Comparison study on measurement of rail weld joint between inertial reference method and multi-point chord reference method

Purpose – Straightness measurement of rail weld joint is of essential importance to railway maintenance. Dueto the lack of efficient measurement equipment, there has been limited in-depth research on rail weld joint with a5-m wavelength range, leaving a significant knowledge gap in this field.Design/methodology/approach – In this study, the authors used the well-established inertial referencemethod (IR-method), and the state-of-the-art multi-point chord reference method (MCR-method). Two methodshave been applied in different types of rail straightness measurement trollies, respectively. These instrumentswere tested in a high-speed rail section within a certain region of China. The test results were ultimatelyvalidated through using traditional straightedge and feeler gauge methods as reference data to evaluate the railweld joint straightness within the 5-m wavelength range.Findings – The research reveals that IR-method and MCR-method produce reasonably similar measurementresults for wavelengths below 1 m. However, MCR-method outperforms IR-method in terms of accuracy forwavelengths exceeding 3 m. Furthermore, it was observed that IR-method, while operating at a slower speed,carries the risk of derailing and is incapable of detecting rail weld joints and low joints within the track.Originality/value – The research compare two methods’ measurement effects in a longer wavelength rangeand demonstrate the superiority of MCR-method.

Weakening of Interannual Variability in the Summer East Asian Upper-tropospheric Westerly Jet since the Mid-1990s

In this study,we found that the intensity of interannual variability in the summer upper-tropospheric zonal wind has significantly weakened over Northeast Asia and the subtropical western North Pacific（WNP） since the mid-1990s,concurrent with the previously documented decrease of the westerly jet over North China and Northwest China.Corresponding to this weakening of zonal wind variability,the meridional displacement of the East Asian westerly jet（EAJ） manifested as the leading mode of zonal wind variability over the WNP and East Asia（WNP-EA） before the mid-1990s but not afterward.The energetics of the anomalous pattern associated with the meridional displacement of the EAJ suggests that barotropic energy conversion,from basic flow to anomalous patterns,has led to the weakening of the variability in the EAJ meridional displacement and to a change in the leading dominant mode since the mid-1990s.The barotropic energy conversion efficiently maintained the anomalies associated with the variability in the EAJ meridional displacement during 1979-1993 but acted to dampen the anomalies during 1994-2008.A further investigation of the energetics suggests that the difference in the patterns of the circulation anomaly associated with either the first leading mode or the meridional displacement of the EAJ,i.e.,a southwest-northeast tilted pattern during 1979-1993 and a zonally oriented pattern during 1994-2008,has contributed greatly to the change in barotropic energy conversion.

A Decadal Shift of Summer Surface Air Temperature over Northeast Asia around the Mid-1990s

This study identifies a decadal shift of summer surface air temperature （SAT） over Northeast Asia,including southeastern parts of Russia,Mongolia and northern China,around the mid-1990s.The results suggest that the SAT over the Northeast Asia experienced a significant warming after 1994 relative to that before 1993.This decadal shift also extends to northern China,and leads to a warmer summer over Northeast China and North China after the mid-1990s.The decadal warming over Northeast Asia is found to concur with the enhancement of South China rainfall around the mid-1990s.On the one hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift only in summer,but not in other seasons.On the other hand,both the Northeast Asian SAT and South China rainfall exhibit this mid-1990s decadal shift not only in the summer seasonal mean,but also in each month of summer （June,July and August）.Furthermore,the decadal warming is found to result from an anticyclonic anomaly over Northeast Asia,which can be interpreted as the response to the increased precipitation over South China,according to previous numerical results.Thus,we conclude that the warming shift of summer Northeast Asian SAT around the mid-1990s was a remote response to the increased precipitation over South China.

