21,604 research outputs found
The family practitioner family : the use of metaphor in understanding changes in primary health care organizations
Current UK health policy guidance locates primary care at the frontiers of health care modernization. New organizational structures have resulted in general practitioner (GP) practices being brought together in Primary Care Groups (PCGs) and Primary Care Trusts (PCTs) each serving a much larger population group than the traditional GP practice. These changes have been accompanied with a need to explore new ways of working and thinking. This paper draws upon the experiences of nurses and GPs participating in an evaluation of workforce planning issues in primary health care. It explores how practitioners working in PCGs across one geographical area were able to gain a better understanding of what these changes, to both the structure and process of practice, might involve. During this developmental process the respondents used âthe familyâ metaphor, as a form of âshorthandâ to orientate themselves to the new responsibilities, challenges and opportunities presented by these changes to primary health care. It was in the use of terms and constructs that were familiar to their âeveryday lifeâ experiences that made taking the first tentative steps in the change process easier. This paper suggests that using metaphors may be a powerful tool for policy makers, practitioners,managers and for researchers as they seek to communicate a plan for change and in understanding what these changes might mean
Gated rotation mechanism of site-specific recombination by ÏC31 integrase
Integrases, such as that of the Streptomyces temperate bacteriophage ÏC31, promote site-specific recombination between DNA sequences in the bacteriophage and bacterial genomes to integrate or excise the phage DNA. ÏC31 integrase belongs to the serine recombinase family, a large group of structurally related enzymes with diverse biological functions. It has been proposed that serine integrases use a âsubunit rotationâ mechanism to exchange DNA strands after double-strand DNA cleavage at the two recombining att sites, and that many rounds of subunit rotation can occur before the strands are religated. We have analyzed the mechanism of ÏC31 integrase-mediated recombination in a topologically constrained experimental system using hybrid âphesâ recombination sites, each of which comprises a ÏC31 att site positioned adjacent to a regulatory sequence recognized by Tn3 resolvase. The topologies of reaction products from circular substrates containing two phes sites support a right-handed subunit rotation mechanism for catalysis of both integrative and excisive recombination. Strand exchange usually terminates after a single round of 180° rotation. However, multiple processive â360° rotationâ rounds of strand exchange can be observed, if the recombining sites have nonidentical base pairs at their centers. We propose that a regulatory âgatingâ mechanism normally blocks multiple rounds of strand exchange and triggers product release after a single round
Inverse Modelling to Obtain Head Movement Controller Signal
Experimentally obtained dynamics of time-optimal, horizontal head rotations have previously been simulated by a sixth order, nonlinear model driven by rectangular control signals. Electromyography (EMG) recordings have spects which differ in detail from the theoretical rectangular pulsed control signal. Control signals for time-optimal as well as sub-optimal horizontal head rotations were obtained by means of an inverse modelling procedures. With experimentally measured dynamical data serving as the input, this procedure inverts the model to produce the neurological control signals driving muscles and plant. The relationships between these controller signals, and EMG records should contribute to the understanding of the neurological control of movements
Hierarchical and High-Girth QC LDPC Codes
We present a general approach to designing capacity-approaching high-girth
low-density parity-check (LDPC) codes that are friendly to hardware
implementation. Our methodology starts by defining a new class of
"hierarchical" quasi-cyclic (HQC) LDPC codes that generalizes the structure of
quasi-cyclic (QC) LDPC codes. Whereas the parity check matrices of QC LDPC
codes are composed of circulant sub-matrices, those of HQC LDPC codes are
composed of a hierarchy of circulant sub-matrices that are in turn constructed
from circulant sub-matrices, and so on, through some number of levels. We show
how to map any class of codes defined using a protograph into a family of HQC
LDPC codes. Next, we present a girth-maximizing algorithm that optimizes the
degrees of freedom within the family of codes to yield a high-girth HQC LDPC
code. Finally, we discuss how certain characteristics of a code protograph will
lead to inevitable short cycles, and show that these short cycles can be
eliminated using a "squashing" procedure that results in a high-girth QC LDPC
