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This article investigates the exponential stability of generalized neural networks (GNNs) with a time-varying delay. Different from the literatures on the similar topic, the considered time delay contains a few intermittent large-delay periods (LDPs). A new approach is proposed to determine how frequent and how long the LDPs are allowed for guaranteeing the exponential stability by using switching techniques. The GNN is first modeled as a switched time-delay system which may include an unstable subsystem. Then, based on a novel Lyapunov–Krasovskii functional with LDP-based terms, a delay-dependent exponential stability criterion and associated evaluation algorithm are developed. Finally, two numerical examples are provided to show the effectiveness of the proposed method.

This study examined the impact of varying the holding time following an ad libitum laboratory breakfast on acute dietary behaviour and subsequent intake. Twenty-four participants (20 females (age: 23.4 ± 6.3 years; body mass index: 23.9 ± 3.9 kg·m–2, mean ± SD)) completed 3 trials following a quasi-randomised, crossover design. Each trial (7-day separation) incorporated a defined post-prandial delay (DPD) period of either zero (no delay), 1 or 3 hours following a buffet breakfast consumed over 30 minutes. Dietary intake outcomes included energy, macronutrient and core food group intakes. On completion of the DPD period, participants left the laboratory and recorded all food/beverages consumed for the remainder of the day. One-way repeated-measures ANOVA assessed all outcomes, with post hoc analysis conducted on significant main effects. Energy and carbohydrate intakes were significantly lower on no delay vs. 1-hour (p = 0.014) and 3-hour (p = 0.06) DPD trials (energy intake: 1853 ± 814 kJ vs. 2250 ± 1345 kJ vs. 1948 ± 1289 kJ; carbohydrates: 68 ± 34 g vs. 77 ± 44 vs. 69 ± 43 g; respectively). DPD periods did not influence the time to consume next meal or energy, macronutrient and core food group intakes for the remainder of the day. Delaying participants from leaving a laboratory alters dietary intake at an ad libitum test meal. The post-meal holding period is an important methodological consideration when planning laboratory studies to assess appetite. Novelty: Delaying participants from leaving a laboratory alters dietary intake at ad libitum breakfast meals. The length of the delay period did not affect dietary intake at ad libitum breakfast meals.

Introduction Vaccination coverage is widely used as metric of vaccination programme performance. However, VPDs outbreaks were reported in areas with high vaccination coverage. Timeliness and completeness have been considered more important assessment indicators of routine vaccination than overall vaccination coverage, but little is known in rural China. This study aimed to assess the timeliness and completeness of serial routine vaccinations among children in rural Southwest China. Methods A multi-stage stratified cluster survey was conducted among 1062 children aged 18–48 months in rural Guangxi. Vaccination status was obtained from child’s vaccination certificate. We calculated timely vaccination coverage, complete vaccination coverage, timely-and-complete vaccination coverage and 95% CI for routine vaccination through weighted estimation analysis. Weighted Kaplan-Meier analyses were applied to estimate the median delay periods for each dose of serial routine vaccines, including one-dose BCG, three-dose HepB, three-dose OPV, four-dose DTP, two-dose MCV, two-dose JEV and two-dose MPV-A. Complete coverage, and timely-and-complete coverage for combined 5-vaccine series were calculated. Results For each dose of routine vaccines, overall vaccination coverages were over 90%, but timely vaccination coverage ranged from the lowest of 44.4% for JEV1 to the highest of 92.5% for MPV-A1. For multi-dose routine vaccines, complete vaccination coverages varied from the lowest of 92.9% for MCV to the highest of 100% for HepB, and timely-and-complete vaccination coverages were lower than 80%, ranging from the lowest of 30% for JEV to the highest of 77.2% for MPV-A. For combined 5-vaccine series, complete coverage was 77%, while timely-and-complete coverage was 12.1%. MPV-A1 had the longest median delay of 176 days, but BCG and HepB1 had the shortest of 1 day. Conclusions The overall coverages of serial routine vaccinations were high, but the timeliness and completeness were poor. Relevant agencies of vaccination service should address timeliness-and-completeness into the assessment indicators of routine vaccination service quality.

The lateral prefrontal cortex is involved in the integration of multiple types of information, including working memory and motor preparation. However, it is not known how downstream regions can extract one type of information without interference from the others present in the network. Here, we show that the lateral prefrontal cortex of non-human primates contains two minimally dependent low-dimensional subspaces: one that encodes working memory information, and another that encodes motor preparation information. These subspaces capture all the information about the target in the delay periods, and the information in both subspaces is reduced in error trials. A single population of neurons with mixed selectivity forms both subspaces, but the information is kept largely independent from each other. A bump attractor model with divisive normalization replicates the properties of the neural data. These results provide new insights into neural processing in prefrontal regions.

Maturation of basal ganglia (BG) and frontoparietal circuitry parallels developmental gains in working memory (WM). Neurobiological models posit that adult WM performance is enhanced by communication between reward-sensitive BG and frontoparietal regions, via increased stability in the maintenance of goal-relevant neural patterns. It is not known whether this reward-driven pattern stability mechanism may have a role in WM development. In 34 young adolescents (12.16–14.72 years old) undergoing fMRI, reward-sensitive BG regions were localized using an incentive processing task. WM-sensitive regions were localized using a delayed-response WM task. Functional connectivity analyses were used to examine the stability of goal-relevant functional connectivity patterns during WM delay periods between and within reward-sensitive BG and WM-sensitive frontoparietal regions. Analyses revealed that more stable goal-relevant connectivity patterns between reward-sensitive BG and WM-sensitive frontoparietal regions were associated with both greater adolescent age and WM ability. Computational lesion models also revealed that functional connections to WM-sensitive frontoparietal regions from reward-sensitive BG uniquely increased the stability of goal-relevant functional connectivity patterns within frontoparietal regions. Findings suggested (1) the extent to which goal-relevant communication patterns within reward-frontoparietal circuitry are maintained increases with adolescent development and WM ability and (2) communication from reward-sensitive BG to frontoparietal regions enhances the maintenance of goal-relevant neural patterns in adolescents' WM. The maturation of reward-driven stability of goal-relevant neural patterns may provide a putative mechanism for understanding the developmental enhancement of WM.