Role of short-wavelength filtering lenses in delaying myopia progression and amelioration of asthenopia in juveniles

AIM： To evaluate the positive effects of blue-violet light filtering lenses in delaying myopia and relieving asthenopia in juveniles. METHODS： Sixty ametropia juveniles （aged range, 11-15y） were randomized into two groups： the test group （30 children, 60 eyes）, wearing blue-violet light filtering lenses; and the control group （30 children, 60 eyes）, wearing ordinary aspherical lenses. Baseline refractive power of the affected eyes and axial length of the two groups was recorded. After 1-year, the patients underwent contrast sensitivity （glare and non-glare under bright and dark conditions）, accommodation-related testing, asthenopia questionnaire assessment, and adverse reaction questionnaire assessment. RESULTS： After ly of wearing the filtering lenses, changes in refractive power and axial length were not significantly different between the two groups （P〉0.05）. Under bright conditions, the contrast sensitivities at low and medium- frequency grating （vision angles of 6.3, 4.0, and 2.5） with glare in the test group were significantly higher than in the control group （P〈0.05）, while the contrast sensitivity at low-frequency grating （vision angles of 6.3 and 4.0） in the absence of glare in the test group was higher than in the control group （P〈0.05）. Under glare and non-glare dark conditions, the contrast sensitivities of various frequencies in the test group did not show significant differences compared with those in the control group （P〉0.05）. In the test group, the amplitude of accommodation, accommodative lag, and accommodative sensitivity of patients wearing glasses for 6 and 12mo were significantly elevated （P〈0.05）, while the asthenopia gratings were significantly decreased （P〈0.05）. Nevertheless, in the control group,the amplitude of accommodation, accommodative lag, and accommodative sensitivity after 12mo were not significantly altered compared with baseline （P〉0.05）, and the asthenopia grating was not significantly decreased （P〉0.05）. In addition, after wearing glasses for 6 to 12mo, the asthenopia grating of patients in the test group decreased significantly compared with the control group （P〈0.05）. At 12mo, the constituent ratio of adverse reactions did not show significant difference between the two groups （P〉0.05）. CONCLUSION： A l-year follow-up reveal that compare with ordinary glasses, short-wavelength filtering lenses （blue/ violet-light filters） increase the low- and medium-frequency contrast sensitivity under bright conditions and improved accommodation. They effectively relieved asthenopia without severe adverse reactions, suggesting potential for clinical application. However, no significant advantages in terms of refractive power or axial length progression were found compared with ordinary aspheric lenses.

Abrupt Summer Warming and Changes in Temperature Extremes over Northeast Asia Since the Mid-1990s: Drivers and Physical Processes

This study investigated the drivers and physical processes for the abrupt decadal summer surface warming and increases in hot temperature extremes that occurred over Northeast Asia in the mid-1990s. Observations indicate an abrupt increase in summer mean surface air temperature （SAT） over Northeast Asia since the mid-1990s. Accompanying this abrupt surface wanning, significant changes in some temperature extremes, characterized by increases in summer mean daily maximum temperature （Tmax）, daily minimum temperature （Train）, annual hottest day temperature （TXx）, and annual warmest night temperature （TNx） were observed. There were also increases in the frequency of summer days （SU） and tropical nights （TR）. Atmospheric general circulation model experiments forced by changes in sea surface temperature （SST）/sea ice extent （SIE）, anthropogenic greenhouse gas （GHG） concentrations, and anthropogenic aerosol （AA） forcing, relative to the period 1964- 93, reproduced the general patterns of observed summer mean SAT changes and associated changes in temperature extremes, although the abrupt decrease in precipitation since the mid-1990s was not simulated. Additional model experiments with different forcings indicated that changes in SST/SIE explained 76% of the area-averaged summer mean surface warming signal over Northeast Asia, while the direct impact of changes in GHG and AA explained the remaining 24% of the surface warming signal. Analysis of physical processes indicated that the direct impact of the changes in AA （through aerosol- radiation and aerosol-cloud interactions）, mainly related to the reduction of AA precursor emissions over Europe, played a dominant role in the increase in TXx and a similarly important role as SST/SIE changes in the increase in the frequency of SU over Northeast Asia via AA-induced coupled atmosphere-land surface and cloud feedbacks, rather than through a direct impact of AA changes on cloud condensation nuclei. The modelling results also imply that the abrupt summer surface warming and increases in hot temperature extremes over Northeast Asia since the mid-1990s will probably sustain in the next few decades as GHG concentrations continue to increase and AA precursor emissions over both North America and Europe continue to decrease.

