Simple,coupled algorithms for solving creeping flows and their application to electro‐osmotic flows

In this study we developed simple, coupled algorithms for solving low‐Reynolds‐number flows applicable to micro‐scale flows such as electro‐osmotic flows. The most popular scheme, i.e. the projection method, is not suitable for such flows because of its undesirable slip effect on boundaries at low‐Reynolds‐numbers. In our method, the velocity and pressure are strongly coupled, and the momentum and pressure equations are solved iteratively by using the successive over relaxation (SOR) method while exchanging the unknown variables as soon as they have been updated. The developed methods are applied to a model flow for evaluating their performance. It was found that the coupled schemes are indeed superior to a projection method, i.e. the fractional‐step method, in both numerical accuracy and CPU time. The code is then applied to a dc electro‐osmotic flow within a cavity driven by electrical force acting on the ions spread in the fluid. In this application, the system of equations for the fluid flow and that for the ion transport are solved in a decoupled way, but each system is solved by using fully implicit schemes. From the simulations and by introducing the concept of vorticity source, we can identify two roles of the body force, one contributing to build‐up of the osmotic pressure and the other to the fluid flow. The interesting reverse flow occurring after the external potentials applied on the electrodes have been shut off is also investigated in terms of the vorticity source. Copyright © 2010 John Wiley & Sons, Ltd.     

Experimental Investigation of Nozzle Exit Reflector Effect on Supersonic Jet

The present study describes an experimental work to investigate the effect of a nozzle exit reflector on a supersonic jet that is discharged from a convergent–divergent nozzle with a design Mach number of 2.0. An annular reflector is installed at the nozzle exit and its diameter is varied. A high-quality spark schlieren optical system is used to visualize detailed jet structures with and without the reflector. Impact pressure measurement using a pitot probe is also carried out to quantify the reflector’s effect on the supersonic jet which is in the range from an over-expanded to a moderately under-expanded state. The results obtained show that for over-expanded jets, the reflector substantially increases the jet spreading rate and reduces the supersonic length of the jet, compared with moderately under-expanded jets. The reflector’s effect appears more significant in imperfectly expanded jets that have strong shock cell structures, but is negligible in correctly expanded jet.     

Retro-Ene reaction. VI. Functionalization of 4,5-dihalopyridazin-6-ones using 1-acetyloxymethyl-4,5-dihalopyridazin-6-ones as the 1-O, 3-N, 5-O ene-adduct

Functionalization of 1-acetyloxymethyl-4,5-dihalopyridazin-6-ones via retro-ene reaction with some nucleophiles gave regioselectively only 5-halo-4-substitutedpyridazin-6-ones.     

An optimal order convergence for a weak formulation of the compressible Stokes system with inflow boundary condition

Summary. We formulate the compressible Stokes system given in (1.1) into a (new) weak formulation (2.1). A finite element method for this is presented. Existence and uniqueness of the finite element method is shown. An optimal error estimate for the numerical approximation is obtained. Numerical examples are given, showing its efficiency and rates of convergence of the approximate solutions that results from the discrete problem (3.1). Received October 20, 1996 / Revised version received January 21, 1999 / Published online: April 20, 2000     

Radionuclides analysis in hot spring waters in Korea by liquid scintillation counting

Tritium and ¹⁴C concentration in hot spring water in Korea were determined. Tritium in the most hot spring samples could not detected and concentration range was <0.5?C1.31?TU. And ¹⁴C contents were ranged 1.7?C78.6?pMC. From the ³H and ¹⁴C analysis, we found some hot springs are mixed with recent groundwater and hot spring water ages were estimated from 1,940 to 32,800?years. And also, ²²⁶Ra and ²²⁸Ra were determined simultaneously in hot spring water, and some other radionuclides were also analyzed. Content distribution of ²²²Rn was 50?C3,760?pCi/L, ²²⁶Ra was <0.003?C0.15?Bq/L and ²²⁸Ra was below the detection limit.     

