Moscow Institute of Physics and Technology

About: Moscow Institute of Physics and Technology is a education organization based out in Dolgoprudnyy, Russia. It is known for research contribution in the topics: Laser & Plasma. The organization has 8594 authors who have published 16968 publications receiving 246551 citations. The organization is also known as: MIPT & Moscow Institute of Physics and Technology (State University).

VLBI-Gaia offsets favor parsec-scale jet direction in active galactic nuclei

Abstract: Context. The data release 1 (DR1) of milliarcsecond-scale accurate optical positions of stars and galaxies was recently published by the space mission Gaia . Aims. We study the offsets of highly accurate absolute radio (very long baseline interferometry, VLBI) and optical positions of active galactic nuclei (AGN) to see whether or not a signature of wavelength-dependent parsec-scale structure can be seen. Methods. We analyzed VLBI and Gaia positions and determined the direction of jets in 2957 AGNs from their VLBI images. Results. We find that there is a statistically significant excess of sources with VLBI-to-Gaia position offset in directions along and opposite to the jet. Offsets along the jet vary from 0 to tens of mas. Offsets in the opposite direction do not exceed 3 mas. Conclusions. The presense of strong, extended parsec-scale optical jet structures in many AGNs is required to explain all observed VLBI-Gaia offsets along the jet direction. The offsets in the opposite direction shorter than 1 mas can be explained either by a non-point-like VLBI jet structure or a “core-shift” effect due to synchrotron opacity.

Branching fraction measurements of χc0 and χc2 to π0π0 and ηη

Abstract: Using a sample of 1.06 x 10(8) psi' decays collected by the BESIII detector, chi(c0) and chi(c2) decays into pi(0)pi(0) and eta eta are studied. The branching fraction results are Br(chi(c0) -> pi(0)pi(0)) = (3.23 +/- 0.03 +/- 0.23 +/- 0.14) x 10(-3), Br(chi(c2) -> pi(0)pi(0)) = (8.8 +/- 0.2 +/- 0.6 +/- 0.4) x 10(-4), Br(chi(c0) -> eta eta) = (3.44 +/- 0.10 +/- 0.24 +/- 0.2) x 10(-3), and Br(chi(c2) -> eta eta) = (6.5 +/- 0.4 +/- 0.5 +/- 0.3) x 10(-4), where the uncertainties are statistical, systematic due to this measurement, and systematic due to the branching fractions of psi' -> gamma chi(cJ). The results provide information on the decay mechanism of chi(c) states into pseudoscalars.

A test of an engineering model of premixed turbulent combustion

Abstract: The aim of this paper is to test a model of premixed turbulent combustion that joins a closed balance equation for progress variable and a submodel for the chemical timescale that characterizes the maximum possible increase in the local combustion rate under the influence of preferential diffusion into flamelets stretched by turbulent eddies. Since the effect of mixture properties is the main peculiarity of this model, measurements of turbulent combustion velocities, conducted for an extensive set of mixtures with substantially different properties, are chosen to test it. These measurements are simulated by combining the Bray-Moss thermochemistry, the model to be tested, the Bray parameterization of the stretch factor, and the k-∈ submodel of turbulence. Based on the concept of leading points, the dominating role played by critically curved flamelets in premixed turbulent combustion is emphasized. A method for computing a chemical timescale characterizing such flamelets is developed. This method is simple; it involves neither adjustable parameters nor empirical constants but the laminar burning velocity is considered to be an input parameter known from measurements. A comparison between the dependencies of combustion velocities on turbulent velocity, measured previously and computed here for a set of burning mixtures with substantially different properties, is presented. The model quantitatively predicts the dependence of combustion velocities not only on turbulent velocity but also on physicochemical properties of burning mixtures, including the strong effect of preferential diffusion. For moderate turbulence, the quantitative agreement between the measurements and computations has been obtained for various mixtures without any variations in the single remaining model constant unknown a priori.

Effective Connectivity within the Default Mode Network: Dynamic Causal Modeling of Resting-State fMRI Data.

Abstract: The Default Mode Network (DMN) is a brain system that mediates internal modes of cognitive activity, showing higher neural activation when one is at rest. Nowadays, there is a lot of interest in assessing functional interactions between its key regions, but in the majority of studies only association of BOLD (Blood-oxygen-level dependent) activation patterns is measured, so it is impossible to identify causal influences. There are some studies of causal interactions (i.e. effective connectivity), however often with inconsistent results. The aim of the current work is to find a stable pattern of connectivity between four DMN key regions: the medial prefrontal cortex mPFC, the posterior cingulate cortex PCC, left and right intraparietal cortex LIPC and RIPC. For this purpose fMRI (functional magnetic resonance imaging) data from 30 healthy subjects (1000 time points from each one) was acquired and spectral dynamic causal modeling (DCM) on a resting-state fMRI data was performed. The endogenous brain fluctuations were explicitly modeled by Discrete Cosine Set at the low frequency band of 0.0078–0.1 Hz. The best model at the group level is the one where connections from both bilateral IPC to mPFC and PCC are significant and symmetrical in strength (p<0.05). Connections between mPFC and PCC are bidirectional, significant in the group and weaker than connections originating from bilateral IPC. In general, all connections from LIPC/RIPC to other DMN regions are much stronger. One can assume that these regions have a driving role within the DMN. Our results replicate some data from earlier works on effective connectivity within the DMN as well as provide new insights on internal DMN relationships and brain’s functioning at resting state.

Nonlinear Transient Dynamics of Photoexcited Resonant Silicon Nanostructures

Abstract: Optically generated electron–hole plasma in high-index dielectric nanostructures was demonstrated as a means of tuning their optical properties. However, until now an ultrafast operation regime of such plasma-driven nanostructures has not been attained. Here, we perform pump–probe experiments with resonant silicon nanoparticles and report on dense optical plasma generation near the magnetic dipole resonance with an ultrafast (about 2.5 ps) relaxation rate. On the basis of experimental results, we develop an analytical model describing the transient response of a nanocrystalline silicon nanoparticle to an intense laser pulse and show theoretically that plasma-induced optical nonlinearity leads to ultrafast reconfiguration of the scattering power pattern. We demonstrate 100 fs switching to a unidirectional scattering regime upon irradiation of the nanoparticle by an intense femtosecond pulse. Our work lays the foundation for developing ultracompact and ultrafast all-optical signal processing devices.