Now showing items 1-20 of 62659

    • Novel Materials Based on Poly(2-Oxazoline): Synthesis, Molecular Characterization, and Application in Drug Delivery

      Alkattan, Nedah S. (2023-06-01) [Dissertation]
      Advisor: Hadjichristidis, Nikos
      Committee members: Nunes, Suzana Pereira; Khashab, Niveen M.; Avgeropoulos, Apostolos
      Poly(2-oxazolines) (POxs) are a class of polymers that have gained significant interest in biomedical applications. POxs are mainly synthesized using living cationic ring-opening polymerization (CROP) under microwave irradiation. POxs are considered pseudo-polypeptides because they are similar to polypeptides. Nevertheless, they are more chemically stable than polypeptides due to the presence of tertiary amides. POxs The major goal of this research is to synthesize and characterize a novel well-defined amphiphilic block copolymer based on POxs. These amphiphilic block copolymers can comprise core cross-linked star polymers (CCS) or linear block copolymers. This research demonstrates and describes the synthesis of poly(2-methyl-2-oxazoline-b-poly(2,2'-(1,4-phenylene)bis-2-oxazoline)-co-(2-n-2-butyl-2-oxazoline)(PMeOx-b-P(PhenBisOx-co-ButOx) amphiphilic core cross-linked star polymers (CCS) based on POxs. The CCS polymers are synthesized via sequential CROP in two steps by synthesizing Poly(2-methyl-2-oxazoline) (PMeOx) as the living arms followed by cross-linking of the core 2, 2’-(1,4-phenylene)bis-2-oxazoline (PhenBisOx) as the cross-linker and 2-n-butyl-2-oxazoline (ButOx) as a hydrophobic monomer to form the core of the CCS polymers. In addition, this research will clarify the other kinds of amphiphilic copolymers based on aggregation-induced emission (AIE) fluorophores, tetraphenylethylene (TPE) as an initiator that have been synthesized by a combination of cationic and anionic ROP. First, the difunctional initiator TPE-(OH)2 was synthesized via McMurry coupling reaction. Then, two kinds of triblock copolymers, TPE-poly(2-methyl-2-oxazoline)-b-poly(ε-caprolactone) (TPE-(PMeOx-b-PCL)2) and TPE-poly(ε-caprolactone)-b-poly(2-methyl-2-oxazoline) (TPE-(PCL-b-PMeOx)2), were synthesized by altering the sequence of polymerization. The resulting polymers, CCS polymers and the triblock copolymers were loaded with the anticancer drug doxorubicin (DOX) and their in vitro properties, cytotoxicity, and drug release at different pH were studied. Furthermore, the resulting polymers were characterized by size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), dynamic light scattering (DLS), and transmission electron microscopy (TEM). All results in this research showed that the amphiphilic block copolymers, the CCS polymers and the triblock copolymers could be suitable carriers for drug delivery systems.
    • A scanning-to-incision switch in TFIIH-XPG induced by DNA damage licenses nucleotide excision repair

      Bralic, Amer; Tehseen, Muhammad; Sobhy, Mohamed Abdelmaboud; Tsai, Chi-Lin; Alhudhali, Lubna F.; Yi, Gang; Yu, Jina; Yan, Chunli; Ivanov, Ivaylo; Tsutakawa, Susan E; Tainer, John A.; Hamdan, Samir (Nucleic Acids Research, Oxford University Press (OUP), 2022-12-08) [Article]
      Nucleotide excision repair (NER) is critical for removing bulky DNA base lesions and avoiding diseases. NER couples lesion recognition by XPC to strand separation by XPB and XPD ATPases, followed by lesion excision by XPF and XPG nucleases. Here, we describe key regulatory mechanisms and roles of XPG for and beyond its cleavage activity. Strikingly, by combing single-molecule imaging and bulk cleavage assays, we found that XPG binding to the 7-subunit TFIIH core (coreTFIIH) stimulates coreTFIIH-dependent double-strand (ds)DNA unwinding 10-fold, and XPG-dependent DNA cleavage by up to 700-fold. Simultaneous monitoring of rates for coreTFIIH single-stranded (ss)DNA translocation and dsDNA unwinding showed XPG acts by switching ssDNA translocation to dsDNA unwinding as a likely committed step. Pertinent to the NER pathway regulation, XPG incision activity is suppressed during coreTFIIH translocation on DNA but is licensed when coreTFIIH stalls at the lesion or when ATP hydrolysis is blocked. Moreover, ≥15 nucleotides of 5′-ssDNA is a prerequisite for efficient translocation and incision. Our results unveil a paired coordination mechanism in which key lesion scanning and DNA incision steps are sequentially coordinated, and damaged patch removal is only licensed after generation of ≥15 nucleotides of 5′-ssDNA, ensuring the correct ssDNA bubble size before cleavage.
    • Melatonin as a Foliar Application and Adaptation in Lentil (Lens culinaris Medik.) Crops under Drought Stress

