bluuebunny/crossref_metadata_2025 huggingface dataset:
Generator Output Breaker Reliability/Availability Benefits
Authors: Ananos Juan B. , Braun Dieter , Buck Wolfgang
Published: October 2008

The problem of operating power stations with the highest possible availability has become more and more important in recent years, the layout of a power station obviously has a decisive influence in this respect. The present paper is specifically concerned with the reliability assessment of large thermal power stations. It provides significant insights in the optimization of power stations layouts. The application of generator circuit-breakers for the switching of generators at their terminal voltage offers many advantages when compared with the unit connection such as lower first costs, simplified operational procedures and better fault protection. Modern SF6 generator circuit-breakers make it possible to interrupt all types of fault currents within four cycles. This rapid clearance of fault currents helps to avoid expensive secondary damage of power station equipment and consequently long down times for repair. Although they have a low probability of occurrence such outages have a substantial effect on the availability of a generating unit. It is obvious that long unavailability periods as e.g. in the case of disruptive faults on step-up transformers may affect the rate of return of investments related with power stations. With the recent successful certification of a generator circuit-breaker with a rated short-circuit breaking current of 200 kA SF6 generator circuit-breakers are now available for generating units up to 2000 MVA. Another recent development has been the integration of all the associated items of switchgear within the generator circuit-breaker enclosure as an option to their separate installation. This greatly improved functionality of generator switchgear also contributes to the realisation of simpler and more economic layouts of power stations. Beside a substantial reduction of the first costs this new solution, being fully factory assembled and tested, also makes possible considerable saving in time and expenditures for erection and commissioning.
Estimating Cooling Towers for Power Plant Applications
Authors: Cruz Hector L.
Published: October 2008

It has always been difficult to estimate size and cost of well designed counterflow induced-draught cooling towers due to the interrelationship of approach temperature and cooling range associated with each design. Attempts to estimate the cost of a tower by assessing currency per cell, per square foot, per gallon, or currency per other single metric, have never been sufficiently accurate due to the asymptotic nature of the approach temperature versus the tower size arithmetic function. To determine accurate qualitative metrics for cooling tower estimating purposes requires assessing two-variable second-order equations in water-flow-rate/approach-temperature, temperature-range/approach-temperature, wet-bulb-temperature/approach-temperature, and approach-temperature/cost. The design and therefore cost responds to the following variables; 1) Recirculating Water Flow Rate, 2) Inlet Wet Bulb Temperature (WBT), 3) Approach Temperature, and 4) Cooling Tower Range or Heat Duty. With the proper evaluation of these parameters they can be utilized to determine metrics to estimate the following parameters: 1) Number of Cells, 2) Basin Area, 3) Pump Power, 4) Fan Power, and 5) Costs (at today’s prices only). In addition, a percentage breakdown can be calculated for; 1) Structure, 2) Hardware, 3) Mechanical Equipment, 4) Labor, and 5) Miscellaneous items. Although developed for the power industry, the operative model, design, and qualified costing techniques are also valid for large petroleum and chemical process projects, provided the heat duty dissipated, ambient conditions, water quality and flow rate can be accurately predicted. A set of equations are developed which can be used to estimate the significant costs of a proposed cooling tower. Example calculations and data are presented in Annex A.
The Effect of Ambient Conditions on the Performance of Supplementary Fired Gas-Steam Combined Cycle
Authors: Kermani M. J. , Rad Nasab B. , Saffar-Avval M.
Published: October 2008

The effect of ambient conditions, ambient temperature and site location of the power plant (the altitude or ambient pressure), on the performance of a typical supplementary fired (SF) gas-steam combined cycle (CC) is studied, and its performances are compared with that of the unfired case. The CC used in the present study is comprised of two V94.2 gas turbine units, two HR-steam generators and a single steam cycle. For the cases studied, it is observed that SF can increase the total net power of the CC by 5% and the efficiency for the fired-cycle is observed to be about 1% less than that of unfired-cycle case. The variations of the total net power with ambient temperature for both supplementary fired and unfired cases (slope w.r.t. the ambient temperature) are almost identical.
Last Stage Performance Considerations in Low-Pressure Turbines of Power Plants: A Case Study
Authors: Sunder Raj Komandur S.
Published: October 2008

