3,246 research outputs found
The Smith Cloud: HI associated with the Sgr dwarf?
The Smith high velocity cloud (V(LSR) = 98 kms) has been observed at two
locations in the emission lines [OIII]5007, [NII]6548 and H-alpha. Both the
[NII] and H-alpha profiles show bright cores due to the Reynolds layer, and red
wings with emission extending to V(LSR) = 130 kms. This is the first
simultaneous detection of two emission lines towards a high velocity cloud,
allowing us to form the ratio of these line profiles as a function of LSR
velocity. At both cloud positions, we see a clear distinction between emission
at the cloud velocity, and the Reynolds layer emission (V(LSR) = 0). The
[NII]/H-alpha ratio (=0.25) for the Reynolds layer is typical of the warm
ionised medium. At the cloud velocity, this ratio is enhanced by a factor of
3-4 compared to emission at rest with respect to the LSR. A moderately deep
upper limit at [OIII] (0.12R at 3-sigma) was derived from our data. If the
emission arises from dilute photoionisation from hot young stars, the highly
enhanced [NII]/H-alpha ratio, the [OIII] non-detection and weak H-alpha
emission (0.24-0.30R) suggest that the Smith Cloud is 26+/-4 kpc from the Sun,
at a Galactocentric radius of 20+/-4 kpc. This value assumes that the emission
arises from an optically thick slab, with a covering fraction of unity as seen
by the ionizing photons, whose orientation is either (a) parallel to the
Galactic disk, or (b) such as to maximize the received flux from the disk. The
estimated mass and size of the cloud are 4x10^6 Msun and 6 kpc. We discuss a
possible association with the much larger Sgr dwarf, at a galactocentric radius
of 16+/-2 kpc, which lies within 35 degrees (~12 kpc) of the Smith Cloud.Comment: 18 pages, 14 figures, mn.sty. Our first application of a new method
for establishing distances to high velocity clouds. This version matches
paper to appear in MNRAS, 299, 611-624 (Sept. 11 issue
Evolution of displacements and strains in sheared amorphous solids
The local deformation of two-dimensional Lennard-Jones glasses under imposed
shear strain is studied via computer simulations. Both the mean squared
displacement and mean squared strain rise linearly with the length of the
strain interval over which they are measured. However, the
increase in displacement does not represent single-particle diffusion. There
are long-range spatial correlations in displacement associated with slip lines
with an amplitude of order the particle size. Strong dependence on system size
is also observed. The probability distributions of displacement and strain are
very different. For small the distribution of displacement has
a plateau followed by an exponential tail. The distribution becomes Gaussian as
increases to about .03. The strain distributions consist of
sharp central peaks associated with elastic regions, and long exponential tails
associated with plastic regions. The latter persist to the largest studied.Comment: Submitted to J. Phys. Cond. Mat. special volume for PITP Conference
on Mechanical Behavior of Glassy Materials. 16 Pages, 8 figure
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The use of the Continuously Regenerating Trap (CRT<sup>TM</sup>) and SCRT<sup>TM</sup> Systems to meet future emissions legislation
The progressive tightening of particulate matter (PM) legislation presents challenges to the engine development and aftertreatment communities. The Continuously Regenerating Trap (CRTTM) has been developed to enable diesel engines to meet the proposed future legislation. This passive filter system combines an oxidation catalyst with a Diesel Particulate Filter (DPF); the filter traps the PM and the oxidation catalyst generates NO2 which combusts the trapped PM at substantially lower temperatures than is possible using oxygen.
This paper outlines the operating principle of the CRTTM, and describes the performance of the system. It has been shown that the very high PM conversions obtained with the CRTTM can enable even Euro 1 engines to meet the PM limits proposed for introduction in Europe in 2005. In addition, the system removes PM across the whole particle size range, including ultrafine particulates. These results will be discussed, as will in-field durability studies which have shown that the system is still capable of converting 90% of PM after very high mileage operation (up to 600,000 km).
