Surface acoustic wave characteristics of ZnO films grown on a polycrystalline 3C-SiC buffer layer

Zinc oxide (ZnO) thin films were deposited onto a polycrystalline (poly) 3C-SiC buffer layer for surface acoustic wave (SAW) applications using a magnetron sputtering system. Atomic force microscopy (AFM) and X-ray diffraction (XRD) showed that the ZnO grown on 3C-SiC/Si had a smooth surface, a dominant c-axis orientation and a lower residual stress in ZnO thin film compared to that grown directly onto Si substrate. In order to evaluate the SAW characteristics of ZnO films on a 3C-SiC buffer layer, the two-port SAW resonators, based on inter-digital transducer (IDT)/ZnO/3C-SiC/Si and IDT/ZnO/Si structures, were fabricated and measured within a temperature range of 25-135 °C. The resulting 3C-SiC buffer layer improved the insertion loss by approximately 7.3 dB within the SAW resonator and enhanced the temperature stability with TCF = −22 ppm/°C up to 135 °C in comparison to that of TCF = −45 ppm/°C within a temperature range of 25-115 °C of the ZnO/Si structure.     

Sprouting angiogenesis under a chemical gradient regulated by interactions with an endothelial monolayer in a microfluidic platform

Microfluidic cell culture assays are versatile tools for studying cell migration, particularly angiogenesis. Such assays can deliver precisely controlled linear gradients of chemical stimuli to cultured cells in a microfluidic channel, offering excellent optical resolution and in situ monitoring of cellular morphogenesis in response to a gradient. Microfluidic cell culture assays provide a chemical gradient subject to molecular diffusion, although cellular metabolism can perturb it. The actual gradient perturbed by cells has not been precisely described in the context of regulated cellular morphogenesis. We modeled the chemical gradient in a microfluidic channel by simulating the analyte(VEGF) distribution during cellular interactions. The results were experimentally verified by monitoring sprouting angiogenic response from a monolayer of human umbilical vein endothelial cells (hUVECs) into a type 1 collagen scaffold. The simulation provided a basis for understanding a real distribution of the analyte interrupted by cells in microfluidic device. The new protocol enables one to quantify the morphogenesis of hUVECs under a flat, less-steep, or steep gradient.     

In situ curing of sliding SU-8 droplet over a microcontact printed pattern for tunable fabrication of a polydimethylsiloxane nanoslit

A tunable process for polydimethylsiloxane (PDMS) nanoslit fabrication is developed for nanofluidic applications. A microcontact printing (μCP) of a laterally spreading self-assembled hexadecanethiol (HDT) layer, combined with in situ curing of a sliding SU-8 droplet, enables precise and independent tuning of a nanoslit-mold width and height using a single μCP master mold. The SU-8 nanoslit-mold is replicated using a hard-soft composite PDMS to prevent channel collapse at low (<0.2) aspect ratio (height over width). The fluidic characteristics as well as dimensions of nanoslits fabricated with various conditions are analyzed using a fluorescein sample and AFM images. Finally, concentration polarization-based sample preconcentration is successfully demonstrated at the nanoslit boundary where an electric double-layer is overlapped.     

Three-dimensional complex image coding using a circular Dammann grating

Recently, optical image coding using a circular Dammann grating (CDG) has been proposed and investigated. However, the proposed technique is intensity based and could not be used for three-dimensional (3D) image coding. In this paper, we investigate an optical image coding technique that is complex-amplitude based. The system can be used for 3D image coding. The complex-amplitude coding is provided by a circular Dammann grating through the use of a digital holographic recording technique called optical scanning holography. To decode the image, along the depth we record a series of pinhole holograms coded by the CDG. The decoded reconstruction of each depth location is extracted by the measured pinhole hologram matched to the desired depth. Computer simulations as well as experimental results are provided.     

