Tight Bounds for Prefetching and Buffer Management Algorithms for Parallel I/O Systems AbstractÐThe I/O performance of applications in multiple-disk systems can be improved by overlapping disk accesses. This requires the use of appropriate prefetching and buffer management algorithms that ensure the most useful blocks are accessed and retained in the buffer. In this paper, we answer several fundamental questions on prefetching and buffer management for distributed-buffer parallel I/O systems. First, we derive and prove the optimality of an algorithm, P-min, that minimizes the number of parallel I/Os. Second, we analyze P-con, an algorithm that always matches its replacement decisions with those of the well-known demand-paged MIN algorithm. We show that P-con can become fully sequential in the worst case. Third, we investigate the behavior of on-line algorithms for multiple-disk prefetching and buffer management. We define and analyze P-lru, a parallel version of the traditional LRU buffer management algorithm. Unexpectedly, we find that the competitive ratio of P-lru is independent of the number of disks. Finally, we present the practical performance of these algorithms on randomly generated reference strings. These results confirm the conclusions derived from the analysis on worst case inputs. C ONTINUING advances in processor architecture and technology have resulted in the I/O subsystem becoming the bottleneck in many applications. The problem is exacerbated by the advent of multiprocessing systems that can harness the power of hundreds of processors in speeding up computation. Improvements in I/O technology are unlikely to keep pace with processor memory speeds, causing many applications to choke on I/O. The increasing availability of cost-effective multiple disk storage systems [6] , [10] provides an opportunity to improve the I/O performance through the use of parallelism. However, it remains a challenging problem to exploit the increased disk bandwidth to reduce the I/O latency of an application. Effective use of parallel I/O systems requires buffer management algorithms that carefully coordinate the prefetching and caching policies.. Prefetching is a powerful technique that can be used to reduce the I/O latency seen by an application. Prefetching refers to reading a block of data from disk before it is actually required by the computation. In a parallel I/O system, prefetching can be used to overlap the operations of the disks. When the computation demands a disk-resident block of data, anticipatory reads on the other disks can be done concurrently to prefetch blocks that will be referenced later. Prefetched blocks are held in the disk buffers until needed. The overlap in the reads can potentially decrease the number of I/Os by a factor equal to the number of disks. However, reading a block from a disk requires evicting some other block from the buffer to make space for the new block. This may trigger an additional I/O in the future in case the evicted block is referenced again. The buffer manager must choose between the relative benefit of increasing disk parallelism by prefetching now, against the increase in the number of I/Os due to suboptimal eviction choices. The actual disk parallelism achievable depends on the distribution of accesses to the disks, the size of the disk buffers and the buffer management policies.. Several different I/O organizations have been proposed for parallel I/O systems [18] , [9] . A recent taxonomy of storage architectures is presented in [10] . Two logical configurations representing extreme points on the spectrum can be identified, based on centralized or distributed organizations of the I/O system. A traditional multipledisk server represents the canonical globally-shared buffer organization. In such a system, the disks are attached to a centralized server using the system I/O bus, and caching is performed centrally at the server. However, such a scheme has limitations for scalability, as both the bus and the server are potential bottlenecks. Distributed storage architectures consisting of multiple disks interconnected by a high-speed network, such as the Fiber Channel Arbitrated Loop (FC-AL), are an emerging trend [10] , [12] , [15] directed towards distributed operation of the disks. In a typical configuration [10] , [15] I/O requests are made to the server which forwards the I/O request to the appropriate disk using the storage network. The disk then fetches the data and communicates it directly back to the client. Each network-attached disk controls the layout and caching of its data, which is performed locally at that disk. This is similar to the distributed buffer model of parallel I/O used in this paper. A third possibility is to simulate a globally shared buffer organization on the physically distributed buffers. The potential gain is better buffer usage by smoothing local load imbalances between disks. The cost is much greater server complexity required to perform central coordination of the distributed cache, more sophisticated processing ability at the individual disks, and increased communication requirements. Cooperative caching in the environment of a network of workstations consisting of powerful processors with attached disks and executing applications directly was studied in [7] .. In this paper, we describe and analyze buffer management algorithms for a distributed I/O architecture. The I/O system consists of several I/O nodes connected together by a communication network. An I/O node consists of a disk and associated disk buffer. Data from a disk is cached in the local buffer of that I/O node. The data for the computation is spread out among the disks in units of blocks. A block is the unit of retrieval from a disk. In each I/O at most one block from each disk can be read and stored in the disk's I/O buffer. The computation is characterized by a reference string, consisting of the ordered sequence of blocks that the computation accesses. A block must be brought into the I/O buffer before it can be delivered to the computation.. The buffer management algorithm is responsible for prefetching and caching decisions that are necessary to service the reference string. Its goal is to service the reference string in the smallest number of I/Os. To do this, it must decide when to initiate an I/O, from which disks to prefetch in an I/O, and from which blocks to evict the corresponding buffers. In order to prefetch, the buffer management algorithm must have some knowledge of the future accesses to be made by the computation [17] . This is referred to as lookahead. Without lookahead, only the block currently demanded by the computation can be fetched, and the disks will operate serially. By using the lookahead, prefetches from other disks can be made concurrently with the demanded block. Lookahead is also beneficial for caching by allowing the buffer manager to make better eviction decisions. We consider two scenarios: in an off-line situation, the entire reference string is available to the buffer management algorithm at the start of the computation; in an on-line situation, only partial knowledge of the future reference string (see Section 2.1) is known to the buffer manager at any time.. In this paper, we address several fundamental issues dealing with prefetching and caching in a distributed-buffer parallel I/O system. We present three algorithms (P-min, P-con, and P-lru), and study their performance using analysis and simulation. We define and prove the optimality of a greedy off-line algorithm, P-min, that minimizes the number of parallel I/Os. Secondly, we show that P-con, an algorithm that attempts to optimize the number of I/Os on each disk in isolation (by mimicking the eviction decisions of the optimal sequential algorithm), can have very poor parallel performance. The analysis of P-con and the simulation results for randomly generated data (see Section 6) underscore the importance of prefetching even when it necessitates making imperfect eviction decisions.. The P-min and P-con algorithms analyzed in this paper are generalizations of the aggressive and conservative policies proposed by Cao et al. [5] for sequential I/O. However, while aggressive is suboptimal in the single disk I/O model of [5] , P-min is proven to be the optimal algorithm in the distributed-buffer parallel I/O model. It is interesting to note that for a single disk, both