The strong mixing of close levels with two valence electrons in Be-like xenon greatly complicates ab initio QED calculations beyond the first-order approximation. Because of a strong interplay ...between the electron-electron correlation and QED effects, the standard single-level perturbative QED approach may fail, even if it takes into account the second-order screened QED diagrams. In the present Letter, the corresponding obstacles are overcome by working out the QED perturbation theory for quasidegenerate states. The contributions of all the Feynman diagrams up to the second order are taken into account. The many-electron QED effects are rigorously evaluated in the framework of the extended Furry picture to all orders in the nuclear-strength parameter αZ. The higher-order electron-correlation effects are considered within the Breit approximation. The nuclear recoil effect is accounted for as well. The developed approach is applied to high-precision QED calculations of the ground and singly excited energy levels in Be-like xenon. The most accurate theoretical predictions for the binding and excitation energies are obtained. These results deviate from the most precise experimental value by 3σ but perfectly agree with a more recent measurement.
The nuclear recoil effect on the g factor of Li-like ions is evaluated. The one-electron recoil contribution is treated within the framework of the rigorous QED approach to the first order in the ...electron-to-nucleus mass ratio m/M and to all orders in the parameter αZ. These calculations are performed in a range Z=3-92. The two-electron recoil term is calculated for low- and middle-Z ions within the Breit approximation using a four-component approach. The results for the two-electron recoil part obtained in the Letter strongly disagree with the previous calculations performed using an effective two-component Hamiltonian. The obtained value for the recoil effect is used to calculate the isotope shift of the g factor of Li-like ^{A}Ca^{17+} with A=40 and A=48 which was recently measured. It is found that the new theoretical value for the isotope shift is closer to the experimental one than the previously obtained value.
We report on the results of the extensive multi-wavelength campaign from optical to GeV γ-rays of the 2014 periastron passage of PSR B1259−63, which is a unique high-mass γ-ray emitting binary system ...with a young pulsar companion. Observations demonstrate the stable nature of the post-periastron GeV flare and prove the coincidence of the flare with the start of rapid decay of the Hα equivalent width, usually interpreted as a disruption of the Be stellar disc. Intensive X-ray observations reveal changes in the X-ray spectral behaviour happening at the moment of the GeV flare. We demonstrate that these changes can be naturally explained as a result of synchrotron cooling of monoenergetic relativistic electrons injected into the system during the GeV flare.
We report on broad multiwavelength observations of the 2010-2011 periastron passage of the γ-ray loud binary system PSR B1259−63. High-resolution interferometric radio observations establish extended ...radio emission trailing the position of the pulsar. Observations with the Fermi
Gamma-ray Space Telescope reveal GeV γ-ray flaring activity of the system, reaching the spin-down luminosity of the pulsar, around 30 d after periastron. There are no clear signatures of variability at radio, X-ray and TeV energies at the time of the GeV flare. Variability around periastron in the Hα emission line, can be interpreted as the gravitational interaction between the pulsar and the circumstellar disc. The equivalent width of the Hα grows from a few days before periastron until a few days later, and decreases again between 18 and 46 d after periastron. In near-infrared we observe the similar decrease of the equivalent width of Brγ line between the 40th and 117th day after the periastron. For the idealized disc, the variability of the Hα line represents the variability of the mass and size of the disc. We discuss possible physical relations between the state of the disc and GeV emission under assumption that GeV flare is directly related to the decrease of the disc size.
•Light activated chloride channel GtACR2 was expressed in vivo in rat pyramidal neurons.•Light stimulation of GtACR2 can induce both inhibition and excitation of cells.•Light-induced generation of ...action potentials most likely occurs in axonal terminals.•GtACR2 potentially could be used both as cell silencer and cell activator in optogenetics experiments.
Optogenetics is a powerful technique in neuroscience that provided a great success in studying the brain functions during the last decade. Progress of optogenetics crucially depends on development of new molecular tools. Light-activated cation-conducting channelrhodopsin2 was widely used for excitation of cells since the emergence of optogenetics. In 2015 a family of natural light activated chloride channels GtACR was identified which appeared to be a very promising tool for using in optogenetics experiments as a cell silencer. Here we examined properties of GtACR2 channel expressed in the rat layer 2/3 pyramidal neurons by means of in utero electroporation. We have found that despite strong inhibition the light stimulation of GtACR2-positive neurons can surprisingly lead to generation of action potentials, presumably initiated in the axonal terminals. Thus, when using the GtACR2 in optogenetics experiments, its ability to induce action potentials should be taken into account. Our results also open an interesting possibility of using the GtACR2 both as cell silencer and cell activator in the same experiment varying the pattern of light stimulation.
