bluuebunny/crossref_metadata_2025 huggingface dataset:
On-Line Gas Measurements Within PEM Fuel Cell Flow Fields by Electric Arc Emission Spectroscopy
Authors: Bettermann Hans , Fischer Peter , Labus Martin , Reichelt Arno
Published: March 2012

This contribution presents a novel online detector concept for analyzing gas compositions in flow fields of PEM fuel cells. This concept is based on arc emission spectroscopy. At the end of a flow field meander, the exhaust gas is directed to the electrodes of the discharge unit in which the molecules are electronically excited. After excitation, the gas molecules emit radiation that is analyzed by a spectrometer. Applied to the gas exhaust of the anode, the arc emission spectrometer detects hydrogen, water vapor and nitrogen. The detection limit of nitrogen is in the range of a few ppm. This property enables the detector to document the actual permeability of the membrane as well as to monitor pre-stages of membrane degradation.
A Thermal-Electrochemical Model of a Fuel Cell Stack Block
Authors: Beedie David , Knight Christopher , Horsfield Matthew , Moobola Roy
Published: March 2012

RRFCS is developing SOFC fuel cell stack and system technology for a hybrid power generation system. RRFCS is also developing state of the art numerical prediction tools that will be used to support fuel cell product design. One such tool, the Block Thermal Model, is based in the FEMAP-TMG thermal model generator package. This paper describes the constituents of the block and the physics modelled, presents the initial results and states the computer resources used. Full validation could be a subject for later publication. In the RRFCS stack block, aerothermal physics in the anode and cathode gas flows is coupled with electrochemistry, distributed throughout a highly repeated three-dimensional solid geometry. The requirement was to create numerical modelling capability to accurately solve the main coupled behaviours throughout the entire domain of the block, as a function of externally applied conditions. The key distributions are thermal, electrical, chemical and hydraulic. The strength of the couplings determines the robustness of the design. The geometry, mesh density and fidelity required create considerable scope for model size to be enormous, with all the attendant issues around model setup, solution time and stability and post-processing. A finite element (FE) pre- and post-processor with a dedicated thermal solver extended by user-defined subroutines provides detailed thermal mapping and will be able to capture the coupled physics interactions. The FE mesh includes every component in the block including the end fittings and fuel pipes, as the sensible energy in the circulating fuel has significant thermal effects particularly at inlet. These components are less exposed to cooling airflow and will have significant effects in dynamic solutions. In order to capture the non-uniform distribution of fuel cell heat release, anode and cathode mass balances and electrochemical calculations are required at adequate resolution. Distributions of electrical current and fuel flow are currently user-input. Considerable attention was given to careful structuring of the mesh in order to minimise the element count. Full advantage was taken of the reasonable simplifications that can be made of the solid structure, fluid flows and fluid-solid heat exchanges. It was decided at the outset to make these simplifications as without them the model would have required orders of magnitude greater computational capability, probably without appreciably greater accuracy of the thermal distribution. Control of the radiation model setup was also both reasonable and necessary. Some validation of the tube mesh and initial steady-state results will be presented.
Effect of Porosity Gradient in Gas Diffusion Layer on Cell Performance With Thin-Film Agglomerate Model in Cathode Catalyst Layer of a PEM Fuel Cell
Authors: Lee Chun-I , Jung Shiqah-Ping , Hsueh Kan-Lin , Chen Chi-Chang , Chang Wen-Chen
Published: March 2012

A one-dimensional, steady-state, two-phase, isothermal numerical simulations were performed to investigate the effect on cell performance of a PEM fuel cell under non-uniform porosity of gas diffusion layer. In the simulation, the non-uniform porosity of gas diffusion layer was taken into account to analyze the transport phenomena of water flooding and mass transport in the gas diffusion layer. The porosity of the gas diffusion layer is treated as a linear function. Furthermore, the structure of the catalyst layer is considered to be a cylindrical thin-film agglomerate. Regarding the distribution analysis of liquid water saturation, oxygen concentration and water concentration depend on the porosity of gas diffusion layer. In the simulation, the εCG and εGC represent the porosity of the interfaces between the channel and gas diffusion layer and the gas diffusion layer and the catalyst layer, respectively. The simulation results indicate that when the (εCG, εGC) = (0.8, 0.4), higher liquid water saturation appears in the gas diffusion layer and the catalyst layer. On the contrary, when the (εCG, εGC) = (0.4, 0.4), lower liquid water saturation appears. Once the liquid water produced by the electrochemical reaction and condensate of vapor water may accumulate in the open pores of the gas diffusion layer and reduced the oxygen transport to the catalyst sites. This research attempts to use a thin-film agglomerate model, which analyze the significant transport phenomena of water flooding and mass transport under linear porosity gradient of gas diffusion layer in the cathode of a PEM fuel cell.
A Transient Fuel Cell Model to Simulate HTPEM Fuel Cell Impedance Spectra
Authors: Vang Jakob Rabjerg , Andreasen So̸ren Juhl , Kær So̸ren Knudsen
Published: March 2012

