11,110 research outputs found
Scarcity may promote cooperation in populations of simple agents
In the study of the evolution of cooperation, resource limitations are
usually assumed just to provide a finite population size. Recently, however, it
has been pointed out that resource limitation may also generate dynamical
payoffs able to modify the original structure of the games. Here we study
analytically a phase transition from a homogeneous population of defectors when
resources are abundant to the survival of unconditional cooperators when
resources reduce below a threshold. To this end, we introduce a model of simple
agents, with no memory or ability of recognition, interacting in well-mixed
populations. The result might shed light on the role played by resource
constraints on the origin of multicellularity.Comment: 5 pages, 2 figure
Wear of a chute in a rice sorting machine
In a rice sorting machine, rice grains drop onto and slide down an anodised aluminium chute. The purpose of the chute is to separate the grains and provide a controlled distribution. At the bottom of the chute the grains are examined optically and contaminants or defective grains
are removed from the stream by jets of air. The machine has the ability to sort low quality rice which contains a large element of contaminants such as husk. The husk is extremely
abrasive and this, along with other factors, can lead to a reduction in the life of the chute by wear of the surface.
In this work a failure analysis process was undertaken to establish the nature and causes of the chute surface wear and the mechanisms of material removal. Wear occurs initially at the location where the grains first strike the chute and at subsequent regions down the chute where bounce occurs.
An experimental and analytical examination of the rice motion on impacting the chute was also carried out along with some friction testing of potential replacement chute materials. The evidence gathered during the failure analysis along with the experimental analysis was
used to propose possible material/design improvements
Entropic Barriers, Frustration and Order: Basic Ingredients in Protein Folding
We solve a model that takes into account entropic barriers, frustration, and
the organization of a protein-like molecule. For a chain of size , there is
an effective folding transition to an ordered structure. Without frustration,
this state is reached in a time that scales as , with
. This scaling is limited by the amount of frustration which
leads to the dynamical selectivity of proteins: foldable proteins are limited
to monomers; and they are stable in {\it one} range of temperatures,
independent of size and structure. These predictions explain generic properties
of {\it in vivo} proteins.Comment: 4 pages, 4 Figures appended as postscript fil
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