Segment Of Sphere Research Articles

24 hours of an #outcry: The networked publics of a socio-political debate

This article explores the development of a social–political discussion on everyday sexism in Germany, labelled ‘#aufschrei’ (German for ‘outcry’), that started as a small Twitter conversation and evolved into a nationwide debate within 24 hours. After discussing the relationship of social actions, social networks and interlinked digital objects in the construction of networked publics, the authors propose to understand #aufschrei as an ‘ad hoc’ public – a communication sphere evolving around a shared topic within the spaces of the networked public sphere. Applying both computational research approaches and traditional content analysis to a large set of Twitter data, the authors reconstruct the dynamics of the debate in relation to concepts of horizontal and vertical segments of the public sphere. The conclusion calls for a theoretical re-evaluation of how those concepts can be applied to networked publics, and for an increased research effort to develop comprehensive methods for visualising or objectifying networked publics.

Preparation of copper sphere segment void templates for electrochemical SERS and their use to study the interaction of amino acids with copper under potentiostatic control

We describe a simple method to prepare nanostructured copper electrodes based on electrodeposition of copper through a polystyrene nanosphere template to produce a copper sphere segment void (SSV) structure. We show that the SSV copper electrodes give a large SER enhancement under potentiostatic control and we use the SSV copper electrodes to study the adsorption of aromatic and non-aromatic amino acids in basic solution.

Polyhedra faster than spheres?

Purpose – The purpose of this paper is to present a new and efficient technique for discrete element modelling using non-convex polyhedral grain shapes. Design/methodology/approach – The efficiency of the technique follows from the use of grains that are dilated versions of the basic polyhedral grain shapes. Dilation of an arbitrary polyhedral grain is accomplished by placing the center of a sphere of fixed radius at every point on the surface. The dilated vertices become sphere segments and the edges become cylinder segments. The sharpness of the vertices and edges can be adjusted by varying the dilation radius. Contacts between two dilated polyhedral grains can be grouped into three categories; vertex on surface, vertex on edge, and edge on edge, or in the grammar of the model, sphere on polygonal surface, sphere on cylinder, and cylinder on cylinder. Simple, closed-form solutions exist for each of these cases. Findings – The speed of the proposed polyhedral discrete element model is compared to similar models using spherical and ellipsoidal grains. The polyhedral code is found to run about 40 percent as fast as an equivalent code using spherical grains and about 80 percent as fast as an equivalent code using ellipsoidal grains. Finally, several applications of the polyhedral model are illustrated. Originality/value – Few examples of discrete element modeling studies in the literature use polyhedral grains. This dearth is because of the perceived complexity of the polyhedral coding challenges and the slow speed of the codes compared to codes for other grain shapes. This paper presents a much simpler approach to discrete element modeling using polyhedral grain shapes.

In Situ Observation of O-Metal Vibrations at Pt and Au Electrodes By Plasmonic Crystalline-Based SERS

For practical applications of polymer electrolyte fuel cell (PEFC), designing a high performance and low cost membrane electrode assembly (MEA) is necessary, and performance and cost of a MEA is closely related to the properties of catalysts. Improvement of cathode catalyst becomes a key, and fundamental understandings of cathode reaction mechanism has been essential.For the reaction mechanism investigation, in situ, dynamic measurement tools should be required. We have been developing a combination of surface enhanced vibrational spectroscopic techniques, such as surface enhanced Raman scattering (SERS), surface enhanced infrared absorption spectroscopy (SEIRAS) and sum frequency generation (SFG) spectroscopy. Generator-collector regime in the electrochemical microchannel device has been also investigated to realize time-resolved measurement by detecting adsorbed intermediates during electrocatalytic reaction.The recent development in nanofabrication technology affects in the field of plasmonics and various types of novel SERS-active substrates have been reported. We have already prepared the micrometer-scale inverse pyramid-type plasmonic crystalline SERS-active substrates [1-2] with flat (111)-oriented Au surfaces and strong SERS signals from self-assembled monolayers (SAMs) of thiophenol were detected[3]. Although SERS activity of the plasmonic crystalline substrate covered by Pt was not high, strong SERS signal has been reported at sphere segment void (SSV)-type plasmonic crystalline substrates covered with Pt or Pd.[4-5] By tuning the size and depth of SSVs, SERS signal from atomically thickness-controlled Pt thin film covering only the top most surfaces of Au-SSV has proved to give information about adorbates on Pt surfaces selectively. Furthermore, by remaining PS templates, only the Pt surface becomes electrochemically active and SERS intensity from Pt-rim is enhanced much higher. Electrochemical SERS measurement are also carried out in situ at Au- and Pt/Au-SSV substrates. Acknowledgement This work was supported by New Energy, Industrial Technology Development Organization (NEDO), Fuel Cell Promotion Office of the Agency of Natural Resources and Energy, Ministry of Economy, Trade and Industry (METI).

