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Sample records for elevated temperature exposure

  1. Oxidative stress causes coral bleaching during exposure to elevated temperatures

    NASA Astrophysics Data System (ADS)

    Lesser, M. P.

    1997-07-01

    Elevated temperatures and solar ultraviolet (UV) radiation have been implicated as recent causes for the loss of symbiotic algae (i.e., bleaching) in corals and other invertebrates with photoautotrophic symbionts. One hypothesized mechanism of coral bleaching involves the production of reduced oxygen intermediates, or toxic oxygen, in the dinoflagellate symbionts and host tissues that subsequently causes cellular damage and expulsion of symbionts. Measurements of photosynthesis in the Caribbean coral Agaricia tenuifolia, taken during temperature-induced stress and exposure to full solar radiation, showed a decrease in photosynthetic performance followed by bleaching. Exposure of corals to exogenous antioxidants that scavenge reactive oxygen species during temperature-induced stress improves maximum photosynthetic capacity to rates indistinguishable from corals measured at the ambient temperature of their site of collection. Additionally, these antioxidants prevent the coral from " bleaching " and affect the mechanism of symbiont loss from the coral host. These observations confirm a role for oxidative stress, whether caused by elevated temperatures or exposure to UV radiation, in the bleaching phenomenon.

  2. 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.

  3. 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.

  4. 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.

  5. The timing of embryonic exposure to elevated temperature alters stress endocrinology in domestic chickens (Gallus domesticus).

    PubMed

    Wilsterman, Kathryn; Mast, Andrew D; Luu, Thuyvan H; Haussmann, Mark F

    2015-02-01

    Patterns of glucocorticoid (GC) release in response to stimuli vary both among individuals and within individuals across their lifetime. While much work has focused on how the prenatal steroid environment can affect GC release, relatively little is known about how environmental parameters, such as incubation temperature affect GCs. We tested the hypothesis that variation and timing of elevated incubation temperature within the thermoneutral zone can alter the pattern of GC release. We incubated domestic chicken eggs (Gallus domesticus) at the optimal incubation temperature (37.5 °C) or at a slightly higher temperature (+1.1 °C) either early, late, or throughout incubation. At three weeks post-hatch, all birds were (i) exposed to a capture-restraint stress to measure stress-induced GC release (naïve). Three days following the naïve stressor, birds were (ii) exposed to a heat challenge, which was followed the next day by a second capture-restraint stress (post-heat challenge). Regardless of treatment, birds had similar patterns of GC release following the naïve stress series. However, during the post-heat challenge stress series, birds incubated at optimal temperatures increased their peak GC release. In contrast, birds exposed to slightly elevated temperatures for any period of development failed to increase peak GC release, and their specific response varied with timing of exposure to the elevated incubation temperature. Our results demonstrate that subtle variation in the embryonic environment, such as elevated incubation temperature within the thermoneutral zone, can impact the pattern of GC release of offspring. Further work is needed to understand the mechanisms underlying these changes and the relationship between fitness and environmentally-altered phenotypes. PMID:25623149

  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. PMID:24141693

  7. Exposure Of NIF Relevant Polymeric Samples To Deuterium-Tritium Gas At Elevated Temperature And Pressure

    SciTech Connect

    Ebey, P S; Dole, J M; Nobile, A; Schoonover, J R; Burmann, J; Cook, B; Letts, S; Sanchez, J; Nikroo, A

    2005-06-24

    The purpose of the experiments described in this paper was to expose samples of polymeric materials to a mixture of deuterium-tritium (DT) gas at elevated temperature and pressure to investigate the effects (i.e. damage) on the materials. The materials and exposure parameters were chosen with to be relevant to proposed uses of similar materials in inertial fusion ignition experiments at the National Ignition Facility. Two types of samples were exposed and tested. The first type consisted of 10 4-lead ribbon cables of fine manganin wire insulated with polyimide. Wires of this type are proposed for use in thermal shimming of hohlraums and the goal of this experiment was to measure the change in electrical resistance of the insulation due to tritium exposure. The second type of sample consisted of 20 planar polymer samples that may be used as ignition capsule materials. The exposure was at 34.5 GPa (5010 psia) and 70 C for 48 hours. The change in electrical resistance of the wire insulation will be presented. The results for capsule materials will be presented in a separate paper in this issue.

  8. 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

  9. 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.

  10. 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. PMID:20360633

  11. Effects of Long-Term Thermal Exposure on Commercially Pure Titanium Grade 2 Elevated-Temperature Tensile Properties

    NASA Technical Reports Server (NTRS)

    Ellis, David L.

    2012-01-01

    Elevated-temperature tensile testing of commercially pure titanium (CP Ti) Grade 2 was conducted for as-received commercially produced sheet and following thermal exposure at 550 and 650 K (531 and 711 F) for times up to 5000 h. The tensile testing revealed some statistical differences between the 11 thermal treatments, but most thermal treatments were statistically equivalent. Previous data from room temperature tensile testing was combined with the new data to allow regression and development of mathematical models relating tensile properties to temperature and thermal exposure. The results indicate that thermal exposure temperature has a very small effect, whereas the thermal exposure duration has no statistically significant effects on the tensile properties. These results indicate that CP Ti Grade 2 will be thermally stable and suitable for long-duration space missions.

  12. 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.

  13. Acoustic inspection of bond strength of steel-reinforced mortar after exposure to elevated temperatures

    PubMed

    Chiang; Tsai; Kan

    2000-03-01

    In order to evaluate the bond strength between the reinforcement and concrete after fire damage, a combination of acoustic through-transmission and pull-out tests were used. Previous studies have shown a 25% decrease in the ultrasonic pulse velocity at 90% of the maximum load at room temperature. The specimens were kept in the oven at an elevated temperature for 1, 2, or 3 h. They were then removed and cooled to room temperature. Inspection was conducted using a high-power ultrasonic pulse velocity system while a pull-out load was applied. The correlation between preheated temperature, acoustic wave velocity, and the applied load was analyzed. Initial results show that bond strength and pulse velocity decreased substantially as the temperature or the heating time increased. PMID:10829721

  14. Effect of Thermal Exposure on the Tensile Properties of Aluminum Alloys for Elevated Temperature Service

    NASA Technical Reports Server (NTRS)

    Edahl, Robert A., Jr.; Domack, Marcia

    2004-01-01

    Tensile properties were evaluated for four aluminum alloys that are candidates for airframe applications on high speed transport aircraft. These alloys included the Al-Cu-Mg-Ag alloys C415 and C416 and the Al-Cu-Li-Mg-Ag alloys RX818 and ML377. The Al-Cu-Mg alloys CM001, which was used on the Concorde SST, and 1143, which was modified from the alloy used on the TU144 Russian supersonic aircraft, were tested for comparison. The alloys were subjected to thermal exposure at 200 F, 225 F and 275 F for times up to 30,000 hours. Tensile tests were performed on thermally-exposed and as-received material at -65 F, room temperature, 200 F, 225 F and 275 F. All four candidate alloys showed significant tensile property improvements over CM001 and 1143. Room temperature yield strengths of the candidate alloys were at least 20% greater than for CM001 and 1143, for both the as-received and thermally-exposed conditions. The strength levels of alloy RX818 were the highest of all materials investigated, and were 5-10% higher than for ML377, C415 and C416 for the as-received condition and after 5,000 hours thermal exposure. RX818 was removed from this study after 5,000 hours exposure due to poor fracture toughness performance observed in a parallel study. After 30,000 hours exposure at 200 F and 225 F, the alloys C415, C416 and ML377 showed minor decreases in yield strength, tensile strength and elongation when compared to the as-received properties. Reductions in tensile strength from the as-received values were up to 25% for alloys C415, C416 and ML377 after 15,000 hours exposure at 275 F.

  15. Abrasion and fatigue resistance of PDMS containing multiblock polyurethanes after accelerated water exposure at elevated temperature.

    PubMed

    Chaffin, Kimberly A; Wilson, Charles L; Himes, Adam K; Dawson, James W; Haddad, Tarek D; Buckalew, Adam J; Miller, Jennifer P; Untereker, Darrel F; Simha, Narendra K

    2013-11-01

    Segmented polyurethane multiblock polymers containing polydimethylsiloxane and polyether soft segments form tough and easily processed thermoplastic elastomers (PDMS-urethanes). Two commercially available examples, PurSil 35 (denoted as P35) and Elast-Eon E2A (denoted as E2A), were evaluated for abrasion and fatigue resistance after immersion in 85 °C buffered water for up to 80 weeks. We previously reported that water exposure in these experiments resulted in a molar mass reduction, where the kinetics of the hydrolysis reaction is supported by a straight forward Arrhenius analysis over a range of accelerated temperatures (37-85 °C). We also showed that the ultimate tensile properties of P35 and E2A were significantly compromised when the molar mass was reduced. Here, we show that the reduction in molar mass also correlated with a reduction in both the abrasion and fatigue resistance. The instantaneous wear rate of both P35 and E2A, when exposed to the reciprocating motion of an ethylene tetrafluoroethylene (ETFE) jacketed cable, increased with the inverse of the number averaged molar mass (1/Mn). Both materials showed a change in the wear surface when the number-averaged molar mass was reduced to ≈ 16 kg/mole, where a smooth wear surface transitioned to a 'spalling-like' pattern, leaving the wear surface with ≈ 0.3 mm cracks that propagated beyond the contact surface. The fatigue crack growth rate for P35 and E2A also increased in proportion to 1/Mn, after the molar mass was reduced below a critical value of ≈30 kg/mole. Interestingly, this critical molar mass coincided with that at which the single cycle stress-strain response changed from strain hardening to strain softening. The changes in both abrasion and fatigue resistance, key predictors for long term reliability of cardiac leads, after exposure of this class of PDMS-urethanes to water suggests that these materials are susceptible to mechanical compromise in vivo. PMID:23871543

  16. Effects of crude oil exposure and elevated temperature on the liver transcriptome of polar cod (Boreogadus saida).

    PubMed

    Andersen, Øivind; Frantzen, Marianne; Rosland, Marte; Timmerhaus, Gerrit; Skugor, Adrijana; Krasnov, Aleksei

    2015-08-01

    Petroleum-related activities in the Arctic have raised concerns about the adverse effects of potential oil spill on the environment and living organisms. Polar cod plays a key role in the Arctic marine ecosystem and is an important species for monitoring oil pollution in this region. We examined potential interactions of oil pollution and global warming by analysing liver transcriptome changes in polar cod exposed to crude oil at elevated temperature. Adult males and females were kept at high (11°C) or normal (4°C) temperature for 5 days before exposure to mechanically dispersed crude oil for 2 days followed by recovery in clean sea water for 11 days at the two temperatures. Genome-wide microarray analysis of liver samples revealed numerous differentially expressed genes induced by uptake of oil as confirmed by increased levels of bile polycyclic aromatic hydrocarbon (PAH) metabolites. The hepatic response included genes playing important roles in xenobiotic detoxification and closely related biochemical processes, but also of importance for protein stress response, cell repair and immunity. Though magnitude of transcriptome responses was similar at both temperatures, the upregulated expression of cyp1a1 and several chaperone genes was much stronger at 11°C. Most gene expression changes returned to basal levels after recovery. The microarray results were validated by qPCR measurement of eleven selected genes representing both known and novel biomarkers to assess exposure to anthropogenic threats on polar cod. Strong upregulation of the gene encoding fibroblast growth factor 7 is proposed to protect the liver of polar fish with aglomerular kidneys from the toxic effect of accumulated biliary compounds. The highly altered liver transcriptome patterns after acute oil exposure and recovery suggests rapid responses in polar cod to oil pollutants and the ability to cope with toxicity in relatively short time. PMID:26005920

  17. Effect of long-time, elevated-temperature exposures to vacuum and lithium on the properties of a tantalum alloy, T-111

    NASA Technical Reports Server (NTRS)

    Buzzard, R. J.; Sheffler, K. D.

    1974-01-01

    The effect of long-term, elevated-temperature vacuum and lithium exposures on the mechanical properties of T-111 (Ta-8W-2Hf) is determined. Exposure conditions were for 1000 hours at 980 or 1315 C, 5000 hours at 1315 C, and a duplex temperature exposure of 1000 hours at 980 C plus 4000 hours at 1040 C. The exposures resulted in reduced tensile and creep strengths of the T-111 in the 900 to 1100 C temperature range where a dynamic strain-age-strengthening mechanism is operative in this alloy. This strength reduction was attributed to the depletion of oxygen from solid solution in this alloy.

  18. The relationship between specific absorption rate and temperature elevation in anatomically based human body models for plane wave exposure from 30 MHz to 6 GHz

    NASA Astrophysics Data System (ADS)

    Hirata, Akimasa; Laakso, Ilkka; Oizumi, Takuya; Hanatani, Ryuto; Chan, Kwok Hung; Wiart, Joe

    2013-02-01

    According to the international safety guidelines/standard, the whole-body-averaged specific absorption rate (Poljak et al 2003 IEEE Trans. Electromagn. Compat. 45 141-5) and the peak spatial average SAR are used as metrics for human protection from whole-body and localized exposures, respectively. The IEEE standard (IEEE 2006 IEEE C95.1) indicates that the upper boundary frequency, over which the whole-body-averaged SAR is deemed to be the basic restriction, has been reduced from 6 to 3 GHz, because radio-wave energy is absorbed around the body surface when the frequency is increased. However, no quantitative discussion has been provided to support this description especially from the standpoint of temperature elevation. It is of interest to investigate the maximum temperature elevation in addition to the core temperature even for a whole-body exposure. In the present study, using anatomically based human models, we computed the SAR and the temperature elevation for a plane-wave exposure from 30 MHz to 6 GHz, taking into account the thermoregulatory response. As the primary result, we found that the ratio of the core temperature elevation to the whole-body-averaged SAR is almost frequency independent for frequencies below a few gigahertz; the ratio decreases above this frequency. At frequencies higher than a few gigahertz, core temperature elevation for the same whole-body averaged SAR becomes lower due to heat convection from the skin to air. This lower core temperature elevation is attributable to skin temperature elevation caused by the power absorption around the body surface. Then, core temperature elevation even for whole-body averaged SAR of 4 W kg-1 with the duration of 1 h was at most 0.8 °C, which is smaller than a threshold considered in the safety guidelines/standard. Further, the peak 10 g averaged SAR is correlated with the maximum body temperature elevations without extremities and pinna over the frequencies considered. These findings were confirmed

  19. A preliminary report on the effect of elevated temperature exposure on the mechanical properties of titanium-alloy honeycomb-core sandwich panels.

    NASA Technical Reports Server (NTRS)

    Bales, T. T.; Cain, R. L.

    1971-01-01

    A study has been initiated to determine the effects of elevated-temperature exposure on the room-temperature mechanical properties of titanium honeycomb-core sandwich panels fabricated by brazing or spot diffusion bonding. Only flatwise tensile properties following exposure have been determined to date. Preliminary results indicate very little change in the flatwise tensile strength of sandwich panels fabricated by spot diffusion bonding following exposures of 10,000 hr at 600 and 800 F and 1000 hr at 1000 F. Titanium panels fabricated by using a Ti-Zr-Be braze alloy are susceptible to oxidation at elevated temperature and experience flatwise tensile strength degradation after continuous exposures of 7500 hr at 600 F, 1000 hr at 800 F, and less than 100 hr at 1000 F. It is possible that the exposure life of the brazed panels may be substantially increased if the panel edges are sealed to prevent oxidation of the braze alloy.

  20. FDTD analysis of temperature elevation in the lens of human and rabbit models due to near-field and far-field exposures at 2.45 GHz.

