Structural characterization of backbone-expanded helices in hybrid peptides: (αγ) n and (αβ) n sequences with unconstrained β and γ homologues of L-Val

Learning your αβγ's: The diversity of hydrogen-bonding patterns in backbone-expanded hybrid helices is shown by crystal-structure determination of several oligomeric peptides (see scheme; C=gray; H=white; O=red; N=blue). C 12 helices were observed in the αγ peptide series for n=2-8. In comparison, the αα peptide and αβ peptide sequences show C 10 and mixed C 14/C 15 helices, respectively. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Substrate integrated Lead-Carbon hybrid ultracapacitor with flooded, absorbent glass mat and silica-gel electrolyte configurations

Lead-Carbon hybrid ultracapacitors (Pb-C HUCs) with flooded, absorbent-glass-mat (AGM) and silica-gel sulphuric acid electrolyte configurations are developed and performance tested. Pb-C HUCs comprise substrate-integrated PbO2 (SI-PbO2) as positive electrodes and high surface-area carbon with graphite-sheet substrate as negative electrodes. The electrode and silica-gel electrolyte materials are characterized by XRD, XPS, SEM, TEM, Rheometry, BET surface area, and FTIR spectroscopy in conjunction with electrochemistry. Electrochemical performance of SI-PbO2 and carbon electrodes is studied using cyclic voltammetry with constant-current charge and discharge techniques by assembling symmetric electrical-double-layer capacitors and hybrid Pb-C HUCs with a dynamic Pb(porous)/PbSO4 reference electrode. The specific capacitance values for 2 V Pb-C HUCs are found to be 166 F/g, 102 F/g and 152 F/g with a faradaic efficiency of 98%, 92% and 88% for flooded, AGM and gel configurations, respectively.

Sonochemical Synthesis of Pt Ion Substituted TiO2 (Ti0.9Pt0.1O2): A High Capacity Anode Material for Lithium Battery

Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ -> Ti3+ -> Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. Accordingly, 10 atom% Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder X-ray diffraction pattern (XRD), Rietveld refinement and TEM study reveals that Ti0.9Pt0.1O2 nanocrystallites of similar to 4 nm size crystallize in anatase structure. X-ray photo-electron spectroscopy (XPS) study confirms that and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt-0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg(-1) or exchange of similar to 1.5Li/Ti0.9Pt0.1O2. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.029208jes] All rights reserved.

Completely random nanoporous Cu4O3-CuO-C composite thin films for potential application as multiple channel photonic band gap based filter in the telecommunication wavelengths

In 2003, Babin et al. theoretically predicted (J. Appl. Phys. 94:4244, 2003) that fabrication of organic-inorganic hybrid materials would probably be required to implement structures with multiple photonic band gaps. In tune with their prediction, we report synthesis of such an inorganic-organic nanocomposite, comprising Cu4O3-CuO-C thin films that experimentally exhibit the highest (of any known material) number (as many as eleven) of photonic band gaps in the near infrared. On contrary to the report by Wang et al. (Appl. Phys. Lett. 84:1629, 2004) that photonic crystals with multiple stop gaps require highly correlated structural arrangement such as multilayers of variable thicknesses, we demonstrate experimental realization of multiple stop gaps in completely randomized structures comprising inorganic oxide nanocrystals (Cu4O3 and CuO) randomly embedded in a randomly porous carbonaceous matrix. We report one step synthesis of such nanostructured films through the metalorganic chemical vapor deposition technique using a single source metalorganic precursor, Cu-4(deaH)(dea)(oAc)(5) a <...aEuro parts per thousand(CH3)(2)CO. The films displaying multiple (4/9/11) photonic band gaps with equal transmission losses in the infrared are promising materials to find applications as multiple channel photonic band gap based filter for WDM technology.

Meso-Structured Silica-Nafion Hybrid Membranes for Direct Methanol Fuel Cells

A series of novel organic-inorganic hybrid membranes have been prepared employing Nafion and acid-functionalized meso-structured molecular sieves (MMS) with varying structures and surface area. Acid-functionalized silica nanopowder of surface area 60 m(2)/g, silica meso-structured cellular foam (MSU-F) of surface area 470 m(2)/g and silica meso-structured hexagonal frame network (MCM-41) of surface area 900 m(2)/g have been employed as potential filler materials to form hybrid membranes with Nafion framework. The structural behavior, water uptake, proton conductivity and methanol permeability of these hybrid membranes have been investigated. DMFCs employing Nafion-silica MSU-F and Nafion-silica MCM-41 hybrid membranes deliver peak-power densities of 127 mW/cm(2) and 100 mW/cm(2), respectively; while a peak-power density of only 48 mW/cm(2) is obtained with the DMFC employing pristine recast Nafion membrane under identical operating conditions. The aforesaid characteristics of the hybrid membranes could be exclusively attributed to the presence of pendant sulfonic acid groups in the filler, which provide fairly continuous proton-conducting pathways between filler and matrix in the hybrid membranes facilitating proton transport without any trade-off between its proton conductivity and methanol crossover. (C) 2012 The Electrochemical Society. DOI: 10.1149/2.036211jes] All rights reserved.

