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31.
Joë l Benoist Jonathan M. Borwein Nicolae Popovici 《Proceedings of the American Mathematical Society》2003,131(4):1109-1113
The aim of this paper is to characterize in terms of scalar quasiconvexity the vector-valued functions which are -quasiconvex with respect to a closed convex cone in a Banach space. Our main result extends a well-known characterization of -quasiconvexity by means of extreme directions of the polar cone of , obtained by Dinh The Luc in the particular case when is a polyhedral cone generated by exactly linearly independent vectors in the Euclidean space .
32.
Ten insect attractants, a number of intermediates in their synthesis and some related compounds were characterized by their 13C NMR spectra. The chemical shifts of the allylic carbon atoms allowed neat distinction between E and Z isomers of alkenic compounds. 相似文献
33.
Understanding and controlling the band broadening is essential to obtain accurate molar-mass distributions by size-exclusion chromatography (SEC). In this paper, band broadening in SEC is reviewed from a contemporary perspective. The observed band broadening is due to dispersion inside and outside the chromatographic column (undesirable band broadening) and to the polydispersity of the sample (desirable SEC selectivity). The various contributors to band broadening are discussed. Integrity plots are introduced as a tool to evaluate the performance of specific SEC columns at given experimental conditions. For narrow polymer standards on single SEC columns the observed peak width is dominated by the chromatographic dispersion. MALDI-ToF-MS is demonstrated as an alternative to determine the PDI of narrowly distributed samples. The plate heights encountered at very high reduced velocities are found to be lower than expected. This is advantageous for fast separations by SEC. 相似文献
34.
Viorel Cîrcu Mihaela Ilie Monica Iliş Florea Dumitraşcu Ionela Neagoe Simona Păsculescu 《Polyhedron》2009,28(17):3739-3746
A series of cyclometallated 2-phenylpyridine Pt(II) complexes having N-benzoyl thiourea derivatives as ancillary ligands were prepared and characterised by elemental analysis, IR and UV–Vis spectroscopy, 1H and 13C NMR spectroscopy as well as by X-ray diffraction on single-crystal. All complexes were obtained as a single isomer with N atom of the 2-phenylpyridine ligand and S atom of the N-benzoyl thiourea derivatives coordinated in trans positions to the platinum metal as evidenced by using X-ray crystallography and NMR spectroscopy. All Pt(II) complexes show good luminescence properties at room temperature, both in dichloromethane solution and in solid state. 相似文献
35.
C. H. Chao G. Popovici E. J. Charlson E. M. Charlson J. M. Meese M. A. Prelas 《Journal of Crystal Growth》1994,140(3-4):454-458
Smooth diamond films have been grown by hot filament chemical vapor deposition under DC bias on mirror-polished Si(100) substrates. Films of a few micrometers thickness were obtained in 30 min. The films were found to have d-spacing at 2.06 and 2.11 Å by X-ray diffraction. Raman spectra showed very broad peaks at 1329 (1336) and 1591 cm-1. The films have a high density of planar defects and large internal stresses. 相似文献
36.
Ernest Popovici Ion Morjan Victor Ciupina Ladislau Vekas Oana Marinica 《Applied Surface Science》2007,254(4):1048-1052
Well-dispersed nanoparticles with iron/iron carbide core and iron oxide shell structures may constitute an excellent magnetic material for different applications as magnetic nanofluids, contrast agents in magnetic resonance imaging, sensors and catalysts. Based on the ability of the CO2 laser pyrolysis technique to synthesize nanoparticles of the Fe/Fe2O3 core-shell type, we further improve the powder dispersion by first collecting the nanoparticles in a toluene bubbler, positioned downstream and prior to the collection filter. Structural characterisation of the samples by electron microscopy and X-ray diffraction was performed. Conditions in which clusters contain a reduced number of nanoparticles (around 50) are evidenced. Mean core-shell particle sizes of 15 nm were estimated. Finally, preliminary results on the morphology of iron/iron oxide core-shell nanoparticles as hydrocarbon-based magnetic nanofluids are presented. 相似文献
37.
