• Current Optics and Photonics
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• 제2권6호
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• pp.514-518
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• 2018

Carrier diffusion length in the light-sensitive material is one of the key elements in improving the light-current conversion efficiency of solar-cell devices. In this paper, we measured the carrier diffusion length in lead-halide perovskite ($MAPbI_3$) and mixed lead-halide ($MAPbI_{3-x}Cl_x$) perovskite devices using scanning photocurrent microscopy (SPCM). The SPCM signal decreased as we moved the focused laser spot away from the metal contact. By fitting the data with a simple exponential curve, we extracted the carrier diffusion length of each perovskite film. Importantly, the diffusion length of the mixed-halide perovskite was higher than that of the halide perovskite film by a factor of 3 to 6; this is consistent with the general expectation that the carrier mobility will be higher in the case of the mixed lead-halide perovskites. Finally, the diffusion length was investigated as a function of applied bias for both samples, and analyzed successfully in terms of the drift-diffusion model.

• Journal of Information Processing Systems
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• 제18권1호
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• pp.59-74
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• 2022

During the last decade, the security of digital images has received considerable attention in various multimedia transmission schemes. However, many current cryptosystems tend to adopt a single-layer permutation or diffusion algorithm, resulting in inadequate security. A hierarchical bilateral diffusion architecture for color image encryption is proposed in response to this issue, based on a hyperchaotic system and DNA sequence operation. Primarily, two hyperchaotic systems are adopted and combined with cipher matrixes generation algorithm to overcome exhaustive attacks. Further, the proposed architecture involves designing pixelpermutation, pixel-diffusion, and DNA (deoxyribonucleic acid) based block-diffusion algorithm, considering system security and transmission efficiency. The pixel-permutation aims to reduce the correlation of adjacent pixels and provide excellent initial conditions for subsequent diffusion procedures, while the diffusion architecture confuses the image matrix in a bilateral direction with ultra-low power consumption. The proposed system achieves preferable number of pixel change rate (NPCR) and unified average changing intensity (UACI) of 99.61% and 33.46%, and a lower encryption time of 3.30 seconds, which performs better than some current image encryption algorithms. The simulated results and security analysis demonstrate that the proposed mechanism can resist various potential attacks with comparatively low computational time consumption.

• Geomechanics and Engineering
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• 제37권2호
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• pp.97-107
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• 2024

The accurate prediction of grouting upward diffusion height is crucial for estimating the bearing capacity of tip-grouted piles. Borehole construction during the installation of bored piles induces soil unloading, resulting in both radial stress loss in the surrounding soil and an impact on grouting fluid diffusion. In this study, a modified model is developed for predicting grout diffusion height. This model incorporates the classical rheological equation of power-law cement grout and the cavity reverse expansion model to account for different degrees of unloading. A series of single-pile tip grouting and static load tests are conducted with varying initial grouting pressures. The test results demonstrate a significant effect of vertical grout diffusion on improving pile lateral friction resistance and bearing capacity. Increasing the grouting pressure leads to an increase in the vertical height of the grout. A comparison between the predicted values using the proposed model and the actual measured results reveals a model error ranging from -12.3% to 8.0%. Parametric analysis shows that grout diffusion height increases with an increase in the degree of unloading, with a more pronounced effect observed at higher grouting pressures. Two case studies are presented to verify the applicability of the proposed model. Field measurements of grout diffusion height correspond to unloading ratios of 0.68 and 0.71, respectively, as predicted by the model. Neglecting the unloading effect would result in a conservative estimate.

• 품질경영학회지
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• 제51권4호
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• pp.691-700
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• 2023

Purpose: This study aims to analyze the diffusion pattern of the Mongolian mobile phone market. In particular, we used a generalized diffusion model to explore the factors affecting market potenial. Methods: We used three diffusion models to estimate the number of mobile subscribers in Mongolia. Based on the Logistic model with the best fitness, we introduced time-varying market potential and explored the influence of various independent variables such as GDP and inflation. Results: Among the basic diffusion models, the Logistic model was the best in terms of estimation performance and statistical significance. The estimation results of the Generalized Logistic model confirm that investment in the telecommunication sector has a significant positive effect on market potential. The estimation of the Generalized Logistic model effectively describes the continuous growth of the Mongolian telecommunications market until recently. Conclusion: We have analyzed the diffusion pattern of the Mongolian telecommunications market and found that the amount of investment in the sector leads to the growth of the market size. This study is original in terms of its subject - Mongolian telecommunications market and methodology - time-varying market potential.

