6,634 research outputs found
Rapid turnover of hyphae of mycorrhizal fungi determined by AMS microanalysis of C-14
Processes in the soil remain among the least well-characterized components of the carbon cycle. Arbuscular mycorrhizal (AM) fungi are ubiquitous root symbionts in many terrestrial ecosystems and account for a large fraction of photosynthate in a wide range of ecosystems; they therefore play a key role in the terrestrial carbon cycle. A large part of the fungal mycelium is outside the root ( the extraradical mycelium, ERM) and, because of the dispersed growth pattern and the small diameter of the hyphae (<5 micrometers), exceptionally difficult to study quantitatively. Critically, the longevity of these. ne hyphae has never been measured, although it is assumed to be short. To quantify carbon turnover in these hyphae, we exposed mycorrhizal plants to fossil ("carbon-14 - dead") carbon dioxide and collected samples of ERM hyphae ( up to 116 micrograms) over the following 29 days. Analyses of their carbon-14 content by accelerator mass spectrometry (AMS) showed that most ERM hyphae of AM fungi live, on average, 5 to 6 days. This high turnover rate reveals a large and rapid mycorrhizal pathway of carbon in the soil carbon cycle
Electrically charged fluids with pressure in Newtonian gravitation and general relativity in d spacetime dimensions: theorems and results for Weyl type systems
Previous theorems concerning Weyl type systems, including Majumdar-Papapetrou
systems, are generalized in two ways, namely, we take these theorems into d
spacetime dimensions (), and we also consider the very
interesting Weyl-Guilfoyle systems, i.e., general relativistic charged fluids
with nonzero pressure. In particular within Newton-Coulomb theory of charged
gravitating fluids, a theorem by Bonnor (1980) in three-dimensional space is
generalized to arbitrary space dimensions. Then, we prove a new
theorem for charged gravitating fluid systems in which we find the condition
that the charge density and the matter density should obey. Within general
relativity coupled to charged dust fluids, a theorem by De and Raychaudhuri
(1968) in four-dimensional spacetimes in rendered into arbitrary
dimensions. Then a theorem, new in and dimensions, for
Weyl-Guilfoyle systems, is stated and proved, in which we find the condition
that the charge density, the matter density, the pressure, and the
electromagnetic energy density should obey. This theorem comprises, as
particular cases, a theorem by Gautreau and Hoffman (1973) and results in four
dimensions by Guilfoyle (1999). Upon connection of an interior charged solution
to an exterior Tangherlini solution (i.e., a Reissner-Nordstr\"om solution in
d-dimensions), one is able to give a general definition for gravitational mass
for this kind of relativistic systems and find a mass relation with the several
quantities of the interior solution. It is also shown that for sources of
finite extent the mass is identical to the Tolman mass.Comment: 27 page
Neutrinoless Double Beta Decay and Lepton Flavor Violation
We point out that extensions of the Standard Model with low scale (~TeV)
lepton number violation (LNV) generally lead to a pattern of lepton flavor
violation (LFV) experimentally distinguishable from the one implied by models
with GUT scale LNV. As a consequence, muon LFV processes provide a powerful
diagnostic tool to determine whether or not the effective neutrino mass can be
deduced from the rate of neutrinoless double beta decay. We discuss the role of
\mu -> e \gamma and \mu -> e conversion in nuclei, which will be studied with
high sensitivity in forthcoming experiments.Comment: 4 pages, 3 figure
Electric Deflection of Rotating Molecules
We provide a theory of the deflection of polar and non-polar rotating
molecules by inhomogeneous static electric field. Rainbow-like features in the
angular distribution of the scattered molecules are analyzed in detail.
Furthermore, we demonstrate that one may efficiently control the deflection
process with the help of short and strong femtosecond laser pulses. In
particular the deflection process may by turned-off by a proper excitation, and
the angular dispersion of the deflected molecules can be substantially reduced.
We study the problem both classically and quantum mechanically, taking into
account the effects of strong deflecting field on the molecular rotations. In
both treatments we arrive at the same conclusions. The suggested control scheme
paves the way for many applications involving molecular focusing, guiding, and
trapping by inhomogeneous fields
Lepton-mediated electroweak baryogenesis
We investigate the impact of the tau and bottom Yukawa couplings on the
transport dynamics for electroweak baryogenesis in supersymmetric extensions of
the Standard Model. Although it has generally been assumed in the literature
that all Yukawa interactions except those involving the top quark are
negligible, we find that the tau and bottom Yukawa interaction rates are too
fast to be neglected. We identify an illustrative "lepton-mediated electroweak
baryogenesis" scenario in which the baryon asymmetry is induced mainly through
the presence of a left-handed leptonic charge. We derive analytic formulae for
the computation of the baryon asymmetry that, in light of these effects, are
qualitatively different from those in the established literature. In this
scenario, for fixed CP-violating phases, the baryon asymmetry has opposite sign
compared to that calculated using established formulae.Comment: 26 pages, 5 figure
2S hyperfine structure of atomic deuterium
We have measured the frequency splitting between the and hyperfine sublevels in atomic deuterium by an optical differential
method based on two-photon Doppler-free spectroscopy on a cold atomic beam. The
result Hz is the most precise value for
this interval to date. In comparison to the previous radio-frequency
measurement we have improved the accuracy by the factor of three.
The specific combination of hyperfine frequency intervals for metastable- and
ground states in deuterium atom derived from our measurement is in a good agreement with
calculated from quantum-electrodynamics theory.Comment: 7 pages, 7 figure
Collisional shifts in optical-lattice atom clocks
We theoretically study the effects of elastic collisions on the determination
of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom
clocks. Interparticle interactions of bosonic atoms in multiply-occupied
lattice sites can cause a linear frequency shift, as well as generate
asymmetric Ramsey fringe patterns and reduce fringe visibility due to
interparticle entanglement. We propose a method of reducing these collisional
effects in an optical lattice by introducing a phase difference of
between the Ramsey driving fields in adjacent sites. This configuration
suppresses site to site hopping due to interference of two tunneling pathways,
without degrading fringe visibility. Consequently, the probability of double
occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure
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