Thermal Stability Conditions Research Articles

Features of the thermal stabilization theory of composite superconductors: The nonlinear description of the dissipative states

The features of the Joule's energy dissipation in a composite high-temperature superconductor with a power equation of the voltage-current characteristic cooled by liquid helium or hydrogen are discussed. It is shown that the non-standard thermal stabilization conditions of composite superconductors can exist if the nonlinear temperature dependences of the electrical resistivity of the stabilizing matrix and heat flux to liquid refrigerant are considered. First, there may be no minimum currents of the existence and propagation of a normal zone. Second, the intensive cooling of a composite superconductor by liquid refrigerant significantly increases the range of the stable currents, which leads to the existence of the supercritical applied currents. Third, an increase in the temperature of a composite superconductor may occur under the conditions close to adiabatic during irreversible propagation of the thermal instability despite its intensive cooling by liquid refrigerant. This effect must be considered when determining the burnout conditions of a composite superconductor. The performed numerical experiments are compared with the results obtained from the existing thermal stabilization theory of the composite superconductors, which is based on the linear temperature dependence of the critical current density of superconductor and jump-like transition from the superconducting state to the normal.

Dynamics of particles around the time conformal quantum corrected Schwarzschild black hole

Abstract In this paper, we explore the dynamics of neutral and charged particles in presence/absence of magnetic field around the quantum corrected-Schwarzschild black hole as well as the time conformal quantum corrected-Schwarzschild black hole. We investigate the conditions under which the particles move towards or away from the vicinity of black hole when they collide with other particles. We study the effective potential and effective force in presence/absence of magnetic field graphically. Recently many researchers took interest in point particle dynamics and one can initiate the study of a more complex motion of extended celestial bodies. A major area of interest among these important fields, is the particle motions (neutral and charged) around black hole and naked singularities. In this work we want to show that the quantum corrected-Schwarzschild black hole admits the time conformal factor e ϵ g ( t ) without violating the symmetry structure of the black hole, where ϵ is a small parameter that causes perturbation in the proposed spacetime and g ( t ) is a function of time t . The inception of time conformal factor, re-scales all the conservation laws that hold in the given spacetime. This type of study is important because it tells about the formation of gravitational waves and Hawking radiation. The study of thermal stability, horizons and energy conditions corresponding to the time conformal quantum corrected Schwarzschild spacetime is also explored. Furthermore, we analyze and compare the dynamics of charged and neutral particle around time conformal quantum corrected-Schwarzschild black hole with the time conformal Schwarzschild black hole. The effective force and effective potential with magnetic field and angular momentum are given graphically. The stability of the proposed spacetime is also discussed with the help of Lyapunov exponent.

Impact of MCrAlY feedstock powder modification by high-energy ball milling on the microstructure and high-temperature oxidation performance of HVOF-sprayed coatings

Two MCrAlY coatings with micro/nanostructure were deposited by high velocity oxygen-fuel (HVOF) spraying method. The microstructure modification of the feedstock powder was carried out by high energy ball milling. After 12 h of milling, the process produces semi-spherical agglomerates with a nano-scaled single crystalline γ-matrix. The as-milled MCrAlY powder exhibited good thermal stability and favorable powder conditions for thermal spraying. The microstructural investigation of as-sprayed conventional coating revealed a dense coating consisting of well-deformed splats. At the same time, a higher amount of inter-splat porosity was detected for the nanostructured coating which was attributed to the lower deformability of the milled powder. Moreover, high-temperature oxidation behavior and microstructural evolution of thermally-grown oxide (TGO) formed on the coatings were examined. For this purpose, free-standing coatings were subjected to isothermal oxidation at 1050 °C for 100 h in air. The results indicated that the microstructure of coating has a considerable impact on the oxidation performance. The nanostructured MCrAlY coating outperformed its conventional counterpart under the high-temperature oxidizing condition.

