Search

In this paper, a novel scheme is proposed to obtain the single-mode laser using parity-time symmetry breaking. Four analogue micro-rings are optically coupled in the square configuration in a way that two micro-rings on the square diameter experience gain and the other two experience loss. The coupling coefficient for horizontal and vertical coupling between micro-rings is considered to be different. According to this new scheme, the symmetry of structure is destroyed, and thus the degenerate modes that can disrupt the stability of laser, disappeared. Due to the coupling of the resonators, four super-modes, which are coupled pairwise, are generated. The Eigen-frequency and parity-time symmetry breaking of the two super-modes depend on the difference between horizontal and vertical coupling coefficient; however, these parameters depend on the summation of the coupling coefficients for the other two. Results show that the laser output is single mode in a specific condition of coupling coefficient and gains. It is concluded that the threshold of pump parameter is improved in the new scheme, relative to the two coupled micro-rings. [ABSTRACT FROM PUBLISHER]

Raman spectroscopy has been used extensively on meteoritic samples since it is a nondestructive tool that provides information about their structure and mineralogical composition, which can give important clues about planet formation. However, the power of the excitation laser used in this technique can alter the properties of the samples due to thermal effects. In this undergraduate research work, the laser-induced thermal effects produced on the carbonaceous chondritic meteorite Northwest Africa 6603 were studied in detail by analyzing the low- and high-resolution Raman spectra parameters of the minerals found in the inclusions and matrix of this sample as a function of the excitation power. Olivine (forsterite), graphitic carbon, pyroxene (enstatite), hematite and gehlenite were the minerals identified in the studied regions. The Raman parameters of these minerals were affected by the laser power to a greater or lesser extent, indicating an increase in structural disorder. In general, the alterations observed were permanent (reverse changes were not observed). These thermal effects were correlated with the topography of the irradiated regions by analyzing their changes using optical microscopy. The micrographs of a few regions showed changes on their topography after irradiating the regions with the maximum applied power (e.g., more depressed areas). These findings exhibited strong evidence of the thermal effects induced by the laser power on the materials found in this fragment, which must be considered to avoid alterations of the physical and chemical properties of the meteoritic samples. In addition, this work presents the first study done on the mineralogical composition of Northwest Africa 6603 using Raman spectroscopy. Furthermore, from an educational standpoint, this project exposed the involved undergraduate physics students to numerous research steps (e.g., experiment preparation, data acquisition/analysis, and manuscript preparation) which provided them with a broad spectrum of valuable scientific and technical tools for their future careers. [ABSTRACT FROM AUTHOR]

NiCrAl/20%WC coatings were prepared by laser cladding on 45 steel under different technological parameters. The effects of technological parameters on the microstructure, microstructure, hardness and wear resistance were investigated. The results show that with the increase of the scanning speed, the height, width, depth and dilution rate of the cladding layer gradually decrease, the microstructure becomes smaller and smaller, the hardness gradually increases, and the wear amount decreases first and then increases, and the wear amount is the least when the scanning speed is 600 mm/min. With the increase of laser power, the height, width, depth and dilution rate of cladding layer gradually increase. The hardness gradually decreases; The wear decreases first and then increases, and the wear is the least when the laser power is 1.2 kW. [ABSTRACT FROM AUTHOR]

The lack of uniform and objective techniques to evaluate treatment efficacy in photo-epilation studies leads to contradictory results. Thus, there is an urgent need to explore commonly accepted assessment tools. One of the most common methods uses hair counts via digital photography. However, macrophotography may not be able to depict the vellus-like hair induced by photo-epilation. On the other hand, handheld dermatoscopy is practical, affordable and offers high-quality magnification. Hair counts from a handheld dermatoscope and a digital camera were compared in 73 women who underwent 6 sessions with the Alexandrite 755 nm laser. Significantly more hairs were counted using the dermatoscope than using the digital camera (76.9 ± 41.3 vs. 58.6 ± 31.4, p <.005), independently of hair thickness and hair density. The difference in hair counts between the two instruments was inversely related to hair thickness and directly related to hair density. The handheld dermatoscope may be a more effective tool than the widely used digital camera in evaluating the response to laser hair removal treatment. [ABSTRACT FROM AUTHOR]

The high lustre and desirable aesthetics of stainless steels have resulted in their application for decorative purposes in a variety of industries including homeware and automotive, but primarily in architecture. It is possible to further enhance the aesthetics of stainless steel by imparting a thin coloured film on the surface that does not impair any inherent desirable properties, including corrosion resistance. There are two different types of thin coloured films, iridescent and non-iridescent. Iridescent colour can visually change depending on the angle from which it is viewed and is a consequence of a phenomenon known as thin film interference. Non-iridescent colour is created by the absorbance of light waves of all but a given wavelength, the colour is intrinsic to the thin film and does not change with viewing angle. For the purpose of this review, colouring techniques have categorised into three groups, electrochemical, non-electrochemical and laser colouring. Laser colouring can be utilised as either an electrochemical or non-electrochemical process and is particularly suited to colouring small areas and intricate shapes. Non-electrochemical techniques, such as physical vapour deposition (PVD) and thermal tinting, avoid the use of toxic chemicals, however, they present other challenges, including energy consumption and scrappage rate. The use of non-electrochemical and laser techniques to colour stainless steel can negate the use of toxic hexavalent chromium; however, they are yet to be widely adopted by industry for this purpose. Therefore, it is important to consider each technique to understand why this is the case. The present Part 2 of the review discusses non-electrochemical and laser processes used to produce coloured films on stainless steel, whereas Part 1 discussed the electrochemical processes. [ABSTRACT FROM AUTHOR]

