排序方式: 共有38条查询结果,搜索用时 15 毫秒
1.
2.
I.C. Demetriou 《Computational Optimization and Applications》2004,29(2):197-217
We consider n noisy measurements of a smooth (unknown) function, which suggest that the graph of the function consists of one convex and one concave section. Due to the noise the sequence of the second divided differences of the data exhibits more sign changes than those expected in the second derivative of the underlying function. We address the problem of smoothing the data so as to minimize the sum of squares of residuals subject to the condition that the sequence of successive second divided differences of the smoothed values changes sign at most once. It is a nonlinear problem, since the position of the sign change is also an unknown of the optimization process. We state a characterization theorem, which shows that the smoothed values can be derived by at most 2n – 2 quadratic programming calculations to subranges of data. Then, we develop an algorithm that solves the problem in about O(n
2) computer operations by employing several techniques, including B-splines, the use of active sets, quadratic programming and updating methods. A Fortran program has been written and some of its numerical results are presented. Applications of the smoothing technique may be found in scientific, economic and engineering calculations, when a potential shape for the underlying function is an S-curve. Generally, the smoothing calculation may arise from processes that show initially increasing and then decreasing rates of change. 相似文献
3.
制备了甘氨酸-壳聚糖复合膜修饰玻碳电极(Gly-CTS/GCE),研究了抗坏血酸(AA)和尿酸(UA)在该修饰电极上的电化学行为。结果表明在pH=5.59的磷酸盐缓冲溶液中,AA、UA在Gly-CTS/GCE上均产生灵敏的不可逆氧化峰,其峰电流与浓度在一定范围内呈良好的线性关系。对AA和UA混合溶液平行测定7次,相对标准偏差分别为4.6%、2.9%,表明该电极重现性和稳定性良好。AA、UA在Gly-CTS/GCE电极上的氧化峰峰电位相差340mV,据此可实现对二者的同时检测,并可应用于实际样品测定。 相似文献
4.
Michael Davis Michael A. Demetriou David J. Olinger 《Flow, Turbulence and Combustion》2003,71(1-4):75-91
A highly efficient, low-order model for vortex-induced vibration of flexible cables at low Reynolds number has been developed. A coupled map lattice (CML) wake model, based on circle maps, is combined with a cable model (linear wave equation). With this model, both the self-excited response of the cable oscillation in the crossflow direction and the resulting wake structures are examined at Re = 100. This represents an improvement over earlier CML models capable of only modelling wakes behind externally forced cables. For comparison, spectral-element based numerical simulations, in addition to experiments on a freely vibrating cable flow, were conducted. The freely vibrating CML model predicted lace-like structures consistent with these numerical simulations and experimental results. Little difference was noted between the vortex shedding wake patterns determined for forced cables (from previous CML models) and freely vibrating cables. The freely vibrating CML matched experimental data for maximum cable amplitude reasonably well over a range of mass-damping parameter employed in offshore structural applications. 相似文献
5.
By identifying the key characteristic "structural scales" that dictate the resistance of a porous metallic glass against buckling and fracture, stochastic highly porous metallic-glass structures are designed capable of yielding plastically and inheriting the high plastic yield strength of the amorphous metal. The strengths attainable by the present foams appear to equal or exceed those by highly engineered metal foams such as Ti-6Al-4V or ferrous-metal foams at comparable levels of porosity, placing the present metallic-glass foams among the strongest foams known to date. 相似文献
6.
