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991.
A possible cooling of electrons at low temperatures is predicted from a newly-developed approach to steady-state nonlinear transport in the presence of an electric field. The lowering of the electron temperature below the lattice temperature occurs in low-impurity samples and at such a current density for which the average drift velocity of the carriers is near the sound speed.  相似文献   
992.
In the reaction π? + A → π+π?π? + A at 15.1 GeV/c the coherently produced 3π mass spectrum has a broad peak around 1.1 GeV which consists mainly of a JP = 1+ state and of a smaller fraction of 0-. Comparing the observed dependence of the production of these diffractive states on the atomic weight A of the target nuclei with the optical model, we have studied the absorption of the produced states in nuclear matter. We have found the following values of the absorption cross-sections: σ2(0-) = 49?7+9 mb and σ2(1+) = 15.8?1.3+1.5 mb.  相似文献   
993.
A lepton-pair trigger was used to select a hadronic system in different flavour and colour states: properties of the transformation of this system into hadrons were measured in terms of charge flow, multiplicity distribution, and fragmentation function. It is observed that, while the effects of flavour are clearly seen, the colour degrees of freedom are not observed in the region of low pT.  相似文献   
994.
995.
The presence of a hydroxyl group in steroidal amines, amides and imines, may profoundly influence their fragmentation in the mass spectrometer. This fragmentation is initiated by the rearrangement of the hydroxylic hydrogen on the nitrogen containing groups and products ions characteristic of the OH site in the molecule. Sometimes this may occur even when the two groups are situated at remote positions.  相似文献   
996.
(200)-oriented Pt and Ir electrode films have been epitaxially grown on MgO/Si(100) by in situ pulsed-laser deposition (PLD). A comparison of crystallinity and surface morphology of both electrode films was made. It was found that both electrode films featured remarkable atomic-scale smooth surfaces and had the same epitaxial relationship with substrates. Different from the noncompact surface morphology of the Pt film, the morphology of the Ir film offers a rectangular grain shape and the grains are arrayed regularly and compactly. The difference in the surface morphology of both electrode films is briefly explained in terms of the degree of species saturation. PACS 81.15.Fg; 68.55.Jk; 61.14.Hg; 68.55.-a; 81.15.-z; 77.55.+f  相似文献   
997.
Microdomain-macrodomain transformations and phase transitions in 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 single crystals were investigated by studying their relative permittivity under various dc bias at constant heating and cooling rates. The orientation dependence of the bias field effect was revealed by examining the temperature dependence of relative permittivity as a function of crystal orientation (the 111, 011 and 001 directions) and dc bias field. The crystals have a microdomain rhombohedral ferroelectric state in the ferroelectric phase under zero dc bias. External bias field could modulate the domain state and induce a macrodomain state in the crystals. Also, it is proposed that the dc bias applied along the 001 or 011 direction could induce a tetragonal ferroelectric phase or an orthorhombic ferroelectric phase, respectively, in an intermediate temperature range. PACS 77.80.-e; 77.22.-d; 81.40.-z  相似文献   
998.
Zn2SiO4 single-doped and co-doped with Mn2+ ions and Pb2+ ions has been prepared by a sol–gel process. The luminescent properties of the samples have been investigated. From the excitation and emission spectral analysis, it was found that the emission peaks vary with the change of the excitation wavelength. An enhanced luminescent characteristic of Mn2+ ions (in blue and green spectral zones) has been observed, due to the energy transfer from the Pb2+ ion to the Mn2+ ion. The emission peaks originate from the d–d transitions of the Mn2+ ion. However, the relative intensities of the peaks show a dependence on the concentration of the Pb2+ ion. PACS 81.05.Je; 78.55.Hx; 61.72.Ww  相似文献   
999.
Barium ferrite (BaFe12O19) thin films have been deposited by pulsed laser deposition (PLD) on Si substrates with MgO underlayers. The films were deposited in oxygen atmosphere by excimer laser (=248 nm, pulse duration=23 ns) in the temperature range 750–900 °C. The experiments showed that the substrate temperature has remarkable effect on the films magnetic and structural properties. The BaFe12O19 films deposited at 900 °C in 200 mTorr oxygen showed some perpendicular orientation, with a perpendicular squareness of 0.5 and an in-plane squareness of 0.3. Such thin BaFe12O19 films have platelet grains with a size of about 300 nm. The perpendicular saturation magnetization and coercivity are 185 emu/cm3 and 1.4 kOe, respectively. PACS 81.15.Fg.; 75.70.Ak; 75.50.Pp; 68.55.j  相似文献   
1000.
Electron field emission properties of tetrahedral amorphous carbon films (ta-C) with various sp3 fractions, [sp3]/([sp2]+[sp3]), prepared by magnetic filtered plasma deposition system, were investigated. The ta-C films were deposited on (100) n-Si wafer with a resistivity of 0.01–0.02 cm in a substrate bias voltage Vb range from +20 V to -80 V. The relative fraction of sp3-bonded carbon in these films was qualitatively and quantitatively estimated by a fitting of the Raman and XPS spectra, respectively. Results show that ta-C films of high sp3 fraction, more than 80%, can be formed with a substrate bias voltage Vb in the range from -10 to -50 V. A remarkably low turn-on field of about 1.7 V/m was observed for these samples. For Vb outside this range, the sp3 fraction is lower. The surface of such ta-C films was found to be smooth and uniform from the images of atomic force microscopy. The sp3 fraction of the sample is believed to be the main factor affecting field emission properties of ta-C films. PACS 79.70; 78.30; 73.90.+f  相似文献   
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