237 research outputs found
Quantitative constraint-based computational model of tumor-to-stroma coupling via lactate shuttle
Cancer cells utilize large amounts of ATP to sustain growth, relying primarily on non-oxidative,
fermentative pathways for its production. In many types of cancers this leads, even in the presence
of oxygen, to the secretion of carbon equivalents (usually in the form of lactate) in the cell’s
surroundings, a feature known as the Warburg effect. While the molecular basis of this phenomenon
are still to be elucidated, it is clear that the spilling of energy resources contributes to creating a
peculiar microenvironment for tumors, possibly characterized by a degree of toxicity. This suggests
that mechanisms for recycling the fermentation products (e.g. a lactate shuttle) may be active,
effectively inducing a mutually beneficial metabolic coupling between aberrant and non-aberrant
cells. Here we analyze this scenario through a large-scale in silico metabolic model of interacting
human cells. By going beyond the cell-autonomous description, we show that elementary physico-
chemical constraints indeed favor the establishment of such a coupling under very broad conditions.
The characterization we obtained by tuning the aberrant cell’s demand for ATP, amino-acids and
fatty acids and/or the imbalance in nutrient partitioning provides quantitative support to the idea
that synergistic multi-cell effects play a central role in cancer sustainmen
How Quantum Computers Fail: Quantum Codes, Correlations in Physical Systems, and Noise Accumulation
The feasibility of computationally superior quantum computers is one of the
most exciting and clear-cut scientific questions of our time. The question
touches on fundamental issues regarding probability, physics, and
computability, as well as on exciting problems in experimental physics,
engineering, computer science, and mathematics. We propose three related
directions towards a negative answer. The first is a conjecture about physical
realizations of quantum codes, the second has to do with correlations in
stochastic physical systems, and the third proposes a model for quantum
evolutions when noise accumulates. The paper is dedicated to the memory of
Itamar Pitowsky.Comment: 16 page
Randomized Control in Performance Analysis and Empirical Asset Pricing
The present article explores the application of randomized control techniques
in empirical asset pricing and performance evaluation. It introduces geometric
random walks, a class of Markov chain Monte Carlo methods, to construct
flexible control groups in the form of random portfolios adhering to investor
constraints. The sampling-based methods enable an exploration of the
relationship between academically studied factor premia and performance in a
practical setting. In an empirical application, the study assesses the
potential to capture premias associated with size, value, quality, and momentum
within a strongly constrained setup, exemplified by the investor guidelines of
the MSCI Diversified Multifactor index. Additionally, the article highlights
issues with the more traditional use case of random portfolios for drawing
inferences in performance evaluation, showcasing challenges related to the
intricacies of high-dimensional geometry.Comment: 57 pages, 7 figures, 2 table
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