30,489 research outputs found
Size effect and the quadratic temperature dependence of the transverse magnetoresistivity in "size-effect" tungsten single crystals
The transverse magnetoresistivity of pure tungsten single crystals with a residual resistivity ratio ρ293K/ρ4.2K of about 75000 was measured from 4.2 to 20 K and in magnetic fields of up to 15 T. The size effect, i.e. the linear dependence of the magnetoconductivity on the inverse cross sample dimensions, was studied in detail at high fields. We show that the size effect can be used for the separation of the contributions from the electron-surface and the electron-phonon scattering mechanisms to the full conductivity. We demonstrate that the electron-phonon scattering leads to the exponential temperature dependence of the conductivity, and the interference between the electron-phonon and the electron-surface processes leads to a new scattering mechanism "electron-phonon-surface" with a quadratic temperature dependence of the magnetoconductivity. © Published under licence by IOP Publishing Ltd
Developments in quantitative luminescence techniques
Developments in quantitative luminescence technique
Electrical and galvanomagnetic properties of AuAl2+6%Cu intermetallic compounds at low temperatures
The AuAl2 intermetallic compounds are of substantial interest in view of their application potential. The investigated intermetallics AuAl 2+6%Cu were prepared from fine powders of AuAl2 and Cu by vacuum sputtering on a glass substrate and consisted of films with a thickness of about one micrometer. The films were annealed. The temperature and field dependence of the electroresistivity, the magnetoresistivity and the Hall effect of AuAl2+6%Cu films were measured in the temperature interval from 4.2 to 100 K and at magnetic fields of up to 15 T. We demonstrate that the temperature dependence of the electroresistivity has a minimum at T = 20 K and a metallic behavior above this temperature. The magnetoresistivity is very small (less then 1%), positive at low temperatures and negative above 12 K. The Hall coefficient is positive, which corresponds to the holes in a one zone model with a charge carrier concentration of about 1.6 1020 cm-3. © Published under licence by IOP Publishing Ltd
Combustion waves in a model with chain branching reaction and their stability
In this paper the travelling wave solutions in the adiabatic model with
two-step chain branching reaction mechanism are investigated both numerically
and analytically in the limit of equal diffusivity of reactant, radicals and
heat. The properties of these solutions and their stability are investigated in
detail. The behaviour of combustion waves are demonstrated to have similarities
with the properties of nonadiabatic one-step combustion waves in that there is
a residual amount of fuel left behind the travelling waves and the solutions
can exhibit extinction. The difference between the nonadiabatic one-step and
adiabatic two-step models is found in the behaviour of the combustion waves
near the extinction condition. It is shown that the flame velocity drops down
to zero and a standing combustion wave is formed as the extinction condition is
reached. Prospects of further work are also discussed.Comment: pages 32, figures 2
Lubrication effects on the flow of wet granular materials
We investigate the dynamics of a partially saturated grain-liquid mixture
with a rotating drum apparatus. The drum is partially filled with the mixture
and then rotated about its horizontal axis. We focus on the continous
avalanching regime and measure the impact of volume fraction and viscosity of
the liquid on the dynamic surface angle. The inclination angle of the surface
is observed to increase sharply to a peak and then decrease as a function of
liquid volume fraction. The height of the peak is observed to increase with
rotation rate. For higher liquid volume fractions, the inclination angle of the
surface can decrease with viscosity before increasing. The viscosity where the
minima occurs decreases with the rotation rate of the drum. Limited
measurements of the flow depth were made, and these were observed to show only
fractional changes with volume fraction and rotation speeds. We show that the
qualitative features of our observations can be understood by analyzing the
effect of lubrication forces on the timescale over which particles come in
contact.Comment: 7 pages, 8 figure
Dimensionality effects on non-equilibrium electronic transport in Cu nanobridges
We report on non-equilibrium electronic transport through normal-metal (Cu)
nanobridges coupled to large reservoirs at low temperatures. We observe a
logarithmic temperature dependence of the zero-bias conductance, as well as a
universal scaling behavior of the differential conductance. Our results are
explained by electron-electron interactions in diffusive metals in the
zero-dimensional limit.Comment: RevTex, 4 page
Spin Relaxation Times of Single-Wall Carbon Nanotubes
We have measured temperature ()- and power-dependent electron spin
resonance in bulk single-wall carbon nanotubes to determine both the
spin-lattice and spin-spin relaxation times, and . We observe that
increases linearly with from 4 to 100 K, whereas {\em
decreases} by over a factor of two when is increased from 3 to 300 K. We
interpret the trend as spin-lattice relaxation via
interaction with conduction electrons (Korringa law) and the decreasing
dependence of as motional narrowing. By analyzing the latter, we
find the spin hopping frequency to be 285 GHz. Last, we show that the Dysonian
lineshape asymmetry follows a three-dimensional variable-range hopping behavior
from 3 to 20 K; from this scaling relation, we extract a localization length of
the hopping spins to be 100 nm.Comment: 6 pages, 3 figure
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