• The Pure and Applied Mathematics
• /
• v.23 no.3
• /
• pp.205-221
• /
• 2016

We formulate the additive entropy of a natural number in terms of the additive partition function, and show that its multiplicative entropy is directly related to the multiplicative partition function. We give a practical formula for the multiplicative entropy of natural numbers with two prime factors. We use this formula to analyze the comparative density of additive and multiplicative entropy, prove that this density converges to zero as the number tends to infinity, and empirically observe this asymptotic behavior.

• Journal of Powder Materials
• /
• v.31 no.1
• /
• pp.8-15
• /
• 2024

The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBF-processed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

• Journal of Powder Materials
• /
• v.26 no.4
• /
• pp.319-326
• /
• 2019

Additive manufacturing (AM) is a highly innovative method for joining dissimilar materials for industrial applications. In the present work, AM of STS630 and Ti-6Al-4V powder alloys on medium entropy alloys (MEAs) NiCrCo and NiCrCoMn is studied. The STS630 and Ti64 powders are deposited on the MEAs. Joint delamination and cracks are observed after the deposition of Ti64 on the MEAs, whereas the deposition of STS630 on the MEAs is successful, without any cracks and joint delamination. The microstructure around the fusion zone interface is characterized by scanning electron microscopy and X-ray diffraction. Intermetallic compounds are formed at the interfacial regions of MEA-Ti64 samples. In addition, Vicker's hardness value increased dramatically at the joint interface between MEAs and Ti-6Al-4V compared to that between MEAs and STS630. This result is attributed to the brittle nature of the joint, which can lead to a decrease in the joint strength.

• Journal of Powder Materials
• /
• v.29 no.1
• /
• pp.22-27
• /
• 2022

Conventionally, metal materials are produced by subtractive manufacturing followed by melting. However, there has been an increasing interest in additive manufacturing, especially metal 3D printing technology, which is relatively inexpensive because of the absence of complicated processing steps. In this study, we focus on the effect of varying powder size on the synthesis quality, and suggest optimum process conditions for the preparation of AlCrFeNi high-entropy alloy powder. The SEM image of the as-fabricated specimens show countless, fine, as-synthesized powders. Furthermore, we have examined the phase and microstructure before and after 3D printing, and found that there are no noticeable changes in the phase or microstructure. However, it was determined that the larger the powder size, the better the Vickers hardness of the material. This study sheds light on the optimization of process conditions in the metal 3D printing field.

• Journal of Powder Materials
• /
• v.29 no.2
• /
• pp.132-151
• /
• 2022

The CoCrFeMnNi high-entropy alloy (HEA), which is the most widely known HEA with a single face-centered cubic structure, has attracted significant academic attention over the past decade owing to its outstanding multifunctional performance. Recent studies have suggested that CoCrFeMnNi-type HEAs exhibit excellent printability for selective laser melting (SLM) under a wide range of process conditions. Moreover, it has been suggested that SLM can not only provide great topological freedom of design but also exhibit excellent mechanical properties by overcoming the strength-ductility trade-off via producing a hierarchical heterogeneous microstructure. In this regard, the SLM-processed CoCrFeMnNi HEA has been extensively studied to comprehensively understand the mechanisms of microstructural evolution and resulting changes in mechanical properties. In this review, recent studies on CoCrFeMnNi-type HEAs produced using SLM are discussed with respect to process-induced microstructural evolution and the relationship between hierarchical heterogeneous microstructure and mechanical properties.

• Journal of the Korean Chemical Society
• /
• v.25 no.4
• /
• pp.214-218
• /
• 1981

Kinetic studies were carried out on urethane polymerization reaction of hydroxyl-terminated polybutadiene with isophorone diisocyanate under presence of Hexogen as solid additive. The rate was found to increase with the amount of Hexogen added. However the rate acceleration was not a catalytic effect but solely due to an increase of activation entropy. The reaction was a good 2nd order process with nearly constant activation energy of 8.4 kcal/mole.

