1,191,844 research outputs found
The Relation between the Radial Temperature Profile in the Chromosphere and the Solar Spectrum at Centimeter, Millimeter, Sub-millimeter, and Infrared Wavelengths
Solar observations from millimeter to ultraviolet wavelengths show that there
is a temperature minimum between photosphere and chromosphere. Analysis based
on semi-empirical models locate this point at about 500 km over the
photosphere. The consistency of these models has been tested by means of
millimeter to infrared observations.
In the present work, we show that variations of the theoretical radial
temperature profile near the temperature minimum impacts the brightness
temperature at centimeter, submillimeter, and infrared wavelengths, but the
millimeter wavelength emission remains unchanged. We found a region between 500
and 1000 km over the photosphere that remains hidden to observations at the
frequencies under study in this work.Comment: Accepted in Solar Physic
The superconducting gaps in FeSe studied by soft point-contact Andreev reflection spectroscopy
FeSe single crystals have been studied by soft point-contact
Andreev-reflection spectroscopy. Superconducting gap features in the
differential resistance dV/dI(V) of point contacts such as a characteristic
Andreev-reflection double-minimum structure have been measured versus
temperature and magnetic field. Analyzing dV/dI within the extended two-gap
Blonder-Tinkham-Klapwijk model allows to extract both the temperature and
magnetic field dependence of the superconducting gaps. The temperature
dependence of both gaps is close to the standard BCS behavior. Remarkably, the
magnitude of the double-minimum structure gradually vanishes in magnetic field,
while the minima position only slightly shifts with field indicating a weak
decrease of the superconducting gaps. Analyzing the dV/dI(V) spectra for 25
point contacts results in the averaged gap values = 1.8+/-0.4meV and
=1.0+/-0.2 meV and reduced values 2/kTc=4.2+/-0.9 and
2/kTc=2.3+/-0.5 for the large (L) and small (S) gap, respectively.
Additionally, the small gap contribution was found to be within tens of percent
decreasing with both temperature and magnetic field. No signatures in the dV/dI
spectra were observed testifying a gapless superconductivity or presence of
even smaller gaps.Comment: 8 pages, 4 figs., 3 tables. Shortened version without fig.4 and Table
3 is accepted for publication in Phys. Rev.
Surprisingly large uncertainties in temperature extraction from thermal fits to hadron yield data at LHC
The conventional hadron-resonance gas (HRG) model with the Particle Data
Group (PDG) hadron input, full chemical equilibrium, and the hadron type
dependent eigenvolume interactions is employed to fit the hadron mid-rapidity
yield data of ALICE Collaboration for the most central Pb+Pb collisions. For
the case of point-like hadrons the well-known fit result MeV is
reproduced. However, the situation changes if hadrons have different
eigenvolumes. In the case when all mesons are point-like while all baryons have
an effective hard-core radius of 0.3 fm the temperature dependence of
the has a broad minimum in the temperature range of MeV,
with fit quality comparable to the MeV minimum in the
point-particle case. Very similar result is obtained when only baryon-baryon
eigenvolume interactions are considered, with eigenvolume parameter taken from
previous fit to ground state of nuclear matter. Finally, when we apply the
eigenvolume corrections with mass-proportional eigenvolume ,
fixed to particular proton hard-core radius , we observe a second minimum
in the temperature dependence of the , located at the significantly
higher temperatures. For instance, at fm the fit quality is better
than in the point-particle HRG case in a very wide temperature range of
MeV, which gives an uncertainty in the temperature determination from
the fit to the data of 150 MeV. These results show that thermal fits to the
heavy-ion hadron yield data are very sensitive to the modeling of the
short-range repulsion eigenvolume between hadrons, and that chemical freeze-out
temperature can be extracted from the LHC hadron yield data only with sizable
uncertainty.Comment: 8 pages, 3 figures, v3: added calculations for baryon-baryon only
eigenvolume interactions fitted to nuclear ground state, added table with
fitted data, title and discussion modified in order to ensure more clarity
about the presented result
Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field
