Thermal diffusion

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Turbulent thermal diffusion of aerosols in geophysics and in laboratory experiments

Turbulent thermal diffusion of aerosols in geophysics and in laboratory experiments

The number density of particles in our experiments was of the order of 10 10 particles per cubic meter. Therefore, the distance between particles is about 1 mm, and their colli- sion rate is negligibly small. Indeed, calculation of the parti- cle collision rate using the Saffman-Turner formula (Saffman and Turner, 1956) confirmed this finding. Consequently, we did not observe any coalescence of particles. The effect of the gravitational settling of small particles (0.5–1 µm) is neg- ligibly small (the terminal fall velocity of these particles be- ing less than 0.01 cm/s). Thus, we may conclude that the two competitive mechanisms of particle transport, i.e. mixing by turbulent diffusion and accumulation of particles due to tur- bulent thermal diffusion, exist simultaneously and there is a very small effect of gravitational settling of the particles.
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Effects of chemical reaction in thermal and mass diffusion of micropolar fluid saturated in porous regime with radiation and ohmic heating

Effects of chemical reaction in thermal and mass diffusion of micropolar fluid saturated in porous regime with radiation and ohmic heating

The present paper analyzes the chemically reacting free convection magnetohydro- dynamic micropolar flow, heat and mass transfer in porous medium past an infinite vertical plate with radiation, and viscous dissipation. The non-linear coupled par- tial differential equations are solved numerically using an implicit finite difference scheme known as Keller-Box method. The results for concentration, transverse ve- locity, angular velocity, and temperature are obtained and effects of various pa- rameters on these functions are presented graphically. The numerical discussion with physical interpretations for the influence of various parameters also presented. Key words: thermal diffusion, mass diffusion, porous medium, micropolar fluid,
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Diffusion-Thermo and Thermal Radiation of an Optically Thick Gray Gas in Presence of Magnetic Field and Porous Medium

Diffusion-Thermo and Thermal Radiation of an Optically Thick Gray Gas in Presence of Magnetic Field and Porous Medium

heat transfer at the plate and hence the fluid temperature decreases. This means the thermal boundary layer decreases and more uniform temperature distributes across the boundary layer. Further, it is seen from Fig.10 that the fluid temperature  decreases with an increase in Prandtl number Pr . The thermal conductivity of fluid decreases with an increase in Pr , resulting a decrease in thermal boundary layer thickness and the heat is able to diffuse away from the heated surface. Therefore, thermal diffusion has a tendency to reduce the fluid temperature. It is seen from Fig.11 that an increase in Dufour number Du leads to rise in the fluid temperature  . The Dufour number is the ratio of concentration to temperature difference. Higher values of Dufour number Du imply a lower temperature difference, which results in an enhancement in the temperature profiles. As the Dufour number increases, concentration gradients therefore generally assist the flow and enhance thermal energy in the regime and also increase thermal boundary layer thickness. It is also observed from Fig.11 that an increase in chemical reaction parameter K leads to rise in the fluid temperature distribution  . This can be attributed to internal heat generation in the fluid due to Arrhenius kinetics. It is observed from Fig.12 that both the temperature  and concentration  increase as time  progresses. The chemical reaction reduces the local concentration, thus increasing its concentration gradient and its flux. As seen from the Fig.13, an increase in chemical reaction parameter K causes a decrease in the concentration of the chemical species in the boundary layer. Further, Fig.13 shows that the concentration  decreases with an increase in Schmidt number Sc . Physically, it is true since increase of Sc means decrease of molecular diffusivity which results in decreasing of concentration boundary layer. Hence, the concentration of species is higher for small values of Sc . The profiles have the common feature that the fluid temperature and concentration distributions decrease in a monotone fashion from the surface to a zero value far away in the free stream.
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Polímeros  vol.14 número1

Polímeros vol.14 número1

evaluated from the modulation-frequency dependence of the signal amplitude, Eq.4, or its phase, Eq.5. In the derivation of Eqs. 4 and 5, Rousset and co-workers have assumed that the sample is optically opaque and that the heat flux into the surrounding air is negligible. The implicit optical opaqueness condition was ensured by the use of a thin circular absorbing Al foil (14 µm thick and 5 mm diameter) attached to the front surface of the sample using a thin layer of thermal paste to guarantee a good thermal contact between the sample and the Al foil. The thermal diffusion time in this Al foil is in the order of 13.6 ms so that the heat generated in the thin Al absorber is instantaneously transmitted to the sample. Heat capacity measur
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Rev. IBRACON Estrut. Mater.  vol.2 número1

Rev. IBRACON Estrut. Mater. vol.2 número1

In this work a computational model, based on the inite element method was implemented, to simulate the early age concrete behavior, having as a special feature, the evaluation of the cracking risk. The inite element analysis encloses the computational modeling of the following phenomena: chemical, thermal, diffusion and mechanical which occur at the irst days after the concrete cast. The developed software results were compared with experimental values found in the literature, demonstrating an excellent agreement for all the imple- mented analysis.

