3,100 research outputs found
Hubbard-model description of the high-energy spin-spectral-weight distribution in La(2)CuO(4)
The spectral-weight distribution in recent neutron scattering experiments on
the parent compound LaCuO (LCO), which are limited in energy range to
about 450\,meV, is studied in the framework of the Hubbard model on the square
lattice with effective nearest-neighbor transfer integral and on-site
repulsion . Our study combines a number of numerical and theoretical
approaches, including, in addition to standard treatments, density matrix
renormalization group calculations for Hubbard cylinders and a suitable spinon
approach for the spin excitations. Our results confirm that the
magnitude suitable to LCO corresponds to intermediate values smaller than
the bandwidth , which we estimate to be eV for
. This confirms the unsuitability of the conventional linear
spin-wave theory. Our theoretical studies provide evidence for the occurrence
of ground-state d-wave spinon pairing in the half-filled Hubbard model on the
square lattice. This pairing applies only to the rotated-electron spin degrees
of freedom, but it could play a role in a possible electron d-wave pairing
formation upon hole doping. We find that the higher-energy spin spectral weight
extends to about 566 meV and is located at and near the momentum .
The continuum weight energy-integrated intensity vanishes or is extremely small
at momentum . This behavior of this intensity is consistent with that
of the spin waves observed in recent high-energy neutron scattering
experiments, which are damped at the momentum . We suggest that future
LCO neutron scattering experiments scan the energies between 450 meV and 566
meV and momenta around .Comment: 23 pages, 5 figure
Skyrmion morphology in ultrathin magnetic films
Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a
non-invasive, high resolution tool to investigate the morphology of isolated
skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to
be strongly affected by local pinning effects and magnetic field history.
Micromagnetic simulations including static disorder, based on a physical model
of grain-to-grain thickness variations, reproduce all experimental observations
and reveal the key role of disorder and magnetic history in the stabilization
of skyrmions in ultrathin magnetic films. This work opens the way to an
in-depth understanding of skyrmion dynamics in real, disordered media.Comment: 9 pages, 8 figures, including supplementary information
Space Shuttle program communication and tracking systems interface analysis
The Space Shuttle Program Communications and Tracking Systems Interface Analysis began April 18, 1983. During this time, the shuttle communication and tracking systems began flight testing. Two areas of analysis documented were a result of observations made during flight tests. These analyses involved the Ku-band communication system. First, there was a detailed analysis of the interface between the solar max data format and the Ku-band communication system including the TDRSS ground station. The second analysis involving the Ku-band communication system was an analysis of the frequency lock loop of the Gunn oscillator used to generate the transmit frequency. The stability of the frequency lock loop was investigated and changes to the design were reviewed to alleviate the potential loss of data due the loop losing lock and entering the reacquisition mode. Other areas of investigation were the S-band antenna analysis and RF coverage analysis
Implicit Regularization and Renormalization of QCD
We apply the Implicit Regularization Technique (IR) in a non-abelian gauge
theory. We show that IR preserves gauge symmetry as encoded in relations
between the renormalizations constants required by the Slavnov-Taylor
identities at the one loop level of QCD. Moreover, we show that the technique
handles divergencies in massive and massless QFT on equal footing.Comment: (11 pages, 2 figures
Scalar Casimir Effect on a D-dimensional Einstein Static Universe
We compute the renormalised energy momentum tensor of a free scalar field
coupled to gravity on an (n+1)-dimensional Einstein Static Universe (ESU),
RxS^n, with arbitrary low energy effective operators (up to mass dimension
n+1). A generic class of regulators is used, together with the Abel-Plana
formula, leading to a manifestly regulator independent result. The general
structure of the divergences is analysed to show that all the gravitational
couplings (not just the cosmological constant) are renormalised for an
arbitrary regulator. Various commonly used methods (damping function,
point-splitting, momentum cut-off and zeta function) are shown to, effectively,
belong to the given class. The final results depend strongly on the parity of
n. A detailed analytical and numerical analysis is performed for the behaviours
of the renormalised energy density and a quantity `sigma' which determines if
the strong energy condition holds for the `quantum fluid'. We briefly discuss
the quantum fluid back-reaction problem, via the higher dimensional Friedmann
and Raychaudhuri equations, observe that equilibrium radii exist and unveil the
possibility of a `Casimir stabilisation of Einstein Static Universes'.Comment: 37 pages, 15 figures, v2: minor changes in sections 1, 2.5, 3 and 4;
version published in CQ
Renal Transplantation in HIV-Infected Patients: The First Portuguese Review
INTRODUCTION: With the introduction of combination antiretroviral therapy (cART), prognosis of human immunodeficiency virus (HIV) infection has been improved and kidney transplantation (KT) in HIV-positive patients became possible.
