Search results for "Spectral"
showing 10 items of 3116 documents
Modeling the energy thermalization of X-ray photons in a microcalorimeter with superconducting absorber
2003
We present a modeling of the response of a microcalorimeter to the absorption of X-ray photons, based on the main microscopical processes responsible for the energy thermalization. In particular, we have modeled a microcalorimeter with superconducting tin absorber (350 micron x 350 micron x 7 micron) and neutron transmutation doped (NTD) germanium thermistor (75 micron x 50 micron x 150 micron). Such a detector, operated at 60 mK, is expected to achieve a spectral resolution as good as 1 eV FWHM in the soft X-ray energy range, based on the known sources of thermal and electronic noise. Nevertheless, the best spectral resolution measured in laboratory experimental tests is of about 5 eV FWHM…
Branching fraction measurements of arsenic 4p25s-4p3 transitions
2021
Abstract Transition lines of neutral arsenic atom (As I) have been observed in the spectra of stellar and sub-stellar objects. Accurate and reliable data of oscillator strengths of those transitions allow differentiating between different evolution models of those objects. We have measured branching fractions for As I (4p25s-4p3) transition lines in 180–310 nm spectral range with higher increased accuracy using light source powered by inductively coupled radio frequency plasma (RF-ICP) source – not earlier applied in studies of atomic arsenic. The measurements were performed for 7 excited states of As I and compared with data from the literature. We combined them with the selected lifetime …
Transverse velocity fluctuations of hot electrons in n-type GaAs in crossed electric and magnetic fields by Monte Carlo methods
2005
In this work we investigate some steady‐state stochastic properties of hot electron dynamics in bulk n‐type GaAs in the presence of crossed, static electric and magnetic fields. To this aim, a single particle, three valleys‐Monte Carlo method is adopted. In order to include the non‐parabolicity of valleys a local parabolic approximation is performed allowing us to get an analytic expression for k(t) during free flights. It is shown how the room temperature‐spectrum of longitudinal velocity fluctuations is markedly affected by the oscillations at the cyclotron frequency and is lowered or increased by the magnetic field depending on the considered frequency. On the contrary, the transverse sp…
Heating ofAl13−andAl14clusters
2001
Dynamical properties of ${\mathrm{Al}}_{13}^{\ensuremath{-}}$ and ${\mathrm{Al}}_{14}$ clusters at a high-temperature regime are studied using a density functional theory based first-principles simulations method. During the heating ${\mathrm{Al}}_{13}^{\ensuremath{-}}$ shows a significantly different behavior than ${\mathrm{Al}}_{14}$ due to its double-magic nature. We also demonstrate that it is hard to assign any distinct melting transition for the studied cluster sizes. For ${\mathrm{Al}}_{13}^{\ensuremath{-}}$ we observe a solidlike behavior well after the melting temperature of bulk aluminum. In contradiction with the rare gas clusters we notice that the outermost atom of icosahedral …
Solution of the fully-mixed-state problem: Direct deperturbation analysis of theAΣ+1–bΠ3complex in a NaCs dimer
2009
Laser-induced fluorescence (LIF) spectra $(4)\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}\ensuremath{\rightarrow}A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}$ and collisionally enhanced $A\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}--b\phantom{\rule{0.2em}{0ex}}^{3}\ensuremath{\Pi}\ensuremath{\rightarrow}X\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Sigma}^{+}$ LIF spectra measured by Fourier transform spectrometer with the resolution of $0.03--0.05\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ provided about 1160 term values of the $e$-symmetry rovibronic levels of the fully mixed $A\phantom{\rule{…
Atomic transition probabilities of F I spectral lines from3s−3pand3p−3dtransition arrays
1999
We have measured the relative transition probabilities of about $100 3s\ensuremath{-}3p$ and $3p\ensuremath{-}3d$ lines of neutral fluorine in the visible and near-infrared spectrum with a wall-stabilized high-current arc, which is operated under conditions very close to partial local thermodynamic equilibrium. The set of measured lines includes about 40 intersystem transitions. Our data have been placed on an absolute scale by normalizing several strong transitions to the results of the OPACITY Project calculations, which are expected to be quite accurate for such transitions. We estimate that the uncertainties of our absolute transition probability values are in the \ifmmode\pm\else\textp…
Line positions and intensities in the band of ethylene near : An experimental and theoretical study
2008
Abstract Recently, we built a tensorial formalism adapted to the spectroscopy of X2Y4 molecules. It is based on formalisms developed in Dijon for spherical-top molecules. This approach has the advantages to allow a systematic development of rovibrational interactions and to make global analyses easier to perform. We used this tool to carry out an analysis of the ν 12 band of 12C2H4 near 1450 cm - 1 , both in frequencies and intensities. 1240 line positions and 871 intensities, measured in a set of spectra recorded in Brussels, with global root mean square deviations of 1.6 × 10 - 4 cm - 1 and 1.88 % , respectively.
Probing Models of Extended Gravity using Gravity Probe B and LARES experiments
2014
We consider models of Extended Gravity and in particular, generic models containing scalar-tensor and higher-order curvature terms, as well as a model derived from noncommutative spectral geometry. Studying, in the weak-field approximation, the geodesic and Lense-Thirring processions, we impose constraints on the free parameters of such models by using the recent experimental results of the Gravity Probe B and LARES satellites.
High-precision ab initio calculations of the spectrum of Lr$^+$
2019
The planned measurement of optical resonances in singly-ionised lawrencium (Z = 103) requires accurate theoretical predictions to narrow the search window. We present high-precision, ab initio calculations of the electronic spectra of Lr$^+$ and its lighter homologue lutetium (Z = 71). We have employed the state-of-the-art relativistic Fock space coupled cluster approach and the AMBiT CI+MBPT code to calculate atomic energy levels, g-factors, and transition amplitudes and branching-ratios. Our calculations are in close agreement with experimentally measured energy levels and transition strengths for the homologue Lu$^+$ , and are well-converged for Lr$^+$ , where we expect a similar level o…
Further evidence for the presence of a neutron star in 4U 2206+54. INTEGRAL and VLA observations
2005
The majority of High Mass X-ray Binaries (HMXBs) behave as X-ray pulsars, revealing that they contain a magnetised neutron star. Among the four HMXBs not showing pulsations, and that do not show the characteristics of accreting black holes, there is the unusual HMXB 4U 2206+54. Here we present contemporaneous high-energy and radio observations of this system conducted with INTEGRAL and the VLA in order to unveil its nature. The high-energy spectra show clear indications of the presence of an absorption feature at ~32 keV. This is the third high-energy observatory which reveals marginal evidence of this feature, giving strong support to the existence of a cyclotron resonance scattering featu…