Fourth Station Research Articles

Evidence for a rheologically strong chemical mantle root beneath the Ontong–Java Plateau

Shear wave splitting measurements, in conjunction with studies of shear wave velocity structure, indicate that the Ontong^Java Plateau (OJP) large igneous province (LIP) has a thick, compositionally distinct root that diverts asthenospheric mantle flow beneath the Pacific plate. The OJP, the largest of Earth’s LIPs, stands 2 km above adjacent Pacific abyssal plains and is composed of mantle plume derived volcanics erupted at 122 and 90 Ma. Surface wave tomography of the Plateau reveals a seismically slow upper mantle root that extends approximately to 300 km depth. The thickness and juxtaposition of the Plateau and the mantle root imply that the OJP is the preserved ‘head’ of a rising mantle plume formed in situ when the LIP erupted. Thus, it is a far-traveled body currently moving northwestwards with the Pacific plate. Shear wave splitting at four seismic stations along the northern margin of the OJP varies systematically: the fast axis of seismic anisotropy at three stations on the NE OJP margin trend NW, parallel to hotspot-defined Pacific absolute plate motion; at a fourth station, on the NW margin of the Plateau, the fast shear wave trend is NE. Upper mantle flow directions delineated by the shear wave splitting could thus represent mantle flow diverted around the leading, northwestern face of the rheologically strong, chemically distinct OJP root. In sum, the Plateau and its deep root appear to be similar to continental tectosphere, except for contrasting seismic velocities. fl 2001 Elsevier Science B.V. All rights reserved.

Airborne particle accumulation and composition at different locations in the northern Negev desert

Atmospheric desert dust was collected over 36 months in ground-level collectors at four stations in the northern Negev desert, Israel. Three stations (Shivta, Sede Boqer and Avdat) are located in the desert itself whereas the fourth station (Sayeret Shaked) is situated at the desert fringe, in the transition zone between the true desert and the more humid area to the north. The dynamics of the dust in the three desert stations is similar and differs from that at the desert fringe station. In the desert, dust accumulation is highest in summer and lowest in winter, whereas the situation is reverse at the desert fringe. Also, the amount of accumulation is much higher in the desert itself. No important differences are observed with respect to the average grain size of the dust, but the temporal evolution in grain size variability at the desert fringe is different from that in the desert. Mineralogical analysis by means of X-ray diffraction shows that quartz and calcite, and to a lesser extent also dolomite, are the major constituents of the Negev dust. There is a good agreement between the quartz and calcite content of the dust samples and that of the outcropping rocks located slightly upwind of the four stations, suggesting that at least an important part of the dust collected is of rather local origin. However, the regular records of dust haze events in the northern Negev show that part of the dust that accumulates in this region is not of local origin, but originates from distant sources. This dust may later mix with the local dust.

Inclusion of an intravaginal progesterone insert plus GnRH and prostaglandin F2alpha for ovulation control in postpartum suckled beef cows.

Four experiment stations (IL, KS, MN, and MO) conducted experiments to determine effects of introducing a CIDR (controlled internal device release) into an ovulation control program for postpartum suckled beef cows. Five hundred sixty cows were assigned randomly to two treatments: 1) 100 microg of GnRH (i.m.) followed in 7 d with 25 mg of PGF2alpha, followed in 48 h by a second injection of GnRH and one fixed-time insemination (Cosynch; n = 287) or 2) Cosynch plus one CIDR during the 7 d between the first injection of GnRH and PGF2alpha (Cosynch+P; n = 273). Cows at three stations were inseminated at the time of the second GnRH injection (n = 462), whereas 98 cows at the fourth station were inseminated 16 to 18 h after that injection. Blood samples were collected at d -17, -7, 0, and 2 relative to PGF2alpha to determine concentrations of progesterone. Ultrasonography was used to monitor follicle diameter on d 2 and to determine the presence of an embryo at 30 to 35 d after insemination. Pregnancy rates were greater (P < 0.05) for Cosynch+P- (58%) than for Cosynch-treated (48%) cows. No station x treatment interaction occurred; however, cows at MO (62%) and KS (60%) had greater (P < 0.05) pregnancy rates than those at IL (47%) and MN (44%). Cows that had follicles > 12 mm on d 2 had greater (P < 0.01) pregnancy rates than those with follicles < or = 12 mm regardless of treatment. Pregnancy rates were similar between Cosynch and Cosynch+P treatments when cycling cows had elevated concentrations of progesterone at d 0, but pregnancy rates were greater (P < 0.05) in the Cosynch+P (79%) than in the Cosynch (43%) treatment when cycling cows had low concentrations of progesterone on d 0 (at PGF2alpha injection). Similarly, among noncycling cows, pregnancy rates were greater (P < 0.05) in the Cosynch+P (59%) treatment than in the Cosynch (39%) treatment. Cows in greater body condition at the onset of the breeding season experienced improved (P < 0.001) overall pregnancy rates. Pregnancy rates for cows that calved > 50 d before the onset of the breeding season were greater (P < 0.01) than those for cows that calved < or = 50 d. Thus, treatment of suckled cows with Cosynch yielded acceptable pregnancy rates, but addition of a CIDR improved pregnancy rates in noncycling cows. Body condition and days postpartum at initiation of the breeding season affected overall efficacy of the Cosynch and Cosynch+P protocols.

