635 research outputs found
Multi Sector Planning Tools for Trajectory-Based Operations
This paper discusses a suite of multi sector planning tools for trajectory-based operations that were developed and evaluated in the Airspace Operations Laboratory (AOL) at the NASA Ames Research Center. The toolset included tools for traffic load and complexity assessment as well as trajectory planning and coordination. The situation assessment tools included an integrated suite of interactive traffic displays, load tables, load graphs, and dynamic aircraft filters. The planning toolset allowed for single and multi aircraft trajectory planning and data communication-based coordination of trajectories between operators. Also newly introduced was a real-time computation of sector complexity into the toolset that operators could use in lieu of aircraft count to better estimate and manage sector workload, especially in situations with convective weather. The tools were used during a joint NASA/FAA multi sector planner simulation in the AOL in 2009 that had multiple objectives with the assessment of the effectiveness of the tools being one of them. Current air traffic control operators who were experienced as area supervisors and traffic management coordinators used the tools throughout the simulation and provided their usefulness and usability ratings in post simulation questionnaires. This paper presents these subjective assessments as well as the actual usage data that was collected during the simulation. The toolset was rated very useful and usable overall. Many elements received high scores by the operators and were used frequently and successfully. Other functions were not used at all, but various requests for new functions and capabilities were received that could be added to the toolset
Environmental assessment of humic acid coated magnetic materials used as catalyst in photo-fenton processes
Persistent organic pollutants have been increasingly detected in natural waters, and this represents a real challenge to the quality of this resource. To remove these species, advanced treatment technologies are required. Among these technologies, Fenton-like and photo-Fenton-like processes have been investigated for the removal of pollutants from water. Delicate aspects of photo-Fenton processes are that light-driven processes are energy intensive and require a fair amount of chemical inputs, which strongly affects their overall environmental burdens. At present, aside from determining the efficiency of the processes to remove pollutants of a particular technology, it becomes fundamental to assess also the environmental sustainability of the overall process. In this work, the methodology of the life cycle assessment (LCA) was applied to identify the hotspots of using magnetite particles covered with humic acid (Fe3O4/HA) as a heterogeneous photo-Fenton catalyst for water remediation. The sustainability of the overall process was considered, and a comparative LCA study was performed between H2O2 and persulfate activation at different pH. The addition of humic substances to the particles allows the effectiveness of the catalyst to improve without increasing the environmental impacts; these processes are strongly correlated with energy consumption and therefore with the efficiency of the process. For this reason, working at acidic pH allows us to contain the impacts
Effects of various meteorological conditions and spatial emissionresolutions on the ozone concentration and ROG/NO<sub>x</sub> limitationin the Milan area (I)
The three-dimensional photochemical model UAM-V is used to investigate the effects of various meteorological conditions and of the coarseness of emission inventories on the ozone concentration and ROG/NO<sub>x</sub> limitation of the ozone production in the Po Basin in the northern part of Italy. As a base case, the high ozone episode with up to 200ppb on 13 May 1998 was modelled and previously thoroughly evaluated with measurements gained during a large field experiment. Systematic variations in meteorology are applied to mixing height, air temperature, specific humidity and wind speed. Three coarser emission inventories are obtained by resampling from 3x3km<sup>2</sup> up to 54x54km<sup>2</sup> emission grids. The model results show that changes in meteorological input files strongly influence ozone in this area. For instance, temperature changes peak ozone by 10.1ppb/°C and the ozone concentrations in Milan by 2.8ppb/°C. The net ozone formation in northern Italy is more strongly temperature than humidity dependent, while the humidity is very important for the ROG/NO<sub>x</sub> limitation of the ozone production. For all meteorological changes (e.g. doubling the mixing height), the modelled peak ozone remains ROG limited. A strong change towards NO<sub>x</sub> sensitivity in the ROG limited areas is only found if much coarser emission inventories were applied. Increasing ROG limited areas with increasing wind speed are found, because the ROG limited ozone chemistry induced by point sources is spread over a larger area. Simulations without point sources tend to increase the NO<sub>x</sub> limited areas
The UV Continuum of Quasars: Models and SDSS Spectral Slopes
We measure long (2200-4000 ang) and short (1450-2200 ang) wavelength spectral
slopes \alpha (F_\nu proportional to \nu^\alpha) for quasar spectra from the
Sloan Digital Sky Survey. The long and short wavelength slopes are computed
from 3646 and 2706 quasars with redshifts in the z=0.76-1.26 and z=1.67-2.07
ranges, respectively. We calculate mean slopes after binning the data by
monochromatic luminosity at 2200 ang and virial mass estimates based on
measurements of the MgII line width and 3000 ang continuum luminosity. We find
little evidence for mass dependent variations in the mean slopes, but a
significant luminosity dependent trend in the near UV spectral slopes is
observed with larger (bluer) slopes at higher luminosities. The far UV slopes
show no clear variation with luminosity and are generally lower (redder) than
the near UV slopes at comparable luminosities, suggesting a slightly concave
quasar continuum shape. We compare these results with Monte Carlo distributions
of slopes computed from models of thin accretion disks, accounting for
uncertainties in the mass estimates. The model slopes produce mass dependent
trends which are larger than observed, though this conclusion is sensitive to
the assumed uncertainties in the mass estimates. The model slopes are also
generally bluer than observed, and we argue that reddening by dust intrinsic to
the source or host galaxy may account for much of the discrepancy.Comment: To be published in ApJ, 18 pages, 10 figure
Self-Lensing Models of the LMC
All of the proposed explanations for the microlensing events observed towards
the LMC have difficulties. One of these proposed explanations, LMC
self-lensing, which invokes ordinary LMC stars as the long sought-after lenses,
has recently gained considerable popularity as a possible solution to the
microlensing conundrum. In this paper, we carefully examine the set of LMC
self-lensing models. In particular, we review the pertinent observations made
of the LMC, and show how these observations place limits on such self-lensing
models. We find that, given current observational constraints, no purely LMC
disk models are capable of producing optical depths as large as that reported
in the MACHO collaboration 2-year analysis. Besides pure disk, we also consider
alternate geometries, and present a framework which encompasses the previous
studies of LMC self-lensing. We discuss which model parameters need to be
pushed in order for such models to succeed. For example, like previous workers,
we find that an LMC halo geometry may be able to explain the observed events.
