Variation Of Critical Temperature Research Articles

Effect of local chemical disordering on magnetic properties in high entropy manganite of variable hole concentration

A series of high entropy manganite perovskites (La0.2Pr0.2Nd0.2Bi0·2Ba0.2)MnO3, (La1/6Pr1/6Gd1/6Bi1/6Sr1/6Ba1/6)MnO3, (La0.2Nd0.2Gd0.2Sr0·2Ba0.2)MnO3 and (La1/6Pr1/6Nd1/6Ca1/6Sr1/6Ba1/6)MnO3 with variable hole concentration at fixed A-site ionic radius (<rA> = 1.253 Å) have prepared by sol-gel technique. Single phase samples were characterized by the powder X-ray diffraction (PXRD), Field Emission Scanning Electron Microscopy (FE-SEM), Energy Dispersive X-ray (EDX) analysis and elemental mapping which confirm the phase purity of the samples, surface morphology, elemental ratio and chemical homogeneity. X-ray photoelectron spectroscopic (XPS) studies reveal the increase of Mn4+ ions systematically with the substitution of hole concentration at A-site. Magnetization study in this high entropy sample with variable hole concentration at fixed <rA> = 1.253 Å exhibits several contrasting behaviour compare to the conventional hole doped samples. In these high entropy manganites the variation in critical temperature (TC) does not follow expected trend neither with the hole concentration nor to the cationic size disorder parameter, σ2. Though the <rA> is fixed, there is a slight increase in tolerance factor (f) due to hole variation in B-site. Interestingly, TC variation with f shows similar trend to the hole concentration, which is expected to be increased linearly. The effect of f on TC is rather weaker in comparison to σ2. The large drop in TC for high entropy system with respect to the conventional manganite is related to the local structural distortion which severely hampers the Mn3+—O—Mn4+ double exchange interaction. The competing magnetic interactions lead to magnetic phase separation as well as Griffith like phase. Spin pinning is noticed for the samples containing six elements in A-site which is independent on hole concentration. Possible spin clustering is also realized above ferromagnetic TC. Careful analysis of the magnetization data suggests that observed anomaly in magnetic behaviour can be ascribed to the local chemical disordering apart from the size disorder parameter. The possible role on magnetic properties of the number of elements occupying in a crystallographic site is emphasized.

Effect of scanning speed on fatigue behavior of 316L stainless steel fabricated by laser powder bed fusion

The effect of the scanning speed on the fatigue behavior of Laser Powder Bed Fusion (LPBF)-fabricated 316L steel is investigated in this paper. To this end, fatigue limits of specimen manufactured by different scanning speeds are determined by the self-heating approach. EBSD experiments and relative density measurements are carried out to characterize the microstructure and porosity. To analyse the influence of scanning speed on the microstructure (grain morphology, texture, dislocation density and stored energy) and fatigue property, a dislocation-density, crystal plasticity and stored energy-based fatigue model is developed. The inverse optimization method is combined with EBSD experiments and uniaxial tension experiments to identify the model parameters. The experimental results show a critical scanning speed, below which the fatigue limit stays almost unchanged and decreases drastically while the scanning speed is increased beyond. Furthermore, the simulation results show that the predicted fatigue limits correspond well to the experimental fatigue ones. From experimental and numerical results, it is deduced that the critical stored energy density and maximum temperature variation are functions of the porosity and can be used to differentiate the types of fatigue: microstructure-dominated or defect-dominated. This article provides new insights which can be further used in the optimization of fatigue behavior of LPBF 316L steel with respect to the scanning speed.

