Strong blue emission from ZnSe nanowires grown at low temperature

We report optimized photoluminescence of ZnSe nanowires grown by molecular beam epitaxy, obtained by lowering the growth temperature down to 300 °C. The low‐temperature growth method has been developed using Si(111) and GaAs(111)B substrates. On the latter, vertical oriented blue‐emitting nanowires have been obtained. The growth mecha‐ nism is discussed with the help of in‐situ and ex‐situ electronic and structural measurements. We also report strong blue luminescence from ZnSe nanowires grown on ITO‐coated glasses, demonstrating that ZnSe nanowires are optimal candidates for transparent optoelectronics. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The table placement problem: a research challenge at the EWI 2007

The table placement problem consists in deciding how to seat the participants attending a social lunch or dinner so that the total social benefit of the event is maximum. Four different approaches are presented: a linear model, a bin-packing-based-approach, a quadratic assignment problem, and a greedy heuristic. The different formulations are computationally compared over a set of artificial instances and on the real data for the EURO Winter Institute 2007 Gala dinner.     

A G/M/1 retrial queue with constant retrial rate

In this paper, we are concerned with the analytical treatment of an GI/M/1 retrial queue with constant retrial rate. Constant retrial rate is typical for some real world systems where the intensity of individual retrials is inversely proportional to the number of customers in the orbit or only one customer from the orbit is allowed to make the retrials. In our model, a customer who finds the server busy joins the queue in the orbit in accordance with the FCFS (first-come-first-out) discipline and only the oldest customer in the queue is allowed to make the repeated attempts to reach the server. A distinguishing feature of the considered system is an arbitrary distribution of inter-arrival times, while the overwhelming majority of the papers is devoted to the retrial systems with the stationary Poisson arrival process. We carry out an extensive analytical analysis of the queue in steady state using the well-known matrix analytic technique. The ergodicity condition and simple expressions for the stationary distributions of the system states at pre-arrival, post-arrival and arbitrary times are derived. The important and difficult problem of finding the stationary distribution of the sojourn time is solved in terms of the Laplace–Stieltjes transform. Little’s formula is proved. Numerical illustrations are presented.     

Multiplex isothermal solid-phase recombinase polymerase amplification for the specific and fast DNA-based detection of three bacterial pathogens

We report on the development of an on-chip RPA (recombinase polymerase amplification) with simultaneous multiplex isothermal amplification and detection on a solid surface. The isothermal RPA was applied to amplify specific target sequences from the pathogens Neisseria gonorrhoeae, Salmonella enterica and methicillin-resistant Staphylococcus aureus (MRSA) using genomic DNA. Additionally, a positive plasmid control was established as an internal control. The four targets were amplified simultaneously in a quadruplex reaction. The amplicon is labeled during on-chip RPA by reverse oligonucleotide primers coupled to a fluorophore. Both amplification and spatially resolved signal generation take place on immobilized forward primers bount to expoxy-silanized glass surfaces in a pump-driven hybridization chamber. The combination of microarray technology and sensitive isothermal nucleic acid amplification at 38 °C allows for a multiparameter analysis on a rather small area. The on-chip RPA was characterized in terms of reaction time, sensitivity and inhibitory conditions. A successful enzymatic reaction is completed in <20 min and results in detection limits of 10 colony-forming units for methicillin-resistant Staphylococcus aureus and Salmonella enterica and 100 colony-forming units for Neisseria gonorrhoeae. The results show this method to be useful with respect to point-of-care testing and to enable simplified and miniaturized nucleic acid-based diagnostics. Figure

The combination of multiplex isothermal nucleic acid amplification with RPA and spatially-resolved signal generation on specific immobilized oligonucleotides     

Modification of guanosine with cyanopropargylic alcohols

Guanosine has been modified with tertiary cyanopropargylic alcohols under mild conditions (1:1.1–2 molar ratio, K₂CO₃, DMF, 20–25 °C, 19–50 h) to simultaneously give two modifications. The first product (1:1 adduct) is formed by the stereoselective addition of the amide function of the purine ring to the triple bond (38–43% yields), and the second product is the 1:2 adduct, with a second molecule of cyanopropargylic alcohol having reacted with the two vicinal hydroxy groups of the ribose moiety to give a functionalized 1,3-dioxolane ring (29–50% yields).     

