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991.
Diana Q. L. Oliveira Luiz C. A. Oliveira Enver Murad José D. Fabris Adilson C. Silva Lucas Morais de Menezes 《Hyperfine Interactions》2010,195(1-3):27-34
Heterogeneous Fenton or Fenton-like reagents consist of a mixture of an iron-containing solid matrix and a liquid medium with H2O2. The Fenton system is based on the reaction between Fe2?+? and H2O2 to produce highly reactive intermediate hydroxyl radicals (???OH), which are able to oxidize organic contaminants, whereas the Fenton-like reaction is based on the reaction between Fe3?+? and H2O2. These heterogeneous systems offer several advantages over their homogeneous counterparts, such as no sludge formation, operation at near-neutral pH and the possibility of recycling the iron promoter. Some doping transition cations in the iron oxide structure are believed to enhance the catalytic efficiency for the oxidation of organic substrates in water. In this work, goethites synthesized in presence of niobium served as precursors for the preparation of magnetites (niobian magnetites) via chemical reduction with hydrogen at 400°C. These materials were used as Fenton-like catalysts. Both groups of (Nb, Fe)-oxide samples were characterized by 57Fe Mössbauer spectroscopy at 298 K. The results show that increasing niobium contents raise the catalytic potential for decomposition of methylene blue, which was, in this work, used as a model molecule for organic substrates in water. 相似文献
992.
993.
H. Spiering V. Ksenofontov O. Leupold J. Kusz L. Deák Z. Németh C. Bogdán L. Bottyán D. L. Nagy 《Hyperfine Interactions》2016,237(1):58
The effect of selfabsorption in Mössbauer sources is studied in detail. Spectra were measured using an old 57 C o/R h source of 74M B q activity with an original activity of ca. 3.7G B q and a 0.15G B q 57 C o/α ? F e source magnetized by an in-plane magnetic field of 0.2 T. The 57 C o/α ? F e source of a thickness of 25 μ was used both from the active and the inactive side giving cause to very different selfabsorption effects. The absorber was a single crystal of ferrous ammonium sulphate hexahydrate (FAS). Its absorption properties were taken over from a detailed study (Bull et al., Hyperfine Interact. 94(1–3), 1; Spiering et al. 2). FAS (space group P21/c) crystallizes as flat plates containing the (\(\overline {2}\)01) plane. The γ-direction was orthogonal to the crystal plate. The 57 C o atoms of the 57 C o/R h source were assumed to be homogeneously distributed over a 6μ thick Rh foil and to follow a one dimensional diffusion profile in the 25 μ Fe-foil. The diffusion length was fitted to 10 μ. The theory follows the Blume-Kistner equations for forward scattering (Blume and Kistner, Phys. Rev. 171, 417, 3) by integrating over the source sampled up to 128 layers. 相似文献
994.
We prove the existence and uniqueness of a global solution of a damped quasilineat hyperbolic equatiion. We apply a method based on a special integral inequality, to show that the solution decays exponentially, and to obtain precise estimates of the constants in estimates. 相似文献
995.
Acoustical Physics - The propagation of elastic waves in periodic stratified media with arbitrary local anisotropy and in anisotropic plates and bars inhomogeneous in thickness is considered under... 相似文献
996.
Bertalan Pécsi 《Algebra Universalis》2009,60(4):369-380
We prove that the class of weakly representable relation algebras is closed under homomorphic images, hence it is a variety.
As a corollary we classify the subdirectly irreducible algebras in this class.
Received April 3, 2007; accepted in final form February 7, 2008. 相似文献
997.
Multiplication operators in weighted Banach (and locally convex) spaces of functions holomorphic in the unit disc are well
known. In this note we investigate the connection between power boundedness, mean ergodicity and uniform mean ergodicity of
such operators.
Received: 13 October 2008, Revised: 18 November 2008 相似文献
998.
Joaquín Sicilia Luis A. San-José Juan García-Laguna 《Annals of Operations Research》2009,169(1):93-115
We study an inventory system where demand on the stockout period is partially backlogged. The backlogged demand ratio is a
mixture of two exponential functions. The shortage cost has two significant costs: the unit backorder cost (which includes
a fixed cost and a cost proportional to the length of time for which the backorder exists) and the cost of lost sales. A general
procedure to determine the optimal policy and the minimum inventory cost for all the parameter values is developed. This model
generalizes several inventory systems analyzed by different authors. Numerical examples are used to illustrate the theoretical
results. 相似文献
999.
A. Pérez-González J. M. Vilar-Fernández W. González-Manteiga 《Annals of the Institute of Statistical Mathematics》2009,61(1):85-109
The main objective of this work is the nonparametric estimation of the regression function with correlated errors when observations
are missing in the response variable. Two nonparametric estimators of the regression function are proposed. The asymptotic
properties of these estimators are studied; expresions for the bias and the variance are obtained and the joint asymptotic
normality is established. A simulation study is also included. 相似文献
1000.
In this work, we study a single-item inventory model where shortages are allowed. A known constant fraction of the demand
during the stockout period is backlogged, and the rest are lost sales. Usually, in the literature on inventory control, the
unit backorder cost is considered to be a linear function of the waiting time until the customer gets the item. However, in
some real-world situations, the unit cost of a backorder may not be linear. To model this situation, we develop a new approach
by considering that the backlogging unit cost is a nondecreasing, continuous, and positive function of the amount of time
the customers wait before receiving the item. Our objective is to maximize the average profit per unit time. An effective
solution procedure to determine the optimal policy and the maximum average profit is developed. Numerical examples, which
help us to understand the theoretical results, are also presented. 相似文献