Molecular dynamics simulation of martensitic transformations in NiAI

Both thermally induced and stress-induced coherent nucleation and growth of an L1₀ martensitic phase have been examined and analyzed at the atomic level in molecular dynamics (MD) computer simulations of an ordered B2 NiAl lattice array using embedded atom method (EAM) interatomic potentials. Both heterogeneous and homogeneous nucleation are observed, the latter requiring an applied stress. The heterogeneous process occurs at ledge corners on stepped free surfaces and can be analyzed in terms of localized soft modes. The homogeneous nucleation can be understood as resulting from a strain spinodal instability which produces a morphology reminiscent of chemical spinodal decomposition. Self-accommodating martensite variants appear very early in the growth process, and all interfaces remain coherent with no detectable presence of dislocations in these early stages. Formerly Graduate Student, Department of Metallurgy, Institute of Materials Science, University of Connecticut. This article is based on a presentation made during TMS/ASM Materials Week in the symposium entitled “Atomistic Mechanisms of Nucleation and Growth in Solids,” organized in honor of H.I. Aaronson’s 70th Anniversary and given October 3“5, 1994, in Rosemont, Illinois.     

Fracture properties of metals and alloys from molecular dynamics simulations

Molecular dynamics simulations of fracture have been performed on the metals Al and Nb, and the intermetallic alloys RuAl, Nb₃Al and NiAl. The forces and energies were modelled with embedded atom method potentials. The increasing external stress was applied using displacements of the outer boundaries of the array, calculated by anisotropic elasticity theory, until the pre-existing cracks propagated or dislocation nucleation occurred. The resulting critical stress intensity factor was calculated at various orientations and temperatures, and the results compared with theory. Observations of slip systems are reported, as well as values for surface energies and “unstable stacking” energies.     

Endogenous centers: A simple departure from the NUE model

The model departs from the new urban economics (NUE) by allowing a single economic agent (a G-agent, e.g., a corporate headquarters) to contact every location with equal frequency: the G-agent is allowed to travel in every direction. A NUE-like assumption requires all other agents to contact the G-agent, in which case, the G-agent must locate at the center; i.e., the CBD is necessarily endogenous. The evolution of subcenters begins with growth in demand which raises the level of bid rents by enough to outbid agriculture. After one agent moves to the suburbs, interdependency among agents insures that the incipient suburban center becomes more attractive to other agents.     

Multiple inhibitory cytokines induce deregulated progenitor growth and apoptosis in hematopoietic cells from Fac-/- mice

We used a murine model containing a disruption of the murine homologue (Fac) of Fanconi Anemia group C (FAC) to evaluate the role of Fac in the pathogenesis of bone marrow (BM) failure. Methylcellulose cultures of BM cells from Fac-/- and Fac+/+ mice were established to examine the growth of multipotent and lineage-restricted progenitors containing inhibitory cytokines, including interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha), and macrophage inflammatory protein-1alpha (MIP-1alpha). Clonogenic growth of Fac-/- progenitors was reduced by 50% at 50- to 100-fold lower concentrations of all inhibitory cytokines evaluated. We hypothesized that the aberrant responsiveness to inhibitory cytokines in clonogenic cells may be a result of deregulated apoptosis. To test this hypothesis, we performed the TUNEL assay on purified populations of primary BM cells enriched for hematopoietic progenitors or differentiated myeloid cells. After stimulation with TNF-alpha, accentuated apoptosis was observed in both populations of Fac-/- cells. In addition, deregulated apoptosis was also noted in the most immature phenotypic population of hematopoietic cells after stimulation with MIP-1alpha. Together these data suggest a role of Fac in affecting the signaling of multiple cytokine pathways and support cytokine-mediated apoptosis as a major mechanism responsible for BM failure observed in FA patients.     

