Hemispherical Depressions Research Articles

Charcoal-containing microwave electromagnetic radiation absorbers with relief surface

A new technology for manufacturing microwave electromagnetic radiation (EMR) absorbers characterized by a geometrically inhomogeneous surface is presented. The novelty of the presented technology lies in the use of radiotransparent polymer forms with hemispherical depressions of the same volume, which are the component for the formation of the surface layer of absorbers. The technology consists in filling these molds with a mixture of powdered activated (birch) charcoal and the binder in the liquid phase and further drying it in the forms. Compared with analogues, the developed technology is characterized by low complexity of reproduction. Most of the time required to implement the presented technology is associated with the drying process of a mixture of powdered activated birch charcoal and a binder. The experimentally established patterns of changes in the values of electromagnetic radiation reflection and absorption coefficients in the frequency range 1.0–28.0 GHz of the absorbers manufactured in accordance with the presented technology are provided, depending on the type of binder contained in them (polyvinyl acetate aqueous solution, gypsum aqueous solution, polyurethane mastic). It was determined that the most effective of the EMR absorbers studied in the course of establishing the indicated patterns are those ones that contain an aqueous solution of polyvinyl acetate. Electromagnetic radiation absorption coefficient values in the frequency range 1.0–28.0 GHz of such absorbers vary from 0.75 to 0.99. In addition, the mass per unit area of such absorbers is 1.5–2.0 times less than the mass per unit area of absorbers containing an gypsum aqueous solution or polyurethane mastic. Microwave EMR absorbers manufactured using the presented technology are characterized by higher mechanical strength, as well as lower cost compared to analogues and are recommended for use in the creation of anechoic chambers.

Flexible and Speedy Preparation of Large-Scale Polystyrene Monolayer through Hemispherical-Depression-Assisted Self-Assembling and Vertical Lifting

Liquid interfacial self-assembled two-dimensional nanomonolayers are promising as colloidal crystal templates or lithographic masks for the mass production of periodic nanoarrays. However, the interfacial self-assembled monolayers usually suffer various defects such as grain boundaries, line defects, vacancy defects, and multilayers due to imperfect process technology. Here, we demonstrated a series of optimized strategies including the hemispherical-depression-assisted self-assembly, dot coating approach, and vertical lifting transfer protocol to eliminate surface defects especially multilayers jointly. After stabilizing the hemispherical depression height to 1.5 mm with a 40° tilted silicon slide, the self-assembly time was significantly shortened to 10 min for a 1 × 2 cm2 area of PS monolayer. The series of strategies were successfully implemented not only on glass and silicon flat substrates but also on the side and end face of optical fiber, even on flexible substrates, while maintaining great morphologies. Besides, in association with nanospherical lens photolithography and nanosphere lithography technologies, various two-dimensional nanoarrays such as nanotriangles and nanoholes could be successfully obtained for subsequent optical properties research, which present broad application prospects in biochemical sensing, medicine, environmental protection, and other fields.

Morphologic and Morphometric Study of Human Acetabulum and its Clinical Significance

Introduction: The acetabulum is a cup shaped hemispherical depression which is present on the hip bone, contributed by ilium, ischium and pubis. It has a central depressed non-articular part called acetabular fossa, surrounded by a curved lunate articular surface which articulates with the head of femur to form hip joint. The knowledge of acetabular dimensions assists the radiologists in diagnosing acetabular dysplasia and aids the surgeon to determine the correct size of the acetabular cup during total hip arthroplasty and to realign the acetabulum back to normal position. Aim: To measure and analyse the relationship between the depth and diameter of acetabulum and also to study the variations in the morphology of anterior acetabular ridge. Materials and Methods: A cross-sectional study was done on 104 unpaired dry human adult hip bones from February 2017 to September 2019 after obtaining ethical clearance. The diameter and depth of acetabulum was measured using vernier calliper and a metallic strip and correlation between them were analysed using Pearson’s test. Student’s t-test was used to test the significance between the variables. The p-value <0.05 were considered as statistically significant. The different shapes of anterior acetabular ridge were noted. All the recorded data were analysed using Statistical Package for the Social Sciences (SPSS version 16.0). Results: The average measurements of acetabular diameter and depth were 48.98±2.91 mm and 24.12±2.54 mm, respectively. A positive and a significant correlation was found between diameter and depth of the acetabulum (r=0.388, p<0.001). The mean values of diameter and depth of acetabulum in right side were 48.76±2.94 mm and 23.6±2.48 mm, respectively. The average values of diameter and depth in left side were 49.2±2.92 mm and 24.6±2.59 mm, respectively. Though the measurements of acetabular dimensions on left side were slightly greater than right side, they were not statistically significant (p>0.05). Four different shapes of anterior acetabular ridges were noted: angular (23.08%), curved (63.46%), straight (2.88%) and irregular (10.58%). Conclusion: The present study showed weakly positive correlation between diameter and depth of the acetabulum and morphological variations in the shape of anterior acetabular ridge.

