bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the anti‐resorptive ability of an experimental acetazolamide paste for the treatment of late replanted teeth: a study in rats
Authors: Mori Graziela Garrido , Poi Wilson Roberto , Castilho Lithiene Ribeiro
Published: March 2012

Abstract –  When late replantation is performed, the root surface and root canal should be treated. Notwithstanding failures still occur, because of the high rates of root resorption, evidencing the need to search for substances that may inhibit root resorption. The acetazolamide is a known anti‐resorptive agent, and its use as root canal dressing may increase the success rates in the treatment of root resorption. Therefore, this study evaluated the effect of an acetazolamide paste used as root canal dressing in late replanted teeth. The study was conducted on 24 maxillary right incisors of rats, which were avulsed and divided in two groups. In group I, the teeth were kept dry for 30 min, had their root surfaces rubbed with a blade, and were treated with 2% sodium fluoride at pH 5.5 for 20 min; the root canals were instrumented and filled with acetazolamide paste; and then the teeth were replanted. In group II, the treatment was similar to group I, except for the root canal dressing, with utilization of calcium hydroxide in group II. At 15 and 60 days after replantation, the animals were killed and the specimens were processed in a histotechnical laboratory for microscopic and morphometric analysis. The results demonstrated the ability of both intracanal substances to limit root resorption, yet they were unable to completely inhibit the root resorption. Replacement resorption lacunae were present in greater proportion in group II, at 60 days. It was concluded that the acetazolamide paste was effective to limit the root resorption, being more effective in limiting the replacement resorption compared with calcium hydroxide.
Linking variability in brain chemistry and circuit function through multimodal human neuroimaging
Authors: Fisher P. M. , Hariri A. R.
Published: March 2012

Identifying neurobiological mechanisms mediating the emergence of individual differences in behavior is critical for advancing our understanding of relative risk for psychopathology. Neuroreceptor positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) can be used to assay in vivo regional brain chemistry and function, respectively. Typically, these neuroimaging modalities are implemented independently despite the capacity for integrated data sets to offer unique insight into molecular mechanisms associated with brain function. Through examples from the serotonin and dopamine system and its effects on threat‐ and reward‐related brain function, we review evidence for how such a multimodal neuroimaging strategy can be successfully implemented. Furthermore, we discuss how multimodal PET‐fMRI can be integrated with techniques such as imaging genetics, pharmacological challenge paradigms and gene–environment interaction models to more completely map biological pathways mediating individual differences in behavior and related risk for psychopathology and inform the development of novel therapeutic targets.
Estimation of herbaceous biomass from species composition and cover
Authors: Axmanová Irena , Tichý Lubomír , Fajmonová Zuzana , Hájková Petra , Hettenbergerová Eva , Li Ching‐Feng , Merunková Kristina , Nejezchlebová Martina , Otýpková Zdenka , Vymazalová Marie , Zelený David
Published: March 2012

Questions

Biomass is an important ecological property, but its measurement is destructive and time‐consuming and therefore generally missing for historical vegetation plots. Here we propose and test indirect estimation of herbaceous biomass using models based on easily obtainable variables, namely plant height and cover. We compare these models with Ellenberg indicator values for nutrients (EIVs Nutrients), which are sometimes used as an alternative measure of productivity.

Location

Czech Republic, western Slovakia.

Methods

Above‐ground biomass (dry weight; g·m−2) was regressed against the following explanatory variables: (1) Cover E1, total percentage cover of the herb layer visually estimated in the field; (2) Biomass estimate‐raw, ‐adjusted and ‐median, calculated from plant covers and heights (according to a local flora); and (3) mean EIVs Nutrients calculated per plot. For the analyses, we used four data sets containing a total of 469 plots from different vegetation types: ‘Wet meadows’, ‘Dry grasslands’, ‘Fen–dry grassland transects’ and ‘Forest herb layer’. To test the applicability of different biomass estimates we chose an example of a species richness–productivity relationship in the ‘Wet meadows’ data set and describe differences in resulting patterns.

Results

Both cover of herb layer and calculated ‘biomass volumes’ were more accurate in predicting biomass dry weight than EIVs Nutrients. The best results were obtained from the Biomass estimate‐median model that combines median stand height and total cover of the herb layer. Cover E1 showed relatively tight correlations with biomass, particularly in sparse vegetation, but was a rather poor predictor when cover values were high. This was especially noticeable in application of the Cover E1 model in analysis of the species richness–productivity relationship.

