53 research outputs found
On the exact boundary controllability of semilinear wave equations
We address the exact boundary controllability of the semilinear wave equation
posed over a bounded domain of
. Assuming that is continuous and satisfies the condition
for some small enough and some , we
apply the Schauder fixed point theorem to prove the uniform controllability for
initial data in . Then, assuming that is
in and satisfies the condition , we apply
the Banach fixed point theorem and exhibit a strongly convergent sequence to a
state-control pair for the semilinear equation
Particle Effects on the ISGRI Instrument On-Board the INTEGRAL Satellite
The INTEGRAL satellite was launched on October 17, 2002. All on-board
instruments are operating successfully. In this paper, we focus on radiation
effects on the Cadmium Telluride camera ISGRI. The spectral response of the
camera is affected by cosmic particles depositing huge amount of energy,
greater than the high threshold of the electronics. Our study raises the
contribution of cosmic ray protons. Solutions are proposed to limit the
degradation of spectral response of large pixel gamma cameras operating in
space
Impacts of The Radiation Environment At L2 On Bolometers Onboard The Herschel Space Observatory
We present the effects of cosmic rays on the detectors onboard the Herschel
satellite. We describe in particular the glitches observed on the two types of
cryogenic far- infrared bolometer inside the two instruments PACS and SPIRE.
The glitch rates are also reported since the launch together with the SREM
radiation monitors aboard Herschel and Planck spacecrafts. Both have been
injected around the Lagrangian point L2 on May 2009. This allows probing the
radiation environment around this orbit. The impacts on the observation are
finally summarized.Comment: 8 pages, 13 figures, 2 images, Author Keywords: Bolometers, Infrared
detectors, cryogenics, radiation effects, submillimeter wave technology IEEE
Terms: Bolometers, Detectors, Instruments, Picture archiving and
communication systems, Protons, Silicon, Space vehicles; Radiation and Its
Effects on Components and Systems (RADECS), 2011 12th European Conference.
Conference location: Sevilla. Date of Conference: 19-23 Sept. 2011. Session
H: Radiation Environment: Space, Atmospheric and Terrestrial (PH2
Negative energy balance hinders prosocial helping behavior
The internal state of an animal, including homeostatic requirements, modulates its behavior. Negative energy balance stimulates hunger, thus promoting a range of actions aimed at obtaining food. While these survival actions are well established, the influence of the energy status on prosocial behavior remains unexplored. We developed a paradigm to assess helping behavior in which a free mouse was faced with a conspecific trapped in a restrainer. We measured the willingness of the free mouse to liberate the confined mouse under diverse metabolic conditions. Around 42% of ad libitum-fed mice exhibited a helping behavior, as evidenced by the reduction in the latencies to release the trapped cagemate. This behavior was independent of subsequent social contact reward and was associated with changes in corticosterone indicative of emotional contagion. This decision-making process was coupled with reduced blood glucose excursions and higher Adenosine triphosphate (ATP):Adenosine diphosphate (ADP) ratios in the forebrain of helper mice, suggesting that it was a highly energy-demanding process. Interestingly, chronic (food restriction and type 2 diabetes) and acute (chemogenetic activation of hunger-promoting AgRP neurons) situations mimicking organismal negative energy balance and enhanced appetite attenuated helping behavior toward a distressed conspecific. To investigate similar effects in humans, we estimated the influence of glycated hemoglobin (a surrogate of long-term glycemic control) on prosocial behavior (namely charity donation) using the Understanding Society dataset. Our results evidenced that organismal energy status markedly influences helping behavior and that hypothalamic AgRP neurons are at the interface of metabolism and prosocial behavior
X-ray Spectroscopy of MXB 1728-34 with XMM-Newton
We have analysed an XMM-Newton observation of the low mass X-ray binary and
atoll source MXB 1728-34. The source was in a low luminosity state during the
XMM-Newton observation, corresponding to a bolometric X-ray luminosity of
5*10E36 d^2 erg/s, where d is the distance in units of 5.1 kpc. The 1-11 keV
X-ray spectrum of the source, obtained combining data from all the five
instruments on-board XMM-Newton, is well fitted by a Comptonized continuum.