      Yasmeen, Sidra; Wahab, Abdul; Saleem, Muhammad Hamzah; Ali, Baber; Qureshi, Kamal A.; Jaremko, Mariusz (Sustainability, MDPI AG, 2022-12-07) [Article]
      Here, we grow two different varieties of lentil (lentil-2009 and lentil-93) under different drought levels and with different applications of melatonin. Increasing the levels of soil water deficit significantly decreased numerous morphological and biochemical characteristics, including shoot length, total chlorophyll content, and transpiration rate, in both varieties of lentil. Contrastingly, drought stress increased the concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2), and electrolyte leakage, an indicator of oxidative damage to membrane-bound organelles. The activities of enzymatic antioxidants and osmolytes were initially increased up to a drought level of 80% water field capacity (WFC) but gradually decreased with higher levels of drought stress (60% WFC) in the soil. At the same time, the results also showed that the lentil-2009 is more tolerant to drought stress than lentil-93. The negative impact of drought stress can be overcome by the application of melatonin. Melatonin increased plant growth and biomass, photosynthetic pigments, gas exchange characteristics, and enhanced the activities of various enzymatic and non-enzymatic antioxidants and proline content by decreasing oxidative stress. We conclude that foliar application of melatonin offers new possibilities for promoting lentil drought tolerance.
    • A Volatile Solid Additive Enables Oligothiophene All-Small-Molecule Organic Solar Cells with Excellent Commercial Viability

      Hu, Dingqin; Tang, Hua; Karuthedath, Safakath; Chen, Qianqian; Chen, Si; Khan, Jafar Iqbal; Liu, Heng; Yang, Qianguang; Gorenflot, Julien; Petoukhoff, Christopher; Duan, Tainan; Lu, Xinhui; Laquai, Frédéric; Lu, Shirong (Advanced Functional Materials, Wiley, 2022-12-07) [Article]
      The commercial viability of all-small-molecule (ASM) organic solar cells (OSCs) requires high efficiency, long-term stability, and low-cost production. However, satisfying all these factors at the same time remains highly challenging. Herein, a volatile solid additive, namely, 1,8-dichloronaphthalene (DCN) is demonstrated to simultaneously enhance the power conversion efficiency (PCE) and the storage, thermal as well as photo stabilities of oligothiophene ASM-OSCs with concise and low-cost syntheses. The improved PCEs are mainly due to the DCN-induced morphology control with improved exciton dissociation and reduced non-geminate recombination. Notably, the PCE of 16.0% stands as the best value for oligothiophene ASM-OSCs and is among the top values for all types of binary ASM-OSCs. In addition, devices incorporating DCN have shown remarkable long-term stability, retaining over 90% of their initial PCE after dark storage aging of 3000 h and thermal or light stressing of 500 h. The findings demonstrate that the volatile-solid-additive strategy can be a simple yet effective method of delivering highly efficient and stable oligothiophene ASM-OSCs with excellent commercial viability.
    • Comparative Anticancer Potentials of Taxifolin and Quercetin Methylated Derivatives against HCT-116 Cell Lines: Effects of O-Methylation on Taxifolin and Quercetin as Preliminary Natural Leads

