713 research outputs found
Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae
In this paper, we make a comprehensive determination of the Hubble constant
by using two parameters - the B-V color and the rate of decline - to simultaneously standardize the luminosities of all nearby
Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more
distant sample of 29 SNe Ia. Each group is treated in as similar a manner as
possible in order to avoid systematic effects. A simultaneous
minimization yields a standardized absolute luminosity of the
Cepheid-calibrated supernovae as well as the Hubble constant obtained from the
more distant sample. We find and a standardized
absolute magnitude of -19.46. The sensitivity of to a metallicity
dependence of the Cepheid-determined distances is investigated. The total
uncertainty , dominated by uncertainties in the primary Cepheid
distance indicator, is estimated to be 5 km/s Mpc^{-1}.Comment: To appear in Ap
Engineer Intelligence Study No. 191, Terrain Analysis, Alaska Slope Region, Alaska, 1959
The summary on Page 5 is paraphrased as follows. This digital document is a generalized description of the Arctic Slope region -- an area covering approximately 70,000 square miles. Access to the region and the feasibility of various access routes are discussed. Location and extent of natural fuel supplies are given. Factors controlling outdoor work feasibility are summarized graphically on Page 19. A terrain analysis of each of the three major physiographic provinces of the region. Those provinces are the Arctic Coastal Plain, Arctic Foothills, and Brooks Range provinces. Geographic factors which affected cross-country movement, construction, and water supply within those provinces are evaluated. This document contains detailed Landforms and Physiographic Provinces..., Bedrock Geography..., and Surficial Deposits... maps. The distribution list names a number of Corps of Engineers intelligence organizations and the engineering officers of army formations which might be interested in operations in Alaska. The digital document contains a bibliography.
High-resolution scans of the large maps (150 to 350 MB) are attached (below) as related files
Nickel Mixing in the Outer Layers of SN 1987A
Supernova 1987A remains the most well-observed and well-studied supernova to
date. Observations produced excellent broad-band photometric and spectroscopic
coverage over a wide wavelength range at all epochs. Here, we focus on the very
early spectroscopic observations. Only recently have numerical models been of
sufficient detail to accurately explain the observed spectra. In SN 1987A, good
agreement has been found between observed and synthetic spectra for day one,
but by day four, the predicted Balmer lines become much weaker than the
observed lines. We present the results of work based on a
radiation-hydrodynamic model by Blinnikov and collaborators. Synthetic non-LTE
spectra generated from this model by the general radiation transfer code
PHOENIX strongly support the theory that significant mixing of nickel into the
outer envelope is required to maintain strong Balmer lines. Preliminary results
suggest a lower limit to the average nickel mass of 1.0 \times 10^{-5} solar
masses is required above 5000 \kmps by day four. PHOENIX models thus have the
potential to be a sensitive probe for nickel mixing in the outer layers of a
supernova.Comment: 16 pages, 7 figures, ApJ, v556 2001 (in press
Examining Differences in Middle School Student Achievement on a State Mandated Examination: Does a Full Year of Agriscience Really Make a Difference?
Early agricultural education programs in the United States existed to promote new methods and techniques to further agricultural production. Today, extending integration, general knowledge, appreciation, and literacy about agriculture is the goal, especially at the middle school level. Not only is agricultural education designed to encompass academics, but science and technology, literacy, and career preparedness are parts of the total agricultural education program. Since the passage of No Child Left Behind Act (NCLB), more pressure has been put on teachers to generate increased student academic performance and improvement of test scores. The purpose of this research study was to determine if there were statistically significant differences in academic achievement on a state mandated assessment of students who completed a yearlong middle school agricultural education course and students who completed only an eight week middle school agricultural education course in the same school, with the same instructor; the significance in time spent in the course was the main issue in question. The findings showed a statistically significant relationship between the completion of the year-long agricultural education course and math, science, and social studies scores on the state mandated assessment. For example, both 7th and 8th grade students who completed a year-long brain-based agricultural education course had higher mean scores than students who completed only an eight-week brain-based agricultural education course on the math, science, and social studies portions of the assessment
Automatic Identification of Ineffective Online Student Questions in Computing Education
This Research Full Paper explores automatic identification of ineffective
learning questions in the context of large-scale computer science classes. The
immediate and accurate identification of ineffective learning questions opens
the door to possible automated facilitation on a large scale, such as alerting
learners to revise questions and providing adaptive question revision
suggestions. To achieve this, 983 questions were collected from a question &
answer platform implemented by an introductory programming course over three
semesters in a large research university in the Southeastern United States.
