22,646 research outputs found
Learning from the experts: exploring playground experience and activities using a write and draw technique.
BACKGROUND: Qualitative research into the effect of school recess on children's physical activity is currently limited. This study used a write and draw technique to explore children's perceptions of physical activity opportunities during recess. METHODS: 299 children age 7-11 years from 3 primary schools were enlisted. Children were grouped into Years 3 & 4 and Years 5 & 6 and completed a write and draw task focusing on likes and dislikes. Pen profiles were used to analyze the data. RESULTS: Results indicated 'likes' focused on play, positive social interaction, and games across both age groups but showed an increasing dominance of games with an appreciation for being outdoors with age. 'Dislikes' focused on dysfunctional interactions linked with bullying, membership, equipment, and conflict for playground space. Football was a dominant feature across both age groups and 'likes/dislikes' that caused conflict and dominated the physically active games undertaken. CONCLUSION: Recess was important for the development of conflict management and social skills and contributed to physical activity engagement. The findings contradict suggestions that time spent in recess should be reduced because of behavioral issues
Generalized Satisfiability Problems via Operator Assignments
Schaefer introduced a framework for generalized satisfiability problems on
the Boolean domain and characterized the computational complexity of such
problems. We investigate an algebraization of Schaefer's framework in which the
Fourier transform is used to represent constraints by multilinear polynomials
in a unique way. The polynomial representation of constraints gives rise to a
relaxation of the notion of satisfiability in which the values to variables are
linear operators on some Hilbert space. For the case of constraints given by a
system of linear equations over the two-element field, this relaxation has
received considerable attention in the foundations of quantum mechanics, where
such constructions as the Mermin-Peres magic square show that there are systems
that have no solutions in the Boolean domain, but have solutions via operator
assignments on some finite-dimensional Hilbert space. We obtain a complete
characterization of the classes of Boolean relations for which there is a gap
between satisfiability in the Boolean domain and the relaxation of
satisfiability via operator assignments. To establish our main result, we adapt
the notion of primitive-positive definability (pp-definability) to our setting,
a notion that has been used extensively in the study of constraint satisfaction
problems. Here, we show that pp-definability gives rise to gadget reductions
that preserve satisfiability gaps. We also present several additional
applications of this method. In particular and perhaps surprisingly, we show
that the relaxed notion of pp-definability in which the quantified variables
are allowed to range over operator assignments gives no additional expressive
power in defining Boolean relations
Headwaters are critical reservoirs of microbial diversity for fluvial networks
Streams and rivers form conspicuous networks on the Earth and are among nature's most effective integrators. Their dendritic structure reaches into the terrestrial landscape and accumulates water and sediment en route from abundant headwater streams to a single river mouth. The prevailing view over the last decades has been that biological diversity also accumulates downstream. Here, we show that this pattern does not hold for fluvial biofilms, which are the dominant mode of microbial life in streams and rivers and which fulfil critical ecosystem functions therein. Using 454 pyrosequencing on benthic biofilms from 114 streams, we found that microbial diversity decreased from headwaters downstream and especially at confluences. We suggest that the local environment and biotic interactions may modify the influence of metacommunity connectivity on local biofilm biodiversity throughout the network. In addition, there was a high degree of variability in species composition among headwater streams that could not be explained by geographical distance between catchments. This suggests that the dendritic nature of fluvial networks constrains the distributional patterns of microbial diversity similar to that of animals. Our observations highlight the contributions that headwaters make in the maintenance of microbial biodiversity in fluvial networks
RankPL: A Qualitative Probabilistic Programming Language
In this paper we introduce RankPL, a modeling language that can be thought of
as a qualitative variant of a probabilistic programming language with a
semantics based on Spohn's ranking theory. Broadly speaking, RankPL can be used
to represent and reason about processes that exhibit uncertainty expressible by
distinguishing "normal" from" surprising" events. RankPL allows (iterated)
revision of rankings over alternative program states and supports various types
of reasoning, including abduction and causal inference. We present the
language, its denotational semantics, and a number of practical examples. We
also discuss an implementation of RankPL that is available for download
On the static Lovelock black holes
We consider static spherically symmetric Lovelock black holes and generalize
the dimensionally continued black holes in such a way that they asymptotically
for large r go over to the d-dimensional Schwarzschild black hole in dS/AdS
spacetime. This means that the master algebraic polynomial is not degenerate
but instead its derivative is degenerate. This family of solutions contains an
interesting class of pure Lovelock black holes which are the Nth order Lovelock
{\Lambda}-vacuum solu- tions having the remarkable property that their
thermodynamical parameters have the universal character in terms of the event
horizon radius. This is in fact a characterizing property of pure Lovelock
theories. We also demonstrate the universality of the asymptotic Einstein limit
for the Lovelock black holes in general.Comment: 19 page
Glycine decarboxylase deficiency causes neural tube defects and features of non-ketotic hyperglycinemia in mice.
