High rate deformation behavior and extraordinary energy absorption of carbon nanotube mats and glassy polymer thin films

We investigate the energy absorption characteristics and associated deformation behavior of free standing thin films using a micro-projectile impact test for two different materials: (1) multiwall carbon nanotubes (MWCNTs) and (2) glassy polystyrene. Films from 50-250nm thickness are impacted with silica microprojectiles at velocities from 300-900 m/s. The interconnected network of multiwall carbon nanotubes (MWCNT) sample while having quite modest quasi-static mechanical properties shows strong energy absorption at the extreme strain rates resulting from ballistic impact. As the spherical projectile engages the film, the bundles of MWCNT tubes straighten and translate into the impact region, dissipating the kinetic energy of the projectile via frictional interactions between tubes and stretching of the network, ultimately leading to fracture of principal tubes. The specific energy absorption depends on velocity and film thickness and can range up to 9 MJ/kg. For glassy, well entangled high molecular weight polystyrene, the impact of a supersonic micro-projectile initiates extensive crazing, yielding, and adiabatic heating leading to plastic flow of the load-bearing viscoelastic melt prior to film rupture and perforation. The less entangled, more mobile near-surface regions of these freestanding films favorably modify the deformation processes, increasing the specific energy absorption with decreased film thickness and increased impact velocity to impressive values of 2-3 MJ/kg for what is normally considered a brittle material. Please click Additional Files below to see the full abstract

Autonomous Materials Discovery Driven by Gaussian Process Regression with Inhomogeneous Measurement Noise and Anisotropic Kernels

A majority of experimental disciplines face the challenge of exploring large and high-dimensional parameter spaces in search of new scientific discoveries. Materials science is no exception; the wide variety of synthesis, processing, and environmental conditions that influence material properties gives rise to particularly vast parameter spaces. Recent advances have led to an increase in efficiency of materials discovery by increasingly automating the exploration processes. Methods for autonomous experimentation have become more sophisticated recently, allowing for multi-dimensional parameter spaces to be explored efficiently and with minimal human intervention, thereby liberating the scientists to focus on interpretations and big-picture decisions. Gaussian process regression (GPR) techniques have emerged as the method of choice for steering many classes of experiments. We have recently demonstrated the positive impact of GPR-driven decision-making algorithms on autonomously steering experiments at a synchrotron beamline. However, due to the complexity of the experiments, GPR often cannot be used in its most basic form, but rather has to be tuned to account for the special requirements of the experiments. Two requirements seem to be of particular importance, namely inhomogeneous measurement noise (input dependent or non-i.i.d.) and anisotropic kernel functions, which are the two concepts that we tackle in this paper. Our synthetic and experimental tests demonstrate the importance of both concepts for experiments in materials science and the benefits that result from including them in the autonomous decision-making process

Confirming the existence of π-allyl-palladium intermediates during the reaction of meta photocycloadducts with palladium(ii) compounds

The transient existence of π-allyl-palladium intermediates formed by the reaction of Pd(OAc)2 and anisole-derived meta photocycloadducts has been demonstrated using NMR techniques. The intermediates tended to be short-lived and underwent rapid reductive elimination of palladium metal to form allylic acetates, however this degradation process could be delayed by changing the reaction solvent from acetonitrile to chloroform

DNA-directed nanofabrication of high-performance carbon nanotube field-effect transistors

