To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
We present a detailed overview of the cosmological surveys that we aim to carry out with Phase 1 of the Square Kilometre Array (SKA1) and the science that they will enable. We highlight three main surveys: a medium-deep continuum weak lensing and low-redshift spectroscopic HI galaxy survey over 5 000 deg2; a wide and deep continuum galaxy and HI intensity mapping (IM) survey over 20 000 deg2 from
$z = 0.35$
to 3; and a deep, high-redshift HI IM survey over 100 deg2 from
$z = 3$
to 6. Taken together, these surveys will achieve an array of important scientific goals: measuring the equation of state of dark energy out to
$z \sim 3$
with percent-level precision measurements of the cosmic expansion rate; constraining possible deviations from General Relativity on cosmological scales by measuring the growth rate of structure through multiple independent methods; mapping the structure of the Universe on the largest accessible scales, thus constraining fundamental properties such as isotropy, homogeneity, and non-Gaussianity; and measuring the HI density and bias out to
$z = 6$
. These surveys will also provide highly complementary clustering and weak lensing measurements that have independent systematic uncertainties to those of optical and near-infrared (NIR) surveys like Euclid, LSST, and WFIRST leading to a multitude of synergies that can improve constraints significantly beyond what optical or radio surveys can achieve on their own. This document, the 2018 Red Book, provides reference technical specifications, cosmological parameter forecasts, and an overview of relevant systematic effects for the three key surveys and will be regularly updated by the Cosmology Science Working Group in the run up to start of operations and the Key Science Programme of SKA1.
We investigate the contribution of a local over- or under-density to linear estimates of the cosmic dipole. We focus on radio continuum surveys. Recently it was shown that the radio dipole amplitude is larger than expected from the corresponding dipole of the CMB. We show that a significant contribution to this excess could come from local structure.
In the lead-up to the Square Kilometre Array (SKA) project, several next-generation radio telescopes and upgrades are already being built around the world. These include APERTIF (The Netherlands), ASKAP (Australia), e-MERLIN (UK), VLA (USA), e-EVN (based in Europe), LOFAR (The Netherlands), MeerKAT (South Africa), and the Murchison Widefield Array. Each of these new instruments has different strengths, and coordination of surveys between them can help maximise the science from each of them. A radio continuum survey is being planned on each of them with the primary science objective of understanding the formation and evolution of galaxies over cosmic time, and the cosmological parameters and large-scale structures which drive it. In pursuit of this objective, the different teams are developing a variety of new techniques, and refining existing ones. To achieve these exciting scientific goals, many technical challenges must be addressed by the survey instruments. Given the limited resources of the global radio-astronomical community, it is essential that we pool our skills and knowledge. We do not have sufficient resources to enjoy the luxury of re-inventing wheels. We face significant challenges in calibration, imaging, source extraction and measurement, classification and cross-identification, redshift determination, stacking, and data-intensive research. As these instruments extend the observational parameters, we will face further unexpected challenges in calibration, imaging, and interpretation. If we are to realise the full scientific potential of these expensive instruments, it is essential that we devote enough resources and careful study to understanding the instrumental effects and how they will affect the data. We have established an SKA Radio Continuum Survey working group, whose prime role is to maximise science from these instruments by ensuring we share resources and expertise across the projects. Here we describe these projects, their science goals, and the technical challenges which are being addressed to maximise the science return.
Two patients (G01, J02) with chronic nonfluent aphasia and sentence
production deficits received syntactic mapping treatment to improve
sentence production. The patients had dramatically different outcomes in
that improved syntax production generalized to nontreatment tasks for G01,
but not for JO2. To learn how treatment influenced the neural substrates
for syntax production, both patients underwent pre- and posttreatment
functional magnetic resonance imaging (fMRI) of sentence generation. G01
showed more robust activity posttreatment than pretreatment in
Broca's area; ventral temporal activity decreased slightly from pre-
to posttreatment. Comparison of J02's pretreatment and posttreatment
images revealed little change, although activity was more diffuse pre-
than posttreatment. Findings suggest that for G01, rehabilitation led to
engagement of an area (Broca's area) used minimally during the
pretreatment scan, whereas for J02, rehabilitation may have led to more
efficient use of areas already involved in sentence generation during the
pretreatment scan. fMRI findings are discussed in the context of
sentence-production outcome and generalization. (JINS, 2006,
fMRI was used to determine the frontal, basal ganglia, and thalamic
structures engaged by three facets of language generation: lexical
status of generated items, the use of semantic vs. phonological
information during language generation, and rate of generation. During
fMRI, 21 neurologically normal subjects performed four tasks:
generation of nonsense syllables given beginning and ending consonant
blends, generation of words given a rhyming word, generation of words
given a semantic category at a fast rate (matched to the rate of
nonsense syllable generation), and generation of words given a semantic
category at a slow rate (matched to the rate of generating of rhyming
words). Components of a left pre-SMA–dorsal caudate
nucleus–ventral anterior thalamic loop were active during word
generation from rhyming or category cues but not during nonsense
syllable generation. Findings indicate that this loop is involved in
retrieving words from pre-existing lexical stores. Relatively diffuse
activity in the right basal ganglia (caudate nucleus and putamen) also
was found during word-generation tasks but not during nonsense syllable
generation. Given the relative absence of right frontal activity during
the word generation tasks, we suggest that the right basal ganglia
activity serves to suppress right frontal activity, preventing right
frontal structures from interfering with language production. Current
findings establish roles for the left and the right basal ganglia in
word generation. Hypotheses are discussed for future research to help
refine our understanding of basal ganglia functions in language
generation. (JINS, 2003, 9, 1061–1077.)
