287 research outputs found
Effect of the recycling process and binder type on bituminous mixtures with 100% reclaimed asphalt pavement
There is a great interest in increasing the amount of recycled material used in asphalt mixes because of the beneficial impact on the environment. This is leading to the development of different recycling procedures, from cold in-situ to hot in-plant recycling. The objective of the study presented in this paper is to evaluate cracking resistance of recycled mixes manufactured by three types of processes, i.e., cold with emulsion, hot with high penetration bitumens and hot with emulsion (half-warm mixture), using 100% of reclaimed asphalt pavement (RAP) at different temperatures. Differences in their workability and ease of use are also analysed by gyratory compaction.Peer ReviewedPostprint (author's final draft
Theory of Stellar Oscillations
In recent years, astronomers have witnessed major progresses in the field of
stellar physics. This was made possible thanks to the combination of a solid
theoretical understanding of the phenomena of stellar pulsations and the
availability of a tremendous amount of exquisite space-based asteroseismic
data. In this context, this chapter reviews the basic theory of stellar
pulsations, considering small, adiabatic perturbations to a static, spherically
symmetric equilibrium. It starts with a brief discussion of the solar
oscillation spectrum, followed by the setting of the theoretical problem,
including the presentation of the equations of hydrodynamics, their
perturbation, and a discussion of the functional form of the solutions.
Emphasis is put on the physical properties of the different types of modes, in
particular acoustic (p-) and gravity (g-) modes and their propagation cavities.
The surface (f-) mode solutions are also discussed. While not attempting to be
comprehensive, it is hoped that the summary presented in this chapter addresses
the most important theoretical aspects that are required for a solid start in
stellar pulsations research.Comment: Lecture presented at the IVth Azores International Advanced School in
Space Sciences on "Asteroseismology and Exoplanets: Listening to the Stars
and Searching for New Worlds" (arXiv:1709.00645), which took place in Horta,
Azores Islands, Portugal in July 201
Heliospheric Transport of Neutron-Decay Protons
We report on new simulations of the transport of energetic protons
originating from the decay of energetic neutrons produced in solar flares.
Because the neutrons are fast-moving but insensitive to the solar wind magnetic
field, the decay protons are produced over a wide region of space, and they
should be detectable by current instruments over a broad range of longitudes
for many hours after a sufficiently large gamma-ray flare. Spacecraft closer to
the Sun are expected to see orders-of magnitude higher intensities than those
at the Earth-Sun distance. The current solar cycle should present an excellent
opportunity to observe neutron-decay protons with multiple spacecraft over
different heliographic longitudes and distances from the Sun.Comment: 12 pages, 4 figures, to be published in special issue of Solar
Physic
Collective effects of stellar winds and unidentified gamma-ray sources
We study collective wind configurations produced by a number of massive stars, and obtain densities and expansion velocities of the stellar wind gas that is to be target, in this model, of hadronic interactions. We study the expected -ray emission from these regions, considering in an approximate way the effect of cosmic ray modulation. We compute secondary particle production (electrons from knock-on interactions and electrons and positrons from charged pion decay), and solve the loss equation with ionization, synchrotron, bremsstrahlung, inverse Compton, and expansion losses. We provide examples where configurations can produce sources for GLAST satellite, and the MAGIC, HESS, or VERITAS telescopes in non-uniform ways, i.e., with or without the corresponding counterparts. We show that in all cases we studied no EGRET source is expected
Using an Ellipsoid Model to Track and Predict the Evolution and Propagation of Coronal Mass Ejections
We present a method for tracking and predicting the propagation and evolution
of coronal mass ejections (CMEs) using the imagers on the STEREO and SOHO
satellites. By empirically modeling the material between the inner core and
leading edge of a CME as an expanding, outward propagating ellipsoid, we track
its evolution in three-dimensional space. Though more complex empirical CME
models have been developed, we examine the accuracy of this relatively simple
geometric model, which incorporates relatively few physical assumptions,
including i) a constant propagation angle and ii) an azimuthally symmetric
structure. Testing our ellipsoid model developed herein on three separate CMEs,
we find that it is an effective tool for predicting the arrival of density
enhancements and the duration of each event near 1 AU. For each CME studied,
the trends in the trajectory, as well as the radial and transverse expansion
