Collaborative framework for browser games development In this paper we do a review of research in software and game development, game modding communities, open-source development and open content creation. The ideas gathered in this research used to create a conceptual model for the creation of a collaborative on-line framework for browser games development. The generated conceptual model will be used in future work to build and test the framework. Computer games are an increasingly popular application of computer technology [11] , and a very important part of today's entertainment culture.. Game development is a complex and demanding task that typically needs teams with various skills and expertises to create an interesting and viable game [2] [7] . In the context of Free and Open Source Software (FOSS) games, the need to have programmers, designers, graphical artists, musicians and others on the team make the barriers to entry somewhat high.. Various researchers have studied the software development process applied to games development, and its particulars both in commercial and FOSS settings.. In a related movement to FOSS, Open Content and Creative Commons allows for collaboration and sharing in various fields not related software development, like writing, arts, music, and others. The work included in this paper is only the first step in the creation and testing of the collaborative games creation framework. This is the groundwork needed to start with the building of a prototype web application that will flesh out these ideas and give us some metrics on the applicability of these ideas and their success in the field. Browser games are using mostly closed technologies. It is possible to create good quality games using Open Source tools and open collaborative frameworks. Using open licenses both for code and art resources on games allows the creation of a pool of resources that enriches all futures games based on this technology. This approach also allows creators with good game ideas but poor artistic skills to engage in game creation. The opposite is also true, because an artist can take a good game with poor graphics and make a version with better ones.. The ability to remix content to make new things allowed recent revolutions in areas like music, video and software development. Games make use of these things but not in an integrated matter.. The reviewed literature allowed us to create a conceptual model of the framework that incorporated the most important ideas of how on-line collaborative efforts work and create successful communities. Also the study of the methodologies for software and game development guided the division of roles and tasks between the various parts of the framework. The conceptual model that will guide the creation of the framework and allow us to test if these ideas taken from different areas can be applied to collaborative game creation.. 7.

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


A large-scale performance study of cluster-based high-dimensional indexing High-dimensional clustering is used by some content-based image retrieval systems to partition the data into groups; the groups (clusters) are then indexed to accelerate processing of queries. Recently, the Cluster Pruning approach was proposed as a simple way to produce such clusters. While the original evaluation of the algorithm was performed within a text indexing context at a rather small scale, its simplicity motivated us to study its behavior in an image indexing context at a much larger scale. This paper summarizes the results of this study and shows that while the basic algorithm works fairly well, three extensions dramatically improve its performance and scalability, accelerating both query processing and the construction of clusters, making Cluster Pruning a promising basis for building large-scale systems that require a clustering algorithm. Many approximate high-dimensional near neighbor search methods are based on some sort of segmentation of the data collection into groups of descriptors, which are stored together on disk. At query time, an index is then typically used to select the single nearest such group for searching. Several such methods are based on using a k-means approach for clustering the data. k-means, however, has problems at very large scale [8] . Chierichetti et al. [1] proposed a very simple algorithm, called Cluster Pruning, which uses the initial steps of the k-means algorithm to select a number of random cluster leaders and assign each descriptor to a single leader. At search time, the nearest b clusters are read and used to produce the approximate results. To improve result quality, they proposed some parameters affecting the size of clusters and the depth of the cluster index.. Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Many content-based image retrieval systems and techniques rely on clustering to partition data, either for preprocessing or for data retrieval. Recently, the Cluster Pruning algorithm was proposed as a very simple, yet effective, approach for rapidly producing clusters of acceptable quality. Its simplicity and performance was a strong motivation to study its behavior in a large-scale image indexing context.. Building on Cluster Pruning, we have proposed three extensions which increase its performance at large scale. The first extension comes from the observation that disks can not be ignored and taking into account the IO granularity is a key factor to performance. The second extension comes from the observation that good search performance is obtained when clusters are better balanced. The third extension comes from the observation that, at scale, using an index to facilitate the assignment of data points to clusters is mandatory for performance.. Overall, we believe that, with our modifications, Cluster Pruning is a good basis for building large-scale systems that require a clustering algorithm. Not only is the algorithm fast, but it appears to produce clusters of acceptable quality, even at large scale. The seminal Video-Google approach to image retrieval uses k-means to group descriptors into visual words, which are then indexed using information retrieval techniques; in this case, the clusters are not used directly for query processing [11] . Philbin et al. [9] concluded, much like Chierichetti et al., that result quality is enhanced when varying the extent of the search and/or redundancy of the clustering.. Building on Video-Google, Nistér and Stewénius observed that the retrieval quality was increased when the visual vocabulary is significantly enlarged (to several millions) [7] . When k is very large, however, standard k-means fails. They thus proposed a hierarchical k-means approach, which is quite similar to Cluster Pruning, but builds clusters topdown. Data points may be assigned to more than one leaf. Nistér and Stewénius do not study the various options discussed in the Cluster Pruning approach. They subsequently addressed the use of multiple (15-20) clusterings together to ensure quality, requiring one disk IO per cluster for each query descriptor [2] .. Accelerating the clustering of the data collection in the Video-Google context is also the goal of Philbin et al. [8] . Their clustering process is flat, similar to standard k-means. They basically reduce the number of representatives each point must be compared to, boosting the assignment and trading-off speed for accuracy. They start by precomputing a large set of cluster representatives that get indexed into several randomized kd-trees. They assign a data point to its approximate closest representative by first probing each kd-tree with the point to cluster.. Overall, these methods [7, 8, 9, 11] have much in common with Cluster Pruning yet have quite specific properties. First, they never use the data in clusters, but rather the mapping between data points and cluster centers. Therefore, they are free to create poorly balanced clusters, and can rely on tf-idf schemes from information retrieval to compensate for differences in cluster cardinalities. Second, they also create a very large number of clusters since this, in turn, creates very sparse lists, as needed for efficient processing of inverted lists. Last, they are mostly main memory oriented.

