Formation of runoff at the hillslope scale during intense precipitation

On 60 m² hillslope plots, at 18 mainly grassland locations in Switzerland rain was applied at rates of 50–100 mm/h for between 3 and 6 h. The generated flows were measured, including overland flow, near surface and subsurface flow 0.5–1.3 m below the surface. At some locations less than 2% of the rain flowed down the slope either on or below the surface, whereas at some others more than 90% of the rain ran off. At the majority of sites most runoff was overland flow, though at a few sites subsurface flow, usually via macropores was dominant. Data collected during each of 48 high intensity sprinkling experiments were used to distinguish, which processes were dominant in each experiment. Which dominant and subsidiary processes occurred depended on interactions between infiltration rate, change in soil water storage and drainage of the soil water. These attributes were often not directly linked to parameters usually considered important like vegetation, slope, soil clay content and antecedent soil moisture. Considering the structure of the soil in combination with these attributes, process determination was in many cases fairly straightforward, indicating the possibility of reliably predicting runoff processes at a site. However, at some sites, effects occurred that were not easily recognizable and led to surprising results

Alice: The Rosetta Ultraviolet Imaging Spectrograph

We describe the design, performance and scientific objectives of the NASA-funded ALICE instrument aboard the ESA Rosetta asteroid flyby/comet rendezvous mission. ALICE is a lightweight, low-power, and low-cost imaging spectrograph optimized for cometary far-ultraviolet (FUV) spectroscopy. It will be the first UV spectrograph to study a comet at close range. It is designed to obtain spatially-resolved spectra of Rosetta mission targets in the 700-2050 A spectral band with a spectral resolution between 8 A and 12 A for extended sources that fill its ~0.05 deg x 6.0 deg field-of-view. ALICE employs an off-axis telescope feeding a 0.15-m normal incidence Rowland circle spectrograph with a concave holographic reflection grating. The imaging microchannel plate detector utilizes dual solar-blind opaque photocathodes (KBr and CsI) and employs a 2 D delay-line readout array. The instrument is controlled by an internal microprocessor. During the prime Rosetta mission, ALICE will characterize comet 67P/Churyumov-Gerasimenko's coma, its nucleus, and the nucleus/coma coupling; during cruise to the comet, ALICE will make observations of the mission's two asteroid flyby targets and of Mars, its moons, and of Earth's moon. ALICE has already successfully completed the in-flight commissioning phase and is operating normally in flight. It has been characterized in flight with stellar flux calibrations, observations of the Moon during the first Earth fly-by, and observations of comet Linear T7 in 2004 and comet 9P/Tempel 1 during the 2005 Deep Impact comet-collision observing campaignComment: 11 pages, 7 figure

A combined field and numerical approach to investigate flow processes in natural macroporous soils under extreme precipitation

International audienceA procedure involving simultaneous experimental and numerical research is described for the purposes of understanding the mechanisms involved when extreme precipitation is transformed to flood stream discharge. It is shown that experiments and model applications by themselves are not sufficient for process identification, but that their combined application provides considerable insight into the subsurface flow processes. The proposed approach is unconventional in that a numerical model, based on stringent continuity and momentum criteria, is used as a tool for process identification only. Unlike other studies, it is not intended to demonstrate the applicability of the utilised model for general hydrological applications, or to provide evidence of the suitability of particular model simplifications. Rather, different and sometimes conflicting model realisations are used to examine the plausibility of flow processes which may occur on natural hill slopes. Hereby, small scale effects such as those relating to the mechanisms of water entry into the macropores, and the movement of water to the surrounding matrix are identified from the results of well instrumented field experiments

Solvable K-essence Cosmologies and Modified Chaplygin Gas Unified Models of Dark Energy and Dark Matter

This paper is devoted to the investigation of modified Chaplygin gas model in the context of solvable k-essence cosmologies. For this purpose, we construct equations of state parameter of this model for some particular values of the parameter $n$. The graphical behavior of these equations are also discussed by using power law form of potential. The relationship between k-essence and modified Chaplygin gas model shows viable results in the dark energy scenario. We conclude that the universe behaves as a cosmological constant, quintessence phase or phantom phase depending upon $n$.Comment: 14 pages, 6 figure

Spectral Inversion of Multi-Line Full-Disk Observations of Quiet Sun Magnetic Fields

Spectral inversion codes are powerful tools to analyze spectropolarimetric observations, and they provide important diagnostics of solar magnetic fields. Inversion codes differ by numerical procedures, approximations of the atmospheric model, and description of radiative transfer. Stokes Inversion based on Response functions (SIR) is an implementation widely used by the solar physics community. It allows to work with different atmospheric components, where gradients of different physical parameters are possible, e.g., magnetic field strength and velocities. The spectropolarimetric full-disk observations were carried out with the Stokesmeter of the Solar Telescope for Operative Predictions (STOP) at the Sayan Observatory on 3 February 2009, when neither an active region nor any other extended flux concentration was present on the Sun. In this study of quiet Sun magnetic fields, we apply the SIR code simultaneously to 15 spectral lines. A tendency is found that weaker magnetic field strengths occur closer to the limb. We explain this finding by the fact that close to the limb, we are more sensitive to higher altitudes in an expanding flux tube, where the field strength should be smaller since the magnetic flux is conserved with height. Typically, the inversions deliver two populations of magnetic elements: (1) high magnetic field strengths (1500-2000 G) and high temperatures (5500-6500 K) and (2) weak magnetic fields (50-150 G) and low temperatures (5000-5300 K).Comment: 10 pages, 6 figures, accepted for Solar Physic

Salmeterol for the prevention of high-altitude pulmonary edema.

