789 research outputs found
Spatial interference from well-separated condensates
We use magnetic levitation and a variable-separation dual optical plug to
obtain clear spatial interference between two condensates axially separated by
up to 0.25 mm -- the largest separation observed with this kind of
interferometer. Clear planar fringes are observed using standard (i.e.
non-tomographic) resonant absorption imaging. The effect of a weak inverted
parabola potential on fringe separation is observed and agrees well with
theory.Comment: 4 pages, 5 figures - modified to take into account referees'
improvement
Temperature dependence of the electron spin g factor in GaAs
The temperature dependence of the electron spin factor in GaAs is
investigated experimentally and theoretically. Experimentally, the factor
was measured using time-resolved Faraday rotation due to Larmor precession of
electron spins in the temperature range between 4.5 K and 190 K. The experiment
shows an almost linear increase of the value with the temperature. This
result is in good agreement with other measurements based on photoluminescence
quantum beats and time-resolved Kerr rotation up to room temperature. The
experimental data are described theoretically taking into account a diminishing
fundamental energy gap in GaAs due to lattice thermal dilatation and
nonparabolicity of the conduction band calculated using a five-level kp model.
At higher temperatures electrons populate higher Landau levels and the average
factor is obtained from a summation over many levels. A very good
description of the experimental data is obtained indicating that the observed
increase of the spin factor with the temperature is predominantly due to
band's nonparabolicity.Comment: 6 pages 4 figure
Metal Patch Antenna
Disclosed herein is a patch antenna comprises a planar conductive patch attached to a ground plane by a support member, and a probe connector in electrical communication with the conductive patch arranged to conduct electromagnetic energy to or from the conductive patch, wherein the conductive patch is disposed essentially parallel to the ground plane and is separated from the ground plane by a spacing distance; wherein the support member comprises a plurality of sides disposed about a central axis oriented perpendicular to the conductive patch and the ground plane; wherein the conductive patch is solely supported above the ground plane by the support member; and wherein the support member provides electrical communication between the planer conductive patch and the ground plane
Cyclotron resonance of the quasi-two-dimensional electron gas at Hg1-xCdxTe grain boundaries
The magnetotransmission of a p-type Hg0.766Cd0.234Te bicrystal containing a single grain boundary with an inversion layer has been investigated in the submillimetre wavelength range. For the first time the cyclotron resonance lines belonging to the various electric subbands of a quasi-two-dimensional carrier system at a grain boundary could be detected. The measured cyclotron masses and the subband densities determined from Shubnikov-de Haas experiments are compared with theoretical predictions and it is found that the data can be explained very well within the framework of a triangular well approximation model which allows for non-parabolic effects
The intrinsic features of the specific heat at half-filled Landau levels of two-dimensional electron systems
The specific heat capacity of a two-dimensional electron gas is derived for
two types of the density of states, namely, the Dirac delta function spectrum
and that based on a Gaussian function. For the first time, a closed form
expression of the specific heat for each case is obtained at half-filling. When
the chemical potential is temperature-independent, the temperature is
calculated at which the specific heat is a maximum. Here the effects of the
broadening of the Landau levels are distinguished from those of the different
filling factors. In general, the results derived herein hold for any
thermodynamic system having similar resonant states.Comment: 11 pages, 1 figure, to appear in J Low Temp Phys (2010
Allozyme differentiation of two populations of the genus Neoplecostomus Eigenmann & Eigenmann, 1888 (Teleostei, Loricariidae) from the upper Paraná River basin, Brazil
Allozyme electrophoresis was used to examine 12 enzymatic systems in two populations of the genus Neoplecostomus from the Paraná River basin. Samples of Neoplecostomus sp. 1 were collected in Paraitinguinha stream of the Tietê River basin, in the municipality of Salesópolis, São Paulo State, and those of Neoplecostomus sp. 2 from São Domingos stream of the Rio Grande River basin, in the municipality of Muzambinho, Minas Gerais State. The genetic variability of the two populations was estimated by Nei’s expected heterozygosity and was considered lower than average for populations of freshwater fish. The proportion of polymorphic loci was low (only 5.26% for the locus Idh). The low frequency of heterozygosity for both populations revealed a high fixation of alleles for each locus. Homozygote excess was observed in both populations. The values of Nei’s genetic identity and the presence of loci with different allele frequencies in both populations may imply that the two populations belong to different species. The genetic variability between populations was compared to other data for loricariids
Cyclotron effective mass of 2D electron layer at GaAs/AlGaAs heterojunction subject to in-plane magnetic fields
We have found that Fermi contours of a two-dimensional electron gas at
\rmGaAs/Al_xGa_{1-x}As interface deviate from a standard circular shape under
the combined influence of an approximately triangular confining potential and
the strong in-plane magnetic field. The distortion of a Fermi contour manifests
itself through an increase of the electron effective cyclotron mass which has
been measured by the cyclotron resonance in the far-infrared transmission
spectra and by the thermal damping of Shubnikov-de Haas oscillations in tilted
magnetic fields with an in-plane component up to 5 T. The observed increase of
the cyclotron effective mass reaches almost 5 \% of its zero field value which
is in good agreement with results of a self-consistent calculation.Comment: 4 pages, Revtex, figures can be obtained on request from
[email protected]; to appear in Phys. Rev. B (in press). No changes, the
corrupted submission replace
ENCAPSULATION EFFICIENCY AND THERMAL STABILITY OF ORANGE ESSENTIAL OIL MICROENCAPSULATED BY SPRAY DRYING AND BY COACERVATION
Orange essential oil was microencapsulated by spray drying using maltodextrin and modified starch as carrier agents, and also by coacervation using sodium alginate. The influence of different microencapsulation methods and carriers on the microscopic and thermal characteristics of the product and on the encapsulation efficiency of the microparticles was investigated. According to a technique based on headspace extraction coupled to gas chromatography, the encapsulation efficiencies were above 99 % for both methods, and the oil was composed mainly of D-limonene (95.7 %) and mircene (1.66 %). Coacervation and spray drying produced microparticles of 908.63 μm and 1.02 μm, respectively, which increased the thermal stability of the oil. Nonetheless, the coacervated microparticles showed higher thermal stability and boiling point than the spray-dried ones
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