Materials Literature
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We present data concerning the dynamics of photoexcitation of defect centers in germanium-doped silica glass optical fibers and fiber preforms. It is shown that two-photon absorption of mode-locked and Q-switched light at 527 nm results in partial ionization of the germanium oxygen deficiency center (GODC) 400-nm lumi…
We report strong visible photoluminescence (PL) at room temperature from oxidized Si nanometer-sized spheres with a spherical crystalline Si (c-Si) core and an amorphous ${\mathrm{SiO}}_{2}$ (a-${\mathrm{SiO}}_{2}$) surface layer. The peak energy of the broad PL spectrum is about 1.65 eV, which is independent of the c…
Helically coiled forms of the carbon cage on the nanometer scale are theoretically proposed. The optimized surface construction for different types of helically coiled structures consisting of sevenfold, sixfold, and fivefold rings of carbon atoms is given. The thermal stability of various helical structures is studie…
Stealth liposomes have recently emerged as a promising antitumor drug delivery system, yet no studies have been reported to examine their dynamic behavior at the microcirculatory level. In this investigation, we have used in vivo fluorescence videomicroscopy to study the decay in plasma concentration and the interstit…
Abstract Various nylon 6‐clay hybrids, such as molecular composites of nylon 6 and silicate layers of montmorillonite and saponite, NCHs and NCHPs, respectively, have been synthesized. Sorption of water in those hybrids was measured to estimate the resistance to water permeation. The diffusion coefficient D and the pa…
A highly tetrahedrally bonded form on nonhydrogenated amorphous carbon (a-C) is produced by deposition from filtered medium-energy ion beams. A range of such films was grown and the ${\mathit{sp}}^{3}$-bonded fractions, plasmon energies, compressive stresses, and resistivities were measured as a function of ion energy…
The nonlinear optical behaviour of the organic crystal MBA-NP has been investigated at 1064 and 532 nm, with both nanosecond and picosecond pulses. The second-order effective susceptibility for second harmonic generation, and the damage thresholds compare favourably with those of most inorganic crystals. Two-photon ab…
A summary is given of theories founded on concepts such as roughening transitions, kinetic roughening, and connected nets which in principle allow the prediction of the conditions under which a crystal face (hkl) will grow as a flat face, by a layer mechanism, or as a rough face. Starting with Jackson's theory based o…
The growth kinetics of m-chloronitrobenzene crystals from acetone solutions were measured and analysed to see the effects of the presence of microcrystals in the solution. The microcrystals generated by the added fine crystals were found to cause significant enhancement of the growth rate by a factor of 2-5. Possible…
Vogel-Fulcher-Tammann temperature dependence of sigma ( sigma varies as exp(-E a /k(T-T 0 ))) was found in a KTiOPO 4 single crystal for the (001) direction. The values of T 0 and E a were 150 K and 0.16 eV respectively. Below 150 K fast ion transport can therefore be expected to be frozen.
The information required from optical assessment of nonlinear organic materials differs widely depending on the application envisaged for the material in question. Accordingly, a suitable assessment scheme must be devised which will give a reliable indication of the promise of these materials in a wide variety of appl…
The quest for more efficient nonlinear optical materials of increased optical quality is being spurred by the development of optical communication systems that require ultrafast broad band optical signal processing functions. Conversely, nonlinear optical phenomena enlarge traditional spectroscopic approaches to encom…
Atomic force microscopy was used to obtain images of lysozyme crystals growing in their native solution environment. The authors growth by both two-dimensional nucleation and screw dislocation mechanisms. Nucleation centres appeared to occur randomly over the surface, and were uncorrelated from layer to layer. Surface…
Phenytoin crystal growth kinetics have been measured in phosphate buffer as a function of pH, supersaturation, and temperature. Incorporation of growth units into the crystal lattice is controlled by surface integration and follows a screw-dislocation mechanism. This mechanism explains the observed dependence of growt…
The underlying crystal-growth theory and structural molecular chemistry important in the understanding of the methodology behind the theoretical prediction of crystal morphology is presented together with its application to the molecular solid benzophenone. Benzophenone crystallizes in the orthorhombic space group P2…
Tailor-made molecular auxiliaries for the control of nucleation and growth of molecular crystals may be classified into two broad categories: inhibitors and promoters. Tailor-made inhibitors of crystal growth can be used for a variety of purposes which include morphological engineering, reduction of crystal symmetry,…
Polymorphism has critical implications in material design of organic crystals for elucidating specific functions in optics, pharmaceuticals, foods, biology etc. This is because diversified properties are revealed in polymorphic modifications. Depending on the selection of the specific polymorphs, one has to deal with…
Protein and virus crystals commonly grown in the laboratory on earth have also been grown in a microgravity environment on the US Space Shuttle. Two techniques for growth of the crystals were investigated: vapour diffusion and direct liquid-liquid diffusion. Crystals produced in microgravity, although generally isomor…
The production of uniform fine crystalline particles is highly desirable for pharmaceutical products in order to enhance stability and dissolution rates and, thereby, to favour high bioavailability. Precipitation under high-supersaturation conditions favours nucleation over growth processes and will result in smaller…
The effect of solvent in crystallization of polymorphs has been studied using the drug sulphathiazole as a model compound. The solubilities of the four polymorphic forms of sulphathiazole were determined as a function of temperature in various solvents. Within the temperature ranges studied, the rank order of solubili…