Conclusions

In contrast to biomass, cover of the herb layer has a fixed upper limit (100%), which may lead to misinterpretations in dense, structurally diverse vegetation. Most promising is the Biomass estimate‐median method, which can be applied both to already sampled plots by calculating median height from average species heights according to local floras and to newly sampled plots using the median of plant heights measured in the field. Therefore, we propose it as a rapid, non‐destructive alternative to biomass harvest.
Substrate variations that affect the nucleic acid clamp activity of reverse transcriptases
Authors: Oz‐Gleenberg Iris , Herzig Eytan , Voronin Nickolay , Hizi Amnon
Published: March 2012

We have recently shown that reverse transcriptases (RTs) perform template switches when there is a very short (two‐nucleotide) complementarity between the 3′ ends of the primer (donor) strand and the DNA or RNA template acceptor strands [Oz‐Gleenberg et al. (2011) Nucleic Acids Res39, 1042–1053]. These dinucleotide pairs are stabilized by RTs that are capable of ‘clamping’ together the otherwise unstable duplexes. This RT‐driven stabilization of the micro‐homology sequence promotes efficient DNA synthesis. In the present study, we have examined several factors associated with the sequence and structure of the DNA substrate that are critical for the clamp activity of RTs from human immunodeficiency virus type 1 (HIV‐1), murine leukemia virus (MLV), bovine immunodeficiency virus (BIV) and the long terminal repeat retrotransposon Tf1. The parameters studied were the minimal complementarity length between the primer and functional template termini that sustains stable clamps, the effects of gaps between the two template strands on the clamp activity of the tested RTs, the effects of template end phosphorylations on the RT‐associated clamp activities, and clamp activity with a long ‘hairpin’ double‐stranded primer comprising both the primer and the complementary non‐functional template strands. The results show that the substrate conditions for clamp activity of HIV‐1 and MLV RTs are more stringent, while Tf1 and BIV RTs show clamp activity under less rigorous substrate conditions. These differences shed light on the dissimilarities in catalytic activities of RTs, and suggest that clamp activity may be a potential new target for anti‐retroviral drugs.
Perioperative Outcomes of Laparoscopic Radical Nephrectomy for Renal Cell Carcinoma in Patients With Dialysis‐Dependent End‐Stage Renal Disease
Authors: Yamashita Kaori , Ito Fumio , Nakazawa Hayakazu
Published: March 2012

The aims of this study were: (i) to analyze the perioperative outcomes of laparoscopic radical nephrectomy for renal cell carcinoma in patients with dialysis‐dependent end‐stage renal disease and (ii) to reveal perioperative management problems that are unique to these patients. Between June 2004 and June 2011, laparoscopic radical nephrectomy was performed in 39 patients who had renal cell carcinoma and dialysis‐dependent end‐stage renal disease. The operative outcomes of these patients were compared with the operative outcomes of 104 non‐end‐stage renal disease patients with sporadic renal cell carcinoma who underwent laparoscopic radical nephrectomy during the same period. Laparoscopic surgery was completed in thirty‐eight end‐stage renal disease patients. One patient was converted to open surgery because of an intraoperative injury to the inferior vena cava. This patient was excluded from the analysis. The mean operative time was 240 min; blood loss, 157 mL; and postoperative hospital stay, 9.6 days. Postoperative complications were observed in six patients, as follows: retroperitoneal hematoma and abscess in one patient, thrombosis of the arteriovenous fistula in three patients, pneumonia in one patient, and gastrointestinal bleeding in one patient. Eleven patients required blood transfusions. There was no significant difference between the end‐stage renal disease patients and the non‐end‐stage renal disease patients in the mean operative time or the amount of blood loss. In conclusion, laparoscopic radical nephrectomy is feasible for dialysis‐dependent end‐stage renal disease patients, as well as for non‐end‐stage renal disease patients; however, end‐stage renal disease patients may have a higher probability of experiencing non‐life‐threatening complications.
CARE/CEASA Roundtable on: Liquidity and Capital Management
Authors: Calomiris Charles , Campello Murillo , Lang Mark , Vasvari Florin , Richardson Scott
Published: March 2012

Five distinguished banking and accounting scholars explore the role of liquidity at not only the “macro” level of the economy, but also at the level of individual companies. The first of the four main speakers, who is the author of the preceding article, restates his argument that the stability of financial systems can be increased by directing bank regulators and executives to find the optimal combination of liquidity and capital requirements. The second of the four speakers shifts the focus to liquidity management by non‐financial companies, with particular emphasis on their use of lines of credit and their role in helping companies weather the financial crisis. The third speaker places liquidity in the context of capital markets, and presents suggestive evidence that improvements in corporate disclosure and transparency have beneficial effects on both the level and volatility of liquidity in those markets. The panel is rounded out by a discussion of liquidity in corporate bond markets and the proposal of a new way to measure such liquidity.
GEOCHEMISTRY OF CRUDE OILS, SEEPAGE OILS AND SOURCE ROCKS FROM BELIZE AND GUATEMALA: INDICATIONS OF CARBONATE‐SOURCED PETROLEUM SYSTEMS
Authors: Petersen H.I. , Holland B. , Nytoft H.P. , Cho A. , Piasecki S. , de la Cruz J. , Cornec J.H.
Published: March 2012

This study reviews the stratigraphy and the poorly documented petroleum geology of the Belize‐Guatemala area in northern Central America. Guatemala is divided by the east‐west trending La Libertad arch into the North and South Petén Basins. The arch is the westward continuation of the Maya Mountains fault block in central Belize which separates the Corozal Basin in northern Belize from the Belize Basin to the south. Numerous petroleum seeps have been reported in both of these basins. Small‐scale oil production takes place in the Corozal Basin and the North and South Petén Basins. For this study, samples of crude oil, seepage oil and potential source rocks were collected from both countries and were investigated by organic geochemical analyses and microscopy. The oil samples consisted of non‐biodegraded crude oils and slightly to severely biodegraded seepage oils, both of which were generated from source rocks with similar thermal maturities. The crude oils were generated from marine carbonate source rocks and could be divided into three groups:

Group 1 oils come from the North Petén Basin (Guatemala) and the western part of the Corozal Basin (Belize), and have a typical carbonate‐sourced geochemical composition. The oils correlate with extracts of organic‐rich limestones assigned to the Upper Cretaceous “Xan horizon” in the Xan oilfield in the North Petén Basin. The oils were generated from a single source facies in the North Petén Basin, but were charged from two different sub‐basins.

