Dissociable Early Attentional Control Mechanisms Underlying Cognitive and Affective Conflicts

It has been well documented that cognitive conflict is sensitive to the relative proportion of congruent and incongruent trials. However, few studies have examined whether affective conflict processing is modulated as a function of proportion congruency (PC). To address this question we recorded eventrelated potentials (ERP) while subjects performed both cognitive and affective face-word Stroop tasks. By varying the proportion of congruent and incongruent trials in each block, we examined the extent to which PC impacts both cognitive and affective conflict control at different temporal stages. Results showed that in the cognitive task an anteriorly localized early N2 component occurred predominantly in the low proportion congruency context, whereas in the affective task it was found to occur in the high proportion congruency one. The N2 effects across the two tasks were localized to the dorsolateral prefrontal cortex, where responses were increased in the cognitive task but decreased in the affective one. Furthermore, high proportions of congruent items produced both larger amplitude of a posteriorly localized sustained potential component and a larger behavioral Stroop effect in cognitive and affective tasks. Our findings suggest that cognitive and affective conflicts engage early dissociable attentional control mechanisms and a later common conflict response system

Fabrication of Tough Hydrogel Composites from Photoresponsive Polymers to Show Double-Network Effect

Inspired by the toughening mechanism of double-network (DN) gels, tough hydrogel composites with a sandwich structure were fabricated from photoresponsive polymers. By copolymerization of hydrophilic monomers, 2-ureidoethyl methacrylate (UM), and photoresponsive hydrophobic monomers, (2-nitrobenzyloxycarbonylaminoethyl methacrylate (NBOC)) at high concentrations, physical hydrogels that are soft and highly stretchable are formed due to the hydrophobic associations of NBOC, serving as dynamic crosslinkers. By UV irradiation, the physical crosslinking switches into chemical crosslinking, and the soft physical hydrogels transform into rigid and less stretchable chemical hydrogels. By UV curing the surface layers of the physical hydrogels, we prepared hydrogel composites having a sandwiched structure with two rigid outer layers and a soft inner layer. The molecular-level continuous interfaces and matched swelling ratios between the layers ensure the macroscale hydrogel composites’ high strength and toughness with a DN gel effect. The outer layers fracture preferentially at deformation, playing a role like the first network of a DN gel, while the inner layer maintains the integrity, playing a role resembling the second network. The evolution of the fracture morphology of the rigid layers gives useful insight into the internal fracture process of DN gels

Study on the damping properties of magnetorheological elastomers based on cis-polybutadiene rubber

Magnetorheological elastomers (MREs) are composed of magnetizable particles (iron particles) and a soft rubber-like matrix. Their mechanical properties, including modulus and damping capability, can be controlled by an external magnetic field. The damping properties of MREs, which play an important role in applications, depend mainly on particle content. This paper aims to investigate MRE’s damping capabilities by studying two categories of cis-polybutadiene rubber-based MREs: isotropic and structured MREs. Both isotropic and structured MRE samples with various iron particle contents (60, 70, 80 and 85 wt%) were fabricated and their damping properties were measured by using a modified dynamic mechanical analyzer (DMA) and a universal testing machine. The results show that the loss factor in the glass transition region decreases with the increment of iron particle content. The loss factors of structured MREs are lower than those of isotropic MREs when the iron particle contents are the same. Furthermore, dynamic testing was conducted to study the effect of strain amplitude, frequency and magnetic field on the loss factor of MREs. In addition, the stress-softening experiments indicate that the ratio of remaining strain energy versus initial strain energy shows a decreasing trend with iron particle content and loading time

Internal Damage Evolution in Double-Network Hydrogels Studied by Microelectrode Technique

Double-network (DN) hydrogels have attracted considerable attention owing to their unique mechanism to show extraordinary mechanical strength and toughness. Although the toughening mechanism of the DN gels, breaking of the relatively stiff and brittle first network as sacrificial bonds, is widely accepted, the microstructure and morphology evolution of the internal damage have hardly been revealed. In this study, we study the internal structures of the first network in partially damaged DN gels by using the microelectrode technique (MET) based on the Donnan effect of the polyelectrolyte first network. We measure the spatial distribution of the electric potential of the prestretched and then reswelled DN gels. From the anisotropic depth profiles of potential and reswelling ratio, the microstructures of DN gels at a scale larger than the microelectrode probe size (similar to 200 nm) are revealed at the preyielding, yielding, and strain-hardening regimes

