1,001 research outputs found
Six degree of freedom simulation system for evaluating automated rendezvous and docking spacecraft
Future logistics supply and servicing vehicles such as cargo transfer vehicles (CTV) must have full 6 degree of freedom (6DOF) capability in order to perform requisite rendezvous, proximity operations, and capture operations. The design and performance issues encountered when developing a 6DOF maneuvering spacecraft are very complex with subtle interactions which are not immediately obvious or easily anticipated. In order to deal with these complexities and develop robust maneuvering spacecraft designs, a simulation system and associated family of tools are used at TRW for generating and validating spacecraft performance requirements and guidance algorithms. An overview of the simulator and tools is provided. These are used by TRW for autonomous rendezvous and docking research projects including CTV studies
TB94: Chemical and Physical Properties of the Boothbay, Brayton, Croghan, Monarda, Plaisted, Scantic, and Swanville Soil Mapping Units
Seven soil mapping units were each sampled at five locations within Maine. The morphology of the soil was described at each site. The profiles were sampled on a horizonal basis from the soil surface to a depth of 100 cm. The soil samples were taken to the laboratory where their chemical and physical properties were determined. Weighted means and weighted standard deviations were determined for several soil properties. Soil profile descriptions and chemical and physical soil data are presented for each sample site.https://digitalcommons.library.umaine.edu/aes_techbulletin/1101/thumbnail.jp
Hump on upper shelf of ductile-brittle transition temperature curve of a plain carbon steel
The ductileâbrittle transition temperature (DBTT) in a plain carbon steel has been studied in a series of Charpy V notch samples. Both non-standard and standard samples were used in the as drawn, normalised and annealed conditions. In all cases, a hump was recorded on the upper shelf of the DBTT. Examination of fractures in the SEM in the vicinity of the hump showed typical microvoid coalescence. Low temperature fractures showed classical cleavage fractures with river markings. In the normalised and annealed conditions, both yield stress Ïy and impact transition temperature Tc varied inversely with square root of the ferrite grain size, in agreement with previous workers. However, the points for âas drawnâ samples lay off the linear plot. The reasons for this are discussed. The hump on the upper shelf of the DBTT is thought to be associated with dynamic strain aging
Topological Modes in Dual Lattice Models
Lattice gauge theory with gauge group is reconsidered in four
dimensions on a simplicial complex . One finds that the dual theory,
formulated on the dual block complex , contains topological modes
which are in correspondence with the cohomology group ,
in addition to the usual dynamical link variables. This is a general phenomenon
in all models with single plaquette based actions; the action of the dual
theory becomes twisted with a field representing the above cohomology class. A
similar observation is made about the dual version of the three dimensional
Ising model. The importance of distinct topological sectors is confirmed
numerically in the two dimensional Ising model where they are parameterized by
.Comment: 10 pages, DIAS 94-3
Electronic Structure of LuRh2Si2: "Small" Fermi Surface Reference to YbRh2Si2
We present band structure calculations and quantum oscillation measurements
on LuRh2Si2, which is an ideal reference to the intensively studied quantum
critical heavy-fermion system YbRh2Si2. Our band structure calculations show a
strong sensitivity of the Fermi surface on the position of the silicon atoms
zSi within the unit cell. Single crystal structure refinement and comparison of
predicted and observed quantum oscillation frequencies and masses yield zSi =
0.379c in good agreement with numerical lattice relaxation. This value of zSi
is suggested for future band structure calculations on LuRh2Si2 and YbRh2Si2.
LuRh2Si2 with a full f electron shell represents the "small" Fermi surface
configuration of YbRh2Si2. Our experimentally and ab initio derived quantum
oscillation frequencies of LuRh2Si2 show strong differences with earlier
measurements on YbRh2Si2. Consequently, our results confirm the contribution of
the f electrons to the Fermi surface of YbRh2Si2 at high magnetic fields. Yet
the limited agreement with refined fully itinerant local density approximation
calculations highlights the need for more elaborated models to describe the
Fermi surface of YbRh2Si2.Comment: 12 pages 10 figure
Viking navigation
A comprehensive description of the navigation of the Viking spacecraft throughout their flight from Earth launch to Mars landing is given. The flight path design, actual inflight control, and postflight reconstruction are discussed in detail. The preflight analyses upon which the operational strategies and performance predictions were based are discussed. The inflight results are then discussed and compared with the preflight predictions and, finally, the results of any postflight analyses are presented
Isolated Stricture of the Fossa Navicularis Following Transurethral Resection of the Prostate -139 17.2.1.1 Y-V flap Procedures -139 17.2.2.2 Resurfacing of Fossa Navicularis -139 17.2.2.3 Transverse Ventral Penile Skin
Fostering online learning at the workplace : a scheme to identify and analyse collaboration processes in asynchronous discussions
Research has shown that providing participants with highâquality learning material is not sufficient to help them profit most from online education. The level of interaction among participants is another key determinant for learning outcomes. However, merely proposing interaction does not automatically lead to fruitful discussion and collaboration. Specifically, social presence and facilitation activities add value to online discussions. In Murphy's collaboration framework, social presence represents the basis of successful online collaboration from which more reflective discussions and coâconstruction can evolve. In this paper, an adjusted version of this framework was applied in a workplace learning context. The content analysis of 1170 comments in an online course for careers practitioners of a public employment service showed that the extended framework generated deeper insights into the dynamics of online discussions. The results show that involvement in collaborative learning at the workplace was supported by a high social presence and influenced by course topic and tasks. Facilitation played an important role in creating a sympathetic sense of community and stimulating coâcreation processes
Social presence in the 21st Century: an adjustment to the Community of Inquiry framework
The Community of Inquiry framework, originally proposed by Garrison, Anderson and Archer (2000) identifies teaching, social and cognitive presences as central to a successful online educational experience. This article presents the findings of a study conducted in Uruguay between 2007 and 2010. The research aimed to establish the role of cognitive, social and teaching presences in the professional development of 40 English language teachers on Continuous Professional Development (CPD) programmes delivered in blended learning settings. The findings suggest that teaching presence and cognitive presence have themselves 'become social'. The research points to social presence as a major lever for engagement, sense-making and peer support. Based on the patterns identified in the study, this article puts forward an adjustment to the Community of Inquiry framework, which shows social presence as more prominent within the teaching and cognitive constructs than the original version of the framework suggests
Elastic Tensor of YNi_2B_2C
The complete elastic tensor of YNi_2B_2C was determined by application of the
resonant ultrasound spectroscopy technique to a single-crystal sample. Elastic
constants were found to be in good agreement with partial results obtained from
`time-of-flight' measurements performed on samples cut from the same ingot.
From the measured constants, the bulk modulus and Debye temperature are
calculated.Comment: 5 pages, 3 figure
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