In addition to requiring very high PM conversion, the proposed future legislation requires substantial reductions in NOx emissions form heavy duty diesel vehicles. To meet these challenges the SCRTTM has been developed. This combines the CRTTM with SCR (Selective Catalytic Reduction) technology, and enables very high simultaneous conversions of CO, HC, PM and NOx to be achieved. The SCRTTM system is described, and its operating characteristics are discussed. It has been shown that the SCRTTM can potentially meet the legislative limits proposed for introduction in Europe in 2008
A Decade Of Starspot Activity On The Eclipsing Short-Period RS Canum Venaticorum Star WY Cancri: 1988-1997
We present optical photometry of the short-period eclipsing RS CVn system WY Cancri for the years 1988–1997. For each light curve, we model the distortion waves in order to study the behavior of starspots in this system. After removing the spot effects f
The Bolocam 1.1 mm Lockman Hole Galaxy Survey: SHARC II 350 micron Photometry and Implications for Spectral Models, Dust Temperatures, and Redshift Estimation
We present 350 micron photometry of all 17 galaxy candidates in the Lockman
Hole detected in a 1.1 mm Bolocam survey. Several of the galaxies were
previously detected at 850 microns, at 1.2 mm, in the infrared by Spitzer, and
in the radio. Nine of the Bolocam galaxy candidates were detected at 350
microns and two new candidates were serendipitously detected at 350 microns
(bringing the total in the literature detected in this way to three). Five of
the galaxies have published spectroscopic redshifts, enabling investigation of
the implied temperature ranges and a comparison of photometric redshift
techniques.
Lambda = 350 microns lies near the spectral energy distribution peak for z =
2.5 thermally emitting galaxies. Thus, luminosities can be measured without
extrapolating to the peak from detection wavelengths of lambda > 850 microns.
Characteristically, the galaxy luminosities lie in the range 1.0 - 1.2 x 10^13
L_solar, with dust temperatures in the range of 40 K to 70 K, depending on the
choice of spectral index and wavelength of unit optical depth. The implied dust
masses are 3 - 5 x 10^8 M_solar. We find that the far-infrared to radio
relation for star-forming ULIRGs systematically overpredicts the radio
luminosities and overestimates redshifts on the order of Delta z ~ 1, whereas
redshifts based on either on submillimeter data alone or the 1.6 micron stellar
bump and PAH features are more accurate.Comment: In Press (to appear in Astrophysical Journal, ApJ 20 May 2006 v643 1)
47 pages, 10 figures, 4 table
Radial HI Profiles at the Periphery of Galactic Disks: The Role of Ionizing Background Radiation
Observations of neutral hydrogen in spiral galaxies reveal a sharp cutoff in
the radial density profile at some distance from the center. Using 22 galaxies
with known HI distributions as an example, we discuss the question of whether
this effect can be associated exclusively with external ionizing radiation, as
is commonly assumed. We show that before the surface density reaches
(the same for
galaxies of different types), it is hard to expect the gas to be fully ionized
by background radiation. For two of 13 galaxies with a sharp drop in the HI
profile, the "steepening" can actually be caused by ionization. At the same
time, for the remaining galaxies, the observed cutoff in the radial HI profile
is closer to the center than if it was a consequence of ionization by
background radiation and, therefore, it should be caused by other factors.Comment: 15 pages, 6 figure
Exploring the views of students on the use of Facebook in university teaching and learning
Facebook use among students is almost ubiquitous; however, its use for formal academic purposes remains contested. Through an online survey monitoring student use of module Facebook pages and focus groups, this study explores students’ current academic uses of Facebook and their
views on using Facebook within university modules. Students reported using Facebook for academic purposes, notably peer–peer communication around group work and assessment – a use not always conceptualised by students as learning. Focus groups revealed that students are not ready or equipped for the collaborative style of learning envisaged by the tutor and see Facebook as their personal domain, within which they