P-min and Pcon degenerate to the optimal single disk algorithm, MIN [4] . However, in the parallel case, P-min is optimal while P-con can be suboptimal by a factor proportional to the number of disks.. The performance of on-line buffer management algorithms is analyzed in the framework of competitive analysis. In our context, the competitive ratio is the worst case (over all possible reference strings) ratio of the number of I/Os done by the on-line algorithm to the number of I/Os needed by the optimal off-line algorithm P-min, to service the same reference string. We define local lookahead that permits future knowledge of only the next access on each disk, and analyze the performance of P-lru, a parallel online adaptation of the traditional Least Recently Used (LRU) buffer management algorithm, with local lookahead. The competitive ratio of P-lru is shown to be m, the size of each local buffer, and surprisingly, independent of the number of disks. This implies that P-lru reaps the benefits of increased parallelism that P-min gets with an increasing number of disks, while the performance penalty for suboptimal caching due to incomplete future knowledges does not increase. Finally, simulation experiments using synthetic reference strings were performed to study the performance of the algorithms in typical situations.. The rest of the paper is organized as follows: In Section 1.1, we summarize related work. Section 2 discusses the prefetching and caching problem for parallel I/O systems, followed by formal definitions and a summary of the main results. In Section 3, we show that algorithm P-min performs the minimal number of I/Os, and is therefore optimal in the distributed-buffer model. In Section 4, we derive a tight upper bound on the worst case performance of the P-con algorithm. In Section 5, we analyze the worst case performance of the on-line algorithm P-lru. Simulation results that complement and validate the analysis are presented in Section 6. We conclude with a discussion in Section 7. The I/O performance of applications in multiple-disk systems can be improved by overlapping disk accesses. This requires the use of appropriate prefetching and buffer management algorithms that ensure the most useful blocks are accessed and retained in the buffer.. In this paper, we answered several fundamental questions on prefetching and buffer management for a distributed-buffer parallel I/O system. We derived and proved the optimality of a simple greedy prefetching algorithm P-min, that minimizes the number of parallel I/Os. P-min prefetches from a disk whenever the block to be prefetched is required earlier than some block in the buffer.. We analyzed a conservative prefetching algorithm, P-con, that sacrifices prefetching in order to make optimal caching decisions for each disk independently. It only prefetches when it can make the same eviction decisions as the optimal demand-paged sequential algorithm MIN. Both analytical and simulation results indicated that P-con has poor parallel performance that degrades in proportion to the number of disks. The results indicate that greater gains are possible by prefetching, compared to the benefit of making optimal caching decisions.. The importance of prefetching is also demonstrated in the behavior of the on-line algorithm P-lru analyzed in this paper. Because of its ignorance of accesses beyond the block to be prefetched, P-lru's eviction decisions are suboptimal than those of P-min. However, its performance relative to P-min is independent of the number of disks; it therefore gets all the benefits of increased parallelism that P-min gets with increasing the number of disks, while the penalty of suboptimal caching does not increase. Since in practice, LRU is a good caching algorithm with a single disk, the results imply that its parallel counterpart will have good scalable performance with increased I/O-system sizes. (CRIN) in Nancy, France. His main research interests are in the areas of term rewriting and symbolic computation with applications to automated reasoning/verification, functional and equational programming, and computer algebra; storage and access structures for temporal and spatial databases with applications to scientific databases and geographic information systems; and parallel computing. Dr. Verma is a member of the ACM. The formal study of buffer management algorithms for sequential I/O (also known as the paging problem), was pioneered by Belady [4] and Sleator and Tarjan [19] . The sequential paging algorithm MIN, based on the longestforward-distance eviction policy, was shown to minimize the number of page faults [4] . Competitive analysis of online paging algorithms was studied in [19] . It was shown that no deterministic on-line paging algorithm can be better than m-competitive, where m is the size of the mainmemory buffer, and that LRU achieves the best possible competitive ratio. These fundamental results have been expanded to include models that allow different forms of lookahead [1] , [8] , whereby the algorithm has access to some portion of the future request sequence in determining the block to evict. These results deal exclusively with demand-fetched I/O, since in the sequential disk model considered, there is no benefit to be gained by prefetching.. The use of prefetching from a single disk to overlap CPU and I/O operations, was addressed in [5] . As mentioned earlier, two off-line algorithms called aggressive and conservative were analyzed, and bounds on the elapsed time relative to the optimal prefetching algorithm were derived. In a single disk system without prefetching, there is no overlap between the disk and the CPU; in this case, the elapsed time is within a factor two of that achievable by the optimal prefetching algorithm. In the model of [5] , the aggressive algorithm has a worst case ratio between 1 and 2 over optimal prefetching, depending on the relative speeds of the disk and CPU, and the size of the buffer. The issues involved in prefetching in a multiple-disk parallel I/O context were, however, not considered in that paper.. An alternate parallel disk model based on multiple disks sharing a global buffer [21] has been studied from the viewpoint of buffer management. Patterson et al. [17] , Kimbrel and Karlin [13] , Barve et al. [2] , Varman [20] , and Kallahalla and Varman [11] have presented and analyzed different buffer management algorithms under varying assumptions. In the TIP model [17] , Patterson et al. define a cost/benefit model to compare the relative cost of reclaiming a buffer by eviction against the benefit obtained by prefetching a block into that buffer. This is used to guide the decisions of the buffer manager. The approximations made in the model favor the case of shallow prefetching within a small lookahead window and the case when the requests within the lookahead are distributed randomly across the disks. Kimbrel and Karlin [13] considered a more general model with complete off-line knowledge of the reference string and arbitrary load distributions across the disks. They presented a sophisticated approximation algorithm called reverse-aggressive, and analyzed the worst case ratio of the elapsed time relative to the optimal algorithm. Within realistic ranges of technology-related parameters for CPU and disk speeds, typical buffer sizes, and a small number of disks, the approximation ratio was shown to be small. A useful special class of read-once reference strings where each block was accessed exactly once was considered in [2] . On-line algorithms for different models of lookahead were presented and optimal and near-optimal bounds were demonstrated. In [20] , randomized algorithms for read-once reference strings in a global shared-buffer model were presented and analyzed. Recently, in [11] , an on-line algorithm using dynamic, randomized relocation of the blocks for a general reference string was proposed and analyzed.. Parallel prefetching algorithms in the context of specific applications were discussed in [14] , [16] , [3] . In terms of analysis, the shared-buffer model presents a challenging optimization problem for buffer management. At present, there is no known optimal off-line algorithm for general reference strings besides the brute-force search method. In contrast, in this paper we present an optimal off-line algorithm for general reference strings for the distributed buffer model.

