Temporal Delay Research Articles

Fairness in the Field: The Ethics of Resource Allocation in Randomized Controlled Field Experiments

Many in the international development community have embraced the randomized controlled field experiment, akin to a biomedical clinical trial for social interventions, as the new “gold evidential standard” in program impact evaluation. In response, critics have called upon the method’s advocates to consider the moral dimensions of randomization, leading to a debate about the method’s ethics. My research intervenes in this debate by empirically investigating how researchers manage the perception of randomization in the field. Without the possibility of a placebo, researchers rhetorically and materially frame the experiment differently for the control and treatment groups. Three technologies allow for this differential framing: geographic separation, temporal delay, and public randomization ceremonies. Geographic separation is a “technology of opacity” designed to obscure unequal resource distribution by disentangling the intervention and research components of the experiment for the control group. The latter two are technologies of transparency designed to expose the element of randomization but downplay conditions that may affect participant buy in. All three technologies work to preclude collective definitions of fair resource allocation, yet they are not fully successful in preventing modes of confrontation and resistance that lie outside of the experiment’s framing.

Hydrological performance of green roofs in the context of the meteorological factors during the 5‐year monitoring period

AbstractGreen roofs as solutions that can offer varying levels of stormwater management are the topic of current interest. In order to use this form of reconstructing retention capacity, it is important to understand the influence of meteorological conditions on the functioning of living roofs. The study presents the results of research, using of the ANOVA variance analysis method, on retention performance (i.e. volumetric control) and detention (temporal delay run‐off) carried out in the years 2009–2014. The results indicate that the green roof can effectively retain rainfall and delay the initiation of run‐off from the rainfall events included in the analysis. Understanding the hydrological performance of green roofs in different local meteorological conditions is key to the successful implementation and development of sustainable practices to control run‐off in urban areas.

Nucleus Basalis Links Sensory Stimuli with Delayed Reinforcement to Support Learning

Linking stimuli with delayed reinforcement requires neural circuits that can bridge extended temporal gaps. Auditory cortex (ACx) circuits reorganize to support auditory fear learning, but only when afferent sensory inputs temporally overlap with cholinergic reinforcement signals. Here we show that mouse ACx neurons rapidly reorganize to support learning, even when sensory and reinforcement cues are separated by a long gap. We found that cholinergic basal forebrain neurons bypass the temporal delay through multiplexed, short-latency encoding of sensory and reinforcement cues. At the initiation of learning, cholinergic neurons in Nucleus Basalis increase responses to conditioned sound frequencies and increase functional connectivity with ACx. By rapidly scaling up responses to sounds that predict reinforcement, cholinergic inputs jump the gap to align with bottom-up sensory traces and support associative cortical plasticity.

A stronger influence of past rather than present landscape structure on present plant species richness of road-field boundaries

Road verges provide a refuge for numerous plant species, especially in agroecosystems characterized for decades by a general decline in semi-natural habitats and edge density. Beyond the influence of present landscape structure on the local structure and composition of plant communities, past landscape structure could also have a substantial effect. Indeed, a temporal delay could especially be hypothesized between periods of landscape changes and biological responses of plant communities. We surveyed plant communities of three adjacent elements of 190 road-field boundaries in Central-Western France: the berm, the embankment and the field margin. We compared the effects of past (1980) and present (2011) surrounding agricultural landscape structure on the plant species richness of each element and on the Sørensen taxonomic compositional dissimilarity index between pairs of elements using linear models and a model averaging procedure. We characterized the landscape structure at both time periods within three circular buffers of 250, 500 and 1000 m radius around the centre of each sampled road-field boundary. In each buffer, we calculated the proportion of grasslands, the proportion of woodlands and the edge density. Despite a weak explanatory power of the landscape structure, species richness of each road-field element was better explained by past than present landscape structure. Species richness of berms, the element of the road-field boundary having the highest proportion of perennial species, was also the most influenced by past landscape structure. As an example, species richness of berms increased with the proportion of woodlands and the edge density when considering a buffer of 500 m radius. In contrast, compositional dissimilarity between pair of elements was neither affected by past nor present landscape structure. Our results suggest that the taxonomic diversity of plant communities of road-field boundaries have a time-lagged response to landscape changes, emphasising that currently implemented management programs represent high stakes for biodiversity conservation in future decades.

Measurement noise explains lack of full adaptation without the need of forgetting: evidence from temporal delays.

Measurement noise explains lack of full adaptation without the need of forgetting: evidence from temporal delays.

