71,948 research outputs found
Excluding a ladder
A ladder is a grid graph. When does a graph class
exclude some ladder as a minor? We show that this is the case if and only if
all graphs in admit a proper vertex coloring with a bounded
number of colors such that for every -connected subgraph of , there
is a color that appears exactly once in . This type of vertex coloring is a
relaxation of the notion of centered coloring, where for every connected
subgraph of , there must be a color that appears exactly once in .
The minimum number of colors in a centered coloring of is the treedepth of
, and it is known that classes of graphs with bounded treedepth are exactly
those that exclude a fixed path as a subgraph, or equivalently, as a minor. In
this sense, the structure of graphs excluding a fixed ladder as a minor
resembles the structure of graphs without long paths. Another similarity is as
follows: It is an easy observation that every connected graph with two
vertex-disjoint paths of length has a path of length . We show that
every -connected graph which contains as a minor a union of sufficiently
many vertex-disjoint copies of a grid has a grid
minor.
Our structural results have applications to poset dimension. We show that
posets whose cover graphs exclude a fixed ladder as a minor have bounded
dimension. This is a new step towards the goal of understanding which graphs
are unavoidable as minors in cover graphs of posets with large dimension.Comment: v3: revised according to referees' comment
A new measurement of the Hubble constant and matter content of the Universe using extragalactic background light -ray attenuation
The Hubble constant and matter density of the Universe
are measured using the latest -ray attenuation results from Fermi-LAT
and Cherenkov telescopes. This methodology is based upon the fact that the
extragalactic background light supplies opacity for very high energy photons
via photon-photon interaction. The amount of -ray attenuation along the
line of sight depends on the expansion rate and matter content of the Universe.
This novel strategy results in a value of
~km~s~Mpc and
. These estimates are independent and
complementary to those based on the distance ladder, cosmic microwave
background (CMB), clustering with weak lensing, and strong lensing data. We
also produce a joint likelihood analysis of our results from rays and
these from more mature methodologies, excluding the CMB, yielding a combined
value of ~km~s~Mpc and .Comment: 9 pages, 6 figures, 1 table. Accepted by Ap
Transformations to achieve the Sustainable Development Goals Includes the SDG Index and Dashboards. Sustainable Development Report 2019
The Sustainable Development Report 2019 presents an updated SDG Index and Dashboards with a refined assessment
of countries’ distance to SDG targets. The report has been successfully audited for the first time by the European Commission
Joint Research Centre. New indicators have been included, primarily to refine the indicator selection on agriculture, diets, gender
equality and freedom of speech. We have also added more metrics for international spillovers, including on fatal work accidents.
A new website and data visualization tools are available (http://sustainabledevelopment.report).
Once again, Nordic countries – Denmark, Sweden and Finland – top the SDG Index. Yet, even these countries
face major challenges in implementing one or several SDGs. No country is on track for achieving all 17 goals with major
performance gaps even in the top countries on SDG 12 (Responsible Consumption and Production), SDG 13 (Climate
Action), SDG 14 (Life Below Water) and SDG 15 (Life on Land). Income and wealth inequalities, as well as gaps in health
and education outcomes by population groups also remain important policy challenges in developing and developed
countries alike.
The Sustainable Development Report 2019 generates seven major findings:
1. High-level political commitment to the SDGs is falling short of historic promises
In September 2019, heads-of-states and governments will convene for the first time in person at the UN in New York to
review progress on their promises made four years after the adoption of the 2030 Agenda. Yet, our in-depth analyses show
that many have not taken the critical steps to implement the SDGs. Out of 43 countries surveyed on SDG implementation
efforts, including all G20 countries and countries with a population greater than 100 million, 33 countries have endorsed
the SDGs in official statements since January 1st, 2018. Yet in only 18 of them do central budget documents mention the
SDGs. This gap between rhetoric and action must be closed.
2. The SDGs can be operationalized through six SDG Transformations
SDG implementation can be organized along the following Transformations: 1. Education, Gender, and Inequality; 2. Health,
Wellbeing, and Demography; 3. Energy Decarbonization and Sustainable Industry; 4. Sustainable Food, Land, Water, Oceans;
5. Sustainable Cities and Communities; and 6. Digital Revolution for Sustainable Development. The transformations respect
strong interdependencies across the SDGs and can be operationalized by well-defined parts of governments in collaboration
with civil society, business, and other stakeholders. They must be underpinned and guided by the principles of Leave No One
Behind and Circularity and Decoupling of resource use from human wellbeing.
