Spheres Of Different Sizes Research Articles

Modeling the effects of molecular crowding on cerebellar long term depression

the number of released Ca 2+ which was not observed experimentally. We then implemented the presence of large concentrations of non-reactive macromolecules, a condition known as molecular crowding [3,4]. The nonreactive molecules were modeled using spheres of different sizes either placed regularly or randomly throughout the intracellular space of the spine. A classical approach would suggest that the presence of these macromolecules would result in an increase in the amount of Ca 2+ needed to induce LTD, producing a rightward shift of the curve. Instead, our simulations show that the steepness of the sigmoidal curve increased, replicating experimental results. We further studied the effect of molecular crowding on the efficiency of LTD expression. In the control simulation we varied the diffusion coefficient of PKC until no synaptic plasticity was induced. PKC is a key protein in the expression ofLTD that phosphorylates AMPARs. We then ran the simulations with increasing presence of crowding molecules. Interestingly, it was at a crowding value of 45% that LTD was not only recovered, but was 30% stronger. Molecular crowding in other cell types has been calculated to be in the order of 40-45 % [5]. Furthermore, theoretical work suggests that molecular crowding could be a mechanism to increase the efficiency of biochemical reactions [6]. In summary, our results show that there is a strong influence of molecular crowding in the activation of biochemical signals in synapses. Based on our simulations we propose that the regulation of crowding molecules in spines could be a mechanism to control the reliability and strength of synaptic plasticity.

A universal bridge functional for infinitely diluted solutions: A case study for Lennard-Jones spheres of different diameters

We propose a universal bridge functional for closure of the Ornstein-Zernike (OZ) equation for infinitely diluted solutions of Lennard-Jones spheres of different sizes in a Lennard-Jones fluid. The bridge functional is parameterized using data from molecular dynamics (MD) simulations. We show that for all of the investigated systems, the bridge functional can be efficiently parameterized with an exponential function that depends only on the ratio of the sizes of solute and solvent atoms. To check the parameterization, we solve the OZ equation with a closure that includes the parametrized functional, and with a closure without the bridge functional (a hypernetted chain closure). We show that introducing the bridge functional allows us to obtain radial distribution functions (RDFs) close to the MD results, and to improve substantially predictions of the location and height of the first peak of an RDF.

Microfluidic sorting with a moving array of optical traps

Optical sorting was demonstrated by selective trapping of a set of microspheres (having specific size or composition) from a flowing mixture and guiding these in the desired direction by a moving array of optical traps. The approach exploits the fact that whereas the fluid drag force varies linearly with particle size, the optical gradient force has a more complex dependence on the particle size and also on its optical properties. Therefore, the ratio of these two forces is unique for different types of flowing particles. Selective trapping of a particular type of particles can thus be achieved by ensuring that the ratio between fluid drag and optical gradient force on these is below unity whereas for others it exceeds unity. Thereafter, the trapped particles can be sorted using a motion of the trapping sites towards the output. Because in this method the trapping force seen by the selected fraction of particles can be suitably higher than the fluid drag force, the particles can be captured and sorted from a fast fluid flow (about 150 μm/s). Therefore, even when using a dilute particle suspension, where the colloidal trafficking issues are naturally minimized, due to high flow rate a good throughput (about 30 particles/s) can be obtained. Experiments were performed to demonstrate sorting between silica spheres of different sizes (2, 3, and 5 μm) and between 3 μm size silica and polystyrene spheres.

Influence of gravel distribution on the variability of chloride penetration front in saturated uncracked concrete

The concepts of chloride penetration front and critical chloride content in reinforced concrete are not easily quantifiable and the disparity of results in the literature attests a great variability of the causes. The aim of this study is to propose part of the disparity interpretation on a diffusion test by examining the geometrical influence of gravel distribution on the variability of chloride concentration at a given depth and of depth at a given concentration, in an uncracked cover concrete. For this, concrete is considered as a two-phase material with mortar (assumed homogeneous) as one phase and gravels as another. 3D composite specimens are modeled by using a mix of mortar and randomly distributed spheres of different sizes (gravels) to reproduce particle size distribution. An isothermal diffusion model based on Fick’s second law along with Langmuir and Freundlich types interaction is considered. Freundlich parameters are calculated from C3A content of the ciment. Langmuir parameter values are taken from the literature. The finite element method is used for the composition. Simulations are compared with experimental results obtained with an OPC concrete from the BHP2000 French National project.The study shows good agreement between the proposed pure diffusion finite element model and experimental results. It also shows that depth and concentration dispersions are not negligible, especially at 3month of exposure. A part of concentration isovalue location can be 3mm deeper than the mean value location, on the studied concrete.

