To grate a liquid into tiny droplets by its impact on a hydrophobic micro-grid

We report on experiments of drop impacting a hydrophobic micro-grid, of typical spacing a few tens of $\mu$m. Above a threshold in impact speed, liquid emerges to the other side, forming micro-droplets of size about that of the grid holes. We propose a method to produce either a mono-disperse spray or a single tiny droplet of volume as small as a few picoliters corresponding to a volume division of the liquid drop by a factor of up to 10$^5$. We also discuss the discrepancy of the measured thresholds with that predicted by a balance between inertia and capillarity.Comment: 3 pages, 5 figures, Accepted for publication in Applied Physics Letter

Biases in the determination of dynamical parameters of star clusters: today and in the Gaia era

The structural and dynamical properties of star clusters are generally derived by means of the comparison between steady-state analytic models and the available observables. With the aim of studying the biases of this approach, we fitted different analytic models to simulated observations obtained from a suite of direct N-body simulations of star clusters in different stages of their evolution and under different levels of tidal stress to derive mass, mass function and degree of anisotropy. We find that masses can be under/over-estimated up to 50% depending on the degree of relaxation reached by the cluster, the available range of observed masses and distances of radial velocity measures from the cluster center and the strength of the tidal field. The mass function slope appears to be better constrainable and less sensitive to model inadequacies unless strongly dynamically evolved clusters and a non-optimal location of the measured luminosity function are considered. The degree and the characteristics of the anisotropy developed in the N-body simulations are not adequately reproduced by popular analytic models and can be detected only if accurate proper motions are available. We show how to reduce the uncertainties in the mass, mass-function and anisotropy estimation and provide predictions for the improvements expected when Gaia proper motions will be available in the near future.Comment: 14 pages, 8 figures, accepted for publication by MNRA

Are Laparoscopic Staplers Effective for Ligation of Large Intraabdominal Arteries?

AbstractObjectives. To evaluate ligation of aortoiliac arteries with laparoscopic staplers in order to develop specifically designed staplers.Methods. Cadaveric study. Seven human cadaver aortas were stapled using EndoGIA60® staplers. Efficiency was evaluated macroscopically and on a hydrodynamic bench.Clinical study. Twelve patients had ligation of 14 large abdominal arteries (aorta: nine, iliac artery: four, hepatic artery: one) using a laparoscopic stapler. Stapling efficiency was judged on peroperative clinical and postoperative CT scan criteria.Results. Cadaveric study. Stapling was performed perfectly on four moderately calcified aortas, without leakage with a pulsatile pressure of >250 mmHg. For three aortas with severe calcification, stapling was not efficient and major leakage occurred.Clinical study. Stapling appeared clinically efficient on all arteries but one aorta: this severely calcified aorta was ligated conventionally. The staplers are not easy to use due to their shape and their lack of articulation. After a mean follow-up of 31.3 months, all the other stapled arteries were effectively ligated.Conclusion. The commercially available staplers can be used securely on moderately calcified arteries but stapling of severely calcified arteries should be avoided. These devices should be redesigned to facilitate their use in vascular surgery

A rare early-type star revealed in the Wing of the Small Magellanic Cloud

Sk 183 is the visually-brightest star in the N90 nebula, a young star-forming region in the Wing of the Small Magellanic Cloud (SMC). We present new optical spectroscopy from the Very Large Telescope which reveals Sk 183 to be one of the most massive O-type stars in the SMC. Classified as an O3-type dwarf on the basis of its nitrogen spectrum, the star also displays broadened He I absorption which suggests a later type. We propose that Sk 183 has a composite spectrum and that it is similar to another star in the SMC, MPG 324. This brings the number of rare O2- and O3-type stars known in the whole of the SMC to a mere four. We estimate physical parameters for Sk 183 from analysis of its spectrum. For a single-star model, we estimate an effective temperature of 46+/-2 kK, a low mass-loss rate of ~10^-7 Msun yr^-1, and a spectroscopic mass of 46^+9_-8 Msun (for an adopted distance modulus of 18.7 mag to the young population in the SMC Wing). An illustrative binary model requires a slightly hotter temperature (~47.5 kK) for the primary component. In either scenario, Sk 183 is the earliest-type star known in N90 and will therefore be the dominant source of hydrogen-ionising photons. This suggests Sk 183 is the primary influence on the star formation along the inner edge of the nebula.Comment: Accepted by ApJ, 10 pages, 7 figures, v2 after proof

