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Women's Life Worlds 'In-Between' (2011)

Antje Daniel Katharina Fink Lena Kroeker Jaana Schütze

This volume of Bayreuth African Studies Working Papers authored and edited by doctoral students of the Bayreuth International Graduate School of African Studies (BIGSAS) represents challenges and (im-)possibilities of reviewing women’s life worlds in Africa. Therewith we revive an old debate: African thinkers opposed Western concepts, searching for a kind of feminism beyond traditional roles and beyond Western feminism, which basically antagonizes women’s subordination due to patriarchy. Thus, if African women have different positions to Western feminism, how do they perceive themselves? To what extent are women expanding their social, political or economic realm? Does this change result in a re-definition of gender roles? How do women in Africa deal with gendered hierarchies and authority? Are there conflicts or ‘in-betweens’ among ‘traditional roles’ and the behavior of women? All these questions surround one core content: women’s life worlds ‘in-between’. ‘In-betweenness’ refers here to a situation when the life worlds of women transform, resulting from social, political, economic or environmental changes or uncertainties. In such a situation women negotiate between conflicting or contradictory assumed norms, roles, social practices or orders. Opportunities for women may change, expand or become limited. For example, women can rethink their roles and behavior, be it temporary or in long term perspectives. Following this view the authors focus on situations of ‘in-betweenness’ of women in different African countries and in diverse realms of life. Literary scholar Samuel Ndogo analyzes the autobiography of an exceptional Kenyan author and activist: Wangari Maathai. The title of her autobiography, Unbowed (2006), already suggests friction between her life trajectory and cultural notions of womanhood. However, the title also shows pride at having withstood opposition, which at the same time contests a society’s readiness to tolerate an exception. Katharina Nambula’s paper shares Ndogo’s perspective of Literature Studies and shows how the female protagonists in Waiting, written by Goretti Kyomuhendo (2007), survive in a politically instable and male dominated society during the reign of Idi Amin in Uganda. Facing the men's inability to sort out the chaos, Kyomuhendo’s female characters temporarily deploy their hidden strengths to resume some order. As soon as men re-enter their former positions though, gender relations are back to normal. Other aspects of uncertainty and how women deal with it are discussed by Serah Kiragu. With regard to global climate change, Kiragu assesses changes in women’s livelihoods in semi arid Kenya. She describes the women’s recent difficulties and how they are coping with a changing environmental situation. This approach vividly illustrates that a notion of women as passive victims does not hold. Young rural women in Northern Ghana change their social sphere altogether – at least temporarily. In his anthropological article, Christian Ungruhe describes how a whole generation of young girls move out from their rural homes to urban centers. They become actively involved in labor migration and therewith experience economic independence in an attempt to generate their dowry, acquire modern assets, and consummate relationships. Although the journey marks a temporary phase in the women’s lives, it is an important experience which they can bring to their future rural lives and a permanent phenomenon in women’s biographies in West Africa. In contrast, women in Lesotho participate in wage labor on a permanent basis. Lena Kroeker illustrates in a historic and ethnographic overview why Lesotho ranks 8th in the Global Gender Gap Index 2010 and how women’s high level of participation did not change but merely separated gender and generations. Various civil society representatives met at the World Social Forum with the aim of creating a more equal and just world. Antje Daniel portraits the strategies and main features of Brazilian and Kenyan women’s organizations and explains how characteristics of women’s organizations in the national context determine transnational activism within the space of the World Social Forum. All contributions not only illustrate contemporary life worlds of women but depict processes of change within them from the perspectives of African Literature, Geography, Anthropology and Sociology. The articles in this first issue of BIGSASworks! from a broad spectrum of disciplines provide fresh and original perspectives on an evergreen debate as well as unique empirical material.