    PubMed

    Oizumi, Takuya; Laakso, Ilkka; Hirata, Akimasa; Fujiwara, Osamu; Watanabe, Soichi; Taki, Masao; Kojima, Masami; Sasaki, Hiroshi; Sasaki, Kazuyuki

    2013-07-01

    The eye is said to be one of the most sensitive organs to microwave heating. According to previous studies, the possibility of microwave-induced cataract formation has been experimentally investigated in rabbit and monkey eyes, but not for the human eye due to ethical reasons. In the present study, the temperature elevation in the lens, the skin around the eye and the core temperature of numerical human and rabbit models for far-field and near-field exposures at 2.45 GHz are investigated. The temperature elevations in the human and rabbit models were compared with the threshold temperatures for inducing cataracts, thermal pain in the skin and reversible health effects such as heat exhaustion or heat stroke. For plane-wave exposure, the core temperature elevation is shown to be essential both in the human and in the rabbit models as suggested in the international guidelines and standards. For localised exposure of the human eye, the temperature elevation of the skin was essential, and the lens temperature did not reach its threshold for thermal pain. On the other hand, the lens temperature elevation was found to be dominant for the rabbit eye. PMID:23390146

  1. 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.

  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. 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.

  4. Elevated temperature crack growth

    NASA Technical Reports Server (NTRS)

    Kim, K. S.; Vanstone, R. H.

    1992-01-01

    The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.

  5. 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.

  6. The relationship between specific absorption rate and temperature elevation in anatomically based human body models for plane wave exposure from 30 MHz to 6 GHz.

    PubMed

    Hirata, Akimasa; Laakso, Ilkka; Oizumi, Takuya; Hanatani, Ryuto; Chan, Kwok Hung; Wiart, Joe

    2013-02-21

    According to the international safety guidelines/standard, the whole-body-averaged specific absorption rate (Poljak et al 2003 IEEE Trans. Electromagn. Compat. 45 141-5) and the peak spatial average SAR are used as metrics for human protection from whole-body and localized exposures, respectively. The IEEE standard (IEEE 2006 IEEE C95.1) indicates that the upper boundary frequency, over which the whole-body-averaged SAR is deemed to be the basic restriction, has been reduced from 6 to 3 GHz, because radio-wave energy is absorbed around the body surface when the frequency is increased. However, no quantitative discussion has been provided to support this description especially from the standpoint of temperature elevation. It is of interest to investigate the maximum temperature elevation in addition to the core temperature even for a whole-body exposure. In the present study, using anatomically based human models, we computed the SAR and the temperature elevation for a plane-wave exposure from 30 MHz to 6 GHz, taking into account the thermoregulatory response. As the primary result, we found that the ratio of the core temperature elevation to the whole-body-averaged SAR is almost frequency independent for frequencies below a few gigahertz; the ratio decreases above this frequency. At frequencies higher than a few gigahertz, core temperature elevation for the same whole-body averaged SAR becomes lower due to heat convection from the skin to air. This lower core temperature elevation is attributable to skin temperature elevation caused by the power absorption around the body surface. Then, core temperature elevation even for whole-body averaged SAR of 4 W kg(-1) with the duration of 1 h was at most 0.8 °C, which is smaller than a threshold considered in the safety guidelines/standard. Further, the peak 10 g averaged SAR is correlated with the maximum body temperature elevations without extremities and pinna over the frequencies considered. These findings

  7. Ocular temperature elevation induced by threshold in vivo exposure to 1090-nm infrared radiation and associated heat diffusion

    NASA Astrophysics Data System (ADS)

    Yu, Zhaohua; Schulmeister, Karl; Talebizadeh, Nooshin; Kronschläger, Martin; Söderberg, Per G.

    2014-10-01

    An in vivo exposure to 197 W/cm2 1090-nm infrared radiation (IRR) requires a minimum 8 s for cataract induction. The present study aims to determine the ocular temperature evolution and the associated heat flow at the same exposure conditions. Two groups of 12 rats were unilaterally exposed within the dilated pupil with a close to collimated beam between lens and retina. Temperature was recorded with thermocouples. Within 5 min after exposure, the lens light scattering was measured. In one group, the temperature rise in the exposed eye, expressed as a confidence interval (0.95), was 11±3°C at the limbus, 16±6°C in the vitreous behind lens, and 16±7°C on the sclera next to the optic nerve, respectively. In the other group, the temperature rise in the exposed eye was 9±1°C at the limbus and 26±11°C on the sclera next to the optic nerve, respectively. The difference of forward light scattering between exposed and contralateral not exposed eye was 0.01±0.09 tEDC. An exposure to 197 W/cm2 1090-nm IRR for 8 s induces a temperature increase of 10°C at the limbus and 26°C close to the retina. IRR cataract is probably of thermal origin.

  8. Exposure to elevated temperature and Pco(2) reduces respiration rate and energy status in the periwinkle Littorina littorea.

    PubMed

    Melatunan, Sedercor; Calosi, Piero; Rundle, Simon D; Moody, A John; Widdicombe, Stephen

    2011-01-01

    In the future, marine organisms will face the challenge of coping with multiple environmental changes associated with increased levels of atmospheric Pco(2), such as ocean warming and acidification. To predict how organisms may or may not meet these challenges, an in-depth understanding of the physiological and biochemical mechanisms underpinning organismal responses to climate change is needed. Here, we investigate the effects of elevated Pco(2) and temperature on the whole-organism and cellular physiology of the periwinkle Littorina littorea. Metabolic rates (measured as respiration rates), adenylate energy nucleotide concentrations and indexes, and end-product metabolite concentrations were measured. Compared with values for control conditions, snails decreased their respiration rate by 31% in response to elevated Pco(2) and by 15% in response to a combination of increased Pco(2) and temperature. Decreased respiration rates were associated with metabolic reduction and an increase in end-product metabolites in acidified treatments, indicating an increased reliance on anaerobic metabolism. There was also an interactive effect of elevated Pco(2) and temperature on total adenylate nucleotides, which was apparently compensated for by the maintenance of adenylate energy charge via AMP deaminase activity. Our findings suggest that marine intertidal organisms are likely to exhibit complex physiological responses to future environmental drivers, with likely negative effects on growth, population dynamics, and, ultimately, ecosystem processes. PMID:22030851

  9. Effect of service exposure on fatigue crack propagation of Inconel 718 turbine disc material at elevated temperatures

    SciTech Connect

    Jeong, Dae-Ho; Choi, Myung-Je; Goto, Masahiro; Lee, Hong-Chul; Kim, Sangshik

    2014-09-15

    In this study, the fatigue crack propagation behavior of Inconel 718 turbine disc with different service times from 0 to 4229 h was investigated at 738 and 823 K. No notable change in microstructural features, other than the increase in grain size, was observed with increasing service time. With increasing service time from 0 to 4229 h, the fatigue crack propagation rates tended to increase, while the ΔK{sub th} value decreased, in low ΔK regime and lower Paris' regime at both testing temperatures. The fractographic observation using a scanning electron microscope suggested that the elevated temperature fatigue crack propagation mechanism of Inconel 718 changed from crystallographic cleavage mechanism to striation mechanism in the low ΔK regime, depending on the grain size. The fatigue crack propagation mechanism is proposed for the crack propagating through small and large grains in the low ΔK regime, and the fatigue crack propagation behavior of Inconel 718 with different service times at elevated temperatures is discussed. - Highlights: • The specimens were prepared from the Inconel 718 turbine disc used for 0 to 4229 h. • FCP rates were measured at 738 and 823 K. • The ΔK{sub th} values decreased with increasing service time. • The FCP behavior showed a strong correlation with the grain size of used turbine disc.

  10. 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

  11. Elevated Temperature Crack Propagation

    NASA Technical Reports Server (NTRS)

    Orange, Thomas W.

    1994-01-01

    This paper is a summary of two NASA contracts on high temperature fatigue crack propagation in metals. The first evaluated the ability of fairly simple nonlinear fracture parameters to correlate crack propagation. Hastelloy-X specimens were tested under isothermal and thermomechanical cycling at temperatures up to 980 degrees C (1800 degrees F). The most successful correlating parameter was the crack tip opening displacement derived from the J-integral. The second evaluated the ability of several path-independent integrals to correlate crack propagation behavior. Inconel 718 specimens were tested under isothermal, thermomechanical, temperature gradient, and creep conditions at temperatures up to 650 degrees C (1200 degrees F). The integrals formulated by Blackburn and by Kishimoto correlated the data reasonably well under all test conditions.

  12. Elevated temperature strain gages

    NASA Technical Reports Server (NTRS)

    Brittain, J. O.; Geslin, D.; Lei, J. F.

    1986-01-01

    One of the goals of the HOST Program is the development of electrical resistance strain gages for static strain measurements at temperatures equal to or greater than 1273 K. Strain gage materials must have a reproducible or predictable response to temperature, time and strain. It is the objective of this research to investigate criteria for the selection of materials for such applications through electrical properties studies. The results of the investigation of two groups of materials, refractory compounds and binary alloy solid solutions are presented.

  13. Elevated temperature aluminum alloys

    NASA Technical Reports Server (NTRS)

    Meschter, Peter (Inventor); Lederich, Richard J. (Inventor); O'Neal, James E. (Inventor)

    1989-01-01

    Three aluminum-lithium alloys are provided for high performance aircraft structures and engines. All three alloys contain 3 wt % copper, 2 wt % lithium, 1 wt % magnesium, and 0.2 wt % zirconium. Alloy 1 has no further alloying elements. Alloy 2 has the addition of 1 wt % iron and 1 wt % nickel. Alloy 3 has the addition of 1.6 wt % chromium to the shared alloy composition of the three alloys. The balance of the three alloys, except for incidentql impurities, is aluminum. These alloys have low densities and improved strengths at temperatures up to 260.degree. C. for long periods of time.

  14. 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.

  15. 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.

  16. 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.

  17. SEASONAL PATTERNS OF PHOTOSYNTHESIS IN DOUGLAS FIR SEEDLINGS DURING THE THIRD AND FOURTH YEAR OF EXPOSURE TO ELEVATED CO2 AND TEMPERATURE

    EPA Science Inventory

    We examined the interactive effects of elevated atmospheric CO2 and temperature on seasonal patterns of photosynthesis in Douglas-fir (Psuedotsuga menziesii (Mirb.) Franco) seedlings. Seedlings were grown in sunlit chambers controlled to track either ambient (~400 ppm) CO2 or am...

  18. STOMATAL RESPONSES OF DOUGLAS-FIR SEEDLINGS TO ELEVATED CARBON DIOXIDE AND TEMPERATURE DURING THE THIRD AND FOURTH YEARS OF EXPOSURE

    EPA Science Inventory

    Two major components of climate change, increasing atmospheric [CO2] and increasing temperature, may substantially alter the effects of water availability to plants through effects on the rate of water loss from leaves. We examined the interactive effects of elevated [CO2] and t...

  19. 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)

  20. Emiliania huxleyi increases calcification but not expression of calcification-related genes in long-term exposure to elevated temperature and pCO2

    PubMed Central

    Benner, Ina; Diner, Rachel E.; Lefebvre, Stephane C.; Li, Dian; Komada, Tomoko; Carpenter, Edward J.; Stillman, Jonathon H.

    2013-01-01

    Increased atmospheric pCO2 is expected to render future oceans warmer and more acidic than they are at present. Calcifying organisms such as coccolithophores that fix and export carbon into the deep sea provide feedbacks to increasing atmospheric pCO2. Acclimation experiments suggest negative effects of warming and acidification on coccolithophore calcification, but the ability of these organisms to adapt to future environmental conditions is not well understood. Here, we tested the combined effect of pCO2 and temperature on the coccolithophore Emiliania huxleyi over more than 700 generations. Cells increased inorganic carbon content and calcification rate under warm and acidified conditions compared with ambient conditions, whereas organic carbon content and primary production did not show any change. In contrast to findings from short-term experiments, our results suggest that long-term acclimation or adaptation could change, or even reverse, negative calcification responses in E. huxleyi and its feedback to the global carbon cycle. Genome-wide profiles of gene expression using RNA-seq revealed that genes thought to be essential for calcification are not those that are most strongly differentially expressed under long-term exposure to future ocean conditions. Rather, differentially expressed genes observed here represent new targets to study responses to ocean acidification and warming. PMID:23980248

  1. Tolerance of LSS plant component to elevated temperatures.

    PubMed

    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 degrees 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. PMID:12053940

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Ultrahigh pressure liquid chromatography using elevated temperature.

    PubMed

    Xiang, Yanqiao; Liu, Yansheng; Lee, Milton L

    2006-02-01

    Fast liquid chromatographic (LC) methods are important for a variety of applications. Reducing the particle diameter (d(p)) is the most effective way to achieve fast separations while preserving high efficiency. Since the pressure drop along a packed column is inversely proportional to the square of the particle size, when columns packed with small particles (<2 microm) are used, ultrahigh pressures (>689 bar) must be applied to overcome the resistance to mobile phase flow. Elevating the column temperature can significantly reduce the mobile phase viscosity, allowing operation at higher flow rate for the same pressure. It also leads to a decrease in retention factor. The advantage of using elevated temperatures in LC is the ability to significantly shorten separation time with minimal loss in column efficiency. Therefore, combining elevated temperature with ultrahigh pressure facilitates fast and efficient separations. In this study, C6-modified 1.0 microm nonporous silica particles were used to demonstrate fast separations using a temperature of 80 degrees C and a pressure of 2413 bar. Selected separations were completed in 30 s with efficiencies as high as 220,000 plates m(-1). PMID:16376355

  7. 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.

  8. 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.

  9. Effects of long-time elevated temperature exposures on hot-isostatically-pressed power-metallurgy Udimet 700 alloys with reduced cobalt contents

    NASA Technical Reports Server (NTRS)

    Hart, F. H.

    1984-01-01

    Because almost the entire U.S. consumption of cobalt depends on imports, this metal has been designated "strategic'. The role and effectiveness of cobalt is being evaluated in commercial nickel-base superalloys. Udiment 700 type alloys in which the cobalt content was reduced from the normal 17% down to 12.7%, 8.5%, 4.3%, and 0% were prepared by standard powder metallurgy techniques and hot isostatically pressed into billets. Mechanical testing and microstructural investigations were performed. The mechanical properties of alloys with reduced cobalt contents which were heat-treated identically were equal or better than those of the standard alloy, except that creep rates tended to increase as cobalt was reduced. The effects of long time exposures at 760 C on mechanical properties and at 760 C and 845 C on microstructures were determined. Decreased tensile properties and shorter rupture lives with increased creep rates were observed in alloy modifications. The exposures caused gamma prime particle coarsening and formation of sigma phase in the alloys with higher cobalt contents. Exposure at 845 C also reduced the amount of MC carbides.

  10. 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.

  11. Properties of yttria-tetragonal zirconia polycrystal (Y-TZP) materials after long-term exposure to elevated temperatures. Final report

    SciTech Connect

    Swab, J.J.

    1989-03-01

    Seven commercially available yttria-tetragonal zirconia polycrystal (Y-TZP) materials were evaluated. Room temperature properties were measured before and after heat treatments at 1000C. Microstructure and phase stability were also examined. In all but one case, the Y-TZPs showed very little change in room temperature properties after long times at this temperature. Results show that pressure-assisted processing greatly improves the strength by reducing porosity and keeping the grain size extremely fine, but this reduces the toughness because finer grains are more difficult to transform. In addition, a small amount of cubic zirconia appears to enhance the toughness of fine-grained Y-TZP while maintaining good strength. During processing, a small amount of cubic zirconia is formed and allowed to grow. This creates regions poor in yttria which can transform spontaneously in the presence of a crack-tip stress field.

  12. Room Temperature and Elevated Temperature Composite Sandwich Joint Testing

    NASA Technical Reports Server (NTRS)

    Walker, Sandra P.

