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Peak Temperature (peak + temperature)
Selected AbstractsSynchronous peak Barrovian metamorphism driven by syn-orogenic magmatism and fluid flow in southern Connecticut, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008P. J. LANCASTER Abstract Recent work in Barrovian metamorphic terranes has found that rocks experience peak metamorphic temperatures across several grades at similar times. This result is inconsistent with most geodynamic models of crustal over-thickening and conductive heating, wherein rocks which reach different metamorphic grades generally reach peak temperatures at different times. Instead, the presence of additional sources of heat and/or focusing mechanisms for heat transport, such as magmatic intrusions and/or advection by metamorphic fluids, may have contributed to the contemporaneous development of several different metamorphic zones. Here, we test the hypothesis of temporally focussed heating for the Wepawaug Schist, a Barrovian terrane in Connecticut, USA, using Sm,Nd ages of prograde garnet growth and U,Pb zircon crystallization ages of associated igneous rocks. Peak temperature in the biotite,garnet zone was dated (via Sm,Nd on garnet) at 378.9 ± 1.6 Ma (2,), whereas peak temperature in the highest grade staurolite,kyanite zone was dated (via Sm,Nd on garnet rims) at 379.9 ± 6.8 Ma (2,). These garnet ages suggest that peak metamorphism was pene-contemporaneous (within error) across these metamorphic grades. Ion microprobe U,Pb ages for zircon from igneous rocks hosted by the metapelites also indicate a period of syn-metamorphic peak igneous activity at 380.6 ± 4.7 Ma (2,), indistinguishable from the peak ages recorded by garnet. A 388.6 ± 2.1 Ma (2,) garnet core age from the staurolite,kyanite zone indicates an earlier episode of growth (coincident with ages from texturally early zircon and a previously published monazite age) along the prograde regional metamorphic T,t path. The timing of peak metamorphism and igneous activity, as well as the occurrence of extensive syn-metamorphic quartz vein systems and pegmatites, best supports the hypothesis that advective heating driven by magmas and fluids focussed major mineral growth into two distinct episodes: the first at c. 389 Ma, and the second, corresponding to the regionally synchronous peak metamorphism, at c. 380 Ma. [source] Electrospun Silk Fibroin Mats for Tissue EngineeringENGINEERING IN LIFE SCIENCES (ELECTRONIC), Issue 3 2008A. Alessandrino Abstract Processing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set-up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES-SF) mats. Using SEM it was found that the ES-SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5,% w/v SF solution in formic acid, with an electric field of 2.4,kV/cm and a spinneret-collector distance of 10,cm. FT-IR and DSC analyses were performed to investigate the structure of the ES-SF mats before and after immersion in methanol for different times (5, 10, and 15,min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the ,-sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT-IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES-SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7,days at 37,°C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1,day and cell confluence at 7,days. Alamar blue test demonstrated that there were very low differences between cell viability on ES-SF mats and the tissue culture plastic control. [source] Iron Status: A Possible Risk Factor for the First Febrile SeizureEPILEPSIA, Issue 7 2002Azhar S. Daoud Summary: ,Purpose: We conducted a controlled study to investigate the relation of iron status and first febrile seizure (FFS). Methods: Measures of iron sufficiency including hemoglobin concentration (HB), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), and plasma ferritin (PF) were prospectively measured in 75 children with FFS and compared with 75 controls matched for age and sex with febrile illnesses without convulsions. Results: Mean ferritin level was significantly lower in cases with FFS (29.5 ± 21.3 ,g/L) than in controls (53.3 ± 37.6 ,g/L) with p = 0.0001. The proportion of subjects with a PF level ,30 ,g/L was significantly higher among children with FFS (49 of 75 vs. 24 of 75) than in controls (p = 0.000). Mean levels of HB, MCV, and MCH also were lower among FFS cases, but differences failed to attain statistical significance. A higher proportion of cases with FFS had an HB <110 g/L, MCV <72 fL, and MCH <24 pg than did the controls, but the differences were not statistically significant. There were no statistically significant differences between the cases and the controls in the mean peak temperature on admission, types of underlying illness, or family history of epilepsy and of febrile convulsion. Conclusions: PF level was significantly lower in children with FFS than in the reference group, suggesting a possible role for iron insufficiency in FFS. [source] Effect of Ce, Sb, and Sn on Solarization and Crystallization of an X-Ray-Irradiated Photosensitive GlassINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2010Mohamad Hassan Imanieh The effect of Ce, Sb, and Sn photosensitive elements, individually and in combination with each other, on solarization and crystallization of an X-ray irradiated and a nonirradiated lithium silicate-based glass were investigated. According to the results, considering the crystallization behavior of the nonirradiated glasses, they were divided into Ce-bearing and Ce-free groups, in which the former group showed a clearer solarization tendency that manifested as an appearance of an absorbance peak at 318 nm in the spectrophotometry experiment. However, the results showed that in the irradiated glasses, the presence of Sb was more important in terms of improvement in crystallization view. Antimony decreased the differential thermal analysis (DTA) crystallization peak temperature from 655°C to 594°C and, in combination with the two other elements, changed the surface crystallization mechanism to a bulk one. The reactions that seemed to be responsible for the above-mentioned observations were discussed by spectrophotometry, DTA, X-ray diffraction, and scanning electron microscopic methods. [source] Injectable acrylic bone cements for vertebroplasty with improved propertiesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2004Raúl García Carrodeguas Abstract Currently commercially available acrylic bone cements lack adequate radiopacity and viscosity when they are used in percutaneous vertebroplasty (PVP). In this work improved formulations of radiopaque and injectable poly(methyl methacrylate) bone cements were prepared with different amounts (10,50 wt.