8,873 research outputs found
LOFT - a Large Observatory For x-ray Timing
The high time resolution observations of the X-ray sky hold the key to a
number of diagnostics of fundamental physics, some of which are unaccessible to
other types of investigations, such as those based on imaging and spectroscopy.
Revealing strong gravitational field effects, measuring the mass and spin of
black holes and the equation of state of ultradense matter are among the goals
of such observations. At present prospects for future, non-focused X-ray timing
experiments following the exciting age of RXTE/PCA are uncertain. Technological
limitations are unavoidably faced in the conception and development of
experiments with effective area of several square meters, as needed in order to
meet the scientific requirements. We are developing large-area monolithic
Silicon Drift Detectors offering high time and energy resolution at room
temperature, which require modest resources and operation complexity (e.g.,
read-out) per unit area. Based on the properties of the detector and read-out
electronics that we measured in the lab, we developed a realistic concept for a
very large effective area mission devoted to X-ray timing in the 2-30 keV
energy range. We show that effective areas in the range of 10-15 square meters
are within reach, by using a conventional spacecraft platform and launcher of
the small-medium class.Comment: 13 pages, 8 figures, 1 table, Proceedings of SPIE Vol. 7732, Paper
No. 7732-66, 201
Impact of intrauterine growth restriction on cerebral and renal oxygenation and perfusion during the first 3 days after birth
Intrauterine growth restriction (IUGR) is associated with a higher incidence of perinatal complications as well as cardiovascular and renal diseases later on. A better insight into the disease mechanisms underlying these sequalae is important in order to identify which IUGR infants are at a higher risk and find strategies to improve their outcome. In this prospective case–control study we examined whether IUGR had any effect on renal and cerebral perfusion and oxygen saturation in term neonates. We integrated near-infrared spectroscopy (NIRS), echocardiographic, Doppler and renal function data of 105 IUGR infants and 105 age/gender-matched controls. Cerebral and renal regional oxygen saturation values were measured by NIRS during the first 12 h after birth. Echocardiography alongside Doppler assessment of renal and anterior cerebral arteries were performed at 6, 24, 48 and 72 h of age. Glomerular and tubular functions were also assessed. We found a left ventricular dysfunction together with a higher cerebral oxygen saturation and perfusion values in the IUGR group. IUGR term infants showed a higher renal oxygen saturation and a reduced oxygen extraction together with a subclinical renal damage, as indicated by higher values of urinary neutrophil gelatinase-associated lipocalin and microalbumin. These data suggest that some of the haemodynamic changes present in growth-restricted foetuses may persist postnatally. The increased cerebral oxygenation may suggest an impaired transition to normal autoregulation as a consequence of intra-uterine chronic hypoxia. The higher renal oxygenation may reflect a reduced renal oxygen consumption due to a subclinical kidney damage
Characterization of the VEGA ASIC coupled to large area position-sensitive Silicon Drift Detectors
Low-noise, position-sensitive Silicon Drift Detectors (SDDs) are particularly
useful for experiments in which a good energy resolution combined with a large
sensitive area is required, as in the case of X-ray astronomy space missions
and medical applications. This paper presents the experimental characterization
of VEGA, a custom Application Specific Integrated Circuit (ASIC) used as the
front-end electronics for XDXL-2, a large-area (30.5 cm^2) SDD prototype. The
ASICs were integrated on a specifically developed PCB hosting also the
detector. Results on the ASIC noise performances, both stand-alone and bonded
to the large area SDD, are presented and discussed.Comment: 15 pages, 11 figures. Accepted for publication in Journal of
Instrumentation (JINST
Excess Higgs Production in Neutralino Decays
The ATLAS and CMS experiments have recently claimed discovery of a Higgs
boson-like particle at ~5 sigma confidence and are beginning to test the
Standard Model predictions for its production and decay. In a variety of
supersymmetric models, a neutralino NLSP can decay dominantly to the Higgs and
the LSP. In natural SUSY models, a light third generation squark decaying
through this chain can lead to large excess Higgs production while evading
existing BSM searches. Such models can be observed at the 8 TeV LHC in channels
exploiting the rare diphoton decays of the Higgs produced in the cascade decay.
Identifying a diphoton resonance in association with missing energy, a lepton,
or b-tagged jets is a promising search strategy for discovery of these models,
and would immediately signal new physics involving production of a Higgs boson.
