• 제목/요약/키워드: Growth velocity

검색결과 488건 처리시간 0.03초

일방향응고된 $Bi_{2}Te_{3}-PbBi_{4}Te_{7}$ 공정합금의 열전특성 (Thermoelectric properties of unidirectionally solidified $Bi_{2}Te_{3}-PbBi_{4}Te_{7}$ eutectic alloys)

  • 박창근;민병규;이동희
    • 한국재료학회지
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    • 제5권2호
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    • pp.251-258
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    • 1995
  • $Bi_{2}Te_{3}$와 PbTe의 혼합물에서 $Bi_{2}Te_{3}-PbBi_{4}Te_{7}$의 공정조직이 형성됨을 이용, 제2상의 미세조직 제어로 열전도도의 감소에 따른 성능지수 향상을 목적하여 여러 조건에서 제조된 n-type(Bi, Pb)-Te계 공정조성 일방향 응고재의 열전특성을 조사하였다. 일방향응고시 공정상 PbBi_{4}Te_{7}$$Bi_{2}Te_{3}$의 벽개면(0001)을 따라 lamellar 형태로 성장하였으며, 성장속도가 1.4 \times 10^{-4}$cm/sec에서 $8.3 \times 10^{-4}$cm/sec로 증가됨에 따라 4PbBi_[4]Te_{7}$의 상간격은 10.4 $\mu \textrm{m}$에서 3.2$\mu \textrm{m}$로 감소되었다. Seeback계수는 성장방향 및 성장속도와 온도구배에는 관계없이 약 $\mid$$\alpha$$\mid$=29 $\mu$ V/K일정하였다. 전기전도도는 성장속도에 따라 약간 감소하는 경향을 보였고 성장방향에 평행한 경우가 수직한 경우보다 약 3배 정도 컸다. 성능지수는 성장방향과 성장속도 및 온도구배에 따라 약간씩 변화를 보였다. 수직한 경우가 평행한 경우에 비해 상대적으로 증가하는 경향을 나타내었는데 이는 lamellar 간격이 줄어듦에 따른 열전도도의 감속에서 비롯된 것으로 분석되었다.

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SM490B 용접부의 피로균열 성장 거동에 미치는 초고속 용사코팅 효과 (The Effect of High Velocity Oxygen Fuel Thermal Spray Coating on Fatigue Crack Growth Behavior for Welded SM490B)

  • 윤명진;최성종;조원익
    • 한국자동차공학회논문집
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    • 제14권4호
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    • pp.99-106
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    • 2006
  • High velocity oxygen-fuel thermal spray coating of the WC-Co cermet material is a well-established process for modifying the surface properties of the structural components exposed to the corrosive and wear attacks, and also these coating are well-known method to improve the fatigue strength of material. In this study, HVOF coated SM490B are prepared to evaluation of the effect of coating on tension and fatigue crack growth behavior. The pre-crack of the fatigue crack growth test specimens machined at deposited material area, heat affected zone and boundary, respectively. Through these test, the following results are obtained: 1) Tensile strength was about 498 MPa, and fracture occurred on base metal area. 2) The fatigue crack of coated specimens propagated more rapidly than non-coated specimen in all specimens. 3) In the same coating thickness specimens, the specimens with pre-crack at boundary more rapidly propagated than the specimens with pre-crack at HAZ and deposited material area. These results can be used as basic data in a structural integrity evaluation of rolled SM490B weldments considering HVOF coating.

Czochralski 단결정 성장특성제어를 위한 자장형태에 관한 연구 (Effect of Applied Magnetic Fields on Czochralski Single Crystal Growth)

  • 김창녕;김경훈
    • 한국결정성장학회지
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    • 제3권1호
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    • pp.18-30
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    • 1993
  • 균일한 자장과 비균일한 자장이 도가니에 가하여졌을 때의 Czochralski유동장이 수치적으로 해석되었다. 여기에서 부력의 효과, thermocapillarity 효과, 원심력의 효과, 자장의 효과등이 Czochralski유동장을 지배하고 있다. 자오면에서의 속도성분과 회전방향의 속도성분이 구하여졌으며 온도, 전류의 흐름 등이 해석되었다. 균일한 자장의 경우에 세기가 증가하면 모든 속도성분이 작아지고 있으며 결정표면 아래에서 회전방향으로의 전류의 세기가 증가한다. 불균일한 자장의 경우에는 자장의 불균일성이 증가하면 자오면에서의 평면유동은 억제되는 반면 회전방향의 속도성분은 더 증가하게 된다. 이와 같은 여러 형태의 자장의 영향아래에서의 Czochralski 유동장에 대한 이해는 도가니(Crucible)안의 용질 및 불순물의 농도에 관한 거동을 연구할 수 있는 기초를 제공하고 있다.