Large strain response in acceptor- and donor-doped Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-based lead-free ceramics

Effects of Fe and La addition on the dielectric, ferroelectric, and piezoelectric properties of Bi_0.5Na_0.5TiO₃–Bi_0.5Li_0.5TiO₃–BaTiO₃–Mn ceramics were investigated. Similar to the doping effect in lead-based piezoelectric materials, here the Fe-doped ceramic created a hard effect with an improved mechanical quality factor (Q _m) ~ 160, coercive field (E _c) ~ 2.9 kV/mm, decreased dielectric constant ( e₃₃^T /e₀ ) ~ 80 3, \left( {\varepsilon_{33}^{T} /\varepsilon_{0} } \right)\sim 80 3, and loss (tanδ) ~ 0.024 while the La-doped one indicated a soft feature with improved piezoelectric constant (d ₃₃) ~ 184 pC/N, e₃₃^T /e₀   ~ 983, \varepsilon_{33}^{T} /\varepsilon_{0} \,\sim { 983}, tanδ ~ 0.033, and decreased E _c ~ 2.46 kV/mm. In addition, the temperature dependence of the ferroelectric hysteresis loops and strain response under unipolar electric field was also studied. Around the depolarization temperature T _d, large strain value was obtained with the normalized d₃₃^* d_{33}^{*} up to ~1,000 pC/N, which was suggested originated from the development of the short-range order or non-polar phases in the ferroelectric matrix. All these would provide a new way to realize high piezoelectric response for practical application in different temperature scale.     

Anthropogenic and natural radionuclides in caribou and muskoxen in the western Alaskan Arctic and marine fish in the Aleutian Islands in the first half of 2000s

A number of caribou and muskoxen samples from the western Alaskan Arctic and fish samples from the Aleutian Islands were collected between 1998 and 2006 and analyzed for anthropogenic (⁹⁰Sr and ¹³⁷Cs) and natural radionculides (⁴⁰ K, ²¹⁰Pb and ²²⁶Ra), as part of the radiological assessment for the regional subsistence hunting communities in the first half of 2000s. We examined the relationship between the activities of these nuclides with the size of the fish. In caribou samples, concentration of ⁹⁰Sr in muscle was below the detection limit of 0.14 Bq kg^− 1 and ¹³⁷Cs concentration in bones was below the detection limit of 0.15 Bq kg^− 1.¹³⁷Cs activity varied over an order of magnitude in caribou muscle samples with an average value of 2.5 Bq/kg wet wt. Average ¹³⁷Cs activity in muskoxen muscle was found to be 9.7 Bq/kg wet wt. However, there were a little variation (less than 60%) in ²¹⁰Pb, ⁴⁰ K, and ²²⁶Ra in both muscle and bone of both caribou and muskoxen. The activities of total ²¹⁰Pb in caribou and muskox bones were found to be 1-2 orders of magnitude higher than that of parent-supported ²¹⁰Pb indicating the potential for dating of bones of terrestrial mammals (time elapsed since the death of the animal) based on the excess ²¹⁰Pb method exists. In fish muscle samples, ¹³⁷Cs activity varied from below detection limit to 154 mBq/kg wet wt. and its content increased with the size of the fish due to its transfer through the food chain. Among the seven fish species investigated, ²¹⁰Pb activities varied almost an order of magnitude; however, ⁴⁰K and ²²⁶Ra activities varied less than a factor of two. Total annual effective dose due to ⁹⁰Sr and ¹³⁷Cs from the ingestion of those terrestrial and marine meats was estimated to be negligible (ca. 9 μSV/a) compared to the natural radionuclides present thus posing negligible radiological threat to humans.     

Large eddy simulation of flow characteristics in an unconfined slot impinging jet with various nozzle-to-plate distances

To study the detailed flow structure of the unconfined plane impinging jet, a 3-dimensional flow analysis is carried out focused on the flow mechanism with the non-dimensional distance, L/d, as flow parameter by using the LES turbulent technique. The symbols d and L represent the nozzle width and the nozzle-to-plate distance, respectively. Then, the flow structures along both the stream-wise and spanwise direction are investigated. For these purposes, the plane impinging jet with Reynolds number of 11,000 is analyzed. The nozzle width was fixed at 1.5mm, but the nozzle-to-plate distance was varied between 4mm and 24mm. As a result, the plane impinging jet shows different flow patterns with L/d. In conclusion, the plane impinging jet is classified into three types with the non-dimensional variable, L/d. L/d≤4: Stable impinging jet, 4<L/d<11: periodically-stable impinging jet and L/d≥11: Unstable impinging jet.     

