Search PubMed⌕ Search

Biomedical subjects

M E Hayden

Publications and source records attributed to M E Hayden.

17 recordsLinked to original sources
PubMed2005

Active shielding of cylindrical saddle-shaped coils: application to wire-wound RF coils for very low field NMR and MRI.

We provide an exact expression for the magnetic field produced by cylindrical saddle-shaped coils and their ideal shield currents in the low-frequency limit. The stream function associated with the shield surface current is also determined. The results of the analysis are useful for the design of actively shielded radio-frequency (RF) coils. Examples pertinent to very low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) are presented and discussed.

Electromagnetic Fields↗
PubMed2004

Neutron-detected tomography of impurity-seeded superfluid helium.

We describe a neutron radiography technique that can be used to map the distribution of 3He impurities in liquid 4He, providing direct and quantitative access to underlying transport processes. Images reflecting finite normal- and superfluid-component 4He velocity fields are presented.

Journal Article↗
PubMed2004

Restricted diffusion within a single pore.

The time-dependent diffusion of 3Heatoms perpendicular to the axis of a single macroscopically large cylindrical pore is studied using a steady (or constant) gradient-recalled echo sequence. Measurements of the effective 3Hediffusion coefficient extending from the free-diffusion regime to the motionally averaged regime are presented, and are well-described by analytic solutions to the Bloch-Torrey equation based on the gaussian phase approximation. Our data yield the value 0.140(6)m2/s for the self diffusion coefficient of 3Heat a temperature of 296 K and a pressure of 1.00 Torr. Adaptations of these methods should enable the study of complex pore geometries as model systems.

Journal Article↗
PubMed2003

Observation of weak-limit quasiparticle scattering via broadband microwave spectroscopy of a d-wave superconductor.

There has long been a discrepancy between microwave conductivity measurements in high temperature superconductors and the conductivity spectrum expected in the simplest models for impurity scattering in a d-wave superconductor. Here we present a new type of broadband measurement of microwave surface resistance that finally shows some of the spectral features expected for a d(x2-y2) pairing state. Cusp-shaped conductivity spectra, consistent with weak impurity scattering of nodal quasiparticles, were obtained in the 0.6-21 GHz frequency range in highly ordered crystals of YBa2Cu3O6.50 and YBa2Cu3O6.99.

Journal Article↗
PubMed2000

Vocational reentry following TBI: an enablement model.

OBJECTIVE: To illustrate the importance of environmental factors for optimizing return to work following traumatic brain injury (TBI) using illustrative case examples. DESIGN AND PARTICIPANTS: Three case studies are presented that were selected from an overall sample of 57 TBI survivors. SETIING: Postacute, outpatient TBI rehabilitation program. MAIN OUTCOME MEASURES: Outcome was essentially descriptive and focused on factors associated with successful return to work. RESULTS AND CONCLUSIONS: These case examples point out the necessity of specialized treatment that not only focuses on the specific strengths and weakness of the individual, but also on extant environmental factors, including degree of structure or distractions that either reinforce or preclude optimal performance.

Adolescent↗
PubMed2000

Reducing level of handicap in traumatic brain injury: an environmentally based model of treatment.

A treatment model is described that has as its primary focus reducing the level of handicap of individuals with traumatic brain injury (TBI) by addressing the interaction between critical environmental variables and areas of deficit. The model focuses on two primary environmental variables-degree of distraction tolerated and degree of structure required by each individual to function optimally. These variables are systematically addressed in treatment through environmental simulations within the clinic. An outcome measurement system (Pate Environmentally Relevant Program Outcome System [PERPOS]) is presented that quantifies the level of handicap throughout treatment and at discharge as a function of the interplay between deficit and environment. Data are provided that validate the PERPOS scores through comparison with qualitative descriptors of day-to-day functioning in several domains. Outcome data indicate the participants in this treatment model made significant gains with regard to reduction of handicap.

Activities of Daily Living↗
PubMed2000

A comparison of neuropsychological and situational assessment for predicting employability after closed head injury.

The relationships among neuropsychological assessment, situational assessment, and judgments of future employability in 127 survivors of moderate to severe closed head injury were evaluated. Participants received a comprehensive neuropsychological battery and a situational vocational evaluation. Two groups were created, based on employment recommendation from the situational evaluation. A seven-factor model was found to account for the preponderance of variance within the neuropsychological battery used, and one factor was predictive of group assignment from situational assessment. However, the present data reinforce the predominance of findings in the literature that indicate that, in general, no individual neuropsychological test can be used to predict vocational performance in more environmentally relevant environments. Exceptions to this "rule" may occur when comparisons between results of formal neuropsychological tests and situational evaluation are limited to very simple, very circumscribed, and/or very well-defined functions. Thus, situational assessment is seen as a critical adjunct to neuropsychological assessment in making "real-world" predictions. The particular situational assessment used in this study was internally valid, an important finding given the importance of situational assessment in ecologically valid predictions.

Adolescent↗
PubMed1997

Mild traumatic brain injury. A primer for understanding its impact on employee return to work.

1. Mild head injuries are common occurrences in the United States. 2. If not properly understood and managed, mild head injuries can be unnecessarily costly in terms of lost work days, financial expenditures, and human suffering. 3. If properly understood and treated, most victims of mild head injuries can return to productive lifestyles. 4. Factors that place persons at high risk for more severe symptoms and/or more lengthy recovery periods are easy to conceptualize.

Brain Injuries↗
PubMed1991

In vitro studies with five quinolones: evidence for changes in relative potency as quinolone resistance rises.

