Polymer-coated cation-exchange stationary phases on the basis of silica

Summary The procedure of polymer coating of preferably inorganic porous particle support materials for LC has been applied to the preparation of a new type of weak cationexchange phases. A special copolymer of butadiene and maleic acid could be immobilized on silica by cross-linking effected with radical starters such as peroxides or γ-radiation. The chromatographic properties of such materials proved to be excellent regarding efficiency, ion-exchange capacity and selectivity, as well as chemical stability also in comparison to other, commercially available, materials. Test measurements were successfully performed with ionic or ionizable inorganic and organic solutes over the entire applicable pH-range of the mobile phase which also contained organic modifiers. A special feature of the new type of cation-exchange phase is the minor contribution of hydrophobic (lipophilic) interaction to the retention mechanism besides the actual ion-exchange process.     

Fabrication and characterization of thin films of single-walled carbon nanotube bundles on flexible plastic substrates

A convenient method to obtain patterns of films of single-walled carbon nanotubes (SWNT) bundles on flexible plastic is described. Using the Line Patterning method SWNT films of thickness ranging from approximately 300-1500 nm can be obtained from aqueous surfactant-supported dispersions of chemically purified SWNT bundles synthesized by the pulsed-laser ablation method. These films are strongly adherent and are competitive in performance with commercially available films of indium-tin-oxide (ITO) on plastics. For example, an approximately 1500 thick film of SWNT on poly(ethylene terephthalate) (PET) shows a surface resisitvity of approximately 80 Omega/sq, optical transparency >80%, and robust flexibility. Unlike ITO/PET, films of SWNT/PET can be folded and bent to a crease without cracking. The simple techniques involoved in obtaining these films (i.e., those without requiring lithography or ink-jet printing) could help facilitate the rapid fabrication of transparent, flexible electronic devices, heralding what promises to be a new approach towards the development of next-generation optoelectronic devices.     

Appearance of the dielectric instability and its coexistence with the superconductivity in ultrathin metallic filaments with decreasing diameter

Some dielectric instability appears before the superconducting (s/c) transition of Hg, In, Ga, Sn filaments when their diameters are decreased to 20–30 Å. Above the s/c transition the differential conductivity of the filaments may be approximated by the formula σ = σ_a + σ_b exp [-E₀(T)/E], where the electric field E₀ is equal toabout 10–60 mV cm^-1, and falls abruptly before the s/c transition. There are conductivity oscillations along E in the s/c transition region. The results are interpreted in terms of Peierls instability and charge-density wave (CDW) conductivity.     

One-dimensional effects in low-temperature conductivity of ultrathin metallic filaments

The resistance of ultrathin filaments (UF) of Hg (with diameters 20–40 Å) increases as the temperature is lowered as $\text{ΔR/R ～ T}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}\text{(T < 60}\text{K}\text{)}$ and decreases with the applied electrical field as $\text{ΔR/R ～}\text{1}\text{E}$. The magnitude 1113 1104 of this effects increases as the diameter of UF is made smaller. Such temperature dependence is interpreted in terms of weak electron localization in one-dimension. The non-linearity of current-voltage characteristics of UF is due to electron-electron interactions in one-dimensional tunnel junctions.     

Site-Specific Hyperphosphorylation Inhibits,Rather than Promotes,Tau Fibrillization,Seeding Capacity,and Its Microtubule Binding

The consistent observation of phosphorylated tau in the pathology of Alzheimer's disease has contributed to the emergence of a model where hyperphosphorylation triggers both tau disassociation from microtubules and its subsequent aggregation. Herein, we applied a total chemical synthetic approach to site-specifically phosphorylate the microtubule binding repeat domain of tau (K18) at single (pS356) or multiple (pS356/pS262 and pS356/pS262/pS258) residues. We show that hyperphosphorylation of K18 inhibits 1) its aggregation in vitro, 2) its seeding activity in cells, 3) its binding to microtubules, and 4) its ability to promote microtubule polymerization. The inhibition increased with increasing the number of phosphorylated sites, with phosphorylation at S262 having the strongest effect. Our results argue against the hyperphosphorylation hypothesis and underscore the importance of revisiting the role of site-specific hyperphosphorylation in regulating tau functions in health and disease.     

A field test for the detection of peroxide-based explosives

A rapid and simple field test for the detection of triacetone-triperoxide (TATP) and hexamethylenetriperoxidediamine (HMTD), two explosives which find significant illegal use, has been developed. Unknown samples are first treated with a catalase solution to remove hydrogen peroxide traces, in order to provide selectivity towards peroxide-based bleaching agents which are contained in commercial laundry detergents. Subsequently, the peroxide-based explosives are decomposed via UV irradiation, thus yielding hydrogen peroxide, which is determined by the horseradish peroxidase (POD) catalysed formation of the green radical cation of 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS). The limits of detection for this method are 8 x 10(-6) mol dm(-3) for TATP and 8 x 10(-7) mol dm(-3) for HMTD, respectively. As an option, p-hydroxyphenylacetic acid (pHPAA) may be used as peroxidase substrate, resulting in lower limits of detection (8 x 10(-7) mol dm(-3) for TATP and HMTD). The complete method uses a mobile setup to be applied under field conditions.     

Concentration bounds for empirical conditional value-at-risk: The unbounded case

Conditional Value-at-Risk (CVaR) is a popular risk measure for modelling losses in the case of a rare but extreme event. We consider the problem of estimating CVaR from i.i.d. samples of an unbounded random variable, which is either sub-Gaussian or sub-exponential. We derive a novel one-sided concentration bound for a natural sample-based CVaR estimator in this setting. Our bound relies on a concentration result for a quantile-based estimator for Value-at-Risk (VaR), which may be of independent interest.     

Meson production in p + d reactions

Total and differential cross sections for the reactions p + d → ³He + m ⁰ with m=π, η and p + d → ³H+π⁺ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied. Representing the GEM Collaboration