One step to detect the latent fingermarks with gold nanoparticles

A simple and environment friendly chemical route for detecting latent fingermarks by one-step single-metal nanoparticles deposition method (SND) was achieved successfully on several non-porous items. Gold nanoparticles (AuNPs) synthesized using sodium borohydride as reducing agent in the presence of glucose, were used as working solution for latent fingermarks detection. The SND technique just needs one step to obtain clear ridge details in a wide pH range (2.5-5.0), whereas the standard multi-metal deposition (MMD) technique requires six baths in a narrow pH range (2.5-2.8). The SND is very convenient to detect latent fingermarks in forensic scene or laboratory for forensic operators. The SND technique provided sharp and clear development of latent fingermarks, without background staining, dramatically diminished the bath steps.

A meso elastoplastic constitutive model for polycrystalline metals based on equivalent slip systems with latent hardening

A meso material model for polycrystalline metals is proposed, in which the tiny slip systems distributing randomly between crystal slices in micro-grains or on grain boundaries are replaced by macro equivalent slip systems determined by the work-conjugate principle. The elastoplastic constitutive equation of this model is formulated for the active hardening, latent hardening and Bauschinger effect to predict macro elastoplastic stress-strain responses of polycrystalline metals under complex loading conditions. The influence of the material property parameters on size and shape of the subsequent yield surfaces is numerically investigated to demonstrate the fundamental features of the proposed material model. The derived constitutive equation is proved accurate and efficient in numerical analysis. Compared with the self-consistent theories with crystal grains as their basic components, the present theory is much simpler in mathematical treatment.

Supervised Gaussian Process Latent Variable Model for Dimensionality Reduction

The Gaussian process latent variable model (GP-LVM) has been identified to be an effective probabilistic approach for dimensionality reduction because it can obtain a low-dimensional manifold of a data set in an unsupervised fashion. Consequently, the GP-LVM is insufficient for supervised learning tasks (e. g., classification and regression) because it ignores the class label information for dimensionality reduction. In this paper, a supervised GP-LVM is developed for supervised learning tasks, and the maximum a posteriori algorithm is introduced to estimate positions of all samples in the latent variable space. We present experimental evidences suggesting that the supervised GP-LVM is able to use the class label information effectively, and thus, it outperforms the GP-LVM and the discriminative extension of the GP-LVM consistently. The comparison with some supervised classification methods, such as Gaussian process classification and support vector machines, is also given to illustrate the advantage of the proposed method.

Numerical Simulation of Transient Thermal Field in Laser Melting Process

Numerical simulation of thermal field was studied in laser processing. The 3-D finite element model of transient thermal calculation is given by thermal conductive equation. The effects of phase transformation latent are considered. Numerical example is given to verify the model. Finally the real example of transient thermal field is given.

Experimental Study on Convective Boiling Heat Transfer in Narrow-Gap Annulus Tubes

Since convective boiling or highly subcooled single-phase forced convection in micro-channels is an effective cooling mechanism with a wide range of applications, more experimental and theoretical studies are required to explain and verify the forced convection heat transfer phenomenon in narrow channels. In this experimental study, we model the convective boiling behavior of water with low latent heat substance Freon 113 (R-113), with the purpose of saving power consumption and visualizing experiments. Both heat transfer and pressure drop characteristics were measured in subcooled and saturated concentric narrow gap forced convection boiling. Data were obtained to qualitatively identify the effects of gap size, pressure, flow rate and wall superheat on boiling regimes and the transition between various regimes. Some significant differences from unconfined forced convection boiling were found,and also, the flow patterns in narrow vertical annulus tubes have been studied quantitatively.

Numerical simulation of temperature field evolution of metallic alloy surface due to pulsed laser treatment

This paper performed a numerical simulation on temperature field evolution for the surface layer of a metallic alloy subjected to pulsed Nd:YAG laser treatment. The enthalpy method was adopted to solve the moving boundary problem, I.e. Stefan problem. Computational results were obtained to show the temperature field evolution. Effects of latent heat and mushy zone width on the temperature field were investigated. The results also show very high values of temperature gradient and cooling rate, which are typical characteristics during the solidification process.

