Time Lag In Response Research Articles

Population dynamics of microtine rodents: an experimental test of the predation hypothesis

One of the most popular hypotheses to explain the 3–5 year vole cycle in Fennoscandia is the predation hypothesis, which emphasises the role of specialist predators, especially small mustelids, in driving the microtine rodent cycle. I have tested this hypothesis in a field experiment with a focus on the interaction between the least weasel (Mustela nivalis nivalis L.) and the field vole (Microtus agrestis L.). The test involved a perturbation of the natural vole‐weasel dynamics by increasing the numbers of predators. In natural cyclic dynamics, the numbers of weasels follow the numbers of voles with a time lag; the delay in the numerical response of the predators essentially leads to the cyclic dynamics. In this experiment, I attempted to eliminate the time lag in predators' numerical response by adding weasels into the system at a point when vole numbers are increasing but weasels are still scarce. The experiment was conducted in three experimental islands (each 5–10 km2) using adjacent comparable islands as controls. Results of the experiment did not provide strong evidence either for or against the hypothesis. Two of three experimental areas did not show a treatment effect, while one area showed an effect in both population dynamics and population structure. Unexpectedly, the previously clearly cyclic dynamics were much less regular in the study areas (and elsewhere in southern Finland) during the period of the experiment.

Cyclic voles, prey switching in red fox, and roe deer dynamics – a test of the alternative prey hypothesis

Medium‐sized predators sometimes switch to alternative prey species as their main prey declines. Our objective of this study was to test the alternative prey hypothesis for a medium sized predator (red fox, Vulpes vulpes), a small cyclically fluctuating main prey (microtine voles) and larger alternative prey (roe deer fawns, Capreolus capreolus). We used long‐term time series (28 years) on voles, red fox and roe deer from the Grimsö Wildlife Research Area (59°40′N, 15°25′E) in south‐central Sweden to investigate interspecific relationships in the annual fluctuations in numbers of the studied species. Annual variation in number of roe deer fawns in autumn was significantly and positively related to vole density and significantly and negatively related to the number of fox litters in the previous year. In years of high vole density, predation on roe deer fawns was small, but in years of low vole density predation was more severe. The time lag between number of fox litters and predation on fawns was due to the time lag in functional response of red fox in relation to voles. This study demonstrates for the first time that the alternative prey hypothesis is applicable to the system red fox, voles and roe deer fawns.

Variable Response Time Lag Module for Car-Following Models: Development and Structuring with Fuzzy Set Theory

The car-following process consists of a stimulus-response relationship between vehicles in which the driver of the following vehicle reacts to the actions of the lead vehicle after a time lag. Since the 1950s, the car-following phenomenon has been studied and analyzed, resulting in various models and algorithms. Throughout this period, driver response time lag has always been assumed to be a constant value for the driver at all times, regardless of the approach and level of detail of the model. The primary shortcoming of a constant time lag is that it introduces a number of strong assumptions that do not concur with human nature. To address the problems associated with constant time lag, an independent response time lag module was developed that can be used in any car-following model or algorithm without changing its fundamental mathematical structure. One of the most appealing aspects of this module is its flexible and transparent structure that can easily be adapted to and calibrated for any model or simulation algorithm. The development and structure of the module are described, including the fuzzy definitions of driving states, fuzzy rule extraction, and fuzzy time lag assignment. Statistical and graphical evaluations of the module performance are also included by integrating the module to a proportional car-following model. In the graphical evaluation, the module improved the model performance significantly by providing more precise timing for the driver response. Both Kolmogorov–Smirnov and root-mean-square error tests confirmed that the use of the module improves the car-following model performance.

