464 research outputs found
Supergravity Higgs Inflation and Shift Symmetry in Electroweak Theory
We present a model of inflation in a supergravity framework in the Einstein
frame where the Higgs field of the next to minimal supersymmetric standard
model (NMSSM) plays the role of the inflaton. Previous attempts which assumed
non-minimal coupling to gravity failed due to a tachyonic instability of the
singlet field during inflation. A canonical K\"{a}hler potential with
\textit{minimal coupling} to gravity can resolve the tachyonic instability but
runs into the -problem. We suggest a model which is free of the
-problem due to an additional coupling in the K\"{a}hler potential which
is allowed by the Standard Model gauge group. This induces directions in the
potential which we call K-flat. For a certain value of the new coupling in the
(N)MSSM, the K\"{a}hler potential is special, because it can be associated with
a certain shift symmetry for the Higgs doublets, a generalization of the shift
symmetry for singlets in earlier models. We find that K-flat direction has
This shift symmetry is broken by interactions coming from
the superpotential and gauge fields. This direction fails to produce successful
inflation in the MSSM but produces a viable model in the NMSSM. The model is
specifically interesting in the Peccei-Quinn (PQ) limit of the NMSSM. In this
limit the model can be confirmed or ruled-out not just by cosmic microwave
background observations but also by axion searches.Comment: matches the published version at JCA
Expression of a truncated form of hHb1 hair keratin in human breast carcinomas.
Human hHb1 belongs to the type II hard keratin family and is physiologically expressed in hair shafts. In the present study, using specific 3' and 5' probes for hHb1, we established that breast carcinomas ectopically express a hHb1 5'-truncated mRNA, and that this transcript is restricted to malignant epithelial cells. Furthermore, an in vitro study indicated that it could be translated. We concluded that, in breast carcinomas, expression of truncated hHb1 is related to epithelial cell transformation. Because the hHb1 gene maps to 12q11-q13, a chromosome region known to present several breakpoints in solid tumours, we propose that the hHb1 gene might represent a target for such alterations
On the period ratio P<sub>1</sub>/2P<sub>2</sub> in the oscillations of coronal loops
<p>Aims. With strong evidence of fast and slow magnetoacoustic modes arising in the solar atmosphere there is scope for improved
determinations of coronal parameters through coronal seismology. Of particular interest is the ratio P<sub>1</sub>/2P<sub>2</sub>between the period P<sub>1</sub> of the fundamental mode and the period P<sub>2</sub> of its first harmonic; in an homogeneous medium this ratio is one, but in a more complex
configuration it is shifted to lower values.</p>
<p>Methods. We consider analytically the effects on the different magnetohydrodynamic modes of structuring and stratification, pointing
out that transverse or longitudinal structuring or gravitational stratification modifies the ratio P<sub>1</sub>/2P<sub>2</sub>.</p>
<p>Results. The deviations caused by gravity and structure are studied for the fast and slow modes. Structure along the loop is found to
be the dominant effect.</p>
<p>Conclusions. The departure of P<sub>1</sub>/2P<sub>2</sub> from unity can be used as a seismological tool in the corona. We apply our technique to the
observations by Verwichte et al. (2004), deducing the density scale height in a coronal loop.</p>
String Matching and 1d Lattice Gases
We calculate the probability distributions for the number of occurrences
of a given letter word in a random string of letters. Analytical
expressions for the distribution are known for the asymptotic regimes (i) (Gaussian) and such that is finite
(Compound Poisson). However, it is known that these distributions do now work
well in the intermediate regime . We show that the
problem of calculating the string matching probability can be cast into a
determining the configurational partition function of a 1d lattice gas with
interacting particles so that the matching probability becomes the
grand-partition sum of the lattice gas, with the number of particles
corresponding to the number of matches. We perform a virial expansion of the
effective equation of state and obtain the probability distribution. Our result
reproduces the behavior of the distribution in all regimes. We are also able to
show analytically how the limiting distributions arise. Our analysis builds on
the fact that the effective interactions between the particles consist of a
relatively strong core of size , the word length, followed by a weak,
exponentially decaying tail. We find that the asymptotic regimes correspond to
the case where the tail of the interactions can be neglected, while in the
intermediate regime they need to be kept in the analysis. Our results are
readily generalized to the case where the random strings are generated by more
complicated stochastic processes such as a non-uniform letter probability
distribution or Markov chains. We show that in these cases the tails of the
effective interactions can be made even more dominant rendering thus the
asymptotic approximations less accurate in such a regime.Comment: 44 pages and 8 figures. Major revision of previous version. The
lattice gas analogy has been worked out in full, including virial expansion
and equation of state. This constitutes the main part of the paper now.
