Photoelectron spectroscopy beamline on Indus-1 synchrotron radiation source

We describe here a photoelectron spectroscopy beamline installed on Indus-1 storage ring. Initially we give a brief description of optical and mechanical layout of beam-line. The beamline optics was designed to cover energy range from 10 eV to 200 eV and it consists of a pre-focusing mirror, a toroidal grating monochromator and a post-focusing mirror. We then discuss indigenously developed ultra high vacuum compatible work station to carry out angle integrated photoemission experiments. The beamline has been successfully commissioned and photoemission measurements on a variety of standard samples are presented.

The requirements for Ca2+, protein phosphorylation and concurrent protein synthesis for zeatin signaling of acidic chitinase transcript accumulation in Cucumis sativus L

We have previously reported that both Ca2+ and staurosporine-sensitive protein kinase(s) are involved in the cytokinin zeatin induction of cucumber chitinase activity and its protein content (Barwe et al. 2001). To further characterize signal transduction events involved in this cytokinin induction of chitinase gene expression, Northern hybridizations of total RNAs prepared from excised, dark-grown cucumber cotyledons treated with cytokinins and/or various agonists and antagonists of signal transduction components, were carried out using a cucumber acidic chitinase (CACHT) cDNA probe (Metraux et al. 1989). CACHT mRNA increased by approximately 5- to 6-fold in response to exogenous zeatin (Z), zeatin riboside (ZR), and benzyladenine (BA) treatment, but failed to accumulate in response to kinetin (K). Among the cytokinins tested, Z was most effective. The Z-induced accumulation of CACHT mRNA was inhibited by a plasma membrane Ca2+ channel blocker verapamil. Treatment of cotyledons with exogenous CaCl2 and calcium ionophore A23187 in the presence and absence of cytokinin enhanced CACHT mRNA accumulation. These two observations suggest the participation of extracellular calcium in signaling Z-induction. Furthermore, the presence of staurosporine (an inhibitor of protein kinase) in Z treatment reduced CACHT mRNA, suggesting the involvement of phosphorylation of one or more cellular proteins. In addition, we provide evidence that the Z-induction of CACHT mRNA is blocked by protein synthesis inhibitor cycloheximide treatment. Taken together, these results suggest that Ca2+ influx from extracellular space, protein phosphorylation, and concurrent protein synthesis events participate in cytokinin signaling during Z-induced CACHT transcript accumulation.

A cascaded discharge plasma-adsorbent technique for engine exhaust treatment

A cascaded system of electrical discharges (non-thermal plasma) and adsorption process was investigated for the removal of oxides of Nitrogen (NOx) and total hydrocarbons (THC) from an actual diesel engine exhaust. The non-thermal plasma and adsorption processes were separately studied first and then the cascaded process was studied. In this study, different types of adsorbents were used. The NOx removal efficiency was higher with plasma-associated adsorption (cascaded) process compared to the individual processes and the removal efficiency was found almost invariant in time. When associated by plasma, among the adsorbents studied, activated charcoal and MS-13X were more effective for NOx and THC removal respectively. The experiments were conducted at no load and at 50% load conditions. The plasma reactor was kept at room temperature throughout the experiment, while the temperature of the adsorbent reactor was varied. A relative comparison of adsorbents was discussed at the end.

Optical and Electronic Properties of Conjugated Polymer -Nanocluster Semiconductor Hybrid Systems

Conjugated polymers are intensively pursued as candidate materials for emission and detection devices with the optical range of interest determined by the chemical structure. On the other hand the optical range for emission and detection can also be tuned by size selection in semiconductor nanoclusters. The mechanisms for charge generation and separation upon optical excitation, and light emission are different for these systems. Hybrid systems based on these different class of materials reveal interesting electronic and optical properties and add further insight into the individual characteristics of the different components. Multilayer structures and blends of these materials on different substrates were prepared for absorption, photocurrent (Iph), photoluminescence (PL) and electroluminscence (EL) studies. Polymers chosen were derivatives of polythiophene (PT) and polyparaphenylenevinylene (PPV) along with nanoclusters of cadmium sulphide of average size 4.4 nm (CdS-44). The photocurrent spectral response in these systems followed the absorption response around the band edges for each of the components and revealed additional features, which depended on bias voltage, thickness of the layers and interfacial effects. The current-voltage curves showed multi-component features with emission varying for different regimes of voltage. The emission spectral response revealed additive features and is discussed in terms of excitonic mechanisms.