• Computers and Concrete
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• 제34권2호
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• pp.169-178
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• 2024

To circumvent the constraints of time-consuming experimental methods, numerical simulation can be one of the most effective approaches to investigating chloride diffusion behaviors in concrete. However, except for the effect of the external environments, the transport direction of the chloride cannot be neglected when the concrete is exposed to the marine tidal zone, especially in certain areas of concrete members. In this study, based on Fick's second law, considering the effects of timevarying, chloride binding capacity, concrete stress state, ambient temperature, and relative humidity on chloride diffusion coefficient, the modified one-dimensional, two-dimensional, and three-dimensional novel modified chloride diffusion theoretical models were established through defining the current boundary conditions. The simulated results based on the novel modified multi-dimensional model were compared with the experimental results obtained from some previous pieces of literature. The comparing results showed that the modified multi-dimensional model was well-fitted with experimental data, confirming the high accuracy of the novel modified model. The experimental results in literature showed that the chloride diffusion in the corner area of the concrete structure cannot be simulated by a simple one-dimensional diffusion model, where it is necessary to select a suitable multi-dimensional chloride diffusion model for simulation calculation. Therefore, the novel modified multi-dimensional model established in this study has a stronger applicability for practical engineering.

• KIEAE Journal
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• 제17권3호
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• pp.91-97
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• 2017

Purpose: Various studies on a light shelf are in progress, but it has the problem of glare occurrence. The present study suggested a diffusion film as the method for resolving the glare problem, and aimed to establish light shelf-related basic data by conducting the performance evaluation of a light shelf depending on the installation position of the diffusion film. Method: To carry out the light shelf performance evaluation depending on the diffusion film installation position, three cases were established: no diffusion film installation (Case 1), diffusion film installation on the reflector (Case 2), and diffusion film installation on the upper glass surface of the window for light shelf installation (Case 3); and the energy reduction performance, luminance, and luminance contrast were analyzed based on a testbed. Result: The conclusions of this study are as follows. 1) When the diffusion film was applied, the amount of light introduced through the light shelf decreased, and the average indoor illumination decreased accordingly. 2) For Case 3, the lighting energy reduction performance was identical to the lighting energy reduction efficiency of the existing light shelf; and for Case 2, it was found to be inappropriate as the lighting energy consumption increased compared to that of the existing light shelf. 3) The analysis of the glare for the cases established in this study showed that the luminance contrast was low for Case 3, and thus the glare problem could be minimized. 4) The specific angle of the light shelf could induce the glare problem by increasing the luminance depending on the external condition. 5) Based on the aforementioned contents, the installation position of the diffusion film for improving the lighting performance and glare problem of the light shelf was found to be the upper glass surface of the window for light shelf installation.

• 한국재료학회지
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• 제27권7호
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• pp.386-391
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• 2017

Using a customized diffusion bonder, we executed diffusion bonding for ring shaped white gold and red gold samples (inner, outer diameter, and thickness were 15.7, 18.7, and 3.0 mm, respectively) at a temperature of $780^{\circ}C$ and applied pressure of 2300 N in a vacuum of $5{\times}10^{-2}$ torr for 180 seconds. Optical microscopy, field emission scanning electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDS) were used to investigate the microstructure and compositional changes. The mechanical properties were confirmed by Vickers hardness and shear strength tests. Optical microscopy and FE-SEM confirmed the uniform bonding interface, which was without defects such as micro pores. EDS mapping analysis confirmed that each gold alloy was 14K with the intended composition; Ni and Cu was included as coloring metals in the white and red gold alloys, respectively. The effective diffusion coefficient was estimated based on EDS line scanning. Individual values of Ni and Cu were $5.0{\times}10^{-8}cm^2/s$ and $8.9{\times}10^{-8}cm^2/s$, respectively. These values were as large as those of the melting points due to the accelerated diffusion in this customized diffusion bonder. Vickers hardness results showed that the hardness values of white gold and red gold were 127.83 and 103.04, respectively, due to solid solution strengthening. In addition, the value at the interface indicated no formation of intermetallic compound around the bonding interface. From the shear strength test, the sample was found not to be destroyed at up to 100,000 gf due to the high bonding strength. Therefore, these results confirm the successful diffusion bonding of 14K white-red golds with a diffusion bonder at a low temperature of $780^{\circ}C$ and a short processing time of 180 seconds.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1995년도 추계학술발표회논문집(2)
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• pp.707-712
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• 1995

