Significant Parabolic Relationship Research Articles

Biomass distribution patterns of salt marshes: A detailed spatial analysis in central China's coastal wetlands

Wetland vegetation plays a critical role in the health of coastal ecosystems, serving pivotal roles in disaster mitigation and blue carbon sequestration. While extensive research on the effects of sea-level rise on the aboveground biomass of salt marsh vegetation, the spatial patterns of biomass distribution related to surface elevation remain less explored. This study investigates the growth patterns and spatial distribution of Spartina alterniflora in central coast of China through field surveys and the analysis of remote sensing data via Google Earth Engine. We have found a significant parabolic relationship between vegetation biomass and distance from the sea, with the optimal biomass influenced by the location of the marsh front edge. Further, we observe that biomass distribution varies with surface elevation and is influenced by geomorphological features notably creeks, which introduce significant elevation differences and local biomass fluctuations. These findings offer new insights into the spatial distribution of tidal flat vegetation, which are vital for effective coastal management and for modeling the evolution of tidal flats.

Large seasonal variation of soil respiration in a secondary tropical moist forest in Puerto Rico.

Tropical forests are the largest contributors to global emissions of carbon dioxide (CO2) to the atmosphere via soil respiration (R s). As such, identifying the main controls on R s in tropical forests is essential for accurately projecting the consequences of ongoing and future global environmental changes to the global C cycle. We measured hourly R s in a secondary tropical moist forest in Puerto Rico over a 3‐year period to (a) quantify the magnitude of R s and (b) identify the role of climatic, substrate, and nutrient controls on the seasonality of R s. Across 3 years of measurements, mean R s was 7.16 ± 0.02 μmol CO2 m‐2 s‐1 (or 2,710 g C m‐2 year‐1) and showed significant seasonal variation. Despite small month‐to‐month variation in temperature (~4°C), we found significant positive relationships between daily and monthly R s with both air and soil temperature, highlighting the importance of temperature as a driver of R s even in warm ecosystems, such as tropical forests. We also found a significant parabolic relationship between mean daily volumetric soil moisture and mean daily R s, with an optimal moisture value of 0.34 m3 m‐3. Given the relatively consistent climate at this site, the large range in mean monthly R s (~7 μmol CO2 m‐2 s‐1) was surprising and suggests that even small changes in climate can have large implications for ecosystem respiration. The strong positive relationship of R s with temperature at monthly timescales particularly stands out, as moisture is usually considered a stronger control of R s in tropical forests that already experience warm temperatures year‐round. Moreover, our results revealed the strong seasonality of R s in tropical moist forests, which given its high magnitude, can represent a significant contribution to the seasonal patterns of atmospheric (CO2) globally.

Evaluation on the pore and water-permeability of woven conical tubular vascular graft with continuous variable cross sections

Considering the wall smoothness and mechanical continuity of conical tubular vascular grafts, the conical tubular vascular graft with continuous variable cross-sections (CVC) has been successfully woven on the basis of the equal-cover-factor principle. However, the tubular wall property and its effect on water permeability is still unknown, which is one of the fundamental properties for woven vascular grafts. In this study, a series of CVC conical tubular prototypes with different conical degrees and typical fabric weaves were prepared, and their wall features and the water permeability along the tubular walls were measured. And then, the study investigated the uniformity of the wall structure as well as the relationship among water permeability, and porosity and pore sizes. The results show that these samples have statistically uniform pore features and water permeability along the graft wall, but both the pore features and the permeability are sensitive to the conical degree as well as fabric weaves. Moreover, the water permeability has a significant parabolic relationship with the pore size, while there is no significant dependence on the porosity. These results demonstrate advantages of the CVC tubular vascular graft produced in the equal-cover-factor principle, and will facilitate the development of the CVC woven tubular vascular graft.

