Search

Background: To minimize measurement uncertainties and create seamless procedures between tests and simulations for the characterization and prediction of damage in large scale structures, a system capable of monitoring the quantities of interest at different scales throughout the test is required. Objective: The aim of this work is to develop a multiview DIC framework at varying scales in which kinematic fields are expressed on a unique mesh. Methods: A three-point flexural test was performed on a concrete beam and the images acquired by three different cameras were used to perform DIC calculations. Results: Displacement and strain fields were measured using mono and multiview implementations; their associated uncertainties were assessed. Damage initiation and growth within the sample was quantified based on the standard displacement uncertainty. Conclusion: The reported results show that the proposed method reduced the associated displacement uncertainties. The onset and propagation of damage was successfully quantified. [ABSTRACT FROM AUTHOR]

We extend our study of the swarm-based gradient descent method for non-convex optimization, (Lu et al., Swarm-based gradient descent method for non-convex optimization, 2022, arXiv:2211.17157), to allow random descent directions. We recall that the swarm-based approach consists of a swarm of agents, each identified with a position, x , and mass, m . The key is the transfer of mass from high ground to low(-est) ground. The mass of an agent dictates its step size: lighter agents take larger steps. In this paper, the essential new feature is the choice of direction: rather than restricting the swarm to march in the steepest gradient descent, we let agents proceed in randomly chosen directions centered around — but otherwise different from — the gradient direction. The random search secures the descent property while at the same time, enabling greater exploration of ambient space. Convergence analysis and benchmark optimizations demonstrate the effectiveness of the swarm-based random descent method as a multi-dimensional global optimizer. [ABSTRACT FROM AUTHOR]

The purpose of this study is to explore students’ backtracking patterns in using a digital textbook, reveal the relationship between backtracking behaviors and academic performance as well as learning styles. This study was carried out for 2 semesters on 102 university students and they are required to use a digital textbook system called DITeL to review courseware. Students’ backtracking behaviors are characterized by seven backtracking features extracted from interaction log data and their learning styles are measured by Felder–Silverman learning style model. The results of this study reveal that there is a subgroup of students called backtracker who backtrack more frequently and performed better than the average students. Furthermore, the causal inference analysis reveals that a higher initial ability can directly cause a higher frequency of backtracking, thus affecting the final test score. In addition, the significance analysis reveals no significant correlation between backtracking behavior and learning style. Building upon these experimental findings, we offer several suggestions for the future advancement of digital teaching materials development. [ABSTRACT FROM AUTHOR]

Bacterial nucleotide excision repair (NER) has been extensively studied in vitro , but its modus operandi in living cells remains to be fully explored and understood. New studies in Escherichia coli reveal the essential role of RNA polymerase both in locating bulky lesions genome-wide and also in the delivery and assembly of functional NER complexes at the lesion sites. New studies in E. coli reveal the phenomenon of pervasive transcription-coupled NER, which encompasses all parts of the genome – including antisense and intergenic regions – due to suppression of transcription termination. The concept of RNA polymerase-driven DNA repair is likely to be generalizable to other repair pathways to address the common fundamental problem of promptly locating the rare lesions in the genome of a living cell. The nucleotide excision repair (NER) pathway removes helix-distorting lesions from DNA in all organisms. Escherichia coli has long been a model for understanding NER, which is traditionally divided into major and minor subpathways known as global genome repair (GGR) and transcription-coupled repair (TCR), respectively. TCR has been assumed to be mediated exclusively by Mfd, a DNA translocase of minimal NER phenotype. This review summarizes the evidence that shaped the traditional view of NER in bacteria, and reviews data supporting a new model in which GGR and TCR are inseparable. In this new model, RNA polymerase serves both as the essential primary sensor of bulky DNA lesions genome-wide and as the delivery platform for the assembly of functional NER complexes in living cells. [ABSTRACT FROM AUTHOR]

With the rapid development of multimedia technology, it is very important to improve the accuracy of sparse signal reconstruction for image or speech based on compressed sensing technology. In this work, a matching pursuit algorithm for sparse signal reconstruction based on Jaccard coefficient and backtracking strategy is proposed to improve the accurate reconstruction probability. Jaccard coefficient matching criterion and inner product matching criterion are combined to preserve more features of the original vector. A mean-based thresholding strategy is used to selects atoms adaptively, and the backtracking method is introduced to filter out the wrong atoms. Experimental results show that the reconstruction performance of the proposed algorithm is much better than other greedy algorithms when the sparsity K is large (K>35). For speech signals, the proposed algorithm has better reconstruction performance than other algorithms for both male and female voice signals. Under different compression ratios, the AFSNR and the PESQ scores of the reconstructed speech by the proposed algorithm are increased by at least 1.5348 dB and 0.5629, respectively, especially showing superior performance under larger compression ratio. The proposed algorithm has bright application prospect in intelligent speech interaction with accurate reconstruction of speech signal under large compression ratios. [ABSTRACT FROM AUTHOR]

Causal models show promise as a foundation for the semantics of counterfactual sentences. However, current approaches face limitations compared to the alternative similarity theory: they only apply to a limited subset of counterfactuals and the connection to counterfactual logic is not straightforward. This article addresses these difficulties using exogenous interventions, where causal interventions change the values of exogenous variables rather than structural equations. This model accommodates judgments about backtracking counterfactuals, extends to logically complex counterfactuals, and validates familiar principles of counterfactual logic. This combines the interventionist intuitions of the causal approach with the logical advantages of the similarity approach. [ABSTRACT FROM AUTHOR]

