769 research outputs found
Monte Carlo and hydrodynamic simulation of a one dimensional n+ â n â n+ silicon diode
An improved closure relation - based on the entropy principle - is implemented in a Hydrodynamic
model for electron transport. Steady-state electron transport in the "benchmark" n+ - n - n+ submicron silicon diode is simulated and the quality of the model is assessed by comparison
with Monte Carlo results
The role of electron-electron scattering in spin transport
We investigate spin transport in quasi 2DEG formed by III-V semiconductor
heterojunctions using the Monte Carlo method. The results obtained with and
without electron-electron scattering are compared and appreciable difference
between the two is found. The electron-electron scattering leads to suppression
of Dyakonov-Perel mechanism (DP) and enhancement of Elliott-Yafet mechanism
(EY). Finally, spin transport in InSb and GaAs heterostructures is investigated
considering both DP and EY mechanisms. While DP mechanism dominates spin
decoherence in GaAs, EY mechanism is found to dominate in high mobility InSb.
Our simulations predict a lower spin relaxation/decoherence rate in wide gap
semiconductors which is desirable for spin transport.Comment: to appear in Journal of Applied Physic
Creation of Dirac Particles in the Presence of a Constant Electric Field in an Anisotropic Bianchi I Universe
In this article we compute the density of Dirac particles created by a
cosmological anisotropic Bianchi I universe in the presence of a constant
electric field. We show that the particle distribution becomes thermal when one
neglects the electric interaction.Comment: 9 page
Generalized phonon-assisted Zener tunneling in indirect semiconductors with non-uniform electric fields : a rigorous approach
A general framework to calculate the Zener current in an indirect
semiconductor with an externally applied potential is provided. Assuming a
parabolic valence and conduction band dispersion, the semiconductor is in
equilibrium in the presence of the external field as long as the electronphonon
interaction is absent. The linear response to the electron-phonon interaction
results in a non-equilibrium system. The Zener tunneling current is calculated
from the number of electrons making the transition from valence to conduction
band per unit time. A convenient expression based on the single particle
spectral functions is provided, enabling the numerical calculation of the Zener
current under any three-dimensional potential profile. For a one dimensional
potential profile an analytical expression is obtained for the current in a
bulk semiconductor, a semiconductor under uniform field and a semiconductor
under a non-uniform field using the WKB (Wentzel-Kramers-Brillouin)
approximation. The obtained results agree with the Kane result in the low field
limit. A numerical example for abrupt p - n diodes with different doping
concentrations is given, from which it can be seen that the uniform field model
is a better approximation than the WKB model but a direct numerical treatment
is required for low bias conditions.Comment: 29 pages, 7 figure
Characterisation of the secondary-neutron production in particle therapy treatments with the MONDO tracking detector
Particle Therapy (PT) is a non-invasive technique that exploits charged light ions for the irradiation of tumours that cannot be effectively treated with surgery or conventional radiotherapy. While the largest dose fraction is released to the tumour volume by the primary beam, a non-negligible amount of additional dose is due to the beam fragmentation that occurs along the path towards the target volume. In particular, the produced neutrons are particularly dangerous as they can release their energy far away from the treated area, increasing the risk of developing a radiogenic secondary malignant neoplasm after undergoing a treatment. A precise measurement of the neutron flux, energy spectrum and angular distributions is eagerly needed in order to improve the treatment planning system software, so as to predict the normal tissue toxicity in the target region and the risk of late complications in the whole body. The MONDO (MOnitor for Neutron Dose in hadrOntherapy) project is dedicated to the characterisation of the secondary ultra-fast neutrons ([20-400] MeV energy range) produced in PT. The neutron tracking system exploits the reconstruction of the recoil protons produced in two consecutive (n, p) elastic scattering interactions to measure simultaneously the neutron incoming direction and energy. The tracker active media is a matrix of thin squared scintillating fibers arranged in orthogonally oriented layers that are read out by a sensor (SBAM) based on SPAD (Single-Photon Avalanche Diode) detectors developed in collaboration with the Fondazione Bruno Kessler (FBK)
The Influence of Physical Education on Self-Efficacy in Overweight Schoolgirls: A 12-Week Training Program
The purpose of this randomized controlled study was to investigate the impact of a 12- week physical education (PE) program on the self-efficacy of overweight schoolgirls. We randomly assigned 60 overweight schoolgirls (15â17 years) to either an experimental moderate to vigorous aerobic exercise (âŒ90 min, three times a week) group (n = 30) or a control group (CG) (n = 30) that received non-specific regular PE lessons with activities chosen by the curricular teacher mainly focused on team games and sports skills that aimed to achieve general psycho-physical wellness (âŒ90 min, three times a week). To assess the starting level of students and significant changes reached, at baseline and after training, a battery of standardized assessment motor tests and a psychometric scale (generalized self-efficacy scale, GES) were administered. At the end of the intervention, the experimental group reported a considerable decrease in body mass index (BMI) and a large improvement in self-efficacy (p < 0.001). No significant changes were found in the CG. The results suggested that the 12-week moderate to a vigorous aerobic exercise program is an effective weight loss intervention and a vehicle to promote a range of outcomes important to the qualitative growth of adolescents. In fact, it could provide a positive and significant impact on the self-efficacy of overweight schoolgirls
