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Sample records for body-core temperature elevation

  1. FDTD analysis of body-core temperature elevation in children and adults for whole-body exposure

    NASA Astrophysics Data System (ADS)

    Hirata, Akimasa; Asano, Takayuki; Fujiwara, Osamu

    2008-09-01

    The temperature elevations in anatomically based human phantoms of an adult and a 3-year-old child were calculated for radio-frequency whole-body exposure. Thermoregulation in children, however, has not yet been clarified. In the present study, we developed a computational thermal model of a child that is reasonable for simulating body-core temperature elevation. Comparison of measured and simulated temperatures revealed thermoregulation in children to be similar to that of adults. Based on this finding, we calculated the body-core temperature elevation in a 3-year-old child and an adult for plane-wave exposure at the basic restriction in the international guidelines. The body-core temperature elevation in the 3-year-old child phantom was 0.03 °C at a whole-body-averaged specific absorption rate of 0.08 W kg-1, which was 35% smaller than in the adult female. This difference is attributed to the child's higher body surface area-to-mass ratio.

  2. Computational model for calculating body-core temperature elevation in rabbits due to whole-body exposure at 2.45 GHz

    NASA Astrophysics Data System (ADS)

    Hirata, Akimasa; Sugiyama, Hironori; Kojima, Masami; Kawai, Hiroki; Yamashiro, Yoko; Fujiwara, Osamu; Watanabe, Soichi; Sasaki, Kazuyuki

    2008-06-01

    In the current international guidelines and standards with regard to human exposure to electromagnetic waves, the basic restriction is defined in terms of the whole-body average-specific absorption rate. The rationale for the guidelines is that the characteristic pattern of thermoregulatory response is observed for the whole-body average SAR above a certain level. However, the relationship between energy absorption and temperature elevation was not well quantified. In this study, we improved our thermal computation model for rabbits, which was developed for localized exposure on eye, in order to investigate the body-core temperature elevation due to whole-body exposure at 2.45 GHz. The effect of anesthesia on the body-core temperature elevation was also discussed in comparison with measured results. For the whole-body average SAR of 3.0 W kg-1, the body-core temperature in rabbits elevates with time, without becoming saturated. The administration of anesthesia suppressed body-core temperature elevation, which is attributed to the reduced basal metabolic rate.

  3. FDTD analysis of human body-core temperature elevation due to RF far-field energy prescribed in the ICNIRP guidelines

    NASA Astrophysics Data System (ADS)

    Hirata, Akimasa; Asano, Takayuki; Fujiwara, Osamu

    2007-08-01

    This study investigated the relationship between the specific absorption rate and temperature elevation in an anatomically-based model named NORMAN for exposure to radio-frequency far fields in the ICNIRP guidelines (1998 Health Phys. 74 494-522). The finite-difference time-domain method is used for analyzing the electromagnetic absorption and temperature elevation in NORMAN. In order to consider the variability of human thermoregulation, parameters for sweating are derived and incorporated into a conventional sweating formula. First, we investigated the effect of blood temperature variation modeling on body-core temperature. The computational results show that the modeling of blood temperature variation was the dominant factor influencing the body-core temperature. This is because the temperature in the inner tissues is elevated via the circulation of blood whose temperature was elevated due to EM absorption. Even at different frequencies, the body-core temperature elevation at an identical whole-body average specific absorption rate (SAR) was almost the same, suggesting the effectiveness of the whole-body average SAR as a measure in the ICNIRP guidelines. Next, we discussed the effect of sweating on the temperature elevation and thermal time constant of blood. The variability of temperature elevation caused by the sweating rate was found to be 30%. The blood temperature elevation at the basic restriction in the ICNIRP guidelines of 0.4 W kg-1 is 0.25 °C even for a low sweating rate. The thermal time constant of blood temperature elevation was 23 min and 52 min for a man with a lower and a higher sweating rate, respectively, which is longer than the average time of the SAR in the ICNIRP guidelines. Thus, the whole-body average SAR required for blood temperature elevation of 1 °C was 4.5 W kg-1 in the model of a human with the lower sweating coefficients for 60 min exposure. From a comparison of this value with the basic restriction in the ICNIRP guidelines of 0

  4. Telemetric measurement of body core temperature in exercising unconditioned Labrador retrievers

    PubMed Central

    Angle, T. Craig; Gillette, Robert L.

    2011-01-01

    This project evaluated the use of an ingestible temperature sensor to measure body core temperature (Tc) in exercising dogs. Twenty-five healthy, unconditioned Labrador retrievers participated in an outdoor 3.5-km run, completed in 20 min on a level, 400-m grass track. Core temperature was measured continuously with a telemetric monitoring system before, during, and after the run. Data were successfully collected with no missing data points during the exercise. Core temperature elevated in the dogs from 38.7 ± 0.3°C at pre-exercise to 40.4 ± 0.6°C post-exercise. While rectal temperatures are still the standard of measurement, telemetric core temperature monitors may offer an easier and more comfortable means of sampling core temperature with minimal human and mechanical interference with the exercising dog. PMID:21731189

  5. Effects of body core temperature and brain dopamine activity on timing processes in humans.

    PubMed

    Rammsayer, T H

    1997-08-22

    In a placebo-controlled study, the effects of experimentally induced increase in body core temperature and of the dopamine antagonist haloperidol on judgments of an apparent second, a speeded-tapping task, and temporal discrimination of intervals in the range of milliseconds and seconds were investigated in 40 healthy male subjects. A 0.7 degree C-increase in body core temperature due to 3-h exposure to an ambient temperature of 52 degrees C did not cause any statistically significant changes in timing tasks. Unlike heat exposure, 3 mg of haloperidol caused a pronounced impairment of performance on the temporal discrimination of intervals in the range of milliseconds and seconds (P < 0.01 and P < 0.001, respectively) as well as speeded tapping (P < 0.05). For temporal discrimination of intervals in the range of seconds, a significant interaction between ambient temperature and haloperidol could be established (P < 0.05) indicating that haloperidol caused a significant performance decrement only in subjects exposed to an ambient temperature of 28 degrees C but not in those exposed to 52 degrees C. The overall pattern of results suggests that temporal processing of intervals in the range of milliseconds can be considered a function of dopaminergic activity in the basal ganglia while temporal processing of longer intervals appears to be cognitively mediated. Furthermore, the hypothesis that timing processes in humans are modulated by changes in body core temperature could not be established.

  6. Body core temperature of rats subjected to daily exercise limited to a fixed time

    NASA Astrophysics Data System (ADS)

    Shido, O.; Sugimoto, Naotoshi; Sakurada, Sotaro; Kaneko, Yoshiko; Nagasaka, Tetsuo

    Several timed daily environmental cues alter the pattern of nycthemeral variations in body core temperature in rodents. The present study investigated the effect of timed exercise on variations of daily body core temperature. Male rats were housed in cages with a running wheel at an ambient temperature of 24° C with a 12:12 h light/dark cycle. Timed daily exercise rats (TEX) were allowed access to the wheel for 6 h in the last half of the dark phase, freely exercising rats (FEX) could run at any time, and sedentary rats (NEX) were not allowed to run. After a 3-week exercise period, all animals were denied access to the wheel. The intraabdominal temperatures (Tab) and spontaneous activities of rats were measured for 6 days after the exercise period. The Tab values of the TEX rats were significantly higher than those of the other two groups only in the last half of the dark phase, while Tab in the FEX and NEX rats showed no significant difference. The specific Tab changes in the TEX rats lasted for 2 days after the exercise period. Spontaneous activity levels were higher in the TEX rats than the FEX and NEX rats in the last half of the dark phase for 1 day after the exercise period. The results suggest that daily exercise limited to a fixed time per day modifies nycthemeral variations of body core temperature in rats so that the temperature increases during the period when the animals had previously exercised. Such a rise in body core temperature is partly attributed to an increase in the spontaneous activity level.

  7. The ingestible telemetric body core temperature sensor: a review of validity and exercise applications.

    PubMed

    Byrne, Christopher; Lim, Chin Leong

    2007-03-01

    An ingestible telemetric temperature sensor for measuring body core temperature (Tc) was first described 45 years ago, although the method has only recently gained widespread use for exercise applications. This review aims to (1) use Bland and Altman's limits of agreement (LoA) method as a basis for quantitatively reviewing the agreement between intestinal sensor temperature (Tintestinal), oesophageal temperature (Toesophageal) and rectal temperature (Trectal) across numerous previously published validation studies; (2) review factors that may affect agreement; and (3) review the application of this technology in field-based exercise studies. The agreement between Tintestinal and Toesophageal is suggested to meet our delimitation for an acceptable level of agreement (ie, systematic bias <0.1 degrees C and 95% LoA within +/-0.4 degrees C). The agreement between Tintestinal and Trectal shows a significant systematic bias >0.1 degrees C, although the 95% LoA is acceptable. Tintestinal responds less rapidly than Toesophageal at the start or cessation of exercise or to a change in exercise intensity, but more rapidly than Trectal. When using this technology, care should be taken to ensure adequate control over sensor calibration and data correction, timing of ingestion and electromagnetic interference. The ingestible sensor has been applied successfully in numerous sport and occupational applications such as the continuous measurement of Tc in deep sea saturation divers, distance runners and soldiers undertaking sustained military training exercises. It is concluded that the ingestible telemetric temperature sensor represents a valid index of Tc and shows excellent utility for ambulatory field-based applications.

  8. Hypocretin deficiency in narcolepsy with cataplexy is associated with a normal body core temperature modulation.

    PubMed

    Grimaldi, Daniela; Agati, Patrizia; Pierangeli, Giulia; Franceschini, Christian; Guaraldi, Pietro; Barletta, Giorgio; Vandi, Stefano; Cevoli, Sabina; Plazzi, Giuseppe; Montagna, Pasquale; Cortelli, Pietro

    2010-09-01

    Narcolepsy with cataplexy (NC) is a sleep disorder caused by the loss of the hypothalamic neurons producing hypocretin. The clinical hallmarks of the disease are excessive daytime sleepiness, cataplexy, other rapid eye movement (REM) sleep phenomena, and a fragmented wake-sleep cycle. Experimental data suggest that the hypocretin system is involved primarily in the circadian timing of sleep and wakefulness but also in the control of other biological functions such as thermoregulation. The object of this study was to determine the effects of the hypocretin deficit and of the wake-sleep cycle fragmentation on body core temperature (BcT) modulation in a sample of drug-free NC patients under controlled conditions. Ten adult NC patients with low cerebrospinal fluid (CSF) hypocretin levels (9 men; age: 38 ± 12 yrs) were compared with 10 healthy control subjects (7 men; age: 44.9 ± 12 yrs). BcT and sleep-wake cycle were continuously monitored for 44 h from 12:00 h. During the study, subjects were allowed to sleep ad libitum, living in a temperature- and humidity-controlled room, lying in bed except when eating, in a light-dark schedule (dark [D] period: 23:00-07:00 h). Sleep structure was analyzed over the 24-h period, the light (L) and the D periods. The wake-sleep cycle fragmentation was determined by calculating the frame-shift index (number of 30-s sleep stage shifts occurring every 15 min) throughout the 44-h study. The analysis of BcT circadian rhythmicity was performed according to the single cosinor method. The time-course changes in BcT and in frame-shift index were compared between narcoleptics and controls by testing the time × group (controls versus NC subjects) interaction effect. The state-dependent analysis of BcT during D was performed by fitting a mixed model where the factors were wake-sleep phases (wake, NREM stages 1 and 2, slow-wave sleep, and REM sleep) and group. The results showed that NC patients slept significantly more than

  9. Order-picking in deep cold--physiological responses of younger and older females. Part 2: body core temperature and skin surface temperature.

    PubMed

    Baldus, Sandra; Kluth, Karsten; Strasser, Helmut

    2012-01-01

    So far, it was unclear to what extent working in deep cold-storage depots has an influence on female order-pickers body core temperature and skin surface temperature considering different age groups. Physiological effects of order-picking in a chill room (+3°C) and cold store (-24°C) were examined on 30 female subjects (Ss), classified in two age groups (20- to 35- year-olds and 40- to 65-year-olds). The body core temperature was taken every 15 min at the tympanum and the skin surface temperature was recorded continuously at seven different positions. Working in the chill room induced a decrease of the body core temperature up to 0.5K in comparison to the value at the outset for both age groups which could be compensated by all Ss during the breaks. Working in the cold store caused a decline up to 1.1K for the younger Ss and 1.3K for the older Ss. A complete warming-up during the breaks was often not possible. Regarding the skin surface temperature, working in the chill room can be considered as unproblematic, whereas significantly lower temperatures at nose, fingers and toes, associated with substantial negative subjective sensations, were recorded while working in the cold store. PMID:22317178

  10. [Feeding activity, spontaneous activity and body core temperature of saddle-back tamarins (Saguinus fuscicollis)].

    PubMed

    Petry, H

    1991-02-01

    Eating behaviour and spontaneous activity (videometry) as well as deep body temperature (radiotelemetry) of 3 adult Saddle Back Tamarins (Saguinus fuscicollis) were investigated (singly housed, environmental temperature 28 degrees C, relative air humidity 60%, light 6:00-18:00 h, drinking-water and pelleted colony diet ad lib.). The experimental animals (1 female, 2 males; 3-8 years old), born in captivity, showed only some slight individual differences within their inborn species pattern, with regard to the 3 measured parameters. The monkeys were, like wild-living individuals, strictly light-active. They moved in the day-time nearly uninterrupted without special rhythm and slept remarkably deep through the whole night. Food intake occurred during the whole day with varying intensity. The body temperature of the 3 monkeys showed individual daytime-means between 38.8-39.9 degrees C, whereby the temperature fluctuated dependent on their moving activity with a range of about +/- 0.5 degrees C. At night the body temperature of the animals averaged between 35.9-36.6 degrees C.

  11. Deception of ambient and body core temperature improves self paced cycling in hot, humid conditions.

    PubMed

    Castle, Paul C; Maxwell, Neil; Allchorn, Alan; Mauger, Alexis R; White, Danny K

    2012-01-01

    We used incorrect visual feedback of ambient and core temperature in the heat to test the hypothesis that deception would alleviate the decrement in cycling performance compared to a no deception trial. Seven males completed three 30 min cycling time trials in a randomised order on a Kingcycle ergometer. One time trial was in temperate, control conditions (CON: 21.8 ± 0.6°C; 43.3 ± 4.3%rh), the others in hot, humid conditions (HOT: 31.4 ± 0.3°C; 63.9 ± 4.5%rh). In one of the hot, humid conditions (31.6 ± 0.5°C; 65.4 ± 4.3%rh), participants were deceived (DEC) into thinking the ambient conditions were 26.0°C; 60.0%rh and their core temperature was 0.3°C lower than it really was. Compared to CON (16.63 ± 2.43 km) distance covered was lower in HOT (15.88 ± 2.75 km; P < 0.05), but DEC ameliorated this (16.74 ± 2.87 km; P < 0.05). Mean power output was greater in DEC (184.4 ± 60.4 W) than HOT (168.1 ± 54.1 W; P < 0.05) and no difference was observed between CON and DEC. Rectal temperature and iEMG of the vastus lateralis were not different, but RPE in the third minute was lower in DEC than HOT (P < 0.05). Deception improved performance in the heat by creating a lower RPE, evidence of a subtle mismatch between the subconscious expectation and conscious perception of the task demands.

  12. Changes in body core temperatures and heat balance after an abrupt release of lower body negative pressure in humans

    NASA Astrophysics Data System (ADS)

    Tanabe, Minoru; Shido, Osamu

    1994-03-01

    Changes in body core temperature ( T cor) and heat balance after an abrupt release of lower body negative pressure (LBNP) were investigated in 5 volunteers under the following conditions: (1) an ambient temperature ( T a) of 20 °C or (2) 35 °C, and (3) T a of 25 °C with a leg skin temperature of 30°C or (4) 35°C. The leg skin temperature was controlled with water perfusion devices wound around the legs. Rectal ( T re), tympanic ( T ty) and esophageal ( T es) temperatures, skin temperatures (7 sites) and oxygen consumption were measured. The intensity of LBNP was adjusted so that the amount of blood pooled in the legs was the same under all conditions. When a thermal balance was attained during LBNP, application of LBNP was suddenly halted. The skin temperatures increased significantly after the release of LBNP under all conditions, while oxygen consumption hardly changed. The release of LBNP caused significant falls in T cor s under conditions (1) and (3), but lowered T cor s very slightly under conditions (2) and (4). The changes in T es were always more rapid and greater than those of T ty and T re. The falls in T ty and T re appeared to be explained by changes in heat balance, whereas the sharp drop of T es could not be explained especially during the first 8 min after the release of LBNP. The results suggest that a fall in T cor after a release of LBNP is attributed to an increase in heat loss due to reflexive skin vasodilation and is dependent on the temperature of venous blood returning from the lower body. It is presumed that T es may not be an appropriate indicator for T cor when venous return changes rapidly.

  13. Changes in body core and body surface temperatures during prolonged swimming in water of 10°C—a case report

    PubMed Central

    2012-01-01

    Background This case report describes an experienced open-water ultra-endurance athlete swimming in water of 9.9°C for 6 h and 2 min. Methods Before the swim, anthropometric characteristics such as body mass, body height, skinfold thicknesses, and body fat were determined. During and after the swim, body core (rectum) and body surface (forearm and calf) temperatures were continuously recorded. Results The swimmer (53 years old, 110.5 kg body mass, 1.76 m body height, 34.9% body fat, and a body mass index of 35.7 kg/m2) achieved a total distance of 15 km while swimming at a mean speed of 2.48 km/h, equal to 0.69 m/s, in water of 9.9°C. Body core temperature was at 37.8°C before the swim, increased to a maximum of 38.1°C after approximately 20 min of swimming, and then decreased continuously to 36.3°C upon finishing the swim. The lowest body core temperature was 36.0°C between 35 and 60 min after finishing the swim. Sixty minutes after the swim, the body core temperature continuously rose to 36.5°C where it remained. At the forearm, the temperature dropped to 19.6°C after approximately 36 min of swimming and decreased to 19.4°C by the end of the swim. The lowest temperature at the forearm was 17.6°C measured at approximately 47 min before the athlete stopped swimming. At the calf, the temperature dropped to 13.0°C after approximately 24 min of swimming and decreased to 11.9°C at the end of the swim. The lowest temperature measured at the calf was 11.1°C approximately 108 min after the start. In both the forearm and the calf, the skin temperature continuously increased after the swim. Conclusions This case report shows that (1) it is possible to swim for 6 h in water of 9.9°C and that (2) the athlete did not suffer from hypothermia under these circumstances. The high body mass index, high body fat, previous experience, and specific preparation of the swimmer are the most probable explanations for these findings. PMID:23849461

  14. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Yau, J. F.; Malik, S. N.; Kim, K. S.; Vanstone, R. H.; Laflen, J. H.

    1985-01-01

    The objective of the Elevated Temperature Crack Growth Project is to evaluate proposed nonlinear fracture mechanics methods for application to combustor liners of aircraft gas turbine engines. During the first year of this program, proposed path-independent (P-I) integrals were reviewed for such applications. Several P-I integrals were implemented into a finite-element postprocessor which was developed and verified as part of the work. Alloy 718 was selected as the analog material for use in the forthcoming experimental work. A buttonhead, single-edge notch specimen was designed and verified for use in elevated-temperature strain control testing with significant inelastic strains. A crack mouth opening displacement measurement device was developed for further use.

  15. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1984-01-01

    A three year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for non-proportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved undertanding were through several critical non-proportional loading experiments. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C.

  16. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1985-01-01

    A 3 year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for nonproportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved understanding were through several critical nonproportional loading experiments. The direction of cracking observed on failed specimens was also recorded and used to guide the development of the theory. Cyclic deformation responses were permanently recorded digitally during each test. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C. In contrast to some other metals, loading path in nonproportional loading had little effect on fatigue lives. Strain rate had a small effect on fatigue lives at 649 C. Of the various correlating parameters the modified plastic work and octahedral shear stress were the most successful.

  17. Comparing new-technology passive warming versus traditional passive warming methods for optimizing perioperative body core temperature.

    PubMed

    Bender, Miriam; Self, Beverly; Schroeder, Ellen; Giap, Brandon

    2015-08-01

    Hypothermia puts surgical patients at risk for adverse outcomes. Traditional passive warming methods are mostly ineffective in reducing hypothermia. New-technology passive warming holds promise as an effective method for promoting and sustaining normothermia throughout surgery. The purpose of this retrospective cohort study was to compare the effectiveness of new-technology passive warming with traditional methods. We measured core body temperature at anesthesia induction and at the end of surgery for patients undergoing robotic-assisted prostatectomy/hysterectomy in the lithotomy position who received either new-technology passive warming (n = 30) or traditional linens and gel pads (n = 35). The traditionally warmed cohort had no change in temperature (35.9° C ± 0.6° C presurgery vs 35.9° C ± 0.7° C postsurgery; t = 0.47; P = .66). The intervention cohort showed a significant increase in temperature (35.75° C ± 0.52° C presurgery vs 36.30° C ± 0.53° C postsurgery; t = 4.64; P < .001). A repeated-measure analysis of variance adjusting for surgery duration and fluid administration confirmed the significance (F = 17.254; P < .001), suggesting that new-technology passive warming may effectively complement active warming to reduce perioperative hypothermia.

  18. Actinide Thermodynamics at Elevated Temperatures

    SciTech Connect

    Friese, Judah I.; Rao, Linfeng; Xia, Yuanxian; Bachelor, Paula P.; Tian, Guoxin

    2007-11-16

    The postclosure chemical environment in the proposed Yucca Mountain repository is expected to experience elevated temperatures. Predicting migration of actinides is possible if sufficient, reliable thermodynamic data on hydrolysis and complexation are available for these temperatures. Data are scarce and scattered for 25 degrees C, and nonexistent for elevated temperatures. This collaborative project between LBNL and PNNL collects thermodynamic data at elevated temperatures on actinide complexes with inorganic ligands that may be present in Yucca Mountain. The ligands include hydroxide, fluoride, sulfate, phosphate and carbonate. Thermodynamic parameters of complexation, including stability constants, enthalpy, entropy and heat capacity of complexation, are measured with a variety of techniques including solvent extraction, potentiometry, spectrophotometry and calorimetry

  19. Poloxamer-based hydrogels hardening at body core temperature as carriers for cell based therapies: in vitro and in vivo analysis.

    PubMed

    Volkmer, Elias; Leicht, Uta; Moritz, Martina; Schwarz, Christina; Wiese, Hinrich; Milz, Stefan; Matthias, Philipp; Schloegl, Winfried; Friess, Wolfgang; Goettlinger, Michael; Augat, Peter; Schieker, Matthias

    2013-09-01

    Cell-based regenerative therapies for bone defects usually employ bone precursor cells seeded on solid scaffolds. Thermosensitive hydrogels that harden at body core temperature are promising alternative cell carriers as they are applicable minimally invasively. We modified Pluronic® P123 with different chain extenders and assessed rheology and biocompatibility of the resulting hydrogels. The best candidate was tested in a rat's femoral defect model. All gels hardened above 25 °C with butane-diisocyanate-hydrogels (BDI-gels) displaying the highest storage moduli. BDI-gels showed the most favourable biocompatibility and did not affect cellular adipogenic or osteogenic differentiation in vitro. Implantation of BDI-hydrogel into femoral defects did not impede bone healing in vivo as evidenced by μCT and histological analysis. We conclude that thermosensitive BDI-gels are promising alternative cell carriers. The gels harden upon injection in vivo without interfering with bone metabolism. Further experiments will assess the gels' capacity to effectively transport living cells into bone defects. PMID:23712537

  20. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Vanstone, R. H.; Malik, S. N.; Laflen, J. H.

    1988-01-01

    A study was performed to examine the applicability of path-independent (P-I) integrals to crack growth problems in hot section components of gas turbine aircraft engines. Alloy 718 was used and the experimental parameters included combined temperature and strain cycling, thermal gradients, elastic-plastic strain levels, and mean strains. A literature review was conducted of proposed P-I integrals, and those capable of analyzing hot section component problems were selected and programmed into the postprocessor of a finite element code. Detailed elastic-plastic finite element analyses were conducted to simulate crack growth and crack closure of the test specimen, and to evaluate the P-I integrals. It was shown that the selected P-I integrals are very effective for predicting crack growth for isothermal conditions.

  1. Ion implantation at elevated temperatures

    SciTech Connect

    Lam, N.Q.; Leaf, G.K.

    1985-11-01

    A kinetic model has been developed to investigate the synergistic effects of radiation-enhanced diffusion, radiation-induced segregation and preferential sputtering on the spatial redistribution of implanted solutes during implantation at elevated temperatures. Sample calculations were performed for Al and Si ions implanted into Ni. With the present model, the influence of various implantation parameters on the evolution of implant concentration profiles could be examined in detail.

  2. Comparison of two fluid warming devices for maintaining body core temperature during living donor liver transplantation: Level 1 H-1000 vs. Fluid Management System 2000

    PubMed Central

    Han, Sangbin; Choi, Junghee; Ko, Justin Sangwook; Gwak, Misook; Lee, Suk-Koo

    2014-01-01

    Background Rapid fluid warming has been a cardinal measure to maintain normothermia during fluid resuscitation of hypovolemic patients. A previous laboratory simulation study with different fluid infusion rates showed that a fluid warmer using magnetic induction is superior to a warmer using countercurrent heat exchange. We tested whether the simulation-based result is translated into the clinical liver transplantation. Methods Two hundred twenty recipients who underwent living donor liver transplantation between April 2009 and October 2011 were initially screened. Seventeen recipients given a magnetic induction warmer (FMS2000) were matched 1 : 1 with those given a countercurrent heat exchange warmer (Level-1 H-1000) based on propensity score. Matched variables included age, gender, body mass index, model for end-stage liver disease score, graft size and time under anesthesia. Core temperatures were taken at predetermined time points. Results Level-1 and FMS groups had comparable core temperature throughout the surgery from skin incision, the beginning/end of the anhepatic phase to skin closure. (P = 0.165, repeated measures ANOVA). The degree of core temperature changes within the dissection, anhepatic and postreperfusion phase were also comparable between the two groups. The minimum intraoperative core temperature was also comparable (Level 1, 35.6℃ vs. FMS, 35.4℃, P = 0.122). Conclusions A countercurrent heat exchange warmer and magnetic induction warmer displayed comparable function regarding the maintenance of core temperature and prevention of hypothermia during living donor liver transplantation. The applicability of the two devices in liver transplantation needs to be evaluated in various populations and clinical settings. PMID:25368785

  3. [The influence of ultrahigh-frequency electromagnetic radiation and low-intensity laser radiation on the body core temperature and basal metabolism in rats with systemic inflammation].

    PubMed

    Zhavoronok, I P; Molchanova, A Iu; Ulashik, V S

    2012-01-01

    The effects of ultrahigh-frequency electromagnetic radiation (UHF EMR) and low-intensity laser irradiation (LILI) on the body and skin temperature, oxygen consumption, production of carbon dioxide and heat release were investigated in the experiments on intact rats and during LPS-induced polyphasic fever. It was found that UHF EMR with the wavelength of 4,9 mm, 5,6 mm or 7,1 mm and LILI with the wavelength of 0.47 microm, 0.67 microm and 0.87 microm caused modulation of basal metabolism and thermal response to systemically administered lipopolysaccharide (LPS). These findings suggest that the most pronounced antipyretic and hypometabolic effects were observed after the treatment with UHF EMR at 7,1 mm and LILI at 470 microm.

  4. An elevated temperature titration calorimeter

    SciTech Connect

    Smith, J.R.; Zanonato, P.L.; Choppin, G.R. . Dept. of Chemistry)

    1991-06-01

    A variable-temperature (313 K to 353 K) titration calorimeter of high sensitivity has been constructed. The purpose of the calorimeter is to study temperature effects on the enthalpies of complex formation and of other reactions of metal cations such as hydrolysis and precipitation. Operation of the calorimetric system, including that final calculation of the heat released during titration, is automatic via computer control. Calibration tests of the calorimeter using 2-amino-2-hydroxymethyl-1,3-propanediol gave -(46.0 {plus minus} 0.3) kJ mol{sup {minus}1} and -(46.2 {plus minus} 0.2) kJ mol{sup {minus}1} for the enthalpy of protonation, at 318 K and at 343 K, respectively. For titrations of 2-bis(2-hydroxyethyl) amino-2-hydroxymethyl-1,3-propanediol, enthalpy of protonation values of -(28.4 {plus minus} 0.3) kJ mol{sup {minus}1} and -(29.3 {plus minus} 0.2) kJ mol{sup {minus}1} were obtained at 318 K and at 343 K, respectively. 6 refs., 3 figs., 2 tabs.

  5. Temperature elevation in the fetus from electromagnetic exposure during magnetic resonance imaging.

    PubMed

    Kikuchi, Satoru; Saito, Kazuyuki; Takahashi, Masaharu; Ito, Koichi

    2010-04-21

    This study computationally assessed the temperature elevations due to electromagnetic wave energy deposition during magnetic resonance imaging in non-pregnant and pregnant woman models. We used a thermal model with thermoregulatory response of the human body for our calculations. We also considered the effect of blood temperature variation on body core temperature. In a thermal equilibrium state, the temperature elevations in the intrinsic tissues of the woman and fetal tissues were 0.85 and 0.61 degrees C, respectively, at a whole-body averaged specific absorption rate of 2.0 W kg(-1), which is the restriction value of the International Electrotechnical Commission for the normal operating mode. As predicted, these values are below the temperature elevation of 1.5 degrees C that is expected to be teratogenic. However, these values exceeded the recommended temperature elevation limit of 0.5 degrees C by the International Commission on Non-Ionizing Radiation Protection. We also assessed the irradiation time required for a temperature elevation of 0.5 degrees C at the aforementioned specific absorption rate. As a result, the calculated irradiation time was 40 min.

  6. Temperature elevation in the fetus from electromagnetic exposure during magnetic resonance imaging

    NASA Astrophysics Data System (ADS)

    Kikuchi, Satoru; Saito, Kazuyuki; Takahashi, Masaharu; Ito, Koichi

    2010-04-01

    This study computationally assessed the temperature elevations due to electromagnetic wave energy deposition during magnetic resonance imaging in non-pregnant and pregnant woman models. We used a thermal model with thermoregulatory response of the human body for our calculations. We also considered the effect of blood temperature variation on body core temperature. In a thermal equilibrium state, the temperature elevations in the intrinsic tissues of the woman and fetal tissues were 0.85 and 0.61 °C, respectively, at a whole-body averaged specific absorption rate of 2.0 W kg-1, which is the restriction value of the International Electrotechnical Commission for the normal operating mode. As predicted, these values are below the temperature elevation of 1.5 °C that is expected to be teratogenic. However, these values exceeded the recommended temperature elevation limit of 0.5 °C by the International Commission on Non-Ionizing Radiation Protection. We also assessed the irradiation time required for a temperature elevation of 0.5 °C at the aforementioned specific absorption rate. As a result, the calculated irradiation time was 40 min.

  7. Aircraft structures research at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Duberg, John E

    1955-01-01

    A review is made of the test techniques that have been developed and used by the NACA for experimental research in aircraft structures at elevated temperatures. Some experimental results are presented. Remarks are included on the problem of model scaling for testing of structures at high temperatures. (author)

  8. Elevated temperature deformation of TD-nickel.

    NASA Technical Reports Server (NTRS)

    Petrovic, J. J.; Ebert, L. J.

    1973-01-01

    Sensitivity of the elevated temperature (above 0.5 Tm) deformation of TD-nickel to grain size and shape was examined in both tension and creep. Elevated temperature strength increased with increasing grain diameter and increasing L/D ratio. Temperature sensitivity of the yield stress, as well as high (compared to self diffusion) apparent tensile activation enthalpies were the result of the internal stress not being proportional to the shear modulus. Creep activation enthalpies increased with increasing L/D ratio and, to a lesser extent, increasing grain diameter, reaching high values which may be apparent values. The thoria particle dispersion may have been altered by elevated temperature tensile and creep deformation.

  9. Elevated-Temperature Tribology of Metallic Materials

    SciTech Connect

    Blau, Peter Julian

    2010-01-01

    The wear of metals and alloys takes place in many forms, and the type of wear that dominates in each instance is influenced by the mechanics of contact, material properties, the interfacial temperature, and the surrounding environment. The control of elevated-temperature friction and wear is important for applications like internal combustion engines, aerospace propulsion systems, and metalworking equipment. The progression of interacting, often synergistic processes produces surface deformation, subsurface damage accumulation, the formation of tribolayers, and the creation of free particles. Reaction products, particularly oxides, play a primary role in debris formation and microstructural evolution. Chemical reactions are known to be influenced by the energetic state of the exposed surfaces, and that surface energy is in turn affected by localized deformation and fracture. At relatively low temperatures, work-hardening can occur beneath tribo-contacts, but exposure to high temperatures can modify the resultant defect density and grain structure to affect the mechanisms of re-oxidation. As research by others has shown, the rate of wear at elevated temperatures can either be enhanced or reduced, depending on contact conditions and nature of oxide layer formation. Furthermore, the thermodynamic driving force for certain chemical reactions is moderated by kinetics and microstructure. The role of deformation, oxidation, and tribo-corrosion in the elevated temperature tribology of metallic alloys will be exemplified by three examples involving sliding wear, single-point abrasion, and repetitive impact plus slip.

  10. Methods for structural design at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Ellison, A. M.; Jones, W. E., Jr.; Leimbach, K. R.

    1973-01-01

    A procedure which can be used to design elevated temperature structures is discussed. The desired goal is to have the same confidence in the structural integrity at elevated temperature as the factor of safety gives on mechanical loads at room temperature. Methods of design and analysis for creep, creep rupture, and creep buckling are presented. Example problems are included to illustrate the analytical methods. Creep data for some common structural materials are presented. Appendix B is description, user's manual, and listing for the creep analysis program. The program predicts time to a given creep or to creep rupture for a material subjected to a specified stress-temperature-time spectrum. Fatigue at elevated temperature is discussed. Methods of analysis for high stress-low cycle fatigue, fatigue below the creep range, and fatigue in the creep range are included. The interaction of thermal fatigue and mechanical loads is considered, and a detailed approach to fatigue analysis is given for structures operating below the creep range.

  11. Buffer strips in composites at elevated temperature

    NASA Technical Reports Server (NTRS)

    Bigelow, C. A.

    1983-01-01

    The composite material 'buffer strip' concept is presently investigated at elevated temperatures for the case of graphite/polyimide buffer strip panels using a (45/0/45/90)2S layup, where the buffer strip material was 0-deg S-glass/polyimide. Each panel was loaded in tension until it failed, and radiographs and crack opening displacements were recorded during the tests to determine fracture onset, fracture arrest, and the extent of damage in the buffer strip after crack arrest. At 177 + or - 3 C, the buffer strips increased the panel strength by at least 40 percent in comparison with panels without buffer strips. Compared to similar panels tested at room temperature, those tested at elevated temperature had lower residual strengths, but higher failure strains.

  12. Void evolution in polycarbonate at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Chen, Y. H.; Feng Chou, Kuo; Li, C. L.; Lee, Sanboh

    2011-08-01

    The void evolution in polycarbonate (PC) at elevated temperatures was investigated. Internal cylindrical cracks and voids were induced in PC by Nd-YAG laser irradiation. During the annealing at temperatures of 177-197 °C, the spherical void grows to a maximum size, which then decreases, and is finally leveling off. A model of void evolution based on the evaporation and condensation mechanisms for growth and shrinkage is proposed. The theoretical predictions are in good agreement with the experimental data. The activation energies of evaporation and condensation processes are determined to be 477.31 and 611.49 kJ/mol, respectively.

  13. Void evolution in polycarbonate at elevated temperatures

    SciTech Connect

    Chen, Y. H.; Li, C. L.; Lee, Sanboh; Kuo Feng Chou

    2011-08-15

    The void evolution in polycarbonate (PC) at elevated temperatures was investigated. Internal cylindrical cracks and voids were induced in PC by Nd-YAG laser irradiation. During the annealing at temperatures of 177-197 deg. C, the spherical void grows to a maximum size, which then decreases, and is finally leveling off. A model of void evolution based on the evaporation and condensation mechanisms for growth and shrinkage is proposed. The theoretical predictions are in good agreement with the experimental data. The activation energies of evaporation and condensation processes are determined to be 477.31 and 611.49 kJ/mol, respectively.

  14. Elevated temperature forming method and preheater apparatus

    DOEpatents

    Krajewski, Paul E; Hammar, Richard Harry; Singh, Jugraj; Cedar, Dennis; Friedman, Peter A; Luo, Yingbing

    2013-06-11

    An elevated temperature forming system in which a sheet metal workpiece is provided in a first stage position of a multi-stage pre-heater, is heated to a first stage temperature lower than a desired pre-heat temperature, is moved to a final stage position where it is heated to a desired final stage temperature, is transferred to a forming press, and is formed by the forming press. The preheater includes upper and lower platens that transfer heat into workpieces disposed between the platens. A shim spaces the upper platen from the lower platen by a distance greater than a thickness of the workpieces to be heated by the platens and less than a distance at which the upper platen would require an undesirably high input of energy to effectively heat the workpiece without being pressed into contact with the workpiece.

  15. Hypothalamic paraventricular nucleus is critical for renal vasoconstriction elicited by elevations in body temperature.

    PubMed

    Cham, Joo Lee; Badoer, Emilio

    2008-02-01

    Redistribution of blood from the viscera to the peripheral vasculature is the major cardiovascular response designed to restore thermoregulatory homeostasis after an elevation in body core temperature. In this study, we investigated the role of the hypothalamic paraventricular nucleus (PVN) in the reflex decrease in renal blood flow that is induced by hyperthermia, as this brain region is known to play a key role in renal function and may contribute to the central pathways underlying thermoregulatory responses. In anesthetized rats, blood pressure, heart rate, renal blood flow, and tail skin temperature were recorded in response to elevating body core temperature. In the control group, saline was microinjected bilaterally into the PVN; in the second group, muscimol (1 nmol in 100 nl per side) was microinjected to inhibit neuronal activity in the PVN; and in a third group, muscimol was microinjected outside the PVN. Compared with control, microinjection of muscimol into the PVN did not significantly affect the blood pressure or heart rate responses. However, the normal reflex reduction in renal blood flow observed in response to hyperthermia in the control group ( approximately 70% from a resting level of 11.5 ml/min) was abolished by the microinjection of muscimol into the PVN (maximum reduction of 8% from a resting of 9.1 ml/min). This effect was specific to the PVN since microinjection of muscimol outside the PVN did not prevent the normal renal blood flow response. The data suggest that the PVN plays an essential role in the reflex decrease in renal blood flow elicited by hyperthermia.

  16. Crushed salt reconsolidation at elevated temperatures.

    SciTech Connect

    Holcomb, David Joseph; Clayton, Daniel James; Lee, Moo Yul; Bronowski, David R.

    2010-06-01

    There is a long history of testing crushed salt as backfill for the Waste Isolation Pilot Plant program, but testing was typically done at 100 C or less. Future applications may involve backfilling crushed salt around heat-generating waste packages, where near-field temperatures could reach 250 C or hotter. A series of experiments were conducted to investigate the effects of hydrostatic stress on run-of-mine salt at temperatures up to 250 C and pressures to 20 MPa. The results of these tests were compared with analogous modeling results. By comparing the modeling results at elevated temperatures to the experimental results, the adequacy of the current crushed salt reconsolidation model was evaluated. The model and experimental results both show an increase in the reconsolidation rate with temperature. The current crushed salt model predicts the experimental results well at a temperature of 100 C and matches the overall trends, but over-predicts the temperature dependence of the reconsolidation. Further development of the deformation mechanism activation energies would lead to a better prediction of the temperature dependence by the crushed salt reconsolidation model.

  17. Luminescence in crosslinked polyethylene at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Bamji, S. S.; Bulinski, A. T.; Suzuki, H.; Matsuki, M.; Iwata, Z.

    1993-10-01

    Electrical treeing is often responsible for the breakdown of insulating materials used in power apparatus such as high-voltage transformers, cables, and capacitors. Insulation, such as crosslinked polyethylene (XLPE), used in underground high-voltage cables usually operates at temperatures above ambient. This paper describes the characteristics of luminescence, emitted prior to electrical tree inception, at a crosslinked polyethylene-semiconducting material (XLPE-semicon) interface held above room temperature. Use of a sensitive light detection system showed that XLPE subjected to elevated temperatures emits luminescence even without voltage application. This light was attributed to thermoluminescence which decreased with the decrease in the concentration of the crosslinking by-products present in the polymer. The spectra of thermoluminescence were only in the visible range. On the other hand, electroluminescence occurred when the XLPE-semicon interface was held above room temperature and subjected to high electric stress. This light did not depend on the concentration of the crosslinking by-products and the spectra of electroluminescence were in the visible and the ultraviolet ranges. It is proposed that XLPE-semicon interface held at elevated temperature and subjected to long-term voltage application initially emits both thermoluminescence and electroluminescence. As the crosslinking by-products exude out of the polymer, thermoluminescence decreases with time and ultimately ceases, but electroluminescence occurs as long as the voltage is applied to the polymer. Although the intensity of electroluminescence emitted at high temperature was lower than that emitted at ambient, sufficient ultraviolet radiation was emitted. The ultraviolet radiation could photodegrade the polymer and lead to electrical tree inception.

  18. Gas-Alloy Interactions at Elevated Temperatures

    SciTech Connect

    Arroyave, Raymundo; Gao, Michael

    2012-11-07

    The understanding of the stability of metals and alloys against oxidation and other detrimental reactions, to the catalysis of important chemical reactions and the minimization of defects associated with processing and synthesis have one thing in common: At the most fundamental level, all these scientific/engineering problems involve interactions between metals and alloys (in the solid or liquid state) and gaseous atmospheres at elevated temperatures. In this special issue, we have collected a series of articles that illustrate the application of different theoretical, computational, and experimental techniques to investigate gas-alloy interactions.

  19. Molten Composition B Viscosity at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Zerkle, David K.; Núñez, Marcel P.; Zucker, Jonathan M.

    2016-10-01

    A shear-thinning viscosity model is developed for molten Composition B at elevated temperature from analysis of falling ball viscometer data. Results are reported with the system held at 85, 110, and 135°C. Balls of densities of 2.7, 8.0, and 15.6 g/cm3 are dropped to generate a range of strain rates in the material. Analysis of video recordings gives the speed at which the balls fall. Computer simulation of the viscometer is used to determine parameters for a non-Newtonian model calibrated to measured speeds. For the first time, viscosity is shown to be a function of temperature and strain rate-dependent maximum RDX (cyclotrimethylenetrinitramine) particle volume fraction.

  20. Optimization Of Nakazima Test At Elevated Temperatures

    SciTech Connect

    Turetta, A.; Ghiotti, A.; Bruschi, S.

    2007-04-07

    Nowadays hot forming of High Strength Steel is gaining the strict requirements of automotive producer: in fact deformation performed simultaneously with quenching assures a fully martensitic microstructure at room temperature and thus high strength properties that allow the thickness reduction of the body-in-white components. Basic aspects of hot stamping are still under investigation and supplementary achievements are expected for a successful application of sheet metal forming technologies at elevated temperatures. Among data needed to settle a numerical model of the process, information about material formability may help in better designing and optimizing hot stamping operations. In the first part of the work, a new experimental apparatus based on Nakazima concept is presented; process parameters are optimized in order to accurately replicate the thermo-mechanical conditions typical of the industrial process, paying particular attention to the thermal and microstructural evolution. On the other hand, as commercial FE codes require the implementation of Forming Limit Diagrams at constant temperature, numerical investigations have been performed in order to determine the proper testing conditions to obtain FLD at nearly constant temperature.

  1. Strengths of serpentinite gouges at elevated temperatures

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, D.A.; Ma, S.; Summers, R.; Byerlee, J.D.

    1997-01-01

    Serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones. To test these hypotheses, we have measured the strength of chrysotile-, lizardite-, and antigorite-rich serpentinite gouges under hydrothermal conditions, with emphasis on chrysotile, which has thus far received little attention. At 25??C, the coefficient of friction, ??, of chrysotile gouge is roughly 0.2, whereas the lizardite- and antigorite-rich gouges are at least twice as strong. The very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content. When the adsorbed water is removed, chrysotile is as strong as pure antigorite gouge at room temperature. Heating to ???200??C causes the frictional strengths of all three gouges to increase. Limited data suggest that different polytypes of a given serpentine mineral have similar strengths; thus deformation-induced changes in polytype should not affect fault strength. At 25??C, the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities, consistent with previous studies. At temperatures up to ???200??C, however, chrysotile strength is essentially independent of velocity at low velocities. Overall, chrysotile has a restricted range of velocity-strengthening behavior that migrates to higher velocities with increasing temperature. Less information on velocity dependence is available for the lizardite and antigorite gouges, but their behavior is consistent with that outlined for chrysotile. The marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth. The velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip, but in the presence of a hydrostatic fluid pressure gradient, all varieties of serpentine are too strong to explain the apparent weakness of faults such

  2. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... for an Elevated temperature material, liquid, n.o.s.: ER29DE94.000 ... 49 Transportation 2 2014-10-01 2014-10-01 false Elevated temperature materials. 172.325 Section... REQUIREMENTS, AND SECURITY PLANS Marking § 172.325 Elevated temperature materials. (a) Except as provided...

  3. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... for an Elevated temperature material, liquid, n.o.s.: ER29DE94.000 ... 49 Transportation 2 2013-10-01 2013-10-01 false Elevated temperature materials. 172.325 Section... REQUIREMENTS, AND SECURITY PLANS Marking § 172.325 Elevated temperature materials. (a) Except as provided...

  4. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... for an Elevated temperature material, liquid, n.o.s.: ER29DE94.000 ... 49 Transportation 2 2011-10-01 2011-10-01 false Elevated temperature materials. 172.325 Section... REQUIREMENTS, AND SECURITY PLANS Marking § 172.325 Elevated temperature materials. (a) Except as provided...

  5. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... for an Elevated temperature material, liquid, n.o.s.: ER29DE94.000 ... 49 Transportation 2 2010-10-01 2010-10-01 false Elevated temperature materials. 172.325 Section... REQUIREMENTS, AND SECURITY PLANS Marking § 172.325 Elevated temperature materials. (a) Except as provided...

  6. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 49 Transportation 2 2012-10-01 2012-10-01 false Elevated temperature materials. 172.325 Section... REQUIREMENTS, AND SECURITY PLANS Marking § 172.325 Elevated temperature materials. (a) Except as provided in paragraph (b) of this section, a bulk packaging containing an elevated temperature material must be...

  7. Strontium sorption on hematite at elevated temperatures

    SciTech Connect

    Karasyova, O.N.; Ivanova, L.I.; Lakshtanov, L.Z.; Loevgren, L.

    1999-12-15

    Acid-base reactions and surface complexation of Sr(II) at the hematite/water interface have been studied by means of potentiometric titrations at three different temperatures: 25, 50, and 75 C. Equilibrium measurements were performed in 0.1 M NaCl. In the evaluation of equilibrium models for the acid-base reactions and complexation reactions in the three-component system H{sup +} -({triple{underscore}bond}FeOH)-Sr{sup 2+}, the constant capacitance model was applied. During the titrations with Sr, aliquots of the suspension were sampled at in several points. The aqueous concentrations of Sr were analyzed by atomic absorption spectrometry. Treatment of data included tests for formation of both inner-sphere and outer-sphere complexes of different stoichiometric composition. The proposed equilibrium model consists of the following surface complexes of inner sphere type: {triple{underscore}bond}FeOHSr{sup 2+} and {triple{underscore}bond}FeOSrOH. Besides the stability constants for the surface complexes, the thermodynamic parameters {Delta}H and {Delta}S were evaluated. The combined effect of a decrease in pH{sub pzc} with increasing temperature and positive enthalpies of surface complex formation favors adsorption of Sr at elevated temperatures.

  8. Integrated research in constitutive modelling at elevated temperatures, part 1

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.; Allen, D. H.

    1986-01-01

    Topics covered include: numerical integration techniques; thermodynamics and internal state variables; experimental lab development; comparison of models at room temperature; comparison of models at elevated temperature; and integrated software development.

  9. Decomposition reactions in RDX at elevated temperatures and pressures

    NASA Astrophysics Data System (ADS)

    Schweigert, Igor

    2015-03-01

    Mechanisms and rates of elementary reactions controlling condensed-phase decomposition of RDX under elevated temperatures (up to 2000 K) and pressures (up to a few GPa) are not known. Global decomposition kinetics in RDX below 700 K has been measured; however, the observed global pathways result from complex manifolds of elementary reactions and are likely to be altered by elevated temperatures. Elevated pressures can further affect the condensed-phase kinetics and compete with elevated temperatures in promoting some elementary reactions and suppressing others. This presentation will describe density functional theory (DFT) based molecular dynamics simulations of crystalline and molten RDX aimed to delineate the effects of elevated temperatures and pressures on the mechanism of initial dissociation and the resulting secondary reactions. This work was supported by the Naval Research Laboratory, by the Office of Naval Research, and by the DOD High Performance Computing Modernization Program Software Application Institute for Multiscale Reactive Modeling of Insensitive Munitions.

  10. Elevated temperature deformation of TD-nickel base alloys

    NASA Technical Reports Server (NTRS)

    Petrovic, J. J.; Kane, R. D.; Ebert, L. J.

    1972-01-01

    Sensitivity of the elevated temperature deformation of TD-nickel to grain size and shape was examined in both tension and creep. Elevated temperature strength increased with increasing grain diameter and increasing L/D ratio. Measured activation enthalpies in tension and creep were not the same. In tension, the internal stress was not proportional to the shear modulus. Creep activation enthalpies increased with increasing L/D ratio and increasing grain diameter, to high values compared with that of the self diffusion enthalpy. It has been postulated that two concurrent processes contribute to the elevated temperature deformation of polycrystalline TD-nickel: (1) diffusion controlled grain boundary sliding, and (2) dislocation motion.

  11. Ferromagnetic vortex core switching at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Lebecki, Kristof M.; Nowak, Ulrich

    2014-01-01

    An approach for the investigation of vortex core switching is presented. Thermal effects up to the Curie point are included in a micromagnetic framework based on the recently developed Landau-Lifshitz-Bloch equation. In this approach it is easier to avoid numerical discretization artifacts, commonly present when a Bloch point is mediating the switching process. Switching in thin circular permalloy disks caused by the application of a slowly increasing magnetic field oriented orthogonally to the disk is considered. An energy barrier which can be overcome by thermal fluctuations is taken into account, leading to a strong influence of the temperature on the switching field. In particular, the switching field goes to zero at a significantly smaller temperature than the Curie temperature. The deduced nucleation volume is smaller than the typical grain size in permalloy.

  12. Aluminum nanocomposites for elevated temperature applications

    NASA Astrophysics Data System (ADS)

    Borgonovo, C.; Apelian, D.; Makhlouf, M. M.

    2011-02-01

    Aluminum casting alloys conventionally used in the automotive and aerospace industries (i.e., Al-Zn-Mg, and Al-Cu-Mg systems) are able to achieve excellent tensile strength at room temperature. At high temperatures, such alloys lose dimensional stability and their mechanical properties rapidly degrade. Aluminum-based nanocomposites show the potential for enhanced performance at high temperatures. The manufacturing process, however, is difficult; a viable and effective method for large-scale applications has not been developed. In the current study, an innovative and cost-effective approach has been adopted to manufacture Al/AlN composites. A nitrogen-bearing gas is injected into the melt and AlN particles synthesize in-situ via chemical reaction. In a preliminary stage, a model able to predict the amount of reinforcement formed has been developed. AlN dispersoids have been succesfully synthesized in the matrix and the model has been experimentally validated.

  13. Rhenium/Oxygen Interactions at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan; Myers, Dwight; Zhu, Dong-Ming; Humphrey, Donald

    2000-01-01

    The oxidation of pure rhenium is examined from 600-1400 C in oxygen/argon mixtures. Linear weight loss kinetics are observed. Gas pressures, flow rates, and temperatures are methodically varied to determine the rate controlling steps. The reaction at 600 and 800 C appears to be controlled by a chemical reaction step at the surface; whereas the higher temperature reactions appear to be controlled by gas phase diffusion of oxygen to the rhenium surface. Attack of the rhenium appears to be along grain boundaries and crystallographic planes.

  14. Tantalum alloys resist creep deformation at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Buckman, R. W., Jr.

    1966-01-01

    Dispersion-strengthened tantalum-base alloys possess high strength and good resistance to creep deformation at elevated temperatures in high vacuum environments. They also have ease of fabrication, good weldability, and corrosion resistance to molten alkali metals.

  15. Determination of Plate Compressive Strengths at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Heimerl, George J; Roberts, William M

    1950-01-01

    The results of local-instability tests of h-section plate assemblies and compressive stress-strain tests of extruded 75s-t6 aluminum alloy, obtained to determine flat-plate compressive strength under stabilized elevated temperature conditions, are given for temperatures up to 600 degrees F. The results show that methods available for calculating the critical compressive stress at room temperature can also be used at elevated temperatures if the applicable compressive stress-strain curve for the material is given.

  16. Plastic responses to elevated temperature in low and high elevation populations of three grassland species.

    PubMed

    Frei, Esther R; Ghazoul, Jaboury; Pluess, Andrea R

    2014-01-01

    Local persistence of plant species in the face of climate change is largely mediated by genetic adaptation and phenotypic plasticity. In species with a wide altitudinal range, population responses to global warming are likely to differ at contrasting elevations. In controlled climate chambers, we investigated the responses of low and high elevation populations (1200 and 1800 m a.s.l.) of three nutrient-poor grassland species, Trifolium montanum, Ranunculus bulbosus, and Briza media, to ambient and elevated temperature. We measured growth-related, reproductive and phenological traits, evaluated differences in trait plasticity and examined whether trait values or plasticities were positively related to approximate fitness and thus under selection. Elevated temperature induced plastic responses in several growth-related traits of all three species. Although flowering phenology was advanced in T. montanum and R. bulbosus, number of flowers and reproductive allocation were not increased under elevated temperature. Plasticity differed between low and high elevation populations only in leaf traits of T. montanum and B. media. Some growth-related and phenological traits were under selection. Moreover, plasticities were not correlated with approximate fitness indicating selectively neutral plastic responses to elevated temperature. The observed plasticity in growth-related and phenological traits, albeit variable among species, suggests that plasticity is an important mechanism in mediating plant responses to elevated temperature. However, the capacity of species to respond to climate change through phenotypic plasticity is limited suggesting that the species additionally need evolutionary adaptation to adjust to climate change. The observed selection on several growth-related and phenological traits indicates that the study species have the potential for future evolution in the context of a warming climate.

  17. Gas Generation Testing of Neptunium Oxide at Elevated Temperature

    SciTech Connect

    Duffey, JM

    2004-01-30

    Elevated temperature gas generation tests have been conducted using neptunium dioxide produced on a laboratory scale using the HB-Line Phase II flowsheet. These tests were performed to determine what effect elevated temperatures would have on the neptunium dioxide in comparison to neptunium dioxide tested at ambient temperature. The headspace gas compositions following storage at elevated temperatures associated with normal conditions of transport (NCT) have been measured. These test results show an increase in hydrogen generation rate at elevated temperature and significant removal of oxygen from the headspace gas. The elevated temperature gas generation tests described in this report involved heating small test vessels containing neptunium dioxide and measuring the headspace gas pressure and composition at the end of the test period. Four samples were used in these tests to evaluate the impact of process variables on the gas generation rate. Two samples were calcined to 600 degrees Celsius and two were calcined to 650 degrees Celsius. Each test vessel contained approximately 9.5 g of neptunium dioxide. Following exposure to 75 per cent relative humidity (RH) for five days, these samples were loaded in air and then heated to between 105 and 115 degrees Celsius for about one month. At the conclusion of the test period, the headspace gas of each container was analyzed using a micro-gas chromatograph installed in the glovebox where the experiments were conducted. The pressure, volume, and composition data for the headspace gas samples were used to calculate average H2 generation rates.

  18. Performance of MOV Stem Lubricants at Elevated Temperatures

    SciTech Connect

    DeWall, Kevin George; Nitzel, Michael Everett; Watkins, John Clifford

    2001-07-01

    This paper documents the results of recent tests sponsored by the U. S. Nuclear Regulatory Commission (NRC) and performed by the Idaho National Engineering and Environmental Laboratory (INEEL). These tests address the effectiveness of the lubricant used on the threaded portion of the valve stem, where the stem nut turns on the stem. Recent testing indicates that an elevated temperature environment can lead to significant increases in the friction coefficient at the stem/stem-nut interface. Most valve actuator qualification tests are performed at room temperature. Similarly, in-service tests are run at ambient plant temperatures, usually 70 to 100°F. Since design conditions can lead to valve operating temperatures in the 200 to 300°F range, it is important to know whether a temperature-induced increase in friction at the stem/stem-nut interface will prevent the required operation of critical valves. Lubricant aging is another phenomenon that might have deleterious effects on the thrust output of a valve actuator. Laboratory experience and field experience both indicate that after long periods in elevated temperature environments, the lubricants may lose their lubrication qualities. The scope of the current test program includes testing of five different lubricants on four different valve stems. Pending completion of the testing, results of the tests conducted using two of the four stems are discussed. The test series included collection of baseline data at room temperature, single step temperature tests where the temperature of the test setup was elevated directly to 250°F, and step testing where the temperature was elevated in steps to 130, 190, and 250°F, then returned to 70°F. All greases tested showed evidence of physical change after elevated temperature tests. Except for one particular lubricant, all of the greases tested showed increased coefficients of friction at elevated temperatures. Numerous other preliminary conclusions are presented

  19. The elevated temperature behavior of particle reinforced Al matrix composites

    SciTech Connect

    Lloyd, D.J.

    1994-12-31

    The elevated temperature modulus, strength and creep of SiC particle reinforced composites produced by the DURALCAN{trademark} are discussed. It is shown that the reinforcing particles provide an increased modulus over the complete temperature range studied, and the temperature dependence of the composite modulus is controlled by the temperature dependence of the matrix modulus. The composite strength decreases with increasing temperature, reflecting softening of the matrix due to over aging, and as a result, is dependent on the thermal stability of the matrix. The particles provide increased creep resistance, and there are differences between the creep of melt processed composites and those produced by powder metallurgy.

  20. Help-seeking behavior during elevated temperature in Chinese population.

    PubMed

    Chan, Emily Ying Yang; Goggins, William B; Kim, Jacqueline Jakyoung; Griffiths, Sian; Ma, Timothy K W

    2011-08-01

    The negative impact of extreme temperatures on health is well-established. Individual help-seeking behavior, however, may mitigate the extent of morbidity and mortality during elevated temperatures. This study examines individual help-seeking behavior during periods of elevated temperatures among a Chinese population. Help-seeking patterns and factors that influence behavior will be identified so that vulnerable subgroups may be targeted for health protection during heat crises. A retrospective time-series Poisson generalized additive model analysis, using meteorological data of Hong Kong Observatory and routine emergency help call data from The Hong Kong Senior Citizen Home Safety Association during warm seasons (June-September) 1998-2007, was conducted. A "U"-shaped association was found between daily emergency calls and daily temperature. About 49% of calls were for explicit health-related reasons including dizziness, shortness of breath, and general pain. The associate with maximum temperature was statistically significant (p = 0.034) with the threshold temperature at which the frequency of health-related calls started to increase being around 30-32°C. Mean daily relative humidity (RH) also had a significant U-shaped association with daily emergency health-related calls with call frequency beginning to increase with RH greater than 70-74% (10-25% of the RH distribution). Call frequency among females appeared to be more sensitive to high temperatures, with a threshold between 28.5°C and 30.5°C while calls among males were more sensitive to cold temperatures (threshold 31.5-33.5°C). Results indicate differences in community help-seeking behavior at elevated temperatures. Potential programs or community outreach services might be developed to protect vulnerable subgroups from the adverse impact of elevated temperatures.

  1. Friction Tests in Magnesium Tube Hydroforming at Elevated Temperatures

    SciTech Connect

    Hwang, Yeong-Maw; Wang, Kuo-Hsing; Kuo, Tsung-Yu

    2011-05-04

    In metal forming, lubricants have a variety of functions. The top priority is usually reduction of friction in order to increase the formability of the materials and reduce tool wear. Because magnesium alloys have very poor formability at room temperature, it is essential to manufacture a part from Magnesium alloys at elevated temperatures. The aim of this paper is to present a friction test method to evaluate the performance of different kinds of lubricants and determine their coefficients of friction at elevated temperatures in tube hydroforming of magnesium alloys. A self-designed experimental apparatus is used to carry out the experiments of friction tests. The coefficient of friction between the tube and die at guiding zone is determined. The effects of the internal pressure, the axial feeding velocity and temperatures on the friction forces and coefficients of friction for different lubricants are discussed.

  2. Solution hardening and strain hardening at elevated temperatures

    SciTech Connect

    Kocks, U.F.

    1982-10-01

    Solutes can significantly increase the rate of strain hardening; as a consequence, the saturation stress, at which strain hardening tends to cease for a given temperature and strain rate, is increased more than the yield stress: this is the major effect of solutes on strength at elevated temperatures, especially in the regime where dynamic strain-aging occurs. It is shown that local solute mobility can affect both the rate of dynamic recovery and the dislocation/dislocation interaction strength. The latter effect leads to multiplicative solution strengthening. It is explained by a new model based on repeated dislocation unlocking, in a high-temperature limit, which also rationalizes the stress dependence of static and dynamic strain-aging, and may help explain the plateau of the yield stress at elevated temperatures. 15 figures.

  3. Modeling Saturn Ring Temperature Variations as Solar Elevation Decreases

    NASA Astrophysics Data System (ADS)

    Spilker, L.; Flandes, A.; Altobelli, N.; Leyrat, C.; Pilorz, S.; Ferrari, C.

    2008-12-01

    After more than four years in orbit around Saturn, the Cassini Composite Infrared Spectrometer (CIRS) has acquired a wide-ranging set of thermal measurements of Saturn's main rings (A, B, C and Cassini Division). Temperatures were retrieved for the lit and unlit rings over a variety of ring geometries that include solar phase angle, spacecraft elevation, solar elevation and local hour angle. To first order, the largest temperature changes on the lit face of the rings are driven by variations in phase angle while differences in temperature with changing spacecraft elevation and local time are a secondary effect. Decreasing ring temperature with decreasing solar elevation are observed for both the lit and unlit faces of the rings after phase angle and local time effects are taken into account. For the lit rings, decreases of 2- 4 K are observed in the C ring and larger decreases, 7-10 and 10 - 13 K, are observed in the A and B rings respectively. Our thermal data cover a range of solar elevations from -21 to -8 degrees (south side of the rings). We test two simple models and evaluate how well they fit the observed decreases in temperature. The first model assumes that the particles are so widely spaced that they do not cast shadows on one another while the second model assumes that the particles are so close together they essentially form a slab. The optically thinnest and optically thickest regions of the rings show the best fits to these two end member models. We also extrapolate to the expected minimum ring temperatures at equinox. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA and at CEA Saclay supported by the "Programme National de Planetologie". Copyright 2008 California Institute of Technology. Government sponsorship acknowledged.

  4. Effects of microwaves on cell survival at elevated temperatures

    SciTech Connect

    Robinson, J.E.; Harrison, G.H.; McCulloch, D.; McCready, W.A.

    1981-12-01

    Since microwaves are used in human cancer therapy, information on specific biological effects of microwaves at elevated temperatures is important. To help supply this information, we exposed mammalian cells (CHO) and bacteria (Serratia marcescens) to hyperthermal temperatures (43, 44, and 45/sup o/C for CHO and 48, 49, and 50/sup o/C for the bacteria) with and without microwave irradiation. Temperature control was maintained by a refrigeration-reheat system and high-velocity water recirculation. The 2450-MHz microwave source was operated in a pulsed mode with power density up to 500 mW/cm/sup 2/. As expected, the survival curve slopes for both cell types increased rapidly with temperature, doubling for each degree Celsius. Microwave irradiation produced no significant change in extrapolation number for either cell type. However, survival curves of CHO cells which received microwaves were steeper by a factor of 1.25 than their sham-irradiated controls. No significant effect on slope was seen with the bacteria. Liquid crystal thermometry revealed a microwave-induced temperature elevation of 0.3/sup o/C in the glass microcapillary exposure tubes. This temperature elevation closely corresponded to the observed difference in survival curve slopes for the CHO cells and suggests a simple thermal origin for that difference.

  5. Upsettability and forming limit of magnesium alloys at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Park, Heung Sik; Kim, Si Pom; Park, Young Chul; Park, Joon Hong; Baek, Seung Gul

    2012-11-01

    In recent years, Magnesium (Mg) and its alloys have become a center of special interest in the automotive industry. Due to their high specific mechanical properties, they offer a significant weight saving potential in modern vehicle constructions. Most Mg alloys show very good machinability and processability, and even the most complicated die casting parts can be easily produced. In this study, Microstructure, Vickers hardness and tensile tests were examined and performed for each specimen to verify effects of forming conditions. Also to verify upsettability and forming limit of the specimen at room temperature and elevated temperature, upsetting experiments were performed. For comparison, experiments at elevated temperature were performed for various Mg alloy, such as AZ31, AZ91, and AM50. The experimental results were compared with those of CAE analysis to propose forming limit of Magnesium alloys.

  6. Effects of elevated CO2 and temperature on seed quality.

    PubMed

    Hampton, J G; Boelt, B; Rolston, M P; Chastain, T G

    2013-04-01

    Successful crop production depends initially on the availability of high-quality seed. By 2050 global climate change will have influenced crop yields, but will these changes affect seed quality? The present review examines the effects of elevated carbon dioxide (CO2) and temperature during seed production on three seed quality components: seed mass, germination and seed vigour. In response to elevated CO2, seed mass has been reported to both increase and decrease in C3 plants, but not change in C4 plants. Increases are greater in legumes than non-legumes, and there is considerable variation among species. Seed mass increases may result in a decrease of seed nitrogen (N) concentration in non-legumes. Increasing temperature may decrease seed mass because of an accelerated growth rate and reduced seed filling duration, but lower seed mass does not necessarily reduce seed germination or vigour. Like seed mass, reported seed germination responses to elevated CO2 have been variable. The reported changes in seed C/N ratio can decrease seed protein content which may eventually lead to reduced viability. Conversely, increased ethylene production may stimulate germination in some species. High-temperature stress before developing seeds reach physiological maturity (PM) can reduce germination by inhibiting the ability of the plant to supply the assimilates necessary to synthesize the storage compounds required for germination. Nothing is known concerning the effects of elevated CO2 on seed vigour. However, seed vigour can be reduced by high-temperature stress both before and after PM. High temperatures induce or increase the physiological deterioration of seeds. Limited evidence suggests that only short periods of high-temperature stress at critical seed development stages are required to reduce seed vigour, but further research is required. The predicted environmental changes will lead to losses of seed quality, particularly for seed vigour and possibly germination. The seed

  7. Effects of elevated CO2 and temperature on seed quality.

    PubMed

    Hampton, J G; Boelt, B; Rolston, M P; Chastain, T G

    2013-04-01

    Successful crop production depends initially on the availability of high-quality seed. By 2050 global climate change will have influenced crop yields, but will these changes affect seed quality? The present review examines the effects of elevated carbon dioxide (CO2) and temperature during seed production on three seed quality components: seed mass, germination and seed vigour. In response to elevated CO2, seed mass has been reported to both increase and decrease in C3 plants, but not change in C4 plants. Increases are greater in legumes than non-legumes, and there is considerable variation among species. Seed mass increases may result in a decrease of seed nitrogen (N) concentration in non-legumes. Increasing temperature may decrease seed mass because of an accelerated growth rate and reduced seed filling duration, but lower seed mass does not necessarily reduce seed germination or vigour. Like seed mass, reported seed germination responses to elevated CO2 have been variable. The reported changes in seed C/N ratio can decrease seed protein content which may eventually lead to reduced viability. Conversely, increased ethylene production may stimulate germination in some species. High-temperature stress before developing seeds reach physiological maturity (PM) can reduce germination by inhibiting the ability of the plant to supply the assimilates necessary to synthesize the storage compounds required for germination. Nothing is known concerning the effects of elevated CO2 on seed vigour. However, seed vigour can be reduced by high-temperature stress both before and after PM. High temperatures induce or increase the physiological deterioration of seeds. Limited evidence suggests that only short periods of high-temperature stress at critical seed development stages are required to reduce seed vigour, but further research is required. The predicted environmental changes will lead to losses of seed quality, particularly for seed vigour and possibly germination. The seed

  8. Elevated temperature mechanical properties of line pipe steels

    NASA Astrophysics Data System (ADS)

    Jacobs, Taylor Roth

    The effects of test temperature on the tensile properties of four line pipe steels were evaluated. The four materials include a ferrite-pearlite line pipe steel with a yield strength specification of 359 MPa (52 ksi) and three 485 MPa (70 ksi) yield strength acicular ferrite line pipe steels. Deformation behavior, ductility, strength, strain hardening rate, strain rate sensitivity, and fracture behavior were characterized at room temperature and in the temperature range of 200--350 °C, the potential operating range for steels used in oil production by the steam assisted gravity drainage process. Elevated temperature tensile testing was conducted on commercially produced as-received plates at engineering strain rates of 1.67 x 10 -4, 8.33 x 10-4, and 1.67 x 10-3 s-1. The acicular ferrite (X70) line pipe steels were also tested at elevated temperatures after aging at 200, 275, and 350 °C for 100 h under a tensile load of 419 MPa. The presence of serrated yielding depended on temperature and strain rate, and the upper bound of the temperature range where serrated yielding was observed was independent of microstructure between the ferrite-pearlite (X52) steel and the X70 steels. Serrated yielding was observed at intermediate temperatures and continuous plastic deformation was observed at room temperature and high temperatures. All steels exhibited a minimum in ductility as a function of temperature at testing conditions where serrated yielding was observed. At the higher temperatures (>275 °C) the X52 steel exhibited an increase in ductility with an increase in temperature and the X70 steels exhibited a maximum in ductility as a function of temperature. All steels exhibited a maximum in flow strength and average strain hardening rate as a function of temperature. The X52 steel exhibited maxima in flow strength and average strain hardening rate at lower temperatures than observed for the X70 steels. For all steels, the temperature where the maximum in both flow

  9. Modelling of aluminium sheet forming at elevated temperatures

    NASA Astrophysics Data System (ADS)

    van den Boogaard, A. H.; Huétink, J.

    2004-06-01

    The formability of Al-Mg sheet can be improved considerably, by increasing the temperature. By heating the sheet in areas with large shear strains, but cooling it on places where the risk of necking is high, the limiting drawing ratio can be increased to values above 2.5. At elevated temperatures, the mechanical response of the material becomes strain rate dependent. To accurately simulate warm forming of aluminium sheet, a material model is required that incorporates the temperature and strain-rate dependency. In this paper simulations are presented of the deep drawing of a cylindrical cup, using shell elements. It is demonstrated that the familiar quadratic Hill yield function is not capable of describing the plastic deformation of aluminium. Hardening can be described successfully with a physically based material model for temperatures up to 200 °C. At higher temperatures and very low strain rates, the flow curve deviates significantly from the model.

