• Bulletin of the Korean Chemical Society
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• 제24권7호
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• pp.961-966
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• 2003

A quantum-chemical study of conformations and electronic structures of polyheterocyclic derivatives with vinylenediheteroatom substituents at the 3- and 4-positions was performed to search for novel blue-lightemitting conjugated polymers. Conformational potential energy curves of the polymers were constructed as a function of the helical angle (a) through semiempirical Hartree-Fock band calculations at the Austin model 1 level. It is found that poly(3,4-vinylenedioxythiophene) possesses a quite flat curve in the range of α = 51.4°- 120°. Replacing S atoms for O atoms greatly increases repulsion between the neighboring units, and thereby the units become perpendicular to one another. Because of the hydrogen bonding between O and NH, poly(3,4- vinylenedioxypyrrole) is predicted to be anti-coplanar and poly(3,4-vinylenediaminofuran) to be nearly anticoplanar. According to the modified extended Huckel band calculations, the HOMO-LUMO gaps (HLGs) of the polymers, unless the polymer chains are twisted, are close to or slightly smaller than those of their respective mother polymers. Among the polymers, poly(3,4-vinylenedioxythiophene) is presumed to be the most probable candidate for a blue-light emitter because its HLG is within the range of the electronic requirement for blue-light emitters.

• Advances in concrete construction
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• 제5권4호
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• pp.391-405
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• 2017

Cement acts as the most important component of concrete as it binds and holds the concrete together. But it is one of the major $CO_2$ emitters all over the world, during manufacturing (900 kg of $CO_2$ per 1000 kg). Some of the modern construction methods aim at reducing the amount of usage of cement and came out with numerous solutions for replacement of the same. One such supplement in current trend is the Steel dust or the Electric Arc Furnace Dust (EAFD), which is a waste product from the electric arc furnace when the scrap metal is melted. When the concrete containing steel dust is exposed to atmosphere, the environmental oxygen and moisture play role to form rust and ultimately the member becomes harder. As Cement is the binder of conventional concrete, only certain percentage of the same could be replaced by the new material, steel dust. Tests were conducted for the 28 days cube strength of M45 grade (suitable for prestressing) concrete which has 0%, 10%, 20%, 30%, 40% and 50% steel dust instead cement. From the test, the optimum percentage replacement of steel dust was obtained, for which the beams and overhead poles were cast, prestressed and tested for the failure load and deflections. A conventional concrete beam and overhead pole were also cast, prestressed and tested to compare the results with those of the beam and pole that contained steel dust. The load vs. deflection plot and other results from the test is also discussed.

• 반도체디스플레이기술학회지
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• 제9권4호
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• pp.7-12
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• 2010

Field-emission characteristics of carbon nanotubes(CNTs), which were grown on conical-type tungsten micro-tips by using an electrophoretic deposition(EPD) method, were examined. The EPD method proved to be convenient to manipulate and arrange CNTs from well dispersed suspensions onto such tip-type substrates. The growth rate of CNTs was proportional to the applied d.c. bias voltage and the process time. It was observed from the Raman study that the EPDproduced CNTs showed better crystal qualities with the Raman intensity ratio( $I_D$/$I_G$) of 0.41-0.42 than the CVD-produced CNTs and their crystal qualities could be further improved by thermal annealing. The electron emitters based on the EPDCNTs showed excellent field emission properties, such as the threshold voltage for electron emission of about 620 V and the maximum emission current of about 345 ${\mu}A$. In addition, the EPD-CNTs exhibited the stable long-term(up to 40 h) emission capability and the emission stability was enhanced by thermal annealing.

• Bulletin of the Korean Chemical Society
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• 제34권8호
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• pp.2267-2270
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• 2013

A series of blue fluorescent emitters based on triphenylene derivatives were synthesized via the Diels-Alder reaction in moderate yields. The electronic absorption and emission characteristics of the new functional materials were affected by the nature of the substituent on the triphenylene nucleus. Multilayered OLEDs were fabricated with a device structure of: ITO/NPB (50 nm)/EML (30 nm)/Bphen (30 nm)/Liq (2.0 nm)/Al (100 nm). All devices showed efficient blue emissions. Among those, a device using 1 gives the best performances with a high brightness (978 cd $m^{-2}$ at 8.0 V) and high efficiencies (a luminous efficiency of 0.80 cd/A, a power efficiency of 0.34 lm/W and an external quantum efficiency of 0.73% at 20 $mA/cm^2$). The peak wavelength of the electroluminescence was 455 nm with CIEx,y coordinates of (0.17, 0.14) at 8.0 V.

• 천문학회지
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• 제36권3호
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• pp.123-144
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• 2003

The 8m class telescopes in the ground-based optical astronomy together with help from the ultra-sharp eye of the Hubble Space Telescope have enabled us to observe forming galaxies beyond red shift z = 5. In particular, more than twenty Ly$\alpha$-emitting galaxies have already been found at z > 5. These findings provide us with useful hints to investigate how galaxies formed and then evolved in the early universe. Further, detailed analysis of Ly$\alpha$ emission line profiles are useful in exploring the nature of the intergalactic medium because the trailing edge of cosmic reionization could be close to z $\~$ 6 -7, at which forming galaxies have been found recently. We also discuss the importance of superwinds from forming galaxies at high redshift, which has an intimate relationship between galaxies and the intergalactic medium. We then give a review of early cosmic star formation history based on recent progress in searching for Ly$\alpha$-emitting young galaxies beyond red shift 5.

