The Southern Ontario All-sky Meteor Camera Network     

R. J. Weryk  P. G. Brown  A. Domokos  W. N. Edwards  Z. Krzeminski  S. H. Nudds  D. L. Welch 《Earth, Moon, and Planets》2008,102(1-4):241-246

We have developed an automated network of all-sky CCD video systems to detect medium–large meteoroids ablating over Southern Ontario, Canada. The system currently consists of five stations with the largest baseline being 180 km. Each site runs a video rate recorder with sufficient resolution to determine meteoroid trajectories with a typical precision of about 300 m but no worse than 1 km. The sensitivity of the camera is close to a stellar visual magnitude of +1 which allows for astrometric calibrations using field stars. Photometric procedures have also been developed and tested. The system has a limiting magnitude for meteors of about −2 with the current detection algorithm.  相似文献   

Observations on the faunas of two warm streams in the taupo thermal region     

M. J. Winterbourn  T. J. Brown 《新西兰海洋与淡水研究杂志》2013,47(1):38-50

Observations were made on the biota of two warm streams in the Taupo thermal region during December 1965 and June 1966. Distribution of the fauna was related to the observed water temperatures, and the possible effects and importance of high temperature are discussed. The principal “thermal” species were Protozoa, larval and adult Hydrophilidae (Coleoptera), larval and pupal Ephydridae (Diptera), Nematoda, and Rotifera.  相似文献   

Protozoa from Blue Lake,Raoul Island (note)     

Tim J. Brown  John A. Peart 《新西兰海洋与淡水研究杂志》2013,47(1-2):171-178

The protozoan populations of microhabitats in Blue Lake, Raoul Island, Kermadec Group, 28° 30’ S 178° 00’ W are described qualitatively and semi‐quantitatively. The in situ and in vitro pH values of the four micro‐habitats examined were recorded. After two days in vitro there was a marked drop in the pH of the mud zones, a slight drop in pH of the water zone and no decrease in the pH at the surface. The nature of the protozoan populations is discussed in relation to the pH values and the changes which took place in these values.  相似文献   

Colony formation in the Cheilostomatous Bryozoan Fenestrulina Malusii var. Thykeophora     

D. P. Gordon 《新西兰海洋与淡水研究杂志》2013,47(2):342-351

The early stages of colony formation of Fenestrulina malusii var. thyreophora are described, and notes on two other species are included for comparison. In Fenestrulina, early budding patterns are very variable, although some patterns are commoner than others. At the 3‐zooid stage of colony formation there is usually temporary suppression of budding on one side, with the result that the three first‐generation zooids produced from the ancestrula arise 1, 2, 4 in the commonest budding sequence rather than 1, 2, 3; budding patterns may be considerably modified when colonies are obstructed. In Fenestrulina and Eurystomella foraminigera the first zooid budded from the ancestrula lies in the distal midline whereas the second zooid occupies this position in Crassimarginatella papulifera. In all three species the proximal periancestrular zooids are not budded directly from the ancestrula but belong to the third zooidal generation.  相似文献   

Measurements of tagged pups and a population estimate of New Zealand fur seals on Taumaka,open bay Islands,Westland     

M. C. Crawley  D. L. Brown 《新西兰海洋与淡水研究杂志》2013,47(3-4):389-395

In January 1970, 309 pups of the New Zealand fur seal, Arctocephalus forsteri (Lesson, 1828), were tagged on Taumaka Island, one of the Open Bay Islands, Westland, New Zealand (43°52’ S, 168°53’ E). At about 6 weeks old, male pups have longer flippers and are longer and heavier than female pups.

A population estimate of seals on Taumaka Island is based on a count of pups of the year, to which data from related species of fur seals were applied (incidence of pregnancy and age at first pupping from Arctocephalus pusillus, immature mortality from Callorhinus ursinus), and on the assumptions that the sex ratio and sexual mortalities are equal. There were at that time 2,000–3,000 seals, including pups, on the island.  相似文献   

