10,453 research outputs found
Noise suppression due to long-range Coulomb interaction: Crossover between diffusive and ballistic transport regimes
We present a Monte Carlo analysis of shot-noise suppression due to long-range
Coulomb interaction in semiconductor samples under a crossover between
diffusive and ballistic transport regimes. By varying the mean time between
collisions we find that the strong suppression observed under the ballistic
regime persists under quasi-ballistic conditions, before being washed out when
a complete diffusive regime is reached.Comment: RevTex, 3 pages, 4 figures, minor correction
Africanized honey bees (Apis mellifera L.) are more efficient at removing worker brood artificially infested with the parasitic mite Varroa jacobsoni Oudemans than are Italian bees or Italian/Africanized hybrids
Getting science to the citizen : 'food addiction' at the British Science Festival as a case study of interactive public engagement with high profile scientific controversy
Non peer reviewedPublisher PD
Stellar science from a blue wavelength range - A possible design for the blue arm of 4MOST
From stellar spectra, a variety of physical properties of stars can be
derived. In particular, the chemical composition of stellar atmospheres can be
inferred from absorption line analyses. These provide key information on large
scales, such as the formation of our Galaxy, down to the small-scale
nucleosynthesis processes that take place in stars and supernovae. By extending
the observed wavelength range toward bluer wavelengths, we optimize such
studies to also include critical absorption lines in metal-poor stars, and
allow for studies of heavy elements (Z>38) whose formation processes remain
poorly constrained. In this context, spectrographs optimized for observing blue
wavelength ranges are essential, since many absorption lines at redder
wavelengths are too weak to be detected in metal-poor stars. This means that
some elements cannot be studied in the visual-redder regions, and important
scientific tracers and science cases are lost. The present era of large public
surveys will target millions of stars. Here we describe the requirements
driving the design of the forthcoming survey instrument 4MOST, a multi-object
spectrograph commissioned for the ESO VISTA 4m-telescope. We focus here on
high-density, wide-area survey of stars and the science that can be achieved
with high-resolution stellar spectroscopy. Scientific and technical
requirements that governed the design are described along with a thorough line
blending analysis. For the high-resolution spectrograph, we find that a
sampling of >2.5 (pixels per resolving element), spectral resolution of 18000
or higher, and a wavelength range covering 393-436 nm, is the most
well-balanced solution for the instrument. A spectrograph with these
characteristics will enable accurate abundance analysis (+/-0.1 dex) in the
blue and allow us to confront the outlined scientific questions. (abridged)Comment: 14 pages, 8 figures, accepted for publication in A
Dose-finding study of paclitaxel and cyclophosphamide in advanced breast cancer
Background The toxicity profile of prolonged infusions of paclitaxel in combination with cyclophosphamide in metastat-ic breast cancer has already been defined. The objective of this dose-finding study was to determine the maximum tolerable doses (MTDs) of shorter (three-hour) infusions of paclitaxel in combination with i.v. bolus cyclophosphamide in patients who had previously received a maximum of one chemotherapy for advanced breast carcinoma. The MTD of the same regimen with granulocyte colony-stimulating factor (G-CSF) support was then established. Patients and methods Eighty women with metastatic breast cancer received a total of 352 fully evaluable courses of therapy. The starting doses were paclitaxel 135 mg/m2 and cyclophosphamide 750 mg/m2 given every three weeks. At least three patients were treated at each dose level and if there were dose-limiting toxic effects during the first cycles three additional patients were entered. G-CSF support (5 ug/kg s.c.) was added to the second cycle if specific dose-limiting toxicities had occurred during the first cycle. The MTD was defined as the dose level at which more than two of six patients presented dose-limiting toxicities during the first cycle. Results Febrile neutropenia (n = 4) and severe thrombo-cytopenia (n - 1) defined the MTDs of paclitaxel as 200 mg/m2 and of cyclophosphamide as 2,000 mg/m2 with or without G-CSF in patients with and, respectively, without prior chemotherapy for advanced disease. Non-hematologic toxicity was moderate. Recommended doses were 200 mg/m2 of paclitaxel and 1,750 mg/m2 of cyclophosphamide with or without G-CSF in patients with and, respectively, without prior chemotherapy. The overall response rate was 25% and 50%, respectively, in patients with and without prior chemotherapy for metastatic disease. Complete remissions (9%) were reported only in patients without prior chemotherapy; antitumour activity in women with anthracycline-resistant disease, with an 8% response rate (95% CI: 1%-26%), was poor. Conclusion Paclitaxel at 200 mg/m2 and cyclophosphamide at 1,750 mg/m2 can be safely administered every three weeks to women with advanced breast cancer. The moderate antitumour activity observed with the schedule tested argues against its use as initial therapy for advanced breast cance
