766 research outputs found
Response of Vegetation Important to Northern Bobwhites Following Chemical and Mechanical Treatments (Oral Abstract)
Populations of northern bobwhite (Colinus virginianus) have declined since the early 1900s due to large-scale land use changes and habitat destruction. In southern pine stands land managers have used a variety of treatments to control hardwood encroachment, a major contributing factor to the loss of optimal quail habitat. We compared the use of the herbicide Arsenal (imazapyr) and traditional mechanical treatments with and without fire to control hardwood stem encroachment on 2 study areas. On Tall Timbers Research Station, hardwood stem density decreased on herbicide and herbicide + burn plots, but increased on all mechanically treated plots between years. Herbicide and herbicide + burn plots resulted in a 3-fold increase in forb coverage between years, whereas mechanically treated plots did not increase forb coverage. On Foshalee Plantation, hardwood stem density decreased and forb coverage increased between years on chemically treated plots. A one-time application of Arsenal can control hardwood encroachment in pine forests and stimulate herbaceous species growth. Following treatment, vegetative communities likely can be maintained for prolonged periods by using traditional, less expensive, methods of management such as prescribed fire
Antarctic streams as a potential source of iron for the Southern Ocean
Due to ironās role in oceanic primary production, there has been great interest in quantifying the importance of Fe in regions where concentrations are very low and macronutrients, nitrate and phosphate, are available. Measurements of filterable (i.e., \u3c0.4 Ī¼m) Fe concentrations in streams from Taylor Valley, McMurdo Dry Valleys, Antarctica, suggest that coastal-zone stream Fe input to the Southern Ocean could potentially play an important role in primary production in nearshore regions. Filterable Fe (fFe) data from streams in the McMurdo Dry Valleys were used to represent glacier meltwater that flows through ice-free landscape with the potential of transporting Fe to the Antarctic coastal zone. Estimates of potential fFe flux to the Antarctic Peninsula region using our mean fFe concentration of 10.6 Āµg Lā1 combined with an estimate of ice-free area for the Antarctic Peninsula result in an fFe flux of 1.2 Ć 107 g yrā1. Although small compared to iceberg and aeolian Fe fluxes, future stream input to the Southern Ocean could increase due to glacier retreat and melting, thus increasing the fFe flux from glacier meltwater streams
A High-Mass Protobinary System in the Hot Core W3(H2O)
We have observed a high-mass protobinary system in the hot core W3(H2O) with
the BIMA Array. Our continuum maps at wavelengths of 1.4mm and 2.8mm both
achieve sub-arcsecond angular resolutions and show a double-peaked morphology.
The angular separation of the two sources is 1.19" corresponding to 2.43X10^3
AU at the source distance of 2.04 kpc. The flux densities of the two sources at
1.4mm and 2.8mm have a spectral index of 3, translating to an opacity law of
kappa ~ nu. The small spectral indices suggest that grain growth has begun in
the hot core. We have also observed 5 K components of the CH3CN (12-11)
transitions. A radial velocity difference of 2.81 km/s is found towards the two
continuum peaks. Interpreting these two sources as binary components in orbit
about one another, we find a minimum mass of 22 Msun for the system. Radiative
transfer models are constructed to explain both the continuum and methyl
cyanide line observations of each source. Power-law distributions of both
density and temperature are derived. Density distributions close to the
free-fall value, r^-1.5, are found for both components, suggesting continuing
accretion. The derived luminosities suggest the two sources have equivalent
zero-age main sequence (ZAMS) spectral type B0.5 - B0. The nebular masses
derived from the continuum observations are about 5 Msun for source A and 4
Msun for source C. A velocity gradient previously detected may be explained by
unresolved binary rotation with a small velocity difference.Comment: 38 pages, 9 figures, accepted by The Astrophysical Journa
A Pre-Protostellar Core in L1551
Large field surveys of NH3, C2S, 13CO and C18O in the L1551 dark cloud have
revealed a prolate, pre-protostellar molecular core (L1551-MC) in a relatively
quiescent region to the northwest of the well-known IRS 5 source. The kinetic
temperature is measured to be 9K, the total mass is ~2Msun, and the average
particle density is 10^4-10^5 cm^(-3). L1551-MC is 2.25' x 1.11' in projection
oriented at a position angle of 133deg. The turbulent motions are on the order
of the sound speed in the medium and contain 4% of the gravitational energy,
E_{grav}, of the core. The angular momentum vector is projected along the major
axis of L1551-MC corresponding to a rotational energy of 2.5E-3(sin
i)^(-2)|E_{grav}|. The thermal energy constitutes about a third of |E_{grav}|
and the virial mass is approximately equal to the total mass. L1551-MC is
gravitationally bound and in the absence of strong, ~160 microgauss, magnetic
fields will likely contract on a ~0.3 Myr time scale. The line profiles of many
molecular species suggest that the cold quiescent interior is surrounded by a
dynamic, perhaps infalling envelope which is embedded within the ambient
molecular gas of L1551.Comment: 27 pages, 7 figures, ApJ accepte
Respiratory water loss: A predictive model
A steady-state model, based on a combination of empirical and mechanistic relationships, is developed to predict respiratory water loss from terrestrial vertebrates. Model parameters are evaluated from published data for the banner-tail kangaroo rat (Dipodomys spectabilis). A three-dimensional representation of model behavior is presented, emphasizing the interaction of organismal and environmental variables. The model makes possible the calculation of respiratory water and heat losses for animals in both artificial and natural environments.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22956/1/0000523.pd
Als3 is a Candida albicans invasin that binds to cadherins and induces endocytosis by host cells.
