DATA ADJUSTMENT FOR NON-REACTIVE BATCH OR STEADY-STATE PROCESSES

An analytical method was developed to adjust inconsistent process data by a least-sum-of-squares technique to “best” meet all material balance constraints. One complete data set composed of “M” stream flow rates with “N” components in each stream was used from either batch or steady-state non-reactive processes to define an unconstrained sum-of-squares adjustment function

Derivatives of the unconstrained sum-of-squares adjustment function with respect to each variable were set to zero yielding a set of non-linear algebraic equations. The entire non-linear set was solved by converging on only M— 2 search variables as compared to conventional methods requiring N(M — 1) — 1 search variables.     

Multiplicities and instabilities in film blowing

The mechanics of the blown film process are studied for Newtonian and viscoelastic models of the polymer melt. Multiple solutions of the governing equations are possible even for the Newtonian fluid, with the existence of more than one steady-state bubble profile for a given set of operating parameters; steady axisymmetric solutions vanish suddenly at critical combinations of operating variables. Several types of instabilities exist, including one that is analogous to “draw resonance.” The stability of the bubble to infinitesimal disturbances depends on the set of operating parameters that is controlled; control of the bubble inflation pressure is much less stable than control of the amount of inflating air, for example. Heat transfer is stabilizing.     

An algorithm for analysis of polymer filling of molds

A numerical implementation of the Volume of Fluid (VOF) free surface technique, applied to a filling process governed by a potential flow, is introduced. The implementation is based on a finite element control volume space discretization and uses an implicit time integration. This allows for the accurate tracking of the filling front using large simulation time steps in molds with complex geometries. The approach is validated on comparision with the analytical solution for filling a one-dimensional tube and with two-dimensional results obtained with previously-presented filling algorithms. Examples of the application of the approach in the analysis of structural resin transfer molding (SRTM) are presented. The capability of the method is demonstrated on predicting “race tracking” and “dry spotting” phenomena. The CPU requirement for a typical analysis is on the order of 1 to 20 s on pesonal computers.     

A colour harmony model for two‐colour combinations

This study investigates harmony in two‐colour combinations in order to develop a quantitative model. A total of 1431 colour pairs were used as stimuli in a psychophysical experiment for the visual assessment of harmony. These colour pairs were generated using 54 colours selected systematically from CIELAB colour space. During the experiment, observers were presented with colour pairs displayed individually against a medium gray background on a cathode ray tube monitor in a darkened room. Colour harmony was assessed for each colour pair using a 10‐category scale ranging from “extremely harmonious” to “extremely disharmonious.” The experimental results showed a general pattern of two‐colour harmony, from which a quantitative model was developed and principles for creating harmony were derived. This model was tested using an independent psychophysical data set and the results showed satisfactory performance for model prediction. The study also discusses critical issues including the definition of colour harmony, the relationship between harmony and pleasantness, and the relationship between harmony and order in colour. © 2006 Wiley Periodicals, Inc. Col Res Appl, 31, 191–204, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20208     

A comprehensive approach to chemical engineering computational problems

A general programme for the solution of large sparse systems of non-linear equations is presented that allows to afford in a general way most computational problems in chemical engineering.Equipments and plants can, in fact, be represented as networks of “unit cells” to which material and energy balance equations are applied in finite form.The lay-out of the network and the assessment of the equations is a matter of the engineer's judgment and depends upon the aims of the computation and the complexity and importance of the phenomena involved.The solution of the equations then becomes a straightforward procedure that may be committed to the computer.Examples of application to a variety of chemical equipments and to process computation are given.     

An efficient algorithm for community detection in complex weighted networks

Community detection decomposes large-scale, complex networks “optimally” into sets of smaller sub-networks. It finds sub-networks that have the least inter-connections and the most intra-connections. This article presents an efficient community detection algorithm that detects community structures in a weighted network by solving a multi-objective optimization problem. The whale optimization algorithm is extended to enable it to handle multi-objective optimization problems with discrete variables and to solve the problems on parallel processors. To this end, the population's positions are discretized using a transfer function that maps real variables to discrete variables, the initialization steps for the algorithm are modified to prevent generating unrealistic connections between variables, and the updating step of the algorithm is redefined to produce integer numbers. To identify the community configurations that are Pareto optimal, the non-dominated sorting concept is adopted. The proposed algorithm is tested on the Tennessee Eastman process and several benchmark community-detection problems.     