    1998-01-01

    Testing of composite sandwich joint elements has been completed to verify the strength capacity of joints designed to carry specified running loads representative of a high speed civil transport wing. Static tension testing at both room and an elevated temperature of 350 F and fatigue testing at room temperature were conducted to determine strength capacity, fatigue life, and failure modes. Static tension test results yielded failure loads above the design loads for the room temperature tests, confirming the ability of the joint concepts tested to carry their design loads. However, strength reductions as large as 30% were observed at the elevated test temperature, where all failure loads were below the room temperature design loads for the specific joint designs tested. Fatigue testing resulted in lower than predicted fatigue lives.

  13. 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

  14. 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.

  15. Elevated temperature fatigue testing of metals

    NASA Technical Reports Server (NTRS)

    Hirschberg, M. H.

    1981-01-01

    The major technology areas needed to perform a life prediction of an aircraft turbine engine hot section component are discussed and the steps required for life prediction are outlined. These include the determination of the operating environment, the calculation of the thermal and mechanical loading of the component, the cyclic stress-strain and creep behavior of the material required for structural analysis, and the structural analysis to determine the local stress-strain-temperature-time response of the material at the critical location in the components. From a knowledge of the fatigue, creep, and failure resistance of the material, a prediction of the life of the component is made. Material characterization and evaluation conducted for the purpose of calculating fatigue crack initiation lives of components operating at elevated temperatures are emphasized.

  16. EROSION OF ELEVATED TEMPERATURE CORROSION SCALES ON METALS

    SciTech Connect

    Maasberg, J.A.; Levy, A.V.

    1981-05-01

    Combined erosion-corrosion poses a considerable problem to the design of long lifetime metallic components in energy conversion systems. To gain some insight into this problem, scales were formed on stainless steel at elevated temperature and subsequently were eroded at room temperature to determine the nature of the erosion rates and the mechanism of scale removal. Thin corrosion scales were formed on 310 stainless steel and an experimental Fe-18Cr-5Al-1Hf alloy at high temperatures (9ooo and 980°C) in gas mixtures with various levels of oxygen and combined oxygen-sulfur. The corroded specimens were eroded at room temperature in an air-solid particle stream using 50{micro}m SiC at 60 ms{sup -1}. The conditions of the corrosive exposures, the rates of erosion of these scales and the microscopic appearance of the eroded surface were correlated to determine the mechanism of thin scale erosion.

  17. 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

  18. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 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 in paragraph (b) of this section, a bulk packaging containing an elevated temperature material must be...

  19. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 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 in paragraph (b) of this section, a bulk packaging containing an elevated temperature material must be...

  20. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 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 in paragraph (b) of this section, a bulk packaging containing an elevated temperature material must be...

  1. 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...

  2. 49 CFR 172.325 - Elevated temperature materials.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 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 in paragraph (b) of this section, a bulk packaging containing an elevated temperature material must be...

  3. Failure of welds at elevated temperatures

    SciTech Connect

    Stevick, G.R. )

    1994-04-01

    This thesis presents several new insights into creep crack growth problems: (1) the potential for stress concentrations resulting from the mismatch of creep properties between weld and base metals, (2) a creep crack growth model that includes the effects of stress triaxiality, and (3) a crack initiation model based on the statistical distribution of inclusion size and spacing. Longitudinally welded piping is used extensively in the power industry for high temperature applications. An elastic-creep finite element analysis of a typical symmetric, double-V longitudinal weld shows that a material stress concentration will develop in 1--2 years if creep properties of the weld and base metals are different. The stress concentration in the weld peaks mid-wall at the weld fusion line on both sides for the typical case in which creep strain rate of the weld metal is greater than that of the base metal. Finite element analysis results also showed that differences in material properties have a significant effect on the stress field after a crack has formed. The increased stress helps explain recent premature failures of longitudinally welded pipe in the power industry and suggest that the weld efficiency factors permitted by the ASME/ANSI B31.1 Piping Code should be reevaluated for longitudinal pipe welds at elevated temperatures.

  4. Tobacco exposure, weight status, and elevated blood pressure in adolescents.

    PubMed

    Huntington-Moskos, Luz; Turner-Henson, Anne; Rice, Marti

    2014-08-01

    The pathogenesis of hypertension begins in youth. An estimated 4% of US adolescents have diagnosed hypertension and 17% have elevated blood pressures, predisposing them to hypertension and cardiovascular disease (CVD) later in life. There is limited research on the clustering of CVD risk factors such as tobacco exposure and weight status that may be associated with high blood pressure in adolescents. The aim of this exploratory study was to determine the relationships between total smoke exposure (TSE; cigarette smoking and secondhand smoke), waist circumference, and blood pressure in a sample of rural adolescents, ages 15-18. A convenience sample of 148 adolescents ages 15-18 was recruited from two rural high schools (88 female and 60 male, all Caucasian). Adolescents were assessed for tobacco exposure (self-report, salivary cotinine), weight status (body mass index, waist circumference), and blood pressure. Self-report measures of tobacco exposure included the Uptake Continuum and Peer and Family Smoking measure. Age, gender, waist circumference and salivary cotinine contributed to 35% of the variance in systolic blood pressure and 18% in diastolic blood pressure. One-fourth (25%) of adolescent males and 11% of adolescent females had elevated systolic blood pressures. Approximately one-fifth of the sample (22%) had elevated salivary cotinine levels indicative of tobacco use and secondhand smoke exposure. TSE and waist circumference were predictors of elevated blood pressure in adolescents. Public health measures need to address clusters of risk factors including blood pressure, tobacco exposure, and weight status among adolescents in order to reduce CVD. PMID:24519179

  5. 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...

  6. Effect of outdoor exposure at ambient and elevated temperatures on fatigue life of Ti-6Al-4V titanium alloy sheet in the annealed and the solution treated and aged condition

    NASA Technical Reports Server (NTRS)

    Phillips, E. P.

    1974-01-01

    Specimens of Ti-6Al-4V titanium alloy sheet in the annealed and the solution-treated and aged heat-treatment condition were exposed outdoors at ambient and 560 K (550 F) temperatures to determine the effect of outdoor exposure on fatigue life. Effects of exposure were determined by comparing fatigue lives of exposed specimens to those of unexpected specimens. Two procedures for fatigue testing the exposed specimens were evaluated: (1) fatigue tests conducted outdoors by applying 1200 load cycles per week until failure occurred and (2) conventional fatigue tests (continuous cycling until failure occurred) conducted indoors after outdoor exposure under static load. The exposure period ranged from 9 to 28 months for the outdoor fatigue-test group and was 24 months for the static-load group. All fatigue tests were constant-amplitude bending of specimens containing a drilled hole (stress concentration factor of 1.6). The results of the tests indicate that the fatigue lives of solution-treated and aged specimens were significantly reduced by the outdoor exposure at 560 K but not by the exposure at ambient temperature. Fatigue lives of the annealed specimens were essentially unaffected by the outdoor exposure at either temperature. The two test procedures - outdoor fatigue test and indoor fatigue test after outdoor exposure - led to the same conclusions about exposure effects.

  7. 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.

  8. Structural efficiencies of various aluminum, titanium, and steel alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Heimerl, George J; Hughes, Philip J

    1953-01-01

    Efficient temperature ranges are indicated for two high-strength aluminum alloys, two titanium alloys, and three steels for some short-time compression-loading applications at elevated temperatures. Only the effects of constant temperatures and short exposure to temperature are considered, and creep is assumed not to be a factor. The structural efficiency analysis is based upon preliminary results of short-time elevated-temperature compressive stress-strain tests of the materials. The analysis covers strength under uniaxial compression, elastic stiffness, column buckling, and the buckling of long plates in compression or in shear.

  9. 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.

  10. Elevated blood lead levels from exposure via a radiator workshop

    SciTech Connect

    Treble, R.G.; Thompson, T.S.; Morton, D.N.

    1998-04-01

    Elevated lead levels were discovered in blood samples collected from family members where both the father and the mother worked in a radiator repair workshop. The father and mother were found to have blood lead levels of 2.0 and 0.5 {micro}mol/L, respectively. The father`s blood lead level was just below the Canadian occupational health and safety intervention level. The two children had blood lead levels of 1.0 and 0.8 {micro}mol/L, both of which are in excess of the recommended guideline for intervention in the case of children. The exposure of the two children was possibly due to a combination of pathways including exposure at the workshop itself during visits and also the transportation of lead-containing dust to the home environment.

  11. Elevated temperature fiber push-out testing

    SciTech Connect

    Eldridge, J.I.

    1995-10-01

    The potential use of fiber-reinforced composite materials for high temperature applications makes the development of interface test methodology at those high temperatures very desirable. A facility for performing high temperature fiber push-out tests will be described with emphasis on critical issues in experimental procedure. Examples from several composite systems illustrate the temperature dependence and environmental sensitivity of fiber debonding and sliding. Interpretation of the temperature dependence will be made primarily in terms of changes in residual stresses along with additional effects due to changes in matrix ductility and interfacial wear. Examples will show that high temperature fiber push-out testing can often distinguish between chemical and frictional fiber/matrix bonding in cases where room temperature only testing cannot.

  12. Temperature changes across CO2-lased dentin during multiple exposures

    NASA Astrophysics Data System (ADS)

    Zakariasen, Kenneth L.; Barron, Joseph R.; Boran, Thomas L.

    1990-06-01

    The literature increasingly indicates that lasers will have a multitude of applications for dental hard tissue procedures, e.g. preventive therapy, caries removal, laser etching and endodontic therapy. However, it is critical that such laser therapies avoid the production of heat levels which will be damaging to the surrounding vital tissues, such as the dental pulp and periodontal tissues. Our preliminary research on temperature changes across C02 lased dentin indicated that for single preventive therapeutic exposures (1.2 W., 0. 1 sec., 1.0 mm focal spot) the mean temperature rise across 350 j.tm of dentin was 0.57 0C while across 1000 .tm of dentin the mean rise was only 0.18 °C. Further research utilizing multiple preventive therapeutic exposures (1.2 W., 0. 1 sec., 1.0 mm focal spot, 3 x 1.0 sec. intervals) showed mean temperature elevations of 1.56 0C across 350 m of dentin and 0.66 O across 1000 xm of dentin. While these temperature elevations, which would be associated with preventive therapy, are very low and would be biologically acceptable, it must be noted that exposures of higher intensities are required to fuse enamel and porcelain, or remove decay. This current research investigates temperature elevations which occuT during C02 lasing utilizing the following exposure parameters: 8.0 W., 1.0 mm focal spot, 0.1 sec. exposures, 2 or 4 exposures per site pulsed 1.0 sec. apart. Three dentin thicknesses were utilized, i.e. 1000 jim, 1500 p.tm and 2000 .tm. Four sections of each thickness were utilized with four exposure sites per specimen (2 with 2 exposures, 2 with 4 exposures). All dentin sections were prepared from non-carious third molars using a hard tissue microtome. A thermistor was placed on the dentin surface opposite each lased site and temperature changes were recorded for approximately 50 sec. following lasing. Mean temperature elevations ranged from a high of 3.07 C for the 1000 xm section utilizing four exposures to a low of 0.37 0C for the

  13. 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.

  14. 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

  15. Temperature changes across porcelain during multiple exposure CO2 lasing

    NASA Astrophysics Data System (ADS)

    Barron, Joseph R.; Zakariasen, Kenneth L.; Peacocke, Larry

    1990-06-01

    Research indicates that laser energy may provide a useful method for glazing and fusing porcelain for intraoral prosthetic purposes. However, it is not known whether such lasing will result in the production of heat levels that may be damaging to adjacent vital tissues such as the dental pulp and periodontal tissues. This research is designed to measure the magnitude of temperature rise across porcelain observed during multiple exposure C02 lasing. Fifteen porcelain examples of 1000 jim (5), 1500 pm (5) and 2000 tm (5) x each received five C02 laser exposures on the same exposure site at 1.0 sec. intervals at 8.0 watts (0.2 sec. per exposure with a 1 mm focal spot). A YSI 144201 thermilinear precision thermistor was placed on the porcelain surface opposite each laser exposure site. Temperature rise above ambient was recorded by an HP3421A data acquisition unit and HP9816 technical microcomputer. Recording continued for sufficient time to allow temperatures to return to ambient. The mean temperature elevations ranged from a low of 2.97 0C (2000 pm) to a high of 7.77 °C (1000 μm). ANOVA and Duncan's Multiple Range Test indicated significant differences in temperature rise by porcelain thickness. It would appear from the results of this research that temperature elevations adjacent to lased porcelain may be sufficiently controllable that safe intraoral porcelain lasing will be possible.

  16. 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.

  17. Response of sugarcane to carbon dioxide enrichment and elevated temperature

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Four sugarcane cultivars (CP72-2086, CP73-1547, CP88-1508, and CP80-1827) were grown in elongated temperature-gradient greenhouses (TGG) at ambient or elevated carbon dioxide (CO2) of 360 or 720 µmol CO2 mol-1 air, respectively. Each TGG maintained temperatures in four zones at Base temperature wit...

  18. 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.

  19. Elevated-Temperature "Ultra" Fast Fracture Strength of Advanced Ceramics: An Approach to Elevated-Temperature "Inert" Strength

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Gyekenyesi, J. P.

    1999-01-01

    The determination of "ultra" fast fracture strengths of five silicon nitride ceramics at elevated temperatures has been made by using constant stress-rate ("dynamic fatigue") testing with a series of "ultra" fast test rates. The test material included four monolithic and one SiC whisker-reinforced composite silicon nitrides. Of the five test materials, four silicon nitrides exhibited the elevated -temperature strengths that approaches their respective room-temperature strengths at an "ultra" fast test rate of 3.3 x 10(exp 4) MPa/s. This implies that slow cracks growth responsible for elevated-temperature failure can be eliminated or minimized by using the "ultra" fast test rate. These ongoing experimental results have shed light on laying a theoretical and practical foundation on the concept and definition of elevated-temperature "inert" strength behavior of advanced ceramics.

  20. Xanthan stability at elevated temperatures. [xanthan

    SciTech Connect

    Seright, R.S. ); Henrici, B.J. )

    1990-02-01

    Xanthan stability is examined to define more clearly the polymer's temperature limitations as a mobility-control agent. Experiments were performed to probe the relative importance of hydrolysis, oxidation, and helix-coil transitions in xanthan degradation. In the absence of oxidizing agents (i.e., dissolved oxygen), results indicate that free-radical, oxidation/reduction reactions are not the dominant mechanism for xanthan degradation. Depending on the pH, acid-catalyzed hydrolysis and base-catalyzed fragmentation reactions may play important roles. With Arrhenius calculations, it was estimated that under ideal conditions (no dissolved oxygen, pH 7 to 8, and moderate to high salinities), a xanthan solution could maintain at least half of its original viscosity for a period of 5 years if the temperature does not exceed 75 to 80{degrees}C (167 to 176{degrees}F). New polymers will be needed for chemical floods where xanthan does not have sufficient stability.

  1. Raman spectroscopy of vapors at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Laane, Jaan; Haller, Kristjan; Sakurai, Sachie; Morris, Kevin; Autrey, Daniel; Arp, Zane; Chiang, Whe-Yi; Combs, Amanda

    2003-05-01

    The most effective way to obtain high quality vapor-phase Raman spectra is to heat the samples to increase their vapor pressure. Many samples can be heated to 350 °C and higher without decomposition. We have designed a simple Raman cell to allow these high temperature studies to be carried out. The high-temperature Raman spectra of nine molecules will be presented and discussed. Most of these are non-rigid molecules containing aromatic rings for which vibrational potential energy surfaces have been determined from their spectra. Two molecules ( p-cresol and 3-methylindole) are model compounds for amino acids and their vapor-phase spectra are characteristic of environments with no hydrogen bonding.

  2. Apparatus for elevated temperature compression or tension testing of specimens

    NASA Astrophysics Data System (ADS)

    Gates, Thomas S.

