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排序方式: 共有702条查询结果,搜索用时 31 毫秒
41.
42.
Causo MS Ciccotti G Montemayor D Bonella S Coker DF 《The journal of physical chemistry. B》2005,109(14):6855-6865
We generalize the linearized path integral approach to evaluate quantum time correlation functions for systems best described by a set of nuclear and electronic degrees of freedom, restricting ourselves to the adiabatic approximation. If the operators in the correlation function are nondiagonal in the electronic states, then this adiabatic linearized path integral approximation for the thermal averaged quantum dynamics presents interesting and distinctive features, which we derive and explore in this paper. The capability of these approximations to accurately reproduce the behavior of physical systems is demonstrated by calculating the diffusion constant for an excess electron in a metal-molten salt solution. 相似文献
43.
As part of our continuing studies of pyrone-containing natural products, a series 6-methoxypyran-2-ones were synthesized. These were found to react with molecular oxygen at 20 degrees C, and this novel reaction yielded a series of highly functionalized alpha,beta-butenolides. [reaction: see text] 相似文献
44.
Margadonna S Prassides K Fitch AN 《Journal of the American Chemical Society》2004,126(47):15390-15391
Isotropic nearly zero thermal expansion (i.e., negligible volume change) is reported in a large temperature range for Fe[Co(CN)6], a member of the Prussian blue family with electronically active metal sublattices and a cubic framework structure built by a cyanide-bridged network of octahedral units. Suitable selection of metal ions and interstitial units could allow such anomalous thermal behavior to be combined with the variety of unusual electronic, optical, and magnetic properties exhibited by Prussian blue analogues. 相似文献
45.
Arvanitidis J Papagelis K Margadonna S Prassides K 《Dalton transactions (Cambridge, England : 2003)》2004,(19):3144-3146
Sm(2.75)C(60) displays large negative thermal expansion behaviour in the temperature range 4.2-32 K at ambient pressure as a result of a quasi-continuous valence change from the larger Sm(2+) towards the smaller Sm(2.3+) ion. Here we use the powder synchrotron X-ray diffraction technique at ambient temperature and elevated pressures to study the compression behaviour in the pressure range 0-6 GPa. An abrupt hysteretic phase transition, accompanied by a dramatic volume decrease (approximately =6.0%) and a change in colour from black to golden was found at approximately =4 GPa induced by a sudden Sm valence transition from +2.3 towards +3. Such behaviour is typical of highly correlated Kondo insulators like SmS and makes Sm(2.75)C(60) the first known molecular-based member of this fascinating class of materials. 相似文献
46.
Medina E Díaz M León N Guerrero C Hasmy A Serena PA Costa-Krämer JL 《Physical review letters》2003,91(2):026802
Conductance histograms of aluminum and gold nanocontact rupture are studied experimentally and simulated using embedded atom potentials to assess the interplay between electronic and structural properties at room temperature. Our results reveal a crossover from quantized conductance structures to crystalline faceting or geometric shell/subshell structures at 300 K. The absence of electronic shell structure in gold and aluminum is in stark contrast with the behavior of alkaline metal nanowires which emulate their cluster counterparts. Semiclassical arguments suggest why rapid dominance of ionic structures takes place, and possible nanowire architectures are proposed in consistency with both the experimental and simulated nanocontact data. 相似文献
47.
A. Förster M.I. Lepsa D. Freundt J. Stock S. Montanari 《Applied Physics A: Materials Science & Processing》2007,87(3):545-558
This paper reviews the main aspects of the design, fabrication and characterization of GaAs Gunn diodes intended to be used
in advanced driver assistance systems. The corresponding Gunn diode based oscillators operate at the microwave frequency of
77 GHz and deliver an output power up to 19.2 dBm (83.2 mW). To fulfill the high demands of the automotive industry, temperature
stability and a high grade of frequency purity, the Gunn diode structure includes a hot electron injector. This is based on
the heteroepitaxy of a graded gap AlxGa1-xAs layer and an adjacent thin highly doped GaAs layer. The hot electron injector properties are investigated using dc and
rf electrical measurements, including the temperature influence as well. Specific production related data of the cavity oscillators
using our Gunn diodes are presented. New alternatives, such as the resonant tunneling emitter as a hot electron injector and
the Gunn diode based MMIC as oscillator, are introduced.
PACS 85.30.-z; 73.40.-c; 07.57.Hm; 84.30.Ng; 85.30.Fg 相似文献
48.
49.
Peter W. Kenny Carlos A. Montanari Igor M. Prokopczyk Fernanda A. Sala Geraldo Rodrigues Sartori 《Journal of computer-aided molecular design》2013,27(8):655-664
The ability to modify chemical structures in an automated and controlled manner is useful in molecular design. This Perspective introduces the MUDO molecule editor and shows how automated molecule editing can be used to standardize structures, enumerate tautomeric and ionization states, identify matched molecular pairs. Unlike its predecessor Leatherface, MUDO can also process 3D structures and this capability can be used to link non-covalently docked ligands to proteins. 相似文献
50.
Simulated minimum cross-section histograms of breaking Al nanocontacts are produced using molecular dynamics. The results allow a new interpretation of the controverted conductance histogram peaks based on preferential geometrical arrangements of nanocontact necks. As temperature increases, lower conductance peaks decrease in favor of broader and higher conductance structures. This reveals the existence of shell and supershell structures favored by the increased mobility of Al atoms. 相似文献