Cryogenic GaAs FET amplifier

An extremely low noise, cryogenic, gallium arsenide field-effect-transistor amplifier has been developed for the frequency range 3.7 to 4.2 GHz. The amplifier has an average noise temperature of 25 K, with an associated gain of 21 dB, when cooled to a physical temperature of 77 K.     

Nanonet-based hematite heteronanostructures for efficient solar water splitting

We report the highest external quantum efficiency measured on hematite (α-Fe(2)O(3)) without intentional doping in a water-splitting environment: 46% at λ = 400 nm. This result was enabled by the introduction of TiSi(2) nanonets, which are highly conductive and have suitably high surface areas. The nanonets serve a dual role as a structural support and an efficient charge collector, allowing for maximum photon-to-charge conversion. Without the addition of any oxygen-evolving catalysts, we obtained photocurrents of 1.6 and 2.7 mA/cm(2) at 1.23 and 1.53 V vs RHE, respectively. These results highlight the importance of charge transport in semiconductor-based water splitting, particularly for materials whose performance is limited by poor charge diffusion. Our design introduces material components to provide a dedicated charge-transport pathway, alleviating the reliance on the materials' intrinsic properties, and therefore has the potential to greatly broaden where and how various existing materials can be used in energy-related applications.     

Quantifying the elasticity and viscosity of geometrically confined polymer films via thermal wrinkling

We apply thermal wrinkling, which is a surface instability that occurs during thermal annealing of polymer films geometrically confined by a rigid substrate and a flexible superstrate, to study the elasticity and viscosity of chemically crosslinked polymer systems. Specifically, we study the thermal wrinkling of aluminum‐capped polyhydroxystyrene films with different extent of chemical crosslinking and find that that the rate of change of the wrinkling wavelength with annealing time and temperature has unique relationships with the elasticity and viscosity of the polymer network. With the aid of analytical expressions that relate the time‐ and temperature‐dependent evolution of the wrinkle wavelength to the elasticity and viscosity, we are able to quantify the elastic modulus and shear viscosity of geometrically confined polymer thin films as a function of the degree of crosslinking. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Generating regular elements

Let R be a prime right Goldie ring. A useful fact is that, if $a,b\in R$ are such that $aR+bR$ contains a regular element, then there exists $\lambda \in R$ such that $a+b\lambda$ is regular. We show that the analogous result holds for $n?1$ pairs of elements: if R contains a field of cardinality at least $n+1$, and if $a_i,b_i\in R$ are such that $a_{i}R+b_{i}R$ contains a regular element for $1?i?n$, then there exists a single element $\lambda \in R$ such that $a_i+b_i\lambda$ is regular for each i.     

Accelerated passive MR catheter tracking into the carotid artery of canines

Background

Using magnetic resonance (MR) imaging for navigating catheters has several advantages when compared with the current “gold standard” modality of X-ray imaging. A significant drawback to interventional MR is inferior temporal and spatial resolutions, as high spatial resolution images cannot be collected and displayed at rates equal to X-ray imaging. In particular, passive MR catheter tracking experiments that use positive contrast mechanisms have poor temporal imaging rates and signal-to-noise ratio. As a result, with passive methods, it is often difficult to reconstruct motion artifact-free tracking images from areas with motion, such as the thoracic cavity.

Methods

In this study, several accelerated MR acquisition strategies, including parallel imaging and compressed sensing (CS), were evaluated to determine which method is most effective at improving the frame rate and passive detection of catheters in regions of physiological motion. Device navigation was performed both in vitro, through the aortic arch of an anthropomorphic chest phantom, and in vivo from the femoral artery, up the descending aorta into the supra-aortic branching vessels in canines.

Results and Discussion

The different parallel imaging methods produced images of low quality. CS with a two-fold acceleration was found to be the most effective method for generating tracking images, improving the image frame rate to 5.2 Hz, while maintaining a relatively high in-plane resolution. Using CS, motion artifact was decreased and the catheters were visualized with good conspicuity near the heart.

Conclusions

The improvement in the imaging frame rate by image acceleration was sufficient to overcome motion artifacts and to better visualize catheters in the thoracic cavity with passive tracking. CS preformed best at tracking. Navigation with passive MR catheter tracking was demonstrated from the femoral artery to the carotid artery in canines.     

BRANCHING IN THE BACTERIORHODOPSIN PHOTOCHEMICAL CYCLE

Abstract— Kinetics have been determined for the decay of the terminal phototransients M(410) and O(660) and the reappearance of the BR(570) chromophore in flash-photolyzed aqueous suspensions of light-adapted purple membrane fragments from Halobacterium halobium . The results were fitted to a linear model of     

Reversed-phase high-performance liquid chromatographic approach to determine total lymphocyte concentrations of 6-thioguanine, methylmercaptopurine and methylthioguanine in humans.

A reversed-phase high-performance liquid chromatographic (HPLC) procedure was developed to quantify intracellular lymphocyte 6-thioguanine, methylmercaptopurine and methylthioguanine. The free base of each metabolite was obtained by acid hydrolysis, which allowed for a total determination of thiopurine metabolites. 6-Thioguanine was analyzed on an octadecylsilane column using acetonitrile-10 mM sodium phosphate (11:89), pH 7, containing 0.06% tetrabutylammonium chloride. 6-Thioguanine was oxidized with potassium permanganate, and fluorescence was measured at 330 nm excitation and 410 nm emission. Methylmercaptopurine and methylthioguanine were separated on a cyanopropylsilane column using methanol-40 mM sodium phosphate (22:78), pH 2.7, and detected by ultraviolet absorbance at 314 and 290 nm, respectively.     

How to measure the spreading width for the decay of superdeformed nuclei

A new expression for the branching ratio for the decay via the E1 process in the normal-deformed band of superdeformed nuclei is given within a simple two-level model. Using this expression, the spreading or tunneling width gamma (downward arrow) for superdeformed decay can be expressed entirely in terms of experimentally known quantities. We show how to determine the tunneling matrix element V from the measured value of gamma (downward arrow) and a statistical model of the energy levels. The accuracy of the two-level approximation is verified by considering the effects of the other normal-deformed states.     

A 350GHz Radial-Probe SIS Mixer for Astronomical Imaging Arrays

We have developed a 330-370GHz SIS mixer for small-format, heterodyne, astronomical imaging arrays. Fixed-tuned broadband operation is achieved by means of a superconducting radial waveguide probe. A horn-reflector antenna provides high-efficiency optical coupling. Using a variable-temperature cryogenic noise source, we measured a DSB system noise temperature of 32±1K. The mixer contributes 3±3K, supporting the theoretically-predicted result that the noise temperature of a DSB mixer can be less than h/2 (8.6K)