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1.
AIMS: To develop a method to calculate and record theoretical microbial survival curves during thermal processing of foods and pharmaceutical products simultaneously with the changing temperature. Moreover, to demonstrate that the method can be used to calculate nonisothermal survival curves, with widely available software such as Microsoft Excel. METHODS AND RESULTS: It has been assumed that the targeted organism's isothermal survival curves are not log linear and hence, the inactivation rate in nonisothermal processes is a function of the momentary temperature and the corresponding survival ratio. This could be expressed by a difference equation, which is an approximation to the continuous rate model. The concept was tested with the isothermal survival parameters of Clostridium botulinum and Bacillus sporothermodurans spores, and Salmonella enteritidis cells, using different kinds of survival models and under temperature profiles resembling those of commercial processes. As expected, there was an excellent agreement between the curves produced by solving the differential equation of the continuous model and by the incremental method, which has been posted on the web as freeware. CONCLUSIONS: It is possible to calculate nonisothermal survival curves, in real time, with an algorithm that can be written in the language of general purpose software, to follow the inactivation of one or more targeted organisms simultaneously and to simulate microbial survival patterns under existing or planned industrial thermal processes. SIGNIFICANCE AND IMPACT OF THE STUDY: Replacement of the traditional 'F0-value', which requires the log linearity of the organism's isothermal survival curves, by the more realistic theoretical survival ratio estimate as a measure of the thermal process efficacy. 相似文献
2.
Kristel Van Goethem 《Morphology》2008,18(1):27-49
This article analyzes the grammaticalization of adjectives into prefixes in Dutch and French. In the first part, the notion
of ‘affixoids’, hybrid elements that combine properties of free lexemes and bound morphemes, will be defined and illustrated.
It will be claimed that affixoids can be seen as a result of a grammaticalization process for which we will advance phonological,
morphological, semantic and distributional parameters applying to the evolution of adjectives into prefixes. The second part
will be devoted to a specific case study in which these grammaticalization parameters will be applied to the Dutch adjectives
oud ‘old’ and nieuw ‘new’ and their French counterparts ancien ‘old’ and nouveau ‘new’ when used in word-formation. More particularly, we will examine whether these adjectives may develop prefix-like properties
when embedded in a compound structure and determine their degree of grammaticalization.
Kristel Van Goethem is a Postdoctoral fellow of the Research Foundation-Flanders (FWO) 相似文献
3.
Fast test systems fulfilling legislative specifications are required to determine mycotoxin contamination in unprocessed cerealse.g. at grain elevators, import and export terminals, or the milling and brewing industry to prevent contamination of food and
feed.
We describe the first tests of a novel fluorescence-based test for deoxynivalenol (DON), which will be commercially available
within the next few months.
The analytical procedure of the new test takes less than 15 minutes for extraction, purification, derivatization and measurement.
The system’s advantage is its speed and easy procedure providing quantitative DON determination.
To ensure an international standard, the validation procedure for wheat, barley and maize will be performed following USDA/GIPSA
requirements (03/2006) for DON tests.
Presented at the 28th Mykotoxin-Workshop, Bydgoszcz, Poland, May 29–31, 2006
Financial support: Christian Doppler Society and Government of Lower Austria 相似文献
4.
Sergio A. Estay Sabrina Clavijo-Baquet Mauricio Lima Francisco Bozinovic 《Population Ecology》2011,53(1):53-58
The relationship between ectotherm ecology and climatic conditions has been mainly evaluated in terms of average conditions.
Average temperature is the more common climatic variable used in physiological and population studies, and its effect on individual
and population-level processes is well understood. However, the intrinsic variability of thermal conditions calls attention
to the potential effects that this variability could have in ecological systems. Regarding this point, two hypotheses are
proposed. From the allocation principle, it may be inferred that if temperature variability is high enough to induce stress
in the organisms, then this extra-cost should reduce the energetic budget for reproduction, which will be reflected in population
parameters. Moreover, a mathematical property of non-linear functions, Jensen’s inequality, indicates that, in concave functions,
like the temperature–reproduction performance function, variability reduces the expected value of the output variable, and
again modifies population parameters. To test these hypotheses, experimental cultures of Tribolium confusum under two different thermal variability regimens were carried out. With these data, we fitted a simple population dynamics
model to evaluate the predictions of our hypothesis. The results show that thermal variability reduces the maximum reproductive
rate of the population but no other parameters such as carrying capacity or the nonlinear factor in a nonlinear version of
the Ricker model, which confirms our hypotheses. This result has important consequences, such as the paradoxical increase
in population variability under a decrease in thermal variability and the necessary incorporation of climatic variability
to evaluate the net effect of climate change on the dynamics of natural populations. 相似文献
5.
