Showing papers by "Carleton University published in 1997"

The modeling, characterization, and design of monolithic inductors for silicon RF IC's

Abstract: The results of a comprehensive investigation into the characteristics and optimization of inductors fabricated with the top-level metal of a submicron silicon VLSI process are presented. A computer program which extracts a physics-based model of microstrip components that is suitable for circuit (SPICE) simulation has been used to evaluate the effect of variations in metallization, layout geometry, and substrate parameters upon monolithic inductor performance. Three-dimensional (3-D) numerical simulations and experimental measurements of inductors were also used to benchmark the model accuracy. It is shown in this work that low inductor Q is primarily due to the restrictions imposed by the thin interconnect metallization available in most very large scale integration (VLSI) technologies, and that computer optimization of the inductor layout can be used to achieve a 50% improvement in component Q-factor over unoptimized designs.

The Differential Effect of Storybook Reading on Preschoolers' Acquisition of Expressive and Receptive Vocabulary.

Abstract: The present study was conducted to assess the effect of didactic techniques used during storybook reading on young children's acquisition of new vocabulary introduced in storybooks. Thirty children for each group of three- and four-year-old children were read one storybook individually. The study included three storybook reading conditions: single-reading, repeated-reading and questioning. In both the repeated-reading and the questioning conditions, the storybook was read three times. Children in the questioning condition were asked, during each reading of the storybook, to label target items with the novel words. Listening to multiple readings of a storybook facilitated children's acquisition of expressive and receptive vocabulary, whereas answering questions during the multiple readings was more helpful to the acquisition of expressive than receptive vocabulary. These findings suggest that, under certain conditions, didactic techniques used by adults have differential effects on preschoolers' receptive and expressive vocabulary.

Geochemistry, genesis, and health implications of fluoriferous groundwaters in the upper regions of Ghana

Abstract: The most appropriate and widely used source of drinking water for the populations of the upper regions of Ghana is groundwater. In general, groundwater quality is acceptable except for some parts of the Bolgatanga and Bongo Districts, where there are occurrences of elevated levels of natural groundwater fluoride. Concentrations of groundwater fluoride in excess of the World Health Organization (WHO) maximum guideline value (1.5 mg/l) in the Bongo area have been known since 1978. However, the effect of fluoride on people ingesting the water did not receive public and medical attention until October 1993, when health personnel were asked to investigate the cause of stained teeth in school children. The investigation established that 62% of the total population of school children in the Bongo area had dental fluorosis. Against this background, a study was initiated to understand the geochemistry, genesis, and distribution of fluoride in relation to the geology of the area. Groundwater fluoride in the upper regions ranges from 0.11 to 4.60 ppm, with the highest concentrations associated with the fluorine-enriched Bongo coarse-grained hornblende granite and syenite suite. The source of groundwater fluoride within the Bongo granitoids is dissolution of the mineral fluorite and dissolution of and anion exchange with micaceous minerals and their clay products. Applying the WHO recommended guideline values for fluoride in drinking water reveals that 49% of wells in the area deliver water below the optimum level of 0.5 mg/l F–; these populations are thus prone to dental caries. Twenty-eight percent of the wells fall within the optimum interval for good dental health (0.5–1.5 mg/l F–). Twenty-three percent of the wells have concentrations above the recommended maximum guideline limit of 1.5 mg/l F–; this population is susceptible to dental and possibly skeletal fluorosis. Climatic conditions of the area suggest that the individual water consumption is in the order of 3 to 4 l which is higher than the WHO estimate of 2 l/adult/day. In addition, dietary intake for the upper region population is probably higher than WHO baseline values (0.2–0.5 mg/day). This implies that a much higher population is susceptible to developing dental and skeletal fluorosis than originally suspected. Geochemical symbol plot maps help geochemists understand factors controlling the distribution and uptake of fluoride in the upper regions, but they are of minimal value to health officials responsible for planning epidemiological studies and dental health education programs in the region. By casting fluoride data into contoured 'geochemical health-risk maps' using intake interval guidelines more closely aligned to regional climatic and dietary conditions, health officals can better judge the impacts (regional and population based) of fluoride on segments of the population, such as various sex and age groups.

A critique of fixed and progressive ratio schedules used to examine the neural substrates of drug reinforcement.