Performance of Spatially and Temporally Distributed Displays as a Function of Continuous versus Discrete Update Schedules

Generally, there are two ways to present monitored information: a traditional display that spatially distributes information across a screen or a temporally distributed display, which is the presentation of information serially in the center of a screen. Previous studies comparing these display formats have used methodologies in which changes in numerical information only occurred in view of the participant. This is beneficial for tight experimental control, but is not realistic since information can constantly change. The current study compared a spatially distributed display with a temporally distributed display and manipulated the updates to occur either in view, as in previous research, or continuously, even if out of view. Results showed a system response lag time in addition to participant reaction time for realistic settings and an increase in missed events not shown in previous research. These findings suggest that while a temporally distributed display is currently far from implementation, research shows promise for this technology.

Baseflow and peakflow chemical responses to experimental applications of ammonium sulphate to forested watersheds in north‐central West Virginia, USA

AbstractStream water was analysed to determine how induced watershed acidification changed the chemistry of peakflow and baseflow and to compare the relative timing of these changes. Two watersheds in north‐central West Virginia, WS3 and WS9, were subjected to three applications of ammonium sulphate fertilizer per year to induce acidification. A third watershed, WS4, was the control. Samples were collected for 8 years from WS9 and for 9 years from WS3. Prior to analyses, concentration data were flow adjusted, and the influence of natural background changes was removed by accounting for the chemical responses measured from WS4. This yielded residual values that were evaluated using robust locally weighted regression and Mann–Kendall tests. On WS3, analyte responses during baseflow and peakflow were similar, although peakflow responses occurred soon after the first treatment whereas baseflow responses lagged 1–2 years. This lag in baseflow responses corresponded well with the mean transit time of baseflow on WS3. Anion adsorption on WS3 apparently delayed increases in SO4 leaching, but resulted in enhanced early leaching losses of Cl and NO3. Leaching of Ca and Mg was strongly tied, both by timing and stoichiometrically, to NO3 and SO4 leaching. F‐factors for WS3 baseflow and peakflow indicated that the catchment was insensitive to acid neutralizing capacity reductions both before and during treatment, although NO3 played a large role in reducing the treatment period F‐factor. By contrast, the addition of fertilizer to WS9 created an acid sensitive system in both baseflow and peakflow. On WS9, baseflow and peakflow responses also were similar to each other, but there was no time lag after treatment for baseflow. Changes in concentrations generally were not as great on WS9 as on WS3, and several ions showed no significant changes, particularly for peakflow. The lesser response to treatment on WS9 is attributed to the past abusive farming and site preparation before larch planting that resulted in poor soil fertility, erosion, and consequently, physical and chemical similarities between upper and lower soil layers. Even with fertilizer‐induced NO3 and SO4 leaching increases, base cations were in low supplies and, therefore, unavailable to leach via charge pairing. The absence of a time lag in treatment responses for WS9 baseflow indicates that it has substantially different flow paths than WS3. The different hydrologies on these nearby watersheds illustrates the importance of understanding watershed hydrology when establishing a monitoring programme to detect ecosystem change. Published in 2002 by John Wiley & Sons, Ltd.

Multi-scale landscape and seascape patterns associated with marbled murrelet nesting areas on the U.S. west coast

Habitat for wide-ranging species should be addressed at multiple scales to fully understand factors that limit populations. The marbled murrelet (Brachyramphus marmoratus), a threatened seabird, forages on the ocean and nests inland in large trees. We developed statistical relationships between murrelet use (occupancy and abundance) and habitat variables quantified across many spatial scales (statewide to local) and two time periods in California and southern Oregon, USA. We also addressed (1) if old-growth forest fragmentation was negatively associated with murrelet use, and (2) if some nesting areas are more important than others due to their proximity to high quality marine habitat. Most landscapes used for nesting were restricted to low elevation areas with frequent fog. Birds were most abundant in unfragmented old-growth forests located within a matrix of mature second-growth forest. Murrelets were less likely to occupy old-growth habitat if it was isolated (> 5 km) from other nesting murrelets. We found a time lag in response to fragmentation, where at least a few years were required before birds abandoned fragmented forests. Compared to landscapes with little tono murrelet use, landscapes with many murrelets were closer to the ocean's bays, river mouths, sandy shores, submarine canyons, and marine waters with consistently high primary productivity. Within local landscapes (≤ 800ha), inland factors limited bird abundance, but at the broadest landscape scale studied (3200 ha), proximity to marine habitat was most limiting. Management should focus on protecting or creating large, contiguous old-growth forest stands, especially in low-elevation areas near productive marine habitat.

