Ferromagnetic Film on a Superconducting Substrate

We study the equilibrium domain structure and magnetic flux around a ferromagnetic (FM) film with perpendicular magnetization M_0 on a superconducting (SC) substrate. At 4{\pi}M_0<H_{c1} the SC is in the Meissner state and the equilibrium domain width in the film, l, scales as (l/4{\pi}{\lambda}_{L}) = (l_{N}/4{\pi}{\lambda}_{L})^{2/3} with the domain width on a normal (non-superconducting) substrate, l_{N}/4\pi\lambda_L >> 1. Here \lambda_L is the London penetration length. For 4{\pi}M_0 > H_{c1} and l_{N} in excess of about 35 {\lambda}_{L}, the domains are connected by SC vortices. We argue that pinning of vortices by magnetic domains in FM/SC multilayers can provide high critical currents.Comment: 4 pages, 2 figures, submitted to PR

Amphibian Occupancy and Functional Connectivity of Restored Wetlands in the Missouri River Floodplain

Wetland decline may threaten many taxa including shorebirds, amphibians, and fish. As agencies increase restoration of wetland habitat, monitoring is crucial to inform the process. Permeable skin sensitive to water quality and biphasic life histories requiring both terrestrial and aquatic habitat make amphibians good indicators of wetland health. I modeled amphibian occupancy in restored Missouri River bends to determine habitat characteristics associated with the presence of amphibians. Occupancy modeling acknowledges imperfect detection and allows the inclusion of detection covariates. To assess detection I examined two methods currently used to assess anuran occupancy in wetlands, aural anuran surveys and tadpole dip-netting. I assessed survey and site-specific factors that may influence detection success of anuran species using these two methods and found that water temperature appears to play a role in aural detection of some species during call surveys. Slope impacts detection of tadpoles and may be indicative of a sampling bias. I incorporated the top detection models into my candidate models testing the effect of habitat characteristics on amphibian occupancy. My results indicate that the slope of a wetland is driving occupancy of many species at the research sites. In most cases slope had a negative impact on occupancy. Landscape characteristics, like connectivity of wetlands, facilitate between-patch dispersal and may be just as important to the local persistence of amphibians. I assessed connectivity for anurans of wetlands within a bend and recommend locations for new restorations that can improve connectivity of the bend. I found that average connectivity of a bend may not be the best indicator of functional connectivity. All of the research bends had clusters of wetlands that were highly connected to one another but relatively unconnected to the rest of the complex. I suggest that future site selection should focus on shallow, gently sloping wetlands and that a few well-placed restorations could increase functional connectivity of the complex and improve the resilience of amphibian populations to droughts, floods, and localized disturbances like land-use changes. Advisor: Craig Alle

Amphibian Occupancy and Functional Connectivity of Restored Wetlands in the Missouri River Floodplain

Wetland decline may threaten many taxa including shorebirds, amphibians, and fish. As agencies increase restoration of wetland habitat, monitoring is crucial to inform the process. Permeable skin sensitive to water quality and biphasic life histories requiring both terrestrial and aquatic habitat make amphibians good indicators of wetland health. I modeled amphibian occupancy in restored Missouri River bends to determine habitat characteristics associated with the presence of amphibians. Occupancy modeling acknowledges imperfect detection and allows the inclusion of detection covariates. To assess detection I examined two methods currently used to assess anuran occupancy in wetlands, aural anuran surveys and tadpole dip-netting. I assessed survey and site-specific factors that may influence detection success of anuran species using these two methods and found that water temperature appears to play a role in aural detection of some species during call surveys. Slope impacts detection of tadpoles and may be indicative of a sampling bias. I incorporated the top detection models into my candidate models testing the effect of habitat characteristics on amphibian occupancy. My results indicate that the slope of a wetland is driving occupancy of many species at the research sites. In most cases slope had a negative impact on occupancy. Landscape characteristics, like connectivity of wetlands, facilitate between-patch dispersal and may be just as important to the local persistence of amphibians. I assessed connectivity for anurans of wetlands within a bend and recommend locations for new restorations that can improve connectivity of the bend. I found that average connectivity of a bend may not be the best indicator of functional connectivity. All of the research bends had clusters of wetlands that were highly connected to one another but relatively unconnected to the rest of the complex. I suggest that future site selection should focus on shallow, gently sloping wetlands and that a few well-placed restorations could increase functional connectivity of the complex and improve the resilience of amphibian populations to droughts, floods, and localized disturbances like land-use changes. Advisor: Craig Alle

