Numerical analyses for improved terminal velocity of deep water torpedo anchor

Purpose: This research aims to investigate the effects of manipulation of a torpedo’s geometries to attain higher terminal velocity. The parameters of interest include geometric changes of the original design, as well as sea water properties that reflect water depth in South China Sea. Design/methodology/approach: The research make use of computational fluid dynamics (CFD) software, FLUENT, to solve viscous incompressible Navier–Stokes equations with two equations k-epsilon turbulent model. The calculated drag coefficient is subsequently used to calculate the maximum attainable terminal velocity of the torpedo. Findings: It was found that the terminal velocity can be improved by sharper tip angle, greater aspect ratio, greater diameter ratio and optimum rear angle at 30°. Sensitivity of drag coefficient toward each of the parameters is established in this paper. Originality/value: The paper, in addition to verifying the importance of aspect ratio, has also established the tip angle, diameter ratio and rear angle of the torpedo as important geometric aspects that could be tuned to improve its terminal velocity

Superconducting instability in the Holstein-Hubbard model: A numerical renormalization group study

We have studied the d-wave pairing-instability in the two-dimensional Holstein-Hubbard model at the level of a full fluctuation exchange approximation which treats both Coulomb and electron-phonon (EP) interaction diagrammatically on an equal footing. A generalized numerical renormalization group technique has been developed to solve the resulting self-consistent field equations. The $d$-wave superconducting phase diagram shows an optimal T_c at electron concentration ~ 0.9 for the purely electronic Hubbard system. The EP interaction suppresses the d-wave T_c which drops to zero when the phonon-mediated on-site attraction $U_p$ becomes comparable to the on-site Coulomb repulsion $U$. The isotope exponent $\alpha$ is negative in this model and small compared to the classical BCS value $\alpha_{BCS} = 1/2$ or compared to typical observed values in non-optimally doped cuprate superconductors.Comment: 4 pages RevTeX + 3 PS figures include

Intersectionality and Feminist Pedagogy: Lessons from Teaching about Racism and Economic Inequity

This paper utilizes Rochester, NY, as a case study to argue that approaching race intersectionally and across disciplines creates a stronger model of feminist pedagogy. It is based on our work in the classroom and on the Fisher Race Initiatives—a series of three interactive workshops we created on our campus to create change in the aftermath of the Michael Brown shooting in Ferguson, MO, and in the subsequent rise of the #BlackLivesMatter movement. Our goals were to promote dialogue on race, to expose participants to factual information on race, and to emphasize the intersectional causes of poverty in the Rochester region. We use the framework of Gunnar Myrdal’s vicious circle theory about the perpetual cycle of black poverty and white racism to present how racism engenders and promulgates economic inequity, and we describe that framework here in the context of the Rochester region. We look at historical and current examples in the housing and education markets as specific examples of institutionalized racism and how it perpetuates the cycle of poverty. We conclude our paper by reflecting on how this intersectional interdisciplinary approach provides valuable lessons for faculty and students on diminishing unaware/unintentional racism and white privilege and promoting a more equitable campus committed to social justice

Elastic Wavefield Modeling for Arbitrarily Oriented Orthotropic Media

Composite materials have gained a considerable importance, being widely applied e.g. in aerospace industries as unidirectional, layered or woven structures. Through their complex build-up these materials exhibit anisotropic elastic behavior, raising considerable difficulties for ultrasonic nondestructive testing techniques. In modeling the interaction of elastic waves with such media a simple tool of assisting analysis is available. In this respect, simulation and optimization allow for a reduction of experimental work and an increase in reliability of applied testing procedures. For materials exhibiting orthotropic elastic symmetry, fundamental plane wave characteristics are presented in this contribution. These relationships are further applied for transducer-field modeling using the Generalized Point Source Synthesis method [1]. Since for complex-shaped components the material’s natural symmetry planes are in general not identical with the component’s surfaces, a respective transformation has been applied recently to yield a compact elastic tensor representation for such configurations [2]. Based on this formulation, all analytical results are obtained in a coordinate-free form, where the material’s spatial orientation appears as an additional parameter. Since orthotropy includes the higher symmetries tetragonal, transversely isotropic, cubic and isotropic, the results presented cover most of the materials of today’s industrial interest. Numerical results cover slowness and group velocity diagrams as well as field pattern calculations for commercial transducers including time-depedent rf-impulse modeling

Multiple organ dysfunction caused by parathyroid adenoma‑induced primary hyperparathyroidism