Normal aging is associated with a decline in memory and motor learning ability. However, the exact form of these impairments (e.g., the short-term temporal stability and affected learning mechanisms) is largely unknown. Here, we used a sensorimotor adaptation task to examine changes in the temporal stability of two forms of learning (explicit and implicit) because of normal aging. Healthy young subjects (age range, 19–28 years; 20 individuals) and older human subjects (age range, 63–85 years; 19 individuals) made reaching movements in response to altered visual feedback. On each trial, subjects turned a rotation dial to select an explicit aiming direction. Once selected, the display was removed and subjects moved the cursor from the start position to the target. After initial training with the rotational feedback perturbation, subjects completed a series of probe trials at different delay periods to systematically assess the short-term retention of learning. For both groups, the explicit aiming showed no significant decrease over 1.5 min. However, this was not the case for implicit learning; the decay pattern was markedly different between groups. Older subjects showed a linear decrease of the implicit component of adaptation over time, while young subjects showed an exponential decay over the same period (time constant, 25.61 s). Although older subjects adapted at a similar rate, these results suggest natural aging selectively impacts the short-term (seconds to minutes) temporal stability of implicit motor learning mechanisms. This understanding may provide a means to dissociate natural aging memory impairments from deficits caused by brain disorders that progress with aging.

Quarantine disinfestation treatments for Queensland fruit fly (Bactrocera tryoni (Froggatt)) have been developed which use high temperatures to kill preimaginal life stages within fruit prior to export. However, thermal tolerance of individuals can be increased if they are exposed to elevated temperatures before disinfestation treatment. The rate that this thermal conditioning decays after exposure, and the effect of temperature on this decay process, were investigated. Eggs of B. tryoni were exposed to a nonlethal hot water treatment at 38°C for 15 min, 1 or 3 h, then held in air at 25°C for times ranging from 15 min to 12 h, before being exposed to hot water disinfestation at 46°C for various times. From each of these cohorts, the lethal time for 99% mortality (LT99) was calculated. The LT99 of B. tryoni eggs increased with longer conditioning times at 38°C. For each conditioning time, the LT99 decreased with longer delay periods at 25°C prior to disinfestation. The rate of decrease was greatest during the first hour of delay, after which the rate of decrease slowed and tended toward zero. This induction and decay was modeled using a double-exponential equation. These experiments show that thermal conditions prior to disinfestation, and the time delay before the procedure commences, both influence the response of the insect to the disinfestation treatment. These results have implications for the specification of postharvest quarantine treatments, which are usually expressed only in terms of a fruit-center target temperature.

This study is concerned with the observer-based H ∞ stabilisation problem for a class of linear systems with large delay periods (LDPs). Based on the switching technique, the system with LDPs is modelled into a switched delay system which consists of two subsystems. The controller and observer gains are solved under the small delay case. Sufficient conditions are derived to ensure the system is not only exponentially stable, but also possesses an H ∞ performance index. The effectiveness of the proposed method is validated by the simulation of a load frequency control system.

Pigeons and other animals sometimes deviate from optimal choice behavior when given informative signals for delayed outcomes. For example, when pigeons are given a choice between an alternative that always leads to food after a delay and an alternative that leads to food only half of the time after a delay, preference changes dramatically depending on whether the stimuli during the delays are correlated with (signal) the outcomes or not. With signaled outcomes, pigeons show a much greater preference for the suboptimal alternative than with unsignaled outcomes. Key variables and research findings related to this phenomenon are reviewed, including the effects of durations of the choice and delay periods, probability of reinforcement, and gaps in the signal. We interpret the available evidence as reflecting a preference induced by signals for good news in a context of uncertainty. Other explanations are briefly summarized and compared.

Purpose. To examine causes as well as extent of delay in diagnosis and treatment of primary open angle glaucoma patients in a sample of Egyptians.Patients and Methods. 440 patients with primary open angle glaucoma were interviewed to evaluate delay in their diagnosis and treatment. The extent and cause of delay were investigated. The total delay interval, if any, was correlated with socioeconomic and other factors.Results. The median total delay was one year, with 50% of patients having a total delay of 1 year or less, of which 25% exhibited zero total delay. 25% of patients had a delay ranging from 1 to 3 years, and 25% had a total delay ranging from 3 to 27 years. Diagnostic delay accounted for 43.03% of cases. Longer delays were met in patients with certain socioeconomic factors. Patients with a positive family history of glaucoma displayed shorter delay periods.Conclusion. Significant delay in the diagnosis and treatment of glaucoma was found. Poor socioeconomic status seems to hinder timely diagnosis and treatment of POAG. Certain socioeconomic factors seem to correlate with the extent of delay. More effort is thus needed to subsidize the cost of investigations and treatment for glaucoma patients.

Summary: Working memory-guided behaviors require memory retention during delay periods, when subsets of prefrontal neurons have been reported to exhibit persistently elevated firing. What happens to delay activity when information stored in working memory is no longer relevant for guiding behavior? In this study, we perform juxtacellular recording and labeling of delay-tuned (-elevated or -suppressed) neurons in the prelimbic cortex of freely moving rats, performing a familiar delayed cue-matching-to-place task. Unexpectedly, novel task-rules are introduced, rendering information held in working memory irrelevant. Following successful strategy switching within one session, delay-tuned neurons are filled with neurobiotin for histological analysis. Delay-elevated neurons include pyramidal cells with large heterogeneity of soma-dendritic distribution, molecular expression profiles, and task-relevant activity. Rule change induces heterogenous adjustments on individual neurons and ensembles’ activity but cumulates in balanced firing rate reorganizations across cortical layers. Our results demonstrate divergent cellular and network dynamics when an abrupt change in task rules interferes with working memory. : Ozdemir et al. perform juxtacellular recording and labeling of delay-tuned neurons in rats performing a working memory task. They show that these cells are heterogeneous in molecular expression and somato-dendritic organization. Unexpected change of the task rule diversely adjusts firing activity of the delay-tuned neurons and prefrontal networks. Keywords: the medial prefrontal cortex, working memory, adaptive cognitive control, memory delay, cellular heterogeneity, juxtacellular labeling