We report on a compact 808 nm diode-pumped passively Q-switched (PQS) Nd:YVO4 laser at 1064 nm with black phosphorus (BP)/ indium selenide (InSe) heterostructure as a saturable absorber (SA). When the transmission of the output coupler (OC) was 30%, the maximum continuous-wave (CW) output power of 10.3 W was obtained with a slope efficiency of 52.4% under the incident pump power of 22 W. The maximum average output power of 3.1 W was obtained at 9.29 W pump power, corresponding to the repetition rate of 598 kHz and the pulse width of 455 ns during pulse operation, further power scaling was limited by the damage threshold of the saturable absorber mirror (SAM). The results sufficiently validated that two-dimensional (2D) BP/InSe heterostructure could be used as an optical modulator for near-IR pulsed laser sources. [ABSTRACT FROM AUTHOR]

Angled surfaces are significant for obtaining complex 3D glass structures to be employed in precise optical components such as light guides. However, it is challenging to fabricate angled structures in glass with high precision. In this study, femtosecond laser irradiation followed by a chemical etching process is used to create a 45-degree angled surface. The roughness values of the angled top and bottom surfaces are compared and the parameters are optimized to achieve maximum surface quality. A 45-degree angled surface with <300 nm roughness and <±0.5° deviation is obtained in a given area of 1 × 1.5 mm2. Using this approach, various complex structures have been successfully fabricated with high quality and precision. Results indicate that this method can be adapted to the high-precision glass manufacturing industry. [ABSTRACT FROM AUTHOR]

Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080TM pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering. [ABSTRACT FROM AUTHOR]

One of the most revolutionary aspects of Laser Powder Bed Fusion (LPBF) is to be able to lift the design constraints from conventional manufacturing. However, as a rule of thumb, any surfaces lower than 45° with respect to the horizontal plane would still require sacrificial supports in order to complete the printing. Fundamentally, it is unclear whether it is feasible to print a 1st layer 0° overhang nor how the print parameters for the 1st layer can be optimised. This research demonstrates that large 1st layer 0° overhangs can be printed with a coverage above 90%. For the first time, the parameter space of laser power, scan speed and hatch spacing for the 1st layer has been simultaneously explored efficiently. The use of the rate of change of the mushy zone is proposed for the parameter selection instead of the average melt pool temperature. Adaptive Parameter 28 (AP28: 250W_4000 mm/s_50 µm) is the best choice. Several surface morphological phenomena are discussed. The core parameter (285W_960 mm/s_110 µm) causes severe balling and its mechanism is revealed. The average melt pool temperature of the 1st layer by the core parameter is lower than that of the bulk. The ramifications beyond the 1st layer are also illustrated. [ABSTRACT FROM AUTHOR]

Experiments on Laser powder bed fusion (LPBF) of powdered Ti on Al2O3 substrate were conducted and the interface formation was studied using a multi-material fluid dynamics model. Results show that the melt pool is relatively shallow, with relatively flat interlayer interface under LPBF's conduction mode. In this condition, a thin sheath of molten Al2O3 forms and acts as a lubricating film for the molten Ti, leading to Rayleigh instability due to high flow inertia. Keyhole formation penetrates the Al2O3 substrate, resulting in a wavy interlayer interface. The recoil pressure from the keyhole and overall melt inertia are suppressed by the highly viscous molten Al2O3, thereby improving single-track melt pool stability. However, the thermal expansion coefficient difference between Ti and Al2O3 led to the formation of transverse cracks. Achieving a defect-free metal-on-ceramic single track remains a challenge, despite this study serving as a guide for melt track and interface control. [ABSTRACT FROM AUTHOR]

The high cost of laser powder bed fusion (LPBF) fabricated high-strength Sc containing aluminium alloy hinders its applications. To reduce the cost, we reported a LPBF fabricated strong and ductile Al--Mn--Mg--Sc--Zr alloy using large layer thicknesses to improve the fabrication efficiency on coarse powder particles. A high relative density exceeding 99.2% was achieved at layer thicknesses up to 120 μm. In post-process heat-treated specimens, the yield strength only had a slight 6% decrease from layer thickness of 30 to 120 μm; such a decrease in strength was attributed to the larger grain size resulted from the adopted larger layer thickness. The fabricated sample at layer thickness of 120 μm still exhibited high tensile yield strength of 472 MPa and fracture strain of ~10%. This work showed a successful application of improving the LPBF fabrication efficiency of highstrength Al--Mn--Mg--Sc--Zr alloy using large layer thickness in LPBF process. [ABSTRACT FROM AUTHOR]

Laser powder bed fusion (L-PBF) is one of the most widely used metal additive manufacturing technology for fabrication of functional and structural components. However, inconsistency in quality and reliability of L-PBF products is still a significant barrier preventing it from wider adoption. Machine learning (ML) of monitoring data offers a unique solution to effectively identify possible defects and predict the quality of L-PBF products. In this work, we introduce a semi-supervised ML approach to detect anomalies that occurred in L-PBF products. We train the ML model to classify surface appearances in the reference monitoring data. We then correlate the classified appearances to post-process characteristics, e.g. surface roughness, morphology, or tensile strength. We demonstrate that the established correlation enables the determination of key appearances indicative of the quality of the printed samples including anomaly-free, lackof- fusion and overheated. We further validate our ML approach by performing prediction on test samples having various geometries. [ABSTRACT FROM AUTHOR]

In-situ co-axial meltpool monitoring has become a popular tool for digitising the laser powder bed fusion (L-PBF) process, providing baseline data for certification. Each layer produces an image where the pixel position represents the laser coordinates and the pixel intensity denotes the sensor response. The 3D image stacks represent the infrared emission during the manufacturing of the physical component. However, interpreting monitoring data remains a challenge. To address this issue, this study evaluates the performance of a near-infrared photodiode in detecting typical geometrical features such as porosity and overhanging structures ranging from the micro-to-meso scale. Monitoring data is highly sensitive to heat accumulation around overhanging structures and can quantify dross formation based on hotspots. Cold spots, which represent a lack of fusion porosity at scan track intersections, can indicate a probability of defect formation. However, the sensitivity and predictive value of monitoring data for porosity are low due to the healing of defects in subsequent layers. Local process variables, such as the scan strategy and part orientation, significantly influence dross and hot spot formation. This study shows the potential of NIR photodiodes in deriving metrics for in-line certification of L-PBF components, leading to improved process control and quality assurance. [ABSTRACT FROM AUTHOR]

