Hydrogenated carbon clusters produced by highly charged ion impact on solid

The emission of small (hydrogenated) carbon cluster ions C_nHm ⁺ (n =2-22) upon highly charged Xe^q+ (q =20-44) impact on C₈₄ surfaces is studied by means of time-of-flight secondary ion mass spectrometry. The respective stage of hydrogenation/protonation of a certain carbon cluster ion Cn ⁺ is a strong indication for its geometrical structure. From the cluster ion yield as a function of cluster size it can be concluded, that the hydrogenation takes place after the initial carbon cluster formation. The carbon clusters seem to be emitted as an entity in agreement with “equilibrium” and “shock wave” models. Received 4 February 2000     

Strong electromagnetic field localization near the surface of hemicylindrical particles

We theoretically study the forward and backward plane wave illuminations of hemicylindrical dielectric particles with different radii and refractive indices. Near field effects providing strong field enhancement and narrow beam width are obtained from hemicylindrical particles, which can be associated with whispering gallery modes (WGMs) and photonic nano-jets (PNJs). It should be noted that existence of PNJ and WGM effects depending on forward/backward light illuminations is studied for the first time in all-dielectric hemicylindrical particles. Compared to dielectric cylinders, hemicylindrical aided PNJs show relatively small influences of WGM regime, when exists, to PNJ behavior. Under the backward excitation, on the other hand, typical nano-jet is produced. The designed hemicylindrical structure could be implemented in high-resolution optical imaging and sensing applications.     

The Nephroprotective Effect of Zizyphus lotus L. (Desf.) Fruits in a Gentamicin-Induced Acute Kidney Injury Model in Rats: A Biochemical and Histopathological Investigation

Zizyphus lotus L. (Desf.) (Z. lotus) is a medicinal plant largely distributed all over the Mediterranean basin and is traditionally used by Moroccan people to treat many illnesses, including kidney failure. The nephrotoxicity of gentamicin (GM) has been well documented in humans and animals, although the preventive strategies against it remain to be studied. In this investigation, we explore whether the extract of Zizyphus lotus L. (Desf.) Fruit (ZLF) exhibits a protective effect against renal damage produced by GM. Indeed, twenty-four Wistar rats were separated into four equal groups of six each (♂/♀ = 1). The control group was treated orally with distilled water (10 mL/kg); the GM treated group received distilled water (10 mL/kg) and an intraperitoneal injection of GM (80 mg/kg) 3 h after; and the treated groups received ZLF extract orally at the doses 200 or 400 mg/kg and injected intraperitoneally with the GM. All treatments were given daily for 14 days. At the end of the experiment, the biochemical parameters and the histological observation related the kidney function was explored. ZLF treatment has significantly attenuated the nephrotoxicity induced by the GM. This effect was indicated by its capacity to decrease significantly the serum creatinine, uric acid, urea, alkaline phosphatase, gamma-glutamyl-transpeptidase, albumin, calcium, sodium amounts, water intake, urinary volume, and relative kidney weight. In addition, this effect was also shown by the increase in the creatinine clearance, urinary creatinine, uric acid, and urea levels, weight gain, compared to the rats treated only with the GM. The hemostasis of oxidants/antioxidants has been significantly improved with the treatment of ZLF extract, which was shown by a significant reduction in malondialdehydes levels. Histopathological analysis of renal tissue was correlated with biochemical observation. Chemical analysis by HPLC-DAD showed that the aqueous extract of ZLF is rich in phenolic compounds such as 3-hydroxycinnamic acid, catechin, ferulic acid, gallic acid, hydroxytyrosol, naringenin, p- coumaric Acid, quercetin, rutin, and vanillic acid. In conclusion, ZLF extract improved the nephrotoxicity induced by GM, through the improvement of the biochemical and histological parameters and thus validates its ethnomedicinal use.     

Dynamical Localization for Unitary Anderson Models

This paper establishes dynamical localization properties of certain families of unitary random operators on the d-dimensional lattice in various regimes. These operators are generalizations of one-dimensional physical models of quantum transport and draw their name from the analogy with the discrete Anderson model of solid state physics. They consist in a product of a deterministic unitary operator and a random unitary operator. The deterministic operator has a band structure, is absolutely continuous and plays the role of the discrete Laplacian. The random operator is diagonal with elements given by i.i.d. random phases distributed according to some absolutely continuous measure and plays the role of the random potential. In dimension one, these operators belong to the family of CMV-matrices in the theory of orthogonal polynomials on the unit circle. We implement the method of Aizenman-Molchanov to prove exponential decay of the fractional moments of the Green function for the unitary Anderson model in the following three regimes: In any dimension, throughout the spectrum at large disorder and near the band edges at arbitrary disorder and, in dimension one, throughout the spectrum at arbitrary disorder. We also prove that exponential decay of fractional moments of the Green function implies dynamical localization, which in turn implies spectral localization. These results complete the analogy with the self-adjoint case where dynamical localization is known to be true in the same three regimes.     

