•A real-time, nondestructive measurement technique for measuring the in-plane thermal diffusivity of massive, flat orthotropic, and isotropic bodies.•Flash laser heating and IR camera utilized with ...the outputted results being independent of the surface emissivity and absorbed laser radiation.•Deterministic and Bayesian methods for retrieving thermal diffusivity applied.•The technique is applicable to a wide range of diffusivities.
A new technique and device for measuring in-plane heat diffusivity for isotropic and orthotropic media are proposed. This novel method is associated with active thermography, with a laser flash generating temperature changes in the sample and the utilization of an infra-red camera to observe these changes. The model is a semi-infinite body with an adiabatic boundary heated by a Dirac delta impulse. Instead of recording the spatial and temporal changes of the surface temperature, only the time instant at which the intensity of radiation attains a maximum at a selected set of points is recorded and processed. The approach does not require assessment of two, difficult to measure, quantities: the surface emissivity and the amount of heat absorbed by the sample as a result of the laser flash. The time of the measurement is on the order of a second. The solution is a surprisingly simple expression linking the time, at which the temperature attains its maximum, with the diffusivity of the sample. This model has been used to solve the inverse problem of retrieving the diffusivity using the standard least squares method and the Bayesian Monte Carlo Markov Chain technique. The results compare well with those obtained using a commercial Parker flash method equipment.
The sorption curve is an essential feature for the modelling of heat and mass transfer in porous building materials. Several models have been proposed in the literature to represent the amount of ...moisture content in the material according to the water activity (or capillary pressure) level. These models are based on analytical expressions and few parameters that need to be estimated by inverse analysis. This article investigates the reliability of eight models through the accuracy of the estimated parameters. For this, experimental data for a wood fibre material are generated with special attention to the stop criterion to capture long time kinetic constants. Among five sets of measurements, the best estimate is computed. The reliability of the models is then discussed. After proving the theoretical identifiability of the unknown parameters for each model, the primary identifiability is analysed. It evaluates whether the parameters influence on the model output is sufficient to proceed the parameter estimation with accuracy. For this, a continuous derivative-based approach is adopted. Seven models have a low primary identifiability for at least one parameter. Indeed, when estimating the unknown parameters using the experimental observations, the parameters with low primary identifiability exhibit large uncertainties. Finally, an Approximation Bayesian Computation algorithm is used to simultaneously select the best model and estimate the parameters that best represent the experimental data. The GAB and Fredlund-Xing models, together with a proposed model in this work, were the best ones selected by this algorithm.
Thermal ablation is a well‐established successful treatment for cardiac arrhythmia, but it still presents limitations that require further studies and developments. In the rotor‐driven functional ...re‐entry arrhythmia, tissue heterogeneity results on the generation of spiral/scroll waves and wave break dynamics that may cause dangerous sustainable fibrillation. The selection of the target region to perform thermal ablation to mitigate this type of arrhythmia is challenging, since it considerably affects the local electrophysiology dynamics. This work deals with the numerical simulation of the thermal ablation of a cardiac muscle tissue and its effects on the dynamics of rotor‐driven functional re‐entry arrhythmia. A non‐homogeneous two‐dimensional rectangular region is used in the present numerical analysis, where radiofrequency ablation is performed. The electrophysiology problem for the propagation of the action potential in the cardiac tissue is simulated with the Fenton–Karma model. Thermal damage caused to the tissue by the radiofrequency heating is modeled by the Arrhenius equation. The effects of size and position of a heterogeneous region in the original muscle tissue were first analyzed, in order to verify the possible existence of the functional re‐entry arrhythmia during the time period considered in the simulations. For each case that exhibited re‐entry arrhythmia, six different ablation procedures were analyzed, depending on the position of the radiofrequency electrode and heating time. The obtained results revealed the effects of different model parameters on the existence and possible mitigation of the functional re‐entry arrhythmia.
