Showing papers by "A.K. Pal published in 2003"

Galactose toxicity in the rat as a model for premature ovarian failure: an experimental approach readdressed.

Abstract: Background The pathophysiological mechanisms underlying premature ovarian failure (POF) are largely unknown. Our objective was to develop a working animal model to explore the pathogenesis of POF. Since galactosaemic women eventually develop POF, we evaluated the potential of experimental galactose toxicity as the proposed model. Methods Pregnant rats were fed pellets supplemented with or without 35% galactose from day 3 of conception continuing through weaning of the litters. Female offspring were evaluated for serum levels of galactose and galactose-1-phosphate, growth rate, onset of puberty, reproductive cyclicity, ovarian complement of follicles, hypothalamo-pituitary-ovarian function and follicular response to gonadotrophins. Results Galactose toxicity delayed the onset of puberty and developed a state of hypergonadotrophic hypoestrogenism. The characteristic low FSH levels at weaning followed by pubertal spurts of gonadotrophins and estradiol (E(2)) secretion of the controls was replaced by a sustained high level of FSH and a low level of E(2) under galactose toxicity. The ovary developed with apparently normal or deficient complement of follicles. Ovarian response to exogenous gonadotrophin stimulation was blunted, but the response improved significantly when the stimulation was preceded by pituitary desensitization. Conclusion Experimental galactose toxicity may serve as a model for exploring some of the basic tenets of POF.

Effect of particle shape distribution on the surface plasmon resonance of Ag–SiO2 nanocomposite thin films

Abstract: Silver?silica nanocomposite thin films were prepared by high pressure d.c.?sputtering technique. Films deposited at lower substrate temperature showed a narrow distribution of nanoparticles with nearly spherical shape. Increase in substrate temperature resulted in films with a non-uniform size and shape due to the agglomeration of the nanoparticles. This size and shape distribution has a profound effect on the optical absorbance spectra and results in a broad and asymmetric surface plasmon band. A?shape distribution introduced in the Maxwell?Garnett or Bruggeman effective medium theory was found to give a reasonable description of the experimentally observed optical absorption spectra.

Effect of interfacial alloying on the surface plasmon resonance of nanocrystalline Au-Ag multilayer thin films

Abstract: Nanocrystalline Au and Ag in multilayer thin film form with Au/Ag/Au structure were prepared by high pressure (∼40 Pa) d.c. sputtering techniques. The Ag concentrations in AgxAu1-x films were changed from x = 0 to 1. These multilayer films with varying Ag concentration showed significant changes in microstructures obtained from TEM and XRD analyses. The optical absorption spectra of these multilayer films showed a single plasmon band confirming the formation of Au-Ag alloy. We ascribe this alloying to the interfacial reactions in nanophase limited at the Au-Ag interface. The red-shift and broadening of the plasmon bands with the increase in silver concentration could be associated to the increase in size of the nanoparticles and its distribution. The observed red shift in the plasmon band may be associated with the change in electronic structure at the Au-Ag interface due to configuration mixing of the atomic energy levels of Au and Ag.

Prenatal exposure to high galactose adversely affects initial gonadal pool of germ cells in rats

Abstract: BACKGROUND: In rats, prenatal exposure to high concentrations of galactose may contribute to a condition that is equivalent to the premature ovarian failure (POF) component of human galactosaemia. We investigated if development of POF under experimental galactosaemia-like conditions was attributed to impaired germ cell migration. METHODS: Pregnant rats were fed pellets supplemented with, or without, 35% galactose from day 3 of conception continuing through parturition. Between days 12-15, embryos from one uterine horn were dissected out. Primordial germ cells (PGC) were histochemically localized and counted on the basis of binding of Dolichos biflorus agglutinin, a lectin specific for terminal N-acetylgalactosamine (GalNAc), to the surface glycoconjugate of the germ cells. The embryos from the other uterine horn were maintained until parturition. Liver activity of uridine diphosphate galactose 4-epimerase, the enzyme involved at multiple steps in the process of synthesis of GalNAc, was assayed in 1-2 day old female pups. RESULTS: The numbers of PGC at the day-specific sites on all days of examination were significantly lower (P ≤ 0.0003), and liver epimerase activity was significantly (P = 0.000001) reduced in the galactose-exposed group. CONCLUSION: Impaired germ cell migration leading to the development of gonads with deficient initial pools of germ cells may form the causal link between galactosaemia and POF.

Studies on CdS nanoparticles dispersed in silica matrix prepared by sol-gel technique

Abstract: SiO2/CdS-nanoparticle composite films (SiO2:CdS=85:15, 80:20, 75:25 and 70:30) were prepared by the sol-gel route. The films were characterized by studying microstructural (XRD and TEM) and optical (transmittance and photoluminescence) properties. Band gaps of these films annealed at different temperatures (373-473 K) for different times (10-120 min) indicated that the signature of nanocrystallinity is retained throughout the range of our experimental conditions. A thermal diffusion process controlled growth in the crystallite size with increasing annealing time and temperature. The average radii of the nanoparticles varied as the cube root of the annealing time but showed exponential dependence on the inverse of annealing temperature. Photoluminescence (PL) studies of the composite films indicated excitonic transitions. Theoretical analysis of the line shapes of the PL peaks recorded at 300 K and 80 K could be accounted for by the combined effects of size distribution and phonon broadening. It was observed that the deformation potential (E d) effectively controlled the line shapes of the PL measurements.

An ellipsometric investigation of Ag/SiO $\mathsf{_2}$ nanocomposite thin films

Abstract: Dielectric properties of silver/SiO2 nanocomposite thin films grown by high-pressure dc sputtering technique were studied by spectroscopic ellipsometry (300-800 nm) The dielectric behavior of the nanocomposite thin films largely depended on the particle size, its number density and the surrounding environments The films showed semiconductor-like behavior up to a critical particle size and concentration, beyond which the films exhibited the typical surface plasmon resonance characteristics in their optical properties The refractive index was also found to have a strong dependence on the particle size and its dispersion in the matrix The results were found to be consistent with those obtained from UV-VIS optical absorbance data Bruggeman effective medium theory was used to explain the experimental results

Effect of ion energy and ion current on the synthesis of c-BN films by r.f. plasma CVD

Abstract: Boron nitride films were synthesized by r.f. plasma CVD technique using borane-ammonia, nitrogen and argon as the precursor gases. The films were deposited onto Si (100) and fused silica substrates kept at different substrate temperatures (573–703 K). Hot emissive probe was utilized to measure the ion energy of the radicals bombarding the substrate during deposition. Effects of substrate temperature, ion energy and ion current on the c-BN content in the films were determined. Bombardment of energetic ions during growth has profound effect on the film quality. Initial layer seemed to contain boron rich hexagonal B51–2 N phase.