Size-selective sliding of sessile drops on a slightly inclined plane using low-frequency AC electrowetting

When placed on an inclined solid plane, drops often stick to the solid surface due to pinning forces caused by contact angle hysteresis. When the drop size or the plane's incline angle is small, the drop is difficult to slide due to a decrease in gravitational force. Here we demonstrate that small drops (0.4-9 μL) on a slightly inclined plane (~12°, Teflon and parylene-C surface) can be mobilized through patterned electrodes by applying low-frequency ac electrowetting under 400 Hz (110-180 V(rms)), which has a mechanism different from that of the high-frequency ac method that induces sliding by reducing contact angle hysteresis. We attribute the sliding motion of our method to a combination of contact angle hysteresis and interfacial oscillation driven by ac electrowetting instead of the minimization of contact angle hysteresis at a high frequency. We investigated the effects of ac frequency on the sliding motion and terminal sliding of drops; the terminal sliding velocity is greatest at resonance frequency. Varying the electrowetting number (0.21-0.56) at a fixed frequency (40 Hz) for 5 μL drops, we found an empirical relationship between the electrowetting number and the terminal sliding velocity. Using the relationship between the drop size and ac frequency, we can selectively slide drops of a specific size or merge two drops along an inclined plane. This simple method will help with constructing microfluidic platforms with sorting, merging, transporting, and mixing of drops without a programmable control of electrical signals. Also, this method has a potential in heat transfer applications because heat removal capacity can be enhanced significantly through drop oscillation.     

Improvement of the electrical properties of TiO2-doped Bi5Nb3O15 thin films by the addition of MnO2

The leakage current density of a 1.0 mol% TiO₂-doped Bi₅Nb₃O₁₅ (TB₅N₃) film was high, and the breakdown electric field was low. This could be attributed to the presence of intrinsic oxygen vacancies and free electrons. The electrical properties of the TB₅N₃ film improved upon the addition of MnO₂ because of the formation of extrinsic oxygen vacancies, which caused the number of intrinsic oxygen vacancies to decrease in order to maintain the equilibrium concentration of oxygen vacancies in the film. However, the electric properties degraded when the MnO₂ content exceeded 15.0 mol% because of the formation of interstitial oxygen ions and holes. The dielectric constant (?_r) of the TB₅N₃ film slightly decreased upon the addition of a small amount of MnO₂. The TB₅N₃ film with 15.0 mol% MnO₂, which exhibited a small leakage current density of 2.5 × 10^?11 A/cm² at 0.15 MV/cm and a high breakdown electric field of 0.47 MV/cm, still maintained a large ?_r of 118 with a small loss tangent of 2.0% at 100.0 kHz.     

Edge directional 2D LMS filter for infrared small target detection

In this paper, we introduce an edge directional 2D least mean squares (LMSs) filter for small target detection in infrared (IR) images. Generally, the 2D LMS filter functions as a background prediction to apply to IR small target detection field. In order to accurately predict background objects as well as regions covered by small targets, the proposed 2D LMS filter take full advantage of edge information of prediction pixels corresponding to surrounding blocks around current filter window. And, to adjust adaptively its step size in the background and small target region, the adaptive region-dependent nonlinear step size is calculated by using the variance of the prediction pixels of the surrounding blocks. This prediction structure and adaptive step size of the proposed 2D LMS filter is applied to the background region including objects such as cloud edge and small target region differently. Through this way, the proposed 2D LMS filter predicts the background excluding small targets. Then, by subtracting the predicted background from the original IR image, small targets can be extracted. Experimental results show that the proposed 2D LMS filter has stronger target extraction and better background suppression ability compared to the existing 2D LMS filters.     