Short-wavelength infrared InAs/GaSb superlattice hole avalanche photodiode

We demonstrate two short-wavelength infrared avalanche photodiodes based on InAs/GaSb superlattice grown by metal-organic chemical vapor deposition.The difference between the two devices,namely,p+n-n+and p+nn-n+,is that the p+nn-n+device possesses an additional middle-doped layer to separate the multiplication region from the absorption region.By properly controlling the electric field distribution in the p+nn-n+device,an electric field of 906 kV/cm has been achieved,which is 2.6 times higher than that in the p+n-n+device.At a reverse bias of-0.1 V at 77 K,both devices show a 100%cut-off wavelength of 2.25μm.The p+n-n+and p+nn-n+show a dark current density of 1.5×10^-7 A/cm^2 and 1.8×10^-8 A/cm^2,and a peak responsivity about 0.35 A/W and 0.40 A/W at 1.5μm,respectively.A maximum multiplication gain of 55 is achieved in the p+nn-n+device while the value is only less than 2 in the p+n-n+device.Exponential nature of the gain characteristic as a function of reverse bias confirms a single carrier hole dominated impact ionization.

Back Illuminated N/P/P⁺Bifacial Silicon Solar Cell under Modulated Short-Wavelength: Determination of Base Optimum Thickness

A bifacial silicon solar cell under monochromatic illumination in frequency modulation by the rear side is being studied for the optimization of base thickness. The density of photogenerated carriers in the base is obtained by resolution of the continuity equation, with the help of boundary conditions at the junction surface (n+/p) and the rear face (p/p+) of the base. For a short wavelength corresponding to a high absorption coefficient, the AC photocurrent density is calculated and represented according to the excess minority carrier’s recombination velocity at the junction, for different modulation frequency values. The expression of the AC recombination velocity of excess minority carriers at the rear surface of the base of the solar cell is then deduced, depending on both, the absorption coefficient of the silicon material and the thickness of the base. Compared to the intrinsic AC recombination velocity, the optimal thickness is extracted and modeled in a mathematical relationship, as a decreasing function of the modulated frequency of back illumination. Thus under these operating conditions, a maximum short-circuit photocurrent is obtained and a low-cost bifacial solar cell can be achieved by reducing material (Si) to elaborate the base thickness.

Performance of dual-band short-or mid-wavelength infrared photodetectors based on InGaAsSb bulk materials and InAs/GaSb superlattices

In this paper,we demonstrate bias-selectable dual-band short-or mid-wavelength infrared photodetectors based on In0.24Ga0.76As0.21Sb0.79 bulk materials and InAs/GaSb type-II superlattices with cutoff wavelengths of 2.2μm and 3.6μm,respectively.At 200 K,the short-wave channel exhibits a peak quantum efficiency of 42%and a dark current density of5.93×10^-5）/cm^2at 500 mV,thereby providing a detectivity of 1.55×10^11cm·Hz^1/2/W.The mid-wave channel exhibits a peak quantum efficiency of 31%and a dark current density of 1.22×10^-3A/cm^2at-300 mV,thereby resulting in a detectivity of 2.71×10^10cm·Hz^1/2/W.Moreover,we discuss the band alignment and spectral cross-talk of the dual-band n-i-p-p-i-n structure.

What Mineral Resources will China Need to Discover by the Mid-21st Century？

In the past 40 years of China＇s reform and opening up, China＇s economy has been developing rapidly, and industrialization and urbanization have begun to take shape. At present, China is heading towards an information society. Mineral resources have played a great supporting role during this process. During the whole of 2017, China consumed 2.344 billion tons of iron ore, 2.4 billion tons of cement and 3.65 billion tons of raw coal （Fig. 1）.