The national geophysical data center bathymetric program     

Maureen R. Kenny  Kurt E. Brown 《Marine Geodesy》2013,36(2-3):165-175

The National Geophysical Data Center's (NGDC's) mission is data management in the broadest sense, playing a role in the nation's research into the environment and providing data to a wide group of users. NGDC also operates components of the International Council of Scientific Unions (ICSU) World Data Center A. The Marine Geology and Geophysics Division of NGDC handles bathymetric data acquisition, manipulation, archival, and dissemination and operates the International Hydrographic Organization Data Center for Digital Bathymetry. Four major data bases have been developed to manage the large volume of data received: the Global Marine Geophysical Data Base (geophysical data acquired in a time series); the NOAA National Ocean Service Hydrographic Data Base; the International Hydrographic Data Base (contains bathymetric data, other than NOS surveys, with no time‐tagging); and the Multibeam Bathymetric Data Base. In addition, gridded data sets such as ETOPO5 are available from NGDC. Bathymetric data are acquired by NGDC through data exchange, funded and contract programs, processing of long‐term data holdings, data digitization from hardcopy sources, and national and international linkages. NGDC personnel participate nationally and internationally on numerous committees associated with studies of the seafloor including charting and bathymetric needs.  相似文献   

Polar cap particle precipitation and aurora: Review and commentary     

Patrick T. Newell  Kan Liou  Gordon R. Wilson 《Journal of Atmospheric and Solar》2009,71(2):199-215

Polar rain has a beautiful set of symmetry properties, individually established, but not previously discussed collectively, which can be organized by a single unifying principle. The key polar rain properties are favored hemisphere (controlled by the interplanetary magnetic field B_x), dawn/dusk gradient (IMF B_y), merging rate (IMF B_z or more generally dΦ_MP/dt), nightside/dayside gradient, and seasonal effect. We argue that all five properties involve variants on a single theme: the further downstream a field line exits the magnetosphere (or less directly points toward the solar wind electron heat flux), the weaker the polar rain. This effect is the result of the requirements of charge quasi-neutrality, and because the ion thermal velocity declines and the tailward ion bulk flow velocity rises moving down tail from the frontside magnetopause.Polar cap arcs (or more properly, high-latitude sun-aligned arcs) are largely complementary to the polar rain, occurring most frequently when the dayside merging rate is low, and thus when polar rain is weak. Sun-aligned arcs are often considered as originating either in the polar rain or the expansion of the plasma sheet into the polar cap. In fact three quite distinct types of sun-aligned high-latitude arcs exist, two common, and one rare. One type of arc occurs as intensifications of the polar rain, and is common, but weak, typically <0.1 ergs/cm² s, and lacks associated ion precipitation. A second category of Sun-aligned arcs with energy flux >0.1 ergs/cm² s usually occurs adjacent to the auroral oval, and includes ion precipitation. The plasma regime of these common, and at times intense, arcs is often distinct from the oval which they abut. Convection alone does not specify the open/closed nature of these arcs, because multiple narrow convection reversals are common around such arcs, and the arcs themselves can be embedded within flows that are either sunward or anti-sunward. These observational facts do not neatly fit into either a plasma sheet origin or a polar rain origin (e.g., the necessity to abut the auroral oval, and the presence of ions does not fit the properties of polar rain, which can in any event be nearly absent for northward interplanetary magnetic field). One theory is that such arcs are associated with merging tailward of the cusp. Both of these common types of sun-aligned arcs fade within about 30 min of a southward IMF turning.The third, and rarest, category of sun-aligned arcs are intense, well detached from the auroral oval, contain plasma sheet origin ion precipitation as well as electrons, and persist for hours after a southward turning. These intense detached sun-aligned arcs can rapidly cross the polar cap, sometimes multiple times. Most events discussed in the literature as “theta-aurora” do not fit into this category (for example, although they may appear detached in images, they abut the oval in particle data, and do not have the persistence of detached events under southward IMF turnings). It is possible that no single theory can account for all three types of sun-aligned arcs.Solar energetic particle (SEP) events are at times used to demarcate polar cap open/closed boundaries. Although this works at times, examples exist where this method fails (e.g., very quiet conditions for which SEP reaches below L=4), and the method should be used with caution. Finally, it is shown that, although it is rare, the polar cap can at times completely close.  相似文献   

The IDC Seismic,Hydroacoustic and Infrasound Global Low and High Noise Models     

David Brown  Lars Ceranna  Mark Prior  Pierrick Mialle  Ronan J. Le Bras 《Pure and Applied Geophysics》2014,171(3-5):361-375

