44 research outputs found
Overcoming Student Resistance to a Teaching Innovation
This mixed-methods study investigated student perceptions of an innovative educational tool and the instructor strategies that helped change initial student resistance into acceptance and engagement. The educational tool in this study is Calibrated Peer Review (CPR)™, a web-based program that uses writing as a learning and assessment tool. Evaluations of CPR were analyzed from students in a general chemistry course over seven semesters involving 1515 students. Analysis revealed reasons for students’ like or dislike of CPR and how the instructor modified implementation to provide students a more positive experience. Analysis of student perceptions suggests that successful implementation of new tools requires attention to potential sources of student resistance at the outset as well as active listening and response to student concerns
How Do You Get Student Buy-In to A Wonderful (to You) Teaching Innovation?
One difficulty in adopting new classroom tools is persuading students to accept an educational technique out of their comfort zone. Our study investigated student perceptions when Calibrated Peer Review (CPR)™, a web-based program that uses writing for learning and assessing, was introduced into a general chemistry college classroom, and the strategies that helped convert initial intense opposition into acceptance and engagement. We will share the mistakes made, the reasons for students\u27 like or dislike of CPR, the 4 year path taken to understand the issues and modify its implementation for a more positive classroom experience, and why the instructor persisted in the face of resistance. Our findings can be generalized easily to the introduction of any new teaching tool. The audience will have opportunities to pair/share with neighbors about their good, bad and ugly experiences with a teaching innovation and two easy statistical data-handling methods will be explained
The Quasar / Galaxy Pair PKS 1327-206 / ESO 1327-2041: Absorption Associated with a Recent Galaxy Merger
We present HST/WFPC2 broadband and ground-based Halpha images, H I 21-cm
emission maps, and low-resolution optical spectra of the nearby galaxy ESO
1327-2041, which is located 38 arcsec (14 kpc in projection) west of the quasar
PKS 1327-206. Our HST images reveal that ESO 1327-2041 has a complex optical
morphology, including an extended spiral arm that was previously classified as
a polar ring. Our optical spectra show Halpha emission from several H II
regions in this arm located ~5 arcsec from the quasar position (~2 kpc in
projection) and our ground-based Halpha images reveal the presence of several
additional H II regions in an inclined disk near the galaxy's center.
Absorption associated with ESO 1327-2041 is found in H I 21-cm, optical, and
near-UV spectra of PKS 1327-206. We find two absorption components at cz = 5255
and 5510 km/s in the H I 21-cm absorption spectrum, which match the velocities
of previously discovered metal-line components. We attribute the 5510 km/s
absorber to disk gas in the extended spiral arm and the 5255 km/s absorber to
high-velocity gas that has been tidally stripped from the disk of ESO
1327-2041. The complexity of the galaxy/absorber relationships for these very
nearby H I 21-cm absorbers suggests that the standard view of high redshift
damped Lyman-alpha absorbers is oversimplified in many cases.Comment: Replaced with accepted version; 16 page
Gamma-Rays and the Far-Infrared-Radio Continuum Correlation Reveal a Powerful Galactic Centre Wind
We consider the thermal and non-thermal emission from the inner 200 pc of the
Galaxy. The radiation from this almost star-burst-like region is ultimately
driven dominantly by on-going massive star formation. We show that this
region's radio continuum (RC) emission is in relative deficit with respect to
the expectation afforded by the Far- infrared-Radio Continuum Correlation
(FRC). Likewise we show that the region's gamma-ray emission falls short of
that expected given its star formation and resultant supernova rates. These
facts are compellingly explained by positing that a powerful (400-1200 km/s)
wind is launched from the region. This wind probably plays a number of
important roles including advecting positrons into the Galactic bulge thus
explaining the observed ~kpc extension of the 511 keV positron annihilation
signal around the GC. We also show that the large-scale GC magnetic field falls
in the range ~100-300 microG and that - in the time they remain in the region -
GC cosmic rays do not penetrate into the region's densest molecular material.Comment: Version accepted for publication in MNRAS Letters. Discussion
extended and references adde
Cosmic Origins Spectrograph and FUSE Observations of T ~ 10^5 K Gas In A Nearby Galaxy Filament
We present a detection of a broad Ly-alpha absorber (BLA) with a matching O
VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high
S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The
Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) =
33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by
FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well
aligned with the broader HI component. The different line widths of the BLA and
OVI suggest a temperature of T = 1.4 x 10^5 K in the absorber. The observed
line strength ratios and line widths favor an ionization scenario in which both
ion-electron collisions and UV photons contribute to the ionization in the gas.
