Effects of global atmospheric perturbations on forest ecosystems: Predictions of seasonal and cumulative effects

The physical effects of certain large events, such as giant impacts, explosive volcanism, or combined nuclear explosions, have the potential of inducing global catastrophes in our terrestrial environment. Such highly energetic events can inject substantial quantities of material into the atmosphere. In turn, this changes the amount of sunlight reaching the Earth's surface and modifies atmospheric temperatures to produce a wide range of global effects. One consequence is the introduction of serious stresses in both plants and animals throughout the Earth's biosphere. For example, recent studies predict that forest lands, crop lands, and range lands would suffer specific physical and biological degradations if major physical and chemical disruptions occurred in our atmosphere. Forests, which cover over 4 times 10 to the 9th power hectares (4 times 10 to the 7th power sq km) of our planet, or about 3 times the area now cultivated for crops, are critical to many processes in the biosphere. Forests contribute heavily to the production of atmospheric oxygen, supply the major volume of biomass, and provide a significant percentage of plant and animal habitats

Research core drilling in the Manson impact structure, Iowa

The Manson impact structure (MIS) has a diameter of 35 km and is the largest confirmed impact structure in the United States. The MIS has yielded a Ar-40/Ar-39 age of 65.7 Ma on microcline from its central peak, an age that is indistinguishable from the age of the Cretaceous-Tertiary boundary. In the summer of 1991 the Iowa Geological Survey Bureau and U.S. Geological Survey initiated a research core drilling project on the MIS. The first core was beneath 55 m of glacial drift. The core penetrated a 6-m layered sequence of shale and siltstone and 42 m of Cretaceous shale-dominated sedimentary clast breccia. Below this breccia, the core encountered two crystalline rock clast breccia units. The upper unit is 53 m thick, with a glassy matrix displaying various degrees of devitrification. The upper half of this unit is dominated by the glassy matrix, with shock-deformed mineral grains (especially quartz) the most common clast. The glassy-matrix unit grades downward into the basal unit in the core, a crystalline rock breccia with a sandy matrix, the matrix dominated by igneous and metamorphic rock fragments or disaggregated grains from those rocks. The unit is about 45 m thick, and grains display abundant shock deformation features. Preliminary interpretations suggest that the crystalline rock breccias are the transient crater floor, lifted up with the central peak. The sedimentary clast breccia probably represents a postimpact debris flow from the crater rim, and the uppermost layered unit probably represents a large block associated with the flow. The second core (M-2) was drilled near the center of the crater moat in an area where an early crater model suggested the presence of postimpact lake sediments. The core encountered 39 m of sedimentary clast breccia, similar to that in the M-1 core. Beneath the breccia, 120 m of poorly consolidated, mildly deformed, and sheared siltstone, shale, and sandstone was encountered. The basal unit in the core was another sequence of sedimentary clast breccia. The two sedimentary clast units, like the lithologically similar unit in the M-1 core, probably formed as debris flows from the crater rim. The middle, nonbrecciated interval is probably a large, intact block of Upper Cretaceous strata transported from the crater rim with the debris flow. Alternatively, the sequence may represent the elusive postimpact lake sequence

Sifting Convolution on the Sphere

A novel spherical convolution is defined through the sifting property of the Dirac delta on the sphere. The so-called sifting convolution is defined by the inner product of one function with a translated version of another, but with the adoption of an alternative translation operator on the sphere. This translation operator follows by analogy with the Euclidean translation when viewed in harmonic space. The sifting convolution satisfies a variety of desirable properties that are lacking in alternate definitions, namely: it supports directional kernels; it has an output which remains on the sphere; and is efficient to compute. An illustration of the sifting convolution on a topographic map of the Earth demonstrates that it supports directional kernels to perform anisotropic filtering, while its output remains on the sphere.Comment: 5 pages, 3 figure

Computer modeling of large asteroid impacts into continental and oceanic sites: Atmospheric, cratering, and ejecta dynamics

