Hemispherical Shape Research Articles

In Situ Contact Angle Tuning of Silver Nanostructures by Laser Heating in Different Fluid Ambient.

It has been theoretically suggested by Yan et al. (Colloids Surf., A 2013, 429, 142-148) that the contact angle θc of a liquid droplet on any given surface can be controlled by immersing it in an appropriate surrounding environment. Here, we report the first experimental demonstration of such an in situ contact angle tuning of silver (Ag) nanoparticles on quartz substrates via nanosecond pulsed laser heating under various fluid ambients, like air, water, and glycerol. Nanosphere lithography (NSL) was used to deposit Ag nanopyramids on quartz substrates. This system was subsequently melted by laser heating inside the various fluids to form nanoparticles. By using a combination of top and side view scanning electron microscopy (SEM) imaging, we show that the contact angle of Ag nanoparticles could be increased by going from heating in air to heating under fluids, with a near hemispherical shape (θc ∼ 99°) under air irradiation to nearly spherical (θc ∼ 167°) under glycerol irradiation. The mechanism of this contact angle change could be explained qualitatively by the changing interfacial energies of the substrate and metal in the various fluids. Similar contact angle control was also achieved for nanoparticles created by dewetting of Ag thin films in the various fluids. One practical implication of this contact angle tunability is the ability to change the intensity ratio of the quadrupolar to dipolar localized surface plasmon resonances in the Ag nanoparticles. This work also has implications to those applications in which nanoparticles on a substrate are heated in various gas or fluid ambients, such as in catalysis, as the ensuing shape change can modify properties.

Analytical design of all-dielectric grating as a narrowband absorber

All dielectric grating absorbers due to the high potential of providing reliable applications in modern devices and technology are being investigated. Periodic structures based on high-index all dielectric materials are particularly attractive due to the low ohmic loss. In this work, we have proposed and investigated all dielectric grating absorbers by an analytical model. Firstly, we have compared the results of the proposed analytical method with the existent experimental outcomes. Secondly, using the impedance matching concept we have proposed another structure of a hemisphere shape and compared the results of the proposed method with those of the full-wave simulations. With this novel structure, we have achieved high absorptance of approximately 100% and high-quality factor (Q=14.23). Additionally, our proposed method reduces the calculation time and needs less memory compared to the full-wave simulations. The results of the analytical method have an acceptable agreement with the experimental data and those of the full-wave simulations.

3D warp interlocks p-aramid fabrics for composite reinforcement and ballistic vest applications: Effect of yarn density on its formability characteristics

The material forming capability becomes one of the most important characteristic of textile performance in the manufacturing of three-dimensional (3D) components to fit a 3D surface in various technical applications. In this study, different forming characteristics of 3D warp interlock fabrics in dry fabric condition were investigated. 3D warp interlock architecture with different areal density from same para-aramid yarn with a linear density of 168dtex were systematically designed and produced on automatic dobby loom with standard atmospheric conditions. The approach utilizes a low speed forming process with a predefined hemispherical shape of punch for the analysis of different forming behaviour of the fabrics specimen. The same blank-holder pressure was chosen for all the samples for better comparisons. Among several forming properties, some important characteristics have been observed, measured and analysed for a better understanding of the material forming behaviour of the different samples specimen. The research results with independent warp and weft yarn densities show a significant impact on the forming behaviours 3D warp interlock fabric. Moreover, the result of the investigation also will give a better understanding on different forming behaviours of 3D warp interlock fabric with various densities while applying in different textile application including women soft body armour.

Three new species of the spiral nematode genus helicotylenchus steiner, 1945 (nematoda: hoplolaimidae) from Vietnam

Investigations on entomopathogenic and plant parasitic nematodes in some natural forests in the Ngoc Linh mountain (Quang Nam province) and the Thuong Xuan forest (Thanh Hoa province) revealed three new species of plant parasitic nematodes belonging to the genus Helicotylenchus Steiner, 1945 (Nematoda: Hoplolaimidae). These new species were named Helicotylenchus castanus sp. n., Helicotylenchus madhucus sp. n. and Helicotylenchus digitus sp. n. with morphological characteristics described and illustrated. The new species Helicotylenchus castanus sp.n. is characterized by the highly hemispherical shape of the lip region, extremely short and rounded tail without projection. The second new species Helicotylenchus madhucus sp. n. is characterized by high lip region with 4-5 annuli, hemispherical and not set off from body contour, stylet 31.3-35.9 (33.3 ± 1.3) µm long, tail with a short ventral projection and the presence of males in the population. The third new species, Helicotylenchus digitus sp.n. was recognized by broad rounded tail with strong annulated projection in the digital shape, and also the presence of males in population.

