46,860 research outputs found
Microlensing of Broad Absorption Line Quasars
The physical nature of the material responsible for the high--velocity,
broad-absorption line features seen in a small fraction of quasar spectra has
been the subject of debate since their discovery. This has been especially
compounded by the lack of observational probes of the absorbing region. In this
paper we examine the role of ``microlenses'' in external galaxies on observed
variability in the profiles of broad absorption lines in multiply-imaged
quasars. Utilizing realistic models for both the broad absorption line region
and the action of an ensemble of microlensing masses, we demonstrate that stars
at cosmological distances can provide an important probe of the physical state
and structure of material at the heart of these complex systems. Applying these
results to the macrolensed BAL quasar system, H1413+117, the observed spectral
variations are readily reproduced, but without the fine-tuning requirements of
earlier studies which employ more simplistic models.Comment: 7 pages, 4 figures (included), Latex (mn.sty), Submitted to MNRA
Gravitational microlensing of planets: the influence of planetary phase and caustic orientation
Recent studies have demonstrated that detailed monitoring of gravitational
microlensing events can reveal the presence of planets orbiting the microlensed
source stars. With the potential of probing planets in the Galactic Bulge and
Magellanic Clouds, such detections greatly increase the volume over which
planets can be found. This paper expands on these original studies by
considering the effect of planetary phase on the form of the resultant
microlensing light curve. It is found that crescent-like sources can undergo
substantially more magnification than a uniformly illuminated disk, the model
typically employed in studying such planets. In fact, such a circularly
symmetric model is found to suffer a minimal degree of magnification when
compared to the crescent models. The degree of magnification is also a strong
function of the planet's orientation with respect to the microlensing caustic.
The form of the magnification variability is also strongly dependent on the
planetary phase and from which direction it is swept by the caustic, providing
further clues to the geometry of the planetary system. As the amount of light
reflected from a planet also depends on its phase, the detection of extreme
crescent-like planets requires the advent of 30-m class telescopes, while light
curves of planets at more moderate phases can be determined with today's 10-m
telescopes.Comment: 7 pages, 7 figures, to appear in the MNRA
Automatic transponder
A method and apparatus for the automatic, remote measurement of the internal delay time of a transponder at the time of operation is provided. A small portion of the transmitted signal of the transponder is converted to the receive signal frequency of the transponder and supplied to the input of the transponder. The elapsed time between the receive signal locally generated and the receive signal causing the transmission of the transmitted signal is measured, said time being representative of or equal to the internal delay time of the transponder at the time of operation
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Seven-year climatology of dust opacity on Mars
This paper describes the procedure we have used to produce multi-annual dust scenarios for Martian years 24 to 30 from a multi-instrument dataset of total dust opacity observations. This procedure includes gridding the observations on a pre-defined longitude-latitude grid with 1 sol resolution in time, and spatially interpolating the results to obtain complete daily maps of total dust opacity. We used weighted binning as gridding technique, and spatial kriging as method of interpolation. The new dust scenarios are available as NetCDF files, easy to interface to any model including global circulation and mesoscale models for the Martian atmosphere
Association between obesity and bacterial vaginosis as assessed by Nugent score
Background
Bacterial vaginosis is one of the most common vaginal conditions in the U.S. Recent studies have suggested obese women have an abnormal microbiota reminiscent of BV; however, few studies have investigated the prevalence of bacterial vaginosis in overweight and obese populations. Moreover, despite the increased prevalence of obesity and bacterial vaginosis in black women, it is not known whether racial disparities exist in the relationship between obesity and bacterial vaginosis.
Objective
The objective of this study was to examine the relationship between body mass index and bacterial vaginosis as determined by Nugent score and to determine the influence of race in this context.
Study Design
We performed a cross-sectional study using patient data and vaginal smears from 5,918 participants of the Contraceptive CHOICE Project. Gram stained vaginal smears were scored using the Nugent method and categorized as BV-negative (Nugent score 0-3), BV-intermediate (Nugent score 4-6), or BV-positive (Nugent score 7-10). Body mass index was determined using Centers for Disease Control and Prevention guidelines and obese individuals were categorized as Class I, II, or III obese based on NIH and World Health Organization body mass index parameters. Linear regression was used to model mean differences in Nugent scores and Poisson regression with robust error variance was used to model prevalence of bacterial vaginosis.
Results
In our cohort, 50.7% of participants were black, 41.5% were white, and 5.1% were of Hispanic ethnicity with an average age of 25.3 years old. Overall, 28.1% of participants were bacterial vaginosis-positive. Bacterial vaginosis was prevalent in 21.3% of lean, 30.4% of overweight, and 34.5% of obese women (p<0.001). The distribution of bacterial vaginosis-intermediate individuals was similar across all body mass index categories. Compared to lean women, Nugent scores were highest among overweight and obese Class I women (adjusted mean difference; overweight 0.33 [95% CI 0.14, 0.51] and Class I obese 0.51 [95% CI 0.29, 0.72]). Consistent with this, overweight and obese women had a higher frequency of bacterial vaginosis compared to lean women, even after adjusting for variables including race. Among white women, the prevalence of BV was higher for overweight and Class I and Class II/III obese white women compared to lean white women, a phenomenon not observed among black women, suggesting an effect modification.
Conclusion
Overweight and obese women have higher Nugent scores and a greater occurrence of bacterial vaginosis compared to lean women. Black women have a greater prevalence of bacterial vaginosis independent of their body mass index compared to white women
Investigation of new concepts of adaptive devices Quarterly technical report, 3 Dec. 1968 - 2 Mar. 1969
Conduction mechanisms and transient behavior of memory device using semiconductor device
Investigation of new concepts of adaptive devices Quarterly technical report, 3 Mar. - 2 Jun. 1969
Charge decay processes in memory device and in new metal nitride semiconductor light-sensitive memory elemen
A new comparison between solid-state thermionics and thermoelectrics
It is shown that equations for electrical current in solid-state thermionic
and thermoelectric devices converge for devices with a width equal to the mean
free path of electrons, yielding a common expression for intensive electronic
efficiency in the two types of devices. This result is used to demonstrate that
the materials parameters for thermionic and thermoelectric devices are equal,
rather than differing by a multiplicative factor as previously thought
Valuing an ecotourism resource : a case study of the Boulders Beach African penguin colony
The colony of African Penguins at Boulders, Simon's Town on the southern Cape Peninsula, Western Cape formed in 1985, and is now a major ecotourism destination. The African Penguin is listed as Endangered due in part to competition with commercial fisheries. Improvements in the spatial management of these fisheries could assist with the conservation of the penguins, but would be costly. Various techniques were used to estimate the value of the colony, and to assess its impact on the economy of the southern Peninsula
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