Imaging Atomic Scale Dynamics on III-V Nanowire Surfaces During Electrical Operation.

As semiconductor electronics keep shrinking, functionality depends on individual atomic scale surface and interface features that may change as voltages are applied. In this work we demonstrate a novel device platform that allows scanning tunneling microscopy (STM) imaging with atomic scale resolution across a device simultaneously with full electrical operation. The platform presents a significant step forward as it allows STM to be performed everywhere on the device surface and high temperature processing in reactive gases of the complete device. We demonstrate the new method through proof of principle measurements on both InAs and GaAs nanowire devices with variable biases up to 4 V. On InAs nanowires we observe a surprising removal of atomic defects and smoothing of the surface morphology under applied bias, in contrast to the expected increase in defects and electromigration-related failure. As we use only standard fabrication and scanning instrumentation our concept is widely applicable and opens up the possibility of fundamental investigations of device surface reliability as well as new electronic functionality based on restructuring during operation.

Atomic scale surface structure and morphology of InAs nanowire crystal superlattices: the effect of epitaxial overgrowth.

While shell growth engineering to the atomic scale is important for tailoring semiconductor nanowires with superior properties, a precise knowledge of the surface structure and morphology at different stages of this type of overgrowth has been lacking. We present a systematic scanning tunneling microscopy (STM) study of homoepitaxial shell growth of twinned superlattices in zinc blende InAs nanowires that transforms {111}A/B-type facets to the nonpolar {110}-type. STM imaging along the nanowires provides information on different stages of the shell growth revealing distinct differences in growth dynamics of the crystal facets and surface structures not found in the bulk. While growth of a new surface layer is initiated simultaneously (at the twin plane interface) on the {111}A and {111}B nanofacets, the step flow growth proceeds much faster on {111}A compared to {111}B leading to significant differences in roughness. Further, we observe that the atomic scale structures on the {111}B facet is different from its bulk counterpart and that shell growth on this facet occurs via steps perpendicular to the ⟨112⟩B-type directions.

Direct imaging of atomic scale structure and electronic properties of GaAs wurtzite and zinc blende nanowire surfaces.

Using scanning tunneling microscopy and spectroscopy we study the atomic scale geometry and electronic structure of GaAs nanowires exhibiting controlled axial stacking of wurtzite (Wz) and zinc blende (Zb) crystal segments. We find that the nonpolar low-index surfaces {110}, {101[overline]0}, and {112[overline]0} are unreconstructed, unpinned, and without states in the band gap region. Direct comparison between Wz and Zb GaAs reveal a type-II band alignment and a Wz GaAs band gap of 1.52 eV.

Self-organized formation of GaSb/GaAs quantum rings.

Ring-shaped GaSb/GaAs quantum dots, grown by molecular beam epitaxy, were studied using cross-sectional scanning tunneling microscopy. These quantum rings have an outer shape of a truncated pyramid with baselengths around 15 nm and heights of about 2 nm but are characterized by a clear central opening extending over about 40% of the outer baselength. They form spontaneously during the growth and subsequent continuous capping of GaSb/GaAs quantum dots due to the large strain and substantial As-for-Sb exchange reactions leading to strong Sb segregation.

Association of cyclophosphamide pharmacokinetics to polymorphic cytochrome P450 2C19.

Cyclophosphamide (CP), a widely used cytostatic, is metabolized by polymorphic drug metabolizing enzymes particularly cytochrome P450 (CYP) enzymes. Its side effects and clinical efficacy exhibit a broad interindividual variability, which might be due to differences in pharmacokinetics. CP-kinetics were determined in 60 patients using a global and a population pharmacokinetic model considering functionally relevant polymorphisms of CYP2B6, CYP2C9, CYP2C19, CYP3A5, and GSTA1. Moreover, metabolic ratios were calculated for selected CP metabolites, analyzed by (31)P-NMR-spectroscopy. Analysis of variance revealed that the CYP2C19*2 genotype influenced significantly pharmacokinetics of CP at doses

Validation of a stages of exercise change questionnaire.

