Peak Shift Method Research Articles

Groundwater recharge estimation in Mediterranean mountain environments by isotope profiles – Partitioning of macropore and matrix flow

Developing and continuously improving effective and feasible methods to estimate groundwater recharge is essential to ensure sustainable resource assessment. Mountain environments represent key areas for the regional water balance. In this study, the isotope profile method was used to investigate water fluxes through the vadose zone and subsequent groundwater recharge in a Mediterranean mountain environment. Six high-resolution soil water isotope profiles were taken at two different locations in the Troodos Massif (Cyprus) in the eastern Mediterranean, focusing on estimating recharge in the soil of hillslopes. Analysis of the isotope profiles yielded recharge rates ranging from 30–70 mm/year, leading to a re-evaluation of previous studies on groundwater recharge. The comparison of results obtained by the peak-shift method and mathematical modeling was used to partition matrix and macropore flow, reaching up to 39 %. Potential methodological limits of the environmental isotope profile method in skeleton-rich soils were found.

The peak‐shift method for the description of structural relaxation in glassy materials: a critical review

AbstractNowadays, the glass transition kinetics is most commonly described in terms of the Tool–Narayanaswamy–Moynihan (TNM) model. Evaluation of one of the most prominent features of the structural relaxation motions—the relaxation nonlinearity—was traditionally done using the peak‐shift (PS) method. This paper introduces, for the first time, extensive testing of the PS method by means of theoretical simulations for all practically observable types of structural relaxation behavior and all types of glassy/amorphous materials (tested range of the glass transition temperatures: −55 to 1000°C; tested range of the relaxation activation energies: 300–1300 kJ⋅mol−1). For the majority of types of structural relaxation behavior, the PS method tends to slightly overestimate the value of the TNM nonlinearity parameter x (by ∼ 0.05–0.10). In the specific cases of the highly linear behavior (↑ x) combined with a broad distribution of relaxation times, the PS method systematically vastly underestimates the value of x. A new, improved temperature program was proposed for the PS method, eliminating the major intrinsic drawback of the originally proposed version of the PS methodology. In addition, based on the comparison between the theoretically simulated and real‐life experimental data, a new approach (based on the characteristic PS dependence shape) was introduced to estimate the width of the relaxation times distribution.

Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone depth profiles

Profiles of the stable isotope ratios of pore water within the vadose zone provide fingerprints of the history of water percolation into a soil. These profiles, combined with profiles of the volumetric water content, can determine the timing and amount of water that has percolated during specific periods. This study aims to: (1) understand water percolation at two sites in Quebec (Canada) that experience thick snow coverage during the winter season; (2) calculate groundwater recharge rates using the peak-shift method; and (3) estimate the transpiration rate based on the water balance budget. A 7-m-deep borehole was drilled at two sites: one site is sparsely covered by vegetation (S1), while the second underlies a pine forest (S2). For all subsamples, δ18O and δ2H from the soil pore water were analyzed, volumetric water content of the cores was measured, and grain-size analyses to estimate the hydraulic properties were performed. For both boreholes, the winter–spring and summer–autumn periods were determined. Given the limited evapotranspiration occurring during the winter–spring period, recharge rates were high at both sites (71 and 75%), while the summer–autumn period had lower recharge rates of 63% (S1) and 41% (S2). A transpiration rate of 0.7 mm/day was estimated for the pine trees covering site S2. This study provides new field observations for estimating recharge based on water stable isotope profiles in a humid northern region dominated by snowmelt. Moreover, it confirms the accuracy of the peak-shift method for assessing groundwater recharge and estimating transpiration.

Monte Carlo study on the surface potential measurement using the peak-shift method

The accurate surface potential measurements in charging phenomena of insulating materials are highly desired as important information about charging can be inferred from surface potential. The interaction of the charged particle, induced by probe particles and emitted from sample surfaces, with surface potential enables its determination from the shift in the characteristic peak in the energy spectrum—the “peak-shift” method. However, important features, which are believed to be correlated with charging, are presented in the energy spectrum, and on the other hand, the peak-shift method is not suited for all charging phenomena. We use a Monte Carlo method to evaluate the charging of the semi-infinite SiO2 bulk induced by primary-electron irradiation and clarify the correlation of energy spectral features with charging and the applicability range of the peak-shift method. To take into account the charge trapping by defects, vacancies, and impurities etc., trapping sites are assumed to uniformly distribute in the sample, with the depth distribution described by a Gaussian function. Furthermore, the trapping of low-energy secondary electrons is also included to model their emissions more accurately. With simulation reliability evidenced by the agreement on the peak-shift magnitude with experiment, this work advances our understanding of the peak-shift method.

