GaN nanowires for piezoelectric generators

We demonstrate the high potential of GaN nanowires (NWs) to convert mechanical energy into electric energy. Using an atomic force microscope equipped with a Resiscope module, an average output voltage of –74 mV and a maximum of –443 mV ± 2% per NW were measured. This latter value is the highest reported so far for GaN NWs. By considering these output signals, we have estimated an average and a maximum power density generated by one layer of GaN NWs of the order of 5.9 mW/cm² and 130 mW/cm², respectively. These results offer promising prospects for the use of GaN NWs for high‐efficiency ultracompact piezogenerators. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microwave measurements of proton tunneling and structural parameters for the propiolic acid-formic acid dimer

Microwave spectra of the propiolic acid-formic acid doubly hydrogen bonded complex were measured in the 1 GHz to 21 GHz range using four different Fourier transform spectrometers. Rotational spectra for seven isotopologues were obtained. For the parent isotopologue, a total of 138 a-dipole transitions and 28 b-dipole transitions were measured for which the a-dipole transitions exhibited splittings of a few MHz into pairs of lines and the b-type dipole transitions were split by ~580 MHz. The transitions assigned to this complex were fit to obtain rotational and distortion constants for both tunneling levels: A(0+) = 6005.289(8), B(0+) = 930.553(8), C(0+) = 803.9948(6) MHz, Δ(0+)(J) = 0.075(1), Δ(0+)(JK) = 0.71(1), and δ(0+)(j) = -0.010(1) kHz and A(0-) = 6005.275(8), B(0-) = 930.546(8), C(0-) = 803.9907(5) MHz, Δ(0-)(J) = 0.076(1), Δ(0-)(JK) = 0.70(2), and δ(0-)(j) = -0.008(1) kHz. Double resonance experiments were used on some transitions to verify assignments and to obtain splittings for cases when the b-dipole transitions were difficult to measure. The experimental difference in energy between the two tunneling states is 291.428(5) MHz for proton-proton exchange and 3.35(2) MHz for the deuterium-deuterium exchange. The vibration-rotation coupling constant between the two levels, F(ab), is 120.7(2) MHz for the proton-proton exchange. With one deuterium atom substituted in either of the hydrogen-bonding protons, the tunneling splittings were not observed for a-dipole transitions, supporting the assignment of the splitting to the concerted proton tunneling motion. The spectra were obtained using three Flygare-Balle type spectrometers and one chirped-pulse machine at the University of Virginia. Rotational constants and centrifugal distortion constants were obtained for HCOOH···HOOCCCH, H(13)COOH···HOOCCCH, HCOOD···HOOCCCH, HCOOH···DOOCCCH, HCOOD···DOOCCCH, DCOOH···HOOCCCH, and DCOOD···HOOCCCH. High-level ab initio calculations provided initial rotational constants for the complex, structural parameters, and some details of the proton tunneling potential energy surface. A least squares fit to the isotopic data reveals a planar structure that is slightly asymmetric in the OH distances. The formic OH···O propiolic hydrogen bond length is 1.8 ? and the propiolic OH···O formic hydrogen bond length is 1.6 ?, for the equilibrium configuration. The magnitude of the dipole moment was experimentally determined to be 1.95(3) × 10(-30) C m (0.584(8) D) for the 0(+) states and 1.92(5) × 10(-30) C m (0.576(14) D) for the 0(-) states.     

The Influence of Adnectin Binding on the Extracellular Domain of Epidermal Growth Factor Receptor

The precise and unambiguous elucidation and characterization of interactions between a high affinity recognition entity and its cognate protein provides important insights for the design and development of drugs with optimized properties and efficacy. In oncology, one important target protein has been shown to be the epidermal growth factor receptor (EGFR) through the development of therapeutic anticancer antibodies that are selective inhibitors of EGFR activity. More recently, smaller protein derived from the 10th type III domain of human fibronectin termed an adnectin has also been shown to inhibit EGFR in clinical studies. The mechanism of EGFR inhibition by either an adnectin or an antibody results from specific binding of the high affinity protein to the extracellular portion of EGFR (exEGFR) in a manner that prevents phosphorylation of the intracellular kinase domain of the receptor and thereby blocks intracellular signaling. Here, the structural changes induced upon binding were studied by probing the solution conformations of full length exEGFR alone and bound to a cognate adnectin through hydrogen/deuterium exchange mass spectrometry (HDX MS). The effects of binding in solution were identified and compared with the structure of a bound complex determined by X-ray crystallography. ?      

