Nonexistence of conformally flat slices of the Kerr spacetime

Initial data for black hole collisions are commonly generated using the Bowen-York approach based on conformally flat 3-geometries. The standard (constant Boyer-Lindquist time) spatial slices of the Kerr spacetime are not conformally flat, so that use of the Bowen-York approach is limited in dealing with rotating holes. We investigate here whether there exist foliations of the Kerr spacetime that are conformally flat. We limit our considerations to foliations that are axisymmetric and that smoothly reduce in the Schwarzschild limit to slices of constant Schwarzschild time. With these restrictions, we show that no conformally flat slices can exist.Comment: 5 LaTeX pages; no figures; to be submitted to Phys. Rev.

Apparatus for establishing flow of a fluid mass having a known velocity

An apparatus for establishing a flow of fluid mass, such as gas, having a known velocity is introduced. The apparatus is characterized by an hermetically sealed chamber conforming to a closed-loop configuration and including a throat and a plurality of axially displaceable pistons for sweeping through the throat a stream of gas including a core and an unsheared boundary layer. Within the throat there is a cylindrical coring body concentrically related to the throat for receiving the core, and a chamber surrounding the cylindrical body for drawing off the boundary layer, whereby the velocity of the core is liberated from the effects of the velocity of the boundary layer

How Much Time for the General Chemistry Laboratory?

The method of teaching science in which a certain amount of opportunity is given each student for work by himself in the laboratory (the so-called individual laboratory method) is of fairly recent development. Many of the early American professors of chemistry did not believe that the beginning student should be allowed to set foot in a laboratory. This was undoubtedly due to the fact that these instructors were educated under the German system of class-room demonstration. According to Lucasse (1) the credit for the development of the first chemistry laboratory for instruction goes to Lomonossoff (1748). Later the passage of the Morrill Land Grant Act of 1862 caused a great development of the laboratory method, in that during the period 1880-1900 there were a great number of university laboratories constructed

The Second Virial Coefficient as a Measure of Gas Imperfection

The combined laws of Boyle and of Gay-Lussac give the familiar formula pv = nRT for the equation of state of any gas. No single gas, however, obeys this law exactly under all conditions. The classical experiment of Joule, moreover, seemed to show that the internal energy of a gas is independent of the volume, or (δU/δV)τ . More exact measurements subsequently performed by Joule and Thomsen established the fact that this conclusion is also inexact for all real gases, but that it is approached more closely the more a gas approaches the \u27ideal state\u27. Deviations from these two laws are caused by the same phenomena, namely, the complexities of the force fields surrounding the molecules and other properties of the individual molecules composing the gas. It may be said that no real gas is ideal and that every gas approaches ideality as the pressure approaches zero or the volume approaches infinity

Numerical simulation of liquid sloshing in a partially filled container with inclusion of compressibility effects

A numerical scheme of study is developed to model compressible two-fluid flows simulating liquid sloshing in a partially filled tank. For a two-fluid system separated by an interface as in the case of sloshing, not only a Mach-uniform scheme is required, but also an effective way to eliminate unphysical numerical oscillations near the interface. By introducing a preconditioner, the governing equations expressed in terms of primitive variables are solved for both fluids (i.e. water, air, gas etc.) in a unified manner. In order to keep the interface sharp and to eliminate unphysical numerical oscillations in unsteady fluid flows, the non-conservative implicit Split Coefficient Matrix Method (SCMM) is modified to construct a flux difference splitting scheme in the dual time formulation. The proposed numerical model is evaluated by comparisons between numerical results and measured data for sloshing in an 80% filled rectangular tank excited at resonance frequency. Through similar comparisons, the investigation is further extended by examining sloshing flows excited by forced sway motions in two different rectangular tanks with 20% and 83% filling ratios. These examples demonstrate that the proposed method is suitable to capture induced free surface waves and to evaluate sloshing pressure loads acting on the tank walls and ceiling

Continuous-flow laboratory simulation of stream water quality changes downstream of an untreated wastewater discharge.

In regions of the world with poor provision of wastewater treatment, raw sewage is often discharged directly into surface waters. This paper describes an experimental evaluation of the fate of two organic chemicals under these conditions using an artificial channel cascade fed with a mix of settled sewage and river water at its upstream end and operated under continuous steady-state conditions. The experiments underpin an environmental risk assessment methodology based on the idea of an “impact zone” (IZ) – the zone downstream of wastewater emission in which water quality is severely impaired by high concentrations of unionised ammonia, nitrite and biochemical oxygen demand (BOD). Radiolabelled dodecane-6-benzene sulphonate (DOBS) and aniline hydrochloride were used as the model chemical and reference compound respectively. Rapid changes in 14C counts were observed with flow-time for both these materials. These changes were most likely to be due to complete mineralisation. A dissipation half-life of approximately 7.1 h was observed for the 14C label with DOBS. The end of the IZ was defined as the point at which the concentration of both unionised ammonia and nitrite fell below their respective predicted no-effect concentrations for salmonids. At these points in the cascade, approximately 83 and 90% of the initial concentration of 14C had been removed from the water column, respectively. A simple model of mineral nitrogen transformations based on Michaelis–Menten kinetics was fitted to observed concentrations of NH4, NO2 and NO3. The cascade is intended to provide a confirmatory methodology for assessing the ecological risks of chemicals under direct discharge co

Exploring the potential of ivr technology to promote collaborative learning in science experiences

This poster explores how different types of virtual reality technology (VR) allow for various degrees of collaborative enactment within virtual environments. This two-staged study analyzed the engagement and reflections of 27 students with three forms of VR hardware. Findings from direct observations and students’ perceptions suggest that the capabilities of high-end immersive virtual reality (IVR) can allow for more meaningful and natural forms of embodied interactions, locomotion, and verbal communication