Circular-polarization reconfigurable monopole antenna with enhanced boresight gain for GNSS applications

A circular-polarization (CP) reconfigurable monopole antenna with enhanced boresight-gain for GNSS applications is proposed. The antenna consists of two meandered monopoles placed perpendicular to each other, a feeding network using the Wilkinson power divider, two switchable 90°-phase-shifters, a defected ground structure (DGS) and a metallic reflector. The metallic reflector is placed at the back of the antenna to improve efficiency and boresight gain. Simulation results show that the metallic reflector can substantially increase the efficiency and boresight-gain of the antenna by about 20% and 5 dB, respectively, in the operating band, yet retaining the impedance bandwidth and axial-ratio bandwidth.postprin

Compact frequency reconfigurable slot antenna with continuous tuning range for cognitive radios

The design of a compact frequency-reconfigurable slot antenna for cognitive radios is proposed in this paper. The antenna consists of a rectangular-ring slot, a T-shaped feed line, an inverted T-shaped stub and two varactors. The length of the rectangular-ring slot is designed to resonate at about 2.4 GHz. The inverted T-shaped stub is used to extend the current path, making the total size of the antenna smaller for low frequency operation. The two varactors are used to achieve continuous tuning. The proposed antenna is studied and designed using computer simulation. The simulated return loss, radiation pattern, realized peak gain and efficiency of the antenna are presented. Results show that the antenna has a wide tuning range from 2.14 to 3.33 GHz (43.51%) and is a potential candidate for use in cognitive radios.postprin

Circularly polarized monopole antenna using CRLH TL feed network

A circularly polarized (CP) monopole antenna with the feed network designed based on using composite right/left-handed transmission line (CRLH TL) is proposed. The CP antenna consists of two monopole elements, a 90°-phase shifter implemented using a CRLH TL unit cell and a Wilkinson power divider. The two monopole elements are designed to operate at a frequency of about 2.3 GHz and placed in perpendicular to each other to generate two orthogonal-electric fields. The power divider divides the input signal into two signals with equal amplitude and phase. One of the signals is fed to a monopole element via the phase shifter, while the other signal is fed directly to the other monopole element. The two signals at the corresponding monopole elements are therefore in phase quadrature, hence generating a CP signal. Simulation results show that the antenna has an impedance bandwidth (S11 < -10 dB) of 1.89-3.20 GHz and a wide axial-ratio bandwidth (AR < 3 dB) of 2.08-2.36 GHz.postprin

Optically powered WDM signal transmission system with distributed parametric amplification

We report, for the first time to our knowledge, an optically powered wavelength-division-multiplexing (WDM) communication system with distributed parametric amplification in the dispersion-shifted fiber. The parametric pump for the amplification of WDM signals also acts as the power supply for the receiver component. The proposed scheme is also a potential candidate for the last mile transmission. Successful musical signal transmission has been demonstrated. Additionally, four channels of 10-Gb/s WDM signals are used to get more precise performance evaluation of the system. The power penalties of less than or equal to 1.35 dB at a bit-error rate of 10-9 are achieved for all WDM channels in the presence of 10-dB parametric gain. © 2006 IEEE.published_or_final_versio

Optically powered WDM signal transmission system with distributed parametric amplification

We report an optically-powered WDM communication system with distributed parametric amplification in dispersion-shifted fiber. The parametric pump also supplies power for the receiver. Power penalties less than 2-dB for each channel at the BER of 10-9 are demonstrated with 10-dB gain. © 2010 IEEE.published_or_final_versionThe IEEE Photonics Society Summer Topical Meetings, Playa del Carmen, Mexico, 19-21 July 2010. In Proceedings of PHOSST, 2010, p. 125-12

Effect of Hawthorn on Drosophila Melanogaster Antioxidant-Related Gene Expression

Purpose: To study the effects of various doses of hawthorn extract on Drosophila lifespan, antioxidant enzyme activity and expression of antioxidant-related regulation genes.Methods: Experiments with Drosophila as an animal model were conducted. The effects of hawthorn on Drosophila melanogaster antioxidant related gene expression were investigated by lifespan tests of Drosophila,  antioxidant enzyme activity assay of Drosophila, and mRNA expression of antioxidant genes by real time-PCR assay.Results: The results indicate that hawthorn extract prolonged the life span of Drosophila, with 50 % survival time of 0.8 and 4 mg/mL groups being increased from 52 days (control) to 56 and 62 days, respectively. Addition of 0.8 mg/mL hawthorn extract increased CuZn-SOD enzyme activity significantly (p < 0.05); the 4 mg/mL extract significantly increased CuZn-SOD enzyme (p < 0.01) and CAT enzyme activity (p < 0.05), but decreased MDA levels. Real time-PCR results show that the 4 mg/mL extract significantly improved the expression levels of CuZn-SOD and CAT mRNA (p < 0.05); on the other hand, both extract concentrations improved PHGSH-Px mRNA level significantly compared with that of control group (p < 0.05).Conclusion: The antioxidant activity of hawthorn in vivo may be achieved by increasing endogenous antioxidant enzymes.Keywords: Drosophila melanogaster, Hawthorn, Lifespan, Enzyme, Gene expression, Phospholipid hydroperoxide glutathione peroxidase,  Superoxide dismutase, Catalas

Overall Evolution of Realistic Gamma-ray Burst Remnant and Its Afterglow

Conventional dynamic model of gamma-ray burst remnants is found to be incorrect for adiabatic blastwaves during the non-relativistic phase. A new model is derived, which is shown to be correct for both radiative and adiabatic blastwaves during both ultra-relativistic and non-relativistic phase. Our model also takes the evolution of the radiative efficiency into account. The importance of the transition from the ultra-relativistic phase to the non-relativistic phase is stressed.Comment: 9 pages, aasms4 style, 3 ps figures, minor changes, will be published in Chin. Phys. Let

An overview of epigenetics and chemoprevention

AbstractIt is now appreciated that both genetic alteration, e.g. mutations, and aberrant epigenetic changes, e.g. DNA methylation, cause cancer. Epigenetic dysregulation is potentially reversible which makes it attractive as targets for cancer prevention. Synthetic drugs targeting enzymes, e.g. DNA methyltransferase and histone deacetylase, that regulate epigenetic patterns are active in clinical settings. In addition, dietary factors have been suggested to have potential to reverse aberrant epigenetic patterns. Uncovering the human epigenome can lead us to better understand the dynamics of DNA methylation in disease progression which can further assist in cancer prevention