• 대한기계학회논문집B
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• 제23권1호
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• pp.33-42
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• 1999

The effects of wan thermal boundary condition were investigated for a uniform wall temperature, a uniform wall heat flux, and for coupled heat conduction In the channel wall with transverse rectangular ribs. Numerical investigations for steady laminar flow show behavior similar to that observed experimentally in the separated flow region for flow over a cylinder. Conjugate heat transfer with a low solid-fluid thermal conductivity ratio does not lead to the same results as for the uniform heat flux boundary condition, and heat transfer reversal is found on the back sides of the ribs.

• 한국진공학회지
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• 제11권2호
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• pp.103-107
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• 2002

Metal/ferroelectric/semiconductor field effect transistors(MFSFET′s) with various gate electrodes, that are aluminum, platinum and poly-Si, using rapid thermal annealed $LiNbO_3$/Si(100) structures were fabricated and the properties of the FET′s have been discussed. The drain current of the "on" state of FET with Pt electrode was more than 3 orders of magnitude larger than the "off" state current at the same "read" gate voltage of 1.5 V, which means the memory operation of the MFSFET. A write voltage as low as about $\pm$4 V, which is applicable to low power integrated circuits, was used for polarization reversal. The retention properties of the FET using Al electrode were quite good up to about $10^3$ s and using Pt electrode remained almost the same value of its initial value over 2 days at room temperature.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제44회 동계 정기학술대회 초록집
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• pp.304-305
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• 2013

We report a positive exchange bias (HE) in thinmultilayered filmscontaining nano-oxide layer. The positive HE, obtained for our system results from an antiferromagnetic coupling between the ferromagnetic (FM) CoFe and the antiferromagnetic (AFM) CoO layers, which spontaneously form on top of the nano-oxide layer (NOL). The shift in the hysteresis loop along the direction of thecooling field and the change in the sign of exchange bias are evidence of antiferromagnetic interfacial exchange coupling between the CoO and CoFe layers. Our calculation indicates that uncompensated oxygen moments in the NOL results in antiferromagnetic interfacial exchange coupling between the CoO and CoFe layers. One of the interesting features observed with our system is that it displays the positive HE even above the bulk Neel temperature (TN) of CoO. Although the positive HEsystem has a different AFM/FM interfacial spin structure compare to that of the negative HE one, the results of the angular dependence measurements show that the magnetization reversal mechanism can be considered within the framework of the coherent rotation model.

• Journal of Magnetics
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• 제7권1호
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• pp.4-8
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• 2002

The magnetoresistance (MR) and the magnetization reversal of a lateral spin-injection device based on a spin-polarized field effect transistor (spin FET) have been investigated. The device consists of a two-dimensional electron gas (2DEG) system in an InAs single quantum well (SQW) and two ferromagnetic $(Ni_{80}Fe_{20})$ contacts: all injector (source) and a detector (drain). Spin-polarized electrons are injected from the first contact and, after propagating through the InAs SQW are collected by the second contact. By engineering the shape of the permalloy contacts, we were able to observe distinct switching fields $(H_c)$ from the injector and the collector by using scanning Kerr microscopy and MR measurements. Magneto-optic Kerr effect (MOKE) hysteresis loops demonstrate that there is a range of magnetic field (20~60 Oe), at room temperature, over which the magnetization in one contact is aligned antiparallel to that in the other. The MOKE results are consistent with the variation of the magnetoresistance in the spin-injection device.

• Korea-Australia Rheology Journal
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• 제20권1호
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• pp.27-34
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• 2008

Clay suspensions in liquid polymers exhibit a time-dependent behaviour that includes viscoelastic as well as thixotropic features. Because of the presence of interacting clay platelets, particulate networks can develop, which are broken down during flow and rebuild upon cessation of the flow. Here, the use of thixotropic techniques in probing flow-induced structures in nanocomposites is explored with data on a hectorite-poly(isobutylene) model system. By means of fast stress jump measurements the hydrodynamic contributions to the steady state stresses are determined as well as those caused by the stretching of the clay floes. Flow reversal measurements do not provide a clear indication of flow-induced anisotropy in the present case. The recovery of the clay microstructure upon cessation of flow is followed by means of overshoot and dynamic measurements. The development of a particulate network is detected by the appearance and growth of a low frequency plateau of the storage moduli. The modulus-frequency curves after various rest times collapse onto universal master curves, regardless of the pre-shear history or temperature. The scaling factors for this master curve are the crossover parameters. The crossover moduli are nearly a linear function of the crossover frequency, the relation being identical for recovery after shearing at different shear rates. This function depends, however, on temperature.

• 폴리머
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• 제25권2호
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• pp.279-292
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• 2001

몰치환도 (MS)가 다른 두 종류의 (hydroxypropyl)celluloses (HPCs)와 이들로부터 3가지의 유도체, 즉 (acetoxypropyl)celluloses, (ethoxypropyl)celluloses와 (cyanoethoxypropyl) celluloses들을 합성함과 동시에 이들의 열 및 액정상의 특성을 검토하였다. 모든 시료들은 상온에서 cholesteric 상의 반사색깔들을 나타내며 온도상승에 의해 광학 pitch(λ$_{ms}$ )가 증가하는 우측방향의 나선구조를 형성하였다. 그러나, 검토한 유도체들의 액정상에서 등방상액체로의 전이온도($T_{i}$)와 유리전이온도, 동일한 온도에서 액정상이 나타내는 λ$_{m}$ 의 크기 그리고 λ$_{m}$ 의 온도의존성은 MS와 HPC에 도입된 측쇄의 길이 및 화학구조에 크게 의존하였다. 이들의 결과를 치환기의 극성과 유연성의 차이 그리고 주쇄들간의 거리 등과의 관련하에서 검토하였다. 모든 유도체들에 있어서, λ$_{m}$ 값들은 액정상의 $T_{i}$보다 높은 온도에서 무한대로 접근하므로 온도에 의한 나선방향의 역전은 검출되지 않았다.

