4,182 research outputs found
Flow instabilities of magnetic flux tubes IV. Flux storage in the solar overshoot region
We consider the effects of material flows on the dynamics of toroidal
magnetic flux tubes located close to the base of the solar convection zone,
initially within the overshoot region. The problem is to find the physical
conditions in which magnetic flux can be stored for periods comparable to the
dynamo amplification time, which is of the order of a few years. We carry out
nonlinear numerical simulations to investigate the stability and dynamics of
thin flux tubes subject to perpendicular and longitudinal flows. We compare the
simulations with the results of simplified analytical approximations. We
determine ranges of the flow parameters for which a linearly Parker-stable
magnetic flux tube is stored in the middle of the overshoot region for a period
comparable to the dynamo amplification time. The residence time for magnetic
flux tubes with fluxes of 2x10^{21} Mx in the convective overshoot layer is
comparable to the dynamo amplification time, provided that the average speed
and the duration of the downflow do not exceed about 50 m/s and 100 days,
respectively, and that the lateral extension of the flow is smaller than about
10 degrees.Comment: Accepted to be published in Astronomy and Astrophysics. 16 pages, 16
figures. To access GIF animations, use
http://www.mps.mpg.de/homes/ishik/flute/frict_inst.gif,
http://www.mps.mpg.de/homes/ishik/flute/TF60.gif and
http://www.mps.mpg.de/homes/ishik/flute/TF180.gi
An Index Of Management Intensity For Coffee Agroecosystems To Evaluate Butterfly Species Richness
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117238/1/eap20031351491.pd
Linking Shade Coffee Certification To Biodiversity Conservation: Butterflies And Birds In Chiapas, Mexico
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/117232/1/eap2004143642.pd
Holographic Floquet states in low dimensions
We study the response of a (2+1)-dimensional gauge theory to an external
rotating electric field. In the strong coupling regime such system is
formulated holographically in a top-down model constructed by intersecting D3-
and D5-branes along 2+1 dimensions, in the quenched approximation, in which the
D5-brane is a probe in the AdS_5 x S^5 geometry. The system has a
non-equilibrium phase diagram with conductive and insulator phases. The
external driving induces a rotating current due to vacuum polarization (in the
insulator phase) and to Schwinger effect (in the conductive phase). For some
particular values of the driving frequency the external field resonates with
the vector mesons of the model and a rotating current can be produced even in
the limit of vanishing driving field. These features are in common with the
(3+1) dimensional setup based on the D3-D7 brane model and hint on some
interesting universality. We also compute the conductivities paying special
attention to the photovoltaic induced Hall effect, which is only present for
massive charged carriers. In the vicinity of the Floquet condensate the optical
Hall coefficient persists at zero driving field, signalling time reversal
symmetry breaking.Comment: 56 pages, 19 figure
Post-release mortality of shortfin mako in the Atlantic using satellite telemetry: preliminary results
This paper provides an update of the study on post-release mortality of the shortfin mako, Isurus oxyrinchus developed within the ICCAT Shark Research and Data Collection Program (SRDCP). Up to date, 34 tags (14 sPATs and 20 miniPATs) have been deployed by observers on Brazilian, Portuguese, Uruguayan, and US vessels in the temperate NE and NW, Equatorial and SW Atlantic. Data from 28 out of 34 tagged specimens could be used to obtain preliminary information regarding post-release mortality, resulting in a total of 7 mortality and 21 survival events.This study was carried out as part of a cooperative work conducted by the ICCAT Shark species group integrated in
the ICCAT Shark Research and Data Collection Program (SRDCP). The authors are grateful to all fishery observers
and longline skippers from the Nations involved in this study. Tags from additional sources have been contributed
and deployed with several national Projects, specifically: Project "LL-Sharks: Mitigação das capturas de tubarões na
pescaria de palangre de superfĂcie (Ref: 31-03-05-FEP-44, funded by PROMAR)", Project "MAKO-WIDE - "A
wide scale inter-hemispheric and inter-disciplinary study aiming the conservation of the shortfin mako shark in the
Atlantic Ocean (Ref: FAPESP/19740/2014)", funded by FCT (Portuguese Foundation for Science and Technology)
and FAPESP (SĂŁo Paulo Research Foundation, Brazil), and Project SAFEWATERS SC7 (The provision of advice
on the conservation of pelagic sharks associated to fishing activity under EU Sustainable Fisheries Partnership
Agreements in the Atlantic Ocean) under the Framework Contract MARE/2012/21, funded by the European
Commission. Additional satellite tags were acquired by NOAA in US-Uruguay and US-Portugal-Uruguay
collaboration initiatives. Rui Coelho is supported by an Investigador-FCT contract from the Portuguese Foundation
for Science and Technology (FCT) supported by the EU European Social Fund and the Programa Operacional
Potencial Humano (Ref: IF/00253/2014).info:eu-repo/semantics/draf
Holographic Floquet states in low dimensions (II)
We continue the study in [1] of a strongly coupled (2+1)-dimensional gauge
theory subject to an external rotating electric field. The system is modelled
holographically as a D3/D5 probe intersection. We add temperature to the D3
background and analyze the phase diagram. Also here, the conductive phase
extends down to vanishing external electric field at discrete values of the
frequencies where vector meson Floquet condensates form. For all temperatures,
at given intercalated frequencies, we find new dual states that we name Floquet
suppression points, where the vacuum polarization vanishes even in the presence
of an electric field. From the data we infer that these states exist both in
the conductive and insulating phases. In the massless limit we find a linear
and instantaneous conductivity law, recovering known general results in 2+1
dimensions. We also examine the photovoltaic AC and DC current as the response
to an oscillating probe electric field and see that rising the temperature
suppresses the photovoltaic Hall current. All the results obtained carry over
qualitatively unaltered to the case of D3/D7.Comment: 22 pages + appendice
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