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Characteristics of a Chromatic Dispersion Measurement Method Using the Bidirectional Modulation of Optical Intensity Modulator We had recently measured a chromatic dispersion of optical fiber and a time delay of chirped fiber grating based on a bidirectional modulation of an optical intensity modulator. In this paper, we analyze characteristics of the chromatic dispersion measurement method using a bidirectional modulation of an optical intensity modulator, and give a detailed explanation about the selection of measurement setup parameters to achieve an accurate measurement. We also propose modified measurement system to decrease relative intensity noise caused by the bidirectional transmission through a device under test Pulse broadening caused by a chromatic dispersion has been the main limitation on increasing the single channel data rate and transmission distance of optical fiber communication systems. Thus a compensation of the total chromatic dispersion for transmission path is critical to the design and the construction of a long-haul and high speed optical fiber communication system. For accurate compensat ion of the chromatic dispersion, the measurement of the chromatic dispersion must be performed to design and manufacture the optical fiber and components such as chromatic dispersion compensators and wavelength division multiplexing components. The chromatic dispersion must also be measured with the installation of new systems or the upgrade of existing systems to higher bit rate systems in the field. The measurement of chromatic dispersion is commonly carried out using the phase-shift method [1] . Although this method provides highly accurate and reliable measurements, the phase instability and phase resolution are affected by modulation frequency and wavelength step size.. In recent letters [ 2] - [4] , we had proposed a chromatic dispersion measurement method based on bidirectional modulation of an optical intensity modulator (OIM). In [2] - [4] , however, a simple description of the measurement method and measured results of optical fiber and chirped fiber grating were given, but there are no considerations related to their characteristics and problems. In this paper, we give a detailed explanation about the selection of measurement setup parameters to achieve an accurate measurement of chromatic dispersion by the proposed method and also propose the modified measurement system to decrease the relative intensity noise caused by bidirectional transmission through a device under test (DUT). Figure 1 shows a schematic diagram of the modified chromatic measurement system using a bidirectional modulation of an OIM. This system has lower relative intensity noise than the previous system [3] , because there is no bidirectional transmission of a modulated optical signal through the DUT. Light from a tunable laser experiences a co -propagating modulation by the OIM and travels through the optical circulator#2 and the DUT. The modulated light is incident on the output port of the OIM and experiences a counter -propagating modulation by the RF signal with a time delay τ corresponding to the length of the DUT. The bidirectionally modulated light with the time difference is detected by a photodetector through an optical circulator #1. A network analyzer (NA) measures the system transfer function with periodical ripples in the RF domain. In conclusion, we have given detailed explanation about the select ion of measurement setup parameters to achieve an accurate measurement of the chromatic dispersion by using the bidirectional modulation of OIM. We also propose the modified measurement system to decrease relative intensity noise caused by bidirectional transmission through the DUT. The chromatic dispersion of 2.235 km optical fiber has been measured by the proposed method. The variations of the measured dispersion at 1550 nm and the dispersion slope have been less than 0.115 ps/nm/km and 0.0044 ps/nm 2 /km, respectively. This method can be applied to measure the dispersion of various fibers such as dispersionshifted fiber and dispersion compensating fiber.

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Teleoperation of multi-agent systems with nonuniform control input delays Consensus and coordination of multiple teleoperated agents has been a control topic of growing interest over the last decade due, in part, to its many potential applications and related complex challenges. One of these challenges is to guarantee stability and motion coordination in the presence of inherent communication and input delays as well as system nonlinearities in the multi-agent system. Addressing this challenge herein, we report on a model reference robust control framework that guarantees stability, motion coordination, and formation control of N output strictly passive, nonlinear Lagrangian systems with arbitrarily large, nonuniform control input delays. The control framework is comprised of a reference model coupled to the nonlinear systems via the use of N modified scattering transformation blocks. It is shown that the overall control architecture is stable for any large constant delay, robust to system uncertainties, and that the control parameters are delay-independent. A numerical example with four nonlinear planar manipulators and another example with six ground vehicles are finally presented to illustrate the performance of the proposed controller. In this paper, we have proposed and studied the use of a passivity-based MRRC framework for the remote control of N nonlinear Lagrangian systems with nonuniform control input delays. The proposed control framework extends the control architecture introduced in [35] for single, time-delay robotics systems to the general case of multiple nonlinear agents. We showed that the proposed controller, comprised of a linear reference model and N scattering transformation blocks, guarantees the stability, motion coordination, and formation convergence of a group of output strictly passive systems with any large constant input delays using concepts of passivity and Lyapunov stability. Furthermore, we showed that the design control parameters are delay-independent and that the overall controller is robust to model uncertainties, only requiring the knowledge of a lower bound on the dissipation rate ρ i . Along with the theoretical analysis, two numerical examples with planar manipulators and unmanned vehicles were presented to validate the proposed MRRC framework. To the best of our knowledge, this paper constitutes the first time that the concept of passivity-based scattering transformation is employed in the stabilization and control of multiple nonlinear systems with control input delays and one of the first research efforts to address the coordination of nonlinear systems with pure delayed control. Research extensions to the ideas presented in this paper include the stability analysis of the overall system under time-varying delays and data transmission losses, the compensation of initial position errors, and the addition of direct inter-agent communication.