Whole-air relaxed eddy accumulation for the measurement of isotope and trace-gas fluxes (2012)

Johannes Ruppert Michael Riederer Willi A. Brand Thomas Foken

Measuring the isotopic composition of trace gas fluxes can provide additional information on ecosystem gas exchange, when ecosystem processes, like assimilation, discriminate against heavier isotopes. In the case of CO2 exchange, different mass-balances for bulk CO2 and its 13CO2 or CO18O isotopes can be used to separate respiration from photosynthetic assimilation. Up to now, detectors for direct isotope measurements in the field lack the precision needed for fast eddy covariance (EC) flux measurements. The collection of updraft and downdraft whole-air samples using the relaxed eddy accumulation technique (REA) allows simultaneously determining trace gas concentrations and isotope ratios by high precision laboratory analysis. At the same time whole-air REA relaxes several of the technical problems related to REA sampling on traps. In tests using air from a tank the complete whole-air REA sampling system and its foil balloon bag reservoirs showed no signs of contamination after cleaning. The standard deviations of δ13C and δ18O isotope ratios were only slightly higher than the precision specified for the laboratory analysis procedure. First experiment results showed that isotopic differences (up-drafts−downdrafts) were large enough to yield signal to noise ratios greater than five when applying hyperbolic deadbands during REA sampling (HREA). The performance of the instrument and the HREA sampling method are investigated by simulation of the sampling process for bulk CO2, which serves as proxy scalar. Measurements by whole-air HREA in combination with high precision isotope analysis can quantify the isofluxes of 13CO2 and CO18O. Furthermore, additional information is collected on the scalar correlation of bulk CO2 and its stable isotopes, which represents the relatively short timescale of updrafts and downdrafts in the turbulent exchange above an ecosystem. This information is essential to check the scalar similarity assumptions made in the HREA and EC/flask method for the quan-tification of isofluxes.

Water use of forests along elevation gradients in the Berchtesgaden National Park (2005)

Olimpia Kolcun

Forests are major sources of water vapor to the atmosphere and have an important influence on both regional and global climate. Understanding of the water exchange between the vegetation and the atmosphere, and recognition of factors to predict the water fluxes is necessary to estimate the changes in water use according to possible climate change. In this study the processes affecting the transpiration of Norway spruce (Picea abies) in the Berchtesgaden National Park along an elevation gradient were investigated. Sapflow and meteorological measurements were carried out during the summer of 2002. For each stand, structural differences (tree height, circumference, diameter (DBH), tree density, basal area) were also analyzed. For the experiment, three Norway spruce stands – with similar inclination, exposition, LAI and soil conditions, but situated at different elevations a.s.l in the Berchtesgaden National Park were selected. The transpiration rates of spruce were compared with those of other species: Fagus sylvatica, Larix decidua and Pinus mugo. In each stand, six to fifteen trees were selected for sapflow measurements. Xylem sap flux was observed with constant-heating-method according to Granier. Sapflow rates of individual trees were scaled up to the stand level according to the cross-sectional sapwood area of the DBH class (for spruce and beech) or total cross-sectional sapwood area (for larch). Within the sparse Larix decidua stand, both the sapflow in trees and water loss from understory vegetation were measured. Strong correlations between transpiration rates and maximum VPD and daily integrated PPFD were found for the experimental species. For the Norway spruce stands, needle nutrient concentrations were also determined. During the 2002 growing season (May- September), the seasonal patterns of tree canopy transpiration were similar for the different experimental stands. The highest water use was observed in June and July for spruce and dwarf-pine, and in July and August for beech. The seasonal changes in canopy transpiration and conductance, and the variation between spruce stands, may be in part explained by differences in meteorological conditions. Canopy conductance was calculated from canopy transpiration (Ec) and vapor pressure deficit (VPD). Absolute rates of seasonal canopy transpiration within experimental Picea abies sites differed greatly from 78 to 165 mm. The highest transpiration rates occurred in the lowest situated stand and they decreased with increasing elevation. The seasonal water loss from the Fagus sylvatica site (78 mm) was similar to the water loss at the highest situated spruce site. The seasonal transpiration of Pinus mugo site reached 44 mm. Transpiration of Larix decidua was only measured successfully during June and during a few days in July. A strong decrease of canopy conductance (gt) with increasing VPD was observed for all stands. The highest maximum canopy conductance for spruce, 20 mm s-1, was calculated for the 630 m site, while for the 1040 m and the 1360 m sites the maximum gtmax reached 15 mm s-1. In comparison the maximum canopy conductance for the beech site was higher than for the spruce site at the same elevation a.s.l. (630 m) and reached 30 mm s-1. The lowest maximum gt, 10 m s-1, was estimated for dwarf-pine shrub. For the examination of controls on spruce forest water use that were found along the elevation gradient, the GAS-FLUX model was used. Model simulations support two alternative hypotheses, namely that stomatal patchiness as well as carboxylation capacity (Vcmax) may have had an influence on stand water use. The modelled transpiration with changes in Vcmax was similar to estimated transpiration rates obtained by changing the “portion of leaves that are active” (stomatal patchiness). The developed model can be used for estimation of water use for other similar mountainous locations or for examination of ecosystem sensitivities to environmental changes (nitrogen supply, air temperature). The current work should stimulate further research on the detailed study of e.g. stomatal patchiness and its influence on transpiration rates, or to test the results at other sites.