      Mohammed, Hamdoon A.; Almahmoud, Suliman A.; El-Ghaly, El-Sayed M.; Khan, Firdos Alam; Emwas, Abdul-Hamid M.; Jaremko, Mariusz; Almulhim, Fatimah F.; Khan, Riaz A.; Ragab, Ehab A. (ACS Omega, American Chemical Society (ACS), 2022-12-07) [Article]
      Six flavonoids present in Pulicaria jaubertii, i.e., 7,3′-di-O-methyltaxifolin (1), 3′-O-methyltaxifolin (2), 7-O-methyltaxifolin (3), taxifolin (4), 3-O-methylquercetin (5), and quercetin (6), were tested for their anticancer activities. The methylated flavonoids, compounds 1–3 and 5, were evaluated for their anticancer activities in comparison to the non-methylated parent flavonoids taxifolin (4) and quercetin (6). The structures of the known compounds were reconfirmed by spectral analyses using 1H and 13C NMR data comparisons and HRMS spectrometry. The anticancer activity of these compounds was evaluated in colon cancer, HCT-116, and noncancerous, HEK-293, cell lines using the MTT antiproliferative assays. The caspase-3 and caspase-9 expressions and DAPI (4′, 6-diamidino-2-phenylindole) staining assays were used to evaluate the apoptotic activity. All the compounds exhibited antiproliferative activity against the HCT-116 cell line with IC50 values at 33 ± 1.25, 36 ± 2.25, 34 ± 2.15, 32 ± 2.35, 34 ± 2.65, and 36 ± 1.95 μg/mL for compounds 1 to 6, respectively. All the compounds produced a significant reduction in HCT-116 cell line proliferation, except compounds 2 and 6. The viability of the HEK-293 normal cells was found to be significantly higher than the viability of the cancerous cells at all of the tested concentrations, thus suggesting that all the compounds have better inhibitory activity on the cancer cell line. Apoptotic features such as chromatin condensation and nuclear shrinkage were also induced by the compounds. The expression of caspase-3 and caspase-9 genes increased in HCT-116 cell lines after 48 h of treatment, suggesting cell death by the apoptotic pathways. The molecular docking studies showed favorable binding affinity against different pro- and antiapoptotic proteins by these compounds. The docking scores were minimum as compared to the caspase-9, caspase-3, Bcl-xl, and JAK2.
    • Are carotenoids the true colors of crop improvement?

      Moreno, Juan C; Al-Babili, Salim (New Phytologist, Wiley, 2022-12-07) [Article]
    • Analysis of interface mode localization in disordered photonic crystal structure

      Goyal, Amit Kumar; Husain, Mudassir; Massoud, Yehia Mahmoud (Journal of Nanophotonics, SPIE-Intl Soc Optical Eng, 2022-12-06) [Article]
      A disordered photonic crystal (D-PhC) structure is analyzed to study the interface mode localization characteristics. The design comprises a bilayer-disordered PhC structure, where layers are arranged in Thue–Morse sequence (TMS). The impact of local symmetric substructures on eigenstates coupling is also considered over a wider wavelength range. The mode hybridization study is carried out for varying refractive index contrast values of TMS structures at an operating wavelength of 550, 632.8, and 750 nm, respectively. The dispersion analysis confirms the localization of bulk guided, and edge-guided modes for different incidence angles at the structural local resonators. Further, increasing the RI contrast value leads to generation of hybrid interface modes of very high electric field intensity. Thus, showing its potential applications in both sensing and light guiding applications. Moreover, because of the higher surface electric field intensity this structure can also be used for fluorescence-based detection and surface-enhanced Raman spectroscopy as well.
    • Pristine biochar performance investigation to remove metals in primary and secondary treated municipal wastewater for groundwater recharge application