The role of sunlight in the removal and repair of viruses in the sea

We investigated the in situ destruction rates of marine viral particles as well as the decay rates of infectivity for viral isolates along an ~400‐km transect from oligotrophic offshore waters to productive coastal waters in the Gulf of Mexico. Light‐mediated decay rates of viral infectivity averaged over the solar day ranged from 0.7 to 0.85 h−1 in surface waters at all stations and decreased with depth in proportion to the attenuation of UVB (305 nm). The destruction rates of viral particles also decreased with depth, although the rates of particle destruction were only 22–61% of infectivity when integrated over the mixed layer. The rates of viral particle destruction indicated that at three of four stations 6–12% of the daily bacterial production would have to be lysed in order to maintain ambient viral concentrations. At the fourth station, where there was a dense bloom of Synechococcus spp. and the mixed layer was shallower, 34–52% of the daily bacterial production would have to be lysed. A comparison of the difference between destruction rates of viral particles and infectivity integrated over the depth of the mixed layer implies that host‐mediated repair must have restored infectivity to 39–78% of the sunlight‐damaged viruses daily. The calculated frequency of contacts between viral particles and bacterial cells that resulted in infection (contact success) ranged from ~18 to 34% in offshore waters, where the frequency of contacts between viruses and bacteria was much lower, to ~1.0% at the most inshore station, where contact rates are much higher. This suggests that in offshore waters bacterial communities are less diverse, and that there is less selection to be resistant to viral infection. This paper provides a framework for balancing viral production, destruction, and light‐dependent repair in aquatic viral communities.

A FOURTH PUMPING STATION AT TAI PO TAU, HONG KONG

Since 1960 the importation of Chinese water into Hong Kong has played an important part in local water supply. With continued growth, consumption has risen leading to the need for major additional works including a fourth pumping station at Tai Po Tau, the heart of the raw water distribution system. Built in restricted site the D station will have a capacity of over 3000 million litres per day (Mld) (35 m 3 /s) making it the largest water pumping station in Hong Kong, increasing capacity at Tai Po Tau to over 5100 Mld (64 m 3 /s). An intricate arrangement of tunnels and shafts enables the raw water to be drawn from five sources at two distinct hydraulic levels. The two levels vary depending upon the time of year and also upon weather conditions which cause rapid increases in catchment flow. Water is pumped to two high head (110 m) and five low head (40 m) destinations. Because water is taken from local catchments it can contain large quantities of debris. The D station includes a screening facility which comprises raked bar and rotating band screens. Power supplies are provided from the local grid at 132 kV and the project includes construction of a substation. A major factor in the design and contract documentation for the project was the need to integrate construction of the new facilities, including connections, with minimal disruption to the existing system which the client continues to operate. These considerations influenced the contract strategy and required careful programming. Construction has involved traditional techniques but the large pumphouse sump, constructed mainly in bedrock, required special attention. The paper describes the development of the designs for permanent works and indicates how the implementation programme was developed.

