National Institute Of Materials Physics - Romania

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5714 articles found

2851. Transient processes induced by heavy projectiles in silicon

Authors: Lazanu, I; Lazanu, S

Published: JUL 1 2010, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 268, 2245, DOI: 10.1016/j.nimb.2010.04.003

The thermal spike model developed for the electronic stopping power regime is extended to consider both ionization and nuclear energy loss processes of the projectile as electronic and atomic heat distinct sources. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated and discussed for different ions in silicon, at room and cryogenic temperatures, taking into account the peculiarities of electron-phonon interaction in both domains. The model developed contributes to the understanding of transient microscopic processes immediately after the projectile interaction in the target. (c) 2010 Elsevier B.V. All rights reserved.

2852. Improved large mesoporous ordered molecular sieves-Stabilization and acid/base functionalization

Authors: Kosslick, H; Pitsch, I; Deutsch, J; Pohl, MM; Schulz, A; Vu, AT; Nguyen, DT; Frunza, L; Jaeger, C

Published: JUL 1 2010, CATALYSIS TODAY, 152, 60, DOI: 10.1016/j.cattod.2010.03.005

The preparation of nanoporous materials with enhanced stability using an improved synthesis route using reactive inorganic silica and alumina species is reported. This way improved mesoporous molecular sieves were obtained. The synthesized aluminum substituted mesoporous molecular materials (Al-MMS) contain very large pores of 50-200 angstrom size combined with an improved pore wall thickness. Increased wall thickness and Al substitution lead to an improved chemical stability against alkaline solution. The textural, structural and acid properties are investigated by physico-chemical methods. The catalytic performance acidic materials was tested in the benzoylation reaction; amino functionalized materials were studied in the base catalyzed Michael addition. (C) 2010 Elsevier B.V. All rights reserved.

2853. The effect of the inhomogeneities on the propagation of elastic waves in isotropic bodies

Authors: Apostol, BF

Published: JUL 2010, MECHANICS RESEARCH COMMUNICATIONS, 37, 462, DOI: 10.1016/j.mechrescom.2010.05.005

A new method is introduced for estimating the effects of the inhomogeneities on the propagation of the elastic waves in isotropic bodies. The method is based on the Kirchhoff electromagnetic potentials. It is applied here for estimating the effect of a static density inhomogeneity, either extended or localized, on the elastic waves propagating in an infinite, or a semi-infinite (half-space) body. For a semi-infinite body the method leads to coupled integral equations, which are solved. It is shown that such a density inhomogeneity may renormalize the waves velocity, or may even produce dispersive waves, depending on the geometry of the body and the spatial extension of the inhomogeneity. The method can be extended to other types of geometries or inhomogeneities, as, for instance, those occurring in the elastic constants. (C) 2010 Elsevier Ltd. All rights reserved.

2854. Synthesis and structural characteristics of nitrogen doped TiO2 aerogels

Authors: Popa, M; Macovei, D; Indrea, E; Mercioniu, I; Popescu, IC; Danciu, V

Published: JUL 2010, MICROPOROUS AND MESOPOROUS MATERIALS, 132, 86, DOI: 10.1016/j.micromeso.2009.12.024

Nitrogen doped TiO2 aerogels were obtained by sol gel process followed by supercritical drying with liquid CO2. Urea and NH3 (25% aqueous solution) were used as nitrogen sources. The as-prepared aerogels were submitted to thermal treatments performed under different experimental conditions (temperature and heating time). Increasing the temperature from 450 degrees C to 550 degrees C a decrease about 32% and 15.4% of the particle size and surface OH groups' concentration, respectively and an increase about 21.4% of the incorporated nitrogen in TiO2 lattice were observed. The immersion of the TiO2 aerogels in NH3 solution induced a decreasing by 48.86% and by 80% of the S-BET and the aerogel porosity, respectively. The photocatalytic activity of the obtained N-doped TiO2 was found to depend mainly on the nitrogen incorporation in the TiO2 lattice. (C) 2009 Elsevier Inc. All rights reserved.

2855. N,N-dimethylbiguanide complexes displaying low cytotoxicity as potential large spectrum antimicrobial agents

Authors: Olar, R; Badea, M; Marinescu, D; Chifiriuc, MC; Bleotu, C; Grecu, MN; Iorgulescu, EE; Lazar, V

Published: JUL 2010, EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY, 45, 3034, DOI: 10.1016/j.ejmech.2010.03.033

The new complexes M(DMBG)(2)(ClO(4))(2) (M:Mn, Ni, Cu and Zn; DMBG: N,N-dimethylbiguanide) have been synthesized and characterized by IR, EPR, (1)H NMR, (13)C NMR as well as electronic spectroscopy data. Complex [Ni(DMBG)(2)](ClO(4))(2)center dot 2DMF (DMF: N,N-dimethylformamide) crystallizes in the monoclinic P2 (1)/c space group while [Cu(DMBG)(2)](ClO(4))(2) adopt monoclinic P21/c space group as X-ray single crystal data indicate. The redox behavior of complexes was investigated by cyclic voltammetry. The metal-free N, N-dimethylbiguanide and complexes exhibit specific anti-infective properties as demonstrated the low MIC values, a large antimicrobial spectrum and also inhibit the ability of Pseudomonas aeniginosa and Staphylococcus aureus strains to colonize the inert surfaces. The complexes exhibit also a low cytotoxicity levels on HeLa cells. (c) 2010 Elsevier Masson SAS. All rights reserved.

