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01. PhD Thesis

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Open Access
Modelling of residential heat decarbonisation pathways in the republic of Kazakhstan
(Nazarbayev University School of Engineering and Digital Sciences, 2018-03) Kerimray, Aiymgul
Globally, buildings account for one third of final energy consumption and are a significant source of CO2 emissions. Concerns with unsustainable use of energy in buildings, growing greenhouse gases emissions and energy poverty challenges all require effective planning, strategies and actions from policy makers. Energy systems models together with scenario analysis are widely applied tools to aid decision making in energy planning and in the assessments of technology pathways. Studies and analyses using energy systems models tend to focus on energy transition pathways and neglect energy poverty, energy affordability and local pollution. In addition, they generally do not simultaneously incorporate spatial, building type and urban/rural detail. This thesis addresses this gap, by introducing the first sub-nationally disaggregated energy system model with regional detail, representation of the building types (detached, flat) urban/rural disaggregation, and analysis of energy poverty...
Open Access
IMPEDANCE BASED APTASENSOR FOR THE DETECTION OF MYCOBACTERIUM TUBERCULOSIS SECRETED PROTEIN MPT64
(Nazarbayev University School of Engineering and Digital Sciences, 2019) Sypabekova, Marzhan
Tuberculosis (TB) detection remains a significant healthcare issue in the developing world owing to a number of challenges. Current diagnostics are based on microbiological culturing, sputum smear microscopy, and nucleic acid amplification tests. These methods suffer from limitations such as batch to batch variations, frequent contaminations, low sensitivity, and the requirement for special facilities, expensive devises, reagents, and trained personnel. This thesis describes the development of the sensitive oligonucleotide-based aptasensor for the detection of TB biomarker MPT64 protein. The dissertation investigates the selection and use of ssDNA aptamers to detect MPT64 using the electrochemical impedance spectroscopy (EIS). Aptamers serve as bio-recognition elements in this study, and they have numerous advantages including cheap cost, ease of modification and long shelf life. The combination of aptamers with the EIS offers sensitive detection since the change in EIS signal can be recorded as the result of analyte binding event based not only on molecular interaction level but also on electron transfer levels. As the result 17 unique aptamer sequences were purified and analyzed. One aptamer with dissociation equilibrium constant KD of 8.92 nM was selected and the surface chemistry was optimized based on ssDNA aptamer modified with a long linker and 6-mercaptohexanol as a co-adsorbent at 1/100 ratio. The selected aptamer was further immobilized on an interdigitated microelectrode and connected to a portable potentiostat. The detection time for aptasensor was found to be 15 min. The aptasensor was tested on clinical samples and showed increased binding to TB (+) samples as compared to TB (-) samples. The integration of the aptasensor with the in house built fluidic chamber and liquid flow rate within chamber was also investigated. The work in this thesis is significant as it can contribute to the diagnosis of TB (non-invasive), monitoring of anti-TB treatment in infected people and hence to socio-economic development of the country. It is the first portable aptasensor which is developed using aptamers and EIS as a detection technique that can provide fast clinical sample analysis (reduced from 3 h to 15 min) as well as elimination of using of extra reagents, equipment, and personnel.
Open Access
OPTIMAL DESIGN AND CONTROL OF VARIABLE IMPEDANCE ACTUATED ROBOTS
(Nazarbayev University School of Engineering and Digital Sciences, 2019) Zhakatayev, Altay
In this thesis, the challenging problems of design and control of variable impedance actu ated robots are considered. The difficulties arise due to nonlinear dynamics, physical con straints of the system, and presence of additional actuators and nonlinear elastic/damping elements. As a result, we propose a control methodology, which takes into account system constraints and input bounds, guarantees system utilization to its full potential, and closely achieves the system’s target performance level. The thesis consists of seven chapters. The first chapter gives a broad introduction to the problem and provides the literature review. For example, differences between position-controlled robots and variable impedance actu ated robots are discussed, their corresponding advantages and disadvantages are presented and compared, past design and control solutions are reviewed, and the hypothesis is de scribed. The second chapter covers the proposed closed-loop control methodology for variable stiffness actuated robots. This chapter covers the general idea behind closed-loop control of variable impedance actuated robots using model predictive control, and it also includes simulations and experimental results. The augmentation of the variable stiffness robots with reaction wheels is described in chapter three. Specifically, the advantages of using reaction wheels to actuate the variable stiffness robots are discussed. This is fol lowed by a discussion of time-optimal control of variables stiffness robots in chapter four. This chapter presents and describes two time-optimal control problems: minimum time for target performance and minimum time for maximum performance. In chapter five energy optimal control of variable stiffness robots is described. In particular, three energy-optimal control problems are defined: maximum performance with limited energy, target perfor mance with minimum energy and maximum performance with minimum energy. Then chapter six contains successive linearization-based model predictive control of variable stiffness robots. The main idea of this chapter is that linearization might be beneficial for model predictive control of nonlinear systems due to a simpler model and the resulting smaller sampling time. Finally, chapter seven describes the potential impact of our research in the field of robotics and society.
Restricted
EVAPORATION AND WATER BALANCE OF SMALL ENDORHEIC LAKES IN SEMI-ARID NORTHERN KAZAKHSTAN
(Nazarbayev University School of Engineering and Digital Sciences, 2019) Yapiyev, Vadim
Approximately two thirds of global precipitation falling over continental surfaces is reverted to the atmosphere by terrestrial evaporation. Over the terrestrial surfaces, the difference between Precipitation-Evaporation (P-E) is stored as soil- surface- and groundwater and contributes to surface and sub-surface runoff that ultimately returns water back to the ocean by stream and groundwater flow. Chapter 1 sketches the global water cycle and underlines a relative importance of evaporation in endorheic basins. Endorheic basins (i.e., land-locked drainage networks) and their lakes can be highly sensitive to variations in climate and adverse anthropogenic activities, such as overexploitation of water resources. Chapter 2 provides a brief overview of one major endorheic basin on each continent, plus a number of endorheic basins in Central Asia (CA), a region where a large proportion of the land area is within this type of basin. In CA a substantial increase in irrigated agriculture coupled with negative climate change impacts have disrupted the fragile water balance for many endorheic basins and their lakes. Transboundary integrated land and water management approaches must be developed to facilitate adequate climate change adaptation and possible mitigation of the adverse anthropogenic influence on endorheic basins. Subsequently, the focus shifts to the endorheic lakes within Burabay National Nature Park (BNNP), Northern Kazakhstan (the main focus of this thesis). These endorheic lakes have been drying out during the last one hundred years or so with a public perception that the water level decrease accelerated in the past few decades.
