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Hydrogels with embedded functional particulates are widely used to create soft materials with innovative functionalities. In order to advance these soft materials to functional devices and machines, critical technical challenges are the precise positioning of particulates within the hydrogels and the construction of the hydrogels into a complex geometry. Inkjet printing is a promising method for addressing these challenges and ultimately achieving hydrogels with voxelized functionalities, so-called digital hydrogels. However, the development of the inkjet printing process primarily relies on empirical optimization of its printing and curing protocol. In this study, a general scaling law is proposed to predict the transport of particulates within the hydrogel during inkjet printing. This scaling law is based on a hypothesis that water-matrix interaction during the curing of inkjet-printed particle-laden polymeric drops determines the intra-drop particle distribution. Based on the hypothesis, a dimensionless similarity parameter of the water-matrix interaction is proposed, determined by the hydrogel's water evaporation coefficient, particle size, and mechanical properties. The hypothesis was tested by correlating the intra-drop particle distribution to the similarity parameter. The results confirmed the scaling law capable of guiding ink formulation and printing and curing protocol.

The field of printed electronics for highly integrated circuits and energy devices demands very fine and highly conductive electric interconnections. In this study, conductive lines having a high cross-sectional aspect ratio were printed via the inkjet printing of Ag nanoparticle inks assisted by a laser-induced selective surface wetting technique: a hydrophobic layer of self-assembled monolayer-treated ZnO nanorods was coated on a glass substrate and selectively ablated by a laser to form micro-channels for the inkjet, whose surface energy changed from 36.3 mJ/m2 to 51.5 mJ/m2 before and after the laser irradiation. With the varying width of the laser-ablated channels and pitch of jetted ink drops, the 3D shapes of the printed silver lines were measured to investigate their effects on the widths, heights, and uniformities of the printed patterns. The results showed that the present technique realized a uniform line of 35 μm width and 0.46 μm average thickness, having an aspect ratio of 0.013, which is 7.6 times higher than that printed on bare glass.

Simultaneous meteor radar, MLS, and MERRA observations show that the Antarctic mesopause cooled to 26 K, in response to a 66 K warming in the stratosphere during the 2019 minor sudden stratospheric warming (SSW) in the Southern Hemisphere. Depressed gravity wave (GW) activity and the enhanced upward propagation of 10-day planetary waves (PWs) are prominent during SSWs. We observed an enhancement in carbon monoxide through carbon dioxide (CO2) photolysis and a decrease in ozone (O3) at 75 km during peak SSW. Hence, mesospheric cooling (MC) is due to the combined effects of PWs, CO2 infrared cooling, and O3 depletion but not the adiabatic cooling of GWs. PW analysis suggests that the chemical tracers that induced MC were uplifted from the lower atmosphere by anthropogenic and other sources and propagated through meridional circulation. Thus, the polar mesosphere was significantly affected by the 2019 SH SSW. Simultaneous meteor radar, MLS, and MERRA observations show that the Antarctic mesopause cooled to 26 K, in response to a 66 K warming in the stratosphere during the 2019 minor sudden stratospheric warming (SSW) in the Southern Hemisphere. Depressed gravity wave (GW) activity and the enhanced upward propagation of 10-day planetary waves (PWs) are prominent during SSWs. We observed an enhancement in carbon monoxide through carbon dioxide (CO2) photolysis and a decrease in ozone (O3) at 75 km during peak SSW. Hence, mesospheric cooling (MC) is due to the combined effects of PWs, CO2 infrared cooling, and O3 depletion but not the adiabatic cooling of GWs. PW analysis suggests that the chemical tracers that induced MC were uplifted from the lower atmosphere by anthropogenic and other sources and propagated through meridional circulation. Thus, the polar mesosphere was significantly affected by the 2019 SH SSW. &nbsp

We studied the effect of current supply duration at final-step currents during the stepwise electrical sintering of silver (Ag) nanoparticles (NPs). Ag NPs ink was inkjet-printed onto Eagle-XG glass substrates. Constant final-step currents of 0.4 and 0.5 A with various time intervals were applied to the printed samples. The final-step current of 0.5 A damaged the line at a comparatively shorter time duration. On the other hand, the lower final-step current of 0.4 A prevented the line damage at longer time durations while producing comparatively lower Ag NPs specific resistance. The minimum specific resistances of the printed samples sintered at 0.4 and 0.5 A were 3.59 μΩ∙cm and 3.79 μΩ∙cm, respectively. Furthermore, numerical temperature estimation and scanning electron microscope (SEM) analysis were conducted to elaborate on the results. The numerical temperature estimation results implied that the lower estimated peak temperature at the final-step current of 0.4 A helped prevent Ag NP line damage. The SEM micrographs suggested that a high surface porosity—caused by higher sintering peak temperatures—in the case of the 0.5 A final-step current resulted in a comparatively higher Ag NP line-specific resistance. This contribution is a step forward in the development of Ag NP sintering for printed electronics applications.

