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We report a case of Schnyder corneal dystrophy (SCD) treated with deep phototherapeutic keratectomy (PTK). A 33-year-old man presented with a 5-year history of blurred vision and corneal haze in both eyes. Slit-lamp examination revealed needle-like subepithelial crystalline depositions and prominent arcus lipoides bilaterally. Similar clinical findings were observed in the patient's father. A diagnosis of SCD was made on the basis of the clinical presentation. PTK was performed using a multizone, multipass, and shoot and check technique with the WaveLight EX500 excimer laser. After 22 months of follow-up, the best-corrected visual acuity had increased from 0.5 to 0.9 in the right eye and from 0.3 to 0.9 in the left eye. SCD is rare but has a unique ocular presentation, which facilitates the diagnosis. PTK can increase patients' visual acuity and eliminate the need for aggressive management through penetrating keratoplasty or deep anterior lamellar keratoplasty.

Airborne transmission of SARS-CoV-2 mostly occurs indoors, and effective mitigation strategies for specific building types are needed. Most guidance provided during the pandemic focused on general strategies that may not be applicable for all buildings. A systematic evaluation of infection risk mitigation strategies for different public and commercial buildings would facilitate their reopening process as well as post-pandemic operation. This study evaluates engineering mitigation strategies for five selected US Department of Energy prototype commercial buildings (i.e., Medium Office, Large Office, Small Hotel, Stand-Alone Retail, and Secondary School). The evaluation applied the multizone airflow and contaminant simulation software, CONTAM, with a newly developed CONTAM-quanta approach for infection risk assessment. The zone-to-zone quanta transmission and quanta fate were analyzed. The effectiveness of mechanical ventilation, and in-duct and in-room air treatment mitigation strategies were evaluated and compared. The efficacy of mitigation strategies was evaluated for full, 75%, 50% and 25% of design occupancy of these buildings under no-mask and mask-wearing conditions. Results suggested that for small spaces, in-duct air treatment would be insufficient for mitigating infection risks and additional in-room treatment devices would be needed. To avoid assessing mitigation strategies by simulating every building configuration, correlations of individual infection risk as a function of building mitigation parameters were developed upon extensive parametric studies. [ABSTRACT FROM AUTHOR]

The paper presents the results of a study of the optical properties of CdS on the basis of the band anticrossing theory (BAC) with the involvement of the wider source data to the analysis results. Depending on the growth conditions, the presence and change in the concentration of oxygen and intrinsic point defects, which determine the composition of the crystals, have been taken into account. Data from studies of the structural features of crystals have also been used. The concept of nonuniform distribution of oxygen isoelectronic centers in the CdS volume due to their predominant segregation in layers of stacking faults (SFs) and also on dislocations has been introduced. To analyze the optical data, the capabilities of the method for constructing band models, which collect extensive and multilateral information about specific samples have been used. A refined model multizone of CdS ⋅ O with SFs, which determines the spectrum of edge emission, has been presented. The nature of the edge emission A2B6 crystals with a small deviation from stoichiometry (CdS type) was explained as a spectrum of bound excitons at oxygen centers in SF layers. The article gives recommendations for the diagnostics of CdS crystals, suitable for creating stable luminescent systems or lasers. [ABSTRACT FROM AUTHOR]

Airborne transmission of SARS-CoV-2 mostly occurs indoors, and effective mitigation strategies for specific building types are needed. Most guidance provided during the pandemic focused on general strategies that may not be applicable for all buildings. A systematic evaluation of infection risk mitigation strategies for different public and commercial buildings would facilitate their reopening process as well as post-pandemic operation. This study evaluates engineering mitigation strategies for five selected US Department of Energy prototype commercial buildings (i.e., Medium Office, Large Office, Small Hotel, Stand-Alone Retail, and Secondary School). The evaluation applied the multizone airflow and contaminant simulation software, CONTAM, with a newly developed CONTAM-quanta approach for infection risk assessment. The zone-to-zone quanta transmission and quanta fate were analyzed. The effectiveness of mechanical ventilation, and in-duct and in-room air treatment mitigation strategies were evaluated and compared. The efficacy of mitigation strategies was evaluated for full, 75%, 50% and 25% of design occupancy of these buildings under no-mask and mask-wearing conditions. Results suggested that for small spaces, in-duct air treatment would be insufficient for mitigating infection risks and additional in-room treatment devices would be needed. To avoid assessing mitigation strategies by simulating every building configuration, correlations of individual infection risk as a function of building mitigation parameters were developed upon extensive parametric studies.

