2,954 research outputs found
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 versus time follow the
power law, . Our results show the power coefficient exponent
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
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 law, yet for large number of simulation
steps we get , providing random initial population was sufficiently
big to allow for still reliable statistical analysis. The
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 () in the
power law in short time scale, again followed by 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
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