The physics of high-Tc superconducting cuprates is obscured by the effect of strong electronic correlations. One way to overcome this problem is to seek an exact solution at least within a small ...cluster and expand it to the whole crystal. Such an approach is at the heart of cluster perturbation theory (CPT). Here, we developed CPT for the dynamic spin and charge susceptibilities (spin-CPT and charge-CPT), with the correlation effects explicitly taken into account by the exact diagonalization. We applied spin-CPT and charge-CPT to the effective two-band Hubbard model for the cuprates obtained from the three-band Emery model and calculated one- and two-particle correlation functions, namely, a spectral function and spin and charge susceptibilities. The doping dependence of the spin susceptibility was studied within spin-CPT and CPT-RPA, that is, the CPT generalization of the random phase approximation (RPA). In the underdoped region, both our methods resulted in the signatures of the upper branch of the spin excitation dispersion with the lowest excitation energy at the (π,π) wave vector and no presence of low-energy incommensurate excitations. In the high doping region, both methods produced a low energy response at four incommensurate wave vectors in qualitative agreement with the results of the inelastic neutron scattering experiments on overdoped cuprates.
The structural, magnetic, electrical, and dilatation properties of the rare-earth NdCoO3 and SmCoO3 cobaltites were investigated. Their comparative analysis was carried out and the effect of ...multiplicity fluctuations on physical properties of the studied cobaltites was considered. Correlations between the spin state change of cobalt ions and the temperature dependence anomalies of the lattice parameters, magnetic susceptibility, volume thermal expansion coefficient, and electrical resistance have been revealed. A comparison of the results with well-studied GdCoO3 allows one to single out both the general tendencies inherent in all rare-earth cobaltites taking into account the lanthanide contraction and peculiar properties of the samples containing Nd and Sm.
Electronic structure and magnetic properties of Fe3Se4 are calculated using the density functional approach. Due to the metallic properties, magnetic moments of the iron atoms in two nonequivalent ...positions in the unit cell are different from ionic values for Fe3+ and Fe2+ and are equal to M1=2.071μB and M2=−2.042μB, making the system ferrimagnetic. The total magnetic moment for the unit cell is 2.135μB. Under isotropic compression, the total magnetic moment decreases non-monotonically and correlates with the non-monotonic dependence of the density of states at the Fermi level N(EF). For 7% compression, the magnetic order changes from the ferrimagnetic to the ferromagnetic. At 14% compression, the magnetic order disappears and the total magnetic moment becomes zero, leaving the system in a paramagnetic state. This compression corresponds to the pressure of 114 GPa. The magnetic ordering changes faster upon application of an isotropic external pressure due to the sizeable anisotropy of the chemical bondings in Fe3Se4. The ferrimagnetic and paramagnetic states occur under pressures of 5.0 and 8.0 GPa, respectively. The system remains in the metallic state for all values of compression.
We study quench dynamics and defects formation in the one-dimensional quantum Ising chain in a time-dependent transverse magnetic field, given by a semi-infinite pulse and as the pulse of the finite ...width. The system’s final state depends on the quench time and pulse amplitude, resulting in the emergence of topological defects, and consists of a mixture of ground and excited states. We obtain a new analytical expression, generalizing the Landau–Zener (LZ) and adiabatic-impulse (AI) approximation formulas for the asymptotic probability of remaining in the ground state. We show that our theoretical predictions are in good agreement with the results of the numerical simulations, even when the LZ and AI approximations fail.
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•Wearable microwave radiometer can monitor the core body temperature continuously 24/7.•The size of stable wearable microwave radiometer is 32 × 25 × 14 mm3.•The accuracy of the ...radiometer is independent of the antenna reflection coefficient.•The accuracy of the radiometer is independent of the radiometer front-end temperature.
This paper presents a new circuit of the miniature microwave radiometer for wearable devices, which can be used to monitor the core body temperature (CBT) of internal human tissues continuously 24/7. The measurement results of the proposed device, as opposed to the known miniature wearable radiometers, remain unchanged when the impedance of the examined area varies. We have derived an analytical expression for radiometer measurement error based on parameters of device components. This formula allows accuracies to be estimated and optimal parameters of the circuit to be selected to minimise measurement error at a design stage. It is shown that measurement error is independent of the antenna reflection coefficient and the temperature of the radiometer front-end. A prototype of the single-channel miniature radiometer has 32 × 25 × 14 mm3 dimensions and USB interface communication with PC. A 28 -h run of the device has shown that it is highly stable, and a maximum drift in temperature is 0.15 °C. Operating frequency range was 3400−4100 MHz, supply voltage −5 V; power supply of the radiometer in measurement mode is 210 mA; time constant of the radiometer without being averaged is 0.6 s, at the same time, standard deviation δ = 0.17 °C, with further averaging during 4 s δ = 0.052 °C, with averaging during 30 s δ = 0.017 °C; when there were input reflections R2 = 0.25, an error in measuring brightness temperature shifted by 0.2 °C; with 10 °C variations in ambient temperature the shift was 0.15 °C.
