Incomplete Shell Research Articles

X-ray Absorption Spectroscopy Unveils the Formation of Gold Nanoparticles in Corn

In this study, X-ray absorption spectroscopy was used to determine the possible gold biotransformation by Zea mays (corn) var. Golden, germinated and grown in a medium spikedwith KAuCl4. In addition, the gold uptake capacity of corn assisted by thiourea and ammoniumthiocyanate was investigated. Results showed that up to 160 mg/L, gold did no treduce corn seed germination or plant growth. Both thiourea and ammonium thiocyanateresulted in a 6-fold increase of gold concentration in roots and thiourea promoted a 10-fold increase of gold concentration in shoots. X-ray absorption near edge structure studies demonstrated that approximately 91% of the gold present in plant samples was Au(0). Theremaining 9% was present as Au(III). In addition, extended X-ray absorption fi ne structureresults showed that in corn roots, the gold coordination number was around 9,5 neighboringgold atoms at approximately 2,86 Å, indicating an incomplete fi rst coordination shell,which imply the presence of a nano-phase. The results demonstrated that Z. mays was ableto produce gold nanoparticles with a size of 10,36 nm.

TRACING THE ASYMMETRY IN THE ENVELOPE AROUND THE CARBON STAR CIT 6

We present high angular resolution observations of HC3N J = 5 − 4 line and 7 mm continuum emission from the extreme carbon star CIT 6. We find that the 7 mm continuum emission is unresolved and has a flux consistent with blackbody thermal radiation from the central star. The HC3N J = 5 − 4 line emission originates from an asymmetric and clumpy expanding envelope comprising two separate shells of HC3N J = 5 − 4 emission: (1) a faint outer shell that is nearly spherical which has a radius of 8'' and (2) a thick and incomplete inner shell that resembles a one-arm spiral starting at or close to the central star and extending out to a radius of about 5''. A comparison between the data and our excitation modeling results suggests an unusually high abundance of HC3N in the envelope of CIT 6. We discuss the possibility that the envelope might be shaped by the presence of a previously suggested possible binary companion. The abundance of HC3N may be enhanced in spiral shocks produced by the interaction between the circumstellar envelope of CIT 6 and its companion star.

Determination of the effective nuclear charge for free ions of transition metals from experimental spectra

The refined set of values of the effective nuclear charge ( $$ \bar Z_{ef} $$ ) and the set of one-electron spin-orbital constants (ξ 3 teor ) are obtained for ions of transition metals with the help of a semiempirical method of calculation of the spectrum of free ions with allowance for the spin-orbital interaction. The effective nuclear charge, which is a variable theoretical parameter, was determined from a comparison of theoretically calculated ion absorption spectra with experimental ones. The form of the potential for the calculation of the spin-orbital constant was chosen such that the calculated value ξ 3 teor would coincide with the experimental one ξ 3 exp . The calculated set of values $$ \bar Z_{ef} $$ , ξ 3 teor } can be used in semiempirical calculations of energy levels of 3d ions (ions with an incomplete 3d shell).

Propylamine–borane

The title compound, C3H12BN, was solved using data collected from a multiple crystal (note incomplete data shell). The cell packing is dominated by bifurcated attractive N—Hδ+⋯δ−H—B inter­actions.

Standard state thermodynamic properties of aqueous sodium perrhenate using high dilution calorimetry up to 598.15 K

Standard state thermodynamic properties for aqueous sodium perrhenate at temperature in the range of (298.15 to 598.15) K and at p sat were determined by high dilution solution calorimetry down to 10 −4 m. Standard state partial molar heat capacities, C p , 2 ∘ , of aqueous sodium perrhenate calculated from present study are compared to literature values up to T = 398.15 K. The differences between C p , 2 ∘ of ReO 4 - ( aq ) and Cl −(aq) at lower temperature is much greater than that due to their internal molecular motions. Consequently, the perrhenate ion appears to have an ionic incomplete primary hydration shell as compared to the chloride ion. The ReO 4 - / Cl - difference in thermodynamic functions has now been well defined up to T = 598.15 K for other important high temperature calculations.

