69 research outputs found
Collars and partitions of hyperbolic cone-surfaces
For compact Riemann surfaces, the collar theorem and Bers' partition theorem
are major tools for working with simple closed geodesics. The main goal of this
paper is to prove similar theorems for hyperbolic cone-surfaces. Hyperbolic
two-dimensional orbifolds are a particular case of such surfaces. We consider
all cone angles to be strictly less than to be able to consider
partitions.Comment: 11 pages, 9 figures; v2: minor changes, to appear in Geometriae
Dedicat
Extraordinary Biomass-Burning Episode and Impact Winter Triggered by the Younger Dryas Cosmic Impact ∼12,800 Years Ago. 2. Lake, Marine, and Terrestrial Sediments
Part 1 of this study investigated evidence of biomass burning in global ice records, and here we continue to test the
hypothesis that an impact event at the Younger Dryas boundary (YDB) caused an anomalously intense episode of
biomass burning at ∼12.8 ka on a multicontinental scale (North and South America, Europe, and Asia). Quantitative
analyses of charcoal and soot records from 152 lakes, marine cores, and terrestrial sequences reveal a major peak in
biomass burning at the Younger Dryas (YD) onset that appears to be the highest during the latest Quaternary. For the
Cretaceous-Tertiary boundary (K-Pg) impact event, concentrations of soot were previously utilized to estimate the
global amount of biomass burned, and similar measurements suggest that wildfires at the YD onset rapidly consumed
∼10 million km2 of Earth’s surface, or ∼9% of Earth’s biomass, considerably more than for the K-Pg impact. Bayesian
analyses and age regressions demonstrate that ages for YDB peaks in charcoal and soot across four continents are
synchronous with the ages of an abundance peak in platinum in the Greenland Ice Sheet Project 2 (GISP2) ice core and
of the YDB impact event (12,835–12,735 cal BP). Thus, existing evidence indicates that the YDB impact event caused
an anomalously large episode of biomass burning, resulting in extensive atmospheric soot/dust loading that triggered
an “impact winter.” This, in turn, triggered abrupt YD cooling and other climate changes, reinforced by climatic
feedback mechanisms, including Arctic sea ice expansion, rerouting of North American continental runoff, and subsequent ocean circulation changes
Convexity of strata in diagonal pants graphs of surfaces
We prove a number of convexity results for strata of the diagonal pants graph of a surface, in analogy with the extrinsic geometric properties of strata in the Weil-Petersson completion. As a consequence, we exhibit convex flat subgraphs of every possible rank inside the diagonal pants graph
Convexity of strata in diagonal pants graphs of surfaces
We prove a number of convexity results for strata of the diagonal pants graph of a surface, in analogy with the extrinsic geometric properties of strata in the Weil-Petersson completion. As a consequence, we exhibit convex flat subgraphs of every possible rank inside the diagonal pants graph
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