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141.
The influence of stacking fault energy on microvoid coalescence in pure materials has been studied. It was shown that as a material's stacking fault energy (SFE) decreased, the extent of microvoid coalescence that occurred during ductile fracture also decreased. The decrease of microvoid coalescence in low SFE materials was attributed to a hindrance in the development of dislocation cells associated with the restricted motion of dislocations. In pure materials, microvoids are believed to initiate and grow along dislocation cell walls formed during deformation. As such, the absence or scarcity of cells in lower SFE materials limits the formation of these voids during ductile fracture. 相似文献
142.
Richard L. Venezky 《Computers and the Humanities》1988,22(4):285-291
The Dictionary of Old English computing systems have provided access since the 1970s to a database of approximately three million running words. These systems, designed for a variety of machines and written in a variety of languages, have until recently been planned with computing center billing algorithms in mind. With personal workstations emphasis has shifted to building more elegant user interfaces and to providing the entire DOE database to editors around the world. While the shift from sequential files to random access files and the provision of extensive development tools have changed some of the design process, error checking and protection of the database against accidental intrusion have remained as central issues.Richard L. Venezky is Unidel Professor of Educational Studies and professor of Computer and Information Sciences at the University of Delaware. He was formerly professor and chair of Computer Sciences at the University of Wisconsin. His research interests include writing systems, literacy, knowledge representation, and computer-assisted instruction. Among his recent publications are The Subtle Danger: Reflections on the Literacy Abilities of America's Young Adults (Princeton, NJ: ETS, 1987), and Steps Towards a Modern History of American Reading Instruction (Review of Research in Education, 1986, vol. 13, 129–70). 相似文献
143.
Cyclic hot corrosion conducted on Haynes 230 at temperatures of 871 and 1093 C indicated that catastrophic corrosion occurred. The corrosion rate was related to the high content of tungsten and chromium in the alloy. The concept of basic and acid fluxing was applied to explain the dissolution of the protective film of Cr2O3 and volatile WO3 by an Na2SO4-rich liquid due to the formation of Na2CrO4 and Na2WO4. As the basic melts were acidified by continuously consuming oxygen ions, plate-like crystals of Cr2O3 were precipitated on the free surface by conversion from Na2CrO4. Acid fluxing was achieved by the refractory oxide, WO3, consuming oxygen ions. The presence of sulphur suppressed the diffusion of chromium outward to form protective Cr2O3. Internal chromium-rich sulphide particles were observed. It was suggested that at very lowP
O2, sulphur reacted with chromium to form CrS initially. As oxygen penetrated through the porous layer, the CrS was oxidized internally to Cr2O3. 相似文献
144.
Wolfgang Sachse A. N. Netravali A. Richard Baker 《Journal of Nondestructive Evaluation》1992,11(3-4):251-261
In the single-fiber-composite (SFC) test, a fiber imbedded in a matrix is loaded in tension, resulting in a fragmentation of the fiber. In the conventional version of this test, the final fiber fragmentation length distribution is used with a micro-mechanical model to determine the average fiber/matrix interfacial shear stress. In the enhanced version of this test, one also determines the applied stress at each fiber fracture, and from this, one can evaluate the strength of the fiber at short gage lengths. In our measurement system, we utilize an acoustic emission (AE) technique to detect the fiber fractures and to locate the fiber breaks and so determine both the fiber failure stresses as well as the fiber fragmentation lengths while the test is in progress. Critical to the success of this test is a broadband AE system that utilizes point-like AE sensors, procedures for evaluatingin situ, the wavespeed of the first wave arrival and signal processing techniques for determining the arrival time of this signal as precisely as possible for a broad range of wave shapes. Here we describe the application of such an enhanced SFC test procedure to investigate the failure of a Nicalon fiber in an epoxy matrix. 相似文献
145.
Several related algorithms are presented for computing logarithms in fieldsGF(p),p a prime. Heuristic arguments predict a running time of exp((1+o(1))
) for the initial precomputation phase that is needed for eachp, and much shorter running times for computing individual logarithms once the precomputation is done. The running time of the precomputation is roughly the same as that of the fastest known algorithms for factoring integers of size aboutp. The algorithms use the well known basic scheme of obtaining linear equations for logarithms of small primes and then solving them to obtain a database to be used for the computation of individual logarithms. The novel ingredients are new ways of obtaining linear equations and new methods of solving these linear equations by adaptations of sparse matrix methods from numerical analysis to the case of finite rings. While some of the new logarithm algorithms are adaptations of known integer factorization algorithms, others are new and can be adapted to yield integer factorization algorithms. 相似文献
146.
