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Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series compliance. Therefore, this study investigated the impact of changing the activation timing and level (i.e., preactivation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were used to assess muscle fascicle kinematics and muscle activity levels, respectively. Although joint kinematics were similar among MTU-stretch-hold contractions (∼40° rotation amplitude), increasing preactivation increased fascicle shortening and stretch amplitudes (9.9–23.2 mm, P ≤ 0.015). This led to increasing positive and negative fascicle work with increasing preactivation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of preactivation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5–7.6%, P = 0.559) by preactivation, but rFE was strongly correlated with peak fascicle force during stretch (rrm = 0.62, P = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series compliance to better understand the mechanical drivers of adaptation to exercise. NEW & NOTEWORTHY: Apparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depends on the preactivation during the exercise and cannot be estimated from the muscle-tendon unit (MTU) or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series compliance and muscle preactivation need to be considered when eccentric exercise protocols are designed. [ABSTRACT FROM AUTHOR]

Residual force depression (rFD) following active muscle shortening is assumed to correlate most strongly with muscle work, but this has not been tested during voluntary contractions in humans. Using dynamometry, we compared steady‐state ankle joint torques (N = 16) following tibialis anterior (TA) muscle–tendon unit (MTU) lengthening and shortening to the time‐matched torque during submaximal voluntary fixed‐end dorsiflexion reference contractions (REF) at a matched MTU length and EMG amplitude. Ultrasound revealed significantly reduced (P < 0.001) TA fascicle shortening amplitudes during MTU lengthening without a preload over small and medium amplitudes, respectively, relative to REF. MTU lengthening with a preload over a large amplitude significantly (P < 0.001) increased fascicle shortening relative to REF, as well as stretch amplitudes relative to MTU lengthening without a preload (P = 0.001). Significant (P = 0.028) steady‐state fascicle force enhancement relative to REF was observed following MTU lengthening, and was similar among MTU lengthening‐hold conditions (3–5%). MTU shortening with and without a preload over small and large amplitudes significantly (P < 0.001) increased positive fascicle and MTU work relative to REF, but significant (P = 0.006) rFD was observed following MTU shortening with a preload (7–10%) only. rFD was linearly related to positive MTU work [rrm(47) = 0.48, P < 0.001], but not positive fascicle work [rrm(47) = 0.16, P = 0.277]. Our findings indicate that MTU lengthening without substantial fascicle stretch enhances steady‐state force output, which might arise from less shortening‐induced rFD. Our findings also indicate similar rFD following different amounts of positive fascicle/MTU work, which cautions against using work to predict rFD during submaximal voluntary contractions. Key points: Accurately predicting muscle force is challenging because active muscle shortening depresses force output.The residual force depression (rFD) that exists following active muscle shortening is commonly assumed to correlate strongly and positively with muscle work.We found that tibialis anterior muscle fascicle work and muscle–tendon unit work did not accurately predict rFD during submaximal voluntary dorsiflexion contractions.Fascicle shortening during fixed‐end reference contractions also potentially induced rFD of 3–5%, which was similar to the rFD following muscle–tendon unit shortening without a preload.A higher number of active muscle fibres during shortening probably increased rFD, which suggests that motor unit recruitment during shortening might predict rFD. [ABSTRACT FROM AUTHOR]

Sensory responses typically vary depending on the recent history of sensory experience. This is essential for processes, including adaptation, efficient coding, and change detection. In the auditory cortex (AC), the short-term history dependence of sound-evoked (onset) responses has been well characterized. Yet many AC neurons also respond to sound terminations, and little is known about the history dependence of these “offset” responses, whether the short-term dynamics of onset and offset responses are correlated, or how these properties are distributed among cell types. Here we presented awake male and female mice with repeating noise burst stimuli while recording single-unit activity from primary AC. We identified parvalbumin and somatostatin interneurons through optotagging, and also separated narrow-spiking from broad-spiking units. We found that offset responses are typically less depressive than onset responses, and this result was robust to a variety of stimulus parameters, controls, measurement types, and selection criteria. Whether a cell’s onset response facilitates or depresses does not predict whether its offset response facilitates or depresses. Cell types differed in the dynamics of their onset responses, and in the prevalence, but not the dynamics, of their offset responses. Finally, we clustered cells according to spiking responses and found that response clusters were associated with cell type. Each cluster contained cells of several types, but even within a cluster, cells often showed cell type-specific response dynamics. We conclude that onset and offset responses are differentially influenced by recent sound history, and discuss the implications of this for the encoding of ongoing sound stimuli. [ABSTRACT FROM AUTHOR]

We study dynamic signaling in a game of stochastic stakes. Each period, a privately informed agent of binary type chooses whether to continue receiving a return that is an increasing function of both her reputation and an exogenous public stakes variable or to irreversibly exit the game. A strong type has a dominant strategy to continue. In the unique perfect Bayesian equilibrium, the weak type plays a mixed strategy that depends only on current stakes and her historical minimum and she builds a reputation by continuing when the stakes reach a new minimum. We discuss applications to corporate reputation management, online vendor reputation, and limit pricing with stochastic demand. [ABSTRACT FROM AUTHOR]

Background. Following stretch of an active muscle, muscle force is enhanced, which is known as residual force enhancement (rFE). As earlier studies found apparent corticospinal excitability modulations in the presence of rFE, this study aimed to test whether corticospinal excitability modulations contribute to rFE. Methods. Fourteen participants performed submaximal plantar flexion stretch-hold and fixed-end contractions at 30% of their maximal voluntary soleus muscle activity in a dynamometer. During the steady state of the contractions, participants either received subthreshold or suprathreshold transcranial magnetic stimulation (TMS) of their motor cortex, while triceps surae muscle responses to stimulation were obtained via electromyography (EMG), and net ankle joint torque was recorded. B-mode ultrasound imaging was used to confirm muscle fascicle stretch during stretch-hold contractions in a subset of participants. Results. Following stretch of the plantar flexors, an average rFE of 7% and 11% was observed for contractions with subthreshold and suprathreshold TMS, respectively. 41-46 ms following subthreshold TMS, triceps surae muscle activity was suppressed by 19-25%, but suppression was not significantly different between stretch-hold and fixed-end contractions. Similarly, the reduction in plantar flexion torque following subthreshold TMS was not significantly different between contraction conditions. Motor evoked potentials, silent periods and superimposed twitches following suprathreshold TMS were also not significantly different between contraction conditions. Discussion. As TMS of the motor cortex did not result in any differences between stretch-hold and fixed-end contractions, we conclude that rFE is not linked to changes in corticospinal excitability. [ABSTRACT FROM AUTHOR]