On stochastic resonance in a model of double diffusion

ABSTRACTThe double diffusion model was proposed in the late 1970s and extended in 1980s and 1990s by Aifantis and co-workers. It is a continuum model that assumes two local non-equilibrium concentration fields abiding separate mass–momentum equations mediated by a linear mass exchange term. The present work deals with stochastic double diffusion of two competing phase densities to study transport in nanocrystals. We show that the presence of surface inhomogeneities and temporal delay, represented by stochastic dynamics, could have substantial impact at the interface of the two phases. The effect is most pronounced at a critical point (stochastic resonance), where maximum energy transfer occurs, thereby quantifying the impact of surface imperfections in nanocrystal dynamics. The results have been favourably compared with experimental data.This is part of a thematic issue on Small Scale Mechanics - EUROMAT.

Numerical Parametric Analysis of Combustion Instability in Axial-Injected Hybrid Rocket Motors

A computational model of a hybrid rocket motor has been developed for the purpose of simulation of internal ballistics and transient behavior such as combustion instabilities. The numerical model consists of four subcomponents: 1) a quasi-one-dimensional gas dynamics model using Euler equations for flowfield simulation, 2) a chemical model using CEA, 3) an analytical heat-feedback model for transfer of heat from flame to the solid fuel surface, and 4) a one-dimensional thermal conduction model inside the solid fuel. In the unsteady time-dependent simulation, it is seen that upon the application of a temporal boundary layer delay of the wall heat flux to the changes in the regression rate an unstable region ensues. At first, an oscillating periodic increase in the regression rate and chamber pressure is observed (linear regime), which then proceeds into a nonlinear limit cycle. A positive DC shift in the chamber pressure is also observed. The possible reason for the DC shift is explained with an analogy to a simple nonlinear oscillating system. The frequencies of different natural modes (including the intrinsic hybrid oscillation mode) predicted by the model are found to be in good agreement with theoretical prediction. The effect of finite time needed for the unburnt fuel to move from the regressing surface to the flame region is also additionally modeled using a time delay to the heat of combustion. This results in an increased amplitude of oscillations and a higher DC shift. Parametric analyses have been carried out with different boundary layer delays. The effect of the magnitude of boundary layer delay on the values of DC shift and RMS amplitude is also explained.

Flexible dual-soliton manipulation for coherent anti-Stokes Raman scattering spectroscopy.

Though dual soliton is used as the Stokes source in coherent anti-Stokes Raman scattering (CARS) experiments, the mechanism behind it is still not fully investigated. In this paper, dual-soliton pulses generation with a highly birefringent photonic crystal fiber (PCF) is numerically explored and experimentally verified. The simulated pulse exhibits various characteristics in the temporal and spectral domains with respect to the input linear polarization angle, and can be classified into four regions based on distances in the temporal and spectral domain of the soliton pair. By tuning input power and polarization angle, a soliton pair with desirable spectral coverage and temporal delay for CARS applications can be flexibly generated before the two solitons overlap in time domain. The simulated results are then experimentally validated by comparing their temporal and spectral characteristics. In addition, the benefit of using dual-soliton sources, such as Stokes beam, in CARS experiments is also demonstrated. The results and methods presented in this work can improve CARS spectroscopy and microscopy techniques, and may also be beneficial to other dual-wavelength source applications.

Fractional-order-based ACC/CACC algorithm for improving string stability

Traffic flow optimization and driver comfort enhancement are the main contributions of an Adaptive Cruise Control (ACC) system. If communication links are added, more safety and shorter gaps can be reached performing a Cooperative-ACC (CACC). Although shortening the inter-vehicular distances directly improves traffic flow, it can cause string unstable behavior. This paper presents fractional-order-based control algorithms to enhance the car-following and string stability performance for both ACC and CACC vehicle strings, including communication temporal delay effects. The proposed controller is compared with state-of-the-art implementations, exhibiting better performance. Simulation and real experiments have been conducted for validating the approach.

Extinction debt in a biodiversity hotspot: the case of the Chilean Winter Rainfall-Valdivian Forests

Habitat fragmentation has become a major concern of conservation because of negative influences on plant species declines and extinctions. However, local extinction of species can occur with a temporal delay following habitat fragmentation, which is termed extinction debt. Many studies about extinction debt rely on community equilibrium from relationships between species richness and habitat variables. We assumed that the distribution of many vascular plant species in the coastal range of south-central Chile is not in equilibrium with the present habitat distribution. The aim of this research is to quantify patterns of habitat loss and to detect extinction debt from relationships between the current richness of different assemblages of vascular plants (considering longevity and habitat specialization) and both past and current habitat variables. The results showed that native forests have been fragmented and reduced by 53%, with an annual deforestation rate of 1.99%, in the study area between 1979 and 2011. Current richness of plant species was mostly explained by past habitat area and connectivity. Past habitat variables explained best richness of long-lived specialist plants, which are characterized by restricted habitat specialization and slower population turnover. We also showed that habitat fragmentation has resulted in a significant reduction in long-lived plant species’ “dwelling patch sizes (DPS)” between 1979 and 2011. Our analyses provide the first evidence of predicted future losses of plant species in a South American temperate biodiversity hotspot. Consequently, an unknown proportion of the plants in the study area will become extinct if no targeted restoration and conservation action is taken in the near future.