Developing high-performance high-entropy alloys (HEAs) fabricated by laser additive manufacturing (LAM) is the pursuit of the metallic community. In the present work, we designed a series of [(Al6-xNbx)-(FeCoNi)12]Cr3 HEA compositions using a high-entropy alloying strategy based on a cluster-plus-glue-atom model. And their thin-wall-sharped bulks were fabricated by LAM and post-aging treatment. The effects of cracking inhibition and microstructure evolution on the tensile properties were researched in detail. The results show that as the Nb substitutes for Al atoms, the cracking behaviour is ameliorated, ascribed to the tiny Laves phase refined the dendrite spacings and back-filled in the inter-dendritic liquid film. Also, introducing Nb atoms improves the strength but deteriorates the ductility. Significantly, the Nb4 HEA possesses the best tensile-property combination (i.e. σs ~ 419.2 MPa, σb ~ 787.4 MPa, and δ ~ 15.5%) with a strain mechanism of dislocation slip mode. After post-aging for 72 h, the microstructure comprises fully recrystallized equiaxed FCC grains and many tiny needle-like D019 precipitates, leading to high strength and sufficient ductility (i.e. σ0.2 ~ 535.9 MPa, σb ~820 MPa and δ value of 8.9%). These findings provide a new paradigm for the LAM of crackfree HEAs with excellent mechanical properties. [ABSTRACT FROM AUTHOR]

The Invar 36 alloy was additively manufactured by laser powder bed fusion (PBF-LB), and systematical observations and experiments for microstructure, defects, metallography, especially high cycle fatigue behaviour and fractography were conducted. Inadequate laser energy density results in hardly overlapping melting traces, generating numerous defects. Accordingly, the fabricated Invar 36 alloy presents an inferior high cycle fatigue life, as it failures from the rapid aggregation of the defects. In contrast, an adequate laser energy density remarkably enlarges the overlapping between adjacent melting traces. The large molten pools with steady boundaries are beneficially to generate favourable microstructures and low porosity. Consequently, the Invar 36 alloy shows superior high cycle fatigue life, completely generated from small crack propagation, long crack propagation and final fracture stages. Above experimental results and analysis primarily link up the PBF-LB process, microstructures (defects) and high cycle fatigue performance for PBF-LB Invar 36 alloy. [ABSTRACT FROM AUTHOR]

The relationship between processing parameters, microstructure, and mechanical properties of Al-8.3Fe-1.3V-1.8Si alloy processed by laser powder bed fusion is seldom studied. Therefore, fully dense alloys with two parameters were selected to investigate this key issue. The results show that the alloy with low power and scanning speed (S200) shows fan-shell-shaped melt pools and laser tracks while another (S350) shows a deeper and wider melt pool. Both alloys obtain a heterogeneous microstructure without a secondary phase in melt pool (MP) and a nano-sized phase in melt pool boundary (MPB). The difference between solid-solution strengthening and Orowan strengthening in MP and MPB contributes to the difference in compressive yield strength (S200: 380 ± 14 MPa and S350: 705 ± 16 MPa), and heterogeneous nano-hardness results in different crack behaviours and failure strains. This work indicates that adjusting processing parameters is an effective method to control microstructure and mechanical properties of this alloy. [ABSTRACT FROM AUTHOR]

Lattice structures are widely used in the industry for aerospace, automotive and biomedical applications as they are strong yet lightweight. Due to the complex geometry, lattice structures are mostly fabricated with additive manufacturing (AM). Despite AM having many advantages compared to traditional manufacturing methods, defects such as cracks and pores are commonly found in AM-produced samples, which could affect their actual performance. Thus, in this work, finite element analysis (FEA) is used to study the mechanical performances of insitu alloyed titanium-tantalum (TiTa) lattice structures fabricated using laser powder bed fusion (L-PBF). Based on the established experimental data, the CAD models of the as-fabricated samples are reproduced and analysed using two modelling approaches. It is found that the elastic modulus is well-predicted by both simulation methods with high accuracy, while the yield strength is highly underpredicted by the two models for around 50% and 65% respectively. The FEA model is then used to analyse the performances of uniform lattice structures with 50% to 90% porosity and the results are found in agreement with the Gibson- Ashby model. To further improve the prediction accuracy of the simulation, more information on the defect condition is needed. [ABSTRACT FROM AUTHOR]

Node-strengthened hybrid structures with lower relative density inspired by solid solution strengthening mechanism, namely the edge center interstitial lattice (ECIL) structures and vertex node substitutional lattice (VNSL) structures were designed and fabricated by laser powder bed fusion (LPBF). The geometric feature-dependent defects distribution, the intense microstructure sensitivity as well as the node size effect on the mechanical response were investigated. The microstructure sensitivity induced by geometric feature was found to be related to the different supporting condition and distinctive thermal history. ECIL-1.5 structure possessed the highest plateau stress of 1.79 MPa and the largest crush force efficiency of 59.1%, which increased by 59.8% and 15.2% compared to the initial face centre cubic with z-struts (FCCZ)structure. VNSL-1.5 exhibited the greatest specific energy absorption of 14.6 J/g, demonstrating the highest strengthening efficiency was achieved at the critical sphere diameter to strut thickness (Sphstrut) ratio of 3. This method further improved lightweight efficiency, indicating the inherent strengthening mechanism of crystal materials could guide the design of metamaterials. [ABSTRACT FROM AUTHOR]

