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991.
本文考虑的是允许采用比例再保险策略和投资策略的两个保险公司如何寻找最优合并时刻的问题.两个保险公司的风险过程由漂移布朗运动刻画,目标为最大化它们的生存概率.各个公司的安全负荷系数和波动系数在决定两公司是否要合并时起到了关键作用.决定合并后,公司合并费用,合并前后公司的生存概率状况在决定最优合并时刻时起到了关键作用.我们分两种情况讨论了这个问题并分别给出相应情况下的最优策略和值函数. 相似文献
992.
The streamwise fluctuating velocity in the turbulent boundary layer is measured under approximately medium Reynolds Number
by hot wire in order to investigate the scaling properties of the overlapped turbulent spectrum among energy-containing area,
inertial subrange and dissipation range based on FFT analysis. The experiment indicates that the high Reynolds flow reported
before is not indispensable to produce −1 scaling. So far as the measured position is provided with much higher spatial resolution
and enough closing to the wall, −1 scaling is determinate to exist when approaching medium Reynolds. The scaling ranges are
supposed to begin at inner scale and end in outer scale, which reveals the local similarity of the energy spectrum over the
energy-containing eddies near the wall. In the logarithmic area (y
+ > 130), −5/3 scaling occurs in the energy spectrum, while moving away from the wall with Reynolds numbers increasing, the
inertial subrange extends to the lower wavenumbers. On the condition k
1
η ≫ 0.1, the curves of the turbulence spectrum in the logarithmic layer are superposed, which expresses the similarity of turbulence
energy distributed in Komogorov scaling area and exhibits local isotropy characteristics by virtue of the viscous dissipation.
Supported by the National Natural Science Foundation of China (Grant Nos. 10832001 and 10872145), the Program for New Century
Excellent Talents in Universities of Education Ministry of China, and the Plan of Tianjin Science and Technology Development
(Grant No. 06TXTJJC13800) 相似文献
993.
Microcalorimetric Study of the Screening Specific Promoter Bacteria of Nutrient Drug 总被引:3,自引:0,他引:3
H. Zhang X. Yu H. Sun Y. Liu Z. Nan C. Lu M. Ru G. Mai Y. Wang Z. Li 《Journal of Thermal Analysis and Calorimetry》1999,58(2):435-440
The power vs. time curves of the promoter bacteria of a nutrient drug were determined by using a 2277 Thermal Activity Monitor (Sweden). A new experimental model of bacterial growth were established. The growth rate constant, heat output and optimum concentration of specific promoter bacterial of nutrient drug were calculated.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
994.
995.
Zheng‐Ren Xu Xing‐Yun Chai Chang‐Cai Bai Hong‐Yan Ren Ya‐Nan Lu Hai‐Ming Shi Peng‐Fei Tu 《Helvetica chimica acta》2008,91(7):1346-1354
Seven new phenolic glucosides, xylocosides A–G ( 1 – 7 ), together with 18 known compounds were isolated from the stems of Xylosma controversum Clos . In compounds 3 – 6 , the glucose residue is esterified at C(6) by 2‐hydroxycyclopentanecarboxylic acid. These new structures were established by spectroscopic‐data interpretation and chemical methods. 相似文献
996.
997.
A novel method of online microcolumn separation and preconcentration coupled to inductively coupled plasma atomic emission spectrometry (ICP-AES) with the use of acetylacetone-modified silica gel as packing material was developed for the determination of trace rare earth elements (REEs) in environmental and food samples. The main parameters affecting online separation/preconcentration, including pH, sample flow rate, sample volume, elution and interfering ions, have been investigated in detail. Under the optimized operating conditions, the adsorption capacity values for Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu were 25.65, 23.23, 24.01, 19.40, 22.89, 23.77, 24.40, 23.96, 25.58, 25.15, 24.86, 22.75, 16.05, 24.13, 26.51 and 27.93 mg g(-1), respectively. Detection limits (3sigma) based on three times standard deviations of the blanks by 8 replicates were in the range from 48 pg mL(-1) for Lu to 1003 pg mL(-1) for Sm. With 90 s preconcentration time and 10 s elution time, the enrichment factor was 10 and the sample frequency was 28 h(-1). The precisions (RSDs) obtained by determination of a 250 ng mL(-1) (n = 8) REEs standard solution were in the range from 1.7% for Y to 4.4% for Sm. The proposed method was successfully applied to the determination of trace REEs in pig liver, agaric and mushroom. To validate the proposed method, we analyzed three certified reference materials (GBW07401 soil, GBW07301a sediment, and GBW07605 tea leaves). The determined values were in a good agreement with the certified values. The method is rapid, selective, sensitive and applicable to the determination of trace REEs in biological and environmental samples with complicated matrix effects. 相似文献
998.
999.
1000.
Bin Zhang Jun Wang Yu Chen Daniel Früchtl Bo Yu Xiaodong Zhuang Nan He Werner J. Blau 《Journal of polymer science. Part A, Polymer chemistry》2010,48(14):3161-3168
The poly(N‐vinylcarbazole)‐grafted MWNTs (MWNT‐PVK) hybrid materials were synthesized in the presence of S‐1‐Dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate (DDAT)‐covalently functionalized multiwalled carbon nanotubes (MWNT‐DDAT) as reversible addition–fragmentation chain transfer (RAFT) agent. Incorporation of the PVK moieties onto the MWNTs surface can considerably improve the solubility and processability of MWNTs. For all MWNT‐PVK hybrid materials, they are soluble in some common organic solvents such as toluene, THF, chloroform, DMF and others. In contrast to the UV/Vis spectrum of DDAT‐PVK, which was synthesized by use of DDAT as RAFT agent under the same synthetic condition, in the visible region, the absorption spectrum of MWNT‐PVK exhibited a typical electronic absorption characteristics of solubilized carbon nanotubes, in which the absorbance decreases gradually in the range of 350–600 nm. At the same level of linear transmission the MWNT‐PVK with 79.2% PVK moieties in the material structure possesses best optical limiting performance in comparison with the other MWNT‐PVK composites, MWNTs and C60. The significant NLO responses manifest the MWNT‐PVK materials suitable candidate for viable optical limiting devices. Light scattering, originating from the thermal‐induced microplasmas and/or microbubbles, is responsible for the optical limiting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3161–3168, 2010 相似文献