Open Access
Enhanced cognitive radio with energy harvesting and non-ortohogonal multiple access
(Nazarbayev University School of Engineering and Digital Sciences, 2019-04-10) Arzykulov, Sultangali
The increasing demand for wireless applications is making radio spectrum scarce. Meantime, studies show that the assigned spectrum is not thoroughly utilized. The cognitive radio (CR) technology is proposed as a feasible key technology to solve issues related to the spectrum scarcity. CR can improve the spectrum utilization by reusing the unused spectrum occupied by licensed users. Introduction of CR networks produces two kinds of interference: interference from the CR network (secondary network) to the primary network (PN) and the interference among secondary users. All unwanted interference should be adequately managed in order not to jeopardize the performance of the PN and at the same time improve the performance of CR systems. Interference alignment (IA) is a promising technique that can efficiently manage interference. One of the aims of this thesis is to mitigate the interference by deploying multiple antennas at both transmitter and receiver sides in order to improve the performance of CR networks. The rapid growth of data-hungry wireless applications is forcing us to perform energy harvesting (EH) from external power sources for the next-generation of wireless communication systems. Especially, CR networks, where receiver nodes need advanced hardware to process a large amount of data, require higher energy consumption. Thus, another goal of the current thesis is to investigate simultaneous wireless information and power transfer (SWIPT) in CR networks in the presence of intra- and inter-network interference over various channel state conditions. Firstly, a cooperative CR network is investigated over the general α−µ fading channel. The contribution of this study is mainly described by the exact closed-form expression for the outage probability (OP) of secondary users, which clearly shows how the outage saturation paradigm appears when the interference level at primary receiver is applied. Secondly, the proposed cooperative CR is extended by applying multiple-input multiple out (MIMO) antennas and an IA technique to deal with intra- and inter-network interference. The negative effect of interference at both primary and secondary receivers is mitigated by using precoding and interference suppression beamforming matrices. The management of interference at primary receivers allows secondary transmitters to increase the transmit power level. Moreover, the instantaneous capacity performance is assessed for the same CR system by applying two EH methods, i.e., time-switching (TS) and power-splitting (PS). Then, the optimal values of TS and PS portions are determined for different channel state information (CSI) scenarios. In addition, the effect of imperfect CSI on bit error rate and capacity performance is provided. Finally, we jointly study a cooperative CR and non-orthogonal multiple access (NOMA), where we derive closed-form expressions for the OP of NOMA secondary destination users for detect-and-forward and amplify-and-forward relaying techniques. Furthermore, power allocation factors for different distances of secondary NOMA users are found to satisfy OP fairness for all users. In addition, the proposed CR-NOMA network model is further studied with enabled SWIPT technology.
Open Access
REMOVAL OF MERCURY AND IODIDE FROM WATER USING FLY ASH DERIVED ZEOLITES AND NANOCOMPOSITES
(Nazarbayev University School of Engineering and Digital Sciences, 2019-06) Tauanov, Zhandos
With growing issue of the abundance of coal fly ash throughout the world that occupy landfills by creating both environmental and health problems, the requirement for an effective utilization method is constantly growing. Another issue that also needs to be tackled is the contamination of water with hazardous metals and radioactive ions, such as Hg2+ and I-. There is a huge interest of research community in conversion of coal fly ash into zeolites and composites. The impetus is on the optimization of its production process and modification with silver nanoparticles. This, however, requires a thorough understanding of coal fly ash zeolitization conditions and mechanisms. The preferred route of the synthesis of zeolites is the hydrothermal treatment of coal fly ash in a strong alkali solution at elevated temperatures, followed by doping of silver nanoparticles. The process involves several parameters, such as reaction temperature, time, the concentration and L/S ratio, Si/Al ratio in coal fly ash. These parameters appear to have an arbitrary effect on the yield of zeolite and the nanocomposite produced thereof. We propose a conversion model using the fuzzy system and optimize the zeolitization process. The model is designed and developed, using the data, both from literature and experiments, and is later optimized to provide accurate inferences. Further, the doping of silver nanoparticles to produce nanocomposites and using the novel nanocomposite for efficient remediation of Hg2+ and I- from water to study the mechanism by multiple advanced characterization methods....
Open Access
DESIGN AND ENGINEERING OF ADVANCED SI-BASED THIN FILM ANODE MATERIALS FOR LI-ION BATTERIES
(Nazarbayev University, School of Engineering and Digital Science, 2019-06-17) Mukanova, Aliya
Lithium-ion batteries (LIBs) are a versatile way of energy conversion and storage. Thin film batteries are the next generation of Li-ion battery technology with the thickness of tens μm and aimed to power a diverse range of microdevices. In order to increase the storage possibility, i.e. capacity, of such batteries, new high capacity electrode materials should be developed. Silicon-based materials are the most promising anodes due to the highest theoretical capacity and a low potential. However, the current drawbacks of Si such as significant volume expansion, electrical contact loss, and low conductivity impede its practical application in LIBs and commercialization. In this doctoral thesis, the research has been performed in two main directions in order to improve the existing microbatteries and find a way to develop a stable Si-based thin film electrode. The first direction is an investigation of novel silicon carbide thin film (3C-SiC) with a cubic lattice as an anode for LIBs. The advanced method of "single" particle measurement for studying the electrochemical properties of an individual microparticle provided the new data which allowed suggesting the mechanisms of lithiation/delithiation in 3C-SiC film. The use of XRD, TEM, XPS, Raman spectroscopy confirmed that there was no degradation of the 3C-SiC crystal lattice. The obtained results demonstrated that there are in two possible reasons of 3C-SiC thin film electrochemical activity, an intercalation or a capacitance. The second direction is the design of the three-dimensional (3D) amorphous Si (a-Si) thin film anode. The improvement of a-Si thin film anode was achieved through studying the effects of substrate surface condition, dopants incorporation, electrolyte additive and addition of graphene (GF) underlayer. The designed n-type doped porous a-Si thin film and 3D a-Si/GF anode exhibited high electrochemical performance in the lithium cells for several hundred cycles.
