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Showing papers by "University of California, Santa Cruz published in 2000"


Journal ArticleDOI
TL;DR: In this paper, a correlation between the mass Mbh of a galaxy's central black hole and the luminosity-weighted line-of-sight velocity dispersion σe within the half-light radius is described.
Abstract: We describe a correlation between the mass Mbh of a galaxy's central black hole and the luminosity-weighted line-of-sight velocity dispersion σe within the half-light radius. The result is based on a sample of 26 galaxies, including 13 galaxies with new determinations of black hole masses from Hubble Space Telescope measurements of stellar kinematics. The best-fit correlation is Mbh = 1.2(±0.2) × 108 M☉(σe/200 km s-1)3.75 (±0.3) over almost 3 orders of magnitude in Mbh; the scatter in Mbh at fixed σe is only 0.30 dex, and most of this is due to observational errors. The Mbh-σe relation is of interest not only for its strong predictive power but also because it implies that central black hole mass is constrained by and closely related to properties of the host galaxy's bulge.

3,901 citations


Journal ArticleDOI
TL;DR: In this article, the final results of the Hubble Space Telescope Key Project to measure the Hubble constant are presented, and the implications of these results for cosmology are discussed and compared with other, global methods for measuring the Hubble constants.
Abstract: We present here the final results of the Hubble Space Telescope Key Project to measure the Hubble constant. We summarize our method, the results and the uncertainties, tabulate our revised distances, and give the implications of these results for cosmology. The analysis presented here benefits from a number of recent improvements and refinements, including (1) a larger LMC Cepheid sample to define the fiducial period-luminosity (PL) relations, (2) a more recent HST Wide Field and Planetary Camera 2 (WFPC2) photometric calibration, (3) a correction for Cepheid metallicity, and (4) a correction for incompleteness bias in the observed Cepheid PL samples. New, revised distances are given for the 18 spiral galaxies for which Cepheids have been discovered as part of the Key Project, as well as for 13 additional galaxies with published Cepheid data. The new calibration results in a Cepheid distance to NGC 4258 in better agreement with the maser distance to this galaxy. Based on these revised Cepheid distances, we find values (in km/sec/Mpc) of H0 = 71 +/- 2 (random) +/- 6 (systematic) (type Ia supernovae), 71 +/- 2 +/- 7 (Tully-Fisher relation), 70 +/- 5 +/- 6 (surface brightness fluctuations), 72 +/- 9 +/- 7 (type II supernovae), and 82 +/- 6 +/- 9 (fundamental plane). We combine these results for the different methods with 3 different weighting schemes, and find good agreement and consistency with H0 = 72 +/- 8. Finally, we compare these results with other, global methods for measuring the Hubble constant.

2,528 citations


Journal ArticleDOI
TL;DR: A new method to analyse tissue samples using support vector machines for mis-labeled or questionable tissue results and shows that other machine learning methods also perform comparably to the SVM on many of those datasets.
Abstract: Motivation: DNA microarray experiments generating thousands of gene expression measurements, are being used to gather information from tissue and cell samples regarding gene expression differences that will be useful in diagnosing disease. We have developed a new method to analyse this kind of data using support vector machines (SVMs). This analysis consists of both classification of the tissue samples, and an exploration of the data for mis-labeled or questionable tissue results. Results: We demonstrate the method in detail on samples consisting of ovarian cancer tissues, normal ovarian tissues, and other normal tissues. The dataset consists of expression experiment results for 97 802 cDNAs for each tissue. As a result of computational analysis, a tissue sample is discovered and confirmed to be wrongly labeled. Upon correction of this mistake and the removal of an outlier, perfect classification of tissues is achieved, but not with high confidence. We identify and analyse a subset of genes from the ovarian dataset whose expression is highly differentiated between the types of tissues. To show robustness of the SVM method, two previously published datasets from other types of tissues or cells are analysed. The results are comparable to those previously obtained. We show that other machine learning methods also perform comparably to the SVM on many of those datasets. Availability: The SVM software is available at http:// www. cs.columbia.edu/ ∼bgrundy/ svm.

2,464 citations


Journal ArticleDOI
TL;DR: In this paper, a method of functionally classifying genes by using gene expression data from DNA microarray hybridization experiments is introduced based on the theory of support vector machines (SVMs).
Abstract: We introduce a method of functionally classifying genes by using gene expression data from DNA microarray hybridization experiments. The method is based on the theory of support vector machines (SVMs). SVMs are considered a supervised computer learning method because they exploit prior knowledge of gene function to identify unknown genes of similar function from expression data. SVMs avoid several problems associated with unsupervised clustering methods, such as hierarchical clustering and self-organizing maps. SVMs have many mathematical features that make them attractive for gene expression analysis, including their flexibility in choosing a similarity function, sparseness of solution when dealing with large data sets, the ability to handle large feature spaces, and the ability to identify outliers. We test several SVMs that use different similarity metrics, as well as some other supervised learning methods, and find that the SVMs best identify sets of genes with a common function using expression data. Finally, we use SVMs to predict functional roles for uncharacterized yeast ORFs based on their expression data.

