Circular Face Research Articles

Diffuse elastic waves in a nearly axisymmetric body: Distribution, transport, and dynamical localization

We report measurements on the distribution and evolution of diffuse ultrasonic waves in elastic bodies with weakly broken axisymmetry. Aluminum cylinders with dimensions large compared to wavelength were excited by transient point sources at the center of the upper circular face. The resulting power spectral density was then examined as a function of time and frequency and position. It was found that this energy density showed a marked concentration at the center at early times, a concentration that subsequently slowly diminished towards a state of uniformity across the face, over times long compared to ultrasonic transit time across the sample. The evolution is attributed to scattering by symmetry breaking heterogeneities. Relaxation did not proceed all the way to uniformity and equipartition, behavior shown to be consistent with Enhanced Backscatter and with Dynamical Anderson Localization among subspaces of different angular momentum.

Undrained face stability of tunnels in Bangkok subsoils

This paper presents the analysis of undrained face stability of tunnels in Bangkok subsoils. In this study, two-dimensional (2D) and three-dimensional (3D) finite element analyses were employed to analyse the 2D plane strain conditions of transverse (2DT) and longitudinal (2DL) sections as well as the full 3D geometry, respectively. The simplified geometry of 2DT corresponds to the circular face of tunnels subjected to a uniform face pressure, while that of 2DL correspond to the plane strain heading applied by a uniform face pressure at the front plane. For the 2D plane strain transverse and longitudinal sections, the tunnel lining was not considered in the analyses. For 3D cases, tunnel linings were included in the analysis and modelled as the rigid plate element with the fully rough surface along their lengths, while the tunnel face was subjected a face pressure. For all cases, the uniform surcharge was applied all over the ground surface. Strength reduction methods in conjunction with 2D and 3D finite element analyses were employed to determine the stability and the factor of safety of this problem. The stability analyses included ranges of tunnel face pressure measured during the tunnelling process. Effects of three-dimensional stability of tunnel face were also presented and discussed in this paper. Results of analyses were verified and compared with existing methods.

CFD Simulation Of Air-Flow Over A „Quarter-Circular” Object Valided By Experimental Measurement

Abstract A Computer-Fluid-Dynamic (CFD) simulation of air-flow around quarter-circular object using commercial software ANSYS Fluent was used to study iteration of building to air-flow. Several, well know transient turbulence models were used and results were compared to experimental measurement of this object in Boundary Layer Wind Tunnel (BLWT) of Slovak University of Technology (SUT) in Bratislava. Main focus of this article is to compare pressure values from CFD in three different elevations, which were obtained from experimental measurement. Polyhedral mesh type was used in the simulation. Best results on the windward face elevations were obtained using LES turbulence model, where the averaged difference was around 7.71 %. On the leeward face elevations it was SAS turbulence model and averaged differences from was 15.91 %. On the circular face it was SAS turbulence model and averaged differences from all elevations was 12.93 %.

Reliability Analysis of Circular Tunnel Face Stability Obeying Hoek–Brown Failure Criterion Considering Different Distribution Types and Correlation Structures

AbstractA reliability analysis is presented of a circular tunnel face driven by a pressurized shield in a highly fractured Hoek–Brown (HB) rock mass. A limit analysis approach is employed to define a limit state function (LSF) based on an advanced rotational mechanism. The objective is to analyze how different reliability methods, different assumptions about distribution types and correlation structures of the random variables, and different tunnel sizes and support pressures influence the computed reliability results. Results indicate that the reliability method has a limited influence on reliability results, hence suggesting that the LSF is not highly nonlinear and that a computationally efficient method can be employed; and that all random variables under consideration are resistance variables, with their assumed distribution types and correlation structures having a significant effect on the reliability results. This emphasizes the importance of an adequate characterization of geotechnical uncertainti...

Internalization of red blood cell-mimicking hydrogel capsules with pH-triggered shape responses.