GREEDY ALGORITHMS FOR PACKING UNEQUAL SPHERES INTO A CUBOIDAL STRIP OR A CUBOID

Given a finite set of spheres of different sizes, we study the three-dimensional Strip Packing Problem (3D-SPP) as well as the three-dimensional Knapsack Problem (3D-KP). The 3D-SPP asks for a placement of all spheres within a cuboidal strip of fixed width and height so that the variable length of the cuboidal strip is minimized. The 3D-KP requires packing of a subset of the spheres in a given cuboid so that the wasted space is minimized. To solve these problems two greedy algorithms were developed which adapt the algorithms proposed by Huang et al. (2005) to the 3D case with some important enhancements. The resulting methods were tested using the instances provided by Stoyan et al. (2003). Additionally, two series of 12 instances each for the 3D-SPP and for the 3D-KP are introduced and results for these new instances are also reported.

Discrete element modeling of asphalt concrete cracking using a user-defined three-dimensional micromechanical approach

We established a user-defined micromechanical model using discrete element method (DEM) to investigate the cracking behavior of asphalt concrete (AC). Using the “Fish” language provided in the particle flow code in 3-Demensions (PFC3D), the air voids and mastics in asphalt concrete were realistically built as two distinct phases. With the irregular shape of individual aggregate particles modeled using a clump of spheres of different sizes, the three-dimensional (3D) discrete element model was able to account for aggregate gradation and fraction. Laboratory uniaxial complex modulus test and indirect tensile strength test were performed to obtain input material parameters for the numerical simulation. A set of the indirect tensile test were simulated to study the cracking behavior of AC at two levels of temperature, i e, −10 °C and 15 °C. The predicted results of the numerical simulation were compared with laboratory experimental measurements. Results show that the 3D DEM model is able to predict accurately the fracture pattern of different asphalt mixtures. Based on the DEM model, the effects of air void content and aggregate volumetric fraction on the cracking behavior of asphalt concrete were evaluated.

On the theory of heat and mass exchange between contacting spherical particles

The steady-state mass transfer of a chemically active impurity to the surface of a stationary dumbbell-shaped particle consisting of two solid contacting reacting spheres of different sizes is analyzed theoretically. The surrounding medium is at rest, and the numerical concentration of the reagent at a large distance from the aggregate of the spheres is maintained constant. The first-order chemical heterogeneous reaction occurs at a high finite rate and is assumed to be isothermal. The solution to the boundary-value diffusion problem is described by a Laplace axisymmetric equation in the system of tangential-spherical coordinates of revolution. A system of two second-order linear perturbed ordinary differential equations with variable coefficients are obtained using the zero-order integral Hankel transformation and its properties from the boundary conditions for transformed functions. Partial integrals and the mean auxiliary Sherwood numbers are obtained approximately. The solution to the formulated problem is used in various technological applications associated with combustion or chemical reactions at the interface between the continuous and discrete phases in the dispersed system, in meteorology, in analysis of problems associated with environmental pollution, etc.

Wet granular walkers and climbers

Mechanisms of locomotion in microscopic systems are of great interest not only for technological applications but also for the sake of understanding, and potentially harnessing, processes far from thermal equilibrium. Downscaling is a particular challenge and has led to a number of interesting concepts, including thermal ratchet systems and asymmetric swimmers. Here we present a granular ratchet system employing a particularly robust mechanism that can be implemented in various settings. The system consists of wetted spheres of different sizes that adhere to each other, and are subject to a symmetric oscillating, zero average external force field. An inherent asymmetry in the mutual force network leads to force rectification and hence to locomotion. We present a simple model that accounts for the observed behaviour, underscores its robustness and suggests a potential scalability of the concept.

Free-Energy Density Functional of Ions at a Dielectric Interface.