Spatial Structure of Prunus armeniaca L. Populations in the Arid Woodlands of Mountaineous Dagestan

The spatial structure of Prunus armeniaca L. populations was studied at three altitudinal levels in the mountainous Dagestan with respect to the slope steepness. The greatest density of apricot massifs is on the flat slopes of northern exposures and in areas adjacent to river valleys. On the southern slopes, due to their erosion and steepness in comparison with the northern slopes, both the density of apricot trees (r = –0.45) and the diversity of other tree species (r = –0.91) are decreased, which leads to the formation of monodominant apricot woodlands. With increasing density and joint growth with other tree species, the crown of apricot acquires a pyramidal shape; at a low density, it has a hemispherical shape.

On the formation of surface craters by rapid cluster ions

A theoretical approach is developed to describe the dominant features of process by which craters form on the copper, gold and solid argon surfaces under self impacts of high velocity cluster ions. It is showed that, in the shock wave conditions generated at the impact of cluster on the surface, the dynamical process begins when the shock reaches the target free surface inducing the formation of a rarefaction wave(release wave) which propagates inward into the compressed region. The rarefaction causes the shocked material to move toward the free surface and expand into a vacuum forming the crater. It is found that the size of cluster has a significant influence on the mechanism of crater formation. In addition to metals (Cu and Au) the proposed approach has been successfully extended to impact of argon clusters on solid argon substrate. The approach has been validated using molecular dynamics simulated data for copper, gold and argon available in the literature. All simulated crater volumes have been analytically reproduced with a good agreement on the basis of a hemispherical shape.

Rapid, high-quality microfabrication of thermoset polymer PDMS using laser-induced bubbles.

Bubbles can be formed by focusing a high-power laser in a liquid. Based on this phenomenon, the present study demonstrated a novel technique, referred to as microFabrication using Laser-Induced Bubbles (microFLIB), for the microfabrication of the thermoset polymer polydimethylsiloxane (PDMS). A conventional nanosecond green laser was focused at the interface between uncured PDMS and a metal target and scanned to generate a line of bubbles at the boundary. The hemispherical shapes of these bubbles produced a groove on the rear side of the PDMS substrate following subsequent thermal curing. After the fabrication of such specimens, metal films could be selectively deposited along the grooves by electroless plating. This process allows rapid, high-quality microfluidic fabrication with potential applications to biochips.

Systematic evaluation of the interface description for fluid–structure interaction simulations using the isogeometric mortar-based mapping

Within this study the influence of the interface description for partitioned Fluid–Structure Interaction (FSI) simulations is systematically evaluated. In particular, a Non-Uniform Rational B-Spline (NURBS)-based isogeometric mortar method is elaborated which enables the transfer of fields defined on low-order and isogeometric representations of the interface along which the FSI constraints are defined. Moreover, the concept of the Exact Coupling Layer (ECL) using the proposed isogeometric mortar-based mapping method is presented. It allows for smoothing fields that are transferred between two standard low-order surface discretizations applying the exact interface description in terms of NURBS. This is especially important for highly turbulent flows, where the artificial roughness of the low-order faceted FSI interfaces results in spurious flow fields leading to inaccurate FSI solutions. The approach proposed is subsequently compared to the standard mortar-based mapping method for transferring fields between two low-order surface representations (finite volume method for the fluid and finite element method for the structure) and validated on a simple lid-driven cavity FSI benchmark. Then, the physically motivated 3D example of the turbulent flow around a membranous hemisphere (Wood et al., 2016) is considered. Its behavior is predicted by combining the large-eddy simulation technique with the isogeometric analysis to demonstrate the usefulness of the isogeometric mortar-based mapping method for real-world FSI applications. Additionally, the test case of a bluff body significantly deformed in an eigenmode shape of the aforementioned hemisphere is used. For this purpose, both “standard” low-order finite element discretizations and a smooth IGA-based description of the structural surface are considered. This deformation is transferred to the fluid FSI interface and the influence of the interface description on the fluid flow is analyzed. Finally, the computational costs related to the presented methodology are evaluated. The results suggest that the proposed methodology can effectively improve the overall FSI behavior with minimal effort by considering the exact geometry description based on the Computer-Aided Design (CAD) model of the FSI interface.

