Larger Reinforcer Research Articles

Behavioral functions of stimuli signaling transitions across rich and lean schedules of reinforcement

On multiple fixed-ratio schedules, pausing is extended at the start of a component ending in a small reinforcer (a lean component) but only when this component follows a component ending in a large reinforcer (a rich component). In two experiments, we assessed whether a stimulus correlated with a lean component is aversive and how its function is affected by the preceding component. In Experiment 1, pigeons responded on mixed fixed-ratio schedules ending in large or small reinforcers. Observing responses converted the mixed schedule to a multiple one by producing a stimulus correlated with the current component. Overall, the lean stimulus did not suppress observing, suggesting that it was not sufficiently aversive. In Experiment 2, an escape procedure was used, and pigeons could convert a multiple schedule to a mixed one by pecking a key to remove the discriminative stimuli. Pigeons escaped from the lean-schedule stimulus more than they did from the rich one. For two pigeons, this effect was enhanced when a rich component preceded the lean stimulus. The results indicate that a stimulus correlated with the leaner of two reinforcement schedules can acquire aversive functions, but observing and escape procedures may differ in their abilities to detect this effect.

Sex differences in response to amphetamine in adult Long–Evans rats performing a delay-discounting task

The use of animal models to investigate experimental questions about impulsive behavior can provide valuable insight into problems that affect human health. The delay-discounting paradigm involves subjects choosing between smaller reinforcers delivered immediately and larger reinforcers that are delivered after a delay. This is an important experimental paradigm for examining impulsive choice in both laboratory species and humans. However, a shortcoming of previously published delay-discounting studies in animals is that typically only males were studied, reducing the applicability of these studies to human populations. In the present study, both female and male adult Long–Evans rats were trained to perform a delay-discounting task, with delays of 0, 5, 10, 20 and 40s before delivery of the larger reinforcer. Because dopaminergic signaling is important in mediating this task, the effects of d-amphetamine and the dopamine receptor antagonist, cis-flupenthixol, on task performance were then examined. The main experimental measure was percent larger-reinforcer choice, which was defined as the percentage of experimental trials at each delay in which the delayed, larger reinforcer was chosen. There was no sex difference in percent larger-reinforcer choice during baseline performance of the task. However, d-amphetamine administration disrupted choice in females, as evidenced by <80% larger-reinforcer choice in half of the females, but none of the males, at 0.5mg/kg. d-Amphetamine also differentially altered the latency to choose between immediate versus delayed reinforcers in females compared to males. In contrast, cis-flupenthixol did not have a sex-related effect on percent larger-reinforcer choice. These findings parallel the sex differences in response to amphetamine seen in human delay-discounting studies and underscore the importance of evaluating sex-based differences in baseline performance and in response to pharmacologic agents when utilizing animal models.

Forced assembly by multilayer coextrusion to create oriented graphene reinforced polymer nanocomposites

A potential advantage of platelet-like nanofillers as nanocomposite reinforcements is the possibility of achieving two-dimensional stiffening through planar orientation of the platelets. The ability to achieve improved properties through in-plane orientation of the platelets is a challenge and, here, we present the first results of using forced assembly to orient graphene nanoplatelets in poly(methyl methacrylate)/polystyrene (PMMA/PS) and PMMA/PMMA multilayer films produced through multilayer coextrusion. The films exhibited a multilayer structure made of alternating layers of polymer and polymer containing graphene as evidenced by electron microscopy. Significant single layer reinforcement of 118% at a concentration of 2 wt % graphene was achieved—higher than previously reported reinforcement for randomly dispersed graphene. The large reinforcement is attributed to the planar orientation of the graphene in the individual polymer layers. Anisotropy of the stiffening was also observed and attributed to imperfect planar orientation of the graphene lateral to the extrusion flow.

Structure Optimization of the Pressure Vessel with Large Opening and Reinforcement

Aiming at the problems presented in the design of large-size vessels, structure optimization of the pressure vessel with large opening and reinforcement is mainly discussed. Firstly, 3D finite element model was established for the pressure vessel with large opening. Then, the local equivalent stress of the vessel with large opening in the thermal stress coupled field is analyzed based on ANSYS software. Secondly, taking the wall thickness of tank body and connecting pipe, the width and thickness of reinforcement pad as design variables, allowable stress as constrain condition, different structure schemes were proposed. Finally, the optimal scheme was determined through analyzing and comparing different schemes.