Questions were firstly manually classified into three hierarchical categories:
1) learning-irrelevant questions, 2) effective learning-relevant questions, 3)
ineffective learningrelevant questions. The inter-rater reliability of the
manual classification (Cohen's Kappa) was .88. Four different machine learning
algorithms were then used to automatically classify the questions, including
Naive Bayes Multinomial, Logistic Regression, Support Vector Machines, and
Boosted Decision Tree. Both flat and single path strategies were explored, and
the most effective algorithms under both strategies were identified and
discussed. This study contributes to the automatic determination of learning
question quality in computer science, and provides evidence for the feasibility
of automated facilitation of online question & answer in large scale computer
science classes
The Health Sciences and Technology Academy (HSTA): Providing 26 Years of Academic and Social Support to Appalachian Youth in West Virginia
The Health Sciences and Technology Academy’s, (HSTA) goals are to increase college attendance of African American, financially disadvantaged, first generation college and rural Appalachian youth and increase health-care providers and STEM professionals in underserved communities. Students enter in the 9th grade and remain in HSTA four years. They engage in a rigorous academic program within the nurturing environment of small after-school clubs punctuated by yearly summer camps on multiple college campuses. A distinctive piece of HSTA is its students’ development of research projects under the mentorship of teachers and researchers that examine and address health issues faced by their communities. The projects help HSTA students to understand the health dynamics in their local community, transforming them into community advocates who address health and social issues at home as they prepare to move on to college and beyond. Substantial in-state tuition waivers inspire 99% of the 3,021 HSTA graduates to attend college versus 56% of WV high school graduates. Approximately 85% of matriculating HSTA students graduate with a four-year degree or higher versus less than 50% of all college entrants. To date, 57% of HSTA students go into health and other STEM majors, much higher than the state and national figures
The Luminosity of SN 1999by in NGC 2841 and the Nature of `Peculiar' Type Ia Supernovae
We present UBVRIJHK photometry and optical spectroscopy of the so-called
'peculiar' Type Ia supernova 1999by in NGC 2841. The observations began one
week before visual maximum light which is well-defined by daily observations.
The light curves and spectra are similar to those of the prototypical
subluminous event SN 1991bg. We find that maximum light in B occurred on 1999
May 10.3 UT (JD 2,451,308.8 +/- 0.3) with B=13.66 +/- 0.02 mag and a color of
B_max-V_max=0.51 +/- 0.03 mag. The late-time color implies minimal dust
extinction from the host galaxy. Our photometry, when combined with the recent
Cepheid distance to NGC 2841 (Macri et al. 2001), gives a peak absolute
magnitude of M_B=-17.15 +/- 0.23 mag, making SN 1999by one of the least
luminous Type Ia events ever observed. We estimate a decline rate parameter of
dm15(B)=1.90 mag, versus 1.93 for SN 1991bg, where 1.10 is typical for
so-called 'normal' events. We compare SN 1999by with other subluminous events
and find that the B_max-V_max color correlates strongly with the decline rate
and may be a more sensitive indicator of luminosity than the fading rate for
these objects. We find a good correlation between luminosity and the depth of
the spectral feature at 580 nm, which had been attributed solely to Si II. We
show that in cooler photospheres the 580 nm feature is dominated by Ti II,
which provides a simple physical explanation for the correlation. Using only
subluminous Type Ia supernovae we derive a Hubble parameter of H_0=75 +12 -11
km/s Mpc, consistent with values found from brighter events.Comment: 36 preprint pages including 18 figures. Near-IR photometry of the SN
has been added to the paper. Scheduled to appear in ApJ vol. 613 (September
2004). High-resolution version available from
http://www.nd.edu/~pgarnavi/sn99by/sn99by.p
The Nature of SN 1961V
The nature of SN 1961V has been uncertain. Its peculiar optical light curve
and slow expansion velocity are similar to those of super-outbursts of luminous
blue variables (LBVs), but its nonthermal radio spectral index and declining
radio luminosity are consistent with decades-old supernovae (SNe). We have
obtained Hubble Space Telescope STIS images and spectra of the stars in the
vicinity of SN 1961V, and find Object 7 identified by Filippenko et al. to be
the closest to the optical and radio positions of SN 1961V. Object 7 is the
only point source detected in our STIS spectra and only its H-alpha emission is
detected; it cannot be the SN or its remnant because of the absence of
forbidden lines. While the H-alpha line profile of Object 7 is remarkably
similar to that of eta Car, the blue color (similar to an A2Ib supergiant) and
lack of appreciable variability are unlike known post-outburst LBVs. We have
also obtained Very Long Baseline Array (VLBA) observations of SN 1961V at 18
cm. The non-detection of SN 1961V places a lower limit on the size of the
radio-emitting region, 7.6 mas or 0.34 pc, which implies an average expansion
velocity in excess of 4,400 km/s, much higher than the optical expansion
velocity measured in 1961. We conclude the following: (1) A SN occurred in the
vicinity of SN 1961V a few decades ago. (2) If the SN 1961V light maximum
originates from a giant eruption of a massive star, Object 7 is the most
probable candidate for the survivor, but its blue color and lack of significant
variability are different from a post-outburst eta Car. (3) The radio SN and
Object 7 could be physically associated with each other through a binary
system. (4) Object 7 needs to be monitored to determine its nature and
relationship to SN 1961V.Comment: 16 pages, 3 figures, accepted by the Astronomical Journal for the
2004 May issu
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