Comment on: “Lorentz violation in high-energy ions” by Santosh Devasia

In an article “Lorentz violation in high-energy ions” by S. Devasia published in this Journal [EPJ C 69, 343 (2010)], our recent Doppler shift experiments on fast ion beams are reanalyzed. Contrary to our analysis, Devasia concludes that our results provide an “indication of Lorentz violation”. We argue that this conclusion is based on a fundamental misunderstanding of our experimental scheme and reiterate that our results are in excellent agreement with Special Relativity.     

Simulation of round jets with nozzle-dependent inflow conditions using the k−ε turbulence model

In view of the “round jet initial condition anomaly”, discussed in literature, we investigate the effect of inflow conditions resulting from the use of different nozzle geometries to form the jet. RANS simulations in the framework of OpenFOAM using the k − ε turbulence model are performed. As the standard model coefficient C_ε1 = 1.44 is known to overpredict spreading rates for round jets, a value of C_ε1 = 1.6 was recommended for this case already in the 1970's. While this works well for jets issuing from long pipes, it does not give satisfactory results for other nozzle geometries. To overcome this deficiency while keeping the k − ε model, we suggest modified coefficients C_ε1 based on profiles of mean flow and turbulence at the nozzle exit. We determine optimal values of C_ε1 for three different nozzle geometries, and test them at various Reynolds numbers. Good agreement with experimental data is obtained. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evidence of an isomeric pair in furan...HCl: Fourier transform infrared spectroscopy and ab initio calculations

For the first time the coexistence of a sigma- and a pi-complex in the C(4)H(4)O:HCl system has been observed, in the same supersonic expansion of a molecular jet seeded with argon (or helium) or in a flow-cooled cell at 240 K. This is an exception to the third of the Legon-Miller rules which claims the sigma-structure to be the only one to exist. On the grounds of energetic considerations and band contour simulations, two observed bands at 2787.7 and 2795.5 cm(-1) of the nu(s) HCl stretching frequency are assigned to the two complexes, recorded as Fourier transform infrared spectra with a resolution between 0.2 and 0.5 cm(-1). Complementary calculations show that the use of the standard second-order Moller-Plesset perturbation theory may be erroneous for such a complex, due of the overestimation of the dispersion contribution with respect to the electrostatic term. It is finally established that only a balanced version of the second-order Moller-Plesset perturbation method, spin-component scaled-MP2, or a higher level of theory like a coupled-cluster approach, can provide a reliable energetic analysis for this complex.     

Alkyl-Bridged Nitropyrazoles – Adjustment of Performance and Sensitivity Parameters

Starting from 3,5-dinitro-4-methylaminopyrazole ( 2 ), six different energetic salts and three new derivatives of methylene bridged nitropyrazoles were synthesized. The derivatives bear a methylamino ( 4 ), methylnitramino ( 5 ), and azido group ( 7 ). All compounds were intensively characterized using single crystal X-ray diffraction, multinuclear NMR spectroscopy, IR spectroscopy, mass spectrometry, elemental analysis and DTA/TGA measurements. The sensitivities were determined according to BAM standard methods and the energetic properties calculated using the EXPLO5 code. The energetic salts were compared with each other and with ANTA in terms of their energetic properties. On the basis of the methyl- and ethyl bridged derivatives, it was shown how the introduction of methylamino ( 4 ) and methylnitramino ( 5 ) groups in an alkyl-bridged nitropyrazole system modify its properties (performance & sensitivities). In addition, azido compound 7 was contrasted with its literature-known constitutional isomer and investigated for its suitability as a potential metal-free primary explosive.     

Comparative PL study of individual ZnO nanorods,grown by APMOCVD and CBD techniques

The photoluminescence properties of individual ZnO nanorods, grown by atmospheric pressure metalorganic chemical vapor deposition (APMOCV) and chemical bath deposition (CBD) are investigated by means of temperature dependent micro-PL. It was found that the low temperature PL spectra are driven by neutral donor bound exciton emission D⁰X, peaked at 3.359 and 3.363 eV for APMOCVD and CBD ZnO nanorods, respectively. The temperature increase causes a red energy shift of the peaks and enhancement of the free excitonic emission (FX). The FX was found to dominate after 150 K for both samples. It was observed that while APMOCVD ZnO nanorods possess a constant low signal of visible deep level emission with temperature, the ZnO nanorods grown by CBD revealed the thermal activation of deep level emission (DLE) after 130 K. The resulting room temperature DLE was a wide band located at 420–550 nm. The PL properties of individual ZnO nanorods can be of importance for their forthcoming application in future optoelectronics and photonics.     