%) of BaTiO3 or SrTiO3 particles as the radiopaque agent. Two sets of cements were prepared by using untreated or silanated radiopaque particles, respectively. The influence of the content and nature of the radiopaque agent as well as its silanation with 3-(trimethoxysilyl) propyl methacrylate (,-MPS), on the curing parameters, residual monomer content, radiopacity, mechanical properties, and injectability of the resulting materials, was examined. Doughing and setting times, maximum temperature, and compressive strength of all formulations fulfilled the requirements of standard specifications, with values of peak temperature in the range 57,72 °C and those of compressive strength between 114 and 135 MPa. Formulations containing at least 20 wt.% BaTiO3 or SrTiO3 had radiopacities equal to or greater than that corresponding to 2 mm of Al as required for surgical plastics. Injectability of any of the formulations provided 75,80 wt.% of the total mass manually injected through a conventional biopsy needle 4 min after mixing. Silanation of the BaTiO3 or SrTiO3 particles led to formulations with improved mechanical properties and injectability compared to those obtained with the untreated fillers. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 94,104, 2004 [source] Characterization of new acrylic bone cements prepared with oleic acid derivativesJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2002Blanca Vázquez Abstract Acrylic bone-cement formulations were prepared with the use of a new tertiary aromatic amine derived from oleic acid, and also by incorporating an acrylic monomer derived from the same acid with the aim of reducing the leaching of toxic residuals and improving mechanical properties. 4-N,N dimethylaminobenzyl oleate (DMAO) was used as an activator in the benzoyl-peroxide radical cold curing of polymethyl methacrylate. Cements that contained DMAO exhibited much lower polymerization exotherm values, ranging between 55 and 62 °C, with a setting time around 16,17 min, depending on the amine/BPO molar ratio of the formulation. On curing a commercial bone cement, Palacos® R with DMAO, a decrease of 20 °C in peak temperature and an increase in setting time of 7 min were obtained, the curing parameters remaining well within limits permitted by the standards. In a second stage, partial substitution of MMA by oleyloxyethyl methacrylate (OMA) in the acrylic formulations was performed, the polymerization being initiated with the DMAO/BPO redox system. These formulations exhibited longer setting times and lower peak temperatures with respect to those based on PMMA. The glass transition temperature of the experimental cements were lower than that of PMMA cement because of the presence of long aliphatic chains of both activator and monomer in the cement matrix. Number average molecular weights of the cured cements were in the range of 1.2×105. PMMA cements cured with DMAO/BPO revealed a significant (p<0.001) increase in the strain to failure and a significant (p<0.001) decrease in Young's modulus in comparison to Palacos® R, whereas ultimate tensile strength remained unchanged. When the monomer OMA was incorporated, low concentrations of OMA provided a significant increase in tensile strength and elastic modulus without impairing the strain to failure. The results demonstrate that the experimental cements based on DMAO and OMA have excellent promise for use as orthopaedic and/or dental grouting materials. © 2002 Wiley Periodicals, Inc. J Biomed Mater Res (Appl Biomater) 63: 88,97, 2002; DOI 10.1002/jbm.10092 [source] NONCONTACT TEMPERATURE MONITORING OF A PELLETING PROCESS USING INFRARED THERMOGRAPHYJOURNAL OF FOOD PROCESS ENGINEERING, Issue 1 2007C. SALAS-BRINGAS ABSTRACT Contact methods are commonly used to determine temperature during food and feed manufacturing processes. This may, however, result in incorrect temperature measurements, because many food and feed materials easily agglomerate around the thermowell tip of the sensors, decreasing their time response; also, it is difficult to measure temperature from moving objects using contact methods. This article assesses the use of thermography to measure temperature throughout the manufacture of poultry feed. The experiment showed that precaution should be used when the temperature difference, between the meal at the outlet of the conditioner and pellets at the outlet of the pellet press, is associated with the temperature rise across the die. Precaution should also be used when the temperature of the pellets at the outlet of the pellet press is used as the peak temperature during the process. Temperature measurements through infrared emissions require improved instrument design to operate in a dusty, damp, steamy and oily environment. [source] Synchronous peak Barrovian metamorphism driven by syn-orogenic magmatism and fluid flow in southern Connecticut, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 5 2008P. J. LANCASTER Abstract Recent work in Barrovian metamorphic terranes has