259 research outputs found

    Rate-Independent Constructs for Chemical Computation

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    This paper presents a collection of computational modules implemented with chemical reactions: an inverter, an incrementer, a decrementer, a copier, a comparator, a multiplier, an exponentiator, a raise-to-a-power operation, and a logarithm in base two. Unlike previous schemes for chemical computation, this method produces designs that are dependent only on coarse rate categories for the reactions (“fast” vs. “slow”). Given such categories, the computation is exact and independent of the specific reaction rates. The designs are validated through stochastic simulations of the chemical kinetics

    Problematikken rundt bruken av non-GAAP mÄltall og tilhÞrende justeringer med utgangspunkt i det amerikanske REIT-selskapet, Ashford Hospitality Trust Inc.

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    Master's thesis in Industrial economicsRapportering av non-GAAP mĂ„ltall har vĂŠrt et mye omdiskutert tema de siste Ă„rene, spesielt i USA. Det foregĂ„r en rekke justeringer av resultatene som gjĂžr det vanskelig Ă„ se den egentlige verdiskapningen pĂ„ lang sikt. LĂžnninger til toppsjefer er derfor ofte astronomiske uten at dette gjenspeiles i kostnadene til selskapet. I denne oppgaven ser man pĂ„ problematikken rundt bruken av non-GAAP mĂ„ltall og tilhĂžrende justeringer, og hvordan dette kan pĂ„virke vĂ„r oppfatning av verdiskapning.  Oppgaven er basert pĂ„ en case-studie av REIT-selskapet Ashford Hospitality Trust Inc., og tar utgangspunkt i non-GAAP mĂ„ltallet “justert FFO”. Oppgaven har som mĂ„l Ă„ bygge forstĂ„else rundt behov, utfordringer og lĂžsninger knyttet til bruken av non-GAAP-mĂ„ltall. Ettersom GAAP-mĂ„ltall ikke alltid er tilstrekkelig for Ă„ beskrive operasjonell ytelse i REIT-industrien, er det et klart behov for non-GAAP mĂ„ltall som “justert FFO”. Studiet har likevel vist at det foreligger flere potensielle utfordringer knyttet til disse. Ashford Trust har hatt en klar Ăžkende trend i bruken av non-GAAP mĂ„ltall og tilhĂžrende justeringer, hvor antall justeringer ble firedoblet i lĂžpet av perioden 2008 til 2016. Man observerte at selskapet over samme periode fremstilte et resultat som var 8,1 prosent hĂžyere enn det burde vĂŠre for Ă„ beskrive faktisk operasjonell ytelse, tilsvarende 112,9millioner.DenstorebrukenavjusteringergjĂžratselskapetistorgradkanta˚keleggeresultateneogfĂžlgeligvilledeinvestorer.KortsiktigkandettefĂžretilataksjekursenfĂžlgerforventningenetiletoptimistiskresultat,ogdetblirvanskeliga˚sedenegentligeverdiskapningenpa˚langsikt.Pa˚denandresidenharAshfordTrustogsa˚generertengevinstpa˚112,9 millioner. Den store bruken av justeringer gjĂžr at selskapet i stor grad kan tĂ„kelegge resultatene og fĂžlgelig villede investorer. Kortsiktig kan dette fĂžre til at aksjekursen fĂžlger forventningene til et optimistisk resultat, og det blir vanskelig Ă„ se den egentlige verdiskapningen pĂ„ lang sikt. PĂ„ den andre siden har Ashford Trust ogsĂ„ generert en gevinst pĂ„ 781,4 millioner gjennom handel med egne aksjer i samme periode. Dette er finansiell verdiskapning som ikke kommer frem i resultatet. Ettersom gevinsten generert fra kapitalallokering er sĂ„ stor i forhold til selskapets “sminking” pĂ„ det operasjonelle resultatet, kan det tenkes at den finansielle verdiskapningen kompenserer for at selskapet fremstiller en hĂžyere operasjonell verdiskapning enn hva som faktisk er tilfellet, gjennom non-GAAP mĂ„ltall.submittedVersio

