Nazarbayev University Repository (NUR) is an institutional electronic archive designed for the long-term preservation, aggregation, and dissemination of scientific research outcomes and intellectual property produced by the Nazarbayev University community and affiliated organizations.

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    Item type:Item, Access status: Open Access ,
    Effect of KCl/NaCl Composition on Fines Migration Initiation: Experimental Study and DLVO Analysis
    (Nazarbayev University School of Mining and Geosciences, 2026-04-23) Zhomart, Aruzhan; Pourafshary, Peyman
    Fines migration is a major cause of formation damage in sandstone reservoirs. During water injection, changes in brine chemistry can destabilize naturally occurring fines such as kaolinite, clay fragments, and fine quartz. As a result fines detach, migrate with the fluid, and accumulate in pore throats. This accumulation leads to reductions in permeability, increase in pressure drop, and decline in injectivity and hydrocarbon recovery. Since sandstone reservoirs account for a large share of global hydrocarbon production, controlling fines migration remains an important reservoir engineering challenge. The onset of fines migration depends on the physicochemical stability of the sand-fine-brine (SFB) system. Grain surfaces and fines are usually negatively charged in quartz-rich sandstone, and their interaction is governed by the balance between attractive van der Waals and repulsive electrical double-layer (EDL) forces. Fines tend to detach from the rock surface when repulsion becomes dominant over attraction forces. This behavior is described by DLVO theory which connects this interaction energy to salinity, brine composition, zeta potential, and particle size. Among these factors, salinity and brine composition are especially important as they control EDL thickness. Lower salinity increases repulsion, and below the critical salt concentration (CSC), fines migration starts. This study investigates the effect of NaCl/KCl brine composition on the critical salt concentration (CSC) for fines migration initiation in Berea sandstone. Approach used combines zeta potential measurements, machine learning prediction, DLVO modelling, and coreflooding validation. Zeta potential was measured for mixed NaCl/KCl brines using a Malvern Zetasizer, while the 100% KCl case was predicted using machine learning approach. TabM model was chosen to predict zeta potential values for KCl as it has the best performance among nine tested models (test R2 = 0.6983, test RMSE = 7.79 mV). These values were used as inputs to a low- rate DLVO model, which predicted a CSC of 0.03 M for KCl brines. Coreflooding experiments on a Berea sandstone core samples using KCl brines of decreasing concentration (0.20 M-0.01 M) were carried out to validate the DLVO prediction for 100% KCl brines. UV-Vis absorbance analysis of the effluent and pressure drop analysis indicated that a significant increase in fines concentration occurred between 0.03 M and 0.04 M KCl, placing the experimentally observed CSC in the range between 0.03 and 0.04 M. This result is in close agreement with the DLVO-predicted value of 0.03 M that confirms the reliability of the modeling approach. Since 100 % KCl case validated DLVO Model predictions, further models with different compositions of NaCl/KCl brines were constructed. DLVO modeling predicted CSCs of 0.05 M for 80/20 NaCl/KCl, 0.045 M for 50/50, and 0.04 M for 20/80, revealing a clear decrease in CSC with increasing KCl content. The findings show that brine ion composition, even within monovalent systems, has a strong effect on fines stability. Systems dominated by KCl are more likely to experience fines mobilization than systems dominated by NaCl at the same salinity, which has practical importance for injection water design and formation damage control in sandstone reservoirs.
