2,020 research outputs found
Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments
We experimentally investigate mutual information and generalized mutual
information for coherent optical transmission systems. The impact of the
assumed channel distribution on the achievable rate is investigated for
distributions in up to four dimensions. Single channel and wavelength division
multiplexing (WDM) transmission over transmission links with and without inline
dispersion compensation are studied. We show that for conventional WDM systems
without inline dispersion compensation, a circularly symmetric complex Gaussian
distribution is a good approximation of the channel. For other channels, such
as with inline dispersion compensation, this is no longer true and gains in the
achievable information rate are obtained by considering more sophisticated
four-dimensional (4D) distributions. We also show that for nonlinear channels,
gains in the achievable information rate can also be achieved by estimating the
mean values of the received constellation in four dimensions. The highest gain
for such channels is seen for a 4D correlated Gaussian distribution
Phase-coherent lightwave communications with frequency combs
Fiber-optical networks are a crucial telecommunication infrastructure in
society. Wavelength division multiplexing allows for transmitting parallel data
streams over the fiber bandwidth, and coherent detection enables the use of
sophisticated modulation formats and electronic compensation of signal
impairments. In the future, optical frequency combs may replace multiple lasers
used for the different wavelength channels. We demonstrate two novel signal
processing schemes that take advantage of the broadband phase coherence of
optical frequency combs. This approach allows for a more efficient estimation
and compensation of optical phase noise in coherent communication systems,
which can significantly simplify the signal processing or increase the
transmission performance. With further advances in space division multiplexing
and chip-scale frequency comb sources, these findings pave the way for compact
energy-efficient optical transceivers.Comment: 17 pages, 9 figure
Exact localized eigenstates for an extended Bose-Hubbard model with pair-correlated hopping
The impact of sulfur functionalisation on nitrogen-based ionic liquid cations
It has been demonstrated that bonding and interactions within ionic liquids (ILs) can be elegantly tuned by manipulation of structure and the the introduction of functional groups. Here we use XPS to investigate the impact of sulfur containing substituents on the electronic structure of a series N-based cations, all with a common anion, [NTf2]-. The experiments reveal complexity and perturbation of delocalised systems which cannot be easily interpretated by NMR and XPS alone, DFT provides critical insight into bonding and underpins the assignment of spectra and development of deconstruction models for each system studied
Replication-biased genome organisation in the crenarchaeon Sulfolobus
<p>Abstract</p> <p>Background</p> <p>Species of the crenarchaeon <it>Sulfolobus </it>harbour three replication origins in their single circular chromosome that are synchronously initiated during replication.</p> <p>Results</p> <p>We demonstrate that global gene expression in two <it>Sulfolobus </it>species is highly biased, such that early replicating genome regions are more highly expressed at all three origins. The bias by far exceeds what would be anticipated by gene dosage effects alone. In addition, early replicating regions are denser in archaeal core genes (enriched in essential functions), display lower intergenic distances, and are devoid of mobile genetic elements.</p> <p>Conclusion</p> <p>The strong replication-biased structuring of the <it>Sulfolobus </it>chromosome implies that the multiple replication origins serve purposes other than simply shortening the time required for replication. The higher-level chromosomal organisation could be of importance for minimizing the impact of DNA damage, and may also be linked to transcriptional regulation.</p
DNA metabarcoding reveals the dietary profiles of a benthic marine crustacean,Nephrops norvegicus
Norwegian lobster, Nephrops norvegicus, are a generalist scavenger and predator capable of short foraging excursions but can also suspension feed. Existing knowledge about their diet relies on a combination of methods including morphology-based stomach content analysis and stable isotopes, which often lack the resolution to distinguish prey items to species level particularly in species that thoroughly masticate their prey. DNA metabarcoding overcomes many of the challenges associated with traditional methods and it is an attractive approach to study the dietary profiles of animals. Here, we present the diet of the commercially valuable Nephrops norvegicus using DNA metabarcoding of gut contents. Despite difficulties associated with host amplification, our cytochrome oxidase I (COI) molecular assay successfully achieves higher resolution information than traditional approaches. We detected taxa that were likely consumed during different feeding strategies. Dinoflagellata, Chlorophyta and Bacillariophyta accounted for almost 50% of the prey items consumed, and are associated with suspension feeding, while fish with high fisheries discard rates were detected which are linked to active foraging. In addition, we were able to characterise biodiversity patterns by considering Nephrops as natural samplers, as well as detecting parasitic dinoflagellates (e.g., Hematodinium sp.), which are known to influence burrow related behaviour in infected individuals in over 50% of the samples. The metabarcoding data presented here greatly enhances a better understanding of a species’ ecological role and could be applied as a routine procedure in future studies for proper consideration in the management and decision-making of fisheries
The double torus as a 2D cosmos: groups, geometry and closed geodesics
The double torus provides a relativistic model for a closed 2D cosmos with
topology of genus 2 and constant negative curvature. Its unfolding into an
octagon extends to an octagonal tessellation of its universal covering, the
hyperbolic space H^2. The tessellation is analysed with tools from hyperbolic
crystallography. Actions on H^2 of groups/subgroups are identified for SU(1,
1), for a hyperbolic Coxeter group acting also on SU(1, 1), and for the
homotopy group \Phi_2 whose extension is normal in the Coxeter group. Closed
geodesics arise from links on H^2 between octagon centres. The direction and
length of the shortest closed geodesics is computed.Comment: Latex, 27 pages, 5 figures (late submission to arxiv.org
THE "FREELY" FALLING TWO-LEVEL ATOM IN A RUNNING LASER WAVE
The time evolution of a two-level atom which is simultaneously exposed to the
field of a running laser wave and a homogeneous gravitational field is studied.
The result of the coupled dynamics of internal transitions and center-of-mass
motion is worked out exactly. Neglecting spontaneous emission and performing
the rotating wave approximation we derive the complete time evolution operator
in an algebraical way by using commutation relations. The result is discussed
with respect to the physical implications. In particular the long time and
short time behaviour is physically analyzed in detail. The breakdown of the
Magnus perturbation expansion is shown.Comment: 14 Pages, Late
Deuterated molecules in regions of high-mass star formation
We present the results of our studies of deuterated molecules (DCN, DNC,
DCO, ND and NHD) in regions of high-mass star formation, which
include a survey of such regions with the 20-m Onsala radio telescope and
mapping of several objects in various lines with the 30-m IRAM and 100-m MPIfR
radio telescopes. The deuteration degree reaches 10 in these
objects. We discuss its dependencies on the gas temperature and velocity
dispersion, as well as spatial distributions of deuterated molecules. We show
that the HCN/HNC intensity ratio may be a good indicator of the
gas kinetic temperature and estimate densities of the investigated objects.Comment: 8 pages, 4 figures, to be published in Proceedings of Science
(Proceedings of the conference "The Multifaceted Universe: Theory and
Observations - 2022", 23-27 May 2022, SAO RAS, Nizhny Arkhyz, Russia
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