Electron Elevator: Excitations across the Band Gap via a Dynamical Gap State.

We use time-dependent density functional theory to study self-irradiated Si. We calculate the electronic stopping power of Si in Si by evaluating the energy transferred to the electrons per unit path length by an ion of kinetic energy from 1 eV to 100 keV moving through the host. Electronic stopping is found to be significant below the threshold velocity normally identified with transitions across the band gap. A structured crossover at low velocity exists in place of a hard threshold. An analysis of the time dependence of the transition rates using coupled linear rate equations enables one of the excitation mechanisms to be clearly identified: a defect state induced in the gap by the moving ion acts like an elevator and carries electrons across the band gap.

Thermal tweezers for nano-manipulation and trapping of interacting atoms or nanoparticles on crystalline surfaces.

Thermal tweezers is an all-optical nanofabrication technique where surface thermophoresis due to holographically induced strong temperature modulation is used for parallel manipulation and trapping of adatoms and adparticles with nanoscale resolution. This paper conducts the detailed numerical analysis of thermal tweezers in the presence of significant interaction between the adparticles on the surface. In particular, we demonstrate that the considered inter-particle interactions result in a significant enhancement of the surface thermophoretic effect and substantially increases modulation of particle concentration on the surface. In addition, we predict the possibility to achieve adparticle confinement on the surface to strongly sub-wavelength regions ∼12 times smaller than the vacuum wavelength of the optical radiation. A numerical approach to surface diffusion of interacting nanoparticles and adatoms is developed, the Monte Carlo interaction method, and its applicability conditions and limitations are discussed. The obtained results will be important for better understanding of the fundamental aspects of surface thermophoresis, as well as the development of new approaches to nano-patterning of surfaces for engineering their optical, electronic, chemical, and mechanical properties by means of the directed self-assembly of nanoparticles and adatoms.

Electronic excitations and their effect on the interionic forces in simulations of radiation damage in metals.

Using time-dependent tight-binding simulations of radiation damage cascades in a model metal we directly investigate the nature of the excitations of a system of quantum mechanical electrons in response to the motion of a set of classical ions. We furthermore investigate the effect of these excitations on the attractive electronic forces between the ions. We find that the electronic excitations are well described by a Fermi-Dirac distribution at some elevated temperature, even in the absence of the direct electron-electron interactions that would be required in order to thermalize a non-equilibrium distribution. We explain this result in terms of the spectrum of characteristic frequencies of the ionic motion. Decomposing the electronic force into four well-defined components within the basis of instantaneous electronic eigenstates, we find that the effect of accumulated excitations in weakening the interionic bonds is mostly (95%) accounted for by a thermal model for the electronic excitations. This result justifies the use of the simplifying assumption of a thermalized electron system in simulations of radiation damage with an electronic temperature dependence and in the development of temperature-dependent classical potentials.

An empirical potential for simulating vacancy clusters in tungsten.

We present an empirical interatomic potential for tungsten, particularly well suited for simulations of vacancy-type defects. We compare energies and structures of vacancy clusters generated with the empirical potential with an extensive new database of values computed using density functional theory, and show that the new potential predicts low-energy defect structures and formation energies with high accuracy. A significant difference to other popular embedded-atom empirical potentials for tungsten is the correct prediction of surface energies. Interstitial properties and short-range pairwise behaviour remain similar to the Ackford-Thetford potential on which it is based, making this potential well-suited to simulations of microstructural evolution following irradiation damage cascades. Using atomistic kinetic Monte Carlo simulations, we predict vacancy cluster dissociation in the range 1100-1300 K, the temperature range generally associated with stage IV recovery.

An investigation of misoprostol in the promotion of wound healing.

Misoprostol is a synthetic analogue of prostaglandin E1 that is known to attenuate the inflammatory process and promote collagen formation by inhibiting IL-1 and TNF. The objective of this study was to determine if the application of misoprostol wound powder to open wounds in dogs would modulate inflammation and decrease wound healing time. This prospective randomized study included 20 dogs with 281 surgically created 8 mm open wounds over the dorsum. The wounds were assigned to one of three treatments: control (no treatment), treatment (misoprostol powder with 'avicel'), or vehicle ('avicel' alone). Open wounds were digitally photographed on days zero, one, three, seven, 10, and 15 to measure wound size. All wounds were harvested at day 15 and evaluated histologically for evidence of edema, inflammation, necrosis, and collagen characteristics. Amount of epithelialization of open wounds was not significantly different among the groups at days three, seven, 10, and 15. The vehicle treated wounds were found to have a significantly higher degree of necrosis in comparison to control and treatment wounds. The control wounds had significantly lower scores for deep inflammation. All of the other parameters evaluated including location of wound, oedema, and characteristics of collagen fibres in the wound showed no significance among groups. However, the total wound score for the misoprostol was statistically higher than that for the control wounds. Therefore the value of using misoprostol wound powder with 'avicel' as the vehicle to enhance wound healing cannot be substantiated by the results of this study.

