Laser waterjet heat treatment on super-hard materials

The use of the hybrid laser waterjet heat (LWH) treatment process to develop super-hard materials is a new field of research that has the potential to develop materials with hardness characteristics that compare with or exceed that of diamond. The research presented in this dissertation investigated the hardness improvement mechanism of boron nitride (BN) materials by investigating the optimization of LWH process parameters and studying the microstructural refinement of BN materials. The study of the LWH system parameters investigated the relationship between LWH system parameters and the BN materials’ hardness change ratio. Upon the study, the optimal LWH system parameters (laser fluence, laser beam overlap percentage, boron nitride composition, laser pass number, and laser intensity) were identified in order to maximize BN material hardness. For the BN material microstructure refinement study, scanning electron microscopy (SEM), Raman spectroscopy, and finite element methods (FEM) were used to investigate the microstructure of pre- and post-LWH-treated BN materials. Analytical and experimental approaches were conducted throughout all of the studies, and a variety of analysis techniques were applied. Results indicate that LWH treatment is a feasible approach to improve the hardness of select materials while providing a potential method to develop new super-hard materials for the tooling industry

Little Strings, Quasi-topological Sigma Model on Loop Group, and Toroidal Lie Algebras

We study the ground states and left-excited states of the A_{k-1} N=(2,0) little string theory. Via a theorem by Atiyah [1], these sectors can be captured by a supersymmetric nonlinear sigma model on CP^1 with target space the based loop group of SU(k). The ground states, described by L^2-cohomology classes, form modules over an affine Lie algebra, while the left-excited states, described by chiral differential operators, form modules over a toroidal Lie algebra. We also apply our results to analyze the 1/2 and 1/4 BPS sectors of the M5-brane worldvolume theory.Comment: 32 pages. Minor imprecisions and typos corrected. To appear in Nuclear Physics

Ultrahard Polycrystalline Cubic Boron Nitride Composite through Hybrid Laser/Waterjet Heat (LWH) Treatment

Ultra-hard materials that are chemically inert and thermally stable at high temperatures are desirable for enhancing machining and wear performance in demanding chemical and thermal environments. Single and polycrystalline diamonds are the hardest tool materials; however, at high temperatures, diamond reacts with ferrous alloys, losing its chemical inertness and thermal stability. In contrast, cubic boron nitride (cBN) has exceptional chemical and thermal stability but has much lower hardness (35-45 GPa). Increasing the hardness of BN is expected to fill the property gap in state-of-the-art tool materials as shown and to generate huge industrial interest for meeting the stringent design requirements such as machining optical surfaces and reducing the cost and time for machining ferrous materials. A novel laser/waterjet heat treatment (LWH) process is investigated to enhance the surface hardness of a dual phase boron nitride (BN) material composed of 50% cubic and 50% wurtzite phases. Results indicate that experimentally measured hardness increase is dependent on the processing parameter such as laser fluence and overlap between heat treatment passes. Statistical analysis is carried out to identify the processing parameter that result in maximum hardness increase

Ultrahard materials through surface heat treatment

Ultrahard materials that are chemically inert and thermally stable at high temperatures are desirable for enhancing machining and wear performance in demanding chemical and thermal environments. Single and polycrystalline diamonds are the hardest materials (75–100 GPa); however, at high temperatures, diamond loses its chemical inertness and thermal stability. In contrast, cubic boron nitride (cBN) has exceptional chemical and thermal stability but has much lower hardness (35–45 GPa). Increasing the hardness of BN to the level of diamond is expected to result in chemically and thermally inert ultrahard material that is suitable for range of demanding wear and machining applications. An innovative laser/waterjet heat treatment (LWH) technique was designed and applied to polycrystalline 50% cBN/50% wBN tool inserts to reach the hardness level of polycrystalline diamond. The LWH processing consisted of surface heating samples using a continuous wave CO2 laser beam followed by tandem waterjet quenching of the laser beam path to cause stress-induced microstructural changes. Dispersive Raman spectroscopy, high-resolution scanning electron microscope and surface grazing XRD were used to identify the BN phase signatures, grain size changes, and phase transitions. The laser-waterjet heat treatment increased the hardness of binderless cBN sample by 20% (nominal 60 GPa) while it increased the hardness of binderless cBN/wBN sample by 100% (nominal 75 GPa) reaching the hardness of polycrystalline diamond (65–80 GPa). Microstructural analysis of the samples revealed three major features due to heat treatment. First is the formation of amorphous phase as noted by presence of the interfacial layer at grain boundaries. Such phase is expected to introduce the grain-boundary strengthening mechanism via inhibiting ease of dislocation movement across the boundary. Second is the formation of zones with nanosized grains that are expected to increase the energy needed to introduce plastic deformation. Third is the extensive fragmentation and cracking of the lamellas that also reduced the effective grain size and may contribute to the strengthening. A combination of amorphous phase formation at the grain boundaries and nanosized grain formation are suggested as the mechanisms responsible for the increased hardness