We report on naturally inspired hydrogel capsules with pH-induced transitions from discoids to oblate ellipsoids and their interactions with cells. We integrate characteristics of erythrocytes such as discoidal shape, hollow structure, and elasticity with reversible pH-responsiveness of poly(methacrylic acid) (PMAA) to design a new type of drug delivery carrier to be potentially triggered by chemical stimuli in the tumor lesion. The capsules are fabricated from cross-linked PMAA multilayers using sacrificial discoid silicon templates. The degree of capsule shape transition is controlled by the pH-tuned volume change, which in turn is regulated by the capsule wall composition. The (PMAA)15 capsules undergo a dramatic 24-fold volume change, while a moderate 2.3-fold volume variation is observed for more rigid PMAA–(poly(N-vinylpyrrolidone) (PMAA–PVPON)5 capsules when solution pH is varied between 7.4 and 4. Despite that both types of capsules exhibit discoid-to-oblate ellipsoid transitions, a 3-fold greater swelling in radial dimensions is found for one-component systems due to a greater degree of the circular face bulging. We also show that (PMAA–PVPON)5 discoidal capsules interact differently with J774A.1 macrophages, HMVEC endothelial cells, and 4T1 breast cancer cells. The discoidal capsules show 60% lower internalization as compared to spherical capsules. Finally, hydrogel capsules demonstrate a 2-fold decrease in size upon internalization. These capsules represent a unique example of elastic hydrogel discoids capable of pH-induced drastic and reversible variations in aspect ratios. Considering the RBC-mimicking shape, their dimensions, and their capability to undergo pH-triggered intracellular responses, the hydrogel capsules demonstrate considerable potential as novel carriers in shape-regulated transport and cellular uptake.

Bear Gulch style shield heraldry: Iconography of a Protohistoric period Northwestern Plains Warrior Society

The Bear Gulch and Atherton Canyon rock art sites in central Montana contain images of 1024 shield-bearing warriors and an additional 150 freestanding shields. More than 800 of these shields are decorated with heraldic designs characteristic of the Bear Gulch style, and form the largest corpus of Plains decorated shields. Using the system of basic meaningful units, Bear Gulch style designs can be grouped into five geometric and five representational categories, but a count of individual shields shows that the heraldic system was overwhelmingly based on geometric division of the shield's circular face. The various design categories are described and interpreted and the entire corpus of Bear Gulch style shields is compared with Castle Gardens rock art style shields and shields from Historic period Cheyenne culture.

Tunnel face stability and ground settlement in pressurized shield tunnelling

An analysis of the stability of large-diameter circular tunnels and ground settlement during tunnelling by a pressurized shield was presented. An innovative three-dimensional translational multi-block failure mechanism was proposed to determine the face support pressure of large-shield tunnelling. Compared with the currently available mechanisms, the proposed mechanism has two unique features: (1) the supporting pressure applied to the tunnel face is assumed to have a non-uniform rather than uniform distribution, and (2) the method takes into account the entire circular excavation face instead of merely an inscribed ellipse. Based on the discrete element method, a numerical simulation of the Shanghai Yangtze River Tunnel was carried out using the Particle Flow Code in two dimensions. The immediate ground movement during excavation, as well as the behaviour of the excavation face, the shield movement, and the excavated area, was considered before modelling the excavation process.

