26,919 research outputs found
Focused technology: Nuclear propulsion
Five viewgraphs are presented that outline the objectives and elements of the Nuclear Propulsion Program, mission considerations, propulsion technologies, and the logic flow path for nuclear propulsion development
Focused technology: Nuclear propulsion
The topics presented are covered in viewgraph form and include: nuclear thermal propulsion (NTP), which challenges (1) high temperature fuel and materials, (2) hot hydrogen environment, (3) test facilities, (4) safety, (5) environmental impact compliance, and (6) concept development, and nuclear electric propulsion (NEP), which challenges (1) long operational lifetime, (2) high temperature reactors, turbines, and radiators, (3) high fuel burn-up reactor fuels, and designs, (4) efficient, high temperature power conditioning, (5) high efficiency, and long life thrusters, (6) safety, (7) environmental impact compliance, and (8) concept development
Exploring Young Students' Functional Thinking
The Early Years Generalising Project (EYGP) involves Australian Years 1-4 (age 5-9) students and investigates how they grasp and express generalisations. This paper focuses on data collected from six Year 1 students in an exploratory study within a clinical interview setting that required students to identify function rules. Preliminary findings suggest that the use of gestures (both by students and interviewers), self-talk (by students), and concrete acting out, assisted students to reach generalisations and to begin to express these generalities. It also appears that as students become aware of the structure, their use of gestures and self- talk tended to decrease
Nuclear rocket propulsion. NASA plans and progress, FY 1991
NASA has initiated planning for a technology development project for nuclear rocket propulsion systems for space explorer initiative (SEI) human and robotic missions to the moon and Mars. An interagency project is underway that includes the Department of Energy National Laboratories for nuclear technology development. The activities of the project planning team in FY 1990 and 1991 are summarized. The progress to date is discussed, and the project plan is reviewed. Critical technology issues were identified and include: (1) nuclear fuel temperature, life, and reliability; (2) nuclear system ground test; (3) safety; (4) autonomous system operation and health monitoring; and (5) minimum mass and high specific impulse
Design of a Recreational Fishing Survey and Mark-Recapture Study for the Blue Crab, Callinectes sapidus, in Chesapeake Bay
The development of bay wide estimates of recreational harvest has been identified as a high priority by the Chesapeake Bay Scientific Advisory Committee (CBSAC) and by the Chesapeake Bay Program as reflected in the Chesapeake Bay Blue Crab Fishery Management Plan (Chesapeake Bay Program 1996). In addition, the BiState Blue Crab Commission (BBCAC), formed in 1996 by mandate from the legislatures of Maryland and Virginia to advise on crab
management, has also recognized the importance of estimating the levels and trends in catches in the recreational fishery. Recently, the BBCAC has adopted limit and target biological reference points. These analyses have been predicated on assumptions regarding the relative magnitude of the recreational and commercial catch. The reference points depend on determination of the total
number of crabs removed from the population. In essence, the number removed by the various fishery sectors, represents a minimum estimate of the population size. If a major fishery sector is not represented, the total population will be accordingly underestimated. If the relative contribution of the unrepresented sector is constant over time and harvests the same components of
the population as the other sectors, it may be argued that the population estimate derived from the other sectors is biased but still adequately represents trends in population size over time. If either of the two constraints mentioned above is not met, the validity of relative trends over time is suspect. With the recent increases in the human population in the Chesapeake Bay watershed, there is reason to be concerned that the recreational catch may not have been a constant proportion of the total harvest over time. It is important to assess the catch characteristics and the magnitude of the recreational fishery to evaluate this potential bias. (PDF contains 70 pages
Comparison of Nucleon Form Factors from Lattice QCD Against the Light Front Cloudy Bag Model and Extrapolation to the Physical Mass Regime
We explore the possibility of extrapolating state of the art lattice QCD
calculations of nucleon form factors to the physical regime. We find that the
lattice results can be reproduced using the Light Front Cloudy Bag Model by
letting its parameters be analytic functions of the quark mass. We then use the
model to extend the lattice calculations to large values of Q^{2} of interest
to current and planned experiments. These functions are also used to define
extrapolations to the physical value of the pion mass, thereby allowing us to
study how the predicted zero in G_{E}(Q^{2})/G_{M}(Q^{2}) varies as a function
of quark mass.Comment: 31 pages, 22 figure
The Radius of the Proton: Size Does Matter
The measurement by Pohl et al. [1] of the 2S_1/2^F=1 to 2P_3/2^F=2 transition
in muonic hydrogen and the subsequent analysis has led to a conclusion that the
rms charge radius of the proton differs from the accepted (CODATA [2]) value by
approximately 4%, leading to a 4.9 s.d. discrepancy. We investigate the muonic
hydrogen spectrum relevant to this transition using bound-state QED with Dirac
wave-functions and comment on the extent to which the perturbation-theory
analysis which leads to the above conclusion can be confirmed.Comment: Delayed arXiv submission. To appear in 'Proceedings of T(R)OPICALQCD
2010' (September 26 - October 1, 2010). 7 pages, 1 figure. Superseded by
arXiv:1104.297
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