• Journal of Biosystems Engineering
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• v.14 no.3
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• pp.181-187
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• 1989

The mechanical and rheological properties of agricultural materials which influence the machine design or handling are not completely understood. Agricultural materials do not react in a purely elastic manner, and their responses when subjected to stress and strain appear a combination of elastic and viscous behavior. Many researchers have studied the mechanical and rheological properties of the various agricultural materials, but those properties are available mostly for foreign varieties of agricultural products. Rheological properties of rice seedlings become important to formulate the principles governing their mechanical behavior. The objectives of this study were to experimentally determine the creep and recovery behavior of rice seedlings of one japonica-type and one Indica x japonica hybrid in the transplanting age. The results of this study are summarized as follows; 1. The compression creep and recovery behavior of mat-type seedlings could be described by 4-element Burger's model. 2. The steady-state creep appeared at the stress larger than 0.8 MPa and the logarithmic creep appeared at the stress smaller than 0.8 MPa. 3. In the compression creep test of the rice seedlings, the instantaneous elastic modulus of Burger's model showed the range from 20 to 40 MPa. The higher value of absolute viscosity for the rice seedling explained that the rice seedlings were viscoelastic materials. 4. In the recovery test of the rice seedlings, there was a tendency that the higher permanent strain of all samples was observed under the smaller stress being appeared, and the larger permanent strain in Dongjin was observed than in Samkang.

• Journal of Biosystems Engineering
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• v.14 no.1
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• pp.8-15
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• 1989

Agricultural materials do not react in a purely elastic manner, and their responses when subjected to stress and strain are appeared from a combination of elastic and viscous behavior. Various researchers have studied the mechanical and rheological properties of the many agricultural materials, but those properties are available mostly foreign varieties of agricultural products. Rheological properties of rice seedlings become important to formulate the principles governing their mechanical behavior. The objectives of this study were to experimentally determine the stress relaxation properties of rice seedlings such as three Japonica-type and one Indica ${\times}$ Japonica hybrid in the transplanting age. The results of this study are summarized as follows; 1. The stress relaxation behavior could be described by the generalized Maxwell model. 2. The phenomenon of stress relaxation happened abruptly just after loading and this phenomenon weakened with the loading time lapsed. 3. With increase of the initial stress, the stress relaxation intensity and residual stress increased, while the relaxation time was constant with increased, while the relaxation time was constant with increase of the level of initial stress. 4. With increase of loading rate, the stress relaxation intensity increased, while the relaxation time and residual stress decreased.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.11a
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• pp.1247-1250
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• 2005

이 논문은 multicarrier CDMA 이동 통신 시스템에서 직-병렬 혼합 pseudo-noise (PN) 코드 동기 획득 기술을 제안 했으며 다중경로 페이딩 채널에서 multiple access interference (MAI) 의 영향을 분석하였다. 직-병렬 혼합 동기 획득 방식은 입력되는 코드 위상의 불확정 영역 전체를 직렬 획득 방식과 병렬 획득 방식을 조합하여 탐색하는 방식이다. 이러한 방식은 완전 병렬획득보다 MAI의 환경에서 mean acquisition time (MAT)이 조금 늦어지지만 하드웨어의 구조를 훨씬 단순화 할 수 있다. 검파 및 오경보 확률을 closed-form 표현으로 mean acquisition time (MAT)를 유도하였다.

• Journal of the Korean Wood Science and Technology
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• v.33 no.5 s.133
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• pp.66-75
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• 2005

Soybean-based adhesives have recently been reconsidered as alternatives to petroleum-based adhesives due to the uncertainty of availability of petrochemical products and the increased demand for wood adhesives. This study was conducted to investigate the adhesive properties of alkaline phenolic soy (APS) resin for hybrid poplar flakeboard. The APS resin was formulated by crosslinking an alkaline soy flour hydrolyzate with lab-prepared PF resin in the soy hydrolyzate to PF resin weight ratios of 70/30, 60/40, and 50/50. The APS resins were used to fabricate homogeneous hybrid poplar flakeboards with different resin solid levels (5%, 7%, and 9%), press temperatures (175 and $200^{\circ}C$), and press times of 8 and 10 minutes. The IB, wet MOR, and dimensional stability properties of board improved with increasing press time, press temperature, and PF level in APS resins. Increasing press time can be used to offset poor IB strength associated with a 9% resin solid level and the excessive moisture content in the mat. The following conditions were concluded to meet the requirements of the CSA standard for exterior-grade flakeboard: a 50% PF level, a 5% resin content, a $200^{\circ}C$ press temperature, and an 8 minute press time.