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Braz. J. Chem. Eng.  vol.32 número2

Braz. J. Chem. Eng. vol.32 número2

In this communication, an axisymmetric stagna- tion point flow of a Jeffery fluid is considered when thermal-diffusion, diffusion-thermo, magnetic field and Newtonian heating effects are present. Graphs of residual errors are shown to validate the results. The final outcomes of the investigation are:

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Mixed Convection Flow of Couple Stress Fluid in a Vertical Channel with Radiation and Soret Effects

Mixed Convection Flow of Couple Stress Fluid in a Vertical Channel with Radiation and Soret Effects

Dursunkaya and Worek (1992) studied diffusion- thermo and thermal-diffusion effects in transient and steady natural convection from a vertical surface, whereas Kafoussias and Williams (1995) presented the same effects on mixed convective and mass transfer steady laminar boundary layer flow over a vertical flat plate with temperature dependent viscosity. Cheng (2009) studied the Soret and Dufour effects on natural convection heat and mass transfer from a vertical cone in a porous medium. Maleque (2010) examined the Dufour and Soret effects on unsteady MHD convective heat and mass transfer flow due to a rotating disk. Pal and Mondal (2011) analyzed the MHD non-Darcian mixed convection over a non-linear stretching sheet with Soret - Dufour effects with chemical reaction. Recently, Srinivasacharya and Kaladhar (2013) have investigated the Soret and Dufour effects on free convection flow of a couple stress fluid in a vertical channel with chemical reaction. Most recently, they (Srinivasacharya and Kaladhar (2014)) presented the chemical reaction, Soret and Dufour effects on mixed convection flow of couple stress fluid between vertical parallel plates.
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Effects of the thermal history on thermal properties of polymers: an experiment for thermal analysis education.

Effects of the thermal history on thermal properties of polymers: an experiment for thermal analysis education.

Um módulo termogravimétrico deve ser apresentado aos alunos, que devem dispor de todas as condições experimentais necessárias para realizar uma medida termogravimétrica: gás de arraste, medidor de vazão e suporte de amostra. Nos exemplos apresentados, as condi- ções experimentais utilizadas foram: módulo SDT Q600 controlado pelo software Thermal Advantage (4.2.1), ambos da TA-Instruments, suporte de amostra aberto de α-Al 2 O 3 , massa de amostra em torno de 7 mg (± 0,1 mg), amostra de PET de 3 mm de diâmetro, razão de aquecimento de 10 °C min -1 , intervalo de 25 a 800 ºC e atmosfera
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A low-cost, hands-on module to characterize antimicrobial compounds using an interdisciplinary, biophysical approach.

A low-cost, hands-on module to characterize antimicrobial compounds using an interdisciplinary, biophysical approach.

This was the first time this module was implemented as a science outreach tool. As a result, the logistics of executing the module in a resource-limited setting posed formidable challenges, such as shipping delays, a classroom and building not intended for biological work, and tailor- ing the program to suit the available budget. Owing to this, we did not focus on conducting a systematic assessment of the impact of this module on the participants. In the future, we plan to incorporate an evaluation step into this module by implementing the use of pre- and postses- sion surveys (using brief questionnaires) to gain a quantitative estimate of the outcome of this module on participants’ knowledge and attitudes about biophysical research. The questionnaire could be designed to not only measure participants’ understanding of the specific material pre- sented (e.g., the problem of antibiotic resistance, potential modifications of the disc diffusion assay, and incorporating additional parameters into the analytical model) but also to gauge changes in their perceptions of larger concepts such as application of quantitative techniques to biological data and use of interdisciplinary approaches to address scientific challenges.
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Rev. Bras. Psiquiatr.  vol.25 número3

Rev. Bras. Psiquiatr. vol.25 número3

Since its introduction more than two decades ago, Magnetic Resonance Imaging (MRI) has not only allowed for visualization of the macrostructure of the CNS, but also has been able to study dynamic processes which constitute the substrate of currently available MRI variants. While conventional Diffusion Weighted Imaging (DWI) permits a robust visualization of lesions just a few minutes after the onset of cerebral ischemia, Diffusion Tensor Imaging (DTI) measures the magnitude and direction of diffusion, leading to the characterization of cerebral white matter (WM) microstructural integrity. In this paper, the potential role of MRI techniques, particularly DTI, for the study of the relationship between changes in the microstructural integrity of WM and cognitive impairment in the context of cerebrovascular disease are discussed. Significant correlations between scores of behavioral measures of cognitive function and regional anisotropy values are an example of the potential efficacy of DTI for in vivo studies of brain connectivity in vascular neurodegenerative conditions.
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Radiol Bras  vol.49 número6

