Impurity induced structural phase transformations in melt grown single crystals of lead iodide

Lead iodide is a wide‐band gap and highly resistive semiconductor considered to be a promising room temperature nuclear detector. The phenomenon of polytypism is posing interesting problems of phase transformations among its polytypic modifications and formation of polytypic admixture during growth due to native impurities. Transformations have also been observed even when the material is stored for few months that causes deterioration in functioning of the PbI₂ devices. Lead iodide has been purified and single crystals were grown using zone‐refining system. The observed phase transformations during growth and storage have been explained in the light of distortion of [PbI₆]^4‐ octahedron due to impurities present in the material and the known crystal structures of PbI₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoconductivity of Se85−xTe15Hgx thin films

The photoconductive properties such as dark conductivity, steady state and transient characteristics of a-Se_85−xTe₁₅Hg_x thin films, prepared by thermal vacuum evaporation technique have been studied in the temperature range 312–380 K. Analysis of data shows that the activation energy of dark current is greater as compared to the activation energy of photocurrent. The activation energy increases at higher concentration of Hg which shows that the defect density of states decreases. Analysis of intensity dependent photoconductivity shows that the bimolecular recombination is predominant. The transient photoconductivity shows that the carrier lifetime decreases with the increase in Hg concentration and increases at higher concentration of Hg. This decrease is due to the transition trapping process. Further the photosensitivity and carrier lifetime increases at higher concentration of Hg which also confirms that the density of defect states decreases.     

Estimation of time to stationarity in geometrically nonlinear structural responses

The determination of the time to stationarity is defined here through the convergence, to its stationary limit, of the nonstationary variance. This function is estimated through Monte Carlo simulations and a two-step, autoregressive-based modeling approach is employed to minimize the effects of randomness introduced by the limited number of simulations that can be carried out. The methodology is applied extensively to nonlinear single-degree-of-freedom models but is also demonstrated on 8-mode reduced order models of clamped–clamped straight and curved beams. In the latter case, it is found that the time to stationarity is strongly dependent on the excitation level, i.e. varying from one case to another by a factor at least larger than 4, thereby emphasizing the interest in estimating it beforehand. It is finally shown that the single-degree-of-freedom results tabulated here may be used for these reduced order models to obtain a first estimate of the time to stationarity.     

N-methyl Benzimidazole Tethered Cholic Acid Amphiphiles Can Eradicate S. aureus-Mediated Biofilms and Wound Infections

Infections associated with Gram-positive bacteria like S. aureus pose a major threat as these bacteria can develop resistance and thereby limit the applications of antibiotics. Therefore, there is a need for new antibacterials to mitigate these infections. Bacterial membranes present an attractive therapeutic target as these membranes are anionic in nature and have a low chance of developing modifications in their physicochemical features. Antimicrobial peptides (AMPs) can disrupt the microbial membranes via electrostatic interactions, but the poor stability of AMPs halts their clinical translation. Here, we present the synthesis of eight N-methyl benzimidazole substituted cholic acid amphiphiles as antibacterial agents. We screened these novel heterocyclic cholic acid amphiphiles against different pathogens. Among the series, CABI-6 outperformed the other amphiphiles in terms of bactericidal activity against S. aureus. The membrane disruptive property of CABI-6 using a fluorescence-based assay has also been investigated, and it was inferred that CABI-6 can enhance the production of reactive oxygen species. We further demonstrated that CABI-6 can clear the pre-formed biofilms and can mitigate wound infection in murine models.     

Nanoencapsulation and characterization of Albizia chinensis isolated antioxidant quercitrin on PLA nanoparticles

The plant isolated antioxidant quercitrin has been encapsulated on poly-d,l-lactide (PLA) nanoparticles by solvent evaporation method to improve the solubility, permeability and stability of this molecule. The size of quercitrin-PLA nanoparticles is 250 ± 68 nm whereas that PLA nanoparticles is 195 ± 55 nm. The encapsulation efficiency of nanoencapsulated quercitrin evaluated by HPLC and antioxidant assay is 40%. The in vitro release kinetics of quercitrin under physiological condition reveals initial burst release followed by sustained release. Less fluorescence quenching is observed with equimolar concentration of PLA encapsulated quercitrin than free quercitrin. The presence of quercitrin specific peaks on FTIR of five times washed quercitrin loaded PLA nanoparticles provides an extra evidence for the encapsulation of quercitrin into PLA nanoparticles. These properties of quercitrin nanomedicine provide a new potential for the use of such less useful highly active antioxidant molecule towards the development of better therapeutic for intestinal anti-inflammatory effect and nutraceutical compounds.     

Purification,growth and ESR studies of sodium nitrate

Single crystals of sodium nitrate have been purified and grown using zone-refining system fabricated in our laboratory. Laue photographs were employed to check the crystallinity. X-ray irradiated crystals have been studied by electron spin resonance.     

Laser-induced phase transitions in PbI2

Pure crystals of PbI₂ have been grown using zone-refining system. The structural phase transition 12 R → 2 H has been observed when exposed to ruby laser light. The results have been explained on the basis of structural considerations of PbI₂ and compared with the earlier existing findings in literature.     

Nonlinear Luminescence in CdI2 under Pulsed Laser Excitation

Cadmium iodide has been studied from the point of view of nonlinear processes by experiments of optical amplification under two photon excitation. The two photon absorption (2PA) coefficient is determined by nonlinear transmittance technique. By means of two and three photon comparative luminescence measurements carried out using a ruby and neodymium laser, the three photon absorption (3PA) coefficient is determined. The experimental values of the absorption coefficients are compared with the predictions of the existing theories.