Water-air regenerative heat exchanger with increased heat exchange efficiency

According to experts’ forecasts, by 2040 the global demand for energy will increase by 37%, and renewable energy sources in the next 20 years will become the fastest growing segment of the world energy, their share in the next decade will grow by about one and a half times. Solar energy is the fastest growing industry among all non-conventional energy sources and is gaining the highest rates of development in comparison with other renewable energy sources. In this article, the authors provide an overview of the technologies that increase the efficiency and productivity of solar panels, only the investigated methods are described that can speed up the process of introducing solar energy instead of traditional. All the methods described can increase the efficiency of systems that are based on the use of the sun as the main source of energy. The authors presented and described the scheme of a solar-air thermal power plant, which will improve energy efficiency through the use of a regenerative air solar collector with increased heat transfer efficiency. Strengthening will be achieved through the use of hemispherical depressions on the surface that receives solar radiation. A schematic diagram is given and the principle of operation of such a solar collector is described in detail. A comparative calculation of the intensification of the solar collector with the use of depressions and without the use as modernization was carried out, on the basis of which a conclusion was made about the efficiency of using this type of solar collector and the economic effect from the application of this method. A description of the method for calculating the solar collector is given, thanks to which this development can be used and implemented in existing heating and hot water supply systems.

Simple Hierarchical Interface Design Strategy for Accelerating Solar Evaporation

AbstractInterface design is an efficient way to improve the steam generation performance of solar evaporators. Accompanied with the formation of cellulose nanofiber/polylactic acid/polyaniline (PANI) hybrid aerogel (HA) by Pickering emulsion and in situ polymerization, this paper proposes a new perspective of hierarchical interface design strategy to accelerate the water evaporation driven by solar energy. By changing the concentration and type of doped acid, the distribution gap of different PANI forms in HA can be microscopically designed. PANI nanoclusters with smaller gaps facilitate HA to achieve an improved light absorption, photothermal conversion capability and steam generation rate. Moreover, macro interface design introduces hemispherical depression structures to the HA surface through a simple mold. These recessed surfaces not only increase the light absorption by increasing the multiple reflections and refractions of light on the recesses, but also recover part of the heat radiation loss to the environment. A higher evaporation rate of 1.65 kg m−2 h−1 with a steam generation efficiency of 94.6% is achieved under the irradiation of 1 Sun (100 mw cm−2). Finally, HAs have strong purification ability for various raw water, and are promising in terms of their application potential in the field of energy conversion.

Film Cooling with a Plate-Length-Distributed Supply of the Cooling Agent into Hemispherical Depressions in Rotation

Results of computer modeling of fi lm cooling with a plate-length-distributed supply of the cooling agent through angle holes in hemispherical depressions are presented. The calculations have been made in the range of variation in the injection parameter from 0.5 to 2.0 under steady-state conditions and in rotation using the commercial ANSYS CFX 14 software package.

Ductile fracture of an aluminum sheet under proportional loading

The ductile fracture of an AA6111 aluminum sheet after a thermal cycle typical of auto-body paint-baking is investigated with the hybrid experimental-numerical method. The plastic flow of the material is examined by uniaxial tension, plane-strain tension, disk-compression and notched-tension experiments, that are used to calibrate the Yld2004-18p anisotropic yield criterion and the combined Swift-Voce hardening model. Then, the fracture behavior under equibiaxial and plane-strain tension, as well as uniaxial tension and shear, is characterized using a specially-developed cruciform specimen, along with center-hole and shear specimens, respectively. The cruciform fracture specimen proposed here contains two shallow hemispherical depressions (dimples) in the test-section, to initiate fracture. For the fracture characterization, special emphasis is put on specimen design, so that the stress states developed at the neighborhood of the fracture initiation point remain proportional throughout the loading history. In all experiments, the surface strain fields are measured by a stereo-type digital image correlation system. This information is used to validate finite element simulations of the fracture experiments. It is found that the Yld2004-18p model provides a better agreement with experiments than von Mises does, which underscores the sensitivity of the hybrid method to the plasticity models adopted. Once validated, these simulations are used to obtain the fracture loci in terms of two stress-state metrics, i.e., the stress triaxiality and Lode angle parameter.

