排序方式: 共有32条查询结果,搜索用时 21 毫秒
21.
We present evidence for a nonsingular origin of the Universe with intial conditions determined by quantum physics and relativistic
gravity. In particular, we establish that the present temperature of the microwave background and the present density of the
Universe agree well with our predictions from these intial conditions, after evolution to the present age using the Einstein-Friedmann
equation. Remarkably, the quantum origin for the Universe naturally allows its evolution at exactly the critical density.
We also discuss the consequences of these results to some fundamental aspects of quantum physics in the early Universe. 相似文献
22.
23.
Shravankumar KankalaRavikrishna Edulla Sarangapani ModemRavinder Vadde Chandra Sekhar Vasam 《Tetrahedron letters》2011,52(29):3828-3831
The intramolecular crossed aldehyde-ketone benzoin condensation in the chalcone of o-phthalaldehyde (OPA) catalyzed by N-heterocyclic carbene (NHCs) generated in situ from readily available imidazolium and thiazolium salts is described. In this reaction, bicyclic α-hydroxyl ketones (naphthalenone type tertiary alcohol) were selectively produced in good yields (75-94%) in shorter reaction times (20 min) through nucleophilic addition of acyl anion generated by umpolung in OPA-chalcone (regio controlled). 相似文献
24.
Willard M Freeman Melinda E Lull Kruti M Patel Robert M Brucklacher Drake Morgan David CS Roberts Kent E Vrana 《BMC neuroscience》2010,11(1):29
Background
Many studies of cocaine-responsive gene expression have focused on changes occurring during cocaine exposure, but few studies have examined the persistence of these changes with cocaine abstinence. Persistent changes in gene expression, as well as alterations induced during abstinence may underlie long-lasting drug craving and relapse liability. 相似文献25.
Ionic liquids and ionic liquid crystals of imidazolium salts composed of various transition and main group metals have been reviewed. Ionic metal complexes of imidazoles and N-heterocyclic carbenes possess the similar properties were also included. These types of ILs and ILCs have been realized as potential solvents, catalysts, catalyst precursors and reagents for many organic transformations and provide ecofriendly protocols. They have also been found to play key roles in material science. Many of these IL systems are air- and moisture stable and are considered as alternatives for air- and moisture sensitive chloroaluminate-based ILs. 相似文献
26.
W. Meisel CS. Vértes M. Lakatos-Varsányi 《Journal of Radioanalytical and Nuclear Chemistry》1995,190(2):289-298
Integral electron Mössbauer spectroscopy (ICEMS) and additionally some electrochemical methods were used to characterize the passivation process of iron (low carbon steel) in sulfate, sulfate+sulfite (a possible model solution of acid rain) solutions and in phospate buffer. The phase compositions and thicknesses of the passive layers formed due to the electrochemical polarizations were analyzed in dependence on the duration of the anodic passivations and on the pH of the used electrolytes. The passive layer, as determined from the Mössbauer spectra, consists mainly of -FeOOH, however in sulfite containing sulfate aqueous solution at pH 3.5 Fe3C and despite ex-situ circumstances FeSO4·H2O was detected after the shortest polarization time. The film thickness, which was found to grow nearly linearly with polarization time in pure sulfate solution and in phospate buffer, reached a maximum of 60–160 nm (depending on pH) in sulfate+sulfite solution after a passivation time of about 4 hours. It has been proved, that HSO3
–-ion, which is contained by acid rain, initiate pit formation under acid conditions and so enforces the corrosion of iron. The experimental results furthermore suggest, that not the whole oxidic layer is responsible for the passivity but only a very thin intermediate layer formed between an inner oxide layer of a cubic structure and the rhombic oxide (-FeOOH) cover. 相似文献
27.
28.
B. KOVÁCS 《Journal of sound and vibration》2002,254(2):367-378
A new model is presented for the dynamic analysis of a laminated circular ring segment. The differential equations which govern the free vibrations of a circular ring segment and the associated boundary conditions are derived by Hamilton's principle having consideration for the bending and shear deformation of all layers. The author uses a new iterative process to successively refine the stress/strain field in the sandwich arch. The model includes the effects of transverse shear and rotatory inertia. The iterative model is used to predict the modal frequencies and damping of simply-supported sandwich circular arch. The solutions for a three-layer circular arch are compared with a three-layer approximate model. 相似文献
29.
Chandra Sekhar Vasam Sarangapani Modem Shravankumar Kankala Geeta Budige Ravinder Vadde 《应用有机金属化学》2009,23(11):460-466
New dinuclear Rh(I)–Phosphines of the types [Rh(µ‐azi)(CO)(L)]2 ( 1,3 – 7 ) and [Rh(µ‐azi)(L)]2 ( 8 ) with pendant polar groups, and a chealated mononuclear compound [Rh(azi‐H)(CO)(L)] ( 2 ) (where azi = 7‐azaindolate, L = polar phosphine) were isolated from the reaction of [Rh(µ‐Cl)(CO)2]2 with 7‐azaindolate followed by some polar mono‐ and bis‐phosphines ( L 1 – L 8 ). A relationship between Δδ31P‐NMR and ν(CO) values was considered to define the impact of polar‐groups on σ‐donor properties of the phosphines. These compounds were evaluated as catalyst precursors in the hydroformylation of 1‐hexene and 1‐dodecene both in mono‐ and biphasic aqueous organic systems. While the biphasic hydroformylations (water + toluene) gave exclusively the aldehydes, the monophasic one (aqueous ethanol) showed propensity to form both aldehydes and alcohols. The influence of bimetallic cooperative effects, and σ‐donor and hydrophilic properties of the phosphines with pendant polar‐groups in enhancing the yields and selectivity of hydroformylation products was emphasized. In addition, when strong σ‐donor phosphine was used, the π‐acceptor nature of pyridine ring of 7‐azaindolate spacer was found to be a considerable factor in facilitating the facile cleavage of CO group during hydroformylation and in supplementing the cooperative effects. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
30.
A new asymmetric parabolic effective fusion barrier model for heavy ion fusion is developed. 相似文献