Abstract
The effect of hydrostatic pressure up to P = 1.7 GPa on the fluctuation conductivity σ′(T) and pseudogap ∆*(T) in Y
0.95
Pr
0.05
Ba
2
Cu
3
O
7−δ
single crystal with critical temperature Т
с
...= 85.2 K (at P = 0) was investigated. The application of pressure leads to the increase in T
c
with dT
c
/dP = +1.82 K∙GPa
−1
while the resistance decreases as dlnρ(100 K)/dP = −(10.5 ± 0.2) %∙GPa
−1
. Regardless of the pressure, in the temperature interval from T
c
to T
0
(~88 K at P = 0) the behaviour of σ′(T) is well described by the Aslamazov – Larkin (AL – 3D) fluctuation theory, and above the T
0
by the Lawrence – Doniach theory (LD). The Maki-Thompson (MT – 2D) fluctuation contribution is not observed. This indicates the presence of structural defects in the sample induced by Pr. Here it is determined for the first time that when the pressure is applied to the Y
1−x
Pr
x
Ba
2
Cu
3
O
7−δ
single crystal, the pseudogap increases as dlnΔ*/dP = 0.17 GPa
–1
.
Abstract
The effect of annealing both in the oxygen atmosphere and at room temperatures on physical properties such as the pseudogap (Δ*(T)) and excess conductivity (σ′(T)) of untwined YBa
2
Cu
3
O
...7−δ
(YBCO) single crystal with a small deviation from oxygen stoichiometry is studied. It was revealed that as the charge carrier density, n
f
, increases, Т
с
also slightly increases, whereas the temperature of the pseudogap opening, T*, decreases noticeably, which is consistent with the phase diagram (PD) of cuprates. The excess conductivity in the vicinity of T
c
is represented by the Aslamazov-Larkin and Hikami-Larkin fluctuation theories, illustrating the three-dimensional to two-dimensional (i.e. 3D-2D) crossover with an increase in temperature. The crossover temperature T
0
determines the coherence length along the
c
axis is ξ
c
(0) = 0.86 Å, that is 2.6 times larger than for optimally doped YBCO single crystals with defects. Taking into account the short coherence length in high-temperature superconductors, in the model of free charge carriers the phase relaxation time of fluctuating Cooper pairs is determined, τ
φ
(100 K) = (4.55 ± 0.4) · 10
−13
s, which is slightly (1.2 times) larger than in well-structured YBCO films, and as in films, does not depend on n
f
. It is shown that Δ*(T) at different annealing stages practically does not change its shape. As in the well-structured YBCO films, Δ*(T) demonstrates maximum at T
pair
~124 K which depends weakly on n
f
. However, the maximum value of Δ*(T
pair
) increases with increasing n
f
, as it follows from the PD of cuprates. Comparing the experimental data with the Peters-Bauer theory we estimated the density of local pairs <n
↑
n
↓
> ≈ 0.3 near T
c
that is a common value for high-temperature superconductors.
Controlling the growth of thin phthalocyanine films is a long-term challenge for the science of applied nanomaterials. So, this contribution deals with films of unsubstituted zinc phthalocyanine ...(ZnPc) and seeks to acquire structural information that is unavailable
via
physical experiments, thus, finding out how the film morphology can be seriously improved. A model of the vapor-deposited film has been created using the molecular dynamics method. Specifically, the ZnPc molecules are dosed into the simulation box under normal conditions, reproducing key features of the real film, such as the trimolecular wetting layer and the island-like three-dimensional (3D) phase that is structured like the α-polymorph; then all film fragments are characterized
via
their radial distribution functions and mean-squared displacements. The simulation model indicates that the 3D phase starts to develop smoothly through multimolecular cofacial stacking but finally becomes fragmental because the wetting layer is too meager to be a good platform for regular film growth. Accordingly, the film morphology may be improved if the wetting layer is thickened
via
restraining the vertical development of the 3D phase. Following this idea, uniform ZnPc films impaired by neither grain boundaries nor coarser defects were deposited from solutions and visualized at the nanometer scale.
