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We report here a systematic study of the molecular content in the neutral envelope of NGC 7027. The measurements were done in September 1991 with the 30-meter IRAM telescope on Pico Veleta (Spain). The frequencies and transitions covered are given in Table 1. Long integrations were performed in each transitions toward the central position of NGC 7027, and for the strongest lines we obtained detailed maps. The results of the observation are given in Table 1 (in units of main beam temperature).
We report high angular resolution mapping of the CO (J=2→1 and 1→0) lines in three evolved planetary nebulae (PNe): NGC 6781, NGC 6772, and VV47. The CO 2→1 observations of the ring-like nebula NGC 6781 provide the most detailed map to date of the kinematic structure of a PN envelope. The data are well explained with a model consisting of a thin, clumpy, ellipsoidal shell, which is open at the ends and is expanding with a velocity proportional to distance from the star. The molecular shell of NGC 6772 appears similar, but the gas is more confined to an equatorial ring and is much more incomplete. The molecular gas in VV 47 is in two clumpy lobes, which are likely to be the only surviving molecular condensations from an earlier, more extended equatorial distribution of the same kind. The average CO excitation temperature of these PNe is found to be >23 K from the CO 2→1/1→0 line ratio, and the mass of molecular gas is estimated to be 0.1, 0.02, and 0.002 M⊙ in NGC 6781, NGC 6772, and VV 47, respectively. It appears that the ring-like PNe are formed from the dissociation and ionization of neutral ellipsoidal shells; destruction of the envelope begins with the rapid ionization of the least dense polar caps, and continues until the densest molecular material at the nebular waist is fully ionized.
We report high resolution CO (1–0) line imaging of a prominent cometary globule in the Helix Nebula. The results confirm earlier observations (Huggins et al. 1992) that globules consist of dense condensations of neutral gas embedded in the ionized nebula, and they provide new constraints on the structure and kinematics of the gas.
We report the results of an extensive survey of molecular gas in planetary nebulae (PNe) using the millimeter lines of CO. The observations provide a range of information on the kinematics, the structure, and the mass of PN envelopes, which are important for understanding the formation and evolution of the ionized nebulae from the molecular envelopes ejected during the precursor AGB and proto-PNe phases.
We present new, infrared and millimeter views of the Helix nebula which illustrate the critical role of remnant, neutral AGB envelopes in the formation and evolution of planetary nebulae. Large scale ∼ 1 000″ mapping of the entire nebula in the CO (J = 2 − 1) line with the CSO reveals the global structure of the envelope. The CO emission forms the familiar ring structure seen in optical images of the Helix, and indicates a massive remnant with ≳ 50% the mass of the ionized nebula. High resolution CO mapping with the IRAM 30 m telescope shows that the whole envelope is fragmented into an intricate array of small clumps, closely related to the cometary globules seen in the central, ionized cavity. 5–17 μm spectroscopy of the Helix with ISOCAM reveals a remarkable near infrared spectrum, dominated by the pure (v = 0 − 0) rotational lines of H2. The H2 lines are excited to a temperature of ∼ 900 K, and likely arise in warm, outer layers of the small clumps seen in CO. Imaging of the H2 emission with ISOCAM over the whole nebula provides a striking portrait of the fragmented neutral envelope. 3-dimensional views of the envelope are also presented, based on CO mapping and using 3-dimensional visualization techniques. Point symmetries dominate the toroidal structure, and suggest an origin for the Helix in equatorial mass-loss on the AGB, shaped by the action of bipolar outflows or jets.
