Planar silicon microrings as wavelength-multiplexed optical traps for storing and sensing particles

We demonstrate the trapping of particles with silicon microring resonators integrated with waveguides. Multiple microrings with different resonant wavelengths are integrated with each waveguide. We demonstrate that tuning the laser wavelength to the resonance wavelengths of different rings enables trapped particles to be transferred back and forth between the rings. We demonstrate that the change in output power arising from particle-induced resonance shift enables the real-time monitoring of trapped particles, such as their number and velocities, without the need for an external imaging system. The techniques we describe here could form the basis for small footprint systems in which objects are moved between multiple locations on a chip, at each of which different operations are performed and the objects' properties sensed.     

A two-temperature model of radiation damage in α-quartz

Two-temperature models are used to represent the physics of the interaction between atoms and electrons during thermal transients such as radiation damage, laser heating, and cascade simulations. We introduce a two-temperature model applied to an insulator, α-quartz, to model heat deposition in a SiO(2) lattice. Our model of the SiO(2) electronic subsystem is based on quantum simulations of the electronic response in a SiO(2) repeat cell. We observe how the parametrization of the electronic subsystem impacts the degree of permanent amorphization of the lattice, especially compared to a metallic electronic subsystem. The parametrization of the insulator electronic subsystem has a significant effect on the amount of residual defects in the crystal after 10 ps. While recognizing that more development in the application of two-temperature models to insulators is needed, we argue that the inclusion of a simple electronic subsystem substantially improves the realism of such radiation damage simulations.     

Development of liquid chromatography atmospheric pressure chemical ionization tandem mass spectrometry for analysis of halogenated flame retardants in wastewater

Until recently, atmospheric pressure photoionization (APPI) has typically been used for the determination of non-polar halogenated flame retardants (HFRs) by liquid chromatography (LC) tandem mass spectrometry. In this study, we demonstrated the feasibility of utilizing liquid chromatography atmospheric pressure chemical ionization (APCI) tandem mass spectrometry (LC-APCI-MS/MS) for analysis of 38 HFRs. This developed method offered three advantages: simplicity, rapidity, and high sensitivity. Compared with APPI, APCI does not require a UV lamp and a dopant reagent to assist atmospheric pressure ionization. All the isomers and the isobaric compounds were well resolved within 14-min LC separation time. Excellent instrument detection limits (6.1 pg on average with 2.0 μL injection) were observed. The APCI mechanism was also investigated. The method developed has been applied to the screening of wastewater samples for screening purpose, with concentrations determined by LC-APCI-MS/MS agreeing with data obtained via gas chromatography high resolution mass spectrometry.

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Isotopic labelling of quercetin 3-glucoside

The potentially important dietary antioxidant, quercetin 3-O-β-d-glucoside, has been ¹³C-labelled at C-2 of the flavonoid unit by synthesis in 15% yield over five steps from [¹³C]carbon dioxide. The route is appropriate for radiochemical synthesis. Formation of the protected 3-glucosylated flavonol appears to result from [1,7]-sigmatropic rearrangement with migration of a benzyl group followed by cyclisation. A free 5-OH results even when a phosphazene superbase is used.     

Nanoscale heterogeneity in ceria zirconia with low-temperature redox properties

We have investigated nanoscale compositional and structural variations in Ce(0.5)Zr(0.5)O(2) samples with different redox properties. Different samples were prepared using a spray freezing technique, and the synthesis conditions were varied to yield materials with reduction temperatures in the range of 400-750 degrees C. X-ray diffraction and thermal gravimetric analysis were used to characterize the average structures and redox properties of these materials. The nanoscale structural and compositional variations in individual nanoparticles of high activity were determined with atomic-scale electron imaging and nanometer-resolution electron energy loss spectroscopy. During the early stage of particle formation, the crystallization process is initiated via the nucleation of ceria-rich nanodomains. This results in the formation of high-surface-area materials that exhibit nanoscale compositional heterogeneity consisting of Ce-rich cores surrounded by Zr-rich shells. The effect of high-temperature redox cycling on the nanoscale structure, composition, and low-temperature redox properties was also determined. Our analysis suggests that our most active material exhibits significant compositional and structural heterogeneity at the nanometer level.     

An object-oriented designed finite-difference time-domain simulator for electromagnetic analysis and design in MRI--applications to high field analyses

This paper presents a finite-difference time-domain (FDTD) simulator for electromagnetic analysis and design applications in MRI. It is intended to be a complete FDTD model of an MRI system including all RF and low-frequency field generating units and electrical models of the patient. The program has been constructed in an object-oriented framework. The design procedure is detailed and the numerical solver has been verified against analytical solutions for simple cases and also applied to various field calculation problems. In particular, the simulator is demonstrated for inverse RF coil design, optimized source profile generation, and parallel imaging in high-frequency situations. The examples show new developments enabled by the simulator and demonstrate that the proposed FDTD framework can be used to analyze large-scale computational electromagnetic problems in modern MRI engineering.     

Genetic modulation of metalloprotein electron transfer at bare gold

Engineered metalloproteins and enzymes can be self assembled on pristine gold electrodes in robust, electrochemically-addressable, arrays.     

Configuration dependent L = 0 shapes in 32S(t,p)34S

In the ³²S(t,p)³⁴S reaction at 10 MeV, qualitative differences appear in the 0⁺ → 0⁺ angular distributions even at forward angles. Qualitatively similar differences result from simple distorted-wave calculations, using pure microscopic configurations.     

Asymmetric MRI magnet design using a hybrid numerical method

Two-dimensional 1H/13C polarization inversion spin exchange at the magic angle experiments were applied to single crystal samples of amino acids to demonstrate their potential utility on oriented samples of peptides and proteins. High resolution is achieved and structural information obtained on backbone and side chain sites from these spectra. A triple-resonance experiment that correlates the 1H-13Calpha dipolar coupling frequency with the chemical shift frequencies of the alpha-carbon, as well as the directly bonded amide 15N site, is also demonstrated. In this experiment the large 1H-13Calpha heteronuclear dipolar interaction provides an independent frequency dimension that significantly improves the resolution among overlapping 13C resonances of oriented polypeptides, while simultaneously providing measurements of the 13Calpha chemical shift, 1H-13C dipolar coupling, and 15N chemical shift frequencies and angular restraints for backbone structure determination.