5481181 Real-time toxic metals monitor device and method

A rotary cartridge filler for the containerization of hazardous waste in a controlled environment, comprising an upper die module for receiving volumes of shredded waste and a lower canister module for receiving empty containers to be charged with waste from the upper module. The upper and lower modules are axially aligned and separated by a wall containing an opening for the transfer of waste from the upper module to the lower module. Both modules are mounted on a turret which rotates the modules about their axes. The upper and lower modules each contain six chambers uniformly spaced around the outer perimeter of the module and vertically aligned. In a first station, a canister enters a chamber in the lower module, and the modules are then rotated to a second station where both the upper and lower modules are purged with nitrogen. The modules are then rotated to a third station where the upper module is filled with a volume of shredded material before being rotated to a fourth station where the material is discharged to the canister in the lower module by a discharge cylinder located above the upper module. The modules are then rotated to a fifth station where the air in both modules is evacuated before being rotated to a sixth station where the filled canister is removed from the lower module.

Temporal and spatial variability, and the role of dissolved organic carbon (DOC) in methane fluxes from the Sabine River Floodplain (Southeast Texas, U.S.A.)

The Sabine River floodplain, in southeast Texas, U.S.A., is a broad flat watershed which contains a diverse assemblage of blackwater wetland habitats. Methane fluxes were compared across a gradient of three different habitats, within the floodplain, that extended from the outer reaches of the basin to the river proper (i.e., blackgum Nyssa aquatica, cypress Taxodium distichum, and arrowhead Sagittaria spp.), as well as a fourth station (a Spartina marsh) within the Sabine-Neches estuary. Concentrations of dissolved organic carbon (DOC) in the floodplain were very high (15-50 mg/l). Methane emissions were highly variable and ranged from 0.0007 to 1640 mg m -2 d -1 , with the highest rates in July 1993. These highest CH 4 emission rates were observed just after the longest period of flooding (ca. 1 month) at each of the stations. Fluxes were significantly correlated (both positively and negatively) with precipitation (p<0.01) ; natural periods of flooding and drought were primarily responsible for the wide range of emissions. Methane consumption rates had little effect on total emissions because of losses by ebullition and plant-mediated transport mechanisms. Plant-mediated transport accounted for as much as 96% of the total CH 4 emissions at certain stations. Laboratory experiments indicated that UV-B treated humic substances were preferentially utilized by methanogens over untreated humic compounds. Thus, variability of light penetrance across a floodplain may affect the quality and ultimately the availability of DOC to methanogens. Finally, the similarity in peak CH 4 emissions, after a 1 month lag period of flooding, in both agricultural and natural wetlands of southeast Texas, may for the first time demonstrate a similar chronological sequence of microbial reactions for CH 4 production in divergent systems.

Public sector projects in a mathematical modeling course

Student teams in a mathematical modeling course have carried out several projects for the City of Bloomington. IL, a small municipality with a population of 50,000. The first project was a water meter replacement model. Since water meters lose accuracy with age, older meters are a source of lost revenues. The team attempted to determine the optimal meter replacement age. The second project was a police patrol car workload model. This multi-dimensional queueing model involves police call arrival rates, service times, and overall patrol car workloads. The third and fourth projects were carried out for the Bloomington Fire Department. The third project applied various queueing models to the behavior of their three fire stations. The city planned to add a fourth station, and the final project applied a parametric allocation model to the question of where the additional station should be located. Experiences relevant to these projects, as well as the philosophy of student projects in general are discussed.

Simple solutions for hyperbolic and related position fixes

Navigation fixed from range differences to three stations and an additional piece of information are investigated. It is shown that if the additional information is the navigator altitude, or the range difference to a fourth station, the computation of the navigation fix is reduced to finding the roots of a quadratic. If the additional information is the range to another station, or that the navigator is on the Earth ellipsoid, the fix can be obtained by solving a quartic. By emphasizing the underlying geometric interpretations, these fixes and their simple solutions are made clear. The derivations also show that the same solution algorithms are applicable if the basic navigation measurements are range sums instead of range differences.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effects of Submersed Macrophytes on Water Quality in the Tidal Potomac River, Maryland

ABSTRACT In August, 1986, diurnal measurements of temperature, conductivity, dissolved oxygen and pH, and tide-related measurements of suspended-particulate matter and chlorophyll-a were made at three stations within a dense macrophyte bed and at a fourth unvegetated station outside the bed. Light penetration and current velocity were measured at a hole within the bed and at the unvegetated station. Water temperature, dissolved oxygen and pH increased during the day with the steepest vertical gradients and maximum readings occurring within the bed during midafternoon at low tide. Current velocities within the beds were about one-third of those at the open-water site and water clarity was considerably greater inside the bed. Chlorophyll-a and suspended-particulate concentrations were significantly lower at vegetated stations than at the unvegetated open-water station.

