Results 1 - 10 of 36142
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[en] The description of ionization processes in the source with the surface ionization is presented. A limited review of the calculation of the plasma ionization degree as well as the yield of the ionization process in the source is also given. (author)
[en] A test bench for pulse tube refrigerator characterization has been built. In various configurations (basic pulse tube, orifice pulse tube and double inlet pulse tube), the ultimate temperature and the cooling power have been measured as a function of pressure wave amplitude and frequency for various geometries. A lowest temperature of 28 K has been achieved in a single staged double inlet configuration. A modelisation taking into account wall heat pumping, enthalpy flow and regenerator inefficiency is under development. Preliminary calculation results are compared with experimental data
[en] Many years and great effort have been spent constructing the microscopic model for the room temperature multiferroic BiFeO3. However, earlier models implicitly assumed that the cycloidal wavevector was confined to one of the three-fold symmetric axes in the hexagonal plane normal to the electric polarization. Because recent measurements indicate that can be rotated by a magnetic field, it is essential to properly treat the anisotropy that confines at low fields. We propose that the anisotropy energy confines the wavevectors to the three-fold axis and within the hexagonal plane with .
[en] We have carried out a high magnetic field study on single crystalline stoichiometric , a material discussed in terms quantum criticality in itinerant ferromagnets, by means of high field resistivity experiments. Our experiments have been performed at the Laboratoire National des Champs Magnétiques Intenses in Toulouse, France. The resistivity of single crystalline , has been investigated in external fields up to 15.5 T aligned along the c-axis in the temperature range of 1.4–55 K. The main focus of our study lies on the method to extract TN from the magnetoresistivity measurements, because TN could not be easily observed in temperature dependent resistivity for stoichiometric .
[en] Thermoacoustics in cryogenics continues to be a very interesting phenomenon which is still poorly understood but often experienced unexpectedly in experiments where it causes unacceptable heat leaks. The authors report on the appearance and onset of this unwanted occurrence at temperatures below 35 K. A number of physical experiments are presented, where the authors had the means to take quantitative measurements of the heat leak caused by these pressure oscillations in apparatus with bent tubes ranging from 4.55 and 4.7 mm inner diameter, with heat stationing links. The parameters which indicate the likelihood of inadvertently developing these thermoacoustic oscillations are presented and means developed to avoiding them in that instance are given. Furthermore, we had the rare opportunity to record and analyze 4 K TAOs experienced on a test setup and present the simple method that was used to eliminate them. (paper)
[en] Complete text of publication follows. In the previous research of cryogenic complex (dusty) plasma we observed experimentally the possibility of the formation of dust structures in cryogenic environment at 4.2-77 K. It was revealed from the experiments, among others, that the dust structures with high concentration of dust particles can be formed, in which interparticle distance is comparable with particle size - so-called superdense dusty plasma structures. Such structures had exotic properties such as globular (spherical) form, free boundaries, etc. In the present work new results on the experimental investigations of spheroidizing - phenomenon of the transition of dust structures to compact globular shape at cryogenic temperatures - were presented. The experiments were made by means of recently developed techniques and new cryogenic facilities (optical helium cryostat). Possible nature of such phenomenon is discussed.
[en] In this article we present actual projects concerning high resolution measurements developed for future space missions based on ultracold atoms. This work involves the realization of a Bose Einstein Condensate in microgravitational environment and of an inertial atomic quantum sensor
[en] Acoustic properties of alloys of Ge-Pb system have been studied. The temperature dependencies of ultrasound propagation velocity in alloys of Ge-Pb system were investigated in detail. It has been defined that the melting temperature of germanium is 1211 K and lead - 600 K. Based on conducted studies it has been shown that ultrasound propagation velocity depending on temperature decreases linearly.
[en] We report experimental results on the free cooling power available at the level of the second stage regenerator of a 4K pulse tube cooler. By using two localised heat exchangers we obtained additional cooling power, in the range 400 and 600 mW at 4.8 K or between 500 and 700 mW at 18 K. We have investigated in detail the thermal behavior of the system. In this manuscript we report on the evolution of the temperature of the heat exchangers and the pulse tube stages under different distributions of the total heat load.
[en] We investigate one-dimensional arrays of small capacitance Josephson junctions fabricated by conventional e-beam lithography techniques. The arrays are designed to operate in the vicinity of the Coulomb blockade regime. It has been suggested that charges propagate though these arrays in a form similar to solitary waves, following the sine-Gordon model. This system is dual to a long Josephson junction, in which magnetic flux solitons have been thoroughly investigated in the past. Localized charge excitations are of metrological interest because they might offer access to very accurate frequency-to-current conversion. Although previous experiments appear consistent with the existence of solitary charge transport, conclusive evidence is still missing. We present our recent fabrication and measurement results obtained at millikelvin temperatures.