871 research outputs found
Molecular analysis of fungal communities and laccase genes in decomposing litter reveals differences among forest types but no impact of nitrogen deposition
The fungal community of the forest floor was examined as the cause of previously reported increases in soil organic matter due to experimental N deposition in ecosystems producing predominantly high-lignin litter, and the opposite response in ecosystems producing low-lignin litter. The mechanism proposed to explain this phenomenon was that white-rot basidiomycetes are more important in the degradation of high-lignin litter than of low-lignin litter, and that their activity is suppressed by N deposition. We found that forest floor mass in the low-lignin sugar-maple dominated system decreased in October due to experimental N deposition, whereas forest floor mass of high-lignin oak-dominated ecosystems was unaffected by N deposition. Increased relative abundance of basidiomycetes in high-lignin forest floor was confirmed by denaturing gradient gel electrophoresis (DGGE) and sequencing. Abundance of basidiomycete laccase genes, encoding an enzyme used by white-rot basidiomycetes in the degradation of lignin, was 5–10 times greater in high-lignin forest floor than in low-lignin forest floor. While the differences between the fungal communities in different ecosystems were consistent with the proposed mechanism, no significant effects of N deposition were detected on DGGE profiles, laccase gene abundance, laccase length heterogeneity profiles, or phenol oxidase activity. Our observations indicate that the previously detected accumulation of soil organic matter in the high-lignin system may be driven by effects of N deposition on organisms in the mineral soil, rather than on organisms residing in the forest floor. However, studies of in situ gene expression and temporal and spatial variability within forest floor communities will be necessary to further relate the ecosystem dynamics of organic carbon to microbial communities and atmospheric N deposition.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72825/1/j.1462-2920.2007.01250.x.pd
An Effective-Medium Tight-Binding Model for Silicon
A new method for calculating the total energy of Si systems is presented. The
method is based on the effective-medium theory concept of a reference system.
Instead of calculating the energy of an atom in the system of interest a
reference system is introduced where the local surroundings are similar. The
energy of the reference system can be calculated selfconsistently once and for
all while the energy difference to the reference system can be obtained
approximately. We propose to calculate it using the tight-binding LMTO scheme
with the Atomic-Sphere Approximation(ASA) for the potential, and by using the
ASA with charge-conserving spheres we are able to treat open system without
introducing empty spheres. All steps in the calculational method is {\em ab
initio} in the sense that all quantities entering are calculated from first
principles without any fitting to experiment. A complete and detailed
description of the method is given together with test calculations of the
energies of phonons, elastic constants, different structures, surfaces and
surface reconstructions. We compare the results to calculations using an
empirical tight-binding scheme.Comment: 26 pages (11 uuencoded Postscript figures appended), LaTeX,
CAMP-090594-
Biological effects of fulvestrant on estrogen receptor positive human breast cancer: Short, medium and long-term effects based on sequential biopsies.
We report the first study of the biological effect of fulvestrant on ER positive clinical breast cancer using sequential biopsies through to progression. Thirty-two locally/systemically advanced breast cancers treated with first-line fulvestrant (250 mg/month) were biopsied at therapy initiation, 6 weeks, 6 months and progression and immunohistochemically-analyzed for Ki67, ER, EGFR and HER2 expression/signaling activity. This series showed good fulvestrant responses (duration of response [DoR] = 25.8 months; clinical benefit = 81%). Ki67 fell (p < 0.001) in 79% of tumours by 6 months and lower Ki67 at all preprogression time-points predicted for longer DoR. ER and PR significantly decreased in all tumours by 6 months (p < 0.001), with some declines in ER (serine 118) phosphorylation and Bcl-2 (p = 0.007). There were modest HER2 increases (p = 0.034, 29% tumours) and loss of any detectable EGFR phosphorylation (p = 0.024, 50% tumours) and MAP kinase (ERK1/2) phosphorylation (p = 0.019, 65% tumours) by 6 months. While ER remained low, there was some recovery of Ki67, Bcl-2 and (weakly) EGFR/MAPK activity in 45–67% patients at progression. Fulvestrant's anti-proliferative impact is related to DoR, but while commonly downregulating ER and indicators of its signaling and depleting EGFR/MAPK signaling in some patients, additional elements must determine response duration. Residual ER at fulvestrant relapse explains reported sensitivity to further endocrine therapies. Occasional modest treatment-induced HER2 and weakly detectable EGFR/HER2/MAPK signaling at relapse suggests targeting of such activity might have value alongside fulvestrant in some patients. However, unknown pathways must drive relapse in most. Ki67 has biomarker potential to predict fulvestrant outcome and as a quantitative measure of response
Ecological niche and potential geographic distribution of the invasive fruit fly *Bactrocera invadens* (Diptera, Tephritidae)
Two correlative approaches to the challenge of ecological niche modeling (genetic algorithm, maximum entropy) were used to estimate the potential global distribution of the invasive fruit fly, Bactrocera invadens, based on associations between known occurrence records and a set of environmental predictor variables. The two models yielded similar estimates, largely corresponding to Equatorial climate classes with high levels of precipitation. The maximum entropy approach was somewhat more conservative in its evaluation of suitability, depending on thresholds for presence/absence that are selected, largely excluding areas with distinct dry seasons; the genetic algorithm models, in contrast, indicate that climate class as partly suitable. Predictive tests based on independent distributional data indicate that model predictions are quite robust. Field observations in Benin and Tanzania confirm relationships between seasonal occurrences of this species and humidity and temperature
Equation of state for Universe from similarity symmetries
In this paper we proposed to use the group of analysis of symmetries of the
dynamical system to describe the evolution of the Universe. This methods is
used in searching for the unknown equation of state. It is shown that group of
symmetries enforce the form of the equation of state for noninteracting scaling
multifluids. We showed that symmetries give rise the equation of state in the
form and energy density
, which
is commonly used in cosmology. The FRW model filled with scaling fluid (called
homological) is confronted with the observations of distant type Ia supernovae.
