Temperature and interlayer coupling induced thermal transport across graphene/2D-SiC van der Waals heterostructure

Graphene based two-dimensional (2D) van der Waals (vdW) materials have attracted enormous attention because of their extraordinary physical properties. In this study, we explore the temperature and interlayer coupling induced thermal transport across the graphene/2D-SiC vdW interface using non-equilibrium molecular dynamics and transient pump probe methods. We find that the in-plane thermal conductivity κ deviates slightly from the 1/T law at high temperatures. A tunable κ is found with the variation of the interlayer coupling strength χ. The interlayer thermal resistance R across graphene/2D-SiC interface reaches 2.71 $$\times$$ × 10–7$${\text{Km}}^{2} /{\text{W}}$$ Km 2 / W at room temperature and χ = 1, and it reduces steadily with the elevation of system temperature and χ, demonstrating around 41% and 56% reduction with increasing temperature to 700 K and a χ of 25, respectively. We also elucidate the heat transport mechanism by estimating the in-plane and out-of-plane phonon modes. Higher phonon propagation possibility and Umklapp scattering across the interface at high temperatures and increased χ lead to the significant reduction of R. This work unveils the mechanism of heat transfer and interface thermal conductance engineering across the graphene/2D-SiC vdW heterostructure.

Evolutionary Maximization of Energy Amount Harvested by Means of Panel of Thermoelectric Modules

This work proposes the use of a specialized algorithm based on evolutionary computation to the global MPPT regulation of panel of thermoelectric modules connected serially in numerous string sections. Each section of the thermovoltaic panel is equipped with local DC/DC converter controlled by the proposed algorithm and finally this allows the optimization of the total efficiency of conversion. Evolutionary computations adjust PWM signals of switching waveforms of DC/DC sectional simple boost converters, which have outputs configured in parallel. It gives the chance to obtain the highest level of electric energy harvested, i.e., thanks to boost converting operational points precise adaptation to the system temperature profile as well as electric load level. The simulation results of the proposed evolutionary technique confirmed the high speed of the MPPT process that is much better than for perturbation and observation, as well as incremental conductance methods, and it assures concurrent optimization of numerous PWM signals. Next, the work shows practical optimization results achieved by the proposed algorithm implemented to microcontroller module controlling the DC/DC converter during thermal to electric conversion experiment. A laboratory thermovoltaic panel was constructed from a string of Peltier modules and radiator that assured passive cooling. The measurements obtained once more proved the MPPT evolutionary regulation properness and its adaptation effectiveness for different resistive test loads.

Application of Pyroelectric Sensors Based on PVDF Films for EPR Spectra Detection by Heat Release

Pyroelectrics are a wide class of materials that change their polarization when the system temperature varies. This effect is utilized for a number of different commercial and industrial applications ranging from simple thermal sensors and laser interferometers to water vapor harvesting. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for studying the structure and dynamics of materials with unpaired electrons. Since heating accompanies a resonant change of the orientation of electron spins in an external magnetic field, pyroelectrics can be utilized as versatile detectors for so-called indirect detection of the EPR signal. In this work, we investigated three different types of PVDF (polyvinylidene difluoride) standard pyroelectric films with indium tin oxide, Cu/Ni, and Au coatings to determine their sensitivity for detecting EPR signals. All the films were shown to be able to detect the EPR spectra of about 1 μg of a standard stable free radical by heat release. A comparative study based on the calculation of the noise-equivalent power and specific detectivity from experimental spectra showed that the Au coated PVDF film is the most promising active element for measuring the EPR signal. Using the best achieved sensitivity, estimation is given whether this is sufficient for using a PVDF-based pyrodetector for indirectly detecting EPR spectra by recombination heat release or not.

Possible shock-induced crystallization of skeletal quartz from supercritical SiO2-H2O fluid: A case study of impact melt from Kamil impact crater, Egypt

Since its discovery, the Kamil crater (Egypt) has been considered a natural laboratory for studying small-scale impact cratering. We report on a previously unknown shock-related phenomenon observed in impact melt masses from Kamil; that is, the shock-triggered formation of skeletal quartz aggregates from silica-rich fluids. These aggregates are unshocked and characterized by crystallographically oriented lamellar voids and rounded vesicles. The distribution of the aggregates can be correlated with former H2O- and impurity-rich heterogeneities in precursor quartz; i.e., fluid inclusions. The heterogeneities acted as hot spots for local melting. Due to the presence of H2O and the high impact pressure and temperature, the formation of a localized supercritical fluid is plausible. Below the upper critical end point of the SiO2–H2O system (temperature <1100 °C and pressure <1 GPa), SiO2 melt and H2O fluid become immiscible, leading to the rapid and complete crystallization of skeletal quartz.