Few want to do business with a partner who has a bad reputation. Consequently, once a bad reputation is established, it can be difficult to get rid of. This leads on the one hand to the intuitive idea that a good reputation is easy to lose and hard to gain. On the other hand, it can lead to a strong form of history dependence in which a single beneficial or adverse event can cast a shadow over a very long period of time. It gives rise to a reputational trap where an agent rationally chooses not to invest in a good reputation because the chances others will find out is too low. Nevertheless, the same agent with a good reputation will make every effort to maintain it. Here, a simple reputational model is constructed and the conditions for there to be a unique equilibrium that constitutes a reputation trap are characterized. [ABSTRACT FROM AUTHOR]

This paper investigates two scenarios in the external habit formation model with concave utility functions. When the utility function is weakly concave, there exists a unique history‐dependent balanced growth path (BGP) under a knife‐edge existence condition. When the utility function is strictly concave, a unique BGP exists under a more generic condition. I find that the BGPs in the two scenarios are observationally equivalent. The knife‐edge condition limits the applicability of the first scenario. The generic existence condition and the observational equivalence result mitigate this issue. I show that our model can help understand a variety of growth patterns of countries that differ in their fundamentals substantially. [ABSTRACT FROM AUTHOR]

Why do some historical shocks permanently impact local development, while others do not? This paper examines how institutions influence local recovery to population shocks, using a model with multiple regions and increasing returns to economic activity within regions. Extractive institutions crowd out productive activity, making its spatial coordination more difficult in the aftermath of large, negative shocks. Hence, when one region experiences such a shock, extractive institutions can hinder recovery, ensuring a redistribution of productive activity away from that region over the long-run. Using a dataset of major earthquakes and 1860 world cities from 1973 to 2018, I find sustained negative effects of earthquakes on city population growth, with effects being driven by cities located outside of stable democracies, consistent with the theory. [ABSTRACT FROM AUTHOR]

An important yet largely unexamined issue is how the interaction between deforestation and pollution affects economic and environmental sustainability. This article seeks to bridge the gap by introducing a dynamic model of pollution accumulation where polluting emissions can be mitigated and the absorption efficiency of pollution sinks can be restored. We assume that emissions are due to a production activity, and we include deforestation both as an additional source of emissions and as a cause of the exhaustion of environmental absorption efficiency. To account for the fact that the switching of natural sinks to a pollution source can be either possible, and in such a case even reversible, or impossible, we consider that restoration efforts can be either independent from or dependent on environmental absorption efficiency, i.e., state-independent versus state-dependent restoration efforts. We determine (i) whether production or deforestation is the most detrimental from environmental and social welfare perspectives, and (ii) how state-dependent restoration process affects pollution accumulation and deforestation policies and the related environmental and social welfare consequences. [ABSTRACT FROM AUTHOR]

Adaptation is a ubiquitous feature of sensory processing whereby recent experience shapes future responses. The mouse primary visual cortex (V1) is particularly sensitive to recent experience, where a brief stimulus can suppress subsequent responses for seconds. This rapid adaptation profoundly impacts perception, suggesting that its effects are propagated along the visual hierarchy. To understand how rapid adaptation influences sensory processing, we measured its effects at key nodes in the visual system: in V1, three higher visual areas (HVAs: lateromedial, anterolateral, and posteromedial), and the superior colliculus (SC) in awake mice of both sexes using single-unit recordings. Consistent with the feed-forward propagation of adaptation along the visual hierarchy, we find that neurons in layer 4 adapt less strongly than those in other layers of V1. Furthermore, neurons in the HVAs adapt more strongly, and recover more slowly, than those in V1. The magnitude and time course of adaptation was comparable in each of the HVAs and in the SC, suggesting that adaptation may not linearly accumulate along the feed-forward visual processing hierarchy. Despite the increase in adaptation in the HVAs compared with V1, the effects were similarly orientation specific across all areas. These data reveal that adaptation profoundly shapes cortical processing, with increasing impact at higher levels in the cortical hierarchy, and also strongly influencing computations in the SC. Thus, we find robust, brain-wide effects of rapid adaptation on sensory processing. NEW & NOTEWORTHY Rapid adaptation dynamically alters sensory signals to account for recent experience. To understand how adaptation affects sensory processing and perception, we must determine how it impacts the diverse set of cortical and subcortical areas along the hierarchy of the mouse visual system. We find that rapid adaptation strongly impacts neurons in primary visual cortex, the higher visual areas, and the colliculus, consistent with its profound effects on behavior. [ABSTRACT FROM AUTHOR]

