Repeatable Events Research Articles

Numerical investigation of diesel spray combustion characteristics in the ammonia/air atmosphere

Ammonia/diesel dual-fuel combustion mode is a promising strategy for decarbonizing internal combustion engines. However, the impact of a premixed ammonia/air atmosphere on diesel spray combustion characteristics is not fully understood. This study analyzes the effects of premixed ammonia/air atmosphere, including premixed equivalence ratio, the cooling effect of liquid ammonia vaporization, and ambient oxygen concentration on the ignition and combustion characteristics and soot yield potential of diesel spray. Numerical simulations using n-heptane as a single-component diesel surrogate reveal that increasing the premixed ammonia equivalence ratio and lowering ambient oxygen concentration extend the ignition delay times and flame lift-off length of n-heptane spray. Liquid ammonia vaporization further prolongs the ignition delay by lowering the ambient temperature during n-heptane auto-ignition. Moreover, there is a trade-off between ignition delay and soot yield potential as longer ignition delays allow more thorough mixing of diesel and premixed gas, reducing soot formation. Given the substantial extension of ignition delay in ammonia/air atmospheres, it is recommended that ammonia/diesel dual-fuel engines operate with higher charged gas temperatures to ensure stable and repeatable ignition events. The negative effects of increased soot yield could be mitigated by using ammonia to reduce soot precursors. Overall, these results underline the need for further fundamental studies on ammonia/diesel co-combustion to facilitate the commercial adoption of ammonia/diesel dual-fuel engines.

Microbubble collapse near a fiber: Broken symmetry conditions and a planar jet formation

The collapse of microbubbles near a fiber is an example often encountered in water treatment situations and cavitation fibrillation processes. However, due to the broken symmetry conditions, this process has not been studied in detail experimentally or numerically, making it difficult to precisely measure or simulate the rapid bubble evolution during collapse. In this work, we present a novel experimental method, allowing for precisely repeatable cavitation events observation, combined with numerical simulations offering insight into pressure and velocity fields distribution developments in time. Both experimental and numerical works focused on small distances between the bubble and the fiber, where the physical interaction between subjects is the strongest. Four different bubble offsets were considered within the scope of this work, and very good agreement of numerical simulations with experiments was found in all cases. Two modes of bubble collapse were identified, leading to mushroom-shaped bubbles at positions closest to the fiber and a pear-shaped bubble at the farthest position. It is noteworthy that in all four cases, a planar jet formation toward the fiber was observed. The formed jet initially assumes an elongated shape, whereas its stability depends on the mode of bubble collapse. Numerical analysis of the planar jet as the defining feature of the collapse defined lower bounds for the actual values of peak jet velocities, ranging between 250 and 330 m/s, and the resulting impact pressures, which range from 100to 500 MPa.

Moon and Tide: A New Interpretation of Exeter Riddle 22 Based on the Medieval Science of Computus

Abstract Exeter Riddle 22 tells the story of how 60 riders and 15 horses are unable to cross a body of water until a ‘wægn’ (‘wagon’) miraculously transports them to the other shore. Several solutions have been proposed, but none are entirely satisfactory. This article uses medieval scientific lore, as well as the medieval coastal landscape and comparative readings of Old English, Latin and Old Norse texts, to propose a new solution explaining all aspects of the riddle—the full moon. Riddle 22 requires not only an awareness of the relationship between the lunar and tidal cycles, but also a knowledge of the computistical formulae that were taught in monastic schools. The horses and the riders represent the hours of moonlight and the ‘wægn’ represents the moon itself. Additionally, the riddle draws upon images of the coastal landscape, as the riddle also depicts the crossing of a tidal causeway. Solving the riddle in this way is a transformative experience for the scientifically literate reader, who comes to recognize—as per Augustine—that prosaic, repeatable events in nature are everyday miracles.

