GPS for Marine Navigation and Hydrography

Current marine navigation and shipbome surveying accuracy requirements are reviewed. The technical characteristics of GPS are summarized and its single point positioning performance is given and compared with the above requirements. A detailed description and analysis of the three types of observables possible with GPS, namely code, carrier and Doppler frequency measurements, are presented. The following error sources are discussed: cycle slips, Selective Availability, ionospheric and tropospheric effects and multipath. A description of the various receiver measuring techniques currently available, namely C/A code LI, L2 squaring, L2 codeless, P codeless and P code, is given, together with advantages and disadvantages for marine positioning. The single and double differenced observables used in differential GPS (DGPS) mode are analysed in terms of real time versus postmission suitability. The latest techniques for quasi-instantaneous ambiguity resolution such as wide and extra wide-laning are discussed in terms of receiver requirements and operational procedures. An attempt is made at providing DGPS kinematic accuracy estimates for various cases with and without Selective Availability. Trends and prospects are forecast in the following five areas: system enhancements, user equipment, observable types and modelling, marine applications and GPS-related services

Public Attitudes toward Climate Science and Climate Policy in Federal Systems: Canada and the United States Compared 1

Multilevel governance poses several challenges for the politics of climate change. On the one hand, the unequal distribution of power and interests can serve as a barrier to implementing coherent policy at a federal level. On the other, these features also enable policy leadership among sub‐federal units. In the context of wide variation in climate policy at both national and sub‐federal levels in Canada and in the United States, this paper utilizes an original data set to examine public attitudes and perceptions toward climate science and climate change policy in two federal systems. Drawing on national and provincial/state level data from telephone surveys administered in the United States and in Canada, the paper provides insight into where the public stands on the climate change issue in two of the most carbon‐intensive federal systems in the world. The paper includes the first directly comparable public opinion data on how Canadians and Americans form their opinions regarding climate matters and provides insight into the preferences of these two populations regarding climate policies at both the national and sub‐federal levels. Key findings are examined in the context of growing policy experiments at the sub‐federal level in both countries and limited national level progress in the adoption of climate change legislation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91218/1/j.1541-1338.2012.00563.x.pd

EFFECT OF FATIGUE ON DYNAMIC BALANCE AFTER MAXIMUM INTENSITY CROSS-COUNTRY SKIING

Cross-country skiing stresses most of the joints, muscles and tendons in the body giving an overall workout. Skiing requires aerobic and anaerobic power, muscular strength and a variety of complex motor abilities including reaction time, agility, balance, coordination and attention demands (Emily & Arthur, 1989). Muscular fatigue is a key factor which can influence performance via impaired joint proprioception and postural control. Fatigue alters the force generation capacity of the muscle and ultimately leads to task failure (Mahyar et al, 2007). Injury risk increases as time duration of the skiing increases (Smith, Matheson & Meeuwisse, 1996). The maintenance of body posture and balance is an essential requirement for performance of daily tasks and sporting activities. Thus fatigue could affect a skier’s performance through an effect on balance. Fast starts at the beginning of races and short intense efforts required for ascending hills could result in periods of fatigue that could affect balance and performance. Hence fatigue may either result in injury or affect the finish time of the skiers. The main purpose of this study was to evaluate how dynamic balance of the skiers can be influenced by fatigue states following maximum exercis

Comparing the retinal structures and functions in two species of gulls (Larus delawarensis and Larus modestus) with significant nocturnal behaviours

AbstractRing-billed gulls (Larus delawarensis) and gray gulls (Larus modestus) are two species active both by day and night. We have investigated the retinal adaptations that allow the diurnal and nocturnal behaviours of these two species. Electroretinograms and histological analyses show that both species have a duplex retina in which cones outnumber rods, but the number of rods appears sufficient to provide vision at night. Their retinas respond over the same scotopic dynamic range of 3.4logcdm−2, which encompasses all of the light levels occurring at night in their photic environment. The amplitudes of the scotopic saturated a- and b-wave responses as well as the photopic saturated b-wave response and the photopic sensitivity parameter S are however higher in ring-billed gulls than in gray gulls. Moreover, the process of dark adaptation is about 30min faster in gray gulls than in ring-billed gulls. Our results suggest that both species have acquired in the course of their evolution functional adaptations that can be related to their specific photic environment

A note on the appearance of self-dual Yang-Mills fields in integrable hierarchies

A family of mappings from the solution spaces of certain generalized Drinfeld-Sokolov hierarchies to the self-dual Yang-Mills system on R^{2,2} is described. This provides an extension of the well-known relationship between self-dual connections and integrable hierarchies of AKNS and Drinfeld-Sokolov type

