7,775 research outputs found
Plus-Minus-Interesting Exercises To Encourage Student Reflection
It can be difficult to include time for reflection in a problem-solving course, and even more difficult to ensure that students reflect on their problem-solving strategy in a meaningful way. We have found the “plus-minus-interesting’’ or PMI scheme, to be a quick and effective framework for structuring brief, in-class reflection exercises that are completed by teams of students
Study of the application of hydrogen fuel to long-range subsonic transport aircraft, volume 2
The feasibility, practicability, and potential advantages/disadvantages of using liquid hydrogen as fuel in long range, subsonic transport aircraft of advanced design were studied. Both passenger and cargo-type aircraft were investigated. To provide a valid basis for comparison, conventional hydrocarbon (Jet A) fueled aircraft were designed to perform identical missions using the same advanced technology and meeting the same operational constraints. The liquid hydrogen and Jet A fueled aircraft were compared on the basis of weight, size, energy utilization, cost, noise, emissions, safety, and operational characteristics. A program of technology development was formulated
Monotonic Prefix Consistency in Distributed Systems
We study the issue of data consistency in distributed systems. Specifically,
we consider a distributed system that replicates its data at multiple sites,
which is prone to partitions, and which is assumed to be available (in the
sense that queries are always eventually answered). In such a setting, strong
consistency, where all replicas of the system apply synchronously every
operation, is not possible to implement. However, many weaker consistency
criteria that allow a greater number of behaviors than strong consistency, are
implementable in available distributed systems. We focus on determining the
strongest consistency criterion that can be implemented in a convergent and
available distributed system that tolerates partitions. We focus on objects
where the set of operations can be split into updates and queries. We show that
no criterion stronger than Monotonic Prefix Consistency (MPC) can be
implemented.Comment: Submitted pape
Study of advanced fuel system concepts for commercial aircraft and engines
The impact on a commercial transport aircraft of using fuels which have relaxed property limits relative to current commercial jet fuel was assessed. The methodology of the study is outlined, fuel properties are discussed, and the effect of the relaxation of fuel properties analyzed. Advanced fuel system component designs that permit the satisfactory use of fuel with the candidate relaxed properties in the subject aircraft are described. The two fuel properties considered in detail are freezing point and thermal stability. Three candidate fuel system concepts were selected and evaluated in terms of performance, cost, weight, safety, and maintainability. A fuel system that incorporates insulation and electrical heating elements on fuel tank lower surfaces was found to be most cost effective for the long term
Two dimensionality in quasi one-dimensional cobalt oxides
By means of muon spin rotation and relaxation (SR) techniques, we have
investigated the magnetism of quasi one-dimensional (1D) cobalt oxides
CoO (=Ca, Sr and Ba, =1, 2, 3, 5 and
), in which the 1D CoO chain is surrounded by six equally spaced
chains forming a triangular lattice in the -plane, using polycrystalline
samples, from room temperature down to 1.8 K. For the compounds with =1 - 5,
transverse field SR experiments showed the existence of a magnetic
transition below 100 K. The onset temperature of the transition () was found to decrease with ; from 100 K for =1 to 60 K for
=5. A damped muon spin oscillation was observed only in the sample with
=1 (CaCoO), whereas only a fast relaxation obtained even at 1.8
K in the other three samples. In combination with the results of susceptibility
measurements, this indicates that a two-dimensional short-range
antiferromagnetic (AF) order appears below for all
compounds with =1 - 5; but quasi-static long-range AF order formed only in
CaCoO, below 25 K. For BaCoO (=), as decreased
from 300 K, 1D ferromagnetic (F) order appeared below 53 K, and a sharp 2D AF
transition occurred at 15 K.Comment: 12 pages, 14 figures, and 2 table
Towards a time-reversal mirror for quantum systems
The reversion of the time evolution of a quantum state can be achieved by
changing the sign of the Hamiltonian as in the polarization echo experiment in
NMR. In this work we describe an alternative mechanism inspired by the acoustic
time reversal mirror. By solving the inverse time problem in a discrete space
we develop a new procedure, the perfect inverse filter. It achieves the exact
time reversion in a given region by reinjecting a prescribed wave function at
its periphery.Comment: 6 pages, 4 figures. Introduction modified, references added, one
figure added to improve the discussio
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