We analysed all-sky camera images observed at Mt. Bohyun observatory (36.2∘ N, 128.9∘ E) for the period 2017–2019. The image data were acquired with a narrowband filter centred at 557.7 nm for the OI airglow emission at ∼ 96 km altitude. A total of 150 wave events were identified in the images of 144 clear nights. The interquartile ranges of wavelength, phase speed and periods of the identified waves are 20.5–35.5 km, 27.4–45.0 m s−1 and 10.8–13.7 min with the median values of 27.8 km, 36.3 m s−1 and 11.7 min, respectively. The summer and spring bias of propagation directions of north-eastward and northward, respectively, can be interpreted as the effect of filtering by the prevailing winds in the lower atmosphere. In winter the subdominant north-westward waves may be observed due to a nullified filtering effect by slow northward background wind or secondary waves generated in the upper atmosphere. Intrinsic phase speeds and periods of the waves were also derived by using the wind data simultaneously observed by a nearly co-located meteor radar. The nature of vertical propagation was evaluated in each season. The majority of observed waves are found to be freely propagating and thus can be attributed to wave sources in the lower or upper atmosphere.

Owing to its unique properties, silver (Ag) in the form of nanoparticle (NP) ink promises to play a vital role in the development of printed and flexible electronics. Once printed, metal NP inks require a thermal treatment process called sintering to render them conductive. Among the various methods, electrical sintering is a highly selective and rapid sintering method. Here, we studied the electrical sintering of inkjet-printed Ag NP lines via a stepwise current increment sintering (SCIS) technique. In the SCIS technique, the supplied electric current was gradually increased in multiple steps from low electric currents to higher electric currents to avoid thermal damage to the printed Ag NP ink lines. In less than 0.15 s, a line resistivity as low as 6.8 μΩcm was obtained which was comparable with furnace sintered line resistivity of 6.13 μΩcm obtained at 250 °C in 600 s. Furthermore, a numerical model was developed for the SCIS process temperature estimation. The results enabled us to elaborate on the relationship between the Ag NP line resistivity and the process temperature under various electric currents. Under the applied SCIS technique, a stable sintering process was carried out avoiding the conductive ink line and substrate damage.

During the thermal sintering of metal nanoparticles (NPs) the process temperature plays the most important role in the outcome of the sintering results and the selection of a suitable substrate. Here, temperature calculation during pulsed laser sintering of silver (Ag) nanoparticles (NPs) inkjet-printed on glass substrates is presented. During the pulsed laser sintering of Ag NPs, a minimum line resistivity less than twice the bulk silver resistivity was obtained within around 52 s under a laser power of 276 mW. The temperature field during the pulsed laser sintering of Ag NPs was estimated via a three-dimensional numerical model in which a temperature-dependent thermal conductivity of Ag NPs was adopted. An algorithm for treating the thermal conductivity of the heated Ag NPs in a region by a previous laser shot was devised for the improvement of the temperature field estimation. A maximum temperature of approximately 204 °C over the Ag NPs line was obtained with a 276 mW laser power and a scanning speed of 135 μm/s.

In this study, we introduce a thermal sintering process using a heated inert gas as a new sintering method. The heated gas flow is formed by passing nitrogen (N2) gas through a heating head of 300 to 700 °C, and the desired substrates are then exposed to the heated gas flow through a 400 mm long and 5 mm wide slit-nozzle. Sintering performance of Ag films was characterized by analyzing the electrical resistivity and metallographic structures according to the temperature change of the heating head. The temperature distribution of the heating region is analyzed by infrared (IR) thermal imaging and surface temperature measured by thermo-label tape. To test the feasibility of the proposed method for application to printed circuit board (PCB) manufacturing, we performed a reliability evaluation using the printed Ag patterns under the standard of the Institute for Interconnecting and Packaging Electronic Circuit (IPC), TM650. Various reliability test patterns were created by Ag inkjet-printing on both a rigid flame retardant 4 (FR4) substrate and a flexible polyimide (PI) film substrate. The reliability evaluation includes withstanding voltage, adhesive strength, thermal shock, pressure cooker, and bending tests. The surface wettability of the substrates was controlled to obtain high quality fine and uniform patterns by UV/O3 treatment after coating a fluoropolymer thin film.