Abstract: This paper is a critique of fixed and progressive ratio schedules used to examine the neural substrates of cocaine reinforcement. The discussion focuses on problems encountered while examining the effects of neurotoxic lesions and pharmacological pretreatments on cocaine reinforcement. We review the theoretical and interpretational problems associated with the use of the fixed ratio (FR) schedules that have been used in the majority of studies, and we conclude that rate of drug intake cannot directly address the issue of increased or decreased reinforcer efficacy. The progressive ratio (PR) schedule offers some advantages over FR schedules, although it is now clear that the same implementation cannot be applied across all drug classes. It is likely that the motivation to self-administer psychostimulant vs. opiate drugs is qualitatively different. We conclude that there is no single schedule that can quantify all aspects of drug reinforcement and that behavioral paradigms will need to be adapted according to the particular question under study.

Modeling finite-fault radiation from the ωn spectrum

Abstract: The high-frequency seismic field near the epicenter of a large earth- quake is modeled by subdividing the fault plane into subelements and summing their contributions at the observation point. Each element is treated as a point source with an o92 spectral shape, where co is the angular frequency. Ground-motion contributions from the subsources are calculated using a stochastic model. Attenuation is based on simple geometric spreading in a whole space, coupled with regional anelastic atten- uation (Q operator). The form of the co n spectrum with natural n follows from point shear-dislocation theory with an appropriately chosen slip time function. The seismic moment and comer frequency are the two parameters defining the point-source spectrum and must be linked to the subfanlt size to make the method complete. Two coefficients, Aa and K, provide this link. Assigning a moment to a subfault of specified size introduces the stress parameter, Ao-. The relationship between comer frequency (dislocation growth rate) and fault size is established through the coefficient K, which is inherently nonunique. These two parameters control the number of subsources and the ampli- tudes of high-frequency radiation, respectively. Derivation of the model from shear- dislocation theory reveals the unavoidable uncertainty in assigning ogn spectrum to faults with finite size. This uncertainty can only be reduced through empirical vali- dation. The method is verified by simulating data recorded on rock sites near epicenters of the M8.0 1985 Michoacan (Mexico), the M8.0 1985 Valparaiso (Chile), and the M5.8 1988 Saguenay (Qurbec) earthquakes. Each of these events is among the largest for which strong-motion records are available, in their respective tectonic environ- ments. The simulations for the first two earthquakes are compared to the more de- tailed modeling of Somerville et al. (1991), which employs an empirical source function and represents the effects of crustal structure using the theoretical impulse response. Both methods predict the observations accurately on average. The precision of the methods is also approximately equal; the predicted acceleration amplitudes in our model are generally within 15% of observations. An unexpected result of this study is that a single value of a parameter K provides a good fit to the data at high frequencies for all three earthquakes, despite their different tectonic environments. This suggests a simplicity in the modeling of source processes that was unanticipated.

Regime switching in stock market returns

Abstract: An extension of Hamilton's Markov switching techniques (Hamilton, J. B., 1989, A new approach to the economic analysis of nonstationary time series and the business cycle, Econometrica, 57, 357–84) is used to describe and analyse stock market returns. Using new tests, very strong evidence is found for switching behaviour. A major innovation is to use a multivariate specification that allows examination of whether the price/dividend ratio has marginal predictive power for stock market returns after accounting for state-dependent switching. We find strong evidence of predictability. The response of returns to the past price/dividend ratio is strongly asymmetric - about four times larger in the low-return state than in the high-return state. A second innovationis to allow the probability of transitions from one regime to another to depend on economic variables; again there is an asymmetric response to the past price/dividend ratio.

Knowledge-based neural models for microwave design

Abstract: Neural networks have recently been introduced to the microwave area as a fast and flexible vehicle to microwave modeling, simulation and optimization. In this paper, a novel neural network structure, namely, knowledge-based neural network (KBNN), is proposed where microwave empirical or semi-analytical information is incorporated into the internal structure of neural networks. The microwave knowledge complements the capability of learning and generalization of neural networks by providing additional information which may not be adequately represented in a limited set of training data. Such knowledge becomes even more valuable when the neural model is used to extrapolate beyond training data region. A new training scheme employing gradient based l/sub 2/ optimization technique is developed to train the KBNN model. The proposed technique can be used to model passive and active microwave components with improved accuracy, reduced cost of model development and less need of training data over conventional neural models for microwave design.

