19,665 research outputs found
Mean velocity, turbulence intensity and turbulence convection velocity measurements for a convergent nozzle in a free jet wind tunnel
The effect of light on the mean flow and turbulence properties of a 0.056 m circular jet were determined in a free jet wind tunnel. The nozzle exit velocity was 122 m/sec, and the wind tunnel velocity was set at 0, 12, 37, and 61 m/sec. Measurements of flow properties including mean velocity, turbulence intensity and spectra, and eddy convection velocity were carried out using two linearized hot wire anemometers. Normalization factors were determined for the mean velocity and turbulence convection velocity
Dynamical quantum phase transition of a two-component Bose-Einstein condensate in an optical lattice
We study dynamics of a two-component Bose-Einstein condensate where the two
components are coupled via an optical lattice. In particular, we focus on the
dynamics as one drives the system through a critical point of a first order
phase transition characterized by a jump in the internal populations. Solving
the time-dependent Gross-Pitaevskii equation, we analyze; breakdown of
adiabaticity, impact of non-linear atom-atom scattering, and the role of a
harmonic trapping potential. Our findings demonstrate that the phase transition
is resilient to both contact interaction between atoms and external trapping
confinement.Comment: 8 pages, 8 figure
Gravitational Radiation from Black Hole Binaries in Globular Clusters
A populations of stellar mass black hole binaries may exist in globular
clusters. The dynamics of globular cluster evolution imply that there may be at
most one black hole binary is a globular cluster. The population of binaries
are expected to have orbital periods greater than a few hours and to have a
thermal distribution of eccentricities. In the LISA band, the gravitational
wave signal from these binaries will consist of several of the higher harmonics
of the orbital frequency. A Monte Carlo simulation of the galactic globular
cluster system indicates that LISA will detect binaries in 10 % of the clusters
with an angular resolution sufficient to identify the host cluster of the
binary.Comment: 7 pages, 2 eps figures, uses iopart styl
Dilute gas of ultracold two-level atoms inside a cavity; generalized Dicke model
We consider a gas of ultracold two-level atoms confined in a cavity, taking
into account for atomic center-of-mass motion and cavity mode variations. We
use the generalized Dicke model, and analyze separately the cases of a
Gaussian, and a standing wave mode shape. Owing to the interplay between
external motional energies of the atoms and internal atomic and field energies,
the phase-diagrams exhibit novel features not encountered in the standard Dicke
model, such as the existence of first and second order phase transitions
between normal and superradiant phases. Due to the quantum description of
atomic motion, internal and external atomic degrees of freedom are highly
correlated leading to modified normal and superradiant phases.Comment: 10 pages, 7 figure
Self-Similar Graphs
For any graph on vertices and for any {\em symmetric} subgraph of
, we construct an infinite sequence of graphs based on the pair
. The First graph in the sequence is , then at each stage replacing
every vertex of the previous graph by a copy of and every edge of the
previous graph by a copy of the new graph is constructed. We call these
graphs {\em self-similar} graphs. We are interested in delineating those pairs
for which the chromatic numbers of the graphs in the sequence are
bounded. Here we have some partial results. When is a complete graph and
is a special matching we show that every graph in the resulting sequence is
an {\em expander} graph.Comment: 13 pages, 1 tabl
Thermal and hydrodynamic effects in the ordering of lamellar fluids
Phase separation in a complex fluid with lamellar order has been studied in
the case of cold thermal fronts propagating diffusively from external walls.
The velocity hydrodynamic modes are taken into account by coupling the
convection-diffusion equation for the order parameter to a generalised
Navier-Stokes equation. The dynamical equations are simulated by implementing a
hybrid method based on a lattice Boltzmann algorithm coupled to finite
difference schemes. Simulations show that the ordering process occurs with
morphologies depending on the speed of the thermal fronts or, equivalently, on
the value of the thermal conductivity {\xi}. At large value of {\xi}, as in
instantaneous quenching, the system is frozen in entangled configurations at
high viscosity while consists of grains with well ordered lamellae at low
viscosity. By decreasing the value of {\xi}, a regime with very ordered
lamellae parallel to the thermal fronts is found. At very low values of {\xi}
the preferred orientation is perpendicular to the walls in d = 2, while
perpendicular order is lost moving far from the walls in d = 3.Comment: 8 pages, 3 figures. Accepted for publication in Phil. Trans. of Royal
Soc, Ser
Charter 08's Qing Dynasty Precursor
The primary goal of the 1908 petition and the constitutional government petition movement as a whole was national salvation, preventing China from colonization. The petitioners believed that the political system of constitutional government was the source of national wealth and power; that the Qing government and the political system of imperial autocracy were outmoded as they kept China poor and weak; and that China would be as rich and powerful as the Western powers and Japan when the political system of constitutional government was adopted. The movement was a lost opportunity because the Qing court, instead of easing its legitimacy crisis through fundamental democratic reform, treated leaders of the movement as state enemies and intensified its legitimacy crisis in the years prior to its overthrow in the 1911 Revolution
LISA, binary stars, and the mass of the graviton
We extend and improve earlier estimates of the ability of the proposed LISA
(Laser Interferometer Space Antenna) gravitational wave detector to place upper
bounds on the graviton mass, m_g, by comparing the arrival times of
gravitational and electromagnetic signals from binary star systems. We show
that the best possible limit on m_g obtainable this way is ~ 50 times better
than the current limit set by Solar System measurements. Among currently known,
well-understood binaries, 4U1820-30 is the best for this purpose; LISA
observations of 4U1820-30 should yield a limit ~ 3-4 times better than the
present Solar System bound. AM CVn-type binaries offer the prospect of
improving the limit by a factor of 10, if such systems can be better understood
by the time of the LISA mission. We briefly discuss the likelihood that radio
and optical searches during the next decade will yield binaries that more
closely approach the best possible case.Comment: ReVTeX 4, 6 pages, 1 figure, submitted to Phys Rev
- …