155 research outputs found
Photoluminescence signature of skyrmions at \nu = 1
The photoluminescence spectrum of quantized Hall states near filling factor
\nu = 1 is investigated theoretically. For \nu >= 1 the spectrum consists of a
right-circularly polarized (RCP) line and a left-circularly polarized (LCP)
line, whose mean energy: (1) does not depend on the electron g factor for
spin-1/2 quasielectrons, (2) does depend on g for charged spin-texture
excitations (skyrmions). For \nu < 1 the spectrum consists of a LCP line
shifted down in energy from the LCP line at \nu >= 1. The g-factor dependence
of the red shift of the LCP line determines the nature of the negatively
charged excitations.Comment: 11 pages, 2 PostScript figures. Replaced with version to appear in
Physical Review B Rapid Communications. Minor changes, reference adde
Orthogonality catastrophe in a composite fermion liquid
We discuss the emergence of an orthogonality catastrophe in the response of a
composite fermion liquid as the filling factor \nu approaches 1/2m, where
m=1,2,3.... A tunneling experiment is proposed in which dramatic changes in the
I-V characteristic should be observable as \nu is varied. Explicit I-V
characteristics calculated within the so-called Modified Random Phase
Approximation, are provided for \nu=1/3 -> \nu=1/2.Comment: Latex two-column 6 pages including 5 figure
Skyrmionic excitons
We investigate the properties of a Skyrmionic exciton consisting of a
negatively charged Skyrmion bound to a mobile valence hole. A variational wave
function is constructed which has the generalized total momentum P as a good
quantum number. It is shown that the Skyrmionic exciton can have a larger
binding energy than an ordinary magnetoexciton and should therefore dominate
the photoluminescence spectrum in high-mobility quantum wells and
heterojunctions where the electron-hole separation exceeds a critical value.
The dispersion relation for the Skyrmionic exciton is discussed.Comment: 9 pages, RevTex, 2 PostScript figures. Replaced with version to
appear in Phys. Rev. B Rapid Communications. Short discussion of variational
state adde
Linear and nonlinear optical characteristics of the Falicov-Kimball model
We calculate the linear and nonlinear optical properties of the
Falicov-Kimball model for a mixed-valent system within the self-consistent
mean-field approximation. Second-harmonic generation can only occur if the
mixed-valent state has a built-in coherence between the itinerant d-electrons
and the localized f-holes. By contrast, second-harmonic generation cannot occur
for solutions of the model with f-site occupation as a good quantum number. As
an experimental test of coherence in mixed-valent compounds we propose a
measurement of the dynamic second-order susceptibility.Comment: 4 pages, 2 PostScript figures, to appear in Physical Review Letter
Theory of Electronic Ferroelectricity
We present a theory of the linear and nonlinear optical characteristics of
the insulating phase of the Falicov-Kimball model within the self-consistent
mean-field approximation. The Coulomb attraction between the itinerant
d-electrons and the localized f-holes gives rise to a built-in coherence
between the d and f-states, which breaks the inversion symmetry of the
underlying crystal, leading to: (1) electronic ferroelectricity, (2)
ferroelectric resonance, and (3) a nonvanishing susceptibility for
second-harmonic generation. As experimental tests of such a built-in coherence
in mixed-valent compounds we propose measurements of the static dielectric
constant, the microwave absorption spectrum, and the dynamic second-order
susceptibility.Comment: 15 pages, 5 PostScript figures, submitted to Physical Review
Spin degree of freedom in two dimensional exciton condensates
We present a theoretical analysis of a spin-dependent multicomponent
condensate in two dimensions. The case of a condensate of resonantly
photoexcited excitons having two different spin orientations is studied in
detail. The energy and the chemical potentials of this system depend strongly
on the spin polarization . When electrons and holes are located in two
different planes, the condensate can be either totally spin polarized or spin
unpolarized, a property that is measurable. The phase diagram in terms of the
total density and electron-hole separation is discussed.Comment: 4 pages, 3 figures, Accepted for publication in Physical Review
Letter
Treatment of breast cancer with different antiprogestins: Preclinical and clinical studies
Abstract
Treatment with antiprogestins in a new treatment modality for breast cancer. Previously, in rats with DMBA-induced mammary tumors we observed significant growth inhibitory effects of chronic treatment with the antiprogestin mifepristone (RU486). In addition, in 11 postmenopausal breast cancer patients, we observed one objective response, six instances of short-term stable disease, and four instances of progressive disease. Side-effects appeared mainly due to antiglucocorticoid properties of the drug. Increased plasma estradiol levels were observed which probably resulted from ovarian (rat) and adrenal (patients) steroidogenesis.
