Freezing of water in a polymer electrolyte membrane fuel cell ͑PEMFC͒ may cause severe problems in driving a fuel cell vehicle during the winter time. Characteristics of PEMFC which suffered low temperatures below zero celsius were examined with thermal cycles during which the temperature of the environment chamber was cycled from 80 to Ϫ10°C. With the thermal cycles, the cell performance was degraded due to the phase transformation and volume changes of water. Effects of freezing of water in a PEMFC on the electrode structure and polarization resistance were examined by Brunauer, Emmett, Teller analysis, cyclic voltammetry, and ac impedance spectroscopy.

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In this study, we report a neo-conceptive three-dimensionally (3D) crossing manifold micromixer (CMM) embedded in microchannel. Fabricated by sequential processes of photolithography and two photon absorption stereolithography, this leads to a microfluidic system with a built-in micromixer in a site controlled manner. The effectiveness of CMM is investigated numerically and experimentally. Through the numerical simulation, it is estimated that a high mixing ratio of 90% can be obtained even in a channel length shorter than five times the channel width. This compares well with the conventional passive type of micromixers that have a gradual increase in mixing efficiency with the length of the channel. Furthermore, the mixing performance of the realized CMM built-in microchannel is observed by confocal microscopy.

c Hyundai Motor Company, Fuel Cell Vehicle Team, Korea For the mobile application, performance of polymer electrolyte membrane fuel cells ͑PEMFCs͒ should be maintained with being exposed to subzero temperatures in the winter time. To simulate the situation, a PEMFC was operated at 80°C, stopped, cooled to and kept at Ϫ10°C for 1 h, and heated to 80°C for the next operation. With the thermal cycle, cell performance was measured and found to degrade at a degradation rate of 2.3% based on current density at a cell voltage of 0.6 V. The degradation was attributed to freezing of water that was produced during operation and remained in the PEMFC after the operation. To prevent the performance degradation, water was removed from the PEMFC by supplying dry gases or an antifreeze solution to the PEMFC before the cell temperature fell to below 0°C. By using the gas-purging and the solution-purging method designed in this work, the performance degradation rate was successfully reduced to 0.06 and Ϫ0.47%, respectively.The polymer electrolyte membrane fuel cell ͑PEMFC͒ is a promising alternative power source for electric vehicles in the near future. One of the challenges that the PEMFC faces is to maintain its integrity when outdoor temperatures are below 0°C in the winter. During operation of a PEMFC, water is produced at the cathode side by the electrochemical reaction and, in most cases, is supplied through the reactant gases to keep the membrane hydrated. 1,2 If operation of the PEMFC is stopped and outdoor temperature is below 0°C, the water remaining in the PEMFC may freeze with expanding its volume by about 9%, because the density of water and ice at 0°C is 0.9998 and 0.9168 g/cm 3 , respectively. 3 Then when the PEMFC is restarted, ice melts into water again, reducing its volume. Such a repetitive volume change of water occurring inside the PEMFC may degrade cell performance.Recently, effects of water freezing on the performance of PEMFCs have been studied. 4,5 Kagami et al. 4 started a PEMFC at temperatures below 0°C with feeding dry reactant gases and measured cell voltage at various constant current densities. Except at very low current densities, the cell voltage decreased quickly. The higher the current density was, the steeper the decrease in the cell voltage was due to increase in water and ice formation rate. Based on the results, they suggested that for self-starting of PEMFCs without external heating, the start-up temperature of a PEMFC should be above Ϫ5°C. Cho et al. 5 investigated effects of repetitive freezing and melting of water in PEMFCs on their characteristics. To simulate the situation of the mobile application, they operated a PEMFC at an operating temperature of 80°C, stopped, cooled, and kept it at Ϫ10°C for 1 h, and heated it to 80°C again for the next operation. They reported that with repetition of the thermal cycle, performance of the PEMFC degraded due to deformation of the catalytic layers accompanied by a decrease in electrochemical active surface area and an increase in charge-transfe...