Group 2 oils comprise crudes from the South Petén Basin. They have characteristics typical of carbonate‐sourced oils, but these characteristics are less pronounced than those of Group 1 oils. A mixed marine/lacustrine source facies deposited under strongly reducing conditions in a local kitchen area is inferred.

Group 3 oils come from the Corozal Basin, Belize. A carbonate but also a more “shaly” source rock composition for these oils is inferred. A severely biodegraded seepage oil from Belmopan, the capital of Belize, resembles a nearby crude oil. The eastern sub‐basin in the North Petén Basin may potentially be the kitchen area for these oils, and for the seepage oils found in the western part of the Corozal Basin.

The seepage oils from the Corozal and Belize Basins are moderately to severely biodegraded and were generated from carbonate source rocks. Some of the seepage oils have identical C27–29 sterane distributions to the Group 2 oils, but “biodegradation insensitive” biomarker ratios show that the seepage oils can be divided into separate sub‐groups. Severely and slightly biodegraded seepage oils in the Belize Basin were probably almost identical prior to biodegradation.

Lower Cretaceous limestones from the Belize Basin have petroleum generation potential, but the samples are immature. The kitchen for the seepage oils in the Belize Basin remains unknown.
POTENTIAL PETROLEUM SOURCE ROCKS IN THE TERMIT BASIN, NIGER
Authors: Harouna M. , Philp R.P.
Published: March 2012

Potential source rocks from wells in the Termit Basin, eastern Republic of Niger, have been analysed using standard organic geochemical techniques. Samples included organic‐rich shales of Oligocene, Eocene, Paleocene, Maastrichtian, Campanian and Santonian ages. TOC contents of up to 20.26%, Rock Eval S2 values of up to 55.35 mg HC/g rock and HI values of up to 562 mg HC/g TOC suggest that most of the samples analysed have significant oil‐generating potential. Kerogen is predominantly Types II, III and II–III.

Biomarker distributions were determined for selected samples. Gas chromatograms are characterized by a predominance of C17– C21 and C27– C29 n‐alkanes. Hopane distributions are characterized by 22S/(22S+22R) ratios for C32 homohopanes ranging from 0.31 to 0.59. Gammacerane was present in Maastrichtian‐Campanian and Santonian samples. Sterane distributions are dominated by C29 steranes which are higher than C27 and C28 homologues.

Biomarker characteristics were combined with other geochemical parameters to interpret the oil‐generating potential of the samples, their probable depositional environments and their thermal maturity. Results indicate that the samples were in general deposited in marine to lacustrine environments and contain varying amounts of higher plant or bacterial organic matter. Thermal maturity varies from immature to the main oil generation phase. The results of this study will contribute to an improved understanding of the origin of the hydrocarbons which have been discovered in Niger, Chad and other rift basins in the Central African Rift System.
Phosphorylation of epidermal growth factor receptor and chromosome 7 polysomy in gastric adenocarcinoma
Authors: ZHANG Fan , TANG Jian Min , WANG Li , SHEN Jing Ying , ZHENG Lin , WU Ping Ping , ZHANG Mei , YAN Zhao Wen
Published: March 2012

OBJECTIVE:  To investigate the phosphorylation of epidermal growth factor receptor (EGFR) and its potentially associated chromosomal aberrations in gastric adenocarcinoma.

METHODS:  Phosphorylated EGFR (pEGFR) was detected by immunohistochemistry on 145 specimens including 60 tumoral, 60 non‐tumoral, 12 tumor‐adjacent intramucosal dysplasia from patients with gastric adenocarcinoma and 13 mucosae from cancer‐free patients. EGFR gene amplification and chromosome 7 (Chr‐7) polysomy were detected by fluorescence in situ hybridization.

RESULTS:  Positivity of pEGFR was found in 50 tumoral (83.3%) and 42 non‐tumoral specimens (70.0%). There was an association between tumoral and non‐tumoral zones on immunostains of pEGFR (r = 0.353, P = 0.006). Nuclear pEGFR usually presented in mucosae with Helicobacter pylori infection, stromal reaction or vascular invasion. Cytoplasmic pEGFR was correlated with local cancer extension (r = 0.337, P = 0.014) and inversely related with gastrokine 2, which had been previously detected in the same specimens. Eleven intramucosal dysplastic specimens were also positive for pEGFR while 13 mucosae from cancer‐free patients were all negative. No EGFR gene amplification was observed. However, seven tumor specimens showed Chr‐7 polysomy (11.7%) in which 5 were strongly positive for pEGFR.

