595 research outputs found
The Influence of Soil Moisture Conditions on the Absorption of Phosphorus by Plants from Calcareous Soils
Relationship between soil moisture and the absorption of phosphorus and other nutrients
Timing analysis techniques at large core distances for multi-TeV gamma ray astronomy
We present an analysis technique that uses the timing information of
Cherenkov images from extensive air showers (EAS). Our emphasis is on distant,
or large core distance gamma-ray induced showers at multi-TeV energies.
Specifically, combining pixel timing information with an improved direction
reconstruction algorithm, leads to improvements in angular and core resolution
as large as ~40% and ~30%, respectively, when compared with the same algorithm
without the use of timing. Above 10 TeV, this results in an angular resolution
approaching 0.05 degrees, together with a core resolution better than ~15 m.
The off-axis post-cut gamma-ray acceptance is energy dependent and its full
width at half maximum ranges from 4 degrees to 8 degrees. For shower directions
that are up to ~6 degrees off-axis, the angular resolution achieved by using
timing information is comparable, around 100 TeV, to the on-axis angular
resolution. The telescope specifications and layout we describe here are geared
towards energies above 10 TeV. However, the methods can in principle be applied
to other energies, given suitable telescope parameters. The 5-telescope cell
investigated in this study could initially pave the way for a larger array of
sparsely spaced telescopes in an effort to push the collection area to >10 km2.
These results highlight the potential of a `sparse array' approach in
effectively opening up the energy range above 10 TeV.Comment: Published in Astroparticle Physic
Advanced engine study program
A design and analysis study was conducted to provide advanced engine descriptions and parametric data for space transfer vehicles. The study was based on an advanced oxygen/hydrogen engine in the 7,500 to 50,000 lbf thrust range. Emphasis was placed on defining requirements for high-performance engines capable of achieving reliable and versatile operation in a space environment. Four variations on the expander cycle were compared, and the advantages and disadvantages of each were assessed. Parametric weight, envelope, and performance data were generated over a range of 7,500 to 50,000 lb thrust and a wide range of chamber pressure and nozzle expansion ratio
An iterative method to compute the overlap Dirac operator at nonzero chemical potential
The overlap Dirac operator at nonzero quark chemical potential involves the
computation of the sign function of a non-Hermitian matrix. In this talk we
present an iterative method, first proposed by us in Ref. [1], which allows for
an efficient computation of the operator, even on large lattices. The starting
point is a Krylov subspace approximation, based on the Arnoldi algorithm, for
the evaluation of a generic matrix function. The efficiency of this method is
spoiled when the matrix has eigenvalues close to a function discontinuity. To
cure this, a small number of critical eigenvectors are added to the Krylov
subspace, and two different deflation schemes are proposed in this augmented
subspace. The ensuing method is then applied to the sign function of the
overlap Dirac operator, for two different lattice sizes. The sign function has
a discontinuity along the imaginary axis, and the numerical results show how
deflation dramatically improves the efficiency of the method.Comment: 7 pages, talk presented at the XXV International Symposium on Lattice
Field Theory, July 30 - August 4 2007, Regensburg, German
Marine biogeochemical responses to the North Atlantic Oscillation in a coupled climate model
In this study a coupled ocean-atmosphere model containing interactive marine biogeochemistry is used to analyze interannual, lagged, and decadal marine biogeochemical responses to the North Atlantic Oscillation (NAO), the dominant mode of North Atlantic atmospheric variability. The coupled model adequately reproduces present-day climatologies and NAO atmospheric variability. It is shown that marine biogeochemical responses to the NAO are governed by different mechanisms according to the time scale considered. On interannual time scales, local changes in vertical mixing, caused by modifications in air-sea heat, freshwater, and momentum fluxes, are most relevant in influencing phytoplankton growth through light and nutrient limitation mechanisms. At subpolar latitudes, deeper mixing occurring during positive NAO winters causes a slight decrease in late winter chlorophyll concentration due to light limitation and a 10%â20% increase in spring chlorophyll concentration due to higher nutrient availability. The lagged response of physical and biogeochemical properties to a high NAO winter shows some memory in the following 2 years. In particular, subsurface nutrient anomalies generated by local changes in mixing near the American coast are advected along the North Atlantic Current, where they are suggested to affect downstream chlorophyll concentration with 1 year lag. On decadal time scales, local and remote mechanisms act contemporaneously in shaping the decadal biogeochemical response to the NAO. The slow circulation adjustment, in response to NAO wind stress curl anomalies, causes a basin redistribution of heat, freshwater, and biogeochemical properties which, in turn, modifies the spatial structure of the subpolar chlorophyll bloom
Influences motivating smokers in a radon-affected area to quit smoking
Domestic radon gas concentrations in parts of the UK are sufficiently high to increase lung cancer risk among residents, and recent studies have confirmed that the risk of smokers developing lung cancer is significantly enhanced by the presence of radon. Despite campaigns encouraging residents of radon-affected areas (RAEs) to test and remediate their homes, public response to the risks posed by radon remains relatively modest, particularly among smokers and young families, limiting the health benefits and cost-effectiveness achievable by remediation. The observation that smokers, who are most at risk from radon, are not explicitly targeted by current radon remediation campaigns prompted an assessment of the value of smoking-cessation initiatives in reducing radon-induced lung cancers by reaching at-risk subgroups of the population hitherto uninfluenced by radon-awareness programmes. This study addresses the motivation of current quitters in a designated RAE using a postal questionnaire administered around one year after the cessation attempt. Residents of the Northamptonshire RAE who had joined the smoking-cessation programme between July and September 2006 and who remained verifiably tobacco free at four weeks, were subsequently invited to participate in a questionnaire-based investigation into factors affecting their decision to cease smoking. From an initial population of 445 eligible individuals, 205 of those contacted by telephone after 12 months agreed to complete postal questionnaires, and unsolicited questionnaires