The working principle of air-lift pumps can be applied to Direct carbon fuel cell (DCFC) systems, which can handle high-temperature molten coal-laden carbonate fuels. In this study, the pumping performance and essential hydrodynamic features of an air-lift pump with high submergence ratio are studied experimentally. Liquid anode media composed of a mixture of carbonaceous fuels and molten carbonates that surround solid-oxide electrolyte tubular cells in DCFC systems are considered. In this system, a certain amount of CO2 is injected into the liquid fuel media not only to prevent carbonate decomposition, but also to recirculate or transport fuel media. CO2 injection is essential to stabilize the system and enhance reaction. Water and air are selected as simulants of molten fuel and CO2, respectively. Then, a blunt body is inserted into the single hollow tube (Model system), which is then shaped as a tubular cell. Air, which is supplied from the bottom of the tube, flows up in the shape of a bubble and entrains water inside the tube. Then, water is discharged. The flow rate of the water discharged from the top of the tube is measured using the following parameters: Tube diameter, blunt-body diameter, and submergence ratio. Bubble pattern formations in the tube are also observed by varying parameter combinations. Four to five distinct bubble patterns can be observed depending on air flow rate comparisons. The discharge flow rates from the blunt-body-insertion tube are correlated with those from the hollow tube. Finally, two tube parameters, namely, the same cross-sectional flow areas and the same hydraulic diameters, are considered. Good correlations were established for the flow area parameter.

The temperature effect on the electrical characteristics and surface morphology of printed silver ink was investigated for laser irradiation with various laser scanning speeds and intensities. Inkjet-printed silver lines onto a glass substrate were irradiated with a 532 nm continuous wave. The electrical resistance was measured after laser sintering with various scanning speeds and intensities. The temperature field was invoked in the printed silver ink line by laser scanning sintering and this was predicted by numerical analysis. This temperature field show a quasi-steady state behavior since laser irradiation can be considered as a moving heat source. Field emission scanning electron microscope images were then examined with calculated temperatures of printed silver ink. The relation of surface morphology with temperature field were discussed. The effect of a laser scanning speed on the specific resistance of the conductive ink line was intensively investigated.

The present study aims to characterize and understand the dropwise gelation-dehydration phenomena during drop-on-demand (DOD) printing of hydrogel-based soft materials. Functional soft materials have broader impacts on many medical and engineering applications, but constructing soft materials into three-dimensional (3D) configuration with spatially varying properties is still extremely challenging. In order to establish a mechanistic understanding, a hypothesis was postulated that the porosity of hydrogel printed is determined by dropwise gelation and dehydration phenomena during the printing process. The underlying rationale is that many functional properties of the printed hydrogels are closely associated with the structural characteristics at the sub-droplet and droplet scales, specifically porosity. The porosity of a hydrogel droplet is thought to be determined by intra-droplet fluid–structure interactions during gelation and dehydration. In this study, thus, we characterized the gelation-dehydration and consequent microstructure of thermally responsive poly(N-isopropylacrylamind-co-acrylamide) (PNIPAM) copolymer droplets as a model hydrogel material. The gelation kinetics was studied by differential scanning calorimetry. Both macroscopic and microscopic structures of DOD printed hydrogels were characterized by a 3D profiler and scanning electron microscopy. Furthermore, a theoretical model to explain this complex transport processes was also developed. The results showed that the gelation is a rapid process and its impact is mainly observed at the deposition of droplets. Significant structural shrinkage of the printed hydrogel droplets was induced by dehydration. This shrinkage resulted in spatially varying intra-droplet porosity. A computational model of intra-droplet fluid–structure interactions was developed to explain this spatial variation of intra-droplet porosity. In addition, a new dimensionless parameter is proposed to gauge the significance of evaporation and interstitial water transport in the fluid–structure interactions. Significance of gelation kinetics, dehydration and complex fluid–structure interaction within the droplets was discussed to design a DOD printing process for 3D additive manufacturing of hydrogel-based soft materials.

