Sequential Heating Research Articles

Dynamic relaxations of a metallic glass studied on cooling

Metallic glasses have many intrinsic and universal dynamic relaxations observed below the glass-transition temperature. However, these relaxations have mostly been studied on heating and seldom investigated on cooling. In the present work, the slow β and fast β′ relaxations of La60Ni15Al25 metallic glass are studied in sequential heating and cooling experiments under continuous mechanical vibration using a dynamic mechanical analyzer. A slow β relaxation peak is observed on cooling, and compared with the preceding heating step, its peak temperature, activation energy and characteristic relaxation time are all shifted to lower values. On the contrary, a fast β′ relaxation peak is always present on heating, but undetectable on consequent cooling. Only when the metallic glass is cooled below a critical temperature, a certain value of supercooling is achieved, then the fast β′ relaxation is found during subsequent reheating. The work introduces a new approach to investigate dynamic relaxations in metallic glasses and discusses a new possibility of the origin of the fast β’ relaxation.

The effects of sequential heat treatment on microbial reduction and spore inactivation during milk processing

Sequential heating processes are commonly applied to milk by the dairy industry as part of their microbiological control strategy. Often pasteurisation at 72 °C is followed by a sequential high heat treatment step of up to 125 °C; however, such severe heat treatment can lead to reduced protein quality. Nine temperature combinations (80–90 °C) were evaluated to assess microbial reduction and whey protein nitrogen index values during pilot scale milk processing. A total of 110 bacterial isolates were identified to species level by 16S rDNA sequencing, with Bacillus licheniformis identified as the dominant species. While the experimental treatments did not achieve microbial reductions comparable with the control heating process, the results of this study provide a benchmark for milk processors relative to the effects of sequential heat treatments on milk and their impact on the survival of both thermally resistant microbial populations and thermally labile milk components during processing.

Abnormal node detection method for time-sharing heating energy consumption in multi-storey buildings based on drosophila algorithm

In order to solve the problem of high energy consumption of time-sharing heating in multi-storey buildings caused by abnormal node, it is necessary to study the detection method of abnormal node of heating energy consumption. Based on fruit flies algorithm of multi-storey building time-sharing heating energy consumption of the abnormal node detection method, using synchronous sequential PLD multi-storey building heating system of heating time-sharing data, put optimisation algorithm is introduced into EEMD algorithm, noise by flies optimisation calculation the corresponding threshold, remove the noise, the IMF component complete data denoising processing. Based on the recursive dynamic principal component analysis method, the detection model of abnormal heating energy consumption nodes is constructed to realise the detection of abnormal heating energy consumption nodes in multi-storey buildings. Experimental results show that the proposed method has good denoising effect, low false alarm rate and high detection rate.

Estimation of Spatially Distributed Thermal Properties of Heterogeneous Media with Non-Intrusive Measurement

This article deals with estimation of spatially distributed thermal properties of two-dimensional heterogeneous media from the solution of inverse heat conduction problem. The experimental procedure involves sequential heating of sample at four discrete locations on one side and recording transient temperature on the other side non-intrusively. The inverse problem formulation is carried out as parameter estimation problem and the unknown parameters are estimated through minimization of sum of squared error between measured and simulated temperatures using Levenberg–Marquardt algorithm. The huge computational time required to calculate sensitivity matrix is reduced through parallel computation strategy. Numerical estimations are carried out with synthetic temperature and it is found that the resolution and accuracy of estimated spatially distributed thermal conductivity is in better agreement with the exact distribution when compared to volumetric heat capacity even at an error level of ± 0.1 K. Transient temperature response of the fabricated heterogeneous prototype is recorded using infrared radiation camera and the same is used for estimation of unknown parameters. The estimated thermal conductivity closely mimics the actual distribution. Therefore, this simple proposed method can be directly used in thermal tomography applications for identifying the shape and size of inclusions/inhomogeneities from the estimated thermal conductivity distribution alone.

