7,531 research outputs found
The X-ray emission of magnetic cataclysmic variables in the XMM-Newton era
We review the X-ray spectral properties of magnetic cataclysmic binaries
derived from observations obtained during the last decade with the large X-ray
observatories XMM-Newton, Chandra and Suzaku. We focus on the signatures of the
different accretion modes which are predicted according to the values of the
main physical parameters (magnetic field, local accretion rate and white dwarf
mass). The observed large diversity of spectral behaviors indicates a wide
range of parameter values in both intermediate polars and polars, in line with
a possible evolutionary link between both classes.Comment: To appear in the Proceedings of "The Golden Age of Cataclysmic
Variables (Palermo 2011)", in Mem. Soc. Astron. It. (7 pages, 3 figures
The ephemeris, orbital decay, and masses of 10 eclipsing HMXBs
We take advantage of more than 10 years of monitoring of the eclipsing HMXB
systems LMC X-4, Cen X-3, 4U 1700-377, 4U 1538-522, SMC X-1, IGR J18027-2016,
Vela X-1, IGR J17252-3616, XTE J1855-026, and OAO 1657-415 with the ASM
on-board RXTE and ISGRI on-board INTEGRAL to update their ephemeris. These
results are used to refine previous measurements of the orbital period decay of
all sources (where available) and provide the first accurate values of the
apsidal advance in Vela X-1 and 4U 1538-522. Updated values for the masses of
the neutron stars hosted in the ten HMXBs are also provided, as well as the
long-term lightcurves folded on the sources best determined orbital parameters.
These lightcurves reveal complex eclipse ingresses and egresses, that are
understood mostly as being due to the presence of accretion wakes. The results
reported in this paper constitute a database to be used for population and
evolutionary studies of HMXBs, as well as theoretical modelling of long-term
accretion in wind-fed X-ray binaries.Comment: Accepted for publication on A&
Memory Effects in the Standard Model for Glasses
The standard model of glasses is an ensemble of two-level systems interacting
with a thermal bath. The general origin of memory effects in this model is a
quasi-stationary but non-equilibrium state of a single two-level system, which
is realized due to a finite-rate cooling and very slow thermally activated
relaxation. We show that single particle memory effects, such as negativity of
the specific heat under reheating, vanish for a sufficiently disordered
ensemble. In contrast, a disordered ensemble displays a collective memory
effect [similar to that described by Kovacs for glassy polymers], where
non-equilibrium features of the ensemble are monitored via a macroscopic
observable. An experimental realization of the effect can be used to further
assess the consistency of the model.Comment: 4 pages, 6 figure
The eclipsing bursting X-ray binary EXO 0748-676 revisited by XMM-Newton
The bright eclipsing and bursting low-mass X-ray binary EXO 0748-676 has been
observed at several occasions by XMM-Newton during the initial calibration and
performance verification (CAL/PV) phase. We present here the results obtained
from observations with the EPIC cameras. Apart from several type-I X-ray
bursts, the source shows a high degree of variability with the presence of soft
flares. The wide energy coverage and high sensitivity of XMM-Newton allows for
the first time a detailed description of the spectral variability.
The source is found to be the superposition of a central (~2 10^8 cm)
Comptonized emission, most probably a corona surrounding the inner edge of an
accretion disk, associated with a more extended (~3 10^10 cm) thermal halo at a
typical temperature of ~0.6 keV with an indication of non-solar abundances.
Most of the variations of the source can be accounted for by a variable
absorption affecting only the central comptonized component and reaching up to
NH ~1.3 10^23 cm^{-2}. The characteristics of the surrounding halo are found
compatible with an irradiated atmosphere of an accretion disc which intercepts
the central emission due to the system high inclination.Comment: 6 pages, 4 figures, accepted for publication in A&A Letters, XMM
special issu
Reducing the Number of Sputum Samples Examined and Thresholds for Positivity: An Opportunity to Optimise Smear Microscopy.
