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Adsorption of hexavalent and trivalent chromium to a clayey silt soil : batch kinetic and equilibrium studies
Chromium, an element of widespread use, is toxic in some
forms. Improper disposal of waste chromium products has
resulted in contamination of many sites throughout the United
States, including the United Chrome Products Superfund site
in Corvallis, Oregon. A better understanding of chromium
chemistry is needed to facilitate the remediation of these
contaminated sites.
The purpose of this study was to investigate the
characteristics of adsorption of hexavalent and trivalent
chromium (Cr(VI) and Cr(III), respectively) to a clayey silt
soil similar to that found at the United Chrome Products site.
The effects of pH on adsorption rates and magnitudes, and the
effectiveness of selected extractant solutions in removing
adsorbed chromium from soil, were evaluated. Simple
mathematical models were used to describe adsorption kinetics
and equilibrium, and the chemical nature of the adsorption
reactions were postulated.
Cr(VI) adsorption magnitudes and rates increased as pH
decreased. Neither distilled water or groundwater were
effective extractants of adsorbed Cr(VI); an 0.02 molar
orthophosphate solution was a moderately successfull
extractant. Cr(VI) adsorption kinetics were diphasic in
nature, and could be described with an irreversible two-site
adsorption reaction model. Cr(VI) uptake by the soil was
thought to be adsorbed to metallic oxide surfaces rather than
reduced to insoluble Cr(III).
Trivalent chromium (Cr(III)) was most effectively
adsorbed between pH values of four and five. At lower pH
values, Cr(III) adsorption magnitudes decreased proportionally
with hydrogen ion concentration; at higher pH values, the
decrease in Cr(III) adsorption was probably due to
complexation with soluble and colloidal organic matter
released from the soil. EDTA was only moderately effective
in extracting adsorbed Cr(III) from soil
A Search for Water in the Atmosphere of HAT-P-26b Using LDSS-3C
The characterization of a physically-diverse set of transiting exoplanets is
an important and necessary step towards establishing the physical properties
linked to the production of obscuring clouds or hazes. It is those planets with
identifiable spectroscopic features that can most effectively enhance our
understanding of atmospheric chemistry and metallicity. The newly-commissioned
LDSS-3C instrument on Magellan provides enhanced sensitivity and suppressed
fringing in the red optical, thus advancing the search for the spectroscopic
signature of water in exoplanetary atmospheres from the ground. Using data
acquired by LDSS-3C and the Spitzer Space Telescope, we search for evidence of
water vapor in the transmission spectrum of the Neptune-mass planet HAT-P-26b.
Our measured spectrum is best explained by the presence of water vapor, a lack
of potassium, and either a high-metallicity, cloud-free atmosphere or a
solar-metallicity atmosphere with a cloud deck at ~10 mbar. The emergence of
multi-scale-height spectral features in our data suggests that future
observations at higher precision could break this degeneracy and reveal the
planet's atmospheric chemical abundances. We also update HAT-P-26b's transit
ephemeris, t_0 = 2455304.65218(25) BJD_TDB, and orbital period, p =
4.2345023(7) days.Comment: 9 pages, 8 figures, Accepted for publication in Ap
Listening to Students: Voices From the Inner City
What do students in Catholic schools view as important aspects of their unique form of education? They want a safe environment for learning, caring and concerned teachers, high expectations for learning, responsibility and respect in the school community, and a clear sense of how school relates to success in life. This article describes a study which clearly documents student perceptions and values
Detection of Helium in the Atmosphere of the Exo-Neptune HAT-P-11b
The helium absorption triplet at a wavelength of 10,833 \AA\ has been
proposed as a way to probe the escaping atmospheres of exoplanets. Recently
this feature was detected for the first time using Hubble Space Telescope (HST)
WFC3 observations of the hot Jupiter WASP-107b. We use similar HST/WFC3
observations to detect helium in the atmosphere of the hot Neptune HAT-P-11b at
the confidence level. We compare our observations to a grid of 1D
models of hydrodynamic escape to constrain the thermospheric temperatures and
mass loss rate. We find that our data are best fit by models with high mass
loss rates of - g s. Although we do
not detect the planetary wind directly, our data are consistent with the
prediction that HAT-P-11b is experiencing hydrodynamic atmospheric escape.
Nevertheless, the mass loss rate is low enough that the planet has only lost up
to a few percent of its mass over its history, leaving its bulk composition
largely unaffected. This matches the expectation from population statistics,
which indicate that close-in planets with radii greater than 2 R
form and retain H/He-dominated atmospheres. We also confirm the independent
detection of helium in HAT-P-11b obtained with the CARMENES instrument, making
this the first exoplanet with the detection of the same signature of
photoevaporation from both ground- and space-based facilities.Comment: 12 pages, 9 figures, accepted for publication in ApJ
Data from a Public–industry Partnership for Enhancing corn Nitrogen Research
Improving corn (Zeamays L.) N managementis pertinent to economic andenvironmental objectives. However, there are limited comprehensive data sources to develop and test N fertilizer decision aid tools across a wide geographic range of soil and weather scenarios. Therefore, a public-industry partnership was formed to conduct standardized corn N rate response field studies throughout the U.S. Midwest. This research was conducted using a standardized protocol at 49 site-years across eight states over the 2014–2016 growing seasons with many soil, plant, and weather related measurements. This note provides the data (found in supplemental files), outlines the data, summarizes key findings, and highlights the strengths and weakness for those who wish to use this dataset
A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
The water abundance in a planetary atmosphere provides a key constraint on
the planet's primordial origins because water ice is expected to play an
important role in the core accretion model of planet formation. However, the
water content of the Solar System giant planets is not well known because water
is sequestered in clouds deep in their atmospheres. By contrast, short-period
exoplanets have such high temperatures that their atmospheres have water in the
gas phase, making it possible to measure the water abundance for these objects.
