Automated Detection and Characterization of Cracks on Concrete using Laser Scanning

Accurate crack detection and characterization on concrete are essential for the maintenance, safety, and serviceability of various infrastructures. In this paper, an innovative approach was developed to automatically measure the cracks from 3D point clouds collected by a phase-shift terrestrial laser scanner (TLS) (FARO Focus3D S120). The approach integrates several techniques to characterize the cracks, which include the deviation on point normal determined using k-nearest neighbor (kNN) and principal components analysis (PCA) algorithms to identify the cracks, and principal axes and curve skeletons of cracks to determine the projected and real dimensions of cracks, respectively. The coordinate transformation was then performed to estimate the projected dimensions of cracks. Curve skeletons and cross sections of cracks were extracted to represent the real dimensions. Two cases of surface cracks were used to validate the developed approach. Because of the differences in definitions of the crack dimension in the three methods and due to the curve shape of the crack, the width and depth of cracks obtained from the cross-section method and manual measurement were close but slightly smaller than those measured by the projection algorithm; whereas the length of cracks determined by the curve-skeletons method was slightly larger than those obtained by the manual measurement and projection method. The real dimension of a crack has good agreements with real situations when compared with the results of the manual measurement and projection method

Janus-graphene: a two-dimensional half-auxetic carbon allotropes with non-chemical Janus configuration

The asymmetric properties of Janus two-dimensional materials commonly depend on chemical effects, such as different atoms, elements, material types, etc. Herein, based on carbon gene recombination strategy, we identify an intrinsic non-chemical Janus configuration in a novel purely sp$^2$ hybridized carbon monolayer, named as Janus-graphene. With the carbon gene of tetragonal, hexagonal, and octagonal rings, the spontaneous unilateral growth of carbon atoms drives the non-chemical Janus configuration in Janus-graphene, which is totally different from the chemical effect in common Janus materials such as MoSSe. A structure-independent half-auxetic behavior is mapped in Janus-graphene that the structure maintains expansion whether stretched or compressed, which lies in the key role of $p_z$ orbital. The unprecedented half-auxeticity in Janus-graphene extends intrinsic auxeticity into pure sp$^2$ hybrid carbon configurations. With the unique half-auxeticity emerged in the non-chemical Janus configuration, Janus-graphene enriches the functional carbon family as a promising candidate for micro/nanoelectronic device applications

Onset of Tethered Chain Overcrowding

We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature T-x increased, the PEO or PLLA lamellar crystal thickness d(L) increased as well as the reduced tethering density (σ) over tilde of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at (σ) over tilde*similar to3.7-3.8 as evidenced by an abrupt change in the slope between (d(L))(-1) and T-x. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks

Onset of tethered chain overcrowding

Physical Review Letters, 93(2): pp. 028301-1 -- 028301-4. Retrieved September 19, 2006 from http://www.materials.drexel.edu/SRG/chrisli.html. DOI: http://dx.doi.org/10.1103/PhysRevLett.93.028301We proposed an approach to precisely control the density of tethered chains on solid substrates using PEO-b-PS and PLLA-b-PS. As the crystallization temperature T-x increased, the PEO or PLLA lamellar crystal thickness d(L) increased as well as the reduced tethering density (σ) over tilde of the PS chains. The onset of tethered PS chains overcrowding in solution occurs at (σ) over tilde*similar to3.7-3.8 as evidenced by an abrupt change in the slope between (d(L))(-1) and T-x. This results from the extra surface free energy created by the tethered chain that starts to affect the growth barrier of the crystalline blocks

Genetic Interaction Maps in Escherichia coli Reveal Functional Crosstalk among Cell Envelope Biogenesis Pathways

As the interface between a microbe and its environment, the bacterial cell envelope has broad biological and clinical significance. While numerous biosynthesis genes and pathways have been identified and studied in isolation, how these intersect functionally to ensure envelope integrity during adaptive responses to environmental challenge remains unclear. To this end, we performed high-density synthetic genetic screens to generate quantitative functional association maps encompassing virtually the entire cell envelope biosynthetic machinery of Escherichia coli under both auxotrophic (rich medium) and prototrophic (minimal medium) culture conditions. The differential patterns of genetic interactions detected among >235,000 digenic mutant combinations tested reveal unexpected condition-specific functional crosstalk and genetic backup mechanisms that ensure stress-resistant envelope assembly and maintenance. These networks also provide insights into the global systems connectivity and dynamic functional reorganization of a universal bacterial structure that is both broadly conserved among eubacteria (including pathogens) and an important target

How Have Political Incentives for Local Officials Reduced Environmental Pollution in Resource-Depleted Cities?

