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To secure the reliability of flexible electronics, the effect of multicomponent stress on the device properties during complex mechanical deformation needs to be thoroughly understood. The electrical resistances of metal interconnects are investigated by in situ monitoring at different twisting angles and with different pattern positions. As the twisting angle increased, the electrical resistance increased earlier. Furthermore, in the line pattern located far from the central axis, severe electrical degradation and fatigue damage formation were observed. Multicomponent stress evolution during twisting was analyzed by the finite-element simulation method. For easy practical application for estimating the representative twisting strain, an analytic solution of twisting deformation was formulated and compared with the simulation. Using the equivalent strain, the fatigue lifetime was fitted, and the exponents were obtained for lifetime expectation. This systematic study provides the guidelines for highly reliable flexible devices and the tools for determining the expected fatigue lifetime.
The preparation of transmission electron microscopy (TEM) samples from powders is quite difficult and challenging. For powders with particles in the 1–5 μm size range, it is especially difficult to select an adequate sample preparation technique. Epoxy is commonly used to bind powder, but drawbacks, such as differential milling originating from unequal milling rates between the epoxy and powder, remain. We propose a new, simple method for preparing TEM samples. This method is especially useful for powders with particles in the 1–5 μm size range that are vulnerable to oxidation. The method uses solder as an embedding agent together with focused ion beam (FIB) milling. The powder was embedded in low-temperature solder using a conventional hot-mounting instrument. Subsequently, FIB was used to fabricate thin TEM samples via the lift-out technique. The solder proved to be more effective than epoxy in producing thin TEM samples with large areas. The problem of differential milling was mitigated, and the solder binder was more stable than epoxy under an electron beam. This methodology can be applied for preparing TEM samples from various powders that are either vulnerable to oxidation or composed of high atomic number elements.
To date, there have been a number of research proposals to explore the newly emerging wireless charging technologies based on radio-frequency (RF) signals, ambient or dedicated. In particular, research efforts towards achieving the goal of transmitting information and energy at the same time have been rapidly expanding, but the feasibility of this goal has not been fully addressed. Moreover, the respective coverage areas of transmitting information and energy are wildly different, the latter being considerably smaller than the former. This is because the receiver sensitivities are very different, namely -60 dBm for an information receiver and -10 dBm for an energy receiver [1, 2].
Owing to this limitation, recently a commercial implementation of RF energy transfer has been restricted to lower-power sensor nodes with dedicated RF energy transmitters, such as the Powercast wireless rechargeable sensor system  and the Cota system .
In this chapter, we discuss the implementation of long- and short-range RF energy harvesting systems, where the former is to provide far-field-based RF energy transfer over long distances with a 4 × 4 phased antenna array and the latter to provide biosensors with RF energy over short distances. An overall circuit design for these RF energy harvesting systems is described in detail, along with the measurement results to validate the feasibility of far-field-based RF energy transfer. We illustrate the designed test-beds which will be applied to develop sophisticated energy beamforming algorithms to increase the transmission range. Finally, a new research framework is developed through the cross-layer design of the RF energy harvesting system, which is intended to power a low-power sensor node, like the Internet-of-Things (IoT) sensor node. To this end, we present a circuit-layer stored energy evolution model based on the measurements which will be used in designing the upper-layer energy management algorithm for efficient control of the stored energy at the sensor node. The new framework will be useful because the existing works on RF energy harvesting do not explicitly take into account a realistic temporal evolution model of the stored energy in the energy storage device, like such as a supercapacitor.
Decreased hemoglobin levels increase the risk of developing dementia among the elderly. However, the underlying mechanisms that link decreased hemoglobin levels to incident dementia still remain unclear, possibly due to the fact that few studies have reported on the relationship between low hemoglobin levels and neuroimaging markers. We, therefore, investigated the relationships between decreased hemoglobin levels, cerebral small-vessel disease (CSVD), and cortical atrophy in cognitively healthy women and men.
Cognitively normal women (n = 1,022) and men (n = 1,018) who underwent medical check-ups and magnetic resonance imaging (MRI) were enrolled at a health promotion center. We measured hemoglobin levels, white matter hyperintensities (WMH) scales, lacunes, and microbleeds. Cortical thickness was automatically measured using surface based methods. Multivariate regression analyses were performed after controlling for possible confounders.
Decreased hemoglobin levels were not associated with the presence of WMH, lacunes, or microbleeds in women and men. Among women, decreased hemoglobin levels were associated with decreased cortical thickness in the frontal (Estimates, 95% confidence interval, −0.007, (−0.013, −0.001)), temporal (−0.010, (−0.018, −0.002)), parietal (−0.009, (−0.015, −0.003)), and occipital regions (−0.011, (−0.019, −0.003)). Among men, however, no associations were observed between hemoglobin levels and cortical thickness.