Numerous impact cratering events have occurred on the Earth during the last several billion years that have seriously affected our planet and its atmosphere. The largest cratering events, which were caused by asteroids and comets with kinetic energies equivalent to tens of millions of megatons of TNT, have distributed substantial quantities of terrestrial and extraterrestrial material over much or all of the Earth. In order to study a large-scale impact event in detail, computer simulations were completed that model the passage of a 10 km-diameter asteroid through the Earth's atmosphere and the subsequent cratering and ejecta dynamics associated with impact of the asteroid into two different targets, i.e., an oceanic site and a continental site. The calcuations were designed to broadly represent giant impact events that have occurred on the Earth since its formation and specifically represent an impact cratering event proposed to have occurred at the end of Cretaceous time. Calculation of the passage of the asteroid through a U.S. Standard Atmosphere showed development of a strong bow shock that expanded radially outward. Behind the shock front was a region of highly shock compressed and intensely heated air. Behind the asteroid, rapid expansion of this shocked air created a large region of very low density that also expanded away from the impact area. Calculations of the cratering events in both the continental and oceanic targets were carried to 120 s. Despite geologic differences, impacts in both targets developed comparable dynamic flow fields, and by approx. 29 s similar-sized transient craters approx. 39 km deep and approx. 62 km across had formed. For all practical purposes, the atmosphere was nearly completely removed from the impact area for tens of seconds, i.e., air pressures were less than fractions of a bar out to ranges of over 50 km. Consequently, much of the asteroid and target materials were ejected upward into a near vacuum. Effects of secondary volcanism and return of the ocean over hot oceanic crater floor could also be expected to add substantial solid and vaporized material to the atmosphere, but these conditions were not studied

Maintenance of Relationship Functioning For ePREP and OurRelationship for Low-income Couples

Symposium Title: Relationship Health Across Diverse and Underserved Communities: Connecting Theory and Practice to Inform Therapeutic Processes for Couple Distress Chairs: Judith Biesen, M.A., University of Notre Dame; Binghuang A. Wang, M.S., Binghamton University, State University of New York Discussant: Emily Georgia Salivar, Ph.D., Nova Southeastern Universit

Vegetative Characteristics of Pronghorn Bed Sites in Wind Cave National Park, South Dakota

Much of the previous literature on pronghorn (Antilocapra americana) fawns has focused on fawn mortality (Beale 1978, Barrett 1984, Gregg et al. 2001) and social behavior (Kitchen 1974, Autenrieth and Fichter 1975, Bromley 1977). Selection of bed sites by pronghorn fawns is a major factor affecting fawn survival (Bromley 1978, Barrett 1981, O\u27Gara et al. 1986, VanSchmus 1990) because adequate cover is a crucial component of fawn bed site selection (Autenrieth 1984). Alldredge et al. (1991) reported that fawns selected dense shrub cover but avoided the most-dense cover in sagebrush-steppe communities in southcentral Wyoming while Tucker and Gamer (1983) noted that height and density of vegetation provided concealment cover to hiding fawns. Canon and Bryant (1997) also found density and height of vegetation to be factors affecting survival of fawns and suggested that increased grass and forb production provided necessary hiding cover for fawns. Bromley (1978) and Smith and Beale (1980) noted that fawns selected bed sites that offered the greatest opportunity for visual detection of predators rather than concealment The pronghorn was reintroduced into Wind Cave National Park, South Dakota, i 1914 and thus, has been maintained within its boundaries for nearly a century However, no information is available on fawning habitat within Wind Cave National Park. The objective of our study was to quantity vegetative characteris tics of fawn bed sites throughout Wind Cave National Park

Vegetative Characteristics of Pronghorn Bed Sites in Wind Cave National Park, South Dakota

Much of the previous literature on pronghorn (Antilocapra americana) fawns has focused on fawn mortality (Beale 1978, Barrett 1984, Gregg et al. 2001) and social behavior (Kitchen 1974, Autenrieth and Fichter 1975, Bromley 1977). Selection of bed sites by pronghorn fawns is a major factor affecting fawn survival (Bromley 1978, Barrett 1981, O\u27Gara et al. 1986, VanSchmus 1990) because adequate cover is a crucial component of fawn bed site selection (Autenrieth 1984). Alldredge et al. (1991) reported that fawns selected dense shrub cover but avoided the most-dense cover in sagebrush-steppe communities in southcentral Wyoming while Tucker and Gamer (1983) noted that height and density of vegetation provided concealment cover to hiding fawns. Canon and Bryant (1997) also found density and height of vegetation to be factors affecting survival of fawns and suggested that increased grass and forb production provided necessary hiding cover for fawns. Bromley (1978) and Smith and Beale (1980) noted that fawns selected bed sites that offered the greatest opportunity for visual detection of predators rather than concealment The pronghorn was reintroduced into Wind Cave National Park, South Dakota, i 1914 and thus, has been maintained within its boundaries for nearly a century However, no information is available on fawning habitat within Wind Cave National Park. The objective of our study was to quantity vegetative characteris tics of fawn bed sites throughout Wind Cave National Park

