Operation of a high-harmonic gyrofrequency multiplier

The operation of a sixth-harmonic gyrofrequency multiplier is described. The initial experimental results produced 3.5 kW of 17.23 GHz radiation from a 260 keV, 0.3 A, =v/v=4.8 axis-encircling electron beam in a near uniform magnetic field. The output cavity conversion efficiency was measured at 4.5% compared to the predicted value of 8% from a nonlinear simulation code. The design for a higher power, higher efficiency device utilizing magnetic tapering is also presented.     

Simple fabrication of metallic colloidal doublets having electrical connectivity

A method is described for fabricating metallic colloidal doublets of gold-gold, silver-silver, and gold-silver. Individual gold and silver spheres of micrometer diameter were synthesized by the aggregation of nanoparticles. Then, by controlling aggregation using ionic strength, yields of doublets above 20% were obtained by the salting-quenching technique. The gold-gold and silver-silver homodoublets were very stable mechanically, even in sonication; the gold-silver heterodoublets were slightly less stable than the homodoublets in sonication. Electrical connectivity between the gold-silver heterodoublets was verified by observing the autoelectrophoresis of gold-silver doublets in 3% hydrogen peroxide solution. The generality of the salting out and quenching technique is demonstrated here, and the finding that the particles are electrically connected will be of great significance in a number of applications.     

Determination of intracellular glutathione and cysteine using HPLC with a monolithic column after derivatization with monobromobimane

An optimized high‐performance liquid chromatography (HPLC) method is used to show that, as myoblasts differentiate into multinucleated muscle fibers, there is a shift to a more oxidized cell redox state. The HPLC method incorporated derivatization with monobromobimane for the determination of the reduced (GSH) and oxidized (GSSG) forms of glutathione and the reduced (Cys) and oxidized (CysSS) forms of cysteine. The derivatization was optimized to improve the sensitivity of the approach; the limits of detection for glutathione and cysteine were 3 × 10^?8 and 5 × 10^?8 M , respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Musical intervals and relative pitch: frequency resolution, not interval resolution, is special

Pitch intervals are central to most musical systems, which utilize pitch at the expense of other acoustic dimensions. It seemed plausible that pitch might uniquely permit precise perception of the interval separating two sounds, as this could help explain its importance in music. To explore this notion, a simple discrimination task was used to measure the precision of interval perception for the auditory dimensions of pitch, brightness, and loudness. Interval thresholds were then expressed in units of just-noticeable differences for each dimension, to enable comparison across dimensions. Contrary to expectation, when expressed in these common units, interval acuity was actually worse for pitch than for loudness or brightness. This likely indicates that the perceptual dimension of pitch is unusual not for interval perception per se, but rather for the basic frequency resolution it supports. The ubiquity of pitch in music may be due in part to this fine-grained basic resolution.     

Loudness perception and frequency discrimination in subjects with steeply sloping hearing loss: possible correlates of neural plasticity.

Loudness functions and frequency difference limens (DLFs) were measured in five subjects with steeply sloping high-frequency sensorineural hearing loss. The stimuli were pulsed pure tones encompassing a range of frequencies. Loudness data were obtained using a 2AFC matching procedure with a 500-Hz reference presented at a number of levels. DLFs were measured using a 3AFC procedure with intensities randomized within 6 dB around an equal-loudness level. Results showed significantly shallower loudness functions near the cutoff frequency of the loss than at a lower frequency, where hearing thresholds were near normal. DLFs were elevated, on average, relative to DLFs measured using the same procedure in five normally hearing subjects, but showed a local reduction near the cutoff frequency in most subjects with high-frequency loss. The loudness data are generally consistent with recent models that describe loudness perception in terms of peripheral excitation patterns that are presumably restricted by a steeply sloping hearing loss. However, the DLF data are interpreted with reference to animal experiments that have shown reorganization in the auditory cortex following the introduction of restricted cochlear lesions. Such reorganization results in an increase in the spatial representation of lesion-edge frequencies, and is comparable with the functional reorganization observed in animals following frequency-discrimination training. It is suggested that similar effects may occur in humans with steeply sloping high-frequency hearing loss, and therefore, the local reduction in DLFs in our data may reflect neural plasticity.     

Front Tracking Using a Hybrid Analytical Finite Element Approach for Two-Phase Flow Applied to Supercritical CO<Subscript>2</Subscript> Replacing Brine in a Heterogeneous Reservoir and Caprock

Predicting fluid replacement by two-phase flow in heterogeneous porous media is of importance for issues such as supercritical CO₂ sequestration, the integrity of caprocks and the operation of oil water/brine systems. When considering coupled process modelling, the location of the interface is of importance as most of the significant interaction between processes will be happening there. Modelling two-phase flow using grid based techniques presents a problem as the fluid–fluid interface location is approximated across the scale of the discretisation. Adaptive grid methods allow the discretisation to follow the interface through the model, but are computationally expensive and make coupling to other processes (thermal, mechanical and chemical) complicated due to the constant alteration in grid size and effects thereof. Interface tracking methods have been developed that apply sophisticated reconstruction algorithms based on either the ratio of volumes of a fluid in an element (Volume of Fluid Methods) or the advective velocity of the interface throughout the modelling regime (Level set method). In this article, we present an “Analytical Front Tracking” method where a generic analytical solution for two-phase flow is used to “add information” to a finite element model. The location of the front within individual geometrical elements is predicted using the saturation values in the elements and the velocity field of the element. This removes the necessity for grid adaptation, and reduces the need for assumptions as to the shape of the interface as this is predicted by the analytical solution. The method is verified against a standard benchmark solution and then applied to the case of CO₂ pooling and forcing its way into a heterogeneous caprock, replacing hot brine and eventually breaking through. Finally the method is applied to simulate supercritical CO₂ injected into a brine saturated heterogeneous reservoir rock leading to significant viscous fingering and developement of preferential flow paths. The results are compared with to a finite volume simulation.