1,397 research outputs found
Device measures conductivity and velocity of ionized gas streams
Coaxial arrangement of primary coil and two sensing secondary coils contained inside slender quartz tube inserted into ionized stream permits simultaneous determination of conductivity and linear velocity. System results agree favorably with theory
Tracing the development of dust around evolved stars: The case of 47 Tuc
We observed mid-infrared (7.5-22 mum) spectra of AGB stars in the globular
cluster 47 Tuc with the Spitzer telescope and find significant dust features of
various types. Comparison of the characteristics of the dust spectra with the
location of the stars in a logP-K-diagram shows that dust mineralogy and
position on the AGB are related. A 13 mum feature is seen in spectra of low
luminosity AGB stars. More luminous AGB stars show a broad feature at 11.5 mum.
The spectra of the most luminous stars are dominated by the amorphous silicate
bending vibration centered at 9.7 mum. For 47 Tuc AGB stars, we conclude that
early on the AGB dust consisting primarily of Mg-, Al- and Fe oxides is formed.
With further AGB evolution amorphous silicates become the dominant species.Comment: 2 figures, accepted for publication in ApJ Letter
Time-oscillating Lyapunov modes and auto-correlation functions for quasi-one-dimensional systems
The time-dependent structure of the Lyapunov vectors corresponding to the
steps of Lyapunov spectra and their basis set representation are discussed for
a quasi-one-dimensional many-hard-disk systems. Time-oscillating behavior is
observed in two types of Lyapunov modes, one associated with the time
translational invariance and another with the spatial translational invariance,
and their phase relation is specified. It is shown that the longest period of
the Lyapunov modes is twice as long as the period of the longitudinal momentum
auto-correlation function. A simple explanation for this relation is proposed.
This result gives the first quantitative connection between the Lyapunov modes
and an experimentally accessible quantity.Comment: 4 pages, 3 figure
Sds22 regulates aurora B activity and microtubule-kinetochore interactions at mitosis
Sds22 defines protein phosphatase 1 location and function at kinetochores and subsequent activity of aurora B in mitosis
Emergence of order in selection-mutation dynamics
We characterize the time evolution of a d-dimensional probability
distribution by the value of its final entropy. If it is near the
maximally-possible value we call the evolution mixing, if it is near zero we
say it is purifying. The evolution is determined by the simplest non-linear
equation and contains a d times d matrix as input. Since we are not interested
in a particular evolution but in the general features of evolutions of this
type, we take the matrix elements as uniformly-distributed random numbers
between zero and some specified upper bound. Computer simulations show how the
final entropies are distributed over this field of random numbers. The result
is that the distribution crowds at the maximum entropy, if the upper bound is
unity. If we restrict the dynamical matrices to certain regions in matrix
space, for instance to diagonal or triangular matrices, then the entropy
distribution is maximal near zero, and the dynamics typically becomes
purifying.Comment: 8 pages, 8 figure
Time-dependent mode structure for Lyapunov vectors as a collective movement in quasi-one-dimensional systems
Time dependent mode structure for the Lyapunov vectors associated with the
stepwise structure of the Lyapunov spectra and its relation to the momentum
auto-correlation function are discussed in quasi-one-dimensional many-hard-disk
systems. We demonstrate mode structures (Lyapunov modes) for all components of
the Lyapunov vectors, which include the longitudinal and transverse components
of their spatial and momentum parts, and their phase relations are specified.
These mode structures are suggested from the form of the Lyapunov vectors
corresponding to the zero-Lyapunov exponents. Spatial node structures of these
modes are explained by the reflection properties of the hard-walls used in the
models. Our main interest is the time-oscillating behavior of Lyapunov modes.
