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The formation and growth kinetics of the intermetallic compound (IMC) between lead-free solder and Cu substrate in the surface mount process were studied. Optical and scanning electron microscope (OM and SEM) were used to measure the thickness of intermetallic layers and observe the microstructure evolution of solder joint. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffraction (XRD). The grain size of the intermetallic compound /spl eta/-phase Cu/sub 6/Sn/sub 5/ was observed to increase with the increase in peak temperature hold time. The results show that a /spl eta/-phase Cu/sub 6/Sn/sub 5/ IMC layer is formed at solder-Cu substrate interface at a very short time. The growth of intermetallics formation was found not to follow the Fick's law that predicts the mean total thickness increases linearly with the square root of the time. It deviates the Fick's law at the early stage of the growth process and then approaches the parabolic law. To explore the growth kinetics, the IMC growth mechanism is suggested and a lagging diffusion model is presented for predicting the intermetallic compound layer growth. Comparison between the model and experimental results demonstrates that the proposed phase-lag model captures the growth history of IMC layers quite well.

Intermetallics formation between metallization conductor Pd–Ag and solder 62Sn–36Pb–2Ag has been investigated by transmission electron microscopy (TEM) and X-ray diffraction. Energy-dispersive X-ray (EDX) analysis and Selected Area Electron Diffraction (SAED) analysis reveals the formation of the intermetallic compounds Ag 5 Sn, Ag 3 Sn, Pd 2 Sn, PdSn 2, PdSn 4 , and PbPd 3 . X-ray diffraction results further confirm the coexistence of the above phases and additional intermetallic compounds including Pd 3 Sn 2 , PdSn and Pb 3 Pd 5 . Evident single phase intermetallic compound (IMC) layer structure is not observed. The different intermetallic phases coexist near the metallization/solder interface. Silver–tin intermetallic compounds are also observed in the solder.

The Yingxiong Mountains are located in the western Qaidam Basin of China, and the potential for oil reservoirs in this area is significant. Due to the rugged terrain and common inclement weather in the area, there are a number of challenges and difficulties for seismic exploration, so this area was once considered to be a “forbidden zone” for seismic prospecting. 2-D seismic exploration in this area has been attempted since 1995, but the signal-to-noise ratio (S/N) of the seismic data has been poor, owing to the rugged terrain and complex near-surface structure. With the on-going advancement of geophysical techniques, and upgrades to operational equipment in recent years, the data quality has been continuously improved using 2-D wide-line, and the outline of structures can now be interpreted. In 2010, seismic exploration led to the discovery of a big oil reservoir in this area. As a continuation of that work, high-density, 3-D seismic acquisition techniques were employed for the first time in the Yingxiong Mountains in 2011. The quality of the 3-D seismic data has made significant progress using: shot and geophone array joint suppressing noises, high density sampling indoor de-noising, high fold stack, high density pre-migration, and a mark interface verifying static correction. According to detailed 3-D seismic data interpretation, the Yingxiong Mountains oil field may account for over a hundred million tons of oil, and successful drilling in this area would constitute one of the most successful complex mountainous 3-D seismic prospecting projects.

Buildings have more or less changed the microclimate around their surroundings, which will affect natural ventilation of the building and pedestrian's feelings of comfort in the outdoor environment. In this paper, we simulate the distribution of airflow and pressure around buildings of a specific training school utilizing finite volume method and RNG k-ɛ turbulence models. The results indicate that U-shaped building layout has a positive correlation between heat dissipation in summer and wind prevention in winter, providing good conditions for outdoor activities due to the different prevailing wind directions in four seasons; the pressure difference between windward side and leeward side of buildings varies significantly as the height and horizontal position changes, therefore a few rooms in the corner can't ventilate well and need auxiliary approaches to improve. Through the analysis of wind velocity, pressure and air age around the buildings, we conclude suggestions about the improvement of building energy conservation as well as resident comfort.