Ions at dielectric interfaces are found in a wide range of applications including biology, nanofluidics, and fuel cells. Often, the excluded volume of the ions has first-order effects on measured properties. Here, density functional theory of fluids is used to develop a statistical mechanical theory of how ions (charged hard spheres of different sizes) arrange around a dielectric interface.

Radial voidage variation in randomly-packed beds of spheres of different sizes

Abstract The packing arrangement of the particles in a tablet die, before pressing, has no hitherto been considered as a variable in the tabletting process. Because of the complexity of this subject, the present investigation has been restricted to monosized and binary mixtures of spheres in a cylindrical container. The container could be revolved at speeds in excess of 1,000 rpm so that the thickness of an annular layer of water could be measured. From this, the voidage at any radial position could be found. The plot of voidage against distance from the cylindrical wall is a wave form which is damped out after about 5 particle diameters. For packings of monosized spheres the oscillations are regular. There appear to be two kinds of binary mixtures, those in which the particle sizes are similar, and those where the diameter ratio is greater than 0·4. The voidages calculated by suitably weighting the values for each component are in agreement with the measured voidages of the first kind but not with those of the second. Because there is an initial distribution of voidage, it is concluded that there must be some radial movement of the particles during the compacting operation.

Energy Absorption Behavior of a Hyperelastic Membrane for Micro Air Vehicle Wings: Experimental and Finite Element Approaches

The rubber latex membrane is used for micro air vehicles construction and plays an important role in their wings performance. This paper presents finite element (FE) models for investigating the deformation and energy absorption behavior of the latex membrane at static loading, validated by the experimental results. The membrane at different pre-tension levels are attached to a circular steel ring and statically loaded using steel spheres of different sizes placed at the center of the membrane. The deformation of the membrane is measured by the visual image correlation (VIC), a non-contact measurement system and strain energy is calculated based on the Mooney–Rivlin hyperelastic material model. It is found that the deflection and strain energy of the membrane estimated by experiments and FE models are correlated well although discrepancy is expected among experimental and FE results within reasonable limits due to the variation of the thickness of the membrane. The deformation and energy absorption of the membrane increase with the weight of the sphere. But the deformation decreases and the energy absorption increases with increase of the pre-tension level of the membrane due to a specific weight of the sphere.

Supervision of new phenomena in a flow-pattern of viscous liquid

After the exact decision of the equations of movement of a viscous liquid (the equations of Navier-Stokes) under condition of the established current and non compressible liquids it has been revealed that only limited number of lines can appear as the real currents trajectories. This number includes direct lines, concentric circles and some spirals, axis symmetrical currents and currents at which the whirlwind of speed is constant (or equal to zero). It is essential that the established flow of a sphere or the cylinder is impossible, since trajectories of such current are not present among the specified ones. For revealing of sphere flow features, the uniform movement observation was carried out (both single spheres of different size and rigidly connected ones). These spheres formed a figure similar to the single «dumbbells» Or doubled at right angle to two «dumbbells». Experiences have found out the fact of a spontaneous twisting of spheres and «dumbbells» With the speed of a circular motion proportional to linear speed of spheres in motionless water of lake. Thus the twisting occurred always if there was no initial indignation, only counter-clockwise as at movement of spheres in directions the north-south, and the east-West, and upwards-downwards that proves that on rotation of spheres rotation of the Earth cannot render influence.

Heating within Spheres of Different Size Irradiated by an Electromagnetic Plane Wave

This paper presents the results obtained by multiphysics (electromagnetic and thermal) numerical simulations which show the influence of the size in two different spheres that are irradiated by an electromagnetic plane wave. Each sphere is constituted by a series of concentric layers that emulate the tissues in the head. A 10 mW/cm2 plane wave is used as source, and the frequency is setup to 1.8 GHz. The power absorbed per unit volume by the tissues (W/m3) is calculated by using the 3-D Finite Difference Time Domain (FDTD) method. Then, temperature inside the spheres is calculated by using a Finite Differences (FD) formulation of the heat diffusion equation. Two different ways of calculating the power-loss density are presented, and validated with analytical results. It is observed that the increase of temperatures inside a 66 mm sphere, in diameter, is higher than inside a 100 mm sphere. However, the power absorbed per unit volume in the brain zone is six times higher in the 100 mm sphere.

