Horticultural markets promote alien species invasions : an Estonian case study of herbaceous perennials

Gardening is a popular pastime, but commercial horticulture is responsible for the introduction of alien species and contributes to invasions in a variety of ways. Although an extensive international literature is available on plant invasions, it is still important at the national level to examine the influence of local factors. Accordingly, 17 nurseries in Estonia that cultivated and sold perennial alien species were selected, and a list of species and prices was compiled. The relationships between species status, and factors such as their abundance in the wild were examined statistically. A qualitative list of the nationally problematic species among herbaceous perennials was also completed. A total of 880 taxa were recorded, of which 10.3% were native and 89.7% alien. In all, 87.3% of the alien species were still confined to cultivated areas. The ecological and socio-economic characteristics of the taxa were described, and lists of the families of casual, naturalised and invasive aliens were provided. Both native and increasing wild alien species have a very similar profile on the market. Alien species that are less expensive, widely available and have more cultivars per species on the market are also more likely to escape. The invasive status and abundance of escaped aliens in an area increases with residence time. In general, socio-economic factors create new and reflect previous propagule pressures from commercial horticulture, which continuously increase the likelihood of alien species surviving and invading new areas. Our findings suggest that these national socioeconomic market-related factors explain much of the invasiveness of various perennial ornamental species, and therefore regional and national authorities urgently need to regulate and control the ornamental plant trade to diminish the risk of new invasions

Identification and verification of frequency-domain models for XV-15 tilt-rotor aircraft dynamics

Frequency-domain methods are used to extract the open-loop dynamics of the XV-15 tilt-rotor aircraft from flight test data for the cruise condition (V = 170 knots). The frequency responses are numerically fitted with transfer-function forms to identify equivalent model characteristics. The associated handling quality parameters meet or exceed Level 2, Category A, requirements for fixed-wing military aircraft. Step response matching is used to verify the time-domain fidelity of the transfer-function models for the cruise and hover flight conditions. The transient responses of the model and aircraft are in close agreement in all cases, except for the normal acceleration response to elevator deflection in cruise. This discrepancy is probably due to the unmodeled rotor rpm dynamics. The utility of the frequency-domain approach for dynamics identification and analysis is clearly demonstrated

Simultaneous structural and control optimization via linear quadratic regulator eigenstructure assignment

A method for simultaneous structural and control design of large flexible space structures (LFSS) to reduce vibration generated by disturbances is presented. Desired natural frequencies and damping ratios for the closed loop system are achieved by using a combination of linear quadratic regulator (LQR) synthesis and numerical optimization techniques. The state and control weighing matrices (Q and R) are expressed in terms of structural parameters such as mass and stiffness. The design parameters are selected by numerical optimization so as to minimize the weight of the structure and to achieve the desired closed-loop eigenvalues. An illustrative example of the design of a two bar truss is presented

Suppression of biodynamic interference in head-tracked teleoperation

The utility of helmet-tracked sights to provide pointing commands for teleoperation of cameras, lasers, or antennas in aircraft is degraded by the presence of uncommanded, involuntary heat motion, referred to as biodynamic interference. This interference limits the achievable precision required in pointing tasks. The noise contributions due to biodynamic interference consists of an additive component which is correlated with aircraft vibration and an uncorrelated, nonadditive component, referred to as remnant. An experimental simulation study is described which investigated the improvements achievable in pointing and tracking precision using dynamic display shifting in the helmet-mounted display. The experiment was conducted in a six degree of freedom motion base simulator with an emulated helmet-mounted display. Highly experienced pilot subjects performed precision head-pointing tasks while manually flying a visual flight-path tracking task. Four schemes using adaptive and low-pass filtering of the head motion were evaluated to determine their effects on task performance and pilot workload in the presence of whole-body vibration characteristic of helicopter flight. The results indicate that, for tracking tasks involving continuously moving targets, improvements of up to 70 percent can be achieved in percent on-target dwelling time and of up to 35 percent in rms tracking error, with the adaptive plus low-pass filter configuration. The results with the same filter configuration for the task of capturing randomly-positioned, stationary targets show an increase of up to 340 percent in the number of targets captured and an improvement of up to 24 percent in the average capture time. The adaptive plus low-pass filter combination was considered to exhibit the best overall display dynamics by each of the subjects

