Journal articles on the topic 'Silberberg'

An experimental study of the inertial migration of neutrally buoyant spherical particles suspended in the Poiseuille flow through circular tubes has been conducted at Reynolds numbers $(Re)$ from 100 to 1100 for particle-to-tube diameter ratios of ${\sim}$0.1. The distributions of particles in the tube cross-section were measured at various distances from the tube inlet and the radial probability function of particles was calculated. At relatively high $Re$, the radial probability function was found to have two peaks, corresponding to the so-called Segre–Silberberg annulus and the inner annulus, the latter of which was first reported experimentally by Matas et al. (J. Fluid Mech. vol. 515, 2004, pp. 171–195) to represent accumulation of particles at smaller radial positions than the Segre–Silberberg annulus. They assumed that the inner annulus would be an equilibrium position of particles, where the resultant lateral force on the particles disappears, similar to the Segre–Silberberg annulus. The present experimental study showed that the fraction of particles observed on the Segre–Silberberg annulus increased and the fraction on the inner annulus decreased further downstream, accompanying an outward shift of the inner annulus towards the Segre–Silberberg annulus and a decrease in its width. These results suggested that if the tubes were long enough, the inner annulus would disappear such that all particles would be focused on the Segre–Silberberg annulus for $Re<1000$. At the cross-section nearest to the tube inlet, particles were absent in the peripheral region close to the tube wall including the expected Segre–Silberberg annulus position for $Re>700$. In addition, the entry length after which radial migration has fully developed was found to increase with increasing $Re$, in contrast to the conventional estimate. These results may be related to the developing flow in the tube entrance region where the radial force profile would be different from that of the fully developed Poiseuille flow and there may not be an equilibrium position corresponding to the Segre–Silberberg annulus.

AbstractCross-streamline migration of soft particles in suspensions is essential for cell and DNA sorting, blood flow, polymer processing and so on. Pioneering work by Poiseuille on blood flow in vivo revealed an erythrocyte-free layer close to blood vessel walls. The formation of this layer is related to a viscous lift force caused by cell deformation that pushes cells towards the centre of blood capillaries. This lift force has in this case a strong impact on blood flow. In contrast, rigid spherical particles migrate from the centre towards the periphery, owing to inertia (the Segré–Silberberg effect). An important open issue is to elucidate the interplay between particle deformation and inertia. By using a capsule suspension model, Krueger, Kaoui & Harting (J. Fluid Mech., 2014, vol. 751, pp. 725–745) discovered that capsule flexibility can suppress the Segré–Silberberg effect and inertia promotes overall flow efficiency thanks to a strong inertial flow focusing effect.

The inertial migration of a small sphere in a Poiseuille flow is calculated for the case when the channel Reynolds number is of order unity. The equilibrium position is found to move towards the wall as the Reynolds number increases. The migration velocity is found to increase more slowly than quadratically. These results are compared with the experiments of Segré & Silberberg (1962 a, b).

A technique, based on the stress-integration method, for the evaluation of hydrodynamic forces on solid boundaries is proposed to simulate the solid-fluid flow systems in three dimensions in lattice Boltzmann simulations. The accuracy of the scheme is demonstrated by simulating the sphere migrating in a pressure-driven Newtonian fluid flow in a cylindrical tube. The numerical simulation results recover the Segré–Silberberg effect. Using this scheme, we investigate the behavior of a pair of spheres in a tube Poiseuille flow. Oscillatory states are observed for two spheres with different radii placed on opposite sides. The simulation results show that the present model is an effective and efficient direct numerical simulation method for simulating particle motions in fluid flows at finite Reynolds numbers in three dimensions.

In inertial microfluidics colloidal particles in a Poiseuille flow experience the Segré-Silberberg lift force, which drives them to specific positions in the channel cross section. An external force applied along the microchannel induces a cross-streamline migration to a new equilibrium position because of the Saffman effect. We apply optimal control theory to design the time protocol of the axial control force in order to steer a single particle as precisely as possible from a channel inlet to an outlet at a chosen target position. We discuss the influence of particle radius and channel length and show that optimal steering is cheaper than using a constant control force. Using a single optimized control-force protocol, we demonstrate that even a pulse of particles spread along the channel axis can be steered to a target and that particles of different radii can be separarted most efficiently.

AbstractThe lattice Boltzmann method (LBM) for multicomponent immiscible fluids is applied to the simulations of solid-fluid mixture flows including spherical or non-spherical particles in a square pipe at Reynolds numbers of about 100. A spherical solid particle is modeled by a droplet with strong interfacial tension and large viscosity, and consequently there is no need to track the moving solid-liquid boundary explicitly. Nonspherical (discoid, flat discoid, and biconcave discoid) solid particles are made by applying artificial forces to the spherical droplet. It is found that the spherical particle moves straightly along a stable position between the wall and the center of the pipe (the Segré-Silberberg effect). On the other hand, the biconcave discoid particle moves along a periodic helical path around the center of the pipe with changing its orientation, and the radius of the helical path and the polar angle of the orientation increase as the hollow of the concave becomes large.

Evaluation criteria are adapted from previous textbook analyses on the nature of science (NOS) in general chemistry textbooks. These criteria are used to determine how certain NOS dimensions are mentioned and elaborated in those textbooks. Such dimensions emphasize that chemistry is (1) tentative, (2) empirical, (3) model-based, (4) inferential, (5) has technological products, (6) employs instrumentation, and (7) possesses social and societal dimensions. Three book chapters were read and evaluated: the first (on chemistry in general); the second (on atomic structure); and the sixth or seventh chapters (on the electronic structure of atoms). The relevant content in each textbook were rated using the following rubric: Satisfactory and Explicit (S, 2 points); Mention and Implicit (M, 1 point); and No Mention (N, 0 point). Silberberg (2009) has the highest score among the six textbooks with 12 points out of the maximum of 14. It was rated S for five criteria, the most among the six textbooks. Despite the presence of some N evaluations, all textbooks have mentioned some or all of the NOS dimensions formulated, resulting to M and S ratings. This study concludes that NOS dimensions are already present in various ways and varying degrees in each textbook.