A numerical study on extinction and NOx formation in nonpremixed flames with syngas fuel

The flame structure, extinction, and NO_x emission characteristics of syngas/air nonpremixed flames, have been investigated numerically. The extinction stretch rate increased with the increase in the hydrogen proportion in the syngas and with lower fuel dilution and higher initial temperature. It also increased with pressure, except for the case of highly diluted fuel at high pressure. The maximum temperature and the emission index of nitric oxides (EINO_x) also increased in aforementioned conditions. The EINO_x decreased with stretch rate in general, while the decreasing rate was found to be somewhat different between the cases of N₂ and CO₂ dilutions. The reaction paths of NO_x formation were analyzed and represented as NO reaction path diagram. The increase in N radical resulted in larger NO_x production at high initial temperature and pressure. As the pressure increases, EINO_x increases slower due to the third-body recombination. The thermal NO mechanism is weakened for high dilution cases and non-thermal mechanisms prevail. The combustion conditions achieving higher extinction stretch rate can be lead to more NO_x emission, therefore that the selection of optimum operation range is needed in syngas combustion.     

Cyclic behavior of prefabricated circular composite columns with low steel ratio

Improved economy and speed of construction can be achieved through the use of prefabricated structural members. As a step toward the advancement of prefabricated substructures, a precast composite column for seismic regions is proposed in this paper. Concrete-encased composite columns with core structural steel can be utilized for a fast construction method using steel connections. Six concrete-encased composite specimens with low steel ratio were fabricated. Quasi-static tests were conducted to investigate the cyclic response of the prefabricated composite columns. For composite columns with bolt connections, the cyclic behavior in terms of ultimate load and post-cracking behavior was enhanced significantly as the transverse reinforcement ratio increases. Higher prestressing gave greater flexural strength to the composite columns with prestressing and better energy absorption capacity, while displacement ductility of the prestressed composite column was decreased as the prestressing increased.     

The analysis of PM2.5 and associated elements and their indoor/outdoor pollution status in an urban area

In this study, elemental composition of PM2.5 and the status of indoor/outdoor pollution were investigated in a commercial building near a roadside area in Daejeon, Korea. A total of 60 parallel PM2.5 samples were collected both on the roof (outdoor) and in an indoor office of a building near a highly congested road during the spring and fall of 2008. The concentrations of 23 elements were analysed from these PM2.5 samples using instrumental neutron activation analysis. PM2.5 levels in indoor environment (47.6 ± 16.5 μg/m(3)) were noticeably higher than the outdoor levels (37.7 ± 17.2 μg/m(3)) with the I/O concentration ratio of 1.37 ± 0.33 [correlation coefficient (r) = 0.89, P < 0.001]. Principal component analysis results coincidently showed the predominance of sources such as soil dust, traffic, oil/coal combustion and road dust for both indoor and outdoor microenvironments. An isolated source in the indoor environment was assigned to environmental tobacco smoke (ETS) with high factor loading of Ce, Cl, I, K, La and Zn. The overall results of our study indicate that the sources of indoor constituents were strongly dependent on outdoor processes except for the ones affected by independent sources such as ETS. PRACTICAL IMPLICATIONS: An improved understanding of the factors affecting the indoor PM2.5 concentration levels can lead to the development of an efficient management strategy to control health risks from exposure to indoor PM2.5 and related toxic components. A comparison of our comprehensive data sets indicated that most indoor PM2.5 and associated elemental species were strongly enriched by indoor source activities along with infiltration of ambient outdoor air for a naturally ventilated building.