Division of Computer and Network Systems

Dynamic spectrum access is a new spectrum sharing paradigm that allows secondary users to access the abundant spectrum holes or white spaces in the licensed spectrum bands. DSA is a promising technology to alleviate the spectrum scarcity problem and increase spectrum utilization. While DSA has attracted many research efforts recently, in this article, we discuss the challenges of DSA and aim to shed light on its future. We first give an introduction to the state-of- the-art in spectrum sensing and spectrum sharing. Then, we examine the challenges that prevent DSA from major commercial deployment. We believe that, to address these challenges, a new DSA model is critical, where the licensed users cooperate in DSA and hence much more flexible spectrum sharing is possible. Furthermore, the future DSA model should consider the political, social, economic, and technological factors all together, to pave the way for the commercial success of DSA. To support this future DSA model, the future cognitive radio is expected to have additional components and capabilities, to enforce policy, provide incentive and coexistence mechanisms, etc. We call the future cognitive radio with the expanded capabilities a network radio, and discuss its architecture as well as the design issues for future DSA.

For multiuser communications networks, lightwave technology offers the potential to supply a pool of capacity — to be shared among users — far above that provided by any alternative technology. However, the bandwidth limitation of the electro-optic converters needed to attach each user to the optical medium prevents any one user from accessing more than a tiny fraction of the overall capacity. This paper discusses the problems with conventional approaches for tapping the capacity contained within the optical communications band. It then proposes a new network architecture that permits tapping lightwave's vast capacity potential without requiring a technological breakthrough. With this approach, it becomes possible to create networks that offer hundreds of thousands of gigabits-per-second total capacity, to be shared among users, each limited to a peak rate of 1 Gb/s.

Various possibilities for improving the performance of communications protocols and interfaces so that the slow-software-fast-transmission bottleneck can be alleviated are investigated. An architecture that is an alternative to the existing layered architectures is proposed. The novel feature of the proposed architecture is the reduction in the vertical layering; services that correspond to the definitions of layers four to six in the Open Systems Interconnection Reference Model are combined into a single, horizontally structured layer. This approach lends itself more naturally to parallel implementation. Moreover, the delay of a set of processes implemented in parallel is determined by the delay of the longest process, not by the sum of all the process delays, as is the case in a sequential implementation. In the same way, the total throughput need not be limited by the lowest-capacity process, but can be increased by concurrently performing the function on several devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Model-Driven Engineering (MDE) advocates the use of models at every step of the software development process. Within this context, a team of engineers collectively and collaboratively contribute to a large set of interrelated models. Even if the main focus can be on a single model (e.g. a class diagram model), related elements in other models (e.g. a requirement model) often have to be considered and/or accessed. Moreover, all the involved models do not necessarily conform to the same metamodel and thus may have been built using different independent Domain-Specific Languages (DSLs). Such a situation has already been frequently observed in many large-scale industrial deployments of MDE. Manually coordinating all the involved models, i.e. being able to both manage and use the links existing between them, can become a cumbersome and difficult task. As a proposal to solve this inter-DSL coordination issue, we introduce in this paper a generic and extensible inter-model traceability and navigation environment based on the complementary use of megamodeling and model weaving. We illustrate our solution with a concrete working example.

Checksum and CRC algorithms have historically been studied under the assumption that the data fed to the algorithms was entirely random. This paper examines the behavior of checksums and CRCs over real data from various UNIX&reg; file systems. We show that, when given real data in small to modest pieces (e.g., 48 bytes), all the checksum algorithms have skewed distributions. In one dramatic case, 0.01% of the check values appeared nearly 19% of the time. These results have implications for CRCs and checksums when applied to real data. They also cause a spectacular failure rate for the both TCP and Fletcher's checksums when trying to detect certain types of packet splices.

The process control industry has many uses for multimedia, from incorporating diverse imaging sensors to visualizing, monitoring and controlling time-critical processes. A distributed client-server architecture, together with specialized image-processing hardware and a number of commercial products, demonstrates the effectiveness of using multimedia data in a simulated film-coating process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The simulation of blood flow in the cardiac system has the potential to become an attractive diagnostic tool for many cardiovascular diseases, such as in the case of aneurysm. This potential could be reached if the simulations were to be completed in hours rather than days and without resorting to the use of expensive supercomputers. Therefore we have investigated a possibility of acceleratingmedical computational fluid dynamics (CFD) simulations using graphics processing units (GPUs). Our results for the 3D blood flow in the human abdominal aorta show that by transferring only a part of the computations (linear system solvers) to the GPU, it is possible to make the typical CFD simulations three to four times faster depending on the CFD model being used. Since these simulations were performed on widely available GPUs that had been designed as mass-market PC extension cards, our results suggest that porting larger parts of CFD to GPUs could really bring the technology into hospitals.

