SciCombinator

Discover the most talked about and latest scientific content & concepts.

Concept: Halting problem

154

We created a system using a triad of change management, electronic surveillance, and algorithms to detect sepsis and deliver highly sensitive and specific decision support to the point of care using a mobile application. The investigators hypothesized that this system would result in a reduction in sepsis mortality.

Concepts: Decision theory, Decision support system, Decision engineering, Data warehouse, Halting problem, Discrete mathematics, Knowledge engineering, Self service software

16

The spectral gap-the energy difference between the ground state and first excited state of a system-is central to quantum many-body physics. Many challenging open problems, such as the Haldane conjecture, the question of the existence of gapped topological spin liquid phases, and the Yang-Mills gap conjecture, concern spectral gaps. These and other problems are particular cases of the general spectral gap problem: given the Hamiltonian of a quantum many-body system, is it gapped or gapless? Here we prove that this is an undecidable problem. Specifically, we construct families of quantum spin systems on a two-dimensional lattice with translationally invariant, nearest-neighbour interactions, for which the spectral gap problem is undecidable. This result extends to undecidability of other low-energy properties, such as the existence of algebraically decaying ground-state correlations. The proof combines Hamiltonian complexity techniques with aperiodic tilings, to construct a Hamiltonian whose ground state encodes the evolution of a quantum phase-estimation algorithm followed by a universal Turing machine. The spectral gap depends on the outcome of the corresponding ‘halting problem’. Our result implies that there exists no algorithm to determine whether an arbitrary model is gapped or gapless, and that there exist models for which the presence or absence of a spectral gap is independent of the axioms of mathematics.

Concepts: Mathematics, Quantum mechanics, Existence, Quantum state, Standard Model, Halting problem, Turing machine, Undecidable problem

6

Collective animal behavior, such as the flocking of birds or the shoaling of fish, has inspired a class of algorithms designed to optimize distance-based clusters in various applications, including document analysis and DNA microarrays. In a flocking model, individual agents respond only to their immediate environment and move according to a few simple rules. After several iterations the agents self-organize, and clusters emerge without the need for partitional seeds. In addition to its unsupervised nature, flocking offers several computational advantages, including the potential to reduce the number of required comparisons.

Concepts: DNA, Algorithm, Bird, Computer, DNA microarray, Halting problem, Discrete mathematics, Shoaling and schooling

4

Many bioinformatics algorithms are designed for the analysis of sequences of some uniform length, conventionally referred to as k-mers. These include de Bruijn graph assembly methods and sequence alignment tools. An efficient algorithm to enumerate the number of unique k-mers, or even better, to build a histogram of k-mer frequencies would be desirable for these tools and their downstream analysis pipelines. Among other applications, estimated frequencies can be used to predict genome sizes, measure sequencing error rates, and tune runtime parameters for analysis tools. However, calculating a k-mer histogram from large volumes of sequencing data is a challenging task.

Concepts: Algorithm, Bioinformatics, Mathematics, Sequence, Natural number, Halting problem, De Bruijn graph, De Bruijn sequence

2

Advanced Automatic Crash Notification algorithms use vehicle telemetry measurements to predict risk of serious motor vehicle crash injury. The objective of the study was to develop an Advanced Automatic Crash Notification algorithm to reduce response time, increase triage efficiency, and improve patient outcomes by minimizing undertriage (<5%) and overtriage (<50%), as recommended by the American College of Surgeons.

Concepts: Algorithm, Improve, Halting problem

2

Tractography uses diffusion MRI to estimate the trajectory and cortical projection zones of white matter fascicles in the living human brain. There are many different tractography algorithms and each requires the user to set several parameters, such as curvature threshold. Choosing a single algorithm with specific parameters poses two challenges. First, different algorithms and parameter values produce different results. Second, the optimal choice of algorithm and parameter value may differ between different white matter regions or different fascicles, subjects, and acquisition parameters. We propose using ensemble methods to reduce algorithm and parameter dependencies. To do so we separate the processes of fascicle generation and evaluation. Specifically, we analyze the value of creating optimized connectomes by systematically combining candidate streamlines from an ensemble of algorithms (deterministic and probabilistic) and systematically varying parameters (curvature and stopping criterion). The ensemble approach leads to optimized connectomes that provide better cross-validated prediction error of the diffusion MRI data than optimized connectomes generated using a single-algorithm or parameter set. Furthermore, the ensemble approach produces connectomes that contain both short- and long-range fascicles, whereas single-parameter connectomes are biased towards one or the other. In summary, a systematic ensemble tractography approach can produce connectomes that are superior to standard single parameter estimates both for predicting the diffusion measurements and estimating white matter fascicles.

