Effect of traveling magnetic field on dendrite growth of Pb-Sn alloy during directional solidification

The influence of melt convection on dendrite growth during the upward-directional solidification of Pb-33%Sn binary alloys was investigated.The melt convection was modulated by traveling magnetic field.When the direction of traveling magnetic field was changed from upward to downward,the primary dendrite spacing gradually increased,and the distribution peak of the primary dendrite spacing shifted to the field of narrower spacing.These result from the different intensities of melt convection,which are controlled by the traveling magnetic field.The effects of the traveling magnetic field on melt convection are similar to those of adjustment in the gravity level,thus,the primary dendrite spacing varies.When the intensity of the traveling magnetic field was 1 mT,and the drawing speed was 50 μm/s,the gravity acceleration reached 0.22g for the downward-traveling magnetic field and 3.07g for the upward-traveling magnetic field.

Effect of travelling magnetic field on interface morphology in directionally solidified Sn-Cd alloy

The diversity of interface morphologies is observed for directionally solidified Sn-0.65%Cd alloy under a travelling magnetic field （TMF） in the 4 mm-diameter sample. Under an upward TMF, planar and cellular interface morphologies transform alternately with increasing magnetic flux density （B≤10.3 mT）. The interface morphology transforms from shallow cellular to deep cellular morphology under a weak downward TMF （B=3.2 mT）. When the magnetic flux density increases further, both sides of the interface morphology appear to be slightly inconsistent, but they roughly tend to be planar under a strong downward TMF （BS10.3 mT）. The interface instability may be attributed to the flow driven by the TMF. Moreover, the shape of interface appears to be almost flat under an upward TMF, but deflective under a downward TMF.

Control of In Vitro Regeneration of Individual Reproductive and Vegetative Organs in Dracaena fragrans cv. massangeana Hort. Regularities of the Direct Regenerationof Individual Organs In Vitro

Various individual organs (tepal, flower bud, inflorescence branch, inflorescence, adult vegetative bud and juvenile vegetative bud) were directly regenerated respectively by callus in Dracaena fragrans cv. massangeana Hort. During the regeneration of these individual organs some regularity phenomena were observed. Firstly, the kind range of the individual organs, which are directly regenerated in vitro, is in close relationship to the differentiated stages of the organs used for explant excision during plant ontogeny. The explants excised from the epigeous organ that is differentiated at some stage (stage A) during plant ontogeny must be able to separately regenerate all of those individual epigeous organs: ones differentiated slightly later than the stage A, ones differentiated at the stage A and all ones differentiated earlier than the stage A. Secondly, within this range which kind of organ is regenerated depends on the exogenous auxin concentrations in medium. With the gradual increase of 2,4-D concentration from 0.005 mg/L to 0.5 mg/L, the kinds of regenerated organs will change by the order as follows: vegetative bud, inflorescence, inflorescence branch, flower bud, tepal. These regularities will be able to be used for inducing the direct regeneration of a given epigeous organ in angiosperms.

服务业进出口、OFDI和全要素生产率的动态关系研究——基于VAR模型的实证分析

研究服务业贸易、投资与服务业之间的影响关系,对提升我国服务行业国际竞争力、促进其高质量发展具有重要意义。论文使用我国2000—2021年数据,构建VAR模型对服务业进出口、服务业对外直接投资(OFDI)和全要素生产率的动态交互关系进行实证分析。研究结果显示,服务业进出口对服务业对外直接投资具有正相关关系,且长期支持效果明显;服务业进出口对OFDI、全要素生产率提升具有促进作用;在短期内,全要素生产率与OFDI之间存在双向促进作用,从长期来看则存在一定负向影响。基于实证研究结论,文中提出制定政策鼓励服务企业参与国际化竞争、发挥服务业进出口对OFDI的促进效应、提升服务企业自主创新能力等相关对策建议。

OFDI与区域碳排放的非线性关系——基于技术创新的门槛效应研究

随着我国外部市场的扩大和经济对外开放政策的推进,对外直接投资(OFDI)呈现出迅猛增长的趋势。然而,由于过去采用粗放式增长模式,生态环境发展不充分,且由于“双碳”目标政策的实施,碳排放已成为对环境产生重大影响的关键因素,并被纳入总排放控制体系。基于此,本文选取中国2005—2019年30个省份(西藏、港澳台地区除外)的面板数据进行分析。结果表明,在不考虑技术创新作为门槛变量的情况下,整体上我国OFDI对本地碳排放具有显著的抑制作用。然而,在引入技术创新作为门槛变量后,处于技术创新水平较高的地区通过加大OFDI带来的逆向技术溢出效应可以降低本地区碳排放水平;中等技术创新水平的地区增大OFDI反而会增加地区碳排放;较低技术创新水平的地区对外直接投资的碳减排效应则不显著,OFDI对区域碳减排效应存在门槛。文章提出建议:技术创新水平较高地区进一步加大对外开放力度,充分发挥OFDI的逆向技术溢出效应;技术创新水平较低地区扩大OFDI规模,优化调整OFDI结构,坚持绿色导向型OFDI,积极引进国外先进技术、管理经验等,缓解全球温室效应等问题。