Response times of carbon fiber microelectrodes to dynamic changes in catecholamine concentration.

The electrode response time and the measured concentrations during dynamic catecholamine changes were compared using constant potential amperometry and fast-scan cyclic voltammetry. The amperometric response to a rectangular pulse of catecholamine is more rectangular than the cyclic voltammetric response; however, the response times are very similar when, during cyclic voltammetry, the temporal lag due to adsorption and desorption of catecholamine to the electrode is removed by deconvolution. Deconvolution of cyclic voltammetry data was applied to stimulated dopamine release in vivo, allowing for modeling of release and uptake kinetics and to measure catecholamine release from single cells, resulting in better resolution of peaks from single vesicles. In vitro postcalibrations were performed to calculate concentrations of catecholamine measured with cyclic voltammetry and amperometry. The addition of 600 microM ascorbic acid to the postcalibration buffer, allowing a catalytic reaction to regenerate dopamine, resulted in similar calculated concentrations for stimulated release of dopamine using amperometry and cyclic voltammetry. Using deconvoluted cyclic voltammetry to remove the response time lag and adding ascorbic acid to the calibration buffer, the shape and concentration of dynamic catecholamine changes are very similar when measured with constant potential amperometry and cyclic voltammetry.

Vegetational response of rainfall in Rajasthan using AVHRR imagery

The purpose of this paper is to demonstrate the suitability of NOAA-AVHRR imagery for monitoring vegetal cover. Of course, climate is recognized as the most important control on natural vegetation. However, spatial and seasonal changes in land cover are dependent on several factors including the crop species, soil hydrology, grazing conditions, harvest timing and above all on the frequency and amount of rainfall. The analysis is based on six maximum value composite (MVC) NDVI images with a spatial resolution of approximately 5.5 km. An attempt has also been made to examine the serial relationship between the NDVI and the rainfall occurrences at different stations. ‘Thar Desert’ is clearly visible in the images of summer months. A transitional zone is situated between the arid and semi-arid areas along the western fringe of the Aravalli Range. The elimination of time lag in vegetational response of rainfall indicates expected positive relationship between vegetal cover and rainfall.

Prescribed Burning to Restore Mixed‐Oak Communities in Southern Ohio: Effects on Breeding‐ Bird Populations

Abstract: Fire is being experimentally reintroduced to the forests of southern Ohio to determine its effectiveness in restoring and maintaining mixed‐oak ( Quercus spp.) forest communities. We studied the effects of repeated burning (1–4 years of annual burning) and recovery (1 year after burning ) on the breeding bird community. Burning resulted in incremental but temporary reductions in the availability of leaf litter, shrubs, and saplings, but it did not affect trees, snags, or understory vegetation cover. Of 30 bird species monitored, 4 were affected negatively and 2 were affected positively by burning. Population densities of Ovenbirds ( Seiurus aurocapillus), Worm‐eating Warblers ( Helmitheros vermivorus), and Hooded Warblers ( Wilsonia citrina) declined incrementally in response to repeated burning and did not recover within 1 year after burning, suggesting a lag time in response to the changes in habitat conditions. Densities of Northern Cardinals ( Cardinalis cardinalis) fluctuated among years in the control units, but remained low in the burned units. Densities of American Robins ( Turdus migratorius) and Eastern Wood‐Pewees ( Contopus virens) increased in response to burning, but these increases were apparent only after several years of repeated burning. In general, burning resulted in short‐term reductions in the suitability of habitat for ground‐ and low‐shrub‐nesting birds, but it improved habitat for ground‐ and aerial‐foraging birds. Overall, there were no changes in the composition of the breeding‐bird community. Total breeding bird population levels were also unaffected by burning. Our results suggest that prescribed burning applied on a long‐term basis or across large spatial scales is likely to have adverse effects on ground‐ and low‐shrub‐nesting bird species, but other changes in the composition of the breeding‐bird community are likely to be minimal as long as the closed‐canopy forest structure is maintained within the context of prescribed burning.