found that rocks experience peak metamorphic temperatures across several grades at similar times. This result is inconsistent with most geodynamic models of crustal over-thickening and conductive heating, wherein rocks which reach different metamorphic grades generally reach peak temperatures at different times. Instead, the presence of additional sources of heat and/or focusing mechanisms for heat transport, such as magmatic intrusions and/or advection by metamorphic fluids, may have contributed to the contemporaneous development of several different metamorphic zones. Here, we test the hypothesis of temporally focussed heating for the Wepawaug Schist, a Barrovian terrane in Connecticut, USA, using Sm,Nd ages of prograde garnet growth and U,Pb zircon crystallization ages of associated igneous rocks. Peak temperature in the biotite,garnet zone was dated (via Sm,Nd on garnet) at 378.9 ± 1.6 Ma (2,), whereas peak temperature in the highest grade staurolite,kyanite zone was dated (via Sm,Nd on garnet rims) at 379.9 ± 6.8 Ma (2,). These garnet ages suggest that peak metamorphism was pene-contemporaneous (within error) across these metamorphic grades. Ion microprobe U,Pb ages for zircon from igneous rocks hosted by the metapelites also indicate a period of syn-metamorphic peak igneous activity at 380.6 ± 4.7 Ma (2,), indistinguishable from the peak ages recorded by garnet. A 388.6 ± 2.1 Ma (2,) garnet core age from the staurolite,kyanite zone indicates an earlier episode of growth (coincident with ages from texturally early zircon and a previously published monazite age) along the prograde regional metamorphic T,t path. The timing of peak metamorphism and igneous activity, as well as the occurrence of extensive syn-metamorphic quartz vein systems and pegmatites, best supports the hypothesis that advective heating driven by magmas and fluids focussed major mineral growth into two distinct episodes: the first at c. 389 Ma, and the second, corresponding to the regionally synchronous peak metamorphism, at c. 380 Ma. [source] Variations in the transient prograde geothermal gradient from chloritoid-staurolite equilibria: a case study from the Barrovian and Buchan-type domains in the Bohemian MassifJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2007M. KO Abstract Thermodynamic modelling of metamorphic rocks increases the possibilities of deciphering prograde paths that provide important insights into early orogenic evolution. It is shown that the chloritoid,staurolite transition is not only an indicator of temperature on prograde P,T paths, but also a useful indicator of pressure. The approach is applied to the Moravo-Silesian eastern external belt of the Bohemian Massif, where metamorphic zones range from biotite to staurolite-sillimanite. In the staurolite zone, inclusions of chloritoid occur in garnet cores, while staurolite is included at garnet rims and is widespread in the matrix. Chloritoid XFe = 0.91 indicates transition to staurolite at 5 kbar and 550 °C and consequently, an early transient prograde geothermal gradient of 29 °C km,1. The overall elevated thermal evolution is then reflected in the prograde transition of staurolite to sillimanite and in the achievement of peak temperature of 660 °C at a relatively low pressure of 6.5 kbar. To the south and to the west of the studied area, high-grade metamorphic zones record a prograde path evolution from staurolite to kyanite and development of sillimanite on decompression. Transition of chloritoid to staurolite was reported in two places, with chloritoid XFe = 0.75,0.80, occurring at 8,10 kbar and 560,580 °C, and indicating a transient prograde geothermal gradient of 16,18 °C km,1. These data show variable barric evolutions along strike and across the Moravo-Silesian domain. Elevated prograde geothermal gradient coincides with areas of Devonian sedimentation and volcanism, and syn- to late Carboniferous intrusions. Therefore, we interpret it as a result of heat inherited from Devonian rifting, further fuelled by syntectonic Carboniferous intrusions. [source] Reactive flow of mixed CO2,H2O fluid and progress of calc-silicate reactions in contact metamorphic aureoles: insights from two-dimensional numerical modellingJOURNAL OF METAMORPHIC GEOLOGY, Issue 7 2003X. Cui Abstract Previous models of hydrodynamics in contact metamorphic aureoles assumed flow of aqueous fluids, whereas CO2 and other species are also common fluid components in contact metamorphic aureoles. We investigated flow of mixed CO2,H2O fluid and kinetically controlled progress of calc-silicate reactions using a two-dimensional, finite-element model constrained by the geological relations in the Notch Peak aureole, Utah. Results show that CO2 strongly affects fluid-flow patterns in contact aureoles. Infiltration of magmatic water into a homogeneous aureole containing CO2,H2O sedimentary fluid facilitates upward, thermally driven flow in the inner aureole and causes downward flow of the relatively dense CO2 -poor fluid in the outer aureole. Metamorphic CO2 -rich fluid tends to promote upward flow in the inner aureole and the progress of devolatilization reactions causes local fluid expulsion at reacting fronts. We also tracked the temporal evolution of P-T-XCO2conditions of calc-silicate reactions. The progress of low- to medium-grade (phlogopite- to diopside-forming) reactions is mainly driven by heat as the CO2 concentration and fluid pressure and temperature increase simultaneously. In contrast, the progress of the high-grade wollastonite-forming reaction is mainly driven by infiltration of chemically out-of-equilibrium, CO2 -poor fluid during late-stage heating and early cooling of the inner aureole and thus it is significantly enhanced when magmatic water is involved. CO2 -rich fluid dominates in the inner aureole during early heating, whereas CO2 -poor fluid prevails at or after peak