Reinforcement Efficacy Research Articles

Evaluating the reinforcing potential of enzymatic cellulose nanocrystals in polypropylene nanocomposite

Cellulose nanocrystals (CNCs) produced through enzymatic hydrolysis exhibit physicochemical properties that make them attractive as eco-friendly reinforcing agents in polymer composites. However, the extent of their efficacy within a polymeric matrix is yet to be fully established. This study investigated the reinforcing capabilities of enzymatic CNC (approximately 3 nm in diameter) isolated from bleached eucalyptus Kraft pulp (BEKP), focusing on its application in polypropylene (PP) nanocomposites produced by injection molding. The study compared the performance of this enzymatic CNC (1–5 % wt) with PP composites reinforced with micro-sized cellulose fibers (BEKP at 10–30 % wt, approximately 13 μm) and additionally with commercial CNC produced by sulfuric acid hydrolysis. Despite enzymatic CNC experiencing agglomeration during spray-drying, leading to an average diameter increase to 3 μm, it still significantly increased the crystallization and glass transition temperature of the PP matrix. However, this agglomeration likely hindered the improvement of the mechanical properties within the nanocomposites. The results also showed that enzymatic CNC provided higher thermal stability at lower reinforcement levels compared to BEKP, but this came with a reduction in stiffness, posing a significant consideration in composite design. The addition of a coupling agent greatly enhanced the dispersion of reinforcements and the interfacial adhesion within the matrix, contributing to the enhanced performance of the composite properties. Additionally, enzymatic CNC demonstrated potential for superior reinforcement efficacy compared to commercially available CNC produced by sulfuric acid hydrolysis. In conclusion, enzymatic CNC exhibited a promising role as nano-reinforcement for thermoplastic polymer nanocomposites, exhibiting higher thermal properties at lower reinforcing loads than traditional micro-sized fiber reinforcements. The absence of sulfur, coupled with its higher thermal stability and sustainable potential, positions enzymatic CNC as a particularly favorable choice for applications involving direct contact with food, cosmetics, pharmaceuticals, and biomedical materials.

Evaluation of composites based on virgin rubber/devulcanized rubber reinforced with chemically and radiation activated polyurethane scrap for possible applications

AbstractReusing industrial waste is one of the new tactics being used to fight the dumping of solid waste for environmental protection. In the current work, the waste polyurethane (WPU) was ground to a fine powder and used for reinforcement of devulcanized waste rubber/styrene butadiene rubber (DWR/SBR) blends. DWR/SBR/WPU composites were prepared using (0, 3, 6, 9, 15, 30) phr (parts per hundred of rubber) of WPU. It was hypothesized that the treatment of WPU with trimethylolpropane triacrylate (TMPTMA) and irradiated at 10 kGy would improve its compatibility with the DWR/SBR blend and, consequently, its reinforcement efficacy. The incorporation of 30 phr of treated WPU (TWPU) improved the tensile strength (TS) by 47.7% and 8.6% compared to neat DWR/SBR and composites containing 30 phr of untreated WPU (UWPU). In addition, the incorporation of TWPU improved other mechanical characteristics such as tear strength, hardness, and abrasion resistance. As a result of increasing polarity and cross‐link density within the DWR/SBR blend after the addition of polar WPU, the resistance to motor oil was improved. The outcomes are encouraging from the standpoint of the circular economy and help produce high‐performing, reasonably priced DWR/SBR composites for a range of industrial uses, especially in the floor tiles application.Highlights Waste polyurethane (WPU) was activated using gamma irradiation in the presence of TMPTMA. The treatment of WPU improved its compatibility with DWR/SBR blend. The impact of WPU treatment on the properties of DWR/SBR blend was investigated. TWPU improved the mechanical properties of DWR/SBR blend more than UWPU. TWPU increased the motor oil resistance of DWR/SBR blend more than UWPU.

