TA Curves Research Articles

Thermal optima of gross primary productivity are closely aligned with mean air temperatures across Australian wooded ecosystems

Gross primary productivity (GPP) of wooded ecosystems (forests and savannas) is central to the global carbon cycle, comprising 67%-75% of total global terrestrial GPP. Climate change may alter this flux by increasing the frequency of temperatures beyond the thermal optimum of GPP (Topt ). We examined the relationship between GPP and air temperature (Ta) in 17 wooded ecosystems dominated by a single plant functional type (broadleaf evergreen trees) occurring over a broad climatic gradient encompassing five ecoregions across Australia ranging from tropical in the north to Mediterranean and temperate in the south. We applied a novel boundary-line analysis to eddy covariance flux observations to (a) derive ecosystem GPP-Ta relationships and Topt (including seasonal analyses for five tropical savannas); (b) quantitatively and qualitatively assess GPP-Ta relationships within and among ecoregions; (c) examine the relationship between Topt and mean daytime air temperature (MDTa) across all ecosystems; and (d) examine how down-welling short-wave radiation (Fsd) and vapour pressure deficit (VPD) influence the GPP-Ta relationship. GPP-Ta relationships were convex parabolas with narrow curves in tropical forests, tropical savannas (wet season), and temperate forests, and wider curves in temperate woodlands, Mediterranean woodlands, and tropical savannas (dry season). Ecosystem Topt ranged from 15℃ (temperate forest) to 32℃ (tropical savanna-wet and dry seasons). The shape of GPP-Ta curves was largely determined by daytime Ta range, MDTa, and maximum GPP with the upslope influenced by Fsd and the downslope influenced by VPD. Across all ecosystems, there was a strong positive linear relationship between Topt and MDTa (Adjusted R2 : 0.81; Slope: 1.08) with Topt exceeding MDTa by >1℃ at all but two sites. We conclude that ecosystem GPP has adjusted to local MDTa within Australian broadleaf evergreen forests and that GPP is buffered against small Ta increases in the majority of these ecosystems.

Enthalpy Relaxation Study of Poly(Vinyl Chloride) Films Based on the Time-Temperature Superposition Principle

In the enthalpy relaxation of poly(vinyl chloride), a decrease in enthalpy upon the isothermal ageing was measured using the differential scanning calorimetry method as a function of ageing time (tA) and ageing temperature. The range of the ageing temperature was from 56 °C (Tg − 25 °C) to 72 °C (Tg − 9 °C) where Tg denotes the glass transition temperature. The limiting value of the decrease in enthalpy was determined by applying a stretched exponential function to the measured enthalpy data. The relaxation function (ϕ) was derived from the measured enthalpy and the construction of a master curve was tried by shifting the ϕ − tA curves of the respective ageing temperatures horizontally. Although there was no agreement between the shift factors (aT) and the relaxation times of the ϕ − tA curves, the superposition was successfully constructed and the aT values obtained for the poly(vinyl chloride) sample were found to be comparable to those reported for viscoelastic experiments over a broad temperature range above and below Tg carried out for different polymers. The origin of the decrease in enthalpy was briefly discussed in terms of the chain dynamics in the isothermal condition.

Time-temperature superposition in the enthalpy relaxation study of polystyrene

Enthalpy recovery measurement was used to study the physical aging behavior of a polystyrene. The aging experiments at temperatures (TA) near Tg were conducted with aging times (tA) ranging from several minutes to several days. The recovered enthalpy, ΔH(tA, TA), increased with tA, and then a plateau value of ΔHplate appeared in the long time aging experiment. The master curve was successfully constructed concerning the normalized relaxation isotherm of ϕ for the temperature range of Tg−16 < TA < Tg−8 if ΔHplate was used to calculate the normalized term. This implies that the enthalpy relaxation evolves with the same molecular dynamics in respective TA. The shift factor in the master curve was interpreted in terms of the WLF (Williams–Landel–Ferry) equation to determine the coefficients for the superposition of ϕ–tA curves. A smaller value was found in c1 in comparison with those reported in the literature on polystyrene viscoelastic data, which was discussed in terms of temperature dependence of the relaxation rate in the enthalpy decay. POLYM. ENG. SCI., 56:561–565, 2016. © 2016 Society of Plastics Engineers

Hysteresis responses of evapotranspiration to meteorological factors at a diel timescale: patterns and causes.

