Spherical Shell Structure Research Articles

An X-ray-emitting blast wave from the recurrent nova RS Ophiuchi

Stellar explosions such as novae and supernovae produce most of the heavy elements in the Universe. The onset of a nova is well understood as driven by runaway thermonuclear fusion reactions on the surface of a white dwarf in a binary star system; but the structure, dynamics and mass of the ejecta are not well known. In rare cases, the white dwarf is embedded in the wind nebula of a red-giant companion, and the explosion products plough through the nebula and produce X-ray emission. Here we report X-ray observations of such an event, from the eruption of the recurrent nova RS Ophiuchi. The hard X-ray emission from RS Ophiuchi early in the eruption emanates from behind a blast wave, or outward-moving shock wave, that expanded freely for less than 2 days and then decelerated owing to interaction with the nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from the standard spherical shell structure. The early onset of deceleration indicates that the ejected shell had a low mass, the white dwarf has a high mass, and that RS Ophiuchi is therefore a progenitor of the type of supernova (type Ia) integral to studies of the expansion of the Universe.

Structural properties of zinc nitride empty balls

Zinc nitride empty balls can be synthesized by the nitridation reaction of zinc powders with ammonia gas in 500 ml/min at 600 °C for 120 min. Surveys by using X-ray diffraction confirm that zinc nitride has a cubic structure with lattice constants a=0.9788 nm. Observations by using scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy show that zinc nitride is of spherical shell structure. X-ray photoelectron spectroscopy tells the differences in chemical bonding states between zinc nitride and zinc oxide, which confirmed the formation of N–Zn bonds.

Effect of Core Materials on the Formation of Hollow Alumina Microspheres by Mechanofusion Process

Core/shell structures have been prepared via a mechanofusion system by employing several kinds of spherical polymers as a core material and Al2O3 powder or a mixture of Al2O3 and SiO2 powders as a shell material. The effect of the kind of core polymers on the quality of the resulting hollow alumina microspheres has been discussed on the basis of the thermal decomposition behavior of spherical polymers used as a core material. A large fraction of hollow alumina microspheres reflecting the shape and the particle size distribution of the core polymer could be fabricated after sintering at 1600°3C for 3 h, when highly cross‐linked poly(methyl methacrylate) (PMMA) microspheres with a gel fraction of 99.03% were used as a core polymer, and abrupt firing at temperatures higher than 500°3C was adopted to remove the PMMA microspheres. The addition of 5 mass% SiO2 to the Al2O3 shell layer was found to be useful for maintaining the spherical shell structure during the firing process and for fabricating a large fraction of hollow alumina microspheres after the sintering.

Fabrication of W–20 wt % Cu composite nanopowder and sintered alloy with high thermal conductivity

The reduced W–20% Cu powder with W particle sizes of about 30–100 nm and uniform distribution of components was successfully synthesized by mechano-thermochemical process. This process consists of three steps: the producing of oxide powder, the wet ball milling of oxide powder and the final reduction. W/Cu composite oxide clusters with a spherical shell structure were prepared by spray drying of aqueous solution of Cu and W salts with subsequent oxidation at 750 °C for 2 h. These oxide clusters were fragmented to fine oxide powders by wet milling and reduced at 600–800 °C in hydrogen. The sintering behavior of composite powder and thermal conductivity of sintered alloys were also investigated. This composite powder showed higher sinterability comparatively with conventional blended powders. The thermal conductivity of W–20% Cu alloys prepared by this work is 239±5.0 W/mK, which is equal to the theoretical value. Superior properties of the present powder are due to the homogeneous mixing state of nanosized W and Cu particles in powder, homogeneous redistribution of W solid particles in liquid Cu and high purity of powder. This alloy did not contain such impurities as Fe and Co that can be easily introduced in powder in conventional processing.

A study on the free vibration of the joined cylindrical–spherical shell structures

The free vibration characteristics of the joined spherical–cylindrical shell with various boundary conditions are investigated. The boundary conditions considered herein are free–free, simply supported–free and clamped–free for the joined cylindrical–spherical shell structures. The Flügge shell theory and Rayleigh’s energy method are applied in order to analyze the free vibration characteristics of the joined shell structure and individual shell components. In the modal test, the I-DEAS test module is used to calculate mode shapes and natural frequencies of the joined shell structure. The natural frequencies and mode shapes are calculated numerically and they are compared with those of the FEM and modal test to confirm the reliability of the analytical solution. The effects of the shallowness of the spherical shell and length of the cylindrical shell to the free vibrational behavior of joined shell structure are investigated.

