Modeling and analysis of thickness gradient and variations in vacuum‐assisted resin transfer molding process

As vacuum‐assisted resin transfer molding (VARTM) is being increasingly used in aerospace applications, the thickness gradient and variation issues are gaining more attention. Typically, thickness gradient and variations result from the infusion pressure gradient during the process and material variations. Pressure gradient is the driving force for resin flow and the main source of thickness variation. After infusion, an amount of pressure gradient is frozen into the preform, which primarily contributes to the thickness variation. This study investigates the mechanism of the thickness variation dynamic change during the infusion and relaxing/curing processes. A numerical model was developed to track the thickness change of the bagging film free surface. A time‐dependent permeability model as a function of compaction pressure was incorporated into an existing resin transfer molding (RTM) code for obtaining the initial conditions for relaxing/curing process. Control volume (CV) and volume of fluid (VOF) methods were combined to solve the free surface problem. Experiments were conducted to verify the simulation results. The proposed model was illustrated with a relatively complex part. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Evaluation of harassment of migrating double-crested cormorants to limit depredation on selected sport fisheries in Michigan

Diverse management techniques have been used to mitigate conflicts between humans and double-crested cormorants (Phalacrocorax auritus) including harassment methods supplemented by lethal take. In this study we evaluated impacts of programs to harass spring migrating cormorants on the walleye (Sander vitreus) fishery in Brevoort Lake and the yellow perch (Perca flavescens) and walleye fisheries at Drummond Island. Cormorant foraging declined significantly (p < 0.05) at both locations subsequent to initiation of harassment programs. Overall harassment deterred 90% of cormorant foraging attempts while taking less than 6% lethally on average at each site. Yellow perch were a predominate prey item in number and biomass at both locations. Walleye made up a small proportion of the diet at both locations. However, both walleye and yellow perch abundance increased significantly (p < 0.05) at Drummond Island. Walleye abundance at age 3 increased to record levels in 2008 following 3 years of cormorant management at Brevoort Lake. The estimated cormorant consumption of age-1 walleye in the absence of management at Brevoort Lake during 2005 would account for 55% of the record 2006 age-1 walleye population. These results support the hypothesis that cormorant predation on spawning aggregations of sportfish was a significant mortality factor and cormorant management reduced sportfish mortality and increased abundance at both locations. Continuation of harassment programs and fishery assessments will determine whether improvement of targeted sport fisheries through control of spring migrating cormorants is sustainable.     

Condensation of vapor in the presence of non-condensable gas in condensers

This paper presents a set of differential and algebraic equations that model heat and mass transfer in condensers in which a mixture of water vapor and non-condensable gas is cooled. The model has been used to predict the condensation rate, the bulk temperatures of the coolant and the gas–vapor mixture, and the surface temperatures of the condenser wall. The predicted results for counter flow tube condensers are compared with three sets of published experimental data for system in which air is the non-condensable gas. It is found that the predicted condensation rates and coolant bulk temperatures agree very well with all the three sets of experimental data, the predicted wall temperatures agree reasonably well with the experimental results, and the agreement between the predictions and the experimental results on the bulk temperature of the air–vapor mixture is excellent for one set of the experimental data, reasonable for the second set of experimental data, but poor for the third set of experimental data. It is suggested that the poor agreement between the predicted and measured bulk temperatures of the mixture for the third set of experimental data arises from the experimental errors. The results from this study show that when modeling vapor condensation in the presence of a non-condensable gas, a simple model for the mixture channel alone may not be sufficient since neither the temperature nor the heat flux at the wall can be assumed to be constant. The results also show that the wall temperature in the coolant channel can be quite high, and careful modeling of the heat transfer in the coolant channel is needed in order to achieve good agreement between the model predictions and the experimental results.     

Relative potencies and combination effects of steroidal estrogens in fish

The natural steroids estradiol-17beta (E2) and estrone (E1) and the synthetic steroid ethynylestradiol-17alpha (EE2) have frequently been measured in waters receiving domestic effluents. All of these steroids bind to the estrogen receptor(s) and have been shown to elicit a range of estrogenic responses in fish at environmentally relevant concentrations. At present, however, no relative potency estimates have been derived for either the individual steroidal estrogens or their mixtures in vivo. In this study the estrogenic activity of E2, E1, and EE2, and the combination effects of a mixture of E2 and EE2 (equi-potent fixed-ratio mixture), were assessed using vitellogenin induction in a 14-day in vivo juvenile rainbow trout screening assay. Median effective concentrations, relative to E2, for induction of vitellogenin were determined from the concentration-response curves and the relative estrogenic potencies of each of the test chemicals calculated. Median effective concentrations were between 19 and 26 ng L(-1) for E2, 60 ng L(-1) for E1, and between 0.95 and 1.8 ng L(-1) for EE2, implying that EE2 was approximately 11 to 27 times more potent than E2, while E2 was 2.3 to 3.2 times more potent than E1. The median effective concentration, relative to E2, for the binary mixture of E2 and EE2 was 15 ng L(-1) (comprising 14.4 ng L(-1) E2 and 0.6 ng L(-1) EE2). Using the model of concentration addition it was shown that this activity of the binary mixture could be predicted from the activity of the individual chemicals. The ability of each individual steroid to contribute to the overall effect of a mixture, even at individual no-effect concentrations, combined with the high estrogenic potency of the steroids, particularly the synthetic steroid EE2, emphasizes the need to consider the total estrogenic load of these chemicals in our waterways.     