Evapotranspiration (ET) is an important component of the water cycle in terrestrial ecosystems. Understanding the ways in which ET changes with meteorological factors is central to a better understanding of ecological and hydrological processes. In this study, we used eddy covariance measurements of ET from a typical alpine shrubland meadow ecosystem in China to investigate the hysteresis response of ET to environmental variables including air temperature (T a), vapor pressure deficit (VPD) and net radiation (R n) at a diel timescale. Meanwhile, the simulated ET by Priestly-Taylor equation was used to interpret the measured ET under well-watered conditions. Pronounced hysteresis was observed in both T a and VPD response curves of ET. At a similar T a and VPD, ET was always significantly depressed in the afternoon compared with the morning. But the hysteresis response of ET to R n was not evident. Similar hysteresis patterns were also observed in the T a/VPD response curves of simulated ET. The magnitudes of the measured and simulated hysteresis loops showed similar seasonal variation, with relatively smaller values occurring from May to September, which agreed well with the lifetime of plants and the period of rainy season at this site. About 62% and 23% of changes in the strength of measured ET-T a and ET-VPD loops could be explained by the changes in the strength of simulated loops, respectively. Thus, the time lag between R n and T a/VPD is the most important factor generating and modulating the ET-T a/VPD hysteresis, but plants and water status also contribute to the hysteresis response of ET. Our research confirmed the different hysteresis in the responses of ET to meteorological factors and proved the vital role of R n in driving the diel course of ET.

Effect of experimental conditions on parameters derived from TG-DSC measurements of low-temperature oxidation of coal

The process of oxygen chemisorption on coal in the temperature range ≈150–300 °C was studied under different experimental conditions using TG-DSC apparatus. As changing experimental conditions, oxygen flow (20 or 200 cm3 min−1), material of crucible (α-Al2O3 or Pt–Rh alloy), and initial sample mass (2–13 mg) were examined with respect to reliability and reproducibility of the parameters derived from TA curves. As parameters quantifying coal oxidation, temperatures of minimal Tmin and maximal Tmax sample mass, mass changes (mass loss WH below Tmin and mass increase WO above Tmin), heat evolution during oxygen chemisorption QO (related to the coal mass increase), and kinetic parameters (activation energy E and frequency factor A) were evaluated. Values of Tmax, E, and A were found to lie in very close intervals independently on experimental conditions (95% confidence intervals were Tmax = 270.2 ± 0.7 °C, E = 81 ± 3 kJ mol−1, log10A = 5.9 ± 0.3 s−1). Thus, these parameters can be used as actual characteristics of oxygen chemisorption stage of coal oxidation irrespective on conditions of TA measurements. Opposite, parameter QO was confirmed to depend clearly on initial sample mass. The dependence is different for crucible materials used; however, it tends to the same value (≈50 kJ g−1) with increasing sample mass. Further, precision of values WH, WO, and Tmin determined from TG was found to be poor. This fact complicates evaluation of the effect of experimental conditions. Finally, the effect of oxygen flow on all above parameters was found to be negligible. Its influence (if any) was hidden by common experimental errors.

Thermal behaviour of cephalexin in different mixtures

Abstract The thermoanalytical curves (TA), i.e. TG, DTG and DTA for pure cephalexin and its mixtures with talc, magnesium stearate, starch and microcrystalline cellulose, respectively, were drawn up in air and nitrogen at a heating rate of 10 °C min−1. The thermal degradation was discussed on the basis of EGA data obtained for a heating rate of 20 °C min−1. Until 250 °C, the TA curves are similar for all mixtures, up this some peculiarities depending on the additive appears. These certify that between the pure cephalosporin and the excipients do not exists any interaction until 250 °C. A kinetic analysis was performed using the TG/DTG data in air for the first step of cephalexin decomposition at four heating rates: 5, 7, 10 and 12 °C min−1. The data processing strategy was based on a differential method (Friedman), an integral method (Flynn–Wall–Ozawa) and a nonparametric kinetic method (NPK). This last one allowed an intrinsic separation of the temperature, respective conversion dependence on the reacti...

