Results 21 - 30 of 110195
Results 21 - 30 of 110195. Search took: 0.064 seconds
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[en] We consider the one-loop effective potential at zero and finite temperature in field theories with anisotropic space-time scaling, with critical exponent z=2, including both scalar and gauge fields. Depending on the relative strength of the coupling constants for the gauge and scalar interactions, we find that there is a symmetry breaking term induced at one loop at zero temperature and we find symmetry restoration through a first-order phase transition at high temperature.
[en] We report the performance of room temperature terahertz sources based on intracavity difference-frequency generation in mid-infrared quantum cascade lasers with a dual-upper-state (DAU) active region. DAU active region design is theoretically expected to produce larger optical nonlinearity for terahertz difference-frequency generation, compared to the active region designs of the bound-to-continuum type used previously. Fabricated buried heterostructure devices with a two-section buried distributed feedback grating and the waveguide designed for Cherenkov difference-frequency phase-matching scheme operate in two single-mode mid-infrared wavelengths at 10.7 μm and 9.7 μm and produce terahertz output at 2.9 THz with mid-infrared to terahertz conversion efficiency of 0.8 mW/W"2 at room temperature
[en] This paper presents the results of the calculation the thermal field distribution on the surface of processed partunder the influence of a moving heat source (of the low-temperature plasma). (paper)
[en] Ionized gas in low-temperature conditions, are in general characterized by the presence of molecular species, which can strongly affect the system properties and its evolution. In particular, when non-equilibrium conditions exists, the interactions occurring among the particles at a microscopic level, give rise to a complex collisional physics, largely dominated by molecules in different internal quantum states which act as different chemical species. So the modeling of these systems requires the characterization of a plethora of collisional processes, involving molecules, where exchanges of ro-vibronic energies, dissociation, ionization, reactive processes etc., may occur. In this frame, the availability of large sets of cross section data becomes a crucial prerequisite for a realistic simulation of plasma system.
[en] The effect of interfacial scattering on anomalous Hall effect (AHE) was studied in the multilayers. Field-dependent Hall resistivity was measured in the temperature range of 5–300 K with the magnetic field up to 50 kOe. The anomalous Hall resistivity () was enhanced by more than six times at 5 K from n = 1 to n = 12 due to the increased interfacial scattering, whereas the longitudinal resistivity () was increased nearly three times. A scaling relation with was obtained for and measured at 5 K, indicating that the dominant mechanism(s) of the AHE in these multilayers should be side-jump or/and intrinsic in nature. The new scaling relation (Tian et al 2009 Phys. Rev. Lett. 103 087206) has been applied to our data to identify the origin of the AHE in this type of multilayer. (paper)
[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.
[en] Cryogen-free operation of Josephson voltage standards requires a low-noise cryocooler that provides a cooling power of 100 mW or less at 4.2 K, and about 1 W of precooling at an intermediate temperature near 70 K. Due to its intrinsic low level of mechanical vibrations a pulse tube cooler (PTC) appears to be a suitable candidate for such an application. In this work, a two-stage pulse tube cooler has been developed and optimized for cooling of a 1 V or 10 V Josephson voltage standard near 4 K. The performance of the PTC, which is driven by a compressor with a rated input power of 1.7 kW, is optimized under three different conditions. So far, a minimum temperature of 2.66 K and a maximum cooling power of 202 mW at 4.2 K with coefficient of performance (COP) of 1.15x10-4 have been achieved. The performance of the cryocooler is expected to fully satisfy the cooling requirement of the voltage standard. In addition, the experimental results are also compared with those obtained by driving the same cooler by use of a 6 kW compressor
[en] High-temperature micro-/nanomechanics has attracted much interest over the last decade, primarily because of the urgent need to understand the mechanical and tribological properties of advanced engineering materials at micro-/nanoscale and the underlying physics controlling such properties at operationally relevant conditions. Recent years have subsequently witnessed the swift growth and development of new high-temperature micro- and nanoscratching/tribology instruments. Here, we present an overview of fundamental principles and developments in these instruments, discuss pertinent findings on the topic in detail, and outline current challenges and promising future directions in the field.