AbstractThe interplay of inertia and deformability has a substantial impact on the transport of soft particles suspended in a fluid. However, to date a thorough understanding of these systems is still missing, and only a limited number of experimental and theoretical studies are available. We combine the finite-element, immersed-boundary and lattice-Boltzmann methods to simulate three-dimensional suspensions of soft particles subjected to planar Poiseuille flow at finite Reynolds numbers. Our findings confirm that the particle deformation and inclination increase when inertia is present. We observe that the Segré–Silberberg effect is suppressed with respect to the particle deformability. Depending on the deformability and strength of inertial effects, inward or outward lateral migration of the particles takes place. In particular, for increasing Reynolds numbers and strongly deformable particles, a hitherto unreported distinct flow focusing effect emerges, which is accompanied by a non-monotonic behaviour of the apparent suspension viscosity and thickness of the particle-free layer close to the channel walls. This effect can be explained by the behaviour of a single particle and the change of the particle collision mechanism when both deformability and inertia effects are relevant.

This paper reports the results of a two-dimensional finite element simulation of the motion of a circular particle in a Couette and a Poiseuille flow. The size of the particle and the Reynolds number are large enough to include fully nonlinear inertial effects and wall effects. Both neutrally buoyant and non-neutrally buoyant particles are studied, and the results are compared with pertinent experimental data and perturbation theories. A neutrally buoyant particle is shown to migrate to the centreline in a Couette flow, and exhibits the Segré-Silberberg effect in a Poiseuille flow. Non-neutrally buoyant particles have more complicated patterns of migration, depending upon the density difference between the fluid and the particle. The driving forces of the migration have been identified as a wall repulsion due to lubrication, an inertial lift related to shear slip, a lift due to particle rotation and, in the case of Poiseuille flow, a lift caused by the velocity profile curvature. These forces are analysed by examining the distributions of pressure and shear stress on the particle. The stagnation pressure on the particle surface are particularly important in determining the direction of migration.

This paper provided important experimental PVT data of the Sudanese reservoir fluids. It includes composition analysis of 11 mixtures and about 148 PVT data points of constant mass expansion (CME) tests at pressures below the bubble point. The datasets are compared with eight equations of state (EOS), namely, Peng Robinson (PR), Soave-Redlich-Kwong (SRK), Lawal-Lake-Silberberg (LLS), Adachi-Lu-Sugie (ALS), Schmidt-Wenzel (SW), Patel-Teja (PT), Modified-Nasrifar-Moshfeghian (MNM), and Harmens-Knapp (HK). The results of comparison reveals that, with the exception of PR and ALS EOSs, all other EOSs yield consistently a higher average absolute percent deviation (AAPD) in the prediction of molar volume; it exceeds 20% by all mixtures. The grand average AAPD of all mixtures is 17 and 16 for PR and ALS, respectively. ALS is selected to represents the mixtures. It is modified by replacing the coefficient (Ωb1) of the parameter (b1) in the dominator of repulsive term by that of PR. This procedure enhanced the accuracy of ALS by 30 to 90% for individual mixtures and the grand average AAPD is significantly reduced from 16 to about 7.

The connection density of nearby neurons in the cortex has been observed to be around 0.1, whereas the longer-range connections are present with much sparser density (Kalisman, Silberberg, & Markram, 2005 ). We propose a memory association model that qualitatively explains these empirical observations. The model we consider is a multiassociative, sparse, Willshaw-like model consisting of binary threshold neurons and binary synapses. It uses recurrent synapses for iterative retrieval of stored memories. We quantify the usefulness of recurrent synapses by simulating the model for small network sizes and by doing a precise mathematical analysis for large network sizes. Given the network parameters, we can determine the precise values of recurrent and afferent synapse densities that optimize the storage capacity of the network. If the network size is like that of a cortical column, then the predicted optimal recurrent density lies in a range that is compatible with biological measurements. Furthermore, we show that our model is able to surpass the standard Willshaw model in the multiassociative case if the information capacity is normalized per strong synapse or per bits required to store the model, as considered in Knoblauch, Palm, and Sommer ( 2010 ).

A method for light and electron microscopic demonstration of mercury sulfides and mercury selenides in mammalian tissue is presented. Silver ions adhering to the surface of submicroscopic traces of mercury sulfides or selenides in the tissue are reduced to metallic silver by hydroquinone. Physical development thereupon renders deposits of mercury sulfides or mercury selenide visible as spheres of solid silver. Examples of localization of mercury in the central nervous system and various organs from animals exposed to mercury chloride or methyl mercury chloride with or without additional sodium selenide treatment are presented. Selenium treatment results in a considerable increase in the amount of mercury that can be made visible by silver amplification. After mercury chloride treatment, most of the mercury is localized in lysosomes and is only rarely seen in secretory granules. After simultaneous selenium treatment, mercury is also found in nuclei of proximal tubule cells in the kidney and in macrophages. The "sulfide-osmium" method for ultrastructural localization of mercury suggested by Silberberg, Lawrence, and Leider (Arch Environ Health 19:7, 1969) and the light microscopic method using a photographic emulsion suggested by Umeda, Saito, and Saito (Jpn J Exp Med 39:17, 1969) have been experimentally analyzed and commented on.