  10. Thermal Behavior of Cylindrical Buckling Restrained Braces at Elevated Temperatures

    PubMed Central

    Talebi, Elnaz; Tahir, Mahmood Md.; Yasreen, Airil

    2014-01-01

    The primary focus of this investigation was to analyze sequentially coupled nonlinear thermal stress, using a three-dimensional model. It was meant to shed light on the behavior of Buckling Restraint Brace (BRB) elements with circular cross section, at elevated temperature. Such bracing systems were comprised of a cylindrical steel core encased in a strong concrete-filled steel hollow casing. A debonding agent was rubbed on the core's surface to avoid shear stress transition to the restraining system. The numerical model was verified by the analytical solutions developed by the other researchers. Performance of BRB system under seismic loading at ambient temperature has been well documented. However, its performance in case of fire has yet to be explored. This study showed that the failure of brace may be attributed to material strength reduction and high compressive forces, both due to temperature rise. Furthermore, limiting temperatures in the linear behavior of steel casing and concrete in BRB element for both numerical and analytical simulations were about 196°C and 225°C, respectively. Finally it is concluded that the performance of BRB at elevated temperatures was the same as that seen at room temperature; that is, the steel core yields prior to the restraining system. PMID:24526915

  11. Corrosion resistant coatings suitable for elevated temperature application

    DOEpatents

    Chan, Kwai S.; Cheruvu, Narayana Sastry; Liang, Wuwei

    2012-07-31

    The present invention relates to corrosion resistance coatings suitable for elevated temperature applications, which employ compositions of iron (Fe), chromium (Cr), nickel (Ni) and/or aluminum (Al). The compositions may be configured to regulate the diffusion of metals between a coating and a substrate, which may then influence coating performance, via the formation of an inter-diffusion barrier layer. The inter-diffusion barrier layer may comprise a face-centered cubic phase.

  12. Promoted Metals Combustion at Ambient and Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Engel, Carl D.; Herald, Stephen D.; Davis, S. Eddie

    2005-01-01

    Promoted combustion testing of materials, Test 17 of NASA STD-6001, has been used to assess metal propensity to burn in oxygen rich environments. An igniter is used at the bottom end of a rod to promote ignition, and if combustion is sustained, the burning progresses from the bottom to the top of the rod. The physical mechanisms are very similar to the upward flammability test, Test 1 of NASA STD-6001. The differences are in the normal environmental range of pressures, oxygen content, and sample geometry. Upward flammability testing of organic materials can exhibit a significant transitional region between no burning to complete quasi-state burning. In this transitional region, the burn process exhibits a probabilistic nature. This transitional region has been identified for metals using the promoted combustion testing method at ambient initial temperatures. The work given here is focused on examining the transitional region and the quasi-steady burning region both at conventional ambient testing conditions and at elevated temperatures. A new heated promoted combustion facility and equipment at Marshall Space Flight Center have just been completed to provide the basic data regarding the metals operating temperature limits in contact with oxygen rich atmospheres at high pressures. Initial data have been obtained for Stainless Steel 304L, Stainless Steel 321, Haynes 214, and Inconel 718 at elevated temperatures in 100-percent oxygen atmospheres. These data along with an extended data set at ambient initial temperature test conditions are examined. The pressure boundaries of acceptable, non-burning usage is found to be lowered at elevated temperature.

  13. Temperature variation of Saturn's Rings with Solar Elevation

    NASA Astrophysics Data System (ADS)

    Flandes, A.; Spilker, L.; Altobelli, N.; Leyrat, C.; Pilorz, S.; Edgington, S. G.

    2008-12-01

    In its four-year orbit around Saturn, the spacecraft Cassini has achieved a large number of infrared observations of Saturn's main rings through the CIRS experiment (Cassini Composite Infrared Spectrometer). We analyze the change of temperature in the main rings (A, B and C) as function of the solar elevation with respect to the plane of the rings at very low (<6°) and high (>120°) phase angles. Specific regions of every ring were chosen in every case to rule out other effects that may produce variations in temperature as well and to account only effects due to the solar latitudinal variations. For solar elevations that cover a range from -10.1° to -23.5°, in average, the temperature variations of the A, B and C rings are around ~{8 K}, near ~{12 K} and barely ~{3 K} respectively. Simple analytical functions which depend on the solar elevation angle and the heliocentric distance are used to fit the trends observed in the data assuming either a continuous slab or idependent particle models. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA and at CEA Saclay supported by the "Programme National de Planetologie". Copyright 2008 California Institute of Technology. Government sponsorship acknowledged.

  14. Elevated temperature strength of Cr-W alloys

    SciTech Connect

    Dogan, Omer N.; Schrems, Karol K.

    2004-09-01

    Cr alloys containing 0-30 weight percent W were investigated for their strength and ductility. These experimental alloys are intended for use in elevated temperature applications. Alloys were melted in a water-cooled, copper-hearth arc furnace. Microstructure of the alloys was studied using X-ray diffraction, scanning electron microscopy, and light microscopy. A hot hardness tester was used to study the strength of these materials up to 1200ºC. Compression tests at the same temperature range were also conducted.

  15. High strain rate behavior of pure metals at elevated temperature

    NASA Astrophysics Data System (ADS)

    Testa, Gabriel; Bonora, Nicola; Ruggiero, Andrew; Iannitti, Gianluca; Domenico, Gentile

    2013-06-01

    In many applications and technology processes, such as stamping, forging, hot working etc., metals and alloys are subjected to elevated temperature and high strain rate deformation process. Characterization tests, such as quasistatic and dynamic tension or compression test, and validation tests, such as Taylor impact and DTE - dynamic tensile extrusion -, provide the experimental base of data for constitutive model validation and material parameters identification. Testing material at high strain rate and temperature requires dedicated equipment. In this work, both tensile Hopkinson bar and light gas gun where modified in order to allow material testing under sample controlled temperature conditions. Dynamic tension tests and Taylor impact tests, at different temperatures, on high purity copper (99.98%), tungsten (99.95%) and 316L stainless steel were performed. The accuracy of several constitutive models (Johnson and Cook, Zerilli-Armstrong, etc.) in predicting the observed material response was verified by means of extensive finite element analysis (FEA).

  16. Complexation of Neptunium(V) with Fluoride at Elevated Temperatures

    SciTech Connect

    Rao, Linfeng; Tian, Guoxin; Xia, Yuanxian; Friese, Judah I.

    2008-06-16

    Complexation of neptunium(V) with fluoride at elevated temperatures was studied by spectrophotometry and microcalorimetry. Two successive complexes, NpO{sub 2}F(aq) and NpO{sub 2}F{sub 2}{sup -}, were identified by spectrophotometry in the temperature range of 10-70 C. Thermodynamic parameters, including the equilibrium constants and enthalpy of complexation between Np(V) and fluoride at 10-70 C were determined. Results show that the complexation of Np(V) with fluoride is endothermic and that the complexation is enhanced by the increase in temperature - a two-fold increase in the stability constants of NpO{sub 2}F(aq) and more than five-fold increase in the stability constants of NpO{sub 2}F{sub 2}{sup -} as the temperature is increased from 10 to 70 C.

  17. Tolerance of LSS Plant Component to Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Ushakova, S. A.; Tikhomirov, A. A.

    2002-06-01

    Stability of LSS based on biological regeneration of water, air and food subject to damaging factors is largely dependent on the behavior of the photosynthesizing component represented, mainly, by higher plants. The purpose of this study is to evaluate the tolerance of uneven-aged wheat and radish cenoses to temperature effects different in time and value. Estimation of thermal tolerance of plants demonstrated that exposure for 20 h to the temperature increasing to 45°C brought about irreversible damage both in photosynthetic processes (up to 80% of initial value) and the processes of growth and development. Kinetics of visible photosynthesis during exposure to elevated temperatures can be used to evaluate critical exposure time within the range of which the damage of metabolic processes is reversible. With varying light intensity and air temperature it is possible to find a time period admissible for the plants to stay under adverse conditions without considerable damage of metabolic processes.

  18. Cardiac responses to elevated seawater temperature in Atlantic salmon

    PubMed Central

    2014-01-01

    Background Atlantic salmon aquaculture operations in the Northern hemisphere experience large seasonal fluctuations in seawater temperature. With summer temperatures often peaking around 18-20°C there is growing concern about the effects on fish health and performance. Since the heart has a major role in the physiological plasticity and acclimation to different thermal conditions in fish, we wanted to investigate how three and eight weeks exposure of adult Atlantic salmon to 19°C, previously shown to significantly reduce growth performance, affected expression of relevant genes and proteins in cardiac tissues under experimental conditions. Results Transcriptional responses in cardiac tissues after three and eight weeks exposure to 19°C (compared to thermal preference, 14°C) were analyzed with cDNA microarrays and validated by expression analysis of selected genes and proteins using real-time qPCR and immunofluorescence microscopy. Up-regulation of heat shock proteins and cell signaling genes may indicate involvement of the unfolded protein response in long-term acclimation to elevated temperature. Increased immunofluorescence staining of inducible nitric oxide synthase in spongy and compact myocardium as well as increased staining of vascular endothelial growth factor in epicardium could reflect induced vascularization and vasodilation, possibly related to increased oxygen demand. Increased staining of collagen I in the compact myocardium of 19°C fish may be indicative of a remodeling of connective tissue with long-term warm acclimation. Finally, higher abundance of transcripts for genes involved in innate cellular immunity and lower abundance of transcripts for humoral immune components implied altered immune competence in response to elevated temperature. Conclusions Long-term exposure of Atlantic salmon to 19°C resulted in cardiac gene and protein expression changes indicating that the unfolded protein response, vascularization, remodeling of connective

  19. Elevated temperature deformation of thoria dispersed nickel-chromium

    NASA Technical Reports Server (NTRS)

    Kane, R. D.; Ebert, L. J.

    1974-01-01

    The deformation behavior of thoria nickel-chromium (TD-NiCr) was examined over the temperature range 593 C (1100 F) to 1260 C (2300 F) in tension and compression and at 1093 C (2000 F) in creep. Major emphasis was placed on: (1) the effects of the material and test related variables (grain size, temperature, stress and strain rate) on the deformation process; and (2) the evaluation of single crystal TD-NiCr material produced by a directional recrystallization process. Elevated temperature yield strength levels and creep activation enthalpies were found to increase with increasing grain size reaching maximum values for the single crystal TD-NiCr. Stress exponent of the steady state creep rate was also significantly higher for the single crystal TD-NiCr as compared to that determined for the polycrystalline materials. The elevated temperature deformation of TD-NiCr was analyzed in terms of two concurrent, parallel processes: diffusion controlled grain boundary sliding, and dislocation motion.

  20. Void nucleation at elevated temperatures under cascade-damage irradiation

    NASA Astrophysics Data System (ADS)

    Semenov, A. A.; Woo, C. H.

    2002-07-01

    The effects on void nucleation of fluctuations respectively due to the randomness of point-defect migratory jumps, the random generation of free point defects in discrete packages, and the fluctuating rate of vacancy emission from voids are considered. It was found that effects of the cascade-induced fluctuations are significant only at sufficiently high total sink strength. At lower sink strengths and elevated temperatures, the fluctuation in the rate of vacancy emission is the dominant factor. Application of the present theory to the void nucleation in annealed pure copper neutron-irradiated at elevated temperatures with doses of 10-4-10-2 NRT dpa showed reasonable agreement between theory and experiment. This application also predicts correctly the temporal development of large-scale spatial heterogeneous microstructure during the void nucleation stage. Comparison between calculated and experimental void nucleation rates in neutron-irradiated molybdenum at temperatures where vacancy emission from voids is negligible showed reasonable agreement as well. It was clearly demonstrated that the athermal shrinkage of relatively large voids experimentally observable in molybdenum at such temperatures may be easily explained in the framework of the present theory.

  1. Literature survey on oxidations and fatigue lives at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Oshida, Y.

    1984-01-01

    Nickel-base superalloys are the most complex and the most widely used for high temperature applications such as aircraft engine components. The desirable properties of nickel-base superalloys at high temperatures are tensile strength, thermomechanical fatigue resistance, low thermal expansion, as well as oxidation resistance. At elevated temperature, fatigue cracks are often initiated by grain boundary oxidation, and fatigue cracks often propagate along grain boundaries, where the oxidation rate is higher. Oxidation takes place at the interface between metal and gas. Properties of the metal substrate, the gaseous environment, as well as the oxides formed all interact to make the oxidation behavior of nickel-base superalloys extremely complicated. The important topics include general oxidation, selective oxidation, internal oxidation, grain boundary oxidation, multilayer oxide structure, accelerated oxidation under stress, stress-generation during oxidation, composition and substrate microstructural changes due to prolonged oxidation, fatigue crack initiation at oxidized grain boundaries and the oxidation accelerated fatigue crack propagation along grain boundaries.

  2. Compressive Strength of Stainless-Steel Sandwiches at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E.; Pride, Richard A.

    1959-01-01

    Experimental results are presented from crippling tests of stainless-steel sandwich specimens in the temperature range from 80 F to 1,200 F. The specimens included resistance-welded 17-7 PH stainless-steel sandwiches with single-corrugated cores, type 301 stainless-steel sandwiches with double-corrugated cores, and brazed 17-7 PH stainless-steel sandwiches with honeycomb cores. The experimental strengths are compared with predicted buckling and crippling strengths. The crippling strengths were predicted from the calculated maximum strength of the individual plate elements of the sandwiches and from a correlation procedure which gives the elevated-temperature crippling strength when the experimental room-temperature crippling strengths are known. Photographs of some of the tested specimens are included to show the modes of failure.

  3. Emerging disease of amphibians cured by elevated body temperature.

    PubMed

    Woodhams, Douglas C; Alford, Ross A; Marantelli, Gerry

    2003-06-20

    The emerging infectious disease chytridiomycosis is thought to have contributed to many of the recent alarming declines in amphibian populations. Mortalities associated with these declines have often occurred during cooler seasons and at high elevations, suggesting that environmental temperature may be an important factor in disease emergence. We found that thermal environment affects the progress of the disease, and that housing frogs Litoria chloris at an environmental temperature of 37 degrees C for less than 16 h can clear them of the chytrid pathogen Batrachochytrium dendrobatidis. Our experiment demonstrated that elevated body temperatures similar to those experienced in behavioral fever and during normal thermoregulation can clear frogs of chytrid infection; therefore, variation in thermoregulatory opportunities and behaviors are likely to contribute to the differences in disease incidence observed among host species, populations, and regions. Although further refinement of the technique is needed to encompass various host species, appropriately applied thermal manipulations of amphibians and their enclosures may prove to be a safe and effective way of eliminating the fungal pathogen from captive amphibian populations and: preventing accidental spread of the pathogen when animals are translocated or released from captivity. PMID:12887256

  4. Description of a system for interlocking elevated temperature mechanical tests

    SciTech Connect

    Schmale, D.T.; Poulter, G.A.

    1995-07-01

    Long term mechanical creep and fatigue testing at elevated temperatures requires reliable systems with safeguards to prevent destruction of equipment, loss of data and negative environmental impacts. Toward this goal, a computer controlled system has been developed and built for interlocking tests run on elevated temperature mechanical test facilities. Sensors for water flow, water pressure, water leakage, temperature, power and hydraulic status are monitored to control specimen heating equipment through solid state relays and water solenoid valves. The system is designed to work with the default interlocks present in the RF generators and mechanical tests systems. Digital hardware consists of two National Instruments 1/0 boards mounted in a Macintosh IIci computer. Software is written in National Instruments LabVIEW. Systems interlocked include two MTS closed loop servo controlled hydraulic test frames, one with an RF generator and one with both an RF generator and a quartz lamp furnace. Control for individual test systems is modularized making the addition of more systems simple. If any of the supporting utilities fail during tests, heating systems, chill water and hydraulics are powered down, minimizing specimen damage and eliminating equipment damage. The interlock control is powered by an uninterruptible power supply. Upon failure the cause is documented in an ASCII file.

  5. Description of a system for interlocking elevated temperature mechanical tests

    NASA Astrophysics Data System (ADS)

    Schmale, D. T.; Poulter, G. A.

    1995-07-01

    Long term mechanical creep and fatigue testing at elevated temperatures requires reliable systems with safeguards to prevent destruction of equipment, loss of data, and negative environmental impacts. Toward this goal, a computer controlled system has been developed and built for interlocking tests run on elevated temperature mechanical test facilities. Sensors for water flow, water pressure, water leakage, temperature, power, and hydraulic status are monitored to control specimen heating equipment through solid state relays and water solenoid valves. The system is designed to work with the default interlocks present in the RF generators and mechanical tests systems. Digital hardware consists of two National Instruments I/O boards mounted in a Macintosh IIci computer. Software is written in National Instruments LabVIEW. Systems interlocked include two MTS closed loop servo controlled hydraulic test frames, one with an RF generator and one with both an RF generator and a quartz lamp furnace. Control for individual test systems is modularized making the addition of more systems simple. If any of the supporting utilities fail during tests, heating systems, chill water, and hydraulics are powered down, minimizing specimen damage and eliminating equipment damage. The interlock control is powered by an uninterruptible power supply. Upon failure the cause is documented in an ASCII file.

  6. Elevated temperature crack growth in advanced powder metallurgy aluminum alloys

    NASA Technical Reports Server (NTRS)

    Porr, William C., Jr.; Gangloff, Richard P.

    1990-01-01

    Rapidly solidified Al-Fe-V-Si powder metallurgy alloy FVS0812 is among the most promising of the elevated temperature aluminum alloys developed in recent years. The ultra fine grain size and high volume fraction of thermally stable dispersoids enable the alloy to maintain tensile properties at elevated temperatures. In contrast, this alloy displays complex and potentially deleterious damage tolerant and time dependent fracture behavior that varies with temperature. J-Integral fracture mechanics were used to determine fracture toughness (K sub IC) and crack growth resistance (tearing modulus, T) of extruded FVS0812 as a function of temperature. The alloy exhibits high fracture properties at room temperature when tested in the LT orientation, due to extensive delamination of prior ribbon particle boundaries perpendicular to the crack front. Delamination results in a loss of through thickness constraint along the crack front, raising the critical stress intensity necessary for precrack initiation. The fracture toughness and tensile ductility of this alloy decrease with increasing temperature, with minima observed at 200 C. This behavior results from minima in the intrinsic toughness of the material, due to dynamic strain aging, and in the extent of prior particle boundary delaminations. At 200 C FVS0812 fails at K levels that are insufficient to cause through thickness delamination. As temperature increases beyond the minimum, strain aging is reduced and delamination returns. For the TL orientation, K (sub IC) decreased and T increased slightly with increasing temperature from 25 to 316 C. Fracture in the TL orientation is governed by prior particle boundary toughness; increased strain localization at these boundaries may result in lower toughness with increasing temperature. Preliminary results demonstrate a complex effect of loading rate on K (sub IC) and T at 175 C, and indicate that the combined effects of time dependent deformation, environment, and strain aging

  7. Effects of elevated temperature and elevated CO{sub 2} on foliar senescence of Acer seedlings

    SciTech Connect

    Hartz, J.S.; Norby, R.J. |

    1995-06-01

    An important response mechanism of trees to a warmer, CO{sub 2}-enriched atmosphere could be an alteration of phenological relationships. Autumn leaf senescence and abscission were tracked in sugar maple (Acer saccharum) and red maple (A. rubrum) seedlings growing in open-top chambers in ambient or elevated CO{sub 2} in combination with ambient or elevated temperature. Chlorophyll concentration was estimated weekly with a portable reflectance meter calibrated against conventional analysis of chlorophyll in leaf extracts. Abscission was quantified as the percentage of total plant leaf area that had abscised by certain dates. In both species chlorophyll loss from mid-October to mid-November was retarded in plants grown since May at a constant temperature offset 4{degrees}C higher than ambient. Likewise, leaf abscission began later and progressed more slowly in the warmer chambers. These plants still had 80% of their leaf area attached, and the leaves were still green, at the end of the growing season. Carbon dioxide concentration had little effect on leaf senescence or abscission. The results demonstrate the potential for climate warming to extend the growing season, which could enhance plant productivity. However, delayed senescence could also cause nutrient loss by disrupting retranslocation from leaves prior to the end of the growing season.

  8. Theoretical Determination of Lifetime of Compressed Plates at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Herrmann, George; Chu, Hu-Nan

    1959-01-01

    A method for the theoretical determination of the lifetime of com- pressed plates at elevated temperatures is presented. In this approach, linearized equations are used throughout with the assumption that the plate material is a standard linear solid. The critical time (lifetime) is determined by reducing the time-dependent behavior to the time- independent response of purely elastic buckling. Theoretically predicted lifetimes of 2024-T3 (formerly 24S-T3) aluminum-alloy plates at 450 F are compared with experimental values obtained in previous work.

  9. Hydrologic property alterations due to elevated temperatures at Yucca Mountain

    SciTech Connect

    Flint, A.L.; Nash, M.H.; Nash, M.S.

    1994-12-31

    Yucca Mountain is currently being evaluated as a potential site for a high level nuclear waste repository. The pre-emplacement hydrologic properties of the rock are important in determining the suitability of the site; however, post emplacement thermal loads and associated drying may permanently alter the character of the rock. A preliminary study was undertaken to determine the effects of elevated temperatures on hydrologic properties of the welded Topopah Spring member of the Paintbrush Tuff and a zeolitic, nonwelded tuff from the Tuffaceous Beds of Calico Hills. Rock outcrop samples were collected and dried in the laboratory at different temperatures (up to 400 degrees C). Hydrologic and physical properties -were tested before and after each of the drying cycles.

  10. Thermodynamics of Neptunium (V) Complexes with Phosphate at Elevated Temperatures

    SciTech Connect

    Xia, Y.; Friese, Judah I.; Bachelor, Paula P.; Moore, Dean A.; Rao, Linfeng

    2009-06-01

    Abstract – The complexation of Np(V) with phosphate at elevated temperatures was studied by a synergistic extraction method. A mixed buffer solution of TRIS and MES was used to maintain an appropriate pH value during the distribution experiments. The distribution ratio of Np(V) between the organic and aqueous phases was found to decrease as the concentrations of phosphate were increased. Stability constants of the 1:1 and 1:2 Np(V)-HPO42- complexes, dominant in the aqueous phase under the experimental conditions, were calculated from the effect of [HPO42-] on the distribution ratio. The thermodynamic parameters including enthalpy and entropy of complexation between Np(V) and HPO42- at 25o C – 55o C were calculated by the temperature coefficient method.

  11. Do fluctuating temperature environments elevate coral thermal tolerance?

    NASA Astrophysics Data System (ADS)

    Oliver, T. A.; Palumbi, S. R.

    2011-06-01

    In reef corals, much research has focused on the capacity of corals to acclimatize and/or adapt to different thermal environments, but the majority of work has focused on distinctions in mean temperature. Across small spatial scales, distinctions in daily temperature variation are common, but the role of such environmental variation in setting coral thermal tolerances has received little attention. Here, we take advantage of back-reef pools in American Samoa that differ in thermal variation to investigate the effects of thermally fluctuating environments on coral thermal tolerance. We experimentally heat-stressed Acropora hyacinthus from a thermally moderate lagoon pool (temp range 26.5-33.3°C) and from a more thermally variable pool that naturally experiences 2-3 h high temperature events during summer low tides (temp range 25.0-35°C). We compared mortality and photosystem II photochemical efficiency of colony fragments exposed to ambient temperatures (median: 28.0°C) or elevated temperatures (median: 31.5°C). In the heated treatment, moderate pool corals showed nearly 50% mortality whether they hosted heat-sensitive (49.2 ± 6.5% SE; C2) or heat-resistant (47.0 ± 11.2% SE; D) symbionts. However, variable pool corals, all of which hosted heat-resistant symbionts, survived well, showing low mortalities (16.6 ± 8.8% SE) statistically indistinguishable from controls held at ambient temperatures (5.1-8.3 ± 3.3-8.3% SE). Similarly, moderate pool corals hosting heat-sensitive algae showed rapid rates of decline in algal photosystem II photochemical efficiency in the elevated temperature treatment (slope = -0.04 day-1 ± 0.007 SE); moderate pool corals hosting heat-resistant algae showed intermediate levels of decline (slope = -0.039 day-1 ± 0.007 SE); and variable pool corals hosting heat-resistant algae showed the least decline (slope = -0.028 day-1 ± 0.004 SE). High gene flow among pools suggests that these differences probably reflect coral acclimatization

  12. Ethanol production at elevated temperatures using encapsulation of yeast.

    PubMed

    Ylitervo, Päivi; Franzén, Carl Johan; Taherzadeh, Mohammad J

    2011-10-20

    The ability of macroencapsulated Saccharomyces cerevisiae CBS 8066 to produce ethanol at elevated temperatures was investigated in consecutive batch and continuous cultures. Prior to cultivation yeast was confined inside alginate-chitosan capsules composed of an outer semi-permeable membrane and an inner liquid core. The encapsulated yeast could successfully ferment 30 g/L glucose and produce ethanol at a high yield in five consecutive batches of 12 h duration at 42°C, while freely suspended yeast was completely inactive already in the third batch. A high ethanol production was observed also through the first 48 h at 40°C during continuous cultivation at D=0.2 h(-1) when using encapsulated cells. The ethanol production slowly decreased in the following days at 40°C. The ethanol production was also measured in a continuous cultivation in which the temperature was periodically increased to 42-45°C and lowered to 37°C again in periods of 12h. Our investigation shows that a non-thermotolerant yeast strain improved its heat tolerance upon encapsulation, and could produce ethanol at temperatures as high as 45°C for a short time. The possibility of performing fermentations at higher temperatures would greatly improve the enzymatic hydrolysis in simultaneous saccharification and fermentation (SSF) processes and thereby make the bioethanol production process more economically feasible.

  13. Rotating disk electrode system for elevated pressures and temperatures

    SciTech Connect

    Fleige, M. J.; Wiberg, G. K. H.; Arenz, M.

    2015-06-15

    We describe the development and test of an elevated pressure and temperature rotating disk electrode (RDE) system that allows measurements under well-defined mass transport conditions. As demonstrated for the oxygen reduction reaction on polycrystalline platinum (Pt) in 0.5M H{sub 2}SO{sub 4}, the setup can easily be operated in a pressure range of 1–101 bar oxygen, and temperature of 140 °C. Under such conditions, diffusion limited current densities increase by almost two orders of magnitude as compared to conventional RDE setups allowing, for example, fuel cell catalyst studies under more realistic conditions. Levich plots demonstrate that the mass transport is indeed well-defined, i.e., at low electrode potentials, the measured current densities are fully diffusion controlled, while at higher potentials, a mixed kinetic-diffusion controlled regime is observed. Therefore, the setup opens up a new field for RDE investigations under temperature and current density conditions relevant for low and high temperature proton exchange membrane fuel cells.

  14. Binder/HMX interaction in PBX9501 at Elevated Temperatures

    SciTech Connect

    K., S C; M., T C

    2003-10-02

    Plastic bonded explosives (PBX) generally consist of 85 - 95 % by weight energetic material, such as HMX, and 5 - 15 % polymeric binder. Understanding of the structure and morphology at elevated temperatures and pressures is important for predicting of PBX behavior in accident scenarios. The crystallographic behavior of pure HMX has been measured as functions of temperature and grain size. The investigation is extended to the high temperature behavior of PBX 9501 (95% HMX, 2.5 % Estane, 2.5 % BDNPA/F). The results show that the HMX {beta}-phase to {delta}-phase transition in PBX 9501 is similar to that in neat HMX. However, in the presence of the PBX 9501 binder, {delta}-phase HMX readily converts back to {beta}-phase during cooling. Using the same temperature profile, the conversion rate decreases for each subsequent heating and cooling cycle. As observed in earlier experiments, no reverse conversion is observed without the polymer binder. It is proposed that the reversion of {delta}-phase to {beta}-phase is due to changes in the surface molecular potential caused by the influence of the polymer binder on the surface molecules of the {delta}-phase. Upon thermal cycling, the polymer binder segregates from the HMX particles and thus reduces the influence of the binder on the surface molecules. This segregation increases the resistance for the {delta}-phase to {beta}-phase transition, as demonstrated in an aged PBX 9501 material for which the reversion is not observed.

  15. Performance Evaluation of Fiber Bragg Gratings at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Juergens, Jeffrey; Adamovsky, Grigory; Floyd, Bertram

    2004-01-01

    The development of integrated fiber optic sensors for smart propulsion systems demands that the sensors be able to perform in extreme environments. In order to use fiber optic sensors effectively in an extreme environment one must have a thorough understanding of the sensor s limits and how it responds under various environmental conditions. The sensor evaluation currently involves examining the performance of fiber Bragg gratings at elevated temperatures. Fiber Bragg gratings (FBG) are periodic variations of the refractive index of an optical fiber. These periodic variations allow the FBG to act as an embedded optical filter passing the majority of light propagating through a fiber while reflecting back a narrow band of the incident light. The peak reflected wavelength of the FBG is known as the Bragg wavelength. Since the period and width of the refractive index variation in the fiber determines the wavelengths that are transmitted and reflected by the grating, any force acting on the fiber that alters the physical structure of the grating will change what wavelengths are transmitted and what wavelengths are reflected by the grating. Both thermal and mechanical forces acting on the grating will alter its physical characteristics allowing the FBG sensor to detect both temperature variations and physical stresses, strain, placed upon it. This ability to sense multiple physical forces makes the FBG a versatile sensor. This paper reports on test results of the performance of FBGs at elevated temperatures. The gratings looked at thus far have been either embedded in polymer matrix materials or freestanding with the primary focus of this paper being on the freestanding FBGs. Throughout the evaluation process, various parameters of the FBGs performance were monitored and recorded. These parameters include the peak Bragg wavelength, the power of the Bragg wavelength, and total power returned by the FBG. Several test samples were subjected to identical test conditions to

  16. Stability of CdTe solar cells at elevated temperatures: Bias, temperature, and Cu dependence

    NASA Astrophysics Data System (ADS)

    Hiltner, Jason F.; Sites, James R.

    1999-03-01

    A systematic study of the stability of CdTe solar cells fabricated by SCI and NREL has been made. Cells were stressed at elevated temperatures under various bias conditions, both with illumination (˜2 suns) and in the dark. An activation energy of approximately 1 eV is implied from cells stressed at various elevated temperatures. The stability of CdTe solar cells was found to be bias dependent and device-specific. Cells made with thick CdTe and no back-contact copper as well as by at least one SCI recipe were very stable. Extrapolation of effects assuming Arrhenius behavior yields estimated lifetime expectations for the cells stressed at elevated temperatures.

  17. Electromigration in Sintered Nanoscale Silver Films at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Calata, Jesus N.; Lu, Guo-Quan; Ngo, Khai; Nguyen, Luu

    2014-01-01

    Sintered nanoscale silver is a promising interconnection material for semiconductor devices because it provides improved joint properties compared with solder and wire bonds. It has higher electrical and thermal conductivity and is capable of higher operating temperature. Joints with die shear strength above 20 MPa can be formed at around 250°C even without applied pressure. Sintered silver joints were also found to be an order of magnitude more reliable than solder joints and wire bonds. In this work, the electromigration behavior of sintered nanosilver material under conditions of high applied current density and elevated temperature was investigated. Thin strips of sintered nanosilver formed on ceramic substrates were tested under current densities exceeding 150 kA/cm2 at temperatures of 150°C and above. Results based on the percentage change in sample resistance showed that the sintered silver lasted at least ten times longer than aluminum wire bonds. Examination of failed strips revealed that hairline cracks formed during sintering were the main cause of failure. Otherwise, defect-free samples exhibited a 10-fold increase in lifetime over wire bonds under similar conditions.

  18. Isobutanol production at elevated temperatures in thermophilic Geobacillus thermoglucosidasius.

    PubMed

    Lin, Paul P; Rabe, Kersten S; Takasumi, Jennifer L; Kadisch, Marvin; Arnold, Frances H; Liao, James C

    2014-07-01

    The potential advantages of biological production of chemicals or fuels from biomass at high temperatures include reduced enzyme loading for cellulose degradation, decreased chance of contamination, and lower product separation cost. In general, high temperature production of compounds that are not native to the thermophilic hosts is limited by enzyme stability and the lack of suitable expression systems. Further complications can arise when the pathway includes a volatile intermediate. Here we report the engineering of Geobacillus thermoglucosidasius to produce isobutanol at 50°C. We prospected various enzymes in the isobutanol synthesis pathway and characterized their thermostabilities. We also constructed an expression system based on the lactate dehydrogenase promoter from Geobacillus thermodenitrificans. With the best enzyme combination and the expression system, 3.3g/l of isobutanol was produced from glucose and 0.6g/l of isobutanol from cellobiose in G. thermoglucosidasius within 48h at 50°C. This is the first demonstration of isobutanol production in recombinant bacteria at an elevated temperature.

  19. Microfaunal evidences for elevated pliocene temperatures in the arctic ocean

    NASA Astrophysics Data System (ADS)

    Cronin, Thomas M.; Whatley, Robin; Wood, Adrian; Tsukagoshi, Akira; Ikeya, Noriyuki; Brouwers, E. M.; Briggs, W. M.

    1993-04-01

    The migration of thermophilic marine Ostracoda into the Arctic Ocean during the Pliocene indicates that winter and summer ocean temperatures around Arctic margins were ≥ 0 °C and > 3 °C, respectively, and that ice-free conditions existed for most or all of the Arctic. By at least 3.5-3.0 Ma, probably earlier, the opening of the Bering Strait allowed marine organisms to migrate through the Arctic Ocean, mostly from the Pacific Ocean. Migrant taxa such as Cythere, Hemicythere, and Neomonoceratina are known from Pliocene deposits of Alaska and Canada as well as Neogene deposits of the North Pacific and Atlantic oceans. On the basis of ecological and Zoogeographic information on ostracode species from more than 800 modern "core top" samples for the North Atlantic, North Pacific, and Arctic Oceans, we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 °C and 3 °C. This suggests ice-free summers, and probably, a perennially ice-free Arctic Ocean in some regions. Elevated water temperatures in the Arctic Ocean between 3.5 and 2.0 Ma is supported by evidence for late Pliocene increased meridional heat transport in the North Atlantic Ocean.

  20. Elevated Temperature Testing and Modeling of Advanced Toughened Ceramic Materials

    NASA Technical Reports Server (NTRS)

    Keith, Theo G.

    2005-01-01

    The purpose of this report is to provide a final report for the period of 12/1/03 through 11/30/04 for NASA Cooperative Agreement NCC3-776, entitled "Elevated Temperature Testing and Modeling of Advanced Toughened Ceramic Materials." During this final period, major efforts were focused on both the determination of mechanical properties of advanced ceramic materials and the development of mechanical test methodologies under several different programs of the NASA-Glenn. The important research activities made during this period are: 1. Mechanical properties evaluation of two gas-turbine grade silicon nitrides. 2) Mechanical testing for fuel-cell seal materials. 3) Mechanical properties evaluation of thermal barrier coatings and CFCCs and 4) Foreign object damage (FOD) testing.

  1. ELEVATED CO2 AND ELEVATED TEMPERATURE AFFECT CARBON AND NITROGEN CONCENTRATIONS BUT NOT ACCUMULATION IN PSEUDOTSUGA MENZIESII SEEDLINGS

    EPA Science Inventory

    To determine the impact of climate change on concentrations and accumulation of C and N in trees, we grew Pseudotsuga menziesii (Mirb.) Franco (Douglas-fir) seedlings treated with ambient or elevated (+180 mol mol-1) CO2, and with ambient or elevated (+3.5 C) temperature for f...

  2. Elevated Temperature, In Situ Micromechanical Characterization of a High Temperature Ternary Shape Memory Alloy

    NASA Astrophysics Data System (ADS)

    Wheeler, J. M.; Niederberger, C.; Raghavan, R.; Thompson, G.; Weaver, M.; Michler, J.

    2015-12-01

    The microthermomechanical behavior of a precipitation-hardenable Ni-48Ti-25Pd (at.%) shape memory alloy has been investigated as a function of temperature. Micropillars were fabricated within a large <145>-oriented grain and compressed in situ in the SEM at elevated temperatures corresponding to the martensite and austenite phase transformation temperatures. The precipitation-strengthened alloys exhibited stable pseudoelastic behavior with little or no residual strains when near the transformation temperatures. In the plastic regime, slip was observed to occur via pencil glide, circumventing the fine scale precipitates along multiple slip planes.

  3. Durability of polymeric composites after elevated temperature aging

    NASA Astrophysics Data System (ADS)

    Poole, Eric Luther

    The Compression After Impact (CAI) strength of polymeric composites after long term elevated temperature aging is studied. Aging temperatures range from 149sp°C to 204sp°C (300sp°F to 400sp°F). Two types of matrix material are studied, a thermoset bismaleimide (5260) and a thermoplastic polyimide (K3B). Glass transition temperature (Tsb{g}) and fracture toughness are measured after aging. Microscopy and Secondary Ion Mass Spectroscopy (SIMS) are used to evaluate the aged composites. Out-of-plane bending of the CAI specimens during compression is measured by shadow moire. Moire interferometry is used to determine in-plane displacement and strain fields around the impact damage. Results show that the CAI strength degrades with aging for both K3B and 5260. The 5260 matrix suffers from thermo-oxidative degradation at higher temperatures. Surface decomposition causes weight loss and reduces mechanical properties. The CAI strength of the K3B matrix composite also decreases after aging. Evidence of an oxidation reaction is found in the K3B polymer by SIMS, but no weight loss is associated with this chemical reaction. Measured changes in fracture toughness and Tsb{g} do not correlate with CAI strength degradation. Stiffness changes due to aging are insignificant in this study. The degradation region is measured by microscopy near the surface of composites after long aging times. The depth of the degradation zone is dependent on aging time. Degradation growth is modeled with finite elements using diffusion/reaction governing equations. Finite element results agree well with the experimental data.

  4. Elevated Temperature Compressive Properties of Zr-Modified Nial

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Noebe, R. D.

    1996-01-01

    Small Zr additions are known to substantially affect the deformation behavior and strength of polycrystalline NiAl, yet little information is currently available regarding the high-temperature properties of such alloys. Utilizing prealloyed powder technology, a series of four NiAl alloys have been produced containing from 0.05 to 0.7 at. pct Zr. The creep behavior of these alloys was characterized in compression between 1000 and 1400 K at strain rates ranging from approx. O.1 to 10(exp -9)/ sec. All the Zr-modified alloys were significantly stronger than binary NiAl under lower temperature and faster strain-rate conditions; however, the single-phase materials (Zr less than or equal to 0.1 at. pct) and binary NiAl had similar strengths at high temperatures and slow strain rates. The two-phase NiAl-Ni, AlZr alloys containing 0.3 and 0.7 at. pct Zr had nearly identical strengths. While the two-phase alloys were stronger than the single-phase materials at all test conditions, the degree of microstructural damage in the two-phase alloys due to internal oxidation during testing appeared to increase with Zr level. Balancing the poor oxidation behavior with the consistent strength advantage of the two-phase alloys, it is concluded that optimum elevated-temperature properties could be obtained in Heusler-strengthened NiAl containing between 0.1 and 0.3 at. pct Zr.

  5. Factors Controlling Elevated Temperature Strength Degradation of Silicon Carbide Composites

    NASA Technical Reports Server (NTRS)

    2005-01-01

    For 5 years, the cooperative agreement NCC3-763 has focused on the development and understanding of Sic-based composites. Most of the work was performed in the area of SiC fiber-reinforced composites for UEET and NGLT and in collaboration with Goodrich Corporation under a partially reimbursable Space Act Agreement. A smaller amount of work was performed on C fiber-reinforced SiC matrix composites for NGLT. Major accomplishments during this agreement included: Improvements to the interphase used in melt-infiltrated (MI) SiC/SiC composites which increases the life under stressed-oxidation at intermediate temperatures referred to as "outside-debonding". This concept is currently in the patent process and received a Space Act Award. Mechanistic-based models of intermediate temperature degradation for MI SiC/SiC Quantification and relatively robust relationships for matrix crack evolution under stress in SiC/SiC composites which serve as the basis for stress-strain and elevated temperature life models The furthering of acoustic emission as a useful tool in composite damage evolution and the extension of the technique to other composite systems Development of hybrid C-SiC fiber-reinforced SiC matrix composites Numerous presentations at conferences, industry partners, and government centers and publications in recognized proceedings and journals. Other recognition of the author's accomplishments by NASA with a TGIR award (2004), NASA's Medal for Public Service (2004), and The American Ceramic Society s Richard M. Fulrath Award (2005). The following will briefly describe the work of the past five years in the three areas of interest: SiC/SiC composite development, mechanistic understanding and modeling of SiC/SiC composites, and environmental durability of C/SiC composites. More detail can be found in the publications cited at the end of this report.

  6. 49 CFR 173.247 - Bulk packaging for certain elevated temperature materials.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials. When... constructed of carbon steel which is in elevated temperature material service is excepted from § 178.345-7(d... of the packaging material at any temperature within the design temperature range. Stress...

  7. 49 CFR 173.247 - Bulk packaging for certain elevated temperature materials.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials. When... constructed of carbon steel which is in elevated temperature material service is excepted from § 178.345-7(d... of the packaging material at any temperature within the design temperature range. Stress...

  8. Moisture Retention Curves of Topopah Spring Tuff at Elevated Temperatures

    SciTech Connect

    Lin, W.; Roberts, J.; Carlberg, E.; Ruddle, D.; Pletcher, R.

    2001-11-30

    Knowledge of unsaturated flow and transport in porous media is critical for understanding the movement of water and solute through the unsaturated zone. The suction potential of rock determines the imbibition of water and, therefore, the moisture retention in the matrix. That, in turn, affects the relative importance of matrix flow and fracture flow, and their interaction, because greater suction potential moves more water from fractures into the matrix and therefore retards fracture flow. The moisture content as a function of the suction potential is called a moisture retention curve or a characteristic curve. Moisture-retention data are important input for numerical models of water movement in unsaturated porous media. Also important are the effect of sample history on the moisture-retention curves and whether there is significant hysteresis between wetting and drying measurements. The Yucca Mountain Site Characterization Project (YMP) of the U.S. Department of Energy is studying the suitability of the tuffaceous rock at Yucca Mountain, Nevada, for a potential high-level nuclear waste repository. The potential repository horizon will be in the unsaturated zone of the Topopah Spring member (densely welded) of the Paintbrush Tuff unit at Yucca Mountain. This unit is highly fractured. Therefore, transport of water within the near field of the nuclear waste package in the repository is strongly influenced by the suction potential of the repository host rocks at elevated temperatures. In a high-level nuclear waste repository, the rock mass around the waste packages will become dry because of the thermal load of the waste but will then re-wet during the cool-down period as the thermal output of the waste packages declines. Much of this process will occur at temperatures above ambient temperature. The goal of our work is to determine the importance of temperature and the wetting-drying hysteresis on the measured moisture retention curves of the densely welded tuff. For

  9. Trihalomethane hydrolysis in drinking water at elevated temperatures.

    PubMed

    Zhang, Xiao-Lu; Yang, Hong-Wei; Wang, Xiao-Mao; Karanfil, Tanju; Xie, Yuefeng F

    2015-07-01

    Hydrolysis could contribute to the loss of trihalomethanes (THMs) in the drinking water at elevated temperatures. This study was aimed at investigating THM hydrolysis pertaining to the storage of hot boiled water in enclosed containers. The water pH value was in the range of 6.1-8.2 and the water temperature was varied from 65 to 95 °C. The effects of halide ions, natural organic matter, and drinking water matrix were investigated. Results showed that the hydrolysis rates declined in the order following CHBrCl2 > CHBr2Cl > CHBr3 > CHCl3. THM hydrolysis was primarily through the alkaline pathway, except for CHCl3 in water at relatively low pH value. The activation energies for the alkaline hydrolysis of CHCl3, CHBrCl2, CHBr2Cl and CHBr3 were 109, 113, 115 and 116 kJ/mol, respectively. No hydrolysis intermediates could accumulate in the water. The natural organic matter, and probably other constituents, in drinking water could substantially decrease THM hydrolysis rates by more than 50%. When a drinking water was at 90 °C or above, the first order rate constants for THM hydrolysis were in the magnitude of 10(-2)‒10(-1) 1/h. When the boiled real tap water was stored in an enclosed container, THMs continued increasing during the first few hours and then kept decreasing later on due to the competition between hydrolysis and further formation. The removal of THMs, especially brominated THMs, by hydrolysis would greatly reduce one's exposure to disinfection by-products by consuming the boiled water stored in enclosed containers.

  10. Mechanisms of time-dependent crack growth at elevated temperature

    SciTech Connect

    Saxena, A.; Stock, S.R.

    1990-04-15

    Objective of this 3-y study was to conduct creep and creep-fatigue crack growth experiments and to characterize the crack tip damage mechanisms in a model material (Cu-1wt%Sb), which is known to cavitate at grain boundaries under creep deformation. Results were: In presence of large scale cavitation damage and crack branching, time rate of creep crack growth da/dt does not correlate with C[sub t] or C[sup *]. When cavitation damage is constrained, da/dt is characterized by C[sub t]. Area fraction of grain boundary cavitated is the single damage parameter for the extent of cavitation damage ahead of crack tips. C[sub t] is used for the creep-fatigue crack growth behavior. In materials prone to rapid cavity nucleation, creep cracks grow faster initially and then reach a steady state whose growth rate is determined by C[sub t]. Percent creep life exhausted correlates with average cavity diameter and fraction of grain boundary area occupied by cavities. Synchrotron x-ray tomographic microscopy was used to image individual cavities in Cu-1wt% Sb. A methodology was developed for predicting the remaining life of elevated temperature power plant components; (C[sub t])[sub avg] was used to correlate creep-fatigue crack growth in Cr-Mo and Cr-Mo-V steel and weldments.

  11. Palladium based cermet composite for hydrogen separation at elevated temperature

    NASA Astrophysics Data System (ADS)

    Tsai, Yen-Chang; Lin, Chien-Cheng; Lin, Wei-Lin; Wang, Jeng-Han; Chen, San-Yuan; Lin, Pang; Wu, Pu-Wei

    2015-01-01

    A cermet composite consisting of palladium and BaCe0.4Zr0.4Gd0.1Dy0.1O3-x (BCZGD) is fabricated by mixing palladium and BCZGD powders in a ball mill, followed by pressing and sintering at 1450 °C for 24 h in air. The Pd-BCZGD cermet demonstrates impressive hydrogen permeation flux in a mixture of hydrogen and carbon dioxide at elevated temperature, in which the palladium plays the predominant role of facile transport in the hydrogen atoms whereas the BCZGD provides channels for proton conduction. Material characterization including scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermo-gravimetric analysis (TGA) are performed. XRD patterns indicate pure phases of fcc palladium and perovskite BCZGD. SEM images and element mapping suggest a homogeneous mixture of cermet without noticeable defect and phase segregation. TGA results confirm stability of the cermet against carbon dioxide without chemical decomposition. The hydrogen permeation flux is determined via a gas chromatography from 400 to 700 °C at various hydrogen concentration gradients. We record a hydrogen flux of 1.25 cm3 min-1 cm-2 in 50% hydrogen and 50% carbon dioxide at 700 °C, with a selectivity of H2/CO2 approaching infinity.

  12. RHYTHMIC RESPONSE OF SERRATIA MARCESCENS TO ELEVATED TEMPERATURE.

    PubMed

    DIMMICK, R L

    1965-03-01

    Dimmick, Robert L. (University of California, Berkeley). Rhythmic response of Serratia marcescens to elevated temperature. J. Bacteriol. 89:791-798. 1965.-Populations of Serratia marcescens of varied ages and pretreatments, which had been grown in a chemically defined medium, were subjected to thermal stress at 50 to 56 C. The numbers of survivors were plotted vs. time to form survivor curves, and the curves were assembled to form three-dimensional models. The manner in which survivors varied as a function of age and time of heating was variable and often rhythmic. Different three-dimensional patterns were found when different inoculum for the test culture was used. Apparently some "dead" cells again produced colonies after extended heating periods (recuperation); this tendency varied with the age of the culture. Diminutive colony forms, which produced normal colonies upon transfer, appeared and disappeared during heating; this tendency fluctuated with age. It is suggested that survivor curves represent a distribution of resistant forms within the population, and that this distribution varies in a manner best described in terms of servomechanistic response within each cell and within a given culture. Difficulties of attempting to relate changes in specific molecular species to subsequent whole-cell responses are discussed.

  13. The Effect of Elevated Temperature on Concrete Materials and Structures - a Literature Review.

    SciTech Connect

    Naus, Dan J

    2006-03-01

    The objective of this limited study was to provide an overview of the effects of elevated temperature on the behavior of concrete materials and structures. In meeting this objective the effects of elevated temperatures on the properties of ordinary Portland cement concrete constituent materials and concretes are summarized. The effects of elevated temperature on high-strength concrete materials are noted and their performance compared to normal strength concretes. A review of concrete materials for elevated-temperature service is presented. Nuclear power plant and general civil engineering design codes are described. Design considerations and analytical techniques for evaluating the response of reinforced concrete structures to elevated-temperature conditions are presented. Pertinent studies in which reinforced concrete structural elements were subjected to elevated temperatures are described.

  14. Estimation of surface temperature variations due to changes in sky and solar flux with elevation.

    USGS Publications Warehouse

    Hummer-Miller, S.

    1981-01-01

    Sky and solar radiance are of major importance in determining the ground temperature. Knowledge of their behavior is a fundamental part of surface temperature models. These 2 fluxes vary with elevation and this variation produces temperature changes. Therefore, when using thermal-property differences to discriminate geologic materials, these flux variations with elevation need to be considered. -from Author

  15. Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature.

    PubMed

    Jauregui, Iván; Aroca, Ricardo; Garnica, María; Zamarreño, Ángel M; García-Mina, José M; Serret, Maria D; Parry, Martin; Irigoyen, Juan J; Aranjuelo, Iker

    2015-11-01

    Although climate scenarios have predicted an increase in [CO(2)] and temperature conditions, to date few experiments have focused on the interaction of [CO(2)] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO(2). The main goal of this study was to analyze the effect of interacting [CO(2)] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO(2)] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO(2)] (400 vs 700 µmol mol(-1)) and temperature (ambient vs ambient + 4°C) in CO(2) gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO(2)] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO(2)] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO(2)] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity.

  16. Nitrogen assimilation and transpiration: key processes conditioning responsiveness of wheat to elevated [CO2] and temperature.

    PubMed

    Jauregui, Iván; Aroca, Ricardo; Garnica, María; Zamarreño, Ángel M; García-Mina, José M; Serret, Maria D; Parry, Martin; Irigoyen, Juan J; Aranjuelo, Iker

    2015-11-01

    Although climate scenarios have predicted an increase in [CO(2)] and temperature conditions, to date few experiments have focused on the interaction of [CO(2)] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO(2). The main goal of this study was to analyze the effect of interacting [CO(2)] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO(2)] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO(2)] (400 vs 700 µmol mol(-1)) and temperature (ambient vs ambient + 4°C) in CO(2) gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO(2)] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO(2)] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO(2)] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity. PMID:25958969

  17. Elevated exhaust temperature, zoned, electrically-heated particulate matter filter

    DOEpatents

    Gonze, Eugene V [Pinckney, MI; Bhatia, Garima [Bangalore, IN

    2012-04-17

    A system includes an electrical heater and a particulate matter (PM) filter that is arranged one of adjacent to and in contact with the electrical heater. A control module selectively increases an exhaust gas temperature of an engine to a first temperature and that initiates regeneration of the PM filter using the electrical heater while the exhaust gas temperature is above the first temperature. The first temperature is greater than a maximum exhaust gas temperature at the PM filter during non-regeneration operation and is less than an oxidation temperature of the PM.

  18. 49 CFR 173.247 - Bulk packaging for certain elevated temperature materials.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 101 and IM 102 portable tanks; UN portable tanks; marine portable tanks conforming to 46 CFR part 64... 49 Transportation 2 2013-10-01 2013-10-01 false Bulk packaging for certain elevated temperature... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials....

  19. 49 CFR 173.247 - Bulk packaging for certain elevated temperature materials.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 101 and IM 102 portable tanks; UN portable tanks; marine portable tanks conforming to 46 CFR part 64... 49 Transportation 2 2012-10-01 2012-10-01 false Bulk packaging for certain elevated temperature... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials....

  20. 49 CFR 173.247 - Bulk packaging for certain elevated temperature materials.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 101 and IM 102 portable tanks; UN portable tanks; marine portable tanks conforming to 46 CFR part 64... 49 Transportation 2 2014-10-01 2014-10-01 false Bulk packaging for certain elevated temperature... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials....

  1. Zeta potential in intact natural sandstones at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Vinogradov, Jan; Jackson, Matthew D.

    2015-08-01

    We report measurements of the zeta potential of natural sandstones saturated with NaCl electrolytes of varying ionic strengths at temperatures up to 150°C. The zeta potential is always negative but decreases in magnitude with increasing temperature at low ionic strength (0.01 M) and is independent of temperature at high ionic strength (0.5 M). The pH also decreases with increasing temperature at low ionic strength but remains constant at high ionic strength. The temperature dependence of the zeta potential can be explained by the temperature dependence of the pH. Our findings are consistent with published models of the zeta potential, so long as the temperature dependence of the pH at low ionic strength is accounted for and can explain the hitherto contradictory results reported in previous studies.

  2. Static tensile and tensile creep testing of four boron nitride coated ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Coguill, Scott L.; Adams, Donald F.; Zimmerman, Richard S.

    1989-01-01

    Six types of uncoated ceramic fibers were static tensile and tensile creep tested at various elevated temperatures. Three types of boron nitride coated fibers were also tested. Room temperature static tensile tests were initially performed on all fibers, at gage lengths of 1, 2, and 4 inches, to determine the magnitude of end effects from the gripping system used. Tests at one elevated temperature, at gage lengths of 8 and 10 inches, were also conducted, to determine end effects at elevated temperatures. Fiber cross sectional shapes and areas were determined using scanning electron microscopy. Creep testing was typically performed for 4 hours, in an air atmosphere.

  3. Interactive effect of elevated CO2 and temperature on coral physiology

    NASA Astrophysics Data System (ADS)

    Grottoli, A. G.; Cai, W.; Warner, M.; Melman, T.; Schoepf, V.; Baumann, J.; Matsui, Y.; Pettay, D. T.; Hoadley, K.; Xu, H.; Wang, Y.; Li, Q.; Hu, X.

    2011-12-01

    Increases in ocean acidification and temperature threaten coral reefs globally. However, the interactive effect of both lower pH and higher temperature on coral physiology and growth are poorly understood. Here, we present preliminary findings from a replicated controlled experiment where four species of corals (Acorpora millepora, Pocillopora damicornis, Montipora monasteriata, Turbinaria reniformis) were reared under the following six treatments for three weeks: 1) 400ppm CO2 and ambient temperature, 2) 400ppm CO2 and elevated temperature, 3) 650ppm CO2 and ambient temperature, 4) 650ppm CO2 and elevated temperature, 5) 800ppm CO2 and ambient temperature, 6) 800ppm CO2 and elevated temperature. Initial findings of photophysiological health (Fv/Fm), calcification rates (as measured by both buoyant weight and the total alkalinity methods), and energy reserves will be presented.

  4. The effect of elevated temperature on the toxicity of the laboratory cultured dinoflagellate Ostreopsis lenticularis (Dinophyceae).

    PubMed

    Ashton, Mayra; Tosteson, Thomas; Tosteson, Carmen

    2003-06-01

    Ostreopsis lenticularis Fukuyo 1981, is the major benthic dinoflagellate vector implicated in ciguatera fish poisoning in finfish on the southwest coast of Puerto Rico. Clonal laboratory cultures of O. lenticularis (clone 301) exposed to elevated temperatures (30-31 degrees C) for 33 and 54 days showed significant increases in the quantity of extractable toxin they produced as compared to their toxicities versus cells grown at temperatures of 25-26 degrees C. O lenticularis samples collected directly from the field following exposure to elevated temperatures for comparable periods of time also showed significant increases in extractable toxin. The increased toxicity of both field sampled and laboratory grown O. lenticularis exposed to elevated temperatures may result from the effects of elevated temperatures on their metabolism and/or the bacterial symbionts found associated with these microalgae. The number of bacteria associated with cultured O. lenticularis exposed to elevated temperatures was significantly reduced. Increased toxin recovery from O. lenticularis exposed to elevated temperatures may have resulted from the direct effect of temperature on toxin production and/or the reduction of Ostreopsis associated bacterial flora that consume toxin in the process of their growth. This reduction in the quantity of associated bacterial flora in temperature treated cultures may result in increased toxin recovery from O. lenticularis due to a reduction in the consumption of toxin by these symbiont bacteria. PMID:15264548

  5. Shell structures in aluminum nanocontacts at elevated temperatures

    PubMed Central

    2012-01-01

    Aluminum nanocontact conductance histograms are studied experimentally from room temperature up to near the bulk melting point. The dominant stable configurations for this metal show a very early crossover from shell structures at low wire diameters to ionic subshell structures at larger diameters. At these larger radii, the favorable structures are temperature-independent and consistent with those expected for ionic subshell (faceted) formations in face-centered cubic geometries. When approaching the bulk melting temperature, these local stability structures become less pronounced as shown by the vanishing conductance histogram peak structure. PMID:22325572

  6. Shell structures in aluminum nanocontacts at elevated temperatures.

    PubMed

    Costa-Krämer, José Luis; León, Natalia; Guerrero, Carlo; Díaz, Marisel

    2012-01-01

    Aluminum nanocontact conductance histograms are studied experimentally from room temperature up to near the bulk melting point. The dominant stable configurations for this metal show a very early crossover from shell structures at low wire diameters to ionic subshell structures at larger diameters. At these larger radii, the favorable structures are temperature-independent and consistent with those expected for ionic subshell (faceted) formations in face-centered cubic geometries. When approaching the bulk melting temperature, these local stability structures become less pronounced as shown by the vanishing conductance histogram peak structure.

  7. Undercoat prevents blistering of silver plating at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Kuster, C. A.

    1967-01-01

    Gold undercoat prevents blistering in the silver plating of Inconel 718 seals from steam at high temperatures. The undercoat is diffused into the surface of the parent metal by baking prior to silver plating.

  8. Investigating the Stability of eLiposomes at Elevated Temperatures.

    PubMed

    Husseini, Ghaleb A; Pitt, William G; Javadi, Marjan

    2015-08-01

    eLiposomes encapsulate a perfluorocarbon nanoemulsion droplet inside a liposome. Ultrasound is then used as a trigger mechanism to vaporize the perfluorocarbon, break the liposome, and release the desired drug to the tumor tissue. The purpose of this research is to show that eLiposomes synthesized using perfluoropentane are stable above the normal boiling point of the perfluoropentane and at body temperature and thus has potential for use in vivo. Experiments involving the release of fluorescent calcein molecules were performed on eLiposomes to measure the release of calcein at various temperatures in the absence of ultrasound. Results showed that eLiposomes are stable at body temperatures and that as the temperature increases above 40°C, calcein release from these novel nanocarriers increases.

  9. Deflagration Behavior of PBX 9501 at Elevated Temperature and Pressure

    SciTech Connect

    Maienschein, J L; Koerner, J G

    2008-04-15

    We report the deflagration behavior of PBX 9501 at pressures up to 300 MPa and temperatures of 150-180 C where the sample has been held at the test temperature for several hours before ignition. The purpose is to determine the effect on the deflagration behavior of material damage caused by prolonged exposure to high temperature. This conditioning is similar to that experienced by an explosive while it being heated to eventual explosion. The results are made more complicated by the presence of a significant thermal gradient along the sample during the temperature ramp and soak. Three major conclusions are: the presence of nitroplasticizer makes PBX 9501 more thermally sensitive than LX-04 with an inert Viton binder; the deflagration behavior of PBX 9501 is more extreme and more inconsistent than that of LX-04; and something in PBX 9501 causes thermal damage to 'heal' as the deflagration proceeds, resulting in a decelerating deflagration front as it travels along the sample.

  10. Elevated temperature mechanical behavior of new low CTE superalloys

    SciTech Connect

    Cowen, C.J.; Jablonski, P.D.

    2008-09-01

    This paper presents the high temperature mechanical properties of several experimental low coefficient of thermal expansion (CTE) alloys. The use of such alloys facilitate the extension of advanced ferritic stainless steels to higher use temperature in advanced power generation systems. We find that one of these alloys, J5 appears to be favorable for bridging ferritic alloys (operating up to ~600°C) to traditional nickel based superalloys (operating at 750°C).

  11. Fluorescence spectroscopy of anisole at elevated temperatures and pressures

    NASA Astrophysics Data System (ADS)

    Tran, K. H.; Morin, C.; Kühni, M.; Guibert, P.

    2014-06-01

    Laser-induced fluorescence of anisole as tracer of isooctane at an excitation wavelength of 266 nm was investigated for conditions relevant to rapid compression machine studies and for more general application of internal combustion engines regarding temperature, pressure, and ambient gas composition. An optically accessible high pressure and high temperature chamber was operated by using different ambient gases (Ar, N2, CO2, air, and gas mixtures). Fluorescence experiments were investigated at a large range of pressure and temperature (0.2-4 MPa and 473-823 K). Anisole fluorescence quantum yield decreases strongly with temperature for every considered ambient gas, due to efficient radiative mechanisms of intersystem crossing. Concerning the pressure effect, the fluorescence signal decreases with increasing pressure, because increasing the collisional rate leads to more important non-radiative collisional relaxation. The quenching effect is strongly efficient in oxygen, with a fluorescence evolution described by Stern-Volmer relation. The dependence of anisole fluorescence versus thermodynamic parameters suggests the use of this tracer for temperature imaging in specific conditions detailed in this paper. The calibration procedure for temperature measurements is established for the single-excitation wavelength and two-color detection technique.

  12. Ignitability of DMSO vapors at elevated temperature and reduced pressure

    SciTech Connect

    Bergman, W; Ural, E A; Weisgerber, W

    1999-03-08

    Ignitability of DMSO vapors have been evaluated at 664 mm Hg pressure. The minimum temperature at which the DMSO vapors that are in equilibrium with liquid DMSO has been determined using two types of strong ignition sources. This temperature is 172 F for chemical igniters, and 178 F for spark ignition. Numerous tests have been conducted using controlled intensity sparks to define the shape of the minimum ignition energy curve as a function of temperature. The ignition energies spanned four orders of magnitude (approximately from 20,000 to 2 mJ) while the DMSO vapor mixture temperature varied from 185 to 207 F. The Sandia Generator was used to simulate worst case electrostatic sparks that can be produced by the human body. Although it was not designed for air discharges, this device had been used by LLNL for 1 mm spark gap and the resultant spark energy had been measured to fall within the range from 3.2 to 8.8 mJ. CRC tests using this device showed that the minimum ignition temperature strongly depends on the spark gap. The minimum ignition temperature was 207 F at 1 mm spark gap, 203 F at 3 mm spark gap, and 197 F at 6 mm spark gap. This strong dependence on the spark gap is believed to be partly due to the changes in the spark energy as the spark gap changes.

  13. Caustic consumption by a sandstone at elevated temperatures

    SciTech Connect

    Dehghani, K.; Handy, L.L.

    1984-04-01

    The effect of temperature on caustic loss due to its reaction with a representative sandstone was investigated in a series of laboratory experiments. Consumption was measured for sodium hydroxide concentrations from 0.01 to 0.1 N at temperatures from 80/sup 0/ to 180/sup 0/C in fired and unfired Berea sandstone. Three types of experiment were performed. One of these was a static, batch experiment with disaggregated sandstone for different contact times. The others were flow experiments in consolidated cores at various flow rates. In one case caustic was injected and effluent concentration were measured, and, in the other case, the produced fluids were recycled through the core. The results show that caustic concentration is caused by a fast reversible Langmuir-type ion exchange and an irreversible reaction of dissolution of silica. An increase in temperature results in a higher amount of ion exchange for the same initial concentration and a higher rate of dissolution. The heat of the ion exchange reaction is constant in the range of temperature studied and as a result the equilibrium constant of ion exchange can be found for other temperatures. Dissolution for the lowest caustic initial concentration (0.01 N) can be represented by first order reaction but not for the higher injection concentration. Batch experimental results show that equilibrium is established in the caustic-silica reaction with stabilization of pH.

  14. Elevated temperature stress strain behavior of beryllium powder product

    SciTech Connect

    Abeln, S.P.; Field, R.; Mataya, M.C.

    1995-09-01

    Several grades of beryllium powder product were tested under isothermal conditions in compression over a temperature range of room temperature to 1000 C and a strain rate range from 0.001 s{sup {minus}1} to 1 s{sup {minus}1}. Samples were compressed to a total strain of 1 (64% reduction in height). It is shown that all the grades are strain rate sensitive and that strain rate sensitivity increases with temperature. Yield points were exhibited by some grades up to a temperature of 500 C, and appeared to be primarily dependent on prior thermal history which determined the availability of mobile dislocations. Serrated flow in the form of stress drops was seen in all the materials tested and was most pronounced at 500 C. The appearance and magnitude of the stress drops were dependent on accumulated strain, strain rate, sample orientation, and composition. The flow stress and shape of the flow curves differed significantly from grade to grade due to variations in alloy content, the size and distribution of BeO particles, aging precipitates, and grain size. The ductile-brittle transition temperature (DBTT) was determined for each grade of material and shown to be dependent on composition and thermal treatment. Structure/property relationships are discussed using processing history, microscopy (light and transmission), and property data.

  15. Impact Response of Single Crystal Potassium Chloride at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Golkov, R.; Kleiman, D.; Zaretsky, E.

    2004-07-01

    Two types of planar impact experiments were performed with [100]-oriented single crystals of potassium chloride (KCl) having initial temperatures ranged from 293 to 523 K. In the experiments of the first type the maximum impact strength did not exceed the pressure Ptr of B1-B2 transformation in KCl. In these experiments the aluminum buffers were placed between the impactor and the sample and the velocity of aluminum-KCl interface was measured by VISAR. The impact strength in the experiments of the second type (with copper buffers) was higher than Ptr and the VISAR was used for monitoring the free surface velocity of the KCl samples. Temperature dependencies of the longitudinal and the bulk sound velocities obtained in the experiments of the first type were used for the treatment of the results of the second-type experiments. The results show clearly the deceleration of the B1-B2 transformation kinetics and the increase of the KCl yield strength with temperature. Similar temperature-induced strengthening was observed recently in aluminum single crystals [G.I. Kanelet et al, J. Appl. Phys. 90, (2001) 136]. The value of the transformation entropy determined from the temperature dependence of Ptr is found to be close to zero.

  16. Reduction of permeability in granite at elevated temperatures.

    PubMed

    Moore, D E; Lockner, D A; Byerlee, J D

    1994-09-01

    The addition of hydrothermal fluids to heated, intact granite leads to permeability reductions in the temperature range of 300 degrees to 500 degrees C, with the rate of change generally increasing with increasing temperature. The addition of gouge enhances the rate of permeability reduction because of the greater reactivity of the fine material. Flow rate is initially high in a throughgoing fracture but eventually drops to the level of intact granite. These results support the fault-valve model for the development of mesothermal ore deposits, in which seals are formed at the base of the seismogenic zone of high-angle thrust faults. The lower temperature results yield varying estimates of mineral-sealing rates at shallower depths in fault zones, although they generally support the hypothesis that such seals develop in less time than the recurrence interval for moderate to large earthquakes on the San Andreas fault.

  17. Reduction of permeability in granite at elevated temperatures

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, D.A.; Byerlee, J.D.

    1994-01-01

    The addition of hydrothermal fluids to heated, intact granite leads to permeability reductions in the temperature range of 300?? to 500??C, with the rate of change generally increasing with increasing temperature. The addition of gouge enhances the rate of permeability reduction because of the greater reactivity of the fine material. Flow rate is initially high in a throughgoing fracture but eventually drops to the level of intact granite. These results support the fault-valve model for the development of mesothermal ore deposits, in which seals are formed at the base of the seismogenic zone of high-angle thrust faults. The lower temperature results yield varying estimates of mineral-sealing rates at shallower depths in fault zones, although they generally support the hypothesis that such seals develop in less time than the recurrence interval for moderate to large earthquakes on the San Andreas fault.

  18. Technology for Elevated Temperature Tests of Structural Panels

    NASA Technical Reports Server (NTRS)

    Thornton, E. A.

    1999-01-01

    A technique for full-field measurement of surface temperature and in-plane strain using a single grid imaging technique was demonstrated on a sample subjected to thermally-induced strain. The technique is based on digital imaging of a sample marked by an alternating line array of La2O2S:Eu(+3) thermographic phosphor and chromium illuminated by a UV lamp. Digital images of this array in unstrained and strained states were processed using a modified spin filter. Normal strain distribution was determined by combining unstrained and strained grid images using a single grid digital moire technique. Temperature distribution was determined by ratioing images of phosphor intensity at two wavelengths. Combined strain and temperature measurements demonstrated on the thermally heated sample were DELTA-epsilon = +/- 250 microepsilon and DELTA-T = +/- 5 K respectively with a spatial resolution of 0.8 mm.

  19. Behavior of reinforcement SCC beams under elevated temperatures

    NASA Astrophysics Data System (ADS)

    Fathi, Hamoon; Farhang, Kianoosh

    2015-09-01

    This experimental study focuses on the behavior of heated reinforced concrete beams. Four types of concrete mixtures were used for the tested self-compacting concrete beams. A total of 72 reinforced concrete beams and 72 standard cylindrical specimens were tested. The compressive strength under uniaxial loading at 23 °C ranged from 30 to 45 MPa. The specimens were exposed to different temperatures. The test parameters of interest were the compressive strength and the temperature of the specimens. The effect of changes in the parameters was examined so as to control the behavior of the tested concrete and that of the reinforced concrete beam. The results indicated that flexibility and compressive strength of the reinforced concrete beams decreased at higher temperatures. Furthermore, heating beyond 400 °C produced greater variations in the structural behavior of the materials in both the cylindrical samples and the reinforced concrete beams.

  20. Response of microalgae to elevated CO2 and temperature: impact of climate change on freshwater ecosystems.

    PubMed

    Li, Wei; Xu, Xiaoguang; Fujibayashi, Megumu; Niu, Qigui; Tanaka, Nobuyuki; Nishimura, Osamu

    2016-10-01

    To estimate the combined effects of elevated CO2 and temperature on microalgae, three typical and worldwide freshwater species, the green alga Scenedesmus acuminatus, the diatom Cyclotella meneghiniana, and the cyanobacterium Microcystis aeruginosa, as well as mixes of these three species were continuously cultured in controlled environment chambers with CO2 at 390 and 1000 ppm and temperatures of 20, 25, and 30 °C. CO2 and temperature significantly affected the production of microalgae. The cell productivity increased under elevated CO2 and temperature. Although the green alga dominated in the mixed culture within all CO2 and temperature conditions, rising temperature and CO2 intensified the competition of the cyanobacterium with other microalgae. CO2 affected the extracellular polymeric substances (EPS) characteristics of the green alga and the cyanobacterium. Elevated CO2 induced the generation of humic substances in the EPS fractions of the green alga, the cyanobacterium, and the mixed culture. The extracellular carbohydrates of the diatom and the extracellular proteins of the cyanobacterium increased with elevated CO2 and temperature, while the extracellular carbohydrates and proteins of the green alga and the mixes increased under elevated CO2 and temperature. There were synergistic effects of CO2 and temperature on the productivity and the EPS of microalgae. Climate change related CO2 and temperature increases will promote autochthonous organic carbon production in aquatic ecosystems and facilitate the proliferation of cyanobacteria, which potentially changes the carbon cycling and undermines the functioning of ecosystems. PMID:27421856

  1. Response of microalgae to elevated CO2 and temperature: impact of climate change on freshwater ecosystems.

    PubMed

    Li, Wei; Xu, Xiaoguang; Fujibayashi, Megumu; Niu, Qigui; Tanaka, Nobuyuki; Nishimura, Osamu

    2016-10-01

    To estimate the combined effects of elevated CO2 and temperature on microalgae, three typical and worldwide freshwater species, the green alga Scenedesmus acuminatus, the diatom Cyclotella meneghiniana, and the cyanobacterium Microcystis aeruginosa, as well as mixes of these three species were continuously cultured in controlled environment chambers with CO2 at 390 and 1000 ppm and temperatures of 20, 25, and 30 °C. CO2 and temperature significantly affected the production of microalgae. The cell productivity increased under elevated CO2 and temperature. Although the green alga dominated in the mixed culture within all CO2 and temperature conditions, rising temperature and CO2 intensified the competition of the cyanobacterium with other microalgae. CO2 affected the extracellular polymeric substances (EPS) characteristics of the green alga and the cyanobacterium. Elevated CO2 induced the generation of humic substances in the EPS fractions of the green alga, the cyanobacterium, and the mixed culture. The extracellular carbohydrates of the diatom and the extracellular proteins of the cyanobacterium increased with elevated CO2 and temperature, while the extracellular carbohydrates and proteins of the green alga and the mixes increased under elevated CO2 and temperature. There were synergistic effects of CO2 and temperature on the productivity and the EPS of microalgae. Climate change related CO2 and temperature increases will promote autochthonous organic carbon production in aquatic ecosystems and facilitate the proliferation of cyanobacteria, which potentially changes the carbon cycling and undermines the functioning of ecosystems.

