Small Hollows Research Articles

Plasma PVD by small spiral Ta hollow cathodes

Spiral hollow cathodes represent interesting options for local PVD applications. Radio frequency powered small diameter spiral hollow cathodes made from 0.45 mm diameter Ta wire rolled around 0.5 mm diameter rod were tested in PVD regimes on silicon substrates at the gas pressure of 400 Pa (3 Torr). The PVD of Ta and reactive PVD of Ta-N resulted in deposition rates of about 130 nm/min with maximum thickness in the center of the coating spots. However, part of the coating spots can be heavily eroded. At higher RF powers droplets from the melted Ta tip of the spiral can damage the coating and melt the Si substrate. The PVD rates of Ta in argon were similar as those for TaN. However, lower number of droplets of the melted Ta were formed in argon. The heating of the spiral outlet and its effect on the coating was also more intense in nitrogen than in argon. The temperature of the Si substrate table reached about 500 °C in 20 min in the nitrogen plasma and up to 400 °C in argon. This heating was higher on electrically grounded substrates than on the floating substrates. The effect of sharp outlet on possible eroding of the sample was confirmed by a sharp ended 1 mm diameter stainless steel medical needle used as a hollow cathode.

Narrowband stimulated Raman scattering and molecular modulation in anti-resonant hollow-core fibres

Raman scattering is the inelastic process where photons bounce off molecules, losing energy and becoming red-shifted. This weak effect is unique to each molecular species, making it an essential tool in, e.g., spectroscopy and label-free microscopy. The invention of the laser enabled a regime of stimulated Raman scattering (SRS), where the efficiency is greatly increased by inducing coherent molecular oscillations. However, this phenomenon required high intensities due to the limited interaction volumes, and this limitation was overcome by the emergence of anti-resonant fibres (ARFs) guiding light in a small hollow channel over long distances. Based on their unique properties, this Perspective reviews the transformative impact of ARFs on modern SRS-based applications ranging from development of light sources and convertors for spectroscopy and materials science, to quantum technologies for the future quantum networks, providing insights into future trends and the expanding horizons of the field.

Effect of variations hollow of octagon porous media on heat and mass transfer

This study investigates stream function, temperature distribution, and concentration distortion of porous media with three types of hollow. The key factors in conductive heat and mass transfer are the number of vanes in hollows and various hollows, including semi-circle, square, and triangle vanes, which are the novelty of this research. Furthermore, the valuable result of the present study is that hollows with semi-circle vanes had a higher conductive heat transfer than hollows with square and triangle vanes. It is a matter to analyze and study porous media in heat and mass phenomena which are used in three mutually coupled equations in FEM. The finite element approach is employed to compare concentration distribution in porous media with small and large square hollows. Based on the obtained numerical results, the most effect was in the reduction of stream function, temperature distribution, and concentration distortion related to square vanes in hollow. On the other hand, the Nusselt phenomena in the bottom wall influence extremely, and the results depended on some parameters such as ε, Diffusion, Radiation, and Rayleigh number. Finally, Stream function, temperature distribution, concentration distortion, and Nusselt phenomena of octagon porous media are analyzed to develop knowledge in conductive heat and mass transfer.

Enhancing thermal insulation and mechanical strength of porous ceramic through size-graded MA Hollow Spheres

In this study, a series of porous ceramics were prepared using different ratios of small and large size MA hollow ceramic spheres as pore-forming agents, and their thermal insulation properties were investigated. The results showed that increasing the proportion of small size hollow ceramic spheres could effectively decrease the thermal conductivity and improve the compressive strength of the porous ceramics. The optimal porous ceramic was prepared with a ratio of 10∼50 of small and large size hollow ceramic spheres, which had a thermal conductivity of 0.368 W/(m·K) at 800 °C and a compressive strength of 22.43 MPa. Microscopic analysis indicated that the enhanced thermal insulation and mechanical properties were due to the improved pore structure and the enhanced bonding strength between the ceramic spheres and the matrix. The findings provide valuable insights for the development of high-performance thermal insulation materials.