Summary Objectives Motor-evoked potentials (MEPs) to transcranial magnetic stimulation (TMS) show a profound suppression when elicited during the instructed-delay of reaction time (RT) tasks. One predominant hypothesis is that this phenomenon, called “preparatory inhibition”, reflects the operation of processes that suppress motor activity to withhold prepared (but delayed) responses, a form of impulse control. In addition, a startling acoustic stimulus (SAS) – a loud and narrow sound – can trigger the release of prepared responses in RT tasks. We predicted that, if such premature release is clearly forbidden, then anticipating a SAS during delay periods may be associated with increased preparatory inhibition for greater impulse control. Methods Subjects performed a behavioural (n = 16) and TMS (n = 11) experiment. Both used a choice RT task that required subjects to choose a response based on a preparatory cue but to only release it after an imperative signal. SAS and TMS pulses were elicited at the end of the delay period and subjects were asked to do their best to only release their response after the imperative signal, even in the presence of SAS. SAS could be either rare or frequent, in separate blocks. Results Consistent with the literature, SAS shortened RTs, especially when they occurred frequently. Moreover, MEPs were suppressed when subjects delayed prepared responses but this preparatory inhibition did not depend on whether SAS were frequent or rare. Discussion The stronger RT shortening with frequent rather than rare SAS may be due to increased attention and/or reduced reactive inhibition to SAS, leaving preparatory inhibition unaffected.

This paper investigates the problem of guaranteed cost load frequency control (LFC) for a class of uncertain power systems with large delay periods (LDPs). The model of LFC for power systems with LDPs has been firstly modeled as a switched delay system, which includes a potentially unstable subsystem caused by LDPs and a stable subsystem caused by small delay periods (SDPs). Based on the switching technique and under the constraint conditions of the length ratio and the frequency of LPD, the guaranteed cost load frequency controller can be obtained such that the closed-loop system is exponentially stable and a weighted guaranteed cost upper bound is achieved. Finally, an example is provided to demonstrate the applicability of the proposed method.

Cellular combustion regime of a 40% H2–air mixture in the presence of Pt wire at 270–350 °C was observed for the first time. The regime is caused by the catalytic action of Pt-containing particles formed by the decomposition of volatile platinum oxide in a gas phase.

The hippocampus and medial temporal lobes (MTL) support the successful formation of new memories without succumbing to interference from related, older memories. Computational models and animal findings have implicated the dentate gyrus (DG), CA3, CA1, and entorhinal cortex (EC) in the disambiguation and encoding of well-established, episodic events that share common elements. However, it is unknown if these hippocampal subfields and MTL (entorhinal, perirhinal, parahippocampal) cortices also contribute during working memory when overlapping stimuli that share related features are rapidly encoded and subsequently maintained over a brief temporal delay. We hypothesized that activity in CA3/DG hippocampal subfields would be greater for the rapid encoding of stimuli with overlapping features than for the rapid encoding of stimuli with distinct features. In addition, we predicted that CA1 and EC, regions that are associated with creating long-term episodic representations, would show greater sustained activity across both encoding and delay periods for representations of stimuli with overlapping features than for those with distinct features. We used high-resolution fMRI during a delayed matching-to-sample (DMS) task using face pairs that either shared (overlapping condition, OL) or did not share (non-overlapping condition, NOL) common elements. We contrasted the OL condition with the NOL condition separately at sample (encoding) and during a brief delay (maintenance). At sample, we observed activity localized to CA3/DG, the subiculum, and CA1. At delay, we observed activity localized to the subiculum and CA1 and activity within the entorhinal, perirhinal, and parahippocampal cortices. Our findings are consistent with our hypotheses and suggest that CA3/DG, CA1 and the subiculum support the disambiguation and encoding of overlapping representations while CA1, subiculum and entorhinal cortex maintain these overlapping representations during working memory.

Several lines of evidence suggest that the striatum has an important role in spatial working memory. The neural dynamics in the striatum have been described in tasks with short delay periods (1–4 s), but remain largely uncharacterized for tasks with longer delay periods. We collected and analyzed single unit recordings from the dorsomedial striatum of rats performing a spatial working memory task with delays up to 10 s. We found that neurons were activated sequentially, with the sequences spanning the entire delay period. Surprisingly, this sequential activity was dissociated from stimulus encoding activity, which was present in the same neurons, but preferentially appeared towards the onset of the delay period. These observations contrast with descriptions of sequential dynamics during similar tasks in other brains areas, and clarify the contribution of the striatum to spatial working memory. DOI: http://dx.doi.org/10.7554/eLife.19507.001

In previous reports, we described neuronal activity in the polar (PFp), dorsolateral (PFdl), and orbital (PFo) PFC as monkeys performed a cued strategy task with two spatial goals. On each trial, a cue instructed one of two strategies: Stay with the previous goal or shift to the alternative. A delay period followed each cue, and feedback followed each choice, also at a delay. Our initial analysis showed that the mean firing rate of a population of PFp cells encoded the goal chosen on a trial, but only near the time of feedback, not earlier in the trial. In contrast, PFdl cells encoded goals and strategies during the cue and delay periods, and PFo cells encoded strategies in those task periods. Both areas also signaled goals near feedback time. Here we analyzed trial-to-trial variability of neuronal firing, as measured by the Fano factor (FF): the ratio of variance to the mean. Goal-selective PFp neurons had two properties: (1) a lower FF from the beginning of the trial compared with PFp cells that did not encode goals and (2) a weak but significant inverse correlation between FF throughout a trial and the degree of goal selectivity at feedback time. Cells in PFdl and PFo showed neither of these properties. Our findings indicate that goal-selective PFp neurons were engaged in the task throughout a trial, although they only encoded goals near feedback time. Their lower FF could improve the ability of other cortical areas to decode its selected-goal signal.