2,395 citations


Journal ArticleDOI
15 Nov 2000-Proteins
TL;DR: Analysis of amino acid sequences, based on the normalized net charge and mean hydrophobicity, has been applied to two sets of proteins and shows that “natively unfolded” proteins are specifically localized within a unique region of charge‐hydrophobia phase space.
Abstract: "Natively unfolded" proteins occupy a unique niche within the protein kingdom in that they lack ordered structure under conditions of neutral pH in vitro. Analysis of amino acid sequences, based on the normalized net charge and mean hydrophobicity, has been applied to two sets of proteins: small globular folded proteins and "natively unfolded" ones. The results show that "natively unfolded" proteins are specifically localized within a unique region of charge-hydrophobicity phase space and indicate that a combination of low overall hydrophobicity and large net charge represent a unique structural feature of "natively unfolded" proteins.

2,029 citations


Journal Article
D. E. Groom1, M. Aguilar-Benitez, Claude Amsler2, R. M. Barnett1, Patricia R. Burchat3, C. D. Carone4, C. Caso5, G. Conforto6, O. I. Dahl1, Michael Doser7, Semen Eidelman8, Jonathan L. Feng, L. K. Gibbons9, Maury Goodman10, Christoph Grab11, Atul Gurtu12, K. Hagiwara, K. G. Hayes13, J. J. Hernandez14, Ken Ichi Hikasa15, K. Honscheid16, Christopher Kolda1, Michelangelo L. Mangano7, Aneesh V. Manohar17, A. Masoni, Klaus Mönig, Hitoshi Murayama18, Hitoshi Murayama1, Koji Nakamura, S. Sánchez Navas19, Keith A. Olive20, Luc Pape7, A. Piepke21, Matts Roos22, Masaharu Tanabashi15, Nils A. Tornqvist22, T. G. Trippe1, Petr Vogel23, C. G. Wohl1, Ron L. Workman24, W-M. Yao1, B. Armstrong1, J. L. Casas Serradilla7, B. B. Filimonov, P. S. Gee1, S. B. Lugovsky, F. Nicholson7, K. S. Babu, D. Z. Besson25, Otmar Biebel26, P. Bloch7, Robert N. Cahn1, Ariella Cattai7, R. S. Chivukula27, R. Cousins28, Thibault Damour29, K. Desler, R. J. Donahue1, D. A. Edwards, Jens Erler30, V. V. Ezhela, A. Fassò3, W. Fetscher11, Daniel Froidevaux7, Masataka Fukugita31, Thomas K. Gaisser32, L. A. Garren33, S. Geer33, H J Gerber11, Frederick J. Gilman34, Howard E. Haber35, C. A. Hagmann36, Ian Hinchliffe1, Craig J. Hogan37, G. Höhler38, P. Igo-Kemenes39, John David Jackson1, Kurtis F Johnson40, D. Karlen41, Boris Kayser42, S. R. Klein1, Konrad Kleinknecht43, I.G. Knowles44, Edward W. Kolb45, Edward W. Kolb33, P. Kreitz3, R. Landua7, Paul Langacker30, L. S. Littenberg46, David Manley47, John March-Russell, T. Nakada48, Helen R. Quinn3, Georg G. Raffelt49, B. Renk43, L. Rolandi7, Michael T Ronan1, L.J. Rosenberg50, H. F.W. Sadrozinski35, A. I. Sanda51, Michael Schmitt52 
TL;DR: In this article, a biennial review summarizes much of particle physics using data from previous editions., plus 2778 new measurements from 645 papers, including measurements of gauge bosons, leptons, quarks, mesons, and baryons.
Abstract: This biennial Review summarizes much of particle physics. Using data from previous editions., plus 2778 new measurements from 645 papers, we list, evaluate, and average measured properties of gauge bosons, leptons, quarks, mesons, and baryons. We also summarize searches for hypothetical particles such as Higgs bosons, heavy neutrinos, and supersymmetric particles. All the particle properties and search limits are listed in Summary Tables. We also give numerous tables, figures, formulae, and reviews of topics such as the Standard Model, particle detectors., probability, and statistics. Among the 108 reviews are many that are new or heavily revised including those on CKM quark-mixing matrix, V-ud & V-us, V-cb & V-ub, top quark, muon anomalous magnetic moment, extra dimensions, particle detectors, cosmic background radiation, dark matter, cosmological parameters, and big bang cosmology.

1,520 citations


Journal ArticleDOI
TL;DR: This paper analyzed the adjustment dynamics of real exchange rates through impulse response analysis and found that the dynamic response pattern suggests that the shock response is initially amplified before dissipating and that such non-monotonic dynamics can contribute to more than one-third of the observed persistence of the real exchange rate.

