• Journal of Microbiology and Biotechnology
• /
• v.14 no.3
• /
• pp.599-606
• /
• 2004

Gram-positive antagonistic bacilli were isolated from agricultural soils for possible use in biocontrol of plant pathogenic fungi, Fusarium oxysporum, Rhizoctonia solani, and/or Pythium ultimum. Among the 65 antagonistic Gram-positive soil isolates, 22 strains were identified as Bacillus species by 16S rDNA sequence analyses. Four strains, including DF14, especially exhibited multiple antagonistic properties against the three damping-off fungi. Genotypic properties of the Bacillus isolates were characterized by rapid molecular fingerprinting methods using repetitive extragenic palindromic-PCR (REP-PCR), ribosomal intergenic spacer-length polymorphisms (RIS-LP), 16S rDNA PCR-restriction fragment length polymorphisms (PCR-RFLP), and strain-specific PCR assays. The results indicated that the REP-PCR method was more valuable than the RIS-LP and 16S rDNA PCR-RFLP analyses as a rapid and reliable approach for bacilli typing and identification. The use of strain-specific primers designed based on 16S rDNA sequence comparisons enabled it to be possible to selectively detect a strain, DF14, which is being used as a biocontrol agent against damping-off fungi.

• Geomechanics and Engineering
• /
• v.7 no.3
• /
• pp.297-316
• /
• 2014

This paper presents a detailed study focused on investigating the effects of silt content on the static and dynamic properties of sand-silt mixtures. Specimens with a low-plastic silt content of 0, 15, 30 and 50% by weight were tested in static triaxial, cyclic triaxial, and resonant columns in addition to consolidation tests to determine such parameters as compression index, internal friction angle, cohesion, cyclic stress ratio, maximum shear modulus, normalized shear modulus and damping ratio. The test procedures were performed on specimens of three cases: constant void ratio index, e = 0.582; same peak deviator stress of 290 kPa; and constant relative density, $D_r$ = 30%. The test results obtained for both the constant-void-ratio-index and constant-relative-density specimens showed that as silt content increased, the internal friction angle, cyclic stress ratio and maximum shear modulus decreased, but cohesion increased. In testing of the same deviator stress specimens, both cohesion and internal friction angle were insignificantly altered with the increase in silt content. In addition, as silt content increased, the maximum shear modulus increased. The cyclic stress ratio first decreased as silt content increased to reach the threshold silt content and increased thereafter with further increases in silt content. Furthermore, the damping ratio was investigated based on different silt contents in three types of specimens.

• Journal of the Korean Society for Precision Engineering
• /
• v.7 no.2
• /
• pp.74-84
• /
• 1990

The machine tool structures for ultra-precision machining muxt be manufactured with materials which have high static and dynamic stiffness, high damping, a long term dimensional and thermal stability. This study aims at the development of new composite material Epoxy-Granite which exhibits the satisfactory characteristics as a material of ultra-precision mchine tool bed. The Epoxy-Granite testpieces that use epoxy resins as a binder and granite particles as a aggregate have been manufactured so as to examine the material properties about mechanical, thermal and damping characteristics. Experiments were carried out to obtain the proper manufacturing conditions of Expoxy-Granite specimens by varying the several testing conditions such as types of epoxy resins, particle sizes of granite and mixture ratio of epoxy resin and aggregate. Also, when Epoxy-Granite was compared with cast iron, GRANITAN which was imported from CMS of U.K. and granite materials, it has exhibited the superior or almost the same mechanical and damping properties and thermal conductivity, except for the thermal expansion.

• Journal of the Korean Society for Precision Engineering
• /
• v.29 no.9
• /
• pp.1035-1040
• /
• 2012

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has been found to be effective treatment of Parkinson's disease (PD). This study aims to evaluate the effect of DBS for rigidity during DBS surgery. Six Parkinsonian patients who received STN-DBS surgery participated in this study. The examiner imposed flexion and extension of a patient's wrist randomly. Resistance to passive movement was quantified by viscoelastic properties (two damping constants for each of flexion and extension phase and one spring constant throughout both phases). All Viscoelastic constants decreased by DBS (p<0.01). Specifically, reduction in damping constant during flexion ($B_f$) was greater than those of damping constant during extension ($B_e$) and of spring constant (p<0.05). $B_f$ would be appropriate for evaluation of effect of DBS for rigidity during DBS surgery.

