1,710 research outputs found
Relationship between Allan variances and Kalman Filter parameters
A relationship was constructed between the Allan variance parameters (H sub z, H sub 1, H sub 0, H sub -1 and H sub -2) and a Kalman Filter model that would be used to estimate and predict clock phase, frequency and frequency drift. To start with the meaning of those Allan Variance parameters and how they are arrived at for a given frequency source is reviewed. Although a subset of these parameters is arrived at by measuring phase as a function of time rather than as a spectral density, they all represent phase noise spectral density coefficients, though not necessarily that of a rational spectral density. The phase noise spectral density is then transformed into a time domain covariance model which can then be used to derive the Kalman Filter model parameters. Simulation results of that covariance model are presented and compared to clock uncertainties predicted by Allan variance parameters. A two state Kalman Filter model is then derived and the significance of each state is explained
Collaborative multidisciplinary learning : quantity surveying students’ perspectives
The construction industry is highly fragmented and is known for its adversarial culture, culminating
in poor quality projects not completed on time or within budget. The aim of this study is thus to
guide the design of QS programme curricula in order to help students develop the requisite
knowledge and skills to work more collaboratively in their multi-disciplinary future workplaces.
A qualitative approach was considered appropriate as the authors were concerned with gathering an
initial understanding of what students think of multi-disciplinary learning. The data collection
method used was a questionnaire which was developed by the Behaviours4Collaboration (B4C)
team.
Knowledge gaps were still found across all the key areas where a future QS practitioner needs to be
collaborative (either as a project contributor or as a project leader) despite the need for change
instigated by the multi-disciplinary (BIM) education revolution.
The study concludes that universities will need to be selective in teaching, and innovative in
reorienting, QS education so that a collaborative BIM education can be effected in stages, increasing
in complexity as the students’ technical knowledge grows. This will help students to build the
competencies needed to make them future leaders. It will also support programme currency and
delivery
Plant Competition In Relation To Neighbor Biomass: An Intercontinental Study With Poa Pratensis
Long-Toed Salamanders in Harvested and Intact Douglas-Fir Forests of Western Montana
There is little known about how timber harvest practices have affected terrestrial amphibians in the northern Rocky Mountains. Especially lacking is information on the effects of revised harvest methods that fall within the framework of environmental or New Forestry. We estimated the relative abundance of a common forest amphibian, the long-toed salamander (Ambystoma macrodactylum) captured in pitfall arrays on intact, environmentally harvested, and overstory-removal harvested sites in mixed-conifer forests of western Montana. Pitfall data from 1994 through 1996 showed that previously logged sites contained significantly fewer long-toed salamanders regardless of harvest method used. The number of salamanders captured on intact sites (3.1 salamanders·[array]−1·[100 d]−1) was nearly three times the number captured on logged sites (1.2 salamanders·[array]−1·[100 d]−1). Habitat conditions measured in conjunction with trapping efforts indicated that lower amphibian abundance was associated with decreased numbers of large live trees. Declines in amphibian abundance occurred in the absence of changes in understory vegetation that typically occur when forest canopy is reduced. Our findings suggest that long-toed salamanders responded to changes in the physical environment, probably increased temperatures and decreased moisture. That salamanders should respond so dramatically indicates that immediate changes in physical conditions may profoundly alter habitat quality even when other components of the habitat are unaffected
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Shaping public opinion about regional integration: the rhetoric of justification and party cues
The article investigates how justifications used by politicians to explain their positions on policies of regional integration shape public opinion about these policies. I argue that support for a policy position increases when politicians tailor their justifications to the expectations of their audience; and I suggest that this happens even when party cues offer a less effortful way of forming opinions. I test my theoretical expectations in laboratory experiments with diverse samples, which manipulate party cues and justifications for a policy of European integration. I find that citizens use justifications and cues to form opinions. The relative importance of the two factors depends on individual dispositions and political context. In a non-competitive context (study 1), politically invested citizens use cues, while uninvested citizens use justifications. In a competitive context (study 2), the opinions of politically invested citizens are shaped by both factors, while the opinions of uninvested citizens become erratic
New approaches to model and study social networks
We describe and develop three recent novelties in network research which are
particularly useful for studying social systems. The first one concerns the
discovery of some basic dynamical laws that enable the emergence of the
fundamental features observed in social networks, namely the nontrivial
clustering properties, the existence of positive degree correlations and the
subdivision into communities. To reproduce all these features we describe a
simple model of mobile colliding agents, whose collisions define the
connections between the agents which are the nodes in the underlying network,
and develop some analytical considerations. The second point addresses the
particular feature of clustering and its relationship with global network
measures, namely with the distribution of the size of cycles in the network.