1,390 citations


Journal ArticleDOI
TL;DR: In this paper, the angular momenta for the iron core and overlying material of typical presupernova stars along with their detailed chemical structure are determined, for the first time, the angular momentum distribution in typical pre-main-sequence stars.
Abstract: The evolution of rotating stars with zero-age main-sequence (ZAMS) masses in the range 8-25 M☉ is followed through all stages of stable evolution. The initial angular momentum is chosen such that the star's equatorial rotational velocity on the ZAMS ranges from zero to ~ 70% of breakup. The stars rotate rigidly on the ZAMS as a consequence of angular momentum redistribution during the pre-main-sequence evolution. Redistribution of angular momentum and chemical species are then followed as a consequence of Eddington-Sweet circulation, Solberg-Hoiland instability, the Goldreich-Schubert-Fricke instability, and secular and dynamic shear instability. The effects of the centrifugal force on the stellar structure are included. Convectively unstable zones are assumed to tend toward rigid rotation, and uncertain mixing efficiencies are gauged by observations. We find, as noted in previous work, that rotation increases the helium core masses and enriches the stellar envelopes with products of hydrogen burning. We determine, for the first time, the angular momentum distribution in typical presupernova stars along with their detailed chemical structure. Angular momentum loss due to (nonmagnetic) stellar winds and the redistribution of angular momentum during core hydrogen burning are of crucial importance for the specific angular momentum of the core. Neglecting magnetic fields, we find angular momentum transport from the core to the envelope to be unimportant after core helium burning. We obtain specific angular momenta for the iron core and overlying material of 1016-1017 cm2 s-1. These values are insensitive to the initial angular momentum and to uncertainties in the efficiencies of rotational mixing. They are small enough to avoid triaxial deformations of the iron core before it collapses, but could lead to neutron stars which rotate close to breakup. They are also in the range required for the collapsar model of gamma-ray bursts. The apparent discrepancy with the measured rotation rates of young pulsars is discussed.

981 citations


Journal ArticleDOI
TL;DR: Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s-1 and a period of 3.5239 days, which is indicative of a "51 Peg-like" planet with a minimum mass (Msini) of 0.62 MJup and a semimajor axis of0.046 AU.
Abstract: Doppler measurements from Keck exhibit a sinusoidal periodicity in the velocities of the G0 dwarf HD 209458, having a semiamplitude of 81 m s 21 and a period of 3.5239 days, which is indicative of a “51 Peg‐like” planet with a minimum mass ( ) of 0.62 MJup and a semimajor axis of 0.046 AU. Follow-up photometry reveals M sin i a drop of 0.017 mag at the predicted time (within the errors) of transit by the companion based on the velocities. This is the first extrasolar planet observed to transit its star. The radius of the planet derived from the magnitude of the dimming is 1.42 RJup, which is consistent with models of irradiated Jupiter-mass planets. The transit implies that , leading to a true mass of 0.62 MJup for the planet. The resulting mean density of 0.27 g cm 23 sin i 1 0.993 implies that the companion is a gas giant. Subject headings: planetary systems — stars: individual (HD 209458)

940 citations


Journal ArticleDOI
06 Jan 2000-Nature
TL;DR: Findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.
Abstract: Over 400 California sea lions (Zalophus californianus) died and many others displayed signs of neurological dysfunction along the central California coast during May and June 1998. A bloom of Pseudo-nitzschia australis (diatom) was observed in the Monterey Bay region during the same period. This bloom was associated with production of domoic acid (DA), a neurotoxin1 that was also detected in planktivorous fish, including the northern anchovy (Engraulis mordax), and in sea lion body fluids. These and other concurrent observations demonstrate the trophic transfer of DA resulting in marine mammal mortality. In contrast to fish, blue mussels (Mytilus edulus) collected during the DA outbreak contained no DA or only trace amounts. Such findings reveal that monitoring of mussel toxicity alone does not necessarily provide adequate warning of DA entering the food web at levels sufficient to harm marine wildlife and perhaps humans.