  2. Wear Potential Due to Low EHD Films During Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Leville, Alan; Ward, Peter

    2014-01-01

    An earlier study showed that EHD films could be accurately measured in a running bearing and that the EHD film eventually runs-in to a steady state value [1]. In the present paper, we report on additional tests conducted on bearings with more lubricants, wider speeds, and higher temperatures. The new results consistently show that all lubricants tested, including MAC-based lubricants have EHD film levels that are lower than model predictions in some situations. In addition, the MAC lubricants studied have lower film thickness than traditional hydrocarbons. Figure 1 is taken from [1] and shows room temperature data of MAC oil and Corey 100 oil, illustrating the smaller EHD film results when using this MAC oil. Since higher temperatures produce lower films by changing the viscosity, the concern we have is that the EHD films may be too small to prevent ball/race metal contact and resulting wear at lower speeds. Best bearing practices would have the EHD film thickness be at least three (3) times the composite surface roughness. In this paper, we will present measured EHD thicknesses of lubricant films at speeds up to several thousand RPM for bearing bore sizes from as low as 6 mm (0.2 in) to as large as 35 mm (1.4 in) using MAC, Corey and KG-80. Ambient temperatures from room temperature to 52C (125F) are used. Testing was done with the base oils as well as formulated greases. Greases eventually ran in to the same EHD values as the base oil but took longer times to get there. The results clearly indicate that wear is very possible in all steel bearings when using MAC lubricants and that this condition worsens with higher temperatures and smaller bearing size.

  3. Whey protein concentrate storage at elevated temperature and humidity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Dairy processors are finding new export markets for whey protein concentrate (WPC), a byproduct of cheesemaking, but they need to know if full-sized bags of this powder will withstand high temperature and relative humidity (RH) levels during unrefrigerated storage under tropical conditions. To answ...

  4. Effects of Elevated Temperature on Concrete with Recycled Coarse Aggregates

    NASA Astrophysics Data System (ADS)

    Salau, M. A.; Oseafiana, O. J.; Oyegoke, T. O.

    2015-11-01

    This paper discusses the effects of heating temperatures of 200°C, 400°C and 600°C each for 2 hours at a heating rate of 2.5°C/min on concrete with the content of Natural Coarse Aggregates (NCA) partially replaced with Recycled Coarse Aggregates (RCA), obtained from demolished building in the ratio of 0%, 15% and 30%.There was an initial drop in strength from 100°C to 200°C which is suspected to be due to the relatively weak interfacial bond between the RCA and the hardened paste within the concrete matrix;a gradual increase in strength continued from 200°C to 450°C and steady drop occurred again as it approached 600°C.With replacement proportion of 0%, 15% and 30% of NCA and exposure to peak temperature of 600°C, a relative concrete strength of 23.6MPa, 25.3MPa and 22.2MPa respectively can be achieved for 28 days curing age. Furthermore, RAC with 15% NCA replacement when exposed to optimum temperature of 450°C yielded high compressive strength comparable to that of control specimen (normal concrete). In addition, for all concrete samples only slight surface hairline cracks were noticed as the temperature approached 400°C. Thus, the RAC demonstrated behavior just like normal concrete and may be considered fit for structural use.

  5. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    NASA Astrophysics Data System (ADS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1992-06-01

    The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  6. Elevated and Low Temperature Deformation of Cast Depleted Uranium

    SciTech Connect

    Vogel, Sven C.

    2015-02-20

    Goals: Understand crystal structure and micro-structure changes during high and low temperature deformation of uranium, in particular texture, and develop constitutive micro-structure based model for uranium deformation. Deliverables achieved: Completed texture measures for 11 pre- and post-dU compression samples, quantified texture pre- and post-deformation, and provided data to constrain deformation models.

  7. Measurements of the CO first overtone bandstrength at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Caledonia, G. E.; Krech, R. H.; Wilkerson, T.

    1985-08-01

    The spectrally resolved emission from the CO first overtone vibration-rotation band has been studied over the temperature range of 1100-2600 K in a shock-tube experiment. First overtone bandstrengths have been deduced from the data. These compare favorably with theoretical expectations.

  8. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1995-01-01

    The results are reported for high-temperature axial and torsional low-cycle fatigue experiments performed at 760 C in air on thin-walled tubular specimens of Haynes 188, a wrought cobalt-based superalloy. Data are also presented for mean coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. This data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME Boiler and Pressure Code), Manson-Halford, modified multiaxiality factor (proposed in this paper), modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The modified multiaxiality factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  9. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1992-01-01

    The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  10. Response of sugarcane to carbon dioxide enrichment and elevated air temperature

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Four sugarcane cultivars (CP 72-2086, CP 73-1547, CP 88-1508, and CP 80-1827) were grown in elongated temperature-gradient greenhouses (TGG) at ambient or elevated carbon dioxide (CO2) of 360 or 720 µmol CO2 mol-1 air (ppm, mole fraction basis), respectively. Elevated CO2 was maintained by injection...

  11. MONOTERPENE LEVELS IN NEEDLES OF DOUGLAS-FIR EXPOSED TO ELEVATED CO2 AND TEMPERATURE

    EPA Science Inventory

    Levels of monoterpenes in current year needles of douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) seedlings were measured at the conclusion of four years of exposure to ambient or elevated CO2 (+ 179 mmol.mol-1), and ambient or elevated temperature (+ 3.5 C). Eleven monoterpen...

  12. Carbon fluxes acclimate more strongly to elevated growth temperatures than to elevated CO2 concentrations in a northern conifer.

    PubMed

    Kroner, Yulia; Way, Danielle A

    2016-08-01

    Increasing temperatures and atmospheric CO2 concentrations will affect tree carbon fluxes, generating potential feedbacks between forests and the global climate system. We studied how elevated temperatures and CO2 impacted leaf carbon dynamics in Norway spruce (Picea abies), a dominant northern forest species, to improve predictions of future photosynthetic and respiratory fluxes from high-latitude conifers. Seedlings were grown under ambient (AC, c. 435 μmol mol(-1) ) or elevated (EC, 750 μmol mol(-1) ) CO2 concentrations at ambient, +4 °C, or +8 °C growing temperatures. Photosynthetic rates (Asat ) were high in +4 °C/EC seedlings and lowest in +8 °C spruce, implying that moderate, but not extreme, climate change may stimulate carbon uptake. Asat , dark respiration (Rdark ), and light respiration (Rlight ) rates acclimated to temperature, but not CO2 : the thermal optimum of Asat increased, and Rdark and Rlight were suppressed under warming. In all treatments, the Q10 of Rlight (the relative increase in respiration for a 10 °C increase in leaf temperature) was 35% higher than the Q10 of Rdark , so the ratio of Rlight to Rdark increased with rising leaf temperature. However, across all treatments and a range of 10-40 °C leaf temperatures, a consistent relationship between Rlight and Rdark was found, which could be used to model Rlight in future climates. Acclimation reduced daily modeled respiratory losses from warm-grown seedlings by 22-56%. When Rlight was modeled as a constant fraction of Rdark , modeled daily respiratory losses were 11-65% greater than when using measured values of Rlight . Our findings highlight the impact of acclimation to future climates on predictions of carbon uptake and losses in northern trees, in particular the need to model daytime respiratory losses from direct measurements of Rlight or appropriate relationships with Rdark .

  13. Comparison of MODIS Satellite Land Surface Temperature with Air Temperature along a 5000-metre Elevation Transect on Kilimanjaro, Tanzania.

    NASA Astrophysics Data System (ADS)

    Pepin, N. C.; Williams, R.; Maeda, E. E.

    2015-12-01

    There is concern that high elevations may be warming more rapidly than lower elevations, but there is a lack of observational data from weather stations in the high mountains. One alternative data source is satellite LST (Land Surface Temperature) which has extensive spatial coverage. This study compares instantaneous values of LST (1030 and 2230 local solar time) as measured by the MODIS MOD11A2 product at 1 km resolution with equivalent screen level air temperatures (in the same pixel) measured from a transect of 22 in situ weather stations across Kilimanjaro ranging in elevation from 990 to 5803 m. Data consists of 11 years on the SW slope and 3 years on the NE slope, equating to >500 and ~140 octtads (8-day periods) respectively. Results show substantial differences between LST and local air temperature, sometimes up to 20C. During the day the LST tends to be higher than air temperature and the reverse is true at night. The differences show large variance, particularly during the daytime, and tend to increase with elevation, particularly on the NE slope of the mountain which faces the sun when the daytime observations are taken (1030 LST). Differences between LST and air temperature are larger in the dry seasons (JF and JJAS), and reduce when conditions are more cloudy. Systematic relationships with cloud cover and vegetation characteristics (as measured by NDVI and MAIAC for the same pixel) are displayed. More vegetation reduces daytime surface heating above the air temperature, but this relationship weakens with elevation. Nighttime differences are more stable and show no relationship with vegetation indices. Therefore the predictability of the LST/air temperature differences reduces at high elevations and it is therefore much more challenging to use satellite data at high elevations to complement in situ air temperature measurements for climate change assessments, especially for daytime maximum temperatures.

  14. Effects of elevated water temperature on physiological responses in adult freshwater mussels

    USGS Publications Warehouse

    Ganser, Alissa M.; Newton, Teresa J.; Haro, Roger J.

    2015-01-01

    These data suggest that elevated temperatures can alter metabolic rates in native mussels and may decrease the amount of energy that is available for key biological processes, such as survival, growth and reproduction.

  15. Production of recalcitrant organic matter under the influence of elevated carbon dioxide and temperature.

    PubMed

    Ki, Bomin; Park, Suyoung; Choi, Jung Hyun

    2014-09-01

    The effects of elevated CO2 and temperature on the quantity and quality of dissolved organic carbon (DOC) of wetland sediments were investigated by measuring organic matter decomposition rates and phenolic compounds as target recalcitrant organic matter. Mean rates of anaerobic microbial metabolism were consistently higher both in vegetated sediments and in elevated CO2 and temperature, although the differences were not statistically significant (P < 0.05). Concentrations of phenolic compounds in sediments with vegetation are significantly different (P < 0.05) from those in sediments without vegetation. Regarding the biodegradability of the phenolic compounds, vegetated sediments showed higher concentrations of 2-chlorophenol and 2,4-dimethylphenol under elevated CO2 and temperature conditions, which means that more refractory material can be produced through enhanced organic matter degradation by elevated CO2 and temperature. The produced phenolic compounds can be transported to the freshwater ecosystem and influence the recalcitrance of DOC.

  16. Alumina Volatility in Water Vapor at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Opila, Elizabeth J.; Myers, Dwight L.

    2003-01-01

    The volatility of alumina in high temperature water vapor was determined by a weight loss technique. Sapphire coupons were exposed at temperatures between 1250 and 1500 C, water partial pressures between 0.15 and 0.68 atm in oxygen, total pressure of 1 atm, and flowing gas velocities of 4.4 cm/s. The pressure dependence of sapphire volatility was consistent with AI(OH)3(g) formation. The enthalpy of reaction to form Al(OH)3(g) from sapphire and water vapor was determined to be 210 +/- 20 kJ/mol, comparing favorably to other studies. Microstructural examination of tested sapphire coupons revealed surface etching features consistent with a volatilization process.

  17. Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Johnson, R D; Young, A P; Schwope, A D

    1956-01-01

    This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

  18. Microscopic structure of water at elevated pressures and temperatures

    PubMed Central

    Sahle, Christoph J.; Sternemann, Christian; Schmidt, Christian; Lehtola, Susi; Jahn, Sandro; Simonelli, Laura; Huotari, Simo; Hakala, Mikko; Pylkkänen, Tuomas; Nyrow, Alexander; Mende, Kolja; Tolan, Metin; Hämäläinen, Keijo; Wilke, Max

    2013-01-01

    We report on the microscopic structure of water at sub- and supercritical conditions studied using X-ray Raman spectroscopy, ab initio molecular dynamics simulations, and density functional theory. Systematic changes in the X-ray Raman spectra with increasing pressure and temperature are observed. Throughout the studied thermodynamic range, the experimental spectra can be interpreted with a structural model obtained from the molecular dynamics simulations. A spatial statistical analysis using Ripley’s K-function shows that this model is homogeneous on the nanometer length scale. According to the simulations, distortions of the hydrogen-bond network increase dramatically when temperature and pressure increase to the supercritical regime. In particular, the average number of hydrogen bonds per molecule decreases to ≈0.6 at 600 °C and p = 134 MPa. PMID:23479639

  19. Failure mechanisms of thermal barrier coatings exposed to elevated temperatures

    NASA Technical Reports Server (NTRS)

    Miller, R. A.; Lowell, C. E.

    1982-01-01

    The failure of a ZrO2-8%Y2O3/Ni-14% Al-0.1% Zr coating system on Rene 41 in Mach 0.3 burner rig tests was characterized. High flame and metal temperatures were employed in order to accelerate coating failure. Failure by delamination was shown to precede surface cracking or spalling. This type of failure could be duplicated by cooling down the specimen after a single long duration isothermal high temperature cycle in a burner rig or a furnace, but only if the atmosphere was oxidizing. Stresses due to thermal expansion mismatch on cooling coupled with the effects of plastic deformation of the bond coat and oxidation of the irregular bond coat are the probable life limiting factors. Heat up stresses alone could not fail the coating in the burner rig tests. Spalling eventually occurs on heat up but only after the coating has already failed through delamination.

  20. Elevated temperature properties of boron/aluminum composites

    NASA Technical Reports Server (NTRS)

    Sullivan, P. G.

    1978-01-01

    The high temperature properties of boron/aluminum composites, fabricated by an air diffusion bonding technique utilizing vacuum-bonded monolayer tape are reported. Seventeen different combinations of matrix alloy, reinforcement diameter, reinforcement volume percent, angle-ply and matrix enhancement (i.e. titanium cladding and interleaves) were fabricated, inspected, and tested. It is shown that good to excellent mechanical properties could be obtained for air-bonded boron/aluminum composites and that these properties did not decrease significantly up to a test temperature of at least 260 C. Composites made with 8 mil B/W fiber show a much greater longitudinal strength dependence on volume percent fiber than composites made with 5.6 mil fiber. The addition of titanium caused difficulties in composite bonding and yielded composites with reduced strength.

  1. Shock sensitivity of LX 04 at elevated temperatures

    SciTech Connect

    Urtiew, P.A.; Tarver, C.M.; Gorbes, J.W.; Garcia, G.

    1997-07-01

    Hazard scenarios can involve multiple stimuli, such as heating followed by fragment impact (shock). The shock response of LX-04 (85 weight % HMX and 15 weight % Viton binder) preheated to temperatures hear 170C is studied in a 10.2 cm bore diameter gas gun using embedded manganin pressure gauges. The pressure histories at various depths in the LX-04 targets and the run distances to detonation at several input shock pressures are measured and compared to those obtained in ambient temperature LX-04. The hot LX-04 is significantly more shock sensitive than ambient LX-04. Ignition and Growth reactive flow models are developed for ambient and hot LX-04 to allow predictions of impact scenarios that a can not be tested directly.

  2. Potent Induction of Arabidopsis thaliana Flowering by Elevated Growth Temperature

    PubMed Central

    Balasubramanian, Sureshkumar; Sureshkumar, Sridevi; Lempe, Janne; Weigel, Detlef

    2006-01-01

    The transition to flowering is an important event in the plant life cycle and is modulated by several environmental factors including photoperiod, light quality, vernalization, and growth temperature, as well as biotic and abiotic stresses. In contrast to light and vernalization, little is known about the pathways that mediate the responses to other environmental variables. A mild increase in growth temperature, from 23 °C to 27 °C, is equally efficient in inducing flowering of Arabidopsis plants grown in 8-h short days as is transfer to 16-h long days. There is extensive natural variation in this response, and we identify strains with contrasting thermal reaction norms. Exploiting this natural variation, we show that FLOWERING LOCUS C potently suppresses thermal induction, and that the closely related floral repressor FLOWERING LOCUS M is a major-effect quantitative trait locus modulating thermosensitivity. Thermal induction does not require the photoperiod effector CONSTANS, acts upstream of the floral integrator FLOWERING LOCUS T, and depends on the hormone gibberellin. Analysis of mutants defective in salicylic acid biosynthesis suggests that thermal induction is independent of previously identified stress-signaling pathways. Microarray analyses confirm that the genomic responses to floral induction by photoperiod and temperature differ. Furthermore, we report that gene products that participate in RNA splicing are specifically affected by thermal induction. Above a critical threshold, even small changes in temperature can act as cues for the induction of flowering. This response has a genetic basis that is distinct from the known genetic pathways of floral transition, and appears to correlate with changes in RNA processing. PMID:16839183

  3. A complex permittivity and permeability measurement system for elevated temperatures

    NASA Technical Reports Server (NTRS)

    Friederich, Paul

    1990-01-01

    The three goals of this research include: (1) to fully develop a method to measure the permittivity and permeability of special materials as a function of frequency in the range of 2.6 to 18 GHz, and of temperatures in the range of 25 to 1100 C; (2) to assist LeRC in setting up an in-house system for the measurement of high-temperature permittivity and permeability; and (3) to measure the complex permittivity and permeability of special materials as a function of frequency and temperature to demonstrate the capability of the method. The method chosen for characterizing the materials relies on perturbation of a resonant cavity with a small volume of sample material. Different field configurations in the cavity can be used to separate electric and magnetic effects. The cavity consists of a section of rectangular waveguide terminated at each end of a vertical slot iris. The center of one wall is a small hole through which the sample is introduced.

  4. A complex permittivity and permeability measurement system for elevated temperatures

    NASA Technical Reports Server (NTRS)

    Friederich, Paul

    1990-01-01

    The three goals of this research include: (1) to fully develop a method to measure the permittivity and permeability of special materials as a function of frequency in the range of 2.6 to 18 GHz, and of temperature in the range of 25 to 1100 C; (2) to assist LeRC in setting up an in-house system for the measurement of high-temperature permittivity and permeability; and (3) to measure the complex permittivity and permeability of special materials as a function of frequency and temperature to demonstrate the capability of the method. The method chosen for characterizing the materials relies on perturbation of a resonant cavity with a small volume of sample material. Different field configurations in the cavity can be used to separate electric and magnetic effects. The cavity consists of a section of rectangular waveguide terminated at each end of a vertical slot iris. In the center of one wall is a small hole through which the sample is introduced.

  5. Influence of Elevated Temperatures on Pet-Concrete Properties

    NASA Astrophysics Data System (ADS)

    Albano, C.; Camacho, N.; Hernández, M.; Matheus, A.; Gutiérrez, A.

    2008-08-01

    Lightweight aggregate is an important material in reducing the unit weight of concrete complying with special concrete structures of large high-rise buildings. Besides, the use of recycled PET bottles as lightweight aggregate in concrete is an effective contribution for environment preservation. So, the objective of the present work was to study experimentally the flexural strength of the PET -concrete blends and the thermal degradation of the PET in the concrete, when the blends with 10 and 20% in volume of PET were exposed to different temperatures (200, 400, 600 °C). The flexural strength of concrete-PET exposed to a heat source is strongly dependent on the temperature, water/cement ratio, as well as the content and particle size of PET. However, the activation energy is affected by the temperature, location of the PET particles on the slabs and the water/cement ratio. Higher water content originates thermal and hydrolytic degradation on the PET, while on the concrete, a higher vapor pressure which causes an increase in crack formation. The values of the activation energy are higher on the center of the slabs than on the surface, since concrete is a poor heat conductor.

  6. Effect of Preloading on Fatigue Strength in Dynamic Fatigue Testing of Ceramic Materials at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.

    1995-01-01

    Previously derived solutions of fatigue strength as a function of preloading were verified by applying preloads to elevated temperature dynamic fatigue tests of 96 wt% alumina at 1000 C and NC 132 silicon nitride at 1100 C. The technique was found very useful in identification and control of the governing failure mechanism when multiple failure mechanisms, such as slow crack growth, creep and oxidation occurred simultaneously at elevated temperatures.

  7. Elevated temperature tribology of cobalt and tantalum-based alloys

    DOE PAGES

    Scharf, T. W.; Prasad, S. V.; Kotula, P. G.; Michael, J. R.; Robino, C. V.

    2014-12-31

    This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volumemore » gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10–4 mm3/N•m) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. Furthermore, the results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.« less

  8. Elevated temperature tribology of cobalt and tantalum-based alloys

    SciTech Connect

    Scharf, T. W.; Prasad, S. V.; Kotula, P. G.; Michael, J. R.; Robino, C. V.

    2014-12-31

    This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volume gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10–4 mm3/N•m) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. Furthermore, the results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.

  9. Solid/liquid lubrication of ceramics at elevated temperatures

    SciTech Connect

    Erdemir, A.; Erck, R.A.; Fenske, G.R.; Hong, H.

    1996-04-01

    This study investigates the effect of solid and liquid lubrication on friction and wear performance of silicon nitride (Si{sub 3}N{sub 4}) and cast iron. The solid lubricant was a thin silver film ({approx}2 {mu}m thick) produced on Si{sub 3}N{sub 4} by ion-beam-assisted deposition. A high-temperature polyol-ester-base synthetic oil served as the liquid lubricant. Friction and wear tests were performed with pin-on-disk and oscillating-slider wear test machines at temperatures up to 300{degrees}C. Without the silver films, the friction coefficients of Si{sub 3}N{sub 4}/Si{sub 3}N{sub 4} test pairs were 0.05 to 0.14, and the average wear rates of Si{sub 3}N{sub 4} pins were {approx}5 x 10{sup -8} mm{sup 3} N{sup -1}. The friction coefficients of Si{sub 3}N{sub 4}/cast iron test pairs ranged from 0.08 to 0.11, depending on test temperature. The average specific wear rates of cast iron pins were {approx}3 x 10{sup -7} mm{sup 3} N{sup -1} m{sup -1}. However, simultaneous use of the solid-lubricant silver and synthetic oil on the sliding surfaces reduced friction coefficients to 0.02 to 0.08. Moreover, the wear of Si{sub 3}N{sub 4} pins and silver-coated Si{sub 3}N{sub 4} disks was so low that it was difficult to assess by a surface profilometer. The wear rates of cast iron pins were {approx}7 x 10{sup -9} mm{sup 3} N{sup -1} m{sup -1} up to 250{degrees}C, but showed a tendency to increase slightly at much higher temperatures. In general, the test results demonstrated that the solid/liquid lubrication of ceramic and/or metallic components is both feasible and effective in controlling friction and wear.

  10. Interactions of Water Vapor with Oxides at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Jacobson, Nathan; Opila, Elizabeth; Copland, Evan; Myers, Dwight

    2003-01-01

    Many volatile metal hydroxides form by reaction of the corresponding metal oxide with water vapor. These reactions are important in a number of high temperature corrosion processes. Experimental methods for studying the thermodynamics of metal hydroxides include: gas leak Knudsen cell mass spectrometry, free jet sampling mass spectrometry, transpiration and hydrogen-oxygen flame studies. The available experimental information is reviewed and the most stable metal hydroxide species are correlated with position in the periodic table. Current studies in our laboratory on the Si-O-H system are discussed.

  11. Bacterial adaptation to extremes of low temperature and elevated pressure

    NASA Astrophysics Data System (ADS)

    Bartlett, Douglas

    The largest portion of Earth's biosphere is represented by low temperature, high pressure deepsea environments which are exposed to reduced and recalcitrant forms of organic carbon and which are far removed from sun light. Progress that has been made in recent years examining the biodiversity, genomics and genetics of microbial life at great ocean depths will be described. Particular focus will be given to the comparative genomics of members of Colwellia, Photobacterium, Moritella, Shewanella, Psychromonas and Carnobacterium genera. The genomes of piezophiles (high pressure adapted microbes) are characterized by possessing large intergenic regions, large numbers of rRNA operons, rRNA of a modified secondary structure, a reliance on unsaturated and poly-unsaturated fatty acids in their membrane lipids, a diversity of transport and physiological capabilities, and large numbers of transposable elements. Genetic studies in Photobacterium profundum have highlighted roles for extracellular polysaccharide production and DNA replication and protein synthesis in low temperature and high pressure growth. Recent advances in the cultivation of novel piezophiles from a deep-trench environment will also be described.

  12. Thermal diffusivity of igneous rocks at elevated pressure and temperature

    SciTech Connect

    Durham, W.B.; Mirkovich, V.V.; Heard, H.C.

    1987-10-10

    Thermal diffusivity measurements of seven igneous rocks were made to temperatures of 400 /sup 0/C and pressures of 200 MPa. The measuring method was based on the concept of cylindrical symmetry and periodic heat pulses. The seven rocks measured were Westerly (Rhode Island) granite, Climax Stock (Nevada) quartz monzonite, Pomona (Washington) basalt, Atikokan (Ontario, Canada) granite, Creighton (Ontario, Canada) gabbro, East Bull Lake (Ontario, Canada) gabbro, and Stripa (Sweden) granite. The diffusivity of all the rocks showed a positive linear dependence on inverse temperature and, excluding the East Bull Lake gabbro, showed a linear dependence on quartz content. (Quartz content varied from 0 to 31% by volume.) Diffusivity in all cases rose or remained steady with increasing confining pressure. The pressure effect was strongest at lowest pressures and vanished by levels between 10 and 100 MPa, depending on rock type. The pressure effect (measured as a percentage change in diffusivity) is stronger in the four rocks of granite composition than in the three of basaltic composition. Our results agree well with existing thermal diffusivity measurements at atmospheric pressure.

  13. HINDERED DIFFUSION OF ASPHALTENES AT ELEVATED TEMPERATURE AND PRESSURE

    SciTech Connect

    James A. Guin; Ganesh Ramakrishnan

    1999-10-07

    During this time period, experiments were performed to study the diffusion controlled uptake of quinoline and a coal asphaltene into porous carbon catalyst pellets. Cyclohexane and toluene were used as solvents for quinoline and the coal asphaltene respectively. The experiments were performed at 27 C and 75 C, at a pressure of 250 psi (inert gas) for the quinoline/cyclohexane system. For the coal asphaltene/toluene system, experiments were performed at 27 C, also at a pressure of 250 psi. These experiments were performed in a 20 cm{sup 3} microautoclave, the use of which is advantageous since it is economical from both a chemical procurement and waste disposal standpoint due to the small quantities of solvents and catalysts used. A C++ program was written to simulate data using a mathematical model which incorporated both diffusional and adsorption mechanisms. The simulation results showed that the mathematical model satisfactorily fitted the adsorptive diffusion of quinoline and the coal asphaltene onto a porous activated carbon. For the quinoline/cyclohexane system, the adsorption constant decreased with an increase in temperature. The adsorption constant for the coal asphaltene/toluene system at 27 C was found to be much higher than that of the quinoline/cyclohexane system at the same temperature. Apparently the coal asphaltenes have a much greater affinity for the surface of the carbon catalyst than is evidenced by the quinoline molecule.

  14. Elevated temperature enhances normal early embryonic development in the coral Platygyra acuta under low salinity conditions

    NASA Astrophysics Data System (ADS)

    Chui, Apple Pui Yi; Ang, Put

    2015-06-01

    To better understand the possible consequences of climate change on reef building scleractinian corals in a marginal environment, laboratory experiments were conducted to examine the interactive effects of changes in salinity and temperature on percent fertilization success and early embryonic development of the coral Platygyra acuta. In the present study, a salinity of 24 psu (ambient 32 psu) reduced fertilization success by 60 %. Normal embryonic development was reduced by >80 % at 26 psu (ambient 33 psu) with 100 % abnormal development at 22 psu under ambient temperature. Elevated temperature (+3 °C) above the ambient spawning temperature did not show any negative effects on fertilization success. However, there was a trend for more abnormal embryos to develop at elevated temperature in the 2 d of the spawning event. The interactive effects between salinity and temperature are statistically significant only on normal embryonic development of P. acuta, but not on its fertilization success. Salinity was revealed to be the main factor affecting both fertilization success and normal embryonic development. Interestingly, the much lower fertilization success (76 %) observed in the second day of spawning (Trial 2) under ambient temperature recovered to 99 % success under elevated (+3 °C) temperature conditions. Moreover, elevated temperature enhanced normal early embryonic development under lowered salinity (26 psu). This antagonistic interactive effect was consistently observed in two successive nights of spawning. Overall, our results indicate that, in terms of its fertilization success and embryonic development, P. acuta is the most tolerant coral species to reduced salinity thus far reported in the literature. Elevated temperature, at least that within the tolerable range of the corals, could apparently alleviate the potential negative effects from salinity stresses. This mitigating role of elevated temperature appears not to have been reported on corals before.

  15. Reaction of cobalt in SO2 atmospheric at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Worrell, W. L.

    1983-01-01

    The reaction rate of cobalt in SO2 argon environments was measured at 650 C, 700 C, 750 C and 800 C. Product scales consist primarily of an interconnected sulfide phase in an oxide matrix. At 700 C to 800 C a thin sulfide layer adjacent to the metal is also observed. At all temperatures, the rapid diffusion of cobalt outward through the interconnected sulfide appears to be important. At 650 C, the reaction rate slows dramatically after five minutes due to a change in the distribution of these sulfides. At 700 C and 750 C the reaction is primarily diffusion controlled values of diffusivity of cobalt (CoS) calculated from this work show favorable agreement with values of diffusivity of cobalt (CoS) calculated from previous sulfidation work. At 800 C, a surface step becomes rate limiting.

  16. Constitutive equations for meeting elevated-temperature-design needs

    SciTech Connect

    Pugh, C.E.; Robinson, D.N.

    1981-01-01

    Constitutive equations for representing the inelastic behavior of structural alloys at temperatures in the creep regime are discussed from the viewpoint of advances made over the past decade. An emphasis is placed on the progress that has been made in meeting the needs of the program whose design process is based in part on a design-by-inelastic-analysis approach. In particular, the constitutive equations that have been put into place for current use in design analyses are discussed along with some material behavior background information. Equations representing short-term plastic and long-term creep behaviors are considered. Trends towards establishing improved equations for use in the future are also described. Progress relating to fundamentals of continuum mechanics, physical modeling, phenomenological modeling, and implementation is addressed.

  17. Permittivity measurement of thermoplastic composites at elevated temperature.

    PubMed

    Ku, H S; Horsfield, B; Ball, J A; Siores, E

    2001-01-01

    The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity epsilon = epsilon'-jepsilon", and the loss tangent, tan delta = epsilon"/epsilon'. This paper describes two convenient laboratory based methods to obtain epsilon', epsilon" and hence tan delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyzer in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe. PMID:15040528

  18. Permittivity measurement of thermoplastic composites at elevated temperature.

    PubMed

    Ku, H S; Horsfield, B; Ball, J A; Siores, E

    2001-01-01

    The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity epsilon = epsilon'-jepsilon", and the loss tangent, tan delta = epsilon"/epsilon'. This paper describes two convenient laboratory based methods to obtain epsilon', epsilon" and hence tan delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyzer in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe.

  19. Reaction of cobalt in SO2 atmospheres at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Jacobson, N. S.; Worrell, W. L.

    1984-01-01

    The reaction rate of cobalt in SO2 argon environments was measured at 650 C, 700 C, 750 C and 800 C. Product scales consist primarily of an interconnected sulfide phase in an oxide matrix. At 700 C to 800 C, a thin sulfide layer adjacent to the metal is also observed. At all temperatures, the rapid diffusion of cobalt outward through the interconnected sulfide appears to be important. At 650 C, the reaction rate slows dramatically after five minutes due to a change in the distribution of these sulfides. At 700 C and 750 C, the reaction is primarily diffusion controlled; values of diffusivity of cobalt (CoS) calculated from this work show favorable agreement with values of diffusivity of cobalt (CoS) calculated from previous sulfidation work. At 800 C, a surface step becomes rate limiting. Previously announced in STAR as N83-35104

  20. A Flow Stress Formulation of Magnesium Alloy at Elevated Temperature

    SciTech Connect

    Liu Juan; Cui Zhenshan; Ruan Liqun

    2007-05-17

    Dynamic recrystallization (DRX) is the main softening mechanism of magnesium alloy AZ31B in hot deformation. Theoretically, in the flow rule the atomic diffusibility and the driving force of dislocation migration are dependent on the temperature, and the dislocation density and the cumulation of grain boundary energy are dependent on the strain rate. The peak stress will appear when the flow driving force and resistance force reach a balance, after which the stress descending will take place due to recrystallization fraction. Since the DRX is a thermally activated process, the recrystallized volume fraction can be regarded as the function of strain through Avrami equation. Based on this idea, the paper proposes a new constitutive model characterizing dynamic recrystallization for magnesium alloy AZ31B. The model is described by a peak stress and a strain softening rate, in which the peak stress depends only on Zener-Hollomon parameter and is determined through creep equation, and the strain softening rate is mainly dominated by the recrystallized volume fraction. As a result, the formulation of flow stress takes into account of temperature, strain and strain rate, and is characterized by DRX. The thermomechanical simulation tests of magnesium alloy AZ31B by using Gleeble-1500 were conducted, through which the parameters in flow stress model can be easily determined. Comparison shows that the maximum difference of flow stress between the model predictions and test values is approximately 2.32%. This indicates that the proposed constitutive model can be employed to represent the DRX behaviour of AZ31B.

  1. Elevated temperature fretting fatigue of nickel based alloys

    NASA Astrophysics Data System (ADS)

    Gean, Matthew C.

    This document details the high temperature fretting fatigue of high temperature nickel based alloys common to turbine disk and blade applications. The research consists of three area of focus: Experiments are conducted to determine quantitatively the fretting fatigue lives of advanced nickel based alloys; Analytical tools are developed and used to investigate the fretting fatigue response of the material; Fractographic analysis of the experimental results is used to improve the analytical models employed in the analysis of the experiments. Sixty three fretting fatigue experiments were conducted at 649 °C using a polycrystalline Nickel specimen in contact with directionally solidified and single crystal Nickel pads. Various influences on the fretting fatigue life are investigated. Shot peened Rene' 95 had better fretting fatigue life compared to shot peened Rene' 88. Shot peening produced a 2x increase in life for Rene' 95, but only a marginal improvement in the fretting fatigue life for Rene' 88. Minor cycles in variable amplitude loading produces significant damage to the specimen. Addition of occasional overpeaks in load produces improvements in fretting fatigue life. Contact tractions and stresses are obtained through a variety of available tools. The contact tractions can be efficiently obtained for limited geometries, while FEM can provide the contact tractions for a broader class of problems, but with the cost of increased CPU requirements. Similarly, the subsurface contact stresses can be obtained using the contact tractions as a boundary condition with either a semi-analytical FFT method or FEM. It is found that to calculate contact stresses the FFT was only marginally faster than FEM. The experimental results are combined with the analysis to produce tools that are used to design against fretting fatigue. Fractographic analysis of the fracture surface indicates the nature of the fretting fatigue crack behavior. Interrupted tests were performed to analyze

  2. Effects of elevated CO2 and temperature on Gynostemma pentaphyllum physiology and bioactive compounds.

    PubMed

    Chang, Jia-Dong; Mantri, Nitin; Sun, Bin; Jiang, Li; Chen, Ping; Jiang, Bo; Jiang, Zhengdong; Zhang, Jialei; Shen, Jiahao; Lu, Hongfei; Liang, Zongsuo

    2016-06-01

    Recently, an important topic of research has been how climate change is seriously threatening the sustainability of agricultural production. However, there is surprisingly little experimental data regarding how elevated temperature and CO2 will affect the growth of medicinal plants and production of bioactive compounds. Here, we comprehensively analyzed the effects of elevated CO2 and temperature on the photosynthetic process, biomass, total sugars, antioxidant compounds, antioxidant capacity, and bioactive compounds of Gynostemma pentaphyllum. Two different CO2 concentrations [360 and 720μmolmol(-1)] were imposed on plants grown at two different temperature regimes of 23/18 and 28/23°C (day/night) for 60days. Results show that elevated CO2 and temperature significantly increase the biomass, particularly in proportion to inflorescence total dry weight. The chlorophyll content in leaves increased under the elevated temperature and CO2. Further, electron transport rate (ETR), photochemical quenching (qP), actual photochemical quantum yield (Yield), instantaneous photosynthetic rate (Photo), transpiration rate (Trmmol) and stomatal conductance (Cond) also increased to different degrees under elevated CO2 and temperature. Moreover, elevated CO2 increased the level of total sugars and gypenoside A, but decreased the total antioxidant capacity and main antioxidant compounds in different organs of G. pentaphyllum. Accumulation of total phenolics and flavonoids also decreased in leaves, stems, and inflorescences under elevated CO2 and temperature. Overall, our data indicate that the predicted increase in atmospheric temperature and CO2 could improve the biomass of G. pentaphyllum, but they would reduce its health-promoting properties. PMID:27054772

  3. Microstructure and tensile properties of tungsten at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Shen, Tielong; Dai, Yong; Lee, Yongjoong

    2016-01-01

    In order to support the development of the 5 MW spallation target for the European Spallation Source, the effect of fabrication process on microstructure, ductile-to-brittle transition temperature (DBTT), tensile and fracture behaviour of powder-metallurgy pure tungsten materials has been investigated. A hot-rolled (HR) tungsten piece of 12 mm thickness and a hot-forged (HF) piece of about 80 mm thickness were used to simulate the thin and thick blocks in the target. The two tungsten pieces were characterized with metallography analysis, hardness measurement and tensile testing. The HR piece exhibits an anisotropic grain structure with an average size of about 330 × 140 × 40 μm in rolling, long transverse and short transverse (thickness) directions. The HF piece possesses a bimodal grain structure with about 310 × 170 × 70 μm grain size in deformed part and about 25 μm sized grains remained from sintering process. Hardness (HV0.2) of the HR piece is slightly greater than that of the HF one. The ductility of the HR tungsten specimens is greater than that of the HF tungsten. For the HF tungsten piece, specimens with small grains in gauge section manifest lower ductility but higher strength. The DBTT evaluated from the tensile results is 250-300 °C for the HR tungsten and about 350 °C for the HF tungsten.

  4. Elevated Temperature Deformation of Cr3Si Alloyed with Mo

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Whittenberger, J. Daniel; Zeumer, B.; Sauthoff, G.

    1998-01-01

    Four-point bend, constant load compressive creep and constant engineering strain rate tests were conducted on arc-melted and powder-metallurgy (PM) processed Cr40Mo30Si30 specimens in the temperature range 1400 and 1700 K. This is a two phase alloy consisting of (CrMo)3Si and (Cr,Mo)5Si3 phases. The PM specimens, which were substantially weaker than the arc-melted materials, exhibited a stress exponent n, of about 2 and an apparent activation energy for creep, Q(sub 3), of 485 kJ/mol. The mechanism in these specimens appeared to be controlled by creep of a glassy phase. In the case of arc-melted specimens for which nis approximately 3 and Q(sub 3) is approximately 430 kJ/mol, the rate-controlling creep mechanism appeared to be that dominant in the (Cr,Mo)5Si3 phase. In this case, it is suggested that the Nabarro creep mechanism, where dislocation climb is controlled by Bardeen-Herring vacancy sources, is the dominant creep mechanism. Finally, an analysis of the present and literature data on Cr3Si alloyed with Mo appeared to suggest that the creep rate decreases sharply with an increase in the Mo/Si ratio.

  5. Microwave sensor design for noncontact process monitoring at elevated temperature

    NASA Astrophysics Data System (ADS)

    Yadam, Yugandhara Rao; Arunachalam, Kavitha

    2016-02-01

    In this work we present a microwave sensor for noncontact monitoring of liquid level at high temperatures. The sensor is a high gain, directional conical lensed horn antenna with narrow beam width (BW) designed for operation over 10 GHz - 15 GHz. Sensor design and optimization was carried out using 3D finite element method based electromagnetic (EM) simulation software HFSS®. A rectangular to circular waveguide feed was designed to convert TE10 to TE11 mode for wave propagation in the conical horn. Swept frequency simulations were carried out to optimize antenna flare angle and length to achieve better than -10 dB return loss (S11), standing wave ratio (SWR) less than 2.0, 20° half power BW (HPBW) and 15 dB gain over 10 GHz - 15 GHz. The sensor was fabricated using Aluminum and was characterized in an anechoic test box using a vector network analyzer (E5071C, Agilent Technologies, USA). Experimental results of noncontact level detection are presented for boiling water in a metal canister.

  6. Kinetics of Death of Bacterial Spores at Elevated Temperatures

    PubMed Central

    Wang, Daniel I-C.; Scharer, Jeno; Humphrey, Arthur E.

    1964-01-01

    The kinetics of death of Bacillus stearothermophilus spores (FS 7954) suspended in phosphate buffer (pH 7) were studied over a temperature range of 127.2 to 143.8 C and exposure times of 0.203 to 4.150 sec. These short exposure were achieved by use of a tubular flow reactor in which a suspension of spores was injected into a hot flowing stream at the entrance of the reactor. Thermal equilibria of the suspension with the hot stream was achieved within 0.0006 sec. After flow through a fixed length of reactor, the stream containing the spores was cooled by flash vaporization and then assayed for viable count. The death rate data were fitted by a logarithmic expression. However, logarithmic death rate was only approximated in the tail or high-kill regions of exposure. Death rate constants obtained from this portion of the data were found to correlate by Arrhenius as well as Absolute Reaction Rate Theory relationships. Thermal-death time curves were found to correlate the data rather poorly. The activation energy and frequency constant for an Arrhenius relationship fit of the data were found to be 83.6 kcal/gmole and 1047.2 min-1, respectively. The standard enthalpy and entropy changes for an Absolute Reaction Rate Theory relationship fit of the data were found to be 84.4 kcal/gmole and 157 cal/gmole-K, respectively. PMID:14215978

  7. Thermorecovery of cyanobacterial fatty acids at elevated temperatures.

    PubMed

    Liu, Xinyao; Curtiss, Roy

    2012-11-15

    We have developed a genetic system we call "thermorecovery" that allows us to lyse cyanobacterial cultures and hydrolyze membrane lipids to release free fatty acids (FFAs), a biofuel precursor. The system uses thermostable lipases encoded by genes from thermophilic organisms that have been transferred into the cyanobacterial genome and can be synthesized by turning off CO(2) availability and subsequently activated by increasing the concentrated culture temperature. When synthesized in FFA-producing strains, the lipase Fnl from Fervidobacterium nodosum Rt17-B1 released the most FFA. Of the seven candidate lipases investigated, Fnl-synthesizing strains yielded 42.7±1.5 mg/l FFA at 47°C. We also determined that the optimal production conditions for SD338, the Synechocystis strain synthesizing Fnl, was to keep the cell concentrates at 46°C for two days after a one-day CO(2) limitation pretreatment of the culture. A 4-l continuous semi-batch production experiment with SD338 showed that daily harvested cultures (1l) released an average of 43.9±6.6 mg fatty acid and this productivity lasted for at least 20 days without significant decline. This improved thermorecovery process can be used in conjunction with other means to genetically engineer cyanobacteria to produce biofuels or biofuel precursors as the final step in recovery of membrane lipids. PMID:22944207

  8. The Environmental Cost of Misinformation: Why the Recommendation to Use Elevated Temperatures for Handwashing is Problematic

    PubMed Central

    Carrico, Amanda R.; Spoden, Micajah; Wallston, Kenneth A.; Vandenbergh, Michael P.

    2013-01-01

    Multiple government and health organizations recommend the use of warm or hot water in publications designed to educate the public on best practices for washing one’s hands. This is despite research suggesting that the use of an elevated water temperature does not improve handwashing efficacy, but can cause hand irritation. There is reason to believe that the perception that warm or hot water is more effective at cleaning one’s hands is pervasive, and may be one factor that is driving up unnecessary energy consumption and greenhouse gas emissions. We examine handwashing practices and beliefs about water temperature using a survey of 510 adults in the United States. The survey included measures of handwashing frequency, duration, the proportion of time an elevated temperature was used, and beliefs about water temperature and handwashing efficacy. We also estimate the energy consumed and resultant carbon dioxide equivalent emissions (CO2eq) in the U.S. due to the use of elevated temperatures during handwashing. Participants used an elevated temperature 64% of the time, causing 6.3 million metric tons (MMt) of CO2eq which is 0.1% of total annual emissions and 0.3% of commercial and residential sector emissions. Roughly 69% of the sample believed that elevated temperatures improve handwashing efficacy. Updating these beliefs could prevent 1 MMt of CO2eq annually, exceeding the total emissions from many industrial sources in the U.S. including the Lead and Zinc industries. In addition to causing skin irritation, the recommendation to use an elevated temperature during handwashing contributes to another major threat to public health—climate change. Health and consumer protection organizations should consider advocating for the use of a “comfortable” temperature rather than warm or hot water. PMID:23814480

  9. The Environmental Cost of Misinformation: Why the Recommendation to Use Elevated Temperatures for Handwashing is Problematic.

    PubMed

    Carrico, Amanda R; Spoden, Micajah; Wallston, Kenneth A; Vandenbergh, Michael P

    2013-07-01

    Multiple government and health organizations recommend the use of warm or hot water in publications designed to educate the public on best practices for washing one's hands. This is despite research suggesting that the use of an elevated water temperature does not improve handwashing efficacy, but can cause hand irritation. There is reason to believe that the perception that warm or hot water is more effective at cleaning one's hands is pervasive, and may be one factor that is driving up unnecessary energy consumption and greenhouse gas emissions. We examine handwashing practices and beliefs about water temperature using a survey of 510 adults in the United States. The survey included measures of handwashing frequency, duration, the proportion of time an elevated temperature was used, and beliefs about water temperature and handwashing efficacy. We also estimate the energy consumed and resultant carbon dioxide equivalent emissions (CO2eq) in the U.S. due to the use of elevated temperatures during handwashing. Participants used an elevated temperature 64% of the time, causing 6.3 million metric tons (MMt) of CO2eq which is 0.1% of total annual emissions and 0.3% of commercial and residential sector emissions. Roughly 69% of the sample believed that elevated temperatures improve handwashing efficacy. Updating these beliefs could prevent 1 MMt of CO2eq annually, exceeding the total emissions from many industrial sources in the U.S. including the Lead and Zinc industries. In addition to causing skin irritation, the recommendation to use an elevated temperature during handwashing contributes to another major threat to public health-climate change. Health and consumer protection organizations should consider advocating for the use of a "comfortable" temperature rather than warm or hot water. PMID:23814480

  10. Qualification of diesel generator exhaust carbon steel piping to intermitted elevated temperatures

    SciTech Connect

    Ratiu, M.D.; Moisidis, N.T.

    1996-02-01

    The diesel generator exhaust piping, usually made up of carbon steel piping (e.g., ASME SA-106, SA-53), is subjected to successive short time exposures at elevated temperatures up to 1,000 F (538 C). A typical design of this piping, without consideration for creep-fatigue cumulative damage, is at least incomplete, if not inappropriate. Also, a design for creep-fatigue, usually employed for long-term exposure to elevated temperatures, would be too conservative and will impose replacement of the carbon steel piping with heat-resistant CrMo alloy piping. The existing ASME standard procedures do not explicitly provide acceptance criteria for the design qualification to withstand these intermittent exposures to elevated temperatures. The serviceability qualification proposed is based on the evaluation of equivalent full temperature cycles which are presumed/expected to be experienced by the exhaust piping during the design operating life of the diesel engine. The proposed serviceability analysis consists of: (a) determination of the permissible stress at elevated temperatures, and (b) estimation of creep-fatigue damage for the total expected cycles of elevated temperature exposures following the procedure provided in ASME Code Cases N-253-6 and N-47-28.

  11. Elevated CO2 and temperature increase soil C losses from a soy-maize ecosystem

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Warming temperatures and increasing CO2 are likely to have large effects on the amount of carbon stored in soil, but predictions of these effects are poorly constrained. We elevated temperature (canopy: +2.8 °C; soil growing season: +1.8 °C; soil fallow: +2.3 °C) for three years within the 9th-11th ...

  12. A unique elevated-temperature tension-torsion fatigue test rig

    NASA Astrophysics Data System (ADS)

    Jordan, E. H.; Chan, C. T.

    1987-06-01

    A unique tension-torsion fatigue test set up is described that allows strain-controlled tests at temperatures exceeding 649 C. The machine uses a large die set as a load frame resulting in lower cost and superior parallel positioning of the crossheads. Disposable weld-on grips were found to be cost effective for elevated-temperature testing. A new extensometer using commercially available capacitance probes was developed which can operate at the elevated temperature without cooling. Capacitance ring probes were utilized in an attempt to measure through-thickness strains. The characteristic behavior of the ring probes is discussed. Design modifications needed to make a successful measurement of through-thickness strains at elevated temperatures are presented.

  13. Leaf physiological responses of mature Norway Spruce trees exposed to elevated carbon dioxide and temperature

    NASA Astrophysics Data System (ADS)

    Lamba, Shubhangi; Uddling, Johan; Räntfors, Mats; Hall, Marianne; Wallin, Göran

    2014-05-01

    Leaf photosynthesis, respiration and stomatal conductance exert strong control over the exchange of carbon, water and energy between the terrestrial biosphere and the atmosphere. As such, leaf physiological responses to rising atmospheric CO2 concentration ([CO2]) and temperature have important implications for the global carbon cycle and rate of ongoing global warming, as well as for local and regional hydrology and evaporative cooling. It is therefore critical to improve the understanding of plant physiological responses to elevated [CO2] and temperature, in particular for boreal and tropical ecosystems. In order to do so, we examined physiological responses of mature boreal Norway spruce trees (ca 40-years old) exposed to elevated [CO2] and temperature inside whole-tree chambers at Flakaliden research site, Northern Sweden. The trees were exposed to a factorial combination of two levels of [CO2] (ambient and doubled) and temperature (ambient and +2.8 degree C in summer and +5.6 degree C in winter). Three replicates in each of the four treatments were used. It was found that photosynthesis was increased considerably in elevated [CO2], but was not affected by the warming treatment. The maximum rate of photosynthetic carboxylation was reduced in the combined elevated [CO2] and elevated temperature treatment, but not in single factor treatments. Elevated [CO2] also strongly increased the base rate of respiration and to a lesser extent reduced the temperature sensitivity (Q10 value) of respiration; responses which may be important for the carbon balance of these trees which have a large proportion of shaded foliage. Stomatal conductance at a given VPD was reduced by elevated temperature treatment, to a degree that mostly offset the higher vapour pressure deficit in warmed air with respect to transpiration. Elevated [CO2] did not affect stomatal conductance, and thus increased the ratio of leaf internal to external [CO2]. These results indicate that the large elevated

  14. Shifting and extension of phenological periods with increasing temperature along elevational transects in southern Bavaria.

    PubMed

    Schuster, C; Estrella, N; Menzel, A

    2014-03-01

    The impact of global warming on phenology has been widely studied, and almost consistently advancing spring events have been reported. Especially in alpine regions, an extraordinary rapid warming has been observed in the last decades. However, little is known about phenological phases over the whole vegetation period at high elevations. We observed 12 phenological phases of seven tree species and measured air temperature at 42 sites along four transects of about 1000 m elevational range in the years 2010 and 2011 near Garmisch-Partenkirchen, Germany. Site- and species-specific onset dates for the phenological phases were determined and related to elevation, temperature lapse rates and site-specific temperature sums. Increasing temperatures induced advanced spring and delayed autumn phases, in which both yielded similar magnitudes. Delayed leaf senescence could therefore have been underestimated until now in extending the vegetation period. Not only the vegetation period, but also phenological periods extended with increasing temperature. Moreover, sensitivity to elevation and temperature strongly depends on the specific phenological phase. Differences between species and groups of species (deciduous, evergreen, high elevation) were found in onset dates, phenological response rates and also in the effect of chilling and forcing temperatures. Increased chilling days highly reduced forcing temperature requirements for deciduous trees, but less for evergreen trees. The problem of shifted species associations and phenological mismatches due to species-specific responses to increasing temperature is a recent topic in ecological research. Therefore, we consider our findings from this novel, dense observation network in an alpine area of particular importance to deepen knowledge on phenological responses to climate change.

  15. A comparison of deflagration rates at elevated pressures and temperatures with thermal explosion results

    NASA Astrophysics Data System (ADS)

    Glascoe, Elizabeth A.; Springer, Harry Keo; Tringe, Joseph; Maienschein, Jon L.

    2012-03-01

    The deflagration rate of HMX-based explosives has previously been correlated with the violence of thermal explosion experiments. In particular, HMX-based materials that experience deconsolidative burning at elevated pressures (i.e. P = 200 - 600 MPa) also produce significantly more violent thermal explosions. We now report deflagration rates at elevated temperatures (i.e. T = 150 - 180C) and moderate pressures (i.e. P = 10 - 100 MPa). These conditions more closely mimic the pressures and temperatures of an explosive shortly after ignition of a thermal explosion. Here, we discuss the deflagration rates of HMX-based explosives at elevated temperatures and their usefulness to predict the thermal explosion violence of the same materials.

  16. Temperature Variations with Changing Solar Elevation in Saturn's Main Rings as Seen by Cassini CIRS

    NASA Astrophysics Data System (ADS)

    Spilker, Linda J.; Flandes, A.; Altobelli, N.; Leyrat, C.; Pilorz, S.; Ferrari, C.

    2008-09-01

    During four years in orbit around Saturn, the Cassini Composite Infrared Spectrometer (CIRS) has acquired an extensive set of thermal measurements of Saturn's main rings (A, B, C and Cassini Division). Temperatures were retrieved for the lit and unlit rings over a variety of ring geometries that include solar phase angle, spacecraft elevation, solar elevation and local hour angle. To first order, the largest temperature changes on the lit face of the rings are driven by variations in phase angle while differences in temperature with changing spacecraft elevation and local time are a secondary effect. Once phase angle and local time effects are taken into account, decreases in ring temperature with decreasing solar elevation are observed for both the lit and unlit faces of the rings. For the lit rings,decreases of 2- 4 K are observed in the C ring and larger decreases, 7-10 and 10 - 13 K, are observed in the A and B rings respectively. Our thermal data cover a range of solar elevations from -21 to -12 degrees (south side of the rings). We test two simple models to assess how well they fit the observed decreases in temperature. The first model assumes that the particles are so widely spaced that they do not cast shadows on one another while the second model assumes that the particles are so close together they essentially form a slab. The optically thinnest and optically thickest regions of the rings show the best fits to these two end member models. We present a preliminary report on ring temperature variations as a function of solar elevation in Saturn's rings. This research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with NASA. Copyright 2008 California Institute of Technology. Government sponsorship acknowledged.

  17. Additive pressures of elevated sea surface temperatures and herbicides on symbiont-bearing foraminifera.

    PubMed

    van Dam, Joost W; Negri, Andrew P; Mueller, Jochen F; Altenburger, Rolf; Uthicke, Sven

    2012-01-01

    Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F'(m)), while elevated temperatures (>30 °C, only 2 °C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (F(v)/F(m)), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced F(v)/F(m) and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥ 1 µg L(-1)). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures. PMID:22439012

  18. Additive Pressures of Elevated Sea Surface Temperatures and Herbicides on Symbiont-Bearing Foraminifera

    PubMed Central

    van Dam, Joost W.; Negri, Andrew P.; Mueller, Jochen F.; Altenburger, Rolf; Uthicke, Sven

    2012-01-01

    Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F′m), while elevated temperatures (>30°C, only 2°C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (Fv/Fm), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced Fv/Fm and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥1 µg L−1). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures. PMID:22439012

  19. Additive pressures of elevated sea surface temperatures and herbicides on symbiont-bearing foraminifera.

    PubMed

    van Dam, Joost W; Negri, Andrew P; Mueller, Jochen F; Altenburger, Rolf; Uthicke, Sven

    2012-01-01

    Elevated ocean temperatures and agrochemical pollution individually threaten inshore coral reefs, but these pressures are likely to occur simultaneously. Experiments were conducted to evaluate the combined effects of elevated temperature and the photosystem II (PSII) inhibiting herbicide diuron on several types of symbiotic algae (diatom, dinoflagellate or rhodophyte) of benthic foraminifera in hospite. Diuron was shown to evoke a direct effect on photosynthetic efficiency (reduced effective PSII quantum yield ΔF/F'(m)), while elevated temperatures (>30 °C, only 2 °C above current average summer temperatures) were observed to impact photosynthesis more indirectly by causing reductions in maximum PSII quantum yield (F(v)/F(m)), interpreted as photodamage. Additionally, elevated temperatures were shown to cause bleaching through loss of chlorophyll a in foraminifera hosting either diatoms or dinoflagellates. A significant linear correlation was found between reduced F(v)/F(m) and loss of chlorophyll a. In most cases, symbionts within foraminifera proved more sensitive to thermal stress in the presence of diuron (≥ 1 µg L(-1)). The mixture toxicity model of Independent Action (IA) described the combined effects of temperature and diuron on the photosystem of species hosting diatoms or dinoflagellates convincingly and in agreement with probabilistic statistics, so a response additive joint action can be assumed. We thus demonstrate that improving water quality can improve resilience of symbiotic phototrophs to projected increases in ocean temperatures. As IA described the observed combined effects from elevated temperature and diuron stress it may therefore be employed for prediction of untested mixtures and for assessing the efficacy of management measures.

  20. Behaviour during elevated water temperatures: can physiology explain movement of juvenile Atlantic salmon to cool water?

    PubMed

    Breau, Cindy; Cunjak, Richard A; Peake, Stephan J

    2011-07-01

    1. Temperature governs most physiological processes in animals. Ectotherms behaviourally thermoregulate by selecting habitats with temperatures regulating their body temperature for optimal physiological functioning. However, ectotherms can experience temperature extremes forcing the organisms to seek temperature refuge. 2. Fish actively avoid potentially lethal temperatures by moving to cool-water sites created by inflowing tributaries and groundwater seeps. Juvenile Atlantic salmon (Salmo salar) of different age classes exhibit different behavioural responses to elevated temperatures (>23 °C). Yearling (1+) and 2-year-old (2+) Atlantic salmon often cease feeding, abandon territorial behaviour and swim continuously in aggregations in cool-water sites; whereas young-of-the-year (0+) fish continue defending territories and foraging. 3. This study determined whether the behavioural shift in older individuals (2+) occurred when basal metabolic rate, driven by increasing water temperature, reached the maximum metabolic rate such that anaerobic pathways were recruited to provide energy to support vital processes. Behaviour (feeding and stress responses), oxygen consumption, muscle lactate and glycogen, and circulating blood lactate and glucose concentrations were measured in wild 0+ and 2+ Atlantic salmon acclimated to water temperatures between 16 and 28 °C. 4. Results indicate that oxygen consumption of the 2+ fish increased with temperature and reached a plateau at 24 °C, a temperature that corresponded to cessation of feeding and a significant increase in muscle and blood lactate levels. By contrast, oxygen consumption in 0+ fish did not reach a plateau, feeding continued and muscle lactate did not increase, even at the highest temperatures tested (28 °C). 5. To conclude, the experiment demonstrated that the 0+ and 2+ fish had different physiological responses to the elevated water temperatures. The results suggest that wild 2+ Atlantic salmon employ behavioural

  1. Apparatus for production, measurement and reaction studies of dissociated gases at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Christian, J. D.; Gilbreath, W. P.

    1975-01-01

    An apparatus is described which is used for the controlled production, characterization, and study of dissociated gases in a microwave discharge at elevated temperatures. A unique feature is the ability to produce and study a microwave discharge plasma in the heated zone. This allows elevated temperature reactions to be studied in high concentrations of dissociated gases. Further, the system permits weight change measurements of specimens in the plasma, thus facilitating reaction rate determinations. Included is a description of a cavity for use on a 50-mm diameter cylindrical reactor. The effects of flow rate, pressure, temperature, power, metal sample, and sampling position on dissociation percentage of oxygen in the apparatus are described as well as a technique for sample temperature measurements in the plasma which permits determination of high temperature recombination coefficients and reaction rates.

  2. High-resolution absorption cross sections of C2H6 at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Hargreaves, Robert J.; Buzan, Eric; Dulick, Michael; Bernath, Peter F.

    2015-11-01

    Infrared absorption cross sections near 3.3 μm have been obtained for ethane, C2H6. These were acquired at elevated temperatures (up to 773 K) using a Fourier transform infrared spectrometer and tube furnace with a resolution of 0.005 cm-1. The integrated absorption was calibrated using composite infrared spectra taken from the Pacific Northwest National Laboratory (PNNL). These new measurements are the first high-resolution infrared C2H6 cross sections at elevated temperatures.

  3. Reliability and life prediction of ceramic composite structures at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Duffy, Stephen F.; Gyekenyesi, John P.

    1994-01-01

    Methods are highlighted that ascertain the structural reliability of components fabricated of composites with ceramic matrices reinforced with ceramic fibers or whiskers and subject to quasi-static load conditions at elevated temperatures. Each method focuses on a particular composite microstructure: whisker-toughened ceramics, laminated ceramic matrix composites, and fabric reinforced ceramic matrix composites. In addition, since elevated service temperatures usually involve time-dependent effects, a section dealing with reliability degradation as a function of load history has been included. A recurring theme throughout this chapter is that even though component failure is controlled by a sequence of many microfailure events, failure of ceramic composites will be modeled using macrovariables.

  4. Mechanisms of fatigue crack growth in Ti-48Al at ambient and elevated temperature

    SciTech Connect

    Soboyejo, W.O.; Mercer, C.; Aswath, P.B.

    1995-10-01

    Gamma-based titanium aluminides are of practical interest due to their potential to replace nickel- and cobalt-based alloys in aeroengines. The results of a study of crack-tip deformation on the mechanisms of fatigue crack growth in a model powder metallurgy (P/M) gamma-based titanium aluminide intermetallic (Ti-48Al) are presented in this paper. Note that compositions are quoted in atomic % unless stated otherwise. Crack-tip deformation is shown to occur by a combination of deformation-induced twinning and conventional slip at room temperature, and conventional reversed plasticity/slip only at elevated temperature (700 C). Differences between crack-tip deformation mechanisms at room- and elevated-temperature are explained by crack-tip transmission electron microscopy (TEM) analysis. The potential effects of twin toughening are also quantified using optical interference measurements of twin process zones and micromechanical models. The implications of the different crack-tip deformation mechanisms for cyclic irreversibility are discussed for crack growth at room- and elevated-temperature. The results suggest that slower fatigue crack growth rates at elevated-temperature are due to differences in crack-tip deformation and closure mechanisms.

  5. Physiological, biochemical and molecular responses of the potato (Solanum tuberosum L.) plant to moderately elevated temperature.

    PubMed

    Hancock, Robert D; Morris, Wayne L; Ducreux, Laurence J M; Morris, Jenny A; Usman, Muhammad; Verrall, Susan R; Fuller, John; Simpson, Craig G; Zhang, Runxuan; Hedley, Pete E; Taylor, Mark A

    2014-02-01

    Although significant work has been undertaken regarding the response of model and crop plants to heat shock during the acclimatory phase, few studies have examined the steady-state response to the mild heat stress encountered in temperate agriculture. In the present work, we therefore exposed tuberizing potato plants to mildly elevated temperatures (30/20 °C, day/night) for up to 5 weeks and compared tuber yield, physiological and biochemical responses, and leaf and tuber metabolomes and transcriptomes with plants grown under optimal conditions (22/16 °C). Growth at elevated temperature reduced tuber yield despite an increase in net foliar photosynthesis. This was associated with major shifts in leaf and tuber metabolite profiles, a significant decrease in leaf glutathione redox state and decreased starch synthesis in tubers. Furthermore, growth at elevated temperature had a profound impact on leaf and tuber transcript expression with large numbers of transcripts displaying a rhythmic oscillation at the higher growth temperature. RT-PCR revealed perturbation in the expression of circadian clock transcripts including StSP6A, previously identified as a tuberization signal. Our data indicate that potato plants grown at moderately elevated temperatures do not exhibit classic symptoms of abiotic stress but that tuber development responds via a diversity of biochemical and molecular signals.

  6. Plasma hyperosmolality elevates the internal temperature threshold for active thermoregulatory vasodilation during heat stress in humans.

    PubMed

    Shibasaki, Manabu; Aoki, Ken; Morimoto, Keiko; Johnson, John M; Takamata, Akira

    2009-12-01

    Plasma hyperosmolality delays the response in skin blood flow to heat stress by elevating the internal temperature threshold for cutaneous vasodilation. This elevation could be because of a delayed onset of cutaneous active vasodilation and/or to persistent cutaneous active vasoconstriction. Seven healthy men were infused with either hypertonic (3% NaCl) or isotonic (0.9% NaCl) saline and passively heated by immersing their lower legs in 42 degrees C water for 60 min (room temperature, 28 degrees C; relative humidity, 40%). Skin blood flow was monitored via laser-Doppler flowmetry at sites pretreated with bretylium tosylate (BT) to block sympathetic vasoconstriction selectively and at adjacent control sites. Plasma osmolality was increased by approximately 13 mosmol/kgH(2)O following hypertonic saline infusion and was unchanged following isotonic saline infusion. The esophageal temperature (T(es)) threshold for cutaneous vasodilation at untreated sites was significantly elevated in the hyperosmotic state (37.73 +/- 0.11 degrees C) relative to the isosmotic state (36.63 +/- 0.12 degrees C, P < 0.001). A similar elevation of the T(es) threshold for cutaneous vasodilation was observed between osmotic conditions at the BT-treated sites (37.74 +/- 0.18 vs. 36.67 +/- 0.07 degrees C, P < 0.001) as well as sweating. These results suggest that the hyperosmotically induced elevation of the internal temperature threshold for cutaneous vasodilation is due primarily to an elevation in the internal temperature threshold for the onset of active vasodilation, and not to an enhancement of vasoconstrictor activity.

  7. Seawater acidification and elevated temperature affect gene expression patterns of the pearl oyster Pinctada fucata.

    PubMed

    Liu, Wenguang; Huang, Xiande; Lin, Jianshi; He, Maoxian

    2012-01-01

    Oceanic uptake of anthropogenic carbon dioxide results in decrease in seawater pH and increase in temperature. In this study, we demonstrated the synergistic effects of elevated seawater temperature and declined seawater pH on gene expression patterns of aspein, calmodulin, nacrein, she-7-F10 and hsp70 in the pearl oyster Pinctada fucata. Under 'business-as-usual' scenarios, four treatments were examined: (1) ambient pH (8.10) and ambient temperature (27 °C) (control condition), (2) ambient pH and elevated temperature (+3 °C), (3) declined pH (7.70) and ambient temperature, (4) declined pH and elevated temperature. The results showed that under warming and acidic seawater conditions, expression of aspein and calmodulin showed no significant differences among different time point in condition 8.10 T. But the levels of aspein and calmodulin in conditions 8.10 T+3, 7.70 T and 7.70 T+3, and levels of nacrein, she-7-F10 in all the four treatments changed significantly. Low pH and pH × temperature interaction influenced the expression of aspein and calmodulin significantly after hours 48 and 96. Significant effects of low pH and pH × temperature interaction on the expression of nacrein were observed at hour 96. The expression level of she-7-F10 was affected significantly by pH after hours 48 and 96. The expression of hsp70 was significantly affected by temperature, pH, temperature × pH interaction at hour 6, and by temperature × pH interaction at hour 24. This study suggested that declined pH and pH × temperature interaction induced down regulation of calcification related genes, and the interaction between declined seawater pH and elevated temperature caused up regulation of hsp70 in P. facata. These results demonstrate that the declined seawater pH and elevated temperature will impact the physiological process, and potentially the adaptability of P. fucata to future warming and acidified ocean.

  8. Effect of temperature elevation on rabbit cochlear function as measured by distortion-product otoacoustic emissions.

    PubMed

    Noyes, W S; McCaffrey, T V; Fabry, D A; Robinette, M S; Suman, V J

    1996-12-01

    Low-intensity laser stapedotomy has been shown to produce temperature elevations of 3 degrees to 4 degrees C within the cochlea. This study investigates the effect of temperature elevations in this range on cochlear outer hair cell function by use of distortion-product otoacoustic emissions in rabbits. Using esophageal temperature monitoring, we compared 2f1-f2 distortion-product otoacoustic emissions over a range of frequencies (1806 to 8691 Hz) at rabbit normothermia, normothermia plus 3 degrees C, and normothermia after passive cooling. Cochlear temperature was found to exceed changes in esophageal temperature by as much as 1.2 degrees C. We found that a maximum of 3 degrees C elevation in esophageal temperature did not permanently impair outer hair cell function in the rabbit cochlea. Results of this study suggest that moderate changes in cochlear temperature, such as those produced by low-intensity CO2 and holmium-yttrium aluminum garnet lasers, may not produce irreversible thermal damage to the cochlear outer hair cells.

  9. Compartment-specific transcriptomics in a reef-building coral exposed to elevated temperatures.

    PubMed

    Mayfield, Anderson B; Wang, Yu-Bin; Chen, Chii-Shiarng; Lin, Chung-Yen; Chen, Shu-Hwa

    2014-12-01

    Although rising ocean temperatures threaten scleractinian corals and the reefs they construct, certain reef corals can acclimate to elevated temperatures to which they are rarely exposed in situ. Specimens of the model Indo-Pacific reef coral Pocillopora damicornis collected from upwelling reefs of Southern Taiwan were previously found to have survived a 36-week exposure to 30°C, a temperature they encounter infrequently and one that can elicit the breakdown of the coral-dinoflagellate (genus Symbiodinium) endosymbiosis in many corals of the Pacific Ocean. To gain insight into the subcellular pathways utilized by both the coral hosts and their mutualistic Symbiodinium populations to acclimate to this temperature, mRNAs from both control (27°C) and high (30°C)-temperature samples were sequenced on an Illumina platform and assembled into a 236 435-contig transcriptome. These P. damicornis specimens were found to be ~60% anthozoan and 40% microbe (Symbiodinium, other eukaryotic microbes, and bacteria), from an mRNA-perspective. Furthermore, a significantly higher proportion of genes from the Symbiodinium compartment were differentially expressed after two weeks of exposure. Specifically, at elevated temperatures, Symbiodinium populations residing within the coral gastrodermal tissues were more likely to up-regulate the expression of genes encoding proteins involved in metabolism than their coral hosts. Collectively, these transcriptome-scale data suggest that the two members of this endosymbiosis have distinct strategies for acclimating to elevated temperatures that are expected to characterize many of Earth's coral reefs in the coming decades.

