Electron Delocalization on the Silicon Nanoparticles Surface

The specific properties of tubular and fullerenlike silicon nanoparticles depend on theirs electronic structure, which is directly related to the surface geometry. Using density functional approach, a novel dual nature of the surface structure of silicon nanotubes which depends on the type of nanotube have been revevaled. The rippled form of the surface has shown to be a favorable one for (n, n) type structure and the most stable form for (n, 0) Si NT is the nanotube with a smooth-walled graphene-like surface. The phenomenon is explained by the relative position of the non-hybridized p orbitals on the surface.

The Effect of Surface Geometry of Solid Wall On the Collapse of a Cavitation Bubble

The objective of this paper is to reveal the influence of different surface geometric conditions on the dynamic behavior characteristics of a laser-induced bubble collapse. A high-speed camera system was used to record the oscillation process of the laser-induced bubble on plane solid walls with different roughness and a wall containing reentrant cavities full of water or gas. The focus is on the quantitative analysis of the morphological characteristics of the cavitation bubble near the solid wall under different surface forms during the first two oscillation period. The results show that the dimensionless ratio γ, defined as the distance from the center of the bubble to the wall divided by the maximum radius of the bubble, has a great influence on the change of the cavitation shape in the direction of the vertical wall. Different surface geometries without gas in our cases have no significant effect on the collapse time of cavitation bubbles. While for the surface containing gas, the direction of movement of the bubble accompanying the micro-jet will greatly change during the collapse of the cavitation bubble, and the collapse time seems to be independent of the dimensionless ratio γ. These achievements shed the light for the engineering to avoid the damage of the micro-jet caused by design suitable surface geometry.

Drone Surveying of Volumetric Ice Growth in a Steep River

Representative ice thickness data is essential for accurate hydraulic modelling, assessing the potential for ice induced floods, understanding environmental conditions during winter and estimation of ice-run forces. Steep rivers exhibit complex freeze-up behaviour combining formation of columnar ice with successions of anchor ice dams to build a complete ice cover, resulting in an ice cover with complex geometry. For such ice covers traditional single point measurements are unrepresentative. Gathering sufficiently distributed measurements for representativeness is labour intensive and at times impossible with hard to access ice. Structure from Motion (SfM) software and low-cost drones have enabled river ice mapping without the need to directly access the ice, thereby reducing both the workload and the potential danger in accessing the ice. In this paper we show how drone-based photography can be used to efficiently survey river ice and how these photographic surveys can be processed into digital elevation models (DEMs) using Structure from Motion. We also show how DEMs of the riverbed, riverbanks and ice conditions can be used to deduce ice volume and ice thickness distributions. A QGIS plugin has been implemented to automate these tasks. These techniques are demonstrated with a survey of a stretch of the river Sokna in Trøndelag, Norway. The survey was carried out during the winter 2020–2021 at various stages of freeze-up using a simple quadcopter with camera. The 500 m stretch of river studied was estimated to have an ice volume of up to 8.6 × 103 m3 (This corresponds to an average ice thickness of ∼67 cm) during the full ice cover condition of which up to 7.2 × 103 m3 (This corresponds to an average ice thickness of ∼57 cm) could be anchor ice. Ground Control Points were measured with an RTK-GPS and used to determine that the accuracy of these ice surface geometry measurements lie between 0.03 and 0.09 m. The ice thicknesses estimated through the SfM methods are on average 18 cm thicker than the manual measurements. Primarily due to the SfM methods inability to detect suspended ice covers. This paper highlights the need to develop better ways of estimating the volume of air beneath suspended ice covers.

The methods for the formation of optimal acoustic conditions for the transmission of speech content in small rooms

The subject of research in the article is the methodology for the examination of small-volume premises with a predominance of speech content. The aim of the work is to analyze all stages of acoustic expertise for meeting rooms, conference rooms, press centers, to determine the volume and sequence of the stages, taking into account the specific restrictions and conditions that arise in small rooms. All stages of acoustic expertise are considered in the work on examples of real premises of meeting rooms, conference halls, press centers. The sequence of stages of the examination, when it was carried out for premises of small volumes, did not undergo any changes, compared to the sequence that is used for spectator halls. The main distinctive feature of the first stage of acoustic examination in small rooms with a predominance of speech content is the analysis of the structures of the reverberation process in listening places in order to identify the drawbacks of the formation of a diffuse field, instead of checking the geometry of the wall and ceiling panel walls using geometric theory. A feature of the second stage is the development of recommendations for improving the sound-absorbing properties of enclosing surfaces and eliminating the effect of multiple re-reflections of sound energy between parallel surfaces through the use of partial replacement of surface geometry, work with suspended ceiling structures and the use of sound-absorbing curtains (to correct the properties of glass surfaces). The third and fourth stages of the examination remained unchanged.