The last stage blades (LSB) of low-pressure (LP) turbines power plants have been historically specified and designed on the basis of optimization studies by matching the turbine to the condenser/cooling system for a specified unit rating. LSB sizes for U.S. nuclear applications currently range from 38” to 52” for unit ratings of 600 Mwe to 1200 Mwe. LP turbine arrangements usually consist of two or three double-flow sections in parallel. Last stage end loadings (last stage mass flow divided by the last stage annulus area) vary from approximately 8,000 lb/hr-sq.ft to 14,000 lb/hr-sq.ft, with corresponding unit loadings (electrical output in megawatts divided by last stage annulus area) of 1.1 Mwe/sq.ft to 2.1 Mwe/sq.ft. Several power plants have been upgrading/replacing their LP turbines. Considerations include efficiency, reliability, power uprates, operating license renewals (nuclear), aging, inspection and, maintenance. In some cases, LP turbine rotors are being replaced with new rotors, blading and steam path. Others are replacing LP turbines with new and advanced designs incorporating improved technology, better materials, optimized steam paths, more efficient blading, longer LSB sizes, redesigned exhaust hoods, etc. Unlike the other stages in the LP turbine, the last stage performance is affected by both the upstream (load) and downstream (condenser) conditions. While the LP turbines are being upgraded or replaced, no major modifications or upgrades are being made to the condensers. To address vibration effects due to increased flows and velocities from power uprates, the condenser tubes may be staked. Circulating water pumps may or may not be upgraded depending upon the particular application. Consequently, while improvements in LP turbines lead to more efficient utilization of the available energy and higher output, the last stage performance may be out of synch with the existing condenser/cooling system. Undersized or oversized LSB sizes in relation to the unit rating and end loading may result in less than optimum performance depending upon the design and operating range of the condenser/cooling system. This paper examines the various factors that affect last stage performance of LP turbines. Using a case study, it discusses the relationships between the last stage, the unit rating, the end loading and, the operating range of the condenser/cooling system. It examines different last stage exhaust loss curves and provides recommendations for selection of LSB sizes for optimum performance.
A Novel Boiler Ash Deposit Removal System
Authors: Bussing Thomas R. A. , Hochstein James R. , Harty J. Patrick
Published: October 2008

Pratt & Whitney has developed a novel boiler cleaning product based on pulse detonation combustion to efficiently remove ash deposits from coal-fired power plants as well as other industrial boiler applications. This new product, the SHOCKSystem™, offers significant advantages relative to conventional boiler cleaning methodology, including a likely reduction of erosion wear, as well as non-line-of-sight cleaning while online, which not only enhances overall plant performance but also enables a reduction and/or elimination of plant outages caused by fouling. As a result, the online detonation cleaning method has been shown to save millions of dollars in annual power generation costs for the typical coal-fired utility boiler. This paper briefly describes the pulse detonation cycle, presents the new online detonation cleaning method, and discusses demonstrated plant performance improvements and power generation cost savings using this method.
A Method for Estimating Moisture Separator Effectiveness on a Reheat Nuclear Unit
Authors: Kautzmann David E. , Ransom Robert A.
Published: October 2008

Having a better understanding of the level of moisture separator performance is an important component in evaluating the cost benefit of a turbine or MSR improvement or retrofit. The documented methods of determining Moisture Separator Effectiveness (MS η) on a reheat nuclear cycle require extensive station instrumentation, which may not be available in many power plants, or the introduction of radioactive (or other) tracers into the plant system. Because of these difficulties and associated costs, moisture separator performance is typically not adequately evaluated or monitored. This situation can lead to significant misconceptions about the actual operating moisture separator effectiveness. Using data from field tests of multiple GE-designed horizontal moisture separators, important relationships between MS performance and certain operating parameters were established that form the basis of this proposed Moisture Separator test method. This test method is specifically designed to remove many of the known difficulties associated with the current testing methods while maintaining reasonable accuracy levels. By removing many of the roadblocks in testing moisture separators, MS η can now be calculated on a regular basis and will allow for periodic performance monitoring and performance degradation detection.
Advancements in Gas Turbine Vane Repair
Authors: McGraw Julie , Van Deventer George , Anton Reiner , Burns Andrew
Published: October 2008

The evolution of industrial gas turbines has been a driving factor in the advancement of repair techniques for industrial gas turbine components. Turbine vane segments (also known as stationary blades, non-rotational airfoils, or nozzles) are among the many components that have been a focus for repair development. Due to increasing engine efficiencies, the design of gas turbine vane segments continues to become progressively more complex. Neoteric vanes are cast of highly developed superalloys, have complex cooling designs, and are coated with the latest generation coating systems which utilize advanced oxidation resistant bondcoatings combined with thermal barrier coatings. While advanced technologies enable these vanes to operate at the extreme hot gas path running temperatures of today’s engines, they also significantly increase the level of technology required to successfully repair them. The ability to repair these components is essential to minimize the operators’ life cycle cost of the gas turbine. Recoating, reestablishing of critical cooling, dimensional restoration, along with surface and structural restoration using high strength weld and braze techniques are essential for these vanes. Conventional and advanced repair techniques are key elements in the continuing evolution of industrial gas turbine component repair development. This paper will focus on a variety of Siemens’ technical competencies applied during the restoration of service run vane segments for the turbine section of a gas turbine. These repair competencies and technology/service options include: • Dimensional restoration techniques utilizing hot and cold straightening; • Utilization of refurbished blade rings for completed roll-in/roll-out exchanges; • Coupon repair techniques; • Braze restoration of cracks; • Laser etching; • Strain tolerant coatings; • Future technologies under development.
Condenser Tube Fouling and Failures: Cause and Mitigation
Authors: Howell Andrew G. , Saxon George E.
Published: October 2008

The two most common condenser tube problems faced by chemists are internal tube fouling and tube failure. Fouling can have a major impact on power station generating efficiency and capacity, and tube leaks can seriously impact unit availability and reliability. Fundamental understanding of the root cause(s) of these issues, and their mitigation, is essential to resolving these problems and/or preventing their occurrence.
Collaborative Modeling Using System Dynamics for Water Resource Management
Authors: Sun A. C. , Tidwell V. C. , Thomas R. , Brainard J. R. , Kobos P. H. , Malczynski L. A. , Klise G.
Published: October 2008