      Fseha, Yohanna Haile; Sizirici, Banu; Yildiz, Ibrahim; Yavuz, Cafer Tayyar (PloS one, Public Library of Science (PLoS), 2022-12-06) [Article]
      In this study, pristine biochar derived from date palm at 500°C was used in batch reactors (simulating blending adsorbent in aeration tank) and fixed-bed columns (simulating holding adsorbent in fixed-bed reactors). The removal performance of the biochar was assessed toward single and mixed-metal solutions as well as synthetic primary and secondary treated wastewater for copper (Cu2+), iron (Fe2+), nickel (Ni2+) and zinc (Zn2+). The order of maximum adsorption capacities of the metal ions at pH 7 followed: Fe2+ (2.92/2.94 mg/g)>Cu2+(2.69/2.78 mg/g) >Zn2+(2.03/2.19 mg/g)>Ni2+(1.69/1.02 mg/g) in single/mixed-metal solutions and Zn2+(2.91/11.26 mg/g)>Fe2+(0.60/5.29 mg/g)>Cu2+(0.56/5.05 mg/g)>Ni2+(0.13/2.02 mg/g) in synthetic primary/secondary treated wastewater. Blending biochar in aeration tank reduced metal concentrations. The metal ion concentrations in the final effluent were below the World Health Organization drinking water limits (2, 0.3, 0.1 and 3 mg/L for Cu2+, Fe2+, Ni2+ and Zn2+, respectively) suggesting that treated secondary wastewater can be spread into potable aquifers following disinfection. The Freundlich and the Pseudo-second order models fit best the batch experimental data. Experimental data from column analysis fit well to the Thomas model. The adsorption of metal ions on the surface of biochar was confirmed by Scanning electron microscopy, Energy dispersive X-ray studies, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Desorption studies using different eluents demonstrated the reusability potential of the studied biochar.
    • MoStGAN: Video Generation with Temporal Motion Styles

      Shen, Xiaoqian (2022-12-06) [Poster]
      Video generation remains a challenging task due to spatiotemporal complexity and the requirement of synthesizing diverse motions with temporal consistency. Previous works attempt to generate videos in arbitrary lengths either in an autoregressive manner or regarding time as a continuous signal. However, they struggle to synthesize detailed and diverse motions with temporal coherence and tend to generate repetitive scenes after a few time steps. In this work, we argue that a single time-agnostic latent vector of style-based generator is insufficient to model various and temporally-consistent motions. Hence, we introduce additional time-dependent motion styles to model diverse motion patterns. In addition, a extbf{Mo}tion extbf{St}yle extbf{Att}ention modulation mechanism, dubbed as MoStAtt, is proposed to augment frames with vivid dynamics for each specific scale (i.e., layer), which assigns attention score for each motion style w.r.t deconvolution filter weights in the target synthesis layer and softly attends different motion styles for weight modulation. Experimental results show our model achieves state-of-the-art performance on four unconditional $256^2$ video synthesis benchmarks trained with only 3 frames per clip and produces better qualitative results with respect to dynamic motions.
    • Learning The Rules of Minihack Environment Using DreamerV2

      Alkhayat, Hussain (2022-12-06) [Poster]
      DreamerV2 is proven to be able to simulate a visually-dominated environments such as Atari games. However, is it able to simulate environments with hidden rules that are not visual? In this paper I will answer if the world-model of dreamerv2 is capable of learning non-visual rules of the environment minihack.
    • Therapeutic Properties of Vanadium Complexes

      Sharfalddin, Abeer A.; Al-Younis, Inas; Mohammed, Hamdoon A.; Dhahri, Manel; Mouffouk , Fouzi; Abu Ali, Hijazi; Anwar, Md. Jamir; Qureshi, Kamal A.; Hussien, Mostafa A.; Alghrably, Mawadda; Jaremko, Mariusz; Alasmael, Noura Salman; Lachowicz, Joanna Izabela; Emwas, Abdul-Hamid M. (Inorganics, MDPI AG, 2022-12-06) [Article]
      Vanadium is a hard, silver-grey transition metal found in at least 60 minerals and fossil fuel deposits. Its oxide and other vanadium salts are toxic to humans, but the toxic effects depend on the vanadium form, dose, exposure duration, and route of intoxication. Vanadium is used by some life forms as an active center in enzymes, such as the vanadium bromoperoxidase of ocean algae and nitrogenases of bacteria. The structure and biochemistry of vanadate resemble those of phosphate, hence vanadate can be regarded as a phosphate competitor in a variety of biochemical enzymes such as kinases and phosphatases. In this review, we describe the biochemical pathways regulated by vanadium compounds and their potential therapeutic benefits for a range of disorders including type 2 diabetes, cancer, cardiovascular disease, and microbial pathology.
    • Current switching of the antiferromagnetic Néel vector in Pd/CoO/MgO(001)