    1992-05-01

    In order to support materials selection for the next generation supersonic civilian passenger transport aircraft, a testing apparatus was developed to evaluate certain materials under conditions of high load and elevated temperature. In order to elevate the temperature of the material during standard tension and compression testing the test specimen is surrounded by a pair of supports which include internal heating means. These supports also prevent buckling of the specimen during compression testing.

  3. Shock sensitivity of IHE at elevated temperatures

    SciTech Connect

    Urtiew, P.A.; Cook, T.M.; Maienschein, J.L.; Tarver, C.M.

    1993-06-01

    Insensitive high explosives (IHE`s) based on triamino-trinitrobenzene (TATB) have been demonstrated to be very insensitive to shock, thermal, friction and other stimuli. Hazard scenarios can involve more than one stimulus, such as heating followed by fragment impact (shock). The shock sensitivity of the IHE`s LX-17 and PBX-9502 preheated to a temperature (250{degree}C) just below thermal runaway is quantitatively studied using embedded manganin pressure gauges. The thermal expansion of TATB to 250{degree}C is measured to determine the state of the explosive prior to shock initiation. LX-17 and PBX-9502 are found to be significantly more sensitive at 250{degree}C than at lower temperatures, but still less sensitive than ambient temperature HMX-based explosives. An ignition and growth reactive flow computer model of the shock initiation of hot IHE is developed to allow predictions of the response of hot IHE to impact scenarios which can not be tested directly.

  4. 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.

  5. Elevated temperature effects on fatigue and fracture

    SciTech Connect

    Piascik, R.S.; Gangloff, R.P.; Saxena, A.

    1997-12-31

    The intent of this meeting was to reinforce the recent merger of ASTM Committees E09 on Fatigue and E24 on Fracture Mechanics, forming Committee E08 on Fatigue and Fracture. This special technical publication highlights a topical subset of the meeting, that is, research on the critical effect of temperature on the fatigue and fracture of structural materials. Papers highlighted: Integration of damage evolution, from the distributed form to that focused at a crack tip; High-resolution experimental probes of fatigue and fracture processes; Measurement and modeling of the important role of time in microstructural degradation, damage evolution, and crack growth; Models that provide quantitative predictions and are tested by high-quality experimentation; and Performance of next-generation structural metals and composites, characterized within a framework useful in component life prediction. Papers have been processed separately for inclusion on the data base.

  6. The emittance of space radiator materials measured at elevated temperatures

    SciTech Connect

    Mirtich, M.J.; DiFilippo, F.; Barry, J.; Kussmaul, M.

    1994-09-01

    The spectral emittances of textured space radiator materials between 1.7 and 14.7 {mu}m have been evaluated at room temperature and elevated temperature (630{degrees}C) in air. Heating in air caused a permanent increase in spectral emittance for all materials tested: HCl/ion beam textured 304 stainless steel, untextured Ti (6 percent Al, 4 percent V), and sandblasted Ti (6 percent Al, 4 percent V). Changes in the surface chemistry and/or surface morphology of these materials were also observed. Elevated temperature spectral emittance was measured in an argon atmosphere and compared to the measurements in air. Similarity between the room temperature and elevated temperature spectral emittance measurements was also investigated, and limited agreement was found.

  7. Hypercoagulability in response to elevated body temperature and central hypovolemia

    PubMed Central

    Meyer, Martin A.S.; Ostrowski, Sisse R.; Overgaard, Anders; Ganio, Matthew S.; Secher, Niels H.; Crandall, Craig G.; Johansson, Pär I.

    2016-01-01

    Background Coagulation abnormalities contribute to poor outcomes in critically ill patients. In trauma patients exposed to a hot environment, a systemic inflammatory response syndrome, elevated body temperature, and reduced central blood volume occur in parallel with changes in hemostasis and endothelial damage. The objective of this study was to evaluate whether experimentally elevated body temperature and reduced central blood volume (CBV) per se affects hemostasis and endothelial activation. Methods Eleven healthy volunteers were subjected to heat stress, sufficient to elevate core temperature, and progressive reductions in CBV by lower body negative pressure (LBNP). Changes in hemostasis were evaluated by whole blood haemostatic assays, standard hematologic tests and by plasma biomarkers of coagulation and endothelial activation/disruption. Results Elevated body temperature and decreased CBV resulted in coagulation activation evidenced by shortened activated partial tromboplastin time (−9% [IQR −7; −4]), thrombelastography: reduced reaction time (−15% [−24; −4]) and increased maximum amplitude (+4% (2; 6)), all P < 0.05. Increased fibrinolysis was documented by elevation of D-dimer (+53% (12; 59), P = 0.016). Plasma adrenaline and noradrenaline increased 198% (83; 346) and 234% (174; 363) respectively (P = 0.006 and P = 0.003). Conclusions This experiment revealed emerging hypercoagulability in response to elevated body temperature and decreased CBV, whereas no effect on the endothelium was observed. We hypothesize that elevated body temperature and reduced CBV contributes to hypercoagulability, possibly due to moderate sympathetic activation, in critically ill patients and speculate that normalization of body temperature and CBV may attenuate this hypercoagulable response. PMID:23856126

  8. Elevated bulk-silica exposures and evidence for multiple aqueous alteration episodes in Nili Fossae, Mars

    NASA Astrophysics Data System (ADS)

    Amador, Elena S.; Bandfield, Joshua L.

    2016-09-01

    The Nili Fossae region of Mars contains some of the most mineralogically diverse bedrock on the planet. Previous studies have established three main stratigraphic units in the region: a phyllosilicate-bearing basement rock, a variably altered olivine-rich basalt, and a capping rock. Here, we present evidence for the localized alteration of the northeast Nili Fossae capping unit, previously considered to be unaltered. Both near-infrared and thermal-infrared spectral datasets were analyzed, including the application of a method for determining the relative abundance of bulk-silica (SiO2) over surfaces using thermal emission imaging system (THEMIS) images. Elevated bulk-silica exposures are present on surfaces previously defined as unaltered capping rock. Given the lack of spectral evidence for phyllosilicate, hydrated silica, or quartz phases coincident with the newly detected exposures-the elevated bulk-silica may have formed under a number of aqueous scenarios, including as a product of the carbonation of the underlying olivine-rich basalt under moderate water: rock scenarios and temperatures. Regardless of formation mechanism, the detection of elevated bulk-silica exposures in the Nili Fossae capping unit extends the history of aqueous activity in the region to include all three of the main stratigraphic units.

  9. 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

  10. Effects of nuclear radiation and elevated temperature storage on electroexplosive devices

    NASA Technical Reports Server (NTRS)

    Menichelli, V. J.

    1976-01-01

    Aerospace type electroexplosive devices (EEDs) were subjected to nuclear radiation. Components and chemicals used in the EEDs were also included. The kind of radiation and total dosage administered were those which may be experienced in a space flight of 10 years duration, based on information available at this time. After irradiation, the items were stored in elevated constant-temperature ovens to accelerate early effects of the exposure to radiation. Periodically, samples were withdrawn for visual observation and testing. Significant changes occurred which were attributed to elevated-temperature storage and not radiation.

  11. 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. PMID:25898249

  12. EFFECTS OF ELEVATED CO2 AND TEMPERATURE ON SOIL C AND N: RESULTS OF A DOUGLAS FIR MESOCOSM STUDY

    EPA Science Inventory

    We conducted a 4-year study on the effects of elevated CO2 and elevated air temperature on Douglas fir seedlings growing under controlled exposure conditions in outdoor sun-lit mesocosms. 1+1 seedlings were planted in mesocosms in Corvallis, OR in the spring of 1993 in a reconstr...

  13. EFFECTS OF ELEVATED CO2 AND TEMPERATURE ON SOIL C AND N IN A DOUGLAS FIR MESOCOSM STUDY

    EPA Science Inventory

    We conducted a 4-year study on the effects of elevated CO2 and elevated air temperature on Douglas fir seedlings growing under controlled climate and exposure conditions in outdoor sun-lit mesocosms. 1+1 seedlings were planted in mesocosms in Corvallis, OR in the spring of 1993 i...

  14. 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.

  15. Mechanical properties of polyimide coated optical fibers at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Huang, Lei; Dyer, Robert S.; Lago, Ralph J.; Stolov, Andrei A.; Li, Jie

    2016-03-01

    High temperature mechanical strength and reliability of optical fibers have become important subjects as optical fibers are increasingly used for harsher environments. Theories and models of fiber mechanical properties established for traditional telecommunications applications may need to be validated for applications at elevated temperatures. In this paper, we describe the test setup for high temperature tensile strength of fiber and report initial results of dynamic tensile strength of polyimide coated optical fiber at 300 and 350ºC for different heating time intervals. The results are compared with room temperature strength data, data available in the literature, and our earlier work on thermogravimetric analysis (TGA) weight loss of the polyimide coating and the observations on surface morphology at elevated temperatures. Interesting observations are discussed and possible explanations are proposed.

  16. Evaluation of components on a ductwork system at elevated temperatures

    SciTech Connect

    Shen, J.K.; Chern, C.Y.

    1995-12-31

    This paper evaluates the adequacy of a Deactivation Furnace System (DFS) for operation at elevated temperatures (from 1,100 F to 1,800 F). The piping components included in this evaluation are ductwork, flanges, expansion joints, duct support structures, bolts and other load bearing elements. The DFS is designed in accordance with ANSI/ASME B31.1 and B31.3 Codes. However, for the evaluations of elevated temperature conditions, ASME III Code Case N-253-6, Construction of Class 2 or Class 3 components for Elevated Temperature Service, and Code Case N-47-28, Class 1 components in Elevated Temperature Service, are used. To consider creep effects, the primary membrane stresses of piping components are calculated and compared with the stress to rupture based on the duration of operation temperature. The primary-membrane-plus-bending stresses are calculated to determine the use-fraction sum due to service loadings. If the calculated use-fraction sum of a component should exceed the allowable, the limited useful life could be predicted.

  17. 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.

  18. Estimation of temperature elevation generated by ultrasonic irradiation in biological tissues using the thermal wave method

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-Zhou; Zhu, Yi; Zhang, Fei; Gong, Xiu-Fen

    2013-02-01

    In most previous models, simulation of the temperature generation in tissue is based on the Pennes bio-heat transfer equation, which implies an instantaneous thermal energy deposition in the medium. Due to the long thermal relaxation time τ (20 s-30 s) in biological tissues, the actual temperature elevation during clinical treatments could be different from the value predicted by the Pennes bioheat equation. The thermal wave model of bio-heat transfer (TWMBT) defines a thermal relaxation time to describe the tissue heating from ultrasound exposure. In this paper, COMSOL Multiphysics 3.5a, a finite element method software package, is used to simulate the temperature response in tissues based on Pennes and TWMBT equations. We further discuss different factors in the bio-heat transfer model on the influence of the temperature rising and it is found that the temperature response in tissue under ultrasound exposure is a rising process with a declining rate. The thermal relaxation time inhibits the temperature elevation at the beginning of ultrasonic heating. Besides, thermal relaxation in TWMBT leads to lower temperature estimation than that based on Pennes equation during the same period of time. The blood flow carrying heat dominates most to the decline of temperature rising rate and the influence increases with temperature rising. On the contrary, heat diffusion, which can be described by thermal conductivity, has little effect on the temperature rising.

  19. 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.

  20. 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.

  1. Zeta Potential in Intact Natural Carbonates at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Al-Mahrouqi, D.; Vinogradov, J.; Jackson, M.

    2015-12-01

    Measurements of zeta potential have been used to monitor subsurface flows in many natural brine systems. Numerous studies report zeta potentials in carbonates using crushed samples at low ionic strength and laboratory temperatures. However, natural brines have much higher salinity; moreover, temperatures are considerably higher in many subsurface settings. The variation of zeta potentials with temperature has not been examined in natural carbonates. We report zeta potential values interpreted from streaming potential measurements in two intact carbonate rock samples, saturated with artificial brines at elevated temperatures. We measure streaming potential using an experimental set-up that incorporates in-situ measurements of saturated rock conductivity, brine temperature, brine pH, brine electrical conductivity, pressure difference and voltage at temperatures up to 120oC. The streaming potential measurements are complemented with brine effluent studies. We find that the interpreted zeta potential is negative and decreases in magnitude with increasing temperature at low ionic strength (0.01M) and independent of temperature at high ionic strength (0.5M); consistent with published zeta potential in intact natural sandstones. The concentration of Ca2+ (main potential determining ion) also decreases with temperature at low ionic strength, but remains constant at high ionic strength. The temperature dependence of the zeta potential is consistent between two different natural carbonate samples and can be explained by the temperature dependence of pCa2+. We suggest that zeta potential of carbonate is independent of temperature or pH when pCa2+ remains constant. A linear variation of pH vs. pCa2+ is exhibited, at ambient and elevated temperatures, when pCa2+ is allowed to change with pH. This linear variation explains the numerous published data that shows apparent relationship between zeta potential of carbonates and pH.

  2. Young's modulus of cement paste at elevated temperatures

    SciTech Connect

    Odelson, Joshua B.; Kerr, Elizabeth A.; Vichit-Vadakan, Wilasa . E-mail: WVichitVadakan@ctlgroup.com

    2007-02-15

    Calcium silicate hydrate is a porous hydrate that is sensitive to temperature and readily loses strength at elevated temperatures. Mechanical and chemical changes in the microstructure, due to escaping water, can significantly affect the mechanical properties, but these changes occur over different temperature ranges. By measuring Young's modulus as a function of temperature using the dynamic mechanical analyzer, the temperature range in which the greatest change in stiffness occurs can be identified. Additional mineralogy, pore size distribution, and composition analysis from high temperature X-ray diffraction, nitrogen sorption, and thermogravimetric analysis will demonstrate the changes in the microstructure. The results demonstrate that over 90% of the loss in stiffness occurs below 120 deg. C. Therefore, the damage is due to microcracking caused by pore water expansion and evaporation and not the change in mineralogy or composition. More damage, as indicated by greater loss in stiffness, occurs in stiffer and less permeable samples where higher stresses can develop.

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. Thermal behavior of cylindrical buckling restrained braces at elevated temperatures.

    PubMed

    Talebi, Elnaz; Tahir, Mahmood Md; Zahmatkesh, Farshad; Yasreen, Airil; Mirza, Jahangir

    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

  8. Effect of Phenol on Bacillus subtilis Spores at Elevated Temperatures

    PubMed Central

    Russell, A. D.; Loosemore, Muriel

    1964-01-01

    The nature of the recovery medium is shown to influence the number of Bacillus subtilis spores which, after exposure to 2.5 or 5% phenol at high temperatures, can produce a visible colony. Higher survivor counts were obtained in nutrient agar containing L-alanine and D-glucose than in plain nutrient agar. PMID:14215968

  9. 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.

  10. Diffusive Gas Loss from Silica Glass Ampoules at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Palosz, W.

    1998-01-01

    Changes in the pressure of hydrogen, helium and neon due to diffusion through the wall of silica crystal growth ampoules at elevated temperatures were determined experimentally. We show that, while both He- and Ne-losses closely follow conventional model of diffusive gas permeation through the wall, hydrogen losses, in particular at low fill pressures, can be much larger. This is interpreted in terms of the high solubility of hydrogen in silica glasses.

  11. 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.

  12. 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.

  13. Grain boundary oxidation and fatigue crack growth at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Oshida, Y.

    1986-01-01

    Fatigue crack growth rate at elevated temperatures can be accelerated by grain boundary oxidation. Grain boundary oxidation kinetics and the statistical distribution of grain boundary oxide penetration depth were studied. At a constant delta K-level and at a constant test temperature, fatigue crack growth rate, da/dN, is a function of cyclic frequency, nu. A fatigue crack growth model of intermittent micro-ruptures of grain boundary oxide is constructed. The model is consistent with the experimental observations that, in the low frequency region, da/dN is inversely proportional to nu, and fatigue crack growth is intergranular.

