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排序方式: 共有944条查询结果,搜索用时 31 毫秒
51.
为研究高强度桩复合地基加筋垫层的作用机理与筋带拉力的计算方法,采用一套自制的桩土差异沉降控制装置,进行了4组不同桩帽尺寸的大比例静力模型试验。测试了各级荷载作用下的加筋垫层筋带拉力,分析了筋带拉力的大小及分布随荷载增加的变化规律。结果表明:随桩顶和桩间土沉降差增加,筋带拉力逐渐增大,筋带拉力最大值出现在桩顶位置;随着桩帽覆盖率增加,桩间土范围内筋带拉力缓慢减小,桩顶范围筋带拉力变化较大,先增大后减小。加筋垫层的破坏模式表现为桩帽边缘的筋带断裂。 相似文献
52.
Difficulty in imposing essential boundary conditions in the standard element-free Galerkin method (EFG) is due to the lack of Kronecker’s delta function property of shape functions generated by moving least square approximation (MLS). In this paper, we further apply a meshfree model based on the moving Kriging interpolation method (MK) to free vibration analysis of first-order shear deformable plates. The deflection and two rotation field variables of plate are approximated by the MK method, which is employed to construct the shape functions having the delta function property. With this approach, the drawback in enforcement of the boundary conditions caused by the MLS is now avoided. The present formulation is based on the first-order shear deformation plate theory (FSDT) associated with an effective elimination of the shear-locking phenomenon completely, and hence the approach is applicable to both moderately thick and thin plates. Numerical examples considering various aspect ratios and different boundaries are examined and solutions on natural frequencies obtained by the present method are then compared with existing reference solutions, and very good agreements are observed. 相似文献
53.
Discovery of a Short‐Chain Dehydrogenase from Catharanthus roseus that Produces a New Monoterpene Indole Alkaloid
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Dr. Anna K. Stavrinides Dr. Evangelos C. Tatsis Dr. Thu‐Thuy Dang Dr. Lorenzo Caputi Dr. Clare E. M. Stevenson Dr. David M. Lawson Dr. Bernd Schneider Prof. Sarah E. O'Connor 《Chembiochem : a European journal of chemical biology》2018,19(9):940-948
Plant monoterpene indole alkaloids, a large class of natural products, derive from the biosynthetic intermediate strictosidine aglycone. Strictosidine aglycone, which can exist as a variety of isomers, can be reduced to form numerous different structures. We have discovered a short‐chain alcohol dehydrogenase (SDR) from plant producers of monoterpene indole alkaloids (Catharanthus roseus and Rauvolfia serpentina) that reduce strictosidine aglycone and produce an alkaloid that does not correspond to any previously reported compound. Here we report the structural characterization of this product, which we have named vitrosamine, as well as the crystal structure of the SDR. This discovery highlights the structural versatility of the strictosidine aglycone biosynthetic intermediate and expands the range of enzymatic reactions that SDRs can catalyse. This discovery further highlights how a sequence‐based gene mining discovery approach in plants can reveal cryptic chemistry that would not be uncovered by classical natural product chemistry approaches. 相似文献
54.
Jong-Soo Kim Yong-Bim Im Ngoc-Hung Bui 《Journal of Mechanical Science and Technology》2005,19(9):1790-1800
The examination on the operating mechanism of a pulsating heat pipe (PHP) using visualization revealed that the working fluid
in the PHP oscillated to the axial direction by the contraction and expansion of vapor plugs. This contraction and expansion
is due to the formation and extinction of bubbles in the evaporating and condensing section, respectively. In this paper,
a theoretical model of PHP was presented. The theoretical model was based on the separated flow model with two liquid slugs
and three vapor plugs. The results show that the diameter, surface tension and charge ratio of working fluid have significant
effects on the performance of the PHP. The following conclusions were obtained. The periodic oscillations of liquid slugs
and vapor plugs were obtained under specified parameters. When the hydraulic diameter of the PHP was increased to d=3mm, the
frequency of oscillation decreased. By increasing the charging ratio from 40 to 60 by volume ratio, the pressure difference
between the evaporating section and condensing section increased, the amplitude of oscillation reduced, and the oscillation
frequency decreased. The working fluid with higher surface tension resulted in an increase in the amplitude and frequency
of oscillation. Also the average temperature of vapor plugs decreased. 相似文献
55.
