91,630 research outputs found
Thermal electron heating rate: A derivation
The thermal electron heating rate is an important heat source term in the ionospheric electron energy balance equation, representing heating by photoelectrons or by precipitating higher energy electrons. A formula for the thermal electron heating rate is derived from the kinetic equation using the electron-electron collision operator as given by the unified theory of Kihara and Aono. This collision operator includes collective interactions to produce a finite collision operator with an exact Coulomb logarithm term. The derived heating rate O(e) is the sum of three terms, O(e) = O(p) + S + O(int), which are respectively: (1) primary electron production term giving the heating from newly created electrons that have not yet suffered collisions with the ambient electrons; (2) a heating term evaluated on the energy surface m(e)/2 = E(T) at the transition between Maxwellian and tail electrons at E(T); and (3) the integral term representing heating of Maxwellian electrons by energetic tail electrons at energies ET. Published ionospheric electron temperature studies used only the integral term O(int) with differing lower integration limits. Use of the incomplete heating rate could lead to erroneous conclusions regarding electron heat balance, since O(e) is greater than O(int) by as much as a factor of two
Regimes of heating and dynamical response in driven many-body localized systems
We explore the response of many-body localized (MBL) systems to periodic
driving of arbitrary amplitude, focusing on the rate at which they exchange
energy with the drive. To this end, we introduce an infinite-temperature
generalization of the effective "heating rate" in terms of the spread of a
random walk in energy space. We compute this heating rate numerically and
estimate it analytically in various regimes. When the drive amplitude is much
smaller than the frequency, this effective heating rate is given by linear
response theory with a coefficient that is proportional to the optical
conductivity; in the opposite limit, the response is nonlinear and the heating
rate is a nontrivial power-law of time. We discuss the mechanisms underlying
this crossover in the MBL phase, and comment on its implications for the
subdiffusive thermal phase near the MBL transition.Comment: 17 pages, 9 figure
A comparison of recently introduced instruments for measuring rice flour viscosity
The Rapid Visco-Analyser (RVA) and the Micro Visco-Amylograph (MVA) were compared in measuring the viscosity properties of rice flours. A total of 72 rice samples were procured from three cultivars harvested at two locations and three moisture contents and separated into thin, medium, and thick kernel-thickness fractions. A fast and a slow heating rate was used in the procedure for both instruments. Cultivar, kernel thickness, and harvest location affected rice viscosity. The RVA viscosity profiles using a fast heating rate were best correlated with those of the MVA using a slow heating rate. The RVA slow heating rate resulted in lower final viscosities than those using the MVA because of the spindle structure of the RVA. For both the RVA and the MVA, greater rice flour peak viscosities and less trough and final viscosities were obtained with a slow rather than a fast heating rat
A simplified method for calculating the atmospheric heating rate by absorption of solar radiation in the stratosphere and mesosphere
Calculations of the atmospheric heating rate by absorption of solar radiation by O3, H2O, and CO2 are reported. The method needs only seven parameters for each molecule and is particularly useful for heating calculations in three-dimensional global circulation models below 80 km. Applying the formula to the observed distributions of O3, H2O, and CO2 produces reasonable latitudinal and seasonal variations in the heating rate. The calculated heating rate, however, is sensitive to the global distributions of the absorbing gases, and uncertainties in the O3 distribution above approximately 50 km and the H2O distribution below approximately 20 km may seriously affect the global distributions of the heating rate in these regions
Transitions to improved confinement regimes induced by changes in heating in zero-dimensional models for tokamak plasmas
It is shown that rapid substantial changes in heating rate can induce
transitions to improved energy confinement regimes in zero-dimensional models
for tokamak plasma phenomenology. We examine for the first time the effect of
step changes in heating rate in the models of E-J.Kim and P.H.Diamond,
Phys.Rev.Lett. 90, 185006 (2003) and M.A.Malkov and P.H.Diamond, Phys.Plasmas
16, 012504 (2009) which nonlinearly couple the evolving temperature gradient,
micro-turbulence and a mesoscale flow; and in the extension of H.Zhu,
S.C.Chapman and R.O.Dendy, Phys.Plasmas 20, 042302 (2013), which couples to a
second mesoscale flow component. The temperature gradient rises, as does the
confinement time defined by analogy with the fusion context, while
micro-turbulence is suppressed. This outcome is robust against variation of
heating rise time and against introduction of an additional variable into the
model. It is also demonstrated that oscillating changes in heating rate can
drive the level of micro-turbulence through a period-doubling path to chaos,
where the amplitude of the oscillatory component of the heating rate is the
control parameter.Comment: 8 pages, 14 figure
Measuring the temperature and heating rate of a single ion by imaging
We present a technique based on high resolution imaging to measure the
absolute temperature and the heating rate of a single ion trapped at the focus
of a deep parabolic mirror. We collect the fluorescence light scattered by the
ion during laser cooling and image it onto a camera. Accounting for the size of
the point-spread function and the magnification of the imaging system, we
determine the spatial extent of the ion, from which we infer the mean phonon
occupation number in the trap. Repeating such measurements and varying the
power or the detuning of the cooling laser, we determine the anomalous heating
rate. In contrast to other established schemes for measuring the heating rate,
one does not have to switch off the cooling but the ion is always maintained in
a state of thermal equilibrium at temperatures close to the Doppler limit
- …