Chinese resource-exhausted cities face more severe environmental pollution problems than other cities. In addressing these problems, the way local officials (usually senior party and government leaders) operate is very important, as their focus on political achievements may complicate how they manage environmental pollution in these cities. On the one hand, the traditional Gross Domestic Product-based quest for political achievement may lead top leaders to de-emphasize environmental pollution. On the other hand, changes made in 2003 to the way the performance of Chinese officials is evaluated have encouraged some local senior party and government leaders to pay more attention to environmental problems. Based on this, we analyze the relationship between political incentives and environmental pollution by applying the 2004–2014 panel data from 37 resource-exhausted cities. The findings reveal that firstly, among the factors which impact the environmental pollution of resource-exhausted cities, investment in fixed assets, foreign direct investment, industrial structure, per-capita education expenditure, and population density do not have a significant impact, thus indicating that local openness levels, the degree of industrial upgrading, and local investment in fixed assets are not the key variables in environmental pollution control. Secondly, the extent to which officials vie for political achievement affects environmental pollution in resource-exhausted cities. This depends upon whether the officials are municipal party secretaries or mayors; the former play a greater dynamic role in environmental pollution and have stronger robustness than the latter. The conclusion verifies both the existing authority structure of China and its effectiveness in the control of environmental pollution of resource-exhausted cities. That is to say, in contrast to the principles of the party committees, the mayors are in a subordinate position and often fail to fully and effectively exercise their functions. Accordingly, we point out that the selection of municipal party secretaries, rather than mayors, is particularly important in coming to terms with local environmental pollution

Thermotropic and Lyotropic Transitions of Concentrated Solutions of Liquid Crystalline Block Copolymers in a Liquid Crystalline Solvent

Rich phase structures and evolutions of the blends of smectic–nematic (S–N) liquid crystalline (LC) diblock copolymers and a nematic solvent (5CB) are investigated in a concentrated regime. These types of fully LC systems are macroscopically homogeneous with ordered phase-separated structures on the nanometer scale. By varying the temperature as well as the content of 5CB, the phase diagram of the blends is constructed, where the order-to-order transition (OOT) between lamellar and cylindrical nanostructures can be induced either lyotropically or thermotropically. The temperature and concentration dual-responsive properties are found to be closely related to the selectivity and distribution of 5CB, in addition to its phase transformation at the nematic–isotropic transition. As inferred from the miscibility and phase behaviors of its blends with the respective smectic and nematic homopolymers, the partition of 5CB in the S–N diblock copolymers and its influence on the phase structures reveal the important role of the LC interactions on the self-assembly of the diblock copolymers

Anomalous anisotropic negative Poisson's ratio in novel X2_2Y2_2-type transition metal chalcogenides with promising optical absorption

The search for two-dimensional (2D) materials with intrinsic auxetic behavior has always been a desire in materials science. Herein, from advanced first-principles calculations, we identify a novel two-dimensional transition metal chalcogenides (TCMs) monolayer X$_2$Y$_2$-type (X=Cu, Ag, Au and Y=O, S, Se) TCMs. Further, its mechanical, electrical and optical properties are investigated. X$_2$Y$_2$-type TCMs electrically possess semi-metallic and semiconducting properties and optically exhibit excellent phonon absorption. Most importantly the Cu$_2$Se$_2$ monolayer unconventionally demonstrates an anisotropic negative Poisson's ratio (NPR) while other binary compounds of the same main group are absent. The combination of these excellent properties offers splendid potential for further applications of X$_2$Y$_2$-TCMs. In particular, the intrinsic negative Poisson's ratio can make Cu$_2$Se$_2$ monolayer a promising mechanical material in electronics and mechanics

Dielectric Chain Dynamics of Side-Chain Liquid Crystalline Polymer

Both chain dynamics and statistics of side-chain liquid crystalline polymer are experimentally explored. Dielectric measurements over a wide range of frequencies and temperature windows demonstrate that the chain dynamics in the liquid crystalline phase (SmA) is retarded and has higher apparent activation energy compared to that in isotropic melt. The molecular weight dependence of the normal mode relaxation time in the isotropic melt conforms to the Zimm model with excluded volume effect, while it shows Rouse behavior in the liquid crystalline phase. The mean squared end-to-end distance of polymer chain in the liquid crystalline phase decreases compared to that in the isotropic melt. The main chain takes a self-avoiding walk with ⟨<i>R</i>_e²⟩ ∼ <i>N</i>^2ν, ν = 0.54–0.6 in the isotropic melt, whereas a random walk between smectic layers with ν ≅ 0.5, consistent with the results from chain dynamics

Hierarchical Nanostructures and Self-Assemblies in Smectic-Nematic Liquid Crystalline Diblock Copolymers

Coexistence of smectic and nematic orders in 3D curvaceous bicontineous cubic or hexagonal hierarchical structures is observed in a novel class of nanophase separated, flexible double liquid crystalline (LC) diblock copolymers of different molecular weights (MWs) but similar compositions, obtained via sequential anionic polymerization. The diblock copolymer of higher MW exhibits an exceptional order–order transition (OOT) from lamellae (Lam) to hexagonal-packed cylinder (HPC) upon nematic ordering. In contrast, the polymer with lower MW forms a thermodynamically stable, ordered gyroid structure, interwining with LC defects on nanoscale. Delicate balance of collective LC interactions and geometric frustration dictates this unique behavior, which offers a genuine way to fine-tune 2D and 3D complex structures with sub-10 nm feature sizes