Water resource management for most Southwestern states requires collaborative solutions that cross regional, state, and federal judicial boundaries. As most of the region experiences drought-like conditions as well as population growth, there is a growing concern about sustainability of the water resource to meet industrial, agricultural, and residential demands. Technically, seeking a consensus path requires modeling of the hydrologic cycle within a prescribed region. Credible models must capture key interdependencies of various water resources, use historical data for calibration, and provide temporal/spatial resolutions that are aligned with the interests of the decision makers.
Creating Sustainable Water Supplies That Benefit Industries and Communities
Authors: Sundstrom Glen , Pethick Fred
Published: October 2008

For many years, the world enjoyed an abundance of high-quality fresh water that was inexpensive to obtain, treat and transport. Now, many communities and industries face water shortages, deteriorating water quality from seawater intrusion and greater demands due to population growth, tourism, recreational use, drought and industrial expansion. Many water and wastewater treatment plants are struggling to keep up with these higher demands or achieve the quality standards set forth by regulatory agencies. As fresh water becomes harder to obtain and its demand rises, the cost to individual consumers and industrial users increases.
Determination of Water-Soluble Organophosphorus Herbicides by Ion Chromatography With Inductively Coupled Plasma Mass Spectrometry Detection
Authors: Guo Zhongxian , Cai Qiantao , Yang Zhaoguang
Published: October 2008

There is a high risk for human exposure to organophosphorus pesticides through contaminated drinking water. Glyphosate, glufosinate, fosamine and ethephon are among the water-soluble herbicides used currently. Sensitive and rapid analytical methodologies are critical for evaluating their residuals in a broad variety of samples, including environmental waters. However, challenges arise from the inherent chemical properties of the herbicides: strong polarity, high solubility in water, insolubility in organic solvent (except ethephon), absence of chromophore or fluorophore in their molecular structures. So far very rare analytical methods are available for ethephon [1] and fosamine [2], while glyphosate and glufosinate are often determined by gas chromatography [3], high performance liquid chromatography (HPLC) [4] and capillary electrophoresis (CE) [5]. Inductively coupled plasma mass spectrometry (ICP-MS) is sensitive, rapid, selective, and is more powerful when hyphenated with appropriate separation. For the analysis of glufosinate, glyphosate and its metabolite aminomethylphosphonic acid (AMPA), ICP-MS was recently coupled to CE [6] or ion-pairing reversed-phase LC [7].
Development of an Optimized Dose for Coformulation of Zidovudine with Drugs That Select for the K65R Mutation Using a Population Pharmacokinetic and Enzyme Kinetic Simulation Model
Authors: Hurwitz Selwyn J. , Asif Ghazia , Kivel Nancy M. , Schinazi Raymond F.
Published: October 2008

In vitro selection studies and data from large genotype databases from clinical studies have demonstrated that tenofovir disoproxil fumarate and abacavir sulfate select for the K65R mutation in the human immunodeficiency virus type 1 polymerase region. Furthermore, other novel non-thymine nucleoside reverse transcriptase (RT) inhibitors also select for this mutation in vitro. Studies performed in vitro and in humans suggest that viruses containing the K65R mutation remained susceptible to zidovudine (ZDV) and other thymine nucleoside antiretroviral agents. Therefore, ZDV could be coformulated with these agents as a “resistance repellent” agent for the K65R mutation. The approved ZDV oral dose is 300 mg twice a day (b.i.d.) and is commonly associated with bone marrow toxicity thought to be secondary to ZDV-5′-monophosphate (ZDV-MP) accumulation. A simulation study was performed in silico to optimize the ZDV dose for b.i.d. administration with K65R-selecting antiretroviral agents in virtual subjects using the population pharmacokinetic and cellular enzyme kinetic parameters of ZDV. These simulations predicted that a reduction in the ZDV dose from 300 to 200 mg b.i.d. should produce similar amounts of ZDV-5′-triphosphate (ZDV-TP) associated with antiviral efficacy (>97% overlap) and reduced plasma ZDV and cellular amounts of ZDV-MP associated with toxicity. The simulations also predicted reduced peak and trough amounts of cellular ZDV-TP after treatment with 600 mg ZDV once a day (q.d.) rather than 300 or 200 mg ZDV b.i.d., indicating that q.d. dosing with ZDV should be avoided. These in silico predictions suggest that 200 mg ZDV b.i.d. is an efficacious and safe dose that could delay the emergence of the K65R mutation.
Impact of Self-Assembly Properties on Antibacterial Activity of Short Acyl-Lysine Oligomers
Authors: Sarig Hadar , Rotem Shahar , Ziserman Lior , Danino Dganit , Mor Amram
Published: October 2008

