Unsteady discharge of ideal fluids from vertical,constant cross-section reservoirs

Zusammenfassung Die Arbeit befasst sich mit der exakten Lösung des bekannten Ausflussproblems für ideale Flüssigkeiten. Die abgeleiteten Ausdrücke sind gültig für Gefässe von konstantem Querschnitt. Die exakte Lösung für die Ausflusszeit wird mit dem Fall vernachlässigbar kleiner Trägheitshöhe verglichen. Wo eine exakte Lösung in geschlossener Form unmöglich erschien, wurde ein Analogrechner benutzt.     

pH-dependent magnetic phase transition of iron oxide nanoparticles synthesized by gamma-radiation reduction method

In this study, the influence of pH variation on structural and magnetic phase transition of gamma radiolytic synthesized iron oxide nanoparticles is investigated. The structure and magnetic properties of irradiated samples are characterized using X-ray diffraction, Fourier transfer infrared spectroscopy, transmission electron microscopy, and vibrating sample magnetometer. It was found that, in acidic irradiated solution, Fe³⁺ ions make various complexes with polyvinyl alcohol and water molecules which exhibit a multiphase magnetic property as a mixture of dia and paramagnetic materials. On the other hand, in basic condition, rate of radiation induced reduction of Fe³⁺ ions increased which leads to the formation of superparamagnetic Fe₃O₄ nanoparticles. By increasing pH value, in strong basic condition, the tendency of paramagnetic iron (III) oxy-hydroxide formation was high compared to other phases. This variation in the magnetic properties was explained based on iron ions reduction mechanism and the variation of the ligands’ properties during formation of nanoparticles under irradiation.     

Regioselective formation of chlorohydrins from ring-opening of steroidal epoxides using silica-supported BiCl3: A spectral and X-ray crystallographic study

The ring opening of steroidal epoxides are carried out in a regioselective manner using bismuth chloride, ferric chloride, indium chloride, silica supported BiCl₃, FeCl₃ and InCl₃ under mild condition in variable yields. The products obtained were identified by various spectroscopic techniques. The structure of one of the compound has been determined by X-ray diffraction using the direct method and was refined on F2 by the full-matrix least-squares. A general mechanistic scheme for the reaction is proposed on the basis of current and previous results and the mode of epoxide ring-opening. The 3D Hirshfeld surfaces and the associated 2D fingerprint plots were also drawn in order to explore plausible intermolecular interactions. The fingerprint plots evidenced subtle distinctions in the intermolecular contacts for the independent molecules.     

Anomalous ferromagnetism in manganites by finite block spin phenomenology

We investigate the relation between ferromagnetism and spin glasses which have been observed in manganese oxides.We want to explain the spin-glass phase on the basis of finite-sized block spin concepts.Then the phase of colossal ferromagnetism in manganites may be considered as the ferromagnetic ordering between block spins comprised of many random spins with respective majority spin directions. Using the Curie law for block spins, the magnetization and susceptibility are obtained in the lower-temperature and higher-temperature approximations of Brillouin function. The resistivity is also obtained from the electric susceptibility.     

Phytochemical investigation of the seeds of <Emphasis Type="Italic">Butea monosperma</Emphasis>

Phytochemical investigation of the methanolic extract of the seeds of Butea monosperma (Lam.) Taub. (Fabaceae) led to the isolation of three higher fatty acids, viz., n-docosanoic, n-octacosanoic, and n-dotriacontanoic acids, together with /-sitosterol xyloside and a zingiberene diglucoside, characterized as 3,4-dihydrozingiberen-14-ol-β-D-glucopyranosyl-(1→4)-/-D-glucopyranoside. All these phytoconstituents were reported from the seeds of B. monosperma for the first time and their structures were established on the basis of spectral data analysis and chemical reactions.     

