Secondary Transport Systems Research Articles

Proton conductance and regulation of proton/potassium fluxes in Escherichia coli FhlA-lacking cells during fermentation of mixed carbon sources

Escherichia coli uptake potassium ions with the coupling of proton efflux and energy utilization via proton FOF1-ATPase. In this study contribution of formate hydrogen lyase (FHL) complexes in the proton/potassium fluxes and the formation of proton conductance (CMH+) were investigated using fhlA mutant strain. The proton flux rate (JH+) decreased in fhlA by ∼ 25 % and ∼70 % during the utilization of glucose and glycerol, respectively, at 20 h suggesting H+ transport via or through FHL complexes. The decrease in JK+ in fhlA by ∼40 % proposed the interaction between FHL and Trk secondary transport system during mixed carbon fermentation. Moreover, the usage of N,N′-dicyclohexylcarbodiimide (DCCD) demonstrated the mediation of FOF1-ATPase in this interaction. CMH+ was 13.4 nmol min−1 mV−1 in WT at 20 h, which decreased by 20 % in fhlA. Taken together, FHL complexes have a significant contribution to the modulation of H+/K+ fluxes and the CMH + for efficient energy transduction and regulation of the proton motive force during mixed carbon sources fermentation.

Detection of major facilitator superfamily (MFS) transporter in Enterobacteriaceae isolated from chicken

A major facilitator superfamily (MFS) transporter is an active secondary transport system that uses a chemiosmotic ion gradient to transport small molecules. MFS is part of the efflux pump group of proteins and is responsible for releasing toxic compounds and contributing to the antimicrobial resistance mechanisms. In this study, we aimed to detect MFS genes from a collection of Enterobacteriaceae (n=60) isolated from cloacal swabs of chickens. After DNA extraction and amplification, only four isolates (6.7%) were regarded positive for MFS genes and subjected to Sanger dideoxy sequencing. A BlastX search in GenBank® showed that four positive samples with approximate length 300 bp were identified as MSF transporter from Klebsiella pneumoniae with a similarity of 97-98%. This finding warrants further study to confirm both phenotypic and genotypic resistance profiles that correlate with bacterial multidrug efflux pump mechanism.

Neutronics and thermal-hydraulics coupling analyses on transient and accident behaviors of molten chloride salt fast reactor

ABSTRACT Neutronics and thermal-hydraulics coupling transient analyses have been carried out to investigate the intrinsic safety characteristics and fuel temperature ranges of a molten chloride salt fast reactor. The analysis system includes a primary heat transport system and a secondary heat transport system connected by aheat exchanger and a decay heat removal system connected to the secondary system. The neutronics and thermal-hydraulics coupling analysis was performed with the RELAP5-3D code to analyze the entire plant behavior of each event, the temperature and velocity of the reactor inlet flow were obtained, and the reactor power was analyzed in detail following the FLUENT code. Through these analyses, the most severe events for the reactor were revealed. Analysis using the two codes showed that the reactor power calculated by RELAP5-3D was in good agreement with that of FLUENT although the detailed flow inside the core could not be reproduced.

Modeling of Safety Basis Events in the VTR

The Versatile Test Reactor (VTR) is a fast spectrum test reactor currently being developed in the United States under the direction of the U.S. Department of Energy, Office of Nuclear Energy. Safety analysis of the conceptual VTR design is being performed using the SAS4A/SASSYS-1 fast reactor safety analysis code with a model representing the reactor core, primary and secondary heat transport systems, reactor vessel auxiliary cooling system, and reactor protection system. The system’s response and safety performance are being evaluated for a wide spectrum of event initiators and accident sequences. This paper presents an overview of the activities that are ongoing in support of the modeling and analysis of safety basis events (SBEs) in the VTR, including the VTR SAS4A/SASSYS-1 model development, an overview of the SAS4A/SASSYS-1 verification and validation efforts, and a summary of key model development activities to improve the predictive capability of the code. A summary of the results and an analysis of several key SBEs are also presented. VTR authorization from the U.S. Department of Energy will require transient simulations that are demonstrated to be accurate.

Role of Na+/K+-ATPase in ischemic stroke: in-depth perspectives from physiology to pharmacology.