temperature is reached. Low-grade metamorphic rocks are predicted to record the presence of CO2 -rich fluid, and high-grade rocks reflect the presence of CO2 -poor fluid, consistent with geological observations in many calc-silicate aureoles. The distribution of mineral assemblages predicted by our model matches those observed in the Notch Peak aureole. [source] One-dimensional thermal modelling of Acadian metamorphism in southern Vermont, USAJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2000T. R. Armstrong One-dimensional thermal (1DT) modelling of an Acadian (Devonian) tectonothermal regime in southern Vermont, USA, used measured metamorphic pressures and temperatures and estimated metamorphic cooling ages based on published thermobarometric and geochronological studies to constrain thermal and tectonic input parameters. The area modelled lies within the Vermont Sequence of the Acadian orogen and includes: (i) a western domain containing garnet-grade pre-Silurian metasedimentary and metavolcanic rocks from the eastern flank of an Acadian composite dome structure (Rayponda,Sadawga Dome); and (ii) an eastern domain containing similar, but staurolite- or kyanite-grade, rocks from the western flank of a second dome structure (Athens Dome), approximately 10 km farther east. Using reasonable input parameters based on regional geological, petrological and geochronological constraints, the thermal modelling produced plausible P,T paths, and temperature,time (T ,t) and pressure,time (P,t) curves. Information extracted from P,T ,t modelling includes values of maximum temperature and pressure on the P,T paths, pressure at maximum temperature, predicted Ar closure ages for hornblende, muscovite and K-feldspar, and integrated exhumation and cooling rates for segments of the cooling history. The results from thermal modelling are consistent with independently obtained pressure, temperature and Ar cooling age data on regional metamorphism in southern Vermont. Modelling results provide some important bounding limits on the physical conditions during regional metamorphism, and indicate that the pressure contemporaneous with the attainment of peak temperature was probably as much as 2.5 kbar lower than the actual maximum pressure experienced by rocks along various particle paths. In addition, differences in peak metamorphic grade (garnet-grade versus staurolite-grade or kyanite-grade) and peak temperature for rocks initially loaded to similar crustal depths, differences in calculated exhumation rates, and differences in 40Ar/39Ar closure ages are likely to have been consequences of variations in the duration of isobaric heating (or ,crustal residence periods') and tectonic unroofing rates. Modelling results are consistent with a regional structural model that suggests west to east younging of specific Acadian deformational events, and therefore diachroneity of attainment of peak metamorphic conditions and subsequent 40Ar/39Ar closure during cooling. Modelling is consistent with the proposition that regional variations in timing and peak conditions of metamorphism are the result of the variable depths to which rocks were loaded by an eastward-thickening thrust-nappe pile rooted to the east (New Hampshire Sequence), as well as by diachronous structural processes within the lower plate rocks of the Vermont Sequence. [source] Fe3+ Ions Acting as Probes and Agents in Aggregation Processes and Solid-State Reactions in AlO(OH)/Al2O3 MatricesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 5 2010Reinhard Stößer The fate of doped iron species during various mechanically and thermally initiated redox reactions and aggregation processes in crystalline and amorphous AlO(OH) or Al2O3 matrices was investigated. The amorphization of the matrix was performed by chemical (i.e., via sol,gel processes) or mechanochemical treatment (high-energy ball milling). Thermal analysis, coupled with mass spectrometry (TA-MS), Mössbauer spectroscopy, and electron spin resonance (ESR), was used. The TA under various gas atmospheres allowed preparing samples under a controlled temperature regime, together with a controlled gas influence. Both the effect of mechanical activation and the influence of the iron doping could be followed macroscopically via the down-shift of the peak temperature of the corundum formation. The ESR data characterize the Fe3+ ions and their interaction with the magnetic surrounding based on the fine structure parameters. The Mössbauer data allowed the characterization of the Fe(0), Fe2+, and Fe3+ species, together with providing information about their coordinative surrounding. Both methods provided general complementary spectroscopical information. Unexpectedly, (FeOx)n and (FexAl1,x)2O3 aggregates could also be detected in the range of low Fe concentrations. It was demonstrated that even in the low-level doped systems [(FexAl1,x)2O3 with x,0.01], all the essential spectroscopic phenomena occur. At higher Fe concentrations, they were discovered to be caused by magnetic and spin exchange interactions as well as by solid-state reactions during and after the mechanical activation. [source] Pressure Effect on the Homogeneity of Spark Plasma-Sintered Tungsten Carbide PowderJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2009Salvatore Grasso A combined experimental/numerical methodology was developed to aid full densification of pure ultrafine tungsten carbide powder by means of Spark Plasma Sintering (SPS) operating in Current Control mode. Applied pressure ranged from 5 to 80 MPa while the current intensity was set and held constant at 1400 A. The developed SPS model used a moving-mesh technique to account for the electrothermal contact resistance change during both shrinkage and punch sliding follow-up. The pressure dependence on the electrothermal contact resistance was also taken into account by the model. The