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


Health GIS and HIV/AIDS studies: Perspective and retrospective a b s t r a c t GIS (Geographic Information System) is a useful tool that aids and assists in health research, health education, planning, monitoring and evaluation of health programmes that are meant to control and eradicate certain life threatening diseases and epidemics. HIV/AIDS is one such epidemic that poses a serious challenge and threatens the overall human welfare. This communication is an attempt to link and understand the health scenario in a GIS context with emphasis on HIV/AIDS. Various GIS based functionalities for health studies and their scope in analyzing and controlling epidemiological diseases are explored. Overall scenario of the spread of HIV/AIDS around the world is presented along with the Indian perspective. Finally, we conclude with the general management problems, issues and challenges related to HIV/ AIDS prevailing in India. Health is vital for all of us and understanding the determinants of a disease, its spread from person to person and community to community has become increasingly global [1] . As expressed by Scholten and De Lepper [40] , ''health and ill-health are affected by a variety of life-style and environmental factors, including where people live". There are various factors such as climate, environment, water quality and management, education, air pollution, natural disasters, social and many others which are the reasons for the emergence of diseases as shown in Fig. 1 (also known as the The Dahlgren-Whitehead model). The characteristics of these locations (including socio-demographic and environmental exposure) offer a valuable source for epidemiological research studies on health and the environment.. Epidemiological research ranges from outbreak investigation, data collection, design and analysis including the development of statistical models. Since health is a geographical phenomenon and various factors attributing to the health diagnostics and planning are geography dependent, as such, GIS (Geographic Information System) for health studies serves as an important tool. GIS can be useful for health researchers and planners because it plays a vital role in strengthening the whole process of epidemiological surveillance, information management and analysis. It serves as a common platform for convergence of multi-disease surveillance activities. The standardized geo-referencing of epidemiological data facilitates structured approaches to data management. Once the basic structure is ready, it is easy to convert it to surveillance system for any other study. Public health resources, specific diseases and other health events can be mapped in relation to their surrounding environment and existing health and social infrastructures. GIS is being used by public health administrators and professionals, including policy makers, statisticians, regional and district medical officers [44] . Some of its applications in public health are: (1) geographical distribution and variation of diseases (2) analysis of spatial and temporal trends (3) identifying gaps in immunizations (4) mapping populations at risk and stratifying risk factors (5) documenting health care needs of a community and assessing resource allocations (6) forecasting epidemics (7) planning and targeting interventions (8) monitoring diseases and interventions over time (9) managing patient care environments, materials, supplies and human resources (10) monitoring the utilization of health centers (11) route health workers, equipments and supplies to service locations (12) publishing health information using maps, etc.. Health and ill-health therefore, always have a spatial dimension. More than a century ago, epidemiologist and other medical scientists began to explore the potential of maps for understanding the spatial dynamics of diseases. A study carried out by Dr. Snow, [17] is often cited to show that the importance of spatial dynamics in understanding of diseases, and the use of maps to describe and analyze it, is not so recent [8] . Dr. Snow made the hypothesis that cholera might be spread by the infected water supplies more than a century ago using maps to demonstrate the spatial correlation between cholera deaths and contaminated water supplies in the area of Soho in 1854. Scholten and Lepper [40] use the example of AIDS, stressing the importance of spatial distribution of the disease, which they say has been too often overlooked. Another study highlighted that modeling and spatial distribution of AIDS can contribute to both educational interventions and the planning of health care delivery systems [19] . Mapping can play an important role in both areas as it is an excellent means of communication. In order to be of use to resource planners, prediction of AIDS should include a spatial component. Looking into the spatial aspects of health augments the understanding of particular diseases of interest also serves as means to plan interventions and help planners to take important decisions [2, 47] . It is interesting to study and analyze the domain knowledge of GIS and statistics and integrate it with medical science to understand the advances and gaps. It is being widely used in public health, environmental health and epidemiological research in general. World Health Organization (WHO), United Nations Children's Fund (UNCF), US Center for Diseases, United Nations Member States, Public Health Agencies of different countries have been widely using GIS at large in epidemiology. GIS supported by spatial data infrastructure and vibrant routine health data can give planners valuable information to address the issues related to HIV/AIDS and support monitoring, evaluation and planning. GIS can also be used as an effective tool to manage and monitor HIV/AIDS and related routine activities. As health is largely determined by spatial factors (including the socio-cultural and physical environment, which vary greatly in space), it always has an important spatial dimension. Like all powerful technologies, GIS can be applied by practitioners versed in public health methodologies. It can certainly be a tool of prime importance to health research and education. The spatial modeling capacities offered by GIS can help to understand the spatial variation in the incidence of disease, and its covariation with environmental factors with health care.. The facts and figures presented here for the Indian scenario brings out that it is often misleading to consider a country as a homogenous entity as far as HIV/AIDS is concerned. There is a sharp increase in the estimated number of HIV infections that could translate into large numbers of people becoming infected. An understanding of epidemiological principles and methods is required to structure studies and interpret results for proper socioeconomic development at various levels of the society. GIS based mapping is therefore necessary to generalize, symbolize, and classify data so that maps communicate effectively rather than distorting the data behind the map and can aid in combating with the spread of the disease once the geographical incidence, trend of spread and related social-economic-geographical features are ascertained. An appreciation of this fact is important in planning suitable interventions and effective measures for controlling the epidemic.

