S5 0716+714: GeV variability study

The GeV observations by Fermi-LAT give us the opportunity to characterize the high-energy emission (100 MeV–300 GeV) variability properties of the BL Lac object S5 0716+714. In this study, we performed flux and spectral analysis of more than 3 year long (August 2008 to April 2012) Fermi-LAT data of the source. During this period, the source exhibits two different modes of flux variability with characteristic timescales of ∼75 and ∼140 days, respectively. We also notice that the flux variations are characterized by a weak spectral hardening. The GeV spectrum of the source shows a clear deviation from a simple power law, and is better explained by a broken power law. Similar to other bright Fermi blazars, the break energy does not vary with the source flux during the different activity states. We discuss several possible scenarios to explain the observed spectral break.     

On the nature of coronal loops above the quiet sun network

The structure and dynamics of a box in a stellar corona can be modeled employing a 3D MHD model for different levels of magnetic activity. Depending on the magnetic flux through the surface the nature of the resulting coronal structures can be quite different. We investigate a model of an active region for two sunspots surrounded by magnetic field patches comparable in magnetic flux to the sunspots. The model results in emission from the model corona being concentrated in loop structures. In Gudiksen and Nordlund (2005) the loops seen in EUV and X-ray emission outline the magnetic field, following the general paradigm. However, in our model, where the magnetic field is far from a force-free state, the loops seen in X-ray emission do not follow the magnetic field lines. This result is of interest especially for loops as found in areas where the magnetic field emerging from active regions interacts with the surrounding network.     

Improvement of a technological process for ceramic core removal out of internal cavities of aircraft GTE turbine blade castings

A technological process of removing a complex-shaped ceramic core from the interior of GTE thin-walled blade castings is considered. We propose an aluminium oxide-based method for removing a core by leaching accompanied by process intensification with a carboxylic acid additive.     

Computational modeling of interference between helicopter main and tail rotors based on nonlinear blade vortex model

The Mi-2 helicopter was taken as an example for modeling the main and tail rotors operation with account for the interference at low speed sliding flight. Aerodynamic characteristics were calculated. The form of nonlinear vortical wake was obtained.     

Spatial Metaphors of Web Use

When the web became popular, people had to develop ways to talk and think about it. In the mid-1990s, we analyzed spatial language in “web talk.” We found that people described pages as places, and search as motion, both passive and active motion. Here we investigate web talk nearly two decades later. Our analysis reveals that some spatial language has stayed the same, and some has changed. Of special interest is how far fewer motion verbs are used nowadays. We argue that people naturally produce spatial metaphors when talking about new technological domains, and that over time, the most useful elements persist.     

On the modular approach of a 3D model of the system magnetosheath–magnetosphere

This article presents some preliminary features of a new self consistent model of the system magnetosheath–magnetosphere, recently developed in the Institute of Mechanics, Sofia, Bulgaria. The flow in the magnetosheath is governed by 3D ideal gas-dynamic equations. The positions and the shapes of the bow shock and the magnetopause are calculated iteratively as a part of the solution. These surfaces are essentially three-dimensional (generally non-axially-symmetric). The self-consistency between the regions is ensured via the boundary conditions. The magnetopause cusp indentations are formed, influencing essentially the magnetosheath flow. Prediction of the position and the shape of the bow shock for different values of the sonic Mach number are derived. Distribution of some flow parameters in the magnetosheath is presented. 3D numerical finite element model, calculating the field due to the magnetopause currents for an arbitrary magnetopause geometry, is used in the magnetosphere. The fields due to the current systems inside the magnetosphere(cross-tail current, ring current, and Birkeland current) are taken from the Tsyganenko empirical model. The magnetopause surface is calculated from the requirement the outside gas-dynamic pressure to be balanced by the magnetic pressure inside. The magnetosphere model can be viewed as an improved version of the empirical model but with more realistic magnetopause form and shielding field. Not a final but a beta version is used in this approach. The final model version as well the model details will be presented elsewhere.     

The effect of the longitudinal propagating waves on the electron acceleration in the reconnecting current sheet

Based upon the most efficient electron acceleration near the midplane of 3D non-neutral driven reconnecting current sheet (RCS) and the electrostatic wave excitation by the drift Maxwellian distribution of electrons in Vlasov simulation, we assume that the electrostatic waves mainly propagate opposite to the reconnecting electric field and investigated how these waves affect the electron acceleration. The main results are: (1) when the electron’s velocity equals to the phase speed of the waves, they will be trapped and have the different accelerating characteristics from the untrapped electrons through solving the momentum equations of electrons analytically; (2) the test particle simulations further prove that the number of the energetic electrons decreases with the increasing intensity of unstable waves, and the distribution of the energetic electrons takes on the double power-law.     

Exposure to altered gravity affects all stages of endochondral cartilage differentiation.

Chondrogenesis has a number of well-defined steps: (1) condensation, which involves cell aggregation, adhesion and communication; (2) activation of cartilage genes, which is accompanied by rounding up of the cells and intracellular differentiation; and (3) production and secretion of cartilage specific matrix molecules. Our studies show that each of these steps is affected by exposure to gravitational changes. Clinorotation and centrifugation affected initial aggregation and condensation. In the CELLS experiment, where cells were exposed to microgravity after some condensation occurred preflight, intracellular differentiation and matrix production were delayed relative to controls. Once cartilage has developed, in rats, further differentiation (hypertrophy, matrix production) was also affected by spaceflight and hind limb suspension. For the process of chondrogenesis to proceed as we know it, loading and other factors present at 1g are required at each step of the process. This requirement means that not only will skeletal development and bone healing, processes involving chondrogenesis, be altered by long term exposure to microgravity, but that continuous intervention will be necessary to correct any defects produced by altered gravity environments.     

Comparative Utilization of Limited Energy for Continuous and Pulse Operations

Comparative utilization of a limited amount of energy for continuous and pulse operations was investigated. Under a restriction that the amount of available energy was limited, general equations for operational hours of the energy source for given power output were derived for both continuous and pulse mode operations. This paper points out that due to various adjustable parameters available for pulse mode operation, if properly designed pulse mode operation produces longer utilization of available energy for required output power than continuous mode operation.