Roles of vaporization and thermal decomposition in the dynamic evolution of laser-induced bubble on the surface of a submerged metal plate.

This paper aims to explain when the vaporization or thermal decomposition prevails during laser-induced bubble growth and how they influence bubble morphology. Bubbles were generated by irradiating a 304 stainless steel plate submerged in degassed water using millisecond lasers with a pulse width of 0.4 ms and powers of 1.6 kW and 3.2 kW, respectively. The dynamic evolution of bubbles was recorded by a high-speed camera. Moreover, the numerical models were developed to obtain a vaporization model and a decomposition model by incorporating the source terms due to the vaporization and decomposition mass fluxes into the governing equations, respectively. The simulated dynamic bubble evolution is consistent with the experimental results. When the laser power is 1.6 kW, a thin-layer bubble is formed, which gradually shrinks and eventually disappears after the laser stops irradiating. When the laser power is 3.2 kW, a spherical bubble is formed, and its volume decreases significantly after the laser stops irradiating. Subsequently, it remains relatively stable during the observation period. The fundamental reason for the difference between the bubble morphologies obtained from the vaporization model and the decomposition model lies in the presence of a condensation zone in the gas phase. When water vaporization or thermal decomposition dominates, the temperatures obtained from the models align with the decomposition ratios at varying temperatures reported in the literature. Our findings are significant for understanding the dynamic behavior of bubbles, with implications for various laser processing underwater.

Efficient and Controllable Preparation of Tridirectionally Anisotropic Sliding Surfaces Based on Spatial Light Modulator.

Realizing the efficient and controllable preparation of tridirectionally anisotropic sliding surfaces (TASSs) is extremely important. However, achieving efficient preparation of TASSs remains a great challenge. Using a spatial light modulator combined with an image feedback algorithm to adjust the femtosecond laser beam to multifocus array with a gradient intensity distribution is an efficient solution to achieve this target. Specifically, the two solutions of multifocus combination and focus intensity design are used to realize the efficient and controllable preparation of TASSs, and the structure and performance characterizations are carried out to prove the superiority of this method. It is believed that the proposal of this method can provide more inspiration for solving the high-efficiency processing problems of complex micro/nanostructures.

High orientation consistency and adjustable convex width of laser-induced periodic surface structures using picosecond laser pulse trains.

High orientation consistency and adjustable convex width of the low-spatial-frequency laser-induced periodic surface structures (LSFLs), crucial to the functional surface characteristics, have remained elusive. This paper proposes a new method to fabricate LSFLs with high orientation consistency on the rough surface of titanium by combining laser polishing and laser induction with LSFLs with a tunable convex width via laser melting as the post-treatment. Picosecond pulses trained with a 50-ns interval are applied to regulate the thermal incubation effect and achieve laser polishing and laser nanoscale melting. The melting time of titanium for laser polishing and laser nanoscale melting is determined to be on a microsecond time scale and around 100 ns, respectively. Experimental studies show that the surface texture of titanium lowers the orientation consistency of LSFLs and that its divergence angle is 30°. Picosecond pulses with a sub-pulse number of three are applied to achieve surface polishing and the formation of the rudiment of the LSFLs, followed by the picosecond laser induction. As a result, the divergence angle of LSFLs decreases from 30° to 12°. On this basis, aiming at the problem of the narrow adjustability of the convexity ratio of LSFLs, a nanoscale melting processing method based on picosecond pulse trains with a sub-pulse number of four is proposed, and LSFLs with the tunable convexity ratios from 0.3 to 0.87 are obtained.

Mechanism of near-field optical nanopatterning on noble metal nano-films by a nanosecond laser irradiating a cantilevered scanning near-field optical microscopy probe.

To overcome the diffraction limit, a laser irradiating cantilevered scanning near-field optical microscopy (SNOM) probe has been used in near-field optical nanopatterning. In this paper, the mechanism of nanopatterning on noble metal nano-films by this technique is investigated by the finite element method. It is proposed that the main mechanism of this phenomenon is the melt and reshaping of the nano-film under the SNOM tip. The melt is caused by the surface plasmon polariton-assisted enhancement and restriction within the SNOM tip aperture. The impacts of the gap g between the tip and substrate and the polarization of the laser are further analyzed.

Fabrication of nanostructure on Au nano-film by nanosecond laser coupled with cantilevered scanning near-field optical microscopy probe.