Laser powder bed fused (LPBFed) AlSi10Mg is recognised for its superior mechanical properties. However, its thermal stability has never been justified. Herein, we exposed as-built AlSi10Mg to different temperatures (200-500°C) for only 3 min to evaluate its thermal stability. Results showed that LPBFed AlSi10Mg had relatively low thermal stability. Only 3 min of thermal exposure at 200°C would deteriorate its tensile strength dramatically. Microstructural analysis revealed that with increasing thermal input, as-built AlSi10Mg exhibited a microstructural evolution similar to annealing of cold-worked metals, namely recovery, recrystallisation followed by grain-growth. The excessive energy stored in as-built microstructure due to fast cooling during LPBF was deduced as the driving force for this phenomenon. Therefore, such microstructural change was at the expense of dislocations stored in the as-built material, which in turn caused deterioration in tensile strength. The present findings may provide guidance for the application of LPBFed AlSi10Mg. [ABSTRACT FROM AUTHOR]

Ablative laser technology has been in use for many years now. The large side effect profile however has limited its use. Fractional ablative technology is a newer development which combines a lesser side effect profile along with similar efficacy. In this paper we review fractional ablative laser skin resurfacing. [ABSTRACT FROM AUTHOR]

Provides historical comments on the pumping of masers and lasers. Research in the field of molecular microwave spectroscopy in the decade after World War II; Independent research efforts on the ammonia beam maser by Basov and Prokhorov; Masers and quantum electronics; Methods to obtain an inverted nuclear spin system; Optical pumping; Relevance of the multilevel pumping scheme.

The high-energy lasers of the 1980s were unwieldy assemblages of tanks, tubes, and plumbing that produced light by burning flowing gases, and the space shuttle was not ready for "space trucking." In the decades since then, though, laser technology has come a long way, and the giggle factor of these technologies – dubbed "Star Wars" weapons by their detractors – is gone. High-energy solid-state lasers, not available in the Reagan era, are now being tested to shoot down rockets, mortars, and drones at hundreds of meters or more on the battlefield. Their success so far has led the Pentagon to reconsider high-energy lasers and other directed energy weapons for missile defense and perhaps other military applications on the fringes of space and in orbit. But are new actors merely making the same mistakes again, in an updated setting? [ABSTRACT FROM AUTHOR]

Onychomycosis is difficult to treat due to long treatment durations, poor efficacy rates of treatments, high relapse rates, and safety issues when using systemic antifungal agents. Device-based treatments are targeted to specific regions of the nail, have favorable safely profiles, and do not interfere with systemic agents. They may be an effective alternative therapy for onychomycosis especially with increasing reports of squalene epoxidase gene mutations and potential resistance to terbinafine therapy. In this review, we discuss four devices used as antifungal treatments and three devices used as penetration enhancers for topical agents. Lasers, photodynamic therapy, microwaves, and non-thermal plasma have the capacity to inactivate fungal pathogens demonstrated through in vivo studies. Efficacy rates for these devices, however, remain relatively low pointing toward the need to further optimize device or usage parameters. Ultrasound, nail drilling, and iontophoresis aid in improving the permeability of topical agents through the nail and have been investigated as adjunctive therapies. Due to the paucity in clinical data, their efficacy in treating onychomycosis has not yet been established. While the results of clinical studies point toward the potential utility of devices for onychomycosis, further large-scale randomized clinical trials following regulatory guidelines are required to confirm current results. [ABSTRACT FROM AUTHOR]

This study focuses on the issue of uncontrollable debris generated by laser-matter interactions in high-power laser facilities, which significantly impairs operational efficiency. The maximum motion distance of debris, referred to as the safety distance, is a crucial parameter that this work investigates. Three prediction methods that utilize aerodynamic coefficients and trajectories are proposed, with input parameters derived from velocity curves extracted from high-resolution time-resolved images. The results obtained from these methods show good agreement with experimental data collected under laser fluence conditions ranging from 18 to 79 J/cm2 that damage the rear surface of fused silica. The analytically predicted safety distance, with an input velocity fitted at 0 ns and an upper diameter limit of 10 µm, was closest to the experimental result at 155 mm. Analytically predicted values with input velocities fitted at 13,000 ns and all diameter ranges did not exceed 192.3 mm. Numerically predicted values, with input velocity fitted at 13,000 ns and a median diameter of small debris (5 µm), were 140.4 and 295.2 mm for aspect ratios of 2 and 4, respectively. The numerical method is recommended for predicting the safety distance in high-power laser facilities, but obtaining accurate estimates of transient velocity is crucial for the method's effectiveness. [ABSTRACT FROM AUTHOR]

This work presents a critical overview and an integrated application of two of the most promising digital technologies for the conservation of heritage buildings. On the one hand, the work discusses and evaluates the laser scanning technology and its current applications to preserving heritage buildings. On the other hand, the fundamentals and recent practices in 360° imaging are analysed. Finally, both technologies are integrated in two emblematic study cases, i.e. a large Neo-Manueline church in Portugal and a small Romanesque church in Spain, with the aim of creating geo-referenced enriched digital models and supporting the design of a proper preventive conservation plan. The large differences in terms of shape and extension of the investigated buildings demand the use and combination of different laser scanning and 360° imaging technologies in order to provide the best digital product at the least cost. [ABSTRACT FROM AUTHOR]

Wood-leaf separation from terrestrial laser scanning (TLS) is a crucial prerequisite for quantifying many biophysical properties and understanding ecological functions. In this study, we propose a novel multi-directional collaborative convolutional neural network (MDC-Net) that takes the original 3D coordinates and useful features from prior knowledge (prior features) as input, and outputs the semantic labels of TLS point clouds. The MDC-Net contains two key units: (1) a multi-directional neighborhood construction (MDNC) unit to obtain more representative neighbors and enable directionally aware feature encoding in the subsequent local feature extraction, to mitigate occlusion effects; (2) a collaborative feature encoding (CFE) unit is introduced to incorporate useful features from prior knowledge into the network through a collaborative cross coding to enhance the discrimination for thin structures (e.g. small branches and leaf). The MDC-Net is evaluated on five plots from forests in Guangxi, China, with different branch architectures and leaf distributions. Experimental results showed that the MDC-Net achieved an OA of 0.973 and a mIoU of 0.821 and outperformed other related methods. We believe the MDC-Net would facilitate the usage of TLS in ecology studies for quantifying tree size and morphology and thus promote the development of relevant ecological applications. [ABSTRACT FROM AUTHOR]

