Preparation of atomically clean and flat Si(100) surfaces by low-energy ion sputtering and low-temperature annealing

Si(100) surfaces were prepared by wet-chemical etching followed by 0.3-1.5keV Ar ion sputtering, either at elevated or room temperature. After a brief anneal under ultrahigh vacuum conditions, the resulting surfaces were examined by scanning tunneling microscopy. We find that wet-chemical etching alone cannot produce a clean and flat Si(100) surface. However, subsequent 300eV Ar ion sputtering at room temperature followed by a 973K anneal yields atomically clean and flat Si(100) surfaces suitable for nanoscale device fabrication.Comment: 13 pages, 3 figures, to be published in Applied Surface Scienc

Pricklypear Cactus Control in Western South Dakota

In a range improvement study, both liquid and pelleted forms of Picloram were effective in controlling pricklypear cactus. Higher rates of chemical hastened control and gave more complete control. At lower rates, cactus was recovering in 1985, the fourth year of study, suggesting that higher rates may be most cost effective. In 1983 noncactus vegetation response was minor. In 1984, all perennial grass production increased by more than 50% (312 lb/A) at higher rates of Picloram. Shifts in cool season and “warm season grass components were nonsignificant. In 1985, cool season grass was not generally affected by treatments, but warm season grass increased at several rates of Picloram. Cactus continued to decrease. Grass utilization by cattle in 1984 increased greatly at higher rates of Picloram. It appears likely that desirable grazable forage can be increased when cactus is decreased. Access to forage appears t o improve substantially as cactus pads collapse. Based only on 1984 livestock grazing utilization estimates and on 1984 increases in perennial grass production, potential reductions in acreages required for livestock grazing ranged from 49 t o 72%. Economic analyses will be conducted a t the end of the study

Kansas city cardiomyopathy questionnaire administered to hospitalized patients with heart failure

Background and Purpose: The psychometric properties of the Kansas City Cardiomyopathy Questionnaire (KCCQ) have been examined primarily in community-dwelling patients with heart failure (HF). The objective of this research was to examine the properties of the KCCQ administered to patients hospitalized with HF (N = 233). Methods: Confirmatory factor analysis, Cronbach's alphas, and correlations were performed to examine the scale's dimensions, reliability, and validity. Results: Confirmatory factor analysis indicated a 5-factor solution (63.6% of the variance). The Cronbach's alpha levels were greater than .70, except for the self-efficacy dimension (.60). Convergent validity was not verified between the KCCQ and several illness severity measures. Conclusions: The psychometric properties of the KCCQ may be different based on the population in which the KCCQ is administered, which may have clinical implications

The role of antiphase boundaries during ion sputtering and solid phase epitaxy of Si(001)

The Si(001) surface morphology during ion sputtering at elevated temperatures and solid phase epitaxy following ion sputtering at room temperature has been investigated using scanning tunneling microscopy. Two types of antiphase boundaries form on Si(001) surfaces during ion sputtering and solid phase epitaxy. One type of antiphase boundary, the AP2 antiphase boundary, contributes to the surface roughening. AP2 antiphase boundaries are stable up to 973K, and ion sputtering and solid phase epitaxy performed at 973K result in atomically flat Si(001) surfaces.Comment: 16 pages, 4 figures, to be published in Surface Scienc

Assessing the genetic and pathogenic variability of Pyrenophora teres f. maculata (spot form net blotch of barley) and its ability to overcome currently-used sources of resistance on the Canadian prairies

Non-Peer ReviewedEighty two isolates of the fungus Pyrenophora teres f. maculata, causal agent of spot form net blotch (SFNB) of barley, were collected across the Canadian prairies. Following genetic analysis using 13 microsatellite DNA markers, 27 isolates were selected to assess the degree of pathogenic variation in the fungus. Pathogenic variability was evaluated by inoculating isolates onto 11 barley genotypes as differential hosts at the seedling stage. One week following inoculation, the second and third leaves of each plant were rated on to a 1–9 disease severity scale, and plants with scores of 1–3 and >3 were scored as resistant and susceptible, respectively. The entire experiment was repeated. Cluster analysis revealed 13 distinct pathotype groups (virulence patterns) among the 27 representative isolates. Disease severity ratings ranged from 2.2 to 6.1 with a mean of 4.6. To assess the risk of resistance breakdown, the resistance of four barley cultivars (‘AAC Synergy’, ‘CDC Meredith’, ‘Cerveza’ and ‘Major’), which had been previously identified as resistant to SFNB on the Canadian prairies, was evaluated at the seedling stage against six isolates of P. teres f. maculata representing four different pathotypes. The resistance in ‘CDC Meredith’ was clearly overcome by all isolates tested, while ‘AAC Synergy’, ‘Cerveza’ and ‘Major’ still exhibited resistance against all of the pathotypes. The identification of fungal isolates virulent on ‘CDC Meredith’ suggests that producers should avoid growing the same resistant barley variety in short rotation, and avoid relying on resistance as the sole approach to disease management. Judicious use of fungicides, coupled with rotations of at least two years between barley crops and diversity in the barley varieties grown, will promote effective and sustainable management of spot form net blotch