Tensions generated in a lateral fabellotibial suture model. Comparison of methods of application of tension, fixation of tension and suture material.

OBJECTIVES: To compare suture tension on a simulated lateral fabellotibial suture model using various methods of application of tension, fixation, and suture materials. METHODS: Veterinarians constructed simulated lateral fabellotibial suture constructs on a tying stand with a force sensor. Participants used combinations of 45 kg test monofilament nylon, metric 7 braided polyethylene, crimps, crimper, or knots, with their choice of instruments to secure the constructs. The tension in completed constructs was measured and comparisons were made between nylon and polyethylene, the use of crimps compared to knots, and the use of a mechanical distractor compared to hand tightening techniques. A value of p <0.05 was considered significant. RESULTS: Fifty-eight veterinarians created 72 lateral suture constructs. Final tensions generated ranged from 1.4-171.0N. The median tension of nylon sutures (43.9N ± 44.7N) was significantly greater than polyethylene sutures (9.5 N ± 19.6N). The median tension of constructs secured with crimps (62.8N ± 42.4N) was significantly greater than constructs secured with knots (11.8 N ± 14.8N). The mechanical distractor generated significantly higher median tension (78N ± 50.4N), compared to methods without the device (18.6 N ± 25.1N). CLINICAL SIGNIFICANCE: There was a large variability in the tension generated in simulated lateral fabellotibial constructs. Veterinarians who used nylon, crimps, and the mechanical tensioner generated constructs with greater tensions.

Non-Contact Measurement of Thermal Diffusivity in Ion-Implanted Nuclear Materials.

Knowledge of mechanical and physical property evolution due to irradiation damage is essential for the development of future fission and fusion reactors. Ion-irradiation provides an excellent proxy for studying irradiation damage, allowing high damage doses without sample activation. Limited ion-penetration-depth means that only few-micron-thick damaged layers are produced. Substantial effort has been devoted to probing the mechanical properties of these thin implanted layers. Yet, whilst key to reactor design, their thermal transport properties remain largely unexplored due to a lack of suitable measurement techniques. Here we demonstrate non-contact thermal diffusivity measurements in ion-implanted tungsten for nuclear fusion armour. Alloying with transmutation elements and the interaction of retained gas with implantation-induced defects both lead to dramatic reductions in thermal diffusivity. These changes are well captured by our modelling approaches. Our observations have important implications for the design of future fusion power plants.

The effects of a chemically diverse range of calcium channel antagonists on the AVP-stimulated ACTH response in ovine corticotrophs.

Arginine vasopressin (AVP) stimulates adrenocorticotropin (ACTH) release from pituitary corticotrophs by a mechanism dependent on extracellular calcium (Ca2+e). The involvement, in this response, of Ca2+ influx via L-type voltage sensitive Ca2+ channels (VSCC) was studied using cultured ovine anterior pituitary cells. Representatives of 3 chemically distinct classes of organic antagonists of L-type VSCC (methoxyverapamil (D600), nifedipine and diltiazem) and 2 inorganic blocking ions (Cd2+ and Co2+) were used. All of the blockers reduced AVP-stimulated ACTH release, but none caused complete inhibition. ACTH release in response to raised extracellular K+ concentration was also inhibited by these antagonists, with D600 and Cd2+ completely abolishing the response. These results indicate that there is a considerable, but not total, dependence on Ca2+ influx via L-type VSCC during the ACTH response to AVP in ovine corticotrophs.

Structure-function relationships in pancreatic islets: support for intraislet modulation of insulin secretion.