Glycine decarboxylase (GLDC) acts in the glycine cleavage system to decarboxylate glycine and transfer a one-carbon unit into folate one-carbon metabolism. GLDC mutations cause a rare recessive disease non-ketotic hyperglycinemia (NKH). Mutations have also been identified in patients with neural tube defects (NTDs); however, the relationship between NKH and NTDs is unclear. We show that reduced expression of Gldc in mice suppresses glycine cleavage system activity and causes two distinct disease phenotypes. Mutant embryos develop partially penetrant NTDs while surviving mice exhibit post-natal features of NKH including glycine accumulation, early lethality and hydrocephalus. In addition to elevated glycine, Gldc disruption also results in abnormal tissue folate profiles, with depletion of one-carbon-carrying folates, as well as growth retardation and reduced cellular proliferation. Formate treatment normalizes the folate profile, restores embryonic growth and prevents NTDs, suggesting that Gldc deficiency causes NTDs through limiting supply of one-carbon units from mitochondrial folate metabolism
Uncertainty relations for the realisation of macroscopic quantum superpositions and EPR paradoxes
We present a unified approach, based on the use of quantum uncertainty
relations, for arriving at criteria for the demonstration of the EPR paradox
and macroscopic superpositions. We suggest to view each criterion as a means to
demonstrate an EPR-type paradox, where there is an inconsistency between the
assumptions of a form of realism, either macroscopic realism (MR) or local
realism (LR), and the completeness of quantum mechanics.Comment: 9 pages, 2 figures, to appear Journ Mod Optics work presented at PQE
2007 conferenc
The role of tool geometry in process damped milling
The complex interaction between machining structural systems and the cutting process results in machining instability, so called chatter. In some milling scenarios, process damping is a useful phenomenon that can be exploited to mitigate chatter and hence improve productivity. In the present study, experiments are performed to evaluate the performance of process damped milling considering different tool geometries (edge radius, rake and relief angles and variable helix/pitch). The results clearly indicate that variable helix/pitch angles most significantly increase process damping performance. Additionally, increased cutting edge radius moderately improves process damping performance, while rake and relief angles have a smaller and closely coupled effect
Counterterms in semiclassical Horava-Lifshitz gravity
We analyze the semiclassical Ho\v{r}ava-Lifshitz gravity for quantum scalar
fields in 3+1 dimensions. The renormalizability of the theory requires that the
action of the scalar field contains terms with six spatial derivatives of the
field, i.e. in the UV, the classical action of the scalar field should preserve
the anisotropic scaling symmetry ( ,
with ) of the gravitational action. We discuss the renormalization
procedure based on adiabatic subtraction and dimensional regularization in the
weak field approximation. We verify that the divergent terms in the adiabatic
expansion of the expectation value of the energy-momentum tensor of the scalar
field contain up to six spatial derivatives, but do not contain more than two
time derivatives. We compute explicitly the counterterms needed for the
renormalization of the theory up to second adiabatic order and evaluate the
associated functions in the minimal subtraction scheme.Comment: 8 page
- âŠ