ALBERT

Description: Author(s): Wayne M. Witzel, Rajib Rahman, and Malcolm S. Carroll We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on 73 Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-... [Phys. Rev. B 85, 205312] Published Fri May 11, 2012

Description: Author(s): Matthew D. Grace, Jason M. Dominy, Wayne M. Witzel, and Malcolm S. Carroll Constructing high-fidelity control fields that are robust to control, system, and/or surrounding environment uncertainties is a crucial objective for quantum information processing. Using the two-state Landau-Zener model for illustrative simulations of a controlled qubit, we generate optimal control... [Phys. Rev. A 85, 052313] Published Fri May 18, 2012

Description: Bacterial and yeast antagonists isolated from fruit surfaces have been effective in controlling various postharvest diseases and several microbial antagonists have been developed into commercial products. Our knowledge of the fruit microbial community with the exception of grapes, apples and some citrus fruit is rudimentary, and the potential of the resident yeasts for biocontrol remains largely unknown. We determined the occurrence of yeasts on plum surfaces during fruit development from the pre-hardening stage until harvest during two years. A total of 16 species from 13 genera were isolated. Species from three genera, basidiomycetes Rhodotorula (29.5%) and Sporidiobolus (24.7%) and the dimorphic ascomycete genus Aureobasidium (24.7%) constituted 78.7% of all isolations and were recovered throughout fruit development while Cryptococcus spp. constituted only 6.2% of the total plum isolates. The yeast community in the final sampling was significantly different from the first three samplings, reflecting a rapidly changing fruit habitat during the maturation of fruit. For example, Hanseniaspora , Pichia , Zygosaccharomyces , and Wickerhamomyces occurred only on the most mature fruit. Screening of the yeasts for antagonistic activity against Monilinia fructicola , a fungus that causes brown rot, revealed a range of biocontrol activities. Several isolates provided complete control of the decay on plums challenged with a pathogen suspension of 10 3 conidia/ mL, and more than 90% of control on fruit inoculated with the pathogen at a concentration 10 times higher. Some of the best antagonists included A . pullulans and R . phylloplana . Populations of both of these antagonists increased rapidly by several orders of magnitude in wounds of plums incubated at 24 ºC and 4 ºC. Our results indicate that plum surfaces harbor several yeast species with excellent potential for use in biological control of brown rot of stone fruits. This article is protected by copyright. All rights reserved.

Description: Author(s): Matthew R. Sears and Wayne M. Saslow [Phys. Rev. B 85, 014404] Published Thu Jan 05, 2012

Description: Author(s): Matthew R. Sears and Wayne M. Saslow Recent spin-Seebeck experiments on thin ferromagnetic films apply a temperature difference Δ T x along the length x and measure a (transverse) voltage difference Δ V y along the width y . The connection between these involves: (1) thermal equilibration between sample and substrate, (2) spin currents alon... [Phys. Rev. B 85, 035446] Published Mon Jan 30, 2012

Description: Author(s): Wayne M. Witzel, Kevin Young, and Sankar Das Sarma We present a cluster expansion method for approximating quantum spin-bath dynamics in terms of a classical Gaussian stochastic process. The cluster expansion produces the two-point correlation function of the approximate classical bath, permitting rapid evaluation of noise-mitigating quantum control... [Phys. Rev. B 90, 115431] Published Thu Sep 25, 2014

Description: Author(s): Tomohiro Taniguchi and Wayne M. Saslow Based on spin-dependent transport theory and thermodynamics, we develop a generalized theory of the Joule heating in the presence of a spin current. Along with the conventional Joule heating consisting of an electric current and electrochemical potential, it is found that the spin current and spin a... [Phys. Rev. B 90, 214407] Published Mon Dec 01, 2014

