21,359 research outputs found
Effect of random interactions in spin baths on decoherence
We study the decoherence of a central spin 1/2 induced by a spin bath with
intrabath interactions. Since we are interested in the cumulative effect of
interaction and disorder, we study baths comprising Ising spins with random
ferro- and antiferromagnetic interactions between the spins. Using the
resolvent operator method which goes beyond the standard Born-Markov master
equation approach, we show that, in the weak coupling regime, the decoherence
of the central spin at all times is entirely determined by the local-field
distribution or equivalently, the dynamical structure factor of the Ising bath.
We present analytic results for the Ising spin chain bath at arbitrary
temperature for different distributions of the intrabath interaction strengths.
We find clear evidence of non-Markovian behavior in the low temperature regime.
We also consider baths described by Ising models on higher-dimensional
lattices. We find that interactions lead to a significant reduction of the
decoherence. An important feature of interacting spinbaths is the saturation of
the asymptotic Markovian decay rate at high temperatures, as opposed to the
conventional Ohmic boson bath.Comment: 13 page
Mapping of lymphatic filariasis in loiasis areas: A new strategy shows no evidence for Wuchereria bancrofti endemicity in Cameroon
Condensate fragmentation as a sensitive measure of the quantum many-body behavior of bosons with long-range interactions
The occupation of more than one single-particle state and hence the emergence
of fragmentation is a many-body phenomenon universal to systems of spatially
confined interacting bosons. In the present study, we investigate the effect of
the range of the interparticle interactions on the fragmentation degree of one-
and two-dimensional systems. We solve the full many-body Schr\"odinger equation
of the system using the recursive implementation of the multiconfigurational
time-dependent Hartree for bosons method, R-MCTDHB. The dependence of the
degree of fragmentation on dimensionality, particle number, areal or line
density and interaction strength is assessed. It is found that for contact
interactions, the fragmentation is essentially density independent in two
dimensions. However, fragmentation increasingly depends on density the more
long-ranged the interactions become. The degree of fragmentation is increasing,
keeping the particle number fixed, when the density is decreasing as
expected in one spatial dimension. We demonstrate that this remains,
nontrivially, true also for long-range interactions in two spatial dimensions.
We, finally, find that within our fully self-consistent approach, the
fragmentation degree, to a good approximation, decreases universally as
when only is varied.Comment: 8 pages of RevTex4-1, 5 figure
Cyanobacterial mats: Microanalysis of community metabolism
The microbial communities in two sites were studied using several approaches: (1) light microscopy; (2) the measurement of microprofiles of oxygen and sulfide at the surface of the microbial mat; (3) the study of diurnal variation of oxygen and sulfides; (4) in situ measurement of photosynthesis and sulfate reduction and study of the coupling of these two processes; (5) measurement of glutathione in the upper layers of the microbial mat as a possible oxygen quencher; (6) measurement of reduced iron as a possible intermediate electron donor along the established redoxcline in the mats; (7) measurement of dissolved phosphate as an indicator of processes of break down of organic matter in these systems; and (8) measurement of carbon dioxide in the interstitial water and its delta C-13 in an attempt to understand the flow of CO2 through the systems. Microbial processes of primary production and initial degradation at the most active zone of the microbial mat were analyzed
Renormalization flow of Yang-Mills propagators
We study Landau-gauge Yang-Mills theory by means of a nonperturbative vertex
expansion of the quantum effective action. Using an exact renormalization group
equation, we compute the fully dressed gluon and ghost propagators to lowest
nontrivial order in the vertex expansion. In the mid-momentum regime,
, we probe the propagator flow with various
{\em ans\"atze} for the three- and four-point correlations. We analyze the
potential of these truncation schemes to generate a nonperturbative scale. We
find universal infrared behavior of the propagators, if the gluon dressing
function has developed a mass-like structure at mid-momentum. The resulting
power laws in the infrared support the Kugo-Ojima confinement scenario.Comment: 28 pages, 5 figures. V2: Typos corrected and reference adde
Hall state quantization in a rotating frame
We derive electromagnetomotive force fields for charged particles moving in a
rotating Hall sample, satisfying a twofold U(1) gauge invariance principle. It
is then argued that the phase coherence property of quantization of the line
integral of total collective particle momentum into multiples of Planck's
quantum of action is solely responsible for quantization in the Hall state. As
a consequence, the height of the Hall quantization steps should remain
invariant in a rapidly rotating Hall probe. Quantum Hall particle
conductivities do not depend on charge and mass of the electron, and are
quantized in units of the inverse of Planck's action quantum.Comment: 6 pages, accepted for publication in Europhysics Letter
Ecological study of aquatic midges and some related insects with special reference to feeding habits
Die Schweiz ist ein reiches Land. Sie verfĂŒgt ĂŒber viele MillionĂ€re. Der groĂe Reichtum konzentriert sich auf wenige Familien und Personen. In der Schweiz leben aber auch eine halbe Million der Bevölkerung (7,5 Mio.) in Haushalten von ErwerbstĂ€tigen, die weniger als das Existenzminimum verdienen. Ăber 200â000 Personen sind auf Sozialhilfe angewiesen. Bei den Vermögen und den verfĂŒgbaren Einkommen hat sich in den letzten Jahren die Kluft zwischen den obersten und untersten zehn Prozent verschĂ€rft. Die Zunahme der sozialen Ungleichheit erhöht die soziale Brisanz, was mehr zu ergrĂŒnden ist. Die soziale Differenzierung dokumentiert Prozesse der Globalisierung. Sie reproduziert und spezifiziert alte soziale Ungleichheiten. Wichtig ist, dass die Soziale Arbeit das thematisiert und weiter theoretisiert
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