Epitaxial III−V Nanowires on Silicon Mårtensson, Thomas; Svensson, C. Patrik T; Wacaser, Brent A ...
Nano letters,
10/2004, Letnik:
4, Številka:
10
Journal Article
Recenzirano
We present results of ideal epitaxial nucleation and growth of III−V semiconductor nanowires on silicon substrates. This addresses the long-time challenge of integrating high performance III−V ...semiconductors with mainstream Si technology. Efficient room-temperature generation of light on silicon is demonstrated by the incorporation of double heterostructure segments in such nanowires. We expect that advanced heterostructure devices, such as resonant tunneling diodes, superlattice device structures, and heterostructure photonic devices for on-chip communication, could now become available as complementary device technologies for integration with silicon.
We present a mass transport model based on surface diffusion for metal-particle-assisted nanowire growth. The model explains the common observation that for III/V materials thinner nanowires are ...longer than thicker ones. We have grown GaP nanowires by metal-organic vapor phase epitaxy and compared our model calculations with the experimental nanowire lengths and radii. Moreover, we demonstrate that the Gibbs−Thomson effect can be neglected for III/V nanowires grown at conventional temperatures and pressures.
Maternal stress during pregnancy is associated with a modestly increased risk of fetal growth restriction and pre-eclampsia. Since placental abruption shares similar pathophysiological mechanisms and ...risk factors with fetal growth restriction and pre-eclampsia, we hypothesized that maternal stress may be implicated in abruption risk. We investigated the association between maternal bereavement during pregnancy and placental abruption.
We studied singleton births in Denmark (1978-2008) and Sweden (1973-2006) (n = 5,103,272). In nationwide registries, we obtained data on death of women's close family members (older children, siblings, parents, and partners), abruption and potential confounders.
A total of 30,312 (6/1000) pregnancies in the cohort were diagnosed with placental abruption. Among normotensive women, death of a child the year before or during pregnancy was associated with a 54% increased odds of abruption 95% confidence interval (CI) 1.30-1.82; the increased odds were restricted to women who lost a child the year before or during the first trimester in pregnancy. In the group with chronic hypertension, death of a child the year before or in the first trimester of pregnancy was associated with eight-fold increased odds of abruption (odds ratio 8.17, 95% CI 3.17-21.10). Death of other relatives was not associated with abruption risk.
Loss of a child the year before or in the first trimester of pregnancy was associated with an increased risk of abruption, especially among women with chronic hypertension. Studies are needed to investigate the effect of less severe, but more frequent, sources of stress on placental abruption risk.
Dehydrins (DHNs) compose a family of intrinsically unstructured proteins that have high water solubility and accumulate during late seed development, low temperature or water deficit conditions, and ...are thought to play a protective role in freezing and drought tolerance in plants. Twelve Dhn genes were previously described in the barley genome. Here, we report an additional member of this multigene family, Dhn13. The Dhn13 gene is located in chromosome 4 near marker MWG634 and encodes a 107-amino acid KS-type DHN. Semi-quantitative reverse transcriptase PCR data indicated that Dhn13 is constitutively expressed in seedling tissues and embryos of developing seeds. Microarray data were consistent with these results and showed a considerable increase of Dhn13 transcripts when plants were subjected to chilling and freezing temperatures. The highest transcript levels where observed in anthers. The presence of ABRE, MYC, DRE, and POLLEN1LELAT52 regulatory elements in the putative Dhn13 promoter region is in agreement with expression data.
Plant microspores can be reprogrammed from their normal pollen development to an embryogenic route in a process termed microspore embryogenesis or androgenesis. Stress treatment has a critical role ...in this process, inducing the dedifferentiation of microspores and conditioning the following androgenic response. In this study, we have used three barley doubled haploid lines with similar genetic background but different androgenic response. The Barley1 GeneChip was used for transcriptome comparison of these lines after mannitol stress treatment, allowing the identification of 213 differentially expressed genes. Most of these genes belong to the functional categories “cell rescue, defense, and virulence”; “metabolism”; “transcription”; and “transport”. These genes were grouped into clusters according to their expression profiles among lines. A principal component analysis allowed us to associate specific gene expression clusters to phenotypic variables. Genes associated with the ability of microspores to divide and form embryos were mainly involved in changes in the structure and function of membranes, efficient use of available energy sources, and cell fate. Genes related to stress response, transcription and translation regulation, and degradation of pollen-specific proteins were associated with green plant production, while expression of genes related to plastid development was associated with albino plant regeneration.
Model complexity versus scatter in fatigue SVENSSON, T.
Fatigue & fracture of engineering materials & structures,
November 2004, Letnik:
27, Številka:
11
Journal Article
Recenzirano
ABSTRACT
Fatigue assessment in industry is often based on simple empirical models, such as the Wöhler curve or the Paris' law. In contrast, fatigue research to a great extent works with very complex ...models, far from the engineering practice. One explanation for this discrepancy is that the scatter in service fatigue obscures many of the subtle phenomena that can be studied in a laboratory. Here we use a statistical theory for stepwise regression to investigate the role of scatter in the choice of model complexity in fatigue. The results suggest that the amount of complexity used in different design concepts reflects the appreciated knowledge about input parameters. The analysis also points out that even qualitative knowledge about the neglected complexity may be important in order to avoid systematic errors.