The Production of Thin‐Walled Jointless Gold Beads from the Maykop Culture Megalithic Tomb of the Early Bronze Age at Tsarskaya in the North Caucasus: Results of Analytical and Experimental Research

This study, the first of this kind, reconstructs the technical chaîne operatoire of thin‐walled jointless gold bead production in the Maykop culture on the basis of trace‐wear analysis, experimental research and comparative analysis, using gold beads from the Early Bronze Age dolmen (c. 3200–2900 bc) in kurgan 2 at Tsarskaya (discovered in 1898). The results of the study demonstrate that such beads were produced from a perforated disc‐shaped blank by pressure (with intermittent annealing) within a hemispherical depression in a shaping block (presumably made from stone or bone) and subsequent abrasive treatment of the surface. Most probably, this technique was a regional expression of Near Eastern jewellery traditions that emerged within the urbanized centres of Upper Mesopotamia in the early fourth millennium bc and spread out, through the Caucasus, into the southern boundaries of the Eurasian steppe.

Ultrahigh-Speed Dynamics of Micrometer-Scale Inertial Cavitation from Nanoparticles

Direct imaging of cavitation from solid nanoparticles has been a challenge due to the combined nanosized length and time scales involved. We report on high-speed microscopic imaging of inertial cavitation from gas trapped on nanoparticles with a tunable hemispherical depression (nanocups) at nanosecond time scales. The high-speed recordings establish that nanocups facilitate bubble growth followed by inertial collapse. Nanoparticle size, acoustic pressure amplitude, and frequency influence bubble dynamics and are compared to model predictions. Understanding these cavitation dynamics is critical for applications enhanced by acoustic cavitation.

Ultrasound-induced inertial cavitation from gas-stabilizing nanoparticles.

The understanding of cavitation from nanoparticles has been hindered by the inability to control nanobubble size. We present a method to manufacture nanoparticles with a tunable single hemispherical depression (nanocups) of mean diameter 90, 260, or 650 nm entrapping a nanobubble. A modified Rayleigh-Plesset crevice model predicts the inertial cavitation threshold as a function of cavity size and frequency, and is verified experimentally. The ability to tune cavitation nanonuclei and predict their behavior will be useful for applications ranging from cancer therapy to ultrasonic cleaning.

Borings in gneiss boulders in the Miocene (Upper Tortonian) of the Sorbas Basin, SE Spain

AbstractMarine invertebrate borings are very rare in crystalline rocks, providing evidence of particular strategies producers use to colonise these unfavourable substrates. In the Sorbas Basin (Almería, southern Spain), Upper Miocene transgressive successions contain blocks of metamorphic and igneous rocks of the Nevado–Filabride Complex of the Betic Cordillera. Ichnological analysis of the embedded blocks shows the presence of two types of macroborings located in gneiss boulders, revealed to be an extraordinary case worldwide. The most abundant are regular hemispherical depressions ascribed reservedly to the well-known, mostly bivalve boringGastrochaenolites. The second one is a pouch-like depression, tapering downward, elliptical in outline, and clearly different to other non-circular-in-outline, pouch-shaped macroborings. Thus, a new ichnogenus and ichnospeciesCuenulites sorbasensishas been defined. According to the overall shape, an endolithic or semi-endolithic bivalve using chemical means to bore is suggested as the tracemaker. Colonisation could be determined by sea-level coastal dynamics, with decreasing energy during advancing transgression allowing boring, which was then stopped due to supply of fine-grained sediment that killed the borers.

