Electronic leaf wetness duration sensor: why it should be painted

The purpose of this study was to compare and evaluate the performance of electronic leaf wetness duration (LWD) sensors in measuring LWD in a cotton crop canopy when unpainted and painted sensors were used. LWD was measured with flat, printed-circuit wetness sensors, and the data were divided into two periods of 24 days: from 18 December 2001 to 10 January 2002, when the sensors were unpainted, and from 20 January to 13 February 2002, when the sensors were painted with white latex paint (two coats of paint). The data analysis included evaluating the coefficient of variation (CV%) among the six sensors for each day, and the relationship between the measured LWD (mean for the six sensors) and the number of hours with dew point depression under 2 °C, used as an indicator of dew presence. The results showed that the painting markedly reduced the CV% values. For the unpainted sensors the CV% was on average 67% against 9% for painted sensors. For the days without rainfall this reduction was greater. Comparing the sensor measurements to another estimator of LWD, in this case the number of hours with dew point depression under 2 °C, it was also observed that painting improved not only the precision of the sensors but also their sensitivity, because it increases the ability of the sensor to detect and measure the wetness promoted by small water droplets.     

Models of epidemics: when contact repetition and clustering should be included

Background  

The spread of infectious disease is determined by biological factors, e.g. the duration of the infectious period, and social factors, e.g. the arrangement of potentially contagious contacts. Repetitiveness and clustering of contacts are known to be relevant factors influencing the transmission of droplet or contact transmitted diseases. However, we do not yet completely know under what conditions repetitiveness and clustering should be included for realistically modelling disease spread.     

A fully coupled, mechanistic model for infectious disease dynamics in a metapopulation: movement and epidemic duration

The drive to understand the invasion, spread and fade out of infectious disease in structured populations has produced a variety of mathematical models for pathogen dynamics in metapopulations. Very rarely are these models fully coupled, by which we mean that the spread of an infection within a subpopulation affects the transmission between subpopulations and vice versa. It is also rare that these models are accessible to biologists, in the sense that all parameters have a clear biological meaning and the biological assumptions are explained. Here we present an accessible model that is fully coupled without being an individual-based model. We use the model to show that the duration of an epidemic has a highly non-linear relationship with the movement rate between subpopulations, with a peak in epidemic duration appearing at small movement rates and a global maximum at large movement rates. Intuitively, the first peak is due to asynchrony in the dynamics of infection between subpopulations; we confirm this intuition and also show the peak coincides with successful invasion of the infection into most subpopulations. The global maximum at relatively large movement rates occurs because then the infectious agent perceives the metapopulation as if it is a single well-mixed population wherein the effective population size is greater than the critical community size.     

Traditional and innovative diagnostic tools: when and why they should be applied

The development of new technological methods surely improves the quality of the Diagnostic Services in Parasitology offered to the National Sanitary Service, however, cost and simplicity have not to be neglected, even when the prime consideration is efficiency. Moreover, the mere fact that something can be done by one of these new approaches does not mean that it should be done that way or that it is most cost-effective to do it that way. A review of diagnostic tools in Parasitology is proposed, to evaluate when and why each of them should be applied. Traditional procedures for the diagnosis of parasitosis are only based on the "direct" recovery and recognition of the parasite, with the microscope as main tool and few other instruments as co-operator. The innovative procedures, recently adjusted on the basis of new scientific knowledge and made possible by the development of the laboratory instrument weapons, can evidence the parasites both directly and indirectly. If it is obvious that the direct identification of a pathogen is more reliable than that indirect, is not so evident what is the most useful direct method, and when it would be better to use indirect diagnostic tools. Advantages and disadvantages of each procedure, cost as well as the purpose of the test (diagnosis, post-treatment, research), and the general condition in which the test have to been applied must be taken into account when we are choosing. In general, we can say that the rationale for their use can be summarised as follows: 1) The macroscopic/microscopic analysis of samples is always recommended (with the exception of samples coming from tissues that need surgery). This "old" procedure allows the identification in 20 minutes of all the parasites present in mixed infections, and the evaluation of the parasite load. It is a cost-effective method which relies ultimately on the skill of the observer to detect and identify parasite stages; 2) Parasite antigen detection is an innovative and expensive immunological diagnostic, which can suffer of sensitivity and specificity. It could be useful to directly diagnose "occult" infections; 3) Parasite DNA/RNA direct detection is an innovative, sensitive and specific procedure, which can also identify sibling species. It is expensive, therefore its use is restricted to reference laboratories; 4) Host antibody detection is an innovative indirect tool to evaluate the presence of a parasite by means the evaluation of the host response to infection. It can suffer of sensitivity and specificity, and the interpretation of the test results may be difficult. It could be applied as first step to evaluate the presence of tissue parasites, whose direct diagnosis would require surgery. Some tests can be performed in well-equipped laboratories; other tests are available through research laboratories. The specimens, appropriately collected and preserved, have always to be processed in security for potential risk of infection hazard, and submitted to tests appropriate to the laboratory's goals, where, therefore, field and research diagnostic tools shouldn't be applied. The test selected for routine use has to be chosen taking into account value and limitations of each method. Reduction in excessive and often unnecessary testing is mandatory, and therefore it is critical for the clinical Parasitology to perform relevant testing while maintaining appropriate quality. To date, the microscopic analysis of samples is the only direct method that allows all identifications in short times, at a reduced cost, independently from geographical origin and peculiar status of the patient. It has to be regarded as the first step in diagnostic procedures for all laboratories. Some molecular techniques have greater sensitivity than traditional methods, but at least at the present time, their costs may well preclude their routine use. It is difficult to know, exactly, where diagnostic Parasitology will be moving in the next few years, although many soothsayers feel very strongly that the area of molecular diagnostics will replace more traditional means. It is also possible that immunological or perhaps cytometric procedures will replace our more standard diagnostic approach; nevertheless they will continue to remain oddities on the outside of the general practice and be confined to a few reference laboratories. As far as semi-automated or automated instruments and robotics-based techniques, they are useful when large numbers of the same test are performed. Supposing that they will enter in our laboratory, that will happen in central facility rather than in each local facility. So, the great interest in using new technological methods to solve old problems probably will have to be seen in the right perspective.     