Strobe photography mapping of cell membrane potential with nanosecond resolution

The ability to directly observe membrane potential charging dynamics across a full microscopic field of view is vital for understanding interactions between a biological system and a given electrical stimulus. Accurate empirical knowledge of cell membrane electrodynamics will enable validation of fundamental hypotheses posited by the single shell model, which includes the degree of voltage change across a membrane and cellular sensitivity to external electric field non-uniformity and directionality. To this end, we have developed a high-speed strobe microscopy system with a time resolution of ~ 6 ns that allows us to acquire time-sequential data for temporally repeatable events (non-injurious electrostimulation). The imagery from this system allows for direct comparison of membrane voltage change to both computationally simulated external electric fields and time-dependent membrane charging models. Acquisition of a full microscope field of view enables the selection of data from multiple cell locations experiencing different electrical fields in a single image sequence for analysis. Using this system, more realistic membrane parameters can be estimated from living cells to better inform predictive models. As a proof of concept, we present evidence that within the range of membrane conductivity used in simulation literature, higher values are likely more valid.

Repeating caldera collapse events constrain fault friction at the kilometer scale

Fault friction is central to understanding earthquakes, yet laboratory rock mechanics experiments are restricted to, at most, meter scale. Questions thus remain as to the applicability of measured frictional properties to faulting in situ. In particular, the slip-weakening distance [Formula: see text] strongly influences precursory slip during earthquake nucleation, but scales with fault roughness and is challenging to extrapolate to nature. The 2018 eruption of K̄ılauea volcano, Hawaii, caused 62 repeatable collapse events in which the summit caldera dropped several meters, accompanied by [Formula: see text] 4.7 to 5.4 very long period (VLP) earthquakes. Collapses were exceptionally well recorded by global positioning system (GPS) and tilt instruments and represent unique natural kilometer-scale friction experiments. We model a piston collapsing into a magma reservoir. Pressure at the piston base and shear stress on its margin, governed by rate and state friction, balance its weight. Downward motion of the piston compresses the underlying magma, driving flow to the eruption. Monte Carlo estimation of unknowns validates laboratory friction parameters at the kilometer scale, including the magnitude of steady-state velocity weakening. The absence of accelerating precollapse deformation constrains [Formula: see text] to be [Formula: see text] mm, potentially much less. These results support the use of laboratory friction laws and parameters for modeling earthquakes. We identify initial conditions and material and magma-system parameters that lead to episodic caldera collapse, revealing that small differences in eruptive vent elevation can lead to major differences in eruption volume and duration. Most historical basaltic caldera collapses were, at least partly, episodic, implying that the conditions for stick-slip derived here are commonly met in nature.

Timing of gait events affects whole trajectory analyses: A statistical parametric mapping sensitivity analysis of lower limb biomechanics

Time continuous analyses, such as statistical parametric mapping (SPM), have been increasingly used in biomechanics research to determine differences between populations, interventions and methodologies. Currently, it is not known how sensitive time-continuous analyses are to timing variability that occur in gait data. We evaluated this sensitivity by examining the frequency of significant SPM outcomes between two walking speeds when lower limb kinematics and kinetics were segmented and aligned based on 40 repeatable gait events. These events, defined in the supplementary material, include a commonly used event like foot contact and other events that have been previously demonstrated to be repeatable. Repeatable gait events were determined from joint and segment kinematics, joint kinetics as well as ground reaction forces. We examined the frequency of statistical outcomes for a single subject with different numbers of strides analyzed and for a cohort of 10 subjects. Our findings demonstrate that gait interventions, such as changes in walking speed, can induce temporal shifts that affect time-continuous outcomes for both cohort- and subject-level analyses. As both timing and magnitude are important in gait data, researchers are encouraged to perform additional analyses to understand how both of these variables affect time-continuous analysis outcomes. Finally, we demonstrate that multiple SPM tests can be performed to determine if statistical outcomes are due to temporal shifting or differences in magnitude. It is important to understand how both timing and magnitude of biomechanical data influences time continuous analyses as these analyses inform injury prevention, device development and basic understanding of biomechanics.

Realization of a Novel Free-Piston Engine Generator for Hybrid-Electric Vehicle Applications

Free-piston engine generators (FPEGs) have huge potential to be the principal energy conversion device for generating electricity from fuel as part of a hybrid-electric vehicle (EV) powertrain system. The principal advantages lay in the fact that they are theoretically more efficient, more compact, and more lightweight compared to other competing EV hybrid and range-extender solutions (internal combustion engines, rotary engines, fuel cells, etc.). However, this potential has yet to be realized. This article details a novel dual-piston FPEG configuration and presents the full layout of a system and provides technical evidence of a commercial FPEG system’s likely size and weight. The work also presents the first results obtained from a project which set-out to realize an operational FPEG system in hardware through the development and testing of a flexible prototype test platform. The work presents the performance and control system characteristics, for a first of a kind system; these show great technical potential with stable and repeatable combustion events achieved with around 700 W per cylinder and 26% indicated efficiency.