Summary A study of the effects of various delay periods and handling conditions before freezing on Cape hake in the whole or eviscerated state has been made in order to assess the importance of these to the quality and acceptability of the final product. Increasing delays before gutting lead to increasing discolourations in sea frozen fillets and in fillets cut from sea frozen whole fish, even where a further delay for bleeding occurs before freezing. Increasing bleeding times beyond 30 min does not lead to further reductions in this discolouration which is minimized by holding the fish chilled from catching to freezing. The extent of gaping apparent in fillets from whole fish is related to delay before freezing and can also be reduced by holding at chill temperatures throughout the prefreezing period. Quality deterioration was less in fillets than in fish on the bone during extended chill storage after thawing but freezing and thawing again produced little change in fillet quality.

Extended maintenance delays decrease the accuracy of information stored in spatial working memory. In order to elucidate the network underlying sustained spatial working memory, 16 subjects were scanned using fast event-related fMRI as they performed an oculomotor delayed response task containing trials with “short” (2.5 s) or “long” (10 s) delay periods. Multiple cortical and subcortical regions were common to both delay trial types indicating core task regions. Three patterns of activity were found in a subset of core regions that reflect underlying processes: maintenance-related (e.g., left FEF, right supramarginal gyrus (SMG)), response planning-related (e.g., right FEF, SEF), and motor response-related (e.g., lateral cerebellum (declive)) activation. Several regions were more active during long than short delay trials, including multiple sites in DLPFC (BA 9, 46), indicating a circuitry dynamically recruited to support sustained working memory. Our results suggest that specialized brain processes support extended periods of working memory.

Background This study evaluates the possibility of enhancing the beneficial effect of the delay procedure by using hyperbaric oxygen therapy, and the possibility of lessening the time required for maximal effect of delay procedure. Methods Eight male Wistar rats were used in each of 10 groups. The surgical delay method was applied to the caudally based dorsal rat flap by incising the longitudinal borders and undermining the flap. In the first five groups, 3-, 7-, 10-, 14-, and 21-day delay periods were applied, and in the other five groups, hyperbaric oxygen therapy was applied during the delay periods. Blood circulation was measured with a laser Doppler flowmeter, and flap survival lengths were recorded. Histological analysis for vascular counting and determining vascular areas and microangiographic analysis for monitoring vascular status were performed. Results In addition to the flap viabilities being increased, the maximum effect of the delay procedure could be achieved earlier with hyperbaric oxygen therapy. Blood circulation in the flaps, vascular counts, and vascular areas were increased by applying hyperbaric oxygen during the delay period. Microangiographic results confirmed the beneficial effect of hyperbaric oxygen treatment. Conclusions Hyperbaric oxygen treatment during the delay period can lessen the time period needed for the delay procedure and increase the effect of the delay itself.

This paper investigates the problem of load frequency control (LFC) for power systems with large delay periods (LDPs), which is often present in practical power systems and makes them unstable. LFC for power systems with LDPs has been modeled as switched delay systems, which include an unstable subsystem caused by LDPs. The switching strategy is used to deal with the stability problem of LFC for power systems with LDPs and stability criteria are proposed under the constraint conditions of the length ratio and the frequency of LDP to ensure power systems exponential stable. Finally, the relationship between the gains of PI controller and delay margin is studied and the simulation results show that the proposed method is effective.

© 2015 AIP Publishing LLC. Multidimensional signals are generated by subjecting molecules to sequences of short optical pulses and recording correlation plots related to the various controlled delay periods. These techniques which span all the way from the THz to the x-ray regimes provide qualitatively new structural and dynamical molecular information not available from conventional one-dimensional techniques. This issue surveys the recent experimental and theoretical progresses in this rapidly developing 20 year old field which illustrates the novel insights provided by multidimensional techniques into electronic and nuclear motions. It should serve as a valuable source for experts in the field and help introduce newcomers to this exciting and challenging branch of nonlinear spectroscopy.

WOS: 000354605300013, The aim of the current study was to compare simultaneous prompting (SP) and constant time delay (CTD) in terms of their effectiveness and efficiency in teaching children with autism how to respond to questions about personal information. The adapted alternating treatments model was used in the study. Three male students with autism aged 4, 6, and 9, respectively, were included in the study. The findings of the study did not indicate any significant difference in two students with respect to the effectiveness of SP and CTD procedures. On the other hand, SP was observed to create more positive results and lead to a higher level of learning for the third participant. According to the findings, SP was more effective for one participant with respect to all the parameters studied. While SP was more efficient in the other two subjects in terms of incorrect responses, the difference regarding the instructional time to criterion for these two subjects was at a minimal level in favor of SP.

The present study was to investigate whether neuronal activity in primary somatosensory cortical areas (SI) differs when monkeys expect go-cues of different sensory modalities. Two monkeys made wrist extensions and flexions after steadily holding wrist at a center position. Movements were guided by increases in vibration to the monkey's palm (VIB), visual targets (VIS), or both in combination (COM). Neuronal activity recorded in SI during the early and late phases (i.e., the first and last 250 ms) of the instructed delay periods (IDP) were analyzed. Of 406 neurons recorded during all three paradigms, 263 (64.8%) showed significant changes in firing rates (FR) between the early and late IDP phases during either VIB or VIS trials and were selected for further analyses. The selected neurons were classified as VIB- or VIS-biased, depending on the paradigm (VIB or VIS) in which the greater FR changes occurred. Both increases and decreases in FRs were observed during the analyzed epochs. Most VIB-biased neurons showed the biggest FR changes during VIB trials and the least during VIS trials. Conversely, most VIS-biased neurons had the biggest FR changes during VIS trials and the least during VIB trials. For both VIB- and VIS-biased neurons, however, the FR changes were intermediate during COM trials. These results suggest that SI neurons play an important role in initiating/executing wrist movements. Neurons involved in wrist movements showed biases to the modality of cueing signals. Most SI neurons were biased to only one sensory modality. The expectation-related FR changes suggest different involvement by SI in movement initiation when tasks are guided by vibratory and visual signals.

