Propagation and Ghosts in the Classical Kagome Antiferromagnet

We investigate the classical spin dynamics of the kagome antiferromagnet by combining Monte Carlo and spin dynamics simulations. We show that this model has two distinct low temperature dynamical regimes, both sustaining propagative modes. The expected gauge invariance type of the low energy low temperature out of plane excitations is also evidenced in the non linear regime. A detailed analysis of the excitations allows to identify ghosts in the dynamical structure factor, i.e propagating excitations with a strongly reduced spectral weight. We argue that these dynamical extinction rules are of geometrical origin.Comment: 4+ pages, 4 figures. Accepted for publication in the Physical Review Letter

Quantum interference oscillations of the superparamagnetic blocking in an Fe8 molecular nanomagnet

We show that the dynamic magnetic susceptibility and the superparamagnetic blocking temperature of an Fe8 single molecule magnet oscillate as a function of the magnetic field Hx applied along its hard magnetic axis. These oscillations are associated with quantum interferences, tuned by Hx, between different spin tunneling paths linking two excited magnetic states. The oscillation period is determined by the quantum mixing between the ground S=10 and excited multiplets. These experiments enable us to quantify such mixing. We find that the weight of excited multiplets in the magnetic ground state of Fe8 amounts to approximately 11.6%.Comment: Accepted in Phys. Rev. Let

Magnetic excitations in a new anisotropic Kagom\'{e} antiferromagnet

The Nd-langasite compound contains planes of magnetic Nd3+ ions on a lattice topologically equivalent to a kagom\'{e} net. The magnetic susceptibility does not reveal any signature of long-range ordering down to 2 K but rather a correlated paramagnetism with significant antiferromagnetic interactions between the Nd and a single-ion anisotropy due to crystal field effect. Inelastic neutron scattering on Nd-langasite powder and single-crystal allowed to probe its very peculiar low temperature dynamical magnetic correlations. They present unusual dispersive features and are broadly localized in wave-vector Q revealing a structure factor associated to characteristics short range-correlations between the magnetic atoms. From comparison with theoretical calculations, these results are interpreted as a possible experimental observation of a spin liquid state in an anisotropic kagom\'{e} antiferromagnet.Comment: to appear in Physica

Hierarchical geometric frustration in La3Cu2VO9

The crystallographic structure and magnetic properties of the La3Cu2VO9 were investigated by powder neutron diffraction and magnetization measurements. The compound materializes geometric frustration at two spatial scales, within clusters and between clusters, and at different temperature scales. It is shown by exactly solving the hamiltonian spectrum that collective spins are formed on each clusters at low temperature before inter-clusters coupling operates.Comment: 6 pages, 4 figures. HFM2006 proceeding pape

Current status of waste package designs for the Yucca Mountain Project

Conceptual designs for waste packages containing spent fuel or high-level waste glass have been developed for use in a repository at Yucca Mountain. The basis for these designs reflects the unique nature of the expected service environment associated with disposal in welded tuff in the unsaturated zone. In addition to a set of reference designs, alternative design concepts are being considered that would contain and isolate the waste radionuclides in a more aggressive service environment. Consideration is also being given to the feasibility of a concept known as ``heat tailoring`` that employs the thermal energy released by the wasteforms to enhance and extend the performance of the containers. 5 refs., 3 figs

