Computers for real time flight simulation: A market survey

An extensive computer market survey was made to determine those available systems suitable for current and future flight simulation studies at Ames Research Center. The primary requirement is for the computation of relatively high frequency content (5 Hz) math models representing powered lift flight vehicles. The Rotor Systems Research Aircraft (RSRA) was used as a benchmark vehicle for computation comparison studies. The general nature of helicopter simulations and a description of the benchmark model are presented, and some of the sources of simulation difficulties are examined. A description of various applicable computer architectures is presented, along with detailed discussions of leading candidate systems and comparisons between them

Spin symmetry and spin current of helicity eigenstates of the Luttinger Hamiltonian

A general spin symmetry argument is proposed for spin currents in semiconductors. In particular, due to the symmetry with respect to spin polarization of the helicity eigenstates of the Luttinger Hamiltonian for a hole-doped semiconductor, the spin polarized flux from a single helicity eigenstate induced by an external electric field, is canceled exactly when all such contributions from eigenstates that are degenerate in energy are summed. Thus, the net spin current predicted by Murakami et al, Science 301, 1348 (2003), cannot be produced by such a Hamiltonian. Possible symmetry breaking mechanisms which may generate a spin current are discussed

Four-states phase diagram of proteins

A four states phase diagram for protein folding as a function of temperature and solvent quality is derived from an improved 2-d lattice model taking into account the temperature dependence of the hydrophobic effect. The phase diagram exhibits native, globule and two coil-type regions. In agreement with experiment, the model reproduces the phase transitions indicative of both warm and cold denaturations. Finally, it predicts transitions between the two coil states and a critical point.Comment: 7 pages, 5 figures. Accepted for publication in Europhysics Letter

γZ\gamma Z Pair Production at the Photon Linear Collider

$\gamma\gamma\to\gamma Z$ scattering at the Photon Linear Collider is considered. Explicit formulas for helicity amplitudes due to $W$ boson loops are presented. It is shown that the $Z\gamma$ pair production will be easily observable at PLC and separation of the $W$ loop contribution will be possible at $e^+e^-$ c.m. energy of 300~GeV or higher.Comment: 9 pages of standard LaTeX + 3 PostScript figures (uuencoded and compressed

Bayesian estimates of free energies from nonequilibrium work data in the presence of instrument noise

The Jarzynski equality and the fluctuation theorem relate equilibrium free energy differences to non-equilibrium measurements of the work. These relations extend to single-molecule experiments that have probed the finite-time thermodynamics of proteins and nucleic acids. The effects of experimental error and instrument noise have not previously been considered. Here, we present a Bayesian formalism for estimating free-energy changes from non-equilibrium work measurements that compensates for instrument noise and combines data from multiple driving protocols. We reanalyze a recent set of experiments in which a single RNA hairpin is unfolded and refolded using optical tweezers at three different rates. Interestingly, the fastest and farthest-from-equilibrium measurements contain the least instrumental noise, and therefore provide a more accurate estimate of the free energies than a few slow, more noisy, near-equilibrium measurements. The methods we propose here will extend the scope of single-molecule experiments; they can be used in the analysis of data from measurements with AFM, optical, and magnetic tweezers.Comment: 8 page

Institutions and Emissions Trading in China

Institutions—the formal rules and informal norms that shape human interaction ( North 1991 )—have the potential to influence the oper - ation of an emissions trading system ( ETS ). For instance, preexisting economic regulation has been shown to affect firms’ abatement decisions and costs (Fowlie 2010). Transaction costs can also interfere with cost-effective operation by reducing trading levels and increasing abatement costs (Stavins 1995). As China develops a national ETS for carbon dioxide (CO₂) covering multiple energy-intensive sectors, it is important to consider how its design will interact with prevailing institutional features of the country’s economy. This paper focuses specifically on the role of state control of industry, one source of heterogeneity that will affect efforts to establish an ETS in China’s vast and diverse economic system

Prospects for Plug-in Hybrid Electric Vehicles in the United States and Japan: A General Equilibrium Analysis

Abstract and PDF report are also available on the MIT Joint Program on the Science and Policy of Global Change website (http://globalchange.mit.edu/)The plug-in hybrid electric vehicle (PHEV) may offer a potential near term, low carbon alternative to today's gasoline- and diesel-powered vehicles. A representative vehicle technology that runs on electricity in addition to conventional fuels was introduced into the MIT Emissions Prediction and Policy Analysis (EPPA) model as a perfect substitute for internal combustion engine (ICE-only) vehicles in two likely early-adopting markets, the United States and Japan. We investigate the effect of relative vehicle cost and all-electric range on the timing of PHEV market entry in the presence and absence of an advanced cellulosic biofuels technology and a strong (450ppm) economy-wide carbon constraint. Vehicle cost could be a significant barrier to PHEV entry unless fairly aggressive goals for reducing battery costs are met. If a low cost vehicle is available we find that the PHEV has the potential to reduce CO2 emissions, refined oil demand, and under a carbon policy the required CO2 price in both the United States and Japan. The emissions reduction potential of PHEV adoption depends on the carbon intensity of electric power generation and the size of the vehicle fleet. Thus, the technology is much more effective in reducing CO2 emissions if adoption occurs under an economy-wide cap and trade system that also encourages low-carbon electricity generation.BP Conversion Research Project and the MIT Joint Program on the Science and Policy of Global Change through a consortium of industrial sponsors and Federal grants

Markets versus Regulation: The Efficiency and Distributional Impacts of U.S. Climate Policy Proposals

Regulatory measures have proven the favored approach to climate change mitigation in the U.S., while market-based policies have gained little traction. Using a model that resolves the U.S. economy by region, income category, and sector-specific technology deployment opportunities, this paper studies the magnitude and distribution of economic impacts under regulatory versus market-based approaches. We quantify heterogeneity in the national response to regulatory policies, including a fuel economy standard and a clean or renewable electricity standard, and compare these to a cap–and–trade system targeting carbon dioxide or all greenhouse gases. We find that the regulatory policies substantially exceed the cost of a cap–and–trade system at the national level. We further show that the regulatory policies yield large cost disparities across regions and income groups, which are exaggerated by the difficulty of implementing revenue recycling provisions under regulatory policy designs.We acknowledge support of the MIT Joint Program on the Science and Policy of Global Change through a combination of government, industry, and foundation funding, the MIT Energy Initiative, and additional support for this work from a coalition of industrial sponsors. This work is also supported by the DOE Integrated Assessment Grant (DE-FG02-94ER61937). For development of the USREP-ReEDS model, the authors further acknowledge the support of the Joint Institute for Strategic Energy Analysis, which is operated by the Alliance for Sustainable Energy, LLC, on behalf of the U.S. Department of Energy’s National Renewable Energy Laboratory, the University of Colorado-Boulder, the Colorado School of Mines, the Colorado State University, the Massachusetts Institute of Technology, and Stanford University