Sensuous electronics [Reflections

The entrepreneur had finished talking about the software and processing algorithms for a new camera he was marketing, and as he came down from the stage he left the camera on the podium-perhaps forgotten, but perhaps suggesting that it wasn't expensive enough to worry about. · I was contemplating those processing algorithms when a woman who had been sitting behind me pushed by, heading up the aisle. As she passed by, I heard her urgently muttering to herself, "I have to touch it." · It seemed a curious urge. All the magic was in the software and algorithms; the hardware was simply a lens, a sensor, and a few chips. Yet I understood exactly what she was saying. I felt the same way myself. · Why, I asked myself, did I have this need to touch? I started to think about the look and feel of electronic gadgets instead of their functionality. Meanwhile, another speaker was showing a small intelligent thermostat that promised to learn your heating habits and usage. She said it had been designed to be "pretty and fun." Indeed, it had a certain unadorned beauty, simply a circular face with a small touch screen. It seemed the hardware equivalent of the Google home page-minimal and clean. When I remarked on this, someone told me that the insides of the thermostat were equally beautiful. Looking again up at the stage, I was surprised to recognize the truth of this observation. The uncovered circuit board inside resembled a work of art, having the clean geometric lines of a Mondrian painting, compressed to a minimal size and with no appearance of clutter. It exuded a powerful latent functionality.

Neutron production with a pyroelectric double-crystal assembly without nano-tip

Two cylindrical LiTaO3 crystals facing each other's deuterated circular face were exposed to deuterium gas at an ambient pressure of a few mTorr. With a distance of about 4cm between the z+ and z− cut crystal faces, neutrons were produced via the 2H(d,n)3He fusion reaction upon the heating and cooling of the crystals. The 2.5MeV neutrons were detected with organic liquid scintillation detectors equipped with neutron-gamma pulse-shape discrimination electronics to reject pulses generated by the intense X-ray flux. During the cooling phase of naked crystals, deuterium ion-beam (D2+) energies of up to 400keV were obtained as deduced from the associated electron bremsstrahlung end-point energy. The highest electron-beam energy observed during the heating phase was 360keV. With a layer of deuterated polyethylene evaporated on the front face of the crystals, the maximal energies were about 10% lower. In contrast to earlier studies, an electric-field enhancing nano-tip was not employed. Neutron yields up to 500 per thermal cycle were observed, resulting in a total neutron production yield of about 1.6×104 neutrons per thermal cycle. Our approach has the potential of being substantially improved by reducing the frequency of the discharges we are currently experiencing with our geometry, which was not designed for the unprecedented high potentials produced in the presentwork.

Rotational failure mechanisms for the face stability analysis of tunnels driven by a pressurized shield

AbstractThe aim of this paper is to determine the collapse and blow‐out face pressures of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of the limit analysis theory. Two rotational failure mechanisms are proposed for the active and passive cases. These mechanisms have two significant advantages with respect to the available ones: (i) they take into account the entire circular tunnel face instead of an inscribed ellipse to this circular area, and (ii) they are more consistent with the rotational rigid‐block movement observed in the experimental tests. For both the active and passive cases, the three‐dimensional failure surface was generated ‘point by point’ instead of simple use of the existing standard geometric shapes such as cones or cylinders. This was achieved by employing a spatial discretization technique. The numerical results have shown that the present rotational mechanisms provide, in the case of frictional soils (with or without cohesion), a significant improvement with respect to the translational mechanisms. Finally, an extension of the proposed collapse mechanism to include a tension cut‐off in the classical Mohr–Coulomb failure criterion is presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd.

Face Stability Analysis of Circular Tunnels Driven by a Pressurized Shield

The aim of this paper is to determine the face collapse pressure of a circular tunnel driven by a pressurized shield. The analysis is performed in the framework of the kinematical approach of limit analysis theory. It is based on a translational three-dimensional multiblock failure mechanism. The present failure mechanism has a significant advantage with respect to the existing limit analysis mechanisms developed in the case of a frictional soil: it takes into account the entire circular tunnel face and not only an inscribed ellipse to this circular area. This was made possible by the use of a spatial discretization technique. Hence, the three-dimensional failure surface was generated by point instead of simple use of existing standard geometric shapes such as cones or cylinders. The numerical results have shown that a multiblock mechanism composed of three blocks is a good compromise between computation time and results accuracy. The present method significantly improves the best available solutions of the collapse pressure given by other kinematical approaches. Design charts are given in the case of a frictional and cohesive soil for practical use in geotechnical engineering.