Grain boundary diffusion plays significant role in the fission gas release, which is one of the crucial processes dominating nuclear fuel performance. Gaseous fission products such as Xe and Kr generated inside fuel pellet have to diffuse in the lattice and in the grain boundary before they reach open space in the fuel rod. In the mean time, the grains in the fuel pellet grow and shrink according to grain growth kinetics, especially at elevated temperature at which nuclear reactors are operating. Thus the boundary movement ascribed to the grain growth greatly influences the fission gas release rate by lengthening or shortening the lattice diffusion distance, which is the rate limiting step. Sweeping fission gases by the moving boundary contributes to the increment of the fission gas release as well. Lattice and grain boundary diffusion processes in the fission gas release can be studied by 'tracer diffusion' technique, by which grain boundary diffusion can be estimated and used directly for low burn-up fission gas release analysis. However, even for tracer diffusion analysis, taking both the intragranular grain growth and the diffusion processes simultaneously into consideration is not easy. Only a few models accounting for the both processes are available and mostly handle them numerically. Numerical solutions are limited in the practical use. Here in this paper, an approximate analytical solution of the lattice and stationary grain boundary diffusion in a polycrystalline solid is developed for the tracer diffusion techniques. This short closed-form solution is compared to available exact and numerical solutions and turns out to be acceptably accurate. It can be applied to the theoretical modeling and the experimental analysis, especially PIE (post irradiation examination), of low burn up fission. gas release.

• 기술혁신학회지
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• 제20권4호
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• pp.1243-1261
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• 2017

이동통신시장은 지난 10년 동안 괄목할 만한 가입자 증가로 인해 급격하게 성장했다. 서비스의 확산패턴은 그러한 새로운 서비스를 준비하는 이동통신사에게 주요 관심사이다. 우리는 이러한 서비스의 확산패턴이 이전의 모바일 서비스와 유사할 것으로 가정하며, 이러한 서비스의 확산패턴을 확인하는 것은 차세대 모바일 서비스를 위한 이동통신사에게 필수적이다. 본 연구에서는 이동통신서비스의 유사한 확산패턴을 보여 주는 국가를 분류하였다. 전통적인 확산모델을 사용하여, 25개의 서유럽 국가들의 이동통신 확산패턴을 추정한다. 1993년부터 2004년까지 이들 국가들의 월 보급률 자료를 기초로 하였다. 클러스터 분석을 통해 이동통신 확산패턴측면에서 상위 모방국가와 하위 모방국가의 두 그룹을 분류하였다. 이 연구의 결과는 이동통신서비스의 상이한 확산패턴을 설명하기 위한 인과모형을 개발하거나 차세대 이동통신서비스를 위한 새로운 네트워크를 계획할 때 그 기초를 제공한다.

• 한국정보통신학회논문지
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• 제11권5호
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• pp.889-896
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• 2007

센서기술 및 무선통신 기술의 발달로 센서네트워크에 대한 연구가 가속화되고 있다. 센서노드는 크기 및 용량의 제한 때문에 간단하면서 에너지를 효율적으로 사용할 수 있는 프로토콜을 설계하는 것이 매우 중요하다. 기존 센서네트워크용 라우팅 프로토콜로 널리 알려져 있는 directed diffusion 프로토콜은 간단하다는 장점을 갖지만 Interest/Exploratory data 메시지를 Flooding 기법에 따라 전송하게 됨에 따라 에너지 소모가 크다는 단점을 가지고 있다. 따라서 본 논문에서는 directed diffusion 기법이 가진 단점을 보완하면서 각 센서노드가 에너지를 균형 있게 소비할 수 있는 설계된 센서 네트워크 용 라우팅 기법을 제안하고 시뮬레이션을 통해 성능평가를 수행하였다. 성능평가 결과에 따르면 본 연구에서 제안한 라우팅 프로토콜이 기존 directed diffusion 기법에 비해 에너지를 훨씬 효율적으로 사용하면서 센서노드간 에너지 소비 불균형 문제를 해결하고 있음을 수치계산 결과를 통해 확인할 수 있었다.