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Query expansion is a well-known method for improving average effectiveness in information retrieval. The most effective query expansion methods rely on retrieving documents which are used as a source of expansion terms. Retrieving those documents is costly. We examine the bottlenecks of a conventional approach and investigate alternative methods aimed at reducing query evaluation time. We propose a new method that draws candidate terms from brief document summaries that are held in memory for each document. While approximately maintaining the effectiveness of the conventional approach, this method significantly reduces the time required for query expansion by a factor of 5–10.  相似文献   
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ABSTRACT

Mineral oil hydrocarbons (MOH) are known to be mixtures of non-identified substances, which can migrate from, inter alia, recycled food packaging into food products. Such substances may have carcinogenic potential, which leads to a need to avoid their migration into food. In this article, we investigate the possible use of food simulants and model substances to simplify migration approaches. Tenax and Sorb-Star were chosen as simulant media. To stage the action of known components as a replacement for the migration of MOH, 16 single substances, including n-alkanes and aromatic compounds, were used. Kinetic studies were carried out at a maximum of 60°C with contact times of up to 14 days in touching contact with a medium or in gas-phase transfer to it. The results demonstrated that migration was predominantly a function of temperature, time and contact type, but it was also dependant on the molecular weight and polarity of the substances. Due to their low polarity, alkanes showed higher migration to the lipophilic food simulants than did pure aromatics without alkylation. Additionally, alkylated aromatics represent mineral oil aromatic hydrocarbons (MOAH) more realistically. In contrast to Tenax in the gas-phase transition, Tenax in touching contact may lead to overestimated values at higher temperatures. Migration values for Sorb-Star are in similar regions for both contact types. However, the values of the touching contact experiments were slightly higher than those of the gas-phase transfer. The results for Sorb-Star and Tenax with transport solely over the gas phase are also in good agreement. Sorb-Star generally represents an optimal simulant for chunky foods, whereas Tenax seems a good simulant for food types with a high contact surface. Temperatures up to 40°C are appropriate for most types of migration experiments, whereas 60°C should only be used as an option for experiments with Sorb-Star.  相似文献   
4.
Renhe Shi  Teng Long  Jian Liu 《工程优选》2016,48(7):1202-1225
Radial basis function (RBF) surrogate models have been widely applied in engineering design optimization problems to approximate computationally expensive simulations. Ensemble of radial basis functions (ERBF) using the weighted sum of stand-alone RBFs improves the approximation performance. To achieve a good trade-off between the accuracy and efficiency of the modelling process, this article presents a novel efficient ERBF method to determine the weights through solving a quadratic programming subproblem, denoted ERBF-QP. Several numerical benchmark functions are utilized to test the performance of the proposed ERBF-QP method. The results show that ERBF-QP can significantly improve the modelling efficiency compared with several existing ERBF methods. Moreover, ERBF-QP also provides satisfactory performance in terms of approximation accuracy. Finally, the ERBF-QP method is applied to a satellite multidisciplinary design optimization problem to illustrate its practicality and effectiveness for real-world engineering applications.  相似文献   
5.
A numerical method, called overcomplete basis surrogate method (OBSM), was recently proposed, which employs overcomplete basis functions to achieve sparse representations. While the method can handle nonstationary response without the need of inverting large covariance matrices, it lacks the capability to quantify uncertainty in predictions. We address this issue by proposing a Bayesian approach that first imposes a normal prior on the large space of linear coefficients, then applies the Markov chain Monte Carlo (MCMC) algorithm to generate posterior samples for predictions. From these samples, Bayesian credible intervals can then be obtained to assess prediction uncertainty. A key application for the proposed method is the efficient construction of sequential designs. Several sequential design procedures with different infill criteria are proposed based on the generated posterior samples. Numerical studies show that the proposed schemes are capable of solving problems of positive point identification, optimization, and surrogate fitting.  相似文献   
6.
