373 research outputs found
Critical properties of the XXZ model with long-range interactions on the double chain
The model in a transverse field on a double chain with a
uniform long-range interaction among the components of the spins is
considered. The nearest-neighbour interactions are restricted to the components
in the plane and to the spins within the same chain leg, such that the
Hamiltonian is given by , where is the number of sites of the lattice and
label the chain legs. The model is solved exactly by
introducing the Jordan-Wigner and integral Gaussian transformations, which map
the Hamiltonian in a non-interacting fermion system and corresponds to an
extension of the model recently studied by the authors for a single chain. The
equation of state is obtained in closed form, and the critical classical (at ) and quantum (at ) behaviours can be determined exactly. The
quantum critical surface is determined in the space generated by the transverse
field and interaction parameters, and the crossover lines separating the
different critical regimes are also obtained. It is also shown that,
differently from the results obtained for the single chain, the system can
present multiple quantum transitions.Comment: 02 pages, 02 figures, to appear in JMMM (Proceedings of ICM2006
The XY model on the one-dimensional superlattice: static properties
The XY model (s=1/2) on the one-dimensional alternating superlattice (closed
chain) is solved exactly by using a generalized Jordan-Wigner transformation
and the Green function method. Closed expressions are obtained for the
excitation spectrum, the internal energy, the specific heat, the average
magnetization per site, the static transverse susceptibility and the two-spin
correlation function in the field direction at arbitrary temperature. At T=0 it
is shown that the system presents multiple second order phase transitions
induced by the transverse field, which are associated to the zero energy mode
with wave number equal to 0 or . It is also shown that the average
magnetization as a function of the field presents, alternately, regions of
plateaux (disordered phases) and regions of variable magnetization (ordered
phases). The static correlation function presents an oscillating behaviour in
the ordered phase and its period goes to infinity at the critical point.Comment: 16 pages, 16 figure
Fuzzy control of a water pump for an agricultural plant growth system
At the present time there is a high pressure toward the improvement of all the production processes. Those
improvements can be sensed in several directions in particular those that involve energy efficiency. The definition
of tight energy efficiency improvement policies is transversal to several operational areas ranging from
industry to public services. As can be expected, agricultural processes are not immune to this tendency. This
statement takes more severe contours when dealing with indoor productions where it is required to artificially
control the climate inside the building or a partial growing zone. Regarding the latter, this paper presents an
innovative system that improves energy efficiency of a trees growing platform. This new system requires the
control of both a water pump and a gas heating system based on information provided by an array of sensors.
In order to do this, a multi-input, multi-output regulator was implemented by means of a Fuzzy logic
control strategy. Presented results show that it is possible to simultaneously keep track of the desired growing
temperature set-point while maintaining actuators stress within an acceptable range.This work is financed by the ERDF - European Regional Development Fund through the COMPETE Programme (operational programme for competitiveness) and by National Funds through the FCT -Fundação para a Ciência e a Tecnologia (Portuguese Foundation for Science and Technology) within project “*FCOMP-01-0124-FEDER-037281*
Apple and Pear Model for Optimal Production and Fruit Grade in a Changing Environment
Apple and pear crops are very important to the rural economy of Portugal. Despite
significant improvements in productivity and quality, due to the introduction of new management
techniques, model-based decision support may further increase the revenue of the growers. Available
simulation models of orchard growth and production are scarce and are often highly empirical. This
study presents a mechanistic model for the simulation of productivity and fruit grade of apple and
pear orchards under potential and water-limited conditions. The effects of temperature extremes
and rain on fruit set are addressed. The model was validated on apple and pear datasets derived
from extensive experiments conducted in Central and Southern Portugal. Model performance is high
and depicts the effect of crop load on productivity and fruit-size grade and the distribution of both
crops. A simulation example shows the relationship between productivity and average fruit size for
a hypothetical six-year-olc apple orchard. The model herewith presented is a tool that can be used to
estimate optimal crop load for maximum revenue and productivity, fruit size distribution, water use,
and other variables relevant for pome fruit productioninfo:eu-repo/semantics/publishedVersio
Plágio no ensino superior: mensurar o que os alunos fazem, sabem e julgam saber
A investigação sobre o plágio entre alunos do ensino superior tem comprovado que esta prática, além de assumir diversas formas, tanto pode resultar de um ato intencional revelador de falta de
honestidade, como de uma ação não intencional decorrente de desconhecimentos acerca do plágio e
das normas a cumprir para o evitar. Este carácter plural e não intencional do plágio coloca atualmente desafios à investigação, quer fundamental, quer aplicada, raras vezes explorados no caso português.
