110 research outputs found
Extrinsic models for the dielectric response of CaCu{3}Ti{4}O{12}
The large, temperature-independent, low-frequency dielectric constant
recently observed in single-crystal CaCu{3}Ti{4}O{12} is most plausibly
interpreted as arising from spatial inhomogenities of its local dielectric
response. Probable sources of inhomogeneity are the various domain boundaries
endemic in such materials: twin, Ca-ordering, and antiphase boundaries. The
material in and neighboring such boundaries can be insulating or conducting. We
construct a decision tree for the resulting six possible morphologies, and
derive or present expressions for the dielectric constant for models of each
morphology. We conclude that all six morphologies can yield dielectric behavior
consistent with observations and suggest further experiments to distinguish
among them.Comment: 9 pages, with 1 postscript figure embedded. Uses REVTEX and epsf
macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/mc_ext/index.htm
High renin and prorenin in plasma and pleural exudate of a patient with the ovarian hyperstimulation syndrome
We present the case of a 35-year-old woman with a severe ovarian hyperstimulation syndrome (OHSS) as a complication of ovulation induction for primary infertility. The clinical picture showed massively enlarged ovaries, pleural effusion and haemoconcentration. She needed a thoracentesis for evacuation of the large pleural effusion. High levels of renin and prorenin were observed in plasma and pleural exudate
Towards a first principles description of phonons in NiPt disordered alloys: the role of relaxation
Using a combination of density-functional perturbation theory and the
itinerant coherent potential approximation, we study the effects of atomic
relaxation on the inelastic incoherent neutron scattering cross sections of
disordered NiPt alloys. We build on previous work, where
empirical force constants were adjusted {\it ad hoc} to agree with experiment.
After first relaxing all structural parameters within the local-density
approximation for ordered NiPt compounds, density-functional perturbation
theory is then used to compute phonon spectra, densities of states, and the
force constants. The resulting nearest-neighbor force constants are first
compared to those of other ordered structures of different stoichiometry, and
then used to generate the inelastic scattering cross sections within the
itinerant coherent potential approximation. We find that structural relaxation
substantially affects the computed force constants and resulting inelastic
cross sections, and that the effect is much more pronounced in random alloys
than in ordered alloys.Comment: 8 pages, 3 eps figures, uses revtex
Flat branches and pressure amorphization
After summarizing the phenomenology of pressure amorphization (PA), we
present a theory of PA based on the notion that one or more branches of the
phonon spectrum soften and flatten with increasing pressure. The theory
expresses the anharmonic dynamics of the flat branches in terms of local modes,
represented by lattice Wannier functions, which are in turn used to construct
an effective Hamiltonian. When the low-pressure structure becomes metastable
with respect to the high-pressure equilibrium phase and the relevant branches
are sufficiently flat, transformation into an amorphous phase is shown to be
kinetically favored because of the exponentially large number of both amorphous
phases and reaction pathways. In effect, the critical-size nucleus for the
first-order phase transition is found to be reduced to a single unit cell, or
nearly so. Random nucleation into symmetrically equivalent local configurations
characteristic of the high-pressure structure is then shown to overwhelm any
possible domain growth, and an ``amorphous'' structure results.Comment: 8 pages with 3 postscript figures embedded; Proceedings of the 4th
International Discussion Meeting on Relaxations in Complex Systems,
Hersonissos, Heraklion, Crete, June 16-23, ed. K. L. Ngai, Special Issues of
the Journal of Non-Crystalline Solids, 200
Lattice dielectric response of CdCu{3}Ti{4}O{12} and of CaCu{3}Ti{4}O{12} from first principles
Structural, vibrational, and lattice dielectric properties of
CdCu{3}Ti{4}O{12} are studied using density-functional theory within the local
spin-density approximation, and the results are compared with those computed
previously for CaCu{3}Ti{4}O{12}. Replacing Ca with Cd is found to leave many
calculated quantities largely unaltered, although significant differences do
emerge in zone-center optical phonon frequencies and mode effective charges.
