Identical Spheres Research Articles

Motion space analysis of objects in multiple point contacts with applications to form-closure and kinematic pairs

This paper presents a screw theory based method for determining the set of possible second-order relative motions between two 3D rigid objects which are initially in a finite number of unilateral point contacts. Using adjoint transformation for twist and twist-derivative, the motion space allowed by each contact is referred to a common coordinate system. Thereafter, a set of quadratic inequalities in twist and twist-derivative coordinates are solved for obtaining the resultant allowable motions. We show that a minimum of three frictionless contacts are sufficient for curvature based form-closure. Also, it is shown exactly that a regular tetrahedron can be in second-order form-closure with four identical spheres in point contact.

“Do identity and distinctness facts threaten the PSR?”

One conception of the Principle of Sufficient Reason (PSR) maintains that every fact is metaphysically explained. There are different ways to challenge this version of the PSR; one type of challenge involves pinpointing a specific set of facts that resist metaphysical explanation. Certain identity and distinctness facts seem to constitute such a set. For example, we can imagine a scenario in which we have two qualitatively identical spheres, Castor and Pollux. Castor is distinct from Pollux but it is unclear what could metaphysically explain this distinctness fact. In this paper, I argue that we should not treat identity and distinctness facts as metaphysically fundamental. As such, identity and distinctness facts do not challenge the PSR. We can metaphysically explain them.

The Image of the Yenisei in the Paintings of Krasnoyarsk Artists

The Yenisei river occupies a significant place both in the sphere of regional identity and in paintings and graphic works of Krasnoyarsk artists, since it forms the image of Krasnoyarsk and is a connecting link of the Yenisei Siberia. The article analyses paintings and graphic works of Krasnoyarsk artists to identify the features of the image of the Yenisei in regional art. The study is based on the theoretical principles of the modern theory of visual arts and on the analysis of the selected paintings and graphic works of Krasnoyarsk artists of the 20th and 21st centuries from the collection of the Krasnoyarsk Art Museum named after V.I. Surikov. A wide range of sources, including studies of ethnocultural identity, the specific features of artistic culture and the characteristics of Krasnoyarsk landscapes is considered. In the process of comparing the analysis results, it has been revealed that for Krasnoyarsk artists the Yenisei is not only the embodiment of endless natural forces, but also a connecting and harmonising link between the human world and the natural world, at the same time representing a special identity of Siberians (Amosova, et al., 2019)

A numerical study of acoustic scattering by Janus spheres.

Recently Janus particles have become important in several technological fields because they have interesting properties compared with homogeneous particles. The interaction of Janus particles with sound waves is of particular interest for diagnostic purposes, and also in applications in micro- and nanotechnology. In this paper the authors demonstrate that a method of fundamental solution combined with a T-matrix that is computed from far-field information can be applied with benefit to analyse the scattering of sound waves by a particular type of Janus sphere. Moreover, it is shown that this method converges faster than the conventional T-matrix method introduced by Waterman [(1969). J. Acoust. Soc. Am. 45, 1417-1429]. This is of special importance if orientation averaged scattering quantities are required, or if multiple scattering processes on Janus spheres are considered. This method is used to demonstrate the interesting phenomenon of an enhanced side scattering intensity that is larger than the forward scattering intensity, and that this effect can be strengthened using a particular configuration of two identical Janus spheres. Finally, the authors discuss a useful approximation that can be readily applied for two or more Janus spheres.

Simulation of sedimentation of two spheres with different densities in a square tube

We simulated the sedimentations of two unequal spheres with different densities in a square tube for Galileo numbers (Ga) from 5 to 25, resulting in a Reynolds number range of based on the terminal settling velocity. The sedimentation of spheres with different densities is dynamically more complex than that of identical spheres. At high Ga the spheres oscillate in the centreline plane of the tube, where they are initially released from rest. By contrast, the spheres move to the diagonal or reverse–diagonal plane of the tube at low Ga, reaching a steady or periodic state depending on the density difference between them. A phase diagram illustrates the transitions between different sedimentation behaviours depending on Ga and the density difference. A possible mechanism for these behaviours is also presented. Furthermore, we compare two-dimensional (2-D) and three-dimensional computations for our system to attain a better understanding of the hydrodynamic interactions between two unequal spheres at low but finite Reynolds number. Comparing relative trajectories, periods of oscillation and flow features shows that 2-D circular cylinders oscillate much more strongly and frequently than spheres under the same flow conditions. In particular, spheres do not have the discontinuity in period that arises in the 2-D case from the change in rotation sign of a heavy particle.

