Taxonomy of interpolation constraints on recursive subdivision surfaces

Published online: 14 May 2002     

Proteomic analysis of responses of a new probiotic bacterium Lactobacillus casei Zhang to low acid stress

Tolerance to acid is an important feature for probiotic bacteria during transition through the gastrointestinal tract. Proteomics analysis of a new probiotic bacterium, Lactobacillus casei Zhang, was performed upon 30-min exposure to low acid stress (pH 2.5 vs. pH 6.4) using two-dimensional electrophoresis. Out of 33 protein spots that showed changes of expression between the two pHs, 22 showed 1.5-fold higher expression at pH 2.5 than at pH 6.4, whereas five spots had expression decreased by 1.5-fold at pH 2.5. There were also six protein spots that were exclusively present on different pH maps. Further analysis showed that eight of the enhanced proteins, NagA, NagB, PGM, GlmM, LacC, TDP, GALM and PtsI, were involved in carbohydrate catabolism. Moreover, quantitative RT-PCR showed that the mRNA expression levels of dnaK, nagB, galm, estC, tuf and luxS were consistent with changes in protein expression. We postulate that there might be some relationship between differentially expressed proteins and acid tolerance in L. casei Zhang.     

Antibacterial mechanism of bifidocin A,a novel broad-spectrum bacteriocin produced by Bifidobacterium animalis BB04

Bifidocin A, a novel broad-spectrum bacteriocin produced by Bifidobacterium animalis BB04, was isolated from the feces of a healthy centenarian. To understand the mechanism of the antibacterial action of bifidocin A against gram-negative bacteria, its effects at a minimum inhibitory concentration on cell morphology, intracellular organization, membrane permeability, membrane integrity, and membrane proton motive force (PMF) of Escherichia coli 1.90 were investigated. Scanning and transmission electron microscopy analyses showed that bifidocin A induced alterations in the morphology and intracellular organization of E. coli cells. The intracellular organization was more susceptible to changes induced by bifidocin A than the morphology. Bifidocin A treatment caused the leakage of K⁺ and inorganic phosphate, the release of ATP and UV-absorbing materials, and a collapse of the transmembrane electrical potential and pH gradient in E. coli cells. Confocal laser scanning microscopy images showed that E. coli cells treated with bifidocin A took up propidium iodide. These results suggested that the mechanism of action bifidocin A against E. coli involved dissipation of the PMF of the cytoplasmic membrane, an increase in membrane permeability, pore formation in the cell membrane, a change in membrane integrity, and complete cell disintegration.     

Assessment of the safety and applications of bacteriocinogenic Enterococcus faecium Y31 as an adjunct culture in North-eastern Chinese traditional fermentation paocai

Enterococcus faecium Y31 is a class IIa bacteriocin producer found in traditional Chinese fermented foods. The bacteriocin produced by Y31 (bacteriocin Y31) has a broad inhibitory spectrum. Here, we investigated the safety and behaviours of E. faecium Y31 in North-eastern Chinese traditional fermentation paocai (NCTFP) to assess its suitability as an adjunct culture. E. faecium Y31 showed interesting features, such as the absence of virulence determinants (aggregation substance [agg], enterococcal surface protein [esp], endocarditis antigen [efaAfm], gelatinase [gelE], hemolysin [cylA, cylB, cylM], sex pheromone [cpd, cob, ccf], adhesion of collagen [ace], and hyaluronidase [hyl] genes), sensitivity to various antibiotics, lack of haemolytic compounds, and lack of biogenic amine production. E. faecium Y31 could propagate in raw Chinese cabbage and produce bacteriocin Y31. To evaluate its performance as an adjunct culture for NCTFP, changes in the overall quality of control (noninoculated) and experimental NCTFP (inoculated with E. faecium Y31 under previously optimised fermentation conditions) were determined in duplicate fermentations of Chinese cabbage using chemical, microbiological, texture, and sensory evaluations. In the presence of E. faecium Y31, faster fermentation and higher bacteriocin Y31 production were observed than in the control. Additionally, the nitrite concentration of the fermentation solution decreased more rapidly, the total viability of the culture increased, and the lactic acid bacterium population was higher than those in NCTFP produced by spontaneous fermentation. No yeasts and moulds were detected in NCTFP produced by inoculation fermentation or spontaneous fermentation, and the textural properties of these two products were similar. Sensory evaluation results for NCTFP produced by inoculation fermentation were superior to those produced by spontaneous fermentation. Therefore, E. faecium Y31 was sufficient as an adjunct culture to enhance both the hygienic and sensory attributes of NCTFP and its use may help to address the issues inherent in commercial production of NCTFP.     

3种套保效率评价模型的比较研究

套保效率评价模型能否准确反映套保行为的价值直接影响着套保决策的制定和质量，一旦效率评价出现偏差，将导致投资者做出错误判断，甚至套保行为的失败。本文以沪铜为例，分析了目前普遍采用的3种套保效率评价模型——风险减少程度、夏普比率和Lindal’mean—Lindal’S．D在实际应用中存在的偏差，并提出改进套保效率评价模型的相关建议。     

Antibacterial activity and mechanism of bifidocin A against Listeria monocytogenes

