A LEED study of the Si{100}(1 × 1)H surface structure

Extensive LEED intensity-energy data have been collected for a Si{100}(1 × 1)H surface and dynamical theory LEED calculations have been performed using an ideal unreconstructed Si(100) surface to model this structure. Agreement between experiment and theory is good indicating that the probable structure for this surface does involve (weakly scattering) H atoms on the “dangling bonds” of an unreconstructed Si(100) surface, and that difficulties in achieving good agreement between experiment and theory for the clean Si{100}(2 × 1) surface is more probably due to deficiencies in the model structure than to deficiencies in the non-structural aspects of the LEED theory.     

A digital integrator for controlled-potential coulometry

Accurate electrolysis current integration is required in controlled-potential coulometry. Analog integrators have been shown to deviate from ideal response by as much as —0.1%. A digital integrator was designed to optimize the linearity of the voltage-to-frequency converter used, minimize the effects of temperature, eliminate integration errors caused by small polarity changes and signal noise, and allow interchangeability with an analog integrator in a state-of-the-art coulometer widely used throughout the nuclear field for controlled-potential coulometry. Evaluation of the digital integrator, calibrated versus the Faraday, showed bias-free determinations of plutonium with a relative standard deviation of approximately 0.02%. The integrator was designed specifically for use in the controlled-potential coulometric determination of plutonium, but many of the features incorporated can be adopted to digital integrators for other uses where accurate integration over long periods of time is required.     

Di-2-Pyridylketoxime,a new reagent for the spectrophotometric determination of iron(II)

Di-2-pyridylketoxime is proposed for the spectrophotometric determination of iron(II). The complex is stable and exhibits an absorption maximum at 534 nm in an alkaline citrate medium. Beer's law is obeyed and the molar absorptivity is 1.5·10³. Large amounts of copper and nickel can be tolerated. The method is simple, convenient and reproducible.     

Field-cycled PEDRI imaging of free radicals with detection at 450 mT

This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described.     

Quality control and quality assurance aspects of the routine use of capillary electrophoresis for serum and urine proteins in clinical laboratories

Using capillary electrophoresis (CE) for serum protein electrophoresis, the quality of results begins with monitoring a well-functioning instrument, using scrupulously clean capillaries, well-calibrated methods as well as regular use of an internal quality control material. Quality assurance programs are available in countries such as Australia, United Kingdom, United States, and European countries such as Sweden and Germany. The present commercial control material that is available gives percentages of albumin, alpha 1, alpha 2, beta- and gamma-globulins, the gamma-component being of normal distribution, and not containing any monoclonal protein component. We feel that a quantitative commercial control material containing a monoclonal protein at decision level for treating myeloma patients would be beneficial to all laboratories as a serum protein electrophoresis control, whether the analysis is by CE or agarose gels. The same applies for control material for urinary protein electrophoresis.     

Quantized dispersion of two-dimensional magnetoplasmons detected by photoconductivity spectroscopy

We find that the long-wavelength magnetoplasmon, resistively detected by photoconductivity spectroscopy in high-mobility two-dimensional electron systems, deviates from its well-known semiclassical nature as uncovered in conventional absorption experiments. A clear filling-factor dependent plateau-type dispersion is observed that reveals a so far unknown relation between the magnetoplasmon and the quantum Hall effect.     

Use of a sonogashira-acetylide coupling strategy for the synthesis of the aromatic spiroketal skeleton of gamma-rubromycin

[reaction: see text] The synthesis of the fused aromatic spiroketal core of gamma-rubromycin is described via addition of an aryl acetylide fragment to an aryl acetaldehyde fragment. In turn, the aryl acetylene precursor was readily prepared with use of a Sonogashira reaction.     

An integrated electrochemical capillary liquid chromatography-dual microelectrode system for bromine based reaction detection

Amperometric reaction detection of model peptides containing either a thiol or disulfide was successfully achieved with a novel coupled capillary liquid chromatography-dual microelectrode system. Detection is facilitated via dual platinum wire electrodes fabricated directly on a liquid chromatography capillary column. The detection strategy is based on the electrogeneration of bromine at the upstream working electrode followed by reduction of the bromine to bromide at the downstream working electrode. When bromine reacts with analyte eluting from the capillary column, the amount of bromine that reaches the downstream electrode decreases. As a result, the current at the downstream electrode will decrease in proportion to the amount of analyte eluting from the capillary column. Glutathione, glutathione disulfide, alpha-TGF and oxytocin were used to characterize the system and to determine system parameters. The feasibility of the determination of disulfide containing peptides is demonstrated with glutathione disulfide, alpha-TGF and oxytocin.