Following active lengthening, steady-state isometric (ISO) torque is greater than a purely ISO contraction at the same muscle length, this is referred to as residual torque enhancement (rTE). A phenomenon of rTE is activation reduction, characterized by reduced electromyography (EMG) amplitude for a given torque output. We hypothesized that lower motor unit discharge rates would contribute to activation reduction and lessening torque steadiness. Ten young male subjects performed ISO dorsiflexion contractions at 10 and 20% of maximal voluntary contraction (MVC) torque. During rTE trials, the muscle was activated at 10° of plantar flexion, then the ankle was rotated to the ISO position at 40°. Fine wire electrodes recorded motor unit (MU)-discharge rates and variability from the tibialis anterior. Surface EMG quantified activation reduction, and steadiness was determined as the coefficient of variation of torque. The activation reduction was 44 and 24% at 10 and 20% MVC, respectively (P < 0.05). Fewer MUs were recorded in the rTE than ISO condition at 10% (~47%) and 20% (~36%) MVC (P < 0.05). Discharge rates were 19 and 26% lower in the rTE compared with the ISO condition for 10 and 20% MVC, respectively (P < 0.05), with no difference in variability between conditions (P > 0.05). Steadiness was ~22 and 18% lower for the rTE than ISO condition at 10 and 20% MVC (P < 0.05). Our findings indicate that activation reduction may be attributed to lower MU discharge rate and fewer detectable MUs and that this theoretically contributes to a reduction in steadiness in the rTE condition. NEW & NOTEWORTHY Our findings indicate that lower electromyographic activity during the torque enhanced condition following active lengthening compared with a purely isometric contraction arises from fewer active motor units and a lower discharge rate of those that are active. We used an acute condition of increased torque capacity to induce a decrease in net output of the motor neuron pool during a submaximal task to demonstrate, in humans, the impact of motor unit activity on torque steadiness. [ABSTRACT FROM AUTHOR]

We consider a scalar conservation law with hysteresis in which the flux function depends on the history of the evolution. The work is motivated by the need to account for hysteresis in important applications to transport with adsorption. To model hysteresis we use an auxiliary system of ODEs with constraints known as linear play combined with particularly chosen nonlinear truncation functions. A combination of these allows a quite general shape of hysteresis graph with piecewise linear primary and secondary scanning curves; this is distinct from the well-known Preisach model. We prove well-posedness of the model and stability of an explicit-implicit finite difference scheme. The challenge of history dependence requires auxiliary results in product spaces. Numerical results confirm convergence of linear or slower rate. [ABSTRACT FROM AUTHOR]

We model network formation in a firm. Agents learn about the quality of their working relationships with each other. Their good relationships become their networks. Accumulating relationships becomes increasingly costly, however. Over time agents become less open to forming relationships with others unknown to them, leading their networks to be front-loaded with agents they met near the beginning of their careers. The interaction of this dynamic with turnover yields predictions about the time pattern of history dependence in an agent's network as a function of his tenure. Mutual openness of newly arrived agents in a firm also leads to the cross-section prediction of "cohort attachment," a tendency for members of an agent's hiring cohort to be disproportionately represented in his network. When members of a network formed within a firm are subsequently split across many firms, the desire to renew their successful working relationships can lead to job referrals. Former co-workers who provide referrals will be drawn disproportionately from the referred workers' hiring cohorts at their previous employers. [ABSTRACT FROM AUTHOR]

Farsighted formulations of coalitional formation, for instance, by Harsanyi and Ray and Vohra, have typically been based on the von Neumann–Morgenstern stable set. These farsighted stable sets use a notion of indirect dominance in which an outcome can be dominated by a chain of coalitional "moves" in which each coalition that is involved in the sequence eventually stands to gain. Dutta and Vohra point out that these solution concepts do not require coalitions to make optimal moves. Hence, these solution concepts can yield unreasonable predictions. Dutta and Vohra restricted coalitions to hold common, history‐independent expectations that incorporate optimality regarding the continuation path. This paper extends the Dutta–Vohra analysis by allowing for history‐dependent expectations. The paper provides characterization results for two solution concepts that correspond to two versions of optimality. It demonstrates the power of history dependence by establishing nonemptyness results for all finite games as well as transferable utility partition function games. The paper also provides partial comparisons of the solution concepts to other solutions. [ABSTRACT FROM AUTHOR]

The creep of coral sand is a critical factor that needs to be considered in geotechnical design of engineering facilities along coastal areas. In this study, a new fractional order creep model for coral sand is developed by extending the previous work on fractional (visco)plasticity. Unlike traditional fractional creep models that use viscoelasticity, this model uses a fractional order flow rule to capture the creep behaviour of coral sand. To validate the proposed model, test results of coral sand from the available literature are simulated, where good agreement between the model predictions and test results is observed. [ABSTRACT FROM AUTHOR]

The influence of active lengthening (residual force enhancement: RFE) and shortening (force depression: FD) on the electromyography (EMG)-torque relationship was investigated by matching torque and activation at 20%, 40%, 60%, 80% and 100% maximal voluntary contraction (MVC). Sixteen males performed lengthening and shortening contractions of the dorsiflexors over 25° into an isometric steady-state. There was 5% greater torque, with no change in agonist EMG during the RFE condition as compared to the isometric condition. Sub-maximally, in the force enhanced state, there was less agonist EMG during the torque clamp at all intensities relative to isometric, and greater torque during the activation clamps relative to isometric was observed across all intensities except 20% MVC. During the FD state compared to isometric, there was less torque produced during MVC (∼15%) with no change in agonist EMG. Sub-maximally, in the FD state, there was greater agonist EMG during the torque clamp and less torque during the activation clamp relative to the isometric condition across all intensities. The EMG-torque relationship was bilinear for all contraction types but was shifted to the left and right for FD and RFE, respectively as compared with isometric, indicating altered neuromuscular activation strategies in the history-dependent states of RFE and FD. [ABSTRACT FROM AUTHOR]

