α-catenin is a crucial protein at cell junctions that provides connection between the actin cytoskeleton and the cell membrane. At adherens junctions (AJs), α-catenin forms heterodimers with ...β-catenin that are believed to resist force on F-actin. Outside AJs, α-catenin forms homodimers that regulates F-actin organization and directly connect the cell membrane to the actin cytoskeleton, but their mechanosensitive properties are inherently unknown. By using ultra-fast laser tweezers we found that a single α-β-catenin heterodimer does not resist force but instead slips along F-actin in the direction of force. Conversely, the action of 5 to 10 α-β-catenin heterodimers together with force applied toward F-actin pointed end engaged a molecular switch in α-catenin, which unfolded and strongly bound F-actin as a cooperative catch bond. Similarly, an α-catenin homodimer formed an asymmetric catch bond with F-actin triggered by protein unfolding under force. Our data suggest that α-catenin clustering together with intracellular tension engage a fluid-to-solid phase transition at the membrane-cytoskeleton interface.
In this paper, we present the results of the analysis of the radiation conditions of the diagnostic detector modules Divertor Neutron Flux Monitor (DNFM) of the ITER tokamak reactor. The DNFM ...diagnostic system is designed to measure the total neutron yield and fusion power of ITER. At the final stage of designing the DNFM system, a decision was made to change the location of the diagnostic detector modules, which required refining calculations of the energy distribution of the neutron flux in the area of the diagnostic detectors, the uranium fission reaction rate in the DNFM fission chambers, and the Green’s function of the fission reaction rate. The response of the system to the spatial distribution of the DT neutron yield from the ITER plasma for the standard scenario of 500 MW of fusion power was studied. The simulation was performed in the recommended 3D model of the ITER tokamak reactor using the MCNP code. On the basis of the results of neutronic analysis and the requirements for diagnostics by the ITER Organization, the expected performance characteristics of DNFM diagnostics are confirmed.
We present a brief analytic review of position-sensitive detectors of thermal and cold neutrons based on a
thin-film converter. Most attention is paid to new approaches and technical solutions ...determining trends in development of this technique.
A brief analytical review of position-sensitive thermal and cold neutron detectors based on a
gas converter is presented. Most attention is paid to new approaches and technical solutions that ...determine the developmental trends of the methodology.
Abstract
A prototype of the WEM (Well Electron Multiplier) detector with an active area of 10 × 10 mm
2
and a resistive DLC anode was tested in terms of robustness to electrical discharges induced by ...highly ionizing particles (
241
Am alpha source). The perforated structure of the WEM detector was produced from a 500 μm thick FR4 with drilled holes of 200 μm in diameter and 500 μm in pitch. The resistive anode was made of 100 nm thick DLC layer with 30 MOhm/square sheet resistance deposited on the anode grid electrode. The anode grid electrode is used to distribute voltage to the resistive layer and provide fast charge evacuation. The detector was operated in Ar:CO
2
(90:10) gas mixture at gas gain of 3,500. The alpha source was placed in the drift gap. The WEM detector with intrinsic capacitance of 34 pF did not show visible damage and changes in performance after 1 million accumulated discharges. To simulate a large area detector, we added a capacitance up to 1 nF in parallel with the test device. The results of the experiments with an additional capacitance revealed that a small WEM prototype can't be directly scaled to the dimensions more than 60 × 60 mm
2
without losing the robustness to discharges. We assume that the observed damage could be caused by the design features of the prototype. The grid anode electrode with a thickness of 35 μm results in a gap between the perforated FR4 board and the resistive anode board. Simulations of the electric field distribution with Comsol Multiphysics software revealed a significant electric field strength in this gap. This could lead to electric discharge path bypassing the protective resistive DLC layer. A possible solution to this problem could be additional insulation of the anode grid electrode with a coverlay similar to that used in bulk MicroMegas production.
Results of calculation of nuclear heat deposition rate in the vacuum vessel and magnetic coils of the tokamak with reactor technologies are presented. Results obtained for D–D and D–T plasmas are ...compared with each other. Based on the results of the calculations, a conclusion is reached that the nuclear heat rate for the D–D plasma falls into an acceptable range below 1 mW/cm
3
, and the proposed vacuum vessel design is satisfactory from the point of view of radiation shielding. For the D–T plasma, the question regarding additional protection measures or limitation of discharge time remains open for discussion. Based on calculated spatial and energy distributions of the neutron field, we draw the conclusion that an increase in the thickness of protective water layer has the largest effect from the point of view of increasing radiation shielding. Nevertheless, the thickness of the water layer has to be more than doubled in the vacuum vessel, at least, in the inner segment near the equatorial plane, in order to decrease the heat load on the toroidal field coil to the level allowing long discharge when the system operates with D–T plasma. The sources of energy release in toroidal coils are estimated, along with several variants of shielding. In particular, the statement that using boron enriched with
10
B isotope has nearly no impact on energy release is substantiated. The possibility of operation with D–D plasma is confirmed, and problems of radiation shielding when using D–T plasma are revealed.
