1,214 research outputs found
Nonlegumes, legumes, and root nodules harbor different arbuscular mycorrhizal fungal communities.
Legumes are an important plant functional group since they can form a tripartite symbiosis with nitrogen-fixing Rhizobium bacteria and phosphorus-acquiring arbuscular mycorrhizal fungi (AMF). However, not much is known about AMF community composition in legumes and their root nodules. In this study, we analyzed the AMF community composition in the roots of three nonlegumes and in the roots and root nodules of three legumes growing in a natural dune grassland. We amplified a portion of the small-subunit ribosomal DNA and analyzed it by using restriction fragment length polymorphism and direct sequencing. We found differences in AMF communities between legumes and nonlegumes and between legume roots and root nodules. Different plant species also contained different AMF communities, with different AMF diversity. One AMF sequence type was much more abundant in legumes than in nonlegumes (39 and 13%, respectively). Root nodules contained characteristic AMF communities that were different from those in legume roots, even though the communities were similar in nodules from different legume species. One AMF sequence type was found almost exclusively in root nodules. Legumes and root nodules have relatively high nitrogen concentrations and high phosphorus demands. Accordingly, the presence of legume- and nodule-related AMF can be explained by the specific nutritional requirements of legumes or by host-specific interactions among legumes, root nodules, and AMF. In summary, we found that AMF communities vary between plant functional groups (legumes and nonlegumes), between plant species, and between parts of a root system (roots and root nodules)
Nucleon mass, sigma term and lattice QCD
We investigate the quark mass dependence of the nucleon mass M_N. An
interpolation of this observable, between a selected set of fully dynamical
two-flavor lattice QCD data and its physical value, is studied using
relativistic baryon chiral perturbation theory up to order p^4. In order to
minimize uncertainties due to lattice discretization and finite volume effects
our numerical analysis takes into account only simulations performed with
lattice spacings a5. We have also restricted ourselves to
data with m_pi<600 MeV and m_sea=m_val. A good interpolation function is found
already at one-loop level and chiral order p^3. We show that the
next-to-leading one-loop corrections are small. From the p^4 numerical analysis
we deduce the nucleon mass in the chiral limit, M_0 approx 0.88 GeV, and the
pion-nucleon sigma term sigma_N= (49 +/- 3) MeV at the physical value of the
pion mass.Comment: 12 pages, 4 figures, revised journal versio
Braided algebras and the kappa-deformed oscillators
Recently there were presented several proposals how to formulate the binary
relations describing kappa-deformed oscillator algebras. In this paper we shall
consider multilinear products of kappa-deformed oscillators consistent with the
axioms of braided algebras. In general case the braided triple products are
quasi-associative and satisfy the hexagon condition depending on the
coassociator . We shall consider only the products
of kappa-oscillators consistent with co-associative braided algebra, with Phi
=1. We shall consider three explicite examples of binary kappa-deformed
oscillator algebra relations and describe briefly their multilinear
coassociative extensions satisfying the postulates of braided algebras. The
third example, describing kappa-deformed oscillators in group manifold approach
to kappa-deformed fourmomenta, is a new result.Comment: v2, 13 pages; Proc. of 2-nd Corfu School on Quantum Gravity and
Quantum Geometry, September 2009, Corfu; Gen. Rel. Grav. (2011),special
Proceedings issue; version in pres
Study of the three-dimensional shape and dynamics of coronal loops observed by Hinode/EIS
We study plasma flows along selected coronal loops in NOAA Active Region
10926, observed on 3 December 2006 with Hinode's EUV Imaging Spectrograph
(EIS). From the shape of the loops traced on intensity images and the Doppler
shifts measured along their length we compute their three-dimensional (3D)
shape and plasma flow velocity using a simple geometrical model. This
calculation was performed for loops visible in the Fe VIII 185 Ang., Fe X 184
Ang., Fe XII 195 Ang., Fe XIII 202 Ang., and Fe XV 284 Ang. spectral lines. In
most cases the flow is unidirectional from one footpoint to the other but there
are also cases of draining motions from the top of the loops to their
footpoints. Our results indicate that the same loop may show different flow
patterns when observed in different spectral lines, suggesting a dynamically
complex rather than a monolithic structure. We have also carried out magnetic
extrapolations in the linear force-free field approximation using SOHO/MDI
magnetograms, aiming toward a first-order identification of extrapolated
magnetic field lines corresponding to the reconstructed loops. In all cases,
the best-fit extrapolated lines exhibit left-handed twist (alpha < 0), in
agreement with the dominant twist of the region.Comment: 17 pages, 6 figure
Properties of the random field Ising model in a transverse magnetic field
We consider the effect of a random longitudinal field on the Ising model in a
transverse magnetic field. For spatial dimension , there is at low
strength of randomness and transverse field, a phase with true long range order
which is destroyed at higher values of the randomness or transverse field. The
properties of the quantum phase transition at zero temperature are controlled
by a fixed point with no quantum fluctuations. This fixed point also controls
the classical finite temperature phase transition in this model. Many critical
properties of the quantum transition are therefore identical to those of the
classical transition. In particular, we argue that the dynamical scaling is
activated, i.e, the logarithm of the diverging time scale rises as a power of
the diverging length scale
Evaluation of Irradiated Mandibles Using Emission Tomography, Bone Scans, and Radiography
This study compared radiographs, bone scans, and computed emission tomograms with histologic findings in irradiated mandibles of adult Rhesus monkeys. Although osteocytes were lost in the path of the beam, many vessels were partially or totally occluded, the periosteum degenerated, the marrow became fibrotic, and cancellous bone proliferated abundantly, no changes were noted with radiography, conventional bone scanning, or computed emission tomograms. These clinical methods of examination may misrepresent the true condition of irradiated bone because of inadequate sensitivity or balance among factors that control radioactive tracer uptake in bone.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68112/2/10.1177_00220345800590120201.pd
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
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