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161.
Fernandes AC Fernandes R Romao CC Royo B 《Chemical communications (Cambridge, England)》2005,(2):213-214
The high valent molybdenum-dioxo complex [MoO2Cl2] catalyzes the addition of dimethylphenylsilane to aldehydes and ketones to afford the corresponding dimethylphenylsilyl ethers in quantitative yield. 相似文献
162.
R S Tyler E J Wood M Fernandes 《The Journal of the Acoustical Society of America》1983,74(4):1190-1199
Frequency resolution and three tasks of frequency discrimination were measured at 500 and 4000 Hz in 12 normal and 12 hearing-impaired listeners. A three-interval, two-alternative forced-choice procedure was used. Frequency resolution was measured with an abbreviated psychoacoustical tuning curve. Frequency discrimination was measured for (1) a fixed-frequency standard and target, (2) a fixed-frequency standard and a frequency-transition target, and (3) frequency-transition standard and a frequency-transition target. The 50-ms frequency transitions had the same final frequency as the standards, but the initial frequency was lowered to obtain about 79% discrimination performance. There was a strong relationship between poor frequency resolution and elevated pure-tone thresholds, but only a very weak relationship between poor frequency discrimination and elevated pure-tone thresholds. Several hearing-impaired listeners had normal discrimination performance together with pure-tone thresholds of 80-90 dB HL. A slight correlation was found between word recognition and frequency discrimination, but a detailed comparison of the phonetic errors and either the frequency-discrimination or frequency-resolution tasks failed to suggest any consistent interdependencies. These results are consistent with previous work that has suggested that frequency resolution and frequency discrimination are independent processes. 相似文献
163.
In flow injection analysis, several plugs can be injected simultaneously into the same carrier system, in order to achieve overlapped zones. The potentialities of such sequential injections are studied in model systems with spectrophotometric detection; the procedure is shown to give better precision than the use of concentration gradients. The method is used with atomic absorption spectrometry to allow the determination of a wide range of manganese contents in rocks, and to facilitate the use of standard additions for the determination of copper in ethanol. 相似文献
164.
Fernandes RM VanBebber LH Bhattacharya S Chandra P Keppens V Mandrus D McGuire MA Sales BC Sefat AS Schmalian J 《Physical review letters》2010,105(15):157003
We demonstrate that the changes in the elastic properties of the FeAs systems, as seen in our resonant ultrasound spectroscopy data, can be naturally understood in terms of fluctuations of emerging nematic degrees of freedom. Both the softening of the lattice in the normal, tetragonal phase as well as its hardening in the superconducting phase are consistently described by our model. Our results confirm the view that structural order is induced by magnetic fluctuations. 相似文献
165.
Jonatan Floriano da Silva Henrique Fernandes de Lima Marco Antonio Lázaro Velásquez 《Annali dell'Universita di Ferrara》2018,64(2):427-436
In this paper we provide a characterization for stable hypersurfaces with constant anisotropic mean curvature immersed in the Euclidean space \(\mathbb {R}^{n+1}\) through the analysis of the first eigenvalue of the anisotropic Laplacian operator. 相似文献
166.
José R. Correa Cristina G. Fernandes Yoshiko Wakabayashi 《Mathematical Programming》2010,124(1-2):255-269
In the late seventies, Megiddo proposed a way to use an algorithm for the problem of minimizing a linear function a 0 + a 1 x 1 + . . . + a n x n subject to certain constraints to solve the problem of minimizing a rational function of the form (a 0 + a 1 x 1 + . . . + a n x n )/(b 0 + b 1 x 1 + . . . + b n x n ) subject to the same set of constraints, assuming that the denominator is always positive. Using a rather strong assumption, Hashizume et al. extended Megiddo’s result to include approximation algorithms. Their assumption essentially asks for the existence of good approximation algorithms for optimization problems with possibly negative coefficients in the (linear) objective function, which is rather unusual for most combinatorial problems. In this paper, we present an alternative extension of Megiddo’s result for approximations that avoids this issue and applies to a large class of optimization problems. Specifically, we show that, if there is an α-approximation for the problem of minimizing a nonnegative linear function subject to constraints satisfying a certain increasing property then there is an α-approximation (1/α-approximation) for the problem of minimizing (maximizing) a nonnegative rational function subject to the same constraints. Our framework applies to covering problems and network design problems, among others. 相似文献
167.
We show that if a semigroup T divides a semigroup of full order preserving transformations of a finite chain, then so does any semidirect product S⋊T where S is a finite semilattice whose natural order makes S a chain. 相似文献
168.
Albert E. Fernandes Muritiba Manuel Iori Silvano Martello Marcos J. Negreiros Gomes 《Annals of Operations Research》2010,179(1):5-14
Given a non-convex two-dimensional area and identical rectangular stands, we consider the problem of placing the maximum number
of stands in the area, by satisfying a number of operational constraints. We present linear programming models and show the
total unimodularity of the matrices associated with their constraint sets. We then give computational results obtained by
applying the models to the real-world case of the Beira Mar handcraft fair of Fortaleza (Brazil). 相似文献
169.
L. Jakubowski V.V. Plyusnin K. Malinowski M.J. Sadowski J. Zebrowski M. Rabiński H. Fernandes C. Silva P. Duarte M.J. Jakubowski 《等离子体物理论文集》2013,53(9):615-622
The paper reports on experimental studies of electron beams in the ISTTOK tokamak, those were performed by means of an improved four‐channel detector. The Cherenkov‐type detector measuring head was equipped with four radiators made of two types of alumina‐nitrate (AlN) poly‐crystals: machinable and translucent ones, both of 10 mm in diameter and 2.5 mm in thickness. The movable support that enabled the whole detectors to be placed inside the tokamak vacuum chamber, at chosen positions along the ISTTOK minor radius. Since the electron energy distribution is one of the most important characteristics of tokamak plasmas, the main aim of the study was to perform estimations of an energy spectrum of the recorded electrons. For this purpose the radiators were coated with molybdenum (Mo) layers of different thickness. The technique based on the use of Cherenkov‐type detectors enabled the detection of fast electrons (of energy above 66 keV) and determination of their spatial and temporal characteristics in the ISTTOK experiment. Measurements of hard X‐rays (HXR), which were emitted during ISTTOK discharges, have also been performed. Particular attention was paid to the correlation measurements of HXR pulses with run‐away electron beams. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
170.
Rosário Fernandes 《Linear and Multilinear Algebra》2013,61(8):977-991
We study the behaviour of the covering number of an element of a family of vectors under small perturbations. We apply this study to obtain results on the pairs of matrices that have the same immanent. 相似文献