Hopf bifurcation in a stomatal oscillator

Stomata are microscopic openings in leaves of green plants which permit gas exchange. This paper presents a parameter study of a model of a stomatal oscillator first derived by Delwiche and Cooke in 1977. We prove the existence of an unstable limit cycle by using the theory of the Hopf bifurcation. Other bifurcations exhibited by the model are also discussed.     

Cortisol diurnal patterns,associations with depressive symptoms,and the impact of intervention in older adults: Results using modern robust methods aimed at dealing with low power due to violations of standard assumptions

Advances in salivary bioscience enable the widespread integration of biological measures into the behavioral and social sciences. While theoretical integration has progressed, much less attention has focused on analytical strategies and tactics. The statistical literature warns that common methods for comparing groups and studying associations can have relatively poor power compared to more modern robust techniques. Here we illustrate, in secondary data analyses using the USC Well Elderly II study (n = 460, age 60–95, 66% female), that modern robust methods make a substantial difference when analyzing relations between salivary analyte and behavioral data. Analyses that deal with the diurnal pattern of cortisol and the association of the cortisol awakening response with depressive symptoms and physical well-being are reported. Non-significant results become significant when using improved methods for dealing with skewed distributions and outliers. Analytical strategies and tactics that employ modern robust methods have the potential to reduce the probability of both Type I and Type II errors in studies that compare salivary analytes between groups, across time, or examine associations with salivary analyte levels.     

Adsorption of ethylenediaminetetraacetic dianhydride modified oxalate decarboxylase on calcium oxalate

We used ethylenediaminetetraacetic acid dianhydride (EDTAD) to modify oxalate decarboxylase (OXDC) to improve its adsorption on calcium oxalate stones. The modified sites were identified by Ultra performance liquid chromatography-mass spectrometry (UPLC-MS) and the adsorption mechanism of the EDTAD-modified OXDC on calcium oxalate (CaOx) was investigated. We investigated adsorption time, initial enzyme concentration, temperature and solution pH on the adsorption process. Data were analyzed using kinetics, thermodynamics and isotherm adsorption models. UPLC-MS showed that EDTAD was attached to OXDC covalently and suggested that the chemical modification occurred at both the free amino of the side chain and the α-NH₂ of the peptide. The adsorption capacity of the EDTAD-OXDC on calcium oxalate was 53.37% greater than that of OXDC at the initial enzyme concentration of 5 mg/ml, pH = 7.0, at 37° C. The modified enzyme (EDTAD-OXDC) demonstrated improved oxalate degradation activity at pH 4.5?6.0. Kinetic data fitting analysis suggested a pseudo second order kinetic model. Estimates of the thermodynamic parameters including ΔG⁰, ΔH⁰ and ΔS⁰ of the adsorption process showed it to be feasible, spontaneous and endothermic. Isotherm data fitting analysis indicated that the adsorption process is reduced to monolayer adsorption at a low enzyme concentration and to multilayer adsorption at a high enzyme concentration. It may be possible to apply OXDC to degradation of calcium oxalate stones.     

The structure of a model membrane in relation to the viscoelastic properties of the red cell membrane

The molecular arrangement within a lamellar structure composed of human erythrocyte lipids is determined. The 45 A thick lipid layer, in water, is filled in the interior with a liquid-like configuration of the hydrocarbon chains of phospholipid molecules and is covered on both sides by their hydrophilic polar groups. Cholesterol is located so that part of its steroid nucleus is between the polar groups of the phospholipid molecules while the rest of the molecule extends into the inner hydrocarbon layer. This lipid leaflet would be expected to have the mechanical properties of a purely liquid surface, as other authors have shown for the "black" lipid membranes. Data are presented which demonstrate that the intact erythrocyte membrane is a tough viscoelastic substance with a Young''s modulus of 10⁶–10⁸ dynes/cm² and a viscosity of 10⁷–10¹⁰ poises. The parameters and the kinetics of membrane breakdown are incompatible with the model system of pure lipid. Caution must be exercised in applying various data on the model systems to intact membranes.     

