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Articles 1 - 16 of 16
Full-Text Articles in Physical Sciences and Mathematics
Absolute Quantification Of Gene Expression In Individual Bacterial Cells Using Two-Photon Fluctuation Microscopy, Matthew L. Ferguson, Dominique Le Coq, Matthieu Jules, Stéphane Aymerich, Nathalie Declerck, Catherine A. Royer
Absolute Quantification Of Gene Expression In Individual Bacterial Cells Using Two-Photon Fluctuation Microscopy, Matthew L. Ferguson, Dominique Le Coq, Matthieu Jules, Stéphane Aymerich, Nathalie Declerck, Catherine A. Royer
Matthew L. Ferguson
Quantification of promoter activity or protein expression in gene regulatory networks is generally achieved via measurement of fluorescent protein (FP) intensity, which is related to the true FP concentration by an unknown scaling factor, thereby limiting analysis and interpretation. Here, using approaches originally developed for eukaryotic cells, we show that two-photon (2p) fluorescence fluctuation microscopy, specifically scanning number and brightness (sN&B) analysis, can be applied to determine the absolute concentrations of diffusing FPs in live bacterial cells. First, we demonstrate the validity of the approach, despite the small size of the bacteria, using the central pixels and spatial averaging. We …
Cardinal Invariants And The Borel Tukey Order, Samuel Coskey
Cardinal Invariants And The Borel Tukey Order, Samuel Coskey
Samuel Coskey
Many proofs of inequalities between cardinal characteristics of the continuum are combinatorial in nature. These arguments can be carried out in any model of set theory, even a model of CH where the inequalities themselves are trivial. Thus, such arguments appear to establish a stronger relationship than a mere inequality. The Borel Tukey order was introduced by Blass in a 1996 article to address just this. Specifically, he observed that the combinatorial information linking two cardinal characteristics is often captured by a pair of Borel maps called a Borel Tukey morphism. The existence of a Borel Tukey morphisms between …
The Impact Of ‘‘No Impact Man’’: Alternative Hedonism As Environmental Appeal, Jen Schneider, Glen Miller
The Impact Of ‘‘No Impact Man’’: Alternative Hedonism As Environmental Appeal, Jen Schneider, Glen Miller
Jen Schneider
As ‘‘No Impact Man,’’ writer Colin Beavan conducted a one-year experiment to determine whether he and his family could reduce their environmental impact to zero while living and working in Manhattan. This article examines the No Impact Man (NIM) experiment both as ‘‘alternative hedonism,’’ a reconceptualization of the ‘‘good life’’ that avoids unduly damaging the natural world, and also as a kind of ‘‘eco-stunt,’’ an attempt to garner significant media coverage about positive environmental behaviors. We use DeLuca’s theorization of the ‘‘image event’’ to analyze the No Impact Man franchise—blog, book, and documentary film—though we modify that theory in order …
Meteorological Conditions At Racetrack Playa, Death Valley National Park: Implications For Rock Production And Transport, Ralph D. Lorenz, Brian K. Jackson, Jason W. Barnes, Joseph N. Spitale, Jani Radebaugh, Kevin H. Baines
Meteorological Conditions At Racetrack Playa, Death Valley National Park: Implications For Rock Production And Transport, Ralph D. Lorenz, Brian K. Jackson, Jason W. Barnes, Joseph N. Spitale, Jani Radebaugh, Kevin H. Baines
Brian Jackson
Three decades of weather records at meteorological stations near Death Valley National Park are analyzed in an attempt to gauge the frequency of conditions that might form and erase the famous trails of wind-blown rocks in the mud of Racetrack Playa. Trail formation requires the playa to be wet, followed by strong winds and/or freezing conditions. Weather records are compared with a limited set of meteorological data that were acquired in situ at the playa over three winters and that indicate freezing on 50, 29, and 15 nights during the winters of 2007/08–09/10, respectively, as well as with the hydrological …
Kepler And Ground-Based Transits Of The Exo-Neptune Hat-P-11b, Drake Deming, Pedro V. Sada, Brian Jackson, Steven W. Peterson, Eric Agol, Heather A. Knutson, Donald E. Jennings, Flynn Haase, Kevin Bays
Kepler And Ground-Based Transits Of The Exo-Neptune Hat-P-11b, Drake Deming, Pedro V. Sada, Brian Jackson, Steven W. Peterson, Eric Agol, Heather A. Knutson, Donald E. Jennings, Flynn Haase, Kevin Bays
Brian Jackson
We analyze 26 archival Kepler transits of the exo-Neptune HAT-P-11b, supplemented by ground-based transits observed in the blue (B band) and near-IR (J band). Both the planet and host star are smaller than previously believed; our analysis yields Rp = 4.31 R⊕ ± 0.06 R ⊕ and Rs = 0.683 R☉ ± 0.009 R☉, both about 3σ smaller than the discovery values. Our ground-based transit data at wavelengths bracketing the Kepler bandpass serve to check the wavelength dependence of stellar limb darkening, and the J-band transit provides a precise and independent constraint on the transit duration. Both the limb darkening …
Self-Assembly On (111)-Oriented Iii-V Surfaces, Paul J. Simmonds, Minjoo Larry Lee
Self-Assembly On (111)-Oriented Iii-V Surfaces, Paul J. Simmonds, Minjoo Larry Lee
Paul J. Simmonds
We demonstrate the self-assembly of tensile strained GaP into three-dimensional dots on GaAs(111)A. Size and areal density of the dislocation-free GaPdots are readily tunable with both substrate temperature and deposition thickness. GaP dot growth obeys island scaling theory, allowing us to predict dot size distributions a priori.