Transcription elongation by multi-subunit RNA polymerases (RNAPs) is regulated by auxiliary factors in all organisms. NusG/Spt5 is the only universally conserved transcription elongation factor shared by all domains of life. NusG is a component of antitermination complexes controlling ribosomal RNA operons, an essential antipausing factor, and a transcription-translation coupling factor in Escherichia coli. We employed RNET-seq for genome-wide mapping of RNAP pause sites in wild-type and NusG-depleted cells. We demonstrate that NusG is a major antipausing factor that suppresses thousands of backtracked and nonbacktracked pauses across the E. coli genome. The NusG-suppressed pauses were enriched immediately downstream from the translation start codon but were also abundant elsewhere in open reading frames, small RNA genes, and antisense transcription units. This finding revealed a strong similarity of NusG to Spt5, which stimulates the elongation rate of many eukaryotic genes. We propose a model in which promoting forward translocation and/or stabilization of RNAP in the posttranslocation register by NusG results in suppression of pausing in E. coli. [ABSTRACT FROM AUTHOR]

The simplified partial digest problem (SPDP) models an effective and robust method for the building of a physical map using restriction site analysis. The best known algorithm requires O(n2n) time, using O(n2n) working space. The high complexities in time and space impede its application to genomes of a large number of sites. This article gives two new algorithms. The first improves the time by a factor of O(n) and significantly reduces the space to O(n2). The second improves both the time and space to O(n1.52n/2). Extensive experiments are conducted on real genomes. For instances that can be solved by the best known algorithm, the new algorithms achieve a speedup of up to 4000 times; in addition, due to the reduction in space, the new algorithms can solve many more instances. Experiments also reveal the following advantage of the SPDP method: almost every instance has at most four feasible solutions and for an instance that does not contain any pair of symmetric restriction sites, in all observed examples, the solution is unique. [ABSTRACT FROM AUTHOR]

Summary: The growth of small communication devices has pushed designers to design compact‐size antennas. These antennas must be low cost, lightweight, needed for mechanically robust construction, and ease of installation. In this paper, we use a novel genetic algorithm (GA) to produce an ensemble of compact self‐avoiding (SA) antennas such that the voltage standing wave ratio (VSWR) is less than 2 at the desired frequencies (as a measure of efficiency); an optimization criterion to get a desirable multiband antenna in the ultra high frequency (UHF) band. First, the electromagnetic properties of these antennas are simulated using the method of moments in MATLAB. SA antennas form a particular set of dipoles introduced here by applying a novel backtracking algorithm. We also use a Lindenmayer system that generates the geometries by a Turtle graphics render to reach our goal. Next, we simulate the VSWR for 150,000 SA antennas with lengths L from 0.1 to 0.4 m; 10 different frequencies are chosen randomly within the UHF band to obtain our results. All the VSWR ≤ 2 are clustered using density‐based spatial clustering of applications with noise algorithm (DBSCAN), so our method provides the frequency ranges where this condition is fulfilled. From this, we obtain the VSWR minimums used for the antenna design. Finally, as an instance, we use our results to select the appropriate size of a multiband antenna and, through genetic algorithms, modify the geometry to satisfy the design requirements. [ABSTRACT FROM AUTHOR]

Modernization and the ever-increasing trend of introducing modern technologies into various areas of everyday life require school graduates with programming skills. The ability to program is closely related to computational thinking, which is based on algorithmic thinking. It is well known that algorithmic thinking is the ability of students to work with algorithms understood as a systematic description of problem-solving strategies. Algorithms can be considered as a fundamental phenomenon that forms a point of contact between mathematics and informatics. As part of an algorithmic graph theory seminar, we conducted an experiment where we solved the knight's tour problem using the backtracking method to observe the change in students' motivation to learn algorithms at a higher cognitive level. Seventy-four students participated in the experiment. Statistical analysis of the results of the experiment confirmed that the use of the algorithm with decision-making in teaching motivated students to learn algorithms with understanding. [ABSTRACT FROM AUTHOR]

This study explored children's causal reasoning about the past and future. U.S. adults (n = 60) and 3‐to‐6‐year‐olds (n = 228) from an urban, middle‐class population (49% female; ~45% white) participated between 2017 and 2019. Participants were told three‐step causal stories and asked about the effects of a change to the second event. Given direct interventions on the second event, children of all ages judged that the past event still occurred, suggesting even preschoolers understand time is irreversible. However, children reasoned differently when told that the second event did not occur, with no specific cause. In this case, 6‐year‐olds and adults inferred that the past event also did not occur. In both conditions, inferences that future events would change emerged gradually between 4 and 6. [ABSTRACT FROM AUTHOR]

• Solar tracking is a crucial task in efficiently harvesting solar power in a PV plant. • Horizontal Single-axis tracking systems require a precise estimation of its axis' orientation. • This methodology uses available data to accurately estimate the tracker's orientation. • This methodology estimates height differences in adjacent trackers. • The improve tracking and backtracking strategies increase production by 1%. Photovoltaic (PV) energy production is becoming a more significant part of the energy mix world-wide due to its clean origin, supportive and cost reductions. Therefore, it is increasingly important to develop methodologies to improve efficiency and reduce energy losses. Solar tracking is a way of increasing the irradiance over the PV field and, subsequently, boosting energy production. Both single-axis and double-axis tracking systems (SATS & DATS) are well known methods but both require not only a proper estimation of the sun's position but also precise knowledge of the tracker's position and orientation. Several factors (construction, design, configuration) can cause the values used to calculate the optimal tracking to be inaccurate, thus increasing production losses. This paper proposes a methodology to calculate the actual orientation of the trackers' axis based on the energy production of its associated strings. Additionally, it provides the height differences between adjacent trackers by detecting shading patterns. This information is key to defining more efficient tracking and backtracking strategies the avoid row-to-row shading and, overall increasing energy production. The proposed method is applied to a real 5 MW facility, identifying misalignments of several degrees in most trackers that were causing annual losses (1 %), not only due to inaccurate tracking but also row-to-row shading. [ABSTRACT FROM AUTHOR]