STM characterization of the Si-P heterodimer

We use scanning tunneling microscopy (STM) and Auger electron spectroscopy to study the behavior of adsorbed phosphine (PH$_{3}$) on Si(001), as a function of annealing temperature, paying particular attention to the formation of the Si-P heterodimer. Dosing the Si(001) surface with ${\sim}$0.002 Langmuirs of PH$_{3}$ results in the adsorption of PH$_{x}$ (x=2,3) onto the surface and some etching of Si to form individual Si ad-dimers. Annealing to 350$^{\circ}$C results in the incorporation of P into the surface layer to form Si-P heterodimers and the formation of short 1-dimensional Si dimer chains and monohydrides. In filled state STM images, isolated Si-P heterodimers appear as zig-zag features on the surface due to the static dimer buckling induced by the heterodimer. In the presence of a moderate coverage of monohydrides this static buckling is lifted, rending the Si-P heterodimers invisible in filled state images. However, we find that we can image the heterodimer at all H coverages using empty state imaging. The ability to identify single P atoms incorporated into Si(001) will be invaluable in the development of nanoscale electronic devices based on controlled atomic-scale doping of Si.Comment: 6 pages, 4 figures (only 72dpi

Direct observation by resonant tunneling of the B^+ level in a delta-doped silicon barrier

We observe a resonance in the conductance of silicon tunneling devices with a delta-doped barrier. The position of the resonance indicates that it arises from tunneling through the B^+ state of the boron atoms of the delta-layer. Since the emitter Fermi level in our devices is a field-independent reference energy, we are able to directly observe the diamagnetic shift of the B^+ level. This is contrary to the situation in magneto-optical spectroscopy, where the shift is absorbed in the measured ionization energy.Comment: submitted to PR

The new IOC and IAAF policies on female eligibility: old Emperor, new clothes?

The Caster Semenya debacle touched off by the 2009 Berlin World Athletics Championships resulted finally in IOC and IAAF abandonment of sex testing, which gave way to procedures that make female competition eligibility dependent upon the level of serum testosterone, which must be below the male range or instrumentally countered by androgen resistance. We argue that the new policy is unsustainable because (i) the testosterone-performance connection it posits is uncompelling; (ii) testosterone-induced female advantage is not ipso facto unfair advantage; (iii) the new policy reflects the gender policing impulses endemic to sport as well as the broader cultural impulses to monstrify women and to doctor women who have nothing wrong with them; (iv) female–male performance disparities are not the only reason for sex-segregated sport, but co-exist with respectable cultural and practical reasons, which (v) provide a powerful case for allowing athletes to compete in the sex category congruent with their gender identity

On the recurrence and robust properties of Lorenz'63 model

Lie-Poisson structure of the Lorenz'63 system gives a physical insight on its dynamical and statistical behavior considering the evolution of the associated Casimir functions. We study the invariant density and other recurrence features of a Markov expanding Lorenz-like map of the interval arising in the analysis of the predictability of the extreme values reached by particular physical observables evolving in time under the Lorenz'63 dynamics with the classical set of parameters. Moreover, we prove the statistical stability of such an invariant measure. This will allow us to further characterize the SRB measure of the system.Comment: 44 pages, 7 figures, revised version accepted for pubblicatio

Critical fluctuation conductivity in layered superconductors in strong electric field

The paraconductivity, originating from critical superconducting order-parameter fluctuations in the vicinity of the critical temperature in a layered superconductor is calculated in the frame of the self-consistent Hartree approximation, for an arbitrarily strong electric field and zero magnetic field. The paraconductivity diverges less steep towards the critical temperature in the Hartree approximation than in the Gaussian one and it shows a distinctly enhanced variation with the electric field. Our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations in high-temperature superconductors.Comment: 11 pages, 2 figures, to be published in Phys. Rev.