Such a model requires a low-metallicity of -1.7 dex, ionization parameter of
log U ~ -1.4, a large total hydrogen column density of N(H) ~ 4 x 10^19 cm^-2,
and a path length of 400 kpc. The line of sight to Mrk 290 intercepts at the
redshift of the absorber, a megaparsec scale filamentary structure extending
over 20 deg in the sky, with several luminous galaxies distributed within 1.5
Mpc projected distance from the absorber. The collisionally ionized gas in this
absorber is likely tracing a shock-heated gaseous structure, consistent with a
few different scenarios for the origin, including an over-dense region of the
WHIM in the galaxy filament or highly ionized gas in the extended halo of one
of the galaxies in the filament. In general, BLAs with metals provide an
efficient means to study T ~ 10^5 - 10^6 K gas in galaxy halos and in the
intergalactic medium. A substantial fraction of the baryons "missing" from the
present universe is predicted to be in such environments in the form of highly
ionized plasma.Comment: Astrophysical Journal Accepte
A Kennicutt-Schmidt Law for Intervening Absorption Line Systems
We argue that most strong intervening metal absorption line systems, where
the rest equivalent width of the MgII 2796A line is >0.5A, are interstellar
material in, and outflowing from, star-forming disks. We show that a version of
the Kennicutt-Schmidt law is readily obtained if the MgII equivalent widths are
interpreted as kinematic broadening from absorbing gas in outflowing winds
originating from star-forming galaxies. Taking a phenomenological approach and
using a set of observational constraints available for star-forming galaxies,
we are able to account for the density distribution of strong MgII absorbers
over cosmic time. The association of intervening material with star-forming
disks naturally explains the metallicity and dust content of strong MgII
systems as well as their high HI column densities, and does not require the
advection of metals from compact star-forming regions into the galaxy halos to
account for the observations. We find that galaxies with a broad range of
luminosities can give rise to absorption of a given rest-equivalent width, and
discuss possible observational strategies to better quantify true
galaxy-absorber associations and further test our model. We show that the
redshift evolution in the density of absorbers closely tracks the star
formation history of the universe and that strong intervening systems can be
used to directly probe the physics of both bright and faint galaxies over a
broad redshift range. By identifying strong intervening systems with galaxy
disks and quantifying a version of the Kennicutt-Schmidt law that applies to
them, a new probe of the interstellar medium is found which provides
complementary information to that obtained through emission studies of
galaxies. Implications of our results for galaxy feedback and enrichment of the
intergalactic medium are discussed. [abridged]Comment: 23 pages, 15 figure
Non-Thermal Insights on Mass and Energy Flows Through the Galactic Centre and into the Fermi Bubbles
We construct a simple model of the star-formation- (and resultant supernova-)
driven mass and energy flows through the inner ~200 pc (in diameter) of the
Galaxy. Our modelling is constrained, in particular, by the non-thermal radio
continuum and {\gamma}-ray signals detected from the region. The modelling
points to a current star-formation rate of 0.04 - 0.12 M\msun/year at 2{\sigma}
confidence within the region with best-fit value in the range 0.08 - 0.12
M\msun/year which - if sustained over 10 Gyr - would fill out the ~ 10^9 M\msun
stellar population of the nuclear bulge. Mass is being accreted on to the
Galactic centre (GC) region at a rate ~0.3M\msun/year. The region's
star-formation activity drives an outflow of plasma, cosmic rays, and
entrained, cooler gas. Neither the plasma nor the entrained gas reaches the
gravitational escape speed, however, and all this material fountains back on to
the inner Galaxy. The system we model can naturally account for the
recently-observed ~> 10^6 'halo' of molecular gas surrounding the Central
Molecular Zone out to 100-200 pc heights. The injection of cooler,
high-metallicity material into the Galactic halo above the GC may catalyse the
subsequent cooling and condensation of hot plasma out of this region and
explain the presence of relatively pristine, nuclear-unprocessed gas in the GC.
