4,333 research outputs found
Individual effects and dynamics in count data models
In this paper we examine the panel data estimation of dynamic models for count data that include correlated fixed effects and predetermined variables. Use of a linear feedback model ls proposed. The standard Poisson conditional maximum llkelihood estimator for non-dynamic models, which ls shown to be the same as the Poisson maximum llkelihood estimator in a model with individual specific constants, ls inconsistent when regressors are predetermined. A quasi-differenced GMM estimator ls consistent for the parameters in the dynamic model, but when series are highly persistent, there ls a problem of weak instrument bias. An estimator ls proposed that utilises pre-sample information of the dependent count variable, which is shown in Monte Carlo simulations to possess desirable small sample properties. The models and estimators are applied to data on US patents and R&D expenditure
Universal scaling relations in molecular superconductors
Scaling relations between the superconducting transition temperature , the superfluid stiffness and the normal state conductivity
are identified within the class of molecular
superconductors. These new scaling properties hold as varies over
two orders of magnitude for materials with differing dimensionality and
contrasting molecular structure, and are dramatically different from the
equivalent scaling properties observed within the family of cuprate
superconductors. These scaling relations place strong constraints on theories
for molecular superconductivity.Comment: 4 pages, 4 figure
Are we teaching our students what they need to know about ageing? Results from the National Survey of Undergraduate Teaching in Ageing and Geriatric Medicine
Introduction - Learning about ageing and the appropriate management of older patients is important for all doctors. This survey set out to evaluate what medical undergraduates in the UK are taught about ageing and geriatric medicine and how this teaching is delivered.
Methods – An electronic questionnaire was developed and sent to the 28/31 UK medical schools which agreed to participate.
Results – Full responses were received from 17 schools. 8/21 learning objectives were recorded as taught, and none were examined, across every school surveyed. Elder abuse and terminology and classification of health were taught in only 8/17 and 2/17 schools respectively. Pressure ulcers were taught about in 14/17 schools but taught formally in only 7 of these and examined in only 9. With regard to bio- and socio- gerontology, only 9/17 schools reported teaching in social ageing, 7/17 in cellular ageing and 9/17 in the physiology of ageing.
Discussion – Even allowing for the suboptimal response rate, this study presents significant cause for concern with UK undergraduate education related to ageing. The failure to teach comprehensively on elder abuse and pressure sores, in particular, may be significantly to the detriment of older patients
Structure and Magnetic Fields in the Precessing Jet System SS 433 II. Intrinsic Brightness of the Jets
Deep Very Large Array imaging of the binary X-ray source SS 433, sometimes
classified as a microquasar, has been used to study the intrinsic brightness
distribution and evolution of its radio jets. The intrinsic brightness of the
jets as a function of age at emission of the jet material tau is recovered by
removal of the Doppler boosting and projection effects. We find that
intrinsically the two jets are remarkably similar when compared for equal tau,
and that they are best described by Doppler boosting of the form D^{2+alpha},
as expected for continuous jets. The intrinsic brightnesses of the jets as
functions of age behave in complex ways. In the age range 60 < tau < 150 days,
the jet decays are best represented by exponential functions of tau, but linear
or power law functions are not statistically excluded. This is followed by a
region out to tau ~ 250 days during which the intrinsic brightness is
essentially constant. At later times the jet decay can be fit roughly as
exponential or power law functions of tau.Comment: 30 Pages, 11 Figures, Submitted to Ap
Thermodynamic and magnetic properties of the layered triangular magnet NaNiO2
We report muon-spin rotation, heat capacity, magnetization, and ac magnetic
susceptibility measurements of the layered spin-1/2 antiferromagnet NaNiO2.
These show the onset of long-range magnetic order below T_N = 19.5K. Rapid muon
depolarization persisting to about 5K above T_N is consistent with the presence
of short-range magnetic order. The temperature and frequency dependence of the
ac susceptibility suggests that magnetic clusters persist above 25K in the
paramagnetic state and that their volume fraction decreases with increasing
temperature. A frequency dependent peak in the ac magnetic susceptibility at
T_sf = 3K is observed, consistent with a slowing of spin fluctuations at this
temperature. A partial magnetic phase diagram is deduced.Comment: 4 pages, 4 figure
Impaired bone marrow homing of cytokine-activated CD34<sup>+</sup> cells in the NOD/SCID model
The reduced engraftment potential of hematopoietic stem/progenitor cells (HSPCs) after exposure to cytokines may be related to the impaired homing ability of actively cycling cells. We tested this hypothesis by quantifying the short-term horning of human adult CD34+ cells in nonobese diabetic/severe combined immunodeficient (NOD/SCID) animals. We show that the loss of engraftment ability of cytokine-activated CD34+ cells is associated with a reduction in homing of colony-forming cells (CFCs) to bone marrow (BM) at 24 hours after transplantation (from median 2.8% [range, 1.9%-6.1%] to 0.3% [0.0%-0.7%]; n = 3; P < .01), coincident with an increase in CFC accumulation in the lungs (P < .01). Impaired BM homing of cytokine-activated cells was not restored by using sorted cells in G 0G1 or by inducing cell cycle arrest at the G 1/S border. Blocking Fas ligation in vivo did not increase the BM homing of cultured cells. Finally, we tested cytokine combinations or culture conditions previously reported to restore the engraftment of cultured cells but did not find that any of these was able to reverse the changes in homing behavior of cytokine-exposed cells. We suggest that these changes in homing and, as a consequence, engraftment result from the increased migratory capacity of infused activated cells, leading to the loss of selectivity of the homing process. © 2004 by The American Society of Hematology
The phase transition in the localized ferromagnet EuO probed by muSR
We report results of muon spin rotation measurements performed on the
ferromagnetic semiconductor EuO, which is one of the best approximations to a
localized ferromagnet. We argue that implanted muons are sensitive to the
internal field primarily through a combination of hyperfine and Lorentz fields.
The temperature dependences of the internal field and the relaxation rate have
been measured and are compared with previous theoretical predictions.Comment: 4 pages, 4 figure
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