160 research outputs found
How to Incorporate Agriculture into Family STEM night
Family STEM Night is an evening for students and their families to come together and complete hands-on science, math, and engineering activities. This event will usually include a variety of interactive projects in different topics and connections to STEM careers. Incorporating agriculture science is a beneficial and productive way to connect people in the community to agriculture. The author will research the importance of agriculture in STEM, create and implement an agriculture-based STEM project to present at Monarch Grove Elementary Schoolâs STEM night in San Luis Obispo, California.
The need for agriculture in STEM education is prevalent. When asking a child the question, âWhat is a farmer?â The clipart image of a man in overalls holding a pitchfork with a smile on his face is what often is described. Introducing children to the idea farmers not only grow food but do so by being engineers, mathematicians, and scientists may open the door into an interest in a field to which they had no prior knowledge.
Connecting content knowledge, STEM knowledge, real-world issues, and problemsolving skills are all interchangeable factors that play a role in both, (Stubbs & Meyers, 2015) Twenty-seven percent of the careers in agriculture, food, and natural resources are STEM (Soergel, 2015). Children are natural learners as they are inquisitive and eager to connect what they are taught to the world around them. Learning by doing comes effortlessly, especially in educational settings where they are given the opportunity to do so. All students have the opportunity to benefit from STEM programs. It allows them to explore greater depths of all subjects while it also encourages teamwork, knowledge application, tech use, problem-solving, and adaption, (Lynch, 2019)
Discovery of Candidate HO Disk Masers in AGN and Estimations of Centripetal Accelerations
Based on spectroscopic signatures, about one-third of known HO maser
sources in active galactic nuclei (AGN) are believed to arise in highly
inclined accretion disks around central engines. These "disk maser candidates"
are of interest primarily because angular structure and rotation curves can be
resolved with interferometers, enabling dynamical study. We identify five new
disk maser candidates in studies with the Green Bank Telescope, bringing the
total number published to 30. We discovered two (NGC1320, NGC17) in a survey of
40 inclined active galaxies (v_{sys}< 20000 kms^{-1}). The remaining three disk
maser candidates were identified in monitoring of known sources: NGC449,
NGC2979, NGC3735. We also confirm a previously marginal case in UGC4203. For
the disk maser candidates reported here, inferred rotation speeds are 130-500
kms^{-1}. Monitoring of three more rapidly rotating candidate disks (CG211,
NGC6264, VV340A) has enabled measurement of likely orbital centripetal
acceleration, and estimation of central masses (2-7x10^7 M_\odot) and mean disk
radii (0.2-0.4pc). Accelerations may ultimately permit estimation of distances
when combined with interferometer data. This is notable because the three AGN
are relatively distant (10000<v_{sys}<15000 kms^{-1}). As signposts of highly
inclined geometries at galactocentric radii of \sim0.1-1pc, disk masers also
provide robust orientation references that allow analysis of (mis)alignment
between AGN and surrounding galactic stellar disks, even without
interferometric mapping. We find no preference among published disk maser
candidates to lie in high-inclination galaxies, providing independent support
for conclusions that central engines and galactic plane orientations are not
correlated. (ABRIDGED)Comment: 7 figures, accepted for publication in ApJ, Dec. 10, 200
The Megamaser Cosmology Project: I. VLBI observations of UGC 3789
The Megamaser Cosmology Project (MCP) seeks to measure the Hubble Constant
(Ho) in order to improve the extragalactic distance scale and constrain the
nature of dark energy. We are searching for sources of water maser emission
from AGN with sub-pc accretion disks, as in NGC 4258, and following up these
discoveries with Very Long Baseline Interferometric (VLBI) imaging and spectral
monitoring. Here we present a VLBI map of the water masers toward UGC 3789, a
galaxy well into the Hubble Flow. We have observed masers moving at rotational
speeds up to 800 km/s at radii as small as 0.08 pc. Our map reveals masers in a
nearly edge-on disk in Keplerian rotation about a 10^7 Msun supermassive black
hole. When combined with centripetal accelerations, obtained by observing
spectral drifts of maser features (to be presented in Paper II), the UGC 3789
masers may provide an accurate determination of Ho, independent of luminosities
and metallicity and extinction corrections.Comment: 18 pages, 3 figures, 4 table
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The ParsecâScale Accretion Disk in NGC 3393
We present a Very Long Baseline Interferometry image of the water maser emission in the nuclear region of NGC 3393. The maser emission has a linear distribution oriented at a position angle of ~â34°, perpendicular to both the kiloparsec-scale radio jet and the axis of the narrow-line region. The position-velocity diagram displays a red-blue asymmetry about the systemic velocity and the estimated dynamical center, and is thus consistent with rotation. Assuming Keplerian rotation in an edge-on disk, we obtain an enclosed mass of ( within 0.36 ± 0.02 pc (1.48 ± 0.06 mas), which corresponds to a mean mass density of . We also report the measurement with the Green Bank Telescope of a velocity drift, a manifestation of centripetal acceleration within the disk, of in the maser feature, which is most likely located along the line of sight to the dynamical center of the system. From the acceleration of this feature, we estimate a disk radius of 0.17 ± 0.02 pc, which is smaller than the inner disk radius (0.36 ± 0.02 pc) of emission that occurs along the midline (i.e., the line of nodes). The emission along the line of sight to the dynamical center evidently occurs much closer to the center than the emission from the disk midline, contrary to the situation in the archetypal maser systems NGC 4258 and NGC 1068. The outer radius of the disk as traced by the masers along the midline is about 1.5 pc.Astronom