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


Even Periodic and Odd Periodic Complementary Sequence Pairs from Generalized Boolean Functions A pair of two sequences is called the even periodic (odd periodic) ::: complementary sequence pair if the sum of their even periodic (odd ::: periodic) correlation function is a delta function. The well-known ::: Golay aperiodic complementary sequence pair (Golay pair) is a ::: special case of even periodic (odd periodic) complementary sequence ::: pair. In this paper, we presented several classes of even periodic ::: and odd periodic complementary pairs based on the generalized ::: Boolean functions, but which do not form Gloay pairs. The proposed ::: sequences could be used to design signal sets, which have been ::: applied in direct sequence code division multiple (DS-CDMA) cellular ::: communication systems.

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


OR/MS research in disaster operations management Disasters are large intractable problems that test the ability of communities and nations to effectively protect their populations and infrastructure, to reduce both human and property loss, and to rapidly recover. The seeming randomness of impacts and problems and uniqueness of incidents demand dynamic, real-time, effective and cost efficient solutions, thus making the topic very suitable for OR/MS research. While social sciences and humanities literatures enjoy an abundance of articles on disaster management, the OR/MS community is yet to produce a critical mass. In this paper, we survey the literature to identify potential research directions in disaster operations, discuss relevant issues, and provide a starting point for interested researchers. The experience of the 2004 Indian Ocean Tsunami shows that disasters continue to cause loss of human life, environmental damage, disruption of infrastructure, and economic loss. A review of available databases such as EM-DAT, maintained by the Center for Research on the Epidemiology of Disasters and the United States Office of Foreign Disaster Assistance, DesInventar, a project of La Red and OSSO, and the Disaster Database Project, maintained by the University of Richmond (see Appendix A for the URLs of these databases) demonstrates the scale of the problem. As an example, in 2004 the Disaster Database Project added a variety of events ranging from earthquakes to maritime accidents, averaging three new disasters a day.. On 26 December 2004 the Indian Ocean tsunami killed in excess of 225,000 people and dislocated millions more in countries spread around the 0377-2217/$ -see front matter Ó 2005 Elsevier B.V. All rights reserved. doi: 10.1016/j.ejor.2005.05.016 OceanÕs rim from Kenya to Indonesia. The 2001 bombing of the World Trade Center in New York generated direct and indirect losses that most probably will exceed 50 billion US Dollars. And the human cost of extended genocide in a variety of countries in the last two decades has reached totals varying from 100,000 to 800,000 people per incident. These are large, intractable problems that test the ability of communities, nations, and regions to effectively protect their populations and infrastructure, to reduce both human and property loss, and to rapidly recover. Tens of thousands of dead and billions of dollars of damages signal the existence of significant problems for study by any discipline with the capability of reducing the impacts and improving the response to such events.. There is increasing recognition of the need for study of OR/MS issues in disaster management. Dr. Luk van Wassenhove from INSEAD recently wrote six cases on Humanitarian Logistics in Disaster Situations, commenting that ''the subject of disaster management is an absolutely fascinating one that is growing in importance' ' (Van Wassenhove, 2003) . Another promising development is the announcement of the EURO Management Science Strategic Innovation Prize-MSSIP 2006. The invited topic, OR/MS in Humanitarian Security, is defined as ''all those situations in which the survival, the welfare, the health, or the fundamental rights and liberties of people, whether entire populations or particular social groups, are threatened''. The MSSIP 2006 Jury states that ''from the many challenging problems arising within the humanitarian security area, there is an emerging need to develop new methodologies or new variants of old ones, such as emergency logistics, conflict management and resolution, security assessment, strategic management of crises. . .'' (from http://www.euro-online.org).. The objectives of this paper are to (i) point to issues in disaster operations management, (ii) survey existing OR/MS literature, (iii) suggest future research directions, and (iv) act as a tutorial for interested researchers. We believe operations research has significant application to the management of disaster preparedness programs as part of a unified community effort and to the actual conduct of disaster response operations.. In the following section we explain the boundaries of the study. A review of literature is presented in Section 3. Section 4 suggests future research directions, while Section 5 points to some problems and issues in disaster operations management. Section 6 concludes the paper. Appendix A should direct interested researchers to a sample of organizations and disaster related resources as a starting point. In search for new directions for OR/MS research, disaster operations management shows tremendous potential. Disasters have hit, and will continue hitting our communities, businesses, and economies. It is in everyoneÕs interest to understand how we can manage them effectively and efficiently. Better management of disaster operations will improve readiness, increase response speed, and ease recovery. We have surveyed the OR/MS literature to identify publication trends, issues worthy of further investigation, and problems that have not yet been examined. Appendix A provides a starting point for OR/MS researchers who would like to get a head start in understanding disaster operations and meet others working in this area. The soft, i.e. social and political, nature of DOM problems makes this field suitable for data envelopment analysis, fuzzy systems, systems dynamics, and soft OR. The key question is how do we determine decision rules on what method to use to address specific class of disaster problems? For example, problem structuring methods seem to fit well to unstructured problem situations where multiple actors, multiple perspectives, conflicting interests, important tangibles, and key uncertainties exist in tandem (Mingers and Rosenhead, 2004) . Readers interested in soft OR methods should refer to the special issue of EJOR (v. 152, n. 3 ).. An extension of the question above is whether new techniques could be developed to take advantage of the inherent structure of disaster problems? For situations where our knowledge is incomplete, and uncertainties do not seem to be easily resolved, Bankes (1993) suggests using comprehensive simulation models, preferably of interdisciplinary nature, to capture some aspects of natural phenomena using for example, meteorological or geological principles, and technical details via engineering and social behavior models. Gass (1994) mentions that ''public sector problems are multi-objective, and solutions are good or bad, but not optimal''. One may then consider the option of developing models that satisfy all or most of the system constraints without trying to optimize an objective function. For example, Papamichail and French (1999) use constraint programming to develop feasible evacuation strategies for nuclear emergencies.