This paper presents a spatially resolved transient fuel cell model applied to the simulation of high temperature PEM fuel cell impedance spectra. The model is developed using a 2D finite volume method approach. The model is resolved along the channel and across the membrane. The model considers diffusion of cathode gas species in gas diffusion layers and catalyst layer, transport of protons in the membrane and the catalyst layers, and double layer capacitive effects in the catalyst layers. The model has been fitted simultaneously to a polarisation curve and to an impedance spectrum recorded in the laboratory. A simultaneous fit to both curves is not achieved. In order to investigate the effects of the fitting parameters on the simulation results, a parameter variation study is carried out. It is concluded that some of the fitting parameters assume values which are not realistic. In order to remedy this, phenomena neglected in this version of the model must be incorporated in future versions.
Modeling Water Content Distribution in the Polymer Electrolyte Membrane of PEM Fuel Cell
Authors: Tavakoli Bahareh Alsadat , Roshandel Ramin
Published: March 2012

Models play an important role in fuel cell design and development. One of the critical problems to overcome in the proton exchange membrane (PEM) fuel cells is the water management. In this work a steady state, two dimensional, isothermal model in a single PEM fuel cell using individual computational fluid dynamics code was presented. Special attention was devoted to the water transport through the membrane which is assumed to be combined effect of diffusion, electro osmotic drag and convection. The effect of current density variation distribution on the Water content (λ) in membrane/electrode assembly (MEA) was determined. After that detailed distribution of oxygen concentration, water content in membrane, net water flux and different overpotentials were calculated. Simulation results show that the reduction of reactant concentration in flow channels has a significant effect on electrochemical reaction in the gas diffusion and catalyst layer. Different fluxes are compared to investigate the effect of operating condition on the water fluxes in membrane. The amount of different fluxes is a strong function of current density which is related to external load. The model prediction of water content curves are compared with one dimensional model predictions data reported in the validated open literature and good compatibility were observed. In addition, the model predicted fuel cell polarization curves compared well with experimental and numerical data.
Designing a Recharging Grid for the Hybrid Vehicle System: Part I
Authors: Ubong Etim U. , Dorsey James , Armstrong Kevin , Bucchi Anthony , Cady Robert , Bastarache Marc , Parrish Thomas , Hoffman Scott , Szymanski Kevin , Walker Alec
Published: March 2012

To accelerate the development of the hybrid transportation system, there is a need to set up an infrastructure for the hybrid vehicle battery recharging at parking lots of universities as test grounds for this technology. This work focuses on setting up or implementing a pilot recharging network at Kettering University’s main parking lot with a capacity of over 500 vehicles. As the society is transitioning from the fossil fuel powered vehicles to hybridized systems, recharging outlet from fuel cell, solar and wind turbines sources should be in place to facilitate the transfer by 2015. This project details the infrastructural design using fuel cell energy from the Center for Fuel Cell Research of the University for setting up 50 pilot recharging outlets at the parking lot behind the Mott Engineering Building to recharge hybrid vehicles in the main parking lot of the University. The current resources at the Center include a 5 kW SOFC test station, a 4.4 kW Ballard LT-PEM fuel cell mounted on a 5 kW test stand and 1.5 kW high temperature HT-PEM produced by GEI LLC. The use of solar energy during the day is also considered. The applicable codes and standards regarding such installations are reviewed.
An Efficient Unsteady Two-Phase Flow Model for Cathode Gas Channels of a Polymer Electrolyte Fuel Cell
Authors: Basu Suman , Gopinath Ashok
Published: March 2012

The importance of flow field design in a Polymer Electrolyte Fuel Cell (PEFC) cannot be overemphasized. Experimental evidence suggests the presence of a significant amount of liquid water in the PEFC gas channels and a typical driving cycle in a city suggests that a vehicular PEFC engine is unlikely to reach steady state operation under these conditions. Therefore the need for an unsteady two-phase flow model is critical. The “Multiphase Mixture” (M2) model is used to develop an efficient unsteady two-phase flow model for the cathode gas channels. Liquid water evolution in cathode gas channels and its effect on the cathode pressure drop history is investigated with the help of the model. It is an efficient tool to evaluate the performance of new flow field designs as well as to test performance loss due to channel blockage. The same model could be extended to anode gas channels.
Comparison of tunnel junctions for cascaded InAs/GaSb superlattice light emitting diodes
Authors: Murray L. M. , Norton D. T. , Olesberg J. T. , Boggess T. F. , Prineas J. P.
Published: March 2012

Tunnel junctions in cascaded structures must provide adequate barriers to prevent carriers from leaking from one emission region to the next without first recombining radiatively, while at the same time remain low in tunneling resistance for current recycling. In this study, a variety of tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice light emitting diodes, which past studies have found hole confinement to be problematic. Here we used GaSb on the p-side of the junction, while varying materials on the n-side. The authors find Al0.20In0.80As0.73Sb0.27 tunnel junctions function best due to the low set of the conduction band; Ga0.75In0.25As0.23Sb0.77 also works well, though is more resistive due to a reduced set of the conduction band; and GaSb, while giving good hole confinement, results in a very resistive junction. Graded superlattice junctions can also work well, though they show sensitivity to doping levels, and present some challenges in growing strain-free.
UV capillary force lithography for multiscale structures
Authors: Hansen M. , Ziegler M. , Kohlstedt H. , Pradana A. , Raedler M. , Gerken M.
Published: March 2012

Rapid advances in information technology rely on novel patterning techniques. The authors present a simple UV capillary force lithography process, which allows one to imprint a multiscale system, consisting of 250 nm wide nanobridges and a 8–20 μm wide wiring in one lithography step. An additional annealing step for 5 min at 75 °C improved the capillary rise.
Determination of contact angle from the maximum height of enlarged drops on solid surfaces
Authors: Behroozi F.
Published: March 2012