794 citations


Journal ArticleDOI
TL;DR: In this paper, single stellar population (SSP)-equivalent parameters for 50 local elliptical galaxies were analyzed as a function of their structural parameters, including velocity dispersions, radii, surface brightnesses, masses, and luminosities.
Abstract: This paper analyzes single stellar population (SSP)–equivalent parameters for 50 local elliptical galaxies as a function of their structural parameters. The galaxy sample is drawn from the high-quality spectroscopic surveys of Gonzalez (1993) and Kuntschner (1998). The basic data are central values of SSP-equivalent ages, t, metallicities, [Z/H], and enhancement ratios, [E/Fe], derived in Paper I, together with global structural parameters including velocity dispersions, radii, surface brightnesses, masses, and luminosities. The galaxies fill a two-dimensional plane in the four-dimensional space of [Z/H], log t, log σ, and [E/Fe]. SSP age, t, and velocity dispersion, σ, can be taken as the two independent parameters that specify a galaxy's location in this hyperplane. The hyperplane can be decomposed into two subrelations: (1) a Z-plane, in which [Z/H] is a linear function of log σ and log t and (2) a relation between [E/Fe] and σ in which [E/Fe] is larger in high-σ galaxies. Velocity dispersion is the only structural parameter that is found to modulate the stellar populations; adding other structural variables such as Ie or re does not predict [Z/H] or [E/Fe] more accurately. Cluster and field ellipticals follow the same hyperplane, but their (σ,t) distributions within it differ. Most Fornax and Virgo cluster galaxies are old, with a only a small sprinkling of galaxies to younger ages. The field ellipticals span a larger range in SSP age, with a tendency for lower σ galaxies to be younger. The present sample thus suggests that the distribution of local ellipticals in the (σ,t) plane may depend on environment. Since the (σ,t) distribution affects all two-dimensional projections involving SSP parameters, many of the familiar scaling laws attributed to ellipticals may also depend on environment. Some evidence for this is seen in the current sample. For example, only Fornax ellipticals show the classic mass-metallicity relation, whereas other subsamples do not. The tight Mg-σ relations of these ellipticals can be understood as two-dimensional projections of the metallicity hyperplane showing it edge-on. At fixed σ, young age tends to be offset by high [Z/H], preserving Mg nearly constant. The tightness of the Mg-σ relations does not necessarily imply a narrow range of ages at fixed σ. Although SSP parameters are heavily weighted by young stars, modeling them still places tight constraints on the total star formation history of elliptical galaxies. The relation between [E/Fe] and σ is consistent with a higher effective yield of Type II SNe elements at higher σ. This might occur if the IMF is enhanced in massive stars at high σ, or if more SNe II–enriched gas is retained by deeper galactic potential wells. Either way, modulating Type II yields versus σ seems to fit the data better than modulating Type Ia yields. The Z-plane is harder to explain and may be a powerful clue to star formation in elliptical galaxies if it proves to be general. Present data favor a frosting model in which low apparent SSP ages are produced by adding a small frosting of younger stars to an older base population (assuming no change in σ). If the frosting abundances are close to or slightly greater than the base population, simple two-component models run along lines of constant σ in the Z-plane, as required. This favors star formation from well-mixed pre-enriched gas rather than unmixed low-metallicity gas from an accreted object.

Journal ArticleDOI
TL;DR: It is postulate that tropical endophytes themselves may be hyperdiverse and suggest that extrapolative estimates that exclude them will markedly underestimate fungal species diversity.
Abstract: Fungal endophytes are ubiquitous fungi that inhabit healthy plant tissues without causing disease. Endophytes have been found in every plant species examined to date and may be important, but often overlooked, components of fungal biodiversity. In two sites in a lowland, moist tropical forest of central Panama, we quantified endophyte colonization patterns, richness, host preference, and spatial variation in healthy leaves of two co-occurring, understory tree species [Heisteria concinna (Olacaceae) and Ouratea lucens (Ochnaceae)]. From 83 leaves, all of which were colonized by endophytes, we isolated 418 endophyte morphospecies (estimated 347 genetically distinct taxa), most of which were represented by only a single isolate (59%). Among morphospecies encountered in more than one leaf (nonsingletons), we found evidence of host preference and spatial heterogeneity using both morphospecies frequencies and presence/absence records. Based on these data, we postulate that tropical endophytes themselves may be hyperdiverse and suggest that extrapolative estimates that exclude them will markedly underestimate fungal species diversity.

Journal ArticleDOI
TL;DR: The relative importance of various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks, and their spatial distributions.
Abstract: Improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed. We present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion (e.g., plucking, abrasion, cavitation, solution) is a strong function of substrate lithology, and that joint spacing, fractures, and bedding planes exert the most direct control. The relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks, and their spatial distributions. We find that plucking dominates wherever rocks are well jointed on a submeter scale. Hydraulic wedging of small clasts into cracks, bashing and abrasion by bedload, and chemical and physical weathering all contribute to the loosening and removal of joint blocks. In more massive rocks, abrasion by suspended sand appears to be rate limiting in the systems studied here. Concentration of erosion on downstream sides of obstacles and tight coupling between fluid-flow patterns and fine-scale morphology of erosion forms testify to the importance of abrasion by suspended-load, rather than bedload, particles. Mechanical analyses indicate that erosion by suspended-load abrasion is considerably more nonlinear in shear stress than erosion by plucking. In addition, a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued. Cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive, unjointed rocks that is otherwise attributed to suspended-load abrasion. Direct field evidence of cavitation erosion is, however, lacking. In terms of the well-known shear-stress (or stream-power) erosion law, erosion by plucking is consistent with a slope exponent ( n ) of ∼2/3 to 1, whereas erosion by suspended-load abrasion is more consistent with a slope exponent of ∼5/3. Given that substrate lithology appears to dictate the dominant erosion process, this finding has important implications for long-term landscape evolution and the models used to study it.