SU‐GG‐J‐04: Determination of Tumor Volume Using a Joint Motion‐PVE Correction Technique in PET/CT Imaging

Objective: 4D‐CT has been used to determine the tumor volume (TV) for lung/thoracic radiation therapy treatment planning primarily due to its ability to detect the tumor motion extent and trajectory. However, 4‐D CT is usually characterized by high patient radiation exposure. The objective of this abstract is to propose and evaluate an approach that relies on a single static PET/CT scan than can determine the TV by simultaneously correcting for respiratory motion artifact and partial volume effect (PVE) thereby eliminating the need for 4D‐CT and reducing patient exposure.Materials and Methods: The proposed joint correction approach incorporates a model of motion blurring, PVE and object size/shape. A motion blurring kernel (MBK) is then estimated from the deconvolution of the joint model while the TV is derived from convolving the MBK by the object size/shape obtained from the CT image. To test this technique, two studies were performed using 2 spheres of different sizes moving in a 2cm 1D‐sinusoidal and 2D‐circular waveforms respectively. In both cases, a 4D‐CT and a PET/CT of the 2 spheres were acquired. For both studies, the TV from the proposed technique was compared to the maximum‐intensity projection (MIP) volume of the 4D‐CT. Also a Dice coefficient of the two volumes was calculated. Results: The TV of the proposed technique was on average 3% different from the MIP volume. The average Dice coefficient was 0.87. The motion trajectory derived from the proposed technique is continuous while that of the 4D‐CT is discrete. Conclusion: Using this approach, a single static PET/CT can replace a 4D‐CT to determine the TV. This approach also has the ability to determine the tumor motion extent and trajectory and has the added advantage of reducing patient radiation exposure and determining the tumor locale probability (or MBK) compared to 4D‐CT.

Dense Packings of Hard Spheres of Different Sizes Based on Filling Interstices in Uniform Three-Dimensional Tilings

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionDense Packings of Hard Spheres of Different Sizes Based on Filling Interstices in Uniform Three-Dimensional TilingsT. S. Hudson and Peter Harrowell*Cite this: J. Phys. Chem. B 2010, 114, 20, 7132Publication Date (Web):April 29, 2010Publication History Published online29 April 2010Published inissue 27 May 2010https://doi.org/10.1021/jp103375pCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views252Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (22 KB) Get e-AlertsSUBJECTS:Chemical structure Get e-Alerts

Electrosynthesis of well-organized nanoporous poly(3,4-ethylenedioxythiophene) by nanosphere lithography

The electrodeposition of poly(3,4-ethylenedioxythiophene) (PEDOT) films from aqueous surfactant solution through a two-dimensional poly(styrene) (PS) template onto indium tin oxide (ITO) substrate has been investigated. The polymer grows in the interstitial spaces of the self-assembled PS spheres which were subsequently removed by dissolution in tetrahydrofuran (THF). Surface characterization by scanning electron microscopy (SEM) and atomic force microscopy (AFM) reveals that two-dimensional nanoporous honeycomb PEDOT structures can easily be obtained by using PS spheres of different sizes. Gold electrodeposition onto the nanostructured PEDOT electrode was investigated and SEM images show preferential formation of nanoparticles (NP) on the wall and the rim of the PEDOT film but metal clusters inside the pores are also observed.

Absolute quantification of activity content from PET images using the Philips Gemini TF PET/CT system

Positron emission tomography combined with computed tomography (PET/CT) is a quantitative technique suitable for diagnostics and uptake measurements. The quantitative results can be used for the purpose of the calculating absorbed dose to patients undergoing nuclear medicine investigations. Hence, the accuracy of the quantification of the activity content in organs or tissues is of great importance. When using a planar gamma camera and single photon emission computed tomography (SPECT) images, the activity content in organs and tumours has to be determined by the user, using the number of counts in the organs and the efficiency of the camera. However, when using a Philips Gemini TF PET/CT system, the activity concentration in a region of interest (ROI) is given by the system. The reliability of activity concentration values given by the Philips Gemini TF PET/CT system was studied using a Jaszczak phantom containing hot spheres of different sizes; the influence of the ROI size and the impact of organ size, that is the partial volume effect, was investigated with three different lesion-to-background ratios in the phantom. The use of a small ROI size (40 % of the large ROI size, which covered the entire sphere) showed a 15 % improvement in the recovery of the true activity. Small lesion sizes result in large underestimations of the activity concentration values.