Mechanical Properties of Cu-B/Diamond Composites Prepared by Gas Pressure Infiltration

Diamond particles reinforced boron-alloyed Cu matrix (Cu-xB/diamond, x = 0.1, 0.2, 0.3, 0.4, 0.5, and 1.0 wt.%) composites were prepared by gas pressure infiltration. The size of the diamond particles was ~ 230 μm and the diamond volume fraction in the composites was ~ 66%. The interfacial carbide evolution plays an important role in improving the interfacial bonding and enhancing the mechanical properties of the Cu-B/diamond composites. The tensile, compressive and bending strengths firstly increase and then decrease with increasing boron content, giving a maximum tensile strength of 204 MPa, a maximum compressive strength of 608 MPa, and a maximum bending strength of 513 MPa at 0.5 wt.% B addition. The monotonic uniaxial tensile stress–strain curves of the Cu-B/diamond composites were predicted by using the Mori–Tanaka, generalized self-consistent, and Torquato identical hard spheres approximation models. The results suggest that alloying B to Cu matrix is an effective route to strengthening Cu/diamond composites.

Crystallization in a One-Dimensional Periodic Landscape

We consider the crystallization problem for a finite one-dimensional collection of identical hard spheres in a periodic energy landscape. This issue arises in connection with the investigation of crystalline states of ionic dimers, as well as in epitaxial growth on a crystalline substrate in presence of lattice mismatch. Depending on the commensurability of the radius of the sphere and the period of the landscape, we discuss the possible emergence of crystallized states. In particular, we prove that crystallization in arbitrarily long chains is generically not to be expected.

Jammed hard-sphere hcp crystals permeated with trivacancy tunnels

Supported by simple table-top experiments involving stackings of ball bearings and theoretical analysis, we have discovered crystal packings of identical hard spheres that are permeated by a high concentration of large tunnels and yet are jammed (mechanically stable). We show that starting with a strictly jammed hexagonal close-packed (hcp) crystal of identical hard spheres, removal of certain subsets of those spheres can produce mechanically stable vacancy arrangements involving compact (equilateral triangle) trivacancies such that they produce linear trivacancy tunnels. These tunnels can extend over the entire macroscopic length of the hcp medium, and their width is sufficient to allow contained “test” hard spheres with diameters less than 5−1=1.23606… to migrate over that entire length without contacting the static tunnel-wall spheres. A search for the stable (strictly jammed) periodic framework that hosts the highest density of parallel trivacancy tunnels has identified a structure exhibiting a packing fraction ϕ=π/32=0.55536…, which is equal to 3/4 of the maximum monovalent sphere packing fraction ϕmax=π/18=0.74048…. In that periodic arrangement, filling the interior of the contained tunnels with movable unit-diameter spheres may approach the greatest possible “rattler” density within jammed monovalent sphere systems subject to periodic boundary conditions. It will be of interest to study the physical and chemical properties of these anisotropic porous crystal structures. Our findings may have practical implications for engineered separation and catalytic processes.

El budismo tibetano en el ciberespacio: nuevas tecnologías de la información y la comunicación en la Comunidad Dzogchen Internacional

The article explores the impact that new communication and information technologies have had on the recreation of Buddhism in the West. Taking as a case study the Dzogchen International Community, a group of Tibetan roots with presence in Argentina for more than three decades, the paper aims to understand the role played by the use of the internet in the construction of the ritual, community, corporal, and political dimensions of the aforementioned institution. In this way, the text focuses on analyzing the way in which cyberspace fosters the construction of a transnational religious community in which ritual practices mediated by virtual interfaces are coupled with the daily routines of its members. In addition, it explores the incidence that the virtual experience of religion has in the sphere of identity and corporality as well as in the sphere of power relations. The methodological approach on which the research is based included the ethnographic fieldwork and the investigation of the multiple digital media that the Dzogchen International Community uses, in order to enable the analysis of the interrelation between the online world and the offline field.