We investigated both the structural and functional consequences of modifying the hydrophobic, lipopeptide-mimetic oligo-acyl-lysine (OAK) N
α
-hexadecanoyl-
l
-lysyl-
l
-lysyl-aminododecanoyl-
l
-lysyl-amide (c
16
KKc
12
K) to its unsaturated analog hexadecenoyl-KKc
12
K [c
16(ω7)
KKc
12
K]. Despite similar tendencies for self-assembly in solution (critical aggregation concentrations, ∼10 μM), the analogous OAKs displayed dissimilar antibacterial properties (e.g., bactericidal kinetics taking minutes versus hours). Diverse experimental evidence provided insight into these discrepancies: whereas c
16(ω7)
KKc
12
K created wiry interconnected nanofiber networks, c
16
KKc
12
K formed both wider and stiffer fibers which displayed distinct binding properties to phospholipid membranes. Unsaturation also shifted their gel-to-liquid transition temperatures and altered their light-scattering properties, suggesting the disassembly of c
16(ω7)
KKc
12
K in the presence of bacteria. Collectively, the data indicated that the higher efficiency in interfering with bacterial viability emanated from a wobbly packing imposed by a single double bond. This suggests that similar strategies might improve hydrophobic OAKs and related lipopeptide antibiotics.
Comparison of Disk Diffusion and Agar Dilution Methods for Erythromycin, Ciprofloxacin, and Tetracycline Susceptibility Testing of
Campylobacter coli
and for Tetracycline Susceptibility Testing of
Campylobacter jejuni
subsp.
jejuni
Authors: Gaudreau Christiane , Girouard Yves , Gilbert Huguette , Gagnon Josée , Bekal Sadjia
Published: October 2008

With disk diffusion, the following zone diameters are suggested to be resistant and susceptible breakpoints, respectively: for susceptibility testing of
Campylobacter coli
, no inhibition zone and 15 mm or more for erythromycin, and 20 mm or less and 25 mm or more for ciprofloxacin, in the absence or presence of an inhibition zone around the nalidixic acid disk; and for susceptibility testing of
C. coli
and
Campylobacter jejuni
, 20 mm or less and 26 mm or more for tetracycline.
Drug Resistance Mutation Profile and Accumulation Kinetics in Human Immunodeficiency Virus-Positive Individuals Infected with Subtypes B and F Failing Highly Active Antiretroviral Therapy Are Influenced by Different Viral Codon Usage Patterns
Authors: Waléria-Aleixo A. , Martins A. N. , Arruda M. B. , Brindeiro R. M. , Da-Silva R. M. , Nobre F. F. , Greco D. B. , Tanuri A.
Published: October 2008

The major human immunodeficiency virus type 1 subtype circulating in Brazil is B, followed by F and C. We have genotyped 882 samples from Brazilian patients for whom highly active antiretroviral therapy failed, and we found subtype B and the unique recombinant B/F1 forms circulating. Due to codon usage variation, there is a significantly lower incidence of the substitutions L210W, Q151M, and F116Y in subtype F1 isolates than in the subtype B counterparts.
Incidence and Characteristics of Vancomycin Nonsusceptible Strains of Methicillin-ResistantStaphylococcus aureusat Hershey Medical Center
Authors: Kosowska-Shick Klaudia , Ednie Lois M. , McGhee Pamela , Smith Kathy , Todd Cynthia D. , Wehler Amanda , Appelbaum Peter C.
Published: October 2008

All 982 methicillin-resistantStaphylococcus aureusstrains collected from August 2006 to December 2007 were tested for vancomycin susceptibility by using 3-μg/ml vancomycin brain heart infusion screening plates, a vancomycin Etest, and a vancomycin/teicoplanin macro Etest. Three vancomycin-intermediateStaphylococcus aureus(VISA) (0.3%) and two heterogeneous VISA (0.2%) isolates were identified. The screening method yielded 895 cases of ≤1 colony and 87 positive results (with growth of >1 colony after 48 h); further Etests showed 82/87 isolates with growth on screening plates to be false positive. Repeat testing showed a false-positivity rate of only 15 of the original 87 isolates by plate screening.
Porphyromonas gingivalis, Gamma Interferon, and a Proapoptotic Fibronectin Matrix Form a Synergistic Trio That Induces c-Jun N-Terminal Kinase 1-Mediated Nitric Oxide Generation and Cell Death
Authors: Ghosh Abhijit , Park Ji Young , Fenno Christopher , Kapila Yvonne L.
Published: October 2008

During infection and inflammation, bacterial and inflammatory proteases break down extracellular matrices into macromolecular fragments. Fibronectin fragments are associated with disease severity in arthritis and periodontitis. The mechanisms by which these fragments contribute to disease pathogenesis are unclear. One likely mechanism is that fibronectin fragments induce apoptosis of resident cells, which can be further modulated by nitric oxide. Nitric oxide levels are increased at inflammatory sites in periodontitis patients. The aim of this study was to examine whether a proapoptotic fibronectin matrix (AFn) exerts its action by inducing nitric oxide and whether priming by bacterial and inflammatory components exacerbates this mechanism. Our data demonstrate that AFn increased the levels of nitric oxide and inducible nitric oxide synthase (iNOS) dose and time dependently in periodontal ligament (PDL) cells. These effects and apoptosis were inhibited by iNOS suppression and enhanced by iNOS overexpression. Nitric oxide and iNOS induction were paralleled by increased c-Jun N-terminal kinase 1 (JNK-1) phosphorylation. JNK-1 overexpression enhanced the expression of nitric oxide and iNOS, whereas inhibiting JNK-1 by small interfering RNA or a kinase mutant reversed these findings. Priming PDL cells withPorphyromonas gingivalis, its lipopolysaccharide (LPS), or gamma interferon (IFN-γ) further increased nitric oxide levels and apoptosis.Escherichia coliandStreptococcus mutansinduced lesser effects. Gingival fibroblasts and neutrophils responded to a lesser degree to these stimuli, whereas keratinocytes were resistant to apoptosis. Thus, proapoptotic matrices trigger nitric oxide release via JNK-1, promoting further apoptosis in host cells. LPS and IFN-γ accentuate this mechanism, suggesting that during inflammation, the affected matrices and bacterial and inflammatory components combined exert a greater pathogenic effect on host cells.
Primary Activation of Antigen-Specific Naive CD4+and CD8+T Cells following Intranasal Vaccination with Recombinant Bacteria
Authors: Ciabattini Annalisa , Pettini Elena , Andersen Peter , Pozzi Gianni , Medaglini Donata
Published: October 2008