Surface-Enhanced Raman Scattering on Uniform Pd and Pt Films: From Ill-Defined to Structured Surfaces

We report borrowed surface-enhanced Raman scattering (SERS) at Pd and Pt films deposited on Au sphere segment void (SSV) SERS substrates and show that ultrathin, pinhole-free Pd and Pt films could be easily achieved by choosing constant-current deposition for the Pd deposition and under-potential deposited Cu-mediated deposition for the Pt deposition. The surface enhancement achieved from the Pd and Pt films was reproducible, owing to the ordered SSV structure of their surfaces, and borrowed additional enhancement from the long-range electromagnetic (EM) fields generated by the underlying Au SSV substrate. SERS experiments and theoretical simulations indicate that the distance over which the EM fields generated by a concave Au SSV surface can be transferred to the surface of the transition-metal films is approximately an order of magnitude larger than that for a convex sphere surface. This longer range of the EM fields allowed deposition of thicker, more robust Pd and Pt films while retaining the borrowed enhancement. These properties make such Pd and Pt films attractive as SERS surfaces to reveal surface species and reactive intermediates on these two typical electrocatalyst materials.

(Invited) Micro-to-Nanostructures to Probe Electrocatalysts by SERS

Focusing the void plasmon toward the rim part of the sphere segment void (SSV) type plasmonic crystalline structures are further developed by retaining the polystyrene nanospheres inside the voids. Plasmonic whispering gallery modes (WGMs) are proved to appear in such the hybrid structures by the measurements of reflectance spectroscopy and cause the improvement of signal/background ratio in the SERS spectra. From the detailed experimental analyses, a possibility of the plasmonic WGMs to enhance the molecular signal at the Pt electrode surfaces is shown.

Spatial Distribution of Optical Near-Fields in Plasmonic Gold Sphere Segment Voids

We present a comprehensive experimental and computational study on the electromagnetic field distribution in sphere segment void arrays. Surface plasmon polaritons can be excited in these void arrays, resulting in greatly enhanced electromagnetic fields. With the scanning near-field optical microscope (SNOM) we are able to measure the electromagnetic field distribution at the sample surface. For this purpose, an array of relatively large voids with a sphere diameter of 900 nm was fabricated, allowing for an easy access of the scanning glass-fibre tip and yielding very detailed scans. Complementary, finite-difference time-domain (FDTD) calculations on a complete void array have been performed and compared with the SNOM intensity maps and experimental reflectivity data. We show in a direct way both the existence of extended and localised modes in the Au void array for three different void depths. We also show and discuss the changes that the modes undergo for the different void depths and excitation wavelengths. Moreover, since the simulations were performed for two different void geometries, one containing perfectly spherical void surfaces and another more realistic one, which considers the presence of interstitial wall holes and other imperfections, as observed in scanning electron micrographs, we were able to determine by comparison with the experiment under which conditions an array of idealised sphere segment voids is a meaningful model. This demonstrates that both SNOM and FDTD simulations are powerful tools for understanding the plasmonic response of metallic nanostructures, thus enabling, for instance, a design for applications in ultra-sensitive optical detection.

Formation of a space charge during the interaction of an ion with a metal surface

When an ion approaches a metal surface, an induced charge forms in it, which affects the formation of electronic states in an ion-metal system. The spatial distribution of the electron density near the metal surface has been calculated in the case of the classical consideration and in the framework of the energy density functional approximation. It is shown that the space cloud exists in the form of a sphere segment; in this case, this cloud is shifted toward the approaching ion in the quantum-mechanical consideration.