The plasma outflow from the GC reaches a height of a few kpc and is
compellingly related to the recently-discovered Fermi Bubbles. Our modelling
demonstrates that ~ 10^9 M\msun of hot gas is processed through the GC over 10
Gyr. We speculate that the continual star-formation in the GC over the age of
the Milky Way has kept the SMBH in a quiescent state thus preventing it from
significantly heating the coronal gas, allowing for the continual accretion of
gas on to the disk and the sustenance of star formation on much wider scales in
the Galaxy [abridged].Comment: 30 pages, 35 figures. Accepted for publication in MNRAS (20/04/2012).
Minor textual revision
Environmental geochemistry of radioactive contamination.
This report attempts to describe the geochemical foundations of the behavior of radionuclides in the environment. The information is obtained and applied in three interacting spheres of inquiry and analysis: (1) experimental studies and theoretical calculations, (2) field studies of contaminated and natural analog sites and (3) model predictions of radionuclide behavior in remediation and waste disposal. Analyses of the risks from radioactive contamination require estimation of the rates of release and dispersion of the radionuclides through potential exposure pathways. These processes are controlled by solubility, speciation, sorption, and colloidal transport, which are strong functions of the compositions of the groundwater and geomedia as well as the atomic structure of the radionuclides. The chemistry of the fission products is relatively simple compared to the actinides. Because of their relatively short half-lives, fission products account for a large fraction of the radioactivity in nuclear waste for the first several hundred years but do not represent a long-term hazard in the environment. The chemistry of the longer-lived actinides is complex; however, some trends in their behavior can be described. Actinide elements of a given oxidation state have either similar or systematically varying chemical properties due to similarities in ionic size, coordination number, valence, and electron structure. In dilute aqueous systems at neutral to basic pH, the dominant actinide species are hydroxy- and carbonato-complexes, and the solubility-limiting solid phases are commonly oxides, hydroxides or carbonates. In general, actinide sorption will decrease in the presence of ligands that complex with the radionuclide; sorption of the (IV) species of actinides (Np, Pu, U) is generally greater than of the (V) species. The geochemistry of key radionuclides in three different environments is described in this report. These include: (1) low ionic strength reducing waters from crystalline rocks at nuclear waste research sites in Sweden; (2) oxic water from the J-13 well at Yucca Mountain, Nevada, the site of a proposed repository for high level nuclear waste (HLW) in tuffaceous rocks; and (3) reference brines associated with the Waste Isolation Pilot Plant (WIPP). The transport behaviors of radionuclides associated with the Chernobyl reactor accident and the Oklo Natural Reactor are described. These examples span wide temporal and spatial scales and include the rapid geochemical and physical processes important to nuclear reactor accidents or industrial discharges as well as the slower processes important to the geologic disposal of nuclear waste. Application of geochemical information to remediating or assessing the risk posed by radioactive contamination is the final subject of this report. After radioactive source terms have been removed, large volumes of soil and water with low but potentially hazardous levels of contamination may remain. For poorly-sorbing radionuclides, capture of contaminated water and removal of radionuclides may be possible using permeable reactive barriers and bioremediation. For strongly sorbing radionuclides, contaminant plumes will move very slowly. Through a combination of monitoring, regulations and modeling, it may be possible to have confidence that they will not be a hazard to current or future populations. Abstraction of the hydrogeochemical properties of real systems into simple models is required for probabilistic risk assessment. Simplifications in solubility and sorption models used in performance assessment calculations for the WIPP and the proposed HLW repository at Yucca Mountain are briefly described
Math Skills Review
This math skills review was written for first year college chemistry students who have weak math backgrounds, but is useful for all science students in high school and college. Topics covered include algebraic manipulation, dimensional analysis, significant figures, manipulation of exponents, scientific notation, logarithms, the quadratic equation and standard deviation. Educational levels: High school, Undergraduate lower division