The Late Cenozoic Eridanos delta system in the Southern North Sea Basin: a climate signal in sediment supply?

ABSTRACT The Eridanos fluvio‐deltaic system, draining most of north‐western Europe, developed during the Late Cenozoic as a result of simultaneous uplift of the Fennoscandian shield and accelerated subsidence in the North Sea Basin. This seismo‐stratigraphic study aims to reconstruct the large‐scale depositional architecture of the deltaic portion of the basin fill and relate it to external controls. A total of 27 units have been recognized. They comprise over 62×103 km3 in the Southern North Sea Basin alone, and have an average delta surface area of 28×103 km2, which suggests that the size of the drainage area was about 1.1×106 km2. Water depth in the depocentre is seen to decrease systematically over time. This trend is interrupted by a deepening phase between 6.5 and 4.5 Ma that can be correlated with the simultaneous occurrence of increased uplift of the Fennoscandian shield, increased subsidence of the Southern North Sea Basin, and a long‐term eustatic highstand. All these observations point to a tectonic control on long‐term average rates of accommodation and supply. Controls on short‐term variations are inferred from variations in rates of sediment supply and bifurcation of the delta channel network. Both rates were initially low under warm, moist, relatively stable climate conditions. The straight wave‐dominated delta front gradually developed into a lobate fluvial‐dominated delta front. Two high‐amplitude sea‐level falls affected the Pliocene units, which are characterized by widespread delta‐front failures. Changes in relative sea level and climate became more frequent from the late Pliocene onward, as the system experienced the effects of glacial–interglacial transitions. Peaks in sedimentation and bifurcation rates were coeval with cold (glacial) conditions. The positive correlation between rates of supply and bifurcation on the one hand, and climate proxies (pollen and δ18O records) on the other hand is highly significant. The evidence presented in this study convincingly demonstrates the control of climate on time‐averaged sediment supply and channel‐network characteristics, despite the expected nonuniformity and time lags in system response. The presence of a clearly discernible climate signal in time‐averaged sediment supply illustrates the usefulness of integrated seismo‐stratigraphic studies for basin‐wide analysis of delta evolution on geological time scales.

Intermediate resolution H$\mathsf{\beta}$ spectroscopy and photometric monitoring of 3C 390.3

We have monitored the AGN 3C 390.3 between 1995 and 2000. A historical B-band light curve dating back to 1966 shows a large increase in brightness during 1970-1971, followed by a gradual decrease down to a minimum in 1982. During the 1995-2000 lapse the broad Hβ emission and the continuum flux varied by a factor of ≈3. Two large amplitude outbursts, of different duration, in continuum and light were observed i.e.: in October 1994 a brighter flare that lasted ≈1000 days and in July 1997 another one that lasted ≈700 days were detected. The response time lag of the emission lines relative to flux changes of the continuum has been found to vary with time i.e. during 1995-1997 a lag of about 100 days is evident, while during 1998-1999 a double valued lag of ≈100 days and ≈35 days is present in our data. The flux in the Hβ wings and line core vary simultaneously, a behavior indicative of predominantly circular motions in the BLR. Important changes of the Hβ emission profiles were detected: at times, we found profiles with prominent asymmetric wings, like those normaly seen in Sy1s, while at other times, we observe profiles with weak, almost symmetrical wings, similar to those of Sy1.8s. We further dismiss the hypothesis that the double peaked profiles in this object originate in a massive binary BH. Instead, we found that the radial velocity difference between the red and blue bumps is anticorrelated with the light curves of Hβ and continuum radiation. This implies that the zone that contributes most of the energy to the emitted line changes in radius within the disk. The velocity difference increases, corresponding to smaller radii, as the continuum flux decreases. When the continuum flux increases the hump velocity difference decreases. These transient phenomena are expected to result from the variable accretion rate close to the central source. The optical continuum and the flux variations might be related to changes in X-ray emission modulated by a variable accretion rate, changing the surface temperature of the disk, as a result of a variable X-ray irradiation (Ulrich [CITE]). Theoretical profiles were computed for an accretion disk, the observed profiles are best reproduced by an inclined disk () whose region of maximum emission is located roughly at 200 Rg. The mass of the black hole in 3C 390.3, estimated from the reverberation analysis is , 5 times larger than previous estimates (Wandel et al. [CITE]).