Fading a concurrent activity during self-control training for children with autism

We evaluated a modified technique for teaching self-control and increasing the duration of waiting for access to a preferred item among 3 children with autism. Participants initially chose an immediate small reinforcer over a delayed large reinforcer and a delayed large reinforcer with a concurrent activity requirement for the duration of the delay. When the delay to the larger reinforcer with the concurrent activity requirement was gradually increased from 0 s to the terminal delay, participants switched to and maintained selection of that option, thereby demonstrating increased self-control. Finally, the duration of the concurrent activity was gradually reduced without changing the duration of the delay to the large reinforcer. All 3 participants continued to select the delayed large reinforcer, showing self-controlled responding in the absence of a concurrent activity.

Numerical Analysis of Large Pipe Roof Support Reinforcement in Shallow Expansive Loess Tunnel

Xiaohegou tunnel is an under construction shallow expansive loess tunnel with Large Pipe Roof Support. Large Pipe Roof Support construction and excavation of the tunnel was simulated by the Fast Lagrangian finite difference software Flac3D. The pipe roof loading states and the deformation of surrounding rock in front of the tunnel face was obtained in each step of excavation, and the results was compared with a simulation without Large Pipe Roof Support. The results show that the reinforcement effect of Pipe Roof was to restrain the plastic flow of soft soil, and Pipe Roof help to share soil pressure, which could decrease the tunnel deformation effectively.

Sensitivity to delay is affected by magnitude of reinforcement in rats

Previous research has provided discrepant results about how reinforcement delay and magnitude are combined to determine the value of the alternatives in concurrent-chains schedules. In the present experiment, we analyzed a possible interaction between these characteristics of reinforcement, employing a two component concurrent-chains schedule, with rats as experimental subjects. Non-independent VI schedules were presented in the initial links of each component. In the terminal links, the following pairs of delays to reinforcement were presented in 4 conditions: 2-28, 6-24, 24-6, 28-2s (fixed time schedules for a group, fixed interval schedules for the other). Magnitude of reinforcement was maintained constant within components: one pellet for one component, and four pellets for the other. The results indicated that in both groups, the sensitivity to delay – calculated according to the generalized matching law – was higher in the component with the larger reinforcer. This result is in contrast with those reported in the literature of temporal discounting with human participants.

EFFECTS OF ACUTE AND CHRONIC MORPHINE ON DELAY DISCOUNTING IN PIGEONS

When reinforcers of different magnitudes are concurrently available, choice is greater for a large reinforcer; that choice can be reduced by delaying its delivery, a phenomenon called delay discounting and represented graphically by a delay curve in which choice is plotted as a function of delay to the large reinforcer. Morphine, administered acutely, can alter responding for large, delayed reinforcers. In this study, the impact of morphine tolerance, dependence and withdrawal on choice of delayed reinforcers was examined in six pigeons responding to receive a small amount of food delivered immediately or a larger amount delivered immediately or after delays that increased within sessions. Acutely, morphine decreased responding for the large reinforcer, and the effect was greater when morphine was administered immediately, rather than 6 hr, before sessions. During 8 weeks of daily administration, morphine produced differential effects across pigeons, shifting the delay curve downward in some and upward in others. In all pigeons, tolerance developed to the response-rate-decreasing effects of morphine but not to its effects on delay discounting. When chronic morphine treatment was discontinued, rate of responding decreased in four pigeons, indicating the emergence of withdrawal; choice of the large reinforcer increased, regardless of delay, in all pigeons, an effect that persisted for weeks. These data suggest that chronic morphine administration has long-lasting effects on choice behavior, which might impact vulnerability to relapse in opioid abusers.

Effect of signaled reinforcer magnitude on delayed matching-to-sample performance in individuals with intellectual disabilities

The present study investigated effects of signaled reinforcer magnitude in a delayed identity matching-to-sample procedure. Four individuals with intellectual disabilities were trained on conditional discrimination with three geometric stimuli as sample and comparison stimuli. Retention intervals ranged from 0.1 to 16s. The magnitude of the reinforcer (different durations of access to a video game) was signaled by the background color of the screen. Matching accuracy was overall higher when the larger reinforcer was signaled, independently of retention intervals.