The Micro-Scale Mechanism of Metal Mine Tailings Thickening Concentration Improved by Shearing in Gravity Thickener

Higher concentration is beneficial for the Paste and Thickened Tailings(PTT)operation in metal mine.Partial paste thickeners are produced lower density underflow.Flocculated tailings are intended to form a water entrapped network structure in thickener,which is detrimental to underflow concentration.In this study,the continuous thickening experiment was carried out for ultra-fine tungsten tailings to study the influence of rake shearing on underflow.The micro pores structure and seepage flow in tailings bed before and after shearing are studied by CT and simulation approach to reveal the shearing enhancement mechanism of thickening process.The results shown that,the underflow concentration is increased from 61.4 wt%to 69.6 wt%by rake shearing in a pilot scale thickener,the porosity decreased from 46.48%to 37.46%.The entrapped water discharged from sticks structure more than sphere spaces.In items of seepage,after shearing,the seepage flow channel of tailings underflow is becoming longer,which caused the decreasing average flow rate decreases and absolute permeability.The absolute permeability is negatively correlated with tortuosity.The rake shearing can destroy the flocs structure;change the effective stress to increase the concentration.Higher underflow concentration improves the waste recycling and water recovery rate,especially for arid areas.

Classification of All Single Traveling Wave Solutions to (3 + 1)-Dimensional Breaking Soliton Equation

In order to get the exact traveling wave solutions to nonlinear partial differential equation, the complete discrimination system for polynomial and direct integral method are applied to the considered equation. All single traveling wave solutions to the equation can be obtained. As an example, we give the solutions to (3 + 1)-dimensional breaking soliton equation.

Exact Solutions of the Harry-Dym Equation

The aim of this paper is to generate exact travelling wave solutions of the Harry-Dym equation through the methods of Adomian decomposition, He＇s variational iteration, direct integration, and power series. We show that the two later methods are more successful than the two former to obtain more solutions of the equation.

Reversal of radial glow distribution in helicon plasma induced by reversed magnetic field

In this work, the reversal of radial glow distribution induced by reversed magnetic field is reported. Based on the Boswell antenna which is symmetric and insensitive to the magnetic field direction, it seems such a phenomenon in theory appears impossible. However, according to the diagnostic of the helicon waves by magnetic probe, it is found that the direction of magnetic field significantly affects the propagation characteristic of helicon waves, i.e., the interchange of the helicon waves at the upper and the lower half of tube was caused by reversing the direction of magnetic field. It is suggested that the variation of helicon wave against the direction of magnetic field causes the reversed radial glow distribution. The appearance of the traveling wave does not only improve the discharge strength, but also determines the transition of the discharge mode.

Effectiveness of the flipped classroom on the development of self-directed learning in nursing education:a meta-analysis

Objectives: To examine the best practice evidence of the effectiveness of the flipped classroom（FC） as a burgeoning teaching model on the development of self-directed learning in nursing education.Data sources: The relevant randomized controlled trial（RCT） and non-RCT comparative studies were searched from multiple electronic databases including PubMed, Embase, Web of Science, Cumulative Index to Nursing and Allied Health Literature（CINAHL）, Cochrane Central Register of Controlled Trials（CENTRAL）, Wanfang Data, China National Knowledge Infrastructure（CNKI）, and Chinese Science and Technology Periodical Database（VIP） from inception to June 2017.Review methods: The data were independently assessed and extracted for eligibility by two reviewers. The quality of included studies was assessed by another two reviewers using a standardized form and evaluated by using the Cochrane Collaboration’s risk of bias tool. The self-directed learning scores（continuous outcomes） were analyzed by using the 95% confidence intervals（Cls） with the standard deviation average（SMD） or weighted mean difference（WMD）. The heterogeneity was assessed using Cochran’s I;statistic.Results: A total of 12 studies, which encompassed 1440 nursing students（intervention group = 685, control group = 755）, were eligible for inclusion in this review. Of 12 included studies, the quality level of one included study was A and of the others was B. The pooled effect size showed that compared with traditional teaching models, the FC could improve nursing students’ selfdirected learning skill, as measured by the Self-Directed Learning Readiness Scale（SDLRS）, Self-Directed Learning Readiness Scale for Nursing Education（SDLRSNE）, Self-Regulated Learning Scale（SRL）, Autonomous Learning Competencies scale（ALC）, and Competencies of Autonomous Learning of Nursing Students（CALNS）. Overall scores and subgroup analyses with the SRL were all in favor of the FC.Conclusions: The result of this meta-analysis indicated that FCs could improve the effect of self-directed learning in nursing education.Future studies with more RCTs using the same measurement tools are needed to draw more authoritative conclusions.

