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991.
A new enhanced assumed strain brick element for finite deformations in finite elasticity and plasticity is presented. The
element is based on an expansion of shape function derivatives using Taylor series and an extended set of orthogonality conditions
that have to be satisfied for an hourglassing free EAS formulation. Such approach has not been applied so far in the context
of large deformation three-dimensional problems. It leads to a surprisingly well-behaved locking and hourglassing free element
formulation. Major advantage of the new element is its shear locking free performance in the limit of very thin elements,
thus it is applicable to shell type problems. Crucial for the derivation of the residual and consistent tangent matrix of
the element is the automation of the implementation by automatic code generation. 相似文献
992.
993.
994.
Enhancing the carbon sink in European agricultural soils: including trace gas fluxes in estimates of carbon mitigation potential 总被引:7,自引:0,他引:7
Pete Smith Keith W. Goulding Keith A. Smith David S. Powlson Jo U. Smith Pete Falloon Kevin Coleman 《Nutrient Cycling in Agroecosystems》2001,60(1-3):237-252
The possibility that the carbon sink in agricultural soils can be enhanced has taken on great political significance since
the Kyoto Protocol was finalised in December 1997. The Kyoto Protocol allows carbon emissions to be offset by demonstrable
removal of carbon from the atmosphere. Thus, forestry activities (Article 3.3) and changes in the use of agricultural soils
(Article 3.4) that are shown to reduce atmospheric CO2levels may be included in the Kyoto emission reduction targets. The European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). We have shown recently that there
are a number of agricultural land-management changes that show some potential to increase the carbon sink in agricultural
soils and others that allow alternative forms of carbon mitigation (i.e. through fossil fuel substitution), but the options
differ greatly in their potential for carbon mitigation. The changes examined were, (a) switching all animal manure use to
arable land, (b) applying all sewage sludge to arable land, (c) incorporating all surplus cereal straw, (d) conversion to
no-till agriculture, (e) use of surplus arable land to de-intensify 1/3 of current intensive crop production (through use
of 1/3 grass/arable rotations), (f) use of surplus arable land to allow natural woodland regeneration, and (g) use of surplus
arable land for bioenergy crop production. In this paper, we attempt for the first time to assess other (non-CO2) effects of these land-management changes on (a) the emission of the other important agricultural greenhouse gases, methane
and nitrous oxide, and (b) other aspects of the ecology of the agroecosystems. We find that the relative importance of trace
gas fluxes varies enormously among the scenarios. In some such as the sewage sludge, woodland regeneration and bioenergy production
scenarios, the inclusion of trace gases makes only a small (<10%) difference to the CO2-C mitigation potential. In other cases, for example the no-till, animal manure and agricultural de-intensification scenarios,
trace gases have a large impact, sometimes halving or more than doubling the CO2-C mitigation potential. The scenarios showing the greatest increase when including trace gases are those in which manure
management changes significantly. In the one scenario (no-till) where the carbon mitigation potential was reduced greatly,
a small increase in methane oxidation was outweighed by a sharp increase in N2O emissions. When these land-management options are combined to examine the whole agricultural land area of Europe, most of
the changes in mitigation potential are small, but depending upon assumptions for the animal manure scenario, the total mitigation
potential either increases by about 20% or decreases by about 10%, shifting the mitigation potential of the scenario from
just above the EU's 8% Kyoto emission reduction target (98.9 Tg C y−1) to just below it. Our results suggest that (a) trace gas fluxes may change the mitigation potential of a land management
option significantly and should always be considered alongside CO2-C mitigation potentials and (b) agricultural management options show considerable potential for carbon mitigation even after
accounting for trace gas fluxes.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
995.
For components that are required to function in sliding or rubbing contact with other parts, degradation often occurs through
wear due to friction between the two contacting surfaces. Depending on the nature of the materials being used, the addition
of water as a lubricant may introduce corrosion and accelerate the degradation process. To improve the performance and increase
the life of these components, coatings may be applied to the regions subject to the greatest wear. These coatings may be engineered
to provide internal pockets of solid lubricant in order to improve the tribological performance. In the present study, coatings
containing a solid lubricant were produced by thermal spraying feedstock powders consisting of a blend of tungsten carbide-metal
and a fluorinated ethylene-propylene (FEP) copolymer-based material. The volume content of this teflon-based material in the
feedstock ranged from 3.5 to 36%. These feedstocks were deposited using a high velocity oxy-fuel (HVOF) system to produce
coatings having a level of porosity below 2%. Sliding wear tests in which coated rotors were tested in contact with stationary
carbon-graphite disks identified an optimum level of teflon-based material in the feedstock formulation required to produce
coatings exhibiting minimum wear. This optimum level was in the range of 7 to 17% by volume and depended on the composition
of the cermet constituent. Reductions in mass loss for the couples on the order of 50% (an improvement in performance by a
factor of approximately 2) were obtained for the best performing compositions, as compared to couples in which the coating
contained no solid lubricant. 相似文献
996.