Diffraction limit has been the constraint of the nanostructure fabrication. Because the scanning near-field optical microscopy (SNOM) can work in the evanescent near-field region, its application in nano-processing has received extensive attention from researchers globally. In this paper, we combined nanosecond laser with cantilevered SNOM probe. Utilizing the high precision of the confinement and enhancement effect of probe tip and the high instantaneous energy of the laser, we realized nanostructure fabrication andin situdetection on Au nano-film. Feature sizes down to 47 nm full width at half maximum were fabricated. We investigated the laser propagation through the SNOM tip aperture and the light field intensity distribution on the surface of substrate theoretically. The calculation results demonstrate that the laser is highly restricted within the SNOM aperture and enhanced on the exit plane at the rim of aperture. After the transmission, the light field intensity distribution on the surface of the Au nano-film was enhanced due to the localized surface plasmon resonance. The thermal distribution on the surface of Au nano-film indicates that the peak of the temperature distribution appeared at the surface right underneath the center of the aperture. It is proved that the simulation results are consistent with the experimental results.

Mechanism of nanostructure processing on Au and Ag nano-film by a nanosecond laser illuminating cantilevered scanning near-field optical microscopy tip.

Nanostructure processing by a laser illuminating cantilevered scanning near-field optical microscopy (SNOM) tip is a novel technology that has received extensive attention from researchers. In this paper, theoretical investigations of the mechanism for nanostructure fabrication on Au and Ag nano-film by this technology are realized by the finite element method. The light field intensity and temperature distribution on Au and Ag surfaces at the near-field of the SNOM tip apex after illumination is simulated. The results reveal that the laser is restricted and enhanced within the SNOM tip aperture during illumination. Locally excited surface plasmon polaritons, which induce near-field enhancement on the Au and Ag nano-film at the vicinity of the aperture, are significant for nanostructure fabrication. The impacts of several parameters such as aperture width w, gap between the apex and substrate g, and the initial electric field intensity |E0| of the laser on the temperature of the Au and Ag substrate surfaces during fabrication are deeply studied. It reveals that the surface temperature depends on both the enhancement of the light field intensity and the transmitted laser. The enhancement is dominant in affecting temperature when the gap is small, while the transmittance becomes the main factor influencing the surface temperature with the increase of the gap.

Targeted Nanoscale 3D Thermal Imaging of Tumor Cell Surface with Functionalized Quantum Dots.

Measuring the changes in tumor cell surface temperature can provide insights into cellular metabolism and pathological features, which is significant for targeted chemotherapy and hyperthermic therapy. However, conventional micro-nano scale methods are invasive and can only measure the temperature of cells across a single plane, which excludes specific organelles. In this study, fluorescence quantum dots (QDs) are functionalized with the membrane transport protein transferrin (Tf) as a thermo-sensor specific for tumor cell membrane. The covalent conjugation is optimized to maintain the relative fluorescence intensity of the Tf-QDs to >90%. In addition, the Tf-QDs undergo changes in the fluorescence spectra as a function of temperature, underscoring its thermo-sensor function. Double helix point spread function imaging optical path is designed to locate the probe at nanoscale, and 3D thermal imaging technology is proposed to measure the local temperature distribution and direction of heat flux on the tumor cell surface. This novel targeted nanoscale 3D thermometry method can be a highly promising tool for measuring the local and global temperature distribution across intracellular organelles.

Fabrication of self-aligning convergent waveguides of microlens arrays to collect and guide light.

The optical properties of microlens arrays may be significantly affected by the optical crosstalk effect between adjacent lenses. Recently, this issue has triggered increasing attention in the scientific community. In this study, an integrated microlens array (MLA) consisting of self-aligning convergent waveguides of microlenses was fabricated. The optical crosstalk effect does not influence the performance of such system. Based on the self-focusing effect principle, self-writing of the waveguide array was achieved in a photosensitive polymer. The light collection and guiding performance of the MLA with and without thermal cross-linking treatment was analyzed in depth. The relation between the stray light and the filling rate of the MLA shows that a high filling rate decreases the optical crosstalk. Finally, an integrated MLA with a large area, high uniformity, and excellent optical performance was fabricated.

Advanced mechanism of multiphysics fields tip enhancement induced with varied laser power to fabricate pattern-transformable subdiffraction limit nanostructures.

