28,979 research outputs found
Normal Heat Conduction in a Chain with Weak Interparticle Anharmonic Potential
We analytically study heat conduction in a chain with interparticle
interaction V(x)=lambda[1-cos(x)] and harmonic on-site potential. We start with
each site of the system connected to a Langevin heat bath, and investigate the
case of small coupling for the interior sites in order to understand the
behavior of the system with thermal reservoirs at the boundaries only. We
study, in a perturbative analysis, the heat current in the steady state of the
one-dimensional system with weak interparticle potential. We obtain an
expression for the thermal conductivity, compare the low and high temperature
regimes, and show that, as we turn off the couplings with the interior heat
baths, there is a "phase transition:'' the Fourier's law holds only at high
temperatures
Geoconservation education: the leading role of the University of Minho (Portugal)
In the University of Minho the first works concerning geoconservation were developed in 1996 in the Earth Sciences Department but it was only in 2005 that a major step was taken by this university with the creation of the master course on Geological Heritage and Geoconservation. Since that time, around 70 students were enrolled with an average of 10 new students each year. The University of Minho is also engaged with geoconservation at the PhD level. Several theses have been produced focused of themes centred in Portugal, Cape Verde and Brazil. In addition to post-graduation studies on geoconservation, there are also optional courses (5 ECTS) on geodiversity and geoconservation for the graduations on Geology, Biology and Geography. In what concerns non-formal education, the University of Minho has also some work done on raising public awareness of geoconservation through the organisation of guided fieldtrips to selected geosites, participation in TV documentaries and edition of publications
Quantitative assessment of geosites with national and international relevance in Portugal: methodological procedures
During the last years geoscientists of
various institutions have developed a
project aiming the establishment of a
geoconservation strategy in Portugal.
One of the main goals of this project was the
inventory of the most important Portuguese
the definition of the frameworks representing
the most important geological features in
Portugal and considering all geodiversity.
With the participation of more than seventy geoscientists, twenty-seven geological
frameworks were defined according to their
scientific value at both national and international levels. The scientific value together with the vulnerability was numerically assessed in order to obtain a sorted list of all
geosites with scientific value. The first step geosites. The Portuguese geosites inventory will be used in nature conservation policies and land-use strategies in different levels of country's administration
The inventory of the Portuguese geological heritage: a good example of scientific cooperation between universities
The first systematic inventory of the Portuguese geological heritage is a clear example of the academic collaboration that characterizes the geoconservation in Portugal. Three hundred and twenty six geosites with inter- national or national relevance have been inventoried under the scope of the scientific research project “Identifica- tion, characterisation and conservation of geological heritage: a geoconservation strategy for Portugal”. The geosites were selected exclusively based on their scientific value and support twenty-seven frameworks. For each geological framework a leading geoscientist from a university was responsible for the scientific characterization of the framework, to invite collaborators to identify representative geosites, and to assess the scientific value and vulnerability of the geosites. In the end, seventy geoscientists, mainly from universities, took part in the scientific results that are now important raw data to support nature conservation initiatives
Geoconservation education, research and outreach : the experience of the University of Minho (Portugal)
Geoconservation is an emerging geoscience. In order to gain recognition among the scientific community and in society in general, education lato sensu is of paramount importance. This work presents the experience of the University of Minho with geoconservation education during the past 10 years, namely with graduation and postgraduation courses, teachers training, research, and outreach. Working in those different levels enhanced the university internationalisation with an increase in students and staff exchange. In order to reinforce worldwide recognition universities should strengthen their strategy towards geoconservation by creating courses and developing research projects
The formation of IRIS diagnostics I. A quintessential model atom of Mg II and general formation properties of the Mg II h&k lines
NASA's Interface Region Imaging Spectrograph (IRIS) space mission will study
how the solar atmosphere is energized. IRIS contains an imaging spectrograph
that covers the Mg II h&k lines as well as a slit-jaw imager centered at Mg II
k. Understanding the observations will require forward modeling of Mg II h&k
line formation from 3D radiation-MHD models. This paper is the first in a
series where we undertake this forward modeling. We discuss the atomic physics
pertinent to h&k line formation, present a quintessential model atom that can
be used in radiative transfer computations and discuss the effect of partial
redistribution (PRD) and 3D radiative transfer on the emergent line profiles.
We conclude that Mg II h&k can be modeled accurately with a 4-level plus
continuum Mg II model atom. Ideally radiative transfer computations should be
done in 3D including PRD effects. In practice this is currently not possible. A
reasonable compromise is to use 1D PRD computations to model the line profile
up to and including the central emission peaks, and use 3D transfer assuming
complete redistribution to model the central depression.Comment: 13 pages, 13 figures, accepted for Ap
The formation of IRIS diagnostics II. The formation of the Mg II h&k lines in the solar atmosphere
NASA's Interface Region Imaging Spectrograph (IRIS) small explorer mission
will study how the solar atmosphere is energized. IRIS contains an imaging
spectrograph that covers the Mg II h&k lines as well as a slit-jaw imager
centered at Mg II k. Understanding the observations requires forward modeling
of Mg II h&k line formation from 3D radiation-MHD models.