A Clarification of the Terms Dakhma and Astodān on the Basis of Literary Records and Archeological Research in Fars Province

Abstract The terms dakhma (open-air tomb) and astodān (ossuary) are often used interchangeably despite the fact that they refer to two distinct structures with different meanings in pre-Islamic Iranian burial practices. The present study explores the differences between the two structures, along with burial-related terms used by ancient Persians, by examining ancient and medieval Iranian manuscripts and by conducting a field study of surviving artifacts from ancient times. The results show that dakhma (or dakhmagāh) was a general term referring to the entire burial site and its constituent elements—as opposed to the specific astodān. Both of these structures should be differentiated from small hollowed ledges on the edges or surfaces of mountains, which were engraved as late as the early Islamic period (seventh to ninth centuries), even though the terms dakhma and astodān appear in their inscriptions. Although the latter have led some scholars to conflate the terms, the present study finds that these small stone structures and hollows are neither dakhma nor astodān, but rather served as a symbolic memorial to the departed. Furthermore, other burial-related structures in the environs of the dakhma, including mortar-shaped hollowed stones (sang-ābs) and cascade-like stone grooves (called sor-sor-e hāy-e sangi), which have received scant attention, can be traced back to Zoroastrian rituals in Avestan texts and point to the presence of a dakhma. Finally, the present field study, which explored ancient burial sites in the Marvdasht plain in Fars Province, includes unique information and details that are presented here for the first time.

Complexity and Geoheritage Importance of Granite Pseudokarst from the Belaya River Gorge (Western Caucasus)

New investigations in the Western Caucasus contribute to the understanding of granite pseudokarst (sensu lato) and megaclasts linked to river erosion. A plot on the bank of the Belaya River (Mountainous Adygeya, Western Caucasus) was selected to examine diverse and abundant pseudokarst features (small rock basins, hollows, potholes, and channels) and large clasts. Morphological analysis of these features clarifies their general characteristics and genetic interpretations. Pseudokarst features can be classified into two major categories, namely the relatively small (<1 m) and large (>1 m) features. Potholes, which are usually 1–3 m in size, are the most characteristic features occurring on two levels, i.e., on steep walls of the gorge (half-filled with river water) and on slightly inclined surfaces of a terrace-like landform (subaerial exposure). In both cases, their walls from the side of the river are broken. Apparently, these potholes were formed on the river bottom. Subsequent incision of the gorge elevated potholes and the river has eroded them from one side. Apparently, some pseudokarst features are related to macroturbulent flood flows and granite weathering. Due to its scientific uniqueness and aesthetic attractiveness, this granite pseudokarst constitutes geoheritage, which can be exploited for the purposes of geoscience research and geotourism development.

Investigation of Sterilization Effect for Overlapping Pieces in Non-Thermal Sterilization Method of Packaged Fresh Foods Using Pulsed Barrier Discharge

It is important to secure food safety. If a packaged food can be sterilized, food poisoning can be reduced considerably because the packaged food in a plastic container is useful to prevent attaching microorganisms. However, a fresh food, e.g., a salad or sashimi, cannot be sterilized by thermal sterilization. Therefore, we are studying sterilization methods for packaged fresh foods, such as packed salads. In this study, we have investigated the applicable probability of the sterilization method using cold plasma applied to the packaged fresh food. Especially, we have investigated the probability of the sterilization of microorganisms living in a small hollow between the overlapped fresh foods. A plastic petri dish with a lid was used for simulating the plastic container. The cold plasma was applied into the petri dish by a barrier discharge generated by a pulsed voltage. E. coli was used for a target of sterilization. The E. coli was set on a culture agar medium instead of the salad. The experimental results showed that the sterilization method combining the plastic film and cold plasma of the barrier discharge generated by the pulsed voltage is applicable to sterilize microorganisms living in the hollow between the overlapped fresh foods for the packaged fresh food.