The nanofabrication platform was carried out using an atomic force microscope (AFM) system and a continuous wave (cw) laser to investigate the influence of laser power on the underlying mechanism of nanostructures fabricated by multiphysics fields tip enhancement (MFTE) induced by a cw laser irradiating the AFM probe tip. The nanostructure fabrication of nanopits and grooves and nanodots and lines on a polymethyl methacrylate thin film was conducted in an ambient environment by changing the incident laser power. The dependence of the MFTE on laser power was numerically analyzed, too. The lateral dimensions of nanopits and grooves and nanodots and lines characterized in situ were 154 nm, 96 nm, 188 nm, and 25 nm, respectively, breaking the optical diffraction limit. It turned out that the nanostructures converted from craters (pits and grooves) to protrusions (dots and lines) when altered with the laser power. Different laser powers can trigger the MFTE to change, thus, inducing varied coupling energy, which is the essential mechanism for nanostructure conversion. We also established a model to analyze the nanostructures transition and to predict the dimensions of nanostructures. The simulation results demonstrate that the MFTE has an essential effect on the formation of nanostructures, which are in good agreement with the experimental results.

Realization of Force Detection and Feedback Control for Slave Manipulator of Master/Slave Surgical Robot.

Robot-assisted minimally invasive surgery (MIS) has received increasing attention, both in the academic field and clinical operation. Master/slave control is the most widely adopted manipulation mode for surgical robots. Thus, sensing the force of the surgical instruments located at the end of the slave manipulator through the main manipulator is critical to the operation. This study mainly addressed the force detection of the surgical instrument and force feedback control of the serial surgical robotic arm. A measurement device was developed to record the tool end force from the slave manipulator. An elastic element with an orthogonal beam structure was designed to sense the strain induced by force interactions. The relationship between the acting force and the output voltage was obtained through experiment, and the three-dimensional force output was decomposed using an extreme learning machine algorithm while considering the nonlinearity. The control of the force from the slave manipulator end was achieved. An impedance control strategy was adopted to restrict the force interaction amplitude. Modeling, simulation, and experimental verification were completed on the serial robotic manipulator platform along with virtual control in the MATLAB/Simulink software environment. The experimental results show that the measured force from the slave manipulator can provide feedback for impedance control with a delay of 0.15 s.

Nanoscale 3D temperature gradient measurement based on fluorescence spectral characteristics of the CdTe quantum dot probe.

The existing quantum dot temperature measurement techniques can only measure the planar temperature in the cell but fails in 3D temperature investigation. We present a novel method of measuring the 3D temperature field on nano scale, combining fluorescence spectral characteristics of the CdTe quantum dot probe with optical spatial positioning. Based on dual-helix point spread function, a 3D temperature optical measurement system with a resolution of 0.625 °C is established, providing a new perspective of 3D temperature measurement inside the cell. We thus offer an original research tool for further revealing the evolution process of secretions in cell metabolism.

Mechanism and morphology control of underwater femtosecond laser microgrooving of silicon carbide ceramics.

Silicon carbide (SiC) ceramics have been widely used for microelectronics, aerospace, and other industrial fields due to their excellent chemical stability and thermal tolerance. However, hard machinability and low machining precision of SiC ceramics are the key limitations for their further applications. To address this issue, a novel method of underwater femtosecond laser machining was introduced in this study to obtain high precision and smooth surface of the microgrooves of SiC ceramics. The removal profiles were characterized in terms of width, depth, and surface morphology, which exhibited high dependence on the femtosecond laser processing parameters. The instability during the underwater processing affected by laser-induced gas bubbles and material deposition, however, limits the high surface accuracy of microgrooves and processing efficiency. The process condition transformation from a bubble-disturbed circumstance to a disturbance-free model was carefully investigated through a high speed camera for the femtosecond laser processing of SiC ceramics in water. The experiment results indicated that degree of disturbed effect was heavily dependent on size, distribution, and motion of laser-induced gas bubble. Furthermore, some typical evolution mechanisms of gas bubble and their influence on the removal profiles of microgrooves were discussed in detail. Bubble evolution has been proven to be mainly responsible for the behavior of laser propagation (focus model, total reflection, etc.), which notably affects microstructural characteristic of the microgrooves.

Transmission performance of 90°-bend optical waveguides fabricated in fused silica by femtosecond laser inscription.

The L-shape waveguide was written in fused silica using a femtosecond laser with beam shaping. The guiding structure supports good light turning; 0.88 dB/turn was achieved at the silica-air interface. By using the finite-different time-domain method, the turn loss due to the turning structure and refractive index of the L-shape waveguide has been simulated. The results show that the proposed method has unprecedented flexibility in fabricating a 90°-bend waveguide.

