113 research outputs found
Experimental Method Calibration (MECr): A new relative method for heat flux sensor calibration
Heat flux sensor calibration is often expensive, but it is also a fundamental step to obtain valid results. According to the needs, several calibration procedures could be considered. If experimental interpretations focus on heat flux values comparison rather than true values, a relative calibration with high accuracy can be performed. This paper focuses on a new relative calibration-type method of heat flux sensors (HFSs). In general, the HFSs were originally (even recently) factory and in-house-calibrated, but this method was used to calibrate them to an exact common reading to help in performing accurate experiments and eliminating errors that could result from differences between the HFSs. The developed methodology was adapted from a secondary calibration-type (i.e., absolute) generalization. This method aimed to present a simple, low cost, and accurate way to calibrate heat flux sensors. The proposed calibration method was relative, which means that it did not use any calibration reference. However, an absolute calibration adaptation of this method can easily be performed. In the method presented in this paper, calibration was made via sensor sensitivity correction. The experiment consisted of imposing an identical and homogeneous heat flux across four heat flux sensors during a sufficiently long time to be able to statistically subtract any unwanted influences, such as convective and radiative variation. More precisely, temperatures and heat flux levels of 30-35 °C and 60-70 W.m-2 , respectively, were used. Then, new sensor sensitivity values were found by basic statistical data manipulations. Although the focus of this methodology was for contenting thermopile-based HFSs that used differential temperature measurements, the set-up can be adapted for other types of HFSs. In this paper, the set-up, its conception, and guidelines for using this method are presented
Evaluating The Robustness of Self-Supervised Representations to Background/Foreground Removal
Despite impressive empirical advances of SSL in solving various tasks, the
problem of understanding and characterizing SSL representations learned from
input data remains relatively under-explored. We provide a comparative analysis
of how the representations produced by SSL models differ when masking parts of
the input. Specifically, we considered state-of-the-art SSL pretrained models,
such as DINOv2, MAE, and SwaV, and analyzed changes at the representation
levels across 4 Image Classification datasets. First, we generate variations of
the datasets by applying foreground and background segmentation. Then, we
conduct statistical analysis using Canonical Correlation Analysis (CCA) and
Centered Kernel Alignment (CKA) to evaluate the robustness of the
representations learned in SSL models. Empirically, we show that not all models
lead to representations that separate foreground, background, and complete
images. Furthermore, we test different masking strategies by occluding the
center regions of the images to address cases where foreground and background
are difficult. For example, the DTD dataset that focuses on texture rather
specific objects
Evolution of CODYRUN from Thermal Simulation to Coupled Thermal and Daylight Simulation Software
AbstractCODYRUN is a multi-zone software integrating thermal building simulation, airflow, and pollutant transfer. Described in numerous publications, this software was originally used for the passive design of buildings, both for research and teaching purposes. In this context, the data treated were mainly concerned with volumes (zones), surfaces and thicknesses (walls and windows), materials, and systems, with the aim to determine temperatures, heat fluxes, energy consumed, air transfers, and so on.The question thus arose as to the integration of indoor lighting conditions into the simulation. Hence, previous data structures had to be amended to incorporate the spatial positioning of entities (walls, windows, and artificial lighting sources) through vertexes. A set of procedures was also developed for polygons as well as calculating natural and artificial lighting.The results of this new daylighting module were then compared with other results of simulation codes and experimental cases both in artificial and natural environments. Excellent agreements were obtained, such as the values for luminous efficiencies in a tropical and humid climate.A simulation exercise was conducted in a classroom located in Reunion Island (French overseas territory in the Indian Ocean), thus confirming the interest for thermal and daylighting designs in low-energy buildings
Design and use of radiant barriers as thermal insulation for high inertia houses in tropical conditions - a case study
Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.This paper deals with the thermal design and performance
of a roof-mounted radiant barrier, installed in a high inertia
house in tropical and humid conditions. Using dynamic
simulations of a mathematical model of a whole house
including a radiant barrier installed between the roof slab and
the ceiling, the thermal performance of the roof is calculated
and the thermal comfort in the house is evaluated using the
psychometric chart. The mean method is more particularly used
to assess the thermal resistance of the building roof and lead to
a value which can be compared to those obtained using mass
insulation product such as polyurethane foam or glass wool.