This review of existing back-end networks emphasizes the relationship of their storage aspects to the more general concept of local computer networks.

A new method is proposed for the extraction of three-dimensional (3-D) building structures for simulating radio waves propagation in urban environments. The procedure is based on obtaining readily available high-resolution 2-D images (satellite and/or aerial photos) and images on the Internet (e.g., the google earth); and building accurate 3-D models of structures through a process of coordinates and dimensions matching. The new method provides an efficient and economic way for 3-D structure extraction. Combined with the computationally efficient ray-tracing algorithms recently developed by our group and reported in the literature, it is now possible to carry out radio wave propagation predictions for many outdoor urban areas efficiently and accurately.

Purpose – The purpose of this paper is to study cyber-enabled manufacturing systems (CeMS) for additive manufacturing (AM). The technology of AM or solid free-form fabrication has received considerable attention in recent years. Several public and private interests are exploring AM to find solutions to manufacturing problems and to create new opportunities. For AM to be commercially accepted, it must make products reliably and predictably. AM processes must achieve consistency and be reproducible. Design/methodology/approach – An approach we have taken is to foster a basic research program in CeMS for AM. The long-range goal of the program is to achieve the level of control over AM processes for industrial acceptance and wide-use of the technology. This program will develop measurement, sensing, manipulation and process control models and algorithms for AM by harnessing principles underpinning cyber-physical systems (CPS) and fundamentals of physical processes. Findings – This paper describes the challenges facing AM and the goals of the CeMS program to meet them. It also presents preliminary results of studies in thermal modeling and process models. Originality/value – The development of CeMS concepts for AM should address issues such as part quality and process dependability, which are key for successful application of this disruptive rapid manufacturing technology.

SRAM-based weak physically unclonable functions (PUFs) have shown promise regarding tamper sensitive key storage and device ID generation. Weak PUFs rely on intrinsic process variations to produce repeatable and unique start-up behavior. However, noise in the system can affect the start-up behavior and introduce errors. A number of solutions, such as fuzzy extraction and error correcting codes have been proposed to alleviate the effect of noise and generate stable keys. Unfortunately, the overhead from these techniques grows superlinearly with increasing error rate. Alternatively, accelerating device aging or burn-in has been shown to reduce start-up error rate significantly, which leads to reduced overhead for error correction. Unfortunately, burn-in is a time-intensive process and accrues significant production cost. This paper proposes a method to reduce the cumulative burn-in time via quantification of the minimum burn-in requirements for chip. We propose a low-cost proxy to measure the degree of process variation of each device at birth and use previously proposed device aging models to determine the burn-in requirements. Our results show that this procedure reduces cumulative burn-in cost without compromising the resultant reliability of weak PUFs. Furthermore, we analyze the effect of having additional PUF cells, alternate weak PUF designs and transistor technologies on burn-in requirements.

Persons with advanced human immunodeficiency virus (HIV)-1 infection are susceptible to disseminated mycobacterial infections. In the United States, most such infections are caused by Mycobacterium avium or M. intracellulare (i.e., M. avium complex [MAC]). In less developed countries, M. tuberculosis is equally or more prevalent than MAC in persons with HIV-1 infection. Other mycobacterial species have been reported to cause disseminated infection in HIV-infected persons, including Simiae-Avium (SAV) group mycobacteria. SAV group organisms share characteristics of M. avium and M. simiae. Although disseminated (i.e., the isolation of a mycobacterial species from the blood) infection with M. simiae has been reported in HIV-infected persons, another distinct species within the SAV group, M. triplex, was characterized in 1996. Two cases of disseminated infection caused by M. triplex have been reported in HIV-1-positive persons. This report describes four HIV-infected patients from Bangkok, Thailand, and Lilongwe, Malawi, who were infected with SAV group organisms. Because different mycobacterial species are not susceptible uniformly to antimycobacterial agents, accurate identification of mycobacterial species causing an infection is crucial for directing appropriate therapy.

Checksum and CRC algorithms have historically been studied under the assumption that the data fed to the algorithms was entirely random. This paper examines the behavior of checksums and CRCs over real data from various UNIX&amp;reg; file systems. We show that, when given real data in small to modest pieces (e.g., 48 bytes), all the checksum algorithms have skewed distributions. In one dramatic case, 0.01% of the check values appeared nearly 19% of the time. These results have implications for CRCs and checksums when applied to real data. They also cause a spectacular failure rate for the both TCP and Fletcher's checksums when trying to detect certain types of packet splices.

