52,950 research outputs found
Environmental Superstatistics
A thermodynamic device placed outdoors, or a local ecosystem, is subject to a
variety of different temperatures given by short-tem (daily) and long-term
(seasonal) variations. In the long term a superstatistical description makes
sense, with a suitable distribution function f(beta) of inverse temperature
beta over which ordinary statistical mechanics is averaged. We show that
f(beta) is very different at different geographic locations, and typically
exhibits a double-peak structure for long-term data. For some of our data sets
we also find a systematic drift due to global warming. For a simple
superstatistical model system we show that the response to global warming is
stronger if temperature fluctuations are taken into account.Comment: 37 figures. Significantly extended version, to appear in Physica A.
Added new material in section 6 quantifying the stronger response to global
warming if temperature fluctuations are taken into account. Concluding
section 7 and several new references adde
A new Miconia (Melastomatacaeae) from Bolivia, with remarks on angular-branched species in the Andes
A new species of Melastomataceae frorm Bolivia is described, illustrated and placed in a phenetic context within Miconia, a genus of 1000 species and about 2000 published names. Miconia quadrialata is readily distinguished from its Congeners by two-colored leaves and sharply four-angular
and winged branchlets. A search for quadrangular-branched miconias revealed that 12 of 15 such species (in four sections), including the new species, occur in cloud forest in the Andes, raising the question of the adaptive significance of quadrangular branchlets
The far-infrared - radio correlation in dwarf galaxies
The far-infrared - radio correlation connects star formation and magnetic
fields in galaxies, and has been confirmed over a large range of far-infrared
luminosities. Recent investigations indicate that it may even hold in the
regime of local dwarf galaxies, and we explore here the expected behavior in
the regime of star formation surface densities below 0.1 M_sun kpc^{-2}
yr^{-1}. We derive two conditions that can be particularly relevant for
inducing a change in the expected correlation: a critical star formation
surface density to maintain the correlation between star formation rate and the
magnetic field, and a critical star formation surface density below which
cosmic ray diffusion losses dominate over their injection via supernova
explosions. For rotation periods shorter than 1.5x10^7 (H/kpc)^2 yrs, with H
the scale height of the disk, the first correlation will break down before
diffusion losses are relevant, as higher star formation rates are required to
maintain the correlation between star formation rate and magnetic field
strength. For high star formation surface densities Sigma_SFR, we derive a
characteristic scaling of the non-thermal radio to the far-infrared / infrared
emission with Sigma_SFR^{1/3}, corresponding to a scaling of the non-thermal
radio luminosity L_s with the infrared luminosity L_{th} as L_{th}^{4/3}. The
latter is expected to change when the above processes are no longer steadily
maintained. In the regime of long rotation periods, we expect a transition
towards a steeper scaling with Sigma_SFR^{2/3}, implying L_s~L_th^{5/3}, while
the regime of fast rotation is expected to show a considerably enhanced
scatter. These scaling relations explain the increasing thermal fraction of the
radio emission observed within local dwarfs, and can be tested with future
observations by the SKA and its precursor radio telescopes.Comment: 16 pages, 11 figures, accepted at A&
A new interpretation of the far-infrared - radio correlation and the expected breakdown at high redshift
(Abrigded) Observations of galaxies up to z 2 show a tight correlation
between far-infrared and radio continuum emission. We explain the far-infrared
- radio continuum correlation by relating star formation and magnetic field
strength in terms of turbulent magnetic field amplification, where turbulence
is injected by supernova explosions from massive stars. We calculate the
expected amount of turbulence in galaxies based on their star formation rates,
and infer the expected magnetic field strength due to turbulent dynamo
amplification. We estimate the timescales for cosmic ray energy losses via
synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung
emission, probing up to which redshift strong synchrotron emission can be
maintained. We find that the correlation between star formation rate and
magnetic field strength in the local Universe can be understood as a result of
turbulent magnetic field amplification. If the typical gas density in the
interstellar medium increases at high z, we expect an increase of the magnetic
field strength and the radio emission, as indicated by current observations.
Such an increase would imply a modification of the far-infrared - radio
correlation. We expect a breakdown when inverse Compton losses start dominating
over synchrotron emission. For a given star formation surface density, we
calculate the redshift where the breakdown occurs, yielding z (Sigma_SFR/0.0045
M_solar kpc^{-2} yr^{-1})^{1/(6-alpha/2)}. In this relation, the parameter
\alpha describes the evolution of the characteristic ISM density in galaxies as
(1+z)^\alpha. Both the possible raise of the radio emission at high redshift
and the final breakdown of the far-infrared -- radio correlation at a critical
redshift will be probed by the Square Kilometre Array (SKA) and its
pathfinders, while the typical ISM density in galaxies will be probed with
ALMA.Comment: 13 pages, 14 figures, 1 table, accepted at A&A (proof corrections
included
Statistics of 3-dimensional Lagrangian turbulence
We consider a superstatistical dynamical model for the 3-d movement of a
Lagrangian tracer particle embedded in a high-Reynolds number turbulent flow.
The analytical model predictions are in excellent agreement with recent
experimental data for flow between counter-rotating disks. In particular, we
calculate the Lagrangian scaling exponents zeta_j for our system, and show that
they agree well with the measured exponents reported in [X. Hu et al., PRL 96,
114503 (2006)]. Moreover, the model correctly predicts the shape of velocity
difference and acceleration probability densities, the fast decay of component
correlation functions and the slow decay of the modulus, as well as the
statistical dependence between acceleration components. Finally, the model
explains the numerically [P.K. Yeung and S.B. Pope, J. Fluid Mech. 207, 531
(1989)] and experimentally observed fact [B.W. Zeff et al., Nature 421, 146
(2003)] that enstrophy lags behind dissipation.Comment: 5 pages, 3 figures. Replaced by final version accepted by Phys. Rev.
Let
Transition from a mixed to a pure d-wave symmetry in superconducting optimally doped YBaCuO thin films under applied fields
We have probed the Landau levels of nodal quasi-particles by tunneling along
a nodal direction of (110) oriented YBaCuO thin films with a
magnetic field applied perpendicular to the planes, and parallel to the
film's surface. In optimally doped films and at low temperature, finite energy
nodal states are clearly observed in films thinner than the London penetration
depth. Above a well defined temperature the order parameter reverts to a pure
\emph{d}-wave symmetry.Comment: 4 pages, 4 figure
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