Top-Down Design Method of a Time Domain Accelerometer with Adjustable Resolution.

A top-down design methodology and implementation of a time domain sensor is presented in this paper. The acceleration resolution of the time domain sensor is equal to the time-measurement accuracy divided by the sensor sensitivity. Combined with the sensitivity formula, the acceleration resolution is proportional to the vibration amplitude, the time-measurement accuracy, and the third power of the resonant frequency. According to the available time-measurement accuracy and the desired acceleration resolution, the parameters including the vibration amplitude and the resonant frequency were theoretically calculated. The geometrical configuration of the time domain sensor device was designed based on the calculated parameters. Then, the designed device was fabricated based on a standard silicon-on-insulator process and a matched interface circuit was developed for the fabricated device. Experimental results demonstrated that the design methodology is effective and feasible. Moreover, the implemented sensor works well. In addition, the acceleration resolution can be tuned by adjusting the time-measurement accuracy and the vibration amplitude. All the reported results of this work can be expanded to other time domain inertial sensors, e.g., a gyroscope or tilt sensor.

Characterization of Sensitivity of Time Domain MEMS Accelerometer.

This paper characterizes the sensitivity of a time domain MEMS accelerometer. The sensitivity is defined by the increment in the measured time interval per gravitational acceleration. Two sensitivities exist, and they can be enhanced by decreasing the amplitude and frequency. The sensitivity with minor nonlinearity is chosen to evaluate the time domain sensor. The experimental results of the developed accelerometer demonstrate that the sensitivities span from -68.91 µs/g to -124.96 µs/g and the 1σ noises span from 8.59 mg to 6.2 mg (amplitude of 626 nm: -68.91 µs/g and 10.21 mg; amplitude of 455 nm: -94.51 µs/g and 7.76 mg; amplitude of 342 nm: -124.96 µs/g and 6.23 mg), which indicates the bigger the amplitude, the smaller the sensitivity and the bigger the 1σ noise. The adjustable sensitivity provides a theoretical foundation for range self-adaption, and all the results can be extended to other time domain inertial sensors, e.g., a gyroscope or an inclinometer.

Ultralow-Power RRAM with a High Switching Ratio Based on the Large van der Waals Interstice Radius of TMDs.

Low power and high switching ratio are the development direction of the next generation of resistive random access memory (RRAM). Previous techniques could not increase the switching ratio while reducing the SET power. Here, we report a method to fabricate low-power and high-switching-ratio RRAM by adjusting the interstice radius (rg) between the van der Waals (vdW) layers of transitional-metal dichalcogenides (TMDs), which simultaneously increases the switching ratio and reduces the SET power. The SET voltage, SET power, switching ratio and endurance of the device are strongly correlated with rg. When the ratio of rg to the radius of the metal ions that form the conductive filaments (rg/rAg+) is near 1, the SET voltage and SET power vertically decrease while the switching ratio vertically rises with increasing rg/rAg+. For the fabricated Ag/[SnS2/poly(methyl methacrylate)]/Cu RRAM with an rg/rAg+ of 1.04, the SET voltage, SET power and switching ratio are 0.14 V, 10-10 W and 106, respectively. After 104 switching cycles and a 104 s retention time, the switching ratio of the device can still be stable above 106. Bending has no influence on the performance of the device when the bending radius is not <2 mm.

A mechanism for the variation in the photoelectric performance of a photodetector based on CVD-grown 2D MoS2.

Two-dimensional transition-metal dichalcogenides are considered as promising candidates for next-generation flexible nanoelectronics owing to their compelling properties. The photoelectric performance of a photodetector based on CVD-grown 2D MoS2 was studied. It is found that annealing treatment can make the photoresponsivity and specific detectivity of the CVD-grown 2D MoS2 based photodetector increase from 0.1722 A W-1 and 1014.65 Jones to 0.2907 A W-1 and 1014.84 Jones, respectively, while vulcanization can make the rise response time and fall response time decrease from 0.9013 s and 2.173 s to 0.07779 s and 0.08616 s, respectively. A method to determine the O-doping concentration in the CVD-grown 2D MoS2 has been obtained. The criterion for the CVD-grown 2D MoS2 to transition from an oxygen-doped state to a pure state has been developed. A mechanism explaining the variation in the photoelectric performance of the CVD-grown 2D MoS2 has been proposed. The CVD-grown 2D MoS2 and the annealed CVD-grown 2D MoS2 are oxygen-doped MoS2 while the vulcanized CVD-grown 2D MoS2 is pure MoS2. The variation in the photoelectric performance of CVD-grown 2D MoS2 results from differences in the O-doping concentration and the bandgap.

Structure and Properties of Single-Layer MoS2 for Nano-Photoelectric Devices.

