On finite complete rewriting systems and large subsemigroups

Let $S$ be a semigroup and $T$ be a subsemigroup of finite index in $S$ (that is, the set $S\setminus T$ is finite). The subsemigroup $T$ is also called a large subsemigroup of $S$. It is well known that if $T$ has a finite complete rewriting system then so does $S$. In this paper, we will prove the converse, that is, if $S$ has a finite complete rewriting system then so does $T$. Our proof is purely combinatorial and also constructive.Comment: We have made major changes to the paper and simplified most of the proof

Algorithmic opacity: making algorithmic processes transparent through abstraction hierarchy

In this paper we introduce the problem of algorithmic opacity and the challenges it presents to ethical decision-making in criminal intelligence analysis. Machine learning algorithms have played important roles in the decision-making process over the past decades. Intelligence analysts are increasingly being presented with smart black box automation that use machine learning algorithms to find patterns or interesting and unusual occurrences in big data sets. Algorithmic opacity is the lack visibility of computational processes such that humans are not able to inspect its inner workings to ascertain for themselves how the results and conclusions were computed. This is a problem that leads to several ethical issues. In the VALCRI project, we developed an abstraction hierarchy and abstraction decomposition space to identify important functional relationships and system invariants in relation to ethical goals. Such explanatory relationships can be valuable for making algorithmic process transparent during the criminal intelligence analysis process

Real‐Time Control of Urban Headwater Catchments Through Linear Feedback: Performance, Analysis, and Site Selection

The real‐time control of urban watersheds is now being enabled by a new generation of “smart” and connected technologies. By retrofitting stormwater systems with sensors and valves, it becomes possible to adapt entire watersheds dynamically to individual storms. A catchment‐scale control algorithm is introduced, which abstracts an urban watershed as a linear integrator delay dynamical system, parameterizes it using physical watershed characteristics, and then controls network flows using a Linear Quadratic Regulator. The approach is simulated on a 4‐km2 urban headwater catchment in Ann Arbor, Michigan, demonstrating the gains of a stormwater system that can adaptively balance between flood mitigation and flow reduction. We introduce an equivalence analysis and illustrate the performance of the controlled watershed across large events (30‐year storms) to show the uncontrolled passive watershed can only match it during smaller events (10‐year storm). For these smaller events, the storage volume of the controlled storage nodes (ponds, basins, and wetlands) could be reduced as much as 50% and still achieve the same performance of the controlled watershed. A controller placement analysis is also carried out, whereby all possible combinations of controlled sites are simulated across a wide spectrum of design storms. We show that the control of every storage node may not be needed in a watershed, but rather that in our case study a small subset (30%) of the overall watershed can be controlled in coordination to achieve outcomes that match a fully controlled system, even when tested across a long‐term rainfall record and under noisy sensor measurements.Plain Language SummaryInternet‐connected sensors are changing how we study and manage water systems. By adding valves, gates, and pumps to stormwater systems, it will be possible to adaptively control urban watershed in response to individual storms. Without requiring new and expensive construction, this will allow existing infrastructure to be used more effectively. In this paper, we introduce a control algorithm that can be used to control urban watersheds. We also investigate how many control valves are needed to retrofit an urban watershed and where, which may serve as tools for city managers to reduce flooding and manage flows.Key PointsA linear feedback controller is formulated for the control of urban catchments (1‐5 km2) using physical catchment propertiesSimulations show strong flow control performance when compared to uncontrolled catchmentDesired hydraulic outcomes can be achieved by retrofitting a small number of control sitesPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/146619/1/wrcr23569-sup-0001-WRR_-_2018WR022657R_-_Supporting_Information__final_.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146619/2/wrcr23569.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/146619/3/wrcr23569_am.pd

Interaction log and provenance for sensemaking

This paper describes two visual analytic tools designed to support sensemaking through the visualisation of interaction log and analytic provenance. The first tool, SensePath, aims to reduce the time required for the transcription and coding during qualitative analysis such as thematic analysis (making sense of the experiment data). The second tool, SenseMap, is designed to help online sensemaking with everyday tasks such as buying a digital camera. User evaluation leads to early insight of how the visualisation of interaction log and analytic provenance can help these sensemaking tasks