were sent to a further 112 participants for whom telephone contact had proved impossible. One hundred and three completed questionnaires were returned and analysed, the principal tools being c2, Mann-Whitney and Kruskal-Wallis tests. Individuals decide to quit smoking from self-interest, principally on health grounds, and regard the effects of their smoke on others, particularly children and unborn babies, as less significant. The risk of developing respiratory, coronary/cardiac or cancerous conditions provides the greatest motivation to the decision to quit, with knowledge of radon among the lowest-ranked influences. This study confirms that quitters place risks to their personal health as the highest factors influencing their decision to quit, and health professionals should be aware of this when designing smoking-cessation initiatives. As radon risk is ranked very low by quitters, there would appear to be the potential to raise radon awareness through smoking-cessation programmes, with the objective of increasing the uptake and success rate of such programmes and encouraging participation in radon-remediation programmes
Integrating Abstraction Techniques for Formal Verification of Analog Designs
The verification of analog designs is a challenging and exhaustive task that requires deep understanding of physical
behaviours. In this paper, we propose a qualitative based predicate abstraction method for the verification of a class
of non-linear analog circuits. In the proposed method, system equations are automatically extracted from a circuit
diagram by means of a bond graph. Verification is applied based on combining techniques from constraint solving and
computer algebra along with symbolic model checking. Our methodology has the advantage of avoiding exhaustive
simulation normally encountered in the verification of analog designs. To this end, we have used Dymola, Hsolver,
SMV and Mathematica to implement the verification flow. We illustrate the methodology on several analog examples
including Colpitts and tunnel diode oscillators
Limits on the ultra-bright Fast Radio Burst population from the CHIME Pathfinder
We present results from a new incoherent-beam Fast Radio Burst (FRB) search
on the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Pathfinder. Its
large instantaneous field of view (FoV) and relative thermal insensitivity
allow us to probe the ultra-bright tail of the FRB distribution, and to test a
recent claim that this distribution's slope, , is quite small. A 256-input incoherent beamformer was
deployed on the CHIME Pathfinder for this purpose. If the FRB distribution were
described by a single power-law with , we would expect an FRB
detection every few days, making this the fastest survey on sky at present. We
collected 1268 hours of data, amounting to one of the largest exposures of any
FRB survey, with over 2.4\,\,10\,deg\,hrs. Having seen no
bursts, we have constrained the rate of extremely bright events to
\,sky\,day above \,220 Jy\,ms
for between 1.3 and 100\,ms, at 400--800\,MHz. The non-detection also
allows us to rule out with 95 confidence, after
marginalizing over uncertainties in the GBT rate at 700--900\,MHz, though we
show that for a cosmological population and a large dynamic range in flux
density, is brightness-dependent. Since FRBs now extend to large
enough distances that non-Euclidean effects are significant, there is still
expected to be a dearth of faint events and relative excess of bright events.
Nevertheless we have constrained the allowed number of ultra-intense FRBs.
While this does not have significant implications for deeper, large-FoV surveys
like full CHIME and APERTIF, it does have important consequences for other
wide-field, small dish experiments
Metacommunities, metaecosystems and the environmental fate of chemical contaminants
Although pollution is a major driver of ecosystem change, models predicting the environmental fate of contaminants suffer from critical uncertainties related to oversimplifying the dynamics of the biological compartment.It is increasingly recognized that contaminant processing is an outcome of ecosystem functioning, that ecosystem functioning is contingent on community structure and that community structure is influenced by organismal dispersal. We propose a conceptual organization of the contribution of organismal dispersal to local contaminant fate. Direct dispersal effects occur when the dispersing organism directly couples contaminant stocks in spatially separate ecosystems by transporting contaminants in its biomass. Indirect dispersal effects occur when the dispersing organism indirectly influences contaminant fate via community assembly. This can occur either when the dispersing organism is a contaminant processor or when the dispersing organism alters, via species interactions, the abundance of contaminant biotransporters or processors already established in the ecosystem. The magnitude of direct and indirect dispersal effects is modulated by many factors, including other contaminants. These will influence population growth rates of the dispersing species in the donor ecosystem, or the probability that a dispersing individual reaches the recipient ecosystem.We provide a review of pertinent literature demonstrating that these two mechanisms, and their chemical modulation, are well supported or likely to occur in many natural and humanâmodified landscapes. The literature also demonstrates that they can operate in concert with each other.Synthesis and applications. Managed ecosystems thought to be important contaminant and nutrient sinks, such as artificial ponds and constructed wetlands, should be monitored and controlled for inâandâout animal movement if contaminant export is found to be relevant. Uncontaminated fishing grounds linked to contaminated sites via movement of dispersing species should be monitored and resident species evaluated for health consumption advisories. Assessing the success of contaminated site remediation can be improved by better matching the spatial extent of site remediation and the home range of monitored species. Finally, interagency research fund programmes should be developed that narrow the current gap between the fields of ecology and ecotoxicology.Managed ecosystems thought to be important contaminant and nutrient sinks, such as artificial ponds and constructed wetlands, should be monitored and controlled for inâandâout animal movement if contaminant export is found to be relevant. Uncontaminated fishing grounds linked to contaminated sites via movement of dispersing species should be monitored and resident species evaluated for health consumption advisories. Assessing the success of contaminated site remediation can be improved by better matching the spatial extent of site remediation and the home range of monitored species. Finally, interagency research fund programmes should be developed that narrow the current gap between the fields of ecology and ecotoxicology.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143615/1/jpe13054.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143615/2/jpe13054_am.pd
- âŠ