Previous research on self-control using macaques ( Macaca fascicularis) showed these animals have a strong bias for a delayed, larger reinforcer (Self-control) over an immediate, smaller reinforcer (Impulsive). Typical studies of self-control have used a discrete trials methodology with a secondary discriminative stimulus during the delay periods. This results in a greater exposure to the stimulus representing the self-controlled option and may account for some of the early exclusive preference for self-control observed. The present experiment examined self-control bias in three rhesus macaques ( Macaca mulatta) while controlling for differential durations of stimulus exposure. Subjects were presented stimuli via a computer monitor and made choices by touching the stimulus at which point both stimuli were removed for the delay periods. All three subjects displayed a nearly exclusive bias for the delayed, larger reinforcer (self-control). These results are consistent with previous studies, despite the variations in methodology and species.

We study a complete-information alternating-offer bargaining game in which one “active” player bargains with each of a number of other “passive” players one at a time. In contrast to most existing models, the order of reaching agreements is endogenously determined, hence the active player can “play off” some passive players against others by m oving back and forth bargaining with the passive players. We show that this model has a finite number of Markov Perfect Equilibria, some of which exhibiting wasteful delays. Moreover, the maximum number of delay periods that can be supported in Markov Perfect Equilibria increases in the order of the square of the number of players. We also show that these results are robust to a relaxing of the Markov requirements and to more general surplus functions.

Some precast concrete plants expose freshly made concrete elements to steam curing immediately after casting. This is detrimental to properties of the product; therefore, some delay prior to the steam curing process is beneficial. This paper contains the results of an investigation on the effects of various delay intervals selected based on initial setting time of concrete. Four different delay periods and two different steam curing periods at 80 °C (5 and 10 h) were used with two concrete types, namely C25 and C40. Compressive strength tests were performed at 1, 3, 7, 28, and 90 days. Setting time of the concrete was found to be an important criterion to determine the length of the delay periods.

We investigated the role of saccadic gaze fixations in encoding target locations for planning a future manual task consisting of a sequence of discrete target-oriented actions. We hypothesized that fixations of the individual targets are necessary for accurate encoding of target locations and that there is a transfer of sequence information from visual encoding to manual recall. Subjects viewed four targets presented at random positions on a screen. After various delays following target extinction, the subjects marked the remembered target locations on the screen with the tip of a hand-held stick. When the targets were presented simultaneously among distracting elements, the overall accuracy of marking increased with presentation time and total number of targets fixated because the subjects had to serially fixate the individual targets to locate them. Without distractors, the marking accuracy was similarly high regardless of duration of target presentation (0.25–8 s) and number of targets fixated; it was comparable to that with distractors when all four targets had been fixated. This indicates parallel encoding of target locations largely based on peripheral vision. Location memory was stable in these tasks over the delay periods investigated (0.5–8 s). With parallel encoding there was a “shrinkage” in the visuomotor transformation, i.e., the distances between the markings were systematically smaller than the corresponding inter-target distances. When the targets were presented sequentially without distractors, marking accuracy improved with the total number of targets fixated and shrinkage in the visuomotor transformation occurred only with parallel encoding, i.e., when subjects did not fixate the targets. In all experimental conditions for trials in which targets were fixated during encoding, there was little correspondence between the marking sequence and the sequence in which the targets were fixated. We conclude that subjects benefit from fixating targets for subsequent target-oriented manual actions when the targets are presented among distractors and when presented sequentially; when distinct targets are presented simultaneously against a blank background, they are efficiently encoded in parallel largely by peripheral vision.

A study was carried out to examine the ability of equestrians to accurately report precompetition emotions and thoughts across varying time delays (3,7, and 14 days) after competition. Forty male and female dressage riders were randomly divided into two equal groups: participants who watched their videotaped precompetition routine before responding to the items, and participants who visualized the precompetition routine without any external aid. Each rider completed several questionnaires which measured emotions, items related to horses, and an open-ended question on thoughts and emotions at that moment. After a delay of 3,7, and 14 days, the riders were asked to respond to the same questions after imagining themselves preparing for the competition. Repeated-measures MANOVA indicate that though some decrease in emotional intensity was noted for some emotions in the retrospective report, the stability of reporting precompetition emotions was very high in all delay periods. The horse related items were reported particularly accurately. Watching the videotape did not improve the accuracy of the report. Content analysis, however, indicated that when measurement consisted of free report, many emotions and thoughts were added or omitted in the delayed modes. Ericsson and Simon’s (1980, 1984) verbal reports and protocol analysis conceptualization is used to elaborate upon these results.

The goal of the study was an evaluation of the degree, in which nitric oxide (NO) is involved in the benzodiazepines (BZs)-induced recognition memory impairment in rats. The novel object recognition (NOR) test was used to examine recognition memory. The current research focused on the object memory impairing effects of diazepam (DZ; 0.5 and 1 mg/kg, sc ) and flunitrazepam (FNZ; 0.1 and 0.2 mg/kg; sc ) in 1-hour delay periods in rats. It was found that acute ip injection of l -arginine ( l -arg; 250 and 500 mg/kg; ip ), 5 min before DZ administration (0.5 mg/kg, sc ) prevented DZ-induced memory deficits. On the other hand, it was also proven that l -arg (125, 250 and 500 mg/kg; ip ) did not change the behaviour of rats in the NOR test, following a combined administration with FNZ at a threshold dose (0.05 mg/kg; sc ). It was also found that 7-nitroindazole (7-NI; 10, 20 and 40 mg/kg; ip ) induced amnesic effects in DZ in rats, submitted to the NOR test, following a combined administration of 7-NI with a threshold dose of DZ (0.25 mg/kg; sc ). However, following a combined administration of 7-NI (10, 20 and 40 mg/kg; ip ) with FNZ (0.1 mg/kg; sc ), it was observed that 7-NI inhibited the amnesic effects of FNZ on rats in the NOR test. Those findings led us to hypothesize that NO synthesis suppression may induce amnesic effects of DZ, while preventing FNZ memory impairment in rats, submitted to NOR tasks.