Pancreatic islet B cell function was studied in vitro using three structurally different preparations of islet tissues: isolated, intact islets, dispersed islet cells attached singly to microcarrier beads, and reaggregated islet cells. Mechanisms of intercellular communication are eliminated with single cell preparations, whereas in aggregates cell to cell communications are reestablished and a defined microenvironment restored. Perifusion studies measured nonstimulated and glucose- and arginine-stimulated insulin release from the three islet tissues. Insulin secretion rates were expressed as a function of cellular DNA content, permitting direct comparison between tissues. During perifusion with low (2.8 or 5.5 mM) glucose concentrations, secretion rates of single islet cells were up to 6-fold greater (P less than 0.001) than those of intact islets. Perifusion of islet cells with 2.8 mM glucose and 100 or 500 pg glucagon/ml had no effect whereas GH-release-inhibiting factor (330 and 1000 pg/ml) decreased nonstimulated insulin secretion rates by 15% (P less than 0.05). After reaggregation, basal insulin secretion rates were restored toward those of intact islets. Glucose (5.5-30 mM) and L-arginine (5-20 mM) elicited first phase insulin responses from single islet cells that were not significantly different from those observed with intact islets; in contrast, second phase responses of single islets to glucose were approximately 50% those seen with intact islets, and their second phase responses to arginine were absent. Single islet cell first and second phase insulin responses to 5.5 mM glucose were enhanced 2.2-fold (P less than 0.01) and 2.8-fold (P less than 0.05), respectively, in the presence of exogenous glucagon, resulting in secretory profiles characteristic of intact islets. Reaggregation of single islet cells was associated with markedly increased first and second phase insulin responses to both glucose and arginine stimulation. These data show that disruption of the islet microanatomy results in alteration of insulin secretory responses and that these effects can be reversed, in part by exogenous glucagon and GH-release-inhibiting factor, and by reaggregation. Although different mechanisms appear important for nonstimulated, first and second phase insulin release, the findings support a role for both direct intercellular communication and hormonal secretion by islet A and D cells in the modulation of B cell function.

Homologous down-regulation of gonadotropin-releasing hormone receptor sites and messenger ribonucleic acid transcripts in alpha T3-1 cells.

GnRH is known to down-regulate its pituitary receptors by mechanisms that include endocytosis of the agonist-receptor complex. To evaluate the extent to which changes in receptor synthesis contribute to this process, the effects of GnRH and its analogs on GnRH receptor number and messenger RNA (mRNA) levels were analyzed in the alpha T3-1 gonadotroph cell line. Treatment with GnRH or its potent agonist analog, des-Gly10-[D-Ala6]GnRH N-ethylamide, reduced GnRH receptor number in a time- and dose-dependent manner, with a half-maximal decrease in response to 10(-6) M GnRH or agonist analog by 75 min. The maximum decrease in receptor number (to 31% of the control value) was sustained for up to 72 h. In alpha T3-1 cells incubated with 10(-8) M GnRH or agonist analog, the GnRH receptors fell by 28% and 46% after 2 h, respectively; no change in receptors occurred after treatment with 10(-8) M GnRH antagonist ([D-pGlu1,D-Phe2,D-Trp3,6]GnRH). Time- and dose-dependent reductions in the level of receptor mRNA were also observed after treatment of alpha T3-1 cells with GnRH and the agonist analog. However, the maximal reduction in mRNA levels (to 60-70% of the control value) was consistently less than the decline in receptor number. These results indicate that the mechanism of GnRH receptor down-regulation in alpha T3-1 gonadotrophs includes reduction of receptor synthesis secondary to decreases in receptor mRNA levels. The finding that reductions in mRNA levels were relatively less than the decreases in receptor number is consistent with the involvement of additional mechanisms, including endocytosis and degradation, in down-regulation of the GnRH receptor.

Oxytocin modulates the luteinizing hormone response of the rat anterior pituitary to gonadotrophin-releasing hormone in vitro.

Although GnRH is believed to be the primary secretagogue for LH, oxytocin has also been shown to stimulate LH release from the anterior pituitary. We investigated the possibility that the two secretagogues interact in the modulation of LH release. Anterior pituitaries were removed from adult female rats at pro-oestrus, and tissue pieces were pre-incubated in oxytocin for 3 h prior to being stimulated with 15 min pulses of GnRH. LH output over the 1 h period from the beginning of the GnRH pulse was determined. Control incubations were carried out in the absence of oxytocin, and background secretory activities without GnRH stimulation were also determined. Tissue which was pre-exposed to oxytocin (0.012-1.25 microM) had an increased LH response to GnRH (1.25 nM). The increase was larger than the sum of the LH outputs obtained with oxytocin and GnRH separately, revealing that oxytocin synergistically enhanced LH secretion elicited by GnRH (P < 0.05; ANOVA). If stimulation by GnRH was delayed for 2 h after incubation with oxytocin, an increase in LH secretion was still observed, indicating that oxytocin-induced modulation did not rapidly disappear. Oxytocin pre-incubation was observed to result in an increase of maximal GnRH-induced LH output (P < 0.001; t-test), as well as an increase of intermediate responses. The LH response of the anterior pituitary to subsequent pulses of GnRH was modified by the self-priming process. The effect of oxytocin pretreatment on the response of primed tissue to GnRH was also investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Epidemiology of insulin-dependent diabetes mellitus in Canterbury, New Zealand.