生物自组装结构具有精细的三维形貌，其关键结构参数小于光刻等传统纳米加工手段的分辨率极限。利用自组装的生物分子为加工模板，已经实现了金属、碳基、氧化物等材料的形貌可控合成。然而，基于生物模板的电学器件，其性能往往远落后于通过蚀刻或薄膜方法制备的同类器件，并且缺乏长程取向规整性，制约了生物模板在高性能器件中的应用。针对上述挑战，我校化学化工学院朱志教授课题组与北京大学孙伟研究员课题组、清华大学唐建石研究员课题组、美国国家标准与技术研究院郑明博士合作，探索了生物-碳纳米管复合界面及大面积取向排列的调控新方法。北京大学孙伟研究员团队长期从事核酸引导的精准纳米组装研究，厦门大学朱志教授团队长期从事微纳加工及微流控研究，双方紧密合作，优势互补，联合清华大学和美国国家标准与技术研究院等多团队联合攻关完成该工作。共同第一作者厦门大学化学化工学院2011协同创新中心博士研究生陈雅鸿负责了碳纳米管组装及大面积阵列化工作，孙伟研究员和朱志教授为论文的共同通讯作者。Biofabricated semiconductor arrays exhibit smaller channel pitches than existing lithographic feasibility. However, the metal ions within biolattices and the submicrometer dimensions of typical biotemplates result in both poor transport performance and small array uniformity. Using DNA-templated parallel carbon nanotube (CNT) arrays as model systems, we developed a rinsing-after-fixing approach to improve the key transport performance metrics by more than a factor of 10 folds over previous biotemplated field-effect transistors. We also used spatially confined placement of assembled CNT arrays within polymethyl methacrylate cavities to demonstrate centimeter-scale alignment. At the interface of high-performance electronics and biomolecular self-assembly, current approaches may enable scalable biotemplated electronics sensitive to local biological environments.W.S.,M.Z., Y.C., K.W., and Z.Z. acknowledge the National Science Foundation of China (Grant No. 21875003, 21991134, and 61621061) and PKU for financial support. Y.C., C.Y., and Z.Z. acknowledge the National Science Foundation of China (Grant No. 21775128, 21435004, and 21974113) for financial support. J.K.S., J.A.F., and M.Z. acknowledge NIST internal fund. 该研究工作得到国家自然科学基金等资助

Blood pressure in frail older adults: associations with cardiovascular outcomes and all-cause mortality

Background: Blood pressure (BP) management in frail older people is challenging. An randomised controlled trial of largely non-frail older people found cardiovascular and mortality benefit with systolic (S) BP target <120 mmHg. However, all-cause mortality by attained BP in routine care in frail adults aged above 75 is unclear. Objectives: To estimate observational associations between baseline BP and mortality/cardiovascular outcomes in a primary-care population aged above 75, stratified by frailty. Methods: Prospective observational analysis using electronic health records (clinical practice research datalink, n = 415,980). We tested BP associations with cardiovascular events and mortality using competing and Cox proportional-hazards models respectively (follow-up ≤10 years), stratified by baseline electronic frailty index (eFI: fit (non-frail), mild, moderate, severe frailty), with sensitivity analyses on co-morbidity, cardiovascular risk and BP trajectory. Results: Risks of cardiovascular outcomes increased with SBPs >150 mmHg. Associations with mortality varied between non-frail <85 and frail 75-84-year-olds and all above 85 years. SBPs above the 130-139-mmHg reference were associated with lower mortality risk, particularly in moderate to severe frailty or above 85 years (e.g. 75-84 years: 150-159 mmHg Hazard Ratio (HR) mortality compared to 130-139: non-frail HR = 0.94, 0.92-0.97; moderate/severe frailty HR = 0.84, 0.77-0.92). SBP <130 mmHg and Diastolic(D)BP <80 mmHg were consistently associated with excess mortality, independent of BP trajectory toward the end of life. Conclusions: In representative primary-care patients aged ≥75, BP <130/80 was associated with excess mortality. Hypertension was not associated with increased mortality at ages above 85 or at ages 75-84 with moderate/severe frailty, perhaps due to complexities of co-existing morbidities. The priority given to aggressive BP reduction in frail older people requires further evaluation.This article is freely available via Open Access. Click on the Publisher URL to access it via the publisher's site.J.M. is funded by a National Institute for Health Research (NIHR), Doctoral Research Fellowship DRF-2014-07-177 for this research project. This paper presents independent research funded by the National Institute for Health Research (NIHR). The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.published version, accepted version (12 month embargo), submitted versio

A large-scale genome-wide association study meta-analysis of cannabis use disorder