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Local Load Balancing for Globally Efficient Routing in Wireless Sensor Networks One of the limitations of wireless sensor nodes is their inherent limited energy resource. Besides maximizing the lifetime of the sensor node, it is preferable to distribute the energy dissipated throughout the wireless sensor network in order to minimize maintenance and maximize overall system performance. Any communication protocol that involves synchronization of peer nodes incurs some overhead for setting up the communication. We introduce a new algorithm, e3D (energy-efficient Distributed Dynamic Diffusion routing algorithm), and compare it to two other algorithms, namely directed, and random clustering communication. We take into account the setup costs and analyze the energy-efficiency and the useful lifetime of the system. In order to better understand the characteristics of each algorithm and how well e3D really performs, we also compare e3D with its optimum counterpart and an optimum clustering algorithm. The benefit of introducing these ideal algorithms is to show the upper bound on performance at the cost of astronomical prohibitive synchronization costs. We compare the algorithms in terms of system lifetime, power dissipation distribution, cost of synchronization, and simplicity of the algorithm. Our simulation results show that e3D performs comparable to its optimal counterpart while having significantly less overhead.164In this paper, we attempt to overcome limitations of the wireless sensor networks such as: limited energy resources, varying energy consumption based on location, high cost of transmission, and limited processing capabilities. All of these characteristics of wireless sensor networks are complete opposites of their wired network counterparts, in which energy consumption is not an issue, transmission cost is relatively cheap, and the network nodes have plenty of processing capabilities. Routing approaches that have worked so well in traditional networks for over twenty years will not suffice for this new generation of networks.Besides maximizing the lifetime of the sensor nodes, it is preferable to distribute the energy dissipated throughout the wireless sensor network in order to minimize maintenance and maximize overall system performance [12] . Any communication protocol that involves synchronization between peer nodes incurs some overhead in setting up the communication. In this paper, we attempt to determine whether the benefits of more complex routing algorithms, which overshadow the extra control messages each node needs to communicate. Each node could make the most informed decision regarding its communication options if they had complete knowledge of the entire network topology and power levels of all the nodes in the network. This indeed proves to yield the best performance if the synchronization messages are not taken into account. However, since all the nodes would always need to have global knowledge, the cost of the synchronization messages would ultimately be quite expensive.The usual topology of wireless sensor networks involves having many network nodes dispersed throughout a specific physical area. There is usually no specific architecture or hierarchy in place and therefore, the wireless sensor networks are considered as ad hoc networks. That does not mean that a dynamic organization is not allowed, however it just cannot be predefined in advance.An ad-hoc wireless sensor network is an autonomous system of sensor nodes in which all nodes act as routers connected by wireless links. Although ad-hoc networks usually imply that nodes are free to move randomly and organize themselves arbitrarily, in this paper we considered only ad hoc networks with fixed node positions. On the other hand, wireless links are not very reliable and nodes might stop operating at arbitrary points within the system's life; therefore, the routing protocol utilized must be able to handle arbitrary failure of nodes throughout the network. Such a network may operate in a standalone fashion, or it may be connected to other networks, such as the larger Internet. This architecture leads to the concept of peer-to-peer communication throughout the wireless sensor network for communication between most of the network nodes, and client-server communication between some nodes and the base station [3] . Eventually, the data retrieved by the sensors must be propagated back to a central location, where further processing must be done in order to analyze the data and extract meaningful information from the large amounts of data. Therefore, a base station(s) is usually chosen in order to act as the gateway between the wireless network and IEEE 802.x networks [11], such as wired Ethernet, or perhaps 802.11 Wireless Ethernet [12] . Base stations are usually more complex than mere network nodes since they must have dual purpose functionality: one to communicate with the wireless network and the other to communicate with the wired network. It also usually has an unlimited power supply and therefore, power consumption is not critical for the base station. With enough power consumption, each node could theoretically communicate with the base station, however due to a limited power supply, spatial reuse of wireless bandwidth, and the nature of radio communication cost which is a function of the distance transmitted squared, it is ideal to send information in several smaller distance wise steps rather than one transmission over a long communication distance [8, 4] . Over the last half a century, computers have exponentially increased in processing power and at the same time decreased in both physical size and price. These rapid advancements led to a very fast market in which computers would participate more and more in our society's daily activities. In recent years, one such revolution has been taking place, where computers are becoming so small and so cheap that single-purpose computers with embedded sensors are almost practical from both economical and theoretical points of view. Wireless sensor networks are beginning to become a reality, and therefore some of the long overlooked limitations have become an important area of research. Some typical applications for wireless sensors include the collection of massive amounts of sensor data. Furthermore, the sensors can extend mobile device functionality, such as providing input to mobile computer applications and receiving commands from mobile computers. They can facilitate communication with the user's environment, such as beacons or sources of information throughout the physical space [9] . Some other typical examples are environmental sensors, automotive sensors, highway monitoring sensors, and biomedical sensors.. In our simulation, we use a data collection problem in which the system is driven by rounds of communication, and each sensor node has a packet to send to the distant base station. Our proposed algorithm is based on location, power levels, and load on the node, and its goal is to distribute the power consumption throughout the network so that the majority of the nodes consume their power supply at relatively the same rate regardless of physical location. This leads to better maintainability of the system, such as replacing the batteries all at once rather than one by one, and maximizing the overall system performance by allowing the network to function at 100% capacity throughout most of its lifetime instead of having a steadily decreasing node population.. The rest of the paper is organized as follows. Section 2 covers background information and previous work completed in the field, assumptions, algorithms, findings, and shortcomings. Section 3 covers our evaluation test-bed; we explain our own realistic assumptions based on real world sensors, the sensors hardware on which we based our assumptions, and the distribution of the sensor nodes. Section 4 covers the description and cost analysis of six routing algorithms: direct communication, basic diffusion routing algorithm, e3D routing algorithm (diffusion-based and our contribution), ideal diffusion based routing algorithm, random clustering, and the ideal clustering routing algorithm. We finally conclude with Section 5 in which we talk about the importance of our findings and future work. Due to space constraints, we were not able to include all experimental results we have obtained, but we did present the most relevant information to compare e3D with other proposed algorithms that had similar goals to ours. The proposed algorithm (e3D) performed well in terms of achieving its goal to evenly distribute the power dissipation throughout the network while not creating a very large burden for synchronization purposes.

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A platform for high performance and flexible virtual routers on commodity hardware Multi-core CPUs, along with recent advances in memory and buses, render commodity hardware a strong candidate for software router virtualization. In this context, we present the design of a new platform for virtual routers on modern PC hardware. We further discuss our design choices in order to achieve both high performance and flexibility for packet processing. Recent research has shown that modern PCs are a viable platform for the implementation of high-performance software routers [1, 2] . The functionality provided by software routers combined with recent virtualization technologies allows multiple instances of routers to run concurrently on a single box while offering highly configurable forwarding planes and custom routing protocols. Some recent PC-based virtual router prototypes [3] have been proposed, but none of them exploit recent advances in commodity hardware such as multi-core CPUs or network interface cards with hardware multi-queuing.. In [1] we showed that the main performance bottleneck for PCbased software routers is main memory access. With the memory subsystem as the limiting factor for at least the next few years, the number of spare CPU cycles is likely to increase. To exploit these resources we can certainly consolidate a set of software routers running concurrently on the same hardware, inline with conventional server virtualization. However, the short-lived nature of packets inside a router makes router virtualization challenging and certainly more demanding. Is it possible to have the best of two worlds, building a flexible virtual router platform that also reaches the performance limits of the underlying hardware?. Motivated by this challenge, we present a new platform for software virtual routers on commodity hardware. The platform leverages modern and emerging hardware trends to provide: (i) consolidation of virtual data planes onto a common forwarding domain, (ii) highly configurable forwarding planes for advanced programmability, and (iii) the forwarding tree 1 as the basic resource allocation unit for the mapping of virtual router components to cache hierarchies.

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Exploiting spatial context constraints for automatic image region annotation In this paper we conduct a relatively complete study on how to exploit spatial context constraints for automated image region annotation. We present a straightforward method to regularize the segmented regions into 2D lattice layout, so that simple grid-structure graphical models can be employed to characterize the spatial dependencies. We show how to represent the spatial context constraints in various graphical models and also present the related learning and inference algorithms. Different from most of the existing work, we specifically investigate how to combine the classification performance of discriminative learning and the representation capability of graphical models. To reliably evaluate the proposed approaches, we create a moderate scale image set with region-level ground truth. The experimental results show that (i) spatial context constraints indeed help for accurate region annotation, (ii) the approaches combining the merits of discriminative learning and context constraints perform best, (iii) image retrieval can benefit from accurate regionlevel annotation. In this paper we consider a special task of image annotation, namely region annotation, which aims to automatically assign semantic labels to individual segmented regions rather than entire images.