We demonstrate the enhanced optical and electrical properties of an ultrathin silver (Ag) film by applying an aluminum (Al) seed layer between LiF and Ag as a transparent cathode for higher-transparency organic light-emitting diodes (OLEDs). Although the thickness ranges from 4 to 8 nm, the ultrathin Ag film is a continuous and uniform bulk-like film with an Al seed layer, which suppresses the surface plasmon absorption. Compared to an Ag-only cathode, the measured transmittance spectra were considerably increased, comparable with the theoretical calculations of a bulk Al/Ag bilayer film. The Al/Ag bilayer cathode has a transmittance of 87% at a 550 nm wavelength and a sheet resistance of 19.5 Ω/sq with a 4-nm-thick Ag layer. The transparent OLED devices that employed the Al/Ag cathode showed a transmittance of 72% at a 550 nm wavelength for an Ag thickness of 6 nm.

A three-bit flash analog-to-digital converter (ADC) consisting of inverter-based comparators and logic gates using amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO TFTs) was developed. The TFT has a bottom gate structure with a methyl-siloxane-based organic spin-on-glass passivation layer, which reduces the plasma damage on the active layer. A bootstrapped logic gate structure was used in the proposed ADC to overcome the reduced output swing in the inverters and the NAND gates caused by using only n-type a-IGZO TFTs. The output signals of the developed three-bit flash ADC with a-IGZO TFTs well matched the analog inputs. The output voltage swing was 0.2–3.6 V, well matching the simulation result. The three-bit flash ADC was verified up to the 1 kHz operation frequency, and thus can be used in sensor applications such as the wearable sensor display and the integrated biosensing platform.

The characteristics of gasification reactions for carbon–carbonate mixtures were experimentally investigated at high temperatures up to 900 °C, considering the application of the mixtures to the external anode media of a direct carbon fuel cell. A thermo-gravimetric analysis (TGA) was conducted in either a nitrogen or carbon dioxide ambient environment for Li 2 CO 3 , K 2 CO 3 and a mixture of these two substances with carbon black. Changes in the exit gas composition were also monitored during the heating process. It was shown that gasification in the mixture media occurs much more rapidly than carbonate decomposition at elevated temperatures, even for low concentrations of CO 2 . It was also shown that the loading of carbonates to carbon significantly affects the global gasification reaction; it increased the reaction rate by an order of magnitude and decreased its activation energy. Based on the experimental observations, a simplified reaction model of gasification was suggested for the anode media of a DCFC, regarding carbonate-catalysed and metal-catalysed pathways of Boudouard reactions.

Hydrogel-based soft materials have been used in numerous applications in healthcare, food, pharmaceutical, and cosmetic industries. Manufacturing hydrogels whose functional properties and compositions are voxelized at superior spatial resolutions can significantly improve current applications as well as will enable a new generation of soft materials. However, it remains challenging to control the structure and composition of soft materials reliably. In this context, the drop-on-demand (DOD) printing of hydrogels shows excellent potential to address this manufacturing challenge. Despite this potential, a lack of mechanistic understanding of the behavior of printed hydrogel drops makes it challenging to design and optimize DOD printing protocols for a wide variety of hydrogels. In particular, the curing of hydrogel drops, which requires dehydration of printed hydrogel drops, is poorly understood. In this study, thus, a hypothesis was postulated and tested that water-matrix interaction at drop-drop interfaces during curing processes determine the quality of hydrogels printed. Both computational and experimental studies were performed to establish a mechanism of the water-matrix interaction within printed hydrogel drops. The results were further discussed to establish a dimensionless similarity parameter that can characterize water transports during the hydrogel dehydration process.

Drop-on-demand (DOD) electrohydrodynamic (EHD) jet printing uses a nozzle and pulsated electric fields to eject small ink droplets of functional material to the appointed spot of a substrate at the appointed time, which offers solutions of high resolution patterning for fabrication of printed electronics, bioengineering, and display. Because the EHD jet connects fine drops to yield a fine pattern, it is essential to realize high throughput by generating drops quickly and reliably. In this study, the characteristics of jetting frequency were experimentally investigated as a function of nozzle dimensions by measuring response of jetting frequency to pulsating frequency which is varying from 1 Hz to 2000 Hz. The results showed that, even when the nozzle diameter is the same, the other dimensions of the nozzle significantly change the response of jetting to high pulsating frequency. Using a linear damping model describing hydrodynamic motion of ink inside the nozzle, the different behavior of the jetting frequency was explained via the different damping ratio of the oscillating ink: contrary to an underdamped system, an overdamped system supports a jetting frequency higher than the natural frequency.