Photoelectron spectroscopy on silver electrodes on yttria stabilized zirconia under applied potential

Silver electrode layers of different porosity on yttrium stabilized zirconia (YSZ) were investigated by X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS resp.). By applying different potentials in a three electrode arrangement oxygen could be transported from a gaseous reservoir to the working electrode. The change in the work function of the working electrode as a function of applied potentials was monitored by UPS. It showed significant different behavior for dense and porous silver electrodes. On a dense silver electrode a change in work function of up to 0.6 eV was observed at potentials at which a considerable current passed through the electrolyte. In the UP spectra of the valence band an additional structure appeared at a binding energy of 3.3 eV. These changes were also reflected in the appearance of oxygen O 1s signals in the XP spectra at 529 eV assigned to subsurface oxygen. On a porous silver electrode the work function at equilibrium (open circuit) was higher than that of metallic silver and increased linearly with increasing potential, although yet no current through the electrolyte could be observed. With the onset of considerable currents at larger anodic potentials the work function increase became stronger. As reason for the linear increase of the measured work function contributions of the solid electrolyte YSZ are considered. Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000.     

Holographic recording using two-photon-induced photopolymerization

Molecular excitation via the simultaneous absorption of two photons can lead to improved three-dimensional control of photochemical or photophysical processes due to the quadratic dependence of the absorption probability on the incident radiation intensity. This has lead to the development of improved three-dimensional fluorescence imaging, optical data storage, and microfabrication. The latter of these involves the fabrication of three-dimensional structures using a spatial variation in the incident intensity within a photopolymerizable resin. In the past, the translation of the focal plane of a tightly focused laser beam was used to induce localized photopolymerization and fabrication of three-dimensional structures. Here we report the first successful demonstration of large-area patterning via ultrafast holography-based two-photon polymerization of a commercially available optical resin and a large two-photon cross-section dye (AF380). This opens tremendous possibilities for the wide-spread use of two-photon absorption for the three-dimensional control of photoinduced processes. Received: 21 June 1999 / Accepted: 23 June 1999 / Published online: 8 September 1999     

Simulation of the Solid State Vibrational Spectra of Aminodichloroborane and Ammonia Boron Trichloride

This is the second part of a quantum chemical investigation on the reaction between boron trichloride and ammonia. In part I [9] we focused on the energetic course of successive chlorine substitutions which are relevant for the chemical vapor deposition of BN. In this work we analyze in detail the vibrational spectra of reaction products accessible at room temperature. Regarding an experimental IR spectrum of the condensation product of the reaction between BCl₃ and NH₃ [10], there are more signals than expected for monomeric aminodichloroborane. Since this molecule shows the tendency to oligomerize, we have studied whether the presence of aminodichloroborane dimers or trimers or an impurity of the ammonia boron trichloride complex – an intermediate from which aminodichloroborane is formed – can explain the shape of the measured spectrum. To this end we have calculated the vibrational frequencies of monomeric, dimeric, and trimeric BCl₂NH₂, H₃N · BCl₃, and several van der Waals complexes at the level of a Møller‐Plesset second order perturbation theory. For the verification of the methodology, the vibrational frequencies of the dimethylaminodichloroborane molecule have been determined, in good accord with experimental gas phase spectra. Also the solid state spectrum of H₃N · BCl₃ is well reproduced by the computed vibrational spectrum of the monomeric adduct and a hydrogen‐bonded aggregate. Our studies concerning the spectrum of the condensation product of the reaction of boron trichloride with ammonia indicate that the substance investigated by Kwon and McGee had contained, besides monomeric aminodichloroborane, also its trimer and ammonia boron trichloride.