Comparative Assessment of Digital and Conventional Soil Mapping: A Case Study of the Southern Cis-Ural Region, Russia

Digital mapping was applied for a key site located at the Southern Cis-Ural region near Ufa city (the Republic of Bashkortostan, Russia). The digital soil map (DSM) was created using the open-source GIS software packages and compared to a conventional (CSM) one. As input parameters, we used standard morphometric values of the topography and field descriptions of soils, including the authors’ data. The DSM was created at the same scale (1:25,000) as the CSM, and soils of different classes were grouped according to the principle of genetic homogeneity and regional agroecological value. Comparing DSM and CSM showed several significant differences in the position, areas, and boundaries of hydromorphic soils and chernozems. The DSM has advantages over CSM at estimating smaller soil areas (areals) and their boundaries, in particular, on elevated topography elements (hills and steep slopes) and upper links of the erosion network (small dry valleys, hollows, and gullies). On the other hand, fluvial soils are mapped rather poorly by the digital approach, and CSM is more appropriate for such soils’ areals. The highest discrepancy is confined to the areas of eroded soils and fluvisols (15% and 12% of total area, respectively) due to significant differences in DSM and CSM approaches for such soil groups. We suppose that the digital method is effective and suitable for the Cis-Ural region, despite 57% soil taxa (types) prediction accuracy and the complexity of the territory by its ruggedness, erosion, and suffusion processes. The implementation and further use of digital mapping methods increase the quality of work, reduce its cost and terms in the region.

Dominant Research Contribution of Dr. Eiichi Tanaka in the Field of Very Weak Radioactivity Measurements

This article gives dominant research contributions of the late Dr. Eiichi Tanaka in the field of very weak radioactivity measurements with a new type of an extremely low background β-ray scintillation spectrometer, which consists of a large plastic scintillator and a gas-flow GM counter located in the small hollow in the bottom part of the plastic scintillator. The pulse signals from plastic scintillator are coincidence-gated by the pulses from the GM counter. Dominant background signals due to the energetic muons still appear in the higher region than 3.5 MeV even with coincidence gating mode, but extreme reduction of background can be attained in the 0～3 MeV region which is essentially important in the β-ray spectrometry for most of radionuclides.

Manufacturing and Comparison of Sr Modified or Unmodified AlSi12 Eutectic Alloy Matrix Unimodal and Bimodal Composite Metal Foams

Metallic foams are designed to be generally used by the transportation industry as energy‐absorbing reinforcements in bumper panels or as permanent cores for weight reduction. In composite metal foams (CMFs), the second phase is usually formed by hollow spheres or closed‐wall porous materials responsible for the gas (void) intake. Herein, three types of samples are compared: CMFs with unimodal small, unimodal large, and bimodally mixed small and large ceramic hollow spheres. Unmodified AlSi12 or Sr modified AlSi12 alloy is infiltrated between the spheres with low‐pressure infiltration to form the cellular structure. The effect of Sr modification on the matrix material properties and the matrix–filler interface layer is investigated. The samples are evaluated and compared based on microstructural analysis and standardized compressive tests; the fracture mechanism of the structure is analyzed using computed tomography measurements at different deformation states. The aim of this research is to develop high‐performance unimodal and bimodal CMFs, which have better specific mechanical properties than conventional metal foams, and to investigate the effect of Sr modification on the material properties. With these foams, additional weight reduction and higher energy absorption can be achieved, primarily used as automotive components.

Strain-, curvature- and twist-independent temperature sensor based on a small air core hollow core fiber structure.

