Search results for "Single"
showing 10 items of 4920 documents
Time-energy filtering of single electrons in ballistic waveguides
2019
Characterizing distinct electron wave packets is a basic task for solid-state electron quantum optics with applications in quantum metrology and sensing. A important circuit element for this task is a non-stationary potential barrier than enables backscattering of chiral particles depending on their energy and time of arrival. Here we solve the quantum mechanical problem of single-particle scattering by a ballistic constriction in an fully depleted quantum Hall system under spatially uniform but time-dependent electrostatic potential modulation. The result describes electrons distributed in time-energy space according to a modified Wigner quasiprobability distribution and scattered with an …
Further Comments on a Vanishing Singlet Axial Vector Charge
1998
The recent suggestion of a vanishing flavor-singlet axial charge of nucleon due to a nontrivial vacuum structure is further amplified. A perturbative QCD discussion, applicable for the heavy quark contributions, relates it to the physics of the decoupling theorem. It is also shown that $g_{A}^{0}\simeq 0$ leads to a negative $\eta'$-meson-quark coupling, which has been found to be compatible with the chiral quark model phenomenology.
Quark-mass dependence of baryon resonances
2004
We study the quark-mass dependence of J^P = \frac12^- s-wave and J^P = \frac32^- d-wave baryon resonances. Parameter-free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with m_\pi =m_K \simeq 500 MeV the s-wave resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. Similarly the d-wave resonances turn into bound states forming an octet and a decuplet in this limit. A contrasted result is obtained in the 'light' SU(3) limit with m_\pi =m_K \simeq 140 MeV for which no resonances exist.
Finite Size Effects on the Optical Transitions in Quantum Rings under a Magnetic Field
2006
We present a theoretical study of the energy spectrum of single electron and hole states in quantum dots of annular geometry under a high magnetic field along the ring axis in the frame of uncorrelated electron-hole theory. We predict the periodic disappearance of the optical emission of the electron-hole pair as the magnetic field increases, as a consequence of the finite height of the barriers. The model has been applied to semiconductor rings of various internal and external radii, giving as limiting cases the disk and antidot.
Validation of the Monte Carlo Simulation of a Siemens Biograph mCT PET
2016
Geant4 Application for Tomography Emission (GATE) is a simulation platform based on GEANT4. It is designed to perform numerical simulations in medical imaging and radiotherapy. It is also used to simulate Emission Tomography (Positron Emission Tomography, PET and Single Photon Emission Computed Tomography, SPECT), Computed Tomography (CT) and Radiotherapy experiments. The purpose of this study is to validate a GATE model of the commercial PET/CT Siemens Biograph, the latest acquisition of the Clinical Hospital of Salamanca. The geometry of the system has been implemented in GATE, including the detector ring, the crystal blocks, the PMTs etc. Radionuclides for all measurements shall be \(^{1…
J-File Sum Rule Tests for the 3s-3p Transition Array in Singly Ionized Nitrogen - Comparison of Measured and Calculated Data
2005
1. IntroductionIn recent years quite a large number of transition probabilities of spectrallines of light elements have been determined including data for singly ionizednitrogen [1{7]. Some of these experimental as well as theoretical studies providealso data for a few triplet{singlet intersystem transitions, being very interestinge.g. from astrophysical point of view. The energy level system of NII has adistinguished feature compared to the neighboring two members of the carbonisoelectronic sequence (CI, OIII) | the energy difierence between the excitedterms 3
Diindenoanthracene Diradicaloids Enable Rational, Incremental Tuning of Their Singlet-Triplet Energy Gaps
2020
Summary A fundamental understanding of the inherent electronic and magnetic properties of open-shell diradicaloids is essential so that these properties can be modified to create molecules that meet the potential needs of industry. However, there have been very few attempts to date to systematically accomplish this in diradicaloid compounds. Here, we present the synthetic, spectroscopic, and computational investigation of a series of molecules based on the diindeno[1,2-b:1′,2′-g]anthracene framework. Calculations suggest that by altering the transfer integral term, tab, we are able to manipulate the diradical character and, thus, ΔEST within this series of molecules. Experimentally determin…
gFactor of HydrogenlikeSi13+28
2011
We determined the experimental value of the $g$ factor of the electron bound in hydrogenlike $^{28}\mathrm{Si}^{13+}$ by using a single ion confined in a cylindrical Penning trap. From the ratio of the ion's cyclotron frequency and the induced spin flip frequency, we obtain $g=1.995\text{ }348\text{ }958\text{ }7(5)(3)(8)$. It is in excellent agreement with the state-of-the-art theoretical value of 1.995 348 958 0(17), which includes QED contributions up to the two-loop level of the order of $(Z\ensuremath{\alpha}{)}^{2}$ and $(Z\ensuremath{\alpha}{)}^{4}$ and represents a stringent test of bound-state quantum electrodynamics calculations.
First coincidences in pre-clinical Compton camera prototype for medical imaging
2003
Abstract Compton collimated imaging may improve the detection of gamma rays emitted by radioisotopes used in single photon emission computed tomography (SPECT). We present a crude prototype consisting of a single 500 μm thick, 256 pad silicon detector with pad size of 1.4×1.4 mm 2 , combined with a 15×15×1 cm 3 NaI scintillator crystal coupled to a set of 20 photo multipliers. Emphasis is placed on the performance of the silicon detector and the associated read-out electronics, which has so far proved to be the most challenging part of the set-up. Results were obtained using the VATAGP3, 128 channel low-noise self-triggering ASIC as the silicon detector's front-end. The noise distribution (…
Singlet ground state magnetism: III. magnetic excitons in antiferromagnetic TbP
1981
The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined.