• Journal of Powder Materials
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• v.17 no.2
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• pp.136-141
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• 2010

Bismuth-telluride based $(Bi_{0.2}Sb_{0.8})_2Te_3$ thermoelectric powders were fabricated by two-step planetary milling process which produces bimodal size distribution ranging $400\;nm\;{\sim}\;2\;{\mu}m$. The powders were reduced in hydrogen atmosphere to minimize oxygen contents which cause degradation of thermoelectric performance by decreasing electrical conductivity. Oxygen contents were decreased from 0.48% to 0.25% by the reduction process. In this study, both the as-synthesized and the reduced powders were consolidated by the spark plasma sintering process at $350^{\circ}C$ for 10 min at the heating rate of $100^{\circ}C/min$ and then their thermoelectric properties were investigated. The sintered samples using the reduced p-type thermoelectric powders show 15% lower specific electrical resistivity ($0.8\;m{\Omega}{\cdot}cm$) than those of the as-synthesized powders while Seebeck coefficient and thermal conductivity do not change a lot. The results confirmed that ZT value of thermoelectric performance at room temperature was improved by 15% due to high electric conductivity caused by the controlled oxygen contents present at bismuth telluride materials.

• Journal of the Korean Ceramic Society
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• v.32 no.12
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• pp.1337-1348
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• 1995

TZP/SUS- and ZT/SUS-functionally gradient materials (FGM) were fabricated by pressureless sintering in Ar-atmosphere. The sintering defects such as warping, frustrum formation, splitting and cracking which originated from shrinkage and sintering behaviors of metal and ceramics different from each other could be controlled by the adjustment with respect to the particle size and phase type of zirconia. The residual stresses generated on the metal and ceramic regions in FGM were characterized with X-ray diffraction method, and relaxed as the thickness and number of compositional gradient layer were increased. The residual stress states in TZP/SUS-FGM have irregular patterns by means of the different sintering behavior and cracking at ceramic-monolith. While in ZT/SUS-FGM, compressive stress is induced on ceramic-monolith by the volume expansion of monoclinic ZrO2 at phase transformation. Also, compressive stress is induced on metal-monolith by the constraint of warping which may be created to the metal direction by the difference of coefficient of thermal expansions. As a consequence, it has been verified that the residual stress generated on FGM is dominantly influenced by the thickness and number of compositional gradient layer, and the sintering defects and residual stress can be controlled by the constraint of the difference of shrinkage and sintering behaviors of each component.

• Korean Journal of Materials Research
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• v.21 no.10
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• pp.542-545
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• 2011

Half-Heusler alloys are a potential thermoelectric material for use in high-temperature applications. In an attempt to produce half-Heusler thermoelectric materials with fine microstructures, TiCoSb was synthesized by the mechanical alloying of stoichiometric elemental powder compositions and then consolidated by vacuum hot pressing. The phase transformations during the mechanical alloying and hot consolidation process were investigated using XRD and SEM. A single-phase, half- Heusler allow was successfully produced by the mechanical alloying process, but a minor portion of the second phase of the CoSb formation was observed after the vacuum hot pressing. The thermoelectric properties as a function of the temperature were evaluated for the hot-pressed specimens. The Seebeck coefficients in the test range showed negative values, representing n-type conductivity, and the absolute value was found to be relatively low due to the existence of the second phase. It is shown that the electrical conductivity is relatively high and that the thermal conductivities are compatibly low in MA TiCoSb. The maximum ZT value was found to be relatively low in the test temperature range, possibly due to the lower Seebeck coefficient. The Hall mobility value appeared to be quite low, leading to the lower value of Seebeck coefficient. Thus, it is likely that the single phase produced by mechanical alloying process will show much higher ZT values after an excess Ti addition. It is also believed that further property enhancement can be obtained if appropriate dopants are selectively introduced into this MA TiCoSb System.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.957-958
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• 2006

Fe doped skutterudite $CoSb_3$ with a nominal composition of $Fe_xCo_{1-x}Sb_{12}(0{\leq}x{\leq}2.5)$ have been synthesized by mechanical alloying (MA) of elemental powders, followed by vacuum hot pressing. Phase transformations during mechanical alloying and vacuum hot pressing were systematically investigated using XRD. Single phase skutterudite was successfully produced by vacuum hot pressing using as-milled powders without subsequent annealing. However, second phase of $FeSb_2$ was found to exist in case of $x\geq2$, suggesting the solubility limit of Fe with Co in this system. Thermoelectric properties as functions of temperature and Fe contents were evaluated for the hot pressed specimens. Fe doping up to x=1.5 with Co in $Fe_xCo_{4-x}Sb_{12}$ appeared to increase thermoelectric figure of merit (ZT) and the maximum ZT was found to be 0.78 at 525K in this study.

• Particle and aerosol research
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• v.4 no.1
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• pp.21-25
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• 2008

$Pb(Zr_{0.53}Ti_{0.47})O_3$ (PZT) was synthesized by a multiple wet dry process. Precipitates prepared from reaction between $ZrOCl_2{\cdot}8H_2O$ and $TiOCl_2$ and $NH_4OH$ in an aqueous solution was dried at $100^{\circ}C$, and calcined at $500^{\circ}C$ and $700^{\circ}C$. The mixture mixed with PbO and as-dried or calcined $Zr_{0.53}Ti_{0.47}O_4$ (ZT) powders was calcined again at 700 and $800^{\circ}C$. Well crystallized ZT and PZT were formed at even $700^{\circ}C$. PZT piezoelectric ceramics of more than 98.5% in a relative density was obtained by sintering at as low as $900^{\circ}C$.

• Ceramist
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• v.22 no.2
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• pp.133-145
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• 2019

Thermoelectric energy conversion has attracted much attention because it can convert heat into electric power directly through solid state device and vice versa. Current research is aimed at increasing the thermoelectric figure of merit (ZT ) by improving the power factor and reducing the thermal conductivity. Although there have been significant progresses in increasing ZT of material systems composed of Bi, Te, Ge, Pb, and etc. over the last few decades, their relatively high cost, toxicity, and the scarcity have hindered further development of thermoelectrics to expand practical applications. In this paper, we review the current status of research in the fields of nanostructured thermoelectric materials with eco-friendly and low cost elements, such as skutterudites and oxides, for mid-high temperature applications, highlighting the strategies to improve thermoelectric performance.

• Korean Journal of Materials Research
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• v.31 no.8
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• pp.445-449
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• 2021

Zintl compound Mg₃Sb₂ is a promising candidate for efficient thermoelectric material due to its small band gap energy and characteristic electron-crystal phonon-glass behavior. Furthermore, this compound enables fine tuning of carrier concentration via chemical doping for optimizing thermoelectric performance. In this study, nominal compositions of Mg_3.8Sb_2-xTe_x (0 ≤ x ≤ 0.03) are synthesized through controlled melting and subsequent vacuum hot pressing method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) are carried out to investigate phase development and surface morphology during the process. It should be noted that 16 at. % of excessive Mg must be added to the system to compensate for the loss of Mg during melting process. Herein, thermoelectric properties such as Seebeck coefficient, electrical conductivity, and thermal conductivity are evaluated from low to high temperature regimes. The results show that Te substitution at Sb sites effectively tunes the majority carriers from holes to electrons, resulting in a transition from p to n-type. At 873 K, a peak ZT value of 0.27 is found for the specimen Mg_3.8Sb_1.99Te_0.01, indicating an improved ZT value over the intrinsic value.

• Journal of Veterinary Clinics
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• v.36 no.6
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• pp.306-313
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• 2019

