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RISS 인기검색어
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- 저자 : Dimov (검색결과 6 건)
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Ivan Dimov,Krassimir Atanassov 장전수학회 2013 Proceedings of the Jangjeon mathematical society Vol.16 No.3
A Monte Carlo technique of a finite difference scheme is interpretedby a game method for modelling (GMM). The simple GMM model isapproximated by a second order difference scheme. To estimate thenumber of moves (jumps) from a given point of the domain to theboundary we approximate the finite difference scheme by a boundaryvalue problem for an elliptic partial differential equation. Then weuse the fundamental solution of the problem as an approximation tothe average number of moves needed to reach the boundary from anarbitrary point inside the domain.
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Nasrollahi, Vahid,Penchev, Pavel,Jwad, Tahseen,Dimov, Stefan,Kim, Kyunghan,Im, Changmin Elsevier 2018 Optics and lasers in engineering Vol.110 No.-
<P><B>Abstract</B></P> <P>Micro drilling employing ultra-short pulsed lasers is a promising manufacturing technology for producing high aspect ratio holes, particularly on ceramic substrates due to the growing range of application in electronic industry. Controlling the morphology and quality of the holes is an important factor in fulfilling the requirements of such applications. In this research, the effects of a wide fluence spectrum associated with the use of femto-second lasers on achievable aspect ratios were investigated by employing lenses with different focal distances. The holes’ morphology and quality were analysed utilising a high resolution X-ray tomography (XCT). It was demonstrated that the achievable aspect ratio can be increased from 3 to 25 just by varying the lenses focal distances. In addition, the quality of produced holes in terms of taper angle and cylindricity was investigated and the results showed that the quality would be improved by increasing the fluence and/or decreasing the focal distance. At the same time, the limitations of drilling holes with low focal distance lenses were discussed, i.e. sensitivity to defocusing and increased risks of recast formations inside the holes and bending effects, that should be considered in designing processes for high aspect ratio percussion drilling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effects of different focal distance lenses and fluence on achievable holes’ aspect ratio in percussion drilling with femto-second lasers are investigated. </LI> <LI> The achievable holes’ aspect ratio can be increased significantly by employing lower focal distance lenses. </LI> <LI> Holes’ morphologies, cylindricity and taper angle improve by employing smaller focal distance lenses. </LI> <LI> The use of high fluence and high pulse energy in percussion drilling leads to a high penetration depth. </LI> <LI> Key limitations in using lenses with smaller focal distances are a higher sensitivity to defocusing, risks of recast formations and bending effects. </LI> </UL> </P>
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Thomas B Casale,Vesselin V Dimov 대한천식알레르기학회 2010 Allergy, Asthma & Immunology Research Vol.2 No.4
New information regarding the molecular mechanisms of allergic disorders has led to a variety of novel therapeutic approaches. This article briefly reviews the pathogenesis of asthma and allergic diseases, discusses the rationale behind using immunomodulators in these diseases; and examines the therapeutic effects of immunomodulators on allergic diseases. There are a number of immunomodulators that have been developed for the treatment of allergic disorders. Some have looked very promising in pre-clinical trials, but have not shown significant benefits in human clinical trials thus indicating the disparity between mouse models and human asthma. This review focuses on immunomodulators that are in human clinical trials and not molecules in pre-clinical development.
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Nozzle Designs in Powder-Based Direct Laser Deposition: A Review
Ahmet Guner,Prveen Bidare,Amaia Jiménez,Stefan Dimov,Khamis Essa 한국정밀공학회 2022 International Journal of Precision Engineering and Vol.23 No.9
Laser-based Direct Energy Deposition (L-DED) is one of the most commonly employed metal additive manufacturing technologies. In L-DED, a laser beam is employed as a heat source to melt the metal powder that is deposited on a substrate layer by layer for the generation of a desired component. The powder is commonly fed through a nozzle into the molten pool by means of a carrier gas and therefore, a nozzle design that ensures optimal deposition of the material is of critical importance. Additionally, its design also affects the powder and gas flows that arise in the nozzle and during the deposition. This, in turn will affect the characteristics of the generated clad and the performance of the whole deposition. Therefore, an optimization of deposition nozzle geometry can be as important as the controlling of deposition process parameters in order to obtain best component qualities. In this context, the present review work is aimed at analysing the different nozzle designs employed in powder-based L-DED processes and the influence of different geometrical features and configurations on the resulting powder and gas flows. Concretely, the main characteristics of each design, their advantages and their possible shortcomings are analysed in detail. Additionally, a review of most relevant numerical models employed during the development of new and optimised nozzle designs are also addressed.
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Kee, Youngwook,Liu, Zhe,Zhou, Liangdong,Dimov, Alexey,Cho, Junghun,de Rochefort, Ludovic,Seo, Jin Keun,Wang, Yi IEEE 2017 IEEE Transactions on Biomedical Engineering Vol.64 No.11
<P>Quantitative susceptibility mapping (QSM) solves the magnetic field-to-magnetization (tissue susceptibility) inverse problem under conditions of noisy and incomplete field data acquired using magnetic resonance imaging. Therefore, sophisticated algorithms are necessary to treat the ill-posed nature of the problem and are reviewed here. The forward problem is typically presented as an integral form, where the field is the convolution of the dipole kernel and tissue susceptibility distribution. This integral form can be equivalently written as a partial differential equation (PDE). Algorithmic challenges are to reduce streaking and shadow artifacts characterized by the fundamental solution of the PDE. Bayesian maximum a posteriori estimation can be employed to solve the inverse problem, where morphological and relevant biomedical knowledge (specific to the imaging situation) are used as priors. As the cost functions in Bayesian QSM framework are typically convex, solutions can be robustly computed using a gradient-based optimization algorithm. Moreover, one can not only accelerate Bayesian QSM, but also increase its effectiveness at reducing shadows using prior knowledge based preconditioners. Improving the efficiency of QSM is under active development, and a rigorous analysis of preconditioning needs to be carried out for further investigation.</P>
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