Experimental study on reinforcement of bionic grouser of deep-sea mining vehicle

To fulfill the operational demands of deep-sea tracked mining vehicles traversing soft seabed substrates, an evaluation of the characteristics of these substrates was conducted, drawing a comparison with the land swamp black soil found in the buffalo's habitat. Employing the principles of biomimicry, two distinct types of bionic grouser were devised, replicating the configuration of the buffalo's hooves in both the horizontal and vertical planes. Utilizing self-constructed testing platforms, exhaustive examinations of the reinforcement efficacy of these bionic track grousers were undertaken, spanning from single-grouser to multi-grouser configurations and encompassing the entire track assembly. The findings unequivocally demonstrate a pronounced and consistent enhancement in traction force for both types of bionic grousers. Notably, the W-shaped bionic grouser, mimicking the horizontal contour of the buffalo's hoof, exhibits the most substantial increase in traction force. The maximum enhancement in traction force for individual bionic grouser exceeds 30%, while the overall track achieves an increase of over 19%. This research provides a valuable reference and establishes a foundational framework for the design of equipment tailored for the locomotion of deep-sea tracked mining vehicles across soft substrates.

Magnitude and predictors of elasticity of demand for morphine are similar in male and female rats.

Sex differences in vulnerability to opioid use disorder (OUD) have been reported in some clinical and preclinical studies, but findings are mixed and further research is needed in this area. The goal of this study was to compare elasticity of demand (reinforcement efficacy) in an i.v. morphine self-administration (SA) model in male and female rats using a translationally relevant behavioral economics approach. Rate of acquisition and predictors of individual differences in demand (e.g., cumulative morphine infusions during acquisition) were also evaluated in both sexes. Acquisition of morphine SA (0.4 mg/kg/infusion) under a fixed ratio (FR) 1 schedule of reinforcement was slower and infusions earned were lower in females than in males (n = 30-31/sex), but infusions earned did not differ between sexes during the FR 2 and FR 3 phases of acquisition. Increases in the FR response requirement across sessions during demand testing (FR 1-FR 96) resulted in a progressive reduction in morphine infusions in both sexes. Morphine consumption was well-described by an exponential demand function in both sexes and was associated with considerable individual vulnerability. There were no sex differences in elasticity of demand (rate of decline in morphine consumption with increasing price) or intensity of demand (consumption at zero price). A higher number of infusions earned during the FR 2 and FR 3 phases of acquisition and greater maximum response rates during demand testing were associated with lower demand elasticity (i.e., greater reinforcing efficacy) in both males and females, whereas other relationships were sex-specific (e.g., higher intensity of demand was associated with lower elasticity of demand in males but not in females). Our findings indicate similar elasticity of demand and predictors of individual differences in demand for morphine in male and female rats, although sex differences were observed in initial rate of acquisition and in some correlations between morphine SA measures. These data are consistent with findings of similar OUD vulnerability in males and females in some human and animal studies.

A novel technique for delineating the effect of variation in the learning rate on the neural correlates of reward prediction errors in model-based fMRI.

Computational models play an increasingly important role in describing variation in neural activation in human neuroimaging experiments, including evaluating individual differences in the context of psychiatric neuroimaging. In particular, reinforcement learning (RL) techniques have been widely adopted to examine neural responses to reward prediction errors and stimulus or action values, and how these might vary as a function of clinical status. However, there is a lack of consensus around the importance of the precision of free parameter estimation for these methods, particularly with regard to the learning rate. In the present study, I introduce a novel technique which may be used within a general linear model (GLM) to model the effect of mis-estimation of the learning rate on reward prediction error (RPE)-related neural responses. Simulations employed a simple RL algorithm, which was used to generate hypothetical neural activations that would be expected to be observed in functional magnetic resonance imaging (fMRI) studies of RL. Similar RL models were incorporated within a GLM-based analysis method including derivatives, with individual differences in the resulting GLM-derived beta parameters being evaluated with respect to the free parameters of the RL model or being submitted to other validation analyses. Initial simulations demonstrated that the conventional approach to fitting RL models to RPE responses is more likely to reflect individual differences in a reinforcement efficacy construct (lambda) rather than learning rate (alpha). The proposed method, adding a derivative regressor to the GLM, provides a second regressor which reflects the learning rate. Validation analyses were performed including examining another comparable method which yielded highly similar results, and a demonstration of sensitivity of the method in presence of fMRI-like noise. Overall, the findings underscore the importance of the lambda parameter for interpreting individual differences in RPE-coupled neural activity, and validate a novel neural metric of the modulation of such activity by individual differences in the learning rate. The method is expected to find application in understanding aberrant reinforcement learning across different psychiatric patient groups including major depression and substance use disorder.

