Is dark matter an extra-dimensional effect?

We investigate the possibility that the observed behavior of test particles outside galaxies, which is usually explained by assuming the presence of dark matter, is the result of the dynamical evolution of particles in higher dimensional space-times. Hence, dark matter may be a direct consequence of the presence of an extra force, generated by the presence of extra-dimensions, which modifies the dynamic law of motion, but does not change the intrinsic properties of the particles, like, for example, the mass (inertia). We discuss in some detail several possible particular forms for the extra force, and the acceleration law of the particles is derived. Therefore, the constancy of the galactic rotation curves may be considered as an empirical evidence for the existence of the extra dimensions.Comment: 11 pages, no figures, accepted for publication in MPLA; references adde

New Path Equations in Absolute Parallelism Geometry

The Bazanski approach, for deriving the geodesic equations in Riemannian geometry, is generalized in the absolute parallelism geometry. As a consequence of this generalization three path equations are obtained. A striking feature in the derived equations is the appearance of a torsion term with a numerical coefficients that jumps by a step of one half from equation to another. This is tempting to speculate that the paths in absolute parallelism geometry might admit a quantum feature.Comment: 4 pages Latex file Journal Reference: Astrophysics and space science 228, 273, (1995

Confinement and stability of the motion of test particles in thick branes

We consider the motion of test particles in a thick brane version of Randall-Sundrum type II model. It is known that gravity alone cannot explain the confinement of test particles in this kind of brane. In this paper we show that a stable confinement in a domain wall is possible by admitting a direct interaction between test particles and a scalar field. This interaction is implemented by a modification of the Lagrangian of the particle which is inspired by a Yukawa-type interaction between fermions and scalar fields.Comment: 1 figure. Extended analysis to treat general thick branes RSII-type. Added reference

Water pollution from food production: lessons for optimistic and optimal solutions

Food production is a source of various pollutants in aquatic systems. For example, nutrients are lost from fertilized fields, and pathogens from livestock production. Water pollution may impact society and nature. Large-scale water pollution assessments, however, often focus on single pollutants and not on multiple pollutants simultaneously. This study draws lessons from air pollution control for large-scale water quality assessments, where multi-pollutant approaches are more common. To this end, we present a framework for future water pollution assessments searching for optimistic and optimal solutions. We argue that future studies could shift their focus to better account for societal and economic targets. Participatory approaches can help to ensure the feasibility of future solutions to reduce water pollution from food production

Food and agriculture

Food security has long been a challenge for human societies and will become an increasingly pressing global issue over the coming decades (Fischer, 2018). Although global food production has kept pace with population growth, close to 750 million people (or 10% of the global population) were exposed to severe levels of food insecurity in 2019 (FAO/IFAD/ UNICEF/WFP/WHO, 2020). Unfortunately, this number has increased even further over the course of 2020 due to the COVID-19 pandemic and its economic impacts worldwide. In the 2030 Agenda for Sustainable Development, Sustainable Development Goal (SDG) 2 aims to “end hunger, achieve food security and improved nutrition and promote sustainable agriculture” (UNGA, 2015). The food system is almost entirely supported by water, and agriculture uses the major share of global freshwater resources. However, water use for food production is being questioned continually as intersectoral competition for water intensifies and water scarcity increases. Additionally, in many regions of the world, water for food production is used inefficiently (D’Odorico et al., 2020). This is a major driver of environmental degradation, including depletion of aquifers, reduction of river flows, degradation of wildlife habitats, and pollution (Willett et al., 2019). A fundamental transformation of how water is being managed in the food system is therefore necessary if most of the SDG 2 targets are to be achieved by 2030, without further degradation of water resources to concurrently achieve SDG 6 to “ensure availability and sustainable management of water and sanitation for all” (IFPRI, 2019)

