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PubMed1994

Collective phenomena in spatially extended evolutionary games.

A class of spatially extended evolutionary games with simple local rules is introduced. The emergent properties are studied through two complementary approaches. One is based on a heuristic local analysis, the other on exact global techniques. The local analysis provides criteria to group the games into classes with distinct behavior. The results facilitate numerical simulations and reveal that even simple games allow for complex spatio-temporal phenomena. The global analysis demonstrates that certain games perform an uphill march in a fitness landscape determined by the payoff parameters and the topology of the underlying lattice structure. For generic game parameters, the landscape is rugged owing to competing interactions and generates dynamical phenomena well known from frustrated systems: trapping in local maxima for noiseless dynamics and very long relaxation times for stochastic dynamics. Although the model is a mere caricature of evolutionary processes, some of its emergent properties are reminiscent of those observed in nature. It is argued that similar dynamical phenomena will be present in more elaborate approaches.

Animals↗

PubMedDate not supplied

Experimental evaluation of rigor mortis. III. Comparative study of the evolution of rigor mortis in different sized muscle groups in rats.

The use of new methods and an appropriate apparatus has allowed us to make successive measurements of rigor mortis and a study of its evolution in the rat. By a comparative examination on the front and hind limbs, we have determined the following: (1) The muscular mass of the hind limbs is 2.89 times greater than that of the front limbs. (2) In the initial phase rigor mortis is more pronounced in the front limbs. (3) The front and hind limbs reach maximum rigor mortis at the same time and this state is maintained for 2 hours. (4) Resolution of rigor mortis is accelerated in the front limbs during the initial phase, but both front and hind limbs reach complete resolution at the same time.

Animals↗

PubMedDate not supplied

Experimental evaluation of rigor mortis. IV. Change in strength and evolution of rigor mortis in the case of physical exercise preceding death.

Evolution of rigor mortis in rats exercised before death shows the following characteristics with respect to controls: (1) Its intensity is increased in the initial phase. (2) It reaches its maximum development at the same time. (3) Higher maximum values are reached (in our experiments 1.39 times the maximum values for controls). (4) Higher values are maintained from 100 minutes to 16 hours with statistically significant differences. (5) It attains resolution at the same time.

Animals↗

PubMed2004

A quantitative in silico analysis calculates the angiotensin I converting enzyme (ACE) inhibitory activity in pea and whey protein digests.

Angiotensin I converting enzyme (ACE) inhibitory peptides can induce antihypertensive effects after oral administration. By means of an ACE inhibitory peptide database, containing about 500 reported sequences and their IC(50) values, the different proteins in pea and whey were quantitatively evaluated as precursors for ACE inhibitory peptides. This analysis was combined with experimental data from the evolution in ACE inhibitory activity and protein degradation during in vitro gastrointestinal digestion. Pea proteins produced similar in silico scores and were degraded early in the in vitro digestion. High ACE inhibitory activity was observed after the simulated stomach phase and augmented slightly in the simulated small intestine phase. The major whey protein beta-lactoglobulin obtained the highest in silico scores, which corresponded with the fact that degradation of this protein in vitro only occurred from the simulated small intestine phase on and resulted in a 10-fold increase in the ACE inhibitory activity. Whey protein obtained total in silico scores of about 124 ml/mg, compared to 46 ml/mg for pea protein, indicating that whey protein would be a richer source of ACE inhibitory peptides than pea protein. Although beta-lactoglobulin is only partially digested, a higher ACE inhibitory activity was indeed found in the whey (IC(50) = 0.048 mg/ml) compared to the pea digest (IC(50) = 0.076 mg/ml). In silico gastrointestinal digestion of the highest scoring proteins in pea and whey, vicilin and albumin PA2, and beta-lactoglobulin, respectively, directly released a number of potent ACE inhibitory peptides. Several other ACE inhibitory sequences resisted in silico digestion by gastrointestinal proteases. Briefly, the quantitative in silico analysis will facilitate the study of precursor proteins on a large scale and the specific release of bioactive peptides.

Amino Acid Sequence↗

PubMed2006

Performances under representative pressure and temperature conditions of the gas chromatography-mass spectrometry space experiment to investigate Titan's atmospheric composition.