Response of generalist and specialist insect herbivores to landscape spatial structure

Abstract: The purpose of this study was to investigate the effect of changes in landscape pattern on generalist and specialist insects. We did this by comparing the species richness and abundance of generalist and specialist herbivorous insects in alfalfa (Medicago sativa, L.) fields on 26 agricultural landscapes that differed in spatial structure. The insects were from the families Curculionidae (Coleoptera), weevils, and Cicadellidae (Auchennorhyncha), leafhoppers. We hypothesized that: (1) generalist richness and abundance would be highest in landscapes with high diversity (Shannon-Wiener); (2) specialist richness and abundance would be highest in landscapes with (i) high percent cover alfalfa and (ii) low mean inter-patch distance. We tested for these effects after con- trolling for the patch-level effects of field size, field age, frequency of disturbance and vegetation texture. The important findings of the study are: (1) generalist richness and abundance increased with increas- ing landscape diversity and (2) isolation (percent cover alfalfa in the landscape and/or mean inter-patch distance) does not affect specialist insects. These results are significant because they indicate that both generalist and specialist insects may move over much larger distances than previously thought. This is one of the first studies to demonstrate a large scale effect of spatial structure on insects across a broad range of landscapes.

Nonlinear ground-motion amplification by sediments during the 1994 Northridge earthquake

Abstract: It has been known since at least 1898 (ref 1) that sediments can amplify earthquake ground motion relative to bedrock For the weak ground motion accompanying small earthquakes, the amplification due to sediments is well understood in terms of linear elasticity (Hooke's law)2, but there has been a long-standing debate regarding the amplification associated with the strong ground motion produced by large earthquakes The view of geotechnical engineers, based largely on laboratory studies, is that Hooke's law breaks down at larger strains causing a reduced (nonlinear) amplification Seismologists, on the other hand, have tended to remain sceptical of this nonlinear effect, mainly because the relatively few strong-motion observations seemed to be consistent with linear elasticity Although some recent earthquake studies have demonstrated nonlinear behaviour under certain circumstances3,4, the significance of nonlinearity for the type of stiff-soil sites found in the greater Los Angeles region remains unresolved5 Here we report that ground-motion amplification due to sediments for the main shock of the 1994 Northridge earthquake was up to a factor of two less than the amplification observed for its aftershocks These observations imply significant nonlinearity in such amplification, and bring into question the use of measurements of weak ground motion to predict the strong ground motion at sedimentary sites

The front end of new product development: a Canadian survey

Abstract: Despite the importance of the early stages of a product's life, very little attention has been paid to empirically testing the activities performed in the front end of new product development. This article presents the results of a survey of 53 individuals from fifteen high technology firms in the integrated circuit board industry. Our study adopts Cooper's (1988) ‘predevelopment’ model consisting of idea generation, product definition and project evaluation stages, and probes the activities undertaken in each stage. Particular activities were found to play pivotal roles in achieving the objectives of each stage. The results present a clarified view of front end activities that can be used as a starting point for adequately preparing products for development and market success.

Carbon isotope composition of boreal plants: functional grouping of life forms.

Abstract: We tested the hypothesis that life forms (trees, shrubs, forbs, and mosses; deciduous or evergreen) can be used to group plants with similar physiological characteristics. Carbon isotope ratios (δ13C) and carbon isotope discrimination (Δ) were used as functional characteristics because δ13C and Δ integrate information about CO2 and water fluxes, and so are useful in global change and scaling studies. We examined δ13C values of the dominant species in three boreal forest ecosystems: wet Picea mariana stands, mesic Populus tremuloides stands, and dry Pinus banksiana stands. Life form groups explained a significant fraction of the variation in leaf carbon isotope composition; seven life-form categories explained 50% of the variation in δ13C and 42% of the variation in Δ and 52% of the variance not due to intraspecific genetic differences (n=335). The life forms were ranked in the following order based on their values: evergreen trees

Theoretical Calculation of Substituent Effects on the O−H Bond Strength of Phenolic Antioxidants Related to Vitamin E

Abstract: Calculations on phenol and a large number of phenols substituted with methyl, methoxyl, and amino groups have yielded reliable gas-phase O−H bond dissociation energies, BDE(ArO−H)gas. Geometries for the phenol, ArOH, and aryloxyl radical, ArO, were optimized at the (semiempirical) AM1 level followed by single point density functional theory (DFT) calculations using a 6-31G basis set supplemented with p-functions on the hydrogen atom and the B3LYP density functional. This gave BDE(PhO−H)gas = 86.46 kcal/mol, which is in good agreement with the experimental value of 87.3 ± 1.5 kcal/mol. All but one of the compounds and conformations examined had weaker O−H BDE's than phenol, the exception being o-methoxyphenol with the O−H group pointing toward this substituent (BDE = 87.8 kcal/mol). Where comparison was possible, calculated differences in O−H BDE's were in excellent agreement with experiment (better than 1 kcal/mol). A simple group additivity scheme also gave excellent agreement with calculated BDE (ArO−H)...