New Online Communities and New Identity Making: The Curious Case of the Kurdish Diaspora

The central argument in this paper is that the intimately set of processes—diaspora, transnationalism, and communication technologies—are creating new maps of identities, which are diverging from traditional forms of identity-making within the physical and national territory. By delving into how this triangulated relationship brings out a series of new identity experiences, the aim here is to demonstrate how this can serve as a timely example in a wider context of how traditional spheres of identity (i.e. ethnicity, culture, gender, and religion), which have hitherto provided people with firm identities, are being contested in this age of digital technologies and new transnational and global collaborations. Based on an interdisciplinary and comparative research study, including multi-sited (online-offline) methodology, the empirical examples unveil how diasporic Kurds have through their online activities developed transnational and global consciousness that goes beyond the national or dual diasporic consciousness. They display a growing awareness of identity difference not only between diaspora and homeland Kurds, but also between Kurdish diasporas in various European countries. While the struggle for nation-state building and identity rights are still a central part of their agenda, the new opportunities for self-representation in the online world suggest novel articulations of identity which are challenging old notions of belonging and community. Therefore, rather than speaking of the inflationary “imagined diaspora,” this paper presents the fluidity of diasporic identities and how victim diaspora can morph into transnational and global diaspora. The acknowledgement of identity difference and the de-mythologization of the homeland complicates the concept of the imagined community which until now has not been sufficiently recognized in academic writing.

Digital Identity and Our Remembrance

The text password, which is a section of the secret credentials, is known to be too hard to manage. Secret credentials are absolutely necessary for digital identity in democratic societies. We could look for something other than the text password as the valid secret credential. Three big myths are rampant in the sphere of digital identity. These are ‘Higher security achieved by removal of password’, ‘Passwords killed by the biometrics that is dependent on passwords’ and ‘Passwords displaced by PIN that is no more than a weak form of numbers-only password’. Unraveling these myths, we come to the conclusions that we must look for something really valid in the sphere of ‘Non-Text Password’ and that the identity of ‘citizens’ cannot be separated from their volition and memory while the identity of ‘things’ can be handled only technologically. Our own autobiographic memory, especially episodic memory, enables us to come up with the most reliable digital identity platform, bidding farewell to the unsafe and torturous identity proofing.

Discrete element simulation of surface mechanical attrition treatment with rough-surface sonotrode

Surface mechanical attrition treatment (SMAT) is a specialized cold working method that is used to induce compressive residual stresses and refine crystalline grains at the surface of metal components. This technique is increasingly employed in different industries, and the control and optimization of the method require fundamental understanding and accurate process modelling, in particularly detailed information regarding the shot-target interaction. This paper presents a Discrete Element Method (DEM) study of the shot dynamics with rough sonotrodes. These rough surfaces are created by grouping in a hexagonal packing of identical spheres. Different roughness values are obtained by varying the sphere diameter and spacing. The coefficient of restitution (CoR) between shot and target used in our DEM simulations was obtained from Finite Element Method (FEM) simulations of multiple shot-target impacts. The DEM results are analyzed after the SMAT process has reached the steady state. The relationships between surface roughness and the resulting impact angle and velocity distributions are investigated. Furthermore, based on a parametric study, we conducted correlation analyses between processing parameters and shot dynamics, and identified key conditions, using the mechanistic models. The proposed numerical method and findings of this study could be used to tailor the SMAT processes.

Identity Contradictions in Islamic Awakening: Harmonising Intellectual Spheres of Identity

The Islamic awakening demonstrates the following essential contradictions. First, it calls for the authentic return to Arab-Islamic heritage, while deeming as heretical several traditional doctrines; second, it strives for Arab unity without recognising the needed concessions that should be given to unify non-Muslim Arabs; third, it is proud of the creativity of Islamic heritage in natural and philosophical fields while rejecting the indebtedness to Greek or Zoroastrian influences; fourth, it embraces the Abrahamic path in response to atheistic trends and calling for unity with Jewish and Christian monotheisms, without accepting the possibility of tracing the influence of these traditions on the Qur’an and without admitting the non-Abrahamic traditions such as Hinduism into the spiritual camp; and fifth, it admits the primacy of scientific knowledge, while disparaging its methodological presumptions seen in materialism. The articulation of critical views to resolve these contradictions in the Arab world present creative reformation attempts to harmonise intellectual spheres of identity.

Simulating the mechanics of sea ice using the discrete element method

We developed a technique using the discrete element method (DEM) to simulate the fracture mechanics of ice under flexural, compressive, and tensile loading. In the simulations, virtual blocks of ice are created through a multistep process. First, identical spheres are settled into a random packing. Then, a force network is established at the contact points between spherical elements, which are subsequently replaced by their representative Voronoi volumes. The results of three different sets of tests suggest that the strength of the simulated ice was well characterized using a linear function of the free parameters for the critical bond normal and shear stresses. Additionally, in the flexural strength tests the ratio of the ice thickness to the diameter of the spheres was shown to be sensitive for values less than 4.5, suggesting that a minimum number of bonds was necessary to produce robust estimates for the flexural strength. Overall, the results indicate that the simulations may be calibrated to match the strength properties of various types of ice found in the marginal ice zone (MIZ). The DEM simulations developed here may be used in larger scale models to directly incorporate the effects of ice break up on water waves in the MIZ.