Ossifying Fibromyxoid Tumor in the Mandibular Gingiva: Case Report and Review of the Literature

Ossifying fibromyxoid tumors (OFTs) are uncommon soft tissue neoplasms. Only one case arising in the gingiva has been described. A 21-year-old woman presented with a painless exophytic mass located in the right posterior mandibular gingiva, which was identified 6 months earlier. Radiographs showed irregular calcifications inside the lesion, discrete irregularity of alveolar bone, and integrity of buccal and lingual cortical bone. An incisional biopsy was performed based on the clinical diagnostic hypothesis of peripheral ossifying fibroma or peripheral giant cell granuloma. Microscopic features were compatible with the diagnosis of ossifying fibroma. The entire mass was excised and submitted to histopathologic and immunohistochemical analysis. Histopathologic analysis revealed proliferation of round to spindle-shaped cells arranged in cords and nests and embedded in a fibromyxoid matrix. An incomplete shell of bone trabeculae located beneath the fibrous pseudocapsule was observed at the periphery. Immunohistochemical analysis showed positivity for vimentin and S-100 protein and negativity for smooth muscle actin, muscle-specific actin, and glial fibrillary acidic protein. The definitive diagnosis was OFT. The patient showed no clinical signs of recurrence 7 months after surgical excision. OFTs located in the gingiva are extremely rare. At this site, these tumors are clinically indistinguishable from other reactive or neoplastic lesions. Although many cases present an indolent biologic behavior, the local recurrence of OFTs has been reported; therefore, long-term follow-up is mandatory.

Hydrophilic carbon onions synthesized by millisecond pulsed laser irradiation

Carbon onions with hydrophilic characteristics were synthesized through irradiating carbon black suspension using millisecond pulsed laser at room temperature. Laser energy absorption resulted in the structure transformation of carbon black and the formation of hydrophilic groups on the surface of carbon onion. Carbon onions with hollow cores and the incomplete graphitic shells were produced from the starting materials under high and low laser power density, respectively.

Determination of the intershell conductance in a multiwall carbon nanotube

We have measured the current induced voltage drop along an individual multiwall carbon nanotube as a function of the distance to the current injecting electrode. The measurements have been performed at room temperature using scanning probe potentiometry combined with scanning electron microscopy. For a nanotube with an incomplete outer shell, a sharp potential jump was observed at the end of the outermost shell. The electric potential variation along the carbon nanotube has been used to determine the contact resistance between metal electrodes and the tube, the intrashell resistance, and the intershell conductance.

Two new species and a new subspecies of Tetraclitella (Cirripedia: Thoracica) from the Cainozoic of Australia and New Zealand and a consideration of the significance of tubiferous walls

A tubiferous cirripede Tetraclitella judiciae sp. nov., previously known only from two isolated and incomplete shell wall plates identified as Tetraclitella sp. cf. T. purpurascens (Wood, 1815), is described from the early Miocene of Victoria, Australia; a further taxon, Tetraclitella purpurascens miocenica subsp. nov., occurs in the late Miocene-Pliocene of Victoria, and specimens from the early Miocene of New Zealand, previously recorded as Tetraclitella sp. cf. T. purpurascens (Wood, 1815) are redesignated as Tetraclitella nodicostata sp. nov. Tetraclitella is the first cirripede genus known to have had tubiferous walls. Incorporation of chitinous stringers within the shell wall of early tetraclitids (e.g. Epopella) may have facilitated the development of the tubiferous shell wall, which permitted sessile barnacles to maximise the shell strength to calcite ratio: in doing so, these chitinous stringers not only reduced the diversion of energy required to extract calcium carbonate from seawater, but improved the effectiveness of the shell wall in resisting predators. It is also argued here that the presence of chitin within the shell increased resistance to both corrasion and corrosion, the latter becoming an increasing problem for calcareous shelled organisms following a drop in the pH of seawater after the PalaeoceneEocene Thermal Maximum.