The diffraction maxima (001) and (100) of the Mn1.11Al0.89 alloy have been measured by the neutron powder diffraction method in the temperature range from 23 to 427 C. The Curie temperature is found to be (404 ±2)°C. Temperature dependence of the magnetic structure factor gave the critical exponent β = 0.31±0.02.The disorder parameter has been found to decrease with the temperature. A convenient expression describing this behaviour has been proposed and discussed. 相似文献
38.
Dan Popovici 《Proceedings of the American Mathematical Society》2004,132(8):2303-2314
We obtain a Wold-type decomposition theorem for an arbitrary pair of commuting isometries on a Hilbert space. More precisely, can be uniquely decomposed into the orthogonal sum between a bi-unitary, a shift-unitary, a unitary-shift and a weak bi-shift part, that is, a part that can be characterized by the condition that and are shifts. Moreover, contains bi-shift and modified bi-shift maximal parts.
39.
Dr. Marinela M. Dîrtu France Schmit Dr. Anil D. Naik Dr. Ionela Rusu Prof. Dr. Aurelian Rotaru Sergej Rackwitz Dr. Juliusz A. Wolny Prof. Dr. Volker Schünemann Prof. Dr. Leonard Spinu Prof. Dr. Yann Garcia 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(15):5843-5855
A thermochromic 1D spin crossover coordination (SCO) polymer [Fe(βAlatrz)3](BF4)2 ? 2 H2O ( 1? 2 H2O), whose precursor βAlatrz, (1,2,4‐triazol‐4‐yl‐propionate) has been tailored from a β‐amino acid ester is investigated in detail by a set of superconducting quantum interference device (SQUID), 57Fe Mössbauer, differential scanning calorimetry, infrared, and Raman measurements. An hysteretic abrupt two‐step spin crossover (T1/2↓=230 K and T1/2↑=235 K, and T1/2↓=172 K and T1/2↑=188 K, respectively) is registered for the first time for a 1,2,4‐triazole‐based FeII 1D coordination polymer. The two‐step SCO configuration is observed in a 1:2 ratio of low‐spin/high‐spin in the intermediate phase for a 1D chain. The origin of the stepwise transition was attributed to a distribution of chains of different lengths in 1? 2 H2O after First Order Reversal Curves (FORC) analyses. A detailed DFT analysis allowed us to propose the normal mode assignment of the Raman peaks in the low‐spin and high‐spin states of 1? 2 H2O. Vibrational spectra of 1? 2 H2O reveal that the BF4? anions and water molecules play no significant role on the vibrational properties of the [Fe(βAlatrz)3]2+ polymeric chains, although non‐coordinated water molecules have a dramatic influence on the emergence of a step in the spin transition curve. The dehydrated material [Fe(βAlatrz)3](BF4)2 ( 1 ) reveals indeed a significantly different magnetic behavior with a one‐step SCO which was also investigated. 相似文献
40.
D. Popovici A. I. Barzic I. Stoica M. Butnaru G. E. Ioanid S. Vlad C. Hulubei M. Bruma 《Plasma Chemistry and Plasma Processing》2012,32(4):781-799
Novel copolyimides (cPIs) based on 3,3??,4,4??-benzophenonetetracarboxylic dianhydride, 4,4??-diaminodiphenylmethane (DDM) and 1,6-diaminohexane (DAH) were synthesized. Their surface wettability was improved by plasma enhancement of polar component contribution to surface tension from 10 to 50?%. Interfacial energy reduction up to 2.07?C2.95?mN/m was depicted in spreading work values that reveal the manner in which cPIs interact with blood constituents. The results showed that by increasing of the aliphatic DAH content in the polymer chain, the rejection of platelets is higher, prohibiting thrombosis and favoring cohesion with plasma proteins. The different water sorptions of the samples were evaluated by considering their morphologies and chemical affinities to water. When DAH prevails to DDM, water sorption capacity is lowered from 6.36 to 4.96?%?db, presumably due to a higher chain packing efficiency. Atomic force microscopy data revealed that surface roughness is <8?nm for all polymers, even after plasma treatment, preventing clot formation. 相似文献