Adjacent Bars Research Articles

CZM Applications of Argus Coastal Imaging at the Gold Coast, Australia

Abstract A video-based ARGUS coastal imaging system is being used at the northern Gold Coast, Australia to monitor and quantify the regional-scale coastal response to sand nourishment and construction of the world-first Gold Coast artificial (surfing) reef. This automated monitoring system is used to obtain hourly daylight images from four cameras that combined provide continuous coverage of 4.5 km of the coast. Digital image processing techniques are then applied on a routine (weekly to monthly) basis to extract a range of CZM information from the growing image database. Analyses include: the mapping of changing shoreline position (and hence beach width); the measurement of three-dimensional inter-tidal morphology and resulting changes in subaerial sand volume; and the comparison of wave breaking frequency at the reef and adjacent nearshore bars, to quantify enhanced recreational surfing opportunities at the reef site. Based upon the results of image analysis, to date (January 2003) an additional 20–30 m...

DEVELOPMENT OF VERTICAL WIND AND TURBULENCE PROFILES OF WIND TUNNEL BOUNDARY LAYERS

Ventilation is considered one of the most important factors for livestock and plant environmental control. However,because of the difficulties of conducting field experiments, aerodynamic studies of ventilation and HVAC of agricultural buildingsare difficult and expensive to conduct effectively in full-scale buildings. A wind tunnel can be the most powerful technologyfor studying aerodynamics because it works with real airflow and the boundary conditions can be easily changed. A large,multi-purpose wind tunnel was built at the National Institute of Agricultural Engineering (NIAE) in Korea in 2002. In thisresearch, the formation of boundary layers, such as vertical wind and turbulence profiles, in the test section of the wind tunnelwas studied to determine ventilation efficiency and internal airflow characteristics of naturally ventilated buildings.Compared to measured data, it was found that the optimum wind and turbulence profiles of a 20 m boundary layer could notbe achieved using the theory and experimental procedures of civil and architectural engineering because that would requireseveral hundred meters of boundary layer thickness. Moreover, it was impossible to achieve 30% turbulence intensity justabove the floor. Finally, it was found that lattice and blocks could be effectively used to design an optimum boundary layerfor aerodynamic study of agricultural buildings. When using lattice and blocks, the wind and turbulence profiles were seriouslyaffected by the distance between the lattice and the measurement location, by the distance between adjacent bars of lattice,and by the width of the bars.

Vortex shedding from a row of square bars

Interactions of wakes in a flow past a row of square bars, which is placed across a uniform flow, are investigated by numerical simulations and experiments on the tassumption that the flow is two-dimensional and incompressible. At small Reynolds numbers the flow is steady and symmetric with respect not only to streamwise lines through the center of each square bar but also to streamwise centerlines between adjacent square bars. However, the steady symmetric flow becomes unstable at larger Reynolds numbers and make a transition to a steady asymmetric flow with respect to the centerlines between adjacent square bars in some cases or to an oscillatory flow in other cases. It is found that vortices are shed synchronously from adjacent square bars in the same phase or in anti-phase depending upon the distance between the bars when the flow is oscillatory. The origin of the transition to the steady asymmetric flow is identified as a pitchfork bifurcation, while the oscillatory flows with synchronous shedding of vortices are clarified to originate from a Hopf bifurcation. The critical Reynolds numbers of the transitions are evaluated numerically and the bifurcation diagram of the flow is obtained.

Flood plain and channel dynamics of the Quinault and Queets Rivers, Washington, USA

