919 research outputs found
Development of a Fast and Detailed Model of Urban-Scale Chemical and Physical Processing
Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/).A reduced form metamodel has been produced to simulate the effects of physical, chemical, and meteorological processing of highly reactive trace species in hypothetical urban areas, which is capable of efficiently simulating the urban concentration, surface deposition, and net mass flux of these species. A polynomial chaos expansion and the probabilistic collocation method have been used for the metamodel, and its coefficients were fit so as to be applicable under a broad range of present-day and future conditions. The inputs upon which this metamodel have been formed are based on a combination of physical properties (average temperature, diurnal temperature range, date, and latitude), anthropogenic properties (patterns and amounts of emissions), and the surrounding environment (background concentrations of certain species).
Probability Distribution Functions (PDFs) of the inputs were used to run a detailed parent chemical and physical model, the Comprehensive Air Quality Model with Extensions (CAMx), thousands of times. Outputs from these runs were used in turn to both determine the coefficients of and test the precision of the metamodel, as compared with the detailed parent model. The deviations between the metamodel and the parent mode for many important species (O3, CO, NOx, and BC) were found to have a weighted RMS error less than 10% in all cases, with many of the specific cases having a weighted RMS error less than 1%. Some of the other important species (VOCs, PAN, OC, and sulfate aerosol) usually have their weighted RMS error less than 10% as well, except for a small number of cases. These cases, in which the highly non-linear nature of the processing is too large for the third order metamodel to give an accurate fit, are explained in terms of the complexity and non-linearity of the physical, chemical, and meteorological processing. In addition, for those species in which good fits have not been obtained, the program has been designed in such a way that values which are not physically realistic are flagged.
Sensitivity tests have been performed, to observe the response of the 16 metamodels (4 different meteorologies and 4 different urban types) to a broad set of potential inputs. These results were compared with observations of ozone, CO, formaldehyde, BC, and PM10 from a few well observed urban areas, and in most of the cases, the output distributions were found to be within ranges of the observations.
Overall, a set of efficient and robust metamodels have been generated which are capable of simulating the effects of various physical, chemical, and meteorological processing, and capable of determining the urban concentrations, mole fractions, and fluxes of species, important to human health and the climate.Federal Agencies and industries that sponsor the MIT Joint Program on the Science and Policy of Global Change
Tree-level electron-photon interactions in graphene
Graphene's low-energy electronic excitations obey a 2+1 dimensional Dirac
Hamiltonian. After extending this Hamiltonian to include interactions with a
quantized electromagnetic field, we calculate the amplitude associated with the
simplest, tree-level Feynman diagram: the vertex connecting a photon with two
electrons. This amplitude leads to analytic expressions for the 3D angular
dependence of photon emission, the photon-mediated electron-hole recombination
rate, and corrections to graphene's opacity and dynamic
conductivity for situations away from thermal equilibrium, as
would occur in a graphene laser. We find that Ohmic dissipation in perfect
graphene can be attributed to spontaneous emission.Comment: 5 pages, 3 figure
Early Glycemic Control in Critically Ill Emergency Department Patients: Pilot Trial
Objective: Glycemic control in the critically ill intensive care unit (ICU) patient has been shown to improve morbidity and mortality. We sought to investigate the effect of early glycemic control in critically ill emergency department (ED) patients in a small pilot trial.Methods: Adult non-trauma, non-pregnant ED patients presenting to a university tertiary referral center and identified as critically ill were eligible for enrollment on a convenience basis. Critical illness was determined upon assignment for ICU admission. Patients were randomized to either ED standard care or glycemic control. Glycemic control involved use of an insulin drip to maintain blood glucose levels between 80-140 mg/dL. Glycemic control continued until ED discharge. Standard patients were managed at ED attending physician discretion. We assessed severity of illness by calculation of APACHE II score. The primary endpoint was in-hospital mortality. Secondary endpoints included vasopressor requirement, hospital length of stay, and mechanical ventilation requirement.Results: Fifty patients were randomized, 24 to the glycemic group and 26 to the standard care cohort. Four of the 24 patients (17%) in the treatment arm did not receive insulin despite protocol requirements. While receiving insulin, three of 24 patients (13%) had an episode of hypoglycemia. By chance, the patients in the treatment group had a trend toward higher acuity by APACHE II scores. Patient mortality and morbidity were similar despite the acuity difference.Conclusion: There was no difference in morbidity and mortality between the two groups. The benefit of glycemic control may be subject to source of illness and to degree of glycemic control, or have no effect. Such questions bear future investigation. [West J Emerg Med. 2010; 11(1):20-23]
