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Biomedical subjects

D Fort

Publications and source records attributed to D Fort.

17 recordsLinked to original sources
PubMed2006

Determination of the antiferroquadrupolar order parameters in UPd(3).

By combining accurate heat capacity and x-ray resonant scattering results we have resolved the long standing question regarding the nature of the quadrupolar ordered phases in UPd(3). The order parameter of the highest temperature quadrupolar phase has been uniquely determined to be antiphase Q{zx} in contrast to the previous conjecture of Q{x{2}-y{2}}. The azimuthal dependence of the x-ray scattering intensity from the quadrupolar superlattice reflections indicates that the lower temperature phases are described by a superposition of order parameters. The heat capacity features associated with each of the phase transitions characterize their order, which imposes restrictions on the matrix elements of the quadrupolar operators.

Journal Article↗
PubMed2006

Spontaneous symmetry-breaking vortex lattice transitions in pure niobium.

We report an extensive investigation of magnetic vortex lattice (VL) structures in single crystals of pure niobium with the magnetic field applied parallel to a fourfold symmetry axis, so as to induce frustration between the cubic crystal symmetry and hexagonal VL coordination expected in an isotropic situation. We observe new VL structures and phase transitions; all the VL phases observed (including those with an exactly square unit cell) spontaneously break some crystal symmetry. One phase even has the lowest possible symmetry of a two-dimensional Bravais lattice. This is quite unlike the situation in high-Tc or borocarbide superconductors, where VL structures orient along particular directions of high crystal symmetry. The causes of this behavior are discussed.

Journal Article↗
PubMed2006

Observation of a strongly nested Fermi surface in the shape-memory alloy Ni0.62Al0.38.

The Fermi surface topology of the shape-memory alloy Ni0.62Al0.38 has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of approximately 0.18[1,1,0](2pi/a), which corresponds to the wave vector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting.

Journal Article↗
PubMed2002

Intrinsic behavior of flux lines in pure niobium near the upper critical field.

We report small-angle neutron-scattering (SANS) measurements of flux line properties near H(c2) in an ultrapure sample of niobium with weak pinning of flux in the bulk. These confirm in detail the Abrikosov picture of the flux line lattice to within 20 mK of the upper critical field line. However, it has recently been claimed [X. S. Ling et al., Phys. Rev. Lett. 86, 712 (2001)], on the basis of SANS observations of a disordering of flux lines in niobium, that the flux lattice melts at temperatures clearly separated from the upper critical field line. This discrepancy may possibly arise from differences in sample purity and pinning.

Journal Article↗
PubMed2000

Strategies for assessing the implications of malformed frogs for environmental health.

The recent increase in the incidence of deformities among natural frog populations has raised concern about the state of the environment and the possible impact of unidentified causative agents on the health of wildlife and human populations. An open workshop on Strategies for Assessing the Implications of Malformed Frogs for Environmental Health was convened on 4-5 December 1997 at the National Institute of Environmental Health Sciences in Research Triangle Park, North Carolina. The purpose of the workshop was to share information among a multidisciplinary group with scientific interest and responsibility for human and environmental health at the federal and state level. Discussions highlighted possible causes and recent findings directly related to frog deformities and provided insight into problems and strategies applicable to continuing investigation in several areas. Possible causes of the deformities were evaluated in terms of diagnostics performed on field amphibians, biologic mechanisms that can lead to the types of malformations observed, and parallel laboratory and field studies. Hydrogeochemistry must be more integrated into environmental toxicology because of the pivotal role of the aquatic environment and the importance of fates and transport relative to any potential exposure. There is no indication of whether there may be a human health factor associated with the deformities. However, the possibility that causal agents may be waterborne indicates a need to identify the relevant factors and establish the relationship between environmental and human health in terms of hazard assessment.

Animals↗
PubMed1994

Full-thickness Martius grafts to preserve vaginal depth as an adjunct in the repair of large obstetric fistulas.

We performed a modified bulbocavernosus full-thickness pedicle graft procedure on four patients with large obstetric fistulas in Ghana, West Africa. The bulbocavernosus fat pad was harvested in the usual manner, and the full-thickness skin patch was taken from the medial thigh. All grafts showed 100% take by the tenth postoperative day. Adequate vaginal depth and caliber were obtained in all patients. Sexual function resumed in all patients except one, who suffered a recurrent vesicovaginal fistula. This method of vaginoplasty may be useful in patients who have massive vaginal-wall destruction of either gynecologic or obstetric origin.

Adult↗
PubMed1988

Vesicovaginal fistula revisited.

Vesicovaginal fistulas remain common and serious problems for women in West Africa. Thirty-six surgical repairs done during visiting professorships by American gynecologists between the years 1978-1987 are documented. The overall success rate was 70%. The management of large (greater than 4 cm) obstetric fistulas was especially difficult until the Latzko technique was abandoned for the technique of wide mobilization of vaginal flaps over the fistula site. This technique reduced the failure rate from 75% through 1986 to approximately 25% in 1987. Ongoing controversies and basic principles of surgical techniques in fistula repair are reviewed.

Africa, Western↗