Comparison of historic channel migration rates, modern planform conditions, and overall sediment, wood, and flow conditions and interactions for the Quinault River and Queets River in the western Olympic Peninsula, Washington, reveals decadal- to century-scale interactions between gravel-bed channels and forested flood plains in temperate maritime environments. The downstream alluvial portions of these two rivers can be divided into three reaches of different slope, flow, sediment, and wood regimes: (i) the upper Quinault River is aggrading behind Lake Quinault, a natural lake that traps most sediment and wood transported from the Olympic Mountain headwaters. (ii) The lower Quinault River, downstream of Lake Quinault, transports only sediment and wood derived from reworking of flood-plain deposits and contributed from valley margins. (iii) The Queets River has unimpeded movement of sediment and water from the mountainous headwaters to the Pacific Ocean. Measurements of channel planform characteristics and historic migration rates and patterns show that these three reaches have correspondingly distinct channel and flood-plain morphologies and dynamics. The aggrading and sediment-rich upper Quinault River has the widest flood plain, widest active channel, greatest number of low-flow channels and flanking gravel bars, and an average channel migration rate of 12.7±3.3 m/year between 1900 and 1994. The comparatively sediment-poor lower Quinault River has the narrowest flood plain, narrowest active channel, and lowest channel migration rate (4.0±1.2 m/year); and most flow is through a single channel with few adjacent gravel bars. The Queets River has attributes intermediate between the lower and upper Quinault Rivers, including an average channel migration rate of 7.5±2.9 m/year. Flood-plain turnover rates are similar for all three reaches, with channels eroding the flood plain at the rate of about 0.2% of the flood-plain area per year, and with corresponding flood-plain half-lives of 300 to 500 years. Observations from this study and previous studies on the Queets River show that channel and flood-plain dynamics and morphology are affected by interactions between flow, sediment, and standing and entrained wood, some of which likely involve time frames similar to 200–500-year flood-plain half-lives. On the upper Quinault River and Queets River, log jams promote bar growth and consequent channel shifting, short-distance avulsions, and meander cutoffs, resulting in mobile and wide active channels. On the lower Quinault River, large portions of the channel are stable and flow within vegetated flood plains. However, locally, channel-spanning log jams have caused channel avulsions within reaches that have been subsequently mobile for several decades. In all three reaches, log jams appear to be areas of conifer germination and growth that may later further influence channel and flood-plain conditions on long time scales by forming flood-plain areas resistant to channel migration and by providing key members of future log jams. Appreciation of these processes and dynamics and associated temporal and spatial scales is necessary to formulate effective long-term approaches to managing fluvial ecosystems in forested environments.

A RIFFLE STABILITY INDEX TO EVALUATE SEDIMENT LOADING TO STREAMS1

ABSTRACT: Riffles in moderately entrenched stream reaches with gradients of 2 percent to 4 percent that have received excessive sediment from upstream have a distinctly different and higher proportion of smaller mobile particles than riffles in systems that are in dynamic equilibrium. The mobile fraction on the riffle can be estimated by comparing the relative abundance of various particle sizes present on the riffle with the dominant large particles on an adjacent bar. Riffle particles smaller than the dominant large particles on the bar are interpreted as mobile. The mobile percentile of particles on the riffle is termed “Riffle Stability Index” (RSI) and provides a useful estimate of the degree of increased sediment supply to riffles in mountain streams. The RSI addresses situations in which increases in gravel bedload from headwaters activities is depositing material on riffles and filling pools, and it reflects qualitative differences between reference and managed watersheds. The RSI correlates well with other measures of stream channel physical condition, such as V and the results of fish habitat surveys. Thus, it can be used as an indicator of stream reach and watershed condition and also of aquatic habitat quality.

Temporal phase discrimination depends critically on separation

Temporal phase discrimination was measured as a function of spatial separation of the stimulus components. In contrast to many previous studies, phase discrimination thresholds were measured directly, rather than inferred from the ability to discriminate synchronous from antiphase stimuli, or from segregation or shape tasks. For abutting bars, relative phase thresholds were closely proportional to temporal frequency. The proportionality corresponded to a threshold temporal offset of 2.5–9.5 ms, across subjects. Introduction of a small gap (0.125° or greater) led to a dramatic (3- to 7-fold) increase in thresholds for temporal phase discrimination, and thresholds were no longer proportional to temporal frequency. Insertion of a third bar filling the gap resulted in a recovery of the low thresholds, provided that its modulation was consistent with apparent motion across the three bars. Below 8 Hz, phase discrimination thresholds across three bars were equivalent to thresholds for two abutting bars. Above 8 Hz, phase discrimination thresholds for the three bar combination were lower than thresholds for two adjacent bars, implying that phase information was integrated across all three bars. Phase discrimination thresholds do not appear to reflect the properties of a single mechanism. Especially at high temporal frequencies, low thresholds for phase discrimination are closely tied to the presence of apparent motion. Temporal phase discrimination is markedly impaired by a small separation of stimulus components. Moreover, the inability to detect phase differences across gaps corresponds to the loss of phase-dependence of vernier acuity thresholds across gaps.