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Routing in a cyclic mobispace A key challenge of routing in delay tolerant networks (DTNs) is finding routes that have high delivery rates and low endto-end delays. When oracles are not available for future connectivity, opportunistic routing is preferred in DTNs, in which messages are forwarded to nodes with higher delivery probabilities. We observe that real objects have repetitive motions, but no prior research work has investigated the cyclic delivery probability of messages between nodes. In this paper, we propose to use the expected minimum delay (EMD) as a new delivery probability metric in DTNs with repetitive but non-deterministic mobility. Specifically, we model the network as a probabilistic time-space graph with historical contact information or prior knowledge about the network. We then translate it into a probabilistic state-space graph in which the time dimension is removed. Finally, we apply the Markov decision process to derive the EMDs of the messages at particular times. Our proposed EMD-based routing protocol, called routing in cyclic MobiSpace (RCM), outperforms several existing opportunistic routing protocols when simulated using both real and synthetic traces. Delay tolerant networks (DTNs) are occasionally-connected networks that suffer from frequent network partitioning as the result of high mobility, low density, short radio range, intermittent power, interference, obstruction, attacks, etc. Representative DTNs include sensor networks using scheduled connectivity, terrestrial wireless networks that cannot ordinarily maintain end-to-end connectivity, satellite networks with periodic connectivity, and underwater acoustic networks with moderate delays and frequent interruptions.. Routing in DTNs is an active research area. The Delay Tolerant Network Research Group (DTNRG) [1] has designed a complete architecture to support various protocols in DTNs. A DTN can be described abstractly using a timespace graph, in which each edge contains a set of contacts. A contact is a period of time during which two nodes can communicate with each other. On the Internet, intermittent connectivity causes loss of data. DTNs, in contrast, support communication between intermittently-connected nodes using the store-carry-forward routing mechanism.. Routing in DTNs poses some unique challenges compared to conventional data networks due to the uncertain and time-varying network connectivity. In [2, 3] , optimal routes in a DTN can be discovered by constructing a time-space graph with oracles. In practical situations where no oracle is available to reveal future contacts, opportunistic routing [4, 5] is proposed in which one or more copies of a message is sent along different paths and each copy is always forwarded to the node that has a higher delivery probability. Metrics for delivery probability can be either short-term metrics (e.g., the time that has elapsed since the last encounter), which have short life-spans and require frequent updates, or long-term metrics which are relatively stable over time.. Previous works have proposed a variety of long-term metrics including encounter frequency [5] and social similarity [6] . One advantage of the long-term delivery probability metrics is that they are relatively stable once generated from historical connectivity information or prior knowledge on the contact pattern of the nodes, avoiding expensive and frequent updates. We notice that most real objects have cyclic motion patterns, and therefore it is possible and valuable in practice to use some cyclic metric to increase the accuracy of the estimated delivery probability. In this paper, we propose the use of a cyclic long term metric, called the expected minimum delay (EMD), which is the expected time that an optimal forwarding scheme takes to deliver a message at a specific time from a source to a destination, in a network with cyclic and uncertain connectivity. A MobiSpace is a Euclidean space (or other higher dimensional space) where nodes can be either mobile or static and they can communicate within each other's transmission range. We define a cyclic MobiSpace as a MobiSpace where mobility is cyclic. In a cyclic MobiSpace, if two nodes are often in contact at a particular time in previous cycles, then the probability that they will be in contact at the same time in the next cycle is high. A cyclic MobiSpace can be modeled with a probabilistic time-space graph in which an edge between two nodes contains a set of discretized probabilistic contacts. Each discretized probabilistic contact is associated with a time slot and a contact probability. The contact probability is the probability that the two nodes have contacts during the time slot in every cycle. To calculate the EMD of a message, we translate the probabilistic timespace graph into a probabilistic state-space graph, where the time dimension is removed from the edges. Then, we apply the Markov decision process to calculate the EMD of the state corresponding to the node hosting the message and the current time. With EMDs, we propose a routing protocol, called routing in cyclic MobiSpace (RCM).The contributions of this paper are summarized as follows.. 1. We propose the use of a cyclic, long-term delivery probability metric, called EMD, to improve the performance of opportunistic routing in cyclic MobiSpace.. 2. We model a cyclic MobiSpace as a probabilistic timespace graph and devise a lossless translation of this graph model into a probabilistic state-space graph model.. 3. We apply the Markov decision process (MDP) to solve the EMDs of the states in our probabilistic state-space graph model. We also extend a recent result on solving MDPs and propose an efficient algorithm for calculating the EMDs in our state-space graph model. In this paper we have presented our first research investigating a new cyclic delivery probability metric, expected minimum delay (EMD), and provided methods to achieve it in a cyclic MobiSpace. Our proposed probabilistic routing, routing in cyclic MobiSpace (RCM), is evaluated and compared with the enhanced versions of some existing DTN routing protocols using the NUS student trace, the UMassDieselNet trace, and our synthetic traces. The simulation results demonstrate that RCM outperforms the compared protocols in terms of delivery rate and delay.. Due to space limitation, we left some performance analysis of our protocol to the future work, which includes the impact of size of time slots on the performance of RCM. We will also create more synthetic traces with different maps of metro routes and generalize the conditions where RCM can provide most significant improvement. In [2] , Jain, Fall, and Patra presented a comprehensive investigation on the DTN routing problem with different levels of prior knowledge about the network. Specifically, Dijkstra's algorithm (with future connectivity information) or the linear programming approach (when with information of future connectivity, traffic demands, etc.) is used to obtain an optimal path between a source and a destina-tion. In [3] , Merugu, Ammar, and Zegura proposed a DTN routing algorithm that is similar in spirit to Dijkstra's algorithm in [2] . In [7] , Liu and Wu propose a model for DTNs with repetitive mobility. A hierarchical routing is further proposed to make routing in such DTN models scalable.. Epidemic routing [16] is the first flooding-based routing algorithm. Gossip [4] , forwards with probability p. Opportunistic routings, such as [5] , forward based on the delivery probability. Different delivery probability metrics are proposed including encounter frequency [5] , time elapsed since last encounter [8, 18, 19, 23, 24] , social similarity [6] , location similarity [25] , geometric distance [20] , etc.. Trace data available for the research community [22] include UMassDieselNet trace, the NUS student contact trace, etc. In [26] , several opportunistic routing algorithms are simulated in large realistic contact traces. A timely-contact probability metric is proposed in this paper which captures the contact frequency of the mobile nodes which is similar to [5] and [8] in spirit.

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


Polynomial-time computing over quadratic maps I: sampling in real algebraic sets Abstract. Given a quadratic map Q : K n → K k defined over a computable subring D of a real closed field K, andWe present a procedure that computes, in (dn) O(k) arithmetic operations in D, a set S of (real univariate representations of) sampling points in K n that intersects nontrivially each connected component of Z. As soon as k = o(n), this is faster than the standard methods that all have exponential dependence on n in the complexity. In particular, our procedure is polynomial-time for constant k. In contrast, the best previously known procedure is only capable of deciding in n O(k 2 ) operations the nonemptiness (rather than constructing sampling points) of the set Z in the case of p(Y ) = i Y 2 i and homogeneous Q. A by-product of our procedure is a bound (dn) O(k) on the number of connected components of Z. The procedure consists of exact symbolic computations in D and outputs vectors of algebraic numbers. It involves extending K by infinitesimals and subsequent limit computation by a novel procedure that utilizes knowledge of an explicit isomorphism between real algebraic sets.