Traditional health practitioners' perceptions, herbal treatment and management of HIV and related opportunistic infections
Background: In South Africa, traditional health practitioners? (THPs) explanatory frameworks concerning illness aetiologies are much researched. However there is a gap in the literature on how THPs understand HIV-related opportunistic infections (OIs), i.e. tuberculosis, candidiasis and herpes zoster. This study aimed to comprehend THPs? understandings of the aforementioned; to ascertain and better understand the treatment methods used by THPs for HIV and OIs, while also contributing to the documentation of South African medicinal plants for future conservation. Methods: The study was conducted in two locations: Strand, Western Cape where THPs are trained and Mpoza village, Mount Frere, Eastern Cape from where medicinal plants are ordered or collected. Semi-structured interviews were conducted with 53 THPs of whom 36 were diviners (amagrirha: isangoma) and 17 herbalists (inyanga). THPs were selected through a non-probability ?snowball? method. Data were analysed using a thematic content analysis approach. An ethnobotanical survey was conducted and plants used to manage HIV and OIs were collected. A complete set of voucher specimens was deposited at the University of the Western Cape Herbarium for identification. Plant names were checked and updated with Kew?s online website http://www.theplantlist.org. Results: THPs conceptualise the aetiology of HIV and OIs at two related levels. The first involves the immediate manifestation of the illness/condition because of a viral infection in the blood (HIV), the presence of bacteria in the lungs (tuberculosis), or weakened state of the body making it susceptible to OIs. The presence of OIs is indicative of the probable presence of HIV. The second level of causation affects the first, which includes pollution, changes in cultural sexual norms, witchcraft, environmental factors, and lack of adherence to ancestral rituals. THPs reported using 17 plants belonging to 12 families. Remedies included mixes of up to five plants. Conclusion: This study explored the THPs? perspectives on HIV and commonly associated OIs and their herbal treatment methods. THPs generally rely on biomedical diagnosis before treating a client. They also seek guidance from the ancestors for a particular diagnosis, the plants to use for a specific treatment, when to harvest, and how to administer herbal remedies
The Relationship Between Stellar Light Distributions of Galaxies and their Formation Histories
A major problem in extragalactic astronomy is the inability to distinguish in
a robust, physical, and model independent way how galaxy populations are
related to each other and to their formation histories. A similar, but
distinct, and also long standing question is whether the structural appearances
of galaxies, as seen through their stellar light distributions, contain enough
physical information to offer this classification. We argue through the use of
240 images of nearby galaxies that three model independent parameters measured
on a single galaxy image reveal its major ongoing and past formation modes, and
can be used as a robust classification system. These parameters quantitatively
measure: the concentration (C), asymmetry (A) and clumpiness (S) of a galaxy's
stellar light distribution. When combined into a three dimensional `CAS' volume
all major classes of galaxies in various phases of evolution are cleanly
distinguished. We argue that these three parameters correlate with important
modes of galaxy evolution: star formation and major merging activity. This is
argued through the strong correlation of Halpha equivalent width and broad band
colors with the clumpiness parameter, the uniquely large asymmetries of 66
galaxies undergoing mergers, and the correlation of bulge to total light
ratios, and stellar masses, with the concentration index. As an obvious goal is
to use this system at high redshifts to trace evolution, we demonstrate that
these parameters can be measured, within a reasonable and quantifiable
uncertainty, with available data out to z ~ 3 using the Hubble Space Telescope
GOODS ACS and Hubble Deep Field images.Comment: ApJS, in press, 30 pages, Figures 15 and 16 are in color. For a full
resolution version, please go to http://www.astro.caltech.edu/~cc/cas.p
Finite voltage shot noise in normal-metal - superconductor junctions
