2-Oxo-4-trifluoro­meth­yl-2H-chromen-7-yl 2-bromo-2-methyl­propano­ate

In the title compound, C14H10BrF3O4, the coumarin ring system is almost plannar (r.m.s. deviation = 0.025 Å) and a short C—H⋯F contact occurs. The propano­ate fragment is orientated almost perpendicular to the ring [dihedral angle = 71.80 (12)°]. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, generating [100] chains

Limb observations of the Martian atmosphere with Mars Express’ High Resolution Stereo Camera

Introduction: Good knowledge about the aerosol distribution and compositions is essential for the understanding of thermodynamic processes in the Martian atmosphere, which in turn is important for the understanding of the Martian climate and the altitude of the upper boundary of the atmosphere. The last point is of special interest for spacecraft aerobreaking manoeuvres. The Martian atmosphere often shows horizontal layers of haze up to altitudes of about 80 km. These have been described and analysed e.g. by Jaquin et al., 1986, usingViking Orbiter images and by Montmessin et al., 2006, who used SPICAM stellar occultation data. Both showed seasonal and latitudinal changes in the vertical structure of the aerosol distribution and composition. Apart from SPICAM, the High Resolution Stereo Camera (HRSC) is also on board ESA’s robotic spacecraft Mars Express. HRSC was build and is operated by the German Aerospace Center (Neukum et al. 2004; Jaumann et al. 2007). Mars Express is orbiting Mars in an elliptical orbit, with HRSC scanning the surface of Mars, primarily for geological research. In addition to that, HRSC has been used to sample the planetary limb. We examine the HRSC planetary limb data and analyse the seasonal and latitudinal variations of the maximum altitude of the haze layer and of the occurrence of high altitude detached hazes. We make some comparisons with earlier work. In contrast to the SPICAM instrument, HRSC observes the atmosphere during daytime, which makes it possible to compare night and daytime observations. The HRSC Limb Data: HRSC is a push broom scanner with nine line sensors pointing in different directions to facilitate stereoscopic imaging. Four of the sensors have colour filters at 440 nm, 530 nm, 750 nm and 970 nm, respectively. The five other sensors all have filters centred at 650 nm. These panchromatic filters have a much wider bandpass than the four colour filters. The surface observations which are HRSC’s main purpose, are usually take while the spacecraft is nadirtracking near pericentre. Limb observations, however, are mostly made with a pointing of the spacecraft being inertially fixxed in celestial space. This leaves only a small time window to make observations of the limb during descent or ascent. Therefore, usually only a few of the nine sensors can be used for the limb observation. Due to the motion of the spacecraft, the individual image lines are taken at different geographical locations and altitudes. The position of each image pixel above the limb has to be calculated from the spacecraft positioning information (Scholten, pers. comm.). The typical difference in altitude between two neighbouring pixels is between a couple of dozen metres and 150 m. HRSC has been observing the limb occasionally throughout the mission since 2004. So far the northern hemisphere and especially the north polar region, were particularly well covered (Figure 1 and 2). In Figure 2, we give an overview of the available data, sorted by season (LS) and latitude. The channel in which the observations have been made is colourcoded. Most observations were made with the panchromatic channels. There are also many observations with the blue and green sensors and only a few were made in the red and infra red channels. We find the best data coverage in northern spring in the northern most latitudes. For obvious reasons, we do not have any data during polar nights. For most of our actual analysis we sample the five central pixels of the sensor lines. This allows for minimal