Surface energy gradient driven convection for generating nanoscale and microscale patterned polymer films using photosensitizers

The Marangoni effect describes how fluid flows in response to gradients in surface energy. This phenomenon could be broadly harnessed to pattern the surface topography of polymer films if generalizable techniques for programming surface energy gradients existed. Here, a near UV–visible light (NUV–vis) photosensitizer, 9,10‐dibromo‐anthracene (DBA), was doped into thin films of a model polymer, poly(isobutyl methacrylate). After exposure to light through a photomask and heating above the glass transition, thermolysis of photo‐oxidized DBA and grafting to the polymer promoted flow of the film material into the exposed regions. This mechanism did not significantly alter the molecular weight of PiBMA or the film's glass transition temperature, but resulted in an increase in film surface energy as indicated by a decrease in water contact angle. Film height variations of 580 nm were produced using a mask with 12.5 μm features; a mask with 800 nm features was also employed to generate topographic features of corresponding width without expensive contacting equipment. Due to the broad absorbance spectra of DBA, highly accessible and/or unconventional light sources may be employed in this process; this advantage was demonstrated by patterning with sunlight. The nonspecific radical‐mediated nature of the DBA grafting reaction makes this a promising approach for many classes of polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1195–1202     

Molecular Beam Epitaxy of Nonstoichiometric Semiconductors and Multiphase Material Systems

When arsenides are grown by molecular beam epitaxy at low substrate temperatures, as much as 2% excess arsenic can be incorporated into the epilayer. This excess arsenic is in the form of antisites, but there is also a substantial concentration of gallium vacancies. With anneal, there is a significant decrease in the arsenic antisite and gallium vancancy concentrations as the excess arsenic precipitates. With further anneal, the arsenic precipitates coarsen. This combination of low substrate temperature molecular beam epitaxy and a subsequent anneal results in a broad spectrum of materials, from highly defected epilayers to a two-phase system of semimetallic arsenic precipitates in an arsenide semiconductor matrix. These materials exhibit some very interesting and useful electrical and optical properties.     

Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction

Electrospun polystyrene (PS) nanofibers (130–500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25–1.0 μg L^?1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 μg L^?1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 μg L^?1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.     

Agropine,a new amino acid derivative from crown gall tumours

Agropine, an unusual compound produced in plant tumours was shown by mass spectrometry and proton and carbon-13 nmr spectroscopy to be a bicyclic derivative of glutamic acid and a hexitol sugar.     

Meeting Reports: International Workshop on the Protein Circular Dichroism Data Bank

The International Workshop on the Protein Circular Dichroism Data Bank (PCDDB) was held on April 11–13, 2005, at Birkbeck College, University of London, UK, under the sponsorship of the UK Biotechnology and Biological Sciences Research Council. The meeting was chaired by Bonnie Ann Wallace, Professor in the Department of Crystallography at Birkbeck College. The workshop organizing committee consisted of Dr. Robert W. Janes, Queen Mary, University of London, and Dr. Lee Whitmore, also of Birkbeck College.

Participants included experts in both conventional circular dichroism (CD) spectroscopy and representatives from synchrotron radiation circular dichroism (SRCD) beamlines: Prof. J. Sutherland of the NSLS SRCD beamlines U9b and U11 and East Carolina University (USA);     

Deterministic global optimization in ab-initio quantum chemistry

A large number of problems in ab-initio quantum chemistry involve finding the global minimum of the total system energy. These problems are traditionally solved by numerical approaches equivalent to local optimization. While these approaches are relatively efficient, they do not provide guarantees of global optimality unless a starting point sufficiently close to the global minimum is known apriori. Due to the enormous amount of computational effort required to solve these problems, more mathematically rigorous alternatives have so far received very little attention. Taking the above issue into consideration, this paper explores the use of deterministic global optimization in the context of Hartree-Fock theory, an important mathematical model applied in many quantum chemistry methods. In particular, it presents a general purpose approach for generating linear relaxations for problems arising from Hartree-Fock theory. This was then implemented as an extension to the ${{\tt COUENNE}}$ (Convex Over and Under ENvelopes for Nonlinear Estimation) branch and bound mixed integer non-linear programs solver. Proof of concept calculations that simultaneously optimise the orbital coefficients and the location of the nuclei in closed-shell Hartree-Fock calculations are presented and discussed.