The purpose of this study was to examine evidence for the validity of a stages of change measure of the Transtheoretical Model for exercise behavior. Participants were 152 university students (53.3% women, 71.6% Caucasian, M age = 19.18 years) who completed processes of change, self-efficacy, decisional balance, stages of change, and exercise behavior questionnaires as well as a maximal treadmill test. Participants in the action and maintenance stages had the highest strenuous (PC/C/P < A/M) and moderate (PC/C < A/M) self-reported exercise behavior. Those in the maintenance stage had the highest estimated aerobic fitness (PC/P < MA). The differences between the early stages (PC, C, and P) and the later stages (A and M) as described by the first function were primarily due to the behavioral process of change. The differences between the extreme stages (PC and M) and the middle stages (C, P, and A) were due to the experiential processes of change and the pros of decisional balance. The hypothesized patterns of stage differences were partially supported. Failure to obtain full support may have been due to methodological issues or inherent difficulties in detecting evidence for the validity of stages of change measures.

Mechanical measures of uncooked beef longissimus muscle can predict sensory panel tenderness and Warner-Bratzler shear force of cooked steaks.

Two experiments were conducted to investigate mechanical measures of tenderness on uncooked USDA Select longissimus muscle as a means to predict Warner-Bratzler shear force (WBSF) and trained sensory panel tenderness (SPT) of cooked steaks. In Exp. 1, strip loins (n = 24) were aged 14 d postmortem and fabricated into steaks (2.54 cm). Medial, center, and lateral locations within uncooked steaks were evaluated by a plumb bob device and correlated with WBSF and SPT of cooked steaks. In Exp. 2, 24 strip loins were used to evaluate how well plumb bob and needle probe devices used on uncooked steaks predicted WBSF and SPT of cooked steaks. At 2 d postmortem, two steaks were fabricated from the anterior end. One uncooked steak (2.54 cm) was assigned to the plumb bob treatment and the other uncooked steak (5.08 cm) was assigned to needle probe treatment. At 14 d postmortem, one uncooked steak (5.08 cm) was assigned to needle probe treatment, a second uncooked steak (2.54 cm) was assigned to plumb bob treatment, whereas the remaining steaks (2.54 cm) were cooked and evaluated by a trained sensory panel and WBSF device. In Exp. 1, average plumb bob values were negatively correlated (P < 0.05) to average SPT scores (r = -0.48). However, correlations between WBSF and plumb bob values for medial, lateral, and average of all sections were not significant (P > 0.05). In Exp. 2, regression models to predict SPT from needle probe and plumb bob measurements individually taken at 2 d postmortem had R2 of 0.54 and 0.51, respectively. Combining needle probe and plumb bob measurements resulted in an R2 of 0.76; when quadratic terms for both variables were in the model, the R2 was 0.80. Regressing needle probe and plumb bob measurements at 2 d postmortem with WBSF produced R2 values of 0.51 and 0.45, respectively. If linear terms of both probes were combined to predict WBSF, the R2 increased to 0.77. An equation to predict WBSF, including both the linear and quadratic terms of needle probe and plumb bob measurements, resulted in an R2 of 0.84. Using plumb bob and needle probe devices on uncooked longissimus muscle at 2 d postmortem can predict cooked WBSF and SPT of USDA Select Grade steaks at 14 d postmortem.

Hoplopleura janzeni n. sp. (Phthiraptera: Anoplura), a new sucking louse from a Central American swimming mouse.

Both sexes of a new species of sucking louse Hoplopleura janzeni (Phthiraptera: Hoplopleuridae) are described and illustrated from the Central American ichthyomyine swimming mouse Rheomys raptor (Rodentia: Muridae) collected in Costa Rica. The morphology of the new species is compared with that of Hoplopleura exima Johnson, the only other species of sucking louse known to parasitize an ichthyomyine rodent. Hoplopleura janzeni is unique in having posteriorly directed spurs on the first antennal segment, the fore- and midcoxae, and the hind femora of both sexes.