We express the low-frequency shot noise in a disordered normal-metal -
superconductor (NS) junction at finite (subgap) voltage in terms of the normal
scattering amplitudes and the Andreev reflection amplitude. In the multichannel
limit, the conductance exhibits resonances which are accompanied by an
enhancement of the (differential) shot noise. In the study of multichannel
single and double barrier junctions we discuss the noise properties of coherent
transport at low versus high voltage with respect to the Andreev level spacing.Comment: 6 pages, Latex, 2 eps-figures, to be published in PRB, Appendix on
Bogoliubov equation
Hybrid modeling of biological networks: mixing temporal and qualitative biological properties
<p>Abstract</p> <p>Background</p> <p>Modeling a dynamical biological system is often a difficult task since the a <it>priori </it>unknown parameters of such models are not always directly given by the experiments. Despite the lack of experimental quantitative knowledge, one can see a dynamical biological system as (i) the combined evolution tendencies (increase or decrease) of the biological compound concentrations, and: (ii) the temporal features, such as delays between two concentration peaks (i.e. the times when one of the components completes an increase (resp. decrease) phase and starts a decrease (resp. increase) phase).</p> <p>Results</p> <p>We propose herein a new hybrid modeling framework that follows such biological assumptions. This hybrid approach deals with both a qualitative structure of the system and a quantitative structure. From a theoretical viewpoint, temporal specifications are expressed as equality or inequality constraints between delay parameters, while the qualitative specifications are expressed as an ordered pattern of the concentrations peaks of the components. Using this new hybrid framework, the temporal specifications of a biological system can be obtained from incomplete experimental data. The model may be processed by a hybrid model-checker (e.g. Phaver) which is able to give some new constraints on the delay parameters (e.g. the delay for a given transition is exactly 5 hours after the later peak of a gene product concentration). Furthermore, by using a constraint solver on the previous results, it becomes possible to get the set of parameters settings which are consistent with given specifications. Such a modeling approach is particularly accurate for modeling oscillatory biological behaviors like those observed in the Drosophila circadian cycles. The achieved results concerning the parameters of this oscillatory system formally confirm the several previous studies made by numerical simulations. Moreover, our analysis makes it possible to propose an automatic investigation of the respective impact of per and tim on the circadian cycle.</p> <p>Conclusions</p> <p>A new hybrid technique for an automatic formal analysis of biological systems is developed with a special emphasis on their oscillatory behaviors. It allows the use of incomplete and empirical biological data.</p
The RAVE survey: the Galactic escape speed and the mass of the Milky Way
We construct new estimates on the Galactic escape speed at various
Galactocentric radii using the latest data release of the Radial Velocity
Experiment (RAVE DR4). Compared to previous studies we have a database larger
by a factor of 10 as well as reliable distance estimates for almost all stars.
Our analysis is based on the statistical analysis of a rigorously selected
sample of 90 high-velocity halo stars from RAVE and a previously published data
set. We calibrate and extensively test our method using a suite of cosmological
simulations of the formation of Milky Way-sized galaxies. Our best estimate of
the local Galactic escape speed, which we define as the minimum speed required
to reach three virial radii , is km/s (90%
confidence) with an additional 5% systematic uncertainty, where is
the Galactocentric radius encompassing a mean over-density of 340 times the
critical density for closure in the Universe. From the escape speed we further
derive estimates of the mass of the Galaxy using a simple mass model with two
options for the mass profile of the dark matter halo: an unaltered and an
adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the
local circular velocity the latter profile yields a significantly higher mass
than the un-contracted halo, but if we instead use the statistics on halo
concentration parameters in large cosmological simulations as a constraint we
find very similar masses for both models. Our best estimate for , the
mass interior to (dark matter and baryons), is M (corresponding to M). This estimate is in good agreement with recently published
independent mass estimates based on the kinematics of more distant halo stars
and the satellite galaxy Leo I.Comment: 16 pages, 15 figures; accepted for publication in Astronomy &
Astrophysic
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