• Advanced Composite Materials
• /
• v.16 no.2
• /
• pp.167-180
• /
• 2007

The tensile strength of unidirectional carbon fiber reinforced plastics under a high strain rate was experimentally investigated. A high-strain-rate test was performed using the tension-type split Hopkinson bar technique. In order to obtain the tensile stress-strain relations, a special fixture was used for the impact tensile specimen. The experimental results demonstrated that the tensile modulus and strength in the longitudinal direction are independent of the strain rate. In contrast, the tensile properties in the transverse direction and the shear properties increase with the strain rate. Moreover, it was observed that the strain-rate dependence of the shear strength is much stronger than that of the transverse strength. The tensile strength of off-axis specimens was measured using an oblique tab, and the experimental results were compared with the tensile strength predicted based on the Tsai-Hill failure criterion. It was concluded that the tensile strength can be characterized quite well using the above failure criterion under dynamic loading conditions.

• The Journal of Korean Academy of Prosthodontics
• /
• v.58 no.4
• /
• pp.321-327
• /
• 2020

Purpose: The purpose of this study was to measure and compare the strain value exerted on the cervical area using different screw tightening protocols in implant-supported, screw-retained 3-unit prostheses. Materials and methods: Strain gauges were attached to four implants: two external and two internal. Thereafter, two study model were designed each type using acrylic resin. CAD-CAM was used to design hex and nonhex abutments for each group (EH, ENH, IH, and INH group) and Screw-cement-retained prostheses were also designed using a nonprecious base metal. Abutment was fixed with 10 Ncm torque, and the prosthesis was cemented. Screws were fixed with 30 Ncm torque using different three protocols. After 5 min, the strain gauge level was measured, and group analysis was performed (α=.05). Results: External group showed significantly lower strain values than internal group and the EH group showed significantly lower strain values than the ENH group (P<.05). There was no difference in strain value based on the types of screw tightening protocols in same group (P>.05). The IH group exhibited significantly higher strain values than the INH group and the IH group showed a significant difference in strain values based on the types of screw tightening protocols used (P<.05). Conclusion: There was no significant effect on the external type in the implant-supported, screw-retained prostheses. However, strain values were high in the internal type, and the types of screw tightening protocol significantly affected these implants.

• Korean Journal of Materials Research
• /
• v.28 no.6
• /
• pp.317-323
• /
• 2018

Crystal structure of the $L1_2$ type $(Al,X)_3Ti$ alloy (X = Cr,Cu) is analyzed by X-ray diffractometry and the nonuniform strain behavior at high temperature is investigated. The lattice constants for the $L1_2$ type $(Al,X)_3Ti$ alloys decrease in the order of the atomic number of the substituted atom X, and the hardness tends to increase. In a compressive test at around 473K for $Al_{67.5}Ti_{25}Cr_{7.5}$, $Al_{65}Ti_{25}Cr_{10}$ and $Al_{62.5}Ti_{25}Cu_{12.5}$ alloys, it is found that the stress-strain curves showed serration, and deformation rate dependence appeared. It is assumed that the generation of serration is due to dynamic strain aging caused by the diffusion of solute atoms. As a result, activation energy of 60-95 kJ/mol is obtained. This process does not require direct involvement. In order to investigate the generation of serrations in detail, compression tests are carried out under various conditions. As a result, in the strain rate range of this experiment, serration is found to occur after 470K at a certain critical strain. The critical strain increases as the strain rate increases at constant temperature, and the critical strain tends to decrease as temperature rises under constant strain rate. This tendency is common to all alloys produced. In the case of this alloy system, the serration at around 473K corresponds to the case in which the dislocation velocity is faster than the diffusion rate of interstitial solute atoms at low temperature.