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


Enteral versus Parenteral Nutrition: Effect on Intestinal Barrier Function Total parenteral nutrition (TPN), or the complete absence of enteral nutrients, is commonly used in a clinical setting. However, a major consequence of TPN administration is the development of mucosal atrophy and a loss of epithelial barrier function (EBF); and this loss may lead to an increase in clinical infections and septicemia. Our laboratory has investigated the mechanism of this TPN-associated loss of EBF using a mouse model. We have demonstrated that the mucosal lymphoid population significantly changes with TPN, and leads to a rise in interferon gamma (IFN-γ) and decline in interleukin-10 (IL-10) expression-both of which contribute to the loss of EBF. Associated with these cytokine changes is a dramatic decline in the expression of tight junction and adherens junction proteins. This article discusses the potential mechanisms responsible for these changes, and potential strategies to alleviate this loss in EBF. The intestinal epithelium undergoes both morphological and functional changes during total parenteral nutrition (TPN) administration. Many patients, because of either gastrointestinal dysfunction or a lack of intestinal length, are unable to tolerate enteral feedings. These patients are confined to a prolonged course of TPN. It is estimated that over 250,000 patients receive TPN in the United States alone on a yearly basis, 1 resulting in over 11.5 million patient days of care per year. Increasingly, investigators have found that the intestine undergoes significant changes during the administration of TPN with an absence of enteral nutrition. In several TPN animal models, the intestinal epithelium shows a loss of villus height and a decline in epithelial growth. 2, 3 Further analysis of the mucosa shows a loss of epithelial barrier function (EBF) during the administration of TPN. 4 This loss of barrier function may result in endotoxins and even bacteria entering the systemic circulation. TPN results in a loss of villus height, loss of EC proliferation, rise in EC apoptosis, and a marked decline in EBF. Using a mouse model of TPN, the IEL has been shown to undergo significant changes. Such changes may partially account for the mechanism of EBF loss with TPN, and may contribute to the increased incidence of septicemia with TPN administration. The mechanisms by which IEL change with TPN are not known, but data suggests that such changes are due to a lack of enteral nutrition and may be mediated by a decline in EC-derived IL-7. Understanding the mechanisms that are responsible for such changes may lead to the potential for therapeutic options in patients receiving TPN. Further, understanding the changes in the IEL with TPN administration may also yield important information in how EC-IEL interactions take place. Such interactions appear to directly influence observed alterations in the physiology of the intestinal mucosa. Thus, these cell-cell interactions may have important applications in other processes, such as gut adaptation after bowel resection, or during autoimmune processes, such as inflammatory bowel disease.

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


Network Coded Transmission in a Wireless Grid Network with an Energy Constraint Abstract: In wireless networks, routing based on packet forwarding does hardly yield optimum transmission performance in terms of network utilization and throughput. As an alternative to routing, network coding has been introduced in the recent years, where nodes are mixing the data instead of forwarding. In applications, random linear network coding is the most used method, due to its decentralized mode, and due to preserving the achievability of multicast capacity bounds. In this paper, we study the performance of network coding used for multicast transmission of messages in a wireless grid network with an energy constraint. Several energy saving schemes have been proposed in the literature, but in this study we will focus on duty cycling scheme, in which nodes are not always in on state. The performance is measured as the end-to-end delay, i.e. the duration until each node can decode the message sent by the source, and the CDF of observations is used to make analysis. Energy saving is an important factor in wireless transmissions, especially in autonomous devices, i.e. battery operated nodes. In applications like battlefield surveillance, environment and habitat monitoring, sometimes it is hostile, hazardous or impractical to replace or recharge the batteries. The performance of wireless network applications highly depends on the lifetime of the network. For practical applications we expect the lifetime to be from several months to several years, so energy saving is crucial in designing the network.. Energy consumption in a network node can be due to useful sources (transmitting, receiving or processing data) or wasteful sources (channel idle listening, retransmissions due to packet collisions, overhearing, control packets used for errors control). The critical issue is to minimize the energy consumption of network nodes while meeting the application requirements. This paper is organized as follows. In Section II we explain how network coding is applied for wireless networks, marking some advantages of using it. In Section III we describe the scenario of a general multicast transmission in a wireless network. In Section IV we present the problem of energy consumption optimization using duty cycling. Finally, in Section V we present simulation results. This article presents methods for saving energy in a wireless network, in the case of general multicast transmission. The routing of packets inside the network is not store and forward, but mix and forward, namely network coding. We observed the end-to-end delay inside a wireless Network Coded Transmission in a Wireless Grid Network with an Energy Constraint 937 grid network that uses network coding, for different area sizes (i.e. different node density) and for various reception windows for energy saving. A good tradeoff between area and end-toend delay is to choose half of the maximal area, while obtaining at least 30% improvement in speed. Simulations show that energy consumption can be reduced to between 30% and 50%, depending on the duration of the full power on -power off cycle. For sparse networks, the energy