The power saving mechanism with binary exponential traffic indications in the IEEE 802.16e/m

In IEEE 802.16e (air interface standard for MWiMAX) and IEEE 802.16m (evolution of MWiMAX for IMT-Advanced), power saving is one of the important issues for the battery-powered mobile stations (MSs). According to IEEE 802.16e standard, when an MS switches from awake mode to sleep mode, the MS is required to send a sleep request (MOB-SLP-REQ) message and to receive a sleep response (MOB-SLP-RSP) message. In this paper we propose a new sleep mode scheme, called the power saving mechanism with binary exponential traffic indications. This sleep mode scheme omits MOB-SLP-REQ/RSP messages and has a traffic indication (TRF-IND) interval as a main system parameter, applying the truncated binary exponential increasing method for its length. The proposed scheme in this paper is quite well aligned with the design policy of sleep mode in discussion at IEEE 802.16m in the sense that it tries to minimize the overhead for the state transition between awake mode and sleep mode, and hence it can reduce the delay due to the state transition and enhance the power saving efficiency. We present a mathematical analysis for the proposed scheme and investigate its performance. As performance measures, we provide the sleep interval ratio, the average power consumption, and the mean delay. Using the analytical results, the system parameters such as the initial TRF-IND interval and the maximum binary exponent for TRF-IND intervals can be optimized while satisfying the QoS constraint on the mean delay. The numerical results show that the proposed scheme consumes less energy than the power saving class of type I in the IEEE 802.16e standard. This research was supported by the MKE (Ministry of Knowledge Economy), Korea, under the ITRC (Information Technology Research Center) support program supervised by the IITA (Institute for Information Technology Advancement) (IITA-2008-C1090-0801-0013).     

STM/STS observation of polyoxoanions on HOPG surfaces: the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36-

A combination of scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) techniques have been performed on the wheel-shaped [Cu20Cl(OH)24(H2O)12(P8W48O184)]25- and the ball-shaped [{Sn(CH3)2(H2O)}24{Sn(CH3)2}12(A-PW9O34)12]36- deposited on highly oriented pyrolytic graphite surfaces. Small, regular molecule clusters, as well as separated single molecules, were observed. The size of the molecules is in agreement with the data determined by X-ray crystallography. In STS measurements, we found a rather large contrast at the expected location of the Cu metal centers in our molecules, i.e., the location of the individual Cu ions in their organic matrix is directly addressable by STS.     

Thallophilic interactions in aryloxide compounds: the [Tl2(mu2-OAr)4] structural motif in (TlOAr)4 and Tl2Cu(OAr)4 compounds

Two thallium aryloxide compounds TlOC6F5 (TlOAr(F)) and bis-3,5-TlOC6H3(CF3)2 (TlOAr') have been recrystallized from THF and crystallographically characterized in different isomeric forms. The latter compound forms a solvated tetrameric cubane, [TlOAr']4.THF, 1. The TlOAr(F) compound crystallized with a similar stoichiometry, [TlOAr(F)]4.2 THF, 2, but contains a [Tl2(mu2-OAr(F))4] unit that includes a thallophilic interaction at a distance of 3.5943(15) angstroms. Solution 205Tl and 203Tl NMR studies of 1 and 2 support the retention of a cubane structure for 1 in solution and suggest a similar structure for 2 with coupled thallium centers down to -90 degrees C. Fluorescence spectroscopy data for both compounds 1 and 2 in THF are consistent with LMCT. DFT calculations of 1, 2, and three models of the [Tl2(mu2-OAr(F))4] unit show a bonding overlap of the bridged thallium atoms in 2 and are also used to describe the bonding in 1. The structures of two heterobimetallic compounds, Tl2Cu(OAr(F))4, 4, and Tl2Cu(OAr')4, 5, with the [Tl2(mu2-OAr(F))4] structural motif and thallophilic contacts of 3.86(6) and 3.564(1) angstroms, respectively, are described. The crystal structures of the unsolvated of TlOAr(F), 2b, solvated heterobimetallic derivative Tl2Cu(OAr')4.2THF, 5b, and the monomeric (18-crown-6)TlOAr(F), 3, and 205Tl NMR spectra of TlOC6H5, 6, are also reported for comparison purposes.