34 research outputs found
Fluctuation-stabilized marginal networks and anomalous entropic elasticity
We study the elastic properties of thermal networks of Hookean springs. In
the purely mechanical limit, such systems are known to have vanishing rigidity
when their connectivity falls below a critical, isostatic value. In this work
we show that thermal networks exhibit a non-zero shear modulus well below
the isostatic point, and that this modulus exhibits an anomalous, sublinear
dependence on temperature . At the isostatic point, increases as the
square-root of , while we find below the isostatic
point, where . We show that this anomalous dependence
is entropic in origin.Comment: 9 pages, 7 figure
Exact sequence matches in genomic studies
The purpose of this article is to review usage of exact sequence matches in different field of genomic studies. Methods. The presentation is built in the form of a brief review of clearly non-exhaustive list of works in which the authors inferred biological knowledge using statistical properties of exact matches between different genomic texts or self-matches along the same genomic sequence. Results. Often, in genomic studies, different genomic loci exhibit different statistical properties, while their boundaries are not known a priory. In such cases we conclude that studying statistical properties of exact sequence matches is a useful alternative to other methods, for instance, based on arbitrary-size (non-)sliding windowing of the genome. Conclusion. This review demonstrates that exact sequences matches are not only an important auxiliary alignment step, but also helpful in other contexts. Their statistical properties are relatively easy to calculate analytically or numerically under various assumptions and compare to empirical data, validating models and fitting the models’ parameters
Detecting LLM-Generated Text in Computing Education: A Comparative Study for ChatGPT Cases
Due to the recent improvements and wide availability of Large Language Models
(LLMs), they have posed a serious threat to academic integrity in education.
Modern LLM-generated text detectors attempt to combat the problem by offering
educators with services to assess whether some text is LLM-generated. In this
work, we have collected 124 submissions from computer science students before
the creation of ChatGPT. We then generated 40 ChatGPT submissions. We used this
data to evaluate eight publicly-available LLM-generated text detectors through
the measures of accuracy, false positives, and resilience. The purpose of this
work is to inform the community of what LLM-generated text detectors work and
which do not, but also to provide insights for educators to better maintain
academic integrity in their courses. Our results find that CopyLeaks is the
most accurate LLM-generated text detector, GPTKit is the best LLM-generated
text detector to reduce false positives, and GLTR is the most resilient
LLM-generated text detector. We also express concerns over 52 false positives
(of 114 human written submissions) generated by GPTZero. Finally, we note that
all LLM-generated text detectors are less accurate with code, other languages
(aside from English), and after the use of paraphrasing tools (like QuillBot).
Modern detectors are still in need of improvements so that they can offer a
full-proof solution to help maintain academic integrity. Further, their
usability can be improved by facilitating a smooth API integration, providing
clear documentation of their features and the understandability of their
model(s), and supporting more commonly used languages.Comment: 18 pages total (16 pages, 2 reference pages). In submissio
Decay of Quantum Accelerator Modes
Experimentally observable Quantum Accelerator Modes are used as a test case
for the study of some general aspects of quantum decay from classical stable
islands immersed in a chaotic sea. The modes are shown to correspond to
metastable states, analogous to the Wannier-Stark resonances. Different regimes
of tunneling, marked by different quantitative dependence of the lifetimes on
1/hbar, are identified, depending on the resolution of KAM substructures that
is achieved on the scale of hbar. The theory of Resonance Assisted Tunneling
introduced by Brodier, Schlagheck, and Ullmo [9], is revisited, and found to
well describe decay whenever applicable.Comment: 16 pages, 11 encapsulated postscript figures (figures with a better
resolution are available upon request to the authors); added reference for
section
First passage time distribution for a random walker on a random forcing energy landscape
We present an analytical approximation scheme for the first passage time
distribution on a finite interval of a random walker on a random forcing energy
landscape. The approximation scheme captures the behavior of the distribution
over all timescales in the problem. The results are carefully checked against
numerical simulations.Comment: 16 page
Molecular motors robustly drive active gels to a critically connected state
Living systems often exhibit internal driving: active, molecular processes
drive nonequilibrium phenomena such as metabolism or migration. Active gels
constitute a fascinating class of internally driven matter, where molecular
motors exert localized stresses inside polymer networks. There is evidence that
network crosslinking is required to allow motors to induce macroscopic
contraction. Yet a quantitative understanding of how network connectivity
enables contraction is lacking. Here we show experimentally that myosin motors
contract crosslinked actin polymer networks to clusters with a scale-free size
distribution. This critical behavior occurs over an unexpectedly broad range of
crosslink concentrations. To understand this robustness, we develop a
quantitative model of contractile networks that takes into account network
restructuring: motors reduce connectivity by forcing crosslinks to unbind.
Paradoxically, to coordinate global contractions, motor activity should be low.
Otherwise, motors drive initially well-connected networks to a critical state
where ruptures form across the entire network.Comment: Main text: 21 pages, 5 figures. Supplementary Information: 13 pages,
8 figure
Effects of intersegmental transfers on target location by proteins
We study a model for a protein searching for a target, using facilitated
diffusion, on a DNA molecule confined in a finite volume. The model includes
three distinct pathways for facilitated diffusion: (a) sliding - in which the
protein diffuses along the contour of the DNA (b) jumping - where the protein
travels between two sites along the DNA by three-dimensional diffusion, and
finally (c) intersegmental transfer - which allows the protein to move from one
site to another by transiently binding both at the same time. The typical
search time is calculated using scaling arguments which are verified
numerically. Our results suggest that the inclusion of intersegmental transfer
(i) decreases the search time considerably (ii) makes the search time much more
robust to variations in the parameters of the model and (iii) that the optimal
search time occurs in a regime very different than that found for models which
ignore intersegmental transfers. The behavior we find is rich and shows
surprising dependencies, for example, on the DNA length.Comment: 40 pages, 14 figure
How evolution of genomes is reflected in exact DNA sequence match statistics
Genome evolution is shaped by a multitude of mutational processes, including point mutations, insertions, and deletions of DNA sequences, as well as segmental duplications. These mutational processes can leave distinctive qualitative marks in the statistical features of genomic DNA sequences. One such feature is the match length distribution (MLD) of exactly matching sequence segments within an individual genome or between the genomes of related species. These have been observed to exhibit characteristic power law decays in many species. Here, we show that simple dynamical models consisting solely of duplication and mutation processes can already explain the characteristic features of MLDs observed in genomic sequences. Surprisingly, we find that these features are largely insensitive to details of the underlying mutational processes and do not necessarily rely on the action of natural selection. Our results demonstrate how analyzing statistical features of DNA sequences can help us reveal and quantify the different mutational processes that underlie genome evolution