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Variations in the surface chemistry of methanol with CeO 2 (100) at low and elevated pressures
The reactions of methanol with and without O 2 were studied on a flat, highly crystalline CeO 2 (100) thin‐film surface with ambient pressure XPS. In the absence of O 2 , the ambient pressure XPS results indicate that in both low‐pressure (≤10 −5 Torr) and high‐pressure regimes (≥10 −1 Torr), the dominant surface species is methoxy. Methanol decomposition substantially reduces the ceria and C X deposit build‐up on the surface. When O 2 is present, C X does not accumulate on the surface and the dominant surface species is different in the low‐pressure and high‐pressure regimes. Methoxy dominates at low pressure, while formate dominates at the higher pressure. The type of surface species appears to be related to the ability of O 2 to fully oxidize the ceria surface during the methanol reaction.
Prognosticating Survival in Hepatocellular Carcinoma with Elevated Baseline Alpha-fetoprotein Treated with Radioembolization Using a Novel Laboratory Scoring System: Initial Development and Validation
Aims: To investigate laboratory parameters as predictors of overall survival (OS) for hepatocellular carcinoma (HCC) treated with radioembolization and develop/validate a scoring system. Methods: With IRB approval, we included all patients with baseline alpha-fetoprotein (AFP) > 100 ng/dL from our prospectively acquired HCC radioembolization database. Neutrophil–lymphocyte ratio, albumin–bilirubin (ALBI), and AFP were measured at baseline and at 1-, 3-, and 6-month post-radioembolization Landmarks. OS was assessed from these Landmarks. Univariate/multivariate analyses were performed to evaluate OS predictability of these parameters. Baseline Imaging, Laboratory, and Combination scoring systems were developed. Developing/validating groups were created to investigate/validate the score’s OS predictability. Time-dependent receiver operating characteristics (ROC) were evaluated. Patients were stratified into groups I, II, and III by using 25th and 75th percentile cutoffs according to change in Laboratory Score from baseline. Results: 345/401 (86%), 238/401 (59%), and 167/401 (42%) patients had laboratory parameters available at the 1-, 3-, and 6-month Landmarks, respectively. ALBI and AFP were significant OS prognosticators at all Landmarks. The Laboratory Score [ALBI + (0.3 × LnAFP)] was developed/internally validated to predict OS from these Landmarks. Areas under the curve of time-dependent ROCs of the Baseline Imaging vs. Laboratory scores in predicting patient OS post 3 and 6 months Landmarks were 0.56 versus 0.82 and 0.57 versus 0.77, respectively. OS differences in groups I, II, and III according to change in Laboratory Score from baseline were significant (p < 0.001). Conclusions: Post-radioembolization AFP and ALBI scores were significant OS prognosticators. A decrease in post-therapeutic Laboratory Score, which combines AFP and ALBI, correlates with an improved OS.
VARIATION IN FOLIAR NITROGEN AND ALBEDO IN RESPONSE TO NITROGEN FERTILIZATION AND ELEVATED CO2
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Mechanical response and microprocesses of reconsolidating crushed salt at elevated temperature
Design, analysis and performance assessment of potential salt repositories for heat-generating nuclear waste require knowledge of thermal, mechanical, and fluid transport properties of reconsolidating granular salt. So, to inform salt repository evaluations, we have undertaken an experimental program to determine Bulk and Young’s moduli and Poisson’s ratio of reconsolidated granular salt as a function of porosity and temperature and to establish the deformational processes by which the salt reconsolidates. Our tests were conducted at 100, 175, and 250 °C. In hydrostatic tests, confining pressure is increased to 20 MPa with periodic unload/reload loops to determine K. Volume strain increases with increasing temperature. In shear tests at 2.5 and 5 MPa confining pressure, after confining pressure is applied, the crushed salt is subjected to a differential stress, with periodic unload/reload loops to determine E and ν. At predetermined differential stress levels the stress is held constant and the salt consolidates. Displacement gages mounted on the samples show little lateral deformation until the samples reach a porosity of ~10 %. Interestingly, vapor is vented only for 250 °C tests and condenses at the vent port. It is hypothesized that the brine originates from fluid inclusions, which were made accessible by heating and intragranular deformational processes including decrepitation. Furthermore, identification and documentation of consolidation processes are inferred from optical and scanning electron microstructural observations. As a result, densification at low porosity is enhanced by water film on grain boundaries that enables solution-precipitation phenomena.
