Atomic-scale modeling of the deformation of nanocrystalline metals

Nanocrystalline metals, i.e. metals with grain sizes from 5 to 50 nm, display technologically interesting properties, such as dramatically increased hardness, increasing with decreasing grain size. Due to the small grain size, direct atomic-scale simulations of plastic deformation of these materials are possible, as such a polycrystalline system can be modeled with the computational resources available today. We present molecular dynamics simulations of nanocrystalline copper with grain sizes up to 13 nm. Two different deformation mechanisms are active, one is deformation through the motion of dislocations, the other is sliding in the grain boundaries. At the grain sizes studied here the latter dominates, leading to a softening as the grain size is reduced. This implies that there is an ``optimal'' grain size, where the hardness is maximal. Since the grain boundaries participate actively in the deformation, it is interesting to study the effects of introducing impurity atoms in the grain boundaries. We study how silver atoms in the grain boundaries influence the mechanical properties of nanocrystalline copper.Comment: 10 pages, LaTeX2e, PS figures and sty files included. To appear in Mater. Res. Soc. Symp. Proc. vol 538 (invited paper). For related papers, see http://www.fysik.dtu.dk/~schiotz/publist.htm

Lateralizing Value of Interictal Spikes on Overnight Sleep-EEG Studies in Temporal Lobe Epilepsy

Purpose: To determine the lateralizing value of interictal epileptiform discharges (IEDs) recorded during overnight sleep-EEG studies in temporal lobe epilepsy. Because IEDs are more prevalent in non-rapid eye movement (NREM) sleep than in wakefulness, overnight sleep-EEG recordings may contribute additional lateralizing information to the epilepsy surgery evaluation beyond daytime EEGs. Methods: Twenty-four subjects with medically refractory temporal lobe epilepsy underwent continuous overnight sleep-EEG recordings. Subjects were seizure free ≤24 h before study and receiving stable doses of medication. The IED foci recorded on overnight studies were compared with daytime EEGs, interictal samples, and ictal recordings during long-term monitoring, brain magnetic resonance images (MRIs), and surgical outcome. Results: (a) In all 24 subjects, including 13 without IEDs on daytime EEGs, temporal IEDs were present during NREM sleep and were exclusively or predominantly (<95%) unilateral in 15 and bitemporal in nine. (b) Unilateral NREM IEDs were concordant with surface or depth ictal-onset regions in 14 subjects, even if MRIs were normal (three subjects) or surface ictal-onset regions were bilateral (five subjects). Eleven of 12 subjects with unilateral concordant NREM IEDs who have undergone surgery are seizure free. (c) Bitemporal IEDs were associated with postoperative seizures in all subjects with normal MRIs or widespread MRI abnormalities. However, all subjects with bitemporal IEDs and MRI hippocampal abnormalities concordant with ictal-onset regions had good to excellent surgical outcomes. Conclusions: When combined with other investigations, IEDs recorded on overnight studies add prognostic data to the epilepsy surgery evaluation not provided by daytime EEGs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66154/1/j.1528-1157.1999.tb02044.x.pd

Improvements to the Synthesis of Polyimide Aerogels

Cross-linked polyimide aerogels are viable approach to higher temperature, flexible insulation for inflatable decelerators. Results indicate that the all-polyimide aerogels are as strong or stronger than polymer reinforced silica aerogels at the same density. Currently, examining use of carbon nanofiber and clay nanoparticles to improve performance. Flexible, polyimide aerogels have potential utility in other applications such as space suits, habitats, shelter applications, etc. where low dusting is desire

Environmental enrichment intervention for Rett syndrome: An individually randomised stepped wedge trial

Background: Rett syndrome is caused by a pathogenic mutation in the MECP2 gene with major consequences for motor and cognitive development. One of the effects of impaired MECP2 function is reduced production of Brain Derived Neurotrophic Factor (BDNF), a protein required for normal neuronal development. When housed in an enriched environment, MECP2 null mice improved motor abilities and increased levels of BDNF in the brain. We investigated the effects of environmental enrichment on gross motor skills and blood BDNF levels in girls with Rett syndrome. Methods: A genetically variable group of 12 girls with a MECP2 mutation and younger than 6 years participated in a modified individually randomised stepped wedge design study. Assessments were conducted on five occasions, two during the baseline period and three during the intervention period. Gross motor function was assessed using the Rett Syndrome Gross Motor Scale (maximum score of 45) on five occasions, two during the baseline period and three during the intervention period. Blood levels of BDNF were measured at the two baseline assessments and at the end of the intervention period. The intervention comprised motor learning and exercise supplemented with social, cognitive and other sensory experiences over a six-month period. Results: At the first assessment, the mean (SD) age of the children was 3 years (1 year 1 month) years ranging from 1 year 6 months to 5 years 2 months. Also at baseline, mean (SD) gross motor scores and blood BDNF levels were 22.7/45 (9.6) and 165.0 (28.8) ng/ml respectively. Adjusting for covariates, the enriched environment was associated with improved gross motor skills (coefficient 8.2, 95%CI 5.1, 11.2) and a 321.4 ng/ml (95%CI 272.0, 370.8) increase in blood BDNF levels after 6 months of treatment. Growth, sleep quality and mood were unaffected. Conclusions: Behavioural interventions such as environmental enrichment can reduce the functional deficit in Rett syndrome, contributing to the evidence-base for management and further understanding of epigenetic mechanisms. Environmental enrichment will be an important adjunct in the evaluation of new drug therapies that use BDNF pathways because of implications for the strengthening of synapses and improved functioning. Trial registration: ACTRN12615001286538