A prospective study of incidence and prevalence of insulin-dependent diabetes mellitus in persons under 20 years was conducted over a 4-year period (1 February 1982-1 February 1986) for the Canterbury Hospital Board (total population 342,000) area in New Zealand. A central register for the area was established at the beginning of the study period. Degree of ascertainment was close to 100%. Average annual incidence was 11.7 persons per 100,000 (females: 10.6 per 100,000; males: 12.7 per 100,000) with no significant sex difference or temporal trends. Incidence peaks were seen for both sexes in the pubertal ages (females: 11 years; males: 13 years), with minor peaks occurring for both sexes in the pre-school ages. Age of onset was significantly younger in females than males. A seasonal variation in incidence was seen for males, with peaks in late autumn and mid-winter. 5.7% of the new diabetics had a first-degree relative with insulin-dependent diabetes mellitus. Islet cell cytoplasmic antibodies were detected in 68% of new diabetics and in 0% of age- and sex-matched healthy controls. Thyroid, gastric and adrenal auto-antibodies were seen more frequently in diabetics than in controls, but this difference was not significant. Prevalence of insulin-dependent diabetes on 1 February 1982 was 1.00 per 1000 and 1.05 per 1000 on 1 February 1986. The insulin-dependent diabetes mellitus incidence characteristics noted for the Canterbury Hospital Board area are similar to those reported for European and North American populations.

Insulin deficiency in non-insulin-dependent diabetics.

In this study, the prevalence of severe insulin deprivation amongst 104 non-insulin-dependent diabetes mellitus (NIDDM) patients was determined using a mixed meal pancreatic stimulation test (2.4 MJ). Of the 104 patients, 62 were recently diagnosed and 42 had been diabetic for between 1 and 40 years, but were not adequately controlled on diet and oral hypoglycaemic agents. Twenty-one (34%) of the recently diagnosed patients and 13 (31%) of the poorly controlled patients had peak post-testmeal insulin responses less than 160 pmol/l (less than 23 mU/l)--values 3 SD below normal--and were therefore considered to have severe blunting of beta cell response to nutrient secretagogues. Amongst recently diagnosed diabetics, these patients, as a group, had higher blood glucose levels (P less than 0.05) and lower body weights (P less than 0.01) but overall these parameters correlated poorly with insulin responses. Islet cell antibodies were positive in only one patient, whereas they were present in three others with less severe insulin secretory defects. For the treated diabetics, insulin release showed very low non-significant correlations with duration of diabetes, age, weight and glycaemic control. Islet cell antibodies were present in five patients, one only showing peak insulin values less than 160 pmol/l. These data suggest that about one-third of new diabetics and one-third of treated diabetics with poor glycaemic control are insulin deficient. Clinical and biochemical parameters, including islet cell antibodies, appear to be of no value in identifying this sub-group requiring insulin therapy. Their early recognition is best facilitated by routine pancreatic function tests.

Interaction between arginine vasopressin- and raised extracellular potassium-stimulated pathways in adrenocorticotropin secretion.

The intracellular regulation of adrenocorticotropin (ACTH) secretion from pituitary corticotroph cells was investigated by simultaneously exposing cultured ovine corticotrophs to arginine vasopressin (AVP) and raised extracellular K+ concentration ([K+]e). Both of these secretagogues activate L-type voltage-sensitive calcium channels (L-VSCC) as part of their respective ACTH secretory responses. When given together at high concentrations, AVP and raised [K+]e caused ACTH responses that were smaller in magnitude than the sum of the individual responses. However, at low agonist concentrations the simultaneous responses were greater in magnitude (i.e., synergistic). Further investigation suggested that activation of protein kinase C (PKC), which is part of the AVP-induced intracellular signalling pathway, is necessary and sufficient for the generation of the synergistic response, although it is not obligatory for AVP-induced ACTH release.

Oxytocin augmentation of gonadotropin-releasing hormone-stimulated luteinizing hormone release is modulated by cyclic AMP.

Oxytocin has been previously shown to augment GnRH-stimulated LH release. However it is currently unknown which intracellular mediators participate in the process. In this study, after preincubation with oxytocin for 3 hours, quartered pituitaries were stimulated for 15 minutes with GnRH. The effects of diBucAMP, a cell permeable analog of cAMP, and DDA, an adenyl cyclase inhibitor, on the augmentation by oxytocin were investigated. Although addition of diBucAMP increased GnRH-stimulated LH release, it inhibited the augmentation by oxytocin of the response to GnRH. On the other hand addition of DDA induced an increased augmentation by oxytocin. These results indicate that intracellular cAMP inhibits the augmentory activity of oxytocin, and suggest that oxytocin modulation of GnRH action in vivo would be optimal when the hormonal milieu results in reduced levels of cAMP.

