218 research outputs found
Reconnaissance Survey of Nitrate Concentrations in Ground Water in Howard and Pike Counties, Arkansas
In recent years, the rapid growth of poultry and hog production in Arkansas has caused concern regarding nitrate contamination of the ground water. In the study area of Pike and Howard Counties, the number of hogs has increased from 3,300 hogs in 1970 to 75,000 hogs in 1990. Poultr¥ production for the area has increased from 38,933,000 per year 1n 1970 to 62,774,000 per year in 1990. As animal production increases, so does the amount of animal waste that must be disposed. Hog production is of particular concern. Typical hog operations store concentrated animal waste in lagoons prior to land application. If the lagoons are improperly constructed and leak, they can contaminate ground water with bacteria and nitrate. Disposal of chicken litter on pastureland is also a significant source of 9round water nitrate. In response to these concerns, a study of n1trate concentrations in rural water wells was conducted for Pike and Howard Counties during wet and dry seasons in 1991. Approximately fifty samples were collected from each county and analyzed for nitrate as well as other chemical parameters. Pike and Howard Counties are divided into two distinct physiographic regions; the Ouachita Mountains and the Gulf CoastalPlain. Comparisons of nitrate concentrations indicates that the Gulf Coastal Plain portion of the study area may be more susceptible to surface contamination than the Ouachita Mountainportion. Average mean nitrate plus nitrite (NO3-N) values for the Gulf Coast portion of the study area was 1.06 mg/L as compared to 0.59 mg/L for the Ouachita Mountains. Also, nitrate data from a 1955 study indicates that the increased animal production in pike and Howard Counties corresponds with increased levels of groundwater nitrate. In 1955 the average mean NO3-N value was 0.26 mg/L (Gulf Coastal Plain area) as compared to 1.06 mg/L in 1991. Wet season average mean NO3-N values for the Gulf Coast region (0.22mg/L) and the Ouachita Mountain region (0.06 mg/L) were higher than dry season NO3-N values (0.16 mg/L and 0.02 mg/L,respectively). Nitrate levels in ground water for pike and Howard Counties were all below the 10 mg/L NO3-N drinking water standard
A Bioinspired Astrocyte-Derived Coating Promotes the In Vitro Proliferation of Human Neural Stem Cells While Maintaining Their Stemness
The repair of neuronal tissue is a challenging process due to the limited proliferative capacity of neurons. Neural stem cells (NSCs) can aid in the regeneration process of neural tissue due to their high proliferation potential and capacity to differentiate into neurons. The therapeutic potential of these cells can only be achieved if sufficient cells are obtained without losing their differentiation potential. Toward this end, an astrocyte-derived coating (HAc) was evaluated as a promising substrate to promote the proliferation of NSCs. Mass spectroscopy and scanning electron microscopy were used to characterize the HAc. The proliferation rate and the expression of stemness and differentiation markers in NSCs cultured on the HAc were evaluated and compared to the responses of these cells to commonly used coating materials including Poly-L-Ornithine (PLO), and a Human Induced Pluripotent Stem Cell (HiPSC)-based coating. The use of the HAc promotes the in vitro cell growth of NSCs. The expression of the stemness markers Sox2 and Nestin, and the differentiation marker DCX in the HAc group was akin to the expression of these markers in the controls. In summary, HAc supported the proliferation of NSCs while maintaining their stemness and neural differentiation potential
A Sample of Very Young Field L Dwarfs and Implications for the Brown Dwarf "Lithium Test" at Early Ages
Using a large sample of optical spectra of late-type dwarfs, we identify a
subset of late-M through L field dwarfs that, because of the presence of
low-gravity features in their spectra, are believed to be unusually young. From
a combined sample of 303 field L dwarfs, we find observationally that
7.6+/-1.6% are younger than 100 Myr. This percentage is in agreement with
theoretical predictions once observing biases are taken into account. We find
that these young L dwarfs tend to fall in the southern hemisphere (Dec < 0 deg)
and may be previously unrecognized, low-mass members of nearby, young
associations like Tucana-Horologium, TW Hydrae, beta Pictoris, and AB Doradus.