[ 1 12] Cu–7at.%Al single crystals as well as [ 1 23], [ 1 17] and [023] Cu–16at.%Al single crystals were cyclically deformed under constant plastic strain control at room temperature. The cyclic hardening curve of [ 1 12] Cu–7at.%Al single crystal can be divided into three stages, namely initial non-hardening stage, rapid hardening stage and saturation stage. The cyclic stress–strain (CSS) curve exhibited a plateau region in the range of γpl, from 1.1×10−3 to 4.5×10−3. The saturation stress of the plateau is about 27 MPa. The occurrence of strain burst depends on the applied plastic strain amplitude γpl. No strain burst was detected when γpl, was below 4.4×10−4 or above 1.1×10−3. The cyclic deformation and strain burst behavior of [ 1 23], [ 1 17] and [023] Cu–16at.%Al single crystals are different from that of [ 1 12] Cu–7at.%Al single crystal. The cyclic deformation of all three differently oriented Cu–16%Al single crystals is unstable with the frequent occurrence of irregular strain bursts. The specimens cyclically hardened at a very low rate and saturation was not attained at high strain amplitudes. The experimental results indicate that the crystallographic orientation has almost no effect on the cyclic deformation and strain burst behavior of Cu–16at.%Al single crystals. The evolution of slip bands during cyclic deformation in both Cu–7at.%Al and Cu–16at.%Al single crystals is similar to the development of Luders band. The percolation of slip bands along the gauge length is generally accompanied by strain bursts. The above experimental results were explained in terms of the variation of slip mode with Al content in the alloys and the corresponding strain localization during cycling.

Explicit finite element procedures for the simulation of sheet-metal-forming processes are reviewed. Improved techniques for contact searching and contact force evaluation are then proposed and discussed. In the contact searching algorithm, a new contact territory definition is introduced and only node-to-segment contact pairs are defined, which makes the post-contact searching more efficient and easy to implement. For contact force evaluation, a novel approach is employed to make the simulation of sheet forming processes more accurate. The algorithms are implemented and examined via experiments.

An accurate and efficient shell element is presented. The stiffness of the shell element is decomposed into two parts with one part corresponding to stretching and bending deformation and the other part corresponding to shear deformation of the shell. Both parts of the stiffness are calculated with reduced integration rules, thereby improving computational efficiency. Shear strains are averaged on the reference surface such that neither locking phenomena nor any zero energy mode can occur. The satisfactory behaviour of the element is demonstrated in several numerical examples.

Interdiffusion and intermetallics formation between metallization conductor Pd–Ag and solder 62Sn-36Pb-2Ag have been studied. Silver and palladium dot mapping images of solder joints demonstrate that the Pd–Ag metallization layer gradually disappears after 11 days of ageing. It is observed that silver-rich areas exist in the bulk of the 62Sn-36Pb-2Ag solder after ageing but palladium-rich areas are not evident. The diffusion coefficient of the silver in the solder joints for this material system was measured. The activation energy and pre-exponential factor for the silver diffusion were found to be about 0.475 eV and 0.56×10 -10 m 2 s −1 , respectively for the configuration of surface mount thick film solder joints studied. X-ray diffraction results reveal the formation of the intermetallic compounds Ag 5 Sn, Ag 3 Sn, Pd 3 Sn 2, Pd 2 Sn , PdSn 2 , PdSn 4, PdSn , PbPd 3 , and Pb 3 Pd 5 .

In this paper, we describe sex-related health risks among hostesses in two metropolises in China based on data obtained from in-depth interviews. The data show that hostesses, many engaging in commercial sex, are vulnerable to HIV infection, unwanted pregnancies and reproductive tract infections. Nevertheless, many obstacles still are present that hinder them from engaging in safe sex. The findings from our study illustrate the need for targeted interventions in order to improve reproductive health and promote safe sex among this group.

