Search results for "SPECTRA"
showing 10 items of 3542 documents
Decompositions and asymptotic limit for bicontractions
2012
The asymptotic limit of a bicontraction T (that is, a pair of commuting contractions) on a Hilbert space H is used to describe a Nagy–Foias–Langer type decomposition of T. This decomposition is refined in the case when the asymptotic limit of T is an orthogonal projection. The case of a bicontraction T consisting of hyponormal (even quasinormal) contractions is also considered, where we have ST∗=S2T∗.
SPECTRAL INVARIANCE FOR CERTAIN ALGEBRAS OF PSEUDODIFFERENTIAL OPERATORS
2001
We construct algebras of pseudodifferential operators on a continuous family groupoid G that are closed under holomorphic functional calculus, contain the algebra of all pseudodifferential operators of order 0 on G as a dense subalgebra, and reflect the smooth structure of the groupoid G, when G is smooth. As an application, we get a better understanding on the structure of inverses of elliptic pseudodifferential operators on classes of non-compact manifolds. For the construction of these algebras closed under holomorphic functional calculus, we develop three methods: one using two-sided semi-ideals, one using commutators, and one based on Schwartz spaces on the groupoid.
A coupled-cluster study of lanthanum trihalide structures
2002
Coupled-cluster calculations were carried at the CCSD(T)-level in order to determine the structures and vibrational spectra of the lanthanum trihalides LaF3 and LaCl3. Two different approaches were employed to describe scalar relativistic effects; the quasi-relativistic Effective Core Potential approach and the all-electron Douglas–Kroll approach. We find LaF3 to be of pyramidal structure and LaCl3 to be planar. The obtained vibrational frequencies accord well with experimental measurements except for the ν2 mode. This disagreement is attributed to the intrinsic uncertainty of harmonic frequencies of this fluxional mode as extracted from spectra which were obtained at high temperature and f…
Stationarity Test for Wireless Communication Channels
2009
In this article, we propose a new test to determine the intervals of stationarity for wireless communication channels. The intervals of stationarity are identified by comparing the delay power spectral density (PSD) estimated at different time instances. The performance of the proposed stationarity test has been evaluated based on the synthetic data generated using a channel simulator. The analysis of the stationarity intervals for two radio communication channels measured in different propagation scenarios reveals that the number and the length of the stationarity intervals decrease as the dimensions of the channel matrix increase.
On the nature of slow β-relaxation in supercooled liquids
2000
We propose a model for reorientational motions of molecules associated with secondary beta-relaxation in supercooled liquids. The secondary relaxation is attributed to relaxation within a given local minimum, while the primary relaxation is attributed to transitions between distinct free-energy minima. We find that (i) at the temperature where the peak frequency of the extrapolated beta-relaxation intersects the alpha-relaxation, the actual and the extrapolated spectra differ in their time constants by approximately one decade; (ii) there is no clear division between the imaginary part of the dielectric susceptibility for the alpha- and the beta-relaxation for temperatures larger than 1.1 T…
Mass spectra of chlorinated esters: 2—Methyl mono- and dichlorobutanoates
1982
The mass spectral fragmentations of methyl mono- and dichlorobutanates have been studied. Deutrium labelling and metastable ion analysis were used to elucidate the fragmentation mechanisms. The molecular ion peaks of the esters are weak and show only in the spectra of the monochloro isomers. A McLafferty rearrangement gives the base peaks in the spectra of methyl 2-chloro-, 4-chloro- and 4,4-dichlorobutanoate; α-cleavage, [COOCH3]+, in methyl 2,2- and 2,4-dichlorobutanoate; [MCl]+, in methyl 3-chlorobutanoate; [MClHCl]+, in methyl 3,4-dichlorobutanoate; [MClCH2CO]+, in methyl 3,3-dichlorobutanoate and [MClCOOCH3]+˙, in methyl erythro- and threo-2,3-dichlorobutanoate. The mass spectra of the…
Use of Guided Regularized Random Forest for Biophysical Parameter Retrieval
2018
This paper introduces a feature selection method based on random forest -the Guided Regularized Random Forest (GRRF)- which can be used in classification and regression tasks. The method is based on the regularization of the information gain in the random forest nodes to obtain a subset of relevant and non-redundant features. The proposed method is used as a preliminary step In the process of retrieving biophysical parameters from a hyperspectral image. Preliminary experiments show that we can reduce the RMSE of the retrievals by around 7% for the Leaf Area Index and around 8% for the fraction of vegetation cover when compared to the results using random forest features.
Demultiplexing Visible and Near-Infrared Information in Single-Sensor Multispectral Imaging
2016
In this paper, we study a single-sensor imaging system that uses a multispectral filter array to spectrally sample the scene. Our system captures information in both visible and near-infrared bands of the electromagnetic spectrum. Due to manufacturing limitations, the visible filters in this system also transmit the NIR radiation. Similarly, visible light is transmitted by the NIR filter, leading to inaccurate mixed spectral measurements. We present an algorithm that resolves this issue by separating NIR and visible information. Our method achieves this goal by exploiting the correlation of multispectral images in both spatial and spectral domains. Simulation results show that the mean squa…
Performance of TES method over urban areas at a high spatial resolution scale
2013
The Temperature and Emissivity Separation (TES) algorithm is used to retrieve the LSE and LST values from hyperspectral sensors. In this work we analyse the performance of this methodology over urban areas. Three different sources of error in the processing chain of the remote sensing imagery are detected: the algorithm itself, the atmospheric correction and the 3D structure of the urban scenes. The TITAN tool is used to model all the radiative components of the signal registered by a sensor. Results show that: first, the TES algorithm used reproduces the LSE (LST) of urban materials within an RMSE of 0.017 (0.9 K). Second, 20 % of uncertainty in the water vapour content of the total atmosp…
A low cost and easy re-configurable instrument for power quality survey
2004
In this document the development of a low cost and user friendly PC-based instrument for power quality measurement is proposed, according to IEC 61000-4-7 and standard IEC 61000-4-30. It is an easily re-configurable instrument able to measure harmonics, interharmonics and amplitude disturbances and supply unbalance. In order to verify its accuracy, the instrument has been tested according standard test procedures, by means of a built-up calibration test bench.