Na+/K+-ATPase (NKA) is a large transmembrane protein expressed in all cells. It is well studied for its ion exchanging function, which is indispensable for the maintenance of electrochemical gradients across the plasma membrane and herein neuronal excitability. The widely recognized pump function of NKA closely depends on its unique structure features and conformational changes upon binding of specific ions. Various Na+-dependent secondary transport systems are rigorously controlled by the ionic gradients generated by NKA and are essential for multiple physiological processes. In addition, roles of NKA as a signal transducer have also been unveiled nowadays. Plethora of signaling cascades are defined including Src-Ras-MAPK signaling, IP3R-mediated calcium oscillation, inflammation, and autophagy though most underlying mechanisms remain elusive. Ischemic stroke occurs when the blood flow carrying nutrients and oxygen into the brain is disrupted by blood clots, which is manifested by excitotoxicity, oxidative stress, inflammation, etc. The protective effect of NKA against ischemic stress is emerging gradually with the application of specific NKA inhibitor. However, NKA-related research is limited due to the opposite effects caused by NKA inhibitor at lower doses. The present review focuses on the recent progression involving different aspects about NKA in cellular homeostasis to present an in-depth understanding of this unique protein. Moreover, essential roles of NKA in ischemic pathology are discussed to provide a platform and bright future for the improvement in clinical research on ischemic stroke.

Utilization of woody pruning residues of apple trees

Utilize agricultural residues from pruning brings many advantages including employment, social and economic benefit, rural development, natural forest protection, increased energy efficiency, and lower costs of raw material for the production of particleboard industry. In this study, the use of wood utilization of pruning residues from apple trees has been investigated by using chipping at the landing chipping methods (LCMs) and farm chipping methods (FCM). These methods were conducted on seven farms, totaling 9.2 ha. A time study was used to estimate operation time and cost. Transportation of chips from the study area to factories was done with semi-trailers, trucks, and pickup trucks. The residue yield was between 1.8 and 2.0 green ton per hectare. The maximum time was related to chipping and the collection of residues and the most delay was mechanical. The residues were collected, chipped, and transported to the particleboard factory at a cost between US$10.18 and US$19.46 per ton, and the profit rate between US$15.5 and US$24.8 per ton depending on chipping methods and secondary transport system. Cost and the total time of LCM were lower than the FCM, and also production rate of LCM was higher than the FCM; therefore, this method was more effective in processing residues from apple trees. Regression techniques showed that in LCM, the effect of diameter and age was significant on residue processing time and in FCM, the effect of diameter, age, residue density, and functional the area was significant in residue processing time.

New insights into transport capability of sugars and its impact on growth from novel mutants of Escherichia coli.

The fast-growing capability of Escherichia coli strains used to produce industrially relevant metabolites relies on their capability to transport efficiently glucose or potential industrial feedstocks such as sucrose or xylose as carbon sources. E. coli imports extracellular glucose into the periplasmic space across the outer membrane porins: OmpC, OmpF, and LamB. As the internal membrane is an impermeable barrier for sugars, the cell employs several primary and secondary active transport systems, and the phosphoenolpyruvate (PEP)-sugar phosphotransferase (PTS) system for glucose transport. PTS:glucose is the preferred system by E. coli to transport and phosphorylate the periplasmic glucose; nevertheless, PTS imposes a strict metabolic control mechanism on the preferential consumption of glucose over other carbon sources in sugar mixtures such as glucose and xylose resulting from the hydrolysis of lignocellulosic biomass, by the carbon catabolite repression. In this contribution, we summarize the major sugar transport systems for glucose and disaccharide transport, the exhibited substrate plasticity, and their impact on the growth of E. coli, highlighting the relevance of PTS in the control of the expression of genes for the transport and catabolism of other sugars as xylose. We discuss the strategies developed by evolved mutants of E. coli during adaptive laboratory evolution experiments to overcome the nutritional stress condition imposed by inactivation of PTS as a strategy for the selection of fast-growing derivatives in glucose, xylose, or mixtures of glucose:xylose. This approach results in the recruitment of other primary and secondary active transporters, demonstrating relevant sugar plasticity in derivative-evolved mutants. Elucidation of the molecular and biochemical basis of sugar-transport substrate plasticity represents a consistent approach for sugar-transport system engineering for the design of efficient E. coli derivative strains with improved substrate assimilation for biotechnological purposes.

