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901.
S. Ravy P. A. Albouy S. Megtert R. Moret J. P. Pouget R. Comes 《Phase Transitions》2013,86(1-4):193-210
X-Ray diffuse scattering from a series of examples where the reason for the existence of incommensurable features is fairly well understood, is described. They include in particular non stoichiometric compounds such as [DIPS Φ4(l3)0.76] and such as intercalated graphite RbC24. and quasi one dimensional conductors. A particular emphasis is given on various 1 - D conductors and to the relation of the incommensurability to the characteristics of the electron conduction bands. 相似文献
902.
Two examples of the study of phase transitions by means of electron diffraction and electron microscopy are discussed. 相似文献
903.
Dr. Brice Kauffmann Dr. Gilles Guichard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15684-15692
Anion binding properties of neutral helical foldamers consisting of urea type units in their backbone have been investigated. 1H NMR titration studies in various organic solvents including DMSO suggest that the interaction between aliphatic oligoureas and anions (CH3COO?, H2PO4?, Cl?) is site‐specific, as it largely involves the urea NHs located at the terminal end of the helix (positive pole of the helix), which do not participate to the helical intramolecular hydrogen‐bonding network. This mode of binding parallels that found in proteins in which anion‐binding sites are frequently found at the N‐terminus of an α‐helix. 1H NMR studies suggest that the helix of oligoureas remains largely folded upon anion binding, even in the presence of a large excess of the anion. This study points to potentially useful applications of oligourea helices for the selective recognition of small guest molecules. 相似文献
904.
D. G. Pettifor 《辐射效应与固体损伤》2013,168(3-4):121-126
The different roles played by the valence s and d electrons in determining the bulk properties of pure transition metals is described. In the light of this the expected behaviour of the inert gas-metal and metal-metal interatomic potentials is discussed. 相似文献
905.
Copper Causes Regiospecific Formation of C4F8‐Containing Six‐Membered Rings and their Defluorination/Aromatization to C4F4‐Containing Rings in Triphenylene/1,4‐C4F8I2 Reactions
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Kerry C. Rippy Dr. Eric V. Bukovsky Dr. Tyler T. Clikeman Dr. Yu‐Sheng Chen Dr. Gao‐Lei Hou Dr. Xue‐Bin Wang Dr. Alexey A. Popov Dr. Olga V. Boltalina Prof. Steven H. Strauss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(3):874-877
The presence of Cu in reactions of triphenylene (TRPH) and 1,4‐C4F8I2 at 360 °C led to regiospecific substitution of TRPH ortho C(β) atoms to form C4F8‐containing rings, completely suppressing substitution on C(α) atoms. In addition, Cu caused selective reductive‐defluorination/aromatization (RD/A) to form C4F4‐containing aromatic rings. Without Cu, the reactions of TRPH and 1,4‐C4F8I2 were not regiospecific and no RD/A was observed. These results, supported by DFT calculations, are the first examples of Cu‐promoted 1) regiospecific perfluoroannulation, 2) preparative C?F activation, and 3) RD/A. HPLC‐purified products were characterized by X‐ray diffraction, low‐temperature PES, and 1H/19F NMR. 相似文献
906.
This work presents an analysis of the main requirements for semiconductor detectors of ionising radiation that can be operated over a wide temperature range. The analysis shows that wide-gap semiconductors with a band gap greater than 2.0 eV are a better option for effective detection of ionising radiation at high temperatures. The results of an experimental investigation into the luminescent, electrical and spectrometric properties of the wide-gap semiconductor ZnSe are shown as an example. Undoped monocrystalline ZnSe has an extremely low leakage current over a wide range of temperatures up to 167 °C and can be used as a radiometric X-ray detector in pulse-counting mode over a wide temperature range up to at least 130 °C. 相似文献
907.
《Ultrasonics sonochemistry》2014,21(6):1954-1957
A sonochemical approach was employed to prepare Vulcan carbon XC-72R supported by Sn nanoparticles at room temperature in the presence of ethylene glycol. The reduction of metallic Sn ion and ethylene glycol takes place and in turn the glycolate ion as formed acts as a stabilizing agent. Transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy have illustrated that the metallic Sn nanoparticles are successfully embedded on the carbon. The significantly observed reduction over potential for oxygen reduction reaction displays a higher catalytic activity of carbon supported by Sn nanoparticles due to the large surface area of the modified electrode. 相似文献
908.
Dr. Dumitru-Claudiu Sergentu Dr. Corwin H. Booth Prof. Dr. Jochen Autschbach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(25):7239-7251
The Ce L3 edge XAS spectra of CeO2 and cerocene [Ce(C8H8)2] were calculated with relativistic ab-initio multireference wavefunction approaches capable of reproducing the observed spectra accurately. The study aims to resolve the decades-long puzzle regarding the relationship between the number and relative intensities of the XAS peaks and the 4f electron occupation in the ground state (GS) versus the core-excited states (ESs). CeO2 and cerocene exemplify the different roles of covalent bonding and wavefunction configurational composition in the observed intensity patterns. Good agreement is found between the calculated GS 4f-shell occupations and the value derived from XAS measurements using peak areas (nf). The identity of the two-peaked Ce L3 edge is fully rationalized from the perspective of the relaxed wavefunctions for the GS and core ESs. The states underlying the different peaks differ from each other in a surprisingly simple way that can be associated with 4f1 vs. 4f0 sub-configurations. Furthermore, part of one of the cerocene spectral peaks is associated with 4f2 sub-configurations. The pattern therefore reveals excited states that can be interpreted in terms of Ce IV and III oxidation numbers, as long assumed, with Ce II states additionally appearing in the cerocene spectrum. While this work demonstrates the rough accuracy of the conventional approach to determining nf from Ce L3-edge XAS, limitations are highlighted in terms of the ultimate accuracy of this approach and the potential of observing new types of excited states. The need to determine the sources of nf by calculations, is stressed. 相似文献
909.
910.
Maja Musse François De GuioStéphane Quellec Mireille CambertSylvain Challois Armel Davenel 《Magnetic resonance imaging》2010
Microstructure determines the mechanical and transport properties of fruit tissues. One important characteristic of the microstructure is the relative volume fraction of gas-filled intercellular spaces, i.e., the tissue microporosity. Quantification of this microporosity is fundamental for investigating the relationship between gas transfer and various disorders in fruit. 相似文献