The Casimir effect for fields with arbitrary spin

The Casimir force arises when a quantum field is confined between objects that apply boundary conditions to it. In a recent paper we used the two-spinor calculus to derive boundary conditions applicable to fields with arbitrary spin in the presence of perfectly reflecting surfaces. Here we use these general boundary conditions to investigate the Casimir force between two parallel perfectly reflecting plates for fields up to spin-2. We use the two-spinor calculus formalism to present a unified calculation of well-known results for spin-1/2 (Dirac) and spin-1 (Maxwell) fields. We then use our unified framework to derive new results for the spin-3/2 and spin-2 fields, which turn out to be the same as those for spin-1/2 and spin-1. This is part of a broader conclusion that there are only two different Casimir forces for perfectly reflecting plates—one associated with fermions and the other with bosons.     

Effects of Rh on the thermoelectric performance of the p-type Zr0.5Hf0.5Co1−xRhxSb0.99Sn0.01 half-Heusler alloys

We show that Rh substitution at the Co site in Zr_0.5Hf_0.5Co_1−xRh_xSb_0.99Sn_0.01 (0≤x≤1) half-Heusler alloys strongly reduces the thermal conductivity with a simultaneous, significant improvement of the power factor of the materials. Thermoelectric properties of hot-pressed pellets of several compositions with various Rh concentrations were investigated in the temperature range from 300 to 775 K. The Rh “free” composition shows n-type conduction, while Rh substitution at the Co site drives the system to p-type semiconducting behavior. The lattice thermal conductivity of Zr_0.5Hf_0.5Co_1−xRh_xSb_0.99Sn_0.01 alloys rapidly decreased with increasing Rh concentration and lattice thermal conductivity as low as 3.7 W/m*K was obtained at 300 K for Zr_0.5Hf_0.5RhSb_0.99Sn_0.01. The drastic reduction of the lattice thermal conductivity is attributed to mass fluctuation induced by the Rh substitution at the Co site, as well as enhanced phonon scattering at grain boundaries due to the small grain size of the synthesized materials.     

The crystallization kinetics and morphology of nitric acid trihydrate

Crystallization kinetics of stable and metastable nitric acid trihydrate (NAT) were investigated by time dependent X-ray powder diffraction (XRD) measurements. Kinetic conversion curves were evaluated adopting the Avrami model. The growth and morphology of the respective crystallites were monitored in situ on the cryo-stage of an environmental scanning electron microscope (ESEM) under a partial pressure of nitrogen gas (0.3 Torr, 40 Pa). The results show a close relationship between the presence of ice in the sample and the crystallization mechanism of NAT, which results in different shapes and sizes of NAT crystal particles.     

Morphology control of the produced Ag nanoparticles by soft-template technique

The morphology of the produced Ag nanoparticle is controlled successfully by UV irradiating the reaction solution of AgAc/ethyl alcohol/1-octadeconal/1-dodecanethiol. With use of a novel solution such as soft template, Ag nanorods with different sizes and different ratios of length to diameter can be obtained by adjusting the concentrations of the solution compositions.     

Organic peroxide assisted transition metal hydrosilylation catalysis

Summary The catalytic activity of rhodium complexes for the hydrosilylation of substrates such as alkenes, 1,3-dienes, 1-alkynes, or ketones, is enhanced by the addition of organic oxidizing agents, such ast-butyl hydroperoxide, hydrogen peroxide, orm-chloroperbenzoic acid. Similar enhancement is found for the Group VIA hexacarbonyls in the hydrosilylation of 1,3-dienes.     

Quantitative Fourier transform ion cyclotron resonance mass spectrometry--the determination of creatinine by isotope dilution mass spectrometry

Accurate quantitation has been demonstrated on many different types of mass spectrometer. However, quantitative applications of Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) have been limited. In this study, the quantitative potential of FTICRMS has been investigated using an exact matching isotope dilution method for the determination of creatinine in serum. Creatinine is an important clinical biomarker and its measurement is used as an assessment of renal function. The quantitation of creatinine was selected because a high-accuracy high-performance liquid chromatography/mass spectrometry (HPLC/MS) determination using a triple quadrupole mass spectrometer has already been successfully developed in-house. Therefore, a direct comparison of the quantitative capability of FTICRMS could be made against an established method. The accuracy of the quantitation of creatinine was found to be equivalent to that obtained using LC/MS. However, the expanded measurement uncertainty (k = 2) was larger, at 6%, when using FTICRMS compared with 1% when using HPLC/MS with the triple quadrupole mass spectrometer.     

Detection of E. coli using a microfluidics-based antibody biochip detection system

This work demonstrates the detection of E. coli using a 2-dimensional photosensor array biochip which is efficiently equipped with a microfluidics sample/reagent delivery system for on-chip monitoring of bioassays. The biochip features a 4 x 4 array of independently operating photodiodes that are integrated along with amplifiers, discriminators and logic circuitry on a single platform. The microfluidics system includes a single 0.4 mL reaction chamber which houses a sampling platform that selectively captures detection probes from a sample through the use of immobilized bioreceptors. The independently operating photodiodes allow simultaneous monitoring of multiple samples. In this study the sampling platform is a cellulosic membrane that is exposed to E. coli organisms and subsequently analyzed using a sandwich immunoassay involving a Cy5-labeled antibody probe. The combined effectiveness of the integrated circuit (IC) biochip and the immunoassay is evaluated for assays performed both by conventional laboratory means followed by detection with the IC biochip, and through the use of the microfluidics system for on-chip detection. Highlights of the studies show that the biochip has a linear dynamic range of three orders of magnitude observed for conventional assays, and can detect 20 E. coli organisms. Selective detection of E. coli in a complex medium, milk diluent, is also reported for both off-chip and on-chip assays.     

Investigation of the chemical solubility of mixed-alkali fluorcanasite forming glasses

There is currently significant interest in all-ceramic dental restorations due to the demand to replace metals as the primary load-bearing tooth restorative material. A promising non-metallic material for such restorations is fluorcanasite, a chain-silicate glass-ceramic that is castable using conventional dental metal-casting techniques and which exhibits enhanced fracture toughness and flexural strength compared with currently available resin-bonded ceramics. Unfortunately, because of its relatively low silica content, it exhibits poor chemical durability. The aim of this study was to assess the influence of compositional changes on the formation and chemical solubility of the fluorcanasite forming glass, crystalline phase and residual glass. To this end, mixed-alkali compositions have been investigated and it has been shown that the solubility of the glass is a function of the alkali species present in the glass. By changing the alkali ratio of the fluorcanasite forming glass from 0.33 ([K]/[K + Na]) of the base composition derived from stoichiometry to 0.47, it was possible to reduce the chemical solubility of the fluorcanasite material significantly. The addition of extra CaF₂ to refine the grain structure resulted in a decrease in the durability of the material, making it currently unacceptable for dental applications. The glass-ceramic exhibits a minimum chemical solubility at the composition K⁷/Na⁸. The residual glass may have a slightly elevated K content compared to the original glass. The addition of extra CaF₂ to refine the grain structure resulted in an unacceptable decrease in the durability of the material.     

New approach to nonlinear dynamics of fullerenes and fullerites

A new type of nonlinear (anharmonic) excitations—bushes of vibrational modes—in physical systems with point or space symmetry is discussed. All infrared-active and Raman-active bushes for C₆₀ fullerene are found by means of special group-theoretical methods.     

Measurement of the flux of ultrahigh energy cosmic rays from monocular observations by the High Resolution Fly's Eye experiment

We have measured the cosmic ray spectrum above 10(17.2) eV using the two air-fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, phototube, and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extragalactic sources.