Synthesis of oligo(phenyleneethynylene)-tetrathiafulvalene cruciforms for molecular electronics

[reaction: see text] Novel oligo(phenyleneethynylene) (OPE)-tetrathiafulvalene (TTF) cruciform molecules containing thiol end-groups have been prepared and characterized. These redox-active molecules are interesting for future applications as molecular wires/transistors for molecular electronics.     

Bragg selectivity of space-charge gratings in multidomain lithium niobate crystals

It is shown experimentally and theoretically that a partial domain reversal in ferroelectric lithium niobate crystals containing a previously imprinted photorefractive space-charge grating results in a highly unusual change of the angular Bragg selectivity. This carries important in situ information about domain structures, including the quality of periodically poled samples.     

A cyclic dinucleotide with a four-carbon 5'-C-to-5'-C connection; synthesis by RCM, NMR-examination and incorporation into secondary nucleic acid structures

A 5'-C-allylthymidine derivative was prepared from thymidine by the application of a stereoselective allylation procedure and its 5'(S)-configuration was confirmed. From this nucleoside derivative, appropriately protected building blocks were prepared and coupled using standard phosphoramidite chemistry to afford a dinucleotide with two 5'-C-allylgroups. This molecule was used as a substrate for a ring-closing metathesis (RCM) reaction and after deprotection, a 1 : 1 mixture of E- and Z-isomers of a cyclic dinucleotide with an unsaturated 5'-C-to-5'-C connection was obtained. Alternatively, a hydrogenation of the double bond and deprotection afforded a saturated cyclic dinucleotide. An advanced NMR-examination confirmed the constitution of this molecule and indicated a restriction in its overall conformational freedom. After variation of the protecting group strategy, a phosphoramidite building block of the saturated cyclic dinucleotide with the 5'-O-position protected as a pixyl ether and the phosphate protected as a methyl phosphotriester was obtained. This building block was used in the preparation of two 14-mer oligonucleotides with a central artificial bend due to the cyclic dinucleotide moiety. These were found to destabilise duplexes, slightly destabilise bulged duplexes but, to some extent, stabilise a three-way junction in high Mg(2+)-concentrations.     

Reverse Schreinemakers Method for Experimental Analysis of Mixed-Solvent Electrolyte Systems

A method based on Schreinemakers’s tie-line theory of 1893 is derived for determining the composition and phase amounts in solubility experiments for multi-solvent electrolyte systems. The method uses the lever rule in reverse compared to Schreinemakers’s wet residue method, and is therefore called the reverse Schreinemakers (RS) method. The method is based on simple mass balance principles similar to the wet residues method. It allows for accurate determination of the mixed-solvent phase composition even though part of the solvent may precipitate as complexes between solvent and salt. Discrepancies from determining the composition of salt mixtures by pH titration are discussed, and the derived method significantly improves the obtained result from titration. Furthermore, the method reduces the required experimental work needed for analysis of phase composition. The method is applicable to multi-solvent systems and may be used for the determination of solid-phase compositions, similar to Schreinemakers’s original “rest” method. An example calculation is presented for the Na₂CO₃-NaHCO₃-MEG-H₂O system.     

Representing Medical Protocols for Organizational Simulation: An Information-Processing Approach

Organizational simulations have been used in business, manufacturing, and engineering design tasks to gain insight into organizational process bottlenecks, and to improve the quality and efficiency of processes within these industries. As market pressures demand increased efficiencies within the health care industry, organizational simulation techniques could provide similar insight into the design of better medical care processes, or protocols, in medical organizations. To simulate the process of medical care within a specific organization however, requires models that can represent (1) unpredictable patient responses to care, (2) the flexibility needed to adapt to different patients, and (3) different preferences of health care professionals and the implicit preferences contained within the protocol. Using previous work on simulation in the Virtual Design Team (VDT), and an example protocol drawn from an existing protocol in bone marrow transplantation, we describe extensions to the VDT information-processing representation that will allow us to simulate the performance characteristics of a medical protocol used within a medical organization. Our representational extensions capture the uncertainty of medical care for patients, the activity flexibility within the organization, and the preferences of health care professionals that will make information-processing organizational simulations in the medical domain possible. We believe our representation will provide a robust simulation tool box that can be used to investigate the performance of specific medical protocols within different hospital settings, and explore organizational theory within the health care industry.     

Sampling to provide or to bound: With applications to fully dynamic graph algorithms

In dynamic graph algorithms the following provide-or-bound problem has to be solved quickly: Given a set S containing a subset R and a way of generating random elements from S testing for membership in R, either (i) provide an element of R, or (ii) give a (small) upper bound on the size of R that holds with high probability. We give an optimal algorithm for this problem. This algorithm improves the time per operation for various dynamic graph algorithms by a factor of O(log n). For example, it improves the time per update for fully dynamic connectivity from O(log³n) to O(log²n). © 1997 John Wiley & Sons, Inc. Random Struct. Alg., 11 , 369–379 (1997)     

Perturbation-based prediction of vibration phase shift along fluid-conveying pipes due to Coriolis forces,nonuniformity, and nonlinearity

This paper investigates the influence of tread conicity variation on hunting dynamical changing features for railway vehicle. Nonlinear contact force between wheels and rail is estimated by Vermeulen–Johnson creep force law. And a piecewise linear function is employed to appropriate the collision between wheel flange and rail. Hunting asymmetrical motions are analyzed by lateral bifurcation behaviors between maximum and minimum of car body lateral displacement. The result shows that the critical speed decreases with the increase in tread conicity, while the speed gap between linear and nonlinear speeds is narrowing. Compared with wheelsets, lateral amplitudes of the bogies are vulnerable to the tread conicity and decrease gradually. Besides, more asymmetrical motions are put into consideration with regard to tread conicity variation. Similarly, one asymmetrical behavior with small amplitude difference originates from the same chaotic attractor at both sides. And small interactive amplitude jumps in two sides at chaotic or periodic occasions are revealed. Distinguishingly, the other new asymmetrical type is found at a certain tread conicity that amplitudes of the hunting motion in positive and reverse directions no longer coincide and go away in opposite directions when the tread conicity increases to a certain value. And this particular asymmetrical motion disappears with further growth of tread conicity.