22,289 research outputs found
Semi-Classical Description of Antiproton Capture on Atomic Helium
A semi-classical, many-body atomic model incorporating a momentum-dependent
Heisenberg core to stabilize atomic electrons is used to study antiproton
capture on Helium. Details of the antiproton collisions leading to eventual
capture are presented, including the energy and angular momentum states of
incident antiprotons which result in capture via single or double electron
ionization, i.e. into [He or He], and the
distribution of energy and angular momentum states following the Auger cascade.
These final states are discussed in light of recently reported, anomalously
long-lived antiproton states observed in liquid He.Comment: 15 pages, 9 figures may be obtained from authors, Revte
Preliminary Results from Recent Measurements of the Antiprotonic Helium Hyperfine Structure
We report on preliminary results from a systematic study of the hyperfine
(HF) structure of antiprotonic helium. This precise measurement which was
commenced in 2006, has now been completed. Our initial analysis shows no
apparent density or power dependence and therefore the results can be averaged.
The statistical error of the observable M1 transitions is a factor of 60
smaller than that of three body quantum electrodynamic (QED) calculations,
while their difference has been resolved to a precision comparable to theory (a
factor of 10 better than our first measurement). This difference is sensitive
to the antiproton magnetic moment and agreement between theory and experiment
would lead to an increased precision of this parameter, thus providing a test
of CPT invariance.Comment: 6 pages, 4 figure
Study of spin-scan imaging for outer planets missions: Executive summary
The development and characteristics of spin-scan imagers for interplanetary exploration are discussed. The spin-scan imaging photopolarimeter instruments of Pioneer 10 and 11 are described. In addition to the imaging function, the instruments are also used in a faint-light mode to take sky maps in both radiance and polarization. The performance of a visible-infrared spin-scan radiometer (VISSR), which operates in both visible and infrared wavelengths, is reported
Improved simulation of aerosol, cloud, and density measurements by shuttle lidar
Data retrievals are simulated for a Nd:YAG lidar suitable for early flight on the space shuttle. Maximum assumed vertical and horizontal resolutions are 0.1 and 100 km, respectively, in the boundary layer, increasing to 2 and 2000 km in the mesosphere. Aerosol and cloud retrievals are simulated using 1.06 and 0.53 microns wavelengths independently. Error sources include signal measurement, conventional density information, atmospheric transmission, and lidar calibration. By day, tenuous clouds and Saharan and boundary layer aerosols are retrieved at both wavelengths. By night, these constituents are retrieved, plus upper tropospheric, stratospheric, and mesospheric aerosols and noctilucent clouds. Density, temperature, and improved aerosol and cloud retrievals are simulated by combining signals at 0.35, 1.06, and 0.53 microns. Particlate contamination limits the technique to the cloud free upper troposphere and above. Error bars automatically show effect of this contamination, as well as errors in absolute density nonmalization, reference temperature or pressure, and the sources listed above. For nonvolcanic conditions, relative density profiles have rms errors of 0.54 to 2% in the upper troposphere and stratosphere. Temperature profiles have rms errors of 1.2 to 2.5 K and can define the tropopause to 0.5 km and higher wave structures to 1 or 2 km
Distribution of BoLA-DRB3
The role of the major histocompatibility complex (MHC) in the immune response makes it an attractive candidate gene for associations with disease resistance and susceptibility. This study describes genetic variability in the BoLA-DRB3 in Iranian buffaloes. Heminested PCR-RFLP method was used to identify the frequency of BoLA-DRB3 alleles. The BoLA-DRB3 locus is highly polymorphic in the study herd (12 alleles). Almost 63.50% of the alleles were accounted for by four alleles (BoLA-DRB3.2 *48, *20, *21, and obe) in Iranian buffalo. The DRB3.2 *48 allele frequency (24.20%) was higher than the others. The frequencies of the DRB3.2 *20 and DRB3.2 *21 are 14.52 and 14.00, respectively, and obe and gbb have a new pattern. Significant distinctions have been found between Iranian buffalo and other cattle breed studied. In the Iranian buffaloes studied alleles associated with resistance to various diseases are found
Growth states of catalytic reaction networks exhibiting energy metabolism
All cells derive nutrition by absorbing some chemical and energy resources
from the environment; these resources are used by the cells to reproduce the
chemicals within them, which in turn leads to an increase in their volume. In
this study, we introduce a protocell model exhibiting catalytic reaction
dynamics, energy metabolism, and cell growth. Results of extensive simulations
of this model show the existence of four phases with regard to the rates of
both the influx of resources and the cell growth. These phases include an
active phase with high influx and high growth rates, an inefficient phase with
high influx but low growth rates, a quasi-static phase with low influx and low
growth rates, and a death phase with negative growth rate. A mean field model
well explains the transition among these phases as bifurcations. The
statistical distribution of the active phase is characterized by a power law
and that of the inefficient phase is characterized by a nearly equilibrium
distribution. We also discuss the relevance of the results of this study to
distinct states in the existing cells.Comment: 21 pages, 5 figure
Contest based on a directed polymer in a random medium
We introduce a simple one-parameter game derived from a model describing the
properties of a directed polymer in a random medium. At his turn, each of the
two players picks a move among two alternatives in order to maximize his final
score, and minimize opponent's return. For a game of length , we find that
the probability distribution of the final score develops a traveling wave
form, , with the wave profile unusually
decaying as a double exponential for large positive and negative . In
addition, as the only parameter in the game is varied, we find a transition
where one player is able to get his maximum theoretical score. By extending
this model, we suggest that the front velocity is selected by the nonlinear
marginal stability mechanism arising in some traveling wave problems for which
the profile decays exponentially, and for which standard traveling wave theory
applies
A study of factors related to primary grade spelling: correlations of factors studied.
Thesis (Ed.M.)--Boston Universit
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