Design principles of the paradoxical feedback between pancreatic alpha and beta cells

Mammalian glucose homeostasis is controlled by the antagonistic hormones insulin and glucagon, secreted by pancreatic beta and alpha cells respectively. These two cell types are adjacently located in the islets of Langerhans and affect each others’ secretions in a paradoxical manner: while insulin inhibits glucagon secretion from alpha cells, glucagon seems to stimulate insulin secretion from beta cells. Here we ask what are the design principles of this negative feedback loop. We systematically simulate the dynamics of all possible islet inter-cellular connectivity patterns and analyze different performance criteria. We find that the observed circuit dampens overshoots of blood glucose levels after reversion of glucose drops. This feature is related to the temporal delay in the rise of insulin concentrations in peripheral tissues, compared to the immediate hormone action on the liver. In addition, we find that the circuit facilitates coordinate secretion of both hormones in response to protein meals. Our study highlights the advantages of a paradoxical paracrine feedback loop in maintaining metabolic homeostasis.

Manometric recordings bring out post-stimulus refractory states in the anal canal in neonates.

Anorectal manometry is a diagnostic technique used to investigate the correct mechanical performance of the internal anal sphincter (IAS). By distending the rectal ampulla while recording changes in the luminal pressure, this method allows for characterizing the anorectal reflex. It can also provide, indirectly, information about the electrical activity of the IAS. In this study, seventeen neonates having 24-hour delayed passage of meconium or presenting distal intestinal obstruction symptoms underwent anorectal manometry to discard Hirschsprung's disease. All patients had normal anorectal reflex. The time delay between stimulation of the rectal ampulla and the relaxation of the anal canal was studied. The average period of the pressure fluctuations was 5.44 ± 0.13s. The overall duration of the relaxation time was 9.71 ± 0.21s. The maximum lag between the onset of the stimulus and the relaxation of the IAS was 2.90 s, and was achieved when the stimulus was applied following a local maximum of the pressure wave. The existence of a refractory period during the suprathreshold depolarization of smooth muscle cells can explain the evidence of a temporal delay between the stimulus and the mechanical response. In occasions, relaxation appeared first distally. This phenomenon can be explained by the arrangement and morphology of bipolar cells, which may evidence the anisotropic propagation of the mechanical activity. These data may contribute to depict the alterations in excitability underlying the relaxation reflex by means of manometric recording of the anal canal.

When Infamy Becomes Fame: The Positive Side of Negative Athlete Publicity

This study attempted to uncover the paradoxical effects of an athlete’s negative publicity based on the theories of negativity bias, fuzzy trace, and processing fluency. The researcher tested a boundary condition in which repeated claims about an athlete’s negative publicity interacted with the temporal delay of consumers’ evaluation, which, in turn, led to a decrease in the adverse effects of negative publicity. The results of two online experiments demonstrated that dividing attention and cognitive resources in order to encode and retrieve various types of information caused the detailed contextual memory of each account of the athlete’s negative publicity to fade over time, leaving behind merely a gist memory of the celebrities. In the current study, infamy turned into fame, and the consumer’s judgment of the athletes became more positive. The current study may help expand existing research paradigms by further developing our theoretical understanding of the negative publicity effects.

Additional Haptic Information Provided by Anchors Reduces Postural Sway in Young Adults Less Than Does Light Touch.