The extensional and failure properties of polymer melts

The extensional and failure properties of polystyrene melts were studied by pulling sample rods in a special “weight dropping” extensiometer. This apparatus allows pulling to long final lengths and at relatively high rates; except for the highest rates, the experiment is one of constant applied force. Various commercial (broad molecular weight distribution) and special (narrow molecular weight distribution) samples were studied at various temperatures and applied forces. The striking result was that the former (BMWD) samples stretched reasonably uniformly and displayed what has been described as “viscoelastic failure”; the latter (NMWD) samples necked in the final stages and showed what might be called “viscous” failure. In the case of the BMWD material, the stress–time behavior was analyzed theoretically by independently determining the parameters in a nonlinear constitutive equation from GPC and rheogoniometer (shear) data. The theoretical tensile stresses compared quite well with the experimental values. An interesting result came from comparing the complete viscoelastic theory with a viscous (Trouton viscosity) asymptote. These two theoretical curves closely approximated the experimental data until just short of the failure point; at this incipient point, the stresses from the complete theory grew to very large values compared with the viscous stresses. That is, the material could not relax fast enough to allow steady stresses to develop, and the sample failed shortly thereafter.     

合成氨变换工段饱和热水循环系统的优化方法研究

本文将不可行路径法推广到复杂模块中,提出了一种新的不可行路径法,该法与现有不可行路径法的区别在于:在每轮优化迭代计算中,不要求复杂模块的模拟收敛.本文还对初值及标度因子的选取进行了讨论,提出了相应的选取原则.通过对合成氨变换工段循环热水系统以饱和塔出口半水煤气温度最大为目标函数进行优化计算,证明本文方法是成功的.     

Composition control and temperature inferential control of dividing wall column based on model predictive control and PI strategies

The dividing wall column (DWC) is considered as a major breakthrough in distillation technology and has good prospect of industrialization. Model predictive control (MPC) is an advanced control strategy that has acquired extensive applications in various industries. In this study, MPC is applied to the process for separating ethanol, n-propanol, and n-butanol ternary mixture in a fully thermally coupled DWC. Both composition control and temperature inferential control are considered. The multiobjective genetic algorithm function “gamultiobj” in Matlab is used for the weight tuning of MPC. Comparisons are made between the control performances of MPC and PI strategies. Simulation results show that although both MPC and PI schemes can stabilize the DWC in case of feed disturbances, MPC generally behaves better than the PI strategy for both composition control and temperature inferential control, resulting in a more stable and superior performance with lower values of integral of squared error (ISE).     

Amplicon Competition Enables End‐Point Quantitation of Nucleic Acids Following Isothermal Amplification

It is inherently difficult to quantitate nucleic acid analytes with most isothermal amplification assays. We developed loop‐mediated isothermal amplification (LAMP) reactions in which competition between defined numbers of “false” and “true” amplicons leads to order of magnitude quantitation by a single endpoint determination. These thresholded LAMP reactions were successfully used to directly and quantitatively estimate the numbers of nucleic acids in complex biospecimens, including directly from cells and in sewage, with the values obtained closely correlating with qPCR quantitations. Thresholded LAMP reactions are amenable to endpoint readout by cell phone, unlike other methods that require continuous monitoring, and should therefore prove extremely useful in developing one‐pot reactions for point‐of‐care diagnostics without needing sophisticated material or informatics infrastructure.     

SEQUENTIAL METHODS FOR DETECTING CHANGES IN THE VARIANCE OF ECONOMIC TIME SERIES

In this paper EWMA charts and CUSUM charts are introduced for detecting changes in the variance of a GARCH process. The moments of the EWMA statistics are calculated. They permit a better understanding of the underlying control procedure. In an extensive simulation study all control schemes are compared with each other. “Optimal” smoothing parameters and “optimal” reference values are tabulated. It is shown how these charts can be applied to monitor stock market returns.     