Open Access
PERFORMANCE OPTIMIZATION OF NEUROEVOLUTION FOR IMPROVED PROGNOSIS OF THE BREAST CANCER
(Nazarbayev University School of Engineering and Digital Sciences, 2020) Abdikenov, Beibit
Cancer is the second largest cause of mortality, responsible for one in every six deaths globally. Cancer has a significant socio-economic impact and its global cost is estimated to be close to $150 billion. Breast cancer is the most common female cancer and its high incidence places it among Kazakhstan’s most challenging public health problems. Advances in computing and sensing technologies and increased storage availability means that vast quantities of data are now available. While the data is sure to help practitioners understand what causes breast cancer and the best treatment approaches, the number of oncologists understanding its use is limited. Accurate and reliable prognoses are increasingly difficult because of the enormous amounts of data about breast cancer and the low survival rates. The available data’s heterogeneity adds to the challenges for data analytics posed by sheer data volume. Moreover, categorical variables in the heterogeneous dataset require accurate pre-processing if enhanced interpretation is to make progress towards prognosis possible. An advanced research in estimating the missing values in databases is also introduced in this thesis work. Rigorous research efforts have brought about the development of a novel entity embedding scheme based on neural networks capable of addressing effectively the encoding of categorical variables with high cardinality during the presented research. Employing our proposed scheme, it is now possible to represent the categorical variables as real values in high-dimensional space capable of greatly improved interpretation. Neuroevolution, which is a Meta heuristic approach, has been suggested through our work as a robust way of modelling prognosis from the breast cancer database. Neuroevolution also results in multiple equitable solutions of DNNs (Deep Neural Networks) thereby providing users with many options to choose from. Neuroevolution performance has been optimized using the EAs (Evolutionary Algorithms), namely, MOEA/D, NSGAIII, and SPEA2, but this research revealed a number of limitations in existing EAs and so this thesis proposes an improved EA: FIEA (Fuzzy Inspired Evolutionary Algorithm) which uses a fuzzy analytical approach to perform multi-criteria optimization and is also instrumental in selecting a final DNN model from the Pareto optimal set. This approach also provides insight into how the hyper-parameters control accuracy, sensitivity, F1 and other performance metrics. This is a change from traditional approaches which apply DNNs as a black box. The interpretability improved in this way can be used to advance or adjust DNNs’ behaviour and there is evidence that FIEA-optimized DNNs perform better than other algorithms described in the literature.
Open Access
NOVEL MARKER FOR RHEUMATOID ARTHRITIS DISEASE ACTIVITY
(Nazarbayev University School of Engineering and Digital Sciences, 2020) Myngbay, Askhat
RATIONALE: Rheumatoid arthritis (RA) is a chronic autoimmune disease, characterized by pain in affected joints, stiffness, and symmetrical synovitis. Synovial membrane inflammation of diarthrodial joints is a distinctive feature of RA, leading to articular damage, decline in motility and eventually complications, such as cardiomyopathy, neurologic and metabolic disorders. Currently available biomarkers are not satisfactory in terms of monitoring disease activity of RA. AIM: The objective of this study is to show Collagen triple helix repeat containing 1 (CTHRC1) protein`s potential in monitoring RA disease activity HYPOTHESIS: CTHRC1 is a potential biomarker for assessing RA disease activity. The diagnosis of RA depends primarily on clinical assessments. Serology tests routinely used in RA diagnosis are Anti-citrullinated peptide antibody (ACPA) and Rheumatoid factor (RF) level determination in serum/plasma. However, the value of RF for assessing RA remains debatable, because it is also detected in connective tissue diseases, chronic infections, malignancy and in healthy individuals. In comparison, ACPA’s are present in the peripheral blood of almost 80% of RA patients with higher diagnostic specificity. However, in our study ACPA was not associated with disease activity in patients with established diagnosis of RA. Demand for quantitative assessment of disease activity in RA for the improvement of disease diagnosis, prognosis and management is still high. Here I had proposed that the CTHRC1 is a marker of differential diagnosis of RA from OA, ReA and showed high potential to be used to monitor disease activity. METHODS: For this clinical cross sectional study in total 148 individuals with established diagnosis of RA (57), Osteoarthritis (OA-65), Reactive arthritis (ReA-12) and healthy volunteers (14) were recruited. All patients were undergoing treatment at the time of enrollment. Prior collecting and testing plasma samples of patients, they were clinically assessed, including current status, number of swollen and tender joints, tested for complete blood count parameters, current level of RF and ACPA, and also MRI and X-ray of knee joints were performed. Collected plasma samples were tested for the levels of CTHRC1, pro-inflammatory cytokines, such as interleukin 1 beta (IL-1b), interleukin 6 (IL-6), interleukin 8 (IL-8), and interferon gamma (IFN g). All collected data were analyzed including comparison among groups, correlation within each group and Receiver operating characteristic (ROC) analysis was further performed to assess the diagnostic value of CTHRC1. CONCLUSION: This study showed high levels of CTHRC1 protein in RA plasma. These results indicate that CTHRC1 can be used as a novel plasma biomarker to evaluate disease activity in RA. Also it can be used for the differential diagnosis of RA from similar joint diseases, such as OA and ReA.
