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D Gaskell

Publications and source records attributed to D Gaskell.

At least 19 recordsLinked to original sources
PubMed2006

Determination of the pion charge form factor at Q2=1.60 and 2.45 (GeV/c)2.

The 1H(e,e'pi+)n cross section was measured at four-momentum transfers of Q2=1.60 and 2.45 GeV2 at an invariant mass of the photon nucleon system of W=2.22 GeV. The charged pion form factor (F(pi)) was extracted from the data by comparing the separated longitudinal pion electroproduction cross section to a Regge model prediction in which F(pi) is a free parameter. The results indicate that the pion form factor deviates from the charge-radius constrained monopole form at these values of Q2 by one sigma, but is still far from its perturbative quantum chromodynamics prediction.

Journal Article↗
PubMed2005

Measurement of the tensor structure function b1 of the deuteron.

The Hermes experiment has investigated the tensor spin structure of the deuteron using the 27.6 GeV/c positron beam of DESY HERA. The use of a tensor-polarized deuteron gas target with only a negligible residual vector polarization enabled the first measurement of the tensor asymmetry A(d)zz and the tensor structure function b(d)1 for average values of the Bjorken variable 0.01< <0.45 and of the negative of the squared four-momentum transfer 0.5 GeV2 < <5 GeV2. The quantities A(d)zz and b(d)1 are found to be nonzero. The rise of b(d)1 for decreasing values of x can be interpreted to originate from the same mechanism that leads to nuclear shadowing in unpolarized scattering.

Journal Article↗
PubMed2005

Strange-quark contributions to parity-violating asymmetries in the forward g0 electron-proton scattering experiment.

We have measured parity-violating asymmetries in elastic electron-proton scattering over the range of momentum transfers 0.12 < or =Q2 < or =1.0 GeV2. These asymmetries, arising from interference of the electromagnetic and neutral weak interactions, are sensitive to strange-quark contributions to the currents of the proton. The measurements were made at Jefferson Laboratory using a toroidal spectrometer to detect the recoiling protons from a liquid hydrogen target. The results indicate nonzero, Q2 dependent, strange-quark contributions and provide new information beyond that obtained in previous experiments.

Journal Article↗
PubMed2005

Precision Rosenbluth measurement of the proton elastic form factors.

We report the results of a new Rosenbluth measurement of the proton electromagnetic form factors at Q2 values of 2.64, 3.20, and 4.10 GeV2. Cross sections were determined by detecting the recoiling proton, in contrast to previous measurements which detected the scattered electron. Cross sections were determined to 3%, with relative uncertainties below 1%. The ratio mu(p)G(E)/G(M) was determined to 4%-8% and showed mu(p)G(E)/G(M) approximately 1. These results are consistent with, and much more precise than, previous Rosenbluth extractions. They are inconsistent with recent polarization transfer measurements of similar precision, implying a systematic difference between the techniques.

Journal Article↗
PubMed2004

Flavor decomposition of the sea-quark helicity distributions in the nucleon from semiinclusive deep inelastic scattering.

Double-spin asymmetries of semiinclusive cross sections for the production of identified pions and kaons have been measured in deep inelastic scattering of polarized positrons on a polarized deuterium target. Five helicity distributions including those for three sea quark flavors were extracted from these data together with reanalyzed previous data for identified pions from a hydrogen target. These distributions are consistent with zero for all three sea flavors. A recently predicted flavor asymmetry in the polarization of the light quark sea appears to be disfavored by the data.

Journal Article↗
PubMed2004

The role of nipple discharge cytology in the diagnosis of breast disease: a study of 1948 nipple discharge smears from 1530 patients.

In this study a review of 1948 nipple discharge (ND) samples from 1530 patients in the age range of 18-83 years was undertaken to determine whether cytological findings from ND smears could provide useful diagnostic information regarding various breast lesions. The study included 1494 females and 36 males and was carried out during a period of 20 years 8 months. The clinical information in all patients was obtained from clinicians (coauthors), medical records and a review of biopsies in 205 patients who had undergone surgery following the cytodiagnosis. Of the ND samples examined, 1480 were unilateral while 468 were from 234 bilateral ND. The cytodiagnoses were: benign 624, inadequate (despite two to three repeat samples) 492, inflammatory 96, papillary lesion not otherwise specified (NOS) 229, suspicious 22 (21 females, one male) and malignant 67 (63 females, four males). A breast biopsy in the 22 suspicious cases revealed breast carcinoma in 18 cases (females n = 17, male n = 1), atypical ductal hyperplasia (female n = 1), fibroadenoma (female n = 1) and a papilloma in two females. In the 67 cases with a diagnosis of malignancy 65 revealed a breast carcinoma in the biopsy (female n = 62, male n = 3) while one female was diagnosed as fibroadenoma and one male as florid gynaecomastia. In 63 cases (females n = 61; males n = 2) with clinical lumpy areas consistent with the diagnosis of fibrocystic condition in ND, the biopsy confirmed a fibrocystic process. In 53 of 229 cases with ND findings suggestive of a papillary lesion (NOS) the biopsy revealed a papilloma in 41 cases while in 12 cases no lesion was found. In the remaining cases of all the groups only a clinical follow-up and appropriate investigations were performed with no untoward outcome. Based on our study it is felt that cytological examination of ND smears seems to be a reasonably specific method in the diagnosis of malignant and suspicious cases but may be somewhat less specific for other diagnoses.