CONCLUSIONS:  EGFR phosphorylation may be one of the mechanisms that promote tumor initiation and expansion in gastric adenocarcinoma. Detection of pEGFR with analysis of its nuclear or cytoplasmic patterns could be clinicopathologically valuable. Chr‐7 polysomy may partially contribute to EGFR activation in gastric adenocarcinoma, although its role does not predominate.
Recent developments in gastroesophageal reflux disease and Barrett's esophagus: ANNO 2012
Authors: TYTGAT Guido NJ
Published: March 2012

The incidence of gastroesophageal reflux disease (GERD) and esophageal columnar metaplasia is rising worldwide. Both mechanical and functional factors perturb the double sphincter barrier at the esophagogastric junction (EGJ). Discovery of the acid pocket is fundamental in understanding postprandial acid reflux. Adding impedencemetry to pH measurements allows detection of non‐acid or weakly acidic reflux. Histologic and endoscopic injury of the squamous mucosa rises from dilation of the intercellular spaces, papillary extension, accentuated intrapapillary looping, red streaks, erosive tissue loss, etc., graded with the Los Angeles system. Seventy percent of patients have no recognizable abnormalities (non‐erosive or neGERD). Treatment of GERD mainly relates to the control of acid secretion but a revival of alginate/antacid obliterating the acid pocket is to be expected. Weaker heartburn control in neGERD is a misnomer because most studies included patients with no evidence of reflux disease. Traditional (delayed‐release) proton pump inhibitors (PPIs) are powerful suppressors of acid secretion but do have limitations such as gradual build up of acid control, weak control of nocturnal acid recovery, possibility of rebound, occasional need for dose escalation, etc.

Barrett's esophagus (BE) is endoscopically diagnosed also in the absence of intestinal metaplasia. A prerequisite is the precise location of the EGJ (proximal end of gastric folds, esophageal sphincter pinch, distal extent of palisade vessels). BE is graded with the Prague C & M system. Barrett's cancer develops usually via low‐grade and high‐grade dysplasia. Endoscopic examination may indicate suspicious areas, amenable for targeted biopsy. Otherwise, four quadrant biopsies are obtained when searching for neoplasia. Low‐grade dysplasia, especially when it is multifocal and p53 positive, high‐grade dysplasia and mucosal cancer should be treated with endoscopic resection of the target area, followed by radiofrequency ablation of the adjacent non‐neoplastic columnar mucosa, followed with powerful acid suppressant therapy. The long‐term results of the combination of resection and ablation are exiting and at least comparable to surgical resection.
Non‐inflammatory centrilobular sinusoidal fibrosis in pediatric liver transplant recipients under tacrolimus withdrawal
Authors: Egawa Hiroto , Miyagawa‐Hayashino Aya , Haga Hironori , Teramukai Satoshi , Yoshizawa Atsushi , Ogawa Kohei , Ogura Yasuhiro , Okamoto Shinya , Kaido Toshimi , Uemoto Shinji
Published: March 2012

Aim:  We hypothesized that non‐inflammatory central sinusoidal fibrosis (NICSF) is a sign of inadequate immunosuppression in children after living‐donor liver transplantation.

Methods:  In study 1, liver biopsy specimens of 158 patients who had undergone liver transplantation 10 years before or earlier were examined to study the relationship between NICSF and tacrolimus withdrawal. In study 2, tacrolimus was resumed in 18 patients with NICSF in follow‐up biopsies after tacrolimus withdrawal and the subsequent histological changes were analyzed.

Results:  In study 1, after excluding 95 patients with ongoing vascular, biliary and immunological complications, 47 of 63 patients (75%) had NICSF and significant (P = 0.0285) contributing factors were found to be episodes of tacrolimus withdrawal. In study 2, during withdrawal, tacrolimus administration had been discontinued in nine, reduced to once per month in three, twice per month in two, once a week in two and twice a week in two patients, and then finally resumed to daily administration in all. NICSF was scored as 4 in one, 3 in seven, 2 in four and 1 in six patients using modified Dixon's criteria (score, 0–4). After resumption, NICSF was improved in six, unchanged in 11 and aggravated in one patient. C4d deposition was improved in all NICSF‐improved patients. Incidence of positive C4d prior to resumption was significantly greater in improved patients than non‐improved patients (P = 0.0245).

Conclusion:  NICSF might be an indicator of inadequate immunosuppression in long‐term followed recipients and its mechanism may be due to immune reactions including humoral immunity.
Elimination half‐life of intravenously administered equine cardiac troponin I in healthy ponies
Authors: KRAUS M. S. , KAUFER B. B. , DAMIANI A. , OSTERRIEDER N. , RISHNIW M. , SCHWARK W. , GELZER A. R. , DIVERS T. J.
Published: March 2012

Reasons for performing study: To date, no information is available on the true biological elimination half‐life (T1/2) of cardiac troponin I (cTnI) in the equine species. Such data are required to better evaluate the optimal time to acquire the cTnI sample following acute myocardial injury.

Objective: To determine the T1/2 of equine cTnI.

Methods: Four healthy ponies received i.v. injections of recombinant equine cTnI. Plasma cTnI concentrations were measured with a point‐of‐care cTnI analyser at multiple time points after injection. Standard pharmacokinetic analysis was performed to establish the T1/2 of cTnI.

Results: The average T1/2 of cTnI was determined to be 0.47 h using a single rate elimination model.