Water solubility in diopside (2008)

Polina Gavrilenko

(1) Water solubility in pure diopside was measured. Water-saturated diopside crystals were synthesized using piston-cylinder and multi-anvil presses at 20-30 and 100 kbar and 800-1100oC from an oxide and hydroxide starting mixture containing 10 % excess silica. The water concentration in diopside was determined from polarized infrared measurements on doubly polished single crystals. Water contents were calculated by integrating the absorption bands and using published extinction coefficients for water in diopside. All measured infrared spectra of pure diopside fall into two groups. The differences in the spectra point towards substitution mechanisms involving different vacancies, which in turn could be the result of different oxide activities in the starting material. Therefore, a separate series of experiments was carried out with starting materials with an excess or deficiency of MgO or SiO2. These experiments yielded diopside with different absorption spectra. Starting materials with low silica activity yielded Type I bands, which are therefore likely to be related to Si vacancies. Type II bands form at high silica activity and may therefore be related to Mg or Ca vacancies. Water solubility in pure diopside varies from 121 up to 568 ppm H2O. Water solubility at 30 kbar increases from 700 to 1000oC and drops again above 1000oC. At 900oC, water solubility increases to a maximum at 25 kbar and then decreases rapidly to higher pressures. Due to the low solubility of aluminum in clinopyroxene at high pressure, the data on pure diopside are probably a good guide for the water solubility in clinopyroxenes under the conditions of the deeper upper mantle. Since water solubility in diopside under those conditions is order of magnitude below the water solubility in olivine, clinopyroxene is not expected to be a major storage site for water in the deeper upper mantle, even if its modal abundance is significant. (2) Water-saturated Al-containing diopside was synthesized in an end-loaded piston-cylinder apparatus at 1.5-2.5 GPa and 900-1100oC. The compositions of the starting materials for Al-bearing diopside are along the join diopside (CaMgSi2O6) – Ca-Tschermak’s component (CaAl2SiO6) with different ratios of these two end members. The water solubility strongly increases with the presence of Al up to 2500 ppm H2O. The water solubility in aluminous diopside increasing with decreasing temperature. Estimated partition coefficients of water between clinopyroxene and orthopyroxene are close to unity, with Dcpx/opx possibly increasing with temperature. Together with previously published data on water in orthopyroxene, the results of this study clearly show that in the uppermost mantle, most of the water is dissolved in the pyroxenes. The relative importance of clinopyroxene and orthopyroxene is primarily a function of their modal abundance. This observation is consistent with the model of Mierdel et al (2007), which suggests that the Earth’s asthenosphere is due to a minimum in water solubility in nominally anhydrous minerals. (3) In order to determine the effect of water on the equation of state of diopsides, high-pressure single crystal X-ray diffraction experiments with a diamond anvil cell were performed. The compressibility of diopside decreases with increasing water and Al content in the structure. The bulk modulus Ko and its first pressure derivative K’ for the four diopside crystals are 106(1) GPa and 6.1(5) for pure anhydrous diopside (0 ppm H2O); 107(1) GPa and 6.5(4) for pure diopside with 63 ppm of H2O; 108(1) GPa and 6.3(4) for pure diopside with 600 ppm H2O; and 113(1) GPa and 5.7(5) for Al-bearing hydrous (containing 0.374 Al a.p.f.u.) diopside with 2510 ppm H2O. The results on compressibility of diopside contrast with previous work, which showed that compressibility of most other main mantle phases increases with water content. In addition, from the refinement of the crystal structures of both hydrous and dry diopside and comparison with the structure of Ca-Tschermak’s pyroxene it was possible to see the influence of protonation of oxygen atoms. Because of the contrasting effect of water on the equation of state of olivine and of pyroxenes in the upper mantle, detecting water from observations of seismic velocities alone is probably nearly impossible.

