91 research outputs found
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Shining Light in Dark Places: A Study of Anonymous Network Usage ; CU-CS-1032-07
Stable Magnetostatic Solitons in Yttrium Iron Garnet Film Waveguides for Tilted in-Plane Magnetic Fields
The possibility of nonlinear pulses generation in Yttrium Iron Garnet thin
films for arbitrary direction between waveguide and applied static in-plane
magnetic field is considered. Up to now only the cases of in-plane magnetic
fields either perpendicular or parallel to waveguide direction have been
studied both experimentally and theoretically. In the present paper it is shown
that also for other angles (besides 0 or 90 degrees) between a waveguide and
static in-plane magnetic field the stable bright or dark (depending on
magnitude of magnetic field) solitons could be created.Comment: Phys. Rev. B (accepted, April 1, 2002
Initiation, Establishment, and Maintenance of Heritable MuDR Transposon Silencing in Maize Are Mediated by Distinct Factors
Paramutation and transposon silencing are two epigenetic phenomena that have intrigued and puzzled geneticists for decades. Each involves heritable changes in gene activity without changes in DNA sequence. Here we report the cloning of a gene whose activity is required for the maintenance of both silenced transposons and paramutated color genes in maize. We show that this gene, Mop1 (Mediator of paramutation1) codes for a putative RNA-dependent RNA polymerase, whose activity is required for the production of small RNAs that correspond to the MuDR transposon sequence. We also demonstrate that although Mop1 is required to maintain MuDR methylation and silencing, it is not required for the initiation of heritable silencing. In contrast, we present evidence that a reduction in the transcript level of a maize homolog of the nucleosome assembly protein 1 histone chaperone can reduce the heritability of MuDR silencing. Together, these data suggest that the establishment and maintenance of MuDR silencing have distinct requirements
Using Phylogenomic Patterns and Gene Ontology to Identify Proteins of Importance in Plant Evolution
We use measures of congruence on a combined expressed sequenced tag genome phylogeny to identify proteins that have potential significance in the evolution of seed plants. Relevant proteins are identified based on the direction of partitioned branch and hidden support on the hypothesis obtained on a 16-species tree, constructed from 2,557 concatenated orthologous genes. We provide a general method for detecting genes or groups of genes that may be under selection in directions that are in agreement with the phylogenetic pattern. Gene partitioning methods and estimates of the degree and direction of support of individual gene partitions to the overall data set are used. Using this approach, we correlate positive branch support of specific genes for key branches in the seed plant phylogeny. In addition to basic metabolic functions, such as photosynthesis or hormones, genes involved in posttranscriptional regulation by small RNAs were significantly overrepresented in key nodes of the phylogeny of seed plants. Two genes in our matrix are of critical importance as they are involved in RNA-dependent regulation, essential during embryo and leaf development. These are Argonaute and the RNA-dependent RNA polymerase 6 found to be overrepresented in the angiosperm clade. We use these genes as examples of our phylogenomics approach and show that identifying partitions or genes in this way provides a platform to explain some of the more interesting organismal differences among species, and in particular, in the evolution of plants
Origins Space Telescope: baseline mission concept
The Origins Space Telescope will trace the history of our origins from the time dust and heavy elements permanently altered the cosmic landscape to present-day life. How did galaxies evolve from the earliest galactic systems to those found in the Universe today? How do habitable planets form? How common are life-bearing worlds? To answer these alluring questions, Origins will operate at mid- and far-infrared (IR) wavelengths and offer powerful spectroscopic instruments and sensitivity three orders of magnitude better than that of the Herschel Space Observatory, the largest telescope flown in space to date. We describe the baseline concept for Origins recommended to the 2020 US Decadal Survey in Astronomy and Astrophysics. The baseline design includes a 5.9-m diameter telescope cryocooled to 4.5 K and equipped with three scientific instruments. A mid-infrared instrument (Mid-Infrared Spectrometer and Camera Transit spectrometer) will measure the spectra of transiting exoplanets in the 2.8 to 20āāĪ¼m wavelength range and offer unprecedented spectrophotometric precision, enabling definitive exoplanet biosignature detections. The far-IR imager polarimeter will be able to survey thousands of square degrees with broadband imaging at 50 and 250āāĪ¼m. The Origins Survey Spectrometer will cover wavelengths from 25 to 588āāĪ¼m, making wide-area and deep spectroscopic surveys with spectral resolving power Rāāā¼āā300, and pointed observations at Rāāā¼āā40,000 and 300,000 with selectable instrument modes. Origins was designed to minimize complexity. The architecture is similar to that of the Spitzer Space Telescope and requires very few deployments after launch, while the cryothermal system design leverages James Webb Space Telescope technology and experience. A combination of current-state-of-the-art cryocoolers and next-generation detector technology will enable Originsā natural background-limited sensitivity
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