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1.
2.
The Huber criterion for data fitting is a combination of thel
1 and thel
2 criteria which is robust in the sense that the influence of wild data points can be reduced. We present a trust region and a Marquardt algorithm for Huber estimation in the case where the functions used in the fit are non-linear. It is demonstrated that the algorithms converge under the usual conditions. 相似文献
3.
Madsen SJ Sun CH Tromberg BJ Wallace VP Hirschberg H 《Photochemistry and photobiology》2000,72(1):128-134
The response of human glioma spheroids to 5-aminolevulinic acid (ALA)-mediated photodynamic therapy (PDT) is investigated. A two-photon fluorescence microscopy technique is used to show that human glioma cells readily convert ALA to protoporphyrin IX throughout the entire spheroid volume. The central finding of this study is that the response of human glioma spheroids to ALA-mediated PDT depends not only on the total fluence, but also on the rate at which the fluence is delivered. At low fluences (< or = 50 J cm-2), lower fluence rates are more effective. At a fluence of 50 J cm-2, near-total spheroid kill is observed at fluence rates of as low as 10 mW cm-2. The fluence rate effect is not as pronounced at higher fluences (> 50 J cm-2), where a favorable response is observed throughout the range of fluence rates investigated. The clinical implications of these findings are discussed. 相似文献
4.
M S Patterson S J Madsen B C Wilson 《Journal of photochemistry and photobiology. B, Biology》1990,5(1):69-84
Singlet oxygen (1O2) is thought to be the cytotoxic agent in photodynamic therapy (PDT) with current photosensitizers. Direct monitoring of 1O2 concentration in vivo would be a valuable tool in studying biological response. Attempts were made to measure 1O2 IR luminescence during PDT of cell suspensions and two murine tumour models using the photosensitizers Photofrin II and aluminium chlorosulphonated phthalocyanine. Instrumentation was virtually identical to that devised by Parker in the one positive report of in vivo luminescence detection in the literature. Despite the fact that our treatments caused cell killing and tissue necrosis, we were unable to observe 1O2 emission under any conditions. We attribute this negative result to a reduction in 1O2 lifetime in the cellular environment. Quantitative calibration of our system allowed us to estimate that the singlet oxygen lifetime in tissue is less than 0.5 microsecond. Some technical improvements are suggested which would improve detector performance and perhaps make such measurements feasible. 相似文献
5.
Measurements of acoustic absorption and velocity as a function of frequency and concentration in KH2PO4–K2HPO4 buffers at 4°C and pH 5-7 are reported. The dependence of the observed acoustic relaxation parameters on concentration is consistent with that to be expected from perturbation of a monomer-dimer equilibrium with an equilibrium constant [for 2H2PO
4
–
(H2PO4)2
2–] of 0.21 M–1, a bimolecular rate constant of 5×108 M–1-sec–1 and a standard volume change of –5 cm3 mole. The equilibrium constant for H2PO
4
–
+ HPO4
2–H3(PO4)2
3– is estimated to be 0.7 M–1. 相似文献
6.
Hansen MR Madsen GK Jakobsen HJ Skibsted J 《The journal of physical chemistry. A》2005,109(9):1989-1997
The refinement of borate structures using DFT calculations combined with experimental (11)B quadrupole coupling parameters from solid-state NMR spectroscopy is presented. The (11)B electric field gradient (EFG) tensors, calculated using the WIEN2k software for trigonal and tetrahedral boron sites in a series of model compounds, exhibit a convincing linear correlation with the quadrupole coupling tensor elements, determined from (11)B MAS NMR spectra of the central or satellite transitions. The model compounds include Li(2)B(4)O(7), Mg(2)B(2)O(5), Mg(3)B(2)O(6), NH(4)B(C(6)H(5))(4), and colemanite (CaB(3)O(4)(OH)(3).H(2)O). The (11)B quadrupole moment, Q = 0.0409 +/- 0.0002 barn, derived from the linear correlation, is in excellent agreement with the accepted value for Q((11)B). This demonstrates that DFT (WIEN2k) calculations can provide precise (11)B quadrupole coupling parameters on an absolute scale. On the other hand, DFT calculations based on the reported crystal structures for datolite (CaBSiO(4)(OH)) and danburite (CaB(2)Si(2)O(8)) cannot reproduce the experimental (11)B quadrupole coupling parameters to the same high precision. However, optimization of these structures by minimization of the forces between the atoms (obtained by DFT) results in a significant improvement between the calculated and experimental (11)B quadrupole coupling parameters, which indicates that reliable refinements of the borate structures are obtained by this method. Finally, the DFT calculations also provide important structural information about the sign and orientation of the EFG tensor elements in the crystal frame, a kind of information that cannot be achieved from (11)B NMR experiments on powdered samples. 相似文献
7.
A heuristic method for dispatching repair men 总被引:2,自引:0,他引:2
A company has to provide service to its customers. A service consists of a visit to the customer plus the spending of some given time at the scene. The future customer demand is not known but the probability distribution for the demand may be known. When a customer call comes in, the company must immediately specify a time window within which the start of service will be provided. The problem is for a fixed service level to determine an optimal strategy of route design and time window setting so that the total distance travelled is minimized over the time horizon given. A heuristic method BARTOC (Booking Algorithm for Routing and Timing Of Customers) to solve the problem mentioned above is suggested. BARTOC is based on a cluster-first route-second approach. Some computational results are presented. The results indicate that BARTOC produces high quality solutions.Peter Matthiesen, Inc.Dano Chemo, Inc. 相似文献
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