Open Access
DEVELOPMENT OF A PATIENT-SPECIFIC OCULAR MODEL FOR RISK ASSESSMENT OF GLAUCOMA DEVELOPMENT AND PROGRESSION
(Nazarbayev University School of Engineering and Digital Sciences, 2020) Kharmyssov, Chingis
Glaucoma is the leading cause of blindness worldwide. Once the retinal ganglion cell axons are lost they cannot be cured. Therefore, preventative risk assessment measures are important. To be able to perform these tasks, one needs to understand the mechanism behind the axonal blockage that leads to glaucoma. Biomechanical factors are thought to play a role in glaucoma, but the specific mechanism is not explored. In a Finite Element (FE) ocular model, the complex shape of the optic nerve components can be modeled and relevant mechanical quantities, such as stresses and strains due to intraocular (IOP) and/or intracranial (ICP) pressure, can be estimated and their effects assessed. Furthermore, optic nerve head (ONH) morphology and especially lamina cribrosa shape and properties, which are tightly linked to Glaucoma onset and development, vary greatly between individuals. This consequently suggests the development of patient-specific FE ocular models. A method to generate patient-specific ocular models was contrived based on the geometry extracted from Optical Coherence Tomography (OCT) scans. Specifically, retinal layers were segmented using intensity and graph-based algorithms and the segmented layers were then reconstructed with a thin plate spline method. Finally, solid models were created from the reconstructed surfaces and meshed with tetrahedral elements. The geometric details of the generated ONH model correlate well with those of generic models from pertinent literature and special attention was paid to meshing so that the optic nerve region of the ocular model exhibits analysis-suitable element quality. The suggested reconstruction method is semiautomatic and although we aimed to fully capture the complete ONH region, some anatomical structures, which are generally considered relevant and important, could not be extracted from OCT images in vivo. These include the pia arachnoid complex (dura mater and pia mater) that contains cerebrospinal fluid material and is considered to exert ICP. These were handled by carrying out a parametric analysis, using generic models with linear elastic material properties, to establish the degree of importance of the pia arachnoid complex. It was found that pia and dura mater properties can affect post laminar neural tissue and lamina cribrosa biomechanics. As it is currently infeasible to obtain high-quality patient-specific geometries for the pia arachnoid complex in vivo, we embed generic models of the pia and dura mater in our patient-specific ONH model. Viscoelastic material properties of dura mater and sclera were additionally retrieved from physical unidimensional tensile stress-relaxation tests. The influence of viscoelastic material properties at certain levels of ICP/IOP with a generic ocular model was examined, and results indicated, as expected, the importance of viscoelastic properties. Parametric analysis of patient-specific models was performed via the principal component analysis method deriving statistical shape models (SSM). Qualitative, quantitative and biomechanical assessments were performed with the aid of the generated SSM. For the biomechanical assessment, finite element modeling was employed and several patient-specific models, based on SSM shape modes, were generated and tested. We anticipate further enhancements and developments for this approach in the future. Based on the so far obtained results, we find evidence that patient-specific, anatomically detailed 3D ocular models allow for a better understanding of employed biomechanics and can benefit glaucoma risk assessment.
Open Access
MACROPOROUS CRYOGEL COMPOSITES FOR REMOVAL OF HEAVY METALS FROM AQUEOUS AND BIOLOGICAL MEDIA
(Nazarbayev University School of Engineering and Digital Sciences, 2020) Baimenov, Alzhan
The deficiency of clean water is intensely associated with poor health, poverty and a general decline in living standards. Water is important not only for life but it is also the main resource for food and crops production and is used in most industrial processes. In spite of the natural source of water contamination, a continuous rise of heavy metals discharges to aquatic bodies caused by fast industrial development over the last century has been observed. Heavy metals such Cd2+ and Hg2+ are of the most toxic and, as all heavy metals, have a tendency to accumulate in the food chain potentially causing serious health disorders. Another source of water contamination is the nuclear power plants. Among the harmful radionuclides discharged are the radioisotopes of I-, Cs+ and Sr2+. To improve the availability of clean water, low-cost and effective treatment methods must be developed to remove toxic metal ions. Several water treatment technologies are available with adsorption/ion-exchange combined to chelation/complexation are the most effective. In this work, highly effective adsorbents based on polymeric cryogels were developed for the removal of Cd2+ Hg2+, Sr2+, Cs+ and silver-modified forms for targeted removal of I-. Two types of macroporous cryogels were synthesized by free-radical co-polymerization of acrylate-based precursors with allylamine under sub-zero temperature conditions. The adsorption/ion exchange capacity of cryogels is due to the presence of key monomers, methacrylic acid and 2-acrylamido-2-methyl-1-propansulfonic acid. The cryogels were comprehensively characterized and used for the removal of the above mentioned ions from model solutions. Kinetics and equilibrium studies were conducted, models were applied and in combination to post-sorption characterizations potential removal mechanisms were proposed. Finally, the cryogels were tested under environmentally relevant conditions (tap water, river water and sea water) and compared to commercial adsorbents (zeolite Y, ion exchange resin and activated carbon) for the removal of Hg2+ showing excellent behavior. After successful experiments on water, cryogels were used as enterosorbents in animal experiments by using rats. The rats were poisoned with LD50 dose of metals and were treated by cryogels. The results showed high survival rate and an overall decline of concentration of metals in animal tissues. The discoveries of this work demonstrate that cryogelic sorbents have possible implementation in water treatment and as poisoning antidotes.
