Properties of the jet in M87 revealed by its helical structure imaged with the VLBA at 8 and 15 GHz

We present full-track high-resolution radio observations of the jet of the galaxy M87 at 8 and 15 GHz. These observations were taken over three consecutive days in May 2009 using the Very Long Baseline Array (VLBA), one antenna of the Very Large Array (VLA), and the Effelsberg 100 m telescope. Our produced images have dynamic ranges exceeding 20,000:1 and resolve linear scales down to approximately 100 Schwarzschild radii, revealing a limb-brightened jet and a faint, steep spectrum counter-jet. We performed jet-to-counter-jet analysis, which helped estimate the physical parameters of the flow. The rich internal structure of the jet is dominated by three helical threads, likely produced by the Kelvin-Helmholtz (KH) instability developing in a supersonic flow with a Mach number of approximately 20 and an enthalpy ratio of around 0.3. We produce a CLEAN imaging bias-corrected 8-15GHz spectral index image, which shows spectrum flattening in regions of helical thread intersections. This further supports the KH origin of the observed internal structure of the jet. We detect polarised emission in the jet at distances of approximately 20 milliarcseconds from the core and find Faraday rotation which follows a transverse gradient across the jet. We apply Faraday rotation correction to the polarisation position angle and find that the position angle changes as a function of distance from the jet axis, which suggests the presence of a helical magnetic field.Comment: 15 pages, 10 figures, 1 table, Submitted to MNRAS on 25th March 202

Resistive and magnetoresistive properties of CrO2 pressed powders with different types of inter-granular dielectric layers

Resistive, magnetoresistive and magnetic properties of four kinds of pressed CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been investigated. The particles in powders constituted of rounded particles (diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm and average length of 302 nm. All of the particles had a surface dielectric shell of varying thickness and different types (such as oxyhydroxide -CrOOH or chromium oxide Cr2O3). For all the samples at low temperatures we found non-metallic temperature dependence of resistivity and giant negative magnetoresistance (MR). The maximum value of MR at low temperatures (T \approx 5 K) is \approx 37% in relatively small fields (0.5 T). At higher temperatures there was a rapid decrease of MR (up to \approx 1% / T at T \approx 200 K). The main objective of this work was studying the influence of properties and thickness of the intergranular dielectric layers, as well as CrO2 particle shape, on the magnitude of the tunneling resistance and MR of the pressed powder. The new results obtained in this study include: (1) detection at low temperatures in powders with needle-like particles a new type of MR hysteresis, and nonmonotonic MR behaviour with increasing magnetic field (absolute value of the MR at first grows rather rapidly with the field, and then begins diminishing markedly, forming a maximum), and (2) detection of non-monotonic temperature dependence, where - a field in which the resistance in a magnetic field has a maximum, as well as finding discrepancies in values of and coercivity fields, (3) detection of the anisotropy of MR, depending on the relative orientation of the transport current and the magnetic field, (4) a new method of synthesis, to regulate the thickness of dielectric coating.Comment: 19 pages, 8 figure

Pressure effect on magnetic susceptibility of LaCoO3_3

The effect of pressure on magnetic properties of LaCoO$_3$ is studied experimentally and theoretically. The pressure dependence of magnetic susceptibility $\chi$ of LaCoO$_3$ is obtained by precise measurements of $\chi$ as a function of the hydrostatic pressure $P$ up to 2 kbar in the temperature range from 78 K to 300 K. A pronounced magnitude of the pressure effect is found to be negative in sign and strongly temperature dependent. The obtained experimental data are analysed by using a two-level model and DFT+U calculations of the electronic structure of LaCoO$_3$. In particular, the fixed spin moment method was employed to obtain a volume dependence of the total energy difference $\Delta$ between the low spin and the intermediate spin states of LaCoO$_3$. Analysis of the obtained experimental $\chi(P)$ dependence within the two-level model, as well as our DFT+U calculations, have revealed the anomalous large decrease in the energy difference $\Delta$ with increasing of the unit cell volume. This effect, taking into account a thermal expansion, can be responsible for the temperatures dependence of $\Delta$, predicting its vanishing near room temperature.Comment: 7 pages, 9 figure