The simulation of surface resolved particles is a valuable tool to gain more insights in the behaviour of particulate flows in engineering processes. In this work the homogenized lattice Boltzmann method as one approach for such direct numerical simulations is revisited and validated for different scenarios. Those include a 3D case of a settling sphere for various Reynolds numbers. On the basis of this dynamic case, different algorithms for the calculation of the momentum exchange between fluid and particle are evaluated along with different forcing schemes. The result is an updated version of the method, which is in good agreement with the benchmark values based on simulations and experiments. The method is then applied for the investigation of the tubular pinch effect discovered by Segré and Silberberg and the simulation of hindered settling. For the latter, the computational domain is equipped with periodic boundaries for both fluid and particles. The results are compared to the model by Richardson and Zaki and are found to be in good agreement. As no explicit contact treatment is applied, this leads to the assumption of sufficient momentum transfer between particles via the surrounding fluid. The implementations are based on the open-source C++ lattice Boltzmann library OpenLB.

The Drosophila gene gurken participates in a signaling process that occurs between the germ line and the somatic cells (follicle cells) of the ovary. This process is required for correct patterning of the dorsoventral axis of both the egg and the embryo. gurken produces a spatially localized transcript which encodes a TGF-alpha-like molecule (Neuman-Silberberg and Schupbach, Cell 75, 165–174, 1993). Mutations in gurken cause a ventralized phenotype in egg and embryo. To determine whether the gurken gene product plays an instructive role in dorsoventral patterning, we constructed females containing extra copies of a gurken transgene. Such females produce dorsalized eggs and embryos, which is expected if gurken acts as a limiting factor in the dorsoventral patterning process. In addition, the expression pattern of the gene rhomboid in the follicle cells is altered in ovaries of females containing extra copies of gurken. Our results indicate that changing gurken dosage in otherwise wild-type ovaries is sufficient to alter the number of somatic follicle cells directed to the dorsal fate. Therefore the gurken-torpedo signaling process plays an instructive role in oogenesis. It induces dorsal cell fates in the follicle cell epithelium and it controls the production of maternal components that will direct the embryonic dorsoventral pattern after fertilization.

In this work, we have generalized different parametric forms of cubic equations of state (EoSs) to predict complete Joule-Thomson (J-T) inversion curves for methane at wide temperature and pressure ranges. EoSs of the Soave-Redlich-Kwong (SRK), Peng-Robinson (PR), Patel-Teja (PT), Esmaeilzadeh-Roshanfekr (ER) and the Hagtalab-Kamali-Mazloumi-Mahmoodi (HKMM) along with frequently used cohesion functions α(Tr) have been considered for plot of J-T inversion curves. The PR EoS along with different cohesion functions such as those of the Soave, Antonin Chapoy and the Tau-Sim-Tassone have been also tested for accurate prediction of the inversion curves. The four parametric EoSs of Adachi-Lu-Sugie (ALS), and Lawal-Lake-Silberberg (LLS) with their associated cohesion functions have been used for the prediction of J-T inversion curves. It has been observed that for the plot of inversion curves the LLS EoS is inadequate while the ER EoS agrees well with the previous measurements made in Laboratory. Besides, the J-T coefficient measurements from EoSs have been made for carbon dioxide and nitrogen gases at temperatures from 273.15 to 473.15 K and at pressures from 10 to 1000 atm, respectively. The uncertainties of experimental J-T coefficients data of carbon dioxide from values calculated using EoSs at constant pressure of 1 atm and 20 atm and with varying temperatures have been studied.

Radial migration (particle motion transverse to streamlines) in a system which combines frequent entry, straight pore, and exit regions were investigated experimentally for small particle and pore sizes. Pore diameters were less than 30 μm and typical particle to pore diameter ratios were about 0.25. Our new modification of the resistive pulse technique based on pressure reversal, extends this experimental technique to also include single-particle flow dynamics. By pressure drive, a particle in an electrolyte enters a current-carrying pore and an increase in resistance proportional to the particle volume is detected. When the particle exits the pore, the pressure can be reversed such that the particle re-enters the pore. Detailed studies of particle flow properties in a size range relevant to flow in porous media is now possible. The emphasis in this investigation is on radial migration. The effect of particle sedimentation has been negligible, while particle diffusion becomes significant for submicron particles. The measured evolution of the transit time as the particle migrates compares well with an empirical relationship for the migration velocity first proposed by Segré & Silberberg (1962 a, b) and later verified by Ishii & Hasimoto (1980). Entrance and exit effects do not seem to be important for long pores, the results scale very nicely when the pore length is changed.

The concept of community involvement and the effect that the act of “making” has on the community itself is a key consideration in the placemaking discussion (Project for Public Spaces, 2015a; Silberberg, Lorah, Disbrow, &amp; Muessig, 2013). From a historical perspective, community development has been placed in the hands of individuals who are considered experts in the creative process. This approach often results in targeted criticism of the proposed development by the host community and a lack of trust in the motives and priorities of the professionals involved (Nikitin, 2012) and diminishes community involvement in the development of public space, a practice that empowers communities and fosters a sense of place among community members. This article discusses the theoretical foundations of community participation and the value of coproduction in the planning and design process, explores the role of placemaking as a strategy for developing a host community’s sense of place, and proposes a continuum of placemaking strategies based on Arnstein’s ladder of citizen participation to increase the likelihood that a sense of place within the host community will be developed as an outcome of the planning and design process. This continuum is designed to help planning and design professionals better understand how they might include the community in a co-produced process and to highlight the degree to which a placemaking approach to community planning and design promotes a sense of place as an outcome of the process.