Spatial scale of motion segmentation from speed cues

For the accurate perception of multiple, potentially overlapping, surfaces or objects, the visual system must distinguish different local motion vectors and selectively integrate similar motion vectors over space to segment the retinal image properly. We recently showed that large differences in speed are required to yield a percept of motion transparency. In the present study, to investigate the spatial scale of motion segmentation from speed cues alone, we measured the speed-segmentation threshold (the minimum speed difference required for 75% performance accuracy) for ‘corrugated’ random-dot patterns, i.e. patterns in which dots with two different speeds were alternately placed in adjacent bars of variable width. In a first experiment, we found that, at large bar widths, a smaller speed difference was required to segment and perceive the corrugated pattern of moving dots, while at small bar-widths, a larger speed difference was required to segment the two speeds and perceive two transparent surfaces of moving dots. Both the perceptual and segmentation performance transitions occurred at a bar width of around 0.4°. In a second experiment, speed-segmentation thresholds were found to increase sharply when dots with different speeds were paired within a local pooling area. The critical pairing distance was about 0.2° in the fovea and increased linearly with stimulus eccentricity. However, across the range of eccentricities tested (up to 15°), the critical pairing distance did not change much and remained close to the receptive field size of neurons within the primate primary visual cortex. In a third experiment, increasing dot density changed the relationship between speed-segmentation thresholds and bar width. Thresholds decreased for large bar widths, but increased for small bar widths. All of these results are well fit by a simple stochastic model, which estimates the probabilities of having identical or different motion vectors within a local pooling area whose size is the same as that of primate V1 neurons. Altogether, these results demonstrate that speed-based segmentation can function well, even at small spatial scales (i.e. high-spatial frequencies of spatial corrugation) and thereby emphasizes the critical role of a local pooling process early in the cortical motion-processing pathway.

Mortality of newly metamorphosed eastern oysters ( Crassostrea virginica ) in mesohaline Chesapeake Bay

Stocks of eastern oysters, Crassostrea virginica (Gmelin), in mesohaline Chesapeake Bay, USA, exhibit a high degree of inter-annual and spatial variability in recruitment. We found that cumulative oyster spatfall on off-bottom collector plates, measured throughout the summer in 14 years over a span of three decades, was highly positively correlated (r2 = 0.8) with juvenile oyster recruitment on adjacent oyster bars. Total abundances of juvenile oysters on these bars were, however, generally 99.7% lower than predicted from cumulative seasonal larval settlement on collector plates. We propose that although the number of larvae metamorphosing was the key factor in determining the gross annual pattern of recruitment to these mesohaline oyster bars, the actual magnitude of recruitment was governed by post-settlement processes, such as competition for limited resources and predation. We tested the hypothesis that predation may be partly responsible for high post-settlement juvenile oyster mortality. We performed a series of 3-d field investigations over two summers (1989, 1990) at a mesohaline site, employing cages of various mesh sizes (400, 800, 1500 μm) to protect hatchery-reared spat of 0.5 to 4.0 mm shell height. Mortality rates for spat held for 3 d in the estuary (17.8%) were significantly higher (P = 0.0001) for the smallest spat (0.5 to 2.0 mm) compared with those of 2.01 to 4.0 mm (4.2%). In 1990, but not in 1989, enclosure within 400 and 800 μm mesh cages significantly (P = 0.004) increased survival during 3-d deployments (9.4 and 10.1%, respectively) compared with spat unprotected by mesh cages (21.9%). In a series of laboratory predation studies that used the entire community of invertebrates that could penetrate the cages, microscopic juvenile polyclad flatworms, Stylochus ellipticus, were the only organisms that we observed crawling into living oysters and feeding on oyster tissue. Large flatworms (50 to 200 mm2) are known to be important predators on oysters, but this ability of flatworms that were so small (<ca. 5 mm2) and translucent as to be almost invisible without magnification to feed on immediate post-metamorphic oysters has not been documented previously. Our results suggest that the rate of mortality due to predation in mesohaline Chesapeake Bay is much reduced once spat survive for 2 to 3 weeks post-metamorphosis. Thus, it is likely that predation in the 1 to 2 week period immediately after settlement may be a crucial factor in the structuring of eastern oyster populations.