Candida albicans is the most common cause of hematogenously disseminated and oropharyngeal candidiasis. Both of these diseases are characterized by fungal invasion of host cells. Previously, we have found that C. albicans hyphae invade endothelial cells and oral epithelial cells in vitro by inducing their own endocytosis. Therefore, we set out to identify the fungal surface protein and host cell receptors that mediate this process. We found that the C. albicans Als3 is required for the organism to be endocytosed by human umbilical vein endothelial cells and two different human oral epithelial lines. Affinity purification experiments with wild-type and an als3delta/als3delta mutant strain of C. albicans demonstrated that Als3 was required for C. albicans to bind to multiple host cell surface proteins, including N-cadherin on endothelial cells and E-cadherin on oral epithelial cells. Furthermore, latex beads coated with the recombinant N-terminal portion of Als3 were endocytosed by Chinese hamster ovary cells expressing human N-cadherin or E-cadherin, whereas control beads coated with bovine serum albumin were not. Molecular modeling of the interactions of the N-terminal region of Als3 with the ectodomains of N-cadherin and E-cadherin indicated that the binding parameters of Als3 to either cadherin are similar to those of cadherin-cadherin binding. Therefore, Als3 is a fungal invasin that mimics host cell cadherins and induces endocytosis by binding to N-cadherin on endothelial cells and E-cadherin on oral epithelial cells. These results uncover the first known fungal invasin and provide evidence that C. albicans Als3 is a molecular mimic of human cadherins
Abundances of Molecular Species in Barnard 68
Abundances for 5 molecules (C18O, CS, NH3, H2CO, and C3H2) and 1 molecular
ion (N2H+) and upper limits for the abundances of 1 molecule (13CO) and 1
molecular ion (HCO+) are derived for gas within the Bok globule Barnard 68
(B68). The abundances were determined using our own BIMA millimeter
interferometer data and single-dish data gathered from the literature, in
conjunction with a Monte Carlo radiative transfer model. Since B68 is the only
starless core to have its density structure strongly constrained via extinction
mapping, a major uncertainty has been removed from these determinations. All
abundances for B68 are lower than those derived for translucent and cold dense
clouds, but perhaps only significantly for N2H+, NH3, and C3H2. Depletion of CS
toward the extinction peak of B68 is hinted at by the large offset between the
extinction peak and the position of maximum CS line brightness. Abundances
derived here for C18O and N2H+ are consistent with other, recently determined
values at positions observed in common.Comment: 16 pages, 1 figure, accepted by AJ, typo corrected, reference removed
in Section 4.
Rapid Mineral Precipitation During Shear Fracturing of CarbonateāRich Shales
Target subsurface reservoirs for emerging lowācarbon energy technologies and geologic carbon sequestration typically have low permeability and thus rely heavily on fluid transport through natural and induced fracture networks. Sustainable development of these systems requires deeper understanding of how geochemically mediated deformation impacts fracture microstructure and permeability evolution, particularly with respect to geochemical reactions between pore fluids and the host rock. In this work, a series of triaxial direct shear experiments was designed to evaluate how fractures generated at subsurface conditions respond to penetration of reactive fluids with a focus on the role of mineral precipitation. Calciteārich shale cores were directly sheared under 3.5Ā MPa confining pressure using BaCl2ārich solutions as a working fluid. Experiments were conducted within an Xāray computed tomography (xCT) scanner to capture 4āD evolution of fracture geometry and precipitate growth. Three shear tests evidenced nonuniform precipitation of barium carbonates (BaCO3) along throughāgoing fractures, where the extent of precipitation increased with increasing calcite content. Precipitates were strongly localized within fracture networks due to mineral, geochemical, and structural heterogeneities and generally concentrated in smaller apertures where rock:water ratios were highest. The combination of elevated fluid saturation and reactive surface area created in freshly activated fractures drove nearāimmediate mineral precipitation that led to an 80% permeability reduction and significant flow obstruction in the most reactive core. While most previous studies have focused on mixingāinduced precipitation, this work demonstrates that fluidārock interactions can trigger precipitationāinduced permeability alterations that can initiate or mitigate risks associated with subsurface energy systems.Key PointsBarium carbonates precipitate nearāimmediately with injection of BaCl2ārich fluid into freshly sheared calciteārich shalesPrecipitation reactions are strongly localized, favoring narrow apertures and zones of extensive fragmentationFluidārock interactions can promote significant precipitationāinduced permeability alterations that remain challenging to predictPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/1/jgrb54184_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/2/jgrb54184-sup-0001-2019JB018864-SI.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155917/3/jgrb54184.pd
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