Effect of canopy gap size on soil respiration in a mixed broadleaved-Korean pine forest: Evidence from biotic and abiotic factors

Understanding the effects of forest structure, the frequency and size of canopy gaps is pivotal for precisely modelling forest soil carbon budgets. We aimed to determine the differences in soil respiration between closed canopy areas and canopy gaps with various sizes and how soil respiration is affected by biotic and abiotic factors, e.g., soil nutrients, soil microbial biomass and community composition, enzyme activities and fine root biomass. Soil respiration and these environmental factors were measured in eleven tree fall gaps (separated into small, medium and large with sizes ranging from 20 m2 to 450 m2) and three control plots in a mixed broadleaved-Korean pine forest during the growing season. Our results showed that soil respiration was similar between the control and small canopy gaps, while it was 17–49% lower in the medium and large canopy gaps compared to that of the control. There was a significant parabolic relationship between soil respiration and soil moisture, and the optimum moisture was approximately 40%. Fine root biomass and soil enzyme activities showed positive effects on soil respiration across different levels of canopy gaps. Furthermore, soil respiration was significantly declined with increasing soil microbial diversity (OTUs of bacteria). Our findings demonstrate that canopy gap has significant impact on soil CO2 emission in a temperate mixed forest, however, further studies concerning other forest ecosystem types and larger scale are warranted.

Bioelectrical Impedance as a Technique for Estimating Postmortem Interval,.

Estimation of postmortem interval (PMI) is a critical component of death investigation. A cadaver can be hypothesized to be a resistor-capacitor (RC) circuit the impedance (Z) of which changes in a quantifiable manner as the cadaver decomposes. This hypothesis was tested using bioelectrical impedance analysis (BIA) equipment to apply a current with a fixed amplitude at a single frequency to four cadavers over time and measuring two components of Z, resistance (R) and reactance (Xc ). Quadratic regression analysis between Z and accumulated degree days (ADD) showed a statistically significant parabolic relationship. The parabolic relationship poses an initial challenge to the use of the method, and additional research is needed to address this issue. However, the results of the reported research support the hypothesis that Z measured using BIA has a relationship to PMI.

Environmental impacts on recruitment migrations of Patagonian longfin squid (Doryteuthis gahi) in the Falkland Islands with reference to stock assessment

Doryteuthis gahi squid stocks in the Falkland Islands are assessed by depletion models which may include in-season recruitment pulses. Occurrences of in-season recruitment pulses are inferred by sharp peaks in CPUE, but this ad hoc approach does not distinguish between true recruitments into the fishery and aggregations of squid already in situ. Data were therefore investigated from 13 fishing seasons in which true recruitments could be identified by changes in D. gahi size distributions, and related to environmental variables of sea wind, sea surface temperature, and geostrophic currents. Changes in size distributions showed 30% of CPUE peaks to be true recruitments. Recruitment peaks followed a significant parabolic relationship between east-west and north-south sea wind vectors. Recruitment peaks occurring under west sea winds were characterized by a positive correlation between west and north wind speeds. Recruitment peaks occurring under east sea winds were characterized by a positive correlation between east and north wind speeds. The wind speed criteria were used to classify CPUE peaks in all D. gahi fishing seasons from 2002 to 2012. Among winter seasons, D. gahi abundance estimates correlated best with CPUE when depletion models included all recruitment peaks. Among summer seasons, which are shorter, abundance estimates correlated best with CPUE when depletion models included only the last overall peak. We hypothesize that identifying recruitment peaks improves the accuracy of depletion models, but time series must be sufficiently long for multi-peak models to fit optimally.

Structure-Function Relationship Between the Octopus Perimeter Cluster Mean Sensitivity and Sector Retinal Nerve Fiber Layer Thickness Measured With the RTVue Optical Coherence Tomography and Scanning Laser Polarimetry