Computational 4D imaging of light-in-flight with relativistic effects

Light-in-flight imaging enables the visualization and characterization of light propagation, which provides essential information for the study of the fundamental phenomena of light. A camera images an object by sensing the light emitted or reflected from it, and interestingly, when a light pulse itself is to be imaged, the relativistic effects, caused by the fact that the distance a pulse travels between consecutive frames is of the same scale as the distance that scattered photons travel from the pulse to the camera, must be accounted for to acquire accurate space–time information of the light pulse. Here, we propose a computational light-in-flight imaging scheme that records the projection of light-in-flight on a transverse x−y plane using a single-photon avalanche diode camera, calculates z and t information of light-in-flight via an optical model, and therefore reconstructs its accurate ( x , y , z , t ) four-dimensional information. The proposed scheme compensates the temporal distortion in the recorded arrival time to retrieve the accurate time of a light pulse, with respect to its corresponding spatial location, without performing any extra measurements. Experimental light-in-flight imaging in a three-dimensional space of 375 mm × 75 mm × 50 mm is performed, showing that the position error is 1.75 mm, and the time error is 3.84 ps despite the fact that the camera time resolution is 55 ps, demonstrating the feasibility of the proposed scheme. This work provides a method to expand the recording and measuring of repeatable transient events with extremely weak scattering to four dimensions and can be applied to the observation of optical phenomena with ps temporal resolution.

A new approach to creating and deploying audio description for live theater

Audio description is an accessibility service used by blind or visually impaired individuals. Often accompanying movies, television shows, and other visual art forms, the service provides spoken descriptions of visual content, allowing people with vision loss the ability to access information that sighted people obtain visually. At live theatrical events, audio description provides spoken descriptions of scenes, characters, props, and other visual elements that those with vision loss may otherwise find inaccessible. This paper explores a novel approach to automate the creation and deployment of audio description for repeatable live theatrical events, both musical and non-musical. Using readily available tools and established sound-processing techniques, we describe a framework to automate several aspects of audio description for theater. The method uses a reference audio recording and an online time warping algorithm to align audio description with live performances, including a process for handling unexpected interruptions. We also show how a reference audio recording and descriptive tracks can be generated automatically from a show’s script and used to facilitate the deployment of audio description without sufficient resources for multiple performances or a live audio describer. Finally, a software implementation that is integrated into an existing theatrical workflow is also described. This system is used in three evaluation experiments that show the method successfully aligns multiple recordings of works of musical theater and non-musical plays in order to automatically trigger pre-recorded, descriptive audio in real time.

Introduction of Viral Hemorrhagic Septicemia Virus into Freshwater Cultured Rainbow Trout Is Followed by Bursts of Adaptive Evolution.

Viral hemorrhagic septicemia virus (VHSV), a rhabdovirus infecting teleost fish, has repeatedly crossed the boundary from marine fish species to freshwater cultured rainbow trout. These naturally replicated cross-species transmission events permit the study of general and repeatable evolutionary events occurring in connection with viral emergence in a novel host species. The purpose of the present study was to investigate the adaptive molecular evolution of the VHSV glycoprotein, one of the key virus proteins involved in viral emergence, following emergence from marine species into freshwater cultured rainbow trout. A comprehensive phylogenetic reconstruction of the complete coding region of the VHSV glycoprotein was conducted, and adaptive molecular evolution was investigated using a maximum likelihood approach to compare different codon substitution models allowing for heterogeneous substitution rate ratios among amino acid sites. Evidence of positive selection was detected at six amino acid sites of the VHSV glycoprotein, within the signal peptide, the confirmation-dependent major neutralizing epitope, and the intracellular tail. Evidence of positive selection was found exclusively in rainbow trout-adapted virus isolates, and amino acid combinations found at the six sites under positive selection pressure differentiated rainbow trout- from non-rainbow trout-adapted isolates. Furthermore, four adaptive sites revealed signs of recurring identical changes across phylogenetic groups of rainbow trout-adapted isolates, suggesting that repeated VHSV emergence in freshwater cultured rainbow trout was established through convergent routes of evolution that are associated with immune escape.IMPORTANCE This study is the first to demonstrate that VHSV emergence from marine species into freshwater cultured rainbow trout has been accompanied by bursts of adaptive evolution in the VHSV glycoprotein. Furthermore, repeated detection of the same adaptive amino acid sites across phylogenetic groups of rainbow trout-adapted isolates indicates that adaptation to rainbow trout was established through parallel evolution. In addition, signals of convergent evolution toward the maintenance of genetic variation were detected in the conformation-dependent neutralizing epitope or in close proximity to disulfide bonds involved in the structural conformation of the neutralizing epitope, indicating adaptation to immune response-related genetic variation across freshwater cultured rainbow trout.

