Antibiotic lock: In vitro stability of vancomycin and four percent sodium citrate stored in dialysis catheters at 37°C

Catheter-related bacteremia (CRB) is a major cause of morbidity and mortality especially among patients receiving hemodialysis (HD). Antibiotic lock therapy represents a promising technique in the treatment of CRB. Several studies have evaluated antibiotics in combination with heparin as an interdialytic locking solution as adjunctive therapy for CRB. The objective of this study was to evaluate the chemical stability of the vancomycin in 4% sodium citrate in HD catheters as an interdialytic lock. Vancomycin was prepared and diluted with sodium citrate 4% and stored in polyvinyl chloride syringes, 2 carbothane dialysis catheters (Hemostar^®) and 2 dual floating HD catheters (CardioMed^®). Syringes were stored at 4 °C or 23 °C and the catheters were stored in an incubator at 37 °C for 72 hours. Samples underwent daily chromatographic analysis and the luminal concentration of vancomycn was determined on study days 0, 1, and 3. When vancomycin is reconstituted with normal saline to achieve a concentration of 50 mg/mL, and then further diluted in 4% sodium citrate, to achieve concentrations of either 1 or 3 mg/mL, and then stored at 4 °C, room temperature, or 37 °C, solutions were observed to retain >92% of the initial concentration for the study period of 3 days. Based on the fastest degradation rate determined with 95% confidence interval, >90% is retained for 6.53 days. We conclude that vancomycin—4% citrate solutions stored in polyvinyl chloride syringes or HD catheters are not significantly affected by temperature or concentration within the 72 hours storage period. Therefore, these solutions can be anticipated to be suitable as a HD interdialytic antibiotic lock in standard HD catheters.     

About thaumasite formation in Portland-limestone cement pastes and mortars––effect of heat treatment at 95 °C and storage at 5 °C

Owing to the presence of finely divided calcite, mortars and concretes made with Portland-limestone cements are particularly susceptible to damaging thaumasite formation during sulfate attack at lower temperatures. This work reports the results of investigations on mortars made according to DIN/EN 196 and pastes (w/c ratio of 0.5) with CEM I 42,5 R, as well as with mixtures of cement with limestone filler. Some of the samples were heat-treated at 95 °C. The length changes and resonant frequencies of the samples were measured during long-term water-storage at 20 and 5 °C. There was no evidence from X-ray diffraction data of thaumasite formation in the samples. Only for pastes containing 30 wt.% limestone filler were small areas found by SEM and X-ray microanalysis whose chemical analysis matched thaumasite or a thaumasite–ettringite solid solution.     

Effects of Modified Atmosphere Packaging with Various Carbon Dioxide Composition on Biogenic Amines Formation in Indian Mackerel (Rastrelliger kanagurta) stored at 5 ± 1°C

The profile of major biogenic amines was investigated in Indian mackerel packed in modified atmosphere for up to 12 days at 5 ± 1°C. Beheaded and gutted Indian mackerel was packed under different carbon dioxide compositions to study the effects on biogenic amines formation. The treatments were control air (C), vacuum packaging (VP), 30% CO₂/65% N₂/5% O₂ (M30C), 60% CO₂/35% N₂/5% O₂ (M60C), 80% CO₂/15% N₂/5% O₂ (M80C) and 100% CO₂ (M100C). Each amine responded differently to different CO₂ levels. After 12 days of storage, concentrations of histamine were reduced by 6.4%, 8.5%, 70.3%, 78.8% and 90.2% in fish packed under VP, M30C, M60C, M80C and M100C, respectively as compared with control air. Changes in putrescine and cadaverine showed a similar pattern. Gas mix of M30C and VP stimulated the formation of tyramine reaching 203 and 172 ppm, respectively. Higher composition of CO₂ had a significant inhibitory effect on tyramine concentration (p < 0.05). There were parallel increases of putrescine and spermidine in C, VP and M30C. No significant effect of CO₂ was observed on spermine (p > 0.05). After 9 days of storage, more than 300 ppm of histamine was detected in mackerel packed in VP and M30C; therefore, these atmospheres pose a histamine intoxication risk. Copyright © 2013 John Wiley & Sons, Ltd.     

