Peaks and Troughs in Helioseismology: The Power Spectrum of Solar Oscillations

I present a matched-wave asymptotic analysis of the driving of solar oscillations by a general localised source. The analysis provides a simple mathematical description of the asymmetric peaks in the power spectrum in terms of the relative locations of eigenmodes and troughs in the spectral response. It is suggested that the difference in measured phase function between the modes and the troughs in the spectrum will provide a key diagnostic of the source of the oscillations. I also suggest a form for the asymmetric line profiles to be used in the fitting of solar power spectra. Finally I present a comparison between the numerical and asymptotic descriptions of the oscillations. The numerical results bear out the qualitative features suggested by the asymptotic analysis but suggest that numerical calculations of the locations of the troughs will be necessary for a quantitative comparison with the observations.Comment: 18 pages + 8 separate figures. To appear in Ap

A dual Stage ion engine for high impulse missions

In this paper, the applicability of dual stage ion opticsand in particular of the so-called dual stage ion engine to highpower, high specific impulse missions will be evaluated. First, theperformance limits of conventional two gridded ion engines (GIE)will be discussed and the advantages provided by dual stage ionengines reported. The limits of applicability of a dual stage ionengine will be analyzed analytically and the results confirmednumerically. The lifetime and performance of a three griddeddual stage ion engine (DS3G) will be numerically investigated andcompared to those of a conventional GIE assessing for the firsttime in the open literature under what condition dual stage ionoptics provide performance improvements over conventional GIEsand what is its impact on the thruster lifetime. Dual stage ionengines have been found to be capable of providing higher thrustdensity and longer lifetime with respect to conventional griddedion engines

Hollow cathode chemical modelling

In this paper the state of hollow cathode life time modelling at the University of Southampton will be reported. Two models have been developed: one for BaO depletion from the hollow cathode insert and another for low work function compounds deposition and desorption. The model developed to predict BaO depletion from hollow cathode insert will be presented together with some comparison between experimental and numerical data to prove its validity.A model for low work function compounds deposition and desorption will also be presented. This model will be used to simulate the NSTAR cathode showing a very conservative estimate of the cathode life due to conservative character of the hypotheses made in the model development and due to the chosen criteria for the end of life

The train has left the station: Do markets value intra-city access to inter-city rail connections?

This paper analyzes the impact of access to inter-city rail connections on property prices using hedonic, difference-in-difference and time-difference estimation strategies. We investigate the reorganization of the rail system in post-unification Berlin, Germany, which provides much variation in accessibility. Evidence does not support the existence of localized effects. Neither in proximity to stations nor at city-level are there significant price adjustments. No significant price effect is revealed on distance to stations, even when allowing for a complementary relationship. An increase in the attractiveness of central locations coinciding with the final announcement of the train schedule is not attributable to the intervention.Property prices; transport innovation; inter-city connection; railroad; Berlin

Valuing iconic design: Frank Lloyd Wright architecture in Oak Park, Illinois

This study investigates the willingness of homebuyers to pay for co-location with iconic architecture. Oak Park, Illinois was chosen as the study area given its unique claim of having 24 residential structures designed by world-famous American architect Frank Lloyd Wright, in addition to dozens of other designated landmarks and three preservation districts. This study adds to the limited body of existing literature on the external price effects of architectural design and is unique in its focus on residential architecture. We find a premium of about 8.5% within 50-100m of the nearest Wright building and about 5% within 50-250m. These results indicate that an external premium to iconic architecture does exist, although it may partially be attributable to the prominence of the architec

If Alonso was Right: Residual Land Price, Accessibility and Urban Attraction

This study investigates whether accessibility shapes the attractiveness of residential land as predicted by theory. A spatial hedonic analysis is conducted for the metropolitan area of Berlin, Germany, using a large set of georeferenced property transactions and micro-level data. We find that the nuclei of residential land price and employment density gradients are separated by approx. 10 km, which essentially contradicts theoretical implications. Also, environmental externalities arising from the residential composition or the building structure and density in the neighborhood are more important determinants than access to the city center, which, if at all, impacts negatively on residential land prices. Moreover, a new gravity-based accessibility indicator is employed that incorporates the effective distribution of employment as well as the rapid transit network architecture in order to disentangle the effects of proximity to employment opportunities from a more general urban attraction effect. After controlling for accessibility, we find a negative effect of urban attraction, respectively an effect of urban repulsion, indicating a relatively higher attractiveness of peripheral locations. This effect is partially counterbalanced by the benefits arising from access to employment opportunities that are, although relatively dispersed, more concentrated within downtown areas. In the tension between both forces, the land price gradient tends to be, if at all significant, positive. After all, we conclude that if transport costs are very low, commuting costs lose their role as the most striking determinant of land price. These results are robust to spatial dependency.Accessibility, gradient inversion, land price, urban attraction, Berlin