Manfred Ehrhardt 《Bulletin of mathematical biology》1983,45(4):579-590
In this paper we are concerned with problems of the long-term behavior for nonlinear systems in random environment. The general
model is assumed to be given by an ordinary differential equation with random parameters or random input. The disturbance
process can be taken from a fairly general class of Markov processes having a bounded state space. In terms of the system’s
dynamics we give sufficient conditions for the existence and uniqueness of invariant probabilities. Finally, we apply these
results to the two-dimensional biochemical model which is known as the Brusselator.
This work is part of a research project supported by the ‘Stiftung Volkswagenwerk’. 相似文献
6.
Peter J. Mumby 《Coral reefs (Online)》2009,28(3):761-773
Caribbean coral reefs are widely thought to exhibit two alternate stable states with one being dominated by coral and the
other by macroalgae. However, the observation of linear empirical relationships among grazing, algal cover and coral recruitment
has led the existence of alternate stable states to be questioned; are reefs simply exhibiting a continuous phase shift in
response to grazing or are the alternate states robust to certain changes in grazing? Here, a model of a Caribbean forereef
is used to reconcile the existence of two stable community states with common empirical observations. Coral-depauperate and
coral-dominated reef states are predicted to be stable on equilibrial time scales of decades to centuries and their emergence
depends on the presence or absence of a bottleneck in coral recruitment, which is determined by threshold levels of grazing
intensity and other process variables. Under certain physical and biological conditions, corals can be persistently depleted
even while increases in grazing reduce macroalgal cover and enhance coral recruitment; only once levels of recruitment becomes
sufficient to overwhelm the population bottleneck will the coral-dominated state begin to emerge. Therefore, modest increases
in grazing will not necessarily allow coral populations to recover, whereas large increases, such as those associated with
recovery of the urchin Diadema antillarum, are likely to exceed threshold levels of grazing intensity and set a trajectory of coral recovery. The postulated existence
of alternate stable states is consistent with field observations of linear relationships between grazing, algal cover and
coral recruitment when coral cover is low and algal exclusion when coral cover is high. The term ‘macroalgal dominated’ is
potentially misleading because the coral-depauperate state can be associated with various levels of macroalgal cover. The
term ‘coral depauperate’ is preferable to ‘macroalgal dominated’ when describing alternate states of Caribbean reefs. 相似文献
7.
G. Galletta F. Ferri G. Fanti M. D’Alessandro G. Bertoloni D. Pavarin C. Bettanini P. Cozza P. Pretto G. Bianchini S. Debei 《Origins of life and evolution of the biosphere》2006,36(5-6):625-627
The Martian Environment Simulator (SAM “Simulatore di Ambiente Marziano”) is a interdisciplinary project of Astrobiology done at University of Padua. The research is aimed to the study of the survival
of the microorganisms exposed to the “extreme” planetary environment. The facility has been designed in order to simulate
Mars’ environmental conditions in terms of atmospheric pressure, temperature cycles and UV radiation dose. The bacterial cells,
contained into dedicated capsules, will be exposed to thermal cycles simulating diurnal and seasonal Martian cycles. The metabolism
of the different biological samples will be analysed at different phases of the experiment, to study their survival and eventual
activity of protein synthesis (mortality, mutations and capability of DNA reparing). We describe the experimental facility
and provide the perspectives of the biological experiments we will perform in order to provide hints on the possibility of
life on Mars either autochthonous or imported from Earth.
Presented at: National Workshop on Astrobiology: Search for Life in the Solar System, Capri, Italy, 26 to 28 October, 2005. 相似文献
8.
