Nucleation studies and characterization of potassium thiocyanate added KDP crystals grown by seed rotation technique

The effect of the addition of potassium thiocyanate on potassium dihydrogen phosphate (KDP) crystals, grown from aqueous solution by the temperature lowering method using a microcontroller based seed rotation technique has been studied. As part of nucleation studies, metastable zone width, induction period and crystal growth rate of additive added KDP are determined and analyzed with the pure system. Dielectric measurements were carried out on pure and doped crystals at various temperatures ranging from 313 to 423 K and compared. The crystalline perfection of the grown crystal was studied by the high resolution X-ray diffraction analysis. The crystal grown from additive added solution was subjected to structural, optical transmission, second harmonic generation and hardness studies and the effect of additive on pure system is investigated.     

An Extremal Eigenvalue Problem for a Two-Phase Conductor in a Ball

The pioneering works of Murat and Tartar (Topics in the mathematical modeling of composite materials. PNLDE 31. Birkhäuser, Basel, 1997) go a long way in showing, in general, that problems of optimal design may not admit solutions if microstructural designs are excluded from consideration. Therefore, assuming, tactilely, that the problem of minimizing the first eigenvalue of a two-phase conducting material with the conducting phases to be distributed in a fixed proportion in a given domain has no true solution in general domains, Cox and Lipton only study conditions for an optimal microstructural design (Cox and Lipton in Arch. Ration. Mech. Anal. 136:101–117, 1996). Although, the problem in one dimension has a solution (cf. Kre?n in AMS Transl. Ser. 2(1):163–187, 1955) and, in higher dimensions, the problem set in a ball can be deduced to have a radially symmetric solution (cf. Alvino et al. in Nonlinear Anal. TMA 13(2):185–220, 1989), these existence results have been regarded so far as being exceptional owing to complete symmetry. It is still not clear why the same problem in domains with partial symmetry should fail to have a solution which does not develop microstructure and respecting the symmetry of the domain. We hope to revive interest in this question by giving a new proof of the result in a ball using a simpler symmetrization result from Alvino and Trombetti (J. Math. Anal. Appl. 94:328–337, 1983).     

Superficial wrinkles in stretched, drying gelatin films

When a thin film of initially hydrated gelatin is allowed to dry from the surface, superficial changes in the structure of the material affect the local mechanical properties of the drying region. If the film is simultaneously subjected to large strain deformation (above 20%), a periodic pattern of wrinkles appears on the surface of the gelatin along the length of the sample in the direction of the applied force. These wrinkles are uniformly distributed on the surface of the gelatin with a wavelength that is much smaller than the sample thickness, which changes with sample composition, aging time, and deformation rate. We investigate these patterns via in situ environmental scanning electron microscopy (ESEM) and provide a theory for their origin.     

A simple microscopic model for the dynamics of adhesive failure

We consider a microscopic model for the failure of soft adhesives in tension based on ideas of bond rupture under dynamic loading. By focusing on adhesive failure under loading at constant velocity, we demonstrate that bimodal curves of stress against strain may occur due to effects of finite polymer chain or bond length and characterize the loading conditions under which such bimodal behavior is observed. The results of this analysis are in qualitative agreement with experiments performed on unconfined adhesives in which failure does not occur by cavitation.     

Enhancement of stability of growth,structural and NLO properties of KDP crystals due to additive along with seed rotation

Potassium Acetate (CH₃COOK) and Potassium Citrate (K₃C₆H₅O₇) as new additives were added into the potassium dihydrogen phosphate (KDP) solutions in different molar ratios. The metastable zone width and induction period with and without these additives were determined and compared. Dielectric measurements on pure and doped KDP crystals at various temperatures ranging from 313 to 423 K were carried out by the conventional parallel plate capacitor method which results low dielectric constant value dielectrics in doped crystals. The high resolution XRD studies show that CH₃COOK doped KDP crystal and K₃C₆H₅O₇ doped KDP crystal do not contain any internal structural grain boundaries and indicates that the crystalline perfection is very good. Moreover, the addition of these potassium additives improves the quality of the crystal and yields highly transparent crystals with well defined features. The effect of additives on the growth, nucleation kinetics, structural, NLO and optical properties has been investigated. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Defect induced local moment in ZnO as a consequence of Stoner mechanism

We have examined the formation of a local moment by considering various defects in ZnO. The localization of the defect induced state is found to determine the presence/absence of a local moment. A lot of attention on the probable origin of magnetism in wide band gap oxides has focused on cation vacancies. Here we show that oxygen interstitial atoms give rise to a large magnetic moment which results in a spin polarization of both the conduction and valence bands, in addition to spin polarized gap states. A Stoner mechanism is invoked and the relevant Stoner parameters are determined to be 0.7 eV for an oxygen atom in the presence of an oxygen interstitial but reduced to 0.2 eV on oxygen in the presence of a Zn vacancy.     

High-throughput screening assay for the quantification of Cer d18:1/16:0, d18:1/24:0, d18:1/24:1, d18:1/18:0, d18:1/14:0, d18:1/20:0, and d18:1/22:0 in HepG2 cells using RapidFire mass spectrometry

Ceramides are known to be involved in various biological processes with their physiological levels elevated in various disease conditions such as diabetes, Alzheimer's, atherosclerosis. To facilitate the rapid screening of Cer d18:1/16:0, d18:1/24:0, d18:1/24:1, d18:1/18:0, d18:1/14:0, d18:1/20:0, and d18:1/22:0 inhibition in HepG2 cells, a RapidFire coupled to tandem mass spectrometry (RF–MS/MS) method has been developed. The RF platform provides an automated solid-phase extraction system that gave a throughput of 12.6 s per sample to an MS/MS system using electrospray ionization under the positive ion mode. Chromatographic separation of Cer d18:1/16:0, d18:1/24:0, d18:1/24:1, d18:1/18:0, d18:1/14:0, d18:1/20:0, and d18:1/22:0 was achieved using a ternary gradient on C₈ type E cartridge. The MS/MS ion transitions monitored were 538.2 → 264.2, 650.7 → 264.2, 648.6 → 264.2, 566.4 → 264.2, 510.4 → 264.2, 594.4 → 264.2, 622.5 → 264.2, and 552.3 → 250.2 for Cer d18:1/16:0, d18:1/24:0, d18:1/24:1, d18:1/18:0, d18:1/14:0, d18:1/20:0, d18:1/22:0, and the internal standard (Cer d17:1/18:0), respectively. The RF–MS/MS methodology showed an excellent performance with an average Z′ value of 0.5–0.7. This is the first report of an RF–MS/MS assay for screening of ceramides which is amenable for high-throughput screening.     

Tuning of Bistability,Thermal Stability of the Metastable States,and Application Prospects in the C3-Symmetric Designs of Multiple Azo(hetero)arenes Systems

Light-responsive molecular systems with multiple photoswitches in C₃-symmetric designs have enormous application potential. The design part of such molecular systems is critical due to its influence in several properties associated with the photoswitches. In order to tune, and in the evaluation of the design–property relationship, we synthesized 18 tripodal systems with variations in the core, linkers, connectivity, and azo(hetero)arene photoswitches. Through extensive spectroscopic and computational studies, we envisaged the factors controlling near-quantitative photoisomerization in both the directions (bistability) and the thermal stability of the metastable states. Furthermore, we also evaluated the impact of designs in obtaining reversible photo-responsive sol-gel phase transitions, solvatochromism, photo- and thermochromism.