Siegfried Noack und Richard Wohlgemuth 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1985,180(2):101-108
Zusammenfassung In Modellversuchen wurden Haselnüsse, Sojabohnen und Weizen bei zeitlich nicht konstanter Konzentration mit Phosphin begast. Dabei wurden — in Anlehnung an die Begasungspraxis —verschiedene Konzentrationsverläufe mit zunächst ansteigender und nach Überschreiten eines Maximums wieder abfallender PH3-Konzentration hinsichtlich des Einflusses auf die Rückstandsbildung bzw. den Rückstandsabbau untersucht. Die Rückstandshöhe während der Begasung als auch das Rückstandsverhalten bei der anschließenden Lagerung der behandelten Produkte wurde mit einem gaschromatographischen Verfahren überwacht. Die sich bildenden Phosphin-Rückstände folgen dabei der Tendenz nach dem Konzentrationsprofil, sie durchlaufen ebenfalls ein Maximalwert. Rückstände, die in der Phase der ansteigenden Konzentration entstehen, bauen jedoch bei der Lagerung schneller ab als gleich hohe Rückstände, die sich in der Zeit der absinkenden Konzentration bilden. Bei sehr flach verlaufender Konzentration tritt der Maximal-Rückstand gegenüber dem Konzentrationsmaximum zeitlich verzögert auf, bei sehr steilem Konzentrationsverlauf fallen beide Maxima zusammen. Die Vorgänge lassen sich durch das Diffusions- und Sorptionsverhalten des Phosphins begründen. Es wird ein Vergleich mit dem Konzentrationsverlauf bei Praxisbegasungen geführt. Die Einflüsse, die ein stetiges Konzentrationsprofil mit nur einem Maximum bzw. einen Verlauf mit häufig steigender und fallender Konzentration bedingen, werden erläutert und das in beiden Fällen unterschiedliche Rückstandsverhalten untersucht und diskutiert. Schlußfolgerungen für die Begasungspraxis werden gezogen.
Gefördert im Rahmen einer Sachbeihilfe der Deutschen Forschungsgemeinschaft an Dr. R. Wohlgemuth, Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Vorratsschutz, Berlin-Dahlem, zum Thema: Untersuchungen zum Einfluß verschiedener Parameter auf die Rückstandsbildung bei der Begasung von Lebensmitteln gegen Schädlinge 相似文献
Phosphine residues in hazelnuts, soybeans, and wheat after fumigation with non constant cocentrations
Summary In model tests hazelnuts, soy beans and wheat were fumigated with phosphine (PH3) at non constant concentrations. The influence of different concentration characteristics on the fumigation and the decomposition of phosphine residues was investigated in accordance with the fumigation technique. At the beginning the concentration increases, and after attaining the maximum gradually decreases to zero. The level of residues during the fumigation as well as the behaviour of residues during the storage of the fumigated products was monitored with a gaschromatographic method. The residues correlate with the concentration of phosphine, they also pass through a peak. The rate of decomposition of residues which had been formed in the phase of increasing concentration is greater than the rate of residues of equal magnitude which had been formed during the decreasing phase. When the concentration is even the maximum residue occurs later than the maximum concentration; when there is a steep trend both maximums coincide. This behaviour can be explained by the sorption and diffusion of phosphine. A comparison is made with the phosphine concentration which occurs during fumigation in practice. The parameters which produce a constant concentration trend with only one maximum and a non constant trend with an often increasing and decreasing concentration are discussed. The different behaviour of residues in these cases is described. Conclusions are drawn for the practice of fumigation.
Gefördert im Rahmen einer Sachbeihilfe der Deutschen Forschungsgemeinschaft an Dr. R. Wohlgemuth, Biologische Bundesanstalt für Land- und Forstwirtschaft, Institut für Vorratsschutz, Berlin-Dahlem, zum Thema: Untersuchungen zum Einfluß verschiedener Parameter auf die Rückstandsbildung bei der Begasung von Lebensmitteln gegen Schädlinge 相似文献
147.
