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991.
A parameter whose coupling to a quantum probe of n constituents includes all two-body interactions between the constituents can be measured with an uncertainty that scales as 1/n3/2, even when the constituents are initially unentangled. We devise a protocol that achieves the 1/n3/2 scaling without generating any entanglement among the constituents, and we suggest that the protocol might be implemented in a two-component Bose-Einstein condensate. 相似文献
992.
993.
Sergio Luigi Cacciatori Francesco Dalla Piazza Bert Van Geemen 《Letters in Mathematical Physics》2008,85(2-3):185-193
A main issue in superstring theory are the superstring measures. D’Hoker and Phong showed that for genus two these reduce to measures on the moduli space of curves which are the product of modular forms of weight eight and the bosonic measure. They also suggested a generalisation to higher genus. We showed that their approach works, with a minor modification, in genus three and we announced a positive result also in genus four. Here we give the modular form in genus four explicitly. Recently, S. Grushevsky published this result as part of a more general approach. 相似文献
994.
Lozano-Perez S 《Micron (Oxford, England : 1993)》2008,39(3):320-328
The preparation of samples containing stress corrosion crack tips for 3D atom-probe tomography and transmission electron microscopy is of ultimate importance for understanding the mechanisms controlling crack propagation. In this paper, it will be shown that a focused ion beam machine equipped with an in situ micromanipulator is an ideal tool to systematically prepare such demanding samples. The methodology is described and discussed in detail, and several results are presented to demonstrate the potential of the technique. 相似文献
995.
Guido Cognola Monica Gastaldi Sergio Zerbini 《International Journal of Theoretical Physics》2008,47(4):898-910
Motivated by the dark energy issue, a minisuperspace approach to the stability for modified gravitational models in a four
dimensional cosmological setting is investigated. Specifically, after revisiting the f(R) case, R being the Ricci curvature, we present a stability condition around a de Sitter solution valid for modified gravitational
models of generalized type F(R,G,Q), G and Q being the Gauss-Bonnet and quadratic Riemann invariants respectively. A generalization to higher order invariants is presented. 相似文献
996.
Carsten Carstensen Sergio Conti Antonio Orlando 《Continuum Mechanics and Thermodynamics》2008,20(5):275-301
The modeling of the finite elastoplastic behaviour of single crystals with one active slip system leads to a nonconvex variational
problem, whose minimization produces fine structures. The computation of the quasiconvex envelope of the energy density involves
the solution of a nonconvex optimization problem and faces severe numerical difficulties from the presence of many local minima.
In this paper, we consider a standard model problem in two dimensions and, by exploiting analytical relaxation results for
limiting cases and the special structure of the problem at hand, we obtain a fast and efficient numerical relaxation algorithm.
The effectiveness of our algorithm is demonstrated with numerical examples. The precision of the results is assessed by lower
bounds from polyconvexity.
相似文献
997.
Fernando C. Moraes Tiago A. Silva Ivana Cesarino Marcos R. V. Lanza Sergio A. S. Machado 《Electroanalysis》2013,25(9):2092-2099
A sensitive way to determine levofloxacin using a sensor based on vertical aligned carbon nanotubes is described. The morphology and the electrochemical performance of the electrodes were characterised by atomic force microscopy, cyclic voltammetry and square wave voltammetry. A scan‐rate study and electrochemical impedance spectroscopy showed that the levofloxacin oxidation product is adsorbed on the electrode surface. Differential pulse voltammetry in phosphate‐buffer solution allowed the development of a method to determine levofloxacin levels in the range of 1.0–10.0 µmol L?1, with a detection limit of 75.2 nmol L?1. The proposed sensor was successfully applied in the determination of levofloxacin in urine, and the obtained results were in full agreement with those from the HPLC procedure. 相似文献
998.
Jansat S Gómez M Philippot K Muller G Guiu E Claver C Castillón S Chaudret B 《Journal of the American Chemical Society》2004,126(6):1592-1593
Palladium nanoparticles (4 nm, fcc) were prepared through decomposition of [Pd2(dba)3] by H2 in the presence of a chiral xylofuranoside diphosphite. These particles catalyze the allylic alkylation of rac-3-acetoxy-1,3-diphenyl-1-propene with dimethyl malonate leading to an almost total conversion of the (R) enantiomer and almost no reaction with the (S). This gives rise to 97% ee for the alkylation product and a kinetic resolution of the substrate recovered with ca. 90% ee. This behavior was compared to that of a molecular catalyst at various dilutions, and the differences between the two systems are discussed. This is the first colloidal system shown to display such a high enantioselectivity besides the well-known Pt/cinchonidine system. 相似文献
999.
Sergio Baggio M. Enriqueta Díaz de Vivar María Teresa Garland Ricardo Baggio 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(4):m157-m158
The title compound, {[Zn2(SO3)2(C10H8N2)]·H2O}n, is a two‐dimensional polymer built up of a [ZnSO3]n chain evolving around a 21 axis and interconnected by a 4,4′‐bipyridine spacer. The resulting two‐dimensional structures are linked, in turn, by hydrogen bonding mediated by the solvent water molecule. The organic ligand lies on a centre of symmetry located on the mid‐point of the bond between the rings, while the solvent water molecule is halved by a twofold axis passing through the O atom. 相似文献
1000.
Lamberti C Groppo E Prestipino C Casassa S Ferrari AM Pisani C Giovanardi C Luches P Valeri S Boscherini F 《Physical review letters》2003,91(4):046101
Geometric parameters of NiO films epitaxially grown on Ag(001) were determined using two independent experimental techniques and ab initio simulations. Primary beam diffraction modulated electron emission experiments determined that the NiO films grow with O on top of Ag and that the oxide/metal interface distance is d=2.3+/-0.1 A. Polarization-dependent x-ray absorption, at the Ni-K edge, determined the tetragonal strain (r( parallel )=2.046+/-0.009 A, r( perpendicular )=2.12+/-0.02 A) and d=2.37+/-0.05 A. Periodic slab model results agree with the experiments (d=2.40, r( parallel )=2.07, r( perpendicular )=2.10 A; the O-on-top configuration is the most stable). 相似文献