Laser-induced plasma formation in water with up to 400 mJ double-pulse LIBS

Double-pulse LIBS is a promising technique for deep-sea applications.LIBS measurements in shallow water with up to 400 mJ each pulse were done to select laser parameters which promote optimized spectral line emission from plasma even at elevated pressures,where line broadening until loss of most of the spectral information can occur.Optical emission spectroscopy,using a Czerny-Turner spectrometer,has been applied to investigate the dependence of the emitted radiation on laser parameters and hydrostatic pressure.It has been found,that higher laser pulse energies,especially with short pulse delay as required in high water pressure,can also have an adverse effect on the measured spectrum.

Analysis of Aluminum Alloy Double-Pulse MIG Welding Arc Signal Characteristics Based on Broadband Mode Decomposition

Welding voltage and current in arc signals are directly related to arc stability and welding quality.Process experiments with different parameters were organized according to the orthogonal experimental design method by constructing an aluminum alloy double-pulse metal inert gas(MIG)welding arc electric signal test platform.The data acquisition system of the aluminum alloy MIG welding process was established to obtain real-time arc signal information reflecting the welding process.The aluminum alloy’s collected double-pulse arc current signals are decomposed adaptively by broadband mode decomposition(BMD).The direct current(DC)signal,pulse signal,distortion signal,ripple signal,and noise signal are separated and extracted,and the composite multiscale fuzzy entropy(CMFE)is calculated for the component set of the electrical signal.The experimental results show that the current waveform obtained by the double-pulse MIG welding current signal is consistent with the corresponding weld forming diagram.Simultaneously,the composite multiscale fuzzy entropy is calculated for the arc characteristic parameters.The rationality of matching process parameters and arc stability of aluminum alloy’s double-pulse MIG welding were evaluated.

Convergence Phenomenon with Fourier Series of tg(x2)and Alike

The Fourier series of the 2π-periodic functions tg(x2)and 1sin(x)and some of their relatives (first of their integrals) are investigated and illustrated with respect to their convergence. These functions are Generalized functions and the convergence is weak convergence in the sense of the convergence of continuous linear functionals defining them. The figures show that the approximations of the Fourier series possess oscillations around the function which they represent in a broad band embedding them. This is some analogue to the Gibbs phenomenon. A modification of Fourier series by expansion in powers cosn(x)for the symmetric part of functions and sin(x)cosn−1(x)for the antisymmetric part (analogous to Taylor series) is discussed and illustrated by examples. The Fourier series and their convergence behavior are illustrated also for some 2π-periodic delta-function-like sequences connected with the Poisson theorem showing non-vanishing oscillations around the singularities similar to the Gibbs phenomenon in the neighborhood of discontinuities of functions. .

Effect of welding current on morphology and microstructure of Al alloy T-joint in double-pulsed MIG welding

The effect of current on the morphology of Al alloy T-joint in double-pulsed metal inert gas（DP-MIG） welding process was investigated by simulation and experiment.A three-dimensional finite element model and the DP-MIG heat source of double-ellipsoidal volumetric model were developed to simulate the temperature and stress fields under different welding conditions.The macro-morphology and microstructure of welding joints at the corresponding currents were observed in the experiment.The results show that the best condition is at an average current of 90 A and current difference of 40 A,when the maximum temperature is 200 °C higher than the fusion points,with the temperature difference of about 100 °C and stress change of 10 MPa between thermal pulse and thermal base.Under these conditions,Al alloy T-joint with proper fusion condition has smooth fish-scale welding appearance and finer microstructure.Furthermore,the thermal curves and stress distribution in the experiment are consistent with those in the simulation,verifying the precision of the welding simulation.

Application of Stand-off Double-Pulse Laser-Induced Breakdown Spectroscopy in Elemental Analysis of Magnesium Alloy

In this study, a stand-off and collinear double pulse laser-induced breakdown spectroscopy （DP LIBS） system was designed, and the magnesium alloy samples at a distance of 2.5 m away from the LIBS system were measured. The effect of inter-pulse delay on spectra was studied, and the signal enhancement was observed compared to the single pulse LIBS （SP LIBS）. The morphology of the ablated crater on the sample indicated a higher efficiency of surface pretreatment in DP LIBS. The calibration curves of Ytterbium （Y） and Zirconium （Zr） were investigated. The square of the correlation coefficient of the calibration curve of element Y reached up to 0.9998.

