Resonant X-Ray Scattering on the M-Edge Spectra from Triple-k Structure Phase in U_{0.75}Np_{0.25}O_{2} and UO_{2}

We derive an expression for the scattering amplitude of resonant x-ray scattering under the assumption that the Hamiltonian describing the intermediate state preserves spherical symmetry. On the basis of this expression, we demonstrate that the energy profile of the RXS spectra expected near U and Np M_4 edges from the triple-k antiferromagnetic ordering phase in UO_{2} and U_{0.75}Np_{0.25}O_{2} agree well with those from the experiments. We demonstrate that the spectra in the \sigma-\sigma' and \sigma-\pi' channels exhibit quadrupole and dipole natures, respectively.Comment: 3 pages, 3 figures, to be published in J. Phys. Soc. Jpn. Supp

An x-ray resonant diffraction study of multiferroic DyMn2O5

X-ray resonant scattering has been used to measure the magnetic order of the Dy ions below 40K in multiferroic DyMn$_{2}$O$_{5}$. The magnetic order has a complex behaviour. There are several different ordering wavevectors, both incommensurate and commensurate, as the temperature is varied. In addition a non-magnetic signal at twice the wavevector of one of the commensurate signals is observed, the maximum intensity of which occurs at the same temperature as a local maximum in the ferroelectric polarisation. Some of the results, which bear resemblence to the behaviour of other members of the RMn$_{2}$O$_{5}$ family of multiferroic materials, may be explained by a theory based on so-called acentric spin-density waves.Comment: 8 pages, 8 figure

Groundwater Flow Models of Illinois: Data, Processes, Model Performance, and Key Results

The Illinois State Water Survey (ISWS) has a long history of developing groundwater flow models to simulate water supply and groundwater contamination issues in the state of Illinois. However, past local- and regional-scale models developed by the ISWS have traditionally been project based; thus models are archived when the project is completed and may not be updated for many years. This report presents the first version of the Evolving Network of Illinois Groundwater Monitoring and Modeling Analyses (ENIGMMA), which is the framework of data, procedures, protocols, and scripts that facilitate the development of a single, continuously updated groundwater flow model and other outputs (hydrographs, maps, animations of groundwater potentiometric surfaces). This report focuses on five aspects of ENIGMMA: 1. The archived models and high-resolution datasets that serve as inputs to ENIGMMA 2. The procedures for developing model-ready datasets from these inputs 3. The Illinois Groundwater Flow Model (IGWFM), which serves as the single model that will be continuously updated by ENIGMMA 4. The ISWS Calibration Toolbox, used to facilitate a transient calibration of the IGWFM 5. Animations of groundwater potentiometric surfaces using head-specified models This report is a living document that will be updated periodically. Future updates to this report will focus on additional aspects of ENIGMMA, including the automated development of model-ready inputs and display of model outputs. Updates to this report will also chronicle any additional geologic data added to ENIGMMA, and subsequently, to the Illinois Groundwater Flow Model. Updates will also highlight both local- and regional-scale advancements made with the model, including any key results from these models. The current version of the IGWFM combines and expands on two existing groundwater flow models: 1) the Northeastern Illinois Cambrian-Ordovician Sandstone Aquifer model and 2) the East-Central Illinois Mahomet Aquifer model. In addition, the model incorporates new geologic information developed by the Illinois State Geological Survey in the Middle Illinois Water Supply Planning region. The current model domain covers large portions of Illinois, Wisconsin, Indiana, and Michigan. This large spatial extent is necessary to capture the far-reaching regional head declines in the deep Cambrian-Ordovician sandstone aquifer system, which can extend beyond state boundaries. Depicting some shallow, unconsolidated aquifers also requires a simultaneous simulation of the deep sandstone to account for flow exchange between units. This is because the low-permeable stratigraphic units (aquitards) overlying the sandstone aquifers are absent over large areas of northern Illinois or are locally punctured by wells with long, open intervals. To capture these complex flow pathways, the three-dimensional IGWFM explicitly simulates all geologic materials from the land surface to the impermeable Pre-Cambrian crystalline bedrock. The IGWFM does not currently include a groundwater flow simulation of the southern portion of the state where the deep basin sandstones are highly saline and not used for water supply. Incorporating the shallow aquifers in the southern portion of the state into the IGWFM is a long-term goal. The primary datasets currently incorporated into IGWFM include surface water elevations, annual groundwater withdrawals, well information such as open intervals, geologic 2 surfaces, measured water levels, and aquifer properties inferred from previous modeling studies. These datasets are input at their best available spatial and temporal resolutions, allowing for the development of refined local-scale models. Such local-scale models are essential for simulating groundwater-surface water interactions, well interference, and contaminant transport. Major local-scale models already exist for the Mahomet Aquifer, Kane County, and McHenry County. The IGWFM can address a number of water supply planning questions, particularly the impacts of historic, modern, and future high-capacity groundwater withdrawals on heads and groundwater discharging to surface waters. In addition, where detailed geologic information of the shallow aquifers is available, the IGWFM can also simulate the subsurface migration of point (e.g., volatile organic compounds) and nonpoint (e.g., chloride and nitrate) contaminants.published or submitted for publicationis peer reviewedOpe