      Yang, M.; Li, Q.; Wang, T.; Hong, B.; Klewe, C.; Li, Z.; Huang, X.; Shafer, P.; Zhang, F.; Hwang, C.; Yan, W. S.; Ramesh, R.; Zhao, W. S.; Wu, Y. Z.; Zhang, Xixiang; Qiu, Z. Q. (Physical Review B, American Physical Society (APS), 2022-12-05) [Article]
      Recently, the electrical switching of antiferromagnetic (AFM) order has been intensively investigated because of its application potential in data storage technology. Herein, we report the current switching of the AFM Néel vector in epitaxial Pd/CoO films as a function of temperature. Using combined measurements of Hall resistance (HR) and x-ray magnetic linear dichroism (XMLD) below and above the AFM Néel temperature, we unambiguously identified both magnetic and nonmagnetic contributions to the current-induced HR change. Through magnetic field-induced HR measurements, we quantitatively determined the percentage of current-induced CoO spin switching. Further, we showed that the thermal effect dominated the CoO magnetic switching more in samples with a thinner Pd layer and that samples with a thicker CoO layer required higher thermal activation for current-induced magnetic switching. These results provide a clear and comprehensive picture of current-induced AFM spin switching across the AFM Néel temperature.
    • Continuous and discrete data assimilation with noisy observations for the Rayleigh-Bénard convection: a computational study

      Hammoud, Mohamad Abed El Rahman; Le Maître, Olivier; Titi, Edriss S.; Hoteit, Ibrahim; Knio, Omar (Computational Geosciences, Springer Science and Business Media LLC, 2022-12-05) [Article]
      Obtaining accurate high-resolution representations of model outputs is essential to describe the system dynamics. In general, however, only spatially- and temporally-coarse observations of the system states are available. These observations can also be corrupted by noise. Downscaling is a process/scheme in which one uses coarse scale observations to reconstruct the high-resolution solution of the system states. Continuous Data Assimilation (CDA) is a recently introduced downscaling algorithm that constructs an increasingly accurate representation of the system states by continuously nudging the large scales using the coarse observations. We introduce a Discrete Data Assimilation (DDA) algorithm as a downscaling algorithm based on CDA with discrete-in-time nudging. We then investigate the performance of the CDA and DDA algorithms for downscaling noisy observations of the Rayleigh-Bénard convection system in the chaotic regime. In this computational study, a set of noisy observations was generated by perturbing a reference solution with Gaussian noise before downscaling them. The downscaled fields are then assessed using various error- and ensemble-based skill scores. The CDA solution was shown to converge towards the reference solution faster than that of DDA but at the cost of a higher asymptotic error. The numerical results also suggest a quadratic relationship between the ℓ2 error and the noise level for both CDA and DDA. Cubic and quadratic dependences of the DDA and CDA expected errors on the spatial resolution of the observations were obtained, respectively.
    • Vegetation assessments under the influence of environmental variables from the Yakhtangay Hill of the Hindu-Himalayan range, North Western Pakistan

      Ullah, Hameed; Khan, Shujaul Mulk; Jaremko, Mariusz; Jahangir, Sadia; Ullah, Zahid; Ali, Iftikhar; Ahmad, Zeeshan; Badshah, Hussain (Scientific Reports, Springer Science and Business Media LLC, 2022-12-05) [Article]
      Vegetation structures and dynamics are the result of interactions between abiotic and biotic factors in an ecosystem. The present study was designed to investigate vegetation structure and species diversity along various environmental variables in the Yakhtangay Hills of the Hindu-Himalayan Mountain Pakistan, by using multivariate statistical analysis. Quadrat quantitative method was used for the sampling of vegetation. PC-ORD version 5 software was used to classify the vegetation into different plants communities using cluster analysis. The results of regression analysis among various edaphic variables shows that soil organic matter, total dissolved solids, electrical conductivity, CaCO3 and moisture contents shows a significant positive correlation with species abundance, while the soil pH has inverse relationship with plant species abundance. Similarly, species richness increases with increase in soil organic matter, CaCO3 and moisture contents, while decrease with increase in soil pH, total dissolved solids and electrical conductivity (p < 0.05). The vegetation was classified into four major plant communities and their respective indicators were identified using indicator species analysis. Indicator species analysis reflects the indicators of the study area are mostly the indicators to the Himalayan or moist temperate ecosystem. These indicators could be considered for micro-habitat conservation and respective ecosystem management plans not only in the study area but also in other region with similar sort of environmental conditions.
    • Implementing structural equation modelling and multiple mediator models for management information systems