In the frame of the calibration of the aerosol collector and pyrolyser, and gas chromatography-mass spectrometry experiments of the Huygens probe arrived at Titan, systematic experimental studies were led to estimate the influence of the operating conditions on the analyses that should have been achieved in the Titan's atmosphere. The primary objective of this study was to estimate the influence of operating conditions variations induced by (i) instrumental modifications made shortly before the probe launch which can have changed the operating pressures; (ii) the change of the probe environmental conditions (pressure, temperature) during its descent in the atmosphere; (iii) a possible deviation of pressure and temperature regulations from their nominal values because of the long journey of the instrument in space, or of other external events. The secondary objective of this work was to create an analytical database that can be used as a reference to treat the chromatograms obtained in situ, and help to identify chromatographically the analyzed species, complementary to mass spectrometry. Beyond the application to a specific instrument, this work was also useful to experimentally estimate the fundamental evolution of the separation as a function of the changes of operating conditions with time. The obtained results show (i) the significant influence of inlet and outlet pressure variation on the time of analysis, but not on the separation power. It thus enables to significantly shorten the analysis duration, and thus to analyze more compounds within the fixed time of analysis of the instrument; (ii) the significant influence of temperature on the retention. In this frame, the enthalpies of exchange between the gas phase and the stationary phase of the species were determined to be used to retrieve the analyzed species in case of deviation of the operating temperature; (iii) that the possible aging of the columns does not have influence on the columns efficiency and separation power; (iv) the analytical capabilities of the gas chromatography-mass spectrometry experiment within operating conditions representative of those encountered in situ. Finally, in spite of possible operating condition changes, it is shown that results coming from the gas chromatograph-mass spectrometer experiment, which are currently under analysis, could bring important information on the Titan's atmosphere and its history.

Atmosphere↗

PubMed2005

GInaFiT, a freeware tool to assess non-log-linear microbial survivor curves.

This contribution focuses on the presentation of GInaFiT (Geeraerd and Van Impe Inactivation Model Fitting Tool), a freeware Add-in for Microsoft Excel aiming at bridging the gap between people developing predictive modelling approaches and end-users in the food industry not familiar with or not disposing over advanced non-linear regression analysis tools. More precisely, the tool is useful for testing nine different types of microbial survival models on user-specific experimental data relating the evolution of the microbial population with time. As such, the authors believe to cover all known survivor curve shapes for vegetative bacterial cells. The nine model types are: (i) classical log-linear curves, (ii) curves displaying a so-called shoulder before a log-linear decrease is apparent, (iii) curves displaying a so-called tail after a log-linear decrease, (iv) survival curves displaying both shoulder and tailing behaviour, (v) concave curves, (vi) convex curves, (vii) convex/concave curves followed by tailing, (viii) biphasic inactivation kinetics, and (ix) biphasic inactivation kinetics preceded by a shoulder. Next to the obtained parameter values, the following statistical measures are automatically reported: standard errors of the parameter values, the Sum of Squared Errors, the Mean Sum of Squared Errors and its Root, the R(2) and the adjusted R(2). The tool can help the end-user to communicate the performance of food preservation processes in terms of the number of log cycles of reduction rather than the classical D-value and is downloadable via the KULeuven/BioTeC-homepage at the topic "Downloads" (Version 1.4, Release date April 2005).

Bacteria↗

PubMed2004

Dynamic surface tension measurements with submillisecond resolution using a capillary-jet instability technique.

An oscillating capillary jet method is implemented to measure surface tension of aqueous nonionic surfactant solutions as a function of surface age from the jet orifice. The experimental technique captures the evolution of jet swells and necks continuously along the jet propagation axis and is used in conjunction with an existing linear, axisymmetric, constant-property model to determine surface tension of liquids. The method is first validated using deionized water and isopropyl alcohol (constant surface tension test fluids) and a procedure is described to identify the optimum wavelength from the breakup point, which produces the smallest error in surface tension measurements. Dynamic surface tension data of concentrated aqueous Tergitol NP-8 surfactant solutions is then presented. The measurements are performed over a spatial length of approximately 1.5 wavelengths, a span corresponding to 0.6-4.2 ms time window from the jet orifice. Submillisecond surface age measurements are made possible by decreasing the jet diameter. Increased surfactant concentrations make the liquid jet more stable and allow measurements at higher surface ages. The correlation of Hua and Rosen fits well the dynamic surface tension data, which includes submillisecond surface ages. Finally, the time required for surface tension to reach equilibrium levels is estimated using a simple adsorption kinetics theory of surfactant molecules on the liquid/air interface.