This paper presents results for five uniform and two multizone liners based on data acquired in the NASA Langley Grazing Flow Impedance Tube. Two methods, Prony and CHE, are used to educe the impedance spectra for each of these liners for many test conditions. The Prony method is efficient and generally provides accurate results for uniform liners, but is not well suited for multizone liners. The CHE method supports assessment of both uniform and multizone liners, but is much more computationally expensive. The results from these liners demonstrate the efficacy of both eduction methods, but also clearly demonstrate that sufficient attenuation is required to support accurate impedance eduction. For the liners considered in this study, the data indicate approximately 3 dB attenuation is needed for each zone of a multizone liner in order to ensure quality impedance eduction results. This study was conducted in response to two acoustic liner research challenges in support of a collaboration of multiple national laboratories under the International Forum for Aviation Research. [ABSTRACT FROM AUTHOR]

The very intensive calculations necessary to define a performance map requiring evaluation of over a hundred individual operating points can be efficiently conducted with accelerated multizone for engine cycle simulation, leading to a definition of regions of acceptable and optimum homogeneous charge compression ignition operation. Accelerated multizone for engine cycle simulation has the virtue of enabling accurate evaluation of many operating conditions based on thermal stratification data from a single fluid mechanics run at motored conditions. This is possible because thermal stratification is more sensitive to engine geometry than to operating conditions. In this article, accuracy of accelerated multizone for engine cycle simulation is demonstrated by comparison with experimental data for iso-octane homogeneous charge compression ignition operation over a broad range of lean equivalence ratios (0.14–0.28). The validated accelerated multizone for engine cycle simulation model is then applied to generating a performance map for an engine controlled by appropriately adjusting equivalence ratio and internal exhaust gas recirculation. Regions of acceptable and optimum combustion are identified. It is finally demonstrated that while indicated mean effective pressure remains low for optimum homogeneous charge compression ignition operation (1–4 bar), this is sufficient for a large fraction of typical driving in light-duty vehicles. Much driving including idle can therefore be done in homogeneous charge compression ignition mode at high efficiency and low (essentially zero) NO x and particulate matter emissions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Hybrid ventilation is an effective approach to reduce cooling energy consumption by combining natural and mechanical ventilation. Previous studies of full-scale whole-building measurements of high-rise hybrid ventilation are quite limited due to the complexities of buildings and variable ambient conditions. As a result, validated and accurate whole-building simulations of hybrid ventilation often cannot be found in the literature. This paper reports a series of full-scale measurements of hybrid ventilation in a 17-storey high-rise building and associated whole-building simulations by 15-zone detailed and a 5-zone simplified multizone models. The paper is one of the first studies of using multizone models and real-world full-scale data and sharing key operational and performance experience and case studies of high-rise hybrid ventilation. Both the test data and the validated simulation models can be used for the comparison and validation of simulation models. The 5-zone simplified model developed from this study was able to model such a complex high-rise building by only a few zones, making possible the on-line model predictive control of a high-rise building. This was illustrated in this paper by an example of optimizing the uniformity of the hybrid ventilation on different floors by modifying inlet areas. [ABSTRACT FROM AUTHOR]

This paper reports the development of methods for calculating a ventilation performance metric that is a measure of the airflow pattern in a room or zone of a multi-zone ventilation system. Temporal mixing theory is used as the basis for these methods. The methods are applicable to all ventilated systems that can be modeled as a set of interconnected chambers. Relations between the ventilation performance metric defined in this paper and those defined previously are derived. The theoretical results of this paper are consistent with published experimental findings. They also illustrate that the conclusions in some experimental studies about the airflow patterns in working buildings may be incorrect. Re-analysis of previously published detail illustrates how common features of mechanically ventilated buildings, such as recirculation of return air and multiple chambers, confound information about airflow patterns in tracer gas data. The calculation methods developed in this paper can be used to undo this confounding.