AbstractWe report a unique tuneable analogue trend in particle focusing in the laminar and weak viscoelastic regime of elasto-inertial flows. We observe experimentally that particles in circular cross-section microchannels can be tuned to any focusing bandwidths that lie between the “Segre-Silberberg annulus” and the centre of a circular microcapillary. We use direct numerical simulations to investigate this phenomenon and to understand how minute amounts of elasticity affect the focussing of particles at increasing flow rates. An Immersed Boundary Method is used to account for the presence of the particles and a FENE-P model is used to simulate the presence of polymers in a Non-Newtonian fluid. The numerical simulations study the dynamics and stability of finite size particles and are further used to analyse the particle behaviour at Reynolds numbers higher than what is allowed by the experimental setup. In particular, we are able to report the entire migration trajectories of the particles as they reach their final focussing positions and extend our predictions to other geometries such as the square cross section. We believe complex effects originate due to a combination of inertia and elasticity in the weakly viscoelastic regime, where neither inertia nor elasticity are able to mask each other’s effect completely, leading to a number of intermediate focusing positions. The present study provides a fundamental new understanding of particle focusing in weakly elastic and strongly inertial flows, whose findings can be exploited for potentially multiple microfluidics-based biological sorting applications.

An experimental and numerical study on the inertial focusing of neutrally buoyant spherical particles suspended in laminar circular tube flows was performed at Reynolds numbers ($Re$) ranging from 100 to 1000 for particle-to-tube diameter ratios of ${\sim}0.1$. In the experiments, we measured the cross-sectional distribution of particles in dilute suspensions flowing through circular tubes several hundreds of micrometres in diameter. In the cross-section located at 1000 times the tube diameter from the tube inlet, all particles were highly concentrated on one annulus or two annuli, depending on $Re$. At low $Re$, the particles were focused on the so-called Segré–Silberberg (SS) annulus, in accordance with previous studies (regime (A)). At higher $Re$, two particle focusing annuli appeared, with the outer annulus corresponding to the SS annulus (regime (B)). We call the annulus closer to the tube centre ‘the inner annulus’, although this term was used by Matas et al. (J. Fluid Mech., vol. 515, 2004, pp. 171–195) for a significantly broader annulus which included the transient accumulation of particles observed in regime (A). At even higher $Re$, particles were focused on the inner annulus (regime (C)), indicating that the radial position of the SS annulus is no longer a stable equilibrium position. These experimental results were confirmed by a numerical simulation based on the immersed boundary method. The results of this study also indicate that the critical Reynolds numbers between two neighbouring regimes decrease with the increase of the particle-to-tube diameter ratio.

The cross-stream migration of a deformable drop in two-dimensional Hagen–Poiseuille flow at finite Reynolds numbers is studied numerically. In the limit of a small Reynolds number (< 1), the motion of the drop depends strongly on the ratio of the viscosity of the drop fluid to the viscosity of the suspending fluid. For viscosity ratio 0.125 a drop moves toward the centre of the channel, while for ratio 1.0 it moves away from the centre until halted by wall repulsion. The rate of migration increases with the deformability of the drop. At higher Reynolds numbers (5–50), the drop either moves to an equilibrium lateral position about halfway between the centreline and the wall – according to the so-called Segre–Silberberg effect or it undergoes oscillatory motion. The steady-state position depends only weakly on the various physical parameters of the flow, but the length of the transient oscillations increases as the Reynolds number is raised, or the density of the drop is increased, or the viscosity of the drop is decreased. Once the Reynolds number is high enough, the oscillations appear to persist forever and no steady state is observed. The numerical results are in good agreement with experimental observations, especially for drops that reach a steady-state lateral position. Most of the simulations assume that the flow is two-dimensional. A few simulations of three-dimensional flows for a modest Reynolds number (Re = 10), and a small computational domain, confirm the behaviour seen in two dimensions. The equilibrium position of the three-dimensional drop is close to that predicted in the simulations of two-dimensional flow.

Editorial Summary In »Architecture Schools and Their Relationship with Research: It’s Complicated«, Jan Silberberger describes the problematic divide between practicing architects that teach design at architecture schools and scholars investigating the practices of designing from a theoretical or social scientific perspective. Identifying three recurrent misunderstandings between these two groups, he stresses the lack of awareness about genuine research approaches within the discipline of architecture. Emphasizing the interconnectivity of research and practice, Silberberger highlights the potential for further development of the discipline that thorough reflections on the methodologies applied in architectural design afford. [Katharina Voigt]

The Drimolen Palaeocave System Main Quarry deposits (DMQ) are some of the most prolific hominin and primate-bearing deposits in the Fossil Hominids of South Africa UNESCO World Heritage Site. Discovered in the 1990s, excavations into the DMQ have yielded a demographically diverse sample ofParanthropus robustus(including DNH 7, the most complete cranium of the species recovered to date), earlyHomo,Papio hamadryas robinsoniandCercopithecoides williamsi. Alongside the hominin and primate sample is a diverse macromammalian assemblage, but prior publications have only provided a provisional species list and an analysis of the carnivores recovered prior to 2008. Here we present the first description and analysis of the non-primate macromammalian faunas from the DMQ, including all 826 taxonomically identifiable specimens catalogued from over two decades of excavation. We also provide a biochronological interpretation of the DMQ deposits and an initial discussion of local palaeoecology based on taxon representation.The current DMQ assemblage consists of the remains of minimally 147 individuals from 9 Orders and 14 Families of mammals. The carnivore assemblage described here is even more diverse than established in prior publications, including the identification ofMegantereon whitei,Lycyaenops silberbergi, and first evidence for the occurrence ofDinofeliscf.barlowiandDinofelisaff.piveteauiwithin a single South African site deposit. The cetartiodactyl assemblage is dominated by bovids, with the specimen composition unique in the high recovery of horn cores and dominance ofAntidorcas reckiremains. Other cetartiodactyl and perissodactyl taxa are represented by few specimens, as areHystrixandProcavia; the latter somewhat surprisingly so given their common occurrence at penecontemporaneous deposits in the region. Equally unusual (particularly given the size of the sample) is the identification of single specimens of giraffoid, elephantid and aardvark (Orycteropuscf.afer) that are rarely recovered from regional site deposits. Despite the diversity within the DMQ macromammalian faunas, there are few habitat- or biochronologically-sensitive species that provide specific ecologic or age boundaries for the deposits. Recovered species can only support the non-specific, mixed open-to-closed palaeohabitats around Drimolen that have been reconstructed for the other penecontemporaneous South African palaeokarst deposits. The identifiedEquus quaggassp. specimens recovered from the floor of the current excavation (∾−4.5–5 m below datum) suggests that most, if not all the DMQ specimens, were deposited after 2.33 Ma. Simultaneously, the carnivore specimens (D.cf.barlowi, L. silberbergi) suggest earlier Pleistocene (pre- 2.0–1.8 Ma) to maximally 1.6 Ma deposition (D.aff.piveteaui) for most of the DMQ fossil assemblage.