Modification of nanostructured gold surfaces with organic functional groups using electrochemical and solid-phase synthesis methodologies

Anthraquinone and nitrobenzene redox probes were covalently attached to nanostructured sphere segment void (SSV) gold substrates prepared using templated electrodeposition. Anthraquinone was attached to the SSV gold surface through an (aminomethyl)phenyl (NH2CH2C6H4) linker using a combination of electrochemical coupling and solid-phase modification. The nitrobenzene probe was directly immobilized by electrochemical reduction of the corresponding diazonium salt or by self-assembly of 4-nitrobenzene thiol. The surface coverages and stabilities of the modified gold surfaces were characterised by electrochemical and surface enhanced Raman scattering (SERS) techniques. The results demonstrate that electrochemical coupling followed by solid phase coupling is a flexible method for the functionalisation of nanostructured SSV, or other, gold surfaces. The use of the SSV gold substrate allows us to follow the different steps in the modification process using SERS. We find that that diazonium attachment to gold gives greater stability than the more commonly used thiol self-assembly approach.

Axisymmetric Finite-Element Analysis for Interface Migration-Controlled Shape Instabilities of Plate-Like Double-Crystal Grains

An axisymmetric finite-element method is developed to predict the evolution behavior of microstructures by interface migration. The formulation of the method is conducted on the basis of the energy principle during the interface motion. The computations extend earlier models by accounting in detail for the effects of grain-boundary energy, surface energy and chemical potential difference. The eventual shape of the plate-like double-crystal grain depends on both the initial β and the thermal grooving angle Ψ. For a given β, a critical Ψcexists. When Ψ>Ψc, the eventual shape is one made of two sphere segments with a thermal groove. When Ψ≤Ψc, grain splitting along the grain boundary occurs, and the splitting segments evolve into two spheres, respectively. Both the spheroidization time and the splitting time increase with Ψ and β increasing. The volume shrinkage rate decreases with increasing Ψ.

Incident Wavelength Resolved Resonant SERS on Au Sphere Segment Void (SSV) Arrays

Sphere segment void (SSV) arrays allow the reproducible engineering of plasmon-polariton modes from the near-infrared to the ultraviolet through the tuning of the void height and diameter. The wavelength dependence of surface-enhanced Raman scattering (SERS) can then in principle be controlled by selecting these parameters. Using 4-mercaptopyridine as a covalently bonded nonresonant molecular probe, we report a detailed study of such wavelength dependence of SERS in Au SSV arrays as a function of void diameter and height. We conclude that the SERS mechanism on SSV arrays depends on the plasmonic properties of the substrates and also that additional effects contribute significantly to the observed enhancement including a chemical contribution related to the molecular probe and a nanostructuring induced surface plasmon localization existent for the smaller cavity dimensions.

Information and Communication Technologies in Turkey and Other OECD Member Countries

This paper investigates the economic effects of the ICT revolution. In this regard, economic impacts of ICT are evaluated by touching various segments of social and economic spheres that are deeply affected by the ICT revolution. Further, we present summary of a comprehensive survey of previous studies in the literature on the relationship between economic growth and ICT. Then, we examine the ICT sector in OECD area in general and specifically in Turkey. Depending on the results of all these attempts, we propose some policy suggestions for Turkey.

Nanostructures to Probe Electrocatalytic Reactions II

Two dimensional plasmonic structures provide rigid and stable SERS-active substrate. For example, sphere segment void (SSV) structure seems to be attractive, since this structure can be prepared only by wet chemistry and the SERS enhancement coupled with various plasmon modes is available. On the other hand, the SERS-active sites become unclear from the contribution of various plasmon modes and the distribution of them should be understood to investigate the electrocatalytic reactions with in situ electrochemical SERS measurements. In this study, the localization of SERS-active sites in Au-SSV and the focusing the plasmon field to different metals are investigated.

Theory and simulation of chain molecules with multiple bonding sites in an associating solvent

Although polyethylene oxide (PEO) is soluble in water, polymethylene oxide (PMO) is not, even though PMO has more association sites. Some suggest this is due to orientation effects in the water hydrogen-bond network. A simulation and theory study of the effect of bonding site density on thermodynamic properties and extent of bonding of a linear flexible chain in a hydrogen-bonding solvent is performed. Predictions from Wertheim's theory are compared against simulation results. Thermodynamic properties and extent of bonding were obtained. The solvent molecules are modeled as hard spheres with four association sites in a tetrahedral arrangement. The chains are flexible and consist of six tangent segments of hard spheres with bonding sites that interact with the solvent molecules. A solvent molecule can also form a bond with a second solvent molecule. The association interaction is modeled with an orientation-dependent square-well. The total number of bonding sites on each chain is varied and the effects studied. This is another test of the theory for the case of mixtures of associating molecules of different sizes. The Metropolis Monte Carlo technique was chosen to perform simulations in the canonical and isothermal–isobaric ensembles. Good agreement was found between theory and simulation.

