Estimating a minimum set of physically based dynamic parameters to enhance statistical inference in block-oriented modeling

In process identification (i.e., dynamic model development) information on the precision and reliability of a parameter estimate is conveyed by a confidence interval. The best confidence interval is the one with the shortest width for a given level of confidence. Confidence intervals widen as the standard error increases or as the number of estimated parameters increases. When the value of a parameter is needed for physical understanding of process characteristics, its precision and reliability, i.e., certainty, is crucial. Parameter certainty increases as the number of estimated parameters decreases because this causes confidence intervals to shorten and confidence levels to increase. Hence, this article focuses on maximizing parameter certainty of physically interpretable dynamic parameters under block-oriented modeling by obtaining accurate values for all the dynamic parameters from a minimum set of estimated parameters. This objective is accomplished by the development of a procedure that identifies equivalent sets of parameters and estimates one parameter for each set. For a seven (7) input, five (5) output, simulated CSTR, its 84 physically based dynamic parameters were accurately determined from 23 estimated parameters that resulted in an increase in confidence level from 50% to 99.9% for a fixed interval width.     

Comparison of reflector designs for stationary tubular solar collectors

We consider a number of alternative designs for reflectors which are used in conjunction with cylindrical tubular solar collectors. The annual relative optical performance of the collectors is assessed, data being presented for a variety of tube absorptances and reflector reflectances. Both North-South (NS) and East-West (EW) orientations of tubes are considered. This performance data may be combined by the reader with his own local tube and reflector unit costs to make cost-effectiveness judgements between rival collector designs. The method is illustrated using some current Sydney prices, on which basis we make the following assessments: A reflector is always cost-effective, the best option being a stainless steel reflector of Winston-Hinterberger type with a geometric concentration ratio (C) of about 1.2, mounted either NS or EW. At higher C values EW is favoured over NS. Back-silvered glass mirrors are not competitive. A plane diffuse reflector with C 1.2 is also cost-effective for NS orientation. Since no allowance is made for thermal losses in the present work these conclusions should be regarded as tentative only.     

Prediction of turbulent gas‐solid flow in a duct with a 90° bend using an Eulerian‐Lagrangian approach

A dilute, particle‐laden turbulent flow in a square cross‐sectioned duct with a 90° bend is modeled using a three‐dimensional Eulerian‐Lagrangian approach. Predictions are based on a second‐moment turbulence closure, with particles simulated using a Lagrangian particle tracking technique, coupled to a particle‐wall interaction algorithm and a random Fourier series method used to model particle dispersion. The performance of the model is tested for a gas‐solid flow in a horizontal‐to‐vertical duct, with predictions showing good agreement with experimental data. In particular, the consistent use of anisotropic and fully three‐dimensional approaches throughout yields predictions that result in fluctuating particle velocities in acceptable agreement with data. © 2011 American Institute of Chemical Engineers AIChE J, 2012     

Atomic scale characterization of the conformational dynamics of a thermo-sensitive and a non-thermo-sensitive oligomer using vibrational spectra obtained from molecular dynamics

Molecular dynamics simulations (MD) are used to calculate the vibrational spectra of a thermo-sensitive oligomer, namely, poly(N-isopropylacrylamide) (PNIPAM) and a non-thermo-sensitive oligomer, namely, poly(acrylamide) (PAAM) and characterize the atomic scale conformations. Despite the structural similarity between the two polymers, the response of PNIPAM and PAAM to a thermal stimulus is widely different; a coil-to-globule transition is observed for PNIPAM above a lower critical solution temperature (LCST) of 305 K whereas the same is absent in PAAM. Simulations in both the cases are performed above and below the LCST of PNIPAM, namely at 278 K and 310 K, to evaluate the effect of temperature on the polymer conformations. The vibrational spectra of bonds involving atoms from the polymer backbone and the various side-groups (amide I, amide II, and isopropyl group of PNIPAM and amide I and amide II group of PAAM) of the polymers were analyzed to study the conformational changes in the polymer. The differences in the vibrational spectra are used to understand the dynamics of conformational transitions in the two polymers and identify the changes in the relative interactions between various atoms in the backbone and in the side groups of the polymer with water at two different temperatures, namely at 278 K and 310 K. The systematic trends in the observed peak intensities and frequency shifts at the low, medium, and high frequency end of the spectrum for the various atoms in the two polymers are rationalized on the basis of bond-lengths, local coordination, strength of hydrogen bonding, and neighboring solvation environment. The analysis of the vibrational spectra for amide I and amide II regions of PNIPAM suggests a coil-to-globule transition in going from 278 K to 310 K. The differences are evaluated in terms of the strength, stability, and structure of the hydrogen-bond network between polymer and polymer and between polymer and water. Comparison of the vibrational spectra of isopropyl groups in PNIPAM at 278 K and 310 K suggests dehydration of the isopropyl moieties at 310 K. In the case of PNIPAM, we observe that polymer-water interactions are dominant below the LCST whereas polymer–polymer interactions dominate above the LCST. On the other hand, the vibrational spectra of amide I and amide II group of PAAM, at 278 K and 310 K, do not show any significant difference in terms of the interactions between polymer and polymer and interactions between polymer and water. Analysis of the peak intensities, of the amide II stretching band, observed in the frequency range 3500–3700 cm^?1 suggests that the fraction of bonded and non-bonded hydrogen atoms are similar at both 278 K and 310 K. This indicates that the interactions between polymer and polymer and between polymer and water are similar at both the temperatures. The interactions between PAAM and its surrounding environment are found to be unaffected as the temperature is raised from 278 K to 310 K. Comparisons with experimental studies are made where possible. Our study provides useful insights into the nature of various inter-molecular interactions and their role in influencing the atomic scale conformational dynamics in oligomers.     

