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J Mitchell

Publications and source records attributed to J Mitchell.

At least 55 records · Page 3Linked to original sources
PubMed2001

Measurement of the electric form factor of the neutron through d-->(e-->,e(')n)p at Q2 = 0.5 (GeV/c)(2).

We report the first measurement using a solid polarized target of the neutron electric form factor G(n)(E) via d-->(e-->,e(')n)p. G(n)(E) was determined from the beam-target asymmetry in the scattering of longitudinally polarized electrons from polarized deuterated ammonia ( 15ND3). The measurement was performed in Hall C at Thomas Jefferson National Accelerator Facility in quasifree kinematics with the target polarization perpendicular to the momentum transfer. The electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle segmented detector. We find G(n)(E) = 0.04632+/-0.00616(stat)+/-0.00341(syst) at Q2 = 0.495 (GeV/c)(2).

Journal Article↗
PubMed2001

Thyroxine induces transitions in red muscle kinetics and steady swimming kinematics in rainbow trout (Oncorhynchus mykiss).

During normal development, rainbow trout undergo a shift in red muscle contraction kinetics and swimming kinematics. Young trout parr have faster muscle kinetics and faster tailbeat frequency during swimming than older, larger juvenile trout. In this study, the thyroid hormone thyroxine (T(4)) was used to induce these changes in trout parr. This allowed a comparison of swimming kinematics, through the use of video analysis and electromyography, and red muscle contractile properties, through the use of in vitro muscle preparations, between natural parr and same-sized induced juveniles. The red muscle of natural parr has faster contractile properties than induced juveniles, including faster twitch time and a faster maximum shortening velocity (V(max)). Further, natural parr swim with faster tailbeat frequencies than induced juveniles. The results suggest that the natural shift in red muscle contraction kinetics observed during parr-smolt transfomation in trout directly affects swimming behavior in these fish. Also, thyroid hormones appear to induce a shift towards slower isoforms of the muscle protein myosin heavy chain (MHC), a result distinct from work on rats where thyroid hormones induce shifts towards faster forms of MHC. J. Exp. Zool. 290:115-124, 2001.

Animals↗
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

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↗
PubMed2001

Pathways mediating sexual abuse and eating disturbance in children.

OBJECTIVE: To examine the relationship between childhood maltreatment and eating disorders in a sample of children. METHOD: Twenty 10-15-year-old female children who were receiving treatment following reported childhood sexual abuse and 20 age-matched controls were compared on a series of measures assessing eating disorder behaviors, body image concerns, substance use, mood, impulsive behavior, and self-concept. RESULTS: Sexually abused children reported higher levels of eating disorder behaviors, impulsive behaviors, and drug abuse than controls. Furthermore, behavioral impulsivity provided the strongest mediational effect between a history of childhood sexual abuse and purging and restrictive dieting behavior. Drug use proved to be a significant secondary mediator of the childhood sexual abuse eating disorder behavior association. DISCUSSION: These data support the hypothesis that childhood sexual abuse is related to disordered eating in children, and extend similar findings that have been previously reported with adults. Behavioral impulsivity and drug use appear to be significant mechanisms that influence eating disorder behavior following childhood sexual abuse.

Adolescent↗
PubMed2001

The use of ecological momentary assessment approaches in eating disorder research.

OBJECTIVE: Eating disorder (ED) research is increasingly focusing on the proximal antecedents to disordered eating behavior. Such antecedents may include cognitions, environmental stimuli, social interactions, and affective states. Current ED theories suggest that the relationships between antecedents and eating behavior may be complex, including interaction associations, time-lagged effects, and associations that persist only for brief periods of time. Similarly, these theories often include the consequences of behavior-influencing variables of interest (e.g., short-term reductions in negative affect). Careful examination of such theories, however, has been limited by a reliance on data collection methods not appropriate for testing these effects. METHOD: This study examines alternative methods for data collection and analysis that overcome previously noted limitations, using data collected in several studies with eating-disordered participants. RESULTS: The development of a technique called ecological momentary assessment (EMA) allows the ongoing study of behavior in its natural context and reduces biases associated with retrospective recall. The development of technology that allows the sophisticated collection and storage of such data (e.g., palm-top computers), along with statistical procedures for analyzing hierarchically nested, repeated measures data, allow precise testing of complex theoretical models. DISCUSSION: We demonstrate several important features of this research: (1) patients are willing and able to engage in EMA studies, (2) data not possible to collect using other designs are obtainable, (3) complex theoretical models can be evaluated using these data and appropriate statistical methods, and (4) the collection and analysis of EMA data present unique difficulties to ED researchers. Finally, we endorse and provide recommendations for the use of EMA in future ED research and practice.

Data Collection↗
PubMed2001

Administering cognitive-behavioral therapy for bulimia nervosa via telemedicine in rural settings.

OBJECTIVE: This report describes the therapy of 2 women with bulimia nervosa who were treated using cognitive-behavioral therapy delivered via telemedicine. METHOD: The telecommunication link was established using a 128-Kbps ISDN switchable data line. RESULTS: Both cases were treated successfully and were doing well at 1-month follow-up. DISCUSSION: These cases illustrate that this methodology may make it possible to deliver manual-based psychotherapies to patients with eating disorders in remote areas.

