Critical problems of computational aeroacoustics

The aeroacoustics of rigid boundaries is discussed. Lighthill gave a formulation of this problem in which he showed that the sources of the acoustic field were quadrupole in nature. We have preferred a different formulation of the problem, in which the quadrupoles are sources for a nonlinear wave equation, as opposed to the linear one used by Lighthill. This is given here in a figure which also gives further details of a solution procedure for the Euler equations appropriate for the aeroelastic problem and motivated by the analysis of Crow. In accordance with our formulation, we contend that an algorithm for accurate solutions of an inhomogeneous nonlinear wave equation is of prime importance

Project Fog Drops 5. Task 1: A numerical model of advection fog. Task 2: Recommendations for simplified individual zero-gravity cloud physics experiments

A two-dimensional numerical model was used to investigate the formation of marine advection fog. The model predicts the evolution of potential temperature, horizontal wind, water vapor content, and liquid water content in a vertical cross section of the atmosphere as determined by vertical turbulent transfer and horizontal advection, as well as radiative cooling and drop sedimentation. The model is designed to simulate the formation, development, or dissipation of advection fog in response to transfer of heat and moisture between the atmosphere and the surface as driven by advection over horizontal discontinuities in the surface temperature. Results from numerical simulations of advection fog formation are discussed with reference to observations of marine fog. A survey of candidate fog or cloud microphysics experiments which might be performed in the low gravity environment of a shuttle-type spacecraft in presented. Recommendations are given for relatively simple experiments which are relevent to fog modification problems

Understanding Corporate Responsibility: Culture and Complicity

Kipnis's fictional account of the televised treatment of Elaine Robbins clearly shows the surgeon's negligence (Kipnis 2011). The problems with Anodyne's support for the telesurgery breakfast are harder to discern, but show up clearly when we take into consideration how surgical evidence is generated, evaluated, and used by surgeons. Current evidentiary practices in surgery have two major weaknesses, related to the epistemic culture of surgery and to practices of knowledge transmission. We argue that this is a systemic problem, which companies such as Anodyne both contribute to and benefit from. Thus, while we agree with Kipnis's claim that Anodyne is complicit in creating “conditions of danger,” we believe that Anodyne's contributory roles extend beyond creating moral hazards for susceptible surgeons and harms for individual patients. The Epistemic Culture of Surgery By the epistemic culture of surgery, we mean the traditions and practices surrounding the generation, transmission, and uptake of new knowledge in surgery. The traditional research-totreatment pathway starts with a series of clinical trials to test the safety and efficacy of a new drug or device. Such research results are communicated to practitioners via publications in reputable peer-reviewed journals, and used by regulatory bodies such as the U.S. Food and Drug Administration in decisions about whether to approve use of the novel treatment. For several reasons this ideal pathway does not function well in surgery

Vitrification and determination of the crystallization time scales of the bulk-metallic-glass-forming liquid Zr58.5Nb2.8Cu15.6Ni12.8Al10.3

The crystallization kinetics of Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 were studied in an electrostatic levitation (ESL) apparatus. The measured critical cooling rate is 1.75 K/s. Zr58.5Nb2.8Cu15.6Ni12.8Al10.3 is the first bulk-metallic-glass-forming liquid that does not contain beryllium to be vitrified by purely radiative cooling in the ESL. Furthermore, the sluggish crystallization kinetics enable the determination of the time-temperature-transformation (TTT) diagram between the liquidus and the glass transition temperatures. The shortest time to reach crystallization in an isothermal experiment; i.e., the nose of the TTT diagram is 32 s. The nose of the TTT diagram is at 900 K and positioned about 200 K below the liquidus temperature

Analysis of a turbine rotor containing a transverse crack at Oak Creek Unit 17

Transient increases in one, two and three per revolution vibration characteristics of a low pressure steam turbine were observed during steam temperature reduction operations. Vibration and fracture mechanics analyses suggested the presence of a transverse shaft crack which was eventually identified by ultrasonic inspection and confirmed by destructive sectioning. Signature analyses of vibration data recorded over a two-year period prior to crack identification are correlated with fatigue crack growth, which occurred intermittently during transient temperature decreases. The apparent increased response of the rotor to vibration is due to asymmetric stiffness changes introduced by the growing transverse crack. The vibration response is predicted to increase with increasing crack depths in excess of 10% of the shaft diameter. Fracture mechanics analyses predict that fatigue crack growth occurred during periods of steam temperature decrease, when high surface tensile stresses are present. These same transient thermal stresses are shown to have retarded and prevented subsequent fatigue crack growth during steady operation

Equity under the knife: justice and evidence in surgery.

Surgery is an increasingly common and expensive mode of medical intervention. The ethical dimensions of the surgeon-patient relationship including respect for personal autonomy and informed consent are much discussed, but broader equity issues have not received the same attention. This paper extends the understanding of surgical ethics by considering the nature of evidence in surgery and its relationship to a just provision of healthcare for individuals and their populations. Keywords: Surgery; Equity; Justice; Evidence; Health technology assessments; Public health ethic