• Journal of Korean Society for Geospatial Information Science
• /
• v.16 no.4
• /
• pp.59-64
• /
• 2008

We need to use the strength of each Species Distribution Model(SDM) because presence location data were only collected due to time and economic limitations in Korea. This study investigated and compared GAM(Generalized Additive Model) which is one of presence-absence models with Maxent(Maximum Entropy Model) which is one of presence only models according to location data(presence/absence data). The target species was Fisher(Martes pennanti) which is an endangered species in California, USA. We implemented environmental data such as topography, climate and vegetation, and applied models to sub-regions and study area. The results of this study were as follows. Firstly, GAM which used real presence and absence data was better than GAM which used pseudo-absence data and Maxent which used presence-only data. Secondly, Maxent was better than GAM when presence-only data were used. Lastly, each model which applied to different regions didn't predict other area well due to the difference of habitat environment and over-predicted outside of study area. We need to select an optimal model to predict a suitable habitat according to the type and distribution of location data.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.13 no.1
• /
• pp.452-472
• /
• 2019

Most existing wavelet-based multiplicative watermarking methods are affected by geometric attacks to a certain extent. A serious limitation of wavelet-based multiplicative watermarking is its sensitivity to rotation, scaling, and translation. In this study, we propose an image watermarking method by using dual-tree complex wavelet transform with a multi-objective optimization approach. We embed the watermark information into an image region with a high entropy value via a multiplicative strategy. The major contribution of this work is that the trade-off between imperceptibility and robustness is simply solved by using the multi-objective optimization approach, which applies the watermark error probability and an image quality metric to establish a multi-objective optimization function. In this manner, the optimal embedding factor obtained by solving the multi-objective function effectively controls watermark strength. For watermark decoding, we adopt a maximum likelihood decision criterion. Finally, we evaluate the performance of the proposed method by conducting simulations on benchmark test images. Experiment results demonstrate the imperceptibility of the proposed method and its robustness against various attacks, including additive white Gaussian noise, JPEG compression, scaling, rotation, and combined attacks.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.27 no.2
• /
• pp.87-95
• /
• 1990

Conventional methods to estimate natural frequencies and damping ratios of structures from measured response time series obtained during impact tests are reviewed. Maximum Entropy Method and Least Square Prony Method are introduced to alleviate the inherent limitation of the conventional methods. The performance of the methods are explored through computer simulation. As an example of application, they are applied to the time series obtained from an anchor drop-and-snup test of a container ship and the result is compared to that of conventional FFT method. As a result of the computer simulation, it is found that Maximum Entropy Method is very efficient to estimate natural frequencies of structures when two neighboring natural frequencies are close enough and short data records are only available, but it is not a reliable estimator for damping ratios. And it is also found that Least Square Prony Method is efficient to estimate the natural frequencies and damping ratios of highly damped structural system, but the estimation efficiency of damping ratios is significantly deteriorated in the presence of significant additive noise.

• Journal of Communications and Networks
• /
• v.14 no.1
• /
• pp.1-9
• /
• 2012

We consider a receiving node, located at the origin, and a Poisson point process (PPP) that models the locations of the desired transmitter as well as the interferers. Interference is known to be non-Gaussian in this scenario. The capacity bounds for additive non-Gaussian channels depend not only on the power of interference (i.e., up to second order statistics) but also on its entropy power which is influenced by higher order statistics as well. Therefore, a complete statistical characterization of interference is required to obtain the capacity bounds. While the statistics of sum of signal and interference is known in closed form, the statistics of interference highly depends on the location of the desired transmitter. In this paper, we show that there is a tradeoff between entropy power of interference on the one hand and signal and interference power on the other hand which have conflicting effects on the channel capacity. We obtain closed form results for the cumulants of the interference, when the desired transmitter node is an arbitrary neighbor of the receiver. We show that to find the cumulants, joint statistics of distances in the PPP will be required which we obtain in closed form. Using the cumulants, we approximate the interference entropy power and obtain bounds on the capacity of the channel between an arbitrary transmitter and the receiver. Our results provide insight and shed light on the capacity of links in a Poisson network. In particular, we show that, in a Poisson network, the closest hop is not necessarily the highest capacity link.