Finite-key security analysis for multilevel quantum key distribution

We present a detailed security analysis of a d-dimensional quantum key distribution protocol based on two and three mutually unbiased bases (MUBs) both in an asymptotic and finite key length scenario. The finite secret key rates are calculated as a function of the length of the sifted key by (i) generalizing the uncertainly relation-based insight from BB84 to any d-level 2-MUB QKD protocol and (ii) by adopting recent advances in the second-order asymptotics for finite block length quantum coding (for both d-level 2- and 3-MUB QKD protocols). Since the finite and asymptotic secret key rates increase with d and the number of MUBs (together with the tolerable threshold) such QKD schemes could in principle offer an important advantage over BB84. We discuss the possibility of an experimental realization of the 3-MUB QKD protocol with the orbital angular momentum degrees of freedom of photons.Comment: v4: close to the published versio

The GHZ state in secret sharing and entanglement simulation

In this note, we study some properties of the GHZ state. First, we present a quantum secret sharing scheme in which the participants require only classical channels in order to reconstruct the secret; our protocol is significantly more efficient than the trivial usage of teleportation. Second, we show that the classical simulation of an n-party GHZ state requires at least n log n - 2n bits of communication. Finally, we present a problem simpler than the complete simulation of the multi-party GHZ state, that could lead to a no-go theorem for GHZ state simulation.Comment: 5 page

Exact bond percolation thresholds in two dimensions

Recent work in percolation has led to exact solutions for the site and bond critical thresholds of many new lattices. Here we show how these results can be extended to other classes of graphs, significantly increasing the number and variety of solved problems. Any graph that can be decomposed into a certain arrangement of triangles, which we call self-dual, gives a class of lattices whose percolation thresholds can be found exactly by a recently introduced triangle-triangle transformation. We use this method to generalize Wierman's solution of the bow-tie lattice to yield several new solutions. We also give another example of a self-dual arrangement of triangles that leads to a further class of solvable problems. There are certainly many more such classes.Comment: Accepted for publication in J. Phys

Hippocampal Infusion of Zeta Inhibitory Peptide Impairs Recent, but Not Remote, Recognition Memory in Rats.

Spatial memory in rodents can be erased following the infusion of zeta inhibitory peptide (ZIP) into the dorsal hippocampus via indwelling guide cannulas. It is believed that ZIP impairs spatial memory by reversing established late-phase long-term potentiation (LTP). However, it is unclear whether other forms of hippocampus-dependent memory, such as recognition memory, are also supported by hippocampal LTP. In the current study, we tested recognition memory in rats following hippocampal ZIP infusion. In order to combat the limited targeting of infusions via cannula, we implemented a stereotaxic approach for infusing ZIP throughout the dorsal, intermediate, and ventral hippocampus. Rats infused with ZIP 3-7 days after training on the novel object recognition task exhibited impaired object recognition memory compared to control rats (those infused with aCSF). In contrast, rats infused with ZIP 1 month after training performed similar to control rats. The ability to form new memories after ZIP infusions remained intact. We suggest that enhanced recognition memory for recent events is supported by hippocampal LTP, which can be reversed by hippocampal ZIP infusion

Reserve Bank Operations in the Foreign Exchange Market: Effectiveness and Profitability

Since the float of the Australian dollar in December 1983, the Reserve Bank has intervened in the foreign exchange market in order to exert a stabilising influence. Whether this intervention has been stabilising cannot be directly observed since the behaviour of the exchange rate in its absence cannot be known. However, there are a number of ways of assessing it indirectly. The best known is the Friedman “profits test”. Friedman (1953) argued that a central bank which was stabilising the exchange rate would tend to buy foreign exchange when its price was low, and sell when its price is high, and hence its operations would be profitable. This paper applies the profits test to the Bank’s foreign exchange operations since the exchange rate was floated. The main conclusion is that over this period the Bank’s foreign exchange operations have produced total profits of around $A3.4 billion, suggesting that intervention has tended to be stabilising. Other statistical tests developed by Wonnacott (1982) and Mayer and Taguchi (1983), also presented in this paper, support this conclusion.

Critical surfaces for general bond percolation problems

We present a general method for predicting bond percolation thresholds and critical surfaces for a broad class of two-dimensional periodic lattices, reproducing many known exact results and providing excellent approximations for several unsolved lattices. For the checkerboard and inhomogeneous bow-tie lattices, the method yields predictions that agree with numerical measurements to more than six figures, and are possibly exact

Transcriptome Analysis of \u3ci\u3eBifidobacterium Longum\u3c/i\u3e Strains that Show a Differential Response to Hydrogen Peroxide Stress

Consumer and commercial interest in foods containing probiotic bifidobacteria is increasing. However, because bifidobacteria are anaerobic, oxidative stress can diminish cell viability during production and storage of bioactive foods. We previously found Bifidobacterium longum strain NCC2705 had signifi- cantly greater intrinsic and inducible resistance to hydrogen peroxide (H2O2) than strain D2957. Here, we explored the basis for these differences by examining the transcriptional responses of both strains to sub-lethal H2O2 exposure for 5- or 60-min. Strain NCC2705 had 288 genes that were differentially expressed after the 5-min treatment and 114 differentially expressed genes after the 60-min treatment. In contrast, strain D2957 had only 21 and 90 differentially expressed genes after the 5- and 60-min treatments, respectively. Both strains showed up-regulation of genes coding enzymes implicated in oxidative stress resistance, such as thioredoxin, thioredoxin reductase, peroxiredoxin, ferredoxin, glutaredoxin, and anaerobic ribonucleotide reductase, but induction levels were typically highest in NCC2705. Compared to D2957, NCC2705 also had more up-regulated genes involved in transcriptional regulation and more down-regulated genes involved in sugar transport and metabolism. These results provide a greater understanding of the molecular basis for oxidative stress resistance in B. longum and the factors that contribute to strain-to-strain variability in survival in bioactive food products

Genetic and Physiological Responses of \u3ci\u3eBifidobacterium animalis\u3c/i\u3e subsp. \u3ci\u3elactis\u3c/i\u3e to Hydrogen Peroxide Stress

Consumer interest in probiotic bifidobacteria is increasing, but industry efforts to secure high cell viability in foods is determined by these anaerobes’ sensitivity to oxidative stress. To address this limitation, we investigated genetic and physiological responses of two fully sequenced Bifidobacterium animalis subsp. lactis strains, BL-04 and DSM 10140, to hydrogen peroxide (H2O2) stress. Although the genome sequences for these strains are highly clonal, prior work showed they differ in both intrinsic and inducible H2O2 resistance. Transcriptome analysis of early stationary phase cells exposed to a sub-lethal H2O2 concentration detected significant (P2O2 stress resistance might be due to a mutation in a BL-04 gene encoding long chain fatty acid-coA ligase. To explore this possibility, membrane fatty acids were isolated and analyzed by GC-MS. Results confirmed the strains had significantly different lipid profiles; the BL-04 membrane contained higher percentages of C14:0 and C16:0, and lower percentages of C16:1n7 and C18:1n9. Alteration of the DSM 10140 membrane lipid composition using modified growth medium to more closely mimic that of BL-04 yielded cells that showed increased intrinsic resistance to lethal H2O2 challenge, but did not display an inducible H2O2 stress response. Results show deliberate stress induction or membrane lipid modification can be employed to significantly improve H2O2 resistance in B. animalis subsp. lactis strains