A Ti3C2 MXene/Ti composite powder was developed through surface modification and powder coating for producing a high-performance titanium matrix composites (TMCs) by laser power bed fusion. Introducing MXene rarely changed the original sphericity and flowability of Ti powder while it slightly enhanced the laser absorption capacity of Ti powder. The printing conditions in turn affected the morphology and distribution of MXene in as-printed composites. At optimised printing parameters, majority of MXene with high structural integrity and uniform distribution remained along the grain boundaries of as-printed composites, and a combination of high surface quality, geometrical accuracy and densification was obtained. The remaining MXene played the synergy of pulling-out effect and load transfer role, which increased the yield strength from 530 to 710 MPa, while retaining good ductility (elongation of 19.8%). Compared with ASTM standard cast Ti64 alloy, our MXene/Ti composites also exhibited superior comprehensive tensile properties and excellent strength-ductility synergy. [ABSTRACT FROM AUTHOR]

In recent years, mobile laser scanning (MLS) has attracted increasing interest for road network three-dimensional mapping, where one of the applications of MLS data is automation in urban road manhole covers detection and their information measurement for monitoring and management of manhole covers on regular-basis. Therefore, a multi-step method is proposed based on geometric and radiometric constraints on manhole covers for their extraction and maintenance-related information measurement. The proposed method was implemented using graphics processing unit (GPU)- based parallel computing framework with improved computation time. The method performance was evaluated using MLS datasets of two complex urban roadway test sites, which included partially overlapping objects, occluded road surfaces, and intra-class variability. The manhole covers were extracted at average completeness, correctness and quality of 96.69%, 98.32%, and 95.12%, respectively. The proposed method performed satisfactorily in the challenging cases of road manhole covers and achieves significant improvement in comparison with several state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Although multi-temporal acquisitions are a widely accepted way to reduce occlusions in point clouds, occlusion analysis continues to be a visual analysis. The objective of this work is the design of an automatic method for the detection and characterization of street point cloud occlusions acquired with Mobile Laser Scanning (MLS). The proposed method consists of four main phases: alignment of the point cloud, rasterization, generation of occluded point clouds and visibility analysis. The proposed method was tested with point clouds of TerraMobil-ita/iQmulus dataset. The result shows a correct detection of 98.71% of the occlusions on ground and 83.37% on façades. All detected occlusions were correctly characterized. In the case studies, cars generated the largest amount of occluded area on the ground, with an occluded area per object of 15.36 m2. The main source of occlusions on facçdes was the building geometry and windows. [ABSTRACT FROM AUTHOR]

The COVID-19 pandemic has had a profound effect on the delivery of healthcare in the United States and globally. The aim of this study was to evaluate the impact of COVID-19 on common ophthalmic procedure utilization and normalization to pre-pandemic daily rates. Leveraging a national database, Clinformatics™ DataMart (OptumInsight, Eden Prairie, MN), procedure frequencies and daily averages, defined by Current Procedural Terminology codes, of common elective and non-elective procedures within multiple ophthalmology sub-specialties were calculated. Interrupted time-series analysis with a Poisson regression model and smooth spline functions was used to model trends in pre-COVID-19 (January 1, 2018–February 29, 2020) and COVID-19 (March 1, 2020–June 30, 2020) periods. Of 3,583,231 procedures in the study period, 339,607 occurred during the early COVID-19 time period. Anti-vascular endothelial growth factor injections (44,412 to 39,774, RR 1.01, CI 0.99–1.02; p =.212), retinal detachment repairs (1,290 to 1,086, RR 1.07, CI 0.99–1.15; p =.103), and glaucoma drainage implants/trabeculectomies (706 to 487, RR 0.93, CI 0.83–1.04; p =.200) remained stable. Cataract surgery (61,421 to 33,054, RR 0.77; CI 0.76–0.78; p <.001), laser peripheral iridotomy (1,875 to 890, RR 0.82, CI 0.76–0.88; p <.001), laser trabeculoplasty (2,680 to 1,753, RR 0.79, CI 0.74–0.84; p <.001), and blepharoplasty (1,522 to 797, RR 0.71, CI 0.66–0.77; p <.001) all declined significantly. All procedures except laser iridotomy returned to pre-COVID19 rates by June 2020. Most ophthalmic procedures that significantly declined during the COVID-19 pandemic were elective procedures. Among these, the majority returned to 2019 daily averages by June 2020. [ABSTRACT FROM AUTHOR]

Selective laser melting technique is used to manufacture Al-25 wt.%Si and Al-30 wt.%Si surface layers with a thickness of 0.5–0.6 mm followed by a laser rapid solidification process to refine the silicon to a nano-size and increase the hardness. The as-produced alloyed layers were heterogeneous and composed of clustered aggregates of primary Si crystals of size 5–7 µm, decorated with α-Al cells/dendrites, and embedded in a matrix consisting of α-Al dendritic crystals and Al-Si eutectic. However, after several remelting scanning treatments at a fast speed and low power, significant refinement of all phases was achieved, and a dramatic increase in the proportion of the interwoven nano-sized Al-Si fibrous eutectic. The primary Si sizes were reduced to ≤1 µm, while the eutectic spacing decreased and approached as low as 10–15 nm at the highest cooling rate. The high cooling rate significantly reduced the size and the amount of the α-Al cells/dendrites especially those surrounding the primary Si, thereby stimulating ultrafine Al-Si fibrous eutectic to grow adjacent to the primary Si crystals and spread massively, which in turn contributed to the increase in hardness. Transmission electron microscopy revealed block-like primary Si, worm-like Si, and nanoscale fibrous eutectic Si, which was internally nano-twinned. [ABSTRACT FROM AUTHOR]

