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Oyebola Fatima Etudaiye-Muhtar,Rubi Ahmad,Bolaji Tunde Matemilola 연세대학교 동서문제연구원 2017 Global economic review Vol.46 No.4
An appropriate debt maturity structure is essential for firms to enable them align asset structure to liabilities to prevent a mismatch. This study investigates the role of firm-level and institutional variables on debt maturity structure in selected African countries. Using panel generalised method of moment that addresses endogeneity problem; our findings reveal a dynamic process of adjustment to optimal debt maturity structure. Furthermore, firm-level variables (leverage, asset structure and firm size) provide support for the contracting cost, signalling and matching principle theories of debt maturity structure. Results of institutional variables suggest that better developed institutions promote long-term debt maturity structures.
고영호,Muhtar Ahart,고재현,송종현 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.4
High-pressure Brillouin spectroscopy was applied to clarify quantitatively the physical and mechanical differences of a polymer with distinct structures consisting of the same elements. The pressure dependences of elastic properties, Young’s modulus, the shear modulus, the bulk modulus, and Poisson’s ratio for an amorphous poly (-ethylene terephthalate-) [(-PET-)] and a semi-crystalline PET were compared for pressures up to 11 GPa. A collapse of the free volume for the two PETs was ascertained at the different values of the pressure with different slopes for the elastic properties, Young’s modulus, the shear modulus, and the bulk modulus. Although the Poisson’s ratios of a semi-crystalline PET increased linearly with increasing pressure, those of an amorphous PET were almost constant. The P-V equation of state (EOS) for an amorphous PET was also determined, and isothermal bulk moduli extracted from the Birch-Murnaghan and the Vinet EOSs were 6.3 ± 0.2 GPa and 6.7 ± 0.1 GPa, respectively.
Raman Scattering Study of Relaxor Ferroelectric Pb(Sc1/2Nb1/2)O3 Crystals
Kohei Suzuki,SeijiKojima,Muhtar Ahart,Yonghong Bing,Zuo-Guang Ye 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.8
The effects of B-site ordering and vacancies were studied in the relaxor ferroelectric Pb(Sc1/2Nb1/2)O3 (PSN) family by using Raman scattering spectroscopy. Differences with Raman spectra and the depolarization ratios were clearly observed among B-site disordered PSN (PSN-D),B-site ordered with lead/oxygen vacancies PSN (PSN-OV ), and 0.7Pb(Sc1/2Nb1/2)O3-0.3PbTiO3(PSN-30PT) single crystals. The temperature dependence of the depolarization ratio of PSN-30PT was also studied to clarify the ferroelectric phase transitions and the polarization fluctuations in the polar nanoregions.
김재현,최진영,Min-Seok Jeong,고재현,Muhtar Ahart,고영호,김광주 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
A high-pressure Brillouin spectrometer with which the elastic properties of condensed matter could be measured over a wide pressure range was developed. A wide-angle, symmetric-type diamond anvil cell and an optical microscope were combined with a tandem Fabry-Perot interferometer and an optical stage to carry out both symmetric forward scattering and backscattering experiments under the same conditions. The constructed high-pressure Brillouin spectrometer was applied to ethylene-vinyl acetate (EVA) over a pressure range from ambient pressure to ∼13 GPa. The observed Brillouin spectra consisted of one Brillouin doublet caused by longitudinal acoustic waves. The Brillouin shift and the corresponding longitudinal sound velocity increased with increasing pressure. The combination of the two scattering geometries enabled us to obtain the refractive index of EVA at ambient pressure. This experimental technique will be useful in obtaining the equation of states of various types of condensed matter.
Industrial symbiosis: Boron waste valorization through CO2 utilization
Mehmet Çopur,Turgay Pekdemir,Mehmet Muhtar Kocakerim,Haluk Korucu,Rövşen Guliyev 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.10
Various wastes being generated globally and dumped on land by mineral processing activities pose great ecological and health problems. An example is the boron mineral beneficiation solid wastes. Even greater threat is anthropogenic carbon dioxide (CO2) emissions among key causes of prevalent climate change. By this work, we propose a symbiotic solution to alleviate both environmental threats through recovering valuable boron products from boron wastes (BW), while also utilizing and sequestering CO2 stably and permanently. This article presents the results on the effect of important operation parameters for the performance of such a process within the following ranges determined by preliminary tests: temperature: 20-60 oC, solid-to-liquid ratio: 0.1-0.5 g/ml, reaction time: 15-120 min, stirring speed: 300-700 rpm and particle size: 150-600 m. CO2 gas (99.9%) flow rate was maintained continuously at 1.57 l/min under atmospheric pressure. The important findings are (1) per ton of BW production of commercially valuable either (a) 310 kg sodium penta-borate or (b) 350 kg sodium penta-borate mixed with Na2CO3, depending on the process configuration, (c) 725 kg relatively pure CaCO3, a potential source for precipitated calcium carbonate (PCC) and (d) 72 kg CO2 utilization, (2) effective parameters for CO2 utilization, in decreasing order are temperature, solid-toliquid ratio and time, while stirring speed and particle size are ineffective within the range investigated and (3) the optimum operating conditions as: temperature: 60 oC, solid-to liquid ratio: 0.1 g/ml, time: 90 min, stirring speed: 500 rpm and particle size: <180 m.
A Survey of Uyghur Person Name Recognition
Tashpolat Nizamidin,Palidan Tuerxun,Askar Hamdulla,Muhtar Arkin 보안공학연구지원센터 2016 International Journal of Signal Processing, Image Vol.9 No.3
Uyghur is one of the most populous and civilized groups with Turkic ethnicity and mainly located Xinjiang Uyghur Autonomous Region of China. Uyghur language belongs to the Karluk branch of the Turkic language family in Altaic language system, and holds agglutinative characteristics in morphological structure. Named Entity Recognition (NER) is an Information Extraction task that has become an essential part of Natural Language Processing (NLP) tasks, such as Machine Translation and Information Retrieval. In this paper, as a subtask of NER, the importance of Uyghur Named Entity Recognition (UPNR) task is demonstrated, the main characteristics of the Uyghur language are highlighted, and the aspects of standardization in annotating named entities are illustrated. Moreover, the approaches used in Uyghur NPNR field are explained and the features of common tools used in Uyghur NPNR are described. A brief review of the state of the art of Uyghur NPNR research is discussed, too. Finally, we present our conclusions. Throughout the presentation, illustrative examples are used for clarification.