Performance of neat and gelled monomethylhydrazine and red fuming nitric acid in an unlike-doublet combustor

ABSTRACTIgnition and combustion characteristics of neat and gelled monomethylhydrazine (MMH) and red fuming nitric acid (RFNA) were investigated through the use of an unlike doublet injector. MMH gelled with either hydroxypropylcellulose or fumed silica was tested with RFNA gelled with fumed silica. High-speed video results showed that the type of gelling agent has a major impact on the ignition and combustion of the hypergolic propellants. Mismatched rheological properties hinder rapid and repeatable ignition events. Gels with matched rheological properties produce repeatable ignition delays similar to those observed with neat propellants. An elevated pressure combustion chamber was developed to allow direct comparison of combustion efficiency between neat and gelled propellants. Experimental combustion efficiencies were 83% for neat propellants compared to 68% for fumed silica gelled propellants. The results indicate that gelled propellants can operate with acceptable ignition delays but suffer from reduced combustion efficiency and stability when compared to neat propellants.

Hybridization Associated with Cycles of Ecological Succession in a Passerine Bird.

Identifying the diversity of contexts that can lead to hybridization is important for understanding its prevalence and dynamics in natural populations. Despite the potential of ecological succession to dramatically alter species co-occurrence and abundances, it is unknown whether it directly promotes hybridization and, if so, has long-lasting consequences. Here, we summarize 30 years of survey data across 10 populations to show that in western and mountain bluebirds, heterospecific pairing occurs during repeatable and transient colonization events at the early stages of species turnover. Despite mixed pairing occurring only during early succession, genetic data showed presence of hybrids at both early and late successional stages. Moreover, hybrids showed novel patterns of variation in morphology and behavior, emphasizing that even ephemeral contexts for hybridization can have important evolutionary consequences. Our results suggest that because ecological succession often brings together closely related competitors in disparate numbers but lasts for only a brief period of time, it may be a widespread but underappreciated context for hybridization.

How J M Keynes's Logical Theory of Probability Totally Refutes All Attacks on the Concept of Probability

J Derbyshire has recently repeated G L S Shackle’s original attack on the concept of probability in a number of recent articles. He adds nothing new to Shackle’s arguments of forty to eighty years ago that were completely refuted in 1959 by R. Weckstein, who based his refutation of Shackle on a relatively limited understanding of chapters 1-3 and 6 of Keynes’s A Treatise on Probability (1921). Shackle never replied to Weckstein’s repeated demonstrations in 1959 that Keynes’s approach refuted his arguments, which held only against the limiting frequency, relative frequency, propensity and subjective interpretations of probability. Shackle’s arguments failed completely when confronted with Keynes’s theory of logical probability. J M Keynes’s theory of probability is a logical, objective, epistemological approach that is based on partial ordering and not complete orderings. This results in non additive, non linear interval valued probabilities, specified and operationalized in terms of logical propositions about any kind of event. It can easily deal with unique events, single events, crucial events, infrequent events, frequent events, non repeatable events, irreversible events, path dependence, sensitivity to initial conditions, emergence, complex causation, attractor states, partial uncertainty, complete and total uncertainty, fundamental uncertainty, irreducible uncertainty, by means of Keynes’s weight of the evidence analysis, which, when combined with his interval valued probability, can demonstrate that Shackle’s theory is a very special theory that applies only to situations of complete and total uncertainty, which Keynes categorized as ignorance. There is not a single one of Derbyshire’s objections to the concept of probability left standing if Keynes’s logical approach to probability is used.