In underwater turbulent medium, field correlations are found when the incidence is a laser beam array. Variations of the field correlations against the variations in the ring radius of laser array beam, number of beamlets composing the laser array, source size, underwater turbulence parameters, i.e. the ratio of temperature to salinity contributions to the refractive index spectrum, rate of dissipation of mean-squared temperature and rate of dissipation of kinetic energy per unit mass of fluid, are investigated. Field correlations of laser arrays are found to be larger than the field correlations of the single beams. The effect of underwater turbulence is to reduce the field correlation of laser arrays. [ABSTRACT FROM AUTHOR]

In this study, a thermal–phase–mechanical coupled numerical model was presented for the prediction of the distribution of temperature, phase and residual stress of 42CrMo steel during two-track laser hardening process. Austenite and tempering transformation were simulated based on the isoconversional method. K-M equation was used to calculate the fraction of martensite. Residual stress was calculated considering the thermal strain, transformation strain and transformation plasticity. The accuracy of the numerical model was verified according to the comparison with experimental results. The stress distribution of two-track laser hardening process was studied according to numerical simulation results. And the effect of the second track on the residual stress produced by the first track in two-track laser hardening was also analyzed by using this numerical model. [ABSTRACT FROM AUTHOR]

The therapy for unilateral spatial neglect (USN) is unclear. This case report investigated the effect of standing and walking training using a laser pointer based on stimulus-driven attention for USN. The patient was a right-handed 79-year-old man with cardiogenic cerebral embolism in the right middle and posterior cerebral arteries. Initially, we evaluated the absence of hemiparalysis in the lower limb and sensory disorder; almost all daily activities were performed independently. Intervention effects were verified using the BABA method. The course of the four phases (B1, A1, B2, A2) was conducted for 5 days. In the B1 and B2 phases, standing and walking training using a laser pointer was performed additionally to conventional physical therapy. Outcomes were measured using the Behavioural Inattention Test conventional subtest (BIT-c), Catherine Bergego Scale (CBS), and modified Posner task (MPT). The BIT-c remained unchanged in each phase. CBS scores improved after B1 and B2. In the MPT, the reaction time in the left space reduced after B1 and B2 compared with those in the A1 and A2 control phases. In this case, training may have contributed to the improvement in the response to the neglected space and behavioural assessment of USN. [ABSTRACT FROM AUTHOR]

Micro- and nanopatterning of metal oxide materials is an important process to develop electronic or optoelectronic devices. ZnO is a material of choice for its semiconducting and photoluminescence properties. In the frame of the nanoarchitectonics concept, we have developed and investigated a new process that relies on direct writing laser patterning in the Deep-UV (DUV) range to prepare photoluminescent microstructures of ZnO at room temperature, under air. This process is based on a synthesis of colloidal ZnO nanocrystals (NCs) with a careful choice of the ligands on the surface to obtain an optimal (i) stability of the colloids, (ii) redissolution of the non-insolated parts and (iii) cross-linking of the DUV-insolated parts. The mechanisms of photocrosslinking are studied by different spectroscopic methods. This room temperature process preserves the photoluminescence properties of the NCs and the wavelength used in DUV allows to reach a sub-micrometer resolution, which opens new perspectives for the integration of microstructures on flexible substrates for optoelectronic applications. [ABSTRACT FROM AUTHOR]

In this study, we investigate the transferability of the process-property relationship between two Inconel alloys for laser powder bed fusion (LPBF). By developing a Bayesian learning approach, the process-property model of Inconel 625 learned from Inconel 718 demonstrates high accuracy with R of 0.95, which verifies the feasibility of this innovative concept. It is further found that the accuracy of the knowledge transfer model of Inconel 625 is increased if the data on Inconel 625 is more abundant. In this regard, the mean RMSE and MAE on relative density are decreased by about 0.45% and 0.35% when the Inconel 625 dataset size is increased from 15 to 60. In addition, both accuracy and robustness of the Inconel 625 model are increased with transferred knowledge from Inconel 718 regardless of the dataset size of Inconel 625, in which the mean RMSE and MAE are decreased by up to 0.7% and 0.5%, respectively. [ABSTRACT FROM AUTHOR]

Few-body interactions offer the opportunity to study the isolated atom to few-body coupled molecules, and to condensed matter transitions. Atoms in molecules and in condensed matters are coupled by different orders of multipole–multipole interactions, which all stem from different orders of approximations from coulomb interactions between multiple charges. The lowest order multipole–multipole interaction is the dipole–dipole interaction, which is proportional to the size of the dipole. In this article, we use Rydberg atoms, which have more than 1000 times greater electric dipoles than the ground state atoms, to study the van der Waals interaction between few bodies. In addition to the large dipoles, the kinetic energy of the atoms is significantly reduced by reducing the temperature, which makes these interactions stable and observable. Here, we report on the 2D and 3D few-body interaction potentials and possible ways of creating semistable molecules in such an ultracold Rydberg gas with a temperature of ≈100 nK. Although we use Rydberg atoms in this article, this calculation can be applied to other states too. The results reported here are useful for studying repulsive van der Waals interactions and creating ultracold molecules. [ABSTRACT FROM AUTHOR]

In this work, titanium aluminide alloy have been fabricated via the laser deposition technique. The effect of some selected deposition parameters on the microstructure and mechanical properties of produced deposits were studied. The relationship between the laser power, and the microhardness of deposited samples on laser preheated substrate showed an incremental change in laser power from 200 to 600 W. This led to an overall decrease in microhardness of deposited samples from 426 to 373 HV. Sample deposited at 500 W gave the lowest Icorr of 1.8 x 10-8 and the highest Ecorr of -0.138 V. It is evident from the nanoindentation results that indentation modulus and stiffness of sample deposited at 600 W laser power had a lower value compared with 400 W laser power. However, the modulus of both samples fell within titanium alloy modulus range between 105-120 GPa. The microstructures of the deposits are mainly characterized with γ-TiAl and α2-Ti3Al phases and an improved hardness property almost two times higher than that of commercially pure titanium were achieved. It was concluded that changes in the laser power directly causes changes in the microstructure, hardness, stiffness, modulus of elasticity and corrosion resistance of the deposits. [ABSTRACT FROM AUTHOR]

