铌/硅化物原位自生复合材料微米棒状向纳米层片状共晶组织转变及其硬化行为

以Nb−18Si(摩尔分数,%)复合材料为研究对象,分析共晶组织几何形态对电子束表面熔化(EBSM)快速凝固条件的响应机理及其对材料硬度的影响规律。研究结果表明,Nbss/Nb3Si共晶在电弧熔炼凝固条件下以棒状形态为主,而在EBSM凝固条件下转变为层片状形态。利用原子尺度的扫描透射电子显微镜(STEM)和近原子尺度的三维原子探针(APT)对样品进行表征,获得纳米Nbss/Nb_(3)Si共晶的三维层片状结构特征及其组分。与棒状共晶相比,EBSM凝固条件下形成的层片状共晶组织显著细化(共晶间距为39.5 nm),Nbss相体积分数大幅增加(约41%)。随着显微组织由微米棒状共晶转变为纳米层片状共晶,材料硬度显著增加,达到13.9 GPa。

Discrimination of pp solar neutrinos and^(14)C double pile-up events in a large-scale LS detector

As a unique probe,the precision measurement of pp solar neutrinos is important for studying the sun’s energy mechanism as it enables monitoring the thermodynamic equilibrium and studying neutrino oscillations in the vacuum-dominated region.For a large-scale liquid scintillator detector,a bottleneck for pp solar neutrino detection is the pile-up events of intrinsic14C decay.This paper presents a few approaches to discriminating between pp solar neutrinos and ^(14)C pile-up events by considering the differences in their time and spatial distributions.In this study,a Geant4-based Monte Carlo simulation is conducted.Multivariate analysis and deep learning technology are adopted to investigate the capability of ^(14)C pile-up reduction.The BDTG (boosted decision trees with gradient boosting) model and VGG network demonstrate good performance in discriminating pp solar neutrinos and ^(14)C double pile-up events.Under the ^(14)C concentration assumption of 5×10-18g/g,the signal significance can achieve 10.3 and 15.6 using the statistics of only one day.In this case,the signal efficiency for discrimination using the BDTG model while rejecting 99.18% ^(14)C double pile-up events is 51.1%,and that for the case where the VGG network is used while rejecting 99.81%of the ^(14)C double pile-up events is 42.7%.

Relationship between acute stress and sleep disorder in grass-root military personnel:Mediating effect of social support

Background: To explore the relationship between acute stress, social support and sleep disorder in grass-root military personnel, and construct the relational model through structural equation modeling. Methods: A total of 2,411 grass-root military personnel were randomly selected by cluster sampling, and administered the Chinese Military Personnel Sleep Disorder Scale, Military Acute Stress Scale and Social Support Rating Scale.Results: The total score of acute stress scale was positively correlated with the total score and factor scores of sleep disorder scale(r=0.209~0.465, P【0.01); The total score of social support scale was positively correlated with the total score of acute stress scale and the total score and factor scores of sleep disorder scale(r=0.356~0.537, P【0.01). The analysis of mediating effects showed that lack of social support partially mediated between acute stress and the factors of sleep disorder. The analysis of structural equation model showed that acute stress not only had a direct effect on sleep disorder(the path coefficient was 0.29, P=0.000), but also on lack of social support(the path coefficient was 0.39, P=0.000); lack of social support had a direct effect on sleep disorder(the path coefficient was 0.48, P=0.000).Conclusions: Acute stress and lack of social support are two significant factors of sleep disorder in grass-root military personnel. Well-established social support could alleviate sleep disorder induced by acute stress. Lack of social support was a partial mediator between acute stress and sleep disorder.

Priming strategies for controlling stem cell fate: Applications and challenges in dental tissue regeneration

Mesenchymal stromal cells(MSCs)have attracted intense interest in the field of dental tissue regeneration.Dental tissue is a popular source of MSCs because MSCs can be obtained with minimally invasive procedures.MSCs possess distinct inherent properties of self-renewal,immunomodulation,proangiogenic potential,and multilineage potency,as well as being readily available and easy to culture.However,major issues,including poor engraftment and low survival rates in vivo,remain to be resolved before large-scale application is feasible in clinical treatments.Thus,some recent investigations have sought ways to optimize MSC functions in vitro and in vivo.Currently,priming culture conditions,pretreatment with mechanical and physical stimuli,preconditioning with cytokines and growth factors,and genetic modification of MSCs are considered to be the main strategies;all of which could contribute to improving MSC efficacy in dental regenerative medicine.Research in this field has made tremendous progress and continues to gather interest and stimulate innovation.In this review,we summarize the priming approaches for enhancing the intrinsic biological properties of MSCs such as migration,antiapoptotic effect,proangiogenic potential,and regenerative properties.Challenges in current approaches associated with MSC modification and possible future solutions are also indicated.We aim to outline the present understanding of priming approaches to improve the therapeutic effects of MSCs on dental tissue regeneration.

