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- ItemThe Line-of-Sight Depth of Populous Clusters in the Small Magellanic Cloud(The American Astronomical Society, 2001-07) Crowl, Hugh H.; Sarajedini, Ata; Piatti, Andrés E.; Geisler, Doug; Bica, Eduardo; Clariá, Juan J.; João, F. C. Santos, Jr.We present an analysis of age, metal abundance, and positional data on populous clusters in the Small Magellanic Cloud (SMC) with the ultimate aim of determining the line-of-sight (LOS) depth of the SMC by using these clusters as proxies. Our data set contains 12 objects and is limited to clusters with the highest-quality data for which the ages and abundances are best known and can be placed on an internally consistent scale. We have analyzed the variation of the clustersÏ properties with position on the sky and with line-of-sight depth. Based on this analysis, we draw the following conclusions : (1) The observational data indicate that the eastern side of the SMC (facing the Large Magellanic Cloud) contains younger and more metal-rich clusters as compared with the western side. This is not a strong correlation because our data set of clusters is necessarily limited, but it is suggestive and warrants further study. (2) Depending on how the reddening is computed to our clusters, we find a mean distance modulus that ranges from (m-M)^0 = 18.71± 0.06 to 18.82 ± 0.05. (3) The intrinsic ±1 σ LOS depth of the SMC populous clusters in our study is between ~ 6 and ~ 12 kpc, depending primarily on whether we adopt the Burstein & Heiles reddenings or those from Schlegel et al. (4) Viewing the SMC as a triaxial galaxy with declination, right ascension, and LOS depth as the three axes, we find axial ratios of approximately 1:2:4. Taken together, these conclusions largely agree with those of previous investigators and underscore the utility of populous star clusters as probes of the structure of the Small Magellanic Cloud.
- ItemAnalytic torsion and Faddeev-Popov ghosts(2002) McIntyre, AndrewThe regularized determinant of the Laplacian on n-differentials on a hyperbolic Riemann surface is studied. The main result is an intrinsic characterization of the connection form for the determinant line bundle, endowed with the Quillen metric, over the Teichmüller space, in terms of the Green’s function of the Cauchy-Riemann operator. Further, an explicit series representation of that Green’s function, on a Schottky uniformization of the surface, is established. This is a rigorous version of physical heuristics due to Martinec and Verlinde & Verlinde, relating the determinant to the stress-energy tensor of Faddeev-Popov ghost fields on the Riemann surface. One corollary is a simpler proof of the rigorous hyperbolic Belavin-Knizhnik formula, due to Zograf and Takhtajan, which is an intrinsic characterization of the curvature form of the determinant line bundle with Quillen metric. Another corollary is a proof of an explicit holomorphic factorization formula for n = 1 and genus greater than 1, due to Zograf, which generalizes the well known formula for n = 1 and genus 1 relating the determinant of the Laplacian to the Dedekind eta function.
- ItemGlobal Justice and the Challenge of Radical Pluralism(2004-08) Voice, PaulPolitical philosophy has been under the sway of a certain picture since Rawls's A Theory of Justice was published in 1971. This picture combines the idea that the problem of justice should be approached from the direction oi ideal normative theory, and that there are some anchoring ideas that secure the justificatory role of a hypothetical agreement. I think this picture and the hold it has over political philosophy is beginning to fragment. This fragmentation I think is most evident in the skepticism that has become a routine response to the Kantian idea that 'we' can 'discover' the terms of an agreement that has both a categorical force and a universal scope. But as the picture fragments we are still left with the framework and vocabulary of Rawls's difficult and elaborate theory. The major difficulty confronting the Rawlsian project (the problem of pluralism as I will argue below) is itself defined in terms of Rawls's conceptual language. And this serves only to obscure the real challenge and keep us 'bewitched' by Rawls's narrow way of seeing issues. In being bewitched in this way we do not see that the problem of pluralism confronts Rawls's project as a whole, rather than requiring adjustments and accommodations.
