Superconductivity and superconducting order parameter phase fluctuations in a weakly doped antiferromagnet

The superconducting properties of a recently proposed phenomenological model for a weakly doped antiferromagnet are analyzed, taking into account fluctuations of the phase of the order parameter. In this model, we assume that the doped charge carriers can't move out of the antiferromagnetic sublattice they were introduced. This case corresponds to the free carrier spectra with the maximum at ${\bf k}=(\pm \pi /2 ,\pm \pi /2)$, as it was observed in ARPES experiments in some of the cuprates in the insulating state [1]. The doping dependence of the superconducting gap and the temperature-carrier density phase diagram of the model are studied in the case of the $d_{x^{2}-y^{2}}$ pairing symmetry and different values of the effective coupling. A possible relevance of the results to the experiments on high-temperature superconductors is discussed.Comment: 16 pages, 4 figure

Control of the unsteady flow in a stator blade row interacting with upstream moving wakes

January 1993Includes bibliographical references (pages 63-66)A computational study of the unsteady flow in a 2-D stator blade row interacting with upstream rotor wakes has been carried out. A direct spectral-element Navier-Stokes solver has been used for the laminar flow regime (Re106 are based on the Baldwin-Lomax turbulence model. The rotor wakes are represented by velocity distortions moving along the inlet boundary of the computational domain. After interception, the rotor wake migrates towards the pressure surface of the stator blades where it forms a pair of counter-rotating vortices. A moving series of such vortex pairs is the dominant form of unsteady flow over the pressure surface. The unsteady flow over the suction surface is characterized by a street of co-rotating vortices, produced in the leading edge region. These vortices consist of boundary layer fluid distorted and detached by the passing wakes.Downstream of the leading edge, each of these vortices induces an associated, opposite-sign vortex. The blade loading fluctuations arising from wake interaction, are of two kinds. First, a strong pressure pulse occurs on the leading edge upon wake interception. This pulse is a potential flow effect associated with the excess tangential velocity in the wake. Second, a moving pattern of pressure fluctuations, associated with the vortices, is present over the blade surface. The pressure fluctuations are negative on the suction surface, and positive on the pressure surface. The unsteady flow features over the suction surface can be adequately represented by linearized perturbation calculations, where the disturbance flow associated with the wakes is linearized about a steady viscous flow. Three parameters influence the unsteady flow over the suction surface-stator blade loading, excess wake momentum in the stator frame, and wake reduced frequency.The strength of the disturbance flow vortices is directly proportional to the wake momentum and decreases at higher reduced frequencies. An adverse pressure gradient results in stronger vortices and pressure fluctuations. On the pressure surface, the amount of unsteady flow depends on the excess wake momentum only. Strategies for controlling the unsteady flow are simulated using appropriate blade surface boundary conditions. Fluid removal from the suction surface prevents formation of vortices and reduces the associated loading disturbances. Fluid injection from the pressure surface reduces the pressure fluctuations there.Supported by the Applied Research Laboratory at Pennsylvania State Universit

Control of the unsteady flow in a stator blade row interacting with upstream moving wakes

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1992.Includes bibliographical references (leaves 63-66).by Theodore V. Valkov.M.S

The effect of upstream rotor vortical disturbances on the time-average performance of axial compressor stators

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997.Includes bibliographical references (p. 121-130).by Theodore V. Valkov.Sc.D

Direct Ascription of Missing Categorical Values in Survey Research Data

The complete datasets are a prerequisite for sustainable analyses, robust an- alytics and unbiased interpretation of results. Missing values in a survey occur when no data value is stored for the variable in an observation. Missing data can have a significant effect on the conclusions that can be drawn from the data. Direct ascription is the process of replacing missing data with predicted values. The aim of this work is to describe an approach to direct ascription of missing categorical values in survey research data based both on the assumption that values in a data set are missing at random and on the implementation of the correspondence analysis

Effects of low-dosage radiotherapy for knee osteoarthritis on the incidence of knee arthroplasty: Results of a randomized controlled trial with 9-year follow-up

The aim. To compare the incidence of knee arthroplasty in patients receiving standard treatment with non-steroidal anti-inflammatory drugs (NSAIDs) in combination with symptomatic slow acting drugs for osteoarthritis (SYSADOA), or combination of NSAIDs and SYSADOA with low-dose radiation therapy (LDRT) in patients with stage 0–2 knee osteoarthritis (OA). Materials and methods. The article presents the results of randomized controlled study of 292 patients with confirmed knee OA according to Altman’s criteria (1991) and Kellgren – Lawrence radiographic stages 0–2 who were randomized into two groups. The control group (n = 146) received standard therapy of NSAIDs + SYSADOA. Patients of the study group (n  =  146) received combination of standard therapy and  LDRT up to a total dose of 4.5  Gy. The  cumulative risk of knee arthroplasty was assessed using actuarial analysis and the Kaplan – Meier method. Attributable (AF) and population attributable (PAF) fractions were calculated to assess LDRT preventive potential. Results. The total observation period was 2131.2 person-years. Knee arthroplasty was performed in 4.1 % (n = 6) of patients in the study group against 7.5 % (n = 11) in the control group. The  incidence density ratio was 0.60 (95%  CI: 0.18–1.88), which corresponds to a risk reduction by 67 %, but the differences were not statistically significant due to the small number of cases (p = 0.340). The AF was 40 % while the PAF was 21 %. Conclusions. The use of LDRT reduces the risk of knee arthroplasty by two-thirds and has the potential to prevent 21 % cases of knee arthroplasty in patients with knee OA. A study on a larger sample is required

Rare earth elements materials production from apatite ores

The paper deals with the study of processing apatite ores with nitric acid and extraction of the rare earth elements. The rare earth elements can be successfully separated and recovered by extraction from the nitrate- phosphate solution, being an tributyl phosphate as extraction agent. The developed scheme of the processing apatite concentrate provides obtaining rare earth concentrates with high qualitative characteristics

Extraction of rare earth elements from hydrate-phosphate precipitates of apatite processing

The features of extraction of rare earth elements (REE) were considered from hydrate-phosphate precipitates of REE of apatite processing by nitric acid technology. The preliminary purification of nitrate solution of REE from impurities of titanium, aluminum, iron, uranium and thorium was suggested to obtain stable solutions not forming precipitates. Washing the extract was recommended with the evaporated reextract that allows to obtain directly on the cascade of REE extraction the concentrated solutions suitable for the separation into groups by the extraction method. Technical decisions were suggested for the separation of REE in groups without the use of salting-out agent