Groundwater Availability in Northeastern Illinois from Deep Sandstone Aquifers

published or submitted for publicationis peer reviewedOpe

Groundwater Depletion in Chicago's Southwestern Suburbs

Sandstone aquifers in Illinois have been important sources of water for municipalities and industries since the mid-1800s, and remain important in Will, Kendall, Kane, and McHenry Counties (Figure 1a). Long-term withdrawals have resulted in declining groundwater levels (also known as heads), with the greatest declines of over 900 feet in Will County, locally exceeding 1,100 feet when wells are pumping.published or submitted for publicationis peer reviewedOpe

Resonant magnetic x-ray and neutron diffuse studies of transition metal multilayers

Electron scattering mechanisms within metallic multilayers are affected by both structural and magnetic disorders. Off-specular x-ray scattering has long been used to probe the structural interfaces, and it is only recently that it has been applied to the study of magnetic disorder. We compare the resonant magnetic x-ray scattering with off-specular neutron studies from magnetron-sputtered Co/Cu and Co/Ru multilayers grown at the second antiferromagnetic coupling peak. Both techniques yield similar results for the Cu system, and a simple domain model can be applied to extract the magnetic interface morphological parameters. For the Cu system, the in-plane correlation length is field dependent and is 880+/-20 Å after saturation along the hard axis, but increases to 7000+/-100 Å after saturation along the orthogonal easy axis. Both systems show strong out-of-plane correlations in both the structural and magnetic disorders. In all cases, the out-of-plane correlation length for the structural interfaces is 200-250 Å, but the ratio of the magnetic to structural correlations length is dependent on the magnitude of the exchange coupling and ranges from 0.4 to 1.4.

X-ray Resonant Scattering Study of the Order Parameters in Multiferroic TbMnO3_3

We report on an extensive investigation of the multiferroic compound TbMnO$_3$. Non-resonant x-ray magnetic scattering (NRXMS) revealed a dominant $A$-type domain. The temperature dependence of the intensity and wavevector associated with the incommensurate magnetic order was found to be in good agreement with neutron scattering data. XRS experiments were performed in the vicinity of the Mn $K$ and Tb $L_3$ edges in the high-temperature collinear phase, the intermediate temperature cycloidal/ferroelectric phase, and the low-temperature phase. In the collinear phase resonant $E1-E1$ satellites were found at the Mn $K$ edge associated with $A$-type but also $F$-type peaks. The azimuthal dependence of the $F$-type satellites (and their absence in the NRXMS experiments) indicates that they are most likely non-magnetic in origin. We suggest instead that they may be associated with an induced charge multipole. At the Tb $L_3$ edge resonant $A$- and $F$-type satellites ($E1-E1$) were observed in the collinear phase. These we attribute to a polarisation of the Tb 5$d$ states by the ordering of the Mn sublattice. In the cycloidal/ferroelectric phase a new set of resonant satellites appear corresponding to $C$-type order. These appear at the Tb $L_3$ edge only. In addition to a dominant $E1-E1$ component in the $\sigma-\pi^\prime$ channel, a weaker component is found in the pre-edge with $\sigma-\sigma^\prime$ polarization. Calculations of the XRS were performed using the $FDMNES$ code showing that the unrotated $\sigma-\sigma^\prime$ component of the Tb $L_3$ $C$-type peaks appearing in the ferroelectric phase contains a contribution from a multipole that is odd with respect to both space and time, known in various contexts as the anapole.Comment: Phys. Rev. B (In press

Changing Groundwater Levels in the Cambrian-Ordovician Sandstone Aquifers of Northern Illinois, 1980-2014

published or submitted for publicationis peer reviewedOpe