Results 1 - 10 of 97161
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[en] The problem on identification of parameters of three-layered Cu/Nb/Cu and Nb/Cu/Nb structures is concerned. It is shown that in the last case the presence of free outer edges of superconductor leads to the distortion of the material parameters that describe the properties of this structure. (authors)
[en] Recently, a great deal of attention has been devoted to trilayer graphene because it displays stacking and electric-field–dependent electronic properties well-suited for electronic and photonic applications. Several theoretical studies have predicted the electronic dispersion of Bernal (ABA) and rhombohedral (ABC) stacked trilayers. However, a direct experimental visualization of a well-resolved band structure has not yet been reported. In this work, angle resolved photoemission spectroscopy data which show with high resolution the electronic band structure of trilayer graphene on 6H-SiC(0001) are presented. Electronic bands obtained from tight-binding calculations are fitted to the experimental data to extract the interatomic hopping parameters for Bernal and rhombohedral stacked trilayers. The presented results suggest that on SiC substrates the occurrence of rhombohedral stacked trilayer is significantly higher than in natural bulk graphite.
[en] Limited-range ionograms have revealed the presence of quasi-horizontal trace (QHT) segments during daylight hours. This subdivision into component segments of both main traces and the extra traces produced by travelling ionospheric disturbances (TIDs) is seen regularly on limited-range ionograms in mid-latitude regions. F1-region TID wavetrains of 5 or 6 cycles are reported with periods around 10 min. The identification of wavetrains when extra traces are absent is made possible by QHT segments which are found as a function of time to move to lower frequencies in the manner similar to that found for the extra traces. Furthermore particular QHT patterns are ephemeral. It is suggested that the segments result from small-scale stratifications produced by saturation effects of atmospheric gravity waves. Daytime ionograms also record spreading on first-and second-hop traces as a result of very weak signals probably produced by reflections from field-aligned columns which could be embedded in the stratified regions. This spreading appears on ionograms as qusi-horizontal (QH) patches
[en] Ozone is a minor and naturally produced component in the stratosphere which encircles the earth some 15 to 45 Km above its surface. It is not an abundant chemical in the atmosphere but it is highly significant due to its property of shielding the earth from much of the potentially damaging ultraviolet radiation coming from the sun. Should ozone disappear, the earth would become uninhabitable for most forms of life. Due to this property, ozone depletion in the stratosphere is now recognized as a major environmental problem with potentially catastrophic effects. Approximately 90% of ozone is found in the stratosphere where its peak concentrations are about 300 ppb. The altitude of peak concentrations varies from about 25 Km near the equator to approximately 15 Km in the polar region (Botkin and Keller, 1995). Ozone concentration is measured in Dobson Units (D.U.) One D.U. is equivalent to a concentration of 1 ppb of ozone. If brought to normal pressure at sea level, all of the existing atmospheric ozone would form a band of no more than 3 mm thick around the earth. (Kemp. 1994). Concentrations of ozone in the stratosphere have been measured for more than 70 years. Today there is nearly a 30-years record of ozone concentrations available from more than 30 locations around the world. It was found that in the Antarctic zone, the ozone concentrations, taken each year in October, decreased from 300 D.U. in 1970 to 200 D.U. in 1984 and a low of about 90 D.U. in 1993. The records indicate that the ozone concentrations in the stratosphere have been decreasing since mid 1960s. (Botkin and Keller, 1995). The concentration of ozone in Polar Regions is more than that near equator. In fact much of ozone is produced near the equator but moves from equator towards poles with global circulation patterns which are not well understood. (author)
[en] Growing evidence of global depletion of stratospheric ozone has emphasised the need to establish an ultraviolet radiation (UVR) status and trends network, to increase our knowledge of human health effect and to better educate the public about the need to modify personal behaviour in order to minimise UVR exposure. The results presented highlight some of the difficulties that will be faced in developing a consistent approach to solar UVR protection in Australia. (author)
[en] Electronic energy transfer from molecules to metal surfaces at distances < 50 Angstroem has been measured. A monolayer of luminescent molecules is separated from a single crystal metal surface by a layer of physisorbed Ar. The luminescence quantum yield is measured as a function of the Ar spacer thickness. A cubic distance dependence is observed, in agreement with classical image dipole theory. (orig.)
[en] A multi-layer model of terrestrial cosmic space at high and medium latitudes is considered in the approximation of infinite conductivity of the Earth taking into account the ambipolar diffusion processes in upper layers of ionosphere. 14 refs
[en] The IRI (International Reference Ionosphere)-1990 system includes a new option for calculating the bottomside electron density profile shape based on strong dependence of the F2 layer half-density height h0.5 on the F2 layer peak height hmF2. These formulae should be distinct for A class cases when h0.5 belongs to the F2 layer and B class when h0.5 occurs below hmF1. In such cases an influence of the F1 layer significantly distorts the profile shape. 6 refs, 2 figs, 1 tab
[en] This paper describes the structure of the electric current generated by external kink modes at the plasma edge using the ideally conducting plasma model. It is found that the edge current layer is created by both wall touching and free boundary kink modes. Near marginal stability, the total edge current has a universal expression as a result of partial compensation of the (delta)-functional surface current by the bulk current at the edge. The resolution of an apparent paradox with the pressure balance across the plasma boundary in the presence of the surface currents is provided.