Unipolar resistive switching behavior of BiFeO3 thin films prepared by chemical solution deposition

Bismuth ferrite (BiFeO₃, BFO) thin films were spin-coated on Pt/Ti/SiO₂/Si substrates by a chemical solution deposition method. The ferroelectric BFO films annealed at 500 °C and 550 °C were found to possess unipolar resistive switching behaviors. The resistance ratio of the high resistance state (HRS) to the low resistance state (LRS) of the unipolar resistance switching is about 10³ for the ferroelectric BFO films. The conduction mechanisms are concluded to be space charge-limited conduction for the initial state and Ohmic conduction for the LRS. As for the HRS, the Poole-Frenkel emission fits well in the whole voltage region. Traps composed of oxygen vacancies are considered to play a key role in forming conducting paths. The relaxation time of electronic carriers is much shorter than that of ionic oxygen vacancies; therefore, the resistance switching is considered more probably due to carrier injection and emission through the Poole-Frenkel model after forming.     

Luminescence mechanism and carrier dynamic studies of InGaN-based dichromatic light emitting diodes with ultraviolet and blue emissions

In this study, to investigate the luminescence mechanism and carrier dynamics of dichromatic InGaN-based light emitting diodes (LEDs) with two active regions, an ultraviolet (UV)-blue LED (UV active region above the blue one) and a blue-UV LED (blue active region above the UV one) were prepared. Photoluminescence (PL), cathodoluminescence (CL), and time-resolved photoluminescence measurements were performed. For the PL spectra of both LEDs, the blue emissions are stronger than the UV emissions. This trend shows that the higher degree of carrier localization of the blue active region, in either the upper or lower portions of the LEDs, can enhance carrier capture and recombination efficiency. Due to the large and bright light spots emitted from indium-rich clusters in the blue active region, CL images showed that the blue emission is dominant in the image shape for both samples. Furthermore, it was shown that the optical properties and carrier dynamics of dichromatic InGaN-based LEDs could be well explained by the combined effects of the carrier localization effect, structures, extraction efficiency, defect density, and carrier capture efficiency in the UV and blue active regions. Also, thermal effect plays an important role in carrier transport behavior in such dichromatic LEDs. The research results provide important information for operation mechanisms and device designs of dichromatic LEDs.     

Inhibition of gastric emptying and intestinal transit by amphetamine through a mechanism involving an increased secretion of CCK in male rats

1. The effect of amphetamine on gastrointestinal (GI) transit and the plasma levels of cholecystokinin (CCK) were studied in male rats. 2. Gastric emptying was inhibited both acutely and chronically by the administration of amphetamine. GI transit was decreased by the acute administration of amphetamine but not affected by the chronic administration of amphetamine. 3. Plasma CCK levels were increased dose-dependently by amphetamine. 4. Proglumide, a CCK receptor antagonist, prevented amphetamine-induced inhibition of gastric emptying and the decrease in GI transit in male rats. 5. The selective CCK(A) receptor antagonist, lorglumide, dose-dependently attenuated the amphetamine-induced inhibition of gastric emptying in male rats. In contrast, the selective CCK(B) receptor antagonist, PD 135,158, did not reverse the effect of amphetamine on gastric emptying. 6. Both lorglumide and PD 135,158 reversed the inhibitory effect of amphetamine on GI transit in male rats. 7. These results suggest that amphetamine-induced inhibition of gastric emptying and intestinal transit is due in part to a mechanism associated with the hypersecretion of endogenous CCK.     

Glucocorticoids and aging

In this review we analyze the morphologic changes, hypothalamic-pituitary-adrenal (HPA) axis functions, glucocorticoid (GC) receptors, and steroidogenic enzyme activities in both animals and humans during aging. In rodent studies, older animals tend to show: 1) hypertrophy of adrenal zona fasciculata (ZF) cells; 2) neuronal loss in the hypothalamic area; 3) loss of GC receptors in the hippocampus; 4) raised circulating adrenocorticotropic hormone (ACTH) and GC levels, and increased release of corticotropin-releasing hormone from the hypothalamus; 5) reduced suppression of endogenous GC secretion after administration of dexamethasone; 6) decreased attenuation of response to chronic stress; and 7) increased activity of P450scc and 21-hydroxylase. According to the GC cascade hypothesis, stress and GCs facilitate the aging process in rats. Stress induces downregulation of GC receptors in the hippocampus, then impairs GC feedback on stress-induced HPA axis activation. Finally, an increase in the basal level of corticosterone and extended GC secretion following stress occurs. Because activation of the hippocampus decreases HPA axis function, the unrestrained elevation of GC concentration and the reduction in the level of GC receptors in the hippocampus may gradually weaken the feedback mechanisms and halt the response to stress. In humans, there are conflicting reports of HPA axis function during aging, so it is difficult to make a final conclusion regarding the relationship between aging and HPA axis function.     