Conclusion: The elimination of recombinant equine cTnI following i.v. administration is very rapid. Establishing the T1/2 of troponin provides critical information in understanding the clinical application of this cardiac biomarker in equine practice.
Left ventricular mechanics in humans with high aerobic fitness: adaptation independent of structural remodelling, arterial haemodynamics and heart rate
Authors: Stöhr Eric J. , McDonnell Barry , Thompson Jane , Stone Keeron , Bull Tom , Houston Rory , Cockcroft John , Shave Rob
Published: March 2012

Key points 

During cardiac contraction, left ventricular (LV) mechanics play an important role in equalising transmural fibre stress and ensuring efficient ejection of blood.

The factors responsible for altered LV mechanics in humans with high aerobic exercise capacity are unknown but are believed to be related to changes in LV structure or heart rate.

We performed a comprehensive assessment of LV mechanics and cardiovascular function at rest and during dynamic exercise in individuals with moderate and high aerobic exercise capacity.

Our novel data indicate that there is no direct association between altered LV mechanics in humans with high aerobic fitness and classic indicators of cardiovascular adaptation.

The findings provide evidence of a previously unknown type of physiological LV adaptation that may have important implications for exercise training in various healthy and diseased populations.
Effects of chemostimuli on [Ca2+]i responses of rat aortic body type I cells and endogenous local neurons: comparison with carotid body cells
Authors: Piskuric Nikol A. , Nurse Colin A.
Published: March 2012

Key points 

Mammalian aortic bodies (ABs) are putative peripheral chemoreceptor cells presumed to monitor the oxygen content of arterial blood, although their direct chemosensitivity has never been previously demonstrated at the cellular level.

We used Ca2+ imaging to show for the first time that a variety of stimuli, including hypoxia, isohydric and acidic hypercapnia, and isocapnic acidosis, caused increases in cytosolic [Ca2+] in AB chemoreceptor cells.

We also showed that some local neurons, known to be uniquely associated with these AB paraganglia in situ, generated robust [Ca2+]i responses to these chemostimuli, suggesting that they may subserve a sensory function.

These results will help us better understand how AB cells sense the composition of the blood in their local environment near the heart, and how they communicate with sensory neurons to initiate homeostatic reflexes during situations of low oxygen supply, like anaemia.
The Kinetics Effect in SOFCs on Heat and Mass Transfer Limitations: Interparticle, Interphase and Intraparticle Transport
Authors: Paradis Hedvig , Andersson Martin , Yuan Jinliang , Sunde´n Bengt
Published: March 2012

The transport processes in the porous, micro-structured electrodes are one of the least understood areas of research of the solid oxide fuel cell (SOFC). To enhance the knowledge of the transport process’ impact on the performance in the electrodes, the micro-structure needs to be modeled in detail. But at these smaller scales, it can be both cost and time saving to first conclude at which scales, the limiting action on the transport processes occurs. This study investigates the limiting effect of the kinetic parameters’ on the heat and mass transfer at interparticle, interphase and intraparticle transport level. The internal reaction and the electrochemical reaction rates are studied at three levels in the microscopic range or even smaller. At the intraparticle level the effect of temperature distribution, i.e., heat transfer, within a catalyst particle is often less limiting than the internal mass diffusion process, while at the interphase level the former is more limiting. In this study, no severe risk for transport limitations for the anode and the cathode of the SOFC was found with the chosen kinetic parameters. It was found that the reaction rates constitute the largest risk. A parameter study was conducted by increasing the steam reforming and the electrochemical reaction rates by a factor of 100 without any transport limitations for the same kinetic parameters. The result of this study provides one type of control of the kinetic parameters which in turn have an impact on the reforming reaction rates and the cell performance.
The U.S. Department of Energy’s Research and Development Portfolio of Hydrogen Production Technologies
Authors: Garland Roxanne , Dillich Sara , Miller Eric , Babick Kristine , Weil Kenneth
Published: March 2012

The goal of the US Department of Energy (DOE) hydrogen production portfolio is to research and develop low-cost, highly efficient and environmentally friendly production technologies based on diverse, domestic resources. The DOE Hydrogen Program integrates basic and applied research, as well as technology development and demonstration, to adequately address a diverse range of technologies and feedstocks. The program encompasses a broad spectrum of coordinated activities within the DOE Offices of Energy Efficiency and Renewable Energy (EERE), Nuclear Energy (NE), Fossil Energy (FE), and Science (SC). Hydrogen can be produced in small, medium, and larger scale facilities, with small-scale distributed facilities producing from 100 to 1,500 kilograms (kg) of hydrogen per day at fueling stations, and medium-scale (also known as semi-central or city-gate) facilities producing from 1,500 to 50,000 kg per day on the outskirts of cities. The largest central facilities would produce more than 50,000 kg of hydrogen per day. Specific technologies currently under program development for distributed hydrogen production include bio-derived renewable liquids and water electrolysis. Centralized renewable production pathways under development include water electrolysis integrated with renewable power (e.g., wind, solar, hydroelectric, or geothermal), biomass gasification, solar-driven high-temperature thermochemical water splitting, direct photoelectrochemical water splitting, and biological production methods using algal/bacterial processes. To facilitate commercialization of hydrogen production via these various technology pathways in the near and long terms, a “Hydrogen Production Roadmap” has been developed which identifies the key challenges and high-priority research and development needs associated with each technology. The aim is to foster research that will lead to hydrogen production with near-zero net greenhouse gas emissions, using renewable energy sources, nuclear energy, and/or coal (with carbon capture and storage). This paper describes the research and development needs and activities by various DOE offices to address the key challenges in the portfolio of hydrogen production technologies.
Modeling the Effective Thermal Conductivity of an Anisotropic Gas Diffusion Layer in a Polymer Electrolyte Membrane Fuel Cell
Authors: Yablecki J. , Bazylak A.
Published: March 2012