Water permeability of plant cells measured by pressure probes: effects of light and turgor, and the role of unstirred layers (2008)

Yangmin Kim

The dissertation focuses (i) on an analysis of effects of unstirred layers (USLs) during measurements of water permeability (hydraulic conductivity) at the level of single cells, during measurements with the cell pressure probe (CPP) and (ii) on the use of the latter technique to investigate changes in water permeability of leaf cells in response to light. Internodes of the giant green alga Chara corallina and parenchyma cells of corn leaves were used in the studies. Besides the water, the CPP has been employed to study solute flows across cell membranes. This allowed evaluating the role of different types of USLs. In response to claims, recently raised by Tyree et al. (2005) that USLs play a significant or even dominating role in measurements of transport coefficients with the cell pressure probe, a rigorous re-examination of effects of USLs with Chara internodes has been performed indicating a minor role of USLs. For the first time, responses of cell water relations to light have been worked in some detail. Light effects have been separated from those of turgor in intact tissue cells by compensating for transpiration. At low light (LL) intensity (100 to 650 micromol m-2 s-1), hydraulic conductivity of a cell (cell Lp) increased with increasing light intensity by a factor of 2 to 6 in 10 min. However, at high light (HL) intensities of 800 and 1800 micromol m-2 s-1, there was a decline of cell Lp with increasing light intensity at constant cell turgor by factors of 14 and 35, respectively. The effects of LL refer to literature data of overall measurements of the leaf conductances (Kleaf). Decreases of Kleaf at HL have not yet been separated for effects of turgor or light intensity, respectively (as done here). The responses to HL were most likely caused by an oxidative gating of water channels (aquaporins; AQPs), as indicated by the fact that (i) application of reactive oxygen species (ROS) resulted in responses similar to those of HL and (ii) HL effects could be reversed in the presence of the antioxidant glutathione. For the first time, the data indicate an interaction between water relations and light intensity/photosynthesis, which is most likely related to changes in the redox status of leaves.

Water in the Earth’s Interior: Thermodynamics and kinetics of hydrogen incorporation in olivine and wadsleyite (2004)

