Key role of surface plasmon polaritons in generation of periodic surface structures following single-pulse laser irradiation of a gold step edge

Understanding the mechanisms and controlling the possibilities of surface nanostructuring is of crucial interest for both fundamental science and application perspectives. Here, we report a direct experimental observation of laser-induced periodic surface structures (LIPSS) formed near a predesigned gold step edge following single-pulse femtosecond laser irradiation. Simulation results based on a hybrid atomistic-continuum model fully support the experimental observations. We experimentally detect nanosized surface features with a periodicity of ∼300 nm and heights of a few tens of nanometers. We identify two key components of single-pulse LIPSS formation: excitation of surface plasmon polaritons and material reorganization. Our results lay a solid foundation toward simple and efficient usage of light for innovative material processing technologies.

Features of smaller ribosomes in Candidate Phyla Radiation (CPR) bacteria revealed with a molecular evolutionary analysis

The Candidate Phyla Radiation (CPR) is a large bacterial group consisting mainly of uncultured lineages. They have small cells and small genomes, and often lack ribosomal proteins L1, L9, and/or L30, which are basically ubiquitous in ordinary (non-CPR) bacteria. Here, we comprehensively analyzed the genomic information of CPR bacteria and identified their unique properties. In the distribution of protein lengths in CPR bacteria, the peak was at around 100–150 amino acids, whereas the position of the peak varies in the range of 100–300 amino acids in free-living non-CPR bacteria, and at around 100–200 amino acids in most symbiotic non-CPR bacteria. These results show that CPR bacteria have smaller proteins on average, like symbiotic non-CPR bacteria. We found that ribosomal proteins L28, L29, L32, and L33 are also deleted in CPR bacteria, in a lineage-specific manner. Moreover, the sequences of approximately half of all ribosomal proteins in CPR differ, in part, from those of non-CPR bacteria, with missing regions or specific added region. We also found that several regions of the 16S, 23S, and 5S rRNAs are lacking in CPR bacteria and that the total predicted length of the three rRNAs in CPR bacteria is smaller than that in non-CPR bacteria. The regions missing in the CPR ribosomal proteins and rRNAs are located near the surface of the ribosome, and some are close to one another. These observations suggest that ribosomes are smaller in CPR bacteria than in free-living non-CPR bacteria, with simplified surface structures.

Multiobjective optimization of internal and surface structure of high-speed and heavy-duty brake disc

The brake disc plays a crucial role to keep the stable braking of a high-speed and heavy-duty disc brake. There is always high temperature, brake vibration, and even serious deformation under braking pressure and frictional resistance. To improve brake performance, this paper aims to find new internal and surface structures of the brake disc. An equivalent moving load (EML) topology optimization method for internal structure is proposed. Topography optimization method oriented to displacement and stress control for surface structure is carried out. Multiobjective functions containing thermal-structural coupled rigidity and natural frequency of the brake disc are established in the internal and surface structure optimizations. Internal and surface structures of the brake disc are optimized, and the mechanic properties of the brake disc are improved. Thermal-structural coupling and modal analyses are verified with high-speed and heavy-duty brake working conditions. The results show that new brake disc structures meet the requirements, and the effectiveness of the proposed EML topology optimization and topography optimization methods has been proved.

Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 $$\upmu $$ μ J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences $$({F}_{\mathrm{th}})$$ ( F th ) and the incubation factor $$(\zeta )$$ ( ζ ) were also determined. Graphic abstract

Surface patterning techniques for proteins on nano- and micro-systems: A modulated aspect in hierarchical structures

The surface patterning of protein using fabrication or external functionalization of structures demonstrate advanced applications in fields of biomedical research for optics, bioengineering, biosensing and antifouling. Alteration of surface structures...

Diversity and distribution patterns of antennal sensilla in Hydropsychidae (Insecta, Trichoptera)

Structure and distribution of antennal sensilla were studied in males of 19 species of the caddisfly family Hydropsychidae by using scanning electron microscopy (SEM). Eleven types of sensilla were found: long trichoid, chaetoid, thick chaetoid, curved trichoid, coronary, basiconic, styloconic and four types of pseudoplacoid sensilla (mushroom-like, auricillic, ribbed, and T-shaped). Thick chaetoid, ribbed pseudoplacoid, and T-shaped pseudoplacoid sensilla were found only in Macronematinae. The great diversity of pseudoplacoid sensilla originated from a mushroom-like type, which also has a variable structure. Basal flagellomeres in the majority of studied species are equipped with ventrally positioned sensory fields of curved trichoid sensilla. In contrast to Arctopsychinae and Hydropsychinae, the increased number of these sensilla in the fields was noted for Diplectroninae and Smicrideinae. Most Macronematinae show a reduction of sensory fields and a strongly decreased average number of curved trichoid sensilla on distal segments. The great differences found in the studied family probably indicate a rapid function-related evolution of the antennal sensory surface structures in the caddisfly family Hydropsychidae.