New approaches for representing,analyzing and visualizing complex kinetic transformations

Complex kinetic mechanisms involving thousands of reacting species and tens of thousands of reactions are currently required for the rational analysis of modern combustion systems. In order to represent, analyze and visualize effectively the ignition process, advanced computational techniques will be required. Recently, we introduced a novel approach that captured the principal elemental transformations in complex reaction mechanisms in the form of graphs. In this work, we propose new approaches in order to arrive at a compact representation of the information content of these graphs utilizing machine learning principles, such as feature selection in time series and hashing. These approaches allow the projection of the totality of the information contained in the graphs describing the chemical transformations onto a single scalar. The temporally evolving graphs are treated as streaming data and locality-preserving hashing allows the unique assignment of a scalar “motif” value to each such graph. Analysis of those motifs allows the quick identification of “clusters” of identical reaction graphs that correspond to regimes with similar kinetic characteristics. The approach is illustrated with highly complex kinetic mechanisms describing pentane autoignition. It is demonstrated how this novel representation allows the identification of regions where similar temporal history of the chemical transformations is experienced.     

Gas absorption and desorption with reversible instantaneous chemical reaction

The general problem of gas absorption and desorption accompanied by an instantaneous, reversible chemical reaction is approached from the viewpoint that chemical equilibrium prevails everywhere in the liquid phase. The approach allows absorption and desorption to be analysed along the same lines. A complete analytical solution is given for the film theory model and the penetration theory equations are set up in general form.The equations for the enhancement factor reduce to the classical “irreversible” result for absoption when the driving force, φ, becomes very large, rather than in the limit of very large equilibrium constant as the word irreversible seems to suggest. The corresponding asymptote for desorption is obtained by setting φ = 0. A third asymptotic region, in which φ is in the neighborhood of unity, is established for both absorption and desorption. Physically this is the region where driving forces are very small, which from an industrial viewpoint is what happens in absorption and desorption units near pinches.The asymptotic analysis for the pinch region is applied to hydrogen sulfide absorption and desorption from aqueous diisopropanolamine solution. For this system use of the “irreversible” equations grossly overestimates the enhancement factor. Gas-phase controls mass transfer at the lean end of the absorber but at the other terminal locations of the towers the liquid-phase resistance cannot be neglected.     

Solve separation units by combining sure and fast models

Problems met in countercurrent separation units have been solved by means of a proper combination of two different models, referred to as sure and fast, to describe the whole set of theoretical stages.The “sure” model is employed for trays showing particular features, or disturbances, i.e. feed trays, partial condensers, reboilers, side cuts, intercoolers, etc. as well as for trays adjacent to the previous ones. This model is written in terms of single theoretical tray equations. The “fast” model is applied to multitray sections, provided that no “disturbance” exists, with an assumption that molar flowrates and temperatures vary according to prefixed laws. The adoption of effective K-values allows one to use formally the same operating equations for the multitray sections as for single theroretical trays.A Newton—Raphson procedure, combined with a B. P. method, is employed to converge the set of equations describing the problem.     

Molecular reconstruction of heavy petroleum residue fractions

Molecular reconstruction techniques are methods that allow to create mixtures of molecules from partial analytical data. In this article, a two-step reconstruction algorithm will be presented. The first step, called “stochastic reconstruction” step, assumes that oil mixtures can be described by distributions of structural blocks. The choice of the blocks and distributions is based on expert knowledge. The transformation from a set of distributions into a mixture of molecules is obtained by Monte–Carlo sampling, while a genetic algorithm adjusts the parametric distributions. The second step, termed “reconstruction by entropy maximization”, improves the representativeness of the set of constructed molecules by adjusting their molar fractions. The estimation of these molar fractions is carried out by maximizing an information entropy criterion under linear constraints. The two-step reconstruction algorithm allows to rebuild mixtures that resemble the petroleum fractions more closely than the approaches used previously. To illustrate the approach, the technique is applied to petroleum vacuum residue fractions.     