A laser profilometry technique was upgraded to detect underwater bed level evolution with a laser and a single camera for highly transient laboratory experiments. The proposed procedure is simple, but achieves a similar performance as that met by more complex and expensive methods. This technique was applied to a dam-break test case over a mobile bed in a channel with a 90° bend, for which water and bed levels were both continuously recorded at five different places. Photogrammetry was then used to reconstruct the final topography, whose main features could be explained by analysing only a few appropriately chosen linear bed profiles. This cheap, simple, flexible and accurate method thus proves to be an interesting alternative to more complex methods for morphodynamics investigations in the case of fast transient flows. [ABSTRACT FROM AUTHOR]

Flexible vibration sensors applied to acoustic recognition have been studied for using as skin-like electronics. However, the development of vibration sensors to recognise the human voice accurately with stable frequency response, high sensitivity and flexible/conformable form factor has proved to be a major challenge. A flexible capacitive acoustic sensor made of convex array microstructured polydimethylsiloxane film has been proposed to detect the acoustic range of human beings. Performances in the voice response range, including sensitivity, detection limit and dynamic response, were explored and delivered an excellent result due to its unique air void structures. The sensor with such a dielectric layer exhibited high sensitivity (at least 2.01 kPa−1 under 1.06 Pa), wide strength range (0–833.33 kPa), low detection limit (~0.14 Pa) and good cyclic stability (>2000 cycles of different pressures). Our device is suitable for several promising voice-recognition applications, such as home automation, remote control systems and vocal healthcare. [ABSTRACT FROM AUTHOR]

It was aimed to evaluate the effects of conventional surface treatment techniques and femtosecond (FS) laser on shear bond strength (SBS) between zirconia and resin cement. 84 zirconia blocks (2Ã--10Ã--10mm) (Zirkonzahn, Zirkonzahn USA Inc, USA) were divided into six groups (n=14): group FS, FS laser application; group SB-FS, sandblasting followed by FS laser treatment; group FS-SB, FS laser treatment followed by sandblasting, group PS, plasma sputtering; group R, tribochemical silica coating; group SB, sandblasting with 110 µm Al2O3. The resin cement (Panavia F 2.0, Kuraray Medical Inc., Tokyo, Japan) was applied to the samples and polymerized with a LED curing light. SBS test was performed on 72 samples (12 samples from each group) with a universal testing machine. The other two samples of each group were analyzed with SEM and profilometer. For statistical analysis, ANOVA and Tukey HSD tests were used. Although, there were no significant differences between the group SB (7.66 ± 2.04MPa), group PS (7.39 ± 2.98MPa) and group R (5.62 ± 1.39 MPa) (p>0.05), the SBS values of the group FS (13.35 ± 2.48MPa), group SBþFS (13.23 ± 1.84MPa) and group FSþSB (11.31 ± 2.07 MPa) were higher than them with a statistically significant difference (p<0.05). SEM images showed differences in surface morphology among the groups. According to the 3-D profilometer images, the Ra values of Group SB, Group R, Group PS, Group FS, Group FS-SB and Group SB-FS were 0.93, 0.98, 0.16, 6.40, 10.70 and 9.11, respectively. The FS laser surface treatment provided a significantly higher bond strength than the conventional techniques. It is not recommended to combine FS laser treatment with sandblasting. [ABSTRACT FROM AUTHOR]

Because of the essential difference between micro-toughness and macro-toughness, the indiscriminate application of deep notch tests may result in serious errors of micro-toughness associated with shallow cracks or flaws in ceramics. Here, the micro-toughness values of ZrB2, ZrB2-SiC and ZrB2-SiC-Grapite ceramics were successfully measured through ultra-shallow sharp V-notches (depth less than 40 μm, the ratio of notch depth to sample height less than 0.01) produced by nanosecond laser on the surface of bending bars for the first time. Results indicated that the micro-toughness values obtained from these three typical ceramics were significantly lower than the macro-toughness values measured from deep notches. Furthermore, conflicts may arise when comparing the micro- with macro-toughness between different materials, such as the macro-toughness of ZrB2-SiC-G was larger than that of ZrB2-SiC, while a contrary result was obtained for micro-toughness. Compared with the indentation method, improved accuracy of micro-toughness measurement could be obtained by this method. [ABSTRACT FROM AUTHOR]

The aim of the present study was to investigate the feasibility of fabrication of a Fe53.4Cr20Mo16Cu0.6C10 amorphous and amorphous-crystalline crack-free layer with desirable corrosion resistance and hardness using the laser surface melting technique The phase analysis of clad layers has been characterised by X-ray diffraction (XRD). Also, the microstructure and phase analysis of the cross-section of clad layers has been studied by scanning electron microscopy, field emission scanning electron microscopy, and energy dispersive spectrometry. The effect of laser scanning speed on microstructure, corrosion behaviour, and hardness was investigated at 4, 6, and 8 mm s-1. The results showed that a high fraction of amorphous phase (90%) has been obtained at an 8 mm s−1 scan rate. The coating thickness is more than 150 μm, fully dense having low porosity. The corrosion resistance of Fe-based coatings was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopic tests, and pitting corrosion evaluated in HCl solutions. The laser-treated material coatings had a lower current density than the substrate due to the formation of an amorphous phase, and the corrosion resistance values were 56, 162, and 141 Ω.cm2 for 4, 6, and 8 mm s−1 scanning rate samples respectively. It was found that high corrosion resistance is related to coating with a 6 m s−1 scan rate due to the mixture of galvanic effects and amorphous structure. The average measured micro-hardness of the coatings demonstrated that the sample formed from the highest scan rate possessed the highest micro-hardness, which was 824 HV. [ABSTRACT FROM AUTHOR]