Cross-sensitivity (crosstalk) to multiple parameters is a serious but common issue for most sensors and can significantly decrease the usefulness and detection accuracy of sensors. In this work, a high sensitivity temperature sensor based on a small air core (10 µm) hollow core fiber (SACHCF) structure is proposed. Co-excitation of both anti-resonant reflecting optical waveguide (ARROW) and Mach-Zehnder interferometer (MZI) guiding mechanisms in transmission are demonstrated. It is found that the strain sensitivity of the proposed SACHCF structure is decreased over one order of magnitude when a double phase condition (destructive condition of MZI and resonant condition of ARROW) is satisfied. In addition, due to its compact size and a symmetrical configuration, the SACHCF structure shows ultra-low sensitivity to curvature and twist. Experimentally, a high temperature sensitivity of 31.6 pm/°C, an ultra-low strain sensitivity of -0.01pm/µε, a curvature sensitivity of 18.25 pm/m-1, and a twist sensitivity of -22.55 pm/(rad/m) were demonstrated. The corresponding temperature cross sensitivities to strain, curvature and twist are calculated to be -0.00032 °C/µε, 0.58 °C/m-1 and 0.71 °C/(rad/m), respectively. The above cross sensitivities are one to two orders of magnitude lower than that of previously reported optical fiber temperature sensors. The proposed sensor shows a great potential to be used as a temperature sensor in practical applications where influence of multiple environmental parameters cannot be eliminated.

Semi local hollow modules

To consider (R) is a commutative ring with unitary, (X) be a non--Zero unity left (R - module); (X) is known hollow module if each proper sub module of (X) is semi small local hollow module if (X) has a unique maximal submodule which contains each semi small submodule. The current study deals with this class of modules and give several fundamental properties related with this concept.

Role of Dispersion Interactions in Endohedral TM@(ZnS)12 Structures.

II–VI semiconducting materials are gaining attention due to their optoelectronic properties. Moreover, the addition of transition metals, TMs, might give them magnetic properties. The location and distance of the TM are crucial in determining such magnetic properties. In this work, we focus on small hollow (ZnS)12 nanoclusters doped with TMs. Because (ZnS)12 is a cage-like spheroid, the cavity inside the structure allows for the design of endohedral compounds resembling those of C60. Previous studies theoretically predicted that the first-row TM(ZnS)12 endohedral compounds were thermodynamically unstable compared to the surface compounds, where the TM atom is located at the surface of the cluster. The transition states connecting both structure families were calculated, and the estimated lifetimes of these compounds were predicted to be markedly small. However, in such works dispersion effects were not taken into account. Here, in order to check for the influence of dispersion on the possible stabilization of the desired TM(ZnS)12 endohedrally doped clusters, several functionals are tested and compare to MP2. It is found that the dispersion effects play a very important role in determining the location of the metals, especially in those TMs with the 4s3d shell half-filled or completely filled. In addition, a complete family of TM doped (ZnS)12 nanoclusters is explored using ab initio molecular dynamics simulations and local minima optimizations that could guide the experimental synthesis of such compounds. From the magnetic point of view, the Cr(7S)@(ZnS)12 compound is the most interesting case, since the endohedral isomer is predicted to be the global minimum. Moreover, molecular dynamics simulations show that when the Cr atom is located at the surface of the cluster, it spontaneously migrates toward the center of the cavity at room temperature.

Holocene expansion of the Caledonian pinewoods: Spatial and temporal patterns at regional and landscape scales

Background : To facilitate climatic change adaptation, landscape and conservation managers require understanding of spatio-temporal patterns of expansion of potential dominant species. Studying past expansions of canopy-dominant trees can contribute such understanding. Aims : Test hypotheses about expansions of dominants using as a model the mid-Holocene expansion of forests dominated by Pinus sylvestris in the Scottish Highlands. Methods : Pollen analysis and radiocarbon dating of Holocene sediments of a larger basin and several small hollows were performed in three landscapes along a north–south transect. A larger basin records expansion timing at landscape scale, whilst small hollows evidence within-landscape spatio-temporal patterns. Results : Vegetation existing prior to the expansion of pinewoods influenced landscape-scale spatio-temporal expansion patterns of P. sylvestris. Open vegetation generally was invaded earlier and/or to a greater extent; invasion was often later, or did not occur, where woodland with a substantial temperate broadleaved tree and shrub component (e.g. Corylus avellana, Quercus spp.) was present. Most small hollows, not just those where pinewoods became locally established, recorded vegetation change during the expansion. Some present landscape-scale forest composition patterns were established at that time. Conclusions : Studying past expansions of dominants provides evidence relevant to planning conservation and landscape management to facilitate ecological adaptation as species adjust their distributions and abundances in response to climatic change.

