5,208 research outputs found

    The Korteweg-de Vries equation and water waves. Part 2. Comparison with experiments

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    The Korteweg-de Vries (KdV) equation is tested experimentally as a model for moderate amplitude waves propagating in one direction in relatively shallow water of uniform depth. For a wide range of initial data, comparisons are made between the asymptotic wave forms observed and those predicted by the theory in terms of the number of solitons that evolve, the amplitude of the leading soliton, the asymptotic shape of the wave and other qualitative features. The KdV equation is found to predict accurately the number of evolving solitons and their shapes for initial data whose asymptotic characteristics develop in the test section of the wave tank. The accuracy of the leading-soliton amplitudes computed by the KdV equation could not be conclusively tested owing to the viscous decay of the measured wave amplitudes; however, a procedure is presented for estimating the decay in amplitude of the leading wave. Computations suggest that the KdV equation predicts the amplitude of the leading soliton to within the expected error due to viscosity (12%) when the non-decayed amplitudes are less than about a quarter of the water depth. Indeed, agreement to within about 20% is observed over the entire range of experiments examined, including those with initial data for which the non-decayed amplitudes of the leading soliton exceed half the fluid depth

    Actors: The Ideal Abstraction for Programming Kernel-Based Concurrency

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    GPU and multicore hardware architectures are commonly used in many different application areas to accelerate problem solutions relative to single CPU architectures. The typical approach to accessing these hardware architectures requires embedding logic into the programming language used to construct the application; the two primary forms of embedding are: calls to API routines to access the concurrent functionality, or pragmas providing concurrency hints to a language compiler such that particular blocks of code are targeted to the concurrent functionality. The former approach is verbose and semantically bankrupt, while the success of the latter approach is restricted to simple, static uses of the functionality. Actor-based applications are constructed from independent, encapsulated actors that interact through strongly-typed channels. This paper presents a first attempt at using actors to program kernels targeted at such concurrent hardware. Besides the glove-like fit of a kernel to the actor abstraction, quantitative code analysis shows that actor-based kernels are always significantly simpler than API-based coding, and generally simpler than pragma-based coding. Additionally, performance measurements show that the overheads of actor-based kernels are commensurate to API-based kernels, and range from equivalent to vastly improved for pragma-based annotations, both for sample and real-world applications

    The U.S. economy: a brighter outlook after a bumpy ride

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    Economic conditions - United States

    On-board processing satellite network architecture and control study

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    The market for telecommunications services needs to be segmented into user classes having similar transmission requirements and hence similar network architectures. Use of the following transmission architecture was considered: satellite switched TDMA; TDMA up, TDM down; scanning (hopping) beam TDMA; FDMA up, TDM down; satellite switched MF/TDMA; and switching Hub earth stations with double hop transmission. A candidate network architecture will be selected that: comprises multiple access subnetworks optimized for each user; interconnects the subnetworks by means of a baseband processor; and optimizes the marriage of interconnection and access techniques. An overall network control architecture will be provided that will serve the needs of the baseband and satellite switched RF interconnected subnetworks. The results of the studies shall be used to identify elements of network architecture and control that require the greatest degree of technology development to realize an operational system. This will be specified in terms of: requirements of the enabling technology; difference from the current available technology; and estimate of the development requirements needed to achieve an operational system. The results obtained for each of these tasks are presented

    Exchange-Rate Risk Mitigation with Price-Level-Adjusting Mortgages: The Case of the Mexican UDI

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    In 1995, Mexico introduced a credit system based on a price-level-adjusting unit of account called the Unidad de Inversion (UDI, pronounced “oo-dee”), which is Spanish for “unit of investment.” The Bank of Mexico maintains an UDI Index, which sets the peso value of an UDI on any given day. Loans denominated in UDIs maintain their purchasing power and provide a real rate of return in the local currency, pesos. The focus of this study is the real rate of return earned by dollar investors in UDI mortgages. Most dollar investors fear exposure to exchange rate losses in unstable currencies. In this paper, we examine the real-dollar rate of return and the extent to which the inflation adjusting aspect of the UDI mitigates the losses from currency devaluations. We also examine exchange-rate patterns relative to purchasing-power-parity to find investment strategies that increase the real-dollar rate of return on investments in Mexico’s UDI mortgages.

    Evidence

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    The principal developments and trends to be noted in the law of evidence appeared this year in appellate Court decisions. The legislative changes were few. Only one legislative change seems likely to be of any significance and will be felt primarily by drivers accused of being under the influence of intoxicating liquor. For lawyers, the notable developments appear in the case law; it is likely that the courts will remain the primary arena for the development of the law of evidence for some time to come

    Action of diatoms on clay

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    With the recent trend toward the use of higher temperatures and more severe service conditions in the metallurgical and refractories industries there has developed a constantly greater demand for high-alumina clays, that is, clays in which the alumina content is considerably above that of pure kaolinite, Al₂O₃2SiO₂·H₂O. However, the known reserves of good diaspors are so small that ceramic engineers are already turning to basic refractories in order to have sufficient materials for work at high temperatures. Even the slightest reflection on the needs of the refractories industry will show that such substitutions are strictly limited, and possible only where the new material does not introduce further complications and difficulties. Since 1891 it has been known that diatoms can decompose clay to obtain the silica for their frustules. Recent research in the Academy of Science of the USSR has elucidated some of the finer points of this action of diatoms, but as the work was done in pure culture, and in minute quantities, there remains the question, can diatoms be induced to grow on a large enough scale so that man can use them to raise the alumina content of clays? In the conviction that in the near future there will be a demand for high-alumina clays greater than the supply, this study was undertaken in order to learn whether an industrially practical process could be worked out, and if not, at least some further addition to knowledge could be made --Introduction, page 1

    Evidence

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    On January 1, 1967, the California Evidence Code began to govern trials held in California courts. Because of the delays necessarily incident to litigation, the appellate courts were not called upon to review trials held under the new rules in significant numbers until 1968. With the 1968 decisions, however, the impact of the Code upon California practice has become fairly apparent. At the same time, the courts have continued to develop rules of evidence designed to implement the various procedural guarantees found in the Constitution of the United States, and some of these court-developed rules have had significant effect, particularly in criminal cases. Meanwhile, the legislature was content to make few, and only minor, changes in the statutory law of evidence. Thus the principal arena for securing changes in evidence law has shifted from the legislature to the courts
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