Biomedical subjects

J C Davis

Publications and source records attributed to J C Davis.

At least 19 recordsLinked to original sources

PubMed2006

The ground state of the pseudogap in cuprate superconductors.

We present studies of the electronic structure of La(2-x)BaxCuO4, a system where the superconductivity is strongly suppressed as static spin and charge orders or "stripes" develop near the doping level of x = (1/8). Using angle-resolved photoemission and scanning tunneling microscopy, we detect an energy gap at the Fermi surface with magnitude consistent with d-wave symmetry and with linear density of states, vanishing only at four nodal points, even when superconductivity disappears at x = (1/8). Thus, the nonsuperconducting, striped state at x = (1/8) is consistent with a phase-incoherent d-wave superconductor whose Cooper pairs form spin-charge-ordered structures instead of becoming superconducting.

Journal Article↗

PubMed2006

Effects of pairing potential scattering on Fourier-transformed inelastic tunneling spectra of high-Tc cuprate superconductors with bosonic modes.

Recent scanning tunneling microscopy (STM) experimentally observed strong gap inhomogeneity in Bi2Sr2CaCu2O(8+delta) (BSCCO). We argue that disorder in the pair potential underlies the gap inhomogeneity, and investigate its role in the Fourier-transformed inelastic tunneling spectra as revealed in the STM. We find that the random pair potential induces unique q-space patterns in the local density of states (LDOS) of a d-wave superconductor. We consider the effects of electron coupling to various bosonic modes and find the pattern of LDOS modulation due to coupling to the B(1g) phonon mode to be consistent with the one observed in the inelastic electron tunnneling STM experiment in BSCCO. These results suggest strong electron-lattice coupling as an essential part of the superconducting state in high-Tc materials.

Journal Article↗

PubMed2006

Interplay of electron-lattice interactions and superconductivity in superconductivity in Bi2Sr2CaCu2O8+delta.

Formation of electron pairs is essential to superconductivity. For conventional superconductors, tunnelling spectroscopy has established that pairing is mediated by bosonic modes (phonons); a peak in the second derivative of tunnel current d2I/dV2 corresponds to each phonon mode. For high-transition-temperature (high-T(c)) superconductivity, however, no boson mediating electron pairing has been identified. One explanation could be that electron pair formation and related electron-boson interactions are heterogeneous at the atomic scale and therefore challenging to characterize. However, with the latest advances in d2I/dV2 spectroscopy using scanning tunnelling microscopy, it has become possible to study bosonic modes directly at the atomic scale. Here we report d2I/dV2 imaging studies of the high-T(c) superconductor Bi2Sr2CaCu2O8+delta. We find intense disorder of electron-boson interaction energies at the nanometre scale, along with the expected modulations in d2I/dV2 (refs 9, 10). Changing the density of holes has minimal effects on both the average mode energies and the modulations, indicating that the bosonic modes are unrelated to electronic or magnetic structure. Instead, the modes appear to be local lattice vibrations, as substitution of 18O for 16O throughout the material reduces the average mode energy by approximately 6 per cent--the expected effect of this isotope substitution on lattice vibration frequencies. Significantly, the mode energies are always spatially anticorrelated with the superconducting pairing-gap energies, suggesting an interplay between these lattice vibration modes and the superconductivity.

Journal Article↗

PubMed2006

Community-dwelling seniors who present to the emergency department with a fall do not receive Guideline care and their fall risk profile worsens significantly: a 6-month prospective study.