Windrow burning is one of several harvest weed seed control strategies that have been developed and evaluated in Australia to address the widespread evolution of multiple herbicide resistance in annual weeds. Herbicide-resistant Italian ryegrass populations are common in the Palouse region of eastern Washington and northern Idaho. Field and greenhouse studies were conducted to evaluate the effects of burning standing stubble and narrow windrows on the survival of Italian ryegrass seed on the soil surface and to determine the amount of crop residue remaining after both practices. Italian ryegrass emergence was 63, 48, and 1% for the nonburned check, burned standing stubble, and burned windrow treatments, respectively. Crop-residue dry weights were 9.94, 5.69, and 5.79 Mg ha−1 for these same treatments. Windrow burning can be an effective tactic in an integrated weed management strategy for Italian ryegrass control in the Palouse region of eastern Washington and northern Idaho.
Observations have been made of J=2-1 CO in eleven circumstellar clouds including seven carbon stars and four oxygen-rich stars. Observations in four sources, including IRC+10216 have already been published (Wannier et al. 1979, henceforth Paper I) and the remaining observations are being prepared for publication (Knapp et al. 1980, henceforth Paper II). Several results are discussed below with special emphasis on the implications for two sources, namely IRC+10216 and Mira (o Ceti). The observations of IRC+10216 show CO emission over a diameter of 6 arcmin (∼ 0.5pc), a result suggesting a very large mass-loss rate. Mira is unique among the objects studied in displaying a small CO opacity and a high CO excitation temperature. It is suggested that this heating results from the orbital velocity of Mira due to its close binary companion.
Ba6Ta2O11 with an oxygen—deficient perovskite—related structure, was prepared through solid state reaction of BaCO3 and Ta2O5 powders. The electrical conductivity of sintered Ba6Ta2O11 pellets was measured by a.c. impedance spectroscopy inthe temperature range between 200 and 800ºC. The conductivity at 800ºC was3.7x10-3 Ω-1 cm-1; the activation energy for bulk conduction was 0.93 eV at temperatures between 500 and 800ºC and 1.22 eV below 500ºC. The bulk conductivity was independent of atmosphere, while the grain boundary conductivity, with an activation energy of 1.08 eV, decreased as oxygen partial pressure increased. The oxygen ion transport number obtained from concentration cell measurements was 0.5 to 0.65 at temperatures from 450 to 820ºC.
Double molybdates, KLn(MoO4)2 and K5Ln(MoO4)4 have been synthesised utilising the solid state reactions of KIO3 Ln203 and MoO3 (Ln=La,Gd,Dy) in appropriate mole ratios, employing thermal analysis techniques. The solid phases have been characterised by IR, XRD studies and magnetic measurements. The d.c. electrical conductivity values of the two molybdates measured in the temperature range 373–623K are found to increase with rise in temperature. This observation together with the calculated jump activation enthalpies and the supposed ‘layered’ type structure with the loosely held K+ ion between the layers support the ionic conductivity mechanism in these samples.
The effect of intercalated lithium on the electronic band structure of the γ-polytype of InSe has been investigated using a tight-binding method. The energy bands of the pure polytype were calculated and the results compared with previous work. The modifications of the energy bands produced by the introduction of one lithium atom per unit cell were calculated for the lowest potential energy position of the lithium atom in the Van der Waals gap between layers. The results for the changes in the smallest and next-to-smallest direct band gaps are compared with experimental data. An interpretation of a photoluminescence peak produced by lithium intercalation is given.
We report results of a nuclear magnetic resonance (NMR) study of lead(II) cations in β"-alumina. Measurements of line positions and spin-lattice relaxation times (T1) as a function of temperature are presented. The results show that Pb ions possess both static and dynamic disorder in low and intermediate temperature regimes, respectively. Also, a comparison is made between Lorentzian and logarithmic spectral density functions, from which we conclude that the latter provides a better fit to the dataat short correlation times (ωºτºα). The logarithmic form has been proposed to describe diffusive motion in 2-dimensional conductors.
Semiconducting Bi2Sr2CaCu208 and La2CuO4 can be made superconducting following their oxidation in an electrochemical cell. Experimental evidence suggests that the deintercalation of copper, ie. the oxidation of the copper oxide planes is responsible. Intercalation, ie. reduction, reverses the above trends. The mechanism controlling superconductivity is therefore sensitive to the Cu/O ratio, which can be reversibly controlled at room temperature.