Adult↗
PubMed2001

A model of visual-spatial memory across saccades.

This paper describes a neural network model that directs saccades back to targets after they disappear and other saccades intervene. This is a simple example of knowing where something is after it is no longer visible and the observer has moved. These tasks require a short-term memory that can store continuous values of spatial location. The model was generated by training a neural network with a recurrently connected hidden layer to specify memory-guided saccades. The trained network maintains stored locations accurately for a few seconds. It uses a leaky integrator mechanism in which there is a slow decay of the stored value to a small number of fixed point attractors. Similar mechanisms have been used to model oculomotor integration (Cannon, S., Robinson, D., & Shamma, S. (1983). A proposed neural network for the integrator of the oculomotor system. Biological Cybernetics, 49, 127-136; Seung, H. (1998). Continuous attractors and oculomotor control. Neural Networks, 11, 1253-1258). The mechanism is robust to parameters such as the input and output format and the constraints in training. However, the receptive field properties of the hidden units do depend on these parameters. It was possible to find biologically plausible parameters that produced hidden unit behavior similar to that of real neurons involved in saccade memory. In particular, training the model to simultaneously represent the target location in both eye- and head-based reference frames produces units similar to neurons in parietal saccade areas.

Humans↗
PubMed2001

Assessment of cancer risk from ethylene oxide residues in spices imported into New Zealand.

Quantitative estimates of cancer risks from ethylene oxide (ETO) residues were constructed based on 200 retail samples of various spices in New Zealand. Two samples of cinnamon contained detectable ETO. The highest value encountered was 15 ppm. ETO was not detected in the remaining 198 samples. However, 31 samples had detectable levels of ethylene chlorohydrin (ECH) and/or ethylene bromohydrin (EBH). A conservative estimate of ETO intake, based on average spice consumption, was 3.4 x 10(-6) mg/kg/day. Cancer potency factors for ETO ranging from 0.29 to 0.55 (mg/kg/day)(-1) were used to form cancer risk estimates. The resulting estimates of average lifetime excess cancer risk was 0.8 x 10(-6) to 1.7 x 10(-6). The US 97.5 percentile value for spice consumption (2.8 kg spices per year), gave an extreme upper-end estimate of lifetime cancer risk of approximately 1.4 x 10(-5). These risks are practically negligible considering the conservative assumptions used in estimating exposure to ETO. The exposures to ECH and EBH are 200-300-fold higher than to ETO. These compounds are of lesser potency to ETO in terms of mutagenicity or carcinogenicity in studies to date. However, the precise contribution of these compounds to the cancer risk estimate is uncertain due to large toxicological data gaps, including the absence of a 2-year cancer bioassay by the oral route.

Algorithms↗
PubMed2001

Qualitative methodologies and community participation in examining reproductive experiences: the Harlem Birth Right Project.

OBJECTIVES: Racial disparities in health present a challenge to public health because of the complexity of interacting social forces. The Harlem Birth Right Project sought to improve understanding of these forces by using qualitative and community participatory methods. In this paper we 1) describe the process of qualitative inquiry and community involvement, 2) evaluate the impact of community participation, and 3) present a brief summary of the findings on social context as it relates to pregnancy outcomes of women in Harlem. METHODS: We operationalized the qualitative method by combining participant observation, longitudinal case studies, and focus groups. An ethnographic survey was used to verify and triangulate findings across methods of data collection. We involved the community in the design, implementation, and analysis by collaborating with community-based organizations, setting up a community advisory board, and the use of dialogue groups and community meetings. RESULTS: The use of qualitative methods and community partnership uncovered important aspects of the social context of women's lives that may not have emerged through traditional epidemiologic research. We found that pregnancy may serve as a catalyst to increase perception of the magnitude of preexisting social stressors. Several stressors and chronic strains associated with structural forces were identified. For example, the high percentage of households headed by women is seen as one consequence of larger structural forces. While social support networks serve as an important coping mechanism to buffer against the stress caused by these structural forces, the types of support women seek differs by social strata, and some strategies were identified as being substantially more effective than others. CONCLUSIONS: Qualitative and community participatory research can be successfully conducted to support public health goals and can derive important new information on the social context of women's lives.

Community Participation↗
PubMed2001

Psychometric evaluation of the 12-item Well-being Questionnaire for use with people with macular disease.

This paper reports the evaluation of a generic measure of psychological well-being, the 12-item Well-being Questionnaire (W-BQ12), for use with people who have the chronic eye condition, macular disease (MD). The W-BQ12 was incorporated in a self-administered questionnaire which was completed by 1421 members of the Macular Disease Society (MD Society). Unforced factor analysis elicited the expected three factors representing constructs of positive well-being, energy and negative well-being. A forced single-factor solution supported use of the whole scale to measure total general well-being. High Cronbach's alpha coefficients demonstrated good internal consistency reliability in the entire scale (alpha = 0.87) and in subscales (alpha > 0.78). The factor structure matched that found in samples of people with diabetes for whom the W-BQ12 was first developed, indicating construct validity. Expected subgroup differences in the MD sample indicated significantly poorer well-being in women than in men and also in participants who were registered blind or partially sighted compared to those who were not registered. The W-BQ12 will be useful in measuring outcomes in rehabilitative and medical interventions and in researching factors affecting adjustment to MD.