      Osman, Esam; Hardaker, Glenn; Glenn, Liyana Eliza (The International Journal of Information and Learning Technology, Emerald, 2022-12-05) [Article]
      Purpose Overall quantitative research aims to observe certain fundamental principles of logic and scientific frame of reasoning. There continues to be challenges on how quantitative research is conducted in the field of information systems. Design/methodology/approach Structured equation modelling (SEM) research identifies concerns about the standard of scientific enquiry method, the issue of the misconception of sustaining the consequent and the issue of collective validity. Therefore, rigor and robustness in instrument validity, constructs validity and path analysis validity maybe better achieved by attending to these three concerns. Measuring a multiple mediator construct in a hypothetical model continues to be a challenge for researchers in information systems research and related fields. Findings This paper aims to provide a thoughtful assessment of the contemporary issues of structural equation modelling methodology (SEMM), by providing rigid and robust SEMM that has several stages in specifying valid multiple mediators construct and the process to measuring in a path analysis model. This paper attempts to develop each stage of the methodology using relevant research to construct a methodology specified to test effects in multiple mediators in SEM using AMOS software. The methodology developed contains the two main phases; first is prior to data collection phase and the second phase is after the data collection, the use of this methodology design, for implementation, intended to support high methodological standards and subsequent quality in MIS research findings. Originality/value The research paper provides SEMM that has several stages in specifying valid multiple mediators construct and the process to measuring in a path analysis model.
    • Correct estimation of permeability using experiment and simulation

      Khirevich, Siarhei; Yutkin, Maxim; Patzek, Tadeusz (Physics of Fluids, AIP Publishing, 2022-12-05) [Article]
      Estimation of permeability of porous media dates back to Henry Darcy [H. Darcy, Les Fontaines Publiques de la Ville de Dijon (Victor Dalmont, 1856)], and its knowledge is essential in many scientific and engineering endeavors. Despite apparent simplicity of permeability measurements, the literature data are scattered, and this scatter not always can be attributed to the precision of experiment or simulation or to sample variability. Here, we demonstrate an excellent agreement (<1%) between experiments and simulations, where experimental results are extensive and stable, while flow is simulated from first principles, directly on three-dimensional images of the sample, and without fitting parameters. Analyzing when experiments and simulations agree reveals a major flaw affecting many experimental measurements with the out-of-sample placement of pressure ports, including industry standards. The flaw originates from (1) incorrect calculation of the applied pressure gradient, (2) omitting virtual part of the measured system, and (3) pressure loss at the sample–tube contact. Contrary to common wisdom, the relative magnitude of (3) is defined by the sample–tube diameter ratio and is independent of the size of sample pores. Our findings are applicable to a wide range of permeability measurements, including geological-sample-type (Hassler cell) and membrane-type. The reported pressure loss (3) also affects two-phase flow measurements, such as capillary pressure estimation. Removing or taking the flaw into account advances the understanding and control of flow-related processes in complex geometries.
    • Development of a steady detonation reactor with state-to-state thermochemical modeling

      Vargas, J.; Mével, R.; Lino da Silva, M.; Lacoste, Deanna (Shock Waves, Springer Science and Business Media LLC, 2022-12-05) [Article]
      In recent years, several studies have been dedicated to modeling of detonations including assumptions of thermal non-equilibrium. Modeling using two-temperature models has shown that non-equilibrium affects detonation dynamics. However, the deployment of state-to-state models, one of the foremost non-equilibrium modeling tools, in detonation modeling remains under-explored. In this work, we detail the implementation of a STS model of N2 and O2 in a Zel’dovich–von Neumann–Döring reactor for a mixture of H2–air. Certain modifications to the usual theory and models must be performed before the deployment of aforementioned model, namely in the thermodynamics formulation. Additionally, since most codes are not compatible with STS models, a validation of an in-house code is carried out against CHEMKIN. Results indicate that the multi-temperature approach adopted in earlier works is likely not appropriate to model the internal distribution function of O2 and therefore should be used with caution. A comparison of an estimated cell width with experimental values confirms the potential of the STS framework for a more accurate detonation modeling.
    • Effects of low-temperature chemistry on direct detonation initiation by a hot spot under engine conditions