Summary Background Variation in liability to cannabis use disorder has a strong genetic component (estimated twin and family heritability about 50–70%) and is associated with negative outcomes, including increased risk of psychopathology. The aim of the study was to conduct a large genome-wide association study (GWAS) to identify novel genetic variants associated with cannabis use disorder. Methods To conduct this GWAS meta-analysis of cannabis use disorder and identify associations with genetic loci, we used samples from the Psychiatric Genomics Consortium Substance Use Disorders working group, iPSYCH, and deCODE (20 916 case samples, 363 116 control samples in total), contrasting cannabis use disorder cases with controls. To examine the genetic overlap between cannabis use disorder and 22 traits of interest (chosen because of previously published phenotypic correlations [eg, psychiatric disorders] or hypothesised associations [eg, chronotype] with cannabis use disorder), we used linkage disequilibrium score regression to calculate genetic correlations. Findings We identified two genome-wide significant loci: a novel chromosome 7 locus (FOXP2, lead single-nucleotide polymorphism [SNP] rs7783012; odds ratio [OR] 1·11, 95% CI 1·07–1·15, p=1·84 × 10−9) and the previously identified chromosome 8 locus (near CHRNA2 and EPHX2, lead SNP rs4732724; OR 0·89, 95% CI 0·86–0·93, p=6·46 × 10−9). Cannabis use disorder and cannabis use were genetically correlated (rg 0·50, p=1·50 × 10−21), but they showed significantly different genetic correlations with 12 of the 22 traits we tested, suggesting at least partially different genetic underpinnings of cannabis use and cannabis use disorder. Cannabis use disorder was positively genetically correlated with other psychopathology, including ADHD, major depression, and schizophrenia. Interpretation These findings support the theory that cannabis use disorder has shared genetic liability with other psychopathology, and there is a distinction between genetic liability to cannabis use and cannabis use disorder. Funding National Institute of Mental Health; National Institute on Alcohol Abuse and Alcoholism; National Institute on Drug Abuse; Center for Genomics and Personalized Medicine and the Centre for Integrative Sequencing; The European Commission, Horizon 2020; National Institute of Child Health and Human Development; Health Research Council of New Zealand; National Institute on Aging; Wellcome Trust Case Control Consortium; UK Research and Innovation Medical Research Council (UKRI MRC); The Brain & Behavior Research Foundation; National Institute on Deafness and Other Communication Disorders; Substance Abuse and Mental Health Services Administration (SAMHSA); National Institute of Biomedical Imaging and Bioengineering; National Health and Medical Research Council (NHMRC) Australia; Tobacco-Related Disease Research Program of the University of California; Families for Borderline Personality Disorder Research (Beth and Rob Elliott) 2018 NARSAD Young Investigator Grant; The National Child Health Research Foundation (Cure Kids); The Canterbury Medical Research Foundation; The New Zealand Lottery Grants Board; The University of Otago; The Carney Centre for Pharmacogenomics; The James Hume Bequest Fund; National Institutes of Health: Genes, Environment and Health Initiative; National Institutes of Health; National Cancer Institute; The William T Grant Foundation; Australian Research Council; The Virginia Tobacco Settlement Foundation; The VISN 1 and VISN 4 Mental Illness Research, Education, and Clinical Centers of the US Department of Veterans Affairs; The 5th Framework Programme (FP-5) GenomEUtwin Project; The Lundbeck Foundation; NIH-funded Shared Instrumentation Grant S10RR025141; Clinical Translational Sciences Award grants; National Institute of Neurological Disorders and Stroke; National Heart, Lung, and Blood Institute; National Institute of General Medical Sciences.Peer reviewe

Shared genetic risk between eating disorder- and substance-use-related phenotypes:Evidence from genome-wide association studies

First published: 16 February 202

DAN (NBL1) promotes collective neural crest migration by restraining uncontrolled invasion

