Sensitivity of cropping patterns in Africa to transient climate change

The detailed analysis of current cropping areas in Africa presented here reveals significant climate sensitivities of cropland density and distribution across a variety of agro-ecosystems. Based on empirical climate-cropland relationships, cropland density responds positively to increases in precipitation in semi-arid and arid zones of the sub-tropics and warmer temperatures in higher elevations. As a result, marginal increases in seasonal precipitation lead to denser cropping areas in arid and semi-arid regions. Warmer temperatures, on the other hand, tend to decrease the probability of cropping in most parts of Africa (the opposite is true for increases in rainfall and decreases in temperatures relative to current conditions). Despite discrepancies and uncertainties in climate model output, the analysis suggests that cropland area in Africa is likely to decrease significantly in response to transient changes in climate. The continent is expected to have lost on average 4.1 percent of its cropland by 2039, and 18.4 percent is likely to have disappeared by the end of the century. In some regions of Africa the losses in cropland area are likely to occur at a much faster rate, with northern and eastern Africa losing up to 15 percent of their current cropland area within the next 30 years or so. Gains in cropland area in western and southern Africa due to projected increases in precipitation during the earlier portions of the century will be offset by losses later on. In conjunction with existing challenges in the agricultural sector in Africa, these findings demand sound policies to manage existing agricultural lands and the productivity of cropping systems.Climate Change,Crops&Crop Management Systems,Global Environment Facility,Common Property Resource Development,Rural Poverty Reduction

Towards novel C–N materials

Two modifications of the novel guanidinium dicyanamide have been obtained by means of ion-exchange reaction in aqueous or methanolic solution. The hygroscopic compounds were characterized by solution state NMR, mass spectrometry and vibrational spectroscopy. The crystal structures of the polymorphs were elucidated by means of single-crystal X-ray diffraction at 200 K {β-[C(NH2)3][N(CN)2]: Pna21, Z=8, a=1373.1(3), b=495.5(1), c=1802.9(4) pm, U=1226.7(4)×106 pm3; α-[C(NH2)3][N(CN)2]: P21/c, Z=8, a=1924.9(4), b=496.0(1), c=1372.4(3) pm, β=110.46(3)°, U=1227.5(4)×106 pm3} and were found to be largely equivalent in terms of the overall assembly of the molecular ions. Thermodynamic and kinetic aspects of the temperature behaviour of the polymorphs, which is characterized by a succession of thermal events in the temperature region between 240 and 440 K, were assessed by means of temperature-dependent X-ray powder diffraction and thermal analysis. Due to the chemical composition of the novel dicyanamide (C3N6H6), which is formally identical with that of melamine C3N3(NH2)3, and its thermal reactivity, which is represented by the facile conversion into melamine around 400 K, guanidinium dicyanamide may be ideally suited as a molecular precursor for chemical approaches toward highly condensed graphitic carbon nitride materials

From Triazines to Heptazines

The first non-metal tricyanomelaminates have been synthesized via metathesis reactions and characterized by means of single-crystal X-ray diffraction and vibrational and solid-state NMR spectroscopy. The crystal structures of [NH4]2[C6N9H] (1) (P21/c, a = 1060.8(2) pm, b = 1146.2(2) pm, c = 913.32(18) pm, β = 112.36(3)°, V = 1027.0(4) × 106 pm3), [C(NH2)3]3[C6N9]·2 H2O (2) (P212121, a = 762.12(15) pm, b = 1333.6(3) pm, c = 1856.6(4) pm, V = 1887.0(7) × 106 pm3) and [C3N6H7]2[C6N9H]·2.5 H2O (3) (P1̄, a = 1029.5(2) pm, b = 1120.3(2) pm, c = 1120.7(2) pm, α = 104.22(3)°, β = 112.74(3)°, γ = 104.62(3)°, V = 1064.8(4) × 106 pm3) are composed of singly protonated (1 and 3) or nonprotonated (2) tricyanomelaminate ions, which, together with the respective counterions, form two-dimensional, layered structures (1 and 3) or a quasi three-dimensional network (2). Particular emphasis has been placed on the elucidation of the thermal reactivity of the three molecular salts by means of thermal analysis and vibrational and NMR spectroscopy, as well as temperature-dependent X-ray powder diffraction. The title compounds were found to be promising candidates as molecular CNx precursors for the synthesis of graphitic carbon nitride materials. Upon being heated, ammonium and guanidinium tricyanomelaminate uniformly pass the crystalline, heptazine (C6N7)-based intermediate melem (C6N7(NH2)3), which decomposes and forms a semi-amorphous CNxHy material with a pronounced layered structure. Identical pyrolysis products are obtained for the melaminium salt, a classical triazine (C3N3)-based CNx precursor, after passing an intermediate, possibly cross-linked phase at low temperatures. Preliminary solid-state NMR investigations of the final products best conform to heptazine-based structure models for g-C3N4 that have commonly been rather disregarded in favor of triazine-based ones

Fresnel laws at curved dielectric interfaces of microresonators

We discuss curvature corrections to Fresnel's laws for the reflection and transmission of light at a non-planar refractive-index boundary. The reflection coefficients are obtained from the resonances of a dielectric disk within a sequential-reflection model. The Goos-H\"anchen effect for curved light fronts at a planar interface can be adapted to provide a qualitative and quantitative extension of the ray model which explains the observed deviations from Fresnel's laws.Comment: submitted to Phys. Rev.