The primary activation of T-helper and T-cytotoxic cells following mucosal immunization with recombinantStreptococcus gordoniiwas studied in vivo by adoptive transfer of ovalbumin (OVA)-specific transgenic CD8+(OT-I) and CD4+(OT-II) T cells. A recombinant strain, expressing on the surface the vaccine antigen Ag85B-ESAT-6 fromMycobacterium tuberculosisfused to OVA T-helper and T-cytotoxic epitopes (peptides 323 to 339 and 257 to 264), was constructed and used to immunize C57BL/6 mice by the intranasal route. Recombinant, but not wild-type, bacteria induced OVA-specific CD4+and CD8+T-cell clonal expansion in cervical lymph nodes, lung, and spleen. OVA-specific CD4+and CD8+T-cell proliferation appeared first in cervical lymph nodes and later in the spleen, suggesting a possible migration of activated cells from the inductive site to the systemic district. A significant correlation between the percentages of CD4+and CD8+proliferating T cells was observed for each animal. The expression of CD69, CD44, and CD45RB on proliferating T lymphocytes changed as a function of the cell division number, confirming T-cell activation following the antigen encounter. These data indicate that intranasal immunization with recombinantS. gordoniiis capable of inducing primary activation of naive antigen-specific CD4+and CD8+T cells, both locally and systemically.
Iatrogenic lesions and artefacts in gynaecological pathology
Authors: Clarke B , McCluggage W G
Published: October 2008

Increasingly in the field of medicine, new therapeutic modalities, both surgical and non-surgical, are being introduced. Some of these may significantly alter the pathological appearance of normal and neoplastic tissue and result in problems for the pathologist. In this review, iatrogenic pathology within the female genital tract is described, especially concentrating on the recent literature. Pathological artefacts within the female genital tract are also reviewed. Topics covered include mechanical displacement of normal and neoplastic elements into vascular or tissue spaces and thermal artefacts. Recently described pathological findings in neoplastic and non-neoplastic tissue secondary to hormonal, chemotherapeutic and other medications are discussed. Changes associated with non-surgical management of uterine leiomyomas are also described. It behoves the pathologist to be aware of these iatrogenic lesions and artefacts in order to prevent diagnostic errors.
Hypothesis: huntingtin may function in membrane association and vesicular traffickingThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Truant Ray , Atwal Randy , Burtnik Anjee
Published: October 2008

Huntington’s disease is a progressive neurodegenerative genetic disorder that is caused by a CAG triplet-repeat expansion in the first exon of the IT15 gene. This CAG expansion results in polyglutamine expansion in the 350 kDa huntingtin protein. The exact function of huntingtin is unknown. Understanding the pathological triggers of mutant huntingtin, and distinguishing the cause of disease from downstream effects, is critical to designing therapeutic strategies and defining long- and short-term goals of therapy. Many studies that have sought to determine the functions of huntingtin by determining huntingtin’s protein–protein interactions have been published. Through these studies, huntingtin has been seen to interact with a large number of proteins, and is likely a scaffolding protein for protein–protein interactions. Recently, using imaging, integrative proteomics, and cell biology, huntingtin has been defined as a membrane-associated protein, with activities related to axonal trafficking of vesicles and mitochondria. These functions have also been attributed to some huntingtin-interacting proteins. Additionally, discoveries of a membrane association domain and a palmitoylation site in huntingtin reinforce the fact that huntingtin is membrane associated. In Huntington’s disease mouse and fly models, axonal vesicle trafficking is inhibited, and lack of proper uptake of neurotrophic factors may be an important pathological trigger leading to striatal cell death in Huntington’s disease. Here we discuss recent advances from many independent groups and methodologies that are starting to resolve the elusive function of huntingtin in vesicle transport, and evidence that suggests that huntingtin may be directly involved in membrane interactions.
Computer simulations of ABC transporter componentsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Oloo Eliud O. , Kandt Christian , O’Mara Megan L. , Tieleman D. Peter
Published: October 2008

Current computer simulation techniques provide robust tools for studying the detailed structure and functional dynamics of proteins, as well as their interaction with each other and with other biomolecules. In this minireview, we provide an illustration of recent progress and future challenges in computer modeling by discussing computational studies of ATP-binding cassette (ABC) transporters. ABC transporters have multiple components that work in a well coordinated fashion to enable active transport across membranes. The mechanism by which members of this superfamily execute transport remains largely unknown. Molecular dynamics simulations initiated from high-resolution crystal structures of several ABC transporters have proven to be useful in the investigation of the nature of conformational coupling events that may drive transport. In addition, fruitful efforts have been made to predict unknown structures of medically relevant ABC transporters, such as P-glycoprotein, using homology-based computational methods. The various techniques described here are also applicable to gaining an atomically detailed understanding of the functional mechanisms of proteins in general.
Why bicarbonate?This paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Casey Joseph R.
Published: October 2008

