2,271 research outputs found
The not-so-massive black hole in the microquasar GRS1915+105
We present a new dynamical study of the black hole X-ray transient GRS1915+105 making use of near-infrared spectroscopy obtained with X-shooter at the VLT. We detect a large number of donor star absorption features across a wide range of wavelengths spanning the H and K bands. Our 24 epochs covering a baseline of over 1 year permit us to determine a new binary ephemeris including a refined orbital period of P=33.85 +/- 0.16 d. The donor star radial velocity curves deliver a significantly improved determination of the donor semi-amplitude which is both accurate (K_2=126 +/- 1 km/s) and robust against choice of donor star template and spectral features used. We furthermore constrain the donor star's rotational broadening to vsini=21 +/-4 km/s, delivering a binary mass ratio of q=0.042 +/- 0.024. If we combine these new constraints with distance and inclination estimates derived from modelling the radio emission, a black hole mass of M_BH=10.1 +/- 0.6 M_sun is inferred, paired with an evolved mass donor of M_2=0.47 +/- 0.27 M_sun. Our analysis suggests a more typical black hole mass for GRS1915+105 rather than the unusually high values derived in the pioneering dynamical study by Greiner et al. (2001). Our data demonstrate that high-resolution infrared spectroscopy of obscured accreting binaries can deliver dynamical mass determinations with a precision on par with optical studies
(Ti,Sn) solid solution-based gas sensors for new monitoring of hydraulic oil degradation
The proper operation of a fluid power system in terms of efficiency and reliability is directly related to the fluid state; therefore, the monitoring of fluid ageing in real time is fundamental to prevent machine failures. For this aim, an innovative methodology based on fluid vapor analysis through metal oxide (shortened: MOX) gas sensors has been developed. Two apparatuses were designed and realized: (i) a dedicated test bench to fast-age the fluid under controlled conditions; (ii) a laboratory MOX sensor system to test the headspace of the aged fluid samples. To prepare the set of MOX gas sensors suitable to detect the analytes’ concentrations in the fluid headspace, different functional materials were synthesized in the form of nanopowders, characterizing them by electron microscopy and X-ray diffraction. The powders were deposited through screen-printing technology, realizing thick-film gas sensors on which dynamical responses in the presence of the fluid headspace were obtained. It resulted that gas sensors based on solid solution TixSn1–xO2 with x = 0.9 and 0.5 offered the best responses toward the fluid headspace with lower response and recovery times. Furthermore, a decrease in the responses (for all sensors) with fluid ageing was observed
Influence of Topological Edge States on the Properties of Al/Bi2Se3/Al Hybrid Josephson Devices
In superconductor-topological insulator-superconductor hybrid junctions, the
barrier edge states are expected to be protected against backscattering, to
generate unconventional proximity effects, and, possibly, to signal the
presence of Majorana fermions. The standards of proximity modes for these types
of structures have to be settled for a neat identification of possible new
entities. Through a systematic and complete set of measurements of the
Josephson properties we find evidence of ballistic transport in coplanar
Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the
topological edge state. The shunting effect of the bulk only influences the
normal transport. This behavior, which can be considered to some extent
universal, is fairly independent of the specific features of superconducting
electrodes. A comparative study of Shubnikov - de Haas oscillations and
Scanning Tunneling Spectroscopy gave an experimental signature compatible with
a two dimensional electron transport channel with a Dirac dispersion relation.
