10,387 research outputs found
Extracting HI cosmological signal with Generalized Needlet Internal Linear Combination
HI intensity mapping is a new observational technique to map fluctuations in
the large-scale structure of matter using the 21 cm emission line of atomic
hydrogen (HI). Sensitive radio surveys have the potential to detect Baryon
Acoustic Oscillations (BAO) at low redshifts (z < 1) in order to constrain the
properties of dark energy. Observations of the HI signal will be contaminated
by instrumental noise and, more significantly, by astrophysical foregrounds,
such as Galactic synchrotron emission, which is at least four orders of
magnitude brighter than the HI signal. Foreground cleaning is recognised as one
of the key challenges for future radio astronomy surveys. We study the ability
of the Generalized Needlet Internal Linear Combination (GNILC) method to
subtract radio foregrounds and to recover the cosmological HI signal for a
general HI intensity mapping experiment. The GNILC method is a new technique
that uses both frequency and spatial information to separate the components of
the observed data. Our results show that the method is robust to the complexity
of the foregrounds. For simulated radio observations including HI emission,
Galactic synchrotron, Galactic free-free, radio sources and 0.05 mK thermal
noise, we find that we can reconstruct the HI power spectrum for multipoles 30
< l < 150 with 6% accuracy on 50% of the sky for a redshift z ~ 0.25.Comment: 20 pages, 13 figures. Updated to match version accepted by MNRA
Mechanical response of composite materials with through-the-thickness reinforcement
An experimental investigation was conducted to identify the key geometrical parameters and quantify their influence on the mechanical response of through-the-thickness (TTT) reinforced composite materials. Composite laminates with TTT reinforcement fibers were fabricated using different TTT reinforcement materials and reinforcement methods and laminates were also fabricated of similar construction but without TTT reinforcement fibers. Coupon specimens were machined from these laminates and were destructively tested. TTT reinforcement yarns enhance damage tolerance and improve interlaminar strength. Thick-layer composites with TTT reinforcement yarns have equal or superior mechanical properties to thin-layer composites without TTT reinforcement yarns. A significant potential exists for fabrication cost reduction by using thick-layer composites with TTT reinforcement yarns. Removal of the surface loop of the TTT reinforcement improves compression strength. Stitching provides somewhat higher mechanical properties than integral weaving
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Patients’ willingness to complete written incident report forms in one UK tertiary cancer hospital
This article examines patients’ willingness to complete incident report forms (IRF), providing a description of the event or concern. Differing from other studies, its design enabled patients to report incidents when and if they felt this necessary, rather than responding to researchers’ questions. 145 patients receiving treatment for cancer in a UK hospital were invited to participate. Of the 100 patients who agreed to participate, only 13 completed a total of 22 forms. The form’s purpose was not easily understood, often perceived as complaining and patients tended to report relatively trivial matters. Contrary to previous studies, this study found little evidence that IRFs are the right tool for enabling patients’ proactive involvement in safety improvement. Asking patients to monitor their safety by completing IRFs may serve to undermine patients’ trust in their clinicians while duplicating resources
Keck/MOSFIRE Spectroscopy of z=7-8 Galaxies: Ly Emission from a Galaxy at z=7.66
We report the results from some of the deepest Keck/Multi-Object Spectrometer
For Infra-Red Exploration data yet obtained for candidate
galaxies. Our data show one significant line detection with 6.5
significance in our combined 10 hr of integration which is independently
detected on more than one night, thus ruling out the possibility that the
detection is spurious. The asymmetric line profile and non-detection in the
optical bands strongly imply that the detected line is Ly emission from
a galaxy at (Ly, making it the fourth
spectroscopically confirmed galaxy via Ly at . This galaxy is
bright in the rest-frame ultraviolet (UV; ) with a
moderately blue UV slope (), and exhibits a
rest-frame Ly equivalent width of EW(Ly) \AA. The non-detection of the 11 other 7-8
galaxies in our long 10 hr integration, reaching a median 5 sensitivity
of 28 \AA\ in the rest-frame EW(Ly), implies a 1.3 deviation
from the null hypothesis of a non-evolving distribution in the rest-frame
EW(Ly) between and 7-8. Our results are consistent with
previous studies finding a decline in Ly emission at , which may
signal the evolving neutral fraction in the intergalactic medium at the end of
the reionization epoch, although our weak evidence suggests the need for a
