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1.
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
2.
Evaluating the accuracy of theoretical one‐bond 13C─13C scalar couplings and their ability to predict structure in a natural product 下载免费PDF全文
Jacob Powell Domenic Valenti Harley Bobnar Erika Drain Blaine Elliott Sydney Frank Tyler McCullough Sean Moore Andrew Kettring Robbie Iuliucci James K. Harper 《Magnetic resonance in chemistry : MRC》2017,55(11):979-989
This study explores the feasibility of using a combination of experimental and theoretical 1‐bond 13C─13C scalar couplings (1JCC) to establish structure in organic compounds, including unknowns. Historically, nJCC and nJCH studies have emphasized 2 and 3‐bond couplings, yet 1JCC couplings exhibit significantly larger variations. Moreover, recent improvements in experimental measurement and data processing methods have made 1JCC data more available. Herein, an approach is evaluated in which a collection of theoretical structures is created from a partial nuclear magnetic resonance structural characterization. Computed 1JCC values are compared to experimental data to identify candidates giving the best agreement. This process requires knowledge of the error in theoretical methods, thus the B3LYP, B3PW91, and PBE0 functionals are evaluated by comparing to 27 experimental values from INADEQUATE. Respective errors of ±1.2, ±3.8, and ±2.3 Hz are observed. An initial test of this methodology involves the natural product 5‐methylmellein. In this case, only a single candidate matches experimental data with high statistical confidence. This analysis establishes the intramolecular hydrogen‐bonding arrangement, ring heteroatom identity, and conformation at one position. This approach is then extended to hydroheptelidic acid, a natural product not fully characterized in prior studies. The experimental/theoretical approach proposed herein identifies a single best‐fit structure from among 26 candidates and establishes, for the first time, 1 configuration and 3 conformations to complete the characterization. These results suggest that accurate and complete structural characterizations of many moderately sized organic structures (<800 Da) may be possible using only 1JCC data. 相似文献
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Ohne Zusammenfassung 相似文献
4.
An approach to the valuation and decision of ERP investment projects based on real options 总被引:1,自引:0,他引:1
The risks and uncertainties inherent in most enterprise resources planning (ERP) investment projects are vast. Decision making
in multistage ERP projects investment is also complex, due mainly to the uncertainties involved and the various managerial
and/or physical constraints to be enforced. This paper tackles the problem using a real-option analysis framework, and applies
multistage stochastic integer programming in formulating an analytical model whose solution will yield optimum or near-optimum
investment decisions for ERP projects. Traditionally, such decision problems were tackled using lattice simulation or finite
difference methods to compute the value of simple real options. However, these approaches are incapable of dealing with the
more complex compound real options, and their use is thus limited to simple real-option analysis. Multistage stochastic integer
programming is particularly suitable for sequential decision making under uncertainty, and is used in this paper and to find
near-optimal strategies for complex decision problems. Compared with the traditional approaches, multistage stochastic integer
programming is a much more powerful tool in evaluating such compound real options. This paper describes the proposed real-option
analysis model and uses an example case study to demonstrate the effectiveness of the proposed approach. 相似文献
5.
This paper analyses the use of multiple suppliers to replenish one stock item. The replenishment order is split into several portions, one for each supplier, and orders for these portions are placed simultaneously with the respective suppliers. Approximate expressions are derived for the mean and variance of the effective lead time, which is the minimum of the individual lead times of each supplier. These results give effective lead-time-demand mean and variance that are smaller than those of the individual suppliers. The results can be used to lower the operating cost of the stocking policy. 相似文献
6.
Schneider JF Lauber MB Muhr V Kratzer D Paradies J 《Organic & biomolecular chemistry》2011,9(11):4323-4327
This paper focuses on readily accessible thiourea hydrogen bond catalysts derived from amino acids, whose steric and electronic features are modulated by their degree of substitution at the carbinol carbon center. These catalysts were applied in the asymmetric transfer hydrogenation of nitroolefins furnishing the chiral products in up to 99% yield and 86% enantiomeric excess. The proposed catalyst's mode of action is supported by mechanistic investigations. 相似文献
7.
S. Chiamsiri D. Sculli J. Y. Wong✠ 《The Journal of the Operational Research Society》1984,35(4):289-295
This paper presents the results of an attempt to estimate the number of computer terminals required to issue export licences to waiting callers. The problem differs from classical queueing studies in that the arrival pattern is non-stationary, and the measure of performance used to judge the quality of service is the size of the remaining queue at closing time. A stimulation approach is used to evaluate the measures of performance for a given number of service counters. The simulation approach used consists of concatenated independent trials taken at half-hourly intervals. This approach enables a large number of working days to be simulated, thus increasing the reliability of the results. 相似文献
8.
Sefzik TH Turco D Iuliucci RJ Facelli JC 《The journal of physical chemistry. A》2005,109(6):1180-1187
The NMR chemical shift, a six-parameter tensor property, is highly sensitive to the position of the atoms in a molecule. To extract structural parameters from chemical shifts, one must rely on theoretical models. Therefore, a high quality group of shift tensors that serve as benchmarks to test the validity of these models is warranted and necessary to highlight existing computational limitations. Here, a set of 102 13C chemical-shift tensors measured in single crystals, from a series of aromatic and saccharide molecules for which neutron diffraction data are available, is used to survey models based on the density functional (DFT) and Hartree-Fock (HF) theories. The quality of the models is assessed by their least-squares linear regression parameters. It is observed that in general DFT outperforms restricted HF theory. For instance, Becke's three-parameter exchange method and mpw1pw91 generally provide the best predicted shieldings for this group of tensors. However, this performance is not universal, as none of the DFT functionals can predict the saccharide tensors better than HF theory. Both the orientations of the principal axis system and the magnitude of the shielding were compared using the chemical-shift distance to evaluate the quality of the calculated individual tensor components in units of ppm. Systematic shortcomings in the prediction of the principal components were observed, but the theory predicts the corresponding isotropic value more accurately. This is because these systematic errors cancel, thereby indicating that the theoretical assessment of shielding predictions based on the isotropic shift should be avoided. 相似文献
9.
Three-dimensional classical trajectory calculations have been carried out for the quenching of Br*(2P1/2) by collision with ground-state H2, using an approach that describes the electronic as well as heavy-particle (i.e. transition, rotation, vibration) degrees of freedom by classical mechanics. We find a sizeable quenching cross section (≈ Å2), with essentially all of the collision products having H2 vibrationally excited to υ = 1, i.e. near-resonant EV transfer dominates the non-resonant ET,R processes. This is in agreement with experimental results. 相似文献
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