Dual-Frequency Induction Heating Generator With Adjustable Impedance Matching

This paper presents a new resonant generator topology for dual-frequency induction heating. The design offers functionalities that are not present in other solutions, which allow the ratio of equivalent resistance to be controlled at high (HF) and medium (MF) resonant frequencies. A simulation is performed of its interactive work during dual-frequency induction heating, using a specially developed software algorithm. The simulation combines coupled numerical calculations of the electromagnetic and thermal fields during dual-frequency heating of the workpiece with the analysis and modification of the resonance frequencies and power at HF and MF, in accordance with a user-imposed duty cycle. The results are used as the basis for a 100-kW physical model of the generator. The proposed LCLC topology for a dual-frequency resonant inverter with adjusted series inductance allows better use of the ac-dc power supply system, easier implementation of sequential dual-frequency heating, and easier control of MF and HF power waveforms.

Thermodynamic equilibrium analysis of steam methane reforming based on a conjugate solution of material balance and law action mass equations with the detailed energy balance

Thermodynamic equilibrium analysis of the steam methane reforming (SMR) process to synthesis gas was studied. For this purpose, the system equations of the material balance and the equations of law mass action were solved by dichotomy method. The investigation was performed for a wide range of operational conditions such as a temperature, pressure, and inlet steam-to-methane ratio. The results obtained, with the help of developed algorithms, were compared with the results obtained via different commercial and open-source programs. All results are in excellent agreement. The operational conditions for the probable formation of carbon were determined. It was established that for the temperature range above 1100 K, the probability of carbon formation is absent for steam-to-methane ratio above units. In order to determine the amount of heat supplied per 1 mol to the reformer, the heat balance equation was obtained to achieve a targeted degree of methane conversion. With the help of the heat balance equation, it was established that the resulting transformation of substances in the steam methane reformer can be presented as a sequential heating of feed streams of methane and steam from the inlet temperature T1 to the outlet temperature T2, heat for SMR reaction at the temperature T2, and heat for transformation of the part of the produced carbon monoxide (CO) via the water-gas shift (WGS) reaction at the temperature T2. The presented algorithm of thermodynamic analysis gives an appearance of the dependence of the product composition and the amount of required heat from operating conditions such as the temperature, pressure, and steam-to-methane ratio.

Numerical Study of Hyper-Thermic Laser Lipolysis With 1,064 nm Nd:YAG Laser in Human Subjects.

The aim of this study was to develop a numerical model for hyperthermic laser lipolysis in human subjects to improve understanding of the procedure and find optimal therapeutic parameters. A numerical model of hyperthermic laser lipolysis (HTLL) on human subjects was developed that is based on light and heat transport, including the effects of blood perfusion and forced air cooling. Tissue damage was evaluated using the Arrhenius model. Three irradiation scenarios were considered: single skin area irradiation without and with forced air cooling, and sequential heating of four adjacent skin areas in a cyclical manner. An evaluation of the numerical model was made by comparing the recorded skin surface temperature evolution during an experimental HTLL procedure performed on the abdomen of ten human volunteers using a 1,064 nm Nd:YAG laser irradiation. A good agreement was obtained between the simulated skin surface temperatures and thatas measured during the HTLL procedure. The temperature difference between the simulations and experiments was in the range of 0.2-0.4°C. The model parameters, which were fitted to the experiment were the perfusion parameter (0.36-0.79 and 0.18-0.49 kg/m 3 ·s for dermis and subcutis) and the subcutaneous tissue absorption coefficient (0.17-0.21 cm -1 ). By using the developed HTLL model and the determined parameters, temperature depth distributions and the resulting thermal injury to adipocytes were simulated under different treatment conditions. Optimal ranges of the HTTL treatment parameters were determined for different skin types, damaging adipocytes while preserving skin cells. The target subcutaneous temperatures were in the range of 43-47°C, which has been found to lead to programmed adipocyte death. The optimal treatment parameters were further used to define a range of recommended protocols for safe and effective multiarea cycled HTLL treatment of large body surfaces. Specifically, for the set of chosen optimal treatment parameters (4-5 treatment cycles, 1.2 W/cm 2 radiant exposure, and 60-130 W/cm 2 forced air heat-transfer coefficient) the threshold surface temperature during irradiation was found to be in the range of 31-38°C, depending on the skin type and heat-transfer coefficient. The developed numerical model allows for the calculation of the temperature distribution and the resulting injury to adipocyte cells within deeper lying fatty tissuesunder different clinical treatment conditions. It is demonstrated that by measuring the temporal evolution of the skin surface temperatureand by stopping the laser irradiation at predefined skin surface threshold temperatures, it may be possible to monitor and control the effects of the HTLL procedure deeper within the tissue. As such, the model provides a better insight into the HTLL, and may become a tool for defining the range of safe and effective HTLL treatment protocols for patients with different skin types. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Parameters of Charge Carrier Traps in ZnSe

