102 research outputs found
Three Dimensional MHD Wave Propagation and Conversion to Alfven Waves near the Solar Surface. I. Direct Numerical Solution
The efficacy of fast/slow MHD mode conversion in the surface layers of
sunspots has been demonstrated over recent years using a number of modelling
techniques, including ray theory, perturbation theory, differential eigensystem
analysis, and direct numerical simulation. These show that significant energy
may be transferred between the fast and slow modes in the neighbourhood of the
equipartition layer where the Alfven and sound speeds coincide. However, most
of the models so far have been two dimensional. In three dimensions the Alfven
wave may couple to the magneto-acoustic waves with important implications for
energy loss from helioseismic modes and for oscillations in the atmosphere
above the spot. In this paper, we carry out a numerical ``scattering
experiment'', placing an acoustic driver 4 Mm below the solar surface and
monitoring the acoustic and Alfvenic wave energy flux high in an isothermal
atmosphere placed above it. These calculations indeed show that energy
conversion to upward travelling Alfven waves can be substantial, in many cases
exceeding loss to slow (acoustic) waves. Typically, at penumbral magnetic field
strengths, the strongest Alfven fluxes are produced when the field is inclined
30-40 degrees from the vertical, with the vertical plane of wave propagation
offset from the vertical plane containing field lines by some 60-80 degrees.Comment: Accepted for the HELAS II/ SOHO 19/ GONG 2007 Topical Issue of Solar
Physic
A Soluble Phase Field Model
The kinetics of an initially undercooled solid-liquid melt is studied by
means of a generalized Phase Field model, which describes the dynamics of an
ordering non-conserved field phi (e.g. solid-liquid order parameter) coupled to
a conserved field (e.g. thermal field). After obtaining the rules governing the
evolution process, by means of analytical arguments, we present a discussion of
the asymptotic time-dependent solutions. The full solutions of the exact
self-consistent equations for the model are also obtained and compared with
computer simulation results. In addition, in order to check the validity of the
present model we confronted its predictions against those of the standard Phase
field model and found reasonable agreement. Interestingly, we find that the
system relaxes towards a mixed phase, depending on the average value of the
conserved field, i.e. on the initial condition. Such a phase is characterized
by large fluctuations of the phi field.Comment: 13 pages, 8 figures, RevTeX 3.1, submitted to Physical Review
Active Brownian Particles. From Individual to Collective Stochastic Dynamics
We review theoretical models of individual motility as well as collective
dynamics and pattern formation of active particles. We focus on simple models
of active dynamics with a particular emphasis on nonlinear and stochastic
dynamics of such self-propelled entities in the framework of statistical
mechanics. Examples of such active units in complex physico-chemical and
biological systems are chemically powered nano-rods, localized patterns in
reaction-diffusion system, motile cells or macroscopic animals. Based on the
description of individual motion of point-like active particles by stochastic
differential equations, we discuss different velocity-dependent friction
functions, the impact of various types of fluctuations and calculate
characteristic observables such as stationary velocity distributions or
diffusion coefficients. Finally, we consider not only the free and confined
individual active dynamics but also different types of interaction between
active particles. The resulting collective dynamical behavior of large
assemblies and aggregates of active units is discussed and an overview over
some recent results on spatiotemporal pattern formation in such systems is
given.Comment: 161 pages, Review, Eur Phys J Special-Topics, accepte
Recommended Cross Sections for Electron-Indium Scattering
20 pags., 7 figs., 6 tabs.We report, over an extended energy range, recommended angle-integrated cross sections for elastic scattering, discrete inelastic scattering processes, and the total ionization cross section for electron scattering from atomic indium. In addition, from those angle-integrated cross sections, a grand total cross section is subsequently derived. To construct those recommended cross-section databases, results from original B-spline R-matrix, relativistic convergent close-coupling, and relativistic optical-potential computations are also presented here. Electron transport coefficients are subsequently calculated, using our recommended database, for reduced electric fields ranging from 0.01 Td to 10 000 Td using a multiterm solution of Boltzmann's equation. To facilitate those simulations, a recommended elastic momentum transfer cross-section set is also constructed and presented here.The work of K.R.H., O.Z., and K.B. was supported by the United
States National Science Foundation under Grant Nos. OAC-1834740
and PHY-1803844 and by the XSEDE supercomputer Allocation
No. PHY-090031. The (D)BSR calculations were carried out on
Stampede2 at the Texas Advanced Computing Center. The work of
D.V.F. and I.B. was supported by the Australian Research Council and
resources provided by the Pawsey Supercomputing Centre with
funding from the Australian Government and the Government of
Western Australia. F.B. and G.G. acknowledge partial financial
support from the Spanish Ministry MICIU (Project Nos. FIS2016-
80440 and PID2019-104727-RB-C21) and CSIC (Project No.