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Defining the $M_{BH}-sigma_*$ relation using the uniformly measured stellar velocity dispersions in the near-IR

  • 강월랑;우종학
    • 천문학회보
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    • 제36권2호
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    • pp.62.2-62.2
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    • 2011
  • The correlation between black hole mass and stellar velocity dispersion provides an important clue on the black hole growth and galaxy evolution. In the case of AGN, however, it is extremely difficult to measure stellar velocity dispersions in the optical since AGN continuum dilutes stellar absorption features. In contrast, stellar velocity dispersions of active galaxies can be measured in the near-IR, where AGN-to-star flux ratio is much smaller. Expecting that more stellar velocity dispersion measurements will be available using future near-IR facilities, it is crucial to test whether the stellar velocity dispersions measured from the near-IR spectra are consistent with those measured from the optical spectra. For a sample of 35 nearby galaxies, for which optical stellar velocity dispersion measurements and dynamical black hole masses are available, we obtained high quality H-band spectra, using the TripleSpec at the Palomar 5-m Telescope, in order to calibrate the stellar velocity dispersions and define the $M_{BH}-sigma_*$ relation in the near-IR. Based on the spatially resolved kinematics, we correct for the rotation component and determine the luminosity-weighted stellar velocity dispersion of the spheroid component in each galaxy. In this presentation, we will show the comparison between optical and near-IR stellar velocity dispersion measurements and define the $M_{BH}-sigma_*$ relation based on uniformly measured stellar velocity dispersion in the near-IR.

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PHV 연령별 신장 발육의 특징에 관한 연구 -7~18세의 종단적 자료를 이용하여- (Study on the Characteristics of Height Growth by PHV Age -Using longitudinal data of age 7 to 18-)

  • 박주미;김명
    • 보건교육건강증진학회지
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    • 제8권2호
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    • pp.74-86
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    • 1991
  • This study tried to clear the characteristics of height growth pattern depending on Peak Height Velocity age in early, average and late groups. And in it, height growth tendency of girl students in age 7 to 18 years old was compared and investigated in order to know influencing factors, menarcheal age relation. The samples were senior girl students at high school in Seoul. Longitudinal data and survey data were collected in August, 1990. The results could be summarized as follows: 1. On distance curve, the height growth line in early group tended to be the highest and in late group the lowest. On the other hand, on velocity curve late group showed the highest peak and early group showed the lowest peak. In late group, velocity curve was too steep. Of course, these early, average and late groups were classified by PHV age. 2. In these three groups, late group showed the most growth amount per year. However, on distance curve, early group showed higher line than late group. Perhaps this means that peak growth amount in late group might have an effect on mean. 3. Growth amount of adolescence spurt age in these three groups was 6.86cm at age 9(early group), 7.27cm at l1(average group) and 7.65cm at 13(late group). In early group, because. PHV age came too early, it was difficult to find exact adolescence spurt period. In early group, the adolescence spurt period is considered to come at about age 7 to 9. In average group, at 9 to 11 and at 12 to 13 in late group. Especially, spurt of late group was remarkable. 4. When the growth amount of PA, before PA and after PA was compared, growth amount of PA in all three groups was about 20%. In early group, growth amount of APV tended to be large and in late group, that of APV tended to be large and in late group, that of BPV was large. In average group, growth amount of BPV was larger than that of APV. 5. For the purpose of comparing total height growth amount of these groups at age 18, the height growth was assumed to be over. And then, the difference of three groups was studied but it's not significant. 6. Although the difference between height growth and family environment, dietary habits, exercise, disease history in these three groups was investigated, only the income was significant. The significance of all the other factors was not approved. 7. When menarcheal age was compared with PA, generally we know menarche appeared after 1∼2 years of PHV age. But in case of early group, the difference between PHV age and menarcheal age was 5.34 years. In average group, 2.45 years and 0.82 years in late group.

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Cosmology with peculiar velocity surveys

  • Qin, Fei
    • 천문학회보
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    • 제46권2호
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    • pp.43.5-44
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    • 2021
  • In the local Universe, the gravitational effects of mass density fluctuations exert perturbations on galaxies' redshifts on top of Hubble's Law, called 'peculiar velocities'. These peculiar velocities provide an excellent way to test the cosmological model in the nearby Universe. In this talk, we present new cosmological constraints using peculiar velocities measured with the 2MASS Tully-Fisher survey (2MTF), 6dFGS peculiar-velocity survey (6dFGSv), the Cosmicflows-3 and Cosmicflows-4TF compilation. Firstly, the dipole and the quadrupole of the peculiar velocity field, commonly named 'bulk flow' and 'shear' respectively, enable us to test whether our cosmological model accurately describes the motion of galaxies in the nearby Universe. We develop and use a new estimators that accurately preserves the error distribution of the measurements to measure these moments. In all cases, our results are consistent with the predictions of the Λ cold dark matter model. Additionally, measurements of the growth rate of structure, fσ8 in the low-redshift Universe allow us to test different gravitational models. We developed a new estimator of the "momentum" (density weighted peculiar velocity) power spectrum and use joint measurements of the galaxy density and momentum power spectra to place new constraints on the growth rate of structure from the combined 2MTF and 6dFGSv data. We recover a constraint of fσ8=0.404+0.082-0.081 at an effective redshift zeff=0.03. This measurement is also fully consistent with the expectations of General Relativity and the Λ Cold Dark Matter cosmological model.