Structured DC Electric Fields With and Without Associated Plasma Density Gradients Observed with the C/NOFS Satellite

DC electric field observations and associated plasma drifts gathered with the Vector Electric Field Investigation on the Air Force Communication/Navigation Outage Forecasting System (C/NOFS) satellite typically reveal considerable variation at large scales (approximately 100's of km), in both daytime and nighttime cases, with enhanced structures usually confined to the nightside. Although such electric field structures are typically associated with plasma density depletions and structures, as observed by the Planar Langmuir Probe on C/NOFS, what is surprising is the number of cases in which large amplitude, structured DC electric fields are observed without a significant plasma density counterpart structure, including their appearance at times when the ambient plasma density appears relatively quiescent. We investigate the relationship of such structured DC electric fields and the ambient plasma density in the C/NOFS satellite measurements observed thus far, taking into account both plasma density depletions and enhancements. We investigate the mapping of the electric fields along magnetic field lines from distant altitudes and latitudes to locations where the density structures, which presumably formed the original seat of the electric fields, are no longer discernible in the observations. In some cases, the electric field structures and spectral characteristics appear to mimic those associated with equatorial spread-F processes, providing important clues to their origins. We examine altitude, seasonal, and longitudinal effects in an effort to establish the origin of such structured DC electric fields observed both with, and without, associated plasma density gradient

Persistent Longitudinal Variations of Plasma Density and DC Electric Fields in the Low Latitude Ionosphere Observed with Probes on the C/NOFS Satellite

Continuous measurements using in situ probes on consecutive orbits of the C/N0FS satellite reveal that the plasma density is persistently organized by longitude, in both day and night conditions and at all locations within the satellite orbit, defined by its perigee and apogee of 401 km and 867 km, respectively, and its inclination of 13 degrees. Typical variations are a factor of 2 or 3 compared to mean values. Furthermore, simultaneous observations of DC electric fields and their associated E x B drifts in the low latitude ionosphere also reveal that their amplitudes are also strongly organized by longitude in a similar fashion. The drift variations with longitude are particularly pronounced in the meridional component perpendicular to the magnetic field although they are also present in the zonal component as well. The longitudes of the peak meridional drift and density values are significantly out of phase with respect to each other. Time constants for the plasma accumulation at higher altitudes with respect to the vertical drift velocity must be taken into account in order to properly interpret the detailed comparisons of the phase relationship of the plasma density and plasma velocity variations. Although for a given period corresponding to that of several days, typically one longitude region dominates the structuring of the plasma density and plasma drift data, there is also evidence for variations organized about multiple longitudes at the same time. Statistical averages will be shown that suggest a tidal "wave 4" structuring is present in both the plasma drift and plasma density data. We interpret the apparent association of the modulation of the E x B drifts with longitude as well as that of the ambient plasma density as a manifestation of tidal forces at work in the low latitude upper atmosphere. The observations demonstrate how the high duty cycle of the C/NOFS observations and its unique orbit expose fundamental processes at work in the low latitude, inner regions of geospace

Catalytic N_2-to-NH_3 Conversion by Fe at Lower Driving Force: A Proposed Role for Metallocene-Mediated PCET

We have recently reported on several Fe catalysts for N_2-to-NH_3 conversion that operate at low temperature (−78 °C) and atmospheric pressure while relying on a very strong reductant (KC_8) and acid ([H(OEt_2)_2][BArF_4]). Here we show that our original catalyst system, P_3^BFe, achieves both significantly improved efficiency for NH_3 formation (up to 72% for e^– delivery) and a comparatively high turnover number for a synthetic molecular Fe catalyst (84 equiv of NH_3 per Fe site), when employing a significantly weaker combination of reductant (Cp*_2Co) and acid ([Ph_2NH_2][OTf] or [PhNH_3][OTf]). Relative to the previously reported catalysis, freeze-quench Mössbauer spectroscopy under turnover conditions suggests a change in the rate of key elementary steps; formation of a previously characterized off-path borohydrido–hydrido resting state is also suppressed. Theoretical and experimental studies are presented that highlight the possibility of protonated metallocenes as discrete PCET reagents under the present (and related) catalytic conditions, offering a plausible rationale for the increased efficiency at reduced driving force of this Fe catalyst system