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排序方式: 共有4663条查询结果,搜索用时 15 毫秒
101.
On the mechanical performance of closed cell Al alloy foams 总被引:8,自引:0,他引:8
Y. Sugimura J. Meyer M.Y. He H. Bart-Smith J. Grenstedt A.G. Evans 《Acta Materialia》1997,45(12):5245-5259
The mechanical properties of three different commercially available closed cell Al alloys all made by foam casting are examined. The objective is to assess the roles of cell morphology and of imperfections in governing the basic properties: stiffness, yield strength and fracture resistance. This assessment provides goals for manufacturing strategies that enable attainment of good mechanical performance with affordable process technologies. A prevalent role of curves and wiggles in the cell walls on stiffness and strength (anticipated by models) is affirmed by the present measurements. Systematically larger stiffnesses and yield strengths found in tension than in compression are consistent with a prominent role exerted by such imperfections. Moreover, foam casting is apparently capable of cell morphologies that impart properties approaching the best achievable values for an isotropic closed cell solid, devoid of imperfections. There are associated implications for performance and affordability. Fracture measurements indicate crack growth occurring along the cell walls by a mechanism analogous to the plastic tearing of thin sheets. The crack growth resistances are in the range of 1 kJm−2. This mechanism infers a toughness that scales with the cell wall thickness and its yield strength. 相似文献
102.
本文分析空压机原联动控制系统的运行特点,对系统进行改造,利用自制电子式两位差动可调控制器取代压力控制器,克服原系统的缺陷。达到了改造的目的。 相似文献
103.
104.
105.
Eggbeer D Evans P 《Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine》2011,225(1):94-99
This case study presents a method of utilizing computer-aided design technologies to provide bespoke, external breast prostheses. The technique is illustrated through a case study of a mastectomy patient. Photogrammetry methods were used to capture the breast form when supported by a brassiere and the unsupported breast and defect side. Computer-aided design techniques were used to generate a digital prosthesis based upon the supported breast shape and with a fitting surface that matched the defect side. Furthermore, a two-part mould was designed and fabricated using rapid prototyping methods. A colour-matched prosthesis was then fabricated in a gel-based, platinum-cured silicone. 相似文献
106.
107.
David Evans, BCS government relations, looks at what it couldtake to convince kids that the hard stuff is worth doing. 相似文献
108.
Model-based 3-D segmentation of multiple sclerosis lesions in magnetic resonance brain images 总被引:2,自引:0,他引:2
Kamber M Shinghal R Collins DL Francis GS Evans AC 《IEEE transactions on medical imaging》1995,14(3):442-453
Human investigators instinctively segment medical images into their anatomical components, drawing upon prior knowledge of anatomy to overcome image artifacts, noise, and lack of tissue contrast. The authors describe: 1) the development and use of a brain tissue probability model for the segmentation of multiple sclerosis (MS) lesions in magnetic resonance (MR) brain images, and 2) an empirical comparison of the performance of statistical and decision tree classifiers, applied to MS lesion segmentation. Based on MR image data obtained from healthy volunteers, the model provides prior probabilities of brain tissue distribution per unit voxel in a standardized 3-D "brain space". In comparison to purely data-driven segmentation, the use of the model to guide the segmentation of MS lesions reduced the volume of false positive lesions by 50-80% 相似文献
109.
S. A. Matar M. J. Edirisinghe J. R. G. Evans E. H. Twizell J. H. Song 《Journal of Materials Science》1995,30(15):3805-3810
A shrinking undegraded core and a porous outer layer result, if the organic vehicle used for shaping ceramic or metal powder mouldings recedes in the interparticle space of the moulded body during pyrolysis. In the present work, a numerical model has been used which simulates the undegraded shrinking core situation and quantifies degradation of the organic vehicle and the diffusion of the resulting products in solution in the organic phase during pyrolysis of a ceramic moulding. This model is extended to include gaseous mass transport in the porous outer layer for a moulding in the shape of an infinite cylinder. The effect of resistance to gaseous mass transport in the porous outer region on defects originating in inner regions was estimated. It is shown that the greatest obstruction to mass transport is diffusion of degradation products in solution in the organic phase. However, the permeability coefficient for gas transport in the outer region begins to affect the critical heating rate required for avoidance of defects only when it is less than 10–15m2.Nomenclature
C
Concentration,C=C (r, t), based on the total volume of ceramic suspension
-
d
Effective molecular diameter of alphamethylstyrene
-
D
Diffusion coefficient,D=D (C, T)
-
e
Porosity of powder
-
E
Activation energy for thermal degradation
-
h
Remaining weight fraction of polymer
- Hvap
Enthalphy of vaporization
-
i
Node number
-
I
Pre-exponential constant in Equation 13
-
j
Time step
-
K
p
Permeability coefficient
-
K
0
Specific rate constant
-
m
Mass of monomer displaced
-
M
Mass of one alphamethylstyrene molecule
-
P
Monomer vapour pressure
-
P
s
Monomer vapour pressure at outer surface of the cylinder
-
P
1
0
Vapour pressure of monomer over its pure liquid
-
Q
Rate of production of monomer, based on the total volume of ceramic suspension
-
r
Radius of the cylinder
-
r
j
Distance from central axis to the inner surface of the porous layer at time stepj
-
r
0
Initial radius of the cylinder
-
R
Universal gas constant
-
S
0
Specific surface area of powder per unit solid volume
-
t
Time
-
T
Absolute temperature
-
T
c
Temperature at maximum vapour pressure of monomer and atZ
c
-
V
Volume of monomer
-
V
c
Ceramic volume fraction
-
V
p
Polymer volume fraction
-
w
Mass of monomer stored in the porous annulus
-
Z
Heating rate
-
Z
c
Critical heating rate
- 1
Volume fraction of monomer in the polymer-monomer solution
-
Viscosity of the monomer vapour
- p
Density of the polymer
-
Polymer-monomer interaction constant 相似文献
110.
Evans Michael G. Al-Shakli Arwa Jenkins Stuart I. Chari Divya M. 《Nano Research》2017,10(8):2881-2890
The development of safe technologies to genetically modify neurons is of great interest in regenerative neurology,for both translational and basic science applications.Such approaches have conventionally been heavily reliant on viral transduction methods,which have safety and production limitations.Magnetofection (magnet-assisted gene transfer using iron oxide nanoparticles as vectors) has emerged as a highly promising non-viral alternative for safe and reproducible genetic modification of neurons.Despite the high potential of this technology,there is an important gap in our knowledge of the safety of this approach,namely,whether it alters neuronal function in adverse ways,such as by altering neuronal excitability and signaling.We have investigated the effects of magnetofection in primary cortical neurons by examining neuronal excitability using the whole cell patch clamp technique.We found no evidence that magnetofection alters the voltage-dependent sodium and potassium ionic currents that underpin excitability.Our study provides important new data supporting magnetofection as a safe technology for bioengineering of neuronal cell populations. 相似文献