Attenuation of the herbicide glyphosate along railroad corridors in Alaska

Thesis (M.S.) University of Alaska Fairbanks, 2011Following the application of glyphosate in the formulation of AquaMaster® at two contrasting sub-arctic zones along the railroad corridor in Alaska, attenuation of the herbicide glyphosate was investigated. Study sites were established in continental and coastal zones. Glyphosate soil attenuation was similar to temperate regions during the growing season but exhibited an extended persistence during the winter months. Although glyphosate microbial degradation likely slowed during winter, both sites showed evidence of slight glyphosate degradation during the winter months. The coastal site attenuated more rapidly than the continental site which is presumably due to increased rainfall relative to the continental site. Glyphosate attenuation at the coastal site was likely driven by dispersion while microbial degradation was responsible for the attenuation of glyphosate at the continental site. Movement to subsurface soils (10-25 cm) at low concentrations was observed at both sites with slightly more transport at the coastal site than the continental site. Glyphosate transport to groundwater along railroad corridors was not conclusive. Vegetation cover reduction was reduced at the continental site but could not be determined at the coastal site.1. Introduction -- 1.1. Project scope -- 1.2. Methodology overview -- 2. Glyphosate background -- 2.1. Glyphosate -- 2.2. Properties of glyphosate -- 2.3. Glyphosate in the environment -- 2.3.1. Vegetation of uptake, translocation and metabolism -- 2.3.2. Mode of action -- 2.3.3. Fate in soil -- 2.3.3.1. Sorption -- 2.3.3.1. Movement -- 2.3.4. Degradation and persistence -- 2.3.5. Fate in aquatic environments -- 2.3.6. Atmosphere -- 2.3.7. Glyphosate in cold climates -- 3. Materials and methods -- 3.1. Site descriptions -- 3.1.1. Continental study site description -- 3.1.2. Coastal study site description -- 3.2. Field experiment -- 3.3. Analytical methods -- 3.3.1. GC methodology and analysis -- 3.4. LC methodology and analysis -- 4. Results and discussion -- 4.1. Continental site results and discussion -- 4.1.1. Continental site glyphosate -- 4.1.2. Continental site AMPA -- 4.1.3. Continental site glyphosate mass -- 4.2. Coastal site results and discussion -- 4.2.1. Coastal site glyphosate -- 4.2.2. Coastal stie AMPA -- 4.2.3. LC soil and water results and discussion -- 4.3. Comparison of GC coastal results and continental results -- 4.4. Vegetation efficacy results -- 5. Conclusions -- 5.1. Future research needs -- References -- Appendices

Waste package for a repository located in tuff

The development of waste packages for emplacement in a tuff repository has been proceeding during the past year on a broad front. Experimental work has been focused on determination of important package environment parameters and testing the response of waste forms and package materials to the anticipated environment. Conceptual designs have been selected with alternatives to accommodate present uncertainties in the environment and material performance. Computational capabilities are being adapted to provide analyses of anticipated package performance, and plans are being developed for in-situ testing. The waste package activities have been integrated into the overall NNWSI project to assure timely completion consistent with the statutory and regulatory requirements leading to repository site selection around the end of the decade. 7 references

Plowshare sequential device test

For over a year we have been advocating the development of a hardened or ruggedized version of Diamond which will be suitable for sequential detonation of multiple explosives in one emplacement hole. A Plowshare-sponsored device development test, named `Yacht` is proposed for execution in Area 15 at the Nevada Test Site [NTS] in late September 1972. The test is designed to evaluate the ability of a ruggedized Diamond-type explosive assembly to withstand the effects of an adjacent nuclear detonation in the same emplacement hole and then be sequentially fired. The objectives and experimental plan for this concept is provided

Inhomogeneous magnetism in the doped kagome lattice of LaCuO2.66

The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical resistivity, bulk magnetization and specific heat measurements. For temperatures above ~180 K, the spin and charge properties show an activated behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the results indicate an insulating ground state which may or may not be charge ordered. While the frustrated spins in remaining patches of the original kagome lattice might not be directly detected here, the observation of coexisting non-magnetic sites, free spins and frozen moments reveals an intrinsically inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice rationalize this magnetic state in terms of a heterogeneous distribution of cluster sizes and morphologies near the site-percolation threshold

Kondo Screening and Magnetic Ordering in Frustrated UNi4B

UNi4B exhibits unusual properties and, in particular, a unique antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the low temperature behavior of this compound, we propose that the remaining 1/3 U sites are nonmagnetic due to the Kondo effect. We derive a model in which the coexistence of magnetic and nonmagnetic U sites is the consequence of the competition between frustration of the crystallographic structure and instability of the 5f moments.Comment: 4 pages, 2 figure