Practical Issues in the Application of Direct Metal Laser Sintering

Direct Metal Laser Sintering (DMLS) was introduced to meet the objective of producing metal parts directly from CAD data. CRDM has accumulated six years of experience in applying this technique, mostly to prototyping parts for evaluation. For some applications, such as blow moulds, porosity generated in DMLS has proved to be beneficial, but for others a concession on tolerances or finish are necessary and/or complementary operations are required, which add to manufacturing time and cost. This paper examines such issues through some well chosen examples of parts to demonstrate both the strengths and weaknesses of the DMLS process.Mechanical Engineerin

Pilot evaluation of sailplane handling qualities

The evaluation sailplanes were found generally deficient in the area of cockpit layout. The pilots indicated general dissatisfaction with high pitch sensitivity especially when coupled with inertially induced stick forces. While all sailplanes were judged satisfactory for centering thermals and in the ease of speed control in circling flight, pilot opinions diverged on the maneuvering response, pull-out characteristics from a dive, and on phugoid damping. Lateral-directional control problems were noted mainly during takeoff and landing for most sailplanes with the landing wheel ahead of center of gravity. Pilot opinion of in-flight lateral-directional stability and control was generally satisfactory. Five of the evaluation sailplanes exhibited a very narrow airspeed band in which perceptible stall warning buffet occurred. However, this characteristic was considered not objectionable when stall recovery was easy. The pilots objected to the characteristics of a wide airspeed band of stall warning followed by a stall with yawing and rolling tendency and substantial loss of altitude during the stall. Glide path control for the evaluation sailplanes was found to be generally objectionable

Hadronic light-by-light scattering contribution to the muon anomalous magnetic moment revisited

We discuss hadronic light-by-light scattering contribution to the muon anomalous magnetic moment a_\mu^{\rm lbl}, paying particular attention to the consistent matching between the short- and the long-distance behavior of the light-by-light scattering amplitude. We argue that the short-distance QCD imposes strong constraints on this amplitude overlooked in previous analyses. We find that accounting for these constraints leads to approximately 50 per cent increase in the central value of a_\mu^{\rm lbl}, compared to existing estimates. The hadronic light-by-light scattering contribution becomes a_\mu^{\rm lbl}=136(25) \times 10^{-11}, thereby shifting the Standard Model prediction closer to the experimental value.Comment: 16 pages, 2 figure

Constructing N-qubit entanglement monotones from anti-linear operators

We present a method to construct entanglement measures for pure states of multipartite qubit systems. The key element of our approach is an antilinear operator that we call {\em comb} in reference to the {\em hairy-ball theorem}. For qubits (or spin 1/2) the combs are automatically invariant under SL(2,\CC). This implies that the {\em filters} obtained from the combs are entanglement monotones by construction. We give alternative formulae for the concurrence and the 3-tangle as expectation values of certain antilinear operators. As an application we discuss inequivalent types of genuine four-qubit entanglement.Comment: 5 pages, revtex4; more detailed illustration of the metho

Workshop on Applications of Phase Diagrams in Metallurgy and Ceramics

A workshop was held to assess the current national and international status of phase diagram determinations and evaluations for alloys, ceramics, and semiconductors; to determine the needs and priorities, especially technological, for phase diagram determinations and evaluations; and to estimate the resources being used and potentially available for phase diagram evaluation. Highlights of the workshop, description of a new poster board design used in the poster sessions, lists of attendees and demonstrations, the program, and descriptions of the presentations are included

Marriage Patterns in the United States

This paper analyzes cohort marriage patterns in the United States in order to determine whether declining rates of first marriage are due to changes in the timing of marriage, the incidence of marriage, or both. Parametric models, which are well-suited to the analysis of censored or truncated data, are fit separately to information on age at first marriage derived from three data sets which were collected independently and at different points in time. Extended versions of the models are also estimated in which the parameters of the model distributions are allowed to depend on social and, economic variables.The results provide evidence that the incidence of first marriage is declining and that there is only a slight tendency for women to delay marriage. In addition, education is the most important correlate of decisions about the timing of first marriage whereas race is the most important correlate of decisions about its incidence.

Hydrogen-methane fuel control systems for turbojet engines

Design, development, and test of a fuel conditioning and control system utilizing liquid methane (natural gas) and liquid hydrogen fuels for operation of a J85 jet engine were performed. The experimental program evaluated the stability and response of an engine fuel control employing liquid pumping of cryogenic fuels, gasification of the fuels at supercritical pressure, and gaseous metering and control. Acceptably stable and responsive control of the engine was demonstrated throughout the sea level power range for liquid gas fuel and up to 88 percent engine speed using liquid hydrogen fuel

Money Stock Control with Reserve and Interest Rate Instruments Under Rational Expectations

This paper conducts a theoretical comparison of the potential effectiveness, in terms of money stock controllability, of interest rate and reserve instruments. Whereas previous studies have been basically static, the present analysis is carried out in the context of a dynamic macroeconomic model with rational expectations. Particular attention is paid to the distinction between contemporaneous and lagged reserve accounting (CRA and LRA). The criterion employed is the expectation of squared deviations of the (log of the) money stock from target values that are reset each period. Analysis in the basic model suggests the following substantive conclusions. (1) With a reserve instrument, monetary control will be more effective under CRA than LRA. (2) With a reserve instrument and LRA, control will be poorer than with an interest rate instrument. (3) For a wide range of parameter values, control will be better with a reserve instrument and CRA than with an interest rate instrument.