Journal ArticleDOI
TL;DR: In this article, a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra was conducted to determine the star formation and chemical evolution histories of present-day galaxies.
Abstract: This paper commences a series of investigations into the stellar populations of local elliptical galaxies as determined from their integrated spectra. The goal of the series is to determine the star formation and chemical evolution histories of present-day elliptical galaxies. The primary galaxy sample analyzed is that of Gonzalez, which consists of 39 elliptical galaxies drawn primarily from the local field and nearby groups, plus the bulge of Messier 31. Single-burst stellar population (SSP)–equivalent ages, metallicities, and abundance ratios are derived from Hβ, Mg b, and Fe line strengths using an extension of the Worthey models that incorporates nonsolar line-strength "response functions" by Tripicco & Bell. These functions account for changes in the Lick/IDS indices caused by nonsolar abundance ratios, allowing us to correct the Worthey models for the enhancements of Mg and other α-like elements relative to the Fe-peak elements. SSP-equivalent ages of the Gonzalez elliptical galaxies are found to vary widely, 1.5 Gyr t 18 Gyr, while metallicities [Z/H] and enhancement ratios [E/Fe] are strongly peaked around [Z/H] = +0.26 and [E/Fe] = +0.20 (in an aperture of radius re/8). The enhancement ratios [E/Fe] are milder than previous estimates because of the application of nonsolar abundance corrections to both Mg b and Fe for the first time. While [E/Fe] is usually greater than zero, it is not the "E" elements that are actually enhanced but rather the Fe-peak elements that are depressed; this serves not only to weaken Fe but also to strengthen Mg b, accounting for the overall generally mild enhancements. Based on index strengths from the Lick/IDS galaxy library (Trager et al.), C is not depressed with Fe but rather seems to be on a par with other elements such as Mg in the E group. Gradients in stellar populations within galaxies are found to be mild, with SSP-equivalent age increasing by 25%, metallicity decreasing by [Z/H] = 0.20 dex, and [E/Fe] remaining nearly constant out to an aperture of radius re/2 for nearly all systems. Our ages have an overall zero-point uncertainty of at least ~25% because of uncertainties in the stellar evolution prescription, the oxygen abundance, the effect of [E/Fe] ≠ 0 on the isochrones, and other unknowns. However, the relative age rankings of stellar populations should be largely unaffected by these errors. In particular, the large spread in ages appears to be real and cannot be explained by contamination of Hβ by blue stragglers or hot horizontal-branch stars, or by fill-in of Hβ by emission. Correlations between these derived SSP-equivalent parameters and other galaxy observables will be discussed in future papers.

Journal ArticleDOI
TL;DR: In this paper, the Tully-fisher relation, the fundamental plane of elliptical galaxies, Type Ia supernovae, and surface brightness fluctuations are combined with a model of the velocity field to yield the best available estimate of the value of H0 within the range of these secondary distance indicators and its uncertainty.
Abstract: Since the launch of Hubble Space Telescope (HST) 9 yr ago, Cepheid distances to 25 galaxies have been determined for the purpose of calibrating secondary distance indicators. Eighteen of these have been measured by the HST Key Project team, six by the Supernova Calibration Project, and one independently by Tanvir. Collectively, this work sets out an array of survey markers over the region within 25 Mpc of the Milky Way. A variety of secondary distance indicators can now be calibrated, and the accompanying four papers employ the full set of 25 galaxies to consider the Tully-Fisher relation, the fundamental plane of elliptical galaxies, Type Ia supernovae, and surface brightness fluctuations. When calibrated with Cepheid distances, each of these methods yields a measurement of the Hubble constant and a corresponding measurement uncertainty. We combine these measurements in this paper, together with a model of the velocity field, to yield the best available estimate of the value of H0 within the range of these secondary distance indicators and its uncertainty. The uncertainty in the result is modeled in an extensive simulation we call the "virtual Key Project." The velocity-field model includes the influence of the Virgo cluster, the Great Attractor, and the Shapley supercluster, but does not play a significant part in determining the result. The result is H0 = 71 ± 6 km s-1 Mpc-1. The largest contributor to the uncertainty of this 67% confidence level result is the distance of the Large Magellanic Cloud, which has been assumed to be 50 ± 3 kpc. This takes up the first 6.5% of our 9% error budget. Other contributors are the photometric calibration of the WFPC2 instrument, which takes up 4.5%, deviations from uniform Hubble flow in the volume sampled (2%), the composition sensitivity of the Cepheid period-luminosity relation (4%), and departures from a universal reddening law (~1%). These are the major components that , when combined in quadrature, make up the 9% total uncertainty. If the LMC distance modulus were systematically smaller by 1 σ than that adopted here, the derived value of the Hubble constant would increase by 4 km s-1 Mpc-1. Most of the significant systematic errors are capable of amelioration in future work. These include the uncertainty in the photometric calibration of WFPC2, the LMC distance, and the reddening correction. A NICMOS study is in its preliminary reduction phase, addressing the last of these concerns. Various empirical analyses have suggested that Cepheid distance moduli are affected by metallicity differences. If we adopted the composition sensitivity obtained in the Key Project's study of M101, and employed the oxygen abundances measured spectroscopically in each of the Cepheid fields we have studied, the value of the Hubble constant would be reduced by 4% ± 2% to 68 ± 6 km s-1 Mpc-1.

Posted Content
TL;DR: In this article, the authors provide an empirical investigation of the medium-term determinants of current accounts for a large sample of industrial and developing countries and find that current account balances are positively correlated with government budget balances and initial stocks of net foreign assets.
Abstract: This paper provides an empirical investigation of the medium-term determinants of current accounts for a large sample of industrial and developing countries. The analysis is based on a structural approach that highlights the roles of the fundamental macroeconomic determinants of saving and investment. Cross-section and panel regression techniques are used to characterize the properties of current account variation across countries and over time. We find that current account balances are positively correlated with government budget balances and initial stocks of net foreign assets. Among developing countries, measures of financial deepening are positively associated with current account balances while indicators of openness to international trade are negatively correlated with current account balances.

