977 research outputs found
Comparison of robust optimization and info-gap methods for water resource management under deep uncertainty
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.This paper evaluates two established decision-making methods and analyzes their performance and suitability within a water resources management (WRM) problem. The methods under assessment are info-gap (IG) decision theory and robust optimization (RO). The methods have been selected primarily to investigate a contrasting local versus global method of assessing water system robustness to deep uncertainty, but also to compare a robustness model approach (IG) with a robustness algorithm approach (RO), whereby the former selects and analyzes a set of prespecified strategies and the latter uses optimization algorithms to automatically generate and evaluate solutions. The study presents a novel area-based method for IG robustness modeling and assesses the applicability of utilizing the future flows climate change projections in scenario generation for water resource adaptation planning. The methods were applied to a case study resembling the Sussex North Water Resource Zone in England, assessing their applicability at improving a risk-based WRM problem and highlighting the strengths and weaknesses of each method at selecting suitable adaptation strategies under climate change and future demand uncertainties. Pareto sets of robustness to cost are produced for both methods and highlight RO as producing the lower cost strategies for the full range of varying target robustness levels. IG produced the more expensive Pareto strategies due to its more selective and stringent robustness analysis, resulting from the more complex scenario ordering process.This work was financially supported by the UK Engineering and Physical Sciences Research
Council, HR Wallingford and The University of Exeter through the STREAM Industrial
Doctorate Centre. The authors are grateful to Dr Steven Wade, now at the Met Office, and Chris
Counsell of HR Wallingford for providing data for the Sussex North case study
Method for machining holes in composite materials
A method for boring well defined holes in a composite material such as graphite/epoxy is discussed. A slurry of silicon carbide powder and water is projected onto a work area of the composite material in which a hole is to be bored with a conventional drill bit. The silicon carbide powder and water slurry allow the drill bit, while experiencing only normal wear, to bore smooth, cylindrical holes in the composite material
Effects of seawater and deionized water at 0 to 80 deg C on the flexural properties of a glass/epoxy composite
The effect on the flexural properties of a glass/epoxy composite of immersion in deionized water or seawater at 0, 25, and 80 C for 451 hr was examined. The percent weight gain at 0 and 25 C was low (0.06 to 0.17 percent) and there was no significant change in the flexural properties for these environmental conditions. At 80 C there was a decrease in the flexural strength of 17 and 20 percent in seawater and deionized water, respectively. This is a comparison to control samples exposed to 80 C heat alone. These decreases were found to be nearly reversible once the samples were dried. Optical microscopy did not reveal cracking of the matrix. The flexural modulus was essentially unaffected by exposure to deionized water and seawater at 80 C
Orientation-to-alignment conversion and spin squeezing
The relationship between orientation-to-alignment conversion (a form of
atomic polarization evolution induced by an electric field) and the phenomenon
of spin squeezing is demonstrated. A "stretched" state of an atom or molecule
with maximum angular-momentum projection along the quantization axis possesses
orientation and is a quantum-mechanical minimum-uncertainty state, where the
product of the equal uncertainties of the angular-momentum projections on two
orthogonal directions transverse to the quantization axis is the minimum
allowed by the uncertainty relation. Application of an electric field for a
short time induces orientation-to-alignment conversion and produces a
spin-squeezed state, in which the quantum state essentially remains a
minimum-uncertainty state, but the uncertainties of the angular-momentum
projections on the orthogonal directions are unequal. This property can be
visualized using the angular-momentum probability surfaces, where the radius of
the surface is given by the probability of measuring the maximum
angular-momentum projection in that direction. Brief remarks are also given
concerning collective-spin squeezing and quantum nondemolition measurements.Comment: 7 pages, 6 figure
Physical properties of thermoelectric zinc antimonide using first-principles calculations
We report first principles calculations of the structural, electronic,
elastic and vibrational properties of the semiconducting orthorhombic ZnSb
compound. We study also the intrinsic point defects in order to eventually
improve the thermoelectric properties of this already very promising
thermoelectric material. Concerning the electronic properties, in addition to
the band structure, we show that the Zn (Sb) crystallographically equivalent
atoms are not exactly equivalent from the electronic point of view. Lattice
dynamics, elastic and thermodynamic properties are found to be in good
agreement with experiments and they confirm the non equivalency of the zinc and
antimony atoms from the vibrational point of view. The calculated elastic
properties show a relatively weak anisotropy and the hardest direction is the y
direction. We observe the presence of low energy modes involving both Zn and Sb
atoms at about 5-6 meV, similarly to what has been found in Zn4Sb3 and we
suggest that the interactions of these modes with acoustic phonons could
explain the relatively low thermal conductivity of ZnSb. Zinc vacancies are the
most stable defects and this explains the intrinsic p-type conductivity of
ZnSb.Comment: 33 pages, 8 figure
Direct Observation of Propagating Gigahertz Coherent Guided Acoustic Phonons in Free Standing Single Copper Nanowires
We report on gigahertz acoustic phonon waveguiding in free-standing single
copper nanowires studied by femtosecond transient reflectivity measurements.