Using tracer-derived groundwater transit times to assess storage within a high-elevation watershed of the upper Colorado River Basin, USA
Previous watershed assessments have relied on annual baseflow to evaluate the groundwater contribution to streams. To quantify the volume of groundwater in storage, additional information such as groundwater mean transit time (MTT) is needed. This study determined the groundwater MTT in the West Fork Duchesne watershed in Utah (USA) with lumped-parameter modeling of environmental tracers (SF{sub 6}, CFCs, and {sup 3}H/{sup 3}He) from 21 springs. Approximately 30% of the springs exhibited an exponential transit time distribution (TTD); the remaining ~70% were best characterized by a piston-flow TTD. The flow-weighted groundwater MTT for the West Fork watershed is about 40 years with approximately 20 years in the unsaturated zone. A cumulative distribution of these ages revealed that most of the groundwater is between 30 and 50 years old, suggesting that declining recharge associated with 5–10-year droughts is less likely to have a profound effect on this watershed compared with systems with shorter MTTs. The estimated annual baseflow of West Fork stream flow based on chemical hydrograph separation is ~1.7 × 10{sup 7} m{sup 3}/year, a proxy for groundwater discharge. Using both MTT and groundwater discharge, the volume of mobile groundwater stored in the watershed was calculated to be ~6.5 × 10{sup 8} m{sup 3}, or ~20 m thickness of active groundwater storage and recharge of ~0.09 m/year (assuming porosity = 15%). Future watershed-scale assessments should evaluate groundwater MTT, in addition to annual baseflow, to quantify groundwater storage and more accurately assess watershed susceptibility to drought, groundwater extraction, and land-use change.
Trends in wetting behavior for Ag–CuO braze alloys on Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O (3-δ) at elevated temperatures in air
Ba 0.5 Sr 0.5 Co 0.8 0.2 O (3-δ) (BSCF) is a potential oxygen separation membrane material for advanced coal based power plants. For this application, BSCF must be joined to a metal. In the current study, Ag-CuO, a reactive air brazing (RAB) alloy was evaluated for brazing BSCF. In-situ contact angle tests were performed on BSCF using Ag-CuO binary mixtures at 950 and 1000°C and the interfacial microstructures were evaluated. Wetting contact angles (θ< 90°) were obtained at short times at 950°C and the contact angles remained constant at 1000°C for 1, 2 and 8 mol% CuO contents. Microstructural analysis revealed the dissolution of copper oxide into the BSCF matrix to form copper-cobalt-oxygen rich dissolution products along the BSCF grain boundary. The formation of a thick interfacial reaction product layer and ridging at the sessile drop triple point indicate that the reaction kinetics are very rapid and that it will require careful process control to obtain the desired thin but continuous interfacial product layer.
Effects of Elevated Atmospheric Carbon Dioxide and Tropospheric Ozone on Phytochemical Composition of Trembling Aspen ( Populus tremuloides ) and Paper Birch ( Betula papyrifera )
Not provided.
Performance of Tantalum STJ X-ray Detectors at Elevated Count Rates
Here, we have developed an X-ray detector system based on Ta superconducting tunnel junctions (STJs) with an energy resolution below 10 eV under 1 keV. A principal advantage of STJs over other low-temperature detectors is their high count rate capability. In this work, we have optimized the operating conditions and digital pulse processing parameters for input count rates up to 25 kcps/pixel. Resolution below 10 eV is maintained up to 2.5 kcps/pixel, and at input rates of 25 kcps per pixel the resolution is 26 eV FWHM at 525 eV.