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Pb-20wt%Cu 합금의 일방향 응고시 Cu 수지상 결정성장에 대한 시험편의 회전효과 (The Effects of Sample Rotation on Cu-Dendritic Growth During the Directional Solidification of Pb-20wt%Cu Alloy)

  • 김신우
    • 한국주조공학회지
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    • 제14권6호
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    • pp.508-513
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    • 1994
  • For Pb-20wt%Cu alloys, severe macrosegregation due to density difference of the resulting phases in normal directional solidification has been minimized and a uniformly aligned dendritic structure has been produced by axially rotating the sample of 5mm diameter in conjunction with horizontal directional solidification. Under the constant growth velocity of $20{\mu}m/sec$, increasing the rotation rate from 0.18 to 12rpm results in a transition from an aligned columnar to an equiaxed Cu-dendritic structure. With a constant rotation rate of 0.18rpm, increasing the growth velocity from 10 to $50{\mu}m/sec$ also has promoted a transition from columnar to equiaxed structure.

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Numerical Analysis on the Flow Pattern in the Melt of Cold Model for the Czochralski system

  • Kim, Min-Cheol;Lee, Sang-Ho;Yi, Kyung-Woo
    • 한국결정성장학회:학술대회논문집
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    • 한국결정성장학회 1998년도 PROCEEDINGS OF THE 15TH KACG TECHNICAL MEETING-PACIFIC RIM 3 SATELLITE SYMPOSIUM SESSION 4, HOTEL HYUNDAI, KYONGJU, SEPTEMBER 20-23, 1998
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    • pp.113-116
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    • 1998
  • A numerical study was performed on the fluid flow in the melt of the cold model for Czochralski growth system. The fluid flow in the melt of Woods metal with crucible diameter of 20cm was calculated using a three dimensional finite difference method. Since the crucible size is large, fully turbulent model as well as laminar model was used in the calculation. The effects of crucible rotation rate, crystal rotation rate and wall temperature difference on the velocity and temperature distribution were also investigated. For the purpose of verifying the results of calculation, a cold model experiment using Woods metal was also conducted and the velocity distribution in the melt of the model was measured.

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PEM 연료전지의 단순화된 공기극 채널 내 단일 물방울의 성장 및 이동 특성에 대한 실험적 연구 (Experimental investigation of growth and transport behavior of single water droplet in a simplified channel of PEM fuel cell)

  • 김보경;김한상;민경덕
    • 한국신재생에너지학회:학술대회논문집
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    • 한국신재생에너지학회 2006년도 춘계학술대회
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    • pp.81-84
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    • 2006
  • To investigate the characteristics of water droplet on the gas diffusion layer from both upper-view and side-view of flow channel, a rig test apparatus was designed and fabricated with L-shape acryl plate in a $1mm{\times}1mm$ micro-channel. This experimental device is used to simulate the single droplet growth and its transport process under fuel cell operating condition. As a first step, we investigated the growth and transport of single water droplet with working temperature and air flow velocity. The contact angle and its hysteresis of water droplet at departing moment are measured and analyzed. It is expected that this study can provide the basic understanding of liquid water droplet behavior in gas flow channel and GDL interface during the PEM fuel cell operation.

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베타(Betta splendens)의 부화 후 로티퍼(Brachionus calyciflor)와 물벼룩(Moina macrocopa)의 섭취, 소화속도 및 성장 (The Rotifer Brachionus calyciflorus and Water Flea Moina macrocopa as Alternative Foods for Production of the Fighting Fish Betta splendens)

  • 권오남;박기영;박흠기
    • 한국수산과학회지
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    • 제46권4호
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    • pp.393-398
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    • 2013
  • The purpose of this study was to determine how an ornamental fish, such as the fighting fish, Betta splendens would respond to the use of freshwater live-prey, such as rotifers Brachionus calyciflorus and water fleas Moina macrocopa. Ingested quantity, digestive velocity and somatic growth were compared between larvae fed a freshwater rotifer and those fed boiled yolk. Food efficiency and somatic growth were compared between larvae that were fed freshwater water fleas and those fed a micro-diet developed for flounder ($250{\mu}m$, I-hwa Ltd.). The number of rotifers ingested by larvae reached a maximum of 191 per day. However, based on the number ingested per hour and the digestive velocity of consumed rotifers, the maximum ingestible and digestible number of rotifers was calculated to be 272 per day. A maximum of 67 individuals (mean, 49.8 individuals) could be completely digested within the 1-h period from 90 to 180 min after feeding. Somatic growth was enhanced in larvae that were fed rotifers compared to those fed boiled yolk. Larvae exhibited greater growth at rotifer densities of 30 and 40 per mL than at lower densities. Among the water-flea (M. macrocopa and Bosmina sp.) and micro-particle diets, feeding with M. macrocopa resulted in the greatest somatic growth of larvae during the water-flea feeding stage.