Taking zinc selenide (ZnSe) crystals as an example, a procedure of determination of the main parameters of traps is proposed. At first, the conductivity type (electron or hole one) in a crystal of phosphor at its excitation is determined with the help of photoelectric studies or studies of the thermionic emission or thermal or photo-thermal emf. Then the energy of the thermal electron delocalization is determined, e.g., by using the method of thermally stimulated luminescence with sequential fractional heating. As a result, the frequency factors of corresponding traps are found as well. Knowing the effective electron mass, it is easy to calculate the effective density of electron states in the conduction band. Finally, the cross sections of the free-electron localization and their temperature dependences can be determined for all traps from a simple equation.

Reducing the Sonic Boom Level by Heating the Oncoming Airflow

We present the results of calculations of the level of sonic boom in the presence of local heating of the airflow in front of a slender body during its supersonic flight in thermal wake behind the heated regions. The Mach number of a cold oncoming airflow was M = 2. Calculations were performed using a combined method of “phantom bodies.” It is established that sequential local heating of the oncoming airflow in two regions in front of the flying body can reduce the sonic boom level by more than 30% as compared to that in the cold airflow.

Thermal stability and temperature dependent electron spin resonance characteristics of the As acceptor in geological 2H-MoS2

Electron spin resonance (ESR) results are presented on the thermal stability and temperature dependence of the ESR spectral characteristics of the As acceptor dopant (As substituting for S site) in geological 2H-MoS2. Under sequential isochronal heating in H2 (1.1 atm), the As dopant density is found to remain unaffected for anneal temperatures (Tans) up to 525 °C, above which the density moderately decreases (∼3 times) for Tan → 840 °C. In turn, vacuum annealing is seen to result in a gradual increase (2–3 times) of the As acceptor density for Tan increasing from 400 °C → 840 °C, pointing to a positive ‘regain’ of misconfigured As impurities in pristine geo-MoS2. Finally, meticulous monitoring of the ESR signal intensity versus tempertaure at X-band confirms the previously inferred As acceptor activation energy of 0.7 ± 0.2 meV at K-band. The appropriateness of the latter ESR probing and analysis approach has been consolidated by application to the archetypal case of decoupled P donors in n-Si, resulting in an ESR-determined activation energy (42 ± 4 meV) well in agreement with the generally accepted one. In light of these findings, As is confirmed as a promising candidate for stable covalently bonded p-type doping of MoS2.

Strengthening of Reinforced Concrete Beams with Externally Mounted Sequentially Activated Iron-Based Shape Memory Alloys.

Iron based shape memory alloys (Fe-SMA) have recently been used as active flexural strengthening material for reinforced concrete (RC) beams. Fe-SMAs are characterized by a shape memory effect (SME) which allows the recovery of previously induced plastic deformations through heating. If these deformations are restrained a recovery stress is generated by the SME. This recovery stress can be used to prestress a SMA applied as a strengthening material. This paper investigates the performance and the load deformation behavior of RC beams strengthened with mechanical end anchored unbonded Fe-SMA strips activated by sequentially infrared heating. The performance of a single loop loaded and a double loop loaded SMA strengthened RC beam are compared to an un-strengthened beam and a reference beam strengthened with commercially available structural steel. In these tests the SMA strengthened beam had the highest cracking load and the highest ultimate load. It is shown that the serviceability behavior of a concrete beam can be improved by a second thermal activation. The sequential heating procedure causes different temperature and stress states during activation along the SMA strip that have not been researched previously. The possible effect of this different temperature and stress states on metal lattice phase transformation is modeled and discussed. Moreover the role of the martensitic transformation during the cooling process on leveling the inhomogeneity of phase state in the overheated section is pointed out.

