16,189 research outputs found
Relational interpretation of the wave function and a possible way around Bell's theorem
The famous ``spooky action at a distance'' in the EPR-szenario is shown to be
a local interaction, once entanglement is interpreted as a kind of ``nearest
neighbor'' relation among quantum systems. Furthermore, the wave function
itself is interpreted as encoding the ``nearest neighbor'' relations between a
quantum system and spatial points. This interpretation becomes natural, if we
view space and distance in terms of relations among spatial points. Therefore,
``position'' becomes a purely relational concept. This relational picture leads
to a new perspective onto the quantum mechanical formalism, where many of the
``weird'' aspects, like the particle-wave duality, the non-locality of
entanglement, or the ``mystery'' of the double-slit experiment, disappear.
Furthermore, this picture cirumvents the restrictions set by Bell's
inequalities, i.e., a possible (realistic) hidden variable theory based on
these concepts can be local and at the same time reproduce the results of
quantum mechanics.Comment: Accepted for publication in "International Journal of Theoretical
Physics
Evaluating case studies of community-oriented integrated care.
This paper summarises a ten-year conversation within London Journal of Primary Care about the nature of community-oriented integrated care (COIC) and how to develop and evaluate it. COIC means integration of efforts for combined disease-treatment and health-enhancement at local, community level. COIC is similar to the World Health Organisation concept of a Community-Based Coordinating Hub - both require a local geographic area where different organisations align their activities for whole system integration and develop local communities for health. COIC is a necessary part of an integrated system for health and care because it enables multiple insights into 'wicked problems', and multiple services to integrate their activities for people with complex conditions, at the same time helping everyone to collaborate for the health of the local population. The conversation concludes seven aspects of COIC that warrant further attention
Force Dependence of the Michaelis Constant in a Two-State Ratchet Model for Molecular Motors
We present a quantitative analysis of recent data on the kinetics of ATP
hydrolysis, which has presented a puzzle regarding the load dependence of the
Michaelis constant. Within the framework of coarse grained two-state ratchet
models, our analysis not only explains the puzzling data, but provides a
modified Michaelis law, which could be useful as a guide for future
experiments.Comment: 4 pages, 3 eps figures, accepted for publication on Physical Review
Letter
Coulomb drag of Luttinger liquids and quantum-Hall edges
We study the transconductance for two coupled one-dimensional wires or edge
states described by Luttinger liquid models. The wires are assumed to interact
over a finite segment. We find for the interaction parameter that the
drag rate is finite at zero temperature, which cannot occur in a Fermi-liquid
system. The zero temperature drag is, however, cut off at low temperature due
to the finite length of the wires. We also consider edge states in the
fractional quantum Hall regime, and we suggest that the low temperature
enhancement of the drag effect might be seen in the fractional quantum Hall
regime.Comment: 5 pages, 2 figures; to appear in Phys. Rev. Let
Photon-assisted tunneling in a Fe8 Single-Molecule Magnet
The low temperature spin dynamics of a Fe8 Single-Molecule Magnet was studied
under circularly polarized electromagnetic radiation allowing us to establish
clearly photon-assisted tunneling. This effect, while linear at low power,
becomes highly non-linear above a relatively low power threshold. This
non-linearity is attributed to the nature of the coupling of the sample to the
thermostat.These results are of great importance if such systems are to be used
as quantum computers.Comment: 4 pages, 4 figure
A Database of 2MASS Near-Infrared Colors of Magellanic Cloud Star Clusters
The (rest-frame) near-IR domain contains important stellar population
diagnostics and is often used to estimate masses of galaxies at low as well as
high redshifts. However, many stellar population models are still relatively
poorly calibrated in this part of the spectrum. To allow an improvement of this
calibration we present a new database of integrated near-infrared JHKs
magnitudes for 75 star clusters in the Magellanic Clouds, using the 2-Micron
All-Sky Survey (2MASS). The majority of the clusters in our sample have robust
age and metallicity estimates from color-magnitude diagrams available in the
literature, and populate a range of ages from 10 Myr to 15 Gyr and a range in
[Fe/H] from -2.17 to +0.01 dex. A comparison with matched star clusters in the
2MASS Extended Source Catalog (XSC) reveals that the XSC only provides a good
fit to the unresolved component of the cluster stellar population. We also
compare our results with the often-cited single-channel JHK photometry of
Persson and collaborators, and find significant differences, especially for
their 30"-diameter apertures up to ~2.5 mag in the K-band, more than 1 mag in
J-K, and up to 0.5 mag in H-K. Using simulations to center apertures based on
maximum light throughput (as performed by Persson et al, we show that these
differences can be attributed to near-IR-bright cluster stars (e.g., Carbon
stars) located away from the true center of the star clusters. The wide age and
metallicity coverage of our integrated JHKs photometry sample constitutes a
fundamental dataset for testing population synthesis model predictions, and for
direct comparison with near-IR observations of distant stellar populations.Comment: AJ August 2006 issue, 67 pages, 8 tables, 17 figure
Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac
It is shown that our multi-high-frequency (40-200 GHz) resonant cavity
technique yields distortion-free high field EPR spectra for single crystal
samples of the uniaxial and biaxial spin S = 10 single molecule magnets (SMMs)
[Mn12O12(CH3COO)16(H2O)4].2CH3COOH.4H2O and [Fe8O2(OH)12(tacn)6]Br8.9H2O. The
observed lineshapes exhibit a pronounced dependence on temperature, magnetic
field, and the spin quantum numbers (Ms values) associated with the levels
involved in the transitions. Measurements at many frequencies allow us to
separate various contributions to the EPR linewidths, including significant
D-strain, g-strain and broadening due to the random dipolar fields of
neighboring molecules. We also identify asymmetry in some of the EPR lineshapes
for Fe8, and a previously unobserved fine structure to some of the EPR lines
for both the Fe8 and Mn12 systems. These findings prove relevant to the
mechanism of quantum tunneling of magnetization in these SMMs.Comment: Phys. Rev. B, accepted with minor revision
Crossover between Thermally Assisted and Pure Quantum Tunneling in Molecular Magnet Mn12-Acetate
The crossover between thermally assisted and pure quantum tunneling has been
studied in single crystals of high spin (S=10) uniaxial molecular magnet Mn12
using micro-Hall-effect magnetometry. Magnetic hysteresis and relaxation
experiments have been used to investigate the energy levels that determine the
magnetization reversal as a function of magnetic field and temperature. These
experiments demonstrate that the crossover occurs in a narrow (0.1 K) or broad
(1 K) temperature interval depending on the magnitude of the field transverse
to the anisotropy axis.Comment: 5 pages, 4 figure
Predicting the environmental suitability for onchocerciasis in Africa as an aid to elimination planning
Recent evidence suggests that, in some foci, elimination of onchocerciasis from Africa may be feasible with mass drug administration (MDA) of ivermectin. To achieve continental elimination of transmission, mapping surveys will need to be conducted across all implementation units (IUs) for which endemicity status is currently unknown. Using boosted regression tree models with optimised hyperparameter selection, we estimated environmental suitability for onchocerciasis at the 5 × 5-km resolution across Africa. In order to classify IUs that include locations that are environmentally suitable, we used receiver operating characteristic (ROC) analysis to identify an optimal threshold for suitability concordant with locations where onchocerciasis has been previously detected. This threshold value was then used to classify IUs (more suitable or less suitable) based on the location within the IU with the largest mean prediction. Mean estimates of environmental suitability suggest large areas across West and Central Africa, as well as focal areas of East Africa, are suitable for onchocerciasis transmission, consistent with the presence of current control and elimination of transmission efforts. The ROC analysis identified a mean environmental suitability index of 0·71 as a threshold to classify based on the location with the largest mean prediction within the IU. Of the IUs considered for mapping surveys, 50·2% exceed this threshold for suitability in at least one 5 × 5-km location. The formidable scale of data collection required to map onchocerciasis endemicity across the African continent presents an opportunity to use spatial data to identify areas likely to be suitable for onchocerciasis transmission. National onchocerciasis elimination programmes may wish to consider prioritising these IUs for mapping surveys as human resources, laboratory capacity, and programmatic schedules may constrain survey implementation, and possibly delaying MDA initiation in areas that would ultimately qualify
Climate change, climatic variation and extreme biological responses
Extreme climatic events could be major drivers of biodiversity change, but it is unclear whether extreme biological changes are (i) individualistic (species- or group-specific), (ii) commonly associated with unusual climatic events and/or (iii) important determinants of long-term population trends. Using population time series for 238 widespread species (207 Lepidoptera and 31 birds) in England since 1968, we found that population 'crashes' (outliers in terms of species' year-to-year population changes) were 46% more frequent than population 'explosions'. (i) Every year, at least three species experienced extreme changes in population size, and in 41 of the 44 years considered, some species experienced population crashes while others simultaneously experienced population explosions. This suggests that, even within the same broad taxonomic groups, species are exhibiting individualistic dynamics, most probably driven by their responses to different, short-term events associated with climatic variability. (ii) Six out of 44 years showed a significant excess of species experiencing extreme population changes (5 years for Lepidoptera, 1 for birds). These 'consensus years' were associated with climatically extreme years, consistent with a link between extreme population responses and climatic variability, although not all climatically extreme years generated excess numbers of extreme population responses. (iii) Links between extreme population changes and long-term population trends were absent in Lepidoptera and modest (but significant) in birds. We conclude that extreme biological responses are individualistic, in the sense that the extreme population changes of most species are taking place in different years, and that long-term trends of widespread species have not, to date, been dominated by these extreme changes.This article is part of the themed issue 'Behavioural, ecological and evolutionary responses to extreme climatic events'
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