Surface-induced melting of metal nanoclusters

We investigate the size effect on melting of metal nanoclusters by molecular dynamics simulation and thermo dynamic theory based on Kofman's melt model. By the minimization of the free energy of metal nanoclusters with respect to the thickness of the surface liquid layer, it has been found that the nanoclusters of the same metal have the same premelting temperature T-pre = T-0 - T-0(gamma(su) - gamma(lv) - gamma(sl))/(rhoLxi) (T-0 is the melting point of bulk metal, gamma(sv) the solid-vapour interfacial free energy, gamma(sl) the liquid-vapour interfacial free energy, gamma(sl),l the solid-liquid interfacial free energy, p the density of metal, L the latent heat of bulk metal, and xi the characteristic length of surface-interface interaction) to be independent of the size of nanoclusters, so that the characteristic length of a metal can be obtained easily by T-pre, which can be obtained by experiments or molecular dynamics (MD) simulations. The premelting temperature T-pre of Cu is obtained by AID simulations, then xi is obtained. The melting point T-cm is further predicted by free energy analysis and is in good agreement with the result of our MD simulations. We also predict the maximum premelting-liquid width of Cu nanoclusters with various sizes and the critical size, below which there is no premelting.

A new expression of hardening coefficients for fcc-crystal and calibration of the material constants

In order to describe the effect of latent hardening on the macro-plastic behavior of foc-crystal, a new expression for hardening coefficient is proposed in which there are 12 material constants, each having clear physical meaning. And a method of material constant calibration is suggested and used to determine the material constants of copper and aluminum crystal. The simulated load-elongation curves along various crystallographic orientations are comparable with the experimental ones.

The inhomogeneity of plastic-deformation in ductile single-crystals

A discrete slip model which characterizes the inhomogeneity of material properties in ductile single crystals is proposed in this paper. Based on this model rate-dependent finite element investigations are carried out which consider the finite deformation, finite rotation, latent hardening effect and elastic anisotropy. The calculation clearly exhibits the process from microscopic inhomogeneous and localized deformation to necking and the formation of LSBS and reveals several important features of shear localization. For example, the inhomogeneous deformation is influenced by the imperfections and initial non-uniformities of material properties. The inhomogeneous deformation may either induce necking which results in the lattice rotation and leads to geometrical softening, which in turn promotes the formation of CSBS, or induces heavily localized deformation. The microscopic localized deformation eventually develops into the LSBS and results in a failure. These results are in close agreement with experiment. Our calculations also find that the slip lines on the specimen's surface at necking become curved and also find that if the necking occurs before the formation of LSBS, this band must be misoriented from the operative slip systems. In this case, the formation of LSBS must involve non-crystallographic effects. These can also be indirectly confirmed by experiment. All these suggest that our present discrete slip model offers a correct description of the inhomogeneous deformation characterization in ductile crystals.