Highlights • Torque steadiness in the isometric steady-state following an eccentric contraction is impaired compared with a purely isometric contraction. • This decrease in torque steadiness is driven by an activation reduction that occurs in the isometric steady-state following an eccentric contraction when torque is matched to that of a purely isometric contraction. • When activation was matched between a purely isometric contraction and the isometric steady-state following an eccentric contraction, there was no difference in torque steadiness. • Residual force enhancement may improve neuromuscular economy but negatively affects torque steadiness at low levels of contraction intensity. Altered motor unit activation strategies in the force enhanced state likely contribute to the unsteadiness following active lengthening. Abstract Background The isometric steady-state following active lengthening is associated with greater torque production and lower activation, as measured by electromyographic activity (EMG), in comparison with a purely isometric contraction (ISO) at the same joint angle. This phenomenon is termed residual force enhancement (RFE). While there has been a great deal of research investigating the basic mechanisms of RFE, little work has been performed to understand the everyday relevance of RFE. The purpose of this study was to investigate whether neuromuscular control strategies differ between ISO and RFE by measuring torque steadiness of the human ankle plantar flexors. Methods Following ISO maximal voluntary contractions in 12 males (25 ± 4 years), an active lengthening contraction was performed at 15°/s over a 30° ankle excursion, ending at the same joint angle as ISO (5° dorsiflexion; RFE). Surface EMG of the tibialis anterior and soleus muscles was recorded during all tasks. Torque steadiness was determined as the standard deviation (SD) and coefficient of variation (CV) of the torque trace in the ISO and RFE condition during activation-matching (20% and 60% integrated EMG) and torque-matching (20% and 60% maximal voluntary contraction) experiments. Two-tailed, paired t tests were used, within subjects, to determine the presence of RFE/activation reduction (AR) and whether there was a difference in torque steadiness between ISO and RFE conditions. Results During the maximal and submaximal conditions, there was 5%–9% RFE with a 9%–11% AR (p < 0.05), respectively, with no difference in antagonist coactivation between RFE and ISO (p > 0.05). There were no differences in SD and CV of the torque trace for the 20% and 60% activation-matching or the 60% and maximal torque-matching trials in either the RFE or ISO condition (p > 0.05). During the 20% torque-matching trial, there were ∼37% higher values for SD and CV in the RFE as compared with the ISO condition (p < 0.05). A significant moderate-to-strong negative relationship was identified between the reduction in torque steadiness following active lengthening and the accompanying AR (p < 0.05). Conclusion It appears that while the RFE-associated AR provides some improved neuromuscular economy, this comes at the cost of increased torque fluctuations in the isometric steady-state following active lengthening during submaximal contractions. [ABSTRACT FROM AUTHOR]

The plane elastic problem of a circular disc shrink fitted into a hole in an elastically similar plane, with a frictional interface, is studied. The disc is subject to a radial force and torque both of which vary with time. In the steady-state the loads vary harmonically, and a relative phase shift is considered. Frictional slip is accounted for by edge dislocations distributed along the interface. It is shown that the steady-state response, which might, for example, be cyclic slip or full adhesion (shakedown) for a particular loading regime, depends on the loading history before the steady-state loading regime is entered. This contrasts with Melan's theorem for elastic–plastic shakedown, and is a consequence of the normal–tangential coupling in this frictional system. • The steady-state behaviour of a continuous coupled contact is studied. • The contact responds with one of four different steady-state modes. • The modes are shakedown, cyclic slip and monotonic or non-monotonic ratchetting. • The frictional energy dissipation during cyclic slip depends on initial conditions. • There are two possible sequences of the steady-state mode if the load is increased. [ABSTRACT FROM AUTHOR]

The aim of the paper is to present spatial variation of social capital in Poland, especially in relation to historical differences between various regions (resulting from the country's partitions and border changes) and the level of urbanization. Previous studies indicate that such variation exists. However, they were carried out on the basis of declarations, an approach which has its drawbacks. This study uses a novel approach to assessing social capital: observing the behaviour of a study group using experimental economics, used in conjunction with a questionnaire which enables us to study the intention-behaviour gap. The study group consisting of 1540 individuals indicates very little variation between the regions. However, there are differences concerning the gap between declarations and behaviour in questions related to trust, trustworthiness, and cooperation, and our results confirm the conclusions from previous studies only weakly. [ABSTRACT FROM AUTHOR]

The sarcomere length non-uniformity theory (SLNT) is a widely accepted explanation for residual force enhancement (RFE). RFE is the increase in steady-state isometric force following active muscle stretching. The SLNT predicts that active stretching of a muscle causes sarcomere lengths (SL) to become non-uniform, with some sarcomeres stretched beyond actin–myosin filament overlap (popping), causing RFE. Despite being widely known, this theory has never been directly tested. We performed experiments on isolated rabbit muscle myofibrils (n = 12) comparing SL non-uniformities for purely isometric reference contractions (I-state) and contractions following active stretch producing RFE (FE-state). Myofibrils were activated isometrically along the descending limb of the force–length relationship (mean ± 1 standard deviation (SD) = 2.8 ± 0.3 µm sarcomere−1). Once the I-state was reached, myofibrils were shortened to an SL on the plateau of the force–length relationship (2.4 µm sarcomere−1), and then were actively stretched to the reference length (2.9 ± 0.3 µm sarcomere−1). We observed RFE in all myofibrils (39 ± 15%), and saw varying amounts of non-uniformity (1 SD = 0.9 ± 0.5 µm) that was not significantly correlated with the amount of RFE, but through pairwise comparisons was found to be significantly greater than the non-uniformity measured for the I-state (0.7 ± 0.4 µm). Three myofibrils exhibited no increase in non-uniformity. Active stretching was accompanied by sarcomere popping in four myofibrils, and seven had popped sarcomeres in the I-state. These results suggest that, while non-uniformities are present with RFE, they are also present in the I-state. Furthermore, non-uniformity is not associated with the magnitude of RFE, and myofibrils that had no increase in non-uniformity with stretch still showed normal RFE. Therefore, it appears that SL non-uniformity is a normal associate of muscle contraction, but does not contribute to RFE following active stretching of isolated skeletal muscle myofibrils.

This paper focuses on the dynamic aspects of individual behavior affected by its social embedding, either at large (society-wide norms or averages) or at a local neighborhood. The emphasis is on how initial conditions can affect the long run outcome and to derive, discuss and apply the conditions for such thresholds. For this purpose, intertemporal social pressure (from peers, from norms, or from fashions) is modelled in two different ways: (i) individual benefit is influenced by the possession of a stock (in the application: weight) and the society wide average, and (ii) individual benefits depend on a norm that follows its own motion, of course driven by agents’ behavior. The topical issue of obesity serves as motivation and corresponding models and examples are presented and analyzed.

