Fracture Mechanism of Nanocomposite of Metal and Graphene with Defect Pores.

Molecular dynamics simulations were performed to investigate the fracture mechanism and mechanical response of Ni/Graphene nanocomposites under nanoindentation. The effects of size and location of defect pores were explored by examining the pore structure transition, microstructure transition, variation of HCP atomic fraction and dislocation density with indentation depth, load-displacement relationship, and stress distribution. It was found that when the long edges of the pore are located along the longer dimension, the pores are fractured by indentation forces from the short edges. The closer the pore is to the indent, the smaller loading force is required for the pores to reach its fracture limit. For the long edges located along the transverse direction, the maximum indentation depth increases with the distance of the pore away from the indenter. The density of HCP atoms and dislocations in the composite gradually increases with the indentation depth. To understand the physical mechanism of the fracture behavior, we also evaluated the stress distribution in graphene at the fracture point.

Immature murine hippocampal neurones do not develop long-term structural changes after a single isoflurane exposure.

BACKGROUND: Studies in developing animals show that a clinically relevant anaesthesia exposure increases neuronal death and alters brain structure. In the hippocampal dentate gyrus, the anaesthetic isoflurane induces selective apoptosis among roughly 10% of 2-week-old hippocampal granule cells in 21-day-old mice. In this work, we queried whether the 90% of granule cells surviving the exposure might be 'injured' and integrate abnormally into the brain. METHODS: The long-term impact of isoflurane exposure on granule cell structure was studied using a transgenic mouse model fate-mapping approach to identify and label immature granule cells. Male and female mice were exposed to isoflurane for 6 h when the fate-mapped granule cells were 2 weeks old. The morphology of the fate-mapped granule cells was quantified 2 months later. RESULTS: The gross structure of the dentate gyrus was not affected by isoflurane treatment, with granule cells present in the correct subregions. Individual isoflurane-exposed granule cells were structurally normal, exhibiting no changes in spine density, spine type, dendrite length, or presynaptic axon terminal structure (P>0.05). Granule cell axon terminals were 13% larger in female mice relative to males; however, this difference was evident regardless of treatment (difference of means=0.955; 95% confidence interval, 0.37-1.5; P=0.010). CONCLUSIONS: A single, prolonged isoflurane exposure did not impair integration of this age-specific cohort of granule cells, regardless of the animal's sex. Nonetheless, although 2-week-old cells were not affected, the results should not be extrapolated to other age cohorts, which may respond differently.

Caudal and intravenous dexamethasone as an adjuvant to pediatric caudal block: A systematic review and meta-analysis.

BACKGROUND: Dexamethasone has become a popular additive for regional anesthesia. The aim of this meta-analysis was to assess the effectiveness of this additive on the duration of postoperative analgesia, postoperative vomiting, and possible adverse events in pediatrics. METHODS: We searched databases, conference records, and registered trials for randomized controlled trials. The databases included the Cochrane Library, JBI Database of Systematic Reviews, PubMed, ISI Web of Knowledge, Science-Direct, and Embase. Odds ratio, weighted mean difference, and the corresponding 95% confidence intervals were calculated using the REVMAN software, version 5.3, for data synthesis and statistical analysis, which following the PRISMA statement. The main outcomes were duration of postoperative analgesia (time from the end of surgery to first administration of analgesics as evidenced by a pain score) and postoperative vomiting. RESULTS: Seven studies were selected for this meta-analysis, involving 647 pediatric patients. All the patients were randomized to receive caudal or intravenous dexamethasone with caudal block (experimental group) or plain caudal block (control group). There was significantly longer duration of postoperative analgesia in the experimental group compared with control group (weighted mean difference: 238.40 minutes; 95% CI: 193.41-283.40; P < .00001). The experimental group had fewer patients who needed analgesics after surgery (odds ratio: 0.18 minutes; 95% CI: 0.05-0.66; P = .009). Additionally, the number of subjects who remained pain-free to 2, 6, 24, and 48 hours after operation was significantly greater in the experimental group than control group. Side effects in these 2 groups were comparable (odds ratio: 0.94; 95% CI: 0.34-2.56; P = .90). The incidence of postoperative vomiting was significantly decreased in the experimental group compared with control group (odds ratio: 0.29; 95% CI: 0.13-0.63; P = .002). CONCLUSION: Caudal and intravenous dexamethasone could provide longer duration of postoperative analgesia and reduced the incidence of postoperative vomiting with comparable adverse effects than plain caudal block. However, any additive to the caudal space carries with it the potential for neurotoxicity and that caution should always be exercised when weighting the risks and benefits of any additive. The result was influenced by small numbers of participants and significant heterogeneity.

Observation of ventilation effects of I-gel™, Supreme™ and Ambu AuraOnce™ with respiratory dynamics monitoring in small children.