Finite control set model predictive control (FCS-MPC) has been widely recognized in the field of electrical drive control during the past decades, due to its merits of quick dynamic response and low switching frequency. However, it is inherently penalized by high tracking deviations in the steady-state as well as exhaustive search among the switching sequences. To cope with this issue, a low-complexity gradient descent-based finite control set predictive current control (GD-FCSPCC) combined with a backtracking iteration approach is proposed in this article, aiming to improve the control performance by effectively tracking the reference value. First, FCS-PCC is reformulated as a quadratic programming (QP) problem from a geometric perspective. Consequently, the convexity of QP problem is proved to underlying the gradient descent, which minimizes the tracking deviations in an effective manner. Thus, the optimal solutions are selected by optimizing the reformulated objective functions. To reduce the number of the searched control inputs, a two-layer generalized decision-tree is employed. The procedures are repeated in several iteration periods optimized via a backtracking method, until the stopping criterion is satisfied. The effectiveness of the proposed GD-FCSPCC is experimentally validated on a 2.2 kW induction machine testbench. [ABSTRACT FROM AUTHOR]

Inertial odometry is a typical localization method that is widely and easily accessible in many devices. Pedestrian positioning can benefit from this approach based on inertial measurement unit (IMU) values embedded in smartphones. Fitting the inertial odometry outputs, namely step length and step heading of a human for instance, with spatial information is an ubiquitous way to correct for the cumulative noises. This so-called map-matching process can be achieved in several ways. In this paper, a novel real-time map-matching approach was developed, using a backtracking particle filter that benefits from the implemented geospatial analysis, which reduces the complexity of spatial queries and provides flexibility in the use of different kinds of spatial constraints. The goal was to generalize the algorithm to permit the use of any kind of odometry data calculated by different sensors and approaches as the input. Further research, development, and comparisons have been done by the easy implementation of different spatial constraints and use cases due to the modular structure. Additionally, a simple map-based optimization using transition areas between floors has been developed. The developed algorithm could achieve accuracies of up to 3 m at approximately the 90th percentile for two different experiments in a complex building structure. [ABSTRACT FROM AUTHOR]

This paper presents a novel backtracking strategy for additive Schwarz methods for general convex optimization problems as an acceleration scheme. The proposed backtracking strategy is independent of local solvers, so that it can be applied to any algorithms that can be represented in an abstract framework of additive Schwarz methods. Allowing for adaptive increasing and decreasing of the step size along the iterations, the convergence rate of an algorithm is improved. The improved convergence rate of the algorithm is analyzed rigorously. In addition, combining the proposed backtracking strategy with a momentum acceleration technique, we propose a further accelerated additive Schwarz method. Numerical results for various convex optimization problems such as nonlinear elliptic problems, nonsmooth problems, and nonsharp problems are presented in order to support our theory. [ABSTRACT FROM AUTHOR]

Supercomputers and datacenters comprise hundreds of thousands of servers. Different network topologies have been proposed to attain such a high scalability, from flattened Butterfly and Dragonfly to the most disruptive Jellyfish, which is based on a random graph. The routing problem on such networks remains a challenge that can be tackled either as a topology-aware solution or with an agnostic approach. The case of random networks is a very special one since no a priori topological clues can be exploited. In this article, we introduce the polarized routing algorithm, an adaptive nonminimal hop-by-hop mechanism that can be used in most of topologies, including Jellyfish. Polarized routing follows two design criteria: a source–destination symmetry in the routes and avoiding backtracking. Experimental evaluation proves that polarized routing not only outperforms other routings in random graphs but also attains the best performance provided by ad hoc solutions for specific outstanding low-diameter interconnection networks. [ABSTRACT FROM AUTHOR]

Beaches are thought to be a large reservoir for marine plastics. To protect vulnerable beaches, it is advantageous to have information on the sources of this plastic. Here, we develop a universally applicable Bayesian framework to map sources of plastic arriving on a specific beach. In this framework, we combine Lagrangian backtracking simulations of drifting particles with estimates of plastic input from coastlines, rivers and fisheries. The advantage over traditional Lagrangian simulations is that the Bayesian framework can consider information on known sources, and thus facilitates spatiotemporal source attribution for plastic arriving at the specified beach. We show that the main sources for our target beach in southwest Netherlands are the east coast of the UK, the Dutch coast, the English Channel (fisheries) and the Thames, Seine, Rhine and Trieux (rivers). We also show that floating time is a major uncertainty in source attribution using backtracking. Plain Language Summary: A large part of plastic in the ocean is located at or near beaches. This plastic can break down into micro‐plastics or be ingested by animals. Therefore, it is important to clean up these beaches. The easiest way to do so is to prevent the plastic from entering the oceans initially by interfering at the source. In this study, we develop a framework to find these sources for a given beach. We first simulate the path that plastic has taken to reach this beach. We do this by releasing virtual plastic particles at the beach where they end up. Next, we calculate their paths back in time, computing their trajectories until they reach this beach. We then combine these simulations with data on the sources of plastic: where and when did plastic enter the ocean? We apply this framework to a beach in southwest Netherlands, near the town of Domburg. We quantify seasonal effects, where time‐varying currents cause the plastic to come from different sources. Lastly, we study how plastic sources vary with plastic age (the time between the plastic entering the ocean and beaching at its final location). Key Points: Combined oceanic backtracking and Bayesian statistics supports source attribution of beached plasticStrong seasonal variability in likely sources is found, due to variability in plastic input and currentsFloating time remains a major uncertainty in determining the origin of beached plastic via backtracking [ABSTRACT FROM AUTHOR]

Local pseudorandom generators are a class of fundamental cryptographic primitives having very broad applications in theoretical cryptography. Following Couteau et al.’s work at ASIACRYPT 2018, this paper further studies the concrete security of one important class of local pseudorandom generators, i.e., Goldreich’s pseudorandom generators. Our first attack is of the guess-and-determine type. Our result significantly improves the state-of-the-art algorithm proposed by Couteau et al., in terms of both asymptotic and concrete complexity, and breaks all the challenge parameters they proposed. For instance, for a parameter set suggested for 128 bits of security, we could solve the instance faster by a factor of about 277, thereby destroying the claimed security completely. Our second attack further exploits the extremely sparse structure of the predicate $P_{5}$ and combines ideas from iterative decoding. This novel attack, named guess-and-decode, substantially improves the guess-and-determine approaches for cryptographic-relevant parameters. All the challenge parameter sets proposed in Couteau et al.’s work in ASIACRYPT 2018 aiming for 80-bit (128-bit) security levels can be solved in about 258 (278) operations. We suggest new parameters for achieving 80-bit (128-bit) security with respect to our attacks. We also extend the attacks to other promising predicates and investigate their resistance. [ABSTRACT FROM AUTHOR]