Swimming ability in three Costa Rican dry forest rodents.

We investigated the swimming abilities of three Costa Rican dry forest rodents (Coues' rice rat. Oryzomys couesi, hispid cotton rat, Sigmodon hispidus, and spiny pocket mouse, Liomys salvini) associated with a large marsh, Laguna Palo Verde, using 90 s swim trials in a plastic container. Swimming ability was evaluated by observing the use of limbs and tail in the water, inclination to the surface, and diving and floating behavior. Rice rats could float, swim and dive, suggesting that they can exploit surface and underwater resources. Cotton rats swam at the water's surface, but were less skilled swimmers than rice rats. Spiny pocket mice tired quickly and had difficulty staying at the water's surface. Results suggest that differential swimming ability is related to the distribution of the three sympatric species within the marsh and adjacent forest habitats.

Polymorphism of the N-acetyltransferase (NAT2), smoking and the potential risk of periodontal disease.

Periodontal disease is a common multifactorial process that leads to bone destruction and tooth loss. Interactions of environmental and genetic factors determine the extent and severity of periodontal disease. Smoking is one of the risk factors for periodontal disease, and the risk may be influenced by the polymorphism of N-acetyltransferase (NAT2) via metabolism of smoke-derived xenobiotics. We therefore hypothesized that a NAT2 genotype would be a risk factor for periodontal disease. A total of 154 Caucasian subjects were assigned to one of two groups (1) no or mild and (2) severe periodontal disease based on radiographic (bone destruction) and clinical criteria (probing depth, attachment loss) and the number of teeth. In all subjects genotyping for mutations on NAT2 was performed by means of PCR and RFLP analysis. In the less-affected group genotyping showed a fraction of predicted slow and rapid acetylators (53.6% and 46.4%, respectively) corresponding to the normal distribution in Caucasians. Severely affected patients were predominantly slow acetylators, the odds ratios being between 2.38 and 5.02 for the NAT2-related risk depending on the outcome parameters chosen. Adjustment for age had no influence on these findings. Our data indicate that the slow acetylator phenotype is associated with a higher risk of periodontitis, especially with respect to the severity of the disease. Possible implications with respect to the risk associated with smoking are discussed.

Azoreductase activity in bacteria associated with the greening of instant chocolate puddings.

Pseudomonas sp. strain AZR1 and Klebsiella sp. strain AZR2 were isolated from reconstituted instant chocolate puddings that had turned green and were found to have azoreductase activity. This activity was inducible and NADH dependent. Differences in dye reduction rates between the two strains were apparent, and substrate specificity related to dye structure was observed.

Athermal alterations in the structure of the canalicular membrane and ATPase activity induced by thermal levels of microwave radiation.

Sprague-Dawley rats (200-250 g) were exposed 30 min/day for 4 days to thermogenic levels (rectal temperature increase of 2.2 degrees C) of microwave radiation [2.45 GHz, 80 mW/cm2, continuous-wave mode (CW)] or to a radiant heat source resulting in an equivalent increase in body temperature of 2.2 degrees C. On the fifth day after the 4 days of exposure to microwave radiation, the animals were sacrificed and their livers removed. The canalicular membranes were isolated and evaluated for adenosinetriphosphatase (ATPase) activity, total fatty acid composition and membrane fluidity characteristics. Mg(++)-ATPase activity (Vmax) decreased by 48.5% in the group exposed to microwave radiation, with no significant change in the group exposed to radiant heat. The decrease in Mg(++)-ATPase was partially compensated by a concomitant increase in Na+/K(+)-ATPase activity (170% increase in Vmax over control) in animals exposed to microwave radiation, while no change occurred in the group exposed to radiant heat. This alteration in ATPase activity in the group exposed to microwave radiation is associated with a large decrease in the ratio of saturated to unsaturated fatty acids. Conversely, the group exposed to radiant heat had an increase in the ratio of saturated to unsaturated fatty acids. The most dramatic changes were found in the levels of arachidonic acid. Finally, the electron paramagnetic resonance (EPR) spin label technique used to measure the fluidity of the canalicular membranes of the animals in the three groups (sham, microwave radiation and radiant heat) indicated that the results were different in the three groups, reflecting the changes found in their fatty acid composition. The physiological response to "equivalent" thermal loads in rats is expressed differently for different types of energy sources. Possible mechanisms producing these divergent thermogenic responses are discussed.