Detection of Intermediates and Kinetic Control during Assembly of Bacteriophage P22 Procapsid

Bacteriophage P22 serves as a model for the assembly and maturation of other icosahedral double-stranded DNA viruses. P22 coat and scaffolding proteins assemble in vitro into an icosahedral procapsid, which then expands during DNA packaging (maturation). Efficient in vitro assembly makes this system suitable for design and production of monodisperse spherical nanoparticles (diameter ≈ 50 nm). In this work, we explore the possibility of controlling the outcome of assembly by scaffolding protein engineering. The scaffolding protein exists in monomer–dimer–tetramer equilibrium. We address the role of monomers and dimers in assembly by using three different scaffolding proteins with altered monomer–dimer equilibrium (weak dimer, covalent dimer, monomer). The progress and outcome of assembly was monitored by time-resolved X-ray scattering, which allowed us to distinguish between closed shells and incomplete assembly intermediates. Binding of scaffolding monomer activates the coat protein for assembly. Excess dimeric scaffolding protein resulted in rapid nucleation and kinetic trapping yielding incomplete shells. Addition of monomeric wild-type scaffold with excess coat protein completed these metastable shells. Thus, the monomeric scaffolding protein plays an essential role in the elongation phase by activating the coat and effectively lowering its critical concentration for assembly.

Hollow Platinum Spheres with Nano-Channels: Synthesis and Enhanced Catalysis for Oxygen Reduction

Hollow nanostructures are a particularly interesting class of materials that have unusual chemical and physical characteristics that are determined by their shape and composition. A facile procedure for the hollow Pt nanosphere catalysts with nanochannels was developed; the catalysts can be simply prepared at room temperature with silver nanoparticles as sacrificial templates. The incomplete shell of hollow nanospheres may provide the interior surface for the catalytic reaction, and the high surface area of Pt nanospheres leads to a higher catalytic activity. Consequently, these results demonstrate a simple route to enhance the catalytic efficiency of Pt catalysts by a simple improvement.

The Electrocatalytic Properties of Arc‐MWCNTs and Associated ‘Carbon Onions’

AbstractFor the first time we report on the electrochemical characteristics of nanometer sized polyhedral graphite onions dispersed amongst arc‐MWCNTs. These are formed during the electric arc discharge method of producing ultrapure MWCNTs (arc‐MWCNTs). The carbon onions are randomly dispersed amongst the arc‐MWCNTs which are produced with very little amorphous carbon deposits or other unwanted impurities and are formed as closed‐ended tubes. By comparison with commercially available open‐ended hollow‐tube multiwalled carbon nanotubes made using the chemical vapor deposition method (cvd‐MWCNTs), a glassy carbon electrode (GCE), an edge‐plane pyrolytic graphite electrode (eppg) and basal plane pyrolytic graphite (bppg) electrode, we can speculate that it is the edge‐plane‐like defect sites that are the electroactive sites responsible for the apparent ‘electrocatalysis’ seen with a wide range of analytes including: ferrocyanide, ruthenium hexaamine(III), nicotinamide adenosine dinucleotide (NADH), epinephrine, norepinephrine, cysteine, and glutathione. The arc‐MWCNTs themselves are produced as closed‐ended tubes with very few, if any, edge‐plane‐like defect sites evident in their HRTEM characterization. Therefore we speculate that it is the carbon onions dispersed amongst the arc‐MWCNTs which have incomplete graphite shells or a rolled‐up ‘Swiss‐roll’ structures that posses the edge‐plane‐like defect sites and are responsible for the observed voltammetric responses. Carbon onions are no more or no less ‘electrocatalytic’ than open‐ended MWCNTs which in turn are no more electrocatalytic than an eppg electrode. As the carbon onions are ubiquitous in MWCNTs formed using the arc‐discharge method the authors advise that caution should be taken before assigning any electrocatalytic behavior to the MWCNTs themselves as any observed electrocatalysis likely arises from the carbon onion impurities.

Zn7Cu6: a magic cluster of brass?

Density functional theory was applied to a series of 13-atom Zn–Cu alloy clusters. We did a thorough search for the low-energy isomers by global optimization, plus explicit optimization of all homotops of the icosahedron. Structures of copper rich clusters tend to be compact, often icosahedra, whereas zinc rich clusters (\({{\rm Zn}_8{\rm Cu}_{5}^{+}}\), Zn9Cu4, Zn11Cu2) have compact copper cores surrounded by an incomplete shell of solvating Zn atoms. The icosahedral structure, low total energy, and large hardness of Zn7Cu6 indicate that it has special stability among ZnxCuy clusters. However, Zn7Cu6 has many low lying isomers and a small cohesive energy compared to brass, which suggest that it is not stable in a broader sense.

