98,274 research outputs found
Forty Years of Celebration of Discipline: An Interview with Richard Foster
Wow, Richard, it’s been 40 years since your first book, Celebration of Discipline, was published, and it’s still a best seller (selling over 2 million copies), having been translated into 25 languages! Reflecting on that now, could you say something about your original vision for the book, and how God has blessed its impact over the years
Magnetic suspension and pointing system
An apparatus is reported for accurate pointing of instruments on a carrier vehicle and for isolation of the instruments from the vehicle's motion disturbances. The apparatus includes two assemblies with connecting interfaces. The first assembly is attached to the carrier vehicle and consists of an azimuth gimbal and an elevation gimbal which provide coarse pointing by allowing two rotations of the instruments relative to the carrier vehicle. The second or vernier pointing assembly is made up of magnetic suspension and fine pointing actuators, roll motor segments, and an instrument mounting plase which provides appropriate magnetic circuits for the actuators and the roll motor segments. The vernier pointing assembly provides attitude fine pointing and roll positioning of the instruments as well as six degree-of-freedom isolation from carrier motion disturbances
Numerical solution of the steady-state Navier-Stokes equations for hypersonic flow about blunt axisymmetric bodies
The steady-state Navier-Stokes equations are solved for hypersonic flow about blunt axisymmetric bodies. The equations of motion are solved by successive approximations using an implicit finite-difference scheme. The results are compared with viscous shock-layer theory, experimental data, and time-dependent solutions of the Navier-Stokes equations. It is demonstrated that viscous shock-layer theory is sufficiently accurate for the range of flight conditions normally encountered by entry vehicles
Viscous shock layer solutions for turbulent flow of radiating gas mixtures in chemical equilibrium
The viscous shock layer equations for hypersonic laminar and turbulent flows of radiating or nonradiating gas mixtures in chemical equilibrium are presented for two-dimensional and axially symmetric flow fields. Solutions are obtained using an implicit finite difference scheme and results are presented for hypersonic flow over spherically blunted cone configurations at free stream conditions representative of entry into the atmosphere of Venus. These data are compared with solutions obtained using other methods of analysis
Numerical solution of the hypersonic viscous-shock-layer equations for laminar, transitional, and turbulent flows of a perfect gas over blunt axially symmetric bodies
The viscous shock layer equations applicable to hypersonic laminar, transitional, and turbulent flows of a perfect gas over two-dimensional plane or axially symmetric blunt bodies are presented. The equations are solved by means of an implicit finite difference scheme, and the results are compared with a turbulent boundary layer analysis. The agreement between the two solution procedures is satisfactory for the region of flow where streamline swallowing effects are negligible. For the downstream regions, where streamline swallowing effects are present, the expected differences in the two solution procedures are evident
Rim inertial measuring system
The invention includes an angular momentum control device (AMCD) having a rim and several magnetic bearing stations. The AMCD is in a strapped down position on a spacecraft. Each magnetic bearing station comprises means, including an axial position sensor, for controlling the position of the rim in the axial direction; and means, including a radial position sensor, for controlling the position of the rim in the radial direction. A first computer receives the signals from all the axial position sensors and computes the angular rates about first and second mutually perpendicular axes in the plane of the rim and computes the linear acceleration along a third axis perpendicular to the first and second axes. A second computer receives the signals from all the radial position sensors and computes the linear accelerations along the first and second axes
Preliminary testing of a prototype portable X-ray fluorescence spectrometer
A portable X-ray fluorescence spectrometer for use as an analyzer in mineral resource investigative work was built and tested. The prototype battery powered spectrometer, measuring 11 by 12 by 5 inches and weighing only about 15 pounds, was designed specifically for field use. The spectrometer has two gas proportional counters and two radioactive sources, Cd (10a) and Fe (55). Preliminary field and laboratory tests on rock specimens and rock pulps have demonstrated the capability of the spectrometer to detect 33 elements to date. Characteristics of the system present some limitations, however, and further improvements are recommended
Approaching the Problem of Time with a Combined Semiclassical-Records-Histories Scheme
I approach the Problem of Time and other foundations of Quantum Cosmology
using a combined histories, timeless and semiclassical approach. This approach
is along the lines pursued by Halliwell. It involves the timeless probabilities
for dynamical trajectories entering regions of configuration space, which are
computed within the semiclassical regime. Moreover, the objects that Halliwell
uses in this approach commute with the Hamiltonian constraint, H. This approach
has not hitherto been considered for models that also possess nontrivial linear
constraints, Lin. This paper carries this out for some concrete relational
particle models (RPM's). If there is also commutation with Lin - the Kuchar
observables condition - the constructed objects are Dirac observables.
Moreover, this paper shows that the problem of Kuchar observables is explicitly
resolved for 1- and 2-d RPM's. Then as a first route to Halliwell's approach
for nontrivial linear constraints that is also a construction of Dirac
observables, I consider theories for which Kuchar observables are formally
known, giving the relational triangle as an example. As a second route, I apply
an indirect method that generalizes both group-averaging and Barbour's best
matching. For conceptual clarity, my study involves the simpler case of
Halliwell 2003 sharp-edged window function. I leave the elsewise-improved
softened case of Halliwell 2009 for a subsequent Paper II. Finally, I provide
comments on Halliwell's approach and how well it fares as regards the various
facets of the Problem of Time and as an implementation of QM propositions.Comment: An improved version of the text, and with various further references.
25 pages, 4 figure
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