12,474 research outputs found
Holographic RG-flows and Boundary CFTs
Solutions of -dimensional gravity coupled to a scalar field are
obtained, which holographically realize interface and boundary CFTs. The
solution utilizes a Janus-like slicing ansatz and corresponds
to a deformation of the CFT by a spatially-dependent coupling of a relevant
operator. The BCFT solutions are singular in the bulk, but physical quantities
such as the holographic entanglement entropy can be calculated.Comment: 26 pages, 11 figure
Deconstructing Superconductivity
We present a dimensionally deconstructed model of an s-wave holographic
superconductor. The 2+1 dimensional model includes multiple charged Cooper pair
fields and neutral exciton fields that have interactions governed by hidden
local symmetries. We derive AdS/CFT-like relations for the current and charge
density in the model, and we analyze properties of the Cooper pair condensates
and the complex conductivity.Comment: 24 pages, 10 eps figures. v2: Sign conventions clarified, references
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Sub-2 cm/s passivation of silicon surfaces by aprotic solutions
Minimizing recombination at semiconductor surfaces is required for the accurate determination of the bulk carrier lifetime. Proton donors, such as hydrofluoric acid and superacids, are well known to provide highly effective short-term surface passivation. We demonstrate here that aprotic solutions based on bis(trifluoromethanesulfonyl)methane (TFSM) in hexane or pentane can also result in excellent passivation of (100)-orientation silicon surfaces. We show that the optimized TFSM-pentane passivation scheme can measure effective lifetimes up to 20 ms, with a surface recombination velocity of 1.7 cm s1 at an excess carrier density of 1015 cm3 . Fitting injection-dependent lifetime curves requires chemical passivation and field effect passivation from a negatively charged layer with a charge density of 1010–1011 q cm2 . The slightly higher recombination velocity of 2.3 cm s1 measured with TFSM-hexane can be explained by a lower charge density in the passivating layer, suggesting that the steric hindrance associated with the solvent size could play a role in the passivation mechanism. Finally, phosphorus nuclear magnetic resonance experiments confirm that TFSM-based solutions have Lewis acidity without being superacids, which opens up opportunities for them to be used in materials systems sensitive to superacidic environments
Booster Obsolescence and Life Extension (BOLE) for Space Launch System (SLS)
A human mission to the moon and Mars is the stated space exploration goal of the United States and the international community. To achieve these goals, NASA is developing the Space Launch System (SLS) and the Orion crew capsule as key elements in the architecture for missions to the moon and Mars. As part of the SLS Booster Obsolescence and Life Extension (BOLE) program, Northrop Grumman Space Systems is working to address booster obsolescence issues in design and manufacturing. The upgraded boosters will also provide increased performance that will benefit future lunar campaigns, science missions, and the eventual Mars campaign
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Development of a Rooftop Collaborative Experimental Space through Experiential Learning Projects
The Solar, Water, Energy, and Thermal Laboratory
(SWEAT Lab) is a rooftop experimental space at the
University of Texas at Austin built by graduate and
undergraduate students in the Cockrell School of
Engineering. The project was funded by the Texas State
Energy Conservation Office and the University’s Green
Fee Grant, a competitive grant program funded by UT
Austin tuition fees to support sustainability-related projects
and initiatives on campus. The SWEAT Lab is an on-going
experiential learning facility that enables engineering
education by deploying energy and water-related projects.
To date, the lab contains a full weather station tracking
weather data, a rainwater harvesting system and rooftop
garden.
This project presented many opportunities for students to
learn first hand about unique engineering challenges. The
lab is located on the roof of the 10 story Engineering
Teaching Center (ETC) building, so students had to design
and build systems with constraints such as weight
limitations and wind resistance. Students also gained
experience working with building facilities and
management for structural additions, power, and internet
connection for instruments.
With the Bird’s eye view of UT Austin campus, this unique
laboratory offers a new perspective and dimension to
applied student research projects at UT Austin.Cockrell School of Engineerin
Making a market for Miscanthus: Can new contract designs solve the biofuel investment hold-up problem?
We present designs for optimal contracts to solve the investment hold-up problem for perennial crops for the biofuel industry. A fixed-price contract is ex-ante efficient but renegotiation-proof for a limited range of discount parameters. A perfectly- indexed contract is both renegotiation-proof and ex-post efficient. Provided long-run land prices are stationary, the expected cost for both contracts converges to the long-run expected price of land for a risk-neutral farmer.Biofuels, Miscanthus, contract theory, industrial organization, renegotiation-proof contract, Marketing,
Advanced Biofuel Production in Louisiana Sugar Mills: an Application of Real Options Analysis
In order to more fully study the risks and uncertainty involved in cellulosic ethanol production, we examine a simulated plant in South Louisiana using Real Options Analysisreal options, risk, uncertainty, cellulosic ethanol, energy cane, sorghum, bagasse, simulation, Agribusiness, Agricultural Finance, Production Economics, Resource /Energy Economics and Policy, Risk and Uncertainty, q42, q14, q16, d81, g31,
Holographic Electroweak Symmetry Breaking from D-branes
We observe several interesting phenomena in a technicolor-like model of
electroweak symmetry breaking based on the D4-D8-D8bar system of Sakai and
Sugimoto. The benefit of holographic models based on D-brane configurations is
that both sides of the holographic duality are well understood. We find that
the lightest technicolor resonances contribute negatively to the
Peskin-Takeuchi S-parameter, but heavy resonances do not decouple and lead
generically to large, positive values of S, consistent with standard estimates
in QCD-like theories. We study how the S parameter and the masses and decay
constants of the vector and axial-vector techni-resonances vary over a
one-parameter family of D8-brane configurations. We discuss possibilities for
the consistent truncation of the theory to the first few resonances and suggest
some generic predictions of stringy holographic technicolor models.Comment: REVTeX, 25 pages, 8 eps figures, version published in PR
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