Re-Heating Effect on the Enhancement of Plasma Emission Generated from Fe Under Femtosecond Double-Pulse Laser Irradiation

In this paper, we present a study on the effect of inter-pulse delay using femtosecond double-pulse laser-induced breakdown spectroscopy in a collinear geometry. The temporal evolution of spectral intensity is performed for the lines of Fe I 423.60 nm, Fe I 425.08 nm and Fe I 427.18 nm. It is found that, by selecting appropriate inter-pulse delay, the signal enhancement can be significantly increased compared with the single-pulse case. A three-fold enhancement in the current experiment is obtained. The plasma temperature and electron density are also investigated based on the theory of Boltzmann plot and Stark broadening. We attribute the main mechanism for emission enhancement to the plasma re-heating effect.

Correction of dynamic Brazilian disc tensile strength of rocks under preloading conditions considering the overload phenomenon and invoking the Griffith criterion

Dynamic tensile failure is a common phenomenon in deep rock practices,and thus accurately evaluating the dynamic tensile responses of rocks under triaxial pressures is of great significance.The Brazilian disc(BD)test is the suggested method by the International Society for Rock Mechanics and Rock Engineering(ISRM)for measuring both the static and dynamic tensile strengths of rock-like materials.However,due to the overload phenomenon and the complex preloading conditions,the dynamic tensile strengths of rocks measured by the BD tests tend to be overestimated.To address this issue,the dynamic BD tensile strength(BTS)of Fangshan marble(FM)under different preloading conditions were measured through a triaxial split Hopkinson pressure bar(SHPB).The fracture onset in BD specimen was captured through a strain gage around the disc center.The discrepancy between the traditional tensile strength(TTS,determined by the peak load P_(f) of the BD specimen)and the nominal tensile strength(NTS,obtained from the load P_(i) when the diametral fracture commences in the tested BD specimen)was applied to quantitatively evaluating the overload phenomenon.The Griffith criterion was used to rectify the calculation of the tensile stress at the disc center under triaxial stress states.The results demonstrate that the overload ratio(s)increases with the loading rate(σ)and decreases with the hydrostatic pressure(σ_(s)).The TTS corrected by the Griffith criterion is independent of theσ_(s)due to the overload phenomenon,while the NTS corrected by the Griffith criterion is sensitive to both the andσ.Therefore,it is essential to modify the tensile stress in dynamic confined BD tests using both the overload correction and the Griffith criterion rectification to obtain the accurate dynamic BTS of rocks.

Asymmetric Environmental Regulation:Mechanism and a Yardstick Phenomenon

In discussing the policy effects of environmental regulation,we should focus not only on whether environmental regulation helps improve the environmental and economic performance of firms,but also on how such improvement is materialized,i.e.whether the obsolete mode of production is reversed.After matching the database of China’s industrial enterprises with that of pollution emissions from these industrial enterprises,this paper identifies the asymmetric scope of clean production standards to test the effect of environmental regulation on the total factor productivity(TFP)of the industrial enterprises.Our empirical research finds that the implementation of clean production standards may induce TFP improvement.However,such improvement only occurs for polluters who cannot or who barely meet clean production standards and does little to improve the production standards of polluters with low pollution emission,reflecting the yardstick phenomenon of the asymmetric environmental regulation policy effect:While polluters are forced to improve,clean enterprises that pollute less are more likely to take no action.Further research finds that such TFP improvement is materialized primarily by means of overall firm optimization;the compensation effect is insignificant and does not reverse the backward mode of production.Polluters cope with the implementation of clean production standards by purchasing more equipment and expanding capacity,which adds to the tension between the expansion of capacity and the abatement of pollution emission.

