664 research outputs found
The Limited Role of Mutually Unbiased Product Bases in Dimension Six
We show that a complete set of seven mutually unbiased bases in dimension
six, if it exists, cannot contain more than one product basis.Comment: 8 pages, identical to published versio
Multi-Qubit Systems: Highly Entangled States and Entanglement Distribution
A comparison is made of various searching procedures, based upon different
entanglement measures or entanglement indicators, for highly entangled
multi-qubits states. In particular, our present results are compared with those
recently reported by Brown et al. [J. Phys. A: Math. Gen. 38 (2005) 1119]. The
statistical distribution of entanglement values for the aforementioned
multi-qubit systems is also explored.Comment: 24 pages, 3 figure
Statistical mechanics of multipartite entanglement
We characterize the multipartite entanglement of a system of n qubits in
terms of the distribution function of the bipartite purity over all balanced
bipartitions. We search for those (maximally multipartite entangled) states
whose purity is minimum for all bipartitions and recast this optimization
problem into a problem of statistical mechanics.Comment: final versio
Affine Constellations Without Mutually Unbiased Counterparts
It has been conjectured that a complete set of mutually unbiased bases in a
space of dimension d exists if and only if there is an affine plane of order d.
We introduce affine constellations and compare their existence properties with
those of mutually unbiased constellations, mostly in dimension six. The
observed discrepancies make a deeper relation between the two existence
problems unlikely.Comment: 8 page
Setting a precautionary catch limit for Antarctic krill
A revised precautionary catch limit for Antarctic krill (Euphausia superba) in the Scotia Sea of 4 million tons was recently adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The limit was based on a total biomass of 44.3 million tons, as estimated from an acoustic and net survey of krill across the Scotia Sea sector of the Southern Ocean, and a harvest rate of 9.1%, as determined from an analysis of the risks of exceeding defined conservation criteria. We caution, however, that before the fishery can expand to the 4-inillion-ton level it will be necessary to establish mechanisms to avoid concentration of fishing effort, particularly in proximity to colonies of land-breeding krill predators, and to consider the effects of krill immigrating into the region from multiple sources
Classical Statistical Mechanics Approach to Multipartite Entanglement
We characterize the multipartite entanglement of a system of n qubits in
terms of the distribution function of the bipartite purity over balanced
bipartitions. We search for maximally multipartite entangled states, whose
average purity is minimal, and recast this optimization problem into a problem
of statistical mechanics, by introducing a cost function, a fictitious
temperature and a partition function. By investigating the high-temperature
expansion, we obtain the first three moments of the distribution. We find that
the problem exhibits frustration.Comment: 38 pages, 10 figures, published versio
Annexin A2 Binds RNA and Reduces the Frameshifting Efficiency of Infectious Bronchitis Virus
Annexin A2 (ANXA2) is a protein implicated in diverse cellular functions, including exocytosis, DNA synthesis and cell proliferation. It was recently proposed to be involved in RNA metabolism because it was shown to associate with some cellular mRNA. Here, we identified ANXA2 as a RNA binding protein (RBP) that binds IBV (Infectious Bronchitis Virus) pseudoknot RNA. We first confirmed the binding of ANXA2 to IBV pseudoknot RNA by ultraviolet crosslinking and showed its binding to RNA pseudoknot with ANXA2 protein in vitro and in the cells. Since the RNA pseudoknot located in the frameshifting region of IBV was used as bait for cellular RBPs, we tested whether ANXA2 could regulate the frameshfting of IBV pseudoknot RNA by dual luciferase assay. Overexpression of ANXA2 significantly reduced the frameshifting efficiency from IBV pseudoknot RNA and knockdown of the protein strikingly increased the frameshifting efficiency. The results suggest that ANXA2 is a cellular RBP that can modulate the frameshifting efficiency of viral RNA, enabling it to act as an anti-viral cellular protein, and hinting at roles in RNA metabolism for other cellular mRNAs
Multipartite Entanglement and Frustration
Some features of the global entanglement of a composed quantum system can be
quantified in terms of the purity of a balanced bipartition, made up of half of
its subsystems. For the given bipartition, purity can always be minimized by
taking a suitable (pure) state. When many bipartitions are considered, the
requirement that purity be minimal for all bipartitions can engender conflicts
and frustration arises. This unearths an interesting link between frustration
and multipartite entanglement, defined as the average purity over all
(balanced) bipartitions.Comment: 15 pages, 7 figure
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Objective determination of the extratropical transition of tropical cyclones in the Northern Hemisphere
Extratropical transition (ET) has eluded objective identification since the realisation of its existence in the 1970s. Recent advances in numerical, computational models have provided data of higher resolution than previously available. In conjunction with this, an objective characterisation of the structure of a storm has now become widely accepted in the literature. Here we present a method of combining these two advances to provide an objective method for defining ET. The approach involves applying K-means clustering to isolate different life-cycle stages of cyclones and then analysing the progression through these stages. This methodology is then tested by applying it to five recent years from the European Centre of Medium-Range Weather Forecasting operational analyses. It is found that this method is able to determine the general characteristics for ET in the Northern Hemisphere. Between 2008 and 2012, 54% (±7, 32 of 59) of Northern Hemisphere tropical storms are estimated to undergo ET. There is great variability across basins and time of year. To fully capture all the instances of ET is necessary to introduce and characterise multiple pathways through transition. Only one of the three transition types needed has been previously well-studied. A brief description of the alternate types of transitions is given, along with illustrative storms, to assist with further stud
Different strategies for recovering metals from CARON process residue
http://dx.doi.org/10.1016/j.jhazmat.2011.03.048The capacity of Acidithiobacillus thiooxidans DMS 11478 to recover the heavy metals contained in
the residue obtained from the CARON process has been evaluated. Different bioreactor configurations
were studied: a two-stage batch system and two semi-continuous systems (stirred-tank reactor
leaching and column leaching). In the two-stage system, 46.8% Co, 36.0% Mg, 26.3% Mn and 22.3% Ni
were solubilised after 6 h of contact between the residue and the bacteria-free bioacid. The results
obtained with the stirred-tank reactor and the column were similar: 50% of the Mg and Co and
40% of the Mn and Ni were solubilised after thirty one days. The operation in the column reactor
allowed the solid–liquid ratio to be increased and the pH to be kept at low values (<1.0). Recirculation
of the leachate in the column had a positive effect on metal removal; at sixty five days
(optimum time) the solubilisation levels were as follows: 86% Co, 83% Mg, 72% Mn and Ni, 62% Fe and
23% Cr. The results corroborate the feasibility of the systems studied for the leaching of metals from
CARON process residue and these methodologies can be considered viable for the recovery of valuable
metals
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