Multiphase Equilibrium of Fluids Confined in Fisher-Tropsch Catalytic Systems

Energy supply and security imposes a significant challenge in our modern world stemming from our dependence on depleting resources such as petroleum and oil. Fischer-Tropsch synthesis (FTS) is considered as a great energy alternative which can significantly reduce our dependence on oil, improve rural economics, reduce greenhouse emissions, and promise energy security. It is a key technology for converting syngas, produced from coal, biomass or natural gas, into a variety of hydrocarbon products. Although this technology was discovered in 1923, commercialization and scale up are limited to the use of few reactor configurations (e.g. multi-tubular fixed-bed reactor, Slurry-bubble column reactor, and fluidized bed reactors). In order to improve the limitations in both reactor configurations, on lab scale near critical media was utilized, since it offers a great combination of the advantages of both the gas-phase reaction (multi-tubular fixed-bed reactor) and the liquid-phase reaction (slurry-bubble column reactor), while simultaneously overcoming their limitations. This work focuses on modeling the phase behavior of the FTS mixture in fixed bed reactor in the bulk phase inside the reactor bed or inter-particle and then zoom into the catalyst (confined phases within the catalyst pores or intra-particle). This is done by using an extended Peng-Robinson (PR) equation of state (EOS) that is capable of accounting for the fluid behavior inside confined pores as well as in the bulk phases. The PR Equation of state model extended to confined fluid (PR-C) has been utilized in multiphase equilibrium algorithm using FORTRAN. The simulation results provide the composition and the condition of each bulk phase and pore phase for a given initial mixture. Two different scenarios were studied for fixed bed reactor: the first one is the conventional gas phase FTS and the second one is for the supercritical phase FTS (SCF-FTS). In each case, the phase behavior of the mixture of the reactants and products was investigated at different conversions along the bed length. The simultaneous assessment of both gas phase FTS and SCF-FTS phase behavior and reaction performance open the door for optimizing the design FTS reactor and enhance the efficiency of the process. Preferential adsorption of hydrogen has been observed and this could be due to the small size of the hydrogen molecules compared to those of the other components. Our studies suggested that the supercritical phase provides superior heat dissipation due to the existence of denser phase in the bulk and the confined regions than the conventional gas phase. On the other hand in the gas phase and for limited carbon number (up to C8) the pore phase is found to be in a vapor state which should provide higher diffusivity of the reactant than that in the supercritical phase. Our study will continue by integrating the developed phase behavior studies in the reactor design model

Using autoregressive models (VAR) to measure and analyze the impact of net foreign investments on the economic variables of sustainable development in Sudan (1990 – 2017)

تهدف هذه الدراسة إلى استخدام نماذج الانحدار الذاتي VAR في قياس وتحليل أثر صافي الاستثمارات الأجنبية على المتغيرات الاقتصادية للتنمية المستدامة في السودان (1990 – 2017م) ومن اختبار ديكي فولر اتضح أن المتغيرات مستقرة عند المستوى عند مستوى معنوية 5%، كذلك أوضح اختبار جوهانسون للتكامل المشترك أنه يوجد متجه واحد للتكامل ومن خلال نتائج الانحدار الذاتي VAR اتضح أن الاستثمارات الأجنبية للفترات السابقة والحالية لم يكن بالشكل المطلوب. لذلك أوصت الدراسة بإزالة كافة العقبات الداخلية التي تواجه الاستثمار والمستثمرين من إجراءات وقوانين وبنى تحتية وخدمات لجذب استثمارات أكثر.The study aims at using the model of self regression VAR in measuring and analyzing the effect of foreign investments on the economical changes on the sustainable development in Sudan(1990-2017), and from Dicky Foller's test appeared that the variables are stable at the level of 5% significant, also Johanson's test of joint integration showed that there is one direction to integration and through the results of self regression VAR appeared that the foreign investments in  the past and present was not as required. For that, the study recommended to removing all the internal obstacles facing the investment and the investors from procedures, rules, infrastructures, and services to attract more investments

Genetic variation within and among five natural populations of endangered Sclerocarya birrea (A. Rich) subsp. Birrea in Sudan