Fluctuating quasi-stable quantum-charged rotating black holes

We are engaged in studying thermodynamics of black holes from quantum mechanical perspective and already have published a series of papers. We first showed, based on certain assumptions for quantum mechanical nature of black holes, that they can be thought to be immersed in a thermal bath, i.e. rest of the universe. Of course, this consideration is required to study the thermodynamics of the black holes. We were able to find out the conditions of thermal stability for a black hole with arbitrary number of hairs in arbitrary dimensional spacetime. They came in form of a series of inequalities, connecting second-order derivatives of black hole mass with respect to its area and all the hairs. We then introduced the concept of “Quasi stability”, based on partial fulfillment of stability criteria, for thermally decaying black holes. We had also calculated the fluctuations for different hairs of a stable black hole. In this paper, we extend this calculation for charged rotating quasi-stable black holes. These fluctuations are interestingly found to be similar to that of stable black holes in certain aspects.

电力变压器热稳定性能试验与状态监测分析与研究

电力变压器热稳定性能试验与状态监测分析与研究

Ellipsometric studies for thin polymer layers of organic photovoltaic cells

In this study, ellipsometry was used to study thin films on organic photovoltaic cells. The investigated cells contained a traditional donor-acceptor structure as the active layer in the form of a bulk heterojunction. The tested photovoltaic cells had the following structure: ITO/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)/poly (3-hexylthiophene-2-diyl) (P3HT) + 1,3-phenyl-6-fluorine-1H-pyrazolo[3,4-b]quinoline (PQ)/Al. The active layer was a blend of P3HT and a compound from the pyrazoloquinoline group with a low molecular weight marked as PQ. The ITO film acted as the electrode collecting the holes. The PEDOT:PSS layer was used to smoothen the ITO film and facilitate the transport of holes. The layers were tested using spectroscopic ellipsometry (SE), and the spectral dispersion of optical constants was determined in a wavelength range of 300–1700 nm. The appropriate theoretical models were then fitted to the SE measurement results. This information was used to determine the thickness of the layers and the dispersion relation of refractive and extinction indices. The temperature dependence of refractive indices of polythiophene layers during the heating and cooling process is also presented for a temperature range of 25–110 °C. Additionally, the authors calculated thermo-optic and thermal expansion coefficients and characterized the conditions of thermal stability of the layers and reversibility issues in thermal processes.

Thermodynamic description and quasinormal modes of adS black holes in Born-lnfeld massive gravity with a non-abelian hair

We construct a new class of asymptotically (a)dS black hole solutions of Einstein-Yang-Mills massive gravity in the presence of Born-Infeld nonlinear electrody­ namics. The obtained solutions possess a Coulomb electric charge, massive term and a non-abelian hair as well. We calculate the conserved and thermodynamic quantities, and investigate the validity of the first law of thermodynamics. Also, we investigate thermal stability conditions by using the sign of heat capacity through canonical ensemble. Next, we consider the cosmological constant as a thermodynamical pressure and study the van der Waals like phase transition of black holes in the extended phase space thermodynamics. Our results indicate the existence of a phase transition which is affected by the parameters of theory. Finally, we consider a massless scalar perturbation in the background of asymptotically adS solutions and calculate the quasinormal modes by employing the pseu­ dospectral method. The imaginary part of quasinormal frequencies is the time scale of a thermal state (in the conformal field theory) for the approach to thermal equilibrium.

Efficiency Estimation of the Induction Machine by Particle Swarm Optimization Using Rapid Test Data With Range Constraints

Temperature rise of an induction machine increases losses and decrease in the efficiency. The temperature rise depends on the machine design. It takes several hours after starting a machine to reach to thermal stability. In most of the in situ efficiency estimation methods, it is required to obtain the operating data of the machine at a thermally stable condition, which needs a long running time of the machine. In this paper, a method based on a particle swarm optimization (PSO) algorithm is proposed, which can estimate the machine efficiency at different loads with thermal stability. The machine operation data at the first 30 min after the start rather than data at a thermal stability condition are used in the method. The proposed algorithm utilizes two approaches to predict a full-load temperature at a thermally stable condition. The first approach is based on the insulation class of the machine and uses the equivalent circuit. The second approach is based on the trend of the temperature rise in the first 30 min of running the machine after the start. Furthermore, a method is proposed to narrow the parameters range, which helps the PSO to converge to the right answer. All results are validated by the experimental results.