Open Access
DEVELOPMENT OF COST-EFFECTIVE COMPONENTS FOR DYE-SENSITIZED SOLAR CELLS
(Nazarbayev University School of Engineering and Digital Sciences, 2020-02) Baptayev, Bakhytzhan
The commercialization of dye-sensitized solar cells (DSSCs) has been hindered by relatively low efficiency and comparatively high cost of the PV. Hence, further development of DSSC field heavily depends on the bringing down of its cost and improvement of its power converting efficiency. Therefore, we focused on the development of cost-effective methods and components for improving the power converting efficiency (PCE) of DSSCs. In our work we have demonstrated that it is possible to modify the photoanode by using a simple cost-effective technic of surface doping of TiO2 via soaking the photoanode in 50 mM In3+ aqueous solution with acidic pH. Indium surface doping of TiO2 film resulted in remarkable suppression of charge recombination and improvement of VOC (from 0.77 V of the reference undoped TiO2 sample to 0.80 V of In surface doped TiO2 sample) leading to 18% efficiency increase. The overall result is comparable with bulk In doped TiO2 solar cells and demonstrate effectiveness of surface doping technic. Moreover, we developed a new strategy of suppressing porphyrin dye aggregation in DSSCs which is based on axial complexation of central Zn metal of the porphyrin dyes with pyridine compounds via D-A bonding. This enables the use of long alkyl-chain free porphyrins that are economical and easier to synthesize compared to traditional analogs. Thus, a simple structured ZnP porphyrin dye axially coordinated with 4,4’-bipyridine ligand reduced dye aggregation on TiO2 surface and led to over 40 % improvement of cell PCE compared to uncoordinated ZnP sensitized cell. Finally, we have prepared several novel Pt-free counter electrodes from less expensive materials like orange fiber derived carbon embedded cobalt sulfide nanoflakes (OFC@CoxSy-300) and ternary Cu-Co-S sulfides (CuxCoySz-3 and CuCo2S4) which are prepared at lower temperature than Pt-based counter electrode. The developed new composite counter electrode OFC@CoxSy-300 based cell outperformed conventional Pt-based DSSCs by almost 7 % in power converting efficiency due to good electrocatalytic activity of the product. Solvothermally prepared ternary copper-cobalt-sulfides as CuxCoySz-3 and nanostructured flower-shaped CuCo2S4 counter electrodes demonstrated better electrocatalytic activity than Pt CE leading to improved fill factor and photocurrent. Thus 11 % and 14 % enhancements in PCE compared to Pt-based DSSCs were observed in solar cells made of CuxCoySz-3 and CuCo2S4, respectively. The CuCo2S4 CE demonstrated excellent stability during aging test for 1000 h.
Open Access
PERFORMANCE ANALYSIS OF FUTURE COMMUNICATIONS SYSTEMS UNDER RESIDUAL HARDWARE IMPAIRMENTS
(Nazarbayev University School of Engineering and Digital Sciences, 2020-04) Tlebaldiyeva, Leila
Cognitive radio (CR) and millimeter wave (mmWave) communication are two potential technologies for future wireless communication systems to meet ever-increasing consumer data demand. The significant advantage of CR is its ability to improve spectrum utilization by introducing spectrum management paradigms between primary and cognitive users. An even more significant enabling technology for future communications is mmWave communication that offers enormous bandwidth at mmWave frequency bands. Low-grade transceiver hardware is often utilized in modern communication systems to lower the cost of potential networks. The residual hardware distortion noise originating from high rate and low-grade transceiver hardware is a vital parameter to consider while designing reliable systems. This dissertation work pursues to model residual transceiver hardware impairments by using the statistical additive Gaussian model, which is mathematically tractable and can be embedded in complex system configurations. In this thesis, we first develop a system model for a dual-hop decode-and-forward underlay CR relay network operating under residual hardware impairments and derive a closed-form expression for the outage probability performance. Moreover, this work provides useful discussions on the design aspects of wireless communication systems in terms of the outage probability given residual transceiver noise level and fading parameters of channel. Secondly, we study the spectrum sensing technique by employing an improved energy detector (ED) under residual hardware constraints. We present a novel test statistic for improved ED that accounts for residual distortion noise when the fading statistics of the received signal follows the 􀀀 distribution. Moreover, we derive closed-form expressions for the probabilities of detection and false alarm and the area under the receiver operating characteristic curve (AUC) for additive white Gaussian and Nakagami-m fading channels. Our work proposes a new diversity concept of p-order-law combining and p-order-law selecting schemes to combat the adverse effect of residual hardware impairments. Thirdly, our study develops an analytical framework for analog beamforming deviceto- device mmWave communication constrained by residual hardware impairments and other random impairments such as multi-user interference, inter-beam radio frequency (RF) power leakage, and imperfect channel state information (CSI). We perform in-depth outage probability and ergodic capacity analysis for the proposed system model. Finally, we propose to implement a maximum sub-array transmission (MST) scheme built on a hybrid beamforming structure that enables multi-user communication and high outage probability and ergodic capacity performance. The MST diversity suffers from RF power leakage and transceiver distortion noise that are addressed in this work. The hardware impaired communication systems transmit at considerably lower rates than the ideal ones, and, therefore, our research emphasizes the importance of residual distortion modeling.
Open Access
FABRICATION AND INTEGRATION OF ONE- AND TWO-DIMENSIONAL MATERIALS FOR ADVANCED NANOSCALE DEVICES
(Nazarbayev University School of Engineering and Digital Sciences, 2020-04) Kemelbay, Aidar
As the miniaturization of electronic circuits reach physical limits, new materials and physical phenomenon need to be exploited to further increase device density and efficiency. A number of approaches have been proposed. One of the common approaches in the scientific community is the search to understand and practically fabricate novel materials and devices at the nanoscale. In this work, we present several nanofabrication processes and unique synthetic methods that we have developed to achieve novel 1D and 2D semiconducting, dielectric, and ferroelectric materials, relevant for the integration in advanced nanoscale devices. In particular, single-walled carbon nanotubes (CNTs) were synthesized and integrated into bottom- and top-gate field effect transistors. We demonstrated a novel CNT surface pretreatment method that enables uniform and conformal ALD coating of suspended nanotubes with various dielectric materials. Obtained all-oxide TiO2-Al2O3 compound high-k dielectric showed an improved dielectric permittivity. Another class of semiconductor that we investigated, was transition metal dichalcogenide (TMD) layered thin film materials. We developed a novel synthetic method that we termed “lateral conversion,” which was used to grow WS2, WSe2, MoS2 and MoSe2 van der Waals materials. In this method, a metal-oxide layer is converted into TMD material using a chalcogenation reaction that propagates laterally between two inert silica layers. The method results in a multilayer structure with TMD material covered by a capping layer that protects it from the environment, contamination, and oxidation. It was shown that the technique provides control over the TMD position, shape, and thickness with sub-micron precision, at wafer scale. A third class of materials that was studied in this work are hafnia-based ferroelectric thin films. The ability to integrate ferroelectric thin films into electronic devices with atomic layer deposition (ALD) has been a long-standing dream. With the discovery of ferroelectric properties in ALD hafnium oxide, the realization of some advanced architecture devices became one step closer. Here, ALD was used to synthesize Hf0.5Zr0.5O2, with precisely tuned stoichiometry. Next, the crystallization of initially amorphous Hf0.5Zr0.5O2 was performed using widely researched rapid thermal annealing (RTA), as well as by using intense pulsed ion beams (IPIBs), which was done for the first time for such application. RTA-produced ferroelectric thin films, showed successful orthorhombic phase stabilization and annealing-temperature-dependent remnant polarization, whereas early IPIBs experiments demonstrated the ability to crystallize HfO2, ZrO2 and Hf0.5Zr0.5O2 thin films, inducing different crystallographic phases.