Differential response of the permeability of the rat liver canalicular membrane to sucrose and mannitol following in vivo acute single and multiple exposures to microwave radiation (2.45 GHz) and radiant-energy thermal stress.

Both acute and chronic exposures to microwave radiation altered the function of the rat canalicular membrane. A single acute exposure to microwave radiation [80 mW/cm2, 2.45 GHz, continuous wave, 30 min exposure (SAR approximately equal to 72 W/kg)] or a matched radiant-energy thermal load, both designed to raise core body temperature approximately 3 degrees C, decreased the permeability of the canalicular membrane of male Sprague-Dawley rats to sucrose. The change in canalicular membrane permeability was demonstrated by a significant increase in the percentage of [3H]sucrose recovered in bile following its administration by a segmented retrograde intrabiliary injection. Similar acute exposures to microwave and radiant-energy thermal sources produced no significant alterations in canalicular membrane permeability to [14C]mannitol. In both acute exposure protocols, a rapidly reversible increase in bile flow rate was observed. Four exposures (30 min/day x 4 days) to either microwave radiation (80 mW/cm2) or a matched radiant-energy thermal load resulted in a significant depression in bile flow rate at normothermic temperatures. Animals receiving multiple exposures to microwave radiation had significant decreases in canalicular membrane permeability to both [3H]sucrose and [14C]mannitol, while similar exposure to radiant-energy thermal load alone altered canalicular membrane permeability to [3H]sucrose. An examination of the hepatic clearance of sucrose and mannitol following acute microwave exposure demonstrated no significant differences. Thus acute single exposure to microwave and radiant-energy thermal loads produced similar alterations in canalicular membrane permeability. Conversely, multiple exposures produced nonreversible changes in bile flow rate and canalicular membrane permeability, with microwave exposure producing greater alterations in the function of the canalicular membrane than an equivalent radiant-energy thermal load.

Fetal protein malnutrition impairs acquisition of a DRL task in adult rats.

Developing rats were either malnourished or adequately nourished during the prenatal period by feeding their dams diets of 6% (low) or 25% (adequate) casein content 5 weeks prior to mating and throughout pregnancy. All pups received adequate nutrition from the day of birth onwards. Beginning at 160 days of age male rats were tested in a DRL-18 sec operant task. It was found that prenatal malnutrition impaired performance during acquisition, though asymptomatic levels were not significantly different. Subsequent limited hold DRL-18 sec schedules in which late as well as early responses went unrewarded indicated that the timing ability of the prenatally malnourished rats was excellent and similar to that of the controls. These late effects of fetal protein malnutrition are discussed in terms of the difficulty in adapting to the change from CRF to DRL-18 sec (possibilities include a reduced ability to develop a timing strategy or increased sensitivity to the change in reinforcement contingencies), while retaining the ability to time responses accurately once the task was acquired.

Unusual nucleotide sequences at the 5' end of actin genes in Dictyostelium discoideum.

The nucleotide sequences at the 5' end of one actin cDNA and six actin genomic clones from Dictyostelium have been determined. The amino acid sequences derived from the nucleotide sequences show strong conservation for six of the seven genes relative to the NH2-terminal region of Physarum actin. The region 5' to the AUG initiating codon is greater than 90% A+T residues in all of the genes.