Measurement of the liquid/solid contact angle provides useful information on the wetting properties of fluids. In 1870, the German physicist Georg Hermann Quincke (1834–1924) published the functional relation between the maximum height of an enlarged drop and its contact angle. Quincke’s relation offered an alternative to the direct measurement of contact angle, which in practice suffers from several experimental uncertainties. In this paper, we review Quincke’s original derivation and show that it is based on a hidden assumption. We then present a new derivation that exposes this assumption and clarifies the conditions under which Quincke’s relation is valid. To explore Quincke’s relation experimentally, we measure the maximum height of enlarged water drops on several substrates and calculate the contact angle in each case. Our results are in good agreement with contact angles measured directly from droplet images.
Denitrification and Nitrogen Fixation Dynamics in the Area Surrounding an Individual Ghost Shrimp (Neotrypaea californiensis) Burrow System
Authors: Bertics Victoria J. , Sohm Jill A. , Magnabosco Cara , Ziebis Wiebke
Published: March 2012

Bioturbated sediments are thought of as areas of increased denitrification or fixed-nitrogen (N) loss; however, recent studies have suggested that not all N may be lost from these environments, with some N returning to the system via microbial dinitrogen (N
2
) fixation. We investigated denitrification and N
2
fixation in an intertidal lagoon (Catalina Harbor, CA), an environment characterized by bioturbation by thalassinidean shrimp (
Neotrypaea californiensis
). Field studies were combined with detailed measurements of denitrification and N
2
fixation surrounding a single ghost shrimp burrow system in a narrow aquarium (15 cm by 20 cm by 5 cm). Simultaneous measurements of both activities were performed on samples taken within a 1.5-cm grid for a two-dimensional illustration of their intensity and distribution. These findings were then compared with rate measurements performed on bulk environmental sediment samples collected from the lagoon. Results for the aquarium indicated that both denitrification and N
2
fixation have a patchy distribution surrounding the burrow, with no clear correlation to each other, sediment depth, or distance from the burrow. Field denitrification rates were, on average, lower in a bioturbated region than in a seemingly nonbioturbated region; however, replicates showed very high variability. A comparison of denitrification field results with previously reported N
2
fixation rates from the same lagoon showed that in the nonbioturbated region, depth-integrated (10 cm) denitrification rates were higher than integrated N
2
fixation rates (∼9 to 50 times). In contrast, in the bioturbated sediments, depending on the year and bioturbation intensity, some (∼6.2%) to all of the N lost via denitrification might be accounted for via N
2
fixation.
Intramolecular Regulation of the Sequence-Specific mRNA Interferase Activity of MazF Fused to a MazE Fragment with a Linker Cleavable by Specific Proteases
Authors: Park Jung-Ho , Yamaguchi Yoshihiro , Inouye Masayori
Published: March 2012

The genomes of human immunodeficiency virus type 1 (HIV-1) and hepatitis C virus (HCV) consist of single-stranded RNA encoding polyproteins, which are processed to individual functional proteins by virus-encoded specific proteases. These proteases have been used as targets for drug development. Here, instead of targeting these proteases to inhibit viral infection, we utilized the protease activity to activate a toxic protein to prevent viral infection. We engineered the MazE-MazF antitoxin-toxin system of
Escherichia coli
to fuse a C-terminal 41-residue fragment of antitoxin MazE to the N-terminal end of toxin MazF with a linker having a specific protease cleavage site for either HIV PR (HIV-1 protease), NS3 protease (HCV protease), or factor Xa. These fusion proteins formed a stable dimer (instead of the MazF
2
-MazE
2
-MazF
2
heterohexamer in nature) to inactivate the ACA (sequence)-specific mRNA interferase activity of MazF. When the fusion proteins were incubated with the corresponding proteases, the MazE fragment was cleaved from the fusion proteins, releasing active MazF, which then acted as an ACA-specific mRNA interferase cleaving single-stranded MS2 phage RNA. The intramolecular regulation of MazF toxicity by proteases as demonstrated may provide a novel approach for preventive and therapeutic treatments of infection by HIV-1, HCV, and other single-stranded RNA viruses.
Antimicrobial Resistance in Escherichia coli Isolates from Raccoons (Procyon lotor) in Southern Ontario, Canada
Authors: Jardine Claire M. , Janecko Nicol , Allan Mike , Boerlin Patrick , Chalmers Gabhan , Kozak Gosia , McEwen Scott A. , Reid-Smith Richard J.
Published: March 2012

We conducted a cross-sectional study to determine the prevalence of antimicrobial resistance (AMR) in fecal
Escherichia coli
isolates from raccoons (
Procyon lotor
) living in Ontario, Canada. From June to October 2007, we trapped raccoons in three areas: one primarily urban site around Niagara, one primarily rural site north of Guelph, and one at the Toronto Zoo. In addition, we conducted a longitudinal study at the Toronto Zoo site to investigate the temporal dynamics of fecal
E. coli
and AMR in raccoons. Reduced susceptibility to ≥1 antimicrobial agent was detected in
E. coli
isolates from 19% of 16 raccoons at the urban site, 17% of 29 raccoons from the rural site, and 42% of 130 samples collected from 59 raccoons at the zoo site. Raccoons from the zoo site were significantly more likely to shed
E. coli
with reduced susceptibility to ≥1 antimicrobial agent than animals from the rural site (odds ratio [OR], 3.41; 95% confidence interval [CI], 1.17 to 12.09;
P
= 0.02). Resistance to expanded-spectrum cephalosporins (and the associated
bla
CMY-2
gene) was detected in two animals from the zoo site and one animal from the rural site. Serotyping and pulsed-field gel electrophoresis analysis show that raccoons on the zoo grounds harbor a diverse assemblage of
E. coli
, with rapid bacterial turnover within individuals over time. Our study indicates that raccoons may shed resistant bacteria of public health significance and that raccoons have the potential to disseminate these bacteria throughout their environment.
Production of
l
-Ribose from
l
-Ribulose by a Triple-Site Variant of Mannose-6-Phosphate Isomerase from Geobacillus thermodenitrificans
Authors: Lim Yu-Ri , Yeom Soo-Jin , Oh Deok-Kun
Published: March 2012

