13,571 research outputs found
‘Walking ... just walking’: how children and young people’s everyday pedestrian practices matter
In this paper we consider the importance of ‘walking… just walking’ for many children and young people’s everyday lives. We will show how, in our research with 175 9-16-year-olds living in new urban developments in south-east England, some particular (daily, taken-for-granted, ostensibly aimless) forms of walking were central to the lives, experiences and friendships of most children and young people. The main body of the paper highlights key characteristics of these walking practices, and their constitutive role in these children and young people’s social and cultural geography. Over the course of the paper we will argue that ‘everyday pedestrian practices’ (after Middleton 2010, 2011) like these require us to think critically about two bodies of geographical and social scientific research. On one hand, we will argue that the large body of research on children’s spatial range and independent mobility could be conceptually enlivened and extended to acknowledge bodily, social, sociotechnical and habitual practices. On the other hand, we will suggest that the empirical details of such practices should prompt critical reflection upon the wonderfully rich, multidisciplinary vein of conceptualisation latterly termed ‘new walking studies’ (Lorimer 2011). Indeed, in conclusion we shall argue that the theoretical vivacity of walking studies, and the concerns of more applied empirical approaches such as work on children’s independent mobility, could productively be interrelated. In so doing we open out a wider challenge to social and cultural geographers, to expedite this kind of interrelation in other research contexts
Forward-Backward Correlations and Event Shapes as probes of Minimum-Bias Event Properties
Measurements of inclusive observables, such as particle multiplicities and
momentum spectra, have already delivered important information on
soft-inclusive ("minimum-bias") physics at the Large Hadron Collider. In order
to gain a more complete understanding, however, it is necessary to include also
observables that probe the structure of the studied events. We argue that
forward-backward (FB) correlations and event-shape observables may be
particulary useful first steps in this respect. We study the sensitivity of
several different types of FB correlations and two event shape variables -
transverse thrust and transverse thrust minor - to various sources of
theoretical uncertainty: multiple parton interactions, parton showers, colour
(re)connections, and hadronization. The power of each observable to furnish
constraints on Monte Carlo models is illustrated by including comparisons
between several recent, and qualitatively different, PYTHIA 6 tunes, for pp
collisions at sqrt(s) = 900 GeV.Comment: 13 page
Proposed Search For The Detection Of Gravitational Waves From Eccentric Binary Black Holes
Most compact binary systems are expected to circularize before the frequency of emitted gravitational waves (GWs) enters the sensitivity band of the ground based interferometric detectors. However, several mechanisms have been proposed for the formation of binary systems, which retain eccentricity throughout their lifetimes. Since no matched-filtering algorithm has been developed to extract continuous GW signals from compact binaries on orbits with low to moderate values of eccentricity, and available algorithms to detect binaries on quasicircular orbits are suboptimal to recover these events, in this paper we propose a search method for detection of gravitational waves produced from the coalescences of eccentric binary black holes (eBBH). We study the search sensitivity and the false alarm rates on a segment of data from the second joint science run of LIGO and Virgo detectors, and discuss the implications of the eccentric binary search for the advanced GW detectors
Galaxy Formation with local photoionisation feedback I. Methods
We present a first study of the effect of local photoionising radiation on
gas cooling in smoothed particle hydrodynamics simulations of galaxy formation.
We explore the combined effect of ionising radiation from young and old stellar
populations. The method computes the effect of multiple radiative sources using
the same tree algorithm used for gravity, so it is computationally efficient
and well resolved. The method foregoes calculating absorption and scattering in
favour of a constant escape fraction for young stars to keep the calculation
efficient enough to simulate the entire evolution of a galaxy in a cosmological
context to the present day. This allows us to quantify the effect of the local
photoionisation feedback through the whole history of a galaxy`s formation. The
simulation of a Milky Way like galaxy using the local photoionisation model
forms ~ 40 % less stars than a simulation that only includes a standard uniform
background UV field. The local photoionisation model decreases star formation
by increasing the cooling time of the gas in the halo and increasing the
equilibrium temperature of dense gas in the disc. Coupling the local radiation
field to gas cooling from the halo provides a preventive feedback mechanism
which keeps the central disc light and produces slowly rising rotation curves
without resorting to extreme feedback mechanisms. These preliminary results
indicate that the effect of local photoionising sources is significant and
should not be ignored in models of galaxy formation.Comment: Accepted for Publication in MNRAS, 13 pages, 13 figure
Neutron scattering study of the magnetic phase diagram of underdoped YBa(2)Cu(3)O(6+x)
We present a neutron triple-axis and resonant spin-echo spectroscopy study of
the spin correlations in untwinned YBCO crystals with x= 0.3, 0.35, and 0.45 as
a function of temperature and magnetic field. As the temperature T approaches
0, all samples exhibit static incommensurate magnetic order with propagation