Basic equations for suspension flows with interphase mass-transfer

In the case of suspension flows, the rate of interphase momentum transfer M(k) and that of interphase energy transfer E(k), which were expressed as a sum of infinite discontinuities by Ishii, have been reduced to the sum of several terms which have concise physical significance. M(k) is composed of the following terms: (i) the momentum carried by the interphase mass transfer; (ii) the interphase drag force due to the relative motion between phases; (iii) the interphase force produced by the concentration gradient of the dispersed phase in a pressure field. And E(k) is composed of the following four terms, that is, the energy carried by the interphase mass transfer, the work produced by the interphase forces of the second and third parts above, and the heat transfer between phases. It is concluded from the results that (i) the term, (-alpha-k-nabla-p), which is related to the pressure gradient in the momentum equation, can be derived from the basic conservation laws without introducing the "shared-pressure presumption"; (ii) the mean velocity of the action point of the interphase drag is the mean velocity of the interface displacement, upsilonBAR-i. It is approximately equal to the mean velocity of the dispersed phase, upsilonBAR-d. Hence the work terms produced by the drag forces are f(dc) . upsilonBAR-d, and f(cd) . upsilonBAR-d, respectively, with upsilonBAR-i not being replaced by the mean velocity of the continuous phase, upsilonBAR-c; (iii) by analogy, the terms of the momentum transfer due to phase change are upsilonBAR-d-GAMMA-c, and upsilonBAR-d-GAMMA-d, respectively; (iv) since the transformation between explicit heat and latent heat occurs in the process of phase change, the algebraic sum of the heat transfer between phases is not equal to zero. Q(ic) and Q(id) are composed of the explicit heat and latent heat, so that the sum Q(ic) + Q(id)) is equal to zero.

Long-Term Evolution Of Delayed Ettringite And Gypsum In Portland Cement Mortars Under Sulfate Erosion

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the 'penetration period', 'enhance period of strength', and 'macro-crack period'. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations occurred in two stages, the 'latent period' and the 'accelerated period'. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum. (C) 2008 Elsevier Ltd. All rights reserved.

Optimization of thermal environment during crystal growth of large-sized Nd : YAG by Temperature Gradient Technique

A finite-element model is employed to analysis the thermal environments in Temperature Gradient Technique (TGT) furnace during the growth of large-sized Nd:YAG crystal. The obtained results show that when the crucible is located at the lower position inside of the heater, a flatter solid-liquid interface is established, which makes it easier to obtain the core-free Nd:YAG crystal. Meanwhile, the lower crucible position can induce higher axial temperature gradient, which is beneficial to the release of latent heat. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

