Quantification of pumping rate of <Emphasis Type="Italic">Chironomus plumosus</Emphasis> larvae in natural burrows

This paper investigates and compares experimentally determined water velocity field above natural macrozoobenthos burrows generated by Chironomus Plumosus larva during their bio-irrigation activity. All experiments were carried out using particle image velocimetry and performed in mesocosms filled with sediment burrowed by larvae, and the water velocity fields near the inlets and outlets of the U-shaped burrows were measured. From water velocity data the average volumetric flow rates between 54.6 and 61.1 mm³/s were calculated. Assuming an average burrow diameter of 2.25 mm, the volumetric flow rates suggest the average flow velocities through burrows during the pumping period between 13.7 and 15.4 mm/s. Two additional interesting phenomena could also be shown by analyzing the flow field generated by the larva. The analysis of the amount of tracers used for visualizations revealed that some of the tracer particles added to the water must have been consumed along their path from the inlet toward the outlet, hinting clearly to the so-called filter-feeding action of C. plumosus. The second phenomenon is due to the form of motion C. plumosus generates. By careful flow visualizations it was found that unlike other organisms such as Urechis caupo that use peristaltic body contractions, C. plumosus worms its body sinusoidally catapulting the fluid far into the overlying water body. This action is of ecological advantage for it avoids generating short oxygen circuits for their respiration and filter feeding.     

Drift compensation and its sensory basis in waterstriders (Gerris paludum F.)

Summary Watestriders (Gerris paludum F.), displaced by flowing water or wind, compensate for this by periodic jumps against the direction of drift so that they keep their average position — relative to the river bank, for instance — constant over long periods of time. To identify the cues used by the animals to compensate for drift, they were kept on an artificial stream with visual patterns along one or both sides. The velocity of the water flow and the pattern motion were varied. It is not possible to induce compensatory jumps in darkness by water or air current alone. Visual cues are indispensable for the reaction. The product of jump amplitude and jump frequency equals the drift velocity on average. The jump amplitudes are more or less independent of the flow velocity while the jump frequency is adjusted to it.     

Common misinterpretations of the “linear,no-threshold” relationship used in radiation protection

Summary Absorbed doseD is shown to be a composite variable, the product of the fraction of cells hit (I _H ) and the mean dose (hit size)z to those cells.D is suitable for use with high level exposure (HLE) to radiation and its resulting acute organ effects because, sinceI _H = 1.0, it approximates closely enough the mean energy density in the cell as well as in the organ. However, with low level exposure (LLE) to radiation and its consequent probability of cancer induction from a single cell, stochastic delivery of energy to cells results in a wide distribution of hit sizesz, and the expected mean value,z, is constant with exposure. Thus, with LLE, onlyI _H varies withD so that the apparent proportionality between dose and the fraction of cells transformed is misleading. This proportionality therefore does not mean that any (cell) dose, no matter how small, can be lethal. Rather, it means that, in the exposure of a population of individual organisms consisting of the constituent relevant cells, there is a small probability of particle-cell interactions which transfer energy. The probability of a cell transforming and initiating a cancer can only be greater than zero if the hit size (dose) to the cell is large enough. Otherwise stated, if the dose is defined at the proper level of biological organization, namely, the cell and not the organ, only a large dosez to that cell is effective.Dedicated to Prof. L.E. Feinendegen on the occasion of his 60th birthday     

Anisotropic adaptive finite element method for modelling blood flow

In this study, we present an adaptive anisotropic finite element method (FEM) and demonstrate how computational efficiency can be increased when applying the method to the simulation of blood flow in the cardiovascular system. We use the SUPG formulation for the transient 3D incompressible Navier–Stokes equations which are discretised by linear finite elements for both the pressure and the velocity field.