Vibrio natriegens as Host for Expression of Multisubunit Membrane Protein Complexes.

Escherichia coli is a convenient host for the expression of proteins, but the heterologous production of large membrane protein complexes often is hampered by the lack of specific accessory genes required for membrane insertion or cofactor assembly. In this study we introduce the non-pathogenic and fast-growing Vibrio natriegens as a suitable expression host for membrane-bound proteins from Vibrio cholerae. We achieved production of the primary Na+ pump, the NADH:quinone oxidoreductase (NQR), from V. cholerae in an active state, as indicated by increased overall NADH:quinone oxidoreduction activity of membranes from the transformed V. natriegens, and the sensitivity toward Ag+, a specific inhibitor of the NQR. Complete assembly of V. cholerae NQR expressed in V. natriegens was demonstrated by BN PAGE followed by activity staining. The secondary transport system Mrp from V. cholerae, another membrane-bound multisubunit complex, was also produced in V. natriegens in a functional state, as demonstrated by in vivo Li+ transport. V. natriegens is a promising expression host for the production of membrane protein complexes from Gram-negative pathogens.

Modulation of antimicrobial efflux pumps of the major facilitator superfamily in Staphylococcus aureus.

Variants of the microorganism Staphylococcus aureus which are resistant to antimicrobial agents exist as causative agents of serious infectious disease and constitute a considerable public health concern. One of the main antimicrobial resistance mechanisms harbored by S. aureus pathogens is exemplified by integral membrane transport systems that actively remove antimicrobial agents from bacteria where the cytoplasmic drug targets reside, thus allowing the bacteria to survive and grow. An important class of solute transporter proteins, called the major facilitator superfamily, includes related and homologous passive and secondary active transport systems, many of which are antimicrobial efflux pumps. Transporters of the major facilitator superfamily, which confer antimicrobial efflux and bacterial resistance in S. aureus, are good targets for development of resistance-modifying agents, such as efflux pump inhibition. Such modulatory action upon these antimicrobial efflux systems of the major facilitator superfamily in S. aureus may circumvent resistance and restore the clinical efficacy of therapy towards S. aureus infection.

Mechanisms and Control of NO2- Inhibition of Anaerobic Ammonium Oxidation (Anammox).

Nitrite (NO2-), one of the main substrates in the anaerobic ammonium oxidation (anammox) process, has the potential to inhibit anammox bacteria. The sensitivity of anammox cells with different energy status to NO2- was evaluated, and addition of nitrate (NO3-) inhibition on the basis of narK gene with the putative function of facilitating NO3-/NO2- antiporter. The results showed that the resistance of anammox bacteria to NO2- inhibition follows the order: active-cells > starved-cells > resting-cells > starved-/resting-cells. Anammmox resting cells have increasing tolerance to NO2- in the pH range from 7.0 to 7.5. Dissipating the proton gradient by using carbonyl cyanide m-chlorophenyl hydrazine (CCCP) caused severe inhibition at all pH values including pH = 7.5. Addition of NO3- enabled activity recovery of NO2--inhibited anammox bacteria regardless of whether the proton gradient was disrupted or not, supporting the hypothesis of NO3--dependent detoxification via a secondary transport system.

Experimental and analytical studies on heat transfer in a scaled intermediate heat exchanger with water

The present paper describes an experimental and analytical study in terms of the temperature distribution and heat transfer of an intermediate heat exchanger (IHX). An experimental apparatus of IHX with the primary heat transport system and the secondary heat transport system is made, and forced and natural circulation experiments are conducted using the apparatus. Temperature distributions inside the shell are measured using the fixed thermocouples as well as traversable thermocouples. The Nusselt numbers are investigated based on the measured temperature distributions. One-dimensional and three-dimensional computations are conducted under the forced circulation and natural circulation conditions in order to simulate the experimental results. One-dimensional computation is conducted during the transient cooling down process using a plant system code for the heat transport systems of primary and secondary loops. For the three-dimensional computations, a quasi-steady state condition is analyzed. Good agreement is obtained between the one-dimensional computational results and the experimental results for both flow patterns. The precise temperature distribution inside the shell is computed by the three-dimensional CFD code. Based on the calculated temperature distribution, the heat transfer coefficients are evaluated and converted into the Nu numbers, and are compared with the experimental results. As a result of the 3D computation, the Nu number levels off to a constant value as the Reynolds number decreases to the laminar flow condition.

