Search results for "BED"
showing 10 items of 1605 documents
System-environment correlations and Markovian embedding of quantum non-Markovian dynamics
2018
We study the dynamics of a quantum system whose interaction with an environment is described by a collision model, i.e. the open dynamics is modelled through sequences of unitary interactions between the system and the individual constituents of the environment, termed "ancillas", which are subsequently traced out. In this setting non-Markovianity is introduced by allowing for additional unitary interactions between the ancillas. For this model, we identify the relevant system-environment correlations that lead to a non-Markovian evolution. Through an equivalent picture of the open dynamics, we introduce the notion of "memory depth" where these correlations are established between the syste…
Sensitivity of UVER enhancement to broken liquid water clouds: A Monte Carlo approach
2016
The study uses a Monte Carlo radiative transfer model to examine the sensitivity of the UV erythemal radiation (UVER) enhancement to broken liquid water clouds of the cumulus and stratocumulus type. The model uses monochromatic radiation at 310 nm corresponding approximately to the peak of the product between irradiance and the erythemal curve. All scattering, absorption, extinction coefficients, and spectral albedos are tuned to this wavelength. In order of importance, fractional cloud cover, the area of individual cloud patches, and cloud thickness exert a strong influence on the enhancement, with smaller contributions from cloud optical depth, cloud base height, and solar zenith angle. I…
The ratio of primary scattering to total scattering of sky radiance
1974
Recently Eschelbach has computed from theory spectral radiance values for a turbid atmosphere taking into account the effect of multiple scattering. In the present work these computational data were used to investigate the ratio of primary to total scattering. This quotient is a measure of multiple scattering because of the relation: Total Scattering (TS) is equal to Primary Scattering (PS) plus Multiple Scattering (MS), i.e. PS/TS = 100 - MS/TS (%). It is discussed in which way multiple scattering in the solar almucantar depends on the solar elevation, turbidity, scattering angle, wavelength and albedo. The present work shows in which way multiple scattering is related to the optical thick…
Collocated measurements of boundary layer cloud microphysical and radiative properties: A feasibility study
2010
[1] First data from collocated, helicopter-based measurements of boundary layer cloud microphysical properties (effective droplet radius Reff, droplet number concentration N) and spectral radiative quantities (cloud optical thickness τ, cloud top albedo ρ, reflectivity ) are presented. The in situ measurements of the microphysical cloud properties were collected by the Airborne Cloud Turbulence Observation System (ACTOS) attached to a helicopter by a 145 m long rope. Cloud spectral reflectivity was derived from radiances measured by grating spectrometers combined with downward looking optical inlets installed underneath the helicopter. Correlations between cloud microphysics and reflected r…
SU-E-T-467: Monte Carlo Dosimetric Study of the New Flexisource Co-60 High Dose Rate Source.
2017
Recently, a new HDR 60Co brachytherapy source, Flexisource Co-60, has been developed (Nucletron B.V.). This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO.Penelope2008 and GEANT4 Monte Carlo codes were used to dosimetrically characterize this source. Water composition and mass density was that recommended by AAPM. Due to the high energy of the 60Co, dose for small distances cannot be approximated by collisional kerma. Therefore, we have considered absorbed dose to water for r0.75 cm and collisional kerma from 0.75r20 cm. To provide adequate spatial resolution, cells were 0.01 cm in thickness for r2 cm from the sour…
A Monte Carlo-based dosimetric characterization of Esteya® , an electronic surface brachytherapy unit
2018
PURPOSE The purpose of this work is threefold: First, to obtain the phase space of an electronic brachytherapy (eBT) system designed for surface skin treatments. Second, to explore the use of some efficiency enhancing (EFEN) strategies in the determination of the phase space. Third, to use the phase space previously obtained to perform a dosimetric characterization of the Esteya eBT system. METHODS The Monte Carlo study of the 69.5 kVp x-ray beam of the Esteya® unit (Elekta Brachytherapy, Veenendaal, The Netherlands) was performed with PENELOPE2014. The EFEN strategies included the use of variance reduction techniques and mixed Class II simulations, where transport parameters were fine-tune…
Effects of Scaling in SEE and TID Response of High Density NAND Flash Memories
2010
Heavy ion single-event effect (SEE) measurements and total ionizing dose (TID) response for Micron Technology single-level cell 1, 2, 4, 8 Gb commercial NAND flash memory and multi-level cell 8, 16, 32 Gb are reported. The heavy ion measurements were extended down to LET 0.1 MeV-cm2/mg. Scaling effects in SEE and TID response are discussed. Floating gate bit error upset cross section does not scale with feature size at high LETs, except for single-level cell 8 Gb device which is built with 51 nm processes. The threshold LET does not change with scaling. Charge pump TID degradation and standby current improves with scaling. In general, the effect of radiation is either unchanged or is less s…
Monte Carlo evaluation of the Filtered Back Projection method for image reconstruction in proton computed tomography
2011
Abstract In this paper the use of the Filtered Back Projection (FBP) Algorithm, in order to reconstruct tomographic images using the high energy (200–250 MeV) proton beams, is investigated. The algorithm has been studied in detail with a Monte Carlo approach and image quality has been analysed and compared with the total absorbed dose. A proton Computed Tomography (pCT) apparatus, developed by our group, has been fully simulated to exploit the power of the Geant4 Monte Carlo toolkit. From the simulation of the apparatus, a set of tomographic images of a test phantom has been reconstructed using the FBP at different absorbed dose values. The images have been evaluated in terms of homogeneity…
Ultrametricity property of energy landscapes of multidisperse packing problems
2009
We consider the problem of finding the densest closed packing of hard disks with proposed different radii in a circular environment, such that the radius of the circumcircle is minimal. The subspace of the quasioptimum configurations of this problem exhibits the property of ultrametricity.
SU(6) Grand Unification of 3-3-1 Model
2018
We discuss a sequential variant of the \(\mathrm { SU(3)_c \times SU(3)_L \times U(1)_X}\) model which fits within a minimal SU(6) grand unification. Interestingly, this minimal SU(6) embedding can allow a \(\mathrm { SU(3)_c \times SU(3)_L \times U(1)_X}\) symmetry breaking scale within the reach of LHC and with seesaw-type neutrino masses.