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


Efficient Schemes for Compressed-Domain Image Resizing Fast schemes for compressed-domain image size change, are proposed. Fast Winograd DCTs are applied to resizing images by a factor of two to one. First, we speed up the DCT domain downsampling scheme which uses the bilinear interpolation. Then, we speed up other image resizing schemes which use DCT lowpass truncated approximations. The schemes proposed here reduce the computational complexities significantly, while there is no difference in the overall quality of the images compared to previous works. Changing the size of a video frame is required to convert between image and video compression standards like JPEG, MPEG-1,2,4, and H.26x series [1] . When browsing a remote image (or video), downsampled images may be sent initially and then images of a larger size are sent later depending on the request from the client [2] . Since images are usually stored in the transformed domain as compressed data, it is more efficient to resize images directly in the compressed domain than in the spatial domain (see Fig. 1 ). In other words, compressed domain manipulation can reduce the computational complexity, will enable manipulation of data at lesser rate, and improve the precision of computations [3] compared to the spatial domain approach.. Another application is of transcoding from the digital video (DV) streams to MPEG-2 intra coded streams. Here, the chroma format conversion from 4:1:1 to 4:2:2 requires 1:2 horizontal upsampling for chrominance blocks [3] .. Exact DCT-domain downsampling is as follows. Given four adjacent 8 × 8 DCT coded blocks, construct the 8 × 8 DCT of the four corresponding image blocks scaled down by a factor of two (see Fig. 2 ). The straightforward spatial domain approach consists of performing the inverse DCT (IDCT) for the four input blocks, scaling down the four input blocks using bilinear interpolation to form a single 8×8 image block, and then computing the DCT of this block [5] .. Multiplication-free approximation methods [6] , [7] Manuscript have shown a PSNR value of 37.4 dB [7] when applied to the Lena image and lower computational complexity over the exact DCT-domain downsampling method. To ensure even greater image quality than this, more exact methods like ours or those described in [3] are necessary. A method taking advantage of a quantizer, which is essential part of compression systems has been developed [3] . Based on this method, we present a faster method by using the DCTdomain downsampling property.. Martucci developed a DCT-domain downsampling property [8] . According to this property, we can reduce a DCT coded block size 8 × 8 to that of a size 4× 4 by operating entirely in the DCT domain. However, image compression systems decode DCT coded blocks size 8×8. Thus we propose in this paper a fast algorithm converting four DCT coded blocks of size 4×4 into one DCT coded block of size 8 × 8. To this end, we use not only fast eight-point but also fast four-point DCTs both of which are based on the Winograd DFT algorithms. The new method saves 58% of the number of multiplications and 34% of the number of additions compared to the method described in [3] .. Other image resizing algorithms in [9] use the fact that taking a 4×4 inverse DCT of the 4×4 low frequency coefficients of an 8 × 8 DCT coded block directly, gives a lowpassed and half-decimated block in the spatial domain. We also apply the Winograd DCTs to these methods to accelerate the processing time.. A fast four-point DCT based on the Winograd algorithm is addressed in Sect. 2. In Sect. 3, we briefly describe the DCT-domain downsampling property [8] to convert it into matrix form. Then we combine it with the DCTsize conversion mentioned above. In Sect. 4 A significant improvement in implementation complexity is shown for the compressed domain size change in images by using Winograd DCTs and quantizers. We have significantly accelerated two downsampling schemes which use the bilinear interpolation and DCT lowpass truncated approximation, respectively. The proposed fast algorithm has image quality similar to that in [3] and with much less computational complexity. Also, we have accelerated the processing time of the upsampling scheme which exploits DCT lowpass truncated approximation. We can additionally reduce the computational complexity of proposed schemes by using fixed-point arithmetic for low-cost/low-power applications. We did not implement our schemes using fixed-point arithmetic. However, the fixed-point implementation of our schemes is quite simpler than the floating-point one and also straightforward. In terms of the PSNR and MSE, the overall performance of the fixed-point implementation will be similar with the floating-point one and will not change much.