Analytical Study on Junction Temperatures of GaInN and AlGaN Ultraviolet Light Emitting Diodes.

Junction temperatures of GaInN and AlGaN UV LEDs are analytically investigated in this paper. GaInN and AlGaN UV LEDs have a wide variety of applications such as lighting, displays, spectrofluometry, photocatalytic processes, and high resolution optics. An analytical method is employed to analyze the junction temperature variations of GaInN and AlGaN UV LEDs with injection currents. The junction temperature is related to material properties, quantum efficiency, thermal resistance, and series resistance of LEDs. The results of GaInN and AlGaN UV LEDs predicted by this study agree with these obtained from emission peak shift method and forward voltage method.

Investigation into cooling-rate dependent residual stresses in ZrB2–SiC composites using improved Raman spectroscopy method

Thermal residual stresses in spark-plasma sintered ZrB2–20 vol% SiC composites were investigated for different cooling rates employed after sintering. A new method using barycenter shift of Raman emission band was developed to determine the surface residual stress in the SiC phase, with improved accuracy compared to measurements using the traditional peak shift method. Effect of cooling rate on thermal residual stress was quantitatively identified and analyzed. The results showed that the Raman spectroscopy method based on the barycenter shift can reduce the measurement scatter caused by small grain sizes and thus has better accuracy for ZrB2–SiC composites with nano-sized SiC particles. It was found that a lower cooling rate reduced the average residual stress, which was attributed to the smaller thermal gradient, lower stain rate and more diffusional creep with reduction in cooling rate. In addition, decreasing grain size could also reduce the residual stress. This study provides an improved measurement method and a better understanding of the development and distribution of thermal residual stresses in ZrB2–SiC composites.

Sedimentary organic matter characterization of the Whitehill shales (Karoo Basin, South Africa): An integrated quantitative approach using FE-EPMA and LA-ICP-MS

Permian black shales of South Africa's Karoo Basin have been classified as potential unconventional gas resources, the Whitehill Formation of the southern basin parts being the main target for future shale gas exploration and production. Here, we present a novel approach of SOM characterization integrating routine palynofacies analysis and high-resolution BSE imaging, modal mineral analysis, quantitative carbon analysis, EPMA trace element analysis, WDS mapping of carbon particles and carbon peak shift method using field emission microprobe as well as LA-ICP-MS trace element analysis. Black shales of the Whitehill Formation intersected in two deep boreholes of the southern Karoo Basin were studied: (1) massive carbonaceous siltstone (borehole KZF-1, southwestern basin) and (2) laminated shale made of alternating silty and clayey–silty laminae (borehole KWV-1, southeastern basin). Palynofacies indicates an outer shelf setting in the southwestern part (KZF-1) and a stratified basin in the southeastern part (KWV-1). The two shale types reveal striking differences in mineralogy, major and trace element concentrations, and shape and texture of organic particles. The EPMA trace element data of SOM show that the concentration of the elements in the organic particles does not correlate with the chemistry of the black shale when SOM is thermally untransformed. However, in the case of thermally affected and mobilized SOM, the organic acid-rich fluids liberated during the transformation and deformation of SOM can differentially dissolve chemical elements from the surrounding minerals. The LA-ICP-MS data show that the Whitehill shales are enriched in S, Mn, Mo, Ag, Cd, Re, Bi and U relative to the standard marine mud MAG-1. Shales from the southeastern basin (KWV-1) are strongly depleted in Cu, Zn, As and Ba. The granulometric and mineralogical properties of the shales suggest an outer shelf setting with low-energy sediment fallout and sediment reworking, consistent with the paleoenvironmental interpretation based on palynofacies analysis. Different burial depths are inferred from different organic textures: KZF-1 shales show organic particles which preserve organic textures, randomly distributed throughout the siltstone, whereas KWV-1 shales show deformed, thermally transformed and mobilized organic particles, located in between distinct laminae. WDS quantitative element mapping allows for identifying various carbon concentrations within the organic particles. This variability of carbon at grain scale may indicate different carbon–hydrogen molecule speciations. The observed peak shift of carbon in EPMA on different textural types of SOM allowed a correlation between the peak shift and the degree of SOM maturation, indicating that this method potentially works as a vitrinite reflectance proxy. Ultimately, the evaluation of the diagenetic conditions of organic-rich shales from different parts of the basin based on textural criteria of the detrital material and organic particles combined with the carbon peak shift in different organic particles contributes to the assessment of the hydrocarbon potential.