Path planning for mobile robot aims to solve the problem of creating a collision‐free path from the start state to the goal state in the given space, which is a key supporting technology for unmanned work. In order to solve the problems of the asymptotic optimal rapidly extended random trees star (RRT*) algorithm, such as its slow convergence rate, the low efficiency of planning and the high cost of path, an improved motion planner (Fast‐RRT*) was proposed based on hybrid sampling strategy and choose parent based on backtracking. Firstly, the goal bias strategy and constraint sampling are combined in the sampling stage to reduce the blindness of sampling. Secondly, to obtain a path with lower cost than the RRT* algorithm, the ancestor of the nearest node is considered until the initial state in the process of choose parent for new node. To ensure the feasibility of the path, the path is smoothed by cubic B‐spline curve. The effectiveness of Fast‐RRT* algorithm was verified based on MATLAB and V‐rep platform. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

The horizontal single-axis tracker system (HSAT) moves collectors changing the East-West orientation to track the sun's position during the day. However, as a limitation, it requires a higher area than the fixed tilt system (SAF) for the same power. Recently, HSAT with backtracking (HSAT-B) has been developed to increase the ground cover ratio (GCR). By backtracking, modules move such that no mutual beam shading occurs. As Cuba is a small country with land constraints for construction of new solar farms, the authors compared the HSAR-B with the SAF and. the East-West orientation system (SEO), and concluded that, facing land restrictions and taking into account the specific characteristics of the site, the backtracking is other technology to assess. [ABSTRACT FROM AUTHOR]

RNA polymerase II (RNA Pol II) can backtrack during transcription elongation, exposing the 3′ end of nascent RNA. Nascent RNA sequencing can approximate the location of backtracking events that are quickly resolved; however, the extent and genome-wide distribution of more persistent backtracking are unknown. Consequently, we developed a method to directly sequence the extruded, "backtracked" 3′ RNA. Our data show that RNA Pol II slides backward more than 20 nt in human cells and can persist in this backtracked state. Persistent backtracking mainly occurs where RNA Pol II pauses near promoters and intron-exon junctions and is enriched in genes involved in translation, replication, and development, where gene expression is decreased if these events are unresolved. Histone genes are highly prone to persistent backtracking, and the resolution of such events is likely required for timely expression during cell division. These results demonstrate that persistent backtracking can potentially affect diverse gene expression programs. [Display omitted] • Human RNA polymerase II backtracks over 20 nt persistently in vivo • Persistent backtracking commonly occurs near splicing junctions and promoters • Histone gene expression is highly affected by persistent backtracking • Persistent backtracking potentially affects diverse gene expression programs Yang et al. reveal that human RNA polymerase II often experiences extensive backtracking, leading to persistent entrapment in a backtracked state in vivo. This phenomenon is commonly observed near splice sites and gene starting points and particularly in histones. Persistent backtracking is likely to impact various gene expression programs significantly. [ABSTRACT FROM AUTHOR]

• Half-cut cells are the new standard for solar photovoltaic modules. • Standard backtracking can be outperformed by more sophisticated approaches. • Yield optimisation can reduce levelised cost of electricity up to 12% • Increasing full load hours of single-axis tracking systems possible with shading. • Power density optimisation important for future solar-driven energy system. Optimisation of horizontal single-axis tracking solar photovoltaic power plants is important for its optimal application. Commonly, standard backtracking has been applied to avoid mutual shading and improve the full load hours and levelised cost of electricity; however, this approach is not always the best solution for state-of-the-art modules with half cell technology. Backtracking has not yet been studied for different test sites with different solar and climatic conditions. This study aims to improve the knowledge on the techno-economic performance of horizontal single-axis tracking systems with half cell modules applying different backtracking strategies in full hourly resolution for nine test sites globally and varying row spacing. In addition to the standard backtracking algorithm, an advanced backtracking algorithm that varies the tracking angle only if the irradiance can be improved, and an advanced sophisticated backtracking algorithm simulating the irradiance for all possible tracking angles, are studied. The results confirm that standard backtracking is only superior for specific conditions. Compared to no backtracking, standard backtracking shows up to ca. 9% higher levelised cost of electricity due to lower full load hours. Advanced backtracking can lower the levelised cost of electricity by up to 9% and advanced sophisticated backtracking by up to 12%, due to improved full load hours. In general, results are similar and comparable for all test sites studied. This study highlights the importance of backtracking for optimised future horizontal single-axis tracking system planning. [ABSTRACT FROM AUTHOR]

In this paper, we provide new results and algorithms (including backtracking versions of Nesterov accelerated gradient and Momentum) which are more applicable to large scale optimisation as in Deep Neural Networks. We also demonstrate that Backtracking Gradient Descent (Backtracking GD) can obtain good upper bound estimates for local Lipschitz constants for the gradient, and that the convergence rate of Backtracking GD is similar to that in classical work of Armijo. Experiments with datasets CIFAR10 and CIFAR100 on various popular architectures verify a heuristic argument that Backtracking GD stabilises to a finite union of sequences constructed from Standard GD for the mini-batch practice, and show that our new algorithms (while automatically fine tuning learning rates) perform better than current state-of-the-art methods such as Adam, Adagrad, Adadelta, RMSProp, Momentum and Nesterov accelerated gradient. To help readers avoiding the confusion between heuristics and more rigorously justified algorithms, we also provide a review of the current state of convergence results for gradient descent methods. Accompanying source codes are available on GitHub. [ABSTRACT FROM AUTHOR]