Spontaneous counter-current imbibition outwards from a hemi-spherical depression

Spontaneous counter-current imbibition occurs when brine spontaneously displaces oil from a very strongly water-wet rock. Past experiments have been performed on cylindrical rock cores, with or without a cylindrical hole drilled through them, that have some or all of their faces open to imbibition. Changes in the area open to imbibition and the boundary conditions of the core plug can make large differences to the rate of imbibition. For example, linear imbibition into a core with one-end-open is significantly slower than imbibition into an all-faces-open core, and radial inwards imbibition goes faster than radial outwards imbibition. For linear imbibition, the volume imbibed with time varies as the square root of time as compared with almost linear variation with time for radial outwards imbibition. The reason for this behaviour during radial outwards imbibition is that most of the flow resistance is in the vicinity of the cylindrical hole, whereas most of the volume is near the closed outer boundary of the core. One would expect similar behaviour (i.e. imbibition volume linear with time) from spherical outwards imbibition. Experimentally, the situation can be realised by imbibition from an open hemi-spherical cavity on one face of a hemi-spherical block which is sealed on all other faces. In the present paper, a theory for spontaneous spherical outwards imbibition is developed assuming piston-like advance of a front from such a hemi-spherical cavity. Results are calculated and compared for various boundary conditions and the spherical outwards prediction is then tested by experimental results obtained for chalk blocks. The predictions and the experiments confirm that, for the spherical outwards boundary condition, the production curves can be almost linear with time.

Translation of a rigid body with gravity–friction seismic dampers

A refined mathematical dynamic model of a rigid body with a gravity–friction seismic damper moving inside a movable hemispherical rough depression is set up. This model describe the frequency and decrement properties of a rigid body undergoing translational vibrations on a gravity–friction seismic-isolation mechanism. The mechanism consists of two platforms. The lower (supporting) platform has spherical supports that contact with the upper (supported) platform within its hemispherical depressions. The equations of motion incorporate the nonideality of the unilateral constraints and the shock interaction of a material point with the sphere. It is shown how to join the models describing the free motion and the sliding motion of the point over a spherical surface

Pore growth on n ‐InP in liquid ammonia: electrode potential and morphology evolution

AbstractIn this paper we report the pore formation onto n ‐InP (100) in acidic liquid ammonia at 223 K, by applying a constant current density of 2 mA·cm–2. The evolution of the electrode potential and the pore morphology has been investigated in this uncommon non‐aqueous medium. This solvent provides true water free and oxygen free conditions. Specific and reproducible electrochemical behaviour have been obtained. An original evolution of the porous structure has been observed by scanning electron microscopy. Tortuous current line oriented pores are formed. Pores are organized in hemispherical depressions and a multilayered structure is also evidenced. A three distinguished steps evolution has been established. In the first step, an insoluble passive layer is formed on surface, followed by the nucleation of the porous layer. The second phase corresponds to the formation of the first porous layer; while the third stage corresponds to the periodic lift‐off of the porous layer constituting thus a multilayered structure. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

“Taming” Rocks and Changing Landscapes

Cupmarks—artificial hemispherical depressions, often appearing in groups on bedrock surfaces—are found worldwide, often near Paleolithic sites and Holocene settlements. The term “bedrock mortars” expresses the interpretation that they were used for pounding/grinding collected plant foods. A re‐examination of the cupmarks near the site of Hatula, on the margin of the Judean Shephelah west of Jerusalem, rules out the traditional functional interpretation in this instance. Instead, the evidence suggests that these cupmarks are remnants of intensive quarrying aimed at extracting flint nodules from the conglomerate beneath the surface and that the quarry was exploited not only for nodules but for limestone slabs. The cupmarks were drilled during the Pre‐Pottery Neolithic A occupation of the site (ca. 9600–8000 Cal BC) and constitute a component of the Neolithic techno‐cultural tradition. Future research should enlarge the data set of cupmarks and furnish a better understanding of their role in the Pre‐Pottery Neolithic and beyond.

Fatigue in porous PMMA: The effect of stress concentrations

This paper reports on an investigation into the effect of notches and other stress concentration features on the high-cycle fatigue strength of polymethylmethacrylate. The material was used in a porous form, as is found in bone cement and other medical applications. Sharp notches and circular holes reduced the fatigue strength significantly and this could be predicted with an approach known as the theory of critical distances (TCD) which uses two parameters: a critical distance and a critical stress. Introducing large, blunt notches or small hemispherical depressions into the porous samples had no effect on fatigue strength. Mixing under vacuum to reduce porosity gave no significant improvement, but pore-free samples had a much higher fatigue strength. These findings could be explained with regard to the role of porosity. The results provide a framework for assessing the effects of stress concentrations in bone cement and thus improving the design of implants and the procedures used in their fixation.