Hepatobilijarna scintigrafija u proceni funkcije transplantirane jetre

The aim of the study is evaluation of hepatocellular function, as well as morphology and patency of the biliary three of the liver transplants by dynamic hepatobiliary scintigraphy. The study was performed in 10 controls and 10 patients after orthotopic transplantation (up to two years). Sixty minutes dynamic acquisition (1 frame/min) was performed with scintillation camera after injection of 360 MBq 99mTc-diethyl- IDA. Hepatobiliary scintigrams were analysed for morphology, and parenchymal and hepatobiliary TA curves were generated and analysed as regard to the time to maximal acitivity (Tmax) and the time to half of maximum acitivity (T1/2). Uptake of the radiopharmaceutical was slightly but not significantly delayed (Tmax=18.5 +/- 2.9 min) in comparison to the controls (Tmax=14.2 +/- 3.4min), while excretion was significantly prolonged (T1/2=59.5 +/- 12.1 min) than physiological (Tmax=34.2 +/- 4.1min). Intrahepatic bile flow was nonsignificantly prolonged (Tmax=31.3 +/- 3.7 min) in comparison to the controls (Tmax=25.7 +/- 3.5 min) while extrahepatic one is high significantly prolonged (T1/2=89.0 +/- 14.3 min) than physiological (T1/2 =45.0 +/- 7.2 min). Biliary phase of hepatobiliary scintigraphy showed increased accumulation of radiopharmaceutical in the left (n=1) or right (n=2) hepatic duct. Radionuclide methods are noninvasive, and apear to be sensitive and valuable for the monitoring of liver transplants.

A new kinetic method of processing TA data

AbstractA new method of investigating the kinetic parameters and mechanism functions of a solid phase reaction is presented. This method is to analyze the data based on the use of these data at the same temperature and the same degree of conversion on a series of TA curves with different heating rates, so that the kinetic triplet–‐the activation energy E, the pre‐exponential factor A and the analytical form of the function of conversion f (α) can be obtained. The main advantage of this method is that the values of E and f(α) are obtained respectively, and the determination of f (α) is not under the influence of the value of E and the calculation of the value of E is not influenced by the f (α) either.

Thermal decomposition of gypsum

The decomposition of CaSO 4 · 2H 2O under the conditions of TA consists of two consecutive reactions, firstly CaSO 4 · 0.5H 2O then CaSO 4III being formed. The dehydration is a two-step process even when the TA curves illustrate that it is a one-step reaction. The water loss process takes place with a significant delay owing to protracted nucleus formation on the one hand and to interface processes occurring within the grains and to the reduction in the degree of dispersion caused by the sintering of the grains on the other hand.

Inelastic neutron scattering study of acoustic modes in a monodomain AlCuFe quasicrystal

Inelastic neutron scattering results evidenced for the first time that acoustic phonon modes can be observed for a quasicrystal. The triple-axes experiments have been performed on a small monodomain Al63Cu 25Fe12 sample. The obtained TA and LA dispersion curves near to strong Bragg peaks do not show any variation with respect to different Q values. Their slopes are isotropic and do not depend on special symmetry directions; they are comparable to those of corresponding curves for pure aluminium. We have not been able to observe energy gaps in our measurements.

Application of artificial intelligence for the determination of reaction mechanisms

TA curves can be interpreted kinetically by pattern recognition. Readily available symbol strings are compared with those of theoretical curves, stored in a data bank. Such kinetic codes fix the dependences of the mechanistic coordinates on the initial concentration ofone of the reactants; obviously, they are scarcely influenced by the prevailing values of the activation parameters. The foundations for a model-determinating computer program and the experiences with its application are presented. The program reveals the possible homogeneous two-reaction models from an experimental DTA- or non-isothermal UV-series; these are listed in the order of their evidence values. Similarly, the best superpositions of two two-reaction models are determined.