About Appearance of the Irreversibility

The inevitability of arising in equations of kinetics and hydrodynamics irreversibility not contained in original equations of classic mechanics is substantiated. It is established that transfer of information about the direction of system evolution from initial conditions to resulting equations is the consequence of losing information about the position of an individual particle in space, which takes place at roughening description. It is shown that the roughening with respect to impact parameters of colliding particles is responsible for appearance of the irreversibility in resulting equations. Direct equations of kinetics and hydrodynamics are the result of roughening distribution functions with respect to impact parameters of particles, which have not yet reached the domain of their interaction. The direct equations are valid for the progressive direction of timing on the time axis pointing from the past to the future. Reverse equations of kinetics and hydrodynamics are the result of roughening distribution functions with respect to impact parameters of particles, which have already left the domain of their interaction. The reverse equations are valid for the progressive direction of timing on the time axis pointing from the future to the past.

INDEX OF DIRECTION CHANGE OF ZONALLY AVERAGED WIND AND CHANGE OF SEASON

In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn.

Enantio-selective preparation of (S)-1-phenylethanol by a novel marine GDSL lipase MT6 with reverse stereo-selectivity

We previously functionally characterized a novel marine microbial GDSL lipase MT6 and identified that the stereo-selectivity of MT6 was opposite to that of other common lipases in trans-esterification reactions.Herein,we have investigated the use of MT6 in stereo-selective biocatalysis through direct hydrolysis reactions.Notably,the stereo-selectivity of MT6 was also demonstrated to be opposite to that of other common lipases in hydrolysis reactions.Parameters,including temperature,organic co-solvents,pH,ionic strength,catalyst loading,substrate concentration,and reaction time,affecting the enzymatic resolution of racemic 1-phenylethyl acetate were further investigated,with the e.e.of the final（S）-l-Phenylethanol product and the conversion being 97%and 28.5%,respectively,after process optimization.The lengths of side chains of 1-phenylethyl esters greatly affected the stereo-selectivity and conversion during kinetic resolutions.MT6 is a novel marine microbial GDSL lipase exhibiting opposite stereo-selectivities than other common lipases in both trans-esterification reactions and hydrolysis reactions.

中国OFDI逆向技术溢出效应的影响因素研究——基于国别面板数据的非线性门槛技术回归

本文首先对对外直接投资逆向技术溢出效应的机理进行了分析,然后以2003—2013年中国对外直接投资的13个主要发达国家的数据为样本,考察了中国对外直接投资逆向技术溢出效应的影响因素。本文的实证结果发现,中国与东道国之间的技术差距、东道国研发(R&D)支出、全要素生产率、人力资本、技术创新能力、制度环境是对外直接投资逆向技术溢出效应的正相关因素。同时,本文以技术差距作为门槛变量进行门槛效应检验,结果表明,技术差距存在单一门槛值,当中国与东道国之间技术差距较大时,技术差距对逆向技术溢出产生了正向影响;当技术差距缩小后,正相关关系仍然存在,但影响程度有所下降。

中国企业OFDI逆向技术溢出如何提升绿色技术创新——基于长江经济带的经验证据

基于CH模型,测算2003-2016年间长江经济带11个省市的绿色技术创新水平,并采用可以有效控制内生性问题的两阶段最小二乘法考察了对外直接投资逆向技术溢出、市场分割以及其他因素对区域绿色技术创新的影响,结果发现:第一,中国企业对外直接投资逆向技术溢出能显著提高绿色技术创新,但市场分割通过扭曲本地市场的交易成本间接阻碍了绿色技术创新水平的提升;第二,考虑市场分割调节作用时,中国企业对外直接投资逆向技术溢出对于技术吸收能力的作用影响具有一定程度的不确定性;第三,从区域角度看,下游生产率的提升主要得益于中国企业对外直接投资逆向技术溢出效应,而中上游则在更大程度上依赖市场分割(即地方保护);且在存有区际差别市场分割程度的情况下,中国企业对外直接投资对于中国吸收逆向溢出技术的作用具有"倒U型"的特征。