For the past 60 years, muscle contraction had been thought to be governed exclusively by the contractile filaments, actin and myosin. This thinking explained most observations for concentric and isometric, but not for eccentric muscle contractions. Just over a decade ago, we discovered that eccentric contractions were associated with a force that could not be assigned to actin and myosin, but was at least in part associated with the filamentous protein titin. Titin was found to bind calcium upon activation, thereby increasing its structural stability, and thus its stiffness and force. Furthermore, there is increasing evidence that the proximal part of titin binds to actin in an activation- and force-dependent manner, thereby shortening its free length, thus increasing its stiffness and force. Therefore, we propose that muscle contraction involves three filaments, actin, myosin and titin, and that titin regulates force by binding calcium and by shortening its spring length by binding to actin.

Some areas of science face the problem that many academics prefer the private sector over academia. This negatively affects the quality and the quantity of the research output as well as the availability of competent lecturers in these areas. The present paper investigates by means of an optimal control model how the reward of competencies in research and teaching in the private sector affects investments into these skills as well as the decision on whether and when to optimally leave academia. As the decision between academia and industry is obvious if a scientist has strong preference for either, we focus on scenarios where this is not the case. We notably show that the dynamic trade-off between academia and industry results in various forms of brain drain. In this regard, we first confirm that if academic competencies are well rewarded in the private sector, the most competent academics will leave academia. Further, we find scenarios where a scholar with intermediate competencies will try to improve his or her skills as much as possible before leaving academia and scenarios in which it is optimal to not put much effort into work and let competencies slowly depreciate before leaving. Even if scientists are highly skilled and motivated to stay, if poor working conditions do not support knowledge acquisition, competencies will inevitably fall and academia will consist solely of mediocre scholars. The results suggest that brain drain can be destructive for academia in the long run. [ABSTRACT FROM AUTHOR]

Highlights: [•] The paper studies long term dynamics of social networks and activity travel needs. [•] Social networks evolve and activity travel needs change with life-cycle events. [•] The structural equation model takes path dependence effects into account. [•] It shows interdependencies between social network and activity travel dynamics. [•] It indicates existence of a threshold size of personal social networks. [ABSTRACT FROM AUTHOR]

Recent experiments have demonstrated that the timescale of adaptation of single neurons and ion channel populations to stimuli slows down as the length of stimulation increases; in fact, no upper bound on temporal time-scales seems to exist in such systems. Furthermore, patch clamp experiments on single ion channels have hinted at the existence of large, mostly unobservable, inactivation state spaces within a single ion channel. This raises the question of the relation between this multitude of inactivation states and the observed behavior. In this work we propose a minimal model for ion channel dynamics which does not assume any specific structure of the inactivation state space. The model is simple enough to render an analytical study possible. This leads to a clear and concise explanation of the experimentally observed exponential history-dependent relaxation in sodium channels in a voltage clamp setting, and shows that their recovery rate from slow inactivation must be voltage dependent. Furthermore, we predict that history-dependent relaxation cannot be created by overly sparse spiking activity. While the model was created with ion channel populations in mind, its simplicity and genericalness render it a good starting point for modeling similar effects in other systems, and for scaling up to higher levels such as single neurons which are also known to exhibit multiple time scales.

Perceptual priming can stabilize the phenomenal appearance of multistable visual displays (Leopold, Wilke, Maier, & Logothetis, Nature Neuroscience, 5, 605-609, ). Prior exposure to such displays induces a sensory memory of their appearance, which persists over long intervals and intervening stimulation, and which facilitates renewed perception of the same appearance. Here, we investigated perceptual priming for the apparent rotation in depth of ambiguous structure-from-motion (SFM) displays. Specifically, we generated SFM objects with different three-dimensional shapes and presented them in random order and with intervening blank periods. To assess perceptual priming, we established the probability that a perceived direction of rotation would persist between successive objects. In general, persistence was greatest between identical objects, intermediate between similar objects, and negligible between dissimilar objects. These results demonstrate unequivocally that sensory memory for apparent rotation is specific to three-dimensional shape, contrary to previous reports (e.g., Maier, Wilke, Logothetis, & Leopold, Current Biology, 13, 1076-1085, ). Because persistence did not depend on presentation order for any pair of objects, it provides a commutative measure for the similarity of object shapes. However, it is not clear exactly which features or aspects of object shape determine similarity. At least, we did not find simple, low-level features (such as volume overlap, heterogeneity, or rotational symmetry) that could have accounted for all observations. Accordingly, it seems that sensory memory of SFM (which underlies priming of ambiguous rotation) engages higher-level representations of object surface and shape. [ABSTRACT FROM AUTHOR]

Force depression observed following active shortening is not well understood. Previous research suggested that force depression might be associated with a stress-induced inhibition of cross-bridges in the newly formed overlap zone following shortening. Our aim was to investigate this theory in skinned fibres and determine whether there was an inhibition of the attachment of cross-bridges or a decrease In the force produced per cross-bridge. The stress-induced inhibition of cross-bridge theory gives testable predictions, including: (1) skinned fibres should show proportional force and stiffness depression, (2) force after shortening should not be lower than force before shortening, (3) stiffness following shortening should not be lower than stiffness before shortening and (4) force depression should decrease when the stress during shortening is decreased. In agreement with these predictions, force and stiffness depression were approximately proportional, and force depression decreased with decreasing stress during shortening. However, in contrast to the predictions of the stress-induced inhibition of cross-bridge theory, force after shortening from sarcomere lengths of 2.8 and 3.0&mgr;m to a sarcomere length of 2.4&mgr;m was smaller than force before shortening, and this was not accompanied by a corresponding decrease in stiffness. We conclude that the stress-induced inhibition of cross-bridge theory, as proposed previously, cannot be the only mechanism for force depression, but that there is an additional, stress-induced inhibition of cross-bridges in the old overlap zone. Furthermore, both mechanisms, inhibition of cross-bridge attachment and reduction of force produced per cross-bridge, contribute to force depression. Inhibition and/or reduction of force depend(s) on the amount of stress imposed on actin during the shortening phase. [ABSTRACT FROM AUTHOR]

