6,834 research outputs found
Magnetic studies of multi-walled carbon nanotube mats: Evidence for the paramagnetic Meissner effect
We report magnetic measurements up to 1200 K on multi-walled carbon nanotube
mats using Quantum Design vibrating sample magnetometer. Extensive magnetic
data consistently show two ferrromagnetic-like transitions at about 1000 K and
1275 K, respectively. The lower transition at about 1000 K is associated with
an Fe impurity phase and its saturation magnetization is in quantitative
agreement with the Fe concentration measured by an inductively coupled plasma
mass spectrometer. On the other hand, the saturation magnetization for the
higher transition phase (1.0 emu/g) is about four orders of magnitude
larger than that expected from the measured concentration of Co or CoFe, which
has a high enough Curie temperature to explain this high transition. We show
that this transition at about 1275 K is not consistent with a magnetic
proximity effect of Fe-carbon systems and ferromagnetism of any carbon-based
materials or magnetic impurities but with the paramagnetic Meissner effect due
to the existence of Josephson junctions in a granular superconductor.Comment: 5 pages, 4 figure
Characterisation of multilayer ramp-type ReBa2Cu3O7-delta structures by scanning probe microscopy and high-resolution electron microscopy
We studied the morphology of ramps in REBa2Cu3O7 (REBCO) epitaxial films on SrTiO3 substrates, fabricated by RF magnetron sputter deposition and pulsed laser deposition (PLD), by scanning probe microscopy (SPM) and high resolution electron microscopy (HREM). The ramps were fabricated by Ar ion beam etching using masks of standard photoresist and TiN. AFM-studies on ramps in sputter deposited films show a strong dependence, i.e. formation of facets and ridges, on the angle of incidence of the ion beam with respect to the substrate surface as well as the rotation angle with respect to the crystal axes of the substrate. Ramps in pulsed laser deposited films did not show this dependence. Furthermore, we studied the effect of an anneal step prior to the deposition of barrier layers (i.e. PrBu2CU3O7, SrTiO3, CeO2) on the ramp. First results show a recrystallization of the ramp surface, resulting in terraces and a non-homogeneous growth of the barrier material on top of it. The thickness variations, for thin layers of barrier material, can even become much larger than expected from the amount of deposited material and are dependent on the deposition and anneal conditions. HREM studies show a well defined interface between barrier layer and electrodes. The angle of the ramp depends on the etch rate of the mask and REBCO, and on the angle of incidence of the ion beam. TiN has a much lower etch rate compared to photoresist, resulting in an angle of the ramp comparable to the angle of incidence, resulting in a low etching rate on the ramp. These results will lead to improved electrical characteristics of ramp-type junctions
About causes of slow relaxation of melted intermetallic alloys
Ascertainment of the nature of the slow relaxation processes observed after
melting in glass-forming eutectic melts is the subject of this work. We claim
that the diffusion processes nonlinearity in heterogeneous melt with inclusions
of refractory stoichiometry is the origin of this phenomenon. The cause for
this nonlinearity is the thermodynamic instability similar to one taking place
at spinodal decomposition, and indispensable condition is the initially
non-homogenous. For confirmation of our devotes, we consider the model of
liquid solution of a binary system, which evolution described by the
Cahn-Hilliard equation with combined Gibbs potential assuming the presence of
remains after melting stoichiometric phase. Exemplified by the Al-Y and Al-Yb
alloys, using Gibbs potentials from a standard database we show that subject to
initial heterogeneity in these systems the instability can develop leading to
the slow relaxation processes, and determine the regions of this instability in
the phase diagrams
Zenith-Angular Characteristics of Particles in EASs with eV According to the Yakutsk Array Data
Particle lateral distributions were investigated in cosmic ray air showers
with energy eV registered at the Yakutsk array with
surface and underground scintillation detectors with ~GeV threshold during the period of continuous observations from
1986 to 2016. The analysis covers events with arrival direction zenith angles
within five intervals with step . Experimental values were compared to simulation results obtained with the
use of CORSIKA code within the framework of QGSJet01 hadron interaction model.
The whole dataset points at probable cosmic ray composition which is close to
protons.Comment: 14 pages, 6 figures. Accepted for publication in Physics of Atomic
Nuclei, volume 86 (2023
Muons in EASs with eV according to data of the Yakutsk Array
Lateral distribution functions of particles in extensive air showers with the
energy eV recorded by ground-based and underground
scintillation detectors with a threshold of GeV at the Yakutsk array during the continuous observations from
1986 to 2016 have been analyzed using events with zenith angles functions have been compared to the predictions obtained with the
QGSJet01 hadron interaction model by applying the CORSIKA code. The entire
dataset indicates that cosmic rays consist predominantly of protons.Comment: 11 pages, 5 figures, 2 tables. Accepted for publication in JETP
Letters (v.117, no.4, 2023), minor typos fixe
Decay of scalar turbulence revisited
We demonstrate that at long times the rate of passive scalar decay in a
turbulent, or simply chaotic, flow is dominated by regions (in real space or in
inverse space) where mixing is less efficient. We examine two situations. The
first is of a spatially homogeneous stationary turbulent flow with both viscous
and inertial scales present. It is shown that at large times scalar
fluctuations decay algebraically in time at all spatial scales (particularly in
the viscous range, where the velocity is smooth). The second example explains
chaotic stationary flow in a disk/pipe. The boundary region of the flow
controls the long-time decay, which is algebraic at some transient times, but
becomes exponential, with the decay rate dependent on the scalar diffusion
coefficient, at longer times.Comment: 4 pages, no figure
The strong influence of substrate conductivity on droplet evaporation
We report the results of physical experiments that demonstrate the strong influence of the thermal conductivity of the substrate on the evaporation of a pinned droplet. We show that this behaviour can be captured by a mathematical model including the variation of the saturation concentration with temperature, and hence coupling the problems for the vapour concentration in the atmosphere and the temperature in the liquid and the substrate. Furthermore, we show that including two ad hoc improvements to the model, namely a Newton's law of cooling on the unwetted surface of the substrate and the buoyancy of water vapour in the atmosphere, give excellent quantitative agreement for all of the combinations of liquid and substrate considered
Normal and Anomalous Scaling of the Fourth-Order Correlation Function of a Randomly Advected Passive Scalar
For a delta-correlated velocity field, simultaneous correlation functions of
a passive scalar satisfy closed equations. We analyze the equation for the
four-point function. To describe a solution completely, one has to solve the
matching problems at the scale of the source and at the diffusion scale. We
solve both the matching problems and thus find the dependence of the four-point
correlation function on the diffusion and pumping scale for large space
dimensionality . It is shown that anomalous scaling appears in the first
order of perturbation theory. Anomalous dimensions are found analytically
both for the scalar field and for it's derivatives, in particular, for the
dissipation field.Comment: 19 pages, RevTex 3.0, Submitted to Phys.Rev. E, revised versio
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