19,834 research outputs found
On the pathwidth of almost semicomplete digraphs
We call a digraph {\em -semicomplete} if each vertex of the digraph has at
most non-neighbors, where a non-neighbor of a vertex is a vertex such that there is no edge between and in either direction.
This notion generalizes that of semicomplete digraphs which are
-semicomplete and tournaments which are semicomplete and have no
anti-parallel pairs of edges. Our results in this paper are as follows. (1) We
give an algorithm which, given an -semicomplete digraph on vertices
and a positive integer , in time either
constructs a path-decomposition of of width at most or concludes
correctly that the pathwidth of is larger than . (2) We show that there
is a function such that every -semicomplete digraph of pathwidth
at least has a semicomplete subgraph of pathwidth at least .
One consequence of these results is that the problem of deciding if a fixed
digraph is topologically contained in a given -semicomplete digraph
admits a polynomial-time algorithm for fixed .Comment: 33pages, a shorter version to appear in ESA 201
Theory of stripes in quasi two dimensional rare-earth tritellurides
Even though the rare-earth tritellurides are tetragonal materials with a
quasi two dimensional (2D) band structure, they have a "hidden" 1D character.
The resultant near-perfect nesting of the Fermi surface leads to the formation
of a charge density wave (CDW) state. We show that for this band structure,
there are two possible ordered phases: A bidirectional "checkerboard" state
would occur if the CDW transition temperature were sufficiently low, whereas a
unidirectional "striped" state, consistent with what is observed in experiment,
is favored when the transition temperature is higher. This result may also give
some insight into why, in more strongly correlated systems, such as the
cuprates and nickelates, the observed charge ordered states are generally
stripes as opposed to checkerboards.Comment: Added contents and references, changed title and figures. Accepted to
PR
Prevalence of cervical disease at age 20 after immunisation with bivalent HPV vaccine at age 12-13 in Scotland: retrospective population study
The manuscript was reviewed by Jo’s Trust, which supports the conclusions. It made the following statement: We think (it has) massive implications for the screening programme, vaccine and also impact on diagnoses in the future. It gives weight for activity to increase vaccine uptake, has implications on screening intervals. The clinically relevant herd protection is very interesting too. It also feeds into our policy calls for a new IT infrastructure (for the screening programme in England) to record and enable invitations based on whether someone has at the vaccine if intervals can be extended. Funding: This study has been undertaken as part of the programme of surveillance of immunisation against human papillomavirus in Scotland, included within the routine work of Health Protection Scotland, a part of the Scottish National Health Service. No funding has been received from industry.Peer reviewedPublisher PD
Inferring effective interactions from the local density of states: application to STM data from BiSrCaCuO
While the influence of impurities on the local density of states (LDOS) in a
metal is notoriously non-local due to interference effects, low order moments
of the LDOS in general can be shown to depend only on the local structure of
the Hamiltonian. Specifically, we show that an analysis of the spatial
variations of these moments permits one to ``work backwards'' from scanning
tunneling microscopy (STM) data to infer the local structure of the underlying
effective Hamiltonian. Applying this analysis to STM data from the high
temperature superconductor, BiSrCaCuO, we find that
the variations of the electro-chemical potential are remarkably small (i.e.,
the disorder is, in a sense, weak) but that there are large variations in the
local magnitude of the d-wave gap parameter.Comment: 7 pages, 7 figure
THE IMPACT OF ACTIVE LEARNING WITH ADAPTIVE LEARNING SYSTEMS IN GENERAL EDUCATION INFORMATION TECHNOLOGY COURSES
An adaptive learning system is an effective educational tool that meets the individual needs of students, but it is limited in fostering student learning by itself. With active engagement, students learn better than with adaptive learning systems alone. In this study, we investigate the impact of an adaptive learning system with active learning projects on student learning in general education information technology courses. We believe that today\u27s classroom calls for adaptive learning to serve the needs of diverse student populations. Active learning through real-life hands-on learning activities can enhance student learning by allowing them to apply their knowledge to authentic projects. In the classroom, we often find that learning computing with authentic hands-on activities is not only useful, but it contributes to improving student motivation and confidence
Uncertainty rescued: Bohr's complementarity for composite systems
Generalized uncertainty relations may depend not only on the commutator
relation of two observables considered, but also on mutual correlations, in
particular, on entanglement. The equivalence between the uncertainty relation
and Bohr's complementarity thus holds in a much broader sense than anticipated.Comment: Accepted for publication in Phys. Lett.