Multichannel Neutron Collimator for TRT Nemtsev, G. E.; Rodionov, R. N.; Khafizov, R. R. ...
Plasma physics reports,
12/2022, Letnik:
48, Številka:
12
Journal Article
Recenzirano
The project is described of the neutron camera for the tokamak with reactor technologies (TRT). The neutron camera is a multichannel neutron collimator covering the plasma neutron source with ...observation chords. The neutron camera is a system designed for measuring the profile of fusion neutron source in the poloidal cross section of the tokamak. The system conceptual design is proposed, which includes ten measuring channels of collimators that monitor the plasma in the radial direction. For more detailed covering the plasma neutron source with observation lines, it is proposed that the system will also be equipped with several vertical collimators. The channels of collimators are located inside the vacuum chamber ports, being partly introduced into the facility cryostat volume. Such a solution makes it possible to improve the coverage of the plasma volume by observation lines. It is proposed to use stainless steel and high-density borated polyethylene as materials for the collimators. It is planned to use diamond detectors and scintillators based on stilbene and lanthanum chloride as neutron detectors. The plasma neutron source is simulated in this work. Using radiative transport calculations, the neutron fluxes and spectra in the channels of collimators were obtained. The neutron camera of the TRT facility will make it possible to measure the profiles of neutron sources in DD and DT plasmas, as well as the ratios of emission intensities of DD and DT neutrons, neutron spectra, total neutron yields, and other parameters.
Ultrafast force-clamp spectroscopy (UFFCS) is a single molecule technique based on laser tweezers that allows the investigation of the chemomechanics of both conventional and unconventional myosins ...under load with unprecedented time resolution. In particular, the possibility to probe myosin motors under constant force right after the actin-myosin bond formation, together with the high rate of the force feedback (200 kHz), has shown UFFCS to be a valuable tool to study the load dependence of fast dynamics such as the myosin working stroke. Moreover, UFFCS enables the study of how processive and non-processive myosin-actin interactions are influenced by the intensity and direction of the applied force. By following this protocol, it will be possible to perform ultrafast force-clamp experiments on processive myosin-5 motors and on a variety of unconventional myosins. By some adjustments, the protocol could also be easily extended to the study of other classes of processive motors such as kinesins and dyneins. The protocol includes all the necessary steps, from the setup of the experimental apparatus to sample preparation, calibration procedures, data acquisition and analysis.
The activation of a neutron generator is modeled for two operating scenarios: continuous for 16 h and 100 h at 4 h/day for one month. The distribution of the equivalent γ-ray dose rate was calculated ...for different times after the generator was shut down. Different grades of steel were considered for the material of the neutron generator flange. The time dependence of the γ-ray dose rate was calculated for each variant of steel. For long holding times, the steel 316L(N)-IG exhibits the lowest dose rate.
Diagnostic "Divertor Neutron Flux Monitor (DNFM)" is one of the diagnostics to determine the neutron yield and the thermonuclear power of the ITER facility. To detect neutrons, this diagnostic uses ...three detector modules. The expected neutron flux in the detector module location is 10 6 -10 13 n <inline-formula> <tex-math notation="LaTeX">\cdot </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">^{-2}\,\,\cdot \,\,\text{s}^{-1} </tex-math></inline-formula>. The neutron flux and the neutron yield should be measured with 1-ms time resolution and 10% maximum relative error. The detector module consisting of six fission chambers (FCs) is used to meet these requirements, and each FC signal is processed by pulse counting, Campbell, and current measurement methods simultaneously. According to the data of each measurement method, the normalized count rates (NCRs) of the FCs and the detector module and the neutron flux at its location are calculated. The data acquisition (DAQ) system processes the signals of the single detector module and transmits the data of the NCR and the neutron flux of each detector and entire detector module to the upper-level system. To verify the technique solutions, the DAQ system prototype was manufactured. To study the characteristics of this prototype, a set of laboratory tests was carried out. This article illustrates the structure of the DAQ system and the implementation of the FC signal processing methods. The results of the study of the DAQ system prototype for a single detector module are given.