• Composites Research
• /
• v.36 no.2
• /
• pp.86-91
• /
• 2023

Thermoplastic polyurethane (TPU) is a material whose mechanical properties change according to the phase separation of its unique internal microstructure and is therefore used in various industries. Use of TPU as composites helps in improving the desirable characteristics and properties in accordance with usage. Eco-friendly fillers one of the fillers are on the rise and those are mostly used for reinforcing role. Suberin, which can be extracted from cork, is the main component of cork. It is known to serve high damping property of elastomer composite. The original chemical structure of Suberin is an aliphatic polyester aggregate. In this research, Suberin is obtained after depolymerization into an oligomer having 2 or 3 ester bonds through alkaline hydrolysis. The extracted suberin was added to the matrix which is thermoplastic polyurethane as an eco-friendly filler for improving vibration damping property. As a result, when 10 wt% of suberin was added into thermoplastic polyurethane the existing trade-off relationship was overcome. And it is attained the elastic modulus and damping factor at room temperature improving 92 and 59%, respectively, compared to the original matrix. Those results are from the interaction between the microstructure of TPU and suberin.

• Advances in nano research
• /
• v.6 no.1
• /
• pp.39-55
• /
• 2018

Forced vibration analysis of a cracked functionally graded microbeam is investigated by using modified couple stress theory with damping effect. Mechanical properties of the functionally graded beam change vary along the thickness direction. The crack is modelled with a rotational spring. The Kelvin-Voigt model is considered in the damping effect. In solution of the dynamic problem, finite element method is used within Timoshenko beam theory in the time domain. Influences of the geometry and material parameters on forced vibration responses of cracked functionally graded microbeams are presented.

• Journal of the Korean Mathematical Society
• /
• v.50 no.1
• /
• pp.173-187
• /
• 2013

This paper studies the properties of solutions of the Riccati equation arising from the quadratic optimal control problem of the general damped second order system. Using the semigroup theory, we establish the weak differential characterization of the Riccati equation for a general class of the second order distributed systems with arbitrary damping terms.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2001.04a
• /
• pp.419-425
• /
• 2001

The shear modulus of 3-bar lap rubber shear dynamic test specimen is investigated through incremented shear strain tests. The shear force-strain relation of rubber specimen is also calculated by ABAQUS using hyper-elastic material properties of high damping rubber. The analysis results are compatible with shear dynamic tests of 3-bar lap rubber specimen and 1/8 reduced-scale laminated rubber bearing

• Elastomers and Composites
• /
• v.47 no.3
• /
• pp.231-237
• /
• 2012

This study measured the mechanical and damping properties of EPDM compounds including fillers. Semi-reinforcing furnace black (SRF), high abrasion furnace black (HAF) and acetylene black were used as fillers. Dicumyl peroxide (DCP) were used as curing agents. The measurements were conducted using a moving die rheometer (MDR), durometer, universal testing machine (UTM), compression set and dynamic mechanical analysis (DMA). The tensile strength and elongation at break increased with increasing SRF contents in EPDM compounds. However, they decreased with increasing the amount of acetylene black. In the inspecting temperature range, EPDM compound filled acetylene black had stable storage modulus. Furthermore, the tan ${\delta}$ of the EPDM compounds obtained was enhanced by compounding with acetylene black.

• Polymer(Korea)
• /
• v.31 no.4
• /
• pp.289-296
• /
• 2007

The material factors influencing the sound absorption of the polyurethane foam were investigated with FT-IR, small-angle X-ray scattering (SAXS), and dynamic mechanical thermal analyzer (DMTA). The measurements were performed using the samples which had a similar cell structure but different absorption coefficients. It was found that the ability of the sound absorption of the polyurethane foams was closely related to the damping behavior over the transition range. In order to confirm the use of the low monol polyol (LMP) in high-performance applications, the polyurethanes based on LMP and polypropylene oxide polyol (PPG) were prepared by the solution polymerization method. The microstructure and the physical properties of these polyurethanes were compared. The PPG-based polyurethane showed a higher level of the phase-separated structure because the considerable amount of monol presented in PPG made a contribution to the increased chain mobility. However the short chains formed due to the monol species deteriorated the damping property. As a result, the LMP-based polyurethane showed the superior damping behavior as compared with the PPG-based one.