3,684 research outputs found
Re-equilibration after quenches in athermal martensites:Conversion-delays for vapour to liquid domain-wall phases
Entropy barriers and ageing states appear in martensitic
structural-transition models, slowly re-equilibrating after temperature
quenches, under Monte Carlo dynamics. Concepts from protein folding and ageing
harmonic oscillators turn out to be useful in understanding these
nonequilibrium evolutions. We show how the athermal, non-activated delay time
for seeded parent-phase austenite to convert to product-phase martensite,
arises from an identified entropy barrier in Fourier space. In an ageing state
of low Monte Carlo acceptances, the strain structure factor makes
constant-energy searches for rare pathways, to enter a Brillouin zone `golf
hole' enclosing negative energy states, and to suddenly release entropically
trapped stresses. In this context, a stress-dependent effective temperature can
be defined, that re-equilibrates to the quenched bath temperature.Comment: 11 pages, 12 figures. Under process with Phys. Rev. B (2015
Analytical results for random walks in the presence of disorder and traps
In this paper, we study the dynamics of a random walker diffusing on a
disordered one-dimensional lattice with random trappings. The distribution of
escape probabilities is computed exactly for any strength of the disorder.
These probabilities do not display any multifractal properties contrary to
previous numerical claims. The explanation for this apparent multifractal
behavior is given, and our conclusion are supported by numerical calculations.
These exact results are exploited to compute the large time asymptotics of the
survival probability (or the density) which is found to decay as . An exact lower bound for the density is found to
decay in a similar way.Comment: 21 pages including 3 PS figures. Submitted to Phys. Rev.
Use of Geotechnical Design Summary Report as a Management Tool for Resolving Disputes on Underground Construction Projects
The Los Angeles Metro Rail Subway project is initially planned for 30 km (18 mi) of twin, 6-m (20-ft) diameter bored tunnels under city streets and a total of 16 stations. This paper describes briefly the history of the project, the geologic setting, and the challenges encountered during design or anticipated during construction. It also introduces, as part of contract documentation, an interpretive geotechnical baseline report which establishes the basis for identification and recognition of site condition baselines . In so doing, this report (known as a GDSR ) has proven to be an effective tool for ameliorating contractual problems and facilitating conflict resolution
Vibration Signature Analysis of Shipboard Machinery
A brief description of Vibration Signature Analysis as an effective tool in anticipation and prevention of Shipboard Machinery failures is provided. A case history of marine steam turbine and gearbox vibration signature analysis is given
Effect of Particle Size on the Structural and Magnetic Properties of Nanocrystalline Zinc Ferrite
ZnFe2O4 is one of the most important technological material having applications in radio engineering, radio technology, semiconductors, bio-medical applications etc. ZnFe2O4 when in bulk form shows paramagnetic behavior at room temperature. When ZnFe2O4 is synthesized by some techniques it was possible to see the ferromagnetic behavior. Also, ZnFe2O4 in nanocrystalline form exhibit different magnetic properties. Therefore in the present work we intend to present the properties of particle size behavior of ZnFe2O4 nanoparticles. ZnFe2O4 nanoparticles were synthesized by oxalic acid based precursor method. The obtained ZnFe2O4 nano powders were thermally annealed from 300 to 600 °C. The structural and magnetic characterization were measured using X-ray diffraction (XRD), scanning electron microscope (SEM), IR measurements and vibrating sample magnetometer (VSM). XRD patterns clearly showed the formation of zinc ferrite. The particle size was observed to increase from 19 to 35 nm with increasing annealing temperature. The lattice constants were observed to decrease with increasing particle size. The nanoparticles size were confirmed using SEM measurements. IR measurements were carried to confirm the phase formation of ZnFe2O4 nanoparticles. The Infrared spectra showed the characteristic features of vibrational bands corresponding to spinel ferrite. Room temperature ferromagnetic properties were observed for zinc ferrite having particle sizes 19 and 21 nm. For the particle size 29 and 35 nm it showed paramagnetic nature. The magnetic properties of zinc ferrite nanoparticles were observed to be dependent on the particle size.Keywords: Nanoferrites Zn ferrite Structural properties Magnetic propertie
Kondo Effect in Fermi Systems with a Gap: A Renormalization Group Study
We present the results of a Wilson Renormalization Group study of the
single-impurity Kondo and Anderson models in a system with a gap in the
conduction electron spectrum. The behavior of the impurity susceptibility and
the zero-frequency response function, are discussed in the
cases with and without particle-hole symmetry. In addition, for the asymmetric
Anderson model the correlation functions, , are computed.Comment: 10 pages, 10 figure
Exactly solvable toy models of unconventional magnetic alloys: Bethe Ansatz versus Renormalization Group method
We propose toy models of unconventional magnetic alloys, in which the density
of band states, , and hybridization, , are energy
dependent; it is assumed, however, that
, and hence an effective
electron-impurity coupling is
energy independent. In the renormalization group approach, the physics of the
system is assumed to be governed by only rather than by
separate forms of and . However, an exact Bethe
Ansatz solution of the toy Anderson model demonstrates a crucial role of a form
of inverse band dispersion .Comment: A final version. A previous one has been sent to Archive because of
my technical mistake. Sorr
Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon
We discuss Kondo behavior of a conduction electron system coupled with local
optical phonon by analyzing the Anderson-Holstein model with the use of a
numerical renormalization group (NRG) method. There appear three typical
regions due to the balance between Coulomb interaction and
phonon-mediated attraction . For , we
observe the standard Kondo effect concerning spin degree of freedom. Since the
Coulomb interaction is effectively reduced as , the
Kondo temperature is increased when is increased. On
the other hand, for , there occurs the Kondo effect
concerning charge degree of freedom, since vacant and double occupied states
play roles of pseudo-spins. Note that in this case, is decreased
with the increase of . Namely, should be maximized for
. Then, we analyze in detail the Kondo behavior
at , which is found to be explained by the polaron
Anderson model with reduced hybridization of polaron and residual repulsive
interaction among polarons. By comparing the NRG results of the polaron
Anderson model with those of the original Anderson-Holstein model, we clarify
the Kondo behavior in the competing region of .Comment: 8 pages, 8 figure
Kondo effect in a magnetic field and the magnetoresistivity of Kondo alloys
The effect of a magnetic field on the spectral density of a
Kondo impurity is investigated at zero and finite temperatures by using
Wilson's numerical renormalization group method. A splitting of the total
spectral density is found for fields larger than a critical value
, where is the Kondo scale. The splitting
correlates with a peak in the magnetoresistivity of dilute magnetic alloys
which we calculate and compare with the experiments on
. The linear magnetoconductance of quantum
dots exhibiting the Kondo effect is also calculated.Comment: 4 pages, 4 eps figure
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