Tuning the mechanical properties of silicene nanosheet by auxiliary cracks: a molecular dynamics study

Silicene has become a topic of interest nowadays due to its potential application in various electro-mechanical nanodevices. In our previous work on silicene, fracture stresses of single crystal and polycrystalline silicene have been investigated. Existence of defects in the form of cracks reduces the fracture strength of silicene nanosheets to a great extent. In this study, an engineering way has been proposed for improving the fracture stress of silicene nanosheets with a pre-existing crack by incorporating auxiliary cracks symmetrically in a direction perpendicular to the main crack. We call this mechanism the “Failure shielding mechanism”. An extensive molecular dynamics simulation based analysis has been performed to capture the atomic level auxiliary crack-main crack interactions. It is found that the main crack tip stress distribution is significantly changed with the presence of auxiliary cracks for loading along both armchair and zigzag directions. The effects of temperature and the crack propagation speed of silicene have also been studied. Interestingly, in the case of loading along the zigzag direction, SW defect formation is observed at the tip of main crack. This leads to a reduction of the tip stress resulting in a more prominent failure shielding in case of zigzag loading than in armchair loading. Moreover, the position and length of the cracks as well as the loading directions have significant impacts on the tip stress distribution. Finally, this study opens the possibilities of strain engineering for silicene by proposing an engineering way to tailor the fracture strength of silicene.

Inclusion of auxiliary cracks increases the fracture stress of silicene nanosheets with a pre existing crack.     

Evaluation of residual stress and texture in isotope based Mg11B2 superconductor using neutron diffraction

Magnesium diboride (MgB₂) superconducting wires have demonstrated commercial potential to replace niobium–titanium (NbTi) in terms of comparable critical current density. Its higher critical temperature makes MgB₂ wire suitable for liquid-helium-free operation. We recently reported boron-11 isotope-based low-activation Mg¹¹B₂ superconducting wire with decent critical current density appropriate for low-cost superconducting fusion magnets. In this study, we have mainly focused on the neutron diffraction technique to measure the residual stress in Mg¹¹B₂ superconducting wire for the first time. The residual stress state was given qualitative and quantitative interpretation in terms of micro- and macrostress generation mechanisms based on the isotropic model confirmed by neutron texture measurements. The relationship between the stress/strain state in the wire and the transport critical current density is also discussed. This investigation could pave the way to further enhancement of the critical current density of low-activation Mg¹¹B₂ superconducting wires suitable for next-generation fusion grade magnets.

Magnesium diboride (MgB₂) superconducting wires have demonstrated commercial potential to replace niobium–titanium (NbTi) in terms of comparable critical current density.     

Validating the 8 CPCSSN Case Definitions for Chronic Disease Surveillance in a Primary Care Database of Electronic Health Records

PURPOSE

The Canadian Primary Care Sentinel Surveillance Network (CPCSSN) is Canada’s first national chronic disease surveillance system based on electronic health record (EHR) data. The purpose of this study was to develop and validate case definitions and case-finding algorithms used to identify 8 common chronic conditions in primary care: chronic obstructive pulmonary disease (COPD), dementia, depression, diabetes, hypertension, osteoarthritis, parkinsonism, and epilepsy.

METHODS

Using a cross-sectional data validation study design, regional and local CPCSSN networks from British Columbia, Alberta (2), Ontario, Nova Scotia, and Newfoundland participated in validating EHR case-finding algorithms. A random sample of EHR charts were reviewed, oversampling for patients older than 60 years and for those with epilepsy or parkinsonism. Charts were reviewed by trained research assistants and residents who were blinded to the algorithmic diagnosis. Sensitivity, specificity, and positive and negative predictive values (PPVs, NPVs) were calculated.

