ABSTRACT
Results of the analysis of the variability of the H β and H α broad emission-line profiles and the He ii λ4686 Å emission-line fluxes in the 3C 390.3 nucleus during 1992–2014 are present. ...The observed velocity-dependent lag for the Balmer lines is similar to that expected from the Keplerian disc configuration, although there are some differences. Probably, a radial infall motion can be present in the broad-line region of 3C 390.3 in addition to the Keplerian rotation. The lag of the broad He ii line is 26 ± 8 d, significantly less than that of the Balmer lines, so the He ii emission region is much smaller in size. In terms of the power-law relationship between line and optical continuum fluxes with slowly varying scale factor c(t): $F_{\rm line}\propto c(t)\, F_{\rm cont}^a$, the power a is 1.03 for the broad He ii line, while according to Paper I, the power is equal to 0.77 and 0.54 for the broad H β and H α lines, respectively. It means that the variability amplitude is the largest in the He ii, less in H β, and more less in H α. However, the Balmer lines contain a long-term trend that is not seen in the helium line. The narrow He ii line is variable with the amplitude (max-to-min ratio) Rmax ≈ 3, which is much greater than the variability amplitudes of both the narrow Balmer lines and the narrow O iii λ5007 Å line.
Spontaneous burst firing is a hallmark attributed to the neuronal network activity. It is known to be accompanied by intracellular calcium Са2+i oscillations within the bursting neurons. Studying ...mechanisms underlying regulation of burst firing is highly relevant, since impairment in neuronal bursting accompanies different neurological disorders. In the present study, the contribution of NMDA and GABA(A) receptors to the shape formation of spontaneous burst -was studied in cultured hippocampal neurons. A combination of inhibitory analysis with simultaneous registration of neuronal bursting by whole-cell patch clamp and calcium imaging was used to assess spontaneous burst firing and Са2+i level.
Using bicuculline and D-AP5 we showed that GABA(A) and NMDA receptors effectively modulate burst plateau phase and Са2+i transient spike which can further affect action potential (AP) amplitudes and firing frequency within a burst. Bicuculline significantly elevated the amplitude and reduced the duration of both burst plateau phase and Са2+i spike resulting in an increase of AP firing frequency and shortening of AP amplitudes within a burst. D-AP5 significantly decreases the amplitude of both plateau phase and Са2+i spike along with a burst duration that correlated with an increase in AP amplitudes and reduced firing frequency within a burst. The effect of bicuculline was occluded by co-addition of D-AP5 revealing modulatory role of GABA(A) receptors to the NMDA receptor-mediated formation of the burst.
Our results provide new evidence on importance of NMDA and GABA(A) receptors in shaping burst firing and Ca2+transient spikes in cultured hippocampal neurons.
•GABA(A)R and NMDAR bi-directionally modulate burst plateau phase amplitude.•GABA(A)R and NMDAR bi-directionally modulate burst Ca2+-spike amplitude.•GABA(A)R and NMDAR modulate burst APs amplitude and firing frequency.•NMDAR plays leading role in tuning parameters of the burst.•GABA(A)R modulates NMDAR-mediated tuning of the burst.
The electronic band structure and features of the charge density distribution in lead oxide phosphate Pb10(PO4)6O and the copper-doped compound Pb9Cu(PO4)6O have been studied by the density ...functional theory. Despite the differences in chemical compositions and crystal structures, the type of chemical bonding in the Pb10(PO4)6O and Pb9Cu(PO4)6O compounds was found to be similar to the type of chemical bonding that we previously revealed in high-temperature superconductors and in parent compounds for their production—monoclinic α-Bi2O3 and orthorhombic La2CuO4. Although the lack of experimental data on the electronic band structure and physical properties of the Pb10(PO4)6O and Pb10−xCux(PO4)6O compounds does not currently allow us to conclude that superconductivity could exist at room temperature and atmospheric pressure in the Pb10−xCux(PO4)6O compound, further studies of the properties of lead oxide phosphate and other minerals of the apatite supergroup might be useful for identifying new types of promising materials for the production of high-temperature superconductors.
