6,975 research outputs found
A multi-color and Fourier study of RR Lyrae variables in the globular cluster NGC 5272 (M3)
We have performed a detailed study of the pulsational and evolutionary
characteristics of 133 RR Lyrae stars in the globular cluster NGC5272 (M3)
using highly accurate BVI data taken on 5 separate epochs. M3 seems to contain
no less than ~32% of Blazhko stars, and the occurrence and characteristics of
the Blazhko effect have been analyzed in detail. We have identified a good
number (~ 14%) of overluminous RR Lyrae stars that are likely in a more
advanced evolutionary stage off the Zero Age Horizontal Branch (ZAHB). Physical
parameters (i.e. temperature, luminosity, mass) have been derived from (B--V)
colors and accurate color-temperature calibration, and compared with Horizontal
Branch evolutionary models and with the requirements of stellar pulsation
theory. Additional analysis by means of Fourier decomposition of the V light
curves confirms, as expected, that no metallicity spread is present in M3.
Evolution off the ZAHB does not affect [Fe/H] determinations, whereas Blazhko
stars at low amplitude phase do affect [Fe/H] distributions as they appear more
metal-rich. Absolute magnitudes derived from Fourier coefficients might provide
useful average estimates for groups of stars, if applicable, but do not give
reliable {\em individual} values. Intrinsic colors derived from Fourier
coefficients show significant discrepancies with the observed ones, hence the
resulting temperatures and temperature-related parameters are unreliable.Comment: 86 pages, 19 figures, 13 tables, in press A
Clinical impact of double protease inhibitor boosting with Lopinavir/Ritonavir and Amprenavir as part of salvage antiretroviral therapy
Purpose: Double protease inhibitor (PI) boosting is being explored as a new strategy in salvage antiretroviral (ARV) therapy. However, if a negative drug interaction leads to decreased drug levels of either or both PIs, double PI boosting could lead to decreased virologic response. A negative drug interaction has been described between amprenavir (APV) and lopinavir/ritonavir (LPV/r). This observational cohort study assessed the virologic impact of the addition of APV to a salvage ARV regimen, which also contains LPV/r, compared to a regimen containing LPV/r alone. Method: Patients initiated on a salvage ARV regimen that included LPV/r obtained from the expanded access program in Toronto, Canada, were evaluated. APV (600-1,200 mg bid) was added at the discretion of the treating physician. Results: Using multivariate Cox proportional hazards models, we found that the addition of APV to a LPV/r-containing salvage regimen was not significantly associated with time to virologic suppression (< 50 copies/mL; adjusted hazard ratio [HR] = 0.75, p = .12) or with time to virologic rebound (adjusted HR = 1.46, p = .34). Those patients who received higher doses of APV had an increased chance of virologic suppression (p = .03). In a subset of 27 patients, the median LPV Ctrough was significantly lower in patients receiving APV (p = .04), and the median APV Ctrough was reduced compared to reported controls. Conclusion: Our data do not support an additional benefit in virologic reduction of double boosting with APV and LPV/r relative to LPV/r alone in salvage ARV therapy. Our study's limitations include its retrospective nature and the imbalance between the two groups potentially confounding the results. Although these factors were adjusted for in the multivariate analysis, a prospective randomized controlled trial is warranted to confirm our findings
Non equilibrium inertial dynamics of colloidal systems
We consider the properties of a one dimensional fluid of brownian inertial
hard-core particles, whose microscopic dynamics is partially damped by a
heat-bath. Direct interactions among the particles are represented as binary,
instantaneous elastic collisions. Collisions with the heath bath are accounted
for by a Fokker-Planck collision operator, whereas direct collisions among the
particles are treated by a well known method of kinetic theory, the Revised
Enskog Theory. By means of a time multiple time-scale method we derive the
evolution equation for the average density. Remarkably, for large values of the
friction parameter and/or of the mass of the particles we obtain the same
equation as the one derived within the dynamic density functional theory (DDF).
In addition, at moderate values of the friction constant, the present method
allows to study the inertial effects not accounted for by DDF method. Finally,
a numerical test of these corrections is provided.Comment: 13 pages+ 3 Postscript figure
The MACHO Project LMC Variable Star Inventory. IX. Frequency Analysis of the First Overtone RR Lyrae Stars and the Indication for Nonradial Pulsations
More than 1300 variables classified provisionally as first overtone RR Lyrae
pulsators in the MACHO variable star database of the Large Magellanic Cloud
(LMC) have been subjected to standard frequency analysis. Based on the remnant
power in the prewhitened spectra, we found 70% of the total population to be
monoperiodic. The remaining 30% (411 stars) are classified as one of 9 types
according to their frequency spectra. Several types of RR Lyrae pulsational
behavior are clearly identified here for the first time. Together with the
earlier discovered double-mode (fundamental & first overtone) variables this
study increased the number of the known double-mode stars in the LMC to 181.