experimental and numerical results showed the effects of pressure on grain growth, residual porosity, and hardness observed along the sample radius. Upon increasing sintering pressure, complete densification was obtained by reducing the peak temperature measured at the die surface. By combining experimental and modeling results, a direct correlation between compact microstructure homogeneity and sintering parameters (i.e., temperature and applied pressure) was established. [source] Formation and Densification Behavior of MgAl2O4 Spinel: The Influence of Processing ParametersJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Ibram Ganesh Different types of dense stoichiometric and nonstoichiometric magnesium aluminate (MgAl2O4) spinel (MAS) ceramics were prepared following a conventional double-stage firing process using different commercially available alumina and magnesia raw materials. Stoichiometric, magnesia-rich, and alumina-rich spinels were sintered at 1500°,1800°C for 1,2.5 h. The influence of the different processing parameters (average particle size, degree of spinel phase, green density, mass of the powder compact, sintering temperature, holding time at the peak temperature, and starting composition) on the densification behavior of MAS was assessed by measuring the bulk density, apparent porosity, and water absorption capacity, and microstructural observations. Most of the MAS compositions tested exhibited excellent sintering properties. [source] Functional properties and retrogradation behaviour of native and chemically modified starch of mucuna bean (Mucuna pruriens)JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 15 2003Kayode O Adebowale Abstract Mucuna bean (Mucuna pruriens) starch was isolated and subjected to chemical modification by oxidation and acetylation. The proximate analysis of the non-starch components of the native starch on a dry weight basis was 92 g kg,1 moisture, 5 g kg,1 ash, 2 g kg,1 fat, 7 g kg,1 crude fibre and 19 g kg,1 protein. Chemical modification reduced the values for all the non-starch components except the moisture level. For all the samples, swelling power and solubility increased as the temperature increased in the range 50,90 °C. The swelling power of mucuna native starch (MNS) and mucuna acetylated starch (MAS) increased with increasing acidity and alkalinity, while that of mucuna oxidised starch (MOS) only increased with increasing pH in the acidic range. The maximal solubility of all the starches was observed at pH 12. All the starch samples absorbed more oil than water. The lowest gelation concentration followed the trend MAS < MNS < MOS. Chemical modification reduced the gelatinisation temperature (Tp), while peak viscosity (Pv), hot paste viscosity (Hv) and cold paste viscosity (Cv) decreased after oxidation but increased following acetylation. The setback tendency of the native starch was reduced significantly after chemical modification. However, the breakdown value of MNS, 65 BU (Brabender units), was lower than that of MOS (78 BU) but higher than that of MAS (40 BU). Differential scanning calorimetry studies of gelatinisation and retrogradation revealed that chemical modification reduced the onset temperature (To), peak temperature (Tp) and conclusion temperature (Tc). Oxidation and acetylation reduced the gelatinisation and retrogradation enthalpies of the native starch. The enthalpy of retrogradation of the starches increased as the length of storage increased. Copyright © 2003 Society of Chemical Industry [source] A thermoluminescence study of the effects of nitrite on photosystem II in spinach thylakoidsLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 3 2006Archna Sahay Abstract The site of action of nitrite on PS II was investigated by measuring the TL profile of nitrite-treated spinach thylakoid membranes. Three bands were observed in control, which were identified as the Q band (7°C), the B band (24°C) and the C band (57°C). In the presence of 20 mmol/L nitrite, the intensity of the Q band decreased, the B band upshifted to 46°C but the C band disappeared. The suppression of the Q band and the upshift of the B band suggested that nitrite caused inhibition at the water oxidizing complex. The effects of nitrite also remained the same in the presence of chloride. In case of ion-sufficient thylakoid membranes, nitrite decreased the Q band peak intensity and caused an upshift in the B band peak temperature. Nitrite showed similar effects in the presence of DCMU. This suggested that the site of action of nitrite is not at the acceptor side but at the donor side of PS II. The inhibition shown by nitrite has been found to be specific for nitrite anion. No other anions such as formate, fluoride or nitrate, were effective. Copyright © 2006 John Wiley & Sons, Ltd. [source] A Kinetic Study on the Thermal Degradation of Multi-Walled Carbon Nanotubes-Reinforced Poly(propylene) CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2004Min-Kang Seo Abstract Summary: The influence of the multi-walled carbon nanotubes (MWNTs) content on the thermal degradation behavior of MWNTs-reinforced poly(propylene) (PP) composites was investigated by using non-isothermal thermogravimetric analysis (TGA). Kinetic parameters of degradation were evaluated by using the Flynn-Wall-Ozawa iso-conversional method and the pseudo first-order method. As a result, compared with pristine PP, MWNTs-PP nanocomposites have lower peak temperatures of degradation, narrower degradation temperature ranges and a higher amount of residual weight at the end of the degradation, which is likely to be a result of specific interactions between complimentary functional groups. The values of the reaction order of MWNTs-PP nanocomposites determined by the Kissinger method are close to 1 in the non-isothermal degradation process. There is a good correlation between the Ea in region