How Important Is SERCA In Neuronal Calcium Homeostasis?

Maintaining intracellular calcium homeostasis is critical for excitation‐contraction coupling in the heart, and is essentially dependent on primary and secondary active transport systems. However, upregulating sarcoendoplasmic reticulum calcium ATPase (SERCA) in cardiomyocytes from patients with heart failure has recently proved inconclusive (CUPID2 trial). Neuronal calcium impairment is also seen in cardiovascular diseases resulting in heightened sympathetic responsiveness that further exacerbate the disease phenotype. We tested whether overexpression of SERCA in cardiac sympathetic neurons could modulate intracellular calcium transients. Isolated neurons were incubated with either Ad‐MCherry‐SERCA2A or Ad‐MCherry‐Empty (control) for 24 hours immediately post isolation. Calcium imaging using fura‐2AM (2.5μM) was carried out three days post transfection. SERCA2A transgene neurons showed greater depolarisation induced intracellular calcium transients, compared to control (Δ 380/340 ratio (au): SERCA 0.75±0.03, n=68; Empty 0.64±0.03, n=57. P<0.01). SERCA2A expressing neurons also showed greater SR calcium storage compared to control, as demonstrated by significantly higher calcium responses to caffeine (10mM: Δ 380/340 ratio (au): SERCA 0.15±0.01, n=45; Empty 0.03±0.01, n=35. P<0.0001) and thapsigargin stimulation (1μM: Δ 380/340 ratio (au): SERCA 0.12±0.02, n=42; Empty 0.03±0.01, n=33. P<0.0001). Additionally mitochondrial calcium uncoupling with FCCP (1μM) resulted in a greater intracellular calcium change in the SERCA2A transgenic neurons (Δ 380/340 ratio (au): SERCA 0.13±0.01, n=22; Empty 0.05±0.01, n=22. P<0.0001), indicating that altering neuronal calcium handling with upregulation of SERCA has also effected mitochondrial calcium handling and potentially metabolic function in these neurons. Within this study we demonstrated that a SERCA2A gene construct can be transfected in isolated sympathetic neurons from the stellate ganglia. Moreover, this transduction caused an increase in intracellular calcium transients that would be expected to facilitate neurotransmission and be potentially deleterious for cardiac function.Support or Funding InformationBritish Heart Foundation

Exogenous nitrate attenuates nitrite toxicity to anaerobic ammonium oxidizing (anammox) bacteria.

Anaerobic ammonium oxidizing bacteria (anammox) can be severely inhibited by one of its main substrates, nitrite (NO2(-)). At present, there is limited information on the processes by which anammox bacteria are able to tolerate toxic NO2(-). Intracellular consumption or electrochemically driven (transmembrane proton motive force) NO2(-) export are considered the main mechanisms of NO2(-) detoxification. In this work, we evaluated the potential of exogenous nitrate (NO3(-)) on relieving NO2(-) toxicity, putatively facilitated by NarK, a NO3(-)/NO2(-) transporter encoded in the anammox genome. The relative contribution of NO3(-) to NO2(-) detoxification was found to be pH dependent. Exposure of anammox cells to NO2(-) in absence of their electron donating substrate, ammonium (NH4(+)), causes NO2(-) stress. At pH 6.7 and 7.0, the activity of NO2(-) stressed cells was respectively 0 and 27% of the non-stressed control activity (NO2(-) and NH4(+) fed simultaneously). Exogenous NO3(-) addition caused the recovery to 42% and 80% of the control activity at pH 6.7 and 7.0, respectively. The recovery of the activity of NO2(-) stressed cells improved with increasing NO3(-) concentration, the maximum recovery being achieved at 0.85 mM. The NO3(-) pre-incubation time is less significant at pH 7.0 than at pH 6.7 due to a more severe NO2(-) toxicity at lower pH. Additionally, NO3(-) caused almost complete attenuation of NO2(-) toxicity in cells exposed to the proton gradient disruptor carbonyl cyanide m-chlorophenyl hydrazone at pH 7.5, providing evidence that the NO3(-) attenuation is independent of the proton motive force. The absence of a measurable NO3(-) consumption (or NO3(-) dependent N2 production) during the batch tests leaves NO3(-) dependent active transport of NO2(-) as the only plausible explanation for the relief of NO2(-) inhibition. We suggest that anammox cells can use a secondary transport system facilitated by exogenous NO3(-) to alleviate NO2(-) toxicity.