Journal Article↗

PubMed2006

Explosion pressures of hydrocarbon-air mixtures in closed vessels.

An experimental study on pressure evolution during closed vessel explosions of several gaseous fuel-air mixtures was performed, at various initial pressures within 0.3-1.2 bar and ambient initial temperature. Explosion pressures and explosion times are reported for methane-, n-pentane-, n-hexane-, propene-, butene-, butadiene-, cyclohexane- and benzene-air mixtures. The explosion pressures measured in a spherical vessel (Phi=10 cm) and in three cylindrical vessels with different diameter/height ratios are examined in comparison with the adiabatic explosion pressures, computed by assuming chemical equilibrium within the flame front. The influence of initial pressure, fuel concentration and heat losses during propagation (determined by the size and shape of the explosion vessel and by the position of the ignition source) on explosion pressures and explosion times are discussed for some of the examined systems.

Air↗

PubMed1995

Membrane mechanics can account for fusion pore dilation in stages.

Once formed, fusion pores rapidly enlarge to semi-stable conductance values. The membranes lining the fusion pore are continuous bilayer structures, so variations of conductance in time reflect bending and stretching of membranes. We therefore modeled the evolution of fusion pores using the theory of the mechanics of deforming homogeneous membranes. We calculated the changes in length and width of theoretical fusion pores according to standard dynamical equations of motion. Theoretical fusion pores quickly achieve semi-stable dimensions, which correspond to energy minima located in a canyon between energy barriers. The height of the barrier preventing pore expansion diminishes along the dimensions of length and width. The bottom of the canyon slopes gently downward along increasing length. As a consequence, theoretical fusion pores slowly lengthen and widen as the dimensions migrate along the bottom of the canyon, until the barrier vanishes and the pore rapidly enlarges. The dynamics of growth is sensitive to tension, spontaneous curvature, bending elasticity, and mobilities. This sensitivity can account for the quantitative differences in pore evolution observed in two experimental systems: HA-expressing cells fusing to planar bilayer membranes and beige mouse mast cell degranulation. We conclude that the mechanics of membranes could cause the phenomenon of stagewise growth of fusion pores.

Animals↗

PubMed2003

The influence of nitrate leaching through unsaturated soil on groundwater pollution in an agricultural area of the Basque country: a case study.

The average nitrate concentration in the groundwater of the Vitoria-Gasteiz (Basque Country) quaternary aquifer rose from 50 mg NO3-/l during 1986 to over 200 mg/l in 1995, which represents an increase of some 20 mg NO3-/l per year. From 1995 to 2002, the nitrate concentration of the groundwater slightly decreased. Nitrate groundwater pollution during the period 1986-1993 was the result of the abusive use of fertilizers and of the modification in the recharge patterns of the aquifer from surface water sources. From 1993 onwards, apart from a possible rationalization in fertilizer use, the change in the origin of water for irrigation and wetland restoration (water is taken now from artificial pools outside the quaternary aquifer) must be explained in order to account for the observed decrease in nitrate concentration in the groundwater. The water of the aquifer and of the unsaturated zone were studied in two experimental plots (one of them cultivated and the other uncultivated) for 18 months (January 1993-June 1994), during the period of maximum contamination, to evaluate the effect of fertilizers on soil water and on the water in the saturated zone. The soil water was sampled using soil lysimeters at various depths. The volumetric water content of the soil was measured at the same depths using time domain reflectrometry (TDR) probes. Samples of groundwater were taken from a network of wells on the aquifer scale, two located close to the two experimental plots. The temporal evolution of nitrate concentrations in soil solutions depends on the addition of fertilizers and on soil nitrate leaching by rain. During episodes of intense rain (>50 mm in a day), the groundwater deposits are recharged with water coming from the leaching of interstitial soil solutions, causing an increase in the groundwater nitrate concentrations. The mass of nitrate leached from the cultivated zone is five times higher than that of the nitrate leached from the uncultivated zone (1147 kg NO3-/ha in the cultivated sector as against 211 kg NO3-/ha in the uncultivated sector), although part of the nitrate leached into the soil had been previously deposited by the rise of the water table. If we consider that the level of groundwater input is similar in both plots, we may conclude that 964 kg NO3-/ha circulated towards the groundwater in the cultivated zone during the period under study, representing 87% of the nitrate applied to the soil in the form of fertilizer during that period.

