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  1. Article ; Online: Statistical and machine learning analysis for the application of microbially induced carbonate precipitation as a physical barrier to control seawater intrusion.

    Konstantinou, Charalampos / Wang, Yuze

    Journal of contaminant hydrology

    2024  Volume 263, Page(s) 104337

    Abstract: Seawater intrusion in coastal aquifers is a significant problem that can be addressed through the construction of subsurface dams or physical cut-off barriers. An alternative method is the use of microbially induced carbonate precipitation (MICP) to ... ...

    Abstract Seawater intrusion in coastal aquifers is a significant problem that can be addressed through the construction of subsurface dams or physical cut-off barriers. An alternative method is the use of microbially induced carbonate precipitation (MICP) to reduce the hydraulic conductivity of the porous medium and create a physical barrier. However, the effectiveness of this method depends on various factors, and the scientific literature presents conflicting results, making it challenging to generalise the findings. To overcome this challenge, a statistical and machine learning (ML) approach is employed to infer the causes for the reduction in hydraulic conductivity and identify the optimum MICP parameters for preventing seawater intrusion. The study involves data curation, exploratory analysis, and the development of various models to fit the input data (k-Nearest Neighbours - kNN, Support Vector Regression - SVR, Random Forests - RF, Gradient Boosting - XgBoost, Linear model with interaction terms, Ensemble learning algorithms with weighted averages - EnL-WA and stacking - EnL-Stack). The models performed reasonably well in the region where permeability reduction is sensitive to carbonate increase capturing the permeability reduction profile with respect to cementation level while demonstrating that they can be used in initial assessments of the specific conditions (e.g., soil properties). The best performing algorithms were the EnL-Stack and RF followed by XgBoost and SVR. The MICP method is effective in reducing hydraulic conductivity provided that the various biochemical parameters are optimised. Critical biochemical parameters for successful MICP formulations are the bacterial optical density, the urease activity, calcium chloride concentration and flow rate as well as the interaction terms across the properties of the porous media and the biochemical parameters. The models were used to identify the optimum MICP formulation for various porous media properties and the maximum permeability reduction profiles across cementation levels have been derived.
    MeSH term(s) Seawater/chemistry ; Seawater/microbiology ; Machine Learning ; Groundwater/chemistry ; Carbonates/chemistry ; Carbonates/metabolism ; Chemical Precipitation ; Water Movements
    Chemical Substances Carbonates
    Language English
    Publishing date 2024-03-20
    Publishing country Netherlands
    Document type Journal Article ; Research Support, Non-U.S. Gov't
    ZDB-ID 1494766-3
    ISSN 1873-6009 ; 0169-7722
    ISSN (online) 1873-6009
    ISSN 0169-7722
    DOI 10.1016/j.jconhyd.2024.104337
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  2. Book ; Audio / Video ; Thesis: Geschlechtsspezifische Analyse des akuten Myokardinfarktes

    Konstantinou, Christos

    von der Zeit vor dem Infarkt bis zum Langzeitverlauf nach Behandlung mit primärer PTCA

    2009  

    Author's details vorgelegt von: Christos Konstantinou
    Subject code 616.1
    Language German
    Size 1 CD-ROM, 12 cm
    Publishing country Germany
    Document type Book ; Audio / Video ; Thesis
    Thesis / German Habilitation thesis Witten, Herdecke, Univ., Diss., 2008
    Note Titel auf dem Behältnis
    HBZ-ID HT016785532
    Database Catalogue ZB MED Medicine, Health

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  3. Book ; Online: Event-Triggered Islanding in Inverter-Based Grids

    Zografopoulos, Ioannis / Konstantinou, Charalambos

    2023  

    Abstract: The decentralization of modern power systems challenges the hierarchical structure of the electric grid and requires the implementation of automated schemes that can overcome adverse conditions. This work proposes an adaptive isolation methodology that ... ...