Multiple patterning lithography has been widely adopted in advanced technology nodes of VLSI manufacturing. As a key step in the design flow, multiple patterning layout decomposition (MPLD) is critical to design closure. Due to the $\mathcal {N} \mathcal {P} $ -hardness of the general decomposition problem, various efficient algorithms have been proposed with high-quality solutions. However, with increasingly complicated design flow and peripheral processing steps, developing a high-quality layout decomposer becomes more and more difficult, slowing down further advancement in this field. This article presents $\mathsf {OpenMPL}$ (2020), an open-source layout decomposition framework, with well-separated peripheral processing and core solving steps. Besides, previous algorithms or techniques are inspected and several issues are discovered. We then propose corresponding new algorithms to resolve these issues. The experiments demonstrate the effectiveness of our proposed algorithms and the efficiency of $\mathsf {OpenMPL}$. [ABSTRACT FROM AUTHOR]

Cellular life depends on transcription of DNA by RNA polymerase to express genetic information. RNA polymerase has evolved not just to read information from DNA and write it to RNA but also to sense and process information from the cellular and extracellular environments. Much of this information processing occurs during transcript elongation, when transcriptional pausing enables regulatory decisions. Transcriptional pauses halt RNA polymerase in response to DNA and RNA sequences and structures at locations and times that help coordinate interactions with small molecules and transcription factors important for regulation. Four classes of transcriptional pause signals are now evident after decades of study: elemental pauses, backtrack pauses, hairpin-stabilized pauses, and regulator-stabilized pauses. In this review, I describe current understanding of the molecular mechanisms of these four classes of pause signals, remaining questions about how RNA polymerase responds to pause signals, and the many exciting directions now open to understand pausing and the regulation of transcript elongation on a genome-wide scale. [ABSTRACT FROM AUTHOR]

Directed self-assembly (DSA) is one of the leading candidates for extending the resolution of optical lithography to sub-7 nm and beyond. By incorporating DSA in multiple patterning lithography (DSA-MP), the flexibility and resolution of contact/via patterning can be further enhanced by using multiple block copolymer (BCP) materials. Prior work faces the dilemma between solution quality and efficiency and is unable to handle 2-D templates. In this article, we capture the essence of template and mask assignment in DSA-MP by a new graph model and a new problem reduction: Our graph model explicitly represents spacing conflict edges and template hyperedges; thus, extra enumeration and manipulation of incompatible via grouping edges can be avoided, and arbitrary 1-D/2-D templates can be natively handled. We further reduce the assignment problem to exact cover, which is encoded by a sparse matrix. Our concise integer linear programming (ILP) formulation and fast backtracking heuristic achieve substantially superior solution quality and efficiency to the state-of-the-art work. Moreover, our problem and graph modelling is flexible and extensible to utilize dummy vias to improve manufacturability. To narrow down the search region of dummy vias, we devise a conflict core finding technique, which is general and applicable to conflict core analysis of exact cover and other multiple patterning layout decomposition problems. Experimental results show the effectiveness and efficiency of our approach. [ABSTRACT FROM AUTHOR]

Immunofixation Electrophoresis (IFE) analysis is of great importance to the diagnosis of Multiple Myeloma, which is among the top-9 cancer killers in the United States, but has rarely been studied in the context of deep learning. Two possible reasons are: 1) the recognition of IFE patterns is dependent on the co-location of bands that forms a binary relation, different from the unary relation (visual features to label) that deep learning is good at modeling; 2) deep classification models may perform with high accuracy for IFE recognition but is not able to provide firm evidence (where the co-location patterns are) for its predictions, rendering difficulty for technicians to validate the results. We propose to address these issues with collocative learning, in which a collocative tensor has been constructed to transform the binary relations into unary relations that are compatible with conventional deep networks, and a location-label-free method that utilizes the Grad-CAM saliency map for evidence backtracking has been proposed for accurate localization. In addition, we have proposed Coached Attention Gates that can regulate the inference of the learning to be more consistent with human logic and thus support the evidence backtracking. The experimental results show that the proposed method has obtained a performance gain over its base model ResNet18 by 741.30% in IoU and also outperformed popular deep networks of DenseNet, CBAM, and Inception-v3. [ABSTRACT FROM AUTHOR]

Backtracking, the reverse motion of the transcriptase enzyme on the nucleic acid template, is a universal regulatory feature of transcription in cellular organisms but its role in viruses is not established. Here we present evidence that backtracking extends into the viral realm, where backtracking by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA-dependent RNA polymerase (RdRp) may aid viral transcription and replication. Structures of SARS-CoV-2 RdRp bound to the essential nsp13 helicase and RNA suggested the helicase facilitates backtracking. We use cryo-electron microscopy, RNA-protein cross-linking, and unbiased molecular dynamics simulations to characterize SARS-CoV-2 RdRp backtracking. The results establish that the single-stranded 3' segment of the product RNA generated by backtracking extrudes through the RdRp nucleoside triphosphate (NTP) entry tunnel, that a mismatched nucleotide at the product RNA 3' end frays and enters the NTP entry tunnel to initiate backtracking, and that nsp13 stimulates RdRp backtracking. Backtracking may aid proofreading, a crucial process for SARS-CoV-2 resistance against antivirals. [ABSTRACT FROM AUTHOR]

Cellular life depends on transcription of DNA by RNA polymerase to express genetic information. RNA polymerase has evolved not just to read information from DNA and write it to RNA but also to sense and process information from the cellular and extracellular environments. Much of this information processing occurs during transcript elongation, when transcriptional pausing enables regulatory decisions. Transcriptional pauses halt RNA polymerase in response to DNA and RNA sequences and structures at locations and times that help coordinate interactions with small molecules and transcription factors important for regulation. Four classes of transcriptional pause signals are now evident after decades of study: elemental pauses, backtrack pauses, hairpin-stabilized pauses, and regulator-stabilized pauses. In this review, I describe current understanding of the molecular mechanisms of these four classes of pause signals, remaining questions about how RNA polymerase responds to pause signals, and the many exciting directions now open to understand pausing and the regulation of transcript elongation on a genome-wide scale. [ABSTRACT FROM AUTHOR]

