1,928 research outputs found
Addendum to “Absorption of a massive scalar field by a charged black hole”
In [1] we studied the absorption cross section of a scalar field of mass m impinging on a static black hole of mass M and charge Q. We presented numerical results using the partial-wave method, and analytical results in the high- and low-frequency limit. Our low-frequency approximation was only valid if the (dimensionless) field velocity v exceeds vc=2πMm. In this addendum we give the complementary result for v≲vc, and we consider the possible physical relevance of this regime
Chaos and Energy Redistribution the Nonlinear Interaction of Two Spatio-Temporal Wave Triplets
In this paper we examine the spatio-temporal dynamics of two nonlinearly
coupled wave triplets sharing two common modes. Our basic findings are the
following. When spatial dependence is absent, the homogeneous manifold so
obtained can be chaotic or regular. If chaotic, it drives energy diffusion from
long to small wavelengths as soon as inhomogeneous perturbations are added to
the system. If regular, one may yet have two distinct cases: (i) energy
diffusion is again present if the inhomogeneous modes are linearly unstable and
triplets are effectively coupled; (ii) energy diffusion is absent if the
inhomogeneous modes are linearly stable or the triplets are uncoupled.Comment: 21 pages, 5 figures, accepted for publication in Physica D (1997
Quantum spherical model with competing interactions
We analyze the phase diagram of a quantum mean spherical model in terms of
the temperature , a quantum parameter , and the ratio ,
where refers to ferromagnetic interactions between first-neighbor
sites along the directions of a hypercubic lattice, and is
associated with competing antiferromagnetic interactions between second
neighbors along directions. We regain a number of known results for
the classical version of this model, including the topology of the critical
line in the space, with a Lifshitz point at , for , and
closed-form expressions for the decay of the pair correlations in one
dimension. In the T=0 phase diagram, there is a critical border,
for , with a singularity at the Lifshitz point if
. We also establish upper and lower critical dimensions, and analyze
the quantum critical behavior in the neighborhood of .Comment: 18 pages, 3 figures, refs added, minor modifications to match
published versio
The Tourism Industry and Plastic Waste Policies - Comparative Perspectives from the Portuguese Experience
This paper investigates the correlations between the tourism industry and plastic waste. It starts by evidencing that increase in tourism is likely to enhance the volume and improper destination of waste, including plastic, which has become a major environmental concern in touristic cities. The paper suggests that, on the other hand, negative environmental impact caused by plastic may disincentivize tourism, due to pollution in beaches and seas. As tourism grew in Portugal, the country experienced an increase in plastic waste and has taken measures to deal with the problem. Portugal passed federal legislation to ban single-use plastic tableware as of 2020. Companies, NGOs, and the government are also joining forces to reduce plastic waste and increase recycling initiatives. These are examples to follow as the European Union and internationally-recognized NGOs, such as WWF, put fighting plastic waste as one of the main goals to cities’ environmental sustainability in the forthcoming decades
Nonintegrable Interaction of Ion-Acoustic and Electromagnetic Waves in a Plasma
In this paper we re-examine the one-dimensional interaction of
electromagnetic and ion acoustic waves in a plasma. Our model is similar to one
solved by Rao et al. (Phys. Fluids, vol. 26, 2488 (1983)) under a number of
analytical approximations. Here we perform a numerical investigation to examine
the stability of the model. We find that for slightly over dense plasmas, the
propagation of stable solitary modes can occur in an adiabatic regime where the
ion acoustic electric field potential is enslaved to the electromagnetic field
of a laser. But if the laser intensity or plasma density increases or the laser
frequency decreases, the adiabatic regime loses stability via a transition to
chaos. New asymptotic states are attained when the adiabatic regime no longer
exists. In these new states, the plasma becomes rarefied, and the laser field
tends to behave like a vacuum field.Comment: 19 pages, REVTeX, 6 ps figures, accepted for publication in Phys.
Rev.
The power of quantum systems on a line
We study the computational strength of quantum particles (each of finite
dimensionality) arranged on a line. First, we prove that it is possible to
perform universal adiabatic quantum computation using a one-dimensional quantum
system (with 9 states per particle). This might have practical implications for
experimentalists interested in constructing an adiabatic quantum computer.
Building on the same construction, but with some additional technical effort
and 12 states per particle, we show that the problem of approximating the
ground state energy of a system composed of a line of quantum particles is
QMA-complete; QMA is a quantum analogue of NP. This is in striking contrast to
the fact that the analogous classical problem, namely, one-dimensional
MAX-2-SAT with nearest neighbor constraints, is in P. The proof of the
QMA-completeness result requires an additional idea beyond the usual techniques
in the area: Not all illegal configurations can be ruled out by local checks,
so instead we rule out such illegal configurations because they would, in the
future, evolve into a state which can be seen locally to be illegal. Our
construction implies (assuming the quantum Church-Turing thesis and that
quantum computers cannot efficiently solve QMA-complete problems) that there
are one-dimensional systems which take an exponential time to relax to their
ground states at any temperature, making them candidates for being
one-dimensional spin glasses.Comment: 21 pages. v2 has numerous corrections and clarifications, and most
importantly a new author, merged from arXiv:0705.4067. v3 is the published
version, with additional clarifications, publisher's version available at
http://www.springerlink.co
Impact of acute exposure to air pollution on the cardiorespiratory performance of military firemen
Surface boundary layer characteristics over caatinga vegetation in tropical semiarid region of N-E Brazil
Some characteristic features of the atmospheric surface layer over
a tropical semiarid station Petrolina (9.9◦S, 40.22◦W, 365.5 m) in N-E Brazil, are
investigated, using data collected from a micrometeorological tower of 9 m height.
This study utilizes the wind, temperature, humidity and carbon dioxide (CO2) data
obtained for the month of July 2004. The diurnal variation of mean parameters
such as temperature, relative humidity, wind speed and CO2 are studied. Turbulent
statistics are computed using the eddy correlation technique, and are studied under
the framework of Monin-Obukhov similarity theory with results compared with other
experimental studies reported in the literature
Scarabaeoidea (Insecta : Coleoptera) in the Brazilian Cerrado : current state of knowledge
Besouros pertencentes à superfamília Scarabaeoidea ocupam habitats variados, possuem hábitos alimentares diversifi cados, desempenham importante papel ecológico e diversas espécies apresentam importância agrícola. No entanto, estudos com esse grupo na região do Cerrado são escassos. Nesta revisão realizou-se um levantamento dos artigos publicados nos últimos 30 anos a respeito dos Scarabaeoidea no Cerrado. Foram recuperados 64 artigos, realizados em nove unidades da federação, que focavam quatro temas principais espécies praga, aspectos bioecológicos, biodiversidade e importância ecológica, e técnicas e metodologias de coleta de Scarabaeoidea. Os resultados desta revisão indicam que poucos estudos foram realizados com os Scarabaeoidea no Cerrado brasileiro nas últimas décadas frente à importância e diversidade desse grupo de insetos.Beetles belonging to the superfamily Scarabaeoidea occupy different habitats, present feeding habits diversifi ed, play an important ecological role and several species have agricultural importance. However, studies with this group in the Brazilian Cerrado are scarce. In this review we carried out a survey of scientifi c articles published in the past 30 years concerning Scarabaeoidea in the Cerrado. Were found 64 studies in nine Brazilian states. The studies focused on four main topics: pest species, bioecology, biodiversity and ecological importance, techniques and methodologies for collecting Scarabaeoidea. The results of this review indicate that few studies have been conducted with Scarabaeoidea in the Cerrado in recent decades compared to the importance and diversity of this group of insects
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