Tadashi Yoshihashi Nguyen Thi Thu Huong Vipa Surojanametakul Patcharee Tungtrakul Warunee Varanyanond 《Journal of food science》2005,70(1):S34-S37
ABSTRACT: The effect of package and temperature on 2–acetyl-1–pyrroline content in milled aromatic rice during storage was investigated. 2 -Acetyl-1 -pyrroline content was decreased faster at higher storage temperature. However, fat acidity of rice was increased during storage and inversely correlated with 2–acetyl-1–pyrroline content at an early stage of storage. The difference in 2–acetyl-1 -pyrroline recovery from the samples, which were extracted with ethanol at 40 °C and 75 °C, revealed that the starch bound and free forms of 2–acetyl-1–pyrroline may occur in aromatic rice. These results suggested that the biosynthesis of 2–acetyl-1 -pyrroline before starch structure formation in rice kernel could play a key role in the aroma quality of aromatic rice. 相似文献
56.
Chen T.-h. Chang K.W. Bui S.B. Wang H. Dow G.S. Liu L.C.T. Lin T.S. Titus W.S. 《Microwave Theory and Techniques》1991,39(12):1980-1986
The design and fabrication of four broadband monolithic passive baluns including CPW Marchand, multilayer MS Marchand, planar-transformer and broadside-coupled line baluns are presented. Operational frequencies range from 1.5 GHz to 24 GHz. Maximum relative bandwidths in excess of 3:1 are achieved. Simulated performances using full wave electromagnetic analysis are shown to agree with the measured results. Two accurate equivalent circuit models constructed from either electromagnetic simulated or measured S-parameters are developed for the MS Marchand and transformer baluns making the optimization of baluns and circuit design using the baluns much more efficient. The design of monolithic double-balanced diode mixer using two planar-transformer baluns is also presented. Without DC bias, the mixer shows a minimum conversion loss of 6 dB with the RF at 5 GHz and a LO drive of 15 dBm at 4 GHz. The measured input IP3 of this mixer is better than 15 dBm over the 4 to 5.75 GHz frequency band 相似文献
57.
This paper presents an investigation of the buckling behaviour of thin-walled sections subjected to general loading conditions. The semi-analytical finite strip method is used. The existing results are only for sections subjected to a uniform loading, namely: uniform compression, uniform bending and uniform distributed loads, which are applied at the shear centre. For a general loading condition, we proposed the realizing linear analysis first to give longitudinal stresses. The stiffness matrix is provided in the standard manner. Each strip is divided into cells and longitudinal stresses are recorded in these cells. The integrations are performed on each cell domain and the sum of them provides the geometric matrix of the strip. 相似文献
58.
59.
Khoa Bui 《Numerical Heat Transfer, Part A: Applications》2013,63(8):590-603
The effective thermal conductivity (K eff) of carbon nanotube (CNT) composites is affected by the thermal boundary resistance (TBR), the dispersion pattern, and geometry distribution of the CNTs. Traditional effective medium theories assume that CNTs are perfectly dispersed without considering TBR. In this work, we report the development of a new algorithm using CNTs with 3-D worm-like geometry and different persistence lengths. We describe how to obtain K eff using simulations of these realistic CNT configurations with off-lattice Monte Carlo simulation. The results are compared with straight cylinder models without effects of persistence length. 相似文献
60.
This paper presents a study on the durability of different types of stabilised and unstabilised rammed earth walls. These rammed earth walls were constructed and exposed for 20 years to natural weathering, in a wet continental climate. None of these walls have shown complete collapse to date. A method to measure the rammed earth walls erosion by stereo-photogrammetry has been developed. The result shows that the mean erosion depth of the studied walls is about 2 mm (0.5% wall thickness) in the case of rammed earth wall stabilised with 5% by dry weight of hydraulic lime and about 6.4 mm (1.6% wall thickness) in the case of unstabilised rammed earth walls. The stabilisation enables to not use any plaster to protect the walls. In the case of the unstabilised rammed earth walls, an extrapolated lifetime longer than 60 years can be assessed. This shows a potential for the use of unstabilised rammed earth in the similar climatic conditions with this study. The method of stereo-photogrammetry used to measure the erosion of rammed earth walls on site may also help to calibrate and develop more pertinent laboratory test to assess the durability of rammed earth wall. 相似文献