The effects of tin diffusion, silver and palladium dispersion, and intermetallic compound growth on the shear fatigue of solder joints between thick film mixed bonded conductor Pd-Ag and solder 62Sn-36Pb-2Ag are investigated. Microstructural analysis reveals that the intermetallic compounds (IMC's) Pd/sub 3/Sn/sub 2/, Pd/sub 3/Sn, Pd/sub 2/Sn, Pd/sub 3/Sn/sub 2/, PdSn, PdSn/sub 2/, PdSn/sub 4/, Ag/sub 5/Sn, Ag/sub 3/Sn, PbPd/sub 3/, and Pb/sub 3/Pd/sub 5/ are formed after aging. X-ray dot maps demonstrate that the longer the aging time, the more serious the silver and palladium dispersion into the solder and the tin diffusion into the conductor. It is observed that the tin diffuses to the interface of the substrate/conductor after 120 h aging. Shear strength tests with different strain rate show that the adhesion strength decreases with prolongation of aging time. Shear cycling tests indicate that the fatigue lifetime of the solder joints depends on the diffusion depth of the silver and palladium, especially the tin diffusion into the thick film conductor. The above results mean that the more serious is the tin and silver interdiffusion, and the more IMC's are formed in the solder joint (effects which are the result of prolonged storage at high temperature or of long term operation in real SMT assemblies), the more sensitive is the solder joint to stress. Eventually fatigue failure of the joint may result. It is argued that volume change and increased brittleness caused by the intermetallic formation, and volume swelling of the conductor layer due to tin diffusion, are major factors in the decrease of fatigue lifetime and degradation of the shear strength of the solder joints.

The novel fluoronitroaryl azo diaminobenzene chromophores for potential NLO applications were synthesized and the effects of the position of the fluorine group on the properties of the chromophores were investigated. These chromophores exhibit high decomposition temperatures whilst keeping molecular hyperpolarizabilities similar to those of the non-fluorinated analogues. The chromophore 2,4-diamino-4′-fluoro-3′-nitroazobenzene (2R-4F-3N-DIAMINE) shows a significant UV blue shift and a combination of good transparency, high thermal stability and nonlinearity in comparison with 2,4-diamino-2′-fluoro-5′-nitroazobenzene (2R-2F-5N-DIAMINE) and its non-fluorinated analogue 2,4-diamino-3′-nitroazobenzene (2R-3N-DIAMINE).

The free vibration problem of unsymmetrical sandwich plates with laminated composite faces and orthotropic core is analysed in the consideration of the effects of bending, transverse shear, plane inertia, rotatory inertia, and coupling inertia. The spline finite point method (SFPM) is selected to solve the present problem and to establish the basic formulae for a computer programme that can be run on microcomputer. A lot of numerical examples of the cross-ply face sandwich plates, with various boundary conditions, are obtained by the present method to make clear for coupling effects of composite material plates and to seek the optimum ply design of engineering structures.

Bicrystals are widely used to demonstrate the grain boundary (GB) effects on plastic deformation behavior of metals and alloys. In a series of reports to be followed the authors will investigate the effect of the slip continuity across GB, the strain incompatibility at GB and the interaction of dislocation with GB on the cyclic deformation behavior by using different type of copper bicrystals. In the present report, the cyclic deformation behavior of a co-axial symmetrical bicrystal of which the component crystals are single-slip-oriented was investigated.

Research on dielectric elastomer generators (DEGs) which can be utilized to convert mechanical energy to electrical energy has gained wide attention lately. However, very few works account for the operating temperature, viscoelasticity and current leakage in the analysis of DEGs simultaneously. In this study, under several compound four-stroke conversion cycles, the electromechanical performance and energy conversion of a dissipative DEG made of a very-high-bond (VHB) elastomer are investigated at different operating temperatures. The performance parameters such as energy density and conversion efficiency are calculated under different temperatures. Moreover, the common failure modes of the generator are considered: material rupture, loss of tension, electrical breakdown and electromechanical instability. The numerical results have distinctly shown that the operating temperature plays an important role in the performance of DEGs, which could possibly make a larger conversion efficiency for the DEG.

This work investigates the effects of Sb on IMC formation and mechanical properties of Sn-3.5Ag-0.7Cu lead-free solder joints. In this work, SEM is used to measure the thickness of intermetallic layer and observe the microstructural evolution of solder joint. The IMC phases are identified by EDX and XRD. Results show that there is a significant drop in IMC thickness when Sb is about 0.8 wt%. The tensile strength of the solder joints can be slightly improved by adding a small amount of Sb in Sn-Ag-Cu alloy system.

