• 한국분말재료학회지
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• 제22권3호
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• pp.163-168
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• 2015

Ti alloys are extensively used in high-technology application because of their strength, oxidation resistance at high temperature. However, Ti alloys tend to be classified very difficult to cut material. In this paper, The powder synthesis, spark plasma sintering (SPS), bulk material properties such as electrical conductivity and thermal conductivity are systematically examined on $Ti_2AlN$ and $Ti_2AlC$ materials having most light-weight and oxidation resistance among the MAX phases. The bulk samples mainly consisted of $Ti_2AlN$ and $Ti_2AlC$ materials with density close to theoretical value were synthesized by a SPS method. Machining characteristics such as machining time, surface quality are analyzed with measurement of voltage and current waveform according to machining condition of micro-electrical discharge machining with micro-channel shape.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.839-844
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• 2014

The gas-phase radical-radical reaction $O(^3P)$ + $C_2H_5$ (ethyl) ${\rightarrow}$ $H(^2S)$ + $CH_3CHO$(acetaldehyde) was investigated by applying a combination of vacuum-ultraviolet laser-induced fluorescence spectroscopy in a crossed beam configuration and ab initio calculations. The two radical reactants $O(^3P)$ and $C_2H_5$ were respectively produced by photolysis of $NO_2$ and supersonic flash pyrolysis of the synthesized precursor azoethane. Doppler profile analysis of the nascent H-atom products in the Lyman-${\alpha}$ region revealed that the average translational energy of the products and the average fraction of the total available energy released as translational energy were $5.01{\pm}0.72kcalmol^{-1}$ and 6.1%, respectively. The empirical data combined with CBS-QB3 level ab initio theory and statistical calculations demonstrated that the title exchange reaction is a major channel and proceeds via an addition-elimination mechanism through the formation of a short-lived, dynamical addition complex on the doublet potential energy surface. On the basis of systematic comparison with several exchange reactions of hydrocarbon radicals, the observed small kinetic energy release can be explained in terms of the loose transition state with a product-like geometry and a small reverse activation barrier along the reaction coordinate.

• 한국통신학회논문지
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• 제34권5A호
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• pp.414-420
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• 2009

본 논문에서는 OFDMA 기반 relay 시스템에서 throughput 성능개선을 위한, Base Station (BS)과 Relay Station (RS)의 sub-cell 커버리지 설정기법을 제안한다. Relay 시스템에서는 BS-RS 링크에서 무선 자원을 추가로 소비하므로, RS간 자원의 재사용을 고려하면 자원의 효과적 사용이 가능하다. 그러나, 이때 신호의 간섭이 증가하므로 단말기의 수신 Signal to Interference and Noise Ratio (SINR)에 영향을 미치게 된다. 그리므로 본 연구에서는 자원 재사용 정도에 따른 사용가능 자원의 증가를 수신 SINR과 함께 sub-cell 커버리지 결정의 요인으로 함께 고려한다. 모의실험을 통한 결과분석을 통해 throughput 성능을 개선할 수 있는 sub-cell 커버리지를, 다양한 자원재사용 패턴에 따라 도출하였다.

• 전기전자학회논문지
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• 제24권3호
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• pp.853-858
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• 2020

본 논문은 통신기기에서 유입 되는 RF 노이즈에 대해 내성을 가진 OLED용 2-채널 DC-DC 변환기를 제안한다. RF 신호 내성을 위해, 입력전압 변동만큼 감쇠시키는 입력전압 변동감쇠 회로가 내장된다. 양의 전압 V_POS를 출력하는 부스트 변환기는 SPWM-PWM 듀얼모드로 동작하고, 데드 타임을 제어함으로써 전력 효율을 제고한다. V_NEG를 출력하는 인버팅 차지펌프는 2-상 출력 구조로 VCO를 이용한 PFM으로 동작해 작은 리플을 갖도록 설계된다. 0.18 ㎛ BCDMOS 공정으로 시뮬레이션 한 결과, 부스트 변환기 출력전압의 오버슈트와 언더슈트는 10 mV에서 각각 2 mV, 5 mV로 감소하였다. 또한, 2-채널 DC-DC 변환기의 전력효율은 39%~93%을 가졌고, 데드 타임 제어기를 적용한 부스트 변환기의 효율은 종전보다 최대 3% 증가하였다.

• Biomolecules & Therapeutics
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• 제28권4호
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• pp.328-336
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• 2020

Diabetes mellitus affects the colonic motility developing gastrointestinal symptoms, such as constipation. The aim of the study was to examine the role of intracellular signaling pathways contributing to colonic dysmotility in diabetes mellitus. To generate diabetes mellitus, the rats were injected by a single high dose of streptozotocin (65 mg/kg) intraperitoneally. The proximal colons from both normal and diabetic rats were contracted by applying an electrical field stimulation with pulse voltage of 40 V in amplitude and pulse duration of 1 ms at frequencies of 1, 2, 4, and 6 Hz. The muscle strips from both normal rats and rats with diabetes mellitus were pretreated with different antagonists and inhibitors. Rats with diabetes mellitus had lower motility than the control group. There were significant differences in the percentage of inhibition of contraction between normal rats and rats with diabetes mellitus after the incubation of tetrodotoxin (neuronal blocker), atropine (muscarinic receptor antagonist), prazosin (α₁ adrenergic receptor antagonist), DPCPX (adenosine A1 receptor antagonist), verapamil (L-type Ca²⁺ channel blocker), U73122 (PLC inhibitor), ML-9 (MLCK inhibitor), udenafil (PDE₅ inhibitor), and methylene blue (guanylate cyclase inhibitor). The protein expression of p-MLC and PDE₅ were decreased in the diabetic group compared to the normal group. These results showed that the reduced colonic contractility resulted from the impaired neuronal conduction and decreased muscarinic receptor sensitivity, which resulted in decreased phosphorylation of MLC via MLCK, and cGMP activity through PDE₅.

• 한국정보통신학회논문지
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• 제24권8호
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• pp.1086-1094
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• 2020

본 논문은 대한민국 서해와 남해에서의 거리에 따른 성능분석을 위해 실해역 측정을 했다. 서해와 남해 선박의 거리와 전송율 관점에서 측정된 실해역 데이터를 기반으로 데이터 반복 전송 횟수와 파일럿 심볼 배치 간격 파라미터를 조절하여 서해와 남해 성능 비교를 통해 수중OFDM 시스템을 성능을 분석하였다. 결론으로는 전송율과 거리에서 남해의 성능을 비교했을 때 파라미터가 같은 조건에서 남해 5km, 서해 1km 거리에서 BER성능이 남해가 성능이 비슷하였으며, 남해 10km,서해 3km에서 파일럿 심볼의 배치간격을 (𝚫f, 𝚫t) = (6, 3)의 심볼과 PRB가 반복되는 (R_f, R_t) = (2, 1)에서 남해는 1078.92bit/s 서해는 1384.57bit/s으로 전송율관점에서도 남해에서 장거리에서 높은 데이터를 보낼 수 있는걸 확인하였다

• International Journal of Oral Biology
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• 제46권4호
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• pp.176-183
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• 2021

Oral squamous cell carcinoma (OSCC) metastasis is characterized by distant metastasis and local recurrence. Combined chemotherapy with cisplatin and 5-fluorouracil is routinely used to treat patients with OSCC, and the combined use of gefitinib with cytotoxic drugs has been reported to enhance the sensitivity of cancer cells in vitro. However, the development of drug resistance because of prolonged chemotherapy is inevitable, leading to a poor prognosis. Therefore, understanding alterations in signaling pathways and gene expression is crucial for overcoming the development of drug resistance. However, the altered characterization of Ca²⁺ signaling in drug-resistant OSCC cells remains unclear. In this study, we investigated alterations in intracellular Ca²⁺ ([Ca²⁺]_i) mobilization upon the development of gefitinib resistance in human tongue squamous carcinoma cell line (HSC)-3 and HSC-4 using ratiometric analysis. This study demonstrated the presence of altered epidermal growth factor- and purinergic agonist-mediated [Ca²⁺]_i mobilization in gefitinib-resistant OSCC cells. Moreover, Ca²⁺ content in the endoplasmic reticulum, store-operated calcium entry, and lysosomal Ca²⁺ release through the transient receptor potential mucolipin 1, were confirmed to be significantly reduced upon the development of apoptosis resistance. Consistent with [Ca²⁺]_i mobilization, we identified modified expression levels of Ca²⁺ signaling-related genes in gefitinib-resistant cells. Taken together, we propose that the regulation of [Ca²⁺]_i mobilization and related gene expression can be a new strategy to overcome drug resistance in patients with cancer.

• 한국응용곤충학회지
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• 제61권1호
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• pp.117-128
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• 2022

본 연구는 피레스로이드계 살충제인 퍼메트린이 Heliothis virescens의 중추신경세포의 나트륨채널에 어떻게 작용하는 가를 전기생리학적으로 관찰하였다. 퍼메트린은 나트륨채널의 꼬리전류(I_Na-tail)를 지속적으로 증가시켰으며 이러한 비정상적인 나트륨 전류증가가 나방류의 신경계에 과도한 흥분을 일으겨 살충작용을 하는 것으로 생각된다. 이러한 살충작용은 전갈독과 함께 사용했을때 약 8배의 증가가 있었음을 확인하였다. 전갈독이 살충제의 독성을 강화하는 분자생리학적 기전연구가 계속되면 해충방제에 많은 기여를 할 것으로 생각된다.

• Korean Circulation Journal
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• 제53권4호
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• pp.239-250
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• 2023

Background and Objectives: Brugada syndrome (BrS) is an inherited arrhythmia syndrome that presents as sudden cardiac death (SCD) without structural heart disease. One of the mechanisms of SCD has been suggested to be related to the uneven dispersion of transient outward potassium current (I_to) channels between the epicardium and endocardium, thus inducing ventricular tachyarrhythmia. Artemisinin is widely used as an antimalarial drug. Its antiarrhythmic effect, which includes suppression of I_to channels, has been previously reported. We investigated the effect of artemisinin on the suppression of electrocardiographic manifestations in a canine experimental model of BrS. Methods: Transmural pseudo-electrocardiograms and epicardial/endocardial transmembrane action potentials (APs) were recorded from coronary-perfused canine right ventricular wedge preparations (n=8). To mimic the BrS phenotypes, acetylcholine (3 μM), calcium channel blocker verapamil (1 μM), and I_to agonist NS5806 (6-10 μM) were used. Artemisinin (100-150 μM) was then perfused to ameliorate the ventricular tachyarrhythmia in the BrS models. Results: The provocation agents induced prominent J waves in all the models on the pseudo-electrocardiograms. The epicardial AP dome was attenuated. Ventricular tachyarrhythmia was induced in six out of 8 preparations. Artemisinin suppressed ventricular tachyarrhythmia in all 6 of these preparations and recovered the AP dome of the right ventricular epicardium in all preparations (n=8). J wave areas and epicardial notch indexes were also significantly decreased after artemisinin perfusion. Conclusions: Our findings suggest that artemisinin has an antiarrhythmic effect on wedge preparation models of BrS. It might work by inhibition of potassium channels including I_to channels, subsequently suppressing ventricular tachycardia/ventricular fibrillation.

• The Korean Journal of Physiology and Pharmacology
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• 제26권6호
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• pp.531-540
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• 2022

Group 1 metabotropic glutamate receptors (mGluRs) can positively affect postsynaptic neuronal excitability and epileptogenesis. The objective of the present study was to determine whether group 1 mGluRs might be involved in synaptically-induced intracellular free Ca²⁺ concentration ([Ca²⁺]_i) spikes and neuronal cell death induced by 0.1 mM Mg²⁺ and 10 µM glycine in cultured rat hippocampal neurons from embryonic day 17 fetal Sprague-Dawley rats using imaging methods for Ca²⁺ and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays for cell survival. Reduction of extracellular Mg²⁺ concentration ([Mg²⁺]_o) to 0.1 mM induced repetitive [Ca²⁺]_i spikes within 30 sec at day 11.5. The mGluR5 antagonist 6-Methyl2-(phenylethynyl) pyridine (MPEP) almost completely inhibited the [Ca²⁺]_i spikes, but the mGluR1 antagonist LY367385 did not. The group 1 mGluRs agonist, 3,5-dihydroxyphenylglycine (DHPG), significantly increased the [Ca²⁺]_i spikes. The phospholipase C inhibitor U73122 significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The IP₃ receptor antagonist 2-aminoethoxydiphenyl borate or the ryanodine receptor antagonist 8-(diethylamino)octyl 3,4,5-trimethoxybenzoate also significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The TRPC channel inhibitors SKF96365 and flufenamic acid significantly inhibited the [Ca²⁺]_i spikes in the absence or presence of DHPG. The mGluR5 antagonist MPEP significantly increased the neuronal cell survival, but mGluR1 antagonist LY367385 did not. These results suggest a possibility that mGluR5 is involved in synaptically-induced [Ca²⁺]_i spikes and neuronal cell death in cultured rat hippocampal neurons by releasing Ca²⁺ from IP₃ and ryanodine-sensitive intracellular stores and activating TRPC channels.