冬枣黑斑病的光学特性检测方法建立

本研究旨在探究冬枣果实黑斑病过程中光学特性的变化,并筛选出病害检测的特征波长。采用单积分球检测系统结合反向倍加(IAD)算法测定冬枣果实在黑斑病过程中短-中波近红外区域(900~1650 nm)内光学吸收和散射特性,通过光学特性与品质指标间的相关性分析获得特征波长,最后通过近红外光谱对特征波长的有效性进行了验证。研究结果表明,随着黑斑病的发展,冬枣果实的失重率和a^(*)呈现明显的上升趋势,L^(*)、可溶性固形物及叶绿素含量则随贮藏时间下降。冬枣果实的吸收系数(μa)和约化散射系数(μs')均表现出明显的下降趋势。μa和μs'分别在1400~1650和900~1360 nm与病害程度(病斑面积)和部分品质指标(失重率、L^(*)、a^(*)、可溶性固形物和叶绿素)呈现高度相关。与全波长和基于算法获得的特征波长模型相比,基于光学特性优选的10个特征变量建立的冬枣黑斑病判别模型效果最佳,建模集和预测集总体正确率分别达到92.53%和92.35%,证明了短-中波近红外光学信号识别不同病害程度冬枣果实的潜力及基于光学特性优选的特征波长的有效性。

InAs/GaSb二类超晶格中/短波双色红外焦平面探测器

InAs/GaSb超晶格材料已经成为了第三代红外焦平面探测器的优选材料。开展了InAs/GaSb二类超晶格中/短波双色焦平面探测器器件结构设计、材料外延、芯片制备,对钝化方法进行了研究,制备出性能优良的320×256双色焦平面探测器。首先以双色叠层背靠背二极管电压选择结构作为基本结构,设计了中/短波双色芯片结构,然后采用分子束外延技术生长出结构完整、表面平整、低缺陷密度的PNP结构超晶格材料。采用硫化与SiO2复合钝化方法,最终制备的器件在77 K下中波二极管的RA值达到13.6 kΩ·cm^2,短波达到538 kΩ·cm^2。光谱响应特性表明短波响应波段为1.7~3μm,中波为3~5μm。双色峰值探测率达到中波3.7×10^11cm·Hz^1/2W^-1以上,短波2.2×10^11cm·Hz^1/2W^-1以上。响应非均匀性中波为9.9%,短波为9.7%。中波有效像元率为98.46%,短波为98.06%。

320×256 InAs/GaSb超晶格中/短波双色探测器组件研制

InAs/GaSb超晶格材料制备的新型红外器件在最近十几年得到了迅速发展。文中开展了InAs/GaSb二类超晶格中/短波双色焦平面探测器组件研制,设计了中/短波双色叠层背靠背二极管芯片结构,用分子束外延技术生长出结构完整、表面平整、低缺陷密度的PNP结构超晶格材料,制备出性能优良的320×256双色焦平面探测器组件,对探测器组件进行了测试分析。结果显示,在77 K下中波二极管RA值达到26.0 kΩ·cm^2,短波的RA值为562 kΩ·cm^2。光谱响应特性表明短波响应波段为1.7~3μm,中波为3~5μm,满足设计要求。双色峰值探测率达到中波3.12×10^11cm·Hz1/2W^-1,短波1.34×10^11cm·Hz1/2W^-1。响应非均匀性中波为9.9%,短波为9.7%。中波有效像元率为98.46%,短波为98.06%。

Prospects of China's Agricultural Development

Remarkable achievements have been made in China＇s agricultural development since the late 1970s. Nevertheless, deep-rooted problems are arising from inefficient farming practices. From mid- and long-term perspectives, migration of China＇s agricultural labor will slow and large-scale operation of farmland will accelerate. Although grain supply and demand have maintained a tight balance, new potentials still exist in improving grain production. Under the pressures of resource and environmental constraints, advancing the green and efficient transition of agriculture will become a new trend in China＇s agricultural development. In this context, the treatment of agricultural pollution, supply-side structural reform and innovation of agricultural subsidy policy are of strategic significance to the transition and upgrade of China＇s agriculture.

