3,263 research outputs found
Measuring X-ray anisotropy in solar flares. Prospective stereoscopic capabilities of STIX and MiSolFA
During the next solar maximum, two upcoming space-borne X-ray missions, STIX
on board Solar Orbiter and MiSolFA, will perform stereoscopic X-ray
observations of solar flares at two different locations: STIX at 0.28 AU (at
perihelion) and up to inclinations of , and MiSolFA in a
low-Earth orbit. The combined observations from these cross-calibrated
detectors will allow us to infer the electron anisotropy of individual flares
confidently for the first time. We simulated both instrumental and physical
effects for STIX and MiSolFA including thermal shielding, background and X-ray
Compton backscattering (albedo effect) in the solar photosphere. We predict the
expected number of observable flares available for stereoscopic measurements
during the next solar maximum. We also discuss the range of useful spacecraft
observation angles for the challenging case of close-to-isotropic flare
anisotropy. The simulated results show that STIX and MiSolFA will be capable of
detecting low levels of flare anisotropy, for M1-class or stronger flares, even
with a relatively small spacecraft angular separation of 20-30{\deg}. Both
instruments will directly measure the flare X-ray anisotropy of about 40 M- and
X-class solar flares during the next solar maximum. Near-future stereoscopic
observations with Solar Orbiter/STIX and MiSolFA will help distinguishing
between competing flare-acceleration mechanisms, and provide essential
constraints regarding collisional and non-collisional transport processes
occurring in the flaring atmosphere for individual solar flares
Phase separation and pairing regimes in the one-dimensional asymmetric Hubbard model
We address some open questions regarding the phase diagram of the
one-dimensional Hubbard model with asymmetric hopping coefficients and balanced
species. In the attractive regime we present a numerical study of the passage
from on-site pairing dominant correlations at small asymmetries to
charge-density waves in the region with markedly different hopping
coefficients. In the repulsive regime we exploit two analytical treatments in
the strong- and weak-coupling regimes in order to locate the onset of phase
separation at small and large asymmetries respectively.Comment: 13 pages, RevTeX 4, 12 eps figures, some additional refs. with
respect to v1 and citation errors fixe
Robust output synchronization of a network of heterogeneous nonlinear agents via nonlinear regulation theory
In this paper, we consider the output synchronization problem for a network
of heterogeneous diffusively-coupled nonlinear agents. Specifically, we show
how the (non-identical) agents can be controlled in such a way that their
outputs asymptotically track the output of a prescribed nonlinear exosystem.
The problem is solved in two steps. In the first step, the problem of achieving
consensus among (identical) nonlinear reference generators is addressed. In
this respect, it is shown how the techniques recently developed to solve the
consensus problem among linear agents can be extended to agents modeled by
nonlinear d-dimensional differential equations, under the assumption that the
communication graph is connected. In the second step, the theory of nonlinear
output regulation is applied in a decentralized control mode, to force the
output of each agent of the network to robustly track the (synchronized) output
of a local reference model.Comment: Submitted to 52nd IEEE Conference on Decision and Contro
BIOMECHANICAL OPTIMIZATION OF CO2ANGIOGRAPHY
Carbon dioxide (CO2) angiography represents an important technique to overcome most clinical problems related to the use of iodine contrast medium. The recent technologic advancements in the fields of gas injection and image reconstructions made CO2 angiography a very efficient method for clinical evaluation of peripheral cardiovascular system. Despite that, some challenges are still open and a better knowledge of the biomechanical behavior of CO2 and its interactions with blood flowing into the vessels is necessary to optimize this technology and to expand its field of application. This paper presents a quick overview about biomechanical behavior of carbon dioxide during injection, suggesting possible optimization tricks to make CO2 angiography procedures more effective to improve imaging and reduce the patients' radiological dose. Particular attention has been also paid to 3D imaging techniques, which can certainly be opened to the use of carbon dioxide
The Local Interstellar Spectrum of Cosmic Ray Electrons
The direct measurements of electrons and positrons over the last 30 years,
corrected for the solar effect in the force-field approximation, are
considered. The resulting overall electron spectrum may be fitted with a single
power law above few GeV with spectral index (),
consistent with the spectral index of the positron spectrum (), therefore suggesting a common acceleration process for both
species. We propose that the engine was a shock wave originating from the last
supernova explosion among those that formed the local bubble. In addition, at
low energy, the electron spectrum measured during the last solar phase is
damped, whereas the positron spectrum is well represented by a single power law
down to the lowest inferred local interstellar energy (0.8 GeV). We suggest
that this difference arises from a time- and charge-dependent effect of the
solar modulation that is not taken into account by the force-field
approximation.Comment: 10 pages, 9 figures, 1 table. OBSOLETE: please refer to ApJ 612
(2004) 262-267, that is the final version of this wor
The Time of Flight System of the AMS-02 Space Experiment
The Time-of-Flight (TOF) system of the AMS detector gives the fast trigger to
the read out electronics and measures velocity, direction and charge of the
crossing particles. The new version of the detector (called AMS-02) will be
installed on the International Space Station on March 2004. The fringing field
of the AMS-02 superconducting magnet is kG where the
photomultiplers (PM) are installed. In order to be able to operate with this
residual field, a new type of PM was chosen and the mechanical design was
constrained by requiring to minimize the angle between the magnetic field
vector and the PM axis. Due to strong field and to the curved light guides, the
time resolution will be ps, while the new electronics will allow
for a better charge measurement.Comment: 5 pages, 4 figures. Proc. of 7th Int. Conf. on Adv. Tech. and Part.
Phys., 15-19 October 2001,Como (Italy
Treatment of squamous cell carcinoma of the anal canal: A new strategies with anti-EGFR therapy and immunotherapy
The incidence of squamous cell carcinoma of the anal canal (SCAC) is increasing in both sexes but the standard treatment remains that of 20 years ago. However, interesting data have recently emerged on the use of anti-epidermal growth factor receptor (EGFR) agents and immunotherapy in advanced disease. Thus, new avenues of research are opening up that will hopefully lead to more effective therapeutic strategies. We provide an overview of the latest studies published on this tumor and discuss the possible future therapeutic options for combination therapy, anti-EGFR treatment and radiotherapy
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