2,655 research outputs found
Predictive Customer Lifetime value modeling: Improving customer engagement and business performance
CookUnity, a meal subscription service, has witnessed substantial annual revenue growth over the past three years. However, this growth has primarily been driven by the acquisition of new users to expand the customer base, rather than an evident increase in customers' spending levels. If it weren't for the raised subscription prices, the company's customer lifetime value (CLV) would have remained the same as it was three years ago. Consequently, the company's leadership recognizes the need to adopt a holistic approach to unlock an enhancement in CLV.
The objective of this thesis is to develop a comprehensive understanding of CLV, its implications, and how companies leverage it to inform strategic decisions. Throughout the course of this study, our central focus is to deliver a fully functional and efficient machine learning solution to CookUnity. This solution will possess exceptional predictive capabilities, enabling accurate forecasting of each customer's future CLV. By equipping CookUnity with this powerful tool, our aim is to empower the company to strategically leverage CLV for sustained growth.
To achieve this objective, we analyze various methodologies and approaches to CLV analysis, evaluating their applicability and effectiveness within the context of CookUnity. We thoroughly explore available data sources that can serve as predictors of CLV, ensuring the incorporation of the most relevant and meaningful variables in our model. Additionally, we assess different research methodologies to identify the top-performing approach and examine its implications for implementation at CookUnity.
By implementing data-driven strategies based on our predictive CLV model, CookUnity will be able to optimize order levels and maximize the lifetime value of its customer base. The outcome of this thesis will be a robust ML solution with remarkable prediction accuracy and practical usability within the company. Furthermore, the insights gained from our research will contribute to a broader understanding of CLV in the subscription-based business context, stimulating further exploration and advancement in this field of study
Optimising multimodal fusion for biometric identification systems
Biometric systems are automatic means for imitating the human brain’s ability of identifying and verifying other humans by their behavioural and physiological characteristics. A system, which uses more than one biometric modality at the same time, is known as a multimodal system. Multimodal biometric systems consolidate the evidence presented by multiple biometric sources and typically provide better recognition performance compared to systems based on a single biometric modality. This thesis addresses some issues related to the implementation of multimodal biometric identity verification systems. The thesis assesses the feasibility of using commercial offthe-shelf products to construct deployable multimodal biometric system. It also identifies multimodal biometric fusion as a challenging optimisation problem when one considers the presence of several configurations and settings, in particular the verification thresholds adopted by each biometric device and the decision fusion algorithm implemented for a particular configuration. The thesis proposes a novel approach for the optimisation of multimodal biometric systems based on the use of genetic algorithms for solving some of the problems associated with the different settings. The proposed optimisation method also addresses some of the problems associated with score normalization. In addition, the thesis presents an analysis of the performance of different fusion rules when characterising the system users as sheep, goats, lambs and wolves. The results presented indicate that the proposed optimisation method can be used to solve the problems associated with threshold settings. This clearly demonstrates a valuable potential strategy that can be used to set a priori thresholds of the different biometric devices before using them. The proposed optimisation architecture addressed the problem of score normalisation, which makes it an effective “plug-and-play” design philosophy to system implementation. The results also indicate that the optimisation approach can be used for effectively determining the weight settings, which is used in many applications for varying the relative importance of the different performance parameters