To determine structure-function relationship between each of 16 Octopus perimeter G2 program clusters and the corresponding 16 peripapillary sector retinal nerve fiber layer thickness (RNFLT) values measured with the RTVue-100 Fourier-domain optical coherence tomography (RTVue OCT) and scanning laser polarimetry with variable corneal compensation (GDx-VCC) and enhanced corneal compensation (GDx-ECC) corneal compensation. One eye of 110 white patients (15 healthy, 20 ocular hypertensive, and 75 glaucoma eyes) were investigated. The Akaike information criterion and the F test were used to identify the best fitting model. Parabolic relationship with logarithmic cluster mean sensitivity and linear sector RNFLT values provided the best fit. For RTVue OCT, significant (P<0.0001) coefficients of determination (R) were found for all 16 RNFLT sectors. The R values were highest for the temporal, superotemporal, and inferotemporal RNFLT sectors (0.4483 to 0.5186). For GDx-VCC/ECC, significant (P<0.01) parabolic relationship was seen for all but the temporal and nasal RNFLT sectors. The overall highest R value (0.6943) was found for a superotemporal RNFLT sector with GDx-ECC. For some RNFLT sectors, the goodness of fit differed significantly between the imaging methods. Structure-function relationship was similar for the total population and the glaucoma subgroup, whereas no relationship (P>0.05) was found for the control eyes. Mean sensitivity of the Octopus visual field clusters showed significant parabolic relationship with the corresponding peripapillary RNFLT sectors. The relationship was more general with the RTVue OCT than GDx-VCC or GDx-ECC. The results show that visual field clusters of the Octopus G program can be applied for detailed structure-function research.

Sensitivity of Soil Respiration to Variability in Soil Moisture and Temperature in a Humid Tropical Forest

Precipitation and temperature are important drivers of soil respiration. The role of moisture and temperature are generally explored at seasonal or inter-annual timescales; however, significant variability also occurs on hourly to daily time-scales. We used small (1.54 m2), throughfall exclusion shelters to evaluate the role soil moisture and temperature as temporal controls on soil CO2 efflux from a humid tropical forest in Puerto Rico. We measured hourly soil CO2 efflux, temperature and moisture in control and exclusion plots (n = 6) for 6-months. The variance of each time series was analyzed using orthonormal wavelet transformation and Haar-wavelet coherence. We found strong negative coherence between soil moisture and soil respiration in control plots corresponding to a two-day periodicity. Across all plots, there was a significant parabolic relationship between soil moisture and soil CO2 efflux with peak soil respiration occurring at volumetric soil moisture of approximately 0.375 m3/m3. We additionally found a weak positive coherence between CO2 and temperature at longer time-scales and a significant positive relationship between soil temperature and CO2 efflux when the analysis was limited to the control plots. The coherence between CO2 and both temperature and soil moisture were reduced in exclusion plots. The reduced CO2 response to temperature in exclusion plots suggests that the positive effect of temperature on CO2 is constrained by soil moisture availability.

Photosynthetic characteristics and productivity of spring rape plants as related to crop density

Optimal density of spring rape (Brassica napus L.) crop stand was determined by plant photosynthetic characteristics at the beginning of flowering. As crop density increased from 100 to 350 plants/m2, leaf surface index (LSI) of the crop was found to increase by 18.2–80.2%, and LSI decreased by 38.8–67.3% as compared with the sparsest crop (50–100 plants/m2). LSI depended on the rate of incident PAR reaching 0.5 and 0.25 heights of the crop stand and to the soil surface. When crop density increased from 100 to 350 plants/m2, the photosynthetic potential (PP) of the crop increased 1.8 times as compared with the sparsest crop. PP of the densest rape crop stand was 3 times lower than in the sparsest crop. When the crop density increased from 100 to 250 plants/m2, the daily increment in biomass calculated per leaf surface unit increased by 27.0% as compared with the sparsest crop and depended on LSI. When leaf area decreased, the daily increment in biomass calculated per leaf surface unit declined; in the densest stand, this characteristic was by 58.3% lower than in the sparsest crop. Rape productivity at the flowering stage depended on the crop density, LSI of plants, rate of PAR reaching 0.5 and 0.25 heights of the crop stand and to the soil surface, PP, and the daily increment in biomass calculated per leaf surface unit. Crop productivity at the flowering stage and the rape seed yield were associated by a significant parabolic relationship. When crop density increased from 100 to 350 plants/m2, seed yield per plant considerably decreased (by 33.1–78.5%) as compared with the sparsest crop. The greatest influence on seed yield per plant was exerted by LSI and the daily increment in biomass calculated per leaf surface unit. When crop density increased to 250–300 plants/m2, the seed yield considerably rose (by 28.6–58.8%) as compared with the sparsest crop; when this index reached 300–350 plants/m2, the seed yield decreased because plant growth was suppressed, with the productivity reduced. The results thus obtained suggest that the photometric characteristics of spring rape were at optimum at crop density of 100–250 plants/m2. The agroclimatic conditions of Lithuania ensure potential for rapid accumulation of total biomass and high seed yield.