Metal-free N-doped carbon blacks as excellent electrocatalysts for oxygen reduction reactions

Electrochemical oxygen reduction reactions (ORRs) require efficient, durable, and cost-effective electrocatalysts. In this regard, the development of metal-free catalysts with excellent activity is essential. Herein we report the development of a novel two-step heating route to produce metal-free N-doped carbon blacks. The prepared materials exhibit superior electrocatalytic performance for ORRs in a basic media, which is comparable to commercial Pt/C catalysts. Among the various heating temperatures tested, sequential two-step heating at 750 and 1000 °C produced the most efficient catalysts with onset and half-wave potentials of 0.97 and 0.82 V, respectively. The prepared materials show excellent selectivity for 4-electron transfer, durability, and stability in response to methanol poisoning. Control experiments with one-step heating and no N-doping confirm the superiority of the two-step heating process for producing efficient electrocatalysts.

Foamability of Natural Rubber via Microwave Assisted Foaming with Azodicarbonamide (ADC) as Blowing Agent

Utilization of microwave in material processing has attracted significant interest due to its advantages such as rapid and volumetric heating capability. However, the use of microwave in rubbers is usually focused on vulcanization and devulcanization of rubber, but very limited on rubber foaming. Therefore in this study, attempt was made to understand the foaming behavior of natural rubber foam (NRF) via microwave assisted processing using azodicarbonamide (ADC) as the blowing agent. The microwave settings were varied and evaluated in relation to expansion behavior and foam structure of the produced NRF. Three settings were used, i.e. microwave heating only, conventional heating only and third heating was sequential heating with microwave and followed by convection heating. The results indicated that the NR can be foamed via microwave heating in less than six minutes. However good foam structure can be produced by the sequential heating setting between microwave and convection heating. The obtained results demonstrated that microwave can be potentially used as alternative heating to conventional oven heating in production of rubber foams.

Crystallographic, optical, and electronic properties of (Cu, Li)GaS2

We synthesized chalcopyrite-type (Cu1-xLix)GaS2 solid solution samples with a composition of 0.00 ≤ x ≤ 0.20 by mechanochemical process and sequential heating at 550 °C in 5% H2S/N2 gas atmosphere. The X-ray powder diffraction (XRD) peaks of (Cu1-xLix)GaS2 shifted by substitution of Li atoms for Cu atoms in CuGaS2. Their crystallographic parameters were refined by Rietveld analysis using XRD data. The lattice constant a of the (Cu1-xLix)GaS2 solid solution increased with increasing Li content, x, while the lattice constant c decreased with increasing Li content, x. We determined band-gap energies of (Cu1-xLix)GaS2 solid solution by diffuse reflectance spectra. The band-gap energy of the (Cu1-xLix)GaS2 solid solution increased from 2.44 eV of CuGaS2 (x = 0.0) to 2.54 eV of (Cu0.8Li0.2)GaS2 (x = 0.2). To understand the band diagram of (Cu1-xLix)GaS2 solid solution, the energy level of the valence band maximum (VBM) was estimated from the ionization energy, which was measured by photoemission yield spectroscopy. The energy level of the conduction band minimum (CBM) was also determined by adding the band-gap energy to the VBM level. The VBM level of the (Cu1-xLix)GaS2 solid solution decreased with increasing Li content, x. On the other hand, the CBM level was approximately constant. Li-doping in CuGaS2 is effective for decreasing the VBM level without increasing the CBM level.

The occurrence, soil parameters and genesis of rubified soils (‘Fuchserden’) of northeastern Germany

