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Synthesis and characterization of 2D-TMDs thin films/flakes by various solution processed deposition methods for different applications
No full textAtomically thin two-dimensional (2D) transition metal dichalcogenides (TMDs) are promising candidates for future electronics. Currently, the growth of large area TMDs thin films/flakes is one of the biggest challenges. A novel method for the growth of ultra-thin and large area tungsten disulfide (WS2) monolayer flakes has been developed by introducing a solution-based temperature-dependent process. This two-dimensional WS2 growth process is low cost and environmentally friendly. Ammonium tetrathiotungstate ((NH4)2WS4, ATTW) was used as WS2 precursor. The process requires a moderate activation temperature as no flakes are formed at room temperature. Successful growth of flakes was observed in an aqueous solution of the precursor at a temperature between 70 and 90 oC. These flakes could be transferred to any substrate by a controlled dip-coating process. Large 2D WS2 flakes with a lateral size of up to 100 μm were obtained. The thickness ranged from a WS2 monolayer to five monolayers, as verified by AFM.
Similarly, large area molybdenum disulfide (MoS2) ultra-thin film deposition is one of the big challenges in the recent years. Electrodeposition provides an opportunity to grow such ultra-thin films on large scale. However, the transfer of the electrochemically grown film to desired substrate is challenging. In this work, the polymer coated electrodeposited MoS2 films on Au are separated mechanically from the underlying substrate by using ultra-sonication. Collapse of micron-sized bubbles produced by ultra-sonication at the interface of Au and silicon substrate provides enough energy for separation due to their weak adhesion. The Au layer is then removed by standard Au-etchant (K/KI) and the polymer coated MoS2 film (two monolayers) is transferred to a desired substrate.
The obtained MoS2 films by electrodeposition and spin coating were also used for hydrogen evolution reaction. The HER activity measurements for electrodeposited MoS2 showed an overpotential for 30 nm thick MoS2 of -0.33 V, whereas for smaller thicknesses below 10 nm a value of -0.22 V was found. This indicates that ultra-thin films of MoS2 show a better HER activity than thick films. The obtained Tafel slope of 44 mV per decade for 5 nm MoS2 is better than values reported for single crystal MoS2 and other 2D materials such as WS2
The Role of Multinational Corporations in the Green Revolution, 1960s and 1970s
No full textThis dissertation examines the role of multinational corporations in the Green Revolution of the 1960s and 1970s. The author understands the Green to be a technocratic and commercial approach to rural development, which promoted a package of agricultural inputs including high-yielding seed varieties, fertilizers, and plant protection chemicals. The research highlights how multinational companies influenced the rural development agendas of their home countries, international organizations, and governments in the Global South. Chapter 1 provides a literature review and discusses the research approach. Chapter 2 examines a philanthropic-government-corporate network that disseminated hybrid maize seeds in the early 1960s in India. Chapter 3 analyzes the interrelationship of development aid and the fertilizer industry in India. With a case study of the Bimas Gotong Royong project, Chapter 4 focusses on public-private partnerships in the dissemination of plant protection chemicals in the framework of development aid. Chapter 5 shifts the analytical focus to the 1970s, examining the transition from the Green Revolution to the Gene Revolution. It illustrates the decision of chemical corporations to invest in the seed business as a counter-reaction to rising environmental and leftist criticism, and assesses the significance of these changes in terms of the larger history of rural development. Chapter 6 concludes the know-how of multinational companies in the production and dissemination of agrichemicals was indispensible in the increasingly commercial logic of rural development strategies. Meanwhile, multinational corporations were dependent on support from, and partnerships with, the development community when it came to expanding their markets to so-called developing countries and turning rural development into a profitable business
Investigation of Arabidopsis thaliana Tha4 pore formation in planar bilayers using electro-optical methods
No full textIn the course of evolution, the structure and topology of cells have changed greatly. From simple cells surrounded only by a single membrane to cells containing multiple membrane-enclosed organelles. The advantage of individual reaction compartments is offset by the fact that proteins required there are almost exclusively nuclear-coded. They have to be targeted to and imported into their compartment post-translationally. One of the protein import systems involved, which can even transport large fully folded proteins, is the twin-arginine translocation (TAT) system. It operates both in the thylakoidal membrane and the plasma membrane of a wide range of bacteria. The thesis focuses on Tha4, the potential channel forming subunit of the TAT system of Arabidopsis thaliana. To verify formation of homo-oligomeric membrane channels purified Tha4 protein was used. The oligomeric topology of