Instruments and Experimental Techniques最新文献

Coordinated Universal Time (UTC) is calculated using the time data of hundreds of remote atomic clocks. These time data are generated by comparing the atomic clocks to another standard clock through time transfer. One-way time transfer using the Global Navigation Satellite Systems (GNSS) is one of the most essential and widely used time transfer techniques. The stability of the transferred time may be degraded due to many phenomena that affect GNSS signals during their path from the transmitter to the receiver. Multipath reflections are one of these phenomena that considerably degrade one way time transfer stability. It is a common notion that the fewer multipath reflections there are, the better the time transfer stability will be. This can be achieved by limiting the reception of GPS signals to high elevation satellites. In this paper, the author studied the effect of satellite elevation on time transfer stability for both GPS and Galileo. The results of this study suggest that the old shape of the relation between the elevation mask and the time transfer stability may have changed. Therefore, the author proposed a new technique for mitigating the effect of multipath on time transfer stability. The proposed technique was applied to real timing data generated from the Golden receiver of the Physikalisch-technische Bundesanstalt (PTB), which is the German national metrology institute.

The article briefly describes the goals and tasks of the planned “Sun–Terahertz” space experiment on board the Russian segment of the ISS. The experiment was aimed at studying radiation from the Sun in the unexplored terahertz range at frequencies of 10¹²–10¹³ Hz and obtaining new data on the terahertz radiation of the Sun, solar active regions, and solar flares. The scientific equipment being developed is a set of eight detectors sensitive to radiation of various frequencies: 0.4, 0.7, 1.0, 3.0, 5.0, 7.0, 10.0, and 12.0 THz. The main components of the electronics unit of the scientific equipment are considered: amplifiers, optical-chopper drivers, the power board, and the electronics board. The accuracy of signal measurements using an ADC on the electronics board was calculated, and the sensitivity of the scientific equipment was assessed.

A method for recording time-of-flight spectra of hyperthermal gas-dynamic seeded molecular beams of alkali and alkaline earth metal halides is described. This method is free of the need to determine and adjust spectra taking hardware time delays into account. The method is based on registering ions, which are formed in the collision-induced dissociation (CID) of molecules with ionic bonds, by two secondary-electron multipliers located at different distances from the beam chopper along the beam passage.

It is shown that capacitance–frequency characterization can help to derive the optimization limits for radiation optimization of the transient properties of the rectifiers. Measurements of the current–voltage, capacitance–voltage, capacitance–frequency characteristics, and reverse recovery profiling were provided for silicon-based rectifiers. p–n-junction rectifiers were irradiated by 5 MeV electrons with fluences from 10¹⁴ to 10¹⁵ cm^–2. It is shown that reverse-recovery time decreases after 5 MeV electron irradiation and this decreasing changes monotonously with irradiation dose (from 2.2 ms to 15 µs for 10¹⁵ cm^–2). At the same time, series resistance increases dramatically (from 0.5 to 90 Ω); it indicates strong degradation of the high-frequency properties. Next criteria for optimal radiation dose can be used: the irradiation level associated with the maximum of boundary frequency indicates the optimum in terms of switching speed. Before this dose, maximum frequency is limited by reverse-recovery time of diode. After this dose, the limiting factor is the relaxation time of RC-circuit, where R is the series resistance of the diode and C is the capacitance of the SRC-region.

An experimental setup has been created for scanning the integral light sum of X-ray luminescence I_S = f(X) and X-ray luminescence spectrum I_XRL = f(hν); the time dependence of integral tunnel luminescence I_TL = f(τ) and its spectral composition T_L = f(hν); the temperature dependence of integral thermally stimulated luminescence I_TSL = f(T) and its spectral composition I_TSL = f(hν); and the spectrum of “flash” I_F = f(hν) and optical stimulation of “flash” I_FOS = f(hν), irradiated with X-rays and uniaxially deformed along the crystallographic directions 〈100〉 or 〈110〉 at low temperature (85 K).

A hardware and software complex designed to control the temperature of a permanent magnet of a magnetic resonance imaging system and to protect it from overheating in case of failures of the temperature-control system is described. The complex consists of several digital temperature sensors and a meter-recorder that measures temperatures, registers them in memory, and switches off the temperature-control system in case of overheating. Interaction with the computer is carried out with the help of a computer application that provides the setting of the meter, receiving recorded data, visualizing them in graphical and digital form, and saving them in files. The exchange between the meter and the computer is carried out through the local network using the Wi-Fi interface. The complex can also be used in other similar applications.

Multiple-Input Buck–Boost (MIBB) dc–dc converters receive energy from two or more energy sources that can Deliver Several Outputs of variable power. There are situations in which it is advantageous to use a buck-boost converter, i.e., when there is no guarantee that the input voltage will always be higher or always lower than the output voltage. This happens for example when there is an input voltage in an inverter that makes the interface between the photovoltaic panels or wind generators and the electrical grid. Here, we present a trigger-controlled MIBB converter topology with various input voltage sources and energy diversification of 0–100% of each source, determined by a pre-determined arbitrary value. The full-range linear transfer function of the controller drives the closed-loop MIBB system to operate as a linear single-input buck–boost converter. The response time of the controller is about 400 μs and therefore allows for high-speed real-time control. The intelligent fixed frequency switching strategy overcomes the limitations of present multiple-input converters by switching period sharing. System performance was verified by simulations and an experimental setup with two source inputs. It is shown that the system can be treated as a linear system, controlled by a single parameter—K. As a result, a simple to control MIBB system with a wide input/output range and fast response time is presented.

The results of research works on improvement of technical characteristics of high-current photoelectron multiplier tubes manufactured by FSUE VNIIA used in scintillation detectors for studies of pulsed gamma-neutron radiation are given. The design is described and the results of introduction of new technological processes of photomultiplier manufacturing are presented.

To study the dependence of the equation of state of high-density nuclear matter on the term characterizing the isospin (proton–neutron) asymmetry of nuclear matter, it is necessary to measure azimuthal flow of neutrons as well as azimuthal flow of charged particles from a dense nuclear matter in the nuclear–nuclear collisions. For this purpose, the Institute for Nuclear Research (Russian Academy of Sciences) is developing a new high-granular neutron detector that will be used in the BM@N experiment at the extracted beam of the Nuclotron accelerator at the Joint Institute for Nuclear Research (JINR, Dubna). This detector will identify neutrons and measure their energies in the heavy-ion collisions up to 4 GeV per nucleon. This article presents the results of measurements of the time resolution and light yields of samples of scintillation detectors with sizes 40 × 40 × 25 mm³ that will be used in a neutron detector based on the currently available fast plastic scintillator manufactured by JINR using an EQR15 11-6060D-S photodetector for light readout. For comparison, the results of measurements for a detector of the same size with a EJ-230 fast scintillator and with the same type of photodetector are given. The measurements were made on cosmic muons as well as on the Pakhra electron synchrotron of the Lebedev Physical Institute of the Russian Academy of Sciences located in Troitsk, Moscow.

A broadband receiver of NMR signals on a modern elemental base is described. The developed receiver is made using broadband components, which allows it to be used in a wide frequency range. This allows it to be used to study various nuclei or to use it in magnetic fields of various strengths. This receiver can be used as a part of various devices based on NMR, such as tomographs and relaxometers. To control the receiver, a device based on a programmable logic chip (FPGA) has been developed. The use of programmable logic chips makes it easy to adapt the receiver to work with various control protocols within the same device or in different devices. Specialized software (firmware) has been created for flashing the FPGA.