Comparison of Sampling Methods for Semi-Volatile Organic Carbon Associated with PM2.5

This study evaluates the influence of denuder sampling methods and filter collection media on the measurement of semi-volatile organic carbon (SVOC) associated with PM_2.5. Two types of collection media, charcoal (activated carbon) and XAD, were used both in diffusion denuders and impregnated back-up filters in two different samplers, the VAPS and the PC-BOSS. The two organic diffusion denuders were XAD-coated glass annular denuders and charcoal-impregnated cellulose fiber filter (CIF) denuders. In addition, recently developed XAD-impregnated quartz filters were compared to CIF filters as back-up filter collection media. The two denuder types resulted in equivalent measurement of particulate organic carbon and particle mass. The major difference observed between the XAD and charcoal BOSS denuders is the higher efficiency of charcoal for collection of more volatile carbon. This more volatile carbon does not contribute substantially to the particle mass or SVOC measured as OC on quartz filters downstream of the denuders. This volatile carbon does result in high OC concentrations observed in charcoal filters placed behind quartz filters downstream of the XAD denuders and would result in overestimating the SVOC in that configuration.     

Visual marking and change blindness: Moving occluders and transient masks neutralize shape changes to ignored objects.

Visual search efficiency improves by presenting (previewing) one set of distractors before the target and remaining distractor items (D. G. Watson & G. W. Humphreys, 1997). Previous work has shown that this preview benefit is abolished if the old items change their shape when the new items are added (e.g., D. G. Watson & G. W. Humphreys, 2002). Here we present 5 experiments that examined whether such object changes are still effective in recapturing attention if the changes occur while the previewed objects are occluded or masked. Overall, the findings suggest that masking transients are effective in preventing both object changes and the presentation of new objects from capturing attention in time-based visual search conditions. The findings are discussed in relation to theories of change blindness, new object capture, and the ecological properties of time-based visual selection. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flexural creep behavior of discontinuous thermoplastic composites: Non-linear viscoelastic modeling and time–temperature–stress superposition

Flexural creep behavior of nylon 6/6, polypropylene and high-density polyethylene long fiber thermoplastic (LFT) composites was studied according to ASTM D-2990. Neat polymers were tested for baseline data and compared with the 40 wt.% E-glass reinforced LFTs, all processed by compression molding. All materials exhibited non-linear viscoelasticity and showed a succession in creep resistance consistent with static flexural yield strength. A four parameter empirical model used for short fiber thermoplastics (SFT), proposed by Hadid et al., was found to provide an excellent fit to the experimental data. Time-compliance data from flexural creep and dynamic mechanical analysis (DMA) were combined to utilize short-term flexural creep tests to predict lifetime of the composites. A time–temperature–stress superposition (TTSSP) procedure was used, where stress-based vertical shifts were applied in addition to horizontal shifts used in a traditional time–temperature superposition (TTSP). Master curves obtained by this method projected the long-term creep properties, the order of creep resistance being consistent with the flexural creep data.     

Frozen herring as raw material for spice‐salting

One batch of herring (Clupea harengus) was spice‐salted fresh and as thawed after 32 days of frozen storage at −24 °C. After salting, samples of both groups were sent to participating laboratories in Iceland, Denmark, Norway, Germany and England. The herring was kept at 5 ± 1 °C and sampled three times during a 26 week storage period. The development of taste and texture characteristics (determined by sensory evaluation and instrumental texture measurements), formation of low‐molecular‐weight nitrogen compounds and changes in proteolytic activity were followed in both groups. The sensory evaluation results showed that thawed salted herring ripened in a similar manner to herring salted fresh, but at a faster rate. Instrumental texture analysis showed a faster rate of tenderising in thawed salted herring. Proteolytic activity measured as general activity and with specific synthetic substrates was higher in the thawed salted herring. The formation of trichloroacetic acid‐soluble nitrogen and free amino acids was faster in the previously frozen herring. The results show an accelerated but similar rate of ripening in thawed spice‐salted herring in comparison with fresh salted herring. © 2000 Society of Chemical Industry