fluorescence-labelled Tha4 was investigated using fluorescence fluctuation spectroscopy (FFS). The functional properties of the membrane reconstituted Tha4 was investigated using the electrophysiological bilayer technique both in the vertical setup and with the combined fluorescence-opto-electrical horizontal bilayer (HLB) technique. Electrophysiological measurements with artificial planar lipid bilayers revealed cation-selective ion-channels for reconstituted Tha4 with a pore width of 1 nm. Similar results were obtained for co-reconstituted Tha4-Hcf106 proteins in vertical planer bilayers. The investigation of the oligomeric state in solution and in artificial planar lipid bilayers using FFS at the single molecule level with fluorescence-labelled proteins revealed that addition of soluble, NBD-labelled Tha4 showed a strong accumulation in the membrane. Subsequent lifetime measurements disclosed that the NBD-labelled parts are located more close to the polar part of the membrane, in close vicinity of the membrane-water interface
A computational framework to study microbial genes of unknown function
No full textMicrobes have an immense and varied functional potential that influences and is influenced by the surrounding environment. Microbial processes affect global biogeochemical cycles and numerous medical, biotechnological, and industrial activities. Over the centuries, the study of microbial systems has progressed through technological and methodological revolutions that greatly expanded our understanding of the microbial world. These discoveries provided insights into the role of microbial communities in the environment, and helped identify and develop beneficial industrial and biotechnological applications. However, the functional characterization of the microbial genetic repertoire has not kept pace with the constant growth of sequenced genomes and metagenomes. This discrepancy has opened a gap between the known and unknown coding sequence space. Several challenges hinder the bridging of this gap. Consequently, the unknown fraction is often excluded from functional microbiome analyses, resulting in a loss of valuable information and limiting our understanding of the functional roles of microbes. In the last decade, several methods have been proposed to address the challenge of uncharacterized genes. However, despite the advances brought by previous studies, an integrated and scalable solution that organizes unknown genes into biologically meaningful categories is still missing, as well as the development of a standard partitioning scale capable of unifying genomic and metagenomic data maximizing the information for the unknown fraction and facilitating its inclusion in the analyses of microbial systems. The work presented in this thesis addresses these challenges by developing the conceptual and computational basis to enable the study of the large pool of genes with unknown function and their inclusion in the analyses of microbial systems
Synthesis and Structural Characterization of Bismuth(III)-, Lead(II)- and Scandium(III)-Containing Heteropolytungstates
No full textPolyoxometalates (POMs) are discrete, anionic metal-oxides of early d-block metals in high oxidation states that exhibit unmatched structural variety and associated physicochemical properties leading to interest in diverse areas including catalysis, magnetism, material science and biomedicine. Chapter 1 covers the historical background, structural properties and some applications of POMs. Chapter 2 presents the state of the art of bismuth(III)-, lead(II)- and scandium(III)-containing POMs. Chapter 3 is about the analytical techniques and synthetic procedures of used POM precursors. Chapter 4 reports the synthesis and structural characterization of eight novel bismuth(III)-containing POMs. This chapter is divided into two subsections, (i) synthesis of four isostructural Keggin-type ions [Bi(α-XW11O39)2]n-, X = Si (1), Ge (2), n = 13; X = P (3), As (4), n = 11) and two Wells-Dawson-type ions [Bi(α2-X2W17O61)2]17- X = P (5), As (6), n = 17, and (ii) synthesis of the 1:1 complexes [{Bi(H2O)SiW11O39}4]20- (7) and {[Bi(H2O)SiW11O39]5-}∞ (8), the latter being an infinite one-dimensional structure in the solid state. Chapter 5 reports two novel lead(II)-substituted Keggin-type heteropolytungstates, [Pb(α-XW11O39)]6- (X = Si (9), Ge (10)). This work suggests that Pb2+ and Bi3+ mimic the structural chemistry of lanthanides in POM chemistry. Chapter 6 presents the synthesis and structural characterization of two scandium(III)-containing heteropolytungstates, [(Na(H2O))2Sc2(P2W15O56)2]16- (11) and [Sc(HPW7O28)2]13- (12). Chapter 7 summarizes the work presented in this dissertation and discusses the future prospects of this work. Chapter 8 shows some incomplete results including the synthesis of [Sc4(H2O)10(B-β-TeIVW9O33)2]4- (13), [Sc4(H2O)10(B-β-AsIIIW9O33)2]6- (14) {[(Sc(H2O)4)2(H2W12O42)]4-}∞ (15), [Bi2(W3O10)(B-α-BiW9O33)3]23- (16), [Bi2(H2O)6W2O4(B-β-BiW9O33)2] (17), [Sc2Na2(H2O)2(B-α-GeW9O34)2]12- (18) and [Sc2(B-β-GeW8O31)2]14- (19) respectively
Understanding the Role of Executive Functions for Decision-Making and Creative Thinking: Computational and Experimental Approaches
No full textModels of cognition-based brain networks and functions are enormous in number and intricate in function. However, it is possible to compare modules of hierarchically segregated models against one another and model them based on a range of empirical data.
