Explosive Burning of a Mechanically Activated Al and CuO Thermite Mixture

The results of experiments to determine the role of structural schemes for the ignition of a mechanically activated thermite mixture Al–CuO and the formation of its combustion flame are presented. The reaction initiated in the bulk of the experimental assembly transforms into torch combustion in an open space. The dynamics of the volume of the flame reaction region was determined. The stage of flame formation has a stochastic character, determined by the random distribution of the reaction centres in the initial volume of the components. A high-speed camera, a pyrometer and electro contact sensors were used as diagnostic tools. The ultimate goal of the study was to optimize the conditions for the flame formation of this mixture for its effective use with a single ignition of various gas emissions.

Active positioning system based on hall-effect sensors

The paper investigates the behavior of Hall-effect sensors (HES) operating in microwave frequency range. In order to evaluate the capabilities of small radars based on HES’s, the calculation of HES output voltage dependence on microwave intensity is carried out. It is shown that at power flow density I(t) = 10 μW/cm2 (a permissible value for a long-term human body exposure) the single GaAs sensor output Hall voltage U H ~ 0.03 μV. It is also demonstrated that integration of signals with due regard for their delays (as in the case of range-difference radar systems) gives an opportunity to obtain electromagnetic image of any point within the antenna coverage area with centimeter-level accuracy. The paper describes the experimental assembly and estimates the distances to the detected contrasting objects.

Adder Box Used in the Heavy Trucks Transmission Noise Reduction

The paper aims to analyze the vibrations of a summing box, used in heavy vehicles. An experimental setup is proposed and used for the analysis of these vibrations transmitted by the box housing, based on the measurement of the mechanical impedance. It is then shown that a simpler measurement, namely that of the generated noise spectrum, can provide equally useful results, with less effort and in a shorter time. The experimental setup is much simpler, involving a sonometer arranged in the experimental assembly. The symmetry of the box allows us to facilitate the execution of the experimental assembly, and the use of the symmetrical structure to facilitate the calculation of vibrations. The results obtained using this method in the case of a redesigned adder box are presented in the paper.

Microtubules form by progressively faster tubulin accretion, not by nucleation–elongation

Microtubules are dynamic polymers that play fundamental roles in all eukaryotes. Despite their importance, how new microtubules form is poorly understood. Textbooks have focused on variations of a nucleation–elongation mechanism in which monomers rapidly equilibrate with an unstable oligomer (nucleus) that limits the rate of polymer formation; once formed, the polymer then elongates efficiently from this nucleus by monomer addition. Such models faithfully describe actin assembly, but they fail to account for how more complex polymers like hollow microtubules assemble. Here, we articulate a new model for microtubule formation that has three key features: (1) microtubules initiate via rectangular, sheet-like structures that grow faster the larger they become; (2) the dominant pathway proceeds via accretion, the stepwise addition of longitudinal or lateral layers; and (3) a “straightening penalty” to account for the energetic cost of tubulin’s curved-to-straight conformational transition. This model can quantitatively fit experimental assembly data, providing new insights into biochemical determinants and assembly pathways for microtubule nucleation.

Технологическое обеспечение качества поверхностного слоя стекловолоконных композитов при концевом фрезеровании

Introduction. Today fiberglass is one of the most common composite materials. Therefore, its mechanical processing continues to be the subject of many studies. In many scientific publications, the influence of cutting modes and structural and geometric parameters of the tool on the roughness of the machined surface, cutting forces and wear of the cutting tool has been established. The purpose of this work is to study the effect of machining modes on delamination and roughness of fiberglass composites during end milling, as well as testing the hypothesis about the effect of torque on the delamination. The relevance of the study is due to the fact that delamination, along with roughness, has a significant impact on the quality of processing and subsequent assembly of the finished product. A criterion is proposed for assessing the magnitude of the delamination of composite materials during its machining. The results of experimental studies of the torque on the cutter, the relative coefficient of delamination and surface roughness from cutting conditions are presented. Methods: factorial experiment using an experimental assembly developed by the authors based on a piezoelectric torque sensor. The installation allows real-time recording of the change in torque during the milling process, depending on the modes of operation. Results and Discussion. A comparative analysis of the obtained dependences showed that the torque is directly related to delamination. To reduce the delamination, the depth of cut should be decreased, and in order to ensure the specified productivity, the feed and the rotational speed of the cutter should be increased. The presented results confirm the prospects of the developed approach aimed at machining new classes of composite materials.