LINKA20085). This work was also financially supported, in part, by
the Australian Research Council (Project No. DP180101655), the
Ministry of Education, Science and Technological Development of
the Republic of Serbia, and the Institute of Physics (Belgrade).Peer reviewe
Transport of electrons and propagation of the negative ionisation fronts in indium vapour
22 pags., 23 figs.We study the transport of electrons and propagation of the negative ionisation fronts in indium vapour. Electron swarm transport properties are calculated using a Monte Carlo simulation technique over a wide range of reduced electric fields E/N (where E is the electric field and N is the gas number density) and indium vapour temperatures in hydrodynamic conditions, and under non-hydrodynamic conditions in an idealised steady-state Townsend (SST) setup. As many indium atoms are in the first metastable state at vapour temperatures of a few thousand Kelvin, the initial Monte Carlo code was extended and generalized to consider the spatial relaxation and the transport of electrons in an idealised SST experiment, in the presence of thermal motion of the host-gas atoms and superelastic collisions. We observe a significant sensitivity of the spatial relaxation of the electrons on the indium vapour temperature and the initial conditions used to release electrons from the cathode into the space between the electrodes. The calculated electron transport coefficients are used as input for the classical fluid model, to investigate the inception and propagation of negative ionisation fronts in indium vapour at various E/N and vapour temperatures. We calculate the electron density, electric field, and velocity of ionisation fronts as a function of E/N and indium vapour temperature. The presence of indium atoms in the first metastable state significantly affects the characteristics of the negative ionisation fronts. The transition from an avalanche into a negative ionisation front occurs faster with increasing indium vapour temperature, due to enhanced ionisation and more efficient production of electrons at higher vapour temperatures. For lower values of E/N, the electron density behind the streamer front, where the electric field is screened, does not decay as one might expect for atomic gases, but it could be increased due to the accumulation of low-energy electrons that are capable of initiating ionisation in the streamer interior.The work of SD, JA, DB, MSR, DS, and BPM was sup- ˇported by the Ministry of Education, Science and Technological Development of the Republic of Serbia, and the Institute of Physics (Belgrade). The work of KRH, OZ, and KB was supported by the United States National Science Foundation under Grant Nos. OAC-1834740, PHY-1803844, and PHY-2110023, and by the XSEDE supercomputer Allocation No. PHY-090031. The work of DVF and IB, was supported by the Australian Research Council and resources provided
by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia. FB and GG acknowledge partial financial support from the Spanish Ministry MICIU (Project Nos. FIS2016-80440 and PID2019-104727-RB-C21) and CSIC (Project No.
