Theoretical modeling of paramagnetic chemical shifts in actinide complexes

Les déplacements chimiques RMN paramagnétiques sont les déplacements induits par un centre paramagnétique par comparaison à un équivalent diamagnétique. Ils comprennent deux termes: i) le terme de pseudo-contact correspond à l'interaction dipôle-dipôle et provient des propriétés magnétiques anisotropes du centre paramagnétique, ii) le terme de contact qui provient de la densité de spin au noyau actif en NMR, induite par la délocalisation de spin du centre paramagnétique. Pour exploiter les résultats de pNMR, il est nécessaire de séparer ces deux termes. Le modèle de Bleaney, élaboré dans les années 1970 pour les complexes de Ln(III) de symétrie axiale, est fondé sur la théorie du champ cristallin, et permet cette séparation à partir de la dépendance en température: les termes de contact et de pseudo-contact ont des dépendances respectives en T^(-1) et en T^(-2). De plus, l'anisotropie magnétique s'exprime à l'aide d'un unique paramètre de champ cristallin B_0^2 , paramètre effectif qui peut être déduit déduire des déplacements chimiques expérimentaux. Lors de cette thèse, nous avons montré que le modèle de Bleaney n'est pas valable dans les complexes d'actinide de symétrie axiale; en effet, l'anisotropie magnétique ne peut pas être décrite par un seul paramètre de champ cristallin, et la dépendance en température n'est pas celle des lanthanides. Ceci a été montré sur des complexes d'actinide de symétrie axiale formés avec les ligands DPA2- , DOTA4-, TEDGA. Leur synthèse et leur caractérisation spectroscopique a été effectuée au CEA Marcoule par l'équipe de Claude Berthon. Les complexes d'actinide montrent différents degrés d'oxydation (+III, +IV, +VI) par comparaison avec les lanthanides (généralement stables sous la forme +III) et leur structure électronique est plus complexe. Au degré d'oxydation +VI, les actinides du début de la série (U, Np, Pu) forment des cations actinyles linéaires AnO22+, qui ne peuvent pas être décrits par la théorie du champ des ligands. Nous avons montré que la théorie de Bleaney échoue totalement à décrire la dépendance en température des déplacements pNMR dans ces complexes. Les calculs ab initio suggèrent que ce sont les deux doublets de Kramers de basse énergie qui induisent la pNMR dans les complexes actinyles 5f1 . Par ailleurs, un doublet non Kramers bien séparé dicte les propriétés magnétiques dans les complexes 5f2 . Dans les chelates An(IV), les déplacements de pseudo-contact sont faibles par rapport aux termes de contact. Le terme de pseudo-contact est en T^(-1) et on doit ajouter un terme en T^(-3) au terme T^(-2) pour bien reproduire les données expérimentales. Les densités de spin sur les ligands peuvent être estimées des déplacements de contact; des calculs DFT permettent de rationaliser les schémas observés. Cette étude est complétée en analysant les tendances des paramètres de champs cristallins (CFP) dans les complexes Ln(III) et An(IV) DPA. Ces paramètres jouent un rôle essentiel pour la chimie des lanthanides et des actinides. Ils décrivent l'interaction des électrons de la couche f avec les ligands et peuvent inclure de façon effective la répulsion électron-électron, le couplage J-J, et la covalence. Notre analyse a mené aux conclusions suivantes: les CFPs décroissent globalement le long de la série des Ln(III) et An(IV) DPA, effet attribué à la diminution de la covalence qui inclue tous les effets au-délà de la théorie électrostatique. L'effet est plus important dans la série des An(IV) due à un large couplage J-J. Les CFPs axiaux d'ordre 4 et 6 (B_0^4, B_0^6) sont plus importants que ceux d'ordre deux B_0^4 dans les actinides. Ceci implique que la modélisation des déplacements pNMR dans les