Calculation of the electron mobility in III-V inversion layers with high-kappa dielectrics
We calculate the electron mobility for a metal-oxide-semiconductor system with a metallic gate, high-kappa dielectric layer, and III-V substrate, including scattering with longitudinal-optical (LO) polar-phonons of the III-V substrate and with the interfacial excitations resulting from the coupling of insulator and substrate optical modes among themselves and with substrate plasmons. In treating scattering with the substrate LO-modes, multisubband dynamic screening is included and compared to the dielectric screening in the static limit and with the commonly used screening model obtained by defining an effective screening wave vector. The electron mobility components limited by substrate LO phonons and interfacial modes are calculated for In0.53Ga0.47As and GaAs substrates with SiO2 and HfO2 gate dielectrics. The mobility components limited by the LO-modes and interfacial phonons are also investigated as a function of temperature. Scattering with surface roughness, fixed interface charge, and nonpolar-phonons is also included to judge the relative impact of each scattering mechanism in the total mobility for In0.53Ga0.47As with HfO2 gate dielectric. We show that InGaAs is affected by interfacial-phonon scattering to an extent larger than Si, lowering the expected performance, but probably not enough to question the technological relevance of InGaAs. (C) 2010 American Institute of Physics. [doi:10.1063/1.3500553
Scintillating fiber devices for particle therapy applications
Particle Therapy (PT) is a radiation therapy technique in which solid tumors are treated with charged ions and exploits the achievable highly localized dose delivery, allowing to spare healthy tissues and organs at risk. The development of a range monitoring technique to be used on-line, during the treatment, capable to reach millimetric precision is considered one of the important steps towards an optimization of the PT efficacy and of the treatment quality. To this aim, charged secondary particles produced in the nuclear interactions between the beam particles and the patient tissues can be exploited. Besides charged secondaries, also neutrons are produced in nuclear interactions. The secondary neutron component might cause an undesired and not negligible dose deposition far away from the tumor region, enhancing the risk of secondary malignant neoplasms that can develop even years after the treatment. An accurate neutron characterization (flux, energy and emission profile) is hence needed for a better evaluation of long-term complications. In this contribution two tracker detectors, both based on scintillating fibers, are presented. The first one, named Dose Profiler (DP), is planned to be used as a beam range monitor in PT treatments with heavy ion beams, exploiting the charged secondary fragments production. The DP is currently under development within the INSIDE (Innovative Solutions for In-beam DosimEtry in hadrontherapy) project. The second one is dedicated to the measurement of the fast and ultrafast neutron component produced in PT treatments, in the framework of the MONDO (MOnitor for Neutron Dose in hadrOntherapy) project. Results of the first calibration tests performed at the Trento Protontherapy center and at CNAO (Italy) are reported, as well as simulation studies
The graceful exit from the anomaly-induced inflation: Supersymmetry as a key
The stable version of the anomaly-induced inflation does not need a fine
tuning and leads to sufficient expansion of the Universe. The non-stable
version (Starobinsky model) provides the graceful exit to the FRW phase. We
indicate the possibility of the inflation which is stable at the beginning and
unstable at the end. The effect is due to the soft supersymmetry breaking and
the decoupling of the massive sparticles at low energy.Comment: 10 pages, 2 figures using axodraw. Modified version. Discussion
concerning the gravitational scale modified, the effect of massive particles
in the last stage of inflation taken into accoun
In-room test results at CNAO of an innovative PT treatments online monitor (Dose Profiler)
The use of C, He and O ions as projectiles in Particle Therapy (PT) treatments is getting more and more widespread as a consequence of their enhanced relative biological effectiveness and oxygen enhancement ratio, when compared to the protons one. The advantages related to the incoming radiation improved efficacy are requiring an accurate online monitor of the dose release spatial distribution. Such monitor is necessary to prevent unwanted damage to the tissues surrounding the tumour that can arise, for example, due to morphological changes occurred in the patient during the treatment with respect to the initial CT scan. PT treatments with ions can be monitored by detecting the secondary radiation produced by the primary beam interactions with the patient body along the path towards the target volume. Charged fragments produced in the nuclear process of projectile fragmentation can be emitted at large angles with respect to the incoming beam direction and can be detected with high efficiency in a nearly background-free environment. The Dose Profiler (DP) detector, developed within the INSIDE project, is a scintillating fibre tracker that allows an online reconstruction and backtracking of such secondary charged fragments. The construction and preliminary in-room tests performed on the DP, carried out using the 12C ions beam of the CNAO treatment centre using an anthropomorphic phantom as a target, will be reviewed in this contribution. The impact of the secondary fragments interactions with the patient body will be discussed in view of a clinical application. Furthermore, the results implications for a pre-clinical trial on CNAO patients, foreseen in 2019, will be discussed
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