Bicarbonate is a simple single carbon molecule that plays surprisingly important roles in diverse biological processes. Among these are photosynthesis, the Krebs cycle, whole-body and cellular pH regulation, and volume regulation. Since bicarbonate is charged it is not permeable to lipid bilayers. Mammalian membranes thus contain bicarbonate transport proteins to facilitate the specific transmembrane movement of HCO3–. This review provides a wide-ranging view of the biochemistry of bicarbonate and its membrane transporters, revealing what makes the study of bicarbonate transport such a rewarding activity.
Effects of site-directed mutations inEscherichia colisuccinate dehydrogenase on the enzyme activity and production of superoxide radicalsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Zhao Zhongwei , Rothery Richard A. , Weiner Joel H.
Published: October 2008

Escherichia coli succinate dehydrogenase (SdhCDAB) catalyzes the oxidation of succinate to fumarate in the Krebs cycle, and during turnover, it produces superoxide radicals. SdhCDAB is a good model system for the succinate dehydrogenase (Sdh) found in the mitochondrial respiratory chain (complex II), as the subunits are structural homologues. Although mutations in sdh genes are reportedly associated with a variety of mitochondria-related diseases, the molecular mechanism of these diseases is poorly understood. We have investigated the effects of site-directed mutations around the heme (SdhD-H71L and SdhC-H91L), and at the ubiquinone-binding site (Q site; SdhC-I28E), on enzyme activity and production of superoxide radicals. The mutations SdhD-H71L and SdhC-I28E, but not SdhC-H91L, significantly reduce the succinate–ubiquinone reductase activity of the enzyme. All 3 mutant enzymes produce more superoxide than the wild-type enzyme, indicating that disturbance of the heme or the Q site can enhance superoxide production. The presence of a Q-site inhibitor reduces superoxide production significantly. Furthermore, the yield of superoxide is substrate dependent and increases with succinate concentration from 0.1 to 10 mmol/L. Our results indicate that, in SdhCDAB, the Q site with bound ubiquinone is an important source of superoxide radicals.
The position of the Gly-xxx-Gly motif in transmembrane segments modulates dimer affinityThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Johnson Rachel M. , Rath Arianna , Deber Charles M.
Published: October 2008

Although the intrinsic low solubility of membrane proteins presents challenges to their high-resolution structure determination, insight into the amino acid sequence features and forces that stabilize their folds has been provided through study of sequence-dependent helix–helix interactions between single transmembrane (TM) helices. While the stability of helix–helix partnerships mediated by the Gly-xxx-Gly (GG4) motif is known to be generally modulated by distal interfacial residues, it has not been established whether the position of this motif, with respect to the ends of a given TM segment, affects dimer affinity. Here we examine the relationship between motif position and affinity in the homodimers of 2 single-spanning membrane protein TM sequences: glycophorin A (GpA) and bacteriophage M13 coat protein (MCP). Using the TOXCAT assay for dimer affinity on a series of GpA and MCP TM segments that have been modified with either 4 Leu residues at each end or with 8 Leu residues at the N-terminal end, we show that in each protein, centrally located GG4 motifs are capable of stronger helix–helix interactions than those proximal to TM helix ends, even when surrounding interfacial residues are maintained. The relative importance of GG4 motifs in stabilizing helix–helix interactions therefore must be considered not only in its specific residue context but also in terms of the location of the interactive surface relative to the N and C termini of α-helical TM segments.
Renal nucleoside transporters: physiological and clinical implicationsThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Elwi Adam N. , Damaraju Vijaya L. , Baldwin Stephen A. , Young James D. , Sawyer Michael B. , Cass Carol E.
Published: October 2008