Structure-reactivity trends are investigated by means of high temperature shock tube ignition and quantum chemical calculations for four alkanoic acid methyl esters—methyl formate (MF), methyl acetate (MA), methyl propanoate (MP), and methyl butanoate (MB). Ignition delay times are compared at constant argon/oxygen ratios, equivalence ratios and average pressures. It is observed that MA consistently shows longer ignition delay times than the other three esters, while MF and MB have comparable ignition delay times but different activation energies. MP ignition delay times are also comparable with MB in most cases but are found to be slightly shorter, especially under lean conditions. Simulated ignition delay times using the chemical kinetic model by Westbrook et al. [1] also show that MA has longer ignition delay times than MF, although the agreement between model prediction and experiment for MA is not as good as that for MF at 10 atm. Simulated ignition delay times for MB using two recent MB chemical kinetic models do not predict the same ignition delay times as the small ester mechanism under conditions where MF and MB experimental ignition delay times are found to be comparable. Ab initio quantum mechanical calculations are performed using the composite method CBS QB3, in order to determine bond dissociation energies for the four esters, as well as activation barriers for possible fuel H-abstraction reactions by H atoms. The concerted unimolecular decomposition of the esters to yield methanol and a ketene (or CO in the case of MF) is also studied. The relative reactivity observed in experiments for the four esters can be partially attributed to differences in bond energies and the calculated rates obtained in this study. Further work on possible reaction pathways and subsequent reactions of resulting primary radicals from small methyl esters is motivated by this study.  相似文献   
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ABSTRACT

Traumatic brain injury (TBI) due to blast exposure or head impacts in accidents or contact sports is one of the most critical and poorly understood areas of research in the 21st century. To date, the unavailability of human brain tissues (grey and white matter especially) due to ethical and biosafety issues has not allowed for much experimental research into the study of the mechanics of brain tissues under impact or dynamic loading. In the current work, for the first time, biofidelic brain tissue surrogates have been developed using a low cost, castable (to any shape or size), two-part silicone-based material system to precisely mimic the nonlinear mechanical properties of both the white and the grey matter. The fabrication methodology involves the iterative mixing of the two parts of silicone at certain mix ratios (by weight) to generate a biomechanical behavior similar to the white and the grey matter tissues, respectively, at two different strain rates (low and high). The nonlinear behavior of these novel brain tissue surrogates have been characterized using five hyperelastic material models. These brain tissue simulant materials would be indispensable not only for the study of TBI, but also to allow doctors to practice brain surgeries (for training purposes) in a clinical setting. Additionally, crucial brain tissue modifications in Alzheimer's disease and dementia can be studied in the future with such accessible biofidelic brain tissue surrogate materials.  相似文献   
8.
Formaldehyde fixation is widely used for long‐term maintenance of tissue. However, due to formaldehyde‐induced crosslinks, fixed tissue proteins are difficult to extract, which hampers mass spectrometry (MS) proteomic analyses. Recent years have seen the use of different combinations of high temperature and solubilizing agents (usually derived from antigen retrieval techniques) to unravel formaldehyde‐fixed paraffin‐embedded tissue proteomes. However, to achieve protein extraction yields similar to those of fresh‐frozen tissue, high‐temperature heating is necessary. Such harsh extraction conditions can affect sensitive amino acids and post‐translational modifications, resulting in the loss of important information, while still not resulting in protein yields comparable to those of fresh‐frozen tissue. Herein, the objective is to evaluate cleavable protein crosslinkers as fixatives that allow tissue preservation and efficient protein extraction from fixed tissue for MS proteomics under mild conditions. With this goal in mind, disuccinimidyl tartrate (DST) and dithiobis(succinimidylpropionate) (DSP) are investigated as cleavable fixating reagents. These compounds crosslink proteins by reacting with amino groups, leading to amide bond formation, and can be cleaved with sodium metaperiodate (cis‐diols, DST) or reducing agents (disulfide bonds, DSP), respectively. Results show that cleavable protein crosslinking with DST and DSP allows tissue fixation with morphology preservation comparable to that of formaldehyde. In addition, cleavage of DSP improves protein recovery from fixed tissue by a factor of 18 and increases the number of identified proteins by approximately 20 % under mild extraction conditions compared with those of formaldehyde‐fixed paraffin‐embedded tissue. A major advantage of DSP is the introduction of well‐defined protein modifications that can be taken into account during database searching. In contrast to DSP fixation, DST fixation followed by cleavage with sodium metaperiodate, although effective, results in side reactions that prevent effective protein extraction and interfere with protein identification. Protein crosslinkers that can be cleaved under mild conditions and result in defined modifications, such as DSP, are thus viable alternatives to formaldehyde as tissue fixatives to facilitate protein analysis from paraffin‐embedded, fixed tissue.  相似文献   
9.
Norharman and harman are two neuroactive β-carbolines present in several plants and thermally processed foods, including roasted coffee. The objective of this study was to evaluate their amounts in commercial instant coffee-based and coffee substitute beverages (n = 48), with variable amounts of coffee, chicory, barley, malt, and rye. All samples contained variable amounts of both β-carbolines, always with a higher proportion of norharman than harman. The highest levels (p < 0.01) were found in 100% instant coffees, with mean amounts of 3.8 μg/g and 1.5 μg/g for NH and H, respectively, followed by plain chicory. The lowest amounts were found in 100% barley, with 1.1 μg/g for NH and 0.3 μg/g for H. The NH and H content was statistically higher (p < 0.01) in all mixtures with coffee when compared to those without it. Nevertheless, and except for 100% barley, the amounts provided by beverages based on coffee substitutes are within those reported for standard coffee brews.  相似文献   
10.
Particle swarm optimization (PSO) is a population-based, heuristic technique based on social behaviour that performs well on a variety of problems including those with non-convex, non-smooth objective functions with multiple minima. However, the method can be computationally expensive in that a large number of function calls is required. This is a drawback when evaluations depend on an off-the-shelf simulation program, which is often the case in engineering applications. An algorithm is proposed which incorporates surrogates as a stand-in for the expensive objective function, within the PSO framework. Numerical results are presented on standard benchmarking problems and a simulation-based hydrology application to show that this hybrid can improve efficiency. A comparison is made between the application of a global PSO and a standard PSO to the same formulations with surrogates. Finally, data profiles, probability of success, and a measure of the signal-to-noise ratio of the the objective function are used to assess the use of a surrogate.  相似文献   
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