Medical and interventional therapy of Kasabach-Merritt phenomenon associated with Kaposiform hemangioendothelioma:A case report

An infant with Kasabach-Merritt Phenomenon(KMP)presented with a giant subcutaneous mass in the right lower limb,severe hypofibrinogenemia,and thrombocytopenia.Glucocorticoids,along with supportive treatments including transfusion of blood products and clotting factors,were administered to reverse fatal disseminated intravascular coagulation and acute hemolysis.The glucocorticoid dose was tapered slowly,and sirolimus was added to treat the hemangiomas.The patient subsequently underwent interventional therapy.After 6 months of medical and interventional therapy,the patient was doing well with a normal platelet count,the tumor volume was markedly reduced,and the primary cutaneous lesion became pale pink.Currently,the patient remains on sirolimus,and no recurrence of thrombocytopenia or further growth of the mass was observed after six months of follow-up.

Tungsten ion source under double-pulse laser ablation system

New tungsten ion source is produced by using single and double-pulse laser ablation system. Combined collinear Nd：YAG laser beams（266＋1064 nm） are optimized to focus on the sample in air. Optimization of the experimental parameters is achieved to enhance the signal-to-noise ratio of the emission spectra. The velocity distribution of the emitted plasma cloud is carefully measured. The influences of the potential difference between the bias electrodes, laser wavelength and intensity on the current signal are also studied. The results show that the increase in the tungsten ion velocity under the double-pulse lasers causes the output current signal to increase by about three folds. The electron density and temperature are calculated by using the Stark-broadened line profile of tungsten line and Boltzmann plot method of the upper energy levels, respectively. The signal intensity dependence of the tungsten ion angular distribution is also analyzed. The results indicate that the double-pulse laser ablation configuration is more potent technique for producing more metal ion source deposition, thin film formation, and activated plasma-facing component material.

Anesthetic management of a patient with preoperative R-on-T phenomenon undergoing laparoscopic-assisted sigmoid colon resection:A case report

BACKGROUND The R-on-T phenomenon is a malignant arrhythmia associated with potentially catastrophic consequences.It may initiate ventricular tachycardia or ventricular fibrillation,which can result in syncope or sudden cardiac death.This manifestation poses a great challenge for anesthesiologists.However,it is rarely encountered in the perioperative setting.CASE SUMMARY We herein present a case in which the R-on-T phenomenon was incidentally revealed by 24-h Holter monitoring in a patient diagnosed with sigmoid colon cancer.Careful evaluation and treatment with mexiletine were carried out preoperatively under consultation with a cardiovascular specialist,and surgery was uneventfully performed under general anesthesia after thorough preparation.CONCLUSION Physicians should be vigilant about this infrequent but potentially fatal arrhythmia.Our experience suggests that the anesthetic process can be greatly optimized with careful preparation.

符号互动:品牌数字传播的社会认同建构

网络化个体主义是推动品牌社会认同加速离散的重要力量,由此造成品牌社会认同的危机,然而,网络个体的重新聚集也成为品牌构建新社会认同的契机。因此,探索全新的品牌数字传播对社会认同的建构理路,对于理解广告品牌研究的理论与实践具有重要意义。研究基于符号互动理论,对“后浪现象”这一数字传播典型案例进行探讨,从个体、群际和社会三重互动情境着手分析,提炼出品牌数字传播构建社会认同的两个关键环节:“情感化的符号生产”与“仪式化的公众文本创作”。在个体间情感认同形成层面,符号的生产促成情感心理空间的连接和扩大,其是形成情感认同的中间纽带;在群际间层面,人们通过互动仪式链参与公众文本创作,促进群际间的意义生产,突破圈层的意义边界,助力群际间认同。

当代大学生消极苦乐观的表征解析、疗愈理论与教育对策——以“摆烂”现象为例

苦乐观是人生观的重要组成部分,体现了个体对自我生存意义的探寻,而当前部分大学生的“摆烂”现象反映了其苦乐观的消极倾向。通过对当代大学生的“摆烂”现象进行分析,可以发现部分大学生在苦乐观方面存在以下表征:片面理解苦乐内涵与关系的怀疑倾向,苦乐态度不端与情感消极为表征的颓废悲观倾向,苦乐信念缺乏与意志薄弱的精神虚无倾向以及苦乐动机功利与行为脱节的精致利己主义倾向。借助积极心理学相关理论探讨大学生苦乐观教育,有助于消解大学生“摆烂”症候,帮助大学生辩证对待人生苦乐矛盾,树立积极向上的苦乐观。