Star Formation in Disk Galaxies. II. The Effect of Star Formation and Photoelectric Heating on the Formation and Evolution of Giant Molecular Clouds
We investigate the effect of star formation and diffuse photoelectric heating
on the properties of giant molecular clouds (GMCs) formed in high resolution
(~< 10 pc) global (~ 20 kpc) simulations of isolated Milky Way-type galaxy
disks. The clouds are formed through gravitational fragmentation and structures
with densities n_H>=100cm^-3 are identified as GMCs. Between 1000-1500 clouds
are created in the simulations with masses M > 10^5 Msolar and 180-240 with
masses M > 10^6 Msolar in agreement with estimates of the Milky Way's
population. We find that the effect of photoelectric heating is to suppress the
fragmentation of the ISM, resulting in a filamentary structure in the warm gas
surrounding clouds. This environment suppresses the formation of a retrograde
rotating cloud population, with 88% of the clouds rotating prograde with
respect to the galaxy after 300 Myr. The diffuse heating also reduces the
initial star formation rate, slowing the conversation of gas into stars. We
therefore conclude that the interstellar environment plays an important role in
the GMCs evolution. Our clouds live between 0-20 Myr with a high infant
mortality (t' < 3 Myr) due to cloud mergers and star formation. Other
properties, including distributions of mass, size and surface density agree
well with observations. Collisions between our clouds are common, occurring at
a rate of ~1/4 of the orbital period. It is not clear whether such collisions
trigger or suppress star formation at our current resolution. Our star
formation rate is a factor of 10 higher than observations in local galaxies.
This is likely due to the absence of localized feedback in our models.Comment: 25 pages. 18 figures. Accepted for publication in Ap
Resilient High Catalytic Performance of Platinum Nanocatalysts with Porous Graphene Envelope.
Despite the innumerable developments of nanosized and well dispersed noble metal catalysts, the degradation of metal nanoparticle catalysts has proven to be a significant obstacle for the commercialization of the hydrogen fuel cell. Here, the formation of Pt nanoparticle catalysts with a porous graphene envelope has been achieved using a single step low temperature vaporization process. While these Pt-Gr core-shell nanoparticles possess superior resilience to degradation, it comes at the cost of degraded overall catalyst efficacy. However, it is possible to combat this lower overall performance through inclusion of low concentrations of nitrogen precursor in the initial stage of single-step synthesis, inhibiting the formation of complete graphene shells, as verified by atomic resolution aberration-corrected transmission electron microscopy (AC-TEM) imaging. The resultant porous graphene encapsulated Pt catalysts are found to have both the high peak performance of the bare Pt nanoparticle catalysts and the increased resilience of the fully shielded Pt-Gr core-shells, with the optimal N-doped Pt-Gr yielding a peak efficiency of 87% compared to bare Pt, and maintaining 90% of its catalytic activity after extended potential cycling. The nitrogen treated Pt-Gr core-shells thus act as an effective substitute catalyst for conventional bare Pt nanoparticles, maintaining their catalytic performance over prolonged use
Finite size effects on the Poynting-Robertson effect: a fully general relativistic treatment
Ever since the first discovery of Poynting and Robertson, the radiation
source has been treated as merely a point. Even in a very few studies where the
size of the source has been taken into account, the treatment of the problem
remained largely non-relativistic. In the present work, we address the issue of
the finite size effects on the Poynting-Robertson effect in a fully
relativistic manner for the first time. As a result, the emergence and the
characteristic of the critical point/suspension orbit can be studied in a
systematic and detailed manner.Comment: 11pages, 3figure
Randomised controlled feasibility trial of an evidence-informed behavioural intervention for obese adults with additional risk factors
Peer reviewedPublisher PD
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