Tracing the Orphan Stream to 55 kpc with RR Lyrae Stars
We report positions, velocities and metallicities of 50 ab-type RR Lyrae
(RRab) stars observed in the vicinity of the Orphan stellar stream. Using about
30 RRab stars classified as being likely members of the Orphan stream, we study
the metallicity and the spatial extent of the stream. We find that RRab stars
in the Orphan stream have a wide range of metallicities, from -1.5 dex to -2.7
dex. The average metallicity of the stream is -2.1 dex, identical to the value
obtained by Newberg et al. (2010) using blue horizontal branch stars. We find
that the most distant parts of the stream (40-50 kpc from the Sun) are about
0.3 dex more metal-poor than the closer parts (within ~30 kpc), suggesting a
possible metallicity gradient along the stream's length. We have extended the
previous studies and have mapped the stream up to 55 kpc from the Sun. Even
after a careful search, we did not identify any more distant RRab stars that
could plausibly be members of the Orphan stream. If confirmed with other
tracers, this result would indicate a detection of the end of the leading arm
of the stream. We have compared the distances of Orphan stream RRab stars with
the best-fit orbits obtained by Newberg et al. (2010). We find that model 6 of
Newberg et al. (2010) cannot explain the distances of the most remote Orphan
stream RRab stars, and conclude that the best fit to distances of Orphan stream
RRab stars and to the local circular velocity is provided by potentials where
the total mass of the Galaxy within 60 kpc is M_{60}~2.7x10^{11} Msun, or about
60% of the mass found by previous studies. More extensive modelling that would
consider non-spherical potentials and the possibility of misalignment between
the stream and the orbit, is highly encouraged.Comment: Submitted to ApJ, 15 pages in emulateapj format, three tables in
machine-readable format (download "Source" from "Other formats"
Wearable activity technology and action-planning (WATAAP) to promote physical activity in cancer survivors: Randomised controlled trial protocol
Background/Objective: Colorectal and gynecologic cancer survivors are at cardiovascular risk due to comorbidities and sedentary behaviour, warranting a feasible intervention to increase physical activity. The Health Action Process Approach (HAPA) is a promising theoretical frame-work for health behaviour change, and wearable physical activity trackers offer a novel means of self-monitoring physical activity for cancer survivors.
Method: Sixty-eight survivors of colorectal and gynecologic cancer will be randomised into 12- week intervention and control groups. Intervention group participants will receive: a Fitbit AltaTM to monitor physical activity, HAPA-based group sessions, booklet, and support phone-call. Participants in the control group will only receive the HAPA-based booklet. Physical activity (using accelerometers), blood pressure, BMI, and HAPA constructs will be assessed at baseline, 12-weeks (post-intervention) and 24-weeks (follow-up). Data analysis will use the Group x Time interaction from a General Linear Mixed Model analysis.
Conclusions: Physical activity interventions that are acceptable and have robust theoretical underpinnings show promise for improving the health of cancer survivors
Lady Gaga as (dis)simulacrum of monstrosity
Lady Gaga’s celebrity DNA revolves around the notion of monstrosity, an extensively
researched concept in postmodern cultural studies. The analysis that is offered in this
paper is largely informed by Deleuze and Guattari’s notion of monstrosity, as well as
by their approach to the study of sign-systems that was deployed in A Thousand
Plateaus. By drawing on biographical and archival visual data, with a focus on the
relatively underexplored live show, an elucidation is afforded of what is really monstrous
about Lady Gaga. The main argument put forward is that monstrosity as sign
seeks to appropriate the horizon of unlimited semiosis as radical alterity and openness
to signifying possibilities. In this context it is held that Gaga effectively delimits her
unique semioscape; however, any claims to monstrosity are undercut by the inherent
limits of a representationalist approach in sufficiently engulfing this concept. Gaga is
monstrous for her community insofar as she demands of her fans to project their
semiosic horizon onto her as a simulacrum of infinite semiosis. However, this simulacrum
may only be evinced in a feigned manner as a (dis)simulacrum. The analysis of
imagery from seminal live shows during 2011–2012 shows that Gaga’s presumed
monstrosity is more akin to hyperdifferentiation as simultaneous employment of
heterogeneous and potentially dissonant inter pares cultural representations. The article
concludes with a problematisation of audience effects in the light of Gaga’s adoption of
a schematic and post-representationalist strategy in the event of her strategy’s emulation
by competitive artists
When Do Stars Go BOOM?
