15,429 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
An early Anglo-Saxon bridle-fitting from South Leckaway, Forfar, Angus, Scotland
[FIRST PARAGRAPH] In February 2003 the Kinnettles Heritage Group made a quite unexpected find during field-walking at South Leckaway farm near Forfar, Angus (NGR NO 4379 4810): the most northerly example in Britain — by about 150 miles — of an Anglo- Saxon object decorated in Salin’s Style I. It lay isolated and face down on the surface. A follow-up field-walk at the end of the month confirmed, partly with the aid of a metal detector, that there were no readily apparent additional pieces of metalwork, associated structures or burial evidence. The find was reported under the Scottish Treasure Trove legislation, duly claimed and allocated in June 2003 to the Meffan Institute, Forfar (part of Angus Cultural Services)
Rotary antenna attenuator
Radio frequency attenuator, having negligible insertion loss at minimum attenuation, can be used for making precise antenna gain measurements. It is small in size compared to a rotary-vane attenuator
A New Chamber for Studying the Behavior of Drosophila
Methods available for quickly and objectively quantifying the behavioral phenotypes of the fruit fly, Drosophila melanogaster, lag behind in sophistication the tools developed for manipulating their genotypes. We have developed a simple, easy-to-replicate, general-purpose experimental chamber for studying the ground-based behaviors of fruit flies. The major innovative feature of our design is that it restricts flies to a shallow volume of space, forcing all behavioral interactions to take place within a monolayer of individuals. The design lessens the frequency that flies occlude or obscure each other, limits the variability in their appearance, and promotes a greater number of flies to move throughout the center of the chamber, thereby increasing the frequency of their interactions. The new chamber design improves the quality of data collected by digital video and was conceived and designed to complement automated machine vision methodologies for studying behavior. Novel and improved methodologies for better quantifying the complex behavioral phenotypes of Drosophila will facilitate studies related to human disease and fundamental questions of behavioral neuroscience
The z=0.8596 Damped Lyman Alpha Absorbing Galaxy Toward PKS 0454+039
We present {\it Hubble Space Telescope} and ground--based data on the
metal line absorption system along the line of sight to PKS
0454+0356. The system is a moderate redshift damped Lyman alpha system, with
~cm as measured from the {\it
Faint Object Spectrograph} spectrum. We also present ground--based images which
we use to identify the galaxy which most probably gives rise to the damped
system; the most likely candidate is relatively underluminous by QSO absorber
standards ( for and \kms Mpc), and
lies kpc in projection from the QSO sightline. Ground--based
measurements of Zn~II, Cr~II, and Fe~II absorption lines from this system allow
us to infer abundances of [Zn/H]=, [Cr/H]=, and [Fe/H]=,
indicating overall metallicity similar to damped systems at , and that
the depletion of Cr and Fe onto dust grains may be even {\it less} important
than in many of the high redshift systems of comparable metallicity. Limits
previously placed on the 21-cm optical depth in the system, together
with our new N(H~I) measurement, suggest a very high spin temperature for the
H~I, K.Comment: changed uuencode header to produce .Z file so that unix uncompress
command will work without modifying file nam
Lyman Break Galaxies in the NGST Era
With SIRTF and NGST in the offing, it is interesting to examine what the
stellar populations of z~3 galaxies models imply for the existence and nature
of Lyman-break galaxies at higher redshift. To this end, we ``turn back the
clock'' on the stellar population models that have been fit to optical and
infrared data of Lyman-break galaxies at z~3. The generally young ages
(typically 10^8 +- 0.5 yr) of these galaxies imply that their stars were not
present much beyond z=4. For smooth star-formation histories SFR(t) and
Salpeter IMFs, the ionizing radiation from early star-formation in these
galaxies would be insufficient to reionize the intergalactic medium at z~6, and
the luminosity density at z~4 would be significantly lower than observed. We
examine possible ways to increase the global star-formation rate at higher
redshift without violating the stellar-population constraints at z~3.Comment: To appear in "The Mass of Galaxies at Low and High Redshift", ed. R.
Bender and A. Renzini, ESO Astrophysics Symposia, Springer-Verlag 7 Pages, 2
figure
Performance of the resurfaced hip. Part 1: the influence of the prosthesis size and positioning on the remodelling and fracture of the femoral neck
Hip resurfacing is an established treatment for osteoarthritis in young active patients. Failure modes include femoral neck fracture and prosthesis loosening, which may be associated with medium-term bone adaptation, including femoral neck narrowing and densification around the prosthesis stem.Finite element modelling was used to indicate the effects of prosthesis sizing and positioning on the bone remodelling and fracture strength under a range of normal and traumatic loads, with the aim of understanding these failure modes better.The simulations predicted increased superior femoral neck stress shielding in young patients with small prostheses, which required shortening of the femoral neck to give an acceptable implant–bone interface. However, with a larger prosthesis, natural femoral head centre recreation in the implanted state was possible; therefore stress shielding was restricted to the prosthesis interior, and its extent was less sensitive to prosthesis orientation. With valgus orientation, the implanted neck strength was, at worst, within 3 per cent of its intact strength.The study suggests that femoral neck narrowing may be linked to a reduction in the horizontal femoral offset, occurring if the prosthesis is excessively undersized. As such, hip resurfacing should aim to reproduce the natural femoral head centre, and, for valgus prosthesis orientation, to avoid femoral neck fracture
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