4,169 research outputs found

    A Thompson Group for the Basilica

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    We describe a Thompson-like group of homeomorphisms of the Basilica Julia set. Each element of this group acts as a piecewise-linear homeomorphism of the unit circle that preserves the invariant lamination for the Basilica. We develop an analogue of tree pair diagrams for this group which we call arc pair diagrams, and we use these diagrams to prove that the group is finitely generated. We also prove that the group is virtually simple.Comment: 23 pages, 31 figure

    Chatter, Clatter, and Blinks: Defective Car Alerts and the Role of Technological Advances in Design Defect/failure to Warn Cases

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    Car owners are familiar with the warning lights on the dashboard and the beeping sound reminding them to use their seatbelt. But, neither the legislature nor courts have concretely defined the legal nature of these alerts. This iBrief will analyze when a deficient alert becomes a defective product tort claim and determine the appropriate theory under which such claims should be brought

    Rearrangement Groups of Fractals

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    We construct rearrangement groups for edge replacement systems, an infinite class of groups that generalize Richard Thompson's groups F, T, and V . Rearrangement groups act by piecewise-defined homeomorphisms on many self-similar topological spaces, among them the Vicsek fractal and many Julia sets. We show that every rearrangement group acts properly on a locally finite CAT(0) cubical complex, and we use this action to prove that certain rearrangement groups are of type F infinity.Comment: 48 pages, 37 figure

    Single-peptide DNA-dependent RNA polymerase homologous to multi-subunit RNA polymerase

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    Transcription in all living organisms is accomplished by multi-subunit RNA polymerases (msRNAPs). msRNAPs are highly conserved in evolution and invariably share a B400 kDa five-subunit catalytic core. Here we characterize a hypothetical B100 kDa single-chain protein, YonO, encoded by the SPb prophage of Bacillus subtilis. YonO shares very distant homology with msRNAPs, but no homology with single-subunit polymerases. We show that despite homology to only a few amino acids of msRNAP, and the absence of most of the conserved domains, YonO is a highly processive DNA-dependent RNA polymerase. We demonstrate that YonO is a bona fide RNAP of the SPb bacteriophage that specifically transcribes its late genes, and thus represents a novel type of bacteriophage RNAPs. YonO and related proteins present in various bacteria and bacteriophages have diverged from msRNAPs before the Last Universal Common Ancestor, and, thus, may resemble the single-subunit ancestor of all msRNAPs

    Racial Minority Lending Trends at the Farm Service Agency

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    A binomial logistic framework is used to determine important linkages between the FSA's decision on each loan application and the applicants financial and demographic attributes. Using data on both rejected and accepted FSA loan applications, empirical results indicate loan approval decisions were not significantly influenced by the borrowers' racial class and that, in contrast to the credit risk assessment standards employed by commercial lenders, the collective influence of more stringent and objective credit scoring measures on FSA loan approval decisions is insignificant.Agricultural Finance,

    Controlling Marangoni induced instabilities in spin-cast polymer films: how to prepare uniform films

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    In both research and industrial settings spin coating is extensively used to prepare highly uniform thin polymer films. However, under certain conditions, spin coating results in films with non-uniform surface morphologies. Although the spin coating process has been extensively studied, the origin of these morphologies is not fully understood and the formation of non-uniform spincast films remains a practical problem. Here we report on experiments demonstrating that the formation of surface instabilities during spin coating is dependent on temperature. Our results suggest that non-uniform spincast films form as a result of the Marangoni effect, which describes flow due to surface tension gradients. We find that both the wavelength and amplitude of the pattern increase with temperature. Finally, and most important from a practical viewpoint, the non-uniformities in the film thickness can be entirely avoided simply by lowering the spin coating temperature.Comment: 8 pages, 6 figures. electronic supplementary material: 3 pages, 4 figure

    Development of a Hard X-Ray Polarimeter for Astrophysics

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    We have been developing a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (100-300 keV) from astrophysical sources. A laboratory prototype polarimeter has been used to successfully demonstrate the reliability of our Monte Carlo simulation code and to demonstrate our ability to generate a polarized photon source in the lab. Our design concept places a self-containedpolarimeter module on the front-end of a a 5-inch position sensitive PMT (PSPMT). We are currently working on the fabrication of a science model based on this PSPMT concept. Although the emphasis of our development effort is towards measuring hard X-rays from solar flares, our design has the advantage that it is sensitive over a rather large field-of-view (\u3e1 steradian), a feature that makes it especially attractive for γ-ray burst studie

    A direct quantitative measure of surface mobility in a glassy polymer

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    Thin polymer films have striking dynamical properties that differ from their bulk counterparts. With the simple geometry of a stepped polymer film on a substrate, we probe mobility above and below the glass transition temperature TgT_{\textrm{g}}. Above TgT_{\textrm{g}} the entire film flows, while below TgT_{\textrm{g}} only the near surface region responds to the excess interfacial energy. An analytical thin film model for flow limited to the free surface region shows excellent agreement with sub-TgT_{\textrm{g}} data. The system transitions from whole film flow to surface localized flow over a narrow temperature region near the bulk TgT_{\textrm{g}}. The experiments and model provide a measure of surface mobility in a sample geometry where confinement and substrate effects are negligible. This fine control of the glassy rheology is of key interest to nanolithography among numerous other applications

    Development of a hard X-ray polarimeter for astrophysics

    Get PDF
    We have been developing a Compton scatter polarimeter for measuring the linear polarization of hard X-rays (100-300 keV) from astrophysical sources. A laboratory prototype polarimeter has been used to successfully demonstrate the reliability of our Monte Carlo simulation code and to demonstrate our ability to generate a polarized photon source in the lab. Our design concept places a self-containedpolarimeter module on the front-end of a a 5-inch position sensitive PMT (PSPMT). We are currently working on the fabrication of a science model based on this PSPMT concept. Although the emphasis of our development effort is towards measuring hard X-rays from solar flares, our design has the advantage that it is sensitive over a rather large field-of-view (\u3e1 steradian), a feature that makes it especially attractive for γ-ray burst studies
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