Design considerations for integrated inductors in conventional CMOS technologies

The skin and proximity effects, substrate dependencies and other factors which modify integrated inductor characteristics in silicon technologies were examined using quasi-static electromagnetic simulations and characterization studies. Results were used to understand the impact of constraints and opportunities for implementing inductors in silicon technologies. It was shown that wider metal lines are more affected by the skin effect and, at frequencies greater than ∼4 GHz, the effectiveness of improving quality factors ( Q) by widening metal lines is degraded. An inductor composed of three metal layers shunted over an entire length of the inductor trace and another with three metal layers shunted only at their ends were characterized. Inductances of the structures were the same, while the resistance was surprisingly lower for the latter structure. It was demonstrated that parasitic metal-to-substrate capacitances of inductors can be reduced by using an underlying biased n-well. Two-dimensional simulations show that frequency dependencies of inductance for inductors fabricated on p-substrates (20 Ω cm) and those fabricated on p on p + (0.01 Ω cm) substrates are small and are the same. These observations were explained in terms of magnetic field strength, conductivities and eddy currents. It was also shown that ground-signal characterization of inductors can result in errors due to mutual inductance between the inductor and adjacent ground bar.

Context-dependent reflex control: some insights into the role of balance.

Recent research suggests that the balance requirements of a task dictate the reflexive response. However, these observations were inferred indirectly from either different tasks or different phases of the same task. This study directly tested the hypothesis of balance-dependent control during recovery from an unexpected trip. The subjects were tripped in two different support conditions: unilimb support (provided by the stance limb) or trilimb support (provided by the stance limb and both arms placed on adjacent parallel bars). The subjects exhibited anticipatory changes: they biased the body center of mass toward the support limb in the mediolateral direction and elevated the swing limb higher when there was a possibility of being tripped. The electromyographic (EMG) latencies were not influenced by the threat to equilibrium. The magnitudes of the EMG reflexive response to the trip were clearly modulated as a function of the threat to stability, not in a simple manner, but rather in a complex manner, which optimized the recovery strategy. It is evident that the overriding concern, equilibrium control during locomotion, has a dominant influence on reflex modulation.

Differential Velocity Detection in Motion Parallax Fields

Processing of motion parallax relies on the ability of the visual system to segregate locally different motion signals and integrate them over space and time in order to reconstruct a 3-D structure. In a series of experiments, we evaluated the thresholds for differential motion detection and their dependences upon the spatial structure of the optic-flow field. Visual stimuli were large moving random-dot displays (80 deg × 60 deg). Each dot was randomly attributed one of two velocities whose difference ranged between 0% and 80% of their average velocity, which ranged between 2 and 64 deg s−1. Stimulus duration was from 130 to 1040 ms. Subjects were instructed to stare at a central fixation mark and had to decide whether the display specified one or two surfaces. At a duration of 130 ms, subjects needed more than 40% difference between the two velocities to reach a 75%-correct detection criterion. Thresholds reached a minimum value of about 20% at a duration of 500 ms. Thresholds always increased with the average velocity and were not affected when a static form segregation cue was added to the displays. They were always larger than thresholds for velocity discrimination in successive displays (about 10% at 260 ms). We finally investigated the spatial properties of differential velocity detection. The visual field was divided into horizontal stripes of equal widths. Adjacent bars alternately contained random dots moving with one of two velocities. Thresholds for differential velocity detection increased monotonically when the bandwidth decreased, up to an asymptotic value, equal to those observed with a transparent display.

