Dynamic modeling and analysis of a shell-and-tube type gas-to-gas membrane humidifier for PEM fuel cell applications

A gas-to-gas humidifier using membranes is the preferred technology for external humidification of fuel cell reactant gases in mobile applications because no extra power supply is required and there are no moving parts. In particular, a shell and tube structure is compact, which allows its easier integration in a fuel cell vehicle.

This paper proposes a mathematical model for the humidifier using the principles of thermodynamics, including analysis of heat and mass transfer and of static and dynamic behaviors. Firstly, the heat and mass transfer behavior was simulated and the results compared with the experimental data. Secondly, the model was used to investigate the sensitivity of the geometric parameters and the effects of various operating conditions on performance. Finally, step responses of the humidifier at various flow rates were analyzed.     

Hierarchical spatial relation based on a contiguity graph

Autonomous agents traversing a natural space need to be knowledgeable of its space configuration. The existing space models in geographic information systems and robotics, however, deal with only the topological relations among numerous types of spatial relations. We aim to develop an enhanced space model that elaborates the spatial relations with respect to their relevant physical relations. Specifically, the spatial relations in a space configuration are further characterized with the gravitation as a potential factor to affect the space configuration. The resulting space model is capable of capturing an extended set of spatial relations over existing models such as a four‐intersection model. © 2005 Wiley Periodicals, Inc. Int J Int Syst 20: 867–892, 2005.     

Analysis of the glow curves obtained from LiF:Mg,Cu,Na,Si TL material using the general order kinetics model

Three-dimensional thermoluminescence (TL) spectra based on temperature, wavelength and intensity for newly developed LiF:Mg,Cu,Na,Si TL material at the Korea Atomic Energy Research Institute (KAERI) were measured and analysed. The glow curves were obtained by integration of luminescence intensity over all wavelengths at each temperature, and various trapping parameters related to the traps were determined by analysing these curves. A computerised glow curve deconvolution (CGCD) method which was based on the general order kinetics (GOK) model was used for the glow curve analysis. The glow curves of LiF:Mg,Cu,Na,Si TL material were deconvoluted to six isolated glow curves which have peak temperatures at 333, 374, 426, 466, 483 and 516 K. The main glow peak of peak temperature at 466 K had activation energy of 2.06 eV and a kinetic order of 1.05. This TL material was also found to have three recombination centres, 1.80 eV, 2.88 eV and 3.27 eV by analysis of the TL spectra.     

Neither dopamine nor dobutamine corrects mesenteric blood flow depression caused by positive end-expiratory pressure in a rat model of acute lung injury

OBJECTIVE: To determine if either dopamine or dobutamine would counteract the deleterious effect that positive end-expiratory pressure (PEEP) has on cardiac output and mesenteric blood flow in a rat model of acute lung injury. DESIGN: Prospective, randomized, controlled trial in a clinically relevant model of acute lung injury. SETTING: Microcirculation research laboratory. SUBJECTS: Male Sprague-Dawley rats. INTERVENTIONS: The animals were anesthetized with pentobarbital (30 mg/kg) by intraperitoneal injection. They underwent tracheostomy, jugular and femoral vein cannulation, femoral artery cannulation, carotid artery thermistor placement, and bowel preparation for in vivo video microscopy. Acute lung injury was created by administering 0.1 N hydrochloric acid (1 mL/kg) via the tracheostomy. Dopamine or dobutamine (2.5 or 12.5 microg/kg/min), followed by two intravenous fluid boluses, was administered to rats ventilated with 5, 10, 15, and 20 cm H2O of PEEP. MEASUREMENTS AND MAIN RESULTS: Mean arterial pressure, thermodilution cardiac output, mesenteric arteriolar diameter, and red blood cell velocity were measured and mesenteric blood flow was calculated. Cardiac output was depressed in rats exposed to 20 cm H2O of PEEP by 32+/-2%. The corresponding values for cardiac output depression at 20 cm H2O of PEEP in rats receiving 2.5 and 12.5 microg/kg/min of dopamine and 2.5 and 12.5 microg/kg/min of dobutamine were 31+/-1%, 21+/-1%, 29+/-0%, and 24+/-2%, respectively. Mesenteric blood flow was depressed in rats ventilated with 20 cm H2O of PEEP by 74+/-3%, while the corresponding values in rats exposed to 20 cm H2O of PEEP and receiving 2.5 or 12.5 microg/kg/min of dopamine or 2.5 or 12.5 microg/kg/min of dobutamine were 86+/-3%, 77+/-3%, 73+/-3%, and 66+/-3%, respectively. Fluid boluses did not correct the deficits in cardiac output or mesenteric blood flow caused by the combination of acute lung injury and PEEP. CONCLUSIONS: The higher doses of dopamine and dobutamine partially, but insignificantly, corrected the cardiac output depression caused by PEEP in a model of acute lung injury. Neither dose of dopamine nor dobutamine was able to improve PEEP-induced mesenteric blood flow depression.     