Nuclear tetrahedral symmetry: possibly present throughout the periodic table.

More than half a century after the fundamental, spherical shell structure in nuclei had been established, theoretical predictions indicated that the shell gaps comparable or even stronger than those at spherical shapes may exist. Group-theoretical analysis supported by realistic mean-field calculations indicate that the corresponding nuclei are characterized by the TD(d) ("double-tetrahedral") symmetry group. Strong shell-gap structure is enhanced by the existence of the four-dimensional irreducible representations of TD(d); it can be seen as a geometrical effect that does not depend on a particular realization of the mean field. Possibilities of discovering the TD(d) symmetry in experiment are discussed.

Measurement of Speed of Sound in Skull Bone and Its Thickness Using a Focused Ultrasonic Wave

To quantitatively improve brain SPECT (single photon emission computed tomography), we propose a noninvasive method for determining the speed of sound in skull bone and its thickness. We assume a spherical shell structure for the skull, and the speed of sound to be constant in the bone layer. Small ultrasonic transducers are arranged on the outer surface of the bone layer to form a transducer array. The array is excited to produce an ultrasonic pulse wave focused at a point on the inner surface by assigning an appropriate time delay to each of the transducers. The pulse is propagated to the focal point, and a reflected spherical pulse wave is produced at that point. The reflected pulse wave is detected by the same transducers, and the output from each transducer is added to give a summed signal. When the time delays are optimized, we obtain the maximum envelope amplitude for the signal. A simulation study is conducted to confirm the method, and the potential error is examined for ideal conditions. From the simulation results, we conclude that the proposed method is suitable for SPECT if the transducers are arrayed with a sufficiently large aperture.

Pulsing system of C 60 beam for the TOF method

In order to analyze the physical properties of fullerene C 60, which has an especially stable spherical shell structure as a cluster, the energy loss is measured when the fullerene C 60 in the energy region of several 100 eV/amu passes a carbon thin foil using the TOF method. The C 60 direct current beam extracted from an electron impact type ion source needs to be converted to a pulsed beam. A chopping method was adopted for the pulsing of this direct current beam, and a high frequency chopper was manufactured. In this way the C 60 direct current beam was changed into a pulsed beam of frequency 50 μs, and about 2.4 μs half width. After accelerating to 100 kV, the beam was passed through carbon foils of 1 and 5 μg/cm 2, and energy loss measurements were performed.

A Study of the Micellization of Zirconyl 2-Ethyl Hexanoate via Small-Angle Neutron and X-ray Scattering

We report the first investigation of zirconyl 2-ethyl hexanoate micelles in decane using small-angle neutron and X-ray scattering. Our results show that the micelles have a spherical shell structure consisting of an inner core region with a radius of 6.3 Å that is surrounded by a shell 5.3 Å thick incorporating the surfactant chain segments. From the contrast variation experiment, we calculated there were 33 surfactant molecules/micelle. Finally, our small-angle neutron scattering experiments performed at 80 °C showed there was no change in the shape or size of the micelles at the higher temperature.

On the effect of crystallinity on the elastic properties of semicrystalline polyethylene

AbstractThe small strain elastic response of a semicrystalline polyethylene has been simulated with a simple finite element model comprising a composite microstructure of alternating amorphous and crystalline layers arranged in a multi‐layered spherical shell structure. The crystalline lamella is modeled as an isotropic solid having the experimentally determined modulus properties of bulk linear polyethylene and extrapolated to 100% crystallinity. The amorphous layer is modeled as an elastomeric solid with the modulus that of molten linear polyethylene extrapolated to room temperature. Assuming constancy of these phase properties, the finite element calculations of elastic modulus versus crystallinity fit quite well the experimental data of Crist for linear polyethylene above 55% crystallinity. At lower crystallinity the experimental modulus data, which are for copolymers, fall below the model calculations. Two possible causes are discussed: the loss of deformation constraint in lamellae of finite and decreasing width as crystallinity declines, and an expansion of the crystal lattice as a result of the crowding of the comonomer units excluded from the crystal lamella. Either effect would reduce both the modulus and the yield stress as is observed.

Isomeric yield ratios of 134I and 136I in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U

Short-lived nuclides of iodine produced in the proton-, 12C- and 19F-induced fission of 235U, 237Np and 238U were separated with a rapid chemical separation system SISAK. Relative yields of the nuclides were determined by γ -ray spectrometry to obtain the isomeric yield ratios of 134mI/134gI and 136mI/136gI. Angular momenta of the fission fragments, 134I and 136I, were derived from the measured isomeric yield ratios by the spin-dependent statistical model. In the light- and heavy-ion fission, variation of the observed angular momenta can be explained by the excitation energies of the fissioning nuclei and the spherical shell structure with N = 82.