The anisotropic and heterogeneous effective thermal conductivity of the gas diffusion layer (GDL) of the polymer electrolyte membrane fuel cell was determined in the through-plane direction using an analytical thermal resistance model. The geometry of the GDL was reconstructed using porosity profiles obtained through microscale computed tomography imaging of four commercially available GDL materials. The effective thermal conductivity increases almost linearly with increasing bipolar plate compaction pressure. The effective thermal conductivity was also seen to increase with increasing GDL thickness as bulk porosity remained almost constant. The effect of the heterogeneous through-plane porosity distribution on the effective thermal conductivity is discussed. The outcomes of this work will provide insight into the effect of heterogeneity and anisotropy of the GDL on the thermal management required for improved PEMFC performance.
Experimental Analysis of a Single Cell Flowing Electrolyte-Direct Methanol Fuel Cell
Authors: Sabet-Sharghi Nasim , Cruickshank Cynthia A. , Matida Edgar
Published: March 2012

A single cell flowing electrolyte - direct methanol fuel cell (FE-DMFC) was studied experimentally. Nafion® NRE-212 was used in the membrane electrode assembly (MEA). The flowing electrolyte channel was formed by a polyethylene porous material. The active area of the fuel cell was approximately 25 cm2. Effects of varying flowing electrolyte conditions (channel thickness, sulfuric acid concentration, channel pressure), methanol concentration, and fuel cell temperature on the overall performance of the cell were studied. It was observed that stopping the flowing electrolyte caused a reduction in the open circuit voltage as well as the current of the cell, indicating that the methanol crossover affected the cell performance. Also, it is presented that a thicker flowing electrolyte channel results in lower power density, and sulfuric acid concentration of 2 molar (18%) was found to be the most advantageous. Raising operating temperature resulted in much better performance of the cell. Increasing flowing electrolyte pressure slightly decreased the performance.
Manufacturing Implementation of Ultrasonic Sealing of Membrane Electrode Assemblies for High Temperature PEM Fuel Cells
Authors: Pyzza Jake M. , Sisson William M. , Puffer Raymond
Published: March 2012

Early research has demonstrated the benefits of ultrasonically bonding PEM fuel cell Membrane Electrode Assemblies (MEAs), in terms of durability [2] and unit cost and cycle time [3]. With these improvements in performance, the next phase in the development of the process is to move from a laboratory setup to an automated production cell capable of producing larger volumes of fuel cells while maintaining a quality ultrasonic bond. The MEAs also need to be produced more affordably and with quality standards meeting or exceeding the level set by current best manufacturing practices.
Modeling of Carbon Dioxide Formation in Flowing Electrolyte-Direct Methanol Fuel Cells
Authors: Ouellette David , Colpan C. Ozgur , Matida Edgar , Cruickshank Cynthia A.
Published: March 2012

A one-dimensional two-phase model has been developed for a direct methanol fuel cell (DMFC) and flowing electrolyte - direct methanol fuel cell (FE-DMFC). The model has been compared to experimental data found in literature and corresponds well. Using this model, the performance of the DMFC and FE-DMFC are evaluated and compared to one another as well as to their respective single phase models. It has been found that there is a substantial difference between a two-phase and single phase model. Furthermore, the FE-DMFC outperformed the DMFC when it came to methanol inlet concentrations and varying operating temperatures due to the FE-DMFC’s ability to reduce the methanol crossover.
The Effect of Flow Channel Surface Properties and Structures on Water Removal and Fuel Cell Performance
Authors: Friess Brooks R. , Yew Samuel C. , Hoorfar Mina
Published: March 2012