A panel of 203 staphylococci, Enterobacteriaceae, Pseudomonas aeruginosa, and miscellaneous nonfermentative gram-negative bacilli were chosen for their various susceptibilities to ciprofloxacin. On the basis of agar dilution susceptibilities, each of the four taxonomic groups was divided into ciprofloxacin-susceptible, moderately resistant, and highly resistant subgroups, and each subgroup was then further analyzed for its susceptibility to the fluoroquinolones CI-960, CI-990, sparfloxacin, and ofloxacin. Although the MICs of each quinolone increased as ciprofloxacin resistance increased, the potency of CI-960 appeared to increase relative to the potencies of the other quinolones. Similarly, the MICs of sparfloxacin and ofloxacin appeared to be less affected by ciprofloxacin resistance than were the MICs of ciprofloxacin or CI-990. Single-step mutants of representative clinical isolates with different levels of ciprofloxacin resistance were selected to determine whether the study quinolones differed in their propensity to select resistant mutants and whether the presence of preexisting ciprofloxacin resistance influenced the subsequent development of resistance. Each of the five fluoroquinolones and nalidixic acid selected mutants that exhibited generally modest decreases in quinolone susceptibility (4- to 16-fold). However, CI-960 inhibited significantly more mutants (80%) than did the other quinolones (39 to 59%) at a concentration of 1 microgram/ml. The presence of preexisting ciprofloxacin resistance appeared to be associated with higher mutational frequencies in coagulase-negative staphylococci exposed to each of the fluoroquinolones and in Serratia marcescens exposed to nalidixic acid. Preexisting ciprofloxacin resistance did not influence the development of resistance in the strains of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, or Pseudomonas aeruginosa that were studied. The results of this study suggest that quinolones are not affected equally by all resistance mechanisms, and although each one can select mutants, some quinolones may be active against these mutants at clinically achievable concentrations.

Anti-Infective Agents↗
PubMed1985

Impairment of remote memory after closed head injury.

Evidence of partial retrograde amnesia for episodic memories of no personal salience was found in head injured patients (n = 10) tested during posttraumatic amnesia or shortly after its resolution (n = 10), but there was no selective preservation of the earliest memories. In contrast, head injured patients tested during posttraumatic amnesia exhibited relatively preserved retention of early autobiographical memories which they recalled as accurately as oriented head injured patients. It is suggested that reminiscence of salient, early events increases their resistance to partial retrograde amnesia and contributes to the observed temporal gradient.

Adolescent↗
PubMed1981

The role of distinctive features in articulation errors.

Articulation errors of 1,077 children of various ages, etiologies, and sexes were taken from several standardized articulation tests. The Singh and Singh (1976) distinctive feature system was used to produce profiles for each subgroup for consonant phonemes in the initial, medial, and final word positions. Distinctive features were used with different degrees of importance causing hierarchial orders among the features. The hierarchy of features established in this study was consistent with those found in previous studies. It was more pronounced for the initial position than for the medial and final positions, and for the younger age groups as compared with the older groups. In addition, the feature hierarchy for the articulation-disordered group was more distinct than that for the language group. Females revealed a generally superior performance to males, but this superiority was in general not statistically significant. Findings are discussed as to their relevance in the overall application of a phonological theory to speech production strategies.

Adolescent↗
PubMed1981

Markedness of features in the articulatory substitutions of children.

This study concerns an analysis of articulatory substitutions of 801 students using markedness theory and a distinctive feature model (Singh & Singh, 1976). The 556 male and 245 female students ranged in age from 3--7 years and were diagnosed as evidencing an articulatory disorder or a linguistic delay. Significantly more feature substitutions moved from marked to unmarked values than from unmarked to marked values (p less than .05, binomial distribution). The study proposed a hierarchy of distinctive features in terms of markedness rather than in terms of features per se. The applications of articulatory and acoustic data to phonological theory and the implications of the findings to speech treatment are discussed.

Articulation Disorders↗
PubMed1979

Role of distinctive features in dichotic perception of 21 English consonants.

The role distinctive features played in the identification of 21 dichotically presented syllable initial English consonants was evaluated. Results were analyzed for the entire stimulus set and for various intra- and inter-manner class comparisons. Consistent with previous dichotic studies of stops alone, stops as a subgroup showed a large right ear advantage, a high incidence of blend errors, and greater accuracy in identification when the competing stimuli contrasted on one (rather than two) distinctive features. Results for manner classes other than stops, for inter-manner comparisons and for the total stimulus set indicated increased correct identification with increasing numbers of distinctive feature differences between the two syllables. Analysis of error patterns revealed that, in addition to the stops, continuants, and stop-continuant, stop-affricate, and stop-nasal pairs revealed significant numbers of blend errors. Error responses also showed a tendency for unmarked feature specifications to predominate significantly over marked feature specifications. Finally, the magnitude of the right ear advantage varied significantly as a function of manner class, but not as a function of number of feature contrasts.

Adult↗
PubMed1978

Use of the Leiter International Performance Scale with adult aphasics.

Considered whether the Leiter International Performances Scales (LIPS), a general intelligence test used successfully with Ss age 2-18, can be adapted for use with aphasic adults. Six aphasic adults and 6 matched controls were given the Reitan Indians Screening Test of Aphasia and the LIPS. Results showed that the aphasic sample had total test scores comparable with the control group; however, the aphasic group required approximately 66% more time than the controls to complete the test. It was concluded that further work is merited based on the following results: (1) the test provided a sufficient range of difficulty so that each S errored on at least one-fourth of the test items; (2) the test could be given to the adult aphasics within a feasible time frame; (3) the aphasic adults were able to work with the test materials despite visual defects and hemiparesis of the dominant side; (4) feasible modifications can be made in the test.

Adult↗