2856. Thermal analysis of two types of dextran-coated magnetite

Authors: Carp, O; Patron, L; Culita, DC; Budrugeac, P; Feder, M; Diamandescu, L

Published: JUL 2010, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 101, 187, DOI: 10.1007/s10973-009-0593-3

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to similar to 450 A degrees C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160-450 A degrees C and the other at 530-800 A degrees C.

2857. Mesoporous Tin-Triflate Based Catalysts for Transesterification of Sunflower Oil

Authors: Verziu, M; El Haskouri, J; Beltran, D; Amoros, P; Macovei, D; Gheorghe, NG; Teodorescu, CM; Coman, SM; Parvulescu, VI

Published: JUL 2010, TOPICS IN CATALYSIS, 53, 772, DOI: 10.1007/s11244-010-9468-x

Unimodal porous system (denoted as SnTf-MCM-41) and bimodal porosity (denoted as SnTf-UVM-7) were prepared in a two-step synthesis. The triflic acid was incorporated into previously synthesized Sn-containing porous silicas. Chemical analysis was carried out by electron probe microanalysis (EPMA), textural properties were determined by transmission electron microscopy (TEM) and from nitrogen adsorption-desorption isotherms (77 K), while structural characterization by X-ray absorption near-edge structure (XANES), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) measurements. The structural characterization provided evidences on the direct interaction of triflate with incorporated tin species. The acidity of these catalysts was determined from the ammonia chemisorption measurements. The catalysts have been tested for transesterification of sunflower oil under both microwave and ultrasound activation. These experiments showed a direct reaction between the acidity of the catalysts and catalytic performances. No leaching of the triflate species or catalyst deactivation have been detected over several runs.

2858. Analyzing the measured phase in the multichannel Aharonov-Bohm interferometer

Authors: Tolea, M; Nita, M; Aldea, A

Published: JUL 2010, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 42, 2236, DOI: 10.1016/j.physe.2010.04.022

We address the quantum dot phase measurement problem in an open Aharonov-Bohm interferometer, assuming multiple transport channels. In such a case, the quantum dot is characterized by more than one intrinsic phase for the electrons transmission. It is shown that the phase which would be extracted by the usual experimental method (i.e. by monitoring the shift of the Aharonov-Bohm oscillations, as in Schuster et al., Nature 385 (1997) 417) does not coincide with any of the dot intrinsic phases, but is a combination of them. The formula of the measured phase is given. The particular case of a quantum dot containing a S = 1/2 spin is discussed and variations of the measured phase with

2859. Comment on "Q-Switched Tm:YAG Laser Intracavity-Pumped by a 1064 nm Laser"

Authors: Nicolaie, P

Published: JUL 2010, CHINESE PHYSICS LETTERS, 27, DOI: 10.1088/0256-307X/27/7/079901

The paper published in Chin. Phys. Lett. 26 (2009) 124211 reported a Q-switched 2-mu m Tm:YAG laser that is intracavity pumped by a Nd:YAG laser with emission at 1.06 mu m. However, analysis of the experimental setup concludes that only the Nd:YAG laser is Q-switched, and the Tm: YAG laser operates in the free-generation regime. Therefore, Q-switch operation for the 2-mu m emission wavelength is not realized.

2860. Prospects for new antimicrobials based on N,N-dimethylbiguanide complexes as effective agents on both planktonic and adhered microbial strains

Authors: Olar, R; Badea, M; Marinescu, D; Chifiriuc, CM; Bleotu, C; Grecu, MN; Iorgulescu, EE; Bucur, M; Lazar, V; Finaru, A

Published: JUL 2010, EUROPEAN JOURNAL OF MEDICINAL CHEMISTRY, 45, 2875, DOI: 10.1016/j.ejmech.2010.03.009

Metal-free N,N-dimethylbiguanidium acetate and novel complexes M(DMBG)(2)(CH(3)COO)(2)center dot nH(2)O (M: Mn (II), Ni(II), Cu(II) and Zn(II)) were screened for their antimicrobial properties against Gram-positive (Bacillus subtilis, Listeria monocytogenes, Staphylococcus aureus), Gram-negative (Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa) bacteria and fungal (Candida albicans) strains. The ability of compounds to inhibit the microbial adherence ability to the inert substratum as well as their cytotoxicity was also assessed. Our results are demonstrating that some of the tested compounds are exhibiting potent antimicrobial activity accompanied by low cytotoxicity on HeLa cells. The complexes were characterized using microanalytical, IR, EPR, (1)H NMR as well as UV-vis methods. The redox behaviour of complexes was investigated by cyclic voltammetry. The new derivative (HDMBG)(CH(3)COO) crystallizes in the monoclinic P2(1)/n space group as X-ray single-crystal data indicate. (C) 2010 Elsevier Masson SAS. All rights reserved.