In this study, the sintering behavior of silver (Ag) nanoparticle inks was investigated when different particle sizes and sintering methods were employed. Ag nanoparticle inks with two different particle sizes were investigated with average particle diameters of 12 nm and 50 nm. The two kinds of Ag nanoparticle inks were inkjet-printed onto glass substrates. The printed inks were sintered by a furnace and a continuous wave (CW) laser at a wavelength of 532 nm. The specific resistance and surface morphology of the Ag nanoparticle (Ag NP) inks were investigated under various furnace temperatures, laser intensities, and time durations. The ex situ specific resistance of each Ag NP ink was measured by a multimeter to determine the effects of various sintering conditions such as the furnace temperature, laser intensity, and sintering duration. To investigate the correlation between the specific resistance and surface morphology of the Ag NP inks, field emission scanning electron microscopy images were obtained. In addition, the effect of the particle size on the specific resistances of the inks annealed by the furnace and CW laser was evaluated.

We introduce a process for the fabrication of a paper-based analytical device (PAD) for multiple colorimetric analysis via paper- cutting and inkjet-printing. To create the selective flow channels, hydrophobic barriers were formed by using hydrophobic polyvinyl chloride tape-cutting and ultraviolet-curable resin printing. Multiple paper channels were isolated by the hydrophobic barriers on a single chip. An assay model was created from bovine serum albumin (BSA) and tetrabromophenol blue (TBPB) to verify the feasibility of the fabricated PAD. A multiple colorimetric analysis was demonstrated a reaction with different BSA concentrations after the TBPB regent was elaborately deposited onto the circular test spot areas by inkjet printing.

In printed electronics applications, specific resistances of conductive lines are critical to the performance of the devices. The specific resistance of a silver (Ag) nanoparticle electrode is affected by surface morphology of the layered nanoparticles which were sintered by the heat treatment after printing. In this work, the relationship between surface morphology and specific resistance was investigated with various sintering temperatures and various layer thicknesses of Ag nanoparticle ink. Ag nanoparticles with an average size of approximately 50 nm were spin-coated on Eagle XG glass substrates with various spin speed to change the layer thickness of Ag nanoparticles from 200 nm to 900 nm. Coated Ag nanoparticle layers were heated from 150°C to 450°C for 30 min in a furnace. The result showed that higher sintering temperature produces larger grains in an Ag layer and decreases specific resistance of the layer, but that the maximum allowable heating temperature is limited by the thickness of the layer. When grain size exceeded the thickness of the layer, the morphology of the Ag nanoparticles changed to submicron-sized islands and the Ag layers did not have electrical conductivity any more.

A threshold voltage compensation pixel circuit was developed for active-matrix organic light emitting diodes (AMOLEDs) using amorphous indium-gallium-zinc-oxide thin-film transistors (a-IGZO-TFTs). Oxide TFTs are n-channel TFTs; therefore, we developed a circuit for the n-channel TFT characteristics. The proposed pixel circuit was verified and proved by circuit analysis and circuit simulations. The proposed circuit was able to compensate for the threshold voltage variations of the drive TFT in AMOLEDs. The error rate of the OLED current for a threshold voltage change of 3 V was as low as 1.5%.

A direct carbon fuel cell (DCFC) generates electricity directly by converting the chemical energy in coal. In particular, a DCFC system with a solid oxide electrolyte and molten carbonate anode media has been proposed by SRI. In this system, however, there are conflicting effects of temperature, which enhances the ion conductivity of the solid electrolyte and reactivity at the electrodes while causing a stability problem for the anode media. In this study, the effect of temperature on the stability of a carbon-carbonate mixture was investigated experimentally. TGA analysis was conducted under either nitrogen or carbon dioxide ambient for Li2CO3, K2CO3, and their mixtures with carbon black. The composition of the exit gas was also monitored during temperature elevation. A simplified reaction model was suggested by considering the decomposition of carbonates and the catalyzed Boudouard reactions. The suggested model could well explain both the measured weight loss of the mixture and the gas formation from it.