larger statistical sample to allow for a more robust conclusion.Comment: 10 pages, 4 figures, ApJ, in pres
A Radio Determination of the Time of the New Moon
The detection of the New Moon at sunset is of importance to communities based
on the lunar calendar. This is traditionally undertaken with visual
observations. We propose a radio method which allows a higher visibility of the
Moon relative to the Sun and consequently gives us the ability to detect the
Moon much closer to the Sun than is the case of visual observation. We first
compare the relative brightness of the Moon and Sun over a range of possible
frequencies and find the range 5--100\,GHz to be suitable. The next
consideration is the atmospheric absorption/emission due to water vapour and
oxygen as a function of frequency. This is particularly important since the
relevant observations are near the horizon. We show that a frequency of GHz is optimal for this programme. We have designed and constructed a
telescope with a FWHM resolution of 0.6 and low sidelobes to
demonstrate the potential of this approach. At the time of the 21 May 2012 New
Moon the Sun/Moon brightness temperature ratio was in agreement
with predictions from the literature when combined with the observed sunspot
numbers for the day. The Moon would have been readily detectable at from the Sun. Our observations at 16\,hr\,36\,min UT indicated that
the Moon would have been at closest approach to the Sun 16\,hr\,25\,min
earlier; this was the annular solar eclipse of 00\,hr\,00\,min\,UT on 21 May
2012.Comment: 11 pages, 15 figures, accepted for publication in MNRA
CBI limits on 31 GHz excess emission in southern HII regions
We have mapped four regions of the southern Galactic plane at 31 GHz with the
Cosmic Background Imager. From the maps, we have extracted the flux densities
for six of the brightest \hii regions in the southern sky and compared them
with multi-frequency data from the literature. The fitted spectral index for
each source was found to be close to the theoretical value expected for
optically thin free-free emission, thus confirming that the majority of flux at
31 GHz is due to free-free emission from ionised gas with an electron
temperature of K.
We also found that, for all six sources, the 31 GHz flux density was slightly
higher than the predicted value from data in the literature. This excess
emission could be due to spinning dust or another emission mechanism.
Comparisons with m data indicate an average dust emissivity of
K (MJy/sr), or a 95 per cent confidence limit of K (MJy/sr). This is lower than that found in diffuse clouds at high
Galactic latitudes by a factor of . The most significant detection
() was found in (RCW49) and may account for up to
per cent of the total flux density observed at 31 GHz. Here, the
dust emissivity of the excess emission is K (MJy/sr) and
is within the range observed at high Galactic latitudes.
Low level polarised emission was observed in all six sources with
polarisation fractions in the range per cent. This is likely to be
mainly due to instrumental leakage and is therefore upper an upper limit to the
free-free polarisation. It corresponds to an upper limit of per cent
for the polarisation of anomalous emission.Comment: Accepted in MNRAS. 12 pages, 10 figures, 5 table
Lyman Break Galaxies at z>4 and the Evolution of the UV Luminosity Density at High Redshift
We present initial results of a survey for star-forming galaxies in the
redshift range 3.8 < z < 4.5. This sample consists of a photometric catalog of
244 galaxies culled from a total solid angle of 0.23 square degrees to an
apparent magnitude of I_{AB}=25.0. Spectroscopic redshifts in the range 3.61 <
z < 4.81 have been obtained for 48 of these galaxies; their median redshift is
=4.13. Selecting these galaxies in a manner entirely analogous to our large
survey for Lyman break galaxies at smaller redshift (2.7 < z < 3.4) allows a
relatively clean differential comparison between the populations and integrated
luminosity density at these two cosmic epochs. Over the same range of UV
luminosity, the spectroscopic properties of the galaxy samples at z~4 and z~3
are indistinguishable, as are the luminosity function shapes and the total
integrated UV luminosity densities (rho_{UV}(z=3)/rho_{UV}(z=4) = 1.1 +/-0.3).
We see no evidence at these bright magnitudes for the steep decline in the star
formation density inferred from fainter photometric Lyman-break galaxies in the
Hubble Deep Field (HDF). If the true luminosity density at z~4 is somewhat
higher than implied by the HDF, as our ground-based sample suggests, then the
emissivity of star formation as a function of redshift is essentially constant
for all z>1 once internally consistent corrections for dust are made. This
suggests that there is no obvious peak in star formation activity, and that the
onset of substantial star formation in galaxies occurs at z > 4.5. [abridged
abstract]Comment: To appear in the ApJ, minor revisions to match accepted versio
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