The effect of temperature on the development of immature stages of the predator Cheyletus malaccensis Oudemans, produced by either fertilized or virgin females, was studied at 17.5, 20, 25, 30, 32.5, and 35°C, 80 ± 5% relative
humidity, in complete darkness, and fed Tyrophagus putrescentiae (Schrank). The population maintained at 15°C failed to reproduce. The thermal data obtained were used for the estimation
of the thermal requirements (developmental thresholds, thermal constant, optimum temperature) of this predator by a linear
and nonlinear model (Logan type I model). Upper and lower developmental thresholds ranged between 37.4–37.8 and 11.6–12.0°C,
respectively. Optimum temperature for development was estimated at between 33.1 and 33.5°C. The thermal constant ranged between
238.1 and 312.5 degree-days. Based on the data of the total pre-imaginal period, immatures’ survival peaked at 25°C. Arrhenotokous
parthenogenesis (haplodiploidy) is confirmed in the species: virgin females always produce males, whereas fertilized females
give rise to offspring of both sexes. Survival of the immature stages and offspring sex ratio were not significantly influenced
by temperature. 相似文献
9.
Paula M. Leddy Timothy D. Paine Thomas S. Bellows Jr. 《Entomologia Experimentalis et Applicata》1993,68(1):43-50
The relationship between ovipositional preference ofSiphoninus phillyreae (Haliday) (Homoptera: Aleyrodidae) and host plant suitability on seven host plant species (Citrus sinensis (L.) cv. ‘Washington’ [navel orange],Fraxinus uhdei (Wenz.) [shamel ash],Heteromeles arbutifolia Roemer [toyon],Malus domestica Mill. cv. ‘Granny Smith’, [apple],Pistacia vera L. cv. ‘Kerman’ [pistachio],Prunus persica (L.) cv. ‘O’Henry’ [peach], andPyrus communis L. cv. ‘Bartlett’ [pear]) was evaluated. Ovipositional preference ofS. phillyreae was determined by measuring egg density after adult female whitefies were given a simultaneous choice of all host plants
for oviposition. Immature survival, developmental time, and adult size were examined to determine host plant suitability forS. phillyreae. All studies were performed under greenhouse conditions.S. phillyreae showed distinct ovipositional preference among host plant species. Host plant species had a significant effect on immature
survival, but little or no effect on developmental time or forewing length. For four of the seven host plant species tested,
there was an association between ovipositional preference and survival. 相似文献
10.
Maren Huck Marcelo Rotundo Eduardo Fernandez-Duque 《International journal of primatology》2011,32(5):1133-1152
Life history predicts that in sexually dimorphic species in which males are the larger sex, males should reach sexual maturity
later than females (or vice versa if females are the larger sex). The corresponding prediction that in sexually monomorphic
species maturational rates will differ little between the sexes has rarely been tested. We report here sex differences in
growth and development to adulthood for 70 female and 69 male wild owl monkeys (Aotus azarai). In addition, using evidence from natal dispersal and first reproduction (mean: 74 mo) for 7 individuals of known age, we
assigned ages to categories: infant, 0–6 mo; juvenile, 6.1–24 mo; subadult, 24.1–48 mo; adult >48 mo. We compared von Bertalanffy
growth curves and growth rates derived from linear piecewise regressions for juvenile and subadult females and males. Growth
rates did not differ between the sexes, although juvenile females were slightly longer than males. Females reached maximum
maxillary canine height at ca. 2 yr, about a year earlier than males, and females’ maxillary canines were shorter than males’. Thus apart from canine eruption
and possibly crown–rump length, the development of Azara’s owl monkeys conforms to the prediction by life history that in
monomorphic species the sexes should develop at similar paces. 相似文献
11.
James S. Berry Thomas O. Holtzer George S. Innis Jesse A. Logan 《Experimental & applied acarology》1988,5(3-4):207-224
The predator functional response to several prey types and densities may be conceptualized as a multi-dimensional version
of the one-dimensional Holling functional-response curves; however, this empirical approach requires inordinate amounts of
data to develop and test. A simulation method of modelling this functional response is to consider the behavior of a predator
faced with the choice of several prey types. In this model, when all prey are available the predator’s selection will depend
on the absolute abundance of the most-preferred prey type, irrespective of the abundances of the less-preferred prey types.
Consequently, the predator will consume only the most-preferred prey types while that type is available in sufficient numbers.
When abundance of the most-preferred type declines below a certain level, the predator will begin to include in its diet the
second-most-preferred prey type along with the most-preferred prey type. This order-of-preference technique holds up well
when the model is compared to population data fromOligonychus pratensis (Acarina: Tetranychidae)/Neoseiulus fallacis (Acarina: Phytoseiidae), and is consistent with optimal foraging theory. Implementation is simple, and the data requirements
are reduced to determining the predator’s order of preference and normalizing the nutritional values of the prey types to
a single type. 相似文献
12.