An empirical study of earthquake source spectra for California earthquakes

Abstract: We generalize source, path, and site effects for California earthquakes as functions of magnitude and distance, based on regression analysis of 1000 Fourier acceleration spectra from 43 California earthquakes in the moment magnitude range from 4.4 to 7.4, recorded at rupture distances from 1 to 200 km. Empirically derived source spectra for California earthquakes are generally inconsistent with the spectral shape implied by a Brune ("omega-squared") point-source model. This is manifested by magnitude- and frequency-dependence of the Brune model parameters. For ex- ample, the Brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at M5.5 to a value near 50 bars at M7.5. At frequencies below 1 Hz, though, source spectra have much lower spectral ampli- tudes than predicted by the Brune point-source model for these values of stress; this discrepancy grows with increasing magnitude. Finite-fault simulations indicate that this is a consequence of the breakdown of the validity of the point-source approxi- mation for large ruptures. A stochastic finite-fault model, in which the fault is dis- cretized as a number of subfaults, each of which is represented by a Brune omega- squared point source, correctly matches the observed spectral shapes and amplitudes. The spectral decay parameter kappa, representing average near-surface attenuation of high-frequency motion at rock sites, increases with increasing magnitude, from values near 0.035 sec at M5.5 to 0.050 sec at M7.5. Magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical California sites subjected to strong ground motion. Comparisons of our empirical source spectra for California to corresponding spec- tra for eastern North America suggest that the spectral amplitudes are similar in the two regions for low-frequency motions (f < 2 Hz for M5.5, f < 0.5 Hz for M7.5), for equivalent crustal conditions. The eastern events appear to have enhanced high- frequency near-source amplitudes relative to the California events; this is particularly pronounced for large-magnitude earthquakes.

The 60-item Boston Naming Test : Norms for cognitively intact adults aged 25 to 88 years

Abstract: Age- and education-stratified norms on the 60-item Boston Naming Test (BNT) are presented for 219 cognitively intact adults aged 25-88 years. The sample size, age range, and education levels of this sample represent an improvement over currently available norms. Eight short forms of the BNT are compared with the 60-item BNT. Frequency of errors for individual BNT items and the distribution of incorrect responses over seven different categories of errors are discussed. Finally, specific probes to overcome difficulties with ambiguous items are suggested.

Some Comparisons Between Recent Ground- Motion Relations

Abstract: We provide an overview of new ground-motion relations for eastern North America (ENA) developed over the last five years. The empirical-stochastic relations of Atkinson and Boore (1995) are compared to relations developed by the Electric Power Research Institute (EPRI, 1993; also Toro et a/., 1994), Frankel et al. (1996), and the consensus ENA ground-motion values as reported by SSHAC (1996). The main difference between our relations and those of EPRI or Frankel is in the low-frequency amplitudes (f 2) than California values at high frequencies. The alternative soil correction leads to the conclusion that our ENA relations are moderately lower (factor<2) than the California relations at low frequencies, and moderately higher at high frequencies. Both of these conclusions imply that ground-motion relations or time series for earthquakes in one region cannot be simply modified for use in engineering analyses in another region.

