734 research outputs found
Observation of superluminal geometrical resonances in Bi2Sr2CaCu2O8+x intrinsic Josephson junctions
We study Fiske steps in small Bi2Sr2CaCu2O8+x mesa structures, containing
only few stacked intrinsic Josephson junctions. Careful alignment of magnetic
field prevents penetration of Abrikosov vortices and facilitates observation of
a large variety of high quality geometrical resonances, including superluminal
with velocities larger than the slowest velocity of electromagnetic waves. A
small number of junctions limits the number of resonant modes and allows
accurate identification of modes and velocities. It is shown that superluminal
geometrical resonances can be excited by subluminal fluxon motion and that
flux-flow itself becomes superluminal at high magnetic fields. We argue that
observation of high-quality superluminal geometrical resonances is crucial for
realization of the coherent flux-flow oscillator in the THz frequency range
Spin-controlled Mott-Hubbard bands in LaMnO_3 probed by optical ellipsometry
Spectral ellipsometry has been used to determine the dielectric function of
an untwinned crystal of LaMnO_3 in the spectral range 0.5-5.6 eV at
temperatures 50 K < T < 300 K. A pronounced redistribution of spectral weight
is found at the Neel temperature T_N = 140 K. The anisotropy of the spectral
weight transfer matches the magnetic ordering pattern. A superexchange model
quantitatively describes spectral weight transfer induced by spin correlations.
This analysis implies that the lowest-energy transitions around 2 eV are
intersite d-d transitions, and that LaMnO_3 is a Mott-Hubbard insulator.Comment: 4 pages, 4 figure
Strong 3D correlations in vortex system of Bi2212:Pb
The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to . At an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for . The
transition temperature does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at . This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure
Diamagnetism above Tc in underdoped Bi2.2Sr1.8Ca2Cu3O10+d
Single crystals of (Bi2223) with were grown by a traveling solvent floating
zone method in order to investigate the superconducting properties of highly
underdoped Bi2223.Grown crystals were characterized by X-ray diffraction, DC
susceptibility and resistivity measurements, confirming Bi2223 to be the main
phase.The crystals were annealed under various oxygen partial pressures to
adjust their carrier densities from optimally doped to highly underdoped.The
fluctuation diamagnetic component above the superconducting transition
temperature extracted from the anisotropic normal state
susceptibilities () and ()
was found to increase with underdoping, suggesting a decrease in the
superconducting dimensionality and/or increase in the fluctuating vortex liquid
region.Comment: 6 pages, 7 figures, corrected fig.4 and references, published in J.
Phys. Soc. Jpn. 79, 114711 (2010
Fractional Models of Cosmic Ray Acceleration in the Galaxy
Possible formulations of the problem of cosmic rays acceleration in the
interstellar galactic medium are considered with the use of fractional
differential equations. The applied technique has been physically justified. A
Fermi result has been generalized to the case of the acceleration of particles
in shock waves in the supernovae remnants fractally distributed in the Galaxy.Comment: 10 page
Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2
We report on the synthesis and measurements of the temperature dependence of
resistivity, R(T), the penetration depth, l(T), and upper critical magnetic
field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride
MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the
normal state with usual Bloch-Gruneisen temperature dependence of resistivity
and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as
compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal
a superconducting transition at Tc=6.0 K. Although a clear exponential
l(T)dependence in MgB2 thin films and ceramic pellets was observed at low
temperatures, this dependence was almost linear for ZrB12 below Tc/2. These
features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state
is possible in ZrB12. A fit to the data gives a reduced energy gap
2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data
for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we
found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET
Investigation of Operational Characteristics of Special-purpose Alloy Castings
Pilot smeltings of the intermetallic titanium alloy are performed during the work in the vacuum induction smelting installation with a “cold crucible” and the blades of a gas-turbine engine are fabricated by the casting method according to investment models in the centrifugal field. The structure of the initial charge billet for casting the intermetallic titanium alloy is investigated and its chemical composition is analyzed. The process parameters of casting and results of metallographic analysis of fabricated blades are presented. It is established that the cast blade structure has a lamellar structure and consists of phases γ and α2. The results of testing mechanical properties are presented. It is established that ultimate tensile strength σB = 765 MPa, yield point σy = 726.5 MPa, and relative elongation δ = 1.6%. The stress distribution on the blade pen is investigated and its distribution diagrams are constructed. Blade samples are tested for long-term strength (t = 650°C, τ = 500 h), fatigue strength, and impact toughness. © 2017, Allerton Press, Inc
Immunobiological properties of inactivated anti-highly pathogenic avian influenza vaccines based on antigens of А/Н5N1 avian influenza virus strains of different virulence
Antigen of H5N1 low pathogenic avian influenza virus Yamal strain included in the inactivated emulsion vaccine is able to induce strong immunity against highly pathogenic avian influenza in chickens. Inactivated emulsion vaccines based on antigen of H5N1 low pathogenic avian influenza virus Yamal strain and antigen of H5N1 highly pathogenic avian influenza virus А/chicken/Primorsky/85/08 strain are capable of inducing dose-dependent cross immunity against current Н5N1 and H5N8 highly pathogenic avian influenza viruses. Thus, inoculation dose of H5N1 low pathogenic avian influenza virus Yamal strain antigen required for protection of 95% of chickens against H5N1 highly pathogenic avian influenza virus А/chicken/Primorsky/85/08 strain and against H5N8 highly pathogenic avian influenza virus A/duck/KChR/1590-20/20 in the vaccine inoculation volume shall be at least 609 HAU and 255 HAU, respectively. The inoculation dose of H5N1 highly pathogenic avian influenza virus А/chicken/Primorsky/85/08 strain antigen for protection from H5N8 highly pathogenic avian influenza virus A/duck/KChR/1590-20/20 strain shall be at least 294 HAU. Protective effect of the tested inactivated vaccines was associated with humoral immunity level in poultry. Predicted titre of antibodies to homologous virus antigens conferring expected 95% protection of vaccinated poultry was 1:538 or 9.1 log2. Inactivated vaccine based on H5N1 low pathogenic avian influenza virus Yamal strain antigen demonstrates its high immunogenicity in chickens infected with Н5N1 and Н5N8 highly pathogenic avian influenza influenza virus
LEED Holography applied to a complex superstructure: a direct view of the adatom cluster on SiC(111)-(3x3)
For the example of the SiC(111)-(3x3) reconstruction we show that a
holographic interpretation of discrete Low Energy Electron Diffraction (LEED)
spot intensities arising from ordered, large unit cell superstructures can give
direct access to the local geometry of a cluster around an elevated atom,
provided there is only one such prominent atom per surface unit cell. By
comparing the holographic images obtained from experimental and calculated data
we illuminate validity, current limits and possible shortcomings of the method.
In particular, we show that periodic vacancies such as cornerholes may inhibit
the correct detection of the atomic positions. By contrast, the extra
diffraction intensity due to slight substrate reconstructions, as for example
buckling, seems to have negligible influence on the images. Due to the spatial
information depth of the method the stacking of the cluster can be imaged down
to the fourth layer. Finally, it is demonstrated how this structural knowledge
of the adcluster geometry can be used to guide the dynamical intensity analysis
subsequent to the holographic reconstruction and necessary to retrieve the full
unit cell structure.Comment: 11 pages RevTex, 6 figures, Phys. Rev. B in pres
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