Comparison and Assessment of the Creep-Fatigue Evaluation Methods With Notched Specimen Made of Mod.9Cr-1Mo Steel

In components design at elevated temperature, creep-fatigue is one of the most important failure modes, and assessment of creep-fatigue life in structural discontinuities is an important issue in evaluating the integrity of components. Therefore, a lot of creep-fatigue life evaluation methods were proposed until now. To compare and assess the evaluation methods, a series of creep-fatigue test was carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo steel, which is a candidate material for primary and secondary heat transport system components of the Japan sodium-cooled fast reactor (JSFR). Mechanical creep-fatigue tests and thermal creep-fatigue test were performed by using a conventional uni-axial push–pull fatigue test machine and a thermal gradient generating system with an induction heating. The stress concentration levels were adjusted by varying the notch radius in the each test. The creep-fatigue lives, crack initiation, and propagation processes were monitored by a digital microscope and the replica method. A series of finite element analysis (FEA) was carried out to predict the number of cycles to failure by the several creep-fatigue life evaluation methods. Then, these predictions were compared with the test results. Several types of evaluation methods such are stress redistribution locus (SRL) method, simple elastic follow-up method and the methods described in the design and constriction code for fast reactor (FR) published by the Japan Society of Mechanical Engineers (JSME FRs code) were applied. Through the comparisons, it was appeared that SRL method gave rational conservative prediction of the creep-fatigue life when the factor of κ = 1.6 was applied for all conditions tested in this study. A comparison of SRL method and simple elastic follow-up method indicated that SRL method applied factor of κ = 1.6 gave the smallest creep-fatigue life in practicable stress range level. The JSME FRs code gave an evaluation 70–100 times conservative lives comparing with the test results.

Saccharomyces cerevisiae Vacuolar H + -ATPase Regulation by Disassembly and Reassembly: One Structure and Multiple Signals

Vacuolar H(+)-ATPases (V-ATPases) are highly conserved ATP-driven proton pumps responsible for acidification of intracellular compartments. V-ATPase proton transport energizes secondary transport systems and is essential for lysosomal/vacuolar and endosomal functions. These dynamic molecular motors are composed of multiple subunits regulated in part by reversible disassembly, which reversibly inactivates them. Reversible disassembly is intertwined with glycolysis, the RAS/cyclic AMP (cAMP)/protein kinase A (PKA) pathway, and phosphoinositides, but the mechanisms involved are elusive. The atomic- and pseudo-atomic-resolution structures of the V-ATPases are shedding light on the molecular dynamics that regulate V-ATPase assembly. Although all eukaryotic V-ATPases may be built with an inherent capacity to reversibly disassemble, not all do so. V-ATPase subunit isoforms and their interactions with membrane lipids and a V-ATPase-exclusive chaperone influence V-ATPase assembly. This minireview reports on the mechanisms governing reversible disassembly in the yeast Saccharomyces cerevisiae, keeping in perspective our present understanding of the V-ATPase architecture and its alignment with the cellular processes and signals involved.

Comparative genomic analysis reveals distinct genotypic features of the emerging pathogen Haemophilus influenzae type f