Imaging the propagation of light through scenes at picosecond resolution

We present a novel imaging technique, which we call femto-photography , to capture and visualize the propagation of light through table-top scenes with an effective exposure time of 1.85 ps per frame. This is equivalent to a resolution of about one half trillion frames per second; between frames, light travels approximately just 0.5 mm. Since cameras with such extreme shutter speed obviously do not exist, we first re-purpose modern imaging hardware to record an ensemble average of repeatable events that are synchronized to a streak sensor, in which the time of arrival of light from the scene is coded in one of the sensor's spatial dimensions. We then introduce reconstruction methods that allow us to visualize the propagation of femtosecond light pulses through the scenes. Given this fast resolution and the finite speed of light, we observe that the camera does not necessarily capture the events in the same order as they occur in reality: we thus introduce the notion of time-unwarping between the camera's and the world's space--time coordinate systems, to take this into account. We apply our femto-photography technique to visualizations of very different scenes, which allow us to observe the rich dynamics of time-resolved light transport effects, including scattering, specular reflections, diffuse interreflections, diffraction, caustics, and subsurface scattering. Our work has potential applications in artistic, educational, and scientific visualizations; industrial imaging to analyze material properties; and medical imaging to reconstruct subsurface elements. In addition, our time-resolved technique has already motivated new forms of computational photography, as well as novel algorithms for the analysis and synthesis of light transport.

Risk Prevention and Deduction in Software Development Using Fuzzy Membership Function

Evidence indicates that risks in IT projects which are not effectively managed and lack of identification and management during the life cycle of a project can contribute to their failures. Traditional risk assessment methods usually model risks with objective probabilities based on the expected frequency of repeatable events. Meanwhile, managers prefer to linguistically represent likelihoods because of the uncertainty and vagueness of risk factors. The objective of this paper is to identify risk mitigation strategies in software development projects from the perspectives of software practitioners and determine the effectiveness of these strategies. We explore the use of fuzzy methods to overcome the problems associated with probabilistic modelling through a set of questionnaire surveys which was conducted among 3000 IT practitioners using Tukey-B test, Kendall's test and Post Hoc Tukey HSD test. We apply Fuzzy Membership Function (Fuzzy-MBF) as an appropriate mechanism in dealing with the subjectivity in the assessment of risk factors in different stages of a software development life cycle. The proposed Fuzzy-MBF offers a quantitative evaluation of risk factors and provides a systemic evaluation of risk and visualization of results.

Nonlinear dynamics of a bistable piezoelectric-composite energy harvester for broadband application

The continuing need for reduced power requirements for small electronic components, such as wireless sensor networks, has prompted renewed interest in recent years for energy harvesting technologies capable of capturing energy from ambient vibrations. A particular focus has been placed on piezoelectric materials and devices due to the simplicity of the mechanical to electrical energy conversion and their high strain energy densities compared to electrostatic and electromagnetic equivalents. In this paper an arrangement of piezoelectric layers attached to a bistable asymmetric laminate is investigated experimentally to understand the dynamic response of the structure and power generation characteristics. The inherent bistability of the underlying structure is exploited for energy harvesting since a transition from one stable configuration to another, or “snap-through”, is used to repeatedly strain the surface bonded piezoelectric and generate electrical energy. This approach has been shown to exhibit high levels of power extraction over a wide range of vibrational frequencies. Using high speed digital image correlation, a variety of dynamic modes of oscillation are identified in the harvester. The sensitivity of such modes to changes in vibration frequency and amplitude are investigated. Power outputs are measured for repeatable snap-through events of the device and are correlated with the measured modes of oscillation. The typical power generated is approximately 3.2 mW, comparing well with the needs of typical wireless senor node applications.