QSAR study for a novel series of ortho disubstituted phenoxy analogues of α 1-adrenoceptor antagonist WB4101

On the basis of the affinities at the α 1a-, α 1b- and α 1d-adrenoceptors and the 5-HT 1A receptor of a previous series of sixteen 2-[(2-phenoxyethyl)aminomethyl]-1,4-benzodioxanes ortho monosubstituted at the phenoxy moiety, a number of ortho disubstituted analogues were designed, synthesized in both the enantiomeric forms and tested in binding assays on the same receptors. The affinity values of the new compounds 1– 11 were compared with those of the enantiomers of the 2,6-dimethoxyphenoxy analogue, the well-known α1 antagonist WB4101, and of the ortho monosubstituted derivatives, suggesting some distinctive aspects of the interaction of the phenoxy moiety, in particular with the α 1a-AR and the 5-HT 1A receptor, of the monosubstituted and the disubstituted compounds. A classical quantitative structure-activity relationship (Hansch) analysis was applied to the whole set of the S enantiomers of the ortho mono- and disubstituted WB4101 analogues (26 compounds), finding a very good correlation for the α 1a affinity. For this latter, a significant parabolic relationship was also found with the volume of the two ortho substituents. Diametrically opposite, the same relationships for the 5-HT 1A exhibit low or insignificant correlation coefficients.

Diffusion of arylpropionate non-steroidal anti-inflammatory drugs into the cerebrospinal fluid: a quantitative structure-activity relationship approach.

A quantitative structure-activity relationship (QSAR) analysis of a series of arylpropionic acid non-steroidal anti-inflammatory drugs (NSAIDs) has been performed to determine which physicochemical properties of these compounds are involved in their diffusion into the cerebrospinal fluid (CSF). The penetration of eight arylpropionic acid derivatives into CSF was studied in male Wistar rats. After intraperitoneal administration of each compound (5 mg/kg), blood and CSF samples were collected at different times (0.5, 1, 3 and 6 h). The fraction unbound to plasma protein was determined using ultrafiltration. The areas under the curve of the free plasma (AUCF) and CSF (AUCCSF) concentrations were calculated according to the trapezoidal rule. The overall drug transit into CSF was estimated by the ratio RAUC (AUCCSF : AUCF). The lipophilicity was expressed as the chromatographic capacity factor (log kIAM) determined by high-performance liquid chromatography on an immobilized artificial membrane (IAM) column. A significant parabolic relationship was sought between lipophilicity (log kIAM) and the capacity of diffusion across the blood-brain barrier (log RAUC) (r = 0.928; P < 0.01). The arylpropionic acid NSAIDs exhibiting a lipophilicity value between 1.1 and 1.7 entered the CSF easily (RAUC > 1). The molecular weight (MW) was included in this parabolic relationship by means of a multiple regression analysis. This physicochemical parameter improved the correlation (r = 0.976; P < 0.005). Based on our findings, diffusion of arylpropionic acid NSAIDs into CSF appears to depend primarily on their lipophilicity and MW.