The micromachining of NiTinol shape memory alloy is exceptionally demanded in industry on account of its wide and expected use in different fields like aviation, biomedical designing. NiTinol shape memory alloy has enormous application in the vehicle and assembling industry. It accomplishes response surface methodology (RSM) approach based on numerical demonstrating of the machining qualities of the pulsed Nd:YAG laser during micro-channelling operation on 1 mm thick NiTinol shape memory alloy sheet. The tests were arranged and done in light of box-behnken design of experiments. Scanning speed, pulse width, frequency and current were the input parameters investigated in this study and furthermore, these parameters were also used to foster the RSM model. The reaction measures choose for the enhancement of upper width deviation (UWD) and lower width deviation (LWD) of the micro-channelling. Based on the experimental box-behnken design (BBD), micro channelling was performed on NiTinol sheet. The results reveal that the input parameters have a considerable impact on the quality of the micro channel. The ideal input parameter for the desired output parameters is found through particle swarm optimisation. The upper and lower width deviation were discovered with the use of a scanning electron microscopic images. [ABSTRACT FROM AUTHOR]

A series of laser-produced Al–Si surface layers of composition 35, 50, and 60 wt%Si was prepared and analysed for microstructure and hardness. Also, laser remelting at different scanning speeds was performed to obtain nano-sized silicon crystals. The results indicated that all the laser fabricated Al–Si layers consisted of fine primary silicon (PSi) crystals of average size 10 µm, surrounded by α-Al cells/dendrites and distributed in dendritic structure of α-Al and Al–Si eutectic. The results of laser remelting at speeds of 10 and 50 mm/s showed slight microstructural refinement. However, a significant reduction of the amount and size of the PSi to <1 µm as well as a favourable change in the morphology of the eutectic have resulted in the sample processed at a speed of 120 mm/s. The high cooling rate led to a dramatic reduction in the amount of the α-Al dendrites and triggers the eutectic silicon fibres to grew from the existing PSi crystals and ramify around its perimeter. The nanoindentation hardness increased as the interlamellar eutectic spacing decreased. The refinement of the PSi crystals and the modification of the eutectic silicon were attributed to the high density of twins which facilitate rapid and directional growth. [ABSTRACT FROM AUTHOR]

Scintillation index of multimode laser beams used for communication systems in vertical paths of weak atmospheric turbulent medium are examined by employing the Rytov method. On-axis scintillation index is examined versus the source size, propagation distance and zenith angle for vertical link including uplink and downlink. At the selected values of source sizes and propagation distances, scintillation responses of multimode laser beams are evaluated. In general, it is found for both uplink and downlink that the laser beam with multimode content has larger scintillation noise as compared to a Gaussian laser beam. However, for the downlink at L=700 km, at the chosen parameters, the multimode beam possessing larger mode content, is found to attain slightly smaller scintillations. [ABSTRACT FROM AUTHOR]

In this work the influence of picosecond laser (ps) irradiation (PLI) on the properties of black Cr electrodeposited on an SS substrate has been investigated. XPS has shown that black Cr treatment by PLI changes the concentrations of elements on the black Cr coating surface. Furthermore, it diminishes the quantity of CrN compound, while increasing the quantity of metallic chromium (Cro). Full reflectance (RD) of black Cr after treatment with PLI and before treatment in the visible region (300–800 nm) were quite close. Thermal tests at a temperature of 200 oC showed that the adhesion between black Cr treated with PLI and SS is better than that of black chromium not treated with PLI. Thus, such a black Cr absorber may be used in solar water heaters. [ABSTRACT FROM AUTHOR]

To investigate the temperature field of the surface of AlSi10Mg(Fe) with the aluminum oxide layer being removed using pulse laser, the physical model of composite material of aluminum oxide, removed using pulse laser, and aluminum alloy is established by using COMSOL Multi-physics, which calculates the temperature field and the removal effect in the case of different laser scanning linear velocity and laser energy density by solving thermo-physics equations. The influence of different laser parameters on the removal effect is also discussed. Based on the simulation and experiment, it shows that the aluminum oxide removal effect peaks in the case of 15 j/cm2 for laser energy density. [ABSTRACT FROM AUTHOR]

Laser processing has been used as a surface preparation before adhesive bonding, which significantly improves the adhesion between the adhesive and the substrates. In this work, a pulsed fiber laser was used to process different microgrooves in the bonding region of a Ti6Al4V substrate. First, the pulse energy was optimized, and then the effects of the microgroove parameters (groove pattern, depth, and distance) on the surface roughness of the substrate and on the shear strength and failure mode of the adhesive joints were studied using a single factor experimental design. The results show that when the pulse energy is greater than 63 μJ, a significant amount of molten residue is generated around the groove. The parallel groove is the most beneficial to improve the shear strength when the groove direction is 90° (when the groove is perpendicular to the loading direction). In contrast, cross grooves easily form pores that are not filled with adhesive, which weakens the shear strength. The shear strength was observed to decrease for greater groove distances and increase with the groove depth. The maximum shear strength of the adhesively bonded joint after laser processing is about 29.71 MPa, which is an increase of 140% compared with that by surface grinder polishing. [ABSTRACT FROM AUTHOR]

In this study, doped strontium fluorapatite (Sr-FAP) nanopowders were synthesised by sol-gel and used as a coating to modify Ti-6Al-4V substrates through CO2 laser cladding. The Ca ions of FAP were substituted by a different amount of Sr ions to increase bone cell differentiation and antibacterial properties. Lattice parameters and crystal size values of different samples decrease with increasing the amount of Sr ion. According to the morphological results, the laser cladding Sr doped FAP nanopowders can create homogenously and crack-free coating on the Ti-6Al-4V substrates. The 0.6SrFAP nanopowder sample had a more hydrophilic nature in comparison to other Sr doped FAP nanopowders. This sample showed antibacterial properties and high cell adhesion, spreading, and viability while provided a bioactive and favourable surface for bone tissue regeneration. Therefore, 0.6SrFAP nanopowder laser cladding on the surface of Ti-6Al-4VV implants seems to be promising for further in-vivo investigations in bone applications. [ABSTRACT FROM AUTHOR]