4,476 research outputs found
Missing hard states and regular outbursts: the puzzling case of the black hole candidate 4U 1630-472
4U 1630-472 is a recurrent X-ray transient classified as a black-hole
candidate from its spectral and timing properties. One of the peculiarities of
this source is the presence of regular outbursts with a recurrence period
between 600 and 730 d that has been observed since the discovery of the source
in 1969. We report on a comparative study on the spectral and timing behaviour
of three consecutive outbursts occurred in 2006, 2008 and 2010. We analysed all
the data collected by the INTErnational Gamma-Ray Astrophysics Laboratory
(INTEGRAL) and the Rossi X-ray timing Explorer (RXTE) during these three years
of activity. We show that, in spite of having a similar spectral and timing
behaviour in the energy range between 3 and 30 keV, these three outbursts show
pronounced differences above 30 keV. In fact, the 2010 outburst extends at high
energies without any detectable cut-off until 150-200 keV, while the two
previous outbursts that occurred in 2006 and 2008 are not detected at all above
30 keV. Thus, in spite of a very similar accretion disk evolution, these three
outbursts exhibit totally different characteristics of the Compton electron
corona, showing a softening in their evolution rarely observed before in a low
mass X-ray binary hosting a black hole. We argue the possibility that the
unknown perturbation that causes the outbursts to be equally spaced in time
could be at the origin of this particular behaviour. Finally we describe
several possible scenarios that could explain the regularity of the outbursts,
identifying the most plausible, such as a third body orbiting around the binary
system.Comment: April 2015: accepted for publication in MNRAS. May 2015: in pres
Cosmological implications of interacting Group Field Theory models: cyclic Universe and accelerated expansion
We study the cosmological implications of interactions between spacetime
quanta in the Group Field Theory (GFT) approach to Quantum Gravity from a
phenomenological perspective. Our work represents a first step towards
understanding Early Universe Cosmology by studying the dynamics of the emergent
continuum spacetime, as obtained from a fundamentally discrete microscopic
theory. In particular, we show how GFT interactions lead to a recollapse of the
Universe while preserving the bounce replacing the initial singularity, which
has already been shown to occur in the free case. It is remarkable that cyclic
cosmologies are thus obtained in this framework without any a priori assumption
on the geometry of spatial sections of the emergent spacetime. Furthermore, we
show how interactions make it possible to have an early epoch of accelerated
expansion, which can be made to last for an arbitrarily large number of
e-folds, without the need to introduce an ad hoc potential for the scalar
field.Comment: 11 pages, 6 figure
Dynamics of anisotropies close to a cosmological bounce in quantum gravity
We study the dynamics of perturbations representing deviations from perfect
isotropy in the context of the emergent cosmology obtained from the group field
theory formalism for quantum gravity. Working in the mean field approximation
of the group field theory formulation of the Lorentzian EPRL model, we derive
the equations of motion for such perturbations to first order. We then study
these equations around a specific simple isotropic background, characterised by
the fundamental representation of \mbox{SU(2)}, and in the regime of the
effective cosmological dynamics corresponding to the bouncing region replacing
the classical singularity, well approximated by the free GFT dynamics. In this
particular example, we identify a region in the parameter space of the model
such that perturbations can be large at the bounce but become negligible away
from it, i.e. when the background enters the non-linear regime. We also study
the departures from perfect isotropy by introducing specific quantities, such
as the surface-area-to-volume ratio and the effective volume per quantum, which
make them quantitative.Comment: 45 pages, 4 figure
An all-glass microfluidic network with integrated amorphous silicon photosensors for on-chip monitoring of enzymatic biochemical assay
A lab-on-chip system, integrating an all-glass microfluidics and on-chip optical detection, was developed and tested. The microfluidic network is etched in a glass substrate, which is then sealed with a glass cover by direct bonding. Thin film amorphous silicon photosensors have been fabricated on the sealed microfluidic substrate preventing the contamination of the micro-channels. The microfluidic network is then made accessible by opening inlets and outlets just prior to the use, ensuring the sterility of the device. The entire fabrication process relies on conventional photolithographic microfabrication techniques and is suitable for low-cost mass production of the device. The lab-on-chip system has been tested by implementing a chemiluminescent biochemical reaction. The inner channel walls of the microfluidic network are chemically functionalized with a layer of polymer brushes and horseradish peroxidase is immobilized into the coated channel. The results demonstrate the successful on-chip detection of hydrogen peroxide down to 18 mu M by using luminol and 4-iodophenol as enhancer agent
Velocity profiles and interface instability in a two-phase fluid: investigations using ultrasonic velocity profiler
In the present study the velocity profiles and the instability at the interface of a two phase water-oil fluid were investigated. The main aim of the research project was to investigate the instability mechanisms that can cause the failure of an oil spill barrier. Such mechanisms have been studied before for a vast variety of conditions (Wicks in Fluid dynamics of floating oil containment by mechanical barriers in the presence of water currents. In: Conference on prevention and control of oil spills, pp 55-106, 1969; Fannelop in Appl Ocean Res 5(2):80-92, 1983; Lee and Kang in Spill Sci Technol Bull 4(4):257-266, 1997; Fang and Johnston in J Waterway Port Coast Ocean Eng ASCE 127(4):234-239, 2001; among others). Although the velocity field in the region behind the barrier can influence the failure significantly, it had not been measured and analyzed precisely. In the present study the velocity profiles in the vicinity of different barriers were studied. To undertake the experiments, an oil layer was contained over the surface of flowing water by means of a barrier in a laboratory flume. The ultrasonic velocity profiler method was used to measure velocity profiles in each phase and to detect the oil-water interface. The effect of the barrier geometry on velocity profiles was studied. It was determined that the contained oil slick, although similar to a gravity current, can not be considered as a gravity current. The oil-water interface, derived from ultrasonic echo, was used to find the velocity profile in each fluid. Finally it was shown that the fluctuations at the rearward side of the oil slick head are due to Kelvin-Helmholtz instabilitie
Prognostic significance of primary-tumor extension, stage and grade of nuclear differentiation in patients with renal cell carcinoma
Surgery remains the preferred therapy for renal cell carcinoma. The various adjunctive or complementary therapies currently yield disappointing results. Identifying reliable prognostic factors could help in selecting patients most likely to benefit from postoperative adjuvant therapies. We reviewed the surgical records of 78 patients who had undergone radical nephrectomy with lymphadenectomy for renal cell carcinoma, matched for type of operation and histology. According to staging (TNM), 5.1% of the patients were classified as stage I, 51.3% as stage II, 29.5% as stage III and 14.5% as stage IV. Of the 78 patients 40 were T2N0 and 21 T3aN0. Tumor grading showed that 39.7% of the patients had well-differentiated tumors(G1), 41.1% moderately-differentiated (G2), and 19.2% poorly-differentiated tumors (G3). Overall actuarial survival at 5 and 10 years was 100% for stage 1; 91.3% at 5 years and 83.1% at 10 years for stage II; 45.5% and 34.1% for stage III; and 29.1% and nil for stage IV (stage II vs stage III p = 0.0001). Patients with tumors confined to the kidney (pT2N0) had better 5- and 10-year survival rates than patients with tumors infiltrating the perirenal fat (pT3aN0) (p = 0.000006). Survival differed according to nuclear grading (G1 vs G3 ; p = 0.000005; G2 vs G3; p = 0.0009). In conclusion our review identified tumor stage, primary-tumor extension, and the grade of nuclear differentiation as reliable prognostic factors in patients with renal cell carcinomas
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