玉米农田水热碳通量动态及其环境控制机理研究

陆地生态系统与大气之间的水热碳交换是物质、能量循环的关键过程，一直以来都为研究者们所关注。进入20 世纪以来，特别是随着人们对全球气候变暖的逐步认识，气候变化对水热碳交换过程的影响及其对气候变化的响应研究更加备受关注。本研究以2004~2006 年近三年的涡度相关系统连续观测数据为依托，分析了雨养玉米农田水热碳通量的动态及其影响因子。研究表明，玉米农田水热通量(WHF) 呈显著的单峰型日变化， 日最大值出现在正午12:00~13:00，WHF 变化同步。潜热通量(LE)的季节变化规律与日变化相似，冬季小夏季大，年最大值与最小值分别出现在7 月和1 月。显热通量(Hs) 季节变化也呈单峰型，但年最大值出现在5 月，这主要与降水以及作物生长有关。半小时尺度上，WHF 主要受辐射控制，而日峰值受辐射峰值以及植被生长的双重影响；日尺度上，只要有降水过程，Hs 就会随土壤水分的增大而减小，降水停止后逐渐恢复。而降水对LE 的影响受到可用能量(AE)的干扰，表现出复杂的变化趋势。总的来说，降水持续时间越长AE 越少，对LE 的抑制越大；季节尺度上，WHF 受热量与水分的双重制约。Hs 随着天气回暖后第一次较大降水过程的出现呈现明显下降，而LE 则呈现相反的变化趋势。随着雨季到来和作物的生长，Hs 在7 月出现低谷，而LE 呈现相反的趋势随着降水量的增加而增大；年际间WHF 的分布规律大体一致，但因气象条件等的差异，特别是降水的差异造成年际间WHF 略有不同。在不同水文年型下，水分因子的影响作用有显著差异，且WHF 对热量与水分条件变化的敏感程度也不相同。欠水年，水分因子的作用更显著，是制约WHF 变化的主要控制因子，WHF 对水分的变化更敏感；而丰水年，水分因子的影响减弱，热量的盈亏决定着WHF 变化的主要方向。在不同水文年型下，水热碳通量对水热条件的变化表现出不同的响应方式，为研究生态系统对气候变化的响应提供了参考。 净碳(C)吸收期，玉米农田净碳交换(NEE)呈显著的日变化，在日出以后由CO2 释放转变为CO2 吸收，12:30 左右达到一天中的吸收峰值，日落前出现相反的转换。而净C 释放期内，NEE 均为正值且无明显日变化。NEE 季节变化也呈单峰型二次曲线，在7 月下旬或8 月上旬达到年最大吸收率。根据NEE 的正负，一年分为三个阶段：两个C 排放期与一个C 吸收期。一般C 吸收期从6月开始到9 月结束，此前此后均为C 排放期。在半小时、日时间尺度上，光通量密度(PPFD)与NEE 有着相似的变化规律，是控制NEE 的主要因子；在日、季节尺度上，叶面积指数(LAI)和气孔导度(gs)是影响NEE 的主要生物因子，且gs 的影响程度随着发育期的变化而变化，而不同年份间LAI 对NEE 的影响没有显著的差异。几乎在所有时间步长上，土壤温度(Ts)均为生态系统呼吸(Re)的主要控制因子，时间尺度愈短，二者的相关性愈好。总的来说，在较短时间尺度上，高PPFD 与夏季低温将会促进C 的吸收，有利于C 累积。 玉米农田日最大净C 吸收速率(NEEmax, daily)以及吸收释放转换点(NEE=0)均受PPFD 控制。NEEmax, daily 出现时间与PPFDmax, daily 出现时间几乎完全一致，当PPFD 达到1 日内极大值时，净C 吸收也相应达到了日最大值。但NEEmax, daily的量值还受到其它因子的影响。当水分条件充足时，还将受到LAI、gs 等生物因子的控制。NEE 由正转为负的转换点也是由PPFD 决定。当PPFD 稳定大于PPFD*( PPFD*=100 μmol•m-2s -1)时，净C 吸收开始；当PPFD 稳定小于PPFD*时，净C 吸收由此结束。1 日内，PPFD 稳定通过PPFD*之间的时间间隔决定了日净C 吸收的时间长度。日净C 吸收的时间越长，吸收量也越大，且有明显的季节变化，7 月最长9 月最短。 按照热量水分状况将三年分组，分为I 组(水分状况相似，热量条件不同)与II 组(热量条件相似，水分状况不同)。 I 组年际间PPFD 波动是造成C 交换格局变化的关键原因。而II 组年际间C 交换格局不同是由降水量及其不同分布引起的土壤含水量(SWC)变化是造成。SWC 可以解释年际间NEE 变异的97%，而大气水汽压亏缺(VPD)可以解释30.7%；温度因子通过影响C 收支中的呼吸项，间接影响着生态系统的NEE，它可以解释年际间NEE 变异的73.9%，也是造成年际间C 交换格局不同的原因之一；另外，PPFD 和发育期早晚以及净C吸收期长度等也同样影响着C 交换格局的变化。综合两组情况来看，由水分条件年际变化引起的NEE 的波动大于能量年际变化引起的波动。总之，在较长时间尺度上，NEE 对SWC 变化比其对PPFD 变化更敏感，说明在半干旱地区土壤水分条件仍然是决定C 交换格局的主导因子。 NEE 与LE 呈线性相关，它们之间的相关性主要受温度和NEE 的控制，温度越高，二者的相关性越弱，而NEE 越大二者相关性越好。同时，作物蒸腾与土壤蒸发的比例也是影响NEE 与LE 之间关系的主要因素。蒸腾作用所占的比例越大，二者的线性关系越显著，而土壤蒸发比例越大，二者的相关性越弱。总的来说，NEE 与LE 之间的线性关系有明显的季节变化，生长季好于非生长季，夏天好于冬天。 总之，雨养玉米农田水热碳通量既具有其它农田生态系统共有的动态特征，也具有其特有特征。