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    Item type:Item, Access status: Open Access ,
    Mechanical Characterization of FDM Printed Fiber Reinforced Polymer
    (Nazarbayev University School of Engineering and Digital Sciences, 2026-04-30) Amanzholova, Sabina; Maulet, Yerassyl; Mukametkali, Aibat; Talamona, Didier; Perveen, Asma
    Additive manufacturing with fused filament fabrication (FFF) is becoming a highly adopted method for production of lightweight polymer components with complex geometries. Regardless of its advantages, the process still involves dimensional deviations that limit the application of the polymers produced by FFF in accuracy-sensitive fields. PETG (Polyethylene terephthalate glycol) can be reinforced with continuous carbon fiber (CCF). The reinforcement further enables the enhancement of stiffness and strength but the influence of CCF on dimensional accuracy and mechanical performance of printed parts were not yet deeply investigated. The project measures the geometrical accuracy and the mechanical behavior of PETG and continuous carbon fiber reinforced PETG (CCF -PETG) printed using an Anisoprint A4 system. A dimensional analysis on the artifact 80 x 80 x 4 mm was held using ZEISS T-scan. First experiments used a Taguchi based experimental design to determine the influence of printing speed and extrusion temperature on dimensional accuracy. Initial results show that CCF-PETG always depicts a smaller dimensional deviation on all axes compared to PETG. These advancements have been correlated with slower print speeds, the greater rigidity of continuous fibers, and alleviated thermal deformation during co-extrusion. Tensile testing of continuous carbon fiber-reinforced PETG (CCF-PETG) specimens printed at 0°, 15°, 30°, 45°, and contour-only fiber orientations revealed a strong dependence of mechanical properties on fiber angle, with 0° specimens achieving the highest mean ultimate tensile strength of 269.3 MPa and a Young's modulus of 44.62 GPa. Both UTS and stiffness decreased monotonically with increasing fiber angle. These results confirm that fiber orientation is an important parameter governing the mechanical performance of FFF-printed CCF-PETG, and that contour-only configurations provide substantial strength and stiffness improvements over the unreinforced polymer.
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    Item type:Item, Access status: Embargo ,
    Quantum-Safe Authentication Protocol For Smart-City Based Iot Devices
    (Nazarbayev University School of Engineering and Digital Sciences, 2026-05-03) Semenov, Pavel; Ghani, Anwar; Chaudhry, Shehzad Ashraf
    Authentication key exchange protocols enable communication entities to agree on a shared secret value over an insecure public channel. Conventional authentication key exchange protocols rely on mathematical problems that can be broken by Shor's algorithm executed on a quantum computer. This study proposes a quantum-safe authentication protocol that uses the CRYSTALS-Kyber post-quantum cryptographic primitive and Elliptic-Curve Cryptography. The primary application area of the proposed scheme is smart-city infrastructures and resource-constrained environments. This protocol is motivated by the scheme of Parameswarath et al. Their solution lacks perfect forward secrecy and protection against denial-of-service attacks, and it is practically infeasible. The proposed scheme addresses those limitations. The scheme presented in this study was analyzed in the Real-or-Random formal security model. Additionally, the formal security verifier ProVerif was used to verify security properties, including message integrity, strong authentication, and session key secrecy. Moreover, this document includes an informal security analysis that demonstrates a wide range of security features. This study also contains a performance analysis of the proposed scheme along with other recently published schemes. The total computation costs at the IoT device and the Cloud Server are 0.2014 and 0.216 milliseconds, respectively. The storage cost for both the IoT device and the Cloud Server is 2545 bytes. The total communication cost for authentication messages is 1687 bytes. Finally, the presented protocol was simulated using the NS3 network simulator. The measured values for Packet Delivery Ratio, End-to-End delay, and Throughput in a scenario with 40 devices are 99.07\%, 3.54 ms, and 162.92 kbps, respectively.