We found the class of model parameters admissible by the statistical analysis
of SNIa data. We showed that the model with scaling fluid fits well to
supernovae data. We found that and (), which can correspond to (hyper) phantom fluid, and to a
high density universe. However if we assume prior that
then the favoured model is close to concordance
CDM model. Our results predict that in the considered model with
scaling fluids distant type Ia supernovae should be brighter than in
CDM model, while intermediate distant SNIa should be fainter than in
CDM model. We also investigate whether the model with scaling fluid is
actually preferred by data over CDM model. As a result we find from
the Akaike model selection criterion prefers the model with noninteracting
scaling fluid.Comment: accepted for publication versio
Proposal for a Joint German-British Interferometric Gravitational Wave Detector
For many years there has been steady progress towards the detection of gravitational radiation. It has now become clear that the next major step should be the construction of a number of long-baseline detectors around the world. An array of detectors of this type is expected to allow the observation of gravitational waves from a range of astrophysical sources, leading to improved insight in many areas including stellar collapse, binary coalescence and the expansion of the Universe.
We propose that one of these detectors be built by a collaboration formed around the gravitational wave groups in Britain and Germany. In this document we present our case for this collaborative venture and outline the design philosophy of our proposed instrument - an interferometric detector with arms of length close to 3km.
Two detectors of the same general type are planned for the USA (LIGO project), one is planned for Italy (Italian/French VIRGO project) and another is proposed for Australia (AIGO project). It is expected that all the long baseline detectors to be built will operate as part of a coordinated worldwide network
Magnetic Field Amplification in Galaxy Clusters and its Simulation
We review the present theoretical and numerical understanding of magnetic
field amplification in cosmic large-scale structure, on length scales of galaxy
clusters and beyond. Structure formation drives compression and turbulence,
which amplify tiny magnetic seed fields to the microGauss values that are
observed in the intracluster medium. This process is intimately connected to
the properties of turbulence and the microphysics of the intra-cluster medium.
Additional roles are played by merger induced shocks that sweep through the
intra-cluster medium and motions induced by sloshing cool cores. The accurate
simulation of magnetic field amplification in clusters still poses a serious
challenge for simulations of cosmological structure formation. We review the
current literature on cosmological simulations that include magnetic fields and
outline theoretical as well as numerical challenges.Comment: 60 pages, 19 Figure
Detector Description and Performance for the First Coincidence Observations between LIGO and GEO
For 17 days in August and September 2002, the LIGO and GEO interferometer
gravitational wave detectors were operated in coincidence to produce their
first data for scientific analysis. Although the detectors were still far from
their design sensitivity levels, the data can be used to place better upper
limits on the flux of gravitational waves incident on the earth than previous
direct measurements. This paper describes the instruments and the data in some
detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial
change
Energy Flow in the Hadronic Final State of Diffractive and Non-Diffractive Deep-Inelastic Scattering at HERA
An investigation of the hadronic final state in diffractive and
non--diffractive deep--inelastic electron--proton scattering at HERA is
presented, where diffractive data are selected experimentally by demanding a
large gap in pseudo --rapidity around the proton remnant direction. The
transverse energy flow in the hadronic final state is evaluated using a set of
estimators which quantify topological properties. Using available Monte Carlo
QCD calculations, it is demonstrated that the final state in diffractive DIS
exhibits the features expected if the interaction is interpreted as the
scattering of an electron off a current quark with associated effects of
perturbative QCD. A model in which deep--inelastic diffraction is taken to be
the exchange of a pomeron with partonic structure is found to reproduce the
measurements well. Models for deep--inelastic scattering, in which a
sizeable diffractive contribution is present because of non--perturbative
effects in the production of the hadronic final state, reproduce the general
tendencies of the data but in all give a worse description.Comment: 22 pages, latex, 6 Figures appended as uuencoded fil
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