Influence of Uniform Compression on the Temperature Dependence of the Pseudogap of Medium-Praseodymium-Doped Y1−xPrxBa2Cu3O7−δ Single Crystals

The effect of high pressure on the conductivity in the basal plane of HTSC single crystals of Y0.77Pr0.23Ba2Cu3O7−δ is investigated. It has been established that the excess conductivity, Δσ(T), of these single crystals in a wide temperature range Tf < T < T* can be described by an exponential temperature dependence. The description of the excess conductivity using the relation Δσ ~ (1 − T/T*)exp(Δ*ab/T) can be interpreted in terms of the mean-field theory, where T* is represented as the temperature pseudogap opening, and the temperature dependence of the pseudogap (PG) is satisfactorily described in the framework of the BCS-BEC crossover theory. An increase in the applied pressure leads to the effect of narrowing the temperature interval for the realization of the PG-regime, thereby expanding the region of the linear dependence ρ(T) in the ab-plane.

Effect of polyoxymethylene (POM-H Delrin) off-gassing within the Pandora head sensor on direct-sun and multi-axis formaldehyde column measurements in 2016–2019

Analysis of formaldehyde measurements by the Pandora spectrometer systems between 2016 and 2019 suggested that there was a temperature-dependent process inside the Pandora head sensor that emitted formaldehyde. Some parts in the head sensor were manufactured from the thermal plastic polyoxymethylene homopolymer (E.I. Du Pont de Nemour &amp; Co., USA; POM-H Delrin®) and were responsible for formaldehyde production. Laboratory analysis of the four Pandora head sensors showed that internal formaldehyde production had exponential temperature dependence with a damping coefficient of 0.0911±0.0024 ∘C−1 and the exponential function amplitude ranging from 0.0041 to 0.049 DU. No apparent dependency on the head sensor age and heating and cooling rates was detected. The total amount of formaldehyde internally generated by the POM-H Delrin components and contributing to the direct-sun measurements were estimated based on the head sensor temperature and solar zenith angle of the measurements. Measurements in winter, during colder (< 10 ∘C) days in general, and at high solar zenith angles (> 75∘) were minimally impacted. Measurements during hot days (> 28 ∘C) and small solar zenith angles had up to 1 DU (2.69×1016 molec. cm−2) contribution from POM-H Delrin parts. Multi-axis differential slant column densities were minimally impacted (<0.01 DU) due to the reference spectrum being collected within a short time period with a small difference in head sensor temperature. Three new POM-H Delrin free Pandora head sensors (manufactured in summer 2019) were evaluated for temperature-dependent attenuation across the entire spectral range (300 to 530 nm). No formaldehyde absorption or any other absorption above the instrumental noise was observed across the entire spectral range.

Effect of Polyoxymethylene (POM-H Delrin) offgassing within Pandora head sensor on direct sun and multi-axis formaldehyde column measurements in 2016–2019

Analysis of formaldehyde measurements by the Pandora spectrometer systems between 2016 and 2019 suggested that there was a temperature dependent process inside Pandora head sensor that emitted formaldehyde. Some parts in the head sensor were manufactured from thermal plastic polyoxymethylene homopolimer (E.I. Du Pont de Nemour &amp; Co., USA: POM-H Delrin®) and were responsible for formaldehyde production. Laboratory analysis of the four Pandora head sensors showed that internal formaldehyde production had exponential temperature dependence with a damping coefficient of 0.0911 ± 0.0024 °C−1 and the exponential function amplitude ranging from 0.0041 DU to 0.049 DU. No apparent dependency on the head sensor age and heating/cooling rates was detected. The total amount of formaldehyde internally generated by the POM-H components and contributing to the direct sun measurements were estimated based on the head sensor temperature and solar zenith angle of the measurements. Measurements in winter, during cold days in general and at high solar zenith angles (> 75 °) were minimally impacted. Measurements during hot days and small solar zenith angles had up to 1 DU contribution from POM-H parts. Multi-axis differential slant column densities were minimally impacted (

Electron irradiation and annealing effects on the pseudogap in optimally doped YBCO single crystals

The effect of room-temperature annealing on the basal-plane conductivity of YBCO single crystals is investigated after their irradiation with fast electrons. It is revealed that the excess conductivity [Formula: see text] of the samples obeys an exponential temperature dependence in a broad temperature range [Formula: see text]. Here, [Formula: see text] is the crossover temperature from the pseudogap to the fluctuation conductivity regime. The description of the excess conductivity with the expression [Formula: see text] can be interpreted in terms of the mean-field theory where [Formula: see text] corresponds to the mean-field transition temperature to the pseudogap state and the dependence [Formula: see text] is described within the framework of the BCS-BEC crossover theory.