Tendencies of Usage of Geometrical Ornaments in Graphic Design Projects of Ukraine in the XXI ct.

The aim of the research is to outline the present tendencies of usage of geometrical ornaments functioning as symbols of national culture and cultural identity of the Ukrainian nation. Methods of research. The basic method applied in the research is method of complex analysis. Scientific novelty. The novelty of the research lies in discovering the tendencies of usage of geometrical ornaments in modern graphic design projects and in identifying the methods of transformation of Ukrainian geometrical ornamentation. It has been found out that in the sphere of brand identity geometrical elements of ornaments, losing their connection with traditional technologies of implementation, come under influence of visual transformations, namely, switching to line graphics, using contrform effect and pixelation effect. At the same time in the sphere of sign formation sign elements of the graphical ornaments largely obtain abundance of colouring or become subject to colored characteristics of letter and type elements (logos). In billposters and posters an integral series of geometrical ornamentation in both one-colour and two-colour (red and black) versions of execution is used. In other advertising vehicles and graphic products, such as packaging and advertising booklets, one-colour, or monochrome implementation of ornamental ribbon is most frequently found, which makes it a unique marker of national culture and national traditions. Conclusions. The research proved the idea that geometrical ornaments and their individual elements are used in a wide range of graphic design products. It should be noted though that most of these elements fall onto the sphere of sign formation, brand identity, billposters and posters, and far less are used in packaging and print advertising products. The design of modern advertising and graphic products still does not sufficiently use the potential of the sign elements of Ukrainian geometrical ornaments. In the course of the research it has also emerged that graphic designers in their projects almost do not use motifs and compositional groups from the art of the Ukrainian pysanka (painting of Easter eggs).

Discrete element modeling of static liquefaction of shield tunnel face in saturated sand

The failure mechanism and limit support pressure are essential factors for the stability assessment of tunnel face during shield tunneling. Previous studies were mostly based on the assumption that soil fails when the plastic limit is reached. The static liquefaction of saturated sand at pre-failure state often largely reduces shear strength; a stable tunnel face could be destabilized and even collapses abruptly. This paper aims to explore the static liquefaction failure of tunnel face in saturated sands by 3D discrete element simulation. The particle shape is considered by using clump composed of two identical spheres, and the micro-material parameters are calibrated by fitting against triaxial tests. The tunnel face is initially supported by the earth pressure at rest, and then the pressure is reduced by applying a displacement on the free surface until soil body completely collapses. The second-order work during the unloading process is calculated, and a negative value denotes the initiation of static liquefaction. The distribution of negative second-order work point shows the initiation and propagation of static liquefaction. The ultimate failure mode is shown to be composed of a sliding wedge and an overlying chimney, and the chimney is confined to a local area for soil arching. The experienced stress path of tunnel face verifies the existence of static liquefaction instability, indicating the stability analysis should consider static liquefaction rather than simply using the conventional plastic limit state analysis.

Investigation of the Pressure Drop Across Packed Beds of Spherical Beads: Comparison of Empirical Models With Pore-Level Computational Fluid Dynamics Simulations

This study uses novel methods, combining discrete element method (DEM) simulations for packing and computational fluid dynamics (CFD) modeling of fluid flow, to simulate the pressure drop across rigid, randomly packed beds of spheres ranging from 1 to 3 mm in diameter, with porosities between 0.34 and 0.45. This modeling approach enables the combined effect of void fraction and particle size to be studied in more depth than that has been previously possible and is used to give insight into the ability of the well-established Ergun equation to predict the pressure drop behavior. The resulting predictions for pressure drop as a function of superficial velocity were processed to yield coefficients α and β in the Ergun equation and were found to be in keeping with equivalent data in the literature. Although the scatter in α with structural variations was very small, the scatter in β was large (±20%), leading to inaccuracies when used to predict pressure drop data at velocities beyond the Darcy regime. Evaluation of the packed particle structures showed that regions of poor packing, in samples with high porosity and large particle sizes, lead to lower β values. The findings bring strong support to the belief that a generalized model, such as that by Ergun, cannot yield a unique value for β, even for identical spheres.