We report on magnetization, sound velocity, and magnetocaloric-effect
measurements of the Ising-like spin-1/2 antiferromagnetic chain system
BaCoVO as a function of temperature down to 1.3 K and applied
transverse magnetic field up to 60 T. While across the N\'{e}el temperature of
K anomalies in magnetization and sound velocity confirm the
antiferromagnetic ordering transition, at the lowest temperature the
field-dependent measurements reveal a sharp softening of sound velocity
and a clear minimum of temperature at T,
indicating the suppression of the antiferromagnetic order. At higher fields,
the curve shows a broad minimum at T, accompanied by a
broad minimum in the sound velocity and a saturation-like magnetization. These
features signal a quantum phase transition which is further characterized by
the divergent behavior of the Gr\"{u}neisen parameter . By contrast, around the critical field, the
Gr\"{u}neisen parameter converges as temperature decreases, pointing to a
quantum critical point of the one-dimensional transverse-field Ising model.Comment: Phys. Rev. Lett., to appea
Entropic gravity, minimum temperature, and modified Newtonian dynamics
Verlinde's heuristic argument for the interpretation of the standard
Newtonian gravitational force as an entropic force is generalized by the
introduction of a minimum temperature (or maximum wave length) for the
microscopic degrees of freedom on the holographic screen. With the simplest
possible setup, the resulting gravitational acceleration felt by a test mass m
from a point mass M at a distance R is found to be of the form of the modified
Newtonian dynamics (MOND) as suggested by Milgrom. The corresponding MOND-type
acceleration constant is proportional to the minimum temperature, which can be
interpreted as the Unruh temperature of an emerging de-Sitter space. This
provides a possible explanation of the connection between local MOND-type
two-body systems and cosmology.Comment: 12 pages, v6: published versio
Gravitational instability of slowly rotating isothermal spheres
We discuss the statistical mechanics of rotating self-gravitating systems by
allowing properly for the conservation of angular momentum. We study
analytically the case of slowly rotating isothermal spheres by expanding the
solutions of the Boltzmann-Poisson equation in a series of Legendre
polynomials, adapting the procedure introduced by Chandrasekhar (1933) for
distorted polytropes. We show how the classical spiral of Lynden-Bell & Wood
(1967) in the temperature-energy plane is deformed by rotation. We find that
gravitational instability occurs sooner in the microcanonical ensemble and
later in the canonical ensemble. According to standard turning point arguments,
the onset of the collapse coincides with the minimum energy or minimum
temperature state in the series of equilibria. Interestingly, it happens to be
close to the point of maximum flattening. We determine analytically the
generalization of the singular isothermal solution to the case of a slowly
rotating configuration. We also consider slowly rotating configurations of the
self-gravitating Fermi gas at non zero temperature.Comment: Submitted to A&
On the relation between azeotropic behavior and minimum / maximum flash point occurrences in binary mixtures of flammable compounds
The flash point temperature and the boiling temperature of a mixture are related by the fact that both can be modeled based on vapor-liquid equilibrium (VLE) of each component. It has been suggested in the literature that there might exist a concomitance between azeotropic behavior and minimum/maximum flash point temperature for binary mixtures. In order to verify this statement, we derive new temperature dependent functions that relate the conditions valid for azeotropic behavior and those valid for minimum/maximum flash point behavior. Analysis of experimental data and predicted results allowed us to propose a heuristic to forecast extremum flash point based on the sole knowledge of azeotropic data and boiling and flash point temperatures differences. Extremum flash point might occur when both components are flammable and when the gap between the flash point temperatures of individual components (ΔT_fp) is of the same order or smaller than the boiling temperature gap (ΔT_b). Hence, we contribute to the assessment of the fire and explosion hazards in binary mixtures eventually presenting a minimum flash point behavio
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