10,705 research outputs found
Facilitated spin models of dissipative quantum glasses
We introduce a class of dissipative quantum spin models with local
interactions and without quenched disorder that show glassy behaviour. These
models are the quantum analogs of the classical facilitated spin models. Just
like their classical counterparts, quantum facilitated models display complex
glassy dynamics despite the fact that their stationary state is essentially
trivial. In these systems, dynamical arrest is a consequence of kinetic
constraints and not of static ordering. These models display a quantum version
of dynamic heterogeneity: the dynamics towards relaxation is spatially
correlated despite the absence of static correlations. Associated dynamical
fluctuation phenomena such as decoupling of timescales is also observed.
Moreover, we find that close to the classical limit quantum fluctuations can
enhance glassiness, as recently reported for quantum liquids.Comment: 7 pages, 6 figure
Multiple peak aggregations for the Keller-Segel system
In this paper we derive matched asymptotic expansions for a solution of the
Keller-Segel system in two space dimensions for which the amount of mass
aggregation is , where Previously available asymptotics
had been computed only for the case in which N=1
Experimental Demonstration of >230{\deg} Phase Modulation in Gate-Tunable Graphene-Gold Reconfigurable Mid-Infrared Metasurfaces
Metasurfaces offer significant potential to control far-field light
propagation through the engineering of amplitude, polarization, and phase at an
interface. We report here phase modulation of an electronically reconfigurable
metasurface and demonstrate its utility for mid-infrared beam steering. Using a
gate-tunable graphene-gold resonator geometry, we demonstrate highly tunable
reflected phase at multiple wavelengths and show up to 237{\deg} phase
modulation range at an operating wavelength of 8.50 {\mu}m. We observe a smooth
monotonic modulation of phase with applied voltage from 0{\deg} to 206{\deg} at
a wavelength of 8.70 {\mu}m. Based on these experimental data, we demonstrate
with antenna array calculations an average beam steering efficiency of 50% for
reflected light for angles up to 30{\deg}, relative to an ideal metasurface,
confirming the suitability of this geometry for reconfigurable mid-infrared
beam steering devices
Can there be neutrino oscillation in Gamma-Ray Bursts fireball ?
The central engine which powers the Gamma-Ray Burst (GRB) fireball, produces
neutrinos in the energy range of about 5-20 MeV. Fractions of these neutrinos
may propagate through the fireball which is far away from the central engine.
We have studied the propagation of these neutrinos through the fireball which
is contaminated by baryons and have shown that, resonant conversion of
neutrinos are possible for the oscillations of nu_e to nu_{mu,tau}, nu_e to
nu_s and anti-nu_(mu,tou) to anti-nu_s if the neutrino mass square difference
and mixing angle are in the atmospheric and/or LSND range. On the other hand it
is probably difficult for neutrinos to have resonant oscillation if the
neutrino parameters are in the solar neutrino range. From the resonance
condition we have estimated the fireball temperature and the baryon load in it.Comment: 4 pages, two column text, To be published in Phys. Rev.
Realisation of Hardy's Thought Experiment
We present an experimental realisation of Hardy's thought experiment [Phys.
Rev. Lett. {\bf 68}, 2981 (1992)], using photons. The experiment consists of a
pair of Mach-Zehnder interferometers that interact through photon bunching at a
beam splitter. A striking contradiction is created between the predictions of
quantum mechanics and local hidden variable based theories. The contradiction
relies on non-maximally entangled position states of two particles.Comment: 5 page
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The tarantula toxin GxTx detains K+ channel gating charges in their resting conformation.