Rear-End Collision–Warning System: Design and Evaluation via Simulation

The design of an innovative rear-end collision-warning system was evaluated for effectiveness. The crash scenario involves a lead vehicle not moving (LVNM) in one lane of a straight, dry, paved arterial road and a following vehicle approaching in the same lane. The LVNM has a rearfacing sensor and is equipped with the rear crash-warning system, which allows the LVNM to flash its brake lights or its center high-mounted stop lamp, warning the following vehicle that it is approaching too rapidly. Because this problem is complex, the scope was narrowed, and it was assumed that the driver of the following vehicle always detected the warning after a response time lag and then applied hard braking. The warning algorithm (i.e., selecting the most appropriate warning distance for each approaching vehicle speed) was designed based on trade-offs to maximize the capability of preventing crashes, reduce the frequency of nuisance alarms, and minimize the severity of crashes. The overall measures of effectiveness of the warning design were then evaluated for a vehicle speed distribution that represented a suburban arterial road. The findings suggest that the warning system should be very effective in preventing crashes. The expected number of nuisance alarms was small, and for the very small percentage of vehicles that would crash, the expected crash severity was negligible. Experimental studies and field operational tests would be required to obtain more accurate numerical values for the design parameters.

Close association between day-to-day fluctuation of atmospheric pressure and blood pressure

We frequently see patients whose symptoms are aggravated by the change of weather. Some people can predict the change of weather by their feeling or symptoms, such as headache, articular pains and dizziness. We can vaguely recognize the association between weather and physical condition but little scientific attention has been paid to this and there insufficient proof about this. The association was examined between 14 consecutive day-to-day fluctuations of atmospheric pressure (AP) and systolic blood pressure (SBP) in community-dwelling individuals in consideration of time lag or precedence of the response of SBP to AP within a few days. The subjects were 406 community -dwelling residents (178 men and 228 women) aged 15 years or older, mean (SD) age 64.8 (14.4) years. Many subjects (42.1 %) showed a significant positive (21.7%, R = 0.52 ∼ 0.88, P < 0.05) or negative (20.4%, R = −0.52 ∼ −0.86, P < 0.05) correlation between AP and SBP. This result showed a close association between the day-to-day fluctuations of AP and BP in consideration of the varying responsiveness of BP to AP, i.e. there was a time lag and precedence of response of BP over AP, which was probably due to the high sensitivity of BP to initial changes in AP. Further investigations are needed on the effects of AP on the human autonomic nervous system and also on the association between AP and the human physiological or pathological condition.