  10. Light, temperature and nutrients as factors in photosynthetic adjustment to elevated carbon dioxide

    SciTech Connect

    Bunce, J.; Lee, D. )

    1991-05-01

    It has been noted many times that the short-term stimulation of photosynthesis by elevated carbon dioxide usually observed in C3 plants may not persist in the long-term. Experiments were designed to test the hypotheses that photosynthetic adjustment to elevated carbon dioxide is due to (a) feedback inhibition resulting from excess photosynthate production relative to use, and (b) nutrient deficiency resulting from more rapid growth. Soybeans and sugarbeets were grown in controlled environment chambers at 350 and 700 ppm carbon dioxide, at two temperatures, two levels of photosynthetically active radiation, and with three nutrient regimes in a factorial design. Net carbon dioxide uptake rates of individual leaves from all growth conditions were measured at both 350 and 700 ppm carbon dioxide to assay photosynthetic adjustment to the elevated carbon dioxide. Growth at elevated carbon dioxide reduced rates of photosynthesis measured at standard carbon dioxide levels in both species. Photosynthetic rates measured at 350 ppm were lower on average by 33% in sugarbeet and 23% in soybean after growth at elevated carbon dioxide. Photosynthetic adjustment to elevated carbon dioxide was not greater after growth at 1.0 than 0.5 mmol m{sup {minus}2}s{sup {minus}1} PPFD, was not greater at 20 than 25C growth temperature, and could not be overcome by high rates of nutrient application. These results do not support either the feedback inhibition nor nutrient deficiency hypotheses of photosynthetic adjustment to elevated carbon dioxide. In soybeans, complete photosynthetic adjustment could be induced by a single night at elevated carbon dioxide.

  11. Control of infectious Hematopoietic Necrosis virus disease by elevating the water temperature

    USGS Publications Warehouse

    Amend, Donald F.

    1970-01-01

    Studies were performed to determine if increasing water temperatures could control infectious hematopoietic necrosis virus (IHN) disease in sockeye salmon (Oncorhynchus nerka). Mortalities could be prevented if the water temperature was raised to at least 18 C within the first 24 hr after infection of the fish and if the fish were maintained at this temperature for 4–6 days. The disease did not recur after the elevated temperature treatment, but the fish would still contract the disease if they were reinfected. Reasons for the protecting action are discussed.

  12. Improved Mechanical Properties of Various Fabric-Reinforced Geocomposite at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Samal, Sneha; Phan Thanh, Nhan; Petríková, Iva; Marvalová, Bohadana

    2015-07-01

    This article signifies the improved performance of the various types of fabric reinforcement of geopolymer as a function of physical, thermal, mechanical, and heat-resistant properties at elevated temperatures. Geopolymer mixed with designed Si:Al ratios of 15.6 were synthesized using three different types of fabric reinforcement such as carbon, E-glass, and basalt fibers. Heat testing was conducted on 3-mm-thick panels with 15 × 90 mm surface exposure region. The strength of carbon-based geocomposite increased toward a higher temperature. The basalt-reinforced geocomposite strength decreased due to the catastrophic failure in matrix region. The poor bridging effect and dissolution of fabric was observed in the E-glass-reinforced geocomposite. At an elevated temperature, fiber bridging was observed in carbon fabric-reinforced geopolymer matrix. Among all the fabrics, carbon proved to be suitable candidate for the high-temperature applications in thermal barrier coatings and fire-resistant panels.

  13. "Ultra"-Fast Fracture Strength of Advanced Structural Ceramic Materials Studied at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Gyekenyesi, John P.

    1999-01-01

    The accurate determination of inert strength is important in reliable life prediction of structural ceramic components. At ambient temperature, the inert strength of a brittle material is typically regarded as free of the effects of slow crack growth due to stress corrosion. Therefore, the inert strength can be determined either by eliminating active species, especially moisture, with an appropriate inert medium, or by using a very high test rate. However, at elevated temperatures, the concept or definition of the inert strength of brittle ceramic materials is not clear, since temperature itself is a degrading environment, resulting in strength degradation through slow crack growth and/or creep. Since the mechanism to control strength is rate-dependent viscous flow, the only conceivable way to determine the inert strength at elevated temperatures is to utilize a very fast test rate that either minimizes the time for or eliminates slow crack growth. Few experimental studies have measured the elevated-temperature, inert (or "ultra"-fast fracture) strength of advanced ceramics. At the NASA Lewis Research Center, an experimental study was initiated to better understand the "ultra"-fast fracture strength behavior of advanced ceramics at elevated temperatures. Fourteen advanced ceramics - one alumina, eleven silicon nitrides, and two silicon carbides - have been tested using constant stress-rate (dynamic fatigue) testing in flexure with a series of stress rates including the "ultra"-fast stress rate of 33 000 MPa/sec with digitally controlled test frames. The results for these 14 advanced ceramics indicate that, notwithstanding possible changes in flaw populations as well as flaw configurations because of elevated temperatures, the strength at 33 000 MPa/sec approached the room-temperature strength or reached a higher value than that determined at the conventional test rate of 30 MPa/sec. On the basis of the experimental data, it can be stated that the elevated-temperature

  14. Elucidating the Effect of Alloying Elements on the Behavior of Austenitic Stainless Steels at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Naghizadeh, Meysam; Mirzadeh, Hamed

    2016-09-01

    The effect of carbon and molybdenum on elevated temperature behavior of austenitic stainless steels was studied. It was revealed that carbon does not alter the overall grain coarsening behavior but molybdenum significantly retards the growth of grains toward higher temperatures and slower kinetics and effectively increases the grain growth activation energy due to an interaction energy between Mo and grain boundaries. These observations were based on especial activation energy plots, which facilitate the interpretation of results.

  15. Response of Hawaiian and other Indo-Pacific reef corals to elevated temperature

    NASA Astrophysics Data System (ADS)

    Jokiel, P. L.; Coles, S. L.

    1990-04-01

    Loss of symbiotic zooxanthellae, or “bleaching” is one of the first visible signs of thermal stress. Critical threshold temperatures for coral bleaching vary geographically, but can be expressed universally as fixed increments relative to the historical mean local summer maximum. Bleaching can be induced by short-term exposure (i.e. 1 2 days) at temperature elevations of 3°C to 4°C above normal summer ambient or by long-term exposure (i.e. several weeks) at elevations of 1°C to 2°C. Corals in both tropical and subtropical locations live at temperatures close to their lethal limits during the summer months. Temperature elevations above summer ambient, but still below the bleaching threshold, can impair growth and reproduction. Temperature and light interact synergistically; high light accelerates bleaching caused by elevated temperature. Bleaching susceptibility is correlated with respiration rate. Any factor that increases respiration (such as high incident light) accelerates bleaching at higher temperatures. Ultraviolet (UV) radiation is a detrimental factor associated with solar radiation. Increased UV due to thinning of the earth's protective ozone layer may aggravate bleaching and mortality caused by global warming. A warming trend in Hawaiian waters has been observed over the past decade. In 1986, 1987 and 1988 Hawaiian corals were perilously close to their bleaching threshold during the summer months, and localized bleachings did occur. In some cases, local warming of surface water on shallow reef flats exceeded this threshold temperature and caused localized coral bleaching. In other cases, heating of large mesoscale eddies in the lee of the larger islands apparently caused wide-scale bleaching of the most sensitive coral species ( Pocillopora meandrina) to depths of 20 m. A continuation of the warming trend in Hawaii would lead to mass bleachings similar to those observed recently in other geographic locations.

  16. Feasibility demonstration of a hyperfiltration technique to reclaim shower wastewater at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Hester, J. C.; Brandon, C. A.

    1972-01-01

    A feasibility demonstration of a hyperfiltration technique to determine its capability to reclaim shower wastewater at elevated temperature was conducted. Approximately twenty (20) gallons of typical shower water were processed through a dynamically formed membrane at a temperature of 167 F. Chemical and bacterial analyses of the product water are presented which show compliance with all potable water requirements established for extended manned space missions. In addition, subsystem characteristics and capabilities are discussed.

  17. Temperature and competition between bull trout and brook trout: A test of the elevation refuge hypothesis.

    Technology Transfer Automated Retrieval System (TEKTRAN)

    We tested the elevation refuge hypothesis that colder water temperatures impart a competitive advantage to bull trout Salvelinus confluentus and thus account for increased biotic resistance to invasion and displacement by brook trout S. fontinalis in headwater streams. Growth, survival, and behavio...

  18. The analysis of fatigue crack growth mechanism and oxidation and fatigue life at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Liu, H. W.

    1988-01-01

    Two quantitative models based on experimentally observed fatigue damage processes have been made: (1) a model of low cycle fatigue life based on fatigue crack growth under general-yielding cyclic loading; and (2) a model of accelerated fatigue crack growth at elevated temperatures based on grain boundary oxidation. These two quantitative models agree very well with the experimental observations.

  19. CHARACTERISTICS OF MERCURY DESORPTION FROM SORBENTS AT ELEVATED TEMPERATURES. (R826694C697)

    EPA Science Inventory

    This study investigated the dynamic desorption characteristics of mercury during the thermal treatment of mercury-loaded sorbents at elevated temperatures under fixed-bed operations. Experiments were carried out in a 25.4 mm ID quartz bed enclosed in an electric furnace. ...

  20. CHARACTERISTICS OF MERCURY DESORPTION FROM SORBENTS AT ELEVATED TEMPERATURES. (R822721C697)

    EPA Science Inventory

    This study investigated the dynamic desorption characteristics of mercury during the thermal treatment of mercury-loaded sorbents at elevated temperatures under fixed-bed operations. Experiments were carried out in a 25.4 mm ID quartz bed enclosed in an electric furnace. ...

  1. Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The chemistry of whey protein concentrate (WPC) under adverse storage conditions was monitored to provide information on shelf life in hot, humid areas. WPC34 (34.9 g protein/100 g) and WPC80 (76.8 g protein/100 g) were stored for up to 18 mo under ambient conditions and at elevated temperature and...

  2. ELEVATED CO2 AND TEMPERATURE ALTER NITROGEN ALLOCATION IN DOUGLAS-FIR

    EPA Science Inventory

    The effects of elevated CO2 and temperature on principal carbon constituents (PCC) and C and N allocation between needle, woody (stem and branches) and root tissue of Pseudotsuga menziesii Mirb. Franco seedlings were determined. The seedlings were grown in sun-lit controlled-envi...

  3. Carbohydrate concentrations and freezing stress resistance of silver birch buds grown under elevated temperature and ozone.

    PubMed

    Riikonen, Johanna; Kontunen-Soppela, Sari; Vapaavuori, Elina; Tervahauta, Arja; Tuomainen, Marjo; Oksanen, Elina

    2013-03-01

    The effects of slightly elevated temperature (+0.8 °C), ozone (O3) concentration (1.3 × ambient O3 concentration) and their combination on over-wintering buds of Betula pendula Roth were studied after two growing seasons of exposure in the field. Carbohydrate concentrations, freezing stress resistance (FSR), bud dry weight to fresh weight ratio, and transcript levels of cytochrome oxidase (COX), alternative oxidase (AOX) and dehydrin (LTI36) genes were studied in two clones (clones 12 and 25) in December. Elevated temperature increased the bud dry weight to fresh weight ratio and the ratio of raffinose family oligosaccharides to sucrose and the transcript levels of the dehydrin (LTI36) gene (in clone 12 only), but did not alter the FSR of the buds. Genotype-specific alterations in carbohydrate metabolism were found in the buds grown under elevated O3. The treatments did not significantly affect the transcript level of the COX or AOX genes. No clear pattern of an interactive effect between elevated temperature and O3 concentration was found. According to these data, the increase in autumnal temperatures and slightly increasing O3 concentrations do not increase the risk for freeze-induced damage in winter in silver birch buds, although some alterations in bud physiology occur. PMID:23425688

  4. Immobilization of imidazole moieties in polymer electrolyte composite membrane for elevated temperature fuel cells

    NASA Astrophysics Data System (ADS)

    Li, Ke; Zhou, Bei; Ye, Gongbo; Pan, Mu; Zhang, Haining

    2015-12-01

    Development of membrane electrolyte with reasonable proton conductivity at elevated temperature without external humidification is essential for practical applications of elevated temperature proton exchange membrane fuel cells. Herein, a novel polymer electrolyte composite membrane using imidazole as anhydrous proton carriers for elevated temperature fuel cells is investigated. The imidazole moieties are immobilized inside the Nafion/poly(tetrafluoroethylene) (PTFE) composite membrane through in situ formation of imidazole functionalized silica nanoparticles in Nafion dispersion. The thus-formed membrane exhibits strong Coulombic interaction between negatively charged sulfonic acid groups of Nafion and protonated imidazole moieties, leading to an anhydrous proton conductivity of 0.018 S cm-1 at 180 °C. With the introduction of PTFE matrix, the mechanical strength of the membrane is greatly improved. The peak power density of a single cell assembled from the hybrid membrane is observed to be 130 mW cm-2 under 350 mA cm-2 at 110 °C without external humidification and it remains stable for 20 h continuous operation. The obtained results demonstrate that the developed composite membranes could be utilized as promising membrane electrolytes for elevated temperature fuel cells.

  5. Carbohydrate concentrations and freezing stress resistance of silver birch buds grown under elevated temperature and ozone.

    PubMed

    Riikonen, Johanna; Kontunen-Soppela, Sari; Vapaavuori, Elina; Tervahauta, Arja; Tuomainen, Marjo; Oksanen, Elina

    2013-03-01

    The effects of slightly elevated temperature (+0.8 °C), ozone (O3) concentration (1.3 × ambient O3 concentration) and their combination on over-wintering buds of Betula pendula Roth were studied after two growing seasons of exposure in the field. Carbohydrate concentrations, freezing stress resistance (FSR), bud dry weight to fresh weight ratio, and transcript levels of cytochrome oxidase (COX), alternative oxidase (AOX) and dehydrin (LTI36) genes were studied in two clones (clones 12 and 25) in December. Elevated temperature increased the bud dry weight to fresh weight ratio and the ratio of raffinose family oligosaccharides to sucrose and the transcript levels of the dehydrin (LTI36) gene (in clone 12 only), but did not alter the FSR of the buds. Genotype-specific alterations in carbohydrate metabolism were found in the buds grown under elevated O3. The treatments did not significantly affect the transcript level of the COX or AOX genes. No clear pattern of an interactive effect between elevated temperature and O3 concentration was found. According to these data, the increase in autumnal temperatures and slightly increasing O3 concentrations do not increase the risk for freeze-induced damage in winter in silver birch buds, although some alterations in bud physiology occur.

  6. Elevated-temperature fracture resistances of monolithic and composite ceramics using chevron-notched bend tests

    NASA Technical Reports Server (NTRS)

    Ghosh, Asish; Jenkins, Michael G.; Ferber, Mattison K.; Peussa, Jouko; Salem, Jonathan A.

    1992-01-01

    The quasi-static fracture behaviors of monolithic ceramics (SiC, Si3N4, MgAl2O4), self-reinforced monoliths (acicular grained Si3N4, acicular grained mullite), and ceramic matrix composites (SiC whisker/Al2O3 matrix, TiB2 particulate/SiC matrix, SiC fiber/CVI SiC matrix, Al2O3 fiber/CVI SiC matrix) were measured over the temperature range of 20 to 1400 C. The chevron notched, bend bar test geometry was essential for characterizing the elevated temperature fracture resistances of this wide range of quasi-brittle materials during stable crack growth. Fractography revealed the differences in the fracture behavior of the different materials at the various temperatures. The fracture resistances of the self-reinforced monoliths were comparable to those of the composites and the fracture mechanisms were found to be similar at room temperature. However at elevated temperatures the differences of the fracture behavior became apparent where the superior fracture resistance of the self-reinforced monoliths were attributed to the minor amounts of glassy, intergranular phases which were often more abundant in the composites and affected the fracture behavior when softened by elevated temperatures.

  7. Static tensile and tensile creep testing of five ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Zimmerman, Richard S.; Adams, Donald F.

    1989-01-01

    Static tensile and tensile creep testing of five ceramic fibers at elevated temperature was performed. J.P. Stevens, Co., Astroquartz 9288 glass fiber; Nippon Carbon, Ltd., (Dow Corning) nicalon NLM-102 silicon carbide fiber; and 3M Company Nextel 312, 380, and 480 alumina/silica/boria fibers were supplied in unsized tows. Single fibers were separated from the tows and tested in static tension and tensile creep. Elevated test temperatures ranged from 400 C to 1300 C and varied for each fiber. Room temperature static tension was also performed. Computer software was written to reduce all single fiber test data into engineering constants using ASTM Standard Test Method D3379-75 as a reference. A high temperature furnace was designed and built to perform the single fiber elevated temperature testing up to 1300 C. A computerized single fiber creep apparatus was designed and constructed to perform four fiber creep tests simultaneously at temperatures up to 1300 C. Computer software was written to acquire and reduce all creep data.

  8. Static tensile and tensile creep testing of five ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Zimmerman, Richard S.; Adams, Donald F.

    1988-01-01

    Static tensile and tensile creep testing of five ceramic fibers at elevated temperature was performed. J.P. Stevens, Co., Astroquartz 9288 glass fiber, Nippon Carbon, Ltd., (Dow Corning) Nicalon NLM-102 silicon carbide fiber, and 3M Company Nextel 312, 380, and 480 alumina/silica/boria fibers were supplied in unsized tows. Single fibers were separated from the tows and tested in static tension and tensile creep. Elevated test temperatures ranged from 400 to 1300 C and varied for each fiber. Room temperature static tension was also performed. Computer software was written to reduce all single fiber test data into engineering constants using ASTM Standard Test Method D3379-75 as a reference. A high temperature furnace was designed and built to perform the single fiber elevated temperature testing up to 1300 C. A computerized single fiber creep apparatus was designed and constructed to perform four fiber creep tests simultaneously at temperatures up to 1300 C. Computer software was written to acquire and reduce all creep data.

  9. Enhancement of photoheterotrophic biohydrogen production at elevated temperatures by the expression of a thermophilic clostridial hydrogenase.

    PubMed

    Lo, Shou-Chen; Shih, Shau-Hua; Chang, Jui-Jen; Wang, Chun-Ying; Huang, Chieh-Chen

    2012-08-01

    The working temperature of a photobioreactor under sunlight can be elevated above the optimal growth temperature of a microorganism. To improve the biohydrogen productivity of photosynthetic bacteria at higher temperatures, a [FeFe]-hydrogenase gene from the thermophile Clostridium thermocellum was expressed in the mesophile Rhodopseudomonas palustris CGA009 (strain CGA-CThydA) using a log-phase expression promoter P( pckA ) to drive the expression of heterogeneous hydrogenase gene. In contrast, a mesophilic Clostridium acetobutylicum [FeFe]-hydrogenase gene was also constructed and expressed in R. palustris (strain CGA-CAhydA). Both transgenic strains were tested for cell growth, in vivo hydrogen production rate, and in vitro hydrogenase activity at elevated temperatures. Although both CGA-CThydA and CGA-CAhydA strains demonstrated enhanced growth over the vector control at temperatures above 38 °C, CGA-CThydA produced more hydrogen than the other strains. The in vitro hydrogenase activity assay, measured at 40 °C, confirmed that the activity of the CGA-CThydA hydrogenase was higher than the CGA-CAhydA hydrogenase. These results showed that the expression of a thermophilic [FeFe]-hydrogenase in R. palustris increased the growth rate and biohydrogen production at elevated temperatures. This transgenic strategy can be applied to a broad range of purple photosynthetic bacteria used to produce biohydrogen under sunlight.

  10. Expression profiling of potato cultivars with contrasting tuberization at elevated temperature using microarray analysis.

    PubMed

    Singh, Anupama; Siddappa, Sunderasha; Bhardwaj, Vinay; Singh, Brajesh; Kumar, Devendra; Singh, Bir Pal

    2015-12-01

    Temperature is one of the most significant factors affecting potato yield. Night temperature beyond 18-22 °C drastically reduces tuber formation, constraining potato cultivation in tropics and subtropics. Identification of genes and pathways affected by high temperature is crucial for developing thermo tolerant cultivars for these regions. In the present study, two cultivars with contrasting tuberization behavior at night temperatures (24 °C) were selected for gene expression analysis using a customized microarray chip representing 39,031 potato genes. A total of 2500 genes were differentially expressed on 21 d and 4096 genes on 14 d after stress. Gene ontology and pathway analysis provided insights into the probable biological processes and pathways governing tuberization at elevated temperature. Pathway maps were constructed to graphically represent the gene expression patterns. Genes associated with photosynthesis, hormonal activity, sugar transporters and transcription factors were differentially expressed. The results are presented and discussed in terms of tuberization at high temperature. The effect of high temperature on expression of genes controlling tuberization was also analyzed. This study provided useful information on potato tuberization at elevated temperature and make available a framework for further investigations into heat stress in potato.

  11. Dry Sliding Wear Behavior of Hafnium-Based Bulk Metallic Glass at Room and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Keshri, Anup Kumar; Behl, Lovish; Lahiri, Debrupa; Dulikravich, George S.; Agarwal, Arvind

    2016-09-01

    Dry sliding wear behavior of hafnium-based bulk metallic glass was studied at two loads (5 and 15 N) and two temperatures (298 and 673 K) using aluminum oxide (Al2O3) ball as a wear counterpart. At 5 N load, wear reduced by ~71% on increasing the temperature from 298 to 673 K. At a higher load of 15 N, the weight loss reduction was much lower (45%) on increasing the temperature from 298 to 673 K. Decreased wear weight loss on increasing the temperature was attributed to the increased hardness of the Hf-based metallic glass at high temperatures. Micro-hardness of the alloy at 293 K was found to be 636 Hv, which gradually increased to 655 Hv on annealing at 673 K. Improvement in the hardness at elevated temperature is attributed to: (1) free volume annihilation, (2) surface oxide formation and (3) nano-crystallites precipitation. Reduced wear at elevated temperature resulted in smaller volume of debris generation that restricted three-body wear to obtain lower coefficient of friction (COF) (0.25-0.35) compared to COF (0.65-0.75) at room temperature.

  12. Dry Sliding Wear Behavior of Hafnium-Based Bulk Metallic Glass at Room and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Keshri, Anup Kumar; Behl, Lovish; Lahiri, Debrupa; Dulikravich, George S.; Agarwal, Arvind

    2016-07-01

    Dry sliding wear behavior of hafnium-based bulk metallic glass was studied at two loads (5 and 15 N) and two temperatures (298 and 673 K) using aluminum oxide (Al2O3) ball as a wear counterpart. At 5 N load, wear reduced by ~71% on increasing the temperature from 298 to 673 K. At a higher load of 15 N, the weight loss reduction was much lower (45%) on increasing the temperature from 298 to 673 K. Decreased wear weight loss on increasing the temperature was attributed to the increased hardness of the Hf-based metallic glass at high temperatures. Micro-hardness of the alloy at 293 K was found to be 636 Hv, which gradually increased to 655 Hv on annealing at 673 K. Improvement in the hardness at elevated temperature is attributed to: (1) free volume annihilation, (2) surface oxide formation and (3) nano-crystallites precipitation. Reduced wear at elevated temperature resulted in smaller volume of debris generation that restricted three-body wear to obtain lower coefficient of friction (COF) (0.25-0.35) compared to COF (0.65-0.75) at room temperature.

  13. Photosynthetic response to elevated temperature in the symbiotic dinoflagellate Symbiodinium microadriaticum in culture.

    PubMed Central

    Iglesias-Prieto, R; Matta, J L; Robins, W A; Trench, R K

    1992-01-01

    Elevated temperature (28-34 degrees C) has been hypothesized as the primary cause of the loss of algal endosymbionts in coral reef-associated invertebrates, a phenomenon observed on a world-wide scale over the last decade. In past studies of this "bleaching" phenomenon, there has been an underlying assumption that temperature adversely affects the animal hosts, the algae thereby being relegated to a more passive role. Because photosynthesis is a sensitive indicator of thermal stress in plants and has a central role in the nutrition of symbiotic invertebrates, we have tested the hypothesis that elevated temperature adversely affects photosynthesis in the symbiotic dinoflagellate Symbiodinium microadriaticum. The results, based on analyses of light-mediated O2 evolution and in vivo fluorescence, indicate that photosynthesis is impaired at temperatures above 30 degrees C and ceases completely at 34-36 degrees C. These observations are discussed in the context of possible mechanisms that may function in the disassociation of algal-invertebrate symbioses in response to elevated temperature. PMID:11607337

  14. Nanoparticle distribution and temperature elevations in prostatic tumours in mice during magnetic nanoparticle hyperthermia.

    PubMed

    Attaluri, Anilchandra; Ma, Ronghui; Qiu, Yun; Li, Wei; Zhu, Liang

    2011-01-01

    Among a variety of hyperthermia methods, magnetic nanoparticle hyperthermia is a highly promising approach for its confined heating within the tumour. In this study we perform in vivo animal experiments on implanted prostatic tumours in mice to measure temperature distribution in the tumour during magnetic nanoparticle hyperthermia. Temperature elevations are induced by a commercially available ferrofluid injected via a single injection to the centre of the tumour, when the tumour is subject to an alternating magnetic field. Temperature mapping in the tumours during magnetic nanoparticle hyperthermia has demonstrated the feasibility of elevating tumour temperatures higher than 50°C using only 0.1 cm(3) ferrofluid injected in the tumour under a relatively low magnetic field (3 kA/m). Detailed 3-D nanoparticle concentration distribution is quantified using a high-resolution microCT imaging system. The calculated nanoparticle distribution volume based on the microCT scans is useful to analyse nanoparticle deposition in the tumours. Slower ferrofluid infusion rates result in smaller nanoparticle distribution volumes in the tumours. Nanoparticles are more confined in the vicinity of the injection site with slower infusion rates, causing higher temperature elevations in the tumours. The increase in the nanoparticle distribution volume in the tumour group after the heating from that in the tumour group without heating suggests possible nanoparticle re-distribution in the tumours during the heating. PMID:21756046

  15. Viscoelastoplastic Deformation and Damage Response of Titanium Alloy, Ti-6Al-4V, at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Lerch, Bradley A.; Saleeb, Atef F.; Kasemer, Matthew P.

    2013-01-01

    Time-dependent deformation and damage behavior can significantly affect the life of aerospace propulsion components. Consequently, one needs an accurate constitutive model that can represent both reversible and irreversible behavior under multiaxial loading conditions. This paper details the characterization and utilization of a multi-mechanism constitutive model of the GVIPS class (Generalized Viscoplastic with Potential Structure) that has been extended to describe the viscoelastoplastic deformation and damage of the titanium alloy Ti-6Al-4V. Associated material constants were characterized at five elevated temperatures where viscoelastoplastic behavior was observed, and at three elevated temperatures where damage (of both the stiffness reduction and strength reduction type) was incurred. Experimental data from a wide variety of uniaxial load cases were used to correlate and validate the proposed GVIPS model. Presented are the optimized material parameters, and the viscoelastoplastic deformation and damage responses at the various temperatures.

  16. Effects of elevated temperature postharvest on color aspect, physiochemical characteristics, and aroma components of pineapple fruits.

    PubMed

    Liu, Chuanhe; Liu, Yan

    2014-12-01

    In this work, 2 separate experiments were performed to describe the influence of elevated temperature treatments postharvest on the color, physiochemical characteristics and aroma components of pineapple fruits during low-temperature seasons. The L* (lightness) values of the skin and pulp of pineapple fruits were decreased. The a* (greenness-redness) and b* (blueness-yellowness) values of the skin and pulp were all markedly increased. The elevated temperature significantly increased the contents of total soluble solids (TSS) and slightly affected contents of vitamin C (nonsignificant). Titratable acidity (TA) of pineapple fruits were notably decreased, whereas the values of TSS/TA of pineapple fruits were significantly increased. The firmness of the pineapple fruits decreased and more esters and alkenes were identified. The total relative contents of esters were increased, and the total relative contents of alkenes were decreased.

  17. Microstructural stability of wrought, laser and electron beam glazed NARloy-Z alloy at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Singh, J.; Jerman, G.; Bhat, B.; Poorman, R.

    1993-01-01

    Microstructure of wrought, laser, and electron-beam glazed NARloy-Z(Cu-3 wt.% Ag-0.5 wt.% Zr) was investigated for thermal stability at elevated temperatures (539 to 760 C (1,100 to 1,400 F)) up to 94 h. Optical and scanning electron microscopy and electron probe microanalysis were employed for studying microstructural evolution and kinetics of precipitation. Grain boundary precipitation and precipitate free zones (PFZ's) were observed in the wrought alloy after exposing to temperatures above 605 C (1,120 F). The fine-grained microstructure observed in the laser and electron-beam glazed NARloy-Z was much more stable at elevated temperatures. Microstructural changes correlated well with hardness measurements.

  18. Warming Amplification of Minimum and Maximum Temperatures over High-Elevation Regions across the Globe

    PubMed Central

    Wang, Mengben; Jiménez, Claudia Villarroel

    2015-01-01

    An analysis of the annual mean temperature (TMEAN) (1961–2010) has revealed that warming amplification (altitudinal amplification and regional amplification) is a common feature of major high-elevation regions across the globe against the background of global warming since the mid-20th century. In this study, the authors further examine whether this holds for annual mean minimum temperature (TMIN) and annual mean maximum temperature (TMAX) (1961–2010) on a global scale. The extraction method of warming component of altitude, and the paired region comparison method were used in this study. Results show that a significant altitudinal amplification trend in TMIN (TMAX) is detected in all (four) of the six high-elevation regions tested, and the average magnitude of altitudinal amplification trend for TMIN (TMAX) [0.306±0.086 °C km-1(0.154±0.213 °C km-1)] is substantially larger (smaller) than TMEAN (0.230±0.073 °C km-1) during the period 1961–2010. For the five paired high- and low-elevation regions available, regional amplification is detected in the four high-elevation regions for TMIN and TMAX (respectively or as a whole). Qualitatively, highly (largely) consistent results are observed for TMIN (TMAX) compared with those for TMEAN. PMID:26461461

  19. Shape of isolated domains in lithium tantalate single crystals at elevated temperatures

    SciTech Connect

    Shur, V. Ya. Akhmatkhanov, A. R.; Baturin, I. S.; Chezganov, D. S.; Lobov, A. I.; Smirnov, M. M.

    2013-12-09

    The shape of isolated domains has been investigated in congruent lithium tantalate (CLT) single crystals at elevated temperatures and analyzed in terms of kinetic approach. The obtained temperature dependence of the growing domain shape in CLT including circular shape at temperatures above 190 °C has been attributed to increase of relative input of isotropic ionic conductivity. The observed nonstop wall motion and independent domain growth after merging in CLT as opposed to stoichiometric lithium tantalate have been attributed to difference in wall orientation. The computer simulation has confirmed applicability of the kinetic approach to the domain shape explanation.

  20. [Effects of drought stress, high temperature and elevated CO2 concentration on the growth of winter wheat].

    PubMed

    Si, Fu-Yan; Qiao, Yun-Zhou; Jiang, Jing-Wei; Dong, Bao-Di; Shi, Chang-Hai; Liu, Meng-Yu

    2014-09-01

    The impacts of climate change on the grain yield, photosynthesis, and water conditions of winter wheat were assessed based on an experiment, in which wheat plants were subjected to ambient and elevated CO2 concentrations, ambient and elevated temperatures, and low and high water conditions independently and in combination. The CO2 enrichment alone had no effect on the photosynthesis of winter wheat, whereas higher temperature and drought significantly decreased the photosynthetic rate. Water conditions in flag leaves were not significantly changed at the elevated CO2 concentration or elevated temperature. However, drought stress decreased the relative water content in flag leaves, and the combination of elevated temperature and drought reduced the water potential in flag leaves. The combination of elevated CO2 concentration, elevated temperature, and drought significantly reduced the photosynthetic rate and water conditions, and led to a 41.4% decrease in grain yield. The elevated CO2 concentration alone increased the grain yield by 21.2%, whereas the elevated temperature decreased the grain yield by 12.3%. The grain yield was not affected by the combination of elevated CO2 concentration and temperature, but the grain yield was significantly decreased by the drought stress if combined with any of the climate scenarios applied in this study. These findings suggested that maintaining high soil water content might be a vital means of reducing the potential harm caused by the climate change.

  1. Elevated temperature crack growth in aluminum alloys: Tensile deformation of 2618 and FVS0812 aluminum alloys

    NASA Technical Reports Server (NTRS)

    Leng, Yang; Gangloff, Richard P.

    1990-01-01

    Understanding the damage tolerance of aluminum alloys at elevated temperatures is essential for safe applications of advanced materials. The objective of this project is to investigate the time dependent subcritical cracking behavior of powder metallurgy FVS0812 and ingot metallurgy 2618 aluminum alloys at elevated temperatures. The fracture mechanics approach was applied. Sidegrooved compact tension specimens were tested at 175, 250, and 316 C under constant load. Subcritical crack growth occurred in each alloy at applied stress intensity levels (K) of between about 14 and 25 MPa/m, well below K (sub IC). Measured load, crack opening displacement and displacement rate, and crack length and growth rate (da/dt) were analyzed with several continuum fracture parameters including, the C-integral, C (sub t), and K. Elevated temperature growth rate data suggest that K is a controlling parameter during time dependent cracking. For FVS0812, da/dt is highest at 175 C when rates are expressed as a function of K. While crack growth rate is not controlled by C (sub t) at 175 C, da/dt appears to better correlate with C (sub t) at higher temperatures. Creep brittle cracking at intermediate temperatures, and perhaps related to strain aging, is augmented by time dependent transient creep plasticity at higher temperatures. The C (sub t) analysis is, however, complicated by the necessity to measure small differences in the elastic crack growth and creep contributions to the crack opening displacement rate. A microstructural study indicates that 2618 and FVS0812 are likely to be creep brittle materials, consistent with the results obtained from the fracture mechanics study. Time dependent crack growth of 2618 at 175 C is characterized by mixed transgranular and intergranular fracture. Delamination along the ribbon powder particle boundaries occurs in FVS0812 at all temperatures. The fracture mode of FVS0812 changes with temperature. At 175 C, it is characterized as dimpled rupture

  2. The vegetative buds of Salix myrsinifolia are responsive to elevated UV-B and temperature.

    PubMed

    Sivadasan, Unnikrishnan; Randriamanana, Tendry R; Julkunen-Tiitto, Riitta; Nybakken, Line

    2015-08-01

    The predicted rise in temperature and variable changes in ultraviolet-B radiation will have marked effects on plant growth and metabolism. Different vegetative parts of trees have been studied to detect the impacts of enhanced temperature and UV-B, but the effects on buds have rarely been considered. In the present study, Salix myrsinifolia clones were subjected to enhanced UV-B and temperature over two growing seasons starting from 2009, and measured springtime bud development and concentrations of phenolic compounds. In 2010 and 2011 the buds under increased temperature were up to 30% longer than those in control plots. On the other hand, UV-B combined with elevated temperature significantly decreased bud length by 4-5% in 2010. This effect was stronger in males than in females. The vegetative buds contained high constitutive amounts of chlorogenic acid derivatives, which may explain the weak increase in hyperin and chlorogenic acid that are usual UV-B sheltering compounds. The elevated temperature treatment significantly increased salicin content (about 18% in males and 22% in females), while triandrin concentration decreased by only 50% in females. Our results indicate that vegetative bud size is highly affected by seasonal temperature, while UV-B induced a weaker and transient effect. PMID:25749271

  3. Physiological acclimation to elevated temperature in a reef-building coral from an upwelling environment

    NASA Astrophysics Data System (ADS)

    Mayfield, A. B.; Fan, T.-Y.; Chen, C.-S.

    2013-12-01

    Recent work has found that pocilloporid corals from regions characterized by unstable temperatures, such as those exposed to periodic upwelling, display a remarkable degree of phenotypic plasticity. In order to understand whether important reef builders from these upwelling reefs remain physiologically uncompromised at temperatures they will experience in the coming decades as a result of global climate change, a long-term elevated temperature experiment was conducted with Pocillopora damicornis specimens collected from Houbihu, a small embayment within Nanwan Bay, southern Taiwan that is characterized by 8-9 °C temperature changes during upwelling events. Upon nine months of exposure to nearly 30 °C, all colony (mortality and surface area), polyp ( Symbiodinium density and chlorophyll a content), tissue (total thickness), and molecular (gene expression and molecular composition)-level parameters were documented at similar levels between experimental corals and controls incubated at 26.5 °C, suggesting that this species can readily acclimate to elevated temperatures that cause significant degrees of stress, or even bleaching and mortality, in conspecifics of other regions of the Indo-Pacific. However, the gastrodermal tissue layer was relatively thicker in corals of the high temperature treatment sampled after nine months, possibly as an adaptive response to shade Symbiodinium from the higher photosynthetically active radiation levels that they were experiencing at that sampling time. Such shading may have prevented high light and high temperature-induced photoinhibition, and consequent bleaching, in these samples.

  4. ELEVATED TEMPERATURE SENSORS FOR ON-LINE CRITICAL EQUIPMENT HEALTH MONITORING

    SciTech Connect

    James Sebastian

    2005-03-01

    The objective of this research program is to improve high temperature piezoelectric aluminum nitride (AlN) sensor technology to make it useful for instrumentation and health monitoring of current and future electrical power generation equipment. The program will extend the temperature range of the sensor from approximately 700 C to above 1000 C, and ultrasonic coupling to objects at these temperatures will be investigated and tailored for use with the sensor. The chemical vapor deposition (CVD) AlN deposition process was successfully transferred from film production on tungsten carbide substrates to titanium alloy and silicon carbide (SiC) substrates in the first year of the program, and additional substrates were evaluated. In the second year of the program, additional substrate research was performed with the goal of improving the performance of using SiC substrates. While greatly improved bandwidth was achieved, sensor survival at elevated temperature remains problematic. The elevated temperature coupling work continued with significant experimentation. Molten glasses were found to work within a limited temperature range, but metal foils applied with heat and pressure were found to have superior performance overall. The final year of the program will be dedicated to making further advances in AlN/ substrate behavior, and the design and implementation of a sensor demonstration experiment at very high temperature in a simulated industrial application.

  5. Study on the Relationship between Delayed Fluorescence and Photosynthetic Capability at Elevated Temperature in Higher Plants

    NASA Astrophysics Data System (ADS)

    Li, Ying; Xu, Wenhai; Wang, Junsheng; Xing, Da

    2011-01-01

    With the continuous elevation of the global temperature, high-temperature stress has been a major environmental factor that affects plant growth and productivity. Effects of short-term heat temperature stress on light-induced delayed fluorescence (DF) decay kinetic curve, intensity and emission spectrum have been investigated in C3 soybean (Jing Huang No.3) and C4 maize (Yun Xi No.5081) species. The temperature responses of DF decay kinetic curve from two different species show that decay rate characteristics are affected by high temperature. The spectroscopy measurements indicate that heat stress influence the shape of DF emission spectra of two species, especially the peak intensities at 685nm and 730nm. Moreover, our results clearly demonstrate that DF intensity of each plant positively correlated with F730/F685 of DF emission spectra at elevated temperatures. In addition, the net photosynthetic rate (Pn) of samples has the same temperature response with DF intensity and F730/F685. Based on these results, we can conclude that there is an excellent correlation between F730/F685 of DF emission spectra, DF intensity and Pn in both C3 and C4 plants. Therefore, we proposed that the F730/F685 of DF emission spectrum can be used to measure the photosynthetic capability of higher plants to heat stress.

  6. The vegetative buds of Salix myrsinifolia are responsive to elevated UV-B and temperature.

    PubMed

    Sivadasan, Unnikrishnan; Randriamanana, Tendry R; Julkunen-Tiitto, Riitta; Nybakken, Line

    2015-08-01

    The predicted rise in temperature and variable changes in ultraviolet-B radiation will have marked effects on plant growth and metabolism. Different vegetative parts of trees have been studied to detect the impacts of enhanced temperature and UV-B, but the effects on buds have rarely been considered. In the present study, Salix myrsinifolia clones were subjected to enhanced UV-B and temperature over two growing seasons starting from 2009, and measured springtime bud development and concentrations of phenolic compounds. In 2010 and 2011 the buds under increased temperature were up to 30% longer than those in control plots. On the other hand, UV-B combined with elevated temperature significantly decreased bud length by 4-5% in 2010. This effect was stronger in males than in females. The vegetative buds contained high constitutive amounts of chlorogenic acid derivatives, which may explain the weak increase in hyperin and chlorogenic acid that are usual UV-B sheltering compounds. The elevated temperature treatment significantly increased salicin content (about 18% in males and 22% in females), while triandrin concentration decreased by only 50% in females. Our results indicate that vegetative bud size is highly affected by seasonal temperature, while UV-B induced a weaker and transient effect.

  7. Implications of High Temperature and Elevated CO2 on Flowering Time in Plants.

    PubMed

    Jagadish, S V Krishna; Bahuguna, Rajeev N; Djanaguiraman, Maduraimuthu; Gamuyao, Rico; Prasad, P V Vara; Craufurd, Peter Q

    2016-01-01

    Flowering is a crucial determinant for plant reproductive success and seed-set. Increasing temperature and elevated carbon-dioxide (e[CO2]) are key climate change factors that could affect plant fitness and flowering related events. Addressing the effect of these environmental factors on flowering events such as time of day of anthesis (TOA) and flowering time (duration from germination till flowering) is critical to understand the adaptation of plants/crops to changing climate and is the major aim of this review. Increasing ambient temperature is the major climatic factor that advances flowering time in crops and other plants, with a modest effect of e[CO2].Integrated environmental stimuli such as photoperiod, temperature and e[CO2] regulating flowering time is discussed. The critical role of plant tissue temperature influencing TOA is highlighted and crop models need to substitute ambient air temperature with canopy or floral tissue temperature to improve predictions. A complex signaling network of flowering regulation with change in ambient temperature involving different transcription factors (PIF4, PIF5), flowering suppressors (HvODDSOC2, SVP, FLC) and autonomous pathway (FCA, FVE) genes, mainly from Arabidopsis, provides a promising avenue to improve our understanding of the dynamics of flowering time under changing climate. Elevated CO2 mediated changes in tissue sugar status and a direct [CO2]-driven regulatory pathway involving a key flowering gene, MOTHER OF FT AND TFL1 (MFT), are emerging evidence for the role of e[CO2] in flowering time regulation.

  8. Spatiotemporal variability of increasing temperature impacts on grassland vegetation along an elevation transect in the Alps

    NASA Astrophysics Data System (ADS)

    Niedrist, Georg; Obojes, Nikolaus; Bertoldi, Giacomo; Della Chiesa, Stefano; Tasser, Erich; Tappeiner, Ulrike

    2013-04-01

    Different manipulative approaches have been developed to study and quantify impacts of temperature increase on grassland ecosystems. Many of them share the problem of unwanted effects on the surrounding microclimatic conditions. Transplantation of grassland mesocosms along elevation gradients can be a realistic alternative, although with some restrictions. Here we present 3 years of data from a double-transplant-experiment, were 70*70*20cm grassland turves were transplanted at two elevations from 2000m to 1500m a.s.l. and from 1500m to 1000m a.s.l. respectively, along an inner-alpine elevation gradient in the Vinschgau Valley (South Tyrol, I). All donor and receiving sites are comparable regarding land use (meadows), soil conditions or exposition and are located within a few km's distance ensuring comparable weather conditions apart from the intended air temperature (0.54°K/100m) and annual precipitation (20mm/100m) lapse rate. Phytodiversity and above ground net primary production (ANPP) of the transplanted mesocosms were assessed and compared with locally transplanted monoliths of the respective donor site. Furthermore, growth dynamics was continuously observed throughout the vegetation season with a non-destructive method based on measurement of light (photosynthetic active radiation) extinction within the canopy. After 3 years no significant changes in absolute species numbers has been detected at all, whereas slight variations have been observed regarding species composition. Those shifts could be differentiated both to transplantation artifacts and effects of the elevated temperature. Total aboveground phytomass, unsurprisingly, showed higher values on transplanted (lower) mesocosms, however: data from single cuts and growth rate analysis reveal differing effects between the two transplantation steps as well as over the course of the vegetation period. Transplanted plots from 2000m to 1500m showed continuously higher productivity from spring to autumn

  9. Behavior and survival of Mytilus congeners following episodes of elevated body temperature in air and seawater.

    PubMed

    Dowd, W Wesley; Somero, George N

    2013-02-01

    Coping with environmental stress may involve combinations of behavioral and physiological responses. We examined potential interactions between adult mussels' simple behavioral repertoire - opening/closing of the shell valves - and thermal stress physiology in common-gardened individuals of three Mytilus congeners found on the West Coast of North America: two native species (M. californianus and M. trossulus) and one invasive species from the Mediterranean (M. galloprovincialis). We first continuously monitored valve behavior over three consecutive days on which body temperatures were gradually increased, either in air or in seawater. A temperature threshold effect was evident between 25 and 33°C in several behavioral measures. Mussels tended to spend much less time with the valves in a sealed position following exposure to 33°C body temperature, especially when exposed in air. This behavior could not be explained by decreases in adductor muscle glycogen (stores of this metabolic fuel actually increased in some scenarios), impacts of forced valve sealing on long-term survival (none observed in a second experiment), or loss of contractile function in the adductor muscles (individuals exhibited as many or more valve adduction movements following elevated body temperature compared with controls). We hypothesize that this reduced propensity to seal the valves following thermal extremes represents avoidance of hypoxia-reoxygenation cycles and concomitant oxidative stress. We further conjecture that prolonged valve gaping following episodes of elevated body temperature may have important ecological consequences by affecting species interactions. We then examined survival over a 90 day period following exposure to elevated body temperature and/or emersion, observing ongoing mortality throughout this monitoring period. Survival varied significantly among species (M. trossulus had the lowest survival) and among experimental contexts (survival was lowest after experiencing

  10. Transcriptome and biomineralization responses of the pearl oyster Pinctada fucata to elevated CO2 and temperature

    PubMed Central

    Li, Shiguo; Liu, Chuang; Huang, Jingliang; Liu, Yangjia; Zhang, Shuwen; Zheng, Guilan; Xie, Liping; Zhang, Rongqing

    2016-01-01

    Ocean acidification and global warming have been shown to significantly affect the physiological performances of marine calcifiers; however, the underlying mechanisms remain poorly understood. In this study, the transcriptome and biomineralization responses of Pinctada fucata to elevated CO2 (pH 7.8 and pH 7.5) and temperature (25 °C and 31 °C) are investigated. Increases in CO2 and temperature induced significant changes in gene expression, alkaline phosphatase activity, net calcification rates and relative calcium content, whereas no changes are observed in the shell ultrastructure. “Ion and acid-base regulation” related genes and “amino acid metabolism” pathway respond to the elevated CO2 (pH 7.8), suggesting that P. fucata implements a compensatory acid-base mechanism to mitigate the effects of low pH. Additionally, “anti-oxidation”-related genes and “Toll-like receptor signaling”, “arachidonic acid metabolism”, “lysosome” and “other glycan degradation” pathways exhibited responses to elevated temperature (25 °C and 31 °C), suggesting that P. fucata utilizes anti-oxidative and lysosome strategies to alleviate the effects of temperature stress. These responses are energy-consuming processes, which can lead to a decrease in biomineralization capacity. This study therefore is important for understanding the mechanisms by which pearl oysters respond to changing environments and predicting the effects of global climate change on pearl aquaculture. PMID:26732540

  11. Electrospun melamine resin-based multifunctional nonwoven membrane for lithium ion batteries at the elevated temperatures

    NASA Astrophysics Data System (ADS)

    Wang, Qingfu; Yu, Yong; Ma, Jun; Zhang, Ning; Zhang, Jianjun; Liu, Zhihong; Cui, Guanglei

    2016-09-01

    A flame retardant and thermally dimensional stable membrane with high permeability and electrolyte wettability can overcome the safety issues of lithium ion batteries (LIBs) at elevated temperatures. In this work, a multifunctional thermoset nonwoven membrane composed of melamine formaldehyde resin (MFR) nano-fibers was prepared by a electro-spinning method. The resultant porous nonwoven membrane possesses superior permeability, electrolyte wettability and thermally dimensional stability. Using the electrospun MFR membrane, the LiFePO4/Li battery exhibits high safety and stable cycling performance at the elevated temperature of 120 °C. Most importantly, the MFR membrane contains lone pair electron in the nitrogen element, which can chelate with Mn2+ ions and suppress their transfer across the separator. Therefore, the LiMn2O4/graphite cells with the electrospun MFR multifunctional membranes reveal an improved cycle performance even at high temperature. This work demonstrated that electrospun MFR is a promising candidate material for high-safety separator of LIBs with stable cycling performance at elevated temperatures.

  12. Transcriptome and biomineralization responses of the pearl oyster Pinctada fucata to elevated CO2 and temperature

    NASA Astrophysics Data System (ADS)

    Li, Shiguo; Liu, Chuang; Huang, Jingliang; Liu, Yangjia; Zhang, Shuwen; Zheng, Guilan; Xie, Liping; Zhang, Rongqing

    2016-01-01

    Ocean acidification and global warming have been shown to significantly affect the physiological performances of marine calcifiers; however, the underlying mechanisms remain poorly understood. In this study, the transcriptome and biomineralization responses of Pinctada fucata to elevated CO2 (pH 7.8 and pH 7.5) and temperature (25 °C and 31 °C) are investigated. Increases in CO2 and temperature induced significant changes in gene expression, alkaline phosphatase activity, net calcification rates and relative calcium content, whereas no changes are observed in the shell ultrastructure. “Ion and acid-base regulation” related genes and “amino acid metabolism” pathway respond to the elevated CO2 (pH 7.8), suggesting that P. fucata implements a compensatory acid-base mechanism to mitigate the effects of low pH. Additionally, “anti-oxidation”-related genes and “Toll-like receptor signaling”, “arachidonic acid metabolism”, “lysosome” and “other glycan degradation” pathways exhibited responses to elevated temperature (25 °C and 31 °C), suggesting that P. fucata utilizes anti-oxidative and lysosome strategies to alleviate the effects of temperature stress. These responses are energy-consuming processes, which can lead to a decrease in biomineralization capacity. This study therefore is important for understanding the mechanisms by which pearl oysters respond to changing environments and predicting the effects of global climate change on pearl aquaculture.

  13. Elevated temperature viscous remanent magnetization of natural and synthetic multidomain magnetite

    NASA Technical Reports Server (NTRS)

    Kelso, Paul R.; Banerjee, Subir K.

    1994-01-01

    The time-temperature relationship of magnetization is a subject of much interest and debate by paleomagnetists, rock magnetists, and magnetic anomaly modellers. We have investigated this relationship by studying the viscous remanent magnetization (VRM) of coarse-grained multidomain (MD) magnetite. Our experiments covered the temperature range from 22 to 400 C, times from minutes to months, and included both Australian granulite samples and multidomain magnetite samples synthesized by the glass ceramic method. VRM acquisition was found to generally increase with temperature but not always at the rate predicted from classical thermal fluctuation theories. Thermal cycling between room temperature (at which the measurements were made) and the VRM acquisition temperature sharply decreased the temperature dependence of the VRM. Room temperature VRM acquisition accelerates with time when plotted on a semilog plot, whereas at elevated temperature the curves are quasilinear against log(time) for both the natural and synthetic samples. This change in behavior may suggest a variation in the VRM acquisition mechanism as a function of temperature for MD magnetite. The granulites have a nearly linear increase in VRM acquisition rate with temperature whereas the glass ceramics display little change in the acquisition rate between 22 and 200 C, but increase by nearly a factor of 3 by 400 C. The increase in VRM of the glass ceramics between 200 and 400 C is in general qualitative agreement with thermal fluctuation theory. There was no systematic change in the rate of VRM acquisition with grain size for the multidomain magnetites used in this study. Elevated temperature (e.g., 400 C) VRM acquisition by the deep crustal granulites, if extrapolated over the Brunhes chron, would produce a magnetization of several A/m which, if true, is of the order required by models for the source of long-wavelength magnetic anomalies.

  14. The effect of elevated temperature on Barley yellow dwarf virus-PAV in wheat.

    PubMed

    Nancarrow, Narelle; Constable, Fiona E; Finlay, Kyla J; Freeman, Angela J; Rodoni, Brendan C; Trebicki, Piotr; Vassiliadis, Simone; Yen, Alan L; Luck, Jo E

    2014-06-24

    Barley yellow dwarf virus-PAV (BYDV-PAV) is associated with yellow dwarf disease, one of the most economically important diseases of cereals worldwide. In this study, the impact of current and future predicted temperatures for the Wimmera wheat growing district in Victoria, Australia on the titre of BYDV-PAV in wheat was investigated. Ten-day old wheat (Triticum aestivum, cv. Yitpi) seedlings were inoculated with BYDV-PAV and grown at ambient (5.0-16.1°C, night-day) or elevated (10.0-21.1°C, night-day) temperature treatments, simulating the current Wimmera average and future daily temperature cycles, respectively, during the wheat-growing season. Whole above-ground plant samples were collected from each temperature treatment at 0 (day of inoculation), 3, 6, 9, 12, 15, 18, 21 and 24 days after inoculation and the titre of BYDV-PAV was measured in each sample using a specific one-step multiplex normalised reverse transcription quantitative PCR (RT-qPCR) assay. Physical measurements, including plant height, dry weight and tiller number, were also taken at each sampling point. The titre of BYDV-PAV was significantly greater in plants grown in the elevated temperature treatment than in plants grown in the ambient treatment on days 6, 9 and 12. Plants grown at elevated temperature were significantly bigger and symptoms associated with BYDV-PAV were visible earlier than in plants grown at ambient temperature. These results may have important implications for the epidemiology of yellow dwarf disease under future climates in Australia.

  15. The effect of elevated temperature on Barley yellow dwarf virus-PAV in wheat.

    PubMed

    Nancarrow, Narelle; Constable, Fiona E; Finlay, Kyla J; Freeman, Angela J; Rodoni, Brendan C; Trebicki, Piotr; Vassiliadis, Simone; Yen, Alan L; Luck, Jo E

    2014-06-24

    Barley yellow dwarf virus-PAV (BYDV-PAV) is associated with yellow dwarf disease, one of the most economically important diseases of cereals worldwide. In this study, the impact of current and future predicted temperatures for the Wimmera wheat growing district in Victoria, Australia on the titre of BYDV-PAV in wheat was investigated. Ten-day old wheat (Triticum aestivum, cv. Yitpi) seedlings were inoculated with BYDV-PAV and grown at ambient (5.0-16.1°C, night-day) or elevated (10.0-21.1°C, night-day) temperature treatments, simulating the current Wimmera average and future daily temperature cycles, respectively, during the wheat-growing season. Whole above-ground plant samples were collected from each temperature treatment at 0 (day of inoculation), 3, 6, 9, 12, 15, 18, 21 and 24 days after inoculation and the titre of BYDV-PAV was measured in each sample using a specific one-step multiplex normalised reverse transcription quantitative PCR (RT-qPCR) assay. Physical measurements, including plant height, dry weight and tiller number, were also taken at each sampling point. The titre of BYDV-PAV was significantly greater in plants grown in the elevated temperature treatment than in plants grown in the ambient treatment on days 6, 9 and 12. Plants grown at elevated temperature were significantly bigger and symptoms associated with BYDV-PAV were visible earlier than in plants grown at ambient temperature. These results may have important implications for the epidemiology of yellow dwarf disease under future climates in Australia. PMID:24374266

  16. Influence of elevated temperature and acid mine drainage on mortality of the crayfish Cambarus bartonii

    USGS Publications Warehouse

    Hartman, K.J.; Hom, C.D.; Mazik, P.M.

    2010-01-01

    Effects of elevated temperature and acid mine drainage (AMD) on crayfish mortality were investigated in the Stony River, Grant County, West Virginia. During summers 2003 and 2004, four-week in situ bioassays were performed along a thermal and AMD gradient with the native crayfish Cambarus bartonii. Crayfish mortality was analyzed in conjunction with temperature and AMD related variables (pH, specific conductivity). Mortality was significantly higher (48-88%) at sites with high temperatures during 2003 (max = 33.0??C), but no significant differences were observed in 2004 (max = 32.0??C). Temperatures were higher in 2003 than 2004 due to increased discharge from a cooling reservoir flowing into the river. Additionally, duration of high temperature was approximately four days in 2003 as compared with only one day in 2004. No significant relationship between acid mine drainage variables and crayfish mortality was apparent.

  17. Increasing testicular temperature by exposure to elevated ambient temperatures restores spermatogenesis in adult Utp14b (jsd) mutant (jsd) mice.

    PubMed

    Comish, P B; Liang, L Y; Yamauchi, Y; Weng, C C; Shetty, G; Naff, K A; Ward, M A; Meistrich, M L

    2015-03-01

    Because mutations in the human UTP14C gene are associated with male infertility, we sought to develop a method for fertility restoration in azoospermic mice with a mutation in the orthologous Utp14b(jsd) (jsd) gene that have spermatogonial arrest. The method is based on our observation that elevation of testicular temperatures restores spermatogonial differentiation in jsd mutant mice. To non-surgically raise intrascrotal temperatures we placed these mice in incubators at different elevated ambient temperatures. Exposure of jsd/jsd mice to ambient temperatures of 34.5 °C or 35.5 °C for 24 days increased the proportion of tubules with spermatocytes from 0% in untreated controls to over 80%. As those higher temperatures interfere with spermatid differentiation, the mice were then transferred to incubators at 32-32.5 °C for the next 24 days. These environments allowed differentiation to progress, resulting in up to 42% of tubules having late spermatids and about half of the mutant mice having spermatozoa in testicular suspensions. When these spermatozoa were used in intracytoplasmic sperm injection, all gave rise to viable healthy offspring with normal weight gain and fertility. The successful restoration of fertility in Utp14b mutant mice suggests that transient testicular warming might also be useful for spermatogenesis recovery in infertile men with UTP14C gene mutations.

  18. Duration of Exposure to Elevated Temperature Affects Competitive Interactions in Juvenile Reef Fishes

    PubMed Central

    Warren, Donald T.; Donelson, Jennifer M.; McCormick, Mark I.; Ferrari, Maud C. O.; Munday, Philip L.

    2016-01-01

    Climate change will affect key ecological processes that structure natural communities, but the outcome of interactions between individuals and species will depend on their thermal plasticity. We tested how short- and long-term exposure to projected future temperatures affects intraspecific and interspecific competitive interactions in two species of coral reef damselfishes. In conspecific contests, juvenile Ambon damselfish, Pomacentrus amboinensis, exhibited no change in aggressive interactions after 4d exposure to higher temperatures. However, after 90d of exposure, fish showed a nonadaptive reduction in aggression at elevated temperatures. Conversely, 4d exposure to higher temperature increased aggression towards conspecifics in the lemon damselfish, Pomacentrus moluccensis. 90d exposure began to reduce this pattern, but overall there was little effect of temperature. Aggression in interspecific contests increased with short-term exposure, but was significantly lower after long-term exposure indicative of acclimation. Our results show how the length of exposure to elevated temperature can affect the outcome of competitive interactions. Furthermore, we illustrate that results from intraspecific contests may not accurately predict interspecific interactions, which will challenge our ability to generalise the effects of warming on competitive interactions. PMID:27736924

  19. Elevated Ambient Temperature Differentially Affects Virus Resistance in Two Tobacco Species.

    PubMed

    Ma, L; Huang, X; Yu, R; Jing, X L; Xu, J; Wu, C A; Zhu, C X; Liu, H M

    2016-01-01

    Antiviral defense of plants is usually enhanced by an elevated temperature under natural conditions. In order to better understand this phenomenon, we carried out temperature shift experiments with Nicotiana glutinosa plants that were infected with Potato virus X (PVX) or the necrotic strain of Potato virus Y (PVY(N)). The virus titer of the plants was found to be much lower when they were maintained at 30°C compared with 22°C, particularly in the upper leaves. PVX resistance at 30°C persisted for a short period even when temperature was shifted back to 22°C. In contrast, N. benthamiana lost the virus resistance immediately after the temperature dropped to 22°C. Expression analysis of two RNA-dependent RNA polymerases in N. glutinosa (NgRDR) showed that a 12-day treatment at 30°C increased the expression of NgRDR1, while NgRDR6 was not affected. In addition, the NgRDR6 mRNA level correlated with the PVX titer but was unaffected by PVY(N) infection. These observations indicate that PVX and PVY(N), although they are both RNA viruses, might trigger different defense responses at elevated temperatures. Our study provides valuable data for a better understanding of the temperature-regulated host virus interaction. PMID:26474332

  20. Deformation and fracture characteristics of Inconel X-750 at room temperature and elevated temperatures

    SciTech Connect

    Mills, W.J.

    1980-06-01

    Electron fractographic and thin foil electron metallographic techniques were used to evaluate the deformation and fracture characteristics of Inconel X-750 at temperatures ranging from 24 to 816/sup 0/C. Operative dislocation mechanisms and fracture surface morphologies were related to the overall tensile response of this nickel-base superalloy. At room temperature, failure occurred primarily by an intergranular dimple rupture mechanism associated with microvoid coalescence along grain boundary denuded regions. A fairly high density of dislocations throughout the matrix resulted in relatively high ductility levels even though failure occurred by an intergranular mechanism. Under intermediate temperature conditions (316 to 427/sup 0/C), increased transgranular fracture coupled with extensive dislocation activity within the Inconel X-750 matrix caused a slight increase in ductility. At progressively higher temperatures, 538 to 704/sup 0/C, all dislocation activity was channeled through narrow slip bands which subsequently initiated localized separation and resulted in a very faceted fracture surface appearance. The absence of a homogeneous dislocation substructure in this temperature regime resulted in a severe degradation in ductility levels. At the highest test temperature (816/sup 0/C), a uniform dislocation network throughout the Inconel X-750 matrix coupled with intense dislocation activity in the grain boundary denuded zone resulted in a marked improvement in ductility. Furthermore, the extensive dislocation activity along grain boundary regions ultimately resulted in an intergranular fracture morphology.

  1. Fatigue crack growth at elevated temperature 316 stainless steel and H-13 steel

    NASA Technical Reports Server (NTRS)

    Chen, W. C.; Liu, H. W.

    1976-01-01

    Crack growths were measured at elevated temperatures under four types of loading: pp, pc, cp, and cc. In H-13 steel, all these four types of loading gave nearly the same crack growth rates, and the length of hold time had negligible effects. In AISI 316 stainless steel, the hold time effects on crack growth rate were negligible if the loading was tension-tension type; however, these effects were significant in reversed bending load, and the crack growth rates under these four types of loading varied considerably. Both tensile and compressive hold times caused increased crack growth rate, but the compressive hold period was more deleterious than the tensile one. Metallographic examination showed that all the crack paths under different types of loading were largely transgranular for both CTS tension-tension specimens and SEN reversed cantilever bending specimens. In addition, an electric potential technique was used to monitor crack growth at elevated temperature.

  2. Comparative performance of geopolymers made with metakaolin and fly ash after exposure to elevated temperatures

    SciTech Connect

    Kong, Daniel L.Y.; Sanjayan, Jay G. Sagoe-Crentsil, Kwesi

    2007-12-15

    This paper presents the results of a study on the effect of elevated temperatures on geopolymers manufactured using metakaolin and fly ash of various mixture proportions. Both types of geopolymers (metakaolin and fly ash) were synthesized with sodium silicate and potassium hydroxide solutions. The strength of the fly ash-based geopolymer increased after exposure to elevated temperatures (800 deg. C). However, the strength of the corresponding metakaolin-based geopolymer decreased after similar exposure. Both types of geopolymers were subjected to thermogravimetric, scanning electron microscopy and mercury intrusion porosimetry tests. The paper concludes that the fly ash-based geopolymers have large numbers of small pores which facilitate the escape of moisture when heated, thus causing minimal damage to the geopolymer matrix. On the other hand, metakaolin geopolymers do not possess such pore distribution structures. The strength increase in fly ash geopolymers is also partly attributed to the sintering reactions of un-reacted fly ash particles.

  3. Constitutive Modeling and Testing of Polymer Matrix Composites Incorporating Physical Aging at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Veazie, David R.

    1998-01-01

    Advanced polymer matrix composites (PMC's) are desirable for structural materials in diverse applications such as aircraft, civil infrastructure and biomedical implants because of their improved strength-to-weight and stiffness-to-weight ratios. For example, the next generation military and commercial aircraft requires applications for high strength, low weight structural components subjected to elevated temperatures. A possible disadvantage of polymer-based composites is that the physical and mechanical properties of the matrix often change significantly over time due to the exposure of elevated temperatures and environmental factors. For design, long term exposure (i.e. aging) of PMC's must be accounted for through constitutive models in order to accurately assess the effects of aging on performance, crack initiation and remaining life. One particular aspect of this aging process, physical aging, is considered in this research.

  4. Evaluation of weldment creep and fatigue strength-reduction factors for elevated-temperature design

    SciTech Connect

    Corum, J.M.

    1989-01-01

    New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plants components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results of a series of long-term, confirmatory, creep-rupture and fatigue tests of simple welded structures. The structures (welded plates and tubes) were made of 316 stainless steel base metal and 16-8-2 weld filler metal. Overall, the results provide further substantiation of the validity of the strength-reduction factor approach for ensuring adequate life in elevated-temperature nuclear component weldments. 16 refs., 7 figs.

  5. An assessment of buffer strips for improving damage tolerance of composite laminates at elevated temperature

    NASA Technical Reports Server (NTRS)

    Bigelow, C. A.

    1981-01-01

    Buffer strips greatly improve the damage tolerance of graphite/epoxy laminates loaded in tension. Graphite/polyimide buffer strip panels were made and tested to determine their residual strength at ambient and elevated (177 C) temperature. Each panel was cut in the center to represent damage. Panels were radiographed and crack-opening displacements were recorded to indicate fracture, fracture arrest, and the extent of damage in the buffer strip after arrest. All panels had the same buffer strip spacing and width. The buffer strip material was 0 deg S-glass/PMR-15. The buffer strips were made by replacing narrow strips of the 0 deg graphite plies with strips of the 0 deg S-glass on either a one-for-one or a two-for-one basis. Half of the panels were heated to 177 + or - 3 C before and during the testing. Elevated temperature did not alter the fracture behavior of the buffer configuration.

  6. FDTD computation of temperature elevation in the elderly for far-field RF exposures.

    PubMed

    Nomura, Tomoki; Laakso, Ilkka; Hirata, Akimasa

    2014-03-01

    Core temperature elevation and perspiration in younger and older adults is investigated for plane-wave exposure at whole-body averaged specific absorption rate of 0.4 W kg(-1). Numeric Japanese male model is considered together with a thermoregulatory response formula proposed in the authors' previous study. The frequencies considered were at 65 MHz and 2 GHz where the total power absorption in humans becomes maximal for the allowable power density prescribed in the international guidelines. From the computational results used here, the core temperature elevation in the older adult model was larger than that in the younger one at both frequencies. The reason for this difference is attributable to the difference of sweating, which is originated from the difference in the threshold activating the sweating and the decline in sweating in the legs.

  7. Growth response and acclimation of CO2 exchange characteristics to elevated temperatures in tropical tree seedlings

    PubMed Central

    Cheesman, Alexander W.; Winter, Klaus

    2013-01-01

    Predictions of how tropical forests will respond to future climate change are constrained by the paucity of data on the performance of tropical species under elevated growth temperatures. In particular, little is known about the potential of tropical species to acclimate physiologically to future increases in temperature. Seedlings of 10 neo-tropical tree species from different functional groups were cultivated in controlled-environment chambers under four day/night temperature regimes between 30/22 °C and 39/31 °C. Under well-watered conditions, all species showed optimal growth at temperatures above those currently found in their native range. While non-pioneer species experienced catastrophic failure or a substantially reduced growth rate under the highest temperature regime employed (i.e. daily average of 35 °C), growth in three lowland pioneers showed only a marginal reduction. In a subsequent experiment, three species (Ficus insipida, Ormosia macrocalyx, and Ochroma pyramidale) were cultivated at two temperatures determined as sub- and superoptimal for growth, but which resulted in similar biomass accumulation despite a 6°C difference in growth temperature. Through reciprocal transfer and temperature adjustment, the role of thermal acclimation in photosynthesis and respiration was investigated. Acclimation potential varied among species, with two distinct patterns of respiration acclimation identified. The study highlights the role of both inherent temperature tolerance and thermal acclimation in determining the ability of tropical tree species to cope with enhanced temperatures. PMID:23873999

  8. Numerical Modeling of Magnesium Alloy Sheet Metal Forming at Elevated Temperature

    SciTech Connect

    Lee, Myeong-Han; Oh, Soo-Ik; Kim, Heon-Young; Kim, Hyung-Jong; Choi, Yi-Chun

    2007-05-17

    The development of light-weight vehicle is in great demand for enhancement of fuel efficiency and dynamic performance. The vehicle weight can be reduced effectively by using lightweight materials such as magnesium alloys. However, the use of magnesium alloys in sheet forming processes is still limited because of their low formability at room temperature and the lack of understanding of the forming process of magnesium alloys at elevated temperatures. In this study, uniaxial tensile tests of the magnesium alloy AZ31B-O at various temperatures were performed to evaluate the mechanical properties of this alloy relevant for forming of magnesium sheets. To construct a FLD (forming limit diagram), a forming limit test were conducted at temperature of 100 and 200 deg. C. For the evaluation of the effects of the punch temperature on the formability of a rectangular cup drawing with AZ31B-O, numerical modelling was conducted. The experiment results indicate that the stresses and possible strains of AZ31B-O sheets largely depend on the temperature. The stress decreases with temperature increase. Also, the strain increase with temperature increase. The numerical modelling results indicate that formability increases with the decrease in the punch temperature at the constant temperature of the die and holder.

  9. Guidelines and procedures for design of Class 1 elevated temperature nuclear system components

    SciTech Connect

    Not Available

    1986-09-01

    This standard provides guidelines and procedures which may be used by the manufacturer in satisfying the requirements given for design of class 1 elevated temperature nuclear system components. Guidance is given regarding planning and control of design analysis. A sequence for calculations is recommended. Methods of analysis, including procedures to account for environmental effects, are given which are acceptable in principle to the owner. A format is provided for use in documentation of design analyses.

  10. The optical functions of silicon at elevated temperatures and their application to pulsed laser annealing

    SciTech Connect

    Jellison, G.E. Jr.; Lowndes, D.H.; Wood, R.F.

    1993-06-01

    The results of measurements of the optical functions of silicon at elevated temperatures are reviewed and the results applied to pulsed laser annealing of silicon. Several optical experiments which were performed to understand the physics of pulsed laser annealing are described, and related to detailed thermal modeling. The fabrication of silicon solar cells using both thermal and laser processing is described, both of which give very goods results.

  11. Mechanical properties of turbine blade alloys in hydrogen at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Deluca, D. P.

    1981-01-01

    The mechanical properties of single crystal turbine blade alloys in a gaseous hydrogen environment were determined. These alloys are proposed for use in space propulsion systems in pure or partial high pressure hydrogen environments at elevated temperatures. Mechanical property tests included: tensile, creep, low fatigue (LCF), and crack growth. Specimens were in both transverse and longitudinal directions relative to the casting solidification direction. Testing was conducted on solid specimens exposed to externally pressurized environments of gaseous hydrogen and hydrogen-enriched steam.

  12. Changes in life history parameters of Rhopalosiphum maidis (Homoptera: Aphididae) under four different elevated temperature and CO2 combinations.

