2,547 research outputs found
Recuperação de atributos fÃsicos de um argissolo em função do seu revolvimento e do tempo de semeadura direta.
A melhoria da qualidade estrutural do solo pelo uso continuado do sistema semeadura direta ocorre junto com o processo de sua (re)acidificação. Em algumas circunstâncias, ocorre também compactação superficial devido ao tráfego de máquinas, que necessita ser corrigida pela mobilização do solo. Assim, em experimento conduzido há 12 anos sob diferentes sistemas de manejo do solo, avaliou-se o tempo necessário para o solo readquirir os atributos fÃsicos iniciais, alterados no processo de revolvimento do solo, por ocasião da reaplicação de calcário. O experimento foi realizado na Estação Experimental Agronômica da UFRGS, em Eldorado do Sul - RS, em um Argissolo Vermelho distrófico tÃpico. Os sistemas de manejo avaliados foram: (a) preparo convencional durante 12 anos, (b) sistema semeadura direta com revolvimento do solo para incorporar calcário a cada quatro anos, (c) sistema semeadura direta durante oito anos e (d) sistema semeadura direta durante 12 anos. Determinaram-se, imediatamente antes e 6, 12, 24, 36 e 48 meses depois da terceira reaplicação de calcário, a densidade, a porosidade total, a macroporosidade, a microporosidade, a estabilidade de agregados e o teor de C orgânico em três camadas (0,0-2,5; 2,5-7,5 e 7,5-15,0 cm) de solo. O revolvimento do solo para incorporação do calcário no sistema semeadura direta de quatro anos propiciou condições mais favoráveis de densidade e porosidade do solo, mas diminuiu a estabilidade de agregados. Houve necessidade de um perÃodo de quatro anos de cultivo do solo no sistema semeadura direta para o retorno da estabilidade de agregados à condição original. Os atributos fÃsicos do solo foram mais uniformes no perfil no preparo convencional, porém com menor estabilidade de agregados na camada superficial, que foi relacionada ao teor de C orgânico
Mist and Edge Computing Cyber-Physical Human-Centered Systems for Industry 5.0: A Cost-Effective IoT Thermal Imaging Safety System
While many companies worldwide are still striving to adjust to Industry 4.0
principles, the transition to Industry 5.0 is already underway. Under such a
paradigm, Cyber-Physical Human-centered Systems (CPHSs) have emerged to
leverage operator capabilities in order to meet the goals of complex
manufacturing systems towards human-centricity, resilience and sustainability.
This article first describes the essential concepts for the development of
Industry 5.0 CPHSs and then analyzes the latest CPHSs, identifying their main
design requirements and key implementation components. Moreover, the major
challenges for the development of such CPHSs are outlined. Next, to illustrate
the previously described concepts, a real-world Industry 5.0 CPHS is presented.
Such a CPHS enables increased operator safety and operation tracking in
manufacturing processes that rely on collaborative robots and heavy machinery.
Specifically, the proposed use case consists of a workshop where a smarter use
of resources is required, and human proximity detection determines when
machinery should be working or not in order to avoid incidents or accidents
involving such machinery. The proposed CPHS makes use of a hybrid edge
computing architecture with smart mist computing nodes that processes thermal
images and reacts to prevent industrial safety issues. The performed
experiments show that, in the selected real-world scenario, the developed CPHS
algorithms are able to detect human presence with low-power devices (with a
Raspberry Pi 3B) in a fast and accurate way (in less than 10 ms with a 97.04%
accuracy), thus being an effective solution that can be integrated into many
Industry 5.0 applications. Finally, this article provides specific guidelines
that will help future developers and managers to overcome the challenges that
will arise when deploying the next generation of CPHSs for smart and
sustainable manufacturing.Comment: 32 page
Pressure of massless hot scalar theory in the boundary effective theory framework
We use the boundary effective theory (BET) approach to thermal field theory
in order to calculate the pressure of a system of massless scalar fields with
quartic interaction. The method naturally separates the infrared physics, and
is essentially non-perturbative. To lowest order, the main ingredient is the
solution of the free Euler-Lagrange equation with non-trivial (time) boundary
conditions. We derive a resummed pressure, which is in good agreement with
recent calculations found in the literature, following a very direct and
compact procedure.Comment: 10 pages, 4 figure
Phase conversion in a weakly first-order quark-hadron transition
We investigate the process of phase conversion in a thermally-driven {\it
weakly} first-order quark-hadron transition. This scenario is physically
appealing even if the nature of this transition in equilibrium proves to be a
smooth crossover for vanishing baryonic chemical potential. We construct an
effective potential by combining the equation of state obtained within Lattice
QCD for the partonic sector with that of a gas of resonances in the hadronic
phase, and present numerical results on bubble profiles, nucleation rates and
time evolution, including the effects from reheating on the dynamics for
different expansion scenarios. Our findings confirm the standard picture of a
cosmological first-order transition, in which the process of phase conversion
is entirely dominated by nucleation, also in the case of a weakly first-order
transition. On the other hand, we show that, even for expansion rates much
lower than those expected in high-energy heavy ion collisions, nucleation is
very unlikely, indicating that the main mechanism of phase conversion is
spinodal decomposition. Our results are compared to those obtained for a
strongly first-order transition, as the one provided by the MIT bag model.Comment: 12 pages, 10 figures; v2: 1 reference added, minor modifications,
matches published versio
Strangeness in Astrophysics and Cosmology
Some recent developments concerning the role of strange quark matter for
astrophysical systems and the QCD phase transition in the early universe are
addressed. Causality constraints of the soft nuclear equation of state as
extracted from subthreshold kaon production in heavy-ion collisions are used to
derive an upper mass limit for compact stars. The interplay between the
viscosity of strange quark matter and the gravitational wave emission from
rotation-powered pulsars are outlined. The flux of strange quark matter nuggets
in cosmic rays is put in perspective with a detailed numerical investigation of
the merger of two strange stars. Finally, we discuss a novel scenario for the
QCD phase transition in the early universe, which allows for a small
inflationary period due to a pronounced first order phase transition at large
baryochemical potential.Comment: 8 pages, invited talk given at the International Conference on
Strangeness in Quark Matter (SQM2009), Buzios, Brasil, September 28 - October
2, 200
Strange quark matter in explosive astrophysical systems
Explosive astrophysical systems, such as supernovae or compact star binary
mergers, provide conditions where strange quark matter can appear. The high
degree of isospin asymmetry and temperatures of several MeV in such systems may
cause a transition to the quark phase already around saturation density.