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Two Sources Are Better than One for Increasing the Kolmogorov Complexity of Infinite Sequences The randomness rate of an infinite binary sequence is characterized by the sequence of ratios between the Kolmogorov complexity and the length of the initial segments of the sequence. It is known that there is no effective procedure that transforms one input sequence into another sequence with higher randomness rate. By contrast, we display such a uniform effective procedure having as input two independent sequences with positive but arbitrarily small constant randomness rate. Moreover the transformation is a truth-table reduction and the output has randomness rate arbitrarily close to 1.

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Classification-based melody transcription The melody of a musical piece-informally, the part you would hum along withis a useful and compact summary of a full audio recording. The extraction of melodic content has practical applications ranging from content-based audio retrieval to the analysis of musical structure. Whereas previous systems generate transcriptions based on a model of the harmonic (or periodic) structure of musical pitches, we present a classification-based system for performing automatic melody transcription that makes no assumptions beyond what is learned from its training data. We evaluate the success of our algorithm by predicting the melody of the ADC 2004 Melody Competition evaluation set, and we show that a simple frame-level note classifier, temporally smoothed by post processing with a hidden Markov model, produces results comparable to state of the art model-based transcription systems. We have described techniques for recovering a sequence of melodic pitch labels from a complex audio signal. Our approach consists of two steps: first, a discriminatively-trained local pitch classifier operating on single time frames, followed by a hidden Markov model trained to apply some of the temporal constraints observed in real melody label sequences to the resulting signal. This combination is ad-hoc: if the task is to exploit local features subject to sequential constraints, then we should look for an approach that optimizes the entire problem at once. Recently, Taskar et al. (2003) have suggested an approach to using the advantages of classifier-margin-maximization from SVMs in a Markov model, but we expect that solving the entire optimization problem would be impractical for the quantities of training data we are using. The important question is whether there are significant differences in how local features would be processed depending on the context in such a scheme, or whether the problem can in fact be separated into the two stages we have implemented without significant impact on performance. Looking at the intermediate posterior representation illustrated in Fig. 5 , we suspect that this is an adequate representation of the acoustic information for the sequential modeling to be operating on. We feel that the most promising areas for improvement are improving the frame-level accuracy of this front end and more sophisticated post-processing (including improved voicing detection), and not a tighter integration between the two stages, which seem comfortably separate from our perspective.. There are several directions in which we plan to continue this work. Although this paper has considered the problem of melody extraction i.e. assigning at most one pitch to each time step, the OVA classifiers can be run and examined independently. With a different kind of decoding scheme running over the output posteriors, it may be possible to report more than one note for each time frame i.e. polyphonic transcription. Alternatively, there may be a direct classification path to polyphonic transcription i.e. training classifiers to recognize entire chords, although this raises serious combinatoric problems.. We believe the local harmonic structure carried by a chord could provide significant additional information and constraints for melody transcription. In conventional western music, there is an underlying harmonic progression of chords, and the melody notes are strongly dependent on the current chord. The chord sequence itself has a strong sequential structure, and is dependent on the overall key of the piece. This hierarchy of hidden states is a natural fit to hidden Markov modeling, based either on separate chord-related features or on the note observations alone, and a system that explicitly represents the current chord can have a more powerful, chord-dependent transition matrix for the pitch state.. We have shown that a pure classification approach to melody transcription is viable, and can be successful even when based on a modest amount of training data. In the MIREX 2005 evaluation, we entered the system denoted "AVA SVM" in this paper, without any HMM smoothing, which ranked third of ten entries; by switching to the OVA architecture, the RBF kernel, and the posterior-based HMM smoothing, we achieve a 5.5% absolute improvement in overall frame accuracy (from 67.7% to 73.2%), and believe this would carry across to the MIREX test. (The MIREX 2005 results are visible at http://www.music-ir.org/ evaluation/mirex-results/audio-melody/ .). The natural question is: what is the upper limit on the performance achievable by this approach? One attraction of data-driven approaches is that further improvements can predictably be obtained by gathering additional training data. Figure 3 is the important example here: if we create ground truth for another 15 excerpts, how high can our accuracy grow? The slope of accuracy vs. excerpt count looks quite promising, but it may be reaching an asymptote. One of the most striking results of the recent MIREX evaluation is that our radically different approach to transcription scored much the same as the traditional model-based approaches; the performance spread across all systems on raw pitch accuracy was within 10%, from 58% to 68%.. This suggests that the limiting factors are not so much in the algorithms, but in the data, which might consist of 60-70% of relatively easy-to-transcribe frames with the pitch of the remaining frames very difficult to transcribe for classifier-or model-based approaches alike. If this were the case, we would not expect rapid improvements from our classifier with modest amounts of training data, although there must be some volume of training data that would allow us to learn these harder cases.. Given the expense of constructing additional training data-either in trying to beg multitrack recordings from studios and artists, or in manually correcting noisy first-pass transcripts, we are also curious about the tradeoff between quantity and quality in training data. Raw musical audio is available in essentially unlimited quantities: given an automatic way to extract and label ground-truth, we might be able to construct a positive-feedback training loop, a system that attempts to transcribe the melody (aided perhaps by weak annotation, such as related but unaligned MIDI files), then retrains itself on the most confidently-recognized frames, then repeats. Bootstrap training based on lightly-annotated data of this flavor has proven successful for building speech recognition systems from very large training sets (Lamel et al., 2002) . However, classification-based transcription has a number of other attractive features that make it interesting even if it cannot provide a significant performance improvement over conventional methods. One application that we find particularly appealing is to train the classifier on the accompaniment data without the lead melody mixed in, but still using the lead melody transcripts as the target labels. Then we will have a classifier trained to predict the 'appropriate' melody from accompaniment alone. With suitable temporal smoothness constraints, as well as perhaps some random perturbation to avoid boring, conservative melody choices, this could turn into a very interesting kind of automatic music generation or robotic improvisor.