Evaluation of global load sharing and shear-lag models to describe mechanical behavior in partially lacerated tendons
The mechanical effect of a partial thickness tear or laceration of a tendon is analytically modeled under various assumptions and results are compared with previous experimental data from porcine flexor tendons. Among several fibril-level models considered, a shear-lag model that incorporates fibrilâmatrix interaction and a fibrilâfibril interaction defined by the contact area of the interposed matrix best matched published data for tendons with shallow cuts (less than 50% of the cross-sectional area). Application of this model to the case of many disrupted fibrils is based on linear superposition and is most successful when more fibrils are incorporated into the model. An equally distributed load sharing model for the fraction of remaining intact fibrils was inadequate in that it overestimates the strength for a cut less than half of the tendon's cross-sectional area. In a broader sense, results imply that shear-lag contributes significantly to the general mechanical behavior of tendons when axial loads are nonuniformly distributed over a cross section, although the predominant hierarchical level and microstructural mediators for this behavior require further inquiry.Peer ReviewedPostprint (published version
Linking the Supermassive Black Hole Growth with the Megamaser Emission
High-resolution observations of the central few 100 pc of the galactic
nuclear environments remain prohibitive for large statistical samples, which
are crucial for tracing the links between central black hole formation, galaxy
formation and AGN activity over cosmic time. With this contribution, we present
novel ways of connecting the physics of black hole accretion with its immediate
environs via a new quantitative evaluation of the degree to which the strength
and spatial configuration of the water maser emission is associated with the
nuclear nebular galactic activity. We discuss possible evolutionary/causal
connections between these two types of emission, together with criteria that
could dramatically enhance our search for mega-maser systems in nearby galactic
centers. These are timely results given the interest in combining
high-resolution observations with extremely large optical telescopes and large
arrays that start to conquer the sub-millimeter window.Comment: 7 pages, 5 figures, to appear in "The Central Kiloparsec in Galactic
Nuclei: Astronomy at High Angular Resolution 2011", open access Journal of
Physics: Conference Series (JPCS), published by IOP Publishin
Probing the Magnetic Field at Sub-Parsec Radii in the Accretion Disk of NGC 4258
We present an analysis of polarimetric observations at 22 GHz of the water
vapor masers in NGC 4258 obtained with the VLA and the GBT. We do not detect
any circular polarization in the spectrum indicative of Zeeman-induced
splitting of the maser lines of water, a non-paramagnetic molecule. We have
improved the 1-sigma upper limit estimate on the toroidal component of the
magnetic field in the circumnuclear disk of NGC 4258 at a radius of 0.2 pc from
300 mG to 90 mG. We have developed a new method for the analysis of spectra
with blended features and derive a 1-sigma upper limit of 30 mG on the radial
component of the magnetic field at a radius of 0.14 pc. Assuming thermal and
magnetic pressure balance, we estimate an upper limit on the mass accretion
rate of ~10^(-3.7) M_sun/yr for a total magnetic field of less than 130 mG. We
discuss the ramifications of our results on current maser models proposed to
explain the observed maser emission structure and the consequences for current
accretion theories. We find from our magnetic field limits that the thin-disk
model and the jet-disk model are better candidates for accounting for the
extremely low-luminosity nature of NGC 4258, than models that include
advection-dominated accretion flows.Comment: 20 pages, including 10 figures and 2 tables. Accepted for publication
in the Astrophysical Journa
Using VLBI to Probe the Orion-KL Outflow on AU Scales
We present the first contemporaneous 43GHz and 86GHz VLBI images of the v=1
J=2-1 and J=1-0 SiO masers in the Orion-KL nebula. Both maser species exhibit
the same general morphology of earlier J=1-0 maser images which appear to trace
the edges of a bi-polar conical outflow. Surprisingly, the J=2-1 masers form
further from the central protostar than the J=1-0 masers, a fact not readily
explained by current SiO maser pumping models. The average magnitude of offsets
between corresponding regions of the two masing transitions is approximately
14% of the total radial extent of the SiO maser emission. This offset indicates
that each transition must trace different physical conditions.Comment: 20 pages, 4 figure
Prevalence of High X-ray Obscuring Columns among AGN that Host HO Masers
Of 104 AGN known to exhibit HO maser emission, X-ray data that enable
estimation of column densities, or lower limits, are available for 42.
Contributing to this, we report analysis of new and archival X-ray data for 8
galaxies and collation of values for three more. Maser emission is indicative
of large columns of cold gas, and in five of the eight new cases, maser spectra
point toward origins in accretion disks viewed close-to edge-on (a.k.a.
"disk-maser" systems). In these, we detect hard continuum and Fe K
emission with equivalent widths on the order of 1 keV, which is consistent with
Compton reflection, fluorescence by cold material, and obscuring columns \ga
10^{24} cm. Reviewing the full sample of 42, 95% exhibit N cm and 60% exhibit N cm. Half of
these are now recognized to be disk masers (up from 13); in this sub-sample,
which is likely to be more homogeneous vis-\'a-vis the origin of maser
emission, 76% exhibit N cm. The probability of a
common parent distribution of columns for disk-masers and other AGN masers is
<3%. Because ground-based surveys of AGN to detect new disk masers are
relatively unbiased with respect to X-ray brightness and comparatively
inexpensive, they may also be efficient guides for the sensitive pointed X-ray
observations required to identify Compton-thick objects outside of shallow
surveys.Comment: 14 pages, 3 tables and 2 figures. Accepted for publication by ApJ
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