Reorientational Dynamics and Solid-Phase Transformation of Ammonium Dicyanamide into Dicyandiamide

The reorientational dynamics of ammonium dicyanamide ND4[N(C≡N)2] and the kinetics as well as the mechanism of the solid-state isomerization reaction from ammonium dicyanamide into dicyandiamide (N≡C-N=C(NH2)2) was studied by means of 2H and 14N solid-state NMR spectroscopy in a temperature range between 38 and 390 K. Whereas in previous investigations the mechanism of the solid-state transformation was investigated by means of vibrational and magic angle spinning solid-state NMR spectroscopy as well as neutron diffraction, we here present a comprehensive 2H study of the ammonium ion dynamics prior to and during the course of the reaction, thereby highlighting possible cross correlations between dynamics and reactivity involving the ammonium ion. The ND4+ group was found to undergo thermally activated random jumps in a tetrahedral potential, which is increasingly distorted with increasing temperature, giving rise to an asymmetrically compressed or elongated tetrahedron with deviations from the tetrahedral angle of up to 6°. The correlation time follows an Arrhenius law with an activation energy of Ea = 25.8(2) kJ mol-1 and an attempt frequency of τ0-1 = 440(80) THz. The spin−lattice relaxation times were fitted according to a simple Bloembergen−Purcell−Pound type model with a T1 minimum of 4 ms at 230 K. Temperature-dependent librational amplitudes were extracted by line-shape simulations between 38 and 390 K and contrasted with those obtained by neutron diffraction, their values ranging between 5 and 28°. The onset and progress of the solid-phase transformation were followed in situ at temperatures above 372 K and could be classified as a strongly temperature-dependent, heterogeneous two-step reaction proceeding with rapid evolution of ammonia and comparatively slow subsequent reintegration into the solid. On the microscopic level, this correlates with a rapid proton transferpossibly triggered by a coupling between the ammonium ion dynamics and phonon modes on the terahertz time scaleand an essentially decoupled nucleophilic attack of ammonia at the nitrile carbon, giving rise to significantly differing time constants for the two processes

Synthetic routes toward MOF nanomorphologies.

As metal–organic frameworks (MOFs) are coming of age, their structural diversity, exceptional porosity and inherent functionality need to be transferred into useful applications. Fashioning MOFs into various shapes and at the same time controlling their size constitute an essential step toward MOF-based devices. Moreover, downsizing MOFs to the nanoscale triggers a whole new set of properties distinguishing nanoMOFs from their bulk counterparts. Therefore, dimensionality-controlled miniaturization of MOFs enables the customised use of nanoMOFs for specific applications where suitable size and shape are key prerequisites. In this feature article we survey the burgeoning field of nanoscale MOF synthesis, ranging from classical protocols such as microemulsion synthesis all the way to microfluidic-based techniques and template-directed epitaxial growth schemes. Along these lines, we will fathom the feasibility of rationally designing specific MOF nanomorphologies—zero-, one- and two-dimensional nanostructures—and we will explore more complex “second-generation” nanostructures typically evolving from a high level of interfacial control. As a recurring theme, we will review recent advances made toward the understanding of nucleation and growth processes at the nanoscale, as such insights are expected to further push the borders of nanoMOF science

HIV/AIDS, climate change and disaster management : challenges for institutions in Malawi

Southern African institutions involved in disaster management face two major new threats: the HIV/AIDS pandemic (eroding organizational capacity and increasing vulnerability of the population), and climate change (higher risk of extreme events and disasters). Analyzing the combined effects of these two threats on six disaster-related institutions in Malawi, the authors find evidence of a growing gap between demand for their services and capacity to satisfy that demand. HIV/AIDS leads to staff attrition, high vacancy rates, absenteeism, increased workload and other negative effects enhanced by human resources policies and financial limitations. Many necessary tasks cannot be carried out adequately with constraints such as the 42 percent vacancy rate in the Department of Poverty and Disaster Management Affairs, or the reduction of rainfall stations operated by the Meteorological Service from over 800 in 1988 to just 135 in 2006. The authors highlight implications of declining organizational capacity for climate change adaptation, and formulate recommendations.Population Policies,HIV AIDS,Hazard Risk Management,Health Monitoring&Evaluation,Climate Change

Tackling the stacking disorder of melon—structure elucidation in a semicrystalline material

