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61.
多级制造系统是现代制造业的主要加工方式,系统的每一级的加工速度和加工周期是系统设计的主要决策变量,正确确定这两个变量是系统得到优化的主要目标。本文导出了系统优化的基本模型,它包括系统各级的生产时间、等待时间、生产速度、生产成本以及系统的循环时间、总成本、产品利润和利润率等,并给出了一个应用实例。 相似文献
62.
Double-diffusive convection due to a cylindrical source submerged in a salt-stratified solution is numerically investigated
in this study. For proper simulation of the vortex generated around the cylinder, a computational domain with irregular shape
is employed. Flow conditions depend strongly on the thermal Rayleigh number, Ra
T
, and the buoyancy ratio, R
ρ. There are two types of onset of instability existing in the flow field. Both types are due to either the interaction of
the upward temperature gradient and downward salinity gradient or the interaction of the lateral temperature gradient and
downward salinity gradient. The onset of layer instability due to plume convection is due to the former, whereas, the onset
of layer instability of layers around the cylinder is due to the latter. Both types can be found in the flow field. The transport
mechanism of layers at the top of the basic plume belongs to former while that due to basic plume and layer around the cylinder
are the latter. The increase in Ra
T
reinforces the plume convection and reduces the layer numbers generated around the cylinder for the same buoyancy ratio.
For the same Ra
T
, the increase of R
ρ suppresses the plume convection but reinforces the layers generated around the cylinder. The profiles of local Nusselt number
reflects the heat transfer characteristics of plume convection and layered structure. The profiles of averaged Nusselt number
are between the pure conduction and natural convection modes and the variation is due to the evolution of layers.
Received on 13 September 1996 相似文献
63.
64.
We established that acetylacetone and acetone photolytically sensitize norbornene to undergo an efficient radical addition
of solvent (ranging from hexane, cyclic ethers, haloalkanes, acetone, alcohols and acetonitrile) across the double bond. In
view of its synthetic applicability, sensitized photoreactions of norbornene were reviewed and their mechanisms were compared.
Photolysis of acetylacetone in the presence of norbornene in hexane induced i) acetylacetone to cycloadd to norbornene giving
the expected 1,5-diketone, and ii) sensitization by triplet excited acetylacetone to generate reactive norbornene, which underwent
dimerization as well as the addition of a solvent molecule by radical chain processes. In other solvents, the radical chain
addition of solvent dominated the photoreaction, and superseded the cycloaddition, to give excellent to good yields of adducts
to norbornene. While the excited species of acetylacetone for the sensitization was deduced to be its spectroscopic triplet
excited state, that for the cycloaddition should involve a different one which may be a twisted triplet acetylacetone; sensitization
experiments showed that the cycloaddition did not occur from the spectroscopic triplet state. Triplet excited acetone sensitized
norbornene to undergo the same solvent addition more efficiently and cleanly than acetylacetone did. In view of various conflicts
existing in the proposed energy transfer mechanism, the sensitized norbornene reactions were rationalized with electron transfer
and a cation radical chain mechanism. 相似文献
65.
M.-K. Chen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(1):13-18
We examine the influence of relativistic and QED effects on the existence of the 1,3P
o
H- resonances between n
= 2 and 3 hydrogen thresholds, the relativistic and QED corrections and the coupling effects between the high singlet and triplet
states are considered as first-order perturbations. We firstly obtain accurate non-relativistic resonant energies and widths
of fifteen 1P
o
resonances, and fifteen 3P
o
resonances. The fifteen 1P
o
resonances are classified to be
3
(2, 0)
-
n
( 4 ?
n
? 12) and
3
(1, 1)
+
n
( 3 ?
n
? 8). The fifteen 3P
o
resonances are classified to be
3
(2, 0)
+
n
( 3 ?
n
? 12) and
3
(1, 1)
-
n
( 4 ?
n
? 8). We found there exist six Feshbach resonances for
3
(2, 0)
-
n
(1P
o
) series, four Feshbach resonances for
3
(1, 1)
+
n
(1P
o
) series, seven Feshbach resonances for
3
(2, 0)
+
n
(3P
o
) series, and three Feshbach resonances for
3
(1, 1)
-
n
(1P
o
) series.
Received 22 February 2002 Published online 24 September 2002 相似文献
66.
67.
This paper presents an analysis of a portfolio model which can be used to assist a property-liability insurance company in determining the optimal composition of the insurance and investment portfolios. By introducing insurer's threshold risk and relaxing some non-realistic assumptions made in traditional chance constraint insurance and investment portfolio models, we propose a method for an insurer to maximize his return threshold for a given threshold risk level. This proposed model can be used to optimize the composition of underwriting and investment portfolios regarding the insurer's threshold risk level, as well as to generate the efficient frontier by adjusting insurer's threshold risk levels. A numerical example is given based on the industry's aggregated data for a sixteen year period. 相似文献
68.
Browder-Petryshyn 型的严格伪压缩映射的粘滞迭代逼近方法 总被引:1,自引:0,他引:1
主要研究Browder-Petryshyn型的严格伪压缩映射的粘滞迭代逼近过程,证明了Browder-Petryshyn型的严格伪压缩映射的不动点集F(T)是闭凸集.在q-一致光滑且一致凸的Banach空间中,对于严格伪压缩映射T,利用徐洪坤在2004年引进的粘滞迭代得到的序列弱收敛于T的某个不动点.同时证明了Hilbert空间中Browder-Petryshyn型的严格伪压缩映射的相应迭代序列强收敛到T的某个不动点,其结果推广与改进了徐洪坤2004年的相应结果. 相似文献
69.
70.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献