Neural crest cells are both highly migratory and significant to vertebrate organogenesis. However, the signals that regulate neural crest cell migration remain unclear. Here, we test the function of DAN, a BMP antagonist we detected by analysis of chick cranial mesoderm. Our analysis shows that, prior to neural crest cell exit from the hindbrain, DAN is expressed in the mesoderm, then it becomes absent along cell migratory pathways. Cranial neural crest and metastatic melanoma cells avoid DAN protein stripes in vitro. Addition of DAN reduces the speed of migrating cells, in vivo and in vitro respectively. In vivo loss-of-function of DAN results in enhanced neural crest cell migration by increasing speed and directionality. Computer model simulations support the hypothesis that DAN restrains cell migration by regulating cell speed. Taken together, our results identify DAN as a novel factor that inhibits uncontrolled neural crest and metastatic melanoma invasion and promotes collective migration in a manner consistent with inhibition of BMP signaling

Transancestral GWAS of alcohol dependence reveals common genetic underpinnings with psychiatric disorders

Liability to alcohol dependence (AD) is heritable, but little is known about its complex polygenic architecture or its genetic relationship with other disorders. To discover loci associated with AD and characterize the relationship between AD and other psychiatric and behavioral outcomes, we carried out the largest genome-wide association study to date of DSM-IV-diagnosed AD. Genome-wide data on 14,904 individuals with AD and 37,944 controls from 28 case-control and family-based studies were meta-analyzed, stratified by genetic ancestry (European, n = 46,568; African, n = 6,280). Independent, genome-wide significant effects of different ADH1B variants were identified in European (rs1229984; P = 9.8 x 10(-13)) and African ancestries (rs2066702; P = 2.2 x 10(-9)). Significant genetic correlations were observed with 17 phenotypes, including schizophrenia, attention deficit-hyperactivity disorder, depression, and use of cigarettes and cannabis. The genetic underpinnings of AD only partially overlap with those for alcohol consumption, underscoring the genetic distinction between pathological and nonpathological drinking behaviors.Peer reviewe

Novel Techniques for Optical Characterization of Single-Walled Carbon Nanotube Samples

Photoluminescence spectroscopy has emerged as a powerful tool for characterizing the structure and optical properties of single-walled carbon nanotube (SWCNT) samples. This thesis will discuss the development and application of new fluorescence-based methods designed to fully characterize bulk SWCNT suspensions by length and structural composition. An efficient new method is demonstrated to measure length distributions of aqueous SWCNT samples by analyzing the diffusional motions of many individual nanotubes captured in sequences of short-wave infrared (SWIR) fluorescence images. This method, termed length analysis by nanotube diffusion (LAND), provides distributions in very good agreement with those obtained by conventional atomic force microscopy analysis. A novel microscopy technique is described to measure the peak emission wavelengths of many individual nanotubes without the use of a spectrometer. We exploit the chromatic aberration of an objective lens to deduce emission wavelength from focal depth. Spectral measurements successfully reproduce bulk emission spectra and also provide relative abundances of specific SWCNT structures. A new approach is applied to find nanotube concentrations by directly counting SWCNTs in SWIR fluorescence images. Concentrations are used to rigorously determine absolute absorption cross sections for the E11 and E22 electronic transitions of the (6,5), (7,5), (7,6), (8,6), (8,7) and (9,7) SWCNT species. It is found that the absorption cross section per carbon atom decreases with increasing nanotube diameter. Finally, the spectral analysis of fluorescence fluctuations (SAFF) method is developed and used to characterize SWCNT samples by structural composition, sample quality, and aggregation state. Fluorescence spectra are sequentially measured from small volumes of slowly flowing dilute samples and the intensity fluctuations resulting from small statistical variations in nanotube concentration are analyzed. The ratio of the squared mean intensity to variance of intensity is plotted as a function of wavelength to give a relative concentration spectrum, reflecting the number of particles contributing to the emission at each wavelength. In addition, mean intensity is divided by abundance to obtain fluorescence efficiency values for all species represented in the sample. Intensity correlations between different emission wavelengths are used to detect the formation of loose nanotube aggregates and also study the broadening components of individual emission line widths