Advantages and challenges of using soil water isotopes to assess groundwater recharge dominated by snowmelt at a field study located in Canada

ABSTRACTSeasonal signals of stable isotopes in precipitation, combined with measurements of isotope ratios in soil water, can be used for quantitative estimation of groundwater recharge rates. This study investigates the applicability of using the piston flow principle and the peak shift displacement method to estimate actual groundwater recharge rates in a humid Nordic region located in the province of Quebec, Canada. Two different sites with and without vegetation (C1 and C2) in an unconfined aquifer were tested by measuring soil water isotope ratios (18O/16O and 2H/1H) and volumetric pore water content. Core samples were obtained along the vadose zone down to the groundwater table at the two sites (2.45 m for Site C1 and 4.15 m for Site C2). The peak shift method to estimate groundwater recharge rates was shown to be accurate only in certain specific conditions inherent to the soil properties and the topographical situation of the investigated sites. Indeed, at Site C2, recharge from the snowmelt could not be estimated because of heterogeneity in the lower part of the vadose zone. At this same site the later recharge after the snowmelt (in the period from late spring to early autumn) could be estimated accurately because the upper part of the vadose zone was homogeneous. Furthermore, at site C1, runoff/runon phenomena hampered calculations of actual infiltration and thus produced inaccurate results for recharge. These two different site effects (heterogeneity in the first site and runoff/runon in the other site) were identified as being limiting factors in the accurate assessment of actual recharge. This study therefore recommends the use of the peak shift method for (1) humid Nordic regions, (2) homogeneous and thick vadose zones, and (3) areas with few or limited site effects (runoff/runon).

Kinetics of glass transition of GeySe94-yIn6 (y = 10, 15 and 20) chalcogenide glasses under non-isothermal condition

ABSTRACTKinetics of glass transition of GeySe94-yIn6 (y = 10, 15 & 20) glassy alloys has been studied under non-isothermal condition using Differential Scanning Calorimetery (DSC). The glassy alloys have been prepared by rapid quenching of melt technique. For structure characterization, XRD and EDAX techniques have been used. DSC thermograms have been recorded at heating rates 5, 10, 15 and 20 K/min. from room temperature to 823 K. Lasocka's empirical relation has been used to study the heating rate dependence of glass transition temperature. Activation energy of glass transition, evaluated from Kissinger Peak shift method, increases with increase of Ge content in GeySe94-yIn6 (y = 10, 15 & 20) glassy series.

Analysis of junction temperatures for groups III–V semiconductor materials of light-emitting diodes

This study utilizes the Shockly equation and Fourier’s law with the optical, electrical and thermal properties of LEDs to predict the variation of the junction temperature with the injection current. It is shown that the relationship of the junction temperature with the injection current can be determined by the effective thermal conductivity, temperature coefficient of junction voltage, series resistance, integral constant (forward voltage at the initial forward current and junction temperature), ambient temperature and external quantum efficiency. The effective thermal conductivity, temperature coefficient of junction voltage, and series resistance are calculated from the material properties based on the structures of LEDs instead of measurements in this study. The junction temperature of AlGaInP/GaInP MQW red LED predicted from this study agrees with the available experimental data and the junction temperatures of GaInN UV LED and AlGaN UV LED calculated by this work are also consistent with these obtained from the emission peak shift method. The elevated temperatures of AlGaN and GaInN are larger than that of AlGaInP/GaInP MQW red LED due to the difference of the thermal conductivity for the LED substrate. This study also presents the effects of the parameters on the variation of the junction temperature with the injection current. The effective thermal conductivity and ambient temperature significantly affect the junction temperature of LEDs.

