Measuring elastic properties of bones and silicon from V(z) curve generated by multiply reflected signals

Acoustic microscopes can be used to measure Rayleigh and longitudinal or P-wave speeds in a specimen at microscopic resolution. The wave speeds are obtained from the interference pattern as a function of the defocus distance or V(z) curve. The received signal voltage amplitude Vis generated by two beams--the normally reflected central beam and a non-specularly reflected beam that strikes the fluid-solid interface at critical angle. It is shown in this paper that instead of analyzing the interference pattern between these two beams if we consider two other beams that follow the same path but travel through the coupling fluid multiple times before interfering then the V(z) curve generated by this higher order interference gives more accurate values for the material properties. The spacing distance between two successive dips of the V(z) curve is smaller for the higher order interference. The higher order interference, although weaker, gives more accurate results. Justification for the greater accuracy of the higher order interference is given in the paper. Material properties of silicon and bone are obtained by the new technique. Bones are microscopically heterogeneous and anisotropic. Anisotropic properties of homogeneous specimens can be obtained by the line focus acoustic microscope; however, it does not work when the specimen is microscopically heterogeneous. An attempt has been made here to obtain anisotropic properties of bones using point focus lens.     

Novel intramolecular rearrangement leading to the synthesis of biheterocyclic indole-benzoimidazole derivatives on solid phase

[reaction: see text] A novel intramolecular SNAr rearrangement observed during the S-alkylation of benzoimidazole-2-thione with alpha-haloacetophenone is reported. The rearrangement led to the formation of a new benzoimidazole-based intermediate, which is further utilized for the generation of a new biheterocyclic indole-benzimidazole derivatives with a two-point diversity.     

Infinite-impulse-response models of the head-related transfer function

Head-related transfer functions (HRTFs) measured from human subjects were approximated using infinite-impulse-response (IIR) filter models. Models were restricted to rational transfer functions (plus simple delays) so that specific models are characterized by the locations of poles and zeros in the complex plane. The all-pole case (with no nontrivial zeros) is treated first using the theory of linear prediction. Then the general pole-zero model is derived using a weighted-least-squares (WLS) formulation of the modified least-squares problem proposed by Kalman (1958). Both estimation algorithms are based on solutions of sets of linear equations and result in efficient computational schemes to find low-order model HRTFs. The validity of each of these two low-order models was assessed in psychophysical experiments. Specifically, a four-interval, two-alternative, forced-choice paradigm was used to test the discriminability of virtual stimuli constructed from empirical and model HRTFs for corresponding locations. For these experiments, the stimuli were 80 ms, noise tokens generated from a wideband noise generator. Results show that sounds synthesized through model HRTFs were indistinguishable from sounds synthesized from original HRTF measurements for the majority of positions tested. The advantages of the techniques described here are the computational efficiencies achieved for low-order IIR models. Properties of the all-pole and pole-zero estimators are discussed in the context of low-order HRTF representations, and implications for basic and applied contexts are considered.     

Resolution-enhanced Fourier transform method for the estimation of multiple phases in interferometry

A phase shifting method based on high-resolution frequency estimation and Fourier transform technique is introduced. This method, also referred to as the eigenvector method, draws on the complementary strengths of both these methods. The salient feature of the method lies in its ability to handle nonsinusoidal wave-forms, multiple piezoelectric transducers, and arbitrary phase steps in an optical configuration. The method does not need the addition of carrier fringes to separate the spectral contents in the intensity fringes. The proposed concept thus overcomes the limitations of methods based on Fourier transform techniques. The robustness of the proposed method is studied in the presence of noise.     

An expedient approach to internally functionalized chiral dendrimers: synthesis of a dendritic molecule incorporating furanoside skeleton

In an approach to chiral dendritic molecules, a dendrimer incorporating pentose units in the interior and hexose units in the periphery is built up on a 1, 3, 5-trisubstituted aromatic core by using 1,2:5,6-diisopropylidene glucose as the carbohydrate precursor and a 3, 5-disubstituted aromatic unit as the branching block. The carbohydrate moiety also provides internal functionalities in the form of hemiacetal moiety of the furanoside ring.     

Baryogenesis and damping in nonminimal electroweak models

We calculate the baryon asymmetry of the Universe in the standard model of the electroweak theory with CP violation appropriate for simple extensions of the Higgs sector. The propagation of quarks of masses up to about 5 GeV are considered, taking into account the effect of damping rate. We find that the contribution of the b quark can still account for the observed baryon asymmetry to within the theoretical uncertainties of such models.

     

Growth of rough epitaxial surfaces

We present here a set of coupled continuum equations to describe atomic deposition. We take into account evaporation due to thermal and mechanical disturbances as well as subsequent accretion at favourable grooves.     

Laser optogalvanic spectroscopy of argon in the wavelength region 605–740 nm

Two-photon optogalvanic transitions in Ar glow discharge with Nd: YAG laser pumped dye laser excitation in the frequency range 13520–16520 cm⁻¹ has been studied using linear and circular polarization. The intensities of two-photon optogalvanic transitions are very sensitive to changes in the incident laser power which is not the case with one-photon transitions. Intensity ratio for circular and linear polarized light for two photon transitions 6s′[1/2]°1←4s[3/2]°2, 6s′[1/2]°0←4s[3/2]°2, and 5d[1/2]°0←4s[3/2]°2, 5d[1/2]°1←4s[3/2]°2 are quite different from the other two-photon transitions. This has been explained as due to near one photon resonance of 4p′[3/2]1 level for the first pair and 4p′[1/2]1 for the second pair of transitions. The ratio of optogalvanic intensity for circular to linear polarized light has been theoretically estimated and compared with the observed results.