Journal ArticleDOI
TL;DR: In this article, the authors synthesize the results of research on tropical montane forest recovery in abandoned pasture in Costa Rica to address the following questions: (1) What factors limit tropical forest recovery, and (2) How can we use this information to design strategies to facilitate ecosystem recovery?
Abstract: Tropical forests are being cleared at an alarming rate although our understanding of their ecology is limited. It is therefore essential to design restoration experiments that both further our basic knowledge of tropical ecology and inform management strategies to facilitate recovery of these ecosystems. Here we synthesize the results of research on tropical montane forest recovery in abandoned pasture in Costa Rica to address the following questions: (1) What factors limit tropical forest recovery in abandoned pasture? and (2) How can we use this information to design strategies to facilitate ecosystem recovery? Our results indicate that a number of factors impede tropical forest recovery in abandoned pasture land. The most important barriers are lack of dispersal of forest seeds and seedling competition with pasture grasses. High seed predation, low seed germination, lack of nutrients, high light intensity, and rabbit herbivory also affect recovery. Successful strategies to facilitate recovery in abandoned pastures must simultaneously overcome numerous obstacles. Our research shows that establishment of woody species, either native tree seedlings or early-successional shrubs, can be successful in facilitating recovery, by enhancing seed dispersal and shading out pasture grasses. On the contrary, bird perching structures alone are not an effective strategy, because they only serve to enhance seed dispersal but do not reduce grass cover. Remnant pasture trees can serve as foci of natural recovery and may enhance growth of planted seedlings. Our results highlight the importance of: (1) understanding the basic biology of an ecosystem to design effective restoration strategies; (2) comparing results across a range of sites to determine which restoration strategies are most generally useful; and (3) considering where best to allocate efforts in large-scale restoration projects.

Journal Article
TL;DR: In this article, the authors provide an overview of the errors associated with shoreline mapping, and a discussion of factors to be considered when selecting a coastal mapping technique, as well as a comparison of different techniques.
Abstract: Numerous coastal mapping techniques have been developed over the last twenty-seven years (STAFFORD, 1971; DOLAN et al., 1978; FISHER and SIMPSON, 1979; LEATHERMAN, 1983; McBRIDE et al., 1991; THIELER and DANFORTH, 1994a, OVERTON et al., 1996). These techniques, used to measure shoreline erosion, barrier island migration, and dune erosion, vary in approach, accuracy, expense and training/time requirements. Some of the more recent coastal mapping techniques apply advances in cartography and photogrammetry providing high-resolution measurements with less error than manual methods that use a photographic comparator or stereo zoom transfer scope. However, such techniques are expensive, require extensive training, and may take longer than manual methods. While many coastal mapping studies would benefit from these advanced techniques, not all studies require the high resolution these more recent techniques offer. When beginning a coastal mapping project or choosing to upgrade laboratory facilities, researching established coastal mapping techniques before choosing from among them requires extensive literature review. To assist researchers, engineers and planners who wish to undertake a coastal mapping project, this paper provides an overview of the errors associated with shoreline mapping, and a discussion of factors to be considered when selecting a coastal mapping technique.

Journal ArticleDOI
TL;DR: A new method for detecting remote protein homologies is introduced and shown to perform well in classifying protein domains by SCOP superfamily using a new kernel function derived from a generative statistical model for a protein family, in this case a hidden Markov model.
Abstract: A new method for detecting remote protein homologies is introduced and shown to perform well in classifying protein domains by SCOP superfamily. The method is a variant of support vector machines using a new kernel function. The kernel function is derived from a generative statistical model for a protein family, in this case a hidden Markov model. This general approach of combining generative models like HMMs with discriminative methods such as support vector machines may have applications in other areas of biosequence analysis as well.

Journal ArticleDOI
TL;DR: In this article, the authors analyze the cosmology of the Randall-Sundrum model and that of compact brane models in general in the presence of a radius stabilization mechanism and find that the expansion of our universe is generically in agreement with the expected effective four dimensional description.
Abstract: We analyze the cosmology of the Randall-Sundrum model and that of compact brane models in general in the presence of a radius stabilization mechanism. We find that the expansion of our Universe is generically in agreement with the expected effective four dimensional description. The constraint (which is responsible for the appearance of nonconventional cosmologies in these models) that must be imposed on the matter densities on the two branes in the theory without a stabilized radius is a consequence of requiring a static solution even in the absence of stabilization. Such constraints disappear in the presence of a stablizing potential, and the ordinary Friedmann-Robertson-Walker (FRW) equations are reproduced, with the expansion driven by the sum of the physical values of the energy densities on the two branes and in the bulk. For the case of the Randall-Sundrum model we examine the kinematics of the radion field, and find that corrections to the standard FRW equations are small for temperatures below the weak scale. We find that the radion field has renormalizable and unsuppressed couplings to standard model particles after electroweak symmetry breaking. These couplings may have important implications for collider searches. We comment on the possibility that matter off the TeV brane could serve as a dark matter candidate.