PREFERENCE REVERSAL BETWEEN IMPULSIVE AND SELF‐CONTROL CHOICE

In a concurrent-chains procedure, pigeons chose between reinforcers varying in delay and amount. Reinforcer amount was determined by duration of access to grain, and delay was determined by fixed-interval schedules in the terminal links. Preference was measured by the ratio of responses in initial links. Dependent scheduling of variable-interval schedules in initial links ensured that delay and amount were not confounded with frequency of outcomes, which remained equal for the two choices. In Experiment 1, in components signaled by red keys in the initial links, small and large reinforcers were delivered after delays of 1 s and 10 s respectively. In components signaled by green, additional time was added to both delays. Smaller-sooner reinforcers were preferred in red components. In green components, smaller-sooner reinforcers were preferred at short delays, and choices for the larger-later reinforcer generally increased with increasing duration of the added delay. At longer delays, up to 15 s, the larger-later reinforcer was preferred. That is, the pigeons showed within-session preference reversal, with impulsive choice at short delays in red components and self-control choice at long delays in green components. In Experiment 2, added delay to both reinforcement and reinforcer amount were varied. Sensitivity of initial-link response ratios to ratios of amount increased with increasing duration of the added delay. This interaction between delay and amount was predicted if the temporal discounting functions assumed the magnitude effect in which discounting rate was inversely proportional to amount. It was also predicted by the contextual choice model of performance in concurrent-chains procedures.

Effect of the Wire Temperature on the Weld Formation in GMAW

An arc-preheating wire GMAW process is proposed in this paper. The welding wire is preheated by a TIG arc to enhance the wire melting. As a result, the welding current is decrease. So the improved GMAW process is aimed at high efficiency welding with a low level heat input. In this paper, the welding system is designed. The wire temperature is measured by a pyrometer. The preheating current effect on the wire temperature is analyzed. In addition, the influence of the wire temperature on the weld current and weld formation are analyzed compared with conventional GMAW. The results show that the preheated wire can significantly enhance the wire melting. By increasing the temperature of the welding wire, the welding current decrease and the heat input of the base metal reduce accordingly. The shallow penetration and large reinforcement height are obtained at the arc-preheating wire GMAW process.

A physical cross-linking process of cellulose nanofibril gels with shear-controlled fibril orientation

Cellulose nanofibrils constitute the smallest fibrous components of wood, with a width of approximately 4 nm and a length in the micrometer range. They consist of aligned linear cellulose chains with crystallinity exceeding 60%, rendering stiff, high-aspect-ratio rods. These properties are advantageous in the reinforcement components of composites. Cross-linked networks of fibrils can be used as templates into which a polymer enters. In the semi-concentrated regime (i.e. slightly above the overlap concentration), carboxy methylated fibrils dispersed in water have been physically cross-linked to form a volume-spanning network (a gel) by reducing the pH or adding salt, which diminishes the electrostatic repulsion between fibrils. By applying shear during or after this gelation process, we can orient the fibrils in a preferred direction within the gel, for the purpose of fully utilizing the high stiffness and strength of the fibrils as reinforcement components. Using these gels as templates enables precise control of the spatial distribution and orientation of the dispersed phase of the composites, optimizing the potentially very large reinforcement capacity of the nanofibrils.

Reinforcement of Polyether Polyurethane with Dopamine-Modified Clay: The Role of Interfacial Hydrogen Bonding

Dopamine-modified clay (D-clay) was successfully dispersed into polyether polyurethane (PU) by solvent blending. It is found that the incorporation of D-clay into PU gives rise to significant improvements in mechanical properties, including initial modulus, tensile strength, and ultimate elongation, at a very low clay loading. The large reinforcement could be attributed to the hydrogen bonds between the hard segments of PU and stiff D-clay layers that lead to more effective interfacial stress transfer between the polymer and D-clay. Besides, the interactions between D-clay and PU are also stronger than those between Cloisite 30B organoclay and the PU chains. Consequently, at a similar clay loading, the PU/D-clay nanocomposite has much higher storage modulus than the PU/organoclay nanocomposite at elevated temperatures.

Thermal and mechanical properties of homogeneous ternary nanocomposites of regioregular poly(3‐hexylthiophene)‐wrapped multiwalled carbon nanotube dispersed in thermoplastic polyurethane: Dynamic‐ and thermomechanical analysis

AbstractAn interesting correlation between initial loading and nature of wrapping of regioregular poly(3‐hexylthiophene) (rrP3HT) on multiwalled carbon nanotube and their combined effect on dynamic‐ and thermomechanical properties in ternary system (thermoplastic polyurethane as matrix) is highlighted. Wrapping of rrP3HT on carbon nanotube (CNT) makes the hexyl side chains thermally nonequivalent and composites more stable. Dynamic‐ and thermomechanical analysis ascertained the miscibility (single Tg = −40°C), large mechanical reinforcement, and improved storage modulus of nanocomposites in the presence of CNT compared to its blends. Two breaks at ∼ −100 and ∼ −40°C for TPU‐P3HT composites (PHs) and TPU‐P3HT‐MWCNT composites (PHCs) in the loss modulus vs. temperature plot indicates two different types of transitions in P3HT chains. Dimensional stability by expansion probe technique measures low coefficient of thermal expansion of PHCs compared to its blends. Softening property by penetration probe technique suggests that 2.5 wt % loading of P3HT exhibits lowest degree of penetration compared to other nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

