Selective, controllable, and reversible aggregation of polystyrene latex microspheres via DNA hybridization

The directed three-dimensional self-assembly of microstructures and nanostructures through the selective hybridization of DNA is the focus of great interest toward the fabrication of new materials. Single-stranded DNA is covalently attached to polystyrene latex microspheres. Single-stranded DNA can function as a sequence-selective Velcro by only bonding to another strand of DNA that has a complementary sequence. The attachment of the DNA increases the charge stabilization of the microspheres and allows controllable aggregation of microspheres by hybridization of complementary DNA sequences. In a mixture of microspheres derivatized with different sequences of DNA, microspheres with complementary DNA form aggregates, while microspheres with noncomplementary sequences remain suspended. The process is reversible by heating, with a characteristic "aggregate dissociation temperature" that is predictably dependent on salt concentration, and the evolution of aggregate dissociation with temperature is observed with optical microscopy.     

Halide glasses based on chlorides, bromides and iodides

There is relatively little information on glasses based on chlorides, bromides and iodides. Because of the recent interest in fluoride it is the objective of this paper to evaluate the potential for preparing new halide glasses and to offer some predictions on the properties of glasses based on chlorides, bromides and iodides. The predictions of glass-forming tendency, viscosity, chemical durability and structures are discussed.     

微波消解-电感耦合等离子体质谱法测定丙烯腈-丁二烯-苯乙烯共聚物塑料中的铅、镉、汞、铬、砷

建立了微波消解技术-电感耦合等离子体质谱(ICP-MS)法同时测定丙烯腈-丁二烯-苯乙烯共聚物(ABS)塑料中的铅、镉、汞、铬、砷五种元素的方法。对仪器的参数设置、进样系统进行了优化,并对此类塑料样品中上述元素分析的前处理条件,如消解体系、消解温度、恒温时间以及酸用量等进行了优化。方法检出限为0.7～6.5 ng·g-1;用加标回收的方法评价了该方法的准确性,加标回收率为89.8%～110.8%;样品测定相对标准偏差为2.8%～11.3%。该方法检出限低、精确度好、准确度高、简单快速、无需基体匹配。     

The radiation of polarized matter in a wave-guide of general cross-section with many dielectrics I

In this first part a straight general wave-guide with a perfectly conducting outer wall and several dielectrics, excited by an electrically generally polarized matter is considered and the electromagnetic field is determined.     

A model for phosphorus segregation at the silicon-silicon dioxide interface

A new model for phosphorus segregation at the Si-SiO₂ interface is derived and verified by experimental data. The model considers for the first time, a third phase, the interface layer itself, in addition to the Si and SiO₂ phases, and the dynamics of the three-phase system is described in terms of rate equations. In particular, the phosphorus compound formation in the interface layer (phosphorus pile-up), which renders the dopant electrically inactive to a large extent, is described as a competition of the dopant in silicon and in silicon dioxide in filling and depleting a constant density of interface traps. Our model allows an unambiguous correlation of the dopant concentration on both sides of the interface with the integral dose of the interface phosphorus pile-up. Experimental data for different phosphorus concentrations, different temperatures, and different oxidation ambients, including inert anneals, are fitted by a single curve.     

Jordan Structures in Harmonic Functions and Fourier Algebras on Homogeneous Spaces

We study the Jordan structures and geometry of bounded matrix-valued harmonic functions on a homogeneous space and their analogue, the harmonic functionals, in the setting of Fourier algebras of homogeneous spaces.Supported by EPSRC grant GR/G91182 and NSERC grant 7679.     

Gyrotron travelling wave amplifier: I. Analysis of oscillations

The operation of the gyrotron travelling wave amplifier is based on the convective cyclotron maser instability. It is found that this convective instability may become absolute (nonconvective) at a sufficiently high current level, resulting in oscillation instead of amplification. This threshold current for the transition depends sensitively on the applied magnetic field. The axial wavelength and the characteristic frequency of oscillation at the onset of absolute instability are given. It is found that momentum spread has virtually no effect on the threshold current. A small amount of resistive wall loss, however, raises the threshold current significantly. Oscillations due to partial reflection at the ends of the system are also examined. Preliminary experimental results on both types of oscillations are reported and are found to be in good agreement with the theory.     

Elastic and inelastic scattering of 18O by 16O and 18O

Angular distributions have been measured for the elastic and inelastic scattering of ¹⁸O by ¹⁶O and ¹⁸O at laboratory bombarding energies of 42 and 52 MeV. The inelastic scattering data are analyzed in terms of collective excitations using a coupled channel approach. Deformation parameters are obtained for the strongly excited states. The relationship between the strength of inelastic scattering and the amount of structure in the elastic scattering distributions is discussed.