The local Petrov-Galerkin method (MLPG) is applied to solve the geometrically nonlinear problem in this paper. The local Petrov-Galerkin method uses the mov- ing least square approximation as a trial function, and involves only integrations over a regular local subdomain and on a local subboundary centered at a node in question. These special properties lead to a more convenient formulation in dealing with nonlinear problems. An incremental and iterative solution proce- dure is used to solve the geometrically nonlinear problem. Formulations for the geometrically nonlinear problems are obtained from virtual work principle. All measures are related back to the original configuration. Several examples are given to show that the local Petrov-Galerkin method has good accuracy in solving the geometrically nonlinear problem.

In this paper, a neural network (NN) model was designated to identify the geo- metric parameters of drawbead in sheet forming processes. The genetic algorithm (GA) was used to determine the neuron numbers of the hidden layers of the neural network, and a sample design method with the strategy of updating training sam- ples was also used for the convergence. The NN model goes through a progressive retraining process and the numerical study shows that this technique can give a good result of the parameter identification of drawbead.

A meshless local Petrov-Galerkin method (MLPG) is presented for solving the elasto-plasticityprobleminthepaper.Itisatrulymeshlessmethodusingthemov- ing least square (MLS) approximation as a trial function and the MLS weighted function as a test function in the weighted residual method. The incremental tangent stiffness method is applied in computation. Numerical examples show that the local Petrov-Galerkin method is applicable and effective for solving the elasto-plasticity problem.

An edge-based smoothed tetrahedron radial point interpolation method (ES-T-RPIM) is formulated for the 3D acoustic problems, using the simplest tetrahedron mesh which is adaptive for any complicated geometry. In present ES-T-RPIM, the gradient smoothing operation is performed with respect to each edge-based smoothing domain, which is also serving as building blocks in the assembly of the stiffness matrix. The smoothed Galerkin weak form is then used to create the discretized system equations. The acoustic pressure is constructed using radial point interpolation method, and two typical schemes of selecting nodes for interpolation using RPIM have been introduced in detail. It turns out that the ES-T-RPIM provides an ideal amount of softening effect, and significantly reduces the numerical dispersion error in low- to mid-frequency range. Numerical examples demonstrate the superiority of the ES-T-RPIM for 3D acoustic analysis, especially at mid-frequency.

To access the saliva level of 3-methoxy-4-hydroxy-phenylglycol (sMHPG) as an index of mental health in normal volunteers, we investigated the relationship between the sMHPG and the scores on the general health questionnaire-28 (GHQ-28). A total of 270 normal volunteers answered the GHQ-28 and the sMHPG levels were determined. The sMHPG levels in women and men were comparable. There was a significant negative correlation between the social dysfunction score on the GHQ-28 and sMHPG levels in women (P = 0.0035), but not in men. Moreover, the sMHPG levels also correlated with the total GHQ-28 score (P = 0.0205), the anxiety and the insomnia score (P = 0.0306) in women. These data indicate a high social dysfunction score on the GHQ-28 to be associated with a reduced noradrenergic neuronal tone thus possibly reflecting psychomotor retardation in women.

We present an optimized face-down die attachment for single-mode ridge-waveguide laser diodes (LDs) using Au80Sn20 solder. Based on this improved technique, a bonding process window has been determined through microstructure and mechanical investigation of the solder joint, and electro-optical characterization of LDs. Metallographical investigation shows that the solder joint comprises of a layer of /spl delta/ phase near the LD/solder and solder/heatsink interfaces, /spl zeta/ phase at the center of the solder joint, and a layer of (Au, Ni)Sn intermetallic compound (IMC) at the solder/heatsink interface. The /spl delta/ phase shifted to the interfaces, while /spl zeta/ phase Au/Sn compound is remaining at the center of the joint, is postulated by the lower surface tension in /spl delta/ phase. Mechanical shear testing demonstrates good bonding integrity, which meets the requirements specified by MIL-STD-883C. Fracture surface characterization shows brittle fracture occurring within the LD, at the GaAs/SiN interface. This optimized bonding process can achieve optical improvement of 2.5-3/spl times/ compared to unbonded LDs due to good thermal management.