INTRODUCTION: Fall risk is a major contributor to fracture risk; implementing fall reduction programmes remains a challenge for health professionals and policy-makers. MATERIALS AND METHODS: We aimed to (1) ascertain whether the care received by 54 older adults after an emergency department (ED) fall presentation met internationally recommended 'Guideline Care', and (2) prospectively evaluate this cohort's 6-month change in fall risk profile. Participants were men and women aged 70 years or older who were discharged back into the community after presenting to an urban university tertiary-care hospital emergency department with a fall-related complaint. American Geriatric Society (AGS) guideline care was documented by post-presentation emergency department chart examination, daily patient diary of falls submitted monthly, patient interview and physician reconciliation where needed. Both at study entry and at a 6-month followup, we measured participants physiological characteristics by Lord's Physiological Profile Assessment (PPA), functional status, balance confidence, depression, physical activity and other factors. RESULTS: We found that only 2 of 54 (3.7%) of the fallers who presented to the ED received care consistent with AGS Guidelines. Baseline physiological fall risk scores classified the study population at a 1.7 SD higher risk than a 65-year-old comparison group, and during the 6-month followup period the mean fall-risk score increased significantly (i.e. greater risk of falls) (1.7+/-1.6 versus 2.2+/-1.6, p=0.000; 29.5% greater risk of falls). Also, functional ability [100 (15) versus 95 (25), p=0.002], balance confidence [82.5 (44.4) versus 71.3 (58.7), p=0.000] and depression [0 (2) versus 0 (3), p=0.000] all worsened over 6 months. Within 6 months of the index ED visit, five participants had suffered six fall-related fractures. DISCUSSION: We conclude that this group of community-dwelling fallers, who presented for ED care with a clinical profile suggesting a high risk of further falls and fracture, did not receive Guideline care and worsened in their fall risk profile by 29.5%. This gap in care, at least in one centre, suggests further investigation into alternative approaches to delivering Guideline standard health service.

Accidental Falls↗

PubMed2006

Definition of disease duration in ankylosing spondylitis: reassessing the concept.

The concept and definition of disease duration in patients with ankylosing spondylitis is ambiguous, and often many years pass between the onset of symptoms and diagnosis. Members of the Assessment in Ankylosing Spondylitis (ASAS) International Working Group by consensus recently recommended identifying specific components of the medical history to better define and document the concept of disease duration. These include (1) the time of onset of the first symptoms of axial manifestations (including inflammatory back pain); (2) the time of onset of the first symptoms of each individual manifestation, which may be an extra-axial sign or symptom of ankylosing spondylitis, such as peripheral arthritis and enthesitis; (3) the time of onset of associated diseases belonging to the spondyloarthritides, in particular acute anterior uveitis, inflammatory bowel disease and psoriasis; and (4) the time since actual diagnosis by a healthcare provider. Such uniformity in data collection will ensure comparability across studies and facilitate future research.

Acute Disease↗

PubMed2005

ASAS/EULAR recommendations for the management of ankylosing spondylitis.

OBJECTIVE: To develop evidence based recommendations for the management of ankylosing spondylitis (AS) as a combined effort of the 'ASsessment in AS' international working group and the European League Against Rheumatism. METHODS: Each of the 22 participants was asked to contribute up to 15 propositions describing key clinical aspects of AS management. A Delphi process was used to select 10 final propositions. A systematic literature search was then performed to obtain scientific evidence for each proposition. Outcome data for efficacy, adverse effects, and cost effectiveness were abstracted. The effect size, relative risk, number needed to treat, and incremental cost effectiveness ratio were calculated. On the basis of the search results, 10 major recommendations for the management of AS were constructed. The strength of recommendation was assessed based on the strength of the literature evidence, risk-benefit trade-off, and clinical expertise. RESULTS: The final recommendations considered the use of non-steroidal anti-inflammatory drugs (NSAIDs) (conventional NSAIDs, coxibs, and co-prescription of gastroprotective agents), disease modifying antirheumatic drugs, treatments with biological agents, simple analgesics, local and systemic steroids, non-pharmacological treatment (including education, exercise, and physiotherapy), and surgical interventions. Three general recommendations were also included. Research evidence (categories I-IV) supported 11 interventions in the treatment of AS. Strength of recommendation varied, depending on the category of evidence and expert opinion. CONCLUSION: Ten key recommendations for the treatment of AS were developed and assessed using a combination of research based evidence and expert consensus. Regular updating will be carried out to keep abreast of new developments in the management of AS.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed2005

Atomic-Scale Sources and Mechanism of Nanoscale Electronic Disorder in Bi2Sr2CaCu2O8+delta.

The randomness of dopant atom distributions in cuprate high-critical temperature superconductors has long been suspected to cause nanoscale electronic disorder. In the superconductor Bi2Sr2CaCu2O8+delta, we identified populations of atomic-scale impurity states whose spatial densities follow closely those of the oxygen dopant atoms. We found that the impurity-state locations are strongly correlated with all manifestations of the nanoscale electronic disorder. This disorder occurs via an unanticipated mechanism exhibiting high-energy spectral weight shifts, with associated strong superconducting coherence peak suppression but very weak scattering of low-energy quasi-particles.

