2,077 research outputs found
Systematic Analysis Method for Color Transparency Experiments
We introduce a data analysis procedure for color transparency experiments
which is considerably less model dependent than the transparency ratio method.
The new method is based on fitting the shape of the A dependence of the nuclear
cross section at fixed momentum transfer to determine the effective attenuation
cross section for hadrons propagating through the nucleus. The procedure does
not require assumptions about the hard scattering rate inside the nuclear
medium. Instead, the hard scattering rate is deduced directly from the data.
The only theoretical input necessary is in modelling the attenuation due to the
nuclear medium, for which we use a simple exponential law. We apply this
procedure to the Brookhaven experiment of Carroll et al and find that it
clearly shows color transparency: the effective attenuation cross section in
events with momentum transfer is approximately $40\ mb\ (2.2\
GeV^2/Q^2)$. The fit to the data also supports the idea that the hard
scattering inside the nuclear medium is closer to perturbative QCD predictions
than is the scattering of isolated protons in free space. We also discuss the
application of our approach to electroproduction experiments.Comment: 11 pages, 11 figures (figures not included, available upon request),
report # KU-HEP-92-2
Hadron Helicity Violation in Exclusive Processes: Quantitative Calculations in Leading Order QCD
We study a new mechanism for hadronic helicity flip in high energy hard
exclusive reactions. The mechanism proceeds in the limit of perfect chiral
symmetry, namely without any need to flip a quark helicity. The fundamental
feature of the new mechanism is the breaking of rotational symmetry of the hard
collision by a scattering plane in processes involving independent quark
scattering. We show that in the impulse approximation there is no evidence for
of the helicity violating process as the energy or momentum transfer is
increased over the region 1 GeV^2 < Q^2 < 100 GeV^2. In the asymptotic region
Q^2> 1000 GeV^2, a saddle point approximation with doubly logarithmic accuracy
yields suppression by a fraction of power of Q^2. ``Chirally--odd" exclusive
wave functions which carry non--zero orbital angular momentum and yet are
leading order in the high energy limit, play an important role.Comment: uuencoded LaTeX file (21 pages) and PostScript figure
The STRS (shortness of breath, tremulousness, racing heart, and sweating): A brief checklist for acute distress with panic-like autonomic indicators; development and factor structure
Background: Peritraumatic response, as currently assessed by Posttraumatic Stress Disorder (PTSD) diagnostic criterion A2, has weak positive predictive value (PPV) with respect to PTSD diagnosis. Research suggests that indicators of peritraumatic autonomic activation may supplement the PPV of PTSD criterion A2. We describe the development and factor structure of the STRS (Shortness of Breath, Tremulousness, Racing Heart, and Sweating), a one page, two-minute checklist with a five-point Likert-type response format based on a previously unpublished scale. It is the first validated self-report measure of peritraumatic activation of the autonomic nervous system.\ud
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Methods: We selected items from the Potential Stressful Events Interview (PSEI) to represent two latent variables: 1) PTSD diagnostic criterion A, and 2) acute autonomic activation. Participants (a convenience sample of 162 non-treatment seeking young adults) rated the most distressing incident of their lives on these items. We examined the factor structure of the STRS in this sample using factor and cluster analysis.\ud
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Results: Results confirmed a two-factor model. The factors together accounted for 68% of the variance. The variance in each item accounted for by the two factors together ranged from 41% to 74%. The item loadings on the two factors mapped precisely onto the two proposed latent variables.\ud
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Conclusion: The factor structure of the STRS is robust and interpretable. Autonomic activation signs tapped by the STRS constitute a dimension of the acute autonomic activation in response to stress that is distinct from the current PTSD criterion A2. Since the PTSD diagnostic criteria are likely to change in the DSM-V, further research is warranted to determine whether signs of peritraumatic autonomic activation such as those measured by this two-minute scale add to the positive predictive power of the current PTSD criterion A2. Additionally, future research is warranted to explore whether the four automatic activation items of the STRS can be useful as the basis for a possible PTSD criterion A3 in the DSM-V
Evidence for Evolution or Bias in Host Extinctions of Type 1a Supernovae at High Redshift
Type 1a supernova magnitudes conventionally include an additive parameter
called the extinction coefficient. We find that the extinction coefficients of
a popular ``gold'' set are well correlated with the deviation of magnitudes
from Hubble diagrams. If the effect is due to bias, extinctions have been
overestimated, which makes supernovas appear more dim. The statistical
significance of the extinction-acceleration correlation has a random chance
probability of less than one in a million. The hypothesis that extinction
coefficients should be corrected empirically provides greatly improved fits to
both accelerating and non-accelerating models, with the independent feature of
eliminating any significant correlation of residuals.Comment: 20 pages, 5 figures, to appear in Ap
Indication of Anisotropy in Electromagnetic Propagation over Cosmological Distances
We report a systematic rotation of the plane of polarization of
electromagnetic radiation propagating over cosmological distances. The effect
is extracted independently from Faraday rotation, and found to be correlated
with the angular positions and distances to the sources. Monte Carlo analysis
yields probabilistic P-values of order 10^(-3) for this to occur as a
fluctuation. A fit yields a birefringence scale of order 10^(25) meters.