    PubMed

    Xie, Haicui; Zhao, Lei; Wang, Wenqiang; Wang, Zhenying; Ni, Xinzhi; Cai, Wanzhi; He, Kanglai

    2014-08-01

    Biological characteristics of corn leaf aphid, Rhopalosiphum maidis (Fitch), on barley, Hordeum vulgare L., were examined for two generations under four different elevated temperature and CO2 combinations. The developmental duration for each life stage was significantly reduced under the elevated temperature (+4 degrees C). The elevated CO2 (700-750 microl/liter) reduced only the development time of fourth-instar nymph. The overall duration of nymphal stage was reduced in the second generation. Thus, the temperature was the dominant factor to development duration of corn leaf aphid. The fecundity of corn leaf aphid was significantly increased under the elevated temperature and CO2, as well as in the later generation. Elevated temperature and CO2 increased the number of alate production, which may enhance the aphid migration or dispersal and the spread of plant viruses. Corn leaf aphid had the highest intrinsic rate of increase under the elevated temperature and CO2 combination in the second generation. These results indicate that the combined effects of both elevated temperature and CO2 on aphid biology may exacerbate aphid damage on barley under the climate change in accompany with elevated temperature and CO2 level. PMID:25195429

  13. ELEVATED CO2 AND TEMPERATURE ALTER THE ECOSYSTEM C EXCHANGE IN A YOUNG DOUGLAS FIR MESOCOSM EXPERIMENT

    EPA Science Inventory

    We investigated the effects of elevated CO2 (EC) [ambient CO2 (AC) + 190 ppm] and elevated temperature (ET) [ambient temperature (AT) + 3.6 °C] on net ecosystem exchange (NEE) of seedling Douglas fir (Pseudotsuga menziesii) mesocosms. As the study utilized seedlings in reconstruc...

  14. A comparison of deflagration rates, at elevated pressures and temperatures, with thermal explosion results

    NASA Astrophysics Data System (ADS)

    Glascoe, Elizabeth; Springer, H. Keo; Tringe, Joseph W.; Maienschein, Jon L.

    2011-06-01

    Previously, the deflagration rate and behavior of HMX-based explosives have been correlated with the violence of thermal explosion experiments. In particular, HMX materials that experience deconsolidative burning at elevated pressures (i.e. P = 200 - 600 MPa) also produce significantly more violent thermal explosions. Recently, we have measured the deflagration rates of HMX-based explosives at elevated temperatures (i.e. T = 150 - 180C) and moderate pressures (i.e. P = 10 - 100 MPa). These conditions more closely mimic the pressure and temperatures of an explosive shortly after ignition of a thermal explosion. We will discuss the deflagration rates of HMX based explosives at elevated temperatures and make comparisons with thermal explosion studies on the same materials. The Joint DoD-DOE Munitions Technology Development Program is acknowledged for funding. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  15. Effects of intermittent flow and irradiance level on back reef Porites corals at elevated seawater temperatures

    USGS Publications Warehouse

    Smith, L.W.; Birkeland, C.

    2007-01-01

    Corals inhabiting shallow back reef habitats are often simultaneously exposed to elevated seawater temperatures and high irradiance levels, conditions known to cause coral bleaching. Water flow in many tropical back reef systems is tidally influenced, resulting in semi-diurnal or diurnal flow patterns. Controlled experiments were conducted to test effects of semi-diurnally intermittent water flow on photoinhibition and bleaching of the corals Porites lobata and P. cylindrica kept at elevated seawater temperatures and different irradiance levels. All coral colonies were collected from a shallow back reef pool on Ofu Island, American Samoa. In the high irradiance experiments, photoinhibition and bleaching were less for both species in the intermittent high-low flow treatment than in the constant low flow treatment. In the low irradiance experiments, there were no differences in photoinhibition or bleaching for either species between the flow treatments, despite continuously elevated seawater temperatures. These results suggest that intermittent flow associated with semi-diurnal tides, and low irradiances caused by turbidity or shading, may reduce photoinhibition and bleaching of back reef corals during warming events. ?? 2006 Elsevier B.V. All rights reserved.

  16. The flammability limits of hydrogen and methane in air at moderately elevated temperatures

    SciTech Connect

    Ale, B.B.; Wierzba, I.

    1997-12-31

    The flammability limits of hydrogen and methane in air were determined experimentally at elevated initial mixture temperatures up to 350 C at atmospheric pressure for upward flame propagation in a conventional steel test tube apparatus. Additionally, the extent to which a prolonged exposure (i.e., residence time) of the mixture to elevated temperatures before spark ignition and, consequently, the existence of pre-ignition reactions that may influence the value of the lean and rich flammability limits was also investigated. It was shown that the flammability limits for methane widened approximately linearly with an increase in the initial mixture temperature over the whole range of temperatures tested. These limits were not affected by the length of the residence time before spark ignition. Different behavior was observed for flammability limits of hydrogen. They were also widened with an increase in the initial temperature but only up to 200 C. In this initial temperature range the limits were not affected by the length of the residence time. However, at initial temperature exceeding 200 C the flammability limits, especially, the rich limits narrowed with an increase in the temperature and were significantly affected by the residence time before spark ignition. It was suggested that the substantial drop in the value of the rich limit with the increase in the residence time was caused by the relatively low temperature catalytic reactions on the stainless steel surface of the flame tube. Simple method for calculating the hydrogen conversion to water was proposed. The results of calculations are in fair agreement with the experimental evidence.

  17. Cell structural changes in the mesophyll of Norway spruce needles by elevated ozone and elevated temperature in open-field exposure during cold acclimation.

    PubMed

    Kivimäenpää, Minna; Riikonen, Johanna; Sutinen, Sirkka; Holopainen, Toini

    2014-04-01

    The effects of elevated ozone (1.4× ambient) and temperature (ambient +1.3 °C) alone and in combination were studied on the needle cell structure of soil-grown Norway spruce seedlings in the late growing season and winter. Temperature treatment continued over winter and lengthened the snow-free period. Elevated temperature caused microscopic changes related to photosynthesis (decreased chloroplast size and increased number), carbon storage (reduced starch and increased cytoplasmic lipids) and defence (decreased mitochondrial size and proportion per cytoplasm, increased peroxisomes and plastoglobuli, altered appearance of tannins). The results suggest increased oxidative stress by elevated temperature and altered allocation of limited carbon reserve to defence. The number of peroxisomes and plastoglobuli remained high in the outer cells of needles of ozone-exposed seedlings but decreased in the inner cells. This may indicate defence allocation to cells close to the stomata and surface, which are experiencing more oxidative stress. Ozone reduced winter hardiness based on seasonal changes in chloroplast shape and location in the cells. The effects of ozone became evident at the end of the growing season, indicating the effect of cumulative ozone dose or that the seedlings were vulnerable to ozone at the later phases of winter hardening. Elevated temperature increased cellular damage in early winter and visible damage in spring, and the damage was enhanced by ozone. In conclusion, the study suggests that modest air temperature elevation increases stress at the cell structural level in spruce seedlings and is enhanced by low ozone elevation. Future climatic conditions where snow cover is formed later or is lacking but temperatures are low can increase the risk of severe seedling damage, and current and future predicted ozone concentrations increase this risk.

  18. Cell structural changes in the mesophyll of Norway spruce needles by elevated ozone and elevated temperature in open-field exposure during cold acclimation.

    PubMed

    Kivimäenpää, Minna; Riikonen, Johanna; Sutinen, Sirkka; Holopainen, Toini

    2014-04-01

    The effects of elevated ozone (1.4× ambient) and temperature (ambient +1.3 °C) alone and in combination were studied on the needle cell structure of soil-grown Norway spruce seedlings in the late growing season and winter. Temperature treatment continued over winter and lengthened the snow-free period. Elevated temperature caused microscopic changes related to photosynthesis (decreased chloroplast size and increased number), carbon storage (reduced starch and increased cytoplasmic lipids) and defence (decreased mitochondrial size and proportion per cytoplasm, increased peroxisomes and plastoglobuli, altered appearance of tannins). The results suggest increased oxidative stress by elevated temperature and altered allocation of limited carbon reserve to defence. The number of peroxisomes and plastoglobuli remained high in the outer cells of needles of ozone-exposed seedlings but decreased in the inner cells. This may indicate defence allocation to cells close to the stomata and surface, which are experiencing more oxidative stress. Ozone reduced winter hardiness based on seasonal changes in chloroplast shape and location in the cells. The effects of ozone became evident at the end of the growing season, indicating the effect of cumulative ozone dose or that the seedlings were vulnerable to ozone at the later phases of winter hardening. Elevated temperature increased cellular damage in early winter and visible damage in spring, and the damage was enhanced by ozone. In conclusion, the study suggests that modest air temperature elevation increases stress at the cell structural level in spruce seedlings and is enhanced by low ozone elevation. Future climatic conditions where snow cover is formed later or is lacking but temperatures are low can increase the risk of severe seedling damage, and current and future predicted ozone concentrations increase this risk. PMID:24718738

  19. Note: A method for minimizing oxide formation during elevated temperature nanoindentation

    SciTech Connect

    Cheng, I. C.; Hodge, A. M.; Garcia-Sanchez, E.

    2014-09-15

    A standardized method to protect metallic samples and minimize oxide formation during elevated-temperature nanoindentation was adapted to a commercial instrument. Nanoindentation was performed on Al (100), Cu (100), and W (100) single crystals submerged in vacuum oil at 200 °C, while the surface morphology and oxidation was carefully monitored using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The results were compared to room temperature and 200 °C nanoindentation tests performed without oil, in order to evaluate the feasibility of using the oil as a protective medium. Extensive surface characterization demonstrated that this methodology is effective for nanoscale testing.

  20. The Thermal Expansion, Elastic and Fracture Properties of Porous Cordierite at Elevated Temperatures

    SciTech Connect

    Shyam, Amit; Lara-Curzio, Edgar; Pandey, Amit; Watkins, Thomas R; More, Karren

    2012-01-01

    The properties that determine the thermal shock resistance in materials are reported for porous cordierite, a leading candidate material for the fabrication of diesel particulate filters. Fracture toughness and slow crack growth tests were performed on test specimens obtained from the walls of diesel particulate filter monolithic substrates using the double-torsion test method at temperatures between 20 C and 900 C. The thermal expansion and elastic properties were characterized between 20 C and 1000 C. The role of the microstructure of porous cordierite in determining its unusual thermal expansion and elevated temperature Young's modulus and fracture toughness are discussed.

  1. The vacancy in silicon: Identical diffusion properties at cryogenic and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Watkins, George D.

    2008-05-01

    The vacancy contribution to self-diffusion in silicon, recently revealed in the study by Shimitzu et al. [Phys. Rev. Lett. 98, 095901 (2007)], is analyzed to demonstrate that the pre-exponential term, as well as the enthalpy term, matches accurately to that of the isolated neutral vacancy, as determined many years earlier at cryogenic temperatures by electron paramagnetic resonance and deep level transient spectroscopy. The persistent suggestion of an "extended" vacancy with very different migrational properties at elevated temperatures is therefore incorrect. There is only one vacancy.

  2. A falsification of the thermal specialization paradigm: compensation for elevated temperatures in Antarctic fishes

    PubMed Central

    Seebacher, Frank; Davison, William; Lowe, Cara J; Franklin, Craig E

    2005-01-01

    Specialization to a particular environment is one of the main factors used to explain species distributions. Antarctic fishes are often cited as a classic example to illustrate the specialization process and are regarded as the archetypal stenotherms. Here we show that the Antarctic fish Pagothenia borchgrevinki has retained the capacity to compensate for chronic temperature change. By displaying astounding plasticity in cardiovascular response and metabolic control, the fishes maintained locomotory performance at elevated temperatures. Our falsification of the specialization paradigm indicates that the effect of climate change on species distribution and extinction may be overestimated by current models of global warming. PMID:17148152

  3. Large-strain cyclic response and martensitic transformation of austenitic stainless steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Hamasaki, H.; Nakano, T.; Ishimaru, E.; Yoshida, F.

    2016-08-01

    Cyclic tension-compression tests were carried out for austenitic stainless steel (SUS304) at elevated temperatures. The significant Bauschinger effect was found in the obtained stress-strain curve. In addition, stagnation of deformation induced martensitic transformation was observed just after stress reversal until the equivalent stress reached the maximum value in the course of experiment. The constitutive model for SUS304 at room temperature was developed, in which homogenized stress of SUS304 was expressed by the weighed summation of stresses of austenite and martensite phases. The calculated stress-strain curves and predicted martensite volume fraction were well correlated with those experimental results.

  4. Final report of comprehensive testing program for concrete at elevated temperatures

    SciTech Connect

    Oland, C.B.; Naus, D.J.; Robinson, G.C.

    1980-10-01

    The objective of this program was to define the variations in physical (thermal) and mechanical (strength) properties of limestone aggregate concrete and lightweight insulating concrete exposed to elevated temperatures that could occur as a result of a postulated large sodium spill in a lined LMFBR equipment cell. To meet this objective, five test series were conducted: (1) unconfined compression, (2) shear, (3) rebar bond, (4) sustained loading (creep), and (5) thermal properties. Mechanical property results are presented for concretes subjected to temperature up to 621{sup 0}C (1150{sup 0}F).

  5. Small angle neutron scattering from nanocrystalline Pd and Co compacted at elevated temperatures

    SciTech Connect

    Sanders, P.G.; Weertman, J.R.; Barker, J.G.; Siegel, R.W.

    1994-05-01

    Nanocrystalline (n-) Cu and Pd, prepared by inert gas condensation and in situ room temperature (RT) and elevated temperature (warm) compactions, have been studied by small angle neutron scattering (SANS). Previous work on RT compacted and subsequently annealed n-Pd seemed to show that all the scattering could be accounted for by a distribution of pores. Analysis of more extensive SANS measurements, together with results of prompt gamma activation analysis, indicates that the SANS can be explained by the presence of pores and hydrogen. Warm compaction reduces the hydrogen impurity level, while increasing the bulk density and decreasing the pore size. This can lead to a dramatic hardness increase in these materials.

  6. Climate change (elevated CO₂, elevated temperature and moderate drought) triggers the antioxidant enzymes' response of grapevine cv. Tempranillo, avoiding oxidative damage.

    PubMed

    Salazar-Parra, Carolina; Aguirreolea, Jone; Sánchez-Díaz, Manuel; Irigoyen, Juan José; Morales, Fermín

    2012-02-01

    Photosynthetic carbon fixation (A(N) ) and photosynthetic electron transport rate (ETR) are affected by different environmental stress factors, such as those associated with climate change. Under stress conditions, it can be generated an electron excess that cannot be consumed, which can react with O₂, producing reactive oxygen species. This work was aimed to evaluate the influence of climate change (elevated CO₂, elevated temperature and moderate drought) on the antioxidant status of grapevine (Vitis vinifera) cv. Tempranillo leaves, from veraison to ripeness. The lowest ratios between electrons generated (ETR) and consumed (A(N) + respiration + photorespiration) were observed in plants treated with elevated CO₂ and elevated temperature. In partially irrigated plants under current ambient conditions, electrons not consumed seemed to be diverted to alternative ways. Oxidative damage to chlorophylls and carotenoids was not observed. However, these plants had increases in thiobarbituric acid reacting substances, an indication of lipid peroxidation. These increases matched well with an early rise of H₂O₂ and antioxidant enzyme activities, superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and catalase (EC 1.11.1.6). Enzymatic activities were maintained high until ripeness. In conclusion, plants grown under current ambient conditions and moderate drought were less efficient to cope with oxidative damage than well-irrigated plants, and more interestingly, plants grown under moderate drought but treated with elevated CO₂ and elevated temperature were not affected by oxidative damage, mainly because of higher rates of electrons consumed in photosynthetic carbon fixation.

  7. Apparatus for Measuring Spectral Emissivity of Solid Materials at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Ren, Dengfeng; Tan, Hong; Xuan, Yimin; Han, Yuge; Li, Qiang

    2016-05-01

    Spectral emissivity measurements at high temperature are of great importance for both scientific research and industrial applications. A method to perform spectral emissivity measurements is presented based on two sample heating methods, the flat plate and tubular furnace. An apparatus is developed to measure the normal spectral emissivity of solid material at elevated temperatures from 1073 K to 1873 K and wavelengths from 2 \\upmu hbox {m} to 25 \\upmu hbox {m}. Sample heating is accomplished by a torch flame or a high temperature furnace. Two different variable temperature blackbody sources are used as standard references and the radiance is measured by a FTIR spectrometer. Following calibration of the spectral response and background radiance of the spectrometer, the effect of the blackbody temperature interval on calibration results is discussed. Measurements are performed of the normal spectral emissivity of SiC and graphite over the prescribed temperature and wavelength range. The emissivity of SiC at high temperatures is compared with the emissivity at room temperature, and the influence of an oxide layer formed at the surface of SiC on the emissivity is studied. The effect of temperature on the emissivity of graphite is also investigated. Furthermore, a thorough analysis of the uncertainty components of the emissivity measurement is performed.

  8. Ratchetting behavior of type 304 stainless steel at room and elevated temperatures

    SciTech Connect

    Ruggles, M.; Krempl, E.

    1988-01-01

    The zero-to-tension ratchetting behavior was investigated under uniaxial loading at room temperature and at 550, 600 and 650/degree/ C. In History I the maximum stress level of ratchetting was equal to the stress reached in a tensile test at one percent strain. For History II the maximum stress level was established as the stress reached after a 2100 s relaxation at one percent strain. Significant ratchetting was observed for History I at room temperature but not at the elevated temperatures. The accumulated ratchet strain increases with decreasing stress rate. Independent of the stress rates used insignificant ratchet strain was observed at room temperature for History II. This observation is explained in the context of the viscoplasticity theory based on overstress by the exhaustion of the viscous contribution to the stress during relaxation. The viscous part of the stress is the driving force for the ratchetting in History I. Strain aging is presumably responsible for the lack of short-time inelastic deformation resulting in a nearly rate-independent behavior at the elevated temperatures. 26 refs., 7 figs., 1 tab.

  9. Theoretical study of temperature elevation at muscle/bone interface during ultrasound hyperthermia.

    PubMed

    Lin, W L; Liauh, C T; Chen, Y Y; Liu, H C; Shieh, M J

    2000-05-01

    This paper examines the distributions of the SAR (specific absorption rate) ratio and temperature elevation when an ultrasound beam propagates through the interface of muscle and bone. This interface is regarded as a flat boundary to partition the energy of the ultrasound beam, and the analytical solution of temperature distribution is based on the steady-state bio-heat transfer equation. The parameters considered are the incident angle of ultrasound beam, the ultrasound frequency, the acoustic attenuation coefficients of refracted longitudinal and shear waves in bone, and the blood perfusion in muscle. The results show that the peak of the SAR ratio is always at the interface of muscle and bone, while the peak of temperature is located in the bone region beyond the interface. A muscle with lower perfusion or a bone with higher acoustic attenuation results in the shifting of the temperature peak closer to the interface. It is more difficult to heat a higher perfused muscle in front of a bone using a lower frequency ultrasound since the temperature elevation for bone relative to muscle is greater.

  10. Lifetimes statistics for single Kevlar 49 aramid filaments in creep-rupture at elevated temperatures

    SciTech Connect

    Wu, H.F.

    1987-01-01

    Kevlar 49 fibrous composites are routinely fabricated to have strengths above 1.5 GPa(200 ksi), but in many applications one would like to sustain such stresses for long time periods, sometimes at elevated temperatures. Thus the temperature dependence of the creep-rupture process in the fibers is of interest. Experimental data are presented for the lifetime of single Kevlar 49 filaments under constant stress at elevated temperatures. The goal of this research was to fully characterize the statistical strength and lifetime behavior of single filaments in order to separate fiber effects from fiber/matrix interactions in the creep-rupture lifetime of Kevlar 49/epoxy composites as described for example in Phoenix and Wu (1983). First we conducted experiments to determine distributions for the strength of filaments from the two distinct spools as a function of temperature. As expected, the data could generally be fitted by a two-parameter Weibull distribution. Lifetime experiments at 80 and 130/sup 0/C were conducted at several stress levels chosen as suitable fractions of the Weibull scale parameter for short-term strength for that temperature. The lifetime data were well modelled by a two-parameter Weibull distribution with large variability.

  11. Response and Tolerance Mechanism of Cotton Gossypium hirsutum L. to Elevated Temperature Stress: A Review

    PubMed Central

    Zahid, Kashif Rafiq; Ali, Farhan; Shah, Farooq; Younas, Muhammad; Shah, Tariq; Shahwar, Durri; Hassan, Waseem; Ahmad, Zahoor; Qi, Chao; Lu, Yanli; Iqbal, Amjad; Wu, Wei

    2016-01-01

    Cotton is an important multipurpose crop which is highly sensitive to both biotic and abiotic stresses. Proper management of this cash crop requires systematic understanding of various environmental conditions that are vital to yield and quality. High temperature stress can severely affect the viability of pollens and anther indehiscence, which leads to significant yield losses. Cotton can respond to withstand adverse environmental condition in several phases among which the accumulation of chemicals is extremely vital. Calcium, kinases, reactive oxygen species, carbohydrate, transcription factors, gene expression regulation, and plant hormones signaling pathways are playing a handy role in activating the major genes responsible to encounter and defend elevated temperature stress. The production of heat shock proteins is up-regulated when crops are unleashed to high temperature stress. Molecular breeding can play a functional role to identify superior genes for all the important attributes as well as provide breeder ready markers for developing ideotypes. The development of high-temperature resistant transgenic cultivars of cotton can grant a stability benefit and can also ameliorate the production capacity in response to elevated temperature. PMID:27446165

  12. Response and Tolerance Mechanism of Cotton Gossypium hirsutum L. to Elevated Temperature Stress: A Review.

    PubMed

    Zahid, Kashif Rafiq; Ali, Farhan; Shah, Farooq; Younas, Muhammad; Shah, Tariq; Shahwar, Durri; Hassan, Waseem; Ahmad, Zahoor; Qi, Chao; Lu, Yanli; Iqbal, Amjad; Wu, Wei

    2016-01-01

    Cotton is an important multipurpose crop which is highly sensitive to both biotic and abiotic stresses. Proper management of this cash crop requires systematic understanding of various environmental conditions that are vital to yield and quality. High temperature stress can severely affect the viability of pollens and anther indehiscence, which leads to significant yield losses. Cotton can respond to withstand adverse environmental condition in several phases among which the accumulation of chemicals is extremely vital. Calcium, kinases, reactive oxygen species, carbohydrate, transcription factors, gene expression regulation, and plant hormones signaling pathways are playing a handy role in activating the major genes responsible to encounter and defend elevated temperature stress. The production of heat shock proteins is up-regulated when crops are unleashed to high temperature stress. Molecular breeding can play a functional role to identify superior genes for all the important attributes as well as provide breeder ready markers for developing ideotypes. The development of high-temperature resistant transgenic cultivars of cotton can grant a stability benefit and can also ameliorate the production capacity in response to elevated temperature. PMID:27446165

  13. Elevated CO2 Reduced Floret Death in Wheat Under Warmer Average Temperatures and Terminal Drought

    PubMed Central

    Dias de Oliveira, Eduardo; Palta, Jairo A.; Bramley, Helen; Stefanova, Katia; Siddique, Kadambot H. M.

    2015-01-01

    Elevated CO2 often increases grain yield in wheat by enhancing grain number per ear, which can result from an increase in the potential number of florets or a reduction in the death of developed florets. The hypotheses that elevated CO2 reduces floret death rather than increases floret development, and that grain size in a genotype with more grains per unit area is limited by the rate of grain filling, were tested in a pair of sister lines contrasting in tillering capacity (restricted- vs. free-tillering). The hypotheses were tested under elevated CO2, combined with +3°C above ambient temperature and terminal drought, using specialized field tunnel houses. Elevated CO2 increased net leaf photosynthetic rates and likely the availability of carbon assimilates, which significantly reduced the rates of floret death and increased the potential number of grains at anthesis in both sister lines by an average of 42%. The restricted-tillering line had faster grain-filling rates than the free-tillering line because the free-tillering line had more grains to fill. Furthermore, grain-filling rates were faster under elevated CO2 and +3°C above ambient. Terminal drought reduced grain yield in both lines by 19%. Elevated CO2 alone increased the potential number of grains, but a trade-off in yield components limited grain yield in the free-tillering line. This emphasizes the need for breeding cultivars with a greater potential number of florets, since this was not affected by the predicted future climate variables. PMID:26635837

  14. Photoluminescence in silicon implanted with erbium ions at an elevated temperature

    SciTech Connect

    Sobolev, N. A. Kalyadin, A. E.; Shek, E. I.; Sakharov, V. I.; Serenkov, I. T.; Vdovin, V. I.; Parshin, E. O.; Makoviichuk, M. I.

    2011-08-15

    Photoluminescence spectra of n-type silicon upon implantation with erbium ions at 600 Degree-Sign C and oxygen ions at room temperature and subsequent annealings at 1100 Degree-Sign C in a chlorine-containing atmosphere have been studied. Depending on the annealing duration, photoluminescence spectra at 80 K are dominated by lines of the Er{sup 3+} ion or dislocation-related luminescence. The short-wavelength shift of the dislocation-related luminescence line observed at this temperature is due to implantation of erbium ions at an elevated temperature. At room temperature, lines of erbium and dislocation-related luminescence are observed in the spectra, but lines of near-band-edge luminescence predominate.

  15. Fatigue life prediction of an intermetallic matrix composite at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Bartolotta, P. A.

    1991-01-01

    A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the 'Universal Slopes' method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio (Vf), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

  16. Fatigue life prediction of an intermetallic matrix composite at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Bartolotta, Paul A.

    1991-01-01

    A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the Universal Slopes method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio, number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.

  17. Complexation of neptunium(V) with fluoride in aqueous solutions at elevated temperatures

    SciTech Connect

    Tian, Guoxin; Rao, Linfeng; Xia, Yuanxian; Friese, Judah I.

    2009-02-01

    Over the past several decades, the production and testing of nuclear weapons in the U.S. have created significant amounts of high-level nuclear wastes (HLW) that are currently stored in underground tanks across the U.S. DOE (Department of Energy) sites. Eventually, the HLW will be made into the waste form and disposed of in geological repositories for HLW. Among the radioactive materials, neptunium is of great concern in the post-closure chemical environment in the repository because of the long half-life of 237Np (2.14•106 years) and the high mobility of Np(V), the most stable oxidation state of neptunium. It is estimated that 237Np, together with 129I and 99Tc, will be the major contributors to the potential total annual dose from the repository beyond 10000 years [1]. Due to the high radiation energy released from the HLW, the postclosure repository is expected to remain at elevated temperatures for thousands of years [1]. If the waste package is breached and becomes in contact with groundwater, neptunium, as well as other radioactive materials will be in aqueous solutions at elevated temperatures. Interactions of radioactive materials with the chemical components in groundwater play an important role in determining their migration in the repository. To predict the migration behavior of neptunium, it is necessary to have sufficient and reliable thermodynamic data on its complexation with the ligands that are present in the groundwater of the repository (e.g., OH–, F–, SO42– ,PO43– and CO32) at elevated temperatures. However, such data are scarce and scattered for 25°C, and nearly nonexistent for elevated temperatures [2]. To provide reliable thermodynamic data, we have conducted investigations of the complexation of actinides, including thorium, uranium, neptunium and plutonium, at elevated temperatures. Thermodynamic parameters, including formation constants, enthalpy and heat capacity of complexation are experimentally determined. This paper

  18. Instrumentation enabling study of plant physiological response to elevated night temperature

    PubMed Central

    Mohammed, Abdul R; Tarpley, Lee

    2009-01-01

    Background Global climate warming can affect functioning of crops and plants in the natural environment. In order to study the effects of global warming, a method for applying a controlled heating treatment to plant canopies in the open field or in the greenhouse is needed that can accept either square wave application of elevated temperature or a complex prescribed diurnal or seasonal temperature regime. The current options are limited in their accuracy, precision, reliability, mobility or cost and scalability. Results The described system uses overhead infrared heaters that are relatively inexpensive and are accurate and precise in rapidly controlling the temperature. Remote computer-based data acquisition and control via the internet provides the ability to use complex temperature regimes and real-time monitoring. Due to its easy mobility, the heating system can randomly be allotted in the open field or in the greenhouse within the experimental setup. The apparatus has been successfully applied to study the response of rice to high night temperatures. Air temperatures were maintained within the set points ± 0.5°C. The incorporation of the combination of air-situated thermocouples, autotuned proportional integrative derivative temperature controllers and phase angled fired silicon controlled rectifier power controllers provides very fast proportional heating action (i.e. 9 ms time base), which avoids prolonged or intense heating of the plant material. Conclusion The described infrared heating system meets the utilitarian requirements of a heating system for plant physiology studies in that the elevated temperature can be accurately, precisely, and reliably controlled with minimal perturbation of other environmental factors. PMID:19519906

  19. Tree and forest water use under elevated CO2 and temperature in Scandinavian boreal forest

    NASA Astrophysics Data System (ADS)

    Berg Hasper, Thomas; Wallin, Göran; Lamba, Shubhangi; Sigurdsson, Bjarni D.; Laudon, Hjalmar; Medhurst, Jane L.; Räntfors, Mats; Linder, Sune; Uddling, Johan

    2014-05-01

    According to experimental studies and models, rising atmospheric carbon dioxide concentration ([CO2]) and temperature have the potential to affect stomatal conductance and, consequently, tree and forest transpiration. This effect has in turn the capacity to influence the terrestrial energy and water balance, including affecting of the magnitude of river runoff. Furthermore, forest productivity is currently water-limited in southern Scandinavia and in a near future, under the projected climatic change, this limitation may become a reality in the central and northern parts of Scandinavia. In this study we examine the water-use responses in 12 40-year old native boreal Norway spruce (Picea abies (L.) Karst.) trees exposed to a factorial combination of two levels of [CO2] (ambient and doubled) and temperature (ambient and +2.8 °C in summer / +5.6 °C in winter), as well as of entire boreal forests to temporal variation in [CO2], temperature and precipitation over the past 50 years in central and northern Sweden. The controlled factorial CO2 and temperature whole-tree chamber experiment at Flakaliden study site demonstrated that Norway spruce trees lacked elevated [CO2]-induced water savings at guard cell, shoot, and tree levels in the years of measurements. Experimentally, elevated temperature did not result in increased shoot or tree water use as stomatal closure fully cancelled the effect of higher vapour pressure deficit in warmed air environment. Consistent with these results, large scale river runoff data and evapotranspiration estimates from large forested watersheds in central Sweden supported lack of elevated CO2-mediated water savings, and rather suggested that the increasing evapotranspiration trend found in this study was primarily linked to increasing precipitation, rising temperature and more efficient forest management. The results from the whole-tree chamber experiment and boreal forested watersheds have important implications for more accurate

  20. Investigation of temperature and aridity at different elevations of Mt. Ailao, SW China.

    PubMed

    You, Guangyong; Zhang, Yiping; Liu, Yuhong; Schaefer, Douglas; Gong, Hede; Gao, Jinbo; Lu, Zhiyun; Song, Qinghai; Zhao, Junbin; Wu, Chuansheng; Yu, Lei; Xie, Youneng

    2013-05-01

    Our current understanding is that plant species distribution in the subtropical mountain forests of Southwest China is controlled mainly by inadequate warmth. Due to abundant annual precipitation, aridity has been less considered in this context, yet rainfall here is highly seasonal, and the magnitude of drought severity at different elevations has not been examined due to limited access to higher elevations in this area.In this study, short-term micrometeorological variables were measured at 2,480 m and 2,680 m, where different forest types occur. Drought stress was evaluated by combining measurements of water evaporation demand (E p) and soil volumetric water content (VWC). The results showed that: (1) mean temperature decreased 1 °C from 2,480 m to 2,680 m and the minimum temperature at 2,680 m was above freezing. (2) Elevation had a significant influence on E p; however, the difference in daily E p between 2,480 m and 2,680 m was not significant, which was possibly due to the small difference in elevation between these two sites. (3) VWC had larger range of annual variation at 2,680 m than at 2,480 m, especially for the surface soil layer.We conclude that the decrease in temperature does not effectively explain the sharp transition between these forest types. During the dry season, plants growing at 2,680 m are likely to experience more drought stress. In seeking to understand the mountain forest distribution, further studies should consider the effects of drought stress alongside those of altitude. PMID:22752399

  1. Effects of elevated temperature and nickel pollution on the immune status of Japanese medaka.

    PubMed

    Prophete, C; Carlson, E A; Li, Y; Duffy, J; Steinetz, B; Lasano, S; Zelikoff, J T

    2006-09-01

    Changes in a host's environment (i.e. physical or chemical) can alter normal immune function. In aquatic organisms, exposure to stress can result in significant changes in innate immunity. In the natural environment, fish are exposed to multiple stressors simultaneously. Temperature change and/or chemical exposure as individual environmental stressors have been shown in various fish species to alter all aspects of the immune response. These same stressors have also been shown to alter plasma steroid levels in exposed fish. For this study, the effects of elevated temperature and nickel pollution on specific immune parameters of Japanese medaka (Oryzias latipes) were determined. Fish were exposed for 1, 7 or 14d to either: waterborne nickel (Ni) at the nominal concentration of 125ppb; a 5 degrees C (+/-0.5 degrees C) rapid increase in water temperature; or, both potential stressors in combination. Medaka maintained at room temperature (25 degrees C+/-1 degrees C) served as the controls. Altered function of the innate and adaptive arms of the immune response was evaluated by assessing kidney macrophage-mediated superoxide (O(2)(-)) production and splenic T-cell proliferation, respectively. Plasma cortisol levels were analysed in the same fish as a marker of the physiological stress response. While kidney cell number was unaffected by exposure of fish to either stressor alone or both factors in combination, spleen cellularity was decreased (compared to control fish) in medaka exposed for 1d to thermal stress in combination with Ni, and to a lesser extent to thermal stress alone. T-lymphocyte proliferation by medaka splenocytes was not affected by any exposure paradigm. Unstimulated intracellular O(2)(-) production by kidney phagocytes was significantly elevated (compared to control) in medaka exposed for 1d to either thermal stress alone or temperature change in combination with Ni; by 7d, only the stressor combination significantly increased baseline O(2

  2. Engineered thermostable fungal cellulases exhibit efficient synergistic cellulose hydrolysis at elevated temperatures.

    PubMed

    Trudeau, Devin L; Lee, Toni M; Arnold, Frances H

    2014-12-01

    A major obstacle to using widely available and low-cost lignocellulosic feedstocks to produce renewable fuels and chemicals is the high cost and low efficiency of the enzyme mixtures used to hydrolyze cellulose to fermentable sugars. One possible solution entails engineering current cellulases to function efficiently at elevated temperatures in order to boost reaction rates and exploit several other advantages of a higher temperature process. Here, we describe the creation of the most stable reported fungal endoglucanase, a derivative of Hypocrea jecorina (anamorph Trichoderma reesei) Cel5A, by combining stabilizing mutations identified using consensus design, chimera studies, and structure-based computational methods. The engineered endoglucanase has an optimal temperature that is 17°C higher than wild type H. jecorina Cel5A, and hydrolyzes 1.5 times as much cellulose over 60 h at its optimum temperature compared to the wild type enzyme at its optimal temperature. This enzyme complements previously engineered highly active, thermostable variants of the fungal cellobiohydrolases Cel6A and Cel7A in a thermostable cellulase mixture that hydrolyzes cellulose synergistically at an optimum temperature of 70°C over 60 h.The thermostable mixture produces three times as much total sugar as the best mixture of the wild type enzymes operating at its optimum temperature of 60°C, clearly demonstrating the advantage of higher temperature cellulose hydrolysis.

  3. The effects of elevated water temperature on native juvenile mussels: implications for climate change

    USGS Publications Warehouse

    Ganser, Alissa M.; Newton, Teresa J.; Haro, Roger J.

    2013-01-01

    Native freshwater mussels are a diverse but imperiled fauna and may be especially sensitive to increasing water temperatures because many species already may be living near their upper thermal limits. We tested the hypothesis that elevated water temperatures (20, 25, 30, and 35°C) adversely affected the survival and physiology of 2-mo-old juvenile mussels (Lampsilis abrupta, Lampsilis siliquoidea, and Megalonaias nervosa) in 28-d laboratory experiments. The 28-d LT50s (lethal temperature affecting 50% of the population) ranged from 25.3 to 30.3°C across species, and were lowest for L. abrupta and L. siliquoidea. Heart rate of L. siliquoidea was not affected by temperature, but heart rate declined at higher temperatures in L. abrupta and M. nervosa. However, for both of these species, heart rate also declined steadily during the experiment and a strong temperature × time interaction was detected. Juvenile growth was low for all species in all treatments and did not respond directly to temperature, but growth of some species responded to a temperature × time interaction. Responses to thermal stress differed among species, but potential laboratory artifacts may limit applicability of these results to real-world situations. Environmentally relevant estimates of upper thermal tolerances in native mussels are urgently needed to assess the extent of assemblage changes that can be expected in response to global climate change.

  4. Engineered thermostable fungal cellulases exhibit efficient synergistic cellulose hydrolysis at elevated temperatures.

    PubMed

    Trudeau, Devin L; Lee, Toni M; Arnold, Frances H

    2014-12-01

    A major obstacle to using widely available and low-cost lignocellulosic feedstocks to produce renewable fuels and chemicals is the high cost and low efficiency of the enzyme mixtures used to hydrolyze cellulose to fermentable sugars. One possible solution entails engineering current cellulases to function efficiently at elevated temperatures in order to boost reaction rates and exploit several other advantages of a higher temperature process. Here, we describe the creation of the most stable reported fungal endoglucanase, a derivative of Hypocrea jecorina (anamorph Trichoderma reesei) Cel5A, by combining stabilizing mutations identified using consensus design, chimera studies, and structure-based computational methods. The engineered endoglucanase has an optimal temperature that is 17°C higher than wild type H. jecorina Cel5A, and hydrolyzes 1.5 times as much cellulose over 60 h at its optimum temperature compared to the wild type enzyme at its optimal temperature. This enzyme complements previously engineered highly active, thermostable variants of the fungal cellobiohydrolases Cel6A and Cel7A in a thermostable cellulase mixture that hydrolyzes cellulose synergistically at an optimum temperature of 70°C over 60 h.The thermostable mixture produces three times as much total sugar as the best mixture of the wild type enzymes operating at its optimum temperature of 60°C, clearly demonstrating the advantage of higher temperature cellulose hydrolysis. PMID:24916885

  5. A meta-analysis of plant physiological and growth responses to temperature and elevated CO(2).

    PubMed

    Wang, Dan; Heckathorn, Scott A; Wang, Xianzhong; Philpott, Stacy M

    2012-05-01

    Atmospheric carbon dioxide (CO(2)) and global mean temperature are expected to be significantly higher by the end of the 21st century. Elevated CO(2) (eCO(2)) and higher temperature each affect plant physiology and growth, but their interactive effects have not been reviewed statistically with respect to higher chronic mean temperatures and abrupt heat stress. In this meta-analysis, we examined the effect of CO(2) on the physiology and growth of plants subjected to different temperature treatments. The CO(2) treatments were categorized into ambient (<400 ppm) or elevated (>560 ppm) levels, while temperature treatments were categorized into ambient temperature (AT), elevated temperature (ET; AT + 1.4-6°C), or heat stress (HS; AT + >8°C). Plant species were grouped according to photosynthetic pathways (C(3), C(4)), functional types (legumes, non-legumes), growth forms (herbaceous, woody), and economic purposes (crop, non-crop). eCO(2) enhanced net photosynthesis at AT, ET, and HS in C(3) species (especially at the HS level), but in C(4) species, it had no effect at AT, a positive effect at ET, and a negative effect at HS. The positive effect of eCO(2) on net photosynthesis was greater for legumes than for non-legumes at HS, for non-crops than crops at ET, and for woody than herbaceous species at ET and HS. Total (W (T)) and above- (W (AG)) and below-ground (W (BG)) biomass were increased by eCO(2) for most species groups at all temperatures, except for C(4) species and W (BG) of legumes at HS. Hence, eCO(2) × heat effects on growth were often not explained by effects on net photosynthesis. Overall, the results show that eCO(2) effects on plant physiology and growth vary under different temperature regimes, among functional groups and photosynthetic pathways, and among response variables. These findings have important implications for biomass accumulation and ecosystem functioning in the future when the CO(2) level is higher and climate extremes, such as heat waves

  6. Geopolymeric materials prepared using Class F fly ash and elevated temperature curing

    SciTech Connect

    Bakharev, T. . E-mail: tanya.bakharev@eng.monash.edu.au

    2005-06-01

    This paper reports the results of the study of the influence of elevated temperature curing on phase composition, microstructure and strength development in geopolymer materials prepared using Class F fly ash and sodium silicate and sodium hydroxide solutions. In particular, the effect of storage at room temperature before the application of heat on strength development and phase composition was studied. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and SEM were utilised in this study. Long precuring at room temperature before application of heat was beneficial for strength development in all studied materials, as strength comparable to 1 month of curing at elevated temperature can develop in this case only after 24 h of heat curing. The main product of reaction in the geopolymeric materials was amorphous alkali aluminosilicate gel. However, in the case of sodium hydroxide activator in addition to it, traces of chabazite, Linde Type A, Na-P1 (gismondine) zeolites and hydroxysodalite were also present. The type of zeolite present and composition of aluminosilicate gel were dependent on the curing history.

  7. Chemical and mechanical stability of sodium sulfate activated slag after exposure to elevated temperature

    SciTech Connect

    Rashad, A.M.; Bai, Y.; Basheer, P.A.M.; Collier, N.C.; Milestone, N.B.

    2012-02-15

    The chemical and mechanical stability of slag activated with two different concentrations of sodium sulfate (Na{sub 2}SO{sub 4}) after exposure to elevated temperatures ranging from 200 to 800 Degree-Sign C with an increment of 200 Degree-Sign C has been examined. Compressive strengths and pH of the hardened pastes before and after the exposure were determined. The various decomposition phases formed were identified using X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The results indicated that Na{sub 2}SO{sub 4} activated slag has a better resistance to the degradation caused by exposure to elevated temperature up to 600 Degree-Sign C than Portland cement system as its relative strengths are superior. The finer slag and higher Na{sub 2}SO{sub 4} concentration gave better temperature resistance. Whilst the pH of the hardened pastes decreased with an increase in temperature, it still maintained a sufficiently high pH for the protection of reinforcing bar against corrosion.

  8. Elevated temperature as a treatment for Batrachochytrium dendrobatidis infection in captive frogs.

    PubMed

    Chatfield, Matthew W H; Richards-Zawacki, Corinne L

    2011-05-01

    The amphibian chytrid fungus Batrachochytrium dendrobatidis (Bd) has been implicated in amphibian declines worldwide. In vitro laboratory studies and those done on wild populations indicate that Bd grows best at cool temperatures between 17 and 25 degrees C. In the present study, we tested whether moderately elevating the ambient temperature to 30 degrees C could be an effective treatment for frogs infected with Bd. We acquired 35 bullfrogs Rana catesbeiana from breeding facilities and 36 northern cricket frogs Acris crepitans from the wild and acclimated them to either 23 or 26 degrees C for 1 mo. Following the acclimation period, frogs were tested for the presence of Bd using qPCR TaqMan assays. The 12 R. catesbeiana and 16 A. crepitans that tested positive for Bd were subjected to 30 degrees C for 10 consecutive days before returning frogs to their starting temperatures. Post-treatment testing revealed that 27 of the 28 frogs that had tested positive were no longer infected with Bd; only a single A. crepitans remained infected following treatment. This result indicates that elevating ambient temperature to a moderate 30 degrees C can be effective as a treatment for Bd infection in captive amphibians, and suggests that heat may be a superior alternative to antifungal drugs.

  9. Development and evaluation of a HEPA filter for increased strength and resistance to elevated temperature

    SciTech Connect

    Gilbert, H.; Bergman, W.; Fretthold, J.K.

    1992-12-31

    We have developed an improved HEPA filter for increased strength and resistance to elevated temperature to improve the reliability of HEPA filters under accident conditions. The improvements to the HEPA filter consist of a silicone rubber sealant and a new HEPA medium reinforced with a glass cloth. Several prototype filters were built and evaluated for temperature and pressure resistance and resistance to rough handling. The temperature resistance test consisted of exposing the HEPA filter to 1,000 scan at 700 degrees F for five minutes. The pressure resistance test consisted of exposing the HEPA filter to a differential pressure of 10 in. w.g. using a water saturated air flow at 95 degrees F. For the rough handling test, we used a vibrating machine designated the Q110. DOP filter efficiency tests were performed before and after each of the environmental tests. In addition to following the standard practice of using a separate new filter for each environmental test, we also subjected the same filter to the elevated temperature test followed by the pressure resistance test. The efficiency test results show that the improved HEPA filter is significantly better than the standard HEPA filter.

  10. Metabolic effects of elevated temperature on organic acid degradation in ripening Vitis vinifera fruit

    PubMed Central

    Sweetman, C.; Sadras, V. O.; Hancock, R. D.; Soole, K. L.; Ford, C. M.

    2014-01-01

    Berries of the cultivated grapevine Vitis vinifera are notably responsive to temperature, which can influence fruit quality and hence the future compatibility of varieties with their current growing regions. Organic acids represent a key component of fruit organoleptic quality and their content is significantly influenced by temperature. The objectives of this study were to (i) manipulate thermal regimes to realistically capture warming-driven reduction of malate content in Shiraz berries, and (ii) investigate the mechanisms behind temperature-sensitive malate loss and the potential downstream effects on berry metabolism. In the field we compared untreated controls at ambient temperature with longer and milder warming (2–4 °C differential for three weeks; Experiment 1) or shorter and more severe warming (4–6 °C differential for 11 days; Experiment 2). We complemented field trials with control (25/15 °C) and elevated (35/20 °C) day/night temperature controlled-environment trials using potted vines (Experiment 3). Elevating maximum temperatures (4–10 °C above controls) during pre-véraison stages led to higher malate content, particularly with warmer nights. Heating at véraison and ripening stages reduced malate content, consistent with effects typically seen in warm vintages. However, when minimum temperatures were also raised by 4–6 °C, malate content was not reduced, suggesting that the regulation of malate metabolism differs during the day and night. Increased NAD-dependent malic enzyme activity and decreased phosphoenolpyruvate carboxylase and pyruvate kinase activities, as well as the accumulation of various amino acids and γ-aminobutyric acid, suggest enhanced anaplerotic capacity of the TCA cycle and a need for coping with decreased cytosolic pH in heated fruit. PMID:25180109

  11. Metabolic effects of elevated temperature on organic acid degradation in ripening Vitis vinifera fruit.

    PubMed

    Sweetman, C; Sadras, V O; Hancock, R D; Soole, K L; Ford, C M

    2014-11-01

    Berries of the cultivated grapevine Vitis vinifera are notably responsive to temperature, which can influence fruit quality and hence the future compatibility of varieties with their current growing regions. Organic acids represent a key component of fruit organoleptic quality and their content is significantly influenced by temperature. The objectives of this study were to (i) manipulate thermal regimes to realistically capture warming-driven reduction of malate content in Shiraz berries, and (ii) investigate the mechanisms behind temperature-sensitive malate loss and the potential downstream effects on berry metabolism. In the field we compared untreated controls at ambient temperature with longer and milder warming (2-4 °C differential for three weeks; Experiment 1) or shorter and more severe warming (4-6 °C differential for 11 days; Experiment 2). We complemented field trials with control (25/15 °C) and elevated (35/20 °C) day/night temperature controlled-environment trials using potted vines (Experiment 3). Elevating maximum temperatures (4-10 °C above controls) during pre-véraison stages led to higher malate content, particularly with warmer nights. Heating at véraison and ripening stages reduced malate content, consistent with effects typically seen in warm vintages. However, when minimum temperatures were also raised by 4-6 °C, malate content was not reduced, suggesting that the regulation of malate metabolism differs during the day and night. Increased NAD-dependent malic enzyme activity and decreased phosphoenolpyruvate carboxylase and pyruvate kinase activities, as well as the accumulation of various amino acids and γ-aminobutyric acid, suggest enhanced anaplerotic capacity of the TCA cycle and a need for coping with decreased cytosolic pH in heated fruit.

  12. Implications of High Temperature and Elevated CO2 on Flowering Time in Plants

    PubMed Central

    Jagadish, S. V. Krishna; Bahuguna, Rajeev N.; Djanaguiraman, Maduraimuthu; Gamuyao, Rico; Prasad, P. V. Vara; Craufurd, Peter Q.

    2016-01-01

    Flowering is a crucial determinant for plant reproductive success and seed-set. Increasing temperature and elevated carbon-dioxide (e[CO2]) are key climate change factors that could affect plant fitness and flowering related events. Addressing the effect of these environmental factors on flowering events such as time of day of anthesis (TOA) and flowering time (duration from germination till flowering) is critical to understand the adaptation of plants/crops to changing climate and is the major aim of this review. Increasing ambient temperature is the major climatic factor that advances flowering time in crops and other plants, with a modest effect of e[CO2].Integrated environmental stimuli such as photoperiod, temperature and e[CO2] regulating flowering time is discussed. The critical role of plant tissue temperature influencing TOA is highlighted and crop models need to substitute ambient air temperature with canopy or floral tissue temperature to improve predictions. A complex signaling network of flowering regulation with change in ambient temperature involving different transcription factors (PIF4, PIF5), flowering suppressors (HvODDSOC2, SVP, FLC) and autonomous pathway (FCA, FVE) genes, mainly from Arabidopsis, provides a promising avenue to improve our understanding of the dynamics of flowering time under changing climate. Elevated CO2 mediated changes in tissue sugar status and a direct [CO2]-driven regulatory pathway involving a key flowering gene, MOTHER OF FT AND TFL1 (MFT), are emerging evidence for the role of e[CO2] in flowering time regulation. PMID:27446143

  13. Implications of High Temperature and Elevated CO2 on Flowering Time in Plants.

    PubMed

    Jagadish, S V Krishna; Bahuguna, Rajeev N; Djanaguiraman, Maduraimuthu; Gamuyao, Rico; Prasad, P V Vara; Craufurd, Peter Q

    2016-01-01

    Flowering is a crucial determinant for plant reproductive success and seed-set. Increasing temperature and elevated carbon-dioxide (e[CO2]) are key climate change factors that could affect plant fitness and flowering related events. Addressing the effect of these environmental factors on flowering events such as time of day of anthesis (TOA) and flowering time (duration from germination till flowering) is critical to understand the adaptation of plants/crops to changing climate and is the major aim of this review. Increasing ambient temperature is the major climatic factor that advances flowering time in crops and other plants, with a modest effect of e[CO2].Integrated environmental stimuli such as photoperiod, temperature and e[CO2] regulating flowering time is discussed. The critical role of plant tissue temperature influencing TOA is highlighted and crop models need to substitute ambient air temperature with canopy or floral tissue temperature to improve predictions. A complex signaling network of flowering regulation with change in ambient temperature involving different transcription factors (PIF4, PIF5), flowering suppressors (HvODDSOC2, SVP, FLC) and autonomous pathway (FCA, FVE) genes, mainly from Arabidopsis, provides a promising avenue to improve our understanding of the dynamics of flowering time under changing climate. Elevated CO2 mediated changes in tissue sugar status and a direct [CO2]-driven regulatory pathway involving a key flowering gene, MOTHER OF FT AND TFL1 (MFT), are emerging evidence for the role of e[CO2] in flowering time regulation. PMID:27446143

  14. Elevation, Temperature, and Aquatic Connectivity All Influence the Infection Dynamics of the Amphibian Chytrid Fungus in Adult Frogs

    PubMed Central

    Sapsford, Sarah J.; Alford, Ross A.; Schwarzkopf, Lin

    2013-01-01

    Infectious diseases can cause population declines and even extinctions. The amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd), has caused population declines and extinctions in amphibians on most continents. In the tropics, research on the dynamics of this disease has focused on amphibian populations in mountainous areas. In most of these areas, high and low elevation sites are connected by an assemblage of streams that may transport the infectious stage of the pathogen from high to low elevations, and, also, this pathogen, which grows well at cool temperatures, may persist better in cooler water flowing from high elevations. Thus, the dynamics of disease at low elevation sites without aquatic connections to higher elevation sites, i.e., non-contiguous low elevation sites, may differ from dynamics at contiguous low elevation sites. We sampled adult common mistfrogs (Litoria rheocola) at six sites of three types: two at high (> 400m) elevations, two at low elevations contiguous with high elevation streams, and two at low elevations non-contiguous with any high elevation site. Adults were swabbed for Bd diagnosis from June 2010 to June 2011 in each season, over a total of five sampling periods. The prevalence of Bd fluctuated seasonally and was highest in winter across all site types. Site type significantly affected seasonal patterns of prevalence of Bd. Prevalence remained well above zero throughout the year at the high elevation sites. Prevalence declined to lower levels in contiguous low sites, and reached near-zero at non-contiguous low sites. Patterns of air temperature fluctuation were very similar at both the low elevation site types, suggesting that differences in water connectivity to high sites may have affected the seasonal dynamics of Bd prevalence between contiguous and non-contiguous low elevation site types. Our results also suggest that reservoir hosts may be important in the persistence of disease at low elevations. PMID:24324786

  15. Elevated Temperature and CO2 Stimulate Late-Season Photosynthesis But Impair Cold Hardening in Pine[OPEN

    PubMed Central

    2016-01-01

    Rising global temperature and CO2 levels may sustain late-season net photosynthesis of evergreen conifers but could also impair the development of cold hardiness. Our study investigated how elevated temperature, and the combination of elevated temperature with elevated CO2, affected photosynthetic rates, leaf carbohydrates, freezing tolerance, and proteins involved in photosynthesis and cold hardening in Eastern white pine (Pinus strobus). We designed an experiment where control seedlings were acclimated to long photoperiod (day/night 14/10 h), warm temperature (22°C/15°C), and either ambient (400 μL L−1) or elevated (800 μmol mol−1) CO2, and then shifted seedlings to growth conditions with short photoperiod (8/16 h) and low temperature/ambient CO2 (LTAC), elevated temperature/ambient CO2 (ETAC), or elevated temperature/elevated CO2 (ETEC). Exposure to LTAC induced down-regulation of photosynthesis, development of sustained nonphotochemical quenching, accumulation of soluble carbohydrates, expression of a 16-kD dehydrin absent under long photoperiod, and increased freezing tolerance. In ETAC seedlings, photosynthesis was not down-regulated, while accumulation of soluble carbohydrates, dehydrin expression, and freezing tolerance were impaired. ETEC seedlings revealed increased photosynthesis and improved water use efficiency but impaired dehydrin expression and freezing tolerance similar to ETAC seedlings. Sixteen-kilodalton dehydrin expression strongly correlated with increases in freezing tolerance, suggesting its involvement in the development of cold hardiness in P. strobus. Our findings suggest that exposure to elevated temperature and CO2 during autumn can delay down-regulation of photosynthesis and stimulate late-season net photosynthesis in P. strobus seedlings. However, this comes at the cost of impaired freezing tolerance. Elevated temperature and CO2 also impaired freezing tolerance. However, unless the frequency and timing of extreme low-temperature

  16. Elevated temperature and drought interact to reduce parasitoid effectiveness in suppressing hosts.

    PubMed

    Romo, Cecilia M; Tylianakis, Jason M

    2013-01-01

    Climate change affects the abundance, distribution and activity of natural enemies that are important for suppressing herbivore crop pests. Moreover, higher mean temperatures and increased frequency of climatic extremes are expected to induce different responses across trophic levels, potentially disrupting predator-prey interactions. Using field observations, we examined the response of an aphid host-parasitoid system to variation in temperature. Temperature was positively associated with attack rates by parasitoids, but also with a non-significant trend towards increased attack rates by higher-level hyperparasitoids. Elevated hyperparasitism could partly offset any benefit of climate warming to parasitoids, and would suggest that higher trophic levels may hamper predictions of predator-prey interactions. Additionally, the mechanisms affecting host-parasitoid dynamics were examined using controlled laboratory experiments that simulated both temperature increase and drought. Parasitoid fitness and longevity responded differently when exposed to each climatic variable in isolation, compared to the interaction of both variables at once. Although temperature increase or drought tended to positively affect the ability of parasitoids to control aphid populations, these effects were significantly reversed when the drivers were expressed in concert. Additionally, separate warming and drought treatments reduced parasitoid longevity, and although temperature increased parasitoid emergence success and drought increased offspring production, combined temperature and drought produced the lowest parasitoid emergence. The non-additive effects of different climate drivers, combined with differing responses across trophic levels, suggest that predicting future pest outbreaks will be more challenging than previously imagined.

  17. Characteristics of ocular temperature elevations after exposure to quasi- and millimeter waves (18-40 GHz)

    NASA Astrophysics Data System (ADS)

    Kojima, Masami; Suzuki, Yukihisa; Tsai, Cheng-Yu; Sasaki, Kensuke; Wake, Kanako; Watanabe, Soichi; Taki, Masao; Kamimura, Yoshitsugu; Hirata, Akimasa; Sasaki, Kazuyuki; Sasaki, Hiroshi

    2015-04-01

    In order to investigate changes in ocular temperature in rabbit eyes exposed to different frequencies (18 to 40 GHz) of quasi-millimeter waves, and millimeter waves (MMW). Pigmented rabbits were anesthetized with both general and topical anesthesia, and thermometer probes (0.5 mm in diameter) were inserted into their cornea (stroma), lens (nucleus) and vitreous (center of vitreous). The eyes were exposed unilaterally to 200 mW/cm2 by horn antenna for 3 min at 18, 22 and 26.5 GHz using a K band exposure system or 26.5, 35 and 40 GHz using a Ka band exposure system. Changes in temperature of the cornea, lens and vitreous were measured with a fluoroptic thermometer. Since the ocular temperatures after exposure to 26.5 GHz generated by the K band and Ka band systems were similar, we assumed that experimental data from these 2 exposure systems were comparable. The highest ocular temperature was induced by 40 GHz MMW, followed by 35 GHz. The 26.5 and 22 GHz corneal temperatures were almost the same. The lowest temperature was recorded at 18 GHz. The elevation in ocular temperature in response to exposure to 200 mW/cm2 MMW is dependent on MMW frequency. MMW exposure induced heat is conveyed not only to the cornea but also the crystalline lens.

  18. Rheological and Mechanical Property Measurements of PMDI Foam at Elevated Temperatures

    SciTech Connect

    Nemer, Martin Bernard; Brooks, Carlton F.; Shelden, Bion; Soehnel, Melissa Marie; Barringer, David Alan

    2014-10-01

    A study was undertaken to determine the viscosity of liquefied 20 lb/ft3 poly methylene diisocyanate (PMDI) foam and the stress required to puncture solid PMDI foam at elevated temperatures. For the rheological measurements the foam was a priori liquefied in a pressure vessel such that the volatiles were not lost in the liquefaction process. The viscosity of the liquefied PMDI foam was found to be Newtonian with a power law dependence on temperature log10(μ/Pa s) = 20.6 – 9.5 log10(T/°C) for temperatures below 170 °C. Above 170 °C, the viscosity was in the range of 0.3 Pa s which is close to the lower measurement limit (≈ 0.1 Pa s) of the pressurized rheometer. The mechanical pressure required to break through 20lb/ft3 foam was 500-800 psi at temperatures from room temperature up to 180 °C. The mechanical pressure required to break through 10 lb/ft3 was 170-300 psi at temperatures from room temperature up to 180 °C. We have not been able to cause gas to break through the 20 lb/ft3 PMDI foam at gas pressures up to 100 psi.

  19. CHARACTERIZATION OF ELEVATED TEMPERATURE PROPERTIES OF HEAT EXCHANGER AND STEAM GENERATOR ALLOYS

    SciTech Connect

    J.K. Wright; L.J. Carroll; C.J. Cabet; T. Lillo; J.K. Benz; J.A. Simpson; A. Chapman; R.N. Wright

    2012-10-01

    The Next Generation Nuclear Plant project is considering Alloy 800H and Alloy 617 for steam generator and intermediate heat exchangers. It is envisioned that a steam generator would operate with reactor outlet temperatures from 750 to 800 C, while an intermediate heat exchanger for primary to secondary helium would operate up to an outlet temperature of 950 C. Although both alloys are of interest due in part to their technical maturity, a number of specific properties require further characterization for design of nuclear components. Strain rate sensitivity of both alloys has been characterized and is found to be significant above 600 C. Both alloys also exhibit dynamic strain aging, characterized by serrated flow, over a wide range of temperatures and strain rates. High temperature tensile testing of Alloy 617 has been conducted over a range of temperatures. Dynamic strain aging is a concern for these materials since it is observed to result in reduced ductility for many solid solution alloys. Creep, fatigue, and creep-fatigue properties of Alloy 617 have been measured as well, with the goal of determining the influence of the temperature, strain rate and atmosphere on the creep fatigue life of Alloy 617. Elevated temperature properties and implications for codification of the alloys will be described.

  20. Gas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures

    SciTech Connect

    Wiberg, Gustav K. H. E-mail: m.arenz@chem.ku.dk; Fleige, Michael; Arenz, Matthias E-mail: m.arenz@chem.ku.dk

    2015-02-15

    We present a detailed description of the construction and testing of an electrochemical cell setup allowing the investigation of a gas diffusion electrode containing carbon supported high surface area catalysts. The setup is designed for measurements in concentrated phosphoric acid at elevated temperature, i.e., very close to the actual conditions in high temperature proton exchange membrane fuel cells (HT-PEMFCs). The cell consists of a stainless steel flow field and a PEEK plastic cell body comprising the electrochemical cell, which exhibits a three electrode configuration. The cell body and flow field are braced using a KF-25 vacuum flange clamp, which allows an easy assembly of the setup. As demonstrated, the setup can be used to investigate temperature dependent electrochemical processes on high surface area type electrocatalysts, but it also enables quick screening tests of HT-PEMFC catalysts under realistic conditions.

  1. Analysis of elevated temperature data for thermodynamic properties of selected radionuclides

    SciTech Connect

    Wruck, D.A.; Palmer, C.E.A.

    1997-08-01

    This report is a review of chemical thermodynamic data for Ni, Zr, Tc, U, Np, Pu and Am in aqueous solutions at elevated temperatures. Thermodynamic data for aqueous reactions over the temperature range 20-150{degrees}C are needed for geochemical modeling studies of the Yucca Mountain Project. The present review is focused on the aqueous complexes relevant to expected conditions in the Yucca Mountain region: primarily the hydroxide, carbonate, sulfate and fluoride complexes with the metal ions. Existing thermodynamic data are evaluated, and means of extrapolating 25{degrees}C data to the temperatures of interest are discussed. There will be a separate review of solubility data for relevant Ni, Zr, Tc, Np, Pu and Am compounds.

  2. THERMODYNAMICS OF NEPTUNIUM(V) FLOURIDE AND SULFATE AT ELEVATED TEMPERATURES

    SciTech Connect

    L. Rao; G. Tian; Y. Xia; J.I. Friese

    2006-03-06

    Complexation of neptunium(V) with fluoride and sulfate at elevated, temperatures was studied by microcalorimetry. Thermodynamic parameters, including the equilibrium constants and enthalpy of protonation of fluoride and sulfate, and the enthalpy of complexation between Np(V) and fluoride and sulfate at 25-70 C were determined. Results show that the complexation of Np(V) with fluoride and sulfate is endothermic and that the complexation is enhanced by the increase in temperature--a threefold increase in the stability constants of NpO{sub 2}F(aq) and NpO{sub 2}SO{sub 4}{sup -} as the temperature is increased from 25 to 70 C.

  3. Generation of Constant Life Diagram under Elevated Temperature Ratcheting of 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

    Sarkar, Aritra; Nagesha, A.; Sandhya, R.; Mathew, M. D.

    2016-04-01

    Combined influence of mean stress and stress amplitude on the cyclic life under elevated temperature (823-923 K) ratcheting of 316LN austenitic stainless steel is discussed. Constant life Haigh diagrams have been generated, using different combinations of stress amplitude and mean stress. In the plastic domain, the allowable stress was found to increase or decrease with mean stress depending on the temperature and combination of mean stress - stress amplitude employed. Strong influence of dynamic strain aging (DSA) was found at 823 K which affected the mode of deformation of the material in comparison with 923 K. Failure mode expressed through a fracture mechanism map was found to change from fatigue to necking depending on the test temperature as well as combinations of mean stress and stress amplitude. Occurrence of DSA at 823 K proved to be beneficial by way of extending the safe zone of operation to higher R-ratios in comparison with 923 K.

  4. Modeling the effects of elevated temperatures on action potential propagation in unmyelinated axons

    NASA Astrophysics Data System (ADS)

    Ganguly, Mohit; Jenkins, Michael W.; Chiel, Hillel J.; Jansen, E. Duco

    2016-03-01

    Infrared lasers (λ=1.87 μm) are capable of inducing a thermally mediated nerve block in Aplysia and rat nerves. While this block is spatially precise and reversible in sensory and motor neurons, the mechanism of block is not clearly understood. Model predictions show that, at elevated temperatures, the rates of opening and closing of the voltage gated ion channels are disrupted and normal functioning of the gates is hindered. A model combining NEURON with Python is presented here that can simulate the behavior of unmyelinated nerve axons in the presence of spatially and temporally varying temperature distributions. Axon behavior and underlying mechanism leading to conduction block is investigated. The ability to understand the photothermal interaction of laser light and temperature dependence of membrane ion channels in-silico will help speed explorations of parameter space and guide future experiments testing the feasibility of selectively blocking pain conduction fibers (Photonic Analgesia of Nerves (PAIN)) in humans.

  5. Analysis of Screen Channel LAD Bubble Point Tests in Liquid Methane at Elevated Temperature

    NASA Technical Reports Server (NTRS)

    Hartwig, Jason; McQuillen, John

    2012-01-01

    This paper examines the effect of varying the liquid temperature and pressure on the bubble point pressure for screen channel Liquid Acquisition Devices in cryogenic liquid methane using gaseous helium across a wide range of elevated pressures and temperatures. Testing of a 325 x 2300 Dutch Twill screen sample was conducted in the Cryogenic Components Lab 7 facility at the NASA Glenn Research Center in Cleveland, Ohio. Test conditions ranged from 105 to 160K and 0.0965 - 1.78 MPa. Bubble point is shown to be a strong function of the liquid temperature and a weak function of the amount of subcooling at the LAD screen. The model predicts well for saturated liquid but under predicts the subcooled data.

  6. Effect of elevated temperature curing on properties of alkali-activated slag concrete

    SciTech Connect

    Bakharev, T.; Sanjayan, J.G.; Cheng, Y.B.

    1999-10-01

    This investigation is focused on the effect of curing temperature on microstructure, shrinkage, and compressive strength of alkali-activated slag (AAS) concrete. Concrete prepared using sodium silicate and sodium hydroxide as the activator had greater early and flexural strength than ordinary Portland cement concrete of the same water/binder ratio, but it also had high autogenous and drying shrinkage. Heat treatment was found to be very effective in reducing drying shrinkage of AAS concrete and promoting high early strength. However, strength of AAS concrete at later ages was reduced. Microstructural study revealed an inhomogeneity in distribution of hydration product in AAS concrete that can be a cause of strength reduction. Pretreatment at room temperature before elevated temperature curing further improved early strength and considerably decreased shrinkage in AAS concrete.

  7. An anisotropic thermomechanical damage model for concrete at transient elevated temperatures.

    PubMed

    Baker, Graham; de Borst, René

    2005-11-15

    The behaviour of concrete at elevated temperatures is important for an assessment of integrity (strength and durability) of structures exposed to a high-temperature environment, in applications such as fire exposure, smelting plants and nuclear installations. In modelling terms, a coupled thermomechanical analysis represents a generalization of the computational mechanics of fracture and damage. Here, we develop a fully coupled anisotropic thermomechanical damage model for concrete under high stress and transient temperature, with emphasis on the adherence of the model to the laws of thermodynamics. Specific analytical results are given, deduced from thermodynamics, of a novel interpretation on specific heat, evolution of entropy and the identification of the complete anisotropic, thermomechanical damage surface. The model is also shown to be stable in a computational sense, and to satisfy the laws of thermodynamics. PMID:16243703

  8. The effect of elevated temperature and substrate on free-living Symbiodinium cultures

    NASA Astrophysics Data System (ADS)

    Nitschke, M. R.; Davy, S. K.; Cribb, T. H.; Ward, S.

    2015-03-01

    Elevated temperatures can produce a range of serious, deleterious effects on marine invertebrate— Symbiodinium symbioses. The responses of free-living Symbiodinium to elevated temperature, however, have been little studied, especially in the context of their natural habitat. In this study, we investigated physiological responses of two Symbiodinium cultures to elevated temperature, an exclusively free-living ITS2 clade A (strain HI-0509) and the symbiosis-forming ITS2 type A1 (strain CCMP2467). Free-living Symbiodinium strains have recently been isolated from benthic sediments, and both cultures were therefore grown with or without a microhabitat of carbonate sediment at 25, 28 or 31 °C. Maximum quantum yield of photosystem II ( F v/ F m) and specific growth rate were measured as response variables. In culture, Symbiodinium cells exhibit motility in a helical swimming pattern, and therefore, revolutions per minute (RPM) were also measured with video microscopy. The exclusively free-living clade A was physiologically superior to Symbiodinium A1 across all measured variables and treatment combinations. F v/ F m remained relatively stable through time (at approximately 0.55) and was not substantially affected by temperature or the presence or the absence of sediment. Populations of the exclusively free-living Symbiodinium A reproduced faster with sediment than without and exhibited high levels of motility across all treatments (surpassing 300 RPM). In contrast, the F v/ F m of A1 dropped to 0.42 in sediment (relative to cultures without sediment) and exhibited dramatic declines in cell concentration, most severely at 31 °C. A > 50 % reduction in motility was also observed at 31 °C. Even in the absence of sediment, elevated temperature was observed to reduce population growth and cell motility of type A1. We suggest that vital behaviours linked to motility (such as vertical migration and the locating of potential hosts) may become impaired during future thermal

  9. Spring photosynthetic recovery of boreal Norway spruce under conditions of elevated [CO(2)] and air temperature.

    PubMed

    Wallin, Göran; Hall, Marianne; Slaney, Michelle; Räntfors, Mats; Medhurst, Jane; Linder, Sune

    2013-11-01

    Accumulated carbon uptake, apparent quantum yield (AQY) and light-saturated net CO2 assimilation (Asat) were used to assess the responses of photosynthesis to environmental conditions during spring for three consecutive years. Whole-tree chambers were used to expose 40-year-old field-grown Norway spruce trees in northern Sweden to an elevated atmospheric CO2 concentration, [CO2], of 700 μmol CO2 mol(-1) (CE) and an air temperature (T) between 2.8 and 5.6 °C above ambient T (TE), during summer and winter. Net shoot CO2 exchange (Anet) was measured continuously on 1-year-old shoots and was used to calculate the accumulated carbon uptake and daily Asat and AQY. The accumulated carbon uptake, from 1 March to 30 June, was stimulated by 33, 44 and 61% when trees were exposed to CE, TE, and CE and TE combined, respectively. Air temperature strongly influenced the timing and extent of photosynthetic recovery expressed as AQY and Asat during the spring. Under elevated T (TE), the recovery of AQY and Asat commenced ∼10 days earlier and the activity of these parameters was significantly higher throughout the recovery period. In the absence of frost events, the photosynthetic recovery period was less than a week. However, frost events during spring slowed recovery so that full recovery could take up to 60 days to complete. Elevated [CO2] stimulated AQY and Asat on average by ∼10 and ∼50%, respectively, throughout the recovery period, but had minimal or no effect on the onset and length of the photosynthetic recovery period during the spring. However, AQY, Asat and Anet all recovered at significantly higher T (average +2.2 °C) in TE than in TA, possibly caused by acclimation or by shorter days and lower light levels during the early part of the recovery in TE compared with TA. The results suggest that predicted future climate changes will cause prominent stimulation of photosynthetic CO2 uptake in boreal Norway spruce forest during spring, mainly caused by elevated T

  10. Spring photosynthetic recovery of boreal Norway spruce under conditions of elevated [CO(2)] and air temperature.

    PubMed

    Wallin, Göran; Hall, Marianne; Slaney, Michelle; Räntfors, Mats; Medhurst, Jane; Linder, Sune

    2013-11-01

    Accumulated carbon uptake, apparent quantum yield (AQY) and light-saturated net CO2 assimilation (Asat) were used to assess the responses of photosynthesis to environmental conditions during spring for three consecutive years. Whole-tree chambers were used to expose 40-year-old field-grown Norway spruce trees in northern Sweden to an elevated atmospheric CO2 concentration, [CO2], of 700 μmol CO2 mol(-1) (CE) and an air temperature (T) between 2.8 and 5.6 °C above ambient T (TE), during summer and winter. Net shoot CO2 exchange (Anet) was measured continuously on 1-year-old shoots and was used to calculate the accumulated carbon uptake and daily Asat and AQY. The accumulated carbon uptake, from 1 March to 30 June, was stimulated by 33, 44 and 61% when trees were exposed to CE, TE, and CE and TE combined, respectively. Air temperature strongly influenced the timing and extent of photosynthetic recovery expressed as AQY and Asat during the spring. Under elevated T (TE), the recovery of AQY and Asat commenced ∼10 days earlier and the activity of these parameters was significantly higher throughout the recovery period. In the absence of frost events, the photosynthetic recovery period was less than a week. However, frost events during spring slowed recovery so that full recovery could take up to 60 days to complete. Elevated [CO2] stimulated AQY and Asat on average by ∼10 and ∼50%, respectively, throughout the recovery period, but had minimal or no effect on the onset and length of the photosynthetic recovery period during the spring. However, AQY, Asat and Anet all recovered at significantly higher T (average +2.2 °C) in TE than in TA, possibly caused by acclimation or by shorter days and lower light levels during the early part of the recovery in TE compared with TA. The results suggest that predicted future climate changes will cause prominent stimulation of photosynthetic CO2 uptake in boreal Norway spruce forest during spring, mainly caused by elevated T

  11. Plant Pathogenic Microbial Communication Affected by Elevated Temperature in Pectobacterium carotovorum subsp. carotovorum.

