Efficient Monte Carlo Simulation of Biological Aging

A bit-string model of biological life-histories is parallelized, with hundreds of millions of individuals. It gives the desired drastic decay of survival probabilities with increasing age for 32 age intervals.Comment: PostScript file to appear in Int.J.Mod.Phys.

Scaling properties of the Penna model

We investigate the scaling properties of the Penna model, which has become a popular tool for the study of population dynamics and evolutionary problems in recent years. We find that the model generates a normalised age distribution for which a simple scaling rule is proposed, that is able to reproduce qualitative features for all genome sizes.Comment: 4 pages, 4 figure

Divergent evolution paths of different genetic families in the Penna model

We present some results of simulations of population growth and evolution, using the standard asexual Penna model, with individuals characterized by a string of bits representing a genome containing some possible mutations. After about 20000 simulation steps, when only a few genetic families are still present from among rich variety of families at the beginning of the simulation game, strong peaks in mutation distribution functions are observed. This known effect is due to evolution rules with hereditary mechanism. The birth and death balance in the simulation game also leads to elimination of families specified by different genomes. Number of families $G(t)$ versus time $t$ follow the power law, $G \propto t^n$. Our results show the power coefficient exponent $n$ is changing as the time goes. Starting from about --1, smoothly achieves about --2 after hundreds of steps, and finally has semi-smooth transition to 0, when only one family exists in the environment. This is in contrast with constant $n$ about --1 as found, for example, in \cite{bib:evolution}. We suspect that this discrepancy may be due to two different time scales in simulations - initial stages follow the $n\approx-1$ law, yet for large number of simulation steps we get $n\approx-2$, providing random initial population was sufficiently big to allow for still reliable statistical analysis. The $n\approx-1$ evolution stage seems to be associated with the Verhulst mechanism of population elimination due to the limited environmental capacity - when the standard evolution rules were modified, we observed a plateau ($n=0$) in the power law in short time scale, again followed by $n\approx -2$ law for longer times. The modified model uses birth rate controlled by the current population instead of the standard Verhulst death factor

Sharp gene pool transition in a population affected by phenotype-based selective hunting

We use a microscopic model of population dynamics, a modified version of the well known Penna model, to study some aspects of microevolution. This research is motivated by recent reports on the effect of selective hunting on the gene pool of bighorn sheep living in the Ram Mountain region, in Canada. Our model finds a sharp transition in the structure of the gene pool as some threshold for the number of animals hunted is reached.Comment: 5 pages, 4 figure

Broad Histogram Monte Carlo

We propose a new Monte Carlo technique in which the degeneracy of energy states is obtained with a Markovian process analogous to that of Metropolis used currently in canonical simulations. The obtained histograms are much broader than those of the canonical histogram technique studied by Ferrenberg and Swendsen. Thus we can reliably reconstruct thermodynamic functions over a much larger temperature scale also away from the critical point. We show for the two-dimensional Ising model how our new method reproduces exact results more accurately and using less computer time than the conventional histogram method. We also show data in three dimensions for the Ising ferromagnet and the Edwards Anderson spin glass.Comment: 6 pages of a TeX file with 4 PS figures. Related papers at http://www.if.uff.br/~tjp

Studies on the disinfection of seed potatoes

1. Experiments to compare the effect of drying washed and disinfected seed tubers in ventilated stacks of 10 cwt. boxes with drying in seed chitting trays indicated that, in general, there were no marked differences produced by the two methods with respect to control of storage disease, crop growth and yield. However, there was a tendency for condensation moisture to form on the top boxes of the stacks which was probably associated with a slight increase in soft rot in 1965 and blackleg in 1966-67 and 1967-68. Covering boxes with straw was found to apparently reduce condensation. 2. Commercial washing and disinfection increased the incidence of blackleg in the field despite modifications aimed at reducing damage before disinfection. The washing machine was shown to assist in some way the entry of the blackleg organism into the potato tissues beyond the reach of the disinfectant. Disinfection of unwashed tubers reduced the level of the disease to below that found in untreated tubers. 3. Some evidence was given to account for the generally higher incidence of blackleg in the trials in 1968 than in 1967. Although experiments were planted in different fields in the same area in the two years, it is suggested that the difference in blackleg incidence was the result of the rainfall pattern. 4. Using hot air drying apparatus, it was shown that disinfected and washed and disinfected tubers could be dried satisfactorily with air temperatures up to 212°F when exposed to the hot air stream for up to 3i min. There was no evidence that the hot air affected control of storage diseases, growth of crop, blackleg or yield. 5. Disinfection of unwashed tubers in a prototype disinfection tank for 1/2 - 3/4 min. with an EEMC concentration of 150 ppm showed that storage disease could be reduced and blackleg controlled in the field. However, the presence of soil slightly affected the efficiency of the disinfection process. 6. In the trials over the three years disinfection usually reduced the incidence of skin spot, dry rot and gangrene to a satisfactory level. When this was not the case, delay in applying the treatment of more than three days after lifting was usually the reason. 7. Generally, disinfected tubers gave sprout stimulation, earlier emergence, greater number of stems and tubers than undisinfected tubers. 8. Despite the higher level of blackleg in crops grown from washed and disinfected seed compared with untreated tubers, the yield was not significantly reduced. Unwashed, disinfected tubers produced yields which compared favourably with untreated tubers, showing that plants grown from undisinfected seed were probably more vigorous