1,120 research outputs found
Hydraulic Conditions Required to Move Unanchored Residue Materials
Hydraulic conditions required to initiate movement of unanchored residue materials are identified in the present study. Selected amounts of corn, cotton, pine needles, sorghum, soybean, sunflower, and wheat residue are placed in a flume on a sand surface, and flow is then introduced at the top of the flume in progressive increments. The discharge rate and flow velocity necessary to cause residue movement are determined. The ratio of critical flow depth to residue diameter, critical Reynolds number, critical shear stress, dimensionless shear stress, and boundary Reynolds number are calculated from hydraulic measurements. Regression equations are developed to relate dimensionless shear stress to boundary Reynolds number and residue diameter. Boundary Reynolds number, in turn, is related to residue diameter and cover. Close agreement is found between predicted and actual parameter values obtained from the regression relations. The regression equations can be used to estimate the beginning of motion for other residue materials if residue diameter and cover are known
Laser frequency locking by direct measurement of detuning
We present a new method of laser frequency locking in which the feedback
signal is directly proportional to the detuning from an atomic transition, even
at detunings many times the natural linewidth of the transition. Our method is
a form of sub-Doppler polarization spectroscopy, based on measuring two Stokes
parameters ( and ) of light transmitted through a vapor cell. This
extends the linear capture range of the lock loop by up to an order of
magnitude and provides equivalent or improved frequency discrimination as other
commonly used locking techniques.Comment: 4 pages, 4 figures Revte
Correcting for Distortions due to Ionization in the STAR TPC
Physics goals of the STAR Experiment at RHIC in recent (and future) years
drive the need to operate the STAR TPC at ever higher luminosities, leading to
increased ionization levels in the TPC gas. The resulting ionic space charge
introduces field distortions in the detector which impact tracking performance.
Further complications arise from ionic charge leakage into the main TPC volume
from the high gain anode region. STAR has implemented corrections for these
distortions based on measures of luminosity, which we present here.
Additionally, we highlight a novel approach to applying the corrections on an
event-by-event basis applicable in conditions of rapidly varying ionization
sources.Comment: 6 pages, 7 figures, proceedings of the Workshop on Tracking in High
Multiplicity Environments (TIME 05) in Zurich, Switzerland, submitted to
Nucl. Instr. and Meth.
Quantum synthesis of arbitrary unitary operators
Nature provides us with a restricted set of microscopic interactions. The
question is whether we can synthesize out of these fundamental interactions an
arbitrary unitary operator. In this paper we present a constructive algorithm
for realization of any unitary operator which acts on a (truncated) Hilbert
space of a single bosonic mode. In particular, we consider a physical
implementation of unitary transformations acting on 1-dimensional vibrational
states of a trapped ion. As an example we present an algorithm which realizes
the discrete Fourier transform.Comment: 6 RevTeX pages with 3 figures, submitted to Phys.Rev.A, see also
http://nic.savba.sk/sav/inst/fyzi/qo
A Research-Based Curriculum for Teaching the Photoelectric Effect
Physics faculty consider the photoelectric effect important, but many
erroneously believe it is easy for students to understand. We have developed
curriculum on this topic including an interactive computer simulation,
interactive lectures with peer instruction, and conceptual and mathematical
homework problems. Our curriculum addresses established student difficulties
and is designed to achieve two learning goals, for students to be able to (1)
correctly predict the results of photoelectric effect experiments, and (2)
describe how these results lead to the photon model of light. We designed two
exam questions to test these learning goals. Our instruction leads to better
student mastery of the first goal than either traditional instruction or
previous reformed instruction, with approximately 85% of students correctly
predicting the results of changes to the experimental conditions. On the
question designed to test the second goal, most students are able to correctly
state both the observations made in the photoelectric effect experiment and the
inferences that can be made from these observations, but are less successful in
drawing a clear logical connection between the observations and inferences.
This is likely a symptom of a more general lack of the reasoning skills to
logically draw inferences from observations.Comment: submitted to American Journal of Physic
Stable Isotope Fractionation in Titan Aerosol Formation
Stable isotope ratio measurements are a powerful tool used to understand both ancient and modern planetary processes. Instruments on the Cassini- Huygens spacecraft along with ground-based observations have measured several isotope pairs, including C-13/C-12 and N-15/N-14, in Titan's atmosphere. This includes isotopic measurements of the major atmospheric species, CH4 and N2, along with HCN, HC3N, C2H2. C2H6 and C4H2. However, the isotopic fractionation of Titan's organic aerosol has not conclusively been measured and therefore the effect of aerosol formation as an isotopic fractionation pathway in Titan's atmosphere has not been considered. Laboratory studies have measured the carbon and/or nitrogen isotopic fractionation of Titan aerosol analogs. [18] found that the carbon fractionation of photochemical organic aerosol analogs are more enriched in C-13. This enrichment in the aerosol analogs is opposite of what is predicted for photochemical products by the kinetic isotope effect. Additionally, both [16] and [18] found that the nitrogen fractionation in the organic aerosol analogs are opposite of what is observed in Titan's atmospheric N2 and HCN, with the aerosol analogs being a light nitrogen sink. Here we monitor the gas phase during photochemical aerosol analog production as a function of reaction time. In a recirculation experiment, the isotopic fractionation of carbon within the gas-phase products is measured as the CH4 reservoir is depleted. This allows us to monitor the isotopic fractionation pathway during photochemical aerosol analog formation
Kinetic Properties of a Bose-Einstein Gas at Finite Temperature
We study, in the framework of the Boltzmann-Nordheim equation (BNE), the
kinetic properties of a boson gas above the Bose-Einstein transition
temperature . The BNE is solved numerically within a new algorithm, that
has been tested with exact analytical results for the collision rate of an
homogeneous system in thermal equilibrium. In the classical regime (), the relaxation time of a quadrupolar deformation in momentum space is
proportional to the mean free collision time .
Approaching the critical temperature (), quantum statistic
effects in BNE become dominant, and the collision rate increases dramatically.
Nevertheless, this does not affect the relaxation properties of the gas that
depend only on the spontaneous collision term in BNE. The relaxation time
is proportional to , exhibiting a critical
slowing down. These phenomena can be experimentally confirmed looking at the
damping properties of collective motions induced on trapped atoms. The
possibility to observe a transition from collisionless (zero-sound) to
hydrodynamic (first-sound) is finally discussed.Comment: RevTeX, 5 figures. Submitted to Phys. Rev.
Exactly solvable models for triatomic-molecular Bose-Einstein Condensates
We construct a family of triatomic models for heteronuclear and homonuclear
molecular Bose-Einstein condensates. We show that these new generalized models
are exactly solvable through the algebraic Bethe ansatz method and derive their
corresponding Bethe ansatz equations and energies.Comment: 11 page
Atomic Resonance and Scattering
Contains research objectives, summary of research and reports on six research projects.Joint Services Electronics Programs (U. S. Army, U. S. Navy, and U. S. Air Force) under Contract DA 28-043-AMC-02536(E)National Science Foundation (Grant GP-13633)National Bureau of Standards (Grant NBS(G)-269
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