    Abstract The decentralization of modern power systems challenges the hierarchical structure of the electric grid and requires the implementation of automated schemes that can overcome adverse conditions. This work proposes an adaptive isolation methodology that can segregate a grid topology in autonomous islands that maintain stable and economic operation in the presence of deliberate (e.g., cyberattacks) or unintentional abnormal events. The adaptive isolation logic is event-triggered to avoid false positives, improve detection accuracy, and reduce computational overheads. A measurement-based stable kernel representation (SKR) triggering mechanism inspects distributed generation controllers for abnormal behavior. The SKR notifies a machine learning (ML) ensemble classifier that detects whether the system behavior is within acceptable operational conditions. The event-triggered adaptive isolation framework is evaluated using IEEE RTS-24 bus system. Simulation results demonstrate that the proposed framework detects anomalous behavior in real-time and identifies stable partitions minimizing operating costs faster than traditional islanding detection techniques.
    Keywords Electrical Engineering and Systems Science - Systems and Control ; Computer Science - Cryptography and Security
    Subject code 621
    Publishing date 2023-06-27
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Book ; Online: Fracture of bio-cemented sands

    Konstantinou, C. / Martínez-Pañeda, E. / Biscontin, G. / Fleck, N. A.

    2023  

    Abstract: Bio-chemical reactions enable the production of biomimetic materials such as sandstones. In the present study, microbiologically-induced calcium carbonate precipitation (MICP) is used to manufacture laboratory-scale specimens for fracture toughness ... ...

    Abstract Bio-chemical reactions enable the production of biomimetic materials such as sandstones. In the present study, microbiologically-induced calcium carbonate precipitation (MICP) is used to manufacture laboratory-scale specimens for fracture toughness measurement. The mode I and mixed-mode fracture toughnesses are measured as a function of cementation, and are correlated with strength, permeability and porosity. A micromechanical model is developed to predict the dependence of mode I fracture toughness upon the degree of cementation. In addition, the role of the crack tip $T$-stress in dictating kink angle and toughness is determined for mixed mode loading. At a sufficiently low degree of cementation, the zone of microcracking in the vicinity of the crack tip is sufficiently large for a crack tip $K$-field to cease to exist and for crack kinking theory to not apply. The interplay between cementation and fracture properties of sedimentary rocks is explained; this understanding underpins a wide range of rock fracture phenomena including hydraulic fracture.
    Keywords Condensed Matter - Materials Science ; Computer Science - Computational Engineering ; Finance ; and Science ; Physics - Applied Physics
    Subject code 669
    Publishing date 2023-11-13
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article ; Online: An anti-inflammatory response of an organic food intervention by reducing pesticide exposures in children of Cyprus: A cluster-randomized crossover trial.

    Abimbola, Samuel Olushola / Konstantinou, Corina / Xeni, Christina / Charisiadis, Pantelis / Makris, Konstantinos C

    Environmental research

    2024  Volume 252, Issue Pt 1, Page(s) 118710

    Abstract: Organic food consumption in children has been shown to reduce the body burden of chemical pesticides. However, there is little evidence of human health benefits associated with the consumption of organic foods. The objectives were to i) determine the ... ...

    Abstract Organic food consumption in children has been shown to reduce the body burden of chemical pesticides. However, there is little evidence of human health benefits associated with the consumption of organic foods. The objectives were to i) determine the effectiveness of an organic food intervention treatment in reducing the magnitude of an inflammation biomarker (C-reactive protein, CRP) in children (10-12 years) and ii) assess the association between the urinary biomarkers of exposure to pesticides and CRP. This work was part of the ORGANIKO cluster-randomized cross-over trial entailing a 40-day organic food treatment in healthy children. Urinary biomarkers of exposure to pesticides and inflammation (CRP) were measured using tandem mass spectrometry and ELISA immunoassay, respectively. Linear mixed-effect regression models of CRP were used to account for the effect and duration of organic food treatment. Multiple comparisons were handled using Benjamini-Hochberg correction. Results supported an anti-inflammatory effect of organic food treatment in children, albeit with mixed results, depending on the creatinine adjustment method; biomarker levels were divided by urinary creatinine (method a1), or urinary creatinine was used as a fixed effect variable (a2). In the a1 method, a time-dependent reduction for creatinine-adjusted CRP (β = -0.019; 95% CI: -0.031, -0.006; q = 0.045) was observed during the organic food intervention period. A statistically significant association (β = 0.104; 95% CI: 0.035, 0.173; q = 0.045) was found between the biomarker of pyrethroids exposure (3-PBA) and CRP inflammatory biomarker, but not for 6-CN. In the a2 method, similar trend of time-dependent reduction for creatinine-adjusted CRP (β = -0.008; 95% CI: -0.021, 0.004; p = 0.197) was observed during the organic food intervention period, but did not reach statistical significance (q > 0.05); the associations of pyrethroid and neonicotinoid biomarkers with CRP were not statistically significant (q > 0.05). More studies are warranted to sufficiently understand the potential anti-inflammatory response of an organic food treatment.
    Language English
    Publishing date 2024-03-16
    Publishing country Netherlands
    Document type Journal Article
    ZDB-ID 205699-9
    ISSN 1096-0953 ; 0013-9351
    ISSN (online) 1096-0953
    ISSN 0013-9351
    DOI 10.1016/j.envres.2024.118710
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  6. Book ; Online: Development of a fracture capture simulator to quantify the instability evolution in porous medium