Therapeutic potential of dental pulp stem cells and their derivatives:Insights from basic research toward clinical applications

For more than 20 years,researchers have isolated and identified postnatal dental pulp stem cells(DPSCs)from different teeth,including natal teeth,exfoliated deciduous teeth,healthy teeth,and diseased teeth.Their mesenchymal stem cell(MSC)-like immunophenotypic characteristics,high proliferation rate,potential for multidirectional differentiation and biological features were demonstrated to be superior to those of bone marrow MSCs.In addition,several main application forms of DPSCs and their derivatives have been investigated,including stem cell injections,modified stem cells,stem cell sheets and stem cell spheroids.In vitro and in vivo administration of DPSCs and their derivatives exhibited beneficial effects in various disease models of different tissues and organs.Therefore,DPSCs and their derivatives are regarded as excellent candidates for stem cell-based tissue regeneration.In this review,we aim to provide an overview of the potential application of DPSCs and their derivatives in the field of regenerative medicine.We describe the similarities and differences of DPSCs isolated from donors of different ages and health conditions.The methodologies for therapeutic administration of DPSCs and their derivatives are introduced,including single injections and the transplantation of the cells with a support,as cell sheets,or as cell spheroids.We also summarize the underlying mechanisms of the regenerative potential of DPSCs.

Analysis of electromagnetic pulses generated from ultrashort laser irradiation of solid targets at CLAPA

Electromagnetic pulses(EMPs)produced by the interaction of a TW femtosecond laser with solid targets at the Compact Laser Plasma Accelerator(CLAPA)are measured and interpreted.The statistical results confirm that the intensities of the EMPs are closely related to both target material and thickness.The signal of the titanium target is more abundant than that of the copper target with the same thickness,and the intensity of EMP is positively correlated with the target thickness for aluminium foil.With the boosted EMP radiations,the energy of accelerated protons is also simultaneously enhanced.In addition,EMPs emitted from the front of the target exceed those from the rear,which are also pertinent to the specific target position.The resonant waveforms in the target chamber are analyzed using the fast Fourier transform,and the local resonance and the attenuation lead to changes of the frequency spectra of EMPs with variation of detecting positions,which is well supported by the modeling results.The findings are beneficial to gaining insight into the mechanism of EMP propagation in a typical target chamber and providing more information for EMP shielding design.

Hypothermia selectively protects the anterior forebrain mesocircuit during global cerebral ischemia

Hypothermia is an important protective strategy against global cerebral ischemia following cardiac arrest.However,the mechanisms of hypothermia underlying the changes in different regions and connections of the brain have not been fully elucidated.This study aims to identify the metabolic nodes and connection integrity of specific brain regions in rats with global cerebral ischemia that are most affected by hypothermia treatment.18F-fluorodeoxyglucose positron emission tomography was used to quantitatively determine glucose metabolism in different brain regions in a rat model of global cerebral ischemia established at 31–33℃.Diffusion tensor imaging was also used to reconstruct and explore the brain connections involved.The results showed that,compared with the model rats established at 37–37.5℃,the rat models of global cerebral ischemia established at 31–33℃had smaller hypometabolic regions in the thalamus and primary sensory areas and sustained no obvious thalamic injury.Hypothermia selectively preserved the integrity of the anterior forebrain mesocircuit,exhibiting protective effects on the brain during the global cerebral ischemia.The study was approved by the Institutional Animal Care and Use Committee at Capital Medical University(approval No.XW-AD318-97-019)on December 15,2019.