CuO atomic thin monolayer (mlCuO) was synthesized recently. Interest in the mlCuO is based on its close relation to CuO2 layers in typical high temperature cuprate superconductors. Here, we present ...the calculation of the band structure, the density of states and the Fermi surface of the flat mlCuO as well as the corrugated mlCuO within the density functional theory (DFT) in the generalized gradient approximation (GGA). In the flat mlCuO, the Cu-3dx2-y2 band crosses the Fermi level, while the Cu-3dxz,yz hybridized band is located just below it. The corrugation leads to a significant shift of the Cu-3dxz,yz hybridized band down in energy and a degeneracy lifting for the Cu-3dx2-y2 bands. Corrugated mlCuO is more energetically favorable than the flat one. In addition, we compared the electronic structure of the considered CuO monolayers with bulk CuO systems. We also investigated the influence of a crystal lattice strain (which might occur on some interfaces) on the electronic structure of both mlCuO and determined the critical strains of topological Lifshitz transitions. Finally, we proposed a number of different minimal models for the flat and the corrugated mlCuO using projections onto different Wannier functions basis sets and obtained the corresponding Hamiltonian matrix elements in a real space.
The magnetic properties of M2AX (M = Mn, Fe; A = Al, Ga, Si, Ge; X = C, N) phases were studied within DFT-GGA. The magnetic electronic ground state is determined. The investigation of the phase ...stability of M2AX phases is performed by comparing the total energy of MAX phases to that of the set of competitive phases for calculation of the phase formation enthalpy. As the result of such an approach, we have found one stable compound (Mn2GaC), and seven metastable ones. It is shown that several metastable MAX phases (Mn2AlC, Fe2GaC, Mn2GeC, and Mn2GeN) become stable at a small applied pressure (1.5–7 GPa). The mechanical, electronic and elastic properties of metastable MAX phases are studied.
Nucleic acid (NA) aptamers bind to their targets with high affinity and selectivity. The three-dimensional (3D) structures of aptamers play a major role in these non-covalent interactions. Here, we ...use a four-step approach to determine a true 3D structure of aptamers in solution using small-angle X-ray scattering (SAXS) and molecular structure restoration (MSR). The approach consists of (i) acquiring SAXS experimental data of an aptamer in solution, (ii) building a spatial distribution of the molecule’s electron density using SAXS results, (iii) constructing a 3D model of the aptamer from its nucleotide primary sequence and secondary structure, and (iv) comparing and refining the modeled 3D structures with the experimental SAXS model. In the proof-of-principle we analyzed the 3D structure of RE31 aptamer to thrombin in a native free state at different temperatures and validated it by circular dichroism (CD). The resulting 3D structure of RE31 has the most energetically favorable conformation and the same elements such as a B-form duplex, non-complementary region, and two G-quartets which were previously reported by X-ray diffraction (XRD) from a single crystal. More broadly, this study demonstrates the complementary approach for constructing and adjusting the 3D structures of aptamers, DNAzymes, and ribozymes in solution, and could supply new opportunities for developing functional nucleic acids.
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YB-1, a multifunctional DNA- and RNA-binding nucleocytoplasmic protein, is involved in the majority of DNA- and mRNA-dependent events in the cell. It consists of three structurally different domains: ...its central cold shock domain has the structure of a β-barrel, while the flanking domains are predicted to be intrinsically disordered. Recently, we showed that YB-1 is capable of forming elongated fibrils under high ionic strength conditions. Here we report that it is the cold shock domain that is responsible for formation of YB-1 fibrils, while the terminal domains differentially modulate this process depending on salt conditions. We demonstrate that YB-1 fibrils have amyloid-like features, including affinity for specific dyes and a typical X-ray diffraction pattern, and that in contrast to most of amyloids, they disassemble under nearly physiological conditions.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The two widely accepted mechanisms of the insulator-metal Mott-Hubbard transitions which have been considered up until now are driven by the band-filling or bandwidth effects. We found a different ...mechanism of the Mott-Hubbard insulator-metal transition, which is controlled instead by the changes in the Mott-Hubbard energy U. In contrast to the changes in the bandwidth W in the 'bandwidth control' scenario or to the variations of the band-filling n parameter in the 'band-filling' scenario, a dramatic decrease in the Mott-Hubbard energy U plays the key role in this mechanism. We have experimentally observed this type of the insulator metal transition in the transition metal oxide BiFeO{sub 3}. The decrease in the Mott-Hubbard energy is caused by the high-spin-low-spin crossover in the electronic d shell of 3d transition metal ion Fe{sup 3+} with d{sup 5} configuration under high pressure. The pressure-induced spin crossover in BiFeO{sub 3} was investigated and confirmed by synchrotron x-ray diffraction, nuclear forward scattering, and x-ray emission methods. The insulator-metal transition at the same pressures was found by the optical absorption and dc resistivity measurements.
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