10,253 research outputs found
”I Speak Hip Hop”: An Informative Interview about Generation Hip Hop and the Universal Hip Hop Museum
”I Speak Hip Hop” is an interview of members of Generation Hip Hop and the Universal Hip Hop Museum. This primary source highlights two Hip Hop organizations with chapters around the world. Tasha Iglesias and Travis Harris posits that Hip Hop scholars have not fully uncovered Hip Hop\u27s history around the world. As such, in addition to being a primary source, I Speak Hip Hop reveals the need for more scholarly attention on the dynamic expansion of Hip Hop cultures
Route training in mobile robots through system identification
Fundamental sensor-motor couplings form the backbone of
most mobile robot control tasks, and often need to be implemented fast, efficiently and nevertheless reliably. Machine learning techniques are therefore often used to obtain the desired sensor-motor competences. In this paper we present an alternative to established machine learning methods such as artificial neural networks, that is very fast, easy to implement, and has the distinct advantage that it generates transparent, analysable sensor-motor couplings: system identification through nonlinear polynomial mapping. This work, which is part of the RobotMODIC project at the universities of Essex and Sheffield, aims to develop a theoretical understanding of the interaction between the robot and its environment. One of the purposes of this research is to enable the principled design of robot control programs. As a first step towards this aim we model the behaviour of the robot, as this emerges from its interaction with the environment, with the NARMAX modelling method (Nonlinear, Auto-Regressive, Moving Average models with eXogenous inputs). This method produces explicit polynomial functions that can be subsequently analysed using established mathematical methods. In this paper we demonstrate the fidelity of the obtained NARMAX models in the challenging task of robot route learning; we present a set of experiments in which a Magellan Pro mobile robot was taught to follow four different routes, always using the same mechanism to obtain the required control law
An investigation of star formation and dust attenuation in major mergers using ultraviolet and infrared data
Merger processes play an important role in galaxy formation and evolution. To
study the influence of merger processes on the evolution of dust properties and
cosmic star formation rate, we investigate a local sample of major merger
galaxies and a control sample of isolated galaxies using GALEX ultraviolet (UV)
and Spitzer infrared (IR) images. Through a statistical study, we find that
dust attenuation in merger galaxies is enhanced with respect to isolated
galaxies. We find this enhancement is contributed mainly by spiral galaxies in
spiral-spiral (S-S) pairs, and increases with the increasing stellar mass of a
galaxy. Combining the IR and UV parts of star formation rates (SFRs), we then
calculated the total SFRs and specific star formation rates (SSFRs). We find
the SSFRs to be enhanced in merger galaxies. This enhancement depends on galaxy
stellar mass and the companion's morphology, but depends little on whether the
galaxy is a primary or secondary component or on the separation between two
components. These results are consistent with a previous study based only on IR
images. In addition, we investigate the nuclear contributions to SFRs. SFRs in
paired galaxies are more concentrated in the central part of the galaxies than
in isolate galaxies. Our studies of dust attenuation show that the nuclear
parts of pairs most resemble ULIRGs. Including UV data in the present work not
only provides reliable information on dust attenuation, but also refines
analyses of SFRs.Comment: 21 pages, 21 figure
Visual task identification and characterisation using polynomial models
Developing robust and reliable control code for autonomous mobile robots is difficult, because the interaction between a physical robot and the environment is highly complex, subject to noise and variation, and therefore partly unpredictable. This means that to date it is not possible to predict robot behaviour based on theoretical models. Instead, current methods to develop robot control
code still require a substantial trial-and-error component to the software design process. This paper proposes a method of dealing with these issues by a) establishing task-achieving sensor-motor couplings through robot training, and b) representing these couplings through transparent mathematical functions that can be used to form hypotheses
and theoretical analyses of robot behaviour. We demonstrate the viability of this approach by teaching a mobile robot to track a moving football and subsequently modelling
this task using the NARMAX system identification technique
Comparing robot controllers through system identification
In the mobile robotics field, it is very common to find different control programs designed to achieve a particular robot task. Although there are many ways to evaluate these controllers qualitatively, there is a lack of formal methodology to compare them from a mathematical point of view. In this paper we present a novel approach to compare robot control codes quantitatively based on system identification: Initially the transparent mathematical models of the controllers are obtained using the NARMAX system identification process. Then we use these models to analyse the general characteristics of the cotrollers from a mathematical point of view. In this way, we are able to compare different control programs objectively based on quantitative measures. We demonstrate our approach by comparing two different robot control programs, which were designed to drive the robot through door-like openings
Model Calculation of Electron-Phonon Couplings in a Dimer with a Non-Degenerate Orbital
We evaluate all the electron-phonon couplings derived from the one-body
electronic interactions, in both the adiabatic and extreme non-adiabatic limit,
for a dimer with a non-degenerate orbital built from atomic wave functions of
Gaussian shape. We find largely different values of the coupling parameters in
the two cases, as well as different expressions of the corresponding terms in
the Hamiltonian.Comment: 5 postscript figure
The inception of Symplectic Geometry: the works of Lagrange and Poisson during the years 1808-1810
The concept of a symplectic structure first appeared in the works of Lagrange
on the so-called "method of variation of the constants". These works are
presented, together with those of Poisson, who first defined the composition
law called today the "Poisson bracket". The method of variation of the
constants is presented using today's mathematical concepts and notations.Comment: Presented at the meeting "Poisson 2008" in Lausanne, July 2008.