During the total 6.5yr time span of the data, 10% of the stars show strong
period changes. We also discovered two additional types of multifrequency
pulsators with low occurrence rates of 2% for each. In the first type there
remains one closely spaced component after prewhitening by the main pulsation
frequency. In the second type the number of remnant components is two, they are
also closely spaced, and, in addition, they are symmetric in their frequency
spacing relative to the central component. This latter type of variables is
associated with their relatives among the fundamental pulsators, known as
Blazhko variables. Their high frequency (~20%) among the fundamental mode
variables versus the low occurrence rate of their first overtone counterparts
makes it more difficult to explain Blazhko phenomenon by any theory depending
mainly on the role of aspect angle or magnetic field. Current theoretical
models invoke nonradial pulsation components in these stars.Comment: 20 pages, 21 figures (bitmapped), 7 tables, to appear in Ap.
Sorption of Water and Polar-Nonpolar Organic Vapors on Microporous Chromia
High surface area, narrow particle size distribution chromic;t
was investigated for its microporosity. Adsorption studies with
argon, water vapor, methanol, isopropanol, butane, isobutane, neopentane,
and heptane indicated alternative approaches to the
determination of micropore volume
Aging, memory and rejuvenation: some lessons from simple models
Many recent experiments probed the off equilibrium dynamics of spin glasses
and other glassy systems through temperature cycling protocols and observed
memory and rejuvenation phenomena. Here we show through numerical simulations,
using powerful algorithms, that such features can already be observed to some
extent in simple models such as two dimensional ferromagnets. We critically
discuss these results and review some aspects of the literature in the light of
our findings.Comment: 10 pages, 8 figures. Contribution to the Proceedings of the
Summerschool "Ageing and the glass transition", Luxembourg 14-25 Sept. 200
ICRF-159 enhancement of radiation response in combined modality therapies. I. Time/dose relationships for tumour response.
The combined effect of the chemotherapeutic agent ICRF-159 and irradiation were evaluated using the Lewis lung tumour (LL). At a daily dose of 25 mg/kg, ICOF given alone prevented the progressive growth of LL. Daily pretreatment also potentiated the effects of radiation (600 rad) on tumour growth, provided the pretreatment kinetics of the tumour permitted a response to radiation alone. Single acute doses of the drug failed to alter the growth of LL, and when combined with radiation failed to enhance the radiation effect. Fractionation of the drug (25 mg/kg; 4 doses at 3h intervals) before irradiation, however, results in immediate effects on tumour growth which are more than additive. The results suggest that a low dose of ICRF-159 for extended periods is more effective in enhancing radiotherapy than a high dose provided acutely
Surfing on a critical line: Rejuvenation without chaos, Memory without a hierarchical phase space
The dynamic behaviour of glassy materials displays strong nonequilibrium
effects, such as ageing in simple protocols, memory, rejuvenation and Kovacs
effects in more elaborated experiments. We show that this phenomenology may be
easily understood in the context of the nonequilibrium critical dynamics of
non-disordered systems, the main ingredient being the existence of an infinite
equilibrium correlation length. As an example, we analytically investigate the
behaviour of the 2D XY model submitted to temperature protocols similar to
experiments. This shows that typical glassy effects may be obtained by `surfing
on a critical line' without invoking the concept of temperature chaos nor the
existence of a hierarchical phase space, as opposed to previous theoretical
approaches. The relevance of this phenomenological approach to glassy dynamics
is finally discussed.Comment: Version to be published in Europhysics Letters. Slight modifs + ref
to "surfing" adde
Mars oxygen production system design
The design and construction phase is summarized of the Mars oxygen demonstration project. The basic hardware required to produce oxygen from simulated Mars atmosphere was assembled and tested. Some design problems still remain with the sample collection and storage system. In addition, design and development of computer compatible data acquisition and control instrumentation is ongoing
Excitons in InGaAs Quantum Dots without Electron Wetting Layer States
The Stranski-Krastanov (SK) growth-mode facilitates the self-assembly of
quantum dots (QDs) using lattice-mismatched semiconductors, for instance InAs
and GaAs. SK QDs are defect-free and can be embedded in heterostructures and
nano-engineered devices. InAs QDs are excellent photon emitters: QD-excitons,
electron-hole bound pairs, are exploited as emitters of high quality single
photons for quantum communication. One significant drawback of the SK-mode is
the wetting layer (WL). The WL results in a continuum rather close in energy to
the QD-confined-states. The WL-states lead to unwanted scattering and dephasing
processes of QD-excitons. Here, we report that a slight modification to the
SK-growth-protocol of InAs on GaAs -- we add a monolayer of AlAs following InAs
QD formation -- results in a radical change to the QD-excitons. Extensive
characterisation demonstrates that this additional layer eliminates the
WL-continuum for electrons enabling the creation of highly charged excitons
where up to six electrons occupy the same QD. Single QDs grown with this
protocol exhibit optical linewidths matching those of the very best SK QDs
making them an attractive alternative to standard InGaAs QDs
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