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Improvement and validation of a flow model for conical vortices
Jihong Ye,Xin Dong 한국풍공학회 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2
Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the correctedquasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.
Kim, Jihong,Khim, Dongyoon,Kang, Rira,Lee, Seung-Hoon,Baeg, Kang-Jun,Kang, Minji,Noh, Yong-Young,Kim, Dong-Yu American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.11
<P>Here, we report the simultaneous attainment of efficient electron injection and enhanced stability under ambient conditions for top-gate/bottom-contact (TG/BC), n-type, organic field-effect transistors (OFETs) using water-soluble polyfluorene derivatives (WPFs). When inserting the WPF interlayers between a semiconductor and the BC Au electrodes, initially the ambipolar (6,6)-phenyl-C<SUB>61</SUB>butyric acid methyl ester (PCBM) OFETs were fully converted to unipolar charge transport characteristics that were exclusively n-type with significantly increased electron mobilities as high as 0.12 cm<SUP>2</SUP>/(V s) and a decreased threshold voltage. These improvements were mostly attributed to the interfacial dipoles of WPF layers that aligned to form a favorable energy band structure for efficient electron injection and to effectively block counter charge carriers. These were confirmed when values for the reduced work function of metal electrodes with WPFs and their correlated contact resistance were measured via the ultraviolet photoemission spectroscopy and the transmission-line method, respectively. Moreover, the WPF interlayers played an important role in air stability of PCBM OFETs that exhibited higher and appreciably enhanced by increasing the ethylene-oxide side chain lengths of WPFs, which presumably was due to the water/oxygen/ion capturing effects in the hydrophilic interlayers.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-11/am500466q/production/images/medium/am-2014-00466q_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am500466q'>ACS Electronic Supporting Info</A></P>
Improvement and validation of a flow model for conical vortices
Ye, Jihong,Dong, Xin Techno-Press 2014 Wind and Structures, An International Journal (WAS Vol.19 No.2
Separation bubble and conical vortices on a large-span flat roof were observed in this study through the use of flow visualization. The results indicated that separation bubble occurred when the flow was normal to the leading edge of the flat roof. Conical vortices that occur under the cornering flow were observed near the leading edge, and their appearance was influenced by the wind angle. When the wind changed from along the diagonal to deviating from the diagonal of the roof, the conical vortex close to the approaching flow changed from circular to be more oblong shaped. Based on the measured velocities in the conical vortices by flow visualization, a proposed two-dimensional vortex model was improved and validated by simplifying the velocity profile between the vortex and the potential flow region. Through measured velocities and parameters of vortices, the intensities of conical vortices and separation bubble on a large-span flat roof under different wind directions were provided. The quasi-steady theory was corrected by including the effect of vortices. With this improved two-dimensional vortex model and the corrected quasi-steady theory, the mean and peak suction beneath the cores of the conical vortices and separation bubble can be predicted, and these were verified by measured pressures on a larger-scale model of the flat roof.
Off-axis Two-mirror System with Wide Field of View Based on Diffractive Mirror
Qingyu Meng,Jihong Dong,DONG WANG,Wenjing Liang 한국광학회 2015 Current Optics and Photonics Vol.19 No.6
An unobstructed off-axis two-mirror system is presented in this paper. First a suitable initial configurationis established based on third-order aberration theory. In order to achieve a wide field of view (FOV) withhigh image quality , the diffractive mirror is adopted in the two-mirror system to increase the optimizationfreedom and the aberration relationship between diffractive phase coefficients and Zernike coefficients isderived. Furthermore, a complete comparison design example with a focal length of 1200 mm, F-numberof 12, and FOV of 40° × 2° is given to verify the aberration correction ability of the diffractive mirror. The system average wavefront error is 0.007 λ (λ=0.6328 μm) developed from 0.061 λ when the systemdidn’t adopt the diffractive mirror. In this system the phase modulation function of the diffractive mirroris established as an even function of x, so we could obtain a symmetrical imaging quality about thetangential plane, and the symmetric aberration performance also brings considerable convenience toalignment and testing for the system
Sensitivity of Mid-latitude Typhoon Forecast to Multiple Physics Parameterization Dchemes
Jinyoung Park,Dong-Hyun Cha,Jihong Moon,Woojin Cho 한국기상학회 2021 한국기상학회 학술대회 논문집 Vol.2021 No.10
Recently, the frequency of typhoons affecting East Asia has been increasing due to climate change. In particular, some typhoons maintain their intensity before making landfall. However, even short-term typhoon predictions still have tens of kilometers of track errors or can not sufficiently simulate the rapid intensification (weakening) of typhoons. This can be a serious problem for people living in coastal areas when typhoons are active. In order to prevent the damage from typhoons in advance, it is necessary to improve the short-term forecast performance of typhoons. In numerical weather prediction models, the typhoon track and intensity forecast performances are highly sensitive to physics parameterization schemes. Thus, in this study, the forecast performance of a typhoon was compared according to the physics schemes using the Weather Research and Forecasting (WRF) model. The model is consisted of three domains with 12km (601x451), 4km (301x301), and 1.33km (301x301) horizontal resolutions (grid points), respectively. We used the two-way moving nesting technique for domains 2 and 3 to resolve the inner core structure of the typhoon realistically. To compare the sensitivity of physics settings to typhoon forecasting and their dissimilar reaction to the synoptic-scale weather phenomena, we selected three cumulus parameterization schemes (CPS) of Kain-Fritsch (KF), Betts-Miller-Janjic (BMJ), modified Tiedtke (TDK), and also three microphysics schemes (MPS) of WRF-single-moment-microphysics class 3 (WSM3), WRF-single-moment-microphysics class 6 (WSM6), Predicted Particle Properties (P3) 1-category. We selected 6 TCs that moved northward to mid-latitudes, and directly (or indirectly) affected the East Asia region in recent years. The results show that there was a significant difference in simulated typhoon track and intensity performances depending on the physics schemes. On average, the typhoon forecast performances were improved when applyingKF for CPS and WSM3 or WSM6 for MPS.