• 대한임상독성학회지
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• 제4권2호
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• pp.147-150
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• 2006

Neurotoxic shellfish poisoning (NSP) can result from eating filter-feeding shellfish carrying brevetoxins produced by the marine dinoflagellate Krenia brevis (formally Gymnodinium breve). Brevetoxins enhance sodium entry into cells via voltage-sensitive sodium channels and have an excitatory effect. The incubation period is three hours (range 15 minutes-18 hours). NSP is characterized by gastroenteritis combined with neurologic symptoms. Gastrointestinal (GI) symptoms include abdominal pain, nausea, diarrhea and burning pain in the rectum. Neurologic symptoms are paresthesia, reversal of hot and cold temperature sensation, myalgia, headache, vertigo, and ataxia. Other symptoms may include malaise, tremor, dysphagia, bradycardia, decreased reflexes, dilated pupils, seizure, and coma. The health problem caused by K. breviscan be associated with a red tide bloom. We encountered 3 cases of neurotoxic shellfish poisoning. They all presented with GI and neurologic symptoms andrecovered after conservative treatment.

• 한국응용약물학회:학술대회논문집
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• 한국응용약물학회 2003년도 Annual Meeting of KSAP : International Symposium on Pharmaceutical and Biomedical Sciences on Obesity
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• pp.15-23
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• 2003

Interest in the regulation of body weight and the pathological physiology of obesity has been rekindled by the cloning of the obese(ob) gene and identification of its product, leptin, in 1994. The first publication appeared in Nature and is a milestone of obesity research. The remarkable metabolic effects of leptin in rodents are: a) inhibition of food intake, b) stimulation of energy expenditure, and c) reversal of obesity. These effects, though mostly desirable, have not been fully demonstrated in humans. The central action of leptin in the regulation of body weight includes two pathways in rodents: a) When the body weight increasing, more leptin is secreted from adipose tissue, which acts on hypothalamus, probably through a POMC or MSH pathway via M4 receptor, initiates a series of response to obesity, i.e. sympathetic tone increased, energy expenditure enhanced and food intake reduced. b) When body weight reduced, leptin concentration decreased with the shrinkage of fat mass, which may also act on the hypothalamus, probably through a NPY-Y5 receptor pathway. Then a cascade of response to hungry was induced, i.e. increase of parasympathetic tone and food intake, decrease of energy expenditure and body temperature, as well as shut-down of the reproductive function.

• 한국세라믹학회지
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• 제23권1호
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• pp.44-50
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• 1986

Si-ZnO n-n heterojunction diodes were prespared by r.f diode sputtering of the sintered ZnO target on n-type Si single crystal wafers and their structures and electrical properties were studied. The films were grown orientedly with the c-axis of crystallites perpendicular to the substrate surface at low r.f. powder and grown to polycrystalline films with random orientation at high r. f. powder. The crystallite size increased with the increasing substrate temperture The oriented texture films only were used to prepare the photovoltaic diodes and these didoes showed the photovoltaic effect veing positive of the ZnO side for the photons in the wavelength range of 380-1450nm. The sign reversal of phootovoltage which is the property os isotype heterojunction was not observed because of the degeneration of the ZnO films. The diode showed the forward rectification when it was biased with the ZnO side positive. The current-voltage characteristics exhibited the thermal-current type relationship J∝exp(qV/nkT) with n=1.23 at the low forward bias voltage and the tunnelling-current type relationship J∝exp($\alpha$V) where $\alpha$ was constant independent of temperature at the high forward bias voltage. The crystallite size of ZnO films were influenced largely on the photovoltaic properties of diodes ; The diodes with the films of the larger crystallites showed the poor photovoltaic properties. This reason may be cosidered that the ZnO films with the large crystallites could not grow to the electrically continuous films because the thickness of films was so thin in this experiment.

• Bulletin of the Korean Chemical Society
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• 제24권3호
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• pp.274-278
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• 2003

New banana-shaped achiral compounds, 1,3-phenylene bis [4-{4-(alkenyloxy) phenyliminomethyl}benzoate]s were synthesized by varying the length of alkenyl group; their ferroelectric properties are described. The smectic mesophases, including a switchable chiral smectic C $(Sm\;C^*)$ phase, were characterized by differential scanning calorimetry, polarizing optical microscopy and triangular wave method. The presence of vinyl groups at the terminals of linear side wings in the banana-shaped achiral molecules containing Schiff's base mesogen induced a decrease in melting temperature and formation of the switchable $(Sm\;C^*)$ phase in the melt. The smectic phases having the octenyloxy group such as $(CH_2)_6CH=CH_2$ showed ferroelctric switching, and their values of spontaneous polarization on reversal of an applied electric field were 120 nC/cm² (X=H) and 225 nC/ cm² (X=F), respectively. We could obtain ferroelectric phases by controlling the number of carbon atom in alkenyloxy chain of a bent-core molecule.