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161.
Holger Brenner 《Transactions of the American Mathematical Society》2004,356(1):371-392
We study different notions of slope of a vector bundle over a smooth projective curve with respect to ampleness and affineness in order to apply this to tight closure problems. This method gives new degree estimates from above and from below for the tight closure of a homogeneous -primary ideal in a two-dimensional normal standard-graded algebra in terms of the minimal and the maximal slope of the sheaf of relations for some ideal generators. If moreover this sheaf of relations is semistable, then both degree estimates coincide and we get a vanishing type theorem.
162.
Adamová D Agakichiev G Appelshäuser H Belaga V Braun-Munzinger P Castillo A Cherlin A Damjanović S Dietel T Dietrich L Drees A Esumi SI Filimonov K Fomenko K Fraenkel Z Garabatos C Glässel P Hering G Holeczek J Kushpil V Lenkeit B Ludolphs W Maas A Marín A Milosević J Milov A Miśkowiec D Panebrattsev Y Petchenova O Petrácek V Pfeiffer A Rak J Ravinovich I Rehak P Sako H Schmitz W Schukraft J Sedykh S Shimansky S Slívová J Specht HJ Stachel J Sumbera M Tilsner H Tserruya I Wessels JP Wienold T 《Physical review letters》2003,90(2):022301
Based on an evaluation of data on pion interferometry and on particle yields at midrapidity, we propose a universal condition for thermal freeze-out of pions in heavy-ion collisions. We show that freeze-out occurs when the mean free path of pions lambda(f) reaches a value of about 1 fm, which is much smaller than the spatial extent of the system at freeze-out. This critical mean free path is independent of the centrality of the collision and beam energy from the Alternating Gradient Synchrotron to the Relativistic Heavy Ion Collider. 相似文献
163.
Directional synthesis of a dye-linked conducting homopolymer 总被引:2,自引:0,他引:2
We report a new synthesis of a 10,20-diphenyl-5,15-bis(4-cyanophenyl)porphyrin (1) and its reduction to give 10,20-diphenyl-5,15-bis(4-formylphenyl)porphyrin (2). When the conducting polymer poly(2',5'-dioctyl-4,4' '-terphenylenecyanovinylene) was prepared in the presence of 2, we obtained a three-domain structure, compound 3, consisting of two homopolymer blocks (J domains) with the porphyrin dye molecule (P domain) in the middle. The JPJ assembly was subjected to photophysical studies where we showed that the J domain could serve as a light-harvesting antenna for the P domain. 相似文献
164.
Pathak Madhvesh Bohra Rakesh Mehrotra Ram C. Lorenz Ingo-Peter Piotrowski Holger 《Transition Metal Chemistry》2003,28(2):187-192
Reactions of cis-dialkoxy-bis(acetylacetonato)titanium(IV), [(acac)2Ti(OR)2] (R = Et, Pr
i
) with alkoxyalkanols (ROCH2CH2OH) (R = Me, Et, n-Bu) in 1:1 and 1:2 molar ratios in refluxing benzene under anhydrous conditions yield [(acac)2Ti(OR)2–n
(OCH2CH2OR)
n
] (n = 1 or 2) complexes, which were purified by distillation under reduced pressure. On the basis of i.r. and n.m.r. (1H- and 13C-) spectral studies, a cis-octahedral environment around TiIV is proposed. On keeping the distilled dark brown-red viscous liquid [(acac)2Ti(OEt)(OCH2CH2OBu)] for 2 weeks, orange yellow crystals of [(acac)2TiO]2 were obtained. A single crystal X-ray diffraction study suggests the product is a new modification of [(acac)2TiO]2. 相似文献
165.
Friedrich HB Govender M Makhoba X Ngcobo TD Onani MO 《Chemical communications (Cambridge, England)》2003,(23):2922-2923
A new Os/Cu-Al-hydrotalcite-like catalyst is described which, with N-methylmorpholine oxide as co-oxidant, heterogeneously catalyses the hydroxylation of olefins to give diols selectively and in high yield. 相似文献
166.
We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the minimal supersymmetric standard model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so-called D parameter, is computed at one-loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient
which mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at
, while QED final state interactions give a value of
. Explicit expressions for all relevant diagrams are given in an appendix.Received: 3 March 2003, Revised: 16 May 2003, Published online: 3 July 2003 相似文献
167.
168.
“Top–down” models explain the observation of ultra-high energy cosmic rays (UHECR; E5×1019 eV) through the decay of very massive, long-lived “X particles”. If superparticles with masses near a TeV exist, X decays also lead to a significant flux of very energetic neutralinos, assumed to be the (stable or long-lived) lightest superparticles. There is a range of energies where neutrinos get absorbed in the Earth, but neutralinos can still traverse it. These neutralinos could in principle be detected. We calculate the detection rate in planned experiments such as OWL and EUSO. For bino-like neutralinos, which have been considered previously, we find detection rates below 1 event per Teraton of target and year in all cases; often the rates are much smaller. In contrast, if the neutralino is higgsino-like, more than ten events per year per Teraton might be observed, if the mass of the X particle is near its lower bound of 1012 GeV. 相似文献
169.
We extend a theory of first order ? corrections to Gutzwiller’s trace formula for systems with a smooth potential to systems with discrete symmetries and, as an example, apply the method to the two-dimensional hydrogen atom in a uniform magnetic field. We exploit the C4v-symmetry of the system in the calculation of the correction terms. The numerical results for the semiclassical values will be compared with values extracted from exact quantum mechanical calculations. The comparison shows an excellent agreement and demonstrates the power of the ? expansion method. 相似文献
170.
Weijuan Jia Jessica McLachlan Jiayan Xu S. Holger Eichhorn 《Journal of Thermal Analysis and Calorimetry》2010,100(3):839-845
Gold nanoparticles (Au-NPs) were prepared by a surfactant-free single-phase reduction of hydrogen tetrachloroaurate(III) hydrate in the presence of different organic thiol ligands. Sizes, size distributions, and crystallinity of the Au-NPs were determined by high-resolution transmission electron microscopy and powder X-ray diffraction, whereas thermogravimetric analysis provided information on the organic ligand-to-gold ratios as well as amounts of contaminants. A systematic decrease in size with increasing conical bulk of the thiolate ligand is observed but large size distributions and contamination of the generated Au-NPs prohibit detailed mechanistic studies. A first-generation Fréchet dendron thiol produced the smallest and cleanest Au-NPs of the narrowest size distribution. 相似文献