Structural changes and surface morphology have been characterizeded by X-ray diffraction, SEM and Raman spectroscopy for the surface of WC-Co substrates, which were preheated by direct radiation from Ta or W filaments under a pure hydrogen atmosphere. A thin diamond film was then deposited on the substrates in a hot filament CVD apparatus under an acetone and hydrogen atmosphere. It was found that the surface structure is very sensitive to the treatment conditions. The hot filament evaporation is beneficial in removing elemental Co in the substrate and enhancing the diamond quality as well as the adhesion.

To determine the effects of noradrenergic neuronal activity on performance in continuous tasks requiring effortful attention, the performance of 23 male students in the Uchida-Kraepelin test (UKT) was examined. The UKT requires continuous arithmetic addition of single-digit figures for 25 min. The relationship of performance with saliva levels of 3-methoxy-4-hydroxyphenylglycol (sMHPG) was analyzed. Saliva samples were taken before, during and after test performance, and sMHPG levels determined by gas chromatography-mass spectrometry. There was no significant change in mean sMHPG as a result of test performance. However, when initial effort was calculated, defined as number of items completed during the 1st min subtracted from the average completed per minute in the 1st and the 2nd halves (blocks) of the test, significant correlations with sMHPG (p = 0.0002 for the 1st block and p < 0.0001 for the 2nd block) were found. Thus the data indicate that noradrenergic neuronal activity affects the performance on continuous tasks requiring effortful attention.

In this paper, direct adaptive neural network control is studied for a class of multi-input and multi-output (MIMO) nonlinear systems based on input-output model with unknown inter connections between subsystems. The proposed adaptive algorithm is very simple and easy to implement. By finding a unitary orthogonal matrix to tune the NN weights, the closed-loop system is proved to be semi-globally uniformly ultimately bounded (SGUUB). The control performance of the closed-loop system is guaranteed by suitably choosing the design parameters.

The effects of antimony on the microstructural evolution and the intermetallic compound (IMC) growth of Sn-3.5Ag-O.7Cu lead-free solder joints were investigated in this work. To investigate the element diffusion and the growth kinetics of IMC formation in solder joint, isothermal aging test is performed at temperatures of 100°C, 150°C, and 190°C respectively. Optical and scanning electron microscope (OM and SEM) were used to measure the thickness of intermetallic layers and observe the microstructure evolution of solder joint. The IMC phases were identified by energy dispersive X-ray (EDX) and X-ray diffraction (XRD). Results show that the thickness of IMC layer reduces and the grain size decreases with the increase in antimony composition. The activation energy and growth rate of the IMC formation were determined. Results reveal that adding antimony in Sn-3.5Ag-0.7Cu solder system could increase the activation energy, and thus reduce the atomic diffusion rate so as to inhibit the excessive growth of IMC. It is also observed that the fme particles precipitated along the grain boundary of IMC increase with the increase of Sb composition. Based on the observation of the microstructural evolution of the solder joints, a grain boundary pinnimg mechanism for the inhibition of IMC growth due to Sb addition was proposed.

Delaminations of the embedded passive components are often associated with reliability problems. Understanding the delamination can help us quickly identify the failure cause at an early stage of the failure analysis. In this work, defects of buried capacitors have been detected by use of scanning acoustic microscopy (SAM). The results show that SAM can be a powerful analytical tool for the nondestructive evaluation of delaminations in buried passive components. T-scan is an effective method for determining the existence of the internal defects, and TAMI-scan is shown to be capable of detecting the location and size of the delamination and void.

