427 research outputs found
Equivalent thermo-mechanical parameters for perfect crystals
Thermo-elastic behavior of perfect single crystal is considered. The crystal
is represented as a set of interacting particles (atoms). The approach for
determination of equivalent continuum values for the discrete system is
proposed. Averaging of equations of particles' motion and long wave
approximation are used in order to make link between the discrete system and
equivalent continuum. Basic balance equations for equivalent continuum are
derived from microscopic equations. Macroscopic values such as Piola and Cauchy
stress tensors and heat flux are represented via microscopic parameters.
Connection between the heat flux and temperature is discussed. Equation of
state in Mie-Gruneisen form connecting Cauchy stress tensor with deformation
gradient and thermal energy is obtained from microscopic considerations.Comment: To be published in proceedings of IUTAM Simposium on "Vibration
Analysis of Structures with Uncertainties", 2009; 14 pages
Analysis of Strong-Coupling Parameters for Superfluid 3He
Superfluid He experiments show strong deviation from the weak-coupling
limit of the Ginzburg-Landau theory, and this discrepancy grows with increasing
pressure. Strong-coupling contributions to the quasiparticle interactions are
known to account for this effect and they are manifest in the five
-coefficients of the fourth order Ginzburg-Landau free energy terms. The
Ginzburg-Landau free energy also has a coefficient to include magnetic
field coupling to the order parameter. From NMR susceptibility experiments, we
find the deviation of from its weak-coupling value to be negligible at
all pressures. New results for the pressure dependence of four different
combinations of -coefficients, _{345}, _{12},
_{245}, and _{5} are calculated and comparison is made with
theory.Comment: 6 pages, 2 figures, 1 table. Manuscript prepared for QFS200
Limits on Cosmological Variation of Strong Interaction and Quark Masses from Big Bang Nucleosynthesis, Cosmic, Laboratory and Oklo Data
Recent data on cosmological variation of the electromagnetic fine structure
constant from distant quasar (QSO) absorption spectra have inspired a more
general discussion of possible variation of other constants. We discuss
variation of strong scale and quark masses. We derive the limits on their
relative change from (i) primordial Big-Bang Nucleosynthesis (BBN); (ii)
Oklo natural nuclear reactor, (iii) quasar absorption spectra, and (iv)
laboratory measurements of hyperfine intervals.Comment: 10 pages 2 figurs: second version have several references added and
some new comment
Towards a sensitive search for variation of the fine structure constant using radio-frequency E1 transitions in atomic dysprosium
It has been proposed that the radio-frequency electric-dipole (E1) transition
between two nearly degenerate opposite-parity states in atomic dysprosium
should be highly sensitive to possible temporal variation of the fine structure
constant () [V. A. Dzuba, V. V. Flambaum, and J. K. Webb, Phys. Rev. A
{\bf 59}, 230 (1999)]. We analyze here an experimental realization of the
proposed search in progress in our laboratory, which involves monitoring the E1
transition frequency over a period of time using direct frequency counting
techniques. We estimate that a statistical sensitivity of |\adota| \sim
10^{-18}/yr may be achieved and discuss possible systematic effects that may
limit such a measurement.Comment: 8 pages, 7 figure
Rashba interferometers: Spin-dependent single and two-electron interference
Quantum transport in semiconductor nanostructures can be described
theoretically in terms of the propagation and scattering of electron
probability waves. Within this approach, elements of a phase-coherent electric
circuit play a role similar to quantum-optical devices that can be
characterised by scattering matrices. Electronic analogues of well-know optical
interferometers have been fabricated and used to study special features of
charge carriers in solids. We present results from our theoretical
investigation into the interplay between spin precession and quantum
interference in an electronic Mach-Zehnder interferometer with spin-orbit
coupling of the Rashba type. Intriguing spin-dependent transport effects occur,
which can be the basis for novel spintronic devices such as a magnet-less
spin-controlled field-effect transistor and a variety of single-qubit gates.
Their functionality arises entirely from spin-dependent interference of each
single input electron with itself. We have also studied two-electron
interference effects for the spin-dependent Mach-Zehnder interferometer,
obtaining analytical expressions for its two-fermion-state scattering matrix.
