A subsystem-independent generalization of entanglement

We present a generalization of entanglement based on the idea that entanglement is relative to a distinguished subspace of observables rather than a distinguished subsystem decomposition. A pure quantum state is entangled relative to such a subspace if its expectations are a proper mixture of those of other states. Many information-theoretic aspects of entanglement can be extended to this observable-based setting, suggesting new ways of measuring and classifying multipartite entanglement. By going beyond the distinguishable-subsystem framework, generalized entanglement also provides novel tools for probing quantum correlations in interacting many-body systems.     

Efficient solvability of Hamiltonians and limits on the power of some quantum computational models

One way to specify a model of quantum computing is to give a set of control Hamiltonians acting on a quantum state space whose initial state and final measurement are specified in terms of the Hamiltonians. We formalize such models and show that they can be simulated classically in a time polynomial in the dimension of the Lie algebra generated by the Hamiltonians and logarithmic in the dimension of the state space. This leads to a definition of Lie-algebraic "generalized mean-field Hamiltonians." We show that they are efficiently (exactly) solvable. Our results generalize the known weakness of fermionic linear optics computation and give conditions on control needed to exploit the full power of quantum computing.     

Organic syntheses with sulfones noxxxvi: conversion of sulfones into aldehydes and ketones.

Alkyl and allyl sulfones can be converted into boronic esters, oxidation of which leads to aldehydes or ketones.     

DC photoelectric signals from bacteriorhodopsin adsorbed on lipid monolayers and thiol/lipid bilayers supported by mercury

Purple membrane (PM) fragments were adsorbed on a dioleoylphosphatidylcholine (DOPC) monolayer and on a mixed alkanethiol/DOPC bilayer supported by mercury to investigate the kinetics of light-driven proton transport by bacteriorhodopsin (bR). The light-on and light-off capacitive currents on an alkanethiol/DOPC bilayer at pH 6.4 were interpreted on the basis of a simple equivalent circuit. The pH dependence of the biphasic decay kinetics of the light-on currents was analyzed to estimate the pK(a) values for the transitions releasing protons to, and taking up protons from, the solution. The linear dependence of the stationary light-on current of bR on a DOPC monolayer self-assembled on mercury upon the applied potential was interpreted on the basis of an equivalent circuit.     

Sulphonium ions: Collision-activated dissociation using fast atom bombardment ionization and a triple quadrupole mass spectrometer

The low-energy collision-activated dissociation of sulphonium cations, including symmetrical trialkyl R³S⁺, dimethylalkyl (CH₃)₂RS⁺, diphenylalkyl Ph₂RS⁺ and cyclic (CH₂)_nS⁺R, has been recorded using fast atom bombardment ionization and a triple quadrupole mass spectrometer. The general trends are easy loss of sulphide to give [R]⁺, except for R ? CH₃, and loss of alkene to give protonated sulphide if β-hydrogens are available. Loss of alkane, generally found in ammonium compounds, is not observed.     

Nanocap-shaped tin phthalocyanines: synthesis, characterization, and corrosion inhibition activity

Thermal and microwave reactions between [PcSn(IV)Cl2] (1) and the potassium salts of eight fatty acids (2 a-h) led to cis-[(RCO2)2Sn(IV)Pc] compounds (3 a-h) in yields ranging from 54 to 90 %. Compounds 3 a-h were fully characterized by elemental analysis, spectroscopy (IR, UV/Vis, multinuclear NMR), and seven X-ray diffraction structures, whereby two different allotropes were observed in two cases. The two carboxylates in 3 have a cis anisobidentate binding mode, octacoordination of the tin atoms with square-antiprismatic geometry, and pi-electron-rich nanocap shapes. On account of the latter characteristics, 3 a-h compounds have anticorrosion properties. LPR and Tafel electrochemical methods were used to characterize the behavior of these derivatives in naturally aerated sour brine, which is a common environment in petroleum production and refinery operations. The measurement of the corrosion rate of carbon steel AISI 1018 in the presence of 3 a-h (500 ppm) gave efficiencies of 61-87 % for the inhibitor performance. Of the different derivatives examined, compounds 3 e and 3 h were the most effective corrosion inhibitor prototypes.     

Continuous dependence of stochastic control models on the noise distribution

Given a discrete-time stochastic control systemx _t+1 =F(x _t ,a _t , _t ),t=0, 1,.., N (N), where the noise process { _t } is a sequence of i.i.d. random elements with distribution, let ^N (x) be the optimal reward function when the initial state isx and the planning horizon isN. We give conditions under whichv ^N is a continuous function in for several reward criteria. The applicability of these results to nonparametric adaptive control of stochastic systems is briefly discussed.This research was supported in part by the Consejo Nacional de Ciencia y Tecnologia (CONACYT) under Grants PCCBBNA-020630 and PCEXCNA-040640.     

Mixed nests

t-nests witht=((q+1)/2+i) are constructed usingi André nets and (q + 1)/2 regulus nets constructed via a group of order ((q + 1)/2)². The constructed planes obtained using these mixed nests are characterized by the existence of two symmetric homology groups of order (q + 1)/2.The research for this article was partially supported by FONDECYT. This work was done during visits to the University of Iowa in 1993 by the second author and to University of Chile in 1994 by the first author. The authors gratefully acknowledge the support of the Universities of Chile and Iowa.     

Conformational distribution of a 14-residue peptide in solution: a fluorescence resonance energy transfer study

We demonstrate here that a nitrile-derivatized phenylalanine residue, p-cyanophenylalanine (Phe(CN)), and tryptophan (Trp) constitute a novel donor-acceptor pair for fluorescence resonance energy transfer (FRET). The F?rster distance of this FRET pair was determined to be approximately 16 A and hence is well suited for determining relatively short separation distances. To validate the applicability of this FRET pair in conformational studies, we studied the conformational heterogeneity of a 14-residue amphipathic peptide, Mastoparan X (MPx peptide), in water and 7 M urea solution as well as at different temperatures. Specifically, seven nitrile-derivatized mutants of the MPx peptide, each containing a Phe(CN) residue that replaces different positions along the peptide sequence (i.e., from position 5 to 11) and serves as a resonance energy donor to the native Trp residue at position 3, were studied spectroscopically. The FRET efficiencies obtained from these peptides allowed us to gain a global picture regarding the conformational distribution of the MPx peptide in different environments. Our results suggest that the MPx molecules exist in water as an ensemble of rather compact conformations, with a radius of gyration of approximately 4.2 A, whereas in 7 M urea the radius of gyration increases to approximately 6.5 A, indicating that the peptide conformations become more extended under this condition. However, we found that temperature had only a negligible effect on the size of the MPx peptide, underlining the difference between the thermally and chemically denatured states of polypeptides. The application of the Gaussian chain or the wormlike chain model allowed us to further obtain the probability distribution function of the separation distance between any two residues along the peptide sequence. We found that the effective bond length of the MPx peptide, obtained by using the Gaussian chain model, is 2.78 A in water and 4.28 A in 7 M urea.