Our findings suggested that decreased hemoglobin levels affected cortical atrophy, but not increased CSVD, among women, although the association is modest. Given the paucity of modifiable risk factors for age-related cognitive decline, our results have important public health implications.
The formation and morphological evolution of germanides formed in a ternary Ni/Ta-interlayer/Ge system were examined by ex situ and in situ annealing experiments. The Ni germanide film formed in the Ni/Ta-interlayer/Ge system maintained continuity up to 550°C, whereas agglomeration of the Ni germanide occurred in the Ni/Ge system without Ta-interlayer. Through microstructural and chemical analysis of the Ni/Ta-interlayer/Ge system during and after in situ annealing in a transmission electron microscope, it was confirmed that the Ta atoms remained uniformly on the top of the newly formed Ni germanide layer during the diffusion reaction. Consequently, the agglomeration of the Ni germanide film was retarded and the thermal stability was improved by the Ta incorporation.
The oxidation mechanism and thermal stability of nickel oxide (NiO)/carbon nanotube (CNT) composites were investigated by examining composites with different NiO contents by thermogravimetric analysis and transmission electron microscopy (TEM). NiO acts as a catalyst in the oxidation of CNT in the composite. CNTs can be oxidized, even in a vacuum, by reducing NiO to nickel at temperatures lower than the normal oxidation temperature of CNTs. This phase transition was confirmed directly by in situ heating TEM observations. In air, reduction by CNT occurs simultaneously with reoxidation by gaseous O2 molecules, and NiO maintains its phase. The thermal stability decreased with increasing NiO content because of defects in the CNT generated by the NiO loading.
Stream development can generate environmental changes that impact fish communities. In temperate streams, the distribution of fish species is associated with environmental gradients. To analyze the relevant factors, large-scale exploration is required. Thus, to evaluate the distribution patterns of fish in Korea, sampling was conducted on a national scale at 720 sites over a 6-week period in 2009. A total of 124 fish species in 27 families were identified; Zacco platypus and Zacco koreanus of the Cyprinidae were the dominant and subdominant species, respectively. Of the species found, 46 (37.1%) were endemic and 4 (3.2%) exotic; of the latter, Micropterus salmoides and Lepomis macrochirus were widely distributed. Upon canonical correspondence analysis (CCA), both altitude and biological oxygen demand (BOD) were highly correlated with CCA axes 1 and 2, respectively. This explained 62.5% of the species–environment relationship. Altitude and stream order were longitudinally related to species distribution. The numbers of both total and endemic species gradually increased as streams grew in size to the fourth–fifth-order, and decreased in sixth-order, streams. Overall, fish communities were stable throughout the entire watershed, whereas some species showed site-specific occurrence patterns due to the paleogeomorphological characteristics of Korean peninsula. However, various anthropogenic activities may negatively affect fish communities. Therefore, both short- and long-term sustainable management strategies are required to conserve native fish fauna.
An organic/inorganic hybrid-type nonvolatile memory TFT was proposed as a core device for the future flexible electronics. The structural feature of this memory TFT was that a ferroelectric copolymer and an oxide semiconductor layers were employed as a gate insulator and an active channel, respectively. The memory TFT with the structure of Au/poly(vinylidene fluoride-trifluoroethylene)/Al2O3/ZnO/Ti/Au/Ti/poly(ethylene naphthalate) could be successfully fabricated at the process temperature of below 150°C. It was confirmed that the TFT well operated as a memory device even under the bending situations.
We aimed to investigate the factors associated with a positive intake of folic acid (FA) during the periconceptional period among Korean women.
In a cross-sectional study of demographic, obstetric and socio-economic data, history of periconceptional intake of FA and awareness of the benefits of FA supplementation in pregnancy were obtained and analysed using the χ2 test, followed by multiple logistic regression analysis.
The Maternity School, Cheil General Hospital and Women’s Healthcare Center, Seoul, South Korea, between October 2005 and March 2006.
In total 1313 pregnant women participating in a two-day training course available every month.
After excluding subjects with incomplete or inconsistent data, there were 1277 women included in the analysis. Participants were aged 29·4 (sd 2·9) years and had a mean gestational age of 27·9 (sd 7·1) weeks. Only 131 (10·3 %) women took FA during the periconceptional period. According to multiple logistic regression analyses, the adjusted OR for FA supplementation was 1·79 (95 % CI 1·10, 2·91) in women who had previous spontaneous abortions, 4·10 (95 % CI 2·43, 6·78) in women who planned their pregnancy and 6·63 (95 % CI 2·08, 21·12) in those who were aware of the protective effects of FA.
