Sharif Digital Repository

A novel phenomenological discrete bubble model was developed and tested for prediction of the hydrodynamic behavior of the dense phase of a 3D gas-solid cylindrical fluidized bed. The mirror image technique was applied to take into account the effects of the bed wall. The simulation results were validated against experimental data reported in the literature that were obtained by positron emission particle tracking. The time-averaged velocity profiles of particles predicted by the developed model were found to agree well with experimental data. The initial bubble diameter had no significant influence on the time-averaged circulating pattern of solids in the bed. The model predictions clearly... 

A discrete bubble model has been developed taking into account multiple bubble-bubble interactions and a delayed coalescence method. The obtained simulation results were compared with experimental data reported in literature. The simulation results predicted by the developed model indicate clearly that the multiple interactions of bubbles lead to more reasonable results than those predicted by a binary interaction model. In addition, two types of interaction models were applied and predicted results were compared. The frequency of gas bubbles passing through the bed cross section versus bed height follows the same trend as the experimental data. A new modified discrete bubble model has been... 

The effects of temperature, seed mass and agitation rate on agglomeration kinetics of aluminum hydroxide in Bayer process have been studied in a batch system. Collected raw data were analyzed and the kinetics data of agglomeration were derived through simulation of the process using a pre-developed software. The results showed that agglomeration kinetics constant (agglomeration kernel) increases with increase in temperature and agitation rate. Moreover a maximum value of agglomeration rate versus added seed mass was observed. Furthermore the magnitude of calculated activation energy of agglomeration was close to that of growth  

Male infertility is mostly related to semen and spermatozoa, and any diagnosis or treatment requires the investigation of the motility patterns of spermatozoa. The movements of spermatozoa are fast and involve collision and occlusion with each other. In order to extract the motility patterns of spermatozoa, multi-target tracking (MTT) of spermatozoa is necessary. One of the most important steps of MTT is data association, in which the newly arrived observations are used to update the previous tracks. Dynamic Bayesian network (DBN) is a powerful tool for modeling and solving various types of problems such as tracking and classification. There can also be a hybrid-DBN (HDBN), in which both... 

A series of polyurethane elastomers (PUEs) based on 4,4′-cyclohexamethylene diisocyanate (H12MDI)/1,2-ethanediol as hard segment with the soft segments having different molecular weights of polycaprolactone diols, were effectively polymerized by two step technique. The structural characterization was performed by FT-IR spectroscopy. The X-ray diffraction (XRD) technique was used to study the crystallinity and hydrophilicity of the prepared polymer films. It was found that crystallinity and hydrophilicity increased with increasing the chain length of soft segments. The effect of molecular weight of polyols on the contact angle, water absorption (%) and swelling behavior of the synthesized... 

We consider the problem of interference management in wireless cellular networks with caches at both base stations and receivers, and we characterize the degrees of freedom (DoFs) per cell to within an additive gap of (1/3) and a multiplicative gap of 2 for all system parameters, under one-shot linear schemes. Our result indicates that the one-shot linear DoF per cell scales linearly with the total amount of cache available in the cell, i.e., the sum of the caches at the central base station and all the receivers within the cell, resembling a similar phenomenon previously observed for the case of fully connected wireless networks. To establish the result, we propose a decentralized and... 

How can we optimally trade extra computing power to reduce the communication load in distributed computing? We answer this question by characterizing a fundamental tradeoff between computation and communication in distributed computing, i.e., the two are inversely proportional to each other. More specifically, a general distributed computing framework, motivated by commonly used structures like MapReduce, is considered, where the overall computation is decomposed into computing a set of “Map” and “Reduce” functions distributedly across multiple computing nodes. A coded scheme, named “coded distributed computing” (CDC), is proposed to demonstrate that increasing the computation load of the... 

Bubble splitting in 2D gas-solid freely bubbling fluidized beds is experimentally investigated using digital image analysis. The quantitative results can be applied for the development of a new breakage model for bubbly fluidized beds, especially discrete bubble models. The variation of splitting frequency with bubble diameter, new resulting bubble volumes, positions, and also the assumptions of mass and momentum conservation for bubbles after breakage are studied in detail. Small bubbles are found to be more stable than large ones and nearly all mother bubbles split into two almost equally sized daughter bubbles. The momentum of gas bubbles in the vertical direction remains approximately... 

A phenomenological discrete bubble model has been developed for freely bubbling dense gas-solid fluidized beds and validated for a pseudo-two-dimensional fluidized bed. In this model, bubbles are treated as distinct elements and their trajectories are tracked by integrating Newton's equation of motion. The effect of bubble-bubble interactions was taken into account via a modification of the bubble velocity. The emulsion phase velocity was obtained as a superposition of the motion induced by individual bubbles, taking into account bubble-bubble interaction. This novel model predicts the bubble size evolution and the pattern of emulsion phase circulation satisfactorily. Moreover, the effects... 

Sustainable development is significantly contributing the environmental degradation due to improvements in financial sector in One Belt and Road Initiative (BRI) region. Thus, the present research work constructs the sustainable development index for BRI. Afterwards, it unfolds the nexus of sustainable development-environmental degradation and also evaluates the role of financial development indicators in BRI economies. By utilizing the robust mean group, the present study quantifies the long-run marginal impacts of sustainable development, financial development indicators, energy consumption, and urban sprawl on environmental degradation, respectively. The marginal impacts infer an inverted... 

In this article, the digital image analysis (DIA) technique has been used to study the bubble size and bubble size distribution evolution in a pseudo-two-dimensional gas-solid fluidized bed. In addition, a numerical discrete bubble model (DBM) based on the bubble-bubble interactions was developed and the model predictions were compared with the experimental data. The developed model can predict the bubble size and bubble size distribution through the bed height and the lateral distribution of bubbles. Comparison between model predictions and the result of DIA measurements shows that bubble breakage has a significant effect on the bubble size distribution especially at heights far from the... 

Background: Accurate and up-to-date assessment of demographic metrics is crucial for understanding a wide range of social, economic, and public health issues that affect populations worldwide. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 produced updated and comprehensive demographic assessments of the key indicators of fertility, mortality, migration, and population for 204 countries and territories and selected subnational locations from 1950 to 2019. Methods: 8078 country-years of vital registration and sample registration data, 938 surveys, 349 censuses, and 238 other sources were identified and used to estimate age-specific fertility. Spatiotemporal... 

Background: In an era of shifting global agendas and expanded emphasis on non-communicable diseases and injuries along with communicable diseases, sound evidence on trends by cause at the national level is essential. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) provides a systematic scientific assessment of published, publicly available, and contributed data on incidence, prevalence, and mortality for a mutually exclusive and collectively exhaustive list of diseases and injuries. Methods: GBD estimates incidence, prevalence, mortality, years of life lost (YLLs), years lived with disability (YLDs), and disability-adjusted life-years (DALYs) due to 369 diseases and... 

Background: Rigorous analysis of levels and trends in exposure to leading risk factors and quantification of their effect on human health are important to identify where public health is making progress and in which cases current efforts are inadequate. The Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2019 provides a standardised and comprehensive assessment of the magnitude of risk factor exposure, relative risk, and attributable burden of disease. Methods: GBD 2019 estimated attributable mortality, years of life lost (YLLs), years of life lived with disability (YLDs), and disability-adjusted life-years (DALYs) for 87 risk factors and combinations of risk factors, at...