Molecular Beam Epitaxy Approach To The Graphitization Of Gaas(100) Surfaces, Paul J. Simmonds, John Simon, Jerry M. Woodall, Minjoo Larry Lee
Molecular Beam Epitaxy Approach To The Graphitization Of Gaas(100) Surfaces, Paul J. Simmonds, John Simon, Jerry M. Woodall, Minjoo Larry Lee
Paul J. Simmonds
The authors present a method for obtaining graphitized carbon on GaAs(100) surfaces. Carbon-doped GaAs is grown by molecular beam epitaxy before controlled thermal etching within the growth chamber. An AlAs layer beneath the carbon-doped GaAs acts as a thermal etch stop. As the GaAs is etched away, the carbondopant atoms remain on the surface due to their low vapor pressure. The total number of carbon atoms available is precisely controllable by the doping density and thickness of the carbon-doped GaAs layer. Characteristic phonon modes in Raman spectra from the thermally etchedsurfaces show that the residual surfacecarbon atoms form sp2 …
Molecular Beam Epitaxy Of Metamorphic InYGa1−YP Solar Cells On Mixed Anion GaasXP1−X/Gaas Graded Buffers, Stephanie Tomasulo, John Simon, Paul J. Simmonds, Jonathan Biagiotti, Minjoo L. Lee
Molecular Beam Epitaxy Of Metamorphic InYGa1−YP Solar Cells On Mixed Anion GaasXP1−X/Gaas Graded Buffers, Stephanie Tomasulo, John Simon, Paul J. Simmonds, Jonathan Biagiotti, Minjoo L. Lee
Paul J. Simmonds
The authors have grown metamorphic InyGa1−yP on optimized GaAsxP1−x/GaAs graded buffers via solid source molecular beam epitaxy(MBE) for multijunction solar cell applications. In this work, the authors show that a previously developed kinetic growth model can be used to predict the composition of mixed anion GaAsxP1−x alloys on GaAs as a function of substrate temperature and group-V flux. The advantages of using a high growth temperature of 700 °C are then described, including the minimized dependence of composition on small temperature variations, a linear dependence of film composition on …
A Comparison Of Two Open Source Lidar Surface Classification Algorithms, Wade T. Tinkham, Hongyu Huang, Alistair M.S. Smith, Rupesh Shrestha, Michael J. Falkowski, Andrew T. Hudak, Timothy E. Link, Nancy F. Glenn, Danny G. Marks
A Comparison Of Two Open Source Lidar Surface Classification Algorithms, Wade T. Tinkham, Hongyu Huang, Alistair M.S. Smith, Rupesh Shrestha, Michael J. Falkowski, Andrew T. Hudak, Timothy E. Link, Nancy F. Glenn, Danny G. Marks
Nancy Glenn
With the progression of LiDAR (Light Detection and Ranging) towards a mainstream resource management tool, it has become necessary to understand how best to process and analyze the data. While most ground surface identification algorithms remain proprietary and have high purchase costs; a few are openly available, free to use, and are supported by published results. Two of the latter are the multiscale curvature classification and the Boise Center Aerospace Laboratory LiDAR (BCAL) algorithms. This study investigated the accuracy of these two algorithms (and a combination of the two) to create a digital terrain model from a raw LiDAR point …
Making The Human Dimensions Of Sustainable Community Development Visible To Engineers, Juan Lucena, Jen Schneider, Jon A. Leydens
Making The Human Dimensions Of Sustainable Community Development Visible To Engineers, Juan Lucena, Jen Schneider, Jon A. Leydens
Jen Schneider
Recently, engineers – particularly those working on sustainability-related initiatives – have increasingly turned their efforts towards under-served communities. This paper summarises the findings in Engineering and Sustainable Community Development (Juan Lucena et al., 2010) aimed at a diversity of these efforts which are grouped here under the term ‘engineering to help’. These initiatives often exist under names such as community service, humanitarian engineering, and engineers without borders or activities such as the Institution of Civil Engineers' co-sponsored workshop ‘Helping local communities to help themselves’. Although there has been a blossoming of engineering-to-help-related programmes around the world, there is a …
How Do Mathematicians Make Sense Of Definitions?, Laurie O. Cavey, Margaret T. Kinzel, Thomas A. Kinzel, Kathleen L. Rohrig, Sharon B. Walen
How Do Mathematicians Make Sense Of Definitions?, Laurie O. Cavey, Margaret T. Kinzel, Thomas A. Kinzel, Kathleen L. Rohrig, Sharon B. Walen
Laurie O. Cavey
