Gas discharge ion source III. Modified Berkeley multifilament ion source

Total ion current, ion energy, mass and current density distributions, and the impurity content of the ion beams produced by a modified Berkeley multifilament ion source (MFIS) were measured as a function of source configuration, gas pressure, and operating conditions: the 'best' configuration produced beams of 200 mA or more at pressures between 0.40 and 2.0 Pa. In comparison with earlier studies of duoplasmatron and duopigatron sources, the MFIS beams contained less D(+), only ca. 33%, but the beams had much narrower energy distributions and flatter current density distributions. The beams contained 1%-2% impurities which consisted mainly of masses 18, 20, and 22.     

Gas discharge ion source. I. Duoplasmatron

The effects of the plasma expansion cup on the operation of a duoplasmatron ion source have been investigated by measuring the total ion current and the distributions of the ion energy, mass, and current density. A copper expansion cup did not affect the magnetic field near the anode of the ion source and consequently the ion current density distribution was sharply peaked near the center of the cup. Ion energy distributions were approximately symmetrical about anode potential. The dominant ionic species were D(+) (3) and D(+) at low and high arc currents, respectively. Changes in the electrical potential of the copper cup with respect to the anode produced negligible changes in the above data. A mild steel plasma expansion cup caused the magnetic field to diverge and intercept the cup walls, resulting in ion current density distributions that were flatter and more amenable to focusing than the ones with the copper cup. With the steel cup at anode potential, the ion mass distribution was similar to that from the copper cup; however, the ion energy distribution was asymmetrical about the anode potential with a peak about 10-20 V above anode potential. The total ion current from this mode of operation was about one-third the value from the copper cup. If the steel cup assumed floating potential, about 50 V below anode potential, the total current increased to the level observed from the copper cup and the ion energy distribution was similar to that observed with the copper cup but the current density distribution was much flatter than that of the copper cup. The ion mass distribution was 60%-70% atomic ions over the entire arc current range investigated. Based on these data, a modified plasma expansion cup was designed with tapered steel walls lined with a boron nitride insert. The overall performance of the duoplasmatron ion source with this cup was superior to any of the previous three modes of operation. The improved design uses a molybdenum anode insert which is far superior to copper in regard to erosion over extended operating times. A total beam current of 200 mA was produced at an arc current of 24 A.     

Further Consideration of Heteroscedasticity in Fitting Kinetic Models

Box and Hill [6] recently proposed a method for using power transformation weighting in least squares analysis to account for changing variance. Such an approach can be useful when the original data are heteroscedastic but adequate weight estimates are not available, and when the original data are homoscedastic but heteroscedasticity is induced by the data analyst in linearising a nonlinear model.

Several aspects of their proposal are examined for practical implications in fitting chemical kinetic models and a more direct algorithm is recommended for fitting nonlinear models to heteroscedastic data. Methods for testing model adequacy and assessing parameter precision in such situations are also discussed.     

Sensory properties of thickened and protein-enriched plant-based frozen desserts

The number of consumers following plant-based diets has increased and in turn, the variety of plant-based foods available on the market has also increased. Many plant-based foods aim to mimic the functionality and sensory properties of conventional dairy products; however, they may not be suitable for specific populations. Dysphagia, for example, is a swallowing condition requiring texture-modified foods that meet specific criteria. While many conventional thickened products exist that are safe for individuals with dysphagia, the growing interest in plant-based eating alongside the increasing prevalence of dysphagia prompts a need for research on the use and safety of thickened plant-based alternatives. This study investigated the sensory properties of a thickened protein-enhanced ice cream (dairy and whey) compared to thickened protein-enhanced plant-based frozen desserts (cashew and pea, and coconut and pea). The formulations were evaluated using the International Dysphagia Diet Standardization (IDDSI) Spoon Tilt Test and a sensory trial (n = 104 participants, 47 flexitarians and 57 typical consumers) using static (hedonic scales and check-all-that-apply [CATA]), and dynamic (temporal check-all-that-apply (TCATA)) methods. The dairy and whey sample consistently passed the IDDSI test, while the plant-based samples did not. TCATA identified that the plant-based samples had an increased cohesiveness and adhesiveness, and decreased slipperiness when compared to the dairy and whey sample. The differences in textural properties may explain why the plant-based samples did not pass the IDDSI test. The study identified that although plant-based foods strive to mimic conventional dairy products, they have different textural and flavor properties.     

