810 research outputs found
Optimal generation of entanglement under local control
We study the optimal generation of entanglement between two qubits subject to
local unitary control. With the only assumptions of linear control and unitary
dynamics, by means of a numerical protocol based on the variational approach
(Pontryagin's Minimum Principle), we evaluate the optimal control strategy
leading to the maximal achievable entanglement in an arbitrary interaction
time, taking into account the energy cost associated to the controls. In our
model we can arbitrarily choose the relative weight between a large
entanglement and a small energy cost.Comment: 4 page
Computational challenges of tumor spheroid modeling
The speed and the versatility of today's computers open up new opportunities
to simulate complex biological systems. Here we review a computational approach
recently proposed by us to model large tumor cell populations and spheroids,
and we put forward general considerations that apply to any fine-grained
numerical model of tumors. We discuss ways to bypass computational limitations
and discuss our incremental approach, where each step is validated by
experimental observations on a quantitative basis. We present a few results on
the growth of tumor cells in closed and open environments and of tumor
spheroids. This study suggests new ways to explore the initial growth phase of
solid tumors and to optimize anti-tumor treatments.Comment: 19 pages, 4 figures, 2 tables. Accepted for publication in Journal of
Bioinformatics and Computational Biolog
Ab initio phenomenological simulation of the growth of large tumor cell populations
In a previous paper we have introduced a phenomenological model of cell
metabolism and of the cell cycle to simulate the behavior of large tumor cell
populations (Chignola R and Milotti E, Phys. Biol. 2 (2005) 8-22). Here we
describe a refined and extended version of the model that includes some of the
complex interactions between cells and their surrounding environment. The
present version takes into consideration several additional energy-consuming
biochemical pathways such as protein and DNA synthesis, the tuning of
extracellular pH and of the cell membrane potential. The control of the cell
cycle - that was previously modeled by means of ad hoc thresholds - has been
directly addressed here by considering checkpoints from proteins that act as
targets for phosphorylation on multiple sites. As simulated cells grow, they
can now modify the chemical composition of the surrounding environment which in
turn acts as a feedback mechanism to tune cell metabolism and hence cell
proliferation: in this way we obtain growth curves that match quite well those
observed in vitro with human leukemia cell lines. The model is strongly
constrained and returns results that can be directly compared with actual
experiments, because it uses parameter values in narrow ranges estimated from
experimental data, and in perspective we hope to utilize it to develop in
silico studies of the growth of very large tumor cell populations (10^6 cells
or more) and to support experimental research. In particular, the program is
used here to make predictions on the behaviour of cells grown in a glucose-poor
medium: these predictions are confirmed by experimental observation.Comment: 67 pages, pdf only, submitted to Physical Biolog
Thresholds, long delays and stability from generalized allosteric effect in protein networks
Post-transductional modifications tune the functions of proteins and regulate
the collective dynamics of biochemical networks that determine how cells
respond to environmental signals. For example, protein phosphorylation and
nitrosylation are well-known to play a pivotal role in the intracellular
transduction of activation and death signals. A protein can have multiple sites
where chemical groups can reversibly attach in processes such as
phosphorylation or nitrosylation. A microscopic description of these processes
must take into account the intrinsic probabilistic nature of the underlying
reactions. We apply combinatorial considerations to standard enzyme kinetics
and in this way we extend to the dynamic regime a simplified version of the
traditional models on the allosteric regulation of protein functions. We link a
generic modification chain to a downstream Michaelis-Menten enzymatic reaction
and we demonstrate numerically that this accounts both for thresholds and long
time delays in the conversion of the substrate by the enzyme. The proposed
mechanism is stable and robust and the higher the number of modification sites,
the greater the stability. We show that a high number of modification sites
converts a fast reaction into a slow process, and the slowing down depends on
the number of sites and may span many orders of magnitude; in this way
multisite modification of proteins stands out as a general mechanism that
allows the transfer of information from the very short time scales of enzyme
reactions (milliseconds) to the long time scale of cell response (hours).Comment: 5 figures, submitted to Physica
The 15-Months Clinical Experience of SARS-CoV-2: A Literature Review of Therapies and Adjuvants
Background: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus responsible for the coronavirus disease of 2019 (COVID-19) that emerged in December 2019 in Wuhan, China, and rapidly spread worldwide, with a daily increase in confirmed cases and infection-related deaths. The World Health Organization declared a pandemic on the 11th of March 2020. COVID-19 presents flu-like symptoms that become severe in high-risk medically compromised subjects. The aim of this study was to perform an updated overview of the treatments and adjuvant protocols for COVID-19. Methods: A systematic literature search of databases was performed (MEDLINE PubMed, Google Scholar, UpToDate, Embase, and Web of Science) using the keywords: “COVID-19”, “2019-nCoV”, “coronavirus” and “SARS-CoV-2” (date range: 1 January 2019 to 31st October 2020), focused on clinical features and treatments. Results: The main treatments retrieved were antivirals, antimalarials, convalescent plasma, immunomodulators, corticosteroids, anticoagulants, and mesenchymal stem cells. Most of the described treatments may provide benefits to COVID-19 subjects, but no one protocol has definitively proven its efficacy. Conclusions: While many efforts are being spent worldwide in research aimed at identifying early diagnostic methods and evidence-based effective treatments, mass vaccination is thought to be the best option against this disease in the near future
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