Persistence problem in two-dimensional fluid turbulence

We present a natural framework for studying the persistence problem in two-dimensional fluid turbulence by using the Okubo-Weiss parameter Λ to distinguish between vortical and extensional regions. We then use a direct numerical simulation of the two-dimensional, incompressible Navier-Stokes equation with Ekman friction to study probability distribution functions (PDFs) of the persistence times of vortical and extensional regions by employing both Eulerian and Lagrangian measurements. We find that, in the Eulerian case, the persistence-time PDFs have exponential tails; by contrast, this PDF for Lagrangian particles, in vortical regions, has a power-law tail with an exponent θ=2.9±0.2.     

High sensitivity (1 ppm) hydrogen detection using an unconventional Pd/n-InP Schottky device

Hydrogen is detected using a Pd/n-InP Schottky diode in which the elongated, very thin Pd electrode is of greater resistance than the underlying semiconductor substrate. Four-probe measurements of the device resistance, as a function of hydrogen concentration, are made by contacting only the Pd electrode, with a sensitivity of 1 ppm being achieved. On hydrogen exposure the device resistance drops from an initial high value, characteristic of the Pd electrode alone, to a lower value due to a hydrogen-induced lowering of the Schottky barrier that opens up the InP substrate as a parallel current carrying channel.     

Methane preconcentration in a microtrap using multiwalled carbon nanotubes as sorbents

The GC monitoring of green house gases is a challenging task because the concentration of organic species such as methane are relatively low (ppm to ppb) and their analysis requires some level of preconcentration. Since methane is highly volatile, it is not easily retained on conventional sorbents. In this paper we present multiwalled carbon nanotubes (MWNTs) as an effective sorbent for a microtrap designed for methane preconcentration. Its performance was compared to other commercially available carbon based sorbents, and it was found to be the most effective sorbent in terms of breakthrough volume and enthalpy of adsorption.     

Search for anomalous interaction mean free paths of charge, 2≦Z≦18 projectile fragments in emulsions exposed to 1.8 A GeV40Ar ions

⁴⁰Ar-emulsion interactions are studied, to investigate the question of anomalons, in twoG- 5 emulsion stacks. In about 4600 primary interactions, projectile fragments of Z≧2 for all generations have been followed until they interact or leave the stack. After careful estimation of charges of these fragments, variation of their mean free paths is studied as a function of distance from the preceding interaction. Generation effect,N _h dependence and production angle effect are investigated. In addition multi-chain events are analysed separately. Our results do not show anomalons at the 6% level and are consistent with non-occurrence of anomalons. However, this experiment is not sensitive enough to rule out anomalons (with a mfp of the order of 2 to 3 cm) produced at about 1% (or less) level.     

A unified set of proposals for control and design of high speed data networks

In this paper we articulate our philosophy and approach to the design and control of high speed data networks. The object is to put into perspective and to explain the coordination of various isolated pieces of detailed technical analyses that have been reported in several recent papers. In the process we summarize what we have learnt in our recent work and, also, we give indications of the direction of our future work. Our scheme integrates feedback and open loop control. The feedback control is exercised by sliding windows; access controllers regulate bursty sources. All our design proposals are rooted in asymptotic analyses; the justification for asymptotics comes from the largeness of the parameters, such as propagation delay, speed, window size, buffer size, and the number of virtual circuits. This analysis makes a strong case for operating in a specific moderate usage regime, and adaptive dynamic windowing algorithms are given that make this happen; moreover, when in this regime, buffers may be sized aggressively small without jeopardizing performance and the simplicity of the retransmission protocol. The topics in the paper are: model of communication, results on the steady-state behavior of the basic model, access control, small buffers and retransmission protocols, dynamic adaptive windows, bursty sources, and contrast with previous work.I. Mitrani's work was done while AT&T Bell Laboratories.     

