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81.
Weighting model is the only valuation model of life cycle impact assessment(LCIA) profile now. It simplifies evaluation function into linear function, and makes the determination of weighting factor complicated. Therefore the valuation of LCIA profile is the most critical and controversial step in life cycle assessment(LCA). Development on valuation models, which are understood easily and accepted widely, is urgently needed in the field of LCA.The modeling approaches for the linear evaluation function were summed up. The modeling approaches for the nonlinear evaluation function were set up by function approximation theory, which include choosing preference products, forming preference data, establishing artificial neural network(ANN) and training ANN by preference data.By selecting 7 material products as preference product, experience was done with modeling approaches of the nonlinear evaluation function. The results show that the modeling approaches and valuation model of the nonlinear evaluation function are more practical than the weighting model. 相似文献
82.
Biaxial forming behavior is investigated for three aluminum sheet alloys (Al 5182 containing 1% Mn (5182+Mn), Al 5754, and
6111-T4) using a heated die and punch in the warm forming temperature range of 200–350 °C. It is found that, while all three
alloys exhibit significant improvement in their formability compared with that at room temperature, the non-heat-treatable
alloys 5182 + Mn and 5754 give higher part depths than that of heat-treatable 6111-T4. The formability generally increases
with decreasing BHP (BHP), but increasing the forming temperature and/or BHP minimizes the wrinkling tendency and improves
the forming performance. The stretchability of the sheet alloys increase with increasing temperature and increasing BHP. For
the alloys and forming conditions involved in the current study, the formability, measured in terms of part depth, comes mainly
from the drawing of metal into the die cavity, although stretching effects do influence the overall forming behavior. The
optimum formability is achieved by setting the die temperature 50 °C higher than the punch temperature to enhance the drawing
component. Setting the die temperature higher than the punch temperature also improves the strain distribution in a part in
such a manner that postpones necking and fracture by altering the location of greatest thinning. 相似文献
83.
Al-18%Si合金在梯度强磁场中凝固时初生硅的行为 总被引:4,自引:1,他引:4
研究了Al-18%Si合金在10 T梯度强磁场下加热至半固态和全熔态后的凝固过程,观察了初生硅的分布和形态,测定了其冷却曲线.结果表明:在磁场的磁感应强度和磁场梯度的乘积Bz·dBz/dz为正时,初生硅向上部聚集;而在Bz·dBz/dz为负时,初生硅向下部聚集;在强磁场下,加热至全熔态冷却下来的凝固组织中初晶硅的形态发生了明显的改变,由板片状转变为块状,初晶硅显著细化.对强磁场细化初晶硅的机制进行了探讨. 相似文献
84.
A new electron beam control system was developed in a general vacuum electron beam machine by assembling with industrial control computer, programmable logic control (PLC), deflection coil, data acquisition card, power amplifier, etc. In this control system, scanning track and energy distribution of electron beam could be edited off-line, real-time adjusted and controlled on-line. Ti-Mo gradient material (GM) with high temperature resistant was fabricated using the technology of electron beam melting. The melting processes include three steps, such as preheating, melting, and homogenizing. The results show that the GM prepared by melting technology has fine appearance, and it has good integrated interface with the Ti alloy. Mo and Ti elements are gradually distributed in the inter.face of the gradient material. The microstructure close to the Ti alloy base metal is α + β basket-waver grain, and the microstructure close to the GM is a single phase of β solid solution. 相似文献
85.
CdZnTeCrystalGrowthbyVerticalGradientFreezingMethodHouQingrun;WangJinyi;DengJincheng;DuBing,(侯清润)(王金义)(邓金诚)(杜冰);LiMeirongandC... 相似文献
86.
本文用WKB近似方法讨论了势垒贯穿问题系数T和其透射反射系数R之和恒等为1,即满足恒等式T R=1,并进一步得出这一结论不仅适用于一般势垒贯穿而且在方势垒贯穿中也成立,最后讨论了势垒贯穿的几种极限情况,例如,h→0(即经典情况),势垒高度v→∞、v→0,势垒宽度a→∞、a→0,等几种特殊情况下的T及R的取值问题。 相似文献
87.
受施工、龄期、环境及服役期大坝承受的反复静动荷载等多因素影响,坝体和层面出现不同程度的劣化损伤,碾压层本体及层面物理参数呈渐变特性。针对碾压层内力学参数渐变的特性,提出了相应物理参数的等效算法,且给出了耦合性态参数间的数学转换关系,分析坝体应力场与渗流场相互影响机理,据此建立了考虑层内参数渐变的碾压混凝土坝渗流场与应力场耦合分析模型,并编制了相应的有限元分析程序。工程实例分析表明,耦合作用致使大坝的渗流场发生改变,坝体的应力较未耦合时普遍偏大,坝踵处的应力集中显著;渗流场与应力场耦合作用激励下的不利因素可为大坝的设计、施工及安全运行提供参考。 相似文献
88.
89.
90.
We consider the problem of scheduling n jobs in batches on a single parallel-batching machine, where the jobs are partitioned into jobs families and the jobs in each family have the same due date. The objective is to minimize the weighted number of tardy jobs. We first devise an efficient pseudo-polynomial time and a fully polynomial time approximation scheme for the weighted problem. Then we present -time and -time algorithms for the case where the jobs have the same weight and for the case where the jobs have the same processing time, respectively. 相似文献