Role of electron–phonon coupling in the superconducting state of MgB2 polycrystals fabricated at different conditions

In this study, the superconducting properties of MgB2 bulk samples fabricated at different conditions were investigated. Ex situ MgB2 samples were further mixed with Mg and B at different amounts and sintered at different times and temperatures. Using Raman spectroscopy, the bearing of electron-phonon (e-ph) coupling (EPC) has been investigated. The dependence of temperature on magnetization, M(T), along with the dependence of magnetic field on magnetization, M(H), were evaluated to analyze the superconducting characteristics. Using the McMillan formular, which is modified by Allen–Dynes, and the frequency of phonon located in the mid peak centre ω2 (E2g), the contribution of EPC, whose value is closely proportional to the variation of critical temperature was reckoned. The lowest EPC value was determined by Raman spectrum analysis to be 1.094 for the MgB2 sample added with 0.5 Mg and sintered at 1000 °C for 1 h. In addition, the sample showed the lowest critical temperature along with the highest critical current density. The small bundle field (Bsb) as well as the large bundle field (Blb) were obtained using the collective pinning theory, demonstrating the expansion of the small also the large bundle regimes under suitable sample fabrication conditions. Based on the dependence of temperature on normalized critical current density (j) and normalized small bundle field (Bsb), δTc pinning is the predominant flux pinning mechanism across totally MgB2 bulk samples. The model of Dew–Hughes confirmed that the addition of Mg along with B creates surface pinning in the matrix by analyzing the pinning properties.

Effect of temperature variation on the fracture process of double-lap FRP-to-steel bonded joint: an analytical study

This paper presents an analytical study on the bond behavior of the double-lap FRP-to-steel bonded joint subjected to temperature variation. Closed-form solutions for the full-range bond behavior are derived and validated based on a fully reversible local interfacial bond-slip relation. Besides, finite element (FE) simulations considering the interfacial damage elasticity were conducted to investigate its influence on the interfacial bond behavior. Results show that unlike single-lap FRP-to-steel bonded joint, there exist critical temperature variations and bonding lengths that govern the fracture process of the bonded joint. Compared to the fully reversible bond-slip assumption, considering the interfacial damage elasticity has a significant influence on the bond behavior in the unloading stage in the case of temperature elevation, the load-carrying capacity is not affected provided that the bonding length is sufficiently long. While for a temperature drop, the local damage behavior in the bond-slip relation shows no influence.

Vibration Characteristics of a Continuously Rotating Superconducting Magnetic Bearing and Potential Influence to TES and SQUID

We measured the vibration of a prototype superconducting magnetic bearing (SMB) operating at liquid nitrogen temperature. This prototype system was designed as a breadboard model for LiteBIRD low-frequency telescope (LFT) polarization modulator unit. We set an upper limit of the vibration amplitude at $36~\mathrm{\mu m}$ at the rotational synchronous frequency. During the rotation, the amplitude of the magnetic field produced varies. From this setup, we compute the static and AC amplitude of the magnetic fields produced by the SMB magnet at the location of the LFT focal plane as $0.24~\mathrm{G}$ and $3\times10^{-5}$$~\mathrm{G}$, respectively. From the AC amplitude, we compute TES critical temperature variation of $7\times10^{-8}$$~\mathrm{K}$ and fractional change of the SQUID flux is $\delta \Phi/\Phi_0|_{ac}=3.1\times10^{-5}$. The mechanical vibration can be also estimated to be $3.6\times 10^{-2}$$~\mathrm{N}$ at the rotation mechanism location.