Connections with existing work is made and references should be up to date
now. To be submitted for publicatio
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The importance of antecedent vegetation and drought conditions as global drivers of burnt area
The seasonal and longer-term dynamics of fuel accumulation affect fire seasonality and the occurrence of extreme wildfires. Failure to account for their influence may help to explain why state-of-the-art fire models do not simulate the length and timing of the fire season or interannual variability in burnt area well. We investigated the impact of accounting for different timescales of fuel production and accumulation on burnt area using a suite of random forest regression models that included the immediate impact of climate, vegetation, and human influences in a given month and tested the impact of various combinations of antecedent conditions in four productivity-related vegetation indices and in antecedent moisture conditions. Analyses were conducted for the period from 2010 to 2015 inclusive. Inclusion of antecedent vegetation conditions representing fuel build-up led to an improvement of the global, climatological out-of-sample R2 from 0.579 to 0.701, but the inclusion of antecedent vegetation conditions on timescales ≥1 year had no impact on simulated burnt area. Current moisture levels were the dominant influence on fuel drying. Additionally, antecedent moisture levels were important for fuel build-up. The models also enabled the visualisation of interactions between variables, such as the importance of antecedent productivity coupled with instantaneous drying. The length of the period which needs to be considered varies across biomes; fuel-limited regions are sensitive to antecedent conditions that determine fuel build-up over longer time periods (g1/44 months), while moisture-limited regions are more sensitive to current conditions that regulate fuel drying
Site effects of the Roio basin, L’Aquila
During the microzonation studies of the April 6th, 2009 L’Aquila earthquake,
we observed local seismic amplifications in the Roio area—a plane separated from L’Aquila
city center by mount Luco. Six portable, digital instruments were deployed across the plain
from 15 April to mid-May 2009. This array recorded 152 aftershocks. We analyzed the
ground motion from these events to determine relative site amplification within the plain
and on surrounding ridges. Horizontal over vertical spectral ratio on noise data (HVSRN),aftershock recordings (HVEQ) and standard spectral ratio (SSR) showed amplifications at 1.3 and 4.0Hz on quaternary deposits. Seismic amplifications in the frequency range of 4 and 6Hz were also observed on a carbonate ridge of Colle di Roio, on the northwestern border
of the plateau. A small amplification was noticed near the top of mount Luco, another rocky site. Large discrepancies in the amplification levels between methods have been observed for these sites, but the HVSRN, HVEQ and SSR gave similar results at the stations located in the Roio plain. On the rocky sites, the SSR was more reliable than the HVSRN at estimating the transfer function of the site, even if the resonance frequency seemed to be well detected by the latter method.Published809–8234.1. Metodologie sismologiche per l'ingegneria sismicaJCR Journalreserve
The Evolution of Sunspot Magnetic Fields Associated with a Solar Flare
Solar flares occur due to the sudden release of energy stored in
active-region magnetic fields. To date, the pre-cursors to flaring are still
not fully understood, although there is evidence that flaring is related to
changes in the topology or complexity of an active region's magnetic field.