- ItemStrain localization on an oceanic detachment fault system, Atlantis Massif, 30 °N, Mid-Atlantic Ridge(Wiley American Geophysical Union, 2004-11) Schroeder, Timothy; John, Barbara E.Abstract: Microstructural observations, mineral chemistry, and the spatial distribution of deformation fabrics recorded in outcrop samples collected from Atlantis Massif, the active inside corner high at 30 °N, Mid- Atlantic Ridge, suggest that strain is localized near the subhorizontal domal surface hypothesized to be an exposed detachment fault. Deformation textures in peridotite and gabbro indicate that high-temperature (>500 °C) strain occurred via crystal-plastic flow and diffusive mass transfer. Low-temperature (<400 °C) shear zones containing brittle and semibrittle microboudinage textures in which tremolite, chlorite, and/or talc replace fractured serpentine or hornblende cut earlier formed high-temperature deformation fabrics in peridotite. Textures indicate strain was localized by cataclasis and reaction softening into zones of intense greenschist and subgreenschist grade metamorphism. Gabbro is only weakly deformed below amphibolite facies (<500° C), indicating that strain was partitioned into altered peridotite at low temperature. There is a clear relationship between deformation intensity and structural depth beneath the subhorizontal surface of the Massif. Discontinuous high-intensity crystal-plastic deformation fabrics are found at all structural depths (0–520 m) beneath the surface, indicating that high-temperature, granulite- and amphibolite-grade deformation was not localized in a single shear zone. In contrast, semibrittle and brittle low-temperature shear zones are concentrated less than 90 m structurally beneath the surface, and the most intensely brittlely deformed samples concentrated in the upper 10 m. Localization of brittle deformation fabrics near the upper surface of the massif supports the hypothesis that it is the exposed footwall of a detachment fault. The structural evolution of Atlantis Massif is therefore analogous to a continental metamorphic core complex. Strain was localized onto the fault by reaction-softening and fluid-assisted fracturing during greenschist- and subgreenschist-grade hydrothermal alteration of olivine, clinopyroxene, serpentine, and hornblende to tremolite, chlorite, and/or talc. Keywords: detachment fault; low-angle normal fault; megamullion; metamorphic core complex; oceanic core complex; slow-spreading ridges.
- ItemFolding and Quality Control of the VHL Tumor Suppressor Proceed through Distinct Chaperone Pathways(Elsevier, 2005-06) McClellan, Amie J.; Scott, Melissa D.; Frydman, JudithThe mechanisms by which molecular chaperones assist quality control of cytosolic proteins are poorly understood. Analysis of the chaperone requirements for degradation of misfolded variants of a cytosolic protein, the VHL tumor suppressor, reveals that distinct chaperone pathways mediate its folding and quality control. While both folding and degradation of VHL require Hsp70, the chaperon in TRiC is essential for folding but is dispensable for degradation. Conversely, the chaperone Hsp90 neither participates in VHL folding nor is required to maintain misfolded VHL solubility but is essential for its degradation. The cochaperone HOP/Sti1p also participates in VHL quality control and may direct the triage decision by bridging the Hsp70-Hsp90 interaction. Our finding that a distinct chaperone complex is uniquely required for quality control provides evidence for active and specific chaperone participation in triage decisions and suggests that a hierarchy of chaperone interactions can control the alternate fates of a cytosolic protein.
