The development of CFD-DEM is critical for investigating particle phenomena and their coupling with reactor transport. However, there continues to be considerable uncertainty in the selection of ...model parameters because of limitations in: (a) experimental measurements of multi-particle interactions, and (b) computational resources which have restricted most numerical studies to 2D simulations, in very small-scale systems (<50k particles) and/or to local sensitivity analysis. The focus of this study is to identify critical model parameters in 3D CFD-DEM simulations of fluidized beds through multivariate sensitivity analysis and quantify their impact on hydrodynamics. Towards this end, thirteen model parameters are considered and the sampling design matrix is constructed using the Morris-One-At-a-Time (MOAT) screening method. 3D CFD-DEM simulations with almost 170,000 glass bead particles (0.4 mm diameter) are conducted in a small rectangular pulsating fluidized bed, selected because of its repeatable bubbling patterns. Detailed bubble and particle dynamics data from 250+ simulations show that: (a) choosing exceedingly low normal spring stiffness has strong implications on particle velocities; (b) the impact of all contact dissipation parameters (normal restitution, friction and tangential damping) is tightly coupled and sensitivity to any one hinges on the choices of others; and (c) the stability of bubble patterns is contingent on their choices and almost-ideal as well as extremely dissipative systems exhibit no patterns. In addition, by investigating particle dynamics inside and around bubbles, we derive a working expression for the optimal choice of spring stiffness. Overall, this first-of-its-kind analysis provides important guidelines for CFD-DEM model parameter selection and the statistical framework developed here provides a robust strategy for the fundamental investigation of other particle-scale phenomena and simulation-based reactor design and optimization.
CFD-DEM, gas-solid fluidization, pulsating reactor, multivariate sensitivity, linear spring-dashpot model, spring stiffness
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The radiation workers in India use extremity dosemeter in occupational areas where there is likelihood of receiving significant dose to extremities of the body. Algorithm used for the estimation of ...whole body dose and extremity dose of wrist are same and is based on slab phantom calibration. However, internationally, different phantoms are recommended for calibration of dosemeter used for extremity and whole body. The recommended quantity for estimation of dose to extremity is the personal dose equivalent Hp(0.07) at 0.07 mm depth. In light of this, an algorithm was developed for estimation of wrist dose in terms of Hp(0.07) based on calibration performed on ISO recommended pillar phantom. Performance of the dosemeter for the estimation of Hp(0.07) with new algorithm was carried out at different angular exposures of photon beams and mixed field of photon and beta. Comparison of results obtained for two types of ISO phantoms (slab and pillar) is also performed for photon beams to highlight the uncertainty caused due to the use of the slab phantom. In case of beta radiation, it was found that the size and shape of the phantom has very little influence in the response of the dosemeter. Performance of the dosemeter using ISO slab and ISO pillar phantoms for beta radiation using the prevalent algorithm was carried out and found to be within the uncertainty limits laid down by ISO except at angle 60°.
Most industrial scale fluidized-bed reactors are cylindrical, and the cylindrical coordinate system is a natural choice for their CFD simulation. There are, however, subtle complexities associated ...with this choice when using the Two-Fluid Model. The center of the grid forms a computational “boundary” and requires special treatment. Conventionally, a free slip no-normal flow condition has been used which does not predict the hydrodynamics accurately even when predicted parameters are in good agreement with measurement. Another difficulty is posed by the extremely small cells near the grid center, especially when simulating small scale experiments. The presence of these small cells raises concerns over the applicability of the Two-Fluid Model and is known to result in slow simulation convergence. These issues are addressed in the present study and appropriate solutions are proposed including the centerline treatment and the use of a non-uniform grid. Finally, the study compares the Cartesian grid with the cylindrical grid for application to fluidization. It is shown that simulating a cylindrical bed using the cylindrical grid is not only more accurate but also more computationally efficient. The analysis presented along with the proven computational efficiency of the cylindrical grid is especially significant considering that modeling commercial scale reactors, with multiple solid phases and chemical reactions, not only will require accurate description of the fluidization process but will also be exceedingly expensive in terms of computational cost.
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•Numerical treatment for the centerline radial velocity in cylindrical coordinates•Spurious accumulation of solids along the axis resolved due to numerical treatment•Use of non-uniform grid prevents small cells at the center enhancing accuracy•Simulation using the Cartesian grid is less accurate and computationally expensive
Summary
Background
Actinic keratoses (AKs) are common premalignant skin lesions triggered by excessive ultraviolet exposure. The majority of AKs regress or persist, but some progress to squamous cell ...carcinomas. Biomarkers associated with their persistence, progression and regression have not been characterized.