Sylvie Demouchy

(1) Hydrogen diffusion in olivine The kinetics of hydration of dry single crystals of San Carlos olivine was determined by performing experiments under water-saturated conditions. The experiments were performed at 1.5 GPa, 1000°C for 5 hours in a piston cylinder apparatus, or at 0.2 GPa, 900°C, for 1 and 20 hours in TZM cold-seal vessels. Polarized Fourier-transform infrared spectrometry (FTIR) was employed to quantify the hydroxyl distributions in the samples after the experiments. The new data obtained show a strong anisotropy of diffusion, with the diffusion coefficient D[100]>D[010]> D[001] at 900°C for short duration experiments. This initial mechanism of diffusion possibly involved a redox-exchange between proton and polaron. After longer duration experiment, the anisotropy of diffusion is different with D[001]>D[010]» D[100]. For this second stage of diffusion a model of hydrogen-metal vacancy associated defects is proposed, where the vacancies are the slower diffusing species with the diffusion laws: [100], [010] = 10-(5.6±3.2) exp [-(175 ± 76)/RT] [001] = 10-(1.4±0.5) exp [-(258 ± 31)/RT] (2) Hydrogen diffusion in forsterite The kinetics of hydration linked to magnesium-vacancy diffusion within dry synthetic forsterite single crystals was determined by performing similar experiments and analyses as in the previous section. The experiments were performed at 1.5 GPa, 1000°C for 3 hours in piston cylinder apparatus, or at 0.2 GPa, 900-1110°C, for 3-20 hours in TZM cold-seal vessels. The chemical diffusion coefficients are marginally slower than in iron-bearing olivine for the same diffusion process, but the anisotropy of diffusion is the same, with the [001] axis the fastest direction of diffusion and [100] the slowest. Fits of the diffusion data to an Arrhenius law yield similar activation energies for each of the crystallographic axes; a global fit to all the diffusion data gave an activation energy around 211 ± 18 kJmol-1. Thus hydration likely occurs by coupled diffusion of protons and octahedrally coordinated metal vacancies. The diffusion rates are fast enough to modify water contents within xenoliths ascending from the mantle but they are probably too slow to permit a total equilibration in a new dry or wet environment. (3)Dehydration profiles in natural mantle-derived olivine within basalt First evidence for water diffusion in a natural mantle-derived olivine are presented from peridotite samples. The samples are olivine crystals within lherzolite xenoliths from the Quaternary alkali basalts of the Pali-Aike volcanic field in Patagonia. Water content and distribution was studied using unpolarized and polarized FTIR and analyses shows that olivine, Cr-diopside and orthopyroxene contain a significant amount of water, with up to 13 wt ppm H2O for olivine and up to 250 wt ppm H2O in the pyroxenes. In contrast, analysis of optically clear-parts of small garnet crystals indicates that they are dry. Oriented Infrared profiles show that olivine grains larger than 0.5 mm have hydroxyl-depleted rims. These water concentration profiles suggest that partial dehydration occurred during the ascent of the xenolith-bearing magma to the Earth’s surface, confirming that dehydration is occurring in the nature. From a combination of analyses of natural xenoliths with experimental diffusion works, ascent duration of the host magma is estimated to several hours, suggesting a fast rise up to the surface. (4)Temperature and pressure dependence of water solubility in iron-free wadsleyite Previous experimental studies indicate that the maximum solubility of water in wadsleyite may vary as a function of pressure and temperature. Therefore wadsleyite samples were synthesized using a multi-anvil press. One series of experiments were performed at a fixed pressure of 15 GPa and at various temperatures and in a second series the temperature was fixed at 1200°C and pressure was varied from 13 to 18 GPa. The starting material corresponds to a composition of Mg2SiO4 + 5wt% H2O. The water content was quantified by ion probe (SIMS). Results show that at 15 GPa, the water concentration decreases significantly with increasing temperature from 2.5 wt% H2O at 900oC down to 0.93 wt% H2O at 1400oC; the corresponding wadsleyite Mg/Si ratios increase from 1.79 to 1.93 over this temperature range. Up to 17 GPa, no significant effect of pressure on the water content was observed. Moreover, together with previous results on ringwoodite, these data imply a strong decrease of the water partition coefficient between wadsleyite and ringwoodite with temperature. (5) Computer simulation on hydrous point defect in iron-free wadsleyite The general utility lattice program (GULP), a semi-empirical method, was used to simulate the formation of point defects (Mott-Littleton method) in wadsleyite and especially hydrogen incorporation and their corresponding infrared frequencies.