The shortcomings of laryngeal mask airway (LMA™), such as upper airway obstruction and gastric distension or airway leakage, may limit its application in small children. The I-gel™ (I-gel), LMA-Supreme™ (LMA-S), and Ambu AuraOnce™ (Ambu) are three improvements upon these shortcomings. This study adopted respiratory dynamic monitoring to observe the ventilation parameters of the three laryngeal masks in small children. A total of 105 children were randomized into Ambu (n = 35), I-gel (n = 35), and LMA-S (n = 35) groups. Primary outcomes included leak pressure and respiratory dynamic data. Secondary outcomes included hemodynamic data and bispectral index values after induction (T0), time after successful laryngeal mask insertion (T1) and at three recording points every 10 min after insertion (T2, T3, and T4), as well as laryngeal mask related adverse reactions. The inspiratory/expiratory tidal volume per kilogram of body weight in the Ambu group was significantly different from those in the other groups (P < 0.05), while the leak pressure in the Ambu group was significantly lower (P < 0.05). At T3 and T4, the expiratory resistance values in the Ambu group were significantly lower than those in the LMA-S group (P < 0.05). We have shown that the three laryngeal masks provided secure ventilation in children <6 years of age by using continuous respiratory dynamic monitoring. We concluded that the I-gel presented a better sealing effect and fewer adverse reactions.

Giant flexoelectric response of uniformly dispersed BT-PVDF composite films induced by SDS-assisted treatment.

Polymer-ceramic composites are commonly used as flexoelectric films. In existing studies, the flexoelectric effect of composites are generally improved by adjusting the material structures or adding ferroelectric materials. Further improvement of flexoelectric response has encountered a bottleneck. Considering from a new perspective, this study innovatively proposes to prepare the uniformly dispersed BT-PVDF composite films with giant flexoelectric response by surfactant SDS-assisted treatment. According to the engineering applications, tilt sensors have been fabricated with the SDS/BT-PVDF composite films. The prepared tilt sensors can accurately sense the tilt change in a small-angle range (0-10°) between the coaxial connecting parts, the response signal changes significantly (49.25-72.35 mV/°), and the response speed can reach 0.166 s. The research provides a new idea for improving the flexoelectric response and also paves a way for developing tilt sensors through a low-cost, facile, and reliable method, showing potential applications including bending sensing and structural health monitoring.

Far-infrared transparent conductors.

The long-standing challenge in designing far-infrared transparent conductors (FIRTC) is the combination of high plasma absorption edge (λp) and high conductivity (σ). These competing requirements are commonly met by tuning carrier concentration or/and effective carrier mass in a metal oxide/oxonate with low optical dielectric constant (εopt = 2-7). However, despite the high σ, the transparent band is limited to mid-infrared (λp < 5 µm). In this paper, we break the trade-off between high σ and λp by increasing the "so-called constant" εopt that has been neglected, and successfully develop the material family of FIRTC with εopt > 15 and λp > 15 µm. These FIRTC crystals are mainly octahedrally-coordinated heavy-metal chalcogenides and their solid solutions with shallow-level defects. Their high εopt relies on the formation of electron-deficiency multicenter bonds resulting in the great electron-polarization effect. The new FIRTC enables us to develop the first "continuous film" type far-infrared electromagnetic shielder that is unattainable using traditional materials. Therefore, this study may inaugurate a new era in far-infrared optoelectronics.

ZFP36 protects against oxygen-glucose deprivation/reoxygenation-induced mitochondrial fragmentation and neuronal apoptosis through inhibiting NOX4-DRP1 pathway.

The imbalance of mitochondrial dynamics plays an important role in the pathogenesis of cerebral ischemia/reperfusion (I/R) injury. Zinc-finger protein 36 (ZFP36) has been documented to have neuroprotective effects, however, whether ZFP36 is involved in the regulation of neuronal survival during cerebral I/R injury remains unknown. In this study, we found that the transcriptional and translational levels of ZFP36 were increased in immortalized hippocampal HT22 neuronal cells after oxygen-glucose deprivation/reoxygenation (OGD/R) treatment. ZFP36 gene silencing exacerbated OGD/R-induced dynamin-related protein 1 (DRP1) activity, mitochondrial fragmentation, oxidative stress and neuronal apoptosis, whereas ZFP36 overexpression exhibited the opposite effects. Besides, we found that NADPH oxidase 4 (NOX4) was upregulated by OGD/R, and NOX4 inhibition remarkably attenuated OGD/R-instigated DRP1 activity, mitochondrial fragmentation and neuronal apoptosis. Further study demonstrated that ZFP36 targeted NOX4 mRNA directly by binding to the AU-rich elements (AREs) in the NOX4 3'-untranslated regions (3'-UTR) and inhibited NOX4 expression. Taken together, our data indicate that ZFP36 protects against OGD/R-induced neuronal injury by inhibiting NOX4-mediated DRP1 activation and excessive mitochondrial fission. Pharmacological targeting of ZFP36 to suppress excessive mitochondrial fission may provide new therapeutic strategies in the treatment of cerebral I/R injury.

mTOR-driven neural circuit changes initiate an epileptogenic cascade.

