Multiple-shell Structure Research Articles

Multiple Shells Driven by Disk Winds: ALMA Observations in the HH 30 Outflow

We present archival Atacama Large Millimeter/submillimeter Array band 6 observations of the 13CO (J = 2–1) and 12CO (J = 2–1) molecular line emission of the protostellar system associated with HH 30. The 13CO molecular line shows the accretion disk while the molecular outflow is traced by the emission of the 12CO molecular line. We estimated a dynamical mass for the central object of 0.45 ± 0.14 M ⊙, and a mass for the molecular outflow of (1.83 ± 0.19) × 10−4 M ⊙. The molecular outflow presents an internal cavity as well as multiple outflowing shell structures. We distinguish three different shells with constant expansion (∼4–6 km s−1) and possible rotation signatures (≤0.5 km s−1). We find that the shells can be explained by magnetocentrifugal disk winds with launching radii R launch ≲ 4 au and a small magnetic lever arm λ ∼ 1.6–1.9. The multiple shell structure may be the result of episodic ejections of the material from the accretion disk associated with three different epochs with dynamical ages of 497 ± 15 yr, 310 ± 9 yr, and 262 ± 11 yr for the first, second, and third shells, respectively. The outermost shell was ejected 187 ± 17 yr before the middle shell, while the middle shell was launched 48 ± 14 yr before the innermost shell. Our estimations of the linear and angular momentum rates of the outflow as well as the accretion luminosity are consistent with the values expected if the outflow of HH 30 is produced by a wide-angle disk wind.

A fluorescent lateral flow immunoassay based on CdSe/CdS/ZnS quantum dots for sensitive detection of olaquindox in feedstuff.

A portable fluorescence immunosensor based on the CdSe/CdS/ZnS quantum dots (QDs) with multiple-shell structure was fabricated for the precise quantification of olaquindox (OLA). The QDs labeled anti-OLA antibody used as bioprobe played an important role in the design and preparation of a lateral flow test strip. Due to the strong fluorescent intensity of QDs, the sensitivity is greatly improved. The quantitative results were obtained using a fluorescent strip scan reader within 8min, and the calculated limit of detection for OLA at 0.12µg/kg, which was 2.7 times more sensitive than that of the conventional colloidal gold-based strips method. Acceptable recovery of 85.0%-95.5% was obtained by the spiked samples. This newly established QDs-based strip immunoassay method is suitable for the on-site detection and rapid initial screening of OLA in swine feedstuff, and is potentially applied for the detection of other veterinary drugs to ensure food safety.

Charge Exchange X-Ray Emission Detected in Multiple Shells of Supernova Remnant G296.1–0.5

Recent high-resolution X-ray spectroscopy revealed the possible presence of charge exchange (CX) X-ray emission in supernova remnants (SNRs). Although CX is expected to take place at the outermost edges of SNR shells, no significant measurement has been reported so far due to the lack of nearby SNR samples. Here we present an X-ray study of SNR G296.1−0.5, which has a complicated multiple-shell structure, with the Reflection Grating Spectrometer on board XMM-Newton. We select two shells in different regions and find that in both regions the O vii line shows a high forbidden-to-resonance (f/r) ratio that cannot be reproduced by a simple thermal model. Our spectral analysis suggests a presence of CX and the result is also supported by our new radio observation, where we discover evidence of molecular clouds associated with these shells. Assuming G296.1−0.5 has a spherical shock, we estimate that CX is dominant in a thin layer with a thickness of 0.2%–0.3% of the shock radius. The result is consistent with a previous theoretical expectation and we therefore conclude that CX occurs in G296.1−0.5.

Formation mechanisms of hollow manganese hexacyanoferrate particles and construction of a multiple-shell structure.

Formation mechanisms of hollow manganese hexacyanoferrate (Mn-HCF) particles have been investigated. Mn-HCF particles, which were precipitated by mixing an aqueous solution of K3[Fe(CN)6] with MnCl2 in the presence of sodium citrate, could be converted into a hollow structure just by washing with distilled water. The powder X-ray diffractometry suggested that the as-prepared particle has a core/shell morphology with different crystal structures: cubic-core and monoclinic-shell. The time evolutions of the particle size and shell thickness indicated that the core was rapidly (but not instantaneously) formed at the initial stage of the precipitation process, followed by a slower shell growth. In addition, the solubility of the cubic core was estimated to be about 2.5 times higher than that of the monoclinic shell, resulting in the preferential dissolution of the interior of the particle by the washing process. The formation procedure has been used to construct multiple-shell hollow Mn-HCF particles containing up to quadruple separated nesting shells by associating an additional growth technique.