Celebrity Studies in the Long Eighteenth Century: An Interdisciplinary Overview

AbstractThe work done to date on the development of celebrity culture in the long 18th century ranges across fields as diverse as theater and criminology, art and boxing, and music and oral culture, as scholars examine how celebrity operates within discrete segments of the public sphere as well as across them. Celebrity studies is more than a simple description of a star’s popularity. Instead, it examines how personal, social, media, political, and economic events create local conditions of popularity, how a celebrity’s popular images circulate within a culture, and what the celebrity means to a culture; it also traces how concepts of merit and fame change over time. Individual studies of celebrities and the fans, audiences, and readers who admire them are joined by interdisciplinary studies that best capture the breadth of celebrity’s foundations and effects.

SERS from two-tier sphere segment void substrates

Sphere segment void, or inverse opal, films prepared from a variety of coinage metals have shown promise as reliable and reproducible substrates for surface enhanced Raman spectroscopy (SERS). Sphere segment void substrates are prepared from colloidal templates consisting of one or more layers of polystyrene spheres. In this paper, we investigate the reflection spectra and SERS for a gold film consisting of two-tiers of spherical cavities, and show that the best SERS enhancements are obtained from substrates consisting of just a single layer of sphere segment voids.

Entropic solvation force between surfaces modified by grafted chains: a density functional approach

The behavior of a hard sphere fluid in slit-like pores with walls modified by grafted chain molecules composed of hard sphere segments is studied using density functional theory. The chains are grafted to opposite walls via terminating segments forming pillars. The effects of confinement and of “chemical” modification of pore walls on the entropic solvation force are investigated in detail. We observe that in the absence of adsorbed fluid the solvation force is strongly repulsive for narrow pores and attractive for wide pores. In the presence of adsorbed fluid both parts of the curve of the solvation force may develop oscillatory behavior dependent on the density of pillars, the number of segments and adsorption conditions. Also, the size ratio between adsorbed fluid species and chain segments is of importance for the development of oscillations. The choice of these parameters is crucial for efficient manipulation of the solvation force as desired for pores of different width.

Understanding the Surface-Enhanced Raman Spectroscopy “Background”

Even 35 years after the discovery of surface-enhanced Raman spectroscopy (SERS) much remains to be learned about the phenomenon.(1-3) Despite broad consensus on the mechanism of SERS, many features remain poorly understood and in particular much less effort has been put into understanding the continuum emission called the “background” observed in SERS spectra. Here the SERS background is studied systematically on sphere segment void (SSV) plasmonic substrates. We establish the physicochemical dependence of the background on plasmons, the identity of the adsorbate, adsorbate coverage and electrochemical potential. In particular, by exchanging electron-donating and electron-withdrawing adsorbates, we demonstrate predictable modulation of the SERS background. Using these observations, we propose a model for the origin of the SERS background. Finally, we test the proposed model against its predictions for anti-Stokes SERS spectra.

The Use of an Electroactive Marker as a SERS Label in an E‐melting Mutation Discrimination Assay

AbstractIn this paper we describe the first example of the use of an electroactive label as a SERS marker for detecting and quantifying target oligonucleotides and distinguishing mutations using a combination of voltammetry and electrochemically induced melting (E‐melting). The experiments were carried out on sphere segment void substrates selected to show strong surface enhancement for SERS at 633 nm. DNA analysis was carried out for CFTR sequences using synthetic 22‐mer oligonucleotides labelled with a modified anthraquinone at the 3′‐end. Discrimination between the wild type, 1653C/T (point mutation) and ΔF508 (triple deletion) is demonstrated.

Size properties of legume seeds of different varieties using image analysis

Image analysis system was used to provide geometric parameters of legume seeds, which are important for designing of engineering processes such as drying, milling, germination etc. Measured features of bean and lentil seeds were projected area, equivalent diameter, MaxFeret, MinFeret and thickness. Three approximation models (an oblate spheroid, two sphere segments and a triaxial ellipsoid) were used to evaluate volume and surface area of lentil and bean seeds of various varieties. The best approximation model was found as the triaxial ellipsoid and the oblate spheroid for bean varieties and two sphere segments for lentil varieties. From the model data estimated specific surface area were ranged from 5.1–5.8 cm 2/g for bean varieties and 11.57–11.95 cm 2/g for lentil varieties. Image analysis system provided fast and accurate values of important technological properties of legume such as geometric parameters, volume and surface area.