357 research outputs found
Improved method for calculation of parameters of electromagnetic and power processes in electric circuits with steel in saturation mode
The reasons for increased degree of saturation of magnetic system of electric machines with a long error-free running
time are substantiated. It is proved that application of the conventional methods of calculation of electromagnetic and
power processes parameters at practical degrees of saturation results in inadmissible errors. During the process of the
problem solution an improved parameter calculation method applicable under the considered conditions is grounded. A
sufficient degree of coincidence of the calculation results with the experimental data as to integral parameters and instantaneous
power and electromagnetic characteristics is obtained.Обґрунтованo причини підвищення ступеню насичення магнітної системи електричних машин із тривалим наробітком
на відмову. Доведено, що застосування існуючих методів розрахунків параметрів електромагнітних та енергетичних
процесів при ступенях насичення, що зустрічаються на практиці, приводить до неприпустимих похибок.
У процесі розв'язку задачі обґрунтовано уточнений метод розрахунку параметрів, застосовний у розглянутих умовах.
Отриманий достатній ступінь збігу результатів розрахунків з даними експериментів за інтегральними параметрами
та миттєвими енергетичними й електромагнітними характеристиками.Обоснованы причины повышения степени насыщения магнитной системы электрических машин с продолжительной
наработкой на отказ. Доказано, что применение существующих методов расчета параметров электромагнитных
и энергетических процессов при встречающихся на практике степенях насыщения приводит к
недопустимым погрешностям. В процессе решения задачи обоснован уточненный метод расчета параметров,
применимый в рассматриваемых условиях. Получена достаточная степень совпадения результатов расчетов
с данными экспериментов по интегральным параметрам и мгновенным энергетическим и электромагнитным
характеристикам
Absence of bimodal peak spacing distribution in the Coulomb blockade regime
Using exact diagonalization numerical methods, as well as analytical
arguments, we show that for the typical electron densities in chaotic and
disordered dots the peak spacing distribution is not bimodal, but rather
Gaussian. This is in agreement with the experimental observations. We attribute
this behavior to the tendency of an even number of electrons to gain on-site
interaction energy by removing the spin degeneracy. Thus, the dot is predicted
to show a non trivial electron number dependent spin polarization. Experimental
test of this hypothesis based on the spin polarization measurements are
proposed.Comment: 13 pages, 3 figures, accepted for publication in PRL - a few small
change
Discriminative stimulus properties of 1.25 mg/kg clozapine in rats: Mediation by serotonin 5-HT2 and dopamine D4 receptors
The atypical antipsychotic drug clozapine remains one of most effective treatments for schizophrenia, given a lack of extrapyramidal side effects, improvements in negative symptoms, cognitive impairment, and in symptoms in treatment-resistant schizophrenia. The adverse effects of clozapine, including agranulocytosis, make finding a safe clozapine-like a drug a goal for drug developers. The drug dis- crimination paradigm is a model of interoceptive stimulus that has been used in an effort to screen experimental drugs for clozapine-like atypical antipsychotic effects. The present study was conducted to elucidate the receptor-mediated stimulus properties that form this clozapine discriminative cue by testing selective receptor ligands in rats trained to discriminate a 1.25 mg/kg dose of clozapine from vehicle in a two choice drug discrimination task. Full substitution occurred with the 5-HT2A inverse agonist M100907 and the two preferential D4/5-HT2/α1 receptor antagonists Lu 37-114 ((S)-1-(3-(2-(4- (1H-indol-5-yl)piperazin-1-yl)ethyl)indolin-1-yl)ethan-1-one) and Lu 37-254 (1-(3-(4-(1H-indol-5-yl) piperazin-1-yl)propyl)-3,4-dihydroquinolin-2(1H)-one). Partial substitution occurred with the D4 re- ceptor antagonist Lu 38-012 and the α1 adrenoceptor antagonist prazosin. Drugs selective for 5-HT2C, 5-HT6 muscarinic, histamine H1, and benzodiazepine receptors did not substitute for clozapine. The present findings suggest that 5-HT2A inverse agonism and D4 receptor antagonism mediate the dis- criminative stimulus properties of 1.25 mg/kg clozapine in rats, and further confirm that clozapine produces a complex compound discriminative stimulus
Mesoscopic fluctuations of the ground state spin of a small metal particle
We study the statistical distribution of the ground state spin for an
