9,610 research outputs found
Titan solar occultation observations reveal transit spectra of a hazy world
High altitude clouds and hazes are integral to understanding exoplanet
observations, and are proposed to explain observed featureless transit spectra.
However, it is difficult to make inferences from these data because of the need
to disentangle effects of gas absorption from haze extinction. Here, we turn to
the quintessential hazy world -- Titan -- to clarify how high altitude hazes
influence transit spectra. We use solar occultation observations of Titan's
atmosphere from the Visual and Infrared Mapping Spectrometer (VIMS) aboard
NASA's Cassini spacecraft to generate transit spectra. Data span 0.88-5 microns
at a resolution of 12-18 nm, with uncertainties typically smaller than 1%. Our
approach exploits symmetry between occultations and transits, producing transit
radius spectra that inherently include the effects of haze multiple scattering,
refraction, and gas absorption. We use a simple model of haze extinction to
explore how Titan's haze affects its transit spectrum. Our spectra show strong
methane absorption features, and weaker features due to other gases. Most
importantly, the data demonstrate that high altitude hazes can severely limit
the atmospheric depths probed by transit spectra, bounding observations to
pressures smaller than 0.1-10 mbar, depending on wavelength. Unlike the usual
assumption made when modeling and interpreting transit observations of
potentially hazy worlds, the slope set by haze in our spectra is not flat, and
creates a variation in transit height whose magnitude is comparable to those
from the strongest gaseous absorption features. These findings have important
consequences for interpreting future exoplanet observations, including those
from NASA's James Webb Space Telescope.Comment: Updated journal reference; data available via
http://sites.google.com/site/tdrobinsonscience/science/tita
Inversion of spinning sound fields
A method is presented for the reconstruction of rotating monopole source
distributions using acoustic pressures measured on a sideline parallel to the
source axis. The method requires no \textit{a priori} assumptions about the
source other than that its strength at the frequency of interest vary
sinusoidally in azimuth on the source disc so that the radiated acoustic field
is composed of a single circumferential mode. When multiple azimuthal modes are
present, the acoustic field can be decomposed into azimuthal modes and the
method applied to each mode in sequence.
The method proceeds in two stages, first finding an intermediate line source
derived from the source distribution and then inverting this line source to
find the radial variation of source strength. A far-field form of the radiation
integrals is derived, showing that the far field pressure is a band-limited
Fourier transform of the line source, establishing a limit on the quality of
source reconstruction which can be achieved using far-field measurements. The
method is applied to simulated data representing wind-tunnel testing of a
ducted rotor system (tip Mach number~0.74) and to control of noise from an
automotive cooling fan (tip Mach number~0.14), studies which have appeared in
the literature of source identification.Comment: Revised version of paper submitted to JASA; five more figures;
expanded content with more discussion of error behaviour and relation to
Nearfield Acoustical Holograph
Exploring the World\u27s Largest ERP Implementation: the Role of ERP in Strategic Alignment
As one of the largest and most complex organizations in the world, the Department of Defense (DoD) faces many challenges in solving its well-documented financial and related business operations and system problems. The DoD is in the process of implementing modern multifunction enterprise resource planning (ERP) systems to replace many of its outdated legacy systems. This paper explores the ERP implementations of the DoD and seeks to determine the impact of the ERP implementations on the alignment of the DoD’s business and IT strategy. A brief overview of the alignment literature and background on ERP are followed by case study analysis of the DoD ERP development and current implementation status. Lastly, the paper explores the current successes and failures of the ERP implementation and the impact on the DoD’s goal of strategic alignment
Exploring Vulnerability and Interdependency of UK Infrastructure Using Key-Linkages Analysis
It has been argued the UK has experienced significant underinvestment in critical infrastructure over the last two decades. This in turn has resulted in infrastructure that is less capable of assisting the UK economy to grow. This article seeks to augment the relevant evidence by under-taking an in-depth analysis of the inter-linkages and economic contributions from infrastructure within the UK. It explores the relationship between nine infrastructure sectors and how these sectors contribute to the rest of the UK economy using key-linkage analysis. Each infrastructure sector is shown to be unique in the way it interacts with other economic sectors and in the form of contribution it makes to the economy overall. Infrastructure is a necessary and important part of economic development. The analysis finds that over the last 23 years there has been a decline in the relative economic contribution from infrastructure to UK GVA. Only two infrastructure sectors increased their relative contribution to GVA since 1992. These were the water transport sector and sewerage and sanitary services sector. Railway transport and gas distribution have had the largest relative decline in contribution towards UK GVA with relative contributions decreasing by over 50% since 1992. The three most important infrastructure sectors contributing to UK GDP are land transport, electricity production and distribution and telecommunications respectively.Funding for this research was provided by the Engineering and Physical Sciences Research Council (EPSRC) grant number EP/101344X/1 through the Infrastructure Transitions Research Consortium (ITRC).This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s11067-015-9302-
Researching trust in the police and trust in justice: a UK perspective
This paper describes the immediate and more distant origins of a programme of comparative research that is examining cross-national variations in public trust in justice and in the police. The programme is built around a module of the fifth European Social Survey, and evolved from a study funded by the European Commission. The paper describes the conceptual framework within which we are operating – developed in large measure from theories of procedural justice. It reviews some of the methodological issues raised by the use of sample surveys to research issues of public trust in the police, public perceptions of institutional legitimacy and compliance with the law. Finally it gives a flavour of some of the early findings emerging from the programme
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