Spectral analysis and generation of certain highly oscillatory curves related to chaos,part 2: Calculation aspects

The Fourier spectrum of a curve on a given interval, as represented by the Fourier series, is very reflective of the oscillatory behavior of the curve as the “weights” of the Fourier coefficients can indicate the individual prominence of frequencies of oscillations. But, unfortunately, the calculations of the Fourier coefficients can often get quite cumbersome.     

Point contact tunnelling studies on ceramic YBCO with scanning tunnelling microscope tips

A detailed study of point contact tunnelling into ceramic YBCO with electrochemically etched tips of Pt, Nb and W is reported. The superconducting gap parameter (Δ) has been extracted fromI —V and dI/dV —V curves using various procedures. Our results indicate a gap value of about 20 meV. We observe that the zero bias conductance is strongly dependent on the junction resistance. The normal state conductance varies linearly with bias voltage and the conductance curves are asymmetric with respect to polarity of the bias voltage. With contacts of very high junction resistance, we observe G(0)/G(100 mV) has a value as low as 1/6. This may be the lowest value reported so far.     

A mild and efficient chemoselective tetrahydropyranylation of primary alcohols using La(NO3)3·6H2O as a catalyst under solvent-free conditions

Primary alcohols undergo selective and efficient tetrahydropyranylation in the presence of a catalytic amount of La(NO₃)₃·6H₂O under solvent-free conditions.     

Solving the Ising model exactly on a 5×5×4 lattice using the Connection machine

We implement a recently proposed exact method for solving distrete statistical models for the 3-dimensional Ising model with open boundary conditions. Our computations were done on the Connection machine because the problem maps very naturally onto massively parallel architectures. We explicitly calculate the number of states of the system at each energy for systems of size 5×4×L _z, forL _z5. On serial or vector computers, the time for the computation scales with the volumeV likeV2 ^LLy . On the Connection Machine, the calculation can be spread across the processors. This decreases the computation requirements by a factor equal to the number of processors. We describe the method, its implementation on the Connection Machine both in PARIS and in FORTRAN, and our results. We also state the requirements for solving larger systems using this method.On leave from Physics Department, San Francisco State University, San Francisco, California, and Supercomputer Computations Research Institute, Florida State University, Tallahassee, Florida.     

Al(OTf)3 as a highly efficient catalyst for the rapid acetylation of alcohols, phenols and thiophenols under solvent-free conditions

Aluminium triflate (0.01-0.1 mol %) was found to be an efficient catalyst for the acylation of alcohols, phenols, thiols and sugars with acetic anhydride in high yields under solvent-free conditions in a short reaction time at room temperature. Racemization of optically active alcohols and epimerization of sugars were not observed. The acylation efficacy of various acyl donors was also investigated.     

Characterization of metal centers in bioinorganic complexes using ab initio calculations of 113Cd chemical shifts

Determination of (113)Cd chemical shift is of significant interest in NMR characterization of metal porphyrins, metal-histidine interactions, and other metal-ligand interactions in many bioinorganic complexes and metalloproteins. In this study, we present a detailed account of a number of quantum chemical investigations aimed at relating isotropic and anisotropic (113)Cd chemical shifts to the structure of several biologically relevant complexes with discrete and polymeric structures. Calculated and experimentally determined chemical shift values are compared to correlate the variation of the chemical shift values with the structural changes around the metal center. Our results infer that the density functional theory using the Sadlej basis set on the cadmium atom is a suitable method for estimating cadmium shielding values to a reasonable accuracy.     

Chemically fabricated magnetic quantum dots of InP:Mn

Quantum dots of InP:Mn are chemically prepared by following hot colloidal nanochemistry with starting precursors that obviate the need for external surfactant. These quantum dots are uniform spheres with 3-nm diameters; they are crystalline, photoluminescent, and magnetic. The crystallographic and optical properties are similar to those of undoped InP nanocrystallites, while the magnetism is consistent with the ferromagnetic response observed in a class of diluted magnetic semiconductors. Because of the ultrafine sizes, the sample shows superparamagnetic behavior, whereas ferromagnetic hysteresis loops are clearly seen below the blocking temperature. Structural characterization and analysis confirm that the magnetism in these quantum dots is not due to segregated binary MnP or MnO phases and that they truly represent a homogeneous dilute magnetic semiconductor.     

Topological properties of the one dimensional exponential random geometric graph

In this article we study the one‐dimensional random geometric (random interval) graph when the location of the nodes are independent and exponentially distributed. We derive exact results and limit theorems for the connectivity and other properties associated with this random graph. We show that the asymptotic properties of a graph with a truncated exponential distribution can be obtained using the exponential random geometric graph. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008