89 research outputs found
Spin gaps and magnetic structure of NaxCoO2
We present two experiments that provide information on spin anisotropy and
the magnetic structure of NaxCoO2. First, we report low-energy neutron
inelastic scattering measurements of the zone-center magnetic excitations in
the magnetically ordered phase of Na0.75CoO2. The energy spectra suggest the
existence of two gaps, and are very well fitted by a spin-wave model with both
in-plane and out-of-plane anisotropy terms. The gap energies decrease with
increasing temperature and both gaps are found to have closed when the
temperature exceeds the magnetic ordering temperature T_m~22 K. Secondly, we
present neutron diffraction studies of Na0.85CoO2 with a magnetic field applied
approximately parallel to the c axis. For fields in excess of ~8T a magnetic
Bragg peak was observed at the (0,0,3) position in reciprocal space. We
interpret this as a spin-flop transition of the A-type antiferromagnetic
structure, and we show that the spin-flop field is consistent with the size of
the anisotropy gap.Comment: 9 pages, 7 figure
Influence of static Jahn-Teller distortion on the magnetic excitation spectrum of PrO2: A synchrotron x-ray and neutron inelastic scattering study
A synchrotron x-ray diffraction study of the crystallographic structure of
PrO2 in the Jahn-Teller distorted phase is reported. The distortion of the
oxygen sublattice, which was previously ambiguous, is shown to be a chiral
structure in which neighbouring oxygen chains have opposite chiralities. A
temperature dependent study of the magnetic excitation spectrum, probed by
neutron inelastic scattering, is also reported. Changes in the energies and
relative intensities of the crystal field transitions provide an insight into
the interplay between the static and dynamic Jahn-Teller effects.Comment: 7 pages, 6 figure
Magnetic order and dynamics of the charge-ordered antiferromagnet La1.5Sr0.5CoO4
We describe neutron scattering experiments performed to investigate the
magnetic order and dynamics of half-doped La1.5Sr0.5CoO4. This layered
perovskite exhibits a near-ideal checkerboard pattern of Co2+/Co3+ charge order
at temperatures below ~ 800 K. Magnetic correlations are observed at
temperatures below ~ 60 K but static magnetic order only becomes established at
31 K, a temperature at which a kink is observed in the susceptibility. On
warming above 31 K we observed a change in the magnetic correlations which we
attribute either to a spin canting or to a change in the proportion of
inequivalent magnetic domains. The magnetic excitation spectrum is dominated by
an intense band extending above a gap of approximately 3 meV up to a maximum
energy of 16 meV. A weaker band exists in the energy range 20-30 meV. We show
that the excitation spectrum is in excellent quantitative agreement with the
predictions of a spin-wave theory generalized to include the full magnetic
degrees of freedom of high-spin Co2+ ions in an axially distorted crystal
field, coupled by Heisenberg exchange interactions. The magnetic order is found
to be stabilized by dominant antiferromagnetic Co2+ -- Co2+ interactions acting
in a straight line through Co3+. No evidence is found for magnetic scattering
from the Co3+ ions, supporting the view that Co3+ is in the S = 0 state in this
material.Comment: 17 pages, 10 figures. Accepted for publication in Phys. Rev.
A critical assessment of the pairing symmetry in NaxCoO2.yH2O
We examine each of the symmetry-allowed pairing states of NaxCoO2.yH2O and
compare their properties to what is experimentally and theoretically
established about the compound. In this way, we can eliminate the vast majority
of states that are technically allowed and narrow the field to two, both of
f-wave type states. We discuss the expected features of these states and
suggest experiments that can distinguish between them. We also discuss
odd-frequency gap pairing and how it relates to available experimental
evidence
Hour-glass magnetic spectrum in an insulating, hole-doped antiferromagnet
Superconductivity in layered copper-oxide compounds emerges when charge
carriers are added to antiferromagnetically-ordered CuO2 layers. The carriers
destroy the antiferromagnetic order, but strong spin fluctuations persist
throughout the superconducting phase and are intimately linked to
super-conductivity. Neutron scattering measurements of spin fluctuations in
hole-doped copper oxides have revealed an unusual `hour-glass' feature in the
momentum-resolved magnetic spectrum, present in a wide range of superconducting
and non-superconducting materials. There is no widely-accepted explanation for
this feature. One possibility is that it derives from a pattern of alternating
spin and charge stripes, an idea supported by measurements on stripe-ordered
La1.875Ba0.125CuO4. However, many copper oxides without stripe order also
exhibit an hour-glass spectrum$. Here we report the observation of an
hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the
family of superconducting copper oxides. Our system has stripe correlations and
is an insulator, which means its magnetic dynamics can conclusively be ascribed
to stripes. The results provide compelling evidence that the hour-glass
spectrum in the copper-oxide superconductors arises from fluctuating stripes.Comment: 13 pages, 4 figures, to appear in Natur
"I feel so stupid because I can't give a proper answer ..." How older adults describe chronic pain: a qualitative study
Background - Over 50% of older adults experience chronic pain. Poorly managed pain threatens independent functioning, limits social activities and detrimentally affects emotional wellbeing. Yet, chronic pain is not fully understood from older adults’ perspectives; subsequently, pain management in later life is not necessarily based on their priorities or needs. This paper reports a qualitative exploration of older adults’ accounts of living with chronic pain, focusing on how they describe pain, with a view to informing approaches to its assessment.