The local occurrence of red subsoils on the Late Pleistocene sandy deposits of the Northern European lowlands invites investigation into the formation and paleoenvironmental significance of these soils. According to the World Reference Base for Soil Resources (WRB), these soils are classified as Rhodic Brunic Arenosols or Chromic Brunic Arenosols; however, because of their unclear origins, these soils are still not considered in the German Guidelines for Soil Mapping. We aim to characterize the genesis of these rubified soils by combining pedological findings with chemical analyses and micromorphological studies at four sites in southeastern Brandenburg, Germany. Our novel analytical approach differentiates pedogenic iron (hydr-)oxides using a combination of Fourier transform infrared-multiple internal reflection (FTIR-MIR) spectroscopy and sequential sample heating (from 21 °C to 100 °C, 250 °C, 500 °C, and 950 °C). Together with a comparison of synthetic iron (hydr-)oxides, the results of this analytical approach demonstrate that the mineralogy of these Rhodic Brunic Arenosols and Chromic Brunic Arenosols are characterized mainly by hematite; some goethite and minor amounts of maghemite are also present. Our results confirm recent findings from Jankowski (2013) that rubification is not primarily a relict process in Central European soils; consequently, the German Guidelines for Soil Mapping require revision. The high total iron contents in the rubified soils suggest strongly that the iron is allochthonous in origin, emphasizing the importance of lateral inputs of iron compounds in the genesis of these soils. This finding is highly consistent with the ‘translocation catena’ concept (Sommer and Schlichting, 1997); i.e., the Rhodic Brunic Arenosols and Chromic Brunic Arenosols studied here formed due to inputs of allochthonous compounds. These rubified soils examined in this study share some genetic features with other soils described from Central Europe, such as the ‘Lockerbraunerden’ or the ‘Ockererden’. Further research should focus on these commonalities and compare the genetic pathways of such soils to support the argument that these soils should be considered in a separate soil class in the German Guidelines for Soil Mapping.

Generation of nanoporous model using sequential annealing and largest cluster selection method

Using molecular dynamics method, we develop a robust algorithm to generate nanoporous material with considerably natural porous structure. The method consists of sequential heating, relaxation, and quenching of Lennard-Jones meta-material. We vary the binding strength, the equilibrium distance, and the cut-off radius of the interaction potential of each sequence, in order to obtain reasonable melt structure, and agglomeration of the particles into nanowires of the nanofoam. The resulted foamy material has good void and wire size distribution, hence can be applied as target material model on computational study of the physical behaviour of porous materials. The method enables fast creation of the porous media with tuneable values of porosity.

Optical properties and electronic structures of Cu2SnS3, Cu2GeS3, and their solid solution Cu2(Ge,Sn)S3

Cu2(GexSn1−x)S3 (CGTS) (0 ≤ x ≤ 1.0) powders were synthesized by mixing elemental powders and sequential heating in 5% H2S gas atmosphere. The crystal structures of CGTS solid solution samples were refined by Rietveld refinement of the powder X-ray diffraction data. CGTS has a monoclinic crystal structure with a space group of Cc (No. 9), and the refined lattice parameters decreased linearly from a = 6.653(7) Å, b = 11.532(5) Å, and c = 6.656(2) Å of Cu2SnS3 (x = 0.0) to a = 6.416(3) Å, b = 11.303(2) Å, and c = 6.434(9) Å of Cu2GeS3 (x = 1.0) with increasing Ge, x. The band-gap energy (Eg) of the Cu2(GexSn1−x)S3 solid solution monotonically increased from 0.87 eV for Cu2SnS3 (x = 0.0) to 1.53 eV for Cu2GeS3 (x = 1.0) with increasing Ge, x. The energy level of the valence band maximum (VBM) from the vacuum level was determined from the ionization energy measured by photoelectron yield spectroscopy (PYS). The determined energy levels of VBM of Cu2SnS3 and Cu2GeS3, and their solid solution samples were shallower than those of Cu2ZnSnS4 and Cu2ZnGeS4, and their solid solution. The energy level of conduction band minimum (CBM) was calculated by adding Eg to VBM level. The energy levels of CBM of Cu2SnS3 and Cu2GeS3, and their solid solution samples were deeper than those of Cu2ZnSnS4 and Cu2ZnGeS4, and their solid solution. Even when the Ge content in Cu2(GexSn1−x)S3 solid solution samples increased, the VBM level did not change significantly but the CBM level increased markedly. We also determined the VBM levels of Cu2SnSe3, Cu2GeSe3, and Cu2(Ge,Sn)Se3 solid solution samples. The energy levels of the VBM of Cu2SnSe3 and Cu2GeSe3, and their solid solution samples were also shallower than those of Cu2ZnSnSe4 and Cu2ZnGeSe4, and their solid solution. On the basis of these results, we discuss the band diagrams of Cu2(Ge,Sn)S3 and Cu2GeSe3 solar cells with the following device structure: absorber layer/CdS buffer layer/ZnO layer.

