4,969 research outputs found
Breakdown of the Fermi-liquid regime in the 2D Hubbard model from a two-loop field-theoretical renormalization group approach
We analyze the particle-hole symmetric two-dimensional Hubbard model on a
square lattice starting from weak-to-moderate couplings by means of the
field-theoretical renormalization group (RG) approach up to two-loop order.
This method is essential in order to evaluate the effect of the
momentum-resolved anomalous dimension which arises in the
normal phase of this model on the corresponding low-energy single-particle
excitations. As a result, we find important indications pointing to the
existence of a non-Fermi liquid (NFL) regime at temperature displaying
a truncated Fermi surface (FS) for a doping range exactly in between the
well-known antiferromagnetic insulating and the -wave singlet
superconducting phases. This NFL evolves as a function of doping into a
correlated metal with a large FS before the -wave pairing
susceptibility finally produces the dominant instability in the low-energy
limit.Comment: 9 pages, 9 figures; published in Phys. Rev.
Capybara (Hydrochoerus hydrochaeris) distribution in agroecosystems: a cross-scale habitat analysis.
Dissipation in planar resonant planetary systems
Close-in planetary systems detected by the Kepler mission present an excess
of periods ratio that are just slightly larger than some low order resonant
values. This feature occurs naturally when resonant couples undergo dissipation
that damps the eccentricities. However, the resonant angles appear to librate
at the end of the migration process, which is often believed to be an evidence
that the systems remain in resonance.
Here we provide an analytical model for the dissipation in resonant planetary
systems valid for low eccentricities. We confirm that dissipation accounts for
an excess of pairs that lie just aside from the nominal periods ratios, as
observed by the Kepler mission. In addition, by a global analysis of the phase
space of the problem, we demonstrate that these final pairs are non-resonant.
Indeed, the separatrices that exist in the resonant systems disappear with the
dissipation, and remains only a circulation of the orbits around a single
elliptical fixed point. Furthermore, the apparent libration of the resonant
angles can be explained using the classical secular averaging method. We show
that this artifact is only due to the severe damping of the amplitudes of the
eigenmodes in the secular motion.Comment: 18 pages, 20 figures, accepted to A&
Surface nano-patterning through styrene adsorption on Si(100)
We present an ab initio study of the structural and electronic properties of
styrene molecules adsorbed on the dimerized Si(100) surface at different
coverages, ranging from the single-molecule to the full monolayer. The
adsorption mechanism primarily involves the vinyl group via a [2+2]
cycloaddition process that leads to the formation of covalent Si-C bonds and a
local surface derelaxation, while it leaves the phenyl group almost
unperturbed. The investigation of the functionalized surface as a function of
the coverage (e.g. 0.5 -- 1 ML) and of the substrate reconstruction reveals two
major effects. The first results from Si dimer-vinyl interaction and concerns
the controlled variation of the energy bandgap of the interface. The second is
associated to phenyl-phenyl interactions, which gives rise to a regular pattern
of electronic wires at surface, stemming from the pi-pi coupling. These
findings suggest a rationale for tailoring the surface nano-patterning of the
surface, in a controlled way.Comment: 19 pages (preprint), 4 figures, supplementary materia
Principal components in the study of soil and plant properties in precision coffee farming
ArticleIn this work, a principal component analysis was performed to evaluate the possibility
of discarding obsolete soil and plant variables in a coffee field to eliminate redundant and
difficult-to-measure information in precision coffee farming. This work was conducted at Brejão
Farm in Três Pontas, Minas Gerais, Brazil, in a coffee field planted with 22 ha of Topázio cultivar.
The evaluated variables were the yield, plant height, crown diameter, fruit maturation index,
degree of fruit maturation, leafing, soil pH, available phosphorus (P), remaining phosphorus
(Prem), available potassium (K), exchangeable calcium (Ca2+), exchangeable magnesium
(Mg2+), exchangeable acidity (Al3+), potential acidity (H + Al), aluminium saturation (N(Al)),
potential CEC (CECp), actual CEC (CECa), sum of bases (SB), base saturation (BS) and organic
matter (OM). The data were evaluated by a principal component analysis, which generated 20
components. Of these, 7 representing 88.98% of the data variation were chosen. The variables
were discarded based on the preservation of the variables with the greatest coefficients in absolute
values corresponding to the first component, followed by the variable with the second highest
absolute value corresponding to the second principal component. Based on the results, the
variables V, OM, fruit maturity index, plant height, yield, leafing and P were selected. The other
variables were discarded
Sistema de produção de banana para a Zona da Mata de Pernambuco.
bitstream/item/27822/1/sp-3.pd
Chirikov Diffusion in the Asteroidal Three-Body Resonance (5,-2,-2)
The theory of diffusion in many-dimensional Hamiltonian system is applied to
asteroidal dynamics. The general formulations developed by Chirikov is applied
to the Nesvorn\'{y}-Morbidelli analytic model of three-body (three-orbit)
mean-motion resonances (Jupiter-Saturn-asteroid system). In particular, we
investigate the diffusion \emph{along} and \emph{across} the separatrices of
the (5,-2,-2) resonance of the (490) Veritas asteroidal family and their
relationship to diffusion in semi-major axis and eccentricity. The estimations
of diffusion were obtained using the Melnikov integral, a Hadjidemetriou-type
sympletic map and numerical integrations for times up to years.Comment: 27 pages, 6 figure
Spatial variability of litter temperature, relative air humidity and skin temperature of chicks in a commercial broiler house
ArticleThe thermal environment inside a broiler house has a great influence on animal welfare
and productivity during the production phase. Among the importance of the chicken litter is the
function of absorbing moisture, provide thermal insulation and provide a soft surface for broilers.