Creep deformation of Alloys 617 and 276 at 750–950 °C

Alloys 617 and 276 were subjected to time-dependent deformation at elevated temperatures under sustained loading of different magnitudes. The results indicate that Alloy 617 did not exhibit strains exceeding 1 percent (%) in 1000 h at 750, 850 and 950 °C when loaded to 10% of its yield strength (YS) values at these temperatures. However, this alloy was not capable of sustaining higher stresses (0.25YS and 0.35YS) for 1000 h at 850 and 950 °C without excessive deformation. Interestingly, Alloy 617 showed insignificant steady-state creep rate at 750 °C irrespective of the applied stress levels. Alloy 276 almost met the maximum creep deformation criterion when tested at 51 MPa–750 °C. Severe creep deformation of both alloys at 950 °C could be attributed to the dissolution of carbides and intermetallic phases remaining after solution annealing or precipitated during quenching.     

Physical mechanisms of dielectric breakdown in SiO2 for the range of −150°C to 150°C

This paper explains the physical nature of breakdown for 10 nm oxide in the range of −150°C to 150°C for N- and P-channel devices (NFETs and PFETs). At 30°C, two mechanisms occur: trap creation and impact ionization; at lower temperatures, the trap creation is significantly suppressed with a corresponding decrease in activation energy. Using the physical model, the reliability of NFETs is compared with what the PFETs relative to processing conditions.     

Micromechanism of cyclic plastic deformation of alloy IN 718 at 600 °C

In the present investigation, an attempt was made to understand the cyclic deformation micromechanism of gas turbine alloy Inconel 718 at 600 °C (i) by conducting low cycle fatigue and creep–fatigue interaction tests and (ii) by studying the microstructure evolution in the material during fatigue tests through extensive electron microscopy. Bilinear slope was obtained in the Coffin–Manson plot for all low cycle fatigue tests, and it was confirmed through transmission electron microscopic examination that microtwinning was the predominant mode of deformation at low plastic strain values, whereas slip and shearing of γ″ precipitates were the predominant mode of deformation at higher plastic strain values. Fatigue life was adversely affected when hold time was introduced at peak tensile strain during creep–fatigue interaction tests. Formation of stepped interface at microtwin boundaries and coarsening of niobium carbide precipitates were observed to be the major microsturctural changes during creep–fatigue interaction tests.     

Experimental research on bolted joint strength and dispersion in steel lattice transmission tower legs under low temperatures (−20°C to −45°C)

Cold regions with subzero temperatures (?20°C to ?45°C) have important impacts on the mechanical properties of structural steel used in lattice steel towers of overhead transmission line systems. The results from regular material tests are not appropriate for the accurate analysis of joint strength in cold weather conditions. This paper presents the tensile test results of 18 coupons of steel material and eight groups (18 specimens per group) of bolted joints with Q345 and Q420 steel under temperatures of 20°C, ?20°C, and ?45°C. The results show that the yield‐to‐ultimate strength ratio of the joints under low temperature conditions is beyond the range of 0.60 to 0.75 for Q420 structural steel. Suggestions are made on how to improve the accuracy of joint design for both the partial resistance factor and the design value of joint yield strength in cold regions.     

Creep Behavior of High‐Nb TiAl Alloy at 800–900 °C by Directional Solidification

Cold crucible directional solidification Ti44Al6Nb1.0Cr alloy is crept at 800–900 °C. Experimental results show that creep lifetime significantly decreases with the increasing creep temperature. When creeping at 900 °C under 130 MPa, the T_Q twinning is activated in lamellar structures. The T_Q twinning shows a strong dependency on temperature during creep under low creep‐stress and it can overcome α₂ lamellae and transfer into adjacent γ lamellae. The hardening by mechanical twinning and the softening by α₂ lamellar dissolution take place at different zones in lamellar structures and the strain incompatibility between hardening zone and softening zone promotes the microcracks to form in lamellar structures. The deformation characteristic of hard and soft lamellae is studied. Moreover, recrystallization γ phase formed in lamellar structures near colony boundary during creep at 900 °C accelerates the creep failure.