COMMITMENT AND SELF‐CONTROL IN A PRISONER'S DILEMMA GAME

Humans often make seemingly irrational choices in situations of conflict between a particular smaller-sooner reinforcer and a more abstract, temporally extended, but larger reinforcer. In two experiments, the extent to which the availability of commitment responses-self-imposed restrictions on future choices-might improve self-control in such situations was investigated. Participants played a prisoner's dilemma game against a computer that played a tit-for-tat strategy-cooperating after a participant cooperated, defecting after a participant defected. Defecting produced a small-immediate reinforcer (consisting of points convertible to gift cards) whereas cooperating increased the amount of subsequent reinforcers, yielding a greater overall reinforcer rate. Participants were normally free to cooperate or defect on each trial. Additionally, they could choose to make a commitment response that forced their choice for the ensuing five trials. For some participants, the commitment response forced cooperation; for others, it forced defection. Most participants, with either commitment response available, chose to commit repeatedly despite a minor point loss for doing so. After extended exposure to these contingencies, the commit-to-cooperate group cooperated significantly more than a control group (with no commitment available). The commit-to-defect group cooperated significantly less than the control group. When both commitment alternatives were simultaneously available-one for cooperation and one for defection-cooperation commitment was strongly preferred. In Experiment 2, the commitment alternative was removed at the end of the session; gains in cooperation, relative to the control group, were not sustained in the absence of the self-imposed behavioral scaffold.

Bending load capacity of reinforced concrete slabs strengthened with textile reinforced concrete

The use of textile reinforced concrete (TRC) is a very effective method for strengthening reinforced concrete (RC) constructions. Within the Collaborative Research Centre 528 of the Technische Universität Dresden (TU Dresden) vast research on TRC was carried out, so as to examine the use of TRC for subsequently strengthening the bending load capacity of existing concrete or reinforced concrete components. As a rule, the experimental research was done at small format reinforced concrete slabs with span widths of 1.60m and slab thicknesses of 0.10m strengthened with TRC. At the same time calculation models were developed to predict the maximum bending load capacity of the reinforced components amongst others.This article describes the experimental and theoretical research reassessing the assignability of the results gained until now to large scale reinforced concrete slabs with a span width of 6.75m and slab thickness of 0.23m. By using textile high-performance carbon reinforcements based on so-called heavy-tow-yarns very high strengthening levels can be realized. The results show significant load bearing capacity increases compared to unreinforced reference slabs. Thus the safe use of bending reinforcements consisting of TRC could be demonstrated for components with even large span widths and high reinforcement degrees. Simultaneously a distinct decrease of deflection with growing reinforcement degree was verified at a comparable load level. Calculation results of the presented simplified calculation model for the estimated bending measurement are consistent with the load carrying capacities determined experimentally. Using the finite element method (FEM) not only the load bearing capacities but also the deformations were calculable keenly.

Effects of pre-trial response requirements on self-control choices by rats and pigeons.

Parallel experiments with rats and pigeons examined whether the size of a pre-trial ratio requirement would affect choices in a self-control situation. In different conditions, either 1 response or 40 responses were required before each trial. In the first half of each experiment, an adjusting-ratio schedule was used, in which subjects could choose a fixed-ratio schedule leading to a small reinforcer, or an adjusting-ratio schedule leading to a larger reinforcer. The size of the adjusting ratio requirement was increased and decreased over trials based on the subject's responses, in order to estimate an indifference point-a ratio at which the two alternatives were chosen about equally often. The second half of each experiment used an adjusting-delay procedure-fixed and adjusting delays to the small and large reinforcers were used instead of ratio requirements. In some conditions, particularly with the reinforcer delays, the rats had consistently longer adjusting delays with the larger pre-trial ratios, reflecting a greater tendency to choose the larger, delayed reinforcer when more responding was required to reach the choice point. No consistent effects of the pre-trial ratio were found for the pigeons in any of the conditions. These results may indicate that rats are more sensitive to the long-term reinforcement rates of the two alternatives, or they may result from a shallower temporal discounting rate for rats than for pigeons, a difference that has been observed in previous studies.