Dynamics of laser-induced cavitation bubbles near a short hole and laser cavitation processing with particles

The interest in pulsation process of laser-induced cavitation bubble in infinite domain or near a solid boundary has increased greatly in recent years. However, studies on dynamics of laser-induced bubbles near a small hole are few. In this work, dynamics of laser-induced cavitation bubbles before and after going through a small hole was studied by high-speed imaging. Various dimensionless parameter, laser energies, hole diameters and hole lengths were selected to investigate the bubble pulsation. Furthermore, a novel surface treatment method of small hole assisted laser cavitation processing in SiO2 particles suspension was proposed to improve surface quality. The surface morphology, residual stress, and roughness of 1060 aluminium alloy after laser cavitation processing were investigated. Results indicate that dimensionless parameter and hole’s size have a great impact on bubble pulsation. Maximum instantaneous velocity of the front and rear walls of the bubbles is about 47 m/s and 119 m/s respectively when the bubble pulsates behind the hole. The movements of the bubbles may cause the particles to impact the surface, producing small hollows and providing concentrated residual stress.

On the 13C‐NMR chemical shift anisotropy patterns and aromatic character in strained fullerenes: Computational analysis of D6h/D2d‐C36 fullerene

AbstractThe NMR characterization of small C36 hollow fullerene exposes a stable cage with structural features based on its strained curved π‐surface in a D6h‐symmetry. Our results indicate that planar‐like aromatic properties of the D6h‐C36 isomer decrease to a nonaromatic cage for D2d‐C36 after Stone‐Wales transformation of an equatorial [6.6] bond. This is given by the decrease of conjugation in the strained π‐surface after Stone‐Wales transformation. Calculated nuclear shielding shows that the main shielding component is always oriented perpendicularly to the cage π‐surface despite the larger curvature degree, as a result of the sp2 character of carbon atoms, resembling C60. Moreover, the D6h‐ and D2d‐C36 cages differ in their charge distribution properties, leading to charge accumulation in the strained cap of the former that leads to a polymerization‐prone cage, which contrasts with that expected for the D2d structure. Hence, structural rearrangements of these non‐Hirsch aromatic fullerenes show that their inherent global behavior requires considering the structural features besides electron counting rules.

Macrovoid-free high performance polybenzimidazole hollow fiber membranes for elevated temperature H2/CO2 separations

Thermally robust membranes are required for H2 production and carbon capture from hydrocarbon fuel derived synthesis (syn) gas. Polybenzimidaole (PBI) materials have exceptional thermal, chemical and mechanical characteristics and high H2 perm-selectivity for efficient syngas separations at process relevant conditions. The large gas volumes processed mandate the use of a high-throughput, small footprint hollow fiber membrane (HFM) platform. In this work, an industrially attractive spinning protocol is developed to fabricate PBI HFMs with unprecedented H2/CO2 separation performance. A unique dope composition incorporating an acetonitrile diluent is discovered enabling asymmetric macro-void free PBI HFM fabrication using a water coagulant. The influences of dope viscosity, coagulant chemistry, and air gap on HFM morphology are evaluated. Elevated temperature (up to 350 °C) H2 permeances of 400 GPU with H2/CO2 selectivities > 20 are achieved. This unprecedented separation performance is a ground breaking achievement at temperatures traditionally considered out-of-reach for polymeric membranes.