A triple-site variant (W17Q N90A L129F) of mannose-6-phosphate isomerase from
Geobacillus thermodenitrificans
was obtained by combining variants with residue substitutions at different positions after random and site-directed mutagenesis. The specific activity and catalytic efficiency (
k
cat
/
K

m

) for
l
-ribulose isomerization of this variant were 3.1- and 7.1-fold higher, respectively, than those of the wild-type enzyme at pH 7.0 and 70°C in the presence of 1 mM Co
2+
. The triple-site variant produced 213 g/liter
l
-ribose from 300 g/liter
l
-ribulose for 60 min, with a volumetric productivity of 213 g liter
−1
h
−1
, which was 4.5-fold higher than that of the wild-type enzyme. The
k
cat
/
K

m

and productivity of the triple-site variant were approximately 2-fold higher than those of the
Thermus thermophilus
R142N variant of mannose-6-phosphate isomerase, which exhibited the highest values previously reported.
Novel Phakopsora pachyrhizi Extracellular Proteins Are Ideal Targets for Immunological Diagnostic Assays
Authors: Luster Douglas G. , McMahon Michael B. , Edwards H. Herb , Boerma Britney L. , Lewis Ivey Melanie L. , Miller Sally A. , Dorrance Anne E.
Published: March 2012

Phakopsora pachyrhizi, the causal agent of Asian soybean rust (ASR), continues to spread across the southeast and midsouth regions of the United States, necessitating the use of fungicides by producers. Our objective in this research was to identify ASR proteins expressed early during infection for the development of immunodiagnostic assays. We have identified and partially characterized a small gene family encoding extracellular proteins in theP. pachyrhiziurediniospore wall, termed PHEPs (forPhakopsoraextracellularprotein). Two highly expressed protein family members, PHEP 107 and PHEP 369, were selected as ideal immunodiagnostic targets for antibody development, after we detected PHEPs in plants as early as 3 days postinfection (dpi). Monoclonal antibodies (MAbs; 2E8E5-1 and 3G6H7-3) generated against recombinant PHEP 369 were tested for sensitivity against the recombinant protein and extracts from ASR-infected plants and for specificity against a set of common soybean pathogens. These antibodies should prove applicable in immunodiagnostic assays to detect infected soybeans and to identify ASR spores from sentinel surveillance plots.
New Sequence Types and Multidrug Resistance among Pathogenic Escherichia coli Isolates from Coastal Marine Sediments
Authors: Vignaroli C. , Luna G. M. , Rinaldi C. , Di Cesare A. , Danovaro R. , Biavasco F.
Published: March 2012

The spread of antibiotic-resistant microorganisms is widely recognized, but data about their sources, presence, and significance in marine environments are still limited. We examined 109
Escherichia coli
strains from coastal marine sediments carrying virulence genes for antibiotic susceptibility, specific resistance genes, prevalence of class 1 and 2 integrons, and sequence type. Antibiotic resistance was found in 35% of strains, and multiple resistances were found in 14%; the resistances detected most frequently were against tetracycline (28%), ampicillin (16.5%), trimethoprim-sulfamethoxazole (13%), and streptomycin (7%). The highest prevalence of resistant strains was in phylogenetic group A, whereas phylogroup B2 exhibited a significantly lower frequency than all the other groups. Sixty percent of multiresistant strains harbored class 1 or 2 integrase genes, and about 50% carried resistance genes (particularly
dfrA
and
aadA
) linked to a class 1 integron. Multilocus sequence typing of 14 selected strains identified eight different types characteristic of extraintestinal pathogens and three new allelic combinations. Our data suggest that coastal marine sediment may be a suitable environment for the survival of pathogenic and antimicrobial-resistant
E. coli
strains capable of contributing to resistance spread via integrons among benthic bacteria, and they highlight a role for these strains in the emergence of new virulent genotypes.
CcrR, a TetR Family Transcriptional Regulator, Activates the Transcription of a Gene of the Ethylmalonyl Coenzyme A Pathway in Methylobacterium extorquens AM1
Authors: Hu Bo , Lidstrom Mary
Published: March 2012