Head-group size or hydrophilicity of surfactants: the major regulator of lipase activity in cationic water-in-oil microemulsions

To determine the crucial role of surfactant head-group size in micellar enzymology, the activity of Chromobacterium Viscosum (CV) lipase was estimated in cationic water-in-oil (w/o) microemulsions of three different series of surfactants with varied head-group size and hydrophilicity. The different series were prepared by subsequent replacement of three methyl groups of cetyltrimethylammonium bromide (CTAB) with hydroxyethyl (1-3, series I), methoxyethyl (4-6, series II), and n-propyl (7-9, series III) groups. The hydrophilicity at the polar head was gradually reduced from series I to series III. Interestingly, the lipase activity was found to be markedly higher for series II surfactants relative to their more hydrophilic analogues in series I. Moreover, the activity remained almost comparable for complementary analogues of both series I and III, though the hydrophilicity was drastically different. Noticeably, the head-group area per surfactant is almost similar for comparable surfactants of both series I and III, but distinctly higher in case of series II surfactants. Thus the lipase activity was largely regulated by the surfactant head-group size, which plays the dominant role over the hydrophilicity. The increase in head-group size presumably allows the enzyme to attain a flexible conformation as well as increase in the local concentration of enzyme and substrate, leading to the higher efficiency of lipase. The lipase showed its best activity in the microemulsion of 6 probably because of its highest head-group size. Furthermore, the observed activity in 6 is 2-3-fold and 8-fold higher than sodium bis(2-ethyl-1-hexyl)sulfosuccinate (AOT) and CTAB-based microemulsions, respectively, and in fact highest ever in any w/o microemulsions.     

Three new pseudohalide bridged dinuclear Zn(II) Schiff base complexes: Synthesis,crystal structures and fluorescence studies

Three new dinuclear Zn(II) complexes [Zn(L)(μ_1,1-N₃)Zn(L)(N₃)] · 1.5H₂O (1), [Zn(L)(μ_1,1-NCO)Zn(L)(NCO)] · 1.5H₂O (2) and [Zn(L)(μ_1,1-NCS)Zn(L)(NCS)(OH₂)] (3) have been synthesized from a potentially tetradentate N₂O₂-donor Schiff base ligand LH, [LH = (OCH₃)(OH)C₆H₃CHN(CH₂)₂N(CH₃)₂], which is the condensation product of o-vanillin and 2-dimethylaminoethylamine. All the three complexes 1, 2 and 3 have been characterized by elemental analysis, IR and ¹H NMR spectroscopy, TGA and fluorescence studies. Finally, their structures have been established by the single crystal X-ray diffraction method. Structural studies reveal that in complexes 1, 2 and 3 the two Zn(II) centers are held together by a μ₂-phenolato oxygen atom and also by an end-on pseudohalide nitrogen (azide for 1; cyanate for 2; thiocyanate for 3) atom. Among the two deprotonated Schiff base ligands present in each complex, one acts as a tetradentate ligand (N₂O₂ donor set) while the other acts as a tridentate ligand (N₂O donor set), having a non-coordinated methoxy group. All the synthesized complexes display intraligand ¹(π–π^∗) fluorescence and can potentially serve as photoactive materials.     

Ion-exchange separation of metal ions with thiosulphate

Summary In a cationic column of Amberlite IR-120 with thiosulphate as the eluting agent it has been possible to separate metal ions from several two to five component mixtures.

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Zusammenfassung Mischungen von 2–5 Metallionen konnten durch Ionenaustausch-chromatographie an Amberlite IR-120 mit Thiosulfat als Eluierungsmittel getrennt werden.

     

Ir(I)–carbonyl complexes of coumarinazoimidazoles: Synthesis structure, electrochemistry, photophysical properties and DFT calculations

The reactions of Vaska’s complex [IrCl(CO)(PPh₃)₂] with 2-(coumaryl-6-azo)imidazole (CZ-H) and its derivatives (CZ-X) have synthesized [Ir(CZ)(CO)(PPh₃)₂] and [Ir(CZ-X)(CO)(PPh₃)₂]. All the complexes have been characterized by FT-IR, UV-Vis, ¹H NMR and FAB-MS spectroscopy. The structural confirmation has been done in one case, by a single crystal X-ray diffraction study, which shows a distorted square pyramidal geometry around the central Ir atom. The complexes are emissive at room temperature. The cyclic voltammetry of the complexes shows a metal centered irreversible oxidation and ligand centered quasireversible reduction couples. To get an insight into the electronic structure, absorption spectra and electrochemical properties, detailed calculations on all three complexes have been performed at the DFT level.