Criteria for the localization of gold deposits within the Ayan–Yuryakh anticlinorium in Magadan oblast have been developed using processed satellite imagery data and the analysis of geological and geophysical materials. The structural elements are linear, arc, ring, and concentric lineaments of the first (11–35 km), second (5–10 km), and third (less than 5 km) rank. The ring structures of the second and third rank form linear chains confined to the hidden linear structures of the northwest and north-northeast strike. Gold deposits occur in the central or peripheral parts of the ring structures of the second rank at the intersections of the latter with regional sublatitudinal faults. The area of ​​the Pavlik deposit has a block structure, due to the dominant faults of the northwestern strike, complicated by faults of the northeastern and meridional strike, as well as arc structural elements. When predicting prospective ore areas, the localization patterns of gold ore, determined by the results of gravimetric and gamma surveys, should be taken into account. [ABSTRACT FROM AUTHOR]

This study proposes a two‐stage stochastic optimisation model for jointly wind turbine (WT) allocation and network reconfiguration (NR) so as to increase the resiliency of distribution system in face of natural disasters. In this regard, in the first level, a possibilistic‐scenario method is proposed to select the line outage scenarios. The proposed model is capable with distribution systems and considers different failure probabilities for system components subject to the intensity of natural disaster in its associated zone. After selecting the line outage scenarios, in the second level, a multi‐stage optimisation framework is proposed for jointly NR and WT allocation in a multi‐zone and multi‐fault system, considering the uncertainty of system load and wind power generation. This strategy makes an interconnection between NR and islanded WTs to increase the resiliency of system and decreases the load shedding. Different economic objectives including, costs of load shedding and power generation are considered in the model. In addition, hardening budget is taken into consideration for the transmission lines, which is minimised during the optimisation process. The simulation results demonstrate the capability and necessity of proposed resiliency‐oriented method and prove the importance of hardening budgets. [ABSTRACT FROM AUTHOR]

The paper investigates the effects on building indoor air quality (IAQ) resulting from the choice of different design ventilation rates. A reference residential building was analysed by means of the multizone modelling software CONTAM, by monitoring the concentration of two pollutants: occupant-generated carbon dioxide (CO2) and total volatile organic compounds (TVOC) from indoor sources. A demand-controlled ventilation strategy based on building occupancy was implemented and users' presence schedules were defined. Specifically, the evolution of indoor pollutant concentrations was investigated when the design ventilation rates, recommended by two IAQ-related standards (the Italian UNI 10339 and the European EN 15251), were implemented through a mechanical ventilation system. Different results regarding the IAQ level were achieved accordingly to the dissimilar ventilation rates. After a statistical analysis on the distributions of CO2 and TVOC concentrations, EN 15251 outcomes showed overall better results of the analysed statistical metrics, i.e. prevalence, sensitivity and accuracy. Indeed, the EN 15251 design airflows led to indoor conditions that were more often classified either in the correct air quality class or in a higher class. Finally, a better alignment between the national and European IAQ standards is recommended, especially in terms of airflows, air quality classes and pollutant limit values. [ABSTRACT FROM AUTHOR]

A study to assess how the fidelity of wind pressure inputs and indoor model complexity affect the predicted air change rate for a study building is presented. The purpose of the work is to support the development of a combined indoor-outdoor hazard prediction tool, which links the CONTAM multizone building simulation tool with outdoor dispersion models. The study building, representing a large office block of a simple rectangular geometry under natural ventilation, was based on a real building used in the Joint Urban 2003 experiment. A total of 1600 indoor model flow simulations were made, driven by 100 meteorological conditions which provided a wide range of building surface pressures. These pressures were applied at four levels of resolution to four different building configurations with varying numbers of internal zones and indoor and outdoor flow paths. Analysis of the results suggests that surface pressures and flow paths across the envelope should be specified at a resolution consistent with the dimensions of the smallest volume of interest, to ensure that appropriate outputs are obtained. [ABSTRACT FROM AUTHOR]