Concepts: Algorithm, Brain, Magnetic resonance imaging, Cerebellum, Programming language, Parameter, Halting problem

1

The third generation PacBio SMRT long reads can effectively address the read length issue of the second generation sequencing technology, but contain approximately 15% sequencing errors. Several error correction algorithms have been designed to efficiently reduce the error rate to 1%, but they discard large amounts of uncorrected bases and thus lead to low throughput. This loss of bases could limit the completeness of downstream assemblies and the accuracy of analysis.

Concepts: Algorithm, Mathematical analysis, Error, Sequence, Numerical analysis, Halting problem, Discrete mathematics, Cauchy sequence

1

One ultimate goal of metabolic network modeling is the rational redesign of biochemical networks to optimize the production of certain compounds by cellular systems. Although several constraint-based optimization techniques have been developed for this purpose, methods for systematic enumeration of intervention strategies in genome-scale metabolic networks are still lacking. In principle, Minimal Cut Sets (MCSs; inclusion-minimal combinations of reaction or gene deletions that lead to the fulfilment of a given intervention goal) provide an exhaustive enumeration approach. However, their disadvantage is the combinatorial explosion in larger networks and the requirement to compute first the elementary modes (EMs) which itself is impractical in genome-scale networks. We present MCSEnumerator, a new method for effective enumeration of the smallest MCSs (with fewest interventions) in genome-scale metabolic network models. For this we combine two approaches, namely (i) the mapping of MCSs to EMs in a dual network, and (ii) a modified algorithm by which shortest EMs can be effectively determined in large networks. In this way, we can identify the smallest MCSs by calculating the shortest EMs in the dual network. Realistic application examples demonstrate that our algorithm is able to list thousands of the most efficient intervention strategies in genome-scale networks for various intervention problems. For instance, for the first time we could enumerate all synthetic lethals in E.coli with combinations of up to 5 reactions. We also applied the new algorithm exemplarily to compute strain designs for growth-coupled synthesis of different products (ethanol, fumarate, serine) by E.coli. We found numerous new engineering strategies partially requiring less knockouts and guaranteeing higher product yields (even without the assumption of optimal growth) than reported previously. The strength of the presented approach is that smallest intervention strategies can be quickly calculated and screened with neither network size nor the number of required interventions posing major challenges.

Concepts: Protein, Metabolism, Metabolic pathway, Intervention, Metabolic network, Optimization, Halting problem, Assumption of Mary

1

Subgraph matching algorithms are designed to find all instances of predefined subgraphs in a large graph or network and play an important role in the discovery and analysis of so-called network motifs, subgraph patterns which occur more often than expected by chance. We present the index-based subgraph matching algorithm (ISMA), a novel tree-based algorithm. ISMA realizes a speedup compared to existing algorithms by carefully selecting the order in which the nodes of a query subgraph are investigated. In order to achieve this, we developed a number of data structures and maximally exploited symmetry characteristics of the subgraph. We compared ISMA to a naive recursive tree-based algorithm and to a number of well-known subgraph matching algorithms. Our algorithm outperforms the other algorithms, especially on large networks and with large query subgraphs. An implementation of ISMA in Java is freely available at http://sourceforge.net/projects/isma/.

Concepts: Algorithm, Graph theory, Design, Programming language, Halting problem, Discrete mathematics, Algorithmic efficiency, Turing machine

0

A total of 1099 breastmilk donations received by the milk bank at the Amiens University Hospital from January to June 2016 were assessed for bacteriological contamination according to French regulations. This consisted in enumerating the total aerobic flora before and after heat treatment as well as the specific enumeration of coagulase-positive staphylococci. Results above the mandatory limits for at least one of these parameters were found in 25.9% of the donations, resulting in the destruction of approximately one-quarter of the volume of the donations (∼195L). This is a huge loss in both economic and health-related terms for neonates, especially for pre-terms. To identify ways to improve the bacteriological assessment results and reduce the percentage of discarded milk, an analysis of the causes was conducted. The two main causes of non-compliance were the detection of a cultivable aerobic flora after heat treatment and the presence of coagulase-positive staphylococci above the mandatory limit (11.7% and 11.2% of the tested donations, respectively). Bacillus spp. were the leading cause of post-heat-treatment non-compliance. Therefore, the implementation of better environmental control could help reduce this kind of contamination. As for samples harboring coagulase-positive staphylococci, a further detection of toxins using molecular biology techniques could help discriminate actual health-hazardous donations that have to be destroyed while enabling the use of toxin-negative donations. Nevertheless, the economic viability of this proposal needs to be further assessed because these techniques are costly. Finally, a change in breastmilk dilutions used to enumerate the total aerobic flora to better reflect the actual level of these bacteria in the milk was proposed. Indeed, the comparison of various combinations of milk dilutions led to the conclusion that the association of the 1/10 and 1/100 dilutions was the best compromise between technical ease of enumeration and ensuring the safety of the donations. Implementing these suggestions would help reduce the rate of non-compliance and give better access to safe breastmilk donations for neonates.

Concepts: Better, Bacteria, Molecular biology, Milk, Breastfeeding, Natural number, Breast milk, Halting problem