- ItemDense Cloud Ablation and Ram Pressure Stripping of the Virgo Spiral NGC 4402(The American Astronomical Society, 2005-07) Crowl, Hugh H.; Kenney, Jeffrey D. P.; van Gorkom, J. H.; Vollmer, BerndWe present optical, H i, and radio continuum observations of the highly inclined Virgo Cluster Sc galaxy NGC 4402, which show evidence for ram pressure stripping and dense cloud ablation. Very Large Array H i and radio continuum maps show a truncated gas disk and emission to the northwest of the main disk emission. In particular, the radio continuum emission is asymmetrically extended to the north and skewed to the west. The H image shows numerous H ii complexes along the southern edge of the gas disk, possibly indicating star formation triggered by the intracluster medium (ICM) pressure. Our BVR images at 0B5 resolution obtained with the WIYN Tip-Tilt Imager show a remarkable dust lane morphology: at half the optical radius, the dust lane of the galaxy curves up and out of the disk, matching the H i morphology. Large dust plumes extend upward for 1.5 kpc from luminous young star clusters at the southeast edge of the truncated gas disk. These star clusters are very blue, indicating very little dust reddening, which suggests dust blown away by an ICM wind at the leading edge of the interaction. To the south of the main ridge of interstellar material, where the galaxy is relatively clean of gas and dust, we have discovered 1 kpc long linear dust filaments with a position angle that matches the extraplanar radio continuum tail; we interpret this angle as the projected ICM wind direction. One of the observed dust filaments has an H ii region at its head.We interpret these dust filaments as large, dense clouds that were initially left behind as the low-density interstellar medium was stripped but were then ablated by the ICM wind. These results provide striking new evidence on the fate of molecular clouds in stripped cluster galaxies.
- ItemProtein Quality Control: Chaperones Culling Corrupt Conformations(Nature Publishing Group, 2005-08) McClellan, Amie J.; Tam, Stephen; Kaganovich, Daniel; Frydman, JudithAchieving the correct balance between folding and degradation of misfolded proteins is critical for cell viability. The importance of defining the mechanisms and factors that mediate cytoplasmic quality control is underscored by the growing list of diseases associated with protein misfolding and aggregation. Molecular chaperones assist protein folding and also facilitate degradation of misfolded polypeptides by the ubiquitin–proteasome system. Here we discuss emerging links between folding and degradation machineries and highlight challenges for future research.
- ItemHolomorphic factorization of determinants of Laplacians using quasi-Fuchsian uniformization(Springer Verlag, 2006) McIntyre, Andrew; Teo, Lee-PengFor a quasi-Fuchsian group Γ with ordinary set Ω, and Δ_n the Laplacian on n-differentials on Γ\Ω, we define a notion of a Bers dual basis ϕ_1,…,ϕ_2_d for ker Δ_n. We prove that det Δ_n/det⟨ϕ_j,ϕ_k⟩, is, up to an anomaly computed by Takhtajan and the second author in (Commun. Math Phys 239(1-2):183–240, 2003), the modulus squared of a holomorphic function F(n), where F(n) is a quasi-Fuchsian analogue of the Selberg zeta function Z(n). This generalizes the D’Hoker–Phong formula det Δ_n=c_g,_nZ(n), and is a quasi-Fuchsian counterpart of the result for Schottky groups proved by Takhtajan and the first author in Analysis 16, 1291–1323, 2006.
- ItemRefractions Off Empire: Untimely Comparisons in Harsh Times(Duke University Press, 2006) Bond, David; Stoler, Ann LauraThe conditions of possibility for what U.S empire looks like today may be deeply embedded in the blunt and elusive nature of a broader range of historical imperial formations.
- ItemHolomorphic factorization of determinants of Laplacians on Riemann surfaces and a higher genus generalization of Kronecker’s first limit formula(Springer Verlag, 2006-09) McIntyre, Andrew; Takhtajan, Leon A.For a family of compact Riemann surfaces X_t of genus g>1 parametrized by the Schottky space S_g, we define a natural basis for the holomorphic n-differentials on X_t which varies holomorphically with t and generalizes the basis of normalized abelian differentials of the first kind for n=1. We introduce a holomorphic function F(n) on S_g which generalizes the classical product \prod(1-q^m)^2 appearing in the Dedekind eta function for n=1 and g=1. We prove a holomorphic factorization formula expressing the regularized determinant of the Laplacian as a product of |F(n)|^2, a holomorphic anomaly depending on the classical Liouville action (a Kahler potential of S_g), and the determinant of the Gram matrix of the natural basis. The factorization formula reduces to Kronecker's first limit formula when n=1 and g=1, and to Zograf's factorization formula for n=1 and g>1.