Melt-growth dynamics in CdTe crystals

We use a new, quantum-mechanics-based bond-order potential (BOP) to reveal melt-growth dynamics and fine-scale defect formation mechanisms in CdTe crystals. Previous molecular dynamics simulations of semiconductors have shown qualitatively incorrect behavior due to the lack of an interatomic potential capable of predicting both crystalline growth and property trends of many transitional structures encountered during the melt $\rightarrow$ crystal transformation. Here we demonstrate successful molecular dynamics simulations of melt-growth in CdTe using a BOP that significantly improves over other potentials on property trends of different phases. Our simulations result in a detailed understanding of defect formation during the melt-growth process. Equally important, we show that the new BOP enables defect formation mechanisms to be studied at a scale level comparable to empirical molecular dynamics simulation methods with a fidelity level approaching quantum-mechanical method

Editorial: In use, in situ: extending field research methods

A case for evaluating in use and in-situ Many authors have argued the need for a broader understanding of context and the situatedness of activity when approaching the evaluation of systems. However, prevailing practice often still tends towards attempting to understand the use of designed artefacts by focusing on a core set of tasks that are thought to define the system. A consequence of such focus is that other tasks are considered peripheral and outside the scope of design and evaluation activities. To illustrate the point, consider the experience, familiar to many of us, of being involved in an evaluation activity where participants provide unstructured qualitative feedback. Irrespective of whether the activity is carried out in a laboratory, in a high fidelity simulation or in a naturalistic setting, participants will frequently volunteer unsolicited feedback about tasks and goals that were not originally within the ambit of the design activity. This unprompted feedback, we suggest, is a cue for the evaluators to pay attention to the relationship between the tool and the practice in which it will be used. In other words a cue to consider the situations in which artefact will be used, the tasks and activities that may be affected by the new system, and so on. These are empirical questions that cannot be answered a priori by the development team, whether the evaluation is taking place in “artificial” or “natural” setting

The influence of the cluster environment on the star formation efficiency of 12 Virgo spiral galaxies

The influence of the environment on gas surface density and star formation efficiency of cluster spiral galaxies is investigated. We extend previous work on radial profiles by a pixel-to pixel analysis looking for asymmetries due to environmental interactions. The star formation rate is derived from GALEX UV and Spitzer total infrared data. As in field galaxies, the star formation rate for most Virgo galaxies is approximately proportional to the molecular gas mass. Except for NGC 4438, the cluster environment does not affect the star formation efficiency with respect to the molecular gas. Gas truncation is not associated with major changes in the total gas surface density distribution of the inner disk of Virgo spiral galaxies. In three galaxies, possible increases in the molecular fraction and the star formation efficiency with respect to the total gas, of factors of 1.5 to 2, are observed on the windward side of the galactic disk. A significant increase of the star formation efficiency with respect to the molecular gas content on the windward side of ram pressure-stripped galaxies is not observed. The ram-pressure stripped extraplanar gas of 3 highly inclined spiral galaxies shows a depressed star formation efficiency with respect to the total gas, and one of them (NGC 4438) shows a depressed rate even with respect to the molecular gas. The interpretation is that stripped gas loses the gravitational confinement and associated pressure of the galactic disk, and the gas flow is diverging, so the gas density decreases and the star formation rate drops. However, the stripped extraplanar gas in one highly inclined galaxy (NGC 4569) shows a normal star formation efficiency with respect to the total gas. We propose this galaxy is different because it is observed long after peak pressure, and its extraplanar gas is now in a converging flow as it resettles back into the disk.Comment: 34 pages, 24 figures, accepted for publication by A&

Magnetic domain walls in constrained geometries

Magnetic domain walls have been studied in micrometer-sized Fe20Ni80 elements containing geometrical constrictions by spin-polarized scanning electron microscopy and numerical simulations. By controlling the constriction dimensions, the wall width can be tailored and the wall type modified. In particular, the width of a 180 degree Neel wall can be strongly reduced or increased by the constriction geometry compared with the wall in unconstrained systems.Comment: 4 pages, 6 figure

A survey of analytic provenance

Analytic provenance research tries to understand a user's reasoning process by examining their interactions with a visual analytic system. This paper presents a survey of analytic provenance literature