How do children learn to cross the street? The process of pedestrian safety training

<p><b>Objective</b>: Pedestrian injuries are a leading cause of child death and may be reduced by training children to cross streets more safely. Such training is most effective when children receive repeated practice at the complex cognitive–perceptual task of judging moving traffic and selecting safe crossing gaps, but there is limited data on how much practice is required for children to reach adult levels of functioning. Using existing data, we examined how children's pedestrian skills changed over the course of 6 pedestrian safety training sessions, each composed of 45 crossings within a virtual pedestrian environment.</p> <p><b>Methods</b>: As part of a randomized controlled trial on pedestrian safety training, 59 children ages 7–8 crossed the street within a semi-immersive virtual pedestrian environment 270 times over a 3-week period (6 sessions of 45 crossings each). Feedback was provided after each crossing, and traffic speed and density were advanced as children's skill improved. Postintervention pedestrian behavior was assessed a week later in the virtual environment and compared to adult behavior with identical traffic patterns.</p> <p><b>Results</b>: Over the course of training, children entered traffic gaps more quickly and chose tighter gaps to cross within; their crossing efficiency appeared to increase. By the end of training, some aspects of children's pedestrian behavior was comparable to adult behavior but other aspects were not, indicating that the training was worthwhile but insufficient for most children to achieve adult levels of functioning.</p> <p><b>Conclusions</b>: Repeated practice in a simulated pedestrian environment helps children learn aspects of safe and efficient pedestrian behavior. Six twice-weekly training sessions of 45 crossings each were insufficient for children to reach adult pedestrian functioning, however, and future research should continue to study the trajectory and quantity of child pedestrian safety training needed for children to become competent pedestrians.</p

Nickel(II)-Catalyzed Site-Selective C–H Bond Trifluoromethylation of Arylamine in Water through a Coordinating Activation Strategy

The first example of nickel­(II)-catalyzed site-selective C–H bond trifluoromethylation of arylamine in water is established. In this transformation, a coordinating activation strategy is performed by the utilization of picolinamide as a directing group, and target products are obtained in moderate to good yields. In addition, the catalyst-in-water system can be reutilized eight times with a slight loss of catalytic activity and applied in the green, concise synthesis of acid red 266. Furthermore, a series of control experiments verify that a single-electron transfer mechanism is responsible for this reaction

Strategy for Fabricating Multiple-Shape-Memory Polymeric Materials via the Multilayer Assembly of Co-Continuous Blends

Shape-memory polymeric materials containing alternating layers of thermoplastic polyurethane (TPU) and co-continuous poly­(butylene succinate) (PBS)/polycaprolactone (PCL) blends (denoted SLBs) were fabricated through layer-multiplying coextrusion. Because there were two well-separated phase transitions caused by the melt of PCL and PBS, both the dual- and triple-shape-memory effects were discussed. Compared with the blending specimen with the same components, the TPU/SLB multilayer system with a multicontinuous structure and a plenty of layer interfaces was demonstrated to have higher shape fixity and recovery ability. When the number of layers reached 128, both the shape fixity and recovery ratios were beyond 95 and 85% in dual- and triple-shape-memory processes, respectively, which were difficult to be achieved through conventional melt-processing methods. On the basis of the classic viscoelastic theory, the parallel-assembled TPU and SLB layers capable of maintaining the same strain along the deforming direction were regarded to possess the maximum ability to fix temporary shapes and trigger them to recover back to original ones through the interfacial shearing effect. Accordingly, the present approach provided an efficient strategy for fabricating outstanding multiple-shape-memory polymers, which may exhibit a promising application in the fields of biomedical devices, sensors and actuators, and so forth

Bioinspired Polylactide Based on the Multilayer Assembly of Shish-Kebab Structure: A Strategy for Achieving Balanced Performances

Achieving balanced mechanical performances in a polymer material has long been attractive, but it is still a significant challenge. Herein, a nonadditive strategy was proposed by tailoring the crystalline structure of neat polylactide (PLA) through a layer-multiplying extrusion. Compared with normal PLA, the layer-multiplied material exhibited a 50% increase in tensile strength, a 4-fold improvement in elongation at break, and greatly enhanced resistance to heat distortion. To comprehensively understand the origin of the balanced performances, we carefully observed and analyzed the tailored crystalline structure. It was demonstrated that the multilayer-assembled shish-kebab structure was fabricated because of the iterative extensional and laminating effects occurring in the layer-multiplying process. Inspired by that process in nacres, the layer-packed shish-kebab skeleton was regarded as the strong phase possessing the ability to offer sufficient strength for resisting mechanical and thermal deformation. Meanwhile, the tenacious interfaces played a significant role in crack deflection and termination in achieving high ductility. More significantly, because no external additives are required, the layer-multiplied PLA is capable of maintaining high transparency as well as good biodegradability and biocompatibility, which gives it competitive advantages in packaging, biomedical, and tissue engineering applications

