Spherical Degree Research Articles

Preparation of solid carbon spheres by pyrolysis of allyl COPNA-BMI resin

The copolymer of allyl condensed polynuclear aromatic (COPNA) resin and 4,4′-bismaleimidodiphenyl methane (BMI) was used to prepare resin microspheres using silicone oil as dispersant by means of suspension polymerization, and solid carbon spheres were prepared by direct pyrolysis of the resin microspheres in this paper. Thermal behavior of the resin microspheres was studied by TG–DTG, FTIR and element analyze instrument. The resultant carbon spheres were characterized by SEM, XRD and nitrogen adsorption–desorption measurement. Results show that the resin microspheres, which have a mean particle diameter of 14.6 μm, possess fine degree of sphericity and smoothness. The resin microspheres possess excellent thermal properties, indicated by that initial decomposition temperature is 420 °C and carbonization yield reaches 49.1% in nitrogen. Furthermore, pyrolysis products of the resin microspheres are made up of solid carbon spheres with a nongraphitized carbonaceous structure. When pyrolysis temperature is 1000 °C, the BET surface area and total pore volume of the carbon spheres arrive at 595 m 2 g −1 and 0.29 cm 3 g −1, respectively.

Ventricular Chamber Sphericity During Spaceflight and Parabolic Flight Intervals of Less Than 1 G

Pathology driven alterations in the geometric shape of the heart have been found to result in regional changes in ventricular wall stress and a remodeling of the myocardium. If reductions in the gravitational forces acting on the heart produce similar changes in the overall contour of the ventricles, this modification might also induce adaptations in the cardiac structure during long-term spaceflight. In this study we examined the changes in left ventricle (LV) shape in spaceflight and during parabolic flights. The diastole dimensions of the human LV were assessed with echocardiography during spaceflight and in parabolic flights which replicated the gravity of the Moon, Mars, and spaceflight and were compared to findings in Earth's gravity. LV dimensions were translated into circularity indices and geometric aspect ratios and correlated with their corresponding gravitational conditions. During parabolic flight, a linear relationship (r = 0.99) was found between both the circularity index and geometric aspect ratio values and the respective gravitational fields in which they were measured. During spaceflight (N = 4) and parabolic flights (N = 3), there was an average 4.1 and 4.4% higher circularity index and a 5.3 and 8.1% lower geometric aspect ratio, respectively. A correlative trend was found between the degree of LV sphericity and the amount of gravitational force directed caudal to the longitudinal orientation of the body. The importance of this finding is uncertain, but may have implications regarding physiologic adaptations in the myocardial structure secondary to changes in LV wall stress upon prolonged exposure to microgravity.

The influence of physicomechanical characteristics of microspherical supporters and dehydrogenation catalysts on their abrasive activity in fluidized bed conditions

In industrial lower paraffin dehydrogenation reactor units with a microspherical chromoalumina catalyst fluidized bed, abrasive wear of internal equipment surfaces proceeds by the fatigue and plastic deformation mechanism, and the wear direction coincides with the catalyst motion trajectory. The wear degree is defined by wearing material and granule physicomechanical properties, which have been taken into account along with hydrodynamic conditions for the formation of fluidized bed to suggest a mathematical model, describing the influence of physicomechanical, structural characteristics and sizes of granule on the abrasive ability of industrial microspherical paraffin dehydrogenation catalysts and aluminum oxide supporters. The most significant factors have been revealed: salient item density on the granule surface, abrasion resistance, microhardness, and sphericity degree. The developed mathematical model permits to predict the abrasive activity of granules under their operation, to estimate the internal reactor surface wear time necessary to attain the critical thickness, and to choose optimal methods for the synthesis of catalysts and supporters with minimal abrasive activities.

ASTEROSEISMOLOGY OF HYBRID PULSATORS MADE POSSIBLE: SIMULTANEOUS MOST SPACE PHOTOMETRY AND GROUND-BASED SPECTROSCOPY OF γ PEG

We have acquired simultaneous high-precision space photometry and radial velocities of the bright hybrid Beta Cep/SPB pulsator Gamma Peg. Frequency analyses reveal the presence of six g modes of high radial order together with eight low-order Beta Cep oscillations in both data sets. Mode identification shows that all pulsations have spherical degrees l = 0 - 2. An 8.5 solar mass model reproduces the observed pulsation frequencies; all theoretically predicted modes are detected. We suggest, contrary to previous authors, that Gamma Peg is a single star; the claimed orbital variations are due to g-mode pulsation. Gamma Peg is the first hybrid pulsator for which a sufficiently large number of high-order g modes and low order p and mixed modes have been detected and identified to be usable for in-depth seismic modeling.