Study on the mechanism of molten aluminum droplets igniting EPS foam

Molten metal droplets with higher fire risk may cause large fires. The ignition by molten metal droplets is more complicated than by solid inert spots due to the latent heat release of solidification and fluid spread involved. There are few studies on the ignition by molten metal with liquid behavior at present. The mechanism of molten aluminum droplets igniting EPS foam was studied in this work. A small spherical aluminum particle (4-12 mm in diameter) was heated and melted to a pre-set temperature (740-1000 °C) and was dropped to a foam sample at a fixed height (20 cm). It was observed that the droplet became a splat after a collision due to the flow of liquid aluminum. The splat diameter was recorded to analyze heat transfer during the collision process. Results show that as the diameter increased from 4 to 12 mm, the critical temperature to ignite decreased from 975 to 760 °C. Compared with solid hot particles, the critical temperatures for ignition and fire spread by molten aluminum droplets were much lower. The internal energy of droplets was also investigated, and the energy per unit contact area was found to be a critical parameter (about 2.5 MJ/m2), which determines whether the ignition will occur. The diffusion of combustible gas was numerically studied and was found consistent with the trend of experimental results. Moreover, the effects of temperature and the initial size of droplets on gas mixing time were also theoretically analyzed. The competition between the gas mixing time and the splat residence time explained the variation of critical ignition temperature with droplet size.

Organic self-assembled monolayers on superconducting NbSe2: interfacial electronic structure and energetics* *This article is dedicated to the memory of Professor Enrico Clementi, our mentor, friend, and a scientific giant on whose shoulders we stand.

While organic self-assembled monolayers (SAMs) have been widely used to modify the work function of metal and metal-oxide surfaces, their application to tune the critical temperature of a superconductor has only been considered recently when SAMs were deposited on NbSe2 monolayers (Calavalle et al 2021 Nano Lett. 21 136–143). Here, we describe the results of density functional theory calculations performed on the experimentally reported organic/NbSe2 systems. Our objectives are: (i) to determine how the organic layers impact the NbSe2 work function and electronic density of states; (ii) to understand the possible correlation with the experimental variations in superconducting behavior upon SAM deposition. We find that, upon adsorption of the organic monolayers, the work-function modulation induced by the SAM and interface dipoles is consistent with the experimental results. However, there occurs no significant difference in the electronic density of states near the Fermi level, a consequence of the absence of any charge transfer across the organic/NbSe2 interfaces. Therefore, our results indicate that it is not a SAM-induced tuning of the NbSe2 density of states near the Fermi level that leads to the tuning of the superconducting critical temperature. This calls for further explorations, both experimentally and theoretically, of the mechanism underlying the superconducting critical temperature variation upon formation of SAM/NbSe2 interfaces.

Thermal stability and buckling analyses of novel encased composite cylinder with polyhedral shapes

The present investigation refers mainly to the thermal buckling performance of an encased polyhedral composite cylinder under a varied temperature field. The cylinder is encased rigidly and tightly so that only radially inward deflection occurs. The interface is smooth between the cylinder and encasement. The radius and bending rigidity of the polyhedral cylinder are approximated, so that the classical shell approach may be used. Combining the energy method and an admissible expression to describe the radial displacement, the potential energy function of a polyhedral cylinder is accomplished explicitly. Two equations of equilibrium are developed by taking the first derivative of the energy function. The critical temperature variation is obtained analytically by solving these two equations. Subsequently, a comparison is carried out to verify the accuracy of the present theoretical predictions. The results indicate the present derivation agrees exactly with other closed-form solutions. An improvement factor is defined as the ratio of the critical temperature variation between the polyhedral and circular cylinder. Finally, parametric evaluations show a higher thickness-to-radius ratio, as well as a higher number of sides, may reduce the improvement factor, respectively. Therefore, one may recommend using a polyhedral cylinder with a low thickness-to-radius ratio and small numbers of sides in engineering applications.

Poplar Sawdust Stack Self-Heating Properties and Variations of Internal Microbial Communities.

