Electro-optic modulators based on polymeric Y-fed directional couplers

textThe performance of current commercially available electro-optical (EO) intensity modulators is adversely affected by the distortions caused by the nonlinearity of their modulation curves. Furthermore, the direct-current biases, required in order to bring these modulators to their best working points, result in more complicated circuit fabrications than are desirable. This current research investigated the feasibility of fabricating bias-free and/or high-linear EO modulators by incorporating the merits of the Y-fed directional couplers (YCMs) with those of the EO polymer materials. To this end, EO polymer-based conventional YCMs were employed to fabricate bias-free EO modulators. A low switching voltage of 3.6V and a high extinction ratio of 26dB were obtained, at a 1.34µm wavelength, with a conventional polymeric YCM having lumped electrodes. A high-speed intrinsic 3dB-biased EO modulator based on a conventional polymeric YCM operating at a 1.55µm wavelength was successfully demonstrated to provide a 22-GHz 3-dB bandwidth, with a performance similar to that of a quadrature-biased Mach-Zehnder modulator (MZM) in terms of nonlinear distortion suppression when no direct-current bias was applied. A broadband high-linear EO modulator based on a ∆β-inverted polymeric YCM was also demonstrated for the first time. This modulator had a 3-dB bandwidth of 20GHz, and a high nonlinear distortion suppression, which was approximately 20dB larger than that of a quadrature-biased MZM in the range between 0 and 8 GHz. The linearity properties of the high-speed ∆β-inverted YCMs were also investigated theoretically. The results show that broadband high-linear modulators can be achieved by taking advantage of the small dispersion in EO polymers’ refractive indexes at microwave and optic frequencies. A systematic study on traveling-wave (TW) electrodes for polymer-based directional couplers was conducted for the first time in order to find the optimal electrode structure and dimensions. A conformal-mapping approach to the optimum TW electrode design of a coplanar waveguide with ground (CPWG) was developed and employed to optimize the electrode dimensions.Electrical and Computer Engineerin

Transcriptome Analysis of Host-Associated Differentiation in \u3cem\u3eBemisia tabaci\u3c/em\u3e (Hemiptera: Aleyrodidae)

Host-associated differentiation is one of the driving forces behind the diversification of phytophagous insects. In this study, host induced transcriptomic differences were investigated in the sweetpotato whitefly Bemisia tabaci, an invasive agricultural pest worldwide. Comparative transcriptomic analyses using coding sequence (CDS), 5′ and 3′ untranslated regions (UTR) showed that sequence divergences between the original host plant, cabbage, and the derived hosts, including cotton, cucumber and tomato, were 0.11–0.14%, 0.19–0.26%, and 0.15–0.21%, respectively. In comparison to the derived hosts, 418 female and 303 male transcripts, respectively, were up-regulated in the original cabbage strain. Among them, 17 transcripts were consistently up-regulated in both female and male whiteflies originated from the cabbage host. Specifically, two ESTs annotated as Cathepsin B or Cathepsin B-like genes were significantly up-regulated in the original cabbage strain, representing a transcriptomic response to the dietary challenges imposed by the host shifting. Results from our transcriptome analysis, in conjunction with previous reports documenting the minor changes in their reproductive capacity, insecticide susceptibility, symbiotic composition and feeding behavior, suggest that the impact of host-associated differentiation in whiteflies is limited. Furthermore, it is unlikely the major factor contributing to their rapid range expansion/invasiveness

Exploring Valid Reference Genes for Quantitative Real-time PCR Analysis in \u3cem\u3ePlutella xylostella\u3c/em\u3e (Lepidoptera: Plutellidae)

Quantitative real-time PCR (qRT-PCR), a primary tool in gene expression analysis, requires an appropriate normalization strategy to control for variation among samples. The best option is to compare the mRNA level of a target gene with that of reference gene(s) whose expression level is stable across various experimental conditions. In this study, expression profiles of eight candidate reference genes from the diamondback moth, Plutella xylostella, were evaluated under diverse experimental conditions. RefFinder, a web-based analysis tool, integrates four major computational programs including geNorm, Normfinder, BestKeeper, and the comparative ΔCt method to comprehensively rank the tested candidate genes. Elongation factor 1 (EF1) was the most suited reference gene for the biotic factors (development stage, tissue, and strain). In contrast, although appropriate reference gene(s) do exist for several abiotic factors (temperature, photoperiod, insecticide, and mechanical injury), we were not able to identify a single universal reference gene. Nevertheless, a suite of candidate reference genes were specifically recommended for selected experimental conditions. Our finding is the first step toward establishing a standardized qRT-PCR analysis of this agriculturally important insect pest

Detecting top-Higgs at high energy e+e−e^{+}e^{-} colliders

We calculate the contributions of the top-Higgs $h_{t}^{0}$ predicted by topcolor assisted technicolor(TC2) models to $e^{+}e^{-}\longrightarrow \overline{t}c\overline{\nu}_{e}\nu_{e}$ and compare the results with the contributions of $h^{0}_{t}$ to the processes $e^{+}e^{-}\longrightarrow Z h^{0}_{t}\longrightarrow Z\overline{t}c$ and $e^+e^-\longrightarrow \gamma h^{0}_{t} \longrightarrow \gamma \overline{t}c$. We find that $e^{+}e^{-} \longrightarrow\overline{t}c\overline{\nu}_{e}\nu_{e}$ is very sensitive to $h^{0}_{t}$, which can be easy detected via this process at high-energy $e^{+}e^{-}$ collider(LC) experiments with $\sqrt{s}\geq 500$ $GeV$, as long as its mass below the $\overline{t}t$ threshold. The process $e^{+}e^{-} \longrightarrow \gamma\overline{t}c$ also can be used to detect $h^{0}_{t}$ at LC experiments.Comment: latex file, 10 pages, 4 eps figure, submitted to Phys. Lett.

Effects of Plant Virus and Its Insect Vector on Encarsia Formosa, a Biocontrol Agent of Whiteflies

In this study, we investigated the tritrophic interactions among a persistently transmitted plant virus, Tomato yellow leaf curl virus (TYLCV), its insect vector, the sweetpotato whitefly Bemisia tabaci, and a parasitoid, Encarsia formosa Gahan, one of the most extensively used biological control agents. As an emerging invasive pest worldwide, the two most damaging whiteflies are B. tabaci B and Q cryptic species. On healthy tomato plants, parasitoid-induced mortality was significantly higher in B. tabaci B than in Q. In contrast, similar mortality levels of B and Q were observed on TYLCV-infected plants. A higher rate of parasitism was consistently observed in B, independent of the TYLCV infection. Similarly, the life history traits of E. formosa were influenced by both TYLCV and the two cryptic species of B. tabaci. Specifically, E. formosa parasitizing B had a greater adult longevity and shorter developmental time on healthy plants, whereas the parasitoids developing from Q has a greater adult longevity on TYLCV-infected plants. The emergence rate of E. formosa was unaffected by either B. tabaci cryptic species or the virus. These results suggest that the vector-borne pathogen can manipulate the host suitability of a parasitoid and hence the parasitoid-host interactions