6,430 research outputs found
Vacuum type I spacetimes and aligned Papapetrou fields: symmetries
We analyze type I vacuum solutions admitting an isometry whose Killing
2--form is aligned with a principal bivector of the Weyl tensor, and we show
that these solutions belong to a family of type I metrics which admit a group
of isometries. We give a classification of this family and we study the
Bianchi type for each class. The classes compatible with an aligned Killing
2--form are also determined. The Szekeres-Brans theorem is extended to non
vacuum spacetimes with vanishing Cotton tensor.Comment: 19 pages; a reference adde
The X-ray flaring activity of the galactic nucleus observed with XMM-Newton
We report the results of XMM-Newton observations of Sgr A*, the radiative
counterpart of the massive black hole at the nucleus of our Galaxy, performed
in the frame of the guaranteed time survey program of the Galactic Center
region. The discovery of bright X-ray flares from Sgr A* with Chandra in
October 2000 have opened new perspectives to understand the processes at work
in this object and in general in black holes accreting at low accretion rates.
We report here the important results obtained with XMM-Newton on the Sgr A*
high-energy flaring activity and we discuss the implications on the models and
the future observational perspectives.Comment: 4 pages, 3 figures, proc. of the SF2A conf. held in Bordeaux, France,
June 2003, eds.: F. Combes, D. Barret and T. Contini, EdP-Sciences Conf.
Serie
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
The emerging population of pulsar wind nebulae in hard X-rays
The hard X-ray synchrotron emission from pulsar wind nebulae (PWNe) probes
energetic particles, closely related to the pulsar injection power at the
present time. INTEGRAL has disclosed the yet poorly known population of hard
X-ray pulsar/PWN systems. We summarize the properties of the class, with
emphasys on the first hard X-ray bow-shock (CTB 80 powered by PSR B1951+32),
and highlight some prospects for the study of Pulsar Wind Nebulae with the
Simbol-X mission.Comment: Proceedings of the 2nd Simbol-X Symposium, AIP Conf. Proc. Series,
Eds. P. Ferrando and J. Rodriguez (4 pages, 2 figures
AC Driven Jumps Distribution on a Periodic Substrate
A driven Brownian particle (e.g. an adatom on a surface) diffusing on a
low-viscosity, periodic substrate may execute multiple jumps. In the presence
of an additional periodic drive, the jump lengths and time durations become
statistically modulated according to a syncronyzation mechanism reminiscent of
asymmetric stochastic resonance. Here, too, bistability plays a key role, but
in a dynamical sense, inasmuch as a particle switches between locked and
running states.Comment: 4 pages, 4 figures, RevTeX, to be published in Surface Science
Letter
XMM-Newton Observation of the Black Hole Microquasar GRS 1758-258
The XMM-Newton X-ray observatory pointed the galactic black hole candidate
and microquasar GRS 1758-258 in September 2000 for about 10 ks during a program
devoted to the scan of the Galactic Center regions. Preliminary results from
EPIC MOS camera data are presented here. The data indicate that the source
underwent a state transition from its standard low-hard state to an
intermediate state. For the first time in this source the ultra-soft component
of the accretion disk, which black hole binaries display in intermediate or
high-soft states, was clearly detected and measured thanks to the high spectral
capabilities of XMM-Newton.Comment: To appear in the Proc. of the Gamma-Ray Astrophysics 2001 Symposium,
4-6 April 2001, Baltimore, Maryland, U.S.A.. American Institute of Physics
(AIP) series: 5 pages, 6 PS figures, latex, uses aipproc.cls aipproc.st
Environmental impact assessment of renewable energy communities: the analysis of an Italian neighbourhood
In recent years, research in renewable energy community (REC) schemes, coupling renewable energy sources and building energy efficiency, is gaining momentum. In this context, Urban Building Energy Modelling tools (UBEMs) have proved to comply with the design requirements of such schemes. However, a clear methodology exploiting UBEMs to support the design of RECs is still missing, especially for assessing the greenhouse gas (GHG) emissions associated with their specific technical configuration. Here, the REC is modelled in “urban modeling interface” (umi), one of the main bottom-up physics-based UBEMs. A building archetype approach is exploited to model the scenarios and assess embodied GHG emissions. The proposed methdology gives the possibility to investigate both the embodied and operational emissions for different REC configuration. A residential neighbourhood in Italy is selected as case study. The results demonstrate the importance of considering building characteristics when analysing emissions reductions in energy-sharing schemes, underlining the necessity of coupling the REC design with energy retrofit interventions
Effects of COVID-19 confinement on the simulation of energy needs and uses of residential buildings in Milan
This paper examines the impact of COVID-19 confinement on the simulation of energy needs and uses of residential buildings in Milan. Data-driven schedules for electricity use before and during lockdown, derived from smart metering data, are applied to an urban building energy model to analyze their effects on energy needs for heating and cooling and the energy use for lighting and for other services. Electricity uses, heating and cooling needs, and total primary energy (TOE) are compared for pre-COVID and during-COVID cases. Electricity increases by 8%, while heating decreases by 10%, and cooling increases by 26%. The 5% decrease in TOE is mainly due to the decrease in heating. The study uses heat maps to display the coefficient of variation of root mean square error (CVRMSE) at different temporal and spatial aggregations, indicating significant differences between pre- and during-COVID cases. The CVRMSE for electricity consumption is highest at the hourly level for single buildings, reaching a maximum of 44, and decreases at higher levels of aggregation. The CVRMSE for TOE is highest at the hourly level for single buildings, reaching a maximum of 230. A scenario is created by combining during-COVID and pre-COVID schedules for a hybrid work model, called post-COVID. The post-COVID scenario results indicate a significant impact of remote work on energy consumption patterns
Comparison of the Laryngeal View during Tracheal Intubation Using Airtraq and Macintosh Laryngoscopes by Unskillful Anesthesiology Residents: A Clinical Study
Background and Objective. The Airtraq laryngoscope (Prodol Meditec, Vizcaya, Spain) is a novel tracheal intubation device. Studies, performed until now, have compared the Airtraq with the Macintosh laryngoscope, concluding that it reduces the intubation times and increase the success rate at first intubation attempt, decreasing the Cormack-Lehane score. The aim of the study was to evaluate if, in unskillful anesthesiology residents during the laryngoscopy, the Airtraq compared with the Macintosh laryngoscope improves the laryngeal view, decreasing the Cormack-Lehane score.
Methods. A prospective, randomized, crossed-over trial was carried out on 60 patients. Each one of the patients were intubated using both devices by unskillful (less than two hundred intubations with the Macintosh laryngoscope and 10 intubations using the Airtraq) anesthesiology residents. The Cormack-Lehane score, the success rate at first intubation attempt, and the laryngoscopy and intubation times were compared. Results. The Airtraq significantly decreased the Cormack-Lehane score (P = 0.04). On the other hand, there were no differences in times of laryngoscopy (P = 0.645; IC 95% 3.1, +4.8) and intubation (P = 0.62; C95% −6.1, +10.0) between the two devices. No relevant complications were found during the maneuvers of intubation using both devices. Conclusions. The Airtraq is a useful laryngoscope in unskillful anesthesiology residents improving the laryngeal view and, therefore, facilitating the tracheal intubation
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