The heat accumulation generated by microbial metabolic activities during the storage of the sawdust may lead to spontaneous combustion accidents. This paper studied the Critical Ambient Temperature (CAT) variation of poplar sawdust at different stack dimensions and investigated the physicochemical properties as well as microbial community dynamics during the self-heating process of poplar sawdust stacks. From the self-heating substances test experiments and Frank-Kamenetskii (FK) theory, it was found that the CAT of poplar sawdust stacks would decrease from 158.27 °C to 102.46 °C with the increase of stack size from 0.1 m to 3.2 m. From the sawdust stack self-heating experiments, microbial metabolic activities were enhanced with the increasing moisture content (by watering) and oxygen (by turning over), which led to a remarkable increase of the sawdust stack temperature and the rapid decomposition of biochemical components (especially cellulose and hemicellulose). From the microbiological community analysis, at the thermophilic stage (around 60 °C, large amounts of heat release in compost bin), the existence of thermostable bacteria (such as Brevibacillus thermoruber, Bacillus thermoamylovorans and Paenibacillus barengoltzii belonging to Firmicutes) played an important role in degrading organic substances. The heat generated by the microbial metabolic activities might lead to spontaneous combustion eventually if sawdust stack is large enough. Therefore, the sawdust should be stacked in a cool and dry area while avoiding large amounts of storage in high humidity environments.

Spatial variation of critical temperatures between snow and rain over Turkey

This study investigates the critical temperatures that separate rain and snow events by using hourly precipitation information, air and dew point temperatures. The study period was taken to be 1997–2016 for air temperatures and 2007–2016 for dew point temperatures. In the study, only the winter season was taken into account, as it includes both snow and rain observations. During the study period, 8 different winter periods were identified for different parts of the country. To define the temperature at the onset of each precipitation event, an interpolation was applied to hourly air temperature values. It is found that critical air temperature values range from 0.5 to 2.2 °C with an average value of 1.4 °C. In addition to critical actual temperature, critical dew point temperatures vary from − 2.1 to 1.3 °C with an average value of − 0.2 °C. As a result of this investigation, only a statistically significant relationship was found between relative humidity and critical dew point temperature. This relationship states that approximately 8–9% increase in relative humidity may cause 1 °C increase in critical dew point temperature.

Nanoscale analysis of superconducting Fe(Se,Te) epitaxial thin films and relationship with pinning properties

The process of developing superconducting materials for large scale applications is mainly oriented to optimize flux pinning and the current carrying capability. A powerful approach to investigate pinning properties is to combine high resolution imaging with transport measurements as a function of the magnetic field orientation, supported by a pinning modelling. We carry out Transmission Electron Microscopy, Electron Energy Loss Spectroscopy and critical current measurements in fields up to 16 T varying the angle between the field and c-axis of Fe(Se,Te) epitaxial thin films deposited on CaF2 substrates. We find evidence of nanoscale domains with different Te:Se stoichiometry and/or rotated and tilted axes, as well as of lattice distortions and two-dimensional defects at the grain boundaries. These elongated domains are tens of nm in size along the in-plane axes. We establish a correlation between these observed microstructural features and the pinning properties, specifically strongly enhanced pinning for the magnetic field oriented in-plane and pinning emerging at higher fields for out-of-plane direction. These features can be accounted for within a model where pinning centers are local variations of the critical temperature and local variations of the mean free path, respectively. The identification of all these growth induced defects acting as effective pinning centers may provide useful information for the optimization of Fe(Se,Te) coated conductors.

Mortality Risk from Respiratory Diseases Due to Non-Optimal Temperature among Brazilian Elderlies.

Over the past decade, Brazil has experienced and continues to be impacted by extreme climate events. This study aims to evaluate the association between daily average temperature and mortality from respiratory disease among Brazilian elderlies. A daily time-series study between 2000 and 2017 in 27 Brazilian cities was conducted. Data outcomes were daily counts of deaths due to respiratory diseases in the elderly aged 60 or more. The exposure variable was the daily mean temperature from Copernicus ERA5-Land reanalysis. The association was estimated from a two-stage time series analysis method. We also calculated deaths attributable to heat and cold. The pooled exposure–response curve presented a J-shaped format. The exposure to extreme heat increased the risk of mortality by 27% (95% CI: 15–39%), while the exposure to extreme cold increased the risk of mortality by 16% (95% CI: 8–24%). The heterogeneity between cities was explained by city-specific mean temperature and temperature range. The fractions of deaths attributable to cold and heat were 4.7% (95% CI: 2.94–6.17%) and 2.8% (95% CI: 1.45–3.95%), respectively. Our results show a significant impact of non-optimal temperature on the respiratory health of elderlies living in Brazil. It may support proactive action implementation in cities that have critical temperature variations.