We compute the vertically emergent h&k intensity from a snapshot of a dynamic
3D radiation-MHD model of the solar atmosphere, and investigate which
diagnostic information about the atmosphere is contained in the synthetic line
profiles. We find that the Doppler shift of the central line depression
correlates strongly with the vertical velocity at optical depth unity, which is
typically located less than 200 km below the transition region (TR). By
combining the Doppler shifts of the h and the k line we can retrieve the sign
of the velocity gradient just below the TR. The intensity in the central line
depression is anticorrelated with the formation height, especially in subfields
of a few square Mm. This intensity could thus be used to measure the spatial
variation of the height of the transition region. The intensity in the
line-core emission peaks correlates with the temperature at its formation
height, especially for strong emission peaks. The peaks can thus be exploited
as a temperature diagnostic. The wavelength difference between the blue and red
peaks provides a diagnostic of the velocity gradients in the upper
chromosphere. The intensity ratio of the blue and red peaks correlates strongly
with the average velocity in the upper chromosphere. We conclude that the Mg II
h&k lines are excellent probes of the very upper chromosphere just below the
transition region, a height regime that is impossible to probe with other
spectral lines.Comment: 15 pages, 12 figures, accepted for ApJ, astro-ph abstract shortened
to confirm to submission requirement
The Framework “Glacial and periglacial landforms and deposits” in the scope of the Portuguese Geological Heritage Inventory
“Geoformas, depósitos glaciários e periglaciários” é um dos contextos geológicos considerados no âmbito da inventariação em curso do património geológico em território nacional. Apesar da reduzida expressão geográfica que as geoformas, os depósitos glaciários e periglaciários têm em Portugal, é-lhes reconhecida importância científica, também por essa via e por resultarem de processos morfodinâmicos raros nas condições climáticas actualmente existentes em Portugal. Após uma avaliação de potenciais geossítios com base em critérios de valor científico, foram seleccionados dezasseis como possuindo relevância nacional.“Glacial and periglacial landforms and deposits” is one of the frameworks included in the
ongoing geological heritage national inventory. The scientific value of these features is connected with
the occurrence of relevant evidences of Quaternary glaciations in the higher mountains of the country
like erosion landforms (U shaped valleys, cirques), depositional landforms (moraines) and deposits
(subglacial tills). Sixteen geosites with national relevance were selected after a potential geosites
assessment focused in scientific criteria.Este trabalho é apoiado pela Fundação para a Ciência e a Tecnologia, através do financiamento
plurianual do CGUP e do projecto de investigação “Identificação, caracterização e conservação do
património geológico: uma estratégia de geoconservação para Portugal” (PTDC/CTEGEX/64966/2006).info:eu-repo/semantics/publishedVersio
Magnetic states of linear defects in graphene monolayers: effects of strain and interaction
The combined effects of defect-defect interaction and of uniaxial or biaxial
strains of up to 10\% on the development of magnetic states on the
defect-core-localized quasi-one-dimensional electronic states generated by the
so-called 558 linear extended defect in graphene monolayers are investigated by
means of {\it ab initio} calculations. Results are analyzed on the basis of the
heuristics of the Stoner criterion. We find that conditions for the emergence
of magnetic states on the 558 defect can be tuned by uniaxial tensile parallel
strains (along the defect direction) at both limits of isolated and interacting
558 defects. Parallel strains are shown to lead to two cooperative effects that
favor the emergence of itinerant magnetism: enhancement of the DOS of the
resonant defect states in the region of the Fermi level and tuning of the Fermi
level to the maximum of the related DOS peak. A perpendicular strain is
likewise shown to enhance the DOS of the defect states, but it also effects a
detunig of the Fermi level that shifts away from the maximum of the DOS of the
defect states, which inhibts the emergence of magnetic states. As a result,
under biaxial strains the stabilization of a magnetic state depends on the
relative magnitudes of the two components of strain.Comment: 9 pages 8 figure
Rephrasing the geodiversity concept under the Ecosystem Services approach and the UN Sustainable Development Goals
The United Nations 2030 Agenda has 17 Sustainable Development Goals (SDG) aiming to achieve a better world for the entire human population. In spite of the fact that human development is dependent on nature and its resources, the non-living (abiotic) natural resources and processes are persistently neglected in international and national policies that foster sustainable development. The current status of abiotic services within the ecosystem services approach is un- satisfactory, inconsistent and confusing, heavily weighting biotic nature and barely including any non-living elements and processes (geodiversity). Furthermore, nature conservation policies at national and regional levels (e.g. EU), usually excludes geodiversity from any effective conservation action. Based on the successful model of promotion of biodiversity, the role of geodiversity on sustainable development also should be founded on the “natural capital” and “ecosystem services” concepts. Geodiversity contributes to “natural capital”, defined as the “world’s stocks of natural assets, which include geology, soil, air, water and all living things”, sometimes also referred to as environmental assets that provide benefits to humanity. Geodiversity contributes to ecosystem services, based on its scientific, educational, economic, cultural, and aesthetic values. Provisioning services refers to the extractable natural resources, the economic base of our modern society, which should be carefully managed. Non-extractable natural resources provide numerous examples of regulation, supporting and cultural services. These non-extractable resources generate scientific, educational and tourism uses, managed by geoconservation. The geodiversity concept is revised making the links with well-established concepts and strategies, namely the ones related with natural capital and ecosystem services, to demonstrate that the UN SDG can only be achieved if the elements and processes of geodiversity are definitely considered in the global agenda. This approach stresses the importance of the sustainable management of geodiversity. The finite character of non-renewable resources and impacts of their extraction should always be emphasized, as well as the conservation of renewable resources, ensuring their sustainable use
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