381 research outputs found
Evaporation induced flow inside circular wells
Flow field and height averaged radial velocity inside a droplet evaporating
in an open circular well were calculated for different modes of liquid
evaporation.Comment: 5 page, 3 figures, submitted to European Physical Journal
Phase diagram of a Bose gas near a wide Feshbach resonance
In this paper, we study the phase diagram of a homogeneous Bose gas with a
repulsive interaction near a wide Feshbach resonance at zero temperature. The
Bose-Einstein-condensation (BEC) state of atoms is a metastable state. When the
scattering length exceeds a critical value depending on the atom density
, , the molecular excitation energy is imaginary and the atomic
BEC state is dynamically unstable against molecule formation. The BEC state of
diatomic molecules has lower energy, where the atomic excitation is gapped and
the molecular excitation is gapless. However when the scattering length is
above another critical value, , the molecular BEC state becomes a
unstable coherent mixture of atoms and molecules. In both BEC states, the
binding energy of diatomic molecules is reduced due to the many-body effect.Comment: 5 pages, 4 figure
Current-density functional theory of time-dependent linear response in quantal fluids: recent progress
Vignale and Kohn have recently formulated a local density approximation to
the time-dependent linear response of an inhomogeneous electron system in terms
of a vector potential for exchange and correlation. The vector potential
depends on the induced current density through spectral kernels to be evaluated
on the homogeneous electron-gas. After a brief review of their theory, the case
of inhomogeneous Bose superfluids is considered, with main focus on dynamic
Kohn-Sham equations for the condensate in the linear response regime and on
quantal generalized hydrodynamic equations in the weak inhomogeneity limit. We
also present the results of calculations of the exchange-correlation spectra in
both electron and superfluid boson systems.Comment: 12 pages, 2 figures, Postscript fil
Thermally fluctuating superconductors in two dimensions
We describe the different regimes of finite temperature dynamics in the
vicinity of a zero temperature superconductor to insulator quantum phase
transition in two dimensions. New results are obtained for a low temperature
phase-only hydrodynamics, and for the intermediate temperature quantum-critical
region. In the latter case, we obtain a universal relationship between the
frequency-dependence of the conductivity and the value of the d.c. resistance.Comment: Presentation completely revised; 4 pages, 2 figure
Studying the local character of Raman features of single-walled carbon nanotubes along a bundle using TERS
Here, we show that the Raman intensity of the G-mode in tip-enhanced Raman spectroscopy (TERS) is strongly dependent on the height of the bundle. Moreover, using TERS we are able to position different single-walled carbon nanotubes along a bundle, by correlating the observed radial breathing mode (RBM) with the AFM topography at the measuring point. The frequency of the G- mode behaves differently in TERS as compared to far-field Raman. Using the RBM frequency, the diameters of the tubes were calculated and a very good agreement with the G--mode frequency was observed
Non-equilibrium coherence dynamics in one-dimensional Bose gases
Low-dimensional systems are beautiful examples of many-body quantum physics.
For one-dimensional systems the Luttinger liquid approach provides insight into
universal properties. Much is known of the equilibrium state, both in the
weakly and strongly interacting regime. However, it remains a challenge to
probe the dynamics by which this equilibrium state is reached. Here we present
a direct experimental study of the coherence dynamics in both isolated and
coupled degenerate 1d Bose gases. Dynamic splitting is used to create two 1d
systems in a phase coherent state. The time evolution of the coherence is
revealed in local phase shifts of the subsequently observed interference
patterns. Completely isolated 1d Bose gases are observed to exhibit a universal
sub-exponential coherence decay in excellent agreement with recent predictions
by Burkov et al. [Phys. Rev. Lett. 98, 200404 (2007)]. For two coupled 1d Bose
gases the coherence factor is observed to approach a non-zero equilibrium value
as predicted by a Bogoliubov approach. This coupled-system decay to finite
coherence is the matter wave equivalent of phase locking two lasers by
injection. The non-equilibrium dynamics of superfluids plays an important role
in a wide range of physical systems, such as superconductors, quantum-Hall
systems, superfluid Helium, and spin systems. Our experiments studying
coherence dynamics show that 1d Bose gases are ideally suited for investigating
this class of phenomena.Comment: to appear in natur
Spacial and temporal dynamics of the volume fraction of the colloidal particles inside a drying sessile drop
Using lubrication theory, drying processes of sessile colloidal droplets on a
solid substrate are studied. A simple model is proposed to describe temporal
dynamics both the shape of the drop and the volume fraction of the colloidal
particles inside the drop. The concentration dependence of the viscosity is
taken into account. It is shown that the final shapes of the drops depend on
both the initial volume fraction of the colloidal particles and the capillary
number. The results of our simulations are in a reasonable agreement with the
published experimental data. The computations for the drops of aqueous solution
of human serum albumin (HSA) are presented.Comment: Submitted to EPJE, 7 pages, 8 figure
Silver nanowire-based transparent, flexible, and conductive thin film
The fabrication of transparent, conductive, and uniform silver nanowire films using the scalable rod-coating technique is described in this study. Properties of the transparent conductive thin films are investigated, as well as the approaches to improve the performance of transparent silver nanowire electrodes. It is found that silver nanowires are oxidized during the coating process. Incubation in hydrogen chloride (HCl) vapor can eliminate oxidized surface, and consequently, reduce largely the resistivity of silver nanowire thin films. After HCl treatment, 175 Ω/sq and approximately 75% transmittance are achieved. The sheet resistivity drops remarkably with the rise of the film thickness or with the decrease of transparency. The thin film electrodes also demonstrated excellent flexible stability, showing < 2% resistance change after over 100 bending cycles
Design and Analysis of Nanotube-Based Memory Cells
In this paper, we proposed a nanoelectromechanical design as memory cells. A simple design contains a double-walled nanotube-based oscillator. Atomistic materials are deposed on the outer nanotube as electrodes. Once the WRITE voltages are applied on electrodes, the induced electromagnetic force can overcome the interlayer friction between the inner and outer tubes so that the oscillator can provide stable oscillations. The READ voltages are employed to indicate logic 0/1 states based on the position of the inner tube. A new continuum modeling is developed in this paper to analyze large models of the proposed nanoelectromechanical design. Our simulations demonstrate the mechanisms of the proposed design as both static and dynamic random memory cells
Probing quantum and thermal noise in an interacting many-body system
The probabilistic character of the measurement process is one of the most
puzzling and fascinating aspects of quantum mechanics. In many-body systems
quantum mechanical noise reveals non-local correlations of the underlying
many-body states. Here, we provide a complete experimental analysis of the
shot-to-shot variations of interference fringe contrast for pairs of
independently created one-dimensional Bose condensates. Analyzing different
system sizes we observe the crossover from thermal to quantum noise, reflected
in a characteristic change in the distribution functions from Poissonian to
Gumbel-type, in excellent agreement with theoretical predictions based on the
Luttinger liquid formalism. We present the first experimental observation of
quasi long-range order in one-dimensional atomic condensates, which is a
hallmark of quantum fluctuations in one-dimensional systems. Furthermore, our
experiments constitute the first analysis of the full distribution of quantum
noise in an interacting many-body system
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