4,771 research outputs found
Mutual effect of thermochemical surface decomposition and viscous interaction during hypersonic flow past a sharp cone
Numerical results on the hypersonic gas flow in viscous interaction regime past sharp circular cones with thermally destructible Teflon surface are presented. Characteristics of the mutual influence between the thermochemical decomposition of the surface and the viscous interaction are revealed
Structure and stability of chiral beta-tapes: a computational coarse-grained approach
We present two coarse-grained models of different levels of detail for the
description of beta-sheet tapes obtained from equilibrium self-assembly of
short rationally designed oligopeptides in solution. Here we only consider the
case of the homopolymer oligopeptides with the identical sidegroups attached,
in which the tapes have a helicoid surface with two equivalent sides. The
influence of the chirality parameter on the geometrical characteristics, namely
the diameter, inter-strand distance and pitch, of the tapes have been
investigated. The two models are found to produceequivalent results suggesting
a considerable degree of universality in conformations of the tapes.Comment: 24 pages, 5 PS figures. Accepted to J. Chem. Phy
The partition function versus boundary conditions and confinement in the Yang-Mills theory
We analyse dependence of the partition function on the boundary condition for
the longitudinal component of the electric field strength in gauge field
theories. In a physical gauge the Gauss law constraint may be resolved
explicitly expressing this component via an integral of the physical
transversal variables. In particular, we study quantum electrodynamics with an
external charge and SU(2) gluodynamics. We find that only a charge distribution
slowly decreasing at spatial infinity can produce a nontrivial dependence in
the Abelian theory. However, in gluodynamics for temperatures below some
critical value the partition function acquires a delta-function like dependence
on the boundary condition, which leads to colour confinement.Comment: 14 pages, RevTeX, submitted to Phys. Rev.
Flexoelectric effect in finite samples
Static flexoelectric effect in a finite sample of a solid is addressed in
terms of phenomenological theory for the case of a thin plate subjected to
bending. It has been shown that despite an explicit asymmetry inherent to the
bulk constitutive electromechanical equations which take into account the
flexoelectric coupling, the electromechanical response for a finite sample is
"symmetric". "Symmetric" means that if a sensor and an actuator are made of a
flexoelectric element, performance of such devices can be characterized by the
same effective piezoelectric coefficient. This behavior is consistent with the
thermodynamic arguments offered earlier, being in conflict with the current
point of view on the matter in literature. This result was obtained using
standard mechanical boundary conditions valid for the case where the
polarization vanishes at the surface. It was shown that, for the case where
there is the polarization is nonzero at the surface, the aforementioned
symmetry of electromechanical response may be violated if standard mechanical
boundary conditions are used, leading to a conflict with the thermodynamic
arguments. It was argued that this conflict may be resolved when using modified
mechanical boundary conditions. It was also shown that the contribution of
surface piezoelectricity to the flexoelectric response of a finite sample is
expected to be comparable to that of the static bulk contribution (including
the material with high values of the dielectric constant) and to scale as the
bulk value of the dielectric constant (similar to the bulk contribution). This
finding implies that if the experimentally measured flexoelectric coefficient
scales as the dielectric constant of the material, this does not imply that the
measured flexoelectric response is controlled by the static bulk contribution
to the flexoelectric effect
Is it possible to assign physical meaning to field theory with higher derivatives?
To overcome the difficulties with the energy indefiniteness in field theories
with higher derivatives, it is supposed to use the mechanical analogy, the
Timoshenko theory of the transverse flexural vibrations of beams or rods well
known in mechanical engineering. It enables one to introduce the notion of a
"mechanical" energy in such field models that is wittingly positive definite.
This approach can be applied at least to the higher derivative models which
effectively describe the extended localized solutions in usual first order
field theories (vortex solutions in Higgs models and so on). Any problems with
a negative norm ghost states and unitarity violation do not arise here.Comment: 16 pp, LaTeX, JINR E2-93-19
Багатовимірна структурна ідентифікація при регулярних сигналах
New structural identification algorithm at a regular signals for the multidimensional objects with unstable poles is discussed in this article. This algorithm is based on the use of transformation of Laplace for the decision of reverse control task. It allows to find the object transfer matrices from the control input and from the indignation input as a result of the quadratic functional minimization. Новий алгоритм структурної ідентифікації багатовимірних можливо нестійких об’єктів при регулярних сигналах розглянуто у статті. Зазначений алгоритм заснований на використанні перетворення Лапласу для розв’язання зворотної задачі керування. Він дозволяє знаходити матриці передатних функцій об’єкта від регульованого входу та від збурення в результаті мінімізації квадратичного функціоналу якості
The Dynamic Characteristics of the Manipulator With Parallel Kinematic Structure Based on Experimental Data
The chapter presents two identification techniques which the authors found
most useful in examining the dynamic characteristics of a manipulator with
a parallel kinematic structure as an object of control. These techniques
emphasize a frequency domain approach. If all input/output signals of an
object can be measured, then the first one of such techniques may be used for
identification. In the case when all disturbances can’t be measured, the second
identification technique may be used
Політичні злочини як елемент політичного життя.