GENERAL COMMENTARY article Front. Physiol., 23 January 2015Sec. Computational Physiology and Medicine Volume 5 - 2014 | https://doi.org/10.3389/fphys.2014.00527

The current evolution of Service-Oriented Computing in ubiquitous systems is leading to the development of context-aware services. These are services whose description is enriched with context information related to the service execution environment and adaptation capabilities. This information is often used for discovery and adaptation purposes. However, in real-life systems context information is naturally dynamic, uncertain and incomplete, which represents an important issue when comparing service description and user requirements. Uncertainty of context information may lead to an inexact match between provided and required service capabilities, and consequently to the non-selection of services. In order to handle uncertain and incomplete context information, we propose a mechanism inspired by graph-comparison for matching contextual service descriptions using similarity measures that allow inexact matching. Service description and requirements are compared using two kinds of similarity measures: local measures, which compare individually required and provided properties, and global measures, which take into account the context description as a whole. We show how the proposed mechanism is integrated in MUSIC, an existing adaptation middleware, and how it enables more optimal adaptation decision making.

The Cancer Research Network (CRN) is a consortium of 12 research groups, each affiliated with a nonprofit integrated health care delivery system, that was first funded in 1998. The overall goal of the CRN is to support and facilitate collaborative cancer research within its component delivery systems. This paper describes the CRN's 20-year experience and evolution. The network combined its members' scientific capabilities and data resources to create an infrastructure that has ultimately supported over 275 projects. Insights about the strengths and limitations of electronic health data for research, approaches to optimizing multidisciplinary collaboration, and the role of a health services research infrastructure to complement traditional clinical trials and large observational datasets are described, along with recommendations for other research consortia.

Research and development work in nanoscience and nanotechnology has generated new fundamental understanding of physical phenomena and material behaviour at the nano-scale. This knowledge has resulted in discoveries of new materials, structures and devices. It is believed that these basic research investments should now lead to new products and applications. The general feeling is that nanotechnology needs to move from fundamentals to practice, from the laboratory to the marketplace. The broad consensus is that we need accelerated research and development investments in nanomanufacturing science to step up transition of nanotechnology and to hasten technology transfer. Such an effort will fulfil nanotechnology’s promise, which to bring about economic and societal benefits. This paper will define and discuss our perspective on nanomanufacturing, describe our manufacturing science programmes ongoing research and development efforts, list manufacturing challenges and discuss how these are being met through our basic research programmes.

In this paper, we propose context-aware profiles and a filtering process for personalising informational content that is delivered to mobile users by Web-based information systems (WIS). The context-aware profiles allow mobile users to express their personal preferences for particular situations they encounter when using a WIS. We argue that the preferences and the needs of a mobile user may vary according to the context in which he uses the system. By defining these profiles, we propose a filtering process that takes into account both the user's current context and the user's preferences for this context. This process selects, in a first step, the context-aware profiles that match the user's current context, and then it filters the available informational content based on the selected profiles.

In order to avoid well-known paradoxes associated with self-referential definitions, higher-order dependent type theories stratify the theory using a countably infinite hierarchy of universes (also known as sorts), Type_0 : Type_1 : *s. Such type systems are called cumulative if for any type A we have that A : Type_i implies A : Type_{i+1}. The Predicative Calculus of Inductive Constructions (pCIC) which forms the basis of the Coq proof assistant, is one such system. In this paper we present the Predicative Calculus of Cumulative Inductive Constructions (pCuIC) which extends the cumulativity relation to inductive types. We discuss cumulative inductive types as present in Coq 8.7 and their application to formalization and definitional translations.

FASTE-CNS is a dynamic communications estimating tool that is accessible through the Internet using a browser such as Internet Explorer or Netscape. It provides means to model the data communications traffic load associated with existing and new applications. FASTE-CNS ultimately resides within NASA GRC's multi-fidelity simulation environment and be an integrated component of GRC's modeling and simulation capability. FASTE-CNS allows a user to dynamically define application message sets and configure communications traffic profiles composed of those message sets. The user also can define a geographical region and assign a number of aircraft to the region. The combination of traffic profiles assigned to regions provides a researcher with an understanding of the quantity and type of air/ground and air/air data link communications that occur in the region. FASTE-CNS also calculates the number of frequencies needed to support communications within the region. This article presents features of FASTE-CNS and the results of field trials conducted in July 2003.