Local structure and superconductivity in (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x compounds

In this work, a close correlation between variations of critical temperature (Tc) and the hole concentration of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x systems was studied. The (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(Fe3O4)x samples were fabricated using the solid-state reaction method, where x ranged from 0 to 0.2. The Tc values of the samples deduced from magnetization versus temperature measurement gradually decreased with increasing the Fe3O4 content (x). To investigate a possible reason for the observed decrease in the values of Tc in the samples, the valence state of copper (V) and the hole concentration (p) in all samples were examined by analyzing the Cu K-edge and Cu L2,3-edge X-ray absorption near edge structure (XANES) spectra. The values of V and p monotonously decreased with the increase in Fe3O4 doping content (x) and agreed with the behavior of Tc. The existence of Fe3+ was confirmed by analyzing Fe L2,3-edge XANES. Hence, Fe3+ ions possibly entered the lattice structure of the samples and filled the holes in CuO2 planes. The degradation of superconductivity in Fe3O4 doped samples was then explained.

Vortex Matter in Heterothermal Superconducting Loops

We studied the (magnetic field-temperature) phase diagram, the resistive state, and the vortex configurations of a rectangular superconducting loop, under an electrical transport current J, and an external applied magnetic field H. We show that the critical current density in the I − V characteristic curve Jc1, at which the first vortex–antivortex (V-Av) pair nucleates in the sample, as well as the number of jumps in the I − V curve (i.e., different resistive states), strongly depends on the temperature of the sample and the spatial variation of critical temperature in the sample.

Behaviour of steel columns with realistic boundary restraints under standard fire

The significance of the occurrence of linearly varying rotational restraint with an increase in temperatures during building fires is outlined. A detailed parametric study conducted on seven hundred and twenty specimens using ABAQUS® investigates the effect of linearly varying rotational restraint on the stability of steel columns under standard fire was presented. Surface plots are drawn to understand the interactive effect of slenderness ratio of a column, axial boundary restraint, and temperature (buckling and critical) with linearly varying rotational restraint for different pre-applied axial load and moment ratios. The prevalence of axial force (Pbuckle/PO) at the ends of the columns due to axial restraint against thermal expansion is also assessed and plotted for the above parameters considered. It was found that buckling temperature and buckling load decreases with an increase in pre-applied axial load and moment while critical temperature variation was insignificant. The interaction equation useful for designers is proposed based on the non-linear regression analysis for assessing the critical temperature of steel columns under standard fire. It was found that the Euro code interaction equation (Eq. 4.21) predicted the critical temperature of a column with varying rotational restraint with reasonable accuracy.

Critical temperature Tc and Pauli limited critical field of Sr2RuO4 : Uniaxial strain dependence

Variations of critical temperature $T_c$ and in-plane critical field $H_{c2}$ of $\text{Sr}_2\text{Ru}\text{O}_4$ under uniaxial stress have recently been reported. We compare the strain dependence of $T_c$ and $H_{c2}$ in various pairing channels ($d$-wave, extended s-wave and $p$-wave) with the experimental observations, by studying a three-band tight-binding model that includes effects of spin-orbit and Zeeman couplings and a separable pairing interaction. Our study helps narrow down the possibility of pairing channels. The importance of the multi-band nature of $\text{Sr}_2\text{Ru}\text{O}_4$ is also highlighted.

