The Effect of Shocks on the Current and Future Behavior of Sudan Economy: Autoregressive Moving-average Approach

This paper attempts to achieve two core objectives. Firstly, it aims to synthesize the information contained in the different expenditure components of GDP for developing a set of Autoregressive Moving-Average (ARMA) models to examine the effect of shocks on the current and subsequent cyclical deviations of Sudan real GDP from what is trending. Secondly, it aims to compare the intensity of those cyclical deviations within the reviewed period (1970-2010) and outside it. ARMA models of different orders are experimented to distinguish, empirically, whether the effect of shocks is transient or permanent and lasts for a long period of time. The major result is that the lingering effect of shocks is permanent causing intensified deviation from the trend outside the reviewed period

A machine learning approach for efficient uncertainty quantification using multiscale methods

Several multiscale methods account for sub-grid scale features using coarse scale basis functions. For example, in the Multiscale Finite Volume method the coarse scale basis functions are obtained by solving a set of local problems over dual-grid cells. We introduce a data-driven approach for the estimation of these coarse scale basis functions. Specifically, we employ a neural network predictor fitted using a set of solution samples from which it learns to generate subsequent basis functions at a lower computational cost than solving the local problems. The computational advantage of this approach is realized for uncertainty quantification tasks where a large number of realizations has to be evaluated. We attribute the ability to learn these basis functions to the modularity of the local problems and the redundancy of the permeability patches between samples. The proposed method is evaluated on elliptic problems yielding very promising results.Comment: Journal of Computational Physics (2017

Parametrization of stochastic inputs using generative adversarial networks with application in geology

We investigate artificial neural networks as a parametrization tool for stochastic inputs in numerical simulations. We address parametrization from the point of view of emulating the data generating process, instead of explicitly constructing a parametric form to preserve predefined statistics of the data. This is done by training a neural network to generate samples from the data distribution using a recent deep learning technique called generative adversarial networks. By emulating the data generating process, the relevant statistics of the data are replicated. The method is assessed in subsurface flow problems, where effective parametrization of underground properties such as permeability is important due to the high dimensionality and presence of high spatial correlations. We experiment with realizations of binary channelized subsurface permeability and perform uncertainty quantification and parameter estimation. Results show that the parametrization using generative adversarial networks is very effective in preserving visual realism as well as high order statistics of the flow responses, while achieving a dimensionality reduction of two orders of magnitude