Optical properties and electronic structures of Cu2ZnSnS4, Cu2ZnGeS4, and Cu2Zn(Ge,Sn)S4 and Cu2Zn(Ge,Sn)Se4 solid solutions

Cu2Zn(GexSn1−x)S4 (CZGTS) samples were synthesized by a mechanochemical process and sequential heating. The phases in the obtained powders were analyzed by X-ray diffraction. The band-gap energies of the CZGTS samples were determined by the diffuse reflectance spectra of UV–vis–NIR spectroscopy. The band gap energy of the CZGTS system linearly increased from 1.49 eV for Cu2ZnSnS4 (x = 0.0) to 2.25 eV for Cu2ZnGeS4 (x = 1.0). Their energy levels of valence band maximum (VBM) from the vacuum level were estimated from the ionization energies measured by photoemission yield spectroscopy (PYS). The energy levels of conduction band minimum (CBM) were determined by addition of the band-gap energies to the VBM levels. The energy level of VBM of the CZGTS solid solution was almost constant. On the other hand, the CBM level of the CZGTS solid solution linearly increased from −3.96 eV for Cu2ZnSnS4 (x = 0.0) to −3.28 eV for Cu2ZnGeS4 (x = 1.0) with the increasing Ge content. For CZGTS solar cells with CdS buffer layer, unfavorable cliff-type conduction band offset was expected. We also synthesized Cu2ZnSnSe4, Cu2ZnGeSe4, and Cu2Zn(Ge,Sn)Se4 (CZGTSe) solid solution samples and determined their energy levels of VBM and CBM. For Cu2Zn(GexSn1−x)Se4 system with 0.3 ≦ x ≦ 1.0, similar cliff-type conduction band offset was is expected. However, desirable positive spike-type conduction band offset was expected for the Cu2Zn(GexSn1−x)Se4 solar cells with 0.0 ≦ x ≦ 0.2 and CdS buffer layer.

Crystallographic, optical, and electronic properties of Li-doped CuIn(S,Se)2, (Cu,Li)In(S,Se)2

(Cu1−xLix)In(S1−ySey)2 (CLISSe) samples with 0.0 ≤ x ≤ 0.4 and y = 0.25, 0.50, and 0.75 were prepared by a mechanochemical process and sequential heating. The X-ray diffraction (XRD) peaks of the (Cu1−xLix)In(S1−ySey)2 shifted to the lower angle side by the substitution of Li atoms for Cu atoms. The solid solution limit of Li for Cu in (Cu1−xLix)In(S1−ySey)2 system widened with increasing Se content, y. The single-phase (Cu1−xLix)In(S1−ySey)2 samples were obtained for the compositions with 0.0 ≤ x ≤ 0.05 for y = 0.25, 0.0 ≤ x ≤ 0.20 for y = 0.50, and 0.0 ≤ x ≤ 0.30 for y = 0.75. The crystallographic parameters such as the lattice constants a and c, c/a, and the atomic coordinate of a S/Se atom for (Cu1−xLix)In(S1−ySey)2 were refined by Rietveld analysis using XRD data. Both the lattice constants a and c of the (Cu1−xLix)In(S1−ySey)2 with a tetragonal chalcopyrite structure increased with increasing Li content, x. The band gaps of (Cu1−xLix)In(S1−ySey)2 solid solutions widened with increasing Li content, x. To understand the band diagram of the solid solutions, the energy level of the valence band maximum (VBM) from the vacuum level was determined from the ionization energy measured by photoemission yield spectroscopy (PYS). The energy level of the conduction band minimum (CBM) was also determined by adding the band-gap energy to the VBM level. The VBM level of the (Cu1−xLix)In(S0.25Se0.75)2 solid solution decreased considerably with increasing Li content, x. The CBM level of the (Cu1−xLix)In(S1−ySey)2 solid solution was approximately constant. The Li doping in CuIn(S,Se)2 is useful for decreasing the VBM of the CuIn(S,Se)2 absorber and increasing the band-gap energy of the CuIn(S,Se)2 absorber without increasing the CBM level.

Selective Synthesis of Monoadduct Derivatives of Triaminopentanoic Acid Anhydride for Time-resolved Fluorescence-mediated Polymer Concentration Measurement

A highly selective method for synthesizing monoadduct derivatives of triaminopentanoic acid anhydride (DTPD) was developed by the sequential heating and cooling of DTPD and an amine catalyst, follo...