Seasonal facilitative and competitive trade‐offs between shrub seedlings and coastal grasses

Shrub expansion is occurring in grasslands globally and may be impacted by the balance of competition and facilitation with existing grasses. Along the mid‐Atlantic and Gulf coasts, the native shrub Morella cerifera (wax myrtle) is rapidly expanding and displacing other native coastal species. Recent research suggests that much of this expansion is due to warming winter temperatures, as temperatures below −15°C kill M. cerifera. The objective of this project was to understand the importance of species interactions with grasses on the growth and physiology of M. cerifera at the seedling life stage through both field and laboratory experiments. In the field, grasses were removed around seedlings and microclimate and shrub physiology and growth were measured. Seeds and seedlings were experimentally frozen to measure the freeze tolerance at both life stages. We found that grasses provided ~1.3°C insulation to shrubs during winter. A freezing threshold for M. cerifera seedlings was experimentally found between −6°C and −11°C, but seeds remained viable after being frozen to the coldest ecologically relevant temperatures. Seedlings competed for light with grasses during warm months and grew more where grasses were clipped, revealing a trade‐off between winter insulation and summer light competition. Morella cerifera exhibits ecosystem engineering at the seedling stage by significantly reducing summer maximum temperatures. When seedlings are very young (less than one year), grasses appear to improve germination and seedling survival. These phenomena enable rapid expansion of M. cerifera across the landscape and likely inform shrub expansion mechanisms in other systems. Although seedlings are small and relatively vulnerable, this life stage appears to have significant implications for ecosystem trajectory in grasslands undergoing shrub encroachment

Quantum repeaters with individual rare-earth ions at telecommunication wavelengths

We present a quantum repeater scheme that is based on individual erbium and europium ions. Erbium ions are attractive because they emit photons at telecommunication wavelength, while europium ions offer exceptional spin coherence for long-term storage. Entanglement between distant erbium ions is created by photon detection. The photon emission rate of each erbium ion is enhanced by a microcavity with high Purcell factor, as has recently been demonstrated. Entanglement is then transferred to nearby europium ions for storage. Gate operations between nearby ions are performed using dynamically controlled electric-dipole coupling. These gate operations allow entanglement swapping to be employed in order to extend the distance over which entanglement is distributed. The deterministic character of the gate operations allows improved entanglement distribution rates in comparison to atomic ensemble-based protocols. We also propose an approach that utilizes multiplexing in order to enhance the entanglement distribution rate.Comment: 13 pages, 4 figure

The Partition Function of Multicomponent Log-Gases

We give an expression for the partition function of a one-dimensional log-gas comprised of particles of (possibly) different integer charge at inverse temperature {\beta} = 1 (restricted to the line in the presence of a neutralizing field) in terms of the Berezin integral of an associated non- homogeneous alternating tensor. This is the analog of the de Bruijn integral identities [3] (for {\beta} = 1 and {\beta} = 4) ensembles extended to multicomponent ensembles.Comment: 14 page

The impact of mild cognitive impairment on decision-making under explicit risk conditions: Evidence from the Personality and Total Health (PATH) Through Life longitudinal study

Objective: Previous research has indicated that cognition and executive function are associated with decision-making, however the impact of mild cognitive impairment (MCI) on decision-making under explicit risk conditions is unclear. This cross-sectional study examined the impact of MCI, and MCI subtypes, on decision-making on the Game of Dice Task (GDT), among a cohort of older adults. Method: Data from 245 older adult participants (aged 72-78 years) from the fourth assessment of the Personality and Total Health Through Life study were analyzed. A diagnostic algorithm identified 103 participants with MCI, with subtypes of single-domain amnestic MCI (aMCI-single; n = 38), multi-domain amnestic MCI (aMCI-multi; n = 31), and non-amnestic MCI (n = 33), who were compared with an age-, sex-, education-, and income-matched sample of 142 cognitively unimpaired older adults. Decision-making scores on the GDT (net score, single number choices, and strategy changes) were compared between groups using nonparametric tests. Results: Participants with MCI showed impaired performance on the GDT, with higher frequencies of single number choices and strategy changes. Analyses comparing MCI subtypes indicated that the aMCI-multi subtype showed increased frequency of single number choices compared to cognitively unimpaired participants. Across the sample of participants, decision-making scores were associated with measures of executive function (cognitive flexibility and set shifting). Conclusion: MCI is associated with impaired decision-making performance under explicit risk conditions. Participants with impairments in multiple domains of cognition showed the clearest impairments. The GDT may have utility in discriminating between MCI subtypes