Given the pulsatile nature of the flow in blood vessels we have pursued adaptivity based on the average flow over a cardiac cycle. Error indicators are derived to define an anisotropic mesh metric field. Mesh modification algorithms are used to anisotropically adapt the mesh according to the desired size field. We demonstrate the efficiency of the method by first applying it to pulsatile flow in a straight cylindrical vessel and then to a porcine aorta with a stenosis bypassed by a graft. We demonstrate that the use of an anisotropic adaptive FEM can result in an order of magnitude reduction in computing time with no loss of accuracy compared to analyses obtained with uniform meshes.     

Small-scale movements of lotic macroinvertebrates with variations in flow

1. The small-scale movements and distribution patterns of invertebrates were observed in an attempt to identify the various mechanisms by which organisms may use flow refugia during flow disturbances. The microdistribution of lotic macroinvertebrates was examined in two replicate, non-circulating laboratory flumes with variations in flow among microhabitat patches (≈ 0.015–0.035 m²). The discharge in one experimental flume was manipulated to mimic spates and alter near-bed flow patterns; the other flume acted as a control. After an initial settling period, the position and behaviour of animals within the flumes was recorded before, during and after a simulated spate. Three species with contrasting flow microhabitat preferences and movement behaviour were examined. 2. At low discharge, the microdistribution of all three study species in flumes was broadly consistent with field observations. In the field, the optimum current speed was lowest for adults of the dytiscid beetle, Oreodytes sanmarkii, and highest for mayfly nymphs, Ephemerella ignita, with nymphs of the stonefly, Leuctra inermis, most abundant at intermediate velocities. In the flumes, O. sanmarkii occurred only in very low velocity areas, L. inermis occurred widely throughout the flumes with highest density in low velocity areas and E. ignita also occurred throughout the flumes, but maximum density was in moderately high velocity areas. 3. Increased discharge did not reduce the total number of individuals in experimental versus control flumes for any of the three species studied, although total numbers did decrease over the observation period in both treatments. Simulated spates resulted in a change in the microdistribution of O. sanmarkii and E. ignita, but not L. inermis, such that numbers were reduced in very high velocity microhabitats and animals accumulated in lower flow areas, analogous to flow refugia. These distributional shifts were attributed to movements of individuals among microhabitats. 4. Both active and passive modes of movement contributed to the accumulation of E. ignita and O. sanmarkii in low flow microhabitats (i.e. flow refugia). Some nymphs of E. ignita actively crawled from high to low flow microhabitats. Both species drifted between microhabitats. Drift entry could be active or passive, whereas regaining the substratum was active: O. sanmarkii swam down and E. ignita altered its body posture to promote sinking.     

A novel method for the observation of membrane transporter dynamics.

A new method is proposed for measuring the dynamic properties of a membrane transporter by means of steady-state fluxes. Any voltage-sensitive transporter will give a flow of substrate in the presence of a steady-state periodic membrane potential. The periodic steady-state flow, averaged over one period, is a flux that can be measured by traditional steady-state techniques, such as the radioactive tracer method. The average flux, solely due to the periodic field, is described by a set of Lorentzian functions that depend on the applied periodic field amplitude and frequency. The normal mode amplitudes and frequencies of these Lorentzians are model-independent parameters of the transport mechanism. Measurement of the average flux as a function of the applied periodic frequency permits determination of system relaxation times as the reciprocals of the midpoints of the Lorentzian curves, which in turn can be used to estimate individual rate constants of specific models. It was found by simulation of a six-state model of the electrogenic Na+/glucose cotransporter, using published estimates of the model rate constants, that the periodic field effects can be large and rich with measurable details that can be used to study the mechanism thoroughly. The new method serves in this case to complement and expand on the information obtainable by means of the voltage clamp method. It was also found by means of simulations of a nonelectrogenic six-state cotransporter model that experimentally measurable effects are expected and that results can be used to distinguished among alternative kinetic models as well as to estimate individual rate constants.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chlorophyll content and factors affecting its spatial distribution in the Middle Volga reservoirs