Colored apparel and its potential influence on heterosexual attraction

The objective of this study is to determine if men would follow the “red effect” when choosing colors for women to wear on a date, and also to determine if the colors that men would wear when going on a date would be the same as the colors that females (their date) would wish them to wear. A set of psychophysical data was generated from this experiment, where participants were asked to rank a set of 10 colored samples based on preference for each question asked. There were three different sets of colored samples. The set of colored samples given to the participant depended on the question. A total of five questions were asked. Scaling analysis was done on the data to organize a set of items according to preferences providing values, an interval scale (Z values), that correspond to the relative perceptual differences among the stimuli. The Z values were graphed to show the general preference of colors for women to wear, and the preference of colors for men to wear. A Spearman's rank-order correlation coefficient (SRCC) was calculated comparing each individual's rank order with the mean rank order for that specific question. An average Spearman's rank order was calculated for each question and each gender in order to determine the variability in answers. Scaling results indicate that men follow the “red effect,” but women preferred to wear other colors such as turquoise, blue, or yellow depending on the outfit. Males and females agreed that no matter the colored bottoms (denim or black), blue was the preferred color top for men to wear. SRCC results showed a lot of variability between individual answers and the mean answer indicating that participants' rankings did not necessarily agree with general color preferences presented in the scaling analysis. While scaling analysis might suggest certain color preferences such as men following the “red effect” and women preferring to wear blue, the poor correlation found using SRCC between the individual answers and the mean rank orders suggests that color preferences for each individual are inherently unique.     

Targeting optimum resource allocation using reverse problem formulations and property clustering techniques

Decoupling the constitutive equations from the balance and constraint equations allows for reformulating a conventional forward problem into two reverse problems. The first reverse problem is the reverse of a simulation problem, where the process model is solved in terms of the constitutive (synthesis/design) variables instead of the process variables, thus providing the synthesis/design targets. The second reverse problem (reverse property prediction) solves the constitutive equations to identify unit operations, operating conditions and/or products by matching the synthesis/design targets. Visualization of the problem is achieved by employing recently developed property clustering techniques, which allows a high-dimensional problem to be visualized in two or three dimensions. The clusters by definition satisfy intra-stream and inter-stream conservation through linear “mixing” rules, which allows for the development of consistent additive rules along with their ternary representation.     

Computation of the near-optimal temperature and initiator policies for a batch polymerization reactor

Optimal control theory is applied to a batch polymerization reactor for PMMA to calculate the near-optimal temperature and initiator policies that are required to produce a polymer with a desired final conversion, and desired number average and weight average molecular weights. The two-point boundary value problem that results from the application of the Pontryagin minimum principle to the mathematical model of the reactor is solved by the discretization control method. According to this, the total reaction time is divided into N equal subintervals. It is assumed that the control variables remain constant in each interval and the Hamiltonian is minimized by a first-order gradient technique. It is shown that the introduction of the “target set” concept, which is well suited to industrial practice, simplifies the numerical solution of the TPBV problem. Results of the simulations demonstrate the potential gains possible from the application of the optimal control theory to the batch polymerization of PMMA.     

Infrared spectroscopic monitoring of urea addition to oriented strandboard resins

One of the variables in phenol formaldehyde adhesive resin formulation is the addition of urea, which allows the resin manufacturer to manipulate both product functionality and cost. Nitrogen content can be used as a measure of the level of urea addition because most of the nitrogen present is derived from urea added at the end of the preparation process. Nitrogen analyses of a set of commercial oriented strandboard resins were first determined by combustion analysis. IR spectroscopic data were then collected and used along with the values for nitrogen content to generate predictive models. First, principal component analysis demonstrated the ability to separate resin mixtures from low to high nitrogen content. Partial least squares regression was then performed and gave excellent correlations between the measured and predicted nitrogen contents for a set of unrelated (test) resins and a set of mixtures prepared through combinations of resins with known nitrogen contents. Similar results were obtained on both a wet and dry mass basis. Given the flexibility of this instrumentation, such analyses could be placed in‐line for real time monitoring of resin applied during panel manufacturing. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci 2007