BackgroundThe incidence of invasive disease caused by encapsulated Haemophilus influenzae type f (Hif) has increased in the post-H. influenzae type b (Hib) vaccine era. We previously annotated the first complete Hif genome from a clinical isolate (KR494) that caused septic shock and necrotizing myositis. Here, the full genome of Hif KR494 was compared to sequenced reference strains Hib 10810, capsule type d (Hid) Rd Kw20, and finally nontypeable H. influenzae 3655. The goal was to identify possible genomic characteristics that may shed light upon the pathogenesis of Hif.ResultsThe Hif KR494 genome exhibited large regions of synteny with other H. influenzae, but also distinct genome rearrangements. A predicted Hif core genome of 1390 genes was shared with the reference strains, and 6 unique genomic regions comprising half of the 191 unique coding sequences were revealed. The majority of these regions were inserted genetic fragments, most likely derived from the closely-related Haemophilus spp. including H. aegyptius, H. haemolyticus and H. parainfluenzae. Importantly, the KR494 genome possessed several putative virulence genes that were distinct from non-type f strains. These included the sap2 operon, aef3 fimbriae, and genes for kanamycin nucleotidyltranserase, iron-utilization proteins, and putative YadA-like trimeric autotransporters that may increase the bacterial virulence. Furthermore, Hif KR494 lacked a hisABCDEFGH operon for de novo histidine biosynthesis, hmg locus for lipooligosaccharide biosynthesis and biofilm formation, the Haemophilus antibiotic resistance island and a Haemophilus secondary molybdate transport system. We confirmed the histidine auxotrophy and kanamycin resistance in Hif by functional experiments. Moreover, the pattern of unique or missing genes of Hif KR494 was similar in 20 Hif clinical isolates obtained from different years and geographical areas. A cross-species comparison revealed that the Hif genome shared more characteristics with H. aegyptius than Hid and NTHi.ConclusionsThe genomic comparative analyses facilitated identification of genotypic characteristics that may be related to the specific virulence of Hif. In relation to non-type f H. influenzae strains, the Hif genome contains differences in components involved in metabolism and survival that may contribute to its invasiveness.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2164-15-38) contains supplementary material, which is available to authorized users.

191 Point mutations in the yeast Pma1 H+-ATPase affect polyphosphate (PolyP) distribution

Yeast plasma membrane Н+-ATPase (Pma1) is a key enzyme of the yeast cell metabolism. It generates electrochemical Н+ gradient providing energy for operating the secondary solute transport systems and maintaining intracellular pH and ion homeostasis. Most of the enzyme molecule anchored in the plasma membrane by M1–M10 segments is located in cytosole and membrane; less than 5% of the Pma1 face extracellular space. Membrane domain contains amino acid residues, which form H+ transport pathway; cytosole parts house the enzyme active center and cytosolic C-terminal tail has regulatory function. The enzyme function and regulation are tightly connected to glucose metabolism: its fermentation triggers activation of Pma1 function, structurally accompanied by the enzyme multiple phosphorylation during intracellular traffic on route to plasma membrane. There are ca. 10 phosphorylation sites; only 3 of them are identified: one single and two tandemly located sites are in the C-terminal tail. Both ATP and PolyP can be used to phosphorylate amino acid residues; however, there are little data on the interactive metabolism of ATP and PolyP. Most of phosphorylable Ser, Thr, Asp, Glu, and Tyr residues are located in the inner parts of the enzyme; however, there are several such residues in the Pma1 outer parts: D714, S716, D718, and D720 in M5–M6 loop and S846, E847, T850, and D851 in M9–M10 loop, close to the enzyme regulatory C-tail. It seems reasonable that multiple phosphorylation of Pma1 goes subsequently, and first of such sites could be located in the enzyme extracytosolic part. The M5–M6 loop phosphorylable residues, except D714, were found to be unimportant for the enzyme structure-function relationship; D714A mutant was poorly expressed and inactive (Petrov, 2011). However, D714N did not disturb the enzyme functioning, thus excluding the role of D714 in the enzyme phosphorylation. Therefore, we choose to study further residues in the M9–M10 loop by replacing them with Ala. The ATPase activity of these mutants ranged from the wild-type level (S846A) to 2- (E847A) to 3-fold (T850A) drop. Changes of activity were accompanied by changes in PolyP fractions (Figure 1), which were most significant for S846A and T850A. S846A had 1.5–1.7-fold increase in PolyP1 (found mostly in cytosole and vacuoles) and PolyP3 (localized near the cell surface) and dramatic 3-fold decrease in PolyP4-5 fractions (associated with cell wall), while T850A had stable 1.5-fold increase in all PolyP but PolyP4-5 fractions. Both mutants also had 20% (S846A) to 37% (T850A) increase in total PolyP. These data may point to lack of one or more phosphorylation sites and/or participation of PolyP in the Pma1 ATPase phosphorylation. Possibly, the sites at S846 and T850 act jointly, similarly to tandemly located and acting S911 and T912 in the regulatory C-tail (Lecchi et al., 2007). Further study of these mutants, although methodologically challenging, seems certain to yield more useful insights into functioning and regulation of the Pma1 ATPase as well as into the interactive mechanisms of ATP and PolyP metabolism.