Using this result, we consider ways to generate two-electron output states for
which the Rashba spin-subband quantum number and the output-arm index are
entangled. Combining spin-dependent interference in our proposed Mach-Zehnder
interferometer with a projective charge measurement at the output enables
entanglement generation. As our particular scheme involves tuneable spin
precession, electric-field control of entanglement production can be achieved.Comment: 7 pages, 5 figures, Elsevier style, submitted to special issue of
Solid State Communications, v2: replacement to rectify formatting problems,
v3: minor changes + 3 references adde
Cosmological Variation of the Fine Structure Constant from an Ultra-Light Scalar Field: The Effects of Mass
Cosmological variation of the fine structure constant due to the
evolution of a spatially homogeneous ultra-light scalar field ()
during the matter and dominated eras is analyzed. Agreement of
with the value suggested by recent observations of
quasar absorption lines is obtained by adjusting a single parameter, the
coupling of the scalar field to matter.
Asymptotically in this model goes to a constant value
in the early radiation and the late
dominated eras. The coupling of the scalar field to (nonrelativistic) matter
drives slightly away from in the epochs when the
density of matter is important.
Simultaneous agreement with the more restrictive bounds on the variation
from the Oklo natural fission reactor and from
meteorite samples can be achieved if the mass of the scalar field is on the
order of 0.5--0.6 , where .
Depending on the scalar field mass, may be slightly smaller or
larger than at the times of big bang nucleosynthesis, the emission
of the cosmic microwave background, the formation of early solar system
meteorites, and the Oklo reactor. The effects on the evolution of due
to nonzero mass for the scalar field are emphasized.
An order of magnitude improvement in the laboratory technique could lead to a
detection of .Comment: 22 pages, 15 figures Version 2: The Oklo event is now considered as
localized in time. The initial conditions for the scalar field have been
refined. The numbers in the Table have been recomputed. Added Ref
Quintessence and variation of the fine structure constant in the CMBR
We study dependence of the CMB temperature anisotropy spectrum on the value
of the fine structure constant and the equation of state of the dark
energy component of the total density of the universe. We find that bounds
imposed on the variation of from the analysis of currently available
CMB data sets can be significantly relaxed if one also allows for a change in
the equation of state.Comment: 5 pages, 3 figures. Several references added and a few minor typos
corrected in the revised versio
Current-induced highly dissipative domains in high Tc thin films
We have investigated the resistive response of high Tc thin films submitted
to a high density of current. For this purpose, current pulses were applied
into bridges made of Nd(1.15)Ba(1.85)Cu3O7 and Bi2Sr2CaCu2O8. By recording the
time dependent voltage, we observe that at a certain critical current j*, a
highly dissipative domain develops somewhere along the bridge. The successive
formation of these domains produces stepped I-V characteristics. We present
evidences that these domains are not regions with a temperature above Tc, as
for hot spots. In fact this phenomenon appears to be analog to the nucleation
of phase-slip centers observed in conventional superconductors near Tc, but
here in contrast they appear in a wide temperature range. Under some
conditions, these domains will propagate and destroy the superconductivity
within the whole sample. We have measured the temperature dependence of j* and
found a similar behavior in the two investigated compounds. This temperature
dependence is just the one expected for the depairing current, but the
amplitude is about 100 times smaller.Comment: 9 pages, 9 figures, Revtex, to appear in Phys. Rev.
Charge conservation and time-varying speed of light
It has been recently claimed that cosmologies with time dependent speed of
light might solve some of the problems of the standard cosmological scenario,
as well as inflationary scenarios. In this letter we show that most of these
models, when analyzed in a consistent way, lead to large violations of charge
conservation. Thus, they are severly constrained by experiment, including those
where is a power of the scale factor and those whose source term is the
trace of the energy-momentum tensor. In addition, early Universe scenarios with
a sudden change of related to baryogenesis are discarded.Comment: 4 page
Constraints on the Variations of the Fundamental Couplings
We reconsider several current bounds on the variation of the fine-structure
constant in models where all gauge and Yukawa couplings vary in an
interdependent manner, as would be expected in unified theories. In particular,
we re-examine the bounds established by the Oklo reactor from the resonant
neutron capture cross-section of 149Sm. By imposing variations in \Lambda_{QCD}
and the quark masses, as dictated by unified theories, the corresponding bound
on the variation of the fine-structure constant can be improved by about 2
orders of magnitude in such theories. In addition, we consider possible bounds
on variations due to their effect on long lived \alpha- and \beta-decay
isotopes, particularly 147Sm and 187Re. We obtain a strong constraint on \Delta
\alpha / \alpha, comparable to that of Oklo but extending to a higher redshift
corresponding to the age of the solar system, from the radioactive life-time of
187Re derived from meteoritic studies. We also analyze the astrophysical
consequences of perturbing the decay Q values on bound state \beta-decays
operating in the s-process.Comment: 25 pages, latex, 5 eps figure
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