Reconstruction of a muon bundle in the JUNO central detector

The Jiangmen Underground Neutrino Observatory(JUNO)is a multi-purpose neutrino experiment.One of the main goals is to determine the neutrino mass ordering by precisely measuring the energy spectrum of reactor antineutrinos.For the detection of reactor antineutrinos,cosmogenic backgrounds,such as^(9)Li/^(8)He and fast neutrons induced by cosmic muons,should be rejected carefully by applying muon veto cuts,which require good muon track reconstruction.With a 20-kton liquid scintillator detector,the simulation shows the proportion of muon bundles(muon multiplicity≥2)to be approximately 8%in JUNO,whereas its reconstruction has been rarely discussed in previous experiments.This study proposes an efficient algorithm for muon track reconstruction based on the charge response of a photomultiplier tube array.This is the first reconstruction of muon bundles in a large-volume liquid scintillator detector.In addition,the algorithm shows good performance and potential for reconstruction for both a single muon and double muons(muon multiplicity=2).The spatial resolution of a single-muon reconstruction was20 cm,and the angular resolution was 0.5°.For doublemuon reconstruction,the spatial and angular resolutions could be 30 cm and 1.0°,respectively.Moreover,this paper also discusses muon classification and the veto strategy.

Mechanism of calcium hydroxide inhibiting methicillin resistant Staphylococcus aureus

Objective:To investigate the inhibitory effect of calcium hydroxide on methicillin-resistant Staphylococcus aureus and the related inhibition mechanism.Methods:To determine the minimum inhibitory concentration of calcium hydroxide using microplate dilution method;to compare the effects of calcium hydroxide at 8MIC,MIC,1/4MIC and 0 concentrations on MRSA using growth curve method;to determine the effects of calcium hydroxide on the cell membrane of methicillin-resistant Staphylococcus aureus using calcium xanthophyll and propidium iodide fluorescence staining The effect of calcium hydroxide on the morphology of methicillin-resistant Staphylococcus aureus was observed by scanning electron microscopy;the inhibition mechanism of calcium hydroxide on MRSA was investigated by sodium dodecyl sulfate polyacrylamide gel electrophoresis of protein bands.Results:The MIC of calcium hydroxide on MRSA was 3.125 mg/mL;the fluorescence intensity showed significant changes after co-culture of calcium hydroxide with bacteria;MRSA appeared to be significantly crumpled and broken in the presence of calcium hydroxide;the SDS-PAGE experimental bands indicated that the protein inside the bacteria decreased accordingly with the increase of calcium hydroxide concentration.Conclusion:Calcium hydroxide has a significant inhibitory effect on the growth of MRSA,and its bactericidal mechanism may be related to the destruction of bacterial body structure.

Preparation and characterization of hemihydrate calcium sulfate-calcium hydroxide composite bone repair materials

Objective:To prepare a bone repair material with certain mechanical strength and biological activity,this paper used calcium sulfate hemihydrate(CSH)powder compounded with calcium hydroxide(Ca(OH)2)powder to prepare a bone repair scaffold material for physicochemical property characterization and testing.Methods:The physical and chemical properties and characterization of the dried and cured bone repair materials were determined by Fourier infrared spectroscopy(FT-IR),X-ray diffraction(XRD),and scanning electron microscopy;Universal material testing machine to determine the mechanical and mechanical strength of composite materials.Results:XRD showed that the structure of the composite material phase at 5%concentration was calcium sulfate hemihydrate and calcium hydroxide after hydration.The FT-IR and XRD analyses were consistent.Scanning electron microscopy(SEM)results showed that calcium hydroxide was uniformly dispersed in the hemihydrate calcium sulfate material.0%,1%,5%,and 10%specimen groups had compressive strengths of 3.86±3.1,5.27±1.28,8.22±0.96,and 14.4±3.28 MPa.10%addition of calcium hydroxide significantly improved the mechanical strength of the composites,but also reduced the the porosity of the material.Conclusion:With the addition of calcium hydroxide,the CSH-Ca(OH)2 composite was improved in terms of mechanical material and is expected to be a new type of bone repair material.

A new risk stratification score for patients with suspected cardiac chest pain in emergency departments,based on machine learning

To the Editor:Chest pain is one of the most common complaints for patients attending emergency departments(EDs)globally.It is important to accurately stratify risk of possible acute coronary syndrome(ACS)for these patients.[1]Several risk stratification scores such as thrombolysis in myocardial infarction(TIMI),global registry for acute coronary events(GRACE),Banach and HEART are helpful.[2]Previous research in our setting compared these four scores and found that the HEART score,with a C-statistic of 0.731,was the best for predicting 7-day major adverse cardiac events(MACE)The purpose of this study was to develop risk stratification prediction models for 7-day MACE in patients with chest pain,utilizing machine learning algorithms such as eXtreme Gradient Boosting(XGBoost),Support Vector Machine(SVM).