II and the peak temperature of degradation for the composites. Activation energies for degradation of different contents of MWNTs-filled PP nanocomposites as a function of conversion. [source] The Fountain Hills unique CB chondrite: Insights into thermal processes on the CB parent bodyMETEORITICS & PLANETARY SCIENCE, Issue 6 2009Dante S. LAURETTA This meteorite is closely related to the CBa class. Mineral compositions and O-isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CBa chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine-grained matrix suggests that Fountain Hills formed in a dust-poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near-CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10,3bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine-spinel geothermometry suggests a peak temperature of metamorphism between 535 °C and 878 °C, similar to type-4 ordinary chondrites. [source] The fine-grained matrix of the Semarkona LL3.0 ordinary chondrite: An induced thermoluminescence studyMETEORITICS & PLANETARY SCIENCE, Issue 5 2009Jonathan P. CRAIG The samples had TL sensitivities comparable with 4 mg of bulk samples of type 3.2,3.4 ordinary chondrites, which is very high relative to bulk Semarkona. The other induced TL properties of these samples, TL peak temperatures, and TL peak widths distinguish them from other ordinary chondrite samples where the TL is caused by feldspar. Cathodoluminescence images and other data suggest that the cause of the luminescence in the Semarkona fine-grained matrix is forsterite. In some respects the matrix TL data resemble that of Semarkona chondrules, in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments. However, differences in the TL peak temperature versus TL peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism. We also note that forsterite appears to be a major component in many primitive materials, such as nebulae, cometary dust, and Stardust particles. [source] Potassium diffusion in melilite: Experimental studies and constraints on the thermal history and size of planetesimals hosting CAIsMETEORITICS & PLANETARY SCIENCE, Issue 12 2004Motoo ITO These observations could be used to provide important constraints on the thermal history and size of the planetesimals into which the CAIs were incorporated, provided the diffusion kinetic properties of K in these minerals are known. Thus, we have experimentally determined K diffusion kinetics in the melilite end-members, åkermanite and gehlenite, as a function of temperature (900,1200 °C) and crystallographic orientation at 1 bar pressure. The closure temperature of K diffusion in melilite, Tc(K:mel), for the observed grain size of melilite in the CAIs and cooling rate of 10,100 °C/Myr, as calculated from our diffusion data, is much higher than that of Mg in anorthite. The latter was calculated from the available Mg diffusion data in anorthite. Assuming that the planetesimals were heated by the decay of 26Al and 60Fe, we have calculated the size of a planetesimal as a function of the accretion time tf such that the peak temperature at a specified radial distance rc equals Tc(K:mel). The ratio (rc/R)3 defines the planetesimal volume fraction within which 41K* in melilite grains would be at least partly disturbed, if these were randomly distributed within a planetesimal. A similar calculation was also carried out to define R versus tf relation such that 26Mg* was lost from ,50% of randomly distributed anorthite grains, as seems to be suggested by the observational data. These calculations suggest that ,60% of melilite grains should retain 41K* if ,50% of anorthite grains had retained 26Mg*. Assuming that tf was not smaller than the time of chondrule formation, our calculations yield minimum planetesimal radius of ,20,30 km, depending on the choice of planetesimal surface temperature and initial abundance of the heat producing isotope 60Fe. [source] Importance of the accretion process in asteroid thermal evolution: 6 Hebe as an exampleMETEORITICS & PLANETARY SCIENCE, Issue 5 2003Amitabha Ghosh Previous simulations of asteroid heat transfer have assumed that accretion was instantaneous. For the first time, we present a thermal model that assumes a realistic (incremental) accretion scenario and takes into account the heat budget produced by decay of 26Al during the accretion process. By modeling 6 Hebe (assumed to be the H chondrite parent body), we show that, in contrast to results from instantaneous accretion models, an asteroid may reach its peak temperature during accretion, the time at which different depth zones within the asteroid attain peak metamorphic temperatures may increase from the center to the surface, and the volume of high-grade material in the interior may be significantly less than that of unmetamorphosed material surrounding the metamorphic core. We show that different times of initiation and duration of accretion produce a spectrum of evolutionary possibilities, and thereby, highlight the importance of the accretion process in shaping an asteroid's thermal history. Incremental accretion models provide a means of linking theoretical models of accretion to measurable quantities (peak temperatures, cooling rates, radioisotope closure times) in meteorites that were determined by their thermal histories. [source] Thermoluminescence sensitivity and thermal history of type 3 ordinary chondrites: Eleven new type 3.0,3.1 chondrites and possible explanations for differences among H, L, and LL chondritesMETEORITICS & PLANETARY SCIENCE, Issue 6 2002P. H. Benoit We have identified 11 UOCs of petrologic types 3.0,3.1: Adrar 003, Elephant Moraine (EET) 90066, EET 90161, Grosvenor Mountains (GRO) 95502, Lewis Cliff (LEW) 88477, Meteorite Hills (MET) 96503, Yamato (Y)-790787, Y-791324, Y-791558, Y-793565, and Y-793596. These samples represent an important new resource for researchers