A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable
step to drive Josephson junctions in the proper regime to detect possible
distinctive features of Majorana fermions.Comment: 11 pages, 14 figure
Age, Metallicity and Star Formation History of Cluster Galaxies at z~0.3 F
We investigate the color-magnitude distribution in the rich cluster AC 118 at
z=0.31. The sample is selected by the photometric redshift technique, allowing
to study a wide range of properties of stellar populations, and is complete in
the K-band, allowing to study these properties up to a given galaxy mass. We
use galaxy templates based on population synthesis models to translate the
physical properties of the stellar populations - formation epoch, time-scale of
star formation, and metallicity - into observed magnitudes and colors. In this
way we show that a sharp luminosity-metallicity relation is inferred without
any assumption on the galaxy formation scenario (either monolithic or
hierarchical). Our data exclude significant differences in star formation
histories along the color-magnitude relation, and therefore confirm a pure
metallicity interpretation for its origin, with an early (z~5) formation epoch
for the bulk of stellar populations. The dispersion in the color-magnitude
diagram implies that fainter galaxies in our sample (K~18) ceased to form stars
as late as z~0.5, in agreement with the picture that these galaxies were
recently accreted into the cluster environment. The trend with redshift of the
total stellar mass shows that half of the luminous mass in AC 118 was already
formed at $z~2, but also that 20% of the stars formed at z<1.Comment: 16 pages, 10 figures. ApJ in pres
The Large-Angle Photon Veto System for the NA62 Experiment at CERN
The branching ratio (BR) for the decay K^+ \rightarrow \pi^+ \nu \bar{\nu} is
a sensitive probe for new physics. The NA62 experiment at the CERN SPS will
measure this BR to within about 10%. To reject the dominant background from
channels with final state photons, the large-angle vetoes (LAVs) must detect
photons of energy as low as 200 MeV with an inefficiency of less than 10^-4, as
well as provide energy and time measurements with resolutions of 10% and 1 ns
for 1 GeV photons. The LAV detectors make creative reuse of lead glass blocks
recycled from the OPAL electromagnetic calorimeter barrel. We describe the
mechanical design and challenges faced during construction, the
characterization of the lead glass blocks and solutions adopted for monitoring
their performance, and the development of front-end electronics to allow
simultaneous time and energy measurements over an extended dynamic range using
the time-over-threshold technique. Our results are based on test-beam data and
are reproduced by a detailed Monte Carlo simulation that includes the readout
chain.Comment: 8 pages, 13 figures. Prepared for the Conference Record of the IEEE
Nuclear Science Symposium, Valencia, Spain, October 201
A novel numerical modelling approach for keratoplasty eye procedure
Objective of the work is to investigate stress and deformation that conrneal tissue and donor graft undergo during endothelial keratoplasty. In order to attach the donor graft to the cornea, different air bubble pressure profiles acting on the graft are considered. This study is carried out by employing a three-dimensional nonlinear finite element methodology, combined with a contact algorithm. The ocular tissues are treated as isotropic, hyper-elastic and nearly-incompressible materials. The contact algorithm, based on the penalty-based node-to-surface approach, is used to model the donor graft-corneal interface region. First, the proposed computational methodology is tested against benchmark data for bending of the plates over a cylinder. Then, the influence of geometrical and material parameters of the graft on the corneal contact-structural response is investigated. The results are presented in terms of Von Mises stress intensity, displacement and mean contact force. Results clearly indicate that the air bubble pressure plays a key role in the corneal stress and strain, as well as graft stiffness and thickness
Effectiveness of flow obstructions in enhancing electro-osmotic flow
In this paper the influence of obstructions on micro-channel electroosmotic flow is investigated for the first time. To carry out such a study, regular obstructions are introduced into micro-channels and flow rates are numerically calculated. The effect of channel width on flow rates is analysed on both free and obstructed channels. The solid material considered for channel walls and obstructions is silicon and the electrolyte is de-ionised water. The parameters studied include channel width, obstruction size and effective porosity of the channel. The effective porosity is varied between 0.4 and 0.8 depending on other chosen parameters. The results clearly demonstrate that, under the analysed conditions, introduction of obstructions into channels wider than100 micro meters enhances the flow rate induced by electro-osmosis
The [1,2,4]Triazolo[4,3-a]pyridine as a New Player in the Field of IDO1 Catalytic Holo-Inhibitors
Inhibitors of indoleamine 2,3-dioxygenase 1 (IDO1) are considered a promising strategy in cancer immunotherapy as they are able to boost the immune response and to work in synergy with other immunotherapeutic agents. Despite the fact that no IDO1 inhibitor has been approved so far, recent studies have shed light on the additional roles that IDO1 mediates beyond its catalytic activity, conferring new life to the field. Here we present a novel class of compounds originated from a structure-based virtual screening made on IDO1 active site. The starting hit compound is a novel chemotype based on a [1,2,4]triazolo[4,3-a]pyridine scaffold, so far underexploited among the heme binding moieties. Thanks to the rational and in silico-guided design of analogues, an improvement of the potency to sub-micromolar levels has been achieved, with excellent in vitro metabolic stability and exquisite selectivity with respect to other heme-containing enzymes
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