A Thermodynamic Model for Nd(III)–Sulfate Interaction at High Ionic Strengths and Elevated Temperatures: Applications to Rare Earth Element Extraction
Neodymium (Nd), a rare earth element (REE), is critical to numerous industries. Neodymium can be extracted from ore concentrates, waste materials, or recycled materials such as recycled Nd-Fe-B permanent magnets. In a standard process, concentrated sulfuric acid (H 2 SO 4 ) is used as an extraction/leaching agent. Therefore, knowledge of Nd(III)–sulfate interaction at high ionic strengths is important for optimization of the extraction process. In addition, sulfate is also a major species in natural surface waters and present in nuclear waste streams. Nd(III) has been used a chemical analog to trivalent actinides in nuclear waste research and development. Consequently, knowledge of Nd(III)-sulfate interactions is also impactful to the field of nuclear waste management. Here, in this study, we have developed a thermodynamic model that can describe the interaction of Nd(III) with sulfate to ionic strengths up to ~ 16.5 mol·kg –1 and to temperatures up to 100 °C. The model adopts the Pitzer formulation to describe activity coefficients of aqueous species. This model can be used to design and optimize a chemical process for REE recovery from ore concentrates, recycled materials, and acid mine drainage (AMD) and to understand the mobility of REEs and actinides in the environment.
Elevated-Temperature Corrosion of CoCrCuFeNiAl0.5Bx High-Entropy Alloys in Simulated Syngas Containing H2S
High-entropy alloys are formed by synthesizing five or more principal elements in equimolar or near equimolar concentrations. Microstructure of the CoCrCuFeNiAl{sub 0.5}B{sub x} (x = 0, 0.2, 0.6, 1) high-entropy alloys under investigation is composed of a mixture of disordered bcc and fcc phases and borides. These alloys were tested gravimetrically for their corrosion resistance in simulated syngas containing 0, 0.01, 0.1, and 1 % H{sub 2}S at 500 °C. The exposed coupons were characterized using XRD and SEM. No significant corrosion was detected at 500 °C in syngas containing 0 and 0.01 % H{sub 2}S while significant corrosion was observed in syngas containing 0.1 and 1 % H{sub 2}S. Cu{sub 1.96}S was the primary sulfide in the external corrosion scale on the low-boron high-entropy alloys, whereas FeCo{sub 4}Ni{sub 4}S{sub 8} on the high-boron high-entropy alloys. Multi-phase Cu-rich regions in the low-B high-entropy alloys were vulnerable to corrosive attack.
Phase transformations in Cd–Ni nanostructured system at elevated temperatures
Using X-ray diffraction (both in vacuum and in air), derivatomass-spectrometry and thermo-programmed oxidation, phase transformations in nanostructured Cd–Ni system occurring while heating up 720 °C were described. These metal powders were obtained by joint reduction from aqueous solutions of salts with hydrazine. When study their composition, earlier unknown phases were detected (intermetallide CdNi{sub 3} and solid solution Cd{sub x}Ni{sub 1–x} with face centered cubic structure) and among the known intermetallides (Cd{sub 5}Ni and CdNi), only Cd{sub 5}Ni was found. As a consequence, phase transformations in the obtained nanostructured powders were remarkably different from those present on the Cd–Ni phase diagram. The intermediates and FCC phase decompose independently with formation of individual initial components (Cd and Ni) without intermediate product. At relatively high Cd concentration in the system, intermediate CdNi{sub 3} phase formation from Cd{sub 5}Ni and Cd{sub x}Ni{sub 1–x} phases, which are polar opposites in composition, is possible. The decomposition temperatures of Cd{sub 5}Ni and melting point of Cd in the nanostructured state were lower than those specified by the phase diagram by 170 and 70 °C, respectively, which well corresponded to the concept of effective (high) temperatures attributed to the nanostructured systems due to the energy saturation of the con stituent nanocrystallites.
Hot Ductility and Compression Deformation Behavior of TRIP980 at Elevated Temperatures
The hot ductility tests of a kind of 980 MPa class Fe-0.31C (wt pct) TRIP steel (TRIP980) with the addition of Ti/V/Nb were conducted on a Gleeble-3500 thermomechanical simulator in the temperatures ranging from 873 K to 1573 K (600 °C to 1300 °C) at a constant strain rate of 0.001 s{sup −1}. It is found that the hot ductility trough ranges from 873 K to 1123 K (600 °C to 850 °C). The recommended straightening temperatures are from 1173 K to 1523 K (900 °C to 1250 °C). The isothermal hot compression deformation behavior was also studied by means of Gleeble-3500 in the temperatures ranging from 1173 K to 1373 K (900 °C to 1100 °C) at strain rates ranging from 0.01 s{sup −1} to 10 s{sup −1}. The results show that the peak stress decreases with the increasing temperature and the decreasing strain rate. The deformation activation energy of the test steel is 436.7 kJ/mol. The hot deformation equation of the steel has been established, and the processing maps have been developed on the basis of experimental data and the principle of dynamic materials model (DMM). By analyzing the processing maps of strains of 0.5, 0.7, and 0.9, it is found that dynamic recrystallization occurs in the peak power dissipation efficiency domain, which is the optimal area of hot working. Finally, the factors influencing hot ductility and thermal activation energy of the test steel were investigated by means of microscopic analysis. It indicates that the additional microalloying elements play important roles both in the loss of hot ductility and in the enormous increase of deformation activation energy for the TRIP980 steel.