However, since all known LMC tracer stellar populations exhibit disk-like
kinematics, such models will have difficulty being reconciled with
observations. For SMC self-lensing, we find predicted optical depths differing
from previous results, but more than sufficient to explain all observed SMC
microlensing. In contrast, for the LMC we find a self-lensing optical depth
contribution between 0.47e-8 and 7.84e-8, with 2.44e-8 being the value for the
set of LMC parameters most consistent with current observations.Comment: 20 pages, Latex, 14 figures, submitted to Ap
Evidence for TP-AGB stars in high redshift galaxies, and their effect on deriving stellar population parameters
We explore the effects of stellar population models on estimating star
formation histories, ages and masses of high redshift galaxies. The focus is on
the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) phase of stellar
evolution, whose treatment is a source of major discrepancy among different
evolutionary population synthesis. In particular, besides the models usually
adopted in the literature, we use models (by Maraston 2005), in which the
contribution of the TP-AGB phase is observationally calibrated and is the
dominant source of near-IR energy for stellar populations in the age range 0.2
to 2 Gyr. We use a sample of high-z galaxies in the HUDF, with spectroscopic
redshifts, and Spitzer IRAC and MIPS photometry from GOODS. We find that the
TP-AGB phase plays a key role in the interpretation of Spitzer data for high-z
galaxies, when the rest-frame near-IR is sampled. When fitting without dust
reddening, the models with the empirically-calibrated TP-AGB phase always
reproduce better the observed spectral energy distributions (SEDs). Allowing
for dust reddening improves the fits with literature models in some cases. In
both cases, the results from Maraston models imply younger ages by factors up
to 6 and lower stellar masses (by ~60 % on average). The observed strengths of
the MgUV spectral feature compare better to the predicted ones in the case of
the Maraston models, implying a better overall consistency of SED fitting.
Finally, we find that photometric redshifts improve significantly using these
models on the SEDs extending over the IRAC bands. This work provides the first
direct evidence of TP-AGB stars in the primeval Universe.Comment: 14 pages, 10 figures, 3 tables, submitted to the Astrophysical
Journa
A Quantitative Comparison of SMC, LMC, and Milky Way UV to NIR Extinction Curves
We present an exhaustive, quantitative comparison of all of the known
extinction curves in the Small and Large Magellanic Clouds (SMC and LMC) with
our understanding of the general behavior of Milky Way extinction curves. The
R_V dependent CCM relationship and the sample of extinction curves used to
derive this relationship is used to describe the general behavior of Milky Way
extinction curves. The ultraviolet portion of the SMC and LMC extinction curves
are derived from archival IUE data, except for one new SMC extinction curve
which was measured using HST/STIS observations. The optical extinction curves
are derived from new (for the SMC) and literature UBVRI photometry (for the
LMC). The near-infrared extinction curves are calculated mainly from 2MASS
photometry supplemented with DENIS and new JHK photometry. For each extinction
curve, we give R_V = A(V)/E(B-V) and N(HI) values which probe the same dust
column as the extinction curve. We compare the properties of the SMC and LMC
extinction curves with the CCM relationship three different ways: each curve by
itself, the behavior of extinction at different wavelengths with R_V, and
behavior of the extinction curve FM fit parameters with R_V. As has been found
previously, we find that a small number of LMC extinction curves are consistent
with the CCM relationship, but majority of the LMC and all of the SMC curves do
not follow the CCM relationship. For the first time, we find that the CCM
relationship seems to form a bound on the properties of all of the LMC and SMC
extinction curves. This result strengthens the picture of dust extinction
curves exhibit a continuum of properties between those found in the Milky Way
and the SMC Bar. (abridged)Comment: 18 pages, 10 figures, ApJ in pres
Large-Scale Gravitational Instability and Star Formation in the Large Magellanic Cloud
Large-scale star formation in disk galaxies is hypothesized to be driven by
global gravitational instability. The observed gas surface density is commonly
used to compute the strength of gravitational instability, but according to
this criterion star formation often appears to occur in gravitationally stable
regions. One possible reason is that the stellar contribution to the
instability has been neglected. We have examined the gravitational instability
of the Large Magellanic Cloud (LMC) considering the gas alone, and considering
the combination of collisional gas and collisionless stars. We compare the
gravitationally unstable regions with the on-going star formation revealed by
Spitzer observations of young stellar objects. Although only 62% of the massive
young stellar object candidates are in regions where the gas alone is unstable,
some 85% lie in regions unstable due to the combination of gas and stars. The
combined stability analysis better describes where star formation occurs. In
agreement with other observations and numerical models, a small fraction of the
star formation occurs in regions with gravitational stability parameter Q > 1.
