4,900 research outputs found
Muscle atrophy and metal-on-metal hip implants
Background and purpose — Muscle atrophy is seen in patients with metal-on-metal (MOM) hip implants, probably because of inflammatory destruction of the musculo-tendon junction. However, like pseudotumors, it is unclear when atrophy occurs and whether it progresses with time. Our objective was to determine whether muscle atrophy associated with MOM hip implants progresses with time.
Patients and methods — We retrospectively reviewed 74 hips in 56 patients (32 of them women) using serial MRI. Median age was 59 (23–83) years. The median time post-implantation was 83 (35–142) months, and the median interval between scans was 11 months. Hip muscles were scored using the Pfirrmann system. The mean scores for muscle atrophy were compared between the first and second MRI scans. Blood cobalt and chromium concentrations were determined.
Results — The median blood cobalt was 6.84 (0.24–90) ppb and median chromium level was 4.42 (0.20–45) ppb. The median Oxford hip score was 34 (5–48). The change in the gluteus minimus mean atrophy score between first and second MRI was 0.12 (p = 0.002). Mean change in the gluteus medius posterior portion (unaffected by surgical approach) was 0.08 (p = 0.01) and mean change in the inferior portion was 0.10 (p = 0.05). Mean pseudotumor grade increased by 0.18 (p = 0.02).
Interpretation — Worsening muscle atrophy and worsening pseudotumor grade occur over a 1-year period in a substantial proportion of patients with MOM hip implants. Serial MRI helps to identify those patients who are at risk of developing worsening soft-tissue pathology. These patients should be considered for revision surgery before irreversible muscle destruction occurs
Spreading Width for Decay out of a Superdeformed Band
The attenuation factor F responsible for the decay out of a superdeformed
(SD) band is calculated with the help of a statistical model. This factor is
given by 1/F = (1 + Gamma(down) / Gamma(S)). Here, Gamma(S) is the width for
the collective E2 transition within the superdeformed band, and Gamma(down) is
the spreading width which describes the mixing between a state in the SD band
and the normally deformed (ND) states of equal spin. The attenuation factor F
is independent of the statistical E1 decay widths Gamma(N) of the ND states
provided that the Gamma(N) are much larger than both Gamma(down) and Gamma(S).
This condition is generically met. Previously measured values of F are used to
determine Gamma(down).Comment: Submitted to Physical Review Letter
Finite size effects on transport coefficients for models of atomic wires coupled to phonons
We consider models of quasi-1-d, planar atomic wires consisting of several,
laterally coupled rows of atoms, with mutually non-interacting electrons. This
electronic wire system is coupled to phonons, corresponding, e.g., to some
substrate. We aim at computing diffusion coefficients in dependence on the wire
widths and the lateral coupling. To this end we firstly construct a numerically
manageable linear collision term for the dynamics of the electronic occupation
numbers by following a certain projection operator approach. By means of this
collision term we set up a linear Boltzmann equation. A formula for extracting
diffusion coefficients from such Boltzmann equations is given. We find in the
regime of a few atomic rows and intermediate lateral coupling a significant and
non-trivial dependence of the diffusion coefficient on both, the width and the
lateral coupling. These results, in principle, suggest the possible
applicability of such atomic wires as electronic devices, such as, e.g.,
switches.Comment: 9 pages, 5 figures, accepted for publication in Eur. Phys. J.
Development of a pulsar-based timescale
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA)
project we develop the first pulsar-based timescale that has a precision
comparable to the uncertainties in international atomic timescales. Our
ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the
free atomic timescale Echelle Atomique Libre (EAL). The EPS can be used to
detect fluctuations in atomic timescales and therefore can lead to a new
realisation of Terrestrial Time, TT(PPTA11). We successfully follow features
known to affect the frequency of the International Atomic Timescale (TAI) and
we find marginally significant differences between TT(PPTA11) and TT(BIPM11).
We discuss the various phenomena that lead to a correlated signal in the pulsar
timing residuals and therefore limit the stability of the pulsar timescale.Comment: Accepted for publication in MNRA
Mapping the structure of Borneo's tropical forests across a degradation gradient
South East Asia has the highest rate of lowland forest loss of any tropical region, with logging and deforestation for conversion to plantation agriculture being flagged as the most urgent threats. Detecting and mapping logging impacts on forest structure is a primary conservation concern, as these impacts feed through to changes in biodiversity and ecosystem functions. Here, we test whether high-spatial resolution satellite remote sensing can be used to map the responses of aboveground live tree biomass (AGB), canopy leaf area index (LAI) and fractional vegetation cover (FCover) to selective logging and deforestation in Malaysian Borneo. We measured these attributes in permanent vegetation plots in rainforest and oil palm plantations across the degradation landscape of the Stability of Altered Forest Ecosystems project. We found significant mathematical relationships between field-measured structure and satellite-derived spectral and texture information, explaining up to 62% of variation in biophysical structure across forest and oil palm plots. These relationships held at different aggregation levels from plots to forest disturbance types and oil palms allowing us to map aboveground biomass and canopy structure across the degradation landscape. The maps reveal considerable spatial variation in the impacts of previous logging, a pattern that was less clear when considering field data alone. Up-scaled maps revealed a pronounced decline in aboveground live tree biomass with increasing disturbance, impacts which are also clearly visible in the field data even a decade after logging. Field data demonstrate a rapid recovery in forest canopy structure with the canopy recovering to pre-disturbance levels a decade after logging. Yet, up-scaled maps show that both LAI and FCover are still reduced in logged compared to primary forest stands and markedly lower in oil palm stands. While uncertainties remain, these maps can now be utilised to identify conservation win–wins, especially when combining them with ongoing biodiversity surveys and measurements of carbon sequestration, hydrological cycles and microclimate
Route to nonlocality and observation of accessible solitons
We develop a general theory of spatial solitons in a liquid crystalline
medium exhibiting a nonlinearity with an arbitrary degree of effective
nonlocality. The model accounts the observability of "accessible solitons" and
establishes an important link with parametric solitons.Comment: 4 pages, 2 figure
Relative spins and excitation energies of superdeformed bands in 190Hg: Further evidence for octupole vibration
An experiment using the Eurogam Phase II gamma-ray spectrometer confirms the
existence of an excited superdeformed (SD) band in 190Hg and its very unusual
decay into the lowest SD band over 3-4 transitions. The energies and dipole
character of the transitions linking the two SD bands have been firmly
established. Comparisons with RPA calculations indicate that the excited SD
band can be interpreted as an octupole-vibrational structure.Comment: 12 pages, latex, 4 figures available via WWW at
http://www.phy.anl.gov/bgo/bc/hg190_nucl_ex.htm
The Parkes Observatory Pulsar Data Archive
The Parkes pulsar data archive currently provides access to 144044 data files
obtained from observations carried out at the Parkes observatory since the year
1991. Around 10^5 files are from surveys of the sky, the remainder are
observations of 775 individual pulsars and their corresponding calibration
signals. Survey observations are included from the Parkes 70cm and the
Swinburne Intermediate Latitude surveys. Individual pulsar observations are
included from young pulsar timing projects, the Parkes Pulsar Timing Array and
from the PULSE@Parkes outreach program. The data files and access methods are
compatible with Virtual Observatory protocols. This paper describes the data
currently stored in the archive and presents ways in which these data can be
searched and downloaded.Comment: Accepted by PAS
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