Synthesis and applications of tert-alkoxysiloxane linkers in solid-phase chemistry

Straightforward syntheses of two tert-alkoxysilyl chloride functionalised resins 3 and 31 that allow facile attachment of 1°, 2°, 3° alcohols and phenols to the solid-phase have been achieved. Resin 3 displayed useful loading levels (0.7 mmol/g), and it was stable to storage in activated form. Siloxanes from reaction of 3 with alcohols and phenols were compatible with a variety of reaction conditions commonly used in solid-phase synthesis.     

Effect of a static magnetic field on silicon transport in liquid phase diffusion growth of SiGe

Liquid phase diffusion experiments have been performed without and with the application of a 0.4 T static magnetic field using a three‐zone DC furnace system. SiGe crystals were grown from the germanium side for a period of 72 h. Experiments have led to the growth of single crystal sections varying from 0 to 10 mm thicknesses. Examination of the processed samples (single and polycrystalline sections) has shown that the effect of the applied static magnetic field is significant. It alters the temperature distribution in the system, reduces mass transport in the melt, and leads to a much lower growth rate. The initial curved growth interface was slightly flattened under the effect of magnetic field. There were no growth striations in the single crystal sections of the samples. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrogen-antihydrogen interactions at low energies

The main cause of loss of trapped AH is due to collisions with H₂ and He. As a first step towards treating these reactions we are studying the interaction of AH with H. We have carried out variational calculations to determine an upper bound to the smallest internuclear distance at which the light particles are still bound to the nuclei. We are currently in the process of taking into account the motion of the nuclei. This will enable us to calculate cross-sections for low energy H-AH scattering. This revised version was published online in August 2006 with corrections to the Cover Date.     

A least-squares method applied to the hydrogen molecule

A least-squares approach is proposed to remedy some of the weaknesses of the method of moments. It is shown by an application to the hydrogen molecule that the least-squares procedure yields reliable results in cases where the method of moments fails. The prediction of equilibrium internuclear distances by the least-squares method is also found to be more reliable than the corresponding results obtained by the method of moments.     

A novel laser scanning camera

A camera has been developed for low light level, high resolution viewing and uses a HeNe laser beam raster-scanned across the field-of-view. By synchronously detecting the reflected light with a photomultiplier the subject can be reconstructed in a video frame and viewed on a conventional television monitor. Advantages of this system include large depth-of-field, electronic zoom, on- or off-axis optical zoom, ability to view at ranges greater than 10 m in regions that are difficult to illuminate, such as nuclear reactor gas ducts, and resolution better than 200 μm in the near-field.     

The structural and compositional analysis of single crystal surfaces using low energy ion scattering

The use of ion scattering for surface composition and structure analysis has been reviewed. The extreme surface specificity of this technique has been widely used to obtain qualitative information in a straightforward way, but the occurrence of charge exchange processes, thermal lattice vibrations and multiple scattering have precluded quantitative analysis of experimental data. Examples are quoted to illustrate the progress that has been made in understanding these fundamental processes and in applying this knowledge to the development of the analytical capabilities of the technique.     

Scattering of low-energy positrons by the hydrogen molecular ion

A first application of the Kohn method is made to the calculation of scattering parameters for positron collisions with the hydrogen molecular ion below the positronium formation threshold at 9.45 eV. Phase shifts from the two-centre Coulomb value are obtained for the lowest spheroidal partial wave of _g ⁺ symmetry. For energies as low as 1.2 eV, it is found that a very flexible trial function must be used if accurate results are to be obtained.     

Ultralow energy ion beam surface modification of low density polyethylene

Ultralow energy Ar+ and O+ ion beam irradiation of low density polyethylene has been carried out under controlled dose and monoenergetic conditions. XPS of Ar+-treated surfaces exposed to ambient atmosphere show that the bombardment of 50 eV Ar+ ions at a total dose of 10(16) cm(-2) gives rise to very reactive surfaces with oxygen incorporation at about 50% of the species present in the upper surface layer. Using pure O+ beam irradiation, comparatively low O incorporation is achieved without exposure to atmosphere (approximately 13% O in the upper surface). However, if the surface is activated by Ar+ pretreatment, then large oxygen contents can be achieved under subsequent O+ irradiation (up to 48% O). The results show that for very low energy (20 eV) oxygen ions there is a dose threshold of about 5 x 10(15) cm(-2) before surface oxygen incorporation is observed. It appears that, for both Ar+ and O+ ions in this regime, the degree of surface modification is only very weakly dependent on the ion energy. The results suggest that in the nonequilibrium plasma treatment of polymers, where the ion flux is typically 10(18) m(-2) s(-1), low energy ions (<50 eV) may be responsible for surface chemical modification.     

Aperiodic stochastic resonance in a hysteretic population of cardiac neurons

Aperiodic stochastic resonance (ASR) is studied for a densely interconnected population of excitatory and inhibitory neurons that exhibit hysteresis. Switching between states in the presence of noisy external forcing is represented as a "competition between averages" and this is further explained through a semianalytical model. In contrast to energy-based approaches where only the timing of a switch between states is represented, the competition between averages also identifies the input history responsible for a switch. This last point leads to some interesting conclusions regarding cause and effect in the presence of noisy forcing of a hysteretic system. For example, at subthreshold inputs, it is found that the input history causing a switch between states is primarily dependent upon the noise level even though the corresponding time to switch is sensitive to both the distance from the threshold and the noise level. Since the application considered here is to cardiac neuronal control, control performance is considered over the full input range. Noise tuning for adequate control performance is found to be unnecessary if the noise level is high enough. This is consistent with studies of ASR for sensory neurons. Another observation made here that may be of clinical significance is that at higher noise levels, constraints placed upon inputs to ensure adequate control performance are likely to depend upon the switching direction.     

Effects of starvation for 4-20 days on the amino acid content of Biomphalaria glabrata as determined by cellulose HPTLC-densitometry with confirmation of identity using silica gel and RP-18 W plates with two mobile phases causing inversion of the separation mechanism

The effects of starvation at 4, 7, 10, 14, and 20 days on the amino acid content of Biomphalaria glabrata was determined by high performance thin layer chromatography (HPTLC)-densitometry. Cultures of control and starved snails were prepared for each duration of time. Samples were extracted using ethanol-water (70:30), and supernatant was collected after multiple centrifugations. Samples and standards were applied as bands using a CAMAG Linomat 4 onto cellulose HPTLC plates and developed in a 2-butanol-pyridine-acetic acid-water (39:34:10:26) mobile phase before spraying with ninhydrin detection reagent and scanning with a CAMAG 3 scanner to quantify ornithine (Orn), glycine (Gly), alanine (Ala), valine (Val), and leucine (Leu). Amino acid identification was confirmed by HPTLC on silica gel plates and RP-18?W plates using two different mobile phases causing inversion of the separation mechanism. Starvation led to an overall decrease in amino acid content in comparison to the control snails, however, the amount of amino acids in the starved snails had no correlation with the duration of starvation.