We present a precise determination of the water abundance in the atmosphere of
the 2 short-period exoplanet WASP-43b based on thermal
emission and transmission spectroscopy measurements obtained with the Hubble
Space Telescope. We find the water content is consistent with the value
expected in a solar composition gas at planetary temperatures (0.4-3.5x solar
at 1 confidence). The metallicity of WASP-43b's atmosphere suggested
by this result extends the trend observed in the Solar System of lower metal
enrichment for higher planet masses.Comment: Accepted to ApJL; this version contains three supplemental figures
that are not included in the published paper. See also our companion paper
"Thermal structure of an exoplanet atmosphere from phase-resolved emission
spectroscopy" by Stevenson et a
Duality Cascade in Brane Inflation
We show that brane inflation is very sensitive to tiny sharp features in
extra dimensions, including those in the potential and in the warp factor. This
can show up as observational signatures in the power spectrum and/or
non-Gaussianities of the cosmic microwave background radiation (CMBR). One
general example of such sharp features is a succession of small steps in a
warped throat, caused by Seiberg duality cascade using gauge/gravity duality.
We study the cosmological observational consequences of these steps in brane
inflation. Since the steps come in a series, the prediction of other steps and
their properties can be tested by future data and analysis. It is also possible
that the steps are too close to be resolved in the power spectrum, in which
case they may show up only in the non-Gaussianity of the CMB temperature
fluctuations and/or EE polarization. We study two cases. In the slow-roll
scenario where steps appear in the inflaton potential, the sensitivity of brane
inflation to the height and width of the steps is increased by several orders
of magnitude comparing to that in previously studied large field models. In the
IR DBI scenario where steps appear in the warp factor, we find that the
glitches in the power spectrum caused by these sharp features are generally
small or even unobservable, but associated distinctive non-Gaussianity can be
large. Together with its large negative running of the power spectrum index,
this scenario clearly illustrates how rich and different a brane inflationary
scenario can be when compared to generic slow-roll inflation. Such distinctive
stringy features may provide a powerful probe of superstring theory.Comment: Corrections in Eq.(5.47), Eq (5.48), Eq(5.49) and Fig
DBI Inflation using a One-Parameter Family of Throat Geometries
We demonstrate the possibility of examining cosmological signatures in the
DBI inflation setup using the BGMPZ solution, a one-parameter family of
geometries for the warped throat which interpolate between the Maldacena-Nunez
and Klebanov-Strassler solutions. The warp factor is determined numerically and
subsequently used to calculate cosmological observables including the scalar
and tensor spectral indices, for a sample point in the parameter space. As one
moves away from the KS solution for the throat the warp factor is qualitatively
different, which leads to a significant change for the observables, but also
generically increases the non-Gaussianity of the models. We argue that the
different models can potentially be differentiated by current and future
experiments.Comment: 17 pages, 10 figures; v2: section 4 expanded, references added; v3:
typos fixe
The Antarctic Submillimeter Telescope and Remote Observatory (AST/RO)
AST/RO, a 1.7 m diameter telescope for astronomy and aeronomy studies at
wavelengths between 200 and 2000 microns, was installed at the South Pole
during the 1994-1995 Austral summer. The telescope operates continuously
through the Austral winter, and is being used primarily for spectroscopic
studies of neutral atomic carbon and carbon monoxide in the interstellar medium
of the Milky Way and the Magellanic Clouds. The South Pole environment is
unique among observatory sites for unusually low wind speeds, low absolute
humidity, and the consistent clarity of the submillimeter sky. Four heterodyne
receivers, an array receiver, three acousto-optical spectrometers, and an array
spectrometer are installed. A Fabry-Perot spectrometer using a bolometric array
and a Terahertz receiver are in development. Telescope pointing, focus, and
calibration methods as well as the unique working environment and logistical
requirements of the South Pole are described.Comment: 57 pages, 15 figures. Submitted to PAS
Reconstructing Single Field Inflationary Actions From CMBR Data
This paper describes a general program for deriving the action of single
field inflation models with nonstandard kinetic energy terms using CMBR power
spectrum data. This method assumes that an action depends on a set of
undetermined functions, each of which is a function of either the inflaton wave
function or its time derivative. The scalar, tensor and non-gaussianity of the
curvature perturbation spectrum are used to derive a set of reconstruction
equations whose solution set can specify up to three of the undetermined
functions. The method is then used to find the undetermined functions in
various types of actions assuming power law type scalar and tensor spectra. In
actions that contain only two unknown functions, the third reconstruction
equation implies a consistency relation between the non-gaussianty, sound speed
and slow roll parameters. In particular we focus on reconstructing a
generalized DBI action with an unknown potential and warp factor. We find that
for realistic scalar and tensor spectra, the reconstructed warp factor and
potential are very similar to the theoretically derived result. Furthermore,
physical consistency of the reconstructed warp factor and potential imposes
strict constraints on the scalar and tensor spectral indices.Comment: 33 pages, 3 figures: v3 - References adde
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