Periconceptional intake of FA was more likely among Korean women with a history of previous spontaneous abortion, who planned their pregnancy or who were aware of the protective effects of FA during pregnancy. However, the proportion of women who took FA in the periconceptional period was low.
The role of folate, vitamin B12 and homocysteine levels in
depression is not clear.
To investigate cross-sectional and prospective associations between
folate, B12 and homocysteine levels and late-life
A total of 732 Korean people aged 65 years or over were evaluated at
baseline. Of the 631 persons who were not depressed, 521 (83%) were
followed over a period of 2–3 years and incident depression was
ascertained with the Geriatric Mental State schedule. Serum folate, serum
vitamin B12 and plasma homocysteine levels were assayed at
both baseline and follow-up.
Lower levels of folate and vitamin B12 and higher homocysteine
levels at baseline were associated with a higher risk of incident
depression at follow-up. Incident depression was associated with a
decline in vitamin B12 and an increase in homocysteine levels
over the follow-up period.
Lower folate, lower vitamin B12 and raised homocysteine levels
may be risk factors for late-life depression.
Cellulose electro-active paper (EAPap) has attracted much attention as a new smart electronic material to be utilized as mechanical sensors, bio compatible applications and wireless communications. The thin EAPap film has many advantages such as lightweight, flexible, dryness, biodegradable, easy to chemically modify, cheap and abundance. Also EAPap film has a good reversibility for mechanical performance, such as bending movement, under electric field. The main actuation mechanism governed by piezoelectric property can be modulated by material direction and stretching ratio during process. In this paper we present the overview as well as fabrication process of cellulose EAPap as a novel smart material. Also we propose the method to enhance the piezoelectricity, its mechanical and electromechanical properties. In addition, the fabrication of high quality metal patterns with Schottky diode on the cellulose surface is an initiating stage for the integration of the EAPap actuator and electronic components. The integration of flexible actuator and electronic elements has huge potential application including flying magic carpets, microwave driven flying insets and micro-robots and smart wall papers.
We have fabricated a new magnetic field enhanced solid phase crystallization (FESPC) polycrystalline silicon (poly-Si) thin film transistors (TFTs), which shows the excellent electrical characteristics and superior stability compared with hydrogenated amorphous silicon (a-Si:H) TFTs. The mobility (μ) and threshold voltage (VTH) of p-type TFTs of which the channel width and length are 5 μm and 7 μm, respectively are 31.98 cm2/Vs and -6.14 V, at VDS=-0.1 V. In the FESPC TFTs, the characteristics caused by grain boundary are remarkable due to large number of grain boundaries in the channel compared with poly-Si TFTs. The VTH of the TFT which have 5 μm channel length is smaller than that of 18 μm channel length by 1.36 V, which is considerably large value. It is due to the large number of grain boundaries in the channel and the high lateral electric field. The grain boundary potential barrier height is decreased, when the large lateral electric field is applied (which is called DIGBL effect). As a result of increased mobility, the drain current is increased, and VTH can be decreased. The activation energy (Ea) is strongly depended on the drain bias and the number of grain boundaries. is decreased, caused by the large drain bias and/or smaller number of grain boundaries. This decreased Ea can be reduced VTH due to increased the drain current. VTH of p-type poly-Si TFT employing FESPC on the glass substrate is affected by channel length and VDS due to energy barrier lowering effect at the grain boundary by increased lateral electrical field.
We have investigated the shift of threshold voltage in the a-Si:H TFT due to the various negative pulse width stress. The drain bias dependent threshold voltage shift in the pulsed stress of a-Si:H TFT for AMOLED backplane is also measured and analyzed. When a positive gate and drain bias is applied to a-Si:H TFT (W/L = 200/4 Ým), VTH of a-Si:H TFT is increased during the stress time due to the defect state creation and charge trapping. VTH of a-Si:H TFT is increased from 1.645V to 2.53V (δVTH=0.885V) after the DC gate bias stress of VGS=15V, VDS=0V for 20,000sec. When the pulsed negative bias stress is applied to the gate electrode of the current driving a-Si:H TFT with the drain bias, VTH shift is considerably reduced due to the hole trapping into the gate insulator during the stress. When a negative pulse width is 16msec (pulse of 60Hz), the VTH is increased form 1.594V to 2.195V (δVTH=0.601V). When a negative pulse width increases from 16msec to 5sec without drain bias (VDS=0V), VTH is increased from 1.615V to 2.055V (δVTH=0.44V). When a drain bias is increased from 0V to 15V, VTH is slightly decreased from 1.58V to 1.529V (δVTH=-0.051V) due to large (-30V) VGD (VG=-15V, VD=15V) bias, while it is increased from 1.66V to 2.078V (δVTH=0.418V) width DC gate bias stress of VGS=15V, VDS=15V for 20,000sec.
