The design concept of the 6-degree-of-freedom hydraulic shaker at ESTEC

The European Space Agency (ESA) has decided to extend its test facilities at the European Space and Technology Center (ESTEC) at Noordwijk, The Netherlands, by implementing a 6-degree-of-freedom hydraulic shaker. This shaker will permit vibration testing of large payloads in the frequency range from 0.1 Hz to 100 Hz. Conventional single axis sine and random vibration modes can be applied without the need for a configuration change of the test set-up for vertical and lateral excitations. Transients occurring during launch and/or landing of space vehicles can be accurately simulated in 6-degrees-of-freedom. The performance requirements of the shaker are outlined and the results of the various trade-offs, which are investigated during the initial phase of the design and engineering program are provided. Finally, the resulting baseline concept and the anticipated implementation plan of the new test facility are presented

Thermodynamics of an incommensurate quantum crystal

We present a simple theory of the thermodynamics of an incommensurate quantum solid. The ground state of the solid is assumed to be an incommensurate crystal, with quantum zero-point vacancies and interstitials and thus a non-integer number of atoms per unit cell. We show that the low temperature variation of the net vacancy concentration should be as $T^4$, and that the first correction to the specific heat due to this varies as $T^7$; these are quite consistent with experiments on solid $^4$He. We also make some observations about the recent experimental reports of ``supersolidity'' in solid $^4$He that motivate a renewed interest in quantum crystals.Comment: revised, new title, somewhat expande

Geometric dependence of Nb-Bi2{_2}Te3{_3}-Nb topological Josephson junction transport parameters

Superconductor-topological insulator-superconductor Josephson junctions have been fabricated in order to study the width dependence of the critical current, normal state resistance and flux periodicity of the critical current modulation in an external field. Previous literature reports suggest anomalous scaling in topological junctions due to the presence of Majorana bound states. However, for most realised devices, one would expect that trivial $2\pi$-periodic Andreev levels dominate transport. We also observe anomalous scaling behaviour of junction parameters, but the scaling can be well explained by mere geometric effects, such as the parallel bulk conductivity shunt and flux focusing

Improved determination of VOCs in marine biota by using on-line purge and trap-gas chromatography-mass spectrometry

A Tekmar LSC-2000 Purge and Trap (P&T) apparatus was further modified in order to improve the on-line P&T gas chromatographic etermination of Volatile Organic Compounds (VOCs) in biological tissue. The standard needle sparger of the Tekmar was replaced by a system consisting of two needles (purge gas in- and outlet) and a moisture trap. This modification allows a rapid throughput of samples and minimizes the risk of contamination or losses. Addition of 1-octanol proved successful in eliminating the severe sample foaming that generally occurs when biological material is purged. For separation of the analytes a J&W DB-VRX column (60 m, 0.25 mm i.d., 1.4 µm film) was used, which allowed the elimination of the cryofocusing step prior to injection. The method was tested for 13 priority VOCs and detection limits were obtained ranging from 0.003 ng/g (tetrachloromethane) to 0.16 ng/g (m- and p-xylene) using single ion monitoring-mass spectrometry. The reproducibility was around 15 % for most compounds and the recoveries were better than 80 % for all analytes except 1,1-dichloroethane (59 %).Although the method was originally validated for 13 VOCs, it was found to be applicable for a broader range of VOCs and was tested an eel from the Scheldt estuary. Apart from the priority VOCs several other VOCs turned up rather unexpectedly in these samples. They were identified on the basis of their mass spectra and quantified using selected ion monitoring

Improved determination of VOCs in marine biota by using on-line purge and trap-gas chromatography-mass spectrometry

A Tekmar LSC-2000 Purge and Trap (P&T) apparatus was further modified in order to improve the on-line P&T gas chromatographic etermination of Volatile Organic Compounds (VOCs) in biological tissue. The standard needle sparger of the Tekmar was replaced by a system consisting of two needles (purge gas in- and outlet) and a moisture trap. This modification allows a rapid throughput of samples and minimizes the risk of contamination or losses. Addition of 1-octanol proved successful in eliminating the severe sample foaming that generally occurs when biological material is purged. For separation of the analytes a J&W DB-VRX column (60 m, 0.25 mm i.d., 1.4 µm film) was used, which allowed the elimination of the cryofocusing step prior to injection. The method was tested for 13 priority VOCs and detection limits were obtained ranging from 0.003 ng/g (tetrachloromethane) to 0.16 ng/g (m- and p-xylene) using single ion monitoring-mass spectrometry. The reproducibility was around 15 % for most compounds and the recoveries were better than 80 % for all analytes except 1,1-dichloroethane (59 %).Although the method was originally validated for 13 VOCs, it was found to be applicable for a broader range of VOCs and was tested an eel from the Scheldt estuary. Apart from the priority VOCs several other VOCs turned up rather unexpectedly in these samples. They were identified on the basis of their mass spectra and quantified using selected ion monitoring

Volatile organic compounds in various marine organisms from the southern North Sea

The concentration levels of 12 priority volatile organic compounds (VOCs) were determined in two species of vertebrates and four species of invertebrates from sampling stations in the Southern North Sea, using a modified Tekmar LSC 2000 purge and trap system coupled to GC-MS. In general, concentration levels of VOCs found in this study were of the same order of magnitude as those previously reported in the literature. The concentrations of the chlorinated hydrocarbons (CHCs), with the exception of chloroform, tended to be lower than those of the monocyclic aromatic hydrocarbons (MAHs). The experimental data were statistically evaluated using both cluster and principal component analysis (PCA). From the results of cluster analysis and PCA, no specific groups could be distinguished on the basis of geographical, temporal or biological parameters. However, based on the cluster analysis and the PCA, the VOCs could be divided into three groups, C2-substituted benzenes, CHCs and benzene plus toluene. This division could be related to different types of sources. Finally, it was shown that organisms can be used to monitor the presence of VOCs in the marine environment and the observed concentrations levels were compared with proposed safety levels

Generalization of Gutzwiller Approximation

We derive expressions required in generalizing the Gutzwiller approximation to models comprising arbitrarily degenerate localized orbitals.Comment: 6 pages, 1 figure, to appear in J.Phys.Soc.Jpn. vol.6