BACKGROUND: Pulmonary edema results from a persistent imbalance between forces that drive water into the air space and the physiologic mechanisms that remove it. Among the latter, the absorption of liquid driven by active alveolar transepithelial sodium transport has an important role; a defect of this mechanism may predispose patients to pulmonary edema. Beta-adrenergic agonists up-regulate the clearance of alveolar fluid and attenuate pulmonary edema in animal models. METHODS: In a double-blind, randomized, placebo-controlled study, we assessed the effects of prophylactic inhalation of the beta-adrenergic agonist salmeterol on the incidence of pulmonary edema during exposure to high altitudes (4559 m, reached in less than 22 hours) in 37 subjects who were susceptible to high-altitude pulmonary edema. We also measured the nasal transepithelial potential difference, a marker of the transepithelial sodium and water transport in the distal airways, in 33 mountaineers who were prone to high-altitude pulmonary edema and 33 mountaineers who were resistant to this condition. RESULTS: Prophylactic inhalation of salmeterol decreased the incidence of high-altitude pulmonary edema in susceptible subjects by more than 50 percent, from 74 percent with placebo to 33 percent (P=0.02). The nasal potential-difference value under low-altitude conditions was more than 30 percent lower in the subjects who were susceptible to high-altitude pulmonary edema than in those who were not susceptible (P<0.001). CONCLUSIONS: Prophylactic inhalation of a beta-adrenergic agonist reduces the risk of high-altitude pulmonary edema. Sodium-dependent absorption of liquid from the airways may be defective in patients who are susceptible to high-altitude pulmonary edema. These findings support the concept that sodium-driven clearance of alveolar fluid may have a pathogenic role in pulmonary edema in humans and therefore represent an appropriate target for therapy

Photonic crystal carpet: Manipulating wave fronts in the near field at 1550 nm

Ground-plane cloaks, which transform a curved mirror into a flat one, and recently reported at wavelengths ranging from the optical to the visible spectrum, bring the realm of optical illusion a step closer to reality. However, all carpet-cloaking experiments have thus far been carried out in the far-field. Here, we demonstrate numerically and experimentally that a dielectric photonic crystal (PC) of a complex shape made of a honeycomb array of air holes can scatter waves in the near field like a PC with a at boundary at stop band frequencies. This mirage effect relies upon a specific arrangement of dielectric pillars placed at the nodes of a quasi-conformal grid dressing the PC. Our carpet is shown to work throughout the range of wavelengths 1500nm to 1650nm within the stop band extending from 1280 to 1940 nm. The device has been fabricated using a single- mask advanced nanoelectronics technique on III-V semiconductors and the near field measurements have been carried out in order to image the wave fronts's curvatures around the telecommunication wavelength 1550 nm.Comment: 6 page

Boundary Terms and Junction Conditions for Generalized Scalar-Tensor Theories

We compute the boundary terms and junction conditions for Horndeski's panoptic class of scalar-tensor theories, and write the bulk and boundary equations of motion in explicitly second order form. We consider a number of special subclasses, including galileon theories, and present the corresponding formulae. Our analysis opens up of the possibility of studying tunnelling between vacua in generalized scalar-tensor theories, and braneworld dynamics. The latter follows because our results are independent of spacetime dimension.Comment: 13 pages, Equation corrected. Thanks to Tsutomu Kobayashi for informing us of the typ

RHESSI images and spectra of two small flares

We studied the evolution of two small flares (GOES class C2 and C1) that developed in the same active region with different morphological characteristics: one is extended and the other is compact. We analyzed the accuracy and the consistency of different algorithms implemented in RHESSI software to reconstruct the image of the emitting sources, for energies between 3 and 12 keV. We found that all tested algorithms give consistent results for the peak position whil the other parameters can differ at most by a factor 2. Pixon and Forward-fit generally converge to similar results but Pixon is more reliable for reconstructing a complex source. We investigated the spectral characteristics of the two flares during their evolution in the 3--25 keV energy band. We found that a single thermal model of the photon spectrum is inadequate to fit the observations and we needed to add either a non-thermal model or a hot thermal one.The non-thermal and the double thermal fits are comparable. If we assume a non-thermal model, the non-thermal energy is always higher than the thermal one.Only during the very final decay phase a single thermal model fits fairly well the observed spectrum.Comment: 26 pages, 11 figures, accepted by Solar Physic