Disease surveillance and data collection issues in epidemic modelling

This paper is founded on a tutorial session given to the School on Modern Statistical Methods in Medical Research which was held at the International Centre for Theoretical Physics, Trieste in September 1999. We review the aims, scope and purposes of infectious disease surveillance including determining transmission information to underpin model structure and parameterization in epidemic modelling. The practical problems inherent in collecting surveillance data are illustrated by a study of HIV/AIDS in Cambodia. We also review the basic elements of mathematical models developed to represent the transmission dynamics of infectious diseases, and discuss reasons for the gap between mathematical epidemic models and available data.     

Polymerisation of methyl methacrylate in a pilot-scale tubular reactor: modelling and experimental studies

A pilot-scale tubular reactor fitted with in-line static mixers is experimentally and theoretically evaluated for the polymerisation of methyl methacrylate (MMA). A non-isothermal and non-adiabatic axially dispersed plug-flow model is used to describe the flow characteristics of the reactor. The model is applied to the polymerisation of a concentrated MMA solution (up to 72% (v/v)). Key model parameters were attained through independent bench and pilot-scale experiments. Measured monomer conversions and polymer molecular weight were accurately predicted by model simulation. The presence of static mixers is shown to give near-ideal plug-flow operation for the experimental conditions of this study. Furthermore, an approximately four-fold increase in overall heat transfer coefficient is indicated due to the radial mixing incited by the mixers. Studies also demonstrated the importance of inhibitor kinetics on the dynamic and steady-state performance of the reactor.     

Cervical mucus symptom and daily fecundability: first results from a new database

With the collaboration of Italian centres providing services on natural family planning, a prospective study collected data on 2755 menstrual cycles of 193 women. A database was constructed using information on the daily characteristics of cervical mucus and episodes of intercourse. Taking the day of peak mucus as a conventional marker of ovulation, the database identified the length (12 days) and location of a 'window' of potential fertility, the highest level of conception probability being confined to the central five to six days. Univariate analysis provided evidence of the impact on fecundability of the woman's age and the basic infertile pattern of a cycle. Several analytical approaches highlighted the relationship between daily mucus characteristics and levels of fecundability     

Experimental and modelling studies of the catalytic combustion of methane

Ceramic honeycomb monoliths with a noble metal-alumina based washcoat were used as burners for the combustion of very lean methane-air mixtures below the conventional lower flammability limit without the emission of CO, NO_x, or unburned fuel gas. Measurements and modelling in the steady state proved that the near zero emissions could have been equally due to gas phase combustion than to catalytic combustion for the long monoliths. However, only catalytic oxidation reactions could account for the complete and clean combustion observed for the shortest burners, indicating that even in the longest monoliths, the combustion had been catalytic. Thus the onset of gas phase combustion was inhibited by catalytic combustion. This phenomenon was investigated using numerical modelling and experimental studies on a catalytic stagnation point flow reactor, with a polycrystalline Pt foil as the catalyst. These studies showed the extent of the phenomenon of inhibition of gas phase ignition and how catalytic combustion is an extremely stable and clean process.     

Analysis of uncertainty in health care cost-effectiveness studies: an introduction to statistical issues and methods

Cost-effectiveness analysis is now an integral part of health technology assessment and addresses the question of whether a new treatment or other health care program offers good value for money. In this paper we introduce the basic framework for decision making with cost-effectiveness data and then review recent developments in statistical methods for analysis of uncertainty when cost-effectiveness estimates are based on observed data from a clinical trial. Although much research has focused on methods for calculating confidence intervals for cost-effectiveness ratios using bootstrapping or Fieller's method, these calculations can be problematic with a ratio-based statistic where numerator and/or denominator can be zero. We advocate plotting the joint density of cost and effect differences, together with cumulative density plots known as cost-effectiveness acceptability curves (CEACs) to summarize the overall value-for-money of interventions. We also outline the net-benefit formulation of the cost-effectiveness problem and show that it has particular advantages over the standard incremental cost-effectiveness ratio formulation.     

