"Is There a Wage Payoff to Innovative Work Practices?"

During the 1980s, wage inequality increased dramatically and the American economy lost many high wage, low- to medium-skill jobs, which had provided middle class incomes to less skilled workers. Increasingly, less skilled workers seemed restricted to low wage jobs lacking union or other institutional protections. Although "good" jobs for less skilled workers are unlikely to return in their previous form, a number of sociologists, economists, and industrial relations scholars have suggested that a new paradigm of work, often called "high performance," is emerging, which offers such workers more skilled jobs and higher wages. Using a unique national data set we find little evidence that high performance work systems are associated with higher wages.

Superconductor transition temperatures study

Compounds having beta tungsten structure exist as solid solutions over composition range of several percent. However, for most of these compounds, relationship between composition and superconducting transition temperature is not known

Mind the Gap: Experimental Tests to Improve Efficacy of Fladry for Nonlethal Management of Coyotes

Coyotes (Canis latrans) are the top predator of livestock in the contiguous United States. Developing more effective nonlethal tools to prevent coyote depredation will facilitate coexistence between livestock producers and coyotes. Fladry is a nonlethal deterrent designed to defend livestock by creating a visual barrier to wolves (C. lupus). Fladry may also be effective with coyotes, but large gap spacing between flags may reduce its efficacy. To address this issue, we performed 2 experiments on captive coyotes using fladry modified to reduce gap spacing at the U.S. Department of Agriculture, Predator Research Facility in Millville, Utah, USA, during 2015–2016 and 2017–2018. In 2015–2016, we tested 2 styles for attaching flags (top‐knot and shower‐curtain) to the rope‐line that reduce gaps by preventing coiling of individual flags. In 2017–2018, we tested the efficacy of gap spacing (27.9 cm vs. 45.7 cm) between flags for preventing coyote crossings. For both tests, we compared the time until coyotes crossed the fladry between treatment types. We found no differences in time to crossing between the 2 attachment designs. In our second experiment, fladry with smaller gaps between flags had greater efficacy of preventing coyote crossings than did fladry with larger gaps. Our results also indicated that for each additional minute coyotes spent interacting with fladry overall (i.e., increased persistent behavior), survival of the barrier decreased. These results suggest that persistent coyotes may overcome neophobia more rapidly than coyotes that do not exhibit persistent behaviors. Furthermore, use of top‐knot fladry and coyote‐width spacing will increase protection of livestock from coyotes

Absence of Dipole Transitions in Vortices of Type II Superconductors

The response of a single vortex to a time dependent field is examined microscopically and an equation of motion for vortex motion at non-zero frequencies is derived. Of interest are frequencies near $\Delta^{2}/E_{F}$, where $\Delta$ is the bulk energy gap and $E_{F}$ is the fermi energy. The low temperature, clean, extreme type II limit and maintaining of equilibrium with the lattice are assumed. A simplification occurs for large planar mass anisotropy. Thus the results may be pertinent to materials such as $NbSe_2$ and high temperature superconductors. The expected dipole transition between core states is hidden because of the self consistent nature of the vortex potential. Instead the vortex itself moves and has a resonance at the frequency of the transition.Comment: 12 pages, no figure

Depinning transition in type-II superconductors

The surface impedance Z(f) of conventional isotropic materials has been carefully measured for frequencies f ranging from 1 kHz to 3 MHz, allowing a detailed investigation of the depinning transition. Our results exhibit the irrelevance of classical ideas to the dynamics of vortex pinning. We propose a new picture, where the linear ac response is entirely governed by disordered boundary conditions of a rough surface, whereas in the bulk vortices respond freely. The universal law for Z(f) thus predicted is in remarkable agreement with experiment, and tentatively applies to microwave data in YBaCuO films.Comment: 4 pages, 4 figures, 14 reference

Composite vortex model of the electrodynamics of high-TcT_c superconductor

We propose a phenomenological model of vortex dynamics in which the vortex is taken as a composite object made of two components: the vortex current which is massless and driven by the Lorentz force, and the vortex core which is massive and driven by the Magnus force. By combining the characteristics of the Gittleman-Rosenblum model (Phys. Rev. Lett. {\bf 16}, 734 (1966)) and Hsu's theory of vortex dynamics (Physica {\bf C 213},305 (1993)), the model provides a good description of recent far infrared measurements of the magneto-conductivity tensor of superconducting YBa$_2$Cu$_3$O$_{7-\delta }$ films from 5 cm$^{-1}$ to 200 cm$^{-1}$.Comment: LaTex file (12 pages) + 3 Postscript figures, uuencoded. More information on this paper, please check http://www.wam.umd.edu/~lihn/newmodel

The influence of past and present climate on the biogeography of modern mammal diversity

Within most terrestrial groups of animals, including mammals, species richness varies along two axes of environmental variation, representing energy availability and plant productivity. This relationship has led to a search for mechanistic links between climate and diversity. Explanations have traditionally focused on single mechanisms, such as variation in environmental carrying capacity or evolutionary rates. Consensus, though, has proved difficult to achieve and there is growing appreciation that geographical patterns of species richness are a product of many interacting factors including biogeographic history and biological traits. Here, we review some current hypotheses on the causes of gradients in mammal richness and range sizes since the two quantities are intimately linked. We then present novel analyses using recent datasets to explore the structure of the environment–richness relationship for mammals. Specifically, we consider the impact of glaciation on present day mammalian diversity gradients. We conclude that not only are multiple processes important in structuring diversity gradients, but also that different processes predominate in different places

Measurement of the Far Infrared Magneto-Conductivity Tensor of Superconducting YBa2_2Cu3_3O7−δ_{7-\delta } Thin Films

We report measurements of the far infrared transmission of superconducting YBa$_2$Cu$_3$O$_{7-\delta }$ thin films from 5 cm$^{-1}$ to 200 cm$^{-1}$ in fields up to 14$T$. A Kramers-Kronig analysis of the magneto-transmission spectrum yields the magneto-conductivity tensor. The result shows that the magneto-conductivity of YBa$_2$Cu$_3$O$_{7-\delta }$ is dominated by three terms: a London term, a low frequency Lorentzian ($\omega _1\approx$ 3 cm$^{-1}$) of width $\Gamma _1=$ 10 cm$^{-1}$ and a finite frequency Lorentzian of width $\Gamma _2=$ 17 cm$^{-1}$ at $\omega _2=$ 24 cm$^{-1}$ in the hole cyclotron resonance active mode of circular polarization.\\Comment: Revised LaTex file (12 pages) + 4 Postscript figures, uuencoded. In response to referees' comments, we refined the paper a lot; we encourage you to download this revised versio

Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers

Recently, it has been shown that magnetic tunnel junctions with thin MgO tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR) values at room temperature1, 2. However, the physics of spin dependent tunneling through MgO barriers is only beginning to be unravelled. Using planar magnetic tunnel junctions in which ultra-thin layers of magnetic metals are deposited in the middle of a MgO tunnel barrier here we demonstrate that the TMR is strongly modified when these layers are discontinuous and composed of small pancake shaped nanodots. At low temperatures, in the Coulomb blockade regime, for layers less than ~1 nm thick, the conductance of the junction is increased at low bias consistent with Kondo assisted tunneling. In the same regime we observe a suppression of the TMR. For slightly thicker layers, and correspondingly larger nanodots, the TMR is enhanced at low bias, consistent with co-tunneling.Comment: Nano Letters (in press