Allosteric ligands modulate protein activity by altering the energy landscape of conformational space in ligand-protein complexes. Here we investigate how ligand binding to a K+ channel's voltage sensor allosterically modulates opening of its K+-conductive pore. The tarantula venom peptide guangxitoxin-1E (GxTx) binds to the voltage sensors of the rat voltage-gated K+ (Kv) channel Kv2.1 and acts as a partial inverse agonist. When bound to GxTx, Kv2.1 activates more slowly, deactivates more rapidly, and requires more positive voltage to reach the same K+-conductance as the unbound channel. Further, activation kinetics are more sigmoidal, indicating that multiple conformational changes coupled to opening are modulated. Single-channel current amplitudes reveal that each channel opens to full conductance when GxTx is bound. Inhibition of Kv2.1 channels by GxTx results from decreased open probability due to increased occurrence of long-lived closed states; the time constant of the final pore opening step itself is not impacted by GxTx. When intracellular potential is less than 0 mV, GxTx traps the gating charges on Kv2.1's voltage sensors in their most intracellular position. Gating charges translocate at positive voltages, however, indicating that GxTx stabilizes the most intracellular conformation of the voltage sensors (their resting conformation). Kinetic modeling suggests a modulatory mechanism: GxTx reduces the probability of voltage sensors activating, giving the pore opening step less frequent opportunities to occur. This mechanism results in K+-conductance activation kinetics that are voltage-dependent, even if pore opening (the rate-limiting step) has no inherent voltage dependence. We conclude that GxTx stabilizes voltage sensors in a resting conformation, and inhibits K+ currents by limiting opportunities for the channel pore to open, but has little, if any, direct effect on the microscopic kinetics of pore opening. The impact of GxTx on channel gating suggests that Kv2.1's pore opening step does not involve movement of its voltage sensors
The importance of flavor in leptogenesis
We study leptogenesis from the out-of-equilibrium decays of the lightest
heavy neutrino in the medium (low) temperature regime, T\lsim 10^{12}
GeV ( GeV), where the rates of processes mediated by the (and
) Yukawa coupling are non negligible, implying that the effects of lepton
flavors must be taken into account. We find important quantitative and
qualitative differences with respect to the case where flavor effects are
ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of
magnitude; (ii) The sign of the asymmetry can be opposite to what one would
predict from the sign of the total lepton asymmetry ; (iii)
Successful leptogenesis is possible even with .Comment: 27 pages, 2 figures. Added 3 reference
Scaling properties of growing noninfinitesimal perturbations in space-time chaos
We study the spatiotemporal dynamics of random spatially distributed
noninfinitesimal perturbations in one-dimensional chaotic extended systems. We
find that an initial perturbation of finite size grows in time
obeying the tangent space dynamic equations (Lyapunov vectors) up to a
characteristic time , where is the largest Lyapunov exponent and
is a constant. For times perturbations exhibit spatial
correlations up to a typical distance . For times larger than
finite perturbations are no longer described by tangent space
equations, memory of spatial correlations is progressively destroyed and
perturbations become spatiotemporal white noise. We are able to explain these
results by mapping the problem to the Kardar-Parisi-Zhang universality class of
surface growth.Comment: 4.5 pages LaTeX (RevTeX4) format, 3 eps figs included. Submitted to
Phys Rev
CP violation in scatterings, three body processes and the Boltzmann equations for leptogenesis
We obtain the Boltzmann equations for leptogenesis including decay and
scattering processes with two and three body initial or final states. We
present an explicit computation of the CP violating scattering asymmetries. We
analyze their possible impact in leptogenesis, and we discuss the validity of
their approximate expressions in terms of the decay asymmetry. In scenarios in
which the initial heavy neutrino density vanishes, the inclusion of CP
asymmetries in scatterings can enforce a cancellation between the lepton
asymmetry generated at early times and the asymmetry produced at later times.
We argue that a sizeable amount of washout is crucial for spoiling this
cancellation, and we show that in the regimes in which the washouts are
particularly weak, the inclusion of CP violation in scatterings yields a
reduction in the final value of the lepton asymmetry. In the strong washout
regimes the inclusion of CP violation in scatterings still leads to a
significant enhancement of the lepton asymmetry at high temperatures; however,
due to the independence from the early conditions that is characteristic of
these regimes, the final value of the lepton asymmetry remains approximately
unchanged.Comment: 24 pages, 6 figures. One appendix added. Some numerical results and
corresponding figures (mainly fig. 3) corrected. Final version to be
published in JHE
The Trainer Project: A New Simulator-Based Driver Training Curriculum
The purpose of the EU funded TRAINER project is to develop a new cost-effective Pan-European driver training curriculum, includingcomputer-based interactive multimedia and simulator technology. Thecurriculum will pay significant attention to higher order skills including riskawareness. For this purpose a number of scenarios were developed thataddresses the most important needs of learner drivers. These scenarios are usedin a PC-based interactive multimedia tool as well as in a driving simulator. Theinteractive multimedia tool allows training and assessment of higher cognitiveskills (i.e., strategic and manoeuvring tasks), familiarisation of novice driverswith the basic principles of driving, and contributing to a better understandingof (potential) risks. A low cost stationary driving simulator is used for acquiringskills in vehicle handling and negotiating common traffic situations (i.e.,manoeuvring and control tasks). In addition, a mean cost semi-dynamic drivingsimulator is developed for supporting the needs of specific driver cohorts, suchas novice drivers with enhanced knowledge problems and drivers in high-riskgroups. Application of such an advanced computer-based curriculum alsoimplies development of criteria to allow driving instructors to determinetraining progress. These criteria are based on a database of normative driverbehaviour. This paper mainly focuses on the description of the technical (softandhardware) requirements for both low-cost and mean-cost simulators
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