315 research outputs found
Expressed emotion as an assessment of family environment with mothers and fathers of 1-year-old children.
Background: High levels of expressed emotion (EE) in parents have been found to put children at risk for emotional and behavioural problems. However, the majority of existing studies have focused on mothers of school-aged children and adolescents rather than younger children, and have only rarely included fathers. Methods: The present study examined the reliability of EE in mothers and fathers of 1-year old children. It also investigated whether depression and marital problems in the postnatal period predicted EE toward the child at 12 months. EE was assessed with the Preschool Five Minute Speech Sample in 163 families. Results: The rater-interrater and code-recode reliability was high for most EE dimensions. Mothers and fathers were found to display quite similar EE scores. Regression analyses showed that depression and couple relationship significantly predicted EE in mothers, but not fathers. Conclusions: The findings suggest that EE provides a reliable and useful assessment of the family environment in families of young children. © 2012 John Wiley & Sons Ltd
Temperature dependence of the superheating field for superconductors in the high-k London limit
We study the metastability of the superheated Meissner state in type II
superconductors with k >> 1 beyond Ginzburg-Landau theory, which is applicable
only in the vicinity of the critical temperature. Within Eilenberger's
semiclassical approximation, we use the local electrodynamic response of the
superconductor to derive a generalized thermodynamic potential valid at any
temperature. The stability analysis of this functional yields the temperature
dependence of the superheating field. Finally, we comment on the implications
of our results for superconducting cavities in particle accelerators.Comment: 7.5 pages, 2 figure
Heat capacity at the glass transition
A fundamental problem of glass transition is to explain the jump of heat
capacity at the glass transition temperature without asserting the
existence of a distinct solid glass phase. This problem is also common to other
disordered systems, including spin glasses. We propose that if is defined
as the temperature at which the liquid stops relaxing at the experimental time
scale, the jump of heat capacity at follows as a necessary consequence
due to the change of system's elastic, vibrational and thermal properties. In
this picture, we discuss time-dependent effects of glass transition, and
identify three distinct regimes of relaxation. Our approach explains widely
observed logarithmic increase of with the quench rate and the correlation
of heat capacity jump with liquid fragility
Is demagnetization an efficient optimization method?
Demagnetization, commonly employed to study ferromagnets, has been proposed
as the basis for an optimization tool, a method to find the ground state of a
disordered system. Here we present a detailed comparison between the ground
state and the demagnetized state in the random field Ising model, combing exact
results in and numerical solutions in . We show that there are
important differences between the two states that persist in the thermodynamic
limit and thus conclude that AC demagnetization is not an efficient
optimization method.Comment: 2 pages, 1 figur
Dislocation Kinks in Copper: Widths, Barriers, Effective Masses, and Quantum Tunneling
We calculate the widths, migration barriers, effective masses, and quantum
tunneling rates of kinks and jogs in extended screw dislocations in copper,
using an effective medium theory interatomic potential. The energy barriers and
effective masses for moving a unit jog one lattice constant are close to
typical atomic energies and masses: tunneling will be rare. The energy barriers
and effective masses for the motion of kinks are unexpectedly small due to the
spreading of the kinks over a large number of atoms. The effective masses of
the kinks are so small that quantum fluctuations will be important. We discuss
implications for quantum creep, kink--based tunneling centers, and Kondo
resonances
Nonlinear Waves in Disordered Diatomic Granular Chains
We investigate the propagation and scattering of highly nonlinear waves in
disordered granular chains composed of diatomic (two-mass) units of spheres
that interact via Hertzian contact. Using ideas from statistical mechanics, we
consider each diatomic unit to be a "spin", so that a granular chain can be
viewed as a spin chain composed of units that are each oriented in one of two
possible ways. Experiments and numerical simulations both reveal the existence
of two different mechanisms of wave propagation: In low-disorder chains, we
observe the propagation of a solitary pulse with exponentially decaying
amplitude. Beyond a critical level of disorder, the wave amplitude instead
decays as a power law, and the wave transmission becomes insensitive to the
level of disorder. We characterize the spatio-temporal structure of the wave in
both propagation regimes and propose a simple theoretical interpretation for
such a transition. Our investigation suggests that an elastic spin chain can be
used as a model system to investigate the role of heterogeneities in the
propagation of highly nonlinear waves.Comment: 10 pages, 8 figures (some with multiple parts), to appear in Physical
Review E; summary of changes: new title, one new figure, additional
discussion of several points (including both background and results
Similarity of fluctuations in correlated systems: The case of seismicity
We report a similarity of fluctuations in equilibrium critical phenomena and
non-equilibrium systems, which is based on the concept of natural time. The
world-wide seismicity as well as that of San Andreas fault system and Japan are
analyzed. An order parameter is chosen and its fluctuations relative to the
standard deviation of the distribution are studied. We find that the scaled
distributions fall on the same curve, which interestingly exhibits, over four
orders of magnitude, features similar to those in several equilibrium critical
phenomena (e.g., 2D Ising model) as well as in non-equilibrium systems (e.g.,
3D turbulent flow).Comment: 5 pages, 9 figure
Fracture Strength of Disordered Media: Universality, Interactions, and Tail Asymptotics
We study the asymptotic properties of fracture strength distributions of disordered elastic media by a combination of renormalization group, extreme value theory, and numerical simulation. We investigate the validity of the “weakest-link hypothesis” in the presence of realistic long-ranged interactions in the random fuse model. Numerical simulations indicate that the fracture strength is well-described by the Duxbury-Leath-Beale (DLB) distribution which is shown to flow asymptotically to the Gumbel distribution. We explore the relation between the extreme value distributions and the DLB-type asymptotic distributions and show that the universal extreme value forms may not be appropriate to describe the nonuniversal low-strength tail.Peer reviewe
Real-Time Wavelet-transform spectrum analyzer for the investigation of 1/f^\alpha noise
A wavelet transform spectrum analyzer operating in real time within the
frequency range 3X10^(-5) - 1.3X10^5 Hz has been implemented on a low-cost
Digital Signal Processing board operating at 150MHz. The wavelet decomposition
of the signal allows to efficiently process non-stationary signals dominated by
large amplitude events fairly well localized in time, thus providing the
natural tool to analyze processes characterized by 1/f^alpha power spectrum.
The parallel architecture of the DSP allows the real-time processing of the
wavelet transform of the signal sampled at 0.3MHz. The bandwidth is about
220dB, almost ten decades. The power spectrum of the scattered intensity is
processed in real time from the mean square value of the wavelet coefficients
within each frequency band. The performances of the spectrum analyzer have been
investigated by performing Dynamic Light Scattering experiments on colloidal
suspensions and by comparing the measured spectra with the correlation
functions data obtained with a traditional multi tau correlator. In order to
asses the potentialities of the spectrum analyzer in the investigation of
processes involving a wide range of timescales, we have performed measurements
on a model system where fluctuations in the scattered intensities are generated
by the number fluctuations in a dilute colloidal suspension illuminated by a
wide beam. This system is characterized by a power-law spectrum with exponent
-3/2 in the scattered intensity fluctuations. The spectrum analyzer allows to
recover the power spectrum with a dynamic range spanning about 8 decades. The
advantages of wavelet analysis versus correlation analysis in the investigation
of processes characterized by a wide distribution of time scales and
non-stationary processes are briefly discussed.Comment: 12 pages, 6 figure
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