Causal relationships between vascular factors and late-life depression are controversial.
To investigate prospective associations between risk factors for vascular disease and incidence of late-life depression.
Of 661 community participants aged 65 years or over, without depression at baseline, 521 (79%) were re-evaluated 2 years later. At baseline and follow-up, a diagnostic interview for depression was carried out and information on vascular status, disability and cognitive function was gathered.
Pre-existing heart disease, incident stroke and lower baseline high-density lipoprotein cholesterol level were significantly associated with incidence of late-life depression, independently of disability and cognitive function.
These results provide some support for a vascular aetiology of late-life depression. However, important risk factors for cerebrovascular disease such as hypertension and diabetes were not implicated, and the associations with lipid levels might still be explained by affective states earlier in life.
We report on the insulator-charging-effects of poly-4-vinylphenol (PVP) gate dielectric on the reliabilities of pentacene thin-film transistors (TFTs). Our PVP films were prepared by spin coating and curing at various temperatures (155, 175, and 200 °C). Evaluated using Au/PVP/p+−Si structures, the dielectric strength of PVP films cured at 175 °C was superior to those of the other PVP films cured at different temperatures. Although saturation current and field mobility (∼0.13 cm2/Vs) obtained from a TFT with PVP film cured at 200 °C appeared higher than those (∼0.07 cm2/Vs) from the device with 175 °C-cured polymer film, the TFT prepared at 200 °C revealed a low on/off current ratio of less than 104 due to its high off-state current and also unreliable saturation behavior under repetitive gate voltage sweep. The unreliable behavior is due to the dielectric-charging caused by gate-electron-injection. We thus conclude that there are some optimal PVP-curing conditions to improve the reliability of pentacene TFT.
Purpose: We investigated the quality and usefulness of spiral computed tomography and threedimensional reconstruction in children with obstruction of the central airways as a complication of congenital heart disease. Materials and methods: Spiral computed tomography with three-dimensional reconstruction was performed in 49 children with obstruction of the central airways seen as a complication of congenital heart disease. Spiral scanning was performed during breathing in 40, and after sedation with chloral hydrate in 38. Contrast medium was administered through a pedal venous route in 42. We analyzed the motion artifact, additional information provided by, and clinical usefulness, of the three-dimensional images. We also investigated the factors influencing the quality of the images. Results: Stenoses were seen in the trachea in 21 patients, and in bronchuses in 28. Their causes were an anomaly of the aortic arch in 6, posterior displacement of the aortic arch in 7, posterior displacement of the ascending aorta in 5, compression of the brachiocephalic artery in 5, absent pulmonary valve syndrome in 6, displaced or dilated cardiovascular structure in 17, and pulmonary arterial sling in 2. Motion artifact caused mild or negligible degradation of images in all patients except 6. Breath-holding in non-sedated children produced more severe motion artifact than did cardiovascular pulsation. Threedimensional images provided additional information over two-dimensional images in 11, and provided clinically useful information in 10. Contrast injection via the pedal route was better for the quality of threedimensional images than brachiocephalic injection (p = 0.013). Conclusions: Three-dimensional computed tomography is useful in evaluation of obstruction of the central airways in children with congenital heart disease. Despite the fact that motion artifact is unavoidable, the quality of three-dimensional images is acceptable for making a proper and accurate diagnosis. A pedal route is recommended for injection of contrast medium.
Inflammatory pseudotumour (IPT) is an idiopathic condition characterized by sclerosing inflammation, which mimics a neoplastic process. IPT involving the skull base and cervical spine is distinctly rare and usually indistinguishable from aggressive neoplasms or infection. We report a case of IPT involving the skull base and cervical spine. Initially the patient complained of headache and hearing loss without other neurological dysfunction. Two cycles of oral systemic steroid therapy resulted in only partial responses. Low dose radiotherapy was followed by quadriparesis as the lesion infiltrated into the cervical vertebral bodies. Subsequently a second course of radiation was administered to the whole cervical spine. Marked improvement was observed clinically and radiologically; however, the patient gradually deteriorated and died of sepsis. Given the aggressive nature of disease and the complications related to the long-term treatment, we suggest that a more aggressive therapeutic approach is suitable in extensive IPT of the skull base.