Copper nanoparticles are preferred as a printable conductive material in printed electronics because they cost less than noble nano particles such as gold and silver. Only disadvantage is that copper is easily oxidized, which may deteriorate the conductivity. Copper is thermodynamically unstable at atmospheric condition and is easily oxidized into either Cu2O or CuO, both of which are less conductive compared to pure copper. To alleviate these problems, we propose a sintering process using laser in the study. The laser source in this study is a laser having 532 nm wavelength and 5 W maximum output power. The size of used copper particle is 100∼120 nm. In order to measure the absorptivity at 532 nm, UV visible-spectrometer was used. Copper nano ink was spin-coated on the glass substrate, and various irradiated laser powers and scan rates were applied in air. The resistivity of the conductive film, after laser sintering under the condition of air, was below 5.3 μΩcm which was three times as much as that of bulk copper.

The morphologies of inkjet-printed narrow silver lines on fluorocarbon film-coated glass substrates were measured with varying contact angles and drop spacing to study the actual stability of line printing by using a practical inkjet system. From a practical stability point of view, three types of the lines were observed: stable, unstable, and meta-stable. The stable lines were free from any bulging or breaking; the unstable lines had repetitive and periodic instabilities; and the meta-stable lines had no repetitive instability but had irregular bulges that appear sparsely. Unstable line printing resulted from either the dynamic or static instability of bead flow, which arose when the pressure-driven bead flow was too large or too small compared with droplet deposition rate, respectively. Whether the printing would be stable or meta-stable was determined by the anti-bulging stability of the flow against other disturbances. The anti-bulging stability increased when the bead flow rate was balanced with the printing rate, whereas it decreased for the present system when the flow-balance became sensitive to drop spacing.

Air-lift pump can pump liquid and sediments in it by using air-induced lift force. This working principle can be applied to direct carbon fuel cell (DCFC) to carry or transport high-temperature molten fuel or carbonate in the DCFC system. For this application, pumping performance and essential hydrodynamic features of air-lift pump with high submergence ratio are investigated experimentally. In this study, a model system of air-lift pump is designed and made for this purpose, where air is supplied from the bottom of the tube, flows up with a shape of bubble formed, entrains water inside the tube, and discharges it. Flow rate of water discharged from the top is measured with two variable parameters of tube diameter and submergence ratio. Bubble patterns formed in the tube are observed with various combinations of the two parameters and show four distinct patterns depending on air flow rate. A theoretical model is employed to predict discharge flow rate and it is comparable with the experimental results in slug-flow regime. Cracking flow rate, at which discharge of water is initiated, increases as tube diameter increases and submergence ratio decreases. The flow-rate ratio of water to air, i.e., pumping effectiveness, provides a feasible operating range of air-lift pump in terms of the two parameters.

In this work, an experiment on furnace thermal sintering with printed silver (Ag) nanoparticle ink was carried out. The Ag nanoparticle ink employed in this study has a particle size of around 50 nm and particles constitute 34 wt% of the ink. The Ag nanoparticle ink was printed by inkjet printing. A thermal sintering process in a furnace was conducted at temperatures of 150, 200, and 250 degrees C for 20 to 3000 seconds. After sintering, electrical conductivities and cross-sectional images were measured. The specific resistance and the cross-sectional area of the sintered ink decrease as the sintering temperature increases. The SEM images indicate that surface premelting caused sintering below the melting temperature of silver, 960 degrees C, which increased neck growth and lowered the electrical resistance. Lastly, the minimum specific resistance of 7.08 microOmgega x cm was obtained after sintering for 3000 s at 250 degrees C. This specific resistance value was 4.4 times larger than that of bulk silver.

An airlift pump can be used to pump liquids and sediments within itself, which cannot easily be pumped up by a conventional method, by using the airlift effect. This characteristic of the airlift pump can be exploited in a DCFC (Direct Carbon Fuel Cell) so that molten fuel with high temperature may be carried or transported. The basic characteristics of airlift are investigated. A simple system is constructed, where the reservoir is filled with water, a tube is inserted, and air is supplied from the bottom of the tube. Then, water is lifted and its flow rate is measured. Bubble patterns in the tube are observed in a range of air flow rates with the parameters of the tube diameter and submergence ratio, leading to four distinct regimes. The pumping performance is predicted, and the correlation between the supplied gas flow rate and the induced flow rate of water is found.

