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141.
A. Frei Yu. Sobolev I. Altarev K. Eberhardt A. Gschrey E. Gutsmiedl R. Hackl G. Hampel F. J. Hartmann W. Heil J. V. Kratz Th. Lauer A. Liźon Aguilar A. R. Müller S. Paul Yu. Pokotilovski W. Schmid L. Tassini D. Tortorella N. Trautmann U. Trinks N. Wiehl 《The European Physical Journal A - Hadrons and Nuclei》2007,34(2):119-127
The production rates of ultracold neutrons (UCN) with a solid deuterium converter have been measured at the pulsed reactor
TRIGA Mainz. Exposed to a thermal neutron fluence of
n·cm^-2·pulse^-1, the number of detected very cold and ultracold neutrons ranges up to 200 000 at 7mol of solid deuterium
(sD2) in combination with a pre-moderator (mesitylene). About 50% of the measured neutrons can be assigned to UCN with energies
E of
where V
F(sD
2) = 105 neV and V
F(guide) = 190 neV are the Fermi potentials of the sD2 converter and our stainless steel neutron guides, respectively. Thermal cycling of solid deuterium, which was frozen out
from the gas phase, considerably improved the UCN yield, in particular at higher amounts of sD2. 相似文献
142.
Dendronized Hyperbranched Macromolecules: Soft Matter with a Novel Type of Segmental Distribution 下载免费PDF全文
Priv.‐Doz. Dr. Albena Lederer Prof. Dr. Walther Burchard Tobias Hartmann Johannes S. Haataja Dr. Nikolay Houbenov Andreas Janke Dr. Peter Friedel Dr. Ralf Schweins Dr. Peter Lindner 《Angewandte Chemie (International ed. in English)》2015,54(43):12578-12583
Dendronization of a hyperbranched polyester with different generation dendrons leads to pseudo‐dendritic structures. The hyperbranched core is modified by the divergent coupling of protected monomer units to the functional groups. Compared to dendrimers, the synthetic effort is significantly less, but the properties are very close to those of high‐generation dendrimers. The number of functional groups, molar mass, and rheology behavior even in the early generation (G1–G4) pseudo‐dendrimers strongly resembles the behavior of dendrimers in higher generations (G5–G8). Comparison of the segmental and internal structure with perfect dendrimers is performed using SANS, dynamic light scattering and viscosity analysis, microscopy and molecular dynamics simulation. The interpretation of the results reveals unique structural characteristics arising from lower segmental density of the core, which turns into a soft nano‐sphere with a smooth surface even in the first generation. 相似文献
143.
This paper proposes a method to improve the reliability of construction schedules by optimizing schedule robustness of construction projects. The schedule robustness is measured by a criterion evaluating the impact of deviations from the initial schedule on the makespan, which arise during the realization phase of a construction project. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
144.
Summary In the treatment of saddle point problems with finite elements a discrete Babuka-Brezzi condition is encountered. We demonstrate what this discrete Babuka-Brezzi condition entails and explain the mechanical background of this somewhat abstract inf sup condition.
Die diskrete Babuka-Brezzi-Bedingung
Übersicht Behandelt man Sattelpunktprobleme mit Finiten Elementen, dann stößt man auf eine diskrete Babuka-Brezzi Bedingung. Wir zeigen, welche Rolle diese diskrete Babuka-Brezzi-Bedingung bei der numerischen Behandlung spielt und verdeutlichen den mechanischen Hintergrund dieser etwas abstrakten inf sup Bedingung.相似文献
145.
In this experimental work, we investigate the influence of an organic counterion, sodium tosylate, on the rheological properties
of an aqueous solution of CTAB at the concentration of 0.05M. With this system we can clearly see shear thickening for small
salt concentrations C
s
and only shear thinning behavior at higher C
s
characterized by a linear evolution of η=f(γ) in a log-log representation. In these evolutions it is only in a very small domain of concentrations of the salt (near
C
s
=0.035M) that we can observe a nearly constant plateau of the shear stress against shear rate. The values of σ0 (characterizing the stress plateau), G
0 (the plateau modulus) and τR (the relaxation time) obtained by dynamical rheological measurements, allow to compare experimental results obtained to predicted
values of the theory of Cates corresponding to the occurrence of shear induced banding structures.
Received: 22 July 1997 Accepted: 3 February 1998 相似文献
146.
We investigate the Ar(+)-Fe asymmetric charge transfer (ACT) reaction using a combination of plasma diagnostics methods and a kinetic model of the afterglow plasma, which allow monitoring of the temporal evolution of the densities of different species. The iron vapor is created inside a discharge cell by cathode sputtering; its density is measured by atomic absorption spectroscopy. The rate coefficient of the reaction is evaluated from the emission intensity decay of Fe(+)? lines pumped by the ACT process in the He-Ar-Fe and Ar-Fe afterglow plasmas. The measurements yield a rate coefficient k = 7.6( ± 3.0) × 10(-9) cm(3) s(-1) at T = 300 K. 相似文献
147.
The direct enantioselective 1,4-addition of water to α,β-unsaturated acceptors is an open challenge in asymmetric catalysis. Enantioselective conjugate addition of either silicon or boron nucleophiles and subsequent enantiospecific oxidative degradation of the carbon-element bond represents, however, an attractive detour. A single extra step thereby enables an indirect enantiocontrolled construction of (in a broader sense) aldols from α,β-unsaturated carbonyl and carboxyl compounds. While that strategy had been obvious for a long time, it was recent stunning progress in transition metal-catalysed activation of interelement linkages that brought about the solution to that long-standing problem. A concise introduction of existing protocols for stereoselective 1,4-addition of oxygen nucleophiles is followed by a comprehensive summary of the recent rapid advances in transition metal-catalysed (and metal-free) asymmetric conjugate transfer of nucleophilic silicon and boron onto α,β-unsaturated acceptors. 相似文献
148.
Michael Hartmann 《Contemporary Physics》2013,54(2):89-102
We review a recent approach to determine the minimal spatial length scales on which local temperature exists. After mentioning an experiment where such considerations are of relevance, we first discuss the precise definition of the existence of local temperature and its physical relevance. The approach to calculate the length scales in question considers homogenous chains of particles with nearest-neighbour interactions. The entire chain is assumed to be in a thermal equilibrium state and it is analysed when such an equilibrium state at the same time exists for a local part of it. The result yields estimates for real materials, the liability of which is discussed in the sequel. We finally consider a possibility to detect the existence or non-existence of a local thermal state in experiment. 相似文献
149.
In contrast to their carbocyclic aniline analogues, N,N-diarylsubtituted 2-aminothiophenes are not protonated at their N-atoms but at the 5-position or, to a smaller extent, at the 3-position of the thiophene nucleus giving rise to cationic species of the Wheland type. However, 5-formyl and 5-acetyl-substituted 2-(N,N-diarylamino)thiophenes are protonated at the corresponding carbonyl moieties. This finding not only enables insight into the mechanism of electrophilic substitution of N,N-disubstituted 2-aminothiophenes but also allows to prepare deurated 2-aminothiophenes by treatment their non-deuterated parent compounds with CF3COOD. 相似文献
150.