473 research outputs found
Nuclear and Non-Ionizing Energy-Loss for Coulomb Scattered Particles from Low Energy up to Relativistic Regime in Space Radiation Environment
In the space environment, instruments onboard of spacecrafts can be affected
by displacement damage due to radiation. The differential scattering cross
section for screened nucleus--nucleus interactions - i.e., including the
effects due to screened Coulomb nuclear fields -, nuclear stopping powers and
non-ionization energy losses are treated from about 50 keV/nucleon up to
relativistic energies.Comment: Accepted for publication in the Proceedings of the ICATPP Conference
on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo (Como,
Italy), 7--8 October, 2010, to be published by World Scientifi
Antiproton modulation in the Heliosphere and AMS-02 antiproton over proton ratio prediction
We implemented a quasi time-dependent 2D stochastic model of solar modulation
describing the transport of cosmic rays (CR) in the heliosphere. Our code can
modulate the Local Interstellar Spectrum (LIS) of a generic charged particle
(light cosmic ions and electrons), calculating the spectrum at 1AU. Several
measurements of CR antiparticles have been performed. Here we focused our
attention on the CR antiproton component and the antiproton over proton ratio.
We show that our model, using the same heliospheric parameters for both
particles, fit the observed anti-p/p ratio. We show a good agreement with
BESS-97 and PAMELA data and make a prediction for the AMS-02 experiment
Coherent ultrafast spin-dynamics probed in three dimensional topological insulators
Topological insulators are candidates to open up a novel route in spin based
electronics. Different to traditional ferromagnetic materials, where the
carrier spin-polarization and magnetization are based on the exchange
interaction, the spin properties in topological insulators are based on the
coupling of spin- and orbit interaction connected to its momentum. Specific
ways to control the spin-polarization with light have been demonstrated: the
energy momentum landscape of the Dirac cone provides spin-momentum locking of
the charge current and its spin. The directionality of spin and momentum, as
well as control with light has been demonstrated. Here we demonstrate a
coherent femtosecond control of spin-polarization for states in the valence
band at around the Dirac cone.Comment: 14 pages, 4 figure
Electrical Characterization of SiPM as a Function of Test Frequency and Temperature
Silicon Photomultipliers (SiPM) represent a promising alternative to
classical photomultipliers, for instance, for the detection of photons in high
energy physics and medical physics. In the present work, electrical
characterizations of test devices - manufactured by ST Microelectronics - are
presented. SiPMs with an area of 3.5x3.5 micron^2 and a cell pitch of 54 micron
were manufactured as arrays of 64x64 cells and exhibiting a fill factor of 31%.
The capacitance of SiPMs was measured as a function of reverse bias voltage at
frequencies ranging from from 20 Hz up to 1 MHz and temperatures from 300 K
down to 85 K. While leakage currents were measured at temperatures from 400 K
down to 85 K. Thus, the threshold voltage - i.e., voltage corresponding to that
at which the multiplication regime for the leakage current begins - could be
determined as a function of temperature. Finally, an electrical model suited to
reproduce the dependence of the frequency dependence of capacitance is
presented.Comment: To appear on the Proceedings of the 13th ICATPP Conference on
Astroparticle, Particle, Space Physics and Detectors for Physics
Applications, Villa Olmo (Como, Italy), 3-7 October, 2011, to be published by
World Scientific (Singapore
Proton Modulation in the Heliosphere for Different Solar Conditions and Prediction for AMS-02
Spectra of Galactic Cosmic Rays (GCRs) measured at the Earth are the
combination of several processes: sources production and acceleration,
propagation in the interstellar medium and propagation in the heliosphere.
Inside the solar cavity the flux of GCRs is reduced due to the solar
modulation, the interaction which they have with the interplanetary medium. We
realized a 2D stochastic simulation of solar modulation to reproduce CR spectra
at the Earth, and evaluated the importance in our results of the Local
Interstellar Spectrum (LIS) model and its agreement with data at high energy.
We show a good agreement between our model and the data taken by AMS-01 and
BESS experiments during periods with different solar activity conditions.
Furthermore we made a prediction for the flux which will be measured by AMS-02
experiment.Comment: Accepted for publication in the Proceedings of the ICATPP Conference
on Cosmic Rays for Particle and Astroparticle Physics, Villa Olmo (Como,
Italy), 7-8 October, 2010, to be published by World Scientific (Singapore
Latitudinal Dependence of Cosmic Rays Modulation at 1 AU and Interplanetary-Magnetic-Field Polar Correction
The cosmic rays differential intensity inside the heliosphere, for energy
below 30 GeV/nuc, depends on solar activity and interplanetary magnetic field
polarity. This variation, termed solar modulation, is described using a 2-D
(radius and colatitude) Monte Carlo approach for solving the Parker transport
equation that includes diffusion, convection, magnetic drift and adiabatic
energy loss. Since the whole transport is strongly related to the
interplanetary magnetic field (IMF) structure, a better understanding of his
description is needed in order to reproduce the cosmic rays intensity at the
Earth, as well as outside the ecliptic plane. In this work an interplanetary
magnetic field model including the standard description on ecliptic region and
a polar correction is presented. This treatment of the IMF, implemented in the
HelMod Monte Carlo code (version 2.0), was used to determine the effects on the
differential intensity of Proton at 1\,AU and allowed one to investigate how
latitudinal gradients of proton intensities, observed in the inner heliosphere
with the Ulysses spacecraft during 1995, can be affected by the modification of
the IMF in the polar regions.Comment: accepted for publication inAdvances in Astronom
Suprathermal particle addition to solar wind pressure: possible influence on magnetospheric transmissivity of low energy cosmic rays?
Energetic (suprathermal) solar particles, accelerated in the interplanetary
medium, contribute to the solar wind pressure, in particular during high solar
activity periods. We estimated the effect of the increase of solar wind
pressure due to suprathermal particles on magnetospheric transmissivity of
galactic cosmic rays in the case of one recent solar event
Emergence of pseudogap from short-range spin-correlations in electron doped cuprates
Electron interactions are pivotal for defining the electronic structure of
quantum materials. In particular, the strong electron Coulomb repulsion is
considered the keystone for describing the emergence of exotic and/or ordered
phases of quantum matter as disparate as high-temperature superconductivity and
charge- or magnetic-order. However, a comprehensive understanding of
fundamental electronic properties of quantum materials is often complicated by
the appearance of an enigmatic partial suppression of low-energy electronic
states, known as the pseudogap. Here we take advantage of ultrafast
angle-resolved photoemission spectroscopy to unveil the temperature evolution
of the low-energy density of states in the electron-doped cuprate
NdCeCuO, an emblematic system where
the pseudogap intertwines with magnetic degrees of freedom. By photoexciting
the electronic system across the pseudogap onset temperature T*, we report the
direct relation between the momentum-resolved pseudogap spectral features and
the spin-correlation length with an unprecedented sensitivity. This transient
approach, corroborated by mean field model calculations, allows us to establish
the pseudogap in electron-doped cuprates as a precursor to the incipient
antiferromagnetic order even when long-range antiferromagnetic correlations are
not established, as in the case of optimal doping.Comment: 17 pages, 3 figure
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