Intermediate Disk Research Articles

Evolution of Radial Abundances Gradients from Planetary Nebulae

The presence of radial abundance gradients is now well established, both in our Galaxy and in other spirals. These gradients were originally derived from oxygen abundance in HII regions, but in the past few years, other elements produced by massive stars have also been shown to display radial abundance gradients similar to the oxygen gradient, which amounts to −0.07 dex kpc−1. Moreover, planetary nebulae (PN), belonging to the intermediate disk population (the so–called Peimbert “type II” PN) also exhibit gradients of the same order of magnitude as the HII regions.

The local velocity distribution from a stellar system with two Gaussian components

The superposition of two stellar velocity distribution functions of Gaussian type is applied in order to study the velocity distribution of a stellar sample in the galactic plane. Assuming that the Galaxy is symmetric respect to this plane, the relationships to be fulfilled by the central velocity moments of the total stellar sample are obtained. If the total velocity distribution is consistent with this type of superposition, the partial moments of the subsamples, which are associated with the Gaussian components, can be calculated and, also, the population percentage. Our results show that first component corresponds to young disk population and the second one to intermediate disk population.

Large scale structure and kinematics of the LMC from a study of long-period variable stars

A recently completed study of the kinematics of Long-Period (or red) Variables (LPVs) in the LMC by Hughes et al. (1990) has shown that those with short periods (100 to 225 days) have spheroidal kinematics (high velocity dispersion and low rotational velocity about the LMC). This is the first evidence of the LMC's possessing a spheroidal population. The spheroid is flattened (with axial ratio c/a ˜0.3 to 0.5), and is not much thicker than the intermediate age disk. The velocity distribution of the old LPVs indicates that the mass of the LMC is ˜ 6.2 ± 1.5 × 109M, and that of the spheroid represented by the old LPVs is ˜2 % of the LMC's total mass. If these old LPVs are members of the LMC's disk, then their velocity dispersion implies that they have an age of ˜10 Gyr. The LPVs with intermediate periods (225 to 450 days) are members of the LMC's rotating disk population, with an age ˜4 Gyr derived from their velocity dispersion, and similar to that of the planetary nebulae, CH stars and old cluster populations.

Excitation energy transfer in phycobilisomes at −196°C isolated from the cyanobacterium Anabaena variabilis (M-3): evidence for the plural transfer pathways to the terminal emitters

Excitation energy transfer in phycobilisomes at −196°C was studied by means of the time-resolved fluorescence spectroscopy in the picosecond time-range. Supplemental data were obtained from the allophycocyanin-core complex. When the phycobilisomes were excited at 580 nm, at leastnine fluorescence components were resolved by the time-resolved spectra and deconvolution of thosespectra. Energy transfer among these components is not straightforward. At the phycocyanin level, two transfer pathways are probable; one may be among the β-155 chromophores, and another among α-84 chromophores along the long axis of the phycobilisome rods. The β-84 chromophores in intermediate discs of the rods might function as an energy pool by a fast equilibrium between αa-84 and β-84 chromophores. The β-84 chromophores in the trimer next to the core-complex is the energy donor to the core-complex. At allophycocyanin level, two pathways of the energy transfer were also found; one from F660 to F686 through the F673. This corresponds to the energy flow from β-84 chromophore without linker to 18.3 kDa polypeptide and finally to the ‘anchor’ polypeptide. The other pathway is from the F666 to F680, i.e., from the β-84 with a linker polypeptide to the α-subunit of allophycocyanin B. Two independent pathways in the energy transfer shown in this study basically agreewith the assembly model of the core components proposed by Glazer (cf. Biochim. Biophys. Acta 768 (1984) 29–51).

Stress-strain state of a rod-type piezoceramic sensor

1. The finite elements method was used to develop an algorithm for calculating the natural frequencies and modes and the stress-strain state of piezoelectric sensors in an axisymmetric formulation. 2. A study was made of the deformation of a rod-type piezoelectric sensor subjected to preliminary static compression and subsequent vibrational loading by means of electrical harmonic excitation. 3. It was shown that the stress distribution in the piezoelements is nonuniform due to design features of the sensor. 4. It was established that an increase in the stiffness of the intermediate disk between the piezoceramic column and the radial cover plate of the sensor lowers the tensile hoop stresses in the adjacent piezoelement by 15–20%.

Past and present metal abundance gradient in the galactic disc

A critical discussion of some determinations of metal abundance gradient in the galactic disc is presented with an attempt to homogenize the results related to local and large-scale gradients. A new estimation of the palaeogradient in intermediate and old disc population is presented. The gradient is found to depend on galactocentric distance, and to be nearly constant with time during the lifetime of the galactic disc.

Simultaneous X-ray and optical observations of GX 339-4 in an X-ray high state

Optical emission, soft X-rays, and hard X-rays have been observed simultaneously from the black hole candidate GX 3339-4 in a typical high state. Each of these components is interpreted as arising from a characteristic region of the accretion disk. Considered as a black hole, GX 339-4 lacks the variable 2 keV blackbody component that would be emitted from the 'solid' surface of a neutron star in the low-mass neutron star binaries. The X-ray emission in the high state is therefore extremely soft and stable in time. The intermediate disk region is optically thick and geometrically thin. The observed soft X-ray component with a 'disk blackbody' spectrum comes from this region. The innermost disk region is dynamically unstable due to the effect of general relativity and possibly due to radiation pressure. This region is responsible for the generation of the hard X-ray tail through Comptonization.

Vibration isolator coupling

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The lunate bone: a weak link in the articular column of the wrist

This study deals with the two degrees of freedom of the wrist joint allowing flexion-extension and radioulnar inclination (deviation). Based on the movements of the wrist the author proposes an articular model comprising an antebrachial socket and a bony unit formed by the distal carpal row and metacarpal bones. The articulation of these two units is afforded by a composite intermediate disc comprising the proximal row of carpal bones with their intercarpal ligaments. The advantages of this model are exposed.

The synovial folds of the knee joint: Anatomical study

Three in number, the plicae are inconstant synovial structures found within the cavity of the knee joint, and have been recognised for some time. The inferior plica in particular was described by Vesalius in 1555. Both the inferior and medial plicae are vestiges of an intermediate articular disc similar to the menisci. The superior plica derives from the wall which in the first instance, separates the bursa and quadriceps cul-de-sac.

The metallography of zirconium hydride precipitation in a magnesium/0.5 wt % zirconium alloy

Transmission electron microscopy has been used to study the precipitation sequence during internal hydriding of a homogenised Mg/0.5wt%Zr alloy. At low hydriding temperatures (435 °C), a fine homogeneous dispersion of coherent, plate-like precipitates containing zirconium and hydrogen is formed on {0001} planes of the Mg matrix. The precipitate is stable for prolonged periods at 435 °C in a hydrogen atmosphere, but dissolves fairly readily at 500 °C in argon. At high hydriding temperatures (530 or 600 °C the first observed precipitate is as porous discs on {0001}Mg, each of which consists of a number of smaller particles. With continued hydriding, the intermediate precipitate discs develop facets and coalesce to eventually form solid hexagonal-shaped plates of the equilibrium ZrH 2, which have an orientation relationship with the Mg matrix given by: (111) zrH 2 //(0001) Mg, [202̄] zrH 2 //[112̄0] Mg.