Efficacy of Interactive Internet‐Based Education in Structural Timber Design

While traditional teaching methods (e.g., real‐time, synchronous lectures) have proven effective for training future engineers, the Internet provides an avenue to reinforce the material and augment student learning, comprehension, and retention of material. This paper presents the integration and assessment of a library of interactive instructional modules specifically for a senior‐level undergraduate elective course in civil engineering. An ongoing, comprehensive assessment process was implemented in the fall 1999 semester. The results of this quantitative assessment indicate that the use of well designed and pedagogically sound Internet‐based supplemental modules provide students with a better understanding of course material. However, when Internet‐based content does not promote critical thinking, little increase in the student performance and understanding of the material is realized. Interactive Web‐based instruction should not be viewed as a “replacement” to traditional instruction, but rather a tool that provides a broader and more dynamic environment for students with a variety of learning styles.     

The degradation of poly(vinyl chloride). I. Hydrogen chloride evolved from solid samples and from solutions

A technique is described for the accurate and reproducible estimation of hydrogen chloride evolved during the degradation of poly(vinyl chloride). Results of degrading PVC in solvents and in the solid state are reported, and explanations are suggested for the differences in the observed behavior.     

Cell population models for bifurcation analysis and nonlinear control of continuous yeast bioreactors

Saccharomyces cerevisiae (baker's yeast) can exhibit sustained oscillations over a wide range of operating conditions when produced in a continuous bioreactor. In this paper the bifurcations leading to these periodic solutions are investigated using an unstructured, segregated model in which the population balance equation (PBE) for the cell mass distribution is coupled to the mass balance of the rate limiting substrate. The PBE model is shown to produce periodic solutions over a range of dilution rates due to the presence of two supercritical Hopf bifurcations. The problem of oscillation attenuation using nonlinear feedback control with four candidate input/output variable pairings is investigated. The controller designs are based on a low dimensional moment representation of the PBE model. The performance of the nonlinear controllers are compared and discussed.     

The Influence of Heat on the Sensitivity of a Photographic Film to Low Intensity Light

A fast radiation monitoring film, the lIford PM I, was exposed at 0 per cent relative humidity to low intensity u-v light from a plastic scintillator, the exposure temperoture being varied between +10 and +75°C. Films were also heated at 60°C. and 0 per cent RH and subsequently exposed to the scintillator light at 30O°C, the results indicating the presence of latent sub-image in the heated film at the end of the heating. From the temperature dependence of the net film density obtained with constant heating time the activation energy of 126 eV was derived, this corresponding to the formation energy of a Frenkel defect in silver bromide. The results suggest that the effect of increased temperature in increasing light absorption is a minor one in this instance.     

Modelling the functional roles of synaptic and extra-synaptic γ-aminobutyric acid receptor dynamics in circadian timekeeping

In the suprachiasmatic nucleus (SCN), γ-aminobutyric acid (GABA) is a primary neurotransmitter. GABA can signal through two types of GABA_A receptor subunits, often referred to as synaptic GABA_A (gamma subunit) and extra-synaptic GABA_A (delta subunit). To test the functional roles of these distinct GABA_A in regulating circadian rhythms, we developed a multicellular SCN model where we could separately compare the effects of manipulating GABA neurotransmitter or receptor dynamics. Our model predicted that blocking GABA signalling modestly increased synchrony among circadian cells, consistent with published SCN pharmacology. Conversely, the model predicted that lowering GABA_A receptor density reduced firing rate, circadian cell fraction, amplitude and synchrony among individual neurons. When we tested these predictions, we found that the knockdown of delta GABA_A reduced the amplitude and synchrony of clock gene expression among cells in SCN explants. The model further predicted that increasing gamma GABA_A densities could enhance synchrony, as opposed to increasing delta GABA_A densities. Overall, our model reveals how blocking GABA_A receptors can modestly increase synchrony, while increasing the relative density of gamma over delta subunits can dramatically increase synchrony. We hypothesize that increased gamma GABA_A density in the winter could underlie the tighter phase relationships among SCN cells.     