ENTROPY GENERATION FOR A NON-NEWTONIAN SHEAR THINNING FLUID WITH VISCOUS HEATING EFFECTS

This paper reports the entropy generation of a two-dimensional, non-isothermal, steady, hydrodynamically and thermally fully-developed flow of an incompressible, non-Newtonian shear thinning fluid between two infinite parallel plates. The inelastic fluid is modeled by a two parameter Carreau constitutive equation with an exponential temperature dependence of viscosity. Temperature dependence of the fluid is modeled through Arrhenius law. Momentum and energy balance equations, which govern the flow, are coupled, and this nonlinear boundary value problem is solved numerically using a Pseudospectral method based on the Chebyshev polynomials. The effect of various flow controlling parameters on velocity, temperature and entropy generation is analyzed. The results indicated that Brinkman number and activation energy have opposite effects on entropy generation due to heat transfer. In contrast to the power-law index, an increase in the material time constant results in a decrease in the Bejan Number.

Peculiarities of Electrical Characteristics of Semi-Insulating CdTe-Сl crystals

Electrical properties of semi-insulating CdTe-Сl crystals, grown by the vertical Bridgman and the travelling heater method, have been studied. It is found that the travelling heater method provides electron conductivity of the crystals, and the vertical Bridgman method – hole conductivity. Specific resistance of the samples is of (108-109) Ohm×сm at 300 K, and Hall mobility of the holes and electrons is of (45 - 55) cm2/V·s and (10 - 20) cm2/V·s respectively. Very low values of electron mobility and an exponential temperature dependence of µn are due to drift barriers with a height of εb ≈ 0.20 eV. Formation of the barriers is caused by the fluctuations of the potential relief resulting from the microheterogeneity of the defect-impurity system. Quasi-photochemical reactions that reduce electron mobility after photo-excitation have been observed in n-CdTe-Cl samples. In p-CdTe-Cl samples, neither drift barriers, nor quasi-photochemical reactions were detected.

Excess conductivity and the pseudogap state in Hf-doped YBa2Cu3O7−δ ceramics

The electrical conductivity of hafnium (Hf)-doped YBa2Cu3O[Formula: see text] ceramics is investigated. Hf doping has been revealed to lead to an increase of the number of effective scattering centers for the normal charge carriers. In a broad temperature range, the excess conductivity of the investigated samples obeys an exponential temperature dependence, while near [Formula: see text] it is satisfactorily described by the Aslamazov–Larkin model. Meanwhile, Hf doping has been shown to lead to a notable broadening of the temperature range for the manifestation of the pseudogap anomaly in the [Formula: see text]-plane.

Viscous dissipation effect on the flow of a thermodependent Herschel-Bulkley fluid

The present study concerns the numerical analysis of both hydrodynamic and thermal properties of a Herschel-Bulkley fluid flow in a pipe. The flow, which involves forced heat transfer convection, is steady and takes place within a pipe of circular cross section with uniform wall temperature. The Herschel-Bulkley model with the Papanastasiou regularization is used and flow index values of 1 and 1.5 are considered. The study focuses on the effect of neglecting both viscous dissipation and temperature dependence of the fluid consistency on its hydrodynamic and thermal properties. For that purpose, we investigate both wall heating (Br<0) and wall cooling (Br>0) as well as the exponential temperature dependence of the consistency. The results show that neglecting both of these parameters results in more than a 50% underestimation of the heat transfer due to the viscous nature of this kind of fluid.

Polyaniline Nanostructures Doped with Fluorescent TPA-BTD-BN

In this paper, a novel fluorescent material with high conductivity as 0.45 S·cm-1 and strong fluorescence has been successfully synthesized basing on polyaniline (PANI) nanostructures doped with a new prepared fluorescein TPABTDBN. The PANI nanostructures were prepared via a simplified template-free method (STFM) with FeCl3 as oxidant and dopant. The resulting sample was characterized by SEM, IR and fluorescence spectroscopy. The fluorescence intensity of synthesized composite improves with the increasing content of TPABTDBN. The electrical properties of pressed composite pellets were measured from room temperature about 291K down to 132K, the conductance follow the exponential temperature dependence of three-dimensional variable-range hopping (VRH) model.

Observations Arising From Exponential Fitting Methods to a Charpy V-Notch Energy Database From Tata Steel

Charpy testing across a range of temperatures is a cost effective way to characterise the ductile-to-brittle transition region. It is often convenient to fit a curve to Charpy data through the transition region: a commonly used method is to use a continuous tan-h fit, a single mathematical expression that links lower shelf, transition region and ductile upper shelf behaviour in one continuous curve. Using this method, the temperature dependence of Charpy energy is a unique feature of each individual steel with some steels exhibiting steep transition curves and some shallow curves. In contrast to Charpy data, fracture toughness data are usually analysed by partitioning upper shelf and transition region data. The transition region data is generally accepted to fit a universal temperature dependence, the Master Curve, as proposed by Wallin [1] and standardised in ASTM E1921 [2]. Recent research on nuclear pressure vessel steels [3, 4] has indicated that when Charpy data is assessed using a similar method to that used for fracture toughness data, a common exponential temperature dependence is observed. This paper presents the current results from an on-going investigation aimed at assessing the effect of exponential curve fitting methods on a large dataset of Charpy V-notch energy data from Tata Steel. The Tata Steel data cover a wide range of parent plate steels. The results are compared to the recent studies on nuclear pressure vessel steels and a similar exponential temperature dependence is observed.