Correlations between Burrowing Owl and Black-Tailed Prairie Dog Declines: A 7-Year Analysis

Concern over the status of species associated with prairie dog colonies has increased with the recent proposed listing of black-tailed prairie dogs (Cynomys ludovicianus). We monitored burrowing owl (Athene cunicularia) populations and prairie dog densities in 17 black-tailed prairie dog colonies in the Nebraska panhandle between 1990 and 1996. All prairie dog colonies were controlled at least once during the study. We observed a 63% decline in nesting pairs of burrowing owls and significant declines in burrow densities. Results indicated a time lag in owl response to changes in active burrow densities. However, in the later years of the study when burrow densities were lowest, owl numbers were positively correlated with the density of active burrows in the same years, indicating active burrows may become more important as burrow density declines. We also monitored fledging success of burrowing owls for 398 nesting attempts over 5 years (1989-93) for a larger set of colonies that included the 17 used in the owl and prairie dog monitoring. Differences in mean fledging success among colonies each year (colony effect) explained most of the variation in fledging success among nesting owls. Vulnerability to badger (Taxidea taxus) predation may in part explain differences in fledging success among colonies; badger predation on owl nests was lower when densities of active prairie dog burrows were high. Efforts are needed to ensure preservation of black-tailed prairie dog colonies for burrowing owls and other species associated with this prairie ecosystem, and to better monitor changes in burrowing owl and prairie dog populations.

Cellular growth of host and symbiont in a cnidarian-zooxanthellar symbiosis.

The hydroid Myrionema ambionense, a fast-growing cnidarian (doubling time = 8 days) found in shallow water on tropical back-reefs, lives in symbiosis with symbiotic dinoflagellates of the genus Symbiodinium (hereafter also referred to as zooxanthellae). The symbionts live in vacuoles near the base of host digestive cells, whereas unhealthy looking zooxanthellae are generally located closer to the apical end of the host cell. Cytokinesis of zooxanthellae occurred at night, with a peak in number of symbionts with division furrows (mitotic index, MI = 12%-20%) observed at dawn. The MI of zooxanthellae decreased to near zero by the middle of the afternoon and remained there until the middle of the next night. Densities of live zooxanthellae living inside of host digestive cells peaked following cytokinesis, whereas densities of unhealthy looking symbionts were highest just before the division peak. Mitosis of host digestive cells was highest in the evening, also preceding the peak in zooxanthellar MI. This is the first study relating phased host cell division to diel zooxanthellar division in marine cnidarians. Food vacuoles were prevalent inside of digestive cells of field-collected hydroids within a few hours after sunset and throughout the night, coinciding with digestion of captured demersal plankton. Laboratory experiments showed that food vacuoles appeared in digestive cell cytoplasm within 2 h of feeding with nauplii of Artemia. The number and size of food vacuoles per digestive cell and the percentage of digestive cells with food vacuoles all decreased 5-7 h following feeding in laboratory experiments, and by mid-day in field-collected hydroids. Light and external food supply were important in maintaining phased division of the symbionts, with a lag in response time to both parameters of 11-36 h. Altering light and feeding during the night did not influence the level of the peak MI the next morning, though in one experiment the absence of light slowed final separation of daughter cells at the end of cytokinesis. In another experiment, hydroids starved for 3-7 d and "pulse-fed" Artemia nauplii for 1 h at the beginning of the dark period showed continued low symbiont division (< 5%) after 11 h, whether maintained in constant light or darkness, implying that most algal division is set more than 24 h prior to actual cytokinesis. Transferred to a 14:10 h light:dark cycle for another 24 h (36 h after feeding), the same hydroids exhibited a "normal" peak MI (ca. 15%) at dawn, but zooxanthellae from hydroids kept in constant darkness still showed a low MI. These results show that mitosis of symbiotic dinoflagellates requires three factors: external food; a minimum period of time following feeding (11-36 h), presumably for digestion; and a period of light following feeding, presumably to provide carbon skeletons necessary for completing cytokinesis.

