Suchergebnisse

Die globale Hungersituation hat sich seit 1990 verbessert, wie der Welthunger-Index 2013 anhand von Daten aus dem Zeitraum 2008-2012 zeigt. Der WHI ist um ein Drittel gesunken. Dennoch ist die weltweite Hungersituation nach wie vor "ernst". 870 Millionen Men­schen hatten laut Schätzungen der Ernährungs- und Landwirtschafts­organisation der Vereinten Nationen (FAO) im Mittel der Jahre 2010-2012 nicht genug zu essen. Südasien und Afrika südlich der Sahara haben die höchsten WHI-Werte. Südasien hat seinen WHI-Wert zwischen 1990 und 1995 deutlich verbessert, vor allem durch einen großen Rückgang des Untergewichts bei Kindern. Der schnelle Fortschritt in dieser Region konnte jedoch nicht aufrechterhalten werden. Soziale Ungleichheit und der schlechte Ernährungszustand, das geringe Bildungsniveau und der niedrige gesellschaftliche Status von Frauen tragen nach wie vor zu einem hohen Anteil von Untergewicht bei Kindern unter fünf Jahren bei. Afrika südlich der Sahara konnte in den 1990er-Jahren den Hun­ger nicht so stark reduzieren wie Südasien. Seit der Jahrtausendwende hat die Region jedoch deutliche Fortschritte gemacht; ihr WHI-Wert liegt nun unter dem von Südasien. Größere politische Stabilität in den Län­dern, die in den 1990er- und 2000er-Jahren von Bürgerkriegen betrof­fen waren, ermöglichte wirtschaftliches Wachstum. Fortschritte im Kampf gegen HIV und AIDS, Erfolge bei der Malariabekämpfung und höhere Impfraten trugen zu einer Senkung der Kindersterblichkeit bei. Seit 1990 haben 23 Länder deutliche Fortschritte gemacht und ihre WHI-Werte um 50 Prozent oder mehr gesenkt. 27 Länder konnten die Kategorien "gravierend" und "sehr ernst" verlassen. Die folgenden zehn Länder haben seit 1990 die größten absoluten Fortschritte erzielt: Angola, Äthiopien, Bangladesch, Ghana, Kambodscha, Malawi, Niger, Ruanda, Thailand und Vietnam. ; Non-PR ; IFPRI2 ; PHND; DGO; COM

Combining on-surface synthetic methods with the power of scanning tunneling microscopy to characterize novel materials at the single molecule level, we show how to steer the reactivity of one anthracene-based precursor towards different product nanostructures. Whereas using a Au(111) surface with three-fold symmetry results in the dominant formation of a starphene derivative, the two-fold symmetry of a reconstructed Au(110) surface allows the selective growth of non-benzenoid linear conjugated polymers. We further assess the electronic properties of each of the observed product structures via tunneling spectroscopy and DFT calculations, altogether advancing the synthesis and characterization of molecular structures of notable scientific interest that have been only scarcely investigated to date, as applies both to starphenes and to non-benzenoid conjugated polymers. ; We acknowledge funding from the European Union's Horizon 2020 programme (Grant Agreement No. 635919 and 863098), from the Spanish Agencia Estatal de Investigación (Grant No. MAT2016-78293-C6, PID2019-107338RB-C63, PID2019-107338RB-C66 and FIS2017-83780-P), Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2019–2022, ED431G 2009/03), Dep. Educación of the Basque Government and UPV/EHU (Grant No. IT-756-13), and the European Regional Development Fund (ERDF). ; Peer reviewed

Trabajo presentado al Symposium on Surface Science (3S), celebrado en Austria del 1 al 7 de marzo de 2020. ; We acknowledge funding from the European Union's Horizon 2020 programme (Grant Agreement Nos. 635919 and 863098 from ERC and FET Open projects, respectively), from the Spanish MINECO (Grant Nos. FIS2017-83780-P and MAT2016-78293-C6) and from the University of the Basque Country (Grant IT1246-19). D. G. O. thanks the Alexander von Humboldt Foundation for supporting his research stay at the MPI, and Klaus Kern for hosting him. ; Peer reviewed

This article is part of the themed collection: 2020 Chemical Science HOT Article Collection. ; Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reactions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from adequate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchitectures with pre-defined handedness. ; We acknowledge funding from the European Union's Horizon 2020 Programme (Grant Agreement No. 635919 ("SURFINK") and 863098 ("SPRING")), from the Spanish MINECO (Grant No. MAT2016-78293-C6), Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2016–2019, ED431G/09), and the Fondo Europeo de Desarrollo Regional (FEDER). ; Peer reviewed