It is shown that the largest time-oscillating period of the Lyapunov modes is
twice as long as the time-oscillating period of the longitudinal momentum
auto-correlation function. This relation is satisfied irrespective of the
particle number and boundary conditions. A simple explanation for this relation
is given based on the form of the Lyapunov vector.Comment: 39 pages, 21 figures, Manuscript including the figures of better
quality is available from http://www.phys.unsw.edu.au/~gary/Research.htm
Lyapunov spectra of billiards with cylindrical scatterers: comparison with many-particle systems
The dynamics of a system consisting of many spherical hard particles can be
described as a single point particle moving in a high-dimensional space with
fixed hypercylindrical scatterers with specific orientations and positions. In
this paper, the similarities in the Lyapunov exponents are investigated between
systems of many particles and high-dimensional billiards with cylindrical
scatterers which have isotropically distributed orientations and homogeneously
distributed positions. The dynamics of the isotropic billiard are calculated
using a Monte-Carlo simulation, and a reorthogonalization process is used to
find the Lyapunov exponents. The results are compared to numerical results for
systems of many hard particles as well as the analytical results for the
high-dimensional Lorentz gas. The smallest three-quarters of the positive
exponents behave more like the exponents of hard-disk systems than the
exponents of the Lorentz gas. This similarity shows that the hard-disk systems
may be approximated by a spatially homogeneous and isotropic system of
scatterers for a calculation of the smaller Lyapunov exponents, apart from the
exponent associated with localization. The method of the partial stretching
factor is used to calculate these exponents analytically, with results that
compare well with simulation results of hard disks and hard spheres.Comment: Submitted to PR
Hopping dynamics for localized Lyapunov vectors in many-hard-disk systems
The dynamics of the localized region of the Lyapunov vector for the largest
Lyapunov exponent is discussed in quasi-one-dimensional hard-disk systems at
low density. We introduce a hopping rate to quantitatively describe the
movement of the localized region of this Lyapunov vector, and show that it is a
decreasing function of hopping distance, implying spatial correlation of the
localized regions. This behavior is explained quantitatively by a brick
accumulation model derived from hard-disk dynamics in the low density limit, in
which hopping of the localized Lyapunov vector is represented as the movement
of the highest brick position. We also give an analytical expression for the
hopping rate, which is obtained us a sum of probability distributions for brick
height configurations between two separated highest brick sites. The results of
these simple models are in good agreement with the simulation results for
hard-disk systems.Comment: 28 pages, 13 figure
From Lyapunov modes to the exponents for hard disk systems
We demonstrate the preservation of the Lyapunov modes by the underlying
tangent space dynamics of hard disks.
This result is exact for the zero modes and correct to order for
the transverse and LP modes where is linear in the mode number.
For sufficiently large mode numbers the dynamics no longer preserves the mode
structure.
We propose a Gram-Schmidt procedure based on orthogonality with respect to
the centre space that determines the values of the Lyapunov exponents for the
modes.
This assumes a detailed knowledge of the modes, but from that predicts the
values of the exponents from the modes.
Thus the modes and the exponents contain the same information
The “hidden strength” of active citizenship: the involvement of local residents in public safety projects
The past two decades or so have seen a growing interest in 'active' (or 'responsible') citizenship within local public safety projects and programmes, but little is known about how such projects function in practice. Besides presenting theoretical debates on community safety projects, this article reports empirical insights into the wealth and variety of informal, citizen-based contributions, specifically to handling communal crime and disorder in Amsterdam, capital city of the Netherlands. Subsequently, it assesses the kind of lessons empirical studies provide about the importance of 'social capital' for public participation, the perils of social exclusion and the nature of relationships between citizens and professionals. It is argued that enthusiastic efforts of individual citizens are equally important, if not more so, than strong social ties. Moreover, in overall terms, active participation tends to have a significant bias in favour of the white, middle-aged, middle-class population. Finally, benevolent citizens regularly encounter professional barriers and bureaucratic ceilings that inhibit their desire to participate. All rhetoric to the contrary notwithstanding, promoting genuine active citizenship is easier said than done. © The Author(s) 2011
- …