Thermal nonlinear performance of the porous metal cylinders with composite graphene nanofiller reinforcement encased in elastic mediums

This paper investigates the nonlinear thermal performance of the functionally graded porous (FGP) cylinder with the graphene nanofillers (GNF) encased in elastic mediums. An initial out-of-roundness imperfection (dent) was considered on the crown of the cylinder body, which may be induced by a concentrated load. This imperfection is described analytically. The total potential energy function of the cylinder during the heating process is expressed theoretically for the cylinder with symmetrical distributions of both the pores and GNF to the mid-surface of the cross-section. By variation of the potential energy function, the nonlinear equilibrium equations and the critical temperature variation values are obtained. Furthermore, the results of the present study are compared with other available expressions for a homogeneous metal cylinder. Finally, a numerical parametric investigation is taken, focusing on the differences of the nonlinear equilibrium curves and the critical temperature variations induced by different magnitudes of the initial out-of-roundness imperfections, pores contents, weight fractions of nanofillers, and geometric properties of the graphene platelets.

Calculations of Some Doping Nanostructurations and Patterns Improving the Functionality of High-Temperature Superconductors for Bolometer Device Applications

We calculate the effects of doping nanostructuration and the patterning of thin films of high-temperature superconductors (HTS) with the aim of optimizing their functionality as sensing materials for resistive transition-edge bolometer devices (TES). We focus, in particular, on spatial variations of the carrier doping into the CuO layers due to oxygen off-stoichiometry, (that induce, in turn, critical temperature variations) and explore following two major cases of such structurations: First, the random nanoscale disorder intrinsically associated to doping levels that do not maximize the superconducting critical temperature; our studies suggest that this first simple structuration already improves some of the bolometric operational parameters with respect to the conventional, nonstructured HTS materials used until now. Secondly, we consider the imposition of regular arrangements of zones with different nominal doping levels (patterning); we find that such regular patterns may improve the bolometer performance even further. We find one design that improves, with respect to nonstructured HTS materials, both the saturation power and the operating temperature width by more than one order of magnitude. It also almost doubles the response of the sensor to radiation.

Research on the crystallization behavior occurred in the process of preparing bulk metallic glass with selective laser melting

The crystallization behavior occurred in the heat affected zone in the process of bulk metallic glasses preparation with selective laser melting has been studied with molecular dynamics simulation. Cyclical heating conditions are applied with three different temperature variation rates in the simulation cases, while the heating rate is ten times of the cooling rate in each case. The results reveal that the newly formed crystal cluster has more Ni atoms than the parent phase. When the cooling rate is about one third of the critical cooling rate for the formation of metallic glass, the crystallization behaviors happen in the first cooling process, which is controlled alternately by growth mechanism and nucleation mechanism. In the following heating process, the numbers of both crystal clusters and crystal atoms first increase and then decrease. When the cooling rate is about two fifths of the critical cooling rate, the crystallization behaviors happen in the second cooling process. When the cooling rate increases to about two thirds of the critical cooling rate, massive crystallization behavior is not observed, showing that the crystallization occurred in the HAZ in the process of preparing BMGs with SLM can be suppressed with a critical temperature variation rate.

Non-dimensional analysis of the criticality of Li-ion battery thermal runaway behavior.

Lithium-ion batteries are the most popular used portable energy storage technology due to the relatively high energy density. While thermal instability induced safety concerns impede the pace of developing large scale applications, the practical applications have no tolerance for the catastrophic failure. To learn more about the characteristics of battery failure, the criticality of battery thermal runaway is studied in this paper. Semenov and Thomas models are employed to analyze the criticality of battery thermal runaway in uniform and nonuniform temperature distribution situations. In order to improve accuracy of prediction, the critical parameters of overall reaction are taken as a weighted average of four exothermic reactions and the critical criteria are revised by the consumption of reactants. Results from revised model are consistence with oven model. According to the revised thermal abuse models, the critical criterion (ψcr,δcr) and critical temperature distribution (θcr) are analyzed in different composite materials, convective heat transfer coefficients and cell deformations. Results give the variation of critical criteria and critical temperature with these factors.