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R J Holt

Publications and source records attributed to R J Holt.

At least 19 recordsLinked to original sources
PubMed2003

Cross-section measurement of charged-pion photoproduction from hydrogen and deuterium.

We have measured the differential cross section for the gamman-->pi(-)p and gammap-->pi(+)n reactions at theta(c.m.)=90 degrees in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at E(gamma) greater, similar 3.3 GeV exhibit a global scaling behavior for both pi(-) and pi(+) photoproduction, consistent with the constituent counting rule and the existing pi(+) photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive pi(-) to pi(+) photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.

Journal Article↗
PubMed2003

Evidence for quark-hadron duality in the proton spin asymmetry A1.

Spin-dependent lepton-nucleon scattering data have been used to investigate the validity of the concept of quark-hadron duality for the spin asymmetry A1. Longitudinally polarized positrons were scattered off a longitudinally polarized hydrogen target for values of Q2 between 1.2 and 12 GeV2 and values of W2 between 1 and 4 GeV2. The average double-spin asymmetry in the nucleon resonance region is found to agree with that measured in deep-inelastic scattering at the same values of the Bjorken scaling variable x. This finding implies that the description of A1 in terms of quark degrees of freedom is valid also in the nucleon resonance region for values of Q2 above 1.6 GeV2.

Journal Article↗
PubMed2003

Measurement of the tensor analyzing powers T20 and T21 in elastic electron-deuteron scattering.

The tensor analyzing power components T20 and T21 have been measured in elastic electron-deuteron scattering at the 2 GeV electron storage ring VEPP-3, Novosibirsk, in a four-momentum transfer range from 8.4 to 21.6 fm(-2). A new polarized internal gas target with an intense cryogenic atomic beam source was used. The new data determine the deuteron form factors G(C) and G(Q) in an important range of momentum transfer where the first node of the deuteron monopole charge form factor is located. The new results are compared with previous data and with some theoretical predictions.

Journal Article↗
PubMed2001

Measurement of the high energy two-body deuteron photodisintegration differential cross section.

The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

Journal Article↗
PubMed2001

Polarization measurements in high-energy deuteron photodisintegration.

We present measurements of the recoil proton polarization for the d(gamma-->,p-->)n reaction at straight theta(c.m.) = 90 degrees for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization p(y) vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(gamma,p)n cross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.

Journal Article↗
PubMed2001

Evidence for a three-nucleon-force effect in proton-deuteron elastic scattering.

Developments in spin-polarized internal targets for storage rings have permitted measurements of 197 MeV polarized protons scattering from vector polarized deuterons. This work presents measurements of the polarization observables A(y), iT11, and C(y,y) in proton-deuteron elastic scattering. When compared to calculations with and without three-nucleon forces, the measurements provide further evidence that three-nucleon forces make a contribution to the observables. This work indicates that three-body forces derived from static nuclear properties appear to be crucial to the description of dynamical properties.

Journal Article↗
PubMed1996

Phylogenetic analysis of tnpR genes in mercury resistant soil bacteria: the relationship between DNA sequencing and RFLP typing approaches.

The diversity of resolvase (tnpR) genes carried by a number of mercury resistant soil bacteria has been investigated by DNA sequencing. The resulting DNA sequence information was compared to previously published tnpR DNA sequences and to previously published restriction fragment length polymorphism (RFLP) data, permitting the relationships between DNA sequencing and RFLP approaches to be studied by the use of phylogenetic trees. DNA maximum likelihood and DNA parsimony were used to construct a variety of phylogenetic trees. DNA sequencing confirmed the validity of RFLP analysis and highlighted the importance of restriction endonuclease choice upon the resulting RFLP patterns and dendrogram topology. The tnpR genes of two previously uncharacterised mercury resistant bacteria, T2-7 and T2-12 were also studied. DNA sequence data placed T2-7 in a previously described gene class, tnpR-D and T2-12 in a new gene class, tnpR-F. The significance of this data with respect to the recombination and evolution events occurring within bacterial populations are discussed.

Base Sequence↗
PubMed1986

Neuroleptic drug-induced coagulopathy: mechanism of reaction and duration of effect.

Patients (N = 32) with documented phenothiazine-induced reductions in platelet levels were evaluated after drug substitution with haloperidol; 28 (88%) patients had normal platelet levels after 1 year of treatment with haloperidol. Coagulation studies indicated that activated partial thromboplastin time (APTT) elevations were more common in patients previously treated with chlorpromazine than in those previously treated with fluphenazine. There was no relationship between attenuation of reduced platelet levels and reduced APTT ratios. This preliminary study indicates that there may be two mechanisms of phenothiazine-induced coagulopathy.

Adult↗
PubMed1984

Alprazolam reversal of reserpine-induced depression in patients with compensated tardive dyskinesia.

Two patients are described who developed neuroleptic drug-induced tardive dyskinesia (TD) secondary to the treatment of schizophrenia. In both patients, neuroleptic drug discontinuation brought about a decrease in the severity of the TD and an increase in schizophrenic symptomatology. Reserpine was added for both antipsychotic coverage and reported beneficial effects in the treatment of TD. The patients' schizophrenia was controlled using reserpine 1 mg/d; the TD dissipated in one patient and decreased in the other. After about seven weeks of reserpine therapy, both patients developed depressive symptoms that required the addition or alprazolam. Within a month of the initiation of alprazolam, the depressions had cleared. Alprazolam may block reserpine-induced increases in beta-adrenergic receptors in the brain and may account for the antidepressive effects in these two patients.

Adult↗
PubMed1984

An analysis of poison control center reports of ciguatera toxicity in Puerto Rico for one year.

Forty-five cases of ciguatera poisoning in Puerto Rico (P.R.) are described. These cases represent all those reported to the P.R. Poison Control Center in 1982. Most of the cases were reported in the spring and summer months. The most common fish ingested was the grouper. The clinical presentation of acute and long term symptoms was similar to that reported in other geographical areas, except the incidence of paresthesias. Paresthesias were reported in 11% of the patients reported to the poison center. A companion telephone survey indicated that persons in P.R. that do not eat fish do so because of fear of ingesting the toxin. Our findings indicate an overall familial contact with the ciguatera toxin in Puerto Rico at 7%. This study is the first to document that ciguatera is a common poisoning reported to the Poison Control Center in Puerto Rico. Our findings also support other authors contentions of geographical variations in clinical symptomatology.

Adolescent↗