水和酸化皮膜に覆われたアルミニウムのアノード酸化 Ｉ 水和酸化物および複合酸化物皮膜の生成挙動

Pure aluminum specimens were covered with hydrous oxide films by immersion in boiling distilled water and then anodized galvanostatically in a neutral borate solution at different temperatures to form composite oxide films. The formation behavior of the hydrous oxide and composite oxide films was examined by gravimetry, XPS, chemical analysis and electron microscopy.It was found that the hydrous oxide films consist of two layers; a fibrous outer layer (thickness δh.o) and a dense inner layer (δh.i). The thickness of the outer layer, δh.o, increased rapidly with time to reach a steady value of ca. 0.3μm but that of the inner layer, δh.i, continued to increase gradually after a rapid increase. The hydrous oxide had a chemical composition of Al2O3⋅2.7H2O and a density of ca. 2.3g/cm3, both of which did not change with immersion time.The composite oxide films consisted of two layers; an outer crystalline oxide layer (thickness δo) and an inner amorphous oxide layer (δi). During anodizing, δh.i decreased linearly, and the total thickness, δo+δi, increased linearly with ta. The δh.i vs. ta and δo+δi vs. ta curves were independent of anodizing temperature, Ta. The outer layer thickness, δo, increased with ta, at a rate increasing with ta. This behavior was pronounced at higher Ta. The rate of increase in δi decreased with ta, and this also became more pronounced at higher Ta. The electric field supported by δi+δo was found to increase with ta from 7.7 to 10.3×106V/cm. This is explained as being due to the formation of the crystalline oxide layer capable of supporting higher electrical field and to the increase in δo/(δi+δo).

Correlation between changes in Curie temperature and electrical resistivity during structural relaxation in Fe27Ni53P14B6 metallic glass

Changes in Curie temperature (ΔTc, electrical resistivity (Δϱ/ϱ) and volume (ΔV/V) caused by isochronal annealing in as-quenched and pre-annealed Fe27Ni53P14B6 metallic glasses were compared. It was found that the ΔTc against annealing temperature (Ta) curves in as-quenched and pre-annealed samples are very similar to the Δϱ/ϱ against Ta curves. Particularly, almost a linear relationship was observed between ΔTc and Δϱ/ϱ in the pre-annealed sample. The results strongly suggest that the origins of both ΔTc and Δϱ/ϱ during structural relaxation in the pre-annealed sample are attributed to identical, reversible, short-range ordering.

Investigation of reactions connected with formation of condensed phosphates by ta methods

Dynamic and quasi-isothermal-isobaric TA curves were used to follow the condensation reactions taking place during calcination of manganese and cobalt dihydrogenphosphates. The products of calcination obtained were analyzed by chromatography, IR and NMR spectroscopy, and X-ray diffraction analysis.

Studies of radiation damage in NaCl single crystals by positron annihilation

Aging and heat treatment of NaCl single crystals after high-energy (100 MeV) electron irradiation was studied by positron lifetime and peak counts of two-photon angular correlation techniques. Three lifetime components, τ1≃0.15, τ2≃0.38, and τ3≃1.10 nsec, with I2≃52% and I3≃4.5%, are clearly observed for the sample aged at room temperature after the electron irradiation. Annealing of the sample up to 300 °C has reduced the value of I3 to &amp;lt;1%. As Ta≳300 °C, the long-lifetime component becomes practically unresolvable. The peak counts of two-photon angular correlation N(0) versus the annealing temperature Ta curves also showed a rapid decrease in the region, 125 °C&amp;lt;Ta&amp;lt;200 °C. The extinction of the long-lived τ3 component and the decrease of N(0) were attributed to rediffusion of the Na from colloidal aggregates to lattice sites in the crystal formerly vacant.

A computer automated thermal analysis laboratory for polymer characterization

Thermal methods of analysis can be used to measure a wide variety of physical and chemical properties of polymer systems. These properties are usually determined by making one or more transformations of the output from the TA instruments. Transformations that are commonly encountered include multiplication, integration, differentiation, logarithms, baseline subtraction and combinations of these to fit complex equations. In many cases, the calculations and/or replotting require more time than the operation time of the instrument. This paper describes a software package that has been developed for use with a DEC PDP 11/40 computer system, which eliminates nearly all of the hand calculations and plotting that are normally encountered for DSC, TG, TMA and evolved gas techniques (TEA, TGC). The package consists of programs to perform direct data acquisition simultaneously from all the instruments, to transform the data as necessary, and to plot the TA curves in a form suitable for reporting. Substantial improvements in efficiency, accuracy and data analysis capabilities have been realized through automation of the TA laboratory. Specific examples of expanded capabilities for polymer characterization are described.