Methods - Cognitively intact men and women aged over sixty-five who lived in the community opted into the study through responding to advertisements in the media and via contacts with groups and organisations in North-East Scotland. Interviews were transcribed and thematically analysed using a framework approach.
Results - Qualitative individual interviews and one group interview were undertaken with 23 older adults. Following analysis, the following main themes emerged: diversity in conceptualising pain using a simple numerical score; personalising the meaning of pain by way of stories, similes and metaphors; and, contextualising pain in relation to its impact on activities.
Conclusions - The importance of attending to individuals’ stories as a meaningful way of describing pain for older adults is highlighted, suggesting that a narrative approach, as recommended and researched in other areas of medicine, may usefully be applied in pain assessment for older adults. Along with the judicious use of numerical tools, this requires innovative methods to elicit verbal accounts, such as using similes and metaphors to help older adults describe and discuss their experience, and contextualising the effects of pain on activities that are important to them
"I try and smile, I try and be cheery, I try not to be pushy. I try to say ‘I’m here for help’ but I leave feeling… worried’’: A qualitative study of perceptions of interactions with health professionals by community-based older adults with chronic pain
Background: Over 50% of community-dwelling older adults experience chronic pain, which threatens their quality of life. Of importance to their pain management is older people’s interaction with health professionals that, if unsatisfactory, may impair the outcome.
Aims: To add to the limited research specific to older people living with chronic pain in the community, we explored how they perceive their experiences of interacting with health professionals, seeking factors that might optimise these interactions.
Methods: Purposive sampling was used to recruit men and women .65 years with self-reported musculoskeletal chronic pain. Qualitative individual interviews and one group interview were undertaken with 23 participants. Data were transcribed verbatim and underwent Framework Analysis.
Results: Three themes were identified. Seeking help illustrates issues around why older people in the community may or may not seek help for chronic pain, and highlights the potential involvement of social comparison. Importance of diagnosis illustrates the desire for professional validation of their condition and an aversion to vague explanations based on the person’s age. Being listened to and being heard illustrates the importance of empathic communication and understanding expectations, with due respect for the person’s age.
Conclusions: In common with people of all ages, an effective partnership between an older person in pain and health professionals is essential if pain is to be reported, appropriately assessed and managed, because of the subjective nature of pain and its treatment responses. For older people with pain, perception about their age, by both parties in the partnership, is an additional factor that can unnecessarily interfere with the effectiveness of this partnership. Health professionals should engage with older adults to clarify their expectations about pain and its management, which may be influenced by perceptions about age; and to encourage expression of their concerns, which may also be affected by perceptions about age
TrpA1 Regulates Thermal Nociception in Drosophila
Pain is a significant medical concern and represents a major unmet clinical need. The ability to perceive and react to tissue-damaging stimuli is essential in order to maintain bodily integrity in the face of environmental danger. To prevent damage the systems that detect noxious stimuli are therefore under strict evolutionary pressure. We developed a high-throughput behavioral method to identify genes contributing to thermal nociception in the fruit fly and have reported a large-scale screen that identified the Ca2+ channel straightjacket (stj) as a conserved regulator of thermal nociception. Here we present the minimal anatomical and neuronal requirements for Drosophila to avoid noxious heat in our novel behavioral paradigm. Bioinformatics analysis of our whole genome data set revealed 23 genes implicated in Ca2+ signaling that are required for noxious heat avoidance. One of these genes, the conserved thermoreceptor TrpA1, was confirmed as a bona fide “pain” gene in both adult and larval fly nociception paradigms. The nociceptive function of TrpA1 required expression within the Drosophila nervous system, specifically within nociceptive multi-dendritic (MD) sensory neurons. Therefore, our analysis identifies the channel TRPA1 as a conserved regulator of nociception
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