412 research outputs found
Universal relationship in gene-expression changes for cells in steady-growth state
Cells adapt to different conditions by altering a vast number of components,
which is measurable using transcriptome analysis. Given that a cell undergoing
steady growth is constrained to sustain each of its internal components, the
abundance of all the components in the cell has to be roughly doubled during
each cell division event. From this steady-growth constraint, expression of all
genes is shown to change along a one-parameter curve in the state space in
response to the environmental stress. This leads to a global relationship that
governs the cellular state: By considering a relatively moderate change around
a steady state, logarithmic changes in expression are shown to be proportional
across all genes, upon alteration of stress strength, with the proportionality
coefficient given by the change in the growth rate of the cell. This theory is
confirmed by transcriptome analysis of Escherichia Coli in response to several
stresses.Comment: 7 pages (5 figures) + 2 Supplementary pages (figures
Void-induced cross slip of screw dislocations in fcc copper
Pinning interaction between a screw dislocation and a void in fcc copper is
investigated by means of molecular dynamics simulation. A screw dislocation
bows out to undergo depinning on the original glide plane at low temperatures,
where the behavior of the depinning stress is consistent with that obtained by
a continuum model. If the temperature is higher than 300 K, the motion of a
screw dislocation is no longer restricted to a single glide plane due to cross
slip on the void surface. Several depinning mechanisms that involve multiple
glide planes are found. In particular, a depinning mechanism that produces an
intrinsic prismatic loop is found. We show that these complex depinning
mechanisms significantly increase the depinning stress
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