Perceptual Model-Driven Authoring of Plausible Vibrations from User Expectations for Virtual Environments
One of the central goals of design is the creation of experiences that are rated favorably in the intended application context. User expectations play an integral role in tactile product quality and tactile plausibility judgments alike. In the vibrotactile authoring process for virtual environments, vibra-tion is created to match the user’s expectations of the presented situational context. Currently, inefficient trial and error approaches attempt to match expectations implicitly. A more efficient, model-driven procedure based explicitly on tactile user expectations would thus be beneficial for author-ing vibrations. In everyday life, we are frequently exposed to various whole-body vibrations. Depending on their temporal and spectral proper-ties we intuitively associate specific perceptual properties such as “tin-gling”. This suggests a systematic relationship between physical parame-ters and perceptual properties. To communicate with potential users about such elicited or expected tactile properties, a standardized design language is proposed. It contains a set of sensory tactile perceptual attributes, which are sufficient to characterize the perceptual space of vibration encountered in everyday life. This design language enables the assessment of quantita-tive tactile perceptual specifications by laypersons that are elicited in situational contexts such as auditory-visual-tactile vehicle scenes. Howev-er, such specifications can also be assessed by providing only verbal de-scriptions of the content of these scenes. Quasi identical ratings observed for both presentation modes suggest that tactile user expectations can be quantified even before any vibration is presented. Such expected perceptu-al specifications are the prerequisite for a subsequent translation into phys-ical vibration parameters. Plausibility can be understood as a similarity judgment between elicited features and expected features. Thus, plausible vibration can be synthesized by maximizing the similarity of the elicited perceptual properties to the expected perceptual properties. Based on the observed relationships between vibration parameters and sensory tactile perceptual attributes, a 1-nearest-neighbor model and a regression model were built. The plausibility of the vibrations synthesized by these models in the context of virtual auditory-visual-tactile vehicle scenes was validat-ed in a perceptual study. The results demonstrated that the perceptual spec-ifications obtained with the design language are sufficient to synthesize vibrations, which are perceived as equally plausible as recorded vibrations in a given situational context. Overall, the demonstrated design method can be a new, more efficient tool for designers authoring vibrations for virtual environments or creating tactile feedback. The method enables further automation of the design process and thus potential time and cost reductions.:Preface III
Abstract V
Zusammenfassung VII
List of Abbreviations XV
1 Introduction 1
1.1 General Introduction 1
1.1 Objectives of the Thesis 4
1.2 Structure of the Thesis 4
2. Tactile Perception in Real and Virtual Environments 7
2.1 Tactile Perception as a Multilayered Process 7
2.1.1 Physical Layer 8
2.1.2 Mechanoreceptor Layer 9
2.1.3 Sensory Layer 19
2.1.4 Affective Layer 26
2.2 Perception of Virtual Environments 29
2.2.1 The Place Illusion 29
2.2.2 The Plausibility Illusion 31
2.3 Approaches for the Authoring of Vibrations 38
2.3.1 Approaches on the Physical Layer 38
2.3.2 Approaches on the Mechanoreceptor Layer 40
2.3.3 Approaches on the Sensory Layer 40
2.3.4 Approaches on the Affective Layer 43
2.4 Summary 43
3. Research Concept 47
3.1 Research Questions 47
3.1.1 Foundations of the Research Concept 47
3.1.2 Research Concept 49