Bulky Surface Ligands Promote Surface Reactivities of [Ag141X12(S-Adm)40]3+ (X = Cl, Br, I) Nanoclusters: Models for Multiple-Twinned Nanoparticles.

Surface ligands play important roles in controlling the size and shape of metal nanoparticles and their surface properties. In this work, we demonstrate that the use of bulky thiolate ligands, along with halides, as the surface capping agent promotes the formation of plasmonic multiple-twinned Ag nanoparticles with high surface reactivities. The title nanocluster [Ag141X12(S-Adm)40]3+ (where X = Cl, Br, I; S-Adm = 1-adamantanethiolate) has a multiple-shell structure with an Ag71 core protected by a shell of Ag70X12(S-Adm)40. The Ag71 core can be considered as 20 frequency-two Ag10 tetrahedra fused together with a dislocation that resembles multiple-twinning in nanoparticles. The nanocluster has a strong plasmonic absorption band at 460 nm. Because of the bulkiness of S-Adm, the nanocluster has a low surface thiolate coverage and thus unusually high surface reactivities toward exchange reactions with different ligands, including halides, phenylacetylene and thiols. The cluster can be made water-soluble by metathesis with water-soluble thiols, thereby creating new functionalities for potential bioapplications.

Vortex shells in mesoscopic triangles of amorphous superconducting thin films

Direct observation of vortex states confined in mesoscopic regular triangle dots of amorphous Mo–Ge thin films was made with a scanning superconducting quantum interference device microscope. The observed magnetic images illustrate clearly how vortices are distributed over the triangle dots by forming not only commensurate triangular clusters, but also unique patterns imposed by incommensurability. We discuss the results in terms of vortex shells and construct the packing sequence of vortices in the multiple shell structure.

Morpho-kinematics of the planetary nebula NGC 3242: an analysis beyond its multiple-shell structure

In this paper we present the results of optical high-resolution imaging and spectroscopy of the complex planetary nebula (PN) NGC~3242. Our study is based on the analysis of the narrowband H$\alpha$ $\lambda$6563\AA , [O III] $\lambda$5007\AA , [N II] $\lambda$6584\AA , and [S II] $\lambda$6724{\AA} images, and high- resolution spectroscopy using spectral ranges centered on the H$\alpha$ $\lambda$6564\AA , [N II] $\lambda$6583\AA , and [O III] $\lambda$5007\AA . We detected and analysed morphological components beyond the multiple shell structure of this PN, to investigate the small-scale morphological components aligned towards its major axis (such as knots and ansae, as well as the arc-like features) and its surroundings. Thus, we investigated the morpho-kinematical properties of NGC~3242, as well as their nature and formation. Our results regarding the elliptical double-shell structure and the distance to this nebula are in concordance with previous studies. Furthermore, we have used the software SHAPE to construct a 3D model of NGC~3242, allowing us to successfully reproduce our observational data. We conclude that the prominent knots emitting in the [N II] line are fast, low-ionisation emission regions (FLIERs) related to high velocity jets and the so-called ansae-like features rather resemble bubbles. The disruptions immersed in the halo, whose emission was detected in the the [O III] high-excitation emission line, remarkably display high velocities and were formed likely in an earlier ejection event, in comparison to the innermost FLIERs and bubbles. Finally, according to our model, the kinematical ages of the structures in NGC~3242 range from 390 to 5400 yr.

Surface properties for α-cluster nuclear matter

We introduce a new microscopic model for α-cluster matter, which simulates the properties of ordinary nuclear matter and α-clustering in a curved surface of a large but finite nucleus. The model is based on a nested icosahedral fullerene-like multiple-shell structure, where each vertex is occupied by a microscopic α-particle. The novel aspect of this model is that it allows a consistent description of nuclear surface properties from microscopic parameters to be made without using the leptodermous expansion. In particular, we show that the calculated surface energy is in excellent agreement with the corresponding coefficient of the Bethe-Weizäcker semi-empirical mass formula. We discuss the properties of the surface α-cluster state, which resembles an ultra cold bosonic quantum gas trapped in an optical lattice. By comparing the surface and interior states we are able to estimate the α preformation probability. Possible extensions of this model to study nuclear dynamics through surface vibrations and departures from approximate sphericity are mentioned.

Synthesis of Multiple‐Shell WO3 Hollow Spheres by a Binary Carbonaceous Template Route and Their Applications in Visible‐Light Photocatalysis

Hollow go lightly: well-defined multiple-shell WO(3) hollow spheres were synthesized by a facile binary carbonaceous spheres template route. Compared with single-shell WO(3) hollow spheres, the unusual porous multiple-shell structure of the WO(3) hollow spheres proves to greatly enhance photocatalytic activity toward degradation of organic pollutants under visible-light irradiation.

