1,929 research outputs found

### Optimization methods applied to hybrid vehicle design

The use of optimization methods as an effective design tool in the design of hybrid vehicle propulsion systems is demonstrated. Optimization techniques were used to select values for three design parameters (battery weight, heat engine power rating and power split between the two on-board energy sources) such that various measures of vehicle performance (acquisition cost, life cycle cost and petroleum consumption) were optimized. The apporach produced designs which were often significant improvements over hybrid designs already reported on in the literature. The principal conclusions are as follows. First, it was found that the strategy used to split the required power between the two on-board energy sources can have a significant effect on life cycle cost and petroleum consumption. Second, the optimization program should be constructed so that performance measures and design variables can be easily changed. Third, the vehicle simulation program has a significant effect on the computer run time of the overall optimization program; run time can be significantly reduced by proper design of the types of trips the vehicle takes in a one year period. Fourth, care must be taken in designing the cost and constraint expressions which are used in the optimization so that they are relatively smooth functions of the design variables. Fifth, proper handling of constraints on battery weight and heat engine rating, variables which must be large enough to meet power demands, is particularly important for the success of an optimization study. Finally, the principal conclusion is that optimization methods provide a practical tool for carrying out the design of a hybrid vehicle propulsion system

### Quantum power correction to the Newton law

We have found the graviton contribution to the one-loop quantum correction to
the Newton law. This correction results in interaction decreasing with distance
as 1/r^3 and is dominated numerically by the graviton contribution. The
previous calculations of this contribution to the discussed effect are
demonstrated to be incorrect.Comment: 10 pages, 5 figures; numerical error corrected, few references adde

### Constraints on the variability of quark masses from nuclear binding

Based on recent work on nuclear binding, we update and extend the anthropic
constraints on the light quark masses, with results that are more tightly
constrained than previously obtained. We find that heavy nuclei would fall
apart (because the attractive nuclear central potential becomes too weak) if
the sum of the light quark masses m_u+m_d would exceed their physical values by
64% (at 95% confidence level). We summarize the anthropic constraints that
follow from requiring the existence both of heavy atoms and of hydrogen. With
the additional assumption that the quark Yukawa couplings do not vary, these
constraints provide a remarkably tight anthropic window for the Higgs vacuum
expectation value: 0.39 < v/v_physical < 1.64.Comment: 21 pages, 7 figure

### Isotropy of the early universe from CMB anisotropies

The acoustic peak in the CMB power spectrum is sensitive to causal processes
and cosmological parameters in the early universe up to the time of last
scattering. We provide limits on correlated spatial variations of the peak
height and peak position and interpret these as constraints on the spatial
variation of the cosmological parameters (baryon density, cold dark matter
density and cosmological constant as well as the amplitude and tilt of the
original fluctuations). We utilize recent work of Hansen, Banday and Gorski
(HBG) who have studied the spatial isotropy of the power spectrum as measured
by WMAP by performing the power spectrum analysis on smaller patches of the
sky. We find that there is no statistically significant correlated asymmetry of
the peak. HBG have also provided preliminary indications of a preferred
direction in the lower angular momentum range(~ 2-40) and we show how possible
explanations of this asymmetry are severely constrained by the data on the
acoustic peak. Finally we show a possible non-gaussian feature in the data,
associated with a difference in the northern and southern galactic hemispheres.Comment: 14 pages, 3 figures, v.2 adds an extra relevant reference and commen

### Asymptotic Limits and Structure of the Pion Form Factor

We use dispersive techniques to address the behavior of the pion form factor
as $Q^2 \to \infty$ and $Q^2 \to 0$. We perform the matching with the
constraints of perturbative QCD and chiral perturbation theory in the high
energy and low energy limits, leading to four sum rules. We present a version
of the dispersive input which is consistent with the data and with all
theoretical constraints. The results indicate that the asymptotic perturbative
QCD limit is approached relatively slowly, and give a model independent
determination of low energy chiral parameters.Comment: 8 pages, Latex, 2 figure

### Study of pesudoscalar transition form factors within light front quark model

We study the transition form factors of the pesudoscalar mesons ($\pi,\eta$
and $\eta^{\prime}$) as functions of the momentum transfer $Q^2$ within the
light-front quark model. We compare our results with the recent experimental
data by CELLO, CLEO, BaBar and Belle. By considering the possible uncertainties
from the quark masses, we illustrate that our predicted form factors can fit
with all the data, including those at the large $Q^2$ regions.Comment: 10 pages, 4 figures, accepted for publication in Phys. Rev.

### The Electromagnetic Mass Differences of Pions and Kaons

We use the Cottingham method to calculate the pion and kaon electromagnetic
mass differences with as few model dependent inputs as possible. The
constraints of chiral symmetry at low energy, QCD at high energy and
experimental data in between are used in the dispersion relation. We find
excellent agreement with experiment for the pion mass difference. The kaon mass
difference exhibits a strong violation of the lowest order prediction of
Dashen's theorem, in qualitative agreement with several other recent
calculations.Comment: 40 pages, Latex, needs axodraw. and psfig. macros, 4 figure

- â€¦