AbstractA long-standing conjecture asserts that every finite nonabelian $p$-group has a noninner automorphism of order $p$. In this paper the verification of the conjecture is reduced to the case of $p$-groups $G$ satisfying ${ Z}_{2}^{\star } (G)\leq {C}_{G} ({ Z}_{2}^{\star } (G))= \Phi (G)$, where ${ Z}_{2}^{\star } (G)$ is the preimage of ${\Omega }_{1} ({Z}_{2} (G)/ Z(G))$ in $G$. This improves Deaconescu and Silberberg’s reduction of the conjecture: if ${C}_{G} (Z(\Phi (G)))\not = \Phi (G)$, then $G$ has a noninner automorphism of order $p$ leaving the Frattini subgroup of $G$ elementwise fixed [‘Noninner automorphisms of order $p$ of finite $p$-groups’, J. Algebra 250 (2002), 283–287].

Abstract One of the fundamental phenomena associated with the transport of rigid particles by the fluid flow in narrow ducts and tubes is the Segre–Silberberg effect. Experimental observations show that a spherical particle transported by the fluid flow in a long channel occupies a position of equilibrium between the wall and the centerline of the channel. In this study, this effect was numerically investigated using a novel semi-implicit immersed boundary method based on the discrete forcing approach. A uniform Cartesian mesh is used for the duct, whereas a moving Lagrangian mesh is used to track the position of the particle. Unlike previous studies, both cases of the duct geometry are considered: a round tube and a flat channel. Good agreement is shown to the available theoretical and numerical results of other studies. The problem is described by two dimensionless parameters, the channel Reynolds number, and the relative particle diameter. Parametric studies to these parameters were carried out, showing fundamental dependencies of equilibrium position on Reynolds number from 20 to 500 and on relative particle diameter from 0.2 to 0.7. It is demonstrated that the position of equilibrium becomes closer to the wall with the increase of Reynolds number, as well as with the decrease of particle diameter. In addition, the dependence of particle velocity on its diameter is investigated. The obtained results are of both theoretical and practical interest, with possible applications ranging from proppant transport to the design of microfluidic devices.

Abstract Following the publication (Granger DE et al., Nature 2015;522:85–88) of an 26Al/10Be burial isochron age of 3.67±0.16 Ma for the sediments encasing hominin fossil StW573 (‘Little Foot’), we consider data on chert samples presented in that publication to explore alternative age interpretations. 10Be and 26Al concentrations determined on individual chert fragments within the sediments were calculated back in time, and data from one of these fragments point to a maximum age of 2.8 Ma for the sediment package and therefore also for the fossil. An alternative hypothesis is explored, which involves re-deposition and mixing of sediment that had previously collected over time in an upper chamber, which has since been eroded. We show that it is possible for such a scenario to yield ultimately an isochron indicating an apparent age much older than the depositional age of the sediments around the fossil. A possible scenario for deposition of StW573 in Member 2 would involve the formation of an opening between the Silberberg Grotto and an upper chamber. Not only could such an opening have acted as a death trap, but it could also have disturbed the sedimentological balance in the cave, allowing unconsolidated sediment to be washed into the Silberberg Grotto. This two-staged burial model would thus allow a younger age for the fossil, consistent with the sedimentology of the deposit. This alternative age is also not in contradiction to available faunal and palaeomagnetic data.

The migration of a bubble inside a two-dimensional converging–diverging channel is investigated numerically. A parametric study is conducted to investigate the effects of the Reynolds and Weber numbers and the amplitude of the converging–diverging channel. It is found that increasing the Reynolds number and the amplitude of the channel increases the oscillation of the bubble and promotes the migration of the bubble toward one of the channel wall. The bubble undergoes oblate–prolate deformation periodically at the early times, which becomes chaotic at the later times. This phenomenon is a culmination of the bubble path instability as well as the Segré–Silberberg effect.

Microfluidic channels have been proposed as a method for removal of cryoprotective agents from cell suspensions [Fleming, Longmire, and Hubel, J. Biomech. Eng. 129, 703 (2007)]. The device tested consists of a rectangular cross section channel of 500 μm depth, 25 mm width, and 160 mm length, through which a cell suspension and wash stream flow in parallel. Cryoprotective agents diffuse from the cell stream to the wash stream and the wash stream is discarded. The washed cell stream is then ready for use. This device must be capable of removing 95% of the dimethyl sulfoxide (DMSO) from the cell stream with minimal cell losses. Our previous studies have demonstrated our ability to remove DMSO [Mata, Longmire, McKenna, Glass, and Hubel, Microfluid. Nanofluid. 5, 529 (2008)]. The next phase of the investigation involves characterizing the influence of flow conditions on cell motion through the device. To that end, Jurkat cells (lymphoblasts) in a 10% DMSO solution were flowed through the microfluidic channel in parallel with a wash stream composed of phosphate buffered saline solution (PBS). Average cell stream velocities were varied from 0.94 to 8.5 mm/s (Re 1.7 to 6.0). Cell viability at the outlet was high, indicating that cells are not damaged during their passage through the device. Gravitational settling caused an accumulation of cells near the bottom of the channel, where flow velocities are low. Cell settling leads results in an initial transient period for cell motion through the device. For the initial portion of cells flowing through the device, cells tend to accumulate in the device until a critical device population time is reached. Cell recovery (number of cells out of the device divided by the number of cells input to the device) is high (90–100%) after the device has been fully populated. For a single stage device with average cell stream velocities of ⩾6 mm/s, cell recovery was 90–100%. As more stages are added to the device, the population time for the device increases. Gravitational settling of cells also leads to a time-varying cell concentration from the input syringe to the inlet of the channel, as well as cell losses due to cells remaining in the horizontally-oriented syringe. Reorienting the syringes to a vertical position eliminates these losses. Cell motion within the channel can be modulated by the flow conditions used. For sufficiently high Reynolds numbers, the Segre-Silberberg effect [Segre and Silberberg, J. Fluid Mech. 14, 115 (1962)] can be used to move cells from the low velocity region of the cell stream to a higher velocity region thereby reducing the transient portion of processing the cells and improving overall recovery of cells through the device.

Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segré–Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.

AbstractWe investigated the association of LHR expression in epithelial ovarian cancer (OC) with clinical and pathologic characteristics of patients. LHR expression was examined immunohistochemically using tissue microarrays (TMAs) of specimens from 232 OC patients. Each sample was scored quantitatively evaluating LHR staining intensity (LHR-I) and percentage of LHR (LHR-P) staining cells in tumor cells examined. LHR-I was assessed as no staining (negative), weak (+ 1), moderate (+ 2), and strong positive (+ 3). LHR-P was measured as 1 to 5, 6 to 50% and > 50% of the tumor cells examined. Positive LHR staining was found in 202 (87%) patients’ tumor specimens and 66% patients had strong intensity LHR expression. In 197 (85%) of patients, LHR-P was measured in > 50% of tumor cells. LHR-I was significantly associated with pathologic stage (p = 0.007). We found that 72% of stage III or IV patients expressed strong LHR-I in tumor cells. There were 87% of Silberberg’s grade 2 or 3 patients compared to 70% of grade 1 patients with LHR expression observed in > 50% of tumor cells, p = 0.037. Tumor stage was significantly associated with overall survival and recurrence free survival, p < 0.001 for both analyses, even after adjustment for age, tumor grade and whether patient had persistent disease after therapy or not. Our study demonstrates that LHR is highly expressed in the majority of OC patients. Both LHR-I and LHR-P are significantly associated with either the pathologic stage or tumor grade.

