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151.
A microwave-assisted desorption method was developed and coupled with solid-phase microextraction and GC-MS for the analysis of pyrethroid residues in strawberries. In the first step, pyrethroid analytes were desorbed from the whole fruits in an aqueous acetonitrile solution at 50% under microwave assistance, so preventing these compounds to be captured with strong matrix effects by endogenous constituents. Then, the 100 microm poly(dimethylsiloxane)-coated fibre was exposed for 30 min in the obtained extracting solution. Calibration curves, realised from blank strawberries spiked at different concentrations with standards, showed a linear range between 1 microg/kg and 250 microg/kg with r2 > 0.992 and variation coefficients below 15%. Limits of detection and quantitation were found lower than 14 microg/kg and 40 microg/kg, respectively. Observed analysis results by using this method and relative to field incurred strawberry samples were also compared to those obtained by two accredited trading laboratories using traditional methods. 相似文献
152.
Suppose that G is a locally compact group and π is a (not necessarily irreducible) unitary representation of a closed normal subgroup N of G on a Hilbert space . We extend results of Clifford and Mackey to determine when π extends to a unitary representation of G on the same space in terms of a cohomological obstruction. 相似文献
153.
Jahnke T Czasch A Schöffler MS Schössler S Knapp A Käsz M Titze J Wimmer C Kreidi K Grisenti RE Staudte A Jagutzki O Hergenhahn U Schmidt-Böcking H Dörner R 《Physical review letters》2004,93(16):163401
Recently Cederbaum et al. [Phys. Rev. Lett. 79, 4778 (1997)]] predicted a new decay channel of excited atoms and molecules termed interatomic Coulombic decay (ICD). In ICD the deexcitation energy is transferred via virtual photon exchange to a neighboring atom, which releases it by electron emission. We report on an experimental observation of ICD in 2s ionized neon dimers. The process is unambiguously identified by detecting the energy of two Ne1+ fragments and the ICD electron in coincidence, yielding a clean, background free experimental spectral distribution of the ICD electrons. 相似文献
154.
Carlyon RP van Wieringen A Long CJ Deeks JM Wouters J 《The Journal of the Acoustical Society of America》2002,112(2):621-633
Two experiments investigated pitch perception for stimuli where the place of excitation was held constant. Experiment 1 used pulse trains in which the interpulse interval alternated between 4 and 6 ms. In experiment 1a these "4-6" pulse trains were bandpass filtered between 3900 and 5300 Hz and presented acoustically against a noise background to normal listeners. The rate of an isochronous pulse train (in which all the interpulse intervals were equal) was adjusted so that its pitch matched that of the "4-6" stimulus. The pitch matches were distributed unimodally, had a mean of 5.7 ms, and never corresponded to either 4 or to 10 ms (the period of the stimulus). In experiment 1b the pulse trains were presented both acoustically to normal listeners and electrically to users of the LAURA cochlear implant, via a single channel of their device. A forced-choice procedure was used to measure psychometric functions, in which subjects judged whether the 4-6 stimulus was higher or lower in pitch than isochronous pulse trains having periods of 3, 4, 5, 6, or 7 ms. For both groups of listeners, the point of subjective equality corresponded to a period of 5.6 to 5.7 ms. Experiment 1c confirmed that these psychometric functions were monotonic over the range 4-12 ms. In experiment 2, normal listeners adjusted the rate of an isochronous filtered pulse train to match the pitch of mixtures of pulse trains having rates of F1 and F2 Hz, passed through the same bandpass filter (3900-5400 Hz). The ratio F2/F1 was 1.29 and F1 was either 70, 92, 109, or 124 Hz. Matches were always close to F2 Hz. It is concluded that the results of both experiments are inconsistent with models of pitch perception which rely on higher-order intervals. Together with those of other published data on purely temporal pitch perception, the data are consistent with a model in which only first-order interpulse intervals contribute to pitch, and in which, over the range 0-12 ms, longer intervals receive higher weights than short intervals. 相似文献
155.
D. Filges F. Goldenbaum M. Enke J. Galin C.-M. Herbach D. Hilscher U. Jahnke A. Letourneau B. Lott R.-D. Neef K. Nünighoff N. Paul A. Péghaire L. Pienkowski H. Schaal U. Schröder G. Sterzenbach A. Tietze V. Tishchenko J. Toke M. Wohlmuther 《The European Physical Journal A - Hadrons and Nuclei》2001,11(4):467-490
A recent renascent interest in energetic proton-induced production of neutrons originates largely from the inception of projects
for target stations of intense spallation neutron sources, like the planned European Spallation Source (ESS), accelerator-driven
nuclear reactors, nuclear waste transmutation, and also from the application for radioactive beams. In the framework of such
a neutron production, of major importance is the search for ways for the most efficient conversion of the primary beam energy
into neutron production. Although the issue has been quite successfully addressed experimentally by varying the incident proton
energy for various target materials and by covering a huge collection of different target geometries --providing an exhaustive
matrix of benchmark data-- the ultimate challenge is to increase the predictive power of transport codes currently on the
market. To scrutinize these codes, calculations of reaction cross-sections, hadronic interaction lengths, average neutron
multiplicities, neutron multiplicity and energy distributions, and the development of hadronic showers are confronted with
recent experimental data of the NESSI collaboration. Program packages like HERMES, LCS or MCNPX master the prevision of reaction
cross-sections, hadronic interaction lengths, averaged neutron multiplicities and neutron multiplicity distributions in thick
and thin targets for a wide spectrum of incident proton energies, geometrical shapes and materials of the target generally
within less than 10% deviation, while production cross-section measurements for light charged particles on thin targets point
out that appreciable distinctions exist within these models.