Tribological characteristics of A356 Al alloy-SiC(P) composite discs

The dry sliding wear and friction behaviour of A356 Al alloy and its composites containing 10 and 20 vol.% SiC(P) have been studied using pin-on-disc set up. In these tests, A356 Al alloy and its composites are used as disc whereas brake pad was used in the form of pins. Wear tests were carried out at a load of 192 N and the sliding speed was varied from 1 to 5 m/s. Tests were done for a sliding distance of 15 km. The effects of sliding velocity on the wear rate, coefficient of friction and nature of tribolayers formed on discs have been studied. Wear rates of composites as calculated by weight loss method, found to be negative at sliding speed of more than 2 m/s. Worn surfaces of pins and discs have been analyzed using scanning electron microscope. SEM and EDAX analysis of worn surfaces of composite discs showed formation of tribolayers, consisting of mixture of oxides of Al, Si, Cu, Ca, Ba, Mg, and Fe. In these layers, copper and barium content found to be increase with sliding speed in the case of composites. (C) 2011 Elsevier B.V. All rights reserved.

Large reduction of leakage current by graded-layer La doping in (Ba0.5, Sr0.5)TiO3 thin films

A large reduction in the leakage current behavior in (Ba, Sr)TiO3 (BST) thin films was observed by graded-layer donor doping. The graded doping was achieved by introducing La-doped BST layers in the grown BST films. The films showed a large decrease (about six orders of magnitude) in the leakage current in comparison to undoped films at an electric field of 100 kV/cm. The large decrease in leakage current was attributed to the formation of highly resistive layers, originating from compensating defect chemistry involved for La-doped films grown in oxidizing environment. Temperature-dependent leakage-current behavior was studied to investigate the conduction mechanism and explanations of the results were sought from Poole–Frenkel conduction mechanism.

Nonlinear dielectric behavior in three-component ferroelectric superlattices

Three-component ferroelectric superlattices consisting of alternating layers of SrTiO3, BaTiO3, and CaTiO3 (SBC) with variable interlayer thickness were fabricated on Pt(111)/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. The presence of satellite reflections in x-ray-diffraction analysis and a periodic concentration of Sr, Ba, and Ca throughout the film in depth profile of secondary ion mass spectrometry analysis confirm the fabrication of superlattice structures. The Pr (remnant polarization) and Ps (saturation polarization) of SBC superlattice with 16.4-nm individual layer thickness (SBC16.4) were found to be around 4.96 and 34 μC/cm2, respectively. The dependence of polarization on individual layer thickness and lattice strain were studied in order to investigate the size dependence of the dielectric properties. The dielectric constant of these superlattices was found to be much higher than the individual component layers present in the superlattice configuration. The relatively higher tunability ( ∼ 55%) obtained around 300 K indicates that the superlattice is a potential electrically tunable material for microwave applications at room temperature. The enhanced dielectric properties were thus discussed in terms of the interfacial strain driven polar region due to high lattice mismatch and electrostatic coupling due to polarization mismatch between individual layers.

Ferroelectric interaction and polarization studies in BaTiO3/SrTiO3 superlattice

Ferroelectric superlattice structures consisting of alternating layers of BaTiO3 and SrTiO3 with variable interlayer thickness were grown on Pt (111)/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. The presence of superlattice reflections in the x-ray diffraction pattern clearly showed the superlattice behavior of the fabricated structures over a range of 6.4–20 nm individual layer thicknesses. Depth profile conducted by secondary ion mass spectrometry analysis showed a periodic concentration of Ba and Sr throughout the film. Polarization hysteresis and the capacitance-voltage characteristics of these films show clear size dependent ferroelectric characteristics. The spontaneous (Ps) and remnant (Pr) polarizations increase gradually with decreasing periodicity, reach a maximum at a finite thickness and then decrease. The competition between the size effect and long-range ferroelectric interaction is suggested as a possible reason for this phenomenon. The temperature dependence of Ps and Pr shows a single ferroelectric phase transition, and the Curie temperature is estimated to be about 316 K. The curve shows that the ferroelectric superlattice tends to form an artificial material, responding as a single structure with an averaged behavior of both the parent systems.

