7,014 research outputs found
An active interferometric method for extreme impedance on-wafer device measurements
Nano-scale devices and high-power transistors present extreme impedances, which are far removed from the 50-Ω reference impedance of conventional test equipment, resulting in a reduction in the measurement sensitivity as compared with impedances close to the reference impedance. This letter describes a novel method based on active interferometry to increase the measurement sensitivity of a vector network analyzer for measuring such extreme impedances, using only a single coupler. The theory of the method is explained with supporting simulation. An interferometry-based method is demonstrated for the first time with on-wafer measurements, resulting in an improved measurement sensitivity for extreme impedance device characterization of up to 9%
THE POLITICAL ECONOMY OF FOOD PRICE INFLATION IN SOUTH AFRICA
This paper reports on a study that investigated the increase in food prices in South Africa. It is set against the scenario of an increasing inflation rate since September 2001. The June 2002 STATSSA figures estimated the annual inflation rate (CPIX) at 8.8% with food inflation being the major contributor with an annual increase of 14%. The high unemployment and poverty rate in South Africa has already lead to concerns about the negative impact of these increases on the cost of living for the poorest. In this paper we show that the sharp depreciation of the exchange rate towards the end of 2001 had a major impact on the producer price of maize one of the key agricultural commodities because of its role as a staple food and as an input in the production of white and red meat and other animal products.Demand and Price Analysis, Political Economy,
Incompatibility of Rotation Curves with Gravitational Lensing for TeVeS
We constrain the one-parameter class of TeVeS models by testing the theory
against both rotation curve and strong gravitational lensing data on galactic
scales, remaining fully relativistic in our formalism. The upshot of our
analysis is that -- at least in its simplest original form, which is the only
one studied in the literature so far -- TeVeS is ruled out, in the sense that
the models cannot consistently fit simultaneously the two sets of data without
including a significant dark matter component. It is also shown that the
details of the underlying cosmological model are not relevant for our analysis,
which pertains to galactic scales. The choice of the stellar Initial Mass
Function -- which affects the estimates of baryonic mass -- is found not to
change our conclusions.Comment: 12 pages, 4 figure
Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
We present a sample of 1317 Infrared-Faint Radio Sources (IFRSs) that, for
the first time, are reliably detected in the infrared, generated by
cross-correlating the Wide-Field Infrared Survey Explorer (WISE) all-sky survey
with major radio surveys. Our IFRSs are brighter in both radio and infrared
than the first generation IFRSs that were undetected in the infrared by the
Spitzer Space Telescope. We present the first spectroscopic redshifts of IFRSs,
and find that all but one of the IFRSs with spectroscopy has z > 2. We also
report the first X-ray counterparts of IFRSs, and present an analysis of radio
spectra and polarization, and show that they include Gigahertz-Peaked Spectrum,
Compact Steep Spectrum, and Ultra-Steep Spectrum sources. These results,
together with their WISE infrared colours and radio morphologies, imply that
our sample of IFRSs represents a population of radio-loud Active Galactic
Nuclei at z > 2. We conclude that our sample consists of lower-redshift
counterparts of the extreme first generation IFRSs, suggesting that the fainter
IFRSs are at even higher redshift.Comment: 23 pages, 17 figures. Submitted to MNRA
Cognitive dysfunction in patients with cerebral microbleeds on T2*-weighted gradient-echo MRI.