乙型肝炎病毒检测方法的现状研究

HBV感染是我国最主要的传染性疾病之一,目前临床主要使用体外诊断试剂对该病毒进行准确快速的检测,体外诊断试剂盒的方法学主要包括:免疫学方法和分子生物学方法。本文通过PubMed(检索时限自2017年1月至2023年12月)和万方数据库(检索时限自2017年1月至2023年12月)检索乙型肝炎病毒(hepatitis B virus,HBV)的检测方法、相关试剂盒的生产和临床应用的相关文献,详细列举最新检测方法的进展并比较不同方法学的优缺点,全面分析和讨论了我国目前乙型肝炎病毒检测的现状和研究进展。研究发现,我国HBV检测用商品化试剂盒的方法学分布存在集中现象,试剂盒的生产存在“东部多,西部少,大分散,小聚集”的特点。

我国闭坑煤矿矿井水水质演化研究进展与展望

随着我国煤矿矿井关闭数量的逐渐增加,闭坑矿井水水质恶化和污染问题日益突出,准确掌握闭坑矿井水水质演化规律及机制,是目前闭坑矿山可持续绿色发展的重大科学难题,也是地下水污染有效防控和水资源合理开发利用的重要前提。在回顾关闭矿井发展历史的基础上,首先阐述了我国关闭矿井的分布情况,之后分别对闭坑矿井水水质特征、水质演化规律及水质演化的多场作用等方面展开综述,最后对我国闭坑矿井水水质研究中存在的关键问题和应用方向进行了展望。研究结果表明:①截至2023年底,我国关闭矿井的数量已经上升到13000多个,主要分布在山西、河南、河北、山东、江苏和安徽北部等地区;②我国部分闭坑矿井水的pH、矿化度、硫酸盐、氟化物和铁锰重金属等水质指标含量超过Ⅲ类水标准,其中酸性矿井水(pH<6.5)主要分布在云贵、鲁西、山西等地区,高矿化度矿井水(TDS>1000 mg/L)主要分布在鲁西、山西、河南、两淮、蒙东、宁东、新疆等地区,硫酸盐矿井水(硫酸盐质量浓度>250 mg/L)主要分布在云贵、鲁西、山西、蒙东、宁东、神东、新疆哈密等地区,氟化物矿井水(F质量浓度>1.0 mg/L)主要分布在两淮、山西、神东等地区,铁锰重金属矿井水(Fe质量浓度>0.3 mg/L、Mn质量浓度>0.1 mg/L)主要分布在云贵、鲁西、山西、蒙东等地区。③在闭坑矿井被完全淹没之前,其水质在空间上会出现明显的分层现象,即浅部的优质水层、中部的过渡水层和深部的劣质水层,这主要与矿井采掘空间分布、地温梯度和盐度等因素有关。④煤矿关闭后,矿井水水质的演变过程大致可分为3个阶段,第Ⅰ阶段为矿井水中典型污染物(硫酸盐和铁离子)质量浓度快速上升达并到峰值阶段,第Ⅱ阶段为污染物浓度快速下降阶段,第Ⅲ阶段为矿井水水质与邻近含水层地下水水质背景值相同并保持相对稳定阶段。⑤系统总结了我国闭坑矿井水动力场、水化学场、微生物场和温度场的研究进展,指出了闭坑矿井多相(水−岩−气−生)多场(水化学场−水动力场−微生物场−温度场)耦合作用机制的研究还不充分。⑥提出了我国闭坑矿井水水质演化问题的研究仍然面临着水质演化规律和水质演化机制不清楚等关键科学问题。

任务协作表示增强的要素及关系联合抽取模型

对文本中诸如实体与关系、事件及其论元等要素及其特定关系的联合抽取是自然语言处理的一项关键任务.现有研究大多采用统一编码或参数共享的方式隐性处理任务间的交互,缺乏对任务之间特定关系的显式建模,从而限制模型充分利用任务间的关联信息并影响任务间的有效协同.为此,提出了一种基于任务协作表示增强的要素及关系联合抽取模型(Task-Collaboration Representation Enhanced model for joint extraction of elements and relationships,TCRE).该模型旨在从多个阶段处理任务间的特定关系,帮助子任务进行更细致的调节和优化,促进整体性能的提升.在三个关系抽取和一个事件抽取数据集上进行实验,TCRE在实体识别和关系提取任务上平均性能分别提高0.57%和0.77%,在触发词识别和论元角色分类任务上分别提高0.7%和1.4%.此外,TCRE还显示出在缓解“跷跷板现象”方面的作用.