Journal Article↗

PubMed2005

Coincidence of checkerboard charge order and antinodal state decoherence in strongly underdoped superconducting Bi2Sr2CaCu2O8 + delta).

The doping dependence of nanoscale electronic structure in superconducting Bi(2)Sr(2)CaCu(2)O(8 + delta) is studied by scanning tunneling microscopy. At all dopings, the low energy density-of-states modulations are analyzed according to a simple model of quasiparticle interference and found to be consistent with Fermi-arc superconductivity. The superconducting coherence peaks, ubiquitous in near-optimal tunneling spectra, are destroyed with strong underdoping and a new spectral type appears. Exclusively in regions exhibiting this new spectrum, we find local "checkerboard" charge ordering of high energy states, with a wave vector of Q = (+/- 2pi/4.5a(0),0); (0, +/- 2pi/4.5a(0)) +/- 15%. Surprisingly, this spatial ordering of high energy states coexists harmoniously with the low energy Bogoliubov quasiparticle states.

Journal Article↗

PubMed2005

Type I interferon correlates with serological and clinical manifestations of SLE.

BACKGROUND: Systemic lupus erythematosus (SLE) is an autoimmune disease affecting multiple organ systems triggered by the production of autoantibodies. Previous clinical studies in humans and murine models suggest that type I interferons (IFNs) are important for the initiation and potentiation of SLE activity. METHODS: 65 consecutive patients with SLE were identified from the University of California, San Francisco Lupus Clinic with moderate-severe disease activity. 94 serological samples were collected. Type I IFN levels and the ability of plasma to induce expression of several surface markers of dendritic cell maturation were measured. RESULTS: Type I IFN levels correlated with the presence of cutaneous manifestations, and there was a trend towards correlation with renal disease. No correlation was found between type I IFN levels and neurological disease. Type I IFN levels correlated positively with the SLEDAI score and anti-dsDNA levels and inversely with C3 levels. Interestingly, type I IFN levels were highest in African American patients. SLE plasma also induced the expression of MHC class I, CD38, and CD123 on monocytes, and was blocked by the addition of a monoclonal antibody to IFNAR1. CONCLUSIONS: The pathogenic role of type I IFN is suggested by the induction of cell surface markers for dendritic cell maturation. The potential therapeutic utility of antibodies directed to either type I IFN or IFNAR1/IFNAR2 may be of interest in further studies.

Adult↗

PubMed2005

Sustained durability and tolerability of etanercept in ankylosing spondylitis for 96 weeks.

OBJECTIVE: To evaluate the continued safety and durability of clinical response in patients with ankylosing spondylitis receiving etanercept. METHODS: 277 patients who had participated in a previous randomised, double blind, placebo controlled 24 week trial were eligible to continue in this open label extension study. All patients who enrolled in the open label extension (n = 257) received subcutaneous etanercept 25 mg twice weekly for up to 72 weeks, for a combined 96 weeks of cumulative trial and open label experience. For the patients who had received etanercept for 24 weeks in the double blind trial, this represented almost 2 years of continuous etanercept treatment. RESULTS: Patients continuing etanercept treatment had a sustained response for almost 2 years, with 74% achieving an ASsessments in Ankylosing Spondylitis 20% (ASAS 20) response after 96 weeks of etanercept treatment. Patients who had received placebo in the preceding double blind trial had similar responses, with 70% of patients attaining an ASAS 20 response after 24 weeks of etanercept treatment and 78% achieving an ASAS 20 response after 72 weeks. Improved spinal mobility was seen in both groups. Etanercept was well tolerated in patients treated for up to 96 weeks. CONCLUSION: The subcutaneous administration of twice weekly doses of etanercept provided sustained durability of response in the improvement of signs and symptoms of ankylosing spondylitis for nearly 2 years.

Adolescent↗

PubMed2005

Lamivudine is not effective in primary Sjögren's syndrome.