The ethylmalonyl coenzyme A (ethylmalonyl-CoA) pathway is one of the central methylotrophy pathways in
Methylobacterium extorquens
involved in glyoxylate generation and acetyl-CoA assimilation. Previous studies have elucidated the operation of the ethylmalonyl-CoA pathway in C
1
and C
2
assimilation, but the regulatory mechanisms for the ethylmalonyl-CoA pathway have not been reported. In this study, a TetR-type activator, CcrR, was shown to regulate the expression of crotonyl-CoA reductase/carboxylase, an enzyme of the ethylmalonyl-CoA pathway involved in the assimilation of C
1
and C
2
compounds in
Methylobacterium extorquens
AM1. A
ccrR
null mutant strain was impaired in its ability to grow on C
1
and C
2
compounds, correlating with the reduced activity of crotonyl-CoA reductase/carboxylase. Promoter fusion assays demonstrated that the activity of the promoter required for
ccr
expression (the
katA-ccr
promoter) decreased as much as 50% in the absence of
ccrR
compared to wild-type
M. extorquens
AM1. Gel mobility shift assays confirmed that CcrR directly binds to the region upstream of the
katA-ccr
promoter. A palindromic sequence upstream of
katA
at positions −334 to −321 with respect to the predicted translational start site was identified, and mutations in this region eliminated the gel retardation of the
katA-ccr
promoter region by CcrR. CcrR does not appear to regulate the expression of other ethylmalonyl-CoA pathway genes, suggesting the existence of additional regulators.
Analyses of MbtB, MbtE, and MbtF Suggest Revisions to the Mycobactin Biosynthesis Pathway in Mycobacterium tuberculosis
Authors: McMahon Matthew D. , Rush Jason S. , Thomas Michael G.
Published: March 2012

The production of mycobactin (MBT) by
Mycobacterium tuberculosis
is essential for this bacterium to access iron when it is in an infected host. Due to this essential function, there is considerable interest in deciphering the mechanism of MBT assembly, with the goal of targeting select biosynthetic steps for antituberculosis drug development. The proposed scheme for MBT biosynthesis involves assembly of the MBT backbone by a hybrid nonribosomal peptide synthetase (NRPS)/polyketide synthase (PKS) megasynthase followed by the tailoring of this backbone by
N

6

acylation of the central
l
-Lys residue and subsequent
N

6

-hydroxylation of the central
N

6

-acyl-
l
-Lys and the terminal caprolactam. A complete testing of this hypothesis has been hindered by the inability to heterologously produce soluble megasynthase components. Here we show that soluble forms of the NRPS components MbtB, MbtE, and MbtF are obtained when these enzymes are coproduced with MbtH. Using these soluble enzymes we determined the amino acid specificity of each adenylation (A) domain. These results suggest that the proposed tailoring enzymes are actually involved in precursor biosynthesis since the A domains of MbtE and MbtF are specific for
N

6

-acyl-
N

6

-hydroxy-
l
-Lys and
N

6

-hydroxy-
l
-Lys, respectively. Furthermore, the preference of the A domain of MbtB for
l
-Thr over
l
-Ser suggests that the megasynthase produces MBT derivatives with β-methyl oxazoline rings. Since the most prominent form of MBT produced by
M. tuberculosis
lacks this β-methyl group, a mechanism for demethylation remains to be discovered. These results suggest revisions to the MBT biosynthesis pathway while also identifying new targets for antituberculosis drug development.
Functional Dissection of
N
-Acetylglutamate Synthase (ArgA) of Pseudomonas aeruginosa and Restoration of Its Ancestral
N
-Acetylglutamate Kinase Activity
Authors: Sancho-Vaello Enea , Fernández-Murga María L. , Rubio Vicente
Published: March 2012

In many microorganisms, the first step of arginine biosynthesis is catalyzed by the classical
N
-acetylglutamate synthase (NAGS), an enzyme composed of N-terminal amino acid kinase (AAK) and C-terminal histone acetyltransferase (GNAT) domains that bind the feedback inhibitor arginine and the substrates, respectively. In NAGS, three AAK domain dimers are interlinked by their N-terminal helices, conforming a hexameric ring, whereas each GNAT domain sits on the AAK domain of an adjacent dimer. The arginine inhibition of
Pseudomonas aeruginosa
NAGS was strongly hampered, abolished, or even reverted to modest activation by changes in the length/sequence of the short linker connecting both domains, supporting a crucial role of this linker in arginine regulation. Linker cleavage or recombinant domain production allowed the isolation of each NAGS domain. The AAK domain was hexameric and inactive, whereas the GNAT domain was monomeric/dimeric and catalytically active although with ∼50-fold-increased and ∼3-fold-decreased

K
m

glutamate
and
k
cat
values, respectively, with arginine not influencing its activity. The deletion of N-terminal residues 1 to 12 dissociated NAGS into active dimers, catalyzing the reaction with substrate kinetics and arginine insensitivity identical to those for the GNAT domain. Therefore, the interaction between the AAK and GNAT domains from different dimers modulates GNAT domain activity, whereas the hexameric architecture appears to be essential for arginine inhibition. We proved the closeness of the AAK domains of NAGS and
N
-acetylglutamate kinase (NAGK), the enzyme that catalyzes the next arginine biosynthesis step, shedding light on the origin of classical NAGS, by showing that a double mutation (M26K L240K) in the isolated NAGS AAK domain elicited NAGK activity.
Checking pregnancy status in adolescent girls before procedures under general anaesthesia
Authors: Donaldson J F , Napier S J , Ward-Jones M , Wheeler R A , Spargo P M
Published: March 2012

Objective

Surgery, ionising radiation and anaesthesia in the presence of an undetected pregnancy could be harmful. British guidelines state that female patients of 'childbearing age' should have their pregnancy status established before surgery. Approaching this topic with an adolescent girl can be challenging.