Thermal and magnetic properties of integrable spin-1 and spin-3/2 chains with applications to real compounds

The ground state and thermodynamic properties of spin-1 and spin-3/2 chains are investigated via exactly solved su(3) and su(4) models with physically motivated chemical potential terms. The analysis involves the Thermodynamic Bethe Ansatz and the High Temperature Expansion (HTE) methods. For the spin-1 chain with large single-ion anisotropy, a gapped phase occurs which is significantly different from the valence-bond-solid Haldane phase. The theoretical curves for the magnetization, susceptibility and specific heat are favourably compared with experimental data for a number of spin-1 chain compounds. For the spin-3/2 chain a degenerate gapped phase exists starting at zero external magnetic field. A middle magnetization plateau can be triggered by the single-ion anisotropy term. Overall, our results lend further weight to the applicability of integrable models to the physics of low-dimensional quantum spin systems. They also highlight the utility of the exact HTE method.Comment: 38 pages, 15 figure

Optimization of Vaccine Virus Accumulation in the Development of Smallpox Drugs Based on Cell Cultures

Objective. Optimization of vaccine virus cultivation in the suspended cell culture BHK-21 for infectious activity increment of virus-containing suspension as the base material for smallpox vaccine preparations. Materials and methods. We used suspended culture line of the cells BHK-21 of 72-hour age and nutrient medium of the MEM type in accordance with the guidelines on preparation in our studies. For challenging of the cells, vaccine virus (strain B-51) was used. The virus was adapted through three consequent passages on horion-allantois shell of developing chicken embryos of commercial dermovaccine series 449а at the premises of the Federal State Budgetary Institution “the 48th Central Research Institute” of the Ministry of Defense of the Russian Federation. Information on its genetic features is absent. Cultivation and precipitation of infected cells BHK-21 was carried out in bioreactor with priming volume of 1 liter at (36.5±0.5) °C and aeration with air mixture with varying content of CO2. Results and conclusions. Gas  massexchange intensity was enhanced alongside simultaneous maintaining of sparing hydrodynamic conditions for mixing suspended cell cultures in bioreactor. Two-fold increase (up to (4.48±0.63)·109 cell/l) in suspended BHK-21 cell culture concentration at the end of reproduction cycle was achieved. Concentration of the vaccine virus was 3–5 times raised, from (8.1±0.3) lg PFU (plaque forming unit)/ml up to the level of infectious activity – (8.8±0.3) lg PFU/ml. Specific multiplicity of cell infection in recalculation per a cell was 1–5 PFU/cell and by virus yield – 20–100 PFU/cell. Enhanced infectious activity of the virus in concentrated suspension of infected BHK-21 cells substantiates the perspectives of the proposed method for improvement of vaccine virus accumulation phase in the development of anti-smallpox preparations based on cell cultures

OJ287: deciphering the 'Rosetta stone of blazars

OJ287 is the best candidate active galactic nucleus (AGN) for hosting a supermassive binary black hole (SMBBH) at very close separation. We present 120 Very Long Baseline Array (VLBA) observations (at 15 GHz) covering the time between April 1995 and April 2017. We find that the OJ287 radio jet is precessing on a time-scale of similar to 22 yr. In addition, our data are consistent with a jet-axis rotation on a yearly time-scale. We model the precession (24 +/- 2 yr) and combined motion of jet precession and jet-axis rotation. The jet motion explains the variability of the total radio flux-density via viewing angle changes and Doppler beaming. Half of the jet-precession time-scale is of the order of the dominant optical periodicity time-scale. We suggest that the optical emission is synchrotron emission and related to the jet radiation. The jet dynamics and flux-density light curves can be understood in terms of geometrical effects. Disturbances of an accretion disc caused by a plunging BH do not seem necessary to explain the observed variability. Although the SMBBH model does not seem necessary to explain the observed variability, an SMBBH or Lense-Thirring precession (disc around single BH) seem to be required to explain the time-scale of the precessing motion. Besides jet rotation also nutation of the jet axis could explain the observed motion of the jet axis. We find a strikingly similar scaling for the time-scales for precession and nutation as indicated for SS433 with a factor of roughly 50 times longer in OJ287