Carbothermal Reduction of Quartz and Carbon Pellets at Elevated Temperatures
In this study, the carbothermal reduction of pellets composed of quartz and carbon at temperatures between 1898 K and 1948 K (1625 °C and 1675 °C) are investigated. The main product from this reaction is silicon carbide (SiC). The reduction of quartz with carbon black, charcoal, coke, coal, and pre-heated coal in the pellet were compared to investigate the different carbon resources used in silicon production. Charcoal and coke have high SiO reactivity, while carbon black and coal (pre-heated coal) have low SiO reactivity. Charcoal and carbon black show better matching between quartz/carbon reactivity and SiO reactivity, and will lose less SiO gas than coke and pre-heated coal. Coal has a high volatile content and is thus not recommended as a raw material for the pellets.
Processing Parameter Control of Lifetime-Limiting Failure Mechanisms in Al-Si Cast Alloys at Room and Elevated Temperatures
Aluminum-silicon cast alloys widely used throughout the transportation sector, A356, 319, and A390, have been studied with respect to chemical compositions and processing parameters that control the resultant mechanical behavior. First, the development of strengthening mechanisms is discussed in terms of the role that alloying elements, solidification behavior, and thermal treatments play. Based on this understanding, an extensive matrix of material conditions was developed and characterized in order to provide practical guidelines for alloy development. In order to provide an understanding of lifetime-limiting failure mechanisms, fatigue crack growth and hot compressive dwell behaviors were further investigated. Fatigue crack growth tests were conducted for all alloys at R = 0.1 and room temperature, and creep–fatigue of 319 was studied at R = − 1.5 and 250 °C. The role of processing parameters in controlling the mechanical properties is identified and discussed, and recommendations for optimized design are made.
Elevated Temperature Corrosion Studies of AlCrN and TiAlN Coatings by PAPVD on T91 Boiler Steel
The present investigation discusses the hot corrosion behavior of AlCrN and TiAlN nano-coatings on T91 boiler steel by PAPVD process subjected to molten salt of Na{sub 2}SO{sub 4}-60%V{sub 2}O{sub 5} at 900 °C for 50 cycles. Surface and cross-sectional studies were performed by AFM, SEM/EDS and XRD techniques to understand the corrosion kinetics and mechanism. T91 bare boiler steel as well as TiAlN-coated specimen has shown higher internal oxidation as well as weight gain. The better corrosion resistance of AlCrN-coated specimen has been observed by virtue of higher availability of Cr and Al in the oxide scale as well as adherent and dense coating. The betterment of AlCrN coating can be attributed to low internal oxidation as well as movement of Cr and Al toward oxide scale to form protective corrosion barriers.
Deformation Behavior of a Coarse-Grained Mg-8Al-1.5Ca-0.2Sr Magnesium Alloy at Elevated Temperatures
The compression tests were carried out on a coarse-grained Mg-8Al-1.5Ca-0.2Sr magnesium alloy samples at temperatures from 300 to 450 °C and strain rates from 0.001 to 10 s{sup −1}. The flow stress curves were analyzed using the double-differentiation method, and double minima were detected on the flow curves. The first set of minima is shown to identify the critical strain for twinning, while the second set indicates the critical strain for the initiation of dynamic recrystallization (DRX). Twin variant selection was numerically identified by comprehensive analysis of the Schmid factors for different deformation modes and the accommodation strains imposed on neighboring grains. It was found that twinning is initiated before DRX. Dynamic recrystallization volume increases with strain rate at a given deformation temperature. At high strain rate, various twin variants are activated to accommodate deformation, leading to the formation of twin intersections and high DRX volume. Fully dynamic recrystallized structure can be obtained at both high and low strain rates due to the high mobility of the grain and twin boundaries at the temperature of 400 °C.