Chemokine receptors in HIV-1 and SIV infection

Glucose-6-phosphatase (G6Pase) activity and the rate of glucose cycling are increased in islets from animal models of Type II (non-insulin-dependent) diabetes mellitus. Glucocorticoid treatment further stimulates these processes and inhibits glucose-induced insulin release. To determine whether these effects result from a direct action of glucocorticoids on the beta-cells, we used isolated islets. The islets were from transgenic mice overexpressing the glucocorticoid receptor in their beta-cells to increase the cells' sensitivity to glucocorticoid. Islets from transgenic and non-transgenic control mice utilized and oxidized the same amount of glucose. In contrast, islet G6Pase activity was 70 % higher, glucose cycling was increased threefold and insulin release was 30 % lower in islets from transgenic mice. Hepatic G6Pase activity was the same in transgenic and control mice. Dexamethasone administration increased G6Pase activity and glucose cycling and decreased insulin release in both transgenic and control mouse islets. We conclude that glucocorticoids stimulate islet G6Pase activity and glucose cycling by acting directly on the beta-cell. That activity may be linked to the inhibition of insulin release.     

Combined salience based person re-identification

Human eye perceives an object as the entity with global information and local information. Human salience is distinctive local information in matching pedestrians across disjoint camera views, and matching on overall foreground guarantees reliable and robust identification. In this paper, we propose a strategy for the matching of mean salience to identify pedestrians. Also, we consider that person re-identification based on the local single directional matching suffers from the variations of pose, illumination and overlapping, and propose a global bi-directional matching to solve the challenging problems of person re-identification. Furthermore, our matching of mean salience is tightly combined with the global bi-directional matching. Patch matching is utilized to handle the misalignment problem in pedestrian images. We test our feature and matching approaches in person re-identification scenario. Experimental results demonstrate that the mean salience and the global bi-directional matching have promising discriminative capability in comparison with other ones.     

The effect of phosphate treatment on nickel dispersion on MCM-41 mesoporous material

The incorporation of nickel into mesoporous molecular sieves MCM-41 was carried out. Ni-PO/MCM41 and Ni-C1/MCM41 were prepared by using Ni(II) acetate solution adjusted to pH=2.5 with phosphoric acid and hydrochloric acid, respectively, by the incipient wetness method. Photoacoustic spectroscopy (PAS) was used to study the local environments of Ni(II) incorporated into mesopores. The PAS of as-prepared Ni/MCM41, Ni-Cl/MCM41, and Ni-PO/MCM41 with Ni(II) acetate solution exhibits two bands of λ_max around 400 nm and 750 nm, which could be assigned to the³A_2g→³T_lg(F) and the³A_2g→³T_lg(P) transition of octahedral Ni(II) species. After calcination, Ni ion within Ni-PO/MCM41 dispersed atomically onto the surface of MCM-41 channel as an octahedral species without the transformation to nickel oxide phase, while Ni ion within Ni-Cl/MCM41 and Ni/MCM41 transformed to nickel oxide phase. It may be attributed to the fact that each Ni ion is separated by the phosphate grafted to surface silanol group. The effects of phosphoric acid on the dispersity of Ni ion within MCM-41 have been investigated using³¹P and²⁹Si MAS NMR spectroscopy and X-ray photoelectron spectroscopy.     

Failure analysis of a boiler tube in USC coal power plant

This paper presents failure analysis of final superheater tube in ultra-supercritical (USC) coal power plant. Visual inspection was performed to find out the characteristics of fracture of the as-received material. And the micro-structural changes such as grain growth and carbide coarsening was examined by scanning electron microscope. Detailed microscopic studies were made to find out the behavior of the scale exfoliation on the waterside of tubes. From those investigations, the creep rupture may be caused by the softened structure induced by carbide coarsening and accelerated by the metal temperature increase by the impediment of heat transfer due to voids.