Loran-C Chains: Determination of Extent of Cover

A mainly theoretical study has been undertaken to demonstrate how the extent of cover from a hyperbolic navigation system chain can be evaluated. The impetus for the study was the need to assess how Loran-C could be extended over Western Europe, particularly in the South western Approaches, North Sea, English Channel and Bay of Biscay sea areas.The technique described in this article leads to an accurate determination of the electric field strength at a distance from each transmitting site and takes into account the complexities of the ground-wave propagation path. This field-strength contour is combined with the geometric effects of station siting (expansion factors) to yield a constant S/N contour (–10 dB) which defines the ¼n.m. error and hence the limit of cover for the hyperbolic chain under study.In order to exercise the analytical methods a hypothetical Loran-C chain was studied comprising a master station at Lessay (France), with secondary stations at Soustons (also in France), at Sylt (dual rated; off the North Sea coast of Germany, near the Danish border) and at a fourth station located in north-west Britain on the Hebridean island of Barra. The study indicated that such a hypothetical chain would significantly improve Loran-C cover over much of western Europe.

Variations of radon content in groundwaters and possible correlation with seismic activities in northern Taiwan

Radon (222Rn) concentration in geothermal waters and CO2-rich cold springwaters collected weekly in duplicate samples from four stations in northern Taiwan were measured from July 1980 to December 1983. Seven spike-like radon anomalies (increases of 2 to 3 times the standard deviation above the mean) were observed at three stations. Following every anomaly except one, an earthquake ofML above 4.6 occurred within 4 to 51 days, at an epicentral distance 14 to 45 km, and at a focal depth of less than 10 km. The distribution of the earthquakes preceded by radon anomalies is skewed in certain directions from the radon stations; the radon stations seem to be insensitive to earthquakes occurring in the other directions. At the fourth station, near a volcanic area, much gas (mainly CO2) is discharged from the well, together with hot water. A very high concentration of radon was detected in the discharged gas; therefore trapping of gas in the water can result in anomalously high radon contents. According to limited measurements, the radon concentration in water appears to be undersaturated with respect to that in gas. This suggests that hot water is very susceptible to radon loss, and monitoring of radon in gas is more desirable.

Étude régionale magnéto-tellurique des structures de la conductivité électrique sur la bordure occidentale du craton ouest africain en République du Sénégal

Magnetotelluric soundings were carried out in the Senegal Republic on the western border of the west African craton by a team of geophysicists from Mbour's Observatory, along an approximately east–west profile. This profile includes four stations about 20 km apart. The purpose of this paper is to analyse and interpret the obtained data. The magnetotelluric data were restricted to a period range of 20–300 s. The measurements were performed individually with a reference station located in the sedimentary basin at approximately 130 km from the craton border, and they allowed one to calculate the amplitude ratios of the electromagnetic field components at the mobile stations. A two-dimensional model indicates the presence of a deep conducting layer at a depth of 80 km for the four stations. For the three stations located on the craton border the introduction of a conducting layer at a depth of 30 km permits a better approximation of the data. On the other hand, the presence of a conducting layer underneath the fourth station located on the craton is not justified by the two-dimensional model.The presence of a conducting zone in the mobile zone crust seems to have resulted from a hydration process. On the craton, the crust became hydrated and the conducting level is not present. [Journal Translation]