Open Access
RECEIVER ARCHITECTURES AND ALGORITHMS FOR NON-ORTHOGONAL MULTIPLE ACCESS
(Nazarbayev University School of Engineering and Digital Sciences, 2020-05) Manglayev, Talgat
Multiple access (MA) schemes in cellular systems aim to provide high throughput to multiple users simultaneously while utilising the network resources efficiently. Traditionally, each user in the network is assigned a fraction of resources (such as slots in time or frequency) to operate so that multi-user interference is avoided. These schemes are named as ‘orthogonal multiple access’ (OMA) and are the basis of most cellular standards – from the earliest first generation up to the current fourth-generation systems. Non-orthogonal multiple access (NOMA) on the other hand is a novel method that allows all the users in the network to operate in the entire available spectrum at the same time which enables significant improvement in the system throughput. While providing increased throughput, NOMA requires high computational power in order to implement sophisticated interference cancellation algorithms at each user terminal, as well as power allocation schemes at the base station. As a potential candidate for the fifth-generation networks (5G), NOMA must meet certain requirements, and computational efficiency is essential for reduced latency. Recently graphics processing units (GPUs), which were initially intended for outputting images to display, appeared as an alternative to multi-core central processing units (CPUs) for general-purpose computing. GPUs have thousands of cores with approximately three times less frequency than a CPU core. With their numerous advantages in executing heavy and time-consuming computations in parallel, GPUs have become attractive platforms in a variety of fields. The overall aim of this research is to significantly increase the scientific understanding and technical knowledge on NOMA. This is achieved by exploring and developing novel methods, models, designs and techniques that will facilitate the implementation of NOMA for future generation networks. First, the achievable data rates for individual users are demonstrated in a successful interference cancellation (SIC) based NOMA network. These results were compared against the conventional orthogonal MA schemes with optimum power allocation and varying fairness. In addition, a further investigation was carried out into the deficiency of SIC receivers which can occur when a user in the networks attempts to decode other users’ signal. Presented in the analysis is the findings from the experimental process where the decoding order of a user with a mismatched signal was observed as well as the significant impact on the computation time. The decoding time-difference between correct and mismatched decoding order as a detection method of deficiency or fraudulence in the network is then discussed. Next, a comparison is presented between the computational times of the SIC receiver with another popular interference cancellation scheme named ‘parallel interference cancellation’ (PIC). This was done using different platforms specifically for an uplink NOMA system. The results showed that the computation time of PIC scheme is significantly lower than SIC on the GPU platform even for a very large number of available users in the network. Then, the execution time of NOMA with SIC in the uplink of a cellular network with user clustering was examined. User clustering is a popular method in NOMA networks that eases the sophisticated resource allocation and network management issues. While most works found in the literature review concentrate on the joint optimisation of user grouping and resources, this research project focused on processing the signal detection of each cluster in parallel on the GPU platform at the base station. Following this, parallel interference cancellation (PIC) was implemented and compared with the existing SIC on both CPU and GPU platforms for uplink NOMAOFDM. Architectures of the receivers were modified to fit into parallel processing. GPU was found applicable to speed up computations in NOMA based next-generation cellular networks outperforming up to 220 times SIC on CPU. Finally, the research presents the power allocation problem from artificial intelligence (AI) perspective and propose a method to predict the power allocation coefficients in a downlink NOMA system. The results of the research show a close-to-optimal sum rate with about 120 times reduced computation time. The achieved results decreases the network latency and assist NOMA to meet 5G requirements.