Modelling disease spread through random and regular contacts in clustered populations

An epidemic spreading through a network of regular, repeated, contacts behaves differently from one that is spread by random interactions: regular contacts serve to reduce the speed and eventual size of an epidemic. This paper uses a mathematical model to explore the difference between regular and random contacts, considering particularly the effect of clustering within the contact network. In a clustered population random contacts have a much greater impact, allowing infection to reach parts of the network that would otherwise be inaccessible. When all contacts are regular, clustering greatly reduces the spread of infection; this effect is negated by a small number of random contacts.     

A modeling exercise to show why population models should incorporate distinct life histories of dispersers

Dispersal is an important form of movement influencing population dynamics, species distribution and gene flow between populations. In population models, dispersal is often included in a simplified manner by removing a random proportion of the population. Many ecologists now argue that models should be formulated at the level of individuals instead of the population level. To fully understand the effects of dispersal on natural systems, it is therefore necessary to incorporate individual-level differences in dispersal behavior in population models. Here, we parameterized an integral projection model, which allows for studying how individual life histories determine population-level processes, using bulb mites, Rhizoglyphus robini, to assess to what extent dispersal expression (frequency of individuals in the dispersal stage) and dispersal probability affect the proportion of successful dispersers and natal population growth rate. We find that allowing for life-history differences between resident phenotypes and disperser phenotypes shows that multiple combinations of dispersal probability and dispersal expression can produce the same proportion of leaving individuals. Additionally, a given proportion of successful dispersing individuals result in different natal population growth rates. The results highlight that dispersal life histories, and the frequency with which disperser phenotypes occur in the natal population, significantly affect population-level processes. Thus, biological realism of dispersal population models can be increased by incorporating the typically observed life-history differences between resident phenotypes and disperser phenotypes, and we here present a methodology to do so.     

The intergenerational transmission of Australian Indigenous languages: why language maintenance programmes should be family-focused

By 2050, the majority of Australia’s surviving Indigenous languages are likely to become extinct. The intergenerational transmission of languages in which children acquire languages from their parents and grandparents is a key mechanism for reversing language shift, but many Australian children whose parents speak an Indigenous language do not speak that language. Using a unique, national survey of Australian Indigenous children, I identify factors associated with the successful intergenerational transmission of Indigenous languages within Aboriginal and Torres Strait Islander families. Results highlight the importance of parents’ language use. Although community-level characteristics account for some of the variance in successful language transmission, parents who use Indigenous languages at home, speak them as well as they speak English, and do not also speak a creole language are more likely to pass those languages onto their children.     