Fleeting small-scale surface magnetic fields build the quiet-Sun corona

Arch-like loop structures filled with million Kelvin hot plasma form the building blocks of the quiet-Sun corona. Both high-resolution observations and magnetoconvection simulations show the ubiquitous presence of magnetic fields on the solar surface on small spatial scales of $\sim$100\,km. However, the question of how exactly these quiet-Sun coronal loops originate from the photosphere and how the magnetic energy from the surface is channeled to heat the overlying atmosphere is a long-standing puzzle. Here we report high-resolution photospheric magnetic field and coronal data acquired during the second science perihelion of Solar Orbiter that reveal a highly dynamic magnetic landscape underlying the observed quiet-Sun corona. We found that coronal loops often connect to surface regions that harbor fleeting weaker, mixed-polarity magnetic field patches structured on small spatial scales, and that coronal disturbances could emerge from these areas. We suggest that weaker magnetic fields with fluxes as low as $10^{15}$\,Mx and or those that evolve on timescales less than 5\,minutes, are crucial to understand the coronal structuring and dynamics.Comment: Accepted for publication in The Astrophysical Journal Letter

East Africa Future Water Scenarios to 2050

We have analysed two possible development scenarios for the extended Lake Victoria Basin (eLVB.) Each scenario combines a plausible socio-economic development pathway with climate change impacts calculated for the GHG concentration pathway RCP6.0 (i.e. medium climate change). A Reference Scenario (REF) applies the storyline and quantification of one of the IPCC’s Shared Socio-economic Pathways (SSP), the ‘Middle of the Road’ scenario (SSP2). The East-Africa Regional Vision scenario (EA-RVS) portrays the vision of the region, as expressed in several vision studies and the first stakeholder workshop of the study. - Data comes as Excel files - Supplementary to the report: East Africa Water Scenarios to 2050 - The Excel Files have been used in the second workshop “East Africa Future Water Scenarios to 2050”, from December 4-6, 2018 in Entebbe, Uganda, for consultation and joint learning and for discussion and fine-tuning of modelling result

Geodesic motion in the neighbourhood of submanifolds embedded in warped product spaces

We study the classical geodesic motions of nonzero rest mass test particles and photons in (3+1+n)- dimensional warped product spaces. An important feature of these spaces is that they allow a natural decoupling between the motions in the (3+1)-dimensional spacetime and those in the extra n dimensions. Using this decoupling and employing phase space analysis we investigate the conditions for confinement of particles and photons to the (3+1)- spacetime submanifold. In addition to providing information regarding the motion of photons, we also show that these motions are not constrained by the value of the extrinsic curvature. We obtain the general conditions for the confinement of geodesics in the case of pseudo-Riemannian manifolds as well as establishing the conditions for the stability of such confinement. These results also generalise a recent result of the authors concerning the embeddings of hypersurfaces with codimension one.Comment: 8 pages, 1 figure. To appear in General Relativity and Gravitation as a contributed paper to Mashhoon Festschrif

Balancing clean water-climate change mitigation tradeoffs

Energy systems support technical solutions fulfilling the United Nations’ Sustainable Development 2 Goal for clean water and sanitation (SDG6), with implications for future energy demands and greenhouse 3 gas emissions. The energy sector is also a large consumer of water, making water efficiency targets in4 grained in SDG6 important constraints for long-term energy planning. Here, we apply a global integrated 5 assessment model to quantify the cost and characteristics of infrastructure pathways balancing SDG6 tar6 gets for water access, scarcity, treatment and efficiency with long-term energy transformations limiting climate warming to 1.5 ◦ 7 C. Under a mid-range human development scenario, we find that approximately 8 1 trillion USD2010 per year is required to close water infrastructure gaps and operate water systems consistent with achieving SDG6 goals by 2030. Adding a 1.5 ◦ 9 C climate policy constraint increases these costs by up to 8 %. In the reverse direction, when the SDG6 targets are added on top of the 1.5 ◦ 10 C policy 11 constraint, the cost to transform and operate energy systems increases 2 to 9 % relative to a baseline 1.5 ◦ 12 C scenario that does not achieve the SDG6 targets by 2030. Cost increases in the SDG6 pathways 13 are due to expanded use of energy-intensive water treatment and costs associated with water conserva14 tion measures in power generation, municipal, manufacturing and agricultural sectors. Combined global spending (capital and operational expenditures) in the integrated SDG6-1.5 ◦ 15 C scenarios to 2030 on water and energy systems increases 92 to 125 % relative to a baseline scenario without 1.5 ◦ 16 C and SDG6 17 constraints. Evaluation of the multi-sectoral policies underscores the importance of water conservation 18 and integrated water-energy planning for avoiding costs from interacting water, energy and climate goals