Thermal transient test and strength evaluation of a thick cylinder model made of Mod.9Cr-1Mo steel

Mod.9Cr-1Mo steel is a candidate material for the primary and secondary heat transport system components of the Japan sodium-cooled fast reactor. However, there is little evidence to support the structural integrity of components made of Mod.9Cr-1Mo steel in a practical environment. To verify the failure mode and assess creep–fatigue damage, a thick cylinder test model made of Mod.9Cr-1Mo steel was subjected to 1873 cycles of accelerated thermal transient loading using a large-scale sodium loop through which liquid sodium at 600°C and 250°C flowed repeatedly, with the period of each transient being 2h and 1h, respectively. After completion of the test, the test model was inspected using liquid penetrant testing. Observations using a scanning electron microscope and hardness testing were then performed to characterize creep–fatigue damage in the structural model subjected to cyclic thermal transient loading in a sodium environment. Heat transfer analysis based on the measured temperature data and elastic and inelastic thermal stress analyses using finite element analysis were performed to evaluate the relationship between creep–fatigue damage and the observed crack conditions. Finally, the characteristics of creep–fatigue damage under cyclic thermal loading in a sodium environment and the evaluation methods were considered.

Sodium removal from sodium wetted under sodium ultra sonic scanner

Sodium is used as a coolant in primary and secondary heat transport systems of Liquid Metal cooled Fast Breeder Reactors (LMFBR). The Prototype Fast Breeder Reactor (PFBR) is in advanced stage of construction at Kalpakkam, India. Under Sodium Ultra Sonic Scanner (USUSS) is used to image the components dipped in sodium and more specifically the gap between Sub Assembly (SA) heads and the control plug. This is essential to confirm that no SA is protruding from its position. USUSS has to be qualified in sodium before its use in the reactor. After sodium testing, sodium adhering to the USUSS needs to be removed to prevent reaction with oxygen and moisture present in air when it is taken out. The sodium removal process is based on the use of moist carbon-di-oxide (CO2) at a temperature of about 353K. The reaction rate is controlled by varying the ratio of CO2 to moisture. Hydrogen released during the reaction of sodium with moisture is continuously monitored to ensure safe limits of hydrogen concentration. This paper describes the details of the experimental setup used in a cleaning pit for the removal of sodium adhering on USUSS and the technical details of the cleaning process.

Verification of the Estimation Methods of Strain Range in Notched Specimens Made of Mod.9Cr-1Mo Steel

Several methods of estimating strain range at a structural discontinuity have been developed in order to assess component reliability. In a component design at elevated temperature, estimation of strain range is required to evaluate the fatigue and creep-fatigue damage. Therefore, estimation of strain range is one of the most important issues when evaluating the integrity of a component during its lifetimes. To verify the methods of estimating strain range for discontinuous structures, low cycle fatigue tests were carried out with notched specimens. All the specimens were made of Mod.9Cr-1Mo steel, because it is a candidate material for a primary and secondary heat transport system components of Japan Sodium-cooled Fast Reactor (JSFR). Displacement control fatigue tests and thermal fatigue tests were performed by ordinary uniaxial push–pull test machine and equipment generating the thermal gradient in the notched plate by induction heating. Several notch radii were employed to vary the stress concentration level in both kinds of tests. Crack initiation and propagation process during the tests were observed by a digital microscope and the replica method to define the failure cycles. Elastic and inelastic finite element analyses were also performed to estimate strain range for predicting fatigue life. Then, these predictions were compared with the test results. Several methods such as stress redistribution locus (SRL) method, simple elastic follow-up (SEF) method, Neuber's law, and the procedures employed by elevated temperature design codes were applied. Through these comparisons, the applicability and conservativeness of these strain range estimation methods, which is the basis of the fatigue and creep-fatigue life prediction, are discussed.