• Journal of Microbiology and Biotechnology
• /
• v.26 no.3
• /
• pp.452-460
• /
• 2016

Acid stress can affect the viability of probiotics, especially Bifidobacterium. This study aimed to improve the acid tolerance of Bifidobacterium longum BBMN68 using adaptive evolution. The stress response, and genomic differences of the parental strain and the variant strain were compared by acid stress. The highest acid-resistant mutant strain (BBMN68m) was isolated from more than 100 asexual lines, which were adaptive to the acid stress for 10^th, 20^th, 30^th, 40^th, and 50^th repeats, respectively. The variant strain showed a significant increase in acid tolerance under conditions of pH 2.5 for 2 h (from 7.92 to 4.44 log CFU/ml) compared with the wild-type strain (WT, from 7.87 to 0 log CFU/ml). The surface of the variant strain was also smoother. Comparative whole-genome analysis showed that the galactosyl transferase D gene (cpsD, bbmn68_1012), a key gene involved in exopolysaccharide (EPS) synthesis, was altered by two nucleotides in the mutant, causing alteration in amino acids, pI (from 8.94 to 9.19), and predicted protein structure. Meanwhile, cpsD expression and EPS production were also reduced in the variant strain (p < 0.05) compared with WT, and the exogenous WT-EPS in the variant strain reduced its acid-resistant ability. These results suggested EPS was related to acid responses of BBMN68.

• Korean Journal of Metals and Materials
• /
• v.56 no.11
• /
• pp.835-843
• /
• 2018

In this work, we report a delta rosette strain sensor based on highly stretchable silver nanowire (AgNW) percolation piezoresistors. The proposed rosette strain sensors were easily prepared by a facile two-step fabrication route. First, three identical AgNW piezoresistive electrodes were patterned in a simple and precise manner on a donor film using a solution-processed drop-coating of the AgNWs in conjunction with a tape-type shadow mask. The patterned AgNW electrodes were then entirely transferred to an elastomeric substrate while embedding them in the polymer matrix. The fabricated stretchable AgNW piezoresistors could be operated at up to 20% strain without electrical or mechanical failure, showing a maximum gauge factor as high as 5.3, low hysteresis, and high linearity ($r^2{\approx}0.996$). Moreover, the sensor responses were also found to be highly stable and reversible even under repeated strain loading/unloading for up to 1000 cycles at a maximum tensile strain of 20%, mainly due to the mechanical stability of the AgNW/elastomer composites. In addition, both the magnitude and direction of the principal strain could be precisely characterized by configuring three identical AgNW piezoresistors in a delta rosette form, representing the potential for employing the devices as a multidimensional strain sensor in various practical applications.

• Journal of Life Science
• /
• v.21 no.8
• /
• pp.1156-1162
• /
• 2011

Equine coital exanthema caused by equine herpesvirus type 3 (EHV-3) is a venereal disease which seriously drops horse reproduction rates. Here, we isolated EHV-3 from infected horses and investigated their biological characteristics. Initial cytopathic effects such as rounding of cells were detected 48 hours post infection of the virus into RK-13 cells. The infected cells were going to detach from the surface of culture flasks 72 hours post infection. The type of isolated viruses from swabbed samples was EHV-3 by PCR analysis. Glycoprotein G (gG) of isolated EHV-3 has a 99.25 percent similarity rate to that of EHV-3 334/74 control strain. The isolated EHV-3 was named Georo strain. Georo strain consisted of four major proteins including 145 kD, 60 kD, 45 kD and 40 kD, as shown by SDS-PAGE analysis. We hope the newly isolated Georo strain of EHV-3 can be used for studying various aspects of Korean equine coital exanthema.

• KSBB Journal
• /
• v.17 no.3
• /
• pp.290-294
• /
• 2002

The present work describes the improvement of an erythritol-producing strain to lower the formation of glycerol, which is a characteristic by-product of the strain and could cause difficulties in the recovery and purification of the final product. The yeast-like fungi Moniliella suaveolens var. nigra, isolated previously in the same laboratory from beehives, was mutated by exposing it to a 4 g/L NTG solution. From a total of 2000 mutated strains, Em6j30-14 was selected as the one having the most desirable properties. Cultivating the strain for seven days in 300 mL flasks containing 30 mL of a 400 g/L glucose medium resulted in an erythritol yield of 43%. The glycerol yield was 5%, which is a value 50% lower as compared with the wild type. However, attempts to reproduce the above results in a 5L-fermenter failed, resulting in a similar erythritol concentration but a much higher formation of glycerol. Possible reasons for such a different behaviour could be oxygen limitation or the aggregation of cells, but the exact mechanism could not yet be identified. Foam formation, which is another major problem in large-scale fermentation, tended to be much lower for the mutant strain.