Single-frequency dielectric relaxation used to characterize the glass transition time of polydextrose

Dielectric relaxation methods are applicable to powdery materials such as carbohydrates. These materials have relaxations that occur in the milli-Hz range while samples are held at fixed temperatures and fixed water activities, aw, (relativity humidity). Under proper conditions these materials undergo physical changes where the initially glassy powder transitions to an amorphous equilibrium state at the glass transition temperature, Tg. Determining this transition involves characterizing the boundary curve (Tg versus aw) which determines Tg and aw conditions where materials are stable with long-shelf life or unstable with very a short shelf-life. This paper serves to illustrate multiple methodologies which can be used to characterize glass transition from frequency-spectra. Three methodologies are described: peak-broadening, peak-shift, and single-frequency. The new single frequency method not only provides results that identical to those of the peak-shift method but increases the data acquisition speeds by a factor of 5. This method is illustrated on polydextrose, a common sugar substitute. The information gathered can then be used to construct the boundary curve which is used to characterize the shelf-life of a material at various conditions.

Enthalpy recovery and its relation to shear response in an amine cured DGEBA epoxy

A description of enthalpy recovery for an amine-cured, digylcidyl ether of bisphenol A (DGEBA) epoxy (Epon 828/Jeffamine T403) was acquired through a series of experiments targeting the effects of the individual parameters: cooling rate, heating rate, aging temperature, and aging time. From these experiments, the peak temperature, Tp, and fictive temperature, Tf, were tracked as measures of the extent of structural relaxation. The KAHR formalism provides a standard for comparison to similar epoxies and was parametrized using the peak shift method. The resulting parameterization was then used to assess the relation between volumetric and shear relaxation. In particular, the KAHR model was used to predict volumetric relaxation time-temperature shift factors that are directly compared to measured time-temperature shift factors in shear. This unique methodology to assess equivalence between volumetric and shear relaxation shift factors further establishes the basis for this key assumption of continuum constitutive models based on rheological simplicity.

Characterizing Substrate Properties of Purine-Related Compounds with Purine Metabolism Enzymes for Enzymatic Peak-Shift HPLC Method

We have extended peak-shift method for measuring purine bases to make it suitable for other purine-related compounds. We optimized the reactions of the purine metabolism enzymes 5′-nucleotidase (EC 3.1.3.5), purine nucleoside phosphorylase (PNP) (EC 2.4.2.1), xanthine oxidase (XO) (EC 1.17.3.2), urate hydroxylase (EC 1.7.3.3), adenosine deaminase (ADA) (EC 3.5.4.4), and guanine deaminase (EC 3.5.4.3) by determining their substrate specificity and reaction kinetics. These enzymes eliminate the five purine base peaks (adenine, guanine, hypoxanthine, xanthine, and uric acid) and four nucleosides (adenosine, guanosine, inosine, and xanthosine). The bases and nucleosides can be identified and accurately quantified by comparing the chromatograms before and after treatment with the enzymes. Elimination of the individual purine compound peaks was complete in a few minutes. However, when there were multiple substrates, such as for XO, and when the metabolites were purine compounds, such as for PNP and ADA, it took longer to eliminate the peaks. The optimum reaction conditions for the peak-shift assay methods were an assay mixture containing the substrate (10 μL, 0.1 mg/mL), the combined enzyme solution (10 μL each, optimum concentration), and 50 mM sodium phosphate (up to 120 μL, pH 7.4). The mixture was incubated for 60 minutes at 37°C. This method should be suitable for determining the purine content of a variety of samples, without interference from impurities.

Effect of Carbon Content on Stacking Fault Energy of Fe-20Mn-3Cu TWIP Steel

The influence of carbon content on the stacking fault energy (SFE) of Fe–20Mn–3Cu twinning-induced plasticity (TWIP) steel was investigated by means of X-ray diffraction peak-shift method and thermodynamic modeling. The experimental result indicated that the stacking fault probability decreases with increasing carbon addition, the SFE increases linearly when the carbon content in mass percent is between 0. 23% and 1.41%. The thermodynamic calculation results showed that the SFE varied from 22. 40 to 29. 64 mJ · m−2 when the carbon content in mass percent changes from 0. 23 % to 1.41%. The XRD analysis revealed that all steels were fully austenitic before and after deformation, which suggested that TWIP effect is the predominant mechanism during the tensile deformation process of Fe-20Mn-3Cu-XC steels.

