4,216 research outputs found
A variant of nested dissection for solving n by n grid problems
Nested dissection orderings are known to be very effective for solving the sparse positive definite linear systems which arise from n by n grid problems. In this paper nested dissection is shown to be the final step of incomplete nested dissection, an ordering which corresponds to the premature termination of dissection. Analyses of the arithmetic and storage requirements for incomplete nested dissection are given, and the ordering is shown to be competitive with nested dissection under certain conditions
The Apparent Velocity and Acceleration of Relativistically Moving Objects
Although special relativity limits the actual velocity of a particle to ,
the velocity of light, the observed velocity need not be the same as the actual
velocity as the observer is only aware of the position of a particle at the
time in the past when it emits the detected signal. We consider the apparent
speed and acceleration of a particle in two cases, one when the particle is
moving with a constant speed and the other when it is moving with a constant
acceleration. One curious feature of our results is that in both cases, if the
actual velocity of the particle approaches , then the apparent velocity
approaches infinity when it is moving toward the observer and when it is
moving away from the observer.Comment: 9 pages, LaTeX forma
Ultrasonic studies of the magnetic phase transition in MnSi
Measurements of the sound velocities in a single crystal of MnSi were
performed in the temperature range 4-150 K. Elastic constants, controlling
propagation of longitudinal waves reveal significant softening at a temperature
of about 29.6 K and small discontinuities at 28.8 K, which corresponds to
the magnetic phase transition in MnSi. In contrast the shear elastic moduli do
not show any softening at all, reacting only to the small volume deformation
caused by the magneto-volume effect. The current ultrasonic study exposes an
important fact that the magnetic phase transition in MnSi, occurring at 28.8 K,
is just a minor feature of the global transformation marked by the rounded
maxima or minima of heat capacity, thermal expansion coefficient, sound
velocities and absorption, and the temperature derivative of resistivity.Comment: 4 pages, 4 figure
The FEM-2 design method
The FEM-2 parallel computer is designed using methods differing from those ordinarily employed in parallel computer design. The major distinguishing aspects are: (1) a top-down rather than bottom-up design process; (2) the design considers the entire system structure in terms of layers of virtual machines; and (3) each layer of virtual machine is defined formally during the design process. The result is a complete hardware/software system design. The basic design method is discussed and the advantages of the method are considered. A status report on the FEM-2 design is included
Pigment–protein architecture in the light-harvesting antenna complexes of purple bacteria: does the crystal structure reflect the native pigment–protein arrangement?
AbstractStructural analysis of crystallized peripheral (LH2) and core antenna complexes (LH1) of purple bacteria has revealed circular aggregates of high rotational symmetry (C8, C9 and C16, respectively). Quantum-chemical calculations indicate that in particular the waterwheel-like arrangements of pigments should show characteristic structure-sensitive spectroscopic behavior in the near infrared absorption region. Laser-spectroscopic data obtained with non-crystallized, isolated LH2 of Rhodospirillum molischianum are in line with a highly symmetric (C8) circular aggregate, but deviations have been found for LH2 of Rhodobacter sphaeroides and Rhodopseudomonas acidophila. For both the latter, C-shaped incomplete circular aggregates (as seen only recently in electron micrographs of crystallized LH1–reaction center complexes) may be a suitable preliminary model
Crystal structure and characterization of magnesium carbonate chloride heptahydrate
MgCO·MgCl·7HO is the only known neutral magnesium carbonate containing chloride ions at ambient conditions. According to the literature, only small and twinned crystals of this double salt could be synthesised in a concentrated solution of MgCl. For the crystal structure solution, single-crystal diffraction was carried out at a synchrotron radiation source. The monoclinic crystal structure (space group Cc) exhibits double chains of MgO octahedra linked by corners, connected by carbonate units and water molecules. The chloride ions are positioned between these double chains parallel to the (100) plane. Dry MgCO·MgCl·7HO decomposes in the air to chlorartinite, Mg(OH)Cl(CO)·nHO (n = 2 or 3). This work includes an extensive characterization of the title compound by powder X-ray diffraction, thermal analysis, SEM and vibrational spectroscopy
Experimental demonstration of fractional orbital angular momentum entanglement of two photons
The singular nature of a non-integer spiral phase plate allows easy
manipulation of spatial degrees of freedom of photon states. Using two such
devices, we have observed very high dimensional (D > 3700) spatial entanglement
of twin photons generated by spontaneous parametric down-conversion.Comment: submitted to Phys. Rev. Let
"Честный" и "нечестный" маркетинг: пример DeSheli
В статье рассматриваются критерии "честного" и "нечестного" маркетинга, выделены основные принципы маркетинга, описаны методы "недобросовестного" маркетинга, приводятся приемы "нечестного" маркетинга, используемые компанией DeSheli, приведены рекомендации, как не попасться на нечестных маркетологов, а также, если вы поддались провокациям и оформили кредит на косметику, но после того осознали, что совершили ошибку, несколько правил, как вернуть деньги
Dynamic Problems of Evolution
Evolution and growth of natural and man-made processes have impressed human beings from the very beginning. What is evolution? Is it the passage from an initial to a higher stage? What does "higher" mean in a world of many objectives? Is "higher" bound to the existence of monotonous indicators like entropy, or is it "gambling" within a predetermined combinatoric multifold of possibilities?
Questions of this kind arise from the phenomena in our environment, from the spring-off of new species, but also from processes in our man-made technological world. How is the transition of basic innovation to technology and use of the corresponding products by society, what forecast can be made from increasing CO2, in the atmosphere on the impact on climate, from features of seismologic waves on future events etc. That means there is a strong connection between evolution processes and the emphasis of systems analysis as a help for strategic actions.
This paper deals with general considerations about possible growth mechanisms as a base for creating valid growth models. But the main goal is to show how the parameters in growth models can be estimated using on one hand a fuzzy approach together with vector optimization and on the other hand a Bayesian approach. It can be seen that both approaches are useful and applicable and we get informations from one approach which the other one cannot give us. We studied already the growth of cracks in materials, processes well described in [10]. Preliminary results are contained in [13].
Research will be continued to identify the superposition of driving forces and of coupled systems in which oscillations can arise because of time delays between their driving-force pulses
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