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Evidence for suboxic nitrification in recent marine sediments
The classical scheme of biogeochemical zones (BGZ) is known to be an oversimplification
of the microbial processes that occur in organic-rich marine sediments. Results from a coupled
deployment of pore-water gel probes in Loch Duich, Scotland, provide direct evidence for rapid
recycling within the iron reduction (FeR) and sulphate reduction (SR) zones. High resolution porewater
profiles obtained using diffusive equilibrium in thin films (DET) gel probes found a nitrate peak
at the boundary between the FeR and SR zones. This non-steady state feature is consistent with recycling
of reduced N occurring throughout the FeR zone. Both conventional pore-water iron profiles
and results from diffusive gradient in thin films (DGT) probes indicate that iron is solubilised and precipitated
in rapid Fe/S recycling reactions throughout the SR zone. The presence of such complex
recycling reactions confirms the oversimplification of the classical BGZ scheme
Quantum theory of resonantly enhanced four-wave mixing: mean-field and exact numerical solutions
We present a full quantum analysis of resonant forward four-wave mixing based
on electromagnetically induced transparency (EIT). In particular, we study the
regime of efficient nonlinear conversion with low-intensity fields that has
been predicted from a semiclassical analysis. We derive an effective nonlinear
interaction Hamiltonian in the adiabatic limit. In contrast to conventional
nonlinear optics this Hamiltonian does not have a power expansion in the fields
and the conversion length increases with the input power. We analyze the
stationary wave-mixing process in the forward scattering configuration using an
exact numerical analysis for up to input photons and compare the results
with a mean-field approach. Due to quantum effects, complete conversion from
the two pump fields into the signal and idler modes is achieved only
asymptotically for large coherent pump intensities or for pump fields in
few-photon Fock states. The signal and idler fields are perfectly quantum
correlated which has potential applications in quantum communication schemes.
We also discuss the implementation of a single-photon phase gate for continuous
quantum computation.Comment: 10 pages, 11 figure
High-resolution pore-water sampling with a gel sampler
Sediment pore-water profiles were sampled at high resolution (millimeter scale) with a polyacrylamide gel probe. This simple procedure involves inserting a 1-mm-thick gel held in a plastic probe into sediment. The gel reaches diffusive equilibrium in <1-2 h. For anions, the gel was sectioned, back-equilibrated into distilled-deionized water, and anions determined by high-performance liquid chromatography. Laboratory trials showed recovery of 104+/-4% Cl, 102+/-2% NO3, 101+/-1% SO4, and 102+/-2% NH4. For Fe and Mn, the gel was fixed in 0.01 M NaOH for similar to 3 h, subsectioned, extracted with 1 M HNO3, and analyzed by atomic absorption spectrometry. Field trials were undertaken in Esthwaite Water, a seasonally anoxic lake in the English Lake District. Gel probe data compared well with conventional pore-water extractions
(In,Ga)N/GaN microcavities with double dielectric mirrors fabricated by selective removal of an (Al,In)N sacrificial layer
Comparable microcavities with 3/2 (~240 nm) active regions containing distributed (In,Ga)N quantum wells, grown on GaN substrates and bounded by two dielectric mirrors, have been fabricated by two different routes: one using laser lift-off to process structures grown on GaN-on-sapphire templates and the second using freestanding GaN substrates, which are initially processed by mechanical thinning. Both exploit the properties of an Al0.83In0.17N layer, lattice matched to the GaN substrate and spacer layers. In both cases cavity quality factors >400 are demonstrated by measurements of the cavity-filtered room-temperature excitonic emission near 410 nm
Structured illumination microscopy using micro-pixellated light-emitting diodes
Structured illumination is a flexible and economical method of obtaining optical sectioning in wide-field microscopy [1]. In this technique the illumination system is modified to project a single-spatial frequency grid pattern onto the sample [2, 3]. The pattern can only be resolved in the focal plane and by recording images for different transverse grid positions (or phases) an image of the in-focus parts of the object can be calculated. Light emitting diodes (LEDs) are becoming increasingly popular for lighting and illumination systems due to their low cost, small dimensions, low coherence, uniform illumination, high efficiency and long lifetime. These properties, together with recent developments in high brightness, ultraviolet operation and microstructured emitter design offer great potential for LEDs as light sources for microscopy. In this paper we demonstrate a novel structured illumination microscope using a blue micro-structured light emitting diode as the illumination source. The system is potentially very compact and has no-moving-parts
Deltaron Dibaryon Structure in Chiral SU(3) Quark Model
We discuss the structure of Deltaron dibaryon in the chiral SU(3) quark
model. The energy of Deltaron is obtained by considering the coupling of the
and (hidden color) channels. The effects of various
parameters on the Deltaron mass are also studied. It is shown that the mass of
Deltaron is lower than the mass of but higher than the mass of
.Comment: 15 pages, Late
Entangled light in transition through the generation threshold
We investigate continuous variable entangling resources on the base of
two-mode squeezing for all operational regimes of a nondegenerate optical
parametric oscillator with allowance for quantum noise of arbitrary level. The
results for the quadrature variances of a pair of generated modes are obtained
by using the exact steady-state solution of Fokker-Planck equation for the
complex P-quasiprobability distribution function. We find a simple expression
for the squeezed variances in the near-threshold range and conclude that the
maximal two-mode squeezing reaches 50% relative to the level of vacuum
fluctuations and is achieved at the pump field intensity close to the
generation threshold. The distinction between the degree of two-mode squeezing
for monostable and bistable operational regimes is cleared up.Comment: 7 pages, 4 figures; Content changed: more details added to the
discussion. To be published in Phys. Rev.
Anatomy of Spin-Transfer Torque
Spin-transfer torques occur in magnetic heterostructures because the
transverse component of a spin current that flows from a non-magnet into a
ferromagnet is absorbed at the interface. We demonstrate this fact explicitly
using free electron models and first principles electronic structure
calculations for real material interfaces. Three distinct processes contribute
to the absorption: (1) spin-dependent reflection and transmission; (2) rotation
of reflected and transmitted spins; and (3) spatial precession of spins in the
ferromagnet. When summed over all Fermi surface electrons, these processes
reduce the transverse component of the transmitted and reflected spin currents
to nearly zero for most systems of interest. Therefore, to a good
approximation, the torque on the magnetization is proportional to the
transverse piece of the incoming spin current.Comment: 16 pages, 8 figures, submitted to Phys. Rev.
A self-consistent treatment of non-equilibrium spin torques in magnetic multilayers
It is known that the transfer of spin angular momenta between current
carriers and local moments occurs near the interface of magnetic layers when
their moments are non-collinear. However, to determine the magnitude of the
transfer, one should calculate the spin transport properties far beyond the
interface regions. Based on the spin diffusion equation, we present a
self-consistent approach to evaluate the spin torque for a number of layered
structures. One of the salient features is that the longitudinal and transverse
components of spin accumulations are inter-twined from one layer to the next,
and thus, the spin torque could be significantly amplified with respect to
treatments which concentrate solely on the transport at the interface due to
the presence of the much longer longitudinal spin diffusion length. We conclude
that bare spin currents do not properly estimate the spin angular momentum
transferred between to the magnetic background; the spin transfer that occurs
at interfaces should be self-consistently determined by embedding it in our
globally diffuse transport calculations.Comment: 21 pages, 6 figure
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