Device characteristics and thermal analysis of AlGaInP-based red monolithic light-emitting diode arrays

We investigated the device characteristics of AlGaInP/GaInP multiple quantum wells monolithic light-emitting diode (LED) arrays operating at λ ∼ 630 nm, together with experimental and theoretical thermal analysis. The optical and electrical properties were experimentally measured. The junction temperature of a single LED with 300 × 300 µm2 was experimentally determined by the electroluminescence emission peak shift method, which led to a thermal resistance of ∼47 K W−1. As the number of LEDs in arrays was increased, the optical power output (Popt) was also increased. For 1 × 4 and 2 × 2 LED arrays, the Popt was about 15 mW at 300 mA and it was maximized to ∼23 mW at 670 mA. From the measured light–current–voltage data, the detailed theoretical calculations on the thermal properties were carried out by a three-dimensional steady-state heat dissipation model using the measured heat source densities. The internal temperature profiles were obtained for different separation distances, array sizes and injection currents. The internal temperature was largely increased with the increase in array size and the decrease in the separation distance.

Feasibility analysis of junction temperature measurement for GaN-based high-power white LEDs by the peak-shift method

Transient thermal impedance of GaN-based high-power white light emitting diodes (LEDs) is created using a thermal transient tester. An electro-thermal simulation shows that LED junction temperature (JT) rises to a very low degree under low duty cycle pulsed current. At the same JT, emission peaks are equivalent at pulsed and continuous currents. Moreover, the difference in peak wavelength when a LED is driven by pulsed and continuous currents initially decreases then increases with increasing pulse width. Thus, selecting an appropriate pulse width decreases errors in JT measurement.

Kinetics of Phase Transformations and Thermal Stability of Ge<sub>x</sub>Se<sub>70</sub>Sb<sub>30-x</sub> (x = 5, 10, 15, 20) Chalcogenide Glasses

Kinetic studies of two-phase transformations i.e. glass transition and crystallization for GexSe70Sb30-x (x = 5, 10, 15, 20) glasses have been performed using differential scanning calorimetry (DSC) at different heating rates under non-isothermal condition. The glass transition and crystallization regions have been investigated in terms of their characteristic temperatures i.e. glass transition temperature Tg and crystallization temperature Tc and activation energy. The activation energies of glass transition and crystallization have been calculated by employing peak shift method of Kissinger and isoconversional methods. Activation energies have been found to be dependent on the composition. The thermal stabili- ty is determined from the temperature difference ΔT = Tc — Tg where Tc and Tg are the onset crystallization and glass transition temperature respectively. It has been found that Ge15Se70Sb15 glass is thermally more stable as compared to the other members of the series.

An Improvement on the Junction Temperature Measurement of Light-Emitting Diodes by using the Peak Shift Method Compared with the Forward Voltage Method

The junction temperature of red, green and blue high power light emitting diodes (LEDs) is measured by using the emission peak shift method and the forward voltage method. Both the emission peak shift and the forward voltage decrease show a linear relationship relative to junction temperature. The linear coefficients of the red, green and blue LEDs for the peak shift method and the forward voltage method range from 0.03 to 0.15 nm/°C and from 1.33 to 3.59 mV/°C, respectively. Compared with the forward voltage method, the peak shift method is almost independent of bias current and sample difference. The variation of the slopes is less than 2% for the peak shift method and larger than 30% for the forward voltage method, when the LEDs are driven by different bias currents. It is indicated that the peak shift method gives better stability than the forward voltage method under different LED working conditions.

Stacking fault energy in some single crystals

The stacking fault energy of single crystals has been reported using the peak shift method. Presently studied all single crystals are grown by using a direct vapor transport (DVT) technique in the laboratory. The structural characterizations of these crystals are made by XRD. Considerable variations are shown in deformation (α) and growth (β) probabilities in single crystals due to off-stoichiometry, which possesses the stacking fault in the single crystal.

Protein Secondary Structure Imaging with Ultrabroadband Multiplex Coherent Anti-Stokes Raman Scattering (CARS) Microspectroscopy

Protein secondary structures in human hair have been studied with ultrabroadband multiplex coherent anti-Stokes Raman scattering (CARS) microspectroscopy. The CARS peak-shift mapping method has been developed and applied to hair samples with and without treatments by chemical reduction and mechanical extension. It clearly visualizes the treatment induced changes in protein secondary structures and their spatial distributions. Using the new imaging technique, we found a multilayered structure in the human hair cortex.