The lithium derivatives from anhydrous niobium (Y) phosphate were made through NbOPO4.H20 and LiCl by solid state reaction at 200 ºC and subsequentannealed at 500ºC. The solid with the highest lithium content, exhibits the maximum conductivity of all materials prepared. The electrical conductivity of this solid ranges from 10-10 Ω-1 cm-1 at 373K to 3.62.10-3Ω-1cm-1 at 683K.
Starting from the seminal work of De Wolff , we have developed a structural description, based on two kinds of defects, which accounts for the scattering function of all γand ε-MnO2. Using numerical simulation results, we propose simple methods to estimate the parameters which characterize real manganese dioxide samples. Real time neutron powder diffraction has been used to investigate in situ the transformations undergone by γ-MnO2 during thermal annealing and electrochemical reduction in alkaline solutions. We have found that thermally induced transformation from MnO2 to ∝-Mn2O3 can involve up to seven different steps and that electrochemical reduction of γ-MnO2 in KOD electrolyte proceeds through three stages, the final one leading in most cases to a breakdown of the initial crystal lattice.
The dynamic bond percolation model was developed to deal with dynamic disorder, treating ion mobility by a percolation model in which the assignment of any site-to-site jump as allowed or forbidden changes on a timescale related to the local reorganizational dynamics of the polymer segments (the renewal time). Here we discuss the special cases of highfrequency spectra and partially crystalline electrolytes. At high frequencies, the present hopping model yields unphysical behavior (frequencyindependent response); we trace this back to the incorrect treatment of short-time dynamics, and show how it can be corrected. For partially crystalline materials, we show that a rollover feature in the spectrum, in the microwave range, can be expected when ions are trapped in isolated regions of high conductivity, such as amorphous pockets in largely crystalline PEO.
The search for lithium ion conductors in crystalline or polycrystalline solid state ionic materials has resulted in finding a new class of compounds. Five new, stable, homogeneous compounds formed in the lithium alcohol systems, LiI—(ROH)x for R=CH3CH2OH, CH3CH2CH2OH, CH3CHOHCH3,, and CH3OH have been identified and characterized.
"Overcharging" of pure stage graphite hydrogenosulfate i.e charging of graphene layers with expulsion of H+ from the intercalate layer is modelized by transmission lines which agree quite well with A.C Impedance measurements. The meaning of the apparent Diffusivity Da = 12 /3 R1C1 is discussed as significant of the displacement of H+/e− holes pairs along the blocking interface separating graphene and intercalate layers.
Molecular dynamics simulations were carried out in an attempt to reproduce and explain the differing composition dependencies of the ionic conductivities of Na(I)-Ba(II)- and Na(I)-Sr(II)- ß' '-alumina. Impedance spectroscopy measurements of Na1.67-2xBaxMg0.67Al10.33O17, where x = 0.0 - 0.835, showed a distinct minimum in the conductivity when x = 0.67, or 80% exchange of Ba(II) for Na(I). Evidence for mobile cation ordering at that composition was seen in the simulation results and the general change in conductivity with Ba(II) content was reproduced rather well. The results of a similar experimental study of Na(I)-Sr(II)-ß' '-alumina did not show a minimum in the conductivity, but our simulations incorrectly predicted the Sr(II) system to behave in the same fashion as the Ba(II) system. Possible reasons for this discrepancy are suggested, including problems with transferring potentials between oxides and the influence of absorbed water on the experimental results.
The transport properties and far-infrared reflectivity of BiSI, BiTel, SbTeI, Bi2 Se3 and Bi2S3 have been studied, and the results show a good agreement between the two techniques. Lithium insertion within metal-chalcogen-halogen compounds has been carried out using Li/LiC1O4-PC/MChI galvanic cells at room temperature. Electrochemical potential spectroscopy measurements show the different regimes involved in the insertion reaction.