It is essential to elucidate the neurobiological contribution of executive functions (EFs) to cognitive functions such as decision making (DM) and creative thinking.
The prefrontal cortex (PFC) is associated with several EFs. The PFC is part of a deliberate inhibitory control (IC) network; it is also a central node for problem-solving and the creative ideation process. Nevertheless, several cognitive domains for inhibition and flexibility correspond to distinct cortico-frontal networks. An integrated computational–experimental framework could provide insight into the root of EFs.
This PhD thesis aims to explore the role of models of cognition-related brain networks and functions. The thesis addresses 1) the computational perspective on decision-making and creative thinking and 2) the experimental perspective on creative thinking, supported by relevant peer-reviewed publications.
The computational perspective on DM and creative thinking is concerned with validating computational modeling through spiking neural network (SNN) and connectionist models.
The experimental perspective on creative thinking is concerned with the relationships among creative cognition, creative drive, and their associated neuromodulator systems––a subject on which information has, until now, remained scattered and elusive. The experimental study used a non-invasive brain stimulation method (transcranial direct current stimulation [tDCS]) to examine the role of the inferior frontal gyrus (IFG) in divergent thinking (DT) and whether changes in the activity of the IFGs and IC would mediate variations in DT
Women in Rural Development: The Case Study of the Office du Niger in Mali, 1960-2010
No full textThe Office du Niger [hereafter, ON] in Mali was created by the French colonial authorities in 1932 with the goal of establishing a textile industry and producing rice for the local population. When the former colony of Soudan became independent in 1960, the ON came under the authority of the new Malian state and was nationalized. In the following years, the new Malian authorities made this enterprise in the heart of the Malian development process with an emphasis on achieving food self-sufficiency and increasing food exports. In the context of decolonization and the Cold War, the Malian government has followed the socialist model of development. Specially, its new statesman, Modibo Keita formulated a resolution which was approved in September 1960. According to this resolution, new economic structures were supposed to be established to build a socialist economy by investing into Mali’s people, both men and women as the basis and main driver of the nation’s development. Since then, the ON absorbed a large share of public investment, and collective work at the village level was promoted. Farmers, men as well as women, became organized in agricultural associations in order to increase productivity and to raise the living standard of dwellers. Over times, political changes occurring in Bamako as well as decision-making in the ON management level did influence the functioning of the irrigation scheme, not to mention the international community. This study investigates the historical evolution of women’s situation in the ON and the role they have played in the rural development process initiated through the lens of the irrigation scheme from 1960 to 2010. By analyzing the historical situation of women and their role, this research project came down to asking whether during the study period there a possible change of their position over time was, or whether they remained in the background
Trace elements and their application as geochemical proxies in marine chemical sediments
No full textThe topic of this PhD Thesis is the application of trace elements such as rare earth elements and yttrium (REY), neodymium (Nd) isotopes and gallium (Ga) in combination with its geochemical partner Aluminum (Al) as geochemical proxies in various types of marine chemical sediments from Precambrian to modern formation ages. The marine chemical sediments investigated comprise Precambrian (banded) iron formations ((B)IFs), manganese formations (MnFs) and stromatolitic carbonates, and modern authigenic carbonates from methane seep sites and hydrogenetic ferromanganese (Fe-Mn) crusts. Trace element systematics of these potential geochemical archives can provide valuable insights into the physico-chemical conditions under which their formation occurred and allow conclusions regarding the trace element budget of the precipitating fluid.