Recycling waste fiber-reinforced polymer composites for low-carbon asphalt concrete: The effects of recycled glass fibers on the durability of bituminous composites

Waste Fiber-Reinforced Polymer (FRP) composites have become an environmental issue in China, Europe, and the United States. However, recycling waste FRP composites poses sustainability challenges in the long term because their predominantly cross-linked structure (thermoset matrices coating) typically cannot be re-used or re-processed. Here, for the first time, we studied the merits of introducing recycled glass fibers (rGF) to bitumen to enhance bitumen's durability as measured by resistance to aging and resistance to moisture damage. We compared the reinforcement efficacy of recycled glass fibers (rGF) with recycled glass fibers after the polymer coating was removed (rGFWP) and with virgin glass fibers (vGF). After aging, compared to the bitumen with rGFWP, the bitumen containing rGF showed enhanced resistance to oxidative aging, as evidenced by lower values of two indexes of chemical aging (a 64.5% lower carbonyl index and a 94.5% lower sulfoxide index), a 47.10% lower increase in the ratio of large molecular size, and a 61.41% lower rheological aging index. Moreover, bitumen containing recycled glass fiber demonstrated noticeably improved resistance to moisture damage as compared to base bitumen, particularly for rGFWP, as demonstrated by energy ratio (ER) values that were 478% higher. The resistance to moisture damage of bitumen containing rGF was also significant improved, as evidenced by a 72.78% increase in surface energy, the better MISTI value (the least variation from a value of one), and a 213% higher ER value compared to base bitumen. This indicates that recycled glass fibers have positive effects on the durability of bitumen composites. The outstanding durability of bitumen with recycled glass fibers highlights the feasibility of adding recycled glass fibers to bitumen as a practical application that provides an economic and environmentally friendly solution for waste glass fibers.

Appetitive Pavlovian conditioning of the stimulus effects of nicotine enhances later nicotine self-administration.

Nicotine produces robust stimulus effects that can be conditioned to exert stimulus control over behavior through associative learning. Additionally, nicotine has weak reinforcing effects that are inconsistent with its prevalence of use and the tenacity of nicotine dependence. The present study investigated whether conditioned associations to the nicotine drug stimulus may confer additional reinforcing strength to nicotine that thereby increase its use liability, and presents a new methodological approach to investigating the interaction between the stimulus effects and reinforcing effects of drugs. Male and female Sprague-Dawley rats were divided into groups receiving intravenous infusions of either 0.03 mg/kg nicotine or 0.9% saline that were either Paired (30 s delayed) or explicitly Unpaired (4 to 6 min delayed) with sucrose deliveries over 24 daily conditioning sessions. Thereafter, recessed nosepoke response devices were installed in the chambers and infusions of their assigned drug solutions were contingently available according to a progressive ratio schedule. Rats in the Paired Nicotine condition acquired the nosepoke response, expressed active nosepoke discrimination, and self-administered significantly more infusions than rats in any of the other groups. These results demonstrate that the interoceptive stimulus effects of nicotine can form Pavlovian associations with reinforcing events that alter its reinforcement efficacy.

Simultaneously improving strength and ductility of hybrid Al–Si matrix composite with polyphasic and multi-scale ceramic particles

Hybrid aluminum matrix composites have received widespread attention because of their superior performance to single-phase reinforced aluminum matrix composites. In situ VB2–AlN–Al4C3–VSi2/Al ribbons with polyphasic and multi-scale reinforcement particles were prepared by powder metallurgy method and controlled by melt-spinning and then verified the reinforcement efficacy in Al–12Si alloy. It was found that the addition of VB2–AlN–Al4C3–VSi2/Al ribbons not only refined the grain of α-Al, but also optimized the morphology of eutectic silicon for Al–12Si matrix composite. Thereafter, the mechanical properties of the VB2–AlN–Al4C3–VSi2/Al–12Si composite, including the tensile strength, ductility and hardness were increased by 36.2%, 82.2% and 33.4%, respectively, with the addition of VB2–AlN–Al4C3–VSi2/Al ribbons. The excellent mechanical properties can be attributed to the micron-sized VSi2 particles, nano-sized AlN, VB2, and Al4C3 as well as the well-bonded particle/matrix interface. In addition, multiple strengthening mechanisms have also made outstanding contributions to the improvement of the mechanical properties, including (1) Orowan strengthening; (2) Coefficient of thermal expansion (CTE) mismatch strengthening; (3) the Hall-Petch effect caused by grain refinement. The present experimental results provide an insight into the understanding of polyphasic and multi-scale reinforcement particles, and extend the effort for the development of Al–Si composite.