are studied from 0 to ~.3 AU to create predictions at 1 AU with an average
accuracy of 2.9 hours.Comment: 18 pages, 11 figure
Influence of Low-Degree High-Order p-Mode Splittings on the Solar Rotation Profile
The solar rotation profile is well constrained down to about 0.25 R thanks to
the study of acoustic modes. Since the radius of the inner turning point of a
resonant acoustic mode is inversely proportional to the ratio of its frequency
to its degree, only the low-degree p modes reach the core. The higher the order
of these modes, the deeper they penetrate into the Sun and thus they carry more
diagnostic information on the inner regions. Unfortunately, the estimates of
frequency splittings at high frequency from Sun-as-a-star measurements have
higher observational errors due to mode blending, resulting in weaker
constraints on the rotation profile in the inner core. Therefore inversions for
the solar internal rotation use only modes below 2.4 mHz for l < 4. In the work
presented here, we used an 11.5 year-long time series to compute the rotational
frequency splittings for modes l < 4 using velocities measured with the GOLF
instrument. We carried out a theoretical study of the influence of the
low-degree modes in the region 2 to 3.5 mHz on the inferred rotation profile as
a function of their error bars.Comment: Accepted for publication in Solar Physics. 17 Pages, 9 figure
A Model for the Stray Light Contamination of the UVCS Instrument on SOHO
We present a detailed model of stray-light suppression in the spectrometer
channels of the Ultraviolet Coronagraph Spectrometer (UVCS) on the SOHO
spacecraft. The control of diffracted and scattered stray light from the bright
solar disk is one of the most important tasks of a coronagraph. We compute the
fractions of light that diffract past the UVCS external occulter and
non-specularly pass into the spectrometer slit. The diffracted component of the
stray light depends on the finite aperture of the primary mirror and on its
figure. The amount of non-specular scattering depends mainly on the
micro-roughness of the mirror. For reasonable choices of these quantities, the
modeled stray-light fraction agrees well with measurements of stray light made
both in the laboratory and during the UVCS mission. The models were constructed
for the bright H I Lyman alpha emission line, but they are applicable to other
spectral lines as well.Comment: 19 pages, 5 figures, Solar Physics, in pres
Large-scale Bright Fronts in the Solar Corona: A Review of "EIT waves"
``EIT waves" are large-scale coronal bright fronts (CBFs) that were first
observed in 195 \AA\ images obtained using the Extreme-ultraviolet Imaging
Telescope (EIT) onboard the \emph{Solar and Heliospheric Observatory (SOHO)}.
Commonly called ``EIT waves", CBFs typically appear as diffuse fronts that
propagate pseudo-radially across the solar disk at velocities of 100--700 km
s with front widths of 50-100 Mm. As their speed is greater than the
quiet coronal sound speed (200 km s) and comparable to the
local Alfv\'{e}n speed (1000 km s), they were initially
interpreted as fast-mode magnetoacoustic waves ().
Their propagation is now known to be modified by regions where the magnetosonic
sound speed varies, such as active regions and coronal holes, but there is also
evidence for stationary CBFs at coronal hole boundaries. The latter has led to
the suggestion that they may be a manifestation of a processes such as Joule
heating or magnetic reconnection, rather than a wave-related phenomena. While
the general morphological and kinematic properties of CBFs and their
association with coronal mass ejections have now been well described, there are
many questions regarding their excitation and propagation. In particular, the
theoretical interpretation of these enigmatic events as magnetohydrodynamic
waves or due to changes in magnetic topology remains the topic of much debate.Comment: 34 pages, 19 figure
A Kinematically Complete Measurement of the Proton Structure Function F2 in the Resonance Region and Evaluation of Its Moments
We measured the inclusive electron-proton cross section in the nucleon
resonance region (W < 2.5 GeV) at momentum transfers Q**2 below 4.5 (GeV/c)**2
with the CLAS detector. The large acceptance of CLAS allowed for the first time
the measurement of the cross section in a large, contiguous two-dimensional
range of Q**2 and x, making it possible to perform an integration of the data
at fixed Q**2 over the whole significant x-interval. From these data we
extracted the structure function F2 and, by including other world data, we
studied the Q**2 evolution of its moments, Mn(Q**2), in order to estimate
higher twist contributions. The small statistical and systematic uncertainties
of the CLAS data allow a precise extraction of the higher twists and demand
significant improvements in theoretical predictions for a meaningful comparison
with new experimental results.Comment: revtex4 18 pp., 12 figure
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
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