Rutile TiO2 Flocculent Ripples with High Antireflectivity and Superhydrophobicity on the Surface of Titanium under 10 ns Laser Irradiation without Focusing.

We report on the formation of rutile TiO2 flocculent laser-induced periodic surface structures (LIPSSs) with high antireflectivity and superhydrophobicity on the surface of titanium under 10 ns 1064 nm laser irradiation without focusing. The center part of the Gaussian laser beam is used to deposit flocculent structure and the edge part used to produce LIPSSs. The melt and modification thresholds of titanium were determined first, and then, the melt and modification spot-overlap numbers, several responsible for the formation of flocculent structure and LIPSSs, were introduced. It is found that both the melt and modification spot-overlap numbers increase with an increase in laser fluence and spot-overlap number, contributing to the production of flocculent LIPSSs. LIPSSs are obtained with the modification spot-overlap number above 300, and the amount of flocculent structures increases with an increase in the peak laser fluence and spot-overlap number. Then, considering that the fine adjustment of the melt and modification spot-overlop numbers in one-time line scanning is quite difficult, the composite structure, of which both LIPSSs and flocculent structures are distinct, was optimized using laser line scanning twice. On this basis, a characterization test shows the sample full of the flocculent LIPSSs represents best antireflectivity with the value around 10% in the waveband between 260 and 2600 nm (advance 5 times in infrared wavelengths compared to the initial titanium surface), and shows the no-stick hydrophobicity with the contact angle of 160° and roll-off angle of 25° because of the pure rutile phase of TiO2.

Mitochondrial Genomic Evidence of Selective Constraints in Small-Bodied Terrestrial Cetartiodactyla.

Body size may drive the molecular evolution of mitochondrial genes in response to changes in energy requirements across species of different sizes. In this study, we perform selection pressure analysis and phylogenetic independent contrasts (PIC) to investigate the association between molecular evolution of mitochondrial genome protein-coding genes (mtDNA PCGs) and body size in terrestrial Cetartiodactyla. Employing selection pressure analysis, we observe that the average non-synonymous/synonymous substitution rate ratio (ω) of mtDNA PCGs is significantly reduced in small-bodied species relative to their medium and large counterparts. PIC analysis further confirms that ω values are positively correlated with body size (R2 = 0.162, p = 0.0016). Our results suggest that mtDNA PCGs of small-bodied species experience much stronger purifying selection as they need to maintain a heightened metabolic rate. On the other hand, larger-bodied species may face less stringent selective pressures on their mtDNA PCGs, potentially due to reduced relative energy expenditure per unit mass. Furthermore, we identify several genes that undergo positive selection, possibly linked to species adaptation to specific environments. Therefore, despite purifying selection being the predominant force in the evolution of mtDNA PCGs, positive selection can also occur during the process of adaptive evolution.

Different Evolutionary Trends of Galloanseres: Mitogenomics Analysis.

The two existing clades of Galloanseres, orders Galliformes (landfowl) and Anseriformes (waterfowl), exhibit dramatically different evolutionary trends. Mitochondria serve as primary sites for energy production in organisms, and numerous studies have revealed their role in biological evolution and ecological adaptation. We assembled the complete mitogenome sequences of two species of the genus Aythya within Anseriformes: Aythya baeri and Aythya marila. A phylogenetic tree was constructed for 142 species within Galloanseres, and their divergence times were inferred. The divergence between Galliformes and Anseriformes occurred ~79.62 million years ago (Mya), followed by rapid evolution and diversification after the Middle Miocene (~13.82 Mya). The analysis of selective pressure indicated that the mitochondrial protein-coding genes (PCGs) of Galloanseres species have predominantly undergone purifying selection. The free-ratio model revealed that the evolutionary rates of COX1 and COX3 were lower than those of the other PCGs, whereas ND2 and ND6 had faster evolutionary rates. The CmC model also indicated that most PCGs in Anseriformes exhibited stronger selective constraints. Our study suggests that the distinct evolutionary trends and energy requirements of Galliformes and Anseriformes drive different evolutionary patterns in the mitogenome.

Thermal error modeling of machine tool based on dimensional error of machined parts in automatic production line.