Quadripartite Surface Wave Method: Development

Summary In general, accurate surface wave phase velocities are obtained from the tripartite method only when the epicentre-to-network path is nearly parallel to one leg of the array. This limitation can be removed by adding a fourth station to the network and assuming wavefronts in the form of circular arcs. The addition of two stations permits the use of such wavefronts to estimate the lateral heterogeneity of the structure beneath the array. This can also be done with a five-station network if two separate events are employed. Tests of the quadripartite method in the presence of lateral heterogeneity, show that a roughly rectangular configuration of stations yields a phase velocity which is a good approximation to the true velocity at the centre of the array. Tests of a triangular network which includes a central station indicate that such an array may provide the means for determining the phase-velocity gradient with only four stations. The quadripartite method is used to test the feasibility of network measurement of local attenuation of surface waves due to the intrinsic attenuation of the Earth. Our results demonstrate that amplitude errors are not the only important consideration in the measurement of accurate attenuation. Timing errors and the ratio of network dimensions to wavelength are important as well. We conclude that even under ideal conditions, the present measurement and data-processing techniques appear to offer little hope for accurate network measurement of local attenuation.

The distribution of siphonophores in a transect across the North Atlantic Ocean at 32°N

A study has been made of the distribution of siphonophores in a series of twelve oblique (0–1000 m) hauls made in a transect across the North Atlantic at 32°N, from 16°W to 60°W. A total of 66 species was identified, of which twelve were physonect siphonophores and the remainder calycophorans. In order to assess the changes in the population of the nineteen most abundant species, the species correlation coefficient matrix was calculated and six factors were extracted and rotated to simple structure. The first two factors indicated a clear east-west trend in the distributional pattern for thirteen of these siphonophore species. The coefficient of proportional similarity between stations was also calculated using the data for all of the species present. From this it was possible to divide the stations into two clear zones, namely the first three and the last eight, while the fourth station was intermediate. A comparison of these results with the TSD data for these stations showed that the fourth station was in the transitional zone between the eastern North Atlantic water and that characteristic of the Sargasso Sea, and that these two major water masses were distinguishable at all the depths where siphonophores would be expected to be found. It is concluded that there was some interrelationship between the physical features of the separate water masses and the composition of the siphonophore populations found in each. The problems involved in deciding on a sampling programme for such a study as this are also discussed.

Velocities of compressional and shear waves in marine sediments determined in situ from a research submersible

In situ measurements of the velocity and attenuation of compressional waves, and velocities of Stoneley waves from which shear-wave velocities were computed, were made at three stations in the sea floor off San Diego, California, from a research submersible; a fourth station was occupied by divers. Sediment types and water depths ranged from medium sand at 20 meters to clayey silt at 986 meters. Sediment densities, porosities, and grain sizes were measured in sediment samples taken at each station. These unique data allowed tentative evaluations of models and equations, and computations of constants, for elastic and viscoelastic saturated, porous media. For the range in sediment types, results included:Property Sediment type Sand Clayey siltRatio, Vp sediment/Vp bottom water 1.20 0.98Attenuation, db/m at 14 kHz 7 1Sediment density, g/cm3 2.01 1.33Shear-wave velocity, m/sec 197 88Rigidity modulus μ × 1010 dynes/cm2 0.08 0.01Lame's constant λ × 1010 dynes/cm2 6.34 2.80 It is concluded that either Hookean-elastic or viscoelastic equations can be used to compute compressional-wave and shear-wave velocities and other elastic constants. To account for absorption in sediments, a ‘viscoelastic’ solid model is used in which frequency-independent, complex Lame constants, (μ + iμ′) and (λ + iλ′) replace μ and λ in the equations of elasticity; with this model and equations, and data taken on the four stations, μ, μ′, λ and λ′ were computed. In this viscoelastic model, the mechanics of absorption are not specified, and the assumption of frequency-independent, complex Lame constants leads to a linear dependence of attenuation on frequency and no dispersion of velocity with frequency in the range of frequencies of interest in underwater acoustics and marine geophysics. The evidence of this study and others indicates that almost all open-ocean sediments have finite regidities and transmit shear waves.

A numerical method for calculating unsteady two-dimensional laminar boundary layers

A method for calculating unsteady two dimensional boundary layers in laminar incompressible flow has been developed and tested. No restrictive assumptions are made regarding the time-dependent terms in the boundary-layer equation. The differential equations are solved with an implicit difference scheme similar to that employed for steady two-dimensional boundary layers. At each step, here, known conditions at three stations are used to calculate the conditions at a new (fourth) station. The entire field is covered by a succession of these steps.

The ecology of shallow water meiofauna in two New England estuaries.