We use a homogeneously observed sample of roughly one hundred and fifty
6300-10000 Angstrom spectra of L and T dwarfs taken with the Low-Resolution
Imaging Spectrometer at the W. M. Keck Observatory to examine the strength of
the 6708-A Li I line as a function of spectral type and further corroborate the
trends noted by Kirkpatrick et al. (2000). We use our low-gravity spectra to
investigate the strength of the Li I line as a function of age. The data weakly
suggest that for early- to mid-L dwarfs the line strength reaches a maximum for
a few 100 Myr, whereas for much older (few Gyr) and much younger (<100 Myr) L
dwarfs the line is weaker or undetectable. We show that a weakening of lithium
at lower gravities is predicted by model atmosphere calculations, an effect
partially corroborated by existing observational data. Larger samples
containing L dwarfs of well determined ages are needed to further test this
empirically. If verified, this result would reinforce the caveat first cited in
Kirkpatrick et al. (2006) that the lithium test should be used with caution
when attempting to confirm the substellar nature of the youngest brown dwarfs.Comment: 73 pages with 22 figures; to appear in ApJ (Dec 20, 2008, v689n2
issue
Discoveries from a Near-infrared Proper Motion Survey using Multi-epoch 2MASS Data
We have conducted a 4030-square-deg near-infrared proper motion survey using
multi-epoch data from the Two Micron All-Sky Survey (2MASS). We find 2778
proper motion candidates, 647 of which are not listed in SIMBAD. After
comparison to DSS images, we find that 107 of our proper motion candidates lack
counterparts at B-, R-, and I-bands and are thus 2MASS-only detections. We
present results of spectroscopic follow-up of 188 targets that include the
infrared-only sources along with selected optical-counterpart sources with
faint reduced proper motions or interesting colors. We also establish a set of
near-infrared spectroscopic standards with which to anchor near-infrared
classifications for our objects. Among the discoveries are six young field
brown dwarfs, five "red L" dwarfs, three L-type subdwarfs, twelve M-type
subdwarfs, eight "blue L" dwarfs, and several T dwarfs. We further refine the
definitions of these exotic classes to aid future identification of similar
objects. We examine their kinematics and find that both the "blue L" and "red
L" dwarfs appear to be drawn from a relatively old population. This survey
provides a glimpse of the kinds of research that will be possible through
time-domain infrared projects such as the UKIDSS Large Area Survey, various
VISTA surveys, and WISE, and also through z- or y-band enabled, multi-epoch
surveys such as Pan-STARRS and LSST.Comment: To appear in the September 2010 issue of The Astrophysical Journal,
Supplement Serie
A New Method for the Generation of Realistic Atomistic Models of Siliceous MCM-41
A new method is outlined for constructing realistic models of the mesoporous amorphous silica adsorbent, MCM-41. The procedure uses the melt-quench molecular dynamics technique. Previous methods are either computationally expensive or overly simplified, missing key details necessary for agreement with experimental data. Our approach enables a whole family of models spanning a range of pore widths and wall thicknesses to be efficiently developed and yet sophisticated enough to allow functionalisation of the surface – necessary for modelling systems such as self-assembled monolayers on mesoporous supports (SAMMS), used in nuclear effluent clean-up.
The models were validated in two ways. The first method involved the construction of adsorption isotherms from grand canonical Monte Carlo simulations, which were in line with experimental data. The second method involved computing isosteric heats at zero coverage and Henry law coefficients for small adsorbate molecules. The values obtained for carbon dioxide gave good agreement with experimental values.
We use the new method to explore the effect of increasing the preparation quench rate, pore diameter and wall thickness on low pressure adsorption. Our results show that tailoring a material to have a narrow pore diameter can enhance the physisorption of gas species to MCM-41 at low pressure
A molten salt test loop for component and instrumentation testing
Molten salt is an effective coolant for a wide range of applications, including nuclear reactors, concentrated solar power, and other high temperature industrial heat transfer processes. The technical readiness level of components and instrumentation for high-temperature molten salt applications needs improvement for molten salt to be more widely adopted. A molten salt test loop was designed, built, and commissioned as a test bed to address these issues. The molten salt test loop at Abilene Christian University was built out of 316 stainless steel with a forced flow centrifugal-type pump, and was instrumented for remote operation. A low-temperature molten nitrate salt was used in this system, which was designed to operate at temperatures up to 300 ◦C and flow rates up to 90 liters per minute.
This paper describes the loop design, computational fluid dynamics modeling, construction, and commissioning details. An outline of the data acquisition and control systems is presented. Salt samples were taken before and after introduction into the loop, and melting points were measured both before and after salt circulation. Performance of the system is discussed as well as improvements required for higher temperature loops envisioned for the future
The Society for Immunotherapy of Cancer statement on best practices for multiplex immunohistochemistry (IHC) and immunofluorescence (IF) staining and validation.
OBJECTIVES: The interaction between the immune system and tumor cells is an important feature for the prognosis and treatment of cancer. Multiplex immunohistochemistry (mIHC) and multiplex immunofluorescence (mIF) analyses are emerging technologies that can be used to help quantify immune cell subsets, their functional state, and their spatial arrangement within the tumor microenvironment.
METHODS: The Society for Immunotherapy of Cancer (SITC) convened a task force of pathologists and laboratory leaders from academic centers as well as experts from pharmaceutical and diagnostic companies to develop best practice guidelines for the optimization and validation of mIHC/mIF assays across platforms.
RESULTS: Representative outputs and the advantages and disadvantages of mIHC/mIF approaches, such as multiplexed chromogenic IHC, multiplexed immunohistochemical consecutive staining on single slide, mIF (including multispectral approaches), tissue-based mass spectrometry, and digital spatial profiling are discussed.
CONCLUSIONS: mIHC/mIF technologies are becoming standard tools for biomarker studies and are likely to enter routine clinical practice in the near future. Careful assay optimization and validation will help ensure outputs are robust and comparable across laboratories as well as potentially across mIHC/mIF platforms. Quantitative image analysis of mIHC/mIF output and data management considerations will be addressed in a complementary manuscript from this task force
The impact range for smooth wall–liquid interactions in nanoconfined liquids
Bulk and nanoconfined liquids have initially very different physics; for
instance, nanoconfined liquids show stratification and position-dependent
relaxation processes. A number of similarities between bulk and nanoconfined
liquids have nevertheless been reported in computer simulations during the last
decade. Inspired by these observations, we present results from molecular
dynamics computer simulations of three nanoconfined liquids (i.e.,
single-component Lennard-Jones (LJ) liquid, Kob-Andersen binary LJ mixture, and
an asymmetric dumbbell model) demonstrating also a microscopic similarity
between bulk and nanoconfined liquids. The results show that the interaction
range for the wall-liquid and liquid-liquid interactions of the nanoconfined
liquid are identical to the bulk liquid as long as the liquid remains "Roskilde
simple" in nanoconfinement, i.e., the liquid has strong correlations between
virial and potential energy equilibrium fluctuations in the NVT ensemble.Comment: 8 page
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