Starphenes show promising optoelectronic properties. Notably, HOMO–LUMO energy gap presumably decreases with their increasing size, making larger homologues extremely desirable. Unfortunately, with the size, their instability and insolubility also increase, challenging classical synthetic ways. A new method has been developed, enabling synthesis of large starphenes in a quantity sufficient for their full characterisation and further applications. ; Starphenes are attractive compounds due to their characteristic physicochemical properties that are inherited from acenes, making them interesting compounds for organic electronics and optics. However, the instability and low solubility of larger starphene homologs make their synthesis extremely challenging. Herein, we present a new strategy leading to pristine [16]starphene in preparative scale. Our approach is based on a synthesis of a carbonyl-protected starphene precursor that is thermally converted in a solid-state form to the neat [16]starphene, which is then characterised with a variety of analytical methods, such as 13C CP-MAS NMR, TGA, MS MALDI, UV/Vis and FTIR spectroscopy. Furthermore, high-resolution STM experiments unambiguously confirm its expected structure and reveal a moderate electronic delocalisation between the pentacene arms. Nucleus-independent chemical shifts NICS(1) are also calculated to survey its aromatic character. ; This research has been funded in parts by foundation EXPERIENTIA, ERDF/ESF "UOCHB MSCA Mobility" (No. CZ.02.2.69/0.0/0.0/17 050/0008490), and has received funding from the EraNET Cofund Initiatives Quan-tERA under the European Union's Horizon 2020 research and innovation programme grant agreement ORQUID. This project has received financial support from the CNRS through the MITI interdisciplinary programs and JST-ERATO (No. JPMJER1903) and JSPS-WPI. Financial support is also acknowledged from the Spanish Ministry of Science and Innovation (MAT2016-78293-C6, PID2019-107338RB-C63), from the Basque Government (IT-1255-19), from the Spanish National Research Council (CSIC, COOPB20432), from the Euro-pean Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (contract no. EFA 194/16 TNSI) and from the European Research Council (grant agreement no. 635919). The authors thank Yannick Coppel (LCC-CNRS, Toulouse) for recording CP-MAS spectra, Jean-Francois Meunier (LCC-CNRS, Toulouse) for thermogravimetric analysis and Vladimir Vrkoslav (IOCB-Prague) for recording MS MALDI spectra. ; Peer reviewed

Open-shell graphene nanoribbons have become promising candidates for future applications, including quantum technologies. Here, we characterize magnetic states hosted by chiral graphene nanoribbons (chGNRs). The substitution of a hydrogen atom at the chGNR edge by a ketone effectively adds one pz electron to the π-electron network, producing an unpaired π-radical. A similar scenario occurs for regular ketone-functionalized chGNRs in which one ketone is missing. Two such radical states can interact via exchange coupling, and we study those interactions as a function of their relative position, which includes a remarkable dependence on the chirality, as well as on the nature of the surrounding ribbon, that is, with or without ketone functionalization. Besides, we determine the parameters whereby this type of system with oxygen heteroatoms can be adequately described within the widely used mean-field Hubbard model. Altogether, we provide insight to both theoretically model and devise GNR-based nanostructures with tunable magnetic properties. ; We acknowledge financial support from the MCIN/AEI/10.13039/501100011033 (Grants PID2019-107338RB-C62, PID2019-107338RB-C63, PID2020-115406GB-I00, PCI2019-111933-2 (FLAG-ERA grant LEGOCHIP), and Juan de la Cierva Grant FJC2019-041202-I), the European Union's Horizon 2020 research and innovation program (FET-OPEN project SPRING, Grant No. 863098 and Marie Skłodowska-Curie Actions Individual Fellowship No. 101022150), the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, Grant ED431G2019/03), the European Regional Development Fund, the Basque Government (IT-1255-19), the Basque Government (PIBA Grant PI_2020_1_0014), the Basque Departamento de Educación through the Ph.D. scholarship No. PRE_2020_2_0049 (S.S.), the Spanish Research Council (LINKC20002). ; Peer reviewed

Monolayer hexagonal boron nitride (hBN) is attracting considerable attention because of its potential applications in areas such as nano- and opto-electronics, quantum optics and nanomagnetism. However, the implementation of such functional hBN demands precise lateral nanostructuration and integration with other two-dimensional materials, and hence, novel routes of synthesis beyond exfoliation. Here, a disruptive approach is demonstrated, namely, imprinting the lateral pattern of an atomically stepped one-dimensional template into a hBN monolayer. Specifically, hBN is epitaxially grown on vicinal Rhodium (Rh) surfaces using a Rh curved crystal for a systematic exploration, which produces a periodically textured, nanostriped hBN carpet that coats Rh(111)-oriented terraces and lattice-matched Rh(337) facets with tunable width. The electronic structure reveals a nanoscale periodic modulation of the hBN atomic potential that leads to an effective lateral semiconductor multi-stripe. The potential of such atomically thin hBN heterostructure for future applications is discussed. ; The authors acknowledge financial support from the Spanish Ministry of Science and Innovation (Grants MAT-2017-88374-P, PID2019-107338RB-C63, MAT2017-88492-R, and Severo Ochoa CEX2019-000910-S), the CSIC (Grant 2020AEP178), the Basque Government (Grant IT-1255-19), the Marie Sklodowska-Curie European Union's Horizon 2020 program (grant MagicFACE 797109), the European Research Council (Advanced Grant 789104-eNANO), and Elettra Sincrotrone Trieste for providing access to its synchrotron radiation facilities. I.P. and F.B. acknowledge funding from EUROFEL, and D.U. from the Ministry of Science and Higher Education of the Russian Federation [Grant No. 075-15-2020-797 (13.1902.21.0024)]. A.A.M. acknowledges the German Ministry for Education and Research (Grant 05K19KER). ; Peer reviewed