ensemble of small metallic grains, using a random-matrix toy model. Using the
Hartree Fock approximation, we find that already for interaction strengths well
below the Stoner criterion there is an appreciable probability that the ground
state has a finite, nonzero spin. Possible relations to experiments are
discussed.Comment: 4 pages, RevTeX; 1 figure included with eps
On the computation of zone and double zone diagrams
Classical objects in computational geometry are defined by explicit
relations. Several years ago the pioneering works of T. Asano, J. Matousek and
T. Tokuyama introduced "implicit computational geometry", in which the
geometric objects are defined by implicit relations involving sets. An
important member in this family is called "a zone diagram". The implicit nature
of zone diagrams implies, as already observed in the original works, that their
computation is a challenging task. In a continuous setting this task has been
addressed (briefly) only by these authors in the Euclidean plane with point
sites. We discuss the possibility to compute zone diagrams in a wide class of
spaces and also shed new light on their computation in the original setting.
The class of spaces, which is introduced here, includes, in particular,
Euclidean spheres and finite dimensional strictly convex normed spaces. Sites
of a general form are allowed and it is shown that a generalization of the
iterative method suggested by Asano, Matousek and Tokuyama converges to a
double zone diagram, another implicit geometric object whose existence is known
in general. Occasionally a zone diagram can be obtained from this procedure.
The actual (approximate) computation of the iterations is based on a simple
algorithm which enables the approximate computation of Voronoi diagrams in a
general setting. Our analysis also yields a few byproducts of independent
interest, such as certain topological properties of Voronoi cells (e.g., that
in the considered setting their boundaries cannot be "fat").Comment: Very slight improvements (mainly correction of a few typos); add DOI;
Ref [51] points to a freely available computer application which implements
the algorithms; to appear in Discrete & Computational Geometry (available
online
Ground-state energy and spin in disordered quantum dots
We investigate the ground-state energy and spin of disordered quantum dots
using spin-density-functional theory. Fluctuations of addition energies
(Coulomb-blockade peak spacings) do not scale with average addition energy but
remain proportional to level spacing. With increasing interaction strength, the
even-odd alternation of addition energies disappears, and the probability of
non-minimal spin increases, but never exceeds 50%. Within a two-orbital model,
we show that the off-diagonal Coulomb matrix elements help stabilize a ground
state of minimal spin.Comment: 10 pages, 2 figure
Spin magnetization of strongly correlated electron gas confined in a two-dimensional finite lattice
The influence of disorder and interaction on the ground state polarization of
the two-dimensional (2D) correlated electron gas is studied by numerical
investigations of unrestricted Hartree-Fock equations. The ferromagnetic ground
state is found to be plausible when the electron number is lowered and the
interaction and disorder parameters are suitably chosen. For a finite system at
constant electronic density the disorder induced spin polarization is cut off
when the electron orbitals become strongly localized to the individual network
sites. The fluctuations of the interaction matrix elements are calculated and
brought out as favoring the ferromagnetic instability in the extended and weak
localization regime. The localization effect of the Hubbard interaction term is
discussed.Comment: 7 pages, 9 figure
Classification of integrable Weingarten surfaces possessing an sl(2)-valued zero curvature representation
In this paper we classify Weingarten surfaces integrable in the sense of
soliton theory. The criterion is that the associated Gauss equation possesses
an sl(2)-valued zero curvature representation with a nonremovable parameter.
Under certain restrictions on the jet order, the answer is given by a third
order ordinary differential equation to govern the functional dependence of the
principal curvatures. Employing the scaling and translation (offsetting)
symmetry, we give a general solution of the governing equation in terms of
elliptic integrals. We show that the instances when the elliptic integrals
degenerate to elementary functions were known to nineteenth century geometers.
Finally, we characterize the associated normal congruences
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