Mutations in genes regulating mTOR pathway signaling are now recognized as a significant cause of epilepsy. Interestingly, these mTORopathies are often caused by somatic mutations, affecting variable numbers of neurons. To better understand how this variability affects disease phenotype, we developed a mouse model in which the mTOR pathway inhibitor Pten can be deleted from 0 to 40 % of hippocampal granule cells. In vivo, low numbers of knockout cells caused focal seizures, while higher numbers led to generalized seizures. Generalized seizures coincided with the loss of local circuit interneurons. In hippocampal slices, low knockout cell loads produced abrupt reductions in population spike threshold, while spontaneous excitatory postsynaptic currents and circuit level recurrent activity increased gradually with rising knockout cell load. Findings demonstrate that knockout cells load is a critical variable regulating disease phenotype, progressing from subclinical circuit abnormalities to electrobehavioral seizures with secondary involvement of downstream neuronal populations.

Transport of polymer-modified nanoparticles in nanochannels coated with polymers.

Using molecular dynamics simulations based on explicit-solvent model, we study migration of polymer-modified nanoparticles through nanochannels coated with polymers. The polymers densely grafted on the spherical nanoparticle and the channel surface form spherical polymer brush (SPB) and planar polymer brush (PPB), respectively. The migration of the neutral polymer-modified nanoparticle is driven by electroosmotic flow (EOF). The effects of the electric field strength and the SPB-PPB interaction on polymer conformations and transport dynamics of the SPB are explored. The migration velocity of the SPB reduces as the interaction between the SPB and the PPB increases. For strong SPB-PPB interaction, the directional migration of the SPB can be triggered only after the electric field strength exceeds a critical value. The high EOF velocity forces the center of mass of the spherical nanoparticle to keep near the central region of the channel due to high shear rate close to the brush-fluid interface. Unlike electrophoresis of charged polymer-grafted spherical particles, the SPB adopts a more extended conformation in the plane perpendicular to the EOF direction.

Impact of mTOR hyperactive neurons on the morphology and physiology of adjacent neurons: Do PTEN KO cells make bad neighbors?

Hyperactivation of the mechanistic target of rapamycin (mTOR) pathway is associated with epilepsy, autism and brain growth abnormalities in humans. mTOR hyperactivation often results from developmental somatic mutations, producing genetic lesions and associated dysfunction in relatively restricted populations of neurons. Disrupted brain regions, such as those observed in focal cortical dysplasia, can contain a mix of normal and mutant cells. Mutant cells exhibit robust anatomical and physiological changes. Less clear, however, is whether adjacent, initially normal cells are affected by the presence of abnormal cells. To explore this question, we used a conditional, inducible mouse model approach to delete the mTOR negative regulator phosphatase and tensin homolog (PTEN) from <1% to >30% of hippocampal dentate granule cells. We then examined the morphology of PTEN-expressing granule cells located in the same dentate gyri as the knockout (KO) cells. Despite the development of spontaneous seizures in higher KO animals, and disease worsening with increasing age, the morphology and physiology of PTEN-expressing cells was only modestly affected. PTEN-expressing cells had smaller somas than cells from control animals, but other parameters were largely unchanged. These findings contrast with the behavior of PTEN KO cells, which show increasing dendritic extent with greater KO cell load. Together, the findings indicate that genetically normal neurons can exhibit relatively stable morphology and intrinsic physiology in the presence of nearby pathological neurons and systemic disease.

New design for highly durable infrared-reflective coatings.

The fundamental challenge in designing durable infrared-reflective coatings is achieving the ideal combination of both high reflectivity and durability. Satisfying these competing demands is traditionally achieved by deposition of durable layers on highly reflective metals. We overturn the traditional logic of 'first reflectivity and then durability' and propose an alternative of 'first durability and then reflectivity': First, a transition-metal compound is selected as a durable base; then its reflectivity is improved by incorporating silver/gold to form an alloy or by overcoating a multilayer stack. Two validation experiments prove that the new strategy works extremely well: the coatings thus obtained have infrared reflectivities close to that of aluminum, and their hardness and acid and salt corrosion resistances are 27-50, 400-1 500 and 7 500-25 000 times that of aluminum. The traditional mirror coating (e.g., Al/SiO2 films) is more suitable for moderate environments, while our mirror coating that was obtained by the new strategy (e.g., an Ag-doped hafnium nitride film) is more suitable for harsh environments, such as ones with dust, windblown sand, moisture, acid rain or salt fog. This work opens up new opportunities for highly durable infrared-reflective coatings and rejuvenates the study of transition metal compounds in a completely new area of optics.