Regular Incidence Complexes, Polytopes, and C-Groups

Regular incidence complexes are combinatorial incidence structures generalizing regular convex polytopes, regular complex polytopes, various types of incidence geometries, and many other highly symmetric objects. The special case of abstract regular polytopes has been well-studied. The paper describes the combinatorial structure of a regular incidence complex in terms of a system of distinguished generating subgroups of its automorphism group or a flag-transitive subgroup. Then the groups admitting a flag-transitive action on an incidence complex are characterized as generalized string C-groups. Further, extensions of regular incidence complexes are studied, and certain incidence complexes particularly close to abstract polytopes, called abstract polytope complexes, are investigated.Comment: 24 pages; to appear in "Discrete Geometry and Symmetry", M. Conder, A. Deza, and A. Ivic Weiss (eds), Springe

Using sonic anemometer temperature to measure sensible heat flux in strong winds

Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind (<i>w</i>') and sonic temperature (<i>T</i><sub>s</sub>'), and are commonly used to measure sensible heat flux (<i>H</i>). Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared <i>H</i> calculated with <i>T</i><sub>s</sub> to <i>H</i> calculated with a co-located thermocouple and found that, for horizontal wind speed (<i>U</i>) less than 8 m s<sup>−1</sup>, the agreement was around ±30 W m<sup>−2</sup>. However, for <i>U</i> ≈ 8 m s<sup>−1</sup>, the CSAT <i>H</i> had a generally positive deviation from <i>H</i> calculated with the thermocouple, reaching a maximum difference of ≈250 W m<sup>−2</sup> at <i>U</i> ≈ 18 m s<sup>−1</sup>. With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus <i>T</i><sub>s</sub> in high winds (due to a delayed detection of the sonic pulse), which resulted in the large CSAT heat flux errors. Although this <i>T</i><sub>s</sub> error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of <i>T</i><sub>s</sub>; however, a <i>T</i><sub>s</sub> error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the <i>T</i><sub>s</sub> error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed

Adsorption hysteresis and capillary condensation in disordered porous solids: a density functional study

We present a theoretical study of capillary condensation of fluids adsorbed in mesoporous disordered media. Combining mean-field density functional theory with a coarse-grained description in terms of a lattice-gas model allows us to investigate both the out-of-equilibrium (hysteresis) and the equilibrium behavior. We show that the main features of capillary condensation in disordered solids result from the appearance of a complex free-energy landscape with a large number of metastable states. We detail the numerical procedures for finding these states, and the presence or absence of transitions in the thermodynamic limit is determined by careful finite-size studies.Comment: 30 pages, 18 figures. To appear in J. Phys.: Condens. Matte

Polarized Secretory Trafficking Directs Cargo for Asymmetric Dendrite Growth and Morphogenesis

SummaryProper growth of dendrites is critical to the formation of neuronal circuits, but the cellular machinery that directs the addition of membrane components to generate dendritic architecture remains obscure. Here, we demonstrate that post-Golgi membrane trafficking is polarized toward longer dendrites of hippocampal pyramidal neurons in vitro and toward apical dendrites in vivo. Small Golgi outposts partition selectively into longer dendrites and are excluded from axons. In dendrites, Golgi outposts concentrate at branchpoints where they engage in post-Golgi trafficking. Within the cell body, the Golgi apparatus orients toward the longest dendrite, and this Golgi polarity precedes asymmetric dendrite growth. Manipulations that selectively block post-Golgi trafficking halt dendrite growth in developing neurons and cause a shrinkage of dendrites in mature pyramidal neurons. Further, disruption of Golgi polarity produces neurons with symmetric dendritic arbors lacking a single longest principal dendrite. These results define a novel polarized organization of neuronal secretory trafficking and demonstrate a mechanistic link between directed membrane trafficking and asymmetric dendrite growth

Capillary condensation in disordered porous materials: hysteresis versus equilibrium behavior

We study the interplay between hysteresis and equilibrium behavior in capillary condensation of fluids in mesoporous disordered materials via a mean-field density functional theory of a disordered lattice-gas model. The approach reproduces all major features observed experimentally. We show that the simple van der Waals picture of metastability fails due to the appearance of a complex free-energy landscape with a large number of metastable states. In particular, hysteresis can occur both with and without an underlying equilibrium transition, thermodynamic consistency is not satisfied along the hysteresis loop, and out-of-equilibrium phase transitions are possible.Comment: 4 pages, 4 figure

A Radial Velocity Survey of the Cygnus OB2 Association

We conducted a radial velocity survey of the Cygnus OB2 Association over a 6 year (1999 - 2005) time interval to search for massive close binaries. During this time we obtained 1139 spectra on 146 OB stars to measure mean systemic radial velocities and radial velocity variations. We spectroscopically identify 73 new OB stars for the first time, the majority of which are likely to be Association members. Spectroscopic evidence is also presented for a B3Iae classification and temperature class variation (B3 - B8) on the order of 1 year for Cygnus OB2 No. 12. Calculations of the intial mass function with the current spectroscopic sample yield Gamma = -2.2 +/- 0.1. Of the 120 stars with the most reliable data, 36 are probable and 9 are possible single-lined spectroscopic binaries. We also identify 3 new and 8 candidate double-lined spectroscopic binaries. These data imply a lower limit on the massive binary fraction of 30% - 42%. The calculated velocity dispersion for Cygnus OB2 is 2.44 +/- km/s, which is typical of open clusters. No runaway OB stars were found.Comment: 56 pages, 23 figures, 5 tables, accepted for publication in the Astrophysical Journa