LINKA20085). This work was also financially supported by
the Australian Research Council (Project No. DP180101655).Peer reviewe
Expanding the genetic architecture of nicotine dependence and its shared genetics with multiple traits
Cigarette smoking is the leading cause of preventable morbidity and mortality. Genetic variation contributes to initiation, regular smoking, nicotine dependence, and cessation. We present a Fagerström Test for Nicotine Dependence (FTND)-based genome-wide association study in 58,000 European or African ancestry smokers. We observe five genome-wide significant loci, including previously unreported loci MAGI2/GNAI1 (rs2714700) and TENM2 (rs1862416), and extend loci reported for other smoking traits to nicotine dependence. Using the heaviness of smoking index from UK Biobank (N = 33,791), rs2714700 is consistently associated; rs1862416 is not associated, likely reflecting nicotine dependence features not captured by the heaviness of smoking index. Both variants influence nearby gene expression (rs2714700/MAGI2-AS3 in hippocampus; rs1862416/TENM2 in lung), and expression of genes spanning nicotine dependence-associated variants is enriched in cerebellum. Nicotine dependence (SNP-based heritability = 8.6%) is genetically correlated with 18 other smoking traits (r(g) = 0.40-1.09) and co-morbidities. Our results highlight nicotine dependence-specific loci, emphasizing the FTND as a composite phenotype that expands genetic knowledge of smoking
Biomassa e teor de óleo essencial em Aloysia triphylla (l'hérit) Britton submetida a diferentes níveis de reposição hídrica e à variação sazonal das condições ambientais
Invasão biológica de Artocarpus heterophyllus Lam. (Moraceae) em um fragmento de Mata Atlântica no Nordeste do Brasil: impactos sobre a fitodiversidade e os solos dos sítios invadidos
Toward ‘post-REDD+ landscapes’: Mexico’s community forest enterprises provide a proven pathway to reduce emissions from deforestation and forest degradation
Regions where community forest enterprises dominate the landscape have low to non-existent deforestation, sustainable forest management, enhancement of carbon stocks, forest conservation and substantial generation of sustainable livelihoods. Corruption and deforestation are also associated with some Mexican forest communities, but these regions have created a sector with hundreds of well-managed community forests that contribute to the mitigation of, and adaptation to, climate change. Some 60–70% of Mexican forests are now owned by communities. Forests and land redistribution to local communities that began with the Mexican Revolution (1910–1917) continued until 1992, with a major surge from 1958 to 1976. The agrarian and forest tenure reforms in Mexico served as a foundation for village-level democratic decision-making around forest management. This model clearly defines rights holders and the agricultural and forest territory that they own. Mexico experienced a period of industrial logging concessions on community lands, but both government and communities sought reform in the 1970s, so that timber rights and greater authority over forest management devolved to communities. Mexican forest laws in recent decades have frequently provided a supportive policy environment for community forestry. An estimated 2300 communities regularly log under management plans in Mexico . Mexican community forest enterprises with forest common properties operate at all levels of this vertically integrated industrial sector
Manejo forestal comunitario y el surgimiento de instituciones de gobernanza a múltiples escalas
Las iniciativas para reducir las emisiones de la deforestación y la degradación forestal (REDD) dependerán fundamentalmente de la población rural para manejar los recursos forestales. Aunque el diseño de marcos, mecanismos y acuerdos para implementar los programas de REDD ha sido objeto de considerable atención, todavía no está claro cómo funcionará REDD+ en la práctica y cómo se garantizará la participación de la población local. El manejo forestal comunitario (MFC) puede ser una opción para REDD+ dependiendo de cómo se gestione, debido principalmente a las expectativas de que el MFC podría reducir las emisiones de la deforestación y degradación forestal. El estudio de los factores institucionales que favorecen el surgimiento de sistemas exitosos de MFC y empresas forestales locales puede proporcionar valiosas lecciones a los planificadores de REDD. En este documento analizamos iniciativas de manejo forestal comunitario en México, Brasil y Bolivia para evaluar el papel que las instituciones de gobernanza a escalas múltiples tienen en su desarrollo. Al comparar y contrastar sistemas avanzados de MFC con las regiones en las que todavía está surgiendo, mostramos la necesidad imperativa de una base organizativa local para el manejo de los recursos comunitarios
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