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


Characteristics of wap traffic ABSTRACT Wireless Application Protocol (WAP) [1] is a protocol for the transmission of web like content to mobile phones and other (usually wireless) devices with lowbandwidth links. Although commercial take-up has been slower than originally hoped, WAP is still offers considerable promise as more content tailored to small devices becomes available.. The standard WAP configuration is to have a WAP terminal communicating with a WAP gateway, which is then connected to the web. The terminal sends its request to the gateway, which then requests the content from the web server. The web server replies to the request with WML (Wireless Markup Language) files which the gateway can then optimise for transmission over the low bandwidth link to the terminal. A modified approach which allows the browsing of standard web pages is to use an HTML filter to convert the HTML pages to WML, but on devices with small displays this is unlikely to be successful, with content having to be tailored to the device. Proposals for WAP 2.0 allow selection of information depending on the capabilities of the device, but this paper deals with the current WAP specification (1.2).. There is little in the literature on the modelling of WAP traffic. One approach to modelling WAP traffic would be to modify an existing web traffic model, taking into account the optimising (effectively compression) which is carried out by the gateway and HTML filter. However, with the exception of some PDAs which now have WAP browsers, most WAP devices have a very limited user interface which affects the way people use the device. Most WAP browsing uses WML pages directly rather than the HTML filter, and a simple conversion from a web model is not therefore appropriate. In addition, the relatively high costs of using WAP on a mobile phone in many cases reduces casual browsing. Information retrieved through high cost WAP services needs to be of value, and for it to be accessed on the move, time sensitive, at least from the point of view of the user. Another difficulty with a web model is that a web page usually consists of a main page with a number of other files, such as images, included within it. Web models therefore differentiate between the reading time for a complete page between page requests, and the loading times of files within a page [2] . WAP traffic has fewer images and smaller pages which are read more quickly, reducing this distinction.. As well as constructing a model for WAP traffic, it is interesting to consider the effect of WAP traffic on the overall aggregate traffic through the system. One major difficulty in the dimensioning of capacity for Internet traffic is due to the self-similarity of Web browsing traffic pattern. Self-similar traffic possesses the property that, when aggregated over time, the distribution of the trace remains. Web traffic displays structural self-similarities, and is therefore is bursty, over different time scales. This means that neither the aggregation of the series over longer periods nor the superimposition of multiple sources would result in a smoother traffic pattern. In other words, the total traffic in the core network is just as bursty as the traffic being generated by one single Web user. This would imply that the amount of buffering or allowance that needs to be provisioned in the network to enable sufficient resources at all time has to be infinite, which is obviously impossible from a practical point of view. Therefore, it becomes difficult to both efficiently and adequately provision capacity to handle internet traffic, when up to 70% comes from Web browsing traffic [8] , a highly self-similar type of traffic. Our results show WAP traffic varies significantly from web traffic, particularly due to the way it is accessed. This means that modifications to web based models are unlike to model WAP traffic satisfactory. Of particular note is that even though the page sizes are significantly smaller, interarrival time is increased due to the reduced user interface increasing reading time.. Note that the nature of the experiments means that the results will be affected by the user interface, and so would not be representative of WAP traffic on a device with a different interface such as a pen based one. Reading and scrolling times are also likely to be dependent on the screen size, although the one used here was fairly typical of a WAP-enabled GSM phone.. WAP traffic itself is self-similar, but not significantly so. When aggregated with web traffic, it does not greatly change the high degree of selfsimilarity present in that traffic. A summary of the simulation runs being conducted, as well as the corresponding traffic characteristics in terms of the selfsimilarity indicator, the Hurst parameter, is presented below in Table 4 . Simulation results from the Web only model suggested that Web traffic on its own is highly selfsimilar, as indicated by its Hurst parameter in the order of 0.85. This value corresponds quite well with other results already published in literature [4] . In fact, it is this high degree of self-similarity of Web traffic, together with the fact that Web traffic constitutes for a majority of the overall internet traffic nowadays, that has caused the infamous problem that it is extremely difficult to provision sufficient resources to handle internet traffic both reliably and efficiently. In order to fulfil the requirements for both the initial model verification and the actual evaluation of WAP traffic characteristics, various scenarios were established and simulation runs were conducted to obtain the necessary traces for investigation. The scenarios considered were: The simulated WAP traffic was aggregated into various time frames to roughly illustrate the existence or not of self-similarity.. After that, the Hurst parameter estimation program was then utilised to give a more precise indication of the self-similarity property of WAP traffic. The corresponding aggregation plot and log-scale graph for WAP only traffic were shown below in Figures 5 and 6 respectively. From the degree of burstiness of the signal depicted in Figure 5 , we could predict that WAP traffic was indeed slightly self-similar. This is confirmed by the wavelet based estimator. The average value of the Hurst parameter estimated by the program over 20 simulation runs was calculated to be 0.59, where a value above 0.5 indicates self-similarity. This compares to Hurst parameters of 0.39 for speech and 0.85 for web, which is line with expectations. Actual traffic traces captured from Web browsing activity exhibits a Hurst parameter in the range between 0.76 and 0.83 [4] .. Sample aggregation plots for web and speech traffic are shown in figure 7 and 8 respectively. The aggregation plot clearly illustrates that the combined traffic still exhibits self-similarity, which was confirmed by the Hurst parameter as obtained via the log-scale graph in Figure 10 . The Hurst parameter for this particular simulation was estimated to be 0.826. Table 2 shows the variation in Hurst parameter with diffferent proportions of web and WAP traffic. With the proportion of WAP traffic increasing all the way up to three quarters of the total traffic, the estimated Hurst parameter only dropped slightly by approximately 0.06, which was considered to be insignificant in regards to the degree of self-similarity of the combined traffic. Traffic with Hurst parameter of 0.85 and 0.80 would be considered as equally self-similar. In other words, WAP traffic does not seem to be "helpful" in terms of lessening the problem of self-similarity. Simulations were also run with all three traffic types with various contributions from each traffic type, with the percentage of Web traffic ranging from 22% to 54%, that of speech from 27% to 53%, while the share of WAP traffic ranges from 13% to 40%. As an example, a single iteration from the pool of simulation runs was identified to have a ratio of Web to speech to WAP traffic volume being 35% : 32% : 33%, and its aggregation traces and log-scale graph were shown below in Figures 11 and 12 respectively. It is quite obvious from the persistence of burstiness in the above aggregation plots that a combined load with approximately equal share of Web, speech and WAP traffic exhibit a degree of self-similarity not much different from that of a pure Web traffic source. This observation was verified by processing the aggregated trace with the wavelet estimator. The Hurst parameter for this sample was estimated to be 0.819. The results from each set of runs for each traffic split are summarised below in Table 3 .

