1,819 research outputs found
How the Implementation of Honors Sections Affects the Academic Performance of Non-Honors Students
Research in honors education generally credits honors students with elevating the academic experience for all students at an institution (see Andrews; Clauss; Brimeyer et al.). Honors students are seen as having a positive peer effect: setting a standard for other students to follow as well as stimulating and challenging faculty, thereby raising the level of the classroom for all ( Joseph W. Cohen, cited by Andrews 38). Thus, many assume that moving honors students into separate sections adversely affects the academic performance of non-honors students, an assumption we faced at our institution. In the context of a study done in a college of engineering, that perception is even stronger because peer-to-peer and group projects are such important pedagogical elements of the engineering undergraduate curriculum. We are unaware of any research on how honors sections of general education courses affect the academic performance of non-honors students taking those same courses, but our study indicates that the implementation of honors sections for selected core courses in the University of Iowa (UI) College of Engineering did not adversely affect non-honors engineering students taking those same core courses.
In the fall of 2015, the UI College of Engineering inaugurated honors sections of core engineering courses for two reasons. First, the undergraduate engineering population had become large enough for honors sections to be economically and logistically feasible. The college’s enrollment had increased from about 1,200 students to more than 2,000 over six years. New sections of the core first- and second-year courses were necessary, thus providing an opportunity to add honors sections. The second motivating factor came from the UI Honors Program, which had recently changed the criteria for eligibility and graduation requirements, reducing the total number of honors students and making an increased proportion of first-year engineering majors eligible for honors. Although engineering students had previously made up a large fraction of honors-eligible students, they were not easily retained because of scheduling constraints and the absence of honors courses in the engineering curriculum. The honors program and the college of engineering were both interested in attracting more engineering students to the honors program and graduating more engineering students with the honors credential
A Radial Velocity Study of CTCV J1300-3052
We present time-resolved spectroscopy of the eclipsing, short period
cataclysmic variable CTCV J1300-3052. Using absorption features from the
secondary star, we determine the radial velocity semi-amplitude of the
secondary star to be K2 = 378 \pm 6 km/s, and its projected rotational velocity
to be v sin i = 125 \pm 7 km/s. Using these parameters and Monte Carlo
techniques, we obtain masses of M1 = 0.79 \pm 0.05 MSun for the white dwarf
primary and M2 = 0.198 \pm 0.029 MSun for the M-type secondary star. These
parameters are found to be in excellent agreement with previous mass
determinations found via photometric fitting techniques, supporting the
accuracy and validity of photometric mass determinations in short period CVs.Comment: Accepted for publication in MNRAS (24th January 2012). 10 pages, 9
figures (black and white
Spatial coherence effects on second- and fourth-order temporal interference
We report the results of two experiments performed with two-photon light,
produced via collinear degenerate optical spontaneous parametric downconversion
(SPDC), in which both second-order (one-photon) and fourth-order (two-photon)
interferograms are recorded in a Mach-Zehnder interferometer (MZI). In the
first experiment, high-visibility fringes are obtained for both the second- and
fourth-order interferograms. In the second experiment, the MZI is modified by
the removal of a mirror from one of its arms; this leaves the fourth-order
interferogram unchanged, but extinguishes the second-order interferogram. A
theoretical model that takes into consideration both the temporal and spatial
degrees-of-freedom of the two-photon state successfully explains the results.
While the temporal interference in the MZI is independent of the spatial
coherence of the source, that of the modified MZI is not
T Pyxidis: The First Cataclysmic Variable with a Collimated Jet
We present the first observational evidence for a collimated jet in a
cataclysmic variable system; the recurrent nova T Pyxidis. Optical spectra show
bipolar components of H with velocities , very similar
to those observed in the supersoft X-ray sources and in SS 433. We argue that a
key ingredient of the formation of jets in the supersoft X-ray sources and T
Pyx (in addition to an accretion disk threaded by a vertical magnetic field),
is the presence of nuclear burning on the surface of the white dwarf.Comment: 10 pages 2 figures to appear in ApJ Letter
VLT spectroscopy of XTE J2123-058 during quiescence
We present VLT low resolution spectroscopy of the neutron star X-ray
transient XTE J2123-058 during its quiescent state. Our data reveal the
presence of a K7V companion which contributes 77 % to the total flux at 6300 A
and orbits the neutron star at K_2 = 287 +/- 12 km/s. Contrary to other soft
X-ray transients (SXTs), the Halpha emission is almost exactly in antiphase
with the velocity curve of the optical companion. Using the light-center
technique we obtain K_1 = 140 +/- 27 km/s and hence q=K_1/K_2=M_2/M_1= 0.49 +/-
0.10. This, combined with a previous determination of the inclination angle
(i=73 +/- 4) yields M_1 = 1.55 +/- 0.31 Msun and M_2 = 0.76 +/- 0.22 Msun. M_2
agrees well with the observed spectral type. Doppler tomography of the Halpha
emission shows a non-symmetric accretion disc distribution mimicking that seen
in SW Sex stars. Although we find a large systemic velocity of -110 +/- 8 km/s
this value is consistent with the galactic rotation velocity at the position of
J2123-058, and hence a halo origin. The formation scenario of J2123-058 is
still unresolved.Comment: 10 pages, 3 figures, accepted for publication in MNRAS with very
minor change
Observables in Topological Yang-Mills Theories
