Foraminal and paraspinal extraforaminal attachments of the sixth and seventh lumbar spinal nerves in large breed dogs.

Fresh cadaveric lumbar spines of 20 adult large breed dogs were used to study the sixth and seventh lumbar spinal nerves along their course through their respective intervertebral foramen. The relationship between the periosteum lining the vertebral canal (endorhachis; peridural membrane) and the vessels inside the vertebral canal, and the relationship between the nerves and the wall of the intervertebral foramen and the extraspinal suspensory apparatus were investigated. Each intervertebral foramen contained a fibrous septum that divided it into two sub-compartments by connecting the fibrous capsule of the facet joints with the intervertebral disc and the adjoining vertebral body. The lumbar nerves and the main artery passed through the cranial sub-compartment and the main vein passed through the caudal sub-compartment. In all cases, there was a circumneural sleeve that connected the ventral branches of the lumbar nerves extraspinally with the fibrous capsule of the facet joints dorsally, the fibrous septum caudally, and the caudal vertebral notch and accessory process cranioventrally. The deep layer of the circumneural sleeve was formed by the periosteum lining the vertebral canal pouching laterally through the intervertebral foramen; the superficial (lateral) layer was formed by the deep sheet of the thoracolumbar fascia. The deep sheet of the thoracolumbar fascia continued cranially and caudally to the circumneural sleeve to attach it to the vertebral body and the intervertebral disc. Regional and individual differences were noted in the composition and length of the circumneural sleeve. The potential biomechanical and clinical roles of these variations are discussed.

Imaging spin filter for electrons based on specular reflection from iridium (001).

As Stern-Gerlach type spin filters do not work with electrons, spin analysis of electron beams is accomplished by spin-dependent scattering processes based on spin-orbit or exchange interaction. Existing polarimeters are single-channel devices characterized by an inherently low figure of merit (FoM) of typically 10⁻4-10⁻³. This single-channel approach is not compatible with parallel imaging microscopes and also not with modern electron spectrometers that acquire a certain energy and angular interval simultaneously. We present a novel type of polarimeter that can transport a full image by making use of k-parallel conservation in low-energy electron diffraction. We studied specular reflection from Ir (001) because this spin-filter crystal provides a high analyzing power combined with a "lifetime" in UHV of a full day. One good working point is centered at 39 eV scattering energy with a broad maximum of 5 eV usable width. A second one at about 10 eV shows a narrower profile but much higher FoM. A relativistic layer-KKR SPLEED calculation shows good agreement with measurements.

Spin-resolved mapping of spin contribution to exchange-correlation holes.

By means of spin-polarized electron coincidence spectroscopy we explore the fundamental issue of spin-resolved contributions to the exchange-correlation hole in many-electron systems. We present a joint experimental and theoretical study of correlated electron pair emission from a ferromagnetic Fe(001) surface induced by spin-polarized low-energy electrons. We demonstrate that the contribution to the exchange-correlation hole due to exchange is more extended than the contribution due to the screened Coulomb interaction.

Positron-induced emission of electron-positron pairs from solid surfaces.

The collision of a low-energy positron, which impinges on a crystalline surface, with a valence electron may result in the emission of a spatially separated time-correlated electron-positron pair. We present a method for calculating the cross section for this positron surface reaction channel, which we briefly refer to as (p, ep) in analogy to electron-induced pair emission (e, 2e). The two-particle final state is represented by a product of an electron and a positron diffraction state coupled by a 'correlation factor', which accounts for the screened Coulomb interaction. The electron-solid and positron-solid quasi-particle potentials are based on first-principles calculations within density functional theory. Numerical (p, ep) results are presented for Cu(111) and compared to their (e, 2e) counterparts. Energy distributions for constant emission angles reflect, to a large extent, the valence electron density of states. In equal-energy (p, ep) angular distributions, the Coulomb interaction produces a central accumulation zone-in contrast to a depletion zone for (e, 2e)-the relative weight and the extension of which are subject to 'matrix element effects'. At larger angles sharp features arise from single-particle surface resonances.