•The mathematical model for nanoparticles capture from sulfur is proposed.•Concentration and size distribution analysis is performed by laser ultramicroscopy.•The efficiency of crystallization ...methods for sulfur high purification is shown.
High-purity sulfur used in nanotechnology, assumes a total impurity content at the level of 1 · 10−3–1 · 10−4 wt% and also limiting impurities at the level of 1 · 10−7–1 · 10−8 wt%, which include both molecular and heterogenous nanoparticles. The mathematical model for the efficiency of the capture of nanosized particles by the directional crystallization has been developed. The model was verified on the experimental data on the capture of nanosized particles (silver and germanium (30–60 nm)) by the crystallization front of benzene and then it has been used for calculation of sulfur purification process. It is found that the rate of the crystal growth increases, the energy of the particle that is due to the motion of the melt also increases and, consequently, the rate of transition of particles from the melt into the crystal increases too. It is found that as the rate of the crystal growth increases, the distribution coefficient decreases but at the rate greater than 1 cm/h it begins to increase. With an increase in the rate of crystallization, the rate of the transition of particles from the melt to the crystal increases exponentially with a linear increase of the crystallization rate. The calculations showed that the value of the potential of the disjoining pressure is determined by the values of interaction constant and particle size. Since the value of the particle distribution coefficient between the crystal and the melt in the process of the crystal growth differs from unity, crystallization methods can be sufficiently effective for sulfur high purification.
The results of the theoretical and experimental studies of the ignition processes of a completely new class of fuel - Bio water-coal (Bio-WCF) based on charcoal and coal. Based on the results of a ...high-speed video recording of the ignition process, the main stages of thermal preparation (evaporation of moisture from the surface layer of the particle, thermal decomposition of the organic part of the coal) and the ignition of Bio-WCF drops have been identified.
The experiments have been carried out on the setup providing a low level of error (not more than 11.2%) of the main recorded values (ignition delay time (t
ign
), a characteristic size of the fuel particles at the initial time d, temperature of the oxidizing agent T
e
). The temperature regime has varied over a wide range (873≤ Te≤1273 K) and corresponded to the actual operating conditions of the steam and hot water boilers.
It is established that the addition of charcoal to the structure of a water-coal suspension leads to a significant acceleration of the ignition process. It has been shown that at relatively low temperatures (Te = 873 K) the addition of charcoal to the WCF structure accelerates the ignition process by 40%. Under conditions of high oxidizer temperatures, the ignition delay times of Bio-WCF and WCF are identical. According to the results of the experiments, it has been found that when particles of bio-coal-carbon fuel based on high-volatile A bituminous coal are ignited, dispersion of the surface fuel layer is possible. In the case of the ignition of Bio-WCF based on semi-anthracite, such an effect has not been registered.
Based on a detailed analysis of the video frames, a mathematical model of the ignition process of suspension fuel based on water, coal, and charcoal is developed. The numerical simulation of the ignition process has been carried out and the ignition delay times have been calculated. A comparative analysis of the theoretical and experimental values of t
ign
has shown their good agreement. According to the results of a mathematical modeling, the values of the concentrations of the components of the gas mixture at the moment of ignition of a particle of bio water-coal fuel have been established. It is shown that a vapor-gas mixture is formed in the particle boundary layer with a large concentration gradient and with a complex topology caused by a convective-diffusive motion in the "volatile-oxidizer" system.
The article presents the experimental research results of the flame propagation processes in the small vicinity of Bio-WCF particles during their ignition. According to the experimental researches, ...there have been obtained characteristic ignition delay times (t
ign
) and times of full engulfment of the fuel particle in fire (t
sf
). We have analyzed the influence of metamorphism degree of fuel basic component (coal) and sort of biomass on characteristics of these processes. It has been shown that increase in concentration of biomass in fuel leads to decrease in ignition delay times and fire propagation in boundary layer of the Bio-WCF particle. We have recognized that the oxidizer temperature (T
g
) strongly influences the fire propagation dynamic in small volume vicinity of fuel particles. Also, we have observed that the effect of influence of oxidizer temperature (T
g
) on the time of full engulfment of the fuel particle in fire (t
sf
) differs from the predicted once. Increase in T
g
in a certain period of changes in its values (T
g
= 1073-1273 K) leads to increase in time of full engulfment of the Bio-WCF particle in fire. The hypothesis describes the influence of ambient temperature on t
sf
was formulated.
We have substantiated the hypothesis using the results of mathematical modeling. This hypothesis describes the physical mechanism of the influence of water vapors, which are formed during intrapore moisture evaporation on characteristics and conditions of volatile combustion in the boundary layer of the fuel particle.
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