ESR measurements of phosphorus dimers in isotopically enriched 28Si silicon

Dopants in silicon have been studied for many decades using optical and electron spin resonance (ESR) spectroscopy. Recently, new features have been observed in the spectra of dopants in isotopically enriched 28Si since the reduced inhomogeneous linewidth in this material improves spectral resolution. With this in mind, we measured ESR on exchange coupled phosphorus dimers in 28Si and report two results. First, a new fine structure is observed in the ESR spectrum arising from state mixing by the hyperfine coupling to the 31P nuclei, which is enhanced when the exchange energy is comparable to the Zeeman energy. This fine structure enables us to spectroscopically address two separate dimer sub-ensembles, the first with exchange (J) coupling ranging from 2 to 7 GHz and the second with J ranging from 6 to 60 GHz. Next, the average spin relaxation times, T1 and T2 of both dimer sub-ensembles were measured using pulsed ESR at 0.35 T. Both T1 and T2 for transitions between triplet states of the dimers were found to be identical to the relaxation times of isolated phosphorus donors in 28Si, with T2 = 4 ms at 1.7 K limited by spectral diffusion due to dipolar interactions with neighboring donor electron spins. This result, consistent with theoretical predictions, implies that an exchange coupling of 2 - 60 GHz does not limit the dimer T1 and T2 in bulk Si at the 10 ms timescale.Comment: 24 pages, 9 figure

MODELING TIMBER SUPPLY, FUEL-WOOD, AND ATMOSPHERIC CARBON MITIGATION

There is general agreement that global warming is occurring and that the main contributor to this probably is the buildup of green house gases, GHG, in the atmosphere. Two main contributors are the utilization of fossil fuels and the deforestation of many regions of the world. This paper examines a number of current issues related to mitigating the global warming problem through forestry. We use discrete time optimal control to model a simplified carbon cycle. The burning of fossil fuels increases atmospheric carbon while the burning of fuel-wood along with its forest source maintain an atmospheric carbon level. The standing timber in the forests is a carbon sink, as are wood buildings and structures, and fossil fuel in the ground. Through time the buildings and structures decay and release carbon to the atmosphere. We also present a numerical example to help illustrate the characteristics of the model. The conclusions are that the forest sector can have a significant impact.Environmental Economics and Policy,

Anisotropic Stark Effect and Electric-Field Noise Suppression for Phosphorus Donor Qubits in Silicon

We report the use of novel, capacitively terminated coplanar waveguide (CPW) resonators to measure the quadratic Stark shift of phosphorus donor qubits in Si. We confirm that valley repopulation leads to an anisotropic spin-orbit Stark shift depending on electric and magnetic field orientations relative to the Si crystal. By measuring the linear Stark effect, we estimate the effective electric field due to strain in our samples. We show that in the presence of this strain, electric-field sources of decoherence can be non-negligible. Using our measured values for the Stark shift, we predict magnetic fields for which the spin-orbit Stark effect cancels the hyperfine Stark effect, suppressing decoherence from electric-field noise. We discuss the limitations of these noise-suppression points due to random distributions of strain and propose a method for overcoming them

Mercury in the environment

Problems in assessing mercury concentrations in environmental materials are discussed. Data for situations involving air, water, rocks, soils, sediments, sludges, fossil fuels, plants, animals, foods, and man are drawn together and briefly evaluated. Details are provided regarding the toxicity of mercury along with tentative standards and guidelines for mercury in air, drinking water, and food

VALUING WILDLIFE MANAGEMENT: A UTAH DEER HERD

Managers of public wildlife resources generally are concerned with enhancing the quality of recreation by increasing wildlife through habitat manipulation. However, current recreation valuation studies have focused upon variables that are inappropriate for use in these management decisions. The economic criterion for these decisions should be the value of a change in the stock of the wildlife population compared to its cost. An estimate of such a value was made for the Oak Creek deer herd in Utah, using a household production function approach in an optimal control framework. The value of an additional deer in the herd was estimated to be approximately $40.00.Resource /Energy Economics and Policy,

Do you pass it on? An examination of the consequences of perceived cyber incivility

Purpose: The emerging literature on computer-mediated communication at the study lacks depth in terms of elucidating the consequences of the effects of incivility on employees. This study aims to compare face-to-face incivility with incivility encountered via e-mail on both task performance and performance evaluation. Design/methodology/approach: In two experimental studies, the authors test whether exposure to incivility via e-mail reduces individual task performance beyond that of face-to-face incivility and weather exposure to that incivility results in lower performance evaluations for third-parties. Findings: The authors show that being exposed to cyber incivility does decrease performance on a subsequent task. The authors also find that exposure to rudeness, both face-to-face and via e-mail, is contagious and results in lower performance evaluation scores for an uninvolved third party. Originality/value: This research comprises an empirically grounded study of incivility in the context of e-mail at study, highlights distinctions between it and face-to-face rudeness and reveals the potential risks that cyber incivility poses for employees