261 research outputs found
Anomalous Dynamic Arrest in a Mixture of Big and Small Particles
We present molecular dynamics simulations on the slow dynamics of a mixture
of big and small soft-spheres with a large size disparity. Dynamics are
investigated in a broad range of temperature and mixture composition. As a
consequence of large size disparity, big and small particles exhibit very
different relaxation times. As previously reported for simple models of
short-ranged attractive colloids and polymer blends, several anomalous dynamic
features are observed: i) sublinear behavior for mean squared displacements,
ii) concave-to-convex crossover for density-density correlators, by varying
temperature or wavevector, iii) logarithmic decay for specific wavevectors of
density-density correlators. These anomalous features are observed over time
intervals extending up to four decades, and strongly resemble predictions of
the Mode Coupling Theory (MCT) for state points close to higher-order MCT
transitions, which originate from the competition between different mechanisms
for dynamic arrest. For the big particles we suggest competition between
soft-sphere repulsion and depletion effects induced by neighboring small
particles. For the small particles we suggest competition between bulk-like
dynamics and confinement, respectively induced by neighboring small particles
and by the slow matrix of big particles. By increasing the size disparity, a
new relaxation scenario arises for the small particles. Self-correlators decay
to zero at temperatures where density-density correlations are frozen. The
behavior of the latters resembles features characteristic of type-A MCT
transitions, defined by a zero value of the critical non-ergodicity parameter.Comment: Version 2. Added major new result
Multimode theory of measurement-induced non-Gaussian operation on wideband squeezed light
We present a multimode theory of non-Gaussian operation induced by an
imperfect on/off-type photon detector on a splitted beam from a wideband
squeezed light. The events are defined for finite time duration in the time
domain. The non-Gaussian output state is measured by the homodyne detector with
finite bandwidh . Under this time- and band-limitation to the quantm states,
we develop a formalism to evaluate the frequency mode matching between the
on/off trigger channel and the conditional signal beam in the homodyne channel.
Our formalism is applied to the CW and pulsed schemes. We explicitly calculate
the Wigner function of the conditional non-Gaussian output state in a realistic
situation. Good mode matching is achieved for BT\alt1, where the discreteness
of modes becomes prominant, and only a few modes become dominant both in the
on/off and the homodyne channels. If the trigger beam is projected nearly onto
the single photon state in the most dominant mode in this regime, the most
striking non-classical effect will be observed in the homodyne statistics. The
increase of and the dark counts degrades the non-classical effect.Comment: 20 pages, 14 figures, submitted to Phys. Rev.
Design and evaluation of in-line product repair strategies for defect reduction in the production of electric drives
Manufacturing companies are continuously facing the challenge of operating their manufacturing processes and systems in order to deliver the required production rates of high quality products of increasing complexity, with limited use and waste of resources. This aspect is particularly critical in emerging sectors, such as the e-mobility industry, where state of the art quality and process control technologies show strong limitations. This paper proposes new solutions for implementing in-line product repair strategies in the production of electric drives for the automotive industry. Moreover, it develops an innovative quantitative tool to estimate the impact of the proposed strategies on the overall process-chain performance. The benefits of the approach are validated within a real industrial context
Optimal focusing for maximal collection of entangled narrow-band photon pairs into single-mode fibers
We present a theoretical and experimental investigation of the emission
characteristics and the flux of photon pairs generated by spontaneous
parametric downconversion in quasi-phase matched bulk crystals for the use in
quantum communication sources. We show that, by careful design, one can attain
well defined modes close to the fundamental mode of optical fibers and obtain
high coupling efficiencies also for bulk crystals, these being more easily
aligned than crystal waveguides. We distinguish between singles coupling,
conditional coincidence, and pair coupling, and show how each of these
parameters can be maximized by varying the focusing of the pump mode and the
fiber-matched modes using standard optical elements. Specifically we analyze a
periodically poled KTP-crystal pumped by a 532 nm laser creating photon pairs
at 810 nm and 1550 nm. Numerical calculations lead to coupling efficiencies
above 94% at optimal focusing, which is found by the geometrical relation L/z_R
to be ~ 1 to 2 for the pump mode and ~ 2 to 3 for the fiber-modes, where L is
the crystal length and z_R is the Rayleigh-range of the mode-profile. These
results are independent on L. By showing that the single-mode bandwidth
decreases as 1/L, we can therefore design the source to produce and couple
narrow bandwidth photon pairs well into the fibers. Smaller bandwidth means
both less chromatic dispersion for long propagation distances in fibers, and
that telecom Bragg gratings can be utilized to compensate for broadened photon
packets--a vital problem for time-multiplexed qubits. Longer crystals also
yield an increase in fiber photon flux proportional to sqrt{L}, and so,
assuming correct focusing, we can only see advantages using long crystals.Comment: 19 pages, 15 figures, ReVTeX4, minor revisio
Mode-coupling theory for structural and conformational dynamics of polymer melts
A mode-coupling theory for dense polymeric systems is developed which
unifyingly incorporates the segmental cage effect relevant for structural
slowing down and polymer chain conformational degrees of freedom. An ideal
glass transition of polymer melts is predicted which becomes molecular-weight
independent for large molecules. The theory provides a microscopic
justification for the use of the Rouse theory in polymer melts, and the results
for Rouse-mode correlators and mean-squared displacements are in good agreement
with computer simulation results.Comment: 4 pages, 3 figures, Phys. Rev. Lett. in pres
Quantum state reconstruction of the single-photon Fock state
We have reconstructed the quantum state of optical pulses containing single
photons using the method of phase-randomized pulsed optical homodyne
tomography. The single-photon Fock state |1> was prepared using conditional
measurements on photon pairs born in the process of parametric down-conversion.