A model for the compressive buckling of extended chain polymers 总被引:1,自引:0,他引:1
Steven J. DeTeresa Roger S. Porter Richard J. Farris 《Journal of Materials Science》1985,20(5):1645-1659
A model for the compressive buckling of an extended polymer chain is presented. The application of classical elastic instability analysis to an idealized polymer chain reveals that the bending rigidity and critical buckling loads for a chain are proportional to the force constants for valence bond angle bending and torsion. Highly oriented polymer fibres are treated as a collection of elastic chains that interact laterally. The critical stresses to buckle this collection of chains are calculated following a procedure developed to predict the compressive strengths of fibre-reinforced composites. This buckling stress is predicted to be equal to the shear modulus of the fibres and is the limiting value of compressive strength. Comparison of experimental and predicted values shows that the theory overestimates the compressive strength, but that there is a correlation of shear modulus with axial compressive strength. Consideration of flaws in both the theory and the material indicate that the compressive strength should be proportional to either the shear modulus or shear strength of the fibres.Nomenclature
P
axial compressive load (force)
-
P
cr
critical buckling load (force)
-
M,M
i
bending moments
-
l
length of a link
-
p
number of links
-
k
elastic hinge constant
-
,
i
angular rotation of hinges
-
L
overall chain or column length
-
v,v
i
lateral deflection of buckled chain or column
-
x, y, z
Cartesian coordinate axes
-
E
Young's modulus of isotropic column
-
I
moment of inertia
-
a
ij
matrix coefficients
-
A
p
coefficient for exact buckling loads of chains
- T
energy change due to work of external load on buckled column or chain
- U
1
bending strain energy change of buckled column or chain
- U
2, U
2
e
, U
2
s
strain energy changes in elastic foundation, where e refers to extension mode buckling and s refers to shear mode buckling
-
E
t
transverse modulus
-
G
longitudinal shear modulus
-
b
dimension associated with chain packing
-
A
cross-sectional area per chain (=b
2)
-
f(x)
curve fitted to shape of buckled chain
-
m,n,r
integers
-
a
n
coefficients of trigonometric series
-
y
normal strain iny-direction
-
y
normal stress iny-direction
-
xy
shear strain inxy plane
-
xy
shear stress inxy plane
-
u
x
displacement inx-direction
-
u
y
displacement iny-direction
-
V
volume 相似文献
148.
Low-density microcellular carbon foams 总被引:3,自引:0,他引:3
A method has been developed to produce vitreous carbon foams having both low densities (0.03 to 0.10gcm–3) and small cell sizes ( 20 m). This process involves the replication of a porous sacrificial substrate, i.e. sodium chloride. The salt is pressed initially into bars and sintered to give a structure with continuous porosity. The pores are infused with a phenolic solution, the solvent is evaporated, and the resin is pyrolysed within the salt substrate. Extraction of the salt and freeze drying lead to the final carbon foam. The substrate serves two purposes in this process: (1) it prevents shrinkage of the foam during pyrolysis, and (2) it dictates the cell size of the foam. 相似文献
149.
Kester Bruce E. Gilliland J. L. Fritts Stewart S. Bell Zeb G. Smith Hubert Berby Richard H. 《Industry Applications, IEEE Transactions on》1972,(1):8-18
MAN is but a part of the universe; his capabilities make him a significant link, in the cycle of life. To ensure this life, man must live in harmony with his environment. Recently, a disharmony has been discovered which could have grave effects upon the existence of man. It appears that man in his great thrust forward is destroying his own environment. The gravity of this threat to man's own existence carries some intrinsic problems of its own: man must allow his reason rather than his emotion to take command. 相似文献
150.
Lawrence K. Wang Richard P. Leonard Dennis W. Goupil Mu Hao Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1975,25(7):491-502
Industrial effluents usually include multicomponent organic solutes. The optimum pH for adsorption of a specific industrial effluent on activated carbon should be determined experimentally because, in general, more than one mechanism is involved. A series of experiments was conducted to establish the influence of the initial hydrogen ion concentration on carbon adsorption of organic solutes. For these studies, powdered activated carbon was used, and the water systems studied included both single component pure organic compounds as well as multicomponent organic wastes. Results indicate that the pH effect upon the effectiveness of carbon adsorption mainly depends upon the nature of the adsorbed substance. In general, the degree of ionisation is the controlling factor for adsorption of ionic organic solutes on activated carbon. Adsorption reaches a maximum at the point of least ionisation of the adsorbate. As the organic compounds become more complex (i.e. longer hydrocarbon chains, higher molecular weights, increased branching), the electrical adsorption forces between activated carbon and ionic organic solutes will govern. Anionic surfactants meet with decreased electronegative repulsive forces at low pH levels, which increase the effectiveness of carbon adsorption. However, the adsorption of a cationic surfactant is increased by an increase in the electronegative carbon surface at high pH levels. When ionic organic solutes become much more complex, like a polymer, the effects of both ionisation and electrical adsorption forces become less important. Instead, the adsorption rate will be controlled by the extent of hydrolysis caused by the pH adjustment. For non-ionic organic solutes, chemical reaction(s) between the adsorbate and the added chemical (acid or base) for pH adjustment is an important controlling factor. Again, hydrolysis is responsible for the breakdown of larger size molecules to smaller sizes. Then an increase in adsorption rate with decreasing molecular weight of adsorbate is expected. 相似文献