Observable signals from the appearance of quark matter can be predicted and
studied in astrophysical simulations. As input in such simulations, an equation
of state with an integrated quark matter phase transition for a large
temperature, density and proton fraction range is required. Additionally,
restrictions from heavy ion data and pulsar observation must be considered. In
this work we present such an approach. We implement a quark matter phase
transition in a hadronic equation of state widely used for astrophysical
simulations and discuss its compatibility with heavy ion collisions and pulsar
data. Furthermore, we review the recently studied implications of the QCD phase
transition during the early post-bounce evolution of core-collapse supernovae
and introduce the effects from strong interactions to increase the maximum mass
of hybrid stars. In the MIT bag model, together with the strange quark mass and
the bag constant, the strong coupling constant provides a parameter
to set the beginning and extension of the quark phase and with this the mass
and radius of hybrid stars.Comment: 6 pages, 5 figures, talk given at the International Conference on
Strangeness in Quark Matter (SQM2009), Buzios, Brasil, September 28 - October
2, 2009, to be published in Journal Phys.
Hydrodynamical instabilities in an expanding quark gluon plasma
We study the mechanism responsible for the onset of instabilities in a chiral
phase transition at nonzero temperature and baryon chemical potential. As a
low-energy effective model, we consider an expanding relativistic plasma of
quarks coupled to a chiral field, and obtain a phenomenological chiral
hydrodynamics from a variational principle. Studying the dispersion relation
for small fluctuations around equilibrium, we identify the role played by
chiral waves and pressure waves in the generation of instabilities. We show
that pressure modes become unstable earlier than chiral modes.Comment: 7 pages, 4 figure
Holographic rho mesons in an external magnetic field
We study the rho meson in a uniform magnetic field eB using a holographic
QCD-model, more specifically a D4/D8/Dbar8 brane setup in the confinement phase
at zero temperature with two quenched flavours. The parameters of the model are
fixed by matching to corresponding dual field theory parameters at zero
magnetic field. We show that the up- and down-flavour branes respond
differently to the presence of the magnetic field in the dual QCD-like theory,
as expected because of the different electromagnetic charge carried by up- and
down-quark. We discuss how to recover the Landau levels, indicating an
instability of the QCD vacuum at eB = m_rho^2 towards a phase where charged rho
mesons are condensed, as predicted by Chernodub using effective QCD-models. We
improve on these existing effective QCD-model analyses by also taking into
account the chiral magnetic catalysis effect, which tells us that the
constituent quark masses rise with eB. This turns out to increase the value of
the critical magnetic field for the onset of rho meson condensation to eB = 1.1
m_rho^2 = 0.67 GeV^2. We briefly discuss the influence of pions, which turn out
to be irrelevant for the condensation in the approximation made.Comment: 26 pages, 10 .pdf figures, v2: version accepted for publication in
JHE
Modification of the epigenome in human cancer cells by expression of a DNA demethylase from plants
Dense quark matter in compact stars
The densest predicted state of matter is colour-superconducting quark matter,
in which quarks near the Fermi surface form a condensate of Cooper pairs. This
form of matter may well exist in the core of compact stars, and the search for
signatures of its presence is an ongoing enterprise. Using a bag model of quark
matter, I discuss the effects of colour superconductivity on the mass-radius
relationship of compact stars, showing that colour superconducting quark matter
can occur in compact stars at values of the bag constant where ordinary quark
matter would not be allowed. The resultant ``hybrid'' stars with colour
superconducting quark matter interior and nuclear matter surface have masses in
the range 1.3-1.6 Msolar and radii 8-11 km. Once perturbative corrections are
included, quark matter can show a mass-radius relationship very similar to that
of nuclear matter, and the mass of a hybrid star can reach 1.8 \Msolar.Comment: 11 pages, for proceedings of SQM 2003 conference; references added,
abstract reworde
- …