Este artigo debruça-se sobre a discussão metodológica em curso acerca da mensuração da incidência
do plágio no ensino superior, trazendo à colação dados recentes sobre estudantes portugueses e refletindo sobre os prolongamentos dessa discussão na prevenção desta prática fraudulenta. Verifica-se
que a combinação de distintos indicadores permite mensurar de forma mais holística a incidência do
plágio e que a sua prevenção carece de maior aposta em formação sobre uma correta utilização e creditação de fontes
A new plant growth system rig based on thermodynamic solar energy: a study for energy efficiency assessment
At the present there is a high pressure toward the improvement
of all production processes. Those improvements can target distinct
factors along the production chain. In particular, and due to recent tight
energy efficiency policies, those that involve energy efficiency. As can be
expected, agricultural processes are not immune to this tendency. Even
more when dealing with indoor productions. In this context, this work
presents an innovative system that aims to improve the energy efficiency
of a trees growing platform. This improvement in energy consumption
is accomplished by replacing an electric heating system by one based
on thermodynamic panels. The assessment of the heating fluid caudal
and its temperature was experimentally obtained by means of a custom
made scaled prototype whose actuators status are commanded by a
Fuzzy-based controller. The obtained results suggest that the change in
the heating paradigm will lead to overall savings that can easily reach
60% on the energy bill.This work is financed by the Project TEC4Growth - Pervasive Intelligence, Enhancers and Proofs of Concept with Industrial Impact / NORTE-01-0145-FEDER-000020”, which is financed by the North Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, and through the European Regional Development Fund (ERDF)
Pilot Study to Reduce Added Salt on a University Canteen through the Use of an Innovative Dosage Equipment
Background: This study aims to demonstrate the practical application of an innovative easy-to-use equipment to dosage cooking salt, and evaluate the effectiveness in reducing 30% of the added salt in meals and the impact on consumers satisfaction and food waste. Methods: Two canteens from one public university where randomized in one control arm and one intervention arm. The first step was to evaluate the salt added to food through atomic emission spectrophotometry in both canteens, and the second step was to perform gradual reductions of up to 30% of cooking salt in the intervention canteen using the Salt Control-C (SC-C) equipment. Consumer acceptability was assessed through satisfaction questionnaires and food waste was evaluated by weighing. Results: The intervention canteen achieved to a reduction of more than 30% of added salt in soup (34.3% per 100 g), fish dish (41.1% per 100 g) and meat dish (48.0% per 100 g), except for the vegetarian dish (6.1% per 100 g). There was no decrease in consumer satisfaction, with a significant satisfaction increase of 15.7% (p = 0.044) regarding the flavor of the main dish. Also, no significant differences were found in food waste. Conclusions: SC-C seems to be effective in reducing 30% of added salt levels in canteen meals, and may be a good strategy to control and reach adequate levels of added salt in meals served outside-the-home, promoting benefits to the individuals health. (c) 2022 by the authors. Licensee MDPI, Basel, Switzerland
Validation of a cable speedometer for butterfly evaluation
Getting fast results from the evaluation of swimmers is one of
the most important goals to achieve with technological development
in the field. The purpose of this study was to validate a
real-time velocimetric device (speedometer) through the comparison
of their results with computer assisted videogrametry.
The sample included 7 international level swimmers (3 females
and 4 males). Each swimmer performed four 25m trials, two at
200m race pace and two at 50m race pace. For each trial, two
stroke cycles were studied, resulting on a total of 28 cycles
SWIMMING EVALUATION, ADVICE AND BIOFEEDBACK
Rev Port Cien Desp 6(Supl.2) 201–282 237
analysed. Hip v(t) curves obtained from speedometer and
videogrametry were compared, as well as the speedometer hip
curve with the one of the centre of mass (CM). The higher
mean correlation obtained was between vhip1 and vhip2
(0.955±0.028), followed by vhip1 with vCM (0.920±0.049). The
lower correlation was vhip2 vs. vCM (0.878±0.053). It was concluded
that the speedometer is a reliable, fast and interactive
tool for training advice
Time limit at the minimum velocity of VO2max and intracyclic variation of the velocity of the centre of mass
The purpose of this study was to analyse the relationship
between time limit at the minimum velocity that elicits maximal
oxygen consumption (TLim-vVO2max) and intra-cyclic variations
of the velocity of the centre of mass (dv) in the four
competitive swimming techniques. Twelve elite male swimmers
SWIMMING BIOENERGETICS
Rev Port Cien Desp 190 6(Supl.2) 185–197
swam their own best technique until exhaustion at their previously
determined v O2max to assess TLim-v O2max. The test
was videotaped in the sagittal plan and the APAS software was
used to evaluate the horizontal velocity of the centre of mass
(Vcm) and its intra-cyclic variation (dv) per swimming technique.
Results pointed out that the strokes that presented
higher intra-cyclic variations also presented larger values of
TLim. Intra-cyclic speed fluctuations (dv) decreased during the
TLim test in the four strokes studied, probably due to fatigue.
Key words: VO2, intra-cyclic velocity variations, time limit, centre
of mass.Authors want to express their gratitude to the Portuguese
National Team, and the Portuguese Swimming Federation, for
their cooperation
Some peculiarities of motion of neutral and charged test particles in the field of a spherically symmetric charged object in General Relativity
We propose the method of investigation of radial motions for charged and
neutral test particles in the Reissner-Nordstr\"{o}m field by means of mass
potential. In this context we analyze special features of interaction of
charges and their motions in General Relativity and construct the radial motion
classification. For test particles and a central source with charges and
, respectively, the conditions of attraction (when ) and repulsion
(when ) are obtained. The conditions of motionless test particle states
with respect to the central source are investigated and, in addition, stability
conditions for such static equilibrium states are found. It is shown that
stable states are possible only for the bound states of weakly charged
particles in the field of a naked singularity. Frequencies of small
oscillations of test particles near their equilibrium positions are also found.Comment: 15 pages, 9 figure
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