Measurement and shaping of biphoton spectral wavefunctions

In this work we present a simple method to reconstruct the complex spectral wavefunction of a biphoton, and hence gain complete information about the spectral and temporal properties of a photon pair. The technique, which relies on quantum interference, is applicable to biphoton states produced with a monochromatic pump when a shift of the pump frequency produces a shift in the relative frequencies contributing to the biphoton. We demonstrate an example of such a situation in type-II parametric down-conversion (SPDC) allowing arbitrary paraxial spatial pump and detection modes. Moreover, our test cases demonstrate the possibility to shape the spectral wavefunction. This is achieved by choosing the spatial mode of the pump and of the detection modes, and takes advantage of spatiotemporal correlations.Comment: Supplementary information also available. Comments and feedback appreciated. Compared to the previous version, here we have made the following changes: -corrected a typo in the text between Eq. (11) and (12) -corrected a typo in the references -added reference

Combinatorial RNA interference in Caenorhabditis elegans reveals that redundancy between gene duplicates can be maintained for more than 80 million years of evolution

BACKGROUND: Systematic analyses of loss-of-function phenotypes have been carried out for most genes in Saccharomyces cerevisiae, Caenorhabditis elegans, and Drosophila melanogaster. Although such studies vastly expand our knowledge of single gene function, they do not address redundancy in genetic networks. Developing tools for the systematic mapping of genetic interactions is thus a key step in exploring the relationship between genotype and phenotype. RESULTS: We established conditions for RNA interference (RNAi) in C. elegans to target multiple genes simultaneously in a high-throughput setting. Using this approach, we can detect the great majority of previously known synthetic genetic interactions. We used this assay to examine the redundancy of duplicated genes in the genome of C. elegans that correspond to single orthologs in S. cerevisiae or D. melanogaster and identified 16 pairs of duplicated genes that have redundant functions. Remarkably, 14 of these redundant gene pairs were duplicated before the divergence of C. elegans and C. briggsae 80-110 million years ago, suggesting that there has been selective pressure to maintain the overlap in function between some gene duplicates. CONCLUSION: We established a high throughput method for examining genetic interactions using combinatorial RNAi in C. elegans. Using this technique, we demonstrated that many duplicated genes can retain redundant functions for more than 80 million years of evolution. This provides strong support for evolutionary models that predict that genetic redundancy between duplicated genes can be actively maintained by natural selection and is not just a transient side effect of recent gene duplication events

Using art for public engagement: reflections on the Dementia and Imagination project

Creative outputs engage the public and can be used to share research. This paper reports on public engagement activities that were part of the research project Dementia and Imagination (D&I). We found that artwork and creative activities effectively engaged a range of audiences and challenged negative ideas about dementia. For the project team, public engagement developed relationships with collaborators and connected the research to different community settings, influencing future programmes of work. Further work could explore public engagement in diverse settings to assess which approaches are effective in maximising research value and wider community benefit

Electron-hole and plasmon excitations in 3d transition metals: Ab initio calculations and inelastic x-ray scattering measurements

We report extensive all-electron time-dependent density-functional calculations and nonresonant inelastic x-ray scattering measurements of the dynamical structure factor of 3d transition metals. For small wave vectors, a plasmon peak is observed which is well described by our calculations. At large wave vectors, both theory and experiment exhibit characteristic low-energy electron-hole excitations of d character which correlate with the presence of d bands below and above the Fermi level. Our calculations, which have been carried out in the random-phase and adiabatic local-density approximations, are found to be in remarkable agreement with the measured dynamical structure factor of Sc and Cr at energies below the semicore onset energy (M-edge) of these materials.Comment: To appear in Phys. Rev.