Regolith textures on Mercury: Comparison with the Moon

Surfaces of atmosphereless planetary bodies, including the Moon and Mercury, are covered with regolith. Regolith-related processes define surface morphology at scales of meters and tens of meters. We systematically surveyed all available images of the surface of Mercury with image resolution better than 2.5 m per pixel, and compared the observed regolith textures with those on the Moon. In a manner similar to the Moon, a typical surface contains many impact craters of different degrees of degradation, which indicates that regolith gardening smooths all topographic features. Textures characteristic of surfaces of large young craters with thin regolith are similar on both bodies. There are several types of sharp geologically young textures on Mercury that do not have lunar analogs. Hollows are young sharp irregular depressions on Mercury; they were discovered in images of lower resolution and attributed to sublimation of unidentified, moderately volatile material. Our survey reveals small, decameter-size hollows both spatially associated with known large hollow clusters and scattered at great distances from them. The existence of small hollows provides new constraints on the nature of these enigmatic features. Two types of fresh, geologically young regolith textures on Mercury, finely textured slope patches and chevron texture, have no analogs on the Moon, and their formation mechanism is unclear. We propose that sintering of regolith particles due to high peak surface temperatures cause formation of a slightly indurated decimeter-thick crust at the regolith surface on Mercury. We hypothesize that such a crust can play a key role in formation of these uniquely regolith textures of Mercury.

Biomimetic porous polypropylene foams with special wettability properties

Nowadays, the subject of wettability still has received little attention in the scientific literature, especially in the cellular solids, despite its significant role in the pervasiveness of the water treatment. Herein, inspired by the mussel, a green method was developed to construct nano-/micro-structures on the multi-structural polypropylene (like the dense solids, big hollow, small hollow and hierarchical open/closed-cell porous structure) by the surface-adherent polydopamine. Moreover, the relationship between both surface chemical and physical (such as pore structure and size) properties of the porous media, and wettability were studied. Besides, water–glycerol mixture solutions with various viscosities were used to study the spreading and imbibition behavior in the porous polypropylene foams, and the surface free energy of the different cellular solids (before and after modification) was estimated by Owens-Wendt equation. More interestingly, different kinds of the super-wetting materials like super-amphiphilic and hierarchical super-hydrophilic/super-hydrophobic, etc., were successful prepared. Both fundamental theoretical and numerical analysis were also conducted to reveal the mechanism of the penetration or surface repellency toward a drop, and to predict the transport of fluids in porous media. We believe that this work may serve as a source of inspiration in designing other advanced functional materials.

Characteristics of vector beams in mid-infrared waveband in an As2Se3 photonic crystal fiber with small hollow core

Abstract Characteristics of vector beams in mid-infrared waveband are analyzed numerically in an As2Se3 photonic crystal fiber (PCF) with small central hollow core (SCHH), including the mode fields, confinement loss, effective refractive index and chromatic dispersion. In the PCFs with the SCHH diameter d0 of 0–1.5 μm, the confinement losses of the four vector beams (HE11, TM01, TE01, and HE21) are smaller than 1.0 dB/m for the wavelengths up to ~5 μm. For the SCHH diameter d0 of 0.5–1.5 μm, the field enhancement of the HE11 mode occurs in the SCHHs in the central area for the wavelengths ≥5 μm. This happens because the evanescent light penetrates into the SCHH. With d0 increasing, the effective refractive index separations (δneff) between the HE11 mode and high-order modes (TM01, TE01, and HE21) decreases, while the δneff among the high-order modes increases. At the wavelength of 5 μm, the δneff of HE11-TE01, TE01-HE21, and HE21-TM01 is 0.03098, 0.03960, and 0.06867, respectively, when d0 is 1.5 μm. The second ZDWs of TE01, HE21 and TM01 mode are blueshifted with the increase of d0, but they are longer than 5 μm. The negative dispersion regions of the high-order modes (TE01, HE21, and TM01) are much wider than the HE11 modes. With the increase of d0, the HE11 mode dispersion curves have no obvious change, while the high-order modes (TE01, HE21, and TM01) dispersion curves become steep at the longer wavelength, the TM01 mode changes most obviously, and the depression appears. The transmission property for the waveband of 5–10 μm could be improved by increasing the ring number or core diameter of the fiber. The fiber losses at 10 μm are 4.81, 7.65, 5.95 and 2.47 dB/m for the four kinds of vector beams, respectively, when the diameters of the central area and SCHH are increased to 15.09 and 5.25 μm. Our simulated results will be useful for the optical applications in mid-infrared waveband, such as the generation of cylindrical vector mode and orbital angular momentum (OAM) and the particle manipulation by optical fields.