  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. Microchip Electrophoresis at Elevated Temperatures and High Separation Field Strengths

    PubMed Central

    Mitra, Indranil; Marczak, Steven P.; Jacobson, Stephen C.

    2014-01-01

    We report free-solution microchip electrophoresis performed at elevated temperatures and high separation field strengths. We used microfluidic devices with 11-cm long separation channels to conduct separations at temperatures between 22 (ambient) and 45 °C and field strengths from 100 to 1000 V/cm. To evaluate separation performance, N-glycans were used as a model system and labeled with 8-aminopyrene-1,3,6-trisulfonic acid to impart charge for electrophoresis and render them fluorescent. Typically, increased diffusivity at higher temperatures leads to increased axial dispersion and poor separation performance; however, we demonstrate that sufficiently high separation field strengths can be used to offset the impact of increased diffusivity in order to maintain separation efficiency. Efficiencies for these free-solution separations are the same at temperatures of 25, 35, and 45 °C with separation field strengths ≥500 V/cm. PMID:24114979

  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. Friction Properties of Molybdenum Alloyed Steel at Elevated Temperatures

    SciTech Connect

    Li Jianliang; Xiong Dangsheng; Wu Hongyan

    2011-01-17

    The high-temperature properties of steel surface can be improved by molybdenum surface alloying. Molybdenzing was carried out on carbon steel in the multi-function double glow plasma surface alloying furnace. The friction and wear tests were conducted on a high temperature ball-on-disk tribometer under the temperature of 25 deg. C{approx}600 deg. C. The contents of alloy element varied with alloyed layer were detected by SEM attached with EDS. The molybdenized layer is composed of the deposited layer and diffused layer. The micro-hardness of alloyed layer decreases from HV650 on the top layer to HV240. The friction coefficient of molybdenized layer decreases from 0.5{approx}0.6 to 0.2{approx}0.3 and wear rate decreases by 20% at elevated temperature after molybdenizing.

  18. Helium and deuterium implantation in tungsten at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Cipiti, B. B.; Kulcinski, G. L.

    2005-12-01

    High temperature helium and deuterium implantation on tungsten has been studied using the University of Wisconsin inertial electrostatic confinement device. Helium or deuterium ions from a plasma source were driven into polished tungsten powder metallurgy samples. Deuterium implantation did not damage the surface of the specimens at elevated temperatures (˜1200 °C). Helium implantation resulted in a porous surface structure above 700 °C. A helium fluence scan, ion energy scan, and temperature scan were all completed. With 30 keV ions, the pore formation started just below 4 × 10 16 He +/cm 2. The pore size increased and the pore density decreased with increasing fluence and temperature. The energy scan from 20 to 80 keV showed no consistent trend.

  19. 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).

  20. Elevated temperature alters carbon cycling in a model microbial community

    NASA Astrophysics Data System (ADS)

    Mosier, A.; Li, Z.; Thomas, B. C.; Hettich, R. L.; Pan, C.; Banfield, J. F.

    2013-12-01

    Earth's climate is regulated by biogeochemical carbon exchanges between the land, oceans and atmosphere that are chiefly driven by microorganisms. Microbial communities are therefore indispensible to the study of carbon cycling and its impacts on the global climate system. In spite of the critical role of microbial communities in carbon cycling processes, microbial activity is currently minimally represented or altogether absent from most Earth System Models. Method development and hypothesis-driven experimentation on tractable model ecosystems of reduced complexity, as presented here, are essential for building molecularly resolved, benchmarked carbon-climate models. Here, we use chemoautotropic acid mine drainage biofilms as a model community to determine how elevated temperature, a key parameter of global climate change, regulates the flow of carbon through microbial-based ecosystems. This study represents the first community proteomics analysis using tandem mass tags (TMT), which enable accurate, precise, and reproducible quantification of proteins. We compare protein expression levels of biofilms growing over a narrow temperature range expected to occur with predicted climate changes. We show that elevated temperature leads to up-regulation of proteins involved in amino acid metabolism and protein modification, and down-regulation of proteins involved in growth and reproduction. Closely related bacterial genotypes differ in their response to temperature: Elevated temperature represses carbon fixation by two Leptospirillum genotypes, whereas carbon fixation is significantly up-regulated at higher temperature by a third closely related genotypic group. Leptospirillum group III bacteria are more susceptible to viral stress at elevated temperature, which may lead to greater carbon turnover in the microbial food web through the release of viral lysate. Overall, this proteogenomics approach revealed the effects of climate change on carbon cycling pathways and other

  1. 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

  2. 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.

  3. Elevated temperature fracture of RS/PM aluminum alloy 8009

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    The fracture behavior of advanced powder metallurgy Al-Fe-V-Si alloy 8009 (previously called FVS0812) is being characterized under monotonic loads, as a function of temperature. Particular attention is focused on contributions to the fracture mechanism from the fine grained dispersoid strengthened microstructure, dissolved solute from rapid solidification, and the moist air environment. Time-dependent crack growth is characterized in advanced aluminum alloys at elevated temperatures with the fracture mechanics approach, and cracking mechanisms are examined with a metallurgical approach. Specific tasks were to obtain standard load crack growth experimental information from a refined testing system; to correlate crack growth kinetics with the j-integral and time dependent C(sub t)(t); and to investigate the intermediate temperature embrittlement of 8009 alloy in order to understand crack growth mechanisms.

  4. 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.

  5. 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.

  6. Elevated Temperature Crack Growth Behavior in HSCT Structural Materials

    NASA Technical Reports Server (NTRS)

    Saxena, Ashok

    1998-01-01

    Structures in super-sonic aircraft are subjected to conditions of high temperature and cyclic and sustained loading for extended periods of time. The durability of structures fabricated from aluminum and certain titanium alloys in such demanding conditions is of primary concern to the designers and manufacturers of futuristic transport aircraft. Accordingly, the major goal of this project was to evaluate the performance and durability of high temperature aluminum and titanium alloys for use in high speed civil transport (HSCT) structures. Additional goals were to develop time-dependent fracture mechanics methodology and test methods for characterizing and predicting elevated temperature crack growth behavior in creep-brittle materials such as ones being considered for use in HSCT structures and to explore accelerated methods of simulating microstructural degradation during service and measuring degraded properties in these materials.

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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. PMID:25354956

  12. 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.

  13. Electride-like phases at extreme compression and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Bonev, Stanimir; Dubois, Jonathan

    The transformation of materials into electride-like structures under the application of extreme pressure has attracted a lot of interest recently. Theoretical studies have predicted the existence of low-coordinated crystal phases, where the conduction electrons are localized in the interstitial atomic regions, for a number of elements at high density. Most of these works have been limited to static lattice calculations. The pressures where such transformations are projected to occur are accessible in shock-wave experiments, but at elevated temperatures. In this talk I will discuss the temperature dependence of elecride structures, both solids and liquids, as well as the requirements for their accurate simulation. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  14. 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.

  15. Evidence that elevated water temperature affects the reproductive physiology of the European bullhead Cottus gobio.

    PubMed

    Dorts, Jennifer; Grenouillet, Gaël; Douxfils, Jessica; Mandiki, Syaghalirwa N M; Milla, Sylvain; Silvestre, Frédéric; Kestemont, Patrick

    2012-04-01

    Climate change is predicted to increase the average water temperature and alter the ecology and physiology of several organisms including fish species. To examine the effects of increased water temperature on freshwater fish reproduction, adult European bullhead Cottus gobio of both genders were maintained under three temperature regimes (T1: 6-10, T2: 10-14 and T3: 14-18°C) and assessed for gonad development (gonadosomatic index-GSI and gonad histology), sex steroids (testosterone-T, 17β-estradiol-E2 and 11-ketotestosterone-11-KT) and vitellogenin (alkali-labile phosphoprotein phosphorus-ALP) dynamics in December, January, February and March. The results indicate that a 8°C rise in water temperature (T3) deeply disrupted the gonadal maturation in both genders. This observation was associated with the absence of GSI peak from January to March, and low levels of plasma sex steroids compared with T1-exposed fish. Nevertheless, exposure to an increasing temperature of 4°C (T2) appeared to accelerate oogenesis with an early peak value in GSI and level of plasma T recorded in January relative to T1-exposed females. In males, the low GSI, reduced level of plasma 11-KT and the absence of GSI increase from January to March support the deleterious effects of increasing water temperature on spermatogenesis. The findings of the present study suggest that exposure to elevated temperatures within the context of climate warming might affect the reproductive success of C. gobio. Specifically, a 4°C rise in water temperature affects gametogenesis by advancing the spawning, and a complete reproductive failure is observed at an elevated temperature of 8°C. PMID:21638008

  16. 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.

  17. Binder/HMX Interaction in PBX9501 at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Saw, Cheng K.; Tarver, Craig M.

    2004-07-01

    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 β- to δ-phase transition in PBX 9501 is similar to that in neat HMX. However, in the presence of the PBX 9501 binder, δ-phase HMX readily converts back to β-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 δ-phase to β-phase is due to changes in the surface molecular potential caused by the influence of the polymer binder on the δ-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 δ-phase to β-phase transition, as demonstrated in an aged PBX 9501 material for which the reversion is not observed.

  18. 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.

  19. Rotating disk electrode system for elevated pressures and temperatures

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 H2SO4, 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.

  20. Rotating disk electrode system for elevated pressures and temperatures.

    PubMed

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

    2015-06-01

    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 H2SO4, 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. PMID:26133849

  1. 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

  2. Elevated temperature reduces survivorship and settlement of the larvae of the Caribbean scleractinian coral, Favia fragum (Esper)

    NASA Astrophysics Data System (ADS)

    Randall, C. J.; Szmant, A. M.

    2009-06-01

    The effect of elevated seawater temperatures, such as those plaguing tropical seas during the summers of anomalously warm years, on early life stages of reef corals remains poorly studied. To redress this situation, survivorship of larvae of the brooding coral, Favia fragum, was studied in the laboratory, using both short term (48 h) and long term (156-191 h) exposures to 28, 29, and 31°C. Ability to settle when presented with induction substrates and survival after settlement, at the same exposure temperature and after reciprocal transfers to the other experimental temperatures, were also measured. No significant effect of temperature on survivorship was detected after 48 h of exposure, but larvae incubated for 156 h at the highest temperature (31°C) exhibited a 13% reduced survivorship compared to larvae at 28°C. Induction of settlement further increased mortality at the highest temperature (31°C); survivorship after settlement at 31°C was 27% lower than when larvae were simply maintained at the elevated temperature. These results indicate that elevated temperatures are more detrimental to coral larvae undergoing the developmentally complex settlement process than to the swimming planula stage. This may bode poorly for Caribbean corals with late summer reproductive seasons.

  3. 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...

  4. 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.

  5. Microscopic evaluation of vesicles shed by erythrocytes at elevated temperatures.

    PubMed

    Moore, Timothy; Sorokulova, Iryna; Pustovyy, Oleg; Globa, Ludmila; Pascoe, David; Rudisill, Mary; Vodyanoy, Vitaly

    2013-11-01

    The images of human erythrocytes and vesicles were analyzed by a light microscopy system with spatial resolution of better than 90 nm. The samples were observed in an aqueous environment and required no freezing, dehydration, staining, shadowing, marking, or any other manipulation. Temperature elevation resulted in significant concentration increase of structurally transformed erythrocytes (echinocytes) and vesicles in the blood. The process of vesicle separation from spiculated erythrocytes was video recorded in real time. At a temperature of 37°C, mean vesicle concentrations and diameters were found to be 1.50 ± 0.35 × 10(6) vesicles per microliter and 0.365 ± 0.065 μm, respectively. The vesicle concentration increased approximately threefold as the temperature increased from 37 to 40°C. It was estimated that 80% of all vesicles found in the blood are smaller than 0.4 μm. Accurate account of vesicle numbers and dimensions suggest that 86% of the lost erythrocyte material is lost not by vesiculation but by another, as yet, unknown mechanism. PMID:23964014

  6. Interface degradation in CAS/Nicalon during elevated temperature aging

    SciTech Connect

    Plucknett, K.P.; Cain, R.L.; Lewis, M.H.

    1995-03-01

    A CaO-Al{sub 2}O{sub 3}-SiO{sub 2} (CAS)/Nicalon glass-ceramic matrix composite has been subjected to elevated temperature oxidation heat-treatments between 375 and 1200{degrees}C, for up to 100 hours. Micro- and macro-mechanical properties have been determined by fiber push-down, using a mechanical properties microprobe, and flexure testing, respectively. Aging between 450 and 800{degrees}C results in significant property degradation, with reduced bending modulus and flexure strength, increased fiber sliding stress, and a transition to a purely brittle failure mode. Aging degradation is due to oxidative removal of the carbon interlayer, with the subsequent formation of a silica bond between fiber and matrix. At higher temperatures, carbon is retained due to the formation of a protective silica plug at exposed fiber ends, with the subsequent retention of composite properties. Short duration pre-treatment schedules, at 1000 or 1100{degrees}C, were developed to prevent intermediate temperature property degradation.

  7. 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.

  8. 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.

  9. Powder processing of NiAl for elevated temperature strength

    SciTech Connect

    Whittenberger, J.D.; Hebsur, M.; Grahle, P.; Arzt, E.; Behr, R.; Zoeltzer, K.

    1997-12-31

    In an effort to superimpose two different elevated temperature strengthening mechanisms in NiAl, one lot of an oxide dispersion strengthened (ODS) NiAl powder has been milled in liquid nitrogen (cryomilled) to introduce AlN particles at the grain boundaries, and a second lot of ODS powder was simply roasted in gaseous nitrogen as an alternative means to produce AlN reinforced grain boundaries. Powder from both of these lots as well as the starting material have been consolidated by hot extrusion and tested at 1,300 K. Both nitrogen roasting and cryomilling produced AlN within the ODS NiAl matrix which strengthened the alloy; however, based on the AlN content, cryomilling is more effective.

  10. 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.

  11. Hot deformation behaviour of alloys for applications at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Voyzelle, Benoit

    The present study investigated the deformation behaviour, microstructure evolution and fracture behaviour under hot working conditions of alloys designed for elevated-temperature applications. For this purpose, iron-aluminum and titanium-aluminum alloys were selected and their compositions are: Fe-8.5wt%Al-5.5Cr-2.0Mo-0.2Zr-0.03C, Fe-16.5Al-5.5Cr-1.0Nb-0.05C and Ti-33.3Al-2.8Mn-4.8Nb. These alloys were tested in the as-cast condition and in the form of hot-rolled + annealed plate for the iron-aluminum alloys and in the HIP'ed condition for the titanium-aluminum alloy. Isothermal compression tests were carried out with a Gleeble 2000 over a range of temperatures from 800 to 1250°C and constant strain rates from 10-3 to 10 s-1. In general, the flow curves are marked by a peak stress and softening which decline as temperature rises, and a flow stress which diminishes with rise in temperature and decrease in strain rate. The flow behaviour at peak stress (sigmap) and 0.5 true strain of these materials was described well by the Zener-Hollomon parameter Z=3˙exp /RTQHW , where Z=K3sinha sn . A numerical curve-fitting method was used to yield values of the following parameters: (i) stress exponent, n and (ii) activation energy, QHW . The dynamic material modeling approach was performed to extract from hot compression data: (i) the strain rate sensitivity parameter, m, (ii) the efficiency of power dissipation, eta, and (iii) the instability parameter, xi. The microstructure evolution and fracture behaviour were assessed using optical and electron microscopy. The deformation processes occuring were determined by correlation of the sigma-epsilon curves, m and microstructural observations. The resulting deformation map indicates that at lower temperatures and higher strain rates, the dominant restoration occurs by dynamic recovery, while at lower strain rates and higher temperatures dynamic recrystallization is the operative mode. At the highest temperatures, dynamic

  12. Brief oral stimulation, but especially oral fat exposure, elevates serum triglycerides in humans.

    PubMed

    Mattes, Richard D

    2009-02-01

    Oral exposure to dietary fat results in an early initial spike, followed by a prolonged elevation, of serum triglycerides in humans. The physiological and pathophysiological implications remain unknown. This study sought to determine the incidence of the effect, the required fat exposure duration, and its reliability. Thirty-four healthy adults participated in four to six response-driven trials held at least a week apart. They reported to the laboratory after an overnight fast, a catheter was placed in an antecubital vein, and a blood sample was obtained. Participants then ingested 50 g of safflower oil in capsules with 500 ml of water within 15 min to mimic a high fat meal but without oral fat exposure. Blood was collected 0, 10, 20, 30, 40, 50, 60, 120, 240, 360, and 480 min after capsule ingestion with different forms (full fat, nonfat, none) and durations of oral fat exposures (10 s, 5 min, 20 min, and/or 2 h). A triglyceride response (increase of triglyceride >10 mg/dl within 30 min) was observed in 88.2%, 70.5%, and 50% of participants with full-fat, nonfat, and no oral exposure, respectively. Test-retest reliability was 75% with full-fat exposure but only 45.4% with nonfat exposure. Full-fat and nonfat exposures led to comparable significant elevations of triglyceride over no oral stimulation with 10-s exposures, but full fat led to a greater rise than nonfat with 20 min of exposure. These data indicate that nutritionally relevant oral fat exposures reliably elevate serum triglyceride concentrations in most people. PMID:19074638

  13. 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

  14. 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.

