1,057 research outputs found
Covid-19 vaccines and the competition between independent and politicised models of regulation
The regulatory approaches used to approve Covid-19 vaccines vary substantially across different countries. While some states assign responsibility for vaccine approval to independent regulatory agencies, politicians in other states have greater scope to influence decision-making. Eva Heims and Slobodan Tomic write that the current push to roll out vaccination programmes as quickly as possible is shining a light on competition between these independent and politicised models of regulation
Coexistence of Superconductivity and Spin Density Wave orderings in the organic superconductor (TMTSF)_2PF_6
The phase diagram of the organic superconductor (TMTSF)_2PF_6 has been
revisited using transport measurements with an improved control of the applied
pressure. We have found a 0.8 kbar wide pressure domain below the critical
point (9.43 kbar, 1.2 K) for the stabilisation of the superconducting ground
state featuring a coexistence regime between spin density wave (SDW) and
superconductivity (SC). The inhomogeneous character of the said pressure domain
is supported by the analysis of the resistivity between T_SDW and T_SC and the
superconducting critical current. The onset temperature T_SC is practically
constant (1.20+-0.01 K) in this region where only the SC/SDW domain proportion
below T_SC is increasing under pressure. An homogeneous superconducting state
is recovered above the critical pressure with T_SC falling at increasing
pressure. We propose a model comparing the free energy of a phase exhibiting a
segregation between SDW and SC domains and the free energy of homogeneous
phases which explains fairly well our experimental findings.Comment: 13 pages, 10 figures, revised v: fig.9 added, section 4.2 rewritten,
accepted v: sections 4&5 improve
Fiber-optic interferometric sensor of magnetic field for structural health monitoring
AbstractIn this paper we report on results of measurement of AC and DC magnetic field by fiber-optic interferometric sensor. Principle of operation is based on change of length of optical path cavity between the magnetostrictive wire and fiber-optic tip. Any change of the outside magnetic field causes elongation or contraction of the sensing wire. Using a fiber-optic sensing configuration based on single-mode 3×3 coupler and low-coherence interferometry we were able to read the instant separation between the wire and fiber ends with accuracy of about 50 nm. This separation corresponds with the intensity of the magnetic field in the range of 50 nT to 800 μT what is measured by using well calibrated magnetometer. The sensor is dedicated for on-line structural health monitoring of composite materials made of carbon reinforced epoxy matrix with integrated magnetic particles. Due to final purpose to be embedded in the structure, the sensor is designed to have small overall size of about 250 μm in outside diameter
Linearization of multichannel amplifiers with the injection of second harmonics into the amplifier and predistortion circuit
A linearization technique that uses the injection of the fundamental signal second harmonics together with the fundamental signals at the amplifier input has been extended in this paper by introducing the injection the second harmonics into nonlinear microwave amplifier and so-called predistortion circuit. Predistortion circuit produces the third-order intermodulation signals that are injected at the amplifier input together with the second harmonics making the linearization procedure more independent on the phase variation of the second harmonics. In addition, a considerably better improvement is attained for the power of fundamental signals close to 1-dB compression point by applying the linearization technique proposed in this paper in comparison to the linearization with the injection of the second harmonics merely in the nonlinear amplifier
4-Lump kinetic model for hydrotreated gas oil catalytic cracking
This study has monitored the influence of one of the hydrodesulphurisation process parameters - H2/CH ratio on the properties of three catalytic cracking products (gas, petrol, light cyclic oil, and heavy cyclic oil ).
The microactivity test (MAT) was applied to all kinetic measurements. A 4-lump, non-isothermal and non-stationary kinetic model for the fixed, plug-flow MAT reactor was developed to model catalytic cracking of hydrotreated gas oil. Kinetic constants were estimated by the Nelder Mead method. The product yields predicted by the model showed good confirmity with experimental data
Dry Matter Variability and Quality in Some Perspective Populations of some Agrostis Species
Important goals in forage grass breeding are improvement in forage yield and quality. The objective of this study was the examination of dry matter variability of autochtonous populations of three species from the genus Agrostis L. in order to choose the best ones for creating cultivars. Since we have not had domestic cultivars of these species so far, and it is known that they can be used for various purposes like cutting and grazing and having good quality, this research is made reasonable in many ways. The present results refer to the variability of genetic potentiality of the dry matter production in the year of usage. They refer to the basic parameters of quality on the chosen families originating from 14 populations of colonial bentgrass, Agrostis capillaris L., 22 populations creeping bentgrass, Agrostis stolonifera L. and 7 families originating from redtop, Agrostis gigantea Roth. With all the three species, the most productive family, with statistically significant higher yield, present the initial material for creating the first cultivars in our country
Enhanced Thermoelectric Power and Electronic Correlations in RuSe
We report the electronic structure, electric and thermal transport properties
of RuIrSe (). RuSe is a semiconductor that
crystallizes in a cubic pyrite unit cell. The Seebeck coefficient of RuSe
exceeds -200 V/K around 730 K. Ir substitution results in the suppression
of the resistivity and the Seebeck coefficient, suggesting the removal of the
peaks in density of states near the Fermi level. RuIrSe
shows a semiconductor-metal crossover at about 30 K. The magnetic field
restores the semiconducting behavior. Our results indicate the importance of
the electronic correlations in enhanced thermoelectricity of RuSb.Comment: 6 pages, 4 figure
Anisotropic charge dynamics in the quantum spin-liquid candidate -(BEDT-TTF)Cu(CN)
We have in detail characterized the anisotropic charge response of the dimer
Mott insulator -(BEDT-TTF)\-Cu(CN) by dc conductivity, Hall
effect and dielectric spectroscopy. At room temperature the Hall coefficient is
positive and close to the value expected from stoichiometry; the temperature
behavior follows the dc resistivity . Within the planes the dc
conductivity is well described by variable-range hopping in two dimensions;
this model, however, fails for the out-of-plane direction. An unusually broad
in-plane dielectric relaxation is detected below about 60 K; it slows down much
faster than the dc conductivity following an Arrhenius law. At around 17 K we
can identify a pronounced dielectric anomaly concomitantly with anomalous
features in the mean relaxation time and spectral broadening. The out-of-plane
relaxation, on the other hand, shows a much weaker dielectric anomaly; it
closely follows the temperature behavior of the respective dc resistivity. At
lower temperatures, the dielectric constant becomes smaller both within and
perpendicular to the planes; also the relaxation levels off. The observed
behavior bears features of relaxor-like ferroelectricity. Because
heterogeneities impede its long-range development, only a weak tunneling-like
dynamics persists at low temperatures. We suggest that the random potential and
domain structure gradually emerge due to the coupling to the anion network.Comment: 14 pages, 13 figure
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