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891.
A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
892.
893.
894.
A stereoselective synthesis of (2S,3R)-β-methoxyphenylalanine, an amino acid contained within the cyclic peptide cyclomarin A, was successfully synthesized from Lajoie’s serine aldehyde. 相似文献
895.
H. Hansen G. Chanfray D. Davesne P. Schuck 《The European Physical Journal A - Hadrons and Nuclei》2002,14(4):397-411
An application of a self-consistent version of RPA to quantum field theory with broken symmetry is presented. Although our
approach can be applied to any bosonic field theory, we specifically study the ϕ4 theory in 1 + 1 dimensions. We show that the standard RPA approach leads to an instability which can be removed when going
to a superior version, i.e. the renormalized RPA. We present a method based on the so-called charging formula of the many-electron problem to calculate
the correlation energy and the RPA effective potential.
Received: 18 February 2002 / Accepted: 8 May 2002 相似文献
896.
The kinetics of the aquation of (H2O)5Cr(O2CCCl3)2+ have been examined at 35–55°C and 1.00M ionic strength with [H+] = 0.01?1.00M. The reaction follows the rate equation -d ln [Crtotal]/dt = (a[H+]?1 + b + c[H+])/(1 + d[H+]), where [Crtotal] is the stoichiometric concentration of the complex. At 45°C a = (1.41 ± 0.03) × 10?7M/s, b = (1.66 ± 0.02) × 10?5 s?1, c = (7.0 ± 0.8) × 10?5M?1·S?1 and d = 2.3 ± 0.3M?1. Two mechanisms consistent with this rate law are discussed, with evidence being presented in favor of an ester hydrolysis mechanism involving steady-state intermediates. Equilibrium and activation parameters were determined. 相似文献
897.
D. Cline M.J.A. De Voigt P.B. Vold Ole Hansen O. Nathan D. Sinclair 《Nuclear Physics A》1974,233(1):91-104
Energy levels in 40Ca up to 10.2 MeV have been studied in the neutron pickup reaction 41Ca(τ, α)40Ca with 20 MeV bombarding energy. Thirty excited states have been identified and angular distributions have been measured in the interval from 5° to 40° by means of a split-pole magnetic spectrometer. The angular distributions together with DW calculations have been used to extract ln values and spectroscopic factors. The ln = 2 strength distribution for the particle-hole levels is compared to the lp = 3 strength distribution from pr stripping data. 相似文献
898.
L. Eskildsen D. S. Olesen B. Mikkelsen J. Farr T. Durhuus Z. Wang P. B. Hansen K. E. Stubkjaer 《Fiber and Integrated Optics》1990,9(3):231-236
A new approach to automatic gain control has been demonstrated and a signal polarization independent operation over a 35-nm wavelength range at a gain level of 17 dB has been obtained. 相似文献
899.
Mickel J. Hansen Michael M. Lerch Dr. Wiktor Szymanski Prof. Dr. Ben L. Feringa 《Angewandte Chemie (International ed. in English)》2016,55(43):13514-13518
A straightforward synthesis of azobenzenes with bathochromically‐shifted absorption bands is presented. It employs an ortho‐lithiation of aromatic substrates, followed by a coupling reaction with aryldiazonium salts. The products are obtained with good to excellent yields after simple purification. Moreover, with the presented methodology, a structurally diverse panel of different azobenzenes, including unsymmetric tetra‐ortho‐substituted ones, can be readily obtained, which paves the way for future development of red‐light‐addressable azobenzene derivatives for in vivo application. 相似文献
900.
We introduce and analyze a framework and corresponding method for compressed sensing in infinite dimensions. This extends the existing theory from finite-dimensional vector spaces to the case of separable Hilbert spaces. We explain why such a new theory is necessary by demonstrating that existing finite-dimensional techniques are ill suited for solving a number of key problems. This work stems from recent developments in generalized sampling theorems for classical (Nyquist rate) sampling that allows for reconstructions in arbitrary bases. A conclusion of this paper is that one can extend these ideas to allow for significant subsampling of sparse or compressible signals. Central to this work is the introduction of two novel concepts in sampling theory, the stable sampling rate and the balancing property, which specify how to appropriately discretize an infinite-dimensional problem. 相似文献