interested in the nature of primitive solar system materials. Previously reported trends in which TL sensitivity increases with TL peak temperature and TL peak width, which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism, are confirmed by the new data. Importantly, the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by UOCs increases along the series LL, L and H. This suggests either different burial depths for the UOCs from each class, or formation at similar depths in regoliths of different thickness. [source] GaN HEMT thermal behavior and implications for reliability testing and analysisPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008Daniel S. Green Abstract GaN HEMT reliability evaluation in a typical Arrhenius manner requires establishing peak junction temperature for a particular stress condition. Several new techniques have yielded promising results toward establishing peak temperature for these devices in combination with detailed physical modeling, particularly micro-Raman imaging. This paper compares results from finite element modeling to measurements by infrared imaging and micro-Raman imaging. The limitations of IR imaging were confirmed similar to earlier reports. Two techniques for establishing temperature from micro-Raman measurements were used to reveal excellent correlation to the model, and also provide insight into the relationship between temperature and structural change in the device. Temperature modeling data is reported for base plate temperature from 85°C to 250°C for practical GaN HEMT devices. Implications of the measurements for GaN HEMT reliability stress testing and analysis will be discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effect of zeolite 5A on the crystalline behavior of polypropylene (PP) in PP/,-nucleating agent systemPOLYMER COMPOSITES, Issue 12 2008Zhiping Lv The effect of zeolite 5A on the crystalline behavior of polypropylene (PP) in PP/,-nucleating agent system was investigated with X-ray diffractometer (XRD), differential scanning calorimeter (DSC), and polarized light microscope (PLM) in this study. Zeolite 5A has less effect on crystalline phase of PP/,-nucleating agent than does n -CaCO3, which is ascribed to the stronger surficial polarity and better dispersibility of zeolite 5A. The data of DSC indicated that the crystallization peak temperature of PP increases by 8.3°C in the presence of zeolite 5A, and n -CaCO3 increases 5.7°C in PP/TMB-5 system, relative to pure PP. And the initial crystallization temperature (Tc0) and the relative crystallinity (Xc) of PP is much more dramatically raised in the presence of zeolite 5A than CaCO3. The efficiency of zeolite 5A in reducing the spherulites size of PP was seen clearly from the PLM photographs. The mechanical testing results showed that the flexural strength and impact strength of PP/,-nucleating agent system increased in the presence of zeolite 5A. POLYM. COMPOS., 2008. © Society of Plastics Engineers [source] Mechanical and viscoelastic properties of semi-interpenetrating polymer networks of poly(vinyl chloride)/thermosetting resin blendsPOLYMER ENGINEERING & SCIENCE, Issue 6 2000Charles U. Pittman Jr. Semi-interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepared by premixing porous, 150 ,m diameter particles of PVC and a small quantity (from 5 to 15% by weight) of a single thermosetting liquid preresin from one of five types (e.g. methylene bis-phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, and vinyl ester resins, respectively). Two roll milling of these mixtures was followed by hot-press curing. Mechanical testing indicated that most of these blends exhibited increased tensile, impact, and flexural strengths. The strength increments were greater when going from 0 to 5% thermoset content than when going from 5 to 10% or 10 to 15% thermoset. In many cases, increasing thermoset content from 10 to 15% gave slightly decreased or unchanged tensile, impact, and flexural strengths. This behavior is in accord with a "thermoset dilution effect" in PVC. Most of these SIPN blends exhibited a tan , peak temperature lower than that for pure PVC in the glass transition region. The tan , peak temperatures were progressively lowered as the amounts of thermoset increased. Also, a single distinct peak existed in the E, curves for most of the blends. Only the PVC/epoxy (90/10) blend showed two peak maxima in E, vs. temperature curves. All blends exhibited peak E, values at a lower temperature than those of PVC which had been exposed to the same processing temperatures. These observations seem to rule out the presence of large domains of PVC, which are phase-separated from PVC/thermoset SIPN, and pure thermoset domains. A substantial amount of the added thermoset appears to exist in SIPN type phases in these five blend types. [source] Synthesis and characterization of radio-opaque thermosensitive poly[N -isopropylacrylamide-2,2,-(ethylenedioxy)bis(ethylamine)-2,3,5-triiodobenzamide]POLYMER INTERNATIONAL, Issue 8 2009Christine M Leon Abstract BACKGROUND:In situ gelling polymers, like poly(N -isopropylacrylamide) (poly(NIPAAm)), have many potential medical applications due to their biocompatibility and thermosensitivity. RESULTS: Radio-opaque thermosensitive poly(NIPAAm) grafted with 10.7 wt% 2,2,-(ethylenedioxy)bis(ethylamine)-2,3,5-triiodobenzamide was successfully synthesized and characterized. The conjugated polymer showed good visibility with X-ray fluoroscopy. The polymer had a lower critical solution temperature of 30 °C after conjugation with triiodobenzamide as determined by cloud point determination and a transition peak temperature of 33.3 ± 0.57 °C as determined by differential scanning calorimetry. CONCLUSION: The polymer synthesized was highly visible under X-rays, based upon the percentage incorporation of triiodobenzamide. After conjugation of the NIPAAm to the