First prototyping of a dedicated PET system with the hemisphere detector arrangement

A strong demand is expected for high-sensitivity, high-resolution and low-cost brain positron emission tomography (PET) imaging for early diagnosis of dementia, as well as for general neuroscience studies. Therefore, we have proposed novel geometries of a hemisphere detector arrangement for high-sensitivity brain imaging, in which an add-on detector at the chin position or neck position helps in sensitivity uniformity improvement. In this study, we developed the first prototype system for proof-of-concept using four-layer depth-of-interaction detectors, each of which consisted of 16 × 16 × 4 Zr-doped GSO crystals with dimensions of 2.8 × 2.8 × 7.5 mm3 and a high-sensitivity 64-channel flat-panel photomultiplier tube. We used 47 detectors to form a hemisphere detector with a hemisphere shape of 25 cm inner diameter and 50 cm outer diameter, and we used seven detectors for each of the add-on detectors. The total detector number of 54 was about one-fourth that of a typical whole-body PET scanner. The hemisphere detector for the prototype system was realized by multiple rings having different numbers of detectors and a cross-shaped top detector unit covering the top. Performance evaluation showed uniform spatial resolutions of 3–4 mm by the filtered back-projection method. Imaging tests of a hot-rod phantom done with an iterative method were able to resolve 2.2 mm rods. Peak sensitivity was measured as more than 10% at a region near the top of the head, which was achieved with the help of the top detector unit. In addition, using the prototype system, we performed the first FDG clinical test with a healthy volunteer. The results showed that the proposed geometries had high potential for realizing high-sensitivity, high-resolution, and low-cost brain PET imaging. As for the add-on detector position, it was shown that the neck position resulted in higher sensitivity and wider field of view (FOV) than the chin position because the add-on detector at the neck position can be placed continuously to the hemisphere detector and close to the FOV.

Template-Free Synthesis and Selective Filling of Janus Nanocups.

We report on the formation of shape- and surface-anisotropic Janus nanocups (JNCs) by evaporation-induced confinement assembly (EICA) of ABC triblock terpolymers. During microphase separation in spherical confinement, the triblock terpolymer spontaneously adopted a hemispherical shape with an inner concentric lamella-lamella (ll) morphology. Cross-linking and disassembly of the microparticles resulted in well-defined JNCs with different chemistry on the inside and outside. By synthesizing polymers with increasing length of the cross-linkable block, we tuned the mechanical stability of the nanocups, which is relevant to control opening and closing of the cup cavity. We utilize the Janus properties for selective uptake of cargo exemplified by the filling of JNCs with polymer or gold nanoparticles. The directional properties of JNCs suggest applications in locomotion, oil-spill recovery, storage and release, templating, and as nanoreactors with attoliter volume.

Ultraselective acetone-gas sensor based ZnO flowers functionalized by Au nanoparticle loading on certain facet

ZnO flowers with thin sheet and hemisphere shapes were fabricated via thermal decomposition in an organic solvent. Especially, typical hemisphere morphology with exposed (002) crystal face were created for the first time. Because of exposed (002) facet increased, a facet-like heterostructure of ZnO formed to get enhanced sensor performance, especially after loading Au nanoparticles (NPs) using a supersonic chemistry way. Gas sensing tests indicate that the hemisphere Au/ZnO sensor with the best performance and a nice selectivity to acetone. This is ascribed that the unique second-level structure provides more active centers and diffusion channels for acetone molecules. Au NPs increases the thickness of the surface electron depletion layer, which enhanced the sensitivity of the gas sensor.

