2,219 research outputs found
State detection using coherent Raman repumping and two-color Raman transfers
We demonstrate state detection based on coherent Raman repumping and a
two-color Raman state transfer. The Raman coupling during detection selectively
eliminates unwanted dark states in the fluorescence cycle without compromising
the immunity of the desired dark state to off-resonant scattering. We
demonstrate this technique using where a combination of
Raman coupling and optical pumping leaves the
metastable state optically dark and immune to off-resonant scattering. All
other states are strongly coupled to the upper levels. We achieve a
single shot state-detection efficiency of in a
integration time, limited almost entirely by technical imperfections. Shelving
to the state before detection is performed via a two-color
Raman transfer with a fidelity of
Kinetic Theory of Response Functions for the Hard Sphere Granular Fluid
The response functions for small spatial perturbations of a homogeneous
granular fluid have been described recently. In appropriate dimensionless
variables, they have the form of stationary state time correlation functions.
Here, these functions are expressed in terms of reduced single particle
functions that are expected to obey a linear kinetic equation. The functional
assumption required for such a kinetic equation, and a Markov approximation for
its implementation are discussed. If, in addition, static velocity correlations
are neglected, a granular fluid version of the linearized Enskog kinetic theory
is obtained. The derivation makes no a priori limitation on the density, space
and time scale, nor degree of inelasticity. As an illustration, recently
derived Helfand and Green-Kubo expressions for the Navier-Stokes order
transport coefficients are evaluated with this kinetic theory. The results are
in agreement with those obtained from the Chapman-Enskog solution to the
nonlinear Enskog kinetic equation.Comment: Submitted to J. Stat. Mec
Solidity of viscous liquids. IV. Density fluctuations
This paper is the fourth in a series exploring the physical consequences of
the solidity of highly viscous liquids. It is argued that the two basic
characteristics of a flow event (a jump between two energy minima in
configuration space) are the local density change and the sum of all particle
displacements. Based on this it is proposed that density fluctuations are
described by a time-dependent Ginzburg-Landau equation with rates in k-space of
the form with where is the average
intermolecular distance. The inequality expresses a long-wavelength dominance
of the dynamics which implies that the Hamiltonian (free energy) may be taken
to be ultra local. As an illustration of the theory the case with the simplest
non-trivial Hamiltonian is solved to second order in the Gaussian
approximation, where it predicts an asymmetric frequency dependence of the
isothermal bulk modulus with Debye behavior at low frequencies and an
decay of the loss at high frequencies. Finally, a general
formalism for the description of viscous liquid dynamics, which supplements the
density dynamics by including stress fields, a potential energy field, and
molecular orientational fields, is proposed
Solidity of viscous liquids. V. Long-wavelength dominance of the dynamics
This paper is the fifth in a series exploring the physical consequences of
the solidity of glass-forming liquids. Paper IV proposed a model where the
density field is described by a time-dependent Ginzburg-Landau equation of the
nonconserved type with rates in space of the form . The
model assumes that where is the average intermolecular
distance; this inequality expresses a long-wavelength dominance of the dynamics
which implies that the Hamiltonian (free energy) to a good approximation may be
taken to be ultralocal. In the present paper we argue that this is the simplest
model consistent with the following three experimental facts: 1) Viscous
liquids approaching the glass transition do not develop long-range order; 2)
The glass has lower compressibility than the liquid; 3) The alpha process
involves several decades of relaxation times shorter than the mean relaxation
time. The paper proceeds to list six further experimental facts characterizing
equilibrium viscous liquid dynamics and shows that these are readily understood
in terms of the model; some are direct consequences, others are quite natural
when viewed in light of the model
Brain-inspired computing with fluidic iontronic nanochannels
The unparalleled energy efficiency of the brain is driving researchers to
seek out new brain-inspired (neuromorphic) computing paradigms. Artificial
aqueous ion channels are emerging as an exciting new platform for neuromorphic
computing, representing a departure from conventional solid-state devices by
directly mimicking the fluidic ion transport found in the brain. However,
despite recent interest, a tangible demonstration of neuromorphic computing
remains a challenge. Here we successfully perform neuromorphic reservoir
computing using easy to fabricate tapered microchannels that embed a conducting
network of fluidic nanochannels between colloids, which we show to be a novel
memristor (memory resistor). Remarkably, a wide range of typical conductance
memory timescales can easily be achieved by constructing channels of different
length, a unique and highly desirable feature. This work is inspired and
supported by a new theoretical model, which stems directly from traditional
diffusion-conduction equations and shows excellent agreement with the
experiments, predicting the features and relevant parameters presented here.