Perceptual after-effects decay over time at a rate that depends on several factors, such as the duration of adaptation and the duration of the test stimuli. Whether this decay is accelerated by exposure to other faces after adaptation is not known. Our goal was to determine if the appearance of other faces during a delay period after adaptation affected the face identity after-effect. In the first experiment we investigated whether, in the perception of ambiguous stimuli created by morphing between two faces, the repulsive after-effects from adaptation to one face were reduced by brief presentation of the second face in a delay period. We found no effect; however, this may have been confounded by a small attractive after-effect from the interference face. In the second experiment, the interference stimuli were faces unrelated to those used as adaptation stimuli, and we examined after-effects at three different delay periods. This showed a decline in after-effects as the time since adaptation increased, and an enhancement of this decline by the presentation of intervening faces. An exponential model estimated that the intervening faces caused an 85% reduction in the time constant of the after-effect decay. In conclusion, we confirm that face after-effects decline rapidly after adaptation and that exposure to other faces hastens the re-setting of the system.

We show how event extraction can be used for handling delayed response tasks with arbitrary delay periods between the stimulus and the cue for response. We use a simple recurrent network for solving the task. Our approach is based on a number of information processing levels, where the lowest level works on raw time-step based sensory data. This data is classified using an unsupervised clustering mechanism. The second level works on this classified data, but still on the individual time-step basis. An event extraction mechanism detects and signals transitions between classes; this forms the basis for the third level. As this level only is updated when events occur, it is independent of the time-scale of the lower level interaction. We also sketch how an event filtering mechanism could be constructed which discards irrelevant data from the event stream. Such a mechanism would output a fourth level representation which could be used for delayed response tasks where irrelevant, or distracting, events could occur during the delay.

We investigate self-sustaining stable states (attractors) in networks of integrate-and-fire neurons. First, we study the stability of spontaneous activity in an unstructured network. It is shown that the stochastic background activity, of 1-5 spikes/s, is unstable if all neurons are excitatory. On the other hand, spontaneous activity becomes self-stabilizing in presence of local inhibition, given reasonable values of the parameters of the network. Second, in a network sustaining physiological spontaneous rates, we study the effect of learning in a local module, expressed in synaptic modifications in specific populations of synapses. We find that if the average synaptic potentiation (LTP) is too low, no stimulus specific activity manifests itself in the delay period. Instead, following the presentation and removal of any stimulus there is, in the local module, a delay activity in which all neurons selective (responding visually) to any of the stimuli presented for learning have rates which gradually increase with the amplitude of synaptic potentiation. When the average LTP increases beyond a critical value, specific local attractors (stable states) appear abruptly against the background of the global uniform spontaneous attractor. In this case the local module has two available types of collective delay activity: if the stimulus is unfamiliar, the activity is spontaneous; if it is similar to a learned stimulus, delay activity is selective. These new attractors reflect the synaptic structure developed during learning. In each of them a small population of neurons have elevated rates, which depend on the strength of LTP. The remaining neurons of the module have their activity at spontaneous rates. The predictions made in this paper could be checked by single unit recordings in delayed response experiments.

Human subjects were exposed to concurrent-chains schedules in which reinforcer amounts or delays were varied in the terminal links and consummatory responses were required to receive points later exchangeable for money. Two independent variable-interval 30-s schedules or a single variable-interval 15-s schedule were in effect during the initial links and delay periods were defined by fixed-time schedules used in the terminal links. In addition to varying reinforcer amount and delay, two different choice procedures were studied for two different groups and a monetary deduction procedure was studied, within subjects, under independent scheduling procedure. The human subjects preferred the larger of two different reinforcer amounts and the shorter of two different reinforcer delays. The degree of preference was higher in the independent scheduling procedure than in the nonindependent scheduling procedure and there was no substantial difference in preference between the absence and presence of the monetary deduction procedure.

Background: In order to minimize the influence of glycolysis on diabetes mellitus (DM) diagnostic tests, we have compared the behavior of citric/citrate, fluoride additives and gel-serum with plasma-heparin under careful preanalytical conditions. Subsequently, we compared the effectiveness of both fluoride and citric additives at different pre-centrifugation times. Finally, the influence of citric/citrate collection tube on diagnostic tests results was evaluated. Methods: The first study of 80 voluntary patients assessed the glucose bias of citric/citrate, fluoride additive tubes and gel-serum tubes versus plasma-heparin tubes at several medical decision cut-offs (MDC). The second study performed with 72 volunteers evaluated additives, simulating transport times to the laboratory and centrifugation delay periods. Final evaluation compares the proportion of positive tests in total tests carried out in two different periods. Results: When citric/citrate (n=79) and fluoride tubes (n=60) were compared with plasma-heparin under controlled preanalytical conditions, both met the bias specification for plasma glucose (±1.8%) at seven MDC. On the contrary, serum samples (n=15) did not meet it at five MDC. In the second study, differences in glucose values at distinct pre-centrifugation times were not statistically significant for citric/citrate tubes, but significant for fluoride tubes and also for comparison of fluoride and citric/citrate tubes. Hemolysis in fluoride tubes was higher. Citric/citrate tube implementation in our laboratory caused an increase in positive diagnostic tests that were only statistically significant for gestational diabetes mellitus (GDM) screening. Conclusions: Citric/citrate additive tube is equivalent to plasma-heparin avoiding glycolysis completely and immediately under careful preanalytical conditions even with a 3-h delay in plasma separation. According to used MDC we have not statistically significantly increased the diagnoses of DM cases.