Gradient echo T2*-weighted MRI has high sensitivity in detecting cerebral microbleeds, which appear as small dot-like hypointense lesions. Microbleeds are strongly associated with intracerebral haemorrhage, hypertension, lacunar stroke and ischaemic small vessel disease, and have generated interest as a marker of bleeding-prone microangiopathy. Microbleeds have generally been considered to be clinically silent; however, since they are located in widespread cortical and basal ganglia regions and are histologically characterized by tissue damage, we hypothesized that they would cause cognitive dysfunction. We therefore studied patients with microbleeds (n = 25) and a non-microbleed control group (n = 30) matched for age, gender and intelligence quotient. To avoid the confounding effects of coexisting cerebrovascular disease, the groups were also matched for the extent of MRI-visible white matter changes of presumed ischaemic origin, location of cortical strokes, and for the proportion of patients with different stroke subtypes (including lacunar stroke). A battery of neuropsychological tests was used to assess current intellectual function, verbal and visual memory, naming and perceptual skills, speed and attention and executive function. Microbleeds were most common in the basal ganglia but were also found in frontal, parieto-occipital, temporal and infratentorial regions. There was a striking difference between the groups in the prevalence of executive dysfunction, which was present in 60% of microbleed patients compared with 30% of non-microbleed patients (P = 0.03). Logistic regression confirmed that microbleeds (but not white matter changes) were an independent predictor of executive impairment (adjusted odds ratio = 1.32, 95% confidence interval 1.01-1.70, P = 0.04). Patients with executive dysfunction had more microbleeds in the frontal region (mean count 1.54 versus 0.03; P = 0.002) and in the basal ganglia (mean 1.17 versus 0.32; P = 0.048). There was a modest correlation between the number of microbleeds and the number of cognitive domains impaired (r = 0.44, P = 0.03). This study provides novel evidence that microbleeds are associated with cognitive dysfunction, independent of the extent of white matter changes of presumed ischaemic origin, or the presence of ischaemic stroke. The striking effect of microbleeds on executive dysfunction is likely to result from associated tissue damage in the frontal lobes and basal ganglia. These findings have implications for the diagnosis of stroke patients with cognitive impairment, and for the appropriate use of antihypertensive and antiplatelet treatments in these patients
Singularities of the Magnon Boundstate S-Matrix
We study the conjectured exact S-matrix for the scattering of BPS magnon
boundstates in the spin-chain description of planar N=4 SUSY Yang-Mills. The
conjectured S-matrix exhibits both simple and double poles at complex momenta.
Some of these poles lie parametrically close to the real axis in momentum space
on the branch where particle energies are positive. We show that all such poles
are precisely accounted for by physical processes involving one or more
on-shell intermediate particles belonging to the known BPS spectrum.Comment: 32 pages, 9 figure
How do I sound to me? Perceived changes in communication in Parkinson's disease
Objective: To examine self and carer perceived changes in communication associated with Parkinson's disease and relate these to speech intelligibility, gender, age and other disease measures.
Design: Cross-sectional survey of a hospital- and community-based sample of 176 people with Parkinson's disease and their carers using a questionnaire based on semantic differential techniques.
Participants: One hundred and four people with Parkinson's disease with no history of communication difficulties prior to onset of their Parkinson's disease and 45 primary carers who returned completed questionnaires.
Main outcome measures: Differences in ratings for `before' the onset of Parkinson's disease versus present status.
Results: There was a strong perception of negative impact on communication between `before' and `now', irrespective of age and gender and largely independent of disease severity and duration, intelligibility and cognitive status. Activities of daily living (assessed by Unified Parkinson's Disease Rating Scale (UPDRS) II) and depression rating scale scores had the strongest association with change (adjusted R 2 0.27). There was a significant correlation between the rank order of perceived change in features examined in people with Parkinson's disease versus their carers, though in general carers rated change as having less impact.
Conclusions: Parkinson's disease exercises a strong influence on communication even before apparent alterations to intelligibility or motor status
The statistical mechanics of a polygenic characterunder stabilizing selection, mutation and drift
By exploiting an analogy between population genetics and statistical
mechanics, we study the evolution of a polygenic trait under stabilizing
selection, mutation, and genetic drift. This requires us to track only four
macroscopic variables, instead of the distribution of all the allele
frequencies that influence the trait. These macroscopic variables are the
expectations of: the trait mean and its square, the genetic variance, and of a
measure of heterozygosity, and are derived from a generating function that is
in turn derived by maximizing an entropy measure. These four macroscopics are
enough to accurately describe the dynamics of the trait mean and of its genetic
variance (and in principle of any other quantity). Unlike previous approaches
that were based on an infinite series of moments or cumulants, which had to be
truncated arbitrarily, our calculations provide a well-defined approximation
procedure. We apply the framework to abrupt and gradual changes in the optimum,
as well as to changes in the strength of stabilizing selection. Our
approximations are surprisingly accurate, even for systems with as few as 5
loci. We find that when the effects of drift are included, the expected genetic
variance is hardly altered by directional selection, even though it fluctuates
in any particular instance. We also find hysteresis, showing that even after
averaging over the microscopic variables, the macroscopic trajectories retain a
memory of the underlying genetic states.Comment: 35 pages, 8 figure
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