SETTING: Urban health clinic, Nairobi. OBJECTIVE: To evaluate the impact on tuberculosis (TB) case detection and laboratory workload of reducing the number of sputum smears examined and thresholds for diagnosing positive smears and positive cases. DESIGN: In this prospective study, three Ziehl-Neelsen stained sputum smears from consecutive pulmonary TB suspects were examined blind. The standard approach (A), > or = 2 positive smears out of 3, using a cut-off of 10 acid-fast bacilli (AFB)/100 high-power fields (HPF), was compared with approaches B, > or = 2 positive smears (> or = 4 AFB/100 HPF) out of 3, one of which is > or = 10 AFB/100 HPF; C, > or = 2 positive smears (> or = 4 AFB/100 HPF) out of 3; D, > or = 1 positive smear (> or = 10 AFB/100 HPF) out of 2; and E, > or = 1 positive smear (> or = 4 AFB/100 HPF) out of 2. The microscopy gold standard was detection of at least one positive smear (> or = 4 AFB/100 HPF) out of 3. RESULTS: Among 644 TB suspects, the alternative approaches detected from 114 (17.7%) (approach B) to 123 cases (19.1%) (approach E) compared to 105 cases (16.3%) for approach A (P < 0.005). Sensitivity ranged between 82.0% (105/128) for A and 96.1% (123/128) for E. The single positive smear approaches reduced the number of smears by 36% compared to approach A. CONCLUSION: Reducing the number of specimens and the positivity threshold to define a positive case increased the sensitivity of microscopy and reduced laboratory workload
Short report: molecular markers associated with Plasmodium falciparum resistance to sulfadoxine-pyrimethamine in the Democratic Republic of Congo.
Sulfadoxine-pyrimethamine (SP) is the first line antimalarial treatment in the Democratic Republic of Congo. Using polymerase chain reaction, we assessed the prevalence of mutations in the dihydrofolate reductase (dhfr) (codons 108, 51, 59) and dihydropteroate synthase (dhps) (codons 437, 540) genes of Plasmodium falciparum, which have been associated with resistance to pyrimethamine and sulfadoxine, respectively. Four hundred seventy-four patients were sampled in Kilwa (N = 138), Kisangani (N = 112), Boende (N = 106), and Basankusu (N = 118). The proportion of triple mutations dhfr varied between sites but was always > 50%. The proportion of dhps double mutations was < 20%, with some sites as low as 0.9%. A quintuple mutation was present in 12.8% (16/125) samples in Kilwa; 11.9% (13/109) in Kisangani, 2.9% (3/102) in Boende, and 0.9% (1/112) in Basankusu. These results suggest high resistance to pyrimethamine alone or combined with sulfadoxine. Adding artesunate to SP does not seem a valid alternative to the current monotherapy
Quark propagator in a covariant gauge
Using mean--field improved gauge field configurations, we compare the results
obtained for the quark propagator from Wilson fermions and Overlap fermions on
a \3 lattice at a spacing of fm.Comment: 5 pages, 8 figures, talk given by F.D.R. Bonnet at LHP 2001 workshop,
Cairns, Australi
The method of Gaussian weighted trajectories. V. On the 1GB procedure for polyatomic processes
In recent years, many chemical reactions have been studied by means of the
quasi-classical trajectory (QCT) method within the Gaussian binning (GB)
procedure. The latter consists in "quantizing" the final vibrational actions in
Bohr spirit by putting strong emphasis on the trajectories reaching the
products with vibrational actions close to integer values. A major drawback of
this procedure is that if N is the number of product vibrational modes, the
amount of trajectories necessary to converge the calculations is ~ 10^N larger
than with the standard QCT method. Applying it to polyatomic processes is thus
problematic. In a recent paper, however, Czako and Bowman propose to quantize
the total vibrational energy instead of the vibrational actions [G. Czako and
J. M. Bowman, J. Chem. Phys., 131, 244302 (2009)], a procedure called 1GB here.
The calculations are then only ~ 10 times more time-consuming than with the
standard QCT method, allowing thereby for considerable numerical saving. In
this paper, we propose some theoretical arguments supporting the 1GB procedure
and check its validity on model test cases as well as the prototype four-atom
reaction OH+D_2 -> HOD+D
Effect of the reservoir size on gas adsorption in inhomogeneous porous media
We study the influence of the relative size of the reservoir on the
adsorption isotherms of a fluid in disordered or inhomogeneous mesoporous
solids. We consider both an atomistic model of a fluid in a simple, yet
structured pore, whose adsorption isotherms are computed by molecular
simulation, and a coarse-grained model for adsorption in a disordered
mesoporous material, studied by a density functional approach in a local
mean-field approximation. In both cases, the fluid inside the porous solid
exchanges matter with a reservoir of gas that is at the same temperature and
chemical potential and whose relative size can be varied, and the control
parameter is the total number of molecules present in the porous sample and in
the reservoir. Varying the relative sizes of the reservoir and the sample may
change the shape of the hysteretic isotherms, leading to a "reentrant" behavior
compared to the grand-canonical isotherm when the latter displays a jump in
density. We relate these phenomena to the organization of the metastable states
that are accessible for the adsorbed fluid at a given chemical potential or
density.Comment: 16 page
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