18,720 research outputs found
Recommended from our members
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
Photovoltaic system costs using local labor and materials in developing countries
The use of photovoltaic (PV) technology in countries that do not presently have high technology industrial capacity was investigated. The relative cost of integrating indigenous labor (and manufacturing where available) into the balance of the system industry of seven countries (Egypt, Haiti, the Ivory Coast, Kenya, Mexico, Nepal, and the Phillipines) was determined. The results were then generalized to other countries, at most levels of development. The results of the study imply several conclusions: (1) the cost of installing and maintaining comparable photovoltaic systems in developing countries is less than in the United States; (2) skills and some materials are available in the seven subject countries that may be applied to constructing and maintaining PV systems; (3) there is an interest in foreign countries in photovoltaics; and (4) conversations with foreign nationals suggest that photovoltaics must be introduced in foreign markets as an appropriate technology with high technology components rather than as a high technology system
Developmental program for 8-watt, 2.3- gigahertz, n-p-n, silicon transistor Final report, 12 Oct. 1966 - 30 Oct. 1968
Silicon microwave transistor with hermetic coaxial packag
Top Down Implementation Plan for system performance test software
The top down implementation plan used for the development of system performance test software during the Mark IV-A era is described. The plan is based upon the identification of the hierarchical relationship of the individual elements of the software design, the development of a sequence of functionally oriented demonstrable steps, the allocation of subroutines to the specific step where they are first required, and objective status reporting. The results are: determination of milestones, improved managerial visibility, better project control, and a successful software development
Destroying black holes with test bodies
If a black hole can accrete a body whose spin or charge would send the black
hole parameters over the extremal limit, then a naked singularity would
presumably form, in violation of the cosmic censorship conjecture. We review
some previous results on testing cosmic censorship in this way using the test
body approximation, focusing mostly on the case of neutral black holes. Under
certain conditions a black hole can indeed be over-spun or over-charged in this
approximation, hence radiative and self-force effects must be taken into
account to further test cosmic censorship.Comment: Contribution to the proceedings of the First Mediterranean Conference
on Classical and Quantum Gravity (talk given by T. P. S.). Summarizes the
results of Phys. Rev. Lett. 103, 141101 (2009), arXiv:0907.4146 [gr-qc] and
considers further example
Ride quality evaluation 1: Questionnaire studies of airline passenger comfort
As part of a larger effort to assess passenger comfort in aircraft, two questionnaires were administered: one to ground-based respondents; the other to passengers in flight. Respondents indicated the importance of various factors influencing their satisfaction with a trip, the perceived importance of various physical factors in determining their level of comfort, and the ease of time spent performing activities in flight. The in-flight sample also provided a rating of their level of comfort and of their willingness to fly again. Comfort ratings were examined in relation to (1) type of respondent, (2) type of aircraft, (3) characteristics of the passengers, (4) ease of performing activities, and (5) willingness to fly again
Minimum noise impact aircraft trajectories
Numerical optimization is used to compute the optimum flight paths, based upon a parametric form that implicitly includes some of the problem restrictions. The other constraints are formulated as penalties in the cost function. Various aircraft on multiple trajectores (landing and takeoff) can be considered. The modular design employed allows for the substitution of alternate models of the population distribution, aircraft noise, flight paths, and annoyance, or for the addition of other features (e.g., fuel consumption) in the cost function. A reduction in the required amount of searching over local minima was achieved through use of the presence of statistical lateral dispersion in the flight paths
Strengthening Community Colleges' Influence on Economic Mobility
Examines the role of community colleges in enhancing upward mobility. Compares family incomes of community college and four-year college students and incomes by degree attained. Recommends ways to help more students obtain degrees in high-earning fields
Effect of aluminum phosphate additions on composition of three-component plasma-sprayed solid lubricant
Image analysis (IA) and electron microprobe X-ray analysis (EMXA) were used to characterize a plasma-sprayed, self-lubricating coating, NASA LUBE PS106, specified by weight percent as 35NiCr-35Ag-30CaF2. To minimize segregation of the powder mixture during the plasma-spraying procedure, monoaluminum phosphate was added to form agglomerate particles. Three concentrations of AlPO4 were added to the mixtures: 1.25, 2.5, and 6.25 percent by weight. Analysis showed that 1.25 wt% AlPO4 yielded a CaF2 deficiency, 2.5 wt% kept the coating closest to specification, and 6.25 wt% yielded excess CaF2 as well as more impurities and voids and a deficiency in silver. Photomicrographs and X-ray maps are presented. The methods of IA and EMXA complement each other, and the reasonable agreement in the results increases the confidence in determining the coating composition
Origin of the Thermal Radiation in a Solid-State Analog of a Black-Hole
An effective black-hole-like horizon occurs, for electromagnetic waves in
matter, at a surface of singular electric and magnetic permeabilities. In a
physical dispersive medium this horizon disappears for wave numbers with
. Nevertheless, it is shown that Hawking radiation is still emitted if
free field modes with are in their ground state.Comment: 13 Pages, 3 figures, Revtex with epsf macro
- …