This study investigated the effect of adding haptic information to the control of posture, as well as comparing the effect of both the “light touch” (LT) and “anchor system” (AS) paradigms on postural sway. Additionally, it compared the effect of location and number of points of contact to the control of posture in young adults. The location consisted of using the anchors tied to the finger and held by the hands, and, for LT, the fingertip. For the number of points of contact, participants used two hands, and then separately the dominant hand, and the non-dominant hand, for both anchor and LT paradigms. Participants stood upright with feet-together and in tandem position while performing tasks that combined the use of anchors and LT, points of contact (hand grip and finger), and number of points of contact (two hands and one hand). In this study, the anchors consist of holding in each hand a flexible cable with the other end attached to the ground. The LT consists of slightly touching a rigid surface with the tip of the index finger. The results showed, first, that the anchors improved postural control less than did the LT. Second, they revealed that holding the anchors with the hands or with them tied to the fingertip resulted in a similar reduction in postural sway only in the tandem position. For the feet-together position, the anchors tied to the fingertip were ineffective. Similarly, the use of one or two hands did not affect the contribution of the anchors. However, using two hands in the LT condition was more effective than was one hand. Third, our results showed the presence of a temporal delay between force and center-of-pressure (COP) for the anchors, only in the AP direction with feet-together. In conclusion, overall, the anchors were less effective in reducing postural sway than was the LT. The anchors attached to fingertips were as effective as the hand-held anchors in the tandem position, yet ineffective during foot-together standing. Force-COP timing explains reduced postural sway with LT but not for the anchor; hence, exploratory and supra-postural components may be involved.

Evidence of gradual loss of precision for simple features and complex objects in visual working memory.

Previous studies have suggested that people can maintain prioritized items in visual working memory for many seconds, with negligible loss of information over time. Such findings imply that working memory representations are robust to the potential contaminating effects of internal noise. However, once visual information is encoded into working memory, one might expect it to inevitably begin degrading over time, as this actively maintained information is no longer tethered to the original perceptual input. Here, we examined this issue by evaluating working memory for single central presentations of an oriented grating, color patch, or face stimulus, across a range of delay periods (1, 3, 6, or 12 s). We applied a mixture-model analysis to distinguish changes in memory precision over time from changes in the frequency of outlier responses that resemble random guesses. For all 3 types of stimuli, participants exhibited a clear and consistent decline in the precision of working memory as a function of temporal delay, as well as a modest increase in guessing-related responses for colored patches and face stimuli. We observed a similar loss of precision over time while controlling for temporal distinctiveness. Our results demonstrate that visual working memory is far from lossless: while basic visual features and complex objects can be maintained in a quite stable manner over time, these representations are still subject to noise accumulation and complete termination. (PsycINFO Database Record

Experimental evidence for delayed contingent cooperation among wild dwarf mongooses

Many animals participate in biological markets, with strong evidence existing for immediate cooperative trades. In particular, grooming is often exchanged for itself or other commodities, such as coalitionary support or access to food and mates. More contentious is the possibility that nonhuman animals can rely on memories of recent events, providing contingent cooperation even when there is a temporal delay between two cooperative acts. Here we provide experimental evidence of delayed cross-commodity grooming exchange in wild dwarf mongooses (Helogale parvula). First, we use natural observations and social-network analyses to demonstrate a positive link between grooming and sentinel behavior (acting as a raised guard). Group members who contributed more to sentinel behavior received more grooming and had a better social-network position. We then used a field-based playback experiment to test a causal link between contributions to sentinel behavior and grooming received later in the day. During 3-h trial sessions, the perceived sentinel contributions of a focal individual were either up-regulated (playback of its surveillance calls, which are given naturally during sentinel bouts) or unmanipulated (playback of its foraging close calls as a control). On returning to the sleeping refuge at the end of the day, focal individuals received more grooming following surveillance-call playback than control-call playback and more grooming than a matched individual whose sentinel contributions were not up-regulated. We believe our study therefore provides experimental evidence of delayed contingent cooperation in a wild nonprimate species.

A two-stage optical parametric amplifier for femtosecond fiber laser generation at 920 nm

We demonstrate a cascaded, two-stage, fiber-based optical parametric amplifier (OPA) in which the signal pulses are generated in the first stage via spontaneous degenerate four-wave mixing (DFWM) mechanism and subsequently are used as the seed pulse for the stimulated DFWM in the second stage. A compact femtosecond fiber laser provides the pump pulse with 220-fs duration at 20-MHz repetition rate. Large-mode area (LMA) photonic crystal fibers (PCFs) with zero dispersion wavelength at 1054 nm and a dispersion slope of 0.20 ps/km/nm2 provide the parametric gain. Pulses with 2-mW average power in spectral range from 850 to 1000 nm are obtained from the first-stage OPA, and they are further amplified to 23.4 mW in the second stage OPA, corresponding to 10.7-dB parametric gain. The output pulse duration and spectral bandwidth are closely related to the temporal delay between the signal and pump pulses in the second stage. With an optimized time delay, pulses with >1 nJ energy and <200 fs duration are obtained at the spectral range from 850 to 1000 nm.