To meet the need for preparing high-performance nano-optoelectronic devices based on single-layer MoS2, the effects of the heating method (one-step or two-step heating) and the temperature of the MoO3 source on the morphology, size, structure, and layers of an MoS2 crystal grown on a sapphire substrate using chemical vapor deposition are studied in this paper. The results show that MoS2 prepared by two-step heating (the heating of the S source starts when the temperature of the MoO3 source rises to 837 K) is superior over that of one-step heating (MoO3 and S are heated at the same time). One-step heating tends to form a mixture of MoO2 and MoS2. Neither too low nor too high of a heating temperature of MoO3 source is conducive to the formation of MoS2. When the temperature of MoO3 source is in the range of 1073 K to 1098 K, the size of MoS2 increases with the rise in temperature. A uniform large-sized triangle with a side length of 100 µm is obtained when the heating temperature of MoO3 is 1098 K. The triangular MoS2 crystals grown by the two-step heating method have a single-layer structure.

(-)-Epicatechin-3-O-ß-D-allopyranoside from Davallia formosana prevents diabetes and dyslipidemia in streptozotocin-induced diabetic mice.

The objective of this study was to evaluate the effects and molecular mechanism of (-)-epicatechin-3-O-ß-D-allopyranoside from Davallia formosana (BB) (also known as Gu-Sui-Bu) on type 1 diabetes mellitus and dyslipidemia in streptozotocin (STZ)-induced diabetic mice. This plant was demonstrated to display antioxidant activities and possess polyphenol contents. Diabetic mice were randomly divided into six groups and were given daily oral gavage doses of either BB (at three dosage levels), metformin (Metf) (at 0.3 g/kg body weight), fenofibrate (Feno) (at 0.25 g/kg body weight) or vehicle (distilled water) and a group of control (CON) mice were gavaged with vehicle over a period of 4 weeks. Treatment with BB led to reduced levels of blood glucose, HbA1C, triglycerides and leptin and to increased levels of insulin and adiponectin compared with the vehicle-treated STZ group. The diabetic islets showed retraction from their classic round-shaped as compared with the control islets. The BB-treated groups (at middle and high dosages) showed improvement in islets size and number of Langerhans islet cells. The membrane levels of skeletal muscular glucose transporter 4 (GLUT4) were significantly higher in BB-treated mice. This resulted in a net glucose lowering effect among BB-treated mice. Moreover, BB enhanced the expression of skeletal muscle phospho-AMPK in treated mice. BB-treated mice increased expression of fatty acid oxidation enzymes, including peroxisome proliferator-activated receptor α (PPARα) and mRNA levels of carnitine palmitoyl transferase Ia (CPT1a). These mice also expressed lower levels of lipogenic genes such as fatty acid synthase (FAS), as well as lower mRNA levels of sterol regulatory element binding protein 1c (SREBP1c) and liver adipocyte fatty acid binding protein 2 (aP2). This resulted in a reduction in plasma triglyceride levels. BB-treated mice also expressed lower levels of PPARγ and FAS protein. This led to reduced adipogenesis, fatty acid synthesis and lipid accumulation within adipose tissue, and consequently, to lower triglyceride levels in liver, blood, and adipose tissue. Moreover, BB treatment not only displayed the activation Akt in liver tissue and skeletal muscle, but also in C2C12 myotube to cause an increase in phosphorylation of Akt in the absence of insulin. These results demonstrated that BB act as an activator of AMPK and /or regulation of insulin pathway (Akt), and the antioxidant activity within the pancreas. Therefore, BB treatment ameliorated the diabetic and dyslipidemic state in STZ-induced diabetic mice.

(-)-Epicatechin-3-O-ß-D-allopyranoside from Davallia formosana, Prevents Diabetes and Hyperlipidemia by Regulation of Glucose Transporter 4 and AMP-Activated Protein Kinase Phosphorylation in High-Fat-Fed Mice.

The purpose of this experiment was to determine the antidiabetic and lipid-lowering effects of (-)-epicatechin-3-O-ß-D-allopyranoside (BB) from the roots and stems of Davallia formosana in mice. Animal treatment was induced by high-fat diet (HFD) or low-fat diet (control diet, CD). After eight weeks of HFD or CD exposure, the HFD mice were treating with BB or rosiglitazone (Rosi) or fenofibrate (Feno) or water through gavage for another four weeks. However, at 12 weeks, the HFD-fed group had enhanced blood levels of glucose, triglyceride (TG), and insulin. BB treatment significantly decreased blood glucose, TG, and insulin levels. Moreover, visceral fat weights were enhanced in HFD-fed mice, accompanied by increased blood leptin concentrations and decreased adiponectin levels, which were reversed by treatment with BB. Muscular membrane protein levels of glucose transporter 4 (GLUT4) were reduced in HFD-fed mice and significantly enhanced upon administration of BB, Rosi, and Feno. Moreover, BB treatment markedly increased hepatic and skeletal muscular expression levels of phosphorylation of AMP-activated (adenosine monophosphate) protein kinase (phospho-AMPK). BB also decreased hepatic mRNA levels of phosphenolpyruvate carboxykinase (PEPCK), which are associated with a decrease in hepatic glucose production. BB-exerted hypotriglyceridemic activity may be partly associated with increased mRNA levels of peroxisome proliferator activated receptor α (PPARα), and with reduced hepatic glycerol-3-phosphate acyltransferase (GPAT) mRNA levels in the liver, which decreased triacylglycerol synthesis. Nevertheless, we demonstrated BB was a useful approach for the management of type 2 diabetes and dyslipidemia in this animal model.