Structural Evolution and Toughening Mechanism of β‑Transcrystallinity of Polypropylene Induced by the Two-Dimensional Layered Interface during Uniaxial Stretching

The structure and morphology of β-crystals of isotactic polypropylene (iPP) are of great significance because β-crystals can improve the toughness and ductility of iPP. Toughening of β-spherulites, which was ascribed to phase transformation, has been extensively investigated. However, the toughening mechanism of other β-crystals with special structures and morphologies is not clear. In this study, β-transcrystallinity (β-TC), which showed a greater toughening effect than that of β-spherulite, was constructed through microlayered coextrusion. During uniaxial stretching, β-TC preferred to transform into an α-crystal, whereas β-spherulite preferred to transform to a smectic mesophase. The transformation degree of β-TC was much higher than that of β-spherulite. More importantly, the lamellar fragments from β-TC gradually rearranged along the stretching direction, accompanied by continuous absorption of energy. The special β–α phase transformation, high transformation rate, and rearrangement of lamellar fragments led to the highly improved toughness of the layered samples

Enhancing the Oxygen-Barrier Properties of Polylactide by Tailoring the Arrangement of Crystalline Lamellae

The gas-barrier properties of semicrystalline polymers can be significantly adjusted by tailoring the arrangement of their impermeable crystalline lamellae. In particular, the highest barrier efficiency is achieved when the arrangement of the lamellae stacks is perpendicular to the direction of gas diffusion. The work reported on in this paper provides a strategy to achieve such a lamellar arrangement with the aid of a self-assembly nucleator and a two-dimensional (2D) interface. PT (PLA + TMC-300) and PTG (PLA + TMC-300 + graphene) were coextruded to form alternating PT/PTG multilayers with different layer numbers. During isothermal treatment at 140 °C, the dissolved TMC-300 first self-assembles into solid-state fibrils that are perpendicular to the 2D PT/PTG-layered interface due to the induced effects of the graphene. Subsequently, these TMC-300 fibrils induce the epitaxial growth of PLA lamellae with a normal parallel to the fibrillar direction of the TMC-300. In this way, a designed arrangement where the PLA lamellae stack perpendicular to the direction of gas diffusion is achieved. As expected, the resulting PLA exhibits impressively enhanced gas-barrier properties: a decrease of 85.4% in the oxygen permeability coefficient (<i>P</i>_O₂) was observed for the 16-layer sample (0.7 × 10^–19 (m³·m)/(m²·s·Pa)) compared with the sample without layer structure. Through the construction of “lamellae-barrier walls” by tailoring the arrangement of the lamellae, this work provides a route to fabricate semicrystalline polymers with superior gas-barrier properties with great potential for use in high-barrier applications such as food packing, beverage bottles and fuel tanks

In Situ Formation of Microfibrillar Crystalline Superstructure: Achieving High-Performance Polylactide

As a biobased and biodegradable polyester, polylactide (PLA) is widely applied in disposable products, biomedical devices, and textiles. Nevertheless, due to its inherent brittleness and inferior strength, simultaneously reinforcing and toughening of PLA without sacrificing its biodegradability is highly desirable. In this work, a robust assembly consisting of compact and well-ordered microfibrillar crystalline superstructure (FCS) surrounded by slightly oriented amorphism, is achieved by a combined external force field. Unlike the classic crystalline superstructures such as shish-kebabs, cylindrites, and lamellae, the newfound FCS with diameter of about 100 nm and length of several tens of micrometers is aggregated with well-aligned crystalline nanofibers. FCS can serve as discontinuous fiber to self-reinforce the amorphous PLA; more importantly, FCS can also act as rivets to pin the propagating fibrillar crazes leading to the formation of dense fibrillar crazes during stretching, which dissipates much energy and translates the failure of PLA from brittle to ductile. Consequently, PLA with FCS exhibits exceptionally simultaneous enhancement in ductility, strength, and stiffness, outperforming normal PLA with increments of 728, 55, and 70% in elongation at break, strength, and modulus, respectively. Therefore, FSC exhibits competitive advantages in achieving high-performance PLA even for other semicrystalline polymers. More significantly, this newfound crystalline superstructure (FCS) provides a new structural model to establish the correlation between structure and performance