Abstract: Stretch of activated muscles leads to enhanced forces compared to isometric contractions at the same muscle length and the same level of activation. This so-called residual force enhancement (RFE) is thought to be a property of all muscles and preparations. However, observations concerning the existence, amount and duration of RFE are inconsistent, especially for voluntary activated large human muscles. Therefore, physiological relevance for daily activity is still questionable and the purpose of this study was to examine whether RFE is present in voluntary sub-maximal activated quadriceps femoris (QF). Seated in a rotational dynamometer with EMG attached to superficial parts of QF, 30 subjects performed isometric and isometric–eccentric–isometric contractions (20° stretch, ω =60°s−1) at 30% and 60% of maximum voluntary activation (MVA) and contraction (MVC). To account for the complexity of the multi-headed QF, a compensation model based on physiological cross-sectional area and individual EMG–torque relations was used to interpret EMG data. For both levels of intensity and both feedback control strategies, ANOVA identified significant RFE (at the same level of activation) and reduced activation (at the same level of torque). Against expectations, RFE was independent of the level of activation. [Copyright &y& Elsevier]

Almost all democratic societies evolved socially and politically out of authoritarian and nondemocratic regimes. These changes not only altered the allocation of economic resources in society but also the structure of political power. In this paper, we develop a framework for studying the dynamics of political and social change. The society consists of agents that care about current and future social arrangements and economic allocations; allocation of political power determines who has the capacity to implement changes in economic allocations and future allocations of power. The set of available social rules and allocations at any point in time is stochastic. We show that political and social change may happen without any stochastic shocks or as a result of a shock destabilizing an otherwise stable social arrangement. Crucially, the process of social change is contingent (and history-dependent): the timing and sequence of stochastic events determine the long-run equilibrium social arrangements. For example, the extent of democratization may depend on how early uncertainty about the set of feasible reforms in the future is resolved. [ABSTRACT FROM AUTHOR]

A general form of temporal strength conditions under variable creep loading is employed to formulate several new phenomenological accumulation rules based on the constant-loading durability diagram. Unlike the well-known Robinson rule of linear accumulation of partial life-times, the new rules allow to describe the life-time sensitivity to the load sequence observed in experiments. Comparison of the new rules with experimental data shows that they fit the data much more accurately than the Robinson rule. [ABSTRACT FROM AUTHOR]

Despite the importance of hysteresis of water diffusion in polymeric materials, only limited literature is available on this subject. The FT-IR-ATR spectroscopy technique was used to investigate the effect of cycling moisture boundary conditions on the diffusivity of moisture of three asphalt binders. Each sample passed through three hydration cycles and two dehydration cycles. The existence of hysteresis of moisture diffusivity in asphalt binders is validated. The increase in moisture diffusivity is primarily attributed to the change in microstructure of the asphalt binder after being exposed to moisture. This is supported by atomic force microscope images of asphalt binder before and after exposure to water. Evidence to an increase of water trapped in the form of vapour even after dehydration was observed, and this may also contribute to the increase in diffusivity. This topic is still under investigation by this research group. [ABSTRACT FROM AUTHOR]

This paper focuses on the dynamic aspects of individual behavior affected by its social embedding, either at large (society-wide norms or averages) or at a local neighborhood. The emphasis is on how initial conditions can affect the long run outcome and to derive, discuss and apply the conditions for such thresholds. For this purpose, intertemporal social pressure (from peers, from norms, or from fashions) is modelled in two different ways: (i) individual benefit is influenced by the possession of a stock (in the application: weight) and the society wide average, and (ii) individual benefits depend on a norm that follows its own motion, of course driven by agents' behavior. The topical issue of obesity serves as motivation and corresponding models and examples are presented and analyzed. [ABSTRACT FROM AUTHOR]

Force depression after active shortening has been observed in different muscle preparations. It has been assumed that force depression is caused by the development of sarcomere length nonuniformities after shortening. However, this hypothesis has never been investigated in a preparation where individual sarcomere lengths could be directly measured. Here, we investigated force depression in single myofibnls (n = 11) and tracked simultaneously the changes in individual sarcomere lengths (n = 60) before, during, and after shortening and after a purely isometric contraction performed at the final length. Shortening produced force depression in all myofibrils (mean ± SE; 30.9 ± 3.9%). During shortening, all sarcomeres shortened, but not by the same amount. Sarcomere lengths were nonuniform, with the same mean SD before (0.11 ± 0.06 μm) and after shortening (0.11 ± 0.06 μm) and after a purely isometric contraction at the final length (0.10 ± 0.05 μm). Furthermore, greater shortening magnitudes were found for sarcomeres that were long in the initial isometric configuration. Nonuniformities of half-sarcomere lengths were also the same before (SD = 0.13 μm) and after (SD = 0.14 μm) shortening. We conclude from these results that the development of sarcomere (or half-sarcomere) length nonuniformities does not play a major role in force depression. Rather, force depression seems an intrinsic property of individual (half-) sarcomeres and muscle contraction. [ABSTRACT FROM AUTHOR]

Abstract: The steady-state force following active muscle shortening or stretch differs from the maximum isometric force associated with the final length. This phenomenon proves that the isometric force production is not only dependent on current muscle length and length time derivative, but depends on the preceding contraction history. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this history-dependent force modification. The muscles were pre-stimulated at a fixed length, then different stretch/shortening episodes were introduced, whereafter changes of the active force were recorded while the muscles were held isometrically to approach a steady-state force before de-stimulation. The mechanical work during active stretch and shortening was evaluated by integrating the product of force and ramp velocity over the length-varying period. The results show a negative linear correlation between the force modification and the mechanical work produced on or by the muscle, continuous between shortening and stretch. A corresponding modification of the passive force component following each stimulation was also observed. The conclusion is that the isometric force attained after stretch or shortening is well described by an asymptotic force which is determined by the mechanical work. [Copyright &y& Elsevier]

