European Airport Concessions: Retail Strategies to Improve Commercial Revenue from Leisure Travelers

Aeronautical revenue from landing and handling charges to carriers is falling significantly below 60% of total revenue and will not persist as the main source of income for airports. Airports in Europe cannot continue to rely on profits from airlines; operating companies need to improve the competitiveness through commercial income from different traveler types. The purpose of this multiple case study was to understand the elements of successful sales strategies by concessionaires (retailers) at the metropolitan airport system of Zurich and Basel in hopes of improving the nonaeronautical revenue from leisure travelers, a price-sensitive customer segment. The conceptual framework was corporate strategic planning with the underlying concept of sustainable business operations. Semistructured interviews included 9 executives and senior managers of concessions and retail operations at Zurich International and Basel EuroAirport, and covered major themes such as managing the shopping experience of passengers as well as collaboration between concessionaires, airports, and airlines. The key findings, which emerged from an inductive analysis of the data, were that the identification of personalized offerings and the inclusion of individual travelers\u27 needs are required to ensure a flexible approach by each airport and shop location throughout the terminal. The collected data contained indicators for holistic and targeted concepts by retail concessions in cooperation with airport stakeholders. Social implications include sustainable retail strategies by promoting value adding products and services, improving the passenger\u27s travel experience, and ensuring the profitability of concessionaires in a changing aviation market

In Situ Abiotic Detoxification and Immobilization of Hexavalent Chromium

Detailed site characterization data from the former electroplating shop at the U.S. Coast Guard Air Support Center, Elizabeth City, North Carolina, suggested that the elevated Cr(VI) in the capillary fringe area had contaminated the ground water at the site. Most of the mobile Cr(VI) is present in the capillary fringe zone of the aquifer under an oxidizing environment. Current literature suggests that the reduction of Cr(VI) to Cr(Ill) through in situ redox manipulation in the presence of a reductant is an innovative technique for remediating chromate-contaminated sediments and ground water. The objective of this study was to evaluate the effectiveness of sodium dithionite in creating a reductive environment to remediate Cr(VI) present in soil. Sodium dithionite, a strong reductant, was injected into a small area of the vadose zone where elevated Cr(VI) was identified. Several striking changes observed in the target zone during the post-injection monitoring periods include a significant decrease in Eh(SHE), as much as ~ 700 m V, absence of dissolved oxygen for 48 weeks, and the increase of Fe(II) concentrations. Results indicated that the in situ remedial treatment of Cr(VI) in the capillary fringe area was effective and consequently the concentration of Cr(VI) in ground water dropped below the MCLG level. This research demonstrated the effectiveness of in situ abiotic remediation by reducing Cr(VI) concentrations, mobility, and toxicity in soils and ground water within a short period of time. Therefore, sodium dithionite would be a feasible and cost-effective option for a full-scale remedial approach for the contaminated site at the U.S. Coast Guard Facility

The Discordance of Mass-Loss Estimates for Galactic O-Type Stars

We have determined accurate values of the product of the mass-loss rate and the ion fraction of P^{4+}, Mdot q(P^{4+}), for a sample of 40 Galactic O-type stars by fitting stellar-wind profiles to observations of the P V resonance doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P^{4+} is the dominant ion in the wind, Mdot q(P^{4+}) approximates the mass-loss rate to within a factor of 2. Theory predicts that P^{4+} is the dominant ion in the winds of O7-O9.7 stars, though an empirical estimator suggests that the range from O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P V wind profiles are systematically smaller than those obtained from fits to Halpha emission profiles or radio free-free emission by median factors of about 130 (if P^{4+} is dominant between O7 and O9.7) or about 20 (if P^{4+} is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from "density squared" diagnostics have been systematically over-estimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.Comment: 26 pages, 4 figures; accepted for publication in Ap

Radiation-driven winds of hot luminous stars XVII. Parameters of selected central stars of PN from consistent optical and UV spectral analysis and the universality of the mass-luminosity relation

