity properties [14, 20] and important efficiency and robustness properties [3, 12] .. Buffer sizing is an important issue for RCP, as for other protocols. If links are run close to capacity, then buffers need to be large, so that new flows can be given a high starting rate. But if links are run with some spare capacity, then this may be sufficient to cope with new flows, and allow buffers to be small.. In previous work the local stability of RCP has been studied for a single resource with a large buffer [1] and for a network with small buffers under the max-min criterion [25] . In this paper we model a variant of RCP which achieves α-fairness when buffers are small, and we establish, in Section 3, a simple decentralized sufficient condition for the local stability of this algorithm. In Sections 4 and 5 we show that, with small buffers, feedback based on queue size has a major impact on equilibrium utilization. In Section 6 we study whether the presence of feedback based on queue size is helpful or not, given the presence of feedback based on rate mismatch: we show that it may cause the queue to be less accurately controlled.. Finally, under weighted proportional fairness, we explore the scale of the step-change in rate necessary at a resource to accommodate a new flow. We show that it can be estimated from the aggregate flow through the resource, and without knowledge of individual flow rates. In Section 7 we illustrate the effectiveness of a step-change algorithm, which we introduce, under various traffic scenarios. The parameter a is the same as in the original model (1) of RCP. But the parameter bj is a rescaled version of β,. and its units are the reciprocal of the units in which the queue size is measured. The parameter a controls the speed of convergence at each resource, while the parameter bj controls the utilization of resource j at the equilibrium point. From (10-11) we can deduce that the utilization of resource j is. and hence that. For example, if σj = 1, corresponding to Poisson arrivals of packets of constant size, then a value of bj = 0.022 produces a utilization of 90%. Figure 2 plots the function (15), under the label 'Gaussian analysis' and shows how utilization decreases as bj increases.. It is important to note that setting the parameter bj to control utilization produces a very different scaling for β from that of [1] , as a consequence of the presence of the bandwidth-delay product CjT j in the relation (14) . In particular, if the bandwidth-delay product Cj T j is large, then the values we consider for β are much larger than those considered in [1] .. If the parameters bj are all set to zero, and the algorithm uses as Cj not the actual capacity of resource j, but instead a target, or virtual, capacity of say 90% of the actual capacity, then this too will achieve an equilibrium utilization of 90%. In this case the equivalent sufficient condition for local stability is. (cf. [23] , [11] Section 6.2, [24] ). An outstanding question, to be considered more fully in Section 6, is whether it is advantageous to set the parameters bj to be positive, or equivalently whether to include a queueing term in the definition of the protocol. We note here that although the presence of a queueing term is associated with a smaller choice for the parameter a -note the factor two difference between conditions (13) and (16) -nevertheless, close to the equilibrium the local responsiveness is comparable, since the queueing term contributes roughly the same feedback as the term measuring rate mismatch. Below equilibrium, the b = 0 case is more responsive (up to a factor of 2); above equilibrium, the b > 0 case is more responsive (how much more responsive depends on the buffer size). We remark that, in the taxonomy of [11] , we are considering fair dual algorithms rather than delay-based dual algorithms [13, 16] , and this is important for the form of the sufficient conditions (13) and (16).

O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 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 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 O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Video segmentation by MAP labeling of watershed segments AbstractÐThis paper addresses the problem of spatio-temporal segmentation of video sequences. An initial intensity segmentation method (watershed segmentation) provides a number of initial segments which are subsequently labeled, with a known number of labels, according to motion information. The label field is modeled as a Markov Random Field where the statistical spatial and temporal interactions are expressed on the basis of the initial watershed segments. The labeling criterion is the maximization of the conditional a posteriori probability of the label field given the motion hypotheses, the estimate of the label field of the previous frame, and the image intensities. For the optimization, an iterative motion estimation-labeling algorithm is proposed and experimental results are presented. ONE of the key issues in the design of many vision systems is their ability to decompose image sequences into the ªobjectsº that are depicted in them. Motion information is one of the main elements that are used for segmenting video sequences. However, extracting and coupling motion information with the segmentation process is by no means a trivial task. For the estimation of motion, spatial constraints need to be imposed in a form of a support region where the motion is assumed either to be smooth or to follow a parametric model. In general, if the region of support is arbitrarily chosen then the motion estimate will be deteriorated either because the single motion assumption within the region is violated or because the texture pattern is too low to constrain enough the estimation. Furthermore, in the motion-based segmentation framework issues like the occlusions and the temporal coherency of the segmentation mask need to be addressed.. In this paper, we present an approach in which spatial and temporal constraints are incorporated into a single framework to allow the joint estimation of the segmentation field and of the motion information. The method operates in two levels ( Fig. 1) . At the lower level (LEVEL 1 in Fig. 1 ), a segmentation algorithm operating on the current frame's intensities provides a set of segments with relatively small intensity variation. At the next level, (LEVEL 2 in Fig.1 ) these segments are grouped into regions that move with the same motion parameters by assigning an ªobjectº label to each segment. We use the well-known notion of Markov Random Fields (MRF) in order to express spatial and temporal constraints at the level of the ªintensityº segments. The labeling criterion is the maximization