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Biomedical subjects

M J Naughton

Publications and source records attributed to M J Naughton.

At least 19 recordsLinked to original sources
PubMed2005

Field-enhanced diamagnetism in the pseudogap state of the cuprate Bi2Sr2CaCu2O(8+delta) superconductor in an intense magnetic field.

In hole-doped cuprates, Nernst experiments imply that the superconducting state is destroyed by spontaneous creation of vortices which destroy phase coherence. Using torque magnetometry on Bi2Sr2CaCu2O(8+delta), we uncover a field-enhanced diamagnetic signal M above the transition temperature Tc that increases with applied field to 32 Tesla and scales just like the Nernst signal. The magnetization results above Tc distinguish M from conventional amplitude fluctuations and strongly support the vortex scenario for the loss of phase coherence at Tc.

Journal Article↗
PubMed2005

Coexistence of superconductivity and antiferromagnetism probed by simultaneous nuclear magnetic resonance and electrical transport in (TMTSF)2PF6 system.

We report simultaneous NMR and electrical transport experiments in the pressure range near the boundary of the antiferromagnetic spin density wave (SDW) insulator and the metallic/superconducting (SC) phase in (TMTSF)2PF6. Measurements indicate a tricritical point separating a line of second-order SDW/metal transitions from a line of first-order SDW/metal(SC) transitions with coexistence of macroscopic regions of SDW and metal(SC) order, with little mutual interaction but strong hysteretic effects. NMR results quantify the fraction of each phase.

Journal Article↗
PubMed2004

Magic angle effects and angular magnetoresistance oscillations as dimensional crossovers.

Interference effects between velocity and density of states, which occur as electrons move along open orbits in the extended Brillouin zone in anisotropic conductors, result in a change of wave functions' dimensionality at magic angle (MA) directions of a magnetic field. In particular, these 1D-->2D dimensional crossovers result in the appearance of sharp minima in a resistivity component rho perpendicular (H,alpha), perpendicular to conducting layers. This explains the main qualitative features of MA and angular magnetoresistance oscillations' phenomena observed due to the existence of quasi-one-dimensional sheets of Fermi surface in (TMTSF)2X, (DMET-TSeF)2X, and kappa-(ET)2Cu(NCS)(2) conductors.

Journal Article↗
PubMed2004

Magnetic determination of H(c2) under accurate alignment in (TMTSF)2ClO4.

Cantilever magnetometry has been used to measure the upper critical magnetic field H(c2) of the quasi-one-dimensional molecular organic superconductor (TMTSF)2ClO4. From simultaneous resistivity and torque magnetization experiments conducted under precise field alignment, H(c2) at low temperature is shown to reach 5 T, nearly twice the Pauli paramagnetic limit imposed on spin singlet superconductors. These results constitute the first thermodynamic evidence for a large H(c2) in this system and provide support for spin triplet pairing in this unconventional superconductor.

Journal Article↗
PubMed2003

Interference commensurate oscillations in quasi-one-dimensional conductors.

We suggest an analytical theory to describe angular magnetoresistance oscillations recently discovered in the quasi-one-dimensional conductor (TMTSF)2PF6 [see Phys. Rev. B 57, 7423 (1998)]] and define the positions of the oscillation minima. The origin of these oscillations is related to interference effects resulting from Bragg reflections which occur as electrons move along quasiperiodic and periodic ("commensurate") electron trajectories in the extended Brillouin zone. We reproduce via calculations existing experimental data and predict some novel effects.

Journal Article↗
PubMed2002

Intersubband transport in quantum wells in strong magnetic fields mediated by single- and two-electron scattering.

We show theoretically that in quantum wells subjected to a strong magnetic field the intersubband current peaks at magnetic field values, which reveal the underlying specific intersubband scattering mechanism. We have designed and grown a superlattice structure in which such current oscillations are clearly visible, and in which the transition from the purely single-electron to the mixed single- and two-electron scattering regimes can be observed by tuning the applied voltage bias. The measurements were conducted in ultrahigh magnetic fields (up to 45 T) to obtain the full spectrum of the current oscillations.