     

The mechanism of the low-temperature hot corrosion of pure iron and manganese at 600–800°C

The corrosion of pure iron and manganese in simulated combustion gases at 600–800°C in the presence of sodium sulfate deposits is faster than the same reaction without salt deposits. This effect is due to the formation of a liquid solution between sodium sulfate and the sulfates of the corroded metals. The nature of these liquid solutions is examined together with the possible mechanisms for the transport of matter through the liquid and the dissolution-reprecipitation of solid metal compounds in the liquid salt. Finally, the reasons for the formation of sulfides in mixture with oxides in the inner solid region of the scale and the effects produced by the presence of sulfides on the overall reaction rate are considered.     

Short crack initiation and growth at 600 °C in notched specimens of Inconel718

The natural initiation and growth of short cracks in Inconel®718 U-notch specimens has been studied at 600 °C in air. U notches were introduced through broaching, and hardness traces and optical microscopy on cross-sections through the U notch broaching showed that the broaching process had introduced a deformed, work hardened layer. Fatigue tests were conducted under load control using a 1-1-1-1 trapezoidal waveform, on specimens with as-broached and polished U-notches. Multi-site crack initiation occurred in the notch root. Many of the cracks initiated at bulge-like features formed by volume expansion of oxidising (Nb,Ti)C particles. In unstressed samples, oxidation of (Nb,Ti)C particles occurred readily, producing characteristic surface eruptions. Scanning electron microscopy on metallographic sections revealed some sub-surface (Nb,Ti)C oxidation and localised matrix deformation around oxidised particles. A mechanism for crack initiation by carbide expansion during oxidation is discussed. Surface short crack growth rates in the notch root of polished specimens were measured using an acetate replica technique. Observed short-crack growth rates were approximately constant across a wide range of crack lengths. However, there was a transition to rapid, accelerating crack growth once cracks reached several hundred micrometers in length. This rapid propagation in the latter stages of the fatigue life was assisted by crack coalescence. Polishing the U-notch to remove broaching marks resulted in a pronounced increase in fatigue life.     

Embrittlement of a superduplex stainless steel in the range of 550–700 °C

Duplex stainless steels are very attractive materials, combining high mechanical properties with improved corrosion resistance. However, these steels present technical limitations because they can experience embrittlement as a consequence of thermal cycles. Moreover, the higher level of alloying elements (Cr and Mo) in the new duplex generation, called superduplex, accelerates the precipitation kinetics of harmful intermetallic phases, which are the responsible of embrittlement. This fact raises the question of the influence of these cycles on the actual performance of duplex components and structures and on its possible failure during service.

In order to investigate this question, heat treatments in the range of 550–700 °C, with different exposure times and cooling rates, have been made on a superduplex stainless steel type EN 1.4507. The evolution of mechanical properties has been followed by means of hardness measurements, impact and fracture toughness tests, whereas microstructural changes have been identified by using optical and transmission electron microscopy analysis. A correlation between the degree of embrittlement and the different types of precipitates has been established.     

Oxidation of iron, aluminium and titanium films in the temperature range 50–200 °C

The oxidation kinetics of iron, aluminium and titanium films have been studied in the temperature range 50–200 °C at a pressure of 0.7 Pa with a piezoelectric quartz microbalance. For titanium, additional measurements in the pressure range 7 × 10⁻³ – 70 Pa have been carried out. All three metals under investigation showed qualitatively common features in their oxidation behaviour: a very fast initial oxygen absorption step, completed in less than 1 min, followed by a slow, temperature-independent oxide growth with logarithmic time law at lower temperatures, and an enhancement of the oxidation rate at higher temperatures. The oxidation curves are compared with the results of model calculations based on the Cabrera-Mott theory.     

