75,554 research outputs found
Voltage-Controlled Spin Selection in a Magnetic Resonant Tunnelling Diode
We have fabricated all II-VI semiconductor resonant tunneling diodes based on
the (Zn,Mn,Be)Se material system, containing dilute magnetic material in the
quantum well, and studied their current-voltage characteristics. When subjected
to an external magnetic field the resulting spin splitting of the levels in the
quantum well leads to a splitting of the transmission resonance into two
separate peaks. This is interpreted as evidence of tunneling transport through
spin polarized levels, and could be the first step towards a voltage controlled
spin filter.Comment: To be published in Phys. Rev. Let
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
Consideration of the relationship between Kepler and cyclotron dynamics leading to prediction of a non-MHD gravity-driven Hamiltonian dynamo
Conservation of canonical angular momentum shows that charged particles are
typically constrained to stay within a poloidal Larmor radius of a poloidal
magnetic flux surface. However, more detailed consideration shows that
particles with a critical charge to mass ratio can have zero canonical angular
momentum and so be both immune from centrifugal force and not constrained to
stay in the vicinity of a specific flux surface. Suitably charged dust grains
can have zero canonical angular momentum and in the presence of a gravitational
field will spiral inwards across poloidal magnetic surfaces toward the central
object and accumulate. This accumulation results in a gravitationally-driven
dynamo, i.e., a mechanism for converting gravitational potential energy into a
battery-like electric power source.Comment: 14 pages, 1 figur
Codimension-two critical behavior in vacuum gravitational collapse
We consider the critical behavior at the threshold of black hole formation
for the five dimensional vacuum Einstein equations satisfying the
cohomogeneity-two triaxial Bianchi IX ansatz. Exploiting a discrete symmetry
present in this model we predict the existence of a codimension-two attractor.
This prediction is confirmed numerically and the codimension-two attractor is
identified as a discretely self-similar solution with two unstable modes.Comment: 4 pages, 5 figures, typos correcte
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