Design

The authors conducted an observational study and a survey in their institution and a national survey of Association of Paediatric Anaesthetists (APA) linkmen.

Setting

Local: Southampton. National: UK.

Results

Both surveys demonstrate widespread concerns about inconsistent and informal practices. Only 45% of respondents in the authors' institution stated they ask adolescent girls if they could be pregnant. 40% of APA linkmen were unaware of national guidelines.

Conclusions

This work illustrates the need for consistent national guidance. We propose that all girls who have reached menarche should be routinely offered a urine pregnancy test before any procedure under general anaesthesia.
Restless legs syndrome and risk of incident cardiovascular disease in women and men: prospective cohort study
Authors: Winter Anke C , Schürks Markus , Glynn Robert J , Buring Julie E , Gaziano J Michael , Berger Klaus , Kurth Tobias
Published: March 2012

Objectives

To evaluate the association between restless legs syndrome (RLS) and incident cardiovascular disease (CVD).

Design

Prospective cohort study.

Setting

Women's Health Study (WHS) and Physicians' Health Study (PHS), USA.

Participants

29 756 female health professionals aged ≥45 years and 19 182 male physicians aged ≥40 years at baseline.

Main outcome measures

Main outcome was incidence of major CVD; secondary outcomes were first incidence of myocardial infarction, stroke, death due to CVD or coronary revascularisation.

Results

3487 (11.7%) women and 1373 (7.2%) men met International Restless Legs Study Group criteria for RLS. In the WHS 450 major CVD events occurred and 1064 major CVD events were confirmed in the PHS. In both cohorts, RLS was not associated with increased risk of major CVD, stroke, myocardial infarction, CVD death or coronary revascularisation. After adjustment for major vascular risk factors, the HRs (95% CI) for major CVD were 1.15 (0.88 to 1.50) in women and 1.01 (0.81 to 1.25) in men. Highest multivariable-adjusted HRs were 1.29 (0.91 to 1.82) for total stroke in women and 1.22 (0.87 to 1.70) for CVD death in men. Excluding participants with comorbidities potentially leading to RLS did not substantially change the effect estimates.

Conclusions

In these large prospective studies of female and male health professionals, RLS was not associated with an increased risk of any incident CVD event. The data do not support the hypothesis that RLS is a marker of increased risk of vascular disease.
Building information for systematic improvement of the prevention of hospital-acquired pressure ulcers with statistical process control charts and regression
Authors: Padula William V , Mishra Manish K , Weaver Christopher D , Yilmaz Taygan , Splaine Mark E
Published: March 2012

Objectives

To demonstrate complementary results of regression and statistical process control (SPC) chart analyses for hospital-acquired pressure ulcers (HAPUs), and identify possible links between changes and opportunities for improvement between hospital microsystems and macrosystems.

Methods

Ordinary least squares and panel data regression of retrospective hospital billing data, and SPC charts of prospective patient records for a US tertiary-care facility (2004–2007). A prospective cohort of hospital inpatients at risk for HAPUs was the study population.

Results

There were 337 HAPU incidences hospital wide among 43 844 inpatients. A probit regression model predicted the correlation of age, gender and length of stay on HAPU incidence (pseudo R2=0.096). Panel data analysis determined that for each additional day in the hospital, there was a 0.28% increase in the likelihood of HAPU incidence. A p-chart of HAPU incidence showed a mean incidence rate of 1.17% remaining in statistical control. A t-chart showed the average time between events for the last 25 HAPUs was 13.25 days. There was one 57-day period between two incidences during the observation period. A p-chart addressing Braden scale assessments showed that 40.5% of all patients were risk stratified for HAPUs upon admission.

Conclusion

SPC charts complement standard regression analysis. SPC amplifies patient outcomes at the microsystem level and is useful for guiding quality improvement. Macrosystems should monitor effective quality improvement initiatives in microsystems and aid the spread of successful initiatives to other microsystems, followed by system-wide analysis with regression. Although HAPU incidence in this study is below the national mean, there is still room to improve HAPU incidence in this hospital setting since 0% incidence is theoretically achievable. Further assessment of pressure ulcer incidence could illustrate improvement in the quality of care and prevent HAPUs.
Withdrawal of artificial nutrition and hydration in the Neonatal Intensive Care Unit: parental perspectives
Authors: Hellmann Jonathan , Williams Constance , Ives-Baine Lori , Shah Prakesh S
Published: March 2012

Objective

To review the experience of the practice of withdrawal of artificial nutrition and hydration (WANH) and to describe parental perspectives on the process.

Design

A retrospective chart review and parental survey.

Setting

Tertiary level Neonatal Intensive Care Unit (NICU).

Participants

Infants who had WANH after withdrawal of other life-sustaining treatment, and their parents.

Main outcome measure

Parental perspectives on the care and process were obtained through a survey administered 1 to 4 years after the death of their infant.

Results

Fifteen cases (5.5% of all mortality and 0.5% of all admissions) of WANH were identified, and 10 parents participated in the survey. The median (range) gestational age was 40 weeks (31–42) and birth weight was 3409 g (2000–4640). The reason for WANH was predicted poor outcome due to severe neurological injury/disease. The median (range) time between WANH and death was 16 days (2–37). All parents reported favourable perceptions of preparation, support, communication and care. Seven parents reported concerns regarding pain experienced by their infant. Parents reported the ability to spend quality time, creating tangible memories and the virtues and professional qualities of the caregivers to be helpful, but identified that consistency and continuity of care could be improved.