Effects of electrode parameters on sewage disinfection by underwater pulsed arc discharge

Underwater pulsed arc discharge is a potential method applying on sewage disinfection. The disinfection effect may be influenced by electrode parameters. In this paper, effects of different electrode materials, gap distances and electrode shapes were studied with underwater pulsed arc discharge. The following results were obtained through experiments. Reactive species production of different materials are arranged from largest to smallest is W, Titanium alloy and Ti. However, the difference of pressure amplitude among three materials is less than 0.88%. Under the influence of these physical and chemical effects, with 800 s’ treatment, the residual Escherichia coli content of W, Titanium alloy, and Ti is 103.77 CFU/L, 104.29 CFU/L, and 104.87 CFU/L. W shows the best disinfection effect, which generated 2.2 orders reduction with an energy density of 0.6 J/mL. It can be found that the disinfection effect has a positive correlation with the electron work function of material. When the voltage is constant, the discharge dispersion increases as the gap distance increases. At a discharge voltage of 4.5 kV, with the gap distance changing from 0.25 to 1.50 mm, the total spectral intensity decreases, and the pressure amplitude increases first and then decreases. The study shows disinfection efficiency keeps the same trend with the change of pressure wave. And there is an optimal distance in sewage disinfection. Under the experimental conditions in this manuscript, the optimal distance is 1 mm. For the three electrode shapes, the pressure amplitude and total spectral intensity of rod shape are higher than hemisphere and cone shape. As a result, the rod electrode presented the highest disinfection effect, which residual Escherichia coli content is 103.63 CFU/L after 800 s’ treatment.

From 2D to 3D: Strain- and elongation-free topological transformations of optoelectronic circuits

Optoelectronic circuits in 3D shapes with large deformations can offer additional functionalities inaccessible to conventional planar electronics based on 2D geometries constrained by conventional photolithographic patterning processes. A light-sensing focal plane array (FPA) used in imagers is one example of a system that can benefit from fabrication on curved surfaces. By mimicking the hemispherical shape of the retina in the human eye, a hemispherical FPA provides a low-aberration image with a wide field of view. Due to the inherently high value of such applications, intensive efforts have been devoted to solving the problem of transforming a circuit fabricated on a flat wafer surface to an arbitrary shape without loss of performance or distorting the linear layouts that are the natural product of this fabrication paradigm. Here we report a general approach for fabricating electronic circuits and optoelectronic devices on nondevelopable surfaces by introducing shear slip of thin-film circuit components relative to the distorting substrate. In particular, we demonstrate retina-like imagers that allow for a topological transformation from a plane to a hemisphere without changing the relative positions of the pixels from that initially laid out on a planar surface. As a result, the resolution of the imager, particularly in the foveal region, is not compromised by stretching or creasing that inevitably results in transforming a 2D plane into a 3D geometry. The demonstration provides a general strategy for realizing high-density integrated circuits on randomly shaped, nondevelopable surfaces.

Solvent-free growth of carbon dots by sputter-plasma assisted chemical vapour deposition over large areas

Planar graphene quantum dots synthesized using wet chemistry have been widely investigated for their optoelectronic properties, but less work exists on deposition of curved carbon dots (CDs) by physical techniques. In this work, a bottom-up growth method termed sputter-plasma assisted chemical vapour deposition (SPA-CVD) is used to grow curved CDs in vacuum, reminiscent of graphene fabricated on copper foil using chemical vapour deposition. In SPA-CVD, ∼10-nm thick Cu layers with an ultrathin carbon film on top are nucleated into copper nanoparticles (Cu-NP) by thermal annealing resulting in curved CDs on their surfaces. CD morphology and dimensions are determined by the hemispherical shape of the nucleated Cu-NPs. With this method, a uniform layer of CDs of tuneable size can be grown on a substrate such as aluminum over wafer-size-areas, without the use of solvents. CD diameter and concentration can be tuned over a wide range by manipulating the SPA-CVD sputtering and evaporation parameters. It is shown that SPA-CVD grown curved CDs embedded in a poly(methyl methacrylate) matrix show resistive memory effects. This work provides a new insight towards the development of high-quality, curved CDs with tuneable properties for device applications, for which planar and solution processed CDs may not be suitable.