The effects of Sn diffusion, Ag and Pd dispersion and intermetallic compound growth on the shear fatigue of solder joints between thick film mixed bonded Pd-Ag conductor and 62Sn-36Pb-2Ag solder are investigated. The samples were prepared by assembling leadless ceramic chip carrier (LCCC) passive components on a 96% Al/sub 2/O/sub 3/ substrate and ageing at 150/spl deg/C for varying times. Microstructural analysis reveals that the intermetallic compounds (IMC) Pd/sub 3/Sn/sub 2/, Pd/sub 3/Sn, Pd/sub 2/Sn, PdSn, PdSn/sub 2/, PdSn/sub 4/, Ag/sub 5/Sn, Ag/sub 3/Sn, PbPd/sub 3/, and Pb/sub 3/Pd/sub 5/ are formed after ageing. X-ray dot maps demonstrate that the longer the ageing time, the more serious the Ag and Pd dispersion into the solder and the Sn diffusion into the conductor. It is noted that the Sn diffuses to the interface of the substrate/conductor after 120 hours ageing. Shear strength tests at varying strain rates show that adhesion strength decreases with prolonged ageing time. Shear cycling tests indicate that the solder joint fatigue lifetime depends on the Ag and Pd diffusion range, and especially on Sn diffusion into the thick film conductor. These results mean that the more serious the Sn and Ag interdiffusion, and the more IMC is formed in the solder joint (which can be due to prolonged high temperature storage or long term operation of SMT assemblies), the more sensitive is the solder joint to stress, eventually leading to fatigue failure. It is argued that volume change and increased brittleness due to intermetallic formation, and conductor layer volume swelling due to Sn diffusion are major factors in the decrease of solder joint fatigue lifetime and shear strength.

The frequency selective surfaces (FSS) on both normally and in-plane biased ferrite slab is analyzed using the full-wave moment method solution in this paper. The extra degree of freedom offered by the biased ferrite can be used to tune the resonance characteristics of FSS. Numerical results show that the reflection band center frequencies can be adjusted by several gigahertz.

In this paper, anodic bonding between silicon wafer and glass wafer (Pyrex 7740) has been successfully achieved at low temperature. The bonding strength is measured using a tensile testing machine. The interfaces are examined and analyzed by scanning acoustic microscopy (SAM), scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS). Prior to bonding, the wafers are cleaned in RCA solutions, and the surfaces become hydrophilic. The effects of the bonding parameters, such as bonding temperature, voltage, bonding time and vacuum condition, on bonding quality are investigated using Taguchi method, and the feasibility of bonding silicon and glass wafers at low temperature is explored. The bonding temperature used ranges from 200 °C to 300 °C. The sensitivity of the bonding parameters is analyzed and it is found that the bonding temperature is the dominant factor for the bonding process. Therefore, the effects of bonding temperature are investigated in detail. High temperatures cause high ion mobility and bonding current density, resulting in the short transition period to the equilibrium state. Almost bubble-free interfaces have been obtained. The bonded area increases with increasing the bonding temperature. The unbonded area is less than 1.5% within the whole wafer for bonding temperature between 200 °C to 300 °C. The bonding strength is higher than 10 MPa, and increases with the bonding temperature. Fracture mainly occurs inside the glass wafer other than in the interface when the bonding temperature is higher than 225 °C. SIMS results show that the chemical bonds of Si-O form in the interface. Higher bonding temperature results in more oxygen migration to the interface and more Si-O bonds. The bonding mechanisms consist of hydrogen bonding and Si-O chemical reaction.