The structure of thin phthalocyanine films is modeled for practical purposes.
The behavior of space charges in both all the volume and local zones of the working volume of solid polymer dielectrics is studied during long-term applying a dc and pulsed voltages up to the ...formation of breakdown channels. The studies show that the larger negative space charge, the smaller the dielectric breakdown time; the appearance of a positive space charge near the anode the cathode and its increase lead to an increase in the lifetime of solid polymeric insulation. The experimental method of measuring space charges during service is proposed to use for monitoring the state of insulation.
Nucleoid-associated proteins (NAPs) control the structure and functions of bacterial nucleoid. Histone-like HU proteins are most abundant NAPs in dividing bacterial cells. Previously, structural ...ensembles of conformations of HU proteins from pathogenic mycoplasmas
Spiroplasma melliferum
and
Mycoplasma gallisepticum
were obtained using NMR spectroscopy. A structural study of these mycoplasma proteins is performed by small-angle X-ray scattering (SAXS). The occurrence of individual conformations from the ensemble, obtained by NMR, is estimated from the scattering data on HU protein solutions. In particular, an approach based on characterization of equilibrium mixtures in terms of volume fractions of their components was applied. The general shape of the proteins and their oligomeric state are independently confirmed using ab initio bead modelling. The flexibility of DNA-binding protein domains is analyzed by the ensemble optimization method, which is based on comparison of the structural characteristics of conformations fitting the SAXS data to the distribution of these characteristics in a randomly generated set. The results obtained give a new insight on the variability of the structure of HU proteins, which is necessary for their functioning.
Purpose. To consider problems of electric machines optimization within a wide range of many variables variation as well as the presence of many calculation constraints in a single-criteria ...optimization search tasks. Results. A structural model for optimizing electric machines of arbitrary type using Microsoft Azure machine learning technology has been developed. The obtained results, using several optimization methods from the Microsoft Azure database are demonstrated. The advantages of cloud computing and optimization based on remote servers are shown. The results of statistical analysis of the results are given. Originality. Microsoft Azure machine learning technology was used for electrical machines optimization for the first time. Recommendations for modifying standard algorithms, offered by Microsoft Azure are given. Practical value. Significant time reduction and resources spent on the optimization of electrical machines in a wide range of variable variables. Reducing the time to develop optimization algorithms. The possibility of automatic statistical analysis of the results after performing optimization calculations.
Typical zinc phthalocyanines (ZnPc) exhibit poor solubility in common solvents and, hence, are processed into thin films mostly from the vapor phase. The present work discloses how these limitations ...can be effectively overcome. Specifically, highly concentrated molecular solutions of unsubstituted ZnPc are prepared by combining a weakly structured ZnPc polymorph with binary liquid systems composed of a π-accepting solvent and a simple nitrogenous base, such as ammonia or tertiary aliphatic amine. The amine-assisted solubilization of ZnPc is rationalized by quantitative analysis of optical spectra and electrostatic potential maps of the dye molecule. A volatile aminoalcohol is proposed in order to rationally modify the habit of ZnPc crystallites and concurrently to produce uniform deposition of the crystallites by drop-casting the dye solutions onto a glass substrate. Finally, a versatile algorithm for wet-processed ZnPc films is declared.
Wet-processing of unsubstituted zinc phthalocyanine into polycrystalline films is mastered.