Objectives
We performed skin biopsies in patients with extensive actinic damage to identify biomarkers that correlate with clinical progression and regression of AKs.
Methods
This was an observational study of a cohort of patients with extensive actinic damage. AKs were mapped on a clear plastic template in 26 patients at months 3, 6, 9 and 11. Biopsies were taken from randomly selected, predetermined AKs and were evaluated for p53, E‐cadherin, Snail, Slug and Twist. The study is registered at Clinicaltrials.gov: NCT00027976.
Results
p53 exhibited greater expression in clinically apparent AKs (histological score 2·89 ± 1·45) than in regressed AKs (0·75 ± 0·96); P < 0·01. There was also significantly less membrane E‐cadherin, the lack of which is a marker of epithelial–mesenchymal transition, in clinically apparent AKs (1·89 ± 1·81) than in sun‐exposed skin (3·07 ± 1·75); P < 0·005. The E‐cadherin transcription repressors Snail, Slug and Twist were increased in AKs compared with sun‐exposed skin. A limitation of the study is that measurement of histological biomarkers was not a primary end point. In addition, patients were allowed to apply sunscreens.
Conclusions
At the molecular level, loss of E‐cadherin and an increase in p53 are linked to the dynamic interplay between the persistence, progression and regression of AKs.
What's already known about this topic?
Actinic keratoses (AKs) are common dysplastic epidermal lesions that result from chronic and excessive ultraviolet exposure.
Biomarkers associated with progression and regression of AK have not been characterized.
What does this study add?
Decreased E‐cadherin and increased p53, Snail, Slug and Twist (E‐cadherin transcription factors) were associated with progression from AK to nonmelanoma skin cancer.
What is the translational message?
Strategies targeting these molecules may be effective in reversing rising skin cancer rates.
E‐cadherin, p53, Snail, Slug and Twist are potential biomarkers that may be used to assess the efficacy of existing chemopreventive agents.
Linked Comment: O’Shaughnessy. Br J Dermatol 2020; 182:834–835.
In this review, we summarised the different methods for copper nanoparticle synthesis, including green methods. We highlighted that the synthesis of the copper nanoparticles from green sources is ...preferable as they serve as stable and reducing entities. Furthermore, we critically reviewed the effectiveness of copper- based nanoparticles in oncogenic treatments emphasizing breast, lung, colorectal, and skin cancers. Finally, we have summarised the recent progress made in copper-based nanoparticles and their applications to amplify and rectify present cancer treatment options. The synthesis, characterization, stabilization, and functionalization techniques of various copper-based nanoparticles have also been highlighted in each section. In conclusion, the review provides the outlook of copper nanoparticles in cancer diagnostics and therapeutics.
A comprehensive measurement of concentrations of the natural radionuclides
238
U,
232
Th and
40
K, and
226
Ra in the soil and rocks along with natural uranium and tritium activity levels in lake ...water were carried out during the Indian expedition to Antarctica. The samples were collected from the Larsemann Hills region in Antarctica (latitude 69°20′ S to 69°25′S, longitude 76°6′ E to 76°23′E). The data on the natural radioactivity for this region is limited. The study was carried out to establish baseline levels of radioactivity in different terrestrial matrices of this region such as soil, rocks, and lake water. A radiation survey mapping for terrestrial radioactivity was conducted in the region before collection of soil and rock samples. The soil and rock samples were analyzed for natural radioactivity concentrations using high-resolution gamma spectroscopy system. The major contributor to elevated gamma radiation background is attributed to the higher concentration of
232
Th and
40
K radionuclides in both soil and rocks. Terrestrial components of gamma dose rate due to natural radioactivity have been estimated from the measured radioactivity concentrations and dose conversion coefficients. Several “hotspots” and high background areas in the region have been identified having significantly higher concentration of
232
Th and
40
K. Rocks in Larsemann Hills region showed high reserve of thorium mineralization in monazites and
40
K in K-feldspar. The concentrations of
232
Th in soil are found to be in the range of 106–603 Bq/kg, whereas in rock it is in the range of 8–4514 Bq/kg. Natural radioactivity U (nat) and
3
H contents in the lake water samples in Larsemann Hills region were estimated as 0.4 and 1.3 Bq/L and are well within the prescribed limit of radioactivity in drinking water as recommended by World Health Organization.
LiMgPO4:Tb,B – A new sensitive OSL phosphor for dosimetry Dhabekar, Bhushan; Menon, S.N.; Alagu Raja, E. ...
Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms,
08/2011, Letnik:
269, Številka:
16
Journal Article
Recenzirano
Optically Stimulated Luminescence (OSL) technique has emerged as a serious competitor to Thermally Stimulated Luminescence (TSL) technique in various dosimetric applications, especially after the ...development of crystalline alumina (Al2O3:C) doped with carbon. Since then, several attempts are being made to develop other possible materials for OSL based dosimetric applications. Efforts conducted in our laboratory in this direction have led to the development of a new phosphor, Lithium Magnesium Phosphate doped with terbium and boron (LiMgPO4:Tb,B). This phosphor is prepared by solid-state diffusion method involving conventional air furnaces with operating temperature 1000 degree C and easily amenable to large scale production without compromising primary dosimetric advantages. In this work we present some of the dosimetric OSL characteristics of this phosphor. The phosphor exhibits a main TSL peak at 250 degree C. The phosphor also emits OSL, when the irradiated phosphor is stimulated with 470nm light with the OSL sensitivity 1.3 times that of commercially available Al2O3:C. Photoluminescence (PL) emission spectrum consists of sharp lines characteristics of Tb3+ emission. The OSL discs made out of this phosphor are reusable up to at least 50 cycles, the phosphor exhibits dose linearity up to 1kGy. Minimum detectable dose is found to be 20 mu Gy and fading of the OSL signal is found to be about 16% in four days, after which the OSL signal stabilizes.
Gas-flow distribution plays a critical role in the performance of fluidized beds because it directly affects gas residence-time and solids mixing. However, measuring it accurately in the harsh ...conditions of larger reactors is not possible. Therefore, this study is focused on the development of a rigorous computational framework for quantifying gas-flow distribution during fluidization. To this end, fine-grid simulations are conducted for the bubbling fluidization of two distinct Geldart B particles - 1.15mm LLDPE and 0.50mm glass particles, at superficial gas velocities U/Umf=2 and 3 in a 50cm diameter bed. The two-fluid model (TFM) is employed to describe the solids motion efficiently and in-house developed tool MS3DATA (Multiphase-flow Statistics using 3D Detection and Tracking Algorithm) to compute detailed bubble statistics. The overall gas flow is divided into three phases: (a) dense flow in areas relatively rich is solids concentration (b) “visible” bubble flow associated with rising bubbles and (c) throughflow accounting for the gas flow which mostly bypasses through bubbles. It is found that conditions within the dense-phase depend largely on the particle properties while bubbling dynamics are significantly affected by superficial gas velocity. Calculations show that the throughflow increases in areas frequented by bubbles because the voidage distribution around bubbles increases the local dense-phase permeability. Throughflow may account for up to 40% of the overall gas flow, especially in the fluidization of large particles. This is not desirable because its residence-time is almost 2× shorter (as compared to the dense flow) and contributes minimally to solids mixing. Finally, it is shown that in comparison to lab-scales, larger beds exhibit more homogeneous gas mixing. Insights from this study and the methodology developed will be useful in investigating gas flow distribution in complex fuel conversion systems.
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•Computational framework developed for gas-flow and residence-time distribution•Flow-field coupled with bubble detection tool (MS3DATA) for detailed analysis•Dense-phase close to minimum fluidization, except near bubble boundaries•Bypass related to solids permeability and bubble rise; increases in bubble chains•Throughflow constitutes 30–40% of gas flow with gas residence 50% shorter.
•MS3DATA predicts multiphase flow characteristics using simulation data.•Bubble statistics computed using novel detection and tracking algorithm.•Algorithm capabilities exemplified by application to ...bubbling fluidized bed case.•3D detection accurately captures small bubbles, slugs and their azimuthal velocity.•Algorithm is scalable and computes high-resolution statistics with insignificant cost.
Bubble dynamics play a critical role in the hydrodynamics of fluidized beds and significantly affect reactor performance. In this study, MS3DATA (Multiphase-flow Statistics using 3D Detection And Tracking Algorithm) is developed, validated and applied to numerical simulations of large-scale fluidized beds. Using this algorithm, bubbles are detected using void fraction data from simulations and are completely characterized by their size, shape and location while their velocities are computed by tracking bubbles across successive time frames. A detailed analysis of 2D (across vertical sections) and 3D bubble statistics using 3D simulations of lab-scale (diameter 14.5cm) and pilot-scale bed (diameter 30cm) is presented and it is shown that the former (a) under-predicts sizes of larger bubbles, (b) cannot detect a large fraction of small bubbles (<3cm) and (c) is unable to track the azimuthal motion of bubbles in the larger bed. The scalability of the algorithm is discussed by comparing the computational cost of computing bubble statistics on highly resolved grids. Even though 3D bubble detection is significantly more expensive than 2D detection, the cost is still negligible compared to the cost of accurate simulations. Besides application to fluidization simulation data of large fluidized beds, this algorithm can be easily extended to characterize bubbles, droplets and clusters in other areas of multiphase flows.
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