In this work we tackle the stacking disorder of melon, a layered carbon imide amide polymer with the ideal composition (C6N7(NH)(NH2)). Although its existence has been postulated since 1834 the structure of individual melon layers could only recently be solved via electron diffraction and high-resolution 15N solid-state NMR spectroscopy. With only weak van der Waals interactions between neighboring layers its long range stacking order is poorly defined preventing an efficient use of diffraction techniques. We, therefore, rely on a combination of solid-sate NMR experiments and force field calculations. The key information is obtained based on heteronuclear (1H–13C) and homonuclear (1H–1H) second moments M2 acquired from 1H–13C cross polarization experiments. To allow for an interpretation of the polarization transfer rates the resonances in the 13C MAS spectra have to be assigned and the hydrogen atoms have to be located. The assignment was performed using a two-dimensional 15N–13C iDCP experiment. For the determination of the position of the hydrogen atoms NH and HH distances were measured via 1H–15N Lee–Goldburg CP and 1H–1H double-quantum build-up curves, respectively. Furthermore, the homogeneity of the material under examination was investigated exploiting 15N spin-diffusion. Based on force field methods 256 structure models with varying lateral arrangements between neighboring layers were created. For each model the M2 were calculated allowing them to be ranked by comparing calculated and measured M2 as well as via their force field energies. This allows the creation of markedly structured hypersurfaces with two distinctly favored shift vectors for the displacement of neighboring layers

From Molecular Building Blocks to Condensed Carbon Nitride Networks: Structure and Reactivity

The scope of this thesis was defined by three major issues, which have been arising from the requirement to further extend and to deepen research on carbon nitride chemistry from a materials chemistry point of view. Access to highly condensed CNx species and, ultimately, binary carbon nitride C3N4, was primarily sought by using suitable carbon nitride precursor species, based on the following leitmotifs: 1. Gaining a deeper understanding of the reactivity of precursors and the mechanisms governing solid-state reactions, the latter being the key to the directed synthesis of novel precursor systems as well as to extended carbon nitride solids with tailored properties. 2. Developing novel CNx precursors based on the evaluation of reactivity principles and solid-phase reaction trajectories thus established. 3. Providing an experimental basis for the predominantly speculative discussion centered on the structure of graphitic carbon nitride-type systems, with the major focus being on the nature of the structural building-blocks of polymeric CNxHy solids. The interplay between structural requirements of suitable CNx precursors and their thermal reactivity was demonstrated by a combined 2H solid-state NMR and neutron diffraction study of ammonium dicyanamide, as well as by a comprehensive spectroscopic study of the thermal decomposition of ammonium cyanoureate. Various novel non-metal dicyanamides and tricyanomelaminates were synthesized, structurally characterized and screened for potential thermally induced solid-state reactivity. Their suitability as CNx precursors for the synthesis of graphitic carbon nitride g-C3N4 was evaluated, leading to the observation that the formation of melamine C3N3(NH2)3 is favored in all systems at elevated temperatures. Therefore, particular emphasis was placed on the study of the thermal behavior of the prototypic precursor melamine, whose pyrolysis, including the identities of the intermediates, has been a highly controversial issue during the past decades. The present work provides the structures of the two “missing links” in melamine condensation, melam [(H2N)2C3N3]2NH and melon [C6N7NH(NH2)]n. In addition, the identities of two further intermediates were resolved, which could be identified as co-crystallisates made up from melamine and melem in the distinct ratios 2:1 and 1:2, respectively. Ultimately, the identity of a CNxHy polymer obtained by pyrolysis of melamine at T = 893 -913 K was resolved by a concerted approach based on electron diffraction, solid-state NMR spectroscopy, and theoretical investigations. It was demonstrated that the material commonly associated with a hydrogen-contaminated graphitic carbon nitride material is in fact melon, a 1D polymer composed of NH-bridged heptazine rings first described by Liebig in 1834. Melon represents a so far unique example of a structurally characterized, 1D polymeric carbon nitride material, and at the same time sheds new light on the present discussion regarding the identity and structure of graphitic carbon nitride

Mainstreaming climate adaptation into development assistance in Mozambique: Institutional barriers and opportunities

Based on a literature review and expert interviews, this paper analyzes the most important climate impacts on development goals and explores relevant institutions in the context of mainstreaming climate adaptation into development assistance in Mozambique. Climate variability and change can significantly hinder progress toward attaining the Millennium Development Goals and poverty aggravates the country's climate vulnerability. Because Mozambique is one of the major recipients of official development assistance in the world, there is a clear interest in ensuring that the risks of climate impacts are incorporated into the country's development investments. A screening of donor activities at the sub-national level shows that a high share of development assistance is invested in climate-sensitive sectors, partly in areas that are particularly exposed to droughts, floods, and cyclones. The authors find that Mozambique has a supportive legislative environment and donors have a high awareness of climate risks. However, limited individual, organizational, networking, and financial capacity constrain mainstreaming initiatives. Given strong limitations at the national level, bilateral and multilateral donors can play a key role in fostering institutional capacity in Mozambique.Climate Change,Environmental Economics&Policies,Population Policies,Common Property Resource Development,Global Environment Facility