Thermoresponsive Brushes Facilitate Effective Reinforcement of Calcium Phosphate Cements.

Calcium phosphate ceramics are frequently applied to stimulate regeneration of bone in view of their excellent biological compatibility with bone tissue. Unfortunately, these bioceramics are also highly brittle. To improve their toughness, fibers can be incorporated as the reinforcing component for the calcium phosphate cements. Herein, we functionalize the surface of poly(vinyl alcohol) fibers with thermoresponsive poly(N-isopropylacrylamide) brushes of tunable thickness to improve simultaneously fiber dispersion and fiber–matrix affinity. These brushes shift from hydrophilic to hydrophobic behavior at temperatures above their lower critical solution temperature of 32 °C. This dual thermoresponsive shift favors fiber dispersion throughout the hydrophilic calcium phosphate cements (at 21 °C) and toughens these cements when reaching their hydrophobic state (at 37 °C). The reinforcement efficacy of these surface-modified fibers was almost double at 37 versus 21 °C, which confirms the strong potential of thermoresponsive fibers for reinforcement of calcium phosphate cements.

Mechanical reinforcement and creep resistance of coextruded wood flour/polyethylene composites by shell‐layer treatment with nano‐ and micro‐SiO2 particles

Nano‐ and micro‐SiO2 particles (termed nSiO2 and mSiO2, respectively) were incorporated in the shell layer of a coextruded wood flour/high density polyethylene composite (WF/HDPE) to improve the mechanical properties and inhibit creep behavior. The effects of loading content, particle size, and surface treatment of the silica with vinyl trimethoxy silane (VTS) were investigated on the properties of the resulting coextruded WF/HDPE composites. Scanning electron microscopy revealed proper interfacial adhesion between the core and shell layers. nSiO2 exhibited higher reinforcement efficacy than that of mSiO2 for the shell‐layer materials. Incorporation of the VTS‐treated nSiO2 caused an increase in flexural‐ and impact strength of the coextruded composites by 29% and 57%, compared to the non‐silica filled coextruded WF/HDPE controls, respectively. Incorporation of nSiO2, either untreated or VTS‐treated, enhanced creep resistance of shell layer materials; however, only VTS‐nSiO2 worked for the coextruded composites. These findings demonstrate that filling with silica, particularly VTS‐treated nSiO2, in the shell layer substantially and economically reinforces coextruded shell/core‐structured WF/HDPE composites. POLYM. COMPOS., 40:1576–1584, 2019. © 2018 Society of Plastics Engineers

Strong process-structure interaction in stoveable poly(urethane-urea) aligned carbon nanotube nanocomposites

The exceptional static and dynamic physical properties of poly(urethane-urea) (PUU) elastomers make them prime candidates for impulsive loading structural applications, such as blast protection coatings. Since the theoretical physical properties of carbon nanotubes (CNTs) are among the best for any currently known material, a number of previous studies explored the use of CNTs as nanoscale fillers to enhance the properties of PUU nanocomposites. However, due to the challenges inherent in dispersing CNTs in a PUU matrix and the resulting random orientation of the CNTs, these previous works observed marginal improvements in physical properties, and were unable to establish clear structure-property relations. Here, we report the synthesis of aligned-CNT (A-CNT) reinforced PUU polymer nanocomposites (A-PNCs) by infusing A-CNT forests with a stoveable PUU, and establish process-structure-property relations that quantify the contribution of CNT confinement on the PUU mechanical response. This stoveable process was achieved using blocked isocyanate which prevented polymerization until the blocks were removed with heat. PUUs of two distinct compositions were explored: one with 40 wt% hard-segment content (PUU211) and the other with 66 wt% hard-segment content (PUU541). Thermogravimetric analysis indicates that A-CNTs enhance the thermal stability of the hard-segment phase in PUU A-PNCs at 340 °C by up to 45% over the baseline PUUs. Atomic force microscopy reveals that the elongated nanophase hard-segment formations along the CNT axis observed only in the nanocomposites were of similar characteristic size to the average inter-A-CNT spacing (∼70 nm), indicating a strong influence of A-CNTs on the size and orientation of hard-segment nanophases, as corroborated via small angle X-ray scattering. Nanoindentation testing reveals that PUU A-PNCs possess significant elastic anisotropy, and exhibit enhanced longitudinal effective indentation moduli of ∼460 MPa (>3 × that of the PUU211 baseline) and ∼1350 MPa (∼1.5 × that of the PUU541 baseline) for PUU211 and PUU541 nanocomposites, respectively. This difference in magnitude of CNT reinforcement efficacy indicates that CNT confinement leads to significant hard-segment re-organization in the PUU211 A-PNCs, whereas the interconnected network of hard-segments in the PUU541 is affected by CNT templating to a lesser extent. Dynamic nanoindentation testing results are consistent with these interpretations, where longitudinally-loaded PUU211 A-PNCs are found to exhibit a >3 × enhancement in storage modulus at 1 Hz of ∼730 MPa, whereas the longitudinally-loaded PUU541 A-PNCs exhibit a slightly enhanced storage modulus enhancement at 1 Hz of 2190 MPa (∼1.5 × that of the PUU541 baseline). Reinforcement of PUUs with A-CNTs is a promising way to tune the physical properties of the PNCs; higher A-CNT packing densities, where the inter-CNT spacing could approach the nanophase characteristic diameter, could further enhance the PUU performance in ballistic protection applications.