PLANT DIVERSITY IN MANAGED FORESTS: UNDERSTORY RESPONSES TO THINNING AND FERTILIZATION

Although most temperate forests are actively managed for timber production, few data exist regarding the long-term effects of forest management on understory plant communities. We investigated the responses of understory communities to a factorial combination of silvicultural-thinning and nutrient-addition treatments maintained for 12–16 yr in a set of 21–27 yr old Douglas-fir (Pseudotsuga menziesii) plantations. The four thinning levels span those used operationally (final stem densities of 494–1680 trees/ha); the two fertilization levels included a control and N addition in the form of urea at ∼60 kg N·ha−1·yr−1, about twice the dosage used operationally. Understory vegetation cover showed significant effects of thinning, with the highest thinning level resulting in the highest observed cover values. However, in some cases low levels of thinning resulted in a reduction in understory cover compared to unthinned controls. Understory vegetation declined dramatically in response to urea fertilization, with up to a 10-fold drop in herb-layer cover in unthinned stands. Species richness showed a simpler response to treatments, increasing in response to thinning, but decreasing in response to fertilization. Examination of species–area relationships indicated that effects of thinning and fertilization on species richness were similar across the range of spatial scales examined. Tree canopy cover, assessed by means of hemispherical photograph analysis, increased with fertilization, and estimated understory light levels decreased with fertilization, but neither showed a significant response to thinning at the time of measurement (12–16 yr after tree removal). Thus, treatment effects on understory cover and species richness were not a simple function of canopy cover or estimated light availability. Rather, there was a weak positive relationship between estimated understory light flux and vascular plant cover and diversity in nonfertilized plots, and no such relationship in fertilized plots. The lack of correspondence between treatment effects on canopy cover and understory vegetation may be due to time lags in understory response to changes in canopy cover or to treatment effects not mediated by light availability, such as physical disturbance during thinning operations and toxicity responses following application of urea fertilizer. Species-specific responses to treatments were in part predictable as a function of plant life-form and edaphic association: species affinity for high soil moisture was the best predictor of fertilization responses, while life-form was the best predictor of thinning responses, with ferns and graminoids showing the largest positive responses to thinning. The successional status and stature of understory plant species were not significantly related to treatment responses. In sum, our results indicate that silvicultural thinning and fertilization can have large effects on understory plant diversity and community composition. However, such effects were not a simple function of understory light levels, and conventional “functional types” were of only limited value in predicting species-specific responses to silvicultural treatments.

PREDICTION OF ALLUVIAL SYSTEM WITH SAND WAVES UNDER UNSTEADY CONDITIONS IN GRADED SEDIMENT BED

Temporal responses of sand waves, mean flow depth and reach averaged sediment transportation rate due to periodic change of flow discharge were investigated on the basis of flume tests using the graded and the uniform sediment. They were also predicted by taking the reference grain size for sand wave transformation into account. The predicted results were verified with the experimental results. From the results of experiments and predictions, it was found that the width of loop in the graphs of dischargewave height and discharge-flow depth for the graded sediment were smaller than that for the uniform one under same flow discharge condition. Therefore, time lag of response for the graded sediment is smaller than that for the uniform one. And, the peaks of wave length, wave height and flow depth indicated the positive time-lag to the peak of flow discharge, while the peak of sediment transportation rate indicated the negative time-lag to it.

Establishing a therapeutic index for the inhaled corticosteroids: Part I: Pharmacokinetic/pharmacodynamic comparison of the inhaled corticosteroids