The computed phonon frequencies of CdCu{3}Ti{4}O{12} are found to be in
excellent agreement with experiment, and the computed lattice contribution to
the intrinsic static dielectric constant (~60) also agrees exceptionally well
with a recent optical absorption experiment. These results provide further
support for a picture in which the lattice dielectric response is essentially
conventional, suggesting an extrinsic origin for the anomalous low-frequency
dielectric response recently observed in both materials.Comment: 5 pages; uses REVTEX macros. Also available at
http://www.physics.rutgers.edu/~dhv/preprints/lh_cdct/index.htm
Structured analysis of histopathological characteristics of vulvar lichen sclerosus in a juvenile population
Genital lichen sclerosus (LS), a chronic noninfectious dermatosis, is not rare in pediatric
dermatology. The histopathological diagnosis in children and adults in both genital and nongenital
LS is considered to be the same and encompasses a broad range of possible characteristics. Clinical
manifestations and treatment options of genital LS in children are different depending on gender.
The vast majority of boys are treated with circumcision, making for a larger amount of information
on the histopathology of genital LS in boys, whereas substantial information on the histopathology
of juvenile vulvar LS is lacking. In girls, vulvar LS almost always persists beyond puberty and, therefore, presents a particular challenge to clinicians and cause for concern for the patient. Vulvar LS in
childhood and adolescence (juveniles) is underreported, and there are uncertainties with regard to
the long-term course of the disease when it occurs at an age when the vulva is still developing. The
present study investigates biopsi
Local Isoelectronic Reactivity of Solid Surfaces
The quantity w^N(r) = ( 1/ k^2 T_el)[partial n(r, T_el) / partial
T_el]_(v(r),N) is introduced as a convenient measure of the local isoelectronic
reactivity of surfaces. It characterizes the local polarizability of the
surface and it can be calculated easily. The quantity w^N(r) supplements the
charge transfer reactivity measured e.g. by the local softness to which it is
closely related. We demonstrate the applicability and virtues of the function
w^N(r) for the example of hydrogen dissociation and adsorption on Pd(100).Comment: RevTeX, 13 pages, 3 figures, to appear in Phys. Rev. Let
Phonons in random alloys: the itinerant coherent-potential approximation
We present the itinerant coherent-potential approximation(ICPA), an analytic,
translationally invariant and tractable form of augmented-space-based,
multiple-scattering theory in a single-site approximation for harmonic phonons
in realistic random binary alloys with mass and force-constant disorder.
We provide expressions for quantities needed for comparison with experimental
structure factors such as partial and average spectral functions and derive the
sum rules associated with them. Numerical results are presented for Ni_{55}
Pd_{45} and Ni_{50} Pt_{50} alloys which serve as test cases, the former for
weak force-constant disorder and the latter for strong. We present results on
dispersion curves and disorder-induced widths. Direct comparisons with the
single-site coherent potential approximation(CPA) and experiment are made which
provide insight into the physics of force-constant changes in random alloys.
The CPA accounts well for the weak force-constant disorder case but fails for
strong force-constant disorder where the ICPA succeeds.Comment: 19 pages, 12 eps figures, uses RevTex
Isolated rectal buttonhole tears in obstetrics: case series and review of the literature.
INTRODUCTION AND HYPOTHESIS: The management of isolated rectal buttonhole tears is not standardised and can be challenging in an acute obstetric setting. Our aim was to review the published literature and describe management and repair techniques in a case series. METHODS: A literature search was carried out. All results were screened and reviewed. Rectal buttonhole tears following vaginal delivery between April 2012 and January 2020 in our institution were identified. Repair technique and post-operative management were recorded. RESULTS: There were nine published case reports (four instrumental deliveries, two vaginal breech and three normal vaginal deliveries). Four case reports described a two-layer closure and five described a three-layer closure. Two cases were repaired in collaboration with colorectal surgeons. All nine cases made an uneventful recovery. We identified three patients with buttonhole tears all of whom had instrumental deliveries. A colorectal surgeon repaired the tear in two layers in one case, and an obstetrician performed the repair in the other two cases, one in three layers and the other in two layers. One patient had a de-functioning stoma at a later date due to a second breakdown of the recto-vaginal fistula repair. CONCLUSION: Buttonhole tears are rare but techniques of repair vary. Most cases reviewed had an uneventful recovery after repair. We provide standardised steps for repair and management of isolated rectal buttonhole tears along with a video demonstrating the repair technique in an animal tissue (pig) model
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