Reasons People Surrender Unowned and Owned Cats to Australian Animal Shelters and Barriers to Assuming Ownership of Unowned Cats

Most cats surrendered to nonhuman animal shelters are identified as unowned, and the surrender reason for these cats is usually simply recorded as “stray.” A cross-sectional study was conducted with people surrendering cats to 4 Australian animal shelters. Surrenderers of unowned cats commonly gave surrender reasons relating to concern for the cat and his/her welfare. Seventeen percent of noncaregivers had considered adopting the cat. Barriers to assuming ownership most commonly related to responsible ownership concerns. Unwanted kittens commonly contributed to the decision to surrender for both caregivers and noncaregivers. Nonowners gave more surrender reasons than owners, although many owners also gave multiple surrender reasons. These findings highlight the multifactorial nature of the decision-making process leading to surrender and demonstrate that recording only one reason for surrender does not capture the complexity of the surrender decision. Collecting information about multiple reasons for surrender, particularly reasons for surrender of unowned cats and barriers to assuming ownership, could help to develop strategies to reduce the number of cats surrendered.     

Mitochondrial DNA structure and colony expansion dynamics of New Zealand fur seals (Arctocephalus forsteri) around Banks Peninsula

New Zealand fur seals are one of many pinniped species that survived the commercial sealing of the eighteenth and nineteenth centuries in dangerously low numbers. After the enforcement of a series of protection measures in the early twentieth century, New Zealand fur seals began to recover from the brink of extinction. We examined the New Zealand fur seal populations of Banks Peninsula, South Island, New Zealand using the mitochondrial DNA control region. We identified a panmictic population structure around Banks Peninsula. The most abundant haplotype in the area showed a slight significant aggregated structure. The Horseshoe Bay colony showed the least number of shared haplotypes with other colonies, suggesting a different origin of re-colonisation of this specific colony. The effective population size of the New Zealand fur seal population at Banks Peninsula was estimated at approximately 2500 individuals. The exponential population growth rate parameter for the area was 35, which corresponds to an expanding population. In general, samples from adjacent colonies shared 4.4 haplotypes while samples collected from colonies separated by between five and eight bays shared 1.9 haplotypes. The genetic data support the spill-over dynamics of colony expansion already suggested for this species. Approximate Bayesian computations analysis suggests re-colonisation of the area from two main clades identified across New Zealand with a most likely admixture coefficient of 0.41 to form the Banks Peninsula population. Approximate Bayesian computations analysis estimated a founder population size of approximately 372 breeding individuals for the area, which then rapidly increased in size with successive waves of external recruitment. The population of fur seals in the area is probably in the late phase of maturity in the colony expansion dynamic.     

A Comparison of Body Size Evaluations of Obesity Surgery Patients and General Population Adults

RAND, COLLEEN S. W., JAQUELYN LISS RESNIK, AND ALEX M. C. MACGREGOR. A comparison of body size evaluations of obesity surgery patients and general population adults. Obes Res. Objective: To compare post-operative obesity surgery patients and general population adults in their assessments of a wide range of body sizes. Research Methods and Procedures: Obesity surgery patients (n = 274) and general population adults (n = 326) rated ideal and socially acceptable body sizes in separate arrays of babies, children, young adults, and middle-aged and older adults. Nine line figure drawings ranging from very thin to very obese were rated for each array. Results: Both groups selected the same ideal body size for all arrays except for babies. Both groups rejected obese and very thin body sizes as socially acceptable. However, the obesity surgery patients were more restrictive than general population adults in their ratings of socially acceptable body sizes. Current obesity status did not impact ratings for the patient or general population subjects. In the patient sample, time since surgery did not influence body size evaluations. Discussion: The study of body size ratings limited only to the “ideal” size may be misleading because it may mask subtle but meaningful differences between groups. The consistent difference in more restrictive ratings of obesity surgery patients compared to general population adults may be due to patients' greater psychological investment in endorsing the societal ideal body size. It may also be due to patients' status as peripheral group members of the normal weight community. The inability of some patients to maintain their post-operative weight loss may be particularly problematic for those who have defined “socially acceptable” body size most narrowly.     

Some Exploratory Methods for Studying Curvature in Robust Regression

The paper suggests an exploratory method for studying curvature, within the context of robust regression, using an analog of the approached developed by Doksum and Samarov (1995). The strategy begins by approximating the regression surface using a proposed generalization of the so‐called running interval smoother. The generalization consists of estimating the span via arobust measure of scale associated with the residuals. This approximation can then be used to measure linearity using a robust analog of a measure considered by Doksum and Samarov. The results are illustrated with data from a study on predicting reading ability.