13,945 research outputs found
Relation between trees of fragmenting granules and supergranulation evolution
Context: The determination of the underlying mechanisms of the magnetic
elements diffusion over the solar surface is still a challenge. Understanding
the formation and evolution of the solar network (NE) is a challenge, because
it provides a magnetic flux over the solar surface comparable to the flux of
active regions at solar maximum. Aims: We investigate the structure and
evolution of interior cells of solar supergranulation. From Hinode
observations, we explore the motions on solar surface at high spatial and
temporal resolution. We derive the main organization of the flows inside
supergranules and their effect on the magnetic elements. Method: To probe the
superganule interior cell, we used the Trees of Fragmenting Granules (TFG)
evolution and their relations to horizontal Results: Evolution of TFG and their
mutual interactions result in cumulative effects able to build horizontal
coherent flows with longer lifetime than granulation (1 to 2 hours) over a
scale up to 12\arcsec. These flows clearly act on the diffusion of the
intranetwork (IN) magnetic elements and also on the location and shape of the
network. Conclusions: From our analysis during 24 hours, TFG appear as one of
the major elements of the supergranules which diffuse and advect the magnetic
field on the Sun's surface. The strongest supergranules contribute the most to
magnetic flux diffusion in the solar photosphere.Comment: 13 pages, 17 figures, accepted in Astronomy and Astrophysics movie :
http://www.lesia.obspm.fr/perso/jean-marie-malherbe/Hinode2007/hinode2007.htm
Designed Interaction Potentials via Inverse Methods for Self-Assembly
We formulate statistical-mechanical inverse methods in order to determine
optimized interparticle interactions that spontaneously produce target
many-particle configurations. Motivated by advances that give experimentalists
greater and greater control over colloidal interaction potentials, we propose
and discuss two computational algorithms that search for optimal potentials for
self-assembly of a given target configuration. The first optimizes the
potential near the ground state and the second near the melting point. We begin
by applying these techniques to assembling open structures in two dimensions
(square and honeycomb lattices) using only circularly symmetric pair
interaction potentials ; we demonstrate that the algorithms do indeed cause
self-assembly of the target lattice. Our approach is distinguished from
previous work in that we consider (i) lattice sums, (ii) mechanical stability
(phonon spectra), and (iii) annealed Monte Carlo simulations. We also devise
circularly symmetric potentials that yield chain-like structures as well as
systems of clusters.Comment: 28 pages, 23 figure
Mesoscale dynamics on the Sun's surface from HINODE observations
Aims: The interactions of velocity scales on the Sun's surface, from
granulation to supergranulation are still not understood, nor are their
interaction with magnetic fields. We thus aim at giving a better description of
dynamics in the mesoscale range which lies between the two scales mentioned
above. Method: We analyse a 48h high-resolution time sequence of the quiet Sun
photosphere at the disk center obtained with the Solar Optical Telescope
onboard Hinode. The observations, which have a field of view of 100
\arcsec 100 \arcsec, typically contain four supergranules. We monitor
in detail the motion and evolution of granules as well as those of the radial
magnetic field. Results: This analysis allows us to better characterize Trees
of Fragmenting Granules issued from repeated fragmentation of granules,
especially their lifetime statistics. Using floating corks advected by measured
velocity fields, we show their crucial role in the advection of the magnetic
field and in the build up of the network. Finally, thanks to the long duration
of the time series, we estimate that the turbulent diffusion coefficient
induced by horizontal motion is approximately . Conclusions: These results demonstrate that the long living
families contribute to the formation of the magnetic network and suggest that
supergranulation could be an emergent length scale building up as small
magnetic elements are advected and concentrated by TFG flows. Our estimate for
the magnetic diffusion associated with this horizontal motion might provide a
useful input for mean-field dynamo models.Comment: to appear in A&A - 8 pages, 13 figures (degraded quality) - Full
resolution version available @
http://www.ast.obs-mip.fr/users/rincon/hinode_roudier_aa09.pd
Quasi full-disk maps of solar horizontal velocities using SDO/HMI data
For the first time, the motion of granules (solar plasma on the surface on
scales larger than 2.5 Mm) has been followed over the entire visible surface of
the Sun, using SDO/HMI white-light data.
Horizontal velocity fields are derived from image correlation tracking using
a new version of the coherent structure tracking algorithm.The spatial and
temporal resolutions of the horizontal velocity map are 2.5 Mm and 30 min
respectively .