兼容集成中的新型材料系探索与特殊超晶格结构研究年度报告

含边缘元素的III-V族光电子合金材料是近些年逐渐兴起的一种新型材料系,开展相关研究的国家较少,这些合金的基本特性、合成以及器件应用等方面还存在很多未知,亟需推动。为此,该研究在含边缘元素的III-V族光电子材料的理论计算、合成实验与特性表征方面系统地开展基础创新研究。在理论研究方面,我们利用第一性原理重点计算了GaN1-xBix和InP1-xBix三元合金的电子结构与光学特性等,预测了Bi元素并入对合金物理性质的影响。在III-V族含硼材料的合成与特性表征方面,利用低压金属有机化学气相沉积技术,在GaAs上生长出了BGaAsB四元合金与BGaAsSb/GaAs MQW,明确了B并入对于Sb并入以及Ga As Sb/Ga As MQW光致发光特性的影响。基于InAs/GaSb二类超晶格实现短波、甚长波及窄带长波/甚长波双色红外探测器的研究,生长的材料具有极高的材料质量.短波探测器单管器件在77 K条件下50%截止波长为2.56μm,峰值探测率为1.3×1011cm·Hz1/2·W^(-1);中波探测器单管器件在77 K条件下50%截止波长为4.3μm,峰值探测率为2.4×1011 cm·Hz1/2·W^(-1);甚长波红外探测器单管器件在77 K条件下50%截止波长为14.5μm,量子效率为14%,热噪声限制的探测率为4.3×109 cm·Hz1/2 W^(-1).研究了分子束外延生长的中波、长波、甚长波波段的InAs/GaSb二类超晶格吸收层材料在77K和室温条件先非有意掺杂浓度、迁移率、导电率特性。发现随着温度的升高,分子束外延生长的中波、长波、甚长波红外吸收区材料都出现了导电类型由p型向n型的转变,其中中波、长波、甚长波样品的转变温度分别为210、140和85 K,相应的电子激活能为106、71和32 meV。

连接界面不定性对筋板结构中频振动的影响

以一个具有典型中频振动特征的简单梁板组合结构为例,讨论了连接界面不定性对于工程中常用的筋板类结构振动响应的主要影响特征以及对于中频混合模型法(hybrid FE/SEA method)的计算有效性与准确性的一般影响规律。分析表明:连接界面自由度数目不确定性的影响比连接界面位置的不确定性的影响更为显著,尤其是当界面自由度数目较少的情况下,随着筋板间的动态特性差异的增大,连接界面不定性的影响逐渐增强。采用中频混合模型法进行计算时应尽量减小连接界面自由度数目的不确定性,这对于梁板间具有较大动态特性差异的筋板组合结构的中频振动响应的准确预测来说显得尤为重要。

Effect of homogenization annealing on internal residual stress distribution and texture in ME21 magnesium alloy extruded plates

The distribution of residual stresses through thickness of 5 mm-thick ME21 magnesium alloy extruded plates was analyzed non-destructively using short-wavelength X-ray diffraction(SWXRD),and the effect of homogenization annealing before extrusion on the residual stress was discussed.The classic d 0 method with an annealed stress-free reference specimen was employed to determine the residual stress of the extruded plates.The residual stress results showed that the gradient of residual stress in the transverse direction was larger than that of the extrusion direction.The homogenization process prior to extrusion weaken the formed sample’s texture.The maximum residual stress of the as-extruded plate was reduced,and the residual stress distribution was homogenized.