我国OFDI逆向技术溢出效应的研究——基于省际面板数据的门槛回归分析

利用2003—2013年我国29个省级行政区的省际面板数据实证分析我国对外直接投资(OFDI)的逆向技术溢出效应,结果显示,我国OFDI存在逆向技术溢出效应,且这种效应存在显著的地区差异性。门槛模型的回归结果表明,我国OFDI的逆向技术溢出效应不受经济自由度的影响,但受创新能力和金融发展水平的制约,创新能力和金融发展水平均存在门槛效应,当其跨越门槛值时,OFDI的逆向技术溢出效应显著增加。

中国对“一带一路”沿线国家OFDI逆向技术溢出的影响因素研究

基于2003—2014年"一带一路"沿线国家的跨国面板数据,运用随机前沿引力模型,研究了中国对外直接投资逆向技术溢出的影响因素。研究表明,签订双边自贸协定对中国对外直接投资逆向技术溢出存在显著的正向效用,"一带一路"沿线东道国的技术创新水平对中国对外直接投资逆向技术溢出具有显著的正面影响,而东道国与中国之间的文化差异和经济距离在一定程度上阻碍了中国对外直接投资的逆向技术溢出。而对不同国家的分析表明,2003—2014年,中国通过"一带一路"沿线国家OFDI获得的国外研发溢出效率排名前5位的国家分别为新加坡、巴基斯坦、越南、匈牙利和斯里兰卡。技术无效率函数的估计结果发现,东道国法律与腐败监管的严厉程度、东道国经济自由度在降低中国对"一带一路"沿线国家OFDI逆向技术溢出无效程度中发挥着重要的作用。因此,"走出去"的中国企业必须高度重视东道国当地的文化环境,同时应加快向东南亚、南亚及中亚转移劳动密集型产业。最后,应制定政策鼓励国内研发实力强的企业对科技资源密集型的发达国家和地区进行对外直接投资。

OFDI对中国全球价值链嵌入效应研究

对外直接投资作为载体将要素分散到不同的国家,使各产品的生产不再局限于某一国内,进而影响一国在全球价值链嵌入的程度。为探究OFDI对中国全球价值链嵌入的影响效应,对二者关系进行实证检验,得出OFDI对中国全球价值链嵌入度有正向的行业调整效应和技术逆溢出效应的结论。提出为了使投资活动能够更有效地促进中国在全球价值链中的升级,应大力鼓励企业“走出去”、实施创新驱动战略、加速培养尖端复合人才等建议。

OFDI、逆向技术溢出与全要素能源效率——基于PVAR模型分析

在中国企业大规模“走出去”的背景下,探讨了对外直接投资(OFDI)逆向技术溢出对全要素能源效率的作用机制。以2003-2017年中国29个省份的面板数据为样本,运用SBM方向距离函数方法对样本期内各省份的全要素能源效率进行了测算,通过构建包含技术创新在内的面板向量自回归(PVAR)模型系统阐述了OFDI逆向技术溢出对全要素能源效率的动态影响路径。研究结果发现:在样本期内,中国各省全要素能源效率空间分布较为稳定,但存在显著的空间异质性,即东部沿海地区最高,中部地区次之,西部地区最低;OFDI逆向技术溢出能够一定程度上促进全要素能源效率的提高,但目前该作用效果还尚小且存在滞后性特征;OFDI逆向技术溢出与技术创新之间存在良性互动,OFDI逆向技术溢出能够有效促进技术创新,反之,技术创新也能促进对OFDI外溢技术的吸收。

OFDI逆向技术溢出门槛与母国技术进步——基于绿地投资与企业海外并购的比较

对中国企业海外并购与绿地投资两种对外直接投资方式(OFDI)与母国技术进步的关系进行横纵两向比较与探讨分析,结果显示:企业海外并购技术转移度低于绿地投资技术转移度,因而企业海外并购获得的逆向技术溢出包括研发资金溢出与人力资本溢出均高于绿地投资的溢出效应,企业海外并购与绿地投资对母国技术进步均有促进作用。同时,受到母国研发资金投入与人力资本存量约束,二者分别为企业海外并购与绿地投资设立了最低与最高"门槛值",企业海外并购数量超过最低"门槛值"与绿地投资低于最高"门槛值"均会带动母国技术进步,反之两者都抑制母国技术进步。因此,中国应提高对外直接投资中企业海外并购份额,以提高技术进步程度。