From this reconstruction, using the multi-resolution analysis, one can obtain
to the velocity field at different scales with its derivatives such as the
horizontal divergence or the vertical component of the vorticity. The intrinsic
error on the velocity is ~0.25 km/s for a time sequence of 30 minutes and a
mesh size of 2.5 Mm.This is acceptable compared to the granule velocities,
which range between 0.3 km/s and 1.8 km/s. A high correlation between
velocities computed from Hinode and SDO/HMI has been found (85%). From the data
we derive the power spectrum of the supergranulation horizontal velocity field,
the solar differential rotation, and the meridional velocity.Comment: 8 pages, 11 figures, accepted in Astronomy and Astrophysic
PassGAN: A Deep Learning Approach for Password Guessing
State-of-the-art password guessing tools, such as HashCat and John the
Ripper, enable users to check billions of passwords per second against password
hashes. In addition to performing straightforward dictionary attacks, these
tools can expand password dictionaries using password generation rules, such as
concatenation of words (e.g., "password123456") and leet speak (e.g.,
"password" becomes "p4s5w0rd"). Although these rules work well in practice,
expanding them to model further passwords is a laborious task that requires
specialized expertise. To address this issue, in this paper we introduce
PassGAN, a novel approach that replaces human-generated password rules with
theory-grounded machine learning algorithms. Instead of relying on manual
password analysis, PassGAN uses a Generative Adversarial Network (GAN) to
autonomously learn the distribution of real passwords from actual password
leaks, and to generate high-quality password guesses. Our experiments show that
this approach is very promising. When we evaluated PassGAN on two large
password datasets, we were able to surpass rule-based and state-of-the-art
machine learning password guessing tools. However, in contrast with the other
tools, PassGAN achieved this result without any a-priori knowledge on passwords
or common password structures. Additionally, when we combined the output of
PassGAN with the output of HashCat, we were able to match 51%-73% more
passwords than with HashCat alone. This is remarkable, because it shows that
PassGAN can autonomously extract a considerable number of password properties
that current state-of-the art rules do not encode.Comment: This is an extended version of the paper which appeared in NeurIPS
2018 Workshop on Security in Machine Learning (SecML'18), see
https://github.com/secml2018/secml2018.github.io/raw/master/PASSGAN_SECML2018.pd
Lecture Notes on Topological Crystalline Insulators
We give an introduction to topological crystalline insulators, that is,
gapped ground states of quantum matter that are not adiabatically connected to
an atomic limit without breaking symmetries that include spatial
transformations, like mirror or rotational symmetries. To deduce the
topological properties, we use non-Abelian Wilson loops. We also discuss in
detail higher-order topological insulators with hinge and corner states, and in
particular present interacting bosonic models for the latter class of systems.Comment: Lectures given at the San Sebasti\'an Topological Matter School 2017,
published in "Topological Matter. Springer Series in Solid-State Sciences,
vol 190. Springer, Cham
Estrogenic activity, race/ethnicity, and Indigenous American ancestry among San Francisco Bay Area women.
Estrogens play a significant role in breast cancer development and are not only produced endogenously, but are also mimicked by estrogen-like compounds from environmental exposures. We evaluated associations between estrogenic (E) activity, demographic factors and breast cancer risk factors in Non-Latina Black (NLB), Non-Latina White (NLW), and Latina women. We examined the association between E activity and Indigenous American (IA) ancestry in Latina women. Total E activity was measured with a bioassay in plasma samples of 503 women who served as controls in the San Francisco Bay Area Breast Cancer Study. In the univariate model that included all women with race/ethnicity as the independent predictor, Latinas had 13% lower E activity (p = 0.239) and NLBs had 35% higher activity (p = 0.04) compared to NLWs. In the multivariable model that adjusted for demographic factors, Latinas continued to show lower E activity levels (26%, p = 0.026), but the difference between NLBs and NLWs was no longer statistically significant (p = 0.431). An inverse association was observed between E activity and IA ancestry among Latina women (50% lower in 0% vs. 100% European ancestry, p = 0.027) consistent with our previously reported association between IA ancestry and breast cancer risk. These findings suggest that endogenous estrogens and exogenous estrogen-like compounds that act on the estrogen receptor and modulate E activity may partially explain racial/ethnic differences in breast cancer risk
Masses of Fermions in Supersymmetric Models
We consider the mass generation for the usual quarks and leptons in some
supersymmetric models. The masses of the top, the bottom, the charm, the tau
and the muon are given at the tree level. All the other quarks and the electron
get their masses at the one loop level in the Minimal Supersymmetric Standard
Model (MSSM) and in two Supersymmetric Left-Right Models, one model uses
triplets (SUSYLRT) to break -symmetry and the other use
doublets(SUSYLRD).Comment: 24 pages, 2 figures and 3 table
Preparation of a Series of Substituted N-Phenyl-5-Bromo-6-Chloro- and 5-Bromo-6-Chloronicotinates of Potential Agricultural Interest
Substituted phenyl esters of 5-bromo-2-chloronicotinic acid and 5 bromo 6-chloronicotinic acid were prepared. The acids were first converted to their respective acid chlorides using thionyl chloride, and the acid chlorides were immediately transformed to the esters by treatment with the appropriately substituted phenol in sodium hydroxide solution. Aunique chloride displacement of bromide was observed on attempting to convert 5,6-dibromonicotinic acid to its acid chlorid
- âŠ