Femto-photography

We present femto-photography , a novel imaging technique to capture and visualize the propagation of light. With an effective exposure time of 1.85 picoseconds (ps) per frame, we reconstruct movies of ultrafast events at an equivalent resolution of about one half trillion frames per second. Because cameras with this shutter speed do not exist, we re-purpose modern imaging hardware to record an ensemble average of repeatable events that are synchronized to a streak sensor, in which the time of arrival of light from the scene is coded in one of the sensor's spatial dimensions. We introduce reconstruction methods that allow us to visualize the propagation of femtosecond light pulses through macroscopic scenes; at such fast resolution, we must consider the notion of time-unwarping between the camera's and the world's space-time coordinate systems to take into account effects associated with the finite speed of light. We apply our femto-photography technique to visualizations of very different scenes, which allow us to observe the rich dynamics of time-resolved light transport effects, including scattering, specular reflections, diffuse interreflections, diffraction, caustics, and subsurface scattering. Our work has potential applications in artistic, educational, and scientific visualizations; industrial imaging to analyze material properties; and medical imaging to reconstruct subsurface elements. In addition, our time-resolved technique may motivate new forms of computational photography.

Using Discrete-time Event History Fertility Models to Simulate Total Fertility Rates and Other Fertility Measures.

Event history models, also known as hazard models, are commonly used in analyses of fertility. One drawback of event history models is that the conditional probabilities (hazards) estimated by event history models do not readily translate into summary measures, particularly for models of repeatable events, like childbirth. In this paper, we describe how to translate the results of discrete-time event history models of all births into well-known summary fertility measures: simulated age- and parity-specific fertility rates, parity progression ratios (PPRs), and the total fertility rate (TFR). The method incorporates all birth intervals, but permits the hazard functions to vary across parities. It also can simulate values for groups defined by both fixed and time-varying covariates, such as marital or employment life histories. We demonstrate the method using an example from the National Survey of Family Growth (NSFG) and provide an accompanying data file and Stata program.

Causes and Triggers of Coups d'état: An Event History Analysis

What explains the propensities of countries to experience coups d'état? This article tests various, at times competing, theories of coups using event history analysis by modeling coups as repeatable events. We highlight the different roles that political regimes play in inducing or deterring coups, and argue that political regimes that are not clearly democratic or autocratic are the most vulnerable to coups. Features of hybrid regimes increase their underlying coup vulnerability and the impact of coup‐triggering events. While existing literature has noted higher coup frequency in nondemocratic regimes than in democratic regimes, we note the impact of differences within the nondemocratic regimes, with particular emphasis on the timing of a coup event. Contributing to growing research on variations in nondemocratic regimes and their consequences, our analysis of global coup data in 152 countries indicates that very autocratic regimes are much less vulnerable to coups than hybrid regimes.Related Articles Kim, Hae S. “.” Politics & Policy 37 (): 395‐414. http://onlinelibrary.wiley.com/doi/10.1111/j.1747‐1346.2009.00177.x/abstract Rhoads Jr., James C., and Tung‐wen Sun. 1994. “.” Southeastern Political Review 22 (): 159‐170. http://onlinelibrary.wiley.com/doi/10.1111/j.1747‐1346.1994.tb00325.x/abstract Boehmer, Charles. 2007. “.” Politics & Policy 35 (): 774‐809. http://onlinelibrary.wiley.com/doi/10.1111/j.1747‐1346.2007.00084.x/abstract

Who Receives Food Stamps During Adulthood? Analyzing Repeatable Events With Incomplete Event Histories

Using data from the Panel Study of Income Dynamics (PSID) from 1968 to 2005, we estimate the cumulative probability that young adults in the United States will receive food stamps during adulthood, and examine how that probability varies with an individual's income and education at age 25 as well as by race and gender. We find that the probability of first food stamp receipt as an adult declines sharply with age, indicating that most adult recipients do so by age 40. Also, those receiving food stamps in early adulthood are likely to receive them again. For these reasons, and because food stamp receipt is a repeatable event, life table analyses that include individuals who are not observed until after they become exposed to the risk of food stamp receipt (whom we label "late entrants") are likely to overstate cumulative participation during adulthood. For example, one often-cited study included individuals who enter their sample after age 20 (late entrants) and report that 50.8% of 20-year-olds are recipients by age 65. In contrast, when we exclude late entrants, we find that 39.2% of 20-year-olds and 29.7% of 25-year-olds receive benefits during adulthood.