On the fatigue behaviour of quenched and tempered at 300 and 600 °C SAE 1045 steel in an environment of sugar cane juice

SAE 1045 steel is widely used for manufacturing shafts in the sugar cane mills of the sugar industry. These shafts are designed with an expectation of a long lifetime. However, fatigue failures occur frequently. The sugar cane juice processed in these mills has corrosive properties that can alter the fatigue life of these shafts. In this research, the fatigue strength of SAE 1045 steel between 1 × 10⁴ and 2 × 10⁵ cycles in air and in sugar cane juice, with two different microstructures (tempered martensite at 300 °C and tempered martensite at 600 °C), was determined in rotating bending. The microstructure of the materials was characterized using optical microscopy, and the fracture surfaces were characterized using scanning electron microscopy. The results show that the fatigue strength at 2 × 10⁵ cycles for the tempered condition at 600 °C decreases 7% because of the sugar cane juice effect, and for the tempered condition at 300 °C, the fatigue strength decreases 15%.     

Anomalous Tensile Strength and Fracture Behavior of Polycrystalline Iridium from Room Temperature to 1600 °C

The nature of the brittleness of Iridium crystal is still unclear. The aim of this study is to explore the mechanism of ductile‐to‐brittle transition (DBT) and the fracture behavior in polycrystalline Iridium. Tensile tests are conducted from room temperature to 1600 °C. Furthermore, fracture morphology and deformation substructures are characterized by OM, SEM, and TEM. The results show that the tensile strength increases anomalously below 600 °C and then decreases with the increasing temperature. The elongation increases slowly from room temperature to 700 °C, and it then changes sharply from 9.88% at 700 °C to 31% at 800 °C. Below 700 °C, the polycrystalline Iridium exhibits intergranular and partial transgranular cleavage fracture pattern. In contrast, the ductile fracture morphologies associated with microvoids coalescence are observed between 800 and 1600 °C. Massive tangling screw dislocations form at 700 °C and less tangles appear when stretching at 900 °C, manifesting that the DBT is around 800 °C in polycrystalline Iridium.

     

Characterisation and simulation of the creep behaviour of Nicrofer 6025HT wire material at 650 °C

Thermal efficiency of combined cycle power plants can be improved by increasing temperature and pressure in the steam turbine. Since typical power plant materials have presently reached their operation limit with higher steam temperature, the application of a new cooling system could reduce the material temperature to tolerable conditions. For this purpose, a new sandwich structure was developed comprising a woven wire mesh interlayer between two plane sheets. Cooling steam is fed into the interlayer where it can flow without severe losses. This sandwich structure is applied to the steam turbine casing as a wall cladding.Due to the combination of constant overpressure of cooling steam and high temperature exposure of hot steam, the structures are stressed parallel and perpendicular to the intermediate layer primarily by creep loads. To simulate the creep behaviour via the finite element method the exact knowledge of the creep behaviour of the constituents, the wire and the sheet, is essential. Therefore, creep tests at 650 °C on wire material, manufactured from the nickel base alloy Nicrofer 6025HT, were carried out to determine constitutive equations. The creep behaviour was simulated on the basis of the concept of the internal backstress, which was implemented in an adequate user subroutine of the commercial FEM-software Abaqus.     

Experimental assessment of the Ru–Al–Ni ternary phase diagram at 1000 and 1100 °C

Knowledge of phase equilibria in the Ru–Al–Ni ternary system is relevant to the development of new single crystal Ni-based superalloys as well as to new high temperature protective coating systems for these alloys. A series of diffusion couple investigations have been performed across the Ru–Al–Ni ternary system in order to establish phase fields and possible diffusion paths. A continuous B2 phase has been shown to exist across the Ru–Al–Ni ternary between the RuAl and NiAl phases at temperatures of 1000 and 1100 °C. Ternary isothermal sections for Ru–Al–Ni at 1000 and 1100 °C are presented.