Viral surface geometry shapes influenza and coronavirus spike evolution through antibody pressure

The evolution of circulating viruses is shaped by their need to evade antibody response, which mainly targets the viral spike. Because of the high density of spikes on the viral surface, not all antigenic sites are targeted equally by antibodies. We offer here a geometry-based approach to predict and rank the probability of surface residues of SARS spike (S protein) and influenza H1N1 spike (hemagglutinin) to acquire antibody-escaping mutations utilizing in-silico models of viral structure. We used coarse-grained MD simulations to estimate the on-rate (targeting) of an antibody model to surface residues of the spike protein. Analyzing publicly available sequences, we found that spike surface sequence diversity of the pre-pandemic seasonal influenza H1N1 and the sarbecovirus subgenus highly correlates with our model prediction of antibody targeting. In particular, we identified an antibody-targeting gradient, which matches a mutability gradient along the main axis of the spike. This identifies the role of viral surface geometry in shaping the evolution of circulating viruses. For the 2009 H1N1 and SARS-CoV-2 pandemics, a mutability gradient along the main axis of the spike was not observed. Our model further allowed us to identify key residues of the SARS-CoV-2 spike at which antibody escape mutations have now occurred. Therefore, it can inform of the likely functional role of observed mutations and predict at which residues antibody-escaping mutation might arise.

Adaptive surface geometry determination in multi-material x-ray computed tomography using fringe projection

One of the main challenges during digital post-processing of x-ray computed tomographic (XCT) measurement data is the reconstruction of the surface geometry of the measured objects. Conventionally, the surface geometry is defined as an isosurface of identical greyscale values, i.e. the x-ray absorbance of the material, based on a linear interpolation between neighboring voxels. Due to the complex surface geometry and rough surface, XCT measurements of additively manufactured (AM) parts are particularly prone to measurement artefacts caused by various physical effects when the x-rays penetrate the material. The irregular greyscale values at the measured surface geometry render commonly used single threshold greyscale value based isosurfaces as insufficient for representing the external and internal surface of the measured objects. This issue becomes particularly apparent when measuring multi-material objects, such as additively manufactured objects with integrated RFID tags. To address this challenge, this study presents a methodology for reliable surface geometry determination of XCT data based on previously acquired fringe projection (FP) data. For this purpose, the conventionally acquired surfaces geometries from the XCT and FP measurements are extracted, pre-processed and registered to each other before being merged into a single mesh. This merged data set is subsequently used as a starting point or reference for a locally adaptive threshold surface detection algorithm, which is able to capture the surface geometry at a sub-voxel resolution. In order to validate the methodology and confirm the envisaged benefits, selected geometry elements of the resulting surface geometry from measurements samples manufactured by additive manufacturing with integrated RIFD tags are compared to coordinate measurement machine (CMM) reference measurements. The results indicate a more robust surface geometry detection against artifacts especially for multi-material applications.

Lorentz resonance in the homogenization of plasmonic crystals

We explain the Lorentz resonances in plasmonic crystals that consist of two-dimensional nano-dielectric inclusions as the interaction between resonant material properties and geometric resonances of electrostatic nature. One example of such plasmonic crystals are graphene nanosheets that are periodically arranged within a non-magnetic bulk dielectric. We identify local geometric resonances on the length scale of the small-scale period. From a materials perspective, the graphene surface exhibits a dispersive surface conductance captured by the Drude model. Together these phenomena conspire to generate Lorentz resonances at frequencies controlled by the surface geometry and the surface conductance. The Lorentz resonances found in the frequency response of the effective dielectric tensor of the bulk metamaterial are shown to be given by an explicit formula, in which material properties and geometric resonances are decoupled. This formula is rigorous and obtained directly from corrector fields describing local electrostatic fields inside the heterogeneous structure. Our analytical findings can serve as an efficient computational tool to describe the general frequency dependence of periodic optical devices. As a concrete example, we investigate two prototypical geometries composed of nanotubes and nanoribbons.

New Approach to Three-Coordinate Milling of Large-Sized Surfaces of Second Order

The study introduces a new approach to precision machining of large-sized surfaces of second order on a three-coordinate horizontal milling machine. The new technology does not require the use of unique large-size boring lathes or five-axis milling machines. Three-axis horizontal milling machines do not need to be equipped with additional equipment that provides the workpiece with the missing rotational and translational movements relative to the machine table. The proposed technology is based on the use of a new approach that combines the geometric parameters of the second-order machined surface, the spherical surface of the cutting tool, i.e. cutter, and their position relative to the working table. The use of the developed technology will improve the efficiency and accuracy of machining the surface of second order, as well as simplify the control program and technological support due to the absence of movable equipment. The study gives an example of practical implementation and shows the possibility of independent control of the machined parabolic surface geometry using a three-coordinate horizontal milling machine.

Tool-Workpiece Interaction in the Cutting Process and Its Use

The paper analyzes the influence of natural tool wear on parameters of chip shaping and machining forces and proposes the adjustment of tool geometry based on natural shape of crater wear to extend time of machining. The contact of the cutting tool and the workpiece at actual cutting speed is a complex physical process, the result of which is a specific shape and characteristics of the machined surface and the modification of tool cutting characteristics. Due to the fact that there is no existing cutting material which would resist wear in the conditions of working high stress and temperature, it is necessary to take into account that tool cutting conditions change with cutting time. This is caused by the change in tool geometry after its functional areas become worn out. One of the practical effects of those changes is gradual modification of machined surface geometry, its fortification, formation of residual stress, character of chip formation and shaping, the development of friction temperature and deformation in the zone of the contact of the tool and workpiece. This means that the cut part changes its characteristics. It is up to date to eliminate or at least mitigate this negative influence of tool wear based on the results of cutting.