Jürgen Kröller 《Biological cybernetics》1995,74(1):9-20
The response of primary muscle spindle afferent fibers to muscle stretch is nonlinear. Now spindle responses (trains of action
potentials) to band-limited Gaussian white noise length perturbations of the gastrocnemius muscles (input signal) are described
in cats. The input noise upper cutoff frequency was clearly above the frequency range of physiological length changes in cat
hindleg muscles. The input–output relation was analyzed by means of peri-spike averages (PSAs), which could be shown to correspond
to the kernels of Wiener’s white noise approach to systems identification. The present approach (the reverse correlation analysis)
was applied up to the third order. An experiment consisted of two recordings: one (the source recording) to determine PSAs
and the other (the test recording) to provide an input signal for predicting responses. The predictions of different orders
were compared with the actual neuronal response (the observation) of the test recording. Four different approximation procedures
were developed to adapt prediction and observation and to determine weighting factors for the predictions of different orders.
The approximations also yielded the value of the power density P of the input noise signal: at a variety of stimulus parameters,
P from approximations had the same magnitude as P determined directly from the input signal amplitude spectrum. The prediction of a sequence of action potentials improved
the higher the order of components. 37 of 42 action potentials of a test recording (the observation) could be confidently
predicted from PSAs or kernels. Compared with the size of the linear first-order prediction curve, the relative sizes of the
second and third-order prediction curves were: 1.0 : 0.47 : 0.26.
Received: 15 November 1994/Accepted in revised form: 23 May 1995 相似文献
13.
A constant ratio between species richness estimated at the local and regional scale is interpreted as a proof of quasi-neutral unsaturated communities. Based on Zobel’s model of plant community (Zobel,Folia Geobot. 36: 3–8, 2001) we tested the methodology of the species-pool concept by comparing the saturated and unsaturated communities generated by spatially-explicit mechanistic simulations with known assembly rules. Tests show that local-regional species plots can be applied to distinguish saturated vs. unsaturated communities, however, the outcome of tests, i.e. the relationship between local and regional richness depends on the size of the areas compared. Independently from the mechanisms controlling diversity, trivial saturation will appear if one of the scales is either too small or too broad because species-area curves are bound at these extreme scales. Similarly, trivial unsaturaton will appear if the two scales compared are close to each other. The application of species-area curves is useful because they help to find scales for non-trivial relationships. Field tests reporting quasi-neutrality and unsaturated plant communities were performed at the intermediate scales of the corresponding species-area curves, and they were estimated from heterogeneous samples. Therefore, this field evidence might be biased by scaling artefacts. We propose to reanalyze the field evidence with solid scaling conventions and to restrict the concept of quasi-neutrality to subordinated functional groups based on the following hypotheses: (1) neutrality will appear within subordinated guilds as a consequence of the hierarchical structure of plant communities; (2) the lower a guild in the hierarchy the higher neutrality of within-layer processes detected; (3) quasi-neutrality found at the community level is not a proof of community-level neutrality but it is due to the higher number of subordinated species in the samples. 相似文献
14.
Summary A study of the bacterial microflora of muds colonized bySpartina townsendii agg. in healthy and ‘die-back’ sites in the Lymington estuary was made. No important qualitative differences were found between
the microfloras of the two types of site. Fewer species, however, were present in the die-back sites. It is suggested that
under anaerobic conditions, such as occur in a ‘die-back’ site, the bacteria will utilise such oxygen as is present, and will
then engage in anaerobic metabolic processes, producing reduced ions which will reduce the oxidation-reduction potential still
further. The occurrence of abundant sulphate reducers in the ‘die-back’ sites may be particularly significant in this respect.
No evidence was obtained of any more direct relationship between bacterial flora and the development of ‘die-back’. 相似文献
15.
Using linear stability analysis, the qualitative stability properties of open nonlinear chemical systems, in which reactions
of any order may occur, will be studied. Systems will be classified in three fundamental classes: trees, cycles and loops,
according to their knot graphs. The study of the Jacobian matrix for the kinetic equations of the system shows that the symmetrizability
by a particular procedure (calledD-symmetrizability) is a sufficient condition for stability. It has been proved that tree-graphs always satisfy the above condition.
