3,819 research outputs found
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.
Conformational transitions of heteropolymers in dilute solutions
In this paper we extend the Gaussian self-consistent method to permit study
of the equilibrium and kinetics of conformational transitions for
heteropolymers with any given primary sequence. The kinetic equations earlier
derived by us are transformed to a form containing only the mean squared
distances between pairs of monomers. These equations are further expressed in
terms of instantaneous gradients of the variational free energy. The method
allowed us to study exhaustively the stability and conformational structure of
some periodic and random aperiodic sequences. A typical phase diagram of a
fairly long amphiphilic heteropolymer chain is found to contain phases of the
extended coil, the homogeneous globule, the micro-phase separated globule, and
a large number of frustrated states, which result in conformational phases of
the random coil and the frozen globule. We have also found that for a certain
class of sequences the frustrated phases are suppressed. The kinetics of
folding from the extended coil to the globule proceeds through non-equilibrium
states possessing locally compacted, but partially misfolded and frustrated,
structure. This results in a rather complicated multistep kinetic process
typical of glassy systems.Comment: 15 pages, RevTeX, 20 ps figures, accepted for publication in Phys.
Rev.
Dynamics of thermoelastic thin plates: A comparison of four theories
Four distinct theories describing the flexural motion of thermoelastic thin
plates are compared. The theories are due to Chadwick, Lagnese and Lions,
Simmonds, and Norris. Chadwick's theory requires a 3D spatial equation for the
temperature but is considered the most accurate as the others are derivable
from it by different approximations. Attention is given to the damping of
flexural waves. Analytical and quantitative comparisons indicate that the
Lagnese and Lions model with a 2D temperature equation captures the essential
features of the thermoelastic damping, but contains systematic inaccuracies.
These are attributable to the approximation for the first moment of the
temperature used in deriving the Lagnese and Lions equation. Simmonds' model
with an explicit formula for temperature in terms of plate deflection is the
simplest of all but is accurate only at low frequency, where the damping is
linearly proportional to the frequency. It is shown that the Norris model,
which is almost as simple as Simmond's, is as accurate as the more precise but
involved theory of Chadwick.Comment: 2 figures, 1 tabl
Vibration and buckling of thin-walled composite I-beams with arbitrary lay-ups under axial loads and end moments
A finite element model with seven degrees of freedom per node is developed to study vibration and buckling of thin-walled composite I-beams with arbitrary lay-ups under constant axial loads and equal end moments. This model is based on the classical lamination theory, and accounts for all the structural coupling coming from material anisotropy. The governing differential equations are derived from the Hamilton’s principle. Numerical results are obtained for thin-walled composite I-beams to investigate the effects of axial force, bending moment and fiber orientation on the buckling moments, natural frequencies, and corresponding vibration mode shapes as well as axial-moment-frequency interaction curves
Conditions of yield and cyclic plasticity around inclusions
n this paper the stress field in the proximity of a circular (cylindrical) inclusion is considered. The conditions for in-plane plastic flow in the matrix are examined from a classical elasticity solution obtained by Goodier. Elementary cases are considered such as remote loading ranging from pure tensile and pure shear to equibiaxial tension. For proportional loading, it is argued that the upper bound to the shakedown limit is always twice the elastic limit; therefore, within the limits of our assumptions, if the elastic stress concentration for the equivalent stress is greater than two, there is a possibility of cyclic plasticity before bulk yielding, which means that possibly an arbitrarily large plastic strain can cumulate with increasingly high risk of exhaustion of ductility and void nucleation or detachment of the interface Consequently, conditions under which it is possible to reach twice the elastic limit before full-scale yielding are shown in the Dundurs plane representing all possible combinations of elastic parameters. Following these lines, it is shown that there is no possibility of cyclic plasticity under remote shear; there is a limited area of the Dundurs plane for tension, including the hole case; finally, in the equibiaxial limiting case, cyclic plasticity is always possible for any combination of elastic properties
Local probing of ionic diffusion by electrochemical strain microscopy: spatial resolution and signal formation mechanisms
Electrochemical insertion-deintercalation reactions are typically associated
with significant change of molar volume of the host compound. This strong
coupling between ionic currents and strains underpins image formation
mechanisms in electrochemical strain microscopy (ESM), and allows exploring the
tip-induced electrochemical processes locally. Here we analyze the signal
formation mechanism in ESM, and develop the analytical description of operation
in frequency and time domains. The ESM spectroscopic modes are compared to
classical electrochemical methods including potentiostatic and galvanostatic
intermittent titration (PITT and GITT), and electrochemical impedance
spectroscopy (EIS). This analysis illustrates the feasibility of spatially
resolved studies of Li-ion dynamics on the sub-10 nanometer level using
electromechanical detection.Comment: 49 pages, 17 figures, 4 tables, 3 appendices, to be submitted to J.