Midbrain dopamine neurons in vivo discharge in a single-spike firing pattern or in a burst-firing pattern. Such activity in vivo strikingly contrasts with the pacemaker activity of the same dopamine ...neurons recorded in vitro. We have recently shown that burst activity in vivo of midbrain dopamine neurons is due to the local activation of excitatory amino acid receptors, as microapplication of the broad-spectrum antagonist of excitatory amino acids, kynurenic acid, strongly regularized the spontaneous firing pattern of these dopamine neurons. In the present study, we investigated which subtypes of excitatory amino acid receptors are involved in the burst-firing of midbrain dopamine neurons in chloral hydrate-anaesthetized rats, iontophoretic or pressure microejections of 6-cyano, 7-nitroquinoxaline-2,3-dione (CNQX), a non-N-methyl-D-aspartate (NMDA) receptor antagonist, did not alter the spontaneous burst firing of dopamine neurons (n = 36). In contrast, similar ejections of (+-)2-amino,5-phosphonopentanoic acid (AP-5), a specific antagonist at NMDA receptors, markedly regularized the firing pattern by reducing the occurrence of bursts (n = 52). In addition, iontophoretic ejections of NMDA, but not kainate or quisqualate, elicited a discharge of these dopamine neurons in bursts (n = 20, 12 and 14, respectively). These data suggest that burst-firing of midbrain dopamine neurons in vivo results from the tonic activation of NMDA receptors by endogenous excitatory amino acids. In view of the critical dependency of catecholamine release on the discharge pattern of source neurons, excitatory amino acid inputs to midbrain dopamine neurons may constitute a major physiological substrate in the control of the dopamine level in target areas.
Hypoaigic zones are aquifer volumes close to and beneath the shores of saline surface water bodies, and are characterized by the presence of time-dependent natural convection and chemical ...stratification. When transient and cyclic processes are involved there is significant potential for complex flow and reaction in the near-shore aquifer, presenting a unique challenge to pollutant risk assessment methodologies. This work considers the nature of some hypoaigic processes generated by the seasonally saline Canning River of Western Australia near a site contaminated by petroleum hydrocarbons. A dissolved hydrocarbon plume migrates within the shallow superficial aquifer to the nearby bank of the Canning River. Beneath the river bank a zone of complex fluid mixing is established by seasonal and tidal influences. Understanding this complexity and the subsequent ramifications for local biogeochemical conditions is critical to inferring the potential for degradation of advecting contaminants. A range of modelling approaches throws light on the overall topographic controls of discharge to the river, on the saline convection processes operating under the river bank, on the potential for fluid mixing, and on the various important time scales in the system. Saline distributions simulated within the aquifer hypoaigic zone are in at least qualitative agreement with previous field measurements at the site and are strongly affected by seasonal influences. Groundwater seepage velocities at the shoreline are found to be positively correlated with river salinity. Calculations of fluid age distributions throughout the system show sensitivity to dispersivity values; however, maximum fluid ages under the river appear to be diffusion limited to a few decades. The saline convection cell in the aquifer defines a zone of strong dispersive dilution of aged (many decades) deep aquifer fluids with relatively young (several months) riverine fluids. Seasonal recharge and river salinity cycles induce regular perturbations to the convection cell, yielding intra-annual variations of 50% in seepage velocity and almost 30% in wedge penetration distance at the plume location.
A nicotine vaccine could prevent relapse to smoking by hindering blood nicotine from reaching the brain. Niccine® is a nicotine hapten tetanus-toxoid conjugate vaccine. The present study evaluated ...the clinical efficacy of Niccine for tobacco smoking relapse prevention.
Cigarette smokers (n = 355) aged 25-50 years were enrolled in a randomized, double-blind, parallel group 1-year trial encompassing 16 visits and 16 telephone calls. Niccine 40 μg or placebo was administered on Days 0, 28, 56, 90, 150, and 210. Between Days 56-98, subjects were treated with varenicline to aid cessation, targeted for Day 70. Only individuals abstinent between Days 90-98 (n = 265) were allowed to continue to 1 year (n = 219). Relapse to smoking was defined as >5 cigarettes within 7 days or since the last contact, or smoking on >5 occasions within 7 days or since the last contact.
At 1 year, nonrelapse was 43.3% in the Niccine versus 51.1% in the placebo groups (difference = -7.9%; 95% CI = -20.6% to 4.9%). There was no benefit of Niccine on smoking status at 6 or 9 months, exhaled carbon monoxide levels, time to relapse, abstinence, withdrawal symptoms, or smoking reinforcement. Nicotine antibody levels increased (mean = 1.34 μg/ml; SD = 2.84 μg/ml) in the Niccine group, but were not related to relapse. Adverse events except hypersensitivity and compensatory smoking did not differ between groups.
This nicotine vaccine appeared well tolerated but did not influence trajectories of relapse possibly because of insufficient antibody levels or lack of efficacy of the vaccine concept for relapse prevention.
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