Surface enhanced Raman scattering of light by ZnO nanostructures

Raman scattering (including nonresonant, resonant, and surface enhanced scattering) of light by optical and surface phonons of ZnO nanocrystals and nanorods has been investigated. It has been found that the nonresonant and resonant Raman scattering spectra of the nanostructures exhibit typical vibrational modes, E ₂(high) and A ₁(LO), respectively, which are allowed by the selection rules. The deposition of silver nanoclusters on the surface of nanostructures leads either to an abrupt increase in the intensity (by a factor of 10³) of Raman scattering of light by surface optical phonons or to the appearance of new surface modes, which indicates the observation of the phenomenon of surface enhanced Raman light scattering. It has been demonstrated that the frequencies of surface optical phonon modes of the studied nanostructures are in good agreement with the theoretical values obtained from calculations performed within the effective dielectric function model.     

Photoemission of a doped Mott insulator: spectral weight transfer and a qualitative Mott-Hubbard description

The spectral weight evolution of the low-dimensional Mott insulator TiOCl upon alkali-metal dosing has been studied by photoelectron spectroscopy. We observe a spectral weight transfer between the lower Hubbard band and an additional peak upon electron doping, in line with quantitative expectations in the atomic limit for changing the number of singly and doubly occupied sites. This observation is an unconditional hallmark of correlated bands and has not been reported before. In contrast, the absence of a metallic quasiparticle peak can be traced back to a simple one-particle effect.     

Giant nonmonotonic stretching response of a self-associating polymer in shear flow

Self-associating polymers are ubiquitous in synthetic and biological systems. Here, we use a combination of simulation and theory to show that these polymers exhibit a counterintuitive strong nonmonotonic stretching response in shear flow. Furthermore, we demonstrate that this behavior can be tuned by controlling the barrier for dissociation of the bonds and develop a quantitative and predictive theory based on conformational transitions to explain the observed behavior. Our results can be important in understanding previous experimental and theoretical observations and further aid in the development of novel smart materials.     

A Biomimetic Synthesis of (±)‐Basiliolide B

A highly diastereoselective and practical biomimetic total synthesis of (±)‐basiliolide B has been achieved through the study of the two proposed biosynthetic pathways (O‐methylation and O‐acylation) for the unprecedented 7‐methoxy‐4,5‐dihydro‐3H‐oxepin‐2‐one (C ring). The synthesis featured a cyclopropanation/ring opening strategy for establishing the stereogenic centers at C8 and C9, a biomimetic 2‐pyrone Diels–Alder cycloaddition for the synthesis of the ABD ring system, and finally a highly efficient biomimetic intramolecular O‐acylation for the C ring formation. This result provides an important perspective on the biosynthetic origin of the unprecedented 7‐membered acyl ketene acetal moiety of the C ring.     

Crystallographic report: Phenyl(N,N‐di‐n‐propyldithiocarbamato)mercury(II)

The structure of PhHg(S₂CNPr₂) shows a distorted linear geometry about mercury defined by a sulfur and a carbon atom. Centrosymmetric molecules aggregate via Hg?S interactions to form loosely associated dimers. Copyright © 2003 John Wiley & Sons, Ltd.     

Crystallographic report: Tris(N,N‐dimethyldithiocarbamato)arsenic(III) dichloromethane solvate

The structure of As(S₂CNMe₂)₃ has approximate threefold symmetry and features essentially monodentate dithiocarbamate ligands, so that the geometry is trigonal pyramidal. Copyright © 2003 John Wiley & Sons, Ltd.     

Crystallographic report: (4,7‐Diphenyl‐1,10‐phenanthroline) bis(pyrrolinedithiocarbamato)zinc(II) chloroform solvate

The mononuclear structure of Zn(S₂CN(CH₂)₄)₂(4,7‐Ph₂‐1,10‐phenanthroline) shows the zinc atom in each of the two independent molecules comprising the asymmetric unit to exist in a distorted octahedral geometry defined by an N₂S₄ donor set. Copyright © 2003 John Wiley & Sons, Ltd.     

On the sum of two N0-matrices

In this paper, we study the Fan product of two N₀-matrices and inequalities for two N₀-matrices A,B with A ≤ B. Necessary and sufficient conditions are given for the sum of two symmetric N₀-matrices to be an N₀-matrix.     

Exact analysis of asymmetric random polling systems with single buffers and correlated input process

We introduce a simple approach for modeling and analyzing asymmetric random polling systems with single buffers and correlated input process. We consider two variations of single buffers system: the conventional system and the buffer relaxation system. In the conventional system, at most one customer may be resided in any queue at any time. In the buffer relaxation system, a buffer becomes available to new customers as soon as the current customer is being served. Previous studies concentrate on conventional single buffer system with independent Poisson process input process. It has been shown that the asymmetric system requires the solution ofm 2 ^m –1) linear equations; and the symmetric system requires the solution of 2 ^m–1–1 linear equations, wherem is the number of stations in the system. For both the conventional system and the buffer relaxation system, we give the exact solution to the more general case and show that our analysis requires the solution of 2 ^m –1 linear equations. For the symmetric case, we obtain explicit expressions for several performance measures of the system. These performance measures include the mean and second moment of the cycle time, loss probability, throughput, and the expected delay observed by a customer.