Water flow paths in soils of an undisturbed and landslide affected mature montane rainforest in South Ecuador (2010)

Folkert Christian Bauer

The number of previous hydrological studies concerning water flow paths in tropical montane rainforest is small. However, due to the increasing pressure of deforestation and land use change comprehensive knowledge of these natural ecosystems is needed if sustainable land use strategies should keep negative effects of human impacts on water flow paths as low as possible. In this context, present work addresses the identification, characterisation, and modelling of water flow paths in soils of an undisturbed and landslide affected natural Andean forest ecosystem in the south of Ecuador whose deforestation rate is one of the highest in South America. In an investigation area situated in the Andes of South Ecuador, in gentler slopes and altitudes above 2100 m ASL mainly Stagnosols and Histosols with stagnic colour pattern and low to negligible rock fragment content prevail. With increasing altitude the abundance of these soils increase, while the presence of Cambisols and Regosols is most pronounced below 2100 m ASL and clearly correlated with the slope angle. Therefore, these soils were mainly encountered in steeper, particularly landslide affected sites often resembling a melange of fine soil and high contents of rock fragments. Aside the investigation of the influence of the rock fragment content on soil hydrological- and physical parameters such as the relationship between rock fragment content and saturated hydraulic conductivity of the soil, present study aims particularly to investigate flow paths of water in soils of landslide affected and unaffected hillslopes. Therefore, we employed conventional field- and laboratory methods, dye tracer experiments including an appropriate image processing technique, as well as statistical models. Results show that both rock fragment content and bulk density control significantly, but not largely the saturated hydraulic conductivity of the mineral soils. Dye tracer experiments and soil parameters document a deeper percolation in the landslide affected hillslopes than in the landslide unaffected hillslopes, where we found preferential flow in root channels with low soil matrix interaction as dominant flow mechanism. A surface near quasi impervious layer along the interface between topsoil and subsoil limits percolation of the water giving the prerequisites of a lateral shallow subsurface flow along the interface between topsoil and organic layer. This is in line with previous studies performed in the same investigation area which already proved indirectly the existence of this flow. However, in none of these studies the shallow subsurface flow was assigned to certain slope inclinations or altitudes. Due to a recently published digital soil map and the results we obtained from the landslide unaffected sites, we know that particularly in hillslopes of less than 30 degrees above 2100 m ASL prerequisites are given for spatially extended shallow subsurface flow. However, even if these prerequisites are not evident for the landslide affected hillslopes, we cannot exclude the possibility of shallow subsurface flow occurrence here since soil cover of the steep terrain is relatively shallow while rainfall is high throughout the year. Therefore, and given that key parameters such as permeability of subsoil and bedrock, interception and evaporation remain unclear or were investigated exclusively such as the spatial variability of the saturated hydraulic conductivity, we conducted a series of virtual experiments in order to assess the potential occurrence of shallow subsurface flow in Cambisols below 2100 m ASL. In these experiments we also included the organic layer being highly abundant in the investigation area, whose hydraulic parameters were estimated by means of inverse numerical modelling. The virtual experiments were based on a two dimensional finite element model representing a steep forested hillslope transect of approx. 54 m length. Aside soil properties, evapotranspiration and interception, the model included the spatial variability of the saturated hydraulic conductivity, the pressure head and their spatial trends. The results of virtual experiment series show that a sound evidence of the key parameters aforementioned is obligate if process conceptualisation regarding shallow subsurface flow generation, but also landslide initiation, solute and matter transport is in the spotlight.

Vulnerability to Drought Risk and Famine: Local Responses and External Interventions among the Afar of Ethiopia, a study on the Aghini Pastoral Community (2008)

