25,848 research outputs found
Exchange interaction and correlations radically change behaviour of a quantum particle in a classically forbidden region
Exchange interaction strongly influences the long-range behaviour of
localised electron orbitals and quantum tunneling amplitudes. It violates the
oscillation theorem (creates extra nodes) and produces a power-law decay
instead of the usual exponential decrease at large distances. For inner
orbitals inside molecules decay is , for macroscopic systems , where is the Fermi momentum and for 1D, 3.5
for 2D and 4 for 3D crystal. Correlation corrections do not change these
conclusions. Slow decay increases the exchange interaction between localized
spins and the under-barrier tunneling amplitude. The under-barrier transmission
coefficients in solids (e.g. for point contacts) become temperature-dependent
Observation of a 2D Bose-gas: from thermal to quasi-condensate to superfluid
We present experimental results on a Bose gas in a quasi-2D geometry near the
Berezinskii, Kosterlitz and Thouless (BKT) transition temperature. By measuring
the density profile, \textit{in situ} and after time of flight, and the
coherence length, we identify different states of the gas. In particular, we
observe that the gas develops a bimodal distribution without long range order.
In this state, the gas presents a longer coherence length than the thermal
cloud; it is quasi-condensed but is not superfluid. Experimental evidence
indicates that we observe the superfluid transition (BKT transition).Comment: 5 pages, 6 figure
Range Corrections to Three-Body Observables near a Feshbach Resonance
A non-relativistic system of three identical particles will display a rich
set of universal features known as Efimov physics if the scattering length a is
much larger than the range l of the underlying two-body interaction. An
appropriate effective theory facilitates the derivation of both results in the
|a| goes to infinity limit and finite-l/a corrections to observables of
interest. Here we use such an effective-theory treatment to consider the impact
of corrections linear in the two-body effective range, r_s on the three-boson
bound-state spectrum and recombination rate for |a| much greater than |r_s|. We
do this by first deriving results appropriate to the strict limit |a| goes to
infinity in coordinate space. We then extend these results to finite a using
once-subtracted momentum-space integral equations. We also discuss the
implications of our results for experiments that probe three-body recombination
in Bose-Einstein condensates near a Feshbach resonance.Comment: 28 pages, 3 figure
The Extended Methanol Maser Emission in W51
The European VLBI Network (EVN) has been used to make phase referenced,
wide-field (several arcminute) spectral line observations of the 6.7-GHz
methanol maser emission towards W51. In the W51main region, the bulk of the
methanol is offset from an UCHII region. This probably indicates the methanol
emission arises at the interface of the expanding UCHII region and not from an
edge-on circumstellar disc, as previously suggested. Near the W51 IRS2 region,
the methanol emission is associated with a very compact, extremely embedded
source supporting the hypothesis that methanol masers trace the earliest stages
of massive star formation. As well as these two previously well studied sites
of star formation, many previously unknown regions star formation are detected,
demonstrating that methanol masers are powerful means of detection young
massive stars.Comment: 5 pages, 3 figure
Quantum and Classical Dynamics of a BEC in a Large-Period Optical Lattice
We experimentally investigate diffraction of a Rb-87 Bose-Einstein condensate
from a 1D optical lattice. We use a range of lattice periods and timescales,
including those beyond the Raman-Nath limit. We compare the results to quantum
mechanical and classical simulations, with quantitative and qualitative
agreement, respectively. The classical simulation predicts that the envelope of
the time-evolving diffraction pattern is shaped by caustics: singularities in
the phase space density of classical trajectories. This behavior becomes
increasingly clear as the lattice period grows.Comment: 7 pages, 6 figure
DESIGNING GRADUATE EDUCATION FOR AGRIBUSINESS STUDENTS
For several years, universities in the U.S. have been struggling with defining and refining undergraduate and graduate agribusiness education programs. With the release of the recommendations of the National Agribusiness Education Commission, the search for the key ingredients of a Masters-level program has intensified. Mississippi State University has been among those universities attempting to define the parameters of a "cutting edge" agribusiness program. Faculty interest within the College of Business and Industry and the Agricultural Economics Department to develop a joint program has precipitated intensive efforts to achieve this goal. A nationally recognized agribusiness group of six academic leaders served as a Cooperative State Research Service team to assess the University's potential, using the concept of an agribusiness institute as an integrating and management vehicle. Efforts in this direction have been aided by a USDA planning grant now moving into its second year. A survey of Mid-South agribusiness leaders indicates the interest of the industry in development of the program. The final step is to address the logistical details required to convert the current Master of Agribusiness Management in the Department of Agricultural Economics to a jointly administered program of study.Teaching/Communication/Extension/Profession,
RHESSI Observations of the Solar Flare Iron-line Feature at 6.7 keV
Analysis of RHESSI 3--10 keV spectra for 27 solar flares is reported. This
energy range includes thermal free--free and free--bound continuum and two line
features, at 6.7keV and 8keV, principally due to highly ionized iron (Fe). We
used the continuum and the flux in the so-called Fe-line feature at 6.7keV to
derive the electron temperature T_e, the emission measure, and the Fe-line
equivalent width as functions of time in each flare. The Fe/H abundance ratio
in each flare is derived from the Fe-line equivalent width as a function of
T_e. To minimize instrumental problems with high count rates and effects
associated with multi-temperature and nonthermal spectral components, spectra
are presented mostly during the flare decay phase, when the emission measure
and temperature were smoothly varying. We found flare Fe/H abundance ratios
that are consistent with the coronal abundance of Fe (i.e. 4 times the
photospheric abundance) to within 20% for at least 17 of the 27 flares; for 7
flares, the Fe/H abundance ratio is possibly higher by up to a factor of 2. We
find evidence that the Fe XXV ion fractions are less than the theoretically
predicted values by up to 60% at T_e=25 MK appear to be displaced from the most
recent theoretical values by between 1 and 3 MK.Comment: To be published, Ap
1967 Recommended Small Grains-Planting Dates, Varieties, and Description
Wheat
Planting Dates - - - September 15 to October 20Varieties - - - - - Benhur, Knox 62, Monon, Red Coat
Barley
Planting Dates - - - September 15 to October 20Varieties - - -- - Barsoy, Datyon, Harrison, Kenbar, Will
Oats (Fall varieties)
Planting Dates - - - August 20 to October 1 Varieties - - - - - Dubois and Nor lin
Barsoy-A New Winter Barley
The early maturity of Barsoy winter barley will fill a gap in the maturity dates of the barley varieties presently recommended. Double cropping of small grain and wheat has grown to the extent that 30,000 to 40,000 acres in Kentucky grow two crops each year. This practice will continue to develop and become more important on grain farms. The early maturity characteristic of Barsoy will allow an earlier planting of soybeans than will other barley varieties
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