lanthanides et actinides de symétrie axiale par la théorie de Bleaney inclue de façon effective les effets d'ordres supérieurs. Et montre la limitation de cette théorie.Paramagnetic NMR (pNMR) shifts are the extra induced chemical shifts in a paramagnetic complex compared to its diamagnetic counterpart. The pNMR shift of a nucleus can be divided into two terms: the pseudocontact shift which is a 'through-space magnetic dipole-dipole interaction and originates from the anisotropic magnetic properties of the metal center, and the contact shift which arises from the presence of spin density at the nuclear position, a phenomenon due to the spin delocalization. In the 1970s, Bleaney had proposed a simple model based on crystal field theory (CFT) which permits the separation of the two terms based on their temperature dependency in the axially symmetric lanthanide complexes. According to his theory, the contact and the pseudocontact shifts behave as functions of T^(-1) and T^(-2) , respectively. Furthermore, his theory relates the magnetic anisotropy responsible for the pNMR shifts with only one crystal field parameter (CFP) B_0^2: an effective parameter that can be extracted from the experimental pNMR shifts, helps to model the zero field splitting and molecular magnetism. In this thesis, we have shown that Bleaney's model fails to describe pNMR shifts in axially symmetric actinide complexes, neither their magnetic anisotropy can be modeled with only one CFP nor the shifts follow the temperature dependency as proposed for lanthanides. This is shown by detailed studies performed in axially symmetric actinide complexes with DPA2- , DOTA4-, TEDGA ligands. Actinides show variable oxidation numbers (+III, +IV, +VI) compared to the Ln (mostly stable in +III) and the electronic structure is more complicated. In the +VI oxidation state, the earlier actinides (U, Np, Pu) form linear actinyl cations AnO22+, which cannot be described with the ligand field theory. We have shown that Bleaney's theory completely fails to describe the temperature dependency of the pNMR shifts in these complexes. Ab initio calculations suggest that two low-lying Kramers doublets are responsible for the pNMR shifts in the 5f1 actinyl complexes, whereas a well-isolated ground non-Kramers doublet dictates the magnetic properties in the 5f2 complexes. In the axially symmetric An(IV) DPA chelates, the pseudocontact shifts are small compared to the contact shifts, temperature dependency of the contact shifts mostly follow T^(-1) relationship whereas the pseudocontact shifts require T^(-3) term in addition to the T^(-2) to properly fit the experimental data. Spin density distributions on the ligands are estimated from the contact shifts; DFT-based evaluation plays an important role in support of the observed patterns. The survey is completed by analyzing the trends of the CFPs in the Ln(III) and An(IV) DPA complexes. CFT parametrically describe the interaction of the f electrons with the ligands and the CFPS effectively include various effects as the electron-electron repulsion, J-J coupling, covalency etc. Our analysis leads to the following conclusions- the overall magnitude of the CFPs decreases along both the Ln(III) and An(IV) DPA series, these declining trends are attributed to the decrease of covalency that includes all the effects beyond the electrostatic picture, the decrease was much larger in the An(IV) series due to large J-J coupling. The fourth and sixth orders axial CFPs (B_0^4, B_0^6) are larger than the second-order order B_0^2which implies that the modeling of the pNMR shifts in the axially symmetric Ln or An complexes according to Bleaney's theory effectively includes the higher-order effects in B_0^2 and denotes a limitation to this theory