will discuss academic topics where they see a strong relevance and purpose, notably in connection with assessment. Students use Facebook for their own mutually defined purposes and a change in student mind- and skill-sets is required to appropriate the collaborative learning benefits of Facebook in formal educational contexts
Three Body Interactions, Angular Momentum and Black Hole Moduli Spaces
We investigate the dynamics of a pair of (4+1)-dimensional black holes in the
moduli approximation and with fixed angular momentum. We find that spinning
black holes at small separations are described by the de Alfaro, Fubini and
Furlan model. For more than two black holes, we find an explicit expression for
the three-body interactions in the moduli metric by associating them with the
one-loop three-point amplitude of a four-dimensional theory. We also
investigate the dynamics of a three black hole system in various
approximations.Comment: 20 pages, phyzz
Safety of overlapping inpatient orthopaedic surgery: A multicenter study
BackgroundAlthough overlapping surgery is used to maximize efficiency, more empirical data are needed to guide patient safety. We conducted a retrospective cohort study to evaluate the safety of overlapping inpatient orthopaedic surgery, as judged by the occurrence of perioperative complications.MethodsAll inpatient orthopaedic surgical procedures performed at 5 academic institutions from January 1, 2015, to December 31, 2015, were included. Overlapping surgery was defined as 2 skin incisions open simultaneously for 1 surgeon. In comparing patients who underwent overlapping surgery with those who underwent non-overlapping surgery, the primary outcome was the occurrence of a perioperative complication within 30 days of the surgical procedure, and secondary outcomes included all-cause 30-day readmission, length of stay, and mortality. To determine if there was an association between overlapping surgery and a perioperative complication, we tested for non-inferiority of overlapping surgery, assuming a null hypothesis of an increased risk of 50%. We used an inverse probability of treatment weighted regression model adjusted for institution, procedure type, demographic characteristics (age, sex, race, comorbidities), admission type, admission severity of illness, and clustering by surgeon.ResultsAmong 14,135 cases, the frequency of overlapping surgery was 40%. The frequencies of perioperative complications were 1% in the overlapping surgery group and 2% in the non-overlapping surgery group. The overlapping surgery group was non-inferior to the non-overlapping surgery group (odds ratio [OR], 0.61 [90% confidence interval (CI), 0.45 to 0.83]; p < 0.001), with reduced odds of perioperative complications (OR, 0.61 [95% CI, 0.43 to 0.88]; p = 0.009). For secondary outcomes, there was a significantly lower chance of all-cause 30-day readmission in the overlapping surgery group (OR, 0.67 [95% CI, 0.52 to 0.87]; p = 0.003) and shorter length of stay (e, 0.94 [95% CI, 0.89 to 0.99]; p = 0.012). There was no difference in mortality.ConclusionsOur results suggest that overlapping inpatient orthopaedic surgery does not introduce additional perioperative risk for the complications that we evaluated. The suitability of this practice should be determined by individual surgeons on a case-by-case basis with appropriate informed consent.Level of evidenceTherapeutic Level III. See Instructions for Authors for a complete description of levels of evidence
Observations of the Extended Distribution of Ionized Hydrogen in the Plane of M31
We have used the Wisconsin H-Alpha Mapper (WHAM) to observe the spatially
extended distribution of ionized hydrogen in M31 beyond the stellar disk. We
obtained five sets of observations, centered near the photometric major axis of
M31, that extend from the center of the galaxy to just off the edge of the
southwestern HI disk. Beyond the bright stellar disk, but within the HI disk,
weak H-alpha is detected with an intensity I(H-alpha) = 0.05 (+0.01 / -0.02)
Rayleighs. Since M31 is inclined 77 degrees with respect to the line of sight,
this implies that the ambient intergalactic ionizing flux onto each side of M31
is Phi_0 <= 1.6 x 10^4 photons cm^-2 s^-1. Just beyond the outer boundary of
the HI disk we find no significant detection of H-alpha and place an upper
limit I(H-alpha) <= 0.019 Rayleighs.Comment: To appear in ApJ Letters; 12 pages, 4 figure
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