Nonpoint Source Abatement Costs in the Kentucky River Watershed

A growing share of water pollution in the U.S. can be attributed to nonpoint sources (USEPA 2002). Some of this trend can be attributed to declining point source (PS) emissions as a result of regulation under the Clean Water Act (CWA). However, fertilizer-intensive practices used to improve agricultural productivity over recent decades have also increased nitrate loads and resulted in water quality impairments. Nonpoint source (NPS) pollution from agricultural practices is generally exempt from federal regulation. However, some voluntary programs allow point sources subject to the CWA’s effluent limitations to meet their standards by purchasing offset credits reflecting reductions in NPS discharges to the same waters (USEPA 2004). Such water quality trading (WQT) programs have been implemented in a number of states to reduce pollution abatement costs (Breetz et al 2004). In this setting, NPS supply pollution abatement when they implement best management practices (BMP) that reduce nutrient loads, and the cost of BMPs form a supply curve for credits. WQT programs are supported by the EPA as an important means for efficiently pursuing water quality goals (USEPA 2003a). Among the BMPs available for water quality management, riparian buffer strips have proven effective in mitigating the movement of nutrients and other pollutants into surface waters (Qiu et al 2006). Estimates of riparian buffer costs would be valuable for developing policy related to WQT and other conservation programs. This paper estimates the annual costs of buffer strips in six counties in the Lower Kentucky River Basin, as part of a project evaluating the feasibility of WQT programs in that area.Environmental Economics and Policy,

Naughty or nice? Punishment and the interaction of formal and informal incentives in long-term contractual relationships

The paper develops a model of repeated interaction between a buyer and a seller, which is then tested via laboratory experiments. The model allows for both formal and informal incentives in the contractual relationship between the parties. Formal incentives are explicit, performance-conditioned obligations enforced by third parties, such as a binding bonus paid for meeting an objectively measurable criterion. Informal incentives are non-binding promises to reward good performance. Although they are not enforced by external institutions, parties engaged in long-term interactions have incentives to “keep their words” about these promises and such payments can provide motivation for desirable performance. The current literature posits that these two types of incentives can function either as complements, so that joint use leads to better outcomes than either alone, or as substitutes, so that the availability of formal incentives may actually undermine the effectiveness of informal incentives. This study uses laboratory experiments to provide a rigorous test of hypotheses about the interaction of these incentives. The observed results suggest that the complementarity effect occurs in certain situations, but that the substitution effect does not occur as predicted, possibly because people do not punish transgressions in the manner that the theoretical model assumes.Relational contracts, experimental economics

Interface bonding of a ferromagnetic/semiconductor junction : a photoemission study of Fe/ZnSe(001)

We have probed the interface of a ferromagnetic/semiconductor (FM/SC) heterojunction by a combined high resolution photoemission spectroscopy and x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example of a very low reactivity interface system and it expected to constitute large Tunnel Magnetoresistance devices. We focus on the interface atomic environment, on the microscopic processes of the interface formation and on the iron valence-band. We show that the Fe contact with ZnSe induces a chemical conversion of the ZnSe outermost atomic layers. The main driving force that induces this rearrangement is the requirement for a stable Fe-Se bonding at the interface and a Se monolayer that floats at the Fe growth front. The released Zn atoms are incorporated in substitution in the Fe lattice position. This formation process is independent of the ZnSe surface termination (Zn or Se). The Fe valence-band evolution indicates that the d-states at the Fermi level show up even at submonolayer Fe coverage but that the Fe bulk character is only recovered above 10 monolayers. Indeed, the Fe 1-band states, theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe junctions, are strongly modified at the FM/SC interface.Comment: 23 pages, 5 figures, submitted to Physical review

k-space spin filtering effect in the epitaxial Fe/Au/Fe/GaAs(001) spin-valve

International audienceThe hot-electron magnetotransport of epitaxial Fe/Au/Fe/GaAs(001) spin-valves is investigated by ballistic-electron magnetic microscopy. A magnetocurrent amplitude larger than 500% is observed at room temperature close to the Schottky barrier energy. Remarkably, this magnetocurrent is not significantly affected by the thickness reduction of ferromagnetic films, down to 5 atomic layers of the Fe(001) top electrode. This rather suggests a dominant interfacial spin-filtering effect. Finally, the magnetocurrent is strongly reduced when the effective mass of the semiconductor collector is increased. These observations are consistent with recent theoretical prediction of k-space spin-filtering effect in epitaxial spin-valves attached to a semiconducting lead

Transport property study of MgO-GaAs(001) contacts for spin injection devices

International audienceThe electrical properties of Au/MgO/n-GaAs(001) tunnel structures have been investigated with capacitance-voltage and current-voltage measurements at room temperature with various MgO thicknesses between 0.5 and 6.0nm. For an oxide thickness higher than 2nm and for low bias voltages, the voltage essentially drops across the oxide and the structure progressively enters the high-current mode of operation with increasing reverse bias voltage, the property sought in spin injection devices. In this mode, we demonstrate that a large amount of charge accumulates at the MgO/GaAsinterface in interface traps located in the semiconductor band gap

Induced work function changes at Mg-doped MgO/Ag(001) interfaces: Combined Auger electron diffraction and density functional study