Published in Letters in Mathematical Physics. 22 page
AKARI/IRC Broadband Mid-infrared data as an indicator of Star Formation Rate
AKARI/Infrared Camera (IRC) Point Source Catalog provides a large amount of
flux data at {\it S9W} () and {\it L18W} ()
bands. With the goal of constructing Star-Formation Rate(SFR) calculations
using IRC data, we analyzed an IR selected
GALEX-SDSS-2MASS-AKARI(IRC/Far-Infrared Surveyor) sample of 153 nearby
galaxies. The far-infrared fluxes were obtained from AKARI diffuse maps to
correct the underestimation for extended sources raised by the point-spread
function photometry. SFRs of these galaxies were derived by the spectral energy
distribution fitting program CIGALE. In spite of complicated features contained
in these bands, both the {\it S9W} and {\it L18W} emission correlate with the
SFR of galaxies. The SFR calibrations using {\it S9W} and {\it L18W} are
presented for the first time. These calibrations agree well with previous works
based on Spitzer data within the scatters, and should be applicable to
dust-rich galaxies.Comment: PASJ, in pres
A general framework for nonholonomic mechanics: Nonholonomic Systems on Lie affgebroids
This paper presents a geometric description of Lagrangian and Hamiltonian
systems on Lie affgebroids subject to affine nonholonomic constraints. We
define the notion of nonholonomically constrained system, and characterize
regularity conditions that guarantee that the dynamics of the system can be
obtained as a suitable projection of the unconstrained dynamics. It is shown
that one can define an almost aff-Poisson bracket on the constraint AV-bundle,
which plays a prominent role in the description of nonholonomic dynamics.
Moreover, these developments give a general description of nonholonomic systems
and the unified treatment permits to study nonholonomic systems after or before
reduction in the same framework. Also, it is not necessary to distinguish
between linear or affine constraints and the methods are valid for explicitly
time-dependent systems.Comment: 50 page
Effects of dust scattering albedo and 2175 A bump on ultraviolet colours of normal disc galaxies
We discuss dust properties in the interstellar medium (ISM) of nearby normal
galaxies, by comparing observations in the ultraviolet (UV) with simulations by
a radiative transfer model. The observed UV colours of nearby galaxies show a
reddening relative to their expected intrinsic colours. Some authors argued
that the Milky Way dust cannot reproduce the reddening because of the prominent
2175 \AA absorption bump. Other authors proposed a reduction mechanism of the
bump strength in an {\it attenuation law} derived from the ratio of the
observed intensity to the intrinsic one through an age-selective attenuation
(i.e., young stars are more attenuated selectively). We newly find that the
wavelength dependence of the scattering albedo also has a strong effect on the
UV colour; an albedo decreasing toward shorter wavelengths (except for the
absorption bump range) produces a significant UV reddening. After comparing the
observed UV colours of nearby normal galaxies with those expected from
radiative transfer simulations assumed several dust models, we find two sorts
of dust suitable for these galaxies: (1) dust with a bump and a smaller albedo
for a shorter wavelength (except for the bump range), and (2) dust without any
bump but with an almost constant albedo. If very small carbonaceous grains
responsible for the common unidentified infrared emission band are also the
bump carrier, the former dust is favorable. Finally, we derive mean attenuation
laws of various dust models as a function of the UV attenuation, and derive
some relations between the UV attenuation and observable/theoretical
quantities.Comment: MNRAS in pres
- …