The world has faced tremendous challenges during the COVID-19 pandemic since 2020, and effective clean air strategies that mitigate infectious risks indoors have become more essential. In this study, a novel approach based on the Wells-Riley model applied to a multizone building was proposed to simulate exposure to infectious doses in terms of " quanta ". This modeling approach quantifies the relative benefits of different risk mitigation strategies so that their effectiveness could be compared. A case study for the US Department of Energy large office prototype building was conducted to illustrate the approach. The infectious risk propagation from the infection source throughout the building was evaluated. Different mitigation strategies were implemented, including increasing outdoor air ventilation rates and adding air-cleaning devices such as Minimum Efficiency Reporting Value (MERV) filters and portable air cleaners (PACs) with HEPA filters in-room/in-duct germicidal ultraviolet (GUV) lights, layering with wearing masks. Results showed that to keep the risk of the infection propagating low the best strategy without universal masking was the operation of in-room GUV or a large industrial-sized PAC; whereas with masking all strategies were acceptable. This study contributes to a better understanding of the airborne transmission risks in multizone, mechanically ventilated buildings and how to reduce infection risk from a public health perspective of different mitigation strategies. • A new method was developed for simulating SARS-CoV-2 airborne quanta transmission in multizone buildings using CONTAM. • Whole-building exposure risk was modeled for a large office building , considering dynamic zone pressures and ambient conditions. • System level mitigation was more effective to reduce overall building risk when the location of the infected individual was unknown. • In-room mitigation reduced local transmission risk more effectively when the individual was in the same zone. [ABSTRACT FROM AUTHOR]

Highlights: [•] Real-time zero-dimensional three-zone diagnostic combustion model. [•] Capable of evaluating in-cylinder temperatures, HRR and NOx in DI diesel engines. [•] Able to be integrated in the engine ECU for control applications. [•] Able to be integrated in the test bed acquisition software for calibration tasks. [•] Tested under both steady state and fast transient conditions. [Copyright &y& Elsevier]

The ingress of exterior contaminants into buildings is often assessed by treating the building interior as a single well-mixed space. Multizone modelling provides an alternative way of representing buildings that can estimate concentration time series in different internal locations. A state-space approach is adopted to represent the concentration dynamics within multizone buildings. Analysis based on this approach is used to demonstrate that the exposure in every interior location is limited to the exterior exposure in the absence of removal mechanisms. Estimates are also developed for the short term maximum concentration and exposure in a multizone building in response to a step-change in concentration. These have considerable potential for practical use. The analytical development is demonstrated using a simple two-zone building with an inner zone and a range of existing multizone models of residential buildings. Quantitative measures are provided of the standard deviation of concentration and exposure within a range of residential multizone buildings. Ratios of the maximum short term concentrations and exposures to single zone building estimates are also provided for the same buildings. [ABSTRACT FROM AUTHOR]

Abstract: A simple mathematical model of stack ventilation flows in multi-compartment buildings is developed with a view to providing an intuitive understanding of the physical processes governing the movement of air and heat through naturally ventilated buildings. Rules of thumb for preliminary design can be ascertained from a qualitative examination of the governing equations of flow, which elucidate the relationships between ‘core’ variables – flow rates, air temperatures, heat inputs and building geometry. The model is applied to an example three-storey office building with an inlet plenum and atrium. An examination of the governing equations of flow is used to predict the behaviour of steady flows and to provide a number of preliminary design suggestions. It is shown that control of ventilation flows must be shared between all ventilation openings within the building in order to minimise the disparity in flow rates between storeys, and ensure adequate fresh air supply rates for all occupants. [Copyright &y& Elsevier]

A multizone droplet burn model is developed to account for changes in the thermal and transport properties as a function of droplet radius. The formulation is semi-analytical – allowing for accurate and computationally efficient estimates of flame structure and burn rates. Zonal thermal and transport properties are computed using the Cantera software, pre-tabulated for rapid evaluation during run-time. Model predictions are compared to experimental measurements of burningn-heptane, ethanol and methanol droplets. An adaptive zone refinement algorithm is developed that minimizes the number of zones required to provide accurate estimates of burn time without excess zones. A sensitivity study of burn rate and flame stand-off with far-field oxygen concentration is conducted with comparisons to experimental data. Overall agreement to data is encouraging with errors typically less than 20% for predictions of burn rates, stand-off ratio and flame temperature for the fuels considered. [ABSTRACT FROM AUTHOR]