Correlation Functions for an Elastic String in a Random Potential: Instanton Approach

We develop an instanton technique for calculations of correlation functions characterizing statistical behavior of the elastic string in disordered media and apply the proposed approach to correlations of string free energies corresponding to different low-lying metastable positions. We find high-energy tails of correlation functions for the case of long-range disorder (the disorder correlation length well exceeds the characteristic distance between the sequential string positions) and short-range disorder with the correlation length much smaller then the characteristic string displacements. The former case refers to energy distributions and correlations on the distances below the Larkin correlation length, while the latter describes correlations on the large spatial scales relevant for the creep dynamics.Comment: 5 pages; 1 .eps figure include

The VLT-FLAMES Tarantula Survey. VII. A low velocity dispersion for the young massive cluster R136

Detailed studies of resolved young massive star clusters are necessary to determine their dynamical state and evaluate the importance of gas expulsion and early cluster evolution. In an effort to gain insight into the dynamical state of the young massive cluster R136 and obtain the first measurement of its velocity dispersion, we analyse multi-epoch spectroscopic data of the inner regions of 30 Doradus in the Large Magellanic Cloud (LMC) obtained as part of the VLT-FLAMES Tarantula Survey. Following a quantitative assessment of the variability, we use the radial velocities of non-variable sources to place an upper limit of 6 km/s on the line-of-sight velocity dispersion of stars within a projected distance of 5 pc from the centre of the cluster. After accounting for the contributions of undetected binaries and measurement errors through Monte Carlo simulations, we conclude that the true velocity dispersion is likely between 4 and 5 km/s given a range of standard assumptions about the binary distribution. This result is consistent with what is expected if the cluster is in virial equilibrium, suggesting that gas expulsion has not altered its dynamics. We find that the velocity dispersion would be ~25 km/s if binaries were not identified and rejected, confirming the importance of the multi-epoch strategy and the risk of interpreting velocity dispersion measurements of unresolved extragalactic young massive clusters.Comment: 18 pages, 7 figures, accepted by A&

Antioxidant properties and heat damage of water biscuits enriched with sprouted wheat and barley

The nutritional value of cereal kernels is markedly improved by the germination process. Aim of this study was to evaluate protein, ash, sugars, heat damage (furosine, hydroxymethylfurfural, glucosylisomaltol), carotenoids, tocols, phenolics and antioxidant capacity (FRAP, ABTS, DPPH, reducing power, superoxide anion, beta-carotene bleaching tests) of water biscuits enriched with increasing quantities (0, 5, 10 and 20%) of sprouted bread wheat or barley. The wholemeals from sprouted wheat and barley showed high concentrations of total carotenoids (82.6 and 119.7 mg/kg, respectively), tocols (53.4 and 88.2 mg/kg), conjugated (368.0 and 564.2 mg/kg) and bound (1811.6 and 3022.0 mg/kg) phenolics. Therefore, the enriched water biscuits had higher carotenoids, tocols and phenolics content, heat damage and antioxidant capacity than the controls. The greatest increase was recorded in barley-enriched samples. The addition of 15%-20% sprouted wheat or 5%-10% sprouted barley improved the nutritional quality of water biscuits while limiting heat damage

Free-energy distribution of the directed polymer at high temperature

We study the directed polymer of length $t$ in a random potential with fixed endpoints in dimension 1+1 in the continuum and on the square lattice, by analytical and numerical methods. The universal regime of high temperature $T$ is described, upon scaling 'time' $t \sim T^5/\kappa$ and space $x = T^3/\kappa$ (with $\kappa=T$ for the discrete model) by a continuum model with $\delta$-function disorder correlation. Using the Bethe Ansatz solution for the attractive boson problem, we obtain all positive integer moments of the partition function. The lowest cumulants of the free energy are predicted at small time and found in agreement with numerics. We then obtain the exact expression at any time for the generating function of the free energy distribution, in terms of a Fredholm determinant. At large time we find that it crosses over to the Tracy Widom distribution (TW) which describes the fixed $T$ infinite $t$ limit. The exact free energy distribution is obtained for any time and compared with very recent results on growth and exclusion models.Comment: 6 pages, 3 figures large time limit corrected and convergence to Tracy Widom established, 1 figure changed