A 3-dimensional hemispherical brain phantom for compact dedicated brain PET scanners

A new brain-dedicated compact PET scanner with hemispherical detector arrangement has been recently proposed for high-sensitivity brain imaging. An appropriate standard phantom is highly required for an objective performance evaluation. The Hoffman 3-dimensional (3D) brain phantom has been widely used as a de-facto standard brain phantom. However, the Hoffman phantom cannot be inserted into hemispherical PET scanners because the phantom has a cylindrical shape outside, which is different from the actual human head. Therefore, the purpose of this study is to develop a 3D ‘hemispherical’ brain phantom which is applicable to various scanners including the scanners with hemispherical detector arrangement. Changing outer shell into a hemispherical shape while maintaining the same radioactivity distribution as the original Hoffman phantom was the key. We performed a simulation study and an actual PET/CT study comparing the original Hoffman and hemispherical phantoms. In the simulation, we evaluated the count characteristics, image noise and voxel-by-voxel differences between phantom images and the digital reference. In the actual PET/CT study, we compared the PET images of the two phantoms using a commercial PET/CT scanner. As a result, in the simulation study, the noise equivalent count rate of the hemispherical phantom was higher than that of the original Hoffman phantom by about 20%. On the other hand, the difference in the image noise was not considerable and average global absolute voxel-by-voxel differences from the reference were almost same between the cylindrical and hemispherical phantoms. In the actual PET/CT study, the hemispherical phantom was validated to use imaging performance evaluation, and the obtained percent contrast was comparable with the original Hoffman phantom. The developed hemispherical phantom is useful for compact PET scanners with hemispherical detector arrangement in view of evaluation of appropriate scanning/reconstruction parameters and validation of the imaging performance towards clinical and widespread applications.

Development of button shear keys to improve the debonding resistance of sandwich composite panel

Abstract In the composite sandwich panel, debonding between the foam core and face sheet is due to its inability to withstand shear loads. In the present study shear resistance capability of sandwich panel is enhanced by introducing button shaped shear key inserts in between facesheet and foam core. The sandwich panel is composed of glass fibre reinforced polymer (GFRP) skin with PVC (Polyvinylchloride) foam core impregnated with epoxy resin while the button keys are made up of chopped strands. By using the present methodology, the bonding of the facesheet and foam core of sandwich model will be improved by the participation of the core through button keys. Also, the button shapes distribute the stress concentration uniformly on the inner layer of the foam surface. Parametric finite element (FE) investigation using ANSYS software has also been performed to evaluate the foam core performance by the introduction of button shaped grooves in the foam material. The shapes of the button keys comprising of hemisphere, frustum and cylindrical shapes are analysed numerically and compared with experimental results.

Description of Rotylenchus rhomboides n. sp. and a Belgian population of Rotylenchus buxophilus (Tylenchomorpha: Hoplolaimidae).

During a survey in the Botanical garden of Ghent University, a new species Rotylenchus rhomboides n. sp. and a population of Rotylenchus buxophilus were found. Rotylenchus rhomboides n. sp. is characterized by the presence of a rhomboid-like widening of the mid-ridge of lateral field at the level of vulva, a feature previously unknown within the genus. The population of the new species, composed only by females, has a rounded labial region with 4 to 5 annuli, robust stylet (31–37 μm long), short dorsal esophageal gland (9–19 μm) overlap of the intestine, vulva located slightly posterior to mid-body, and hemispherical or rounded tail shape with large phasmids located 3 to 5 annuli anterior to the level of anus. The hierarchical cluster analysis based on morphological features indicated that the new species closely resembles R. corsicus, R. gracilidens, and R. rugatocuticulatus. The DNA analyses of the D2-D3 of 28S rDNA, ITS rDNA, and COI mtDNA sequences of Rotylenchus rhomboides n. sp. show a close relationship with R. buxophilus, R. goodeyi, R. laurentinus, R. pumilus, and R. incultus, all of which can also be differentiated from the new species by morphological features. The combination of morphological, morphometric, and molecular characteristics confirmed the new species and the first report of R. buxophilus on yam (Dioscorea tokoro) in Belgium.