Mit hygrothermischer Gebäudesimulation lässt sich der Feuchte- und Wärmetransport in einem Gebäude und über dessen Bauteile detailliert berechnen. Der natürliche oder mechanisch angetriebene Luftwechsel mit dem Außenklima sowie der Luftwechsel zwischen definierten Zonen innerhalb des Gebäudes tragen erheblich zu einem energetisch sinnvollen und behaglichen Raumklima bei. Es ist bei der Erstellung des Gebäudemodells möglich, den Luftwechsel je Zeitschritt vorzugeben. Jedoch ist dieser in Realität vom vorherrschenden Raumklima abhängig. Wird die hygrothermische Gebäudesimulation mit einem Mehrzonen-Gebäudedurchströmungsmodell gekoppelt, so werden das Innenklima und der Luftwechsel je Zeitschritt, gegenseitig beeinflussend, simuliert. Dieser Beitrag erzielt einen Einblick in das Berechnungsverfahren des Durchströmungsmodells und dessen Kopplung mit dem hygrothermischen Gebäudemodell. Ferner ist ein Beispiel der erweiterten Simulation mit Infiltration und interzonalem Luftaustausch, auch im Vergleich zum fest definierten eingegeben Luftwechsel, enthalten. Hygrothermal building simulation coupled with multizone air flow model. With hygrothermal whole building software it is possible to calculate heat and moisture transport within a building and its components. The natural or mechanical driven air exchange between indoor and outdoor climate as well as airflow between defined building zones are significant contributors to an energetically and comfortable indoor environment. At the design of the building model it is possible to set the ventilation per time step. However, the ventilation depends on the indoor climate. The hygrothermal whole building software coupled with a multizone building airflow model can simulate the indoor climate and the natural and interzonal air exchange influencing each other. This paper gives an insight into the airflow model and its implementation and shows some results of an example simulation. [ABSTRACT FROM AUTHOR]

The prohibitive number of speakers required for the reproduction of isolated soundfields is the major limitation preventing solution deployment. This paper addresses the provision of personal soundfields (zones) to multiple listeners using a limited number of speakers with an underlying assumption of fixed virtual sources. For such multizone systems, optimization of speaker positions and weightings is important to reduce the number of active speakers. Typically, single stage optimization is performed, but in this paper a new two-stage pressure matching optimization is proposed for wideband sound sources. In the first stage, the least-absolute shrinkage and selection operator (Lasso) is used to select the speakers' positions for all sources and frequency bands. A second stage then optimizes reproduction using all selected speakers on the basis of a regularized least-squares (LS) algorithm. The performance of the new, two-stage approach is investigated for different reproduction angles, frequency range and variable total speaker weight powers. The results demonstrate that using two-stage Lasso-LS optimization can give up to 69 dB improvement in the mean squared error (MSE) over a single-stage LS in the reproduction of two isolated audio signals within control zones using e.g. 84 speakers. [ABSTRACT FROM PUBLISHER]

Air leakage through the building envelope into the building interiors has a considerable impact on the energy loads and consequently energy demand and energy costs of buildings. This phenomenon known as infiltration happens through various openings and venues in the building envelope varying from large openings such as doors and windows to minute cracks and crevices. In addition to impacting building energy loads, infiltration impacts indoor air quality and can result in moisture accumulation problems in the building envelope. A generalized review of infiltration that includes evaluation techniques and models, quantification, and interaction with other heat transfer phenomena is presented in this article. [ABSTRACT FROM PUBLISHER]

Abstract: Experimental measurements from a converted indirect injection diesel Kubota D905 engine fueled with a simulated biomass derived gas are compared with simulation results using a multizone homogeneous charge compression ignition (HCCI) engine model. Two different fuel blends were tested and each consisted of varying amounts of CH4, CO2, N2, H2, and CO to mimic the gaseous constituents of producer gas. The multizone model was originally developed as a 32 bit serial application for use with primary reference fuels (PRFs). However, for the purpose of this study, the model has been parallelized using Message Passing Interface (MPI) for Fortran and is executed in a 64 bit environment to further reduce computational time. Once calibration was complete, the numerical model showed good pressure trace matching with the experimental data across both fuel mixture compositions and various equivalence ratios. Correspondingly, heat release rate (HRR) curves showed good matching as well. Calibration settings from one engine operating point for a given fuel mixture were readily transferable to other operating points and the second fuel mixture. However, there were some discrepancies in predicting pressure traces when operating the model near the misfire limit of the engine due to cyclic variability, which exceeds the limitations of the model. [Copyright &y& Elsevier]