Dependence on redshift z rules out a local effect. Barring hidden systematic
bias in the data, the correlation indicates a new cosmological effect.Comment: 5 pages, 1 figure, ReVTeX. For more information, see
http://www.cc.rochester.edu/college/rtc/Borge/aniso.htm
Behavioral Deficits and Axonal Injury Persistence after Rotational Head Injury Are Direction Dependent
Pigs continue to grow in importance as a tool in neuroscience. However, behavioral tests that have been validated in the rodent model do not translate well to pigs because of their very different responses to behavioral stimuli. We refined metrics for assessing porcine open field behavior to detect a wide spectrum of clinically relevant behaviors in the piglet post-traumatic brain injury (TBI). Female neonatal piglets underwent a rapid non-impact head rotation in the sagittal plane (n=8 evaluable) or were instrumented shams (n=7 evaluable). Open field testing was conducted 1 day prior to injury (day −1) in order to establish an individual baseline for analysis, and at days +1 and +4 after injury. Animals were then killed on day +6 after injury for neuropathological assessment of axonal injury. Injured piglets were less interested in interacting with environmental stimuli and had a lower activity level than did shams. These data were compared with previously published data for axial rotational injuries in neonatal piglets. Acute behavioral outcomes post-TBI showed a dependence on the rotational plane of the brain injury, with animals with sagittal injuries demonstrating a greater level of inactivity and less random usage of the open field space than those with axial injuries. The persistence of axonal injury is also dependent on the rotational plane, with sagittal rotations causing more prolonged injuries than axial rotations. These results are consistent with animal studies, finite element models, and studies of concussions in football, which have all demonstrated differences in injury severity depending upon the direction of head impact rotation
Exclusive Hadronic Processes and Color Transparency
We review the current status of high energy exclusive processes and color
transparency.Comment: 17 pages, 8 figures, based on talk given at International Symposium
on Nuclear Physics, Mumbai, Dec 18-22, 200
Premedication With Meloxicam Exacerbates Intracranial Hemorrhage in an Immature Swine Model of Non-impact Inertial Head Injury
Meloxicam is a cyclo-oxgenase-2 preferential non-steroid anti-inflammatory drug with very effective analgesic and anti-inflammatory effects in swine. Previous reports in piglets have demonstrated that meloxicam also inhibits cyclo-oxgenase-1 and reduces production of thromboxane significantly. We use pre-injury analgesia in our immature swine (3–5 day old piglets) model of brain injury using rapid head rotations without impact. In 23 consecutive subjects we found that premedication with meloxicam (N=6) produced a significantly higher mortality rate (5/6 or 83%) than buprenorphine (N =17, 1/17 or 6%, p \u3c 0.02). On gross neuropathologic examination of the meloxicam-treated swine, we observed massive subdural and subarachnoid bleeding which were not present in buprenorphine-premedicated animals. To our knowledge there are no previous reports in swine of increased bleeding or platelet inhibition associated with meloxicam administration and further research is needed to define mechanisms of action in piglets. We caution the use of meloxicam in swine when inhibition of platelet aggregation might adversely affect refinement of experimental research protocols, such as in stroke, trauma, and cardiac arrest models
QCD Form Factors and Hadron Helicity Non-Conservation
Recent data for the ratio shocked the
community by disobeying expectations held for 50 years. We examine the status
of perturbative QCD predictions for helicity-flip form factors. Contrary to
common belief, we find there is no rule of hadron helicity conservation for
form factors. Instead the analysis yields an inequality that the leading power
of helicity-flip processes may equal or exceed the power of helicity conserving
processes. Numerical calculations support the rule, and extend the result to
the regime of laboratory momentum transfer . Quark orbital angular
momentum, an important feature of the helicity flip processes, may play a role
in all form factors at large , depending on the quark wave functions.Comment: 25 pages, 5 figure
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