Spin asymmetry and GDH sum rule for real and virtual photons for the deuteron

An explicit evaluation of the spin asymmetry of the deuteron and the associated GDH sum rule is presented which includes disintegration, single and double pion and eta production. For the GDH integral a large cancellation is found between the disintegration channel and the meson production channels. Furthermore, first results for the contribution of the disintegration channel to the generalized GDH integral at constant four-momentum transfer reveal a dominance of the isovector M1 transition to the $^1$S$_0$-state near threshold resulting in a negative contribution with a minimum around $Q^2\approx 0.2$ fm$^{-2}$ which is driven by the nucleon anomalous isovector magnetic moment.Comment: 9 pages, 7 figures, World Scientific style, invited talk at GDH 2004 Symposiu

Incoherent single pion electroproduction on the deuteron with polarization effects

Incoherent pion electroproduction on the deuteron is studied from threshold up to the second resonance region with special emphasis on the influence of final state interaction, in particular on polarization observables. The elementary $\gamma N\to\pi N$ amplitude is taken from the MAID-2003 model. Final state interaction is included by considering complete rescattering in the final $NN$ and $\pi N$ subsystems. Their influence on the structure functions governing the semi-exclusive differential cross section, where besides the scattered electron only the produced pion is detected, is investigated in detail. For charged pion-production the effect of $NN$-rescattering is moderate whereas $\pi N$-rescattering is almost negligible, except very close to threshold. $NN$-rescattering appears much stronger in neutral pion production for which the primary mechanism is the elimination of a significant spurious coherent contribution in the impulse approximation. Sizeable effects are also found in some of the polarization structure functions for beam and/or target polarizations.Comment: 20 pages including 14 figure

Life History, Diet and Habitat of the Federally Endangered Laurel Dace (Chrosomus saylori)

Laurel Dace (Chrosomus saylori) is a small, freshwater minnow that is endemic to headwater streams on Walden Ridge, Tennessee. The species was listed as federally endangered in 2011 and the U.S. Fish and Wildlife Service Recovery Plan indicates a need for life history, diet and habitat studies. A literature review, samples of archived specimens, and a surrogate species, the Tennessee Dace (Chrosomus tennesseensis), were used to describe the life history and diet of the Laurel Dace. A total of 370 Tennessee Dace were collected from Laurel Ford Branch, a stream 8.6 km from the Laurel Dace type-locality, over an 18-month period. The standard length of 370 Tennessee Dace was measured and the age of 72 individuals was determined with otolith microstructure analysis. We examined patterns of growth with a von Bertalanffy model and length relationships. Mortality estimates were derived from model parameters. Tennessee Dace exhibit positive allometric growth, 4+ age groups and estimated annual natural mortality of 73%. Tennessee Dace reproductive biology was determined by identifying and weighing gonads and counting mature ova in all sexually-mature females. The female-to-male sex-ratio was 1.3:1, reproductive maturity began at age-2, and mature ova counts ranged from 64 to 143. Variation in ova maturity between individuals during the March-to-July spawning season indicated that Tennessee Dace are multiple-clutch spawners. Morphometric analysis revealed pectoral fin length-to-standard length ratio as a sexually-dimorphic characteristic. Tennessee Dace and Laurel Dace diets were quantified through multiple season; both species were opportunistic feeders that consumed aquatic and terrestrial invertebrates, plant matter, and algae. The habitat of the northern population of Laurel Dace was characterized in pools in four segments of three streams. Pool volume, water depth, silt depth, canopy cover, and substrate were measured in the field and the sub-watershed land cover of each stream was quantified with ArcGIS. Laurel Dace inhabit streams that are characterized by large pools with predominantly bedrock substrate, dense riparian vegetation and heavily-forested watersheds. The results of this study indicate that to conserve Laurel Dace populations managers may encourage responsible land use on Walden Ridge and change federal permitting to protect individuals during the spawning season

Incoherent pion photoproduction on the deuteron with polarization observables I: Formal expressions

Formal expressions are developed for the general five-fold differential cross section of incoherent $\pi$-photoproduction on the deuteron including beam and target polarization. The polarization observables of the cross section are described by various beam, target and beam-target asymmetries for polarized photons and/or polarized deuterons. They are given as bilinear hermitean forms in the reaction matrix elements divided by the unpolarized cross section. In addition, the corresponding observables for the semi-exclusive reaction $\vec d(\vec \gamma,\pi)NN$ are also given.Comment: 11 pages, 1 figur

Cooperative quantum tunneling of the magnetization in Fe-doped Li3_3N

The spin-reversal in dilute Li$_2$(Li$_{1-x}$Fe$_{x}$)N with $x < 1$ % is dominated by resonant quantum tunneling of spatially well-separated states. We report on the effect of finite couplings between those states that give rise to cooperative, simultaneous quantum tunneling of two spins. This phenomenon, known as spin-spin cross relaxation, effectively elucidates the fine-structure observed in isothermal magnetization loops, a previously unresolved aspect. Temperature and field-dependent magnetization measurements were conducted over a range from T = 2 K to 300 K in applied fields of up to $\mu_0H$ = 7 T. Magnetic dipole fields are computed numerically. Our findings affirm the absence of stoichiometric defects in Li$_2$(Li$_{1-x}$Fe$_{x}$)N and underscore its exemplary suitability as a model system for investigating spin-reversal processes at the microscopic level. This is attributed to its comparatively simple crystal structure, the availability of large single crystals, elevated characteristic energies, and well-defined energy levelsComment: 7 pages, 4 figure

Iron single crystal growth from a lithium-rich melt

\alpha-Fe single crystals of rhombic dodecahedral habit were grown from a melt of Li$_{84}$N$_{12}$Fe$_{\sim 3}$. Crystals of several millimeter along a side form at temperatures around $T \approx 800^\circ$C. Upon further cooling the growth competes with the formation of Fe-doped Li$_3$N. The b.c.c. structure and good sample quality of \alpha-Fe single crystals were confirmed by X-ray and electron diffraction as well as magnetization measurements and chemical analysis. A nitrogen concentration of 90\,ppm was detected by means of carrier gas hot extraction. Scanning electron microscopy did not reveal any sign of iron nitride precipitates.Comment: 13 pages, 4 figure