Room temperature growth of wafer-scale silicon nanowire arrays and their Raman characteristics

Journal of Nanoparticle Research - We report a simple, inexpensive, and rapid process for large area growth of vertically aligned crystalline silicon nanowires (SiNWs) of diameter...     

Performance of a rotating membrane emulsifier for production of coarse droplets

A versatile and high capacity membrane emulsification system which utilises a rotating membrane for the precision manufacture of oil-in-water (o/w) emulsions is investigated. The o/w emulsions produced used a low viscosity paraffin wax as the dispersed phase, Tween 20 or sodium dodecyl sulphate (SDS) as the emulsifier and carbomer as the stabiliser, respectively. The ability to generate coarse monodisperse emulsions was demonstrated with droplets of average diameter 80–570 μm and coefficient of variation ranging from 9.8% to 33.6%. The effects of key process parameters on the droplet size and distribution are discussed, including requirements for future developments of the membrane.     

Electronic and structural shell closure in AgCu and AuCu nanoclusters

The structures of AgCu clusters containing 40 atoms are investigated. The most promising structural families (fcc clusters, capped decahedra, and two types of capped polyicosahedra) are singled out by means of global optimization techniques within an atom-atom potential model. Then, representative clusters of each family are relaxed by means of density-functional methods. It is shown that, for a large majority of compositions, a complex interplay of geometric and electronic shell-closure effects stabilizes a specific polyicosahedral family, whose clusters are much lower in energy and present large HOMO-LUMO gaps. Within this family, geometric and quantum effects concur to favor magic structures associated with core-shell chemical ordering and high symmetry, so that these clusters are very promising from the point of view of their optical properties. Our results also suggest a natural growth pathway of AgCu clusters through high-stability polyicosahedral structures. Results for AuCu clusters of the same size are reported for comparison, showing that the interplay of the different effects is highly material specific.     

(29)Si NMR shifts and relative stabilities calculated for hypercoordinated silicon-polyalcohol complexes: role in sol-gel and biogenic silica synthesis

Penta- and hexa-coordinated silicon is rare, occurring as a transient species in some glasses, nonaqueous organosilicon solutions and organosilicon gels such as silicone, and is stable at high pressures within the earth in dense phases such as stishovite. The stable form expected in aqueous solution is quadra-coordinated silicon. A recent study proposed the existence of hypercoordinated silicon-polyalcohol complexes in aqueous solution, based on (29)Si NMR shifts at -102 to -103 ppm and -145 to -147 ppm. Here, we report ab initio molecular orbital calculations of (29)Si NMR chemical shifts and relative stabilities of silicon-polyalcohol monocyclic and spirocyclic complexes, from ethylene glycol (C(2)H(6)O(2)) to arabitol (C(5)H(12)O(5)) with Si in quadra-, penta- and hexa-coordination ((Q)Si, (P)Si, (H)Si), calculated at the HF/6-311+G(2d,p)//HF/6-31G* level. Calculated shifts are accurate with a 1-8% error for (Q)Si and 2-9% for (P)Si. Shifts calculated for the hypercoordinated silicon complexes having structures proposed in the literature are much more negative (-128 and -180 ppm for (P)Si and (H)Si) than observed. We propose that cyclic trimers complexed by polyalcohols can explain the -102 ppm shift, where the Si atoms are all (Q)Si, or where two silicons are (Q)Si and one is (P)Si with rapid exchange between the Si sites. The -145 ppm resonance results from structures similar to those proposed in the experimental NMR study for the -102 ppm peak. Our relative stability calculations indicate that structures proposed in the literature for hypercoordinated silicon complexes are thermodynamically unstable in aqueous solution at acidic to neutral conditions but may exist in degrading silicone-gel breast-implants. Thus, aqueous hypercoordinated silicon-polyalcohol complexes are unlikely to play an important role in biological silicon uptake and hold little promise for novel silica synthesis routes from aqueous solutions under nonextreme conditions.     

Refractometric studies of molecular complexes ofDDT with some compounds of biological interest

Formation of molecular complexes betweenDDT as acceptor and indole, 2-methylindole, 3-methylindole, benzene and naphthalene as donors have been studied in carbon tetrachloride using refractometric and differential refractometric measurements. Titration techniques through these measurements have indicated11 stoichiometry of these complexes. Equilibrium constants (K ₁) and extent of electronic polarization were calculated. Two types of complexes were observed, one association involving primarily the benzhydryltrichloromethyl grouping ofDDT with a polar complexing agents, and the other interaction of theDDT aromatic -electron system with -electrons of donors in the complexing molecule. These data support the charge-transfer complex formation hypothesis for the mode of action ofDDT on molecular level.

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Refraktometrische Untersuchungen an Molekülkomplexen von DDT mit einigen biologisch relevanten Verbindungen

Zusammenfassung Es wurde die Bildung von Molekülkomplexen zwischenDDT als Acceptor und Indol, 2-Methyl-indol, 3-Methyl-indol, Benzol und Naphthalin als Donor in CCl₄ mittels Refraktometrie und differenzieller Refraktometrie untersucht. Es wurde11-Stöchiometrie der Komplexe festgestellt, Gleichgewichtskonstanten und das Ausmaß der Elektronenpolarisation wurden berechnet. Zwei Typen von Komplexen wurden beobachtet; in einem Fall erfolgt die Assoziation primär über die Benzhydryltrichlormethyl-Gruppierung desDDT, im anderen Fall über -Elektronenwechselwirkungen. Die Daten unterstützen ein chargetransfer-Modell der Komplexbildung vonDDT mit geeigneten Donormolekülen.

     

Synchronization and control of spatiotemporal chaos using time-series data from local regions

In this paper we show that the analysis of the dynamics in localized regions, i.e., sub-systems can be used to characterize the chaotic dynamics and the synchronization ability of the spatiotemporal systems. Using noisy scalar time-series data for driving along with simultaneous self-adaptation of the control parameter representative control goals like suppressing spatiotemporal chaos and synchronization of spatiotemporally chaotic dynamics have been discussed. (c) 1998 American Institute of Physics.     

An integrated economic lot-size model for vendor–buyer inventory system when input is random

An integrated strategy is discussed for both vendor and buyer when the input is random. It is shown numerically that the cooperative approach is beneficial to reduce the cost when compared with an independent decision by both the parties. Though the integrated total cost decreases, the buyer’s cost increases due to random input in his inventory. To encourage the buyer to order a large quantity, a trade credit is offered by the vendor to the buyer to settle the account. A conciliation factor is suggested to share the benefits.     

An analysis of the complexation between poly(aspartic acid) and poly(ethylene glycol)

The compatibility between poly(aspartic acid) and poly(ethylene glycol) for the formation of an interpolymer complex (IPC) was investigated by dynamic rheology and evaluation of zeta potential values. The homogeneity of the realized IPC was observed by near infrared chemical imagistic (NIR-CI) technique. The data were sustained and underlined by the assessment of the compatibility between the polymeric compounds.     

Modulation of the nucleation rate preexponential in a low-temperature Ising system

A metastable lattice gas with nearest-neighbor interactions and continuous-time dynamics is studied using a generalized Becker-D?ring approach in the multidimensional space of cluster configurations. The preexponential of the metastable-state lifetime (inverse of nucleation rate) is found to exhibit distinct peaks at integer values of the inverse supersaturation. Peaks are unobservable (infinitely narrow) in the strict limit T-->0, but become detectable and eventually dominate at higher temperatures.