ANALYSIS OF FAST NEUTRON TRANSPORT IN CHLORIDE SALTS USING MONTE CARLO METHOD

The aim of this paper is to present results of fast neutron behavior analysis within the chloride salts environment using simulations based on Monte Carlo method (MCNP 6.2). Three non-fueled salts (NaCl, KCl, MgCl2) and two salts containing fissile material (UCl3, ThCl4) were studied. Results of this theoretical study will be used for design of an experimental assembly, which will serve to achieve goals of the international research project ADAR (Accelerator Driven Advanced Reactor). One of the project objectives is to investigate chloride salts as potential coolant and a dissolved fuel carrier of advanced nuclear reactor cooled by molten salts and driven by an accelerator.

Thermal Conductivity of Superfluid $$^3$$He-B in a Tubular Channel Down to 0.1$$T_\mathrm{c}$$ at the $$^{4}$$He Crystallization Pressure

We studied the thermal conductivity of superfluid $$^{3}$$ 3 He in a 2.5-mm effective diameter and 0.15-m-long channel connecting the two volumes of our experimental assembly. The main volume contained pure solid $$^{4}$$ 4 He, pure liquid $$^{3}$$ 3 He and saturated liquid $$^{3}$$ 3 He–$$^{4}$$ 4 He mixture at varying proportions, while the separate heat-exchanger volume housed sinter and was filled by liquid $$^{3}$$ 3 He. The system was cooled externally by a copper nuclear demagnetization stage, and, as an option, internally by the adiabatic melting of solid $$^{4}$$ 4 He in the main volume. The counterflow effect of superfluid just below the transition temperature $$T_\mathrm{c}$$ T c resulted in the highest observed conductivity about five times larger than that of the normal fluid at the $$T_\mathrm{c}$$ T c . Once the hydrodynamic contribution had practically vanished below $$0.5T_\mathrm{c}$$ 0.5 T c , we first observed almost constant conductivity nearly equal to the normal fluid value at the $$T_\mathrm{c}$$ T c . Finally, below about $$0.3T_\mathrm{c}$$ 0.3 T c , the conductivity rapidly falls off toward lower temperatures.

ANALYSIS OF NEUTRON FIELDS GENERATED IN SPALLATION TARGETS OF B-URAN EXPERIMENTAL ASSEMBLY USING MONTE CARLO METHOD

The aim of this paper is to introduce experimental assembly B-URAN and the results of Monte Carlo simulations of neutron fields, which will be generated by using various spallation targets. This experimental assembly was constructed in Joint Institute of Nuclear Research in Dubna, Russian Federation, in order to study accelerator driven systems fundamental characteristics. Beam of 660 MeV protons should be used for that purpose. The MCNP model of such set-up has been developed at Brno University of Technology, Czech Republic. The goal is to get data needed for prediction of reaction rates in detectors placed in B-URAN experimental channels. Such data will be experimentally validated later. Furthermore, simulations of radiation exposure around this xperimental assembly were performed.

Visualización de un flujo de convección mediante un arreglo tipo Schlieren

In this work a Schlieren system is proposed. It is used to visualizing a convection flow, caused by the cooling surface a Peltier cell. The experimental assembly elements are a white LED light source (450 nm – 650 nm) that consumes 300 nW of measured electrical power, a Z-type optical reflective relay, a knife, an image acquisition system based on an Edmund EO02018C camera with CMOS RGB sensor and optomechanical components. A program for the analysis of the reference and the convection flow video was designed. As a first step, numerical integration and the phase unwrapping were carrid out to obtain the temperature gradients of the phenomenon under study and its temporal evolution. Then, each detection layer was analyzed, processing the data that provide more information on this phenomenon. It is important to note that the red layer of the camera has a better contrast in the visualization of the phenomenon, however, it is more affected by undesirable light diffraction. Therefore, the green layer of the camera is optimal for analyzing the phenomenon, this study confirms that that the Schlieren technique is ideal for observing phenomena where the temperature gradient is small and there are convection flows.

Microtubules form by progressively faster tubulin accretion, not by nucleation-elongation

Microtubules are dynamic polymers that play fundamental roles in all eukaryotes. Despite their importance, how new microtubules form is poorly understood. Textbooks have focused on variations of a nucleation-elongation mechanism in which monomers rapidly equilibrate with an unstable oligomer (nucleus) that limits the rate of polymer formation; once formed, the polymer then elongates efficiently from this nucleus by monomer addition. Such models faithfully describe actin assembly, but they fail to account for how more complex polymers like hollow microtubules assemble. Here we articulate a new model for microtubule formation that has three key features: i) microtubules initiate via rectangular, sheet-like structures which grow faster the larger they become; ii) the dominant pathway proceeds via accretion, stepwise addition of longitudinal or lateral layers; iii) a ‘straightening penalty’ to account for the energetic cost of tubulin’s curved-to-straight conformational transition. This model can quantitatively fit experimental assembly data, providing new insights into biochemical determinants and assembly pathways for microtubule nucleation.