Conflict analysis using surrogate safety measures (SSMs) has become an efficient approach to investigate safety issues. The state-of-the-art studies largely resort to video images taken from high buildings. However, it suffers from heavy labor work, high cost of maintenance, and even security restrictions. Data collection and processing remains a common challenge to traffic conflict analysis. Unmanned Aerial Systems (UASs) or Unmanned Aerial Vehicles (UAVs), known for easy maneuvering, outstanding flexibility, and low costs, are considered to be a novel aerial sensor. By taking full advantage of the bird’s eye view offered by UAV, this study, as a pioneer work, applied UAV videos for surrogate safety analysis of pedestrian-vehicle conflicts at one urban intersection in Beijing, China. Aerial video sequences for a period of one hour were analyzed. The detection and tracking systems for vehicle and pedestrian trajectory data extraction were developed, respectively. Two SSMs, that is, Postencroachment Time (PET) and Relative Time to Collision (RTTC), were employed to represent how spatially and temporally close the pedestrian-vehicle conflict is to a collision. The results of analysis showed a high exposure of pedestrians to traffic conflict both inside and outside the crosswalk and relatively risking behavior of right-turn vehicles around the corner. The findings demonstrate that UAV can support intersection safety analysis in an accurate and cost-effective way.
In nature, the folding and conformation of proteins can control the cell or organelle membrane permeability and regulate the life activities. Here we report the first example of synthetic polypeptide vesicles that regulate their permeability via ordered transition of secondary conformations, in a manner similar to biological systems. The polymersomes undergo a β‐sheet to α‐helix transition in response to reactive oxygen species (ROS), leading to wall thinning without loss of vesicular integrity. The change of membrane structure increases the vesicular permeability and enables specific transport of payloads with different molecular weights. As a proof‐of‐concept, the polymersomes encapsulating enzymes could serve as nanoreactors and carries for glucose‐stimulated insulin secretion in vivo inspired by human glucokinase, resulting in safe and effective treatment of type 1 diabetes mellitus in mouse models. This study will help understand the biology of biomembranes and facilitate the engineering of nanoplatforms for biomimicry, biosensing, and controlled delivery applications.
In this paper, we demonstrated the encapsulation of CdTe quantum dots (QDs) and ZnO nanorods (NRs) with a layer of mesoporous SiO 2 shell (pore size: 4.1 nm) for the purpose of integrating dualemission property into one common nanostructure. Within the core-shell CdTe/ZnO@SiO 2 nanocomposites, CdTe QDs and ZnO NRs provide visible emission and UV emission, respectively. The fluorescence intensity ratio of the dual emission can be tuned by altering the hydrolysis time of tetraethyl orthosilicate (TEOS). The core-shell CdTe/ZnO@SiO 2 nanocomposites exhibit very interesting photoluminescent behaviors after interactions with heavy-metal ions such as Hg 2+ , Pb 2+ , and Cu 2+ . The visible emission contributed by CdTe QDs was abnormally enhanced in a range of 20-90% at the concentration of Hg 2+ < 10 -8 M, Pb 2+ < 10 -5 M, and Cu 2+ < 10 -6 M, whereas the intensity of UV emission by ZnO NRs was kept constant in all cases. Consequently, the UV emission may serve as a reference. The mechanism of the fluorescence enhancement is presumed to be the adsorption of the metal ions by the trap sites and the resulting surface passivation of the QDs. The mesoporous silica shell of the nanocomposites also plays a key role in the process of fluorescence enhancement, which helps to protect the surface characteristics of QDs, prevent the flocculation of the particles, and promote the adsorption of Cu 2+ , Hg 2+ , and Pb 2+ ions. The variable visible emission in combination with the constant UV emission indicates that the as-prepared CdTe/ZnO@SiO 2 core/shell nanostructures may serve as novel biluminescent materials as well as reliable and sensitive fluorescence probes.
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