Renal handling of physiological and pharmacological nucleosides is a major determinant of their plasma levels and tissue availabilities. Additionally, the pharmacokinetics and normal tissue toxicities of nucleoside drugs are influenced by their handling in the kidney. Renal reabsorption or secretion of nucleosides is selective and dependent on integral membrane proteins, termed nucleoside transporters (NTs) present in renal epithelia. The 7 known human NTs (hNTs) exhibit varying permeant selectivities and are divided into 2 protein families: the solute carrier (SLC) 29 (SLC29A1, SLC29A2, SLC29A3, SLC29A4) and SLC28 (SLC28A1, SLC28A2, SLC28A3) proteins, otherwise known, respectively, as the human equilibrative NTs (hENTs, hENT1, hENT2, hENT3, hENT4) and human concentrative NTs (hCNTs, hCNT1, hCNT2, hCNT3). The well characterized hENTs (hENT1 and hENT2) are bidirectional facilitative diffusion transporters in plasma membranes; hENT3 and hENT4 are much less well known, although hENT3, found in lysosomal membranes, transports nucleosides and is pH dependent, whereas hENT4–PMAT is a H+-adenosine cotransporter as well as a monoamine–organic cation transporter. The 3 hCNTs are unidirectional secondary active Na+-nucleoside cotransporters. In renal epithelial cells, hCNT1, hCNT2, and hCNT3 at apical membranes, and hENT1 and hENT2 at basolateral membranes, apparently work in concert to mediate reabsorption of nucleosides from lumen to blood, driven by Na+gradients. Secretion of some physiological nucleosides, therapeutic nucleoside analog drugs, and nucleotide metabolites of therapeutic nucleoside and nucleobase drugs likely occurs through various xenobiotic transporters in renal epithelia, including organic cation transporters, organic anion transporters, multidrug resistance related proteins, and multidrug resistance proteins. Mounting evidence suggests that hENT1 may have a presence at both apical and basolateral membranes of renal epithelia, and thus may participate in both selective secretory and reabsorptive fluxes of nucleosides. In this review, the renal handling of nucleosides is examined with respect to physiological and clinical implications for the regulation of human kidney NTs and adenosine signaling, intracellular nucleoside transport, and nephrotoxicities associated with some nucleoside drugs.
Shedding light on drug transport: structure and function of the P-glycoprotein multidrug transporter (ABCB1)This paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Sharom Frances J.
Published: October 2008

P-glycoprotein (Pgp; ABCB1), a member of the ATP-binding cassette (ABC) superfamily, exports structurally diverse hydrophobic compounds from the cell, driven by ATP hydrolysis. Pgp expression has been linked to the efflux of chemotherapeutic drugs in human cancers, leading to multidrug resistance (MDR). The protein also plays an important physiological role in limiting drug uptake in the gut and entry into the brain. Substrates partition into the lipid bilayer before interacting with Pgp, which has been proposed to function as a hydrophobic vacuum cleaner. Low- and medium-resolution structural models of Pgp suggest that the 2 nucleotide-binding domains are closely associated to form a nucleotide sandwich dimer. Pgp is an outwardly directed flippase for fluorescent phospholipid and glycosphingolipid derivatives, which suggests that it may also translocate drug molecules from the inner to the outer membrane leaflet. The ATPase catalytic cycle of the protein is thought to proceed via an alternating site mechanism, although the details are not understood. The lipid bilayer plays an important role in Pgp function, and may regulate both the binding and transport of drugs. This review focuses on the structure and function of Pgp, and highlights the importance of fluorescence spectroscopic techniques in exploring the molecular details of this enigmatic transporter.
Coupling between apical and paracellular transport processesThis paper is one of a selection of papers published in this Special Issue, entitled CSBMCB — Membrane Proteins in Health and Disease.
Authors: Kapus András , Szászi Katalin
Published: October 2008

Transcellular transport affects the paracellular flux through 2 distinct mechanisms: by determining the driving force and by altering the permeability of the paracellular pathway. Such coordination ensures efficient transepithelial transport by preventing the build-up of large electrical and osmotic gradients. The regulation of paracellular permeability was originally recognized as increased paracellular flux of water and solutes upon the activation of the intestinal Na+-coupled glucose uptake. Despite great advances in the molecular characterization of the tight junctions that form the structural basis of epithelial barrier functions, the mechanisms whereby apical transporters alter the paracellular pathways remains unresolved. Recent studies suggest that myosin-based contractility is central to this coupling. In this minireview, we summarize our current knowledge of paracellular permeability, its regulation by contractility, and the various signaling events that link apical Na+-glucose cotransport to myosin phosphorylation. While the role of myosin phosphorylation appears to be universal, the mechanism(s) whereby apical transport triggers this process is likely cell specific. The current model suggests that in intestinal cells, a key factor is a p38 MAP kinase-induced Na+/H+-exchanger-mediated alkalinization. We propose an alternative, nonexclusive mechanism in kidney tubular cells, in which the key event may be a Na+-cotransport-triggered plasma membrane depolarization, which in turn leads to Rho-mediated myosin phosphorylation.
Spruce budworm populations, defoliation, and changes in stand condition during an uncontrolled spruce budworm outbreak on Cape Breton Island, Nova Scotia
Authors: Ostaff Donald P. , MacLean David A.
Published: October 2008

Effects of an uncontrolled spruce budworm (Choristoneurafumiferana (Clem.)) outbreak in 20 mature balsam fir (Abiesbalsamea (L.) Mill.) stands on Cape Breton Island, Nova Scotia, were studied from 1976 to 1985. Spruce budworm populations were extremely high, higher than peak levels recorded for other outbreaks, and averaged over 380 third-instar larvae per square metre of foliage from 1976 to 1980. As many as 1570 third-instar larvae per square metre occurred 5 to 7 years after the start of the outbreak, resulting in complete current defoliation and back-feeding on older foliage. Stands were divided into three groups, based on the pattern of cumulative current defoliation; the sum of current annual defoliation during the outbreak was 343, 445, and 543% for these groups, equivalent to the removal of 3.5 to 5.5 age-classes of foliage. Budworm defoliation caused the death of 78, 80, and 89% of the merchantable balsam fir volume in the three groups of stands, respectively, as well as 27% of the spruce (Picea sp.) volume; another 39% of the spruce volume died as a result of spruce beetle (Dendroctonusrufipennis Kby.) activity. Fir mortality commenced 3 years after the start of the outbreak and spruce mortality 2 to 3 years later. About one-half of the total mortality occurred in the 4 years after budworm populations and defoliation returned to low levels. Tree mortality and loss of foliage opened the stands, and 4 years after the collapse of the outbreak, 4% of the surviving trees and 17% of the dead trees had blown down, whereas 60% of all trees had broken tops.
Detection and analysis of T-DNA in crown gall tumors and kanamycin-resistant callus of Robiniapseudoacacia
Authors: Davis John M. , Keathley Daniel E.
Published: October 2008