Received: 22 May 2001 / Accepted: 3 September 2001 相似文献
156.
In optical communications, four-dimensional (4D) modulation formats encode information onto the quadrature components of two arbitrary orthogonal states of polarisation of the optical field. Many analytical models available in the optical communication literature allow, within a first-order perturbation framework, the computation of the average power of the nonlinear interference (NLI) accumulated in coherent fibre-optic transmission systems. However, all such models only operate under the assumption of transmitted polarisation-multiplexed two-dimensional (PM-2D) modulation formats, which only represent a limited subset of the possible dual-polarisation 4D (DP-4D) formats. Namely, only those where data transmitted on each polarisation channel are mutually independent and identically distributed. This paper presents a step-by-step mathematical derivation of the extension of existing NLI models to the class of arbitrary DP-4D modulation formats. In particular, the methodology adopted follows the one of the popular enhanced Gaussian noise model, albeit dropping most assumptions on the geometry and statistic of the transmitted 4D modulation format. The resulting expressions show that, whilst in the PM-2D case the NLI power depends only on different statistical high-order moments of each polarisation component, for a general DP-4D constellation, several other cross-polarisation correlations also need to be taken into account. 相似文献
157.
Mathias Eisenhut Xinghua Guo Astrid H. Paulitsch-Fuchs Elmar C. Fuchs 《Central European Journal of Chemistry》2011,9(4):750-751
The original version of the article was published in Cent. Eur. J. Chem. 9(3) (2011), pp 391–403. Unfortunately, the original
version of this article contains mistakes in the caption of the y-axis of Figs. 5,6 and 10 due to a font conversion problem.
The actual units on the y-axis of these figures should be μS cm−1, not mS cm−1. 相似文献
158.
Dr. Astrid Maronna Dr. Olaf Hübner Prof. Dr. Markus Enders Dr. Elisabeth Kaifer Prof. Dr. Hans‐Jörg Himmel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(27):8958-8977
Herein, we report on the synthesis, protonation, and coordination chemistry of chelating guanidine ligands with biphenyl, binaphthyl, and bipyridyl backbones. The ligands are shown to be proton sponges, and this protonation was studied experimentally and by using quantum‐chemical calculations. Group 10 metal (Ni, Pd, and Pt) complexes with different metal/ligand ratios were synthesized. In the case of the bipyridyl systems, coordination occurs exclusively at the pyridine N atoms, as opposed to protonation. The spin‐density distribution and the magnetism were evaluated for a series of paramagnetic NiII complexes with the aid of paramagnetic NMR spectroscopic studies in alliance with quantum‐chemical calculations and magnetic (SQUID) measurements. Through direct delocalization from the singly occupied molecular orbitals (SOMOs), a significant amount of spin density is placed on the guanidinyl groups, and spin polarization also transports spin density onto the aromatic backbone. 相似文献
159.
Stefan Barthel Kolja Schuh Oliver Marquardt Tilmann Hickel Jörg Neugebauer Frank Jahnke Gerd Czycholl 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(11):1-11
In this paper we systematically analyze the electronic structures of polar and nonpolar wurtzite-InN/GaN quantum dots and their modification due to the quantum-confined Stark effect caused by intrinsic fields. This is achieved by combining continuum elasticity theory with an effective-bond orbital model to describe the elastic and single-particle electronic properties in these nitride systems. Based on these results, a many-body treatment is used to determine optical absorption spectra. The efficiency of optical transitions depends on the interplay between the Coulomb interaction and the quantum-confined Stark effect. We introduce an effective confinement potential which represents the electronic structure under the influence of the intrinsic polarization fields and calculate the needed strength of Coulomb interaction to diminish the separation of electrons and holes. 相似文献
160.
Self‐Assembled Cyclic d,l‐α‐Peptides as Generic Conformational Inhibitors of the α‐Synuclein Aggregation and Toxicity: In Vitro and Mechanistic Studies 下载免费PDF全文
Dr. Marina Chemerovski‐Glikman Eva Rozentur‐Shkop Dr. Michal Richman Dr. Asaf Grupi Asaf Getler Prof. Haim Y. Cohen Dr. Hadassa Shaked Cecilia Wallin Dr. Sebastian K. T. S. Wärmländer Prof. Elisha Haas Prof. Astrid Gräslund Prof. Jordan H. Chill Prof. Shai Rahimipour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(40):14236-14246
Many peptides and proteins with large sequences and structural differences self‐assemble into disease‐causing amyloids that share very similar biochemical and biophysical characteristics, which may contribute to their cross‐interaction. Here, we demonstrate how the self‐assembled, cyclic d,l ‐α‐peptide CP‐2 , which has similar structural and functional properties to those of amyloids, acts as a generic inhibitor of the Parkinson′s disease associated α‐synuclein (α‐syn) aggregation to toxic oligomers by an ?off‐pathway“ mechanism. We show that CP‐2 interacts with the N‐terminal and the non‐amyloid‐β component region of α‐syn, which are responsible for α‐syn′s membrane intercalation and self‐assembly, thus changing the overall conformation of α‐syn. CP‐2 also remodels α‐syn fibrils to nontoxic amorphous species and permeates cells through endosomes/lysosomes to reduce the accumulation and toxicity of intracellular α‐syn in neuronal cells overexpressing α‐syn. Our studies suggest that targeting the common structural conformation of amyloids may be a promising approach for developing new therapeutics for amyloidogenic diseases. 相似文献