Appl. Phys
Anti-corrosion ceramic coatings on the surface of Nd-Fe-B repelling magnets
The results of vacuum-arc deposition of thin ZrO₂coatings to protect the surface of Nd-Fe-B permanent magnets used as repelling devices in orthodontics are presented. The structure, phase composition and mechanical properties of zirconium dioxide films have been investigated by means of SEM, XRD, EDX, XRF and nanoindentation method. It was revealed the formation of polycrystalline ZrO₂ films of monoclinic modification with average grain size 25 nm. The influence of the ZrO₂ coating in terms of its barrier properties for corrosion in quasi-physiological 0.9 NaCl solution has been studied. Electrochemical measurements indicated good barrier properties of the coating on specimens in the physiological solution environment
Point-loaded discs and blocks applicable to tensile testing of brittle materials
A method of numerically approximating the solutions of plane-stress or plane-strain elasticity problems with boundary conditions consisting of concentrated forces or distributed loads is presented herein. The effect of each concentrated force (commonly termed a point load) that acts on the boundary is represented by a Flamant solution. Usually, the combined effect of these Flamant solutions indicates the presence of distributed loadings or ‘residual stresses’ on some portions of the boundary that are not consistent with the actual boundary conditions. The negatives of these ‘residual stresses’ are used as stress boundary conditions in a singular integral method of numerical analysis that is applicable to plane elasticity problems involving distributed loadings on the boundaries. Since the method presented herein involves only stress boundary conditions, the solutions are valid for both plane stress and plane strain.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline
Dynamic Behavior in Piezoresponse Force Microscopy
Frequency dependent dynamic behavior in Piezoresponse Force Microscopy (PFM)
implemented on a beam-deflection atomic force microscope (AFM) is analyzed
using a combination of modeling and experimental measurements. The PFM signal
comprises contributions from local electrostatic forces acting on the tip,
distributed forces acting on the cantilever, and three components of the
electromechanical response vector. These interactions result in the bending and
torsion of the cantilever, detected as vertical and lateral PFM signals. The
relative magnitudes of these contributions depend on geometric parameters of
the system, the stiffness and frictional forces of tip-surface junction, and
operation frequencies. The dynamic signal formation mechanism in PFM is
analyzed and conditions for optimal PFM imaging are formulated. The
experimental approach for probing cantilever dynamics using frequency-bias
spectroscopy and deconvolution of electromechanical and electrostatic contrast
is implemented.Comment: 65 pages, 15 figures, high quality version available upon reques
Wavelet treatment of the intra-chain correlation functions of homopolymers in dilute solutions
Discrete wavelets are applied to parametrization of the intra-chain two-point
correlation functions of homopolymers in dilute solutions obtained from Monte
Carlo simulation. Several orthogonal and biorthogonal basis sets have been
investigated for use in the truncated wavelet approximation. Quality of the
approximation has been assessed by calculation of the scaling exponents
obtained from des Cloizeaux ansatz for the correlation functions of
homopolymers with different connectivities in a good solvent. The resulting
exponents are in a better agreement with those from the recent renormalisation
group calculations as compared to the data without the wavelet denoising. We
also discuss how the wavelet treatment improves the quality of data for
correlation functions from simulations of homopolymers at varied solvent
conditions and of heteropolymers.Comment: RevTeX, 19 pages, 7 PS figures. Accepted for publication in PR
- …