RESULTS

We obtained data from 1,920 charts from 4 different EHR systems (Wolf, Med Access, Nightingale, and PS Suite). For the total sample, sensitivity ranged from 78% (osteoarthritis) to more than 95% (diabetes, epilepsy, and parkinsonism); specificity was greater than 94% for all diseases; PPV ranged from 72% (dementia) to 93% (hypertension); NPV ranged from 86% (hypertension) to greater than 99% (diabetes, dementia, epilepsy, and parkinsonism).

CONCLUSIONS

The CPCSSN diagnostic algorithms showed excellent sensitivity and specificity for hypertension, diabetes, epilepsy, and parkinsonism and acceptable values for the other conditions. CPCSSN data are appropriate for use in public health surveillance, primary care, and health services research, as well as to inform policy for these diseases.     

Accuracy of peak-power compensation in fiber-guided and free-space acoustic-resolution photoacoustic microscopy

Acoustic resolution photoacoustic microscopy (AR-PAM) has gained much attention in the past two decades due to its high contrast, scalable resolution, and relatively higher imaging depth. Multimode optical fibers (MMF) are extensively used to transfer light to AR-PAM imaging scan-head from the laser source. Typically, peak-power-compensation (PPC) is used to reduce the effect of pulse-to-pulse peak-power variation in generated photoacoustic (PA) signals. In MMF, the output intensity profile fluctuates due to the coherent nature of light and mode exchange caused by variations in the bending of the fibers during scanning. Therefore, using a photodiode (PD) to capture a portion of the total power of pulses as a measure of illuminated light on the sample may not be appropriate for accurate PPC. In this study, we have investigated the accuracy of PPC in fiber-guided and free-space AR-PAM systems. Experiments were conducted in the transparent and highly scattering medium. Based on obtained results for the MMF-based system, to apply PPC to the generated PA signals, tightly focused light confocal with the acoustic focus in a transparent medium must be used. In the clear medium and highly focused illumination, enhancement of about 45% was obtained in the homogeneity of an optically homogeneous sample image. In addition, it is shown that, as an alternative, free-space propagation of the laser pulses results in more accurate PPC in both transparent and highly scattering mediums. In free-space light transmission, enhancement of 25-75% was obtained in the homogeneity of the optically homogeneous sample image.     

Use of stents to treat kinks causing obstruction in a left internal mammary artery graft

Left internal mammary arteries (LIMA) are used routinely as grafts to the left anterior descending coronary artery (LAD) in selected patients undergoing coronary artery bypass graft (CABG) surgery because of better long-term patency rates. Pathology other than fibrointimal hyperplasia, accelerated atherosclerosis, or thrombus can sometimes cause obstructive lesions in such grafts. This report illustrates a kink in a LIMA graft to the LAD causing an obstructive lesion shortly after surgery and describes the subsequent management of this lesion with intracoronary stents. Cathet. Cardiovasc. Intervent. 46:223–226, 1999. © 1999 Wiley-Liss, Inc.     

Morphologic Studies of the Placenta and Autopsy Findings in Neonatal-onset Glutaric Acidemia Type II

A case of neonatal-onset glutaric acidemia type II with electron-transfer flavoprotein (ETF) deficiency is presented. The morphological pattern of disease in the male infant included hypospadias, cryptorchidism, bilateral 13 ribs, nuclear cataract, cystic dysplasia of kidneys, lipid accumulation in the liver and renal tubular epithelium, and immature brain with white matter gliosis. The morphologic examination of the placenta revealed features of delayed maturation, including large-for-gestational-age size and abundant immature intermediate villi with cellular syncytiotrophoblast, persistent villous cytotrophoblast, and decreased syncytial knots. In addition, immature intermediate villi showed exaggeration of lacunar interstitial spaces consistent with nonhydropic villous edema. Marked lipid accumulation was seen within extravillous trophoblasts of placental septa and cell islands. Light lipid accumulation was also noted within fibroblasts of stem villi. These findings suggest that in glutaric acidemia type II, fatty acid oxidation could also be affected in the placenta.