Thermal and oxidative decomposition of ibuprofen-based ionic liquids

Pharmaceuticals are often discharged into the environment and later detected in drinking water, plants, and soil. Thus, the decomposition or biodegradability of these compounds is a constant concern. The objective of this work was to show the decomposition of pharmaceutical ionic liquids (IL-APIs) via thermal and oxidative methods. Long- and short-term thermal decomposition and oxidative processes in the presence and absence of H2O2 and UV-C irradiation were investigated for four IL-APIs derived from ibuprofen. The results of short-term thermal stability experiments showed that the IL-APIs were thermally stable up to 160–200 °C, and have an activation energy of 60–100 kJ mol−1 for decomposition, which indicates that thermal decomposition requires high energy consumption. Under long thermal stability condition they were stable up to 50 °C; however, they were totally decomposed after 24 h at 100 °C. At 20–40 °C they can take days (t1/2 = 18–72 days) to years (t1/2 = 13–35 years) to be decomposed. On the other hand, oxidative decomposition in water with or without H2O2 (4–12 min and 2–5 h, respectively) was faster, resulting in decomposition of the IL-APIs in minutes to hours. The decomposition products from the oxidative process were characterized by mass spectrometry, which indicated that the presence of H2O2 facilitates an alternative, efficient, and faster method for decomposition of IL-APIs.

Study of half metallicity, structural and mechanical properties in inverse Heusler alloy Mn2ZnSi(1-x)Ge x and a superlattice.

The electronic and magnetic properties of Mn2ZnSi(1−x)Gex (x = 0.0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875, and 1.0) inverse Heusler alloys and Mn2ZnSi/Mn2ZnGe superlattice have been investigated using first-principles calculations. All these alloys are stable in the fcc magnetic phase and satisfies the mechanical and thermal stability conditions as determined from the elastic constants and negative formation energy. The spin-polarized electronic band structures and the density of states indicate half-metallicity with 100% spin polarization at the Fermi energy level for x = 0.0, 0.125, 0.25, 0.50, and 1.0, with the integral values of the total magnetic moments per formula unit at their equilibrium lattice constants, following the Slater–Pauling rule. The electronic properties and the magnetic moments are mostly contributed by two Mn atoms and are coupled anti-parallel to each other, making them ferrimagnetic in nature. The presence of the half-metallic bandgap with an antiparallel alignment of Mn atoms makes these Heusler alloys a potential candidate for spintronic applications.

Numerical Study of Noise Barriers’ Side Edge Effects on Pollutant Dispersion near Roadside under Various Thermal Stability Conditions

Roadside noise barrier helps to reduce downwind pollutant concentrations from vehicle emission. This positive characteristic of the construction feature can be explained by its interaction with flow distribution and species dispersion. In this paper, a three-dimensional numerical model has been developed to simulate highway pollutant dispersion—a realizable k-ε model was employed to model turbulent flow, and a non-reaction species dispersion model was applied to simulate species transport. First, numerical models were validated with experimental data, and good agreement was observed. Then, detailed simulations were conducted to study double barriers’ effects on highway pollutant dispersion under different settings: noise barriers with different heights, noise barriers with and without edge effects, and different atmospheric thermal boundary conditions. Results show that: (1) Noise barriers without edge effects cause bigger downwind velocity and turbulence intensity than noise barriers with edge effects. (2) At ground level, lower downwind pollutant concentration and higher pollutant concentration, near upwind barrier and between barriers, are observed for noise barriers without edge effect cases; higher on-road pollutant concentration can be seen near barrier side edges for cases with edge effect. (3) Downwind velocity and turbulence intensity increase as barrier height increases, which causes reduced downwind pollutant concentration. (4) With the same barrier height, under unstable atmospheric boundary condition, the lowest pollutant concentration can be found for both downwind and between barriers. Overall, these findings will provide valuable inputs to noise barrier design, so as to improve roadside neighborhood air quality.

