8,367 research outputs found
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
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
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
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
The Levinthal paradox: yesterday and today
A change in the perception of the protein folding problem has taken place recently. The nature of the change is outlined and the reasons for it are presented. An essential element is the recognition that a bias toward the native state over much of the effective energy surface may govern the folding process. This has replaced the random search paradigm of Levinthal and suggests that there are many ways of reaching the native state in a reasonable time so that a specific pathway does not have to be postulated. The change in perception is due primarily to the application of statistical mechanical models and lattice simulations to protein folding. Examples of lattice model results on protein folding are presented. It is pointed out that the new optimism about the protein folding problem must be complemented by more detailed studies to determine the structural and energetic factors that introduce the biases which make possible the folding of real proteins
Pair Production at the Photon Linear Collider
scattering at the Photon Linear Collider is
considered. Explicit formulas for helicity amplitudes due to boson loops
are presented. It is shown that the pair production will be easily
observable at PLC and separation of the loop contribution will be possible
at 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
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