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    Examining the Nature, Effectiveness and Implications of English Private Tutoring among Undergraduate Students at an EMI University in Kazakhstan
    (Nazarbayev University Graduate School of Education, 2026-04-16) Marat, Amina; Hajar, Anas
    This study examines the nature, effectiveness, and broader implications of fee-charging English private tutoring (EPT) among undergraduate students enrolled in English-medium instruction (EMI) programmes in Kazakhstan. While fee-charging private tutoring has been widely associated with school-level exam preparation, no research has examined how EMI university students engage with and evaluate EPT in higher education contexts in Kazakhstan. Addressing this lacuna, the study adopts a qualitative design to investigate eight undergraduate university students’ motivations for participation in EPT, their learning experiences, and their perceptions of EPT’s role in supporting academic and linguistic development. Using a phenomenological study approach, data were collected through narrative writing and individual semi-structured interviews with 8 EMI undergraduate students who had recently engaged in EPT. The analysis was guided by Benson’s (2011) framework of language learning beyond the classroom, focusing on the dimensions of location, formality, locus of control, and pedagogy. The findings reveal that students primarily engage in EPT as a strategic response to the linguistic and academic demands of studying in English. Participants reported improvements in speaking confidence, vocabulary, grammatical accuracy, and their ability to manage EMI-related academic tasks. EPT was consistently valued for its personalised, flexible, and goal-oriented nature, which contrasted with the perceived limitations of formal university instruction. However, the study also highlights critical concerns about unequal access, inconsistent tutor quality, and inadequate regulation. Participants recognised that while EPT can enhance learning opportunities, it may simultaneously reproduce educational inequalities. Overall, the study argues that EPT should be understood not merely as supplementary support but as a significant and structured response to institutional gaps and the growing marketisation of English in Kazakhstan’s higher education system. Pedagogically, the findings suggest that EMI institutions should integrate more personalised, student-centred, and language-supportive practices into formal curricula to reduce reliance on private tutoring. In addition, policymakers and educators should consider developing quality assurance frameworks and professional guidelines to enhance the effectiveness and equity of EPT provision. Keywords: shadow education, English private tutoring (EPT), English-medium instruction (EMI), undergraduate students, Kazakhstan, qualitative inquiry
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    Metal-Doped Porous Titanium Dioxide Particles For Photocatalytic Degradation Of Emerging Pollutants And Hydrogen Evolution
    (Nazarbayev University School of Engineering and Digital Sciences, 2026-05-05) Imanzhussip Serkul; Poulopoulos, Stavros; Atabaev, Timur
    This research addresses critical global challenges in environmental protection and sustainable energy by synthesizing and characterizing multifunctional, metal-doped porous titanium dioxide (pTiO2) nanoparticles. The study’s objective was to develop an effective photocatalyst for dye degradation, hydrogen evolution, and antibacterial treatment. Porous TiO2 was successfully synthesized using a solvothermal method, followed by systematic optimization of the diethylenetriamine (DETA)/titanium isopropoxide (TIP) precursor ratio and annealing temperature. The optimal bare pTiO2 sample (50 µL DETA / 200 µL TIP, annealed at 400 °C) exhibited a pure anatase crystalline phase and a high BET surface area of 199.67 m²/g. This bare catalyst achieved an exceptional total removal efficiency of 98.28% for Methylene Blue (MB) dye in 90 minutes, comprising 49.97% dark adsorption and 48.31% photocatalytic degradation. To enhance its performance and multifunctionality, the optimized pTiO2 was doped with silver (Ag) up to 1 wt%. The resulting Ag-pTiO2 composite demonstrated superior catalytic activity across both key applications. In hydrogen evolution experiments via sodium borohydride (NaBH₄) hydrolysis, the 4 mg optimal dosage of 1% Ag-pTiO2 yielded the highest total hydrogen volume (31.3 mL in 20 minutes), surpassing the bare pTiO2 (25.0 mL) and the uncatalyzed reaction (25.63 mL). Furthermore, the Ag-pTiO2 exhibited markedly superior broad-spectrum antimicrobial efficacy compared to the bare material against both Staphylococcus aureus (Gram-positive) and Escherichia coli BL21 (Gram-negative). Under light activation, the Ag-pTiO2 achieved complete bacterial growth suppression for S. aureus at approximately 0.125 mg/mL. This enhanced activity is attributed to a synergistic mechanism where the silver dopant acts as an electron sink, minimizing electron-hole recombination and increasing the generation of lethal reactive oxygen species (ROS). By precisely tuning the precursor chemistry and silver dopant levels, this study provides a versatile platform for synthesizing high surface area pTiO2 that simultaneously addresses water purification, clean energy production, and pathogen control. These findings offer a scalable pathway for developing multifunctional nanomaterials capable of tackling complex, interlinked environmental and public health crises.