Polymer microfabrication by scanning based microstereolithography: Optical design and material functionality

Several research groups have attempted to optimize photopolymerization parameters to increase the throughput of scanning based microstereolithography (MSL) systems through modified beam scanning techniques. Efforts in reducing the curing line width have been implemented through high numerical aperture (NA) optical setups. However, the intensity contour symmetry and the depth of field of focus have led to grossly non-vertical and non-uniform curing profiles. This work tries to review the photopolymerization process in a scanning based MSL system from the aspect of material functionality and optical design. The focus has been to exploit the rich potential of photoreactor scanning system in achieving desired fabrication modalities (minimum curing width, uniform depth profile, and vertical curing profile) even with a reduced NA optical setup and a single movable stage. The present study tries to manipulate to its advantage the effect of optimized lower c] (photoinitiator (PI) concentration) in reducing the minimum curing width to similar to 10-20 mu m even with a higher spot size (similar to 21.36 mu m) through a judiciously chosen ``monomer-PI'' system. Optimization on grounds of increasing E-max (maximum laser exposure energy at surface) by optimizing the scan rate provides enough time for the monomer or resin to get cured across the entire resist thickness (surface to substrate similar to 10-100 mu m), leading to uniform depth profiles along the entire scan lengths. (C) 2012 American Institute of Physics. http://dx.doi.org/10.1063/1.4750975]

Hybrid molecules of carvacrol and benzoyl urea/thiourea with potential applications in agriculture and medicine

Benzoyl phenyl urea, a class of insect growth regulator's acts by inhibiting chitin synthesis. Carvacrol, a naturally occurring monoterpenoid is an effective antifungal agent. We have structurally modified carvacrol (2-methyl-5-1-methylethyl] phenol) by introducing benzoylphenyl urea linkage. Two series of benzoylcarvacryl thiourea (BCTU, 4a-f) and benzoylcarvacryl urea (BCU, 5a-f) derivatives were prepared and characterized by elemental analysis, IR, H-1 and C-13 NMR and Mass spectroscopy. Derivatives 4b, 4d, 4e, 4f and 5d, 5f showed comparable insecticidal activity with the standard BPU lufenuron against Dysdercus koenigii. BCTU derivatives 4c, 4e and BCU 5c showed good antifungal activity against phytopathogenic fungi viz. Magnaporthe grisae, Fusarium oxysporum, Dreschlera oryzae; food spoilage yeasts viz. Debaromyces hansenii, Pichia membranifaciens; and human pathogens viz. Candida albicans and Cryptococcus neoformans. Compounds 5d, 5e and 5f showed potent activity against human pathogens. Moderate and selective activity was observed for other compounds. All the synthesized compounds were non-haemolytic. These compounds have potential application in agriculture and medicine. (C) 2012 Elsevier Ltd. All rights reserved.

Metal cholate hydrogels: versatile supramolecular systems for nanoparticle embedded soft hybrid materials

This work describes the formation of hydrogels from sodium cholate solution in the presence of a variety of metal ions (Ca2+, Cu2+, Co2+, Zn2+, Cd2+, Hg2+ and Ag+). Morphological studies of the xerogels by electron microscopy reveal the presence of helical nanofibres. The rigid helical framework in the calcium cholate hydrogel was utilised to synthesize hybrid materials (AuNPs and AgNPs). Doping of transition metal salts into the calcium cholate hydrogel brings out the possibility of synthesising metal sulphide nano-architectures keeping the hydrogel network intact. These novel gel-nanoparticle hybrid materials have encouraging application potentials.

Space-vector-based hybrid pulse width modulation technique to reduce line current distortion in induction motor drives

Pulse width modulation (PWM) techniques involving different switching sequences are used in space vector-based PWM generation for reducing line current ripple in induction motor drives. This study proposes a hybrid PWM technique employing five switching sequences. The proposed technique is a combination of continuous PWM, discontinuous PWM (DPWM) and advanced bus clamping PWM methods. Performance of the proposed PWM technique is evaluated and compared with those of the existing techniques on a constant volts per hertz induction motor drive. In terms of total harmonic distortion in the line current, the proposed method is shown to be superior to both conventional space vector PWM (CSVPWM) and DPWM over a fundamental frequency range of 32-50 Hz at a given average switching frequency. The reduction in harmonic distortion is about 42% over CSVPWM at the rated speed of the drive.