Open Access
Fabrication and Properties of Nickel Nanotubes Synthesized by Template-Assisted Electrochemical Deposition
(Nazarbayev University School of Engineering and Digital Sciences, 2020-09-20) Kalkabay, Gulnar
One of the important topics today is the controlled synthesis of nanostructured materials, in particular nanotubes (NT) or nanowires, the interest in which is due to the great potential for their use as devices in microelectronics [1], catalysts [2], biomedicine [3], sensors [4], etc. The interest in metal nanotubes is due to the great prospects for practical applications associated with a larger specific surface area for nanotubes compared to nanowires, the possibility of obtaining single-domain isotropic walls along the entire length and the unique magnetic properties. Although a large number of recent research aimed at perfecting methods for producing metal nanowires/nanotubes and studying their properties, there are still many blank spots and unresolved issues [5]. In particular, the controlled synthesis of nanotubes with a predetermined isotropic wall thickness along the entire nanotube length, well-ordered crystalline structure, controlled orientation of domain structures, and high corrosion resistance to external influences remains unsolved and research active. Nickel nanowires and nanotubes deserve special attention due to their unique structural, conductive and magnetic properties. While the popular template-assisted electrochemical deposition of nickel nanowires is not difficult, the synthesis of highly ordered nickel nanotubes with controlled properties needs further research. Although there are many works devoted to the Ni nanotubes synthesis, showing that Ni NTs strongly depends on fabrication method and parameters, mechanism of NT growth is still not fully explored. The aim of this work is comprehensive study of template-assisted electrochemical deposition of nickel nanotubes with controlled isotropic geometry of the diameter and wall thickness. The driving motive is the search for optimal fabrication conditions of Ni nanotubes with a high degree of structural ordering, as well as establishing controlled nanotubes synthesis with given structural parameters and aspect ratio. Electrochemical deposition of Ni nanotubes was studied at various synthesis conditions, including the composition and temperature of the electrolyte, the difference in applied potentials, alcohol additives and the acidity of the solution. Detailed model for the Ni nanotube growth and formation of nanotube walls in the pores of polymer templates is developed. According to the model, at the initial stage of Ni nanotube formation the transverse component of growth rate prevails, which is responsible for nanotube wall growth in width. At the next stage characterized by a decrease in current density due to the depletion of the electrolyte solution the nanotube grows uniformly in both transverse and longitudinal directions. Next, the concentration of metal ions dominate near the top end of the nanotube, resulting that the longitudinal component of the growth rate of the nanotubes prevails and the tubes grow predominantly along the walls of the pores. The influence of various factors such as difference in the applied potential, temperature and the level of acidity of the electrolyte solution on the wall thickness, grain sizes and the degree of texturing of nanotubes, was evaluated. In particular, it was found that an increase in the applied potentials in the range of 1.5 – 2.0 V and the deposition temperature range 35-50°C leads to the formation of nanotubes with one dominant direction of texture orientation and to the increase in the number of defects in the nanotubes crystal structure due to an increase in the average crystallite size and the degree of microstresses. Adding ethanol to the electrolyte increases Ni nanotubes conductivity due to an improvement in the crystal structure and decrease in amorphous inclusions. It was found that lowering the acidity level of the solution leads to a decrease in the nanotubes wall thickness and the size of crystallites. Based on the conducted experiments, the most optimal parameters for the synthesis of nanotubes were selected: the difference of the applied potentials is 1.5-1.75 V, pH = 3 and the electrolyte temperature is 25 °C. These parameters were used to fabricate Ni nanotubes for experiments to study the influence of the geometry of the template matrix on the structure of the resulting nanotubes, as well as for corrosion tests experiments. The main magnetic characteristics of fabricated Ni nanotubes were explored. Ni nanotubes arrays coercivity and squareness ratio exhibit unusual dependence on nanotubes diameter: it rises for samples with nanotubes 100 to 300 nm diameters and falls down for nanotubes 400 and 500 nm diameters. Ni nanotubes corrosion resistance to external influences of aggressive media was studied. The kinetics of degradation of Ni nanotubes was determined depending on the acidity of the solution and time being in the solution. It has been shown that the main mechanism of degradation of nickel nanotubes is the formation of the metastable phase of nickel oxide, which decays due to instability, which leads to partial destruction of the structure. It was found that the speed of degradation of nanotubes depends on the degree of crystallinity of the initial nanotubes, as well as the acidity of the solution.
Restricted
Multiphase Flow Simulation using Lattice Boltzmann Model incorporating a Crossover Equation of State
(Nazarbayev University School of Engineering and Digital Sciences, 2020-09-25) Kabdenova, Bagdagul
Multiphase flows are involved in many practical applications such as CO2 injection in porous media initially saturated with brine water, spray combustions, oil and gas, nuclear power plants and other industrial and agricultural processes. Conventional Computational Fluid Dynamics (CFD) techniques, which assumes the fluid as a continuum, faces challenges in tracking the interface in multiphase flows. This is majorly due to the fact that the generic phase interface forms and is maintained because of inter-molecular forces that originate at meso- or micro-scales. An effective representation scale of such forces at continuum can be achieved only by models that come at a high computational cost. In this work, we use a multiphase Lattice Boltzmann Model (LBM) which offers a meso-scale solving framework with the purpose to study multiphase systems and the corresponding fluid behavior at the given conditions in pore-scale domains. More specifically, we apply the multiphase Shan-Chen’s pseudopotential Lattice Boltzmann Model due to its proven ability to capture the sharp interface in intricate microscopic domains and to its efficient parallelization. In pseudopotential LBM, the phase separation is maintained thanks to the introduction of a body force depending on the gradient of a scalar function, called effective mass. By choosing the specific forms of the effective mass, different equations of state (EoS) can be incorporated into the model, including the most popular cubic ones such as the Van der Waals, the Peng-Robinson or the Carnahan-Staring. Such cubic EoS are known for their high accuracy when applied to fluids at subcritical conditions. However, these EoS fail in representing the non-analytical behavior of a generic fluid in the vicinity of the critical point evidenced by long-scale density fluctuations. This limitation can be amended by using a crossover formulation of the considered EoS. The crossover EoS uses non-analytic scaling laws asymptotically close to the critical point, while away from the critical point it becomes the original classical EoS; besides in the limit of zero density it reproduces ideal gas behavior. Accurate prediction of fluid properties at super/near-critical conditions is important for different applications including the flow in porous media where surface tension plays a major role.In this thesis, a crossover formulation of a generic EoS is incorporated into the pseudopotential LBM. That significantly extends the capability of pseudopotential LBM to model fluid properties closer and above the critical point. This work also shows simulation results for multicomponent flows in complex geometries. This is motivated by the goal to build a model which can accurately predict the supercritical CO2 flow in brine-saturated porous media, as found in deep saline aquifers. Specifically, two-component flow in a T-mixer passing cylindrical obstacles and immiscible multicomponent flow in a channel to study fingering effects are presented.