The spatial structure of the logarithmic region in very-high-Reynolds-number rough wall turbulent boundary layers

Using super-large-scale particle image velocimetry (SLPIV), we investigate the spatial structure of the near-wall region in the fully rough atmospheric surface layer with Reynolds number$Re_{\unicode[STIX]{x1D70F}}\sim O(10^{6})$. The field site consists of relatively flat, snow-covered farmland, allowing for the development of a fully rough turbulent boundary layer under near-neutral thermal stability conditions. The imaging field of view extends from 3 m to 19 m above the ground and captures the top of the roughness sublayer and the bottom of an extensive logarithmic region. The SLPIV technique uses natural snowfall as seeding particles for the flow imaging. We demonstrate that SLPIV provides reliable measurements of first- and second-order velocity statistics in the streamwise and wall-normal directions. Our results in the logarithmic region show that the structural features identified in laboratory studies are similarly present in the atmosphere. Using instantaneous vector fields and two-point correlation analysis, we identify vortex structures sharing the signature of hairpin vortex packets. We also evaluate the zonal structure of the boundary layer by tracking uniform momentum zones (UMZs) and the shear interfaces between UMZs in space and time. Statistics of the UMZs and shear interfaces reveal the role of the zonal structure in determining the mean and variance profiles. The velocity difference across the shear interfaces scales with the friction velocity, in agreement with previous studies, and the size of the UMZs scales with wall-normal distance, in agreement with the attached eddy framework.

Exploring atmospheric stagnation during a severe particulate matter air pollution episode over complex terrain in Santiago, Chile

A severe air quality degradation event occurred in the Santiago Metropolitan Area (SMA), Chile, in June 2014. Meteorological and air quality measurements from 11 stations in the area as well as numerical simulations using the Weather and Research Forecasting (WRF) model were used to explain the main reasons for the occurrence of elevated particulate matter (PM) concentrations. The conditions were characterized with formation of a coastal low in central Chile between the southeastern anticyclone and a high-pressure system over Argentina. At a local scale, these conditions generated a depression at the base of the inversion layer, an increase in the vertical thermal stability, lower humidity and low-wind conditions, which were conducive to a decrease in pollutant dispersion and insufficient ventilation of the polluted air. Measurements and simulations using the WRF model revealed a vertical structure of the boundary layer during these stagnant conditions and provided a basis for a trajectory analysis. The back-trajectory calculation showed that the transport of air parcels was contained in the valley during the highest concentrations. The analysis also enabled the definition of the threshold values of a simple indicator of air pollution (ventilation coefficient, VC), which confirmed the evolution of the episode and divided the observed daily concentrations into two groups, with one including values above the limits prescribed by the national air quality standards (NAQS) and the other including values below these limits. For the SMA, the daily PM concentrations above the NASQ limits were associated with an overall mean threshold value of VC below 500 m2 s−1 (for PM2.5) and 300 m2 s−1 (for PM10). To apply the VC analysis to other pollutants and different geographic locations, different threshold values should be evaluated.

Thermal fluctuations of charged black holes in gravity’s rainbow

Quantum fluctuation effects have an irrefutable role in high energy physics. Such fluctuation can be often regarded as a correction of infrared (IR) limit. In this paper, the effects of the first-order correction of entropy, caused by thermal fluctuation, on the thermodynamics of charged black holes in gravity's rainbow will be discussed. It will be shown that such correction has profound contributions to high energy limit of thermodynamical quantities, stability conditions of the black holes and interestingly has no effect on thermodynamical phase transitions. The coupling between gravity's rainbow and the first-order correction will be addressed. In addition, the measurement of entropy as a function of fluctuation of temperature will be done and it will be shown that de Sitter (dS) case enforces an upper limit on the values of temperature and produces cyclic like diagrams. While for the anti-de Sitter (AdS) case, a lower limit on the entropy is provided and although for special cases a cyclic like behavior could be observed, no upper or lower limit exists for the temperature. In addition, a comparison between non-correction and correction included cases on the thermodynamical properties of solutions will also be discussed and the effects of the first-order correction will be highlighted. It will be shown that the first-order correction provides the solutions with larger classes of thermal stability conditions which may result into existence of a larger number of thermodynamical structures for the black holes.