On the basis of the data obtained during field observations in the summer low water period of 2001, the patterns of chlorophyll distribution and its relation to hydrological and hydrochemical factors in two eutrophic reservoirs of the Middle Volga are studied. The hydrological structure of the Gorky Reservoir, where the Volga water mass dominates, is homogeneous, while in the Cheboksary Reservoir along with the eutrophic Volga waters, the mesotrophic Oka water masses can be distinguished keeping their abiotic and biotic features over a long distance. Phytoplankton in the two contiguous reservoirs with different flow regimens and anthropogenic loads responds differently to the external influence. An autotrophic community in the Gorky Reservoir is more stable and depends little on abiotic factors which account for ∼63% of the explained chlorophyll variation. In the Cheboksary Reservoir under maximal for the Volga cascade flow velocity and anthropogenic load, the development and distribution of phytoplankton are almost completely (R ² = 0.93) controlled by these factors. The trophic state of the reservoirs has not changed as compared to the beginning of the 1990s.     

Periodic orbits near heteroclinic cycles in a cyclic replicator system

A species is semelparous if every individual reproduces only once in its life and dies immediately after the reproduction. While the reproduction opportunity is unique per year and the individual’s period from birth to reproduction is just n years, the individuals that reproduce in the ith year (modulo n) are called the ith year class, i = 1, 2, . . . , n. The dynamics of the n year-class system can be described by a differential equation system of Lotka–Volterra type. For the case n = 4, there is a heteroclinic cycle on the boundary as shown in previous works. In this paper, we focus on the case n = 4 and show the existence, growth and disappearance of periodic orbits near the heteroclinic cycle, which is a part of the conjecture by Diekmann and van Gils (SIAM J Appl Dyn Syst 8:1160–1189, 2009). By analyzing the Poincaré map near the heteroclinic cycle and introducing a metric to measure the size of the periodic orbit, we show that (i) when the average competitive degree among subpopulations (year classes) in the system is weak, there exists an asymptotically stable periodic orbit near the heteroclinic cycle which is repelling; (ii) the periodic orbit grows in size when some competitive degree increases, and converges to the heteroclinic cycle when the average competitive degree tends to be strong; (iii) when the average competitive degree is strong, there is no periodic orbit near the heteroclinic cycle which becomes asymptotically stable. Our results provide explanations why periodic solutions expand and disappear and why all but one subpopulation go extinct.     

Head movements of the mealworm beetle Tenebrio molitor

Tethered walking imagines of the mealworm beetle Tenebrio molitor wave their heads in random fashion. If a periodic pattern of vertical black and white stripes is rotated around the animal a regular nystagmic head movement is superimposed upon the random waving, the frequency of the latter equals the contrast frequency within large ranges of the angular velocity of the pattern. The nystagmus is inverted: After a short period of tracking, during which the angular velocity of the head is the same as that of the panorama, the head returns slowly toward its normal position according to an exponential-like function. Resting animals do not wave their heads. However, if the above panorama is rotated, the beetle turns its head in the direction of the movement of the panorama and holds it in a side-way position, as long as the rotation is maintained. The angular position reached depends in the same manner on the angular velocity of the panorama as the turning tendency of walking animals established in open loop experiments using the spherical Y-maze method.     