Heating of blue compact dwarf galaxies: gas distribution and photoionization by stars in I Zw 18

Photoionization models so far are unable to account for the high electron temperature Te([O III]) implied by the line ratio [O III]4363A/[O III]5007A in low-metallicity blue compact dwarf galaxies, casting doubts on the assumption of photoionization by hot stars as the dominant source of heating of the gas in these objects. Combinations of runs of the 1-D photoionization code NEBU are used to explore alternative models for the giant H II region shell I Zw 18 NW. Acceptable models are obtained, which represent schematically an incomplete shell comprising radiation-bounded condensations embedded in a low-density matter-bounded diffuse medium. The thermal pressure contrast between gas components is about a factor 7. The diffuse phase can be in pressure balance with the hot superbubble fed by mechanical energy from the inner massive star cluster. The failure of previous modellings is ascribed to (1) the adoption of an inadequate small-scale gas density distribution, which proves critical when the collisional excitation of hydrogen contributes significantly to the cooling of the gas, and possibly (2) a too restrictive implementation of Wolf-Rayet stars in synthetic stellar cluster spectral energy distributions. A neutral gas component heated by soft X-rays, whose power is less than 1% of the star cluster luminosity and consistent with CHANDRA data, can explain the low-ionization fine-structure lines detected by SPITZER. [O/Fe] is slightly smaller in I Zw 18 NW than in Galactic Halo stars of similar metallicity and [C/O] is correlatively large. Extra heating by, e.g., dissipation of mechanical energy is not required to explain Te([O III]) in I Zw 18. Important astrophysical developments are at stakes in the 5% uncertainty attached to [O III] collision strengths.

Transformed initial dent as a trigger of the post-buckling process

A procedure for determination of critical loads of imperfect shells is proposed with allowance for the technique of stability and load carrying capacity of incomplete shells in an inhomogeneous stress–strain state developed earlier in the monographs [Gavrylenko GD. Stability of ribbed cylindrical shells in inhomogeneous stress–strain state. Kiev: Nauk. Dumka; 1989. 176pp [in Russian]; Gavrylenko GD. Stability of ribbed shells of incomplete form. Ukraine: Institute of Mathematics of NAS; 1999. 190pp [in Russian]]. New method of numerical estimation of carrying capacity of a shell is suggested and realized. Results from a joint theoretical and experimental investigation of the buckling of cylindrical shells containing localized dent damage are presented.

Oxidation of Alumina-Supported Co and Co−Pd Model Catalysts for the Fischer−Tropsch Reaction

Cobalt and bimetallic Co-Pd systems are well-known Fischer-Tropsch catalysts. Compared to Co, the bimetallic systems exhibit an increased activity toward CO hydrogenation and methane conversion, attributed to resistance against oxidation. To study the oxidation behavior, model catalysts have been generated by depositing either Co or first Co and subsequently Pd onto a thin epitaxial alumina film grown on NiAl(110). Pure Co particles and bimetallic particles with a Co core and a Pd shell have been studied before and after exposure to oxygen and after thermal treatments, using X-ray photoelectron spectroscopy (XPS), temperatureprogrammed CO desorption (TPD), ferromagnetic resonance (FMR), and infrared reflection absorption spectroscopy (IRAS) in ultrahigh vacuum. Large doses of O2 (1000 langmuirs; 1 langmuir ) 10 -6 Torr‚s) at 300 K lead to complete oxidation of Co particles. Upon annealing to temperatures above 530 K, XPS indicates that the cobalt oxide is mostly reduced by transfer of oxygen to the alumina support, resulting in its thickening. TPD, however, indicates the existence of persistent surface oxygen species, reducing the CO adsorption energy on the particles. Exposures to small doses of O2 (30-50 langmuirs) were also studied by a careful comparison of XPS, TPD, and FMR data. In this case, XPS indicates Co in a metallic state, whereas TPD and FMR indicate oxidic behavior. We conclude that small amounts of non-stoichiometric subsurface oxygen or subsurface and surface oxygen are present which are not detectable in the Co 2p XPS signal but have a pronounced effect on the surface chemistry and the magnetism, i.e., on certain bulk properties. In the case of bimetallic Co/Pd particles, an incomplete Pd shell on the Co particles even promotes oxygen uptake, while only a complete Pd shell inhibits oxidation.