Shallow Surveying in Hazardous Waters

Of order one importance to any study of nearshore processes is knowledge of the bathymetry in shallow water. This is true for studies on open coast sandy beaches where surf zone dynamics drive the system, inlet environments where bathymetric evolution can rapidly change navigation channels, and in more benign, lower-energy coastal environments that evolve slowly over 10’s to 100’s of years. Difficulties in obtaining shallow bathymetry where depth-limited wave breaking occurs, submerged hazards are present, or other harsh environments has led to the development of survey systems on highly maneuverable personal watercraft (Beach, et al., 1994; Cote, 1999; Dugan, et al., 1999; MacMahan, 2001). In this work we discuss shallow water surveying from the Coastal Bathymetry Survey System (CBASS), a Yamaha Waverunner equipped with differential GPS, single-beam 192 KHz acoustic echo-sounder, and onboard navigation system. Data obtained with the CBASS in three regions will be discussed, including an energetic surf zone located in southern California during the 2003 Nearshore Canyon Experiment (NCEX), on Lake Erie in 2002 (and compared with historical surveys dating back 150 years), and around Piscataqua River Inlet, NH, in 2007. Estimated accuracy (for sandy bottoms) in water depths ranging 1–10 m are 0.07-0.10 m in the vertical, and on the order of 0.1-1 m horizontally depending on water depth and bottom slope. The high maneuverability of the personal watercraft makes very shallow water bathymetric surveys possible with acoustic altimeters, particularly in regions where airborne remote sensing systems fail (owing to water clarity issues) or where repeated high resolution surveys are required (e.g., where an erodible bottom is rapidly evolving)

Reconstruction of Residual Stress in a Welded Plate Using the Variational Eigenstrain Approach

We present the formulation for finding the distribution of eigenstrains, i.e. the sources of residual stress, from a set of measurements of residual elastic strain (e.g. by diffraction), or residual stress, or stress redistribution, or distortion. The variational formulation employed seeks to achieve the best agreement between the model prediction and some measured parameters in the sense of a minimum of a functional given by a sum over the entire set of measurements. The advantage of this approach lies in its flexibility: different sets of measurements and information about different components of the stress-strain state can be incorporated. We demonstrate the power of the technique by analysing experimental data for welds in thin sheet of a nickel superalloy aerospace material. Very good agreement can be achieved between the prediction and the measurement results without the necessity of using iterative solution. In practice complete characterisation of residual stress states is often very difficult, due to limitations of facility access, measurement time or specimen dimensions. Implications of the new technique for experimental analysis are all the more significant, since it allows the reconstruction of the entire stress state from incomplete sets of data.Comment: 16 pages, 17 figure

Quantum Interest in (3+1) dimensional Minkowski space

The so-called "Quantum Inequalities", and the "Quantum Interest Conjecture", use quantum field theory to impose significant restrictions on the temporal distribution of the energy density measured by a time-like observer, potentially preventing the existence of exotic phenomena such as "Alcubierre warp-drives" or "traversable wormholes". Both the quantum inequalities and the quantum interest conjecture can be reduced to statements concerning the existence or non-existence of bound states for a certain one-dimensional quantum mechanical pseudo-Hamiltonian. Using this approach, we shall provide a simple proof of one version of the Quantum Interest Conjecture in (3+1) dimensional Minkowski space.Comment: V1: 8 pages, revtex4; V2: 10 pages, some technical changes in details of the argument, no change in physics conclusions, this version essentially identical to published versio

Macroscopic Observables Detecting Genuine Multipartite Entanglement and Partial Inseparability in Many-Body Systems

We show a general approach for detecting genuine multipartite entanglement (GME) and partial inseparability in many-body-systems by means of macroscopic observables (such as the energy) only. We show that the obtained criteria, the "GME gap" and "the k-entanglement gap", detect large areas of genuine multipartite entanglement and partial entanglement in typical many body states, which are not detected by other criteria. As genuine multipartite entanglement is a necessary property for several quantum information theoretic applications such as e.g. secret sharing or certain kinds of quantum computation, our methods can be used to select or design appropriate condensed matter systems.Comment: 4 pages, 3 figures, published version, title extende