Normal mode oscillation of a sphere with solid–gas–solid structure

A free oscillation study was made for a heterogeneous sphere with three-layered spherical shell structure composed of an inner spherical sample, middle gas, and outer solid layers in order to apply resonant sphere technique (RST) to elasticity measurements at high pressures. The spheroidal modes of the sphere are classified into “sample,” “gas,” and “container” modes, whose strain energy distributions are localized in the sample, gas, and outer layers, respectively. The sample modes, whose frequencies provide information about the elastic constants of the spherical sample, are more strongly excited than the gas and container modes when putting a vibrational source on the surface of spherical sample in the three-layered sphere and measuring the resonance spectrum on the sample sphere. The localization of strain energy is due to a large difference in acoustic impedance between gas and solid layers. All the resonant frequencies increase with increasing pressure in the gas layer, but the pressure derivatives of resonant frequencies of gas modes are larger than those of sample and container modes. Thus the pressure curves of gas modes frequently intersect those of sample and container modes. At pressures where the sample or container modes intersect the gas modes, modal interchange takes place only between spheroidal modes of Sln and Sl′n′ satisfying the conditions of l=l′ and n−n′=±1. To avoid such an interchange, the gas layer should be kept thin.

Neutron radii and skins in the Hartree-Fock-Bogoliubov calculations

We examine the systematic predictions for proton and neutron radii in even-even nuclei made by the self-consistent Skyrme-Hartree-Fock-Bogoliubov theory. Such an approach allows us to describe nuclei far from stability, where the spatial extensions of a nuclear system crucially depend on the continuum effects. We concentrate on the influence of spherical shell structure on global behavior of radii. The (N, Z)-localization of neutron and proton skins is discussed.

Measurements for pressure and temperature dependencies of elastic moduli by the resonant sphere technique, RST.

The resonant sphere technique, RST, has been developed for measurements of elasticity and anelasticity of small crystal specimens. This method has advantages over other methods, especially in high‐temperature and high‐pressure measurements. New methods of data acquisition have made it convenient to measure resonance frequency at high temperatures (using a buffer rod), making a 1 K temperature interval measurement possible; this opens up many possibilities in the determination of physical properties of solids. Preliminary measurements of resonance frequency were performed by RST up to 100 MPa, which showed interference of vibration modes between the specimen and the pressure medium, even for helium gas as the pressure medium. This interference may become more serious at higher pressures or under liquid pressure. In order to evaluate such effects, the cavity resonance method was developed by Ohno in 1993, with a spherical shell structure with a spherical specimen at the center. This gives clear boundary conditions in the wave equations. Theoretical evaluation of the resonant frequency on such a system shows the necessity of correction to pressure derivatives of elastic moduli, even in measurements up to 100 MPa.

Structural properties of 3-dimensional carbon clusters

Structural properties of 3d carbon clusters were calculated employing recently developed model potential energy functions for carbon. Primarily, spherical shell structures were included in the present investigation. Configurations corresponding to local energy minima were calculated for various shells of an icosahedron containing different number of C atoms. For C60, the two low-lying isomers, the buckminsterfullerene and truncated dodecahedron, were found to be almost isoenergetic. It was also found that fully relaxed structures of C90 and C120 have energies very comparable to that of C60. Furthermore, a systematic analysis carried out in this study for carbon clusters with varying dimensionalities, revealed an interesting relationship between the bond lengths and the distribution of bond angles. In all cases, shorter bond distances were found to be associated with larger bond angles.

The influence of shells, electron thermodynamics, and evaporation on the abundance spectra of large sodium metal clusters

Measurements of the mass abundance spectra of sodium clusters containing up to 600 atoms are presented. The clusters are produced in a seeded supersonic expansion of Ar or Kr gas, and the spectra are obtained by a time-of-flight technique. The sawtooth features in the spectra are interpreted as evidence of a regular spherical shell structure with magic numbers,N0, scaling approximately with the cube root of the number of sodium atoms. Altogether twelve shell closings are observed,N0=2, 8, 20, 40, 58, 92, 138, 196, 260, 344, 440 and 558. There is also a pronounced odd-even staggering all the way up toN=70. The experimentally observed intensity changes for the clusters around the magic numbers are discussed in terms of the electronic free energy,F(N), calculated at finite temperature, and the second differences of the free energy Δ2F(N)=F(N−1)−2F(N)+F(N+1). The processes behind the non-uniform abundance distributions, and the thermodynamics of finite electron systems with non-uniform level spacings are discussed on this basis.