Envelope density pattern around wide binary AGB stars: a dynamical model

The goal is to build up a simple dynamical model for the out-flowing circumstellar envelope around AGB stars in a wide binary system to explore the parameter dependence of the geometrical characteristics of column density patterns. An AGB star in a wide binary system is considered as a 3-D piston model that can induce a 3-D quasi-spherical density structure in the circumstellar envelope by orbital motion of the AGB star. The column density pattern only depends on two parameters: eccentricity of the orbit e and the terminal outflow velocity to mean orbital velocity ratio gamma. When viewed perpendicular to the orbital plane, spiral, broken spiral, and incomplete concentric shell patterns can be seen, while when viewed along the orbital plane, alternative concentric half-shell, egg-shell, and half-shell half-gap patterns will develop. Non-zero eccentricity causes asymmetry, while larger gamma makes a weaker pattern and helps bring out asymmetry. A spiral pattern may becomes broken when e > 0.4. The spiral center is always less than 12% of spiral pitch away from the orbit center. One should have more chances (~ 80%) seeing spiral-like patterns than seeing concentric shells (~ 20%) in the circumstellar envelope of wide binary AGB stars.

Photostability of Colloidal PbSe and PbSe/PbS Core/Shell Nanocrystals in Solution and in the Solid State

The photostability of semiconductor PbSe nanocrystals (NCs) under different storage conditions and the photoluminescence of PbSe NC films on Si substrates under vacuum and under different atmospheres were investigated. The NCs show a small blue shift in both the emission and absorption spectra when stored in solution. This blue shift is accelerated when the particles are stored in room light compared to when the particles are stored in the dark, which indicates that photooxidation is an important process. The photooxidation process is accelerated by irradiating NC solutions with a 450 W xenon lamp. The photobleaching and appearance of a precipitate are attributed to ligand desorption followed by agglomeration. Reversible O2-induced luminescence quenching was observed on a PbSe NC film on Si substrates, which could be addressed by two mechanisms: indirect quenching by alteration of PbSe charging and neutralization dynamics or quenching through direct interaction of O2 with the exciton. To improve the photostability of PbSe NCs, PbSe/PbS core/shell NCs using (TOP)S (TOP = trioctylphosphine) and TMS2S (TMS2 = bis(trimethylsilyl)) as sulfur sources were prepared. However, PbSe/PbS core/shell NCs did not show an increased stability in solution upon irradiation with a xenon lamp when compared with PbSe core NCs. Either the PbS shell is not able to confine the charge carriers or there is incomplete shell passivation with the PbSe core, and as a result these core/shell NCs have comparable stability.

Magnetic anisotropy and geometrical frustration in the Ising spin-chain system Sr 5Rh 4O 12

A structural and thermodynamic study of the newly synthesized single crystal Sr 5Rh 4O 12 is reported. Sr 5Rh 4O 12 consists of a triangular lattice of spin chains running along the c -axis. It is antiferromagnetically ordered below 23 K with the intrachain and interchain coupling being ferromagnetic (FM) and antiferromagnetic (AFM), respectively. There is strong evidence for an Ising character in the interaction and geometrical frustration that causes incomplete long-range AFM order. The isothermal magnetization exhibits two step-like transitions leading to a ferrimagnetic state at 2.4 T and a FM state at 4.8 T, respectively. Sr 5Rh 4O 12 is a unique frustrated spin-chain system ever found in 4d and 5d based materials without a presence of an incomplete 3d-electron shell.

Shell structure and strengthening of superconducting pair correlation in nanoclusters

The existence of shell structure and the accompanying high degeneracy of electronic levels leads to the possibility of strong superconducting pairing in metallic nanoclusters with N~100-1000 delocalized electrons. The most favorable cases correspond to (a) "magic" clusters with strongly degenerate highest occupied and lowest unoccupied shells and a relatively small energy spacing between them as well as to (b) clusters with slightly incomplete shells and small Jahn-Teller splitting. It is shown that realistic sets of parameters lead to very high values of Tc as well as to a strong alteration of the energy spectrum. The impact of fluctuations is analyzed. Spectroscopic experiments aimed at detecting the presence of pair correlations are proposed. The pairing should also manifest itself via odd-even effects in cluster spectra, similar to the case of nuclei.