Herein, the electronic band structure and charge density distribution are theoretically studied in trigonal Se and Te to clarify the uncertainty stemming from the different views on the types of ...chemical bonding in their crystals and to reconsider the role of valence s- and p-electrons in bonding. The lack of overlapping of the lower and upper bands of valence p-electrons in trigonal Se and the large band separation of valence s- and p-electrons present an opportunity to estimate the contributions of valence s- and p-electrons to the charge densities of two types of bond critical points (BCPs) in trigonal Se. Valence s-electrons and lower p-electrons significantly contribute to the charge density of BCPs of the first type, covalently connecting the nearest neighboring atoms within helical chains. In contrast, the lower and upper valence p-electrons are mainly responsible for the BCPs of the second type linking the neighboring chains in the Se and Te trigonal crystal structures. The nonlocal long-range van der Waals (vdW) correlation functional vdW-DF2, which is important for determining lattice constants, has a minimal effect on BCP parameters, which define the chemical bonding types. The exchange potential of Becke and Johnson modified by Tran and Blaha and the short-range electron–electron correlations considered in the local density approximation correctly reproduce not only the energy bandgap values but also various peculiarities in the electronic band structure of trigonal Se and Te, such as band crossings (Weyl nodes) of the valence p-electrons recently found in trigonal Te via angle-resolved photoemission spectroscopy experiments.
We discuss the origin of the optical variations in the narrow-line Seyfert 1 galaxy NGC 4051 and present the results of a cross-correlation study using X-ray and optical light curves spanning more ...than 12 years. The emission is highly variable in all wavebands, and the amplitude of the optical variations is found to be smaller than that of the X-rays, even after correcting for the contaminating host galaxy flux falling inside the photometric aperture. The optical power spectrum is best described by an unbroken power-law model with slope α= 1.4+0.6−0.2 and displays lower variability power than the 2–10 keV X-rays on all time-scales probed. We find the light curves to be significantly correlated at an optical delay of 1.2+1.0−0.3 d behind the X-rays. This time-scale is consistent with the light traveltime to the optical emitting region of the accretion disc, suggesting that the optical variations are driven by X-ray reprocessing. We show, however, that a model whereby the optical variations arise from reprocessing by a flat accretion disc cannot account for all the optical variability. There is also a second significant peak in the cross-correlation function, at an optical delay of 39+2.7−8.4 d. The lag is consistent with the dust sublimation radius in this source, suggesting that there is a measurable amount of optical flux coming from the dust torus. We discuss the origin of the additional optical flux in terms of reprocessing of X-rays and reflection of optical light by the dust.
The electronic band structure of orthorhombic compound La
2
CuO
4
, which is the parent for a number of high-temperature superconductor families, has been calculated in terms of the density ...functional theory using the WIEN2k program package. Calculations have been performed by means of two exchange-correlation functionals. The former is a sum of the Tran- and Blaha-modified Becke–Johnson exchange potential and correlations in a local approximation, whereas the latter is the Perdew–Burke–Ernzerhof functional. Calculations taking into account spin polarization have shown the presence of an antiferromagnetic ground state in orthorhombic La
2
CuO
4
. Using the former functional, the magnetic moment of copper atoms and a semiconductor gap have been found to be
M
Cu
= 0.725μ
B
and
E
g
= 2 eV. The latter has yielded
M
Cu
= 0.278μ
B
and
E
g
= 0. Calculations results for the optical properties of orthorhombic La
2
CuO
4
: the electron energy losses, the real part of optical conductivity, and reflection coefficient, are in good agreement with experimental data. The calculated spatial distribution of the charge density in orthorhombic compound La
2
CuO
4
has been analyzed with the aim of finding critical saddle points with parameters making it possible to classify the types of chemical bonds in crystals. The set of critical point parameters for orthorhombic La
2
CuO
4
has turned out to be similar to that previously found by us for tetragonal La
2
CuO
4
and related high temperature superconductors. In particular, the positive sign of the charge density Laplacian at bond critical points indicates the absence of covalent bonding in La
2
CuO
4
according to the chemical bond classification proposed by Bader in his “Quantum Theory of Atoms in Molecules and Crystals.”