Non-orthogonal cavity modes near exceptional points in the far field

Non-orthogonal eigenstates are a fundamental feature of non-Hermitian systems and are accompanied by the emergence of nontrivial features. However, the platforms to explore non-Hermitian mode couplings mainly measure near-field effects, and the far-field behaviour remain mostly unexplored. Here, we study how a microcavity with non-Hermitian mode coupling exhibits eigenstate non-orthogonality by investigating the spatial field and the far-field polarization of cavity modes. The non-Hermiticity arises from asymmetric backscattering, which is controlled by integrating two scatterers of different size and location into a microdisk. We observe that the spatial field overlaps of two modes increases abruptly to its maximum value, whilst different far-field elliptical polarizations of two modes coalesce when approaching an exceptional point. We demonstrate such features experimentally by measuring the far-field polarization from the fabricated microdisks. Our work reveals the non-orthogonality in the far-field degree of freedom, and the integrability of the microdisks paves a way to integrate more non-Hermitian optical properties into nanophotonic systems.Comment: 11pages, 4 figure

Hybrid Nanosecond Laser Processing and Heat Treatment for Rapid Preparation of Super-Hydrophobic Copper Surface

The super-hydrophobic copper surface was obtained by using a nanosecond pulsed laser. Different micro- and nano-structures were fabricated by changing the laser scanning interval and scanning speed, before heating in an electric heater at 150 °C for two hours to explore the effect of laser parameters and heat treatment on the wettability of the copper surface. It was found that the laser-treated copper surface is super-hydrophilic, and then, after the heat treatment, the surface switches to hydrophobic or even super-hydrophobic. The best super-hydrophobic surface’s apparent contact angle (APCA) was 155.6°, and the water sliding angle (WSA) was 4°. Super-hydrophobic copper is corrosion-resistant, self-cleaning, and dust-proof, and can be widely used in various mechanical devices

Development of Overweight Vehicle Permit Fee Structure in Illinois

Permits are one of the most effective and common tools for state agencies to regulate the operation of overweight and oversize vehicles by ensuring the safety of passenger and freight traffic and minimizing damage to pavements and bridges while promoting commerce and the safe movement of goods and services. Although the State of Illinois uses a relatively comprehensive permit system, many of its parts have not been revised for more than 30 years. Therefore, the objective of this study was to revise the current permit system by evaluating up-to-date impacts of overweight vehicles. In this study, impacts of overweight (OW) vehicles were evaluated in three aspects (bridge, pavement, and traffic safety) and individual fees were developed for each. The most recent databases on infrastructure condition and state-of-the-art prediction/ classification algorithms were employed to produce the realistic and up-to-date assessment of OW vehicles' impact. Finally, a combined permit fee was recommended as a function of miles to be traveled, as well as axle and weight information, by aggregating the calculated individual fees.IDOT-R27-152Ope

Longer screen time utilization is associated with the polygenic risk for Attention-deficit/hyperactivity disorder with mediation by brain white matter microstructure