Precipitation of copper-rich clusters is a major cause of in-service hardening of reactor pressure vessel steels and has attracted much attention. Experimental studies of microstructural changes in alloys under various conditions have revealed similarities and differences. It has been established that under ageing the precipitate ensemble experiences normal nucleation, growth and Ostwald ripening, a distinguishing feature of which is the bcc-9R-3R-fcc transformations the precipitates undergo during growth. The main effect of electron irradiation is believed to be enhancement of the diffusion of copper and hence acceleration of the kinetics. In the case of neutron irradiation, however, there are many aspects that are not clear. One is that at temperatures less than about 300°C the precipitate size is observed to be very small (∼1-3 nm), i.e. the coarsening rate is very low. In this paper we study this phenomenon by computer simulations based on the “mean-field” approach for describing microstructural evolution.
Clusters of self-interstitial atoms (SIAs) formed in displacement cascades in metals irradiated with energetic particles play an important role in microstructure evolution under irradiation. They have been studied in the fcc and bcc metals by atomic scale computer simulation and in this paper we present the first results of a similar study of SIA clusters in an hcp crystal. Clusters of 4 to 30 SIAs were modelled over a wide temperature range using molecular dynamics and a many-body Finnis-Sinclair type interatomic potential for Zr. The results show a qualitative similarity of the dynamic properties of clusters to those for cubic metals. In particular, all clusters larger than 4 SIAs exhibit fast thermally-activated one-dimensional glide, which is in a <1120> direction in the hcp case. Due to the crystallographic features of the hcp lattice, this mechanism leads to two-dimensional mass transport in basal planes. Smaller clusters (≤ 4 SIAs) exhibit behaviour peculiar to the hcp structure, however, for they can migrate two-dimensionally in the basal plane. The jump frequency, activation energy and correlation factors of clusters have been estimated and comparison drawn between the behaviour of SIA clusters in different structures.
Primary radiation damage in displacement cascades in metals has been studied extensively by atomistic simulation during the last decade. The variety of defect types observed in cascade simulation is not entirely consistent with experimental data. For example, experiments on copper show a very effective production of stacking fault tetrahedra (SFTs) but this was not observed systematically in cascade simulation. To clarify this and related issues, extensive simulation of displacement cascades in copper have been performed using two different interatomic potentials, a short-range many-body potential and a long-range pair potential. We have studied the damage created by primary knock-on-atoms of energy up to 20keV, i.e. below the energy range for formation of subcascades, at temperatures 100 and 600K. Special attention was paid to cascade statistics and the accuracy of simulation in the collision stage. The former required many simulations for each temperature whereas the latter involved a modification of the simulation method. The results on variety of clusters observed, e.g. SFTs, glissile and sessile interstitial clusters, and faulted and perfect interstitial dislocation loops, lead to conclusions on the effect of the potentials and the significant variation of the number of Frenkel pairs and clustering effects produced in different cascades under the same conditions.
Computer simulation of the atomic structure and movement of twinning dislocations in four twin boundaries in the h.c.p. metal α-Ti is described. These dislocations have the form of steps on the twin boundary, and whereas some have cores which are very widely spread over the interface, others are only an interatomic spacing or so across. These configurations are determined mainly by whether or not atomic shuffles are required to restore the h.c.p. crystal structure when the dislocation is introduced. The mobility of the dislocations is also controlled by the same effect, and is found to correlate well with experiment.
Email your librarian or administrator to recommend adding this to your organisation's collection.