The inhaled corticosteroids contain physicochemical differences that alter both glucocorticoid receptor-binding characteristics and the pharmacokinetic variables of these drugs. Differences in receptor-binding affinity translate into differences in potency for different drugs. Differences in pharmacokinetics, however, determine the topical effect to systemic effect ratio, or the “pulmonary targeting” of the drug. Beneficial pharmacokinetic properties that may improve pulmonary targeting include low oral bioavailability, rapid systemic clearance, and slow absorption from the lung. Delivery devices can produce clinically significant differences in topical activity by altering the dose deposited in the lung and, for orally absorbed drugs, the amount deposited in the oropharynx and swallowed. Clinical trials have confirmed that differences in potency or drug delivery of 2-fold or more can be detected in patients with asthma. However, because of the relatively flat nature of the dose-response curve for morning peak expiratory flow and forced expiratory volume in 1 second, the trials must be adequately powered and well controlled. The use of bronchial provocation measures are problematic because of the prolonged lag time for response. Study design flaws can lead to misinterpretation of results. Clinical studies have indicated the following relative potency differences: fluticasone propionate > budesonide = beclomethasone dipropionate > triamcinolone acetonide = flunisolide. Current evidence suggests that potency differences can be overcome by giving larger doses of the less potent drug. However, because of these potency differences, studies of systemic effects should not be done in isolation of adequate topical activity studies to define the pulmonary targeting of the drugs. (J Allergy Clin Immunol 1998;102:S36-S51)

Computer simulation of transport processes in biosensor microreactors

Abstract Microelectronic ferment reactors are finding increasing employment as base elements of biosensor matrices. In this work, a computer simulation of a microelectronic reactor based on ion-sensitive elements, such as transistor or electrolyte—insulator—semiconductor structure, is presented. Our objective involved elucidation of quantitative relations between the sensor design and its characteristics. The computer simulation is performed for different versions of both enzyme carriers and their positions in the microreactor cell. The results of simulation enabled us to optimise both design and all-over dimensions of the microreactor. The principal sensor parameters (such as response rate, amplitude and time lag) are calculated for the optimum cell. A comparison between the calculated models and the corresponding experimental results obtained with the help of considered types of microreactors is carried out.

Effects of Bacillus thuringiensis israelensis (BTI) and Methoprene on Nontarget Macroinvertebrates in Minnesota Wetlands

We studied the effects of the mosquito larvicides methoprene and Bacillus thuringiensis israelensis (Bti) on the benthic macroinvertebrate communities of 27 wetland ecosystems in Wright County, Minnesota. These larvicides are generally considered safe for nontarget species. After 3 yr of preliminary investigations, including 2 yr of intensive sampling, larvicide treatments were applied during 1991–1993. Nine of the wetlands were experimentally treated with methoprene, which disrupts insect development; an additional set of nine wetlands were treated with Bti, a microbial larvicide; and nine wetlands were left untreated to serve as a control treatment. In general, insecticide treatment had minimal effects on nontarget groups during the first treatment year. However, during 1992, highly significant reductions due to both methoprene and Bti were observed in several insect groups. Predatory insects were reduced on methoprene-treated sites but not Bti-treated sites in 1992. In 1993, treatment with both larvicides resulted in wetland communities that were depauperate in most insects. Although effects were observed broadly across insect taxa, Diptera, which comprised 79% of the insects, were affected most strongly, especially the dipteran suborder Nematocera, which included 71% of total insects and was dominated by Chironomidae. Minimal effects on noninsect macroinvertebrates were observed. Bti- and methoprene-treated sites also showed a reduction in richness of insect genera and an increased tendency to be dominated by one or a few genera. Pretreatment data, collected under drought conditions from the same wetlands, showed that the benthic macroinvertebrate fauna was dominated by mollusks during the drought but became increasingly dominated by insects during the wetter years. On the treated sites, insects remained at low density, very similar to the drought conditions, but the noninsect macroinvertebrates declined on treated sites in the same pattern as on control sites. Both indirect effects and direct toxicity likely contributed to the observed differences. Bti is likely to be directly toxic only to nematoceran Diptera; thus effects of Bti on other insect groups may have resulted from disruption of the invertebrate food web. Methoprene is more broadly toxic; thus observed methoprene effects on nonnematoceran groups may have been due to either direct toxicity or food web effects, or both. The 2–3 yr lag time in response of nontarget insects to larvicide treatment demonstrates the need for long-term studies in wetland ecosystems, and the need to reconsider the conclusions based on previous short-term studies that these larvicides are environmentally safe.