17,191 research outputs found
First-order melting of a weak spin-orbit Mott insulator into a correlated metal
The electronic phase diagram of the weak spin-orbit Mott insulator
(Sr(1-x)Lax)3Ir2O7 is determined via an exhaustive experimental study. Upon
doping electrons via La substitution, an immediate collapse in resistivity
occurs along with a narrow regime of nanoscale phase separation comprised of
antiferromagnetic, insulating regions and paramagnetic, metallic puddles
persisting until x~0.04. Continued electron doping results in an abrupt,
first-order phase boundary where the Neel state is suppressed and a homogenous,
correlated, metallic state appears with an enhanced spin susceptibility and
local moments. As the metallic state is stabilized, a weak structural
distortion develops and suggests a competing instability with the parent
spin-orbit Mott state.Comment: 5 pages, 4 figure
Measurements of the Diffuse Ultraviolet Background and the Terrestrial Airglow with the Space Telescope Imaging Spectrograph
Far-UV observations in and near the Hubble Deep Fields demonstrate that the
Space Telescope Imaging Spectrograph (STIS) can potentially obtain unique and
precise measurements of the diffuse far-ultraviolet background. Although STIS
is not the ideal instrument for such measurements, high-resolution images allow
Galactic and extragalactic objects to be masked to very faint magnitudes, thus
ensuring a measurement of the truly diffuse UV signal. The programs we have
analyzed were not designed for this scientific purpose, but would be sufficient
to obtain a very sensitive measurement if it were not for a weak but
larger-than-expected signal from airglow in the STIS 1450-1900 A bandpass. Our
analysis shows that STIS far-UV crystal quartz observations taken near the limb
during orbital day can detect a faint airglow signal, most likely from NI\1493,
that is comparable to the dark rate and inseparable from the far-UV background.
Discarding all but the night data from these datasets gives a diffuse
far-ultraviolet background measurement of 501 +/- 103 ph/cm2/sec/ster/A, along
a line of sight with very low Galactic neutral hydrogen column (N_HI = 1.5E20
cm-2) and extinction (E(B-V)=0.01 mag). This result is in good agreement with
earlier measurements of the far-UV background, and should not include any
significant contribution from airglow. We present our findings as a warning to
other groups who may use the STIS far-UV camera to observe faint extended
targets, and to demonstrate how this measurement may be properly obtained with
STIS.Comment: 7 pages, Latex. 4 figures. Uses corrected version of emulateapj.sty
and apjfonts.sty (included). Accepted for publication in A
Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn12-acetate
We present detailed angle-dependent single crystal electron paramagnetic
resonance (EPR) data for field rotations in the hard plane of the S=10 single
molecule magnet Mn12-acetate. A clear four-fold variation in the resonance
positions may be attributed to an intrinsic fourth order transverse anisotropy
(O44). Meanwhile, a four-fold variation of the EPR lineshapes confirms a
recently proposed model wherein disorder associated with the acetic acid of
crystallization induces a locally varying quadratic (rhombic) transverse
anisotropy (O22). These findings explain most aspects of the magnetic quantum
tunneling observed in Mn12-acetate.Comment: 7 pages, including figures, accepted for publication in Phys. Rev.
Let
Abundance changes and habitat availability drive species’ responses to climate change
There is little consensus as to why there is so much variation in the rates at which different species’ geographic ranges expand in response to climate warming[1,2]. Here, we show for British butterfly species that the relative importance of species’ abundance trends and habitat availability vary over time. Species with high habitat availability expanded more rapidly from the 1970s to mid-1990s, when abundances were generally stable, whereas habitat availability effects were confined to the subset of species with stable abundances from the mid-1990s to 2009, when abundance trends were generally declining. This suggests that stable (or positive) abundance trends are a prerequisite for range expansion. Given that species’ abundance trends vary over time[3] for non-climatic as well as climatic reasons, assessment of abundance trends will help improve predictions of species’ responses to climate change, and help understand the likely success of different conservation strategies for facilitating their expansions
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
Ethical and methodological issues in engaging young people living in poverty with participatory research methods
This paper discusses the methodological and ethical issues arising from a project that focused on conducting a qualitative study using participatory techniques with children and young people living in disadvantage. The main aim of the study was to explore the impact of poverty on children and young people's access to public and private services. The paper is based on the author's perspective of the first stage of the fieldwork from the project. It discusses the ethical implications of involving children and young people in the research process, in particular issues relating to access and recruitment, the role of young people's advisory groups, use of visual data and collection of data in young people's homes. The paper also identifies some strategies for addressing the difficulties encountered in relation to each of these aspects and it considers the benefits of adopting participatory methods when conducting research with children and young people
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
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
Sudakov Resummation for Subleading SCET Currents and Heavy-to-Light Form Factors
The hard-scattering contributions to heavy-to-light form factors at large
recoil are studied systematically in soft-collinear effective theory (SCET).
Large logarithms arising from multiple energy scales are resummed by matching
QCD onto SCET in two stages via an intermediate effective theory. Anomalous
dimensions in the intermediate theory are computed, and their form is shown to
be constrained by conformal symmetry. Renormalization-group evolution equations
are solved to give a complete leading-order analysis of the hard-scattering
contributions, in which all single and double logarithms are resummed. In two
cases, spin-symmetry relations for the soft-overlap contributions to form
factors are shown not to be broken at any order in perturbation theory by
hard-scattering corrections. One-loop matching calculations in the two
effective theories are performed in sample cases, for which the relative
importance of renormalization-group evolution and matching corrections is
investigated. The asymptotic behavior of Sudakov logarithms appearing in the
coefficient functions of the soft-overlap and hard-scattering contributions to
form factors is analyzed.Comment: 50 pages, 10 figures; minor corrections, version to appear in JHE
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