A mechanistic model of developing immunity to Teladorsagia circumcincta infection in lambs

Acquired immunity influences the severity of parasitic disease, but modelling the effects of acquired immunity in helminth infections has proved challenging. This may be due to a lack of suitable immunological data, or to the perceived complexity of modelling the immune response. We have developed a model of T. circumcincta infection in domestic sheep that incorporates the effects of acquired immunity on parasite establishment and fecundity. A large data set from commercially managed populations of Scottish Blackface sheep was used, which included relationships between IgA activity and worm length, and between worm length and fecundity. Use was also made of a recently published meta-analysis of parasite establishment rates. This realistic but simple model of nematode infection emulates observed patterns of faecal egg counts. The end-of-season faecal egg counts are remarkably robust to perturbations in the majority of the parameters, possibly because of priming of the immune system early in the season, reducing parasite establishment and growth and, therefore, faecal egg counts. Lowering the amount of early infection leads to higher end-of-season egg counts. The periparturient rise in egg counts in ewes appears to have an important role in supplying infection for the priming of the immune response. This feedback in the immune priming suggests that nematode infections may be difficult to eliminate.     

Replicating empirical research in behavioral ecology: how and why it should be done but rarely ever is

That empirical evidence is replicable is the foundation of science. Ronald Fisher a founding father of biostatistics, recommended that a null hypothesis be rejected more than once because "no isolated experiment, however significant in itself can suffice for the experimental demonstration of any natural phenomenon" (Fisher 1974:14). Despite this demand, animal behaviorists and behavioral ecologists seldom replicate studies. This practice is not part of our scientific culture, as it is in chemistry or physics, due to a number of factors, including a general disdain by journal editors and thesis committees for unoriginal work. I outline why and how we should replicate empirical studies, which studies should be given priority, and then elaborate on why we do not engage in this necessary endeavor. I also explain how to employ various statistics to test the replicability of a series of studies and illustrate these using published studies from the literature.     

Viability in a pink environment: why "white noise" models can be dangerous

Analysis of long time series suggests that environmental fluctuations may be accurately represented by 1/ f   noise (pink noise), where temporal correlation is found at several scales, and the range of fluctuations increases over time. Previous studies on the effects of coloured noise on population dynamics used first or second order autoregressive noise. I examined the importance of coloured noise for extinction risk using true 1/ f   noise. I also considered the problem of estimating extinction risk with a limited sample of environmental variation. Pink noise environments increased extinction risk in random walk models where environmental variation affected the growth rate. However, pink noise environments decreased extinction risk in the Ricker model where environmental variation modified the carrying capacity. Underestimation of environmental variance almost always yielded underestimation of extinction risk. For either population viability analysis or management, we should carefully consider the long-term behaviour of the environment as well as how we include environmental noise in population models.     

Developing dynamic mechanistic species distribution models: predicting bird-mediated spread of invasive plants across northeastern North America

Species distribution models are a fundamental tool in ecology, conservation biology, and biogeography and typically identify potential species distributions using static phenomenological models. We demonstrate the importance of complementing these popular models with spatially explicit, dynamic mechanistic models that link potential and realized distributions. We develop general grid-based, pattern-oriented spread models incorporating three mechanisms--plant population growth, local dispersal, and long-distance dispersal--to predict broadscale spread patterns in heterogeneous landscapes. We use the model to examine the spread of the invasive Celastrus orbiculatus (Oriental bittersweet) by Sturnus vulgaris (European starling) across northeastern North America. We find excellent quantitative agreement with historical spread records over the last century that are critically linked to the geometry of heterogeneous landscapes and each of the explanatory mechanisms considered. Spread of bittersweet before 1960 was primarily driven by high growth rates in developed and agricultural landscapes, while subsequent spread was mediated by expansion into deciduous and coniferous forests. Large, continuous patches of coniferous forests may substantially impede invasion. The success of C. orbiculatus and its potential mutualism with S. vulgaris suggest troubling predictions for the spread of other invasive, fleshy-fruited plant species across northeastern North America.     

A model for spread of plant disease with periodic removals

A deterministic model for the spread of infectious disease in a plant population consisting of N interacting groups with periodic removals of the infected plants is considered. In the case of two interacting groups with low infection levels, the problem is solved analytically. In the case of N interacting groups arranged in line, where the interaction between the groups decreases exponentially with distance, the mathematical model consists of N nonlinear equations. Numerical solution of these equations for some values of the parameters shows a pattern similar to the solution for the two interacting groups.Contributed from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1067-E, 1984 series     

Evaluation of the medical curriculum: why, when, by whom and for whom should questionnaires be used

The undergraduate medical curriculum has been modified or even totally reorganized in many countries in recent years, and there are plans to make departmental budgets and the salaries of university professors partially dependent on the outcome of teaching. Questionnaires are often used in such situations as a means of curriculum evaluation. Based on our own experience such evaluations should be done not only during and immediately after a course in the curriculum, but also at later time points, e.g., at the end of the undergraduate and also the postgraduate phase. The clinical relevance of lectures and courses can only be graded adequately after some years of clinical experience. Gross anatomy was graded top at all time points evaluated and reached higher levels of 'clinical relevance' than other typical preclinical and even clinical subjects. Efforts should be made to obtain a high response rate for representative results. After modifying parts of a course detailed questionnaires should also include space for students' suggestions. The results of such evaluations are not only relevant to the head of department as feedback on the individual lecturers but also important for the curriculum committee and the dean. Anatomists should utilize these evaluations to improve teaching.     