The properties of MgO/Ag(001) ultrathin films with substitutional Mg atoms in the interface metal layer have been investigated by means of Auger electron diffraction experiments, ultraviolet photoemission spectroscopy, and density functional theory (DFT) calculations. Exploiting the layer-by-layer resolution of the MgKL23L23 Auger spectra and using multiple scattering calculations, we first determine the interlayer distances as well as the morphological parameters of the MgO/Ag(001) system with and without Mg atoms incorporated at the interface. We find that the Mg atom incorporation drives a strong distortion of the interface layers and that its impact on the metal/oxide electronic structure is an important reduction of the work function (0.5 eV) related to band-offset variations at the interface. These experimental observations are in very good agreement with our DFT calculations which reproduce the induced lattice distortion and which reveal (through a Bader analysis) that the increase of the interface Mg concentration results in an electron transfer from Mg to Ag atoms of the metallic interface layer. Although the local lattice distortion appears as a consequence of the attractive (repulsive) Coulomb interaction between O2− ions of the MgO interface layer and the nearest positively (negatively) charged Mg (Ag) neighbors of the metallic interface layer, its effect on the work function reduction is only limited. Finally, an analysis of the induced work function changes in terms of charge transfer, rumpling, and electrostatic compression contributions is attempted and reveals that the metal/oxide work function changes induced by interface Mg atoms incorporation are essentially driven by the increase of the electrostatic compression effect

Band bending in Mg-colored and O₂-activated ultrathin MgO(001) films

Ultrathin MgO films grown on Ag(001) have been investigated using X-ray and ultraviolet photoemission spectroscopies for oxide films successively exposed to Mg and O₂ flux. Studying work functions and layer-resolved Auger shifts allows us to keep track of band profiles from the oxide surface to the interface and reveal the charge- transfer mechanisms underlying the controlled creation of Mg-induced surface color centers and the catalytic enhancement of O₂ activation. Our results demonstrate that one can intimately probe the catalytic properties of metal-supported ultrathin oxide films by studying the electronic band alignment at interfaces

Virtual collaboration: A Phenomenological Study of Remote Online Adjuncts Virtual Collaboration Lived Experiences

Online education is rapidly growing in higher education. To stay competitive, many colleges and universities have begun to offer online classes. Some institutions even offer complete degree programs online. This has left colleges needing to hire more part-time remote adjuncts to fill the fluctuating number of available courses. Because remote online adjuncts are susceptible to isolation, the need has arisen to study the benefits and barriers of virtual collaboration. The purpose of this phenomenological qualitative study was to examine the virtual collaboration lived experiences of remote online adjuncts. The study helped unveil the motives and lived experiences of virtual collaboration among online adjuncts. The current research is sparse when narrowed down to the population of remote online adjuncts. Because remote online adjuncts are a specific population of professors, the barriers and benefits to virtual collaboration may be different from faculty who work full-time in a brick and mortar building. Because virtual collaboration among remote online adjuncts is not pervasive in the current literature, the phenomenological approach allowed the searching of patterns across participants. The central question asked: What effective virtual collaboration lived experiences are remote online adjuncts using to influence their teaching strategies to develop as professionals? The interview replies from 10 remote online adjuncts created the significant statements about virtual collaboration. The composite description revealed nine themes about how participants experience virtual collaboration. The study suggests that higher education leaders would be well served to focus their efforts on leadership that will promote virtual collaboration practices. It is advisable that higher education leaders look for ways to provide leadership to connect collaborators, create opportunities for collaboration, and define clear roles for virtual collaboration. Remote online adjuncts may find camaraderie, social connections, an opportunity to participate in scholarship, a chance for self-reflection, and develop a sense of pride through virtual collaboration. Barriers that must be overcome for virtual collaboration included trust, a lack of time, and a feeling of pressure to participate

Studies on diversity and coexistence in an experimental microbial community

Biodiversity and the coexistence of species have puzzled and fascinated biologists since decades and is a hotspot in todays’ natural sciences. Preserving this biodiversity is a great challenge as habitats and environments underlying tremendous changes like climate change and the loss of natural habitats, which are mainly due to anthropogenic influences. The coexistence of numerous species even in homogeneous environments is a stunning feature of natural communities and has been summarized under the term ‘paradox of plankton’. Up to now, there are several mechanisms discussed, which may contribute to local and global diversity of organisms. Several interspecific trade offs have been identified maintaining the coexistence of species like their abilities regarding competition and predator avoidance, their capability to disperse in space and time, and their ability to exploit variable resources. Further, micro-evolutionary dynamics supporting the coexistence of species have been added to our knowledge, and deriving from theoretical deterministic models, non-linear dynamics which describe the temporal fluctuation of abundances of organisms. Whereas competition and predation seem to be clue structural elements within interacting organisms, the intrinsic dynamic behavior – by means of temporal changes in abundance - plays an important role regarding coexistence within a community. The present work sheds light on different factors affecting the coexistence of species using experimental microbial model systems consisting of a bacterivorous ciliate as the predator and two bacteria strains as prey organism. Additionally, another experimental setup consisting of two up to five bacteria species competing for one limiting resource was investigated. Highly controllable chemostat systems were established to exclude extrinsic disturbances. According to theoretical analyses I was able to show - experimentally and theoretically - that phenotypic plasticity of one species within a microbial one-predator-two-prey food web enlarges the range of possible coexistence of all species under different dynamic conditions, compared to a food web without phenotypic plasticity. This was accompanied by non-linear (chaotic) population dynamics within all experimental systems showing phenotypic plasticity. The experiments on the interplay of competition, predation and invasion showed that all aspects have an influence on species coexistence. Under undisturbed controlled conditions all aspects were analyzed in detail and in combination. Populations showed oscillations which were shown by quasi-chaotic attractors in phase space diagrams. Competition experiments with two up to five bacteria species competing for one limiting resource showed that all organisms were able to coexist which was mediated by species oscillations entering a regime of chaos. Besides that fact it was found, that the productivity (biomass) as well as the total cell numbers – under the same nutrition supply – increased by an increasing number of species in the experimental systems. Up to now, the occurrence of non-linear dynamics in well controlled experimental studies has been recognized several times and this phenomenon seemed to be more common in natural systems than generally assumed