Ali Hassen Muhaba

In East African countries drought-related famine has been a number one risk. Ethiopia is among those countries that are repeatedly stricken by recurrent famine. Agricultural and pastoral households have increasingly become vulnerable to famine. The successive Ethiopian governments attributed the recurring famine and hunger to natural events, particularly to droughts. However, though drought triggers famines, it does not necessarily lead to famine disaster in every context. This is the current tone of literature in disaster causation. Each famine has its own specific causes in each context and this requires exploring the causal factors thereof. This study in the Afar region, in north-east Ethiopia, attempts to explain the root causes of vulnerability to famine, and assess the local and external responses. The central argument of the research is that pastoralists’ vulnerability to famine and food crisis has increased overtime because of the complex interplay of multiple factors such as environmental or ecological degradation, socio-economic destabilization, and political processes. It is also stated that despite efforts of internal and external actors, vulnerability of the pastoral groups to famine has increased over time. In that respect the study attempts to explain how these factors have led to an increase of vulnerability and livelihood insecurity among the Afar pastoralists. Three specific arguments are addressed through analyzing both secondary and primary data. These are: The Afar pastoralists’ vulnerability to famine has increased over the past decades because of the combined effects of drought, ecological crisis and external pressures (encroachments, loss of key pastoral resources, violent conflict and political instability). Pastoral households/communities are currently less able to cope with stresses through their traditional coping and adaptive strategies. Consequently, pastoral households/communities have become more dependent on public transfer (food aid) to cope with recurring food crisis. The empirical research used both qualitative and quantitative data in addressing the basic research questions. The outline of the research is structured to suit an approach of presenting discussions at macro and micro levels. An assessment of factors both, at macro (regional/national) and micro (community) levels, is made on the basis of secondary and primary data respectively. Accordingly, factors related to ecological degradation, socio-political processes and recurrent droughts, etc. are examined. The extent of these problems at the macro level is assessed mainly based on secondary data, while the magnitude of these problems at micro (community) level is assessed on the basis of primary data gathered through a household survey, and individual and focus group interviews. Based on the analyses of both primary and secondary data the research attempts to answer the question why the Afar pastoralists’ vulnerability to famine has increased over time and how the local and external actors have responded to recurring famine. The search for explanations of vulnerability to famine focuses on highlighting the interplay of multiple causal factors at different levels within historical socio-political and economic processes overlapping with ecological crisis and recurrent drought. Accordingly the research highlights the major factors that have created vulnerability to famine. These include: External pressures which include state intervention, land alienation, encroachment by cultivators, loss of dry season/drought retreats, curtailment of mobility and unfavourable terms of trade. Stresses which include frequent drought, conflicts, political instability, weakening mutual support systems, lack of trust in formal government institutions due to non-participatory, lack of commitment, patron-client relationship, and corruption. Ecological/environmental crises which are reflected in terms of loss of key pastoral resources (grass, natural fodder vegetation, and water). The conclusion of the research is that famine and the increase of vulnerability are not primarily the consequences of drought, but of external domination and uneven development. This suggests that the genesis of food crisis (famine) must be understood as an interaction of institutional, economic and political variables. Natural events like droughts don’t necessarily lead to famine in all contexts. It is only when livelihood assets are eroded, opportunities are constrained and people are not well-prepared that the consequences of natural events develop into famine or food crisis. This suggests that production or yield failures caused by drought do not become famines unless other conditions are propitious. Therefore, the current approach in social science research with regard to disaster causation is to look at the interrelationship between natural risks and social vulnerability.

Visualization, Kinetics, and Thermodynamics of DNA-Protein Interactions (2005)