The distribution and abundance of shallow subtidal meiofauna in four habitats in the Niantic and Pettaquamscutt estuaries in southeastern New England were studied from October 1964 through October 1965. Numbers of individuals ranged from 1,184 to 5,163/10 cm2, and wet weights from 8.5 to 62.5 mg/10 cm2. Nematodes were the dominant group, averaging 83% of the total numbers and 64% of the total biomass. Among the nematodes, epigrowth-feeding species were dominant at all four stations; in addition, deposit-feeding species were abundant at three stations where the amount of detritus was high relative to the fourth station. At these three stations ostracods and deposit-feeding polychaetes were also abundant.Nematodes showed marked seasonal changes i their species composition, with epigrowth-feeding species reaching maximum densities in spring and summer (coincident with observed increases in benthic microflora production), and deposit and omnivorous-feeding species in fall and winter (coincident with observed increases in organic detritus). Increases in the epigrowth feeders were responsible for significant increases in the total nematode populations in spring and summer.Ostracods were most abundant in late summer, fall and winter in association with the increases in detritus. Polychaetes, amphipods and lamellibranchs were most abundant in summer, the first-named in association with elevated water temperatures. Harpactacoid copepods were inconsistent in their seasonal distributions.Approximately 80% of the meiofauna occurred in the upper 3 cm of sediment. Copepods and ostracods were virtually limited to the upper 3 cm, while amphipods and lamellibranchs were limited to the upper 2 cm of sediment. Nematodes and polychaetes extended down to 5 cm (the lowest depth studied), although usually in significantly reduced numbers.

The Pipeline Transportation of Heavy Oils

Abstract Heavy oils tend to be highly viscous. The excessive pressure gradientscaused by high viscosity have discouraged the development of heavy oilpipelines in Western Canada. This paper reviews briefly and comments on some ofthe methods used to overcome this difficulty. The crude may be heated to reduce viscosity. This method is well known, andtemperature profiles along a hot oil pipeline may be calculated by an equation given in the paper. There is some difficulty, however, in accurately predictingheat transfer rates because of unknowns in soil temperature andconductivity. Blending the viscous crude with a diluent to reduce its viscosity isprobably the simplest method of obtaining pipeline access to interprovincialmarkets. If a light diluent such as natural gasoline is used, even small percentages greatly reduce the viscosity. Although there are methods ofestimating the viscosity of a blend from a knowledge of the viscosity of the components, laboratory tests on the actual blends to be transported margin moredependable information. The addition of water to viscous oil lines is known to reduce pressuregradients, and research on this matter has been conducted by several people, including the Alberta Research Council. This method, however, may have certain operating difficulties and more work on the matter, would he helpful. The designer of heavy oil pipelines is advised to give careful consideration to all the alternatives and make detailed studies before deciding on the methodto be used. The paper outlines briefly some of the design features of Husky Pipeline Ltd.'s Lloydminster to Hardisty system, which went into operation late in 1963.This 6 5/8-in. pipeline, 72 miles long, utilizes three pumping stations tohandle a blend of Lloydminster crude and natural gasoline. The pumpage isheated to 130°F at each station. A fourth pumping station at the outlet end(Hardisty) allows pumping in either direction; the reversal is used to batchthe diluent north to the crude source, where it is blended with the Lloydminster crude. The blend pumping rate is 15,000 bbls/day.

Loran Accuracy Diagrams for Four-station Fixes

The idea of portraying the accuracy of a navigational system by means of contours is very old and was first introduced to readers of this Journal by Jessell and Trow. Later writers, Sameshima, Namikawa and Hasegawa, have published accuracy contours for Loran chains. This note is a further contribution in this direction and its aim is to investigate what sort of accuracy can be achieved by marrying a position line from one chain with a position line from another.N. Sameshima has studied the accuracy contours arising from a hyperbolic system where position lines are obtained from two pairs of stations, each pair having one station, the master station, in common. Y. Namikawa and K. Hasegawa, in a later article, constructed accuracy contours for a number of Loran chains, mainly in the Pacific, but also in the Atlantic areas. This article discusses the more difficult case where fixes are obtained through using pairs with no common station, and indicates what improvement may be expected through introducing a fourth station in a number of selected instances.