复合润滑结构改善滑动导轨表面爬行现象研究

滑动导轨在低速重载时产生爬行现象,严重影响机床的加工精度。为了改善滑动导轨的爬行现象,对滑动导轨表面复合润滑结构的设计和摩擦力分阶段表征进行了研究。在激光烧蚀微织构的基础上,采用高温高压镶嵌法制备了复合润滑微织构,基于摩擦试验,提出了摩擦力分阶段表征方法,探索了不同复合润滑结构对各阶段摩擦力特征参数的影响规律,建立了复合润滑结构改善爬行现象的理论模型,找到抑制爬行现象性能最优的复合润滑结构。研究结果表明:表面微织构仅影响摩擦力的严重黏滑和爬升阶段,而复合润滑结构对整个启动阶段都有显著影响。填充二硫化钼(MoS 2)的正弦沟槽与六边形凹坑组合的多级复合润滑结构(SF-3)改善表面接触状态和抑制爬行现象的效果最好。与光滑表面(SS)试样相比,SF-3试样爬行时间缩短了72%,第Ⅰ阶段失稳力减小了69.83%,第Ⅱ阶段和第Ⅲ阶段的摩擦突跃力分别减小了75.91%和80.17%。

2023年我国犯罪学研究述评

2023年我国犯罪学研究重点聚焦了网络暴力犯罪、电信网络诈骗犯罪、新科技犯罪风险等热点问题,基本回应了当前我国犯罪治理的热点和难点,具有鲜明的时代特征。但是,面对当前我国犯罪治理现代化和中国特色犯罪学学科体系建设总体上还是比较薄弱,亟待进一步加强。一是发展中国犯罪学。在适用西方现代犯罪学理论的同时,挖掘中国文化中犯罪学科学基因,发展符合中国实际的犯罪学理论,生产中国犯罪治理经验和话语体系。二是加强我国犯罪学的实证研究。不仅仅是犯罪生成规律的实证研究,还包括犯罪防治效果的实证研究,进而生产高质量的犯罪学成果。三是完善官方犯罪统计,开展犯罪被害调查统计,支持社会组织或学者进行犯罪调查。四是加强犯罪的数字治理研究,以数字化赋能犯罪治理体系和治理能力,构建新型犯罪治理体系。五是加强跨学科研究和交流,科学、全面地认识犯罪规律,为立法和犯罪治理决策提供科学依据。

结构尺寸对两级式厚壁阻尼孔流动特性的影响

目前,两级式阻尼孔的设计使用是参考单级式阻尼孔的流量计算公式以及经验参数,选型误差较大,依靠现场实验去修正压损参数或者采用试错法更换不同尺寸的阻尼孔进行效果补偿。结合实验和CFD仿真深入研究了气穴、不同长径比及加工误差等因素对两级式厚壁阻尼孔流动特性的影响,得到了有或无气穴现象时固定长度、不同直径尺寸的阻尼孔流量系数稳定值,为两级式厚壁阻尼孔正确选型及数学建模中的特征参数设置提供依据。

直角凸壁面附近非对称位置的空泡动力学行为实验研究

空化破坏现象在核电厂中广泛存在。为了更深入地揭示空化破坏的机理,本文借助高速摄影实验系统,研究了直角凸壁面附近非对称位置空泡的动力学行为。具体分析了空泡的轮廓变形,形心的移动距离和方向,以及空泡射流的方向随着空泡与壁面相对位置d、h的变化规律。本文主要结论如下:(1)空泡的变形与空泡和固体壁面的相对位置d、h有关。随着空泡与右壁面的距离d的增大,空泡的非对称性越来越弱。随着空泡与上壁面的距离h的增大,在整个空泡的动力学过程中空泡的非球形特征逐渐减弱。(2)在空泡的溃灭和再生长过程中,空泡形心会持续地向左下方移动,且形心向左移动的距离随着d和h的增大而明显减小。(3)当空泡与上壁面的距离h适当时,会产生明显的斜向左下方的射流现象,且射流方向角θ随着d的增大而增大。