Abstract
Temperature dependencies of excess conductivity,
σ
′
, have been studied in detail for three FeSe
0.94
textured polycrystalline samples prepared by partial melting and solid state reaction. ...It was revealed that both
σ
′
and its temperature dependence are extremely sensitive to the method of sample preparation. Then, it was shown that in the range from the superconducting transition temperature
T
c
~9 K up to the characteristic temperature
T
01
~19 K,
σ
′
(
T
)
obeys the classical fluctuation theories of Aslamazov–Larkin (AL) and Hikami-Larkin (Maki-Thompson (MT) term) pointing to the existence of fluctuating Cooper pairs in FeSe at temperatures exceeding double
T
c
. Like in cuprates, AL–MT crossover at
T
0
<
T
01
is observed, which means the appearance of 3D–2D dimensional transition at this temperature. This allows us to determine the coherence length along the
c
-axis,
ξ
c
(0) ~3 Å, and a set of additional samples’ parameters, including the phase relaxation time,
τ
ϕ
, of fluctuating Cooper pairs (FCPs), within a simple two-dimensional free-carrier picture. It was shown that
τ
ϕ
in FeSe coincides with that found for YBa
2
Cu
3
O
7
−
δ
suggesting that the nature of superconducting fluctuations is very similar for these high-temperature superconductors of different types.
IntroductionThe COVID-19 pandemic poses a serious threat to mental well-being both for patients who have suffered from coronavirus disease and for medical workers of this period. The difference in ...perceptions about COVID-19 in patients and those who care for them reflects the peculiarities of assessing the coronavirus pandemic and their own coping capabilities.ObjectivesThe aim of the research was to compare the perceptions about COVID-19 in patients and medical professionals during the pandemic.MethodsA Short questionnaire of Disease Perception (E. Broadbent) was used to study patients’ perceptions about COVID-19 disease. The same questionnaire was modified for the perceptions about the COVID-19 pandemic to study the peculiarities of the perceptions about COVID-19 by medical professionals.The study was conducted from January 2021 to November 2022. The sample consisted of 314 medical workers (57 men and 255 women), whose average age was 36.97±11.93, and 390 patients (64 men and 326 women), whose average age was 28.58±10.74. 35 people (11%) of the surveyed medical workers worked in the red zone.ResultsMedical professionals and patients tend to assess the impact of the pandemic on life in the same way. However, according to medical professionals, the COVID-19 pandemic will last longer than according to patients (4.93±2.81 vs 3.18±2.29, p=0.000). Doctors assess their ability to control the pandemic significantly worse than patients assess their disease as a result of coronavirus infection (2.82±2.28 vs 5.30±2.88, p=0.000). Medical workers have a worse assessment of the effectiveness of the measures taken to combat the pandemic (4.75±2.63 vs 5.50±2.67, p=0.000). Doctors are less likely to find symptoms of coronavirus (2.88±2.32 vs 4.98±2.75, p=0.000) and less concerned about the spread of COVID-19 (3.75±2.55 vs 4.20±2.63, p=0.023). Whereas patients have a worse understanding of what COVID-19 is (6.32±2.87 vs 5.52±2.83, p=0.000), and they believe that COVID-19 affects their emotional state to a greater extent than doctors did (3.60±2.66 vs 4.39±2.90, p=0.000).ConclusionsThus, the specifics of the perceptions about COVID-19 may largely depend on whether a person is faced with a coronavirus in the role of a patient or a medical worker. The emotional state of patients is more affected by the pandemic combined with a worse understanding of COVID-19, while medical workers feel less control and tend to regard the measures taken to combat the pandemic as less effective.Disclosure: Research is supported by the Russian Science Foundation, project No. 21-18-00624.Disclosure of InterestNone Declared
The development of electric pulse technologies for the destruction of solids states (rocks)—drilling, cutting and crushing requires reduction of high pulse voltages. In this work, for the first time, ...studies are proposed and carried out to determine the breakdown voltages of various dielectric media (air, water, rocks) while simultaneously supplying two pulses to the electrode system by two high voltage generators of different polarity—positive and negative, which halves the operating impulse voltage each generator. In addition, experiments have shown that for all media there is a decrease in breakdown voltage in comparison with a monopolar voltage pulse, which reaches 28%—for the breakdown of sandstone, 23%—granite, 24%—water, 25%—air. A physical explanation of the discovered effect is given.
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