33 research outputs found
Rigorous results of limiting behaviors of total tumor size under cyclic intermittent therapy for the system of reversible phenotype-switchable tumor cells
We are keenly interested in finding the limiting behaviors of total tumor
size when tumor cells are subject to the periodic repetition of therapy and
rest periods, called intermittent cyclic therapy. We hypothesize that each
tumor cell can take either therapy-sensitive or therapy-tolerant phenotype, its
phenotype transition is mainly driven by the presence or absence of
environmental stress, and such a transition is reversible. Even though those
aforementioned hypotheses make the model system simple, most of prior papers
attempted to numerically find the optimal therapeutic scheduling that minimizes
total tumor size, and there is no rigorous proof of the limiting behaviors of
total tumor size to my knowledge. Here we present such long-waited
mathematically rigorous results. In the first part of the paper, we present the
derivation of total tumor size reduction criterion and prove two theorems of
two different limiting behaviors of total tumor size under two different
therapy strategies, one leading to an asymptotic finite tumor size according to
an iterated map method and anther leading to asymptotically diminishing of
total tumor size. In the second part of the paper, we discuss the effects of
the intratumoral competition between sensitive and tolerant phenotypes on the
total tumor size reduction criterion
Bacteriophage-mediated competition in Bordetella bacteria
Apparent competition between species is believed to be one of the principle
driving forces that structure ecological communities, although the precise
mecha nisms have yet to be characterized. Here we develop a model system that
isolates phage-mediated interactions by neutralizing resource competition using
two genetically identical Bordetella bronchiseptica strains that differ only in
that one is the carrier of a phage and the other is susceptible to the phage.
We observe and quantify the competitive advantage of the bacterial strain
bearing the prophage in both invading and in resisting invasion by bacteria
susceptible to the phage, and use our measurements to develop a mathematical
model of phage-mediated competition. The model predicts, and experimental
evidence confirms, that the competitive advantage conferred by the phage
depends only on the relative phage pathology and is independent of other phage
and host parameters. This work combines experimental and mathematical
approaches to the study of phage-driven competition, and provides an
experimentally tested framework for evaluation of the effects of
pathogens/parasites on interspecific competition.Comment: 10pages, 8 figure
Noise-induced oscillatory shuttling of NF-{\kappa}B in a two compartment IKK-NF-{\kappa}B-I{\kappa}B-A20 signaling model
NF-{\kappa}B is a pleiotropic protein whose nucleo-cytoplasmic trafficking is
tightly regulated by multiple negative feedback loops embedded in the
NF-{\kappa}B signaling network and contributes to diverse gene expression
profiles important in immune cell differentiation, cell apoptosis, and innate
immunity. The intracellular signaling processes and their control mechanisms,
however, are susceptible to both extrinsic and intrinsic noise. In this
article, we present numerical evidence for a universal dynamic behavior of
NF-{\kappa}B, namely oscillatory nucleo-cytoplasmic shuttling, due to the
fundamentally stochastic nature of the NF-{\kappa}B signaling network. We
simulated the effect of extrinsic noise with a deterministic ODE model, using a
statistical ensemble approach, generating many copies of the signaling network
with different kinetic rates sampled from a biologically feasible parameter
space. We modeled the effect of intrinsic noise by simulating the same networks
stochastically using the Gillespie algorithm. The results demonstrate that
extrinsic noise diversifies the shuttling patterns of NF-{\kappa}B response,
whereas intrinsic noise induces oscillatory behavior in many of the otherwise
non-oscillatory patterns. We identify two key model parameters which
significantly affect the NF-{\kappa}B dynamic response and deduce a
two-dimensional phase-diagram of the NF-{\kappa}B response as a function of
these parameters. We conclude that if single-cell experiments are performed, a
rich variety of NF-{\kappa}B response will be observed, even if
population-level experiments, which average response over large numbers of
cells, do not evidence oscillatory behavior.Comment: 49 pages, 12 figure
Behavior of susceptible-infected-susceptible epidemics on heterogeneous networks with saturation
We investigate saturation effects in susceptible-infected-susceptible (SIS)
models of the spread of epidemics in heterogeneous populations. The structure
of interactions in the population is represented by networks with connectivity
distribution ,including scale-free(SF) networks with power law
distributions . Considering cases where the transmission
of infection between nodes depends on their connectivity, we introduce a
saturation function which reduces the infection transmission rate
across an edge going from a node with high connectivity . A mean
field approximation with the neglect of degree-degree correlation then leads to
a finite threshold for SF networks with . We
also find, in this approximation, the fraction of infected individuals among
those with degree for close to . We investigate via
computer simulation the contact process on a heterogeneous regular lattice and
compare the results with those obtained from mean field theory with and without
neglect of degree-degree correlations.Comment: 6 figure
Bidirectional two colored light emission from stress-activated ZnS-microparticles-embedded polydimethylsiloxane elastomer films
Bidirectional two-colored mechanoluminescent light emission has been demonstrated by unifying two polydimethylsiloxane elastomer layers functionalized with zinc sulfide doped with Cu (ZnS:Cu) or Cu and Mn (ZnS:Cu,Mn). The bilayered composite films are simply fabricated by dispensing uncured ZnS:Cu,Mn + PDMS onto previously spin-coated and ardened ZnS:Cu + PDMS film. The robust PDMS-PDMS bonding yields a ilm which can simultaneously emit light with color coordinates of (0.25, 0.56) and (0.50, 0.48), similar to the intrinsic colors of ZnS:Cu and ZnS:Cu,Mn, respectively. Composite films can emit light in upper and lower directions without fracture when it is stretched. © 2013 Optical Society of America.1
Population Dynamics in Spatially Heterogeneous Systems with Drift: the generalized contact process
We investigate the time evolution and stationary states of a stochastic,
spatially discrete, population model (contact process) with spatial
heterogeneity and imposed drift (wind) in one- and two-dimensions. We consider
in particular a situation in which space is divided into two regions: an oasis
and a desert (low and high death rates). Carrying out computer simulations we
find that the population in the (quasi) stationary state will be zero,
localized, or delocalized, depending on the values of the drift and other
parameters. The phase diagram is similar to that obtained by Nelson and
coworkers from a deterministic, spatially continuous model of a bacterial
population undergoing convection in a heterogeneous medium.Comment: 8 papes, 12 figure
Substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes
We report substrate thermal conductivity effect on heat dissipation and lifetime improvement of organic light-emitting diodes (OLEDs). Heat dissipation behavior of top-emission OLEDs fabricated on silicon, glass, and planarized stainless steel substrates was measured by using an infrared camera. Peak temperature measured from the backside of each substrate was saturated to be 21.4, 64.5, and 40.5 °C, 180 s after the OLED was operated at luminance of 10 000 cd/m2 and 80% luminance lifetime was about 198, 31, and 96 h, respectively. Efficient heat dissipation through the highly thermally conductive substrates reduced temperature increase, resulting in much improved OLED lifetime.This work supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD, Basic Research Promotion Fund) (Grant No. KRF-2008-331-D00216)