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101.
Making use of exact results and quantum Monte Carlo data for the entanglement of formation, we show that the ground state of anisotropic two-dimensional S=1/2 antiferromagnets in a uniform field takes the classical-like form of a product state for a particular value and orientation of the field, at which the purely quantum correlations due to entanglement disappear. Analytical expressions for the energy and the form of such states are given, and a novel type of exactly solvable two-dimensional quantum models is therefore singled out. Moreover, we show that the field-induced quantum phase transition present in the models is unambiguously characterized by a cusp minimum in the pairwise-to-global entanglement ratio R, marking the quantum-critical enhancement of multipartite entanglement. 相似文献
102.
103.
The evolution of a two-level system subjected to stimulated transitions which is undergoing a sequence of measurements of
the level occupation probability is evaluated. Its time correlation function is compared to the one obtained through the pure
Schr?dinger evolution. Systems of this kind have been recently proposed for testing the quantum mechanical predictions against
those of macrorealistic theories, by means of temporal Bell inequalities. The classical requirement of noninvasivity, needed
to define correlation functions in the realistic case, finds a quantum counterpart in the quantum nondemolition condition.
The consequences on the observability of quantum mechanically predicted violations to temporal Bell inequalities are drawn
and compared to the already dealt case of the rf-SQUID dynamics.
Received: 28 March 1996 / Revised version: 13 August 1996 相似文献
104.
Tommaso Schiavinotto Thomas Stützle 《Journal of Mathematical Modelling and Algorithms》2004,3(4):367-402
The linear ordering problem is an NP-hard problem that arises in a variety of applications. Due to its interest in practice, it has received considerable attention and a variety of algorithmic approaches to its solution have been proposed. In this paper we give a detailed search space analysis of available benchmark instance classes that have been used in various researches. The large fitness-distance correlations observed for many of these instances suggest that adaptive restart algorithms like iterated local search or memetic algorithms, which iteratively generate new starting solutions for a local search based on previous search experience, are promising candidates for obtaining high performing algorithms. We therefore experimentally compared two such algorithms and the final experimental results suggest that, in particular, the memetic algorithm is a new state-of-the-art approach to the linear ordering problem. 相似文献
105.
The second dissociation constant of salicylic acid (H2L) has been determined, at 25 degrees C, in NaCl ionic media by UV spectrophotometric measurements. The investigated ionic strength values were 0.16, 0.25, 0.50, 1.0, 2.0 and 3.0 M. The protolysis constants calculated at the different ionic strengths yielded, with the Specific Interaction Theory, the infinite dilution constant, log beta1(0) = 13.62 +/- 0.03, for the equilibrium L2- + H+ <==> HL-. The interaction coefficient between Na+ and L2-, b(Na+, L2-) = 0.02 +/- 0.07, has been also calculated. 相似文献
106.
107.
Tommaso R. I. Cataldi Giampaolo Ricciardi Giuliana Bianco Daniela Pietrangeli Salvatore Abate 《Rapid communications in mass spectrometry : RCM》2009,23(13):1927-1933
Some newly synthesized 10B nido‐carborane derivatives, i.e., 7,8‐dicarba‐nido‐undecaborane monoanions ([7‐Me‐8‐R‐C2B9H10]‐K+, R = H, butyl, hexyl, octyl and decyl), have been fully characterised and examined by electrospray ionization and Fourier transform ion cyclotron resonance mass spectrometry with liquid chromatographic separation (LC/ESI‐FTICR‐MS). These boron‐containing compounds exhibit abundant molecular ions ([M]?) at m/z 140.22631 [CB9H14]?, m/z 196.28883 [CB9H22]?, m/z 224.32032 [CB9H26]?, m/z 252.35133 [CB9H30]? and m/z 280.38354 [CB9H34]? at the normal tube lens voltage setting of ?90 V, which was an instrumental parameter value selected in the tuning operation. Additional [M–nH2]? (n = 1?4) ions were observed in the mass spectra when higher tube lens voltages were applied, i.e., ?140 V. High‐resolution FTICR‐MS data revealed the accurate masses of fragment ions, bearing either an even or an odd number of electrons. Collision‐induced dissociation of the [M–nH2]? ions (n = 0–4) in the quadrupole linear ion trap (LTQ) analyzer confirmed the loss of hydrogen molecules from the molecular ions. It is suggested that the loss of H2 molecules from the alkyl chain is a consequence of the stabilization effect of the nido‐carborane charged polyhedral skeleton. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
108.
A rapid and very sensitive method for the accurate determination of free iodide in real samples is described. The method is based on anion-exchange chromatographic separation coupled with amperometric detection at a modified platinum electrode under constant applied potential (+0.85 V vs. Ag AgCl). An experimental setup with an in-line and very effective method of electrode modification is proposed using an amperometric thin-layer cross-flow detector and a flowing solution 300 mg/L of iodide; the working electrode is polarised to the limiting current for oxidation of iodide to iodine in acidic solutions with the consequent formation of an iodine-based film. The results indicated that the modified electrode exhibits high analytical response for iodide electrooxidation with good stability and long-life. The signal intensity of daily experimental sessions (8 h), during which standards and real samples were repeatedly injected, exhibits a moderate lowering (i.e. <6%). Using a mixture of 25 mM HNO3 and 50 mM NaNO3 as an eluent phase in ion-exchange chromatography, the detection limit of iodide was estimated to be 0.5 g/L (S/N=3) with an injection volume of 50 L. This method was applied successfully to quantify the iodide content of milk samples and in wastewaters as well as trace amounts in common vegetables and solutions containing high chloride levels. 相似文献
109.
110.