Palatal implant surgery effectiveness in treatment of obstructive sleep apnea: A numerical method with 3D patient-specific geometries

Obstructive sleep apnea (OSA) affects a large percentage of the population and is increasingly recognized as a major global health problem. One surgical procedure for OSA is to implant polyethylene (PET) material into the soft palate, but its efficacy remains to be discussed. In this study, we provide input to this topic based on numerical simulations. Three 3 dimensional (3D) soft palate finite element models including mouth-close and mouth-open cases were created based on three patient-specific computed tomography (CT) images. A simplified material modeling approach with the Neo-Hookean material model was applied, and nonlinear geometry was accounted for. Young’s modulus for the implant material was obtained from uniaxial tests, and the PET implant pillars were inserted to the 3D soft palate model. With the finite element model, we designed different surgical schemes and investigated their efficacy with respect to avoiding the soft palate collapse. Several pillar schemes were tested, including different placement directions, different placement positions, different settings for the radius and the array parameters of the implant pillars, and different Young’s moduli for the pillars. Based on our simulation results, the longitudinal-direction implant surgery improved the stiffness of the soft palate to a small degree, and implanting in the transverse direction was evaluated to be a good choice for improving the existing surgical scheme. In addition, the Young’s modulus of the polyethylene material implants has an influence on the reinforcement efficacy of the soft palate.

The reinforcement efficacy of nano- and microscale silica for extruded wood flour/HDPE composites: the effects of dispersion patterns and interfacial modification

The reinforcement efficacy of nano-silica particles for wood/plastic composites (WPCs) has been inconsistent in previous research. Accordingly, this systematic study was conducted to verify the reinforcement feasibility using silica particles. Micro- and nano-silica particles were incorporated into high-density polyethylene (HDPE) via direct compounding (dry dispersion) or by mixing in a solution (wet dispersion), to determine the effects of dispersion and particle size on the reinforcement efficacy of the resulting wood/HDPE composites. Compared with non-filled WPCs, dry dispersion reduced the WPCs’ mechanical strength for microsilica (> 30%), but increased it for nano-silica (< 10%). Wet dispersion plus a surface treatment of silica with vinyltrimethoxysilane (VTS) improved the mechanical strengths of the WPCs by up to 30%; the creep deformation was also restricted to some extent. This study demonstrates that silica particles can reinforce WPCs to a moderate extent, if they are in the nano-diameter size range and are uniformly dispersed into the matrix of the WPC system.

The role of crystallinity in SWCNT–polyetherimide nanocomposites

Two all-aromatic, high-performance poly(etherimide)s ODPA-P3 (I) and BPDA-P3 (II) are studied as a function of SWCNT loading. Polyetherimide I is amorphous but SWCNTs nucleate crystallization during imidization to produce a nanocomposite (nc-I) with SWCNTs embedded in the crystals. This crystalline interphase, with a radial thickness of ∼8 nm, results in a substantial reinforcement efficacy. Melting the interphase and cooling nc-I yields an amorphous nanocomposite with an interphase thickness (3.6 nm) that is smaller and has a lower reinforcement efficacy. Polyetherimide II was used as a reference since SWCNTs reside in the amorphous fraction of its nanocomposite. Consequently, the reinforcement efficiency of the semi-crystalline nc-II and its amorphous analog (prepared by heating above the crystal melting point and cooling) remains unchanged. A crystalline interphase surrounding SWCNT-reinforced poly(etherimide)s appears to be critical in obtaining high reinforcement efficacies. Most high-performance polyimides and poly(etherimide)s are prepared using a thermal imidization step. Our work emphasizes that care has to be taken in selecting the final imidization temperature to avoid melting the crystalline interphase if one is targeting high modulus materials.