Conclusion

Within the spectrum of palliative care in neonates, WANH can be a tenable, justifiable and humane practice in the NICU.
Activation procedures in the electroencephalograms of healthy and epileptic cats under propofol anaesthesia
Authors: Brauer C. , Kästner S. B. R. , Kulka A. M. , Tipold A.
Published: March 2012

The current study evaluated the diagnostic value of electroencephalographic recordings (EEG) in cats with epilepsy under special consideration of photic stimulation and hyperventilation. EEGs in six healthy cats were recorded under light (mean dose of 0.23 mg/kg/min) and deep (mean dose of 0.7 mg/kg/min) propofol anaesthesia, whereas EEGs in 13 diseased cats were recorded under a propofol anaesthesia which was kept as light as possible (mean dose of 0.39 mg/kg/min). Paroxysmal discharges were detected in six of 13 cats suffering from seizures (two cats with idiopathic epilepsy and four cats with symptomatic epilepsy). Activation techniques did not enhance the diagnostic value of the EEGs. Photic driving was detected in one of six healthy cats under light, in five of six healthy cats under deep propofol anaesthesia and in 11 of 13 cats with seizures. Systematic use of activation techniques does not seem to increase the diagnostic yield of the recorded EEGs and should not be used in a clinical setting until future studies indicate value. Further investigations into the origin of photic driving under propofol anaesthesia are needed and could lead to the development of a reliable animal model to research into drug effects on the EEG.
Recovery of staphylococci from computer keyboards in a veterinary medical centre and the effect of routine cleaning
Authors: Bender J. B. , Schiffman E. , Hiber L. , Gerads L. , Olsen K.
Published: March 2012

Computers are an essential tool in the veterinary clinic for ordering, checking laboratory and image results, updating patient records, providing discharge instructions, and inputing billing information. Few studies have documented the degree of contamination or practical methods to disinfect computer equipment within the veterinary clinic setting. The intent of the present study was to characterise the frequency of recovery of Staphylococcus species from computer keyboards from a veterinary teaching hospital setting and to evaluate the effect of daily cleaning. From three keyboards in a treatment area, three in a dermatology area and one in an office, 70 environmental samples were cultured for Staphylococcus. As an indirect measure to assess cleanliness, samples were collected and tested using the 3M Clean–Trace Luminometer (relative light units [RLU]). Of the 25 Staphylococcus recovered 13 were Staphylococcus species, seven Staphylococcus pseudintermedius, four Staphylococcus aureus and one mixed colony of both Staphylococcus species and S pseudintermedius. The median RLU was 2098 (range 132 to 11,590). Routine cleaning decreased the recovering of Staphylococcus and the RLU values. In summary, the study results demonstrate the value of routine cleaning of keyboards and the need for on‐going and regular education of staff and students about good hand hygiene.
An Early Pleistocene grounded ice sheet in the Central North Sea
Authors: Buckley F. A.
Published: March 2012

Evidence is presented for an Early Pleistocene grounded ice sheet in the Central North Sea (CNS). Dated basal Quaternary deposits from UK well 30/13-2 Josephine coincide with the lowest iceberg ploughmarked horizon in a southern CNS depocentre. This horizon has been traced northwards into the central CNS where it is identified as the Crenulate reflection, which exhibits a series of deep, channel-like features, interpreted as subglacial meltwater channels. Further north, a seismic reflection at the same level is characterized by megascale lineations that are interpreted to be the result of erosion, deposition and deformation of sediment beneath an advancing ice sheet. An overlying seismic reflection is characterized by a well-developed channel system that is thought to have drained the retreating ice sheet prior to a post-glacial marine transgression. A southern CNS Early Pleistocene depocentre is shown to have become inactive sometime in the Early to Middle Pleistocene and was replaced by a developing depocentre in the central and northern CNS that remained active into the Late Pleistocene. Evidence for an Elsterian or older grounded ice sheet in UK Continental Shelf Quad 22 is presented in the form of glaciotectonic thrust features.
A novel, minimally invasive, segmental myocardial infarction with a clear healed infarct borderzone in rabbits
Authors: Ziv Ohad , Schofield Lorraine , Lau Emily , Chaves Lenny , Patel Divyang , Jeng Paul , Peng Xuwen , Choi Bum-Rak , Koren Gideon
Published: March 2012

Ventricular arrhythmias in the setting of a healed myocardial infarction have been studied to a much lesser degree than acute and subacute infarction, due to the pericardial scarring, which results from the traditional open-chest techniques used for myocardial infarction (MI) induction. We sought to develop a segmental MI with low perioperative mortality in the rabbit that allows optimal visualization and therefore improved study of the infarction borderzone. Rabbits underwent MI using endovascular coil occlusion of the first obtuse marginal artery. Three weeks postprocedure, we evaluated our model by echocardiography and electrophysiology studies, optical mapping of isolated hearts, and histological studies. Seventeen rabbits underwent the protocol (12 MI and 5 sham) with a 92% survival to completion of the study (11 MI and 5 sham). MI rabbits demonstrated wall motion abnormalities on echocardiography while shams did not. At electrophysiological study, two MI rabbits had inducible ventricular tachycardia and one had inducible ventricular fibrillation. Isolated hearts demonstrated no pericardial scarring with a smooth, easily identifiable infarct borderzone. Optical mapping of the borderzone region showed successful mapping of peri-infarct reentry formation, with ventricular fibrillation inducible in 11 of 11 MI hearts and 1 of 5 sham hearts. We demonstrate successful high resolution mapping in the borderzone, showing delayed conduction in this region corresponding to late deflections in the QRS on ECG. We report the successful development of a minimally invasive MI via targeted coil delivery to the obtuse marginal artery with an exceptionally high rate of procedural survival and an arrhythmogenic phenotype. This model mimics human post-MI on echocardiography, gross pathology, histology, and electrophysiology.
Inflammation and metabolic dysfunction: links to cardiovascular diseases
Authors: Taube Annika , Schlich Raphaela , Sell Henrike , Eckardt Kristin , Eckel Juergen
Published: March 2012