It seems clear that students’ activity while working with definitions differs from that of mathematicians. The constructs of concept definition and concept image have served to support analyses of both mathematicians’ and students’ work with definitions (c.f. Edwards & Ward, 2004; Tall & Vinner, 1981). As part of an ongoing study, we chose to look closely at how mathematicians make sense of definitions in hopes of informing the ways in which we interpret students’ activity and support their understanding of definitions. We conducted interviews with mathematicians in an attempt to reveal their process when making sense of definitions. A striking …
Graphitized Carbon On Gaas(100) Substrates, J. Simon, P. J. Simmonds, J. M. Woodall, M. L. Lee
Graphitized Carbon On Gaas(100) Substrates, J. Simon, P. J. Simmonds, J. M. Woodall, M. L. Lee
Paul J. Simmonds
We report on the formation of graphitized carbon on GaAs(100) surfaces by molecular beam epitaxy. We grew highly carbon-doped GaAs on AlAs, which was then thermally etched in situ leaving behind carbon atoms on the surface. After thermal etching, Raman spectra revealed characteristic phonon modes for sp2-bonded carbon, consistent with the formation of graphitic crystallites. We estimate that the graphitic crystallites are 1.5–3 nm in size and demonstrate that crystallite domain size can be increased through the use of higher etch temperatures.
A Meta-Analysis Of Global Urban Land Expansion, Karen C. Seto, Michail Fragkias, Burak Güneralp, Michael K. Reilly
A Meta-Analysis Of Global Urban Land Expansion, Karen C. Seto, Michail Fragkias, Burak Güneralp, Michael K. Reilly
Michail Fragkias
The conversion of Earth's land surface to urban uses is one of the most irreversible human impacts on the global biosphere. It drives the loss of farmland, affects local climate, fragments habitats, and threatens biodiversity. Here we present a meta-analysis of 326 studies that have used remotely sensed images to map urban land conversion. We report a worldwide observed increase in urban land area of 58,000 km2 from 1970 to 2000. India, China, and Africa have experienced the highest rates of urban land expansion, and the largest change in total urban extent has occurred in North America. Across all regions …
Metamorphic Gaasp Buffers For Growth Of Wide-Bandgap Ingap Solar Cells, J. Simon, S. Tomasulo, P. J. Simmonds, M. Romero, M. L. Lee
Metamorphic Gaasp Buffers For Growth Of Wide-Bandgap Ingap Solar Cells, J. Simon, S. Tomasulo, P. J. Simmonds, M. Romero, M. L. Lee
Paul J. Simmonds
GaAsxP1−x graded buffers were grown via solid source molecular beam epitaxy(MBE) to enable the fabrication of wide-bandgap InyGa1−yP solar cells. Tensile-strained GaAsxP1−x buffers grown on GaAs using unoptimized conditions exhibited asymmetric strain relaxation along with formation of faceted trenches, 100–300 nm deep, running parallel to the [011] direction. We engineered a 6 μm thick grading structure to minimize the faceted trench density and achieve symmetric strain relaxation while maintaining a threading dislocation density of ≤106 cm−2. In comparison, compressively-strained graded GaAsxP1−x buffers on …
Putting Partnership First: A Dialogue Model For Science And Risk Communication, Jen Schneider, Roel Snieder
Putting Partnership First: A Dialogue Model For Science And Risk Communication, Jen Schneider, Roel Snieder
Jen Schneider
In April 2010, the New York Times reported that Vattenfall AB, an energy company owned by the Swedish government, had built one of the first coal-fired power plants designed to capture ~90% of the CO2 it produced, with plans to sequester that CO2 underground in geologic repositories near its plant in Brandenburg, Germany (Voosen, 2010). By most measures, if the plant's operations were proven to be successful, it could have served as a model for other carbon capture and sequestration plants worldwide.
Ice Rafts Not Sails: Floating The Rocks At Racetrack Playa, Ralph D. Lorenz, Brian K. Jackson, Jason W. Barnes, Joe Spitale, John M. Keller
Ice Rafts Not Sails: Floating The Rocks At Racetrack Playa, Ralph D. Lorenz, Brian K. Jackson, Jason W. Barnes, Joe Spitale, John M. Keller
Brian Jackson
We suggest that the existence of many of the rock-carved trails at Racetrack Playa in Death Valley National Park is predominantly due to the effect of arbitrarily weak winds on rocks that are floated off the soft bed by small rafts of ice, as also occurs in arctic tidal beaches to form boulder barricades. These ice cakes need not have a particularly large surface area if the ice is adequately thick—the ice cakes allow the rocks to move by buoyantly reducing the reaction and friction forces at the bed, not by increasing the wind drag. The parameter space of ice …