For the timely treatment of patients with infections in bloodstream and cerebrospinal fluid, a rapid antimicrobial susceptibility test (AST) is urgently needed. Here, we describe a direct and rapid antimicrobial susceptibility testing (dRAST) system, which can determine the antimicrobial susceptibility of bacteria from a positive blood culture bottle (PBCB) in six hours. The positive blood culture sample is directly mixed with agarose and inoculated into a micropatterned plastic microchip with lyophilized antibiotic agents. Using microscopic detection of bacterial colony formation in agarose, the total time to result from a PBCB for dRAST was only six hours for a wide range of bacterial concentrations in PBCBs. The results from the dRAST system were consistent with the results from a standard AST, broth microdilution test. In tests of clinical isolates (n = 206) composed of 16 Gram-negative species and seven Gram-positive species, the dRAST system was accurate compared to the standard broth microdilution test, with rates of 91.11% (2613/2868) categorical agreement, 6.69% (192/2868) minor error, 2.72% (50/1837) major error and 1.45% (13/896) very major error. Thus, the dRAST system can be used to rapidly identify appropriate antimicrobial agents for the treatment of blood stream infection (BSI) and antibiotic-resistant strain infections.

Experimental studies on the fabrication of sub-30-nm nanofibers using two-photon initiated photopolymerization ͑TPP͒ have been carried out. To generate nanofibers at the interior region of microstructures, a photopolymerization method involving a long laser-exposure technique ͑LET͒ is proposed. A multitude of nanofibers with a notably high resolution ͑about 22 nm͒ in TPP were produced using the LET. Furthermore, it is also demonstrated that thin interconnecting networks were created regularly in a weakly polymerized region existing around the boundary of a densely polymerized voxel, allowing for the creation of various embossing patterns. By controlling the distance between adjacent voxels or lines, a selective generation of nanofibers in a local area is possible, which leads to the fabrication of high-functional filters and mixers. Embossing patterns and microchannels including nanofibers inside were fabricated by the LET so as to demonstrate the practical feasibility of this approach. These sub-30-nm nanofibers may find meaningful applications such as biofilters, mixers, and photon emitters in diverse research fields.

Without appropriate treatment, lignocellulosic biomass is not suitable to be fed into existing combustion systems because of its high moisture content, low bulk energy density and difficulties in transport, handling and storage. The aim of this study was to investigate the effects of torrefaction treatment on the weight loss and energy properties of fast growing species in Malaysia (Acacia spp., and Macaranga spp.) as well as oil palm biomass (oil palm trunk and empty fruit bunch). The lignocellulosic biomass was torrefied at three different temperatures 200, 250 and 300 °C for 15, 30 and 45 min. Response surface methodology was used for optimization of torrefaction conditions, so that biofuel of high energy density, maximized energy properties and minimum weight loss could be manufactured. The analyses showed that increase in heating values was affected by treatment severity (cumulated effect of temperature and time). Our results clearly demonstrated an increased degradation of the material due to the combined effects of temperature and treatment time. While the reaction time had less impact on the energy density of torrefied biomass, the effect of reaction temperature was considerably stronger under the torrefaction conditions used in this study. It was demonstrated that each biomass type had its own unique set of operating conditions to achieve the same product quality. The optimized torrefaction conditions were verified empirically and applicability of the model was confirmed. The torrefied biomass occurred more suitable than raw biomass in terms of calorific value, physical and chemical properties. The results of this study could be used as a guide for the production of high energy density solid biofuel from lignocellulosic biomass available in Malaysia.

In several recent clinical trials on cardiac surgery patients, remote ischaemic preconditioning (RIPC) showed a powerful myocardial protective effect. However, the effect of RIPC has not been studied in patients undergoing off-pump coronary artery bypass graft surgery. We evaluated whether RIPC could induce myocardial protection in off-pump coronary artery bypass graft surgery patients. Patients undergoing elective off-pump coronary artery bypass graft surgery were randomly allocated to the RIPC (n=65) or control group (n=65). After induction of anaesthesia, RIPC was induced by four cycles of five-minute ischaemia and reperfusion on the upper limb using a pneumatic cuff. Anaesthesia was maintained with sevoflurane, remifentanil and vecuronium. Myocardial injury was assessed by troponin I before surgery and 1, 6, 12, 24, 48 and 72 hours after surgery. There were no statistical differences in troponin I levels between RIPC and control groups (P=0.172). Although RIPC reduced the total amount of troponin I (area under the curve of troponin increase) by 26%, it did not reach statistical significance (RIPC group 53.2±72.9 hours.ng/ml vs control group 67.4±97.7 hours.ng/ml, P=0.281). In this study, RIPC by upper limb ischaemia reduced the postoperative myocardial enzyme elevation in offpump coronary artery bypass graft surgery patients, but this did not reach statistical significance. Further study with a larger number of patients may be needed to fully evaluate the clinical effect of RIPC in off-pump coronary artery bypass graft surgery patients.