Search results for "solution"
showing 10 items of 5638 documents
PEEM with high time resolution—imaging of transient processes and novel concepts of chromatic and spherical aberration correction
2006
The potential of time-resolved photoemission electron microscopy (PEEM) for imaging ultrafast processes and for aberration correction in full-field imaging is discussed. In particular, we focus on stroboscopic imaging of precessional magnetic excitations via XMCD-PEEM exploiting the time structure of synchrotron radiation (magnetic field pulse pump–X-ray probe). In a special bunch-compression mode at BESSY, a time resolution of about 15 ps has been obtained. Further, we discuss an all-optical pump–probe technique using femtosecond laser excitation. A highly promising alternative to stroboscopic imaging is an approach using time-resolved image detection. As a second application of time-resol…
Elastic constants in RbI, determined by inelastic neutron scattering
1978
Long-wavelength acoustic phonons have been studied in the whole (100)-plane of RbI at 295 K by means of inelastic neutron scattering. The raw data have been corrected for resolution effects taking into account the curvature of the dispersion surface and variations of the mode eigenvectors. The shifts of the neutron groups due to these resolution effects are discussed in detail. The analysis of the experimental results gives for the zero sound elastic constantsc11=28.15±0.5,c12=3.7±0.5 andc44=2.85±0.1 1010 dyn/cm2. A comparison with first sound elastic constants taken from ultrasonic measurements yields significant differences between the high and low frequency elastic constantsc11 andc″=(c1…
SU-GG-T-70: A Dosimetric Study of the MicroSelectron HDR Ir-192 Brachytherapy Source
2010
Purpose: Recently the manufacturer of the mHDR‐v2 HDR Ir‐192 brachytherapy source clarified design changes that may alter the existing dosimetric data for this source. The object of this study was to obtain new dose rate tables following the TG‐43 formalism and to provide these data in close proximity to the source with high spatial resolution including the electron dosimetric contributions from Ir‐192 disintegration. Methods and Material: To study the source we used three different Monte Carlo codes: MCNP5, GEANT4, and Penelope. The source was located inside a 40 cm radius water phantom. Dose and kerma were obtained using 0.1 mm thick voxels to provide high‐resolution dosimetry near the so…
SU-E-T-508: Monte Carlo Dosimetric Study of the CSM40 Low Dose Rate Source
2013
Purpose: There is a LDR 137Cs brachytherapy source, CSM40, developed by Eckert & Ziegler BEBIG. Fundamental dosimetric datasets to be used on treatment planning systems do not exist for this source. This study aims to obtain quality dosimetric data for this source for its use in clinical practice as required by AAPM and ESTRO. Methods: Penelope2008 and GEANT4 Monte Carlo codes were used to characterize this source dosimetry. Water composition and mass density was that recommended by AAPM. Due to the typical energies of the 137 Cs, dose for small distances can be approximated by collisional kerma. Therefore, we have considered collisional kerma for r<20 cm. To provide adequate spatial resolu…
An approach to using conventional brachytherapy software for clinical treatment planning of complex, Monte Carlo-based brachytherapy dose distributio…
2009
Certain brachytherapy dose distributions, such as those for LDR prostate implants, are readily modeled by treatment planning systems (TPS) that use the superposition principle of individual seed dose distributions to calculate the total dose distribution. However, dose distributions for brachytherapy treatments using high-Z shields or having significant material heterogeneities are not currently well modeled using conventional TPS. The purpose of this study is to establish a new treatment planning technique (Tufts technique) that could be applied in some clinical situations where the conventional approach is not acceptable and dose distributions present cylindrical symmetry. Dose distributi…
MO-D-AUD B-08: Treatment Planning for Complex Brachytherapy Dose Distributions Using High-Z Shields and Conventional Software
2008
Purpose: Certain brachytherapydose distributions, like for LDR prostate implants, are readily modeled by treatment planningsoftware using the superposition principle of individual seeds to replicate the total dose distribution. However, dose distributions for brachytherapy treatments using high‐Z shields are currently not well‐modeled using conventional software.Method and Materials:Dose distributions from complex brachytherapy plaques determined using Monte Carlo methods were used as input data, and included COMS‐based eye plaques using 125 I , 103 Pd , and 131 Cs ; 4–8cm diameter AccuBoost peripheral breast brachytherapy applicators from Advanced Radiation Therapy; and the 2 and 3cm diame…
Switching synchronization in one-dimensional memristive networks: An exact solution.
2017
We study a switching synchronization phenomenon taking place in one-dimensional memristive networks when the memristors switch from the high- to low-resistance state. It is assumed that the distributions of threshold voltages and switching rates of memristors are arbitrary. Using the Laplace transform, a set of nonlinear equations describing the memristors dynamics is solved exactly, without any approximations. The time dependencies of memristances are found, and it is shown that the voltage falls across memristors are proportional to their threshold voltages. A compact expression for the network switching time is derived.
About the link between the detailed description of transitions in an ion and the average-ion models
2009
We study the link which exists between microscopic (detailed) models for the evolution of the electronic configurations in a population of ions and the macroscopic (average ion) models. Rigorous asymptotics are presented in situations where they exist (large temperature; almost empty or almost full shells), and numerical simulations are presented.
High-momentum tails as magnetic-structure probes for strongly correlatedSU(κ)fermionic mixtures in one-dimensional traps
2016
A universal ${k}^{\ensuremath{-}4}$ decay of the large-momentum tails of the momentum distribution, fixed by Tan's contact coefficients, constitutes a direct signature of strong correlations in a short-range interacting quantum gas. Here we consider a repulsive multicomponent Fermi gas under harmonic confinement, as in the experiment of G. Pagano et al. [Nat. Phys. 10, 198 (2014)], realizing a gas with tunable $\text{SU}(\ensuremath{\kappa})$ symmetry. We exploit an exact solution at infinite repulsion to show a direct correspondence between the value of the Tan's contact for each of the $\ensuremath{\kappa}$ components of the gas and the Young tableaux for the ${S}_{N}$ permutation symmetr…
The optical blocking filter for the ATHENA wide field imager: Ongoing activities towards the conceptual design
2015
ATHENA is the L2 mission selected by ESA to pursue the science theme "Hot and Energetic Universe" (launch scheduled in 2028). One of the key instruments of ATHENA is the Wide Field Imager (WFI) which will provide imaging in the 0.1-15 keV band over a 40'x40' large field of view, together with spectrally and time-resolved photon counting. The WFI camera, based on arrays of DEPFET active pixel sensors, is also sensitive to UV/Vis photons. Optically generated electron-hole pairs may degrade the spectral resolution as well as change the energy scale by introducing a signal offset. For this reason, the use of an X-ray transparent optical blocking filter is needed to allow the observation of all …