METHODS: We reviewed the demographic, clinical, laboratory, and therapeutic data of all the HIV-infected patients who underwent KT between 2009 (first KT in Portugal in a HIV-infected patient) and May 2014. Case accrual was through all Portuguese KT centers where a KT in an HIV-infected patient was performed. Patients were transplanted following the American and Spanish guideline recommendations that included maintenance on cART, undetectable plasma HIV RNA copies, and absolute CD4 counts of ≥ 200 cells/μL in the last 6 months.
RESULTS: Fourteen KT were performed on men and 3 on women. The mean age of patients at the time of transplantation was 49.9 ± 11.7 years. HIV status was known for 12 ± 5 years. Eight patients had AIDS in the past and all patients received grafts from deceased donors. Twelve patients (64.7%) underwent induction therapy with basiliximab and 2 patients experienced early graft loss. In 2 patients, humoral rejection was diagnosed and in 3 patients, cellular rejection. Two patients died and an additional patient had early graft loss.
CONCLUSION: KT is a possible, but challenging, renal replacement therapy in selected HIV-positive patients. Even in those with AIDS criteria in the past, when the disease is controlled, and after the reconstitution of the immune system with cART, KT can be performed. Nevertheless, the risk-benefit ratio for each patient needs to be taken in consideration
New Criteria of Indication and Selection of Patients to Cochlear Implant
Numerous changes continue to occur in cochlear implant candidacy. In general, these have been accompanied by concomitant and satisfactory changes in surgical techniques. Together, this has advanced the utility and safety of cochlear implantation. Most devices are now approved for use in patients with severe to profound unilateral hearing loss rather then the prior requirement of a bilateral profound loss. Furthermore, studies have begun utilizing short electrode arrays for shallow insertion in patients with considerable low-frequency residual hearing. This technique will allow the recipient to continue to use acoustically amplified hearing for the low frequencies simultaneously with a cochlear implant for the high frequencies. The advances in design of, and indications for, cochlear implants have been matched by improvements in surgical techniques and decrease in complications. The resulting improvements in safety and efficacy have further encouraged the use of these devices. This paper will review the new concepts in the candidacy of cochlear implant. Medline data base was used to search articles dealing with the following topics: cochlear implant in younger children, cochlear implant and hearing preservation, cochlear implant for unilateral deafness and tinnitus, genetic hearing loss and cochlear implant, bilateral cochlear implant, neuropathy and cochlear implant and neural plasticity, and the selection of patients for cochlear implant
Impact of Renal Dysfunction on Liver Transplantation: a Retrospective Study in 708 Orthotopic Liver Transplant Recipients
Renal dysfunction often complicates the course of orthotopic liver transplant recipients and is associated with increased morbid -mortality.
The aims of this study were to determine the
incidence of chronic renal disease and its impact on patient survival.
Clinical data included age, gender and weight,aetiology of hepatic failure, presence of diabetes,hypertension, hepatitis B and C infection, renal dysfunction pretransplant and immunosuppression.
Laboratory data included serum creatinine at days 1, 7, 21, month 6, 12 and yearly. The glomerular filtration rate was determined by Cockcroft-Gault equation. We studied retrospectively from September 1992 to March 2007 708 orthotopic liver transplant
recipients. Mean age 44±12.6 years, 64% males, 17% diabetic, 18.8% hypertensive, 19.9% with hepatitis C and 3.8% hepatitis B. Renal dysfunction pretransplant was known in 21.6%. Mean follow-up was 3.6 years. Mean transplant survival 75% at 12 months.
154 patients died. Univariate and multivariate analyses were performed and a p<0.05 was considered significant.
Acute kidney injury occurred in 33.2%. Chronic kidney disease stage 3 was observed in 34.3%,stage 4 in 6.2% and stage 5 in 5.1%. At the time of this study, 46.4% were on Cyclosporine A, 44.7% on tacrolimus and 8.9% on sirolimus.
Using multivariate analysis, renal dysfunction was correlated with renal dysfunction pre -orthotopic liver transplant (p<0.001), acute kidney injury (p<0.001), haemodialysis development (p<0.001), and
inversely correlated with the use of mycophenolate mophetil (p<0.001); mortality was positively correlated with renal dysfunction pretransplant (p=0.03),chronic kidney disease stage 4 (p=0.001), chronic
kidney disease stage 5 (p<0.001) and inversely correlated with the use of tacrolimus (p=0.006).
In conclusion orthotopic liver transplant recipients are disposed to renal complications that have a negative impact on survival of these patients
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