Abstract: The paper investigates price formation in a decentralized market with random matching. Agents are assumed to have subdued social preferences: buyers, for example, prefer a lower price to a higher one but experience reduced utility increases below a reference price that serves as a common fairness benchmark. The strategic equilibrium reflects market fundamentals, but it is markedly less sensitive to the buyer–seller ratio near the fair price benchmark. Prices may be sticky around very different reference levels in markets with otherwise identical fundamentals. The implied history dependence turns out to be mitigated rather than exacerbated by friction. [Copyright &y& Elsevier]

The isothermal entropy change of polycrystalline Gd[sub5] Si[sub2 .09] Ge[sub1 .91] during the magneto-structural transition is measured exposing the sample to two different temperature/field histories. The phase fraction involved in the transition is observed by using the Hall probe imaging technique. Both experiments confirm that the entropy change during the first-order phase transition depends on the history of the sample. This is understood by the hysteretic nature of the magneto-structural transition. A Preisach-type model accounting for hysteresis in field and temperature is able to predict the phase fractions involved in the transition. The result can be used to explain differences between different measurement methods of the isothermal entropy change of the magnetocaloric effect. [ABSTRACT FROM AUTHOR]

Abstract: The steady-state force following active shortening does not reach the maximum isometric force associated with the final length. Isolated extensor digitorum longus and soleus muscles from mice (NMRI strain) were used to investigate the force produced by a muscle, and some parameters hypothetically influencing this shortening-induced force depression. The muscles were pre-stimulated at fixed length, shortened and then held isometrically to give maximum post-shortening forces, before de-stimulation. The shortening magnitude was 0.18, 0.36 or 0.72mm (about 2–7% of optimal length), time of shortening was chosen as 0.03, 0.06 and 0.12s, and final length as , 0 and , related to optimal length. The mechanical work during active shortening was evaluated by integrating the product of force and shortening velocity over the shortening period. The results show a positive correlation between the force depression and the mechanical work, whereas the force depression was not correlated to the velocity of shortening. Depression of the passive force component was also observed following all stimulations. Experiments show that the fully stimulated redevelopment of isometric force following concentric contraction follows a time function similar to the creation of force when isometric muscle is initially stimulated. The conclusion is that the isometric force development after active shortening can be well described by an asymptotic force which is decided by the produced work, and the initial isometric time constant. [Copyright &y& Elsevier]

A transferable quota system is analysed in a two-period model with market power. So far, the management mechanisms presented in the literature to remedy market power have either not succeeded in securing efficiency in the distribution of quota within and across time periods, or have resulted in only one of the two inefficiencies being eliminated. In this paper a new mechanism is introduced where allocation of quota is made dependent upon historic quota acquisitions. This opens for a trade-off between distributional and time efficiency, or under specific circumstances securing overall efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Krugman [Krugman, P., 1991a. History versus expectations. Quarterly Journal of Economics 106, 651–667.] links multiple equilibria (the domains of attractions depend on history and possibly also on expectations) to the technological property of increasing returns to scale. It is shown that the recently introduced characterization of (non-moderate) social influence [Glaeser, E.L., Sacerdote, B.I., Scheinkman J.A., 2003. The social multiplier. Journal of the European Economic Association 1, 345–353.] coupled with complementarity provides the proper criterion for thresholds and multiple equilibria instead of technological characterizations (increasing returns). [Copyright &y& Elsevier]

Abstract: It has been stated repeatedly for the past 50 years that the steady-state force depression following shortening of an activated muscle depends on the speed of shortening. However, these statements were based on results from experiments in which muscles were shortened at different speeds but identical activation levels. Therefore, the force during shortening was changed in accordance with the force–velocity relationship of muscles: that is, increasing speeds of shortening were associated with decreasing forces, and vice versa. Consequently, it is not possible at present to distinguish whether force depression is caused by the changes in speed, as frequently stated, or the associated changes in force, or both. The purpose of this study was to test if force depression depends on the speed of shortening. We hypothesized that force depression was dependent on the force but not the speed of contraction. Our prediction is that the amount of force depression after shortening contractions at different speeds could be similar if the force during contraction was controlled at a similar level. Cat soleus muscles () were shortened by 9 or 12mm at speeds of 3, 9, and 27mm/s, first with a constant activation during shortening (30Hz), then with activation levels that were reduced (&#60;30Hz) for the slow speeds (3 and 9mm/s) to approximate the shortening forces of the fast speed contractions (27mm/s). If done properly, force depression could be precisely matched at the three different speeds, indicating that force depression was related to the force during the shortening contraction but not to the speed. However, in order to match force depression, the forces during shortening had to be systematically greater for the slow compared to the fast speeds of shortening, suggesting that force depression also depends on the level of activation, as force depression at constant activation levels can only be matched if the force during shortening, evaluated by the mechanical work, is identical. Therefore, we conclude that force depression depends on the force and activation level during shortening, but does not depend on the speed of shortening as has been assumed for half a century. These results support, but do not prove, the current hypothesis that force depression is caused by a stress-related cross-bridge inhibition in the actin–myosin overlap zone that is newly formed during muscle shortening. [Copyright &y& Elsevier]

Abstract: This paper investigates concave intertemporal optimization problems and derives two mechanisms, either growth or control–state interactions (e.g. due to endogenous preferences), that allow for multiple steady states including an unstable one. Therefore, history dependence is possible in a perfectly governed economy subject to the law of diminishing returns if one of these two mechanisms is present. This result complements a large amount of literature that attributes history dependence to convexities. As a consequence, lock-ins into undesired evolutions are possible beyond the familiar case of increasing returns. [Copyright &y& Elsevier]