Journal Article↗

PubMedDate not supplied

[Paroxysmal discharges in children (author's transl)].

The temporal organisation of infra-clinical paroxysmal discharges was recorded in waking children using biotelemetry. This was studied in terms of two hypotheses: firstly regulation of discharges by an "internal clock" which would explain their periodic modulation; secondly the influence of certain induced or spontaneous psychophysiological situation which could increase or decrease their density. By statistical analysis using semi-automatic programmes, the density of paroxysmal discharges was studied for each experimental situation; the chronological evolution of density was also worked out. These programmes were applied to 6 long biotelemetric recordings. The results obtained show that neither of the hypotheses alone can explain the phenomena observed, and that the paroxysmal discharges probably occur at times determined by a combination of internal factors and multiple situations: modulation linked to more or less stable biological rhythms, and the role of the environment and the subjects' reactions, which intervene to a varying extent to mask natural rhythms.

Child↗

PubMed2003

Homo gets a panning.

New studies suggesting that humans and chimpanzees deserve to share the same genus may do little to improve the parlous status of our relatives in their home environment.

Animal Experimentation↗

PubMed1998

Santa Rosalia revisited: why are there so many species of bacteria?

The diversity of bacteria in the world is very poorly known. Usually less than one percent of the bacteria from natural communities can be grown in the laboratory. This has caused us to underestimate bacterial diversity and biased our view of bacterial communities. The tools are now available to estimate the number of bacterial species in a community and to estimate the difference between communities. Using what data are available, I have estimated that thirty grams of forest soil contains over half a million species. The species difference between related communities suggests that the number of species of bacteria may be more than a thousand million. I suppose that the explanation for such a large number of bacterial species is simply that speciation in bacteria is easy and extinction difficult, giving a rate of speciation higher than the rate of extinction, leading to an ever increasing number of species over time. The idea that speciation is easy is justified from the results of recent experimental work in bacterial evolution.

Bacteria↗

PubMed1993

Experimental host-induced selection in Schistosoma mansoni strains from Guadeloupe and comparison with natural observations.

Allelic frequency variation at the malate dehydrogenase (E.C.1.1.1.37) polymorphic locus (Mdh-1) was analysed during several successive generations in four strains of Schistosoma mansoni from Guadeloupe, maintained experimentally on mice. A rapid evolution of the frequency of the Mdh-1a allele is interpreted as being the result of an interaction between experimental drift and selection induced by the murine laboratory host. These experimental results are compared to the genetic structures observed among the corresponding natural populations of S. mansoni in Guadeloupe (West Indies). They strengthen the hypothesis of a natural host-induced selection by the murine host (Rattus rattus), which, in Guadeloupe, plays the role of host reservoir for this human schistosome.

Alleles↗

PubMed2005

Micro-convection, dissipative structure and pattern formation in polymer blend solutions under temperature gradients.

We report experimental results on time evolution of phase separation in a polymer blend solution under a temperature gradient. This study is aimed at making a self-organized structure by utilizing convection in a polymer blend solution comprising polystyrene (PS) and polybutadiene (PB) as solute with dioctylphthalate (DOP) as solvent. The polymer blend solution (PS/PB/DOP) with various compositions (PS/PB = 20/80, 50/50 or 80/20) was prepared with a total polymer concentration (PS + PB) at 3.0 wt.%. The solution was confined in a layer (0.1 mm thick), which was further subjected to a temperature gradient by controlling top and bottom temperatures (Ttop and Tbot) independently with a 10 or 20 degrees C temperature difference (Ttop < Tbot). For all compositions, micro-convection was generated due to the Soret effect, which is relevant to the fact that the temperature gradient induces a concentration gradient. An unusual phase separating process was observed as a result of dynamic coupling with convective flows. Especially, an interesting hierarchical structure was formed for a PS/PB = 50/50 solution. This structure is characterized by a doubly surrounding "sea-island". Namely, the "sea" contains large "islands" which involve tiny "islands". The large "islands" are spatially arranged and embedded in polygonal convection cells.