Abdominal obesity is a major risk factor for cardiovascular disease, and recent studies highlight a key role of adipose tissue dysfunction, inflammation, and aberrant adipokine release in this process. An increased demand for lipid storage results in both hyperplasia and hypertrophy, finally leading to chronic inflammation, hypoxia, and a phenotypic change of the cellular components of adipose tissue, collectively leading to a substantially altered secretory output of adipose tissue. In this review we have assessed the adipo-vascular axis, and an overview of adipokines associated with cardiovascular disease is provided. This resulted in a first list of more than 30 adipokines. A deeper analysis only considered adipokines that have been reported to impact on inflammation and NF-κB activation in the vasculature. Out of these, the most prominent link to cardiovascular disease was found for leptin, TNF-α, adipocyte fatty acid-binding protein, interleukins, and several novel adipokines such as lipocalin-2 and pigment epithelium-derived factor. Future work will need to address the potential role of these molecules as biomarkers and/or drug targets.
Inositol trisphosphate receptors in smooth muscle cells
Authors: Narayanan Damodaran , Adebiyi Adebowale , Jaggar Jonathan H.
Published: March 2012

Inositol 1,4,5-trisphosphate receptors (IP3Rs) are a family of tetrameric intracellular calcium (Ca2+) release channels that are located on the sarcoplasmic reticulum (SR) membrane of virtually all mammalian cell types, including smooth muscle cells (SMC). Here, we have reviewed literature investigating IP3R expression, cellular localization, tissue distribution, activity regulation, communication with ion channels and organelles, generation of Ca2+signals, modulation of physiological functions, and alterations in pathologies in SMCs. Three IP3R isoforms have been identified, with relative expression and cellular localization of each contributing to signaling differences in diverse SMC types. Several endogenous ligands, kinases, proteins, and other modulators control SMC IP3R channel activity. SMC IP3Rs communicate with nearby ryanodine-sensitive Ca2+channels and mitochondria to influence SR Ca2+release and reactive oxygen species generation. IP3R-mediated Ca2+release can stimulate plasma membrane-localized channels, including transient receptor potential (TRP) channels and store-operated Ca2+channels. SMC IP3Rs also signal to other proteins via SR Ca2+release-independent mechanisms through physical coupling to TRP channels and local communication with large-conductance Ca2+-activated potassium channels. IP3R-mediated Ca2+release generates a wide variety of intracellular Ca2+signals, which vary with respect to frequency, amplitude, spatial, and temporal properties. IP3R signaling controls multiple SMC functions, including contraction, gene expression, migration, and proliferation. IP3R expression and cellular signaling are altered in several SMC diseases, notably asthma, atherosclerosis, diabetes, and hypertension. In summary, IP3R-mediated pathways control diverse SMC physiological functions, with pathological alterations in IP3R signaling contributing to disease.
Activation of the TLR4 signaling pathway and abnormal cholesterol efflux lead to emphysema in ApoE-deficient mice
Authors: Goldklang Monica , Golovatch Polina , Zelonina Tina , Trischler Jordis , Rabinowitz Daniel , Lemaître Vincent , D'Armiento Jeanine
Published: March 2012

Smokers with airflow obstruction have an increased risk of atherosclerosis, but the relationship between the pathogenesis of these diseases is not well understood. To determine whether hypercholesterolemia alters lung inflammation and emphysema formation, we examined the lung phenotype of two hypercholesterolemic murine models of atherosclerosis at baseline and on a high-fat diet. Airspace enlargement developed in the lungs of apolipoprotein E-deficient (Apoe−/−) mice exposed to a Western-type diet for 10 wk. An elevated number of macrophages and lymphocytes accompanied by an increase in matrix metalloproteinase-9 (MMP-9) activity and MMP-12 expression was observed in the lungs of Apoe−/−mice on a Western-type diet. In contrast, low-density lipoprotein receptor-deficient ( Ldlr−/−) mice did not exhibit lung destruction or inflammatory changes. Most importantly, we revealed augmented expression of the downstream targets of the Toll-like receptor (TLR) pathway, interleukin-1 receptor-associated kinase 1, and granulocyte colony-stimulating factor, in the lungs of Apoe−/−mice fed with a Western-type diet. In addition, we demonstrated overexpression of MMP-9 in Apoe−/−macrophages treated with TLR4 ligand, augmented with the addition of oxidized LDL, suggesting that emphysema in these mice results from the activation of the TLR pathway secondary to known abnormal cholesterol efflux. Our findings indicate that, in Apoe−/−mice fed with an atherogenic diet, abnormal cholesterol efflux leads to increased systemic inflammation with subsequent lung damage and emphysema formation.