45 research outputs found
Gate induced monolayer behavior in twisted bilayer black phosphorus
Optical and electronic properties of black phosphorus strongly depend on the
number of layers and type of stacking. Using first-principles calculations
within the framework of density functional theory, we investigate the
electronic properties of bilayer black phosphorus with an interlayer twist
angle of 90. These calculations are complemented with a simple
model which is able to capture most of the low energy
features and is valid for arbitrary twist angles. The electronic spectrum of
90 twisted bilayer black phosphorus is found to be x-y isotropic in
contrast to the monolayer. However x-y anisotropy, and a partial return to
monolayer-like behavior, particularly in the valence band, can be induced by an
external out-of-plane electric field. Moreover, the preferred hole effective
mass can be rotated by 90 simply by changing the direction of the
applied electric field. In particular, a +0.4 (-0.4) V/{\AA} out-of-plane
electric field results in a 60\% increase in the hole effective mass
along the y (x) axis and enhances the ()
ratio as much as by a factor of 40. Our DFT and
simulations clearly indicate that the twist angle in combination with an
appropriate gate voltage is a novel way to tune the electronic and optical
properties of bilayer phosphorus and it gives us a new degree of freedom to
engineer the properties of black phosphorus based devices.Comment: 8 pages, 8 figure
Effect of a novel commercial potassium-oxalate containing tooth-desensitizing mouthrinse on the microhardness of resin composite restorative materials with different monomer compositions
The effects of mouthrinses on dental resin composites have been investigated extensively. However, there is little information available regarding the effects of ‘newly developed mouthrinse’ formulations on the microhardness of different monomer based composite systems. Therefore, the aim of this study was to investigate the effect of a novel potassium-oxalate containing desensitizing mouthrinse on the microhardness of different monomer based composite materials.
A hundred and twenty specimens (6mm in diameter and 2mm in height) were prepared for composite resin groups (methacrylate based, DX-511 monomer based and silorane monomer based) and for storage solution groups (artificial saliva and potassium oxalate-containing tooth-desensitizing mouthrinse). After allowing post-polimerization the baseline Knoop microhardness measurements for all specimens were recorded. The specimens were stored in 20 mL mouthwash and artificial saliva for 12 hours at 37ºC. The post-immersion microhardness values of all specimens were also recorded. Data were subjected to ANOVA/Scheffe’s test at a significance level of 0.05. The intra group (pre and post immersion values) comparison of the mean microhardness values of the specimens was done using Wilcoxon signed rank test.
The microhardness of the silorane based composite was not affected significantly (p>0.05). The hardness values of the DX-511 monomer based composite and the methacrylate based composite exhibited a slight but not significant microhardness change compared to the baseline values (p>0.05).
Studies reported that the effect of mouthrinses on microhardness changes of composite resins may be material dependent, and the hardness change susceptibility of a restorative material may be attributed to its resin matrix or filler type. However, dental monomers as well as the oral care products have an ever-evolving technology and future studies should consider newer products. Potassium oxalate containing mouthrinses, especially alcohol-free ones, may be used safely with dental composites with newly developed low-shrink monomer compositions
Simultaneous multi-slice imaging reduces sensitivity of local-SAR to patient motion at 7T
This study investigates the effect of within-scan patient motion on local-SAR for simultaneous multi-slice (SMS) imaging at 7T. A virtual body model was simulated at 104 different positions. 1-/2-/3-spokes pulses were designed to excite a region of 60 slices covering the cerebellum and the brain, using SMS-factors of 1 through 5. Local-SAR was observed to increase by up to 2.75-fold due to patient motion. Pulses with higher SMS-factors were up to 50% less sensitive against changes in local-SAR due to patient motion, compared to SMS:1 pulses. Pulses with higher SMS-factors yielded more consistent local-SAR throughout the scan
The International Workshop on Osteoarthritis Imaging Knee MRI Segmentation Challenge: A Multi-Institute Evaluation and Analysis Framework on a Standardized Dataset
Purpose: To organize a knee MRI segmentation challenge for characterizing the
semantic and clinical efficacy of automatic segmentation methods relevant for
monitoring osteoarthritis progression.
Methods: A dataset partition consisting of 3D knee MRI from 88 subjects at
two timepoints with ground-truth articular (femoral, tibial, patellar)
cartilage and meniscus segmentations was standardized. Challenge submissions
and a majority-vote ensemble were evaluated using Dice score, average symmetric
surface distance, volumetric overlap error, and coefficient of variation on a
hold-out test set. Similarities in network segmentations were evaluated using
pairwise Dice correlations. Articular cartilage thickness was computed per-scan
and longitudinally. Correlation between thickness error and segmentation
metrics was measured using Pearson's coefficient. Two empirical upper bounds
for ensemble performance were computed using combinations of model outputs that
consolidated true positives and true negatives.
Results: Six teams (T1-T6) submitted entries for the challenge. No
significant differences were observed across all segmentation metrics for all
tissues (p=1.0) among the four top-performing networks (T2, T3, T4, T6). Dice
correlations between network pairs were high (>0.85). Per-scan thickness errors
were negligible among T1-T4 (p=0.99) and longitudinal changes showed minimal
bias (<0.03mm). Low correlations (<0.41) were observed between segmentation
metrics and thickness error. The majority-vote ensemble was comparable to top
performing networks (p=1.0). Empirical upper bound performances were similar
for both combinations (p=1.0).
Conclusion: Diverse networks learned to segment the knee similarly where high
segmentation accuracy did not correlate to cartilage thickness accuracy. Voting
ensembles did not outperform individual networks but may help regularize
individual models.Comment: Submitted to Radiology: Artificial Intelligence; Fixed typo
Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis
BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London
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