Predictive model of the effect of temperature, pH and sodium chloride on growth from spores of non-proteolytic Clostridium botulinum.

Non-proteolytic strains of Clostridium botulinum are capable of growth at chill temperatures and thus pose a potential hazard in minimally-processed chilled foods. The combined effect of pH (5.0-7.3), NaCl concentration (0.1-5.0%) and temperature (4-30 degrees C) on growth of non-proteolytic C. botulinum in laboratory media was studied. Growth curves at various combinations of pH, NaCl concentration and temperature were fitted by the Gompertz and Baranyi models, and parameters derived from the curve-fit were modelled. Predictions of growth from the models were compared with data in the literature and this showed them to be suitable for use with fish, meat and poultry products. This model should contribute to ensuring the safety of minimally-processed foods with respect to non-proteolytic C. botulinum.

Erectile dysfunctions: assessment and care.

Erectile dysfunction is a common sexual problem for males in the United States. Health care practitioners need to consider sexual concerns as part of their holistic approach to clients who have sexual problems. This article examines the etiology, assessment and treatment of erectile dysfunctions in the heterosexual male. Physical and psychological influences on erectile dysfunctions are discussed. History-taking, including sexual history, physical assessment and common diagnostic tests, are described for the practitioner who is caring for the sexually dysfunctional client. General treatment modalities and referral needs are discussed.

Elastic trapping of dislocation loops in cascades in ion-irradiated tungsten foils.

Using in situ transmission electron microscopy (TEM), we have observed nanometre scale dislocation loops formed when an ultra-high-purity tungsten foil is irradiated with a very low fluence of self-ions. Analysis of the TEM images has revealed the largest loops to be predominantly of prismatic 1/2〈111〉 type and of vacancy character. The formation of such dislocation loops is surprising since isolated loops are expected to be highly mobile, and should escape from the foil. In this work we show that the observed size and number density of loops can be explained by the fact that the loops are not isolated-the loops formed in close proximity in the cascades interact with each other and with vacancy clusters, also formed in cascades, through long-range elastic fields, which prevent the escape of loops from the foil. We find that experimental observations are well reproduced by object Kinetic Monte Carlo simulations of evolution of cascades only if elastic interaction between the loops is taken into account. Our analysis highlights the profound effect of elastic interaction between defects on the microstructural evolution of irradiated materials.

Quantum-classical simulations of the electronic stopping force and charge on slow heavy channelling ions in metals.

By simulating the passage of heavy ions along open channels in a model crystalline metal using semi-classical Ehrenfest dynamics we directly investigate the nature of non-adiabatic electronic effects. Our time-dependent tight-binding approach incorporates both an explicit quantum mechanical electronic system and an explicit representation of a set of classical ions. The coupled evolution of the ions and electrons allows us to explore phenomena that lie beyond the approximations made in classical molecular dynamics simulations and in theories of electronic stopping. We report a velocity-dependent charge-localization phenomenon not predicted by previous theoretical treatments of channelling. This charge localization can be attributed to the excitation of electrons into defect states highly localized on the channelling ion. These modes of excitation only become active when the frequency at which the channelling ion moves from interstitial point to equivalent interstitial point matches the frequency corresponding to excitations from the Fermi level into the localized states. Examining the stopping force exerted on the channelling ion by the electronic system, we find broad agreement with theories of slow ion stopping (a stopping force proportional to velocity) for a low velocity channelling ion (up to about 0.5 nm fs(-1) from our calculations), and a reduction in stopping power attributable to the charge localization effect at higher velocities. By exploiting the simplicity of our electronic structure model we are able to illuminate the physics behind the excitation processes that we observe and present an intuitive picture of electronic stopping from a real-space, chemical perspective.

Resonant coupling between bulk waves and guided modes in a dielectric slab with a thick holographic grating.

What we believe to be a new type of resonant coupling of an incident bulk wave into guided modes of a slab with a thick holographic grating is shown to occur in the presence of strong frequency detunings of the Bragg condition. This happens through the reflection of the strongly noneigen +1 diffracted order with the slab-grating boundaries, the resultant reflected waves forming a guided slab mode. Rigorous coupled-wave analysis is used for the numerical analysis of the predicted resonant effects. Possible applications include enhanced options for the design of multiplexing and demultiplexing systems, optical signal-processing devices, optical sensors, and measurement techniques.