  15. Elevated temperature creep properties for selected active metal braze alloys

    SciTech Connect

    Stephens, J.J.

    1997-02-01

    Active metal braze alloys reduce the number of processes required for the joining of metal to ceramic components by eliminating the need for metallization and/or Ni plating of the ceramic surfaces. Titanium (Ti), V, and Zr are examples of active element additions which have been used successfully in such braze alloys. Since the braze alloy is expected to accommodate thermal expansion mismatch strains between the metal and ceramic materials, a knowledge of its elevated temperature mechanical properties is important. In particular, the issue of whether or not the creep strength of an active metal braze alloy is increased or decreased relative to its non-activated counterpart is important when designing new brazing processes and alloy systems. This paper presents a survey of high temperature mechanical properties for two pairs of conventional braze alloys and their active metal counterparts: (a) the conventional 72Ag-28Cu (Cusil) alloy, and the active braze alloy 62.2Ag- 36.2Cu-1.6Ti (Cusil ABA), and (b) the 82Au-18Ni (Nioro) alloy and the active braze alloy Mu-15.5M-0.75Mo-1.75V (Nioro ABA). For the case of the Cusil/Cusil ABA pair, the active metal addition contributes to solid solution strengthening of the braze alloy, resulting in a higher creep strength as compared to the non-active alloy. In the case of the Nioro/Nioro ABA pair, the Mo and V additions cause the active braze alloy to have a two-phase microstructure, which results in a reduced creep strength than the conventional braze alloy. The Garofalo sinh equation has been used to quantitatively describe the stress and temperature dependence of the deformation behavior. It will be observed that the effective stress exponent in the Garofalo sinh equation is a function of the instantaneous value of the stress argument.

  16. 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.

  17. Temperature regulation in the unrestrained rabbit during exposure to 600-MHz radiofrequency radiation

    SciTech Connect

    Gordon, C.J.; Long, M.D.; Fehlner, K.S.

    1986-01-01

    Six male New Zealand white rabbits were individually exposed to 600-MHz radiofrequency (RF) radiation for 90 min in a waveguide exposure system at an ambient temperature (Ta) of 20 or 30 C. Immediately after exposure, the rabbit was removed from the exposure chamber and its colonic and ear skin temperatures were quickly measured. The whole-body specific absorption rate (SAR) required to increase colonic and ear skin temperature was determined. At a Ta of 20 C, the threshold SAR for elevating colonic and ear skin temperature was 0.64 and 0.26 W/kg, respectively. At a Ta of 30 C, the threshold SARs were slightly less than at 20 C, with values of 0.26 W/kg for elevating colonic temperature and 0.19 W/kg for elevating ear skin temperature. The relationship between heat load and elevation in deep body temperature shown in the study at 600 MHz is similar to past studies that employed much-higher frequencies of RF radiation (2450-2884 MHz).

  18. 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.

  19. 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.

  20. Dynamic Fracture Initiation Toughness at Elevated Temperatures With Application to the New Generation of Titanium Aluminide Alloys. Chapter 8

    NASA Technical Reports Server (NTRS)

    Shazly, Mostafa; Prakash, Vikas; Draper, Susan; Shukla, Arun (Editor)

    2006-01-01

    Recently, a new generation of titanium aluminide alloy, named Gamma-Met PX, has been developed with better rolling and post-rolling characteristics. I'revious work on this alloy has shown the material to have higher strengths at room and elevated temperatures when compared with other gamma titanium aluminides. In particular, this new alloy has shown increased ductility at elevated temperatures under both quasi-static and high strain rate uniaxial compressive loading. However, its high strain rate tensile ductility at room and elevated temperatures is limited to approx. 1%. In the present chapter, results of a study to investigate the effects of loading rate and test temperature on the dynamic fracture initiation toughness in Gamma-Met PX are presented. Modified split Hopkinson pressure bar was used along with high-speed photography to determine the crack initiation time. Three-point bend dynamic fracture experiments were conducted at impact speeds of approx. 1 m/s and tests temperatures of up-to 1200 C. The results show that thc dynamic fracture initiation toughness decreases with increasing test temperatures beyond 600 C. Furthermore, thc effect of long time high temperature air exposure on the fracture toughness was investigated. The dynamic fracture initiation toughness was found to decrease with increasing exposure time. The reasons behind this drop are analyzed and discussed.

  1. 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.

  2. Stress induced by hooking, net towing, elevated sea water temperature and air in sablefish: Lack of concordance between mortality and physiological measures of stress

    USGS Publications Warehouse

    Davis, M.W.; Olla, B.L.; Schreck, C.B.

    2001-01-01

    In a series of laboratory studies designed to simulate bycatch processes, sablefish Anoplopoma fimbria were either hooked for up to 24 h or towed in a net for 4 h and then subjected to an abrupt transfer to elevated sea water temperature and air. Mortality did not result from hooking or net towing followed by exposure to air, but increased for both capture methods as fish were exposed to elevated temperatures, reflecting the magnifying effect of elevated temperature on mortality. Hooking and exposure to air resulted in increased plasma cortisol and lactate concentrations, while the combination of hooking and exposure to elevated temperature and air resulted in increased lactate and potassium concentrations. In fish that were towed in a net and exposed to air, cortisol, lactate, potassium and sodium concentrations increased, but when subjected to elevated temperature and air, no further increases occurred above the concentrations induced by net towing and air, suggesting a possible maximum of the physiological stress response. The results suggest that caution should be exercised when using physiological measures to quantify stress induced by capture and exposure to elevated temperature and air, that ultimately result in mortality, since the connections between physiological stress and mortality in bycatch processes remain to be fully understood.

  3. 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.

  4. Gasket performance of SWG in ROTT and short term estimation at elevated temperature

    SciTech Connect

    Asahina, M.; Nishida, T.; Yamanaka, Y.

    1996-12-01

    This paper deals with the sealability at room temperature and the durability at elevated temperature of SWG (spiral wound gasket). The fillers in the gasket specimens are chosen as newly developed non-asbestos, asbestos and flexible graphite. The effects of inner and outer rings inserted in the gasket specimens on the new PVRC gaskets constants are examined by using the ROTT test procedure (room temperature tightness test). The durability of SWG at elevated temperature is estimated by using the weight loss of filler and the stress-deflection curve of SWG obtained after aging at elevated temperatures. As a result, the sealability and the durability of newly developed non-asbestos SWG is the same as asbestos SWG, and the durability of flexible graphite SWG at elevated temperatures in this method conform to the boundary temperature in field and it is shown that this method is available to estimate the durability of gaskets at elevated temperatures.

  5. 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

  6. 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

  7. Effects of elevated CO 2 and temperature on monoterpene emission of Scots pine ( Pinus sylvestris L.)

    NASA Astrophysics Data System (ADS)

    Räisänen, Tommi; Ryyppö, Aija; Kellomäki, Seppo

    2008-06-01

    The aim of this study was to evaluate the long-term (5 years) effects of elevated CO2 concentration (doubling of ambient CO2 concentration) and temperature (2-6 °C elevation) on the monoterpene emission of Scots pine (Pinus sylvestris L.) saplings (ca. 20 years old) grown in closed-top environmental chambers. The chamber treatments included: (1) ambient temperature and CO2, (2) ambient temperature and elevated CO2, (3) elevated temperature and ambient CO2, and (4) elevated temperature and elevated CO2. The variability of emissions during and after tree shoot growth was studied, and additionally the total cumulative emission of monoterpenes through a growing period (May-September) was estimated. When compared to the controls, the combination of elevated CO2 and temperature significantly increased normalized monoterpene emission rate for the whole growing period (+23%), whereas elevated CO2 had no significant effect (-4%), and elevated temperature even decreased (-41%) the emission rate. The increasing effect of the combination of elevated CO2 and temperature was strongest during shoot growth (+54%). After shoot growth, no significant differences in emission rate were found among the treatments. Emission modeling showed that the total amount of monoterpenes emitted from May to September was 2.38 mg gdw-1 in ambient conditions. The total emission in elevated CO2 was 5% greater and in elevated temperature 9% lesser than in ambient conditions. The combination of elevated CO2 and temperature increased the amount of emitted monoterpenes over the growing period by 126% compared to the total emission in ambient conditions.

  8. 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

  9. A National Assessment of Sea Level Rise Exposure Using Lidar Elevation Data

    NASA Astrophysics Data System (ADS)

    Strauss, B.; Kulp, S. A.; Tebaldi, C.

    2014-12-01

    The Third National Climate Assessment addressed sea level rise and aggravated coastal flood exposure in all regions, but was completed before high quality lidar-based elevation data became available throughout the entire coastal United States (excluding Alaska). Here we present what we believe to be the first full national assessment incorporating these data. The assessment includes tabulation of land less than 1-6 m above the local high tide line, and of a wide range of features sitting on that land, including total population, socially vulnerable population, housing, property value, road miles, power plants, schools, hospitals, and a wide range of other infrastructure and critical facilities, as well as EPA-listed facilities that are potential sources of contamination during floods or permanent inundation. Tabulations span from zip code to national levels. Notable patterns include the strong concentration of exposure across multiple scales, with a small number of states accounting for most of the total national exposure; and a small number of zip codes accounting for a large proportion of the exposure within many states. Additionally, different features show different exposure patterns; in one example, land and road miles have relatively high exposure but population and property have relatively low exposure in North Carolina. The assessment further places this exposure analysis in the context of localized sea level rise projections integrated with coastal flood risk.

  10. 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.

  11. 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

  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. PMID:25462972

  13. Parental exposure to elevated pCO2 influences the reproductive success of copepods

    PubMed Central

    Cripps, Gemma; Lindeque, Penelope; Flynn, Kevin

    2014-01-01

    Substantial variations are reported for egg production and hatching rates of copepods exposed to elevated carbon dioxide concentrations (pCO2). One possible explanation, as found in other marine taxa, is that prior parental exposure to elevated pCO2 (and/or decreased pH) affects reproductive performance. Previous studies have adopted two distinct approaches, either (1) expose male and female copepoda to the test pCO2/pH scenarios, or (2) solely expose egg-laying females to the tests. Although the former approach is more realistic, the majority of studies have used the latter approach. Here, we investigated the variation in egg production and hatching success of Acartia tonsa between these two experimental designs, across five different pCO2 concentrations (385–6000 µatm pCO2). In addition, to determine the effect of pCO2 on the hatching success with no prior parental exposure, eggs produced and fertilized under ambient conditions were also exposed to these pCO2 scenarios. Significant variations were found between experimental designs, with approach (1) resulting in higher impacts; here >20% difference was seen in hatching success between experiments at 1000 µatm pCO2 scenarios (2100 year scenario), and >85% at 6000 µatm pCO2. This study highlights the potential to misrepresent the reproductive response of a species to elevated pCO2 dependent on parental exposure. PMID:25221371

  14. Nicotine and elevated body temperature reduce the complexity of the genioglossus and diaphragm EMG signals in rats during early maturation

    NASA Astrophysics Data System (ADS)

    Akkurt, David; Akay, Yasemin M.; Akay, Metin

    2009-10-01

    In this paper, we examined the effect of nicotine exposure and increased body temperature on the complexity (dynamics) of the genioglossus muscle (EMGg) and the diaphragm muscle (EMGdia) to explore the effects of nicotine and hyperthermia. Nonlinear dynamical analysis of the EMGdia and EMGg signals was performed using the approximate entropy method on 15 (7 saline- and 8 nicotine-treated) juvenile rats (P25-P35) and 19 (11 saline- and 8 nicotine-treated) young adult rats (P36-P44). The mean complexity values were calculated over the ten consecutive breaths using the approximate entropy method during mild elevated body temperature (38 °C) and severe elevated body temperature (39-40 °C) in two groups. In the first (nicotine) group, rats were treated with single injections of nicotine enough to produce brain levels of nicotine similar to those achieved in human smokers (2.5 (mg kg-1)/day) until the recording day. In the second (control) group, rats were treated with injections of saline, beginning at postnatal 5 days until the recording day. Our results show that warming the rat by 2-3 °C and nicotine exposure significantly decreased the complexity of the EMGdia and EMGg for the juvenile age group. This reduction in the complexity of the EMGdia and EMGg for the nicotine group was much greater than the normal during elevated body temperatures. We speculate that the generalized depressive effects of nicotine exposure and elevated body temperature on the respiratory neural firing rate and the behavior of the central respiratory network could be responsible for the drastic decrease in the complexity of the EMGdia and EMGg signals, the outputs of the respiratory neural network during early maturation.

  15. Physiological ecology of desert biocrust moss following 10 years exposure to elevated CO2: evidence for enhanced photosynthetic thermotolerance

    USGS Publications Warehouse

    Coe, Kirsten K.; Belnap, Jayne; Grote, Edmund E.; Sparks, Jed P.

    2012-01-01

    In arid regions, biomes particularly responsive to climate change, mosses play an important biogeochemical role as key components of biocrusts. Using the biocrust moss Syntrichia caninervis collected from the Nevada Desert Free Air CO2 Enrichment Facility, we examined the physiological effects of 10 years of exposure to elevated CO2, and the effect of high temperature events on the photosynthetic performance of moss grown in CO2-enriched air. Moss exposed to elevated CO2 exhibited a 46% decrease in chlorophyll, a 20% increase in carbon and no difference in either nitrogen content or photosynthetic performance. However, when subjected to high temperatures (35–40°C), mosses from the elevated CO2 environment showed higher photosynthetic performance and photosystem II (PSII) efficiency compared to those grown in ambient conditions, potentially reflective of a shift in nitrogen allocation to components that offer a higher resistance of PSII to heat stress. This result suggests that mosses may respond to climate change in markedly different ways than vascular plants, and observed CO2-induced photosynthetic thermotolerance in S. caninervis will likely have consequences for future desert biogeochemistry.

  16. Physiological ecology of desert biocrust moss following 10 years exposure to elevated CO₂: evidence for enhanced photosynthetic thermotolerance.