Thermally induced error has proven to be the major source of machining error for the machine tool working in a non-temperature-controlled workshop. Current research on thermal error modeling and compensation is implemented based on the measured thermal deformation of machine tool, and the data is obtained referring to spindle idling rather than metal cutting condition, resulting in the disadvantages of the established model with low adaptability to varying conditions. In this paper, a modeling and compensation method based on the dimensional error of the machined parts is proposed to address the issue and verified through machine tools in an automatic production line. Compared with the modeling based on thermal deformation, the method formulates a more direct relations between temperature rise and machining error. The thermal error modeling is carried out by measuring the dimension deviation of the inner hole diameter of the motor end cover and the screened representative temperature variables. Meantime, considering the temperature coefficient in model is difficult to converge when modeling with the single-day data, the unified modeling with the multi-day data is realized by improving the conventional multiple linear regression model. Finally, the generalized model used for thermal error compensation in x direction of the machine tool is obtained. The real-time compensation of the thermal error based on the established model is realized with the machine tool machining in mass production. The verification results show that this error modeling and compensation method can reduce the machining error of the end cover by more than 52%, irrespective of experiencing various complicated working conditions. Stability and robustness of the modeling are also validated through application on the other machine tool with the same configuration and real machining over seven days.

Cavity structure-based active controllable thermal switch for battery thermal management.

Batteries may degrade fast at extreme temperatures, posing a challenge in meeting the dual requirements of heat preservation at low temperatures and efficient cooling at high temperatures. To address this issue, we propose a cavity structure-based active controllable thermal switch. It has a potential switch ratio (SR) of approximately 300, with an experimental SR of 15.4. Furthermore, the thermal resistance can be actively controlled. The "OFF State" of the thermal switch increases energy discharge at low temperatures. Pre-heating with the "OFF State" consumes only 60% of the energy required in the "ON State". By employing the "ON State" at an ambient temperature of 20°C, the battery temperature can be maintained below 35°C. And the "ON + State" keeps the maximum battery temperature remaining below 42°C under extreme conditions. These findings demonstrate that the implementation of the proposed thermal switch enhances the usability of batteries in extreme environments.

Comparative Analyses of the Fecal Microbiome of Five Wild Black-Billed Capercaillie (Tetrao parvirostris) Flocks.

Black-billed capercaillie (Tetrao parvirostris) was listed as a first-class state-protected animal because it was endangered in China (Category I). This study is the first to examine the diversity and composition of T. parvirostris gut microbiome in the wild. We collected fecal samples from five black-billed capercaillie flock roosting sites (each 20 km apart) in one day. Thirty fecal samples were sequenced with 16S rRNA gene amplicons on the Illumina HiSeq platform. This study is the first to analyze the fecal microbiome composition and diversity of black-billed capercaillie in the wild. At the phylum level, Camplyobacterota, Bacillota, Cyanobacteria, Actinomycetota, and Bacteroidota were the most abundant in the fecal microbiome of black-billed capercaillie. At the genus level, unidentified Chloroplast, Escherichia-Shigella, Faecalitalea, Bifidobacterium, and Halomonas were the dominant genera. Based on alpha and beta diversity analyses, we found no significant differences in the fecal microbiome between five flocks of black-billed capercaillie. Protein families: genetic information processing; protein families: signaling and cellular processes, carbohydrate metabolism; protein families: metabolism and energy metabolism are the main predicted functions of the black-billed capercaillie gut microbiome through the PICRUSt2 method. This study reveals the composition and structure of the fecal microbiome of the black-billed capercaillie under wild survival conditions, and this study provides scientific data for the comprehensive conservation of the black-billed capercaillie.

A chromosome-level genome assembly of the yellow-throated marten (Martes flavigula).

The yellow-throated marten (Martes flavigula) is a medium-sized carnivore that is widely distributed across much of Asia and occupies an extensive variety of habitats. We reported a high-quality genome assembly of this organism that was generated using Oxford Nanopore and Hi-C technologies. The final genome sequences contained 215 contigs with a total size of 2,449.15 Mb and a contig N50 length of 68.60 Mb. Using Hi-C analysis, 2,419.20 Mb (98.78%) of the assembled sequences were anchored onto 21 linkage groups. Merqury evaluation suggested that the genome was 94.95% complete with a QV value of 43.75. Additionally, the genome was found to comprise approximately 39.74% repeat sequences, of which long interspersed elements (LINE) that accounted for 26.13% of the entire genome, were the most abundant. Of the 20,464 protein-coding genes, prediction and functional annotation was successfully performed for 20,322 (99.31%) genes. The high-quality, chromosome-level genome of the marten reported in this study will serve as a reference for future studies on genetic diversity, evolution, and conservation biology.