Search results for "spectrum"
showing 10 items of 2043 documents
New Quasi-Atomic Nanoheterostructures: Superatoms and Excitonic Quasi-Molecules
2016
In this review, the state-of-the-art of research of artificial atoms (superatoms or quasi-atomic nanoheterostructures) and more complex nanostructures based on them—synthetic molecules is discussed, a new model of an artificial atom, which satisfactorily explains its electronic properties, is proposed, and the prospects for development of the new scientific trend are mentioned. В этом обзоре обсуждается современное состояние исследований искусственных атомов (сверхатомов или квазиатомных наногетероструктур) и более сложных наноструктур на их основе — синтетических молекул, предложена новая модель искусственного атома, удовлетворительно объясняющая его электронные свойства, а также указаны п…
Analysis of Rauwolfia Alkaloids Employing Capillary Electrophoresis-Mass Spectrometry
1997
Abstract Capillary electrophoresis-mass spectrometry (CE-MS) was applied to analyse extracts of roots and cell suspension cultures from Rauwolfia serpentina. Most of the alkaloids known to be present in the respective plant material have been resolved via CE and assigned according to their electrospray mass spectra.
Application of 252Cf plasma desorption mass spectrometry in dental research
1993
Abstract Topically applied fluorides introduced in dental hygiene products elevate the concentration levels of fluoride in oral fluids and thus also affect chemical reactions of enamel de- and remineralisation. The chemical reactions on the surface of tooth enamel still are a subject of controversy. Here 252 Cf-plasma desorption mass spectrometry and argon ion etching are used to analyse the molecular structure of the upper layes of enamel. The mass spectrum of untreated enamel is characterised by a series of cluster ions containing phosphate. It is evident that under certain conditions the molecular structure of the surface enamel is completely transformed by treatment with fluorides. The …
Spectrum sensing challenges: blind sensing and sensing optimization
2016
By any measure, wireless communications is one of the most evolving fields in engineering. This, in return, has imposed many challenges, especially in handling the hunger for higher data rates in the next generation wireless networks. Among these challenges is how to provide the needed resources in terms of the electromagnetic radio spectrum for these networks. In this regard, cognitive radio (CR) based on dynamic spectrum access (DSA) has been attracting huge attention as a promising solution for more efficient utilization of the available radio spectrum. DSA is based on finding and opportunistically accessing the free-of-use portions of spectrum. To facilitate DSA, spectrum sensing can be…
Stochastic seismic analysis of MDOF structures with nonlinear viscous dampers
2009
Fluid damper devices in civil structures such as buildings or bridges are commonly used as energy absorbers for seismic protection. The problem in the response analysis of structures with filled dampers mainly consists in the fact that, due to the strongly nonlinear behavior of such equipments, the response spectrum (RS) technique fails. In this paper by using the concept of power spectral density function compatible with the elastic RS and the statistical linearization technique, the equivalent damping ratio is obtained. It is shown that once the system is linearized, results obtained by Monte Carlo simulation and those obtained by stochastic analysis are in good agreement. Copyright © 200…
A PC-based low cost impedance and gain-phase analyzer
2008
Abstract In this paper, we present a practical and inexpensive impedance/gain-phase analyzer (IGPA), which is very useful in the design of electronic circuits. This instrument allows the Bode diagram of any network or electronic circuit with an input and an output to be obtained, even though this implementation was not previously known. It can also obtain the module and phase diagrams of any impedance separately. The device under test (DUT) is connected to a personal computer (PC) via the parallel port by means of an electronic circuit implemented for this purpose. The results are shown on the screen of the PC and can be accessible for use in any further operation. The instrument operates i…
Narrowband digital filtering with random frequency hopping spread spectrum
2014
International audience; In digital signal filtering, channels with narrow bandwidth need high order digital filter to be selected without introducing modulation errors. If a carrier randomly switches from a channel to another as in military applications, or some civilian communication standards, it is necessary to detect and estimate these jumps before transposing and analyzing signals in the baseband. This paper presents a real time solution to filter narrow band signals with random frequency hopping spread spectrum. The proposed method is based on three steps. Firstly, the detection of Signal Frequency Hopping (SFH) using the Fast Fourier Transform (FFT), an algorithm to estimate the Domi…
Combination of modal responses consistent with seismic input representation
2004
The well-known modal superposition method for the evaluation of seismic response by the complete quadratic modal combination rule (CQC) is revisited. The most widely used version of the CQC rule utilizes correlation coefficients derived for white-noise excitation and neglects the influence of peak factor variation on the response. Here a simplified procedure for evaluation of correlation coefficients and peak factors consistent with the power spectral density of seismic excitation is proposed. The procedure is based on an approximate analytic expression for direct evaluation of the power spectral density of the excitation consistent with any prefixed response spectrum, and the evaluation of…
A Systematic Review on the Impact of the Social Confinement on People with Autism Spectrum Disorder and Their Caregivers during the COVID-19 Pandemic.
2021
The COVID-19 pandemic had imposed a variety of containment measures on the general population for prolonged periods. Confinement has had, and still has, social, economic, educational, health, and psychological consequences on the entire population. Objective: In this article, a systematic search has been performed based on studies carried out since the beginning of the pandemic, regarding the impact of these containment measures on the autism spectrum disorder (ASD) population and their caregivers. Method: We consulted six databases (i.e., PubMed, Medline, Embase, Scopus, Web of Science, and Science Direct) and selected ten studies that met the inclusion criteria. The chosen studies have be…
Model compounds of spent bleach liquor: 2,3,6-trichloro-p-cymenene and 2,3,5-trichloro-p-cymenene
1991
Abstract 2,3,6-Trichloro-p-cymene (1) was synthesized by chlorination of p-cymene. A reaction mixture was distilled in a Fischer-Spaltrohr distilling apparatus. One fraction contained small quantities of chlorinated cymenenes (two isomers) which were concentrated by preparative gas chromatography. Their FTIR and mass spectra were recorded. In earlier paper the structures of 2,3,6-trichloro-p-cymenene were verified by means of its coupled 13C NMR and mass spectra. In the present work the mass and FTIR spectral data of 2,3,5-trichloro-p-cymenene and 2,3,6-trichloro-p-cymenene are published.