    PubMed

    Saha, N D; Chaudhary, A; Singh, S D; Singh, D; Walia, S; Das, T K

    2015-11-01

    Gram-negative plant pathogenic bacteria regulate specific gene expression in a population density-dependent manner by sensing level of Acyl-Homoserine Lactone (HSL) molecules which they produce and liberate to the environment, called Quorum Sensing (QS). The production of virulence factors (extracellular enzyme viz. cellulase, pectinase, etc.) in Pectobacterium carotovorum subsp. carotovorum (Pcc) is under strong regulation of QS. The QS signal molecule, N-(3-oxohexanoyl)-L-Homoserine Lactone (OHHL) was found as the central regulatory system for the virulence factor production in Pcc and is also under strict regulation of external environmental temperature. Under seven different incubation temperatures (24, 26, 28, 30, 33, 35, and 37 °C) in laboratory condition, highest amount of OHHL (804 violacein unit) and highest (79 %) Disease Severity Index (DSI) were measured at 33 °C. The OHHL production kinetics showed accumulation of highest concentration of OHHL at late log phase of the growth but diminution in the concentration occurred during stationary phase onwards to death phase. At higher temperature (35 and 37 °C) exposure, OHHL was not at detectable range. The effect of temperature on virulence factor production is the concomitant effect of HSL production and degradation which justifies less disease severity index in cross-inoculated tomato fruits incubated at 35 and 37 °C. The nondetection of the OHHL in the elevated temperature may because of degradation as these signal molecules are quite sensitive and prone to get degraded under different physical factors. This result provides the rationale behind the highest disease severity up to certain elevated temperature and leaves opportunities for investigation on mutation, co-evolution of superior plant pathogen with more stable HSL signals-mediated pathogenesis under global warming context. PMID:26271295

  12. Plant Pathogenic Microbial Communication Affected by Elevated Temperature in Pectobacterium carotovorum subsp. carotovorum.

    PubMed

    Saha, N D; Chaudhary, A; Singh, S D; Singh, D; Walia, S; Das, T K

    2015-11-01

    Gram-negative plant pathogenic bacteria regulate specific gene expression in a population density-dependent manner by sensing level of Acyl-Homoserine Lactone (HSL) molecules which they produce and liberate to the environment, called Quorum Sensing (QS). The production of virulence factors (extracellular enzyme viz. cellulase, pectinase, etc.) in Pectobacterium carotovorum subsp. carotovorum (Pcc) is under strong regulation of QS. The QS signal molecule, N-(3-oxohexanoyl)-L-Homoserine Lactone (OHHL) was found as the central regulatory system for the virulence factor production in Pcc and is also under strict regulation of external environmental temperature. Under seven different incubation temperatures (24, 26, 28, 30, 33, 35, and 37 °C) in laboratory condition, highest amount of OHHL (804 violacein unit) and highest (79 %) Disease Severity Index (DSI) were measured at 33 °C. The OHHL production kinetics showed accumulation of highest concentration of OHHL at late log phase of the growth but diminution in the concentration occurred during stationary phase onwards to death phase. At higher temperature (35 and 37 °C) exposure, OHHL was not at detectable range. The effect of temperature on virulence factor production is the concomitant effect of HSL production and degradation which justifies less disease severity index in cross-inoculated tomato fruits incubated at 35 and 37 °C. The nondetection of the OHHL in the elevated temperature may because of degradation as these signal molecules are quite sensitive and prone to get degraded under different physical factors. This result provides the rationale behind the highest disease severity up to certain elevated temperature and leaves opportunities for investigation on mutation, co-evolution of superior plant pathogen with more stable HSL signals-mediated pathogenesis under global warming context.

  13. Elevated temperature altered photosynthetic products in wheat seedlings and organic compounds and biological activity in rhizopshere soil under cadmium stress

    PubMed Central

    Jia, Xia; Zhao, YongHua; Wang, WenKe; He, Yunhua

    2015-01-01

    The objective of this study was to investigate the effects of slightly elevated atmospheric temperature in the spring on photosynthetic products in wheat seedlings and on organic compounds and biological activity in rhizosphere soil under cadmium (Cd) stress. Elevated temperature was associated with increased soluble sugars, reducing sugars, starch, and total sugars, and with decreased amino acids in wheat seedlings under Cd stress. Elevated temperature improved total soluble sugars, free amino acids, soluble phenolic acids, and organic acids in rhizosphere soil under Cd stress. The activity of amylase, phenol oxidase, invertase, β-glucosidase, and l-asparaginase in rhizosphere soil was significantly improved by elevated temperature under Cd stress; while cellulase, neutral phosphatase, and urease activity significantly decreased. Elevated temperature significantly improved bacteria, fungi, actinomycetes, and total microorganisms abundance and fluorescein diacetate activity under Cd stress. In conclusion, slightly elevated atmospheric temperature in the spring improved the carbohydrate levels in wheat seedlings and organic compounds and biological activity in rhizosphere soil under Cd stress in the short term. In addition, elevated atmospheric temperature in the spring stimulated available Cd by affecting pH, DOC, phenolic acids, and organic acids in rhizosphere soil, which resulted in the improvement of the Cd uptake by wheat seedlings. PMID:26395070

  14. Elevated temperature altered photosynthetic products in wheat seedlings and organic compounds and biological activity in rhizopshere soil under cadmium stress.

    PubMed

    Jia, Xia; Zhao, YongHua; Wang, WenKe; He, Yunhua

    2015-01-01

    The objective of this study was to investigate the effects of slightly elevated atmospheric temperature in the spring on photosynthetic products in wheat seedlings and on organic compounds and biological activity in rhizosphere soil under cadmium (Cd) stress. Elevated temperature was associated with increased soluble sugars, reducing sugars, starch, and total sugars, and with decreased amino acids in wheat seedlings under Cd stress. Elevated temperature improved total soluble sugars, free amino acids, soluble phenolic acids, and organic acids in rhizosphere soil under Cd stress. The activity of amylase, phenol oxidase, invertase, β-glucosidase, and l-asparaginase in rhizosphere soil was significantly improved by elevated temperature under Cd stress; while cellulase, neutral phosphatase, and urease activity significantly decreased. Elevated temperature significantly improved bacteria, fungi, actinomycetes, and total microorganisms abundance and fluorescein diacetate activity under Cd stress. In conclusion, slightly elevated atmospheric temperature in the spring improved the carbohydrate levels in wheat seedlings and organic compounds and biological activity in rhizosphere soil under Cd stress in the short term. In addition, elevated atmospheric temperature in the spring stimulated available Cd by affecting pH, DOC, phenolic acids, and organic acids in rhizosphere soil, which resulted in the improvement of the Cd uptake by wheat seedlings.

  15. Elevated temperature altered photosynthetic products in wheat seedlings and organic compounds and biological activity in rhizopshere soil under cadmium stress

    NASA Astrophysics Data System (ADS)

    Jia, Xia; Zhao, Yonghua; Wang, Wenke; He, Yunhua

    2015-09-01

    The objective of this study was to investigate the effects of slightly elevated atmospheric temperature in the spring on photosynthetic products in wheat seedlings and on organic compounds and biological activity in rhizosphere soil under cadmium (Cd) stress. Elevated temperature was associated with increased soluble sugars, reducing sugars, starch, and total sugars, and with decreased amino acids in wheat seedlings under Cd stress. Elevated temperature improved total soluble sugars, free amino acids, soluble phenolic acids, and organic acids in rhizosphere soil under Cd stress. The activity of amylase, phenol oxidase, invertase, β-glucosidase, and L-asparaginase in rhizosphere soil was significantly improved by elevated temperature under Cd stress; while cellulase, neutral phosphatase, and urease activity significantly decreased. Elevated temperature significantly improved bacteria, fungi, actinomycetes, and total microorganisms abundance and fluorescein diacetate activity under Cd stress. In conclusion, slightly elevated atmospheric temperature in the spring improved the carbohydrate levels in wheat seedlings and organic compounds and biological activity in rhizosphere soil under Cd stress in the short term. In addition, elevated atmospheric temperature in the spring stimulated available Cd by affecting pH, DOC, phenolic acids, and organic acids in rhizosphere soil, which resulted in the improvement of the Cd uptake by wheat seedlings.

  16. Elevated temperature altered photosynthetic products in wheat seedlings and organic compounds and biological activity in rhizopshere soil under cadmium stress.

    PubMed

    Jia, Xia; Zhao, YongHua; Wang, WenKe; He, Yunhua

    2015-01-01

    The objective of this study was to investigate the effects of slightly elevated atmospheric temperature in the spring on photosynthetic products in wheat seedlings and on organic compounds and biological activity in rhizosphere soil under cadmium (Cd) stress. Elevated temperature was associated with increased soluble sugars, reducing sugars, starch, and total sugars, and with decreased amino acids in wheat seedlings under Cd stress. Elevated temperature improved total soluble sugars, free amino acids, soluble phenolic acids, and organic acids in rhizosphere soil under Cd stress. The activity of amylase, phenol oxidase, invertase, β-glucosidase, and l-asparaginase in rhizosphere soil was significantly improved by elevated temperature under Cd stress; while cellulase, neutral phosphatase, and urease activity significantly decreased. Elevated temperature significantly improved bacteria, fungi, actinomycetes, and total microorganisms abundance and fluorescein diacetate activity under Cd stress. In conclusion, slightly elevated atmospheric temperature in the spring improved the carbohydrate levels in wheat seedlings and organic compounds and biological activity in rhizosphere soil under Cd stress in the short term. In addition, elevated atmospheric temperature in the spring stimulated available Cd by affecting pH, DOC, phenolic acids, and organic acids in rhizosphere soil, which resulted in the improvement of the Cd uptake by wheat seedlings. PMID:26395070

  17. Sensitivity of cold acclimation to elevated autumn temperature in field-grown Pinus strobus seedlings

    PubMed Central

    Chang, Christine Y.; Unda, Faride; Zubilewich, Alexandra; Mansfield, Shawn D.; Ensminger, Ingo

    2015-01-01

    Climate change will increase autumn air temperature, while photoperiod decrease will remain unaffected. We assessed the effect of increased autumn air temperature on timing and development of cold acclimation and freezing resistance in Eastern white pine (EWP, Pinus strobus) under field conditions. For this purpose we simulated projected warmer temperatures for southern Ontario in a Temperature Free-Air-Controlled Enhancement (T-FACE) experiment and exposed EWP seedlings to ambient (Control) or elevated temperature (ET, +1.5°C/+3°C during day/night). Photosynthetic gas exchange, chlorophyll fluorescence, photoprotective pigments, leaf non-structural carbohydrates (NSC), and cold hardiness were assessed over two consecutive autumns. Nighttime temperature below 10°C and photoperiod below 12 h initiated downregulation of assimilation in both treatments. When temperature further decreased to 0°C and photoperiod became shorter than 10 h, downregulation of the light reactions and upregulation of photoprotective mechanisms occurred in both treatments. While ET seedlings did not delay the timing of the downregulation of assimilation, stomatal conductance in ET seedlings was decreased by 20–30% between August and early October. In both treatments leaf NSC composition changed considerably during autumn but differences between Control and ET seedlings were not significant. Similarly, development of freezing resistance was induced by exposure to low temperature during autumn, but the timing was not delayed in ET seedlings compared to Control seedlings. Our results indicate that EWP is most sensitive to temperature changes during October and November when downregulation of photosynthesis, enhancement of photoprotection, synthesis of cold-associated NSCs and development of freezing resistance occur. However, we also conclude that the timing of the development of freezing resistance in EWP seedlings is not affected by moderate temperature increases used in our field

  18. Dynamic Mechanical Properties of Ceramics and Ceramic Composites at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Yang, Shuo

    1995-01-01

    Advanced ceramics and ceramic matrix composites (CMCs) have great potential for structural application in combustion engines and other energy generating equipment since the required high operating temperatures in such environments have driven traditional metals and superalloys to their limits due to their melting points. As promising substitutes, ceramics and ceramic matrix composites not only significantly increase service temperature, but also have other salient features, such as low density, good chemical stability, and excellent hardness, which offer additional potential for extending performance limits beyond those offered by metallic materials. Dynamic mechanical properties are significant properties for structural materials which subject to dynamic loading. Because of the challenge of high temperature and vibratory environments in advanced combustion engines and energy generating systems, ceramics and ceramic composites also should have good dynamic properties so as to increase durability, reliability, and reduce noise and vibration levels. But, unfortunately, knowledge regarding dynamic mechanical properties of ceramics and ceramic composites at elevated temperatures is limited. This research has focused on the dynamic mechanical properties of silicon nitride based ceramics and composites reinforced with silicon carbide whiskers. These ceramic materials have been considered to be the most attractive structural materials for engine applications. By conducting experiments up to 1100^circC, this research systematically investigates the damping and elastic behavior, explores the possible mechanisms which dominate the damping properties of these materials, and examines the effects of simulated thermal cycling loads on dynamic mechanical properties and microstructures of these promising high temperature structural materials. This research also studies the experimental methods for dynamic testing of ceramic materials, compares experimental results with some

  19. Hypervelocity impact damage response and characterization of thin plate targets at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Corbett, Brooke Myers

    The performance of a typical International Space Station (ISS) shield against the meteoroid and orbital debris (M/OD) impact threat is generally modeled by damage equations for the outer shield and the rear pressure wall. In their current forms, these damage equations neglect the on-orbit temperature extremes witnessed by the ISS. To address IF and HOW temperature extremes affect the performance of the ISS' typical M/OD shield, a comprehensive study was undertaken that investigated hole diameters in .063" thick 6061-T6 aluminum targets impacted at velocities from ˜2-7 km/s at 20°C, 110°C, and 210°C. Robust graphical and analytical analyses confirmed the existence of a statistically significant temperature effect, i.e., hole diameters in heated targets were larger than those in room temperature targets. A new temperature-dependent model was found via multivariable regression analysis that incorporates a linear velocity term and a temperature term based on a form of the cumulative distribution function. Numerical modeling of hypervelocity impacts (HVI) into elevated temperature targets was also performed to determine whether or not currently available material and failure models can adequately simulate the differences observed between room and elevated temperature target hole diameters. Statistical analyses showed that AUTODYN simulated the heated data almost as well as the room temperature data. However, the slightly worse Goodness of Fit (GOF) values between the heated empirical vs. simulated comparisons suggest that the simulations do not completely account for the observed temperature effect. A series of materials tests and observations were carried out on the post-impacted target plates to help explain the empirical data results with respect to material variability and deformation features. Rockwell B and K macro-hardness tests revealed that the hardness values for the targets impacted at 110°C were statistically significantly higher compared to those

  20. Microstructure and elevated-temperature erosion-oxidation behaviour of aluminized 9Cr-1Mo Steel

    NASA Astrophysics Data System (ADS)

    Huttunen-Saarivirta, E.; Honkanen, M.; Tsipas, S. A.; Omar, H.; Tsipas, D.

    2012-10-01

    Degradation of materials by a combination of erosive wear and atmospheric oxidation at elevated temperatures constitutes a problem in some power generation processes, such as fluidized-bed combustion. In this work, 9Cr-1Mo steel, a common tube material in combustion chambers, is coated by a pack cementation method from an Al-containing pack in order to improve the resistance to erosion-oxidation at elevated temperatures. The resulting coating is studied in terms of microstructure and microhardness and tested for its resistance against impacts by sand particles in air at temperatures of 550-700 °C under several conditions, with thickness changes and appearance of the exposed surfaces being studied. The coating was found to contain several phases and layers, the outermost of which was essentially Al-rich and contained e.g., small AlN precipitates. The microhardness values for such coating ranged from 950 to 1100 HV20g. The coating provided the substrate with increased protection particularly against normal particle impacts, as manifested by smaller thickness losses for coated specimens as compared to uncoated counterparts. However, much of the coating was lost under all test conditions, despite the fact that particle debris formed a homogeneous layer on the surface. These results are described and discussed in this paper.

  1. Near-infrared Laser-induced Temperature Elevation in Optically-trapped Aqueous Droplets in Air.

    PubMed

    Ishizaka, Shoji; Ma, Jiang; Fujiwara, Terufumi; Yamauchi, Kunihiro; Kitamura, Noboru

    2016-01-01

    Near-infrared laser-induced temperature elevation in single aqueous ammonium sulfate droplets levitated in air were evaluated by means of laser trapping and Raman spectroscopy. Since the vapor pressure in an aqueous solution droplet should be thermodynamically in equilibrium with that of water in air, the equilibrium size of the droplet varies sensitively through evaporation/condensation of water in accordance with the temperature change of the droplet. In this study, we demonstrated that the changes in the size of an optically levitated aqueous ammonium sulfate droplet were induced by irradiation of a 1064-nm laser beam as a heat source under an optical microscope. Temperature elevation in the droplet was evaluated successfully by means of Raman spectroscopy, and the values determined were shown to be in good agreement with those by the theoretical calculations based on the absorption coefficient of water at 1064-nm and the thermal conductivity of air. To the best of our knowledge, this is the first experimental demonstration showing that the absorption coefficient evaluated from changes in the size of optically-trapped aqueous droplets is consistent with that of pure water. PMID:27063715

  2. Electrodeposition of germanium at elevated temperatures and pressures from ionic liquids.

    PubMed

    Wu, Minxian; Vanhoutte, Gijs; Brooks, Neil R; Binnemans, Koen; Fransaer, Jan

    2015-05-14

    The electrodeposition of germanium at elevated temperatures up to 180 °C and pressures was studied from the ionic liquids 1-butyl-1-methylpyrrolidinium dicyanamide and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide containing [GeCl4(BuIm)2] (where BuIm = 1-butylimidazole) or GeCl4. Cyclic voltammetry (CV), electrochemical quartz crystal microbalance (EQCM), rotating ring-disk electrode (RRDE), scanning electron microscope (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and Auger electron spectroscopy (AES) were used to investigate the electrochemical behavior and the properties of the electrodeposited germanium. Electrodeposition at elevated temperatures leads to higher deposition rates due to: (1) increase in the diffusion rate of the electroactive germanium compounds; (2) faster electrochemical kinetics in the electrolyte; and (3) higher electrical conductivity of the electrodeposited germanium film. Moreover, the morphology of the germanium film is also of a better quality at higher electrodeposition temperatures due to an increase in adatom mobility.

  3. Control of Thermal Deflection, Panel Flutter and Acoustic Fatigue at Elevated Temperatures Using Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Mei, Chuh; Huang, Jen-Kuang

    1996-01-01

    The High Speed Civil Transport (HSCT) will have to be designed to withstand high aerodynamic load at supersonic speeds (panel flutter) and high acoustic load (acoustic or sonic fatigue) due to fluctuating boundary layer or jet engine acoustic pressure. The thermal deflection of the skin panels will also alter the vehicle's configuration, thus it may affect the aerodynamic characteristics of the vehicle and lead to poor performance. Shape memory alloys (SMA) have an unique ability to recover large strains completely when the alloy is heated above the characteristic transformation (austenite finish T(sub f)) temperature. The recovery stress and elastic modulus are both temperature dependent, and the recovery stress also depends on the initial strain. An innovative concept is to utilize the recovery stress by embedding the initially strained SMA wire in a graphite/epoxy composite laminated panel. The SMA wires are thus restrained and large inplane forces are induced in the panel at elevated temeperatures. By embedding SMA in composite panel, the panel becomes much stiffer at elevated temperatures. That is because the large tensile inplane forces induced in the panel from the SMA recovery stress. A stiffer panel would certainly yield smaller dynamic responses.

  4. Measurements of Young's and shear moduli of rail steel at elevated temperatures.

    PubMed

    Bao, Yuanye; Zhang, Haifeng; Ahmadi, Mehdi; Karim, Md Afzalul; Felix Wu, H

    2014-03-01

    The design and modelling of the buckling effect of Continuous Welded Rail (CWR) requires accurate material constants, especially at elevated temperatures. However, such material constants have rarely been found in literature. In this article, the Young's moduli and shear moduli of rail steel at elevated temperatures are determined by a new sonic resonance method developed in our group. A network analyser is used to excite a sample hanged inside a furnace through a simple tweeter type speaker. The vibration signal is picked up by a Polytec OFV-5000 Laser Vibrometer and then transferred back to the network analyser. Resonance frequencies in both the flexural and torsional modes are measured, and the Young's moduli and shear moduli are determined through the measured resonant frequencies. To validate the measured elastic constants, the measurements have been repeated by using the classic sonic resonance method. The comparisons of obtained moduli from the two methods show an excellent consistency of the results. In addition, the material elastic constants measured are validated by an ultrasound test based on a pulse-echo method and compared with previous published results at room temperature. The measured material data provides an invaluable reference for the design of CWR to avoid detrimental buckling failure.

  5. OSMOTIC COEFFICIENTS, SOLUBILITIES, AND DELIQUESCENCE RELATIONS IN MIXED AQUEOUS SALT SOLUTIONS AT ELEVATED TEMPERATURE

    SciTech Connect

    M.S. Gruszkiewicz; D.A. Palmer

    2006-02-22

    While thermodynamic properties of pure aqueous electrolytes are relatively well known at ambient temperature, there are far fewer data for binary systems extending to elevated temperatures and high concentrations. There is no general theoretically sound basis for prediction of the temperature dependence of ionic activities, and consequently temperature extrapolations based on ambient temperature data and empirical equations are uncertain and require empirical verification. Thermodynamic properties of mixed brines in a wide range of concentrations would enhance the understanding and precise modeling of the effects of deliquescence of initially dry solids in humid air in geological environments and in modeling the composition of waters during heating, cooling, evaporation or condensation processes. These conditions are of interest in the analysis of waters on metal surfaces at the proposed radioactive waste repository at Yucca Mountain, Nevada. The results obtained in this project will be useful for modeling the long-term evolution of the chemical environment, and this in turn is useful for the analysis of the corrosion of waste packages. In particular, there are few reliable experimental data available on the relationship between relative humidity and composition that reveals the eutonic points of the mixtures and the mixture deliquescence RH. The deliquescence RH for multicomponent mixtures is lower than that of pure component or binary solutions, but is not easy to predict quantitatively since the solutions are highly nonideal. In this work we used the ORNL low-temperature and high-temperature isopiestic facilities, capable of precise measurements of vapor pressure between ambient temperature and 250 C for determination of not only osmotic coefficients, but also solubilities and deliquescence points of aqueous mixed solutions in a range of temperatures. In addition to standard solutions of CaCl{sub 2}, LiCl, and NaCl used as references, precise direct

  6. Temperature elevation by HIFU in ex vivo porcine muscle: MRI measurement and simulation study

    SciTech Connect

    Solovchuk, Maxim A.; Hwang, San Chao; Chang, Hsu; Thiriet, Marc; Sheu, Tony W. H.

    2014-05-15

    Purpose: High-intensity focused ultrasound is a rapidly developing medical technology with a large number of potential clinical applications. Computational model can play a pivotal role in the planning and optimization of the treatment based on the patient's image. Nonlinear propagation effects can significantly affect the temperature elevation and should be taken into account. In order to investigate the importance of nonlinear propagation effects, nonlinear Westervelt equation was solved. Weak nonlinear propagation effects were studied. The purpose of this study was to investigate the correlation between the predicted and measured temperature elevations and lesion in a porcine muscle. Methods: The investigated single-element transducer has a focal length of 12 cm, an aperture of 8 cm, and frequency of 1.08 MHz. Porcine muscle was heated for 30 s by focused ultrasound transducer with an acoustic power in the range of 24–56 W. The theoretical model consists of nonlinear Westervelt equation with relaxation effects being taken into account and Pennes bioheat equation. Results: Excellent agreement between the measured and simulated temperature rises was found. For peak temperatures above 85–90 °C “preboiling” or cavitation activity appears and lesion distortion starts, causing small discrepancy between the measured and simulated temperature rises. From the measurements and simulations, it was shown that distortion of the lesion was caused by the “preboiling” activity. Conclusions: The present study demonstrated that for peak temperatures below 85–90 °C numerical simulation results are in excellent agreement with the experimental data in three dimensions. Both temperature rise and lesion size can be well predicted. Due to nonlinear effect the temperature in the focal region can be increased compared with the linear case. The current magnetic resonance imaging (MRI) resolution is not sufficient. Due to the inevitable averaging the measured

  7. Surface mapping of field-induced piezoelectric strain at elevated temperature employing full-field interferometry.

    PubMed

    Stevenson, Tim; Quast, Tatjana; Bartl, Guido; Schmitz-Kempen, Thorsten; Weaver, Paul M

    2015-01-01

    Piezoelectric actuators and sensors are widely used for flow control valves, including diesel injectors, ultrasound generation, optical positioning, printing, pumps, and locks. Degradation and failure of material and electrical properties at high temperature typically limits these applications to operating temperatures below 200°C, based on the ubiquitous Pb(Zr,Ti)O3 ceramic. There are, however, many applications in sectors such as automotive, aerospace, energy and process control, and oil and gas, where the ability to operate at higher temperatures would open up new markets for piezoelectric actuation. Presented here is a review of recent progress and initial results toward a European effort to develop measurement techniques to characterize high-temperature materials. Full-field, multi-wavelength absolute length interferometry has, for the first time, been used to map the electric-field-induced piezoelectric strain across the surface of a PZT ceramic. The recorded variation as a function of temperature has been evaluated against a newly developed commercial single-beam system. Conventional interferometry allows measurement of the converse piezoelectric effect with high precision and resolution, but is often limited to a single point, average measurement and to limited sample environments because of optical aberrations in varying atmospheres. Here, the full-field technique allows the entire surface to be analyzed for strain and, in a bespoke sample chamber, for elevated temperatures. PMID:25585393

  8. Piezoelectric response of BiFeO3 ceramics at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Rojac, Tadej; Makarovic, Maja; Walker, Julian; Ursic, Hana; Damjanovic, Dragan; Kos, Tomaz

    2016-07-01

    The high Curie temperature (TC ˜ 825 °C) of BiFeO3 has made this material potentially attractive for the development of high-TC piezoelectric ceramics. Despite significant advances in the search of new BiFeO3-based compositions, the piezoelectric behavior of the parent BiFeO3 at elevated temperatures remains unexplored. We present here a systematic analysis of the converse, longitudinal piezoelectric response of BiFeO3 measured in situ as a function of temperature (25-260 °C), driving-field frequency, and amplitude. Earlier studies performed at room temperature revealed that the frequency and field dependence of the longitudinal response of BiFeO3 is dominated by linear and nonlinear piezoelectric Maxwell-Wagner mechanisms, originating from the presence of local conductive paths along domain walls and grain boundaries within the polycrystalline matrix. This study shows that the same mechanisms are responsible for the distinct temperature dependence of the piezoelectric coefficient and phase angle and thus identifies the local electrical conductivity as the key for controlling the temperature dependent piezoelectric response of BiFeO3 and possibly other, more complex BiFeO3-based compositions.

  9. Surface mapping of field-induced piezoelectric strain at elevated temperature employing full-field interferometry.

    PubMed

    Stevenson, Tim; Quast, Tatjana; Bartl, Guido; Schmitz-Kempen, Thorsten; Weaver, Paul M

    2015-01-01

    Piezoelectric actuators and sensors are widely used for flow control valves, including diesel injectors, ultrasound generation, optical positioning, printing, pumps, and locks. Degradation and failure of material and electrical properties at high temperature typically limits these applications to operating temperatures below 200°C, based on the ubiquitous Pb(Zr,Ti)O3 ceramic. There are, however, many applications in sectors such as automotive, aerospace, energy and process control, and oil and gas, where the ability to operate at higher temperatures would open up new markets for piezoelectric actuation. Presented here is a review of recent progress and initial results toward a European effort to develop measurement techniques to characterize high-temperature materials. Full-field, multi-wavelength absolute length interferometry has, for the first time, been used to map the electric-field-induced piezoelectric strain across the surface of a PZT ceramic. The recorded variation as a function of temperature has been evaluated against a newly developed commercial single-beam system. Conventional interferometry allows measurement of the converse piezoelectric effect with high precision and resolution, but is often limited to a single point, average measurement and to limited sample environments because of optical aberrations in varying atmospheres. Here, the full-field technique allows the entire surface to be analyzed for strain and, in a bespoke sample chamber, for elevated temperatures.

  10. Identification of possible factors influencing temperatures elevation during implant site preparation with piezoelectric technique

    PubMed Central

    Lamazza, Luca; Laurito, Domenica; Lollobrigida, Marco; Brugnoletti, Orlando; Garreffa, Girolamo; De Biase, Alberto

    2014-01-01

    Summary Background Overheating during implant site preparation negatively affects the osseointegration process as well the final outcome of implant rehabilitations. Piezoelectric techniques seem to provide to a gentle implant preparation although few scientific reports have investigated the heat generation and its underlying factors. Purpose To investigate, through a proper methodological approach, the main factors influencing temperature rise during piezoelectric implant site preparation. Materials and methods Different piezoelectric tips (IM1s, IM2, P2-3, IM3, Mectron Medical Technology, Carasco, Italy) have been tested. The experimental set-up consisted in a mechanical positioning device equipped with a load cell and a fluoroptic thermometer. Results The first tip of the sequence (IM1s) generated the highest temperature increasing (ΔT). The diamond tips (IM1s and P2-3) determined higher ΔT values than the smooth tips (IM2 and IM3). Further tests with IM1s suggested that the temperature elevation during the first thirty seconds may be predictive of the maximal temperature as well as of the overall thermal impact. Conclusions Working load, working movements management and bone features resulted to be the main factors influencing temperature rise during piezoelectric implant site preparation. Irrigant temperature and clogging effect may also synergically contribute to the heat generation. PMID:25774245

  11. Plasticity mechanisms in HfN at elevated and room temperature

    PubMed Central

    Vinson, Katherine; Yu, Xiao-Xiang; De Leon, Nicholas; Weinberger, Christopher R.; Thompson, Gregory B.

    2016-01-01

    HfN specimens deformed via four-point bend tests at room temperature and at 2300 °C (~0.7 Tm) showed increased plasticity response with temperature. Dynamic diffraction via transmission electron microscopy (TEM) revealed ⟨110⟩{111} as the primary slip system in both temperature regimes and ⟨110⟩{110} to be a secondary slip system activated at elevated temperature. Dislocation line lengths changed from a primarily linear to a curved morphology with increasing temperature suggestive of increased dislocation mobility being responsible for the brittle to ductile temperature transition. First principle generalized stacking fault energy calculations revealed an intrinsic stacking fault (ISF) along ⟨112⟩{111}, which is the partial dislocation direction for slip on these close packed planes. Though B1 structures, such as NaCl and HfC predominately slip on ⟨110⟩{110}, the ISF here is believed to facilitate slip on the {111} planes for this B1 HfN phase. PMID:27708354

  12. Soot surface temperature measurements in pure and diluted flames at atmospheric and elevated pressures

    SciTech Connect

    Berry Yelverton, T.L.; Roberts, W.L.

    2008-10-15

    Soot surface temperature was measured in laminar jet diffusion flames at atmospheric and elevated pressures. The soot surface temperature was measured in flames at one, two, four, and eight atmospheres with both pure and diluted (using helium, argon, nitrogen, or carbon dioxide individually) ethylene fuels with a calibrated two-color soot pyrometry technique. These two dimensional temperature profiles of the soot aid in the analysis and understanding of soot production, leading to possible methods for reducing soot emission. Each flame investigated was at its smoke point, i.e., at the fuel flow rate where the overall soot production and oxidation rates are equal. The smoke point was chosen because it was desirable to have similar soot loadings for each flame. A second set of measurements were also taken where the fuel flow rate was held constant to compare with earlier work. These measurements show that overall flame temperature decreases with increasing pressure, with increasing pressure the position of peak temperature shifts to the tip of the flame, and the temperatures measured were approximately 10% lower than those calculated assuming equilibrium and neglecting radiation. (author)

  13. Hindered diffusion of asphaltenes at elevated temperature and pressure. Semiannual report, March 20 - September 20, 1996

    SciTech Connect

    Guin, J.A.; Geelen, R.; Gregory, C.; Yang, X.

    1996-11-01

    The objectives are to: investigate the hindered diffusion of coal and petroleum asphaltenes in the pores of catalyst particles at elevated temperature and pressures; and examine the effects of concentration, temperature, solvent type, and pressure on the intraparticle diffusivity of asphaltenes. Progress was made in several areas during this time period. The high temperature/high pressure autoclave has been received from Parr Instrument Company and is in the process of being set up and checked out. During this time period we mainly worked in two areas. In the first area, we performed some measurements on the adsorption isotherms of the model compound quinoline in cyclohexane onto a Criterion 324 catalyst at three temperatures. We are looking at the effect of temperature on the adsorption isotherms of several model compounds. This area is important since the adsorptive uptake of asphaltenes is being studied and the model compound systems lend insight as to how we may expect the more complex asphaltene systems to behave during adsorption on the surface of the porous particles. We found that even for the simple model compound quinoline, the adsorption behavior vs. temperature was quite 0563 complex. The second area explored during this time period was the application of a mathematical model to adsorptive uptake data for asphaltenes on Criterion 324 catalyst particles. This adsorptive uptake data was obtained during the previous time period and was analyzed by mathematical modeling during the current time period. The detailed findings in both of these areas are presented in this report.

  14. Plasticity mechanisms in HfN at elevated and room temperature

    NASA Astrophysics Data System (ADS)

    Vinson, Katherine; Yu, Xiao-Xiang; de Leon, Nicholas; Weinberger, Christopher R.; Thompson, Gregory B.

    2016-10-01

    HfN specimens deformed via four-point bend tests at room temperature and at 2300 °C (~0.7 Tm) showed increased plasticity response with temperature. Dynamic diffraction via transmission electron microscopy (TEM) revealed ⟨110⟩{111} as the primary slip system in both temperature regimes and ⟨110⟩{110} to be a secondary slip system activated at elevated temperature. Dislocation line lengths changed from a primarily linear to a curved morphology with increasing temperature suggestive of increased dislocation mobility being responsible for the brittle to ductile temperature transition. First principle generalized stacking fault energy calculations revealed an intrinsic stacking fault (ISF) along ⟨112⟩{111}, which is the partial dislocation direction for slip on these close packed planes. Though B1 structures, such as NaCl and HfC predominately slip on ⟨110⟩{110}, the ISF here is believed to facilitate slip on the {111} planes for this B1 HfN phase.

  15. Tensile deformation of 2618 and Al-Fe-Si-V aluminum alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Leng, Y.; Porr, W. C., Jr.; Gangloff, R. P.

    1990-01-01

    The present study experimentally characterizes the effects of elevated temperature on the uniaxial tensile behavior of ingot metallurgy 2618 Al alloy and the rapidly solidified FVS 0812 P/M alloy by means of two constitutive formulations: the Ramberg/Osgood equation and the Bodner-Partom (1975) incremental formulation for uniaxial tensile loading. The elastoplastic strain-hardening behavior of the ingot metallurgy alloy is equally well represented by either formulation. Both alloys deform similarly under decreasing load after only 1-5 percent uniform tensile strain, a response which is not described by either constitutive relation.

  16. Evolution of precipitate in nickel-base alloy 718 irradiated with argon ions at elevated temperature

    NASA Astrophysics Data System (ADS)

    Jin, Shuoxue; Luo, Fengfeng; Ma, Shuli; Chen, Jihong; Li, Tiecheng; Tang, Rui; Guo, Liping

    2013-07-01

    Alloy 718 is a nickel-base superalloy whose strength derives from γ'(Ni3(Al,Ti)) and γ″(Ni3Nb) precipitates. The evolution of the precipitates in alloy 718 irradiated with argon ions at elevated temperature were examined via transmission electron microscopy. Selected-area electron diffraction indicated superlattice spots disappeared after argon ion irradiation, which showing that the ordered structure of the γ' and γ″ precipitates became disordered. The size of the precipitates became smaller with the irradiation dose increasing at 290 °C.

  17. Correlation between mobile continents and elevated temperatures in the subcontinental mantle

    NASA Astrophysics Data System (ADS)

    Jain, Charitra; Rozel, Antoine; Tackley, Paul

    2016-04-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) have previously shown that continents exert a first order influence on Earth's mantle flow by affecting convective wavelength and surface heat flow. With stationary continents, Heron and Lowman (JGR, 2014) highlighted the decreasing role of continental insulation on subcontinental temperatures with higher Rayleigh number (Ra). However, the question whether there exists a correlation between mobile continents and elevated temperatures in the subcontinental mantle or not remains to be answered. By systematically varying parameters like core-mantle boundary (CMB) temperature, continental size, and mantle heating modes (basal and internal); we model thermo-chemical mantle convection with 2D spherical annulus geometry (Hernlund and Tackley, PEPI 2008) using StagYY (Tackley, PEPI 2008). Starting with a simple incompressible model having mobile continents, we observe this correlation. Furthermore, this correlation still holds when the model complexity is gradually increased by introducing internal heating, compressibility, and melting. In general, downwellings reduce the mantle temperature away from the continents, thereby resulting in correlation between mobile continents and elevated temperatures in the subcontinental mantle. For incompressible models (Boussinesq approximation), correlation exists and the dominant degree of convection varies with the continental distribution. When internal heating is switched on, correlation is observed but it is reduced as there are less cold regions in the mantle. Even for compressible models with melting, big continents are able to focus the heat underneath them. The dominant degree of convection changes with continental breakup. Additionally, correlation is observed to be higher in the upper mantle (300 - 1000 km) compared to the lower mantle (1000 - 2890 km). At present, mobile continents in StagYY are simplified into a compositionally distinct field drifting at the top of

  18. Effects of multigenerational exposure to elevated temperature on reproduction, oxidative stress, and Cu toxicity in Daphnia magna.

    PubMed

    Bae, Eunhye; Samanta, Palas; Yoo, Jisu; Jung, Jinho

    2016-10-01

    This study evaluated the effect of temperature (20 and 25°C) on reproduction, oxidative stress, and copper (Cu) toxicity in Daphnia magna across three generations (F0, F1, and F2). Exposing D. magna to elevated temperature significantly decreased the number of offspring per female per day, the time to first brood, and body length compared to exposure to the optimal temperature (p<0.05). In addition, elevated temperature induced a significantly higher production of reactive oxygen species and lipid peroxidation (p<0.05). These findings suggest that D. magna likely responded to thermal stress by investing more energy into defense mechanisms, rather than growth and reproduction. In addition, oxidative stress at the elevated temperature gradually increased with each generation, possibly owing to the reduced fitness of the offspring. Exposing D. magna to 25°C (EC50=34±3µgL(-1)) substantially increased the median effective concentration of Cu in all generations compared to exposure to 20°C (EC50=25±3µgL(-1)), indicating a decrease in acute toxicity at elevated temperature. However, elevated temperature significantly increased the oxidative stress induced by a sublethal concentration of Cu (10µgL(-1)). The interaction between elevated temperature and Cu exposure appears to be synergistic; however, this needs to be confirmed using multiple generations in a long-term experiment. PMID:27376351

  19. Structural characteristics and elevated temperature mechanical properties of AJ62 Mg alloy

    SciTech Connect

    Kubásek, J. Vojtěch, D.; Martínek, M.

    2013-12-15

    Structure and mechanical properties of the novel casting AJ62 (Mg–6Al–2Sr) alloy developed for elevated temperature applications were studied. The AJ62 alloy was compared to commercial casting AZ91 (Mg–9Al–1Zn) and WE43 (Mg–4Y–3RE) alloys. The structure was examined by scanning electron microscopy, x-ray diffraction and energy dispersive spectrometry. Mechanical properties were characterized by Viskers hardness measurements in the as-cast state and after a long-term heat treatment at 250 °C/150 hours. Compressive mechanical tests were also carried out both at room and elevated temperatures. Compressive creep tests were conducted at a temperature of 250 °C and compressive stresses of 60, 100 and 140 MPa. The structure of the AJ62 alloy consisted of primary α-Mg dendrites and interdendritic nework of the Al{sub 4}Sr and massive Al{sub 3}Mg{sub 13}Sr phases. By increasing the cooling rate during solidification from 10 and 120 K/s the average dendrite arm thickness decreased from 18 to 5 μm and the total volume fraction of the interdendritic phases from 20% to 30%. Both factors slightly increased hardness and compressive strength. The room temperature compressive strength and hardness of the alloy solidified at 30 K/s were 298 MPa and 50 HV 5, i.e. similar to those of the as-cast WE43 alloy and lower than those of the AZ91 alloy. At 250 °C the compressive strength of the AJ62 alloy decreased by 50 MPa, whereas those of the AZ91 and WE43 alloys by 100 and 20 MPa, respectively. The creep rate of the AJ62 alloy was higher than that of the WE43 alloy, but significantly lower in comparison with the AZ91 alloy. Different thermal stabilities of the alloys were discussed and related to structural changes during elevated temperature expositions. - Highlights: • Small effect of cooling rate on the compressive strength and hardness of AJ 62 • A bit lower compressive strength of AJ 62 compared to AZ91 at room temperature • Higher resistance of the AJ 62

  20. Evaluation Of Liner Back-pressure Due To Concrete Pore Pressure At Elevated Temperatures

    SciTech Connect

    James, R.J.; Rashid, Y.R.; Liu, A.S.; Gou, B.

    2006-07-01

    GE's latest evolution of the boiling water reactor, the ESBWR, has innovative passive design features that reduce the number and complexity of active systems, which in turn provide economic advantages while also increasing safety. These passive systems used for emergency cooling also mean that the primary containment system will experience elevated temperatures with longer durations than conventional plants in the event of design basis accidents. During a Loss of Coolant Accident (LOCA), the drywell in the primary containment structure for the ESBWR will be exposed to saturated steam conditions for up to 72 hours following the accident. A containment spray system may be activated that sprays the drywell area with water to condense the steam as part of the recovery operations. The liner back-pressure will build up gradually over the 72 hours as the concrete temperatures increase, and a sudden cool down could cause excessive differential pressure on the liner to develop. For this analysis, it is assumed that the containment spray is activated at the end of the 72-hour period. A back-pressure, acting between the liner and the concrete wall of the containment, can occur as a result of elevated temperatures in the concrete causing steam and saturated vapor pressures to develop from the free water remaining in the pores of the concrete. Additional pore pressure also develops under the elevated temperatures from the non-condensable gases trapped in the concrete pores during the concrete curing process. Any buildup of this pore pressure next to the liner, in excess of the drywell internal pressure, will act to push the liner away from the concrete with a potential for tearing at the liner anchorages. This paper describes the methods and analyses used to quantify this liner back-pressure so that appropriate measures are included in the design of the liner and anchorage system. A pore pressure model is developed that calculates the pressure distribution across the concrete

  1. Characterization of Wafer-Level Au-In-Bonded Samples at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Luu, Thi-Thuy; Hoivik, Nils; Wang, Kaiying; Aasmundtveit, Knut E.; Vardøy, Astrid-Sofie B.

    2015-06-01

    Wafer-level bonding using Au-In solid liquid interdiffusion (SLID) bonding is a promising approach to enable low-temperature assembly and MEMS packaging/encapsulation. Due to the low-melting point of In, wafer-level bonding can be performed at considerably lower temperatures than Sn-based bonding; this work treats bonds performed at 453 K (180 °C). Following bonding, the die shear strength at elevated temperatures was investigated from room temperature to 573 K (300 °C), revealing excellent mechanical integrity at these temperatures well above the bonding temperature. For shear test temperatures from room temperature to 473 K (200 °C), the measured shear strength was stable at 30 MPa, whereas it increased to 40 MPa at shear test temperature of 573 K (300 °C). The fracture surfaces of Au-In-bonded samples revealed brittle fracture modes (at the original bond interface and at the adhesion layers) for shear test temperatures up to 473 K (200 °C), but ductile fracture mode for shear test temperature of 573 K (300 °C). The as-bonded samples have a layered structure consisting of the two intermetallic phases AuIn and γ', as shown by cross section microscopy and predicted from the phase diagram. The change in behavior for the tests at 573 K (300 °C) is attributed to a solid-state phase transition occurring at 497 K (224 °C), where the phase diagram predicts a AuIn/ψ structure and a phase boundary moving across the initial bond interface. The associated interdiffusion of Au and In will strengthen the initial bond interface and, as a consequence, the measured shear strength. This work provides experimental evidence for the high-temperature stability of wafer-level, low-temperature bonded, Au-In SLID bonds. The high bond strength obtained is limited by the strength at the initial bond interface and at the adhesion layers, showing that the Au-In SLID system itself is capable of even higher bond strength.

  2. Analysis of wear track and debris of stir cast LM13/Zr composite at elevated temperatures

    SciTech Connect

    Panwar, Ranvir Singh Pandey, O.P.

    2013-01-15

    Particulate reinforced aluminum metal matrix composite is in high demand in automobile industry where the operational conditions vary from low to high temperature. In order to understand the wear mode at elevated temperature, this study was planned. For this purpose we developed a metal matrix composite containing aluminum alloy (LM13) as matrix and zircon sand as particulate reinforcement by stir casting process. Different amounts of zircon sand (5, 10, 15 and 20 wt.%) were incorporated in the matrix to study the effect of reinforcement on the wear resistance. Dispersion of zircon sand particles in the matrix was confirmed by using optical microscopy. Sliding wear tests were done to study the durability of the composite with respect to the base alloy. The effects of load and temperature on wear behavior from room temperature to 300 Degree-Sign C were studied to understand the wear mechanism deeply. Surface morphology of the worn surfaces after the wear tests as well as wear debris was observed under scanning electron microscope. Mild to severe wear transition was noticed in tests at high temperature and high load. However, there is interesting change in wear behavior of the composite near the critical temperature of the composite. All the observed behavior has been explained with reference to the observed microstructure of the wear track and debris. - Highlights: Black-Right-Pointing-Pointer Good interfacial bonding between zircon sand particles and Al matrix was observed. Black-Right-Pointing-Pointer The effect of temperature on the wear behavior of LM13/Zr composites was studied. Black-Right-Pointing-Pointer Wear resistance of the composite was improved with addition of zircon sand. Black-Right-Pointing-Pointer Transition temperature from mild to severe wear also improved in composite. Black-Right-Pointing-Pointer SEM analysis of the tracks and debris was done to establish wear mechanism.

  3. Alterations in gill structure in tropical reef fishes as a result of elevated temperatures.

    PubMed

    Bowden, A J; Gardiner, N M; Couturier, C S; Stecyk, J A W; Nilsson, G E; Munday, P L; Rummer, J L

    2014-09-01

    Tropical regions are expected to be some of the most affected by rising sea surface temperatures (SSTs) because seasonal temperature variations are minimal. As temperatures rise, less oxygen dissolves in water, but metabolic requirements of fish and thus, the demand for effective oxygen uptake, increase. Gill remodelling is an acclimation strategy well documented in freshwater cyprinids experiencing large seasonal variations in temperature and oxygen as well as an amphibious killifish upon air exposure. However, no study has investigated whether tropical reef fishes remodel their gills to allow for increased oxygen demands at elevated temperatures. We tested for gill remodelling in five coral reef species (Acanthochromis polyacanthus, Chromis atripectoralis, Pomacentrus moluccensis, Dascyllus melanurus and Cheilodipterus quinquelineatus) from populations in northern Papua New Guinea (2° 35.765' S; 150° 46.193' E). Fishes were acclimated for 12-14 days to 29 and 31°C (representing their seasonal range) and 33 and 34°C to account for end-of-century predicted temperatures. We measured lamellar perimeter, cross-sectional area, base thickness, and length for five filaments on the 2nd gill arches and qualitatively assessed 3rd gill arches via scanning electron microscopy (SEM). All species exhibited significant differences in the quantitative measurements made on the lamellae, but no consistent trends with temperature were observed. SEM only revealed alterations in gill morphology in P. moluccensis. The overall lack of changes in gill morphology with increasing temperature suggests that these near-equatorial reef fishes may fail to maintain adequate O2 uptake under future climate scenarios unless other adaptive mechanisms are employed.

  4. Temperature-induced elevation of basal metabolic rate does not affect testis growth in great tits.

    PubMed

    Caro, Samuel P; Visser, Marcel E

    2009-07-01

    The timing of reproduction varies from year to year in many bird species. To adjust their timing to the prevailing conditions of that year, birds use cues from their environment. However, the relative importance of these cues, such as the initial predictive (e.g. photoperiod) and the supplemental factors (e.g. temperature), on the seasonal sexual development are difficult to distinguish. In particular, the fine-tuning effect of temperature on gonadal growth is not well known. One way temperature may affect timing is via its strong effect on energy expenditure as gonadal growth is an energy-demanding process. To study the interaction of photoperiod and temperature on gonadal development, we first exposed 35 individually housed male great tits (Parus major) to mid-long days (after 6 weeks of 8 h L:16 h D at 15 degrees C, photoperiod was set to 13 h L:11 h D at 15 degrees C). Two weeks later, for half of the males the temperature was set to 8 degrees C, and for the other half to 22 degrees C. Unilateral laparotomies were performed at weeks 5 (i.e one week before the birds were transferred to mid-long days), 8 and 11 to measure testis size. Two measures of basal metabolic rate (BMR) were performed at the end of the experiment (weeks 11 and 12). Testis size increased significantly during the course of the experiment, but independently of the temperature treatment. BMR was significantly higher in birds exposed to the cold treatment. These results show that temperature-related elevation of BMR did not impair the long-day-induced testis growth in great tits. As a consequence, temperature may not be a crucial cue and/or constraint factor in the fine-tuning of the gonadal recrudescence in male great tits, and testis growth is not a high energy-demanding seasonal process. PMID:19525424

  5. Alterations in gill structure in tropical reef fishes as a result of elevated temperatures

    PubMed Central

    Bowden, A.J.; Gardiner, N.M.; Couturier, C.S.; Stecyk, J.A.W.; Nilsson, G.E.; Munday, P.L.; Rummer, J.L.

    2015-01-01

    Tropical regions are expected to be some of the most affected by rising sea surface temperatures (SSTs) because seasonal temperature variations are minimal. As temperatures rise, less oxygen dissolves in water, but metabolic requirements of fish and thus, the demand for effective oxygen uptake, increases. Gill remodelling is an acclimation strategy well documented in freshwater cyprinids experiencing large seasonal variations in temperature and oxygen as well as an amphibious killifish upon air exposure. However, no study has investigated whether tropical reef fishes remodel their gills to allow for increased oxygen demands at elevated temperatures. We tested for gill remodelling in five coral reef species (Acanthochromis polyacanthus, Chromis atripectoralis, Pomacentrus moluccensis, Dascyllus melanurus and Cheilodipterus quinquelineatus) from populations in northern Papua New Guinea (2° 35.765′ S; 150° 46.193′ E). Fishes were acclimated for 12-14 days to 29 and 31 °C, encompassing their seasonal range (29-31 °C), and 33 and 34 °C to account for end-of-century predicted temperatures. We measured lamellar perimeter, cross-sectional area, base thickness, and length for five filaments on the 2nd gill arches and qualitatively assessed 3rd gill arches via scanning electron microscopy (SEM). All species exhibited significant differences in the quantitative measurements made on the lamellae, but no consistent trends with temperature were observed. SEM only revealed alterations in gill morphology in P. moluccensis. The overall lack of changes in gill morphology with increasing temperature suggests that these near-equatorial reef fishes may fail to maintain adequate O2 uptake under future climate scenarios unless other adaptive mechanisms are employed. PMID:24862962

  6. Elevated temperatures increase the toxicity of pesticide mixtures to juvenile coho salmon.

    PubMed

    Laetz, Cathy A; Baldwin, David H; Hebert, Vincent R; Stark, John D; Scholz, Nathaniel L

    2014-01-01

    Pesticide mixtures and elevated temperatures are parallel freshwater habitat stressors for Pacific salmon in the western United States. Certain combinations of organophosphate (OP) insecticides are known to synergistically increase neurotoxicity in juvenile salmon. The chemicals interact to potentiate the inhibition of brain acetylcholinesterase (AChE) and disrupt swimming behavior. The metabolic activation and detoxification of OPs involve temperature-sensitive enzymatic processes. Salmon are ectothermic, and thus the degree of synergism may vary with ambient temperature in streams, rivers, and lakes. Here we assess the influence of water temperature (12-21°C) on the toxicity of ethoprop and malathion, alone and in combination, to juvenile coho salmon (Oncorhynchus kisutch). A mixture of ethoprop (0.9 μg/L) and malathion (0.75 μg/L) produced synergistic AChE inhibition at 12°C, and the degree of neurotoxicity approximately doubled with a modest temperature increase to 18°C. Slightly lower concentrations of ethoprop (0.5 μg/L) combined with malathion (0.4 μg/L) did not inhibit brain AChE activity but did produce a temperature-dependent reduction in liver carboxylesterase (CaE). The activity of CaE was very sensitive to the inhibitory effects of ethoprop alone and both ethoprop-malathion combinations across all temperatures. Our findings are an example of how non-chemical habitat attributes can increase the relative toxicity of OP mixtures. Surface temperatures currently exceed water quality criteria in many western river segments, and summer thermal extremes are expected to become more frequent in a changing climate. These trends reinforce the importance of pollution reduction strategies to enhance ongoing salmon conservation and recovery efforts.

  7. Alterations in gill structure in tropical reef fishes as a result of elevated temperatures.

    PubMed

    Bowden, A J; Gardiner, N M; Couturier, C S; Stecyk, J A W; Nilsson, G E; Munday, P L; Rummer, J L

    2014-09-01

    Tropical regions are expected to be some of the most affected by rising sea surface temperatures (SSTs) because seasonal temperature variations are minimal. As temperatures rise, less oxygen dissolves in water, but metabolic requirements of fish and thus, the demand for effective oxygen uptake, increase. Gill remodelling is an acclimation strategy well documented in freshwater cyprinids experiencing large seasonal variations in temperature and oxygen as well as an amphibious killifish upon air exposure. However, no study has investigated whether tropical reef fishes remodel their gills to allow for increased oxygen demands at elevated temperatures. We tested for gill remodelling in five coral reef species (Acanthochromis polyacanthus, Chromis atripectoralis, Pomacentrus moluccensis, Dascyllus melanurus and Cheilodipterus quinquelineatus) from populations in northern Papua New Guinea (2° 35.765' S; 150° 46.193' E). Fishes were acclimated for 12-14 days to 29 and 31°C (representing their seasonal range) and 33 and 34°C to account for end-of-century predicted temperatures. We measured lamellar perimeter, cross-sectional area, base thickness, and length for five filaments on the 2nd gill arches and qualitatively assessed 3rd gill arches via scanning electron microscopy (SEM). All species exhibited significant differences in the quantitative measurements made on the lamellae, but no consistent trends with temperature were observed. SEM only revealed alterations in gill morphology in P. moluccensis. The overall lack of changes in gill morphology with increasing temperature suggests that these near-equatorial reef fishes may fail to maintain adequate O2 uptake under future climate scenarios unless other adaptive mechanisms are employed. PMID:24862962

  8. A new MEMS-based system for ultra-high-resolution imaging at elevated temperatures.

    PubMed

    Allard, Lawrence F; Bigelow, Wilbur C; Jose-Yacaman, Miguel; Nackashi, David P; Damiano, John; Mick, Stephen E

    2009-03-01

    In recent years, an increasing number of laboratories have been applying in situ heating (and ultimately, gas reaction) techniques in electron microscopy studies of catalysts and other nanophase materials. With the advent of aberration-corrected electron microscopes that provide sub-Angström image resolution, it is of great interest to study the behavior of materials at elevated temperatures while maintaining the resolution capabilities of the microscope. In collaboration with Protochips Inc., our laboratory is developing an advanced capability for in situ heating experiments that overcomes a number of performance problems with standard heating stage technologies. The new heater device allows, for example, temperature cycling from room temperature to greater than 1000 degrees C in 1 ms (a heating rate of 1 million Centigrade degrees per second) and cooling at nearly the same rate. It also exhibits a return to stable operation (drift controlled by the microscope stage, not the heater) in a few seconds after large temperature excursions. With Protochips technology, we were able to demonstrate single atom imaging and the behavior of nanocrystals at high temperatures, using high-angle annular dark-field imaging in an aberration-corrected (S)TEM. The new capability has direct applicability for remote operation and (ultimately) for gas reaction experiments using a specially designed environmental cell.

  9. Analysis of Screen Channel LAD Bubble Point Tests in Liquid Oxygen at Elevated Temperature

    NASA Technical Reports Server (NTRS)

    Hartwig, Jason; McQuillen, John

    2011-01-01

    The purpose of this paper is to examine the key parameters that affect the bubble point pressure for screen channel Liquid Acquisition Devices in cryogenic liquid oxygen at elevated pressures and temperatures. An in depth analysis of the effect of varying temperature, pressure, and pressurization gas on bubble point is presented. Testing of a 200 x 1400 and 325 x 2300 Dutch Twill screen sample was conducted in the Cryogenics Components Lab 7 facility at the NASA Glenn Research Center in Cleveland, Ohio. Test conditions ranged from 92 to 130K and 0.138 - 1.79 MPa. Bubble point is shown to be a strong function of temperature with a secondary dependence on pressure. The pressure dependence is believed to be a function of the amount of evaporation and condensation occurring at the screen. Good agreement exists between data and theory for normally saturated liquid but the model generally under predicts the bubble point in subcooled liquid. Better correlation with the data is obtained by using the liquid temperature at the screen to determine surface tension of the fluid, as opposed to the bulk liquid temperature.

  10. Responses of trace gas fluxes and N availability to experimentally elevated soil temperatures

    SciTech Connect

    Peterjohn, W.T.; Melillo, J.M.; Steudler, P.A.; Newkirk, K.M. ); Bowles, F.P. ); Aber, J.D. )

    1994-08-01

    A field study is being conducted to determine the long-term response of belowground processes to elevated soil temperatures in a mixed deciduous forest. Eighteen experimental plots were established and randomly assigned them to one of three treatments in six blocks. The treatments are: (1) heated plots in which the soil temperature is raised 5[degrees]C above ambient using buried heating cables; (2) disturbance control plots (cables but no heat); and (3) undisturbed control plots (no cables and no heat). In each plot indexes of N availability, the concentration of N in soil solutions leaching below the rooting zone, and trace gas emissions (CO[sub 2], N[sub 2]O, and CH[sub 4]) were measured. In this paper results are presented from the first 6 mo of this study. The daily average efflux of CO[sub 2] increased exponentially with increasing soil temperature and decreased linearly with increasing soil moisture. A linear regression of temperature and the natural logarithm of CO[sub 2] flux explained 92% of the variability. A linear regression of soil moisture and CO[sub 2] flux could explain only 44% of the variability. The relationship between soil temperature and CO[sub 2] flux is in good agreement with the Arrhenius equation. For these CO[sub 2] flux data, the activation energy was 63 kJ/mol and the Q[sub 10] was 2.5.

  11. Effect of elevated temperature and enhanced drainage on carbon balance of tundra microcosms

    SciTech Connect

    Johnson, L.C.; Shaver, G.R.; Giblin, A.E.; Nadelhoffer, K.J.; Rastetter, E.B.; Laundre, J.A.; Murray, G.L. )

    1994-06-01

    We tested effects of temperature and drainage on C balance of intact soil and tundra vegetation over a simulated season. We measured C budgets (CO[sub 2] and CH[sub 4] emissions and dissolved CO[sub 2], CH[sub 4] and DOC in soil water) of Eriophorum vaginatum tussock and moss-dominated interussock microcosms at two temperatures (7[degrees] and 15[degrees]C, season maxima) and two water regimes (saturated and field capacity). Net ecosystem productivity was strongly affected by water. Averaged over temperature and microhabitat, the rate of net C loss from microcosms at field capacity was [approximately]5[times] the saturated microcosms. Only saturated, 15[degrees]C tussock microcosms showed net C storage integrated over the whole season. Ecosystem respiration was strongly affected by water and less by temperature. Respiration rates at field capacity were [approximately]2[times] the rates under saturated conditions. Elevated temperature caused a 1.5[times] increase. Other C components were <20% of gaseous CO[sub 2] losses. Results indicate that C in tundra exists in a fragile balance between storage and release that is controlled mainly by water regime.

  12. Elevated Temperature Fracture Toughness and Fatigue Testing of Steels for Geothermal Applications

    SciTech Connect

    Cutler, R.A.; Goodman, E.C.; Hendrickson, R.R.

    1981-10-01

    Conventional drill bit steels exhibit increased wear and decreased toughness when run at elevated temperatures in geothermal wells. Bits are therefore run at lower speeds and lighter loads, resulting in lower penetration rates for geothermal drilling than for conventional rock drilling. Carpenter EX-00053, Timken CBS 600, Timken CBS 1000M and Vasco X-2M steels with improved hot hardness (improved wear resistance), were tested in conjunction with the steels used for cones (AISI 4829, 3915 and EX55) in conventional roller cones and lugs (AISI 8620, 9315 and EX55) in conventional roller cone rock bits. Short-rod fracture toughness measurements were made on each of these steels between room temperature and 400{degree}C. Fatigue crack resistance was determined at 300{degree}C for high-temperature steels and at room temperature for conventional steels. Scanning electron microscopy analyses of the fractured short-rod specimens were correlated with observed crack behavior from the test records. Materials testing results are discussed and steel selections made for improved geothermal bits. Carpenter EX-00053 and Timken CBS 1000M steels meet all design requirements for use in stabilizers, lugs and cones at temperatures to 400{degree}C. It is recommended that EX-00053 and CBS 1000M be manufactured for geothermal drilling at the Geysers site. [DJE 2005

  13. Deformation Behavior and Dynamic Recovery Kinetics of Ultrahigh Strength Steel BR1500HS at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Xia, Yufeng; Ji, Shuai; Zhang, Yandong; Wu, Dongsen; Quan, Guozheng

    2015-10-01

    The flow behaviors of ultrahigh strength steel BR1500HS at elevated temperature were studied by performing hot tension tests at the temperatures of 773 K, 873 K, 1023 K and 1173 K, and strain rates of 0.01 s-1, 0.1 s-1 and 1 s-1 on a Gleeble 3500 thermo-mechanical simulator. The true stress-strain curves were obtained and their characteristics were analyzed. Relationships among the maximum stress, temperature and strain rate were described by means of the conventional hyperbolic sine equation. The average deformation activation energy in the whole deformation temperatures was determined as Q = 235.257 KJ/mol by regression analysis. Based on σ(dσ/dɛ) verse σ2 curves, the values of dynamic recovery (DRV) rate coefficient, r, saturated stress, σrec, and yield strength, σ0, under different deformation conditions were calculated. In order to estimate the DRV volume fractions, the modified Avrami type equation including r (r = 106.911351Z-0.059) as a function of the temperature compensating parameter, Z, was established, and then the effects of deformation conditions on the DRV kinetics were described in details.

  14. Electrochemical and physical analysis of a Li-ion cell cycled at elevated temperature

    SciTech Connect

    Shim, Joongpyo; Kostecki, Robert; Richardson, Thomas; Song, Xiangyun; Striebel, Kathryn A.

    2002-06-21

    Laboratory-size LiNi0.8Co0.15Al0.05O2/graphite lithium-ion pouch cells were cycled over 100 percent DOD at room temperature and 60 degrees C in order to investigate high-temperature degradation mechanisms of this important technology. Capacity fade for the cell was correlated with that for the individual components, using electrochemical analysis of the electrodes and other diagnostic techniques. The high-temperature cell lost 65 percent of its initial capacity after 140 cycles at 60 degrees C compared to only 4 percent loss for the cell cycled at room temperature. Cell ohmic impedance increased significantly with the elevated temperature cycling, resulting in some of loss of capacity at the C/2 rate. However, as determined with slow rate testing of the individual electrodes, the anode retained most of its original capacity, while the cathode lost 65 percent, even when cycled with a fresh source of lithium. Diagnostic evaluation of cell components including XRD, Raman, CSAFM and suggest capacity loss occurs primarily due to a rise in the impedance of the cathode, especially at the end-of-charge. The impedance rise may be caused in part by a loss of the conductive carbon at the surface of the cathode and/or by an organic film on the surface of the cathode that becomes non-ionically conductive at low lithium content.

  15. Dolomite-magnesian calcite relations at elevated temperatures and CO2 pressures

    USGS Publications Warehouse

    Graf, D.L.; Goldsmith, J.R.

    1955-01-01

    The equilibrium thermal decomposition curve of dolomite has been determined up to a CO2 pressure of 20,000 lb/in.2, at which pressure dolomite decomposes at 857??C. Equilibrium was approached from both directions, by the breakdown and by the solid-state synthesis of dolomite. At elevated temperatures and pressures, calcites in equilibrium with periclase as well as those in equilibrium with dolomite contain Mg in solid solution. In the former, the Mg content increases with increasing CO2 pressure, and decreases with increasing temperature. In the latter, it is a function of temperature only. The exsolution curve of dolomite and magnesian calcite has been determined between 500?? and 800??C; at 500?? dolomite is in equilibrium with a magnesian calcite containing ~6 mol per cent MgCO2; at 800??, ~22 mol per cent. There appears to be a small but real deviation from the ideal 1 : 1 Ca : Mg ratio of dolomite, in the direction of excess Ca, for material in equilibrium with magnesian calcite at high temperature. The experimental findings indicate that very little Mg is stable in the calcites of sedimentary environments, but that an appreciable amount is stable under higher-temperature metamorphic conditions, if sufficient CO2 pressure is maintained. ?? 1955.

  16. An x-ray absorption spectroscopy study of Mo oxidation in Pb at elevated temperatures

    SciTech Connect

    Liu, Shanshan; Olive, Daniel; Terry, Jeff; Segre, Carlo U.

    2009-06-30

    The corrosion of fuel cladding and structural materials by lead and lead-bismuth eutectic in the liquid state at elevated temperatures is an issue that must be considered when designing advanced nuclear systems and high-power spallation neutron targets. In this work, lead corrosion studies of molybdenum were performed to investigate the interaction layer as a function of temperature by X-ray absorption spectroscopy. In situ X-ray absorption measurements on a Mo substrate with a 3-6 {micro}m layer of Pb deposited by thermal evaporation were performed at temperatures up to 900 C and at a 15{sup o} angle to the incident X-rays. The changes in the local atomic structure of the corrosion layer are visible in the difference extended X-ray absorption fine structure and the linear combination fitting of the X-ray absorption near-edge structure to as-deposited molybdenum sample and molybdenum oxide (MoO{sub 2} and MoO{sub 3}) standards. The data are consistent with the appearance of MoO{sub 3} in an intermediate temperature range (650-800 C) and the more stable MoO{sub 2} phase dominating at high and low temperatures.

  17. Amplitude-Frequency Analysis of Signals of Acoustic Emission from Granite Fractured at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Shcherbakov, I. P.; Chmel‧, A. E.

    2015-05-01

    The problem of stability of underground structures serving to store radioactive waste, to gasify carbon, and to utilize geothermal energy is associated with the action of elevated temperatures and pressures. The acoustic-emission method makes it possible to monitor the accumulation of microcracks arising in stress fields of both thermal and mechanical origin. In this report, the authors give results of a laboratory investigation into the acoustic emission from granite subjected to impact fracture at temperatures of up to 600°C. An amplitude-frequency analysis of acousticemission signals has enabled the authors to evaluate the dimension of the arising microcracks and to determine their character (intergranular or intragranular). It has been shown that intergranular faults on the boundaries between identical minerals predominate at room temperature (purely mechanical action); at a temperature of 300°C (impact plus thermoelastic stresses), there also appear cracks on the quartz-feldspar boundaries; finally, at temperatures of 500-600°C, it is intragranular faults that predominate in feldspar. The dimensions of the above three types of microcracks are approximately 2, 0.8, and 0.3 mm respectively.

  18. Thermo-elastic behavior of deformed woven fabric composites at elevated temperatures: Part 1

    SciTech Connect

    Vu-Khanh, T.; Liu, B.

    1994-12-31

    This paper presents the results of a study on the effects of temperature on the thermo-elastic properties of woven fabric composites. The thermo-mechanical behavior of woven fabric composites is characterized by a laminate composed of four fictional unidirectional plies, called the sub-plies model. The model allows determination of the thermo-elastic properties of deformed fabric composites (non-orthogonal structure) and direct use of layered shell elements in finite element codes. A special procedure is also proposed to measure the fiber undulation effect and to predict the on-axis thermo-elastic coefficients of the equivalent constituent plies. The thermo-elastic behavior at elevated temperature was investigated on graphite/epoxy fabric composites. Experimental measurements were carried out from 23 C to 177 C. The results revealed that the equivalent thermal expansion coefficients of the sub-plies remain almost constant over a wide range of temperature. However, the equivalent elastic moduli and Poison`s ratio of the sub-plies vary nonlinearly with temperature. Semiempirical equations based on the experimental data were also developed to predict the equivalent on-axis thermo-elastic properties of the fictional constituent plies in the sub-plies model as a function of temperature.

  19. Habitat pollution and thermal regime modify molecular stress responses to elevated temperature in freshwater mussels (Anodonta anatina: Unionidae).

