Papers by Almadena Chtchelkanova
Science, Jan 3, 2003
Large-scale three-dimensional numerical simulations of the deflagration stage of a thermonuclear ... more Large-scale three-dimensional numerical simulations of the deflagration stage of a thermonuclear supernova explosion show the formation and evolution of a highly convoluted turbulent flame in a gravitational field of an expanding carbon-oxygen white dwarf. The flame dynamics is dominated by the gravity-induced Rayleigh-Taylor instability that controls the burning rate. The thermonuclear deflagration releases enough energy to produce a healthy explosion. The turbulent flame, however, leaves large amounts of unburnt and partially burnt material near the star center, whereas observations imply these materials only in outer layers. This disagreement could be resolved if the deflagration triggers a detonation.
Bulletin of the American Astronomical Society, Oct 1, 2019
HAL (Le Centre pour la Communication Scientifique Directe), 2011
Many personal computers and workstations have two or four cores (that is, CPUs) that enable multi... more Many personal computers and workstations have two or four cores (that is, CPUs) that enable multiple threads to be executed simultaneously. Computers in the near future are expected to have significantly more cores. To take advantage of the hardware of today and tomorrow, you can parallelize your code to distribute work across multiple processors. In the past, parallelization required low-level manipulation of threads and locks. Visual Studio 2010 and the .NET Framework 4 enhance support for parallel programming by providing a new runtime, new class library types, and new diagnostic tools. These features simplify parallel development so that you can write efficient, fine-grained, and scalable parallel code in a natural idiom without having to work directly with threads or the thread pool. The following illustration provides a high-level overview of the parallel programming architecture in the .NET Framework 4.
ABSTRACT Parallelism pervades all aspects of modern computing, from in-home devices such as cell ... more ABSTRACT Parallelism pervades all aspects of modern computing, from in-home devices such as cell phones to large-scale supercomputers. Recognizing this - and motivated by the premise that every undergraduate student in a computer-related field should be prepared to cope with parallel computing - a working group sponsored by NSF and IEEE/TCPP, and interacting with the ACM CS2013 initiative, has developed guidelines for assimilating parallel and distributed computing (PDC) into the core undergraduate curriculum. Over 100 Early-Adopter institutions worldwide are currently modifying their computer-related curricula in response to the guidelines. Additionally, the CDER Center for Curriculum Development and Educational Resources, which grew out of the working group, is currently assembling a book of contributed essays on how to teach PDC topics in lower-level CS/CE courses, to fill the serious lack of textual material for students and instructors. This session is intended: (i) to report on the current state of this initiative; (ii) to bring together authors of book chapters and Early Adopters and other interested parties for discussions on ongoing activities and needs; (iii) to discuss the initiative and collect direct feedback from the community.
The Astrophysical Journal, Oct 20, 1999
We numerically studied the explosion of a supernova caused by supersonic jets present in its cent... more We numerically studied the explosion of a supernova caused by supersonic jets present in its center. The jets are assumed to be generated by a magneto-rotational mechanism when a stellar core collapses into a neutron star. We simulated the process of the jet propagation through the star, jet breakthrough, and the ejection of the supernova envelope by the lateral shocks generated during jet propagation. The end result of the interaction is a highly nonspherical supernova explosion with two high-velocity jets of material moving in polar directions, and a slower moving, oblate, highly distorted ejecta containing most of the supernova material. The jet-induced explosion is entirely due to the action of the jets on the surrounding star and does not depend on neutrino transport or re-acceleration of a stalled shock. The jet mechanism can explain the observed high polarization of Type Ib,c and Type II supernovae, pulsar kicks, very high velocity material observed in supernova remnants, indications that radioactive material was carried to the hydrogen-rich layers in SN1987A, and some others observations that are very difficult or impossible to explain by the neutrino energy deposition mechanism. The breakout of the jet from a compact, hydrogen-deficient core may account for the gamma-ray bursts and radio outburst associated with SN 1998bw/GRB980425.
Object-oriented analysis (OOA) is an orderly and systematic approach for the development of softw... more Object-oriented analysis (OOA) is an orderly and systematic approach for the development of software systems. Software systems developed in the OOA method are readily tested and validated. There are, however, many systems that were developed either previous to the availability of the OOA methodology or without its use. Many of these systems still exist, are frequently modified and thus must be retested after modification. There is a significant need for a capability for organized and systematic testing of existing software. In this thesis we show how the OOA methodology can be used to develop a test suite for existing software to facilitate maintenance and modification of the existing software. The current practice in testing existing software systems is largely an ad hoc process of trial and error, ranging from random testing to exhaustive testing. Use of the OOA methodology provides an orderly and systematic process for hierarchical development of test suites, even for existing software. This concept is illustrated by development of a test suite for the Unix Sockets Library system. Sockets are abstract objects which implemellt interprocess communication between unrelated processes in Unix.