The International Data Centre (IDC) in Vienna, Austria, is determining, as part of automatic processing, sensor noise levels for all seismic, hydroacoustic, and infrasound (SHI) stations in the International Monitoring System (IMS) operated by the Provisional Technical Secretariat of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). Sensor noise is being determined several times per day as a power spectral density (PSD) using the Welch overlapping method. Based on accumulated PSD statistics a probability density function (PDF) is also determined, from which low and high noise curves for each sensor are extracted. Global low and high noise curves as a function of frequency for each of the SHI technologies are determined as the minimum and maximum of the individual station low and high noise curves, respectively, taken over the entire network of contributing stations. An attempt is made to ensure that only correctly calibrated station data contributes to the global noise models by additionally considering various automatic detection statistics. In this paper global low and high noise curves for 2010 are presented for each of the SHI monitoring technologies. Except for a very slight deviation at the microseism peak, the seismic global low noise model returns identically the Peterson (1993) NLNM low noise curve. The global infrasonic low noise model is found to agree with that of Bowman et al. (2005, 2007) but disagrees with the revised results presented in Bowman et al. (2009) by a factor of 2 in the calculation of the PSD. The global hydroacoustic low and high noise curves are found to be in quantitative agreement with Urick’s oceanic ambient noise curves for light to heavy shipping. Whale noise is found to be a feature of the hydroacoustic high noise curves at around 15 and 25 Hz.  相似文献   

Centrifuge modeling of rocking‐isolated inelastic RC bridge piers          下载免费PDF全文

Marianna Loli  Jonathan A. Knappett  Michael J. Brown  Ioannis Anastasopoulos  George Gazetas 《地震工程与结构动力学》2014,43(15):2341-2359

Experimental proof is provided of an unconventional seismic design concept, which is based on deliberately underdesigning shallow foundations to promote intense rocking oscillations and thereby to dramatically improve the seismic resilience of structures. Termed rocking isolation, this new seismic design philosophy is investigated through a series of dynamic centrifuge experiments on properly scaled models of a modern reinforced concrete (RC) bridge pier. The experimental method reproduces the nonlinear and inelastic response of both the soil‐footing interface and the structure. To this end, a novel scale model RC (1:50 scale) that simulates reasonably well the elastic response and the failure of prototype RC elements is utilized, along with realistic representation of the soil behavior in a geotechnical centrifuge. A variety of seismic ground motions are considered as excitations. They result in consistent demonstrably beneficial performance of the rocking‐isolated pier in comparison with the one designed conventionally. Seismic demand is reduced in terms of both inertial load and deck drift. Furthermore, foundation uplifting has a self‐centering potential, whereas soil yielding is shown to provide a particularly effective energy dissipation mechanism, exhibiting significant resistance to cumulative damage. Thanks to such mechanisms, the rocking pier survived, with no signs of structural distress, a deleterious sequence of seismic motions that caused collapse of the conventionally designed pier. © 2014 The Authors Earthquake Engineering & Structural Dynamics Published by John Wiley & Sons Ltd.  相似文献   

Evapotranspiration and canopy characteristics of two lodgepole pine stands following mountain pine beetle attack   总被引：1，自引：0，他引：1       下载免费PDF全文

Mathew G. Brown  T. Andrew Black  Zoran Nesic  Vanessa N. Foord  David L. Spittlehouse  Arthur L. Fredeen  Rebecca Bowler  Nicholas J. Grant  Philip J. Burton  J. A. Trofymow  Dominic Lessard  Gesa Meyer 《水文研究》2014,28(8):3326-3340

Over the past decade, British Columbia (BC), has experienced the largest mountain pine beetle (MPB) outbreak on record. This study used the eddy‐covariance (EC) technique to examine the impact of the MPB attack on evapotranspiration (E) and associated canopy characteristics of two lodgepole pine stands with secondary structure (trees, saplings and seedlings surviving the attack) located in central BC. MPB‐06, an 85‐year‐old almost pure stand of pine trees, was first attacked in 2006, and by 2010, ~80% of the trees had been killed. MPB‐03, a 110‐year‐old stand with an overstory consisting of over 90% pine and a developed sub‐canopy, was first attacked in 2003 and by 2007 had > 95% pine canopy mortality. EC measurements began in August 2006 at MPB‐06 and in March 2007 at MPB‐03, and continued for four years. Annual total E ranged from 226 mm to 237 mm at MPB‐06, and from 280 to 297 mm at MPB‐03, showing relatively little year‐to‐year change at both sites over the four years. Increased E from the accelerated growth of the surviving vegetation (secondary structure, shrubs and herbs) compensated for reduction in E due to the death of the overstory. Monthly average daytime canopy conductance, the Priestley–Taylor (α), and the canopy–atmosphere decoupling coefficient (Ω) steadily increased during the growing season reaching approximate maximum values of 5 mm s^?1, 0.75 and 0.12, respectively. Potential evapotranspiration was approximated using a vapour pressure deficit‐dependent α obtained at high soil water content. Calculated water deficits indicated some water‐supply limitation to the surviving trees and understory at both sites. Rates of root zone drainage during the growing season were low relative to precipitation. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献