Higher topoisomerase 2 alpha gene transcript levels predict better prognosis in GBM patients receiving temozolomide chemotherapy: identification of temozolomide as a TOP2A inhibitor

The search for molecular markers which predict response to chemotherapy is an important aspect of current neuro-oncology research. MGMT promoter methylation is the only proved marker of glioblastoma. The purpose of this study was to assess the effect of topoisomerase expression on glioblastoma survival and study the mechanisms involved. The transcript levels of all isoforms of the topoisomerase family in all grades of diffuse astrocytoma were assessed. A prospective study of patients with glioblastoma treated by a uniform treatment procedure was performed with the objective of correlating outcome with gene expression. The ability of TOP2A enzyme to relax the super coiled plasmid DNA in the presence of temozolomide was evaluated to assess its effect on TOP2A. The temozolomide cyctotoxicity of TOP2A-silenced U251 cells was assessed. The transcript levels of TOP2A, TOP2B, and TOP3A are upregulated significantly in GBM in comparison with lower grades of astrocytoma and normal brain samples. mRNA levels of TOP2A correlated significantly with survival of the patients. Higher TOP2A transcript levels in GBM patients predicted better prognosis (P = 0.043; HR = 0.889). Interestingly, we noted that temozolomide inhibited TOP2A activity in in-vitro enzyme assays. We also noted that siRNA knock down of TOP2A rendered a glioma cell line resistant to temozolomide chemotherapy. We demonstrated for the first time that temozolomide is also a TOP2A inhibitor and established that TOP2A transcript levels determine the chemosensitivity of glioblastoma to temozolomide therapy. Very high levels of TOP2A are a good prognostic indicator in GBM patients receiving temozolomide chemotherapy.

Polymorphic phase boundaries and enhanced piezoelectric response in extended composition range in the lead free ferroelectric BaTi1-xZrxO3

Neutron powder diffraction study of Ba(Ti1-xZrx)O-3 at close composition intervals has revealed coexistence of ferroelectric phases: orthorhombic (Amm2) + tetragonal (P4mm) for 0.02 <= x <= 0.05 and rhombohedral (R3m) + orthorhombic (Amm2) for 0.07 <= x < 0.09. These compositions exhibit relatively enhanced piezoelectric properties as compared to their single phase counterparts outside this composition region, confirming the polymorphic phase boundary nature of the phase coexistence regions. (C) 2013 AIP Publishing LLC.

Anomalous piezoelectric response due to stabilization of two ferroelectric phases in Zr-modified BaTiO3

The lead-free Ba (Ti1-xZrx)O-3 ceramic has shown enhanced piezo-response (d(33)) in a narrow composition interval (0.01 <= x <= 0.03) exhibiting the coexistence of two ferroelectric phases. The system presents two electric-field-dependent-property regimes: (i) a low field regime (E < 1.7 kV mm(-1)) where d(33) is nearly independent of the poling field, and (ii) (E > 1.7 kV mm(-1)) for which d(33) drops sharply. X-ray diffraction studies revealed that the later phenomenon is related to field driven irreversible structural transformation, which tends to drive the system away from an equilibrium two phase state to a nearly single phase metastable state.

Base Triggered Enhancement of First Hyperpolarizability of a Keto-Enol Tautomer

This work describes the base triggered enhancement of first hyperpolarizability of a tautomeric organic molecule, namely, benzoylacetanilide (BA). We have used the hyper-Rayleigh scattering technique to measure the first hyperpolarizability (beta) of BA which exists in the pure keto form in water and as a keto-enol tautomer in ethanol. Its anion exists in equilibrium with the keto and enol forms at pH 11 in aqueous solution. The beta value of the anion form is 709 X 10(-30) esu, whereas that of the enol is 232 x 10(-3) esu and of the keto is 88 X 10(-30) esu. There is an enhancement of beta by similar to 8 times for the anion and similar to 3 times for the enol compared to the keto form. All these are achieved by altering the equilibrium between the three forms of BA by simple means. MP2 calculations reproduce the experimental trend, but the computed beta values are much lower than the measured values. DFT calculations with the standard B3LYP functional could not predict the right order in the beta values. The difference between experimental and calculated values is, perhaps, due to the fact that electron correlation effects are important in computing optical nonlinearities of large organic molecules and MP2 and B3LYP calculations done here for different forms of BA could not account for such effects adequately.

Structural landscape of the 1: 1 benzoic acid : isonicotinamide cocrystal

The acid-pyridine heterosynthon may be used as a `` molecular'' module to probe the structural landscape of the benzoic acid : isonicotinamide 1 : 1 cocrystal, BA: INA. Experimental structures of 1 : 1 cocrystals of fluorobenzoic acids (FBA) with isonicotinamide (INA) contain this heterosynthon and correspond to high-energy structures of 1 : 1 BA : INA.