Springer eBooks, 2003
This book originated as a series of lectures that were given as part of a Summer School on Spintr... more This book originated as a series of lectures that were given as part of a Summer School on Spintronics in the end of August, 1998 at Lake Tahoe, Nevada. It has taken some time to get these lectures in a form suitable for this book and so the process has been an iterative one to provide current information on the topics that are covered. There are some topics that have developed in the intervening years and we have tried to at least alert the readers to them in the Introduction where a rather complete set of references is provided to the current state of the art. The field of magnetism, once thought to be dead or dying, has seen a remarkable rebirth in the last decade and promises to get even more important as we enter the new millennium. This rebirth is due to some very new insight into how the spin degree of freedom of both electrons and nucleons can play a role in a new type of electronics that utilizes the spin in addition to or in place of the charge. For this new field to mature and prosper, it is important that students and postdoctoral fellows have access to the appropriate literature that can give them a sound basis in the fundamentals of this new field and I hope that this book is a very good start in this direction. The Chapter 1 covers the physical concepts related to the magnetic and electrical properties of transition metal oxides. These materials are important for some of the existing as well as future applications of spintronics. Chapter 2 provides a fundamental description of the origins of magnetocrystalline anisotropy resulting from spin-orbit interactions and magnetism. It also deals with the magneto-optic properties of materials such as the Kerr and Faraday effects which are important tools for understanding magnetic properties of materials. Chapter 3 addresses many of the theoretical aspects of spin transport, mostly in metallic systems. Chapter 4 provides an overview of experimental results on spin transport and covers such topics as GMR and spin dependent tunneling. Chapter 5 describes in detail methods for quantitative measurements of the magnetization of materials. This chapter provides a detailed description of magnetic units and their connection to the measurements of magnetic properties. Instruments described in this chapter are the vibrating sample magnetometer, the SQUID magnetometer, Mossbauer spectrometers and NMR spectrometers. Chapter 6 reviews experimental techniques for looking at surface magnetism and involves Kerr microscopy, scanning electron microscopy with polarization analysis, magnetic force microscopy, x-ray dichroism, etc. v vi PREFACE Chapter 7 discusses the origins of magnetic noise that in some sense is the limiting characteristic for many state of the art magnetic devices including magnetic disk storage. Chapter 8 describes the methods for preparing thin films of magnetic materials that include molecular beam epitaxy (MBE), sputtering and pulsed laser deposition. Chapter 9 is a description of magnetic sensors, Chapter 10 is a detailed description of magneto-resistive memories and Chapter 11 is a description of hybrid magnetic devices. I hope that this book will provide an important introduction to the very exciting and potentially revolutionary field of spin electronics.
Computer Communication Review, Oct 15, 2004
As classical information technology approaches limits of size and functionality, practitioners ar... more As classical information technology approaches limits of size and functionality, practitioners are searching for new paradigms for the distribution and processing of information. Our goal in this Introduction is to provide a broad view of the beginning of a new era in information technology, an era of quantum information, where previously underutilized quantum effects, such as quantum superposition and entanglement, are employed as resources for information encoding and processing. The ability to distribute these new resources and connect distant quantum systems will be critical. We present an overview of network implications for quantum communication applications, and for quantum computing. This overview is a selection of several illustrative examples, to serve as motivation for the network research community to bring its expertise to the development of quantum information technologies.
Combustion and Flame, Apr 1, 1999
The interaction of a shock wave and a sinusoidally perturbed premixed flame was studied by solvin... more The interaction of a shock wave and a sinusoidally perturbed premixed flame was studied by solving the reactive Navier-Stokes equations with flame front resolved. An idealized chemical model was used that reproduces the combustion properties of a stoichiometric acetylene-air mixture. The interaction increases the surface area of the flame and the energy release in the system. The increase in energy release is due to two effects: the increase in surface area and the increase in the density of the compressed material. The timescale of the growth of the energy release is the Richtmyer-Meshkov characteristic timescale. The interaction creates vorticity, and the vortices act to maintain a high level of energy release long after the shock wave has passed through the flame. The strength of this vorticity is not enough to stretch and locally extinguish the flame. Three-dimensional perturbations of the same amplitude and wavelength grow a factor of Ӎ2 faster than the two-dimensional perturbations, and the maximum energy release rate is a factor of Ӎ2 larger. The calculations show that the maximum increase in the energy generation rate due to a single interaction of a shock and a flame does not exceed a factor of 20 to 30. To greatly increase the burning rate, multiple shock-flame interactions are required.