Abrahams I Hawkes GE Ahmed A Di Cristina T Demetriou DZ Ivanova GI 《Magnetic resonance in chemistry : MRC》2008,46(4):316-322
Solid-state (23)Na and (31)P magic-angle spinning nuclear magnetic resonance spectroscopy and X-ray crystallography have been used to study the structures of the chain metaphosphates NaCa(PO(3))(3) and NaSr(PO(3))(3). The compounds are isostructural and crystallise in space group P(-1) with the following parameters: NaCa(PO(3))(3), a = 6.711 A, b = 6.934 A, c = 7.619 A, alpha = 83.44 degrees , beta = 81.41 degrees , gamma = 82.80 degrees ; NaSr(PO(3))(3)a = 6.805 A, b = 7.133 A, c = 7.720 A and alpha = 83.71 degrees , beta = 80.48 degrees , gamma = 82.87 degrees . Both structures contain anionic metaphosphate chains of (PO(3))(n) (n) with ionic contacts to Na(+) ions in distorted octahedral sites and Ca(2+) (or Sr(2+)) in distorted dodecahedral sites. (31)P and (23)Na NMR are entirely consistent with the crystallographic data and an empirical method for assigning (31)P resonances to particular crystallographically unique P atoms is described. 相似文献
7.
C70X2(X=H,F, Cl)的稳定性和电子光谱 总被引:1,自引:0,他引:1
用INDO方法研究C70H2四种异构体的稳定性, 表明其最稳定异构体为1, 9-C70H2和7, 8-C70H2, 两者能量差为16.3KJ.mol^-^1, 与实验值及ab initio计算值接近; 光谱计算表明, 其特征吸收峰与实验值一致。在此基础上预测C70F2和C70Cl2的稳定性和电子光谱, 表明C70F2四种异构体的稳定性顺序与C70H2一致, 而C70Cl2则以21, 42-异构体最为稳定。二者的电子光谱与C70H2极其相似只是在500nm以上有细微差别。 相似文献
8.
9.
I. Abrahams D. Z. Demetriou R. T. Kroemer H. Taylor M. Motevalli 《Journal of solid state chemistry》2001,160(2):382
The formation of cluster orbitals in CsSn2Br5 is discussed and related more generally to tetragonal compounds of the type AB2X5 (A=monovalent cation; B=Sn, Pb; X=Cl, Br, I). The crystal structures of CsSn2Cl5 and CsSn2Br5 have been solved by single-crystal X-ray diffraction. These compounds are isostructural with each other and a range of AB2X5 structural analogues. In many AB2X5 compounds where B is a subvalent main group metal a tetragonal cell is observed with space group I4/mcm. The structures of CsSn2Br5 and CsSn2Cl5 are layered with polymeric sheets of [Sn2X5]n−n separated by the Cs+ cations. Stereochemical considerations suggest that stabilization of this structural form, rather than the more ionic NH4Pb2Cl5 or NaSn2Cl5 structures, is through interaction of the “nonbonding” valence electron pairs on tin with low-lying empty d-orbitals on neighboring X atoms. Electronic structure calculations based on the structural data confirm the likelihood of cluster orbital formation. Crystal data: CsSn2Cl5, tetragonal, I4/mcm, a=8.153(1) Å, c=14.882(4) Å, Z=4, R1=0.0215, wR2=0.0503 [I>2σ(I)], R1=0.0393, wR2=0.0536 (all data); CsSn2Br5, tetragonal, I4/mcm, a=8.483(6) Å, c=15.28(2) Å, Z=4, R1=0.0607, wR2=0.1411 [(I>2σ(I)], R1=0.1579, wR2=0.1677 (all data). 相似文献
10.
P. N. Dimotakis B. D. Symeopoulos M. N. Demetriou 《Journal of Radioanalytical and Nuclear Chemistry》1990,143(2):373-379
Infrared absorption spectra of HNO3 solutions in UO2(NO3)2(TBP)2 have been taken. The formation of a hydrogen bond between HNO3 and nitrate or phosphoryl group in UO2(NO3)2(TBP)2 has been established. On extracting Pu(IV) and Np(IV) by 30% TBP-dodecane, dependence of the distribution coefficients on concentration has been found at UO2(NO3)2 concentrations in the aqueous phase upwards from 0.4M. This dependence appeared in the temperature interval 0–60°C. Such effects may be caused by ordered structure of saturated uranyl nitrate solutions in TBP. 相似文献