NMR and molecular modelling studies on elastase inhibitor-peptides for wound management

Proteases play an important and critical role in the physiological process of wound repair. However, excessive and unregulated release of proteolytic enzymes (e.g., elastase) mediates abnormal degradation of healthy tissues, which leads to inflammatory disorders such as chronic wounds. Thus, it is of therapeutic interest to develop novel synthetic inhibitor-peptides of elastase, which can restore the balance between the free enzyme and the endogenous inhibitors in chronic wounds. In previous works, we have reported two different drug delivery systems to release novel elastase inhibitors to the wound site. In both systems synthetic peptides (KRCCPDTCGIKCL-Pep4 and KRMMPDTMGIKML-Pep4M) based on the primary structure of the endogenous elastase inhibitor, secretory leucocyte protease inhibitor, were used as active material. Phosphorylation of the reported peptides prompts significant structural differences, which reflects in distinct inhibitory capacity towards elastase. These structural modifications were prompted by electrostatic interactions and hydrogen bonds established from the peptide phosphoresidue. The current study was also extended to another synthetic peptide (WCTASVPPQCY-PepBBI) that is based on the reactive loop of another elastase inhibitor, the Bowmen-Birk inhibitor. PepBBI, phosphorylated and non-phosphorylated, displays similar behaviour to Pep4 and Pep4M. The structural modifications reported herein were evaluated by two-dimensional nuclear magnetic resonance and molecular modelling approaches.     

Current efficiency in the Hall–He´roult process for aluminium electrolysis: experimental and modelling studies

Results are presented from a laboratory study of the influence of electrolyte composition, temperature, cathodic current density and interpolar distance on the current efficiency with respect to aluminium (CE). The current efficiency was determined from the weight gain of metal, in a laboratory cell designed to attain good and reproducible convective conditions, and with a flat cathode surface which ensures uniform cathodic current distribution. The cell is believed to more closely represent conditions in industrial cells than traditional small-scale cells, and is a good basis for an experimental study of the influence of isolated variable parameters on the current efficiency with respect to aluminium. The results show a nonlinear decrease of CE with increasing electrolyte temperature, a close to linear decrease of CE with increasing NaF/AlF3 ratio in the electrolyte, a slight increase of CE with increasing electrolyte CaF2 concentration, and no influence of electrolyte Al2O3 concentration on CE. A current efficiency model, based on previous work and theory of electrochemistry and mass transport, shows good agreement with the obtained results.     

Methodologic issues in the design and analysis of epidemiologic studies of pregnancy outcome

Using epidemiology to elucidate the causes of adverse pregnancy outcomes offers unique opportunities and poses distinctive challenges. The context of pregnancy includes contraception and planning, medical interventions altering the natural history, and the tendency for selective participation in demanding research protocols. Several key pervasive issues are considered in detail: 1) the close temporal proximity of determinants and outcomes, which makes separation of causes and effects difficult and introduces the real possibility of reverse causality; 2) non-random allocation of exposure, often done consciously in response to concerns about having a healthy pregnancy or to the health of the pregnancy itself, making confounding a major concern; 3) heterogeneity of pregnancy outcomes, with endpoints such as pregnancy loss and preterm birth arising through diverse pathways that are not easily identified and if grouped, could diminish the magnitude of observed associations; and 4) racial and ethnic disparities, which pose a public health challenge in the USA and offer a potentially important opportunity for identifying preventable causes of adverse pregnancy outcome. Sophisticated biological and statistical methods are needed to advance epidemiologic research in this area.     