Non-ideal behavior of sickle cell hemoglobin (Hb S) and varying experimental conditions have made gelling kinetic studies difficult. A new gelation kinetic procedure is developed in this study. This technique uses low Hb S concentrations (20-fold less than in conventional methods) without the need for a temperature jump. Gelation progress, monitored with a newly developed turbidimetric procedure at 815 nm, was fitted to a mono-exponential and a sigmoid-Emax models. These models allowed precise definitions of gelation delay periods, rate of rapid Hb S gelation and a parameter, T 1/2 which combines information from the delay and rapid gelation stages. All these parameters vary linearly with Hb S concentration. The merits of using T 1/2 are discussed.

This paper deals with an economic order quantity (EOQ) model for a deteriorating item with initial order quantity demand and inventory dependent deterioration under delay in payment scheme. Profit is obtained at different intervals of delay period and maximised. Numerical examples for different delay periods are given and percentage of profit is obtained. Sensitivity analysis of the example having maximum profit is carried out.

Visual working memory (VWM) capacity is affected by motivational influences; however, little is known about how reward-related brain activities facilitate the VWM systems. To investigate the dynamic relationship between VWM- and reward-related brain activities, we conducted time–frequency analyses using electroencephalograph (EEG) data obtained during a monetary-incentive delayed-response task that required participants to memorize the position of colored disks. In case of a correct answer, participants received a monetary reward (0, 10 or 50 Japanese yen) announced at the beginning of each trial. Behavioral results showed that VWM capacity under high-reward condition significantly increased compared with that under low- or no-reward condition. EEG results showed that frontal theta (6 Hz) amplitudes enhanced during delay periods and positively correlated with VWM capacity, indicating involvement of theta local synchronizations in VWM. Moreover, frontal beta activities (24 Hz) were identified as reward-related activities, because delay-period amplitudes correlated with increases in VWM capacity between high-reward and no-reward conditions. Interestingly, cross-frequency couplings between frontal theta and beta phases were observed only under high-reward conditions. These findings suggest that the functional dynamic linking between VWM-related theta and reward-related beta activities on the frontal regions plays an integral role in facilitating increases in VWM capacity.

Imposed postfeedback delays promote discrimination training; the present experiments determined whether they also improve performance in programmed instruction. In two experiments, college students completed 45 sets of Holland and Skinner's (1961) programmed text on behavior analysis in a computerized format in a three-component multiple schedule. In Experiment 1, the conditions were (a) no delay between questions, (b) a 10-s delay after each question (noncontingent delay), and (c) a 10-s delay after each question answered incorrectly (contingent delay). Noncontingent delay produced better performance than no delay and contingent delay. To determine whether performance increased in the noncontingent delay condition because subjects studied the material during delay periods, Experiment 2 tested three conditions: (a) no delay between questions, (b) a 10-s delay after each question (noncontingent delay), and (c) a 10-s delay after each question with the screen blank during the delay period. Noncontingent delay produced better performance than no delay, but there was no difference in performance between no delay and noncontingent delay with blank screen. Hence, noncontingent delay improved performance because students used delay periods to study. Furthermore, subjects preferred noncontingent delay to the other conditions, and session time increased only slightly.

Setting: The mortality and morbidity from childhood tuberculosis may be influenced by the delay from the time of first symptoms until the start of and compliance with treatment. Objective: This study investigated these delay periods and the compliance with therapy in children with tuberculosis. Design: During the study period there were 49 children with probable and 123 with confirmed pulmonary tuberculosis (WHO criteria). The mean period from first symptoms until presentation was 4.3 weeks, from presentation until notification 5 weeks and from notification until therapy 0.9 weeks. 16% of children notified as having tuberculosis never received therapy. Significantly fewer children in the urban squatter communities received therapy than in urban settled ( P = 0.02), rural agricultural ( P = 0.0001) and rural settled ( P = 0.09) communities. 12% of children did not complete their therapy. Conclusion: The delay in presentation (‘patient delay') was shorter than the delay in diagnosis (‘doctor delay'). Failure to trace children and to complete therapy was particularly likely to occur in urban squatter communities. Easier access to health care facilities may shorten the ‘patient delay' while greater awareness of tuberculosis and proper investigation of children may shorten the ‘doctor delay'.

We examined the effect of four different delay periods (15, 30, 45, or 60 min.) on recall of the Rey-Osterrieth Complex Figure (ROCF) in older persons. The 60 subjects were divided into four groups of 15; the groups were equivalent in age, sex, and education. All subjects received the standard copy and immediate recall trials of the ROCF, followed by one of the four delay durations. There were no significant differences between the groups on copy, immediate, or delayed recall trials. Thus, minor variations in delay period did not have significant effects on recall.

Previous studies have established that neurons in the dorsomedial striatum track the behavioral significance of external stimuli, are sensitive to contingencies between actions and outcomes, and show rapid flexibility in representing task-related information. Here, we describe how neural activity in the dorsomedial striatum changes during the initial acquisition of a Go/NoGo task and during an initial reversal of stimulus-response contingencies. Rats made nosepoke responses over delay periods and then received one of two acoustic stimuli. Liquid rewards were delivered after one stimulus (S+) if the rats made a Go response (entering a reward port on the opposite wall of the chamber). If a Go response was made to other stimulus (S−), rats experienced a timeout. On 10% of trials, no stimulus was presented. These trials were used to assess response bias, the animals' tendency to collect reward independent of the stimulus. Response bias increased during the reversal, corresponding to the animals' uncertainty about the stimulus-response contingencies. Most task-modulated neurons fired during the response at the end of the delay period. The fraction of response-modulated neurons was correlated with response bias and neural activity was sensitive to the behavioral response made on the previous trial. During initial task acquisition and initial reversal learning, there was a remarkable change in the percentages of neurons that fired in relation to the task events, especially during withdrawal from the nosepoke aperture. These results suggest that changes in task-related activity in the dorsomedial striatum during learning are driven by the animal's bias to collect rewards.

