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Search Results: 1 - 10 of 95480 matches for " Jim I. Mead "
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Late Pleistocene (Rancholabrean) Glyptodont and Pampathere (Xenarthra, Cingulata) from Sonora, Mexico
Mead, Jim I.;Swift, Sandra L.;White, Richard S.;McDonald, H. Greg;Baez, Arturo;
Revista mexicana de ciencias geológicas , 2007,
Abstract: the fossil-rich deposits of térapa (east-central sonora) contain more than 60 zoological taxa, many with tropical affinities such as crocodylus (crocodylian), hydrochaeris (capybara), and many birds. the deposits also contain the dermal ossicles (osteoderms) of two extinct xenarthrans, a glyptodont (glyptotherium cylindricum) and a pampathere (giant armadillo; pampatherium cf. mexicanum). glyptodont remains are also known from other less-well studied localities in sonora. the faunas from these localities also contain the genus bison, which indicates that the deposits are of the rancholabrean land mammal age, late pleistocene. the presence of pampatherium at térapa and the presence of glyptotherium at térapa and the río mayo/río yaqui sites represent the first published accounts of these species from sonora, and greatly extends their known geographical distribution during the rancholabrean by about 1,100 km into northwestern mexico.
Local Extinction and Unintentional Rewilding of Bighorn Sheep (Ovis canadensis) on a Desert Island
Benjamin T. Wilder, Julio L. Betancourt, Clinton W. Epps, Rachel S. Crowhurst, Jim I. Mead, Exequiel Ezcurra
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0091358
Abstract: Bighorn sheep (Ovis canadensis) were not known to live on Tiburón Island, the largest island in the Gulf of California and Mexico, prior to the surprisingly successful introduction of 20 individuals as a conservation measure in 1975. Today, a stable island population of ~500 sheep supports limited big game hunting and restocking of depleted areas on the Mexican mainland. We discovered fossil dung morphologically similar to that of bighorn sheep in a dung mat deposit from Mojet Cave, in the mountains of Tiburón Island. To determine the origin of this cave deposit we compared pellet shape to fecal pellets of other large mammals, and extracted DNA to sequence mitochondrial DNA fragments at the 12S ribosomal RNA and control regions. The fossil dung was 14C-dated to 1476–1632 calendar years before present and was confirmed as bighorn sheep by morphological and ancient DNA (aDNA) analysis. 12S sequences closely or exactly matched known bighorn sheep sequences; control region sequences exactly matched a haplotype described in desert bighorn sheep populations in southwest Arizona and southern California and showed subtle differentiation from the extant Tiburón population. Native desert bighorn sheep previously colonized this land-bridge island, most likely during the Pleistocene, when lower sea levels connected Tiburón to the mainland. They were extirpated sometime in the last ~1500 years, probably due to inherent dynamics of isolated populations, prolonged drought, and (or) human overkill. The reintroduced population is vulnerable to similar extinction risks. The discovery presented here refutes conventional wisdom that bighorn sheep are not native to Tiburón Island, and establishes its recent introduction as an example of unintentional rewilding, defined here as the introduction of a species without knowledge that it was once native and has since gone locally extinct.
A New Formula Describing the Scaffold Structure of Spiral Galaxies
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2009, DOI: 10.1111/j.1365-2966.2009.14950.x
Abstract: We describe a new formula capable of quantitatively characterizing the Hubble sequence of spiral galaxies including grand design and barred spirals. Special shapes such as ring galaxies with inward and outward arms are also described by the analytic continuation of the same formula. The formula is r(phi) = A/log[B tan(phi/2N)]. This function intrinsically generates a bar in a continuous, fixed relationship relative to an arm of arbitrary winding sweep. A is simply a scale parameter while B, together with N, determine the spiral pitch. Roughly, greater N results in tighter winding. Greater B results in greater arm sweep and smaller bar/bulge while smaller B fits larger bar/bulge with a sharper bar/arm junction. Thus B controls the "bar/bulge-to-arm" size, while N controls the tightness much like the Hubble scheme. The formula can be recast in a form dependent only on a unique point of turnover angle of pitch - essentially a 1-parameter fit, aside from a scale factor. The recast formula is remarkable and unique in that a single parameter can define a spiral shape with either constant or variable pitch capable of tightly fitting Hubble types from grand design spirals to late type large-barred galaxies. We compare the correlation of our pitch parameter to Hubble type with that of the traditional logarithmic spiral for 21 well-shaped galaxies. The pitch parameter of our formula produces a very tight correlation with ideal Hubble type suggesting it is a good discriminator compared to logarithmic pitch, which shows poor correlation here similar to previous works. Representative examples of fitted galaxies are shown.
Simple Fit of Data Relating Supermassive Black Hole Mass to Galaxy Pitch Angle
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2009, DOI: 10.1088/0004-6256/137/6/4716
Abstract: Seigar, et al, have recently demonstrated a new, tight correlation between galactic central supermassive black hole (BH) mass and the pitch angle of the spiral arm in disc galaxies which they attribute to other indirect correlations. They fit a double power law, governed by five parameters, to the BH mass as a function of pitch. Noting the features of their fitted curve, we show that a simple linear proportion of the BH mass to the cotangent of the pitch angle can obtain the same fit, within error. Such a direct, elegant fit may help shed light on the nature of the correlation.
Comment on "Gain-assisted Superluminal Light Propagation"
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2002,
Abstract: Wang, Kuzmich and Dogariu, in their 20 July, 2000, Nature article, describe an experiment ostensibly measuring superluminal speeds of 310c via a few percent shift in time of an optical pulse undergoing anomalous dispersion in a pumped medium. This paper seems to have become part of the superluminal lore and is often referenced as a profound example of superluminality. We have closely examined the article and find serious flaws that need to be addressed.