3. Trends on climate (SDG 13) and biodiversity (SDG 14 and SDG 15) are alarming
On average, countries obtain their worst scores on SDG 13 (Climate Action), SDG 14 (Life Below Water) and SDG 15 (Life on
Land). No country obtains a “green rating” (synonym of SDG achieved) on SDG 14 (Life Below Water). Trends on greenhouse
gas emissions and, even more so, on threatened species are moving in the wrong direction. These findings are in line with
the recent reports from the IPCC and IPBES on climate change mitigation and biodiversity protection, respectively.
4. Sustainable land-use and healthy diets require integrated agriculture, climate and health policy interventions
Land use and food production are not meeting people’s needs. Agriculture destroys forests and biodiversity, squanders
water and releases one-quarter of global greenhouse-gas emissions. In total, 78% of world nations for which data are
available obtain a “red rating” (synonym of major SDG challenge) on sustainable nitrogen management; the highest
number of “red” rating across all indicators included in the report. At the same time, one-third of food is wasted, 800 million
people remain undernourished, 2 billion are deficient in micronutrients, and obesity is on the rise. New indicators on
nations’ trophic level and yield gap closure highlight the depth of the challenge. Transformations towards sustainable landuse
and food systems are required to balance efficient and resilient agriculture and forestry with biodiversity conservation
and restoration as well as healthy diets
Landau-Fermi liquid analysis of the 2D t-t' Hubbard model
We calculate the Landau interaction function f(k,k') for the two-dimensional
t-t' Hubbard model on the square lattice using second and higher order
perturbation theory. Within the Landau-Fermi liquid framework we discuss the
behavior of spin and charge susceptibilities as function of the onsite
interaction and band filling. In particular we analyze the role of elastic
umklapp processes as driving force for the anisotropic reduction of the
compressibility on parts of the Fermi surface.Comment: 10 pages, 16 figure
Absence of extended states in a ladder model of DNA
We consider a ladder model of DNA for describing carrier transport in a fully
coherent regime through finite segments. A single orbital is associated to each
base, and both interstrand and intrastrand overlaps are considered within the
nearest-neighbor approximation. Conduction through the sugar-phosphate backbone
is neglected. We study analytically and numerically the spatial extend of the
corresponding states by means of the Landauer and Lyapunov exponents. We
conclude that intrinsic-DNA correlations, arising from the natural base
pairing, does not suffice to observe extended states, in contrast to previous
claims.Comment: 4 RevTex pages, 4 figures include
Improving entanglement and thermodynamic R\'enyi entropy measurements in quantum Monte Carlo
We present a method for improving measurements of the entanglement R\'enyi
entropies in quantum Monte Carlo simulations by relating them with measurements
of participation R\'enyi entropies. Exploiting the capability of building
improved estimators for the latter allows to obtain very good estimates for
entanglement R\'enyi entropies. When considering a full system instead of a
bipartition, the method can be further ameliorated providing access to the
thermodynamic R\'enyi entropies with high accuracy. We also explore a
recently-proposed method for the reconstruction of the entanglement spectrum
from entanglement R\'enyi entropies and finally show how potential entanglement
Hamiltonians may be tested for their validity using a comparison with thermal
R\'enyi entropies.Comment: 15 pages, 11 figure
Rapid Detection of Avian Eimeria Species Using Denaturing Gradient Gel Electrophoresis
A denaturing gradient gel electrophoresis (DGGE) assay was developed to rapidly discriminate species of avian Eimeria. Amplification by PCR of the small subunit ribosomal RNA gene (approximately 1,600 nucleotides) with Eimeria genus-specific primers followed by cloning and sequencing allowed us to carry out phylogenetic analyses and identify clone sequences to species level in most cases. Clones were subsequently used to amplify a smaller fragment (approximately 120 nucleotides) suitable for DGGE. The fragments were separated on denaturing gradient gel and bands with unique migration distances were mixed to obtain an identification ladder. The identification ladder and PCR products obtained from DNA extracted from fecal samples from several poultry farms were compared. Applying the DGGE method in this study allowed a rapid differentiation of Eimeria species present in fecal samples collected from poultry farms
Phase diagrams of spin ladders with ferromagnetic legs
The low-temperature properties of the spin S=1/2 ladder with anisotropic
ferromagnetic legs are studied using the continuum limit bosonization approach.
The weak-coupling ground state phase diagram of the model is obtained for a
wide range of coupling constants and several unconventional gapless
''spin-liquid'' phases are shown to exist for ferromagnetic coupling. The
behavior of the ladder system in the vicinity of the ferromagnetic instability
point is discussed in detail.Comment: 11 pages, 4 figure
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