The Astrophysical Journal, 1999
We numerically studied the explosion of a supernova caused by supersonic jets present in its cent... more We numerically studied the explosion of a supernova caused by supersonic jets present in its center. The jets are assumed to be generated by a magneto-rotational mechanism when a stellar core collapses into a neutron star. We simulated the process of the jet propagation through the star, jet breakthrough, and the ejection of the supernova envelope by the lateral shocks generated during jet propagation. The end result of the interaction is a highly nonspherical supernova explosion with two high-velocity jets of material moving in polar directions, and a slower moving, oblate, highly distorted ejecta containing most of the supernova material. The jet-induced explosion is entirely due to the action of the jets on the surrounding star and does not depend on neutrino transport or re-acceleration of a stalled shock. The jet mechanism can explain the observed high polarization of Type Ib,c and Type II supernovae, pulsar kicks, very high velocity material observed in supernova remnants, indications that radioactive material was carried to the hydrogen-rich layers in SN1987A, and some others observations that are very difficult or impossible to explain by the neutrino energy deposition mechanism. The breakout of the jet from a compact, hydrogen-deficient core may account for the gamma-ray bursts and radio outburst associated with SN 1998bw/GRB980425.
Bulletin of the American Astronomical Society, Oct 1, 2019
Science, 2001
This review describes a new paradigm of electronics based on the spin degree of freedom of the el... more This review describes a new paradigm of electronics based on the spin degree of freedom of the electron. Either adding the spin degree of freedom to conventional charge-based electronic devices or using the spin alone has the potential advantages of nonvolatility, increased data processing speed, decreased electric power consumption, and increased integration densities compared with conventional semiconductor devices. To successfully incorporate spins into existing semiconductor technology, one has to resolve technical issues such as efficient injection, transport, control and manipulation, and detection of spin polarization as well as spin-polarized currents. Recent advances in new materials engineering hold the promise of realizing spintronic devices in the near future. We review the current state of the spin-based devices, efforts in new materials fabrication, issues in spin transport, and optical spin manipulation.
IBM Journal of Research and Development, 2006
Spintronics is a rapidly emerging field of science and technology that will most likely have a si... more Spintronics is a rapidly emerging field of science and technology that will most likely have a significant impact on the future of all aspects of electronics as we continue to move into the 21st century. Conventional electronics are based on the charge of the electron. Attempts to use the other fundamental property of an electron, its spin, have given rise to a new, rapidly evolving field, known as spintronics, an acronym for spin transport electronics that was first introduced in 1996 to designate a program of the U.S. Defense Advanced Research Projects Agency (DARPA). Initially, the spintronics program involved overseeing the development of advanced magnetic memory and sensors based on spin transport electronics. It was then expanded to included Spins IN Semiconductors (SPINS), in the hope of developing a new paradigm in semiconductor electronics based on the spin degree of freedom of the electron. Studies of spin-polarized transport in bulk and low-dimensional semiconductor structures show promise for the creation of a hybrid device that would combine magnetic storage with gain-in effect, a spin memory transistor. This paper reviews some of the major developments in this field and provides a perspective of what we think will be the future of this exciting field. It is not meant to be a comprehensive review of the whole field but reflects a bias on the part of the authors toward areas that they believe will lead to significant future technologies.
Funded by the Computing Research Association's (CRA) Computing Community Consortium (CCC) as ... more Funded by the Computing Research Association's (CRA) Computing Community Consortium (CCC) as a " visioning exercise " meant to promote forward thinking in computing research and then bring these ideas to a funded program.
In this paper, we introduce a new parallel library effort, as part of the PLAPACK project, that a... more In this paper, we introduce a new parallel library effort, as part of the PLAPACK project, that attempts to address discrepencies between the needs of applications and parallel libraries. A number of contributions are made, including a new approach to matrix distribution, new insights into layering parallel linear algebra libraries, and the application of ``object based'''' programming techniques which have recently become popular for (parallel) scientific libraries. We present an overview of a prototype library, the SL_Library, which incorporates these ideas. Preliminary performance data shows this more application-centric approach to libraries does not necessarily adversely impact performance, compared to more traditional approaches.
We present the results of three-dimensional hydrodynamical simulations of the subsonic thermonucl... more We present the results of three-dimensional hydrodynamical simulations of the subsonic thermonuclear burning phase in type Ia supernovae. The burning front model contains no adjustable parameters so that variations of the explosion outcome can be linked directly to changes in the initial conditions. In particular, we investigate the influence of the initial flame geometry on the explosion energy and find that it appears to be weaker than in 2D. Most importantly, our models predict global properties such as the produced nickel masses and ejecta velocities within their observed ranges without any fine tuning.
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Papers by Almadena Chtchelkanova