Microsolvation of sodium ion in acetonitrile clusters: Structure and energetic trend by first principle study

We report a systematic theoretical study on the growth pattern and energetics of Na +(CH 3CN) n clusters ( n = 1–8,12) using density functional approach at the B3LYP/6-31++G(d,p) level. Geometry optimizations for all these clusters were carried out with various possible initial guess structures without any symmetry restriction and finally the stability of the lowest energy isomer was verified from Hessian calculations. It is found that the incorporation of a sodium ion completely rearrange the equilibrium structure of the neat acetonitrile cluster. The solvated clusters favor multiple shell structure with higher symmetry. The first solvation shell is formed by six CH 3CN molecules, where the nitrogen atoms of each molecule points towards the central sodium ion. Here, the nature of binding between the solute and solvent has been attributed as strong ion–dipole interactions. The onset of the second solvation shell occurs at n = 7 and thereafter additional acetonitrile molecules interact with the molecules of the first solvation shell through N…H interaction. Such interactions are weak compared to the ion–dipole interactions leading to minimal perturbation to the inner shell structure. In consistent with this conjecture, the ion-solvation energy is found to increase very sharply upto n = 6, and becomes less steep from n = 7 onwards. Moreover, the calculated stepwise binding energies are found to be in good agreement with available experimental data, which provide confidence about the equilibrium geometries of the Na +(CH 3CN) n clusters predicted in this study.

BIMA CO Observation of EP Aquarii: The Semiregular Pulsating Star with a Double‐Component Line Profile

This paper reports the results of a Berkeley-Illinois-Maryland Association array interferometric observation of EP Aqr, a semiregular pulsating star with a double-component line profile in the CO J = 1-0 line. The broad component shows a flat-topped profile, and the narrow component shows a spiky strong peak. Although previous single-dish observations suggested that the CO J = 2-1 line exhibits a Gaussian-like profile, the CO J = 1-0 line does not. The spatial distributions of both the narrow and the broad components appear to be roughly round with the same peak positions. No significant velocity gradient is seen. The spatial-kinetic properties of the molecular envelope of EP Aqr are reminiscent of a multiple-shell structure model rather than of a bipolar flow and disk model. A problem with this interpretation is that no evidence of interaction between the narrow- and broad-component regions is seen. A Gaussian-like feature seen in the CO J = 2-1 line might play a key role in understanding the spatiokinetic properties of the molecular envelope of EP Aqr.

Imaging polarimetry of stellar light scattered in detached shells around the carbon stars R Scl and U Ant

Imaging polarimetry has been used to study the extended, detached circumstellar shells around the bright carbon stars R Scl and U Ant. The observations were done in two narrow band filters centred on the resonance lines of neutral K and Na, but much broader than the expected line widths. The polarimetric data reveal brightness distributions, in both cases, which are in perfect agreement with previous observations of scattered light obtained through direct imaging techniques. The total intensity images towards R Scl outline, in both filters, circular disk-like distributions out to a radius of21 00 ,w here the intensity drops sharply. The polarised intensity images reveal, however, that the scattering occurs in a geometrically thin shell. The degree of polarisation reaches values of35% in both filters. The imaging polarimetry observations of U Ant reveal a somewhat more complex structure, where the existence of several shells can be discerned. The polarised scattered light comes from a component, at a radius of50 00 from the star, which lies outside the region where the bulk of the light is scattered. The latter comes from a dominating shell at43 00 , which coincides spatially with the detached gas shell inferred from CO radio line data, and there may be another two shells inside this. The polarisation degree reaches50% in the outer component. We model, with a code based on the Monte Carlo method, the scattered emission under the assumption of dust scattering, using the observed polarised brightness distributions as constraints. In the case of R Scl we found that the polarised, as well as the total, light distributions can be explained by scattering in a 2 00 wide shell of radius 20 00 containing a dust mass of2 10 6 M. This dust shell is also responsible for the thermal dust emission measured by IRAS. There is room, up to 30% of the total scattered flux, for other scattering agents. Comparison with CO radio line data shows that this dust shell probably lies outside the detached CO gas shell. In the case of U Ant the modelling explains the outer component in terms of a 5 00 wide shell at a radius of about 52 00 with a dust mass of4 10 6 M. This is also the dust shell responsible for the emission measured by IRAS. However, the bulk of the scattered light cannot in this case be due to scattering by dust. In accordance with a discussion in a previous paper we attribute the remaining, unpolarised, scattering to the KI and Na D resonance lines. In both cases we found evidence that a dust shell has separated from the rest of the circumstellar medium. This may be due to gas-grain drift, or to hydrodynamical eects, which may also explain the complex multiple-shell structure seen towards U Ant. The model results are very dependent on the grain size distribution, and the observational data can only be reconciled with a very steep decline in grain size.