3.2 Limitations 50
4. Development of the Experimental Setup 53
4.1 Hardware 53
4.1.1 Optical Reproduction System 53
4.1.2 Acoustical Reproduction System 54
4.1.3 Whole-Body Vibration Reproduction System 56
4.2 Software 64
4.2.1 Combination of Reproduction Systems for Unimodal and Multimodal Presentation 64
4.2.2 Conducting Perceptual Studies 65
5. Assessment of a Sensory Tactile Design Language for Characterizing Vibration 67
5.1.1 Design Language Requirements 67
5.1.2 Method to Assess the Design Language 69
5.1.3 Goals of this Chapter 70
5.2 Tactile Stimuli 72
5.2.1 Generalization into Excitation Patterns 72
5.2.2 Definition of Parameter Values of the Excitation Patterns 75
5.2.3 Generation of the Stimuli 85
5.2.4 Summary 86
5.3 Assessment of the most relevant Sensory Tactile Perceptual Attributes 86
5.3.1 Experimental Design 87
5.3.2 Participants 88
5.3.3 Results 88
5.3.4 Aggregation and Prioritization 89
5.3.5 Summary 91
5.4 Identification of the Attributes forming the Design Language 92
5.4.1 Experimental Design 93
5.4.2 Participants 95
5.4.3 Results 95
5.4.4 Selecting the Elements of the Sensory Tactile Design Language 106
5.4.5 Summary 109
5.5 Summary and Discussion 109
5.5.1 Summary 109
5.5.2 Discussion 111
6. Quantification of Expected Properties with the Sensory Tactile Design Language 115
6.1 Multimodal Stimuli 116
6.1.1 Selection of the Scenes 116
6.1.2 Recording of the Scenes 117
6.1.3 Recorded Stimuli 119
6.2 Qualitative Communication in the Presence of Vibration 123
6.2.1 Experimental Design 123
6.2.2 Participants 124
6.2.3 Results 124
6.2.4 Summary 126
6.3 Quantitative Communication in the Presence of Vibration 126
6.3.1 Experimental Design 127
6.3.2 Participants 127
6.3.3 Results 127
6.3.4 Summary 129
6.4 Quantitative Communication in the Absence of Vibration 129
6.4.1 Experimental Design 130
6.4.2 Participants 132
6.4.3 Results 132
6.4.4 Summary 134
6.5 Summary and Discussion 135
7. Synthesis Models for the Translation of Sensory Tactile Properties into Vibration 137
7.1 Formalization of the Tactile Plausibility Illusion for Models 139
7.1.1 Formalization of Plausibility 139
7.1.2 Model Boundaries 143
7.2 Investigation of the Influence of Vibration Level on Attribute Ratings 144
7.2.1 Stimuli 145
7.2.2 Experimental Design 145
7.2.3 Participants 146
7.2.4 Results 146
7.2.5 Summary 148
7.3 Comparison of Modulated Vibration to Successive Impulse-like Vibration 148
7.3.1 Stimuli 149
7.3.2 Experimental Design 151
7.3.3 Participants 151
7.3.4 Results 151
7.3.5 Summary 153
7.4 Synthesis Based on the Discrete Estimates of a k-Nearest-Neighbor Classifier 153
7.4.1 Definition of the K-Nearest-Neighbor Classifier 154
7.4.2 Analysis Model 155
7.4.3 Synthesis Model 156
7.4.4 Interpolation of acceleration level for the vibration attribute profile pairs 158
7.4.5 Implementation of the Synthesis 159
7.4.6 Advantages and Disadvantages 164
7.5 Synthesis Based on the Quasi-Continuous Estimates of Regression Models 166
7.5.1 Overall Model Structure 168
7.5.2 Classification of the Excitation Pattern with a Support Vector Machine 171
7.5.3 General Approach to the Regression Models of each Excitation Pattern 178
7.5.4 Synthesis for the Impulse-like Excitation Pattern 181
7.5.5 Synthesis for the Bandlimited White Gaussian Noise Excitation Pattern 187
7.5.6 Synthesis for the Amplitude Modulated Sinusoidal Excitation Pattern 193
7.5.7 Synthesis for the Sinusoidal Excitation Pattern 199
7.5.8 Implementation of the Synthesis 205
7.5.9 Advantages and Disadvantages of the Approach 208
7.6 Validation of the Synthesis Models 210
7.6.1 Stimuli 212
7.6.2 Experimental Design 212
7.6.3 Participants 214
7.6.4 Results 214
7.6.5 Summary 219
7.7 Summary and Discussion 219
7.7.1 Summary 219
7.7.2 Discussion 222
8. General Discussion and Outlook 227
Acknowledgment 237