Journal Article↗

PubMed1965

THE REGULATION OF UREA-BIOSYNTHESIS ENZYMES IN VERTEBRATES.

1. Carbamoyl phosphate synthetase, ornithine transcarbamoylase, the arginine-synthetase system and arginase were measured in the livers of ammoniotelic, ureotelic and uricotelic animals. The chelonian reptiles, whose nitrogen excretory patterns vary according to the habitat, and the Mexican axolotl, a neotenic species, were also studied. 2. The levels of the activities of the first three enzymes mentioned correlate with the amount of nitrogen excreted as urea. 3. The terrestrial turtle, which excretes mainly uric acid, maintains a high arginase activity but has very low levels of the activities of the other three enzymes. 4. The first three enzymes of the urea cycle vary in the phylogenic scale in a co-ordinated manner, which suggests that they are under the same regulatory mechanism. 5. Urea formation from endogenous arginine in vitro has a low efficiency in the Mexican axolotl. 6. The induction of metamorphosis in the Mexican axolotl by the administration of l-tri-iodothyronine, which causes a shift from ammonio-ureotelism to complete ureotelism, is accompanied by an increase mainly in carbamoyl phosphate synthetase and also by an improvement in the efficiency of hydrolysis of endogenous arginine in vitro to give urea. 7. The results obtained by differential centrifugation of the urea-cycle enzymes in rat and Mexican-axolotl livers are presented. The location requirements for the integration of a metabolic cycle are discussed.

Amino Acids↗

PubMed2001

Hypoxic-ischemic brain injury in the newborn: pathophysiology and potential strategies for intervention.

There is increasing clinical and experimental data describing the evolution of hypoxic-ischemic encephalopathy in the perinatal period. Outcome to the fetus is determined not only by the impact of gross asphyxial insult, but also external factors that sensitize the brain to injury. Delayed neuronal and glial death occurring in the hours and days after the insult by apoptotic and related processes are observed following severe injury, and offer the most promise for pharmacological intervention. Furthermore, new technologies allow the identification of subtle insults with evolving encephalopathies that have implications for long-term neurological outcome. Application of this knowledge will allow us to identify strategies for early intervention and prevent the course of damage caused by hypoxic-ischemic injury.

Female↗

PubMed2005

Absorption cross sections and correlation functions of the NH2 A 2A1-X2B1 Renner-Teller system.

We present a quantum-mechanical study of absorption cross sections and correlation functions of the title system, using a spinless Hamiltonian that includes the nonadiabatic Renner-Teller (RT) coupling between the electronic states, and taking into account the nuclear-spin statistics. We consider also the stimulated emission, assuming a Boltzmann distribution of the molecular levels, and we express correlation functions in terms of wave-packet (WP) overlaps. Assuming that the body-fixed z component of the angular momentum is a constant of motion of isolated NH(2), we calculate X rotational and rovibrational, and X+A rovibronic cross sections and correlation functions at 4.2 and 300 K, up to 26 000 cm(-1) and 3000 fs. We also report the rotational spectrum at 3000 K. The number of absorbing states is large at high T, and the number of lines with appreciably intensity thus increases remarkably with T, from 67 at 4.2 K, to 847 at 300 K, and up to 10 609 at 3000 K. The cold spectrum consists only of Pi lines, due to ground-level absorption. At room and higher T, the hot spectrum presents long progressions of rovibronic lines. The strongest spectral intensities are X Pi and Phi rotational lines and A bending Sigma and Pi lines. We also find many Fermi resonances between A bending and combination states, and that approximately 50% of the lines belong to both electronic states. This latter result points out many RT couplings above 11 000 cm(-1). The theoretical intensities agree very well with the few available experimental data. The time evolution of the correlation functions reflects all internal motions, with periods ranging from approximately 750 to 2 fs, from slow rotational modes to ultrafast electronic dynamics. At low T, the correlation function is proportional to the survival probability of an initial WP, it has many recursions, and can be very regular, without decaying on the average. At high T, the correlation function is associated with the dynamics of many WPs, which present different dephasing times, and the dynamics thus becomes very irregular. The internal dynamics is nonadiabatic above 11 000 cm(-1), because the WPs move from the vertical to the linear region of the excited surface, and can jump to the ground surface owing to RT couplings.

Journal Article↗