horizontal averaging. Analysis: As an example, Fig. 3 shows images and profiles for the blue, nadir, and green channels from orbit 6104. Al three images show a continuously bright limb haze until an altitude of about 20 km. At higher altitudes the limb haze becomes darker and stratified consistent with the limb profiles described by Jacquin et al., 1986. As Mars Express progresses along its orbit, the limb observations are made at different locations above the surface. The locations of the three profiles in Fig. 3 are still in close proximity of each other, in fact they overlap, but none the less they show different vertical aerosol distributions. Beginning above the North Polar cap and going southward, we observe less reflectivity above 20 km and more reflectivity below 20 km, hinting at different compositions or amounts of aerosols. It is not possible to obtain and compare profiles at the same location and at the same time with different sensors, but still, averages of profiles over place and season can provide us with information about typical atmospheric conditions. In Fig. 4 we show spectra from the average profiles at three different latitudinal bands between 70�N–90�N, 30�S–30�N, and 90�S– 70�S, on the left, centre, and right, respectively. The different symbols and colours represent the different altitudes at which the spectra were sampled. The size of the symbol increases with the number of averaged profiles. There are very few observations above the South Polar region (compare Fig. 1). In the North (and South) Polar region there is almost no signal above 30 km altitude, while around the equator the limb haze remains bright until altitudes of about 60 km. At the poles, the spectrum at 10 km is reddish. At higher altitudes the spectrum gets whiter, indicating smaller particles or higher ice content. At the low latitudes the spectra are reddish up to 40 km. At 60 km we see a more or less white spectrum. Figure 5 shows the maximum altitude of the aerosols as seen by HRSC, depending on season. During aphelion (LS � 70�) the maximum altitude of the aerosols that are visible with HRSC is around 40 km. During perihelion (LS � 250�) the maximum altitude is around 70 km. Discussion: Figure 1 and 2 show that there are plenty of visual and near infra red HRSC observations of the Martian limb available. These show aerosol distributions that change with season and latitude (Fig. 3 and 4). The plots in Fig. 4 show the spectra of the average limb profiles at several altitudes for three latitudinal bands. Two important distinctions can be made between the equatorial and the polar regions. First, the altitude at which aerosol occur is higher in the equatorial region and second, the composition of the aerosols at different altitudes is different. While the spectrum is white around 20 km altitude above the north pole, it is red at the low latitudes. The seasonal variations of maximum altitude of the aerosols is in good agreement with Jaquin et al. (1986) and with Montmessin et al. (2006). The similarity between Montmessin’s results and ours is likely to be due to the large annual variation of atmospheric dust load compared to the diurnal cycle. A much closer look at the data, is forseen to analyse the daily variation of aerosols in the Martian atmosphere. The CO2 and waterice aerosols are more likely to change their vertical distribution (above the planetary boundary layer) between day and night than the mineral (dust) aerosols. Spectral information would help to discriminate between these components. HRSC can not provide it, because the observation for the different filters take place at different locations and times (see Fig. 3). An alternative is to fit aerosol models to the inverted profiles. Currently, we are preparing this work. Mars Express’ HRSC limb data present a valuable opportunity to analyse Mars daytime atmospheric dust at a high vertical resolution. This work gives a short overview of the available data and analyses some seasonal and latitudinal properties