Adolescent↗
PubMed2003

Q2 dependence of nuclear transparency for exclusive rho0 production.

Exclusive coherent and incoherent electroproduction of the rho(0) meson from 1H and 14N targets has been studied at the HERMES experiment as a function of coherence length (l(c)), corresponding to the lifetime of hadronic fluctuations of the virtual photon, and squared four-momentum of the virtual photon (-Q2). The ratio of 14N to 1H cross sections per nucleon, called nuclear transparency, was found to increase (decrease) with increasing l(c) for coherent (incoherent) rho(0) electroproduction. For fixed l(c), a rise of nuclear transparency with Q2 is observed for both coherent and incoherent rho(0) production, which is in agreement with theoretical calculations of color transparency.

Journal Article↗
PubMed2001

Longitudinal electroproduction of charged pions from (1)H, (2)H, and (3)He.

Separated longitudinal and transverse cross sections for charged pion electroproduction from (1)H, (2)H, and (3)He were measured at Q(2) = 0.4 (GeV/c)(2) for two values of the invariant mass, W = 1.15 GeV and W = 1.60 GeV, in a search for a mass dependence which would signal the effect of nuclear pions. This is the first such study that includes recoil momenta significantly above the Fermi surface. The longitudinal cross section, if dominated by the pion-pole process, should be sensitive to nuclear pion currents. Comparisons of the longitudinal cross section target ratios to a quasifree calculation reveal a significant suppression in (3)He at W = 1.60 GeV. The W = 1.15 GeV results are consistent with simple estimates of the effect of nuclear pion currents, but are also consistent with pure quasifree production.

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

Measurement of the charged pion electromagnetic form factor.

Separated longitudinal and transverse structure functions for the reaction 1H(e,e(')pi(+))n were measured in the momentum transfer region Q2 = 0.6--1.6 (GeV/c)(2) at a value of the invariant mass W = 1.95 GeV. New values for the pion charge form factor were extracted from the longitudinal cross section by using a recently developed Regge model. The results indicate that the pion form factor in this region is larger than previously assumed and is consistent with a monopole parametrization fitted to very low Q2 elastic data.

Journal Article↗
PubMed2000

Fine-needle aspiration cytology of the breast in a case with abundant acellular calcific material indicative of soft-tissue calcinosis.

Since calcific deposits in soft tissue may clinically resemble a tumor, it is feasible to investigate them by fine-needle aspiration (FNA) cytology. In this presentation we describe a case in the breast with extensive accumulation of acellular liquid calcific material which was sampled by the noninvasive technique of FNA, and which was indicative of nonfamilial soft-tissue calcinosis. A 48-yr-old, perimenopausal woman on a routine mammogram showed a well-defined, 1-cm partially cystic opacity in the left upper quadrant of the breast. All other investigations were normal, and no significant family or medical history was present. Under ultrasound guidance FNA was done, and about 1 ml of thick whitish fluid was obtained. Cytopreparations only showed abundant acellular calcium. The patient refused any further treatment and elected to be under the care of her family physician, according to whom she was clinically well with no changes in mammograms for the last 2 yr. The case is interesting, since the cytohistologic findings in aspirate sample appeared to be strongly indicative of soft-tissue calcinosis, which to our knowledge has not been previously reported.

Biopsy, Needle↗
PubMed1998

Fine-needle aspiration cytology of a minimal carcinoma of the breast with neuroendocrine features.

A case of breast carcinoma with neuroendocrine features is described in a 62-year-old nulliparous female, in which the fine-needle aspiration cytodiagnosis was of a breast carcinoma. Carcinoma of the breast with neuroendocrine features is an unusual variant which may be observed in several histologic types of mammary carcinoma. An awareness of this tumor is essential in view of the increasing use of fine-needle aspiration cytology as a minimally invasive, first line of investigation of a breast abnormality. The case presented here is also of interest since the tumor was only 5 mm in diameter (a minimal carcinoma).

Biopsy, Needle↗
PubMed1986

Practice, problems and compliance with postural drainage: a survey of chronic sputum producers.

Fifty outpatients with chronic respiratory disease, who had previously been requested to perform regular postural drainage, were asked to complete a questionnaire designed to assess their usual practice of postural drainage, their impression of its value and their problems and compliance with it. The group performed a median of one session of postural drainage lasting 15 minutes daily, increasing to two sessions lasting nearly 40 minutes daily during exacerbations of chest symptoms. Seventeen patients had difficulty finding time for postural drainage, 15 found it distasteful and in 17 postural drainage caused discomfort or pain. Twenty-seven patients were judged to be performing inadequate postural drainage, despite individual initial instruction and regular follow-up in a respiratory outpatient clinic. Other diverse reasons for poor compliance revealed by the survey are discussed and recommendations made to encourage improved compliance.

Adolescent↗