Тимошенко, В.О. Політичні злочини як елемент політичного життя. / В.О.Тимошенко // Актуальні проблеми політики : зб. наук. пр. / редкол. : С. В. Ківалов (голов. ред.), Л. І. Кормич (заст. голов. ред.), Ю. П. Аленін [та ін.] ; МОНмолодьспорт України, НУ ОЮА. – Одеса : Фенікс, 2011. – Вип. 43. С.174 - 179.The institute of political crimes as element of political life is examined in
the article. Description of political crimes is given with legal and political
science points of view
Синтез гідрованих тіофенів реакцією [3+2] циклоприєднання тіокарбоніліліду
Aim. To study the use of chloromethyl trimethylsilylmethyl sulfide as a precursor of thiocarbonyl ylide in [3+2] cycloaddition reaction to a number of α,β-unsaturated compounds and to establish the regularities of the reaction course. To develop an effective method for the synthesis of new dihydro- and tetrahydrothiophene derivatives which are convenient for further modification.Results and discussion. The synthetic approach to tetrahydrothiophenes with substituents in positions 3 and 4 was extended by the [3+2] cycloaddition reaction of thiocarbonyl ylide with a number of compounds containing an activated multiple bond. The stereoselectivity and limitations of this reaction were determined. Further functionalization of the obtained compounds was carried out.Experimental part. Thiocarbonyl ylide was obtained by fluoride ion-promoted 1,3-desilylation of the known chloromethyl trimethylsilylmethyl sulfide. The synthesis of the target compounds involved the [3+2] cycloaddition of such an ylide to a series of compounds with an activated multiple bond. The stereochemistry of the target compounds was determined by 1H NOESY experiments. Synthetic derivatives of thiolancarboxylic acids, in particular aldehydes, alcohols, amines, amidines, were obtained by functionalization of the [3+2] adducts.Conclusions. The synthetic approach to functionalized tetrahydrothiophenes by the [3+2] cycloaddition reaction of thiocarbonyl ylide with a number of compounds containing an activated multiple bond has expanded the limits of application of this reaction and allows obtaining the target compounds in multigram quantities. A high stereoselectivity of this reaction was observed. The reaction products are convenient synthetic precursors to the various classes of organic compounds.Мета. Вивчити використання хлорометилтриметилсилілметил сульфіду як попередника тіокарбоніліліду в реакції [3+2] циклоприєднанні з рядом α,β-ненасичених сполук та виявити закономірності перебігу цієї реакції. Розробити ефективний метод синтезу нових похідних дигідро- та тетрагідротіофенового ряду, які можуть бути зручними для подальшої модифікації.Результати та їх обговорення. Розширено синтетичний підхід до дигідро- та тетрагідротіофенів із замісниками в 3 та 4 положеннях через реакцію [3+2]-циклоприєднання тіокарбоніліліду до ряду сполук з активованим кратним зв’язком. Визначено стереоселективність та межі застосування цієї реакції. Проведено подальшу функціоналізацію отриманих сполук.Експериментальна частина. Тіокарбонілілід було отримано шляхом промотованого флуорид-йоном 1,3-десилілювання відомого хлорометилтриметилсилілметил сульфіду. Синтез цільових сполук передбачав [3+2]-циклоприєднання такого іліду до ряду сполук з активованими кратними зв’язками. Стереохімію цільових сполук визначено за допомогою 1H NOESY експериментів. Функціоналізацією отриманих сполук одержано синтетичні похідні тіоланкарбонових кислот, зокрема альдегіди, спирти, аміни, амідини.Висновки. Синтетичний підхід до функціоналізованих дигідро- та тетрагідротіофенів за допомогою реакції [3+2]-циклоприєднання тіокарбоніліліду з рядом сполук, які містять активований кратний зв’язок, розширив межі застосування цієї реакції і дозволив одержати цільові сполуки у мультиграмових кількостях. Виявлено високу стереоселективність цієї реакції. Продукти реакції є зручними синтетичними попередниками різних класів органічних сполук
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