code, although not a hierarchical one. We illustrate our approach with designed
examples of girth-10 QC LDPC codes obtained from protographs of one-sided
spatially-coupled codes.Comment: Submitted to IEEE Transactions on Information THeor
Keck Spectroscopy of Faint 3 < z < 7 Lyman Break Galaxies: III. The Mean Ultraviolet Spectrum at z=4
We present and discuss the mean rest-frame ultraviolet spectrum for a sample
of 81 Lyman Break Galaxies (LBGs) selected to be B-band dropouts with a mean
redshift of z=3.9 and apparent magnitudes z_AB<26. Most of the individual
spectra are drawn from our ongoing survey in the GOODS fields with the Keck
DEIMOS spectrograph, and we have augmented our sample with published data taken
with FORS2 on the VLT. In general we find similar trends in the spectral
diagnostics to those found in the earlier, more extensive survey of LBGs at z=3
undertaken by Shapley et al (2003). Specifically, we find low-ionization
absorption lines which trace the presence of neutral outflowing gas are weaker
in galaxies with stronger Lyman-alpha emission, bluer UV spectral slopes, lower
stellar masses, lower UV luminosities and smaller half-light radii. This is
consistent with a physical picture whereby star formation drives outflows of
neutral gas which scatters Lyman-alpha and gives rise to strong low-ionization
absorption lines, while increasing the stellar mass, size, metallicity, and
dust content of galaxies. Typical galaxies are thus expected to have stronger
Lyman-alpha emission and weaker low-ionization absorption at earlier times
(higher redshifts). Indeed, our mean spectrum at z=4 shows somewhat weaker
low-ionization absorption lines than at z=3 and available data at higher
redshift indicates a rapid decrease in low-ionization absorption strength with
redshift. We argue that the reduced low-ionization absorption is likely caused
by a decrease in the covering fraction and/or velocity range of outflowing
neutral gas at earlier epochs. Our continuing survey will enable us to extend
these diagnostics more reliably to higher redshift and determine the
implications for the escape fraction of ionizing photons which governs the role
of early galaxies in cosmic reionization. [Abridged]Comment: 17 pages, 12 figures, submitted to ApJ. Comments welcom
Keck Spectroscopy of Faint 3<z<7 Lyman Break Galaxies:- II. A High Fraction of Line Emitters at Redshift Six
As Lyman-alpha photons are scattered by neutral hydrogen, a change with
redshift in the Lyman-alpha equivalent width distribution of distant galaxies
offers a promising probe of the degree of ionization in the intergalactic
medium and hence when cosmic reionization ended. This simple test is
complicated by the fact that Lyman-alpha emission can also be affected by the
evolving astrophysical details of the host galaxies. In the first paper in this
series, we demonstrated both a luminosity and redshift dependent trend in the
fraction of Lyman-alpha emitters seen within color-selected Lyman-break
galaxies (LBGs) over the range 3<z<6; lower luminosity galaxies and those at
higher redshift show an increased likelihood of strong emission. Here we
present the results from much deeper 12.5 hour exposures with the Keck DEIMOS
spectrograph focused primarily on LBGs at z~6 which enable us to confirm the
redshift dependence of line emission more robustly and to higher redshift than
was hitherto possible. We find 54+/-11% of faint z~6 LBGs show strong (W_0>25
A) emission, an increase of 1.6x from a similar sample observed at z~4. With a
total sample of 74 z~6 LBGs, we determine the luminosity-dependent Lyman-alpha
equivalent width distribution. Assuming continuity in these trends to the new
population of z~7 sources located with the Hubble WFC3/IR camera, we predict
that unless the neutral fraction rises in the intervening 200 Myr, the success
rate for spectroscopic confirmation using Lyman-alpha emission should be high.Comment: 6 pages, 3 figures, submitted to ApJ
Excess antisense RNA from infectious recombinant SV40 fails to inhibit expression of a transfected, interferon-inducible gene
Visual enhancements in pick-and-place tasks: Human operators controlling a simulated cylindrical manipulator
A teleoperation simulator was constructed with vector display system, joysticks, and a simulated cylindrical manipulator, in order to quantitatively evaluate various display conditions. The first of two experiments conducted investigated the effects of perspective parameter variations on human operators' pick-and-place performance, using a monoscopic perspective display. The second experiment involved visual enhancements of the monoscopic perspective display, by adding a grid and reference lines, by comparison with visual enhancements of a stereoscopic display; results indicate that stereoscopy generally permits superior pick-and-place performance, but that monoscopy nevertheless allows equivalent performance when defined with appropriate perspective parameter values and adequate visual enhancements
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