2,485 research outputs found
Propagation of sound through the Earth's atmosphere
The data collected at a pressure of one atmosphere for the different temperatures and relative humidities of the air-water vapor mixtures is summarized. The dew point hygrometer used in these measurements did not give reliable results for dew points much above the ambient room temperature. For this reason measurements were not attempted at the higher temperatures and humidities. Viscous wall losses in the resonant tube at 0 C so dominate the molecular relaxation of nitrogen, in the air-water vapor mixture, that reliable data could not be obtained using the free decay method in a resonant tube at one atmosphere. In an effort to obtain viable data at these temperatures, measurements were performed at a pressure of 10 atmospheres. Since the molecular relaxation peak is proportional to the pressure and the viscous losses are proportional to the inverse square root of the pressure the peak height should be measurable at the higher pressure. The tradeoff here is that at 10 atmospheres; the highest relative humidity attainable is 10 percent. The data collected at 10 atmospheres is also summarized
Propagation of sound through the Earth's atmosphere. 1: Measurement of sound absorption in the air: 2: Measurement of ground impedance
Parts were fabricated for the acoustic ground impedance meter and the instrument was tested. A rubber hose was used to connect the resonator neck to the chamber in order to suppress vibration from the volume velocity source which caused chatter. An analog to digital converter was successfully hardwired to the computer detection system. The cooling system for the resonant tube was modified to use liquid nitrogen cooling. This produced the required temperature for the tube, but the temperature gradients within each of the four tube sections reached unacceptable levels. Final measurements of the deexcitation of nitrogen by water vapor indicate that the responsible physical process is not the direct vibration-translation energy transfer, but is a vibration-vibration energy transfer
Propagation of sound through the Earth's atmosphere
The infrasonic signatures generated by the main blade slap rate of a helicoper were used in an effort to detect infrasound generated by clear air turbulence. The artificially produced infrasound and the response of the data acquisition system used are analyzed. Flight procedures used by the pilot are described and the helicopter flight information is tabulated. Graphs show the relative frequency amplitudes obtained at various microphone locations
Information on the structure of the a1 from tau decay
The decay is analysed using different methods to
account for the resonance structure, which is usually ascribed to the a1. One
scenario is based on the recently developed techniques to generate axial-vector
resonances dynamically, whereas in a second calculation the a1 is introduced as
an explicit resonance. We investigate the influence of different assumptions on
the result. In the molecule scenario the spectral function is described
surprisingly well by adjusting only one free parameter. This result can be
systematically improved by adding higher order corrections to the iterated
Weinberg-Tomozawa interaction. Treating the a1 as an explicit resonance on the
other hand leads to peculiar properties
Propagation of sound through the Earth's atmosphere. 1: Measurement of sound absorption in the air. 2: Measurement of ground impedance
The fabrication of parts for the acoustic ground impedance meter was completed, and the instrument tested. Acoustic ground impedance meter, automatic data processing system, cooling system for the resonant tube, and final results of sound absorption in N2-H2O gas mixtures at elevated temperatures are described
Proton-induced noise in digicons
The Space Telescope, which carries four Digicons, will pass several times per day through a low-altitude portion of the radiation belt called the South Atlantic Anomaly. This is expected to create interference in what is otherwise anticipated to be a noise-free device. Two essential components of the Digicon, the semiconductor diode array and the UV transmitting window, generate noise when subjected to medium-energy proton radiation, a primary component of the belt. These trapped protons, having energies ranging from 2 to 400 Mev and fluences at the Digicon up to 4,000 P+/sec-sq cm, pass through both the window and the diode array, depositing energy in each. In order to evaluate the effect of these protons, engineering test models of Digicon tubes to be flown on the High Resolution Spectrograph were irradiated with low-flux monoenergetic proton beams at the University of Maryland cyclotron. Electron-hole pairs produced by the protons passing through the diodes or the surrounding bulk caused a background count rate. This is the result of holes diffusing over a distance of many diode spacings, causing counts to be triggered simultaneously in the output circuits of several adjacent diodes. Pulse-height spectra of these proton-induced counts indicate that most of the bulk-related counts overlap the single photoelectron peak. A geometrical model will be presented of the charge collection characteristics of the diode array that accounts for most of the observed effects
Taming the Pion Cloud of the Nucleon
We present a light-front determination of the pionic contribution to the
nucleon self-energy, , to second-order in pion-baryon coupling
constants that allows the pion-nucleon vertex function to be treated in a
model-independent manner constrained by experiment. The pion mass
dependence of is consistent with chiral perturbation theory
results for small values of and is also linearly dependent on for
larger values, in accord with the results of lattice QCD calculations. The
derivative of with respect to yields the dominant
contribution to the pion content, which is consistent with the
difference observed experimentally in the violation of the
Gottfried sum rule.Comment: 11 pages, 3 figure
Infrared regulators and SCETII
We consider matching from SCETI, which includes ultrasoft and collinear
particles, onto SCETII with soft and collinear particles at one loop. Keeping
the external fermions off their mass shell does not regulate all IR divergences
in both theories. We give a new prescription to regulate infrared divergences
in SCET. Using this regulator, we show that soft and collinear modes in SCETII
are sufficient to reproduce all the infrared divergences of SCETI. We explain
the relationship between IR regulators and an additional mode proposed for
SCETII.Comment: 9 pages. Added discussion about relationship between IR regulators
and messenger mode
Top Mass Measurements from Jets and the Tevatron Top-Quark Mass
Theoretical issues are discussed for the measurement of the top-mass using
jets, including perturbative and non-perturbative effects that relate
experimental observables to the Lagrangian mass, and appropriate choices for
mass schemes. Full account for these issues is given for e+e--> t-tbar using a
factorization theorem for event shapes for massive quarks. Implications for the
Tevatron top-mass measurement are discussed. A mass-scheme, the "MSR-mass", is
introduced which allows for a precise description of observables sensitive to
scales R << m, but at the same time does not introduce perturbative matching
uncertainties in conversion to the MSbar mass.Comment: 7 pages, proceedings for the International Workshop on Top Quark
Physics, and the 2nd Workshop on Theory, Phenomenology and Experiment in
Heavy Flavor Physics, 2008. v2: reference added, language in section 5
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