European summer climate variability in a heterogeneous multi-model ensemble

Recent results from an enhanced greenhouse-gas scenario over Europe suggest that climate change might not only imply a general mean warming at the surface, but also a pronounced increase in interannual surface temperature variability during the summer season (Schär etal., Nature 427:332-336, 2004). It has been proposed that the underlying physical mechanism is related to land surface-atmosphere interactions. In this study we expand the previous analysis by including results from a heterogeneous ensemble of 11 high-resolution climate models from the PRUDENCE project. All simulations considered comprise 30-year control and enhanced greenhouse-gas scenario periods. While there is considerable spread in the models' ability to represent the observed summer variability, all models show some increase in variability for the scenario period, confirming the main result of the previous study. Averaged over a large-scale Central European domain, the models simulate an increase in the standard deviation of summer mean temperatures between 20 and 80%. The amplification occurs predominantly over land points and is particularly pronounced for surface temperature, but also evident for precipitation. It is also found that the simulated changes in Central European summer conditions are characterized by an emergence of dry and warm years, with early and intensified depletion of root-zone soil moisture. There is thus some evidence that the change in variability may be linked to the dynamics of soil-moisture storage and the associated feedbacks on the surface energy balance and precipitatio

Adaptive approximate Bayesian computation for complex models

Approximate Bayesian computation (ABC) is a family of computational techniques in Bayesian statistics. These techniques allow to fi t a model to data without relying on the computation of the model likelihood. They instead require to simulate a large number of times the model to be fi tted. A number of re finements to the original rejection-based ABC scheme have been proposed, including the sequential improvement of posterior distributions. This technique allows to de- crease the number of model simulations required, but it still presents several shortcomings which are particu- larly problematic for costly to simulate complex models. We here provide a new algorithm to perform adaptive approximate Bayesian computation, which is shown to perform better on both a toy example and a complex social model.Comment: 14 pages, 5 figure

Evaluation of the QBC-vet autoread haematology system for domestic and pet animal species

A comprehensive evaluation was initiated to determine the suitability of the QBC-Vet Autoread haematology system for veterinary purposes in domestic and pet animal species. The system determines haematocrit (HCT), haemoglobin (HGB), white blood cell (WBC) count, granulocyte count, combined lymphocyte and monocyte count (L/M), platelet count, as well as eosinophil and neutrophil counts (canine samples only), and reticulocyte count (canine and feline samples only). Linearity assessed for a canine sample usually surpassed the physiological range. Within-batch precision was very good for the majority of the parameters in feline and canine samples: Coefficients of variation (CV) were below 5.5% for HCT, HGB and WBC. In order to test the accuracy of the system with respect to reference methods, a total of 300 blood samples from the Clinics of Internal Veterinary Medicine and Surgery (101 canine, 99 feline and 100 equine) were analysed. Strong linear correlation was demonstrated for HCT, HGB (rτ;/0.96) and WBC (rτ;/0.93) based on high correlation coefficients and narrow confidence intervals. A somewhat higher degree of variation from the estimated regression lines was found in differential blood cell counts, especially for eosinophil counts of the dog where the automated reader erroneously attributed some lymphocytes or monocytes to eosinophil counts. Accuracy of the system was also assessed with respect to clinical relevance of results. The majority of leukocytosis (50 of 53), neutrophilias (3 of 4), or eosinophilias (4 of 5) was detected properly by the QBC-Vet Autoread haematology system, but only 20 out of 35 leukopenic samples were identified correctly. The system detected the presence of reticulocytes in the majority of feline (9 of 10) and canine (6 of 7) samples with a regenerative anaemia. Unexpectedly, platelets of cats were measured with high within-batch precision (mean CV=4.64%). No ‘streaming' effect (no discrimination between erythrocytes and granulocytes) was observed with this advanced QBC system. The system was found to be easy both in handling and interpretation of results. The buffy coat profile appeared particularly useful and informative. In conclusion, the QBC-Vet Autoread-System has excellent analytical properties and is well suited for veterinary purpose

An approximate Markov model for the wright-fisher diffusion and its application to time series data