Knowledge of genetic diversity is important for successful conservation and domestication of species. In order to determine genetic diversity within and among Sclerocarya birrea (A. Rich.) Htochst. subsp. birrea populations in Sudan, random amplified polymorphic DNA (RAPD) markers were used. Leaf materials from 75 seedlings from five populations (Rashad, Alfaid, Alkhwi, Aldamazin and Baw) of this species were used to compare the genetic diversity. A total of 37 bands were generated using four primers. Genetic variation within the populations as estimated by Shannon information index ranged from 0.343 to 0.272 with an overall diversity of 0.306. Analysis of molecular variance revealed that 46% of the variation was attributed to differences among the populations and 54% within the populations (P < 0.001). The gene flow among population was small (Nm = 0.297). UPGMA cluster and principal coordinate analyses (PCA) indicated Alfaid as the most distinct population. Since genetic variation was found to occur among and within the populations of S. birrea (A. Rich.) Hochst. Subsp. birrea, conservation of these populations would help in the maintenance of the species.Key words: Sclerocarya birrea subsp. birrea, genetic variation, conservation, random amplified polymorphicDNA (RAPD), Sudan

Responses of Periwinkle (Catharanthus roseus) to soil and foliar applications of Haza (Haplophyllum tuberculatum).

This study aimed to investigate the responses of Periwinkle plants to soil and foliar applications of Haza plant in two separate tests under the conditions of the nursery at Shambat, Khartoum North, Sudan. The foliar treatments were for boiled water extracts of hand crushed Haza shoots in concentrations: 0.0, 5, 10, 15 and 20 g/l, while the soil dressing test was for powder of dry shoots of Haza applied in doses of: 0.0, 5, 10, 15 and 20 g per plant. The Periwinkle transplants were planted in 18 inch plastic pots containing River Nile sedimentary soil. The study was arranged in complete randomized design and each treatment was replicated 7 times. Data were collected 4 months after applications. The results showed substantial increments in vegetative and reproductive growth parameters coupled with high alkaloids content from soil dressing with 10 g/plant Haza treatment or the foliar application of the 10 g/l Haza extract. These findings elucidated the bio-stimulating potential of Haza applications for enhanced vegetative and reproductive growth beside alkaloids content of Periwinkle. This stimulating potential may be of value for trials on organic production of other horticultural crops

Effect of nitrogen fertilizer and irrigation on Acacia senegal seedling biomass and photosynthesis

Seedlings of Acacia senegal were grown in a glass greenhouse to study the effect of nitrogen and irrigation regimes on dry matter production and allocation to different plant organs, net photosynthesis per unit leaf area, and nitrogen content in the different plant organs. Ammonium nitrate (NH4NO3) was used in this study, as the source of inorganic nitrogen. The nitrogen treatment consisted of four levels: 0, 30, 100, and 200 ppm of N which were added with the irrigation solution. Irrigation treatment consisted of irrigation every two, five or ten days. Nitrogen fertilization, irrigation regimes, and their interaction significantly affect the total stem, root, and leaf dry weight. However, low and moderate levels of N with irrigation every two days, resulted in higher total plant dry weight. Contrary to the initial hypothesis of the study, net photosynthesis showed no significant differences among the N treatments, but a decrease occurred after the fifth day since irrigation; this was also followed by a low net CO2 uptake. Stomatal conductance was affected significantly by the N and irrigation treatments. Total N content in the whole seedlings, stems, roots, and leaves was found to be high at low to moderate application of N, with irrigation every two days, while percent N in these parts showed a marked increase with increasing the N added. Moreover, percent N in roots showed the highest increase compared to percent N in stems and leaves

Food Legumes and Rising Temperatures: Effects, Adaptive Functional Mechanisms Specific to Reproductive Growth Stage and Strategies to Improve Heat Tolerance

Ambient temperatures are predicted to rise in the future owing to several reasons associated with global climate changes. These temperature increases can result in heat stress- a severe threat to crop production in most countries. Legumes are well-known for their impact on agricultural sustainability as well as their nutritional and health benefits. Heat stress imposes challenges for legume crops and has deleterious effects on the morphology, physiology, and reproductive growth of plants. High-temperature stress at the time of the reproductive stage is becoming a severe limitation for production of grain legumes as their cultivation expands to warmer environments and temperature variability increases due to climate change. The reproductive period is vital in the life cycle of all plants and is susceptible to high-temperature stress as various metabolic processes are adversely impacted during this phase, which reduces crop yield. Food legumes exposed to high-temperature stress during reproduction show flower abortion, pollen and ovule infertility, impaired fertilization, and reduced seed filling, leading to smaller seeds and poor yields. Through various breeding techniques, heat tolerance in major legumes can be enhanced to improve performance in the field. Omics approaches unravel different mechanisms underlying thermotolerance, which is imperative to understand the processes of molecular responses toward high-temperature stress