AZO (aluminum-doped zinc oxide) is one of the best candidate materials to replace ITO (indium tin oxide) for TCOs (transparent conductive oxides) used in flat panel displays, organic light-emitting diodes (OLEDs), and organic solar cells (OSCs). In the present study, to apply an AZO thin film to the transparent electrode of an organic solar cell, a low-temperature selective atomic layer deposition (ALD) process was adopted to deposit an AZO thin film on a flexible poly-ethylene-naphthalate (PEN) substrate. The reactive gases for the ALD process were di-ethyl-zinc (DEZ) and tri-methyl-aluminum (TMA) as precursors and H2O as an oxidant. The structural, electrical, and optical characteristics of the AZO thin film were evaluated. From the measured results of the electrical and optical characteristics of the AZO thin films deposited on the PEN substrates by ALD, it was shown that the AZO thin film appeared to be comparable to a commercially used ITO thin film, which confirmed the feasibility of AZO as a TCO for flexible organic solar cells in the near future.

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

본 연구에서는 전도성 잉크의 레이저 열경화 공정시 은 나노입자 잉크의 레이저 열경화 공정 온도를 수치해석하였다. 유리기판 위에 잉크젯 프린팅을 이용하여 인쇄한 은 나노 입자 잉크를 532 nm 파장의 CW 레이저를 각기 다른 세기로 60 초 동안 조사하여 가열하였다. 온도계산을 위해서, 열생성항에 들어가는 반사율을 구하였고, 레이저 조사 중 실시간 은 나노입자 잉크의 비저항을 측정하였다. 온도 계산은 2 차원 열전도 방정식에 Wiedemann-Franz law 를 적용하였다. 그 결과, 레이저 조사로 인해 인쇄된 잉크의 온도가 상승할수록 비저항이 떨어지는 결과를 확인하였다.

The fingerprint pixel sensor array was investigated for the application to the mobile phone. For the fingerprint sensing high resolution pixel array is necessary. Therefore, the readout voltage dependence on the resistance of the wires was investigated after composing 450th pixel array. The readout voltage was investigated for the ridge contact and valley contact. The simulated results show that the transparent electrode wire can be applied for the fingerprint pixel sensor array.

Key Words: Membrane Humidifier(막가습기), PEMFC System(PEMFC 시스템), Nafion Tubes(나피온튜브),Local Water Mass Flux(국소물질량유속)초록: 실험과수치해석을이용하여차량용PEMFC 시스템의공기공급부운전환경에따른막가습기의성능특성에대한연구를수행하였다. Nafion 막을이용한Shell-and-Tube 형막가습기의입구온도변화에따른열및물전달특성에알아보기위한실험을수행하였으며, 이로부터가습기막을통한물전달성능이입구온도에대하여비선형적으로변화하는특성을확인하였다. Nafion 막의물전달계수를경계면의온도와상대습도의함수로서모델링하여단일튜브형막에대한수치해석을수행하였으며, 해석결과를실험결과와비교하였다. 막을통한국소물질량유속분포가튜브내에서급격하고도비선형적으로변화하는해석결과를얻을수있었으며, 이로부터입구온도가가습기성능에미치는영향을논의하였다.Abstract: The effect of an increase in the temperature of inlet air on the performance of a membrane humidifierfor a PEMFC (Polymer Electrolyte Membrane Fuel Cell) vehicle was investigated both experimentally andnumerically. A shell-and-tube type gas-to-gas humidifier with Nafion membrane was tested. The experimental resultshowed that water transfer varies nonlinearly with the temperature elevation. Numerical analysis based on detailedmodeling was also conducted in simplified geometry of a single tube to explain this nonlinear behavior. Thesimulation revealed that the local water flux varies nonlinearly and dramatically along the tube. The analysis wasbased on the inverse relationship between the increase in temperature and decrease in relative humidity, both ofwhich seriously affect the water conductivity of the membrane.

The performance of a proton exchange membrane fuel cell (PEMFC) is seriously changed by the humidification capability available when equipped with a PTFE® membrane. Typically, the humidification of a fuel cell is carried out by means of an internal or external humidifier. A membrane humidifier is applied to the external humidification of residential power generation fuel cell due to its convenience and high performance. In this study, a static model is constructed to understand the physical phenomena of the membrane humidifier in terms of geometric parameters and operating parameters. The model utilizes the concept of planar type heat exchanger with mass transport through the membrane. The model is constructed with FORTRAN in a Simulink® environment for consistency with other components of the model we previously developed. The results show that the humidity of the wet gas and the channel length, the membrane thickness and wet gas inlet humidity are critical parameters affecting the performance of the humidifier.

