Search results for "Instrumentation"
showing 10 items of 4914 documents
Visco-elastic behavior through fractional calculus: an easier method for best fitting experimental results
2011
In capturing visco-elastic behavior, experimental tests play a fundamental rule, since they allow to build up theoretical constitutive laws very useful for simulating their own behavior. The main challenge is representing the visco-elastic materials through simple models, in order to spread their use. However, the wide used models for capturing both relaxation and creep tests are combinations of simple models as Maxwell and/or Kelvin, that depend on several parameters for fitting both creep and relaxation tests. This paper, following Nutting and Gemant idea of fitting experimental data through a power law function, aims at stressing the validity of fractional model. In fact, as soon as rela…
Signature of cluster isomers in time-resolved photodissociation experiments
2004
Abstract The unrecognized presence of structure isomers in mass-selected cluster ensembles may obstruct investigations of the systems’ intrinsic properties, since isomers differ not only in geometry, but also in other important properties. By the same token isomers are very interesting objects in the detailed study of atomic clusters. In the present work, different scenarios of isomeric coexistence are presented. They vary in the relative values of the interconversion barrier and the dissociation energies. For some idealized cases the possibility of a distinction of isomers by photodissociation experiments is discussed. In favorable situations isomeric structures may even be selected.
Metastable ion studies. 4—mass spectral fragmentation and isomerization in the esters of chlorinated propenoic acids
1983
Metastable peaks have been used to study the fragmentation pathways of the methyl and trideuteriomethyl chloropropenoates and chloromethyl propenoate. The molecular ion peaks of the unsaturated esters are more intense than those of the saturated esters, α-Cleavage, [MOCH3]+, produces the base peak in almost all compounds, the relative abundances of the additional peaks being low for chloromethyl propenoate. The losses of H2O, CH3. and COOH. indicate the isomerization of some ionized chloro esters to the chlorinated 2-butenoic acid molecular ions. An intense loss of H2O observed for methyl 2-chloropropenoate indicates its most facile isomerization, [ester]+˙ → [acid]+˙, whereas the isomeriza…
Correction of the deterministic part of space–charge interaction in momentum microscopy of charged particles
2015
Abstract Ultrahigh spectral brightness femtosecond XUV and X-ray sources like free electron lasers (FEL) and table-top high harmonics sources (HHG) offer fascinating experimental possibilities for analysis of transient states and ultrafast electron dynamics. For electron spectroscopy experiments using illumination from such sources, the ultrashort high-charge electron bunches experience strong space–charge interactions. The Coulomb interactions between emitted electrons results in large energy shifts and severe broadening of photoemission signals. We propose a method for a substantial reduction of the effect by exploiting the deterministic nature of space–charge interaction. The interaction…
Drift velocity of free electrons in liquid argon
1999
Abstract A measurement of the drift velocity of free electrons in liquid argon has been performed. Free electrons have been produced by photoelectric effect using laser light in a so-called “laser chamber”. The results on the drift velocity vd are given as a function of the electric field strength in the range 0.5 kV / cm ⩽| E |⩽12.6 kV / cm and the temperature in the range 87 K ⩽T⩽94 K . A global parametrization of v d (| E |,T) has been fitted to the data. A temperature dependence of the electron drift velocity is observed, with a mean value of Δ v d /( Δ T v d )=(−1.72±0.08)%/ K in the range of 87–94 K.
Controlling laser assisted radiative recombination with few-cycle laser pulses
2006
We report on the radiative recombination of a free electron with a hydrogenic ion in the presence of a few-cycle pulses. It has been shown that the main features of the emission spectra may be described in the framework of a semiclassical model in which the recombination is viewed as a two-step process. The spectra width of the emitted photon energy is practically confined in a range of values in which the emission is classically allowed. Moreover, it has been found that spectra width can be controlled by varying the carrier envelope phase and/or the pulse peak intensity.
Improved resolution power of electrophoretic fractionation of DNA using a voltage gradient up and down application
2004
The improved resolution power of electrophoretic fractionation of DNA in a wide range of molecular masses is demonstrated using an "up and down" application of voltage gradient gel electrophoresis (VGGE). This application also allows separation of different DNA fragments which are poorly fractionated in conventional electrophoresis.
Thermally Tunable Surface Acoustic Wave Cavities
2020
We experimentally demonstrate the dynamical tuning of the acoustic field in a surface acoustic wave (SAW) cavity defined by a periodic arrangement of metal stripes on LiNbO3 substrate. Applying a dc voltage to the ends of the metal grid results in a temperature rise due to resistive heating that changes the frequency response of the device up to 0.3%, which can be used to control the acoustic transmission through the structure. The timescale of the switching is demonstrated to be of about 200 ms. In addition, we have also performed finite-element simulations of the transmission spectrum of a model system, which exhibits a temperature dependence consistent with the experimental data. The adv…
Partial Discharge Detection Using a Spherical Electromagnetic Sensor
2019
The presence of a partial discharge phenomenon in an electrical apparatus is a warning signal that could determine the failure of the insulation system, terminating the service of the apparatus and/or the network. In this paper, an innovative partial discharge (PD) measurement instrument based on an antenna sensor is presented and analyzed. Being non-intrusive is one of the most relevant features of the sensor. The frequency response of the antenna sensor and the features to recognize different PD sources and automatically synchronize them with the supply voltage are described and discussed in details. The results show the performance of the instrument can make a fast and correct diagnosis …
Improvement of Hall Effect Current Transducer Metrological Performances in the Presence of Harmonic Distortion
2010
The performance of Hall effect current transducers (HECTs), under distorted waveform conditions, is usually characterized by means of a frequency response test. In this paper, it was investigated if frequency response is able to correctly evaluate the ratio and the phase errors under distorted conditions. Two HECTs, with the accuracy class level of 1% and 0.5%, respectively, were experimentally characterized under two conditions: 1) sinusoidal excitation with frequencies ranging from 50 to 750 Hz, which is the well-known frequency response test, and 2) nonsinusoidal excitation using fundamental frequency and one harmonic with adjusted amplitude and phase shift. It was found that ratio and p…