Economics of Cute There are many ways to study cute: for example, neuro-biology (cute as adaptation); anthropology (cute in culture); political economy (cute industries, how cute exploits consumers); cultural studies (social construction of cute); media theory and politics (representation and identity of cute), and so on. What about economics? At first sight, this might point to a money-capitalism nexus (“the cute economy”), but I want to argue here that the economics of cute actually works through choice interacting with fixed costs and what economists call ”the substitution effect”. Cute, in conjunction with the Internet, affects the trade-offs involved in choices people make. Let me put that more starkly: cute shapes the economy. This can be illustrated with internet animals, which at the time of writing means Grumpy Cat. I want to explain how that mechanism works – but to do so I will need some abstraction. This is not difficult – a simple application of a well-known economics model, namely the Allen-Alchian theorem, or the “third law of demand”. But I am going to take some liberties in order to represent that model clearly in this short paper. Specifically, I will model just two extremes of quality (“opera” and “cat videos”) to represent end-points of a spectrum. I will also assume that the entire effect of the internet is to lower the cost of cat videos. Now obviously these are just simplifying assumptions “for the purpose of the model”. And the purpose of the model is to illuminate a further aspect of how we might understand cute, by using an economic model of choice and its consequences. This is a standard technique in economics, but not so in cultural studies, so I will endeavour to explain these moments as we go, so as to avoid any confusion about analytic intent. The purpose of this paper is to suggest a way that a simple economic model might be applied to augment the cultural study of cute by seeking to unpack its economic aspect. This can be elucidated by considering the rise of internet animals as a media-cultural force, as epitomized by “cat videos”. We can explain this through an application of price theory and the theory of demand that was first proposed by Armen Alchian and William Allen. They showed how an equal fixed cost that was imposed to both high-quality and low-quality goods alike caused a shift in consumption toward the higher-quality good, because it is now relatively cheaper. Alchian and Allen had in mind something like transport costs on agricultural goods (such as apples). But it is also true that the same effect works in reverse (Cowen), and the purpose of this paper is to develop that logic to contribute to explaining how certain structural shifts in production and consumption in digital media, particularly the rise of blog formats such as Tumblr, a primary supplier of kittens on the Internet, can be in part understood as a consequence of this economic mechanism. There are three key assumptions to build this argument. The first is that the cost of the internet is independent of what it carries. This is certainly true at the level of machine code, and largely true at higher levels. What might be judged aesthetically high quality or low quality content – say of a Bach cantata or a funny cat video – are treated the same way if they both have the same file size. This is a physical and computational aspect of net-neutrality. The internet – or digitization – functions as a fixed cost imposed regardless of what cultural quality is moving across it. Second, while there are costs to using the internet (for example, in hardware or concerning digital literacy) these costs are lower than previous analog forms of information and cultural production and dissemination. This is not an empirical claim, but a logical one (revealed preference): if it were not so, people would not have chosen it. The first two points – net neutrality and lowered cost – I want to take as working assumptions, although they can obviously be debated. But that is not the purpose of the paper, which is instead the third point – the “Alchian-Allen theorem”, or the third fundamental law of demand. The Alchian-Allen Theorem The Alchian-Allen theorem is an extension of the law of demand (Razzolini et al) to consider how the distribution of high quality and low quality substitutes of the same good (such as apples) is affected by the imposition of a fixed cost (such as transportation). It is also known as the “shipping the good apples out” theorem, after Borcherding and Silberberg explained why places that produce a lot of apples – such as Seattle in the US – often also have low supplies of high quality apples compared to places that do not produce apples, such as New York. The puzzle of “why can’t you get good apples in Seattle?” is a simple but clever application of price theory. When a place produces high quality and low quality items, it will be rational for those in faraway places to consume the high quality items, and it will be rational for the producers to ship them, leaving only the low quality items locally.Why? Assume preferences and incomes are the same everywhere and that transport cost is the same regardless of whether the item shipped is high or low quality. Both high quality and low quality apples are more expensive in New York compared to Seattle, but because the fixed transport cost applies to both the high quality apples are relatively less expensive. Rational consumers in New York will consume more high quality apples. This makes fewer available in Seattle.Figure 1: Change in consumption ratio after the imposition of a fixed cost to all apples Another example: Australians drink higher quality Californian wine than Californians, and vice versa, because it is only worth shipping the high quality wine out. A counter-argument is that learning effects dominate: with high quality local product, local consumers learn to appreciate quality, and have different preferences (Cowen and Tabarrok).The Alchian-Allen theorem applies to any fixed cost that applies generally. For example, consider illegal drugs (such as alcohol during the US prohibition, or marijuana or cocaine presently) and the implication of a fixed penalty – such as a fine, or prison sentence, which is like a cost – applied to trafficking or consumption. Alchian-Allen predicts a shift toward higher quality (or stronger) drugs, because with a fixed penalty and probability of getting caught, the relatively stronger substance is now relatively cheaper. Empirical work finds that this effect did occur during alcohol prohibition, and is currently occurring in narcotics (Thornton Economics of Prohibition, "Potency of illegal drugs").Another application proposed by Steven Cuellar uses Alchian-Allen to explain a well-known statistical phenomenon why women taking the contraceptive pill on average prefer “more masculine” men. This is once again a shift toward quality predicted on falling relative price based on a common ‘fixed price’ (taking the pill) of sexual activity. Jean Eid et al show that the result also applies to racehorses (the good horses get shipped out), and Staten and Umbeck show it applies to students – the good students go to faraway universities, and the good student in those places do the same. So that’s apples, drugs, sex and racehorses. What about the Internet and kittens?Allen-Alchian Explains Why the Internet Is Made of CatsIn analog days, before digitization and Internet, the transactions costs involved with various consumption items, whether commodities or media, meant that the Alchian-Allen effect pushed in the direction of higher quality, bundled product. Any additional fixed costs, such as higher transport costs, or taxes or duties, or transactions costs associated with search and coordination and payment, i.e. costs that affected all substitutes in the same way, would tend to make the higher quality item relatively less expensive, increasing its consumption.But digitisation and the Internet reverse the direction of these transactions costs. Rather than adding a fixed cost, such as transport costs, the various aspects of the digital revolution are equivalent to a fall in fixed costs, particularly access.These factors are not just one thing, but a suite of changes that add up to lowered transaction costs in the production, distribution and consumption of media, culture and games. These include: The internet and world-wide-web, and its unencumbered operation The growth and increasing efficacy of search technology Growth of universal broadband for fast, wide band-width access Growth of mobile access (through smartphones and other appliances) Growth of social media networks (Facebook, Twitter; Metcalfe’s law) Growth of developer and distribution platforms (iPhone, android, iTunes) Globally falling hardware and network access costs (Moore’s law) Growth of e-commerce (Ebay, Amazon, Etsy) and e-payments (paypal, bitcoin) Expansions of digital literacy and competence Creative commons These effects do not simply shift us down a demand curve for each given consumption item. This effect alone simply predicts that we consume more. But the Alchian-Allen effect makes a different prediction, namely that we consume not just more, but also different.These effects function to reduce the overall fixed costs or transactions costs associated with any consumption, sharing, or production of media, culture or games over the internet (or in digital form). With this overall fixed cost component now reduced, it represents a relatively larger decline in cost at the lower-quality, more bite-sized or unbundled end of the media goods spectrum. As such, this predicts a change in the composition of the overall consumption basket to reflect the changed relative prices that these above effects give rise to. See Figure 2 below (based on a blog post by James Oswald). The key to the economics of cute, in consequence of digitisation, is to follow