We examine the problem of finding all solutions of two-sided vector inequalities given in the tropical algebra setting, where the unknown vector multiplied by known matrices appears on both sides of the inequality. We offer a solution that uses sparse matrices to simplify the problem and to construct a family of solution sets, each defined by a sparse matrix obtained from one of the given matrices by setting some of its entries to zero. All solutions are then combined to present the result in a parametric form in terms of a matrix whose columns form a complete system of generators for the solution. We describe the computational technique proposed to solve the problem, remark on its computational complexity and illustrate this technique with numerical examples. [ABSTRACT FROM AUTHOR]

This article examines the problem of balancing modern assembly lines for large-size products typical for the automotive industry. The model of a multimanned assembly line balancing problem is proposed, in which assembly tasks are assigned to specific areas closely related to the place of the performance thereof on the vehicle. The model takes into account additional location restrictions. The proposed approach fits in with current trends aiming at minimizing the space occupied by assembly lines along with reducing the number of stations. A hybrid method is proposed combining modified known heuristics of task assignments to workstations with bounding and backtracking techniques in order to determine the assignment of workers to tasks. [ABSTRACT FROM AUTHOR]

• A new tracking strategy with backtracking for PV plants is analysed. • Maximum irradiance is achieved even during backtracking. • Impacts of the design variables of PV plants with this tracking plan are studied. • Design criteria for PV plants with the suggested tracking strategy are proposed. • PV Plants could provide, at least, 2% more energy using this tracking strategy. Photovoltaics is experiencing significant growth because it is a renewable energy resource capable of contributing positively to the global energy system. However, the high variability in solar resources and the inter-collectors shadows negatively influence the energy conversion of a photovoltaic plant, making it necessary to develop technologies that minimize these negative aspects. Considering these issues, this paper analyses the influence of the design variables of a PV plant with two-axis tracking (collector size and distance between collectors) on its energy conversion. For that purpose, the tracking/backtracking strategy considered has two important advantages: it allows eliminating the inter-collector shading and optimizes the collection of global solar irradiance during both tracking and backtracking, by considering not only the optimization of direct component of solar irradiance but also the diffuse and reflected components. Based on this analysis, specific design recommendations are proposed for two-axis tracking PV plants located in Cordoba (Spain). It has been proved that differences in orientation between the collectors running according to this tracking/backtracking strategy and those with pure astronomical tracking increases when the clearness index decreases. Similarly, the results show that the period of time requiring backtracking during sunrise and sunset is longer when GCR decreases. In any case, it has been shown that photovoltaic plants in Cordoba with this new tracking strategy could provide annually, at least, 2% more energy than plants using some existing tracking strategies, even those defined as ideal. Hence, this tracking/backtracking strategy might significantly contribute to the development of photovoltaic plants with two-axis trackers. [ABSTRACT FROM AUTHOR]

Collins introduced the cylindrical algebraic decomposition method for eliminating quantifiers in real arithmetic formulas. In our work we use this method for satisfiability checking in satisfiability modulo theories solver technologies, and tune it by trying to avoid some computation steps that are needed for quantifier elimination but not for satisfiability checking. We further propose novel data structures and adapt the method to work incrementally and to support backtracking. We verify the effectiveness experimentally by comparing different versions of the cylindrical algebraic decomposition used within a state-of-the-art satisfiability modulo theories solver. [ABSTRACT FROM AUTHOR]

Calibration is vital to improving the accuracy of the strapdown inertial navigation system (SINS). Calibration is one of the crucial phases before the operation of SINS and requires high accuracy and speed. Traditional system-level calibration methods have the disadvantages of long calibration times and complicated path design. A fast calibration method for the lever arm and other error parameters is proposed in this article. To shorten the calibration time and improve the calibration accuracy, a backtracking calibration method in inertial frames based on the reduced-order Kalman filter is proposed. Simulations and experiments are given to illustrate the effectiveness of the novel calibration method. The calibration process can be completed in 10 min, which is greatly shortened compared with traditional methods. The calibration time is shortened, and the calibration accuracy is improved. Furthermore, navigation experiments show that the velocity and position accuracies of the SINS are improved significantly after compensation with the calibration results, fully illustrating the significance of the proposed calibration method in improving the navigation performance. [ABSTRACT FROM AUTHOR]

In bacteria, the first two steps of gene expression--transcription and translation--are spatially and temporally coupled. Uncoupling may lead to the arrest of transcription through RNA polymerase backtracking, which interferes with replication forks, leading to DNA double-stranded breaks and genomic instability. How transcription-translation coupling mitigates these conflicts is unknown. Here we show that, unlike replication, translation is not inhibited by arrested transcription elongation complexes. Instead, the translating ribosome actively pushes RNA polymerase out of the backtracked state, thereby reactivating transcription. We show that the distance between the two machineries upon their contact on mRNA is smaller than previously thought, suggesting intimate interactions between them. However, this does not lead to the formation of a stable functional complex between the enzymes, as was once proposed. Our results reveal an active, energy-driven mechanism that reactivates backtracked elongation complexes and thus helps suppress their interference with replication. [ABSTRACT FROM AUTHOR]

Sudoku has unique solution, and backtracking can guarantee the correct result. In order to improve the efficiency of backtracking method, this paper solved Sudoku by the most basic rule-base strategies during searching, only two or three correct candidates were needed to solve successfully. When the Sudoku was solved by the basic rule-base strategies, the returning result was one of three cases, i.e. the success, the failure, and the uncertainty. Only when the result was uncertain, the search was continued, as a result, the efficient pruning was achieved. Meanwhile, this paper used a number of bit operations in the algorithm implementation. A large number of 9 x 9 Sudoku experiments show that the average calculation time is less than 0.15 ms for most Sudoku and 2 ms for those extremely difficult Sudoku. In addition, the average time to solve a 16 x 16 Sudoku is 224 ms. The 9 x 9 Sudoku dataset with 17 cues is recommended as a standard test dataset due to its diversity. [ABSTRACT FROM AUTHOR]

