7,389 research outputs found
Spatially explicit simulation of long-term boreal forest landscape dynamics: incorporating quantitative stand attributes
Spatial simulation models of long-term dynamics of forest landscapes are needed for investigating how different actual or potential disturbance regimes determine the structure and dynamics of forest landscapes. We propose a new approach to bridge the forest stand and landscape processes. Hence, while interested in the boreal forest dynamics at the landscape level, we develop a submodel of stand-level forest dynamics that responds to the landscape-level processes in a spatially explicit landscape model. Compared to the LANDIS model that we used as a starting point, our approach incorporates, in a spatially explicit and quantitative manner: (1) stand-level prediction of basal area and tree volume, and (2) seed dispersal, and sexual and asexual regeneration. Stand development is partly based on growth tables given as model input which means that stand submodel behavior is constrained within a reasonable range. We tested the approach in simulating the development of mixed boreal forests of Quebec, Canada. The simulations demonstrate that stand dynamics can be calibrated to match specific targets and that responses to changes in the initial conditions are realistic. This new modeling approach should allow addressing various theoretical questions and developing, as well as testing, alternative silvicultural and forest management scenarios
Assessing the effectiveness of business support services in England: evidence from a theory based evaluation
In England, publicly supported advisory services for small firms are organised primarily through the Business Link (BL) network. Based on the programme theory underlying this business support services we develop four propositions and test these empirically using data from a new survey of over 3,000 English small firms. Our empirical results provide a broad validation of the programme theory underlying BL assistance for small firms in England during 2003, and more limited support for its effectiveness. More specifically, we find strong support for the value of BL operators maintaining a high profile as a way of boosting take-up. We also find some support for the approach to market segmentation adopted by BL allowing more intensive assistance to be targeted on younger firms and those with limited liability status. In terms of the outcomes of BL support, and allowing for issues of sample selection, we find no significant effects on growth from âotherâ assistance but do find positive and significant employment growth effects from intensive assistance. This provides partial support for the programme theory assertion that BL support will lead to improvements in business growth performance and stronger support for the proposition that there would be differential outcomes from intensive and other assistance. The positive employment growth outcomes identified here from intensive assistance, even allowing for sample selection, suggest something of an improvement in the effectiveness of the BL network since the late 1990s
Warped Vacuum Statistics
We consider the effect of warping on the distribution of type IIB flux vacua
constructed with Calabi-Yau orientifolds. We derive an analytical form of the
distribution that incorporates warping and find close agreement with the
results of a Monte Carlo enumeration of vacua. Compared with calculations that
neglect warping, we find that for any finite volume compactification, the
density of vacua is highly diluted in close proximity to the conifold point,
with a steep drop-off within a critical distance.Comment: 30 pages, 2 figure
Non-serotinous woody plants behave as aerial seed bank species when a late-summer wildfire coincides with a mast year
1. Trees which lack obvious fire-adaptive traits such as serotinous seed-bearing structures or vegetative resprouting are assumed to be at a dramatic disadvantage in recolonization via sexual recruitment after fire, because seed dispersal is invariably quite constrained. We propose an alternative strategy in masting tree species with woody cones or cone-like structures: that the large clusters of woody tissue in a mast year will sufficiently impede heat transfer that a small fraction of seeds can survive the flaming front passage; in a mast year, this small fraction would be a very large absolute number.
2. In Kootenay National Park in British Columbia, we examined regeneration by Engelmann spruce (Picea engelmannii), a non-serotinous conifer, after two fires, both of which coincided with mast years. Coupling models of seed survivorship within cones and seed maturation schedule to a spatially realistic recruitment model, we show that (1) the spatial pattern of seedlings on a 630 m transect from the forest edge into the burn was best explained if there was in situ seed dissemination by burnt trees; (2) in areas several hundred meters from any living trees, recruitment density was well correlated with local prefire cone density; and (3) spruce was responding exactly like its serotinous codominant, lodgepole pine (Pinus contorta).