Application of power addition as modelling technique for flow processes: Two case studies

In many of the continuum processes typically found in chemical engineering, the functional dependency of the dependent variable is only known for large and small values of the independent variable. Exact solutions in the transitional regime are often obscure for various reasons (e.g. narrow band within which the transition from one regime to the other occurs, inadequate knowledge of the physics in this area, etc.). An established method for the matching of limiting solutions is reviewed and subsequently applied. The method regards the known solutions as asymptotes and proposes addition to a power of such asymptotes. It yields a single, adjustable correlating equation that is applicable over the entire domain. This procedure circumvents the introduction of ad hoc curve fitting measures for the different regions and subsequent, unwanted discontinuities in piece-wise fitted correlative equations for the dependent variables. Experimental data of two diverse processes, namely flow in a straight-through diaphragm valve and the fluidisation of a packed bed, are analysed as case studies. Empirical results are investigated for possible asymptotic bounds whereafter power addition is applied to the functional dependencies. The outcome is compared to those of the empirical models and the results discussed. The procedure is revealed to be highly useful in the summarising and interpretation of experimental data in an elegant and simplistic manner. It may also, in general, aid the setup of experimental apparatus for investigation of continuum processes.     

燃煤锅炉烟气中SO3生成的化学动力学模型和实验研究

燃煤锅炉烟气中SO₃能对锅炉设备、大气环境造成包括低温腐蚀、粘污和蓝烟等一系列的危害。因而,对烟气中SO₃主要影响因素及其影响规律的研究对于预测和控制烟气中SO₃浓度以满足不断增长的节能减排标准有重要意义。基于文献中的C/H/O/N/S化学动力学模型的优化、整合建立了化学动力学模型,对烟气中SO₃主要影响因素及其影响规律进行计算研究。还基于自主设计搭建了全混流反应器测量装置,对上述计算工况中的SO₃浓度进行测量。研究发现,烟气中SO₃浓度主要受SO₂、O₂和H₂O的浓度,以及温度和反应停留时间等影响。SO₃浓度受烟气中CO、NO的影响也较为显著,但是受CO₂的影响不大。另外,随着反应停留时间的增加,烟气中SO₃浓度先后经历了3个不同阶段：急剧增加,增长趋势逐渐减缓和逐渐减少。     

X-ray and molecular modelling studies of 4-[N-alkylamino]azobenzene dyes

4-[N,N-Bisalkyl]amino-2′-chloro-4′-nitroazobenzenes were recrystallized from acetone in either triclinic or monoclinic cells with the space group P-1 or P2₁/c. The asymmetric unit cell of dyes having at least one N-cyanoethyl group contained two molecules that were symmetrically unequivalent. The aromatic rings in the azobenzene skeleton were essentially planar with respect to the plane of the azo group, although the C6–C1–N1–N2 torsion angle was 13.2° when the N,N-dicyanoethyl group was employed. X-ray studies were used as a basis for assessing the utility of nonlocal DFT calculations in predicting the equilibrium molecular geometry and solvatochromic properties of the compounds using MM3/ZINDO-S and the COSMO Solvation Model. Although B3LYP and PBE energy functionals were comparable in predicting bond lengths, PBE was slightly better than B3LYP in predicting torsion angles. Furthermore, the dipolarity/polarizability index (π¹) was the preferred solvent parameter for predicting the effects of solvents on λ_max.     

Competitive removal of malachite green and Rhodamine-B using Amberlite-XAD-4 impregnated with Aliquat 336: experimental and modelling studies

ABSTRACT

Use of solvent impregnated resin in the separation has emerged as a new area of interest. It is a hybrid process with the characteristics of adsorption, ion-exchange and extraction. Here, Aliquat 336 impregnated Amberlite XAD-4 resin was used to remove Rhodamine-B and malachite green individually and from their mixtures in the aqueous solution. The performance of prepared resin was studied in batch mode to analyze the effect of adsorbent dosage, pH, concentration of dye solution, salt concentration, time, and temperature. Characterization (using FE-SEM, EDS, FTIR, and point of zero charge), regeneration, and cost analysis of the adsorbent were also done.     