Predictors of delay discounting among smokers: Education level and a Utility Measure of Cigarette Reinforcement Efficacy are better predictors than demographics, smoking characteristics, executive functioning, impulsivity, or time perception

Ninety-four smokers completed the delay discounting procedure for either hypothetical amounts of money, $10 (money) and $1000 (money) or hypothetical amounts of cigarettes ($10 and $1000 worth of cigarettes). We investigated how variables previously found to be related to rates of delay discounting accounted for the observed results. These variables included the following: demographic information, smoking characteristics, executive function abilities, impulsivity, time perception, and the Utility Measure of Cigarette Reinforcing Efficacy (UMCE). Education level and UMCE were each significantly correlated with 3 out of 4 of the discounting measures. Moreover, the largest effect sizes observed were between these two measures and the four discounting measures. All potential discounting predictors were also investigated using step-wise linear regression with Bayesian Information Criterion (BIC) analysis — these BIC models revealed that education level and UMCE accounted for large portions of the variance. We conclude that education level and UMCE were the most consistent predictors of discounting. This data is discussed within the framework of a widely accepted neuroeconomic model that suggests that two brain systems separately assess two separate facets of decision-making, and the interplay between these two systems determines self-control in smokers. We hypothesize that education level and UMCE may serve as surrogate measures of the functionality of these two systems and that discounting may be a sentinel measure of self-control.

Normal, high and ultra-high modulus carbon fiber-reinforced polymer laminates for bonded and un-bonded strengthening of steel beams

Abstract This paper studies the elastic behavior of steel beams strengthened with normal, high and ultra-high modulus CFRP laminates using bonded and un-bonded systems. The elastic behavior of retrofitted beams provides useful information for design of fatigue strengthening systems. A total of seven steel beams including one control unstrengthened beam and six strengthened beams were tested statically until failure in a simply supported four-point bending set-up. The steel beams were retrofitted by normal modulus (NM), high modulus (HM) and ultra-high modulus (UHM) carbon fiber-reinforced polymer (CFRP) laminates with nominal Young’s moduli, ranging from 165 to 440 GPa. Each type of laminate was attached to the steel beams using bonded reinforcement (BR) and un-bonded reinforcement (UR) systems. There is no direct comparison between the BR and the UR systems in the literature. The main goal of the paper is to provide a better understating about the stress distribution along the beam bottom flange when the BR and the UR systems are used for strengthening. All specimens failed due to lateral-torsional buckling (LTB). The effect of different strengthening methods on buckling capacity of the retrofitted specimens was also studied. Experimental results have shown that strengthening using bonded UHM laminates could increase the stiffness of the composite section so that the steel profile has yielded prior to buckling and a larger reinforcement efficacy was then achieved.

Adenosine A2a receptors activate Nuclear Factor-Kappa B (NF-κB) in rat hippocampus after exposure to different doses of MDMA

MDMA (3,4-methylenedioxy-N-methamphetamine) as an empathogenic drug causes neurotoxicity although the mechanisms have not been fully elucidated. The A2a adenosine receptor modulates the reinforcement efficacy and neurotoxicity of MDMA. A2a receptor activation inhibits Nuclear Factor-Kappa B (NF-κB) activation and nuclear translocation by a known mechanism. In the present study, we aimed to compare the NF-κB activity level in rat hippocampus between two doses of MDMA exposure (10 and 20 mg /kg) using either A2aR agonist (CGS) or A2aR antagonist (SCH). Adult male Sprague-Dawley rats were subjected to MDMA followed by intraperitoneal CGS (0.03 mg/kg) or SCH (0.03 mg/kg) injection. The hippocampi were then removed for western blot and RTPCR analyses. Administration of MDMA dose-dependently increased the expression of NF-κB both at mRNA and protein levels. We also found that administration of CGS following MDMA significantly increased the NF-κB expression especially in MDMA 20 +CGS group. By contrast, administration of the A2a-R antagonist SCH resulted in a dose-dependent decrease in NF-κB mRNA and protein. Our study results revealed that MDMA has powerful detrimental effects on expression of NF-κB in a dose-dependent manner. On the other hand, co-administration of A2a agonist (CGS) can protect against MDMA neurotoxic effects by increasing NF-κB expression levels; suggesting a potential application for protection against the neurotoxic effects observed in MDMA users.