The polymer electrolyte membrane (PEM) fuel cell is a zero emission power generation system that has long been considered as a replacement for conventional fossil fuel combustion systems. However, before constituting a viable market for commercial use, the fuel cell efficiency and reliability need to be improved significantly. It has been shown that water management has significant effect on the power and reliability of the cell as the electrolyte membrane must be well hydrated to allow for ion transfer while excess water blocks the activation sites on the cathode side. The latter effect is known as flooding which occurs at large current densities and compromises the normal operation of the fuel cell. To enhance water management, a prodigious amount of numerical models and experimental studies have been conducted to optimize the properties and structures of different layers. One of the key results of these studies has been the design of the flow field patterns on relatively hydrophobic surface of a graphite plate which is believed to provide a better mechanism for removing water droplets from the cathode flow channel. However, the wettability gradient between the catalyst layer (i.e., hydrophilic) and the flow channel (which is currently hydrophobic) introduces problems as the water droplets formed at the catalyst layer will not likely detach and hence create a film of liquid that will block the activation sites. If the flow channel is made out of a material that is more hydrophilic than the catalyst layer, water removal and transport will be enhanced as water naturally moves from low surface energy to high surface energy sites. Another major factor in controlling water in the PEM fuel cell is the flow field architecture. There has also been a large amount of research on different types of the flow field architectures. However, there have been no studies on the relative performance gains provided by changing the surface properties and the architecture separately. This paper presents an experimental analysis comparing two different flow fields with different surface properties, i.e., a hydrophilic gold flow channel and a hydrophobic graphite flow channel. The paper will also compare three different hydrophilic flow channel architectures: an open gold parallel flow channel, an aluminum foam filled parallel flow channel, and a woven wick filled parallel flow channel. This work will result in finding the optimum geometry and surface properties for achieving maximum performance in the flooding regime.
A Real-Time Spatial SOFC Model for Hardware-Based Simulation of Hybrid Systems
Authors: Hughes Dimitri , Wepfer William J. , Davies Kevin , Ford J. Christopher , Haynes Comas , Tucker David
Published: March 2012

Solid oxide fuel cell (SOFC)/ gas turbine (GT) hybrid systems possess the capability to nearly double the efficiency of standard coal-fired power plants which are currently being used for large scale power production. For the purposes of investigating and developing this technology, a SOFC/GT hybrid test facility was developed at the U.S. DOE National Energy Technology Laboratory (NETL) in Morgantown, WV as part of the Hybrid Performance (HyPer) project. The HyPer facility utilizes hardware-in-the-loop technology to simulate coupled SOFC operation with gas turbine hardware in a hybrid arrangement. This paper describes and demonstrates the capabilities of the one-dimensional, real-time operating SOFC model that has been developed and successfully integrated into the HyPer facility. The model presented is designed to characterize SOFC operation over a broad and extensive operating range including inert heating and cooling, standard “on-design” conditions and extreme off-design conditions. The model receives dynamic, system-dependent modeling inputs from facility hardware and calculates a comprehensive set of SOFC operational responses, thus simulating SOFC operation while coupled with a gas turbine. In addition to characterizing SOFC operation, the model also drives the only heat source in the facility to represent fuel cell subsystem release of thermal effluent to the turbine subsystem. Operating parameters such as solid and oxidant stream temperatures, fuel stream compositions, current density, Nernst potential and polarization losses are produced by the model in spatiotemporal manner. The capability of the model to characterize SOFC operation, within dynamic hybrid system feedback, through inert heat up and a step change in load is presented and analyzed.
Effects of Wettability and Flow Direction of Cathode Channel on Plugging Phenomenon in Polymer Electrolyte Fuel Cell
Authors: Taniguchi Ryo , Nishida Kosuke , Kamada Hisashi , Tsushima Shohji , Hirai Shuichiro
Published: March 2012

Water management in cathode channel of polymer electrolyte fuel cell (PEFC) is essential for achieving high current density operation, because excessive liquid water generated at cathode clogs gas channel and disturbs air flow. This phenomenon known as “channel plugging” is one of the critical issues for high-performance PEFC. In this study, the liquid water behavior in the cathode flow channel of an operating PEFC was directly visualized through the transparent separator using a high-speed camera. Furthermore, the differential pressure between the inlet and outlet of the cathode channel was quantitatively measured to predict the liquid water accumulation, and the effects of wettability (hydrophilic or hydrophobic) and flow direction (vertical or horizontal) of the cathode channel on the plugging phenomena were investigated. It was found that the hydrophobic treatment of the cathode channel is effective in draining liquid water smoothly and reduces the averaged differential pressure. The fluctuation of the differential pressure tends to be large due to the sufficient water removal. On the other hand, in the case of hydrophilic treatment, much water attaches to the channel wall and remains inside the gas channel. In addition, the liquid water transport within the cathode channel is largely affected by the flow direction. The averaged differential pressure in the horizontal flow is much lower than that in the vertical flow. The horizontal flow has the advantage of discharging much water to the outside of the cell because the gravity effect can be neglected.
Validation and Uncertainty Quantification of a Two-Phase, Multidimensional PEMFC Computer Model Using High-Resolution Segmented Current Collector Data
Authors: Carnes Brian , Chen Ken S. , Hao Liang , Luo Gang , Ji Yan , Wang Chao-Yang , Spernjak Dusan
Published: March 2012

We present work towards validating a multidimensional computer model capable of simulating two-phase, non-isothermal transport in PEMFCs under a wide variety of conditions. The specific hardware used to gather the experimental data is a state-of-the-art 10×10 segmented bipolar plate attached to a 50 cm2 single cell. The five-way serpentine flow field, bipolar plates and membrane-electrode assembly are all resolved in the model. The data has been collected at Los Alamos National Laboratories under several sets of operating conditions, including different relative humidity of 25%, 50%, 75% and 100% RH and temperatures of 80 and 60 C. Current best practices for model validation are applied, including uncertainty quantification (UQ). Variability in measured data is incorporated by included uncertainty bounds on the data (using either interval bounds or statistical confidence intervals). Sensitivity analysis of model input parameters on predictions is performed using an interface to the the DAKOTA toolkit. The model is calibrated using cell polarization data with uncertainty and then used to predict the local current distribution data.
Three-Dimensional CFD Modeling of Tubular Solid Oxide Fuel Cells With Different Fuels
Authors: Puthran Sachin L. , Koylu Umit O. , Hosder Serhat , Dogan Fatih
Published: March 2012