Experiments were conducted to study the behaviour of grass and straw stems when cut by sharp and blunt blades at speeds between 5 and 35 m/s; comparative experiments were done with polystyrene tube. Measurements were made of the force and energy during cutting using a piezoelectric force transducer mounted behind the blade on a rotating disc. Stem deflection modes during cutting were recorded photographically by using high-speed film in a camera with an open shutter and firing flash guns sequentially by electronic control, with delay periods ranging from 3 to 425 μs. The lowest speed for efficient cutting (the critical speed) for grass and polystyrene tube was 25–30 m/s. The minimum cutting energy per unit dry matter content for grass with a sharp blade was 55 mJ/mm 2 based on stem wall area. At speeds below the critical speed there was a large stem deflection before cutting was complete, which resulted in long stubble lengths and high cutting energy (up to 400–500 mJ/mm 2 in grass). There was no evidence of a critical speed, however, when cutting straw. The mean peak force for grass per unit dry matter content was 18 N/mm of stem diameter, which was 2.6 times greater than when cutting straw. When cutting above the critical speed for grass (inertia cutting) cutting times were as low as 0.3 ms for the sharp blade, and the stem deflection during cutting was equal to about three stem diameters. For straw, however, the deflection before cutting was complete, represented 8–10 stem diameters, with times of about 1.0 ms. For inefficient cutting at low speeds (c. 5 m/s), cutting times ranged up to 15 ms with stem deflections at the blade of up to 32 diameters for a cutting height of 40mm. The difference between stubble length and nominal cutting height for inertia cutting was about 2 mm for sharp blades but ranged up to 50 mm for inefficient cuts at low speeds. Grass stems showed the widest range of deflection mode immediately after cutting. This varied from stem translation and rotation at low speeds, (c. 5 m/s) to marked bending at intermediate speeds (15–25 m/s) and inertia cutting, with little stem displacement, at higher speeds (>25 m/s). Straw exhibited marked stem translation and rotation with little bending at speeds below 25 m/s but marked bending at higher speeds. Polystyrene tube showed a marked bending over its length at speeds up to 25 m/s, above which cutting was in the inertial mode. The minimum cutting energy for grass stems was three times that required for quasi-static cutting in shear. At low cutting speeds ( The specific cutting energy was twice as large for the blunt blade as for the sharp blade in grass and straw. The difference between stubble length and nominal cutting height was generally about three times greater when using the blunt blade.

Discrete responses of experimentally naive, food-deprived White Carneaux pigeons (key pecks) or Sprague-Dawley rats (bar or omnidirectional lever presses) initiated unsignaled delay periods that terminated with food delivery. Each subject first was trained to eat from the food source, but no attempt was made to shape or to otherwise train the response. In both species, the response developed and was maintained. Control procedures excluded the simple passage of time, response elicitation or induction by food presentation, type of operandum, food delivery device location, and adventitious immediate reinforcement of responding as the basis for the effects. Results revealed that neither training nor immediate reinforcement is necessary to establish new behavior. The conditions that give rise to both the first and second response are discussed, and the results are related to other studies of the delay of reinforcement and to explanations of behavior based on contingency or correlation and contiguity.

Two macaques were trained to perform three self-directed behaviors on signal, and to repeat behaviors after a ‘repeat’ signal. The cognitive processes underlying the monkeys’ repeat performance were evaluated using multiple repetitions of the repeat signal, extended delay periods between target behavior and repeat signal, and by transferring the repeat signal to novel behaviors. The monkeys appear to have used representations of their own past behaviors as a basis for repetition performance, but they mostly failed to correctly repeat target behaviors after extended delays and during transfer tasks. Implications for episodic memory abilities are discussed.

We studied prefrontal cortex activity during a saccade task. On each trial, one of three delay periods elapsed between the onset of a visual stimulus and its offset, which triggered a saccade. After stimulus offset, many neurons showed phasic increases in activity that depended on the duration of the preceding delay period. This delay-dependent activity varied only weakly with reaction time and instead appeared to reflect a more general aspect of elapsed time.

O objetivo deste trabalho foi avaliar os efeitos do retardamento da secagem e do armazenamento aberto na qualidade fisiológica de sementes de azevém anual (Lolium multiflorum Lam.), cultivar Comum-RS. Compararam-se períodos de retardamento da secagem (0, 2, 4, 6, 8, 12, 18, 24, 36 e 48 horas) e períodos de armazenamento (0, 4 e 8 meses). Enquanto submetidas aos períodos de retardamento da secagem, 24 kg de sementes ficaram acondicionadas em 18 caixas de poliestireno. A secagem foi realizada sobre piso de concreto, à sombra, por 12 horas, sendo completada em estufa a 35ºC com circulação forçada de ar. As sementes mantiveram o nível inicial de germinação durante os oito meses de armazenamento, mesmo com até 12 horas de retardamento da secagem; entretanto, com seis horas de retardamento, o vigor das sementes foi reduzido aos oito meses de armazenamento, mas se manteve praticamente inalterado aos quatro meses, com até 11 horas de retardamento. Sementes com germinação acima de 70% mantiveram este valor até oito meses de armazenamento, independentemente do período de retardamento da secagem. The objective of this work was to study drying delay effect on physiological quality of annual ryegrass seeds (Lolium multiflorum Lam.), cultivar Comum-RS. Drying delay periods (0, 2, 4, 6, 8, 12, 18, 24, 36 and 48 hours) and storage periods (0, 4 and 8 months) were compared. Drying delay was performed using 18 polystyrene boxes with 24 kg of seeds each. Following, seeds were placed on a shadowy concrete floor for 12 hours, followed by a drying period in a forced air oven. Seeds retained initial germination percentage after 8-month storage period with drying delay up to 12 hours. From 6-hour drying delay, seed vigor began to be reduced after 8-month storage period. Until 4-month storage period, seed vigor was maintained with up to 11-hour drying delay. Seeds with germination percentage above 70% retained those values until 8-month storage period unrelated to drying delay period.