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951.
Hancock JN van Mechelen JL Kuzmenko AB van der Marel D Brüne C Novik EG Astakhov GV Buhmann H Molenkamp LW 《Physical review letters》2011,107(13):136803
We present a magneto-optical study of the three-dimensional topological insulator, strained HgTe, using a technique which capitalizes on advantages of time-domain spectroscopy to amplify the signal from the surface states. This measurement delivers valuable and precise information regarding the surface-state dispersion within <1 meV of the Fermi level. The technique is highly suitable for the pursuit of the topological magnetoelectric effect and axion electrodynamics. 相似文献
952.
Anoop Gupta Pascal Ifeacho Christof Schulz Hartmut Wiggers 《Proceedings of the Combustion Institute》2011,33(2):1883-1890
Flame synthesis of WO3 and WOx (2.9 < x < 3) nanoparticles is carried out by adding a dilute concentration of WF6 as precursor in a low-pressure H2/O2/Ar premixed flame reactor. The reactor is equipped with molecular-beam sampling and particle mass spectroscopy (PMS) to determine particle composition and sizes as a function of height above burner. Varying the H2/O2 ratio allowed us to tune the stoichiometry of the product. With a H2/O2 ratio of 0.67 white colored stoichiometric WO3 is formed, whereas the H2/O2 ratio >0.8 yields blue colored non-stoichiometric WOx (2.9 < x < 3) nanoparticles. The size of nanoparticles can be controlled by varying the residence time in the high-temperature zone of the reactor as observed by molecular-beam sampling with subsequent analysis using PMS. Transmission electron microscopy (TEM) images of as-synthesized nanoparticles show that particles are non-agglomerated and have an almost spherical morphology. The X-ray diffraction (XRD) pattern of the as-synthesized material indicates that the powders exhibit poor crystallinity, however, subsequent thermal annealing of the sample in air changes its structure from amorphous to crystalline phase. It is observed that particles with sub-stoichiometric composition (WOx) show higher conductivity compared to the stoichiometric WO3 sample. 相似文献
953.
Adhesion measurements were performed by AFM (Atomic Force Microscopy). It was shown that many parameters need to be controlled in order to provide reproducible and quantitative results. Adhesion forces were shown to depend on combination of materials characteristics and testing geometry as well as experimental protocol (contact time, contact force and contact area). This contact area was modified by means of FIB (Focused Ion Beam) milling and deliberate abrasion. As a result, a drastic change in adhesion could be observed. Still, those are problems connected to adjustment of interacting surfaces. 相似文献
954.
Daniela Volke Mohammed Daghish Lothar Hennig Matthias Findeisen Sabine Giesa Ramona Oehme Peter Welzel 《Helvetica chimica acta》2003,86(12):4214-4232
The synthesis of some 3‐aryl‐3‐(trifluoromethyl)3H‐diazirine and benzophenone‐based photoaffinity labels is reported. The photolabile group is bound to a scaffold that also accommodates functional groups to which an indicator unit (biotin) and the bioactive ligand can be attached orthogonally. To three of the labels, moenomycin was conjugated with the aim to provide tools for the identification of the moenomycin binding site within the transglycosylase domain of the enzyme PBP 1b. Some preliminary photoaffinity‐labeling experiments were carried out. 相似文献
955.
956.
957.
Manfred Weidenbruch Hartmut Kilian Martin Stürmann Siegfried Pohl Wolfgang Saak Heinrich Marsmann Dirk Steiner Armin Berndt 《Journal of organometallic chemistry》1997,530(1-2):255-257
Addition of the diarylstannylene R″2Sn (R″ = 2−tBu−4,5,6-Me3C6H) to the cryptodiborylcarbene (Me3Si)2C(BtBu)2C furnishes the stannaethene (Me3Si)2C(BtBu)2C=SnR″2 (10). The X-ray structure analysis of 10 reveals a strictly planar environment of the tricoordinated tin and carbon atoms and a slight twisting of the Sn=C double bond. 相似文献
958.
We demonstrate that the Plancherel transform for Type-I groups provides
one with a natural, unified perspective for the generalized continuous wavelet
transform, on the one hand, and for a class of Wigner functions, on the other. We
first prove that a Plancherel inversion formula, well known for Bruhat functions on
the group, holds for a much larger class of functions. This result allows us to view
the wavelet transform as essentially the inverse Plancherel transform. The wavelet
transform of a signal is an L2-function on an appropriately chosen group while
the Wigner function is defined on a coadjoint orbit of the group and serves as an
alternative characterization of the signal, which is often used in practical applications.
The Plancherel transform maps L2-functions on a group unitarily to fields
of Hilbert-Schmidt operators, indexed by unitary irreducible representations of the
group. The wavelet transform can essentially be looked upon as a restricted inverse
Plancherel transform, while Wigner functions are modified Fourier transforms of
inverse Plancherel transforms, usually restricted to a subset of the unitary dual of
the group. Some known results on both Wigner functions and wavelet transforms,
appearing in the literature from very different perspectives, are naturally unified
within our approach. Explicit computations on a number of groups illustrate the
theory.
Communicated by Gian Michele Graf
submitted 05/06/01, accepted: 19/09/02 相似文献
959.
960.
The photocatalytic heterocyclotrimerisation of ethyne and nitrile initiated by cobalt(I) complexes was studied. General mechanistic features as proposed for the ‘dark’ reaction were found to apply as well under photolytic conditions albeit with modifications. The results suggest that the irradiated light accelerates that stage of reaction, leading to the organometallic species which is believed to be the common intermediate for the formation of pyridine and benzene. The rate of pyridine production is linear dependent from nitrile concentration. Benzene formation may be minimised by keeping the ethyne concentration low. An alternative mechanism, based on the initial coordination of nitrile at cobalt is not confirmed. A novel gas buret system was used, which allowed automatic feed of ethyne under isobaric conditions and to monitor all reactants simultaneously on-line. 相似文献