The figure shows how the S3 wave went around the thermally damaged region (red lines are contours of the fraction of damaged tissue) and then connected back to the top boundary. The reconnection of the wavefront to the boundary before the rotor tip was formed then reshaped the S3 wave, which continued to propagate downstream and the rotor generation was avoided by the thermally damaged region.
Organoid cultivation in suspension culture requires agitation at low shear stress to allow for nutrient diffusion, which preserves tissue structure. Multiplex systems for organoid cultivation have ...been proposed, but whether they meet similar shear stress parameters as the regularly used spinner flask and its correlation with the successful generation of brain organoids has not been determined.
Here we used computational fluid dynamics (CFD) to simulate two multiplex culture conditions: steering plates on an orbital shaker and the use of a previously described bioreactor. The bioreactor had low speed and high shear stress regions that may affect cell aggregate growth, depending on volume, whereas the computed variables of the steering plates were closer to those of the spinning flask.
Our protocol improves the initial steps of the standard brain organoid formation, and the produced organoids displayed regionalized brain structures, including retinal pigmented cells. Overall, we conclude that suspension culture on orbital steering plates is a cost-effective practical alternative to previously described platforms for the cultivation of brain organoids for research and multiplex testing.
Local temperature increase is one of the five classical signs of regions with inflammations. This work is focused on the application of the photoacoustic technique for the estimation of the ...temperature field in the colon, as the solution of an inverse problem, for the detection of inflamed regions. Two‐dimensional cases are examined here involving a cross section of the bowel, which characterize either the inflammation of the whole mucosa layer, or three small inflamed regions. The inverse problem is solved for a rotating laser inside the intestine lumen, which imposes pulses for the generation of the acoustic waves. One single ultrasound detector, also located at the laser rotating shaft, provides the simulated measurements for the inverse analysis. The inverse problem is solved here with the minimization of the maximum a posteriori objective function. Results show that the proposed technique can be applied for accurate estimations of the temperature distribution in the region of interest, which might be used for the diagnosis of inflammatory bowel diseases (IBD).
The figure shows the estimation of three inflamed regions in the bowel mucosa, which are characterized by temperatures higher than those of the other regions. The inverse problem was solved with simulated photoacoustic measurements.
HIGHLIGHTS
The photoacoustic inverse approach was applied to estimate the temperature in the bowel wall, by using numerically simulated measurements, aiming at the identification of inflamed regions at large temperatures.
The laser and the ultrasound transducer were assumed at the tip of a rotating shaft, which was inserted in the intestine lumen via a catheter.
No a priori knowledge regarding the existence of an inflamed region was initially considered for the solution of the inverse problem.
The posterior probability distributions in the inflamed regions were correctly centered at the high temperatures and exhibited small variances, thus demonstrating that the technique advanced in this work might be applicable in the future for the diagnostic of inflammatory bowel diseases (IBD).
Drug delivery to tumors suffers from poor solubility, specificity, diffusion through the tumor micro‐environment and nonoptimal interactions with components of the extracellular matrix and cell ...surface receptors. Nanoparticles and drug–polymer complexes address many of these problems. However, large size exasperates the problem of slow diffusion through the tumor. Three‐dimensional tumor spheroids are good models to evaluate approaches to mitigate these difficulties and aid in design strategies to improve the delivery of drugs to treat cancer effectively. Diffusion of drug carriers is highly dependent on cell uptake rate parameters (association/dissociation) and temperature. Hyperthermia increases molecular transport and is known to act synergistically with chemotherapy to improve treatment. This study presents a new inverse estimation approach based on Bayesian probability for estimating nanoparticle cell uptake rates from experiments. The parameters were combined with a finite element computational model of nanoparticle transport under hyperthermia conditions to explore its effect on tumor porosity, diffusion and particle binding (association and dissociation) at cell surfaces. Carboxy‐PEG‐silane (cPEGSi) nanoparticles showed higher cell uptake compared to methoxy‐PEG‐silane (mPEGSi) nanoparticles. Simulations were consistent with experimental results from Skov‐3 ovarian cancer spheroids. Amorphous silica (cPEGSi) nanoparticles (58 nm) concentrated at the periphery of the tumor spheroids at 37°C but mild hyperthermia (43°C) increased nanoparticle penetration. Thus, hyperthermia may enhance cancer treatment by improving blood delivery to tumors, enhancing extravasation and penetration into tumors, trigger release of drug from the carrier at the tumor site and possibly lead to synergistic anti‐cancer activity with the drug.