Since in social bipartite networks it is not possible to measure the clustering
from standard procedures, we propose an alternative clustering coefficient that
can be used to extract an improved normalized cycle distribution in any
network. Finally, the third point addresses dynamical processes occurring on
networks, namely when studying the propagation of information in them. In
particular, we focus on the particular features of gossip propagation which
impose some restrictions in the propagation rules. To this end we introduce a
quantity, the spread factor, which measures the average maximal fraction of
nearest neighbors which get in contact with the gossip, and find the striking
result that there is an optimal non-trivial number of friends for which the
spread factor is minimized, decreasing the danger of being gossiped.Comment: 16 Pages, 9 figure
Fitness benefits of prolonged post-reproductive lifespan in women
Most animals reproduce until they die, but in humans, females can survive long after ceasing reproduction. In theory, a prolonged post-reproductive lifespan will evolve when females can gain greater fitness by increasing the success of their offspring than by continuing to breed themselves. Although reproductive success is known to decline in old age, it is unknown whether women gain fitness by prolonging lifespan post-reproduction. Using complete multi-generational demographic records, we show that women with a prolonged post-reproductive lifespan have more grandchildren, and hence greater fitness, in pre-modern populations of both Finns and Canadians. This fitness benefit arises because post-reproductive mothers enhance the lifetime reproductive success of their offspring by allowing them to breed earlier, more frequently and more successfully. Finally, the fitness benefits of prolonged lifespan diminish as the reproductive output of offspring declines. This suggests that in female humans, selection for deferred ageing should wane when one's own offspring become post-reproductive and, correspondingly, we show that rates of female mortality accelerate as their offspring terminate reproduction
Tensile Fracture of Welded Polymer Interfaces: Miscibility, Entanglements and Crazing
Large-scale molecular simulations are performed to investigate tensile
failure of polymer interfaces as a function of welding time . Changes in the
tensile stress, mode of failure and interfacial fracture energy are
correlated to changes in the interfacial entanglements as determined from
Primitive Path Analysis. Bulk polymers fail through craze formation, followed
by craze breakdown through chain scission. At small welded interfaces are
not strong enough to support craze formation and fail at small strains through
chain pullout at the interface. Once chains have formed an average of about one
entanglement across the interface, a stable craze is formed throughout the
sample. The failure stress of the craze rises with welding time and the mode of
craze breakdown changes from chain pullout to chain scission as the interface
approaches bulk strength. The interfacial fracture energy is calculated
by coupling the simulation results to a continuum fracture mechanics model. As
in experiment, increases as before saturating at the average
bulk fracture energy . As in previous simulations of shear strength,
saturation coincides with the recovery of the bulk entanglement density. Before
saturation, is proportional to the areal density of interfacial
entanglements. Immiscibiltiy limits interdiffusion and thus suppresses
entanglements at the interface. Even small degrees of immisciblity reduce
interfacial entanglements enough that failure occurs by chain pullout and
The Pattern Speeds of M51, M83 and NGC 6946 Using CO and the Tremaine-Weinberg Method
In spiral galaxies where the molecular phase dominates the ISM, the molecular
gas as traced by CO emission will approximately obey the continuity equation on
orbital timescales. The Tremaine-Weinberg method can then be used to determine
the pattern speed of such galaxies. We have applied the method to single-dish
CO maps of three nearby spirals, M51, M83 and NGC 6946 to obtain estimates of
their pattern speeds: 38 +/- 7 km/s/kpc, 45 +/- 8 km/s/kpc and 39 +/- 8
km/s/kpc, respectively, and we compare these results to previous measurements.
We also analyze the major sources of systematic errors in applying the
Tremaine-Weinberg method to maps of CO emission.Comment: 33 pages, figures already in pdf. To appear in 2004 ApJ 607 28
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