Vessel contents during transpiration—embolisms and refilling

Abstract: A test was made of the previous unexpected observation that embolized vessels were refilled during active transpiration. The contents of individual vessels in petioles of sunflower plants were examined, after snap-freezing at 2-h intervals during a day’s transpiration, in the cryo-scanning electron microscope, and assessed for the presence of liquid or gas (embolism) contents. Concurrent measurements were made of irradiance, leaf temperature, transpiration rate, and leaf water potential (by pressure chamber). Up to 40% of the vessels were already embolized by 0900 (transpiration rate ;5 mg·cm 22·s21, water potential about 2300 J/kg), and the proportion declined to a minimum (as low as 4%) at 1500. This was the time of highest transpiration rate (;25 mg·cm 22·s21) and most negative water potential (2600 to 2700 J/kg). Images of vessels with mixed gas and liquid contents showed water being extruded through pits in the walls of the vessels to refill them. The data indicate that: (1) the water columns are weak and break under quite small tensions; (2) embolisms are repaired by refilling the vessels with water on a short time scale (minutes) throughout the day; (3) the vigor of this refilling process is adjusted by the plant on a longer time scale (hours) to the intensity of the water stress; (4) the pressure chamber balance pressure ( P) does not measure tension in the vessels; (5) P is also not a measure of water stress (as measured by vessel embolization); and (6) P is a measure of the plant’s response to water stress, i.e., a measure of the vigor of the refilling process. The test confirms the previous observations and negates all the assumptions and evidences of the Cohesion Theory. The data are fully consistent with the Compensating Pressure Theory, which predicted the relations demonstrated in this experiment. Using the assumptions of that theory it is easy to outline a simple mechanism by which the refilling of vessels might be achieved by reverse osmosis, and the adjustment in (3) might be achieved by osmoregulation in the starch sheath.

Baclofen suppression of cocaine self-administration: demonstration using a discrete trials procedure.

Abstract: We have previously reported that rats display a circadian pattern of cocaine self-administration if access to drug is limited to 10-min discrete trials that are separated by at least 20 min. In the present study, the pattern of cocaine intake (1.5 mg/kg per injection) was studied in two large groups of animals that were maintained on different 12-h light/dark cycles (3 a.m. to 3 p.m. versus 10 a.m. to 10 p.m.). Regardless of the time of light onset, a circadian pattern of cocaine self-administration was observed. Maximum cocaine intake occurred during the final 6 h of the dark period and was followed by a relative abstinence period during the light phase. This highly predictable pattern of drug taking behavior provided an opportunity to explore the effect of baclofen, a GABAB agonist, on the initiation of self-administration behavior. In two separate studies, acute treatment with baclofen (1.25–5.0 mg/kg) was shown to suppress cocaine intake for at least 4 h. Baclofen had no significant effect on responding for food reinforcement. Previous results have indicated that baclofen appears to reduce specifically the motivation to respond for cocaine. Together, these data suggest that baclofen should be considered as a possible pharmacotherapeutic agent in cocaine addiction.

Antioxidant systems and anoxia tolerance in a freshwater turtle Trachemys scripta elegans.

Abstract: The effects of anoxic submergence (20 h at 5°C) and subsequent 24 h aerobic recovery on the antioxidant systems of six organs were examined in freshwater turtles, Trachemys scripta elegans. Both xanthine oxidase and xanthine dehydrogenase were detected in turtle tissues with xanthine oxidase composing 36–75% of the total activity. Turtle organs displayed high constitutive activities of catalase (CAT), superoxide dismutase (SOD), and alkyl hydroperoxide reductase (AHR). Measurements of lipid peroxidation damage products (conjugated dienes, lipid hydroperoxides, thiobarbituric acid reactive substances) showed minimal changes during anoxia or recovery suggesting that natural anoxic-aerobic transitions occur without the free radical damage that is seen during ischemia-reperfusion in mammals. Anoxia exposure led to selected decreases in enzyme activities in organs, consistent with a reduced potential for oxidative damage during anoxia: SOD decreased in liver by 30%, CAT decreased in heart by 31%, CAT and total glutathione peroxidase (GPOX) decreased in kidney (by 68 and 41%), and CAT and SOD decreased in brain (by 80 and 15%). AHR, however, increased 2 and 3.5 fold during anoxia in heart and kidney respectively. Most anoxia-induced changes were reversed during aerobic recovery although brain enzyme activities remained suppressed. Some specific changes occurred during the recovery period: SOD increased from controls in heart by 45%, AHR increased to 200 and 168% of control values in red and white muscle respectively, and total GPOX decreased from controls in heart and white muscle by 75 and 77% respectively. The results show that biochemical adaptation for natural anoxia tolerance in turtles includes well-developed antioxidant defenses that minimize or prevent damage by reactive oxygen species during the reoxygenation of organs after anoxic submergence.