Here, the evolution of the magnetic field in active region NOAA 10953 was
examined using Hinode/SOT-SP data, over a period of 12 hours leading up to and
after a GOES B1.0 flare. A number of magnetic-field properties and low-order
aspects of magnetic-field topology were extracted from two flux regions that
exhibited increased Ca II H emission during the flare. Pre-flare increases in
vertical field strength, vertical current density, and inclination angle of ~
8degrees towards the vertical were observed in flux elements surrounding the
primary sunspot. The vertical field strength and current density subsequently
decreased in the post-flare state, with the inclination becoming more
horizontal by ~7degrees. This behaviour of the field vector may provide a
physical basis for future flare forecasting efforts.Comment: Accepted for Publication in Solar Physics. 16 pages, 4 figure
Site effect variability of the Roio basin in the near-source area of the L'Aquila mainshock
In the frame of the microzonation studies of the April 6th, 2009 L'Aquila earthquake near-source area, we observed local seismic amplifications in the Roio area, a plain separated from L'Aquila city center by mount Luco. Six portable, digital instruments were deployed across the plain from the 15th of April until mid-May 2009. This array recorded up to 152 aftershocks. We analysed the ground motion from these events to determine relative site amplification within the plain and on the surrounding ridges. Horizontal over Vertical spectral ratio on noise data (HVSRN) and on aftershock recordings (HVEQ)as well as standard spectral ratio (SSR) show amplifications at 1.3 Hz and 4.0 Hz on the quaternary deposits. Seismic amplifications in the frequency range between 4 and 6 Hz were also observed on a carbonate ridge of Colle di Roio located on the northwest border of the plateau. A small amplification has also been noticed close to the top of mount Luco, another rocky site. This paper details the results we have obtained and addresses their interpretation.Submitted4.1. Metodologie sismologiche per l'ingegneria sismicaJCR Journalope
A Nanoflare Distribution Generated by Repeated Relaxations Triggered by Kink Instability
Context: It is thought likely that vast numbers of nanoflares are responsible
for the corona having a temperature of millions of degrees. Current
observational technologies lack the resolving power to confirm the nanoflare
hypothesis. An alternative approach is to construct a magnetohydrodynamic
coronal loop model that has the ability to predict nanoflare energy
distributions.
Aims: This paper presents the initial results generated by such a model. It
predicts heating events with a range of sizes, depending on where the
instability threshold for linear kink modes is encountered. The aims are to
calculate the distribution of event energies and to investigate whether kink
instability can be predicted from a single parameter.
Methods: The loop is represented as a straight line-tied cylinder. The
twisting caused by random photospheric motions is captured by two parameters,
representing the ratio of current density to field strength for specific
regions of the loop. Dissipation of the loop's magnetic energy begins during
the nonlinear stage of the instability, which develops as a consequence of
current sheet reconnection. After flaring, the loop evolves to the state of
lowest energy where, in accordance with relaxation theory, the ratio of current
to field is constant throughout the loop and helicity is conserved.
Results: The results suggest that instability cannot be predicted by any
simple twist-derived property reaching a critical value. The model is applied
such that the loop undergoes repeated episodes of instability followed by
energy-releasing relaxation. Hence, an energy distribution of the nanoflares
produced is collated.
Conclusions: The final energy distribution features two nanoflare populations
that follow different power laws. The power law index for the higher energy
population is more than sufficient for coronal heating.Comment: 13 pages, 18 figure
Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities
The coronal magnetic field is the primary driver of solar dynamic events.
Linear and circular polarization signals of certain infrared coronal emission
lines contain information about the magnetic field, and to access this
information, either a forward or an inversion method must be used. We study
three coronal magnetic configurations that are applicable to polar-crown
filament cavities by doing forward calculations to produce synthetic
polarization data. We analyze these forward data to determine the
distinguishing characteristics of each model. We conclude that it is possible
to distinguish between cylindrical flux ropes, spheromak flux ropes, and
sheared arcades using coronal polarization measurements. If one of these models
is found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds certain
quiescent filaments, which will lead to a greater understanding of how they
form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis
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