BackgroundAmazona vittata is a critically endangered Puerto Rican endemic bird, the only surviving native parrot species in the United States territory, and the first parrot in the large Neotropical genus Amazona, to be studied on a genomic scale.FindingsIn a unique community-based funded project, DNA from an A. vittata female was sequenced using a HiSeq Illumina platform, resulting in a total of ~42.5 billion nucleotide bases. This provided approximately 26.89x average coverage depth at the completion of this funding phase. Filtering followed by assembly resulted in 259,423 contigs (N50 = 6,983 bp, longest = 75,003 bp), which was further scaffolded into 148,255 fragments (N50 = 19,470, longest = 206,462 bp). This provided ~76% coverage of the genome based on an estimated size of 1.58 Gb. The assembled scaffolds allowed basic genomic annotation and comparative analyses with other available avian whole-genome sequences.ConclusionsThe current data represents the first genomic information from and work carried out with a unique source of funding. This analysis further provides a means for directed training of young researchers in genetic and bioinformatics analyses and will facilitate progress towards a full assembly and annotation of the Puerto Rican parrot genome. It also adds extensive genomic data to a new branch of the avian tree, making it useful for comparative analyses with other avian species. Ultimately, the knowledge acquired from these data will contribute to an improved understanding of the overall population health of this species and aid in ongoing and future conservation efforts.
We present an experimental and theoretical study of a self-pulsing (GaAl)As injection laser operating in an external cavity. We have observed suppression of the self-pulsations when the external cavity is in the range 6 < L < 10 em. Suppression of self-pulsations can also be obtained by using a multimode graded index optical fiber as the external resonator. These results can be explained by a model which includes the effects of an external cavity and electron trapping. For long cavity lengths, the self-pulsation frequency locks to an external cavity harmonic with no significant quenching, as observed in some earlier experiments.PACS numbers: 42.55. Px, 42.60.By In recent months there has been renewed interest in studying intensity self-pulsatons in injection lasers. It has been reported that in a large percentage of aged lasers there is a tendency for self-sustaining oscillations to develop with a frequency ranging from 0.2-2 GHz. Most of the present models assume that self-pulsations are produced by either a saturable absorber 3 · 4 · 6 · 7 or a superlinear gain which increases with photon density.The saturable absorption can arise from nonuniform current flow, 3 · 4 absorption centers distributed throughout the active region/' or localized absorption centers near the laser facets.7 The superlinear gain can result from electron traps distributed throughout the active region 1 or from a phenomenological origin. K.9 There exists little experimental data to verify any one model conclusively. The correlation between theory and experiment is further complicated by the different laser geometries and the mathematical similarities between the different models.In a recent publication Chinone eta/. 10 reported on a method for the suppression of intensity pulsations by using a short external cavity (0.3-2 em). Experimental results by Paoli eta/.11 showed that the external cavity locks the selfpuslation frequency to a cavity harmonic, with no significant quenching effect. These results are not adequately explained by the conventional rate equations, which do not predict sustained pulsations. In this letter we report a study of a selfpulsing (GaAl)As injection laser operation in an external cavity. We use the conventional set of rate equations widely used to analyze relaxation oscillation in lasers. These are modified by the addition, in the manner of Copeland, 1 of absorbing electron traps, and also by a term accounting for the feedback due to the external resonator. Using these equations, we show that the aforementioned observations are not independent, and fit well within the scope of a single model.12 Our analysis is confirmed by experimental results on a self-pulsing laser. Although we use Copeland's equations in our calculations, we believe that other well known models for self-pulsation, when modified to include the external cavity, would produce similar results. Second, we describe a novel method to suppress self-pulsations using an optical fiber resonator. The compactness of the laser-fiber system makes it a ver...
We report on a new high-speed InP-based InxGa1−xAs Schottky barrier photodiode for infrared detection. The photodiodes were fabricated on both p- and n-InGaAs epilayers. For this application, Schottky barrier height enhancement on InGaAs has been demonstrated. The photodiodes had responsivities as high as 0.55 A/W and quantum efficiencies of up to 45% in the range of 1.3–1.6 μm without antireflection coating. The response speed of photodiodes was measured by the impulse response and autocorrelation methods; rise times of 85 ps for p-InGaAs and 180 ps for n-InGaAs photodiodes were obtained. Recently, a barrier height enhancement of 0.35 eV was obtained in n-InGaAs photodiodes, resulting in a great reduction of leakage currents. This would lead to further improvement in the device performance of the photodiodes. Based on measured RC time constants, we estimate the intrinsic response speed to be 12 GHz for n-InGaAs and 18 GHz for p-InGaAs photodiodes. These results show that InP-based InxGa1−xAs Schottky barrier photodiodes can be very useful for high-speed infrared receivers in fiber-optic communications.
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