Solar tracking is a technique required to increase energy production in multiple photovoltaic (PV) facilities. In these plants, during low-elevation solar angle hours, shadows appear between the collectors causing a dramatic decrease in production. This paper presents a novel optimal tracking strategy to prevent the creation of these shadows. The presented method determines whether or not there is shading between collectors. Thus, when the collectors are not shaded, a tracking trajectory for maximum irradiance on the collectors is suggested. However, when the collectors are shaded, backtracking is proposed. Therefore, energy production in plants with this novel tracking method can be 1.31% higher than that in PV installations with astronomical tracking. Moreover, this method allows the study of PV facilities for which there have been no published approaches, such as plants with non-rectangular collectors or those located on topographically heterogeneous surfaces. • A novel approach for optimal tracking in PV collectors preventing shadows is proposed. • The method presented shows how backtracking improve other usual solutions. • Non-rectangular collectors or non-flat topography can be analysed with this approach. • Increases of 5% in energy production in two-axis tracking PV plants can be achieved. [ABSTRACT FROM AUTHOR]

With the access of renewable distributed generations and the uncertainty of demand‐side response, the operation states of the active distribution network (ADN) are uncertain. This study proposes a novel optimal strategy taking active management costs of the source–network–load as the goal and considering the site selection and the incentive price for the responsive load to optimise the ADN. To deal with uncertainties, a chance‐constrained optimisation model is established and the Monte Carlo sampling method is used. Then, the uncertain model is settled by the improved backtracking search algorithm, which uses an adaptive mutation scale factor. Finally, the practicability of the proposed strategy and the performance of the algorithm are verified by the modified IEEE 33‐bus distribution system and an actual distribution system in China. [ABSTRACT FROM AUTHOR]

Calibration is vital to improving the accuracy of the strapdown inertial navigation system (SINS). Calibration is one of the crucial phases before the operation of SINS and requires high accuracy and speed. Traditional system-level calibration methods have the disadvantages of long calibration times and complicated path design. A fast calibration method for the lever arm and other error parameters is proposed in this article. To shorten the calibration time and improve the calibration accuracy, a backtracking calibration method in inertial frames based on the reduced-order Kalman filter is proposed. Simulations and experiments are given to illustrate the effectiveness of the novel calibration method. The calibration process can be completed in 10 min, which is greatly shortened compared with traditional methods. The calibration time is shortened, and the calibration accuracy is improved. Furthermore, navigation experiments show that the velocity and position accuracies of the SINS are improved significantly after compensation with the calibration results, fully illustrating the significance of the proposed calibration method in improving the navigation performance. [ABSTRACT FROM AUTHOR]

The minimum backward Fréchet distance (MBFD) problem is a natural optimization problem for the weak Fréchet distance, a variant of the well-known Fréchet distance. In this problem, a threshold ε and two polygonal curves, T 1 and T 2 , are given. The objective is to find a pair of walks on T 1 and T 2 , which minimizes the union of the portions of backward movements (backtracking) while maintaining, at any time, a distance between the moving entities of at most ε. In this paper, we generalize this model to capture scenarios when the cost of backtracking on the input polygonal curves is not homogeneous. More specifically, each edge of T 1 and T 2 has an associated non-negative weight. The cost of backtracking on an edge is the Euclidean length of backward movement on that edge multiplied by the corresponding weight. The objective is to find a pair of walks that minimizes the sum of the costs on the edges of the curves, while guaranteeing that the weak traversal of the curves maintains a weak Fréchet distance of at most ε. We propose two exact algorithms, a simple algorithm with O (n 4) time and space complexities and an improved algorithm whose time and space complexities are O (n 2 log 3 / 2 ⁡ n) , where n is the maximum number of the edges of T 1 and T 2. A solution to weighted MBFD also implies a solution to the more general optimization problem in which both backward and forward movements have associated costs. [ABSTRACT FROM AUTHOR]

State space traversal is a very popular approach to detect concurrency errors and test concurrent programs. However, it is not practically feasible for complex programs with many thread interleavings and a large state space. Many techniques explore only a part of the state space in order to find errors quickly—building upon the observation that errors can often be found in a particular small part of the state space. Great improvements in performance have been achieved also through randomization. In the context of this research direction, we present the DFS-RB algorithm that augments the standard algorithm for depth-first traversal with early backtracking. Specifically, it is possible to backtrack early from a state before all outgoing transitions have been explored. The DFS-RB algorithm is non-deterministic—it uses random numbers, together with values of several parameters, to determine when and how early backtracking takes place in the search. To evaluate DFS-RB, we performed a large experimental study with our prototype implementation in Java Pathfinder on several Java programs. The results show that DFS-RB achieves better performance in terms of speed and error detection than many state-of-the-art techniques for many benchmarks in our set. Nevertheless, it is difficult to find a single configuration of DFS-RB that works well for many different benchmarks. We designed a ranking algorithm whose purpose is to identify configurations that yield overall consistently good performance with a small variation. [ABSTRACT FROM AUTHOR]

Successful navigation can require realizing the current path choice was a mistake and the best strategy is to retreat along the recent path: 'back-track'. Despite the wealth of studies on the neural correlates of navigation little is known about backtracking. To explore the neural underpinnings of backtracking we tested humans during functional magnetic resonance imaging on their ability to navigate to a set of goal locations in a virtual desert island riven by lava which constrained the paths that could be taken. We found that on a subset of trials, participants spontaneously chose to backtrack and that the majority of these choices were optimal. During backtracking, activity increased in frontal regions and the dorsal anterior cingulate cortex, while activity was suppressed in regions associated with the core default-mode network. Using the same task, magnetoencephalography and a separate group of participants, we found that power in the alpha band was significantly decreased immediately prior to such backtracking events. These results highlight the importance for navigation of brain networks previously identified in processing internally-generated errors and that such error-detection responses may involve shifting the brain from default-mode states to aid successful spatial orientation. [ABSTRACT FROM AUTHOR]

We present and analyze a backtracking strategy for a general fast iterative shrinkage/thresholding algorithm proposed by Chambolle and Pock [Acta Numer., 25 (2016), pp. 161{319] for strongly convex composite objective functions. Unlike classical Armijo-type line searching, our backtracking rule allows for local increasing and decreasing of the descent step size (i.e., proximal parameter) along the iterations. We prove accelerated convergence rates and show numerical results for some exemplar problems. [ABSTRACT FROM AUTHOR]