The joint and accurate inference of selection and demography from genetic data is considered a particularly challenging question in population genetics, since both process may lead to very similar patterns of genetic diversity. However, additional information for disentangling these effects may be obtained by observing changes in allele frequencies over multiple time points. Such data is common in experimental evolution studies, as well as in the comparison of ancient and contemporary samples. Leveraging this information, however, has been computationally challenging, particularly when considering multi-locus data sets. To overcome these issues, we introduce a novel, discrete approximation for diffusion processes, termed mean transition time approximation, which preserves the long-term behavior of the underlying continuous diffusion process. We then derive this approximation for the particular case of inferring selection and demography from time series data under the classic Wright- Fisher model and demonstrate that our approximation is well suited to describe allele trajectories through time, even when only a few states are used. We then develop a Bayesian inference approach to jointly infer the population size and locus-specific selection coefficients with high accuracy, and further extend this model to also infer the rates of sequencing errors and mutations. We finally apply our approach to recent experimental data on the evolution of drug resistance in Influenza virus, identifying likely targets of selection and finding evidence for much larger viral population sizes than previously reported

Simultaneous Swift X-ray and UV views of comet C/2007 N3 (Lulin)

We present an analysis of simultaneous X-Ray and UV observations ofcomet C/2007 N3 (Lulin) taken on three days between January 2009 and March 2009 using the Swift observatory. For our X-ray observations, we used basic transforms to account for the movement of the comet to allow the combination of all available data to produce an exposure-corrected image. We fit a simple model to the extracted spectrum and measured an X-ray flux of 4.3+/-1.3 * 10^-13 ergs cm-2 s-1 in the 0.3 to 1.0 keV band. In the UV, we acquired large-aperture photometry and used a coma model to derive water production rates given assumptions regarding the distribution of water and its dissociation into OH molecules about the comet's nucleus. We compare and discuss the X-ray and UV morphology of the comet. We show that the peak of the cometary X-ray emission is offset sunward of the UV peak emission, assumed to be the nucleus, by approximately 35,000 km. The offset observed, the shape of X-ray emission and the decrease of the X-ray emission comet-side of the peak, suggested that the comet was indeed collisionally thick to charge exchange, as expected from our measurements of the comet's water production rate (6--8 10^28 mol. s-1). The X-ray spectrum is consistent with solar wind charge exchange emission, and the comet most likely interacted with a solar wind depleted of very highly ionised oxygen. We show that the measured X-ray lightcurve can be very well explained by variations in the comet's gas production rates, the observing geometry and variations in the solar wind flux.Comment: Paper accepted for publication in Astronomy and Astrophysics, 6 March 2012, 12 pages, 8 colour figures, one tabl

Nuclear Shape Fluctuations in Fermi-Liquid Drop Model

Within the nuclear Fermi-liquid drop model, quantum and thermal fluctuations are considered by use of the Landau-Vlasov-Langevin equation. The spectral correlation function of the nuclear surface fluctuations is evaluated in a simple model of an incompressible and irrotational Fermi liquid. The dependence of the spectral correlation function on the dynamical Fermi-surface distortion is established. The temperature at which the eigenvibrations become overdamped is calculated. It is shown that, for realistic values of the relaxation time parameter and in the high temperature regime, there is a particular eigenmode of the Fermi liquid drop where the restoring force is exclusively due to the dynamical Fermi-surface distortion.Comment: 23 pages, revtex, file and 3 figures, accepted for publication in Nuclear Physics

Spectral Analysis of the Chandra Comet Survey

We present results of the analysis of cometary X-ray spectra with an extended version of our charge exchange emission model (Bodewits et al. 2006). We have applied this model to the sample of 8 comets thus far observed with the Chandra X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1 (LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005 (Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include a broad variety of comets, solar wind environments and observational conditions. The interaction model is based on state selective, velocity dependent charge exchange cross sections and is used to explore how cometary X-ray emission depend on cometary, observational and solar wind characteristics. It is further demonstrated that cometary X-ray spectra mainly reflect the state of the local solar wind. The current sample of Chandra observations was fit using the constrains of the charge exchange model, and relative solar wind abundances were derived from the X-ray spectra. Our analysis showed that spectral differences can be ascribed to different solar wind states, as such identifying comets interacting with (I) fast, cold wind, (II), slow, warm wind and (III) disturbed, fast, hot winds associated with interplanetary coronal mass ejections. We furthermore predict the existence of a fourth spectral class, associated with the cool, fast high latitude wind.Comment: 16 pages, 16 figures, and 7 Tables; accepted A&A (Due to space limits, this version has lower resolution jpeg images.