Radiol Bras vol.49 número6

DW-MRI simultaneously provides information on dif- fusion and perfusion. When only high b values are applied, the influence of perfusion is largely cancelled out and the ADC value approximates true diffusion (1) . ADC values may Figure 2. ADC values of the adrenal glands. Box-and-whisker plot of ADC measurements of the right and left adrenal glands (A and B, respectively). Boxes represent interquartile ranges. Whiskers represent ranges for all values. Horizontal lines within boxes are median values. Although there is a slight overlap of PreP and PostP group boxes, the means were significantly higher and different in the PostP group (p = 0.013 for the right side; p = 0.003 for the left side).
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Dissertação para obtenção do Grau de Mestre em Engenharia Biomédica Orientador: Sónia Gonçalves, Professora Auxiliar Convidada, FM-UC Co-orientador: Mário Forjaz Secca, Professor Associado, FCT-UNL

Dissertação para obtenção do Grau de Mestre em Engenharia Biomédica Orientador: Sónia Gonçalves, Professora Auxiliar Convidada, FM-UC Co-orientador: Mário Forjaz Secca, Professor Associado, FCT-UNL

ADC on DWI. The inverse correlation between HFF and ADC could be explained by the fact that increasing fat content of liver cells and extracellular fat accumulation would lead to reduced interstitial space and consequent increased restriction to water diffusion, resulting in lower ADCs. Guiu et al. [23], used IVIM DWI to study the difference between D, D* and fp in patients with type 2 diabetes with and without liver steatosis. Results showed that while D and D* are significantly decreased in steatotic when compared to non-steatotic livers, fp shows the opposite behaviour. It is suggested that the presence of large fat droplets in the cytoplasm of hepatocytes causes the displacement of the remaining contents of the cell peripherally, which leads to the decreased mobility of water molecules in the extra-cellular environment. In addition, the decrease in D* indicates that this structural change is associated with decreased parenchymal perfusion. Finally, the increase in fp is probably due to the shorter T2 of the tissue compartment signal, when compared to that of the vascular compartment, which causes an overestimation of the signal fraction of the vascular compartment [17, 20].
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Brain diffusion weighted and diffusion tensor imaging findings in an infant with biotinidase deficiency.

Brain diffusion weighted and diffusion tensor imaging findings in an infant with biotinidase deficiency.

internal capsules, corona radiata, and parieto-occipital gray matter. In our patient, a different pattern was observed, with moderately reduced diffusion and increased fractional anisotropy in the perirolandic white matter and centra semiovalia. This could be due to accelerated myelina- tion of those areas, induced by the repeated neuronal electric activity of the seizures, as was previously reported in children with Stu¨rge-Weber syndrome 6 and in experimental studies in mice. 7 Vacuolating myeli-

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Objective value on Apparent diffusion coefficient (ADC) map to categorize the intensity of diffusion-weighted imaging (DWi) restriction for prostate cancer detection on multiparametric prostate Mri

Objective value on Apparent diffusion coefficient (ADC) map to categorize the intensity of diffusion-weighted imaging (DWi) restriction for prostate cancer detection on multiparametric prostate Mri

Materials and Methods: Retrospective study, IRB approved, including 122 patients who had suspicious lesion on MRI and who underwent prostate biopsy with ultraso- nography (US)/MRI imaging fusion. There were 60 patients with positive biopsies and 62 with negative biopsies. MRI of these patients were randomized and evaluated inde- pendently by two blinded radiologists. The following variables were analyzed in each lesion: morphology, contours, T2 signal, diffusion restriction (subjective impression and objective values), hyper-enhancement, contact with transition zone or prostatic contour, prostatic contour retraction, Likert and PIRADS classification.
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Drying kinetics of pineapple agro-industrial residues: a new approach / Cinética de secagem de resíduos agro-industriais de abacaxi: uma nova abordagem

Drying kinetics of pineapple agro-industrial residues: a new approach / Cinética de secagem de resíduos agro-industriais de abacaxi: uma nova abordagem

Drying kinetics of pineapple agro-industrial residues was studied using thin-layer of product at 40℃, 50℃, 60℃ and 70℃, and airflow rate of 1.5 m/s. The diffusion model was modified and fitted to experimental data of moisture ratio of pineapple residue to estimate the diffusion coefficient as function of temperature, and a good fitting of Arrhenius equation was obtained, with a variance explained of 99.98 %. Values of diffusion coefficients varied in the range from 4.82 × 10 −10 m 2 ⁄s