An Analytical Incorporation of Power Priority Model with Replication and Expedition based Routing Protocol

Delay tolerant network (DTN) is a class of wireless ad-hoc network. It works when end to end direct path does not exist between source and destination by using the Store and Forwarding routing mechanism. DTN has several features such as long delay, limited resources, high error rate, reliable transmission etc. Its application fields are in wildlife behavior monitoring, military battle field, post disaster communication, under water communication and many more. The purpose of this paper is to compare between two different strategic (Replication and Expedition based) routing protocols with the Power Priority Model, which is proposed in recently. The evaluated result of this performance analysis was obtained from Opportunistic Network Environment (ONE) simulator on various performance metrics such as, Delivery Probability, Overhead ratio, Average latency and Hop count

Impact of training of teachers on their ability, skills, and confidence to teach HIV/AIDS in classroom: a qualitative assessment

BACKGROUND: Considering the significant impact of school-based HIV/AIDS education, in 2007, a curriculum on HIV/AIDS was incorporated in the national curriculum for high school students of Bangladesh through the Government’s HIV-prevention program. Based on the curriculum, an intervention was designed to train teachers responsible for teaching HIV/AIDS in classes. METHODS: In-depth interviews were conducted with teachers to understand their ability, skills, and confidence in conducting HIV/AIDS classes. Focus-group discussions (FGDs) were conducted with students who participated in HIV/AIDS classes. HIV/AIDS classes were also observed in randomly-selected schools. Thematic assessment was made to analyze data. RESULTS: The findings showed that the trained teachers were more comfortable in using interactive teaching methods and in explaining sensitive issues to their students in HIV/AIDS classes. They were also competent in using interactive teaching methods and could ensure the participation of students in HIV/AIDS classes. CONCLUSIONS: The findings suggest that cascading training may be scaled up as it helped increase ability, skills, and confidence of teachers to successfully conduct HIV/AIDS classes

RADIAL DISTRIBUTION OF PARTICLE CLUSTERS IN A DOWNER REACTOR UNIT

This study investigates the formation of clusters at 11 radial positions in a 2.63 cm ID downer reactor using the CREC-GS-Optiprobes. Cluster properties such as dimensions, drag coefficients and velocity across the downer unit radius are established based on the reported data and a probabilistic based model

Outbreak of diarrheal diseases causes mortality in different geographical locations of Bangladesh during the 2021 COVID-19 era

ObjectivesDiarrhea is a major public health problem in low- and middle-income countries, including Bangladesh. Of the different spectrums of diarrheal diseases, cholera occurs every year, causing outbreaks and epidemics following a biannual seasonal pattern. Due to the COVID-19 pandemic, hospitalization for diarrheal diseases decreased in 2020 compared to the previous years. However, in 2021, massive outbreaks occurred in different geographical locations of the country. We described that an outbreak of diarrheal diseases causes mortality in different geographical locations in Bangladesh.MethodIn this study, we present a report of diarrhea outbreaks that were reported in 2018–2021 in different parts of Bangladesh, and data have been captured from different sources such as print and electronic media as well as from a nationwide surveillance system.ResultsAmong these locations, districts of Barisal Division, Kishorganj, Noakhali, Gopalganj, Bandarban, and Chattogram were the major hotspots of the outbreaks where high morbidity due to acute watery diarrhea and even mortality, which is usually low in Bangladesh, were recorded.ConclusionEarly detection and prevention and strengthening of the surveillance system are needed to combat the diarrheal upsurge, take immediate control, and adopt preventive strategies

Characterization of Chickpea Germplasm

In plant breeding, genetic diversity is an important component for crop improvement. An experiment was conducted at Ishurdi, Pabna (Bangladesh) to study the diversity and variability within the core germplasm collection of 93 chickpea accessions, and a total of 13 qualitative and 12 quantitative characteristics were studied. Among the qualitative characteristics more significant variations were observed in plant pigmentation, growth habit, flower color, seed color, seed shape, and texture. A total of 93 accessions were divided into eight clusters. The genotypes in Cluster IV and Cluster VIII were crossed with genotypes in Cluster I and Cluster VII for better yield performance. Correlation co-efficient study was done among the 12 quantitative characters with yield performance of the studied chickpea germplasm. Significant and positive correlation was observed among the days to 50% flowering, branches per plant, pods per plant, seeds per pod, straw yield, but significant and negative correlation was observed among the days to maturity, plant height, canopy width and hundred seeds weight within the yield performance of studied chickpea germplasm. Simultaneously, a more distinguished morphological diversity was found in number of pods per plant, grain yield per plant(g), 100-seed weight (g), harvest index and plant canopy height (cm) among the twelve quantitative traits of 93 chickpea accession. The chickpea accessions BD-6051, BD-6058, BD-6557, BD-6214, BD-6221, BD-6235, BD-6460, BD-6461, BD-6470, BD-6471, BD-6472, BD-6473, BD-6478, BD-6480, BD-6481, 6483, BD-6484, BD-6488, BD- 6491, BD-6500, BD-6505, and BD-6513 could be considered for crop improvement through the future breeding program of chickpea