Using topological Yang-Mills theory as example, we discuss the definition and
determination of observables in topological field theories (of Witten-type)
within the superspace formulation proposed by Horne. This approach to the
equivariant cohomology leads to a set of bi-descent equations involving the
BRST and supersymmetry operators as well as the exterior derivative. This
allows us to determine superspace expressions for all observables, and thereby
to recover the Donaldson-Witten polynomials when choosing a Wess-Zumino-type
gauge.Comment: 39 pages, Late
Time-resolved optical spectroscopy of the pulsating DA white dwarf HS 0507+0434B: New constraints on mode identification and pulsation properties
We present a detailed analysis of time-resolved optical spectra of the ZZ
Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed
mode amplitudes, we deduce the spherical degree, l, of the modes, most of which
have l=1. The presence of a large number of combination frequencies (linear
sums or differences of the real modes) enabled us not only to test theoretical
predictions but also to indirectly infer spherical and azimuthal degrees of
real modes that had no observed splittings. In addition to the above, we
measure line-of-sight velocities from our spectra. We find only marginal
evidence for periodic modulation associated with the pulsation modes: at the
frequency of the strongest mode in the lightcurve, we measure an amplitude of
2.6+/-1.0 km/s, which has a probability of 2% of being due to chance; for the
other modes, we find lower values. Our velocity amplitudes and upper limits are
smaller by a factor of two compared to the amplitudes found in ZZ Psc. We find
that this is consistent with expectations based on the position of HS
0507+0434B in the instability strip. Combining all the available information
from data such as ours is a first step towards constraining atmospheric
properties in a convectionally unstable environment from an observational
perspective.Comment: 16 pages, 12 figs.; accepted for publication in A&
Hard X-ray flares in IGR J08408-4503 unveil clumpy stellar winds
Context : A 1000-s flare from a new hard X-ray transient, IGR J08408-4503,
was observed by INTEGRAL on May 15, 2006 during the real-time routine
monitoring of IBIS/ISGRI images performed at the INTEGRAL Science Data Centre.
The flare, detected during a single one-hour long pointing, peaked at 250 mCrab
in the 20-40 keV energy range.
Aims : Multi-wavelength observations, combining high-energy and optical data,
were used to unveil the nature of IGR J08408-4503.
Methods : A search in all INTEGRAL public data for other bursts from IGR
J08408-4503 was performed, and the detailed analysis of another major flare is
presented. The results of two Swift Target of Opportunity observations are also
described. Finally, a study of the likely optical counterpart, HD 74194, is
provided.
Results : IGR J08408-4503 is very likely a supergiant fast X-ray transient
(SFXT) system. The system parameters indicate that the X-ray flares are
probably related to the accretion of wind clumps on a compact object orbiting
about 1E13 cm from the supergiant HD 74194. The clump mass loss rate is of the
order of 1E-6 solar mass/yr.
Conclusions : Hard X-ray flares from SFXTs allow to probe the stellar winds
of massive stars, and could possibly be associated with wind perturbations due
to line-driven instabilities.Comment: 5 pages with 5 figures. Published as a Letter in Astronomy &
Astrophysic
Mass and Angular Momentum Transfer in the Massive Algol Binary RY Persei
We present an investigation of H-alpha emission line variations observed in
the massive Algol binary, RY Per. We give new radial velocity data for the
secondary based upon our optical spectra and for the primary based upon high
dispersion UV spectra. We present revised orbital elements and an estimate of
the primary's projected rotational velocity (which indicates that the primary
is rotating 7 times faster than synchronous). We use a Doppler tomography
algorithm to reconstruct the individual primary and secondary spectra in the
region of H-alpha, and we subtract the latter from each of our observations to
obtain profiles of the primary and its disk alone. Our H-alpha observations of
RY Per show that the mass gaining primary is surrounded by a persistent but
time variable accretion disk. The profile that is observed outside-of-eclipse
has weak, double-peaked emission flanking a deep central absorption, and we
find that these properties can be reproduced by a disk model that includes the
absorption of photospheric light by the band of the disk seen in projection
against the face of the star. We developed a new method to reconstruct the disk
surface density distribution from the ensemble of H-alpha profiles observed
around the orbit, and this method accounts for the effects of disk occultation
by the stellar components, the obscuration of the primary by the disk, and flux
contributions from optically thick disk elements. The resulting surface density
distribution is elongated along the axis joining the stars, in the same way as
seen in hydrodynamical simulations of gas flows that strike the mass gainer
near trailing edge of the star. This type of gas stream configuration is
optimal for the transfer of angular momentum, and we show that rapid rotation
is found in other Algols that have passed through a similar stage.Comment: 39 pages, 12 figures, ApJ in press, 2004 June 20 issu
Irradiation of the secondary star in X-ray Nova Scorpii 1994 (=GRO J1655--40)
We have obtained intermediate resolution optical spectra of the black-hole
candidate Nova Sco 1994 in June 1996, when the source was in an X-ray/optical
active state (R~15.05). We measure the radial velocity curve of the secondary
star and obtain a semi-amplitude of 279+/-10 km/s; a value which is 30 per cent
larger than the value obtained when the source is in quiescence. Our large
value for K_2 is consistent with 60 +9,-7 per cent of the secondary star's
surface being heated; compared to 35 per cent, which is what one would expect
if only the inner face of the secondary star were irradiated. Effects such as
irradiation-induced flows on the secondary star may be important in explaining
the observed large value for K_2.Comment: 5 pages, 2 figures, accepted by MNRA
- …