The maximum mass of a star that can produce a white dwarf (WD) is an
important astrophysical quantity. One of the best approaches to establishing
this limit is to search for WDs in young star clusters in which only massive
stars have had time to evolve and where the mass of the progenitor can be
established from the cooling time of the WD together with the age of the
cluster. Searches in young Milky Way clusters have not thus far yielded WD
members more massive than about 1.1, well below the Chandrasekhar
mass of , nor progenitors with masses in excess of about
. However, the hunt for potentially massive WDs that escaped their
cluster environs is yielding interesting candidates. To expand the cluster
sample further, we used HST to survey four young and massive star clusters in
the Magellanic Clouds for bright WDs that could have evolved from stars as
massive as 10. We located five potential WD candidates in the
oldest of the four clusters examined, the first extragalactic single WDs thus
far discovered. As these hot WDs are very faint at optical wavelengths, final
confirmation will likely have to await spectroscopy with 30-metre class
telescopes.Comment: 10 pages, 5 figures, accepted to the Astrophysical Journal Letter
Stop the Top Background of the Stop Search
The main background for the supersymmetric stop direct production search
comes from Standard Model ttbar events. For the single-lepton search channel,
we introduce a few kinematic variables to further suppress this background by
focusing on its dileptonic and semileptonic topologies. All are defined to have
end points in the background, but not signal distributions. They can
substantially improve the stop signal significance and mass reach when combined
with traditional kinematic variables such as the total missing transverse
energy. Among them, our variable M^W_T2 has the best overall performance
because it uses all available kinematic information, including the on-shell
mass of both W's. We see 20%-30% improvement on the discovery significance and
estimate that the 8 TeV LHC run with 20 fb-1 of data would be able to reach an
exclusion limit of 650-700 GeV for direct stop production, as long as the stop
decays dominantly to the top quark and a light stable neutralino. Most of the
mass range required for the supersymmetric solution of the naturalness problem
in the standard scenario can be covered.Comment: 16 pages, 5 figure
The SPLASH Survey: A Spectroscopic Analysis of the Metal-Poor, Low-Luminosity M31 dSph Satellite Andromeda X
Andromeda X (And X) is a newly discovered low-luminosity M31 dwarf spheroidal
galaxy (dSph) found by Zucker et al. (2007) in the Sloan Digital Sky Survey
(SDSS - York et al. 2000). In this paper, we present the first spectroscopic
study of individual red giant branch stars in And X, as a part of the SPLASH
Survey (Spectroscopic and Photometric Landscape of Andromeda's Stellar Halo).
Using the Keck II telescope and multiobject DEIMOS spectrograph, we target two
spectroscopic masks over the face of the galaxy and measure radial velocities
for ~100 stars with a median accuracy of sigma_v ~ 3 km/s. The velocity
histogram for this field confirms three populations of stars along the sight
line: foreground Milky Way dwarfs at small negative velocities, M31 halo red
giants over a broad range of velocities, and a very cold velocity ``spike''
consisting of 22 stars belonging to And X with v_rad = -163.8 +/- 1.2 km/s. By
carefully considering both the random and systematic velocity errors of these
stars (e.g., through duplicate star measurements), we derive an intrinsic
velocity dispersion of just sigma_v = 3.9 +/- 1.2 km/s for And X, which for its
size, implies a minimum mass-to-light ratio of M/L =37^{+26}_{-19} assuming the
mass traces the light. Based on the clean sample of member stars, we measure
the median metallicity of And X to be [Fe/H] = -1.93 +/- 0.11, with a slight
radial metallicity gradient. The dispersion in metallicity is large,
sigma([Fe/H]) = 0.48, possibly hinting that the galaxy retained much of its
chemical enrichment products. We discuss the potential for better understanding
the formation and evolution mechanisms for M31's system of dSphs through
(current) kinematic and chemical abundance studies, especially in relation to
the Milky Way sample. (abridged version)Comment: Accepted for Publication in Astrophys. J. 14 pages including 7
figures and 2 tables (journal format
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