Commercial agriculture has come under increasing pressure to reduce nitrogen fertilizer inputs in order to minimize potential nonpoint source pollution of ground and surface waters. This has resulted in increased interest in site specific fertilizer management. One way to solve pollution problems would be to determine crop nutrient needs in real time, using remote detection, and regulating fertilizer dispensed by an applicator. By detecting actual plant needs, only the additional nitrogen necessary to optimize production would be supplied. This research aimed to develop techniques for real time assessment of nitrogen status of corn using a mobile sensor with the potential to regulate nitrogen application based on data from that sensor. Specifically, the research first attempted to determine the system parameters necessary to optimize reflectance spectra of corn plants as a function of growth stage, chlorophyll and nitrogen status. In addition to that, an adaptable, multispectral sensor and the signal processing algorithm to provide real time, in-field assessment of corn nitrogen status was developed. Spectral characteristics of corn leaves reflectance were investigated in order to estimate the nitrogen status of the plants, using a commercial laboratory spectrometer. Statistical models relating leaf N and reflectance spectra were developed for both greenhouse and field plots. A basis was established for assessing nitrogen status using spectral reflectance from plant canopies. The combined effect of variety and N treatment was studied by measuring the reflectance of three varieties of different leaf characteristic color and five different N treatments. The variety effect on the reflectance at 552 nm was not significant (a = 0.01), while canonical discriminant analysis showed promising results for distinguishing different variety and N treatment, using spectral reflectance. Ambient illumination was found inappropriate for reliable, one-beam spectral reflectance measurement of the plants canopy due to the strong spectral lines of sunlight. Therefore, artificial light was consequently used. For in-field N status measurement, a dark chamber was constructed, to include the sensor, along with artificial illumination. Two different approaches were tested (i) use of spatially scattered artificial light, and (ii) use of collimated artificial light beam. It was found that the collimated beam along with a proper design of the sensor-beam geometry yielded the best results in terms of reducing the noise due to variable background, and maintaining the same distance from the sensor to the sample point of the canopy. A multispectral sensor assembly, based on a linear variable filter was designed, constructed and tested. The sensor assembly combined two sensors to cover the range of 400 to 1100 nm, a mounting frame, and a field data acquisition system. Using the mobile dark chamber and the developed sensor, as well as an off-the-shelf sensor, in- field nitrogen status of the plants canopy was measured. Statistical analysis of the acquired in-field data showed that the nitrogen status of the com leaves can be predicted with a SEP (Standard Error of Prediction) of 0.27%. The stage of maturity of the crop affected the relationship between the reflectance spectrum and the nitrogen status of the leaves. Specifically, the best prediction results were obtained when a separate model was used for each maturity stage. In-field assessment of the nitrogen status of corn leaves was successfully carried out by non contact measurement of the reflectance spectrum. This technology is now mature to be incorporated in field implements for on-line control of fertilizer application.

This paper presents an explicit smoothed finite element method (SFEM) for elastic dynamic problems. The central difference method for time integration will be used in presented formulations. A simple but general contact searching algorithm is used to treat the contact interface and an algorithm for the contact force is presented. In present method, the problem domain is first divided into elements as in the finite element method (FEM), and the elements are further subdivided into several smoothing cells. Cell-wise strain smoothing operations are used to obtain the stresses, which are constants in each smoothing cells. Area integration over the smoothing cell becomes line integration along its edges, and no gradient of shape functions is involved in computing the field gradients nor in forming the internal force. No mapping or coordinate transformation is necessary so that the element can be used effectively for large deformation problems. Through several examples, the simplicity, efficiency and reliability of the smoothed finite element method are demonstrated.

This paper presents a curvature-constructed method (CCM) for bending analysis of thin plates using three-node triangular cells and assumed piecewisely linear deflection field. In the present CCM, the formulation is based on the classic thin plate theory, and only deflection field is treated as the field variable that is assumed piecewisely linear using a set of three-node triangular background cells. The slopes at nodes and/or the mid-edge points of the triangular cells are first obtained using the gradient smoothing techniques (GST) over different smoothing domains. Three schemes are devised to construct the curvature in each cell using these slopes at nodes and/or the mid-edge points. The generalized smoothed Galerkin weak form is then used to create the discretized system equations. The essential rotational boundary conditions are imposed in the process of constructing the curvature field, and the translational boundary conditions are imposed in the same way as in the standard FEM. A number of numerical examples, including both static and free vibration analyses, are studied using the present CCM and the numerical results are compared with the analytical ones and those in the published literatures. The results show that outstanding schemes can obtain very accurate solutions.

An internal friction peak (around - 84° C, f = 0.8 hz) was observed in Al-0.5 wt % (0.19 at %) Ga cold-drawn to 12% reduction in area at 20°C. This peak was stable when measurements were taken below 20°C with decending and ascending temperatures and the height of the peak decreased after an anneal at elevated temperatures. It disappeared completely after an anneal at 200°C. The peak height first increased and then decreased with the amount of cold-working at 20° C and a 12% reduction in area seems to be close to the optimum amount of cold-working. The activation enthalpy associated with this internal friction peak measured with the method of changing of frequency is 0.85 ± 0.05 eV. A dislocation-kink dragging model is suggested in which the mobile agents that interact with dislocation kinks are Ga atom-vacancy pairs. The effect of the temperature of previous deformation on the behavior of the internal friction peak is discussed. It is contemplated that the broadening of the peak when the previous plastic deformation was made at -196°C may be due to the formation of Ga atom-divacancy pairs.