Statistics of heavy-ion stopping

Energy-loss straggling of swift heavy ions penetrating through matter has been analysed on the basis of binary stopping theory as well as the modified Bohr model allowing for projectile screening. A program has been written which evaluates the generalized Bothe–Landau formula governing the energy-loss spectrum for penetration through a thin layer, allowing for charge exchange involving an arbitrary number of charge states. This program was generated on the basis of calculational schemes developed originally for swift light ions. Projectile screening and multiple-shell structure of target atoms are allowed for. Explicit energy-loss spectra are given for oxygen in carbon for charge states 6–8 and foil thickness 2, 10 and 50 μg/cm 2. It is also demonstrated that frozen-charge straggling depends only weakly on charge state.

Imaging of detached shells around the carbon stars R Scl and U Ant through scattered stellar light

We present the first optical images of scattered light from large, detached gas/dust shells around two carbon stars, R Scl and U Ant, obtained in narrow band filters centred on the resonance lines of neutral K and Na, and in a Str. b filter (only U Ant). They confirm results obtained in CO radio line observations, but also reveal new and interesting structures. Towards R Scl the scattering appears optically thick in both the K and Na filters, and both images outline almost perfectly circular disks with essentially uniform intensity out to a sharp outer radius of 21. These disks are larger -- by about a factor of two -- than the radius of the detached shell which has been marginally resolved in CO radio line data. In U Ant the scattering in the K filter appears to be, at least partially, optically thin, and the image is consistent with scattering in a geometrically thin (3) shell (radius 43) with an overall spherical symmetry. The size of this shell agrees very well with that of the detached shell seen in CO radio line emission. The scattering in the Na filter appears more optically thick, and the image suggests the presence of at least one, possibly two, shells inside the 43 shell. There is no evidence for such a multiple-shell structure in the CO data, but this can be due to considerably lower masses for these inner shells. Weak scattering appears also in a shell which is located outside the 43 shell. The present data do not allow us to conclusively identify the scattering agent, but we argue that most of the emission in the K and Na filter images is to due to resonance line scattering, and that there is also a weaker contribution from dust scattering in the U Ant data. Awaiting new observational data, our interpretation must be regarded as tentative.

Interralation Between Hume-Rothery Mechanism, Hybridization and Covalent Bonds in Aluminum- and Boron-based Icrosahedral Approximants and Quasicrystals

AbstractMetallic-covalent bonding conversion in icosahedral clusters of Al and B by small changes of the structure was demonstrated by molecular orbital calculations. According to the electron density distribution obtained using the maximum entropy method and the Rietveld method, the bonding conversion phenomenon occurs even in cluster solids such as some Al- and B-based icosahedral approximant phases (Al12Re, α-AlMnSi, α-rhombohedral boron). The multiple-shell atomic structure, the electrical and optical conductivity are compared for metal doped β-rhombohedral boron and AlLiCu or AlPdRe icosahedral quasicrystal. Photoemission and electron energy loss spectroscopy investigations for V doped β-rhombohedral have been discussed. Conclusions are the following two. It is difficult to distinguish a Hume-Rothery, i.e. structure-induced, pseudogap, and a covalent bonding, i.e. hybridization, pseudogap for materials with a highly symmetric Brillouin zone and a strong potential for valence electrons. Because hybridization is necessary not only for covalent bonds but also for metallic ones, it is better to use the covalent bonding pseudogap than the hybridization pseudogap.

Covalency, semiconductor-like and thermoelectric properties of Al-based quasicrystals: icosahedral cluster solids