3. We conclude that non-serotinous species can indeed behave like aerial seed bank species in mast years if the fire takes place late in the seed maturation period. Using the example of the circumpolar boreal forest, while the joint probability of a mast year and a late-season fire will make this type of event rare (we estimate P = 0.1), nonetheless, it would permit a species lacking obvious fire-adapted traits to occasionally establish a widespread and abundant cohort on a large part of the landscape
Orientation of Vortices in a Superconducting Thin-Film: Quantitative Comparison of Spin-Polarized Neutron Reflectivity and Magnetization
We present a quantitative comparison of the magnetization measured by
spin-polarized neutron reflectivity (SPNR) and DC magnetometry on a 1370 \AA\
-thick Nb superconducting film. As a function of magnetic field applied in the
film plane, SPNR exhibits reversible behavior whereas the DC magnetization
shows substantial hysteresis. The difference between these measurements is
attributed to a rotation of vortex magnetic field out of the film plane as the
applied field is reduced. Since SPNR measures only the magnetization parallel
to the film plane whereas DC magnetization is strongly influenced by the
perpendicular component of magnetization when there is a slight sample tilt,
combining the two techniques allows one to distinguish two components of
magnetization in a thin film.Comment: 12 pages, 8 figures, It will be printed in PRB, Oct. 200
The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad Line Region in Mrk 50
We present dynamical modeling of the broad line region (BLR) in the Seyfert 1
galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN
Monitoring Project (LAMP) 2011. We model the reverberation mapping data
directly, constraining the geometry and kinematics of the BLR, as well as
deriving a black hole mass estimate that does not depend on a normalizing
factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is
a nearly face-on thick disk, with a mean radius of 9.6(+1.2,-0.9) light days, a
width of the BLR of 6.9(+1.2,-1.1) light days, and a disk opening angle of
25\pm10 degrees above the plane. We also constrain the inclination angle to be
9(+7,-5) degrees, close to face-on. Finally, the black hole mass of Mrk 50 is
inferred to be log10(M(BH)/Msun) = 7.57(+0.44,-0.27). By comparison to the
virial black hole mass estimate from traditional reverberation mapping
analysis, we find the normalizing constant (virial coefficient) to be log10(f)
= 0.78(+0.44,-0.27), consistent with the commonly adopted mean value of 0.74
based on aligning the M(BH)-{\sigma}* relation for AGN and quiescent galaxies.
While our dynamical model includes the possibility of a net inflow or outflow
in the BLR, we cannot distinguish between these two scenarios.Comment: Accepted for publication in ApJ. 8 pages, 6 figure
Novel TNF Receptor-1 Inhibitors Identified as Potential Therapeutic Candidates for Traumatic Brain Injury
Background: Traumatic brain injury (TBI) begins with the application of mechanical force to the head or brain, which initiates systemic and cellular processes that are hallmarks of the disease. The pathological cascade of secondary injury processes, including inflammation, can exacerbate brain injury-induced morbidities and thus represents a plausible target for pharmaceutical therapies. We have pioneered research on post-traumatic sleep, identifying that injury-induced sleep lasting for 6 h in brain-injured mice coincides with increased cortical levels of inflammatory cytokines, including tumor necrosis factor (TNF). Here, we apply post-traumatic sleep as a physiological bio-indicator of inflammation. We hypothesized the efficacy of novel TNF receptor (TNF-R) inhibitors could be screened using post-traumatic sleep and that these novel compounds would improve functional recovery following diffuse TBI in the mouse.
Methods: Three inhibitors of TNF-R activation were synthesized based on the structure of previously reported TNF CIAM inhibitor F002, which lodges into a defined TNFR1 cavity at the TNF-binding interface, and screened for in vitro efficacy of TNF pathway inhibition (IÎșB phosphorylation). Compounds were screened for in vivo efficacy in modulating post-traumatic sleep. Compounds were then tested for efficacy in improving functional recovery and verification of cellular mechanism.
Results: Brain-injured mice treated with Compound 7 (C7) or SGT11 slept significantly less than those treated with vehicle, suggesting a therapeutic potential to target neuroinflammation. SGT11 restored cognitive, sensorimotor, and neurological function. C7 and SGT11 significantly decreased cortical inflammatory cytokines 3 h post-TBI.
Conclusions: Using sleep as a bio-indicator of TNF-R-dependent neuroinflammation, we identified C7 and SGT11 as potential therapeutic candidates for TBI
Restoring the sting to metric preheating
The relative growth of field and metric perturbations during preheating is
sensitive to initial conditions set in the preceding inflationary phase. Recent
work suggests this may protect super-Hubble metric perturbations from resonant
amplification during preheating. We show that this possibility is fragile and
sensitive to the specific form of the interactions between the inflaton and
other fields. The suppression is naturally absent in two classes of preheating
in which either (1) the vacua of the non-inflaton fields during inflation are
deformed away from the origin, or (2) the effective masses of non-inflaton
fields during inflation are small but during preheating are large. Unlike the
simple toy model of a coupling, most realistic particle
physics models contain these other features. Moreover, they generically lead to
both adiabatic and isocurvature modes and non-Gaussian scars on super-Hubble
scales. Large-scale coherent magnetic fields may also appear naturally.Comment: 6 pages, 3 ps figures, RevTex, revised discussion of backreaction and
new figure. To appear Phys. Rev. D (Rapid Communication
The Strategic Shuffle: Ethnic Geography, the Internal Security Apparatus, and Elections in Kenya
For autocrats facing elections, officers in the internal security apparatus play a crucial role by engaging in coercion on behalf of the incumbent. Yet reliance on these officers introduces a principalâagent problem: Officers can shirk from the autocratâs demands. To solve this problem, autocrats strategically post officers to different areas based on an areaâs importance to the election and the expected loyalty of an individual officer, which is a function of the officerâs expected benefits from the president winning reelection. Using a data set of 8,000 local security appointments within Kenya in the 1990s, one of the first of its kind for any autocracy, I find that the presidentâs coethnic officers were sent to, and the oppositionâs coethnic officers were kept away from, swing areas. This article demonstrates how state institutions from a countryâs previous authoritarian regime can persist despite the introduction of multiâparty elections and thus prevent full democratization.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136510/1/ajps12279_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136510/2/ajps12279.pd
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