Effects of Dietary Vitamin C on the Growth Performance, Antioxidant Activity and Disease Resistance of Fish: A Review

Vitamin C is an essential micronutrient that cannot be synthesized by fish and must be present in fish diets for proper functioning of the physiological conditions. It is required for the biosynthesis of the collagen which is a pre-requisite for the formation of connective tissue and increases the absorption of iron in fish. It prevents various diseases; it is soluble in water and is easily oxidated by heat, light and metal. Most animals can generate vitamin C in sufficient quantities for normal growth and function, but many fish cannot because they lack the enzyme L-gulonolactone oxidase for its manufacture. Vitamin C facilitates the absorption of iron and is necessary for a maximum rate of immune responses and enables a good response to stressors. This updated review presents a general outline of the possible physiological function of vitamin C for fish, with an emphasis on the information on growth performance, antioxidant activity, immune response and disease prevention of fish as well as the synergistic effects of vitamin C with other micronutrients. The diets supplemented with vitamin C promote the growth performance, improve the structure of the intestinal mucosal epithelium, and have a positive impact on the hematological parameter. The addition of different dietary vitamin C to the basal diets significantly improved the growth performance, antioxidant activity, immune response and disease resistance of fish. vitamin C in the aquaculture, having a solid understanding of the positive functions and mechanisms that vitamin C possesses is of the utmost significance

Current Status and Development Trend of Aquaculture: Prospects and Future Potentials

In recent years world aquaculture production has been increased with innovative and technological developments within fisheries sector and scaled up in world total fisheries production. This increasing aquaculture production depends on innovative production systems and technologies, biotechnological developments. The advancements in these cutting-edge technologies have been focused on promoting sustainable aquaculture production, mitigating the risk of disease outbreaks, and contributing to eco-friendly environmental initiatives. This review paper highlights the cutting-edge technologies that have emerged in the field of aquaculture in recent years, up until the present time, with a focus on advancements in fish nutrition. The advancements in aquaculture technology have been instrumental in promoting the achievement of sustainable development goals. As the aquaculture industry continues to evolve, it is expected that there will be further advancements in technology, sustainability practices, and innovative approaches to meet the increasing demand for seafood while minimizing environmental impact. Overall, the future of aquaculture is likely to be characterized by a combination of technological innovation, sustainable practices, and increased focus on environmental and social responsibility. In the arena of aquaculture, this review paper has the potential to nourish the minds of aquaculturists and aquafarmers with a bountiful feast of knowledge. It unveils the latest technologies and developments in the realm of aquaculture, serving as a nutritious resource that can enhance the operation of cultures and promote a fruitful increase in production in the not-so-distant future

Seasonal Price Variation and Market Intregration of Tilapia (Oreochromis Niloticus) Fish in Some Selected Areas of Bangladesh

A study was undertaken to examine the marketing system and price behavior of tilapia fish in selected areas of Mymensingh district of Bangladesh during the month of March-May 2012. The objectives of the study were to estimate costs and margins, seasonal price variation and to test market integration of Tilapia fish. Primary and secondary data were used for this study. The higher marketing cost was incurred by aratdars and the lowest by retailer. On the other hand, retailers earned the highest net marketing margins. Analysis of market integration shows that Tilapia fish market in Bangladesh was well integrated. The study identified some problems related to economic, technical, marketing, social and natural calamities aspects and suggested some measures for solving these problems. The findings of the study revealed that the marketing of tilapia was a profitable business and some recommendations were provided for the improvement of tilapia marketing in the country. Keywords: Engle Granger co-integration, Market integration, marketing system, price behavior, Tilapia