Noise and signal properties in PSF-based fully 3D PET image reconstruction: an experimental evaluation

The addition of accurate system modeling in PET image reconstruction results in images with distinct noise texture and characteristics. In particular, the incorporation of point spread functions (PSF) into the system model has been shown to visually reduce image noise, but the noise properties have not been thoroughly studied. This work offers a systematic evaluation of noise and signal properties in different combinations of reconstruction methods and parameters. We evaluate two fully 3D PET reconstruction algorithms: (1) OSEM with exact scanner line of response modeled (OSEM+LOR), (2) OSEM with line of response and a measured point spread function incorporated (OSEM+LOR+PSF), in combination with the effects of four post-reconstruction filtering parameters and 1–10 iterations, representing a range of clinically acceptable settings. We used a modified NEMA image quality (IQ) phantom, which was filled with 68Ge and consisted of six hot spheres of different sizes with a target/background ratio of 4:1. The phantom was scanned 50 times in 3D mode on a clinical system to provide independent noise realizations. Data were reconstructed with OSEM+LOR and OSEM+LOR+PSF using different reconstruction parameters, and our implementations of the algorithms match the vendor's product algorithms. With access to multiple realizations, background noise characteristics were quantified with four metrics. Image roughness and the standard deviation image measured the pixel-to-pixel variation; background variability and ensemble noise quantified the region-to-region variation. Image roughness is the image noise perceived when viewing an individual image. At matched iterations, the addition of PSF leads to images with less noise defined as image roughness (reduced by 35% for unfiltered data) and as the standard deviation image, while it has no effect on background variability or ensemble noise. In terms of signal to noise performance, PSF-based reconstruction has a 7% improvement in contrast recovery at matched ensemble noise levels and 20% improvement of quantitation SNR in unfiltered data. In addition, the relations between different metrics are studied. A linear correlation is observed between background variability and ensemble noise for all different combinations of reconstruction methods and parameters, suggesting that background variability is a reasonable surrogate for ensemble noise when multiple realizations of scans are not available.

Simulation of lung nodules in chest tomosynthesis

The aim of the present work was to develop an adequate method for simulating lung nodules in clinical chest tomosynthesis images. Based on the visual appearance of real nodules, artificial, three-dimensional nodules with irregular shape and surface structure were created using an approach of combining spheres of different sizes and central points. The nodules were virtually positioned at the desired locations inside the patient and by using the known geometry of the tomosynthesis acquisition, the radiation emitted from the focal spot, passing through the nodule and reaching the detector could be simulated. The created nodules were thereby projected into raw-data tomosynthesis projection images before reconstruction of the tomosynthesis section images. The focal spot size, signal spread in the detector, scattered radiation, patient motion and existing anatomy at the location of the nodule were taken into account in the simulations. It was found that the blurring caused by the modulation transfer function and the patient motion overshadows the effects of a finite focal spot and aliasing and also obscures the surface structure of the nodules, which provides an opportunity to simplify the simulations and decrease the simulation times. Also, the limited in-depth resolution of the reconstructed tomosynthesis section images reduces the necessity to take details of the anatomical structures at the location of the inserted nodule into account.

Wavelength dependence of optical tweezer trapping forces on dye-doped polystyrene microspheres

We present an experimental and numerical study of the wavelength dependence, near resonance, of the optical tweezer trap stiffness on three different dye-doped 1 μm polystyrene spheres with peak absorptions at λ=625, 775, and 840 nm. Experimentally, an increase in the trap stiffness of ~35% on the red side of resonance was observed for the dye-doped spheres relative to polystyrene spheres without dye. Numerical simulations for spheres of different sizes, between 20 nm and 1 μm, and for absorption strengths corresponding to peak extinction coefficient values between 0.0027 and 0.081 were also conducted. Numerical results showed a maximum increase in the trap stiffness of ~35%, which is consistent with experimental results.