3,389 research outputs found
Solitons and kinks in a general car-following model
We study a car-following model of traffic flow which assumes only that a
car's acceleration depends on its own speed, the headway ahead of it, and the
rate of change of headway, with only minimal assumptions about the functional
form of that dependence. The velocity of uniform steady flow is found
implicitly from the acceleration function, and its linear stability criterion
can be expressed simply in terms of it. Crucially, unlike in previously
analyzed car-following models, the threshold of absolute stability does not
generally coincide with an inflection point in the steady velocity function.
The Burgers and KdV equations can be derived under the usual assumptions, but
the mKdV equation arises only when absolute stability does coincide with an
inflection point. Otherwise, the KdV equation applies near absolute stability,
while near the inflection point one obtains the mKdV equation plus an extra,
quadratic term. Corrections to the KdV equation "select" a single member of the
one-parameter set of soliton solutions. In previous models this has always
marked the threshold of a finite- amplitude instability of steady flow, but
here it can alternatively be a stable, small-amplitude jam. That is, there can
be a forward bifurcation from steady flow. The new, augmented mKdV equation
which holds near an inflection point admits a continuous family of kink
solutions, like the mKdV equation, and we derive the selection criterion
arising from the corrections to this equation.Comment: 25 page
Integrating out the heaviest quark in N--flavour ChPT
We extend a known method to integrate out the strange quark in three flavour
chiral perturbation theory to the context of an arbitrary number of flavours.
As an application, we present the explicit formulae to one--loop accuracy for
the heavy quark mass dependency of the low energy constants after decreasing
the number of flavours by one while integrating out the heaviest quark in
N--flavour chiral perturbation theory.Comment: 18 pages, 1 figure. Text and references added. To appear in EPJ
Cusps in K_L --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays,
the strength of which is related to the pi pi S-wave scattering lengths. We
apply an effective field theory framework developed earlier to evaluate the
amplitudes for K_L --> 3 pi decays in a systematic manner, where the strictures
imposed by analyticity and unitarity are respected automatically. The
amplitudes for the decay eta --> 3 pi are also given.Comment: 15 pages, 3 figures, uses Elsevier styl
Chiral Corrections to Lattice Calculations of Charge Radii
Logarithmic divergences in pion and proton charge radii associated with
chiral loops are investigated to assess systematic uncertainties in current
lattice determinations of charge radii. The chiral corrections offer a possible
solution to the long standing problem of why present lattice calculations yield
proton and pion radii which are similar in size.Comment: PostScript file only. Ten pages. Figures included. U. of MD Preprint
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Isospin Violation in Chiral Perturbation Theory and the Decays \eta \ra \pi \ell \nu and \tau \ra \eta \pi \nu
I discuss isospin breaking effects within the standard model. Chiral
perturbation theory presents the appropriate theoretical framework for such an
investigation in the low--energy range. Recent results on the electromagnetic
contributions to the masses of the pseudoscalar mesons and the
amplitudes are reported. Using the one--loop formulae for the
form factors, rather precise predictions for the decay rates of can be obtained. Finally, I present an estimate of
the \tau \ra \eta \pi \nu branching ratio derived from the dominant meson
resonance contributions to this decay.Comment: 10 pages, latex, one figure available upon reques
Strong rescattering in K-> 3pi decays and low-energy meson dynamics
We present a consistent analysis of final state interactions in
decays in the framework of Chiral Perturbation Theory.
The result is that the kinematical dependence of the rescattering phases cannot
be neglected. The possibility of extracting the phase shifts from future
interference experiments is also analyzed.Comment: 14 pages in RevTex, 3 figures in postscrip
Cusps in K --> 3 pi decays
The pion mass difference generates a pronounced cusp in K --> 3 pi decays. As
has recently been pointed out by Cabibbo and Isidori, an accurate measurement
of the cusp may allow one to pin down the S-wave pi pi scattering lengths to
high precision. Here, we present and illustrate an effective field theory
framework that allows one to determine the structure of this cusp in a
straightforward manner. The strictures imposed by analyticity and unitarity are
respected automatically.Comment: 14 pages, 3 figures, uses Elsevier styl
Sexual Differentiation of Circadian Clock Function in the Adrenal Gland
Sex differences in glucocorticoid production are associated with increased responsiveness of the adrenal gland in females. However, the adrenal-intrinsic mechanisms that establish sexual dimorphic function remain ill defined. Glucocorticoid production is gated at the molecular level by the circadian clock, which may contribute to sexual dimorphic adrenal function. Here we examine sex differences in the adrenal gland using an optical reporter of circadian clock function. Adrenal glands were cultured from male and female Period2::Luciferase (PER2::LUC) mice to assess clock function in vitro in real time. We confirm that there is a pronounced sex difference in the intrinsic capacity to sustain PER2::LUC rhythms in vitro, with higher amplitude rhythms in adrenal glands collected from males than from females. Changes in adrenal PER2::LUC rhythms over the reproductive life span implicate T as an important factor in driving sex differences in adrenal clock function. By directly manipulating hormone levels in adult mice in vivo, we demonstrate that T increases the amplitude of PER2::LUC rhythms in adrenal glands of both male and female mice. In contrast, we find little evidence that ovarian hormones modify adrenal clock function. Lastly, we find that T in vitro can increase the amplitude of PER2::LUC rhythms in male adrenals but not female adrenals, which suggests the existence of sex differences in the mechanisms of T action in vivo. Collectively these results reveal that activational effects of T alter circadian timekeeping in the adrenal gland, which may have implications for sex differences in stress reactivity and stress-related disorders
Sigma-term physics in the perturbative chiral quark model
We apply the perturbative chiral quark model (PCQM) at one loop to analyse
meson-baryon sigma-terms. Analytic expressions for these quantities are
obtained in terms of fundamental parameters of low-energy pion-nucleon physics
(weak pion decay constant, axial nucleon coupling, strong pion-nucleon form
factor) and of only one model parameter (radius of the nucleonic three-quark
core). Our result for the piN sigma term of about 45 MeV is in good agreement
with the value deduced by Gasser, Leutwyler and Sainio using
dispersion-relation techniques and exploiting the chiral symmetry constraints.Comment: 19 pages, LaTeX-file, 2 Figure
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