Modeling Tumor Development, Progression and Metastasis in 3D Artificial Tissues: Characterization of Structure and Labeling Patterns in Breast Cancer Hanging‐drop Spheroid Cultures

In this report our laboratory presents the results of a series of studies being conducted to explore the application of 3D artificial tumor tissues as in‐vitro models of breast cancer development, progression and metastasis. In this case, we have employed MCF‐7 breast ductal adenocarcinoma cells and 3D Biomatrix hanging drop plates to evaluate these tumor properties within the context of staged tumor spheroids. A consistent observation of ours in nearly a decade of modeling breast cancer using various natural 3D scaffolds and hydrogel matrices has been that solid tumor models grown in long‐term culture predictably begin to shed both single cells and cell clusters in the form of small groupings of cells as well as progressively larger spheroids. Although we have shown that at least some of these structures have properties consistent with metastasis, including attachment and invasion of target tissues, spontaneously generated versions of cancer clusters also present as pleiomorphic structures and in relatively small numbers which complicates their study. Therefore, we sought to use a system that generates identical clusters and spheres from specific numbers of suspended single cells. The hanging drop system we employ comes in a 96 well format that allows us to generate literally as many spheres as we need for each study. Furthermore, these spheres can be grown out to match any of the sizes commonly found in our tumor models thereby allowing us to study each stage for structure, cell populations and markers. In addition these spheres are also assisting us in systematically studying the process of cancer cell cluster attachment and invasion and to test our working hypothesis that this is controlled through activation of EMT‐like responses through CD44 binding of hyaluronate on the target tissue. Using direct labeling of intact spheres coupled to embedding and sectioning followed by immunolabeling, these studies are demonstrating that over a period of 144 hours our spheroid cultures progress from simple clusters of a few cells to aggregated spheres containing thousands of cells and measuring up to ~600um in diameter. By this later stage, many spheres actually begin to generate their own smaller spheres and clusters as well. In our view this reflects the concept that past 48 hours in culture these spheres transition into being actual tumor organoids themselves. This is supported by development of a complex CD24+ internal structure distinct from an outer shell of CD44+ cells. These studies are ongoing and support our view that 3D artificial tumors are effective tools to study cancer biology in‐vitro.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Pair-wise MHD-interaction of rigid spheres in longitudinal creeping flow

Authors describe and study the mathematical model of two identical rigid spheres immersed in highly viscous fluid with magnetic field acting in it. At infinite distance from suspended particles the flow and the field are uniform. The hypothesis that bulk currents are weak allows to split magnetic and hydrodynamic interactions of the spheres. Distribution of magnetic field is obtained for arbitrary orientation of undisturbed field with respect to line going through the spheres' centers and is written in the form of multipole expansion. This expression is used to calculate magnetic force acting on both particles. Together with known expressions for hydrodynamic forces this result may be applied in study of particle dynamics in uniform flow of viscous magnetic fluid. In the paper particular case of field and flow being parallel to line of centers is examined in more detail. The opportunity of particles' coagulation in such flow is discussed.

Using a discrete element method to investigate seismic response and spin change of 99942 Apophis during its 2029 tidal encounter with Earth

Near-Earth Asteroid 99942 Apophis presents a unique opportunity to study the dynamics, bulk properties, and interior structure of a rubble-pile asteroid when it makes its close encounter with the Earth in 2029. In order to better understand the potential outcomes of a tidal encounter between Earth and Apophis, and to support a potential future mission to Apophis, we perform numerical simulations of the encounter. We represent Earth as a single rigid sphere and the target body as a cohesionless, self-gravitating granular aggregate of identical spheres in a hexagonal-close-packed configuration subject only to gravitational and soft-sphere (elastic) contact forces. We use a radar-derived shape model for the asteroid, along with current best estimates for the orbital solution of Apophis to simulate the encounter trajectory, and perform a large parameter sweep over different potential encounter orientations and bulk densities for the body. We find that the median change in the rotational period for Apophis, sampled for a range of different initial body and spin orientations, is −1.9 h (mean −0.1 ± 6.0 (1-σ) hours) during the encounter. Additionally, we measure that the mean of the largest change in axis length among the 3 primary body axes, also sampled over trials with different initial body and spin orientations, is 0.132 ± 0.066 mm during the encounter, assuming a bulk Young's Modulus of 106 Pa. Such strains on the timescale of peak stress during the encounter may be large enough to be detected by an in-situ seismometer.