Reaction kinetics and pathway of hydrothermal decomposition of aspartic acid

The kinetics and pathway of hydrothermal decomposition of aspartic acid were studied using a continuous‐flow tubular reactor. The reaction was carried out in the temperature range of 200–260°C and at a pressure of 20 MPa. Deamination was the primary reaction, indicated by the presence of significant amount of ammonia, fumaric acid, or maleic acid in the products. Other reaction products were pyruvic acid, malic acid, and traces of succinic and lactic acid. Traces of alanine were also detected, showing the possibility of decomposing high‐molecular weight amino acids to obtain simple amino acids such as glycine or alanine. Results on the effect of reaction parameters demonstrated that decomposition of aspartic acid is highly temperature dependent under hydrothermal conditions. For a slight temperature difference of 60°C (from 200 to 260°C), the first‐order reaction rate constants of 0.003 significantly increased to 0.231 s^?1. The activation energy was 144 kJ/mol, as calculated by the Arrhenius equation. No significant effect was exhibited by other reaction parameters such as pH and pressure. The results are useful in controlling the hydrolysis of proteinaceous materials toward high yield of aspartic acid under hydrothermal conditions. © 2007 Wiley Periodicals, Inc. 39: 175–180, 2007     

Crystal and molecular structure of thiamine monochloride

The crystal and molecular structure of thiamine monochloride (C₁₂H₁₇N₄OSCl) was determined by X-ray diffraction and refined to a finalR value of 0.042. The compound crystallizes in the monoclinic system, space groupP2₁/a, with cell constantsa=18.929(4),b=11.663(2),c=6.376(2) Å and=96.72(8)°. The thiamine molecule is anhydrous and unprotonated, and the torsion angles at the methylene carbon show that it possesses anF conformation. The dihedral angle value of 84.16(6)° between thiazolium and pyrimidine rings is in the normal range found for the thiamine withF conformation, protonated or not, hydrated or not. Thiamine therefore has the same conformation notwithstanding protonation or hydration, with the rings similarly oriented in all the crystal structures containing thiamine.     

Thermal photon production in a strongly coupled anisotropic plasma

Journal of High Energy Physics - For the homogeneous configuration given by the long string limit of the folded string with a spin in AdS 3 and a spin and a winding number in S 1, we solve the...     

The potential of micro-electro-mechanical accelerometers in human vibration measurements

This paper evaluates the advantages and the drawbacks deriving from the use of MEMS (micro-electro-mechanical systems) accelerometers for hand-arm and whole-body vibration measurements. Metrological performances of different transducers were assessed through the identification of their frequency response function, linearity, floor noise and sensitivity to thermal and electromagnetic disturbances. Experimental results highlighted a standard instrumental uncertainty (including the nonlinearity) lower than 5% with the single frequency calibration procedure, such a value was reduced to 2%. The temperature effect was negligible and the electromagnetic disturbances sensitivity was comparable to that of the piezoelectric accelerometers. The compatibility of measurements obtained with MEMS accelerometers with those of piezoelectric-based measurement chains was verified for two specific applications. An example of direct transducer fixation on the skin for vibration transmissibility measurements is also presented. Thanks to the MEMS peculiarities – mainly small sizes and low cost – since novel approaches in the vibration monitoring could be pursued. For instance, it is possible to include by design MEMS accelerometers in any hand-held tool at the operator interface, or inside the seats structures of cars, tractors and trucks. This could be a viable solution to easily obtain repeatable exposure measurements and could also provide diagnostic signals for the tools or seats of functional monitoring.     

An indirect hybrid sound transmission loss controller

The control of sound transmission through panels is an important noise control problem in the aerospace, aeronautical, and automotive industries. The trend towards using lightweight composite materials that have lower sound insulation performance is a negative factor regarding low frequency transmission loss. Double-panel partitions with the gap filled with sound absorption materials are often employed to improve the sound insulation performance with reduced added weight penalty. However, in the low frequency range, the strong coupling between the panels through the air cavity and mechanical paths may greatly reduce the sound transmission performance, making it even lower than the performance of a single panel in some frequency ranges. In this work, an experimental investigation of a new kind of hybrid (active/passive) acoustic actuator is presented. The idea consists of replacing the acoustic absorption material by a hybrid actuator aiming at improving the transmission loss at low frequencies without altering the passive attenuation. A prototype of the system is tested in a plane wave acoustic tube setup. Different kinds of SISO feedforward control implementations were used to attenuate the sound power transmitted through the hybrid active–passive panel using an error microphone or a particle velocity sensor placed downstream with respect to the sample panel. Measurement results of the transmission loss with active and hybrid attenuation are presented and discussed.     

Experimental and theoretical study of the mechanism for the kinetic of elimination of methyl carbazate in the gas phase

The elimination kinetic of methyl carbazate in the gas phase was determined in a static system over the temperature range of 340–390 °C and pressure range of 47–118 Torr. The reaction is homogeneous, unimolecular, and obeys a first order rate law. The decomposition products are methyl amine, nitrous acid, and CO gas. The variation of the rate coefficients with temperatures is given by the Arrhenius expression: log k₁ (s^?1) = (11.56 ± 0.34) ? (180.7 ± 4.1) kJ mol^?1(2.303 RT)^?1. The estimated kinetics and thermodynamics parameters are in good agreement to the experimental values using B3LYP/6‐31G (d,p), and MP2/6‐31G (d,p) levels of theory. These calculations imply a molecular mechanism involving a concerted non‐synchronous quasi three‐membered ring cyclic transition state to give an unstable intermediate, 1,2‐oxaziridin‐3‐one. Bond order analysis and natural charges implies that polarization of O (alkyl)? C (alkyl) bond of the ester is rate determining in this reaction. Copyright © 2008 John Wiley & Sons, Ltd.     

Andreev levels in a graphene–superconductor surface

In order to consider the Dirac-like spectrum of graphene we employ the Bogoliubov de Gennes–Dirac formalism to determine the quasiparticle Andreev levels in an NS surface (normal–superconductor). The normal region is characterized by a width L while the superconducting region is semi-infinite and both regions are made of doped graphene. The quasiparticle energy spectrum is originated by the Andreev reflections that occur in the NS interface. It is shown that this spectrum depends on the width of the normal region and the Fermi energy in each region. When the Fermi energy in the normal metal is lower than the gap of the superconductor region, the spectrum is affected by specular Andreev reflections. The equation that is obtained to find the spectrum is very general and we solve it for some particular cases. We find that the energy spectrum oscillates when the Fermi energy in graphene is changed. Finally we obtain under some approximations an equation for the energy spectrum which is similar in structure as those obtained for an INS conventional junction.     

A version of Stöber synthesis enabling the facile prediction of silica nanospheres size for the fabrication of opal photonic crystals

A sol-gel synthesis procedure based on the method proposed by Stöber et al. (J Colloid Interface Sci 26:302–315, 1968) has been adopted for the one-step preparation of mono-dispersed silica nanospheres. An excellent control of the particle diameter over a wide range is obtained by varying the amount of silicon alkoxide only, while the concentration of all other components is kept fixed: this allows the fabrication of artificial opals with a finely tuned and precisely predictable lattice parameter.