The results are discussed on the basis of the semianalytical resolution of the
Pochhammer and Chree equation. The spreading of the generated Gaussian wave
packet of two different modes is derived analytically and compared with the
observed oscillations of the sample reflectivity. These experiments provide a
unique way to independently obtain geometrical and material characterization.
This direct observation of coherent guided acoustic phonons in a single
nano-object is also the first step toward nanolateral size acoustic transducer
and comprehensive studies of the thermal properties of nanowires
Summary Report on Phase I Results from the 3D Printing in Zero G Technology Demonstration Mission, Volume I
Human space exploration to date has been confined to low-Earth orbit and the Moon. The International Space Station (ISS) provides a unique opportunity for researchers to prove out the technologies that will enable humans to safely live and work in space for longer periods of time and venture beyond the Earth/Moon system. The ability to manufacture parts in-space rather than launch them from Earth represents a fundamental shift in the current risk and logistics paradigm for human spaceflight. In September 2014, NASA, in partnership with Made In Space, Inc., launched the 3D Printing in Zero-G technology demonstration mission to explore the potential of additive manufacturing for in-space applications and demonstrate the capability to manufacture parts and tools on orbit using fused deposition modeling. This Technical Publication summarizes the results of testing to date of the ground control and flight prints from the first phase of this ISS payload
Summary Report for the Technical Interchange Meeting on Development of Baseline Material Properties and Design Guidelines for In-Space Manufacturing Activities
NASA Marshall Space Flight Center (MSFC) and the Agency as a whole are currently engaged in a number of in-space manufacturing (ISM) activities that have the potential to reduce launch costs, enhance crew safety, and provide the capabilities needed to undertake long-duration spaceflight. The recent 3D Printing in Zero-G experiment conducted on board the International Space Station (ISS) demonstrated that parts of acrylonitrile butadiene styrene (ABS) plastic can be manufactured in microgravity using fused deposition modeling (FDM). This project represents the beginning of the development of a capability that is critical to future NASA missions. Current and future ISM activities will require the development of baseline material properties to facilitate design, analysis, and certification of materials manufactured using in-space techniques. The purpose of this technical interchange meeting (TIM) was to bring together MSFC practitioners and experts in materials characterization and development of baseline material properties for emerging technologies to advise the ISM team as we progress toward the development of material design values, standards, and acceptance criteria for materials manufactured in space. The overall objective of the TIM was to leverage MSFC's shared experiences and collective knowledge in advanced manufacturing and materials development to construct a path forward for the establishment of baseline material properties, standards development, and certification activities related to ISM. Participants were asked to help identify research and development activities that will (1) accelerate acceptance and adoption of ISM techniques among the aerospace design community; (2) benefit future NASA programs, commercial technology developments, and national needs; and (3) provide opportunities and avenues for further collaboration
Strong electron-phonon coupling in delta-phase stabilized Pu
Heat capacity measurements of the delta-phase stabilized alloy Pu-Al suggest
that strong electron-phonon coupling is required to explain the moderate
renormalization of the electronic density of states near the Fermi energy. We
calculate the heat capacity contributions from the lattice and electronic
degrees of freedom as well as from the electron-lattice coupling term and find
good overall agreement between experiment and theory assuming a dimensionless
electron-phonon coupling parameter of order unity, lambda ~ 0.8. This large
electron-phonon coupling parameter is comparable to reported values in other
superconducting metals with face-centered cubic crystal structure, for example,
Pd (lambda ~ 0.7) and Pb (lambda ~ 1.5). Further, our analysis shows evidence
of a sizable residual low-temperature entropy contribution, S_{res} ~ 0.4 k_B
(per atom). We can fit the residual specific heat to a two-level system.
Therefore, we speculate that the observed residual entropy originates from
crystal-electric field effects of the Pu atoms or from self-irradiation induced
defects frozen in at low temperatures.Comment: 9 pages, 11 figures, to appear in Phys. Rev.
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