Rebirth of X-ray Emission from the Born-Again Planetary Nebula A 30

The planetary nebula (PN) A30 is believed to have undergone a very late thermal pulse resulting in the ejection of knots of hydrogen-poor material. Using HST images we have detected the angular expansion of these knots and derived an age of 850+280-150 yr. To investigate the spectral and spatial properties of the soft X-ray emission detected by ROSAT, we have obtained Chandra and XMM-Newton observations of A30. The X-ray emission from A30 can be separated into two components: a point-source at the central star and diffuse emission associated with the hydrogen-poor knots and the cloverleaf structure inside the nebular shell. To help us assess the role of the current stellar wind in powering this X-ray emission, we have determined the stellar parameters of the central star of A 30 using a non-LTE model fit to its optical and UV spectrum. The spatial distribution and spectral properties of the diffuse X-ray emission is suggestive that it is generated by the post-born-again and present fast stellar winds interacting with the hydrogen-poor ejecta of the born-again event. This emission can be attributed to shock-heated plasma, as the hydrogen-poor knots are ablated by the stellar winds, under which circumstances the efficient mass-loading of the present fast stellar wind raises its density and damps its velocity to produce the observed diffuse soft X-rays. Charge transfer reactions between the ions of the stellar winds and material of the born-again ejecta has also been considered as a possible mechanism for the production of diffuse X-ray emission, and upper limits on the expected X-ray production by this mechanism have been derived. The origin of the X-ray emission from the central star of A 30 is puzzling: shocks in the present fast stellar wind and photospheric emission can be ruled out, while the development of a new, compact hot bubble confining the fast stellar wind seems implausible.Comment: 29 pages, 11 figures, 4 tables; accepted for publication by Ap

Winery website loyalty: the role of sales promotion and service attributes

Purpose: toward buying wine on mobile phones and m-commerce website loyalty by examining a) the mediating role of sales promotion and b) the moderating role of service attributes of the m-commerce websites in influencing the mediation. Design/methodology/approach: A total of 3,318 completed surveys were collected. Drawing on a large non-probability criterion based purposive sample across six countries (France, Germany, Greece, South Africa, United States and Canada) mediation analysis was performed to examine hypothesized relationships. Findings: Results show that sales promotion mediates the relationship between feelings towards buying wine on mobile phones and m-commerce website loyalty. Moderated mediation reveals that the indirect pathways (sales promotion) through which feelings towards buying wine over mobile exert its effect on m-commerce website loyalty is dependent on the value of service (wine delivery) attributes of the website. The results demonstrate that sales promotion and service are of paramount importance to wineries and wine marketers. Research implications/limitations: Wine producers and retailers should consider the use of sales promotion to enhance sales and loyalty to m-commerce websites. Practical implications: Wine producers and retailers should consider use sales promotion (such as SMS or push notifications) to enhance sales and influence consumer feelings and hence their loyalty. Originality/value: Wine m-commerce studies are limited, especially with an international perspective comparing 6 different countries: 3 from the old world (such as France, Germany and Greece) and 3 from the New World (North America with USA and Canada; and South Africa). Altogether those 6 countries represent around 40% of the world consumption

Don't believe the hype: a grounded exploratory six country wine purchasing study

The purpose of this exploratory study was to understand the extent that consumers report purchasing wine on mobile devices and to empirically examine potential drivers of m-wine purchasing across six countries to guide theoretical research enquiry moving forward. Purposive sampling was employed. An online survey involving 2853 respondents from France, Germany, Greece, Canada, US and South Africa forms the basis for the current study. The results of the study indicate that though mobile phone usage, wine consumption and purchasing rates are high, mobile-wine purchasing prevalence is low within all six countries. While technology hype has us believe an online presence is essential for business revenue growth and performance; the current study indicates wineries should carefully consider consumer readiness towards mobile-wine purchasing. Limitations and recommendations for future research are identified