Structural-functional differences of a crab motoneuron to four stomach muscles.

A motor unit in the stomach of the blue crab, Callinectes sapidus, consists of four separate muscles involved in different aspects of the trituration and filtering of food. Motor nerve terminals to two of the muscles (CPV7a and GM5) release small amounts of transmitter (low-output) while those to the other two muscles (CV2 and CV3) release between three and five-fold greater amounts (high-output). Structural features underlying the disparity in synaptic strength were analysed with thin serial-section electron microscopy. Nerve terminals were similar in their volume percent of mitochondria, clear vesicles and dense core vesicles among the four muscles. This was also the case for the number and size of synaptic contacts. However, presynaptic dense bars representing active zones were longer and occurred more frequently at high-output synapses than at low-output ones. High-output synapses were also characterized by the close spacing of adjacent dense bars. The longer and more closely spaced dense bars at high-output synapses would be factors in the generation of larger synaptic potentials in these terminals compared to their low-output counterparts. Other factors, however, need to be considered to fully account for the physiological differences in synaptic strength among the four muscles.

Rotor cage anomalies and unbalanced magnetic pull in single-phase induction motors

This paper consists of an experimental and theoretical investigation of the effect that rotor cage defects have on the unbalanced magnetic pull (UMP) present in a single-phase motor. The paper presents a detailed development of a mathematical model which can be used to examine both porosity and soldering defects in cage rotors. In the experimental investigation, the UMP developed by a number of nominally identical motors that were known to have rotor defects was measured using a specially designed test rig. The rotors were then divided into two equal groups. The rotor bars in the first group were removed from the rotors and their resistance measured to determine the range and distribution of porosity defects around the periphery of the rotor. The ovality of the rotors of the second group was carefully measured, and their end rings were turned off to enable the bar-to-bar resistance to be measured. This was done for all pairs of adjacent bars in the rotors of the second group, giving again an indication of the range and circumferential distribution of soldering defects.

Interference and negative priming from ignored distractors: the role of selection difficulty.

The relation between distractor interference and negative priming from identical distractors was examined in two experiments. Subjects responded to a target letter, which was indicated by an adjacent bar marker, and attempted to ignore a distracting letter. On prime trials, distracting letters were either compatible or incompatible with the target, allowing for a measure of interference. On subsequent probe trials, previously ignored distractors were sometimes presented as targets, allowing for a measure of negative priming. Reducing the spatial separation between targets and distractors on the prime trial increased the magnitude of interference and negative priming, but these effects appeared to be independent of each other (Experiment 1). In Experiment 2, the prime target location was precued on some trials, but not on others. Precuing attenuated the magnitude of interference, but not that of negative priming effects. This pattern indicates that measures of negative priming and measures of distractor interference on the immediately preceding trial are independent. The results are discussed in terms of a selective inhibition model of selective attention.

Effect of crosspath resistance between adjacent rotor bars on performance of inverter-fed high-speed induction motor

The effects of crosspath resistance between adjacent rotor bars on steady state performance of inverter-fed high-speed cage induction motors are discussed. It is shown that the equivalent rotor resistance and leakage reactance change with crosspath resistance between adjacent rotor bars for various values of the fundamental supply frequency and the slip. The steady state characteristics of the high-speed induction motor drives for various crosspath resistance are discussed on the basis of theoretical and experimental results. The results of this research are applied in the design of a high-speed induction motor with uninsulated rotor bars.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analysis of inverter-fed high-speed induction motor considering crosspath resistance between adjacent rotor bars

The purpose of this work is to analyze the steady state performance of an inverter-fed high-speed induction motor with trapezoidal rotor bars taking into account crosspath resistance between adjacent rotor bars. The performance of the induction motor drives for various crosspath resistances of two kinds of rotor slot shapes, a rectangular bar and a trapezoidal bar, is discussed on the basis of theoretical and experimental results of a 2.2 kW 500 Hz 15000 rev/min three-phase induction motor. It is also shown that the equivalent rotor resistance and leakage reactance change with crosspath resistance between adjacent rotor bars for various values of the fundamental supply frequency, the rotor slip, and the harmonics. The results of this research will be applied for design consideration of a high-speed induction motor with uninsulated rotor bars. >

Impact Vibration Analysis of Group of Hexagonal Bars.