Grounded Ground Birds and Surfing Canopy Birds: Variation of Foraging Stratum Breadth Observed in Neotropical Forest Birds and Tested with Simulation Models Using Boundary Constraints

Vertical stratification of bird species has been intensively studied in temperate as well as tropical forest bird communities. One question that has received less attention is the variation of foraging stratum breadth. Hypotheses trying to explain that variation are based on differences in perception, evasion, adaptation, competition, and environmental and geometric boundary constraints. Although some predict that foraging strata near the ground should be narrower than those near the canopy, others predict that strata in the midstory should be broadest. These hypotheses were tested using observational data of 92 rainforest bird species. Observations were made from or near a 40 m high canopy crane situated close to the Surumoni River (3°10′N, 65°40′W) near Esmeralda, Estado Amazonas, southern Venezuela (Surumoni-Crane-Project). I found a highly significant parabolic relationship between mean foraging height and its standard deviation showing that midstory bird species foraged in a broader stratum than either understory or canopy species. Using a conservative comparative method, I also showed that the relationship was not the result of the phylogenetic relatedness of the species involved. Analysis of previously published data supports the relationship for two other tropical avifaunas. Because the ground and the outer canopy represent geometric boundaries to the movement of most forest birds, two simulation models were used to test whether midstory species may simply have a broader stratum because they are less constrained in their movements than species near the boundaries. The “random model” allowed individuals to move randomly between the two boundaries. It illustrated that boundary constraints alone cannot explain the observed parabolic relationship. In the “preference model,” individuals tended to move back to their preferred height within the forest column. That model simulated the observed parabolic relationship once a sufficient number of time steps had been reached, suggesting that a simple combination of geometric boundaries and preference for a specific foraging height may generate narrower strata near the boundaries. The other hypotheses only explain the parabolic relationship if other factors (e.g. vegetation density) are vertically distributed in such a way as to generate the observed parabolic pattern. Finally, I briefly discuss the advantages and disadvantages of using raw data in across-species analyses versus corrected data in phylogenetically-controlled analyses.

Grounded Ground Birds and Surfing Canopy Birds: Variation of Foraging Stratum Breadth Observed in Neotropical Forest Birds and Tested With Simulation Models Using Boundary Constraints

AbstractVertical stratification of bird species has been intensively studied in temperate as well as tropical forest bird communities. One question that has received less attention is the variation of foraging stratum breadth. Hypotheses trying to explain that variation are based on differences in perception, evasion, adaptation, competition, and environmental and geometric boundary constraints. Although some predict that foraging strata near the ground should be narrower than those near the canopy, others predict that strata in the midstory should be broadest. These hypotheses were tested using observational data of 92 rainforest bird species. Observations were made from or near a 40 m high canopy crane situated close to the Surumoni River (3°10′N, 65°40′W) near Esmeralda, Estado Amazonas, southern Venezuela (Surumoni-Crane-Project). I found a highly significant parabolic relationship between mean foraging height and its standard deviation showing that midstory bird species foraged in a broader stratum than either understory or canopy species. Using a conservative comparative method, I also showed that the relationship was not the result of the phylogenetic relatedness of the species involved. Analysis of previously published data supports the relationship for two other tropical avifaunas. Because the ground and the outer canopy represent geometric boundaries to the movement of most forest birds, two simulation models were used to test whether midstory species may simply have a broader stratum because they are less constrained in their movements than species near the boundaries. The “random model” allowed individuals to move randomly between the two boundaries. It illustrated that boundary constraints alone cannot explain the observed parabolic relationship. In the “preference model,” individuals tended to move back to their preferred height within the forest column. That model simulated the observed parabolic relationship once a sufficient number of time steps had been reached, suggesting that a simple combination of geometric boundaries and preference for a specific foraging height may generate narrower strata near the boundaries. The other hypotheses only explain the parabolic relationship if other factors (e.g. vegetation density) are vertically distributed in such a way as to generate the observed parabolic pattern. Finally, I briefly discuss the advantages and disadvantages of using raw data in across-species analyses versus corrected data in phylogenetically-controlled analyses.

GROUNDED GROUND BIRDS AND SURFING CANOPY BIRDS: VARIATION OF FORAGING STRATUM BREADTH OBSERVED IN NEOTROPICAL FOREST BIRDS AND TESTED WITH SIMULATION MODELS USING BOUNDARY CONSTRAINTS

Abstract Vertical stratification of bird species has been intensively studied in temperate as well as tropical forest bird communities. One question that has received less attention is the variation of foraging stratum breadth. Hypotheses trying to explain that variation are based on differences in perception, evasion, adaptation, competition, and environmental and geometric boundary constraints. Although some predict that foraging strata near the ground should be narrower than those near the canopy, others predict that strata in the midstory should be broadest. These hypotheses were tested using observational data of 92 rainforest bird species. Observations were made from or near a 40 m high canopy crane situated close to the Surumoni River (3°10′N, 65°40′W) near Esmeralda, Estado Amazonas, southern Venezuela (Surumoni-Crane-Project). I found a highly significant parabolic relationship between mean foraging height and its standard deviation showing that midstory bird species foraged in a broader stratum ...