Solution of N-S equations based on the quadtree cut cell method

With the characteristic of the quadtree data structure, a new mesh generation method, which adopts square meshes to decompose a background domain and a cut cell approach to express arbitrary boundaries, is proposed to keep the grids generated with a good orthogonality easily. The solution of N-S equations via finite volume method for this kind of unstructured meshes is derived. The mesh generator and N-S solver are implemented to study two benchmark cases, i.e. a lid driven flow within an inclined square and a natural convection heat transfer flow in a square duct with an inner hot circular face. The simulation results are in agreement with the benchmark values, verifying that the present methodology is valid and will be a strong tool for two-dimensional flow and heat transfer simulations, especially in the case of complex boundaries.

A closed-form solution for the computation of geometric correction factors for four-point resistivity measurements on cylindrical specimens

The present work deals with the evaluation of geometric correction factors for dc four-point probe measurements on finite cylindrical specimens for a random placement of the four probes on a circular face of the specimen. A closed-form (CF) analytical expression is obtained for the potential difference between the voltage probes via the solution of Laplace's equation using the variable-separation technique. The potential difference thus obtained is subsequently used to compute the geometric correction factor. The applicability of the solution is illustrated for two specific cases using a collinear probe-array, namely probes arranged along a radius and normal to a radius. Correction factors obtained from the CF solution are validated in each case by a finite-element simulation solution obtained using COMSOL Multiphysics 3.2. Additionally, the correction factors from the two methods are compared to analytical approximation factors, evaluated using expressions that exist in the literature. A range defined by a lower and an upper analytical approximation factor is computed for each specific case. Correction factors from the CF and COMSOL solutions show an excellent match with each other and lie within the analytical approximation bounds. The application of the CF solution is demonstrated for experimental measurements on copper specimens of different cylindrical geometries.

Packing cylinders on a cylinder with contact constraints

AbstractThe problem of cylinder packing is investigated. The specific problem is to determine the maximum number of congruent cylinders that can be packed around a core cylinder of arbitrary dimensions. The constraint is that their circular face must keep in contact with the core cylinder and there may be no overlapping. Only right circular cylinders are considered. Mathematically, a lower and upper bound is determined. A quantitative result is also found using a modified genetic algorithm. The algorithm was found to reproduce the published results for the top and bottom circular faces of the core which reduces to the problem of packing congruent circles within a circle. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Novel magnetic–acoustic resonator sensors for remote liquid phase measurement and mass detection

Electromagnetic excitation of miniaturized acoustic resonator sensors is a novel approach with distinct advantages over piezoelectric resonators. A much wider range of transducer materials can be utilized, and remote excitation of resonant vibrations in a wide variety of different mode shapes is possible. These resonant modes display similar quality factors and characteristics as those in piezoelectric transducers and can be applied for mass detection as well as liquid phase sensing. In this contribution, we focus on the electromagnetic excitation of acoustic face shear mode (FSM) resonators for liquid property sensing. A variety of non-piezoelectric transducer materials has been investigated. For liquid phase sensing, we have found circular face shear mode resonators to be most sensitive to fluid properties, e.g., density and viscosity, while radial flexural plate modes excite compressional waves and are thus most sensitive to fluid volume, or rather the distance to the liquid surface, i.e. liquid level. Experimental results have been compared with an FEM eigenmode analysis and equivalent circuit models providing a better understanding of the generation and detection mechanisms.

Localised blast loading of fibre–metal laminates with a polyamide matrix

This paper presents the results of localised blast tests on fully clamped square fibre–metal laminate panels, manufactured using sheets of 2024-O aluminium alloy, woven glass–fibre reinforced polyamide and a polypropylene adhesive. The fracture properties of the composite–metal interface were determined using the single cantilever beam geometry and the measured interfacial fracture toughness was between values in the literature for thermosetting composites and aluminium/glass fibre polypropylene. Observations from blast experiments performed on panels with different stacking configurations are reported. Diamond and circular back face damage were observed, along with pitting, global displacement and tearing of the front face. Examinations of sectioned panels are presented and multiple debonding, plastic deformation and fibre fracture were identified within the panels.