triiodobenzamide through a bis(ethylamine) linkage, the resultant polymer retained lower critical solution temperature characteristics in a temperature region that makes it physiologically useful. Copyright © 2009 Society of Chemical Industry [source] Viscoelastic properties of polyacrylonitrile terpolymers during thermo-oxidative stabilization (cyclization)POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 7 2008K. I. Suresh Abstract A study on the thermo-oxidative stabilization (cyclization) of polyacrylonitrile (PAN) terpolymers using dynamic mechanical thermal analysis (DMTA) is reported in this article. When the changes in viscoelastic properties were monitored in a rectangular tension mode, besides the tan , peak characteristic of the glass transition observed below 200°C, the copolymer and the terpolymer displayed a second peak above 200°C due to the cyclization leading to the formation of ladder structures. The initiation temperature of the cyclization process as well as the peak temperature is found to depend on the acid value and the composition of the precursor polymer. The results presented show that monitoring the changes in viscoelastic properties during cyclization provides insight into the material properties as a result of the chemical changes that are taking place. These observations were confirmed by structural characterization using IR spectroscopy, and the observed chemical changes agree with the literature studies, as due to the thermal cyclization process. Copyright © 2008 John Wiley & Sons, Ltd. [source] Enthalpy relaxation of bovine serum albumin and implications for its storage in the glassy state,BIOPOLYMERS, Issue 2 2005Asgar Farahnaky Abstract Two endothermic peaks could be observed for five commercial samples of bovine serum albumin (BSA). The smaller peak observed by differential scanning calorimetry (DSC) corresponded to enthalpy relaxation. This peak was followed on storage of BSA, in its glassy state, after it had been heated above its denaturation temperature. Enthalpy and peak temperature increased with duration of storage. On storage for one week at 60°C, a sample at 8.3% moisture showed a peak at 100°C with an energy value of approximately 2 J per g protein. BSA samples were heated within the DSC sufficiently to eliminate the lower enthalpy peak but without altering the denaturation enthotherm. The amount of physical aging shown by these BSA samples was similar to that of the heat-denatured samples. It was concluded that the heating endotherms of dry BSA reflect both the storage and thermal history of the sample. Possible implications of the enthalpy relaxation of BSA on the behavior of this important protein are considered. © 2005 Wiley Periodicals, Inc. Biopolymers 78: 69,77, 2005 [source] Maturity Control on the Patterns of Hydrocarbon Regeneration from CoalACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 2 2000ZOU Yanrong Abstract Rock-Eval pyrolysis and Py-GC experiments on naturally and artificially matured coal samples were carried out. The results suggest that both depolymerization and defuctionalization exist during the maturation and evolution of coal. The patterns of hydrocarbon regeneration are diverse at different stages of the maturation and evolution. When the vitrinite reflectance (R0) is 0.7%-0.9%, bitumen is the richest in coal while activation energy is the minimum, and the temperature of peak yield is lower than that of primary hydrocarbon generation. However, if reflectance is greater than 0.9%, defunctionalization predominates and the temperature of peak regeneration is shown in lagging compared with the primary hydrocarbon generation. When reflectance is out of the "oil window", the peak temperature of hydrocarbon regeneration and that of the primary hydrocarbon generation seems to be continuous. [source] Thermal Behavior and Non-isothermal Decomposition Reaction Kinetics of NEPE Propellant with Ammonium DinitramideCHINESE JOURNAL OF CHEMISTRY, Issue 5 2010Weiqiang Pang Abstract Thermal decomposition behavior and non-isothermal decomposition reaction kinetics of nitrate ester plasticized polyether NEPE propellant containing ammonium dinitramide (ADN), which is one of the most important high energetic materials, were investigated by DSC, TG and DTG at 0.1 MPa. The results show that there are four exothermic peaks on DTG curves and four mass loss stages on TG curves at a heating rate of 2.5 K·min,1 under 0.1 MPa, and nitric ester evaporates and decomposes in the first stage, ADN decomposes in the second stage, nitrocellulose and cyclotrimethylenetrinitramine (RDX) decompose in the third stage, and ammonium perchlorate decomposes in the fourth stage. It was also found that the thermal decomposition processes of the NEPE propellant with ADN mainly have two mass loss stages with an increase in the heating rate, that is the result of the decomposition heats of the first two processes overlap each other and the mass content of ammonium perchlorate is very little which is not displayed in the fourth stage at the heating rate of 5, 10, and 20 K·min,1 probably. It was to be found that the exothermal peak temperatures increased with an increase in the heating rate. The reaction mechanism was random nucleation and then growth, and the process can be classified as chemical reaction. The kinetic equations of the main exothermal decomposition reaction can be expressed as: d,/dt=1012.77(3/2)(1,,)[,ln(1,,)]1/3 e,1.723×104/T. The critical temperatures of the thermal explosion (Tbe and Tbp) obtained from the onset temperature (Te) and the peak temperature (Tp) on the condition of ,,0 are 461.41 and 458.02 K, respectively. Activation entropy (,S,), activation enthalpy (,H,), and Gibbs free energy (,G,) of the decomposition reaction are ,7.02 J·mol,1·K,1, 126.19 kJ·mol,1, and 129.31 kJ·mol,1, respectively. [source] | |||||||||||||||||||||||||||||||||||||