Cross-continental shelf trends in coral ∂15N on the Great Barrier Reef:further consideration of the reef nutrient paradox

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 180:131-138 (1999) - doi:10.3354/meps180131 Cross-continental shelf trends in coral δ15N on the Great Barrier Reef: further consideration of the reef nutrient paradox P. W. Sammarco1,*, M. J. Risk2, H. P. Schwarcz2, J. M. Heikoop2,** 1Louisiana Universities Marine Consortium (LUMCON), 8124 Hwy. 56, Chauvin, Louisiana 70344, USA 2School of Geography and Geology, McMaster University, 1280 Main St. W., Hamilton, Ontario L8S 4M1, Canada *E-mail: psammarco@lumcon.edu **Present address: EES-1, MS-D462, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA ABSTRACT: In this study, we investigate potential sources of nitrogen for the scleractinian coral Porites lobata in a transect across the central region of the Great Barrier Reef, Australia. The experiment followed a 1-way, Model I, nested ANOVA design. We sampled colonies of P. lobata from 12 reefs spanning the 110 km wide continental shelf at 5 m depth, and determined the δ15N signature in tissue extracts (with zooxanthellae; n = 46). The response curve of the δ15N was found to be curvilinear, yielding a highly significant parabolic relationship with distance from shore (p < 0.001, second-order least-squares polynomial regression). Highest values of δ15N were observed inshore (5.0 to 5.5o/oo), lowest values at the mid-shelf (~3.8o/oo), and high values again offshore (5.2o/oo). We suggest the following causal factors, based on environmental characteristics and phenomena known to occur in this region: (1) inshore corals may be receiving much of their nitrogen from terrigenous sources; (2) mid-shelf corals may be receiving at least some of their nitrogen from associated algal mats known to possess high rates of nitrogen-fixation in this region, which in turn could lower δ15N values; and (3) offshore corals may be receiving their nitrogen from seasonal, nutrient-rich, cold-water intrusions or upwellings, documented to occur in this area. KEY WORDS: δ15N · Corals · Upwelling · Nutrient sources · Trophic shifts Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 180. Publication date: May 03, 1999 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1999 Inter-Research.

Influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid.

The aim of this quantitative structure-activity relationship (QSAR) study was to investigate the influence of lipophilicity on the diffusion of cephalosporins into the cerebrospinal fluid (CSF). The lipophilicity was expressed as the chromatographic capacity factor (log k'w) determined by high-performance liquid chromatography in a reversed-phase system. The penetration of eight cephalosporins into CSF was studied in male Wistar rats receiving the drugs intramuscularly (1.5 mg/kg). One hour after administration, CSF and blood samples were collected, and concentrations of free drug were measured in CSF (CCSF) and in plasma (CP). A significant parabolic relationship was sought between lipophilicity (log k'w) and the capacity of diffusion across the blood-brain barrier expressed as log (CCSF/CP). The cephalosporins exhibiting a moderate lipophilicity diffused well into CSF. A pharmacokinetic study was performed at 1, 2 and 4 h after administration of three cephalosporins: cefazolin, ceftriaxone and cefsulodin. These compounds were choosen according to their lipophilicities (low, moderate and high values, respectively). The AUC0-4h for both free plasma (AUCP) and cerebrospinal fluid (AUCCSF) concentrations were determined. The AUCCSF/AUCP ratio presented a maximum value for a strongly albumin bound cephalosporin, ceftriaxone. In our experimental conditions, the ideal lipophilicity (log k'w) range for diffusion of cephalosporins from plasma into CSF was between 1.6 and 1.8.