    PubMed

    Coe, Kirsten K; Belnap, Jayne; Grote, Edmund E; Sparks, Jed P

    2012-04-01

    In arid regions, biomes particularly responsive to climate change, mosses play an important biogeochemical role as key components of biocrusts. Using the biocrust moss Syntrichia caninervis collected from the Nevada Desert Free Air CO₂ Enrichment Facility, we examined the physiological effects of 10 years of exposure to elevated CO₂, and the effect of high temperature events on the photosynthetic performance of moss grown in CO₂-enriched air. Moss exposed to elevated CO₂ exhibited a 46% decrease in chlorophyll, a 20% increase in carbon and no difference in either nitrogen content or photosynthetic performance. However, when subjected to high temperatures (35-40°C), mosses from the elevated CO₂ environment showed higher photosynthetic performance and photosystem II (PSII) efficiency compared to those grown in ambient conditions, potentially reflective of a shift in nitrogen allocation to components that offer a higher resistance of PSII to heat stress. This result suggests that mosses may respond to climate change in markedly different ways than vascular plants, and observed CO₂-induced photosynthetic thermotolerance in S. caninervis will likely have consequences for future desert biogeochemistry. PMID:22385156

  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. 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

  19. 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....

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

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 101 and IM 102 portable tanks; UN portable tanks; marine portable tanks conforming to 46 CFR part 64... 49 Transportation 2 2011-10-01 2011-10-01 false Bulk packaging for certain elevated temperature... Than Class 1 and Class 7 § 173.247 Bulk packaging for certain elevated temperature materials....

  1. 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....

  2. 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....

  3. 'Effects of Elevated Temperature on Dehalococcoides Dechlorination Performance and DNA and RNA Biomarker Abundance

    SciTech Connect

    Fletcher, Kelly E; Costanza, Jed; Cruz-Garcia, Claribel; Ramaswamy, Nivedhya; Pennell, Kurt; Loeffler, Frank E

    2011-01-01

    Coupling thermal treatment with microbial reductive dechlorination is a promising remedy for tetrachloroethene (PCE) and trichloroethene (TCE) contaminated source zones. Laboratory experiments evaluated Dehalococcoides (Dhc) dechlorination performance, viability, and biomarker gene (DNA) and transcript (mRNA) abundances during exposure to elevated temperatures. The PCE-dechlorinating consortia BDI and OW produced ethene when incubated at temperatures of 30 C, but vinyl chloride (VC) accumulated when cultures were incubated at 35 or 40 C. Cultures incubated at 40 C for less than 49 days resumed VC dechlorination following cooling; however, incubation at 45 C resulted in complete loss of dechlorination activity. Dhc 16S rRNA, bvcA, and vcrA gene abundances in cultures showing complete dechlorination to ethene at 30 C exceeded those measured in cultures incubated at higher temperatures, consistent with observed dechlorination activities. Conversely, biomarker gene transcript abundances per cell in cultures incubated at 35 and 40 C were generally at least one order-of-magnitude greater than those measured in ethene-producing cultures incubated at 30 C. Even in cultures accumulating VC, transcription of the vcrA gene, which is implicated in VC-to-ethene dechlorination, was up-regulated. Temperature stress caused the up-regulation of Dhc reductive dehalogenase gene expression indicating that Dhc gene expression measurements should be interpreted cautiously as Dhc biomarker gene transcript abundances may not correlate with dechlorination activity.

  4. 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.

  5. Dietary exposure to chlorpyrifos alters core temperature in the rat.

    PubMed

    Gordon, Christopher J; Padnos, Beth K

    2002-08-15

    Administration of the organophosphate pesticide chlorpyrifos (CHP) to the male rat at a dose of 25-80 mg/kg (p.o.) results in hypothermia followed by a delayed fever lasting for several days. These are high doses of CHP that cause marked cholinergic stimulation. It is important to understand if chronic exposure to CHP would evoke changes in thermoregulation that are comparable to the acute administration. Male rats of the Long-Evans strain were subjected to dietary treatment of 0, 1, or 5 mg/(kg day) CHP for 6 months. A limited amount of food was given per day to maintain body weight at 350 g. The constant body weight allowed for the regulation of a consistent dosage of CHP per kg body weight throughout the feeding period. Core temperature (T(a)) and motor activity (MA) were monitored by radio telemetric transmitters implanted in the abdominal cavity. After 5 months of treatment, T(c) and MA were monitored in undisturbed animals for 96 h. CHP at 5 mg/(kg day) led to a slight elevation in T(c) without affecting MA. The rats were then administered a challenge dose of CHP (30 mg/kg, p.o.) while T(c) and MA were monitored. Rats fed the 1 and 5 mg/kg CHP diets showed a significantly greater hypothermic response and reduction in MA following CHP challenge compared to controls. The restricted feeding schedule resulted in marked changes in the pattern of the circadian rhythm. Therefore, in another study, rats were treated ad libitum for 17 days with a CHP diet that resulted in a dosage of 7 mg CHP/(mg day). There was a significant increase in T(c) during the daytime but not during the night throughout most of the treatment period. Overall, chronic CHP was associated with a slight but significant elevation in T(c) and greater hypothermic response to a CHP challenge. This latter finding was unexpected and suggests that chronic exposure to CHP sensitizes the rat's thermoregulatory response to acute CHP exposure. PMID:12135625

  6. 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.

  7. Cryogenic and elevated temperature strengths of an Al-Zn-Mg-Cu alloy modified with Sc and Zr

    NASA Astrophysics Data System (ADS)

    Senkova, S. V.; Senkov, O. N.; Miracle, D. B.

    2006-12-01

    The effect of minor additions of Sc and Zr on tensile properties of two developmental Al-Zn-Mg-Cu alloys was studied in the temperature range -196°C to 300°C. Due to the presence of Sc and Zr in a fine dispersoid form, both low-temperature and elevated temperature strengths of these alloys are much higher than those of similar 7000 series alloys that do not contain these elements. After short holding times (up to 10 hours) at 205°C, the strength of these alloys is higher than those of high-temperature Al alloys 2219-T6 and 2618-T6; however, the latter alloys show better strength after longer holding times. It is suggested that additional alloying of the Sc-containing Al-Zn-Mg-Cu alloys with other dispersoid-forming elements, such as Ni, Fe, Mn, and Si, with a respective decrease in the amounts of Zn and Mg may further improve the elevated temperature strength and decrease the loss of strength with extended elevated temperature exposure.

  8. Reduction of the elevator illusion from continued hypergravity exposure and visual error-corrective feedback

    NASA Technical Reports Server (NTRS)

    Welch, R. B.; Cohen, M. M.; DeRoshia, C. W.

    1996-01-01

    Ten subjects served as their own controls in two conditions of continuous, centrifugally produced hypergravity (+2 Gz) and a 1-G control condition. Before and after exposure, open-loop measures were obtained of (1) motor control, (2) visual localization, and (3) hand-eye coordination. During exposure in the visual feedback/hypergravity condition, subjects received terminal visual error-corrective feedback from their target pointing, and in the no-visual feedback/hypergravity condition they pointed open loop. As expected, the motor control measures for both experimental conditions revealed very short lived underreaching (the muscle-loading effect) at the outset of hypergravity and an equally transient negative aftereffect on returning to 1 G. The substantial (approximately 17 degrees) initial elevator illusion experienced in both hypergravity conditions declined over the course of the exposure period, whether or not visual feedback was provided. This effect was tentatively attributed to habituation of the otoliths. Visual feedback produced a smaller additional decrement and a postexposure negative after-effect, possible evidence for visual recalibration. Surprisingly, the target-pointing error made during hypergravity in the no-visual-feedback condition was substantially less than that predicted by subjects' elevator illusion. This finding calls into question the neural outflow model as a complete explanation of this illusion.

  9. Reduction of the elevator illusion from continued hypergravity exposure and visual error-corrective feedback.

    PubMed

    Welch, R B; Cohen, M M; DeRoshia, C W

    1996-01-01

    Ten subjects served as their own controls in two conditions of continuous, centrifugally produced hypergravity (+2 Gz) and a 1-G control condition. Before and after exposure, open-loop measures were obtained of (1) motor control, (2) visual localization, and (3) hand-eye coordination. During exposure in the visual feedback/hypergravity condition, subjects received terminal visual error-corrective feedback from their target pointing, and in the no-visual feedback/hypergravity condition they pointed open loop. As expected, the motor control measures for both experimental conditions revealed very short lived underreaching (the muscle-loading effect) at the outset of hypergravity and an equally transient negative aftereffect on returning to 1 G. The substantial (approximately 17 degrees) initial elevator illusion experienced in both hypergravity conditions declined over the course of the exposure period, whether or not visual feedback was provided. This effect was tentatively attributed to habituation of the otoliths. Visual feedback produced a smaller additional decrement and a postexposure negative after-effect, possible evidence for visual recalibration. Surprisingly, the target-pointing error made during hypergravity in the no-visual-feedback condition was substantially less than that predicted by subjects' elevator illusion. This finding calls into question the neural outflow model as a complete explanation of this illusion. PMID:8668516

  10. Response of sunshine bass to ration at elevated culture temperature

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Temperature and ammonia increase dramatically during summer production of sunshine bass. Global temperatures are projected to increase. A factorial experiment investigated the effects of three digestible protein (DP; 33, 40, 47%), two lipid (L; 10, 18 %) and two ration levels (satiation, restricted)...

  11. Tensile failure behavior of plain carbon steels at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Wray, P. J.

    1984-11-01

    The onset of tensile instability and the occurrence of fracture in plain carbon steels containing up to 1.89C has been examined in the temperature range 500 to 1300 °C and the strain-rate range 6 X lO-6 to 2 × 10-2 s-1. In the ferrite-plus-pearlite mixtures at temperatures below the eutectoid temperature, the work-hardening exponent decreases with increasing amount of pearlite, and there is a corresponding decrease in the Considére strain. However, the onset of necking is delayed to well beyond the Considére strain, and these mixtures are inherently ductile even at the eutectoid composition. In the austenite region, the general intrusion of dynamic recrystallization compctes with intergranular embrittlement at temperatures below about 1050 °C. The embrittlement is related to precipitation which takes place either during cooling (MnS) or at the deformation temperature [AIN, Nb (CN), etc.]. In hypereutectoid steels, the ductility of austenite-plus-cementite and pearlite-plus-cementite mixtures diminishes drastically with decreasing temperature and increasing amount of cementite. The areas of possible fracture modes are mapped in temperature-strain rate and temperature-carbon content space.

  12. Elevated Temperature Fatigue Endurance of Three Ceramic Matrix Composites

    NASA Technical Reports Server (NTRS)

    Kalluri, Sreeramesh; Verrilli, Michael J.

    2007-01-01

    High-cycle fatigue endurance of three candidate materials for the acoustic liners of the Enabling Propulsion Materials Nozzle Program was investigated. The ceramic matrix composite materials investigated were N720/AS (Nextel 720, 3M Corporation), Sylramic S200 (Dow Corning), and UT 22. High-cycle fatigue tests were conducted in air at 910 C on as-machined specimens and on specimens subjected to tensile cyclic load excursions every 160 hr followed by thermal exposure at 910 C in a furnace up to total exposure times of 2066 and 4000 hr. All the fatigue tests were conducted in air at 100 Hz with a servohydraulic test machine. In the as-machined condition, among the three materials investigated only the Sylramic S200 exhibited a deterministic type of high-cycle fatigue behavior. Both the N720/AS and UT-22 exhibited significant scatter in the experimentally observed high-cycle fatigue lives. Among the thermally exposed specimens, N720/AS and Sylramic S200 materials exhibited a reduction in the high-cycle fatigue lives, particularly at the exposure time of 4000 hr.

  13. The effects of elevated temperature and humidity on rectal temperature and respiration rate in the New Zealand white rabbit

    NASA Astrophysics Data System (ADS)

    Kasa, W.; Thwaites, C. J.

    1990-09-01

    In 2 replicated factorial experiments, 7-h climate chamber exposures were used to study the responses of adult NZW rabbits to a range of elevated temperatures and humidities. At 18 mm Hg water vapour pressure, 23.8° C was well tolerated, rectal temperature (RT) and respiration rate (RR) averaging 38.6±0.3° C and 82.9±15.5 breaths/min, respectively. Both parameters were elevated ( P<0.001) at 32.2°, 37.8° and 43.3° C. RT and RR reached plateau levels of 39.5 40.1° C and 410 460/min at 32.2° C, which was tolerated for the full 7-h test period. Test temperatures of 37.8° and 43.3° C, on the other hand, could be tolerated for only 80 and 40 min respectively, before RT reached the safe upper limit of 41.7° C. Final RR values at 37.8° and 43.3° C were 701.6±42.7 and 812±55.1/min, respectively. In a 34.5° C atmosphere a humidity of 21 mm Hg water vapour pressure was classified as “dry”, and was tolerated for 323±123 min. RT and RR increased by 0.6° C and 316/min during the first 20 min of exposure ( P<0.05). Thereafter both parameters increased progressively, but with no significant differences between successive recording periods, until RR reached 550.3±88.8/min at 41.7° C RT. Humidities of 25, 29 and 33 mm Hg water vapour pressure were, on the other hand, classified as “wet” and were tolerated for only 92±22, 81±16 and 119±50 min, respectively. RR at the times that RT reached 41.7° C at these 3 humidities was 732±26, 789±30 and 764±23/min, respectively. The results point to the likelihood that thermal stress will adversely affect the productivity and welfare of NZW rabbits in the tropics unless adequate housing environments are provided. Significant between-individual phenotypic differences in heat tolerance suggest the need for genetic studies of the possibility of selecting for improved heat tolerance.

  14. 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.

  15. Fatigue crack growth behavior of Ti-1100 at elevated temperature

    SciTech Connect

    Maxwell, D.C.; Nicholas, T.

    1995-12-31

    Effects of temperature, frequency, and cycles with superimposed hold times are evaluated in Ti-1100 in order to study the complex creep-fatigue-environment interactions in this material. Crack growth rate tests conducted at cyclic loading frequency of 1.0 Hz show that raising the temperature from 593 to 650 C has only a slightly detrimental effect on crack growth rate, although these temperatures produce growth rates significantly higher than at room temperature. From constant {Delta}K tests, the effects of temperature at constant frequency show a minimum crack growth rate at 250 C. From the minimum crack growth rate at 250 C, the crack growth rate increases linearly with temperature. Increases in frequency at constant temperatures of 593 and 650 C produce a continuous decrease in growth rate in going from 0.001 to 1.0 Hz, although the behavior is primarily cycle dependent in this region. Tests at 1.0 Hz with superimposed hold times from 1 to 1,000 s are used to evaluate creep-fatigue-environment interactions. Hold times at maximum load are found to initially decrease and then increase the cyclic crack growth rate with increasing duration. This is attributed to crack-tip blunting during short hold times and environmental degradation at long hold times. Hold times at minimum load show no change in growth rates, indicating that there is no net environmental degradation to the bulk material beyond that experienced during the baseline 1 Hz cycling.

  16. 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. PMID:22325572

  17. 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. PMID:25261070

  18. 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.

  19. 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).

  20. Elevated temperature creep behavior of Inconel alloy 625

    SciTech Connect

    Purohit, A.; Burke, W.F.

    1984-07-01

    Inconel 625 in the solution-annealed condition has been selected as the clad material for the fuel and control rod housing assemblies of the Upgraded Transient Reactor Test Facility (TREAT Upgrade or TU). The clad is expected to be subjected to temperatures up to about 1100/sup 0/C. Creep behavior for the temperature range of 800/sup 0/C to 1100/sup 0/C of Inconel alloy 625, in four distinct heat treated conditions, was experimentally evaluated.

  1. Anomalous ultrasonic attenuation in ferritic steels at elevated temperatures.

    PubMed

    Hutchinson, Bevis; Lundin, Peter; Lindh-Ulmgren, Eva; Lévesque, Daniel

    2016-07-01

    An unexpected peak in attenuation has been observed at ∼800°C when heating low carbon steels in a laser-ultrasonic instrument. An explanation is given in terms of enhanced crystalline anisotropy with increasing temperature in the bcc ferrite range combined with subsequent transformation to austenite at still higher temperatures. An analysis based on theoretical models of attenuation in the Rayleigh regime is in good agreement with the experimental observations. PMID:27015796

  2. 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.