DEVELOPMENT OF NEW SUPPORTED CATALYSTS FOR DIRECT ETHANOL FUEL CELLS

Fuel cells are electrochemical energy conversion devices to be fed with a fuel and oxidant in order to generate electricity. Ethanol has, recently, shown a promising potential to replace hydrogen as a fuel directly fed into the cell due to its liquid state and sustainability. The challenge, however, is the significantly slow ethanol oxidation kinetics. Therefore, an affordable, highly active, and stable catalyst is necessary for activating such reaction. Platinum (and its alloys) is known as the most active metal for fuel cell catalysis, but its scarce presence has made the fuel cell commercialisation non-feasible. Also, it is very susceptible to poisoning by carbonaceous species which considerably decreases the catalyst lifetime. Palladium has shown a good potential to replace Pt. It is more abundant than Pt and has shown a comparable performance. Furthermore, it is more tolerant for poisoning species. In this thesis, Pd nanoparticles (NPs) are prepared by chemical reduction on five different carbon supports all of which are physically characterised and evaluated for ethanol oxidation. Because of a critical balance amongst the physiochemical characteristics (surface area, porosity, crystallinity extent), Vulcan carbon (XC72) has presented the highest support functionality for Pd ethanol oxidation as measured by the obtained current density. Numerous research efforts have co-concluded that adding a 2nd metal to Pd is beneficial economically and technically. Yet, a few groups have given attention to the trimetallic Pd-based electrocatalysts. Therefore, the main target of this thesis is to investigate various trimetallic combinations and synthesis methods to prepare C-supported trimetallic catalysts. Three different borohydride reduction synthetic protocols were deployed to prepare PdAuNi catalysts. The sodium borhydride-2-propanol (SBIPP) method gives the highest performing PdAuNi/C catalyst with 9-A/mgPd current density peak and - 0.36-V-vs-NHE onset potential while the single Pd counterpart gives only 2 A/mgPd and - 0.26 V, respectively. The physical characterisation shows enhanced physical alloy structure of this PdAuNi. Using the SBIPP protocol, 12 other catalyst combinations from Pd and two other metals were prepared with 12 wt.% metal loading. PdAu-based catalysts have shown significant enhancement of the Pd activity and stability towards ethanol oxidation. PdAuRh, in particular, produces a remarkable oxidation current peak of 10 A/mgPd and - 0.4-V onset potential. The PdAuRh and PdAuNi catalysts seem to present serious candidates to replace Pt and facilitate the transition into an affordable low-carbon technology to supply sustainable electricity.====================================================================================== ِArabic Abstract تعتبر خلايا الوقود أجهزة تحويل طاقة يتم تغذيتها بوقود ومؤكسد لكي تولد كهرباء. وحديثا لاقي وقود الايثانول اهتمام الباحثين كوقود لتغذية الخلية بدلا من الهيدروجين نظرا لطبيعته السائلة واستدامة وجوده. ولكن التحدي امامه هو البطء الشديد في تفاعل اكسدته داخل الخلية. لذا من الضروري إيجاد حفاز نشط جدا لتحفيز اكسدة الايثانول لوقت طويل نسبيا. يعرف معدن البلاتين بأنه انشط المعادن لتحفيز تفاعلات خلايا الوقود ولكن ندرته الشديدة تجعل تسويق خلايا الوقود تجاريا غير مجدي. أيضا فان معدن البلاتين لا يقام السموم الكربونية التي قد توجد على شكل شوائب او تنتج اثناء التفاعلات في خلايا الوقود مما يجعل عمر الحفاز الفعلي قصير جدا. على الجانب الآخر معدن البلاديوم يقدم بديل مناسب للبلاتين حيث انه اقل ندرة من البلاتين في القشرة الأرضية و يعمل بكفاءة تناظر البلاتين. إضافة الي ذلك فان عمر حفاز البلاديوم أطول من البلاتين نظرا لقدرة الأول على مقاومة التسمم بالعينات الكربونية. في هذه الرسالة جسيمات البلاديوم النانوية تم تحضيرها بالاختزال الكيمياء و تم تثبيتها على خمسة أنواع كربون مختلفة كل منهم تم تحليه فيزيائيا و كيميائيا و تم تطبيقها لأكسدة الايثانول. نظرا لتداخل تأثيرات الخواص الفيزوكيميائية مثل المساحة السطحية والمسامية ودرجة التبلور فان الكربون من نوع فولكان 72 قدم افضل أداء هندسي كحامل لحفاز البلاديوم لأكسدة الايثانول يعرف من خلال شدة التيار الكهربي الناتج من التفاعل. العديد من الدراسات السابقة توصلت الى ان إضافة عنصر آخر الي البلاديوم يحقق مصلحة مزدوجة برفع الكفاءة و تقليل الكمية المستهلكة من معدن البلاديوم النبيل. و لكن القليل من الدراسات ركز على دراسة إضافة عنصرين الي البلاديوم بدلا من عنصر واحد. لذا الهدف في هذا العمل هو فحص تركيبات محفزة مختلفة من ثلاث معادن (بلاديوم إضافة الى معدنين اخرين) وطرق تحضير مختلفة. ثلاث طرق اختزال باستخدام البوروهيدريد تم تطبيقاها لانتاج ثلاث حفازات ثلاثية من البلاديوم و الذهب و النيكل. الحفاز المنتج باستخدام تركبية بوروهيدريد الصوديوم و البوروبانول الثنائي هو اعلاهم أداء بكثاقة تيار 9 امبير/مجم (بلاديوم) و جهد بدأ أكسدة -0.36 فولت بينما الحفازي الأحادي من البلاديوم اعطي فقط 2 امبير/مجم (بلاديوم) و ابتدء اكسدة الايثانول مع فرق جهد -0.26 فولت. التشخيص الفيزيائي لهذا الحفاز بينية انشائية محسنة من سبيكة البلاديوم و الذهب و النيكل. و بنفس طريقة التحضير تم تحضير 12 حفاز ثلاثى اخري من البلاديوم و معدنين اخرين و معدل تحميل المعدن على الكربون يكافئ 12% بالوزن. بصفة عامة الحفازات التي تحتوي على بلاديوم و ذهب إضافة الى معدن اخر تقدم أداء محسن تجاه اكسدة الايثانول اكثر من الحفازات الأخرى. انشط هؤلاء هو الحفاز الذي يحتوي على بلاديوم و ذهب و روديوم و الذي انتج كثاقة تيار مرتفعة بقيمة 10 امبير/مجم (بلاديوم) و بدأ أكسدة الايثانول عند تطبيق جهد -0.4 فولت. ان هذا الحفاز الثلاثي و أيضا الحفاز المحتوي على بلاديوم و ذهب و نيكل يقدمون بدائل ناجحة و جدية لاستبدال البلاتين و يمكنهم تسهيل الانتقال الي تقنية منعدمة الكربون لإنتاج الكهرباء بشكل مستدام