Abstract: This work explores analytic solutions to contaminant transport in multizone systems as a means of solving concentration dynamics more rapidly and providing insight into system behaviour. A general formulation is developed that is consistent with state-space theory. This is used to provide general and specific solutions for the concentration time series. In particular, an analytical expression is presented for the case of constant system parameters and constant input conditions using the eigenvalues and eigenvectors for the case of a diagonalisable state matrix for the multizone system. A method for using this expression to solve concentrations over a series of varying building and input states is developed, with potential for use as a rapid means of calculating concentrations at any time. In principle, this method could be used as a complementary method for solving concentration dynamics within multizone software. Analytical expressions for cumulative exposure for the same case are also presented. The characteristic behaviour of the solutions and their dependence on the eigenvalues and eigenvectors of the state matrix are explored for the steady state case and the decay solution. In particular, the behaviour in the late decay phase is shown to be characterised by a single decay rate, given by the smallest magnitude eigenvalue, and a fixed concentration ratio, given by the associated eigenvector. The independence of the concentration ratio in this phase to the initial conditions is also demonstrated. Two example cases are used to illustrate these and additional features. [Copyright &y& Elsevier]

This paper presented an overview of the tools used to predict ventilation performance in buildings. The tools reviewed were analytical models, empirical models, small-scale experimental models, full-scale experimental models, multizone network models, zonal models, and Computational Fluid Dynamics (CFD) models. This review found that the analytical and empirical models had made minimal contributions to the research literature in the past year. The small- and full-scale experimental models were mainly used to generate data to validate numerical models. The multizone models were improving, and they were the main tool for predicting ventilation performance in an entire building. The zonal models had limited applications and could be replaced by the coarse-grid fluid dynamics models. The CFD models were most popular and contributed to 70 percent of the literature found in this review. Considerable efforts were still made to seek more reliable and accurate models. It has been a trend to improve their performance by coupling CFD with other building simulation models. The applications of CFD models were mainly for studying indoor air quality, natural ventilation, and stratified ventilation as they were difficult to be predicted by other models. [Copyright &y& Elsevier]

Multizone network models employ several assumptions, such as uniform temperature and pressure and quiescent air inside a zone, which may lead to inaccurate results in flow calculations. These assumptions can be eliminated in the zones, where the assumptions are inappropriate, by coupling a multizone network program with a computational fluid dynamics (CFD) program. Through theoretical analysis, this paper proves that the solution of air distribution by using the coupled program exists and is unique. Three possible coupling methods have been discussed in the paper. The best method is pressure–pressure coupling that exchanges pressure between the multizone and CFD because it is most stable and can always lead to a converged solution. Numerical tests were further performed to verify the theory and it demonstrated that the coupled program is able to effectively improve the accuracy of the results. Practical Implications The results of this paper provide a theoretical basis for improving the accuracy for modeling airflow and contaminant distributions in buildings. The coupled multizone and computational fluid dynamics can give high fidelity results, so field measurements may not be needed in the future. Designers of indoor environment in the future can use such a tool to evaluate different alternatives in design and identify the best solution for a building that can provide a healthy indoor environment. [ABSTRACT FROM AUTHOR]

We compare model predictions to measurements of SF6 and environmental tobacco smoke particle concentrations in a three-room chamber experiment. To make predictions of multi-room aerosol transport and fate, we linked a multizone airflow model (COMIS) with an indoor aerosol dynamics model (MIAQ4). The linked models provide improved simulation capabilities for predicting aerosol concentrations and exposures in buildings. In this application, we found that the multizone air flow model was vital for predicting the inter-room airflows due to temperature differences between the rooms and when air-sampling pumps were operating during the experiment. Model predictions agree well with measurements, as shown by several comparison metrics. However, predictions of airborne ETS concentrations are slightly lower than measurements. This is mostly attributable to under-stating the source release amount, which we specified independently from literature estimates. Model predictions of ETS particle-size distributions agree with measurements; size bins with the peak concentrations are slightly over-predicted initially, but agree thereafter. [Copyright &y& Elsevier]