In the present work, the mechanical response of a fiber network metamaterial was studied when subjected to 3-point flexure. To account for the initial deformation of the sample due to the fabrication process, backtracking (i.e., the nominal mesh was accurately repositioned in the reference configuration) was implemented in the Digital Volume Correlation (DVC) procedure. Kinematic fields were then measured via DVC at two different scales. Finite element based DVC was validated thanks to a series of initialization steps. The displacement fields were successfully measured and a peculiar deformation mechanism was observed. These measurements were employed to calibrate the constitutive parameters of a second gradient continuum model introduced for modeling this type of metamaterial. Numerical simulations are shown to be in good agreement with experimental measurements at the macroscopic scale. • DVC employed for measuring kinematic fields in pantographs at macro- and mesoscales • Prediction of deformation patterns in 3-point flexure with elastic hinges • Modeling pantographic metamaterial in framework of second gradient continua [ABSTRACT FROM AUTHOR]

Abstract Search and reasoning can be seen as two basic mechanisms for problem solving. Compared with the former, reasoning focuses upon accumulating the changes step by step, to establish a feasible linkage between initial problem state and desired solutions. An algorithmic design grammar, proposed in a prior study, is proved to be a valid approach for layout generation, based on local reasoning which encodes the interactions between design and design contexts in the rules. However, due to the information incompleteness and design complexity, a reasoning can only ensure to be correct at the time while it may pose a threat to subsequent design actions so that it cannot satisfy other design requirements. As such, this study enhances design grammars with heuristics, a kind of search algorithm, which enables the compensation or correction for the prior bad decisions without degenerating the current design. A general perturbation strategy is presented as a logic guidance for the development of grammars, with two sets of rules separately specified for the improvement of adjacency and area satisfaction as case studies. The comparison between design grammars with and without perturbation rules illustrates significant contributions from the real-time perturbation heuristics. Finally, complex algorithmic patterns, as well as their applicability, are extracted for the reuse in other design problems. Highlights • Embedding search heuristics within an algorithmic design grammar • An improved algorithmic design grammar for a layout generation problem • Two perturbation heuristics improving adjacency and area constraint satisfaction • Several complex algorithmic patterns for guiding grammar development [ABSTRACT FROM AUTHOR]

The applicability of different selection methods for power systems on board ships is highly dependent on the number of options possible. With the introduction of new technologies in the maritime sector, this number is increasing. However, its exact value, or even its order of magnitude is still unknown. This article shows the complexity of modern on-board power system by quantifying the number of possible system configurations currently available. A constraint satisfaction algorithm generates different configurations and the results are supported by combinatorics principles. The set of constraints used led to a significant reduction in the design space, and the influence of each of the constraints is investigated independently. Traditional mechanical propulsion is present in less than 1% of the generated configurations, whereas electric and hybrid propulsion are dominant. In particular, the impact of energy storage on the size of the design space is made evident. The order of magnitude of the total number of configurations obtained supports the use of modern selection methods instead of ones based on expert intuition and past experience. The presented work offers a tool to determine and restrict the size of the design space. It can therefore be integrated into existing selection methods and is a starting point for the development of new ones. [ABSTRACT FROM AUTHOR]

During a conventional multiple-point statistics simulation, the algorithm may not find a matched neighborhood in the training image for some unsimulated pixels. These pixels are referred to as the dead-end pixels; the existence of the dead-end pixels means that multiple-point statistics simulation is not a simple sequential simulation. In this paper, the multiple-point statistics simulation is cast as a combinatorial optimization problem, and the efficient backtracking algorithm is developed to solve this optimization problem. The efficient backtracking consists of backtracking, forward checking, and conflict-directed backjumping algorithms that are introduced and discussed in this paper. This algorithm is applied to simulate multiple-point statistics properties of some synthetic training images; the results show that no anomalies occurred in any of the produced realizations as opposed to previously published methods for solving the dead-end pixels. In particular, in simulating a channel system, all the channels generated by this method are continuous, which is of paramount importance in fluid flow simulation applications. The results also show that the presence of hard data does not degrade the quality of the generated realizations. The presented method provides a robust algorithmic framework for performing MPS simulation. [ABSTRACT FROM AUTHOR]

Constraint check plays a central role in establishing generalized arc consistency which is widely used to solve constraint satisfaction problems. In this paper, we propose a new generalized arc consistency algorithm, called GTR, which ensures that the tuples that have been checked to be allowed by a constraint will never be checked again. For each constraint, GTR maintains a dynamic list of the tuples that were checked to be allowed by this constraint and check their validities to identify some values with supports. It is equipped with a mechanism avoiding redundant validity checks. The basic GAC3 algorithm is employed to find a support for the rest values and to add new tuples to the dynamic list. The experiments show that maintaining GTR during search saves a number of constraint checks. It also brings some improvements over cpu time while solving some CSPs with tight constraints. [ABSTRACT FROM AUTHOR]

Veromessor pergandei harvester ants are group foragers which use a combination of social cues (pheromone-marked columns) and individual cues (e.g., self-generated movement, visual cues) when exploring foraging areas for resources. Upon finding food, individuals navigate back to the column, which guides their return to the nest. The direction and length of columns change between foraging bouts, and hence the end of the column (unlike the nest location) is non-stationary. We conducted displacement tests on returning foragers and present three novel findings. First, returning individual ants accurately estimate their distance from the foraging area to the end of the column. Second, ants that reached the column but only traveled a small proportion of the distance to the nest either show homeward or random orientation; random orientation was seen when the column was long. Third, ants that have traveled most of the way back to the nest along the column show backtracking when they are displaced—orienting in the direction opposite to the nest—similar to Australian desert ants Melophorus bagoti. This commonality suggests that some navigation strategies are general across species, and are utilized by ants that navigate individually or socially. [ABSTRACT FROM AUTHOR]