5,286 research outputs found
Cell aging preserves cellular immortality in the presence of lethal levels of damage.
Cellular aging, a progressive functional decline driven by damage accumulation, often culminates in the mortality of a cell lineage. Certain lineages, however, are able to sustain long-lasting immortality, as prominently exemplified by stem cells. Here, we show that Escherichia coli cell lineages exhibit comparable patterns of mortality and immortality. Through single-cell microscopy and microfluidic techniques, we find that these patterns are explained by the dynamics of damage accumulation and asymmetric partitioning between daughter cells. At low damage accumulation rates, both aging and rejuvenating lineages retain immortality by reaching their respective states of physiological equilibrium. We show that both asymmetry and equilibrium are present in repair mutants lacking certain repair chaperones, suggesting that intact repair capacity is not essential for immortal proliferation. We show that this growth equilibrium, however, is displaced by extrinsic damage in a dosage-dependent response. Moreover, we demonstrate that aging lineages become mortal when damage accumulation rates surpass a threshold, whereas rejuvenating lineages within the same population remain immortal. Thus, the processes of damage accumulation and partitioning through asymmetric cell division are essential in the determination of proliferative mortality and immortality in bacterial populations. This study provides further evidence for the characterization of cellular aging as a general process, affecting prokaryotes and eukaryotes alike and according to similar evolutionary constraints
Surface Counterterms and Regularized Holographic Complexity
The holographic complexity is UV divergent. As a finite complexity, we
propose a "regularized complexity" by employing a similar method to the
holographic renormalization. We add codimension-two boundary counterterms which
do not contain any boundary stress tensor information. It means that we
subtract only non-dynamic background and all the dynamic information of
holographic complexity is contained in the regularized part. After showing the
general counterterms for both CA and CV conjectures in holographic spacetime
dimension 5 and less, we give concrete examples: the BTZ black holes and the
four and five dimensional Schwarzschild AdS black holes. We propose how to
obtain the counterterms in higher spacetime dimensions and show explicit
formulas only for some special cases with enough symmetries. We also compute
the complexity of formation by using the regularized complexity.Comment: Published version with some small improvement
Dynamic Studies of Scaffold-dependent Mating Pathway in Yeast
The mating pathway in \emph{Saccharomyces cerevisiae} is one of the best
understood signal transduction pathways in eukaryotes. It transmits the mating
signal from plasma membrane into the nucleus through the G-protein coupled
receptor and the mitogen-activated protein kinase (MAPK) cascade. According to
the current understandings of the mating pathway, we construct a system of
ordinary differential equations to describe the process. Our model is
consistent with a wide range of experiments, indicating that it captures some
main characteristics of the signal transduction along the pathway.
Investigation with the model reveals that the shuttling of the scaffold protein
and the dephosphorylation of kinases involved in the MAPK cascade cooperate to
regulate the response upon pheromone induction and to help preserving the
fidelity of the mating signaling. We explored factors affecting the
dose-response curves of this pathway and found that both negative feedback and
concentrations of the proteins involved in the MAPK cascade play crucial role.
Contrary to some other MAPK systems where signaling sensitivity is being
amplified successively along the cascade, here the mating signal is transmitted
through the cascade in an almost linear fashion.Comment: 36 pages, 9 figure
Periodic Radio Variability in NRAO 530: Phase Dispersion Minimization Analysis
In this paper, a periodicity analysis of the radio light curves of the blazar
NRAO 530 at 14.5, 8.0, and 4.8 GHz is presented employing an improved Phase
Dispersion Minimization (PDM) technique. The result, which shows two persistent
periodic components of and years at all three frequencies,
is consistent with the results obtained with the Lomb-Scargle periodogram and
weighted wavelet Z-transform algorithms. The reliability of the derived
periodicities is confirmed by the Monte Carlo numerical simulations which show
a high statistical confidence. (Quasi-)Periodic fluctuations of the radio
luminosity of NRAO 530 might be associated with the oscillations of the
accretion disk triggered by hydrodynamic instabilities of the accreted flow.
\keywords{methods: statistical -- galaxies: active -- galaxies: quasar:
individual: NRAO 530}Comment: 8 pages, 5 figures, accepted by RA
More on complexity of operators in quantum field theory
Recently it has been shown that the complexity of SU() operator is
determined by the geodesic length in a bi-invariant Finsler geometry, which is
constrained by some symmetries of quantum field theory. It is based on three
axioms and one assumption regarding the complexity in continuous systems. By
relaxing one axiom and an assumption, we find that the complexity formula is
naturally generalized to the Schatten -norm type. We also clarify the
relation between our complexity and other works. First, we show that our
results in a bi-invariant geometry are consistent with the ones in a
right-invariant geometry such as -local geometry. Here, a careful analysis
of the sectional curvature is crucial. Second, we show that our complexity can
concretely realize the conjectured pattern of the time-evolution of the
complexity: the linear growth up to saturation time. The saturation time can be
estimated by the relation between the topology and curvature of SU() groups.Comment: Modified the Sec. 4.1, where we offered a powerful proof: if (1) the
ket vector and bra vector in quantum mechanics contain same physics, or (2)
adding divergent terms to a Lagrangian will not change underlying physics,
then complexity in quantum mechanics must be bi-invariant
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