Confirmation of simultaneous p and g mode excitation in HD 8801 and γ Peg from time-resolved multicolour photometry of six candidate ‘hybrid’ pulsators

We carried out a multi-colour time-series photometric study of six stars claimed as "hybrid" p and g mode pulsators in the literature. Gamma Peg was confirmed to show short-period oscillations of the Beta Cep type and simultaneous long-period pulsations typical of Slowly Pulsating B (SPB) stars. From the measured amplitude ratios in the Stromgren uvy passbands, the stronger of the two short period pulsation modes was identified as radial; the second is l=1. Three of the four SPB-type modes are most likely l=1 or 2. Comparison with theoretical model calculations suggests that Gamma Peg is either an 8.5 solar mass radial fundamental mode pulsator or a 9.6 solar mass first radial overtone pulsator. HD 8801 was corroborated as a "hybrid" Delta Sct Gamma Dor star; four pulsation modes of the Gamma Dor type were detected, and two modes of the Delta Sct type were confirmed. Two pulsational signals between the frequency domains of these two known classes of variables were confirmed and another was newly detected. These are either previously unknown types of pulsation, or do not originate from HD 8801. The O-type star HD 13745 showed small-amplitude slow variability on a time scale of 3.2 days. This object may be related to the suspected new type of supergiant SPB stars, but a rotational origin of its light variations cannot be ruled out at this point. 53 Psc is an SPB star for which two pulsation frequencies were determined and identified with low spherical degree. The behaviour of 53 Ari and Iota Her is consistent with non-variability during our observations, and we could not confirm light variations of the comparison star 34 Psc previously suspected. The use of signal-to-noise criteria in the analysis of data sets with strong aliasing is critically discussed.

Sensitivity of direct radiative forcing by mineral dust to particle characteristics

Airborne dust affects the Earth's energy balance — an impact that is measured in terms of the implied change in net radiation (or radiative forcing, in W m-2) at the top of the atmosphere. There remains considerable uncertainty in the magnitude and sign of direct forcing by airborne dust under current climate. Much of this uncertainty stems from simplified assumptions about mineral dust-particle size, composition and shape, which are applied in remote sensing retrievals of dust characteristics and dust-cycle models. Improved estimates of direct radiative forcing by dust will require improved characterization of the spatial variability in particle characteristics to provide reliable information dust optical properties. This includes constraints on: (1) particle-size distribution, including discrimination of particle subpopulations and quantification of the amount of dust in the sub-10 µm to <0.1 µm mass fraction; (2) particle composition, specifically the abundance of iron oxides, and whether particles consist of single or multi-mineral grains; (3) particle shape, including degree of sphericity and surface roughness, as a function of size and mineralogy; and (4) the degree to which dust particles are aggregated together. The use of techniques that measure the size, composition and shape of individual particles will provide a better basis for optical modelling.

On Coordinating Time Series Spectroscopy with the WET

Die Serie Communications in Asteroseismology (CoAst) stellt eine international gefragte Plattform für wissenschaftliche Publikationen der neuesten Forschungsergebnisse auf dem Gebiet der Asteroseismologie dar. Forschungsgegenstand der Asteroseismologie sind pulsierende Sterne. Neben den halbjährlich erscheinenden regulären Ausgaben mit Beiträgen aus der laufenden Forschung werden auch Sonderausgaben für Konferenzberichte bzw. Programmhandbücher herausgegeben. Der Sammelband Vol. 154 beinhaltet die Konferenzbeiträge des in Delaware 2007 abgehaltenen Delaware Asteroseismic Research Center and Whole Earth Telescope Workshops. Im Rahmen dieses Arbeitstreffens wurden die neuesten theoretischen und beobachtungstechnischen Forschungsergebnisse auf dem Gebiet der Weißen Zwerge präsentiert. Contents: H. L. SHIPMAN: The Whole Earth Telescope Network's August 2008 Workshop S. J. KLEINMAN: Do You Need the WET: A Modest Proposal A. BISCHOFF-KIM: Preliminary Asteroseismology of EC20058-5234 and Limits on Plasmon Neutrinos J. L. PROVENCAL, H. L. SHIPMAN, and the WET TEAM: An Update on XCOV25: GD358 M. H. MONTGOMERY: What We Can Learn from the Light Curves of GD 358 and PG 1351+489 S. E. THOMPSON: On Coordinating Time Series Spectroscopy with the WET M. PAPARÓ, E. PLACHY, L. MOLNÁR, P. I. PÁPICS, Zs. BOGNÁR, N. SZTANKÓ, Gy. KEREKES, A. MÁR & E. BOKOR: Preliminary Results in White Dwarf Research by a New Group H. O. VATS & K. S. BALIYAN: Recent observations of WD1524 at MIRO and participation in WET observing program J. DALESSIO, J. L. PROVENCAL & A. KANAAN: Introducing SPA, "The Stellar Photometry Assistant"