The skin temperature is an important physiological parameter to quantify the thermal comfort of
animals, its variations may occur as a function of thermal variables. So, the aim of this work was
to analyse the magnitude and spatial variability of chicken litter temperature and relative humidity
of the air and to correlate them with the spatial distribution of chicks’ skin surface temperature
throughout the broiler house during the 7th, 14th and 21st days of the chicks’ life, using
geostatistical techniques. The experiment was performed in a commercial broiler house located
in the western mesoregion of Minas Gerais, Brazil, where 28,000 male Cobb chicks were housed.
The heating system consisted of an industrial indirect-fired biomass furnace. The heated air was
inflated by an AC motor, 2,206 W of power, 1,725 RPM. Geostatistical techniques were used
through semivariogram analysis and isochore maps were generated through data interpolation by
kriging. The semivariogram was fitted by the restricted maximum likelihood method. The used
mathematical model was the spherical one. After fitting the semivariograms, the data were
interpolated by ordinary kriging. The semivariograms along with the isochore maps allowed
identifying the non-uniformity of spatial distribution of the broiler litter temperature throughout
the broiler house for 3 days of chicks’ life. It was observed that skin surface presented a positive
correlation with the litter temperature and a negative correlation with the air humidity. The
semivariograms along with the isochore maps allowed identifying the non-uniformity of spatial
distribution of the litter temperature, air humidity and skin temperature of chicks throughout the
broiler aviary for the three days. In addition, the use of geostatistics and distribution maps made
possible to identify different environmental conditions in regions inside the broiler house that
may harm the development of chicks
Design and construction of a low-cost remotely piloted aircraft for precision agriculture applications
ArticleThis study aimed to construct a low cost RPA capable of recording georeferenced
images. For the construction of the prototype of a quadcopter type RPA, only essential materials
were used to allow stable flight. A maximum total weight of 2 kg was stipulated, including frame
weight, electronic components, motors and cameras. The aircraft was programmed using a
low-cost microcontroller widely used in prototyping and automation research. An electronic
circuit board is designed to facilitate the connection of the microcontroller with the other
components of the design. Specific software was used for flight control. The prototype was built
successfully, being able to lift stable and controllable flight. However, we still need to acquire
equipment and programming components capable of enabling autonomous images and flights.
The final cost of the RPA was on average 772.81 to $ 1,288.00
Desempenho motor após palidotomia póstero-ventral e talamotomia ventro-lateral na doença de Parkinson: acompanhamento de um ano
Twenty-three patients with Parkinson's disease underwent stereotactic surgery. To study the long-term motor performance, the patients were evaluated at the pre-operative period and at the 1st, 3rd, 6th, and 12th post-operative months, with the following scales: Unified Parkinson's Disease Rating Scale (UPDRS) motor score and Larsen's Scale for Dyskinesias. The patients under levodopa therapy were assessed both in on and off periods. Fourteen unilateral ventrolateral thalamotomies (VLT), 4 unilateral posteroventral pallidotomies (PVP), 2 bilateral PVP, and 3 VLT with contralateral PVP were performed. The motor improvement was significant and long-lasting in the off period, except for 2 patients. The on period quality improved, mainly due to the control of dyskinesias. The improvement of dyskinesias was long-lasting for the majority of the patients. There was no significant decrease in the levodopa dose. Three patients showed permanent complications, but none was severe.Vinte e três pacientes portadores de doença de Parkinson foram submetidos a cirurgia estereotáxica para tratamento da doença. Com o objetivo de estudar o desempenho motor a longo prazo, os pacientes foram avaliados clinicamente no período pré-operatório, no 1°, 3°, 6°, e 12° mês pós-operatório, com as seguintes escalas: Escala Unificada para Doença de Parkinson (Unified Parkinson's Disease Rating Scale-UPDRS), item III, escore motor e com a Escala de Larsen para Discinesias. Os pacientes que utilizavam levodopa foram avaliados nos estados off e on. Foram realizadas 14 talamotomias ventro-laterais (TVL) unilaterais, 4 palidotomias póstero-ventrais (PPV) unilaterais, 2 PPV bilaterais; 3 TVL associadas à PPV contralateral. O benefício motor foi observado de forma significante no estado off, e manteve-se a longo prazo na maioria dos pacientes, exceto em 2. Houve melhora da qualidade do período on, devido ao controle das discinesias. A melhora das discinesias se manteve a longo prazo na maioria dos pacientes. As cirurgias não promoveram um decréscimo significante na dose de levodopa.Três pacientes tiveram complicações permanentes, mas nenhuma delas foi considerada grave e nem houve prejuízo funcional importante em decorrência das mesmas.Universidade Federal de São Paulo (UNIFESP) Escola Paulista de Medicina Department of Neurology and NeurosurgeryHospital do Servidor Público Estadual Francisco Morato OliveiraUNIFESP, EPM, Department of Neurology and NeurosurgerySciEL
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