THE ECOLOGY OF CLADOPHORA

Cladophora is found in a variety of marine and fresh-waters and provides habitat and food for numerous organisms. It may be the most ubiquitous macroalga in fresh-waters worldwide. This filamentous green alga can reach nuisance levels as a result of cultural eutrophication. Taxonomic identification of Cladophora species is difficult. Taxonomy may be clarified by the simultaneous culture of known taxa and material derived from field collections under the same sets of culture conditions. This should eliminate ecotypic variations in morphology. Cladophora is predominantly benthic and is often found in regions of unidirectional flow or periodic wave action. Its metabolism, and morphology are related to hydrodynamic conditions. Nitrogen and phosphorus are the most commonly reported limiting nutrients. Cladophora is a mid- to late successional species in freshwaters where it is grazer resistant. In marine communities, however, it is considered an early opportunist and relatively palatable to invertebrates. Cladophora is colonized by a wide variety of epiphytes and motile animals because it can offer protection from predation, food (in the form of epiphytes or Cladophora itself), or a substrate that is anchored against flow disturbance. Species interactions that occur within Cladophora communities include 1) competition with other primary producers, 2) top-down control of biomass, 3) association with nitrogen-fixing epiphytes, 4) grazing on epiphytes by invertebrates, and 5) complicated foodwebs in marine intertidal and freshwater communities. Because Cladophora is found in many different habitats, its ecology varies significantly with locale.     

Seasonality of macrophytes and interaction with flow in a New Zealand lowland stream

Introduced submerged macrophytes have come to dominate many shallow water bodies in New Zealand, and are a common component of many lowland streams. We investigated the seasonal variation of macrophyte abundance, its influence on flow and channel volume, and the implications of this on stream habitat and functioning in Whakapipi Stream, a typical lowland stream draining a predominantly agricultural catchment.Abundance of macrophytes over the summer was primarily controlled by the phenological cycles of the two dominant species. Mean minimum total macrophyte biomass (36 g m^–2) and cover (7%) occurred in winter (June and August, respectively), and mean maximum biomass (324 g m^–2), and cover (79%) occurred in late summer (March and February respectively). Egeria densa comprised the majority of both cover and biomass during the study period, except early summer (December) when Potamogeton crispus was prevalent in the shallow stream reaches.Macrophyte beds had a major impact on summer stream velocities, reducing average velocities by an estimated 41%. Stream cross-sectional area was maintained at relatively stable levels similar to that recorded over winter, when stream discharge was in the order of seven times greater. The mean velocity distribution coefficient (), and Manning's roughness coefficient (n) were dependent on and displayed a positive linear relationship with macrophyte abundance. The velocity distribution coefficient is recommended as a better indicator of macrophyte effects on velocity in natural streams, as it does not assume uniform velocity, channel depth and slope within the stream reach.Our study shows that submerged macrophytes play an important structuring role within the stream during the summer period, where macrophyte beds act as semi-permeable dams, retarding flow velocities and increasing stream depth and cross-sectional area. This promotes habitat heterogeneity by creating a greater range of flow velocity variation, and also provides large stable low-flow areas. Other likely ecosystem effects resulting from macrophyte/velocity interactions include increased sedimentation, potential for nutrient processing and increased primary production, both by macrophytes and attached epiphyton. The complex architecture of submerged macrophytes and their influence on stream flow may also provide an increased diversity of habitat for other aquatic biota. We propose that management of degraded lowland streams such as the Whakapipi Stream to maintain stretches with moderate quantities of submerged macrophytes interspersed with shaded areas would optimise stream health during low summer flows.     

Experimental study on the fluid mechanics of blood sucking in the proboscis of a female mosquito

Female mosquitoes are known to have a magnificent micro-scale pumping system that can transport small quantities of blood very effectively. To understand the dynamic characteristics of blood flow inside female mosquitoes, the measurement technique that is capable of measuring instantaneous flow fields of a biological sample at micrometer scales is required. In this study, the blood-sucking flow inside a female mosquito's food canal was measured in vivo using a micro particle image velocimetry (micro-PIV) velocity field measurement technique with high-temporal resolution. The volumetric flow rate (Q) and the time-averaged feeding speed (V) based on the diameter of the food canal (D) was found to be 5.751×10^?3 mm³/s and 0.416 cm/s, respectively. Spectral analysis on the velocity waveform shows a clear peak at 6.1 Hz, indicating distinct pulsatile blood-sucking characteristics. The Womersley number (α) was about 0.117 and the velocity profile of the blood flow inside the proboscis has a parabolic Hagen–Poiseuille flow pattern when α is much smaller than 1.     

