27,566 research outputs found
Ion and polymer dynamics in polymer electrolytes PPO-LiClO4: insights from NMR line-shape analysis
We investigate ion and polymer dynamics in polymer electrolytes PPO-LiClO4
performing 2H and 7Li NMR line-shape analysis. Comparison of temperature
dependent 7Li and 2H NMR spectra gives evidence for a coupling of ion and
polymer dynamics. 2H NMR spectra for various salt concentrations reveal a
strong slow down of the polymer segmental motion when the salt content is
increased. The 2H NMR line shape further indicates that the segmental motion is
governed by dynamical heterogeneities. While the width of the distribution of
correlation times G(log tau) is moderate for low and high salt content, an
extremely broad distribution exists for an intermediate salt concentration 15:1
PPO-LiClO4. For the latter composition, a weighed superposition of two spectral
components, reflecting the fast and the slow polymer segments of the
distribution, describes the 2H NMR line shape over a broad temperature range.
Analysis of the temperature dependent relative intensity of both spectral
components indicates the existence of a continuous rather than a discontinuous
distribution G(log tau). Such continuous distribution is consistent with
gradual fluctuation of the local salt concentration and, hence, of the local
environments of the polymer segments, whereas it is at variance with the
existence of large salt-depleted and salt-rich domains featuring fast and slow
polymer dynamics, respectively. Finally, for all studied mixtures PPO-LiClO4,
the 2H NMR line shape strongly depends on the echo delay in the applied
echo-pulse sequence, indicating that the structural relaxation of the polymer
segments involves successive rotational jumps about small angles gamma<20
degree.Comment: 11 pages, 11 figure
Persistent inequality when learning requires a minimal standard of living
This paper studies the persistence of wealth and utility inequality in a dynamicmodel of skill acquisition with complete credit markets and rational, perfectly altruistic,dynastic utility-maximization, when efficient learning requires a minimal standardof living. The main result is that, if the minimal standard of living is not triviallysmall, at any stationary equilibrium without intergenerational mobility there are?poor?, unskilled and ?rich?, skilled dynasties. Members of rich dynasties inherit morefrom their parents than members of poor dynasties. The former in general acquireskill, while the latter remain unskilled, and - most importantly - members of rich familiesalso enjoy strictly higher utility than members of poor dynasties. This paper studies the persistence of wealth and utility inequality in a dynamicmodel of skill acquisition with complete credit markets and rational, perfectly altruistic,dynastic utility-maximization, when efficient learning requires a minimal standardof living. The main result is that, if the minimal standard of living is not triviallysmall, at any stationary equilibrium without intergenerational mobility there are?poor?, unskilled and ?rich?, skilled dynasties. Members of rich dynasties inherit morefrom their parents than members of poor dynasties. The former in general acquireskill, while the latter remain unskilled, and - most importantly - members of rich familiesalso enjoy strictly higher utility than members of poor dynasties
Linking numbers of measured foliations
We generalise the average asymptotic linking number of a pair of
divergence-free vector fields on homology three-spheres by considering the
linking of a divergence-free vector field on a manifold of arbitrary dimension
with a codimension two foliation endowed with an invariant transverse measure.
We prove that the average asymptotic linking number is given by an integral of
Hopf type. Considering appropriate vector fields and measured foliations, we
obtain an ergodic interpretation of the Godbillon-Vey invariant of a family of
codimension one foliations discussed in math.GT/0111137.Comment: minor corrections, to appear in Ergodic Theory and Dynamical System
Multi-mode density matrices of light via amplitude and phase control
A new method is described for determining the quantum state of correlated
multimode radiation by interfering the modes and measuring the statistics of
the superimposed fields in four-port balanced homodyne detection. The full
information on the -mode quantum state is obtained by controlling both the
relative amplitudes and the phases of the modes, which simplifies the
reconstruction of density matrices to only Fourier transforms. In
particular, this method yields time-correlated multimode density matrices of
optical pulses by superimposing the signal by a sequence of short
local-oscillator pulses.Comment: 6 pages, late
Employment, wage structure, and the economic cycle: differences between immigrants and natives in Germany and the UK
Differences in the cyclical pattern of employment and wages of immigrants relative
to natives have largely gone unnoticed in the migration literature. In this paper we
show that immigrants and natives react differently to the economic cycle. Based on
over two decades of micro data, our investigation is for two of the largest immigrant
receiving countries in Europe which at the same time are characterised by different
immigrant populations as well as different economic cycles, Germany and the UK.
Understanding the magnitude, nature and possible causes of differences in
responses is relevant for assessing the economic performance of immigrant
communities over time. We show that there are substantial differences in cyclical
responses between immigrants and natives. Our analysis illustrates the magnitude of
these differences, while distinguishing between different groups of immigrants.
Differences in responses may be due to differences in the skill distribution between
immigrant groups and natives, or differences in demand for immigrants and natives
of the same skills due to differential allocation of immigrants and natives across
industries and regions. We demonstrate that substantial differences in cyclical
patterns remain, even within narrowly defined groups. Finally, we estimate a more
structural factor type model that, using regional variation in economic conditions,
separates responses to economic shocks from a secular trend and allows us to
obtain a summary measure for these differences within education groups
Limit on T-violating P-conserving rhoNN interaction from the gamma decay of Fe-57
We use the experimental limit on the interference of M1 and E2 multipoles in the Îł decay of 57Fe to bound the time-reversal-violating parity-conserving ĎNN vertex. Our approach is a large-basis shell-model calculation of the interference. We find an upper limit on the parameter gÂŻĎ, the relative strength of the T-violating ĎNN vertex, of close to 10^(-2), a value similar to the best limits from other experiments
RL10A-3-3B high mixture ratio qualification program
The results of the high mixture ratio qualification testing of the RL10 engine for the Shuttle/Centaur program are presented. The objective of the engine qualification test was to demonstrate the suitability of the RL10A-3-3B engine for space vehicle flight by subjecting it to the testing specified in RL10A-3-3B Model Specification Number 2295 dated February 1986. The applicable section of the specification is presented. Due to payload volume advantages which can be achieved by increasing the operating mixture ratio of the RL10, a decision was made to qualify the engine to run at a higher mixture ratio. A program was created to qualify the RL10 engine for operation at 15,000 pounds thrust and a nominal 6.0 to 1 mixture ratio. This model of the engine was designated the RL10A-3-3B. The qualification program included three test series as follows: (1) hardware durability and limits test in which the engine completed 23 firings and 4605.7 seconds with 1588.7 seconds at less than 6.6 mixture ratio; (2) preliminary qualification test in which the engine completed 26 firings and 5750 seconds; and (3) qualification test in which the engine completed 26 hot firings and 5693.4 seconds with 905.9 seconds at 6.7 mixture ratio. Several changes in engine hardware were required for operation of the RL10A-3-3B engine in the Space Shuttle which include a duel pressure switch ignition, an oxidizer flow control, and helium plumbing changes
Nonclassicality filters and quasiprobabilities
Necessary and sufficient conditions for the nonclassicality of bosonic
quantum states are formulated by introducing nonclassicality filters and
nonclassicality quasiprobability distributions. Regular quasiprobabilities are
constructed from characteristic functions which can be directly sampled by
balanced homodyne detection. Their negativities uncover the nonclassical
effects of general quantum states. The method is illustrated by visualizing the
nonclassical nature of a squeezed state.Comment: Significantly revised version, more emphasis on practical applicatio
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