A unified picture of icosahedral cluster solids obtained by comparing Al-based icosahedral quasicrystals to boron-based cluster solids, which consist of icosahedral clusters of the same group III element, B, is discussed. Metallic-covalent bonding conversion in icosahedral clusters of Al and B was demonstrated by molecular orbital calculations. According to theelectron density distribution obtained using the maximum entropy method and the Rietveld method, the bonding conversion phenomenon occurs even in cluster solids such as some Al- and B-based icosahedral approximant phases (Al12Re, α-AlMnSi, α-rhombohedral boron). The covalent bonds observed by the electron density analysis give rise to extremely low carrier density and small density of states at Ef in α-AlMnSi and perhaps in icosahedral quasicrystals. In β-rhombohedral boron, the electronic structure and properties depend on slight variation in atomic environment of the icosahedral multiple-shell structure of the crystals. As metallic atoms are doped into specific atomic sites of β-rhombohedral boron, the atomic structure, the electrical conductivity and its temperature dependence approach those of AlLiCu icosahedral quasicrystal and equal those of AlPdRe icosahedral quasicrystal. From the absolute densitymeasurement, it was revealed that the concept of rigid sphere packing, i.e. metallic bonding, is not applicable to AlPdReicosahedral quasicrystal. Various semiconductor-like behaviors of Al-based icosahedral quasicrystals were demonstrated by means of not only conventional conductivity and Hall coefficient measurements but also modulated photocurrent measurements.In addition, the thermoelectric properties of AlPdRe quasicrystal were estimated. The potential for application of the icosahedral quasicrystals as thermoelectric materials is also discussed.

Multiple shell structured hypercube feature maps for vector quantization of images

Abstract A new neural network architecture is proposed for spatial domain image vector quantization (VQ). The proposed model has a multiple shell structure consisting of binary hypercube feature maps of various dimensions, which are extended forms of Kohonen's self-organizing feature maps (SOFMs). It is trained so that each shell can contain similar-feature vectors. A partial search scheme using the neighborhood relationship of hypercube feature maps can reduce the computational complexity drastically with marginal coding efficiency degradation. This feature is especially proper for vector quantization of a large block or high dimension. The proposed scheme can also provide edge preserving VQ by increasing the number of shells, because shells far from the origin are trained to contain edge block features.

Large shielding factor obtained by a multiple-shell magnetic shield having separate magnetic shaking

Large shielding factors obtained by magnetic shaking techniques are reported. A cylindrical magnetic shield with both ends open (length=120 cm, inner diameter=52 cm) was constructed as a one-half model of an actual size. Metglas 2705M amorphous tapes of 5 cm in width and about 22 μm in thickness were wound helically on the outer surface of a tube (outer diameter=52 cm) to form a thin multiple-shell structure of five shells. The outer three shells, each made of 4 layers of tapes, were subjected to a common magnetic shaking (200 Hz). The fourth shell made of 8 layers was subjected to a different magnetic shaking (536 Hz). The innermost one was a passive shell. The shielding factor in the center of the shield measured for a transversely applied magnetic field (100 mG) showed 1/f-like behavior and extremely large values of 90 900 at 1 Hz and 21 000 at 10 Hz when the opening compensation was on. The shielding factor was much lower and constant at the level of 7000 at frequencies of less than 10 Hz when opening compensation was off. The residual dc magnetic field at the center was as small as 5 μG. It is shown by the experiments that a multiple-shell structure with even narrow spacings exhibits large shielding factors when a magnetic shaking technique is applied. It is also shown that the opening compensation technique is a key to building an open-structure magnetic shield with a large shielding factor.

Plateau de bure observations of IRC+10216: high sensitivity maps of SiC2, SiS, and CS

We have obtained high angular resolution ~ 3”), and high sensitivity maps of IRC+10216. SiC2 is found both in a spherical shell and in the very central region, indicating it is formed both in the inner envelope close to the star, and in the outer shell. The molecules SiS and CS are mostly found in the inner parts of the envelope, but are still detectable in the outer region (r ~ 15”) where the products of photochemistry are found. The maps show that IRC+10216 has a very clumpy envelope, with strong departures from spherical symmetry; an axis oriented NS-SW (P.A. 20°) can be seen in all maps. The radial brightness distribution of CS has secondary maxima, at the radius where the SiC2 shell has its peak emission. A preliminary map shows CN in the same shell, but also in a still larger outer shell. Time variations in the mass loss rate, could be invoked to explain the multiple shell structure of this envelope.

The multiple-shell structure of the planetary nebula NGC 6751

An intriguing bipolar mass outflow and a faint envelope were detected spectroscopically in the planetary nebula NGC 6751 by Gieseking and Solf (1986). To study the physical structure, deep CCD images of this nebula have been obtained which detect not only the morphological counterparts of the aforementioned features but also additional faint halos extending out to a much larger radius. Long-slit echelle spectra are obtained to determine the internal motion and radial velocity, as well as low-dispersion spectra to determine the physical condition and abundances of each feature in the whole nebula. NGC 6751 is apparently a multiple-shell nebula moving through a gas-rich environment. An He abundance difference between the planetary nebula and the ambient medium and an N/O abundance ratio enhancement in the forbidden N II-bright knots in the main nebula are found. From the physical structure of the shells in NGC 6751, information is derived about the average mass-loss rates at various stages. 32 refs.