vector along the a-direction in the CuO2 planes. The incommensurability delta
increases monotonically with hole concentration, as it does in LSCO. However,
delta is generally smaller than in LSCO at the same doping level. The intensity
of the incommensurate Bragg reflections increases with magnetic field for
YBCO(6.45) (superconducting Tc = 35 K), whereas it is field-independent for
YBCO(6.35) (Tc = 10 K). These results suggest that YBCO samples with x ~ 0.5
exhibit incommensurate magnetic order in the high fields used for the recent
quantum oscillation experiments on this system, which likely induces a
reconstruction of the Fermi surface. We present neutron spin-echo measurements
(with energy resolution ~ 1 micro-eV) for T > 0 that demonstrate a continuous
thermal broadening of the incommensurate magnetic Bragg reflections into a
quasielastic peak centered at excitation energy E = 0, consistent with the
zero-temperature transition expected for a two-dimensional spin system with
full spin-rotation symmetry. Measurements on YBCO(6.45) with a triple-axis
spectrometer (with energy resolution ~ 100 micro-eV) yield a crossover
temperature T_SDW ~ 30 K for the onset of quasi-static magnetic order. Upon
further heating, the wavevector characterizing low-energy spin excitations
approaches the commensurate antiferromagnetic wave vector, and the
incommensurability vanishes in an order-parameter-like fashion at an
"electronic liquid-crystal" onset temperature T_ELC ~ 150 K. Both T_SDW and
T_ELC increase continuously as the Mott-insulating phase is approached with
decreasing doping level.Comment: to appear in a special issue on "Fermiology of Cuprates" of the New
Journal of Physic
Significance of Off-Center Rattling for Emerging Low-lying THz Modes in type-I Clathrates
We show that the distinct differences of low-lying THz-frequency dynamics
between type-I clathrates with on-center and off-center guest ions naturally
follow from a theoretical model taking into account essential features of the
dynamics of rattling guest ions. Our model analysis demonstrates the drastic
change from the conventional dynamics shown by on-center systems to the
peculiar dynamics of off-center systems in a unified manner. We claim that
glass-like plateau thermal conductivities observed for off-center systems stem
from the flattening of acoustic phonon dispersion in the regime |k|<|G|/4. The
mechanism is applicable to other systems such as glasses or relaxers
Testing the asymptotic relation for period spacings from mixed modes of red giants observed with the Kepler mission
Dipole mixed pulsation modes of consecutive radial order have been detected
for thousands of low-mass red-giant stars with the NASA space telescope Kepler.
Such modes have the potential to reveal information on the physics of the deep
stellar interior. Different methods have been proposed to derive an observed
value for the gravity-mode period spacing, the most prominent one relying on a
relation derived from asymptotic pulsation theory applied to the gravity-mode
character of the mixed modes. Our aim is to compare results based on this
asymptotic relation with those derived from an empirical approach for three
pulsating red-giant stars. We developed a data-driven method to perform
frequency extraction and mode identification. Next, we used the identified
dipole mixed modes to determine the gravity-mode period spacing by means of an
empirical method and by means of the asymptotic relation. In our methodology,
we consider the phase offset, , of the asymptotic
relation as a free parameter. Using the frequencies of the identified dipole
mixed modes for each star in the sample, we derived a value for the
gravity-mode period spacing using the two different methods. These differ by
less than 5%. The average precision we achieved for the period spacing derived
from the asymptotic relation is better than 1%, while that of our data-driven
approach is 3%. Good agreement is found between values for the period spacing
derived from the asymptotic relation and from the empirical method.
Full abstract in PDF file.Comment: 14 pages, 13 figures, accepted for publication in A&
Design and development of an inexpensive aquatic swarm robotics system
Swarm robotics is a promising approach characterized by large numbers of relatively small and inexpensive robots. Since such systems typically rely on decentralized control and local communication, they exhibit a number of interesting and useful properties, namely scalability, robustness to individual faults, and flexibility. In this paper, we detail the design and development process of a swarm robotics platform composed of autonomous surface robots, which was designed in order to study the use of robotic swarms in real-world environments. Our aquatic surface robots where manufactured using digital fabrication techniques, such as 3D printing and CNC milling, and all hardware and software has been made available as open-source, thus allowing third-parties to customize and further improve our platform.info:eu-repo/semantics/acceptedVersio
The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes
In D-dimensional spacetimes which can be foliated by n-dimensional
homogeneous subspaces, a quantum field can be decomposed in terms of modes on
the subspaces, reducing the system to a collection of (D-n)-dimensional fields.
This allows one to write bare D-dimensional field quantities like the Green
function and the effective action as sums of their (D-n)-dimensional
counterparts in the dimensionally reduced theory. It has been shown, however,
that renormalization breaks this relationship between the original and
dimensionally reduced theories, an effect called the dimensional-reduction
anomaly. We examine the dimensional-reduction anomaly for the important case of
spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references
adde
Educational achievement among long-term survivors of congenital heart defects: a Danish population-based follow-up study
- …