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J. Braz. Chem. Soc.  vol.26 número3

J. Braz. Chem. Soc. vol.26 número3

The aim of this study was to obtain new films based on collagen-chitosan with and without silver for biomedical applications. Membranes with a thin transparent elastic structure were obtained and after immersion in silver nitrate new membranes with silver have been elaborated and their physicochemical properties were assessed using infrared spectroscopy as well as contact angle determinations, and sorption properties. The water absorption has permitted the evaluation of the diffusion coefficient for modified collagen membranes and the values were comparable with diffusion coefficient specific for human cornea. Adsorption and desorption studies of silver ions were investigated based on the concentration of the silver solution. This concentration was determined by an inductively coupled plasma spectrometer. Antimicrobial investigations performed on Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria and hemolytic properties assays have been evaluated measuring optical density. The enhancement of antibacterial activity of membranes with silver content was emphasized.
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Renal water molecular diffusion characteristics in healthy native kidneys: assessment with diffusion tensor MR imaging.

Renal water molecular diffusion characteristics in healthy native kidneys: assessment with diffusion tensor MR imaging.

simulation and experimental studies suggest that the latter is more preferable. One simulation study suggested that at least 20 unique diffusion-encoding directions are required for the robust estimation of anisotropy, and 30 unique diffusion- encoding directions are necessary for the robust estimation of tensor orientation. Liu et al. confirmed that increasing the NDED could improve both the accurate estimation and reproducibility of DTI measurements. Beyond that, acquiring data with more NDED could reduce the difference between inter and intrasession reproducibility, thus promoting the use of DTI measurements in longitudinal studies [36]. Thirdly, the method of selection of ROIs might also influence the DTI results. There is no standard widely accepted method for selection of ROIs and analyzing renal DTI MRI data. In reality, some of the DTI parameters vary gradually from the cortex to the medulla, reaching a most hypoxic zone in the deepest sections of medullary pyramids. Hence, the precision and reproducibility of DTI parameters values are affected by the size and location of the ROI. Larger ROIs that include the entire medullary compartments may provide more
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Int. braz j urol.  vol.35 número5

Int. braz j urol. vol.35 número5

Purpose: To compare the performance of apparent diffusion coeficient (ADC) measurement obtained with diffusion-weighted (DW) magnetic resonance (MR) imaging in the characterization of non-fat-containing T1 hyperintense renal lesions with that of contrast material-enhanced MR imaging, with histopathologic analysis and follow-up imaging as the reference standards.

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Diffusion of nparaffins in carbonaceous materials

Diffusion of nparaffins in carbonaceous materials

This chapter will present the main aspects that influenced the development of this work. Initially, the FTS is briefly described in order to show the relevance of its products (high-value hydrocarbons) taking a special attention in catalysts supported on activated carbons. Next, there will be a short description of the studied porous material, indicating its relevance and application on industrial processes. Then, the fundamentals of diffusion mechanisms are presented in order to provide a better knowledge about the resistances and influences that are on FTS products when they get out from the catalyst. Later, among the different macroscopic and microscopic experimental methods to obtain diffusion values, there is a final section presenting a historical ZLC development, indicating the most important works that supported the obtained results.
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Protein diffusion in mammalian cell cytoplasm.

Protein diffusion in mammalian cell cytoplasm.

We introduce therefore a completely new approach to protein dynamics in the cell based on describing their diffusive motion in a realistic three-dimensional representation of the cell generated from LSCM data. As it is neither useful nor possible to simulate the dynamics of all proteins of a species in an entire cell at a molecular level of detail, we rely here on mesoscopic methods to model protein distributions instead. This approach is applied here to analysis of FRAP data on the same cell. The model cell takes into account the internal structure of the cell using the inhomogeneous fluorophore distribution at equilibrium. We introduce the new methods by determining the diffusion coefficient of a freely-diffusing model protein, enhanced yellow fluorescent protein (EYFP), in two continuous cell lines, fibroblast- like Norden Laboratory Feline Kidney (NLFK) [25] and cervical carcinoma HeLa [26]. We also determine this diffusion coefficient by FFM for the same cell lines so as to be able to compare the results of the new FRAP analysis with those of FFM analysis. Recent studies using single particle tracking and fluctuation methods have shown that proteins may also undergo anomalous diffusion in the cytoplasm [27,28] as well as in the nucleus [29]. These processes are, however, not considered here as the assumption that all diffusive processes are of Brownian nature suffices to interpret the measured (collective) FRAP data (for theoretical studies of anomalous diffusion see, e.g., [30,31]).
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