Are Dark Matter and Dark Energy the Residue of the Expansion-Reaction to the Big Bang ?
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2006,
Abstract: We derive the phenomenological Milgrom square-law acceleration, describing the apparent behavior of dark matter, as the reaction to the Big Bang from a model based on the Lorentz-Dirac equation of motion traditionally describing radiation reaction in electromagnetism but proven applicable to expansion reaction in cosmology. The model is applied within the Robertson-Walker hypersphere, and suggests that the Hubble expansion exactly cancels the classical reaction imparted to matter following the Big Bang, leaving behind a residue proportional to the square of the acceleration. The model further suggests that the energy density associated with the reaction acceleration is precisely the critical density for flattening the universe thus providing a potential explanation of dark energy as well. A test of this model is proposed.
Model-Independent Plotting of the Cosmological Scale Factor as a Function of Lookback Time
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2014, DOI: 10.1088/0004-6256/148/5/94
Abstract: In the present work we describe a model-independent method of developing a plot of scale factor versus lookback time from the usual Hubble diagram of modulus data against redshift. This is the first plot of this type. We follow the model-independent methodology of Daly and Djorgovski (2004) used for their radio-galaxy data. Once the data plot is completed, any model can be applied and will display accordingly as described in standard literature. We then compile an extensive data set to z = 1.8 by combining SNe Ia data from SNLS3 of Conley et al. (2011), High-z SNe data of Riess et al. (2004) and radio-galaxy data of Daly & Djorgovski (2004) to be used to validate the new plot. We first display these data on a standard Hubble diagram to confirm the best fit for LCDM cosmology and thus validate the joined data set. The scale factor plot is then developed from the data and the LCDM model is again displayed from a least-squares fit. The fit parameters are in agreement with the Hubble diagram fit confirming the validity of the new plot. Of special interest is the transition-time of the universe which in the scale factor plot will appear as an inflection point in the data set. Noise is more visible on this presentation which is particularly sensitive to inflection points of any model displayed on the plot unlike on a modulus-z diagram where there are no inflection points and the transition-z is not at all obvious by inspection. We obtain a lower limit of z >0.6. It is evident from this presentation that there is a dearth of SNe data in the range, z = 1-2, exactly the range necessary to confirm a LCDM transition-z in the neighborhood of z = 0.76.
On a Bipolar Model of Hyperbolic Geometry and its Relation to Hyperbolic Robertson-Walker Space
Harry I. Ringermacher,Lawrence R. Mead
Physics , 2012,
Abstract: Negatively curved, or hyperbolic, regions of space in an FRW universe are a realistic possibility. These regions might occur in voids where there is no dark matter with only dark energy present. Hyperbolic space is strange and various "models" of hyperbolic space have been introduced, each offering some enlightened view. In the present work we develop a new bipolar model of hyperbolic geometry, closely related to an existing model - the band model - and show that it provides new insights toward an understanding of hyperbolic as well as elliptic Robertson-Walker space and the meaning of its isometries. In particular, we show that the circular geodesics of a hyperbolic Robertson-Walker space can be referenced to two real centers - a Euclidean center and an offset hyperbolic center. These are not the Euclidean center or poles of the bipolar coordinate system but rather refer to two distinct centers for circular orbits of particles in such systems. Considering the physics of elliptic RW space is so well confirmed in the Lambda-CDM model with respect to Euclidean coordinates from a Euclidean center, it is likely that the hyperbolic center plays a physical role in regions of hyperbolic space.
Induced matter: Curved N-manifolds encapsulated in Riemann-flat N+1 dimensional space
Harry I. Ringermacher,Lawrence R. Mead
Mathematics , 2005, DOI: 10.1063/1.2042968
Abstract: Liko and Wesson have recently introduced a new 5-dimensional induced matter solution of the Einstein equations, a negative curvature Robertson-Walker space embedded in a Riemann flat 5-dimensional manifold. We show that this solution is a special case of a more general theorem prescribing the structure of certain N+1-dimensional Riemann flat spaces which are all solutions of the Einstein equations. These solutions encapsulate N-dimensional curved manifolds. Such spaces are said to "induce matter" in the sub-manifolds by virtue of their geometric structure alone. We prove that the N-manifold can be any maximally symmetric space.
Non-equilibrium excitation of methanol in Galactic molecular clouds: multi-transitional observations at 2 mm
V. I. Slysh,S. V. Kalenskii,I. E. Val'tts,V. V. Golubev,K. Mead
Physics , 1999, DOI: 10.1086/313240
Abstract: We observed 14 methanol transitions near lambda=2 mm in Galactic star-forming regions. Broad, quasi-thermal J(0)-J(-1)E methanol lines near 157 GHz were detected toward 73 sources. Together with the 6(-1)-5(0)E and 5(-2)-6(-1)E lines at 133 GHz and the 7(1)-7(0)E line at 165 GHz, they were used to study the methanol excitation. In the majority of the observed objects, the Class I 6(-1)-5(0)E transition is inverted, and the Class II 5(-2)-6(-1)E and 6(0)-6(-1)E transitions are overcooled. This is exactly as predicted by models of low gain Class I masers. The absence of the inversion of Class II transitions 5(-2)-6(-1)E and 6(0)-6(-1)E means that quasi-thermal methanol emission in all objects arises in areas without a strong radiation field, which is required for the inversion.
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