High material quality growth of AlInAsSb thin films on GaSb substrate by molecular beam epitaxy

In this paper, high material quality Al_(0.4) In_(0.6) AsSb quaternary alloy on GaSb substrates is demonstrated. The quality of these epilayers is assessed using a high-resolution x-ray diffraction, Fourier transform infrared(FTIR) spectrometer,and atomic force microscope(AFM). The x-ray diffraction exhibits high order satellite peaks with a measured period of 31.06 ?(theoretical value is 30.48 ?), the mismatch between the GaSb substrate and AlInAsSb achieves-162 arcsec,and the root-mean square(RMS) roughness for typical material growths has achieved around 1.6 ? over an area of 10 μm×10 μm. At room temperature, the photoluminescence(PL) spectrum shows a cutoff wavelength of 1.617 μm.

NHC-derived carbon-centered luminescent radicals with shortwavelength emission via suppression of Kasha's rule

Luminescent organic radicals have garnered increasing attention owing to their versatile applications in sensing, imaging, and organic light-emitting diodes(OLEDs), attributed to their unique emission properties originating from the doublet spin state.However, the natural narrow bandgap of organic free radicals typically limits their emission to the long-wavelength region.Designing luminescent organic radicals with short-wavelength emission remains a significant challenge. Herein, a series of carbon-centered radicals with short-wavelength emission(383–476 nm) by combining N-heterocyclic carbenes with various polycyclic aromatic hydrocarbons(PAHs)(2-naphthyl, 2a~Ⅰ and 2b~Ⅰ;2-phenanthryl, 2a~Ⅱand 2b~Ⅱ;2-anthryl, 2a~Ⅲand 2b~Ⅲ;3-phenanthryl, 2a~Ⅳand 2b~Ⅳ). Theoretical calculations reveal that the introduction of PAHs significantly increases the ΔE_(D2-D1) in 2a^(Ⅰ–Ⅲ)and 2b^(Ⅰ–Ⅲ)compared to that in phenyl-derived radical congeners. Consequently, the internal transition from D2 to D1 is impeded, leading to a high yield of D2 emission and a suppressed Kasha's rule, thereby overcoming the limitations imposed by their narrow bandgap. For 2a~Ⅳ and 2b~Ⅳ, despite a moderately large ΔED2-D1value, the ΔED3-D1value exceeds 1 e V, indicating that their emission likely originates from the D3 state. Furthermore, we utilized 2a~Ⅲand 2b~Ⅲ as emissive materials in OLEDs,resulting in blue emissions with external quantum efficiencies of 7.5% and 6.5%, respectively.

Large and meso-α scale characteristics of intense rainfall in the mid- and lower reaches of the Yangtze River

Meteorological conditions associated with intense rainfall and great floods over mid- and lower reaches of Yangtze River are studied by analyzing the large-, synoptic-and meso-a-scale circulation systems for 1991, 1996 and 1998. It is found that the advance and retreat of subtropical high over the West Pacific, the monsoon moisture surge from the South China Sea, cold air outbreak over mid- and high-latitudes, and the meso-α scale systems (250-2500 km) from the Tibetan Pleateau as well, are responsible for intense rainfall over the Yangtze River Valley. The persistent and heavy rains and great floods over the Yangtze River Valley occurred when all these four systems are synergetic or in phase lock.

Visible-blind short-wavelength infrared photodetector with high responsivity based on hyperdoped silicon

Developing a low-cost, room-temperature operated and complementary metal-oxide-semiconductor(CMOS)compatible visible-blind short-wavelength infrared(SWIR) silicon photodetector is of interest for security,telecommunications, and environmental sensing. Here, we present a silver-supersaturated silicon(Si:Ag)-based photodetector that exhibits a visible-blind and highly enhanced sub-bandgap photoresponse. The visible-blind response is caused by the strong surface-recombination-induced quenching of charge collection for short-wavelength excitation, and the enhanced sub-bandgap response is attributed to the deep-level electrontraps-induced band-bending and two-stage carrier excitation. The responsivity of the Si:Ag photodetector reaches 504 mA · W^(-1) at 1310 nm and 65 m A · W^(-1) at 1550 nm under-3 V bias, which stands on the stage as the highest level in the hyperdoped silicon devices previously reported. The high performance and mechanism understanding clearly demonstrate that the hyperdoped silicon shows great potential for use in optical interconnect and power-monitoring applications.