Context: The commonly accepted mass-luminosity relation of central stars of planetary nebulae (CSPNs) might not be universally valid. While earlier optical analyses could not derive masses and luminosities independently (instead taking them from theoretical evolutionary models) hydrodynamically consistent modelling of the stellar winds allows using fits to the UV spectra to consistently determine also stellar radii, masses, and luminosities without assuming a mass-luminosity relation. Recent application to a sample of CSPNs raised questions regarding the validity of the theoretical mass-luminosity relation of CSPNs. Aims: The results of the earlier UV analysis are reassessed by means of a simultaneous comparison of observed optical and UV spectra with corresponding synthetic spectra. Methods: Using published stellar parameters (a) from a consistent UV analysis and (b) from fits to optical H and He lines, we calculate simultaneous optical and UV spectra with our model atmosphere code, which has been improved by implementing Stark broadening for H and He lines. Results: Spectra computed with the parameter sets from the UV analysis yield good agreement to the observations, but spectra computed with the stellar parameters from the published optical analysis and using corresponding consistent wind parameters show large discrepancies to both the observed optical and UV spectra. The published optical analyses give good fits to the observed spectrum only because the wind parameters assumed in these analyses are inconsistent with their stellar parameters. By enforcing consistency between stellar and wind parameters, stellar parameters are obtained which disagree with the core-mass-luminosity relation for the objects analyzed. This disagreement is also evident from a completely different approach: an investigation of the dynamical wind parameters.Comment: 22 pages, 18 fugre

Spectral Modelling of Star-Forming Regions in the Ultraviolet: Stellar Metallicity Diagnostics for High Redshift Galaxies

The chemical composition of high redshift galaxies is an important property which gives clues to their past history and future evolution and yet is difficult to measure with current techniques. In this paper we investigate new metallicity indicators, based upon the strengths of stellar photospheric features at rest-frame ultraviolet wavelengths. By combining the evolutionary spectral synthesis code Starburst99 with the output from the non-LTE model atmosphere code WM-basic, we have developed a code that can model the integrated ultraviolet stellar spectra of star-forming regions at metallicities between 1/20 and twice solar. We use our models to explore a number of spectral regions that are sensitive to metallicity and clean of other spectral features. The most promising metallicity indicator is an absorption feature between 1935 A and 2020 A, which arises from the blending of numerous Fe III transitions. We compare our model spectra to observations of two well studied high redshift star-forming galaxies, MS1512-cB58 (a Lyman break galaxy at z = 2.7276), and Q1307-BM1163 (a UV-bright galaxy at z = 1.411). The profiles of the photospheric absorption features observed in these galaxies are well reproduced by the models. In addition, the metallicities inferred from their equivalent widths are in good agreement with previous determinations based on interstellar absorption and nebular emission lines. Our new technique appears to be a promising alternative, or complement, to established methods which have only a limited applicability at high redshifts.Comment: 18 pages, 12 figures, accepted for publication in the Astrophysical Journa

STIS UV spectroscopy of early B supergiants in M31

We analyze STIS spectra in the 1150-1700 Angstrom wavelength range obtained for six early B supergiants in the neighboring galaxy M31. Because of their likely high (nearly solar) abundance, these stars were originally chosen to be directly comparable to their Galactic counterparts, and represent a much-needed addition to our current sample of B-type supergiants, in our efforts to study the dependence of the Wind Momentum-Luminosity Relationship on spectral type and metallicity. As a first step to determine wind momenta we fit the P-Cygni profiles of the resonance lines of N V, Si IV and C IV with standard methods, and derive terminal velocities for all of the STIS targets. From these lines we also derive ionic stellar wind column densities. Our results are compared with those obtained previously in Galactic supergiants, and confirm earlier claims of `normal' wind line intensities and terminal velocities in M31. For half of the sample we find evidence for an enhanced maximum turbulent velocity when compared to Galactic counterparts.Comment: 15 pages, 9 figures, 2 tables. Accepted for publication in The Astrophysical Journa