Attention-deficit/hyperactivity disorder (ADHD) has been reported to be associated with longer screen time utilization (STU) at the behavioral level. However, whether there are shared neural links between ADHD symptoms and prolonged STU is not clear and has not been explored in a single large-scale dataset. Leveraging the genetics, neuroimaging and behavioral data of 11,000+ children aged 9-11 from the Adolescent Brain Cognitive Development cohort, this study investigates the associations between the polygenic risk and trait for ADHD, STU, and white matter microstructure through cross-sectionally and longitudinal analyses. Children with higher polygenic risk scores for ADHD tend to have longer STU and more severe ADHD symptoms. Fractional anisotropy (FA) values in several white matter tracts are negatively correlated with both the ADHD polygenic risk score and STU, including the inferior frontal-striatal tract, inferior frontal-occipital fasciculus, superior longitudinal fasciculus and corpus callosum. Most of these tracts are linked to visual-related functions. Longitudinal analyses indicate a directional effect of white matter microstructure on the ADHD scale, and a bi-directional effect between the ADHD scale and STU. Furthermore, reduction of FA in several white matter tracts mediates the association between the ADHD polygenic risk score and STU. These findings shed new light on the shared neural overlaps between ADHD symptoms and prolonged STU, and provide evidence that the polygenic risk for ADHD is related, via white matter microstructure and the ADHD trait, to STU. This study was mainly supported by NSFC and National Key R&D Program of China. [Abstract copyright: Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.

Entering the Era of Earth Observation-Based Landslide Warning Systems: A novel and exciting framework

Landslide early warning remains a grand challenge due to the high human cost of catastrophic landslides globally and the difficulty of identifying a diverse range of landslide triggering factors. There have been only a very limited number of success stories to date. However, recent advances in earth observation (EO) from ground, aircraft and space have dramatically improved our ability to detect and monitor active landslides and a growing body of geotechnical theory suggests that prefailure behavior can provide clues to the location and timing of impending catastrophic failures. In this paper, we use two recent landslides in China as case studies, to demonstrate that (i) satellite radar observations can be used to detect deformation precursors to catastrophic landslide occurrence, and (ii) early warning can be achieved with real-time in-situ observations. A novel and exciting framework is then proposed to employ EO technologies to build an operational landslide early warning system.This work was supported by the National Natural Science Foundation of China under grants 41801391, 41874005, and 41929001; the National Science Fund for Outstanding Young Scholars of China under grant 41622206; the Fund for International Cooperation under grant NSFCRCUK_NERC; Resilience to Earthquake-Induced Landslide Risk in China under grant 41661134010; the open fund of State Key Laboratory of Geodesy and Earth’s Dynamics (SKLGED2018-5-3-E); Sichuan Science and Technology Plan Project under grant 2019YJ0404; State Key Laboratory of Geohazard Prevention and Geoenvironment Protection Independent Research Project under grant SKLGP2018Z019; the Spanish Ministry of Economy and Competitiveness, the State Agency of Research, and the European Funds for Regional Development under projects TEC2017-85244-C2-1-P and TIN2014-55413-C2-2-P; and the Spanish Ministry of Education, Culture, and Sport under project PRX17/00439. This work was also partially supported by the U.K. Natural Environment Research Council through the Center for the Observation and Modeling of Earthquakes, Volcanoes, and Tectonics under come30001 and the Looking Inside the Continents From Space and Community Earthquake Disaster Risk Reduction in China projects under NE/K010794/1 and NE/N012151/1, respectively, and by the European Space Agency through the ESA-MOST DRAGON-4 project (32244 [4]). Roland Bürgmann acknowledges support by the NASA Earth Surface and Interior focus area

Effects of Sublethal Concentrations of Chlorpyrifos on Olfactory Learning and Memory Performances in Two Bee Species, Apis mellifera and Apis cerana

Chlorpyrifos is a widely used organophosphorus insecticide. The acute oral 24 h median lethal dose (LD50) value of chlorpyrifos in Apis mellifera and in Apis cerana was estimated to assess differential acute chlorpyrifos toxicity in both bee species. The LD50 values of chlorpyrifos in A. mellifera and in A. cerana are 103.4 ng/bee and 81.8 ng/bee, respectively, which suggests that A. cerana bees are slightly more sensitive than A. mellifera bees to the toxicity of chlorpyrifos. Doses half the acute LD50 of chlorpyrifos were selected to study behavioral changes in both bee species using proboscis extension response assay. A. mellifera foragers treated with chlorpyrifos showed significantly lower response to the 10% sucrose solution compared to control bees after 2, 24 and 48 h. Chlorpyrifos significantly impaired the olfactory learning abilities and 2 h memory retention of forager bees regardless of honey bee species, which may affect the foraging success of bees exposed to chlorpyrifos