Description: [1]  Several regions within California have significant air quality issues. Transport of pollutants emitted in one region to another region may add to the impact of local emissions. In this work, Lagrangian particle dispersion model simulations show the amounts of tracers that are transported within and among four regions, Southern California, the San Francisco Bay Area, the Central Valley, and the rest of the state. The simulations cover May and June of 2010, the CalNex experiment period. Tracers of automobile emissions and one type of agricultural emissions are used. Tracer mixing ratios are compared to airborne and ground-based measurements. The age of tracers in each location is also presented. Vertical profiles and diurnal cycles help to clarify the transport process. As is well known, Southern California emissions are transported to the east and affect the desert areas, and Bay Area automobile emissions are an important source of pollutants in the San Joaquin Valley. A novel result is that the Southern California Bight is filled with a mixture of well-aged carbon monoxide tracer from Southern California and the Bay Area. Air over the Bight is also affected by the agricultural emissions represented by the agricultural tracer, dominantly from the Central Valley where its sources are largest. There is no indication of transport from Southern California to the Central Valley. Emissions from the Central Valley do make their way to Southern California, as shown by the agricultural tracer, but automobile emissions from the Valley are insignificant in Southern California.

Description: [1]  The contemporary global carbon cycle is dominated by perturbations from anthropogenic CO 2 emissions. One approach to identify, quantify, and monitor anthropogenic emissions is to focus on intensely emitting urban areas. In this study, we compare the ability of different CO 2 observing systems to constrain anthropogenic flux estimates in the Los Angeles megacity. We consider different observing system configurations based on existing observations and realistic near-term extensions of the current ad hoc network. We use a high-resolution regional model (STILT-WRF) to simulate different observations and observational network designs within and downwind of the Los Angeles basin. A Bayesian inverse method is employed to quantify the relative ability of each network to improve constraints on flux estimates. Ground-based column CO 2 observations provide useful complementary information to surface observations due to lower sensitivity to localized dynamics, but column CO 2 observations from a single site do not appear to provide sensitivity to emissions from the entire LA megacity. Surface observations from remote, down-wind sites contain weak, sporadic urban signals and are complicated by other source/sink impacts, limiting their usefulness for quantifying urban fluxes in LA. We find a network of 8 optimally located in-city surface observation sites provides the minimum sampling required for accurate monitoring of CO 2 emissions in LA, and present a recommended baseline network design. We estimate that this network can distinguish fluxes on 8 week time-scales and 10 km spatial scales to within ~12 g C m -2 d -1 (~10% of average peak fossil CO 2 flux in the LA domain).

Description: [1]  Nitrous oxide (N 2 O) is an important gas for climate and for stratospheric chemistry, with a lifetime exceeding 100 years. Global concentrations have increased steadily since the 18 th century, apparently due to human-associated emissions, principally from the application of nitrogen fertilizers. However, quantitative studies of agricultural emissions at large spatial scales are lacking, inhibited by the difficulty of measuring small enhancements in atmospheric concentration. Here we derive regional emission rates for N 2 O in the agricultural heartland of California, based on analysis of in-situ airborne atmospheric observations collected using a new quantum cascade laser spectrometer. The data were obtained on board the NOAA WP-3 research aircraft during the CalNex (California Research at the Nexus of Air Quality and Climate Change) program in late spring, 2010. We coupled the WRF (Weather Research and Forecasting) model, a meso-scale meteorology model, with the STILT (Stochastic Time-Inverted Lagrangian Transport) model, a Lagrangian particle dispersion model, to link our in-situ airborne observations to surface emissions. We then used a variety of statistical methods to identify source areas and to optimize emission rates. Our results are consistent with the view that fertilizer application is the largest source of N 2 O in the Central Valley. The spatial distribution of surface emissions, based on California land use and activity maps, was very different than indicated in the leading emissions inventory (EDGAR 4.0). Our estimated total emission flux of N 2 O for California in May and June was 3–4 times larger than the annual mean given for the state by EDGAR and other inventories, indicating a strong seasonal variation. We estimated the statewide total annual emissions of N 2 O to be 0.042 ± 0.011 Tg N/yr, roughly equivalent to inventory values if we account for seasonal variations using observations obtained in the Midwestern United States. This state total N 2 O emission is 20.5 Tg CO 2 equivalent (100-year global warming potential (GWP) = 310 CO 2 eq/g N 2 O), accounting for approximately 4% of the state total greenhouse gas emissions.