Spectroscopic observations for asteroseismology

Spectroscopic observations of stellar oscillations provide an indispensable input for asteroseismology. High-resolution and high signal-to-noise ratio time-series spectroscopy can reveal radial velocity variations as well as profile variations in stellar absorption lines which are caused by non-radial pulsations. Oscillations in solar-like stars have been detected in radial velocity measurements obtained with stabilized spectrographs. For hotter stars on the main sequence, besides for the purpose of abundance analyses, spectroscopy is mainly acquired to carry out mode identification, the assignment of the spherical degree l, and the azimuthal order m, to the observed pulsation frequencies. It has been demonstrated for several stars on the main sequence hotter than the sun that only combined spectroscopic and photometric time-series measurements can lead to successful seismic modeling. In this article, I will focus on the application of spectroscopic mode identification on pulsating stars and discuss some recent results.

Deciphering the pulsations of G 29-38 with optical time series spectroscopy

We present optical time series spectroscopy of the pulsating white dwarf star G 29-38 taken at the Very Large Telescope (VLT). By measuring the variations in brightness, Doppler shift and line shape of each spectrum, we explore the physics of pulsation and measure the spherical degree (l) of each stellar pulsation mode. We measure the physical motion of the g modes correlated with the brightness variations for three of the eight pulsation modes in this data set. The varying line shape reveals the spherical degree of the pulsations, an important quantity for properly modelling the interior of the star with asteroseismology. Performing fits to the Hβ, Hy and Hδ lines, we quantify the changing shape of the line and compare them to models and previous time series spectroscopy of G 29-38. These VLT data confirm several l identifications and add four new values, including an additional l = 2 and a possible l = 4. In total, from both sets of spectroscopy of G 29-38, eleven modes now have known spherical degrees.

Comparing Binary Image Analysis Measurements - Euclidean Geometry, Centroids and Corners

Abstract During the past several years, ASTM Subcommittee E04.14 on Quantitative Metallography has been developing an Image Analysis (I/A) methodology to determine the degree of circularity, roundness or sphericity of graphite nodules in ductile cast iron. In the as-polished condition, ideally the iron nodules should appear as dark circular objects in a light gray matrix, Figure 1. When performing Image Analysis measurements for these types of materials, complex gray image procedures should not be required to properly threshold the images to obtain an acceptable binary image on which to perform the measurements.

Mode identification for Balloon 090100001 using combined multicolour photometry and spectroscopy

In this paper, we show that method of mode identification using combined multicolour photometry and spectroscopy can be successfully applied to the pulsating subdwarf B star Balloon 090100001. The method constrains the spherical degree, l.We confirm that the dominant mode is radial and we show that for some other modes the method provides values of l consistent with the observed rotationally split triplet. Moreover, we derive a radius variation of 1.7 per cent for the dominant mode. The identification opens the possibility for constraining the internal structure of the star by means of seismic methods.

A Pulsational Model for the Orthogonal Polarization Modes in Radio Pulsars

In an earlier paper, we introduced a model for pulsars in which non-radial oscillations of high spherical degree (\el) aligned to the magnetic axis of a spinning neutron star were able to reproduce subpulses like those observed in single-pulse measurements of pulsar intensity. The model did not address polarization, which is an integral part of pulsar emission. Observations show that many pulsars emit radio waves that appear to be the superposition of two linearly polarized emission modes with orthogonal polarization angles. In this paper, we extend our model to incorporate linear polarization. As before, we propose that pulsational displacements of stellar material modulate the pulsar emission, but now we apply this modulation to a linearly-polarized mode of emission, as might be produced by curvature radiation. We further introduce a second polarization mode, orthogonal to the first, that is modulated by pulsational velocities. We combine these modes in superposition to model the observed Stokes parameters in radio pulsars.