    PubMed

    Falfushynska, H; Gnatyshyna, L; Yurchak, I; Ivanina, A; Stoliar, O; Sokolova, I

    2014-12-01

    Elevated temperature and pollution are common stressors in freshwater ecosystems. We study cellular stress response to acute warming in Anodonta anatina (Unionidae) from sites with different thermal regimes and pollution levels: a pristine area and an agriculturally polluted site with normal temperature regimes (F and A, respectively) and a polluted site with elevated temperature (N) from the cooling pond of an electrical power plant. Animals were exposed to different temperatures for 14 days and stress response markers were measured in gills, digestive gland and hemocytes. Mussels from site N and A had elevated background levels of lactate dehydrogenase activity indicating higher reliance on anaerobic metabolism for ATP production and/or redox maintenance. Exposure to 25°C and 30°C induced oxidative stress (indicated by elevated levels of lipid peroxidation products) in digestive gland and gills of mussels from A and F sites, while in mussels from N sites elevated oxidative stress was only apparent at 30°C. Temperature-induced changes in levels of antioxidants (superoxide dismutase, metallothioneins and glutathione) were tissue- and population-specific. Acute warming led to destabilization of lysosomal membranes and increased frequencies of nuclear lesions in mussels from F and A sites but not in their counterparts from N site. Elevated temperature led to an increase in the frequency of micronuclei in hemocytes in mussels from F and A sites at 25°C and 30°C and in mussels from N site at 30°C. The mussels from N site also demonstrated better survival at elevated temperature (30°C) than their counterparts from the F and A sites. Taken together, these data indicate that long-term acclimation and/or adaptation of A. anatina to elevated temperatures result in increased thermotolerance and alleviate stress response to moderate temperature rise. In contrast, extreme warming (30°C) is harmful to mussels from all populations indicating limit to this induced

  20. Elevated temperature slow plastic deformation of NiAl/TiB2 particulate composites

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Mannan, S. K.; Sprissler, B.; Viswanadham, R. K.

    1988-01-01

    The 'XD' process for production of discontinuously-reinforced metal-matrix composites has been used to enhance the high-temperature strength of NiAl-TiB2 composites with particulate densities of up to 30 vol pct. SEM, TEM, and optical characterizations of the resulting microstructures showed the average TiB2 particle size to be about 1 micron, while the average grain of the NiAl matrix was of the order of 10 microns. Elevated temperature compression tests conducted at 1200 and 1300 K indicated flow strengths to increase with TiB2 content, so that the 20 vol pct TiB2-reinforced composite was three times stronger than the unreinforced NiAl; this is ascribed to the very high density of microstructural tangled dislocations, loops, and subgrain boundaries connecting the particles.

  1. Elevated Temperature Primary Load Design Method Using Pseudo Elastic-Perfectly Plastic Model

    SciTech Connect

    Carter, Peter; Sham, Sam; Jetter, Robert I

    2012-01-01

    A new primary load design method for elevated temperature service has been developed. Codification of the procedure in an ASME Boiler and Pressure Vessel Code, Section III Code Case is being pursued. The proposed primary load design method is intended to provide the same margins on creep rupture, yielding and creep deformation for a component or structure that are implicit in the allowable stress data. It provides a methodology that does not require stress classification and is also applicable to a full range of temperature above and below the creep regime. Use of elastic-perfectly plastic analysis based on allowable stress with corrections for constraint, steady state stress and creep ductility is described. This approach is intended to ensure that traditional primary stresses are the basis for design, taking into account ductility limits to stress re-distribution and multiaxial rupture criteria.

  2. Research on Softening of A95456 Alloy Deformed Under Elevated Temperatures

    SciTech Connect

    Petrov, Pavel A.; Perfilov, Victor I.

    2007-04-07

    The present paper describes the results of the research on the softening of aluminium alloy A95456 deformed at elevated temperatures. The investigations were carried out within the temperature range of 310-450 deg. C and strain rate of 0.01-0.4 s-1. The strain rate was either constant or variable in performed experiments. In case of variable strain rate two different schemes were observed. Firstly, the deformation of alloy A95456 was performed at constant die velocity and so the strain rate increased monotonically. Secondly, the die velocity was changed suddenly during the deformation of A95456 alloy. In turn, it caused the sudden strain rate change. To describe the softening behaviour of A95456 alloy several equations were investigated. The accuracy of each equation was estimated. Some practical recommendations for use of those equations were given.

  3. Origin of predominance of cementite among iron carbides in steel at elevated temperature.

    PubMed

    Fang, C M; Sluiter, M H F; van Huis, M A; Ande, C K; Zandbergen, H W

    2010-07-30

    A long-standing challenge in physics is to understand why cementite is the predominant carbide in steel. Here we show that the prevalent formation of cementite can be explained only by considering its stability at elevated temperature. A systematic highly accurate quantum mechanical study was conducted on the stability of binary iron carbides. The calculations show that all the iron carbides are unstable relative to the elemental solids, α-Fe and graphite. Apart from a cubic Fe23C6 phase, the energetically most favorable carbides exhibit hexagonal close-packed Fe sublattices. Finite-temperature analysis showed that contributions from lattice vibration and anomalous Curie-Weis magnetic ordering, rather than from the conventional lattice mismatch with the matrix, are the origin of the predominance of cementite during steel fabrication processes.

  4. Constitutive Equations for Use in Design Analyses of Long-life Elevated Temperature Components

    NASA Technical Reports Server (NTRS)

    Pugh, C. E.; Robinson, D. N.

    1983-01-01

    Design analysis needs and procedures relative to elevated temperature components in liquid metal fast breeder reactor (LMFBR) system were examined. The effects of the thermal transients on the pressure boundary components are enhanced by the excellent heat transfer properties of the liquid sodium coolant. Design criteria for high temperature nuclear reactor components recognize the potential occurrence of inelastic structural response. Specifically, criteria and limits were developed which reflect a recognition of this potential and employ design by analysis concepts that requires that inelastic (elastic-plastic and creep) analyses be performed. Constitutive equations to represent multiaxial time-dependent responses of LMFBR alloys are established. The development of equations applicable under cyclic loading conditions are outlined.

  5. Fatigue and flexural response of advanced carbon-carbon composites at room and elevated temperatures

    SciTech Connect

    Mahfuz, H.; Das, P.S.; Jeelani, S.; Baker, D.M.; Johnson, S.A.

    1992-08-01

    The flexural response of SiC-coated carbon-carbon composites (ACC-4) at room and elevated temperatures is presented. Three-point bending tests were performed on virgin and mission-cycled specimens, and the variation in flexural strength is examined. The load-deflection behavior of the material at various temperatures is investigated, and the Weibull (1939) analysis of the strength data is performed. Micrographs of various cross sections in the damaged zone were taken, and the failure mechanisms are discussed. Fatigue tests were conducted under flexural loads, and the S-N diagram with the corresponding Weibull analysis are presented. Untested as well as fractured specimens under static and dynamic loading were C-scanned to identify the damaged zone and visualize the extent of the damage. Failure analyses are presented for both static and cyclic loading on the basis of NDE, the micrographs, and the experimental data. 15 refs.

  6. Fatigue and flexural response of advanced carbon-carbon composites at room and elevated temperatures

    NASA Technical Reports Server (NTRS)

    Mahfuz, Hassan; Das, Partha S.; Jeelani, Shaik; Baker, Dean M.; Johnson, Sigurd A.

    1992-01-01

    The flexural response of SiC-coated carbon-carbon composites (ACC-4) at room and elevated temperatures is presented. Three-point bending tests were performed on virgin and mission-cycled specimens, and the variation in flexural strength is examined. The load-deflection behavior of the material at various temperatures is investigated, and the Weibull (1939) analysis of the strength data is performed. Micrographs of various cross sections in the damaged zone were taken, and the failure mechanisms are discussed. Fatigue tests were conducted under flexural loads, and the S-N diagram with the corresponding Weibull analysis are presented. Untested as well as fractured specimens under static and dynamic loading were C-scanned to identify the damaged zone and visualize the extent of the damage. Failure analyses are presented for both static and cyclic loading on the basis of NDE, the micrographs, and the experimental data.

  7. Elastic Properties and Internal Friction of Two Magnesium Alloys at Elevated Temperatures

    SciTech Connect

    Freels, M.; Liaw, P. K.; Garlea, E.; Morrell, J. S.; Radiovic, M.

    2011-06-01

    The elastic properties and internal friction of two magnesium alloys were studied from 25 C to 450 C using Resonant Ultrasound Spectroscopy (RUS). The Young's moduli decrease with increasing temperature. At 200 C, a change in the temperature dependence of the elastic constants is observed. The internal friction increases significantly with increasing temperature above 200 C. The observed changes in the temperature dependence of the elastic constants and the internal friction are the result of anelastic relaxation by grain boundary sliding at elevated temperatures. Elastic properties govern the behavior of a materials subjected to stress over a region of strain where the material behaves elastically. The elastic properties, including the Young's modulus (E), shear modulus (G), bulk modulus (B), and Poisson's ratio (?), are of significant interest to many design and engineering applications. The choice of the most appropriate material for a particular application at elevated temperatures therefore requires knowledge of its elastic properties as a function of temperature. In addition, mechanical vibration can cause significant damage in the automotive, aerospace, and architectural industries and thus, the ability of a material to dissipate elastic strain energy in materials, known as damping or internal friction, is also important property. Internal friction can be the result of a wide range of physical mechanisms, and depends on the material, temperature, and frequency of the loading. When utilized effectively in engineering applications, the damping capacity of a material can remove undesirable noise and vibration as heat to the surroundings. The elastic properties of materials can be determined by static or dynamic methods. Resonant Ultrasound Spectroscopy (RUS), used in this study, is a unique and sophisticated non-destructive dynamic technique for determining the complete elastic tensor of a solid by measuring the resonant spectrum of mechanical resonance for a

  8. Composite polymer membranes for proton exchange membrane fuel cells operating at elevated temperatures and reduced humidities

    NASA Astrophysics Data System (ADS)

    Zhang, Tao

    Proton Exchange Membrane Fuel Cells (PEMFCs) are the leading candidate in the fuel cell technology due to the high power density, solid electrolyte, and low operational temperature. However, PEMFCs operating in the normal temperature range (60-80°C) face problems including poor carbon monoxide tolerance and heat rejection. The poisoning effect can be significantly relieved by operating the fuel cell at elevated temperature, which also improves the heat rejection and electrochemical kinetics. Low relative humidity (RH) operation is also desirable to simplify the reactant humidification system. However, at elevated temperatures, reduced RH PEMFC performance is seriously impaired due to irreversible water loss from presently employed state-of-the-art polymer membrane, Nafion. This thesis focuses on developing polymer electrolyte membranes with high water retention ability for operation in elevated temperature (110-150°C), reduced humidity (˜50%RH) PEMFCs. One approach is to alter Nafion by adding inorganic particles such as TiO2, SiO2, Zr(HPO 4)2, etc. While the presence of these materials in Nafion has proven beneficial, a reduction or no improvement in the PEMFC performance of Nafion/TiO2 and Nafion/Zr(HPO4)2 membranes is observed with reduced particle sizes or increased particle loadings in Nafion. It is concluded that the PEMFC performance enhancement associated with addition of these inorganic particles was not due to the particle hydrophilicity. Rather, the particle, partially located in the hydrophobic region of the membrane, benefits the cell performance by altering the membrane structure. Water transport properties of some Nafion composite membranes were investigated by NMR methods including pulsed field gradient spin echo diffusion, spin-lattice relaxation, and spectral measurements. Compared to unmodified Nafion, composite membranes materials exhibit longer longitudinal relaxation time constant T1. In addition to the Nafion material, sulfonated styrene

  9. Differences in the Temperature Sensitivity of Soil Organic Carbon Decomposition in a Semi-Arid Ecosystem across an Elevational Gradient

    NASA Astrophysics Data System (ADS)

    Delvinne, H.; Flores, A. N.; Benner, S. G.; Feris, K. P.; De Graaff, M. A.

    2015-12-01

    Semi-arid ecosystems are a significant component of the global carbon (C) cycle as they store approximately 20% of global soil C. Yet, projected increases in mean annual temperatures might alter the amount of soil organic C (SOC) currently stored in these ecosystems. Uncertainties about the temperature sensitivity of SOC decomposition have hindered accurate predictions of C cycle feedbacks to climate change. This study aims to elucidate how the temperature sensitivity of SOC decomposition varies along an elevational (1000m) and climatic (i.e. mean annual temperature and precipitation) gradient. The study sites are located at Reynolds Creek Critical Zone Observatory in Owyhee Mountains of Idaho, USA. We conducted stratified random sampling of soil up to 0-5cm across sagebrush canopy and inter-canopy areas at four elevations. We hypothesized decomposition of SOC pools at lower elevations to have greater temperature sensitivity (more CO2 respired per unit C) compared to upper due to the quality of C that is inherently more temperature sensitive. To assess the temperature sensitivity of SOC decomposition, we used aerobic laboratory incubations (n=40) across a temperature gradient ((15, 20, 25, 30) oC) at constant soil moisture (60% water holding capacity) for 120 days and measured CO2 respired. Cumulative CO2 respired increased with increasing incubation temperature. Cumulative CO2 respired also increased with elevation as upper elevations support greater amounts of C. However, when normalized by SOC, we found that the temperature response of CO2 respiration was greater in soils derived from lower than higher elevations (p<0.05). These results indicate that the response of SOC decomposition to elevated temperatures differs strongly across the landscape in semi-arid ecosystems.

  10. Effects of episodic low aragonite saturation and elevated temperature on the physiology of Stylophora pistillata

    NASA Astrophysics Data System (ADS)

    Lürig, M.; Kunzmann, A.

    2015-05-01

    As global climate change is predicted to gradually alter the oceans' carbonate system and water temperature, knowledge about the effects an altered marine environment has on the physiology of reef building (hermatypic) coral species is more widely established. However, although it is recognized that seawater temperature and the carbonate system of a coral reef can change rapidly and with great amplitude, little is known about how the interaction of these natural fluctuations with long term effects of climate change may affect the metabolism and productivity of hermatypic corals. To investigate this, we acclimated the hermatypic coral Stylophora pistillata to a "worst case" scenario for carbon dioxide emissions (aragonite saturation state [ΩARAG] = 1.6), and tested how exposure to short term (24 h) elevated temperature (+ 3 °C) and further lowered ΩARAG (-1 unit) affected its photosynthesis and respiration. While episodic exposure to very low ΩARAG had only little effect on S. pistillata's physiology, short term heat stress caused a shift from net oxygen production to consumption and partial coral bleaching. Higher gross coral respiration, and lowered photosynthetic activity under episodically elevated temperature may have been the result of photoinhibition and partial coral bleaching. These findings suggest that fluctuating environmental conditions in combination with a low ΩARAG background signal may impair basic metabolic processes in calcifying corals. In a future high-CO2 world short term stress could be relevant for reef ecosystem processes, and may affect the resilience of coral reefs to other external influences and effects of climate change.

  11. Elevated temperature and PCO2 shift metabolic pathways in differentially oxidative tissues of Notothenia rossii.

    PubMed

    Strobel, Anneli; Leo, Elettra; Pörtner, Hans O; Mark, Felix C

    2013-09-01

    Mitochondrial plasticity plays a central role in setting the capacity for acclimation of aerobic metabolism in ectotherms in response to environmental changes. We still lack a clear picture if and to what extent the energy metabolism and mitochondrial enzymes of Antarctic fish can compensate for changing temperatures or PCO2 and whether capacities for compensation differ between tissues. We therefore measured activities of key mitochondrial enzymes (citrate synthase (CS), cytochrome c oxidase (COX)) from heart, red muscle, white muscle and liver in the Antarctic fish Notothenia rossii after warm- (7°C) and hypercapnia- (0.2kPa CO2) acclimation vs. control conditions (1°C, 0.04kPa CO2). In heart, enzymes showed elevated activities after cold-hypercapnia acclimation, and a warm-acclimation-induced upward shift in thermal optima. The strongest increase in enzyme activities in response to hypercapnia occurred in red muscle. In white muscle, enzyme activities were temperature-compensated. CS activity in liver decreased after warm-normocapnia acclimation (temperature-compensation), while COX activities were lower after cold- and warm-hypercapnia exposure, but increased after warm-normocapnia acclimation. In conclusion, warm-acclimated N. rossii display low thermal compensation in response to rising energy demand in highly aerobic tissues, such as heart and red muscle. Chronic environmental hypercapnia elicits increased enzyme activities in these tissues, possibly to compensate for an elevated energy demand for acid-base regulation or a compromised mitochondrial metabolism, that is predicted to occur in response to hypercapnia exposure. This might be supported by enhanced metabolisation of liver energy stores. These patterns reflect a limited capacity of N. rossii to reorganise energy metabolism in response to rising temperature and PCO2.

  12. A semiconductor/mixed ion and electron conductor heterojunction for elevated-temperature water splitting.

    PubMed

    Ye, Xiaofei; Melas-Kyriazi, John; Feng, Zhuoluo A; Melosh, Nicholas A; Chueh, William C

    2013-10-01

    Photoelectrochemical cells (PECs) have been studied extensively for dissociating water into hydrogen and oxygen. Key bottlenecks for achieving high solar-to-hydrogen efficiency in PECs include increasing solar spectrum utilization, surmounting overpotential losses, and aligning the absorber/electrochemical redox levels. We propose a new class of solid-state PECs based on mixed ionic and electronic conducting (MIEC) oxides that operates at temperatures significantly above ambient and utilizes both the light and thermal energy available from concentrated sunlight to dissociate water vapor. Unlike thermochemical and hybrid photo-thermochemical water-splitting routes, the elevated-temperature PEC is a single-step approach operating isothermally. At the heart of the solid-state PEC is a semiconductor light absorber coated with a thin MIEC layer for improved catalytic activity, electrochemical stability, and ionic conduction. The MIEC, placed between the gas phase and the semiconductor light absorber, provides a facile path for minority carriers to reach the water vapor as well as a path for the ionic carriers to reach the solid electrolyte. Elevated temperature operation allows reasonable band misalignments at the interfaces to be overcome, reduces the required overpotential, and facilitates rapid product diffusion away from the surface. In this work, we simulate the behavior of an oxygen-ion-conducting photocathode in 1-D. Using the detailed-balance approach, in conjunction with recombination and electrochemical reaction rates, the practical efficiency is calculated as a function of temperature, solar flux, and select material properties. For a non-degenerate light absorber with a 2.0 eV band-gap and an uphill band offset of 0.3 eV, an efficiency of 17% and 11% is predicted at 723 and 873 K, respectively.

  13. Coralline algal physiology is more adversely affected by elevated temperature than reduced pH.

    PubMed

    Vásquez-Elizondo, Román Manuel; Enríquez, Susana

    2016-01-01

    In this study we analyzed the physiological responses of coralline algae to ocean acidification (OA) and global warming, by exposing algal thalli of three species with contrasting photobiology and growth-form to reduced pH and elevated temperature. The analysis aimed to discern between direct and combined effects, while elucidating the role of light and photosynthesis inhibition in this response. We demonstrate the high sensitivity of coralline algae to photodamage under elevated temperature and its severe consequences on thallus photosynthesis and calcification rates. Moderate levels of light-stress, however, were maintained under reduced pH, resulting in no impact on algal photosynthesis, although moderate adverse effects on calcification rates were still observed. Accordingly, our results support the conclusion that global warming is a stronger threat to algal performance than OA, in particular in highly illuminated habitats such as coral reefs. We provide in this study a quantitative physiological model for the estimation of the impact of thermal-stress on coralline carbonate production, useful to foresee the impact of global warming on coralline contribution to reef carbon budgets, reef cementation, coral recruitment and the maintenance of reef biodiversity. This model, however, cannot yet account for the moderate physiological impact of low pH on coralline calcification. PMID:26740396

  14. Coralline algal physiology is more adversely affected by elevated temperature than reduced pH.

    PubMed

    Vásquez-Elizondo, Román Manuel; Enríquez, Susana

    2016-01-07

    In this study we analyzed the physiological responses of coralline algae to ocean acidification (OA) and global warming, by exposing algal thalli of three species with contrasting photobiology and growth-form to reduced pH and elevated temperature. The analysis aimed to discern between direct and combined effects, while elucidating the role of light and photosynthesis inhibition in this response. We demonstrate the high sensitivity of coralline algae to photodamage under elevated temperature and its severe consequences on thallus photosynthesis and calcification rates. Moderate levels of light-stress, however, were maintained under reduced pH, resulting in no impact on algal photosynthesis, although moderate adverse effects on calcification rates were still observed. Accordingly, our results support the conclusion that global warming is a stronger threat to algal performance than OA, in particular in highly illuminated habitats such as coral reefs. We provide in this study a quantitative physiological model for the estimation of the impact of thermal-stress on coralline carbonate production, useful to foresee the impact of global warming on coralline contribution to reef carbon budgets, reef cementation, coral recruitment and the maintenance of reef biodiversity. This model, however, cannot yet account for the moderate physiological impact of low pH on coralline calcification.

  15. Elevated-Temperature Ferritic and Martensitic Steels and Their Application to Future Nuclear Reactors

    SciTech Connect

    Klueh, RL

    2005-01-31

    In the 1970s, high-chromium (9-12% Cr) ferritic/martensitic steels became candidates for elevated-temperature applications in the core of fast reactors. Steels developed for conventional power plants, such as Sandvik HT9, a nominally Fe-12Cr-1Mo-0.5W-0.5Ni-0.25V-0.2C steel (composition in wt %), were considered in the United States, Europe, and Japan. Now, a new generation of fission reactors is in the planning stage, and ferritic, bainitic, and martensitic steels are again candidates for in-core and out-of-core applications. Since the 1970s, advances have been made in developing steels with 2-12% Cr for conventional power plants that are significant improvements over steels originally considered. This paper will review the development of the new steels to illustrate the advantages they offer for the new reactor concepts. Elevated-temperature mechanical properties will be emphasized. Effects of alloying additions on long-time thermal exposure with and without stress (creep) will be examined. Information on neutron radiation effects will be discussed as it applies to ferritic and martensitic steels.

  16. The Deformation of the Multi-Layered Panel of Sheet Metals Under Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Wook; Woo, Dong-Uk

    A Molten Carbonate Fuel Cell (MCFC) stack consists of several layered unit cells. In each unit cell, the stiff structure of the separator plate contains the softer components, such as electrodes. When surface pressure acts on the stack over an extended period of time at elevated temperatures, the stiffness of the separator plate tends to degrade. Moreover, the demands for large electrode area (to increase the electric capacity of a unit cell) and thinner separator plates (to reduce weight) complicate the design of a separator plate with high stiffness. To evaluate the stiffness of the separator plate at elevated temperatures, we design and test a tiny, multi-layered separator plate specimen using a three-point bending tool. To determine the optimal structure of the separator plate, we investigate three design factors: angle, pitch and height. We adopt the Taguchi method to evaluate the experiments, and use finite element analysis to examine the experimental results. Based on these results, pitch is the most effective of these factors. As the pitch narrows, the stiffness of the separator plate increases. Therefore, we propose the pitch factor as a design criterion for the separator plate of the MCFC stack.

  17. Coralline algal physiology is more adversely affected by elevated temperature than reduced pH

    PubMed Central

    Vásquez-Elizondo, Román Manuel; Enríquez, Susana

    2016-01-01

    In this study we analyzed the physiological responses of coralline algae to ocean acidification (OA) and global warming, by exposing algal thalli of three species with contrasting photobiology and growth-form to reduced pH and elevated temperature. The analysis aimed to discern between direct and combined effects, while elucidating the role of light and photosynthesis inhibition in this response. We demonstrate the high sensitivity of coralline algae to photodamage under elevated temperature and its severe consequences on thallus photosynthesis and calcification rates. Moderate levels of light-stress, however, were maintained under reduced pH, resulting in no impact on algal photosynthesis, although moderate adverse effects on calcification rates were still observed. Accordingly, our results support the conclusion that global warming is a stronger threat to algal performance than OA, in particular in highly illuminated habitats such as coral reefs. We provide in this study a quantitative physiological model for the estimation of the impact of thermal-stress on coralline carbonate production, useful to foresee the impact of global warming on coralline contribution to reef carbon budgets, reef cementation, coral recruitment and the maintenance of reef biodiversity. This model, however, cannot yet account for the moderate physiological impact of low pH on coralline calcification. PMID:26740396

  18. Elevated temperature differently affects foliar nitrogen partitioning in seedlings of diverse Douglas fir provenances.

    PubMed

    Du, Baoguo; Jansen, Kirstin; Junker, Laura Verena; Eiblmeier, Monika; Kreuzwieser, Jürgen; Gessler, Arthur; Ensminger, Ingo; Rennenberg, Heinz

    2014-10-01

    Global climate change causes an increase in ambient air temperature, a major environmental factor influencing plant physiology and growth that already has been perceived at the regional scale and is expected to become even more severe in the future. In the present study, we investigated the effect of elevated ambient air temperature on the nitrogen metabolism of two interior provenances of Douglas fir (Pseudotsuga menziesii var. glauca) originating from contrasting habitats, namely the provenances Monte Creek (MC) from a drier environment and Pend Oreille (PO) from a more humid environment. Three- to four-year-old seedlings of the two provenances were grown for 3 months in controlled environments under either control temperature (day 20 °C, night 15 °C) or high temperature (HT, 30/25 °C) conditions. Total nitrogen (N), soluble protein, chlorophyll and total amino acid (TAA) contents as well as individual amino acid concentrations were determined in both current-year and previous-year needles. Our results show that the foliar total N contents of the two provenances were unaffected by HT. Arginine, lysine, proline, glutamate and glutamine were the most abundant amino acids, which together contributed ∼88% to the TAA pool of current- and previous-year needles. High temperature decreased the contents of most amino acids of the glutamate family (i.e., arginine, proline, ornithine and glutamine) in current-year needles. However, HT did not affect the concentrations of metabolites related to the photorespiratory pathway, such as [Formula: see text], glycine and serine. In general, current-year needles were considerably more sensitive to HT than previous-year needles. Moreover, provenance PO originating from a mesic environment showed stronger responses to HT than provenance MC. Our results indicate provenance-specific plasticity in the response of Douglas fir to growth temperature. Provenance-specific effects of elevated temperature on N-use efficiency suggest

  19. Elevated temperature differently affects foliar nitrogen partitioning in seedlings of diverse Douglas fir provenances.

    PubMed

    Du, Baoguo; Jansen, Kirstin; Junker, Laura Verena; Eiblmeier, Monika; Kreuzwieser, Jürgen; Gessler, Arthur; Ensminger, Ingo; Rennenberg, Heinz

    2014-10-01

    Global climate change causes an increase in ambient air temperature, a major environmental factor influencing plant physiology and growth that already has been perceived at the regional scale and is expected to become even more severe in the future. In the present study, we investigated the effect of elevated ambient air temperature on the nitrogen metabolism of two interior provenances of Douglas fir (Pseudotsuga menziesii var. glauca) originating from contrasting habitats, namely the provenances Monte Creek (MC) from a drier environment and Pend Oreille (PO) from a more humid environment. Three- to four-year-old seedlings of the two provenances were grown for 3 months in controlled environments under either control temperature (day 20 °C, night 15 °C) or high temperature (HT, 30/25 °C) conditions. Total nitrogen (N), soluble protein, chlorophyll and total amino acid (TAA) contents as well as individual amino acid concentrations were determined in both current-year and previous-year needles. Our results show that the foliar total N contents of the two provenances were unaffected by HT. Arginine, lysine, proline, glutamate and glutamine were the most abundant amino acids, which together contributed ∼88% to the TAA pool of current- and previous-year needles. High temperature decreased the contents of most amino acids of the glutamate family (i.e., arginine, proline, ornithine and glutamine) in current-year needles. However, HT did not affect the concentrations of metabolites related to the photorespiratory pathway, such as [Formula: see text], glycine and serine. In general, current-year needles were considerably more sensitive to HT than previous-year needles. Moreover, provenance PO originating from a mesic environment showed stronger responses to HT than provenance MC. Our results indicate provenance-specific plasticity in the response of Douglas fir to growth temperature. Provenance-specific effects of elevated temperature on N-use efficiency suggest

  20. Elevated Temperature and 6-7 Year Outcome of Neonatal Encephalopathy

    PubMed Central

    Laptook, Abbot R.; McDonald, Scott A.; Shankaran, Seetha; Stephens, Bonnie E.; Vohr, Betty R.; Guillet, Ronnie; Higgins, Rosemary D.; Das, Abhik

    2013-01-01

    OBJECTIVE Determine if higher temperature after hypoxia-ischemia is associated with death or IQ < 70 at 6-7 yr among infants treated with intensive care without hypothermia. DESIGN/METHODS Control infants (non-cooled, n=106) of the NICHD Neonatal Research Network hypothermia trial had serial esophageal and skin temperatures over 72hrs. Each infant's temperature was ranked to derive an average of the upper and lower quartile, and median of each site. Temperatures were used in logistic regressions to determine adjusted associations with death or IQ < 70 at 6-7yrs. Secondary outcomes were death, IQ < 70, and moderate/severe CP. IQ and motor function were assessed with Wechsler Scales for Children and Gross Motor Function Classification System. Results are odds ratio (OR, per °C increment within the quartile or median) and 95% confidence interval (CI). RESULTS Primary outcome was available for 89 infants. At 6-7yrs death or IQ < 70 occurred in 54 infants (37 deaths, 17 survivors with IQ < 70) and moderate/severe CP in 15 infants. Death or IQ < 70 was associated with the upper quartile average of esophageal (OR 7.3, 95% CI 2.0-26.3) and skin temperature (OR 3.5, 95% 1.2-10.4). CP was associated with the upper quartile average of esophageal (OR 12.5, 95% CI 1.02-155) and skin temperature (OR 10.3, 95% 1.3-80.2). CONCLUSIONS Among non-cooled infants of a randomized trial, elevated temperatures during the first post-natal days are associated with increase odds of a worse outcome at 6-7yrs. PMID:23595408

  1. Elevated-temperature fracture toughness and fatigue testing of steels for geothermal applications. Annual progress report

    SciTech Connect

    Cutler, R.A.; Goodman, E.C.; Guest, R.V.; Hendrickson, R.R.; Leslie, W.C.

    1980-11-01

    Conventional drill bit steels exhibit increased wear and decreased toughness when run at elevated temperatures in geothermal wells. Bits are therefore run at lower speeds and lighter loads, resulting in lower penetration rates for geothermal wells than for conventional rock drilling. Carpenter EX-00053, Timken CBS 600, Timken CBS 1000M and Vasco X-2M, steels with improved hot hardness (improved wear resistance), were tested in conjunction with the steels used for cones (AISI 4820 and 9315) and lugs (AISI 8620 and 9315) in conventional roller cone rock bits. Shortrod fracture toughness measurements were made on each of these steels between room temperature and 400/sup 0/C. Fatigue crack resistance was determined at 300/sup 0/C for high-temperature steels and at room temperature for conventional steels. Scanning electron microscopy analyses of the fractured short-rod specimens were correlated with observed crack behavior from the test records. Test results are discussed, recommendations made for further testing and preliminary steel selections made for improved geothermal bits.

  2. Defect Monitoring at Elevated Temperatures (>500 °C) Using AN Array of Ultrasonic Waveguides

    NASA Astrophysics Data System (ADS)

    Jarvis, A. J. C.; Cegla, F. B.

    2011-06-01

    This paper describes the development of an array of ultrasonic waveguides that can be permanently installed on high temperature pipework. The work was motivated by the need for monitoring of thermal fatigue cracks in power station boiler outlet pipes. The defect monitoring concept is described and simulated results are presented for the operating envelope of the array. The effects of component geometry, array location and signal to noise ratios on measured defect size were investigated. Results show that the array is capable of measuring defects ranging from the size of an ultrasonic wavelength to 40 percent thickness of the component to within ±0.2 mm of the defect length. Experimental tests using a prototype array attached to a 30 mm thick steel plate containing a 5 mm deep and 0.3 mm wide notch in a furnace at 550 °C showed that monitoring at elevated temperatures is possible. A mean defect length of 5.09 mm with standard deviation of 0.13 mm was measured over a 2 week period. Further tests at even higher temperatures (up to 730 °C) were used to accelerate creep in the attachment mechanism and showed that long-term exposure to temperatures at 550 °C should not have a detrimental effect on the system.

  3. Elevated-Temperature Tests Under Static and Aerodynamic Conditions on Honeycomb-Core Sandwich Panels

    NASA Technical Reports Server (NTRS)

    Groen, Joseph M.; Johnson, Aldie E., Jr.

    1959-01-01

    Stainless-steel honeycomb-core sandwich panels which differed primarily in skin thicknesses were tested at elevated temperatures under static and aerodynamic conditions. The results of these tests were evaluated to determine the insulating effectiveness and structural integrity of the panels. The static radiant-heating tests were performed in front of a quartz-tube radiant heater at panel skin temperatures up to 1,5000 F. The aerodynamic tests were made in a Mach 1.4 heated blowdown wind tunnel. The tunnel temperature was augmented by additional heat supplied by a radiant heater which raised the panel surface temperature above 8000 F during air flow. Static radiant-heating tests of 2 minutes duration showed that all the panels protected the load-carrying structure about equally well. Thin-skin panels showed an advantage for this short-time test over thick-skin panels from a standpoint of weight against insulation. Permanent inelastic strains in the form of local buckles over each cell of the honeycomb core caused an increase in surface roughness. During the aero- dynamic tests all of the panels survived with little or no damage, and panel flutter did not occur.

  4. Liquid oxygen liquid acquisition device bubble point tests with high pressure lox at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Jurns, J. M.; Hartwig, J. W.

    2012-04-01

    When transferring propellant in space, it is most efficient to transfer single phase liquid from a propellant tank to an engine. In earth's gravity field or under acceleration, propellant transfer is fairly simple. However, in low gravity, withdrawing single-phase fluid becomes a challenge. A variety of propellant management devices (PMDs) are used to ensure single-phase flow. One type of PMD, a liquid acquisition device (LAD) takes advantage of capillary flow and surface tension to acquire liquid. The present work reports on testing with liquid oxygen (LOX) at elevated pressures (and thus temperatures) (maximum pressure 1724 kPa and maximum temperature 122 K) as part of NASA's continuing cryogenic LAD development program. These tests evaluate LAD performance for LOX stored in higher pressure vessels that may be used in propellant systems using pressure fed engines. Test data shows a significant drop in LAD bubble point values at higher liquid temperatures, consistent with lower liquid surface tension at those temperatures. Test data also indicates that there are no first order effects of helium solubility in LOX on LAD bubble point prediction. Test results here extend the range of data for LOX fluid conditions, and provide insight into factors affecting predicting LAD bubble point pressures.

  5. Liquid Oxygen Liquid Acquisition Device Bubble Point Tests with High Pressure LOX at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Jurns, John M.; Hartwig, Jason W.

    2011-01-01

    When transferring propellant in space, it is most efficient to transfer single phase liquid from a propellant tank to an engine. In earth s gravity field or under acceleration, propellant transfer is fairly simple. However, in low gravity, withdrawing single-phase fluid becomes a challenge. A variety of propellant management devices (PMD) are used to ensure single-phase flow. One type of PMD, a liquid acquisition device (LAD) takes advantage of capillary flow and surface tension to acquire liquid. The present work reports on testing with liquid oxygen (LOX) at elevated pressures (and thus temperatures) (maximum pressure 1724 kPa and maximum temperature 122K) as part of NASA s continuing cryogenic LAD development program. These tests evaluate LAD performance for LOX stored in higher pressure vessels that may be used in propellant systems using pressure fed engines. Test data shows a significant drop in LAD bubble point values at higher liquid temperatures, consistent with lower liquid surface tension at those temperatures. Test data also indicates that there are no first order effects of helium solubility in LOX on LAD bubble point prediction. Test results here extend the range of data for LOX fluid conditions, and provide insight into factors affecting predicting LAD bubble point pressures.

  6. Microstructure and elevated temperature wear behavior of induction melted Fe-based composite coating

    NASA Astrophysics Data System (ADS)

    Hu, Ge; Meng, Huimin; Liu, Junyou

    2014-10-01

    Fe-based composite coating prepared onto the component of guide wheel using ultrasonic frequency inductive cladding (UFIC) technique has been investigated in terms of microstructure, phase constitutions, microhardness and elevated temperature wear behavior by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), X-ray diffraction (XRD), Vickers microhardness tester and ball-on-disc wear tester. The results indicated that the primary phase in the coating contained austenite γ-Fe, eutectic γ-Fe/(Cr,Fe)2B, boride (Cr,Fe)2B and precipitation enriched in Mo. The average microhardness of the coating was 760 ± 10 HV0.2, which was three times higher than that of the substrate. With increasing temperature, the friction coefficients of the coating and high-chromium cast iron decreased gradually while the wear rates increased during dry sliding wear condition. The relative wear resistance of the coating was 1.63 times higher than that of the high-chromium cast iron at 500 °C, which was ascribed to the hard borides with high thermal stability uniformly embedded in the coating and the formation of dense transfer layer formed onto the worn surface. The high temperature wear mechanism of the coating was dominated by mild abrasive wear. The study revealed that Fe-based composite coating had excellent high temperature wear resistance under dry sliding wear condition.

  7. Production of hydrogen bromide by bromine-methane reactions at elevated temperature.

    SciTech Connect

    Bradshaw, Robert W.; Larson, Richard S.

    2003-05-01

    Hydrogen bromide is a potentially useful intermediate for hydrogen production by electrolysis because it has a low cell potential and is extremely soluble in water. Processes have been proposed to exploit these properties, but among the important issues to be resolved is the efficiency of HBr production from hydrocarbon precursors. This investigation evaluated a fundamental facet of such a technology by studying the reaction of methane and bromine at elevated temperature to determine the yield and kinetics of HBr formation. Laboratory experimentation and computational chemistry were combined to provide a description of this reaction for possible application to reactor design at a larger scale. Experimental studies with a tubular flow reactor were used to survey a range of reactant ratios and reactor residence times at temperatures between 500 C and 800 C. At temperatures near 800 C with excess methane, conversions of bromine to HBr exceeded 90% and reaction products included solid carbon (soot) in stoichiometric amounts. At lower temperatures, HBr conversion was significantly reduced, the products included much less soot, and the formation of bromocarbon compounds was indicated qualitatively. Calculations of chemical equilibrium behavior and reaction kinetics for the experimental conditions were performed using the Sandia CHEMKIN package. An elementary multistep mechanism for the gas-phase chemistry was used together with a surface mechanism that assumed facile deposition of radical species at the reactor walls. Simulations with the laminar-flow boundary-layer code of the CHEMKIN package gave reasonable agreement with experimental data.

  8. Sintering characteristics of FeCuAl green compacts formed at elevated temperature

    NASA Astrophysics Data System (ADS)

    Rahman, M. M.; Zabri, N. H. M.

    2015-07-01

    This paper presents the sintering characteristics of FeCuAl green compacts formed at elevated temperature and sintered at different temperature. Iron ASC 100.29, copper, and aluminum powders were blended mechanically in a low speed mixer. The blended powder mass was subsequently compacted at 150°C. The defect-free green compacts were then sintered at argon gas fired furnace at a heating/cooling rate of 10°C/minute by varying the sintering temperature. The alloyability of the sintered products were examined through XRD whereas the sintered samples were also characterized for their physical and mechanical properties and their microstructures were evaluated. The results revealed that all elements in the samples appeared and single face fcc Cu and bcc Fe (Al) solid solution were found. SEM micrographs revealed that high sintering temperature caused the reduction of pores and loss of grain boundaries in the sample. The metal elements also distributed uniformly. The combination of the iron, copper and aluminum green compacts sintered at 700°C for 90 minutes produced the best mechanical and physical properties.

  9. Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature

    SciTech Connect

    Park, Jingee; Lee, Jongshin; You, Bongsun; Choi, Seogou; Kim, Youngsuk

    2007-05-17

    Using lightweight materials is the emerging need in order to reduce the vehicle's energy consumption and pollutant emissions. Being a lightweight material, magnesium alloys are increasingly employed in the fabrication of automotive and electronic parts. Presently, magnesium alloys used in automotive and electronic parts are mainly processed by die casting. The die casting technology allows the manufacturing of parts with complex geometry. However, the mechanical properties of these parts often do not meet the requirements concerning the mechanical properties (e.g. endurance strength and ductility). A promising alternative can be forming process. The parts manufactured by forming could have fine-grained structure without porosity and improved mechanical properties such as endurance strength and ductility. Because magnesium alloy has low formability resulted form its small slip system at room temperature it is usually formed at elevated temperature. Due to a rapid increase of usage of magnesium sheets in automotive and electronic industry it is necessary to assure database for sheet metal formability and plastic yielding properties in order to optimize its usage. Especially, plastic yielding criterion is a critical property to predict plastic deformation of sheet metal parts in optimizing process using CAE simulation. Von-Mises yield criterion generally well predicts plastic deformation of steel sheets and Hill'1979 yield criterion predicts plastic deformation of aluminum sheets. In this study, using biaxial tensile test machine yield loci of AZ31 magnesium alloy sheet were obtained at elevated temperature. The yield loci ensured experimentally were compared with the theoretical predictions based on the Von-Mises, Hill, Logan-Hosford, and Barlat model.

  10. Effect of Elevated CO2 Concentration, Elevated Temperature and No Nitrogen Fertilization on Methanogenic Archaeal and Methane-Oxidizing Bacterial Community Structures in Paddy Soil

    PubMed Central

    Liu, Dongyan; Tago, Kanako; Hayatsu, Masahito; Tokida, Takeshi; Sakai, Hidemitsu; Nakamura, Hirofumi; Usui, Yasuhiro; Hasegawa, Toshihiro; Asakawa, Susumu

    2016-01-01

    Elevated concentrations of atmospheric CO2 ([CO2]) enhance the production and emission of methane in paddy fields. In the present study, the effects of elevated [CO2], elevated temperature (ET), and no nitrogen fertilization (LN) on methanogenic archaeal and methane-oxidizing bacterial community structures in a free-air CO2 enrichment (FACE) experimental paddy field were investigated by PCR-DGGE and real-time quantitative PCR. Soil samples were collected from the upper and lower soil layers at the rice panicle initiation (PI) and mid-ripening (MR) stages. The composition of the methanogenic archaeal community in the upper and lower soil layers was not markedly affected by the elevated [CO2], ET, or LN condition. The abundance of the methanogenic archaeal community in the upper and lower soil layers was also not affected by elevated [CO2] or ET, but was significantly increased at the rice PI stage and significantly decreased by LN in the lower soil layer. In contrast, the composition of the methane-oxidizing bacterial community was affected by rice-growing stages in the upper soil layer. The abundance of methane-oxidizing bacteria was significantly decreased by elevated [CO2] and LN in both soil layers at the rice MR stage and by ET in the upper soil layer. The ratio of mcrA/pmoA genes correlated with methane emission from ambient and FACE paddy plots at the PI stage. These results indicate that the decrease observed in the abundance of methane-oxidizing bacteria was related to increased methane emission from the paddy field under the elevated [CO2], ET, and LN conditions. PMID:27600710

  11. High-pressure destruction kinetics of Clostridium sporogenes spores in ground beef at elevated temperatures.

    PubMed

    Zhu, Songming; Naim, Fadia; Marcotte, Michèle; Ramaswamy, Hosahalli; Shao, Yanwen

    2008-08-15

    High pressure (HP) is an alternative technique for thermal sterilization of foods with minimum quality loss. HP destruction kinetics of bacterial spores is essential to establishing sterilization process, but knowledge in this field is still very limited. In this study, destruction kinetics was investigated using Clostridium sporogenes PA 3679 (ATCC7955) spores in extra-lean ground beef (5 g each sealed in a sterile plastic bag). Duplicated samples were subjected to HP treatments at 700, 800 and 900 MPa in a HP system equipped with a Polyoxymethylene insulator to maintain constant temperatures at 80, 90 and 100 degrees C during pressure-holding time. The kinetic parameters of the spores (D- and Z-values) were evaluated at these pressures and temperatures. For the pressure from 700 to 900 MPa, D-values ranged from 15.8 to 7.0 and 1.5 to 0.63 min at 80 and 100 degrees C, respectively. The pressure resistance of Z(T)(P) value was 520-563 MPa at 80-100 degrees C. The temperature resistance of Z(P)(T) value was 19.1-19.7 degrees C at 700-900 MPa, much higher than that at atmospheric condition (12.4 degrees C). A regression model was generated which can be used to predict D-value or the death time of a minimum process under given pressure and temperature conditions. HP treatment with elevated temperatures can destroy bacterial spores with a shorter time or lower temperature than conventional thermal processing. This study provides useful information for the achievement of a safe HP sterilization process.

  12. Selected durability studies of geopolymer concrete with respect to carbonation, elevated temperature, and microbial induced corrosion

    NASA Astrophysics Data System (ADS)

    Badar, Mohammad Sufian

    This thesis reports a comprehensive study related to the experimental evaluation of carbonation in reinforced geopolymer concrete, the evaluation of geopolymer concretes at elevated temperature, and the resistance of geopolymer concrete to microbial induced corrosion (MIC). Carbonation: Reinforced concretes, made of geopolymer, prepared from two class F fly ashes and one class C fly ash, were subjected to accelerated carbonation treatment for a period of 450 days. Electrochemical, microstructure and pore structure examinations were performed to evaluate the effect of corrosion caused due to carbonation. GPC specimens prepared from class F fly ash exhibited lower corrosion rates by a factor of 21, and higher pH values (pH>12) when compared with concrete specimens prepared from class C Fly ash (GPCMN). Microstructure and pore characterization of GPC prepared using class F fly ash revealed lower porosity by a factor of 2.5 as compared with thier counterparts made using GPC-MN. The superior performace of GPC prepared with the class F fly ash could be attributed to the dense pore structure and formation of the protective layer of calcium and sodium alumino silicate hydrates (C/N-A-S-H) geopolymeric gels around the steel reinforcement. Elevated Temperature: Geopolymers are an emerging class of cementitious binders which possess a potential for high temperature resistance that could possibly be utilized in applications such as nozzles, aspirators and refractory linings. This study reports on the results of an investigation into the performance of a fly ash based geopolymer binder in high temperature environments. Geopolymer concrete (GPC) was prepared using eleven types of fly ashes obtained from four countries. High content alumina and silica sand was used in the mix for preparing GPC. GPC was subjected to thermal shock tests following ASTM C 1100-88. The GPC samples prepared with tabular alumina were kept at 1093° C and immediately quenched in water. GPC specimens

  13. Emissions of volatile organic compounds and leaf structural characteristics of European aspen (Populus tremula) grown under elevated ozone and temperature.

    PubMed

    Hartikainen, Kaisa; Nerg, Anne-Marja; Kivimäenpää, Minna; Kontunen-Soppela, Sari; Mäenpää, Maarit; Oksanen, Elina; Rousi, Matti; Holopainen, Toini

    2009-09-01

    Northern forest trees are challenged to adapt to changing climate, including global warming and increasing tropospheric ozone (O(3)) concentrations. Both elevated O(3) and temperature can cause significant changes in volatile organic compound (VOC) emissions as well as in leaf anatomy that can be related to adaptation or increased stress tolerance, or are signs of damage. Impacts of moderately elevated O(3) (1.3x ambient) and temperature (ambient + 1 degrees C), alone and in combination, on VOC emissions and leaf structure of two genotypes (2.2 and 5.2) of European aspen (Populus tremula L.) were studied in an open-field experiment in summer 2007. The impact of O(3) on measured variables was minor, but elevated temperature significantly increased emissions of total monoterpenes and green leaf volatiles. Genotypic differences in the responses to warming treatment were also observed. alpha-Pinene emission, which has been suggested to protect plants from elevated temperature, increased from genotype 5.2 only. Isoprene emission from genotype 2.2 decreased, whereas genotype 5.2 was able to retain high isoprene emission level also under elevated temperature. Elevated temperature also caused formation of thinner leaves, which was related to thinning of epidermis, palisade and spongy layers as well as reduced area of palisade cells. We consider aspen genotype 5.2 to have better potential for adaptation to increasing temperature because of thicker photosynthetic active palisade layer and higher isoprene and alpha-pinene emission levels compared to genotype 2.2. Our results show that even a moderate elevation in temperature is efficient enough to cause notable changes in VOC emissions and leaf structure of these aspen genotypes, possibly indicating the effort of the saplings to adapt to changing climate.

  14. Modification of meta-iodobenzylguanidine uptake in neuroblastoma cells by elevated temperature.

    PubMed Central

    Armour, A.; Mairs, R. J.; Gaze, M. N.; Wheldon, T. E.

    1994-01-01

    Successful imaging or treatment of neuroblastoma with 131I-meta-iodobenzylguanidine (131I-mIBG) depends on the selectivity of active (type 1) uptake of mIBG in neuroblastoma cells relative to passive (type 2) uptake present in most normal tissues. This study investigates the effects of moderately elevated temperature (39-41 degrees C) on the cellular uptake of 131I-mIBG in two neuroblastoma cell lines [SK-N-BE(2c) and IMR-32] and in a non-neuronal (ovarian carcinoma) cell line (A2780). In SK-N-BE(2c), a cell line with high active uptake capacity, the specific (type 1) uptake was reduced by 75% (P < 0.001) at 39 degrees C. Both IMR-32 and A2780 have a low capacity for accumulation of mIBG by active uptake. These cell lines demonstrated a statistically significant increase in accumulation at 39 degrees C, mainly as a result of increased non-specific transport. At 41 degrees C uptake of 131I-mIBG was reduced in all cell lines. Thus, the active component of mIBG uptake is more vulnerable to increased temperature than the passive component. It seems probable that moderately increased temperature will have an unfavourable effect on the therapeutic differential for targeted radiotherapy of neuroblastoma using radiolabelled mIBG. PMID:8080728

  15. Low-cycle fatigue of two austenitic alloys in hydrogen gas and air at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Jaske, C. E.; Rice, R. C.

    1976-01-01

    The low-cycle fatigue resistance of type 347 stainless steel and Hastelloy Alloy X was evaluated in constant-amplitude, strain-controlled fatigue tests conducted under continuous negative strain cycling at a constant strain rate of 0.001 per sec and at total axial strain ranges of 1.5, 3.0, and 5.0 percent in both hydrogen gas and laboratory air environments in the temperature range 538-871 C. Elevated-temperature, compressive-strain hold-time experiments were also conducted. In hydrogen, the cyclic stress-strain behavior of both materials at 538 C was characterized by appreciable cyclic hardening at all strain ranges. At 871 C neither material hardened significantly; in fact, at 5% strain range 347 steel showed continuous cyclic softening until failure. The fatigue resistance of 347 steel was slightly higher than that of Alloy X at all temperatures and strain ranges. Ten-minute compressive hold time experiments at 760 and 871 C resulted in increased fatigue lives for 347 steel and decreased fatigue lives for Alloy X. Both alloys showed slightly lower fatigue resistance in air than in hydrogen. Some fractographic and metallographic results are also given.

  16. Electromagnetic Property and Tunable Microwave Absorption of 3D Nets from Nickel Chains at Elevated Temperature.

    PubMed

    Liu, Jia; Cao, Mao-Sheng; Luo, Qiang; Shi, Hong-Long; Wang, Wen-Zhong; Yuan, Jie

    2016-08-31

    We fabricated the nickel chains by a facile wet chemical method. The morphology of nickel chains were tailored by adjusting the amount of PVP during the synthesis process. Both the complex permittivity and permeability of the three-dimensional (3D) nets constructed by nickel chains present strong dependences on temperature in the frequency range of 8.2-12.4 GHz and temperature range of 323-573 K. The peaks in imaginary component of permittivity and permeability mainly derive from interfacial polarizations and resonances, devoting to dielectric and magnetic loss, respectively. The effect from both dielectric and magnetism contribute to enhancing the microwave absorption. The maximum absorption value of the 3D nickel chain nets is approximately -50 dB at 8.8 GHz and 373 K with a thickness of 1.8 mm, and the bandwidth less than -10 dB almost covers the whole investigated frequency band. These are encouraging findings, which provide the potential advantages of magnetic transition metal-based materials for microwave absorption application at elevated temperature. PMID:27509241

  17. Sharper detection of winter temperature changes in the Romanian higher-elevations

    NASA Astrophysics Data System (ADS)

    Croitoru, Adina-Eliza; Drignei, Dorin; Dragotă, Carmen Sofia; Imecs, Zoltan; Burada, Doina Cristina

    2014-11-01

    This paper investigates winter temperature trends in the Romanian higher-altitude areas, for three types of topographies: depression, slope and summit. The main challenge is that some winter temperature trends, by comparison with the other seasons, are milder and harder to detect. We used a change-point regression model with statistically dependent errors and compared it with a standard change-point model with independent errors. Statistical theory ensures that the former model gives a more accurate trend analysis than the latter. The model with statistically dependent errors detects change-points in the mid 70s and statistically significant increasing trends both before and after the change-point. On the other hand, the model with independent errors does not detect statistically significant increasing trends after the change-points for the winter series. These general results occur for all topography types. A separate multiple regression model reveals that the winter temperature trend changes in the Romanian higher-elevations can be described by a linear additive effect of several global atmospheric circulation patterns.

  18. Effects of elevated temperature on the viscoplastic modeling of graphite/polymeric composites

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.

    1991-01-01

    To support the development of new materials for the design of next generation supersonic transports, a research program is underway at NASA to assess the long term durability of advanced polymer matrix composites (PMC's). One of main objectives of the program was to explore the effects of elevated temperature (23 to 200 C) on the constitutive model's material parameters. To achieve this goal, test data on the observed nonlinear, stress-strain behavior of IM7/5260 and IM7/8320 composites under tension and compression loading were collected and correlated against temperature. These tests, conducted under isothermal conditions using variable strain rates, included such phenomena as stress relaxation and short term creep. The second major goal was the verification of the model by comparison of analytical predictions and test results for off axis and angle ply laminates. Correlation between test and predicted behavior was performed for specimens of both material systems over a range of temperatures. Results indicated that the model provided reasonable predictions of material behavior in load or strain controlled tests. Periods of loading, unloading, stress relaxation, and creep were accounted for.

  19. Development of optical tools for the characterization of selective solar absorber at elevated temperature

    NASA Astrophysics Data System (ADS)

    Giraud, Philemon; Braillon, Julien; Delord, Christine; Raccurt, Olivier

    2016-05-01

    Durability of solar components for CSP (Concentrated Solar Power Plant) technologies is a key point to lower cost and ensure their large deployment. These technologies concentrated the solar radiation by means of mirrors on a receiver tube where it is collected as thermal energy. The absorbers are submitted to strong environmental constraints and the degradation of their optical properties (emittance and solar absorbance) have a direct impact on performance. The objective is to develop new optical equipment for characterization of this solar absorber in condition of use that is to say in air and at elevated temperature. In this paper we present two new optical test benches developed for optical characterization of solar absorbers in condition of use up to 800°C. The first equipment is an integrated sphere with heated sample holder which measures the hemispherical reflectance between 280 and 2500 nm to calculate the solar absorbance at high temperature. The second optical test bench measures the emittance of samples up to 1000°C in the range of 1.25 to 28.57 µm. Results of high temperature measurements on a series of metallic absorbers with selective coating and refractory material for high thermal receiver are presented.

  20. Shock Sensitivity of LX-04 Containing Delta Phase HMX at Elevated Temperatures

    SciTech Connect

    Urtiew, P A; Forbes, J W; Tarver, C M; Vandersall, K S; Garcia, F; Greenwood, D W; Hsu, P C; Maienschein, J L

    2003-07-11

    LX-04 is a widely used HMX-based plastic bonded explosive, which contains 85 weight % HMX and 15 weight % Viton binder. The sensitivity of LX-04 to a single stimulus such as heat, impact, and shock has been previously studied. However, hazard scenarios can involve multiple stimuli, such as heating to temperatures close to thermal explosion conditions followed by fragment impact, producing a shock in the hot explosive. The sensitivity of HMX at elevated temperatures is further complicated by the beta to delta solid-state phase transition, which occurs at approximately 165 C. This paper presents the results of shock initiation experiments conducted with LX-04 preheated to 190 C, as well as density measurements and small scale safety test results of the {delta} phase HMX at room temperature. This work shows that LX-04 at 190 C is more shock sensitive than LX-04 at 150 C or 170 C due to the volume increase during the {beta} to {delta} solid phase transition, which creates more hot spots, and the faster growth of reaction during shock compression.

  1. Kinetics of HMX and Phase Transitions: Effects of Grain Size at Elevated Temperature

    SciTech Connect

    Saw, C K

    2002-06-13

    To date a global kinetic rate law has not been written to accurately describe solid-solid phase transformations of HMX and TATB where contributions from grain size effects, binder contents, and impurity levels are explicitly defined. Our recent work presented at the 2001 SCCM topical APS meeting, Atlanta, GA, demonstrated one can not confidently use the second harmonic generation (SHG) diagnostic to study energetic material phase transitions where non-uniform grain size distributions are present. For example, in HMX, the early arrival of SHG before the XRD in the SHG/XRD simultaneous high temperature experiment clearly indicates the partial molecular conversion from centrosymmetric to non-centrosymmetric without any structural changes as exhibit by the XRD pattern. This conversion is attributed to the changes of the surface molecules due to the differences in potential between the surface and the bulk. The present paper reports on accurate XRD measurements following changes of {beta}-HMX to {delta}-HMX at elevated temperature. The results are compared for sample with 2 different grain sizes for HMX. We report accurate temperature dependent lattice parameters and hence volume and linear thermal expansion coefficients along each crystallographic axis. We have also conducted kinetic studies of the behavior of 2 grain-sizes of HMX and concluded that their kinetics, are drastically different.

  2. Reduced group delay dispersion in quantum dot passively mode-locked lasers operating at elevated temperature

    NASA Astrophysics Data System (ADS)

    Mee, J. K.; Raghunathan, R.; Murrell, D.; Braga, A.; Li, Y.; Lester, L. F.

    2014-09-01

    A detailed study of the pulse characteristics emitted from a monolithic Quantum Dot (QD) passively Mode-Locked Laser (MLL) has been performed using a state-of-the-art Frequency Resolved Optical Gating (FROG) pulse measurement system. While traditionally the time-domain pulse characteristics of semiconductor MLLs have been studied using digital sampling oscilloscope or intensity autocorrelation techniques, the FROG measurements allow for simultaneous characterization of time and frequency, which has been shown to be necessary and sufficient for true determination of mode-locked stability. In this paper, FROG pulse measurements are presented on a two-section QD MLL operating over wide temperature excursions. The FROG measurement allows for extraction of the temporal and spectral intensity and phase profiles from which the Group Delay Dispersion (GDD) can be determined. The magnitude of the GDD is found to decrease from 16.1 to 3.5 ps/nm when the temperature is increased from 20 to 50 oC, mirroring the trend of pulse width reduction at elevated temperature, which has been shown to correlate strongly with reduced unsaturated absorption. The possibility to further optimize pulse generation via intra-cavity dispersion compensation in a novel three-section MLL design is also examined, and shows strong potential toward providing valuable insight into the optimal cavity designs and operating parameters for QD MLLs.

  3. Magnetite solubility and phase stability in alkaline media at elevated temperatures

    SciTech Connect

    Ziemniak, S.E.; Jones, M.E.; Combs, K.E.S.

    1994-05-01

    Magnetite, Fe{sub 3}O{sub 4}, is the dominant oxide constituent of the indigenous corrosion layers that form on iron base alloys in high purity, high temperature water. The apparent simultaneous stability of two distinct oxidation states of iron in this metal oxide is responsible for its unique solubility behavior. The present work was undertaken to extend the experimental and theoretical bases for estimating solubilities of an iron corrosion product (Fe{sub 3}O{sub 4}/Fe(OH){sub 2}) over a broader temperature range and in the presence of complexing, pH-controlling reagents. These results indicate that a surface layer of ferrous hydroxide controls magnetite solubility behavior at low temperatures in much the same manner as a surface layer of nickel(II) hydroxide was previously reported to control the low temperature solubility behavior of NiO. The importance of Fe(III) ion complexes implies not only that most previously-derived thermodynamic properties of the Fe(OH){sub 3}{sup {minus}} ion are incorrect, but that magnetite phase stability probably shifts to favor a sodium ferric hydroxyphosphate compound in alkaline sodium phosphate solutions at elevated temperatures. The test methodology involved pumping alkaline solutions of known composition through a bed of Fe{sub 3}O{sub 4} granules and analyzing the emerging solution for Fe. Two pH-controlling reagents were tested: sodium phosphate and ammonia. Equilibria for the following reactions were described in thermodynamic terms: (a) Fe(OH){sub 2}/Fe{sub 3}O{sub 4} dissolution and transformation, (b) Fe(II) and Fe(III) ion hydroxocomplex formation (hydrolysis), (c) Fe(II) ion amminocomplex formation, and (d) Fe(II) and Fe(III) ion phosphatocomplex formation. 36 refs.

  4. 2,5-Dihydroxybenzoic acid: laser desorption/ionisation as a function of elevated temperature

    NASA Astrophysics Data System (ADS)

    Wallace, W. E.; Arnould, M. A.; Knochenmuss, R.

    2005-03-01

    The temperature dependence of laser desorption/ionization (LDI) ion yields has been measured for 2,5-dihydroxybenzoic acid (2,5-DHB) single crystals from room temperature to 160 °C using time-of-flight (TOF) mass spectrometry. A steep rise in ion production occurs at 90 °C, achieving a maximum at 120 °C, then decreases sharply to a minimum at 140 °C, and returns to a second maximum at 150 °C. Above 160 °C, useful information could not be obtained because of rapid volatilization of the sample into the vacuum. The overall trend in ion production, but not some of the details, is well described by a recent two-step theory of the laser desorption/ionization process, which takes into account the temperature-dependent effects of plume expansion. Measuring the background vacuum composition with a quadrupole mass spectrometer residual gas analyzer (RGA) showed an increase in thermal desorption of 2,5-DHB starting at 90 °C and maximizing at 130 °C. The increased neutral production by thermal desorption is believed to be the cause of the decrease in LDI ion production due to reduced pooling probabilities for laser-excited 2,5-DHB molecules. Thermal dehydration, condensation, and decarboxylation increase the volume of gas released at high temperatures which also serve to decrease LDI ion production at elevated temperatures. Lastly, to confirm the mass spectrometry results, the thermal desorption of 2,5-DHB single crystals under vacuum was measured using a quartz-crystal microbalance (QCM). The onset of desorption was found to occur at 90 °C and the maximum desorption rate was found at 135 °C.

  5. MORPHOGENESIS OF DOUGLAS-FIR BUDS IN ALTERED AT ELEVATED TEMPERATURE BUT NOT AT ELEVATED CO21

    EPA Science Inventory

    Global climatic change as expressed by increased CO2 and temperature has the potential for dramatic effects on trees. To determine what its effects may be on Pacific Northwest forests, Douglas-fir (Pseudotsuga menziesii) seedlings were grown in sun-lit controlled environment cham...

  6. In Situ Microstructural Control and Mechanical Testing Inside the Transmission Electron Microscope at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Wang, Baoming; Haque, M. A.

    2015-08-01

    With atomic-scale imaging and analytical capabilities such as electron diffraction and energy-loss spectroscopy, the transmission electron microscope has allowed access to the internal microstructure of materials like no other microscopy. It has been mostly a passive or post-mortem analysis tool, but that trend is changing with in situ straining, heating and electrical biasing. In this study, we design and demonstrate a multi-functional microchip that integrates actuators, sensors, heaters and electrodes with freestanding electron transparent specimens. In addition to mechanical testing at elevated temperatures, the chip can actively control microstructures (grain growth and phase change) of the specimen material. Using nano-crystalline aluminum, nickel and zirconium as specimen materials, we demonstrate these novel capabilities inside the microscope. Our approach of active microstructural control and quantitative testing with real-time visualization can influence mechanistic modeling by providing direct and accurate evidence of the fundamental mechanisms behind materials behavior.

  7. Solar elevation dependent radiosonde temperature bias adjustments back to the 1940s

    NASA Astrophysics Data System (ADS)

    Haimberger, Leopold

    2016-04-01

    The well established RAOBCORE/RICH bias adjustment system for radiosonde temperature records has been enhanced to cope with seasonal changes of solar elevation dependent biases. It is argued that the seasonal cycle of reanalyses is more reliable than that of certain radiosonde types, especially at places where the radiosondes are launched around dawn or dusk, i.e. at high latitudes or near 90E/90W. Furthermore the data set has been extended back to the late 1940s, using JRA-55 and ERA-preSAT background departures as reference. For verification the adjusted data are compared against independent data sets and reanalyses as far as they are available. Suitability of the adjusted data as input for future reanalyses is discussed.

  8. Crop responses to elevated CO2 and interactions with H2O, N, and temperature.

    PubMed

    Kimball, Bruce A

    2016-06-01

    About twenty-seven years ago, free-air CO2 enrichment (FACE) technology was developed that enabled the air above open-field plots to be enriched with CO2 for entire growing seasons. Since then, FACE experiments have been conducted on cotton, wheat, ryegrass, clover, potato, grape, rice, barley, sugar beet, soybean, cassava, rape, mustard, coffee (C3 crops), and sorghum and maize (C4 crops). Elevated CO2 (550ppm from an ambient concentration of about 353ppm in 1990) decreased evapotranspiration about 10% on average and increased canopy temperatures about 0.7°C. Biomass and yield were increased by FACE in all C3 species, but not in C4 species except when water was limiting. Yields of C3 grain crops were increased on average about 19%. PMID:27043481

  9. Elevated Temperature Properties of Titanium Carbide Base Ceramals Containing Nickel or Iron

    NASA Technical Reports Server (NTRS)

    Cooper, A L; Colteryahn, L E

    1951-01-01

    Elevated-temperature properties of titanium carbide base ceramals containing nickel or iron were determined in oxidation, modulus of rupture, tensile strength, and thermal-shock resistance. These materials followed the general growth law and exhibited two stages in oxidation. The following tensile strengths were found at 2000 degrees F: 13.3 weight percent nickel, 16, 150 pounds per square inch; 11.8 weight percent iron, 12,500 pounds per square inch; unalloyed titanium carbide, 16,450 pounds per square inch. Nickel or iron additions to titanium carbide improved the thermal-shock resistance, nickel more. The path of fracture in tensile and thermal-shock specimens was found to progress approximately 50 percent intergranularly and 50 percent transgranularly.

  10. Nucleation and growth of cracks in vitreous-bonded aluminum oxide at elevated temperatures

    SciTech Connect

    Jakus, K.; Wiederhorn, S.M.; Hockey, B.J.

    1986-10-01

    The nucleation and growth of cracks was studied at elevated temperatures on a grade of vitreous-bonded aluminium oxide that contained approx. =8 vol% glass at the grain boundaries. Cracks were observed to nucleate within the vitreous phase, close to the tensile surface of the flexural test specimens used in these experiments. Crack nucleation occurred at a strain of approx. =0.08% to 0.12% which corresponded to a crack nucleation time of approx. =35% of the time to failure by creep rupture. Once nucleated, cracks propagated along grain boundaries, as long as the stress for crack propagation was maintained. The crack velocity for cracks that were nucleated by the creep process was found to be linearly proportional to the apparent stress intensity factor, whereas for cracks that were nucleated by indentation, the crack velocity was proportional to the fourth power of the apparent stress intensity factor.

  11. In situ Measurements of Irradiation-Induced Creep of Nanocrystalline Copper at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Özerİnç, Sezer; Averback, Robert S.; King, William P.

    2016-08-01

    We have measured irradiation-induced creep on nanocrystalline copper micropillars at elevated temperatures. The micropillars, which were ≈1 µm in diameter and ≈2 µm in height, were fabricated from magnetron-sputtered nanocrystalline copper films. The micropillars were compressed during 2.0 MeV Ar+ bombardment and the deformation measured in situ by laser interferometry. The creep rate was measured over the stress range 10-120 MPa at ≈200°C. The results show linear relationships of creep rate with both applied stress and displacement rate, yielding a creep compliance of 0.07 dpa-1 GPa-1 (dpa:displacement per atom). The findings are in good agreement with the previous results obtained using a bulge test on free-standing thin film specimens.

  12. Direct Selective Laser Sintering/Melting of High Density Alumina Powder Layers at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Deckers, J.; Meyers, S.; Kruth, J. P.; Vleugels, J.

    Direct selective laser sintering (SLS) or selective laser melting (SLM) are additive manufacturing techniques that can be used to produce three-dimensional ceramic parts directly, without the need for a sacrificial binder. In this paper, a low laser energy density is applied to SLS/SLM high density powder layers of sub-micrometer alumina at elevated temperatures (up to 800̊C). In order to achieve this, a furnace was designed and built into a commercial SLS machine. This furnace was able to produce a homogeneously heated cylindrical zone with a height of 60 mm and a diameter of 32 mm. After optimizing the layer deposition and laser scanning parameters, two ceramic parts with a density up to 85% and grain sizes as low as 5 μm were successfully produced.

  13. Changes in CdS/CdTe Solar Cells Subjected to Elevated Temperature, Voltage and Illumination

    NASA Astrophysics Data System (ADS)

    Demtsu, Samuel; Nagle, Tim

    2003-10-01

    CdTe/CdS solar cells have been known to exhibit degradation in performance after being subjected to elevated temperature, voltage and illumination. These conditions are collectively referred to as "stress". We have studied and presented CdTe/CdS cell degradation under different stress conditions of devices from First Solar Inc., the University of South Florida and the University of Toledo. All cells were stressed in the light (close to 100 mW/cm2) for 56 days at elevated temperature of 900C at two different biases, short circuit (SC) and open circuit (OC). The stress condition surpasses the operation conditions expected in the field. To characterize the cells, we have measured current density as function of the applied voltage (JV), capacitance vs bias voltage (CV) and quantum efficiency (QE) measurements before and after exposure to stress. To investigate the spatial non-uniformity of photocurrent collection induced by stress we have done Light Beam-Induced Current (LBIC) measurement. The effect of the stress on the photovoltaic parameters short-circuit current (Jsc), open-circuit voltage (Voc), Fill-Factor (FF), and efficiency is presented and discussed. Carrier density as a function of the distance from the semiconductor junction is extracted from the C-V measurements. We have seen some variations between cells and degradation was not monotonic with stress time. The highly probable explanation for the degradation of the cells after the stress is that mobile copper ions diffuse out of the back contact towards the primary junction leaving a depletion of Cu in the back contact, which increases the contact barrier.

  14. Effects of selected thermophilic microorganisms on crude oils at elevated temperatures and pressures. Final report

    SciTech Connect

    Premuzic, E.T.; Lin, M.S.

    1995-07-01

    During the past several years, a considerable amount of work has been carried out showing that microbially enhanced oil recovery (MEOR) is promising and the resulting biotechnology may be deliverable. At the Brookhaven National Laboratory (BNL), systematic studies have been conducted which dealt with the effects of thermophilic and thermoadapted bacteria on the chemical and physical properties of selected types of crude oils at elevated temperatures and pressures. Particular attention was paid to heavy crude oils from Venezuela, California, Alabama, Arkansas, Wyoming, Alaska, and other oil producing areas. Current studies indicate that during the biotreatment several chemical and physical properties of crude oils are affected. The oils are (1) emulsified; (2) acidified; (3) there is a qualitative and quantitative change in light and heavy fractions of the crudes; (4) there are chemical changes in fractions containing sulfur compounds; (5) there is an apparent reduction in the concentration of trace metals; (6) the qualitative and quantitative changes appear to be microbial species dependent; and (7) there is a distinction between {open_quotes}biodegraded{close_quotes} and {open_quotes}biotreated{close_quotes} oils. Preliminary results indicate the introduced microorganisms may become the dominant species in the bioconversion of oils. These studies also indicate the biochemical interactions between crude oils and microorganisms follow distinct trends, characterized by a group of chemical markers. Core-flooding experiments have shown significant additional crude oil recoveries are achievable with thermophilic microorganisms at elevated temperatures similar to those found in oil reservoirs. In addition, the biochemical treatment of crude oils has technological applications in downstream processing of crude oils such as in upgrading of low grade oils and the production of hydrocarbon based detergents.