Blood velocity measurement in human conjunctival vessels

The bulbar conjunctiva is one of the few areas in which blood flow in the peripheral vasculature can be directly and noninvasively observed in the human. Although extensive literature exists describing morphological changes which correlate with a variety of systemic diseases in this vasculature, little quantitative data is available on hemodynamics in either normal or abnormal states. The hemodynamic data available are primarily subjective assessments of "low flow." Approaches to place the subjective assessment on more quantitative grounds have usually been based on photographic techniques that have intrinsic inadequacies. The objective of the work reported here was to develop a system capable of providing sequential blood velocity data potentially useful for providing quantitative information on blood flow and its change in the microvessels of the human conjunctiva. The method that has evolved uses a standard Zeiss slit-lamp to image a subject's conjunctival vessels by using a 1-inch Newvicon TV camera with an electronic magnification of 2x. The video image is simultaneously recorded on a video tape recorder (VTR) to an overall system magnification of approximately 4 microm/raster line. The data acquisition phase requires approximately 5 minutes of patient time, whereas the actual determination of blood velocity in individual vessels is done offline through a modification of the dual-slit videodensimetric method. Two independently controllable video cursors are placed axially over the vessel image with the VTR in the still-frame mode. For each consecutive video field, the position of two reference points on the vessel and the position of each cursor relative to these and to each other are encoded into a computer to track the moving image caused by normal eye movement. The computer then determines new cursor coordinates to ensure a constant position within the vessel. The electrical signals obtained for each cursor site and for each video field are cross-correlated to yield the average blood velocity over the sampled time interval. The system has been calibrated in vitro from 0.2 to 2.5 mm/sec, evaluated in experimental animals, and used to measure blood velocity (0.3 to 1.5 mm/sec) in human conjunctival venules with diameters ranging from 20 to 50 microm. At this writing, blood velocity has been recorded during a period of about 3 months in the same vessel of several postmyocardial infarction patients. Thus, the method appears suitable for determining sequential changes in small vessel blood flow in patients over extended periods of time.     

A contribution to the problem of the concept “biological clock” (part I)

Summary In the first parts of this study on the concept of the biological clock it has been investigated how it is used in the field of biorhythmology. The analysis of the contents of the concept is preceded by a survey of the current research in this field.There are two general hypotheses with respect to the ultimate origin of rhythmic phenomena: the Endogenous Timer Hypothesis and the Exogenous Timer Hypothesis. Within the Endogenous Timer Hypothesis two contrasting viewpoints with respect to the structure of the biological clock can be distinguished, which have been called: the Discrete Entity view, and the Organizational view.It has been shown that in the application of the general clock-idea upon the organism a logical distortion is present. The organism is conceived tobe a clock and tohave a clock simultaneously.In anticipation of the analysis of the explanatory value of the concept of the biological clock in part II, it has been put forward that in a number of cases time-measurement can be considered as a superfluous (redundant) element in the explanation of the phenomena involved.Finally it has been demonstrated that in the case of the Exogenous Timer Hypothesis the concept of the biological clock is not relevant. The Exogenous Timer Hypothesis has been compared with the Endogenous Timer Hypothesis with respect to the criterion of the principle of parsimony, orOccam's razor.List of rhythmological terms autonomous system not under the influence of a periodic source of energy,i.e. selfsustained and free oscillations - non-autonomous system under the influence of a periodic source of energy,i.e. forced oscillations whether in active or passive systems - period time after which a definite phase of the oscillation reoccurs - frequency reciprocal of period - phase instantaneous state of an oscillation within a period, represented by the value of the variable and all its time derivatives - phase angle value of the abscissa corresponding to a point of the curve (phase) given either in radians, in degrees or in other fractions of the whole period. It can be given in units of time, if the length of the period is stated - synchronization state in which two or more oscillations have the same frequency due to mutual or unilateral influences - entrainment coupling of a self-sustained oscillation to a Zeitgeber (forcing oscillation) with the result that either both oscillations have the same frequency (synchronization) or that the frequencies are integral multiples (frequency-demultiplication): possible only within limited ranges of frequencies - Zeitgeber that forcing oscillation which entrains a biological rhythm - free-running rhythms selfsustained oscillations under constant conditions - response-curve indicates, in biology, how the amount and the sign of a phase shift, induced by a single stimulus, depends on the phase in which the stimulus is applied     