Five Agrobacteriumtumefaciens strains, and one A. rhizogenes strain, incited tumors on Robiniapseudoacacia L. (black locust) tissues that were inoculated invitro. Four phytohormone-independent tumors, incited by A. tumefaciens strains A6, A348, A274, and A208, were examined using Southern analysis. T-DNA sequences were detected in, and appeared to be integrated into, the DNA from all the tumors. Some tumors tested negative for the presence of octopine or nopaline. All of these tumors had T-DNAs that were truncated on the right ends, i.e., missing the region in which those particular opine synthetic loci are present on the Ti plasmid. Kanamycin-resistant callus was also obtained after inoculation of cotyledons with A. tumefaciens strain A281 carrying the binary vector pGA472, and Southern analysis indicated that nptII sequences were integrated into the R. pseudoacacia genome.
Vertical distribution of leaf area in Larixoccidentalis: a comparison of two estimation methods
Authors: Bidlake William R. , Black R. Alan
Published: October 2008

Total leaf-area index and the vertical distribution of leaf-area index were described for an unthinned stand (density 11 250 stems/ha) and a thinned stand (density 1660 stems/ha) of 30-year-old Larixoccidentalis Nutt. Two independent methods were used to estimate leaf-area index in each of the two stands. The first method is based on allometric relationships that are applied to stem measurements, and the second method is based on gap-fraction analysis of fisheye photographs. Leaf-area index estimates obtained by the two methods were not significantly different. The gap-fraction method provides a desirable alternative because much less fieldwork is required, however, use of this method is limited to canopies where the light-blocking elements are randomly displayed. Total leaf-area index values for the unthinned and thinned stands were 5.0 and 3.6, respectively. The vertical distribution of leaf-area index in the unthinned stand resembled a normal distribution. The vertical distribution of leaf-area index in the thinned stand would have resembled a normal distribution, except that thinning operations resulted in a truncated distribution of leaf-area index at the canopy base.
The use of notary deeds to estimate the changes in the composition of 19th century forests, in Haut-Saint-Laurent, Quebec
Authors: Bouchard André , Dyrda Stéphan , Bergeron Yves , Meilleur Alain
Published: October 2008

Notary deeds are a new and useful tool for studying the past composition of forest cover, especially when other sources of detailed historical information are not available. When their biases, particularly their nonsystematic survey of the landscape or the influence of market value on the cords sold, are properly taken into consideration, these documents can be used to indicate past forest types and some of the major component species. A case study was developed in the Haut-Saint-Laurent, Quebec, which describes the relative abundance of tree species utilized for forest products in the middle of the 19th century. After the valuable pines and oaks were selectively lumbered at the start of the 19th century, five other species, hemlock, spruce, maple, yellow birch, and beech, were lumbered in a second generation of forest exploitation.
Changes in xylem pressure potential of red spruce seedlings treated with ozone and simulated acid rain
Authors: Roberts Bruce R. , Cannon Jr. William N.
Published: October 2008

Two-year-old containerized seedlings of red spruce (Picearubens Sarg.) were exposed for 8 weeks to charcoal-filtered air (control) or to 7 and 15 parts per hundred million (pphm) ozone (O3) alone and 15 pphm O3 in combination with simulated acid rainfall at pH 4.2 and 3.0 prior to measuring shoot xylem pressure potential. Pressure potential determinations for seedlings treated with O3 alone or O3 + acid rain were always higher (less negative) than similar determinations made on comparable seedlings grown in charcoal-filtered air. These results suggest that exposure to atmospheric deposition may affect xylem pressure potential indirectly by influencing transpirational water loss via stomatal closure and (or) reductions in leaf area expansion. Calculations of osmotic potential and turgor pressure suggest the possibility of some osmotic adjustment in response to deposition stress in this species.
Absorption and translocation of [14C]glyphosate in four woody plant species
Authors: Green Thomas H. , Minogue Patrick J. , Brewer Charles H. , Glover Glenn R. , Gjerstad Dean H.
Published: October 2008

Absorption and translocation patterns of radio-labelled glyphosate (N-(phosphonomethyl)glycine) were examined in four species of woody plants to determine mechanisms of herbicide tolerance in species common to the southeastern United States. Loblolly pine (Pinustaeda L.) and yaupon (Ilexvomitoria (L.) Ait.), both tolerant to the herbicide, absorbed significantly less glyphosate than did red maple (Acerrubrum L.) or white oak (Quercusalba L.), indicating the importance of foliar absorption as a barrier to glyphosate entry. Although herbicide absorption was similar between the sensitive white oak and the tolerant red maple, white oak accumulated more glyphosate in the roots than did red maple, indicating that translocation patterns also contribute significantly to glyphosate tolerance in some woody species.