    Kandasami, Ramesh Kannan / Konstantinou, Charalampos / Biscontin, Giovanna

    2023  

    Abstract: Understanding and controlling fracture propagation is one of the most challenging engineering problems, especially in the oil and gas sector, groundwater hydrology and geothermal energy applications. Predicting the fracture orientation while also ... ...

    Abstract Understanding and controlling fracture propagation is one of the most challenging engineering problems, especially in the oil and gas sector, groundwater hydrology and geothermal energy applications. Predicting the fracture orientation while also possessing a non-linear material response becomes more complex when the medium is non-homogeneous and anisotropic. Fracturing behaviour in geological porous media that exhibit high leak-off potential is not clearly understood. In this context, a novel testing technique is used to simulate the ground conditions in the laboratory and study the instability characteristics of such geo-materials. The bespoke apparatus designed and developed in this research programme is capable of applying true anisotropic boundary stresses, injecting fluid at a predefined flow rate and viscosity while also imaging the instability/ fracture propagation in a porous medium such as sand and weak rock. Pressure profiles and the progression of fracture are recorded simultaneously during the fluid injection process into specimens subjected to different boundary stresses. The fracture propagation data are analysed, which provides information on the evolution of fracture morphology and expansion velocity during the injection event.

    Comment: 12 figures
    Keywords Condensed Matter - Materials Science
    Subject code 550
    Publishing date 2023-03-31
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  7. Book ; Online: Resilient Distributed Integral Control for Multimachine Power Systems with Inherent Input Constraint Satisfaction

    Kavvathas, Theodoros E. / Konstantopoulos, George C. / Konstantinou, Charalambos

    2023  

    Abstract: In this paper, a novel distributed controller for multimachine power systems is proposed to guarantee grid frequency restoration and accurate real and reactive power sharing among the generator units, while maintaining the generator inputs (mechanical ... ...

    Abstract In this paper, a novel distributed controller for multimachine power systems is proposed to guarantee grid frequency restoration and accurate real and reactive power sharing among the generator units, while maintaining the generator inputs (mechanical torque and field excitation voltage) within given bounds. The boundedness of the controller outputs (generator inputs) is rigorously proven using vector field theory. It is additionally shown that even if one generator input reaches its upper/lower limit, the remaining units can still accomplish the desired control tasks without modifying the controller structure or dynamics; hence introducing enhanced system resilience using the proposed approach. This has been accomplished in a unified control structure while using neighbour-to-neighbour communication, thus maintaining the distributed nature of the controller. An example of a 10-bus, 4-machine power system is simulated to verify the proposed controller performance under sudden changes of the load demand.

    Comment: 2023 31st Mediterranean Conference on Control and Automation (MED2023)
    Keywords Electrical Engineering and Systems Science - Systems and Control
    Subject code 629
    Publishing date 2023-05-08
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  8. Book ; Online: Lost at Sea

    Rath, Suman / Intriago, Andres / Sengupta, Shamik / Konstantinou, Charalambos

    Assessment and Evaluation of Rootkit Attacks on Shipboard Microgrids

    2023  

    Abstract: Increased dependence of the maritime industry on information and communication networks has made shipboard power systems vulnerable to stealthy cyber-attacks. One such attack variant, called rootkit, can leverage system knowledge to hide its presence and ...