A novel spectrophotometric method for batch and flow injection determination of sulfite in beverages

A novel spectrophotometric assay method for batch and flow injection determination of sulfite in beverages is described. The method involves a reaction with diaquacobyrinic acid heptamethyl ester (diaquacobester, DACbs) in acetate buffer of pH 3 to form a highly stable sulfite cobester complex (SO₃Cbs). In the absence of sulfite, the reagent displays three absorption maxima at 349, 409 and 525 nm. Addition of sulfite is associated with the development of a new absorption band at 313 nm, an increase in the intensity of the band at 425 nm and a decrease in the absorbance of the bands at 349 and 525 nm. Variations of the absorptions at 313, 349, 425 and 525 nm are linearly proportional to sulfite concentrations over the range of 0.05–25 μg ml⁻¹with a detection limit of 0.01–0.2 μg ml⁻¹. Negligible interferences are caused by most common ions. Validation of the method according to the quality assurance standards shows suitability for quality control assessment of sulfite in complex matrices without prior treatment. The method has the advantages of high selectivity, good sensitivity, fast reaction, high stability of the reagent and reaction product and absorbance measurements at four different wavelengths in the same run. The method is successfully applied to determine the sulfite contents of some beverages. The results compare fairly well with data obtained using the standard method.     

双金属镍-锰／γ-Al2O3催化剂对甲烷二氧化碳重整反应的影响

用浸渍法制备γ-Al2O3负载的Ni-Mn双金属催化剂．在500-700。C按照17：17：2的C02／CHa／N2比例,以36mL／min的载气流速进行甲烷二氧化碳重整反应,利用甲烷二氧化碳的转化率、生成的合成气H2／CO比例以及长期稳定性等指标评价了催化剂的催化性能．实验表明,添加Mn提高催化性能并使双金属催化剂的稳定性更高,比单金属催化剂更好地抑制焦炭生成,Mn最合适的添加量为0．5wt％．通过BET、C02-TPD、TGA、XRD、SEM、EDX和FTIR各种技术对催化剂进行了表征．     

Magnetic resonance imaging of velocity fields, the void fraction and gas dynamics in a cavitating liquid

In acoustic cavitation, the relationship between the bubble dynamics on the microscale and the flow properties on the macroscale is critical in determining sonochemical reaction kinetics. A new technique was developed to measure the void fraction and estimate water mobility in the vicinity of cavitating bubbles using phase-encoded magnetic resonance imaging with short characteristic measurement timescales (0.1–1 ms). The exponential behavior of the NMR signal decay indicated the fast diffusion regime, with the relationship between local mechanical dispersion D _mix and the average bubble radius R, D_mix >> \frac2R²10^-4s, D_{\rm mix}\gg \frac{2R^2}{10^{-4}\hbox{s}}, resulting in dispersion of orders of magnitude greater than diffusion in quiescent water. For two different samples (water and a surfactant solution), the independent measurements of three-dimensional void fraction and velocity fields permitted the calculation of compressibility, divergence and vorticity of the cavitating medium. The measured dynamics of the dissolved gas, compared with that of the surrounding liquid, reflected the difference in the bubble coalescence and lifetimes and correlated with the macroscopic flow parameters.     

Spin-polarized structural, electronic and magnetic properties of intermetallic Dy2Ni2Pb from computational study

We report a first-principles study of structural, electronic and magnetic properties of ternary plumbides (rare earth-transition metal-Plumb) Dy₂Ni₂Pb crystallizes with the orthorhombic structure of the Mn₂AlB₂ type (space group Cmmm), were studied by means of the full-relativistic version of the full-potential augmented plane wave plus local orbital method within the frame work of spin-polarized density functional theory (SP-DFT). The electronic exchange-correlation energy is described by generalized gradient approximation (GGA). We have calculated the lattice parameters, bulk modulii and the first pressure derivatives of the bulk modulii, total densities of states and magnetic properties. The calculated total magnetic moment is found to be equal to 9.52 μB.     

Ligand expansion in ligand-based virtual screening using relevance feedback

Query expansion is the process of reformulating an original query to improve retrieval performance in information retrieval systems. Relevance feedback is one of the most useful query modification techniques in information retrieval systems. In this paper, we introduce query expansion into ligand-based virtual screening (LBVS) using the relevance feedback technique. In this approach, a few high-ranking molecules of unknown activity are filtered from the outputs of a Bayesian inference network based on a single ligand molecule to form a set of ligand molecules. This set of ligand molecules is used to form a new ligand molecule. Simulated virtual screening experiments with the MDL Drug Data Report and maximum unbiased validation data sets show that the use of ligand expansion provides a very simple way of improving the LBVS, especially when the active molecules being sought have a high degree of structural heterogeneity. However, the effectiveness of the ligand expansion is slightly less when structurally-homogeneous sets of actives are being sought.     

A hybrid metaheuristic approach to the university course timetabling problem

This paper describes the development of a novel metaheuristic that combines an electromagnetic-like mechanism (EM) and the great deluge algorithm (GD) for the University course timetabling problem. This well-known timetabling problem assigns lectures to specific numbers of timeslots and rooms maximizing the overall quality of the timetable while taking various constraints into account. EM is a population-based stochastic global optimization algorithm that is based on the theory of physics, simulating attraction and repulsion of sample points in moving toward optimality. GD is a local search procedure that allows worse solutions to be accepted based on some given upper boundary or ‘level’. In this paper, the dynamic force calculated from the attraction-repulsion mechanism is used as a decreasing rate to update the ‘level’ within the search process. The proposed method has been applied to a range of benchmark university course timetabling test problems from the literature. Moreover, the viability of the method has been tested by comparing its results with other reported results from the literature, demonstrating that the method is able to produce improved solutions to those currently published. We believe this is due to the combination of both approaches and the ability of the resultant algorithm to converge all solutions at every search process.