Flow and temperature dynamics in an urban canyon under a comprehensive set of wind directions, wind speeds, and thermal stability conditions

Atmospheric flow and temperature dynamics in the urban roughness sublayer exhibit numerous complexities that cannot all be investigated using models or scaled-down experiments, thus these complexities necessitate careful field observations. Such dynamics were studied under a comprehensive set of wind directions, wind speeds, and thermal stability conditions in a field campaign held in Guelph, Ontario, Canada, from 13th to 25th of August 2017. The urban site was a quasi-two-dimensional canyon with unit canyon aspect ratio. Beside characterizing thermal stability, inertial effects, urban heat island intensity, and mean properties of the atmosphere, the turbulence statistics were studied carefully as functions of roof-level wind angle, diurnal time, the building Reynolds number, or the bulk Richardson number. Turbulence statistics in the vertical direction were observed to be influenced by local conditions, such as flow properties and nearby surface temperatures. These statistics also indicated presence of small integral lengthscales and short integral timescales. On the other hand, turbulence statistics in the horizontal directions were influenced by non-local conditions, such as horizontal heterogeneity in heating or urban morphology. These statistics indicated presence of large integral lengthscales and long integral timescales. In addition, a rigorous scaling analysis was performed to seek significant correlations between turbulence statistics and other known flow variables both locally or as measured at a nearby non-urban rural station. Variances scaled more successfully to mean quantities than covariances (Reynolds stresses and turbulence kinematic heat fluxes). In addition, the statistics in the vertical direction scaled more successfully compared to horizontal directions. Statistics in the horizontal directions, particularly in the along-canyon axis direction, were poorly scaled, suggesting presence of unorganized and irregular turbulence structures influenced by non-local conditions. Temperature difference between the atmosphere and nearby surfaces as well as measured velocity scales showed to scale vertical heat fluxes successfully.

Caracterización térmica, mecánica y morfológica de fibras naturales colombianas con potencial como refuerzo de biocompuestos

Este estudio se enmarca en el campo de la ciencia e ingeniería de materiales enfocada al desarrollo de nuevos compuestos amigables con el medio ambiente. En este contexto, se evaluaron cinco fibras naturales colombianas: damagua (Poulsenia armata), guérregue, palma estera (Astrocaryum malybo), caña flecha (Gynerium sagitatum) e iraca (Carludovica palmata), con el fin de estudiar su viabilidad como refuerzo en materiales compuestos. Mediante diversas mediciones se determinaron las propiedades térmicas, mecánicas y morfológicas de las fibras naturales. El análisis térmico se hizo utilizando termogravimetría (TGA), y se demostró el carácter hidrofílico de las fibras y su estabilidad a elevadas temperaturas. Se ensayó la resistencia de las fibras a la tracción bajo condiciones de fuerzas axiales estáticas, y se encontraron variaciones en las propiedades mecánicas de cada uno de los especímenes. Las fibras de guérregue y caña flecha registraron valores de resistencia máxima competitivos muy similares a los reportados en otras investigaciones con fibras naturales, en tanto que las otras tres fibras tuvieron bajo desempeño. La microestructura de las fibras se examinó mediante microscopía electrónica de barrido (SEM), y las imágenes revelaron una morfología compuesta por el lumen y la pared celular con variación entre los tamaños, comportamiento éste asociado a las propiedades mecánicas de las fibras naturales estudiadas. En conclusión, dos fibras presentaron las mejores propiedades y cumplieron con las condiciones de estabilidad térmica y resistencia mecánica que las hace aptas como refuerzo en la fabricación de biocompuestos con matrices poliméricas. © 2017. Acad. Colomb. Cienc. Ex. Fis. Nat.

Stability of beam positioning in ShenGuangIII

This paper describes how major beam positioning stability challenges faced by ShenGuangIII (SGIII) facility were met and solved by support system designs. The facility must provide vibrational and thermal stability conditions for alignment-sensitive components. The positioning stability error budget is developed for the alignment-sensitive components to provide connections between mechanical designs and performances of the support systems when they are subjected to multiple input sources that can cause structural vibration and drift. The largest allocation for vibration sources is broadband ambient vibration that is specified as acceleration power spectral density (PSD) at top-of-foundation. The components are supported in the laser bay primarily by relatively large and massive hybrid support structures of reinforced concrete (RC) pedestals and steel frames or vessels and in the target bay/switchyard primarily by building and large steel space frames. The support systems are required to afford the fundamental frequencies as best as they could. Finite element models of key modules in the laser bay and the global target bay/switchyard structures have been used to guide the designs of the combined conventional materials and optical system structures. Finite element analyses of broadband ambient vibration have demonstrated that the designs satisfy the positioning error budget. SGIII construction was completed in 2015. Ambient vibration measurements were performed and demonstrated that the acceleration PSDs remaining within guidelines. The dedicated shots to flat gold-plated targets showed that SGIII met its design requirement of ±30μm rms beam pointing to target.