HighP–TNano-Mechanics of Polycrystalline Nickel

We have conducted highP–Tsynchrotron X-ray and time-of-flight neutron diffraction experiments as well as indentation measurements to study equation of state, constitutive properties, and hardness of nanocrystalline and bulk nickel. Our lattice volume–pressure data present a clear evidence of elastic softening in nanocrystalline Ni as compared with the bulk nickel. We show that the enhanced overall compressibility of nanocrystalline Ni is a consequence of the higher compressibility of the surface shell of Ni nanocrystals, which supports the results of molecular dynamics simulation and a generalized model of a nanocrystal with expanded surface layer. The analytical methods we developed based on the peak-profile of diffraction data allow us to identify “micro/local” yield due to high stress concentration at the grain-to-grain contacts and “macro/bulk” yield due to deviatoric stress over the entire sample. The graphic approach of our strain/stress analyses can also reveal the corresponding yield strength, grain crushing/growth, work hardening/softening, and thermal relaxation under highP–Tconditions, as well as the intrinsic residual/surface strains in the polycrystalline bulks. From micro-indentation measurements, we found that a low-temperature annealing (T < 0.4 Tm) hardens nanocrystalline Ni, leading to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of impurity segregation to the grain boundaries of the nanocrystalline Ni

Peer-based behavioral health program for drug users in China: a pilot study

<p>Abstract</p> <p>Background</p> <p>Many injection drug users (IDUs) in China have high risk sexual behaviors that contribute to the spread of HIV infection. Although many IDUs in China move through drug rehabilitation centers, this opportunity for sexual health education has largely been overlooked.</p> <p>Methods</p> <p>A convenience sample of 667 drug users from two rehabilitation centers in South China was recruited in the study. Two hundred and forty seven drug users from a single Guangdong Province rehabilitation center received the peer-based education intervention, while 420 drug users from another rehabilitation center received routine HIV/STI education and was used as the control. One hundred and eighty nine (22.1%) individuals refused to participate in the study. HIV/STI behavioral and knowledge domains were assessed at 3 months in rehabilitation centers after the intervention (first follow-up) and at 2-23 months in the community after release (second follow-up).</p> <p>Results</p> <p>Drug users who completed the intervention reported more frequent condom use with casual sex partners (60.0% vs. 12.5% condom use every time, p = 0.011) and less frequent injection (56.7% vs. 26.4% no injection per day, p = 0.008) at the second follow-up compared to those in the routine education group. Loss to follow up was substantial in both control and intervention groups, and was associated with living far from the detention center and having poor HIV knowledge at baseline.</p> <p>Conclusions</p> <p>This study shows that rehabilitation centers may be a useful location for providing behavioral HIV/STI prevention services and referral of individuals to community-based programs upon release. More research is needed on behalf of detained drug users in China who have complex social, medical, and legal needs.</p

Reduction of Pavlovian bias in schizophrenia: Enhanced effects in clozapine-administered patients

The negative symptoms of schizophrenia (SZ) are associated with a pattern of reinforcement learning (RL) deficits likely related to degraded representations of reward values. However, the RL tasks used to date have required active responses to both reward and punishing stimuli. Pavlovian biases have been shown to affect performance on these tasks through invigoration of action to reward and inhibition of action to punishment, and may be partially responsible for the effects found in patients. Forty-five patients with schizophrenia and 30 demographically-matched controls completed a four-stimulus reinforcement learning task that crossed action ("Go" or "NoGo") and the valence of the optimal outcome (reward or punishment-avoidance), such that all combinations of action and outcome valence were tested. Behaviour was modelled using a six-parameter RL model and EEG was simultaneously recorded. Patients demonstrated a reduction in Pavlovian performance bias that was evident in a reduced Go bias across the full group. In a subset of patients administered clozapine, the reduction in Pavlovian bias was enhanced. The reduction in Pavlovian bias in SZ patients was accompanied by feedback processing differences at the time of the P3a component. The reduced Pavlovian bias in patients is suggested to be due to reduced fidelity in the communication between striatal regions and frontal cortex. It may also partially account for previous findings of poorer "Go-learning" in schizophrenia where "Go" responses or Pavlovian consistent responses are required for optimal performance. An attenuated P3a component dynamic in patients is consistent with a view that deficits in operant learning are due to impairments in adaptively using feedback to update representations of stimulus value

Peer-based behavioral health program for drug users in China: a pilot study

<p>Abstract</p> <p>Background</p> <p>Many injection drug users (IDUs) in China have high risk sexual behaviors that contribute to the spread of HIV infection. Although many IDUs in China move through drug rehabilitation centers, this opportunity for sexual health education has largely been overlooked.</p> <p>Methods</p> <p>A convenience sample of 667 drug users from two rehabilitation centers in South China was recruited in the study. Two hundred and forty seven drug users from a single Guangdong Province rehabilitation center received the peer-based education intervention, while 420 drug users from another rehabilitation center received routine HIV/STI education and was used as the control. One hundred and eighty nine (22.1%) individuals refused to participate in the study. HIV/STI behavioral and knowledge domains were assessed at 3 months in rehabilitation centers after the intervention (first follow-up) and at 2-23 months in the community after release (second follow-up).</p> <p>Results</p> <p>Drug users who completed the intervention reported more frequent condom use with casual sex partners (60.0% vs. 12.5% condom use every time, p = 0.011) and less frequent injection (56.7% vs. 26.4% no injection per day, p = 0.008) at the second follow-up compared to those in the routine education group. Loss to follow up was substantial in both control and intervention groups, and was associated with living far from the detention center and having poor HIV knowledge at baseline.</p> <p>Conclusions</p> <p>This study shows that rehabilitation centers may be a useful location for providing behavioral HIV/STI prevention services and referral of individuals to community-based programs upon release. More research is needed on behalf of detained drug users in China who have complex social, medical, and legal needs.</p