    Detection of interstate liquids pipeline leaks: Feasibility evaluation

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    The approximately 200,000-mile fuel pipeline system in the US operates at flow rates up to 2.5 {times} 10{sup 6} gallons per hour (GPH). Most commercial technologies only provide on-line leak detection at about 0.3% of flow rate, i.e., about 7,500 GPH or larger. Detection of leaks at about 1 GPH or so is desirable both from a regulatory and leak-prevention standpoint. Brookhaven`s commercially-accepted perfluorocarbon tracer (PFT) technology for underground leak detection of utility industry dielectric fluids at leak rates less than 0.1 GPH, with new enhancements, will be able to cost-effectively detect fuel pipeline system leaks to about 1 GPH--3 orders-of-magnitude better than any on-line system. The magnitude of detected leaks would be calculable as well. Proposed mobile surveys (such as those used periodically in the gas pipeline industry) at about 110 to 120 miles per day would allow such small leaks to be detected at 10-ppb tagging levels (less than $1,500 of PFT for a 48-hour tag at the maximum transport rate) under worst-case meteorological dispersion conditions. Smaller leaks could be detected by proportionately larger tagging concentrations. Leaks would be pinpointed by subsequent conventional barholing and vapor analyses. There are no health nor safety issues associated with the use of the proposed technological approach nor any consequential environmental impacts associated with the proposed magnitudes of PFT tagging

    Observations of marine stratocumulus microphysics and implications for processes controlling droplet spectra: Results from the Marine Stratus/Stratocumulus Experiment

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    Journal of Geophysical Research, Vol. 114, D18210The article of record as published may be located at http://dx.doi.org/10.1029/2008JD011035This research was sponsored by the Atmospheric Science Program within the Office of Biological and Environmental Research of U.S. Department of Energy under contract DE-AC02-98CH10886

    The time evolution of aerosol composition over the Mexico City plateau

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    International audienceThe time evolution of aerosol concentration and chemical composition in a megacity urban plume was determined based on 8 flights of the DOE G-1 aircraft in and downwind of Mexico City during the March 2006 MILAGRO field campaign. A series of selection criteria are imposed to eliminate data points with non-urban emission influences. Biomass burning has urban and non-urban sources that are distinguished on the basis of CH3CN and CO. In order to account for dilution in the urban plume, aerosol concentrations are normalized to CO which is taken as an inert tracer of urban emission, proportional to the emissions of aerosol precursors. Time evolution is determined with respect to photochemical age defined as ?Log10 (NOx/NOy). The geographic distribution of photochemical age and CO is examined, confirming the picture that Mexico City is a source region and that pollutants become more dilute and aged as they are advected towards T1 and T2, surface sites that are located at the fringe of the City and 35 km to the NE, respectively. Organic aerosol (OA) per ppm CO is found to increase 7 fold over the range of photochemical ages studied, corresponding to a change in NOx/NOy from nearly 100% to 10%. In the older samples the nitrate/CO ratio has leveled off suggesting that evaporation and formation of aerosol nitrate are in balance. In contrast, OA/CO increases with age in older samples, indicating that OA is still being formed. The amount of carbon equivalent to the deduced change in OA/CO with age is 56 ppbC per ppm CO. At an aerosol yield of 5% and 8% for low and high yield aromatic compounds, it is estimated from surface hydrocarbon observations that only ~9% of the OA formation can be accounted for. A comparison of OA/CO in Mexico City and the eastern U.S. gives no evidence that aerosol yields are higher in a more polluted environment

    Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

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    During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O<sub>3</sub> and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate. Pollutant layers in the free troposphere (FT) can be a result of emissions to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 °C with dry air descending from the upper atmospheric and moist air having a boundary layer (BL) contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (<i>D</i><sub><i>p</i></sub>>100 nm) gives a linear relation up to a number concentration of ~150 cm<sup>−3</sup>, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that ~25 % of aerosol with <i>D</i><sub><i>p</i></sub>>100 nm are interstitial (not activated). A direct comparison of pre-cloud and in-cloud aerosol yields a higher estimate. Artifacts in the measurement of interstitial aerosol due to droplet shatter and evaporation are discussed. Within each of 102 constant altitude cloud transects, CDNC and interstitial aerosol were anti-correlated. An examination of one cloud as a case study shows that the interstitial aerosol appears to have a background, upon which is superimposed a high frequency signal that contains the anti-correlation. The anti-correlation is a possible source of information on particle activation or evaporation

    Aerosol concentration and size distribution measured below, in, and above cloud from the DOE G-1 during VOCALS-REx

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    During the VOCALS Regional Experiment, the DOE G-1 aircraft was used to sample a varying aerosol environment pertinent to properties of stratocumulus clouds over a longitude band extending 800 km west from the Chilean coast at Arica. Trace gas and aerosol measurements are presented as a function of longitude, altitude, and dew point in this study. Spatial distributions are consistent with an upper atmospheric source for O<sub>3</sub> and South American coastal sources for marine boundary layer (MBL) CO and aerosol, most of which is acidic sulfate. Pollutant layers in the free troposphere (FT) can be a result of emissions to the north in Peru or long range transport from the west. At a given altitude in the FT (up to 3 km), dew point varies by 40 °C with dry air descending from the upper atmospheric and moist air having a boundary layer (BL) contribution. Ascent of BL air to a cold high altitude results in the condensation and precipitation removal of all but a few percent of BL water along with aerosol that served as CCN. Thus, aerosol volume decreases with dew point in the FT. Aerosol size spectra have a bimodal structure in the MBL and an intermediate diameter unimodal distribution in the FT. Comparing cloud droplet number concentration (CDNC) and pre-cloud aerosol (<i>D</i><sub><i>p</i></sub>>100 nm) gives a linear relation up to a number concentration of ~150 cm<sup>−3</sup>, followed by a less than proportional increase in CDNC at higher aerosol number concentration. A number balance between below cloud aerosol and cloud droplets indicates that ~25 % of aerosol with <i>D</i><sub><i>p</i></sub>>100 nm are interstitial (not activated). A direct comparison of pre-cloud and in-cloud aerosol yields a higher estimate. Artifacts in the measurement of interstitial aerosol due to droplet shatter and evaporation are discussed. Within each of 102 constant altitude cloud transects, CDNC and interstitial aerosol were anti-correlated. An examination of one cloud as a case study shows that the interstitial aerosol appears to have a background, upon which is superimposed a high frequency signal that contains the anti-correlation. The anti-correlation is a possible source of information on particle activation or evaporation

    Biochemical Programs and Analog-Digital Mixed Algorithms in the Cell

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    International audienceIn this chapter, we take an IT perspective in seeking to understand how computation is carried out in the cell to maintain itself in its environment, process signals and make the decisions that determine its fate. The continuous nature of many protein interactions leads us to consider mixed analog-digital computation models, for which recent results in the theory of analog computability and complexity establish fundamental links with classical programming. We derive from these results a compiler of behavioral specifications into biochemical reactions, which can be compared to natural circuits acquired through evolution. We illustrate this approach through the example of the mitogen-activated protein kinase (MAPK) signaling module, which has a function of analog-digital converter in the cell, and through the cell cycle control

    Simple approximate analytical solution for non-isothermal single-step transformations: kinetic analysis

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    In this paper, we develop a method for obtaining the approximate solution for the evolution of single-step transformations under non-isothermal conditions. We have applied it to many reaction models and obtained very simple analytical expressions for the shape of the corresponding transformation rate peaks. These analytical solutions represent a significant simplification of the system's description allowing easy curve fitting to experiment. A remarkable property is that the evolutions of the transformed fraction obtained at different heating rates are identical when time is scaled by a time constant. The accuracy achieved with our method is checked against several reaction models and different temperature dependencies of the transformation rate constant. It is shown that its accuracy is closely related with that of the Kissinger method
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