It is important to identify the most suitable anesthetic agent that has minimal side effects to be able to control and perform surgeries on bears. In this study, we examined and compared the induction and recovery times as well as the physiological changes occurring during anesthesia induced by medetomidine-zolazepam/tiletamine (MZT) and xylazine-zolazepam/tiletamine (XZT) at general anesthesia for laparoscopic salpingectomy in 326 female Asiatic black bears. The body temperature, heart rate, respiratory rate, and levels of PaO₂ and EtCO₂ were the physiological changes measured during surgical procedures in female bears after anesthesia. In addition, the levels of pO₂, pCO₂, and sO₂ were measured using a portable blood gas analyzer. To induce recovery from anesthesia, bears anesthetized with MZT were intravenously administered atipamezole and bears anesthetized with XZT were intravenously administered yohimbine. The combination MZT, at dosages of 0.019 ± 0.001 mg/kg for medetomidine and 1.4 ± 0.1 mg/kg for ZT, or the combination XZT, at dosages of 2.0 ± 0.1 mg/kg for xylazine and 3.0 ± 0.1 mg/kg for ZT, proved to be reliable and effective in anesthetizing Asiatic black bears for a 40-min handling period for routine clinical procedures. The average anesthesia induction times were 16.5 ± 0.95 min for the bears in the MZT group and 12.0 ± 0.44 min for those in the XZT group. A significant difference was noted between the two drugs (P < 0.001) in terms of the average anesthesia induction time. The anesthesia induction time was shorter for bears with lower body weights than those with higher body weights (P < 0.05). The recovery time of MZT was significantly faster than that of XZT (11.3 ± 0.45 min vs. 18.5 ± 0.83 min) (P < .001). The bears anesthetized with MZT exhibited lower cardiopulmonary suppression than those anesthetized with XZT (P < 0.05). The body temperatures and EtCO₂ of bears in the M ZT group were significantly lower than those in the XZT group as time progressed after anesthesia (P < 0.05). The average pO₂ before the bears were supplied with oxygen was 64.8 ± 3.7 mmHg, but it increased to 211.5 ± 42.5 mmHg afterwards (P < 0.001). In conclusion, our results indicate that bears anesthetized with MZT have longer anesthesia induction time, shorter recovery time, slower heart and respiratory rates, and lower body temperatures and EtCO₂ than those anesthetized with XZT. These findings suggest that XZT is preferable to MZT, warranting further research on its uses and clinical responses in bears.

• East Asian mathematical journal
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• v.22 no.1
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• pp.93-109
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• 2006

The concept of intuitionistic fuzzy set was first introduced by Atanassov in 1986. In this paper, we define the intuitionistic(S,T)-fuzzy left h-ideals of a hemiring by using an s-norm S and a t-norm T and study their properties. In particular, some results of fuzzy left h-ideals in hemirings recently obtained by Jun, $\"{O}zt\"{u}rk$, Song, and others are extended and generalized to intuitionistic (S,T)-fuzzy ideals over hemirings.

• Journal of Plant Biotechnology
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• v.6 no.1
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• pp.55-61
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• 2004

Callus induction and somatic embryogenesis are fundamental to cotton tissue culture biotechnology. An efficient protocol for callus induction, somatic embryogenesis and their maturation have been developed to regenerate plantlets from cotton (Gossypium hirsutum L.) variety coker 312. Embryogenic callus was initiated from hypo-cotyl region that was used as an explant at seedling stage when it was about 7-8 days old. Callus induction was achieved through culturing hypocotyls (5-7mm) on $MS_{1a} medium supplemented with 2,4-D (0.1 mg/L) and KT (0.5 mg/L) for six weeks. A friable, colorless, bulky and well proliferating callus becomes greenish with the addition of NAA (2.0 mg/L), ZT (0.1 mg/L) and removal of 2,4-D (M $S_{1b}$) cultured for two weeks then again transferred to $MS_{1a}. 2,4-dichlorophenoxyacetic acid (2,4-D) promoted the proliferation of embryogenic callus, but had a negative effect on the differentiation and germination of somatic embryos. ZT (0.1mg/L) and activated charcoal (2g/L), both hormones play an important role in differentiation and germination of somatic embryos in hypocotyls derived embryogenic callus but in case of cotton, such a capability have been observed on MS medium with 1.92 g/L $KNO_3$, but it is considered to attain somewhat more improvement. High embryogenesis frequency was achieved through nutrient deficient stress treatment. The frequency of globular embryogenesis (two-three folds) was achieved when well proliferating callus was (from $MS_{1a}$ media) cultured on MS (1/5 strength) medium for four weeks. Here the development of anthocyanins is the best indicator for somatic embryogenesis. However, when embryoid callus was cultured on MS (full strength) medium, the globular embryos were developed into normal plantlets immediately. In this procedure 27.49% cotyledenary embryos were developed. Of that 70% cotyledenary embryos were developed not only into normal plantlets but rooted simultaneously, when cultured on MS (with 0.05 mgg/L giberrelic acid) medium. So complete plants could be regenerated through somatic embryogenesis from hypocotyl explants within 6 months.s.