Image Sensor

A CCD image sensor of the type for providing charge multiplication by impact ionisation has an image area and a plurality of pixels. A separate multiplication register has a plurality of multiplication elements arranged to receive charge from the pixels of the image area. Each multiplication element comprises a sequence of electrodes operable to cause multiplication, the electrodes of each multiplication element being adjacent one another and non-overlapping. The non-overlapping arrangement may be manufactured by a CMOS process thereby providing a CCD image sensor with the advantages of CCD multiplication but using a CMOS manufacturing process

From Buses to BRT: Case Studies of Incremental BRT Projects in North America, MTI Report 09-13

Bus Rapid Transit (BRT) uses different combinations of techniques to improve service, such as bus-only lanes and roads, pre-boarding fare collection, transit priority at traffic signals, stylish vehicles with extra doors, bus stops that are more like light rail stations, and high frequency service. This study examines five approaches to BRT systems as implemented by public transit agencies in California, Oregon, and Ontario. The case studies as a group show that BRT can be thought of as a discretionary combination of elements that can be assembled in many different combinations over time. Every element incrementally adds to the quality or attractiveness of the service. This latitude provides transit agencies with many benefits, including the ability to match infrastructure with operating requirements. For example, a BRT service can combine operations serving free flowing arterial roads in the fringes of the downtown with dedicated lanes in areas closer to city center where congestion is greatest. Buses can operate both on and off the guide way, extending the corridors in which passengers are offered a one-seat ride with no transfer required. Transit agencies also can select specific BRT components and strategies, such as traffic signal priority and increased stop spacing, and apply them to existing local bus operations as a way to increase bus speeds and reduce operating costs. The specific elements selected for a BRT route can be implemented all at once, or in incremental stages either or both geographical extensions or additions of features. All of the case studies showed ridership improvements, but the Los Angeles Metro Rapid bus system illustrates the wide geographic coverage, improved ridership, and moderate cost per new rider that is possible with an approach that includes fewer BRT features spread over more miles of route. Quantitative results from the case studies suggest that incremental improvements, applied widely to regional bus networks, may be able to achieve significant benefits at a lower cost than substantial infrastructure investments focused upon just one or a few corridors

Adjustment of a turbulent boundary layer to a 'canopy' of roughness elements

A model is developed for the adjustment of the spatially averaged time-mean flow of a deep turbulent boundary layer over small roughness elements to a canopy of larger three-dimensional roughness elements. Scaling arguments identify three stages of the adjustment. First, the drag and the finite volumes of the canopy elements decelerate air parcels; the associated pressure gradient decelerates the flow within an impact region upwind of the canopy. Secondly, within an adjustment region of length of order Lc downwind of the leading edge of the canopy, the flow within the canopy decelerates substantially until it comes into a local balance between downward transport of momentum by turbulent stresses and removal of momentum by the drag of the canopy elements. The adjustment length, Lc, is proportional to (i) the reciprocal of the roughness density (defined to be the frontal area of canopy elements per unit floor area) and (ii) the drag coefficient of individual canopy elements. Further downstream, within a roughness-change region, the canopy is shown to affect the flow above as if it were a change in roughness length, leading to the development of an internal boundary layer. A quantitative model for the adjustment of the flow is developed by calculating analytically small perturbations to a logarithmic turbulent velocity profile induced by the drag due to a sparse canopy with L/Lc≪1, where L is the length of the canopy. These linearized solutions are then evaluated numerically with a nonlinear correction to account for the drag varying with the velocity. A further correction is derived to account for the finite volume of the canopy elements. The calculations are shown to agree with experimental measurements in a fine-scale vegetation canopy, when the drag is more important than the finite volume effects, and a canopy of coarse-scale cuboids, when the finite volume effects are of comparable importance to the drag in the impact region. An expression is derived showing how the effective roughness length of the canopy, \z0eff, is related to the drag in the canopy. The value of \z0eff varies smoothly with fetch through the adjustment region from the roughness length of the upstream surface to the equilibrium roughness length of the canopy. Hence, the analysis shows how to resolve the unphysical flow singularities obtained with previous models of flow over sudden changes in surface roughness

Split-beam echosounder observations of natural methane seep variability in the northern Gulf of Mexico

A method for positioning and characterizing plumes of bubbles from marine gas seeps using an 18 kHz scientific split-beam echo sounder (SBES) was developed and applied to acoustic observations of plumes of presumed methane gas bubbles originating at approximately 1400 m depth in the northern Gulf of Mexico. A total of 161 plume observations from 27 repeat surveys were grouped by proximity into 35 clusters of gas vent positions on the seafloor. Profiles of acoustic target strength per vertical meter of plume height were calculated with compensation for both the SBES beam pattern and the geometry of plume ensonification. These profiles were used as indicators of the relative fluxes and fates of gas bubbles acoustically observable at 18 kHz and showed significant variability between repeat observations at time intervals of 1 h–7.5 months. Active gas venting was observed during approximately one third of the survey passes at each cluster. While gas flux is not estimated directly in this study owing to lack of bubble size distribution data, repeat surveys at active seep sites showed variations in acoustic response that suggest relative changes in gas flux of up to 1 order of magnitude over time scales of hours. The minimum depths of acoustic plume observations at 18 kHz averaged 875 m and frequently coincided with increased amplitudes of acoustic returns in layers of biological scatterers, suggesting acoustic masking of the gas bubble plumes in these layers. Minimum plume depth estimates were limited by the SBES field of view in only five instances

