2,789 research outputs found
Instability of the solitary waves for the Generalized Benjamin-Bona-Mahony Equation
In this work, we consider the generalized Benjamin-Bona-Mahony equation
with
. This equation has the traveling wave solutions for
any frequency It has been proved by Souganidis and Strauss
\cite{Strauss-1990} that, there exists a number , such that
solitary waves with is orbitally unstable,
while for is orbitally stable. The linear
exponential instability in the former case was further proved by Pego and
Weinstein \cite{Pego-1991-eigenvalue}. In this paper, we prove the orbital
instability in the critical case .Comment: 32 pages, 1 fictur
Lovastatin arrests CHO cells between the origin decision point and the restriction point
AbstractAsynchronously growing Chinese hamster ovary (CHO) cells treated with the pro-drug, Ξ²-lactone ring form of lovastatin were arrested in G1-phase. Subsequent removal of lovastatin resulted in the synchronous entry of cells into S-phase regardless of the presence of mevalonic acid. Lovastatin-arrested cells contained hypophosphorylated retinoblastoma protein (Rb) and required serum mitogens to enter S-phase after lovastatin removal, indicating that cell-cycle arrest is prior to the restriction point (R-point). However, in contrast to quiescent cells, intact nuclei prepared from lovastatin-arrested cells were competent for DNA replication when introduced into Xenopus egg extracts. Initiation of replication by Xenopus egg cytosol took place specifically within the dihydrofolate reductase (DHFR) origin locus, demonstrating that cells were arrested after the origin decision point (ODP). We conclude that the Ξ²-lactone ring form of lovastatin is an effective reagent with which to synchronize CHO cells between the ODP and R-point, without resulting in the withdrawal of cells from the cell-cycle into a quiescent state
Evolutionary Paths Caused by Feedback between Environment and Finite Population
Natural selection imply that any organisms including human being will evolve
to improve its fitness advantage and the selected genotype or phenotype in
equilibrium state will not vary over the time. However, evolutionary process of
biological organisms in reality is greatly affected by the environmental change
and historical accidents. In this paper, we present a framework for analyzing
the feedback between species and their environment. The framework accounts for
the deterministic effect that species have on their environment, as well as the
stochastic effects that arise due to finite populations. Through a simple
example, we demonstrate that negative feedback between species and environment
negates any advantages that a particular species may possess and results in
species coexistence. In the absence of feedback, the dominant species takes
over the population if the population is large enough. Conversely, we find that
positive feedback generates unpredictable outcomes that depend on the
evolutionary path. Even inferior species can take over the population if they
achieve sufficient abundance early in the process, after which the evolutionary
path becomes locked in. Our results highlight the importance of evolutionary
path and the unpredictability caused by positive feedback between species and
environment
Exploiting the Power of Human-Robot Collaboration: Coupling and Scale Effects in Bricklaying
As an important contributor to GDP growth, the construction industry is
suffering from labor shortage due to population ageing, COVID-19 pandemic, and
harsh environments. Considering the complexity and dynamics of construction
environment, it is still challenging to develop fully automated robots. For a
long time in the future, workers and robots will coexist and collaborate with
each other to build or maintain a facility efficiently. As an emerging field,
human-robot collaboration (HRC) still faces various open problems. To this end,
this pioneer research introduces an agent-based modeling approach to
investigate the coupling effect and scale effect of HRC in the bricklaying
process. With multiple experiments based on simulation, the dynamic and complex
nature of HRC is illustrated in two folds: 1) agents in HRC are interdependent
due to human factors of workers, features of robots, and their collaboration
behaviors; 2) different parameters of HRC are correlated and have significant
impacts on construction productivity (CP). Accidentally and interestingly, it
is discovered that HRC has a scale effect on CP, which means increasing the
number of collaborated human-robot teams will lead to higher CP even if the
human-robot ratio keeps unchanged. Overall, it is argued that more
investigations in HRC are needed for efficient construction, occupational
safety, etc.; and this research can be taken as a stepstone for developing and
evaluating new robots, optimizing HRC processes, and even training future
industrial workers in the construction industry
Absence of a transport signature of spin-orbit coupling in graphene with indium adatoms
Enhancement of the spin-orbit coupling in graphene may lead to various
topological phenomena and also find applications in spintronics. Adatom
absorption has been proposed as an effective way to achieve the goal. In
particular, great hope has been held for indium in strengthening the spin-orbit
coupling and realizing the quantum spin Hall effect. To search for evidence of
the spin-orbit coupling in graphene absorbed with indium adatoms, we carry out
extensive transport measurements, i.e., weak localization magnetoresistance,
quantum Hall effect and non-local spin Hall effect. No signature of the
spin-orbit coupling is found. Possible explanations are discussed.Comment: 5 pages, 4 figures, with supplementary material
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