Bifidocin A, produced by Bifidobacterium animalis BB04, is a novel bacteriocin with antimicrobial activity against a wide range of gram-positive and gram-negative foodborne bacteria. The objective of this study was to investigate the antibacterial activity and mechanism of action of bifidocin A against Listeria monocytogenes, one of the most susceptible bacteria to this bacteriocin. The minimum inhibitory concentration (MIC) of bifidocin A for L. monocytogenes 35152 was 0.029 mg/mL. Time-kill assays showed that bifidocin A effectively inhibited the growth of L. monocytogenes in a time-and concentration-dependent manner. The mechanism of action of bifidocin A was studied by analyzing its effects at a MIC on the cell morphology, intracellular organization, membrane permeability, membrane integrity, and membrane proton motive force (PMF) of L. monocytogenes. Scanning and transmission electron microscopy analyses showed that bifidocin A induced alterations in the morphology and intracellular organization of L. monocytogenes cells. Confocal laser scanning microscopy images showed that L. monocytogenes cells treated with bifidocin A took up propidium iodide. Bifidocin A treatment also induced the leakage of K⁺ and inorganic phosphate, the hydrolysis and release of ATP, and a collapse of the transmembrane electrical potential and pH gradient in L. monocytogenes cells. These results suggested that bifidocin A exerted its anti-Listeria monocytogenes effect through the dissipation of the cytoplasmic membrane PMF, increased membrane permeability, cell membrane pore formation, destruction of membrane integrity, and ultimately complete disintegration of the cells.     

Exploiting colorimetric relationships in characterizing the spectral response functions of the human visual system directly from colour matching functions

The linear relationship between the spectral response functions (SRFs) of a three-colour response system and the set of the corresponding colour matching functions (CMFs) for a particular set of primaries, in the form of three simultaneous equations, is the principal fundamental approach adopted in this article in determining the characteristics of the former. After reviewing, evaluating, and where necessary processing the three sets of 2° field CMFs derived by the historic researchers, Guild, Wright, and Stiles & Burch, they were used with three sets of CMFs to SRFs transforms with adjustable matrix coefficients, respectively, to provide three closely matched sets of SRFs. These close matches then formed the basis for the three sets of potential human visual system (HVS) SRFs, which with three further transforms, whose coefficients are based upon the response of the SRFs at the primary wavelengths, then generate, respectively, a close match to each of the historic sets of CMFs. The precept adopted is that given the relative trichromatic sensitivity of the HVS SRFs and a set of three spectral primaries of defined wavelength and known luminosities, a mathematical relationship may be derived between them that produces a corresponding set of CMFs related to the wavelengths of the primaries selected. In an ideal situation then the three sets of SRFs obtained which each produce a match of the derived CMFs to the original CMFs, should also produce a match with each other and represent the SRFs of the HVS. The same procedure was also applied to the Stiles & Burch 10° SMFs to obtain a 10° version of the HVS SRFs. This article outlines the structure of the mathematical tool evolved and the design of the spreadsheet used to derive and build the various relationships, together with the reasoning for each of the steps in the process. The resulting tool is then used with processed forms of the CMFs of the historic researchers, to show that, within the limits of the experimental errors of the original works, the resulting derived CMFs compare favorably with those originally established by experiment, and furthermore, the three associated individual sets of SRFs match, providing strong evidence that they do indeed represent the SRFs of the human vision system.     

Generic Pareto local search metaheuristic for optimization of targeted offers in a bi-objective direct marketing campaign

Cross-selling campaigns seek to offer the right products to the set of customers with the goal of maximizing expected profit, while, at the same time, respecting the purchasing constraints set by investors. In this context, a bi-objective version of this NP-Hard problem is approached in this paper, aiming at maximizing both the promotion campaign total profit and the risk-adjusted return, which is estimated with the reward-to-variability ratio known as Sharpe ratio. Given the combinatorial nature of the problem and the large volume of data, heuristic methods are the most common used techniques. A Greedy Randomized Neighborhood Structure is also designed, including the characteristics of a neighborhood exploration strategy together with a Greedy Randomized Constructive technique, which is embedded in a multi-objective local search metaheuristic. The latter combines the power of neighborhood exploration by using a Pareto Local Search with Variable Neighborhood Search. Sets of non-dominated solutions obtained by the proposed method are described and analyzed for a number of problem instances.     

Sharpe-ratio pricing and hedging of contingent claims in incomplete markets by convex programming

We analyze the problem of pricing and hedging contingent claims in a financial market described by a multi-period, discrete-time, finite-state scenario tree using an arbitrage-adjusted Sharpe-ratio criterion. We show that the writer’s and buyer’s pricing problems are formulated as conic convex optimization problems which allow to pass to dual problems over martingale measures and yield tighter pricing intervals compared to the interval induced by the usual no-arbitrage price bounds. An extension allowing proportional transaction costs is also given. Numerical experiments using S&P 500 options are given to demonstrate the practical applicability of the pricing scheme.     

Arbitrage pricing theory-based Gaussian temporal factor analysis for adaptive portfolio management

Ever since the inception of Markowitz's modern portfolio theory, static portfolio optimization techniques were gradually phased out by dynamic portfolio management due to the growth of popularity in automated trading. In view of the intensive computational needs, it is common to use machine learning approaches on Sharpe ratio maximization for implementing dynamic portfolio optimization. In the literature, return-based approaches which directly used security prices or returns to control portfolio weights were often used. Inspired by the arbitrage pricing theory (APT), some other efforts concentrate on indirect modelling using hidden factors. On the other hand, with regard to the proper risk measure in the Sharpe ratio, downside risk was considered a better substitute for variance. In this paper, we investigate how the Gaussian temporal factor analysis (TFA) technique can be used for portfolio optimization. Since TFA is based on the classical APT model and has the benefit of removing rotation indeterminacy via temporal modelling, using TFA for portfolio management allows portfolio weights to be indirectly controlled by several hidden factors. Moreover, we extend the approach to some other variants tailored for investors according to their investment objectives and degree of risk tolerance.