Embargo
Design of Aptamer-Functionalized Substrates: Towards Breast Cancer Stem Cell Isolation and Detection
(Nazarbayev University School of Engineering and Digital Sciences, 2020-09-25) Bekmurzayeva, Aliya
Cancer relapse and metastasis remain one of the main problems in treatment of breast cancer (BC). A small subset from bulk tumor cells, called breast cancer stem cells (BCSCs), is found to be responsible for cancer initiation, recurrence, metastasis and resistance to therapy. Therefore, specifically detecting these cells is an important task in BC diagnosis and management. The main goal of this thesis was to develop aptamer-functionalized substrates which in the future could be used for BCSC isolation and detection. To achieve this objective, the project has been divided into three tasks as will be discussed below. Given small number of available specific ligands against BCSC and their importance in BC, one of the tasks of this thesis was to select and characterize new single stranded DNA aptamers against BCSC. Fluorescently activated cell sorting was utilized to enrich oligonucleotides bound to cells while imaging flow cytometry was used to study their binding. Two of the selected aptamers showed increased binding to target cells than to control cells; however, their binding affinity was not fully studied. They are one of the few ligands reported to date to bind BCSC and were selected against well characterized BCSC derived from a triple-negative breast cancer. Another task of this work was to functionalize stainless steel (SS) wire with aptamers specific to BCSC in order to alleviate the problem of “fishing out” such rare events as BCSC. For this, the wire electropolishing conditions were determined. In order to attach ligand, silanization by electrodeposition was optimized thus determining the most suitable applied potential (–0.8 V), pH of the solution (pH 5 and 5.5) and heat treatment temperature after electrodeposition (130°C). The silanized surface was then immobilized with commercially available CD44 aptamers (marker of BCSC) after being activated by a crosslinker to build a functionalized surface. This wire was able to capture the target cells in an in vitro test. The wires were analyzed by such surface characterization methods as atomic force microscopy (AFM), cyclic voltammetry (CV), scanning electron microscopy (SEM) and fluorescence microscopy. In addition, using the same surface chemistry as in functionalized SS wire, another platform – fiber Bragg grating (FBG) sensor has been explored with a well-studied ligand-analyte pair (thrombin and thrombin-binding aptamer). For this, FBG was made sensitive to the surrounding refractive index (RI) by chemical etching and calibrated in solutions with known RI before being functionalized with aptamers. Then the sensor demonstrated increased Bragg wavelength shift when tested in different thrombin concentrations. In conclusion, the main goal of this thesis – developing aptamer-functionalized substrates with a perspective application in BCSC isolation and detection – was achieved, although each task of the project was completed with different level of success. Binding of aptamers selected against BCSC could not be fully studied. However, they are one of the few reported aptamers against an important subtype of BC. Besides, only a small fraction of aptamer candidates were characterized and better binders could still be revealed. Wires functionalized with CD44 aptamers, after further study, have a potential to be used for in vivo capture of target cells in the blood flow, since their small size allows the insertion as a standard guidewire in biomedical devices. For fabricated EGBF biosensor, selective detection of clinically relevant concentration of thrombin has been demonstrated. The used functionalization method allows a facile fabrication of the sensor not requiring thin film fabrication.
Open Access
Optimization of Kazakhstan Coals Gasification Process in the Circulating Fluidized Bed Gasification Process
(Nazarbayev University School of Engineering and Digital Sciences, 2020-09-25) Tokmurzin, Diyar
Coal, coke, and semi-coke are critical feedstock for the production of iron and steel. For over a century coke and semi-coke has been produced from coal using the slow pyrolysis thermal treatment process in fixed bed coke ovens. The coke-oven slow pyrolysis process produces vast quantities of gaseous and liquid emissions associated with coal tar which are not and sometimes cannot be always captured and recycled. Contrary to this, fast pyrolysis associated with gasification processes produces less tar. In this work a novel method incorporating fast pyrolysis to produce semi-coke using circulating fluidized bed partial coal gasification is experimentally studied. The present study includes an investigation of coal fast devolatilization properties, a pilot scale experimental proof of concept, and optimization of the process. Fast pyrolysis characteristics are explored using a wire mesh reactor and a thermobalance reactor experiments, and semi-coke is produced using a high-volatile Shubarkol coal in a custom-built atmospheric lab-scale reactor comprising a riser, a cyclone, a loop seal, and fitted with mechanized systems for semi-coke retrieval. The reactor is operated autothermally, at temperatures varying from 700 to 1000oC. The experimental results indicate the operating conditions for maximum product output. The product characterization revealed that semi-coke gains distinctive characteristics, including lower density, lower volatile matter content, lower ash content, higher porosity, and higher crystallinity of the carbon matrix. In addition, a Computational Fluid Dynamics simulation employing the Eulerian-Lagrangian multiphase particle-in-cell approach reveals fluidization properties and further optimization opportunities.
Open Access
Chitosan Composite Cryogel With Polyelectrolyte Complexes for Tissue Regeneration Application
(Nazarbayev University School of Engineering and Digital Sciences, 2020-09-28) Sultankulov, Bolat
Chitosan has been a successful choice for tissue-engineering applications over the last few decades. Chitosan is a natural polysaccharide with excellent properties for tissue engineering applications, such as biodegradability, biocompatibility, and antimicrobial activity. Available free amine groups in its structure allows further chemical modifications, so new properties could be added for specific tissue engineering application. This dissertation highlights the advances made in biomaterial production and describes novel polyelectrolyte-based (PEC) cryogel that contains chitosan (CHI) and heparin (Hep). We will discuss the preparation of new cryogel material and its physico-chemical properties. Additionally, the measurement of biological activity would be addressed in vitro and in vivo. In particular, the cryogels obtained will be tested to induce differentiation of mesenchymal stem cells (rat BMSCs) derived from rat bone marrow into the osteogenic lineage. Additionally, this study will show potential uses of novel PEC-based cryogel for skin regeneration in vitro and in vivo, demonstrating the broad application of established scaffolding. The research in this dissertation is important because it demonstrates the efficacy of PEC cryogels for tissue engineering applications. This is the first PEC cryogel scaffold based on CHI-Hep made from a one-step reaction with effective loading of growth factors and cytokines.