Evident residuals are present at 6-7 keV which are ascribed to the presence of
a broad iron emission line. This feature can be equally well fitted by a
relativistically smeared line or by a self-consistent, relativistically
smeared, reflection model. Under the hypothesis that the iron line is produced
by reflection from the inner accretion disk, we can infer important information
on the physical parameters of the system, such as the inner disk radius, Rin =
25-100 km, and the inclination of the system, 44{\deg} < i < 60{\deg}.Comment: 7 pages, 3 figures, Accepted by A&A on 29.03.201
The COSPIX Mission: Focusing on the Energetic and Obscured Universe
Tracing the formation and evolution of all supermassive black holes, including the obscured ones, understanding how black holes influence their surroundings and how matter behaves under extreme conditions, are recognized as key science objectives to be addressed by the next generation of instruments. These are the main goals of the COSPIX proposal, made to ESA in December 2010 in the context of its call for selection of the M3 mission. In addition, COSPIX, will also provide key measurements on the non thermal Universe, particularly in relation to the question of the acceleration of particles, as well as on many other fundamental questions as for example the energetic particle content of clusters of galaxies. COSPIX is proposed as an observatory operating from 0.3 to more than 100 keV. The payload features a single long focal length focusing telescope offering an effective area close to ten times larger than any scheduled focusing mission at 30 keV, an angular resolution better than 20 arcseconds in hard X-rays, and polarimetric capabilities within the same focal plane instrumentation. In this paper, we describe the science objectives of the mission, its baseline design, and its performances, as proposed to ESA
The COSPIX mission: focusing on the energetic and obscured Universe
Tracing the formation and evolution of all supermassive black holes,
including the obscured ones, understanding how black holes influence their
surroundings and how matter behaves under extreme conditions, are recognized as
key science objectives to be addressed by the next generation of instruments.
These are the main goals of the COSPIX proposal, made to ESA in December 2010
in the context of its call for selection of the M3 mission. In addition,
COSPIX, will also provide key measurements on the non thermal Universe,
particularly in relation to the question of the acceleration of particles, as
well as on many other fundamental questions as for example the energetic
particle content of clusters of galaxies. COSPIX is proposed as an observatory
operating from 0.3 to more than 100 keV. The payload features a single long
focal length focusing telescope offering an effective area close to ten times
larger than any scheduled focusing mission at 30 keV, an angular resolution
better than 20 arcseconds in hard X-rays, and polarimetric capabilities within
the same focal plane instrumentation. In this paper, we describe the science
objectives of the mission, its baseline design, and its performances, as
proposed to ESA.Comment: 7 pages, accepted for publication in Proceedings of Science, for the
25th Texas Symposium on Relativistic Astrophysics (eds. F. Rieger & C.
van Eldik), PoS(Texas 2010)25
NGC 1624-2: A slowly rotating, X-ray luminous Of?cp star with an extraordinarily strong magnetic field
This paper presents a first observational investigation of the faint Of?cp
star NGC 1624-2, yielding important new constraints on its spectral and
physical characteristics, rotation, magnetic field strength, X-ray emission and
magnetospheric properties. Modeling the spectrum and spectral energy
distribution, we conclude that NGC 1624-2 is a main sequence star of mass M
{\simeq} 30 M{\odot}, and infer an effective temperature of 35 {\pm} 2 kK and
log g = 4.0 {\pm} 0.2. Based on an extensive time series of optical spectral
observations we report significant variability of a large number of spectral
lines, and infer a unique period of 157.99 {\pm} 0.94 d which we interpret as
the rotational period of the star. We report the detection of a very strong -
5.35 {\pm} 0.5 kG - longitudinal magnetic field , coupled with probable
Zeeman splitting of Stokes I profiles of metal lines confirming a surface field
