554 research outputs found
Effective Temperature in a Colloidal Glass
We study the Brownian motion of particles trapped by optical tweezers inside
a colloidal glass (Laponite) during the sol-gel transition. We use two methods
based on passive rheology to extract the effective temperature from the
fluctuations of the Brownian particles. All of them give a temperature that,
within experimental errors, is equal to the heat bath temperature. Several
interesting features concerning the statistical properties and the long time
correlations of the particles are observed during the transition.Comment: to be published in Philosophical Magazin
Gastric perforation and pancreatitis manifesting after an inadvertent nissen fundoplication in a patient with superior mesenteric artery syndrome.
Superior mesenteric artery (SMA) syndrome is an uncommon but well-recognized clinical entity. It can lead to proximal small bowel obstruction and severe morbidity and mortality in lieu of late diagnosis and concomitant existing comorbidities. We report a 54-year-old female, with SMA syndrome which manifested itself after Nissen fundoplication along with two major complications. The diagnosis of SMA was established by clinical symptoms and radiological findings
Symmetric photon-photon coupling by atoms with Zeeman-split sublevels
We propose a simple scheme for highly efficient nonlinear interaction between
two weak optical fields. The scheme is based on the attainment of
electromagnetically induced transparency simultaneously for both fields via
transitions between magnetically split F=1 atomic sublevels, in the presence of
two driving fields. Thereby, equal slow group velocities and symmetric
cross-coupling of the weak fields over long distances are achieved. By simply
tuning the fields, this scheme can either yield giant cross-phase modulation or
ultrasensitive two-photon switching.Comment: Modified scheme, 4 pages, 1 figur
Giant nonlinearity and entanglement of single photons in photonic bandgap structures
Giantly enhanced cross-phase modulation with suppressed spectral broadening
is predicted between optically-induced dark-state polaritons whose propagation
is strongly affected by photonic bandgaps of spatially periodic media with
multilevel dopants. This mechanism is shown to be capable of fully entangling
two single-photon pulses with high fidelity.Comment: 7 pages, 1 figur
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The ISSI international study team on the martian PBL – status report and plan
Dynamical processes in the Martian boundary layer provide the means of communication between surface ice deposits and the free atmosphere, and the means of lifting dust from the surface. The boundary layer is therefore one of the most important components of the Martian climate system. The Martian boundary layer differs from that of the Earth in that it is more strongly forced, it is deeper, and the relative importance of radiative and convective heat fluxes in the lower boundary layer can be quite different. In order to understand the Martian boundary layer, a combination of theoretical, modeling and observational studies are necessary. Interactions between theorists, modelers, and observational scientists are needed to make progress and to provide a basis for analysis of data expected from Phoenix, Mars Science Laboratory, ExoMars and other future landed missions (such as a surface network mission), or missions such as balloons or other aircraft operating in the neutral atmosphere. The prime goal of this project under the auspices of the International Space Science Institute (ISSI) is to review and assess the current knowledge and understanding of Martian planetary boundary layer and its interactions with the surface and free atmosphere. We aim to promote international communication and collaboration to enhance the rate of acquisition of knowledge and understanding. This will be achieved through an International Study Team and publication of overview papers and individual reports on recent advances in this area
Estimate of the free energy difference in mechanical systems from work fluctuations: experiments and models
The work fluctuations of an oscillator in contact with a heat reservoir and
driven out of equilibrium by an external force are studied experimentally. The
oscillator dynamics is modeled by a Langevin equation. We find both
experimentally and theoretically that, if the driving force does not change the
equilibrium properties of the thermal fluctuations of this mechanical system,
the free energy difference between two equilibrium states can be
exactly computed using the Jarzynski equality (JE) and the Crooks relation (CR)
\cite{jarzynski1, crooks1, jarzynski2}, independently of the time scale and
amplitude of the driving force. The applicability limits for the JE and CR at
very large driving forces are discussed. Finally, when the work fluctuations
are Gaussian, we propose an alternative empirical method to compute
which can be safely applied, even in cases where the JE and CR might not hold.
The results of this paper are useful to compute in complex systems
such as the biological ones.Comment: submitted to Journal of Statistical Mechanics: Theory and experimen
Towards deterministic optical quantum computation with coherently driven atomic ensembles
Scalable and efficient quantum computation with photonic qubits requires (i)
deterministic sources of single-photons, (ii) giant nonlinearities capable of
entangling pairs of photons, and (iii) reliable single-photon detectors. In
addition, an optical quantum computer would need a robust reversible photon
storage devise. Here we discuss several related techniques, based on the
coherent manipulation of atomic ensembles in the regime of electromagnetically
induced transparency, that are capable of implementing all of the above
prerequisites for deterministic optical quantum computation with single
photons.Comment: 11 pages, 7 figure
Bose-Einstein condensates in strong electric fields -- effective gauge potentials and rotating states
Magnetically-trapped atoms in Bose-Einstein condensates are spin polarized.
Since the magnetic field is inhomogeneous, the atoms aquire Berry phases of the
Aharonov-Bohm type during adiabatic motion. In the presence of an eletric field
there is an additional Aharonov-Casher effect. Taking into account the
limitations on the strength of the electric fields due to the polarizability of
the atoms, we investigate the extent to which these effects can be used to
induce rotation in a Bose-Einstein condensate.Comment: 5 pages, 2 ps figures, RevTe
Attractively bound pairs of atoms in the Bose-Hubbard model and antiferromagnetism
We consider a periodic lattice loaded with pairs of bosonic atoms tightly
bound to each other via strong attractive on-site interaction that exceeds the
inter-site tunneling rate. An ensemble of such lattice-dimers is accurately
described by an effective Hamiltonian of hard core bosons with strong
nearest-neighbor repulsion which is equivalent to the model with
Ising-like anisotropy. We calculate the ground-state phase diagram for a
one-dimensional system which exhibits incompressible phases, corresponding to
an empty and a fully filled lattice (ferromagnetic phases) and a half-filled
alternating density crystal (anti-ferromagnetic phase), separated from each
other by compressible phases. In a finite lattice the compressible phases show
characteristic oscillatory modulations on top of the anti-ferromagnetic density
profile and in density-density correlations. We derive a kink model which
provides simple quantitative explanation of these features. To describe the
long-range correlations of the system we employ the Luttinger liquid theory
with the relevant Luttinger parameter obtained exactly using the Bethe
Ansatz solution. We calculate the density-density as well as first-order
correlations and find excellent agreement with numerical results obtained with
density matrix renormalization group (DMRG) methods. We also present a
perturbative treatment of the system in higher dimensions.Comment: 10 pages, 9 figure
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