«Города» кочевых скифов

The issue of temporary “cities’ of nomadic Scythians consisting of tent wagons and removable yurts which arose at the site of the Scythian families and the locations of Scythian aristocrats, Tzars and Nomarhs, is considered in the article. The transition to a nomadic way of life, which was based on extensive herding, was impossible without a number of technical achievements: the development of a perfect system for reining a horse, the widespread development of iron and, as a consequence, the emergence of high-tech and reliable weapon. The creation of dwelling, the most adapted to the conditions of nomadic life was of great importance. First of all, a tent wagon covered with felt, became such a dwelling, drawn by slow, but powerful oxen. In our opinion, besides the tent wagons, the Scythians already had such characteristic dwellings for nomads in the form of removable yurts installed on a platform base. During the stay, tent wagons and removable yurts of the Scythians, especially when it comes to influential and populous Scythian cities, as well as the nomadic locations of the Scythian leaders, from a distance could seem to the traveler to be a real city. So-called catacombs are characteristic Scythian burials, especially for IV BC. They consist of a vertical entrance pit (in the mounds of the Scythian aristocracy, its depth could reach 15 m) and one or more burial chambers arranged in the walls or at the corners of the entrance pit. These chambers had an arched vault, resembling a canopy of Scythian tent wagon. Considering that the wheels sometimes appeared on the pledge of these chambers, it can be safely assumed that the Scythian burial chambers recreated the habitual dwelling of the deceased, a tent wagon in which he was born and died. In this case, the “cap” of the Scythian mounds of the hemispherical shape could recreate another nomadic dwelling — a yurt.

High Performance, Tunable Electrically Small Antennas through Mechanically Guided 3D Assembly.

To address demands for increased data transmission rates, electrically small antennas (ESAs) that simultaneously offer large frequency bandwidths and small physical sizes are of growing interest. 3D layouts are particularly important in this context and among various 3D ESAs, systems that adopt hemispherical shapes are very promising, because they can occupy the entire Chu-sphere and offer outstanding electrical performance. Researchers have developed a few different approaches to fabricate high-quality hemispherical ESAs, but most have static layouts and fixed operating frequencies. Here, a mechanically guided 3D assembly approach is introduced for the design and fabrication of deformable hemispherical ESAs that can offer tunable, dynamic properties to adapt to changes in environmental conditions. The strategy exploits controlled compressive buckling of strategically patterned 2D precursor structures, as a low-cost and high-yield scheme that can exploit conventional, planar processing technologies and commercially available platforms. Combined numerical simulations and experimental measurements show outstanding performance characteristics in terms of the quality factor and radiation efficiency. Application of external tensile strains to elastomeric substrates for these systems allows them to be reshaped and reversibly tuned through a wide range of center frequencies. Mechanical testing under different loading conditions demonstrates the ability of these ESAs to accommodate large deformations.

Toward understanding the origin of asteroid geometries

More than a half of the asteroids in the main belt have irregular shapes with ratios of the minor to major axis lengths of less than 0.6. One of the mechanisms that create such shapes is collisions between asteroids. The relationship between the shapes of collisional outcomes and impact conditions such as impact velocities may provide information on the collisional environments and its evolutionary stages when those asteroids are created. In this study, we perform numerical simulations of collisional destruction of asteroids with radii 50 km and subsequent gravitational reaccumulation using smoothed-particle hydrodynamics for elastic dynamics with self-gravity, a model of rock fractures, and a model of friction in completely damaged rock. We systematically vary the impact velocity from 50 to 400 m s−1 and the impact angle from 5° to 45°. We investigate shapes of the largest remnants resulting from collisional simulations. As a result, various shapes (bilobed, spherical, flat, elongated, and hemispherical shapes) are formed through equal-mass and low-velocity (50−400 m s−1) impacts. We clarify a range of the impact angle and velocity to form each shape. Our results indicate that irregular shapes, especially flat shapes, of asteroids with diameters larger than 80 km are likely to be formed through similar-mass and low-velocity impacts, which are likely to occur in the primordial environment prior to the formation of Jupiter.