11,549 research outputs found
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Identification of strategic molecules for future circular supply chains using large reaction networks
Networks of chemical reactions represent relationships between molecules within chemical supply chains and promise to enhance planning of multi-step synthesis routes from bio-renewable feedstocks.</p
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Teaching sustainability as complex systems approach: a sustainable development goals workshop
Purpose
Approaches to solving sustainability problems require a specific problem-solving mode, encompassing the complexity, fuzziness and interdisciplinary nature of the problem. This paper aims to promote a complex systems’ view of addressing sustainability problems, in particular through the tool of network science, and provides an outline of an interdisciplinary training workshop.
Design/methodology/approach
The topic of the workshop is the analysis of the Sustainable Development Goals (SDGs) as a political action plan. The authors are interested in the synergies and trade-offs between the goals, which are investigated through the structure of the underlying network. The authors use a teaching approach aligned with sustainable education and transformative learning.
Findings
Methodologies from network science are experienced as valuable tools to familiarise students with complexity and to handle the proposed case study.
Originality/value
To the best of the authors’ knowledge, this is the first work which uses network terminology and approaches to teach sustainability problems. This work highlights the potential of network science in sustainability education and contributes to accessible material.
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Observation of spin Coulomb drag in a two-dimensional electron gas
An electron propagating through a solid carries spin angular momentum in
addition to its mass and charge. Of late there has been considerable interest
in developing electronic devices based on the transport of spin, which offer
potential advantages in dissipation, size, and speed over charge-based devices.
However, these advantages bring with them additional complexity. Because each
electron carries a single, fixed value (-e) of charge, the electrical current
carried by a gas of electrons is simply proportional to its total momentum. A
fundamental consequence is that the charge current is not affected by
interactions that conserve total momentum, notably collisions among the
electrons themselves. In contrast, the electron's spin along a given spatial
direction can take on two values, "up" and "down", so that the spin current and
momentum need not be proportional. Although the transport of spin polarization
is not protected by momentum conservation, it has been widely assumed that,
like the charge current, spin current is unaffected by electron-electron (e-e)
interactions. Here we demonstrate experimentally not only that this assumption
is invalid, but that over a broad range of temperature and electron density,
the flow of spin polarization in a two-dimensional gas of electrons is
controlled by the rate of e-e collisions
Essential self-adjointness for combinatorial Schr\"odinger operators II- Metrically non complete graphs
We consider weighted graphs, we equip them with a metric structure given by a
weighted distance, and we discuss essential self-adjointness for weighted graph
Laplacians and Schr\"odinger operators in the metrically non complete case.Comment: Revisited version: Ognjen Milatovic wrote to us that he had
discovered a gap in the proof of theorem 4.2 of our paper. As a consequence
we propose to make an additional assumption (regularity property of the
graph) to this theorem. A new subsection (4.1) is devoted to the study of
this property and some details have been changed in the proof of theorem 4.
National Recommendations for Infant and Young Child Feeding in the World Health Organization European Region
OBJECTIVES: Complementary feeding should provide a healthy diet with critical nutrients for growth and development. Information is limited on child and infant feeding recommendations within the World Health Organization (WHO) European Region. METHODS: The WHO Regional Office for Europe and the European Society for Paediatric Gastroenterology, Hepatology and Nutrition (ESPGHAN) performed a survey of national recommendations on infant and young child nutrition aimed at national government departments of health and national paediatric experts. Questions addressed national recommendations on breast-feeding and complementary feeding. RESULTS: Information was available from 48 of the 53 Member States. Forty-five of 48 countries (94%) have national recommendations on infant and young child feeding, of which 41 are endorsed by official public health authorities. Regarding introduction of complementary feeding, 25 countries (out of 34, 74%) recommend 6 months of age as the ideal age. The earliest age of introduction recommended varies from 4 to 5 months in (31/38 countries, 82%) to 6 months (6/38, 16%) and 7 months (1/38, 2.6%). The recommended meal composition varies widely; introduction of iron-rich foods (meat, fish, eggs) at the age of 6 months is recommended in 30 out of 43 countries, whereas 13 (30%) recommend later introduction. CONCLUSIONS: National infant feeding recommendations vary widely between studied countries and partly differ from international recommendations. Too early introduction of complementary feeding can reduce duration of exclusive breast-feeding (EBF). Too late introduction of iron-rich complementary foods might increase anemia risk and adversely affect child development. A review and further harmonization of national recommendations appears desirable
Thermodynamic Properties of Holographic Multiquark and the Multiquark Star
We study thermodynamic properties of the multiquark nuclear matter. The
dependence of the equation of state on the colour charges is explored both
analytically and numerically in the limits where the baryon density is small
and large at fixed temperature between the gluon deconfinement and chiral
symmetry restoration. The gravitational stability of the hypothetical
multiquark stars are discussed using the Tolman-Oppenheimer-Volkoff equation.
Since the equations of state of the multiquarks can be well approximated by
different power laws for small and large density, the content of the multiquark
stars has the core and crust structure. We found that most of the mass of the
star comes from the crust region where the density is relatively small. The
mass limit of the multiquark star is determined as well as its relation to the
star radius. For typical energy density scale of ,
the converging mass and radius of the hypothetical multiquark star in the limit
of large central density are approximately solar mass and 15-27 km.
The adiabatic index and sound speed distributions of the multiquark matter in
the star are also calculated and discussed. The sound speed never exceeds the
speed of light and the multiquark matters are thus compressible even at high
density and pressure.Comment: 27 pages, 17 figures, 1 table, JHEP versio
Isotropy of the velocity of light and the Sagnac effect
In this paper, it is shown, using a geometrical approach, the isotropy of the
velocity of light measured in a rotating frame in Minkowski space-time, and it
is verified that this result is compatible with the Sagnac effect. Furthermore,
we find that this problem can be reduced to the solution of geodesic triangles
in a Minkowskian cylinder. A relationship between the problems established on
the cylinder and on the Minkowskian plane is obtained through a local isometry.Comment: LaTeX, 13 pages, 3 eps figures; typos corrected, added references,
minor changes; to appear in "Relativity in Rotating Frames", ed. G. Rizzi G.
and M.L. Ruggiero, Kluwer Academic Publishers, Dordrecht (2003
Doppler velocimetry of spin propagation in a two-dimensional electron gas
Controlling the flow of electrons by manipulation of their spin is a key to
the development of spin-based electronics. While recent demonstrations of
electrical-gate control in spin-transistor configurations show great promise,
operation at room temperature remains elusive. Further progress requires a
deeper understanding of the propagation of spin polarization, particularly in
the high mobility semiconductors used for devices. Here we report the
application of Doppler velocimetry to resolve the motion of spin-polarized
electrons in GaAs quantum wells driven by a drifting Fermi sea. We find that
the spin mobility tracks the high electron mobility precisely as a function of
T. However, we also observe that the coherent precession of spins driven by
spin-orbit interaction, which is essential for the operation of a broad class
of spin logic devices, breaks down at temperatures above 150 K for reasons that
are not understood theoretically
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