Structure-activity relationship of nitroimidazo (2,1-b) thiazoles in the Salmonella mutagenicity assay.

The mutagenic activity of a series of nitroimidazo (2,1-b) thiazoles was determined in Salmonella typhimurium TA-100 strain by means of the Ames test. A multiple regression analysis showed a highly significant parabolic relationship between mutagenic activity and the Rm values as an expression of the lipophilic character of molecules. The lipophilic character should be important in determining an optimal cell permeation. However when the lipophilic character was expressed by means of the sigma pi values the equation was much less satisfactory. This could be due to the fact that the Rm values of nitroheterocyclic compounds actually represent a measure both of lipophilic and polar character.

Factors affecting the growth of Pennisetum purpureum in the wet tropics. I. Short-term growth and regrowth

Six plantings of elephant grass (Pennisetum purpureurn) were made at 2-monthly intervals in the wet tropics of north Queensland. Each crop was sampled for yield at monthly intervals. After 6 months' growth each crop was ratooned for a further 6 months' growth, with yield samples again being taken at monthly intervals. As well, stem elongation growth was measured twice weekly, together with various climatic parameters and soil moisture to 90 cm. Regrowths after each monthly harvest were sampled 1 month after cutting. Short-term growth, measured as elongation growth and averaged for the whole experimental period, was found to have a significant parabolic relationship with crop age and available soil moisture percentage, but not with average temperature or evaporation. Regrowth yields were found to be linearly and positively correlated with tiller density prior to ratooning and regrowth tiller density, with average regrowth temperature or regrowth degree days but linearly and negatively correlated with moisture regime, whether expressed as average parent-crop soil moisture prior to harvest, average regrowth soil moisture percentage or the summation of stress-free days. It was concluded that environmental limitations to growth in this environment, though relatively short lived, were significant in reducing long-term yields. Growth, however, was possible at all times.

Relationship between degree of renal failure and impairment of intestinal calcium absorption.

The coefficient of true intestinal calcium absorption (a value) was measured by a double radioisotope technique in 29 chronic renal failure patients (serum creatinine levles 2.5-19.5 mg%) aged 20-75 years. The mean log 10 a (+/- standard error) of these subjects (1.197 +/- 0.031) was significantly lower (p less than 0.001) than that of 52 controls (1.532 +/- 0.024), the geometric mean of the renal failure group (15.7%) being approximately half (46%) of that of the controls (33.9%). The decrease of a value of the uremic patients was more pronounced in the younger than in the older subjects as shown by a statistically significant (r = 0.570; p less than 0.001) positive curvilinear, relationship between a value and age. The lowest intestinal calcium absorptions were observed in patients with a serum creatinine level of approximately 11 mg%, the a values increasing progressively with lower or larger than 11 mg% serum creatinine levels, as shown by a statistically significant (r = 0.485; p less than 0.01) parabolic relationship between a value and serum creatinine. The possible mechanism(s) of this relationship are discussed.

Some drug effects influencing barbiturate facilitation of water ingestion.

Pentobarbital was studied in combination with chlorpromazine and a stimulant barbiturate (5 ethyl, 5, 1, 3, dimethyl-2-butenyl barbituric acid) with respect to water intake in the rat. Each depressed water intake when administered alone. Pentobarbital increased drinking in the dosage employed. Chlorpromazine blocked totally the usual pentobarbital facilitation so that the combined effect was the same as that for chlorpromazine alone. The stimulant barbiturate antagonized the pentobarbital effect so that a constant difference between the stimulant and its control was obtained. The effect of the sodium salts of barbital, pentobarbital and phenobarbital upon water intake in the 23 1/2-hour water-deprived rat was also studied. A significant parabolic relationship was found between water intake and dosage, with water intake rising at low dosages and falling at higher dosages. The dosage of the drugs investigated yielding maximum facilitation of water intake varied with the hypnotic dosage. Finally, the extent of facilitation of water intake was found to vary for the different drugs. Two major conclusions are drawn: first, there is a hypnotic dimension of action affecting water intake within the barbiturate family; second, there is another dimension of action which relates to the extent of facilitation.