Journal ArticleDOI
TL;DR: In this paper, the authors presented single stellar population (SSP) equivalent ages, metallicities, and abundance ratios for local elliptical galaxies derived from Hbeta, Mgb, and absorption line strengths.
Abstract: We present single stellar population (SSP) equivalent ages, metallicities, and abundance ratios for local elliptical galaxies derived from Hbeta, Mgb, and absorption line strengths. We use an extension of the Worthey (1994) stellar population models that incorporates non-solar line-strength "response functions" by Tripicco & Bell (1995), allowing us to correct the models for the enhancements of Mg and other alpha-like elements relative to the Fe-peak elements. SSP-equivalent ages of local ellipticals from Gonzalez (1993) are found to vary widely, 1.5 =+0.26 and =+0.20 (in an aperture of radius Re/8). The enhancement ratios are milder than previous estimates, owing to the application of non-solar abundance corrections to both Mgb and for the first time. Gradients in stellar populations within galaxies are found to be mild, with SSP-equivalent age decreasing by 25%, metallicity decreasing by =0.20 dex, and [E/Fe] remaining nearly constant out to an aperture of radius Re/2 for nearly all systems. Our ages have an overall zeropoint uncertainty of at least 25% due to uncertainties in the stellar evolution prescription, the oxygen abundance, the effect of non-solar abundances on the isochrones, and other unknowns. However, the relative age rankings of stellar populations should be largely unaffected by these errors. In particular, the large spread in ages appears to be real and cannot be explained by contamination of Hbeta by blue stragglers or hot horizontal branch stars, or by fill-in of Hbeta by emission. Correlations between these derived SSP-equivalent parameters and other galaxy observables will be discussed in future papers. (Abridged)

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TL;DR: In this article, the authors describe observations and abundance analysis of a high-resolution, high signal-to-noise ratio survey of 168 stars, most of which are metal-poor dwarfs.
Abstract: We describe observations and abundance analysis of a high-resolution, high signal-to-noise ratio survey of 168 stars, most of which are metal-poor dwarfs. We follow a self-consistent LTE analysis technique to determine the stellar parameters and abundances, and we estimate the effects of random and systematic uncertainties on the resulting abundances. Element-to-iron ratios are derived for key α-, odd-Z, Fe-peak, and r- and s-process elements. Effects of non-LTE on the analysis of Fe I lines are shown to be very small on average. Spectroscopically determined surface gravities are derived that are quite close to those obtained from Hipparcos parallaxes.

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TL;DR: In this paper, it was shown that BH masses from reverberation mapping are consistent with the recently discovered relationship between BH mass and galaxy velocity dispersion, not problems with either method of mass measurement.
Abstract: Black hole (BH) masses that have been measured by reverberation mapping in active galaxies fall significantly below the correlation between bulge luminosity and BH mass determined from spatially resolved kinematics of nearby normal galaxies. This discrepancy has created concern that one or both techniques suffer from systematic errors. We show that BH masses from reverberation mapping are consistent with the recently discovered relationship between BH mass and galaxy velocity dispersion. Therefore, the bulge luminosities are the probable source of the disagreement, not problems with either method of mass measurement. This result underscores the utility of the BH mass-velocity dispersion relationship. Reverberation mapping can now be applied with increased confidence to galaxies whose active nuclei are too bright or whose distances are too large for BH searches based on spatially resolved kinematics.

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TL;DR: Nanopore detection and characterization of single molecules represents a new method for directly reading information encoded in linear polymers and it is possible that nucleic acid sequences can be determined at rates exceeding a thousand bases per second.

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TL;DR: In this article, the authors provide a mathematically rigorous foundation for rational vertex operator algebras and their automorphisms in the theory of rational orbifold models in conformal field theory.
Abstract: The goal of the present paper is to provide a mathematically rigorous foundation to certain aspects of the theory of rational orbifold models in conformal field theory, in other words the theory of rational vertex operator algebras and their automorphisms.

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TL;DR: In this article, the effects of mass and force resolution on the density profiles of galaxy-size Cold Dark Matter (CDM) halos in a flat, low-density cosmological model with vacuum energy are studied.
Abstract: We study the effects of mass and force resolution on the density profiles of galaxy-size Cold Dark Matter (CDM) halos in a flat, low-density cosmological model with vacuum energy. We show thatalthough increasing the mass and force resolution allows us to probe deeper into the inner halo regions, it does not lead to steeper inner density profiles. Instead, the halo profiles converge at scales larger than four times the formal resolution or the radius containing more than 200 particles, whichever is larger. In the simulations presented in this paper, we are able to probe density profile of a relaxed isolated galaxy-size halo at scales r=(0.005-1)r_vir. We find that the density distribution can be well approximated by the profile suggested by Moore etal (1998): rho= x^{-1.5}(1+x^{1.5})^-1, where x=r/r_s and r_s is the characteristic radius. The analytical profile proposed by Navarro et al. (1996) rho= x^{-1}(1+x)^-2, also provides a good fit, with the same relative errors of about 10% for radii larger than 1% of the virial radius. Both analytical profiles fit equally well because for high-concentration galaxy-size halos the differences between these profiles become significant only at scales well below 0.01r_vir. We also find that halos of similar mass may have somewhat different parameters (characteristic radius, maximum rotation velocity, etc.) and shapes of their density profiles. We associate this scatter in properties with differences in halo merger histories and the amount of substructure present in the analyzed halos.