•Critical points in charge density of Bi and Sb chalcogenides are found.•Premises for charge density fluctuations in Bi and Sb chalcogenides are revealed.•Charge density fluctuations are proposed to ...be the origin of anomalous properties.•Existence of local magnetic fields in Sb2S3 is found.
Electron band structure calculations and analysis of critical points parameters in the electron density distribution in Bi2Te3, Bi2Se3, Bi2S3, α-Bi2O3, Sb2Te3, Sb2Se3 and Sb2S3 at ambient and high pressures were performed to determine interrelations between the crystal structure, unusual physical (including magnetic and superconducting) properties and peculiarities in the electron density distribution. The programming code WIEN2k was used for band structure calculations. The previously found correlation between the superconducting transition temperature Tc and the electron density Laplacian value in the bond critical point with the highest electron density was confirmed by the calculations made for crystal structures under high pressure. The revealed parameters of bond critical points indicate the significant role of charge density fluctuations in the compounds studied.
The 121, 123Sb NQR spin echo envelopes assigned to the ν1 transition (Δm = 1/2–3/2) were measured for the two crystallographic positions of Sb atoms in the Sb2S3 structure. Unexpectedly deep oscillations of NQR spin echo envelopes were observed in very small (1–3 Oe) external magnetic fields, evidencing for the existence of local magnetic fields in Sb2S3 similar to those earlier observed in bismuth oxide compounds.
We present the results of concurrent X-ray and optical monitoring of the Seyfert 1 galaxy Mrk 79 over a period of more than 5 yr. We find that on short to medium time-scales (days to a few tens of ...days) the 2–10 keV X-ray and optical u- and V-band fluxes are significantly correlated, with a delay between the bands consistent with 0 d. We show that most of these variations may be well reproduced by a model where the short-term optical variations originate from reprocessing of X-rays by an optically thick accretion disc. The optical light curves, however, also display long time-scale variations over thousands of days, which are not present in the X-ray light curve. These optical variations must originate from an independent variability mechanism and we show that they can be produced by variations in the (geometrically) thin disc accretion rate as well as by varying reprocessed fractions through changes in the location of the X-ray corona.
We determine interband lags between variations in the B band and variations in the V, R, and I bands for 14 active galactic nuclei observed at the Crimean Astrophysical Observatory. The computed lags ...range from tenths of a day to several days, and it is positive (that is, V, R, and I bands lag behind the B band) in most cases, except for a few cases for the V filter. In some cases, the lag is greater than zero, with more than 3 sigma confidence. The lag is systematically less for the V filter than for the red filters, and the lag determined from the cross-correlation function (CCF) centroid is systematically greater than the lag determined from the CCF peak. We find that the lag scales with luminosity as L super(b), where b approximately 0.4-0.5. We attribute this lag to the light time travel effect, so it reflects the geometrical size of the region that emits optical continuum. We consider a model in which optical emission is mainly reprocessed emission that arises in the accretion disk heated by an X-ray source above the disk.
Abstract The article is devoted to improving the physical, mechanical and operational characteristics of cast internal combustion engine pistons made of aluminum alloy using secondary charge. The ...advantage of the proposed approach is that these parts are manufactured from any aluminum alloy using the remelting of failed internal combustion engine parts of the same name. The paper shows that while using a secondary charge in the form of remelting failed parts of the same name, the quality of cast products not only does not deteriorate, but, on the contrary, their physical and mechanical characteristics even increase. It should be noted that the high density of the alloy obtained from remelting failed pistons and the high degree of its modification confirmed the authors’ assumption that in this case refining and modification operations can be avoided. The presented approach using the remelting of failed parts makes it possible not only to save fresh charge materials, but also to preserve the chemical composition of the primary parts, and, consequently, the level of their physical, mechanical and operational characteristics.
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