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


Encoding brain network response to free viewing of videos Abstract A challenging goal for cognitive neuroscience researchers is to determine how mental representations are mapped onto the patterns of neural activity. To address this problem, functional magnetic resonance imaging (fMRI) researchers have developed a large number of encoding and decoding methods. However, previous studies typically used rather limited stimuli representation, like semantic labels and Wavelet Gabor filters, and largely focused on voxel-based brain patterns. Here, we present a new fMRI encoding model to predict the human brain's responses to free viewing of video clips which aims to deal with this limitation. In this model, we represent the stimuli using a variety of representative visual features in the computer vision community, which can describe the global color distribution, local shape and spatial information and motion information contained in videos, and apply the functional connectivity to model the brain's activity pattern evoked by these video clips. Our experimental results demonstrate that brain network responses during free viewing of videos can be robustly and accurately predicted across subjects by using visual features. Our study suggests the feasibility of exploring cognitive neuroscience studies by computational image/video analysis and provides a novel concept of using the brain encoding as a test-bed for evaluating visual feature extraction. Brain encoding models provide effective means to understand how brain activity varies along with the variation in external stimuli and how well the brain activity can be predicted from the quantitatively measured external stimuli. It has been receiving increasing interest and a number of papers have been published in recent few years. Especially, several surveys by (Haynes and Rees 2006; Naselaris et al. 2011; Kay and Gallant 2009; Hasson et al. 2010; Sugase-Miyamoto et al. 2011), and Chen et al. (2014) have provided a broad overview of approaches for encoding including image analysis methodologies, functional magnetic resonance imaging (fMRI) analysis algorithms, machine learning algorithms and region of interest (ROI) selection methods and so on. An encoding model mainly consists of four components: structural substrates for brain response modeling, brain response modeling, external stimuli modeling, and the mapping from stimuli to brain response Chen et al. 2014) .. Although previous studies have yielded remarkable results, in our opinion, three problems are required to be revisited in current encoding studies. The first one is that the quantified external stimuli used in previous works are limited. In most fMRI studies [e.g. (Shirer et al. 2012; Haxby et al. 2001; Sterzer et al. 2008; Peelen et al. 2009; Mitchell et al. 2008; Nishimoto et al. 2011)] , visual features were used to represent external stimuli of image/ video, which includes image grid intensity, color Nishimoto et al. 2011; Miyawaki et al. 2008) , semantic category labels [e.g., (Mitchell et al. 2008) ], and participants rated scores about the external stimuli such as face and human body in a naturalistic video stream (Bartels and Zeki 2004) . However, those representations are generally qualitative and subjective, and thus substantially limit the power of encoding models. To alleviate this problem, researchers tried to model the external stimuli via computational image/video descriptors. For example, Kay (Kay et al. 2008 ) and Naselaris (Naselaris et al. 2009 ) adopted Wavelet Gabor filters to model the texture feature of input image. Bartels (Bartels et al. 2008 ) used a motion energy model to describe visual stimuli of free viewing of movie segments. The computer vision community has developed a large amount of visual feature descriptors to represent image/video from different perspectives, for example, color, shape and motion. These features are typically objective and can be automatically derived by computer vision algorithms. However, whether those computer vision based features are feasible for fMRI encoding models has not been fully examined yet. Furthermore, in the computer vision field, the visual features are typically evaluated by conducting recognition or classification experiments based on image/video benchmarks with their human-labeled ground truth. However, this evaluation mechanism is from an engineering view without taking human brain cognition into full consideration. It is of great interest to explore the feasibility of applying brain encoding models to evaluate and compare various visual features.. The second problem is in the component of structural substrates for functional brain response modeling. The structural substrates provide the base for extracting meaningful information from fMRI data. In existing encoding models, voxel-based and ROI-based methods (Thirion et al. 2007; Polyn et al. 2005; Naselaris et al. 2011; Dumoulin and Wandell 2008; Mitchell et al. 2008 ) have been widely adopted. Voxels and ROIs were determined manually based on neuroscience domain knowledge or automatically based on activation detection using task-fMRI. Although voxels and ROIs-based methods are easy to implement and effective in many existing works, their reproducibility, generalizability and reliability have been limited due to the lack of a common and individualized representation of human brain architecture as pointed out in (Liu 2011; Chen et al. 2014) . To be specific, voxel-based methods pose difficulties in assessing the consistency of encoding models across subjects due to the intrinsic variability of brain structure and functions and thus the lack of precise voxelwise correspondence between subjects (Liu 2011) . Recently, we developed and validated a novel data-driven strategy, namely DICCCOL (dense individualized and common connectivity-based cortical landmarks) , to discover consistent and corresponding structural landmarks across various brains. In total, 358 consistent and corresponding functional landmarks were identified, each of which was optimized to possess maximal group-wise consistency of DTI-derived fiber shape patterns . Moreover, this set of the 358 structural brain landmarks can be accurately and reliably predicted in a subject based only on DTI data ). The DICCCOL system provides an appropriate representation of human brain network and enables the opportunity of exploring the consistency of encoding and decoding brain network responses across subjects.. The third problem is in the component of brain response modeling. In previous encoding literatures Kay et al. 2008; Miyawaki et al. 2008 ), fMRI Blood Oxygen-level Dependent (BOLD) intensities have been widely utilized to measure the brain's functional response. However, many literature reports (Logothetis et al. 2001; Chen et al. 2014; Heeger and Ress 2002) have pointed out that fMRI BOLD signals are often sensitive to physiological motion effect and some non-neuronal noises, which may reduce the reliability of encoding models. Another group of methods adopted the brain activation patterns measured by the GLM (general linear model) (e.g., Haxby et al. 2001; Naselaris et al. 2011; Sterzer et al. 2008; Walther et al. 2009; Mitchell et al. 2008) to construct encoding models. Recently, the results reported in the literatures (Richiardi et al. 2011; Shirer et al. 2012) suggest us that functional connectivity is a new, alternative school of methodologies for quantitatively measuring functional brain response. Essentially, brain function is resulted from large-scale functional connectivities (Haynes and Rees 2006; Lynall et al. 2010; Friston 2009; Hagmann et al. 2010) . The brain's comprehension of visual stimuli can be precisely represented by these functional connectivities and interactions among relevant brain networks (Friston 2009; Hagmann et al. 2010; Lynall et al. 2010) . Notably, a few recent studies (Hu et al. 2012; Han et al. 2013) have demonstrated that functional connectivity is an effective tool to model brain response to free viewing of videos.. These three above described problems motivates us to develop a novel fMRI encoding model to predict the brain's responses to free viewing of videos. The architecture of proposed encoding model is illustrated in Fig. 1 . To represent the visual stimuli, we adopt a number of representative features in computer vision research included RGB histogram, color moments, Histogram of Oriented Optical Flow (HOOF) (Nayak et al. 2011 ) and RGB-SIFT (Van De Sande et al. 2010) . To model the universal brain activity in response to video stimuli across subjects, we use the DICCCOL system to localize largescale cortical ROIs and measured the functional connectivities among them. Afterwards, the encoding model bridging feature space and response space is trained via least-squares support vector regression (LSSVR) (Suykens and Vandewalle 1999) . Experimental results demonstrated that brain network responses during free viewing of videos can be robustly and accurately predicted by those visual features and across different subjects.. The rest of this paper is organized as follows. Section ''Materials and methods'' describes the materials and methods adopted in this paper, including the brain response feature representation procedure and the visual feature extraction pipeline and the specifics of the proposed encoding model. The experiments and results are reported in ''Experimental results'' section. Finally, the discussion and conclusions are drawn in ''Conclusion'' section. In this paper, we proposed an fMRI encoding model to predict brain network responses to free viewing of videos. The brain responses were quantified as the functional interactions in large-scale brain networks identified by recently developed and validated DICCCOL brain landmarks localization system. The encoding model which maps the feature space to the brain response space was trained based on LSSVR. Our experimental results demonstrated that the brain network responses to video stimuli can be robustly and accurately predicted across both different feature spaces and different subjects.. Our major contributions are summarized as follows.. (1) We adopted a number of representative visual features in computational vision analysis community to represent a video sample. As mentioned before, the computational representation of stimuli in feature space is quite limited. The idea of taking advantage of visual features in computational vision community will greatly benefit the encoding and decoding studies. (2) We firstly employed the DICCCOOL system to explore the consistency of the encoding and decoding models across different subjects.. The remarkable reproducibility and predictability of DICCCOLs in individual subject demonstrate great advantages of DICCCOL for inter-subject generalization.. (3) Our study revealed the feasibility of using fMRI-based brain encoding techniques to evaluate visual features. Beyond neuroimaging, our results of testing visual features in encoding model are consistent with computational community which implies inherent correlations between the discriminativeness and the encoding capability of a feature. In future, we will improve the proposed work in the following aspects. First, both the number of participants and the number of natural-stimulus video clips are relatively small. In the future, we will collect a larger scale dataset which includes more participants and uses more video clips as external stimuli, are repeat the studies proposed in this paper. Second, a number of structured visual features in computational community will be applied. Meanwhile, we will derive and test more brain response features reflecting the brain's comprehension of video stimuli. Finally, other alternative brain mapping techniques, such as sparsity constrained regression model, will be investigated and compared with the LSSVR algorithm used in this study. We believe that the combination of functional brain imaging and computational vision research will offer great benefit to both fields.