through the qualitative change that, because of the Alchian-Allen effect, moves away from the high-quality, highly-bundled, high-value end of the media goods spectrum. The “pattern prediction” here is toward more, different, and lower quality: toward five minutes of “Internet animals”, rather than a full day at the zoo. Figure 2: Reducing transaction costs lowers the relative price of cat videos Consider five dimensions in which this more and different tendency plays out. Consumption These effects make digital and Internet-based consumption cheaper, shifting us down a demand curve, so we consume more. That’s the first law of demand in action: i.e. demand curves slope downwards. But a further effect – brilliantly set out in Cowen – is that we also consume lower-quality media. This is not a value judgment. These lower-quality media may well have much higher aesthetic value. They may be funnier, or more tragic and sublime; or faster, or not. This is not about absolute value; only about relative value. Digitization operating through Allen-Alchian skews consumption toward the lower quality ends in some dimensions: whether this is time, as in shorter – or cost, as in cheaper – or size, as in smaller – or transmission quality, as in gifs. This can also be seen as a form of unbundling, of dropping of dimensions that are not valued to create a simplified product.So we consume different, with higher variance. We sample more than we used to. This means that we explore a larger information world. Consumption is bite-sized and assorted. This tendency is evident in the rise of apps and in the proliferation of media forms and devices and the value of interoperability.ProductionAs consumption shifts (lower quality, greater variety), so must production. The production process has two phases: (1) figuring out what to do, or development; and (2) doing it, or making. The world of trade and globalization describes the latter part: namely efficient production. The main challenge is the world of innovation: the entrepreneurial and experimental world of figuring out what to do, and how. It is this second world that is radically transformed by implications of lowered transaction costs.One implication is growth of user-communities based around collaborative media projects (such as open source software) and community-based platforms or common pool resources for sharing knowledge, such as the “Maker movement” (Anderson 2012). This phenomenon of user-co-creation, or produsers, has been widely recognized as an important new phenomenon in the innovation and production process, particularly those processes associated with new digital technologies. There are numerous explanations for this, particularly around preferences for cooperation, community-building, social learning and reputational capital, and entrepreneurial expectations (Quiggin and Potts, Banks and Potts). Business Models The Alchian-Allen effect on consumption and production follows through to business models. A business model is a way of extracting value that represents some strategic equilibrium between market forms, organizational structures, technological possibilities and institutional framework and environmental conditions that manifests in entrepreneurial patterns of business strategy and particular patterns of investment and organization. The discovery of effective business models is a key process of market capitalist development and competition. The Alchian-Allen effect impacts on the space of effective viable business models. Business models that used to work will work less well, or not at all. And new business models will be required. It is a significant challenge to develop these “economic technologies”. Perhaps no less so than development of the physical technologies, new business models are produced through experimental trial and error. They cannot be known in advance or planned. But business models will change, which will affect not only the constellation of existing companies and the value propositions that underlie them, but also the broader specializations based on these in terms of skill sets held and developed by people, locations of businesses and people, and so on. New business models will emerge from a process of Schumpeterian creative destruction as it unfolds (Beinhocker). The large production, high development cost, proprietary intellectual property and systems based business model is not likely to survive, other than as niche areas. More experimental, discovery-focused, fast-development-then-scale-up based business models are more likely to fit the new ecology. Social Network Markets & Novelty Bundling MarketsThe growth of variety and diversity of choice that comes with this change in the way media is consumed to reflect a reallocation of consumption toward smaller more bite-sized, lower valued chunks (the Alchian-Allen effect) presents consumers with a problem, namely that they have to make more choices over novelty. Choice over novelty is difficult for consumers because it is experimental and potentially costly due to risk of mistakes (Earl), but it also presents entrepreneurs with an opportunity to seek to help solve that problem. The problem is a simple consequence of bounded rationality and time scarcity. It is equivalent to saying that the cost of choice rises monotonically with the number of choices, and that because there is no way to make a complete rational choice, agents will use decision or choice heuristics. These heuristics can be developed independently by the agents themselves through experience, or they can be copied or adopted from others (Earl and Potts). What Potts et al call “social network markets” and what Potts calls “novelty bundling markets” are both instances of the latter process of copying and adoption of decision rules. Social network markets occur when agents use a “copy the most common” or “copy the highest rank” meta-level decision rule (Bentley et al) to deal with uncertainty. Social network markets can be efficient aggregators of distributed information, but they can also be path-dependent, and usually lead to winner-take all situations and dynamics. These can result in huge pay-offs differentials between first and second or fifth place, even when the initial quality differentials are slight or random. Diversity, rapid experimentation, and “fast-failure” are likely to be effective strategies. It also points to the role of trust and reputation in using adopted decision rules and the information economics that underlies that: namely that specialization and trade applies to the production and consumption of information as well as commodities. Novelty bundling markets are an entrepreneurial response to this problem, and observable in a range of new media and creative industries contexts. These include arts, music or food festivals or fairs where entertainment and sociality is combined with low opportunity cost situations in which to try bundles of novelty and connect with experts. These are by agents who developed expert preferences through investment and experience in consumption of the particular segment or domain. They are expert consumers and are selling their “decision rules” and not just the product. The more production and consumption of media and digital information goods and services experiences the Alchian-Allen effect, the greater the importance of novelty bundling markets. Intellectual Property & Regulation A further implication is that rent-seeking solutions may also emerge. This can be seen in two dimensions; pursuit of intellectual property (Boldrin and Levine); and demand for regulations (Stigler). The Alchian-Allen induced shift will affect markets and business models (and firms), and because this will induce strategic defensive and aggressive responses from different organizations. Some organizations will seek to fight and adapt to this new world through innovative competition. Other firms will fight through political connections. Most incumbent firms will have substantial investments in IP or in the business model it supports. Yet the intellectual property model is optimized for high-quality large volume centralized production and global sales of undifferentiated product. Much industrial and labour regulation is built on that model. How governments support such industries is predicated on the stability of this model. The Alchian-Allen effect threatens to upset that model. Political pushback will invariably take the form of opposing most new business models and the new entrants they carry. Conclusion I have presented here a lesser-known but important theorem in applied microeconomics – the Alchian-Allen effect – and explain why its inverse is central to understanding the evolution of new media industries, and also why cute animals proliferate on the Internet. The theorem states that when a fixed cost is added to substitute goods, consumers will shift to the higher quality item (now relatively less expensive). The theorem also holds in reverse, when a fixed cost is removed from substitute items we expect a shift to lower quality consumption. The Internet has dramatically lowered fixed costs of access to media consumption, and various development platforms have similarly lowered the costs of production. Alchian-Allen predicts a shift to lower-quality, ”bittier” cuter consumption (Cowen). References Alchian, Arman, and William Allen. Exchange and Production. 2nd ed. Belmont, CA: Wadsworth, 1967. Anderson, Chris. Makers. New York: Crown Business, 2012. Banks, John, and Jason Potts. "Consumer Co-Creation in Online Games." New Media and Society 12.2 (2010): 253-70. Beinhocker, Eric. Origin of Wealth. Cambridge, Mass.: Harvard University Press, 2005. Bentley, R., et al. "Regular Rates of Popular Culture Change Reflect Random Copying." Evolution and Human Behavior 28 (2007): 151-158. Borcherding, Thomas, and Eugene Silberberg. 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