BACKGROUND: Retroviral infection has been implicated in the pathogenesis of primary Sjögren's syndrome. OBJECTIVE: To examine the efficacy of the reverse transcriptase inhibitor lamivudine in patients with this syndrome. METHODS: 16 patients with primary Sjögren's syndrome were randomised to receive either lamivudine 150 mg twice daily or placebo for three months. Measures of lacrimal and salivary function, including minor salivary gland biopsies, were obtained before and after treatment. RESULTS: Treatment with lamivudine did not result in significant improvement in the primary outcome measure of unstimulated whole salivary flow or other secondary measures, including minor salivary gland biopsy focus scores. CONCLUSION: Lamivudine is not effective in patients with primary Sjögren's syndrome, suggesting either that a retroviral aetiology is not present or that it may be important only in early disease.

Adult↗

PubMed2005

The post-operative analgesic efficacy and tolerability of lumiracoxib compared with placebo and naproxen after total knee or hip arthroplasty.

BACKGROUND: Lumiracoxib is a novel selective cyclooxygenase-2 (COX-2) inhibitor in development for the treatment of chronic and acute pain. METHODS: This randomized, double-blind multicentre study enrolled 180 patients (aged 18-80 years) with moderate-to-severe pain (>or=2 on a 4-point categorical scale) within 48 h of unilateral total knee or total hip arthroplasty. Patients were randomized to receive lumiracoxib 400 mg once daily (n = 60), placebo (n = 60) or naproxen 500 mg twice daily (n = 60). The study consisted of a 12-h single-dose phase followed by a multiple-dose phase (up to 96 h or until discontinuation). The primary efficacy measure was the summed (time-weighted) pain intensity difference over 0-8 h after the first dose (SPID-8). RESULTS: Lumiracoxib and naproxen were comparable and both treatments were superior to placebo for the primary efficacy measure, SPID-8. Both treatments were generally similar and also superior to placebo for the secondary efficacy measures during both the single- and multiple-dose phases for up to 96 h. Both active treatments were well tolerated. CONCLUSION: Lumiracoxib is an effective alternative to traditional non-selective non-steroidal anti-inflammatory drugs (NSAIDs) for the treatment of post-operative pain.

Adolescent↗

PubMed2004

A 'checkerboard' electronic crystal state in lightly hole-doped Ca2-xNaxCuO2Cl2.

The phase diagram of hole-doped copper oxides shows four different electronic phases existing at zero temperature. Familiar among these are the Mott insulator, high-transition-temperature superconductor and metallic phases. A fourth phase, of unknown identity, occurs at light doping along the zero-temperature bound of the 'pseudogap' regime. This regime is rich in peculiar electronic phenomena, prompting numerous proposals that it contains some form of hidden electronic order. Here we present low-temperature electronic structure imaging studies of a lightly hole-doped copper oxide: Ca2-xNaxCuO2Cl2. Tunnelling spectroscopy (at energies |E| > 100 meV) reveals electron extraction probabilities greatly exceeding those for injection, as anticipated for a doped Mott insulator. However, for |E| < 100 meV, the spectrum exhibits a V-shaped energy gap centred on E = 0. States within this gap undergo intense spatial modulations, with the spatial correlations of a four CuO2-unit-cell square 'checkerboard', independent of energy. Intricate atomic-scale electronic structure variations also exist within the checkerboard. These data are consistent with an unanticipated crystalline electronic state, possibly the hidden electronic order, existing in the zero-temperature pseudogap regime of Ca2-xNaxCuO2Cl2.

Journal Article↗

PubMed2004

The role of balance and agility training in fall reduction. A comprehensive review.

AIM: In the elderly, falls and fall-related injuries are a major problem worldwide and the number of injuries are continuing to increase. It is well established that stability requires a well-functioning muscular-skeletal system as well as an intact balance system. The purpose of this comprehensive review of controlled trials is to examine the evidence for the value of balance and agility training in preventing falls and injuries resulting from falls in older people. METHODS: Thirteen studies meeting our inclusion criteria have been reviewed. RESULTS: Of these 13 studies, 6 demonstrated a significant reduction in the rate of falls. CONCLUSIONS: The conclusion is drawn that an exercise program with a balance component in healthy community dwelling older people is likely to prevent future falls.

Journal Article↗

PubMed2003

Relating atomic-scale electronic phenomena to wave-like quasiparticle states in superconducting Bi2Sr2CaCu2O8+delta.