Canopy nitrogen, carbon assimilation, and albedo in temperate and boreal forests: Functional relations and potential climate feedbacks

The availability of nitrogen represents a key constraint on carbon cycling in terrestrial ecosystems, and it is largely in this capacity that the role of N in the Earth\u27s climate system has been considered. Despite this, few studies have included continuous variation in plant N status as a driver of broad-scale carbon cycle analyses. This is partly because of uncertainties in how leaf-level physiological relationships scale to whole ecosystems and because methods for regional to continental detection of plant N concentrations have yet to be developed. Here, we show that ecosystem CO2 uptake capacity in temperate and boreal forests scales directly with whole-canopy N concentrations, mirroring a leaf-level trend that has been observed for woody plants worldwide. We further show that both CO2 uptake capacity and canopy N concentration are strongly and positively correlated with shortwave surface albedo. These results suggest that N plays an additional, and overlooked, role in the climate system via its influence on vegetation reflectivity and shortwave surface energy exchange. We also demonstrate that much of the spatial variation in canopy N can be detected by using broad-band satellite sensors, offering a means through which these findings can be applied toward improved application of coupled carbon cycle–climate models

Evidence of strong stabilizing effects on the evolution of boreoeutherian (Mammalia) dental proportions.

The dentition is an extremely important organ in mammals with variation in timing and sequence of eruption, crown morphology, and tooth size enabling a range of behavioral, dietary, and functional adaptations across the class. Within this suite of variable mammalian dental phenotypes, relative sizes of teeth reflect variation in the underlying genetic and developmental mechanisms. Two ratios of postcanine tooth lengths capture the relative size of premolars to molars (premolar-molar module, PMM), and among the three molars (molar module component, MMC), and are known to be heritable, independent of body size, and to vary significantly across primates. Here, we explore how these dental traits vary across mammals more broadly, focusing on terrestrial taxa in the clade of Boreoeutheria (Euarchontoglires and Laurasiatheria). We measured the postcanine teeth of N = 1,523 boreoeutherian mammals spanning six orders, 14 families, 36 genera, and 49 species to test hypotheses about associations between dental proportions and phylogenetic relatedness, diet, and life history in mammals. Boreoeutherian postcanine dental proportions sampled in this study carry conserved phylogenetic signal and are not associated with variation in diet. The incorporation of paleontological data provides further evidence that dental proportions may be slower to change than is dietary specialization. These results have implications for our understanding of dental variation and dietary adaptation in mammals

Potential effects of ionizing radiation on the evidentiary value of DNA, latent fingerprints, hair, and fibers: A comprehensive review and new results

An extensive literature review and new post-irradiation experimental results are presented of genotyping blood stains and hair, and physical examinations of latent fingerprints, hairs, and fibers. Results indicate that successful development of nuclear short tandem repeat (STR) and mitochondrial DNA sequence profiles from human blood and hair evidence is possible—up to a point—following exposure to gamma, neutron, beta, and alpha radiation at several levels that would most likely be present at this type of crime scene (i.e., a “dirty bomb,” etc.). Commencing at gamma radiation levels between 90 and 900 kGy, DNA analysis using conventional DNA techniques was unsuccessful. In general, irradiation negatively affected the quality of latent fingerprints. All four radiation types degraded most fingerprint samples at all doses; nevertheless, many fingerprints remained of value for potential use in comparison. Although variable from one hair to another, microscopic changes observed for all types and levels of irradiation could potentially result in false exclusions. Negligible microscopic changes were observed in papers and fibers (used as substrates for fingerprints and bloodstains) up to 90 kGy gamma, but fluorescence of fibers began to change above that dose. Paper and fibers, as well as plastic evidence enclosures, became extremely brittle leading to breakage after a gamma dose of 900 kGy

Light Curves of the Neutron Star Merger GW170817/SSS17a: Implications for R-Process Nucleosynthesis

On 2017 August 17, gravitational waves were detected from a binary neutron star merger, GW170817, along with a coincident short gamma-ray burst, GRB170817A. An optical transient source, Swope Supernova Survey 17a (SSS17a), was subsequently identified as the counterpart of this event. We present ultraviolet, optical and infrared light curves of SSS17a extending from 10.9 hours to 18 days post-merger. We constrain the radioactively-powered transient resulting from the ejection of neutron-rich material. The fast rise of the light curves, subsequent decay, and rapid color evolution are consistent with multiple ejecta components of differing lanthanide abundance. The late-time light curve indicates that SSS17a produced at least ~0.05 solar masses of heavy elements, demonstrating that neutron star mergers play a role in r-process nucleosynthesis in the Universe.Comment: Accepted to Scienc