13,719 research outputs found
The Subpulse Modulation Properties of Pulsars and its Frequency Dependence
A large sample of about two hundred pulsars have been observed to study their
subpulse modulation at an observing wavelength of (when achievable) both 21 and
92 cm using the Westerbork Synthesis Radio Telescope. For 57 pulsars drifting
subpulses are discovered for the first time and are confirmed for many others.
This leads to the conclusion that it could well be that the drifting subpulse
mechanism is an intrinsic property of the emission mechanism itself, although
for some pulsars it is difficult or impossible to detect. It appears that the
youngest pulsars have the most disordered subpulses and the subpulses become
more and more organized into drifting subpulses as the pulsar ages. Drifting
subpulses are in general found at both frequencies and the measured values of
P3 at the two frequencies are highly correlated, showing the broadband nature
of this phenomenon. Also the modulation indices measured at the two frequencies
are clearly correlated, although at 92 cm they are on average possibly higher.
The correlations with the modulation indices are argued to be consistent with
the picture in which the radio emission is composed out of a drifting subpulse
signal plus a quasi-steady signal which becomes, on average, stronger at high
observing frequencies. There is no obvious correlation found between P3 and the
pulsar age (or any other pulsar parameter) contrary to reports in the past.Comment: Proceedings of the 40 Years of Pulsars: Millisecond Pulsars,
Magnetars and More conference in Montrea
Interaction of laser generated ultrasonic waves with wedge-shaped samples
Wedge-shaped samples can be used as a model of acoustic interactions with samples ranging from ocean wedges, to angled defects such as rolling contact fatigue, to thickness measurements of samples with non-parallel faces. We present work on laser generated ultrasonic waves on metal samples; one can measure the dominant Rayleigh-wave mode, but longitudinal and shear waves are also generated. We present calculations, models, and measurements giving the dependence of the arrival times and amplitudes of these modes on the wedge apex angle and the separation of generation and detection points, and hence give a measure of the wedge characteristics
End to end distance on contour loops of random gaussian surfaces
A self consistent field theory that describes a part of a contour loop of a
random Gaussian surface as a trajectory interacting with itself is constructed.
The exponent \nu characterizing the end to end distance is obtained by a Flory
argument. The result is compared with different previuos derivations and is
found to agree with that of Kondev and Henley over most of the range of the
roughening exponent of the random surface.Comment: 7 page
BIM and sensor-based data management system for construction safety monitoring
Purpose
This research aims to investigate the integration of real-time monitoring of thermal conditions within confined work environments through wireless sensor network (WSN) technology when integrated with building information modelling (BIM). A prototype system entitled confined space monitoring system (CoSMoS), which provides an opportunity to incorporate sensor data for improved visualization through new add-ins to BIM software, was then developed.
Design/methodology/approach
An empirical study was undertaken to compare and contrast between the performances (over a time series) of various database models to find a back-end database storage configuration that best suits the needs of CoSMoS.
Findings
Fusing BIM data with information streams derived from wireless sensors challenges traditional approaches to data management. These challenges encountered in the prototype system are reported upon and include issues such as hardware/software selection and optimization. Consequently, various database models are explored and tested to find a database storage that best suits the specific needs of this BIM-wireless sensor technology integration.
Originality value
This work represents the first tranche of research that seeks to deliver a fully integrated and advanced digital built environment solution for automating the management of health and safety issues on construction sites.
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c-axis Josephson Tunnelling in Twinned and Untwinned YBCO-Pb Junctions
Within a microscopic two band model of planes and chains with a pairing
potential in the planes and off diagonal pairing between planes and chains we
find that the chains make the largest contribution to the Josephson tunnelling
current and that through them the d-wave part of the gap contributes to the
current. This is contrary to the usual assumption that for a d-wave tetragonal
superconductor the c-axis Josephson current for incoherent tunnelling into an
s-wave superconductor is zero while that of a d-wave orthorhombic
superconductor with a small s-wave component to its gap it is small but
non-zero. Nevertheless it has been argued that the effect of twins in YBCO
would lead to cancellation between pairs of twins and so the observation of a
current in c-axis YBCO-Pb experiments is evidence against a d-wave type order
parameter. We argue that both theory and experiment give evidence that the two
twin orientations are not necessarily equally abundant and that the ratio of
tunnelling currents in twinned and untwinned materials should be related to the
relative abundance of the two twin orientations.Comment: 6 pages, RevTeX 3.0, 15 PostScript figur
Glueball plus Pion Production in Photon-Photon Collisions.
We here compute the reaction
for various glueball candidates and their assumed quantum states, using a
non-relativistic gluon bound-state model for the glueball.Comment: To appear in Zeit. fur Phys. C; Plain Latex file, 16 pages; 5 figures
appended as a uuencoded postscript file
Possibilities for pedagogy in Further Education: Harnessing the abundance of literacy
In this report, it is argued that the most salient factor in the contemporary communicative landscape is the sheer abundance and diversity of possibilities for literacy, and that the extent and nature of students' communicative resources is a central issue in education. The text outlines the conceptual underpinnings of the Literacies for Learning in Further Education project in a social view of literacy, and the associated research design, methodology and analytical framework. It elaborates on the notion of the abundance of literacies in students' everyday lives, and on the potential for harnessing these as resources for the enhancement of learning. It provides case studies of changes in practice that have been undertaken by further education staff in order to draw upon students' everyday literacy practices on Travel and Tourism and Multimedia courses. It ends with some of the broad implications for conceptualising learning that arise from researching through the lens of literacy practices
Faraday Instability in a Surface-Frozen Liquid
Faraday surface instability measurements of the critical acceleration, a_c,
and wavenumber, k_c, for standing surface waves on a tetracosanol (C_24H_50)
melt exhibit abrupt changes at T_s=54degC above the bulk freezing temperature.
The measured variations of a_c and k_c vs. temperature and driving frequency
are accounted for quantitatively by a hydrodynamic model, revealing a change
from a free-slip surface flow, generic for a free liquid surface (T>T_s), to a
surface-pinned, no-slip flow, characteristic of a flow near a wetted solid wall
(T < T_s). The change at T_s is traced to the onset of surface freezing, where
the steep velocity gradient in the surface-pinned flow significantly increases
the viscous dissipation near the surface.Comment: 4 pages, 3 figures. Physical Review Letters (in press
High-temperature ferromagnetism of electrons in narrow impurity bands: Application to CaB
Ferromagnetism with high Curie temperature , well above room
temperature, and very small saturation moment has been reported in various
carbon and boron systems. It is argued that the magnetization must be very
inhomogeneous with only a small fraction of the sample ferromagnetically
ordered. It is shown that a possible source of high within the
ferromagnetic regions is itinerant electrons occupying a narrow impurity band.
Correlation effects do not reduce the effective interaction which enters the
Stoner criterion in the same way as in a bulk band. It is also shown how, in
the impurity band case, spin wave excitations may not be effective in lowering
below its value given by Stoner theory. These ideas are applied to
CaB and a thorough review of the experimental situation in this material is
given. It is suggested that the intrinsic magnetism of the B and O
dimers might be exploited in suitable structures containing these elements.Comment: 26 pages, 2 figure
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