Journal Article↗
PubMed2002

Critical field enhancement near a superconductor-insulator transition.

We have discovered a phenomenon where the orbital pair breaking effect is reduced, if not eliminated. It appears as a striking enhancement in the upper critical field H(c2) for (TMTSF)2PF6 and a strong upward curvature in the critical field versus temperature in the region of pressure-temperature phase space near the superconductor-spin density wave insulator boundary. A simple model based on self-consistently dividing the superconductor into layers explains the observations remarkably well and provides a unique way around orbital frustration and toward higher critical fields.

Journal Article↗
PubMed2002

The health-related quality of life and survival of small-cell lung cancer patients: results of a companion study to CALGB 9033.

The purposes of this study were 2-fold: to evaluate the impact of the schedule dependency of etoposide (3-day IV short course vs. a 21-day oral prolonged course) with cisplatin on the quality of life of small-cell lung cancer (SCLC) patients; and to examine the effect of baseline quality of life variables on long-term survival, after adjustment for known demographic and clinical prognostic factors. Participants were 70 patients enrolled in the cancer and leukemia group B (CALGB) protocol 9033. Quality of life was assessed at baseline, 6 and 12 weeks by: the EORTC QLQ-30, the Centers for epidemiology studies--Depression short form, the medical outcomes study (MOS) social support questionnaire, and a scale of sleep quality. Contrary to expectations, study results suggested no significant differences in the patients' life quality and treatment response based on whether they received etoposide in a 3-day IV vs. a 21-day oral regimen. The use of the baseline variables in predicting overall survival indicated that patients who were non-white and with liver involvement had decreased survival. Brain involvement, being male, and higher depressive symptoms were also found to be borderline significant in predicting decreased survival in this patient population.

Adult↗
PubMed2001

Triplet superconductivity in an organic superconductor probed by NMR Knight shift.

The nature of the superconducting state in quasi-one-dimensional organic conductors has remained controversial since its discovery. Here we present results of (77)Se NMR Knight shift (K(s)) experiments in (TMTSF)(2)PF(6) under 7 kbar of pressure with a magnetic field aligned along the most conducting a axis. We find no noticeable shift in K(s) upon cooling through the superconducting transition. Since K(s) directly probes the spin susceptibility chi(s), the fact that chi(s) remains unchanged through the superconducting transition strongly suggests spin-triplet superconductivity.

Journal Article↗
PubMed2001

Promoting adherence and retention to clinical trials in special populations: a women's health initiative workshop.

This paper describes a Women's Health Initiative workshop on promoting adherence and retention in randomized clinical trials among ethnic minority women, participants of lower socioeconomic status, and older women. Workshop objectives were: (1) to increase knowledge of demographic and cultural characteristics of diverse groups, (2) to increase awareness of how diversity can affect interactions in clinical research, (3) to explore how research staff behavior can influence adherence and retention, and (4) to increase knowledge of strategies to enhance adherence and retention in special populations. The workshop emphasized the importance of understanding beliefs, values, and experiences that are common in diverse groups of individuals, while at the same time recognizing and respecting individual differences that result from varying life circumstances and experiences. We discuss strategies to increase cultural competence, reduce stereotypes and discrimination, and create a culturally relevant and sensitive research environment.

Age Distribution↗
PubMed2000

Involving minority and underrepresented women in clinical trials: the National Centers of Excellence in Women's Health.

Recent attention to reducing health disparities among population groups has focused on the need to include in clinical studies, especially clinical trials, participants who represent the diversity of the populations to which study results will be applied. While scientists generally applaud the goal of broadening the characteristics of participants in clinical trials, they are faced with multiple challenges as they seek to include historically underrepresented populations in their research. This article examines the historical and sociocultural context of participation by underrepresented groups, especially women and minorities, in clinical trials, identifies major barriers and challenges facing researchers, and suggests strategies for meeting these challenges. The article draws upon the experiences of the investigators affiliated with the National Centers of Excellence of Women's Health (CoEs).

Clinical Trials as Topic↗
PubMed1998

Bone marrow staging in patients with non-Hodgkin's lymphoma: is flow cytometry a useful test?

