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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Mon, 21 Oct 2019 07:00:06 GMT2019-10-21T07:00:06Z3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey
http://hdl.handle.net/10256/17049
3D Object Recognition Based on Point Clouds in Underwater Environment with Global Descriptors: A Survey
Himri, Khadidja; Ridao Rodríguez, Pere; Grácias, Nuno Ricardo Estrela
This paper addresses the problem of object recognition from colorless 3D point clouds in
underwater environments. It presents a performance comparison of state-of-the-art global descriptors,
which are readily available as open source code. The studied methods are intended to assist
Autonomous Underwater Vehicles (AUVs) in performing autonomous interventions in underwater
Inspection, Maintenance and Repair (IMR) applications. A set of test objects were chosen as being
representative of IMR applications whose shape is typically known a priori. As such, CAD models
were used to create virtual views of the objects under realistic conditions of added noise and varying
resolution. Extensive experiments were conducted from both virtual scans and from real data collected
with an AUV equipped with a fast laser sensor developed in our research centre. The underwater
testing was conducted from a moving platform, which can create deformations in the perceived shape
of the objects. These effects are considerably more difficult to correct than in above-water counterparts,
and therefore may affect the performance of the descriptor. Among other conclusions, the testing we
conducted illustrated the importance of matching the resolution of the database scans and test scans,
as this significantly impacted the performance of all descriptors except one. This paper contributes to
the state-of-the-art as being the first work on the comparison and performance evaluation of methods
for underwater object recognition. It is also the first effort using comparison of methods for data
acquired with a free floating underwater platform
Mon, 14 Oct 2019 00:00:00 GMThttp://hdl.handle.net/10256/170492019-10-14T00:00:00ZLong-Term Glucose Forecasting Using a Physiological Model and Deconvolution of the Continuous Glucose Monitoring Signal
http://hdl.handle.net/10256/17048
Long-Term Glucose Forecasting Using a Physiological Model and Deconvolution of the Continuous Glucose Monitoring Signal
Liu, Chengyuan; Vehí, Josep; Avari, Parizad; Reddy, Monika; Oliver, Nick; Georgiou, Pantelis; Herrero, Pau
Blood glucose forecasting in type 1 diabetes (T1D) management is a
maturing field with numerous algorithms being published and a few of them having reached the
commercialisation stage. However, accurate long-term glucose predictions (e.g., >60 min), which
are usually needed in applications such as precision insulin dosing (e.g., an artificial pancreas),
still remain a challenge. In this paper, we present a novel glucose forecasting algorithm that is
well-suited for long-term prediction horizons. The proposed algorithm is currently being used as
the core component of a modular safety system for an insulin dose recommender developed within
the EU-funded PEPPER (Patient Empowerment through Predictive PERsonalised decision support)
project. (2) Methods: The proposed blood glucose forecasting algorithm is based on a compartmental
composite model of glucose–insulin dynamics, which uses a deconvolution technique applied to
the continuous glucose monitoring (CGM) signal for state estimation. In addition to commonly
employed inputs by glucose forecasting methods (i.e., CGM data, insulin, carbohydrates), the
proposed algorithm allows the optional input of meal absorption information to enhance prediction
accuracy. Clinical data corresponding to 10 adult subjects with T1D were used for evaluation
purposes. In addition, in silico data obtained with a modified version of the UVa-Padova simulator
was used to further evaluate the impact of accounting for meal absorption information on prediction
accuracy. Finally, a comparison with two well-established glucose forecasting algorithms, the
autoregressive exogenous (ARX) model and the latent variable-based statistical (LVX) model, was
carried out. (3) Results: For prediction horizons beyond 60 min, the performance of the proposed
physiological model-based (PM) algorithm is superior to that of the LVX and ARX algorithms.
When comparing the performance of PM against the secondly ranked method (ARX) on a 120 min
prediction horizon, the percentage improvement on prediction accuracy measured with the root
mean square error, A-region of error grid analysis (EGA), and hypoglycaemia prediction calculated
by the Matthews correlation coefficient, was 18.8%, 17.9%, and 80.9%, respectively. Although
showing a trend towards improvement, the addition of meal absorption information did not provide
clinically significant improvements. (4) Conclusion: The proposed glucose forecasting algorithm is
potentially well-suited for T1D management applications which require long-term glucose predictions
Tue, 08 Oct 2019 00:00:00 GMThttp://hdl.handle.net/10256/170482019-10-08T00:00:00ZEjection-Collision orbits in the symmetric collinear four–body problem
http://hdl.handle.net/10256/17047
Ejection-Collision orbits in the symmetric collinear four–body problem
Alvarez-Ramírez, Marta; Barrabés Vera, Esther; Medina, Mario; Ollé Torner, Mercè
In this paper, we consider the collinear symmetric four-body problem, where four masses m3=α, m1=1, m2=1, and m4=α, α > 0, are aligned in this order and move symmetrically about their center of mass. We introduce regularized variables to deal with binary collisions as well as McGehee coordinates to study the quadruple collision manifold for a negative value of the energy. The paper is mainly focused on orbits that eject from (or collide to) quadruple collision. The problem has two hyperbolic equilibrium points, located in the quadruple collision manifold. We use high order parametrizations of their stable/unstable manifolds to devise a numerical procedure to compute ejection-collision orbits, for any value of α. Some results from the explorations done for α=1 are presented. Furthermore, we prove the existence of ejection-direct escape orbits, which perform a unique type of binary collisions
Sat, 15 Jun 2019 00:00:00 GMThttp://hdl.handle.net/10256/170472019-06-15T00:00:00ZWellposedness and Decay Rates for the Cauchy Problem of the Moore–Gibson–Thompson Equation Arising in High Intensity Ultrasound
http://hdl.handle.net/10256/17046
Wellposedness and Decay Rates for the Cauchy Problem of the Moore–Gibson–Thompson Equation Arising in High Intensity Ultrasound
Pellicer Sabadí, Marta; Said-Houari, B.
In this paper, we study the Moore–Gibson–Thompson equation in (Formula presented.), which is a third order in time equation that arises in viscous thermally relaxing fluids and also in viscoelastic materials (then under the name of standard linear viscoelastic model). First, we use some Lyapunov functionals in the Fourier space to show that, under certain assumptions on some parameters in the equation, a norm related to the solution decays with a rate (Formula presented.). Since the decay of the previous norm does not give the decay rate of the solution itself then, in the second part of the paper, we show an explicit representation of the solution in the frequency domain by analyzing the eigenvalues of the Fourier image of the solution and writing the solution accordingly. We use this eigenvalues expansion method to give the decay rate of the solution (and also of its derivatives), which results in (Formula presented.) for (Formula presented.) and (Formula presented.) when (Formula presented.)
Tue, 01 Oct 2019 00:00:00 GMThttp://hdl.handle.net/10256/170462019-10-01T00:00:00Z