Printing and spray technologies are the most recent and novel approaches to form organic photovoltaics (OPV) with inexpensive, high speed, and environmentally friendly process. With an electrohydrodynamic atomization (EHDA) approach, the active layer composed of polymer mixture (P3HT:PCBM) was successively fabricated. Operating conditions for obtaining the stable cone jet mode were determined with various applied voltages and liquid feed flow rates. The size distribution of EHDA droplets was characterized by aerodynamic particle sizer (APS) measurement. The mode diameters of the droplets were 580 and 670 nm, respectively, when the liquid flow rates were 1 and 20 μl/min. The maximum power conversion efficiency of 0.48% was obtained under AM 1.5 solar simulation for an OPV device fabricated in air.

In this study, the laser sintering of inkjet-printed silver lines was evaluated. Silver-nanoparticle ink and a drop-ondemand (DOD) inkjet printer were used for printing on glass and polyethylene terephthalate (PET) substrates with various thicknesses. To sinter the printed silver nanoparticles, the silver layer printed on the transparent substrates was irradiated by focused CW laser beams that were incident normal to the substrates; the irradiation was carried out for various beam intensities and for various irradiation times. The electrical conductivity of the laser-sintered silver patterns was measured and compared with the conductivity of silver patterns sintered by using an oven. The increase in the temperature caused by laser irradiation was also calculated on the basis of the laser beam intensity, irradiation time, surface reflectivity, and thermophysical property of the substrate in order to estimate the increase in the electrical conductivity caused by laser sintering.

The variation in electric conductivity was examined for laser irradiation with various beam intensities. A 532-nm continuous wave laser was irradiated onto inkjet-printed silver lines on a glass substrate and the electrical resistance was measured in situ during the irradiation. The results demonstrate that electrical conductivity varies nonlinearly with laser intensity, and has a minimum specific resistance of 3.1 x 10(-8) Ωm at 4 kW/cm2 irradiation. These results are interesting because the specific resistance achieved by the present laser irradiation was approximately 1.9 times lower than the best value obtainable by oven heating, even though it was still higher by 1.9 times than that of bulk silver. It is also demonstrated that the irradiation time required to complete the sintering process decreases with laser intensity. The numerical simulation of laser heating shows that the heating temperature could be as high as 250 degrees C for laser sintering, while it is limited to 250 degrees C for oven sintering. The characteristics of sintering with laser intensity based on the results of field emission scanning electron microscope images are discussed.

Background : Nonalcoholic fatty liver disease (NAFLD) has been more and more often regarded as a serious disorder, because nonalcoholic steatohepatitis (NASH), a part of NAFLD, may progress to the end stage of liver disease. Though an advanced age, obesity, diabetes mellitus (DM) etc. being not infrequent conditions in Korea, are known to exacerbate the severity of this disease, there are only a few Korean reports on this subject. The purpose of this study is to identify possible factors that might add up to the pathological severity of this disorder in Korean patients. Methods : Of 60 patients with steatosis found at liver biopsy, 43 NAFLD patients were reviewed retrospectively after exclusion of other liver diseases. Results : The cases of steatosis were mild, moderate, and severe in 9, 10, and 24 patients, respectively. The degree of necroinflammatory activity was mild, moderate, and severe in 33, 9, and 1 patients, respectively. There were no established factors directly related to these classes. As to fibrosis, the cases were classified as none, mild, moderate, severe, and cirrhotic in 9, 11, 16, 7, and 0 patients, respectively. The stage of fibrosis correlated with the age (p

Sooting characteristics of counterflow ethylene/propane mixture flames have been experimentally studied to investigate the fuel structure effect on PHM and soot formation. Laser-induced incandescene and laser-induced fluorescene techniques were employed to measure soot volume fraction and polycyclic aromatic hydrocarbon (PAH) concentration, respectively. Importance of species on PAH growth as well as the H-abstraction-C addition (HACA) mechanism has been emphasized, considering that PAH growth rate is greater for with mixed fuel than fer pure fuel flames. It was also confirmed that HACA pathways are the dominant soot growth mechanism. A new PAH growth model including both and growth mechanisms is proposed based on the experimental results.