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


A unified platform for archival description and access The archival community has developed content and data structure standards to facilitate access to the diverse and unique sets of archival records, personal papers, and manuscript collections that are held by archival repositories and special collections libraries. However, these standards are difficult for archivists to use and are often implemented in ways that negatively affect materialshandling workflows, depriving archival users of the best possible access to the totality of materials available within an individual repository.The authors propose that archival descriptive problems can be addressed by implementing a web/database application that is tailored specifically to archival needs and can be implemented with little technical knowledge. This paper describes the system architecture of one such tool, the Archon software package, which was developed at the University of Illinois at Urbana-Champaign. Archon automates many technical tasks, such as producing a searchable website, an EAD instance or a MARC record. Although the system utilizes sophisticated algorithms and optimizations, it is easily extensible because most development takes place in an easy-to-use, object-oriented environment. Archival records, personal/family papers, and manuscript collections are among the most valuable materials held by libraries and other cultural institutions. By their very nature, such items are unique and possibly of high research and/or monetary value. Taken collectively, they comprise a major source of primary research materials, and many archival records hold continuing administrative or social value to the organizations or people that produced them.. Archival materials are also difficult for staff to describe and for researchers to access. Both problems are a product of archives' uniqueness. Unlike books or serials, a stack of papers or photographs does not contain supplied titles, authors, or other descriptive data. Nor do archival materials necessarily come to the repository bearing a coherent pattern of arrangement. Furthermore, the many parts of any archival aggregation retain their full significance only when described with reference to the context of their original creation and their relationship to other records of the same or similar provenance. 1 Once materials are arranged, described, housed, and shelved (a time consuming procedure which archivists euphemistically call "processing"), researchers may have to travel great distances to access the materials, assuming they know about or can identify content of interest.. When archivists describe archival materials, they mean to alleviate these problems, but the notion of archival description holds two competing ideas in a somewhat uneasy balance. ISAD(G), the General International Standard for Archival Description, notes that the purpose of archival description is "to identify the context and the content of archival materials in order to facilitate their accessibility [6] ." On the one hand, archivists are admonished to describe materials by making reference to the essential elements of the materials themselves, that is, by 'identifying their context and content [13] .' Doing so ostensibly allows the professional to maintain an impartial record of evidence about how the records were created, so that researchers can authenticate evidence or establish the veracity of the information that they contain [7] . On the other hand, archivists have been criticized for being unduly bureaucratic in exercising the function of writing archival descriptions (commonly known as 'finding aids'). More to the point, they have been accused, with some justice, of subordinating user needs to an idealized notion of archival objectivity [3] . Others have noted that in the past technological obstacles prevented archivists from sharing descriptions of their information outside of their repositories [16] , a fact that certainly encouraged a proliferation of local practices and a lack of standardization. The University of Illinois developed the Archon system to meet the pressing need for improved access to information in the archives of our institutions and to overcome limitations working with EAD in its native format. From an archival user's point of view, Archon automates many technical tasks, such as producing an EAD instance or a MARC record. Staff members do not need to learn technical coding and can concentrate on accomplishing archival work. Little or no training is needed to use the system, assuming the staff member or student worker has at least a passing familiarly with basic principles of archival arrangement and description.. In addition, the public website preserves essential contextual information for users while providing an easily-searchable and browseable interface. The public website can be adapted for local purposes with little or no knowledge of the system's API or the database platform, by modifying the supplied styles and templates and (if necessary) referring to the complete sets of documentation available through the project website. Although the system itself operates using some very sophisticated algorithms and optimizations, Archon is very extensible because all but the most complex development can be done at higher levels of the system. It provides EAD and MARC output, allowing for interoperability with other local, regional, national, or international systems.. UIUC will continue to support the development of Archon, which is used as a production system for four of our archives and special collections units. For future releases, we plan to add an accessions manager and a research cart feature, so that users can tag items for request, and multilingual support. As of this writing, five additional institutions have adopted Archon, and we are actively seeking additional partners who might provide additional input on desired features and extensions.