Abstract: Defining habitual behavior as a positive relation between past and current consumption and addiction as a strong habit, Becker and Murphy (Journal of Political Economy, 1988) studied a model for rational addiction. They identified multiple steady states as another key feature of addiction. In the present paper it is shown how the interplay of addiction with a budget constraint may generate multiple long-run steady states. In the most interesting case, there exist two boundary saddle-point equilibria, as well as an unstable steady state in-between. The basins of attraction of the upper and the lower equilibria are separated by a threshold. Convergence to the lower long-run steady state may be interpreted as ‘cold turkey’, i.e., an immediate exit from consumption. [Copyright &y& Elsevier]

Let X1, X2, .. ., Xn, be independent, identically distributed random variables, uniform on [0, 1]. We observe the Xk sequentially and must stop on exactly one of them. No recollection of the preceding observations is permitted. What stopping rule τ minimizes the expected rank of the selected observation? This full-information expected-rank problem is known as Robbins' problem. The general solution is still unknown, and only some bounds are known for the limiting value as n tends to infinity. After a short discussion of the history and background of this problem, we summarize what is known. We then try to present, in an easily accessible form, what the author believes should be seen as the essence of the more difficult remaining questions. The aim of this article is to evoke interest in this problem and so, simply by viewing it from what are possibly new angles, to increase the probability that a reader may see what seems to evade probabilistic intuition. [ABSTRACT FROM AUTHOR]

The adsorption of protein and other macromolecular species is often strongly history dependent owing to the slow relaxation of nonequilibrium structures. The rate at which molecules adsorb is exquisitely sensitive to, and thus a sensitive measure of, interfacial structure; adsorption kinetics may therefore serve both to identify and to quantify history dependence. Optical waveguide lightmode spectroscopy (OWLS) in multistep mode, where an adsorbing surface is alternately exposed to a protein solution and one free of protein, enables the comparison of adsorption rates onto interfacial layers of identical composition but different formation histories. Contributions to the overall kinetics from the apparent adsorption rate constant, the desorption rate constants of molecules in different adsorbed states, and the interfacial one-body cavity function (a measure of the probability of a “cavity” on the surface free of protein) may be isolated from OWLS kinetic data. We find the rate of adsorption and the corresponding cavity function to increase significantly—for systems of fibronectin, cytochrome c, and lysozyme adsorbing onto Si(Ti)O2—from a first to a subsequent adsorption step and attribute this to a clustering transition among adsorbed protein molecules. From the kinetic data, we determine important structural and temporal information on this event. [Copyright &y& Elsevier]

Three classes of models from evolutionary game theory are studied, which make history-independent predictions: stochastic stability, stochastic stability with local interaction and cheap talk. It is argued that of the three, only local interaction models yield credible history-independent predictions. [ABSTRACT FROM AUTHOR]

Hamstring strain rehabilitation programs with an eccentric bias are effective but have a low adherence rate. Post-stretch isometric (PS-ISO) contractions which incorporate a highly controlled eccentric contraction followed by an isometric contraction resulting in elevated torque during following stretch, compared with isometric contractions at the same joint angle. This study measured torque, activation and musculotendinous unit behaviour of the hamstrings during PS-ISO contractions of maximal and submaximal levels using two stretch amplitudes. Ten male participants (24.6 years ± 2.22 years) completed maximal and submaximal baseline isometric contractions at 90°, 120° and 150° knee flexion and PS-ISO contractions of maximal and submaximal intensity initiated at 90° and 120° incorporating active stretch of 30° and 60° at 60°·s-1. Torque and muscle activation of the knee flexors were simultaneously recorded. Musculotendinous unit behaviour of the biceps femoris long head was recorded via ultrasound during all PS-ISO contractions. Compared with baseline, torque was 8% and 39% greater in the maximal and submaximal PS-ISO conditions respectively with no change in muscle activation. The biceps femoris long head muscle lengthened during all PS-ISO contractions. PS-ISO contractions may be beneficial where the effects of highly controlled eccentric contractions and elevated isometric torque are desired, such as hamstring rehabilitation. [ABSTRACT FROM AUTHOR]

A general deep learning framework based on the Unrolled Attention Sequence-to-Sequence (UA-Seq2Seq) model is developed to address the history-dependent response prediction problem. First, the particular traits of the history-dependent response prediction problem are analyzed, which motivate the incorporation of the unrolled gated recurrent unit (GRU) structure and the attention mechanism into the classical Seq2Seq model in natural language processing. In the UA-Seq2Seq model, the Seq2Seq skeleton frees the restrictions on both the input and target mechanical variables. Meanwhile, the novel unrolled GRU structure conforms to the general process of mechanical simulation and manages to establish the gated links with the historical states, which is further boosted by the powerful attention mechanism dedicated to retrieving the super-long-term memory information. To quickly and informatively validate the UA-Seq2Seq model, a numerical experiment based on the cyclic stress–strain response of low-yield-point steel is conducted, whose constitutive behavior depends highly on the loading history. All the training and testing configurations in the numerical experiment are specified, including a novel data normalization method – named nonlinear reference-value scaling – tailored for mechanical variables. The results verify the effectiveness of the UA-Seq2Seq model to reproduce the history-dependent hysteresis loops and confirm its capability to capture the long-term memory effect. Furthermore, a parametric analysis is carried out to demonstrate the necessity of the unrolled structure and the attention mechanism as well as the advantage of selecting the L1 loss metric, following which a qualitative mechanical interpretation of the UA-Seq2Seq model is provided to aid in the intuitive comprehension. Finally, three feasible applications and extensions of the developed framework are introduced conceptually: integration with finite element analysis, outline analysis, and transfer learning to other similar tasks. Therefore, the proposed deep learning framework is able to cover a wide range of scenarios concerning the mechanical history-dependent response simulation in practice, which facilitates its universal employment in the academic research and engineering design. • A general deep learning framework is developed for the history-dependent response prediction problem. • The first study to apply the Seq2Seq model and attention mechanism to computational mechanics. • A universal data normalization method is tailored for all the mechanical variables. • A mechanical interpretation is provided for the deep learning framework. • The developed framework is scalable and transferable. [ABSTRACT FROM AUTHOR]