923,588 research outputs found
Shift of close-packed basal planes as an order parameter of transitions between antiferromangetic phases in solid oxygen: II. Temperature/pressure dependence of sound velocities and lattice parameters
In the present paper we generalised a phenomenological model developed in
\cite{gomo:2005} for the description of magnetostructural phase transitions and
related peculiarities of elastic properties in solid oxygen under high pressure
and/or low (below 40 K) temperature. We show that variation of all the lattice
parameters in the vicinity of -phase transition is due to both the
shift of basal closed packed planes and appearance of the long-range magnetic
order. Competition between these two factors from one side and lattice
compression below from another produces non monotonic
temperature dependence of lattice parameter (along monoclinic axis). Steep
decrease of the sound velocities in the vicinity of can be
explained by the softening of the lattice with respect to shift of the
close-packed planes (described by the constant ) prior to phase transition
point. We anticipate an analogous softening of sound velocities in the vicinity
of -phase transition and non monotonic pressure dependence of
sound velocities in -phase.Comment: 11 pages, 8 figures, to appear in Low Temperature Physics, v.33, N6,
2007, materails presented at the Conference CC-2006, Kharkov, 200
Comment on Counterintuitive consequence of heating in strongly driven intrinsic junctions of BiSrCaCuO mesas
In a recent paper [Phys.Rev.B 81, 224518 (2010)], C. Kurter et al, analyzed
the effect of strong self-heating in large-area
BiSrCaCuO (Bi-2212) mesa structures. They conclude
that conductance peaks in their mesas occur when mesas are heated to
the superconducting critical temperature . Further on they extrapolate
this statement for all mesas, including much smaller and much better thermally
anchored mesas used in Intrinsic Tunnelling Spectroscopy (ITS). Here I show
that their conclusion does not hold neither for previously reported data, nor
even for their own mesas; the very remote extrapolation to ITS is invalid. I
also point out a number of inconsistencies and misleading references.Comment: 2 page
Jet Methods in Time-Dependent Lagrangian Biomechanics
In this paper we propose the time-dependent generalization of an `ordinary'
autonomous human biomechanics, in which total mechanical + biochemical energy
is not conserved. We introduce a general framework for time-dependent
biomechanics in terms of jet manifolds associated to the extended
musculo-skeletal configuration manifold, called the configuration bundle. We
start with an ordinary configuration manifold of human body motion, given as a
set of its all active degrees of freedom (DOF) for a particular movement. This
is a Riemannian manifold with a material metric tensor given by the total
mass-inertia matrix of the human body segments. This is the base manifold for
standard autonomous biomechanics. To make its time-dependent generalization, we
need to extend it with a real time axis. By this extension, using techniques
from fibre bundles, we defined the biomechanical configuration bundle. On the
biomechanical bundle we define vector-fields, differential forms and affine
connections, as well as the associated jet manifolds. Using the formalism of
jet manifolds of velocities and accelerations, we develop the time-dependent
Lagrangian biomechanics. Its underlying geometric evolution is given by the
Ricci flow equation.
Keywords: Human time-dependent biomechanics, configuration bundle, jet
spaces, Ricci flowComment: 13 pages, 3 figure
Isospin Distillation with Radial Flow: a Test of the Nuclear Symmetry Energy
We discuss mechanisms related to isospin transport in central collisions
between neutron-rich systems at Fermi energies. A fully consistent study of the
isospin distillation and expansion dynamics in two-component systems is
presented in the framework of a stochastic transport theory. We analyze
correlations between fragment observables, focusing on the study of the average
N/Z of fragments, as a function of their kinetic energy. We identify an
EOS-dependent relation between these observables, allowing to better
characterize the fragmentation path and to access new information on the low
density behavior of the symmetry energy.Comment: 4 pages, 4 figures (revtex4
Numerical methods of geomechanics tasks solution during coal deposits’ development
Purpose. Generalization of numerical modeling of geomechanical processes in the vicinity of mine workings by finite elements method and making recommendations for substantiation of suitable construction and behavior of rock massif physical model.