Raman Investigations of Strained Ferroelectrics

<p>This describes research done on a variety of ferroelectric systems over the course of three years during the Ph.D. programme at Victoria University of Wellington. The majority of the work involved using Raman spectroscopy to investigate the lattice dynamics of the ferroelectric materials studied, and by this method measuring the structural phase diagrams in the ferroelectrics. Three material systems were investigated. The first was bulk ceramics of the solid solution of Na₀.₅Bi₀.₅TiO₃ and BaTiO₃ (BNT-BT). The second material was PbTiO₃ (PT) nanowires prepared by annealing `PX' phase lead titanate in air. In these samples we found a tensile strain caused by nanoscopic voids in the wires. The third material studied was thin films of SrTiO₃ (STO) grown epitaxially on lattice mismatch substrates. This introduced strain into the system. In the BNT-BT system, temperature dependent Raman spectra were taken of the various samples. From the spectra, it was discovered that the structural phase transitions of the material did not perfectly correspond to the electrical phase transitions. For one significant phase boundary, no structural change occurs, only a loss of long-range order. The local sensitivity of the Raman spectroscopy technique allowed this to be found. As a consequence of this, no tricritical point is found in the phase diagram of BNT-BT. It was also found that poling the sample in electrical fields shifted the morphotropic phase boundary between 5% and 6% Ba-substitution about 1% towards the high-substitution side, but otherwise did not affect the phase diagram. In the PT nanowires system, temperature dependent Raman spectroscopy and scanning electron microscopy were performed to measure the spectra of single nanowires. A large enhancement of the ferroelectric phase transition temperature was discovered. The enhancement was found to be dependent on the nanowire diameter, with peak enhancements of over 100K measured in wires close to 125 nm. Wires both larger and smaller than this showed smaller degrees of enhancement. It is proposed that the enhancement is caused by tensile strain developed in the wires during their synthesis, where they were transformed from a low-density phase into a high-density phase. In the STO thin films system, temperature dependent ultraviolet Raman spectra and x-ray diffraction spectra were measured to establish a relationship between the biaxial strain developed in the films and their phase diagrams. The XRD found strain in the films of similar substrate which was inversely proportional to thickness up to a threshold point. Beyond that point, there is a discontinuity and additional thickness of film is grown without strain. The strain in the lower layer remains constant. The UV Raman spectroscopy method was able to enhance the signal such that thin films with weak signals could be measured. The spectra showed signs of a phase transition in all of the films. In one film enough of the spectral features were visible to characterise the low temperature phase as the orthorhombic ferroelectric phase of STO. The transition temperature varied from sample to sample, and a relationship between the biaxial strain and the transition temperature was seen.</p>

Raman Investigations of Strained Ferroelectrics

<p>This describes research done on a variety of ferroelectric systems over the course of three years during the Ph.D. programme at Victoria University of Wellington. The majority of the work involved using Raman spectroscopy to investigate the lattice dynamics of the ferroelectric materials studied, and by this method measuring the structural phase diagrams in the ferroelectrics. Three material systems were investigated. The first was bulk ceramics of the solid solution of Na₀.₅Bi₀.₅TiO₃ and BaTiO₃ (BNT-BT). The second material was PbTiO₃ (PT) nanowires prepared by annealing `PX' phase lead titanate in air. In these samples we found a tensile strain caused by nanoscopic voids in the wires. The third material studied was thin films of SrTiO₃ (STO) grown epitaxially on lattice mismatch substrates. This introduced strain into the system. In the BNT-BT system, temperature dependent Raman spectra were taken of the various samples. From the spectra, it was discovered that the structural phase transitions of the material did not perfectly correspond to the electrical phase transitions. For one significant phase boundary, no structural change occurs, only a loss of long-range order. The local sensitivity of the Raman spectroscopy technique allowed this to be found. As a consequence of this, no tricritical point is found in the phase diagram of BNT-BT. It was also found that poling the sample in electrical fields shifted the morphotropic phase boundary between 5% and 6% Ba-substitution about 1% towards the high-substitution side, but otherwise did not affect the phase diagram. In the PT nanowires system, temperature dependent Raman spectroscopy and scanning electron microscopy were performed to measure the spectra of single nanowires. A large enhancement of the ferroelectric phase transition temperature was discovered. The enhancement was found to be dependent on the nanowire diameter, with peak enhancements of over 100K measured in wires close to 125 nm. Wires both larger and smaller than this showed smaller degrees of enhancement. It is proposed that the enhancement is caused by tensile strain developed in the wires during their synthesis, where they were transformed from a low-density phase into a high-density phase. In the STO thin films system, temperature dependent ultraviolet Raman spectra and x-ray diffraction spectra were measured to establish a relationship between the biaxial strain developed in the films and their phase diagrams. The XRD found strain in the films of similar substrate which was inversely proportional to thickness up to a threshold point. Beyond that point, there is a discontinuity and additional thickness of film is grown without strain. The strain in the lower layer remains constant. The UV Raman spectroscopy method was able to enhance the signal such that thin films with weak signals could be measured. The spectra showed signs of a phase transition in all of the films. In one film enough of the spectral features were visible to characterise the low temperature phase as the orthorhombic ferroelectric phase of STO. The transition temperature varied from sample to sample, and a relationship between the biaxial strain and the transition temperature was seen.</p>