Solid oxide fuel cell (SOFC) technology has been of great interest over many years due to its flexibility in using different fuels including the fundamental fuel i.e. hydrogen, for its operation. Various computational and numerical models have been developed along with experimental work to evaluate the performance as well as to identify and overcome the problems faced in the development of SOFC’s. In an attempt to achieve efficient operation with respect to design and combined thermal and electrochemical perspective, the main objective of the proposed study is to present a three-dimensional computational model which will serve as a framework for the analysis and optimization of SOFC’s. A three-dimensional (3-D) model of a tubular SOFC is being developed to study the effect of temperature and electrolyte thickness variations on its performance. A commercial Computational Fluid Dynamics (CFD) software ANSYS-FLUENT was used for the development of the tubular model which incorporates an interactive 3-D electro-thermo-chemical fluid flow analysis. The particular model, after validation against experimental observations for selected benchmark cases, was demonstrated to be compatible for intermediate temperatures using hydrogen as the fuel. The performance of the model was analyzed by varying electrolyte thicknesses from 2–100 μm. The same model was further evaluated using different fuels such as CH4 (methane) and CO (carbon monoxide), including the modeling of the reformation and water-gas shift reactions. The results were compared to other computationally less expensive, analytical and empirical models that could serve as basic models for future research on intermediate temperature SOFC’s.
Parametric Investigations of Direct Methanol Fuel Cell Electrodes Manufactured by Spraying
Authors: Koraishy Babar M. , Solomon Sam , Meyers Jeremy P. , Wood Kristin L.
Published: March 2012

Manufacture of fuel cell electrodes by the thin-film method was originally proposed by Wilson et al. [1, 2] for proton-exchange membrane fuel cells (PEMFCs). This technology was subsequently utilized for the manufacture of direct methanol fuel cell (DMFC) electrodes by Ren et al. [3]. Key processing steps in the thin-film process are catalyst ink formulation and its application. The catalyst ink is typically composed of supported or unsupported catalysts, binder (ionomer), solvents and additives. Rheological properties of the ink, amount of binder, and choice of solvents are tuned to match the particular ink application process used to fabricate the electrode, as each coating process has its own unique requirements. Besides affecting the coating process, the choice and ratios of these components can significantly affect the electrochemical performance of the electrode. In this study, catalyst inks are designed and investigated for the spraying process, for utilization in the continuous fabrication of DMFC electrodes. For this purpose, the effect of the binder (ionomer) content on the performance of the electrodes is studied in detail. Decal-transfer electrodes are fabricated on a custom-built automated spraying apparatus with individually specified anode and cathode binder contents, and assembled to form a catalyst coated membrane (CCM) type membrane electrode assembly (MEA). These electrodes are rigorously tested to specifically identify their electrochemical performance, catalyst utilization and electrode morphology.
Air-Breathing Membraneless Laminar Flow Fuel Cell With Flow-Through Anode
Authors: Mousavi Shaegh Seyed Ali , Nguyen Nam-Trung , Chan Siew Hwa
Published: March 2012

This paper reports the fabrication and characterization of a new concept of flow-through anode for membraneless laminar flow fuel cell (LFFC). To establish a reference case, a fuel cell with flow over and planar anode was fabricated as well. Experimental results indicated that maximum power density was improved from 17 mW/cm2 in planar design to 23 mW/cm2 using the flow-through design. The higher power density of flow-through design is an indicative of higher fuel utilization in the porous anode. Images of the flow obtained experimentally showed that mixing was reduced at the liquid-liquid interface in the channel with flow-through anode leading to increased fuel concentration over anode.
Operation of Carbonate Fuel Cell (MCFC) Using Syngas
Authors: McInerney Joseph , Ghezel-Ayagh Hossein , Sanderson Robert , Hunt Jennifer
Published: March 2012

High temperature fuel cells, such as Molten Carbonate Fuel Cells (MCFC), are prime candidates for power generation using natural gas. Currently MCFC-based products are available for on-site power generation using natural gas and methane-rich biogas. These systems use the most advanced stack configuration utilizing internal reforming of methane. The in-situ reforming within the fuel cell anode provides many operational benefits including stack cooling at high current densities. Syngas from a variety of sources such as coal, biomass and renewables are anticipated to play a key role in the future landscape of power generation. MCFC is capable of utilizing syngss to produce electric power at a very high efficiency. However, because of the differences in the gas compositions between natural-gas and syngas, the fuel cell stack and system designs need to be modified for syngas fuels. The purpose of this study is to develop the design modifications at both the stack and system level needed for operation of internal reforming MCFC using low-methane content syngas without major design changes from the commercial product design. The net outcome of the investigation is a fuel cell system which meets the goals of being able to operate on low methane syngas within thermo-mechanical requirements of the fuel cell stack components. In this paper, we will describe the approach for modification of MCFC design and operating parameters for operation under syngas using both system level modeling and stack level mathematical modeling.