- ItemThe Stellar Population of Stripped Cluster Spiral NGC 4522: A Local Analog to K+A Galaxies?(The American Astronomical Society, 2006-10) Crowl, Hugh H.; Kenney, Jeffrey D. P.We present observations of the stripped Virgo Cluster spiral galaxy NGC 4522, a clear, nearby example of a galaxy currently undergoing interstellar medium-intracluster medium (ISM-ICM) stripping. Utilizing SparsePak integral field spectroscopy on the Wisconsin-Indiana-Yale-NOAO (WIYN) 3.5 m telescope and Galaxy Evolution Explorer (GALEX) UV photometry, we present an analysis of the outer disk (r>3 kpc) stellar population of this galaxy, beyond the H I and Hα truncation radius. We find that the star formation in the gas-stripped outer disk ceased very recently, ~100 Myr ago, in agreement with previous claims that this galaxy is currently being stripped. At the time of this stripping, data and models suggest that the galaxy experienced a modest starburst. The stripping is occurring in a region of the cluster well outside the cluster core, likely because this galaxy is experiencing extreme conditions from a dynamic ICM due to an ongoing subcluster merger. The outer disk has a spectrum of a K+A galaxy, traditionally observed in high-redshift cluster galaxies. In the case of NGC 4522, a K+A spectrum is formed by simple stripping of the interstellar gas by the hot intracluster medium. These data show K+A spectra can be created by cluster processes and that these processes likely extend beyond the cluster core.
- ItemNonvolcanic seafloor spreading and corner-flow rotation accommodated by extensional faulting at 15 °N on the Mid- Atlantic Ridge: A structural synthesis of ODP Leg 209(Wiley American Geophysical Union, 2007-06) Schroeder, Timothy; Cheadle, Michael J.; Dick, Henry J. B.; Faul, Ulrich; Casey, John F.; Kelemen, Peter B.Abstract: Drilling during ODP Leg 209, dredging, and submersible dives have delineated an anomalous stretch of the Mid-Atlantic Ridge north and south of the 15°20'N Fracture Zone. The seafloor here consists dominantly of mantle peridotite with gabbroic intrusions that in places is covered by a thin, discontinuous extrusive volcanic layer. Thick lithosphere (10–20 km) in this region inhibits magma from reaching shallow levels beneath the ridge axis, thereby causing plate accretion to be accommodated by extensional faulting rather than magmatism. The bathymetry and complex fault relations in the drill-core suggest that mantle denudation and spreading are accommodated by a combination of high-displacement, rolling-hinge normal faults and secondary lower-displacement normal faults. These extensional faults must also accommodate corner flow rotation (up to 90 °) of the upwelling mantle within the shallow lithosphere, consistent with remnant magnetic inclinations in denuded peridotite and gabbro from Leg 209 core that indicate up to 90 ° of sub-Curie-temperature rotation. Keywords: seafloor spreading; ocean drilling program; nonvolcanic mid-ocean ridges; extensional faulting.
- ItemDiverse Cellular Functions of the Hsp90 Molecular Chaperone Uncovered Using Systems Approaches(Elsevier, 2007-10) McClellan, Amie J.; Xia, Yu; Deutschbauer, Adam M.; Davis, Ron W.; Gerstein, Mark; Frydman, JudithA comprehensive understanding of the cellular functions of the Hsp90 molecular chaperone has remained elusive. Although Hsp90 is essential, highly abundant under normal conditions, and further induced by environmental stress, only a limited number of Hsp90 ‘‘clients’’ have been identified. To define Hsp90 function, a panelofgenome-wide chemical-genetic screens in Saccharomyces cerevisiae were combined with bioinformatic analyses. This approach identified several unanticipated functions of Hsp90 under normal conditions and in response to stress. Under normal growth conditions, Hsp90 plays a major role in various aspects of the secretory pathway and cellular transport; during environmental stress, Hsp90 is required for the cell cycle, meiosis, and cytokinesis. Importantly, biochemical and cell biological analyses validated several of these Hsp90-dependent functions, highlighting the potential of our integrated global approach to uncover chaperone functions in the cell.