Frank Schubert

In this work the two spectroscopic techniques surface plasmon resonance (SPR) and fluorescence correlation spectroscopy (FCS) as well as the imaging technique cryo-transmission electron microscopy (cryo-TEM) were used to gain kinetic, thermodynamic and structural information about DNA–protein interactions. Furthermore, the micrographs obtained by cryo-TEM were compared to AFM images taken in a previous work. The main goal of this work was to investigate the influence of surfaces on DNA–protein interactions, therefore the methods mentioned above were chosen. Both SPR and AFM deal with molecules attached to a surface, whereas FCS and cryo-TEM monitor the molecules in free solution. As a suitable model system the well characterized interaction between the human replication protein A (RPA) and DNA was chosen. The application of SPR and FCS to analysing the binding of RPA to ssDNA yields information about the kinetics and thermodynamics. No modification of the protein is required and biotinylated and fluorescently labelled DNA strands are available from commercial sources. Salt concentration, pH and temperature can be varied over a wide range. To best of our knowledge, FCS has not been used previously to obtain equilibrium constants at different temperatures. In this work it was demonstrated how temperature dependent SPR and FCS measurements can be performed and evaluated to determine thermodynamic data of DNA–protein interactions. Astonishingly, the equilibrium constant KD for the binding of RPA to ssDNA obtained by FCS is larger than the value obtained by SPR by a factor of 20–25, depending on the temperature. Therefore the values found for the Gibbs free energy were different, whereas the values for the reaction enthalpy were nearly the same for the two methods used. There are clear evidences that the difference in KD and therefore in Gibbs free energy measured by the two methods is due to different reaction entropies. In SPR the reaction is restricted to two dimensions due to immobilization of the DNA molecules to the sensor surface, thus the rate constants obtained might not be the true association and dissociation rates. As a main result, the data obtained by SPR differ from the data gained from the free solution experiments. The reason for this is a loss of one degree of freedom, which in turn results in different entropic terms for the surface and the free solution techniques. In contrast, FCS is able to follow complex formation without spatial restrictions. In consequence, the reaction in three dimensions is entropically less favourable than the reaction at the solid-liquid interface. This might be due to differences in the cratic entropy between the two geometries, however, the role of hydration can not be assessed by our experiments. The picture of the DNA–RPA interaction was completed by further FCS measurements using various dsDNA fragments containing damage sites. The binding of RPA to undamaged dsDNA fragments showed a low affinity to dsDNA (approx. 15%), as expected from previous AFM experiments. Since RPA is known to have a high affinity to singlestranded DNA, this finding may be explained by the binding of RPA to unpaired nucleotides at the end of the dsDNA. Comparing the two imaging techniques AFM and cryo-TEM one does not find a strong influence of the surface on the DNA–RPA interaction. The kinks formed by UV-damaged DNA observed in AFM experiments could not be verified by the cryo-TEM experiments. There might be two reasons for this: First, the kinks in the AFM experiments are induced by the mica surface and therefore do not occur in cryo-TEM experiments. Second, the resolution of the TEM is not as good as in AFM, therefore, the kinks can not be seen in the TEM. The question if the DNA is wrapping around the RPA as stated in earlier works can not be answered using cryo-TEM. The resolution of this method is not as good as in AFM. In order to get micrographs with a better resolution one has to perform simple TEM experiments including staining of the molecules. The drawback of this procedure is that the molecules are influenced by the staining chemicals and therefore not in their natural state. In a very last part of this work the mini-chromosome maintenance com-plex was investigated using FCS and cryo-TEM. It was shown that the protein exhibits a medium affinity to ssDNA and dsDNA. The structure of the DNA substrate does not play an important role, the interaction was the same for simple and bubble dsDNA and dsDNA containing a ssDNA tail.

Vibrational spectroscopy of photosensitizer dyes for organic solar cells (2005)

Carmen Pérez León

Ruthenium(II) complexes containing polypyridyl ligands are intensely investigated as potential photosensitizers in organic solar cells. Of particular interest is their use in dye-sensitized solar cells based on nanocrystalline films of TiO2. Functional groups of the dye allow for efficient anchoring on the semiconductor surface and promote the electronic communication between the donor orbital of the dye and the conduction band of the semiconductor. In the present work a new dye, [Ru(dcbpyH2)2(bpy-TPA2)](PF6)2, and the well known (Bu4N)2[Ru(dcbpyH)2(NCS)2] complex were spectroscopically characterized. The electronic transitions of both dyes showed solvatochromic shifts due to specific interactions of the ligands with the solvent molecules. The surface-enhanced Raman (SER) spectra of the dyes dissolved in water, ethanol, and acetonitrile were measured in silver and gold colloidal solutions. The results demonstrate that the dyes were adsorbed on the metallic nanoparticles in different ways for different solvents. It was also found that in the gold colloid, the aqueous solutions of both dyes did not produce any SERS signal, whereas in ethanolic solution the SERS effect was very weak. Deprotonation, H-bonding, and donor-acceptor interactions seem to determine these different behaviors. Our results indicate the important role of the charge transfer mechanism in SERS. The adsorption of the dye on two different TiO2 substrates, anatase paste films and anatase nanopowder, was also studied to clarify the role of the carboxylate groups in the anchoring process of the dyes on the semiconductor surface. The recorded spectra indicate a strong dependence of the anchoring configuration on the morphology of the semiconductor.

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