• Journal of Korea Foundry Society
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• v.17 no.4
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• pp.338-346
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• 1997

Mechanical properties of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites fabricated by the reaction squeeze casting were compared with those of ($15%Al_2O_3{\cdot}SiO_2$)/Ai composites. Al-Ni intermetallic compounds ($10{\sim}20 {\mu}m$) formed by the reaction between nickel powder and molten aluminum were uniformly distributed in the Al matrix. These intermetallic compounds were identified as $Al_3Ni$ using X-ray diffraction analysis and they resulted in beneficial effects on room and high temperature strength and wear resistance. Microhardness values of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composite were greater by about 100Hv than those of ($15%Al_2O_3{\cdot}SiO_2$)/Al composite. Wear resistance of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites was superior to that of ($15%Al_2O_3{\cdot}SiO_2$)/Al composites regardless of the applied load. While tensile and yield strength of ($10%Al_2O_3{\cdot}SiO_2+5%Ni$)/Al hybrid composites were greater at room temperature and $300^{\circ}C$, strength drop at high temperature was much smaller in hybrid composites.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.416-424
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• 2018

Oil spill and oily wastewater have now become a serious threat to the freshwater and marine environments. Porous materials with super-hydrophobicity and super-oleophilicity are good candidates for the oil adsorption and oil/water separation. Here, flexible hybrid nanofibrous membrane (FHNM) containing $SiO_2$/polyvinylidene fluoride (PVDF) microspheres was prepared by simultaneous electrospinning and electrospraying. The obtained FHNM combined the flexibility of the nanofiber mat and super-hydrophobicity of the microspheres, which could not be achieved by either only electrospinning or only electrospraying. It was found that when the weight ratio between the $SiO_2$ and PVDF reached a critical value, the $SiO_2$ nanoparticles were present on the PVDF microsphere surface, significantly improving the surface roughness and hence the contact angle of the FHNM. Compared with the pure electrospun PVDF nanofiber mat, most of the FHNMs have a higher oil adsorption capacity. The FHNM could separate the oil with water quickly under the gravity and displayed a high efficiency and good reusability for the oil/water separation. More importantly, the FHNM could not only separate the oil with the pure water but also the corrosive solution including the salt, acid and alkali solution.

• Korean Journal of Plant Taxonomy
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• v.53 no.2
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• pp.126-147
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• 2023

The taxonomic identity of Elaeagnus ×maritima and E. ×submacrophylla (Elaeagnaceae) in Korea is unclear, yet they are presumed to be hybrid taxa based on their morphology. To determine their hybrid origins, a morphological analysis (field surveys and specimen examinations) and a molecular analysis involving two nuclear ribosomal DNA (nrDNA) regions (internal transcribed spacer and 5S non-transcribed spacer) and one chloroplast DNA (cpDNA) region (matK) were conducted. The morphological analysis revealed that E. ×maritima showed certain morphological similarities to E. glabra, whereas E. ×submacrophylla showed certain morphological similarities to E. pungens. However, the molecular analysis indicated that E. ×maritima exhibited additive species-specific sites of E. glabra and E. macrophylla in the nrDNA regions. Notably, E. ×submacrophylla showed various aspects, with some individuals exhibiting additive species-specific sites of E. pungens and E. macrophylla in the nrDNA and E. macrophylla sequences in the cpDNA regions, some individuals exhibiting E. macrophylla sequences in the nrDNA and E. pungens sequences in the cpDNA regions, and some individuals displaying E. macrophylla sequences in both the nrDNA and cpDNA regions, despite an intermediate morphology between E. pungens and E. macrophylla. These results indicate that these two species are of hybrid origin and frequently cross between parental and hybrid individuals.

• Journal of Korean Association for Spatial Structures
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• v.1 no.2 s.2
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• pp.101-110
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• 2001

A large floating structure is attracting great attention in recent years from the view of ocean space utilization. Its huge scale in the horizontal directions compared with the wavelength and relatively shallow depth make this type of floating structure flexible and its wave-induced motion be characterized by the elastic deformation. In this paper, a boundary integral equation method is proposed to predict the wave-induced dynamic response mat-like floating offshore structure. The structure is modeled as an elastic plate and its elastic deformation is expressed as a superposition of free-vibration modes in air. This makes it straightforward to expand the well-established boundary integral technique for rigid floating bodies to include the hydroelastic effects. In order to validate the theoretical analysis, we compare with the experimental result of reduced model test. Satisfactory agreement is found between theory and experiment.

• Journal of Mechanical Science and Technology
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• v.14 no.2
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• pp.188-196
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• 2000

In this paper, our aim is to develop a model for two cooperating flexible manipulators handling a rigid object by using lumped parameters. This model is in turn analyzed on MATLAB. In order to validate the model, a precise simulation model is developed using $ADAMS^{TM}$ (Automatic Dynamic Analysis of Mechanical System). Moreover, to clarify the discussion, the motions of a dual-arm experimental flexible manipulator are considered. Using the developed model, we control a robotic system with a symmetric hybrid position/force control scheme. Finally, experiments and simulations are performed, and a comparison of simulation results with experimental results is given to a rerify the validity of our model.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.4
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• pp.433-439
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• 2001

A large floating structure is attracting great attention in recent years from the view of ocean space utilization. Its huge scale in the horizontal directions compared with the wavelength and relatively shallow depth make this type of floating structure flexible and its wave-induced motion be characterized by the elastic deformation. In this paper, a boundary integral equation method is proposed to predict the wave-induced dynamic response mat-like floating offshore structure. The structure is modeled as an clastic plate and its elastic deformation is expressed as a superposition of free-vibration modes in air. This makes it straightforward to expand the well-established boundary integral technique for rigid floating bodies to include the hydroelastic effects. In order to validate the theoretical analysis, we compare with the experimental result of previous model test. Satisfactory agreement is found between theory and experiment.