Methods. Software packages SolidWorks Simulation (COSMOS/М) and ANSYS are used for geomechanical tasks solution.
Findings. Solutions of geomechanical tasks dealing with topical issues of estimating stress-strain state of rock massif around underground workings of different functions are given. Data on the rock massif stress-strain state are received and recommendations on adequate and authentic reflection of its structural peculiarities (stratification and fracturing) are made. Physical model of rock condition (elastic, elastic-plastic, rheological diagrams and complete diagram of deformation taking into account weakening and fracturing) is presented.
Originality. New data about the mechanism of movement processes of coal-bearing massif around mine workings considering stratification and cracks content, limit and out-of-limit deflection state in separate areas, and also the impact of rheological rock properties are received.
Practical implications. Complex of geomechanical tasks solutions allow to increase credibility of rock pressure manifestations prediction and substantiate technical solutions for effective and safe operations at coal mines.Цель. Обобщение опыта численного моделирования методом конечных элементов геомеханических процессов вокруг горных выработок и формирование рекомендаций по обоснованию адекватного строения и поведения физической модели горного массива.
Методика. Для решения задач геомеханики использованы пакеты прикладных программ SolidWorks Simulation (COSMOS/М) и ANSYS.
Результаты. Приведены решения геомеханических задач по актуальным вопросам оценки НДС горного массива вокруг подземных выработок различного назначения. Получены закономерности поведения горного массива и даны рекомендации по адекватному и достоверному отражению его текстурных особенностей (слоистость и трещиноватость) и физической модели состояния горной породы (упругая, упруго-пластическая, реологическая, полная диаграмма деформирования с учетом разупрочнения и разрыхления).
Научная новизна. Получен ряд новых закономерностей развития процессов сдвижения углевмещающего массива вокруг горных выработок с учетом его слоистости и трещиноватости, предельного и запредельного состояния в отдельных областях, а также влияния реологических свойств горных пород.
Практическая значимость. Комплекс решений геомеханических задач позволяет повысить достоверность прогноза проявлений горного давления и обосновать технические решения по эффективному и безопасному ведению горных работ на угольных шахтах.Мета. Узагальнення досвіду чисельного моделювання методом скінченних елементів геомеханічних процесів навколо гірничих виробок і формування рекомендацій з обґрунтування адекватної будови й поведінки фізичної моделі гірського масиву.
Методика. Для розв’язання задач геомеханіки використані пакети прикладних програм Solidworks Simulation (COSMOS/М) і ANSYS.
Результати. Наведено розв’язання геомеханічних задач з актуальних питань оцінки НДС гірського масиву навколо підземних виробок різного призначення. Отримано закономірності поведінки гірського масиву й надано рекомендації з адекватного й достовірного відображення його текстурних особливостей (шаруватість і тріщинуватість) та фізичної моделі стану гірської породи (пружна, пружно-пластична, реологічна, повна діаграма деформування з урахуванням знеміцнення і розпушення).
Наукова новизна. Отримано низку нових закономірностей розвитку процесів зрушення вуглевміщуючого масиву навколо гірничих виробок з урахуванням його шаруватості й тріщинуватості, граничного й позамежного станів в окремих областях, а також впливу реологічних властивостей гірських порід.
Практична значимість. Комплекс розв’язань геомеханічних задач дозволяє підвищити вірогідність прогнозу проявів гірського тиску й обґрунтувати технічні розв’язання з ефективного й безпечного ведення гірничих робіт на вугільних шахтах.The materials discussed in the article were received while performing a complex of research works at the request of a number of industrial enterprises in coal mining in Donbas. The authors are grateful to M. Illiashov, M. Barabash, Yu. Cherednychenko, O. Vivcharenko, V. Chervatiuk, O. Husiev for providing mine-and-geological and technical information on features of conducting mining operations at their enterprises, and also for useful recommendations and fruitful discussion of the received results which are intended to provide an effective solution to mine-technical issues in coal mining
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