Two kinds of mathematical models, i.e. continuous and, discrete models of porulation processes have been justified according to actual demographic statistics of china. Numerical analysis and perspective estimation of dynamic population processes for china been given. A rubber of possible projects of population control and their implications for China have been investiated. Two versions of stability theorem for any population systems are presented. Finally, the structure of large scale population control system has been studied.

The activation enthalpies associated with stress-induced migration of O or N in Ta and Nb were accurately determined on high-purity metals doped with only one type of interstitial atoms. Internal friction and elastic aftereffect measurements were carried out in the same apparatus. New procedures were developed in processing the internal friction and elastic aftereffect data for determining the temperature dependence of the relaxation time. The activation enthalpies obtained for Ta-O, Ta-N, Nb-O and Nb-N are 1.10 5 , 1.67, 1.15, 1.58 eV, respectively, with statistical errors in the range of ±0.01 to 0.02 eV.

Powers and Doyle proposed the existence of pairs of oxygen atoms in interstitial solid solutions of tantalum, based on internal friction measurements from which an asymmetrical broadening of the observed Snoek peak was derived. The present experiments on high-purity tantalum doped only with oxygen in different concentrations show clearly that the oxygen Snoek peak is highly symmetrical for all investigated oxygen contents (up to 5900 at.ppm). The peak is somewhat broadened and shifted to slightly higher temperatures for the higher oxygen contents. Powers' experimental data are carefully reanalyzed and the asymmetry of the Snoek peak cannot be confirmed. It appears thus that the existence of oxygen pairs in tantalum-oxygen solid solutions proposed by Powers is questionable. It has been found that the broadened Snoek peak for the higher oxygen contents can be described by a continuous distribution of relaxation times. Possible physical models to account for the symmetrical broadening and the shift of the Snoek peak are discussed.

In this paper, the adaptive control problem is studied for a class of discrete-time unknown nonlinear systems with general relative degree in the presence of bounded disturbances. To derive the feedback control, a causal state-space model of the plant is obtained. By using an NN observer to estimate the unavailable but predictable states of the system, a Lyapunov-based adaptive state feedback NN controller is proposed. The state feedback control avoids the possible singularity problem in adaptive nonlinear control. The closed-loop system is proven to be semi-globally uniformly ultimately bounded (SGUUB). An arbitrarily small tracking error can be achieved if the size of neural networks is chosen large enough, and the control performance of the closed-loop system is guaranteed by suitably choosing the design parameters.

The state feedback controller is studied for a class of strict-feedback discrete-time nonlinear systems in the presence of bounded disturbances. A Lyapunov-based full state feedback neural network control structure is presented via backstepping, which solves the noncausal problem in the discrete-time backstepping design procedure. The closed-loop system is proven to be semi-globally uniformly ultimately bounded. An arbitrarily small tracking error can be achieved if the size of the neural network is chosen large enough, and the control performance of the closed-loop system is guaranteed by suitably choosing the design parameters.

A new method to evaluate the amount of springback in sheet forming processes based on the explicit finite element method and the orthogonal regression analysis is presented in this paper. To calculate springback accurately, a simple but effective contact searching algorithm is described and Lagrangian multiplier method was used to evaluate the contact force. The loading and unloading process could be simulated within one code. The numerical results by the present method were compared with the results by the commercial dynamic explicit code LS-DYNA3D, also with the experimental results and very good agreement was drawn. In order to obtain the springback conveniently for the purpose of practical use, the orthogonal regression analysis was implemented to establish the explicit relationship between the springback and some design parameters. The present method has been applied to the analysis of some actual sheet forming processes and very good agreement between the numerical results and the experimental results in the final geometry was obtained.