Sorghum [Sorghum bicolor (L.) Moench] landrace variation and classification in North Shewa and South Welo, Ethiopia

Abstract: Fourteen phenotypic characters were chosen for the purpose of obtaining taxonomic evidence on the resemblances of 177 accessions of sorghum from North Shewa and South Welo regions of Ethiopia. Canonical Discriminant Analysis (CDA) and Modeclus cluster analysis were conducted to see if the 177 accessions could form clusters based on their morphological characters, and to test the consistency of farmers’ naming of the five most common Sorghum landraces represented by 44 accessions. Multivariate analyses grouped the 177 accessions into three clusters linked by a few phenotypic intermediate landraces. A botanical key was established for easy classification of the Sorghum crop plants grown in the study area. The number of accessions of the five most common landraces named by the farmers formed dissimilar groups, suggesting that farmers’ naming of these Sorghum landraces are consistent. Midrib color, grain color, grain size, glume color, glume hairiness, and grain shape were the leading morphological characters used by the farmers in naming these Sorghum landraces.

Anorthosites and related granitoids in the Grenville orogen: A product of convective thinning of the lithosphere?

Abstract: In the central and southwestern Grenville province in Canada and the northeastern United States, anorthosites and related granitoids were emplaced during two distinct pulses, at ca. 1.16–1.13 Ga and 1.09–1.05 Ga, each following major crustal thickening events. U-Pb age constraints on movement along major ductile shear zones indicate that they were emplaced within extending crust in an overall convergent orogen. We suggest that convective thinning of the lithosphere played a significant role in their emplacement and in the tectonic evolution of the Grenvillian orogeny.

Isolation of microsatellite DNA markers from a passerine bird, Dendroica petechia (the yellow warbler), and their use in population studies.

Abstract: We describe the isolation and genetic characterization of five microsatellite loci in a passerine bird, the yellow warbler Dendroica petechia, and assess their use for various types of population-level analysis using data from two breeding populations. All five loci show levels of variability comparable to those observed in other vertebrates (Hexp = 0.388-0.989). One locus, Dp mu 05, is highly variable with 46 alleles detected in 41 individuals. All loci appeared to segregate in a Mendelian fashion as judged by patterns of inheritance in known families. However, one locus showed a significant heterozygote deficiency in one population suggesting the possible presence of null alleles at this locus. These markers provide a highly accurate system for determination of parentage in this species: the probability of detecting extrapair fertilization by males given known maternity was 0.999 in each of two separate populations. Comparison of allele frequencies and genetic distances between the two populations showed no evidence for significant differences in allele frequencies at individual loci, whereas the overall genetic distance and FST-value are significantly different from zero suggesting weak differentiation. Finally, cross-species amplification experiments showed that at least one locus appears to amplify products in a wide range of birds including nonpasserine species. Thus, our results demonstrate that these loci will provide a useful set of genetic information for addressing a wide range of population-level analyses in this and other bird species.

Random constraint satisfaction: a more accurate picture

Abstract: Recently there has been a great amount of interest in Random Constraint Satisfaction Problems, both from an experimental and a theoretical point of view. Rather intriguingly, experimental results with various models for generating random CSP instances suggest a "threshold-like" behavior and some theoretical work has been done in analyzing these models when the number of variables becomes large (asymptotic). In this paper we prove that the models commonly used for generating random CSP instances do not have an asymptotic threshold. In particular, we prove that as the number of variables becomes large, almost add instances they generate are trivially overconstrained. We then present a new model for random CSP and, in the spirit of random k-SAT, we derive lower and upper bounds for its parameters so that instances are "almost surely" underconstrained and overconstrained, respectively. Finally, for the case of one of the popular models in Artificial Intelligence we derive sharper estimates for the probability of being overconstrained, as a function of the number of variables. Canada PGS B Scholarship. E-mail: optas@cs.toronto.edu Partially supported by the EU ESPRIT Long-term Research Project ALCOM-IT (Project Nr. 20244). Supported in part by an NSERC grant. Partially supported by the EU ESPRIT Long-term Research Project ALCOM-IT (Project Nr. 20244).

The expansion of maize root‐cap mucilage during hydration. 3. Changes in water potential and water content

Abstract: Root-cap mucilage from aerial nodal roots of maize has been found to have water potential values of -11 MPa or lower when air dried. The value approaches 0 MPa within 2 min of hydration in distilled water. In this time the expanding gel absorbs only about 0.3% of the water content of fully expanded mucilage. It is concluded that the root-cap mucilage per se has almost no capacity to retain water in the rhizosphere. Any function that it may play in the slowing of root desiccation would be indirect. For example, mucilage might decrease pore size between and within soil aggregates by pulling the particles together in a cycle of noctumal efflux of water from the root surface, and diurnal drying during transpiration.