Adult↗
PubMed2001

Retinal phospholipase C from squid is a regulator of Gq alpha GTPase activity.

The phospholipase C (PLC) pathway is the major signaling mechanism of photoactivation in invertebrate photoreceptors. Here we report the cloning of a cDNA encoding a 140-kDa retinal PLC that is uniquely expressed in squid photoreceptors. This cDNA encodes a protein with multiple distinct modular domains: PH, X and Y catalytic, and C2 domains, as well as G- and P-box motifs and two GTP/ATP binding motifs. The PLC was stimulated by activated squid Gq alpha but not by squid Gq beta gamma or mammalian beta gamma subunits. The PLC was inhibited by monophosphate, diphosphate and triphosphate nucleotides but not cyclic nucleosides. We also tested the ability of PLC-140 to regulate the GTPase activity of Gq alpha in the rhabdomeric membranes. Depletion of PLC-140 from the rhabdomeric membranes decreased the GTP hydrolysis but not GTP gamma S binding to the membranes. Reconstitution of purified PLC-140 with membranes accelerated Gq alpha GTPase activity by fivefold at a concentration of 2.5 microM. Our data suggest that PLC-140 plays an important role in both the activation and inactivation pathways of invertebrate visual transduction.

Amino Acid Sequence↗
PubMed2001

Clearance of barium from the oesophagus with diet cola and metoclopramide: a one stop approach to patients with dysphagia.

AIM: To establish a "one-stop" dysphagia service in which a consultation, barium swallow and endoscopy can all be performed in the same hospital visit. MATERIALS AND METHODS: In order to allow both barium swallow examination and endoscopy to be performed on the same day, a novel technique for clearing barium from the upper gastrointestinal tract was established. Following the barium swallow examination, patients were given diet cola and metoclopramide syrup. If appropriate, an upper gastrointestinal endoscopy was then performed shortly afterwards. The service was piloted for 6 months in which time 25 patients were investigated in this way. RESULTS: All patients were seen within 2 weeks of referral. The mean time between barium swallow and endoscopy was 3 h 38 min (range, 1 h 50 min to 5 h 20 min). In all 24 patients in whom an endoscopy was performed, barium had been satisfactorily cleared from the oesophagus and stomach. CONCLUSION: This technique allows both barium swallow and upper gastrointestinal endoscopy to be performed on the same day, providing a rapid, safe and accurate diagnosis with minimum patient inconvenience. Mitchell, J., (2001). Clinical Radiology56, 64-66

Adult↗
PubMed2001

Is the association between dietary fat intake and insulin resistance modified by physical activity?

The rising prevalence of type 2 diabetes, a condition associated with insulin resistance, is commonly attributed to changes in dietary patterns and physical activity levels in susceptible populations. However, few studies have described the independent effects of dietary intake and physical activity on the degree of insulin sensitivity within populations or examined the possibility of interactions between dietary factors and physical activity. This study was undertaken to describe the relationship between the quantity and pattern of dietary fat intake on fasting insulin levels (a marker of insulin sensitivity) and to investigate whether the association was modified by physical activity. A cross-sectional study of 815 nondiabetic men and women (30 to 71 years) recruited from a population-based sampling frame was undertaken. Diet was characterized using a semiquantitative food frequency questionnaire. Physical activity level (PAL), the ratio of total energy expenditure to basal metabolic rate, was estimated using individually calibrated heart rate monitoring, a method previously shown to be an objective and valid method for assessing total energy expenditure. In a linear regression model adjusted for total energy intake, total fat intake bordered on a significant association with fasting insulin (b = 0.000081; P =.058), and the polyunsaturated to saturated fat ratio (P:S ratio) of the diet was negatively associated with fasting insulin concentration (b = -0.37, P <.001). A negative association was observed between the PAL and fasting insulin (b = -0.12, P =.025). The association of the P:S ratio and PAL with fasting insulin remained significant when adjusted for each other and for total fat, total energy intake, body mass index (BMI), waist-to-hip ratio (WHR), age, sex, family history of diabetes, smoking status, and alcohol intake (P:S ratio, b = -0.24, P =.003; PAL, b = -0.13; P =.007). The association with total fat intake was no longer significant in this multivariate model (b = 6.7 x 10(-6); P =.858). There was no evidence for an interaction between total dietary fat intake and PAL (b = -0.000048; P =.243) or between the P:S ratio and PAL (b = -0.013; P =.949). These data demonstrate an independent association between the P:S ratio of the diet, the overall level of physical activity, and the fasting insulin concentration, a marker of insulin sensitivity. There was no evidence that the association between dietary fat intake and insulin resistance was modified by physical activity. The findings provide further support for efforts to promote increases in overall physical activity and modifications in the pattern of dietary fat intake in the whole population.

Adult↗