  3. 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.

  4. Exposure to low levels of hydrogen sulfide elevates circulating glucose in maternal rats

    SciTech Connect

    Hayden, L.J.; Goeden, H.; Roth, S.H. )

    1990-09-01

    Although the lethal effect of hydrogen sulfide (H{sub 2}S) has long been known, the results of exposure to low levels of H{sub 2}S have not been well documented. Rat dams and pups were exposed to low levels of H{sub 2}S (less than or equal to 75 ppm) from d 1 of gestation until d 21 postpartum and analyzed for changes in circulating enzymatic activity and metabolites. Blood glucose was significantly elevated in maternal blood on d 21 postpartum at all exposure levels. This increase in glucose was accompanied by a possible decrease in serum triglyceride in the pups and in the dams on d 21 postpartum. There was no evidence of alterations in serum alkaline phosphatase, lactate dehydrogenase, or serum glutamate oxaloacetate transaminase.

  5. 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.

  6. Diamond structure recovery during ion irradiation at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Deslandes, Alec; Guenette, Mathew C.; Belay, Kidane; Elliman, Robert G.; Karatchevtseva, Inna; Thomsen, Lars; Riley, Daniel P.; Lumpkin, Gregory R.

    2015-12-01

    CVD diamond is irradiated by 5 MeV carbon ions, with each sample held at a different temperature (300-873 K) during irradiations. The defect structures resulting from the irradiations are evident as vacancy, interstitial and amorphous carbon signals in Raman spectra. The observed variation of the full width at half maximum (FWHM) and peak position of the diamond peak suggests that disorder in the diamond lattice is reduced for high temperature irradiations. The dumbbell interstitial signal is reduced for irradiations at 873 K, which suggests this defect is unstable at these temperatures and that interstitials have migrated to crystal surfaces. Near edge X-ray absorption fine structure (NEXAFS) spectroscopy results indicate that damage to the diamond structure at the surface has occurred for room temperature irradiations, however, this structure is at least partially recovered for irradiations performed at 473 K and above. The results suggest that, in a high temperature irradiation environment such as a nuclear fusion device, in situ annealing of radiation-created defects can maintain the diamond structure and prolong the lifetime of diamond components.

  7. 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.

  8. 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.

  9. Simplified Analysis Methods for Primary Load Designs at Elevated Temperatures

    SciTech Connect

    Carter, Peter; Jetter, Robert I; Sham, Sam

    2011-01-01

    The use of simplified (reference stress) analysis methods is discussed and illustrated for primary load high temperature design. Elastic methods are the basis of the ASME Section III, Subsection NH primary load design procedure. There are practical drawbacks with this approach, particularly for complex geometries and temperature gradients. The paper describes an approach which addresses these difficulties through the use of temperature-dependent elastic-perfectly plastic analysis. Correction factors are defined to address difficulties traditionally associated with discontinuity stresses, inelastic strain concentrations and multiaxiality. A procedure is identified to provide insight into how this approach could be implemented but clearly there is additional work to be done to define and clarify the procedural steps to bring it to the point where it could be adapted into code language.

  10. 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. PMID:17801532

  11. 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.

  12. Elevated atmospheric C02 concentration and temperature across an urban-rural transect

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The heat island effect and the high use of fossil fuels in large city centers are well documented, but by how much fossil fuel consumption is elevating atmospheric CO2 concentrations and whether elevations in both atmospheric CO2 and air temperature are consistent from year to year are less well kno...

  13. Response of sugarcane sucrose yields 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...

  14. Heat transfer in quartz, orthoclase, and sanidine at elevated temperature

    NASA Astrophysics Data System (ADS)

    Höfer, M.; Schilling, F.

    The thermal diffusivity of quartz, orthoclase, and sanidine was measured in different directions by a transient method, to determine the second-rank tensor of thermal transport properties as a function of temperature up to 800 °C. Thermal diffusivity of phonons is described as D=1/3 v l, where v is the phonon velocity and l the mean free path length of phonons. In quartz the thermal diffusivity at room temperature is 3.60 mm2 s-1 in [1 0 0] and 7.00 mm2 s-1 in [0 0 1] direction. A 1/T dependency of thermal diffusivity is observed for both directions up to 550 °C with a pronounced anisotropy (A=62% A=(Dmax - Dmin)/Daverage), which decreases with increasing temperature. Close to the α-β-phase transition, we observed a minimum in thermal diffusivity and a negligible anisotropy. Up to 573 °C the maximam of thermal diffusivity, average phonon velocity, and mean free path length are observed in [0 0 1] direction. However, above the temperature of phase transition the maximum values of the properties are observed in [1 0 0] direction. The observed behavior is explained by a model which interrelates velocity and mean free path length of phonons. A further contribution to the thermal diffusivity behavior is related to the higher symmetry of β-quartz, resulting in a reduced phonon-phonon-scattering probability. At ambient temperature, orthoclase and sanidine show similar values of thermal diffusivities ( 1 mm2 s-1) and a temperature-independent anisotropy behavior between 22 and 350 °C of 30%. For both feldspars a small 1/T temperature dependence of thermal diffusivity up to 350 °C is observed. The transparent sanidine in gemstone quality shows a strong increase in thermal diffusivity above 350 °C proportional to T 3. The contribution of the radiative heat-transfer mechanism leads to values more than two times higher in sanidine than in a milky-cloudy orthoclase at 800 °C. For the feldspars the mean free path length of phonons shows a small temperature dependence

  15. Exposures to environmental phenols in Southern California firefighters and findings of elevated urinary benzophenone-3 levels.

    PubMed

    Waldman, Jed M; Gavin, Qi; Anderson, Meredith; Hoover, Sara; Alvaran, Josephine; Ip, Ho Sai Simon; Fenster, Laura; Wu, Nerissa T; Krowech, Gail; Plummer, Laurel; Israel, Leslie; Das, Rupali; She, Jianwen

    2016-03-01

    Firefighters are at increased risk for exposure to toxic chemicals compared to the general population, but few studies of this occupational group have included biomonitoring. We measured selected phenolic chemicals in urine collected from 101 Southern California firefighters. The analytes included bisphenol A (BPA), triclosan, benzophenone-3 (BP-3), and parabens, which are common ingredients in a range of consumer products. BP-3, BPA, triclosan, and methyl paraben were detected in almost all study subjects (94-100%). The BP-3 geometric mean for firefighters was approximately five times higher than for a comparable National Health and Nutrition Examination Survey (NHANES) subgroup. Demographic and exposure data were collected from medical records and via a questionnaire, and covariates were examined to assess associations with BP-3 levels. BP-3 levels were elevated across all firefighter age groups, with the highest levels observed in the 35 to 39year old group. Body fat percentage had a significant inverse association with BP-3 concentrations. Our results indicate pervasive exposure to BP-3, BPA, triclosan, and methyl paraben in this population of firefighters, consistent with studies of other populations. Further research is needed to investigate possible explanations for the higher observed BP-3 levels, such as occupational or California-specific exposures. PMID:26821331

  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. 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.

  18. 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.

  19. An uncoupled viscoplastic constitutive model for metals at elevated temperature

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.; Cronenworth, J.

    1983-01-01

    An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior is presented. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modeled in an incremental form with a yield function, flow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modeled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model is performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.

  20. 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.

  1. 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...

  2. 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 . PMID:26728638

  3. Exothermic and thermal runaway behaviour of some ionic liquids at elevated temperatures.

    PubMed

    Vijayaraghavan, R; Surianarayanan, M; Armel, V; MacFarlane, D R; Sridhar, V P

    2009-11-01

    The exothermic behaviour and intrinsic safety of a number of ionic liquids being considered for battery and solar cell applications have been investigated at elevated temperatures by analysing data from accelerated rate calorimetric (ARC) studies. PMID:19826700

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Enhanced thermoelectric performance of carbon nanotubes at elevated temperature.

    PubMed

    Jiang, P H; Liu, H J; Fan, D D; Cheng, L; Wei, J; Zhang, J; Liang, J H; Shi, J

    2015-11-01

    The electronic and transport properties of the (10, 0) single-walled carbon nanotube are studied by performing first-principles calculations and semi-classical Boltzmann theory. It is found that the (10, 0) tube exhibits a considerably large Seebeck coefficient and electrical conductivity which are highly desirable for good thermoelectric materials. Together with the lattice thermal conductivity predicted by non-equilibrium molecular dynamics simulations, the room temperature ZT value of the (10, 0) tube is estimated to be 0.15 for p-type carriers. Moreover, the ZT value exhibits strong temperature dependence and can reach to 0.77 at 1000 K. Such a ZT value can be further enhanced to as high as 1.9 by isotopic substitution and chemisorptions of hydrogen on the tube surface. PMID:26426972

  10. 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.

  11. 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.

  12. 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

  13. Computation of induced electric field and temperature elevation in human due to lightning current

    NASA Astrophysics Data System (ADS)

    Nagai, T.; Hirata, A.

    2010-05-01

    The present study investigated induced electric field and temperature elevation in specific tissues/organs of an anatomically based human body model for the lightning current. The threshold amplitude of the current inducing ventricular fibrillation and skin burning are estimated from computed induced electric field and temperature elevation with formulas for electrical stimulation and thermal damage. The computational results obtained herein were reasonably consistent with clinical observation.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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.

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

    DOE PAGESBeta

    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

  1. HINDERED DIFFUSION OF ASPHALTENES AT ELEVATED TEMPERATURE AND PRESSURE

    SciTech Connect

    James A. Guin; Ganesh Ramakrishnan; Keiji Asada

    2000-04-07

    During this past six months we continued our ongoing studies of the diffusion controlled uptake of coal and petroleum asphaltenes into a porous carbon catalyst. Toluene was used as the solvent for experiments at 20 C and 75 C while 1-methylnaphthalene was the solvent for the higher temperature experiments at 100 C, 150 C and 250 C. All runs were made at a pressure of 250 psi (inert He gas). Experiments were performed at 20 C and 75 C, for the petroleum asphaltene/toluene system. For the coal asphaltene/toluene system, experiments were performed at 75 C. Experiments were performed at 100 C, 150 C and 250 C for the coal asphaltene/1-methylnaphthalene system. A comparison between the experimental data and model simulated data showed that the mathematical model satisfactorily fitted the adsorptive diffusion of both the coal and petroleum asphaltenes onto a porous activated carbon. The adsorption constant decreases with an increase in temperature for both, the coal asphaltene/1-methylnaphthalene system as well as the petroleum asphaltene/toluene system. It was found that the adsorption constant for the coal asphaltene/toluene system at 75 C was much higher than that of the petroleum asphaltene/toluene system at the same temperature providing evidence of the greater affinity of the coal asphaltenes for the carbon surface. This could be due to the presence of more functional heteroatomic groups in the coal asphaltenes compared to their petroleum counterparts. Also during this time period, a new carbon catalyst support was prepared in our laboratory which will be used in adsorption experiments during the next phase of work.

  2. Exposure to Elevated Carbon Monoxide Levels at an Indoor Ice Arena--Wisconsin, 2014.

    PubMed

    Creswell, Paul D; Meiman, Jon G; Nehls-Lowe, Henry; Vogt, Christy; Wozniak, Ryan J; Werner, Mark A; Anderson, Henry

    2015-11-20

    On December 13, 2014, the emergency management system in Lake Delton, Wisconsin, was notified when a male hockey player aged 20 years lost consciousness after participation in an indoor hockey tournament that included approximately 50 hockey players and 100 other attendees. Elevated levels of carbon monoxide (CO) (range = 45 ppm-165 ppm) were detected by the fire department inside the arena. The emergency management system encouraged all players and attendees to seek medical evaluation for possible CO poisoning. The Wisconsin Department of Health Services (WDHS) conducted an epidemiologic investigation to determine what caused the exposure and to recommend preventive strategies. Investigators abstracted medical records from area emergency departments (EDs) for patients who sought care for CO exposure during December 13-14, 2014, conducted a follow-up survey of ED patients approximately 2 months after the event, and conducted informant interviews. Ninety-two persons sought ED evaluation for possible CO exposure, all of whom were tested for CO poisoning. Seventy-four (80%) patients had blood carboxyhemoglobin (COHb) levels consistent with CO poisoning; 32 (43%) CO poisoning cases were among hockey players. On December 15, the CO emissions from the propane-fueled ice resurfacer were demonstrated to be 4.8% of total emissions when actively resurfacing and 2.3% when idling, both above the optimal range of 0.5%-1.0%. Incomplete fuel combustion by the ice resurfacer was the most likely source of elevated CO. CO poisonings in ice arenas can be prevented through regular maintenance of ice resurfacers, installation of CO detectors, and provision of adequate ventilation. PMID:26583915

  3. 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.

  4. 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.

  5. Hardness of irradiated poly(methyl methacrylate) at elevated temperatures

    SciTech Connect

    Lu, K.-P.; Lee, Sanboh; Cheng, Cheu Pyeng

    2001-08-15

    The decrease in hardness induced by gamma irradiation in poly(methyl methacrylate) (PMMA) has been investigated. The hardness is assumed to decrease linearly with the concentration of radiation-induced defects. Annealing at high temperatures induces defect annihilation as tracked by an increase in hardness. The annihilation follows first-order kinetics during isothermal annealing. The dependence of hardness on the reciprocal of the time constant satisfies the Arrhenius equation, and the corresponding activation energy of the kinetic process decreases with increasing dose. The hardness of postannealed PMMA decreases linearly with increasing dose. {copyright} 2001 American Institute of Physics.

  6. 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.

  7. 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.

  8. 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.

  9. HINDERED DIFFUSION OF ASPHALTENES AT ELEVATED TEMPERATURE AND PRESSURE

    SciTech Connect

    James A. Guin; Ganesh Ramakrishnan; Keiji Asada; Brian Mosley

    2000-09-29

    During this time period work proceeded in two main areas, the performance and analysis of petroleum asphaltene diffusional uptake experiments at 325 C and the preparation and testing of some new carbon based catalysts. In the first area, we performed studies of the diffusion controlled uptake of petroleum asphaltenes into a porous carbon catalyst at 325 C. The experiments were performed under an inert He atmosphere using 1-methylnaphthalene as a solvent. These purpose of these experiments was to extend our previous data which was taken and reported in the prior semi-annual report. These previous experiments were performed only up to a temperature of 250 C. A comparison between the experimental data and model simulated data showed that the mathematical model satisfactorily fitted the adsorptive diffusion of the petroleum asphaltenes onto the porous carbon at 325 C. Comparing with previous results, the adsorption constant continued to decrease with an increase in temperature for the petroleum asphaltene/1-methylnaphthalene system. Also during this time period, some carbon catalyst supports were prepared in our laboratory and several sets of data were obtained in adsorption-diffusion uptake experiments using a petroleum asphaltene with toluene as solvent. These data are presented in this report, although, complete fitting of the data with the mathematical model has not yet been performed. These calculations will be performed during the next time period.

  10. Preliminary investigation of the compressive strength and creep lifetime of 2024-T3 (formerly 24S-T3) aluminum-alloy plates at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E; Deveikis, William D

    1955-01-01

    The results of elevated-temperature compressive strength and creep tests of 2024-T3 (formerly 23S-T3) aluminum-alloy plates supported in V-grooves are presented. For determining elevated-temperature strength, where creep effects are negligible, a relation previously developed for predicting plate compressive strength at room temperature was satisfactory. Creep-lifetime results are presented for the plates in the form of master creep-lifetime curves by using a time-temperature parameter that is convenient for summarizing tensile creep-rupture data. A comparison is made between tensile and compressive creep lifetime for the plates, and the magnitude by which the design stress is decreased because of material creep and loss of strength due to exposure at elevated temperatures is indicated.