909 research outputs found
Thermal Buckling of Composite Tubes
The object was to design and initiate the use of a fixture capable of testing for pre-buckling deflections in a composite tube under thermal loading. The fixture is to be used on a continuing basis to test three types of composites: (1) glass/epoxy, (2) Kevlar/epoxy, and (3) graphite/epoxy. The course of action chosen was to adapt a fixture designed by Tim Streb and Steve Fulkerson in the spring of 1991. The fixture was completed, and one test was performed. An added responsibility was to initiate a course of action such that the volumetric percentage of fiber in the composite may be determined
Mercury in the environment
Problems in assessing mercury concentrations in environmental materials are discussed. Data for situations involving air, water, rocks, soils, sediments, sludges, fossil fuels, plants, animals, foods, and man are drawn together and briefly evaluated. Details are provided regarding the toxicity of mercury along with tentative standards and guidelines for mercury in air, drinking water, and food
F100(3) parallel compressor computer code and user's manual
The Pratt & Whitney Aircraft multiple segment parallel compressor model has been modified to include the influence of variable compressor vane geometry on the sensitivity to circumferential flow distortion. Further, performance characteristics of the F100 (3) compression system have been incorporated into the model on a blade row basis. In this modified form, the distortion's circumferential location is referenced relative to the variable vane controlling sensors of the F100 (3) engine so that the proper solution can be obtained regardless of distortion orientation. This feature is particularly important for the analysis of inlet temperature distortion. Compatibility with fixed geometry compressor applications has been maintained in the model
Nanosecond electro-optical switching with a repetition rate above 20MHz
We describe an electro-optical switch based on a commercial electro-optic
modulator (modified for high-speed operation) and a 340V pulser having a rise
time of 2.2ns (at 250V). It can produce arbitrary pulse patterns with an
average repetition rate beyond 20MHz. It uses a grounded-grid triode driven by
transmitting power transistors. We discuss variations that enable analog
operation, use the step-recovery effect in bipolar transistors, or offer other
combinations of output voltage, size, and cost.Comment: 3 pages, 3 figures. Minor change
Covering Pairs in Directed Acyclic Graphs
The Minimum Path Cover problem on directed acyclic graphs (DAGs) is a
classical problem that provides a clear and simple mathematical formulation for
several applications in different areas and that has an efficient algorithmic
solution. In this paper, we study the computational complexity of two
constrained variants of Minimum Path Cover motivated by the recent introduction
of next-generation sequencing technologies in bioinformatics. The first problem
(MinPCRP), given a DAG and a set of pairs of vertices, asks for a minimum
cardinality set of paths "covering" all the vertices such that both vertices of
each pair belong to the same path. For this problem, we show that, while it is
NP-hard to compute if there exists a solution consisting of at most three
paths, it is possible to decide in polynomial time whether a solution
consisting of at most two paths exists. The second problem (MaxRPSP), given a
DAG and a set of pairs of vertices, asks for a path containing the maximum
number of the given pairs of vertices. We show its NP-hardness and also its
W[1]-hardness when parametrized by the number of covered pairs. On the positive
side, we give a fixed-parameter algorithm when the parameter is the maximum
overlapping degree, a natural parameter in the bioinformatics applications of
the problem
Electronic Correlation and Transport Properties of Nuclear Fuel Materials
Actinide elements, such as uranium and plutonium, and their compounds are
best known as nuclear materials. When engineering optimal fuel materials for
nuclear power, important thermophysical properties to be considered are melting
point and thermal conductivity. Understanding the physics underlying transport
phenomena due to electrons and lattice vibrations in actinide systems is a
crucial step toward the design of better fuels. Using first principle LDA+DMFT
method, we conduct a systematic study on the correlated electronic structures
and transport properties of select actinide carbides, nitrides, and oxides,
many of which are nuclear fuel materials. We find that different mechanisms,
electrons--electron and electron--phonon interactions, are responsible for the
transport in the uranium nitride and carbide, the best two fuel materials due
to their excellent thermophysical properties. Our findings allow us to make
predictions on how to improve their thermal conductivities.Comment: Main article: 5 pages, 3 figures. Supplementary info: 2 pages, 1
figur
APPARATUS FOR DETERMINING LINEAR THERMAL EXPANSIONS OF MATERIALS IN VACUUM OR CONTROLLED ATMOSPHERE
An apparatus for determining linear thermal expansion data up to 1350 deg C for materials that cannot be heated in air is described. Expansion is not measured directly, but is derived from the differential expansion between the material being tested and the materials of construction of the dilatometer. The apparatus is calibrated against published data on the linear thermal expansion of both fused silica and polycrystalline tungsten metal. It can be operated either as a high-vacuum or as a controlled-atmosphere apparatus. Recording of data is either fully automatic or manual. The percentage error is believed to be no greater than plus or minus 0.1 to 0.2%. Original data for linear thermal expansion of materials such as hot-pressed BeO, hafnium-free ZrC/sub 2/, zirconium-free HfO/sub 2/, INOR-8 alloy, siliconized silicon carbide, uranium dioxide, compositions of Be + BeO, and samples of CS 312 graphite, boron nitride, and tungsten metal. (auth
The Potential Cost to New Zealand Dairy Farmers from the Introduction of Nitrate-Based Stocking Rate Restrictions
Introducing a stocking rate restriction is one possible course of action for regulators to improve water quality where it is affected by nitrate pollution. To determine the impact of a stocking rate restriction on a range of New Zealand dairy farms, a whole-farm model was optimised with and without a maximum stocking rate of 2.5 cows per hectare. Three farm systems, which differ by their level of feed-related capital, were examined for the changes to the optimal stocking rate and optimal level of animal milk production genetics when utility was maximised. The whole-farm model was optimised through the use of an evolutionary algorithm called differential evolution. The introduction of a stocking rate restriction would have a very large impact on the optimally organised high feed-related capital farm systems, reducing their certainty equivalent by almost half. However, there was no impact on the certainty equivalent of low feed-related capital systems.environmental regulation, dairy farms, whole-farm model, evolutionary algorithm, Environmental Economics and Policy, Livestock Production/Industries, Q12, Q52, C61,
Bounded Representations of Interval and Proper Interval Graphs
Klavik et al. [arXiv:1207.6960] recently introduced a generalization of
recognition called the bounded representation problem which we study for the
classes of interval and proper interval graphs. The input gives a graph G and
in addition for each vertex v two intervals L_v and R_v called bounds. We ask
whether there exists a bounded representation in which each interval I_v has
its left endpoint in L_v and its right endpoint in R_v. We show that the
problem can be solved in linear time for interval graphs and in quadratic time
for proper interval graphs.
Robert's Theorem states that the classes of proper interval graphs and unit
interval graphs are equal. Surprisingly the bounded representation problem is
polynomially solvable for proper interval graphs and NP-complete for unit
interval graphs [Klav\'{\i}k et al., arxiv:1207.6960]. So unless P = NP, the
proper and unit interval representations behave very differently.
The bounded representation problem belongs to a wider class of restricted
representation problems. These problems are generalizations of the
well-understood recognition problem, and they ask whether there exists a
representation of G satisfying some additional constraints. The bounded
representation problems generalize many of these problems
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