REY distributions and Nd isotope compositions were determined for Paleoproterozoic marine chemical sediments from the Transvaal Supergroup in South Africa to allow insights into (i) the physico-chemical conditions that prevailed during their formation and (ii) the dominant REY sources to the early ocean prior to the Great Oxidation Event (GOE).
Trace element systematics of modern seep carbonates from the Northern Norwegian continental margin show that REY also represent a powerful tool for screening a sample set of marine chemical sediments for detrital components and, thereby, identifying the purest and most reliable geochemical archives.
Gallium-Aluminum systematics of modern marine hydrogenetic Fe-Mn crusts were also investigated in order to better understand the geochemical behavior of the Ga-Al pair in the modern marine environment, especially in the presence of Fe(III)-oxyhydroxides
Effect of Neurofeedback Training Combined with transcranial Direct Current Stimulation on Primary Insomnia
No full textAs insomnia is recognized as a globally prevalent mental disorder with a high comorbidity rate, attempts to cure insomnia have been increasing. Primary insomnia is not attributed to other medical conditions or substance usage but may be due to impaired brain network and dysregulated brain activities. Normally, a bottom-up thalamocortical pathway is targeted with pharmaceutical interventions for neurological and psychiatric disorders, but possibilities to modulate brain mechanisms with a top-down corticothalamic pathway are re-gaining attention and being considered as a potential treatment option. This study focuses on identification of hallmarks of EEG patterns in insomniacs and effects of a combination of two neuromodulation methods: Neurofeedback (NFT) and transcranial direct current stimulation (tDCS). The 12 participants diagnosed with primary insomnia first received 20 sessions of NFT, which was followed by additional 10 sessions of tDCS, and their EEG patterns were measured at baseline and after the completion of the training. The EEG power and coherence in each of theta (1-4 Hz), delta (4-8 Hz), alpha (8-12 Hz), beta (12-30 Hz), gamma (30-50 Hz) frequency bands was analyzed and compared with the EEG of healthy control group. Throughout the research, I found that primary insomniacs tend to have elevated beta and high beta relative power and excessive coherence compared to the norm of healthy population saved in the NeuroGuide database and the healthy control group, respectively. After the intervention, a noticeable reduction in beta power and coherence was observed
Cucurbituril Complexes and their Spectral Characterization
No full textThis doctoral thesis provides insights into the chemistry of host-guest complexes of hydrophobic amino molecules or hydrophobic amines attached with dyes, and their characteristics after complexation with cucurbit[n]urils (n = 7 and 8) was studied. It describes how to calculate the binding constants by different methods and techniques with minimum error and propagation error. Different types of complex can be formed, accompanied by changes in guest luminescence properties after complexation.
The first project in the thesis presents a new fluorophore class for the design of reporter dyes for supramolecular host-guest complex formation with cucurbit[7]uril (CB7). The boron-dipyrromethene group (BODIPY) contains protonatable aniline nitrogen in the meso-position of the BODIPY chromophore, which was functionalized with known binding motifs for CB7.
The second project in the thesis describes the formation of supramolecular complexation between cucurbit[n]urils (n = 7 and 8) and an amphiphilic pyridinium-functionalized anthracene (AnPy) in aqueous solution. The host-guest complexation between CBn and AnPy was studied in detail by using optical spectroscopy.
The third project in the thesis describes how to use different techniques to calculate accurate and precise binding constants with CB7, and how to establish a series of reference compounds to determine CB7 binding affinities by direct and competitive titrations. The compounds have been selected according to their commercial availability to be suitable for various measurement techniques. The binding affinity of berberine chloride was established as a central reference point, which could be measured by fluorescence spectroscopy, ITC, and 1H NMR. The sensitivity of its Ka value to trace impurities in Millipore water was observed in direct titrations but not in competitive titrations. Within a series of competition experiments, reference compounds were established to cover a wide range of affinities (mM-fM)