Constraining Axion Dark Matter with Big Bang Nucleosynthesis

We show that Big Bang Nucleosynthesis (BBN) significantly constrains axion-like dark matter. The axion acts like an oscillating QCD $\theta$ angle that redshifts in the early universe, increasing the neutron-proton mass difference at neutron freeze-out. An axion-like particle that couples too strongly to QCD results in the underproduction of 4He during BBN and is thus excluded. The BBN bound overlaps with much of the parameter space that would be covered by proposed searches for time-varying neutron EDMs. The QCD axion does not couple strongly enough to affect BBN.Comment: 5 pages, 2 figures; v2 typos corrected, numerical values for quark masses update

Bundling Equilibrium in Combinatorial auctions

This paper analyzes individually-rational ex post equilibrium in the VC (Vickrey-Clarke) combinatorial auctions. If $\Sigma$ is a family of bundles of goods, the organizer may restrict the participants by requiring them to submit their bids only for bundles in $\Sigma$. The $\Sigma$-VC combinatorial auctions (multi-good auctions) obtained in this way are known to be individually-rational truth-telling mechanisms. In contrast, this paper deals with non-restricted VC auctions, in which the buyers restrict themselves to bids on bundles in $\Sigma$, because it is rational for them to do so. That is, it may be that when the buyers report their valuation of the bundles in $\Sigma$, they are in an equilibrium. We fully characterize those $\Sigma$ that induce individually rational equilibrium in every VC auction, and we refer to the associated equilibrium as a bundling equilibrium. The number of bundles in $\Sigma$ represents the communication complexity of the equilibrium. A special case of bundling equilibrium is partition-based equilibrium, in which $\Sigma$ is a field, that is, it is generated by a partition. We analyze the tradeoff between communication complexity and economic efficiency of bundling equilibrium, focusing in particular on partition-based equilibrium

Statistical mechanical aspects of joint source-channel coding

An MN-Gallager Code over Galois fields, $q$, based on the Dynamical Block Posterior probabilities (DBP) for messages with a given set of autocorrelations is presented with the following main results: (a) for a binary symmetric channel the threshold, $f_c$, is extrapolated for infinite messages using the scaling relation for the median convergence time, $t_{med} \propto 1/(f_c-f)$; (b) a degradation in the threshold is observed as the correlations are enhanced; (c) for a given set of autocorrelations the performance is enhanced as $q$ is increased; (d) the efficiency of the DBP joint source-channel coding is slightly better than the standard gzip compression method; (e) for a given entropy, the performance of the DBP algorithm is a function of the decay of the correlation function over large distances.Comment: 6 page

Seasonal phenology of the diamondback moth, Plutella xylostella (L.), (Lepidoptera: Plutellidae), and its parasitoids on canola, Brassica napus (L.), in Gauteng province, South Africa

Canola, Brassica napus L. (Brassicaceae), is a relativelynewcrop in SouthAfrica. Several insect pests, including diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), that attack cruciferous vegetables, also attack canola. The aims of this study were to determine the seasonal phenology of P. xylostella populations on canola, and the composition, relative abundance and seasonal phenology of parasitoids attacking P. xylostella on this crop. Diamondback moth adults were monitored with synthetic sex-pheromone traps. Larval and pupal populations of P. xylostella were monitored weekly for three years at Bapsfontein and Rietondale in Gauteng province. Samples of diamondback moth larvae, pupae and parasitoid cocoons were collected and transported to the laboratory. Parasitoids that emerged were identified and their incidence recorded. Berlese funnel catches were used as an indicator of the accuracy of the visual counts. The infestation level of P. xylostella larvae was high from May to August at Rietondale, while at Bapsfontein it was high from September to December. There was a high correlation (r=0.79, P<0.001) between pheromone trap catches and subsequent larval infestations at Bapsfontein. The pheromone traps indicated that diamondback moth adults were present throughout the year. Berlese funnel catches indicated that a large number of larvae, especially first instars, were overlooked during visual plant scouting. Parasitism rates were often very high, reaching 90–100 %. The following parasitoids were recorded from field-collected P. xylostella: the larval parasitoids Cotesia plutellae (Kurdjumov) (Hymenoptera: Braconidae) and Apanteles halfordi Ullyett (Hymenoptera: Braconidae), the larval/pupal parasitoids Diadegma mollipla (Holmgren) (Hymenoptera: Ichneumonidae) and Oomyzus sokolowskii (Kurdjumov) (Hymenoptera: Eulophidae), the pupal parasitoid Diadromus collaris (Gravenhorst) (Hymenoptera: Ichneumonidae), and the hyperparasitoids Mesochorus sp. (Hymenoptera: Ichneumonidae) and Pteromalus sp. (Hymenoptera: Pteromalidae). Cotesia plutellae was the most abundant parasitoid throughout the study