Superior fracture resistance of fiber reinforced polyampholyte hydrogels achieved by extraordinarily large energy-dissipative process zones

Fiber reinforced soft composites (FRSCs) have been developed recently by combining tough but soft polyampholyte hydrogels with stiff yet flexible woven glass fabrics. In this work, we find that the soft composites show increased tearing resistance with sample size and achieve size-independent, exceptionally high tearing energy above a specific size on the centimeter scale. Such size-dependent tearing behavior correlates with the failure mode change from fiber pull-out to fiber fracture. These findings demonstrate that the rigid fibers in the soft matrices transmit force over a large distance, giving the composites very large process zones. Tremendous energy is dissipated in the large process zones, resulting in the superior fracture resistance of FRSCs. By saturation of the process zone size, the soft composites become extraordinarily tough, showing an intrinsic tearing energy of ~1000 kJ m−2 that outperforms other existing tough materials. These novel FRSC materials from hydrated biocompatible hydrogels fill the gap between soft materials and traditional rigid materials, as demonstrated by their high tensile modulus (several GPa) and strength (> 300 MPa), along with exceptionally high tearing toughness

Time-dependent mechanical behavior of tough hydrogels under multiaxial stretching

ABSTRACTUnderstanding the time-dependent mechanical behavior of tough and viscoelastic hydrogels under complex external loading is crucial. In this study, we utilized tough and viscoelastic hydrogels synthesized through the copolymerization of methacrylic acid and methacrylamide as a model system to investigate their mechanical behavior under multiaxial stretching across a wide range of strain rates. Three stretching modes examined were uniaxial, pure shear, and equal biaxial stretching. Our findings show that under equal biaxial stretching, the hydrogels exhibit higher mechanical properties and energy dissipation compared to uniaxial and pure shear stretching, owing to the greater contribution of hydrogen bonds to energy dissipation in the former stretching mode. Additionally, employing the time-elongation separability method during the stretching process, we observed that the relaxation of dynamic hydrogen bonds in the hydrogels only depends on stretching time, independent of the elongation ratio and stretching modes. We anticipate that this study will yield valuable contributions to the design of durable load-bearing soft materials, particularly in dealing with complex deformation and strain rate responses

[Effects of hippocampal stimulus on α₅ subunit of extrasynaptic GABA(A) receptor in kainic acid-induced epileptic rats]

METHODS: A total of 40 healthy male Sprague Dawley (SD) rats were randomly divided into 5 groups of epilepsy, sham operation, low-frequency stimulation (LFS), high-frequency stimulation (HFS) and normal control (n = 8 each). The expression of α₅ subunit of extrasynaptic GABA(A) receptor as well as the association with the curative effects of LFS were evaluated by behavioristics, real-time fluorogenic quantitative polymerase chain reaction (PCR) and Western blot. RESULTS: The kainic acid kindling rats had class V attack with a modeling success rate of 67%. After treatment, as compared with sham operation and epilepsy groups, the number of seizures decreased significantly in LFS and HFS treatment groups (P \u3c 0.01). But LFS and HFS treatment groups were compared, the number of seizures has no statistical significance (P \u3e 0.05). When sham operation and epilepsy groups were compared, the number of seizures was not statistically significant (P \u3e 0.05). The paired inter-group comparisons showed that LFS and HFS treatment groups and sham operation and epilepsy groups had significant differences in α₅ subunit mRNA and protein (P \u3c 0.01). No statistical significance existed between LFS and HFS treatment groups (P \u3e 0.05) or sham operation and HFS treatment groups (P \u3e 0.05). As compared with normal control group, LFS treatment and HFS groups had significant difference (P \u3c 0.01). CONCLUSION: Electrical hippocampal stimulation can effectively inhibit seizures. Both LFS and HFS are equally effective, but the former offers greater benefits. And an inhibition of extrasynaptic α₅ subunit plays an important role in seizure during hippocampal stimulation. OBJECTIVE: To observe the effects of electrical hippocampal stimulation of α₅ subunit of extrasynaptic GABA(A) receptor in kainic acid-induced epileptic rats, explore the optimal therapeutic parameters and elucidate the possible mechanism of electrical stimulation for hippocampal epilepsy