We present a 27‑year‑old male with multiple organ dysfunction caused by parathyroid adenoma‑induced primary hyperparathyroidism (PHPT). Initially, the patient experienced a sudden onset of gastrointestinal symptoms, polyuria, polydipsia, bone pain, renal dysfunction, nephrolithiasis, and acute pancreatitis, symptoms associated with hypercalcemia. Biochemical findings suggested PHPT. Renal biopsy showed an acute tubular injury and massive calcium deposits in the tubular epithelial cells and tubular lumina. Moreover, neck ultrasonography suggested the possibility of a parathyroid tumor. We excised his right parathyroid gland. Histopathological analysis revealed features of a parathyroid adenoma. Post‑operatively this patient had normal serum calcium concentration, but was renally insufficient. A recent repeat biopsy showed chronic renal tubular injury. Our findings illustrate the complications of various systems that can occur in patients with PHPT caused by a parathyroid adenoma.Key words: Hypercalcemia, parathyroid adenoma, parathyroid hormone, primary hyperparathyroidis

The Isotope Effect in d-Wave Superconductors

Based on recently proposed anti-ferromagnetic spin fluctuation exchange models for $d_{x^2-y^2}$-superconductors, we show that coupling to harmonic phonons {\it{cannot}} account for the observed isotope effect in the cuprate high-$T_c$ materials, whereas coupling to strongly anharmonic multiple-well lattice tunneling modes {\it{can}}. Our results thus point towards a strongly enhanced {\it{effective}} electron-phonon coupling and a possible break-down of Migdal-Eliashberg theory in the cuprates.Comment: 12 pages + 2 figures, Postscript files, all uuencoded Phys. Rev. Lett. (1995, to be published

Asymmetric Fermi superfluid with different atomic species in a harmonic trap

We study the dilute fermion gas with pairing between two species and unequal concentrations in a harmonic trap using the mean field theory and the local density approximation. We found that the system can exhibit a superfluid shell structure sandwiched by the normal fermions. This superfluid shell structure occurs if the mass ratio is larger then certain critical value which increases from the weak-coupling BCS region to the strong-coupling BEC side. In the strong coupling BEC regime, the radii of superfluid phase are less sensitive to the mass ratios and are similar to the case of pairing with equal masses. However, the lighter leftover fermions are easier to mix with the superfluid core than the heavier ones. A partially polarized superfluid can be found if the majority fermions are lighter, whereas phase separation is still found if they are heavier.Comment: 12 pages, 7 figure

Fluctuation Exchange Analysis of Superconductivity in the Standard Three-Band CuO2 Model

The fluctuation exchange, or FLEX, approximation for interacting electrons is applied to study instabilities in the standard three-band model for CuO2 layers in the high-temperature superconductors. Both intra-orbital and near-neigbor Coulomb interactions are retained. The filling dependence of the d(x2-y2) transition temperature is studied in both the "hole-doped" and "electron-doped" regimes using parameters derived from constrained-occupancy density-functional theory for La2CuO4. The agreement with experiment on the overdoped hole side of the phase diagram is remarkably good, i.e., transitions emerge in the 40 K range with no free parameters. In addition the importance of the "orbital antiferromagnetic," or flux phase, charge density channel is emphasized for an understanding of the underdoped regime.Comment: REVTex and PostScript, 31 pages, 26 figures; to appear in Phys. Rev. B (1998); only revised EPS figures 3, 4, 6a, 6b, 6c, 7 and 8 to correct disappearance of some labels due to technical problem

Effect of a Normal-State Pseudogap on Optical Conductivity in Underdoped Cuprate Superconductors

We calculate the c-axis infrared conductivity $\sigma_c(\omega)$ in underdoped cuprate superconductors for spinfluctuation exchange scattering within the CuO$_2$-planes including a phenomenological d-wave pseudogap of amplitude $E_g$. For temperatures decreasing below a temperature $T^* \sim E_g/2$, a gap for $\omega < 2E_g$ develops in $\sigma_c(\omega)$ in the incoherent (diffuse) transmission limit. The resistivity shows 'semiconducting' behavior, i.e. it increases for low temperatures above the constant behavior for $E_g=0$. We find that the pseudogap structure in the in-plane optical conductivity is about twice as big as in the interplane conductivity $\sigma_c(\omega)$, in qualitative agreement with experiment. This is a consequence of the fact that the spinfluctuation exchange interaction is suppressed at low frequencies as a result of the opening of the pseudogap. While the c-axis conductivity in the underdoped regime is described best by incoherent transmission, in the overdoped regime coherent conductance gives a better description.Comment: to be published in Phys. Rev. B (November 1, 1999

Stability of condensate in superconductors

According to the BCS theory the superconducting condensate develops in a single quantum mode and no Cooper pairs out of the condensate are assumed. Here we discuss a mechanism by which the successful mode inhibits condensation in neighboring modes and suppresses a creation of noncondensed Cooper pairs. It is shown that condensed and noncondensed Cooper pairs are separated by an energy gap which is smaller than the superconducting gap but large enough to prevent nucleation in all other modes and to eliminate effects of noncondensed Cooper pairs on properties of superconductors. Our result thus justifies basic assumptions of the BCS theory and confirms that the BCS condensate is stable with respect to two-particle excitations