Sang Hyun Sohn Sea Cheon Oh Byung Wan Jo Yeong-Koo Yeo 《Canadian Metallurgical Quarterly》2000,126(8):688-696
The atmospheric ozone concentration in Seoul was forecasted using an artificial neural network and spatiotemporal analysis. The artificial neural network was trained by using hourly pollutant and meteorological data that resulted in complex patterns of ozone formation. The finite-volume method was employed in the spatiotemporal analysis in order to take into account the effects of wind. Time horizons in the forecasts were 1–6 h and 16–21 h. The resulting predictions of ozone formation were compared to measured data. From the comparison, it was found that the neural network method gave reliable accuracy within a limited prediction horizon. 相似文献
997.
The slag system of CaO‐SiO2‐Al2O3‐MgO‐Cr2O3‐MnO‐FetO relevant to refining chromium‐containing steels such as bearing steel is thermodynamically assessed at 1873 K. The activity coefficient of FetO shows an initially rapid increment followed by a gradual reduction according to Cr2O3 content at a constant basicity, and decreases with increasing slag basicity. γMnO is decreased abruptly by increasing Cr2O3 content and thereafter, maintains a nearly constant level. From the standpoint of inclusion control, the Cr2O3 presence in ladle refining slags is thermodynamically harmful in that it minimizes the inclusion level by inducing the increment of γFetO even though Cr2O3 exists in extremely small amounts. However, it is beneficial in that it diminishes AI reoxidation by decreasing γMnO. The presence of carbon in slag decreases γFetO and γMnO, which turns out to be favourable for the reduction of Al reoxidation. The thermodynamic equilibria of chromium and manganese are quantified in terms of FetO and Cr2O3 content as well as slag basicity by using multiple regression analysis. LCr and LMn are increased by the presence of Cr2O3, indicating a low recovery efficiency of Cr and Mn in the treatment of ferroalloy addition. In determining LS values, Cr2O3 is not so important as the basicity of slags. 相似文献
998.
Seong-Mu Jo Wha-Seop Lee Byoung-Sung Ahn Kun-You Park Kyung-A Kim In-Sook Rhee Paeng 《Polymer Bulletin》2000,44(1):1-8
Summary
PMMA homopolymer with CF3(CF2)2CF2- end group was prepared by the ATRP of MMA using CF3(CF2)2CF2-I as an initiator and copper(I) salts/bipy catalysts. This indicated the production of perfluorobutyl radicals by ATRP mechanism
and successful polymerization by them. Di- and triblock copolymers were also prepared by the ATRP of MMA using iodine-terminated
PVDF as (macro)initiators. The kinetic plots (ln[M]o/[M] vs. time) showed nearly first-order with respect to monomer concentration and the Mn,NMR of block copolymers increased linearly with conversion. However, iodine-terminated PVDF showed low initiator efficiency because
propagating rate was much faster than initiating rate
Received: 6 September 1999/Revised version: 27 December 1999/Accepted: 28 December 1999 相似文献
999.
Kee Soo Nam Ju Wook Lee Sang-Gi Kim Tae Moon Roh Hoon Soo Park Jin Gun Koo Kyung Ik Cho 《Electron Device Letters, IEEE》2000,21(7):365-367
A novel simplified fabrication method of a very high density p-channel trench gate power MOSFET using four mask layers and nitride/TEOS sidewall spacers is realized. The proposed process showed improved on-resistance characteristics of the device with increasing cell density and the cost-effective production capability due to the lesser number of processing steps. By using this process technique, a remarkably increased high density (100 Mcell/inch2) trench gate power MOSFET with a cell pitch of 2.5 μm could be effectively realized. The fabricated device had a low specific on-resistance of 1.1 mΩ-cm2 with a breakdown voltage of -36 V 相似文献
1000.
Jo Yew Tham Lixin Shen Seng Luan Lee Hwee Huat Tan 《Signal Processing, IEEE Transactions on》2000,48(2):457-464
This paper proposes a general paradigm for the analysis and application of discrete multiwavelet transforms, particularly to image compression. First, we establish the concept of an equivalent scalar (wavelet) filter bank system in which we present an equivalent and sufficient representation of a multiwavelet system of multiplicity r in terms of a set of r equivalent scalar filter banks. This relationship motivates a new measure called the good multifilter properties (GMPs), which define the desirable filter characteristics of the equivalent scalar filters. We then relate the notion of GMPs directly to the matrix filters as necessary eigenvector properties for the refinement masks of a given multiwavelet system. Second, we propose a generalized, efficient, and nonredundant framework for multiwavelet initialization by designing appropriate preanalysis and post-synthesis multirate filtering techniques. Finally, our simulations verified that both orthogonal and biorthogonal multiwavelets that possess GMPs and employ the proposed initialization technique can perform better than the popular scalar wavelets such as Daubechies'D8 wavelet and the D(9/7) wavelet, and some of these multiwavelets achieved this with lower computational complexity 相似文献