Brain processes associated with target finding

The response execution stage of cognitive skill consists of several substages, including finding the proper response location among available alternatives and moving the effector to the target location. In order to unravel the brain dynamics associated with the finding process, the present experiments used two experimental conditions. In the number condition, which requires both finding and moving, subjects are presented on each trial with a digit, 0–9, are required to find that digit on a circular clock face, and then to move a cursor to that target's location. In the arrow condition, an arrow pointing to the location of the target on the clock face circumference appears simultaneously with the target digit; no target finding is required because subjects need only to move the cursor along the path marked by the arrow. A pilot and the main experiment revealed that response initiation times but not movement times were affected by these experimental manipulations. Analysis of magnetoencephalographic (MEG) activity revealed an early occipital activity which was not affected by experimental manipulations. Later activity with central-parietal and parieto-temporal loci presumably reflected changes in the dorsal and ventral pathways, respectively, and these were affected by experimental conditions. Finally, finding processes seem to be associated with a second late activation of the ventral pathway presumably reflecting ongoing recognition processes.

Experimental Study of Heat Transfer in an Evaporating Meniscus on a Moving Heated Surface

A stable meniscus is formed by a circular nozzle dispensing water over a heated circular face of a rotating cylindrical copper block. The nozzle is offset from the axis of rotation of the copper block and thus a moving meniscus is formed on the surface. The water flow rate, heater surface temperature, and the speed of rotation are controlled to provide a stable meniscus with continuous evaporation of water without any meniscus breakup. The study provides an important insight into the role of the evaporating liquid-vapor interface and transient heat conduction around a nucleating bubble in pool boiling.

Study of Stirling Engine Having Heat Exchangers Consisting of Pin-Fin Arrays

The structure and numerically predicted results of a new Stirling engine with a circular disk heat exchanger consisting of pin-fin arrays are presented. Pin-fin arrays are carved into the circular heat exchanger disk's face. An annular cover plate is attached to these tips. A cooler of similar shape is located. So-called “α”, “β” and “γ” configurations are capable in present engine. Numerical prediction of power employing second-order approximation method is carried out in so-called “β” configuration engine case. The fluid resistances of many parts are regarded and some mechanical friction losses are regarded. The predicted engine output becomes 1 kW with the temperature of 773 and 298 [K] on the heating side and cooling side, respectively. In conclusion, the Stirling engine described here is suitable for biomass and solar use because its heater shape is circular and has unique feature that it doesn't need any heat exchanger pipe.

Influence of Phase Purity on the in Vivo Response to Hydroxyapatite

Two batches of calcium phosphate implants, termed HA1 and HA2 were prepared with calcium to phosphorus ratios of 1.67 and 1.70 respectively. XRD demonstrated that the HA1 implants were composed of phase pure hydroxyapatite, while the phase composition of the HA2 implants contained approximately 5% calcium oxide with the balance being hydroxyapatite. Sintered cylindrical implants, 3 mm in diameter, were prepared from each of the powders, containing slots I mm wide x 2 mm deep in one circular face. The implants were implanted laterally in the distal femur of 6 month old New Zealand white rabbits for a period of 3 weeks. Subsequent histological evaluation demonstrated that the presence of the CaO impurity phase significantly reduced the osteoconductivity, as demonstrated by minimal penetration of new bone within HA2 implant slots and a significant reduction in direct bone apposition on any of the HA2 implant surfaces as compared with HA1 implants. This study has confirmed the need for precise control of the phase purity of hydroxyapatite based bioceramics for optimal biological performance