11,131 research outputs found
Dependence of the Black-body Force on Spacetime Geometry and Topology
In this paper we compute the corrections to the black-body force (BBF)
potential due to spacetime geometry and topology. This recently discovered
attractive force on neutral atoms is caused by the thermal radiation emitted
from black bodies and here we investigate it in relativistic gravitational
systems with spherical and cylindrical symmetries. For some astrophysical
objects we find that the corrected black-body potential is greater than the
flat case, showing that this kind of correction can be quite relevant when
curved spaces are considered. Then we consider four cases: The Schwarzschild
spacetime, the global monopole, the non-relativistic infinity cylinder and the
static cosmic string. For the spherically symmetric case of a massive body, we
find that two corrections appear: One due to the gravitational modification of
the temperature and the other due to the modification of the solid angle
subtended by the atom. We apply the found results to a typical neutron star and
to the Sun. For the global monopole, the modification in the black-body
potential is of topological nature and it is due to the central solid angle
deficit that occurs in the spacetime generated by that object. In the
cylindrical case, which is locally flat, no gravitational correction to the
temperature exists, as in the global monopole case. However, we find the
curious fact that the BBF depends on the topology of the spacetime through the
modification of the azimuthal angle and therefore of the solid angle. For the
static cosmic string we find that the force is null for the zero thickness
case.Comment: 8 pages, 5 figures. Revised versio
Caracterização física química de raízes de mandiocaba.
A mandioca (Manihot esculenta Crantz) é um arbusto de origem brasileira (sudoeste da Amazônia) e que, mesmo antes da chegada dos europeus à América, já estava disseminado para o cultivo alimentar, apresentando diversidades de variedades. Cultivada nas mais diversas regiões do Brasil, sua produção tem sido dirigida tanto para consumo direto como para indústria de transformação. Portanto, objetivou-se avaliar as características físico-químicas das raízes de mandiocaba. Para tal, foram avaliados os teores de umidade 90%, cinzas 0,1%, fibra 0,4%, proteína bruta 0,15%, lipídios totais 0,09%, acidez titulável total 2,2, pH 6,3, sólidos solúveis totais 6,3, açúcar redutor 3,9 e açúcares redutores totais 5,2. Portanto pode-se concluir que a raiz de mandioca doce apresenta atributos que a qualificam para serem utilizadas diretamente para serem fermentadas por leveduras para a obtenção de etanol. Cumpre ressaltar que o rendimento em etanol será proporcional a quantidade de açúcar que existir na raiz de mandioca doce
HPC Cloud for Scientific and Business Applications: Taxonomy, Vision, and Research Challenges
High Performance Computing (HPC) clouds are becoming an alternative to
on-premise clusters for executing scientific applications and business
analytics services. Most research efforts in HPC cloud aim to understand the
cost-benefit of moving resource-intensive applications from on-premise
environments to public cloud platforms. Industry trends show hybrid
environments are the natural path to get the best of the on-premise and cloud
resources---steady (and sensitive) workloads can run on on-premise resources
and peak demand can leverage remote resources in a pay-as-you-go manner.
Nevertheless, there are plenty of questions to be answered in HPC cloud, which
range from how to extract the best performance of an unknown underlying
platform to what services are essential to make its usage easier. Moreover, the
discussion on the right pricing and contractual models to fit small and large
users is relevant for the sustainability of HPC clouds. This paper brings a
survey and taxonomy of efforts in HPC cloud and a vision on what we believe is
ahead of us, including a set of research challenges that, once tackled, can
help advance businesses and scientific discoveries. This becomes particularly
relevant due to the fast increasing wave of new HPC applications coming from
big data and artificial intelligence.Comment: 29 pages, 5 figures, Published in ACM Computing Surveys (CSUR
Generalised verification of the observer property in discrete event systems
The observer property is an important condition to be satisfied by abstractions of Discrete Event Systems (DES) models. This paper presents a generalised version of a previous algorithm which tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure called OP-verifier II overcomes the limitations of the previously proposed verifier while keeping its computational complexity. Results are illustrated by a case study of a transfer line system
Generalised verification of the observer property in discrete event systems
The observer property is an important condition to be satisfied by abstractions of Discrete Event Systems (DES) models. This paper presents a generalised version of a previous algorithm which tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure called OP-verifier II overcomes the limitations of the previously proposed verifier while keeping its computational complexity. Results are illustrated by a case study of a transfer line system
Verification of the observer property in discrete event systems
The observer property is an important condition to be satisfied by abstractions of Discrete Event System (DES) models. This technical note presents a new algorithm that tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure, called OP-Verifier, can be applied to (potentially nondeterministic) automata, with no restriction on the existence of cycles of 'non-relevant' events. This procedure has quadratic complexity in the number of states. The performance of the algorithm is illustrated by a set of experiments
Levantamento e análise de resíduos biodegradáveis destinados a compostagem, originados em campo experimental.
A compostagem é uma pratica usada para o reaproveitamento de resíduos biodegradáveis na adubação orgânica, contribuindo com alguns nutrientes importantes para enriquecimento de solo, e ainda melhorando as condições estruturais do solo. Este trabalho teve como objetivo montar um banco de dados para qualificar os tipos de resíduos biodegradáveis originados nos campos experimentais. O estudo foi desenvolvido nos campos experimentais da Embrapa Amazônia Ocidental, o do KM 30 na rodovia AM 010 em Manaus e o do Caldeirão, no município de Iranduba
Signatures of magnetic activity in the seismic data of solar-type stars observed by Kepler
In the Sun, the frequencies of the acoustic modes are observed to vary in
phase with the magnetic activity level. These frequency variations are expected
to be common in solar-type stars and contain information about the
activity-related changes that take place in their interiors. The unprecedented
duration of Kepler photometric time-series provides a unique opportunity to
detect and characterize stellar magnetic cycles through asteroseismology. In
this work, we analyze a sample of 87 solar-type stars, measuring their temporal
frequency shifts over segments of length 90 days. For each segment, the
individual frequencies are obtained through a Bayesian peak-bagging tool. The
mean frequency shifts are then computed and compared with: 1) those obtained
from a cross-correlation method; 2) the variation in the mode heights; 3) a
photometric activity proxy; and 4) the characteristic timescale of the
granulation. For each star and 90-d sub-series, we provide mean frequency
shifts, mode heights, and characteristic timescales of the granulation.
Interestingly, more than 60% of the stars show evidence for (quasi-)periodic
variations in the frequency shifts. In the majority of the cases, these
variations are accompanied by variations in other activity proxies. About 20%
of the stars show mode frequencies and heights varying approximately in phase,
in opposition to what is observed for the Sun.Comment: Accepted for publication in ApJS, 19(+86) pages, 11(+89) figures,
2(+87) table
Seismic signatures of magnetic activity in solar-type stars observed by Kepler
The properties of the acoustic modes are sensitive to magnetic activity. The
unprecedented long-term Kepler photometry, thus, allows stellar magnetic cycles
to be studied through asteroseismology. We search for signatures of magnetic
cycles in the seismic data of Kepler solar-type stars. We find evidence for
periodic variations in the acoustic properties of about half of the 87 analysed
stars. In these proceedings, we highlight the results obtained for two such
stars, namely KIC 8006161 and KIC 5184732.Comment: 4 pages, 1 figure, to appear in the Proceedings of the IAUS34
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