modulus of 14 {\pm} 1 kG, consistent with a surface dipole of polar
strength >~ 20 kG. This is the largest magnetic field ever detected in an
O-type star, and the first report of Zeeman splitting of Stokes I profiles in
such an object. We also report the detection of reversed Stokes V profiles
associated with weak, high-excitation emission lines of O iii, which we propose
may form in the close magnetosphere of the star. We analyze archival Chandra
ACIS-I X-ray data, inferring a very hard spectrum with an X-ray efficiency log
Lx/Lbol = -6.4, a factor of 4 larger than the canonical value for O-type stars
and comparable to that of the young magnetic O-type star {\theta}1 Ori C and
other Of?p stars. Finally, we examine the probable magnetospheric properties of
the star, reporting in particular very strong magnetic confinement of the
stellar wind, with {\eta}* {\simeq} 1.5 {\times} 10^4, and a very large Alfven
radius, RAlf = 11.4 R*.Comment: 17 pages, MNRAS accepted and in pres
Mitochondrial cristae-remodeling protein OPA1 in POMC neurons couples Ca2+ homeostasis with adipose tissue lipolysis
© 2021 The Authors.Appropriate cristae remodeling is a determinant of mitochondrial function and bioenergetics and thus represents a crucial process for cellular metabolic adaptations. Here, we show that mitochondrial cristae architecture and expression of the master cristae-remodeling protein OPA1 in proopiomelanocortin (POMC) neurons, which are key metabolic sensors implicated in energy balance control, is affected by fluctuations in nutrient availability. Genetic inactivation of OPA1 in POMC neurons causes dramatic alterations in cristae topology, mitochondrial Ca2+ handling, reduction in alpha-melanocyte stimulating hormone (α-MSH) in target areas, hyperphagia, and attenuated white adipose tissue (WAT) lipolysis resulting in obesity. Pharmacological blockade of mitochondrial Ca2+ influx restores α-MSH and the lipolytic program, while improving the metabolic defects of mutant mice. Chemogenetic manipulation of POMC neurons confirms a role in lipolysis control. Our results unveil a novel axis that connects OPA1 in POMC neurons with mitochondrial cristae, Ca2+ homeostasis, and WAT lipolysis in the regulation of energy balance.This work was supported by Agencia Estatal de Investigación y Fondo Social Europeo, Proyecto BFU2016-76973-R FEDER (C.V.A.); AG052005, AG052986, AG051459, DK111178 from NIH and NKFI-KKP-126998 from Hungarian National Research, Development and Innovation Office (T.L.H.); MR/P009824/2 from Medical Research Council UK (G.D.); and Ayudas Fundación BBVA a Investigadores y Creadores Culturales (2015), European Research Council (ERC) under the European Union’s Horizon 2020 Research And Innovation Program (grant agreement 725004) and CERCA Programme/Generalitat de Catalunya (M.C.). A.O. is supported by a Miguel Servet contract (CP19/00083) from Instituto de Salud Carlos III and co-financed by FEDER
Dynamical masses of a nova-like variable on the edge of the period gap
We present the first dynamical determination of the binary parameters of an eclipsing SW Sextantis star in the 3–4 h orbital period range during a low state. We obtained time-resolved optical spectroscopy and photometry of HS 0220+0603 during its 2004–2005 low-brightness state, as revealed in the combined Small & Moderate Aperture Research Telescope System, IAC80 and M1 Group long-term optical light curve. The optical spectra taken during primary eclipse reveal a secondary star spectral type of M5.5 ± 0.5 as derived from molecular band-head indices. The spectra also provide the first detection of a DAB white dwarf in a cataclysmic variable. By modelling its optical spectrum we estimate a white dwarf temperature of 30 000 ± 5000 K. By combining the results of modelling the white dwarf eclipse from ULTRACAM light curves with those obtained by simultaneously fitting the emission- and absorption-line radial velocity curves and I-band ellipsoidal light curves, we measure the stellar masses to be M1 = 0.87 ± 0.09 M⊙ and M2 = 0.47 ± 0.05 M⊙ for the white dwarf and the M dwarf, respectively, and an inclination of the orbital plane of i ≈ 79°. A radius of 0.0103 ± 0.0007 R⊙ is obtained for the white dwarf. The secondary star in HS 0220+0603 is likely too cool and undersized for its mass
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