Localized spectral analysis of global satellite gravity fields for recovering time-variable mass redistributions

A spatiospectral localization method is discussed for processing the global geopotential coefficients from satellite mission data to investigate time-variable gravity. The time-variable mass variation signal usually appears associated with a particular geographical area yielding inherently regional structure, while the dependence of the satellite gravity errors on a geographical region is not so evident. The proposed localization amplifies the signal-to-noise ratio of the (non-stationary) time-variable signals in the geopotential coefficient estimates by localizing the global coefficients to the area where the signal is expected to be largest. The results based on localization of the global satellite gravity coefficients such as Gravity Recovery And Climate Experiment (GRACE) and Gravity and Ocean Circulation Explorer (GOCE) indicate that the coseismic deformation caused by great earthquakes such as the 2004 Sumatra–Andaman earthquake can be detected by the low-low tracking and the gradiometer data within the bandwidths of spherical degrees 15–30 and 25–100, respectively. However, the detection of terrestrial water storage variation by GOCE gradiometer is equivocal even after localization.

MHD waves at a spherical interface modelling EIT waves

AbstractEruptive events such as flares and coronal mass ejections (CMEs) are known to generate global waves propagating over distances comparable to the solar radius in different layers of the solar atmosphere. Here we investigate the propagation of coronal EIT waves, modelled as fast magnetoacoustic modes propagating at a spherical interface in the presence of a purely radial magnetic field. Based on a simplified equilibrium we derive the dispersion relation of the waves. The generation and propagation of EIT waves at the spherical interface is studied numerically for different values of spherical degree and preliminary conclusions are reached regarding the properties of EIT waves. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Best constants of harmonic approximation on classes associated with the Laplace operator

We compute the best constants of approximation by entire functions of spherical type and by trigonometric polynomials of spherical degree on classes of functions f satisfying the condition ∥ Δ k f ∥ L p ⩽ 1 , where p = 1 or 2 and Δ is the Laplace operator.

Polarization lidar at <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>1.54</mn><mspace width="0.3em" /><mi>μ</mi><mi mathvariant="normal">m</mi></mrow></math></inline-formula> and observations of plumes from aerosol generators

The ability to detect relative changes in backscatter polariza- tion from a scanning high-pulse-energy lidar system at 1.54-m wave- length is demonstrated. The new capability was tested during the dis- semination of various biological aerosol simulants and other particulate emissions at the U.S. Army's Dugway Proving Ground. Results demon- strate that the lidar is sensitive to different types of aerosols, and depar- tures from the atmospheric background depolarization ratio are consis- tent with the limited amount of information available on the degree of particle sphericity. We conclude that the polarization-sensitive coatings of the beam-steering unit mirrors are presently the largest source of error and that this error is minimized when scanning with a near-zero elevation angle. This is an encouraging result for aerosol source surveillance ap- plications, where the depolarization information may be useful in deter- mining the aerosol generation mechanism or provide an additional scalar variable for use in delineating the plume from the background. © 2007

A modified kinematic model for particle flow in moving beds

Granular materials are utilized in a wide variety of industrial applications. The complex hydrodynamics of granular flow is still not fully understood. The flow characteristics of solid particles in a two-dimensional moving bed were studied experimentally and theoretically. The effects of mass velocity, properties of particles and the shape of moving bed on flow pattern were examined. The experiments show that the mass velocity of solid particles and the placement of baffles in stagnant zones have no effect on flow pattern. The shape, size and repose angle of particles affect the flow pattern greatly. The particles have more liquidity and the mixture between particles is easier with the increasing of sphericity degree of particles and the decreasing of particle size. The shape of flowing zone becomes more sharp-angled with the increasing of the repose angle, and the stagnant zone becomes larger. The kinematic model was used to simulate the particle flow. For center discharge the simulation results are in agreement with experiment data very well, while for eccentric discharge the simulation couldn't show the effects of side walls on particle flow. An analytic solution of kinematic model was obtained by Lie transformation group. It shows that the velocity of particle flow is the maximum when x equals 0. The method of translational coordinate was used to modify the traditional kinematic model in order to make sure the x value of each point on the maximum particles velocity distribution lines is zero. The modified kinematic model could simulate the eccentric discharge well, and the field of kinematic model applications was expanded.

Study on the microstructure evolution and rheological parameter of semisolid Mg–10Al–4Zn alloys