Carboxy‐PEG‐silane functionalized silica nanoparticle transport through Skov‐3 ovarian tumor spheroids under normal temperature and hyperthermia conditions was modeled by (i) solving Fick's equation with reaction terms, (ii) modeling heat generation and thermal damage to cells, (iii) calculating changes in porosity of the spheroid and membrane rate constants, and (iv) iterating until the stopping criteria is reached. The model accurately predicted the experimentally observed increase in nanoparticle tumor penetration at 43°C compared to 37°C.
This paper deals with the Bayesian estimation of flow parameters in a porous material based on the measurements of local temperature at selected points inside the packed-bed. The unknown probability ...distribution function of estimated parameters was sampled using a Markov Chain Monte Carlo (MCMC) method. The MCMC method is efficient in sampling unknown distributions, but it is extremely time-consuming. The Proper Orthogonal Decomposition was used to construct off-line, low order approximation of the porous media flow problem. This model was further incorporated into the Metropolis-Hastings algorithm to retrieve the posterior distribution of the unknown parameters. This approach allowed us to decrease the computational time necessary to generate an ergodic Markov Chain. The efficiency of the proposed approach was tested on the simulated data generated with commercial CFD tools, and finally, it was applied to the real data acquired on the dedicated experimental stand.
•Research highlight are summarized as follows:•Development of the mathematical model of biomass drying process.•Development of the coupled POD-MCMC inverse methodology estimate unknown parameters of the model.•Analysis of the accuracy of the developed approach.•Application of the inverse method to estimate model parameters for a real measurement data.
In the context of better evaluating the energy balance between the ground surface and the urban thermal environment, the ground diffusivity is a crucial parameter. The aim of this paper is to ...indirectly measure this property of an heterogeneous ground by solving an inverse problem. The conjugate gradient method with adjoint problem formulation was applied to solve the inverse problem with temperature measurements taken at different depths obtained in an experiment reported in the literature. Results show that the inverse problem solution was stable and effective. Estimated values of thermal diffusivity obtained in this works were in accordance with literature values. The reliability of the mathematical model with the estimated thermal diffusivity values was addressed with measurements different from those used for the inverse analysis.
•Estimation of thermophysical properties of the ground.•Enverse heat conduction problem.•Conjugate gradient method.•Practical identifiability.•Reliability of the model.
Abstract
Hyperthermia was shown to be an important co-adjuvant therapy to conventional cancer treatments. Nanoparticles can be used in the hyperthermia therapy to improve the localized absorption of ...energy imposed by external sources, in order to kill tumor cells solely by the effect of heat and with minimum thermal damage to surrounding healthy cells. Nanoparticles can also serve as carriers of drugs that specifically act on the tumor when heated, including hydrogen that can be desorbed to locally promote an antioxidant effect and reduce the viability of cancer cells. In this context, palladium hydride nanoparticles emerge as promising materials for the hyperthermia therapy. In this study, palladium nanocubes (PdNC) and PdCeO
2
nanoparticles were synthesized. Nanofluids produced with these nanomaterials were hydrogenated and then tested to examine their photothermal effects. Nanofluids made of PdH
x
nanoparticles presented significant temperature increases of more than 30 °C under 3 min of diode-laser irradiation. On the other hand, nanofluids with PdCeO
2
H nanoparticles presented temperature increases around 11 °C under the same experimental conditions. The behavior observed with the PdCeO
2
H nanofluids can be attributed to the effect of H
+
in reducing Ce
+4
to Ce
+3
.
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