Study of thermo-oxidative chemical pre-treatment of isotactic polypropylene

A thermo-oxidative pre-treatment with chemical solutions is required in order to provide the adherence of inorganic semiconductor to the isotactic polypropylene (iPP) surface. A few thin films of iPP were treated with oxidizing solution at 90 °C. The crystalline properties were analyzed using XRD, and it had shown the presence of the α-monoclinic phases. The ATR-FTIR spectra had indicated that characteristic iPP peaks after thermo-oxidative chemical pre-treatment diminished sharply. Moreover, the new carbonyl groups (C = O) were observed, which signified oxidation. The UV–Vis spectra had showed a blue shift in the absorption edge, which corresponded to decrease in the optical band gap. The non-isothermal decomposition and crystallization kinetics of iPP films were studied and compared by means of thermogravimetric analysis and differential scanning calorimetric measurement. The values of the melting temperature T _m and the crystallization temperature T _c were found to be iPP surface structure and heating/cooling rate dependent. The activation energy of crystallization E _c was determined.     

Copper‐Chelating Azides for Efficient Click Conjugation Reactions in Complex Media

The concept of chelation‐assisted copper catalysis was employed for the development of new azides that display unprecedented reactivity in the copper(I)‐catalyzed azide–alkyne [3+2] cycloaddition (CuAAC) reaction. Azides that bear strong copper‐chelating moieties were synthesized; these functional groups allow the formation of azide copper complexes that react almost instantaneously with alkynes under diluted conditions. Efficient ligation occurred at low concentration and in complex media with only one equivalent of copper, which improves the biocompatibility of the CuAAC reaction. Furthermore, such a click reaction allowed the localization of a bioactive compound inside living cells by fluorescence measurements.     

Lipid characterization of individual porcine oocytes by dual mode DESI-MS and data fusion

The development of sensitive measurements to analyze individual cells is of relevance to elucidate specialized roles or metabolic functions of each cell under physiological and pathological conditions. Lipids play multiple and critical roles in cellular functions and the application of analytical methods in the lipidomics area is of increasing interest. In this work, in vitro maturation of porcine oocytes was studied. Two independent sources of chemical information (represented by mass spectra in the positive and negative ion modes) from single oocytes (immature oocytes, 24-h and 44-h in vitro matured oocytes) were acquired by using desorption electrospray ionization-mass spectrometry (DESI-MS). Low and mid-level data fusion strategies are presented with the aim of better exploring the large amount of chemical information contained in the two mass spectrometric lipid profiles. Data were explored by principal component analysis (PCA) within the two multi-block approaches to include information on free fatty acids, phospholipids, cholesterol-related molecules, di- and triacylglycerols. After data fusion, clearer differences among immature and in vitro matured porcine oocytes were observed, which provide novel information regarding lipid metabolism throughout oocyte maturation. In particular, changes in TAG composition, as well as increase in fatty acid metabolism and membrane complexity were evidenced during the in vitro maturation process. This information can assist the improvement of in vitro embryo production for porcine species.     

X-ray structure of snow flea antifreeze protein determined by racemic crystallization of synthetic protein enantiomers

Chemical protein synthesis and racemic protein crystallization were used to determine the X-ray structure of the snow flea antifreeze protein (sfAFP). Crystal formation from a racemic solution containing equal amounts of the chemically synthesized proteins d-sfAFP and l-sfAFP occurred much more readily than for l-sfAFP alone. More facile crystal formation also occurred from a quasi-racemic mixture of d-sfAFP and l-Se-sfAFP, a chemical protein analogue that contains an additional -SeCH2- moiety at one residue and thus differs slightly from the true enantiomer. Multiple wavelength anomalous dispersion (MAD) phasing from quasi-racemate crystals was then used to determine the X-ray structure of the sfAFP protein molecule. The resulting model was used to solve by molecular replacement the X-ray structure of l-sfAFP to a resolution of 0.98 A. The l-sfAFP molecule is made up of six antiparallel left-handed PPII helixes, stacked in two sets of three, to form a compact brick-like structure with one hydrophilic face and one hydrophobic face. This is a novel experimental protein structure and closely resembles a structural model proposed for sfAFP. These results illustrate the utility of total chemical synthesis combined with racemic crystallization and X-ray crystallography for determining the unknown structure of a protein.     

Full configuration interaction study of the metal-insulator transition in model systems: LiN linear chains (N=2,4,6,8)

The precursor of the metal-insulator transition is studied at ab initio level in linear chains of equally spaced lithium atoms. In particular, full configuration interaction calculations (up to 1 x 10(9) determinants) are performed, in order to take into account the different nature of the wave function at different internuclear distances. Several indicators of the Metal-Insulator transition (minimum of the energy gap, maximum of the localization tensor or of the polarizability) are considered and discussed. It is shown that the different indicators give concordant results, showing a rapid change in the nature of the wave function at an internuclear distance of about 7 bohrs.