25,420 research outputs found
Fermi distribution of semicalssical non-eqilibrium Fermi states
When a classical device suddenly perturbs a degenerate Fermi gas a
semiclassical non-equilibrium Fermi state arises. Semiclassical Fermi states
are characterized by a Fermi energy or Fermi momentum that slowly depends on
space or/and time. We show that the Fermi distribution of a semiclassical Fermi
state has a universal nature. It is described by Airy functions regardless of
the details of the perturbation. In this letter we also give a general
discussion of coherent Fermi states
Nanoengineered Curie Temperature in Laterally-Patterned Ferromagnetic Semiconductor Heterostructures
We demonstrate the manipulation of the Curie temperature of buried layers of
the ferromagnetic semiconductor (Ga,Mn)As using nanolithography to enhance the
effect of annealing. Patterning the GaAs-capped ferromagnetic layers into
nanowires exposes free surfaces at the sidewalls of the patterned (Ga,Mn)As
layers and thus allows the removal of Mn interstitials using annealing. This
leads to an enhanced Curie temperature and reduced resistivity compared to
unpatterned samples. For a fixed annealing time, the enhancement of the Curie
temperature is larger for narrower nanowires.Comment: Submitted to Applied Physics Letters (minor corrections
Heat pipes for wing leading edges of hypersonic vehicles
Wing leading edge heat pipes were conceptually designed for three types of vehicle: an entry research vehicle, aero-space plane, and advanced shuttle. A full scale, internally instrumented sodium/Hastelloy X heat pipe was successfully designed and fabricated for the advanced shuttle application. The 69.4 inch long heat pipe reduces peak leading edge temperatures from 3500 F to 1800 F. It is internally instrumented with thermocouples and pressure transducers to measure sodium vapor qualities. Large thermal gradients and consequently large thermal stresses, which have the potential of limiting heat pipe life, were predicted to occur during startup. A test stand and test plan were developed for subsequent testing of this heat pipe. Heat pipe manufacturing technology was advanced during this program, including the development of an innovative technique for wick installation
The spectral-curvature parameter: an alternative tool for the analysis of synchrotron spectra
The so-called Spectral Curvature Parameter(SCP), when plotted versus the
high-frequency spectral index () of synchrotron sources, provides
crucial parameters on the continuum spectrum of synchrotron radiation without
the more complex modeling of spectral ageing scenarios. An important merit of
the SCP- diagram is the enhanced reliability of extracting multiple
injection spectra, . Different from the colour-colour diagram,
tracks of different s, especially when the synchrotron particles
are young, exhibit less overlap and less smearing in the SCP- diagram.
Three giant radio galaxies(GRGs) and a sample of Compact steep spectrum(CSS)
souces are presented. GRGs exhibit asymmetries of their injection spectral
indices in the SCP- diagram. The obtained
s and the trends in the sources are cross-checked with the
literature and show remarkable confidence. Besides the spectral steepening,
spectral flattening is prominent in the radio lobes. The spectral flattening is
a clue to efficient re-acceleration processes in the lobes. It implies
interaction with the surrounding intergalactic or intra-cluster medium is an
important characteristic of GRGs. In the SW lobe of DA240, there is a clear
sign of CI and KP/JP bifurcation at the source extremity. This indicates a
highly relativistic energy transportation from the core or in situ acceleration
in this typical FR I lobe. Our analysis proves, if exists, KP spectra imply the
existence of strong field with . In the CSS
sources, our result confirms the CI model and . The
synchrotron self-absorption is significant in the CSS sample.Comment: to be published in A&
Automated Retrieval of Non-Engineering Domain Solutions to Engineering Problems
Organised by: Cranfield UniversityBiological inspiration for engineering design has occurred through a variety of techniques such as creation
and use of databases, keyword searches of biological information in natural-language format, prior
knowledge of biology, and chance observations of nature. This research focuses on utilizing the reconciled
Functional Basis function and flow terms to identify suitable biological inspiration for function based design.
The organized search provides two levels of results: (1) associated with verb function only and (2) narrowed
results associated with verb-noun (function-flow). A set of heuristics has been complied to promote efficient
searching using this technique. An example for creating smart flooring is also presented and discussed.Mori Seiki – The Machine Tool Compan
Magnetic soft modes in the locally distorted triangular antiferromagnet alpha-CaCr2O4
In this paper we explore the phase diagram and excitations of a distorted
triangular lattice antiferromagnet. The unique two-dimensional distortion
considered here is very different from the 'isosceles'-type distortion that has
been extensively investigated. We show that it is able to stabilize a 120{\deg}
spin structure for a large range of exchange interaction values, while new
structures are found for extreme distortions. A physical realization of this
model is \alpha-CaCr2O4 which has 120{\deg} structure but lies very close to
the phase boundary. This is verified by inelastic neutron scattering which
reveals unusual roton-like minima at reciprocal space points different from
those corresponding to the magnetic order.Comment: 5 pages, 3 figures and lots of spin-wave
Anomalous lateral diffusion in a viscous membrane surrounded by viscoelastic media
We investigate the lateral dynamics in a purely viscous lipid membrane
surrounded by viscoelastic media such as polymeric solutions. We first obtain
the generalized frequency-dependent mobility tensor and focus on the case when
the solvent is sandwiched by hard walls. Due to the viscoelasticity of the
solvent, the mean square displacement of a disk embedded in the membrane
exhibits an anomalous diffusion. An useful relation which connects the mean
square displacement and the solvent modulus is provided. We also calculate the
cross-correlation of the particle displacements which can be applied for
two-particle tracking experiments.Comment: 6 pages, 2 figure
Flux through a hole from a shaken granular medium
We have measured the flux of grains from a hole in the bottom of a shaken
container of grains. We find that the peak velocity of the vibration, vmax,
controls the flux, i.e., the flux is nearly independent of the frequency and
acceleration amplitude for a given value of vmax. The flux decreases with
increasing peak velocity and then becomes almost constant for the largest
values of vmax. The data at low peak velocity can be quantitatively described
by a simple model, but the crossover to nearly constant flux at larger peak
velocity suggests a regime in which the granular density near the container
bottom is independent of the energy input to the system.Comment: 14 pages, 4 figures. to appear in Physical Review
Persistence of magnons in a site-diluted dimerized frustrated antiferromagnet
We present inelastic neutron scattering and thermodynamic measurements
characterizing the magnetic excitations in a disordered non-magnetic
substituted spin-liquid antiferromagnet. The parent compound Ba3Mn2O8 is a
dimerized, quasi-two-dimensional geometrically frustrated quantum disordered
antiferromagnet. We substitute this compound with non-magnetic vanadium for the
S = 1 manganese atoms, Ba3(Mn1-xVx)2O8, and find that the singlet-triplet
excitations which dominate the spectrum of the parent compound persist for the
full range of substitution examined, x = 0.02 to 0.3. We also observe
additional low-energy magnetic fluctuations which are enhanced at the greatest
substitution values. These excitations may be a precursor to a low-temperature
random singlet phase which may exist in Ba3(Mn1-xVx)2O8Comment: 30 pages, 9 figure
- …