Melanin synthesis is associated with changes in hyphopodial turgor, permeability, and wall rigidity in gaeumannomyces graminis var. graminis

Mycelia of Gaeumannomyces graminis var. graminis form large cells called hyphopodia with deeply lobed, melanized walls. Like appressoria produced by other pathogens, hyphopodia develop on hydrophobic surfaces, but it is not clear that hyphopodia function as platforms for host penetration. In appressoria, melanin synthesis is linked to the generation of enormous turgor pressures that provide the necessary force for plant penetration. In the present study, hyphopodial turgor was measured in a wild-type strain of G. graminis var. graminis, a mutant exhibiting constitutive synthesis of melanin (referred to as the dark mutant), and a melanin-deficient strain (thr). These experiments demonstrate that hyphopodia of the wild-type strain generate higher pressures than the dark mutant and that nonmelanized thr hyphopodia generate minuscule internal pressures. Melanization of the wall is also associated with an increase in its rigidity. These data correlate with differences in wall permeability consistent with a recent model for turgor generation by appressoria.     

Electrical properties of composite gate oxides formed by rapidthermal processing

In this study, oxide stacks formed by combinations of rapid thermal chemical vapor deposition and rapid thermal oxidation have been investigated as gate dielectrics. This was achieved by performing various types of in situ rapid thermal oxidations both prior to and after oxide deposition to form composite stacked structures. The oxidation ambient and temperature was varied to study the effect on electrical properties such as mobility, leakage current, charge trapping, breakdown and hot carrier degradation. It was found that pre-oxidation prior to depositing an oxide results in a composite structure that greatly reduces the defect density by mismatching pores and weak spots in each film. The mobility behavior of these films was also found to be improved over as-deposited oxides. Post-deposition oxidation in O₂ and N₂O was also found to improve the mobility characteristics. Additionally, post-annealing in N₂ O was effective in improving the reliability of deposited oxides. These N₂O annealed films had low interface trap densities, improved high field mobility, very low charge trapping characteristics and enhanced resistance to hot carrier induced interface state generation. These improvements are attributed to 1) the presence of nitrogen at the interface and 2) to the reduction of nitrogen and hydrogen concentrations in the bulk of the oxide. The role of atomic oxygen during the post-anneal in N₂O is discussed along with differences in annealing ambients     

A PACK STABILITY METHOD FOR MICROBIOLOGICAL TESTING OF LARGE CANS OF BEER

The microbiological stability of four-pint and seven-pint cans of beer can be determined by measuring the curvature of the ends after incubation at 28° C. A simple spherometer, a dial-gauge spherometer and a rig employing depth-transducers have been used in a simple, non-destructive method. This has revealed micro-biological defects more reliably than membrane filtration tests, and before “peaking” was visible to the eye. The method can also be adapted for sorting infected from non-infected cans in the warehouse.     

Ovipositional behavior ofbracon mellitor say (Hymenoptera: Braconidae), a parasitoid of boll weevil (anthonomus grandis Boh.)

FemaleBracon mellitor Say responded to the frass of dietreared boll weevil larvae by probing with the ovipositor. Similar responses were elicited by the hexane and chloroform-methanol fractions after differential extraction of boll weevil feces. The active component of the chloroform-methanol fraction was identified as methylp-hydroxybenzoate (methyl parasept). Because the methyl parasept is an artificial component of the diet, the results suggest that the parasitoid response may be associatively learned. The response to methyl parasept decreased with time in the absence of reinforcement. Results demonstrate that certain chemicals may release behavior normally evoked by kairomones, and may interfere with the isolation of natural kairomones.This paper was approved for publication as TA 12350 by the Director, Texas Agricultural Experiment Station. This study was conducted in cooperation with the USDA. It was supported, in part, by the National Science Foundation and the International Biological Program (NSF-SC-0030) of the University of California. The findings are those of the authors, and not necessarily those of the University of California or the National Science Foundation. Mention of a proprietary or commercial product in this paper does not constitute an endorsement of this product by the USDA.     

Dynamic modeling and linear model predictive control of gas pipeline networks

A linear model predictive control (LMPC) strategy is developed for large-scale gas pipeline networks. A nonlinear dynamic model of a representative pipeline is derived from mass balances and the Virial equation of state. Because the full-order model is ill-conditioned, reduced-order models are constructed using time-scale decomposition arguments. The first reduced-order model is used to represent the plant in closed-loop simulations. The dimension of this model is reduced further to obtain the linear model used for LMPC design. The LMPC controller is formulated to regulate certain pipeline pressures by manipulating production setpoints of cryogenic air separation plants. Both input and output variables are subject to operational constraints. Three methods for handling output constraint infeasibilities are investigated.