A probability distribution of the phase-averaged electric field amplitudes with
a strongly non-Gaussian shape is obtained with the total detection efficiency
of (55+-1)%. The angle-averaged Wigner function reconstructed from this
distribution shows a strong dip reaching classically impossible negative values
around the origin of the phase space.Comment: 4 pages, 4 figures, to appear in Physical Review Letters. Avoid
downloading PDF due to extremely poor figure resolution. Use Postscrip
Simulation study of Non-ergodicity Transitions: Gelation in Colloidal Systems with Short Range Attractions
Computer simulations were used to study the gel transition occurring in
colloidal systems with short range attractions. A colloid-polymer mixture was
modelled and the results were compared with mode coupling theory expectations
and with the results for other systems (hard spheres and Lennard Jones). The
self-intermediate scattering function and the mean squared displacement were
used as the main dynamical quantities. Two different colloid packing fractions
have been studied. For the lower packing fraction, -scaling holds and
the wave-vector analysis of the correlation function shows that gelation is a
regular non-ergodicity transition within MCT. The leading mechanism for this
novel non-ergodicity transition is identified as bond formation caused by the
short range attraction. The time scale and diffusion coefficient also show
qualitatively the expected behaviour, although different exponents are found
for the power-law divergences of these two quantities. The non-Gaussian
parameter was also studied and very large correction to Gaussian behaviour
found. The system with higher colloid packing fraction shows indications of a
nearby high-order singularity, causing -scaling to fail, but the
general expectations for non-ergodicity transitions still hold.Comment: 13 pages, 15 figure
Synthesis and tomographic characterization of the displaced Fock state of light
Displaced Fock states of the electromagnetic field have been synthesized by
overlapping the pulsed optical single-photon Fock state |1> with coherent
states on a high-reflection beamsplitter and completely characterized by means
of quantum homodyne tomography. The reconstruction reveals highly non-classical
properties of displaced Fock states, such as negativity of the Wigner function
and photon number oscillations. This is the first time complete tomographic
reconstruction has been performed on a highly non-classical optical state
Conformational and Structural Relaxations of Poly(ethylene oxide) and Poly(propylene oxide) Melts: Molecular Dynamics Study of Spatial Heterogeneity, Cooperativity, and Correlated Forward-Backward Motion
Performing molecular dynamics simulations for all-atom models, we
characterize the conformational and structural relaxations of poly(ethylene
oxide) and poly(propylene oxide) melts. The temperature dependence of these
relaxation processes deviates from an Arrhenius law for both polymers. We
demonstrate that mode-coupling theory captures some aspects of the glassy
slowdown, but it does not enable a complete explanation of the dynamical
behavior. When the temperature is decreased, spatially heterogeneous and
cooperative translational dynamics are found to become more important for the
structural relaxation. Moreover, the transitions between the conformational
states cease to obey Poisson statistics. In particular, we show that, at
sufficiently low temperatures, correlated forward-backward motion is an
important aspect of the conformational relaxation, leading to strongly
nonexponential distributions for the waiting times of the dihedrals in the
various conformational statesComment: 13 pages, 13 figure
Enhanced response inhibition during intensive meditation training predicts improvements in self-reported adaptive socioemotional functioning.
We examined the impact of training-induced improvements in self-regulation, operationalized in terms of response inhibition, on longitudinal changes in self-reported adaptive socioemotional functioning. Data were collected from participants undergoing 3 months of intensive meditation training in an isolated retreat setting (Retreat 1) and a wait-list control group that later underwent identical training (Retreat 2). A 32-min response inhibition task (RIT) was designed to assess sustained self-regulatory control. Adaptive functioning (AF) was operationalized as a single latent factor underlying self-report measures of anxious and avoidant attachment, mindfulness, ego resilience, empathy, the five major personality traits (extroversion, agreeableness, conscientiousness, neuroticism, and openness to experience), diffi-culties in emotion regulation, depression, anxiety, and psychological well-being. Participants in Retreat 1 improved in RIT performance and AF over time whereas the controls did not. The control participants later also improved on both dimensions during their own retreat (Retreat 2). These improved levels of RIT performance and AF were sustained in follow-up assessments conducted approximately 5 months after the training. Longitudinal dynamic models with combined data from both retreats showed that improvement in RIT performance during training influenced the change in AF over time, which is consistent with a key claim in the Buddhist literature that enhanced capacity for self-regulation is an important precursor of changes in emotional well-being
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