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151.
Jian Ni Lap Keung Chu Feng Wu Domenic Sculli Yuan Shi 《European Journal of Operational Research》2012
This paper addresses the problem of mitigating procurement risk that arises from volatile commodity prices by proposing a hedging strategy within a multi-stage time frame. The proposed multi-stage hedging strategy requires a commodity futures position to be correctly initialised and rebalanced with adequate volumes of short/long positions, so as to reduce the volatility in the total procurement cost that would otherwise be generated by varying commodity spot prices. The novelty in the approach is the introduction of the rebalancing of commodity futures position at defined intermediate stages. To obtain an efficient or near optimal multi-stage hedging strategy, a discrete-time stochastic control model (DSCM) is developed. Numerical experiments and Monte Carlo simulation are used to show that the proposed multi-stage hedging strategy compares favourably with the minimal-variance hedge and the one-stage hedge. A close-form optimal solution is also presented for the case when procurement volume and price are independent. 相似文献
152.
First-principles study of structural stability and elastic property of pre-perovskite PbTiO3
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The structural stability and the elastic properties of a novel structure of lead titanate,which is named preperovskite PbTiO3 (PP-PTO) and is constructed with TiO6 octahedral columns arranged in a one-dimensional manner,are investigated by using first-principles calculations.PP-PTO is energetically unstable compared with conventional perovskite phases,however it is mechanically stable.The equilibrium transition pressures for changing from preperovskite to cubic and tetragonal phases are 0.5 GPa and 1.4 GPa,respectively,with first-order characteristics.Further,the differences in elastic properties between pre-perovskite and conventional perovskite phases are discussed for the covalent bonding network,which shows a highly anisotropic character in PP-PTO.This study provides a crucial insight into the structural stabilities of PP-PTO and conventional perovskite. 相似文献
153.
Xiao-Ling Zhang Li Zhang Ya-Ling Ye Xiang-Hui Li Dr. Bi-Lian Ni Prof. Ying Li Dr. Wei-Ming Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(3):1039-1045
Developing efficient catalysts for the conversion of CO2 into fuels and value-added chemicals is of great significance to relieve the growing energy crisis and global warming. With the assistance of DFT calculations, it was found that, different from Al12X (X=Be, Al, and C), the alkali-metal-like superatom Al12P prefers to combine with CO2 via a bidentate double oxygen coordination, yielding a stable Al12P(η2-O2C) complex containing an activated radical anion of CO2 (i.e., CO2.−). Thereby, this compound could not only participate in the subsequent cycloaddition reaction with propylene oxide but also initiate the radical reaction with hydrogen gas to form high-value chemicals, revealing that Al12P can play an important role in catalyzing these conversion reactions. Considering that Al12P has been produced in laboratory and is capable of absorbing visible light to drive the activation and transformation of CO2, it is anticipated that this work could guide the discovery of additional superatom catalysts for CO2 transformation and open up a new research field of superatom catalysis. 相似文献
154.
Ronghai Xu Xin Sensen Ni Qingzhao Zeng Hongtao Li Moucheng 《Russian Journal of Electrochemistry》2021,57(6):636-643
Russian Journal of Electrochemistry - The corrosion behavior of enamel coating on carbon steel was investigated in the tap water at 80°C (i.e., the simulated electric hot water tank... 相似文献
155.
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157.
??Recurrent event data usually occur in long-term studies which concern
recurrence rates of the disease. In studies of medical sciences, patients who have infected
with the disease, like cancer, were conventionally regarded as impossible to be cured. However,
with the development of medical sciences, recently those patients were found to be possibly
recovered from the disease. The recurrence rate of the events, which is of primary interest,
may be affected by the cure rate that may exist. Therefore, we proposed semiparametric
statistical analysis for recurrent event data with subjects possibly being cured. In our
approach, we present a proportional rate model for recurrence rate with the cure rate adjusted
through a Logistic regression model, and develop some estimating equations for estimation of
the regression parameters, with their large sample properties, including consistency and
asymptotic normality established. Numerical studies under different settings were conducted
for assessing the proposed methodology and the results suggest that they work well for
practical situations. The approach is applied to a bladder cancer dataset which motivated our
study. 相似文献
recurrence rates of the disease. In studies of medical sciences, patients who have infected
with the disease, like cancer, were conventionally regarded as impossible to be cured. However,
with the development of medical sciences, recently those patients were found to be possibly
recovered from the disease. The recurrence rate of the events, which is of primary interest,
may be affected by the cure rate that may exist. Therefore, we proposed semiparametric
statistical analysis for recurrent event data with subjects possibly being cured. In our
approach, we present a proportional rate model for recurrence rate with the cure rate adjusted
through a Logistic regression model, and develop some estimating equations for estimation of
the regression parameters, with their large sample properties, including consistency and
asymptotic normality established. Numerical studies under different settings were conducted
for assessing the proposed methodology and the results suggest that they work well for
practical situations. The approach is applied to a bladder cancer dataset which motivated our
study. 相似文献
158.
V. Cozan A. Butuc A. Stoleru M. Rusu Yushan Ni Mengxian Ding 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(12):899-906
Abstract New copolyether sulfones containing 2,5-bis(4-oxo-benzylidene)-cyclopentanone moieties were prepared in the conventional literature manner by condensing the dipotassium salts of 2,5-bis(4-hydroxyphenzyl- idene)cyclopentanone (I) and 2, 2-bis(4-hydroxyphenyl)propane (Bisphenol A, III) with 4,4′-dichlorodiphenyl sulfone (II), or by condensing the dipotassium salts of I with chlorine-terminated Bisphenol A-4,4′-di-chlorodiphenylsulfone copolymers (V). The resulting copolyether sulfones were confirmed by IR, viscometry, DSC measurements, thermooptical (TOA), and thermogravimetric analysis (TGA). 相似文献
159.
Liyong Chen Mingzu Zhang Zhuang Liu Zixu Gu Yingfeng Tu Peihong Ni 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11):862-871
A biocompatible complex has been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. In the present study, biocompatible complexes have been prepared as gene carrier via electrostatic interaction, which is composed of a polycation, that is, poly[(dimethylamino)ethyl methacrylate] end-capped with cholesterol moiety (Chol-PDMAEMA30), along with a polyanion named poly(aspartic acid)-grafted-poly(ethylene glycol) (PASP-g-PEG). We first synthesized polysuccinimide (PSI) via condensation polymerization of aspartic acid, and then used PEG-NH2 to react with the partial pentacyclic rings of PSI to yield a kind of graft copolymer polysuccinimide-grafted-poly(ethylene glycol) (PSI-g-PEG). After hydrolysis of the residual succinimide units, a new biodegradable and biocompatible graft copolymer PASP-g-PEG was prepared successfully. Chol-PDMAEMA30 was synthesized via oxyanion-initiated polymerization, as reported in our previous literature. We investigated the interactions between every pair among calf thymus DNA, Chol-PDMAEMA30, and PASP-g-PEG by agarose gel retardation assay. The results indicate that the prepared complexes could completely bind DNA and may become more stable during systemic circulation. The complexes have less cytotoxicity compared to the case of alone Chol-PDMAEMA30 or branched polyethylenimine (PEI) system. Furthermore, the physicochemical properties of the complexes were also investigated by zeta potential, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. These biodegradable and biocompatible polymeric carriers have potential applications in gene delivery. 相似文献