Lithium D-Isoascorbate Monohydrate, a New Nonlinear Optical Material

Single crystals of lithium D-isoascorbate monohydrate (LDAM), (C6H7O6Li center dot H2O), are grown by a solution growth method. The crystal structure of LDAM is solved using single crystal X-ray diffraction. The space group is orthorhombic P2(1)2(1)2(1) with four formula units per unit cell and lattice parameters a = 7.7836(3) angstrom, b = 8.7456(3) angstrom, and c = 11.0368(4) angstrom. Solubility of the material in water is determined thermogravimetrically and found to have a positive temperature coefficient of solubility. Large optical quality single crystals are subsequently grown from aqueous solution by a slow cooling method. The crystal has a bulky prismatic habit and among the prominent faces the c face appears as the only principal morphological face. The crystal exhibits a (010) cleavage. Dielectric spectroscopy reveals a nearly Debye type Cole-Cole behavior with anisotropy in relaxation. Optical transmission range is found to be from 300 to 1400 nm. The principal refractive indices of this biaxial crystal, measured using Brewster's angle method, at wavelengths 405, 543, and 632.8 nm, show high dispersion. The crystal is negative biaxial with 2V(z) = 107.8 degrees (405 nm) and belongs to the Hobden class 3. Theoretically generated type 1 and type 2 second order phase matching curves match very well with the experimental results. The second-order nonlinear coefficient d(14) was determined to be 7 x 10(-13) m/V. For the optimum phase matching direction (type 2), the second-order effective nonlinear coefficient and the walk off angle are determined to be 0.84 times d(14) and 3.5 degrees respectively. The crystal possesses high multiple surface damage thresholds of 18 GW/cm(2) and 8 GW/cm(2) at laser wavelengths 1064 and 532 nm, respectively.

A Hybrid Five-Level Inverter With Common-Mode Voltage Elimination Having Single Voltage Source for IM Drive Applications

A new hybrid five-level inverter topology with common-mode voltage (CMV) elimination for induction motor drive is proposed in this paper. This topology has only one dc source, and different voltage levels are generated by using this voltage source along with floating capacitors charged to asymmetrical voltage levels. The pulsewidth modulation (PWM) scheme employed in this topology balances the capacitor voltages at the required levels at any power factor and modulation index while eliminating the CMV. This inverter has good fault-tolerant capability as it can be operated in three-or two-level mode with CMV elimination, in case of any failure in the H-bridges. More voltage levels with CMV elimination can be realized from this topology but only in a limited range of modulation index and power factor. Extensive simulation is done to validate the PWM technique for CMV elimination and balancing of the capacitor voltages. The experimental verification of the proposed inverter-fed induction motor is carried out in the linear modulation and overmodulation regions. The steady-state and transient operations of the drive are verified. The dynamics of the capacitor voltage balancing is also tested. The experimental results demonstrate that the proposed topology can be considered for industrial drive applications.

A 12 V Substrate-Integrated PbO2-Activated Carbon Asymmetric Hybrid Ultracapacitor with Silica-Gel-Based Inorganic-Polymer Electrolyte

A 12 V Substrate-Integrated PbO2-Activated Carbon hybrid ultracapacitor (SI-PbO2-AC HUCs) with silica-gel sulfuric acid electrolyte is developed and performance tested. The performance of the silica-gel based hybrid ultracapacitor is compared with flooded and AGM-based HUCs. These HUCs comprise substrate-integrated PbO2 (SI-PbO2) as positive electrodes and high surface-area activated carbon with dense graphite-sheet substrate as negative electrodes. 12 V SI-PbO2-AC HUCs with flooded, AGM and gel electrolytes are found to have capacitance values of 308 F, 184 F, and 269 F at C-rate and can be pulse charged and discharged for 100,000 cycles with only a nominal decrease in their capacitance values. The best performance is exhibited by gel-electrolyte HUCs.

A Hybrid Multilevel Inverter System Based on Dodecagonal Space Vectors for Medium Voltage IM Drives

Dodecagonal (12-sided) space vector pulsewidth modulation (PWM) schemes are characterized by the complete absence of (6n +/- 1)th-order harmonics (for odd n) in the phase voltages, within the linear modulation range and beyond, including over-modulation. This paper presents a new topology suitable for the realization of such multilevel inverter schemes for induction motor (IM) drives, by cascading two-level inverters with flying-capacitor-inverter fed floating H-bridge cells. Now, any standard IM may be used to get the dodecagonal operation which hitherto was possible only with open-end winding IM. To minimize the current total harmonic distortion (THD), a strategy for synchronous PWM is also proposed. It is shown that the proposed method is capable of obtaining better THD figures, compared to conventional dodecagonal schemes. The topology and the PWM strategy are validated through analysis and subsequently verified experimentally.