We further measure the dependence of the star formation timescale on the
strength of gravitational instability, and quantitatively compare it to the
exponential dependence expected from numerical simulations.Comment: Accepted for publication in ApJ, 10 pages, 5 figure
Exploratory Study of the X-Ray Properties of Quasars With Intrinsic Narrow Absorption Lines
We have used archival Chandra and XMM-Newton observations of quasars hosting
intrinsic narrow UV absorption lines (intrinsic NALs) to carry out an
exploratory survey of their X-ray properties. Our sample consists of three
intrinsic-NAL quasars and one "mini-BAL" quasar, plus four quasars without
intrinsic absorption lines for comparison. These were drawn in a systematic
manner from an optical/UV-selected sample. The X-ray properties of
intrinsic-NAL quasars are indistinguishable from those of "normal" quasars. We
do not find any excess absorption in quasars with intrinsic NALs, with upper
limits of a few times 10^22 cm^-2. We compare the X-ray and UV properties of
our sample quasars by plotting the equivalent width and blueshift velocity of
the intrinsic NALs and the X-ray spectral index against the "optical-to-X-ray"
slope, alpha-ox. When BAL quasars and other AGNs with intrinsic NALs are
included, the plots suggest that intrinsic-NAL quasars form an extension of the
BAL sequences and tend to bridge the gap between BAL and "normal" quasars.
Observations of larger samples of intrinsic-NAL quasars are needed to verify
these conclusions. We also test two competing scenarios for the location of the
NAL gas in an accretion-disk wind. Our results strongly support a location of
the NAL gas at high latitudes above the disk, closer to the disk axis than the
dense BAL wind. We detect excess X-ray absorption only in Q0014+8118, which
does not host intrinsic NALs. The absorbing medium very likely corresponds to
an intervening system at z=1.1, which also produces strong absorption lines in
the rest-frame UV spectrum of this quasar. In the appendix we discuss the
connection between UV and X-ray attenuation and its effect on alpha-ox.Comment: Accepted by the Astrophysical Journa
The Development of a New Questionnaire to Measure the Burden of Immunoglobulin Treatment in Patients with Primary Immunodeficiencies: The IgBoT-35.
Purpose: To describe the development and psychometric testing of a new questionnaire to measure the burden of immunoglobulin treatment (Ig) from the perspective of patients with primary immunodeficiencies (PID). Patients and Methods: An online, cross-sectional survey was administered to PID patients across 10 countries (nine European and Canada) who were receiving either intravenous (IVIg) or subcutaneous (SCIg) immunoglobulin therapy. The range and distribution of the responses (ie, levels of missing data, floor and ceiling effects), exploratory factor analysis (using factor loadings of 0.4 or greater) and measures of internal consistency reliability (ie, Cronbach's alpha coefficient, inter-item and item-total correlations) were used to identify the domain and item pool. Results: In total, 472 patients completed the questionnaire, of which 395 were included in the analysis (32% underwent IVIg and 67% underwent SCIg). The final instrument contained 34 items across eight domains of treatment burden (time, organisation and planning, leisure and social, interpersonal relationships, employment and education, travel, consequences of treatment and emotional) and an additional Ig treatment burden global question at the end of the measure. All the scales achieved good internal reliability (Cronbach's alpha coefficient ranged from 0.70 to 0.85) and, with the exception of one item exceeded the minimum threshold of 0.35 for item-total correlations. Treatment burden was lower than anticipated across the different treatment routes and countries, although overall was more burdensome for patients undergoing IVIg compared to SCIg treatment. Conclusion: The IgBoT-35 appears to be a reliable, patient-generated questionnaire and may help to identify more individualised and preferred therapies for the PID patient when used in clinical practice. A new survey with a sample of US patients is currently being undertaken to further establish its validity and conceptual model. The overall Ig burden of treatment scores appeared to be low. PID patient preferences are important to guide treatment decisions and ensuring patients receive the right treatment at the right time
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