Novel flexible chemical gas sensor based on poly(3,4-ethylenedioxythiophene) nanotube membrane

Poly(3,4-ethylenedioxythiophene) nanotubes (PEDOT NTs) flexible membrane was successfully fabricated by vapor deposition polymerization (VDP) mediated electrospinning for ammonia gas detection. PVA nanofibers (NFs) were electrospun as a core part and polyvinyl alcohol (PVA)/PEDOT coaxial nanocables (NCs) were prepared by VDP method via EDOT monomer adsorption onto the electrospun PVA NFs as templates. To obtain the PEDOT NTs membrane, the PVA NFs were removed from PVA/PEDOT coaxial NCs with distilled water. PVA/PEDOT coaxial NCs and PEDOT NTs had the conductivities of 71 and 61 S cm⁻¹ and were applied as a transducer for ammonia gas detection in the range of 1-100 parts per million (ppm) of NH₃ gas. They exhibited the minimum detectable level of ca. 5 parts per million (ppm) and fast response time (less than 1 s) towards ammonia gas. In a recovery time, the PEDOT NTs membrane sensor was ca. 30 s and shorter compared to that of the membrane sensor based on the PVA/PEDOT NCs (ca. 50 s). In addition, sensor performance of PEDOT NTs membrane was also undertaken as a function of membrane thickness. Thick membrane sensor (30 μm) had the enhanced sensitivity and the sensitivity on the membrane thickness was in the order of 30 μm > 20 μm > 10 μm at 60 ppm of NH₃ gas.     

Effects of Sleep Deprivation on the Sedation of Pediatric Patients Undergoing MRI Examinations

Sedation is an essential factor for pediatric magnetic resonance imaging (MRI) procedure. A long-term failure of sedation has a detrimental effect on a 1 day test plan. Given this background, this study examined the effects of sedation using a sleep deprivation method in pediatric patients scheduled to undergo an MRI examination. The current study examined 54 patients (36 boys and 18 girls) with diseases, such as epilepsy, brain tumor, development delay, mental retardation, and cerebral infarction, who were treated at our medical institution from December 2009 to March 2010. The patients were classified into two groups: group A (n = 27) with sleep deprivation, and group B (n = 27) without sleep deprivation. The mean age of these patients was 4.2 years. Comparative analysis of groups A and B was performed to assess the success rate of pediatric sedation, the time elapsed until complete sedation had been achieved, and the frequency at which patients took Pocral syrup (chloral hydrate). In group A, patients were allowed to start sleep 1 hr later and were woken 1 hr earlier than their mean sleep time. According to this pretreatment, the rate of successful sedation, frequency of the administration of Pocral syrup, and the time elapsed until deep sedation had been achieved were measured. In group A, the rate of successful sedation was 100%, the mean time elapsed until deep sedation had been achieved was 23 min, and the mean frequency of Pocral syrup administration was 1.2 times. In addition, the proportions of patients who had achieved successful sedation after one-time use and two-time use of Pocral syrup were 77.8% and 22.2%, respectively. In group B, successful sedation was achieved in 89%, and the mean time elapsed until deep sedation was 39 min. The mean frequency of Pocral syrup administration was 1.5 times. The proportions of patients who had achieved successful sedation after one-time use and two-time use of Pocral syrup were 51.9% and 48.12%, respectively. The statistical significance was tested using a nonparametric analysis, Mann–Whitney U Test (p < 0.05). Other studies have reported that sleep deprivation had no significant effects. An actual comparison of the sleep-deprived and other patients showed that sleep deprivation affected the rate of successful sedation, the frequency of Pocral syrup administration, and the time elapsed until the patients were sedated. The rate of successful sedation was significantly higher in group A than in group B. The time elapsed until deep sedation had been achieved was also significantly shorter in group A than in group B. In addition, the frequency of Pocral syrup administration (administration dose) was significantly lower in group A than in group B. In conclusion, sleep deprivation increases the effectiveness of pediatric sedation in an MRI examination of pediatric patients and might assist in performing an MRI examination more efficiently in pediatric patients.