13,536 research outputs found
Faraday patterns in dipolar Bose-Einstein condensates
Faraday patterns can be induced in Bose-Einstein condensates by a periodic
modulation of the system nonlinearity. We show that these patterns are
remarkably different in dipolar gases with a roton-maxon excitation spectrum.
Whereas for non-dipolar gases the pattern size decreases monotonously with the
driving frequency, patterns in dipolar gases present, even for shallow roton
minima, a highly non trivial frequency dependence characterized by abrupt
pattern size transitions, which are especially pronounced when the dipolar
interaction is modulated. Faraday patterns constitute hence an optimal tool for
revealing the onset of the roton minimum, a major key feature of dipolar gases.Comment: 4 pages, 10 figure
Interim user's manual for boundary layer integral matrix procedure, version J
A computer program for analyzing two dimensional and axisymmetric nozzle performance with a variety of wall boundary conditions is described. The program has been developed for application to rocket nozzle problems. Several aids to usage of the program and two auxiliary subroutines are provided. Some features of the output are described and three sample cases are included
Boundary layer integral matrix procedure code modifications and verifications
A summary of modifications to Aerotherm's Boundary Layer Integral Matrix Procedure (BLIMP) code is presented. These modifications represent a preliminary effort to make BLIMP compatible with other JANNAF codes and to adjust the code for specific application to rocket nozzle flows. Results of the initial verification of the code for prediction of rocket nozzle type flows are discussed. For those cases in which measured free stream flow conditions were used as input to the code, the boundary layer predictions and measurements are in excellent agreement. In two cases, with free stream flow conditions calculated by another JANNAF code (TDK) for use as input to BLIMP, the predictions and the data were in fair agreement for one case and in poor agreement for the other case. The poor agreement is believed to result from failure of the turbulent model in BLIMP to account for laminarization of a turbulent flow. Recommendations for further code modifications and improvements are also presented
Semi-classical scattering in two dimensions
The semi-classical limit of quantum-mechanical scattering in two dimensions
(2D) is developed. We derive the Wentzel-Kramers-Brillouin and Eikonal results
for 2D scattering. No backward or forward glory scattering is present in 2D.
Other phenomena, such as rainbow or orbiting do show up.Comment: 6 page
TB24: The Caddisflies (Trichoptera) of Maine Excepting the Family Hydroptilidae
A survey of the Trichoptera taken from light trap collections made during July and August, 1959, form the basis of the present paper. A checklist of the family Hydroptilidae known from Maine has been published. The collections were made for the most part in the Boreal Region of Maine.https://digitalcommons.library.umaine.edu/aes_techbulletin/1163/thumbnail.jp
Interaction of vortices in thin superconducting films and Berezinskii-Kosterlitz-Thouless transition
The precondition for the BKT transition in thin superconducting films, the
logarithmic intervortex interaction, is satisfied at distances short relative
to , is the London penetration depth of the
bulk material and is the film thickness. For this reason, the search for
the transition has been conducted in samples of the size . It is
argued below that film edges turn the interaction into near exponential
(short-range) thus making the BKT transition impossible. If however the
substrate is superconducting and separated from the film by an insulated layer,
the logarithmic intervortex interaction is recovered and the BKT transition
should be observable.Comment: 4 pages, no figure
Anomalous fluctuations of active polar filaments
Using a simple model, we study the fluctuating dynamics of inextensible,
semiflexible polar filaments interacting with active and directed force
generating centres such as molecular motors. Taking into account the fact that
the activity occurs on time-scales comparable to the filament relaxation time,
we obtain some unexpected differences between both the steady-state and
dynamical behaviour of active as compared to passive filaments. For the
statics, the filaments have a {novel} length-scale dependent rigidity.
Dynamically, we find strongly enhanced anomalous diffusion.Comment: 5 pages, 3 figure
Sediment Nutrient Accumulation and Nutrient Availability in Two Tidal Freshwater Marshes Along the Mattaponi River, Virginia, USA
Sediment deposition is the main mechanism of nutrient delivery to tidal freshwater marshes (TFMs). We quantified sediment nutrient accumulation in TFMs upstream and downstream of a proposed water withdrawal project on the Mattaponi River, Virginia. Our goal was to assess nutrient availability by comparing relative rates of carbon (C), nitrogen (N), and phosphorus (P) accumulated in sediments with the C, N, and P stoichiometries of surface soils and above ground plant tissues. Surface soil nutrient contents (0.60–0.92% N and 0.09–0.13% P) were low but within reported ranges for TFMs in the eastern US. In both marshes, soil nutrient pools and C, N, and P stoichiometries were closely associated with sedimentation patterns. Differences between marshes were more striking than spatial variations within marshes: both C, N, and P accumulation during summer, and annual P accumulation rates (0.16 and 0.04 g P m−2 year−1, respectively) in sediments were significantly higher at the downstream than at the upstream marsh. Nitrogen:P ratiosbiomass, surface soils, and sediments suggest that N limits primary production in these marshes, but experimental additions of N and/or P did not significantly increase above ground productivity in either marsh. Lower soil N:P ratios are consistent with higher rates of sediment P accumulation at the downstream site, perhaps due to its greater proximity to the estuarine turbidity maximum
Understanding complex magnetic order in disordered cobalt hydroxides through analysis of the local structure
In many ostensibly crystalline materials, unit-cell-based descriptions do not
always capture the complete physics of the system due to disruption in
long-range order. In the series of cobalt hydroxides studied here,
Co(OH)(Cl)(HO), magnetic Bragg diffraction reveals a
fully compensated N\'eel state, yet the materials show significant and open
magnetization loops. A detailed analysis of the local structure defines the
aperiodic arrangement of cobalt coordination polyhedra. Representation of the
structure as a combination of distinct polyhedral motifs explains the existence
of locally uncompensated moments and provides a quantitative agreement with
bulk magnetic measurements and magnetic Bragg diffraction
Derivation of the Planck Spectrum for Relativistic Classical Scalar Radiation from Thermal Equilibrium in an Accelerating Frame
The Planck spectrum of thermal scalar radiation is derived suggestively
within classical physics by the use of an accelerating coordinate frame. The
derivation has an analogue in Boltzmann's derivation of the Maxwell velocity
distribution for thermal particle velocities by considering the thermal
equilibrium of noninteracting particles in a uniform gravitational field. For
the case of radiation, the gravitational field is provided by the acceleration
of a Rindler frame through Minkowski spacetime. Classical zero-point radiation
and relativistic physics enter in an essential way in the derivation which is
based upon the behavior of free radiation fields and the assumption that the
field correlation functions contain but a single correlation time in thermal
equilibrium. The work has connections with the thermal effects of acceleration
found in relativistic quantum field theory.Comment: 23 page
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