28,958 research outputs found
Spin-lattice interactions of ions with unfilled F-shells measured by ESR in uniaxially stressed crystals
Spin-lattice interactions of ions with unfilled F-shells measured by electron spin resonance in uniaxially stressed crystal
Direct one-phonon spin-lattice relaxation times for Nd sup 3 plus and U sup 3 plus ions in CaF sub 2 in sites of tetragonal symmetry
Phonon spin-lattice relaxation times for uranium and neodymium ions in calcium fluorid
Possible Observational Criteria for Distinguishing Brown Dwarfs from Planets
The difference in formation process between binary stars and planetary
systems is reflected in their composition as well as their orbital
architecture, particularly orbital eccentricity as a function of orbital
period. It is suggested here that this difference can be used as an
observational criterion to distinguish between brown dwarfs and planets.
Application of the orbital criterion suggests that with three possible
exceptions, all of the recently-discovered substellar companions discovered to
date may be brown dwarfs and not planets. These criterion may be used as a
guide for interpretation of the nature of sub-stellar mass companions to stars
in the future.Comment: LaTeX, 11 pages including 2 figures, accepted for publication in the
Astrophysical Journal Letter
Light forces in ultracold photoassociation
We study the time-resolved photoassociation of ultracold sodium in an optical
dipole trap. The photoassociation laser excites pairs of atoms to molecular
states of large total angular momentum at high intensities (above 20
kW/cm). Such transitions are generally suppressed at ultracold
temperatures by the centrifugal barriers for high partial waves. Time-resolved
ionization measurements reveal that the atoms are accelerated by the dipole
potential of the photoassociation beam. We change the collision energy by
varying the potential depth, and observe a strong variation of the
photoassociation rate. These results demonstrate the important role of light
forces in cw photoassociation at high intensities.Comment: 7 pages, 3 figure
Spinor Dynamics in an Antiferromagnetic Spin-1 Condensate
We observe coherent spin oscillations in an antiferromagnetic spin-1
Bose-Einstein condensate of sodium. The variation of the spin oscillations with
magnetic field shows a clear signature of nonlinearity, in agreement with
theory, which also predicts anharmonic oscillations near a critical magnetic
field. Measurements of the magnetic phase diagram agree with predictions made
in the approximation of a single spatial mode. The oscillation period yields
the best measurement to date of the sodium spin-dependent interaction
coefficient, determining that the difference between the sodium spin-dependent
s-wave scattering lengths is Bohr radii.Comment: 5 pages, 2 figures. Changes: added reference, minor correction
Winter wheat: A model for the simulation of growth and yield in winter wheat
The basic ideas and constructs for a general physical/physiological process level winter wheat simulation model are documented. It is a materials balance model which calculates daily increments of photosynthate production and respiratory losses in the crop canopy. The partitioning of the resulting dry matter to the active growing tissues in the plant each day, transpiration and the uptake of nitrogen from the soil profile are simulated. It incorporates the RHIZOS model which simulates, in two dimensions, the movement of water, roots, and soluble nutrients through the soil profile. It records the time of initiation of each of the plant organs. These phenological events are calculated from temperature functions with delays resulting from physiological stress. Stress is defined mathematically as an imbalance in the metabolite supply; demand ratio. Physiological stress is also the basis for the calculation of rates of tiller and floret abortion. Thus, tillering and head differentiation are modeled as the resulants of the two processes, morphogenesis and abortion, which may be occurring simulaneously
The Discocyte-Echinocyte Transformation as an Index of Human Red Cell Trauma
Author Institution: Division of Surgical Research, Saint Luke's HospitalScanning electron microscopic observation of blood samples before, during and after cardiopulmonary bypass during cardiovascular surgery revealed that 4 to 25% of the red blood cells undergo a progressive transformation of discocyte to echinocyte. A morphological index, I, was developed and the change in I (Ir) was found to correlate well with measurements of free plasma hemoglobin. Incubation of blood samples form normal subjects for 90 minutes at 37°C resulted in no increase in Ir whereas incubated samples from patients following cardiopulmonary bypass showed an increased Ir to a mean value of 1140 ±185. Incubation therefore appears to uncover sublethal red cell damage caused by extracorporeal circulation. It is suggested that this technique is a sensitive index of red cell trauma which may have useful clinical applications
Web 2.0 Tools Ease Renovation Service Disruptions at The Ohio State University Libraries
The Thompson Library, the main library of The Ohio State University (OSU), began a major renovation in fall 2006 that required the library to close for three years. During this time, the bulk of the circulating collection and many of the personnel relocated to an interim facility. The distance imposed by the renovation created special challenges for service to patrons and communication among library faculty and staff. The OSU Libraries used blogs, podcasts, a wiki, instant messaging, and the campus course management system to reach as many of the constituents of the campus community as possible
High-temperature optically activated GaAs power switching for aircraft digital electronic control
Gallium arsenide high-temperature devices were fabricated and assembled into an optically activated pulse-width-modulated power control for a torque motor typical of the kinds used in jet engine actuators. A bipolar heterojunction phototransistor with gallium aluminum arsenide emitter/window, a gallium arsenide junction field-effect power transistor and a gallium arsenide transient protection diode were designed and fabricated. A high-temperature fiber optic/phototransistor coupling scheme was implemented. The devices assembled into the demonstrator were successfully tested at 250 C, proving the feasibility of actuator-located switching of control power using optical signals transmitted by fibers. Assessments of the efficiency and technical merits were made for extension of this high-temperature technology to local conversion of optical power to electrical power and its control at levels useful for driving actuators. Optical power sources included in the comparisons were an infrared light-emitting diode, an injection laser diode, tungsten-halogen lamps and arc lamps. Optical-to-electrical power conversion was limited to photovoltaics located at the actuator. Impedance matching of the photovoltaic array to the load was considered over the full temperature range, -55 C to 260 C. Loss of photovoltaic efficiency at higher temperatures was taken into account. Serious losses in efficiency are: (1) in the optical source and the cooling which they may require in the assumed 125 C ambient, (2) in the decreased conversion efficiency of the gallium arsenide photovoltaic at 260 C, and (3) in impedance matching. Practical systems require improvements in these areas
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