Spectral techniques in jet noise theory

Spectral analysis techniques applied to Lighthill aerodynamic sound equation for unified jet noise theor

Some applications of jet noise theory

Some applications of jet noise theorie

Theory for the Interdependence of High-Tc_c Superconductivity and Dynamical Spin Fluctuations

The doping dependence of the superconducting state for the 2D one-band Hubbard Hamiltonian is determined. By using an Eliashberg-type theory, we find that the gap function $\Delta_{\bf k}$ has a $d_{x^2-y^2}$ symmetry in momentum space and T$_c$ becomes maximal for $13 \; \%$ doping. Since we determine the dynamical excitations directly from real frequency axis calculations, we obtain new structures in the angular resolved density of states related to the occurrence of {\it shadow states} below T$_c$. Explaining the anomalous behavior of photoemission and tunneling experiments in the cuprates, we find a strong interplay between $d$-wave superconductivity and dynamical spin fluctuations.Comment: 4 pages (REVTeX) with 4 figures (Postscript

Noise reduction evaluation of grids in a supersonic air stream with application to Space Shuttle

Near field acoustic measurements were obtained for a model supersonic air jet perturbed by a screen. Noise reduction potential in the vicinity of the space shuttle vehicle during ground launch when the rocket exhaust flow is perturbed by a grid was determined. Both 10 and 12 mesh screens were utilized for this experiment, and each exhibited a noise reduction only at very low frequencies in the near field forward arc. A power spectrum analysis revealed that a modest reduction of from 3 to 5 decibels exists below a Strouhal number S sub t = 0.11. Above S sub t = 0.11 screen harmonics increased the observed sound pressure level. The favorable noise reductions obtained with screens for S sub t 0.11 may be of substantial interest for the space shuttle at ground launch

Theory for Superconducting Properties of the Cuprates: Doping Dependence of the Electronic Excitations and Shadow States

The superconducting phase of the 2D one-band Hubbard model is studied within the FLEX approximation and by using an Eliashberg theory. We investigate the doping dependence of $T_c$, of the gap function $\Delta ({\bf k},\omega)$ and of the effective pairing interaction. Thus we find that $T_c$ becomes maximal for $13 \; \%$ doping. In {\it overdoped} systems $T_c$ decreases due to the weakening of the antiferromagnetic correlations, while in the {\it underdoped} systems due to the decreasing quasi particle lifetimes. Furthermore, we find {\it shadow states} below $T_c$ which affect the electronic excitation spectrum and lead to fine structure in photoemission experiments.Comment: 10 pages (REVTeX) with 5 figures (Postscript

The relationships between depression and other outcomes of chronic illness caregiving

BACKGROUND: Many caregivers with chronically ill relatives suffer from depression. However, the relationship of depression to other outcomes of chronic caregiving remains unclear. This study tested a hypothesized model which proposed that hours of care, stressful life events, social support, age and gender would predict caregivers' outcomes through perceived caregiver stress. Depression was expected to mediate the relationship between perceived stress and outcomes of chronic caregiving (physical function, self-esteem, and marital satisfaction). METHODS: The sample for this secondary data analysis consisted of 236 and 271 subjects from the Americans' Changing Lives, Wave 1, 1986, and Wave 2, 1989, data sets. Measures were constructed from the original study. Structural equation modeling was used to test the hypothesized model, and an exploratory structural modeling method, specification search, was used to develop a data-derived model. Cross-validation was used to verify the paths among variables. RESULTS: Hours of care, age, and gender predicted caregivers' outcomes directly or through perceived caregiver stress (p < .01). Depression mediated the relationship between perceived stress and psychological outcomes and explained 40% and 11% of the variance in self-esteem and marital satisfaction, respectively. CONCLUSION: Depression predicted psychological outcomes. Whether depression predicts physical health outcomes needs to be further explored

Electron Self-Energy of High Temperature Superconductors as Revealed by Angle Resolved Photoemission

In this paper, we review some of the work our group has done in the past few years to obtain the electron self-energy of high temperature superconductors by analysis of angle-resolved photoemission data. We focus on three examples which have revealed: (1) a d-wave superconducting gap, (2) a collective mode in the superconducting state, and (3) pairing correlations in the pseudogap phase. In each case, although a novel result is obtained which captures the essense of the data, the conventional physics used leads to an incomplete picture. This indicates that new physics needs to be developed to obtain a proper understanding of these materials.Comment: 5 pages, revtex, 3 encapsulated postscript figures, SNS97 proceeding

Influence of anodizing process on fatigue life of a machined aluminium alloy

In order to investigate the coupled effects of machining and anodizing processes on fatigue life of alloy 7010-T7451, a series of rotating bending fatigue tests were conducted at 60Hz. In the as machined condition, test results showed that fatigue life is surface roughness dependent and that fatigue life decreases with an increase in surface roughness and this effect is found to be more pronounced in high cycle fatigue where major portion of fatigue life is consumed in nucleating the cracks. Effects of pretreatments, like degreasing and pickling employed prior to anodizing, on fatigue life of the given alloy were also studied. Results demonstrated that degreasing showed no change in fatigue life while pickling had negative impact on fatigue life of specimens. The small decrease in fatigue life of anodized specimens as compare to pickled specimens is attributed to brittle and microcracking of the coating. Scanning electron microscopic (SEM) examination revealed multi-site crack initiation for the pickled and anodized specimens. SEM examination showed that pickling solution attacked the grain boundaries and intermetallic inclusions present on the surface resulting in pits formation. These pits are of primary concern with respect to accelerated fatigue crack nucleation and subsequent anodized coating formation

Faxen relations in solids - a generalized approach to particle motion in elasticity and viscoelasticity

A movable inclusion in an elastic material oscillates as a rigid body with six degrees of freedom. Displacement/rotation and force/moment tensors which express the motion of the inclusion in terms of the displacement and force at arbitrary exterior points are introduced. Using reciprocity arguments two general identities are derived relating these tensors. Applications of the identities to spherical particles provide several new results, including simple expressions for the force and moment on the particle due to plane wave excitation.Comment: 11 pages, 4 figure

The Pairing Mechanism in HTSC investigated by Electronic Raman Scattering

By means of electronic Raman scattering we investigated the symmetry of the energy gap Delta(k), its temperature dependence and its variation with doping of well characterized Bi2Sr2CaCu2O8+delta single crystals. The oxygen content delta was varied between the under- and the overdoped regime by subsequently annealing the same single crystal in Ar and O2, respectively. The symmetry analysis of the polarized electronic Raman scattering is consistent with a d_x^2-y^2-wave symmetry of the energy gap in both regimes. The gap ratio 2Delta_max/k_BT_c and its temperature dependence changes with doping similar to predictions of theories based on paramagnon coupling.Comment: 3 pages, LaTeX, 2 ps figures available on request to [email protected]