Our results represent a fundamental step in realising the promise of ion
channels as a new platform to emulate the rich aqueous dynamics of the brain
Short-time inertial response of viscoelastic fluids measured with Brownian motion and with active probes
We have directly observed short-time stress propagation in viscoelastic
fluids using two optically trapped particles and a fast interferometric
particle-tracking technique. We have done this both by recording correlations
in the thermal motion of the particles and by measuring the response of one
particle to the actively oscillated second particle. Both methods detect the
vortex-like flow patterns associated with stress propagation in fluids. This
inertial vortex flow propagates diffusively for simple liquids, while for
viscoelastic solutions the pattern spreads super-diffusively, dependent on the
shear modulus of the medium
Multiple-scattering effects on incoherent neutron scattering in glasses and viscous liquids
Incoherent neutron scattering experiments are simulated for simple dynamic
models: a glass (with a smooth distribution of harmonic vibrations) and a
viscous liquid (described by schematic mode-coupling equations). In most
situations multiple scattering has little influence upon spectral
distributions, but it completely distorts the wavenumber-dependent amplitudes.
This explains an anomaly observed in recent experiments
Nonlinear Hydrodynamics of a Hard Sphere Fluid Near the Glass Transition
We conduct a numerical study of the dynamic behavior of a dense hard sphere
fluid by deriving and integrating a set of Langevin equations. The statics of
the system is described by a free energy functional of the
Ramakrishnan-Yussouff form. We find that the system exhibits glassy behavior as
evidenced through stretched exponential decay and two-stage relaxation of the
density correlation function. The characteristic times grow with increasing
density according to the Vogel-Fulcher law. The wavenumber dependence of the
kinetics is extensively explored. The connection of our results with
experiment, mode coupling theory, and molecular dynamics results is discussed.Comment: 34 Pages, Plain TeX, 12 PostScript Figures (not included, available
on request
Post-Eocene coupled oroclines in the Talesh (NW Iran): paleomagnetic constraints
The Talesh Mountains (NW Iran) witnessed a long deformation history from the Triassic Cimmerian orogeny to the ongoing Arabia-Eurasia collision. This protracted multi-stage deformation has generated a remarkably curved orogen with a puzzling kinematic and deformational history. In this study, we investigate the origin of the Talesh curvature through paleomagnetic analyses on rocks of Paleozoic, Mesozoic and Cenozoic age. Our results indicate that at least two major, large-scale, vertical-axis-rotations took place since the Late Cretaceous: 1) a pre-Eocene 73° ± 17° clockwise rotation and 2) post-Eocene differential rotations that formed the Z-shaped mountain belt within a crustal-scale shear zone. The latter involved an increasing amount of clockwise (CW) rotation from south (16°) to north (48°). The orocline formation likely started during the Oligocene where an approximately east-west oriented mountain belt was buckled by the Arabia-Eurasia collision, with Arabia acting as a rigid indenter and the South Caspian basin as a rigid backstop. We hypothesise that the NE-SW oriented Aras and Lahijan fault zones, inherited from transform faults related to the Mesozoic opening of the Caspian-Black Sea back-arc, accommodated the coupled orocline formation
Pressure induced structural and dynamical changes in liquid Si. An ab-initio study
The static and dynamic properties of liquid Si at high-pressure have been
studied using the orbital free ab-initio molecular dynamics method. Four
thermodynamic states at pressures 4, 8, 14 and 23 GPa are considered. The
calculated static structure shows qualitative agreement with the available
experimental data. We analize the remarkable structural changes occurring
between 8 and 14 GPa along with its effect on several dynamic properties.Comment: 10 pages, 11 figures. Accepted for publication in Journal of Physics:
Condensed Matte
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