Learning effectiveness in a Web-based virtual learning environment: a learner control perspective

Web-based technology has a dramatic impact on learning and teaching. A framework that delineates the relationships between learner control and learning effectiveness is absent. This study aims to fill this void. Our work focuses on the effectiveness of a technology-mediated virtual learning environment (TVLE) in the context of basic information technology skills training. Grounded in the technology-mediated learning literature, this study presents a framework that addresses the relationship between the learner control and learning effectiveness, which contains four categories: learning achievement, self-efficacy, satisfaction, and learning climate. In order to compare the learning effectiveness under traditional classroom and TVLE, we conducted a field experiment. Data were collected from a junior high school of Taiwan. A total of 210 usable responses were analysed. We identified four results from this study. (1) Students in the TVLE environment achieve better learning performance than their counterparts in the traditional environment; (2) Students in the TVLE environment report higher levels of computer self-efficacy than their counterparts in the traditional environment; (3) Students in the TVLE environment report higher levels of satisfaction than students in the traditional environment; and (4) Students in the TVLE environment report higher levels of learning climate than their counterparts in the traditional environment. The implications of this study are discussed, and further research directions are proposed.     

Limitation of CMOS supply-voltage scaling by MOSFETthreshold-voltage variation

A fundamental limit of CMOS supply-voltage (V_cc) scaling has been investigated and quantified as a function of the statistical variation of MOSFET threshold-voltage (V_T). Based on the data extracted from a sub 0.5 μm logic technology, the variation of ring-oscillator propagation-delay (T_d) significantly increases as V_cc is scaled down towards the MOSFET V_T. An empirical power-law relationship was then derived to describe the scattering of circuit speed (ΔT_pd ) as a function of MOSFET V_T variation (ΔV_T ) and (V_cc-V_T). Agreement between the model and the experimental data was established for V_cc values from 4.0 to 0.9 V. This fundamental limit of CMOS V_cc, scaling poses an additional challenge for the design and manufacturing of high-performance, low-power portable systems and battery-based equipment     

Elevated Monocytic Interleukin-8 Expression under Intermittent Hypoxia Condition and in Obstructive Sleep Apnea Patients

Obstructive sleep apnea (OSA) is a disease with great cardiovascular risk. Interleukin-8 (IL-8), an important chemokine for monocyte chemotactic migration, was studied under intermittent hypoxia condition and in OSA patients. Monocytic THP-1 cells were used to investigate the effect of intermittent hypoxia on the regulation of IL-8 by an intermittent hypoxic culture system. The secreted protein and mRNA levels were studied by means of enzyme-linked immunosorbent assay and RT/real-time PCR. The chemotactic migration of monocytes toward a conditioned medium containing IL-8 was performed by means of the transwell filter migration assay. Peripheral venous blood was collected from 31 adult OSA patients and RNA was extracted from the monocytes for the analysis of IL-8 expression. The result revealed that intermittent hypoxia enhanced the monocytic THP-1 cells to actively express IL-8 at both the secreted protein and mRNA levels, which subsequently increased the migration ability of monocytes toward IL-8. The ERK, PI3K and PKC pathways were demonstrated to contribute to the activation of IL-8 expression by intermittent hypoxia. In addition, increased monocytic IL-8 expression was found in OSA patients, with disease severity dependence and diurnal changes. This study concluded the monocytic IL-8 gene expression can be activated by intermittent hypoxia and increased in OSA patients.     

KINETICS OF THE SIMULTANEOUS SORPTION OF NONIONIC SURFACTANT AND COPPER(II) BY POLY ACRYLIC ACID - FUNCTIONALIZED ION EXCHANGER

ABSTRACT

Kinetics of the simultaneous sorption of nonionic surfactant oxyethylated alcohols (OS-20) and copper(II) by hydrogen containing form of Purolite C 106 polyacrylic acid-functionalized cation exchanger was investigated: kinetic curves measured, effective coefficients of intraparticle diffusion (D), effective kinetic coefficients of the external mass transfer ((β) were calculated. The sorption of copper (II) and OS-20 is controlled by the intraparticle diffusion. The diffusion rate depends on the solution acidity: on increasing the acidity both the rate of copper (II) intraparticle diffusion and the equilibrium sorption decrease while the rate of intraparticle diffusion and the equilibrium sorption of OS-20 increase. The presence of copper (II) results in an increase in OS-20 diffusion rate but leads to a decrease in the equilibrium sorption of OS-20. The action of OS-20 results in the decrease in the equilibrium sorption of copper (II).The simultaneous sorption of oxyethylated alcohols and copper (II) by Purolite C 106 can be applicable for the purification of sewage including copper plating rinsewater A column filled with Purolite C 106 would not limit the productivity if integrated into the system of sewage purification by ion exchange |The simultaneous sorption of OS-20 and copper (II) by Purolite C 106 ion exchanger can be applicable for the purification of sewage including copper plating rinsewater. With respect to the coefficients of intraparticle diffusion for both copper (II) and OS-20 the column filled with Purolite C 106 would not limit the productivity if integrated into the system of sewage purification using ion exchange,