• Research in Plant Disease
• /
• v.13 no.3
• /
• pp.137-144
• /
• 2007

Fifty nine strains of Agrobacterium vitis, the causal agent of crown-gall disease on grapevine, originating from different geographical regions and 16 grapevine cultivars including 35 Kyoho cultivar of Korea, were characterized by PCR polymorphic analysis using Universal Rice Primer(URP). Of 12 URP primers, primers URP1F, URP2R, URP2F, and URP4R, URP17R were available for detecting PCR polymorphic bands among the A. vitis strains. PCR polymorphic bands produced by primers URP2F and URP17R were profiled to 12 strain types. A. vitis strains originated from Kyoho cultivar of grapevine showed relatively simple genetic diversify of the four PCR types, while the A. vitis strains originated from other grapevine cultivars and type culture strains showed various genetic diversity with 8 types. Unweighted Pair-Group Method with Arithmetic mean(UPGMA) cluster analysis using the URP-PCR polymorphic bands showed 59.4. vitis strains are genetically clustered into large seven groups.

• Journal of Microbiology and Biotechnology
• /
• v.28 no.9
• /
• pp.1536-1541
• /
• 2018

A yellowish, flexirubin-pigment-producing strain $I3-3^T$ was isolated from river water in Iksan, the Republic of Korea. The strain was gram-negative, aerobic, non-motile, showed catalase and oxidase activities, and could grow at a temperature range of $10-35^{\circ}C$, pH 5.0-10 and 0-2.0% (w/v) of NaCl. The major fatty acids were iso-$C_{15:0}$, iso-$C_{17:0}$ 3-OH and summed feature 3 (comprising $C_{16:1}{\omega}7c$ and/or $C_{16:1}{\omega}6c$). The isolate contained phosphatidylethanolamine, one aminolipid, and two unidentified lipids as the major polar lipids. Menaquinone-6 (MK6) was the major respiratory quinone. The G+C content of the genomic DNA of strain $I3-3^T$ was 35.6%. Comparison of the 16S rRNA gene sequence with the sequences of the closely related type strains showed highest sequence similarity of 96.95% and 96.93% to Flavobacterium nitrogenifigens $NXU-44^T$ and Flavobacterium compostarboris $15C3^T$, respectively. Based on phenotypic and phylogenetic distinctiveness, strain $I3-3^T$ is considered as a member of novel species within the genus Flavobacterium, for which Flavobacterium amnigenum sp. nov. is proposed. The type strain is $I3-3^T$ (=KCTC $52884^T$ =NBRC $112871^T$).

• Journal of Mechanical Science and Technology
• /
• v.15 no.1
• /
• pp.44-51
• /
• 2001

One of the recent issues in design of the spot-welded structure such as the automobile body is to develop an economical prediction method of the fatigue design criterion without additional fatigue test. In this paper, as one of basic investigation for developing such methods, fracture mechanical approach was investigated. First, the Model I, Mode II and Mode III, stress intensity factors were analyzed. Second, strain energy density factor (S) synthetically including them was calculated. And finally, in order to decide the systematic fatigue design criterion by using this strain energy density factor, fatigue data of the ΔP-N(sub)f obtained on the various in-plane bending type spot-welded lap joints were systematically re-arranged in the ΔS-N(sub)f relation. And its utility and reliability were verified by the theory of Weibull probability distribution function. The reliability of the proposed fatigue life prediction value at 10(sup)7 cycles by the strain energy density factor was estimated by 85%. Therefore, it is possible to decide the fatigue design criterion of spot-welded lap joint instead of the ΔP-N(sub)f relation.