Central limit theorems for the real eigenvalues of large Gaussian random matrices

Let G be an N×N real matrix whose entries are independent identically distributed standard normal random variables Gij∼N(0,1). The eigenvalues of such matrices are known to form a two-component system consisting of purely real and complex conjugated points. The purpose of this paper is to show that by appropriately adapting the methods of [E. Kanzieper, M. Poplavskyi, C. Timm, R. Tribe and O. Zaboronski, Annals of Applied Probability 26(5) (2016) 2733–2753], we can prove a central limit theorem of the following form: if λ1,…,λNR are the real eigenvalues of G, then for any even polynomial function P(x) and even N=2n, we have the convergence in distribution to a normal random variable 1E(NR)−−−−−√⎛⎝∑j=1NRP(λj/2n−−√)−E∑j=1NRP(λj/2n−−√)⎞⎠→N(0,σ2(P)) as n→∞, where σ2(P)=2−2√2∫1−1P(x)2dx

A Survey for H2O Megamasers III. Monitoring Water Vapor Masers in Active Galaxies

We present single-dish monitoring of the spectra of 13 extragalactic water megamasers taken over a period of 9 years and a single epoch of sensitive spectra for 7 others. Our data include the first K-band science observations taken with the new 100 m Green Bank Telescope (GBT). In the context of a circumnuclear, molecular disk model, our results suggest that either (a) the maser lines seen are systemic features subject to a much smaller acceleration than present in NGC 4258, presumably because the gas is farther from the nuclear black hole, or (b) we are detecting ``satellite'' lines for which the acceleration is in the plane of the sky. We also report a search for water vapor masers towards the nuclei of 58 highly inclined, nearby galaxies.Comment: accepted by ApJ

Quantum Memory with a controlled homogeneous splitting

We propose a quantum memory protocol where a input light field can be stored onto and released from a single ground state atomic ensemble by controlling dynamically the strength of an external static and homogeneous field. The technique relies on the adiabatic following of a polaritonic excitation onto a state for which the forward collective radiative emission is forbidden. The resemblance with the archetypal Electromagnetically-Induced-Transparency (EIT) is only formal because no ground state coherence based slow-light propagation is considered here. As compared to the other grand category of protocols derived from the photon-echo technique, our approach only involves a homogeneous static field. We discuss two physical situations where the effect can be observed, and show that in the limit where the excited state lifetime is longer than the storage time, the protocols are perfectly efficient and noise-free. We compare the technique to other quantum memories, and propose atomic systems where the experiment can be realized.Comment: submitted to New Journal of Physics, Focus on Quantum Memor

Degree Classification: Does the Calculation Model Affect the Award?

Background Universities have the freedom to define their own calculation model to define the degree classification awarded. The output profile features as a key metric in ranking tables, yet this conceptually could be affected by the calculation method and provide a source of inequality. Method The scores from Level 5 & 6 modules from a group of final year students (n=50) was selected. Four different (A,B,C,D) models were applied to the same data to calculate the final degree score and subsequent award classification and analysed based on raw scores and rounded values. Results All four models appear to deliver similar calculated scores (Mean: A=62.9%: B=65.7%: C=64.8%: D=62.7%) however there is a distinct impact on the degree classification profiles. The proportion of students achieving First or Upper Second class awards for models A to D are 72%, 80%, 74%, 70% respectively. If rounding is applied this changes to 72%, 82%, 78%, 70%. Additional application of discretion at classification boundaries may further positively impact the results. Calculation models have minimal impact on lower class awards. Conclusion The results demonstrate that the calculation model has an effect on the degree classification awarded. In particular, models B and C produce more favourable outcomes. Universities using these models may benefit from an improved contribution to ranking performance. Burgess, R. (2007) Beyond the honours degree classification: Burgess Group Final Report, Universities U

Random polynomials, random matrices, and LL-functions

We show that the Circular Orthogonal Ensemble of random matrices arises naturally from a family of random polynomials. This sheds light on the appearance of random matrix statistics in the zeros of the Riemann zeta-function.Comment: Added background material. Final version. To appear in Nonlinearit