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


Indirect quantum control for finite-dimensional coupled systems We present a new analysis on the quantum control for a quantum system coupled to a quantum probe. This analysis is based on the coherent control for the quantum system and a hyperthesis that the probe can be prepared in specified initial states. The results show that a quantum system can be manipulated by probe state-dependent coherent control. In this sense, the present analysis provides a new control scheme which combines the coherent control and state preparation technology. Controlling the time evolution [1, 2, 3, 4, 5, 6, 7, 8] of a quantum system is a major task required for quantum information processing. Several approaches to the control of a quantum system have been proposed in the past decade, which can be divided into coherent (unitary) and incoherent (non-unitary) control, according to how the controls enter the dynamics. In the coherent control scheme, the controls enter the dynamics through the system Hamiltonian. It affects the time evolution of the system state, but not its spectrum, i.e., the eigenvalues of the target density matrix ρ f remain unchanged in the dynamics, due to the unitarity of the evolution. In the incoherent control scheme [9, 10, 11, 12] , an auxiliary system, called probe, is introduced to manipulate the target system through their mutual interaction. This incoherent control scheme is of relevance whenever the system dynamics can not be directly accessed, and it provides a non-unitary evolution which is capable for transferring all initial states (pure or mixed) into an arbitrary pure or mixed state. This breaks the limitation for the coherent control mentioned above.. To be specific, Romano and colleagues [9, 10] have investigated accessibility and controllability of a quantum bit (or a two-level system) coupled to a quantum probe, under the condition that the external control affects only the probe. This analysis is based on the Cartan decomposition [13, 14, 15] of the dynamics, and hence it is involved for high-dimensional systems. In Ref. [16] the authors propose a leaning control with a non-equilibrium environment. The results show that by tailoring the dissipative dynamics we can control the quantum system form a given state to a limited set of states (reachable states).. In this paper, we first examine the controllability for two-dimensional systems, then extend the approach to finite-dimensional quantum systems. This analysis is based on the quantum coherent control scheme and the hypothesis that the probe can be prepared in a specified initial state. The advantages of this scheme are threefold. Firstly, it overcomes the difficulty of the Cartan decomposition based analysis. Secondly, it brings a connection between the coherent control and incoherent control for quantum systems, hence it is easy to be generalized to finite-dimensional systems. Finally, this analysis provides a new control scheme, namely quantum states can be manipulated by probe state-dependent coherent control on the quantum system.. Throughout this paper, we describe the state of the controlled quantum system s by a density matrix ρ s , a positive, unit trace operator on the Hilbert space H s of the system. The convex set of all possible states is represented by P s [9] . Its boundary ∂P s is a set of pure states satisfying ρ 2 s = ρ s . By the definition [9] , the system s is controllable if and only if for all pairs (ρ i , ρ f ) ∈ P s × P s , there exists a set of controls g such that ρ s (t = 0) = ρ i and ρ s (t, g = g fixed ) = ρ f for some t ≥ 0. Suppose that the quantum system s interacts with an initially unentangled probe p, whose density matrix is denoted by ρ p on its Hilbert space H p . The time evolution of the composite system of the controlled system and the probe is governed by H = H s + H p + H I , where H s and H p are the free Hamiltonian for the controlled system and the probe, respectively, while H I denotes the coupling of the system and the probe. Since local transformations do not affect the controllability of the system [9] , H s and H p can be ignored safely in the later analysis.. The paper is organized as follows. In Sec. II, we study the controllability of a two-dimensional system in the indirect control scheme, then we extend the approach to arbitrary finite-dimensional systems in Sec. III. Conclusions and discussions are presented in Sec. IV. In this paper we have presented a scheme for indirect control of a quantum system coupled to a probe. This control scheme is actually a combination of coherent control conditioned on the initial state of the probe. For a two-level system, we have proved that the restriction on the initial state for the quantum system can be partly removed. This simplifies the formulation for the controllability. The scheme has been generalized to arbitrary finite dimensional systems and equations to determine the controls are given. We would like to note that the probe is not required to be initially prepared in an arbitrary state but with a specified spectrum. This requirement can be lifted by adding more controls in the composite systems.. This work was supported by NSF of China under grant No. 10775023 and 10675085.

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


Two-dimensional range search based on the voronoi diagram Abstract: This paper studies the two-dimensional range search problem, and constructs a simple and ecient algorithm based on the Voronoi diagram. In this problem, a set of points and a query range are given, and we want to enumerate all the points which are inside the query range as quickly as possible. In most of the previous researches on this problem, the shape of the query range is restricted to particular ones such as rectangles and triangles, and the improvement o n the worst-case performance has been pursued. On the other hand, the algorithm proposed in this paper is intended to accomplish a good average-case performance, and this performance is actually observed by numerical experiments. In these experiments, we compare the execution time of the proposed algorithm with those of other representative algorithms such as those based on the bucketing technique and the k-d tree. We can observe that our algorithm shows the best performance in almost all the cases. The range search [4] [7] [8] [11] is one of the most fundamental and important geometric problems, and has been researched in the eld of computational geometry. This problem has many applications such as computer graphics (for example, ray tracing and hidden surface removal), geographical information system, data-mining and so on. In this problem, a set S of N points and a query range R are given, and we want to enumerate all the points in S which are inside R. Considering that S is usually xed, and query ranges arise many times; we are interested in preprocessing S in order to decrease the search time.. Most of the previous researches on this problem are restricted to the case where the shape of a query range R is orthogonal [1] , half-planar [6] , circular [3] [5] or spherical [2] [12] . In this paper, on the other hand, we propose an algorithm for solving the two-dimensional range search problem for a general shape of a query range R, b y means of a simple technique using the Voronoi diagram. Furthermore, a good average-case performance is observed by n umerical experiments.. In Section 2, we dene the range search problem. In Section 3, we give an ecient algorithm for this problem, which is based on the Voronoi diagram. In Section 4, we experimentally show the performance of this algorithm. Lastly, conclusions are given in Section 5.

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