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121.
Recent neutron scattering experiments on aqueous salt solutions of amphiphilic t-butanol by Bowron and Finney [Phys. Rev. Lett. 89, 215508 (2002); J. Chem. Phys. 118, 8357 (2003)] suggest the formation of t-butanol pairs, bridged by a chloride ion via O-H...Cl- hydrogen bonds, leading to a reduced number of intermolecular hydrophobic butanol-butanol contacts. Here we present a joint experimental/theoretical study on the same system, using a combination of molecular dynamics (MD) simulations and nuclear magnetic relaxation measurements. Both MD simulation and experiment clearly support the more classical scenario of an enhanced number of hydrophobic contacts in the presence of salt, as it would be expected for purely hydrophobic solutes. [T. Ghosh et al., J. Phys. Chem. B 107, 612 (2003)]. Although our conclusions arrive at a structurally completely distinct scenario, the molecular dynamics simulation results are within the experimental error bars of the Bowron and Finney data. 相似文献
122.
The investigation of quantum mechanical systems mostly concentrates on single elementary particles. If we combine such particles
into a composite quantum system, the number of degrees of freedom of the combined system grows exponentially with the number
of particles. This is a major difficulty when we try to describe the dynamics of such a system, since the computational resources
required for this task also grow exponentially. In the context of quantum information processing, this difficulty becomes
the main source of power: in some situations, information processors based in quantum mechanics can process information exponentially
faster than classical systems. From the perspective of a physicist, one of the most interesting applications of this type
of information processing is the simulation of quantum systems. We call a quantum information processor that simulates other
quantum systems a quantum simulator. 相似文献
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125.
Adrian A. Ammann Petra Macikova Ksenia J. Groh Kristin Schirmer Marc J. F. Suter 《Analytical and bioanalytical chemistry》2014,406(29):7653-7665
A targeted analytical method was established to determine a large number of chemicals known to interfere with the gluco- and mineralocorticoid signalling pathway. The analytes comprise 30 glucocorticoids and 9 mineralocorticoids. Ten out of these corticosteroids were primary metabolites. Additionally, 14 nonsteroids were included. These analytes represent a broader range of possible adverse modes of action than previously reported. For the simultaneous determination of these structurally diverse compounds, a single-step multimode solid-phase extraction and pre-concentration was applied. Extracts were separated by a short linear HPLC gradient (20 min) on a core shell RP column (2.7 μm particle size) and compounds identified and quantified by LC-MS/MS. The method provided excellent retention time reproducibility and detection limits in the low nanograms per litre range. Untreated hospital wastewater, wastewater treatment plant influent, treated effluent and river waters were analysed to demonstrate the applicability of the method. The results show that not all compounds were sufficiently eliminated by the wastewater treatment, resulting in the presence of several steroids (~20 ng/L) and nonsteroids in the final effluent, some of them at high concentrations up to 200 ng/L. Most of the detected mono-hydroxylated steroidal transformation products were found at significantly higher concentrations than their parent compounds. We therefore recommend to include these potentially bioactive metabolites in environmental toxicity assessment. 相似文献
126.
Decoherence is one of the most important obstacles that must be overcome in quantum information processing. It depends on the qubit-environment coupling strength, but also on the spectral composition of the noise generated by the environment. If the spectral density is known, fighting the effect of decoherence can be made more effective. Applying sequences of inversion pulses to the qubit system, we developed a method for dynamical decoupling noise spectroscopy. We generate effective filter functions that probe the environmental spectral density without requiring assumptions about its shape. Comparing different pulse sequences, we recover the complete spectral density function and distinguish different contributions to the overall decoherence. 相似文献
127.
While nuclear magnetic resonance (NMR) is one of the most important experimental tools for the analysis of bulk materials, the low sensitivity of conventional NMR makes it unsuitable for the investigation of small structures. We introduce an experimental scheme that makes NMR spectra of single, nanometer-sized quantum wells possible with excellent sensitivity and selectivity while avoiding the spectral broadening associated with some alternative techniques. The scheme combines optical pumping and pulsed radiofrequency excitation of the nuclei with time-resolved detection of the free induction decay through the polarization of the photoluminescence. 相似文献
128.
Mark T McAuley Rose Anne Kenny Thomas BL Kirkwood Darren J Wilkinson Janette JL Jones Veronica M Miller 《BMC neuroscience》2009,10(1):26
Background
The hippocampus is essential for declarative memory synthesis and is a core pathological substrate for Alzheimer's disease (AD), the most common aging-related dementing disease. Acute increases in plasma cortisol are associated with transient hippocampal inhibition and retrograde amnesia, while chronic cortisol elevation is associated with hippocampal atrophy. Thus, cortisol levels could be monitored and managed in older people, to decrease their risk of AD type hippocampal dysfunction. We generated an in silicomodel of the chronic effects of elevated plasma cortisol on hippocampal activity and atrophy, using the systems biology mark-up language (SBML). We further challenged the model with biologically based interventions to ascertain if cortisol associated hippocampal dysfunction could be abrogated. 相似文献129.
130.
M. Holder J. Knobloch J. May H.P. Paar P. Palazzi D. Schlatter J. Steinberger H. Suter H. Wahl E.G.H. Williams F. Eisele C. Geweniger K. Kleinknecht G. Spahn H-J. Willutzki W. Dorth F. Dydak V. Hepp F.L. Navarria 《Physics letters. [Part B]》1977,70(3):396-398
Forty seven events of the type v + Fe → μ? + μ? + X and nine events of the type have been observed, and zero events with like-sign muons of the opposite sign. Most of the observed events can be attributed to the background of normal charged current events, in which one of the pions or kaons of the hadron shower decays, and so produces a second muon. The remaining events correspond to rates of the order of (3 ± 2) × 10?4 of those for charged current events. They may very well be due to the hadronic production of a charm-anticharm pair, with subsequent decay of one member of the pair. The observed rates correspond to charm-anticharm pair production in 0.5–1% of the hadron showers. No evidence can be found for a lepton-cascade origin of the observed events. 相似文献