A Design of a Solar Fermentation System on Chicken Manure by Fuzzy Logic Temperature Control

Traditional chicken manure fermentation is mostly natural composting or exposure, which is not only time consuming but also susceptible to weather, resulting in uncontrollable quality and environmental pollution. This research aims to build a smart solar chicken manure fermentation system to control the conditions of chicken manure fermentation effectively, improve quality, and solve the problems of environmental pollution. Hot water produced by solar energy is the heat source for the main system of fermentation, and a backup supplemental heat source by gas heater is applied. The mechanism of drive, agitation, ventilation and drying as well as temperature conditions are controlled by the Arduino’s control core. Fuzzy logic is applied to maintain the optimal temperature, so that the system decomposes the bacteria optimally and reduces the consumed time for fermentation. The chicken manure humidity can be decreased from 70% to 30%, and the effective control system temperature is between 40 and 42 °C, while the pH value is changed from 8.7 to 7.4. The sample analysis of the fermentation also shows that there was 13.12% more organic matter in the chicken manure that added the decomposing bacteria than which did not contain the decomposing bacteria.

The Kinetic Aspects of the Dissolution of Slightly Soluble Lanthanoid Carbonates

The problem of the complex use of mineral raw materials is significant in the context of many industries. In the rare earth industry, in the context of limited traditional domestic reserves and dependence on imports of lanthanides, an unambiguous and comprehensive solution has not yet been developed. Promising areas include the involvement of technogenic raw materials in the industrial turnover. The present study examines the kinetics of the dissolution process of poorly soluble lanthanide compounds when changing the parameters of the system. The results obtained reflect the dependence of the degree of extraction of lanthanide on the following variable parameters of the system: temperature, concentration of the complexing agent, and intensity of mixing. On the basis of the experiment, the values of the activation energy and the reaction orders were calculated. The activation energy of the carbonate dissolution process, in kJ/mol, was as follows: 61.6 for cerium, 39.9 for neodymium, 45.4 for ytterbium. The apparent reaction orders of the carbonates are equal to one. The prospect of using the research results lies in the potential to create a mathematical model of the process of extracting a rare earth metal by the carbonate alkaline method.

Polarized Thermal Conductivity of Two-Dimensional Dusty Plasmas

The computation of thermalt properties of dusty plasmas is substantial task in the area of science and technology. The thermal conductivity (λ) has been computed by applying polarization effect through molecular dynamics (MD) simulations of two dimensional (2D) strongly coupled complex dusty plasmas (SCCDPs). The effects of polarization on thermal conductivity have been measured for a wide range of Coulomb coupling (Γ) and Debye screening (κ) parameters using homogeneous non-equilibrium molecular dynamics (HNEMD) method for suitable system sizes. The HNEMD simulation method is employed at constant external force field strength (F*) and varying polarization effects. The algorithm provides precise results with rapid convergence and minute dimension effects. The outcomes have been compared with earlier available simulation results of molecular dynamics, theoretical predictions and experimental results of complex dusty plasma liquids. The calculations show that the kinetic energy of SCCDPS depends upon the system temperature (≡ 1/Г) and it is independent of higher screening parameter. Furthermore, it has shown that the presented HNEMD method has more reliable results than those obtained through earlier known numerical methods.