Seismic anisotropy and mantle flow beneath Africa and Arabia

In spite of numerous studies, the mechanisms for the rifting, uplifting, and volcanism on the African plate remain enigmatic. The most popular hypotheses proposed for explaining these tectonic phenomena involve edge-driven small-scale mantle convection and the thermal or dynamic effects of one or more mantle plumes. In this study we use continental scale shear-wave splitting (SWS) measurements to provide additional constraints on the various models of rifting, uplifting, and volcanism of the Cameroon Volcanic Line (CVL) and the Arabian plate. The splitting of P-to-S converted phases at the core-mantle boundary on the receiver side (XKS including PKS, SKKS, and SKS) is one of the most effective approaches to constrain convective mantle flow patterns. A robust procedure involving automatic and manual batch processing to reliably assess and objectively rank shear-wave splitting parameters were used. The resulting 1532 pairs of splitting parameters show a NNE dominated fast direction. Spatial distribution of the splitting parameters in the CVL and Arabia is not consistent with the edge-driven small-scale mantle convection hypothesis, the mantle plume hypothesis, fossil fabrics formed by past tectonic events, or the fabric-forming process due to the absolute plate motion relative to the deep mantle. The research suggests that the progressive thinning of the lithosphere through basal erosion by the flow leads to decompression melting is responsible for the formation of the CVL, and olivine lattice preferred orientation in the upper asthenosphere associated with the northward motion of the African plate since 150 Ma, most likely causes the observed anisotropy across the Red Sea. --Abstract, page iv

A systematic approach for developing course learning outcomes to fulfill accreditation requirements in Malaysia

Writing appropriate learning outcomes is crucial to course design. Properly written outcomes aids the design of other course elements such as delivery methods and assessment. This paper proposes a systematic approach for writing learning outcomes. The proposed procedure takes advantage of the hierarchical structure of the programme building components. When applied, the procedure helps meet some of the accreditation requirements imposed by the Malaysian Engineering Accreditation Council such as explicit assessment of programme outcomes. Key to success is the careful mapping between course components. Besides, the procedure simplifies course design consequently leading to continual improvement. The procedure can be applied to wide range engineering courses. It also gives more control on planning a balanced assessment

The impact of time and power allocation on the performance of the three-node decode and-forward relay channel

Relying has in use for decades to tackle some of the challenges of wireless communication such as extending transmitting distance, transmitting over rough terrains. Relaying also achieve diversity which was proposed recently as an effective means to combat channel fading. In this work, effect of time and power allocation on relay performance is studied. The channel considered is the three-node channel with half-duplex constraint on the relay. The relaying technique assumed is decode-and-forward. Mutual information is used as the criteria to measure channel performance whereas noise is assumed to be the primary channel impairment. After deriving suitable formula for the mutual information as a function of time and power allocation, numerical results are obtained. Results have shown that the importance of relaying is more apparent when more resources are allocated to the relay. It was also shown that quality of the source to destination link has direct impact on the decision to relay or not to relay. Relatively good source to destination channel makes relaying less useful. The opposite is true for the other two links, namely the source to relay channel and the relay to destination channel. When these two channels are good, relaying becomes advantageous