2-Bromo-2-methyl-N-(4-methyl-2-oxo-2H-chromen-7-yl)propanamide

In the title compound C14H14BrNO3, the coumarin ring system is almost planar (r.m.s. deviation = 0.008 Å) and an intra­molecular C—H⋯O inter­action generates an S(6) ring. In the crystal, mol­ecules are linked by N—H⋯O hydrogen bonds, with the C=O unit of the coumarin ring system acting as the acceptor group, generating [010] C(8) chains. The chain connectivity is reinforced by two C—H⋯O inter­actions

Global scenarios of irrigation water abstractions for bioenergy production: a systematic review

Many scenarios of future climate evolution and its anthropogenic drivers include considerable amounts of bioenergy as a fuel source, as a negative emission technology, and for providing electricity. The associated freshwater abstractions for irrigation of dedicated biomass plantations might be substantial and therefore potentially increase water limitation and stress in affected regions; however, assumptions and quantities of water use provided in the literature vary strongly. This paper reviews existing global assessments of freshwater abstractions for bioenergy production and puts these estimates into the context of scenarios of other water-use sectors. We scanned the available literature and (out of 430 initial hits) found 16 publications (some of which include several bioenergy-water-use scenarios) with reported values on global irrigation water abstractions for biomass plantations, suggesting water withdrawals in the range of 128.4 to 9000 km3 yr−1, which would come on top of (or compete with) agricultural, industrial, and domestic water withdrawals. To provide an understanding of the origins of this large range, we present the diverse underlying assumptions, discuss major study differences, and calculate an inverse water-use efficiency (iwue), which facilitates comparison of the required freshwater amounts per produced biomass harvest. We conclude that due to the potentially high water demands and the tradeoffs that might go along with them, bioenergy should be an integral part of global assessments of freshwater demand and use. For interpreting and comparing reported estimates of possible future bioenergy water abstractions, full disclosure of parameters and assumptions is crucial. A minimum set should include the complete water balances of bioenergy production systems (including partitioning of blue and green water), bioenergy crop species and associated water-use efficiencies, rainfed and irrigated bioenergy plantation locations (including total area and meteorological conditions), and total biomass harvest amounts. In the future, a model intercomparison project with standardized parameters and scenarios would be helpful

Strings on Semisymmetric Superspaces

Several string backgrounds which arise in the AdS/CFT correspondence are described by integrable sigma-models. Their target space is always a Z(4) supercoset (a semi-symmetric superspace). Here we list all semi-symmetric cosets which have zero beta function and central charge c<=26 at one loop in perturbation theory.Comment: 25 pages, 1 figur

Determination of the strong coupling constant based on event shapes

We report on a determination of the strong coupling constant from a fit of QCD predictions for six event-shape variables, calculated at next-tonext-to-leading order (NNLO) and matched to resummation in the next-to-leadinglogarithmic approximation (NLLA). We use data collected by ALEPH at centre-ofmass energies between 91 and 206 GeV. We also investigate the role of hadronisation corrections, using both Monte Carlo generator predictions and analytic models to parametrise non-perturbative power corrections

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

The gradient index coatings and optical filters based on them are a challenge for fabrication. In a round-robin experiment basically the same hybrid antireflection coating for the visible spectral region has been deposited with three different techniques: electron beam evaporation, ion beam sputtering and radio frequency magnetron-sputtering. Spectral performances of such one-side and both-side coated samples have been compared with corresponding theoretical spectra of the designed profile. Also, reproducibility of each process is checked

Calibrated Sub-Bundles in Non-Compact Manifolds of Special Holonomy

This paper is a continuation of math.DG/0408005. We first construct special Lagrangian submanifolds of the Ricci-flat Stenzel metric (of holonomy SU(n)) on the cotangent bundle of S^n by looking at the conormal bundle of appropriate submanifolds of S^n. We find that the condition for the conormal bundle to be special Lagrangian is the same as that discovered by Harvey-Lawson for submanifolds in R^n in their pioneering paper. We also construct calibrated submanifolds in complete metrics with special holonomy G_2 and Spin(7) discovered by Bryant and Salamon on the total spaces of appropriate bundles over self-dual Einstein four manifolds. The submanifolds are constructed as certain subbundles over immersed surfaces. We show that this construction requires the surface to be minimal in the associative and Cayley cases, and to be (properly oriented) real isotropic in the coassociative case. We also make some remarks about using these constructions as a possible local model for the intersection of compact calibrated submanifolds in a compact manifold with special holonomy.Comment: 20 pages; for Revised Version: Minor cosmetic changes, some paragraphs rewritten for improved clarit

Innovation Contests with Entry Auction

We consider procurement of an innovation from heterogeneous sellers. Innovations are random but depend on unobservable effort and private information. We compare two procurement mechanisms where potential sellers first bid in an auction for admission to an innovation contest. After the contest, an innovation is procured employing either a fixed prize or a first-price auction. We characterize Bayesian Nash equilibria such that both mechanisms are payoff-equivalent and induce the same efforts and innovations. In these equilibria, signaling in the entry auction does not occur since contestants play a simple strategy that does not depend on rivals' private information