Simulation of polymer flow through a coat-hanger die: A comparison of two numerical approaches

Coat-hanger dies are commonly used for the extrusion of plastic sheets and films. To describe the flow of a molten polymer through a coat-hanger die, a two-dimensional approach is necessary. Moreover, the thermal effects, which play an important role in the flow distribution, have to be taken into account. In this paper, two numerical models for the simulation of coat-hanger dies are described and compared. These models differ mainly in the simplifying assumptions used and in the treatment of the thermal problem. The simulations obtained with the two models were compared with each other and with experimental data. The discrepancies between the two models can be explained by the different theoretical treatments.     

Effect of human somatotropin-releasing factor and photoperiods on carcass parameters and mammary gland development of dairy heifers

Forty-eight heifers (3 mo old) were subjected for 35 wk to twice daily s.c. injections of saline or human somatotropin-releasing factor (5 microgram.kg-1 BW) and photoperiod of 8 h (short day) or 16 h (long day) of light daily according to a 2 X 2 factorial design. There was no treatment effect on slaughter weight, withers height, and carcass length. Somatotropin-releasing factor increased thymus weight, metacarpal length, and protein content of the carcass but decreased carcass fat content. Long day photoperiod increased chest girth, pituitary weight, and carcass yield. Effects of somatotropin-releasing factor and photoperiod were not additive on volume of mammary parenchymal tissue; there was also a treatment interaction on liver and lung weights. However, extraparenchymal mammary tissue was decreased by human somatotropin-releasing factor and short day photoperiod. In conclusion, use of somatotropin-releasing factor and photoperiod treatments affected carcass parameters and composition and mammary growth.     

Encoding and selective activation of "metabolic memories" in the rat.

Experiment 1 used Pavlovian conditioning procedures to show that rats formed distinct memorial representations of 2 (peanut oil and sucrose pellets) unconditioned stimuli (USs) that could be activated by 2 different conditioned stimuli (CSs). After training in Experiment 2, rats injected with the lipid antimetabolite Na-2-mercaptoacetate (MA) responded more to the CS for oil than to the CS for sucrose. This pattern was not shown by rats that received isotonic saline or systemic 2-deoxy-d-glucose (a glucose antimetabolite). By contrast, intracerebroventricular infusion of the glucose antimetabolite 5-thioglucose selectively promoted responding to the CS for sucrose (Experiment 4). Thus, lipoprivic and glucoprivic treatments selectively promoted the activation of the memories of fat and carbohydrate USs, respectively. In Experiment 3, the capacity of MA to augment responding to a CS for oil was abolished for rats that received subdiaphragmatic vagal deafferentation. This indicates that the capacity of lipoprivic signals to selectively activate the representations of fat USs may depend on vagal afferent fibers. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

3G网络的QoS估算对运营商战略选择产生的影响

介绍了3G网络的优化和升级技术．以及ACP在天线和心共信道功率方面的应用，并结合实际网络利用动态模拟工具对其使用结果进行了阐述。此外．结论了部署40W（而不是20W）PA等网络升级解决方案的优缺点，以及站点功率共享问题．并介绍了比较结果。     

Characterization and Physical Explanation of Energetic Particles on Planck HFI Instrument

The Planck High Frequency Instrument (HFI) has been surveying the sky continuously from the second Lagrangian point (L2) between August 2009 and January 2012. It operates with 52 high impedance bolometers cooled at 100 mK in a range of frequency between 100 GHz and 1 THz with unprecedented sensitivity, but strong coupling with cosmic radiation. At L2, the particle flux is about 5 \(\hbox {cm}^{-2}\,\hbox {s}^{-1}\) and is dominated by protons incident on the spacecraft. Protons with an energy above 40 MeV can penetrate the focal plane unit box causing two different effects: glitches in the raw data from direct interaction of cosmic rays with detectors (producing a data loss of about 15 % at the end of the mission) and thermal drifts in the bolometer plate at 100 mK adding non-Gaussian noise at frequencies below 0.1 Hz. The HFI consortium has made strong efforts in order to correct for this effect on the time ordered data and final Planck maps. This work intends to give a view of the physical explanation of the glitches observed in the HFI instrument in-flight. To reach this goal, we performed several ground-based experiments using protons and \(\alpha \) particles to test the impact of particles on the HFI spare bolometers with a better control of the environmental conditions with respect to the in-flight data. We have shown that the dominant part of glitches observed in the data comes from the impact of cosmic rays in the silicon die frame supporting the micro-machined bolometric detectors propagating energy mainly by ballistic phonons and by thermal diffusion. The implications of these results for future satellite missions will be discussed.     