We also discuss the possibility that excess Higgs production in these SUSY
decays can be responsible for enhancements of up to 50% over the SM prediction
for the observed rate in the existing inclusive diphoton searches, a scenario
which would likely by the end of the 8 TeV run be accompanied by excesses in
the diphoton + lepton/MET and SUSY multi-lepton/b searches and a potential
discovery in a diphoton + 2b search.Comment: 42 pages, 19 figure
Rapid motion adaptation reveals the temporal dynamics of spatiotemporal correlation between ON and OFF pathways
At the early stages of visual processing, information is processed by two major thalamic pathways encoding brightness increments (ON) and decrements (OFF). Accumulating evidence suggests that these pathways interact and merge as early as in primary visual cortex. Using regular and reverse-phi motion in a rapid adaptation paradigm, we investigated the temporal dynamics of within and across pathway mechanisms for motion processing. When the adaptation duration was short (188 ms), reverse-phi and regular motion led to similar adaptation effects, suggesting that the information from the two pathways are combined efficiently at early-stages of motion processing. However, as the adaption duration was increased to 752 ms, reverse-phi and regular motion showed distinct adaptation effects depending on the test pattern used, either engaging spatiotemporal correlation between the same or opposite contrast polarities. Overall, these findings indicate that spatiotemporal correlation within and across ON-OFF pathways for motion processing can be selectively adapted, and support those models that integrate within and across pathway mechanisms for motion processing
Swift follow-up observations of unclassified ASCA sources
We present Swift follow-up observations of a sample of 35 unclassified faint
X-ray sources drawn from the ASCA Galactic centre and plane surveys. Our short
pointed XRT observations allow detections down to a limiting 0.3-10 keV flux of
~1E-13 erg cm-2 s-1, which translates into a luminosity of ~1E33 erg s-1 for an
assumed distance of D=8 kpc. The brightest source in our sample reaches a
maximum 0.3-10 keV luminosity of ~2E36 (D/8kpc)^2 erg s-1 during our
observations. We detect 16 (46%) of the ASCA sources with the XRT, while 19
were not detected during our program. Since we are probing the faint end of the
ASCA source populations, we expect a large fraction of the non-detections to be
due to the Eddington bias. This is strengthened by the fact that we find the
observed XRT count rates to be predominantly lower than expected based on the
reported ASCA intensities. Investigation of the ASCA properties and long-term
X-ray variability leads us to conclude that the non-detections likely include
two spurious ASCA detections and three objects that are variable or transient
X-ray sources. For the 16 XRT-detected sources we obtain positional accuracies
of ~2-4", which significantly improves upon their ASCA uncertainties of ~1'. We
use the X-ray spectra and variability to characterise these objects. Most
appear to be faint, persistent X-ray emitters that have highly absorbed
spectra. Based on their X-ray properties we identify three accreting compact
objects: one confirmed (AX J1754.2-2754) and one candidate (AX J1538.3-5541)
X-ray binary, and one possible magnetically accreting white dwarf (AX
J1620.1-5002). Furthermore, we use the improved positions of XRT-detected
sources to search for counterparts in simultaneously obtained Swift/UVOT images
and possible associations with cataloged sources at various wavelengths. This
reveals three possible main sequence stars amongst our sample.Comment: 14 pages, 7 figures, 7 tables. Accepted for publication in A&A
without revision. Updated a few reference
Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−
The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions
Study of DJ meson decays to D+π−, D0π+ and D∗+π− final states in pp collisions
A study of D+π−, D0π+ and D∗+π− final states is performed using pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected at a centre-of-mass energy of 7 TeV with the LHCb detector. The D1(2420)0 resonance is observed in the D∗+π− final state and the D∗2(2460) resonance is observed in the D+π−, D0π+ and D∗+π− final states. For both resonances, their properties and spin-parity assignments are obtained. In addition, two natural parity and two unnatural parity resonances are observed in the mass region between 2500 and 2800 MeV. Further structures in the region around 3000 MeV are observed in all the D∗+π−, D+π− and D0π+ final states
Study of B0(s)→K0Sh+h′− decays with first observation of B0s→K0SK±π∓ and B0s→K0Sπ+π−
A search for charmless three-body decays of B 0 and B0s mesons with a K0S meson in the final state is performed using the pp collision data, corresponding to an integrated luminosity of 1.0 fb−1, collected at a centre-of-mass energy of 7 TeV recorded by the LHCb experiment. Branching fractions of the B0(s)→K0Sh+h′− decay modes (h (′) = π, K), relative to the well measured B0→K0Sπ+π− decay, are obtained. First observation of the decay modes B0s→K0SK±π∓ and B0s→K0Sπ+π− and confirmation of the decay B0→K0SK±π∓ are reported. The following relative branching fraction measurements or limits are obtained B(B0→K0SK±π∓)B(B0→K0Sπ+π−)=0.128±0.017(stat.)±0.009(syst.), B(B0→K0SK+K−)B(B0→K0Sπ+π−)=0.385±0.031(stat.)±0.023(syst.), B(B0s→K0Sπ+π−)B(B0→K0Sπ+π−)=0.29±0.06(stat.)±0.03(syst.)±0.02(fs/fd), B(B0s→K0SK±π∓)B(B0→K0Sπ+π−)=1.48±0.12(stat.)±0.08(syst.)±0.12(fs/fd)B(B0s→K0SK+K−)B(B0→K0Sπ+π−)∈[0.004;0.068]at90%CL
Search for the decay Bs0→D*∓π±
A search for the decay Bs0→D*∓π± is presented using a data sample corresponding to an integrated luminosity of 1.0 fb-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help us to understand the mechanism behind related decays such as Bs0→π+π- and Bs0→DD- . Systematic uncertainties are minimized by using B0→D*∓π± as a normalization channel. We find no evidence for a signal, and set an upper limit on the branching fraction of B(Bs0→D*∓π±)<6.1(7.8)×10-6 at 90% (95%) confidence level
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