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Search Results: 1 - 10 of 433243 matches for " J. D. Bowman "
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Nearby Doorways, Parity Doublets and Parity Mixing in Compound Nuclear States
N. Auerbach,J. D. Bowman,V. Spevak
Physics , 1994, DOI: 10.1103/PhysRevLett.74.2638
Abstract: We discuss the implications of a doorway state model for parity mixing in compound nuclear states. We argue that in order to explain the tendency of parity violating asymmetries measured in $^{233}$Th to have a common sign, doorways that contribute to parity mixing must be found in the same energy neighbourhood of the measured resonance. The mechanism of parity mixing in this case of nearby doorways is closely related to the intermediate structure observed in nuclear reactions in which compound states are excited. We note that in the region of interest ($^{233}$Th) nuclei exhibit octupole deformations which leads to the existence of nearby parity doublets. These parity doublets are then used as doorways in a model for parity mixing. The contribution of such mechanism is estimated in a simple model.
Consistency of parity-violating pion-nucleon couplings extracted from measurements in 18F and 133Cs
W. S. Wilburn,J. D. Bowman
Physics , 1998, DOI: 10.1103/PhysRevC.57.3425
Abstract: The recent measurement of the nuclear anapole moment of 133Cs has been interpreted to yield a value of the weak pion-nucleon coupling H_pi^1 which contradicts the upper limit from the 18F experiments. We argue that because of the sensitivity of the anapole moment to H_rho^0 in the odd proton nucleus 133Cs, there is a combination of weak meson-nucleon couplings which satisfies both experiments and which is (barely) in agreement with theory. In addition, the anapole moment measurement in 205Tl gives a constraint which is inconsistent with the value from 133Cs, calling into question the theory of nuclear anapole moments. We argue that measurements of directional asymmetry in n+p-->d+gamma and in the photo-disintegration of the deuteron by circularly polarized photons, combined with results from pp scattering, would determine H_pi^1 and several other weak meson-nucleon couplings in a model-independent way.
Impact of surface emissions to the zonal variability of tropical tropospheric ozone and carbon monoxide for november 2004
K. W. Bowman,D. Jones,J. Logan,H. Worden
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: The chemical and dynamical processes governing the zonal variability of tropical tropospheric ozone and carbon monoxide are investigated for November 2004 using satellite observations, in-situ measurements, and chemical transport models in conjunction with inverse-estimated surface emissions. Vertical ozone profile estimates from the Tropospheric Emission Spectrometer (TES) and ozone sonde measurements from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network show the so-called zonal "wave-one" pattern, which is characterized by peak ozone concentrations (70–80 ppb) centered over the Atlantic, as well as elevated concentrations of ozone over Indonesia and Australia (60–70 ppb) in the lower troposphere. Observational evidence from TES CO vertical profiles and Ozone Monitoring Instrument (OMI) NO2 columns point to regional surface emissions as an important contributor to the elevated ozone over Indonesia. This contribution is investigated with the GEOS-Chem chemistry and transport model using surface emission estimates derived from an optimal inverse model, which was constrained by TES and Measurements Of Pollution In The Troposphere (MOPITT) CO profiles (Jones et al., 2007). These a posteriori estimates, which were over a factor of 2 greater than climatological emissions, reduced differences between GEOS-Chem and TES ozone observations by 30–40% and led to changes in GEOS-Chem upper tropospheric ozone of up to 40% over Indonesia. The remaining residual differences can be explained in part by upper tropospheric ozone produced from lightning NOx in the South Atlantic. Furthermore, model simulations from GEOS-Chem indicate that ozone over Indonesian/Australian is more sensitive to changes in surface emissions of NOx than ozone over the tropical Atlantic.
Bright Source Subtraction Requirements For Redshifted 21 cm Measurements
A. Datta,J. D. Bowman,C. L. Carilli
Physics , 2010, DOI: 10.1088/0004-637X/724/1/526
Abstract: The \hi 21 cm transition line is expected to be an important probe into the cosmic dark ages and epoch of reionization. Foreground source removal is one of the principal challenges for the detection of this signal. This paper investigates the extragalactic point source contamination and how accurately bright sources ($\gtrsim 1$ ~Jy) must be removed in order to detect 21 cm emission with upcoming radio telescopes such as the Murchison Widefield Array (MWA). We consider the residual contamination in 21 cm maps and power spectra due to position errors in the sky-model for bright sources, as well as frequency independent calibration errors. We find that a source position accuracy of 0.1 arcsec will suffice for detection of the \hi power spectrum. For calibration errors, 0.05 % accuracy in antenna gain amplitude is required in order to detect the cosmic signal. Both sources of subtraction error produce residuals that are localized to small angular scales, $\kperp \gtrsim 0.05 $Mpc$^{-1}$, in the two-dimensional power spectrum.
Electrostatically Assembled Metallic Point Contacts
A. Korotkov,M. Bowman,H. J. McGuinness,D. Davidovic
Physics , 2001,
Abstract: We describe a method for creating atomic-scale electric contacts. A metal source is deposited on two insulating substrates separated by a 70 nm gap. Electric conductance across the gap is monitored, while protrusions from the bulk extend into the gap and reach corresponding protrusions on the other side of the gap. When the voltage across the gap is large, a pair of corresponding protrusions assembles into a point contact, via equilibrium between electrostatic attraction and a maximum sustained current. The current voltage characteristics of the point contact display crossover from weak link into tunneling junction when its conductance is near 2e2/h, indicating that the point contact is atomic-scale.