Strain differences in delay discounting between Lewis and Fischer 344 rats at baseline and following acute and chronic administration of d-amphetamine

Stimulant drugs have been shown either to increase or decrease rates of delay discounting (impulsive choice). These mixed findings may result from genetic, neurochemical, or environmental factors. Lewis (LEW) and Fischer 344 (F344) rats have neurochemical and behavioral differences that may be relevant to delay discounting and were used to examine effects of acute and chronic administration of d-amphetamine (d-AMP) on impulsive choice using a within-session delay-discounting procedure. Male LEW (n=8) and F344 (n=8) rats chose between one food pellet delivered immediately and three food pellets delivered after an increasing delay. Saline and d-AMP (0.1, 0.3, 1.0, and 1.7mg/kg) were tested acutely and during chronic d-AMP exposure. Choice for the larger reinforcer decreased as the delay to its presentation increased for both strains at baseline. LEW rats made more impulsive choices than F344 rats as indicated by shorter indifference points, and this is consistent with previous research. Acute administration of d-AMP dose dependently increased larger-reinforcer choice and area under the curve (AUC) for LEW, but not F344 rats. During chronic exposure to d-AMP, larger-reinforcer choice and AUC increased relative to acute administration for F344 rats responding in shorter delay series, but not for F344 rats responding in longer delay series or for LEW rats. Differential effects of acute and chronic administration of d-AMP on impulsive choice in LEW and F344 rats may be a result of various factors, including genetic, neurochemical, and environmental variables. Future research should attempt to tease apart the relative contribution of each of these factors on impulsive choice.

Long-term lateral displacement of geosynthetic-reinforced soil segmental retaining walls

The service limit-state design of Geosynthetic-Reinforced Soil (GRS) retaining walls requires accurate estimation of the lateral facing displacement at the end of construction as well as after years of creep. However, before a simplistic but rational methodology for this purpose can be developed, mechanisms governing the short-term and long-term lateral facing displacements must be clarified. In this study, extensive Finite Element analyses were carried out using a calibrated Finite Element procedure to investigate and attempt to better understand the lateral facing displacements of segmental GRS walls at the end of construction and after 10 years of creep under constant gravity loading. The study found that among the two main components of lateral facing displacement, the deformation of reinforced soil zone was largely governed by reinforcement spacing and reinforcement stiffness, while the influence of reinforcement length was negligible. Soil stiffness also played an important role in the lateral deformation if large reinforcement stiffness and/or small reinforcement spacing were used. In contrast, reinforcement length to a very large extent determined the lateral displacement at the back of reinforced soil zone. With constant reinforcement length, the reinforced soil zone could be treated as a deep beam. The displacement at the back of reinforced soil zone was then determined by the earth pressure, beam depth, and beam stiffness, the last of which is a function of soil stiffness, reinforcement spacing, reinforcement stiffness, and facing stiffness. The study found that isochrone stiffness can be used to interpret the lateral deformation of GRS walls under working stress condition.

Pramipexole-Induced Increased Probabilistic Discounting: Comparison Between a Rodent Model of Parkinson's Disease and Controls

The dopamine agonist pramipexole (PPX) can increase impulsiveness, and PPX therapy for neurological diseases (Parkinson's disease (PD) and restless leg syndrome) is associated with impulse control disorders (ICDs) in subpopulations of treated patients. A commonly reported ICD is pathological gambling of which risk taking is a prominent feature. Probability discounting is a measurable aspect of risk taking. We recently developed a probability discounting paradigm wherein intracranial self-stimulation (ICSS) serves as the positive reinforcer. Here we used this paradigm to determine the effects of PPX on discounting. We included assessments of a rodent model of PD, wherein 6-OHDA was injected into the dorsolateral striatum of both hemispheres, which produced persistent PD-like deficits in posture adjustment. Rats were trained to perform ICSS-mediated probability discounting, in which PD-like and control groups exhibited similar profiles. Rats were treated twice daily for 2 weeks with 2 mg/kg (±)PPX (ie, 1 mg/kg of the active form), a dose that improved lesion-induced motor deficits. In both groups, (±)PPX increased discounting; preference for the large reinforcer was enhanced 30-45% at the most uncertain probabilities. Tolerance did not develop with repeated treatments. Increased discounting subsided within 2 weeks of (±)PPX cessation, and re-exposure to (±)PPX reinstated heightened discounting. Such findings emulate the clinical scenario; therefore, ICSS for discounting assessments in rats exhibited high face validity. This model should prove useful in medication development where assessment of the propensity of a putative therapy to induce risk-taking behaviors is of interest.