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TL;DR: In this paper, the evolution of the surface properties of models for rotating massive stars, i.e., their luminosities, effective temperatures, surface rotational velocities, and surface abundances of all isotopes, from the zero-age main sequence to the supernova stage, were investigated.
Abstract: We investigate the evolution of the surface properties of models for rotating massive stars, i.e., their luminosities, effective temperatures, surface rotational velocities, and surface abundances of all isotopes, from the zero-age main sequence to the supernova stage. Our results are based on the grid of stellar models by Heger, Langer, & Woosley, which covers solar metallicity stars in the initial-mass range 8-25 M?. Results are parameterized by initial mass, initial rotational velocity and major uncertainties in the treatment of the rotational mixing inside massive stars. Rotationally induced mixing processes widen the main sequence and increase the core hydrogen-burning lifetime, similar to the effects of convective overshooting. It can also significantly increase the luminosity during and after core hydrogen burning, and strongly affects the evolution of the effective temperature. Our models predict surface rotational velocities for various evolutionary stages, in particular for blue supergiants, red supergiants, and for the immediate presupernova stage. We discuss the changes of the surface abundances due to rotationally induced mixing for main sequence and post-main-sequence stars. We single out two characteristics by which the effect of rotational mixing can be distinguished from that of massive close binary mass transfer, the only alternative process leading to nonstandard chemical surface abundances in massive stars. A comparison with observed abundance anomalies in various types of massive stars supports the concept of rotational mixing in massive stars and indicates that it is responsible for most of the observed abundance anomalies.

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TL;DR: It is found that ISWI mutations affect both cell viability and gene expression during Drosophila development and cause striking alterations in the structure of the male X chromosome.

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TL;DR: The morphometric analysis of submarine landslides in four distinctly different tectonic environments on the continental slopes of Oregon, central California, Texas, and New Jersey provides useful insight into submarine process, including sediment transport mechanisms and slope stability as mentioned in this paper.

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TL;DR: Although higher trophic levels are often considered to be more sensitive to fragmentation, two groups of arthropod predators, spiders and carabid beetles, increased in abundance in older fragments and there was a strong seasonal variation in abundance and diversity in most orders.
Abstract: The distribution of non-ant arthropods was examined in 40 urban habitat fragments in coastal San Diego County, California, USA, to look for effects of fragmen- tation, proximity to developed edge, and the non-native Argentine ant (Linepithema humile). Arthropods were sampled with pitfall traps and by vacuum sampling from California buck- wheat shrubs (Eriogonumfasciculatum). Individual arthropods were identified to order and Recognizable Taxonomic Unit (RTU), or morphospecies. At the fragment scale we looked for correlations in the point diversity and abundance of arthropods as a function of the age and area of the fragment being sampled. At the scale of the individual sample points we looked for correlations of abundance and diversity with variables that describe the species composition of the shrub vegetation and disturbance. As indicators of disturbance we used the cover of native woody and exotic non-woody vegetation, the distance to the nearest developed edge, and the abundance of Argentine ants. The following patterns were found: (1) In general, arthropods showed a fragmentation effect with point diversity and abundance positively correlated with fragment area and negatively correlated with fragment age. (2) The pitfall samples were dominated by three primarily non-native orders, Isopoda (pillbugs), Dermaptera (earwigs), and Blattaria (roaches). Over 35% of all pitfall-captured arthropods belonged to four species in these orders. Dermaptera and Blattaria increased in abundance in smaller and older fragments, respectively. Isopod abundance, in contrast, was unrelated to fragment attributes. None of these groups appeared to be associated with edges, but were distributed throughout the fragments. (3) Point diversity and abundance in ground-active spiders appears to be enhanced by fragmentation. (4) Total pitfall RTU richness and abun- dance, and abundance or richness in the Coleoptera (vacuum), Diptera, non-ant Hymenop- tera, Hemiptera, Microcoryphia, and Acarina had significant partial negative correlations with Argentine ant abundance. The Diptera and Coleoptera had this negative partial rela- tionship with the Argentine ants despite the fact that both they and the ants were positively associated with edges. (5) In general, diversity in most orders was higher in sampling locations dominated by coastal sage scrub habitat than in those with appreciable cover of chaparral shrub species. (6) There was a strong seasonal variation in abundance and diversity in most orders. Diversity and abundance were highest in spring, intermediate in winter, and lowest in the fall. (7) Although higher trophic levels are often considered to be more sensitive to fragmentation, two groups of arthropod predators, spiders and carabid beetles, increased in abundance in older fragments. Abundance of these predators was positively correlated with the abundance of Argentine ants and the non-native Isopods, Dermaptera, and Blattaria.