Impact of Associated Gases on Equilibrium and Transport Properties of a \mathrm{CO}_{2} Stream: Molecular Simulation and Experimental Studies

During the various carbon dioxide capture and storage (CCS) stages, an accurate knowledge of thermodynamic properties of \(\mathrm{CO}_{2}\) streams is required for the correct sizing of plant units. The injected \(\mathrm{CO}_{2}\) streams are not pure and often contain small amounts of associated gaseous components such as \(\mathrm{O}_{2}, \mathrm{N}_{2}\) , \(\mathrm{SO}_{x}, \mathrm{NO}_{x}\) , noble gases, etc. In this work, the thermodynamic behavior and transport properties of some \(\mathrm{CO}_{2}\) -rich mixtures have been investigated using both experimental approaches and molecular simulation techniques such as Monte Carlo and molecular dynamics simulations. Using force fields available in the literature, we have validated the capability of molecular simulation techniques in predicting properties for pure compounds, binary mixtures, as well as multicomponent mixtures. These validations were performed on the basis of experimental data taken from the literature and the acquisition of new experimental data. As experimental data and simulation results were in good agreement, we proposed the use of simulation techniques to generate new pseudo-experimental data and to study the impact of associated gases on the properties of \(\mathrm{CO}_{2}\) streams. For instance, for a mixture containing 92.0 mol% of \(\mathrm{CO}_{2}\) , 4.0 mol% of \(\mathrm{O}_{2}\) , 3.7 mol% of Ar, and 0.3 mol% of \(\mathrm{N}_{2}\) , we have shown that the presence of associated gases leads to a decrease of 14 % and 21 % of the dense phase density and viscosity, respectively, as compared to pure \(\mathrm{CO}_{2}\) properties.     

Direct LED writing of submicron resist patterns： Towards the fabrication of individually-addressable InGaN sub-micron stripe-shaped LED arrays

Submicron stripe-shaped InGaN light-emitting diode （LED） arrays with individually addressable capabilities are demonstrated. The critical submicron- stripe metallic electrodes, which define the emission pattern, are formed by direct LED writing in a mask-free manner. The individually addressable submicron-stripe LEDs show excellent performance in terms of their electrical characteristics （with typical turn-on voltage of 3 V, operational stability and power output up to 28 ~W at 3 mA）. Unlike conventional broad-sized LEDs, the efficiency droop of the submicron-stripe LED is significantly suppressed--in fact, there is no efficiency droop for current densities up to 100 A/cm^2. Furthermore, the submicron-stripe LED shows a lower temperature-dependent shift of the emission wavelength. The lateral emission width is increased with increasing injection current, resulting in a wider lateral emission size than the metallic submicron-stripe electrode. The underlying physics of these phenomena are analysed. Such submicron-stripe LED arrays open up promising applications in nanophotonics and bio-sensing.     

Investigation of electrostrictive polymer efficiency for mechanical energy harvesting

The purpose of this paper is to propose new means for harvesting energy using electrostrictive polymers. Recent trends in energy conversion mechanisms have demonstrated the abilities of electrostrictive polymers for converting mechanical vibrations into electricity. In particular, such materials present advantageous features such as a high productivity, high flexibility, and ease of processing; hence, the application of these materials for energy harvesting purposes has been of significant interest over the last few years. This paper discusses the development of a model that is able to predict the energy harvesting capabilities of an electrostrictive polymer. Moreover, the energy scavenging abilities of an electrostrictive composite composed of terpolymer poly(vinylidenefluoride-trofluoroethylene- chlorofluoroethylene) [P(VDF-TrFE-CFE)] filled with 1 vol% carbon black (C) is evaluated. Experimental measurements of the harvested power and current have been compared with the theoretical behavior predicted by the proposed model. A good agreement was observed between the two sets of data, which consequently validated the proposed modeling to optimize the choice of materials. It was also shown that the incorporation of nanofillers in P(VDF-TrFE-CFE) increased the harvested power.     

Analysis of ac-dc conversion for energy harvesting using an electrostrictive polymer P(VDF-TrFE-CFE)

Harvesting systems capable of transforming unused environmental energy into useful electrical energy have been extensively studied for the last two decades. The recent development of electrostrictive polymers has generated new opportunities for harvesting energy. The contribution of this study lies in the design and validation of electrostrictive polymer- based harvesters able to deliver dc output voltage to the load terminal, making the practical application of such material for self-powered devices much more realistic. Theoretical analysis supported by experimental investigations showed that an energy harvesting module with ac-to-dc conversion allows scavenging power up to 7 μW using a bias electric field of 10 V/μm and a transverse strain of 0.2%. This represents a power density of 280 μW/cm(3) at 100 Hz, which is much higher than the corresponding values of most piezo-based harvesters.     

Universal temperature model for shallow algal ponds provides improved accuracy

While temperature is fundamental to the design and optimal operation of shallow algal ponds, there is currently no temperature model universally applicable to these systems. This paper presents a model valid for any opaque water body of uniform temperature profile. This new universal model was tested against 1 year of experimental data collected from a wastewater treatment high rate algal pond. On the basis of 1 year of data collected every 15 min, the average errors of the predicted afternoon peak and predawn minimum were both only 1.3 °C and the average error between these extremes was just 1.2 °C. In order to demonstrate the improvement in accuracy gained, the expressions for heat fluxes used in nine prior temperature models were systematically substituted into the new universal model and evaluated against the experimental data. Errors in the peak and minimum temperatures increased by up to 2.1 and 3.2 °C, respectively, while the error between these extremes increased by up to 2.9 °C. In practical applications, these levels of inaccuracies could lead to an under/overestimation of the algal productivity and the evaporative water loss by approximately 40% and 300%, respectively.