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


Solving the Bi-Objective Maximum-Flow Network-Interdiction Problem W e describe a new algorithm for computing the efficient frontier of the "bi-objective maximum-flow network-interdiction problem." In this problem, an "interdictor" seeks to interdict (destroy) a set of arcs in a capacitated network that are Pareto-optimal with respect to two objectives, minimizing total interdiction cost and minimizing maximum flow. The algorithm identifies these solutions through a sequence of single-objective problems solved using Lagrangian relaxation and a specialized branch-and-bound algorithm. The Lagrangian problems are simply max-flow min-cut problems, while the branch-and-bound procedure partially enumerates s-t cuts. Computational tests reveal the new algorithm to be one to two orders of magnitude faster than an algorithm that replaces the specialized branch-and-bound algorithm with a standard integer-programming solver. In the deterministic maximum-flow network-interdiction problem (MXFI), an "interdictor" wishes to restrict an "adversary's" use of a capacitated network. Specifically, the adversary seeks to maximize flow through the network, while the interdictor seeks to minimize that maximum flow by interdicting (destroying) arcs using available interdiction resources (Wood 1993) . These resources could be a set of cruise missiles, a given number of aerial sorties, etc. MXFI and related problems appear in the areas of military planning (Whiteman 1999) , drug interdiction (Steinrauf 1991) , and protecting civil infrastructure against terrorist attacks (Salmeron et al. 2004) . The model may be classified as a bilevel, targetselection, or weapons-allocation model; see Matlin (1970) , Bracken and McGill (1974) , Bracken et al. (1977) , and Wen and Hsu (1991) . A simpler version of MXFI, the problem of cutting all flow using minimum interdiction resource, provided one of the earliest applications of maximum flows and the max-flow min-cut theorem. The flow was rail traffic from the Soviet Union into eastern Europe; see Harris and Ross (1955) and Fulkerson (1956, 1957) .. This paper studies an extension of MXFI, which we call the "bi-objective maximum-flow networkinterdiction problem" (BMXFI). In BMXFI, the interdictor wishes to identify all Pareto-optimal solutions for MXFI, i.e., the efficient frontier, with respect to minimizing post-interdiction maximum flow and minimizing "total interdiction cost," i.e., interdictionresource expenditure. A bi-objective formulation is important for a military commander who (i) must pre-plan for various resource availabilities given the uncertainty of warfare, or (ii) may wish to consider cost-to-effectiveness or risk-to-effectiveness tradeoffs that are difficult to include directly in an interdictionplanning model. Steinrauf (1991) and Wood (1993) show that MXFI can be formulated as an integer program (IP). Thus, BMXFI can be solved as a set of IPs for MXFI, one for each plausible level of interdiction resource. But, MXFI is strongly NP-complete and difficult to solve in practice (Wood 1993) . Hence, solution times could be unacceptable, especially in a time-constrained, military setting. Benders decomposition can be helpful, because it incorporates easy-to-solve maximum-flow subproblems, but the computational expense becomes prohibitive because so many subproblems must be solved (Cormican 1995) . Derbes (1997) , Bingol (2001) and Uygun (2002) devise fast heuristics based on Lagrangian relaxation, but these cannot guarantee good solutions. Implicitly, these authors also consider BMXFI, and construct heuristic solution approaches based on weighted-sums scalarization of the two objective functions.. The solution of a sequence of IPs will typically require that a commercial solver be installed on one or more local computers, and that up-to-date licenses be maintained for those computers. But, analysts at Using the arguments in the proof of Proposition 1, we find that BMXFI is equivalent to. In view of this and ignoring the constant R, we see that MXFI-LR R is the reduction of BMXFI-C by means of weighted-sums scalarization of its objectives, using (unscaled) weights 1 and . Hence, the evaluation of f (see (18)) for a range of -values is equivalent to solving weighted-sums scalarizations using various weights. While we cannot expect to identify the full efficient frontier this way (Climaco et al. 1997) , we hope that a substantial portion can be. Thus, for various values of , we perform the following steps:. 1. Using a maximum-flow algorithm, compute. . Set x k ← 1 whenever u k ≥ r k and k ∈ A C , and set. The solution x R is optimal for MXFI R since k∈A r k x k R = R. For problems MXFI R not immediately solved using these steps, we have a head start because, for any R, z R = f − R ≤ z * R for all values of that the procedure examines.. Let R max be the smallest R such that z * R = 0, i.e., the minimum amount of interdiction resource that can force the adversary's maximum flow to 0. The corresponding interdiction plan is found by setting = min k∈A u k /r k in the previously described procedure. Also, for any > max k∈A u k /r k , the solution obtained corresponds to R = 0. Thus, it suffices to examine values of in the range min k∈A u k /r k + max k∈A u k /r k for some > 0.. Since f is a piecewise-linear function with no more than R max break points, a procedure akin to Benders decomposition could map out z R completely by solving at most R max + 1 max-flow problems. The Benders master problem would be simple enough to solve by inspection. However, the sequence of max-flow min-cut problems would involve widely varying arc capacities and would be harder to solve efficiently than one in which arc capacities are nondecreasing. Consequently, we opt for mapping out the function f approximately, starting with a small value for and increasing it according to an empirically derived rule.. We motivate that rule with a network consisting of a set of parallel arcs of the form k = s t , all with unique ratios u k /r k . In this case, f breaks only at points where some arc capacity min u k r k switches from r k to u k , i.e., at = u k /r k . Therefore, we can map out the function f , and thus the functions z R for all R, by evaluating the maximum flow, or minimum cut capacity, at only these values of .. Naturally, the situation is more complex for a general network. But, for simplicity, let us continue to assume that the ratios u k /r k are unique. Suppose some > 0 has been defined, arc capacities u k = min u k r k have been computed, and a minimum cut C is identified such that u k = u k for at least one k ∈ A C . Without loss of generality, assume r k = u k for any k ∈ A. Now, our example implies that f must break somewhere on the interval where = min k∈A C u k /r k u k /r k > , i.e., between its current value and the value where the function would break if C were the only cut in the network. Since G typically contains a huge number of cuts, some other cut may become "the minimum cut" before reaches . Thus, increasing all the way to tends to overshoot the next breakpoint. This observation, along with empirical testing, leads us to adopt the following rule for computing the next :. for some empirically determined > 0 and ∈ 0 1 . We find that = 0 1 min k∈A min u k r k , and = 0 25 work well in general. This paper describes a new procedure, "Algorithm Interdict," for solving the bi-objective maximum-flow interdiction problem. The algorithm first identifies a large portion of the efficient frontier using weightedsums scalarization of the two objectives to be minimized, maximum flow and total interdiction cost.. We interpret this through the theory of Lagrangian relaxation. A specialized branch-and-bound procedure, involving partial cut enumeration, then identifies any missing parts of that frontier.. We have compared Algorithm Interdict to a hybrid algorithm in computational tests; the hybrid algorithm calls a standard integer-programming solver instead of the specialized branch-and-bound procedure, when the Lagrangian solution from Algorithm Interdict is not -optimal. With rare exceptions, our algorithm is one to two orders of magnitude faster than the hybrid algorithm; on average it is 40 times faster. Its efficiency results from the fact that bounds and s-t cuts are computed via the solutions of interrelated, and easily solved maximum-flow problems. The algorithm may require more enumeration than does linear-programming-based branch and bound, but that enumeration is highly efficient. Algorithm Interdict also provides the benefit of not requiring a licensed solver.. We might attempt to reduce enumeration by improving the Lagrangian lower bound. Indeed, it is clear that the standard solver achieves better bounds through the use of integer cutting planes. If such cutting planes could be identified and Lagrangianized with appropriate multipliers, this could improve the lower bound. Wood (1993) identifies some problemspecific cutting planes that could be explored for this purpose.

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Usability context analysis for virtual reality training in South African mines The usability of any tool or system has to be viewed in terms of the context in which it is used, and its appropriateness to that context. According to the ISO definition of usability, the context of use includes the users, tasks, equipment (hardware, software and materials), and the physical and social environments in which a product is used. Context analysis provides a framework to ensure that all factors which may affect the usability of a product are considered.Safety in the South African mining industry is a vital issue. On average, one worker dies every working day, and about 16 are injured in mine-related accidents. Inadequate or insufficient training is often cited as a root cause for many mining fatalities. However, training outside the direct working environment provides only limited real-life opportunities and may fail to make a significant impact within the tense working environment itself. Virtual reality-based training tools can, by contrast, provide simulated exposure to real-world working conditions without the associated risks. This paper discusses contextual analysis for virtual reality (VR) application development, applied to safety training in mines. This contextual analysis has been conducted to contribute to the usability of future system design. It also provides a basis for designing subsequent usability evaluations. The results of the context analysis were applied to the design of a prototype, which was used and evaluated at two large platinum mines. Usability is a general quality of the appropriateness to a purpose of an artefact [Brooke, 1998 ]. This means the usability of any tool or system has to be viewed in terms of the context in which it is used, and its appropriateness to that context. The International Organisation for Standardisation defines usability as the "extent to which a product can be used by specified users to achieve specified goals with effectiveness, efficiency and satisfaction in a specified context of use" [ISO, 1997] . The context of use includes the users, tasks, equipment (hardware, software and materials), and the physical and social environments in which a product is used. In general, it is impossible to specify the usability of a system without first defining who are the intended users of the system, the tasks those users will perform with it, and the characteristics of the physical, organisational and social environment in which it will be used. The introduction of the interactive simulation training system has been beneficial to the workforce. No statistical data is yet available to prove that the accident rate has been reduced. That will require extensive use of such systems and several years of data collection and analysis. The VR prototype system was well received and provided an interesting and enjoyable alternative to other training programs, while at the same time it also improved the safety culture and awareness of the workforce.. Future work will focus on the introduction of training systems that are more immersive, as well as the development of a usability evaluation framework for such systems. There is also scope for extending the development of interactive simulation training systems beyond the generic hazard awareness systems to several other training milieus, such as trackless moving machinery pre-inspections, smelting plant safety aspects, accident reconstruction simulations, isolation procedures, systematic supervision, conveyor procedures and winch operations. Data collection was done in an integrated fashion addressing several of the context-of-use issues in each data collection instrument or session. The methods used were:. • Semi-structured interviews with mine managers and safety, health and environment (SHE) managers.. • Structured interviews with mine workers.

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