Microencapsulation of nisin in alginate-cellulose nanocrystal (CNC) microbeads for prolonged efficacy against Listeria monocytogenes

The present study was undertaken to develop edible nisin-microencapsulated beads in order to inhibit growth of Listeria monocytogenes in ready-to-eat (RTE) ham. Different concentrations of nisin (16, 31, and 63 μg/ml) were microencapsulated into alginate-cellulose nanocrystal beads. Microencapsulation kept the available nisin (63 μg/ml) content 20 times greater compared with free nisin (63 μg/ml) during 28 days of storage at 4 °C. Results showed that 63 μg/ml microencapsulated nisin exhibited 31.26 μg/ml available nisin content after 28 days of storage at 4 °C, whereas there was no available nisin content left for free nisin. Cooked ham slices were then coated by the microencapsulated nisin beads, inoculated with L. monocytogenes [~3 log colony-forming units (CFU)/g], and stored at 4 °C under vacuum packaging for 28 days. The beads containing 16, 31, and 63 μg/ml nisin significantly (P ≤ 0.05) reduced the L. monocytogenes counts by 2.65, 1.50, and 3.04 log CFU/g after 28 days of storage compared with free nisin. Furthermore, microencapsulated nisin beads did not change the physicochemical properties (pH and color) of RTE ham during storage.     

Old Friends Revisited: the Multifractal Nature of Some Classical Functions

We study some explicit functions introduced by Riemann, Jordan, Lévy, Kahane… These functions share the property of having a dense set of discontinuities. We prove that they are examples of multifractal functions.     

Electron spin resonance on carbon nanotubes–polymer composites

Electron spin resonance investigations on styrene–polyisoprene–polystyrene block copolymer loaded with various amounts of multiwalled carbon nanotubes are reported. The temperature dependence of resonance line parameters in the range 290–425 K was analyzed. It was proved that the main resonance line represents a bottleneck of localized and delocalized electrons residing on carbon nanotubes. The temperature dependence of the g-factor and double integral of resonance spectra confirmed this interpretation. The temperature dependence of the resonance linewidth of composites containing various concentrations of nanotubes was explained by the thermally activated narrowing of the resonance spectra. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3406–3412, 2005     

Sol-Gel Coatings on Non-Oxide Planar Substrates and Fibers: A Protection Barrier Against Oxidation and Corrosion

Sol-gel coatings on non-oxide substrates can be used to prevent high temperature degradation and to improve wet corrosion resistance. Alumina coatings were investigated. The starting precursor was aluminium sec-butoxide, modified with chelating ligands such as 2,4-pentanedione or acrylic acid to prevent its precipitation in the presence of water. Stainless steel plates and Hi-Nicalon SiC fibers are often utilized in different kinds of applications and thus were selected as substrates. Thin films were deposited from the modified alkoxide solutions using dip-coating techniques. The parameters governing the process such as the aging of the sols, the viscosity, the withdrawal rate and the thermal treatment were investigated. The films were characterized (morphology, thickness) and showed an interesting behaviour as protection barrier in an aggressive medium.     

Symmetries of directed graphs and the Chinese remainder theorem

It is shown that a permutation group on a finite set is the automorphism group of some directed graph if and only if a generalized Chinese remainder theorem holds for the family of stabilizers. This result can be applied to examine some special permutation groups, including the general linear groups of finite vector spaces.     

Pressure and temperature jump relaxation kinetics of the conformational change in Salmonella typhimurium tryptophan synthase L-serine complex: large activation compressibility and heat capacity changes demonstrate the contribution of solvation

Tryptophan synthase is an alpha2beta2 multienzyme complex that exhibits coupling of the alpha- and beta-subunit reactions by tightly controlled allosteric interactions. A wide range of parameters can affect the allosteric interactions, including monovalent cations, pH, alpha-site and beta-site ligands, temperature, and pressure. Rapid changes in hydrostatic pressure (P-jump) and temperature (T-jump) were used to examine the effects of pressure and temperature on the rates of the interconversion of external aldimine and aminoacrylate intermediates in the Tryptophan synthase-L-Ser complex. The intense fluorescence emission of the Tryptophan synthase L-Ser external aldimine complex at 495 nm, with 420 nm excitation, provides a probe of the conformational state of Trp synthase. P-jump measurements allowed the determination of rate constants for the reactions in the presence of Na(+), Na(+) with benzimidazole (BZI), and NH4(+). The data require a compressibility term, beta(o)(double dagger), to obtain good fits, especially for the NH4(+) and BZI/Na(+) data. The compressibility changes are consistent with changes in solvation in the transition state. The transition state for the relaxation is more similar in volume to the closed aminoacrylate complex in the presence of Na(+), while it is more similar to the open external aldimine in the presence of NH4(+). Differences between the relaxations for positive and negative P-jumps may arise from changing relative populations of microstates with pressure. T-jump experiments of the Na(+) form of the tryptophan synthase-L-Ser complex show large changes in rate and amplitude over the temperature range from 7 to 45 degrees C. The Arrhenius plots show strong curvature, and hence require a heat capacity term, DeltaC(p)(double dagger), to obtain good fits. The values of DeltaC(p)(double dagger) are very large and negative (-3.6 to -4.4 kJ mol(-1) K(-1)). These changes are also consistent with large changes in solvation in the transition state for interconversion of external aldimine and aminoacrylate intermediates in the Tryptophan synthase-L-Ser complex.