安全仪表系统的网络安全考虑：最先还是最后？

对于完整的控制和安全系统，建立强大的防护体系是否是一项可以确保安全仪表系统商业连续性的必要投资？     

An evaluation of two clinically-derived treatments for technophobia

Technology is ubiquitous in our occupational, educational and leisure lives. A fear of interacting with technology can therefore have a major impact on the quality of an individual’s life. This is particularly salient within education as an inability to maximise the benefits of technology may limit academic achievement and subsequent opportunities in life. The severity of the anxiety induced by technology has lead to a plethora of research into the prevalence of ‘technophobia’. This term may have clinical relevance and has been found to be comparable in severity to more traditional phobias [Thorpe, S. J. &; Brosnan, M. (in press). Does computer anxiety reach levels which conform to DSM IV criteria for specific phobia? Computers in Human Behavior]. This paper presents two studies examining the effect of clinically-derived treatments upon levels of anxiety induced by technology. Study 1 was a 10-week selective desensitisation programme with 16 participants (eight computer anxious, eight non-anxious). Over this period computer anxiety and coping cognitions were significantly improved in the computer anxious group and become comparable to those of the matched non-anxious controls. Study 2 was a single treatment session for anxiety. Thirty individuals identified as anxious were assigned to either a one-session treatment (n = 9) or non-treatment (n = 21) group. Initially, both groups were significantly more anxious than the non-anxious control group (n = 59). Subsequent testing established that over the period of an academic year the reduction in anxiety was three times greater in the treated group than the non-treated group such that by the end of the year the treated group no longer differed from the control group, whereas the non-treated group remained significantly more anxious. The implications and limitations of the studies are discussed.     

Modelling the effects of aeration on the persistence of chemical pesticides applied to stored bulk grain

The rates of degradation of common chemical pesticides applied to stored grains are known to be strongly dependent on grain moisture content and temperature. A finite difference mathematical model of the processes of heat and moisture transfer and pesticide decay in aerated grain is presented and its validity is supported by experimental evidence. Aeration is shown to reduce the rate of degradation of pesticides applied to stored grain, and render the rate of decay relatively insensitive to initial grain conditions. In the temperate and sub-tropical wheat growing regions of Australia, aeration can reduce usage of the pesticide methacrifos (0-2-methoxy carbonylprop-1-enyl 0,0-dimethyl phosphorothioate) by factors of 7 and 4 respectively. The effects of initial grain moisture content, initial grain temperature, fan operation, air flow rates and geographic location are modelled. Aeration of pesticide treated grain may reduce uncertainty within the grain handling industry, thus enabling more efficient planning and resource utilization.     

Moisture diffusion through bulk grain

Pixton and Griffiths (1971) describe the diffusion of moisture through bulk grain by means of a diffusion coefficient which is an empirically determined function of grain moisture content and temperature. This paper presents a general analysis of the diffusion mechanism based on the interstitial partial pressure of water vapour derived from hygrothermal data as the driving force, and the properties of porous beds of granular materials are invoked to calculate the resistance to diffusion. An obstructive coefficient, ψ, is determined to be 0.53 which compares excellently with literature values for randomly packed porous media, and is in accord with contention of van Brakel and Heertjes (1974) that the nature of the packing is not an important influence on the value of the obstructive coefficient.     

A new method for defining and managing process alarms and for correcting process operation when an alarm occurs

A new mathematical treatment of alarms that considers them as multi-variable interactions between process variables has provided the first-ever method to calculate values for alarm limits. This has resulted in substantial reductions in false alarms and hence in alarm annunciation rates in field trials. It has also unified alarm management, process control and product quality control into a single mathematical framework so that operations improvement and hence economic benefits are obtained at the same time as increased process safety. Additionally, an algorithm has been developed that advises what changes should be made to Manipulable process variables to clear an alarm. The multi-variable Best Operating Zone at the heart of the method is derived from existing historical data using equation-free methods. It does not require a first-principles process model or an expensive series of process identification experiments. Integral with the method is a new format Process Operator Display that uses only existing variables to fully describe the multi-variable operating space. This combination of features makes it an affordable and maintainable solution for small plants and single items of equipment as well as for the largest plants. In many cases, it also provides the justification for the investments about to be made or already made in process historian systems. Field Trials have been and are being conducted at IneosChlor and Mallinckrodt Chemicals, both in the UK, of the new geometric process control (GPC) method for improving the quality of both process operations and product by providing Process Alarms and Alerts of much high quality than ever before. The paper describes the methods used, including a simple visual method for Alarm Rationalisation that quickly delivers large sets of Consistent Alarm Limits, and the extension to full Alert Management with highlights from the Field Trials to indicate the overall effectiveness of the method in practice.