Crossed cerebellar hypoperfusion in hyperacute ischemic stroke

Objective In chronic stage of cerebral hemispheric infarction, contralateral cerebellar blood flow and metabolism are depressed, which is known as crossed cerebellar diaschisis (CCD). The present study was performed to elucidate (1) whether the diaschisis occurs in hyperacute stage of ischemic stroke when computed tomography (CT) scans is not able to identify infarction, and (2) which site of lesion in the cerebrum is responsible for the depression in contralateral cerebellar blood flow. Methods Single photon emission computed tomography was performed in 21 patients with middle cerebral artery (MCA) embolic infarction within 6 h of the onset (3.2±1.1 h, mean±S.D.). Regions of interest (ROIs) were symmetrically located in the cerebral hemispheres including cerebral cortex and subcortex, and in the cerebellar hemispheres. Results The side-to-side ratio of cerebellar blood flow ipsilateral to that contralateral to cerebral infarct was significantly increased compared with that in normal control ( P<0.001), indicating that contralateral cerebellar blood flow was significantly depressed. In hyperacute stage, the ratio of cerebellar blood flow appeared to be associated with the ratio of cerebral blood flow in whole hemispheres ( r=0.44, P<0.05), in anterior frontal lobe ( r=0.44, P<0.05) and in anterior temporal lobe ( r=0.58, P<0.01), but not in infarct areas ( r=0.26, P=0.3). Stepwise regression analysis revealed that the ratios in cerebellar hemispheres were associated with those in anterior temporal lobe (multiple regression analysis, r=0.58, P<0.01). Conclusions Crossed cerebellar diaschisis occurs at hyperacute stage of stroke of the MCA infarction. It may be related to the hypoperfusion in the anterior frontal and anterior temporal lobes of the cerebrum where regional blood flow is decreased by ischemic infarction per se or by ipsilateral hemispheric depression from infarct area (diaschisis mechanism).

The effect of stress concentrations on the fracture strength of polymethylmethacrylate

Abstract Polymethylmethacrylate (PMMA) is a brittle material whose strength is greatly affected by stress concentrations such as notches and defects. This paper describes a method known as the Theory of Critical Distances (TCD) which uses a critical stress and a critical material distance. The method was tested against experimental data on the fracture strength of PMMA in two forms: commercial Perspex and surgical bone cement. Samples were made containing stress concentrations of various shapes and sizes: notches, holes and hemispherical depressions. Initial predictions were poor, but improved when a modified form of the theory was used, taking the critical stress to be higher than the material’s UTS. One interesting observation, which is well predicted by the theory, is that features with a stress concentration factor less than some critical value (approximately 2) or smaller than a critical size (approximately 0.5 mm) cause no reduction in strength.

Mass/Heat Transfer in Dimpled Two‐Pass Coolant Passages with Rotation

Mass/heat transfer measurements are made in dimpled (hemispherical depressions) inlet and outlet coolant flow passages using the naphthalene sublimation method. The leading and trailing surfaces are dimpled, while the side walls are kept smooth. Measurements are made at a Reynolds number of 21,000 and for Rotation numbers of 0 and 0.2. The measurements indicate that dimples enhance surface mass/heat transfer. This enhancement is stronger in the inlet passage than in the outlet passage. Peak mass/heat transfer occurs immediately downstream of the dimples, while the minimum mass/heat transfer occurs in the dimple region itself. Higher mass/heat transfer is also observed along the lateral edges of the dimple. The location of the Sherwood number peaks suggest the existence of streamwise vortical structures generated from the leading and lateral edges of the dimples.

Aerodynamic Measurements of Regular Depression Roughness

Three plates roughened with regular arrays of cylindrical and hemispherical depressions were tested in a wind tunnel to gain insight into the aerodynamic effects of depression roughness. The term depression roughness refers to configurations where the roughness elements are depressions whose plan area constitutes less than about one-third of the total surface area. The effects of the three depression-roughness configurations on law-of-the-wall parameters were determined. They were found to be much less than that of protrusion roughness of corresponding cross section. Hemispherical depressions produced greater increases in skin friction than cylindrical depressions of the same diameter and depth. Flow development along surfaces with depression roughness can be computed using the same methods used for protrusion roughness, provided that an equivalent protrusion height can be established for the depressions