Microstructure, magneto-transport and magnetic properties of Gd-doped magnetron-sputtered amorphous carbon

The magnetic rare earth element gadolinium (Gd) was doped into thin films of amorphous carbon (hydrogenated \textit{a}-C:H, or hydrogen-free \textit{a}-C) using magnetron co-sputtering. The Gd acted as a magnetic as well as an electrical dopant, resulting in an enormous negative magnetoresistance below a temperature ($T'$). Hydrogen was introduced to control the amorphous carbon bonding structure. High-resolution electron microscopy, ion-beam analysis and Raman spectroscopy were used to characterize the influence of Gd doping on the \textit{a-}Gd$_x$C$_{1-x}$(:H$_y$) film morphology, composition, density and bonding. The films were largely amorphous and homogeneous up to $x$=22.0 at.%. As the Gd doping increased, the $sp^{2}$-bonded carbon atoms evolved from carbon chains to 6-member graphitic rings. Incorporation of H opened up the graphitic rings and stabilized a $sp^{2}$-rich carbon-chain random network. The transport properties not only depended on Gd doping, but were also very sensitive to the $sp^{2}$ ordering. Magnetic properties, such as the spin-glass freezing temperature and susceptibility, scaled with the Gd concentration.Comment: 9 figure

Phonon quarticity induced by changes in phonon-tracked hybridization during lattice expansion and its stabilization of rutile TiO2_2

Although the rutile structure of TiO$_2$ is stable at high temperatures, the conventional quasiharmonic approximation predicts that several acoustic phonons decrease anomalously to zero frequency with thermal expansion, incorrectly predicting a structural collapse at temperatures well below 1000\,K. Inelastic neutron scattering was used to measure the temperature dependence of the phonon density of states (DOS) of rutile TiO$_2$ from 300 to 1373\,K. Surprisingly, these anomalous acoustic phonons were found to increase in frequency with temperature. First-principles calculations showed that with lattice expansion, the potentials for the anomalous acoustic phonons transform from quadratic to quartic, stabilizing the rutile phase at high temperatures. In these modes, the vibrational displacements of adjacent Ti and O atoms cause variations in hybridization of $3d$ electrons of Ti and $2p$ electrons of O atoms. With thermal expansion, the energy variation in this "phonon-tracked hybridization" flattens the bottom of the interatomic potential well between Ti and O atoms, and induces a quarticity in the phonon potential.Comment: 7 pages, 6 figures, supplemental material (3 figures

The Dark Side of Performance Appraisals: A Study of University Librarians Across the U.S.

Performance appraisals are conducted regularly in professional organizations as a means to evaluate employee performance and overall company effectiveness. Employees and employers alike dread appraisal time; appraisals are often time consuming, tedious, and yield minimal positive results. Previous research has shown that employee perceptions of performance appraisals are important to consider when determining their overall effectiveness. In order to build new systems that could be viewed more positively by managers and employees, a deeper examination into the issues of performance appraisals, especially from the manager’s perspective, is needed. Our study looks at data gathered from a survey given to academic library directors, prompting them to evaluate the purposefulness of their current performance appraisal systems. Embedded in this survey is an open-ended response question, asking directors their perceptions of the PA system in their library. Our study seeks to determine if we can use text analytics create a better understanding of manager’s reactions and perceptions of PA systems and formats. We believe that the data gathered from the textual analysis will provide incremental validity into manager perceptions of performance appraisals and further insight into how organizations can improve their own processes

Variation of the density of states in amorphous GdSi at the metal-insulator transition

We performed detailed conductivity and tunneling mesurements on the amorphous, magnetically doped material $\alpha$-Gd$_x$Si$_{1-x}$ (GdSi), which can be driven through the metal-insulator transition by the application of an external magnetic field. Conductivity increases linearly with field near the transition and slightly slower on the metallic side. The tunneling conductance, proportional to the density of states $N(E)$, undergoes a gradual change with increasing field, from insulating, showing a soft gap at low bias, with a slightly weaker than parabolic energy dependence, i.e. $N(E) \sim E^c$, $c \lesssim 2$, towards metallic behavior, with $E^d$, $0.5 \lt d \lt 1$ energy dependence. The density of states at the Fermi level appears to be zero at low fields, as in an insulator, while the sample shows already small, but metal-like conductivity. We suggest a possible explanation to the observed effect.Comment: 6 pages, 6 figure