Psychophysical measures of auditory nonlinearities as a function of frequency in individuals with normal hearing

In order to gain a better understanding of how auditory nonlinear phenomena vary as a function of location along the cochlea, several psychophysical measures of nonlinearity were examined as a function of signal frequency. Six normal-hearing individuals completed three experiments, each designed to measure one aspect of nonlinear behavior: (1) the effects of level on frequency selectivity in simultaneous masking, measured using notched-noise maskers at spectrum levels of 30 and 50 dB, (2) two-tone suppression, measured using forward maskers at the signal frequency (fs) and suppressor tones above fs, and (3) growth of masking, measured using forward maskers below fs at a signal/masker frequency ratio of 1.44. Four signal frequencies (375, 750, 1500, and 3000 Hz) were tested to sample the nonlinear behavior at different locations along the basilar membrane, in order to test the hypothesis that the apical (low-frequency) region of the cochlea behaves more linearly than the basal (high-frequency) region. In general, all three measures revealed a progressive increase in nonlinear behavior as signal frequency increased, with little or no nonlinearity at the lowest frequency, consistent with the hypothesis.     

Structural characterization of the galactoxylomannan of Cryptococcus neoformans Cap67

The galactoxylomannan (GalXM) obtained from the culture supernatant of an acapsular mutant of Cryptococcus neoformans Cap67 was purified by Concanavalin A affinity, ion-exchange, and gel-filtration chromatographies. The structure of GalXM was determined by methylation analysis and by 1D and 2D NMR spectroscopic studies of the intact polysaccharide and of the oligosaccharide fragments generated by Smith degradation and by acetolysis. GalXM is a complex polysaccharide with an alpha-(1-->6) -galactan backbone. The polysaccharide is branched at c-3 of alternate Gal units of the backbone. C-3 is the point of attachment of the oligosaccharide side chains comprised of alpha-D-Man- (1-->3)-alpha-D-Man-(1-->4)- beta-D-Gal-substituted with zero to three terminal beta-Xyl residues as shown in the following structure: [formula: see text].     

Atomic-scale computer simulation of primary irradiation damage effects in metals

Molecular dynamics (MD) has been used extensively to simulate displacement cascades in metals; and this paper contains a summary of the progress made to date. It includes results dealing with the effect of primary knock-on atom energy and irradiation temperature on defect formation in a variety of metals. It is shown that in addition to data on the number of defects produced, quantitative information is available on the distribution of defects created in clusters. Thus, the nature of the primary damage state is now clear. The successful development of multiscale models to describe the evolution of radiation damage microstructure and its impact on material performance requires detailed atomic-level information about the stability, motion and interaction of defects. This is starting to be obtained by MD and some recent results are discussed. The place of atomic-scale modelling in the multiscale problem of radiation damage is shown. This revised version was published online in July 2006 with corrections to the Cover Date.     

Tight-binding molecular dynamics simulations of the vibration properties of α-titanium

Phonon thermal anomalies in α-titanium are studied by means of tight-binding microcanonical molecular dynamics simulations. The frequencies of the zone centre [0001]LO and TO phonons, and the [0001]TA phonon at are determined at different temperatures via the power spectrum of the autocorrelation function associated with the corresponding projections of atomic velocities. It is shown that even at very low temperatures the effects of anharmonicity in vibrational properties are strong and dependent on both wave propagation direction and frequency. In particular, the frequencies of the TO and TA phonons are shown to decrease while the frequency of the [0001]LO phonon increases with crystal temperature, in agreement with experiment.     

Personality stability and change in early adulthood: A behavioral genetic analysis.

79 monozygotic and 48 same-sex dizygotic twin pairs completed the Multidimensional Personality Questionnaire twice, averaging 20 yrs of age at 1st and 30 yrs at 2nd testing. There were significant mean decreases in measures of Negative Emotionality (NE), increases in measures of Constraint (CO), but no significant mean changes for measures of Positive Emotionality (PE). Variance decreased for measures of NE but remained stable for measures of PE and CO. Biometrical analyses revealed that (1) NE variance reduction was due to diminishing genetic influences, (2) personality stability was due largely to genetic factors, and (3) although some evidence for genetic influence on personality change was observed, change was determined largely by environmental factors. It is concluded that the stable core of personality is strongly associated with genetic factors but that personality change largely reflects environmental factors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)