In vivo characterization of 3D skull and brain motion during dynamic head vibration using magnetic resonance elastography.

To introduce newly developed MR elastography (MRE)-based dual-saturation imaging and dual-sensitivity motion encoding schemes to directly measure in vivo skull-brain motion, and to study the skull-brain coupling in volunteers with these approaches. Six volunteers were scanned with a high-performance compact 3T-MRI scanner. The skull-brain MRE images were obtained with a dual-saturation imaging where the skull and brain motion were acquired with fat- and water-suppression scans, respectively. A dual-sensitivity motion encoding scheme was applied to estimate the heavily wrapped phase in skull by the simultaneous acquisition of both low- and high-sensitivity phase during a single MRE exam. The low-sensitivity phase was used to guide unwrapping of the high-sensitivity phase. The amplitude and temporal phase delay of the rigid-body motion between the skull and brain was measured, and the skull-brain interface was visualized by slip interface imaging (SII). Both skull and brain motion can be successfully acquired and unwrapped. The skull-brain motion analysis demonstrated the motion transmission from the skull to the brain is attenuated in amplitude and delayed. However, this attenuation (%) and delay (rad) were considerably greater with rotation (59 ± 7%, 0.68 ± 0.14 rad) than with translation (92 ± 5%, 0.04 ± 0.02 rad). With SII the skull-brain slip interface was not completely evident, and the slip pattern was spatially heterogeneous. This study provides a framework for acquiring in vivo voxel-based skull and brain displacement using MRE that can be used to characterize the skull-brain coupling system for understanding of mechanical brain protection mechanisms, which has potential to facilitate risk management for future injury.

Temporal dynamics of mirror-symmetry perception.

Recent studies have suggested that temporal dynamics rather than symmetrical motion-direction contribute to mirror-symmetry perception. Here we investigate temporal aspects of symmetry perception and implicitly, its temporal flexibility and limitations, by examining how symmetrical pattern elements are combined over time. Stimuli were dynamic dot-patterns consisting of either an on-going alternation of two images (sustained stimulus presentation) or just two images each presented once (transient stimulus presentation) containing different amounts of symmetry about the vertical axis. We varied the duration of the two images under five temporal-arrangement conditions: (a) whole patterns in which a symmetric pattern alternated with a noise pattern; (b) delayed halves—the halves of the symmetric and noise patterns were presented with temporal delay; (c) matched-pairs—two alternating images each containing equal amounts of symmetrical matched-pairs; (d) delayed matched-pairs—the same as arrangement (c), but with matched-pairs presented with delay; and (e) static—both images presented simultaneously as one. We found increased sensitivity in sustained compared to transient stimulus presentations and with synchronous compared to delayed matched-pairs stimuli. For the delayed conditions, sensitivity decreased gradually with longer image durations (>60 ms), prominently for the transient stimulus presentations. We conclude that spatial correlations across-the-symmetry-midline can be integrated over time (∼120 ms), and symmetry mechanisms can tolerate temporal delays between symmetric dot-pairs of up to ∼60 ms.

Post-traumatic stress symptoms are associated with better performance on a delayed match-to-position task.

Many individuals with posttraumatic stress disorder (PTSD) report experiencing frequent intrusive memories of the original traumatic event (e.g., flashbacks). These memories can be triggered by situations or stimuli that reflect aspects of the trauma and may reflect basic processes in learning and memory, such as generalization. It is possible that, through increased generalization, non-threatening stimuli that once evoked normal memories become associated with traumatic memories. Previous research has reported increased generalization in PTSD, but the role of visual discrimination processes has not been examined. To investigate visual discrimination in PTSD, 143 participants (Veterans and civilians) self-assessed for symptom severity were grouped according to the presence of severe PTSD symptoms (PTSS) vs. few/no symptoms (noPTSS). Participants were given a visual match-to-sample pattern separation task that varied trials by spatial separation (Low, Medium, High) and temporal delays (5, 10, 20, 30 s). Unexpectedly, the PTSS group demonstrated better discrimination performance than the noPTSS group at the most difficult spatial trials (Low spatial separation). Further assessment of accuracy and reaction time using diffusion drift modeling indicated that the better performance by the PTSS group on the hardest trials was not explained by slower reaction times, but rather a faster accumulation of evidence during decision making in conjunction with a reduced threshold, indicating a tendency in the PTSS group to decide quickly rather than waiting for additional evidence to support the decision. This result supports the need for future studies examining the precise role of discrimination and generalization in PTSD, and how these cognitive processes might contribute to expression and maintenance of PTSD symptoms.