14,977 research outputs found
Empirical Determinations of Key Physical Parameters Related to Classical Double Radio Sources
Multi-frequency radio observations of the radio bridge of powerful classical
double radio sources can be used to determine: the beam power of the jets
emanating from the AGN; the total time the source will actively produce jets
that power large-scale radio emission; the thermal pressure of the medium in
the vicinity of the radio source; and the total mass, including dark matter, of
the galaxy or cluster of galaxies traced by the ambient gas that surrounds the
radio source. The theoretical constructs that allow a determination of each of
these quantities using radio observations are presented and discussed.
Empirical determinations of each of these quantities are obtained and analyzed.
A sample of 14 radio galaxies and 8 radio loud quasars with redshifts between
zero and two for which there is enough radio information to be able to
determine the physical parameters listed above was studied in detail.
(abridged)Comment: Submitted to ApJ, LaTex, 26 total pages of text which includes
captions & two tables, plus 13 EPS figures & 1 tabl
An empirical study evaluating depth of inheritance on the maintainability of object-oriented software
This empirical research was undertaken as part of a multi-method programme of research to investigate unsupported claims made of object-oriented technology. A series of subject-based laboratory experiments, including an internal replication, tested the effect of inheritance depth on the maintainability of object-oriented software. Subjects were timed performing identical maintenance tasks on object-oriented software with a hierarchy of three levels of inheritance depth and equivalent object-based software with no inheritance. This was then replicated with more experienced subjects. In a second experiment of similar design, subjects were timed performing identical maintenance tasks on object-oriented software with a hierarchy of five levels of inheritance depth and the equivalent object-based software. The collected data showed that subjects maintaining object-oriented software with three levels of inheritance depth performed the maintenance tasks significantly quicker than those maintaining equivalent object-based software with no inheritance. In contrast, subjects maintaining the object-oriented software with five levels of inheritance depth took longer, on average, than the subjects maintaining the equivalent object-based software (although statistical significance was not obtained). Subjects' source code solutions and debriefing questionnaires provided some evidence suggesting subjects began to experience diffculties with the deeper inheritance hierarchy. It is not at all obvious that object-oriented software is going to be more maintainable in the long run. These findings are sufficiently important that attempts to verify the results should be made by independent researchers
Direct Determinations of the Redshift Behavior of the Pressure, Energy Density, and Equation of State of the Dark Energy and the Acceleration of the Universe
One of the goals of current cosmological studies is the determination of the
expansion and acceleration rates of the universe as functions of redshift, and
the determination of the properties of the dark energy that can explain these
observations. Here the expansion and acceleration rates are determined directly
from the data, without the need for the specification of a theory of gravity,
and without adopting an a priori parameterization of the form or redshift
evolution of the dark energy. We use the latest set of distances to SN standard
candles from Riess et al. (2004), supplemented by data on radio galaxy standard
ruler sizes, as described by Daly and Djorgovski (2003, 2004). We find that the
universe transitions from acceleration to deceleration at a redshift of about
0.4. The standard "concordance model" provides a reasonably good fit to the
dimensionless expansion rate as a function of redshift, though it fits the
dimensionless acceleration rate as a function of redshift less well. The
expansion and acceleration rates are then combined with a theory of gravity to
determine the pressure, energy density, and equation of state of the dark
energy as functions of redshift. Adopting General Relativity as the correct
theory of gravity, the redshift trends for the pressure, energy density, and
equation of state of the dark energy out to redshifts of about one are
determined, and are found to be generally consistent with the concordance
model.Comment: 8 pages, 5 figures. Invited presentation at Coral Gables 200
Developing Interventions for Children's Exercise (DICE): a pilot evaluation of school-based exercise interventions for primary school children aged 7 to 8 years.
BACKGROUND: Developing Interventions for Children's Exercise (DICE) is an initiative aimed at determining effective school-based exercise programs. To assess feasibility, we conducted a pilot study of exercise sessions which varied in duration and frequency. METHODS: Exercise interventions were delivered to Year 3 pupils (age 7-8 years; n = 73) in primary schools within Yorkshire, UK. Evaluations were conducted using focus group sessions, questionnaires and observations. RESULTS: The study revealed positive aspects of all interventions, including favorable effects on children's concentration during lessons and identified the value of incorporation of the DICE concept into curriculum lessons. Children appeared enthused and reported well-being and enjoyment. Areas requiring attention were the need for appropriate timetabling of sessions and ensuring the availability of space. CONCLUSION: The concept and sessions were well-accepted by teachers who confirmed their full support of any future implementation There appears to be potential for the encouragement and empowerment of teachers to support physical activity and healthy school environments, and to take an interest in the health of their pupils. Ultimately, these findings should assist in the design of successful exercise interventions in the school setting
Changes in movement symmetry over the stages of the shoeing process in military working horses
Dry Friction due to Adsorbed Molecules
Using an adiabatic approximation method, which searches for Tomlinson
model-like instabilities for a simple but still realistic model for two
crystalline surfaces in the extremely light contact limit, with mobile
molecules present at the interface, sliding relative to each other, we are able
to account for the virtually universal occurrence of "dry friction." The model
makes important predictions for the dependence of friction on the strength of
the interaction of each surface with the mobile molecules.Comment: four pages of latex, figure provide
Water balance complexities in ephemeral catchments with different land uses: Insights from monitoring and distributed hydrologic modeling
Although ephemeral catchments are widespread in arid and semiarid climates, the relationship of their water balance with climate, geology, topography, and land cover is poorly known. Here we use 4 years (2011–2014) of rainfall, streamflow, and groundwater level measurements to estimate the water balance components in two adjacent ephemeral catchments in south-eastern Australia, with one catchment planted with young eucalypts and the other dedicated to grazing pasture. To corroborate the interpretation of the observations, the physically based hydrological model CATHY was calibrated and validated against the data in the two catchments. The estimated water balances showed that despite a significant decline in groundwater level and greater evapotranspiration in the eucalypt catchment (104–119% of rainfall) compared with the pasture catchment (95–104% of rainfall), streamflow consistently accounted for 1–4% of rainfall in both catchments for the entire study period. Streamflow in the two catchments was mostly driven by the rainfall regime, particularly rainfall frequency (i.e., the number of rain days per year), while the downslope orientation of the plantation furrows also promoted runoff. With minimum calibration, the model was able to adequately reproduce the periods of flow in both catchments in all years. Although streamflow and groundwater levels were better reproduced in the pasture than in the plantation, model-computed water balance terms confirmed the estimates from the observations in both catchments. Overall, the interplay of climate, topography, and geology seems to overshadow the effect of land use in the study catchments, indicating that the management of ephemeral catchments remains highly challenging
- …