Statistical Theory of Parity Nonconservation in Compound Nuclei
S. Tomsovic,Mikkel B. Johnson,A. Hayes,J. D. Bowman
Physics , 1999, DOI: 10.1103/PhysRevC.62.054607
Abstract: We present the first application of statistical spectroscopy to study the root-mean-square value of the parity nonconserving (PNC) interaction matrix element M determined experimentally by scattering longitudinally polarized neutrons from compound nuclei. Our effective PNC interaction consists of a standard two-body meson-exchange piece and a doorway term to account for spin-flip excitations. Strength functions are calculated using realistic single-particle energies and a residual strong interaction adjusted to fit the experimental density of states for the targets, ^{238} U for A\sim 230 and ^{104,105,106,108} Pd for A\sim 100. Using the standard Desplanques, Donoghue, and Holstein estimates of the weak PNC meson-nucleon coupling constants, we find that M is about a factor of 3 smaller than the experimental value for ^{238} U and about a factor of 1.7 smaller for Pd. The significance of this result for refining the empirical determination of the weak coupling constants is discussed.
Benefits of laptop computer ergonomics education to graduate students  [PDF]
Peter J. Bowman, Katharine D. Braswell, Jessica R. Cohen, Jenna L. Funke, Hannah L. Landon, Paloma I. Martinez, Julie N. Mossbarger
Open Journal of Therapy and Rehabilitation (OJTR) , 2014, DOI: 10.4236/ojtr.2014.21006
Abstract: Laptop computers are used more often than desktop computers, especially among graduate students. Many common laptop habits can have severe physiological effects on the user ranging from eye strain, poor posture, upper extremity pain, and overuse injuries. Thus, it is important to educate students on the best ergonomic position to use laptops. This study investigates the efficacy of a laptop ergonomic education session and its effects on graduate students’ knowledge and behaviors regarding proper laptop use. A convenience sample of control and experimental groups was used and consisted of 83 occupational therapy (OT), 63 physical therapy (PT), and 26 nurse anesthesia (NA) graduate students. The sample size was 172, with 94 graduate students in the control group and 78 graduate students in the experimental. All study participants completed an initial ergonomics questionnaire. The experimental group was given an ergonomics education session following the questionnaire. Approximately 4 weeks after both groups completed the initial questionnaire; a follow up questionnaire was administered. Results showed that subjects demonstrated a statistically significant improvement in ergonomics knowledge after they completed the ergonomic educational session. Some participants reported making adaptations to laptop positioning and equipment use following the educational session. Thus, participating in ergonomic education can positively influence awareness of body mechanics relative to laptop workstation design.
Scaling Behavior of the Landau Gauge Overlap Quark Propagator
J. B. Zhang,F. D. R. Bonnet,P. O. Bowman,D. B. Leinwebwer,A. G. Williams
Physics , 2003, DOI: 10.1016/S0920-5632(03)02620-3
Abstract: The properties of the momentum space quark propagator in Landau gauge are examined for the overlap quark action in quenched lattice QCD. Numerical calculations are done on three lattices with different lattice spacings and similar physical volumes to explore the approach of the quark propagator towards the continuum limit. We have calculated the nonperturbative momentum-dependent wavefunction renormalization function $Z(p^2)$ and the nonperturbative mass function $M(p^2)$ for a variety of bare quark masses and extrapolate to the chiral limit. We find the behavior of $Z(p^2)$ and $M(p^2)$ are in good agreement for the two finer lattices in the chiral limit. The quark condensate is also calculated.
Towards the Continuum Limit of the Overlap Quark Propagator in Landau Gauge
J. B. Zhang,F. D. R. Bonnet,P. O. Bowman,D. B. Leinweber,A. G. Williams
Physics , 2002, DOI: 10.1016/S0920-5632(03)80474-7
Abstract: The properties of the momentum space quark propagator in Landau gauge are examined for the overlap quark action in quenched lattice QCD. Numerical calculations were done on two lattices with different lattice spacing $a$ and similar physical volumes to explore the quark propagator in the continuum limit. We have calculated the nonperturbative wavefunction renormalization function $Z(p)$ and the nonperturbative mass function $M(p)$ for a variety of bare quark masses and perform a simple linear extrapolation to the chiral limit. We find the behaviour of $Z(p)$ and $M(p)$ in the chiral limit are in good agreement between the two lattices.
Infinite Volume and Continuum Limits of the Landau-Gauge Gluon Propagator
F. D. R. Bonnet,P. O. Bowman,D. B. Leinweber,A. G. Williams,J. M. Zanotti
Physics , 2001, DOI: 10.1103/PhysRevD.64.034501
Abstract: We extend a previous improved action study of the Landau gauge gluon propagator, by using a variety of lattices with spacings from $a = 0.17$ to 0.41 fm, to more fully explore finite volume and discretization effects. We also extend a previously used technique for minimizing lattice artifacts, the appropriate choice of momentum variable or ``kinematic correction'', by considering it more generally as a ``tree-level correction''. We demonstrate that by using tree-level correction, determined by the tree-level behavior of the action being considered, it is possible to obtain scaling behavior over a very wide range of momenta and lattice spacings. This makes it possible to explore the infinite volume and continuum limits of the Landau-gauge gluon propagator.
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