For the cycle-graphs, theD-symmetrizability condition leads to a cyclic relation between forward and reverse steady state flows. The stability may be
assured, even if the cyclic relation is not satisfied, providing that the “symmetry breaking” be lower than an upper bound;
further alternative criteria for stability of cycles have been derived. All these results are independent of the number of
diffusive exchanges with the environment. 相似文献
16.
Shock waves have been proposed in the literature as a mechanism for retinal damage induced by ultra-short laser pulses. For
a spherical absorber, we derive a set of linear equations describing the propagation of pressure waves. We show that the formation
of shock fronts is due to the form of the absorber rather than the inclusion of nonlinear terms in the equations. The analytical
technique used avoids the need for a Laplace transform approach and is easily applied to other absorber profiles. Our analysis
suggests that the ’soft’ nature of the membrane surrounding retinal melanosomes precludes shock waves as a mechanism for the
retinal damage induced by ultra-short pulse lasers. The quantitative estimates of the pressure gradients induced by laser
absorption which are made possible by this work, together with detailed meso-scale or molecular modelling, will allow alternative
damage mechanisms to be identified. 相似文献
17.
N. Rashevsky 《Bulletin of mathematical biology》1968,30(3):501-518
The author’s theory of imitation or mass behavior (N. Rashevsky:Mathematical Biology of Social Behavior, chapter xii, revised edition. Chicago: The University of Chicago Press, 1959; also Rashevsky:Looking at History through Mathematics, Cambridge, Mass.: The MIT Pres, 1968), when society chooses one of two mutually exclusive behaviors, is applied to the interaction
of two social groups, an oppressor group and an oppressed one. Using crude approximations, conditions are derived as to when
the oppressed group will revolt or riot, when the revolt will be suppressed, and when the oppressors will completely give
in and oppression will end. Even in the simple approximation used, the situation depends on 14 parameters showing that a simplistic
view on riots such as mere strong punishments is utterly inadequate. It is also shown that situations may exist in which revolution-like
changes from one type of behavior of a society to another cannot be prevented by any measures. 相似文献
18.
The theoretical foundations of population and community ecology stress the importance of identifying crucial niche requirements
and life history stages of invasive species and, in doing so, give insight into research and management. We focus on Microstegium vimineum, an invasive grass which is causing marked changes in the structure and function of US forests. We describe M. vimineum’s life history and habitat characteristics, infer its niche requirements and synthesize this information in the context of
population dynamics and management. Based on the results synthesized here, M. vimineum’s crucial niche requirements appear to be light (reproductive output), soil moisture (reproductive output, seedling recruitment)
and aboveground coverage by leaf-litter and competing species (seedling recruitment and survival). These data suggest a source-sink
dynamic might allow M. vimineum to disperse and thrive along sunny, and sometimes wet, edge habitats and, in turn, these populations might act as source
populations for adjacent shady forest habitats. By evaluating M. vimineum in the context of its stage-specific requirements, we highlight potential weaknesses in its life history that provide strategies
for effective management. 相似文献
19.
20.
The reproductive period and life-history parameters were investigated for the hoplonemertineAmphiporus lactifloreus found on the tidal flats of the island of Sylt in the northern Wadden Sea. Every six weeks 20 individuals were collected
and then histologically examined to determine the development stage of their reproductive organs.A. lactifloreus reproduces in the late autumn, its peak reproduction being in the second half of November. Individuals from all size classes
>20 mm body length produced gametes. Individuals of the cohorts that reproduced in the late autumn of 1992 persisted and grew
until July 1993, indicating thatA. lactifloreus is an iteroparous species. The length of relaxed individuals was significantly correlated with their length under anaesthetized
conditions, but the regression changed significantly after the reproductive period. Length under ‘relaxed’ conditions was
significantly correlated with weight (wet weight, dry weight, and ash-free dry weight); these relationships did not vary significantly
before or after the reproductive period. Our results show that important life-history data of intertidal nemertines can be
obtained without time-consuming histological studies. On the basis of these findings, recommendations for future studies on
the population biology of intertidal nemertines are given. Regular length measurements of nemertines under ‘relaxed’ conditions
are proposed as a useful tool for tracking the growth and survival of annual cohorts of intertidal nemertines. 相似文献