Semisolid metal (SSM) processing has become an important industry forming process. Now, the traditional casting or forging alloys cannot show all advantages of semisolid metal processing. Especially, the magnesium alloys currently used in SSM processing are restricted to a few commercial alloys such as AZ91, AM50 and AM60. Therefore, in order to vary semisolid alloys, a new Mg–10Al–4Zn alloy is designed on the basis of conventional AZ91D alloys in this paper. The microstructure evolution and rheological parameter of semisolid Mg–10Al–4Zn alloy was investigated. The microstructure of casting consists of α-Mg and β-Mg 17Al 12. After compressed by a ratio of 40% in height at the temperature of 210 °C, the microstructure of Mg–10Al–4Zn alloy changed from developed dendrites to near-equiaxed grains, and all the dendrites oriented in the same orientation. Whereafter, fine recrystallization grains were formed by the release of the stored fault energy induced by deformation at the elevated temperature. The Mg 17Al 12 phase containing zincum firstly melted between boundaries of the primary grains and then penetrated into recrystallization grain boundaries, which resulted in the separation of the fine primary grains suspending in liquid phase. The partially melting was discussed through analyzing the phase transformations. In addition, the research on rheological parameters such as solid fraction, the particle size, the spherical degree, and the distribution of liquid phase showed that the Mg–10Al–4Zn alloy had a good semisolid performance.

Analysis of Errors in Historical Use of Archie's Parameters

Abstract While it is common knowledge that the values of Archie's parameters ‘a’, ‘m’ and ‘n’ may vary for sandstone reservoirs at different conditions ? consolidated/unconsolidated, water-wet/oil-wet, pore geometry, degree of sphericity, clay content and in-situ depositional environment ? the values of a = 1, m = 2 and n = 2 have been linked historically with Archie's equations. Statistically, these values were assumed as the population mean when used in calculations, but the magnitude of errors associated with their use is often neglected. This study shows how a sample of data drawn from experimental and analytical methods determine Archie's parameters. Well logs from sandstone reservoirs are used to draw statistical inferences about the population characteristics of Archie's parameters in sandstone reservoirs. This also shows the magnitude of relative error possible when m = 2 and n = 2 are used to compute water saturation and formation resistivity factors. Introduction The 1942 landmark publication by Gus Archie titled, "The Electrical Resistivity Log as an Aid in Determining Some Reservoir Characteristics "(1) introduced new parameters relevant to describing reservoirs using well logs and set standard parameters for the identification of permeable zones within a reservoir. Basically, Archie's experiments involved measuring the porosity and electrical resistivity of numerous shale-free sandstone cores from the Gulf Coast by saturating them with brine of salinities ranging from 20 to 100,000 ppm of NaCl. Archie's work established the following relationships: Equation (1) (Available In Full Paper) where Ro is the resistivity of the rock fully saturated with brine and Rw is the formation water resistivity. F is termed the formation resistivity factor and is a measure of the effect of formation on the path of electrical current traveling through the electrolytic brine in the rock pore system. The plot of F against porosity (Φ) on log-log scales revealed a linear trend equivalent to: Equation (2) (Available In Full Paper) The ‘m’ parameter represents the trend's negative slope. In deriving the above expression, Archie force-fitted a line to his formation resistivity factor against porosity data such that F = 1.0 at 100% porosity. A replica of Archie's original plot using clean sandstone cores is shown in Figure 1. This was however deemed unnecessary as other research works revealed that when a line is fitted to formation resistivity factor against porosity, the intercept at 100% porosity would not always derive one, but can be greater or less than one. Winsauer et al.(2), for example, duplicated Archie's experiments with sandstone cores from a wide range of reservoirs and arrived at: Equation (3) (Available In Full Paper) Thus, the general form of Archie's formation resistivity factor is expressed as: Equation (4) (Available In Full Paper) Winsauer first referred to Archie's ‘m’ parameter as the cementation factor, while ‘a’ would later be referred to as the tortuosity factor. Archie, again, considered partially saturated hydrocarbon bearing shale-free sandstones and proposed a second factor called the resistivity index (I) that would further increase the rock's resistivity. He expressed this as: Equation (5) (Available In Full Paper) FIGURE 1: Plot of formation resistivity factor against porosity (Available In Full Paper)

Anion and Cation Effects on Imidazolium Salt Melting Points: A Descriptor Modelling Study

The challenge of predicting the melting point of ionic liquids is outlined. A descriptor modelling approach for two separate sets of ionic liquids is presented. In each case, the cations and the anions are modelled separately, using quantitative structure-property relationships. Both models include constitutional, topological and geometric descriptors as well as quantum mechanical ones. This approach gives access to (nxm) ionic liquids using only (n+m) calculations. The protocol is tested and validated for predicting the melting points of two sets, comprised of 22 and 62 imidazolium-based ionic liquids, respectively. Good correlations and predictions are obtained in both cases. Within the data set selected (only monopositive and mononegative ions are studied, and so total charge was not a factor), the degree of sphericity is the most important variable for the anion, while for the cation the main descriptors pertained to three radial distribution functions that describe three different sections in the cation. These characterise the ionic interactions, the symmetry-breaking region, and the length of the side chains.