• 천문학논총
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• 제30권2호
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• pp.433-437
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• 2015

We show the results of a time series analysis of the long-term light curves of four blazars. 3C 279, 3C 345, 3C 446, and BL Lacertae. We used densely sampled light curves spanning 32 years at three frequency bands (4.8, 8, 14.5 GHz), provided by the University of Michigan Radio Astronomy Observatory monitoring program. The spectral indices of our sources are mostly flat or inverted (-0.5 < ${\alpha}$ < 0), which is consistent with optically thick emission. Strong variability was seen in all light curves on various time scales. From the analyses of time lags between the light curves from different frequency bands and the evolution of the spectral indices with time, we find that we can distinguish high-peaking flares and low-peaking flares according to the Valtaoja et al. classification. The periodograms (temporal power spectra) of the light curves are in good agreement with random-walk power-law noise without any indication of (quasi-)periodic variability. We note that random-walk noise light curves can originate from multiple shocks in jets. The fact that all our sources are in agreement with being random-walk noise emitters at radio wavelengths suggests that such behavior is a general property of blazars. We are going to generalize our approach by applying our methodology to a much larger blazar sample in the near future.

• Journal of Information Display
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• 제6권4호
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• pp.45-48
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• 2005

By applying a critical field treatment instead of the conventional surface treatments such as soft rubber roller, ion beam irradiation, adhesive taping, and laser irradiation, electron emission properties of screen-printed carbon nanotubes (CNTs) were enhanced and investigated based on the emission current-voltage characteristics through scanning electron microscopy. After nanotube emitters were activated at the applied electric-field of 2.5 V/um, the electron emission current density with good uniform emission sites reached the value of 2.13 mA/$cm^2$ , which is 400 times higher than that of the untreated sample, and the turn-on voltage decreased markedly from 700 to 460 V. In addition, enhancement of the alignment of CNTs to the vertical direction was observed.

• Journal of Information Display
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• 제12권1호
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• pp.51-55
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• 2011

Efficient two-color-mixed white organic light-emitting diodes are presented herein by employing a sky-blue phosphorescent dopant of iridium(III)bis[4,6-(difluorophenyl)-pyridinato-N,$C^{2'}$]picolinate (FIrpic) and an orange phosphorescent dopant of bis(2-phenylquinoline)(acetylacetonate)iridium(III) ($Ir(phq)_2$acac) on the emissive layer. Very stable color variation under ${\Delta}$0.02 until a 5000 cd/$m^2$ brightness value was realized by efficient carrier control in a multi-stacked emitting layer of blue/red/blue colors. Maximum current and power efficiencies of 23.8 cd/A and 22.9 lm/W in the forward direction were obtained. With balanced emission from the two emitters, the white-light emission of high correlated color temperature of 7308K and the Commission Internationale de I'Eclairage coordinates of (0.30, 0.33) were achieved.

• 한국농공학회논문집
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• 제54권3호
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• pp.19-28
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• 2012

Greenhouse cultivation has been increasing for high quality and four season crop production in South Korea. For the cultivation in a greenhouse, maintaining adequate soil moisture at each crop growth stage is quite important for yield stability and quality while the behavior of moisture movement in the soil has complexity and adequate moisture conditions for crops are vary. Drip irrigation systems have been disseminated in the greenhouse cultivation due to advantages including irrigation convenience and efficiency without savvy consideration of the soil moisture redistribution. This study aims to evaluate soil moisture movement of drip irrigation according to the soil moisture uniformity assessment. Richards equation and finite difference scheme were adapted to simulate soil moisture behavior in soil. Soil container experiment was conducted and the model was validated using the data from the experiment. Two discharge rate (1 ${\ell}/hr$ and 2 ${\ell}/hr$) and three spaces between the emitters (10 cm, 20 cm, and 30 cm) were used for irrigation system evaluation. Christiansen uniformity coefficient was also calculated to assess soil moisture redistribution uniformity. The results would propose design guidelines for drip irrigation system installation in the greenhouse cultivation.

• 전기학회논문지
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• 제61권7호
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• pp.1001-1006
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• 2012

This paper presents a carbon nanotube (CNT) triode-structure field emitter as an ion source in a micro time-of-flight mass spectrometer(TOF-MS). In the ion source by field emission, the electrons emitted from cathodes under an electric field accelerated to the anode and ionize gas molecules by impact before arriving the anode. The generated positive ions are to be accelerated to the ion collector. Whereas most of ions are drawn to the cathodes in diode field emitters, a grid in the triode field emitter prevents the ions from being drawn to the cathodes. The triode field emitter is fabricated by micromachining. The cathode is composed of six CNT cylinders. The total size of the fabricated device is $8.0{\times}7.3{\times}1.9mm^3$. The anode and the grid current of the fabricated CNT field emitter were measured for various anode and grid voltages. When the anode and the grid voltages are 1000 V and 990 V, respectively, the emission current passing through the ionization region is 8.6 ${\mu}A$, which is a sufficient emission current for ionization and mass spectrometry.