Use of a Multi-Reference GPS Station Network for Precise 3D Positioning in Constricted Waterways

Numerous coastal and inland marine operations, including navigation in shallow constricted waterways require time-consuming and expensive maintenance that includes frequent precise multi-beam hydrographic surveys and dredging operations. In addition, environmental and safety concerns lead to the establishment of stringent regulations regarding the minimum under keel clearance for commercial shipping operations. The clearance is partly a function of the navigation channel charting accuracy and the ability to determine the instantaneous water level in real time. The use of real-time kinematic (RTK) GPS to provide a three-dimensional accuracy of better than 10 cm has the potential to improve the effectiveness of channel maintenance and commercial navigation. In order for RTK GPS to yield such a high level of accuracy, carrier phase observables must be used. One of the most important limitations is the requirement for short distances between the ship and shore-based fixed reference stations. With the current GPS capability, the distance should be kept to less than 15 to 20 km to assure a continuous service. Establishing reference stations with such a high density is time-consuming, logistically difficult and results in high maintaining cost and operational reliability issues. In this paper a method to substantially reduce the number of reference stations is investigated through field trials conducted along the St. Lawrence Seaway, Canada, in 1998 and 1999. The proximity of the trials to a solar maximum resulted in a very high level of atmospheric activity and provided an opportunity to examine the advantages and limitations of both the conventional and multi-reference station RTK methods under such conditions. The results of the trials show that the new approach results in a substantial improvement of up to 60%

Characterisation of the clinical importance of porcine group C rotavirus in a swine nursery production network in Quebec

Enteric infectious diseases in swine have considerable economic impact on the industry due either to mortality, cost of treatment or reduced growth rates which can lead to extended production periods. The consequences can be catastrophic especially in nursery sites since young piglets are in a susceptible period associated with immature immune system and are often affected by rapid dehydration related to neonatal diseases

The Discovery of the Most Metal-Rich White Dwarf: Composition of a Tidally Disrupted Extrasolar Dwarf Planet

Cool white dwarf stars are usually found to have an outer atmosphere that is practically pure in hydrogen or helium. However, a small fraction have traces of heavy elements that must originate from the accretion of extrinsic material, most probably circumstellar matter. Upon examining thousands of Sloan Digital Sky Survey spectra, we discovered that the helium-atmosphere white dwarf SDSS J073842.56+183509.6 shows the most severe metal pollution ever seen in the outermost layers of such stars. We present here a quantitative analysis of this exciting star by combining high S/N follow-up spectroscopic and photometric observations with model atmospheres and evolutionary models. We determine the global structural properties of our target star, as well as the abundances of the most significant pollutants in its atmosphere, i.e., H, O, Na, Mg, Si, Ca, and Fe. The relative abundances of these elements imply that the source of the accreted material has a composition similar to that of Bulk Earth. We also report the signature of a circumstellar disk revealed through a large infrared excess in JHK photometry. Combined with our inferred estimate of the mass of the accreted material, this strongly suggests that we are witnessing the remains of a tidally disrupted extrasolar body that was as large as Ceres.Comment: 7 pages in emulateapj, 5 figures, accepted for publication in Ap

A simple mean field model for social interactions: dynamics, fluctuations, criticality

We study the dynamics of a spin-flip model with a mean field interaction. The system is non reversible, spacially inhomogeneous, and it is designed to model social interactions. We obtain the limiting behavior of the empirical averages in the limit of infinitely many interacting individuals, and show that phase transition occurs. Then, after having obtained the dynamics of normal fluctuations around this limit, we analize long time fluctuations for critical values of the parameters. We show that random inhomogeneities produce critical fluctuations at a shorter time scale compared to the homogeneous system.Comment: 37 pages, 2 figure

Brane Bremsstrahlung in DBI Inflation

We consider the effect of trapped branes on the evolution of a test brane whose motion generates DBI inflation along a warped throat. The coupling between the inflationary brane and a trapped brane leads to the radiation of non-thermal particles on the trapped brane. We calculate the Gaussian spectrum of the radiated particles and their backreaction on the DBI motion of the inflationary brane. Radiation occurs for momenta lower than the speed of the test brane when crossing the trapped brane. The slowing down effect is either due to a parametric resonance when the interaction time is small compared to the Hubble time or a tachyonic resonance when the interaction time is large. In both cases the motion of the inflationary brane after the interaction is governed by a chameleonic potential,which tends to slow it down. We find that a single trapped brane can hardly slow down a DBI inflaton whose fluctuations lead to the Cosmic Microwave Background spectrum. A more drastic effect is obtained when the DBI brane encounters a tightly spaced stack of trapped branes.Comment: 20 pages, 1 figur