of the conditional a posteriori probability (MAP) of the label field given the motion hypotheses, the label field of the previous frame, and the image intensities. For the optimization procedure, we propose a method which minimizes the corresponding objective function in an iterative way with respect to the motion parameters and the label field. A three frame approach is adopted in order to deal with occlusions.. In comparison to other works in the area of motion-based segmentation, our method is mostly related to two categories. To the first category belong methods which simultaneously estimate the motion information and its region of support. Depending on if the label field is explicitly defined, temporal and spatial constraints are imposed either on motion [1] , [2] , [3] , [4] and/or on the label field itself [5] , [6] , [7] . Our work can be regarded as an extension of methods of this category that define cliques at pixel level in the Markovian framework and jointly estimate the motion and the label field. We exploit the ability of such approaches to incorporate the spatial and temporal constraints in the optimization procedure. However, by defining cliques on segment level, we provide tighter constraints for the labeling and reduce the dimensionality of the problem. The initial intensity segmentation groups together pixels in which the low degree of texture implies inadequate information about their temporal behavior. These segments are more reliable entities than pixels used as primary elements for the labeling problem. The relation of our approach with existing pixel-based methods will become more apparent once the modeling and the optimization procedure are described. It can be shown [8] that in the degenerate case where the segments that result from the initial segmentation contain a single pixel, our method reduces to an approach that falls in this category.. To the second category belong methods that combine an initial intensity segmentation with motion information. From the prism of our method, we distinguish between the following four general directions: To the first one belong the top-down approaches [9] , [10] . To the second one, methods in which a region merging process is driven by motion-based distance measures [11] , [12] , [13] , [14] , [15] . To the third direction belong methods that utilize an initial intensity segmentation in order to incorporate spatial constraints in the Expectation Maximization framework [16] , [17] . Finally, to the last one belong methods that combine the MRF modeling with an initial segmentation [18] , [19] , [20] . From the above mentioned approaches, the work of Fablet et al. [9] , and Gelgon and Bouthemy [20] , [19] is the most related to our proposal. However, their way of combining the motion information with the labeling is quite different. The dominant motion estimation/outlier detection paradigm which is adopted in [9] has the shortcomings of the hierarchical approaches. Such top-down approaches are faced with the problem of estimating the dominant motion in the presence of multiple independent motion patterns and, furthermore, they impose an artificial hierarchy in determining the motion characteristics of the objects which may lead in situations where outlier segments do not belong to any object [14] . In [20] , [19] , motion is estimated independently per segment. Estimating motion parameters per segment requires sufficient local intensity structure which often implies that the size of segment should be rather large. In search for sufficient texture, the initial intensity segmentation method might violate significant borders. In our approach, where a region-based motion estimation is employed, it is not crucial if some of the segments do not provide sufficient constraints. The ensemble of the constraints in the whole region is what determines the accuracy of the motion estimation. Furthermore, in both [20] and [19] , the temporal constraints are introduced only in the initialization phase for the prediction of the initial label field. In comparison, in our approach, the temporal constraints are incorporated in the optimization procedure itself.. The remainder of the paper is organized as follows: Section 2 briefly discusses the initial intensity segmentation method. Sections 3 and 4 contain the formulation of the labeling problem in the MAP framework and the optimization procedure, respectively. In Section 5, experimental results are presented and, finally, conclusions are drawn in Section 6.. At the lower level of the proposed method ( Fig. 1) , a segmentation algorithm is applied on the intensities in the current frame. We aim for a conservative partitioning of the current frame, such that significant boundaries, that is object boundaries, are not violated. That is, we favor an oversegmentation since the proposed method is not able to recover from an initial undersegmentation by splitting a segment that does not belong entirely to a single object. Although the choice of the segmentation method is not restrictive to the generality of our approach, we favor methods which consider the intensity gradient rather than clustering approaches. For its low-computational complexity and good edge localization accuracy, we use the watershed segmentation algorithm [21] . A filtering with morphological operators [22] with a small (Q Â Q) structuring element is used for a nonlinear smoothing of the current frame. Once the noise level is reduced, the morphological gradient is estimated and segment markers are extracted as areas where the gradient is lower than a threshold. The flooding procedure described by Vincent and Soille [23] provides the final partition (Fig. 2) .. The threshold for the marker extraction is a user-specified prediction of the smallest gradient magnitude of the significant edges. Edges with smaller gradient magnitude are not preserved. It should be noted that the threshold is not directly related with the amount of texture within a segment. During the flooding procedure, a segment will encapsulate some of the pixels which lie between its marker and the marker of the neighboring segment and have higher gradient magnitude than the threshold (Fig. 2) .. Once the intensity segments are extracted, a Region Adjacency Graph (RAG) can be built to express neighborhood relations between them. We denote fs X s P I F F F u g as the set of the watershed segments, q s as the set of the pixels in the watershed segment s, and x s fs H g as the set of neighbors of segment s as they are defined on the Region Adjacency Graph. In this paper, we have proposed a method for segmentation of video sequences in which spatial and temporal consistency is expressed in terms of interactions between segments that result from an initial