Schistosoma mansoni: kinetics of glomerulonephritis in Mongolian gerbils and its correlation with intensity and duration of infection

The frequent occurrence of glomerular lesions in schistosomiasis patients has been reported, although appropriate animal models for the study of schistosomal glomerulonephritis have not been developed. To analyze the relationship between glomerulonephritis and Schistosoma mansoni infection, gerbils, Meriones unguiculatus, were infected with different number of cercariae and sacrificed at different weeks of post infection. Fifty cercariae were the optimum dose to produce the disease, glomerulonephritis, without early death of the animal. Infected gerbils showed heterogeneous types of glomerular lesions with increased serum creatinine level. Immune complex deposition was not detected at glomeruli of infected gerbils even by means of immunuofluorescence and also by transmission electron microscopy. However, infiltration of mononuclear cells in and around some of the altered glomeruli was observed. Immunohistochemical staining, using monoclonal antibody (HUSM-M.g. 15) specific to gerbil's T-cells, revealed significant infiltration of T-cells. These findings suggest that T-cells might be involved in the development of glomerulonephritis. Gerbil could be a useful model to clarify the role of T-cells in the development of glomerulonephritis of schistosomiasis.     

A mechanistic model of photosynthesis in microalgae

A dynamic model of photosynthesis is developed, accounting for factors such as photoadaptation, photoinhibition, and the "flashing light effect." The model is shown to explain the reported photosynthesis-irradiance responses observed under various conditions (constant low light, constant intense irradiance, flashing light, diurnal variation in irradiance). As significant distinguishing features, the model assumes: (1) The stored photochemical energy is consumed in an enzyme-mediated process that obeys Michaelis-Menten kinetics; and (2) photoinhibition has a square-root dependence on irradiance. Earlier dynamic models of photosynthesis assumed a first-order dependence of photoinhibition on irradiance and different kinetics of consumption of the stored energy than used in this work. These earlier models could not explain the photosynthesis-irradiance behavior under the full range of irradiance scenarios-a shortcoming that is overcome in the model developed in this work.     

Posthyperpolarization rebound: Gradualness of intensity and duration effects

Rebound was recorded in the latent pacemaker neuron ofLimnaea stagnalis as an off-response to incoming pulses of constant duration (50 msec) and different strengths (0.17–16.1 nA) or of different duration (10 msec-360 sec) and constant strength (5 nA). To pulses of short duration and weak strength this response consists of a single depolarization wave. With an increase in these parameters the wave gradually grows and is followed by a hyperpolarization wave. At an intensity of 10–12 nA or duration of about 200 msec the rebound response becomes spike-shaped, but the spike is completely formed only at 15.2 nA or 4–5 sec. The last stage of its formation is characterized by "constriction" of the depolarization component. A further increase in pulse intensity of the same duration does not change the rebound response. On the other hand, with a further increase in pulse duration in the corresponding series of experiments fresh spikes were continually added to the first, and depending on the choice of durations, this process could be followed step by step. At a duration of about 190 sec the rebound response reached saturation when it consisted of 8 spikes with a total response duration of about 5 sec. These results are used as the basis for a hypothesis of the possible organization of excitation of the somatic membrane of mollusk pacemaker neurons. Some aspects of the possible mechanism of rebound formation are discussed.Institute of Physiology and Pathology of the Cardiovascular System, Kaunas Medical Institute, Kaunas, Lithuania. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 451–459, September–October, 1973.     

The effects of asymptomatic attacks on the spread of infectious disease: A deterministic model

A deterministic model for a multi-agent disease epidemic with asymptomatic attacks is proposed and investigated. The limitations inherent in the assumptions of the model are discussed in connection with specific agents of disease. The mathematical treatment of the model is separated into analyses of the equilibrium situation and the transient behavior of the disease outbreak. Explicit formulas are derived for the number of susceptibles in the population as well as for the numbers of each type of infective—those with and without symptoms. These theoretical results are followed by a discussion of the practical considerations which must be taken into account to obtain useful information from the model. This work was supported in part by National Library of Medicine Training Grant Number 5 T01 LM00160 and in part by National Institutes of Health National Research Service Award Number 1 F32 GMO 5839 from the Institute of General Medical Sciences.