  15. Computational and Experimental Design of Fe-Based Superalloys for Elevated-Temperature Applications

    SciTech Connect

    Liaw, Peter K.; Fine, Morris E.; Ghosh, Gautam; Asta, Mark D.; Liu, Chain T.; Sun, Zhiqian; Huang, Shenyan; Teng, Zhenke; Wang, Gongyao

    2012-04-13

    Analogous to nickel-based superalloys, Fe-based superalloys, which are strengthened by coherent B2- type precipitates are proposed for elevated-temperature applications. During the period of this project, a series of ferritic superalloys have been designed and fabricated by methods of vacuum-arc melting and vacuum-induction melting. Nano-scale precipitates were characterized by atom-probe tomography, ultrasmall- angle X-ray scattering, and transmission-electron microscopy. A duplex distribution of precipitates was found. It seems that ferritic superalloys are susceptible to brittle fracture. Systematic endeavors have been devoted to understanding and resolving the problem. Factors, such as hot rolling, precipitate volume fractions, alloy compositions, precipitate sizes and inter-particle spacings, and hyperfine cooling precipitates, have been investigated. In order to understand the underlying relationship between the microstructure and creep behavior of ferric alloys at elevated temperatures, in-situ neutron studies have been carried out. Based on the current result, it seems that the major role of β' with a 16%-volume fraction in strengthening ferritic alloys is not load sharing but interactions with dislocations. The oxidation behavior of one ferritic alloy, FBB8 (Fe-6.5Al-10Ni-10Cr-3.4Mo-0.25Zr-0.005B, weight percent), was studied in dry air. It is found that it possesses superior oxidation resistance at 1,023 and 1,123 K, compared with other creep-resistant ferritic steels [T91 (modified 9Cr-1Mo, weight percent) and P92 (9Cr-1.8W-0.5Mo, weight percent)]. At the same time, the calculation of the interfacial energies between the -iron and B2-type intermetallics (CoAl, FeAl, and NiAl) has been conducted.

  16. Small Bioactive Lipoplex (SBL) Nanoparticles Self-Assembled at Elevated Temperature and Pressure

    NASA Astrophysics Data System (ADS)

    Huang, Leaf

    2009-03-01

    Conventional lipoplex (cationic liposome/DNA complex) serves well for gene transfer in cultured cells. However, their in vivo gene delivery activity is limited due to its relatively large size (>100 nm). This is due to incomplete charge neutralization as a result of the steric hindrance during the complexation between DNA and liposomes. Behr et al hypothesized that monomolecular DNA condensate can be prepared if the DNA sees the cationic lipid as monomers. Indeed, small nanoparticles (˜30 nm) were prepared by using a single-chain cationic amphiphile which has a high solubility at the physiological condition. To stabilize the monomolecular condensate, Behr has included a SH group in the cationic amphiphile which could be oxidized to form a dimer. Unfortunately, the stabilized nanoparticles showed no transfection activity when delivered into cells. We hypothesized that similar small lipoplex can be prepared by using a double-chain cationic amphiphile if both DNA and the amphiphile can be soluble in the same solvent. A hydrofluorocarbon HFC-152a is an excellent solvent for the cationic lipid DOTAP at an elevated temperature (˜35 ^oC) and pressure (˜300 atm). Since the solvent can accommodate small amounts of water, DNA or siRNA could be introduced into the system to allow lipoplex formation. The resulting Small Bioactive Lipoplex (SBL) is 30-50 nm in diameter and can transfect cultured cells. Freeze-fracture electron microscopy showed that SBL are solid nanoparticles without any lipid bilayer structure. Since plasmid DNA is fragile at elevated temperature and pressure, we have concentrated our effort in siRNA which is stable under the same conditions. The new formulation shows great promise as an in vivo delivery vector when small particles are required for efficient penetration into the tissues.

  17. Effects of heat stress on photosynthesis of loblolly pine in elevated CO{sub 2} and temperature

    SciTech Connect

    Sasek, T.W.; Thomas, R.B.; Strain, B.R. |

    1995-09-01

    Loblolly pine seedlings were grown from seed in controlled-environment glasshouses from March through October in 4 combinations of elevated CO{sub 2} and temperature; 35 or 70 PaCO{sub 2} and the 30-year average day/night temperatures for central North Carolina (adjusted every 2 weeks) or 5{degrees}C higher than the average. In July, seedlings were exposed to a heat stress of 43{degrees}C/37{degrees}C day/night, representing +10{degrees}C for the high temperature treatments and +15{degrees}C for the low temperature treatments. Leaf gas exchange characteristics were measured at 43{degrees}C early during the second day of stress. Photosynthesis was completely inhibited in seedlings from all 4 CO{sub 2}-temperature combinations. Seedlings were then returned to their normal growth conditions for recovery. After 2 or 4 days of recovery, photosynthesis rates of all seedlings were still decreased; however, elevated-temperature-grown plants recovered more. Elevated CO{sub 2} did not ameliorate the heat stress or speed recovery. Two weeks later, photosynthesis rates in all treatments returned to pre-stress levels. At the October harvest, biomass of nonstressed plants was increased by elevated CO{sub 2} 55% in the ambient temperature and 110% in the elevated temperature treatment. Biomass of heat-stressed seedlings decreased by 40% in elevated CO{sub 2} compared to unstressed controls in either temperature treatment. Results suggest that short-term stochastic events can have important implications for the response of plants to long-term global environmental change.

  18. Influence of Elevated Temperature and Stress Ratio on the Fatigue Response of AM60B Magnesium Alloy

    NASA Astrophysics Data System (ADS)

    Nur-Hossain, Md.; Taheri, Farid

    2012-07-01

    The fatigue response of a high pressure die-cast AM60B Mg alloy is studied at room and elevated temperatures. The fatigue tests are conducted with stress ratio of R = 0.1 and frequency of 30 Hz. The main objective is to determine whether elevated temperature would affect the fatigue response of the alloy. In addition, fatigue crack growth characteristics of the alloy is investigated at room temperature. The purpose of this test is to ascertain the capability and accuracy of a finite element approach coupled with the Walker model in assessing the life cycle of the alloy, in consideration of the influence of stress ratio.

  19. Finite Element Analysis of the Random Response Suppression of Composite Panels at Elevated Temperatures using Shape Memory Alloy Fibers

    NASA Technical Reports Server (NTRS)

    Turner, Travis L.; Zhong, Z. W.; Mei, Chuh

    1994-01-01

    A feasibility study on the use of shape memory alloys (SMA) for suppression of the random response of composite panels due to acoustic loads at elevated temperatures is presented. The constitutive relations for a composite lamina with embedded SMA fibers are developed. The finite element governing equations and the solution procedures for a composite plate subjected to combined acoustic and thermal loads are presented. Solutions include: 1) Critical buckling temperature; 2) Flat panel random response; 3) Thermal postbuckling deflection; 4) Random response of a thermally buckled panel. The preliminary results demonstrate that the SMA fibers can completely eliminate the thermal postbuckling deflection and significantly reduce the random response at elevated temperatures.

  20. Range-wide latitudinal and elevational temperature gradients for the world's terrestrial birds: implications under global climate change.

    PubMed

    La Sorte, Frank A; Butchart, Stuart H M; Jetz, Walter; Böhning-Gaese, Katrin

    2014-01-01

    Species' geographical distributions are tracking latitudinal and elevational surface temperature gradients under global climate change. To evaluate the opportunities to track these gradients across space, we provide a first baseline assessment of the steepness of these gradients for the world's terrestrial birds. Within the breeding ranges of 9,014 bird species, we characterized the spatial gradients in temperature along latitude and elevation for all and a subset of bird species, respectively. We summarized these temperature gradients globally for threatened and non-threatened species and determined how their steepness varied based on species' geography (range size, shape, and orientation) and projected changes in temperature under climate change. Elevational temperature gradients were steepest for species in Africa, western North and South America, and central Asia and shallowest in Australasia, insular IndoMalaya, and the Neotropical lowlands. Latitudinal temperature gradients were steepest for extratropical species, especially in the Northern Hemisphere. Threatened species had shallower elevational gradients whereas latitudinal gradients differed little between threatened and non-threatened species. The strength of elevational gradients was positively correlated with projected changes in temperature. For latitudinal gradients, this relationship only held for extratropical species. The strength of latitudinal gradients was better predicted by species' geography, but primarily for extratropical species. Our findings suggest threatened species are associated with shallower elevational temperature gradients, whereas steep latitudinal gradients are most prevalent outside the tropics where fewer bird species occur year-round. Future modeling and mitigation efforts would benefit from the development of finer grain distributional data to ascertain how these gradients are structured within species' ranges, how and why these gradients vary among species, and the capacity

  1. Drought responses of two gymnosperm species with contrasting stomatal regulation strategies under elevated [CO2] and temperature.

    PubMed

    Duan, Honglang; O'Grady, Anthony P; Duursma, Remko A; Choat, Brendan; Huang, Guomin; Smith, Renee A; Jiang, Yanan; Tissue, David T

    2015-07-01

    Future climate regimes characterized by rising [CO2], rising temperatures and associated droughts may differentially affect tree growth and physiology. However, the interactive effects of these three factors are complex because elevated [CO2] and elevated temperature may generate differential physiological responses during drought. To date, the interactive effects of elevated [CO2] and elevated temperature on drought-induced tree mortality remain poorly understood in gymnosperm species that differ in stomatal regulation strategies. Water relations and carbon dynamics were examined in two species with contrasting stomatal regulation strategies: Pinus radiata D. Don (relatively isohydric gymnosperm; regulating stomata to maintain leaf water potential above critical thresholds) and Callitris rhomboidea R. Br (relatively anisohydric gymnosperm; allowing leaf water potential to decline as the soil dries), to assess response to drought as a function of [CO2] and temperature. Both species were grown in two [CO2] (C(a) (ambient, 400 μl l(-1)) and C(e) (elevated, 640 μl l(-1))) and two temperature (T(a) (ambient) and T(e) (ambient +4 °C)) treatments in a sun-lit glasshouse under well-watered conditions. Drought plants were then exposed to a progressive drought until mortality. Prior to mortality, extensive xylem cavitation occurred in both species, but significant depletion of non-structural carbohydrates was not observed in either species. Te resulted in faster mortality in P. radiata, but it did not modify the time-to-mortality in C. rhomboidea. C(e) did not delay the time-to-mortality in either species under drought or T(e) treatments. In summary, elevated temperature (+4 °C) had greater influence than elevated [CO2] (+240 μl l(-1)) on drought responses of the two studied gymnosperm species, while stomatal regulation strategies did not generally affect the relative contributions of hydraulic failure and carbohydrate depletion to mortality under severe drought. PMID

  2. Drought responses of two gymnosperm species with contrasting stomatal regulation strategies under elevated [CO2] and temperature.

    PubMed

    Duan, Honglang; O'Grady, Anthony P; Duursma, Remko A; Choat, Brendan; Huang, Guomin; Smith, Renee A; Jiang, Yanan; Tissue, David T

    2015-07-01

    Future climate regimes characterized by rising [CO2], rising temperatures and associated droughts may differentially affect tree growth and physiology. However, the interactive effects of these three factors are complex because elevated [CO2] and elevated temperature may generate differential physiological responses during drought. To date, the interactive effects of elevated [CO2] and elevated temperature on drought-induced tree mortality remain poorly understood in gymnosperm species that differ in stomatal regulation strategies. Water relations and carbon dynamics were examined in two species with contrasting stomatal regulation strategies: Pinus radiata D. Don (relatively isohydric gymnosperm; regulating stomata to maintain leaf water potential above critical thresholds) and Callitris rhomboidea R. Br (relatively anisohydric gymnosperm; allowing leaf water potential to decline as the soil dries), to assess response to drought as a function of [CO2] and temperature. Both species were grown in two [CO2] (C(a) (ambient, 400 μl l(-1)) and C(e) (elevated, 640 μl l(-1))) and two temperature (T(a) (ambient) and T(e) (ambient +4 °C)) treatments in a sun-lit glasshouse under well-watered conditions. Drought plants were then exposed to a progressive drought until mortality. Prior to mortality, extensive xylem cavitation occurred in both species, but significant depletion of non-structural carbohydrates was not observed in either species. Te resulted in faster mortality in P. radiata, but it did not modify the time-to-mortality in C. rhomboidea. C(e) did not delay the time-to-mortality in either species under drought or T(e) treatments. In summary, elevated temperature (+4 °C) had greater influence than elevated [CO2] (+240 μl l(-1)) on drought responses of the two studied gymnosperm species, while stomatal regulation strategies did not generally affect the relative contributions of hydraulic failure and carbohydrate depletion to mortality under severe drought.

  3. Microstructural changes to AlCu6Ni1 alloy after prolonged annealing at elevated temperature.

    PubMed

    Wierzbińska, M; Sieniawski, J

    2010-03-01

    This work presents results of microstructure examination of AlCu(6)Ni(1) aluminium alloy. The commercial AlCu(4)Ni(2)Mg(2) (M-309) alloy is widely used for elements of aircraft and automotive engines. Modification its chemical composition was aimed at improving the stability of mechanical properties of the alloy subjected to long-term exposure to high temperature. The alloy after standard T6 heat treatment (solution heat treated at 818 K/10 h/water quenched followed by ageing at 498 K/8 h/air cooled) was annealed for 150 h at elevated temperature of 573 K corresponding to the maximum value at which structural elements of jet piston engines made of aluminium alloys operate. It was found that applied heat treatment caused an increasing in the particles of hardening phase (theta'-Al(2)Cu) size. The significant growth of the length of theta'-Al(2)Cu precipitations was observed in particularly. Nevertheless, it did not strongly result in change of its shape - the 'crystallites' and 'rods' were still characteristic of hardening phase morphology. The phenomena of the growth of theta'-Al(2)Cu precipitates caused decreasing the mechanical properties of the alloy, what is the subject of further investigations by the authors.

  4. Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity.

    PubMed

    Tunick, Michael H; Thomas-Gahring, Audrey; Van Hekken, Diane L; Iandola, Susan K; Singh, Mukti; Qi, Phoebe X; Ukuku, Dike O; Mukhopadhyay, Sudarsan; Onwulata, Charles I; Tomasula, Peggy M

    2016-03-01

    In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100g (WPC34) and 76.8 g of protein/100g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35 °C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35 °C but at least 18 mo at lower temperatures, which should extend the market for these products.

  5. Separation of amino acids, peptides and corresponding Amadori compounds on a silica column at elevated temperature.

    PubMed

    Hao, Zhigang; Lu, Chih-Ying Joey; Xiao, Baiming; Weng, Naidong; Parker, Barry; Knapp, Michael; Ho, Chi-Tang

    2007-04-20

    Maillard reaction of glucose with amino acids and peptides has become a very important experimental model in the food flavor and pharmaceutical industries for better understanding the mechanism of food flavor generation and drug stability. Because of the amino acid and sugar functional groups present in their structures, most of the reaction components formed during the initial stages of Maillard reaction as well as the substrates are relatively polar. These compounds are poorly retained on a conventional reversed phase column. While polar stationary phases like HILIC column do provide better retention for these polar components, method selectivity could still be a challenge due to the structural similarity between these analytes. In this report, parameters such as pH, mobile phase composition and temperature were investigated using different brands of bare silica columns in order to separate glycine (G), diglycine (DG), triglycine (TG), and the corresponding Amadori compounds of glucose-glycine (GG), glucose-diglycine (GDG) and glucose-triglycine (GTG). An excellent separation for glycine, glycine peptides and their Amadori compounds was obtained on a bare silica column at an elevated temperature. PMID:17350634

  6. Thermomechanical model to assess stresses developed during elevated-temperature cleaning of coated optics.

    PubMed

    Liddell, H P H; Lambropoulos, J C; Jacobs, S D

    2014-09-10

    A thermomechanical model is developed to estimate the stress response of an oxide coating to elevated-temperature chemical cleaning. Using a hafnia-silica multilayer dielectric pulse compressor grating as a case study, we demonstrate that substrate thickness can strongly affect the thermal stress response of the thin-film coating. As a result, coatings on large, thick substrates may be susceptible to modes of stress-induced failure (crazing or delamination) not seen in small parts. We compare the stress response of meter-scale optics to the behavior of small-scale test or "witness" samples, which are expected to be representative of their full-size counterparts. The effects of materials selection, solution temperature, and heating/cooling rates are explored. Extending the model to other situations, thermal stress results are surveyed for various combinations of commonly used materials. Seven oxide coatings (hafnia, silica, tantala, niobia, alumina, and multilayers of hafnia-silica and alumina-silica) and three glass substrates (BK7, borosilicate float glass, and fused silica) are examined to highlight some interesting results.

  7. Microstructural changes to AlCu6Ni1 alloy after prolonged annealing at elevated temperature.

    PubMed

    Wierzbińska, M; Sieniawski, J

    2010-03-01

    This work presents results of microstructure examination of AlCu(6)Ni(1) aluminium alloy. The commercial AlCu(4)Ni(2)Mg(2) (M-309) alloy is widely used for elements of aircraft and automotive engines. Modification its chemical composition was aimed at improving the stability of mechanical properties of the alloy subjected to long-term exposure to high temperature. The alloy after standard T6 heat treatment (solution heat treated at 818 K/10 h/water quenched followed by ageing at 498 K/8 h/air cooled) was annealed for 150 h at elevated temperature of 573 K corresponding to the maximum value at which structural elements of jet piston engines made of aluminium alloys operate. It was found that applied heat treatment caused an increasing in the particles of hardening phase (theta'-Al(2)Cu) size. The significant growth of the length of theta'-Al(2)Cu precipitations was observed in particularly. Nevertheless, it did not strongly result in change of its shape - the 'crystallites' and 'rods' were still characteristic of hardening phase morphology. The phenomena of the growth of theta'-Al(2)Cu precipitates caused decreasing the mechanical properties of the alloy, what is the subject of further investigations by the authors. PMID:20500428

  8. Physical and chemical changes in whey protein concentrate stored at elevated temperature and humidity.

    PubMed

    Tunick, Michael H; Thomas-Gahring, Audrey; Van Hekken, Diane L; Iandola, Susan K; Singh, Mukti; Qi, Phoebe X; Ukuku, Dike O; Mukhopadhyay, Sudarsan; Onwulata, Charles I; Tomasula, Peggy M

    2016-03-01

    In a case study, we monitored the physical properties of 2 batches of whey protein concentrate (WPC) under adverse storage conditions to provide information on shelf life in hot, humid areas. Whey protein concentrates with 34.9 g of protein/100g (WPC34) and 76.8 g of protein/100g (WPC80) were stored for up to 18 mo under ambient conditions and at elevated temperature and relative humidity. The samples became yellower with storage; those stored at 35 °C were removed from the study by 12 mo because of their unsatisfactory appearance. Decreases in lysine and increases in water activity, volatile compound formation, and powder caking values were observed in many specimens. Levels of aerobic mesophilic bacteria, coliforms, yeast, and mold were <3.85 log10 cfu/g in all samples. Relative humidity was not a factor in most samples. When stored in sealed bags, these samples of WPC34 and WPC80 had a shelf life of 9 mo at 35 °C but at least 18 mo at lower temperatures, which should extend the market for these products. PMID:26778305

  9. Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Meng, L. J.; Sun, J.; Xing, H.

    2012-08-01

    Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

  10. Elevated temperature creep properties of the 54Fe-29Ni-17Co "Kovar" alloy.

    SciTech Connect

    Stephens, John Joseph, Jr.; Rejent, Jerome Andrew; Schmale, David T.

    2009-01-22

    The outline of this presentation is: (1) Applications of Kovar Alloy in metal/ceramic brazing; (2) Diffusion bonding of precision-photoetched Kovar parts; (3) Sample composition and annealing conditions; (4) Intermediate temperature creep properties (350-650 C); (5) Power law creep correlations--with and without modulus correction; (6) Compressive stress-strain properties (23-900 C); (7) Effect of creep deformation on grain growth; and (8) Application of the power law creep correlation to the diffusion bonding application. The summary and conclusions are: Elevated temperature creep properties of Kovar from 750-900 C obey a power law creep equation with a stress exponent equal to 4.9, modulus compensated activation energy of 47.96 kcal/mole. Grain growth in Kovar creep samples tested at 750 and 800 C is quite sluggish. Significant grain growth occurs at 850 C and above, this is consistent with isothermal grain growth studies performed on Kovar alloy wires. Finite element analysis of the diffusion bonding of Kovar predict that stresses of 30 MPa and higher are needed for good bonding at 850 C, we believe that 'sintering' effects must be accounted for to allow FEA to be predictive of actual processing conditions. Additional creep tests are planned at 250-650 C.

  11. Impact Testing of Stainless Steel Material at Room and Elevated Temperatures

    SciTech Connect

    Dana K. Morton; Spencer D. Snow; Tom E. Rahl; Robert K. Blandford

    2007-07-01

    Stainless steels are used for the construction of numerous spent nuclear fuel or radioactive material containers that may be subjected to high strains and moderate strain rates during accidental drop events. Mechanical characteristics of these base materials and their welds under dynamic loads in the strain rate range of concern are not well documented. However, three previous papers [1, 2, 3] reported on impact testing and analysis results performed at the Idaho National Laboratory using 304/304L and 316/316L stainless steel base material specimens that began the investigation of these characteristics. The goal of the work presented herein is to add the results of additional tensile impact testing for 304/304L and 316/316L stainless steel material specimens. Utilizing a drop-weight impact test machine and 1/4-inch to 1/2-inch thick dog-bone shaped test specimens, additional tests achieved target strain rates of 5, 10, and 22 per second at room temperature, 300, and 600 degrees Fahrenheit. Elevated true stress-strain curves for these materials at each designated strain rate and temperature are presented herein.

  12. Significantly improved cyclability of lithium manganese oxide under elevated temperature by an easily oxidized electrolyte additive

    NASA Astrophysics Data System (ADS)

    Zhu, Yunmin; Rong, Haibo; Mai, Shaowei; Luo, Xueyi; Li, Xiaoping; Li, Weishan

    2015-12-01

    Spinel lithium manganese oxide, LiMn2O4, is a promising cathode for lithium ion battery in large-scale applications, because it possesses many advantages compared with currently used layered lithium cobalt oxide (LiCoO2) and olivine phosphate (LiFePO4), including naturally abundant resource, environmental friendliness and high and long work potential plateau. Its poor cyclability under high temperature, however, limits its application. In this work, we report a significant cyclability improvement of LiMn2O4 under elevated temperature by using dimethyl phenylphonite (DMPP) as an electrolyte additive. Charge/discharge tests demonstrate that the application of 0.5 wt.% DMPP yields a capacity retention improvement from 16% to 82% for LiMn2O4 after 200 cycles under 55 °C at 1 C (1C = 148 mAh g-1) between 3 and 4.5 V. Electrochemical and physical characterizations indicate that DMPP is electrochemically oxidized at the potential lower than that for lithium extraction, forming a protective cathode interphase on LiMn2O4, which suppresses the electrolyte decomposition and prevents LiMn2O4 from crystal destruction.

  13. Mechanical Characterization of Adhesive Bonded Sheet Metal Joints at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Mori, Kiyomi; Azimin, Muhd; Tanaka, Masashi; Ikeda, Takashi

    A new approach is expected for heat resisting metal joints with inorganic adhesive. In the present study, the mechanical characterization of the inorganic adhesive and the strength evaluation of metal joints are realized by an experimental procedure that includes a static test for single lap joints bonded with inorganic adhesives. The inorganic adhesive can be cured at 150°C, and the maximum temperature resistance proposed is up to 1,200°C. A tensile shear test for the joints with a nickel adherend is performed at an elevated temperature of up to 400°C. The effect of material property, overlap length, and thickness of adherend on the joint strength is discussed based on stress analysis for corresponding joint models using a Finite Element Method. It is important to confirm whether fracture occurred in the adhesive layer or at the interface between the adhesive and the adherend. Therefore, the deformation and fracture behavior of the adhesive layer is investigated microscopically by the photographs of a scanning electron microscope (SEM) for the fracture surface.

  14. Aluminum-Silicon Alloy Having Improved Properties at Elevated Temperatures and Articles Cast Therefrom

    NASA Technical Reports Server (NTRS)

    Lee, Jonathan A. (Inventor); Chen, Po-Shou (Inventor)

    2002-01-01

    An aluminum alloy suitable for high temperature applications, such as heavy duty pistons and other internal combustion applications. having the following composition, by weight percent (wt %): Silicon: 11.0-14.0; Copper: 5.6-8.0; Iron: 0-0.8; Magnesium: 0.5-1.5; Nickel: 0.05-0.9; Manganese: 0.5-1.5; Titanium: 0.05-1.2; Zirconium: 0.12-1.2; Vanadium: 0.05-1.2; Zinc: 0.005-0.9; Strontium: 0.001-0.1; Aluminum: balance. In this alloy the ratio of silicon:magnesium is 10-25, and the ratio of copper:magnesium is 4-15. After an article is cast from this alloy, the article is treated in a solutionizing step which dissolves unwanted precipitates and reduces any segregation present in the original alloy. After this solutionizing step, the article is quenched, and is then aged at an elevated temperature for maximum strength.

  15. Elevated temperature strengthening of a melt spun austenitic steel by TiB2

    NASA Technical Reports Server (NTRS)

    Michal, G. M.; Glasgow, T. K.; Moore, T. J.

    1986-01-01

    Mechanical properties of an iron-based alloy containing (by wt pct) 33Ni, 2Al, 6Ti, and 2B (resulting in an alloy containing 10 vol pct TiB2) were evaluated by hardness and tensile testing. The alloy was cast as a ribbon using a dual 'free-jet' variation of Jech et al. (1984) method of chill-block melt-spinning against a copper wheel; to simulate thermal cycles the alloy ribbon would experience during compaction into shapes, various segments of the ribbon were annealed under a vacuum at temperatures ranging from 500 to 1150 C. The results show that maximum strengths at 650 and 760 C were developed in ribbons annealed at 1100 C; in these ribbons an optimal combination of grain coarsening with minimum TiB2 particle growth was observed. However, the elevated-temperature strength of the TiB2-strengthened alloy under optimal annealing conditions was poorer than that of conventional iron-based superalloys strengthened by gamma-prime precipitates.

  16. Elevated-temperature tensile and creep properties of several ferritic stainless steels

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

    The elevated-temperature mechanical properties of several ferritic stainless steels were determined. The alloys evaluated included Armco 18SR, GE 1541, and NASA-18T-A. Tensile and creep strength properties at 1073 and 1273 K and residual room temperature tensile properties after creep testing were measured. In addition, 1273 K tensile and creep tests and residual property testing were conducted with Armco 18SR and GE 1541 which were exposed for 200 hours to a severe oxidizing environment in automotive thermal reactors. Aside from the residual tensile properties for Armco 18SR, prior exposure did not affect the mechanical properties of either alloy. The 1273 K creep strength parallel to the sheet-rolling direction was similar for all three alloys. At 1073 K, NASA-18T-A had better creep strength than either Armco 18SR or GE 1541. NASA-18T-A possesses better residual properties after creep testing than either Armco 18SR or Ge 1541.

  17. Fatigue Hysteresis of Carbon Fiber-Reinforced Ceramic-Matrix Composites at Room and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Li, Longbiao

    2016-02-01

    When the fiber-reinforced ceramic-matrix composites (CMCs) are first loading to fatigue peak stress, matrix multicracking and fiber/matrix interface debonding occur. Under fatigue loading, the stress-strain hysteresis loops appear as fiber slipping relative to matrix in the interface debonded region upon unloading/reloading. Due to interface wear at room temperature or interface oxidation at elevated temperature, the interface shear stress degredes with increase of the number of applied cycles, leading to the evolution of the shape, location and area of stress-strain hysteresis loops. The evolution characteristics of fatigue hysteresis loss energy in different types of fiber-reinforced CMCs, i.e., unidirectional, cross-ply, 2D and 2.5D woven, have been investigated. The relationships between the fatigue hysteresis loss energy, stress-strain hysteresis loops, interface frictional slip, interface shear stress and interface radial thermal residual stress, matrix stochastic cracking and fatigue peak stress of fiber-reinforced CMCs have been established.

  18. Variations of bubble cavitation and temperature elevation during lesion formation by high-intensity focused ultrasound.

    PubMed

    Zhou, Yufeng; Gao, Xiaobin Wilson

    2013-08-01

    High-intensity focused ultrasound (HIFU) is emerging as an effective therapeutic modality in both thermal ablations for solid tumor/cancer and soft-tissue fragmentation. Mechanical and thermal effects, which play an important role in the HIFU treatment simultaneously, are dependent on the operating parameters and may vary with the progress of therapy. Mechanical erosion in the shape of a "squid," a "dumbbell" lesion with both mechanical and thermal lesions, or a "tadpole" lesion with mechanical erosion at the center and thermal necrosis on the boundary in the transparent gel phantom could be produced correspondingly with the pulse duration of 5-30 ms, which is much longer than histotripsy burst but shorter than the time for tissue boiling, and pulse repetition frequency (PRF) of 0.2-5 Hz. Meanwhile, variations of bubble cavitation (both inertial and stable cavitation) and temperature elevation in the focal region (i.e., z = -2.5, 0, and 2.5 mm) were measured by passive cavitation detection (PCD) and thermocouples during the therapeutic procedure, respectively. Stable cavitation increased with the pulse duration, PRF, and the number of pulses delivered. However, inertial cavitation was found to increase initially and then decrease with long pulse duration and high PRF. Temperature in the pre-focal region is always higher than those at the focal and post-focal position in all tests. Great variations of PCD signals and temperature elevation are due to the generation and persistence of large bubble, which is resistant to collapse and occurs with the increase of pulse duration and PRF. Similar lesion pattern and variations were also observed in ex vivo porcine kidneys. Hyperechoes in the B-mode ultrasound image were comparable to the shape and size of lesions in the dissected tissue. Thermal lesion volume increased with the increase of pulse duration and PRF, but mechanical erosion reached its maximum volume with the pulse duration of 20 ms and PRF of 1

  19. Elevated Temperature, Notched Compression Performance of Out of Autoclave Processed Composites

    NASA Technical Reports Server (NTRS)

    Grimsley, Brian W.; Sutter, James K.; Dixon, Genevieve D.; Smeltzer, Satn S.

    2013-01-01

    Curved honeycomb sandwich panels composed of carbon fiber reinforced toughened-epoxy polymer facesheets are being evaluated for potential use as payload fairing components on the NASA heavy-lift space launch system (HL-SLS). These proposed composite sandwich panels provide the most efficient aerospace launch structures, and offer mass and thermal advantages when compared with existing metallic payload fairing structures. NASA and industry are investigating recently developed carbon fiber epoxy prepreg systems which can be fabricated using out-of autoclave (OOA) processes. Specifically, OOA processes using vacuum pressure in an oven and thereby significantly reducing the cost associated with manufacturing large (up to 10 m diameter) composite structures when compared with autoclave. One of these OOA composite material systems, CYCOM(R) 5320-1, was selected for manufacture of a 1/16th scale barrel portion of the payload fairing; such that, the system could be compared with the well-characterized prepreg system, CYCOM(R) 977-3, typically processed in an autoclave. Notched compression coupons for each material were obtained from the minimum-gauge flat laminate [60/-60/0]S witness panels produced in this manufacturing study. The coupons were also conditioned to an effective moisture equilibrium point and tested according to ASTM D6484M-09 at temperatures ranging from 25 C up to 177 C. The results of this elevated temperature mechanical characterization study demonstrate that, for thin coupons, the OHC strength of the OOA laminate was equivalent to the flight certified autoclave processed composite laminates; the limitations on the elevated temperature range are hot-wet conditions up to 163 C and are only within the margins of testing error. At 25 C, both the wet and dry OOA material coupons demonstrated greater OHC failure strengths than the autoclave processed material laminates. These results indicate a substantial improvement in OOA material development and

  20. Limited tolerance by insects to high temperatures across tropical elevational gradients and the implications of global warming for extinction.

    PubMed

    García-Robledo, Carlos; Kuprewicz, Erin K; Staines, Charles L; Erwin, Terry L; Kress, W John

    2016-01-19

    The critical thermal maximum (CTmax), the temperature at which motor control is lost in animals, has the potential to determine if species will tolerate global warming. For insects, tolerance to high temperatures decreases with latitude, suggesting that similar patterns may exist along elevational gradients as well. This study explored how CTmax varies among species and populations of a group of diverse tropical insect herbivores, the rolled-leaf beetles, across both broad and narrow elevational gradients. Data from 6,948 field observations and 8,700 museum specimens were used to map the elevational distributions of rolled-leaf beetles on two mountains in Costa Rica. CTmax was determined for 1,252 individual beetles representing all populations across the gradients. Initial morphological identifications suggested a total of 26 species with populations at different elevations displaying contrasting upper thermal limits. However, compared with morphological identifications, DNA barcodes (cytochrome oxidase I) revealed significant cryptic species diversity. DNA barcodes identified 42 species and haplotypes across 11 species complexes. These 42 species displayed much narrower elevational distributions and values of CTmax than the 26 morphologically defined species. In general, species found at middle elevations and on mountaintops are less tolerant to high temperatures than species restricted to lowland habitats. Species with broad elevational distributions display high CTmax throughout their ranges. We found no significant phylogenetic signal in CTmax, geography, or elevational range. The narrow variance in CTmax values for most rolled-leaf beetles, especially high-elevation species, suggests that the risk of extinction of insects may be substantial under some projected rates of global warming. PMID:26729867

  1. Limited tolerance by insects to high temperatures across tropical elevational gradients and the implications of global warming for extinction.

    PubMed

    García-Robledo, Carlos; Kuprewicz, Erin K; Staines, Charles L; Erwin, Terry L; Kress, W John

    2016-01-19

    The critical thermal maximum (CTmax), the temperature at which motor control is lost in animals, has the potential to determine if species will tolerate global warming. For insects, tolerance to high temperatures decreases with latitude, suggesting that similar patterns may exist along elevational gradients as well. This study explored how CTmax varies among species and populations of a group of diverse tropical insect herbivores, the rolled-leaf beetles, across both broad and narrow elevational gradients. Data from 6,948 field observations and 8,700 museum specimens were used to map the elevational distributions of rolled-leaf beetles on two mountains in Costa Rica. CTmax was determined for 1,252 individual beetles representing all populations across the gradients. Initial morphological identifications suggested a total of 26 species with populations at different elevations displaying contrasting upper thermal limits. However, compared with morphological identifications, DNA barcodes (cytochrome oxidase I) revealed significant cryptic species diversity. DNA barcodes identified 42 species and haplotypes across 11 species complexes. These 42 species displayed much narrower elevational distributions and values of CTmax than the 26 morphologically defined species. In general, species found at middle elevations and on mountaintops are less tolerant to high temperatures than species restricted to lowland habitats. Species with broad elevational distributions display high CTmax throughout their ranges. We found no significant phylogenetic signal in CTmax, geography, or elevational range. The narrow variance in CTmax values for most rolled-leaf beetles, especially high-elevation species, suggests that the risk of extinction of insects may be substantial under some projected rates of global warming.

  2. Limited tolerance by insects to high temperatures across tropical elevational gradients and the implications of global warming for extinction

    PubMed Central

    García-Robledo, Carlos; Kuprewicz, Erin K.; Staines, Charles L.; Erwin, Terry L.; Kress, W. John

    2016-01-01

    The critical thermal maximum (CTmax), the temperature at which motor control is lost in animals, has the potential to determine if species will tolerate global warming. For insects, tolerance to high temperatures decreases with latitude, suggesting that similar patterns may exist along elevational gradients as well. This study explored how CTmax varies among species and populations of a group of diverse tropical insect herbivores, the rolled-leaf beetles, across both broad and narrow elevational gradients. Data from 6,948 field observations and 8,700 museum specimens were used to map the elevational distributions of rolled-leaf beetles on two mountains in Costa Rica. CTmax was determined for 1,252 individual beetles representing all populations across the gradients. Initial morphological identifications suggested a total of 26 species with populations at different elevations displaying contrasting upper thermal limits. However, compared with morphological identifications, DNA barcodes (cytochrome oxidase I) revealed significant cryptic species diversity. DNA barcodes identified 42 species and haplotypes across 11 species complexes. These 42 species displayed much narrower elevational distributions and values of CTmax than the 26 morphologically defined species. In general, species found at middle elevations and on mountaintops are less tolerant to high temperatures than species restricted to lowland habitats. Species with broad elevational distributions display high CTmax throughout their ranges. We found no significant phylogenetic signal in CTmax, geography, or elevational range. The narrow variance in CTmax values for most rolled-leaf beetles, especially high-elevation species, suggests that the risk of extinction of insects may be substantial under some projected rates of global warming. PMID:26729867

  3. Elevated body temperature is linked to fatigue in an Italian sample of relapsing-remitting multiple sclerosis patients.

    PubMed

    Leavitt, V M; De Meo, E; Riccitelli, G; Rocca, M A; Comi, G; Filippi, M; Sumowski, J F

    2015-11-01

    Elevated body temperature was recently reported for the first time in patients with relapsing-remitting multiple sclerosis (RRMS) relative to healthy controls. In addition, warmer body temperature was associated with worse fatigue. These findings are highly novel, may indicate a novel pathophysiology for MS fatigue, and therefore warrant replication in a geographically separate sample. Here, we investigated body temperature and its association to fatigue in an Italian sample of 44 RRMS patients and 44 age- and sex-matched healthy controls. Consistent with our original report, we found elevated body temperature in the RRMS sample compared to healthy controls. Warmer body temperature was associated with worse fatigue, thereby supporting the notion of endogenous temperature elevations in patients with RRMS as a novel pathophysiological factor underlying fatigue. Our findings highlight a paradigm shift in our understanding of the effect of heat in RRMS, from exogenous (i.e., Uhthoff's phenomenon) to endogenous. Although randomized controlled trials of cooling treatments (i.e., aspirin, cooling garments) to reduce fatigue in RRMS have been successful, consideration of endogenously elevated body temperature as the underlying target will enhance our development of novel treatments.

  4. A one-term extrapolation method for estimating equilibrium constants of aqueous reactions at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Gu, Y.; Gammons, C. H.; Bloom, M. S.

    1994-09-01

    A one-term method for extrapolating equilibrium constants for aqueous reactions is proposed which is based on the observation that the change in free energy of a well-balanced isocoulombic reaction is nearly independent of temperature. The current practice in extrapolating log K values for isocoulombic reactions is to omit the ΔCp term but include a ΔS term (i.e., the two-term extrapolation equation of LINDSAY, 1980). However, we observe that the ΔCp and ΔS terms for many isocoulombic reactions are not only small, but are often opposite in sign, and therefore tend to cancel one another. Thus, inclusion of an entropy term often yields estimates which are less accurate than omission of both terms. The one-term extrapolation technique is tested with literature data for a large number of isocoulombic reactions involving ion-ligand exchange, cation hydrolysis, acid-base neutralization, redox, and selected reactions involving solids. In most cases the extrapolated values are in excellent agreement with the experimental measurements, especially at higher temperatures where they are often more accurate than those obtained using the two-term equation of LINDSAY (1980). The results are also comparable to estimates obtained using the modified HKF model of TANGER and HELGESON (1988) and the density model of ANDERSON et al. (1991). It is also found to produce reasonable estimates for isocoulombic reactions at elevated pressure (up to P = 2 kb) and ionic strength (up to I = 1.0). The principal advantage of the one-term method is that accurate estimates of high temperature equilibrium constants may be obtained using only free energy data for the reaction of interest at one reference temperature. The principal disadvantage is that the accuracies of the estimates are somewhat dependent on the model reaction selected to balance the isocoulombic reaction. Satisfactory results are obtained for reactions that have minimal energetic, electrostatic, structural, and volumetric

  5. A New Thermo-Elasto-Viscoplastic Crystal Plasticity Framework to Predict the Formability of Aluminum Alloys at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Inal, Kaan; Cyr, Edward; Mishra, Raja K.

    2016-08-01

    A new thermo-elasto-viscoplastic (TEV) crystal plasticity constitutive formulation is developed and implemented in the well-known Marciniak-Kuczynski analysis to predict the formability of aluminum alloys (AA) 5754 and 3003 at elevated temperatures. The model takes into account the temperature dependence of the single crystal elastic coefficients, single slip hardening parameters, thermal softening and slip rate sensitivity. Temperature dependent single slip hardening parameters are determined from uniaxial tension simulations at room and elevated temperatures. The new model is able to accurately predict the experimental forming limit diagrams (FLDs) without the need for further curve fitting. The effects of elastic constants and thermal softening on FLD predictions are discussed, and a new expression to represent the temperature dependence of the initial imperfection (for the M-K analysis) is developed to enable the model to successfully predict the FLDs for any temperature in the warm forming regime prior to recrystallization.

  6. Laboratory and Numerical Investigations of Frictional Properties of Gabbro at Low Normal Stress and Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Mitchell, E. K.; Brown, K. M.; Fialko, Y. A.

    2013-12-01

    We conducted a series of frictional sliding experiments on fine grained gabbro, a rock representative of oceanic crust, at low normal stress (5 MPa) and elevated temperatures (20 - 450 °C) to explore the rate and state frictional properties at conditions thought to be representative of slow slip events (SSEs) near the bottom of the seismogenic plate interface in subduction zones. We used a direct shear apparatus that is capable of producing large total slip (many tens of centimeters). The gouge layer is naturally introduced between solid rock samples during and after an initial long 'run-in' period. Since this apparatus has a relatively low stiffness (8 MPa/mm) compared to widely used triaxial types (100 MPa/mm), it more readily encourages stick-slip behavior under velocity-weakening conditions. In our experiments, we observed stable sliding at low temperatures (20 -150 °C), stick-slip at high temperatures (400 - 450 °C), and a transitional 'episodic slow slip' behavior at intermediate temperatures (200-350 °C). Our experimental results suggest that there is a continuum of slip modes, as predicted by rate-state theory, and observed on natural faults. The typical SSE velocity in our experiments is about ten times higher than the driving velocity ((0.01 and 0.001 mm/s, respectively). This is similar to the ratio of the geodetically inferred SSE velocity to the plate convergence rate. While the laboratory experiments were conducted at speeds three orders of magnitude greater than the plate convergence rate, the SSE characteristics exhibit intriguing similarities. At temperatures of 150 °C and below, we performed velocity stepping tests between 0.001 and 0.01 mm/s to directly measure the rate-state parameters a, b, Dc, and μo. Since the samples did not stably slide at temperatures above 150 °C, we could not directly measure the rate-state parameters. Instead, we solved the rate-state constitutive equations, and performed a grid search through the rate

  7. Limited Capacity for Faster Digestion in Larval Coral Reef Fish at an Elevated Temperature

    PubMed Central

    Clark, Timothy D.

    2016-01-01

    The prevalence of extreme, short-term temperature spikes in coastal regions during summer months is predicted to increase with ongoing climate change. In tropical systems, these changes are predicted to increase the metabolic demand of coral reef fish larvae while also altering the plankton communities upon which the larvae feed during their pelagic phase. The consequences of these predictions remain speculative in the absence of empirical data on the interactive effects of warm temperatures on the metabolism, postprandial processes and growth responses of coral reef fish larvae. Here, we tested the effect of increased temperature on the metabolism, postprandial performance and fine-scale growth patterns of a coral reef fish (Amphiprion percula) in the latter half of its ~11-d larval phase. First, we measured the length and weight of fed versus fasted larvae (N = 340; mean body mass 4.1±0.05 mg) across fine temporal scales at a typical current summer temperature (28.5°C) and a temperature that is likely be encountered during warm summer periods later this century (31.5°C). Second, we measured routine metabolic rate (Mo2 routine) and the energetics of the postprandial processes (i.e., digestion, absorption and assimilation of a meal; termed specific dynamic action (SDA)) at both temperatures. Larvae fed voraciously when provided with food for a 12-hour period and displayed a temperature-independent increase in mass of 40.1% (28.5°C) and 42.6% (31.5°C), which was largely associated with the mass of prey in the gut. A subsequent 12-h fasting period revealed that the larvae had grown 21.2±4.8% (28.5°C) and 22.8±8.8% (31.5°C) in mass and 10.3±2.0% (28.5°C) and 7.8±2.6% (31.5°C) in length compared with pre-feeding values (no significant temperature effect). Mo2 routine was 55±16% higher at 31.5°C and peak Mo2 during the postprandial period was 28±11% higher at 31.5°C, yet elevated temperature had no significant effect on SDA (0.51±0.06 J at 28.5°C vs

  8. Limited Capacity for Faster Digestion in Larval Coral Reef Fish at an Elevated Temperature.

    PubMed

    McLeod, Ian M; Clark, Timothy D

    2016-01-01

    The prevalence of extreme, short-term temperature spikes in coastal regions during summer months is predicted to increase with ongoing climate change. In tropical systems, these changes are predicted to increase the metabolic demand of coral reef fish larvae while also altering the plankton communities upon which the larvae feed during their pelagic phase. The consequences of these predictions remain speculative in the absence of empirical data on the interactive effects of warm temperatures on the metabolism, postprandial processes and growth responses of coral reef fish larvae. Here, we tested the effect of increased temperature on the metabolism, postprandial performance and fine-scale growth patterns of a coral reef fish (Amphiprion percula) in the latter half of its ~11-d larval phase. First, we measured the length and weight of fed versus fasted larvae (N = 340; mean body mass 4.1±0.05 mg) across fine temporal scales at a typical current summer temperature (28.5°C) and a temperature that is likely be encountered during warm summer periods later this century (31.5°C). Second, we measured routine metabolic rate (Mo2 routine) and the energetics of the postprandial processes (i.e., digestion, absorption and assimilation of a meal; termed specific dynamic action (SDA)) at both temperatures. Larvae fed voraciously when provided with food for a 12-hour period and displayed a temperature-independent increase in mass of 40.1% (28.5°C) and 42.6% (31.5°C), which was largely associated with the mass of prey in the gut. A subsequent 12-h fasting period revealed that the larvae had grown 21.2±4.8% (28.5°C) and 22.8±8.8% (31.5°C) in mass and 10.3±2.0% (28.5°C) and 7.8±2.6% (31.5°C) in length compared with pre-feeding values (no significant temperature effect). Mo2 routine was 55±16% higher at 31.5°C and peak Mo2 during the postprandial period was 28±11% higher at 31.5°C, yet elevated temperature had no significant effect on SDA (0.51±0.06 J at 28.5°C vs

  9. Correlation Between Mobile Continents and Elevated Temperatures in the Subcontinental Mantle

    NASA Astrophysics Data System (ADS)

    Jain, C.; Rozel, A. B.; Tackley, P.

    2015-12-01

    Rolf et al. (EPSL, 2012) and Coltice et al. (Science, 2012) have previously shown that continents exert a first order influence on Earth's mantle flow by affecting convective wavelength and surface heat flow. With stationary continents, Heron and Lowman (JGR, 2014) highlighted the decreasing role of continental insulation on subcontinental temperatures with higher Rayleigh number (Ra). However, the question whether there exists a correlation between mobile continents and elevated temperatures in the subcontinental mantle or not remains to be answered. Continental motion is attributed to the viscous stresses imparted by the convecting mantle and the extent of this motion depends on the heat budget of the mantle. Core-mantle boundary (CMB) heat flux, internal heating from decay of radioactive elements, and mantle cooling contribute to this heat budget. Out of these sources, CMB heat flux is not well defined. However, the recent determination of core's high thermal conductivity requires a CMB heat flow of at least 12 TW (de Koker et al., PNAS 2012; Pozzo et al., Nature 2012; Gomi et al., PEPI 2013). Thus it is necessary to characterize the impact of basal heating on mantle dynamics with mobile continents and self-consistent plate tectonics. By systematically varying parameters such as CMB temperature, continental size, mantle heating modes, and Rayleigh number; we model Boussinesq, incompressible, thermo-chemical mantle convection with 2D spherical annulus geometry using StagYY (Tackley, PEPI 2008). We observe the aforementioned correlation irrespective of the variations in basal heating and continental size (except for very small continents). Moreover, we see episodicity between correlation-anticorrelation with increasing convective vigour. Furthermore, the effect of radioactivity in the continental crust on this correlation is investigated. At present, mobile continents in StagYY are simplified into a compositionally distinct field drifting at the top of the mantle

  10. Elevational variation in body-temperature response to immune challenge in a lizard

    PubMed Central

    Reguera, Senda; Moreno-Rueda, Gregorio

    2016-01-01

    Immunocompetence benefits animal fitness by combating pathogens, but also entails some costs. One of its main components is fever, which in ectotherms involves two main types of costs: energy expenditure and predation risk. Whenever those costs of fever outweigh its benefits, ectotherms are expected not to develop fever, or even to show hypothermia, reducing costs of thermoregulation and diverting the energy saved to other components of the immune system. Environmental thermal quality, and therefore the thermoregulation cost/benefit balance, varies geographically. Hence, we hypothesize that, in alpine habitats, immune-challenged ectotherms should show no thermal response, given that (1) hypothermia would be very costly, as the temporal window for reproduction is extremely small, and (2) fever would have a prohibitive cost, as heat acquisition is limited in such habitat. However, in temperate habitats, immune-challenged ectotherms might show a febrile response, due to lower cost/benefit balance as a consequence of a more suitable thermal environment. We tested this hypothesis in Psammodromus algirus lizards from Sierra Nevada (SE Spain), by testing body temperature preferred by alpine and non-alpine lizards, before and after activating their immune system with a typical innocuous pyrogen. Surprisingly, non-alpine lizards responded to immune challenge by decreasing preferential body-temperature, presumably allowing them to save energy and reduce exposure to predators. On the contrary, as predicted, immune-challenged alpine lizards maintained their body-temperature preferences. These results match with increased costs of no thermoregulation with elevation, due to the reduced window of time for reproduction in alpine environment. PMID:27168981

  11. Carbon balance, partitioning and photosynthetic acclimation in fruit-bearing grapevine (Vitis vinifera L. cv. Tempranillo) grown under simulated climate change (elevated CO2, elevated temperature and moderate drought) scenarios in temperature gradient greenhouses.

    PubMed

    Salazar-Parra, Carolina; Aranjuelo, Iker; Pascual, Inmaculada; Erice, Gorka; Sanz-Sáez, Álvaro; Aguirreolea, Jone; Sánchez-Díaz, Manuel; Irigoyen, Juan José; Araus, José Luis; Morales, Fermín

    2015-02-01

    Although plant performance under elevated CO2 has been extensively studied in the past little is known about photosynthetic performance changing simultaneously CO2, water availability and temperature conditions. Moreover, despite of its relevancy in crop responsiveness to elevated CO2 conditions, plant level C balance is a topic that, comparatively, has received little attention. In order to test responsiveness of grapevine photosynthetic apparatus to predicted climate change conditions, grapevine (Vitis vinifera L. cv. Tempranillo) fruit-bearing cuttings were exposed to different CO2 (elevated, 700ppm vs. ambient, ca. 400ppm), temperature (ambient vs. elevated, ambient +4°C) and irrigation levels (partial vs. full irrigation). Carbon balance was followed monitoring net photosynthesis (AN, C gain), respiration (RD) and photorespiration (RL) (C losses). Modification of environment (13)C isotopic composition (δ(13)C) under elevated CO2 (from -10.30 to -24.93‰) enabled the further characterization of C partitioning into roots, cuttings, shoots, petioles, leaves, rachides and berries. Irrespective of irrigation level and temperature, exposure to elevated CO2 induced photosynthetic acclimation of plants. C/N imbalance reflected the inability of plants grown at 700ppm CO2 to develop strong C sinks. Partitioning of labeled C to storage organs (main stem and roots) did not avoid accumulation of labeled photoassimilates in leaves, affecting negatively Rubisco carboxylation activity. The study also revealed that, after 20 days of treatment, no oxidative damage to chlorophylls or carotenoids was observed, suggesting a protective role of CO2 either at current or elevated temperatures against the adverse effect of water stress. PMID:25462972

  12. Carbon balance, partitioning and photosynthetic acclimation in fruit-bearing grapevine (Vitis vinifera L. cv. Tempranillo) grown under simulated climate change (elevated CO2, elevated temperature and moderate drought) scenarios in temperature gradient greenhouses.

    PubMed

    Salazar-Parra, Carolina; Aranjuelo, Iker; Pascual, Inmaculada; Erice, Gorka; Sanz-Sáez, Álvaro; Aguirreolea, Jone; Sánchez-Díaz, Manuel; Irigoyen, Juan José; Araus, José Luis; Morales, Fermín

    2015-02-01

    Although plant performance under elevated CO2 has been extensively studied in the past little is known about photosynthetic performance changing simultaneously CO2, water availability and temperature conditions. Moreover, despite of its relevancy in crop responsiveness to elevated CO2 conditions, plant level C balance is a topic that, comparatively, has received little attention. In order to test responsiveness of grapevine photosynthetic apparatus to predicted climate change conditions, grapevine (Vitis vinifera L. cv. Tempranillo) fruit-bearing cuttings were exposed to different CO2 (elevated, 700ppm vs. ambient, ca. 400ppm), temperature (ambient vs. elevated, ambient +4°C) and irrigation levels (partial vs. full irrigation). Carbon balance was followed monitoring net photosynthesis (AN, C gain), respiration (RD) and photorespiration (RL) (C losses). Modification of environment (13)C isotopic composition (δ(13)C) under elevated CO2 (from -10.30 to -24.93‰) enabled the further characterization of C partitioning into roots, cuttings, shoots, petioles, leaves, rachides and berries. Irrespective of irrigation level and temperature, exposure to elevated CO2 induced photosynthetic acclimation of plants. C/N imbalance reflected the inability of plants grown at 700ppm CO2 to develop strong C sinks. Partitioning of labeled C to storage organs (main stem and roots) did not avoid accumulation of labeled photoassimilates in leaves, affecting negatively Rubisco carboxylation activity. The study also revealed that, after 20 days of treatment, no oxidative damage to chlorophylls or carotenoids was observed, suggesting a protective role of CO2 either at current or elevated temperatures against the adverse effect of water stress.

  13. Numerical simulation of hydro-thermo-mechanical behavior of concrete structures exposed to elevated temperatures

    NASA Astrophysics Data System (ADS)

    Chung, Jae Hyeon

    In this study, thermal spalling of high-strength concrete structural elements has been investigated by developing numerical models capable of analyzing the combined effects of mass and heat transfer phenomena on thermally induced stresses. Through the use of finite difference simulations, this study investigates moisture effects on thermodynamic states of concrete at elevated temperatures and the influence of pore pressure on development of thermal stress induced by temperature gradients. A finite element stress analysis model is combined with finite difference simulations to predict stress states capable of inducing spalling of the type that has been observed both in the field and in laboratory fire testing of concrete structural elements. The combined hydro-thermo-mechanical analysis procedure presented here may eventually serve as a critical component of stress analysis used for evaluating the fire resistance of high-strength concrete structural systems. The model of concrete exposed to fire that is developed herein involves mass and heat transport phenomena in a multi-phase continuum. Simultaneous flow of multiple fluid phases (i.e., liquid and gaseous) is modeled using newly proposed constitutive relationships that are considered more accurate than those previously available in terms of assessment of thermodynamic state variables of concrete system. In addition, numerical simulations are used to explore the effects that steel reinforcing bars have on internal temperature and pressure within concrete members. Pore pressure and temperature time histories from hydro-thermal finite difference simulations are presented and discussed. Results from the simulations yield an improved understanding of the thermodynamic state variables such as pore pressure, temperature, and degree of liquid water saturation. Selection of constitutive models to describe the flow characteristics of concrete and the procedures implemented for the creation of the concrete models are also

  14. DOES CRITICAL MASS DECREASE AS TEMPERATURE INCREASES: A REVIEW OF FIVE BENCHMARK EXPERIMENTS THAT SPAN A RANGE OF ELEVATED TEMPERATURES AND CRITICAL CONFIGURATIONS

    SciTech Connect

    Yates, K.

    2009-06-10

    Five sets of benchmark experiments are reviewed herein that cover a diverse set of fissile system configurations. The review specifically focused on the change in critical mass of these systems at elevated temperatures and the temperature reactivity coefficient ({alpha}{sub T}) on the system. Because plutonium-based critical benchmark experiments at varying temperatures were not found at the time this review was prepared, only uranium-based systems are included, as follows: (1) HEU-SOL-THERM-010 - UO{sub 2}F{sub 2} solutions with high U{sup 235} enrichment; (2) HEU-COMP-THERM-016 - uranium-graphite blocks with low U concentration; (3) LEU-COMP-THERM-032 - water moderated lattices of UO{sub 2} with stainless steel cladding, and intermediate U{sup 235} enrichment; (4) IEU-COMP-THERM-002 - water moderated lattices of annular UO{sub 2} with/without absorbers, and intermediate U{sup 235} enrichment; and (5) LEU-COMP-THERM-026 - water moderated lattices of UO{sub 2} at different pitches, and low U{sup 235} enrichment. In three of the five benchmarks (1, 3 and 5), modeling of the critical system at room temperature is conservative compared to modeling the system at elevated temperatures, i.e., a greater fissile mass is required at elevated temperature. In one benchmark (4), there was no difference in the fissile mass between the room temperature system and the system at the examined elevated temperature. In benchmark (2), the system clearly had a negative temperature reactivity coefficient. Some of the high temperature benchmark experiments were treated with appropriate (and comprehensive) adjustments to the cross section sets and thermal expansion coefficients, while other experiments were treated with partial adjustments. Regardless of the temperature treatment, modeling the systems at room temperature was found to be conservative for the examined systems, i.e., a smaller critical mass was obtained. While the five benchmarks presented herein demonstrate that, for the

  15. Growth under elevated air temperature alters secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils.

    PubMed

    Zhao, Y H; Jia, X; Wang, W K; Liu, T; Huang, S P; Yang, M Y

    2016-09-15

    Plant secondary metabolites play a pivotal role in growth regulation, antioxidant activity, pigment development, and other processes. As the global climate changes, increasing atmospheric temperatures and contamination of soil by heavy metals co-occur in natural ecosystems, which alters the pH of rhizosphere soil and influences the bioavailability and mobility of metals. Elevated temperatures in combination with heavy metals are expected to affect plant secondary metabolites, but this issue has not been extensively examined. Here, we investigated secondary metabolites in Robiniapseudoacacia seedlings exposed to elevated temperatures using a passive warming device in combination with Cd- and Pb-contaminated soils. Heavy metals significantly stimulated the accumulation of saponins, phenolic compounds, and flavonoids in leaves and stems; alkaloid compounds increased in leaves and decreased in stems, and condensed tannins fluctuated. Elevated temperatures, alone and in combination with Cd and Pb, caused increases in secondary metabolites in the plant tissues. Phenolic compounds showed the greatest changes among the secondary metabolites and significant interactive effects of temperature and metals were observed. These results suggest that slightly elevated temperature could enhance protective and defense mechanisms of Robinia pseudoacacia seedlings exposed to heavy metals by stimulating the production of secondary metabolites.

  16. Plant responses to elevated temperatures: a field study on phenological sensitivity and fitness responses to simulated climate warming.

    PubMed

    Springate, David A; Kover, Paula X

    2014-02-01

    Significant changes in plant phenology have been observed in response to increases in mean global temperatures. There are concerns that accelerated phenologies can negatively impact plant populations. However, the fitness consequence of changes in phenology in response to elevated temperature is not well understood, particularly under field conditions. We address this issue by exposing a set of recombinant inbred lines of Arabidopsis thaliana to a simulated global warming treatment in the field. We find that plants exposed to elevated temperatures flower earlier, as predicted by photothermal models. However, contrary to life-history trade-off expectations, they also flower at a larger vegetative size, suggesting that warming probably causes acceleration in vegetative development. Although warming increases mean fitness (fruit production) by ca. 25%, there is a significant genotype-by-environment interaction. Changes in fitness rank indicate that imminent climate change can cause populations to be maladapted in their new environment, if adaptive evolution is limited. Thus, changes in the genetic composition of populations are likely, depending on the species' generation time and the speed of temperature change. Interestingly, genotypes that show stronger phenological responses have higher fitness under elevated temperatures, suggesting that phenological sensitivity might be a good indicator of success under elevated temperature at the genotypic level as well as at the species level.

  17. Growth under elevated air temperature alters secondary metabolites in Robinia pseudoacacia L. seedlings in Cd- and Pb-contaminated soils.

    PubMed

    Zhao, Y H; Jia, X; Wang, W K; Liu, T; Huang, S P; Yang, M Y

    2016-09-15

    Plant secondary metabolites play a pivotal role in growth regulation, antioxidant activity, pigment development, and other processes. As the global climate changes, increasing atmospheric temperatures and contamination of soil by heavy metals co-occur in natural ecosystems, which alters the pH of rhizosphere soil and influences the bioavailability and mobility of metals. Elevated temperatures in combination with heavy metals are expected to affect plant secondary metabolites, but this issue has not been extensively examined. Here, we investigated secondary metabolites in Robiniapseudoacacia seedlings exposed to elevated temperatures using a passive warming device in combination with Cd- and Pb-contaminated soils. Heavy metals significantly stimulated the accumulation of saponins, phenolic compounds, and flavonoids in leaves and stems; alkaloid compounds increased in leaves and decreased in stems, and condensed tannins fluctuated. Elevated temperatures, alone and in combination with Cd and Pb, caused increases in secondary metabolites in the plant tissues. Phenolic compounds showed the greatest changes among the secondary metabolites and significant interactive effects of temperature and metals were observed. These results suggest that slightly elevated temperature could enhance protective and defense mechanisms of Robinia pseudoacacia seedlings exposed to heavy metals by stimulating the production of secondary metabolites. PMID:27203519

  18. Degradation of flubendiamide as affected by elevated CO2, temperature, and carbon mineralization rate in soil.

    PubMed

    Mukherjee, Irani; Das, Shaon Kumar; Kumar, Aman

    2016-10-01

    An experiment was conducted under three levels of atmospheric CO2 [ambient (398 ± 10 μmol mol(-1)), elevated (570 ± 10 μmol mol(-1)) and open condition], three levels of temperature (4, 25, and 40 °C) to study the degradation pattern of flubendiamide in soil and also carbon mineralization in soil. Results of this study revealed that flubendiamide was found to persist longer under outdoor condition (T1/2, 177.0 and 181.1 days) than ambient (T1/2, 168.4 and 172.3 days) and elevated condition (T1/2, 159.3 and 155.3 days) at 1 and 10 μg g(-1) fortification level, respectively. Results also revealed that flubendiamide dissipated faster at 40 °C (T1/2, 189.4 days) than 25 °C (T1/2, 225.3 days). Slower dissipation was recorded at 4 °C (T1/2, 326.3 days). Thus, increased CO2 levels and temperature following global warming might adversely affect flubendiamide degradation in soil. Laboratory study on microbial biomass carbon (MBC) and carbon mineralization (Cmin) in soil revealed that in des-iodo flubendiamide-treated soils, MBC significantly increased up to 45 days and then decreased. Flubendiamide-treated soil showed a non-significantly decreasing trend of soil MBC with time up to the 15th day of incubation and after 15 days significantly decreased up to 90 days of incubation. In des-iodo flubendiamide-treated soil, the evolution of CO2 decreased up to 45 days, which was increased after 45 days up to 90 days. In flubendiamide-treated soil, CO2 evolution decreased up to 30 days and after 45 days, it increased up to 90 days. PMID:27430656

  19. Elevated temperature triggers human respiratory syncytial virus F protein six-helix bundle formation

    SciTech Connect

    Yunus, Abdul S.; Jackson, Trent P.; Crisafi, Katherine; Burimski, Irina; Kilgore, Nicole R.; Zoumplis, Dorian; Allaway, Graham P.; Wild, Carl T.; Salzwedel, Karl

    2010-01-20

    Human respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infection in infants, immunocompromised patients, and the elderly. The RSV fusion (F) protein mediates fusion of the viral envelope with the target cell membrane during virus entry and is a primary target for antiviral drug and vaccine development. The F protein contains two heptad repeat regions, HR1 and HR2. Peptides corresponding to these regions form a six-helix bundle structure that is thought to play a critical role in membrane fusion. However, characterization of six-helix bundle formation in native RSV F protein has been hindered by the fact that a trigger for F protein conformational change has yet to be identified. Here we demonstrate that RSV F protein on the surface of infected cells undergoes a conformational change following exposure to elevated temperature, resulting in the formation of the six-helix bundle structure. We first generated and characterized six-helix bundle-specific antibodies raised against recombinant peptides modeling the RSV F protein six-helix bundle structure. We then used these antibodies as probes to monitor RSV F protein six-helix bundle formation in response to a diverse array of potential triggers of conformational changes. We found that exposure of 'membrane-anchored' RSV F protein to elevated temperature (45-55 deg. C) was sufficient to trigger six-helix bundle formation. Antibody binding to the six-helix bundle conformation was detected by both flow cytometry and cell-surface immunoprecipitation of the RSV F protein. None of the other treatments, including interaction with a number of potential receptors, resulted in significant binding by six-helix bundle-specific antibodies. We conclude that native, untriggered RSV F protein exists in a metastable state that can be converted in vitro to the more stable, fusogenic six-helix bundle conformation by an increase in thermal energy. These findings help to better define the mechanism of

  20. Selected durability studies of geopolymer concrete with respect to carbonation, elevated temperature, and microbial induced corrosion

    NASA Astrophysics Data System (ADS)

    Badar, Mohammad Sufian

    This thesis reports a comprehensive study related to the experimental evaluation of carbonation in reinforced geopolymer concrete, the evaluation of geopolymer concretes at elevated temperature, and the resistance of geopolymer concrete to microbial induced corrosion (MIC). Carbonation: Reinforced concretes, made of geopolymer, prepared from two class F fly ashes and one class C fly ash, were subjected to accelerated carbonation treatment for a period of 450 days. Electrochemical, microstructure and pore structure examinations were performed to evaluate the effect of corrosion caused due to carbonation. GPC specimens prepared from class F fly ash exhibited lower corrosion rates by a factor of 21, and higher pH values (pH>12) when compared with concrete specimens prepared from class C Fly ash (GPCMN). Microstructure and pore characterization of GPC prepared using class F fly ash revealed lower porosity by a factor of 2.5 as compared with thier counterparts made using GPC-MN. The superior performace of GPC prepared with the class F fly ash could be attributed to the dense pore structure and formation of the protective layer of calcium and sodium alumino silicate hydrates (C/N-A-S-H) geopolymeric gels around the steel reinforcement. Elevated Temperature: Geopolymers are an emerging class of cementitious binders which possess a potential for high temperature resistance that could possibly be utilized in applications such as nozzles, aspirators and refractory linings. This study reports on the results of an investigation into the performance of a fly ash based geopolymer binder in high temperature environments. Geopolymer concrete (GPC) was prepared using eleven types of fly ashes obtained from four countries. High content alumina and silica sand was used in the mix for preparing GPC. GPC was subjected to thermal shock tests following ASTM C 1100-88. The GPC samples prepared with tabular alumina were kept at 1093° C and immediately quenched in water. GPC specimens

  1. ELEVATED TEMPERATURE, SOIL MOISTURE AND SEASONALITY BUT NOT CO2 AFFECT CANOPY ASSIMILATION AND SYSTEM RESPIRATION IN SEEDLING DOUGLAS-FIR ECOSYSTEMS

    EPA Science Inventory

    We investigated the effects of elevated atmospheric CO2 and air temperature on C cycling in trees and associated soil system, focusing on canopy CO2 assimilation (Asys) and system CO2 loss through respiration (Rsys). We hypothesized that both elevated CO2 and elevated temperature...

  2. DOES SOIL CO2 EFFLUX ACCLIMATIZETO ELEVATED TEMPERATURE AND CO2 DURING LONG-TERM TREATMENT OF DOUGLAS-FIR SEEDLINGS?

    EPA Science Inventory

    We investigated the effects of elevated soil temperature and atmospheric CO2 efflux (SCE) during the third an fourth years of study. We hypothesized that elevated temperature would stimulate SCE, and elevated CO2 would also stimulate SCE with the stimulation being greater at hig...

  3. Elevated atmospheric carbon dioxide and temperature effects on seed composition, mineral nutrition, and 15N and 13C dynamics in soybean genotypes under controlled environments

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Seed nutrition of crops can be affected by global climate changes due to elevated CO2 and elevated temperatures. Information on the effects of elevated CO2 and temperature on seed nutrition is very limited in spite of its importance to seed quality and food security. Therefore, the objective of this...

  4. Elevated temperature is more effective than elevated [CO2 ] in exposing genotypic variation in Telopea speciosissima growth plasticity: implications for woody plant populations under climate change.

    PubMed

    Huang, Guomin; Rymer, Paul D; Duan, Honglang; Smith, Renee A; Tissue, David T

    2015-10-01

    Intraspecific variation in phenotypic plasticity is a critical determinant of plant species capacity to cope with climate change. A long-standing hypothesis states that greater levels of environmental variability will select for genotypes with greater phenotypic plasticity. However, few studies have examined how genotypes of woody species originating from contrasting environments respond to multiple climate change factors. Here, we investigated the main and interactive effects of elevated [CO2 ] (CE ) and elevated temperature (TE ) on growth and physiology of Coastal (warmer, less variable temperature environment) and Upland (cooler, more variable temperature environment) genotypes of an Australian woody species Telopea speciosissima. Both genotypes were positively responsive to CE (35% and 29% increase in whole-plant dry mass and leaf area, respectively), but only the Coastal genotype exhibited positive growth responses to TE . We found that the Coastal genotype exhibited greater growth response to TE (47% and 85% increase in whole-plant dry mass and leaf area, respectively) when compared with the Upland genotype (no change in dry mass or leaf area). No intraspecific variation in physiological plasticity was detected under CE or TE , and the interactive effects of CE and TE on intraspecific variation in phenotypic plasticity were also largely absent. Overall, TE was a more effective climate factor than CE in exposing genotypic variation in our woody species. Our results contradict the paradigm that genotypes from more variable climates will exhibit greater phenotypic plasticity in future climate regimes.

  5. Impact of an Elevated Temperature Environment on Sn-Ag-Cu Interconnect Board Level High-G Mechanical Shock Performance

    NASA Astrophysics Data System (ADS)

    Lee, Tae-Kyu; Chen, Zhiqiang; Baty, Greg; Bieler, Thomas R.; Kim, Choong-Un

    2016-09-01

    The mechanical stability of Sn-Ag-Cu interconnects with low and high silver content against mechanical shock at room and elevated temperatures was investigated. With a heating element-embedded printed circuit board design, a test temperature from room temperature to 80°C was established. High impact shock tests were applied to isothermally pre-conditioned ball-grid array interconnects. Under cyclic shock testing, degradation and improved shock performances were identified associated with test temperature variation and non-solder mask defined and solder-mask defined pad design configuration differences. Different crack propagation paths were observed, induced by the effect of the elevated temperature test conditions and isothermal aging pre-conditions.

  6. The effect of time of exposure to elevated temperatures on the flammability limits of some common gaseous fuels in air

    SciTech Connect

    Wierzba, I.; Ale, B.B.

    1999-01-01

    The flammability limits of methane, ethylene, propane, and hydrogen were experimentally determined at elevated initial mixture temperatures up to 350 C at atmospheric pressure for upward flame propagation in a steel test tube apparatus. The existence of preignition reactions at these levels of temperature