E/V Nautilus EM302 Multibeam Echosounder System Review

Introduction The E/V Nautilus undertook leg NA040 to perform a review of the vessel’s Kongsberg EM302 multibeam echosounder in the vicinity of the continental shelf break offshore of St. Petersburg, Florida, from May 4-9, 2014 (Fig. 1). Paul Johnson and Kevin Jerram provided logistical and technical support for data collection and analysis. This report: • Describes the data collected. • Provides an overview of the processing methods used on the data • Presents the EM302 system performance for accuracy and coverage over the expected operational depth range. • Documents changes made to the system configuration prior to the 2014 field season. • Plots the EM302 transducer impedance data to document transducer health

Acoustic and optical observations of methane gas seeps in the Gulf of Mexico

In 2011 and 2012, measurements of acoustic backscatter from natural methane seeps were made in the northern Gulf of Mexico in water depths between 1000-2000 m. The measurementswere made using a calibrated 18 kHz echo sounder with an 11 degree beamwidth in order to estimate the depth-dependent target strength (TS). The TS data indicate a wide variation in the rate of gas seepage from the seafloor. Several of these seeps were revisited with a remotely operated vehicle in order to optically assess the bubble size distribution and to estimate the rate at which gas bubbles were exiting the seafloor. The optical data show bubble sizes between 1-10 mm radius, and similar rates of gas seepage ranging from a few bubbles per second to several tens of bubbles per second. Together, these data help to suggest the requirements for acoustically estimating gas flux from the seafloor over large regions

Acoustic sensing of gas seeps in the deep ocean with split-beam echosounders

When in the form of free gas in the water column, methane seeps emanating from the seabed are strong acoustic targets that are often detectable from surface vessels using echo sounders.In addition to detecting that a seep is present at some location, it is also desirable to characterize the nature of the seep in terms of its morphology and flux rates. Here, we examine how much we can learn about seeps in the deep (\u3e 1000 m) northern Gulf of Mexico using narrow-band split-beam echo sounders operating at fixed frequencies (18 kHz and 38 kHz).Methane seeps in this region are deeper than the methane hydrate stability zone, implying that bubbles of free gas form hydrate rinds that allow them to rise further in the water column than they otherwise would. While this behavior may aid in the classification of gas types in the seep, it is possible that the presence of hydrate rinds may also change the acoustic response of the bubbles and thereby make flux rate estimates more challenging. These and other aspects of seep characterization will be discussed

Does landscape-scale conservation management enhance the provision of ecosystem services?

Biodiversity conservation approaches are increasingly being implemented at the landscape-scale to support the maintenance of metapopulations and metacommunities. However, the impact of such interventions on the provision of ecosystem services is less well defined. Here we examine the potential impacts of landscape-scale conservation initiatives on ecosystem services, through analysis of five case study areas in England and Wales. The provision of multiple ecosystem services was projected according to current management plans and compared with a baseline scenario. Multicriteria analysis indicated that in most cases landscape-scale approaches lead to an overall increase in service provision. Consistent increases were projected in carbon storage, recreation and aesthetic value, as well as biodiversity value. However, most study areas provided evidence of trade-offs, particularly between provisioning services and other types of service. Results differed markedly between study areas, highlighting the importance of local context. These results suggest that landscape-scale conservation approaches are likely to be effective in increasing ecosystem service provision, but also indicate that associated costs can be significant, particularly in lowland areas

To chain or not to chain trade-weighted exchange rate indexes

With the advent of chain calculations for the U.S. national income and product accounts, it seems reasonable to contemplate using the chain approach for other indexes, such as trade-weighted exchange rates (TWEXs). A fundamental criticism of measuring the growth of gross domestic product by a fixed-base-year method is that the estimates are highly sensitive, especially when the economy?s structure is changing dramatically, to the arbitrary choice of the base year. Such a criticism can be levied against TWEXs. In fact, even TWEXs constructed using a Paasche index rather than a Laspeyres index have problems related to base periods. We examine theoretically and empirically the use ofa chain TWEX in relation to two well-known TWEX indexes: the Federal Reserve Bank of Atlanta index, which uses a Laspeyres index, and the Federal Reserve Bank of Dallas index, which uses a Paasche index. The choice of base year alters the behavior ofthe dollar in these two indexes. We contrast this result with the behavior of the dollar in comparable chain TWEXs, where the base year sensitivity is absent. Our results indicate that developers of TWEXs, as well as those revising TWEXs, should consider a chain approach. Furthermore, users need to be aware of the sensitivity of TWEXs to changes in either the base period for trade weights or the reference base period for exchange ratesForeign exchange rates ; Dollar, American

e2v CMOS and CCD sensors and systems for astronomy

e2v designs and manufactures a wide range of sensors for space and astronomy applications. This includes high performance CCDs for X-ray, visible and near-IR wavelengths. In this paper we illustrate the maturity of CMOS capability for these applications; examples are presented together with performance data. The majority of e2v sensors for these applications are back-thinned for highest spectral response and designed for very low read-out noise; the combination delivers high signal to noise ratio in association with a variety of formats and package designs. The growing e2v capability in delivery of sub-systems and cryogenic cameras is illustrated—including the 1.2 Giga-pixel J-PAS camera system