    Abstract Increased dependence of the maritime industry on information and communication networks has made shipboard power systems vulnerable to stealthy cyber-attacks. One such attack variant, called rootkit, can leverage system knowledge to hide its presence and allow remotely located malware handlers to gain complete control of infected subsystems. This paper presents a comprehensive evaluation of the threat landscape imposed by such attack variants on Medium Voltage DC (MVDC) shipboard microgrids, including a discussion of their impact on the overall maritime sector in general, and provides several simulation results to demonstrate the same. It also analyzes and presents the actions of possible defense mechanisms, with specific emphasis on evasion, deception, and detection frameworks, that will help ship operators and maritime cybersecurity professionals protect their systems from such attacks.

    Comment: 2023 IEEE Electric Ship Technologies Symposium (ESTS)
    Keywords Computer Science - Cryptography and Security ; Electrical Engineering and Systems Science - Systems and Control
    Publishing date 2023-05-29
    Publishing country us
    Document type Book ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  9. Article: Tensile Strength of Artificially Cemented Sandstone Generated via Microbially Induced Carbonate Precipitation.

    Konstantinou, Charalampos / Biscontin, Giovanna / Logothetis, Fotios

    Materials (Basel, Switzerland)

    2021  Volume 14, Issue 16

    Abstract: Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, ...

    Abstract Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, particularly tensile stregth. The modes of fracture and the surface characteristics resulting from the indirect tensile strength tests (Brazilian tests) are strongly correlated with the specimen strength and consequently the degree of cementation. This study examines the tensile strength of bio-cemented fine and coarse sands (average particle diameter 0.18 and 1.82 mm, respectively) and investigates failure modes by recording fracture evolution at both sides of specimen and surface characteristics of the reconstructed surfaces. The dimensionless slope parameter Z2 provided the best fit with respect to tensile strength while the power spectral density was a good indicator of surface anisotropy. Finally, wavelet decomposition allowed for comparison of fracture surface characteristics of the two sands ignoring the grain size effects.
    Language English
    Publishing date 2021-08-22
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 2487261-1
    ISSN 1996-1944
    ISSN 1996-1944
    DOI 10.3390/ma14164735
    Database MEDical Literature Analysis and Retrieval System OnLINE

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  10. Article ; Online: Determination of Response Factors for Analytes Detected during Migration Studies, Strategy and Internal Standard Selection for Risk Minimization.

    Kritikos, Nikolaos / Bletsou, Anna / Konstantinou, Christina / Neofotistos, Antonios-Dionysios / Kousoulos, Constantinos / Dotsikas, Yannis

    Molecules (Basel, Switzerland)

    2023  Volume 28, Issue 15

    Abstract: Migration studies are one of the few domains of pharmaceutical analysis employing wide-scope screening methodologies. The studies involve the detection of contaminants within pharmaceutical products that arise from the interaction between the formulation ...

    Abstract Migration studies are one of the few domains of pharmaceutical analysis employing wide-scope screening methodologies. The studies involve the detection of contaminants within pharmaceutical products that arise from the interaction between the formulation and materials. Requiring both qualitative and quantitative data, the studies are conducted using Liquid Chromatography or Gas Chromatography coupled to a mass spectrometer (LC-MS and GC-MS). While mass spectrometry allows wide-scope analyte detection and identification at the very low Analytical Evaluation Threshold (AET) levels used in these studies, MS detectors are far from "universal response" detectors. Regulation brings the application of uncertainty factors into the picture to limit the risk of potential analytes detected escaping report and further evaluation; however, whether the application of a default value can cover any or all relevant applications is still debatable. The current study evaluated the response of species usually detected in migration studies, generating a suitable representative sample, analyzing said species, and creating a strategy and evaluation mechanism for acceptable classification of the detected species. Incorporating novel methodologies, i.e., Design of Experiments (DoE) for Design Space generation, the LC-MS-based methodology is also evaluated for its robustness in changes performed.
    MeSH term(s) Gas Chromatography-Mass Spectrometry ; Mass Spectrometry ; Chromatography, Liquid/methods
    Language English
    Publishing date 2023-07-31
    Publishing country Switzerland
    Document type Journal Article
    ZDB-ID 1413402-0
    ISSN 1420-3049 ; 1431-5165 ; 1420-3049
    ISSN (online) 1420-3049
    ISSN 1431-5165 ; 1420-3049
    DOI 10.3390/molecules28155772
    Database MEDical Literature Analysis and Retrieval System OnLINE

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