      Luong, Minh Bau; Im, Hong G. (Proceedings of the Combustion Institute, Elsevier BV, 2022-12-05) [Article]
      This study investigates the effect of low-temperature chemistry (LTC) on the minimum runup distance, lm, of direct detonation initiation by an autoignitive hot spot under engine conditions. A newly predictive model is proposed to determine an a priori lm . The temperature and pressure increase and the radical build-up prior to the main ignition resulting from LTC are incorporated in the model that allows a better prediction of ignition modes. A series of 1D simulations are performed by varying the initial temperature, the hot spot size and its temperature difference at constant-volume and engine conditions. DME (ethanol) is used to represent a two (single) stage ignition fuel. It was found that taking the transient evolution of the mixture state as an initial condition to the ZND model results in a better representative exothermic characteristic length scale, which exhibits a strong linear correlation with lm regardless of fuel types over a wide range of conditions. The LTC oxidation is found to reduce lm by approximately a factor of two for the low-temperature cases, leading to a comparable value of lm to that of the high-temperature cases. It was also found that the ignition modes are better predicted by identifying an alternative characteristic length scale based on the variation of ignition delay time Tig within its range of monotonic distribution. For a hot spot that has temperature variation spanning across the NTC regime, the runup distance was found to be shortened by approximately a factor of two, such that a longer hot-spot size is required to form detonation. In addition, a better prediction of ignition modes was achieved by defining the normalized front speed as a statistical mean for each runup-distance element than that determined at the midpoint of a hot spot.
    • Complex systems engineering theory is a scientific theory

      Feron, Eric (2022-12-05) [Technical Report]
      The proper design of complex engineering systems is what allows corporations and nations to distinguish themselves in a global competition for technical excellence and economic well-being. After quickly reviewing the central elements of systems engineering, we map all of them onto concepts of mathematics such as theorems and proofs, and onto scientific theories. This mapping allows the protagonists of complex systems engineering and design to map existing techniques from one field to the others; it provides a surprising number of suggestions for improving system design, especially system architecture, by leveraging advanced mathematical and / or scientific concepts in a productive way. In return, mathematicians and computer scientists can benefit from this bridge by bringing to bear many of their automated theorem provers to help with the design of complex systems. Clear classifications of what is "hard" and what is "easy" in mathematical proofs can instantaneously map onto similar appreciations for system design and its reliance on engineers’ creativity. Last, understanding system design from the mathematical-scientific viewpoint can help the system engineer think more maturely about organizing the multitude of tasks required by systems engineering.
    • Experimental investigation of the stability and emission characteristics of premixed formic acid-methane-air flames in a swirl combustor

      Zhu, Xuren; Wang, Shixing; Elbaz, Ayman M.; Younes, Mourad; Jamal, Aqil; Guiberti, Thibault; Roberts, William L. (International Journal of Hydrogen Energy, Elsevier BV, 2022-12-05) [Article]
      Formic acid (FA) is a potential hydrogen energy carrier and low-carbon fuel by reversing the decomposition products, CO2 and H2, back to restore FA without additional carbon release. However, FA-air mixtures feature high ignition energy and low flame speed; hence stabilizing FA-air flames in combustion devices is challenging. This study experimentally investigates the flame stability and emission of swirl flames fueled with pre-vaporized formic acid-methane blends over a wide range of formic acid fuel fractions. Results show that by using a swirl combustor, the premixed formic acid-methane-air flames could be stabilized over a wide range of FA fuel fractions, Reynolds numbers, and swirl numbers. The addition of formic acid increases the equivalence ratios at which the flashback and lean blowout occur. When Reynolds number increases, the equivalence ratio at the flashback limit increases, but that decreases at the lean blowout limit. Increasing the swirl number has a non-monotonic effect on stability limits variation because increasing the swirl number changes the axial velocity on the centerline of the burner throat non-monotonically. In addition, emission characteristics were investigated using a gas analyzer. The CO and NO concentrations were below 20 ppm for all tested conditions, which is comparable to that seen with traditional hydrocarbon fuels, which is in favor of future practical applications with formic acid.