Understanding the catalytic activity of nanoporous gold: Role of twinning in fcc lattice.

Nanoporous gold (NPG) prepared by de-alloying Al2Au exhibits correlation between the high catalytic reactivity towards CO oxidation and the density of twinning defects in the fcc lattice of NPG. It was also discovered that on the internal surface of NPG, quite common twinning defects can create close-packed rows of six-coordinated catalytically active Au atoms denoted as W-chains. In this work, using density functional theory methods, we investigate energy conditions for formation, thermal stability, and chemical reactivity of these active sites. The possibility of dioxygen chemisorption on various surface sites is studied in detail. A contribution from the dispersion interactions is also considered. The calculated surface density of the active six-coordinated atoms in NPG comparable with that of supported gold nanoparticle catalysts, exothermic chemisorption of dioxygen, and the energy profiles of reaction pathways for CO oxidation indicate that the six-coordinated sites created by twinning can significantly contribute to the catalytic activity of NPG.

Short-term variability of gamma radiation at the ARM Eastern North Atlantic facility (Azores)

This work addresses the short-term variability of gamma radiation measured continuously at the Eastern North Atlantic (ENA) facility located in the Graciosa island (Azores, 39N; 28W), a fixed site of the Atmospheric Radiation Measurement programme (ARM). The temporal variability of gamma radiation is characterized by occasional anomalies over a slowly-varying signal. Sharp peaks lasting typically 2–4 h are coincident with heavy precipitation and result from the scavenging effect of precipitation bringing radon progeny from the upper levels to the ground surface. However the connection between gamma variability and precipitation is not straightforward as a result of the complex interplay of factors such as the precipitation intensity, the PBL height, the cloud's base height and thickness, or the air mass origin and atmospheric concentration of sub-micron aerosols, which influence the scavenging processes and therefore the concentration of radon progeny. Convective precipitation associated with cumuliform clouds forming under conditions of warming of the ground relative to the air does not produce enhancements in gamma radiation, since the drop growing process is dominated by the fast accretion of liquid water, resulting in the reduction of the concentration of radionuclides by dilution. Events of convective precipitation further contribute to a reduction in gamma counts by inhibiting radon release from the soil surface and by attenuating gamma rays from all gamma-emitting elements on the ground. Anomalies occurring in the absence of precipitation are found to be associated with a diurnal cycle of maximum gamma counts before sunrise decreasing to a minimum in the evening, which are observed in conditions of thermal stability and very weak winds enabling the build-up of near surface radon progeny during the night.

Thermal stabilization of the resistive states of superconducting composites: Quasilinear approximation

The conditions of the occurrence and development of thermal instabilities in the composite superconductor with a continuously increasing current-voltage characteristic, which is described by the power equation, have been studied. The conditions for thermal stabilization have been analyzed in the general form using dimensionless variables that keep their invariance when varying. For the local temperature disturbance, the critical energies and velocities of its irreversible propagation have been calculated. It has been proved that composites superconductors can have stable states, when the ultimate currents can be higher or lower of the conventionally preset critical current of the composite. Furthermore, superconductivity destruction at supercritical currents takes place not in the form of a stepwise transition from the superconducting to normal state, but due to the formation of thermal and electric switching waves that propagate along the composite superconductor with a constant speed. The condition for full thermal stabilization has been formulated for the superconducting composites with a power current–voltage characteristic. The results of the numerical experiments have proved that the existing theory of thermal stabilization, which assumes a stepwise superconducting–normal transition, leads to the considerable limitation of the range of the stable currents, at which a superconducting state can be kept.