Combined treatment with an antiestrogen in the rat model caused additive growth inhibitory effects. Tumor inhibition after single treatment with mifepristone or tamoxifen was 90 and 75%, respectively. In contrast, when combined, tumor remission similar to that caused by LHRH-agonist treatment (50%) was observed. Even higher tumor remission was found after combined treatment with mifepristone plus LHRH-agonist (75%). In first studies in the rat model we observed significant tumor growth inhibitory effects with two new antiprogestins of seemingly greater potency which cause less unfavorable endocrine side-effects.
In conclusion: combined treatment (antiprogestin plus antiestrogen or LHRH-agonist) may be of value in endocrine therapy of breast cancer
Anomalous magnetic response of the spin-one-half Falicov-Kimball model
The infinite-dimensional spin one-half Falicov-Kimball model in an external
magnetic field is solved exactly. We calculate the magnetic susceptibility in
zero field, and the magnetization as a function of the field strength. The
model shows an anomalous magnetic response from thermally excited local moments
that disappear as the temperature is lowered. We describe possible real
materials that may exhibit this kind of anomalous behavior.Comment: 17 pages, 6 encapsulated postscript figures (included), submitted to
Phys. Rev.
The Diesel Exhaust in Miners Study: IV. Estimating Historical Exposures to Diesel Exhaust in Underground Non-metal Mining Facilities
We developed quantitative estimates of historical exposures to respirable elemental carbon (REC) for an epidemiologic study of mortality, including lung cancer, among diesel-exposed miners at eight non-metal mining facilities [the Diesel Exhaust in Miners Study (DEMS)]. Because there were no historical measurements of diesel exhaust (DE), historical REC (a component of DE) levels were estimated based on REC data from monitoring surveys conducted in 1998–2001 as part of the DEMS investigation. These values were adjusted for underground workers by carbon monoxide (CO) concentration trends in the mines derived from models of historical CO (another DE component) measurements and DE determinants such as engine horsepower (HP; 1 HP = 0.746 kW) and mine ventilation. CO was chosen to estimate historical changes because it was the most frequently measured DE component in our study facilities and it was found to correlate with REC exposure. Databases were constructed by facility and year with air sampling data and with information on the total rate of airflow exhausted from the underground operations in cubic feet per minute (CFM) (1 CFM = 0.0283 m3 min−1), HP of the diesel equipment in use (ADJ HP), and other possible determinants. The ADJ HP purchased after 1990 (ADJ HP1990+) was also included to account for lower emissions from newer, cleaner engines. Facility-specific CO levels, relative to those in the DEMS survey year for each year back to the start of dieselization (1947–1967 depending on facility), were predicted based on models of observed CO concentrations and log-transformed (Ln) ADJ HP/CFM and Ln(ADJ HP1990+). The resulting temporal trends in relative CO levels were then multiplied by facility/department/job-specific REC estimates derived from the DEMS surveys personal measurements to obtain historical facility/department/job/year-specific REC exposure estimates. The facility-specific temporal trends of CO levels (and thus the REC estimates) generated from these models indicated that CO concentrations had been generally greater in the past than during the 1998–2001 DEMS surveys, with the highest levels ranging from 100 to 685% greater (median: 300%). These levels generally occurred between 1970 and the early 1980s. A comparison of the CO facility-specific model predictions with CO air concentration measurements from a 1976–1977 survey external to the modeling showed that our model predictions were slightly lower than those observed (median relative difference of 29%; range across facilities: 49 to –25%). In summary, we successfully modeled past CO concentration levels using selected determinants of DE exposure to derive retrospective estimates of REC exposure. The results suggested large variations in REC exposure levels both between and within the underground operations of the facilities and over time. These REC exposure estimates were in a plausible range and were used in the investigation of exposure–response relationships in epidemiologic analyses
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