Star Formation in the Field and Clusters of NGC 5253

We investigate the star formation history of both the bright star clusters and the diffuse `field star' population in the dwarf starburst galaxy NGC 5253 using STIS longslit ultraviolet spectroscopy. Our slit covers a physical area of 370 x 1.6 pc and includes 8 apparent clusters and several inter-cluster regions of diffuse light which we take to be the field. The diffuse light spectrum lacks the strong O-star wind features which are clearly visible in spectra of the brightest clusters. This discrepancy provides compelling evidence that the diffuse light is not reflected light from nearby clusters, but originates in a UV-bright field star population, and it raises the issue of whether the star formation process may be operating differently in the field than in clusters. We compare our spectra to STARBURST99 evolutionary synthesis models which incorporate a new low metallicity atlas of O-star spectra. We favor a scenario which accounts for the paucity of O-stars in the field without requiring the field to have a different IMF than the clusters: stellar clusters form continuously and then dissolve on ~10 Myr timescales and disperse their remaining stars into the field. We consider the probable contribution of an O-star deficient field population to the spatially unresolved spectra of high redshift galaxies. (Abridged)Comment: 26 pages, 10 figures, accepted for publication in Ap

Ionizing Photon Emission Rates from O- and Early B-type Stars and Clusters

We present new computations of the ionizing spectral energy distributions (SEDs) and Lyman continuum (Lyc) and HeI continuum photon emission rates, for hot O-type and early B-type stars. We consider solar metallicity stars, with effective temperatures ranging from 25,000 to 55,000 K and surface gravities (cm s^-2) logg ranging from 3 to 4, covering the full range of spectral types and luminosity classes for hot stars. We use our updated (WM-basic) code to construct radiation-driven wind atmosphere models for hot stars. Our models include the coupled effects of hydrodynamics and non-LTE radiative transfer in spherically outflowing winds, including the detailed effects of metal line blocking and line blanketing on the radiative transfer and energy balance. We incorporate our hot-star models into our population synthesis code (STARS), and we compute the time-dependent SEDs and resulting Lyc and HeI emission rates for evolving star clusters. We present results for continuous and impulsive star formation for a range of assumed stellar initial mass functions.Comment: 23 pages, 7 figures. To appear in the Astrophysical Journal. For grid of star models see ftp://wise3.tau.ac.il/pub/star

A Simple Scaling Analysis of X-ray Emission and Absorption in Hot-Star Winds

We present a simple analysis of X-ray emission and absorption for hot-star winds, designed to explore the natural scalings of the observed X-ray luminosity with wind and sstellar properties. We show that an exospheric approximation, in which all of the emission above the optical depth unity radius escapes the wind, reproduces very well the detailed expression for radiation transport through a spherically symmetric wind. Using this approximation we find that the X-ray luminosity $L_x$ scales naturally with the wind density parameter \Mdot/\vinf, obtaining L_x \sim (\Mdot/\vinf)^2 for optically thin winds, and L_x \sim (\Mdot/\vinf)^{1+s} for optically thick winds with an X-ray filling factor that varies in radius as $f \sim r^s$. These scalings with wind density contrast with the commonly inferred empirical scalings of X-ray luminosity $L_x$ with bolometric luminosity $L_B$. The empirically derived linear scaling of $L_x \sim L_B$ for thick winds can however be reproduced, through a delicate cancellation of emission and absorption, if one assumes modest radial fall-off in the X-ray filling factor ($s \approx -0.25$ or $s \approx -0.4$, depending on details of the secondary scaling of wind density with luminosity). We also explore the nature of the X-ray spectral energy distribution in the context of this model, and find that the spectrum is divided into a soft, optically thick part and a hard, optically thin part. Finally, we conclude that the energy-dependent emissivity must have a high-energy cut-off, corresponding to the maximum shock energy, in order to reproduce the general trends seen in X-ray spectral energy distributions of hot stars.Comment: 16 pages, 2 figures, requiress aaspp4.sty, accepted by Astrophysical Journal, to appear in the Aug 10, 1999 issue. Several minor changes have been made at the suggestion of the referee. We have added an appendix in which we consider winds with beta-velocity laws, rather than simply constant velocitie

Novel biocatalysts by identification and design

Enzymes produced from bacteria and eukaryotic organisms are presently being used for a large variety of different biotechnological applications. The rapidly increasing demand for enzymes which are active towards novel and often non-natural substrates has triggered the development of novel molecular biological methods of enzyme isolation and design. The metagenome approach is a cultivation-independent method which allows the direct cloning and expression of environmental DNA thereby providing access to a wealth of so-far unknown biocatalysts. Additionally, newly identified or existing biocatalysts can be further optimized by different methods of directed evolution. Here, the principle of the metagenome approach is outlined and a strategy is presented for the optimization of a bacterial lipase using a combination of rational design and directed evolution.