A well-mixed model has been formulated to study the steady-state high pressure free-radical homo- and copolymerization of ethylene and vinyl acetate in an industrial multi-feed multi-zone autoclave reactor system. Using a realistic set of kinetic mechanisms and coefficients, the multi-zone system is modeled as a simple set of well-mixed tank reactors in series. Results from this representation are compared to experimental data in order to estimate apparent initiator efficiencies in each zone. The model is used to calculate monomer conversion and initiator consumption rate, number and weight average molecular weights, and short and long chain branching frequencies at the exit point of each zone and the whole reactor. The effects of zone temperature, feed temperature, and initiator decomposition kinetics on the steady-state reactor performance and polymer properties are considered and simulation results are compared with the industrial data. While estimated initiator efficiencies provide a clear indication of imperfect mixing in the system, the model representation is still able to provide a reasonable estimate of polymer properties. [ABSTRACT FROM AUTHOR]

The multizone approach to steady-state airflow problems models a building as a network of discrete mass flow paths. A nodal formulation of the problem writes the governing equations in terms of the unknown pressures at the points where the flow paths connect. This paper proves conditions under which the nodal equations yield symmetric positive-definite matrices, guaranteeing a unique solution to the flow network. It also establishes relaxed conditions under which a nodal airflow system yields asymmetric matrices with positive eigenvalues, guaranteeing at least one solution.Properly exploiting the system properties greatly reduces the cost of numerical solution. Thus, multizone airflow programs such as CONTAM and COMIS depend on symmetric positive-definite systems. However, the background literature neglects or simplifies the underlying assumptions, does not assert existence and uniqueness, and even contains factual errors. This paper corrects those errors, states the implicit assumptions made in the programs, and discusses implications for modelers and programmers. [Copyright &y& Elsevier]

Engineering controls can be used to reduce the spread of airborne infectious disease, particularly tuberculosis (TB), in high-risk settings. This article evaluates published data on the efficacy of upper-room air ultraviolet germicidal irradiation (UVGI). A three-zone representation of a TB patient room equipped with a germicidal UV lamp is developed. The lamp irradiates the upper-room zone and inactivates airborne mycobacteria; the unirradiated lower-room zone also contains a near-field zone surrounding the TB patient. Infectious particles are generated in the near-field zone and transported throughout the room by air flow between zones. Each zone is independently well-mixed; the whole room, however, is not well-mixed. The three-zone model is applied to a previously published study of UVGI against airborne mycobacteria in a test room. Based on the estimated slopes of the semi-log concentration decay curves for viable mycobacteria, and on the assumption that the test room was essentially well-mixed, the published study reported that UVGI provided 10 to 25 equivalent air changes per hour. However, when the same decay curve slopes are interpreted in the context of the three-zone model, UVGI is seen to be far less effective in reducing exposure intensity near the TB patient. Near-field exposure intensity is relevant because health care workers are usually in close proximity to the TB patients they attend. In general, the interpretation of concentration decay data depends on the specific model of room air mixing that is assumed appropriate. It is recommended that tests of the efficacy of UVGI and other control devices against airborne microorganisms be based on steady-state concentration measurements rather than concentration decay measurements, because the former measurements do not require inferences based on a particular model. [ABSTRACT FROM AUTHOR]

A simplified simulation module has been developed to calculate the thermal performances of multizone buildings, using modal analysis. This technique reduces the computation time and therefore allows architects to perform accurate simulations using a low cost micro computer (type AT for instance). The thermal calculations are based upon a data structure in which the building is decomposed into elements (thermal zones, walls, windows, materials, …). Each building element has been modeled as a computer object. Components of higher complexity are linked to simple components via pointers. Thus, if a component is modified, the modification is automatically transmitted through the whole structure. This environment is particularly adapted to connect the thermal calculation module (COMFIE) to an expert interface. At the moment, no expert system or inference engine is implemented, but simple algorithms which work in the following way. The user inputs a project and several characteristics (heat losses, solar gains, …) are studied by the expert tool, which then proposes alternative designs. The user may test these modifications by repeating the simulation. This tandem simulation/expert interface takes into account the specificity of the project and its climate when applying the expert knowledge. A few expert rules are proposed, in order to enhance the energy savings and the thermal comfort. New expert rules may also be generated and/or validated. This design tool not only provides the user with fast and accurate simulations, but also offers him an opportunity to include the thermal aspects in his design approach with the help of expert rules, and this constitutes a real computer aided design. [ABSTRACT FROM PUBLISHER]