A new strategic framework for water-related health research

The aim of this study was to compile a new strategic framework to guide the funding and management of research in waterrelated human health in South Africa. This framework had to identify the research areas of highest need in the country and provide an effective, yet simple, tool for the management of research projects. A review of current water-related human health research was first undertaken. Using this review as background document, input was solicited from key people in Government, water boards, metro councils, science councils and universities. As part of the study, the country’s research support infrastructure for water-related health research was investigated. The framework was finalised at a stakeholder workshop. A structure of Thrust Areas, with Programmes under each Thrust Area, was suggested for research management and funding. A matrix system of research thrusts versus impacts/risks, interventions and governance was further constructed to assist in the identification of research gaps, rendering the framework a very useful tool in the funding and management of water-related human health research.Keywords: water, public health, research needs, research managemen

On the Global Convergence of Policy Gradient in Average Reward Markov Decision Processes

We present the first finite time global convergence analysis of policy gradient in the context of infinite horizon average reward Markov decision processes (MDPs). Specifically, we focus on ergodic tabular MDPs with finite state and action spaces. Our analysis shows that the policy gradient iterates converge to the optimal policy at a sublinear rate of $O\left({\frac{1}{T}}\right),$ which translates to $O\left({\log(T)}\right)$ regret, where $T$ represents the number of iterations. Prior work on performance bounds for discounted reward MDPs cannot be extended to average reward MDPs because the bounds grow proportional to the fifth power of the effective horizon. Thus, our primary contribution is in proving that the policy gradient algorithm converges for average-reward MDPs and in obtaining finite-time performance guarantees. In contrast to the existing discounted reward performance bounds, our performance bounds have an explicit dependence on constants that capture the complexity of the underlying MDP. Motivated by this observation, we reexamine and improve the existing performance bounds for discounted reward MDPs. We also present simulations to empirically evaluate the performance of average reward policy gradient algorithm.Comment: 29 pages, 5 figure

Helicity-selective phase-matching and quasi-phase matching of circularly polarized high-order harmonics: Towards chiral attosecond pulses

Phase matching of circularly polarized high-order harmonics driven by counter-rotating bi-chromatic lasers was recently predicted theoretically and demonstrated experimentally. In that work, phase matching was analyzed by assuming that the total energy, spin angular momentum and linear momentum of the photons participating in the process are conserved. Here we propose a new perspective on phase matching of circularly polarized high harmonics. We derive an extended phase matching condition by requiring a new propagation matching condition between the classical vectorial bi-chromatic laser pump and harmonics fields. This allows us to include the influence of the laser pulse envelopes on phase matching. We find that the helicity dependent phase matching facilitates generation of high harmonics beams with a high degree of chirality. Indeed, we present an experimentally measured chiral spectrum that can support a train of attosecond pulses with a high degree of circular polarization. Moreover, while the degree of circularity of the most intense pulse approaches unity, all other pulses exhibit reduced circularity. This feature suggests the possibility of using a train of attosecond pulses as an isolated attosecond probe for chiral-sensitive experiments

An N-Terminal Extension to UBA5 Adenylation Domain Boosts UFM1 Activation: Isoform-Specific Differences in Ubiquitin-like Protein Activation

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record.Modification of proteins by the ubiquitin-like protein, UFM1, requires activation of UFM1 by the E1-activating enzyme, UBA5. In humans, UBA5 possesses two isoforms, each comprising an adenylation domain, but only one containing an N-terminal extension. Currently, the role of the N-terminal extension in UFM1 activation is not clear. Here we provide structural and biochemical data on UBA5 N-terminal extension to understand its contribution to UFM1 activation. The crystal structures of the UBA5 long isoform bound to ATP with and without UFM1 show that the N-terminus not only is directly involved in ATP binding but also affects how the adenylation domain interacts with ATP. Surprisingly, in the presence of the N-terminus, UBA5 no longer retains the 1:2 ratio of ATP to UBA5, but rather this becomes a 1:1 ratio. Accordingly, the N-terminus significantly increases the affinity of ATP to UBA5. Finally, the N-terminus, although not directly involved in the E2 binding, stimulates transfer of UFM1 from UBA5 to the E2, UFC1.Marie Curie Career Integration GrantIsrael Science FoundationIsraeli Cancer Associatio