A structural jellium model of cluster electronic structure

A structural jellium model has been developed which accounts for the electronic structures of clusters using a crystal-field perturbation. Although it is related to previous models proposed by Knight et al., this model allows predictions to be made concerning the gross stuctural features of metal clusters; something the original jellium model is incapable of doing. The zero-order potential we derive is of central-field form, depends on the geometry of the cluster, and has a general form that can produce an energy-level ordering similar to that of Knight's rounded well, but can also accommodate other orderings. In particular, qualitative arguments suggest that this potential produces different energy level orderings for clusters with a nucleus with large positive charge at the centre of the cluster, enabling the spherical jellium model to be applied to alkali metal clusters seeded with magnesium and zinc. Analysis of the effects of the non-spherical perturbation on the spherical jellium shell structures leads to the conclusion that for a cluster with a closed-shell electronic structure a high symmetry arrangement which is approximately or precisely close packed will be preferred and provides a basis for rationalising those structures, which have been predicted using ab initio calculations, of clusters with incomplete shell electronic configurations.

Steady-state and transient eddy current predictions using surface impedances in shell structures

Surface impedance techniques are useful means of predicting fields in eddy current problems since they circumvent the need to model the conducting regions themselves. Thus, with their use, two-and three-dimensional field predictions can be made using only scalar potentials. Their use is normally confined to (1) problems where the skin depth is small relative to the other dimensions of the problem and (2) steady-state problems where the skin depth itself is well defined. In this regard, the technique is approximate at best. Presented here is a formulation which can realize an exact prediction of the field, both in steady-state and transient problems. The technique is exact for those problems where knowledge is known as to the nature of the field variation tangential to the conductor shell interface; otherwise, an iterative numerical scheme must be employed to converge on the correct tangential variation. Surface impedances are determined generically and expressed in terms of transfer functions for shell-type structures in three different geometries. The surface impedances happen to be trigometric functions, Bessel functions, and spherical Bessel functions in planar, cylindrical, and spherical shell structures, respectively. Their use is easily implemented in finite difference, finite element, and boundary integral formulations; in this paper, the surface impedances are coupled into a boundary integral approach to verify their use in both two-dimensional cylindrical and a three-dimensional spherical problem. The results are compared to analytical expressions and are shown to disagree by no more than 0.01%.

On the Shape and Orientation Control of Orbiting Shallow Spherical Shell Structure

The dynamics of orbiting shallow flexible spherical shell structures under the influence of control actuators is studied. Control laws are developed to provide both attitude and shape control of the structure. It is seen that the elastic modal frequencies for the fundamental and lower modes are closely grouped due to the effect of the shell curvature. The shell is also assumed to be gravity stabilized by a spring-loaded dumbbell type damper attached at its apex. Control laws are developed based on the pole clustering technique and it is assumed that the dumbbell state information may not be directly observable. Numerical results verify that a significant savings in fuel consumption can be realized by using the hybrid shell-dumbbell system together with point actuators. Other results indicate that for the less robust systems instability may result by not including the orbital and first order gravity-gradient effects in the plant prior to control law design.

Research on Welding Deformations of Spherical Shell Structure (3rd report)

Welding deformations and residual stresses are major factors which affect the collapse strength of externally pressurized vessels. Deflections in spherical shell welded along the equator have been already investigated by some of the authors.In many cases of actual structures, a penetrator is welded circumferentially to a spherical shell. In these cases, the spherical shell near the weld line and the penetrator tend to sink inward.In the 1 St report, the deformations of spherical shell caused by the welding of penetrator were investigated. Experiments were carried out in order to clarify the characteristics of welding deformations under the effects of shell and penetrator dimensions and welding procedures.In the 2 nd report, one-dimensional thermal elasto-plastic analysis using Rayleigh-Ritz method was carried out to solve this problem theoretically. It was clarified by the analysis that the parameter λ and λα, which correlate the rigidity of shell and penetrator, and the parameter (Q/h) β, which correlates welding thermal cycle, are governing the welding deflections.In this report, a method of reducing the welding deformations in spherical shell structures is discussed. Some deflection control methods are considered based on the results obtained by the previous reports. It is proved by experiments that the “thermal-shrinkage-fit method” is effective to produce initial reverse deflection and the “restraint load method” is more effective to reduce welding deflections. The Welding deformations in spherical shells can be prevented almost perfectly by controlling the restraint load together with adopting the initial reverse deflection, and the effectiveness of this proposed method is confirmed by experiments.