Flow velocity underpins microhabitat selection by gobies of the Australian Wet Tropics

1. Water flow is a critical driver of aquatic ecosystem health and function. Amid rising concerns over changing flow regimes, there is an urgent need to understand the functional mechanisms by which flow influences patterns of freshwater biodiversity. 2. We explored the functional link between flow velocity and microhabitat specialisation in a speciose group of freshwater gobies (comprising over half the total fish species richness) within insular streams of the Australian Wet Tropics under base flow conditions. We addressed two particular questions: (i) What is the relative selectivity of species towards streambed composition and water flow velocity? and (ii) Can patterns of microhabitat occupation be explained by differences in intrinsic flow performance among species? To answer these questions, we combined visual field observations of microhabitat use with flow tank assessments of flow speed performance. 3. Tropical freshwater gobies displayed strong specificity towards flow velocities, while being relatively non‐selective towards streambed composition. At opposite extremes of the spectrum, we found Sicyopterus lagocephalus occupying high‐flow (>1.0 ms^?1) microhabitats while Redigobius bikolanus selected slower‐flow (<0.05 ms^?1) areas. These patterns of microhabitat flow specificity were largely explained by the different abilities of species to swim and/or cling to the substratum under these different flow settings. 4. Our findings confirm suggestions that predictable base flows in tropical streams support habitat specialists, which include one species capable of occupying areas of extremely high flow that very few other fishes can withstand. 5. The functional link between flow and gobioid fish distribution patterns could occur throughout tropical streams of the Indo‐Pacific and Caribbean as a widespread phenomenon that may help inform stream flow management guidelines to maintain this substantial component of tropical freshwater biodiversity around the globe.     

Measures of gene flow in the Columbian ground squirrel

From analyses of published data and a review of the literature, I studied indirect and direct measures of gene flow among populations of Columbian ground squirrels, Spermophilus columbianus. New analyses were used to examine an allozyme data set (seven polymorphic loci) that had been collected by Zammuto and Millar (1985a) from six populations of ground squirrels that were spread over 183 km. G-tests indicated significant variation in allele frequencies among populations, but F-statistics revealed relatively little population differentiation (average F _ST=0.026). F _ST values were used to estimate rates of gene flow indirectly and indicated fairly high rates of gene flow (average N _e m=13.5). Recorded dispersal distances of individual ground squirrels were fairly short (most<4 km, maximum recorded distance was 8.5 km), and the minimum distance between populations used to create the allozyme data set was about 25 km. Thus, direct dispersal among the populations in the allozyme data set was highly unlikely. Small genetically effective populations may have experienced high rates of migration over short distances (about 43% of adults in local populations were immigrants), however, resulting in homogeneous allele frequencies over the geographic range. This explanation provides an alternative to invoking gene flow in the recent past to explain discrepancies between dispersal distances in the field and homogenization of allele frequencies over large ranges, Mammalian species that have virtually complete dispersal of subadult males from the natal area might be expected to exhibit relatively high rates of gene flow, regardless of actual dispersal distances. Genetically effective populations may be much smaller than more extensive ecological populations and experience higher rates of gene flow.     