The aim of the study is to evaluate the most appropriate
technical solution to insulate high inertia roofs of buildings,
which can accumulate much energy during the day and create
uncomfortable thermal conditions in the late afternoon and
during the night in summer tropical conditions.cs201
Global attractors for Cahn-Hilliard equations with non constant mobility
We address, in a three-dimensional spatial setting, both the viscous and the
standard Cahn-Hilliard equation with a nonconstant mobility coefficient. As it
was shown in J.W. Barrett and J.W. Blowey, Math. Comp., 68 (1999), 487-517, one
cannot expect uniqueness of the solution to the related initial and boundary
value problems. Nevertheless, referring to J. Ball's theory of generalized
semiflows, we are able to prove existence of compact quasi-invariant global
attractors for the associated dynamical processes settled in the natural
"finite energy" space. A key point in the proof is a careful use of the energy
equality, combined with the derivation of a "local compactness" estimate for
systems with supercritical nonlinearities, which may have an independent
interest. Under growth restrictions on the configuration potential, we also
show existence of a compact global attractor for the semiflow generated by the
(weaker) solutions to the nonviscous equation characterized by a "finite
entropy" condition
Heat Transfer in Buildings: Application to Solar Air Collector and Trombe Wall Design
The aim of this paper is to briefly recall heat transfer modes and explain
their integration within a software dedicated to building simulation (CODYRUN).
Detailed elements of the validation of this software are presented and two
applications are finally discussed. One concerns the modeling of a flat plate
air collector and the second focuses on the modeling of Trombe solar walls. In
each case, detailed modeling of heat transfer allows precise understanding of
thermal and energetic behavior of the studied structures. Recent decades have
seen a proliferation of tools for building thermal simulation. These
applications cover a wide spectrum from very simplified steady state models to
dynamic simulation ones, including computational fluid dynamics modules
(Clarke, 2001). These tools are widely available in design offices and
engineering firms. They are often used for the design of HVAC systems and still
subject to detailed research, particularly with respect to the integration of
new fields (specific insulation materials, lighting, pollutants transport,
etc.). Available from:
http://www.intechopen.com/books/evaporation-condensation-and-heat-transfer/heat-transfer-in-buildings-application-to-solar-air-collector-and-trombe-wall-designComment: Available from:
http://www.intechopen.com/books/evaporation-condensation-and-heat-transfer/heat-transfer-in-buildings-application-to-solar-air-collector-and-trombe-wall-desig
On a diffuse interface model for tumour growth with non-local interactions and degenerate mobilities
We study a non-local variant of a diffuse interface model proposed by
Hawkins--Darrud et al. (2012) for tumour growth in the presence of a chemical
species acting as nutrient. The system consists of a Cahn--Hilliard equation
coupled to a reaction-diffusion equation. For non-degenerate mobilities and
smooth potentials, we derive well-posedness results, which are the non-local
analogue of those obtained in Frigeri et al. (European J. Appl. Math. 2015).
Furthermore, we establish existence of weak solutions for the case of
degenerate mobilities and singular potentials, which serves to confine the
order parameter to its physically relevant interval. Due to the non-local
nature of the equations, under additional assumptions continuous dependence on
initial data can also be shown.Comment: 28 page
Human CD34+/CD90+ ASCs Are Capable of Growing as Sphere Clusters, Producing High Levels of VEGF and Forming Capillaries
Background: Human adult adipose tissue is an abundant source of mesenchymal stem cells (MSCs). Moreover, it is an easily
accessible site producing a considerable amount of stem cells.
Methodology/Principal Findings: In this study, we have selected and characterized stem cells within the stromal vascular
fraction (SVF) of human adult adipose tissue with the aim of understanding their differentiation capabilities and
performance. We have found, within the SVF, different cell populations expressing MSC markers – including CD34, CD90,
CD29, CD44, CD105, and CD117 – and endothelial-progenitor-cell markers – including CD34, CD90, CD44, and CD54.
Interestingly, CD34+/CD90+ cells formed sphere clusters, when placed in non-adherent growth conditions. Moreover, they
showed a high proliferative capability, a telomerase activity that was significantly higher than that found in differentiated
cells, and contained a fraction of cells displaying the phenotype of a side population. When cultured in adipogenic medium,
CD34+/CD90+ quickly differentiated into adipocytes. In addition, they differentiated into endothelial cells (CD31+/VEGF+/Flk-
1+) and, when placed in methylcellulose, were capable of forming capillary-like structures producing a high level of VEGF, as
substantiated with ELISA tests.
Conclusions/Significance: Our results demonstrate, for the first time, that CD34+/CD90+ cells of human adipose tissue are
capable of forming sphere clusters, when grown in free-floating conditions, and differentiate in endothelial cells that form
capillary-like structures in methylcellulose. These cells might be suitable for tissue reconstruction in regenerative medicine,
especially when patients need treatments for vascular disease
Optimal control for a phase field system with a possibly singular potential
In this paper we study a distributed control problem for a phase field system of Caginalp type with logarithmic potential. The main aim of this work would be to force the location of the diffuse interface to be as close as possible to a prescribed set. However, due to the discontinuous character of the cost functional, we have to approximate it by a regular one and, in this case, we solve the associated control problem and derive the related first order necessary optimality conditions
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