BACKGROUND: Flow cytometric analysis of bone marrow often is used as an adjunct to morphologic evaluation in the staging of patients with non-Hodgkin's lymphoma (NHL). The goal of this study was to define objectively the benefit of flow cytometry in this setting. METHODS: The authors reviewed retrospectively all bone marrow specimens submitted between January 1992 and December 1994 to the Washington University Department of Pathology for flow cytometric immunophenotyping to rule out NHL. Results of morphologic examination and flow cytometry were reviewed independently and the ability to detect bone marrow involvement compared. RESULTS: Two hundred and seventy-three bone marrow specimens from 190 patients with an established diagnosis of NHL were submitted for flow cytometric analysis at initial presentation, restaging, and/or recurrence. Morphologic evaluation was negative in 69%, positive in 23%, and equivocal in 8%. Flow cytometry was negative in all but 1 morphologically negative bone marrow specimens and 40% of morphologically involved bone marrow specimens. Two of 23 morphologically equivocal bone marrow specimens were positive by flow cytometry. An additional 86 specimens were obtained to rule out NHL in patients without an established diagnosis of NHL. The majority of patients had a history of human immunodeficiency virus infection, cytopenia, or unexplained fevers. Morphologically, one specimen was involved with NHL, 5 were equivocal, and 80 were negative. All specimens were negative by flow cytometry. CONCLUSIONS: In this study, flow cytometric analysis improved the detection of NHL in bone marrow in only 3 of 273 samples, 2 of which were suspicious morphologically. Flow cytometry of bone marrow aspirates has a limited role in the routine staging and follow-up of patients with an established diagnosis of NHL.

Bone Marrow Examination↗
PubMed1997

Assessment of health-related quality of life in orthopaedic outcomes' studies.

The assessment of health-related quality of life is becoming increasingly important in evaluating the effectiveness of orthopaedic interventions. This report provides an overview of issues related to the assessment of quality of life in orthopaedic populations. Discussed are the definition and dimensions of health-related quality of life: the usefulness of collecting quality of life data; methodological considerations in designing outcomes' studies; the selection of quality of life instruments; modes of instrument administration; and scoring.

Health Status Indicators↗
PubMed1997

Quality of life in geriatric patients with lower urinary tract dysfunction.

Lower urinary tract dysfunctions, such as urinary incontinence, detrusor instability, and benign prostatic hyperplasia, are prevalent in older adults. These conditions, which can occur alone or in combination, result in irritative or obstructive symptoms that can interfere with everyday functioning, leading to negative consequences on health-related quality of life. The nature and severity of these symptoms and the perception of their impact on daily activities can be quite variable. Until recently, relatively little was known about the effect of lower urinary tract dysfunctions on general health status and quality of life. An increasing research base is now available that shows the impact of different urologic dysfunctions in clinical and general populations. This article will provide a brief background on the definition and measurement of health-related quality of life and will summarize the literature about the quality of life of community-dwelling elderly patients with urinary incontinence or prostate conditions. Implications to guide clinical practice and future research will be derived.

Aged↗
PubMed1994

DPB1 locus PCR-RFLP typing of the fourth Asia-Oceania Histocompatibility Workshop cell panel reveals a novel DPB1 allele.

DPB1 locus typing of the 155 cell 4AOHW panel was performed using a PCR-RFLP method. Ambiguity of allele assignment was resolved by amplification using sequence-specific primers. Of the 150 cells for which typings were achieved, three exhibited unusual restriction enzyme fragment patterns, suggesting the possibility of novel DPB1 alleles. Sequence analysis revealed one allele present in the currently reported 46, one novel allele (4AOHW/107) not present among the 46, and one from a non-human primate which is being investigated. Twenty-six (26) of the 34 10IHW cells have been studied previously by cDNA RFLP, and strong haplotypic associations have been demonstrated between DPA1 and DPB1 locus alleles. It is proposed that exploitation of intron polymorphisms making haplotypes will be an integral part of future DPB1 typing as a "first-pass' stratification process to minimize the requirement for sequence-based methods to definitively assign DPB1 alleles.

Alleles↗