Cardiovascular function before, during, and after the first and subsequent pregnancies

This study was designed to test the hypothesis that the vascular remodeling of pregnancy begins early, persists for at least 1 year after delivery, and is accentuated by a second pregnancy. Serial estimates of heart rate, arterial pressure, left ventricular volumes, cardiac output, and calculated peripheral resistance were obtained before pregnancy, every 8 weeks during pregnancy, and 12, 24, and 52 weeks postpartum in 15 nulliparous and 15 parous women using electrocardiography, automated manometry, and M-mode ultrasound. During pregnancy, body weight increased 14.5 +/- 1.8 kg and returned to prepregnancy values 1 year postpartum. Heart rate peaked at term 15 +/- 1 beat/min above prepregnancy levels (57 +/- 1 beat/min). Mean arterial pressure reached its nadir (-6 +/- 1 mm Hg) at 16 weeks, returning to baseline at term. The increases in left ventricular volumes and cardiac output (2.2 +/- 0.2 L/min) peaked at 24 weeks as did the 500 +/- 29 dynes x cm x s(-5) decrease in peripheral resistance, and their magnitude was significantly greater in the parous women. Postpartum they gradually returned toward baseline but remained significantly different from prepregnancy values in both groups at 1 year. We conclude that cardiovascular adaptations to the initial pregnancy begin early, persist postpartum, and appear to be enhanced by a subsequent pregnancy. We speculate that persistence of these changes may lower cardiovascular risk in later life.     

Physical activity in usual occupation and risk of breast cancer (United States)

OBJECTIVE: To identify whether the cause, site of ductal obstruction, and characteristics of fluid aspirates are associated with the cryosurvival and fertility after thawing of sperm obtained during reconstruction of the excurrent ducts with microsurgical epididymal sperm aspiration, vasal sperm aspiration, or both. DESIGN: Prospective study. SETTING: Andrology center at a tertiary care institution. PATIENT(S): Men undergoing reconstruction of the excurrent duct and sperm aspiration (n = 42) or microsurgical epididymal sperm aspiration (n = 11). INTERVENTION(S): Sperm were tested for an association with the cause and site of obstruction. Fertilization and pregnancy rates after sperm aspiration and intracytoplasmic sperm injection (ICSI) were evaluated for fresh and frozen aspirates. MAIN OUTCOME MEASURE(S): Motile sperm count and percentage motility after thawing. RESULT(S): The motile sperm count before freezing was significantly higher in the caput epididymis than in the corpus. The motile sperm count before freezing was related inversely to the distance from the caput where the sperm were aspirated. Sperm from clear and opaque fluid aspirates had better percent motility than those from cloudy and creamy fluid aspirates. High fertilization and pregnancy rates were achieved using both fresh and frozen epididymal sperm. CONCLUSION(S): None of the factors studied was associated with cryosurvival of aspirated epididymal or vasal spermatozoa. Because motility is low after thawing, these specimens are best used with ICSI.     

摄影画廊

旅行及风光摄影专家David Clapp首次为我们展示他最新拍摄的风光照片。     

The structure of distress following trauma: Posttraumatic stress disorder, major depressive disorder, and generalized anxiety disorder.

The current report used confirmatory factor analysis to examine the latent structures of both key features and associated symptoms of three disorders that commonly develop following a traumatic event: posttraumatic stress disorder (PTSD), major depressive disorder (MDD), and generalized anxiety disorder (GAD). Participants were 228 motor-vehicle accident survivors who sought treatment for emotional difficulties. PTSD, MDD, and GAD were assessed with a combination of self-report and interview-based measures. The results of construct level analyses suggested that PTSD, MDD, and GAD are distinguishable but highly correlated disorders following a traumatic event. Symptom level analyses supported a model where the Reexperiencing, Avoidance, and Hypervigilance factors were subsumed under the PTSD construct. However, in this model the Dysphoria factor was a higher order construct correlated with the PTSD, MDD, and GAD factors, suggesting that the Dysphoria cluster may not be unique to PTSD. Diagnostic and theoretical implications of these results are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)