A simulation method was studied to calculate the vibration response during seismic excitation of a group of hexagonal bars installed in a restraint. Since impact phenomena take place between adjacent bars, or between a bar and a restraint, nonlinear force caused by the impact should be considered in the response calculation. The simulation method is a combination of the mode superposition method and the pseudo external force method. Time integration is carried out using the method proposed by Nigam. The nonlinear forces at the next time step can be determined through matrix calculation by introducing influence coefficient matrices which express the influence of impact forces on intersections at impact points. In this report, the influence coefficient matrices are expanded for hexagonal bars in a two-dimensional arrangement, by taking the impact direction of each impact point into consideration. In order to verify the above method, the calculated results were compared with experimental ones. The two results for maximum impact force were similar.

A broad-band position-sensitive phoswich detector for gamma-ray astronomy

A position-sensitive phoswich detector designed to cover a wide energy band from 15 keV to 1 MeV has been investigated. The detector concept is based on the use of an array of discrete 1 × 1 × 5 cm phoswich scintillation bars, the top 3 cm of which is CsI(Na) whilst the rear 2 cm is a GSO (Cerium-doped Gadolinium Orthosilicate Gd 2 SiO 5 (Ce), [1,2]) veto crystal. The array is viewed by a single position-sensitive photomultiplier tube (PSPMT). The test results show that energy resolution ranges from 31% FWHM at 60 keV to 13% FWHM at 511 keV. The FWHM of the point-spread function for the location of each event is smaller than the cross section of a single bar over the entire energy range. This guarantees good separation between energy deposits in adjacent bars. The outputs from the CsI(Na) main detectors and GSO veto crystals can be distinguished by a simple pulse-shape discriminator (PSD). Those multi-bar events which deposit energy only in the CsI(Na) array can be recognised using the position sensing capability of the tube. When used in conjunction with a coded-mask imaging system, an array of such detector modules could provide a competitive telescope for a future gamma-ray astronomy mission.

Impact Vibration Analysis of Bar Group in Single Row.

A simulation method was studied to calculate vibration response of a bar group installed between restraints in a single row under seismic excitation. Because impact phenomena take place between adjacent bars or a bar and a restraint, nonlinear force caused by the impact should be considered in the response calculation. In this study, a new method for determining the nonlinear force without convergence iteration was proposed. The simulation method is basically a combination of the mode superposition method and the pseudo external force method. The method proposed by Nigam is applied for time integration. An impact point is modeled as a set of a gap, a linear spring and a linear damper. The nonlinear forces at the next time step can be determined with matrix calculation by introducing influence coefficient matrices, which express the influence of impact forces on intersections at impact points. In order to verify the above method, the calculation results were compared with experimental ones, which showed that the method can simulate the experimental results well.

The provision of an electric field of controllable penetration into a cylinder

If a cylinder carries on its surface an electric charge of a density which is constant in the axial direction, but which varies sinusoidally with an integral number of wavelengths around the circumference, then inside the cylinder the electric field has its maximum value at points adjacent to the surface, and reduces continuously as the axis is approached. The rate of reduction increases with the number of wavelengths. A rotating cylinder of such charge may be simulated by a number (divisable by three) of equally spaced conducting bars mounted longitudinally on the surface of a stationary cylinder, the bars being connected in sequence to the lines of a three-phase voltage supply. The number of wavelengths of charge around the circumference can be varied by the connection together of a chosen number of adjacent bars effectively to form a single bar, and so fields of varying penetration depths can be produced from a fixed frequency supply. The variation of the resulting currents would be related to the corresponding variation in the complex conductivity of the cylinder material.