intensity segmentation. We express the solution in terms of the MAP criterion and propose an optimization strategy which iteratively maximizes the conditional a posteriori probability of the label field with respect to the motion and the label field.. We have presented results for various image sequences, that show that with the proposed modeling it is possible to group segments that result from a ªfineº initial segmentation, based on motion information. The proposed method exhibits good localization properties, temporal stability and deals successfully with motion occlusions.. For future work, an explicit treatment of the occlusions and, more specifically, of occlusions in the previous frame could be beneficial. This implies the identification of segments that have just appeared in the scene and the relaxation of the assumption of the temporal continuity of the label map in such cases. Finally, the automatic determination of the number of the objects using the Minimum Description Length principle [28] , [29] might be an interesting extension. We have applied the proposed algorithm in a number of sequences in order to test the validity of our approach. We present results for three sequences in each of which different challenges arise. In the first one, the apparent motions of the objects are quite small in magnitude which makes the distinction between them rather difficult. In the second one, the motions are large, a fact which generates large occlusions and even blurs the edges of one of the objects. Finally, in the third sequence, difficulties arise on the one hand because of small deformations in the shape of the moving object and on the other because of the large rotational components which are present in the motion pattern. Extended results for these sequences can be found in [8] .

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 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 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 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 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 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 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


What is cyberinfrastructure Cyberinfrastructure is a word commonly used but lacking a single, precise definition. One recognizes intuitively the analogy with infrastructure, and the use of cyber to refer to thinking or computing -but what exactly is cyberinfrastructure as opposed to information technology infrastructure? Indiana University has developed one of the more widely cited definitions of cyberinfrastructure:Cyberinfrastructure consists of computing systems, data storage systems, advanced instruments and data repositories, visualization environments, and people, all linked together by software and high performance networks to improve research productivity and enable breakthroughs not otherwise possible.A second definition, more inclusive of scholarship generally and educational activities, has also been published and is useful in describing cyberinfrastructure:Cyberinfrastructure consists of computational systems, data and information management, advanced instruments, visualization environments, and people, all linked together by software and advanced networks to improve scholarly productivity and enable knowledge breakthroughs and discoveries not otherwise possible.In this paper, we describe the origin of the term cyberinfrastructure based on the history of the root word infrastructure, discuss several terms related to cyberinfrastructure, and provide several examples of cyberinfrastructure. The term 'cyberinfrastructure' was coined in the late 1990s, and its usage became widespread in 2003 with the publication of "Revolutionizing Science and Engineering Through Cyberinfrastructure: Report of the National Science Foundation Blue-Ribbon Advisory Panel on Cyberinfrastructure" by Atkins et al. [1] .. The development of the term can be traced directly to foundational work in computer science that resulted in creation of computer grids in the 1990s. In 1995, several leading researchers and supercomputer centers collaborated to demonstrate I-WAY at the IEEE/ACM Supercomputing'95 conference, providing a glimpse of the scientific research opportunities that could be created by linking supercomputers and visualization systems via high-speed networks [2] . Noted researcher Ian Foster subsequently published several articles defining grids, starting with the following definition in 1998 [3] :. A computational grid is a hardware and software infrastructure that provides dependable, consistent, pervasive, and inexpensive access to high-end computational capabilities.. Definitions of various types and aspects of computer grids were subsequently expanded upon by Foster and others. This was the catalyst for the concept of cyberinfrastructure, which is very much a generalization of the concept of a computational grid. The 2003 report by Atkins et al., however, did not contain a simple and concise definition of the word cyberinfrastructure. As a result, a number of institutions have attempted to craft their own definitions. The purpose of this paper is to present the history of the word cyberinfrastructure, provide two useful working definitions of cyberinfrastructure (each useful in particular contexts), provide examples of cyberinfrastructure in use today, and explain several concepts related to cyberinfrastructure. The term cyberinfrastructure has become heavily used within the US advanced research and advanced information technology community. We believe there are two definitions that are useable and useful, depending on context: Cyberinfrastructure consists of computing systems, data storage systems, advanced instruments and data repositories, visualization environments, and people, all linked together by software and high performance networks to improve research productivity and enable breakthroughs not otherwise possible.. Cyberinfrastructure consists of computational systems, data and information management, advanced instruments, visualization environments, and people, all linked together by software and advanced networks to improve scholarly productivity and enable knowledge breakthroughs and discoveries not otherwise possible.. Any definition is useful to the extent that it identifies something important and distinguishes it from other things. The definitions above, supplemented by the examples presented here, will we hope help further explain this important concept and aid the development of new cyberinfrastructure technology, features, and functionality that will advance research, education, and workforce development in the US and throughout the world.

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