Dynamic measurement of the volumetric mass transfer coefficient in agitated vessels: Effect of the start-up period on the response of an oxygen electrode

The response of a polarographic oxygen electrode to a step change and to an exponential change in bulk oxygen concentration was studied theoretically and experimentally for the case where there is a significant liquid film resistance at the outerside of the membrane-covered electrode. The probe response has been described considering the start-up period of the concentration changes (the period of time that will elapse before the new concentration level is established and/or before the volumetric mass transfer coefficient k_La regains its steady-state value after the gas supply is opened to the fermentor). A linear change of the pertinent characteristics is assumed during this start-up period. It is shown that a substantial error could be introduced by neglecting the start-up period for cases frequently occurring in practice. In addition, the dependences of the probe response on the direct contact of bubbles with an electrode and on the fluid flow field around it were discussed.     

Evaluation of the heat pulse velocity technique for measurement of sap flow in rainforest and eucalypt forest species of south-eastern Australia

Sap flow in the stems of two cut saplings each of Eucalyptus maculata (a canopy eucalypt forest tree), Doryphora sassafras and Ceratopetalum apetalum (both canopy rainforest trees of south-eastern coastal Australia) was measured by the heat pulse velocity technique and compared with water uptake from a potometer. Scanning electron micrographs of wounding caused by implantation of temperature sensor and heater probes into the sapwood showed that wounding was similar in rainforest and eucalypt species and was elliptical in shape. A circular wound has been implicitly assumed in previous studies. Accurate measurements of sapling water use were obtained using the smaller transverse wound dimension rather than the larger longitudinal dimension because maximum disruption of sap flow through the xylem vessels occurred in the transverse plane. Accurate measurements of sap flux were obtained above a minimum threshold sap velocity. These velocities were 15·7,10·9 and 9·4 cm h^?1 for E. maculata, C. apetalum and D. sassafras, respectively. Below the threshold sap velocity, however, sap flow could not be accurately calculated from measurements of heat pulse velocity. The minimum threshold sap velocity appeared to be determined by probe construction and xylem anatomy. Despite the elliptical wounding and inaccurate measurement of sap flow below the threshold sap velocity, total sap flow over the experimental period for two saplings of each species was within 7% of water use measured by the potometer.     

Pheromone monitoring in the field using single sensillum recording

In order to obtain direct information of stimulus dynamics perceived by a male moth under field conditions a portable device was constructed which enables continuous recording of responses from individual pheromone receptors. The device is suitable for tip recording by means of micro-knives as well as for recording with tungsten electrodes making it applicable for a wide range of insects. A micro thermistor air velocity sensor is placed within 2 mm from the preparation to record the momentary air flow. The signal conditioning electronic circuits are battery powered, and the signals can be stored on a portable tape recorder. Field recordings were made from individual male antennal pheromone receptors ofAegeria myopaeformis andAdoxophyes orana. In all recordings the instantaneous firing frequency of the receptor cells was strongly modulated by the air velocity. Analysis of the data may provide information about the average pheromone concentration and the fine structure of pheromone plumes under various conditions.     

Towards a better model of the effect of prostrate vegetation cover on wind erosion

Vegetation cover is the key to controlling wind erosion. A brief review of wind erosion/cover models is outlined. Fryrear's (1985) soil cover (wheat stubble) model was evaluated against field wind tunnel results from far south-west N.S.W. Fryrear's equation over estimated the soil loss compared to field wind tunnel results.Fryrear's model failed to provide meaningful results at low cover levels with the soil loss ratio, SLR>1 for percent soil cover, % SC<6. A single parameter exponential model was fitted to the wind tunnel data which ensured that SLR did not exceed 1 for 100% SC. Even with this improvement, the exponential model has drawbacks.Results suggest that the SLR is sensitive to wind velocity and that SLR goes to 0 well before % SC=100. A method for approximating the threshold wind velocity required to initiate erosion for various cover levels is described. Using the recurrence interval for a prescribed wind velocity, the probability of erosion hazard for a field can be determined.It is the authors belief that the wind tunnel is underestimating the occurrence of wind erosion events in this study. Three reasons why the wind tunnel may be underestimating erosion events are given.