Analytical Problems and Suggestions in the Analysis of Behavioral Economic Demand Curves

Behavioral economic demand curves (Hursh, Raslear, Shurtleff, Bauman, & Simmons, 1988) are innovative approaches to characterize the relationships between consumption of a substance and its price. In this article, we investigate common analytical issues in the use of behavioral economic demand curves, which can cause inconsistent interpretations of demand curves, and then we provide methodological suggestions to address those analytical issues. We first demonstrate that log transformation with different added values for handling zeros changes model parameter estimates dramatically. Second, demand curves are often analyzed using an overparameterized model that results in an inefficient use of the available data and a lack of assessment of the variability among individuals. To address these issues, we apply a nonlinear mixed effects model based on multivariate error structures that has not been used previously to analyze behavioral economic demand curves in the literature. We also propose analytical formulas for the relevant standard errors of derived values such as P max, O max, and elasticity. The proposed model stabilizes the derived values regardless of using different added increments and provides substantially smaller standard errors. We illustrate the data analysis procedure using data from a relative reinforcement efficacy study of simulated marijuana purchasing.

Thermomechanical properties of nanotubes in a thermosetting polyimide matrix: Relationship to the percolation threshold

The objective of this research is to more fully understand the structure–property relationships in multiwalled carbon nanotube (MWNT)/high performance thermosetting polymer nanocomposites. Nanocomposites containing up to 7wt.% MWNTs and a polyimide matrix (PETI-330) were characterized after curing and these characterization results were compared against similar nanocomposites containing carbon nanofibers (CNFs). Glass transition temperature values and thermomechanical testing indicated that the physical properties of the MWNT nanocomposites followed different trends at MWNT loadings less than and greater than the percolation threshold. In contrast, the CNF nanocomposites roughly showed a single relationship between physical property changes and CNF loading at the loadings studied here, which were all less than the percolation threshold. Overall, these results highlight the challenges in improving the properties of high performance matrices and suggest that MWNT network formation reduces reinforcement efficacy and that MWNTs can interfere with free radical curing processes.

Anti-anhedonic activity of long-term lithium treatment in rats exposed to repeated unavoidable stress

Behavioural and neurochemical responses to palatable food exposure represent an index of hedonic competence. In rats, a palatable meal increases extra-neuronal dopamine levels in the nucleus accumbens shell (NAcS) that confers to it incentive salience and reinforcing value. Repeated stress exposure decreases dopamine output and impairs the NAcS dopaminergic response to palatable food and the competence to acquire a vanilla sugar (VS)-reinforced instrumental behaviour [VS-sustained appetitive behaviour (VAB)]. Moreover, chronic stress exposure disrupts reactivity to aversive stimuli. A 3-wk treatment with lithium, the gold-standard treatment in bipolar disorder, tonically reduces NAcS dopamine output and the reactivity to aversive stimuli. However, it does not affect the dopaminergic response to VS and the competence to acquire VAB. This study investigated whether repeated lithium administration is endowed with anti-anhedonic activity. The NAcS dopaminergic response to VS and the competence to acquire VAB and sucrose self-administration (SA), in terms of fixed-ratio (FR)1, FR5 and progressive ratio schedules of reinforcement, were studied in saline or lithium-treated groups of non-food-deprived rats exposed or not to repeated unavoidable stress. Chronic stress exposure impaired the NAcS dopaminergic response to VS, acquisition of VAB and sucrose SA, in terms of FR1 and FR5 schedules of reinforcement and breaking point score. Repeated lithium treatment restored these parameters to control group values, even when treatment began in rats already showing an anhedonia-like condition. Since the breaking point defines the reinforcement efficacy of a hedonic stimulus, the present data suggest that lithium treatment is endowed with anti-anhedonic activity in rats.