The electronic structure of simple crystalline solids can be completely described in terms either of local quantum states in real space (r-space), or of wave-like states defined in momentum-space (k-space). However, in the copper oxide superconductors, neither of these descriptions alone may be sufficient. Indeed, comparisons between r-space and k-space studies of Bi2Sr2CaCu2O8+delta (Bi-2212) reveal numerous unexplained phenomena and apparent contradictions. Here, to explore these issues, we report Fourier transform studies of atomic-scale spatial modulations in the Bi-2212 density of states. When analysed as arising from quasiparticle interference, the modulations yield elements of the Fermi-surface and energy gap in agreement with photoemission experiments. The consistency of numerous sets of dispersing modulations with the quasiparticle interference model shows that no additional order parameter is required. We also explore the momentum-space structure of the unoccupied states that are inaccessible to photoemission, and find strong similarities to the structure of the occupied states. The copper oxide quasiparticles therefore apparently exhibit particle-hole mixing similar to that of conventional superconductors. Near the energy gap maximum, the modulations become intense, commensurate with the crystal, and bounded by nanometre-scale domains. Scattering of the antinodal quasiparticles is therefore strongly influenced by nanometre-scale disorder.

Journal Article↗

PubMed2003

The treatment of ankylosing spondylitis.

Ankylosing spondylitis is an inflammatory disorder affecting the axial skeleton and periphery. Symptoms can often be debilitating. Current therapy for the disease include physical therapy, non-steroidal anti-inflammatory drugs (NSAIDS, anti-rheumatic disease modifying drugs (DMARDS), and the newly developed biologic agents targeting tumor necrosis factor alpha (TNF-alpha). This paper will provide a comprehensive review of these treatments which focusing on evidence based medicine for the daily clinical practice of rheumatology.

Animals↗

PubMed2003

Lymphocyte depletion with fludarabine in patients with psoriatic arthritis: clinical and immunological effects.

OBJECTIVE: To obtain preliminary information on the safety and efficacy of fludarabine in PsA and analyse its immunomodulatory effects in peripheral blood and synovial tissue. METHODS: 15 patients with active PsA who did not respond to DMARDs were randomly allocated to receive fludarabine every four weeks or placebo. Primary outcomes were the proportion of patients who met the ACR20 and the psoriatic arthritis response criteria (PsARC) at 16 weeks. Secondary outcomes were changes in tender or swollen joint counts and scores of the psoriasis area and severity index (PASI). Phenotypic analysis of peripheral blood mononuclear cells (PBMC), synovial immunohistochemistry, and functional analysis of PBMC were used to determine the immunomodulatory effects of fludarabine. RESULTS: At 16 weeks the ACR20 criteria were met by 3/7 (43%) fludarabine treated v 0/8 placebo treated patients (p=0.08); the PsARC was achieved by 4/7 (57%) fludarabine treated v 2/8 (25%) placebo treated patients; and 3/7 (43%) fludarabine treated v 0/7 placebo treated patients had > or =20% improvement in the PASI. Marked peripheral lymphopenia involving naive (CD4(+) CD45RA(+)) and memory (CD4(+) CD45RO(+)) T cells, CD8(+) T cells, and B cells was seen in fludarabine treated patients. CONCLUSIONS: In PsA fludarabine induces significant peripheral, but modest, synovial lymphopenia, and a trend towards improved clinical response.

Adult↗

PubMed2002

Imaging quasiparticle interference in Bi2Sr2CaCu2O8+delta.

Scanning tunneling spectroscopy of the high-Tc superconductor Bi2Sr2CaCu2O8+delta reveals weak, incommensurate, spatial modulations in the tunneling conductance. Images of these energy-dependent modulations are Fourier analyzed to yield the dispersion of their wavevectors. Comparison of the dispersions with photoemission spectroscopy data indicates that quasiparticle interference, due to elastic scattering between characteristic regions of momentum-space, provides a consistent explanation for the conductance modulations, without appeal to another order parameter. These results refocus attention on quasiparticle scattering processes as potential explanations for other incommensurate phenomena in the cuprates. The momentum-resolved tunneling spectroscopy demonstrated here also provides a new technique with which to study quasiparticles in correlated materials.

Journal Article↗