Experimental studies and molecular modelling of the stress-optical and stress-strain behaviour of poly(ethylene terephthalate). Part III: Measurement and quantitative modelling of birefringence-strain, stress-strain and stress-optical properties

Experimental measurements and Monte-Carlo (MC) modelling of the birefringence-strain, stress-strain and stress-optical behaviour of poly(ethylene terephthalate) (PET) are used, together with the analysis of orientation-strain and conformation-strain behaviour reported in Paper I, to give a detailed, quantitative interpretation and characterisation of its deformation-related properties. The difference between the stress-strain and stress-optical behaviour of PET that had been reported previously is confirmed. Except for the stress, the measured values of all the properties studied are in agreement with those calculated using the MC modelling, which suggests that not all of the junctions or the chains in the entangled PET network are elastically active.The results given by Kuhn and Grün theory are compared with those given by the MC modelling. The expected shortcomings of Kuhn and Grün theory are found. However, distinct from the behaviour reported previously for polyethene, the theory can be used to evaluate, semi-empirically, the stress-optical coefficient of PET.     

Molecular modelling of polyphthalamides thermal properties: Comparison between modelling and experimental results

The aim of this study was to investigate new polyphthalamides (PPA) through the use of molecular modelling techniques and comparison with experimental data. The objectives were to provide a computer simulation method that can be used to predict the properties of polyphthalamides with a good reliability with respect to the experimentally synthesized materials. Several PPA with a variable amount of aromatic units derived from condensation with hexamethylene diamine (HMDA) and terephthalic acid (TPA) or isophthalic acid (IPA) were synthesized. These polymers were characterized using thermal analysis, size-exclusion chromatography, NMR and viscosimetry techniques. The same PPA were modelled at the atomistic level and molecular dynamics simulations were run. The glass transition temperature (T_g) of the various materials was used to make comparisons between simulations and experiments. The results were found to be in good agreement and the simulation method can be used to predict thermal properties of this class of polyamides.     

PVC: Packaging issues and regulations

As a result of reports that vinyl chloride monomer migrated at detectable levels into alcoholic beverages stored in poly(vinyl chloride) bottles, FDA proposed to ban the use of rigid PVC for distilled spirits in 1973. A review is presented of FDA's revised proposal for the regulation of PVC food packaging issued in 1986 and some recent developments that have further delayed FDA's issuance of a rule that would lead to the use of PVC in liquor bottles. Despite significant technological improvements in the manufacture of rigid PVC, which has led to drastic reduction of residual vinyl chloride monomer (RVCM) to safe levels, FDA action on PVC has remained stalled. It is concluded that final action by FDA may well depend not on scientific principles, but on the Agency's ability to effectively reconcile the correct scientific, health and legal solutions with the political pressure being exerted by environmentalist groups.     

白钨矿连续酸浸槽内固体颗粒的流动特性实验及模型研究

以停留时间分布（RTD）为评价指标,对硫磷混酸浸出白钨矿的连续浸出槽内固相颗粒流动行为进行实验研究。同时探究了进料流量、搅拌转速、连续浸出槽中物料进出口位置组合对固相颗粒流动行为的影响。实验结果表明：随着进口流量的增大,一开始槽内的返混程度得到了增强,量纲为1化方差变大,但是继续增大进口流量,进口处物料的横向迁移速度加强,使槽内流体流动趋向平推流,导致量纲为1化方差减小;量纲为1化方差随着搅拌转速的增大而增大,但是此时在槽下部区域会逐渐形成循环死区,槽内死区体积分数随之增大;平均停留时间随着物料进出口位置的变化而发生变化,下进下出的进出料位置组合其平均停留时间最大,且最接近理论平均停留时间。最后利用非理想流动模型来表征实验过程中的停留时间分布,模型拟合的停留时间曲线与实验测量的曲线吻合程度良好。     

喷射环流反应器性能与模化

评述国内外近１０年来有关喷射环流反应器性能及其模化研究的现状及进展，分析了研究中存在的薄弱环节，并对今后的工作提出建议和展望。