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King'ondu CK Iyer A Njagi EC Opembe N Genuino H Huang H Ristau RA Suib SL 《Journal of the American Chemical Society》2011,133(12):4186-4189
Short reaction times and morphology control in the synthesis of inorganic materials under nonthermal conditions remain a challenge. Herein we report a rapid, self-templating, and nonthermal method based on ultraviolet light to prepare metal oxide hierarchical structures. With this method, the morphology of the metal oxides was controlled readily without using templates. 相似文献
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Naftali A. Langberg Ramón V. León James Lynch Frank Proschan 《Probability Theory and Related Fields》1981,57(3):303-310
Summary Since the class of extended decreasing failure rate (EDFR) life distributions (i.e., distributions with support in [0, ]) is compact and convex, it follows from Choquet's Theorem that every EDFR life distribution can be represented as a mixture of extreme points of the EDFR class. We identify the extreme points of this class and of the standard class of decresing failure rate (DFR) life distributions. Further, we show that even though the convex class of DFR life distributions is not compact, every DFR life distribution can be represented as a mixture of extreme points of the DFR class.Research sponsored by the Air Force Office of Scientific Research, AFSC, USAF, under Grant AFOSR 78-3678.Research sponsored by the National Science Foundation MCS-7904698. 相似文献
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Cecil K. King’ondu Naftali Opembe Chun‐hu Chen Katana Ngala Hui Huang Aparna Iyer Hector F. Garcés Steven L. Suib 《Advanced functional materials》2011,21(2):312-323
Self‐assembled multidoped cryptomelane hollow microspheres with ultrafine particles in the size range of 4–6 nm, and with a very high surface area of 380 m2 g?1 have been synthesized. The particle size, morphology, and the surface area of these materials are readily controlled via multiple framework substitutions. The X‐ray diffraction and transmission electron microscopy (TEM) results indicate that the as‐synthesized multidoped OMS‐2 materials are pristine and crystalline, with no segregated metal oxide impurities. These results are corroborated by infrared (IR) and Raman spectroscopy data, which show no segregated amorphous and/or crystalline metal impurities. The field‐emission scanning electron microscopy (FESEM) studies confirm the homogeneous morphology consisting of microspheres that are hollow and constructed by the self‐assembly of pseudo‐flakes, whereas energy‐dispersive X‐ray (EDX) analyses imply that all four metal cations are incorporated into the OMS‐2 structure. On the other hand, thermogravimetric analyses (TGA) and differential scanning calorimetry (DSC) demonstrate that the as‐synthesized multidoped OMS‐2 hollow microspheres are more thermally unstable than their single‐doped and undoped counterparts. However, the in‐situ XRD studies show that the cryptomelane phase of the multidoped OMS‐2 hollow microspheres is stable up to about 450°C in air. The catalytic activity of these microspheres towards the oxidation of diphenylmethanol is excellent compared to that of undoped OMS‐2 materials. 相似文献
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Ephraim Vunain Naftali N. Opembe Kalala Jalama Ajay K. Mishra Reinout Meijboom 《Journal of Thermal Analysis and Calorimetry》2014,115(2):1487-1496
In the present work, we report on the thermal stability of NH2-MCM-41 hybrid material under different atmospheres (nitrogen and air). The thermal stability of this hybrid material is very important because of its common use in catalysis, adsorption, biomedical and biotechnological applications, based on mesoporous and aminopropyl functionalities. Samples were prepared by one pot co-condensation method with different loadings of 3-aminopropyltriethoxysilane (APTES). The thermal stability of hybrid samples (NH2-MCM-41) heat treated in nitrogen and air at 30–800 °C has been investigated. Samples were synthesized under basic media in the presence of cetyltrimethylammonium bromide (CTABr) as structure-directing agent, tetraethyl orthosilicate as silica source, and APTES as functionalizing agent with molar composition of 0.055 CTABr:045 SiO2:0.054 APTES:5.32 NH4OH:14.99 H2O at 50 °C for 24 h at pH 12.4. The obtained hybrid materials have been characterized by thermogravimetric analysis (TG), derivative thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, Fourier-transform infrared spectroscopy, transmission electron microscopy, and surface area determination by the BET method. Based on TG measurements of the treated samples, it was found out that the thermal stability varied greatly in different atmospheres. 相似文献
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We propose a modified version of the Balitsky–Kovchegov (BK) evolution equation, which includes the main NLO corrections. We use the result that the main NLO corrections to the BFKL kernel are the LO DGLAP corrections. We present a numerical solution of the modified non-linear equation, and compare with the solution of the unmodified BK equation. We show that the saturation momentum has a sharp increase in the LHC energy range. Our numerical solution indicates that the influence of the preasymptotic corrections, related to the full anomalous dimensions of the DGLAP equation, are rather large. These corrections moderate the energy behavior of the amplitude, as well as the value of the saturation scale. All our calculations are made with a fixed value of S. 相似文献
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Naftali Kravitsky 《Integral Equations and Operator Theory》1980,3(1):97-124
The notion of the discriminant function of two commuting nonselfadjoint operators A1 and A2 in a Hilbert space H was defined by M.S. Livic in a recent paper [5].In the present paper we study the discriminant function for two special cases of commuting operators. In one case A1 and A2 are rational functions of one and the same operator A in H. In the second case A1 and A2 are Kronecker products of the form A I and I B, where I is the identity operator.As an auxiliary result a relation between the Sylvester and Bezoutian matrices of two polynomials is derived. 相似文献
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Analytic expressions for the first order bias and second order covariance of a general maximum likelihood estimate (MLE) are presented. These expressions are used to determine general analytic conditions on sample size, or signal-to-noise ratio (SNR), that are necessary for a MLE to become asymptotically unbiased and attain minimum variance as expressed by the Cramer-Rao lower bound (CRLB). The expressions are then evaluated for multivariate Gaussian data. The results can be used to determine asymptotic biases. variances, and conditions for estimator optimality in a wide range of inverse problems encountered in ocean acoustics and many other disciplines. The results are then applied to rigorously determine conditions on SNR necessary for the MLE to become unbiased and attain minimum variance in the classical active sonar and radar time-delay and Doppler-shift estimation problems. The time-delay MLE is the time lag at the peak value of a matched filter output. It is shown that the matched filter estimate attains the CRLB for the signal's position when the SNR is much larger than the kurtosis of the expected signal's energy spectrum. The Doppler-shift MLE exhibits dual behavior for narrow band analytic signals. In a companion paper, the general theory presented here is applied to the problem of estimating the range and depth of an acoustic source submerged in an ocean waveguide. 相似文献
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Arnon Neufeld Naftali Landsberg Amir Boag 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,200(1):49-55
A method for enhancing the signal to noise ratio (SNR) in NMR volume coils is described. By introducing inserts made of low-loss, high dielectric constant material into specific locations in the coil, the SNR can often be enhanced by up to 20%, while B1 homogeneity is hardly affected. A model for predicting the limit of the SNR improvement is also presented. The model accurately predicts the SNR gain obtained in both numerical simulations and experiment. An experiment was conducted on a mini-MRI system. Experimental results are in very good agreement with the simulations in regard to both SNR improvement and B1 enhancement in transmission. Inserts made of ultra high dielectric constant materials can be as thin as few millimeters, thus, conveniently fitting into existing coil-sample gaps in volume coils. 相似文献