References 237Eines der zentralen Ziele des Designs von Produkten oder virtuellen Um-gebungen ist die Schaffung von Erfahrungen, die im beabsichtigten An-wendungskontext die Erwartungen der Benutzer erfüllen. Gegenwärtig versucht man im vibrotaktilen Authoring-Prozess mit ineffizienten Trial-and-Error-Verfahren, die Erwartungen an den dargestellten, virtuellen Situationskontext implizit zu erfüllen. Ein effizienteres, modellgetriebenes Verfahren, das explizit auf den taktilen Benutzererwartungen basiert, wäre daher von Vorteil. Im Alltag sind wir häufig verschiedenen Ganzkörper-schwingungen ausgesetzt. Abhängig von ihren zeitlichen und spektralen Eigenschaften assoziieren wir intuitiv bestimmte Wahrnehmungsmerkmale wie z.B. “kribbeln”. Dies legt eine systematische Beziehung zwischen physikalischen Parametern und Wahrnehmungsmerkmalen nahe. Um mit potentiellen Nutzern über hervorgerufene oder erwartete taktile Eigen-schaften zu kommunizieren, wird eine standardisierte Designsprache vor-geschlagen. Sie enthält eine Menge von sensorisch-taktilen Wahrneh-mungsmerkmalen, die hinreichend den Wahrnehmungsraum der im Alltag auftretenden Vibrationen charakterisieren. Diese Entwurfssprache ermög-licht die quantitative Beurteilung taktiler Wahrnehmungsmerkmale, die in Situationskontexten wie z.B. auditiv-visuell-taktilen Fahrzeugszenen her-vorgerufen werden. Solche Wahrnehmungsspezifikationen können jedoch auch bewertet werden, indem der Inhalt dieser Szenen verbal beschrieben wird. Quasi identische Bewertungen für beide Präsentationsmodi deuten darauf hin, dass die taktilen Benutzererwartungen quantifiziert werden können, noch bevor eine Vibration präsentiert wird. Die erwarteten Wahr-nehmungsspezifikationen sind die Voraussetzung für eine anschließende Übersetzung in physikalische Schwingungsparameter. Plausible Vibratio-nen können synthetisiert werden, indem die erwarteten Wahrnehmungs-merkmale hervorgerufen werden. Auf der Grundlage der beobachteten Beziehungen zwischen Schwingungs¬parametern und sensorisch-taktilen Wahrnehmungsmerkmalen wurden ein 1-Nearest-Neighbor-Modell und ein Regressionsmodell erstellt. Die Plausibilität der von diesen Modellen synthetisierten Schwingungen im Kontext virtueller, auditorisch-visuell-taktiler Fahrzeugszenen wurde in einer Wahrnehmungsstudie validiert. Die Ergebnisse zeigten, dass die mit der Designsprache gewonnenen Wahr-nehmungsspezifikationen ausreichen, um Schwingungen zu synthetisieren, die in einem gegebenen Situationskontext als ebenso plausibel empfunden werden wie aufgezeichnete Schwingungen. Die demonstrierte Entwurfsme-thode stellt ein neues, effizienteres Werkzeug für Designer dar, die Schwingungen für virtuelle Umgebungen erstellen oder taktiles Feedback für Produkte erzeugen.:Preface III
Abstract V
Zusammenfassung VII
List of Abbreviations XV
1 Introduction 1
1.1 General Introduction 1
1.1 Objectives of the Thesis 4
1.2 Structure of the Thesis 4
2. Tactile Perception in Real and Virtual Environments 7
2.1 Tactile Perception as a Multilayered Process 7
2.1.1 Physical Layer 8
2.1.2 Mechanoreceptor Layer 9
2.1.3 Sensory Layer 19
2.1.4 Affective Layer 26
2.2 Perception of Virtual Environments 29
2.2.1 The Place Illusion 29
2.2.2 The Plausibility Illusion 31
2.3 Approaches for the Authoring of Vibrations 38
2.3.1 Approaches on the Physical Layer 38
2.3.2 Approaches on the Mechanoreceptor Layer 40
2.3.3 Approaches on the Sensory Layer 40
2.3.4 Approaches on the Affective Layer 43
2.4 Summary 43
3. Research Concept 47
3.1 Research Questions 47
3.1.1 Foundations of the Research Concept 47
3.1.2 Research Concept 49
3.2 Limitations 50
4. Development of the Experimental Setup 53
4.1 Hardware 53
4.1.1 Optical Reproduction System 53
4.1.2 Acoustical Reproduction System 54
4.1.3 Whole-Body Vibration Reproduction System 56
4.2 Software 64
4.2.1 Combination of Reproduction Systems for Unimodal and Multimodal Presentation 64
4.2.2 Conducting Perceptual Studies 65
5. Assessment of a Sensory Tactile Design Language for Characterizing Vibration 67
5.1.1 Design Language Requirements 67
5.1.2 Method to Assess the Design Language 69
5.1.3 Goals of this Chapter 70
5.2 Tactile Stimuli 72
5.2.1 Generalization into Excitation Patterns 72
5.2.2 Definition of Parameter Values of the Excitation Patterns 75
5.2.3 Generation of the Stimuli 85
5.2.4 Summary 86
5.3 Assessment of the most relevant Sensory Tactile Perceptual Attributes 86
5.3.1 Experimental Design 87
5.3.2 Participants 88
5.3.3 Results 88
5.3.4 Aggregation and Prioritization 89
5.3.5 Summary 91
5.4 Identification of the Attributes forming the Design Language 92
5.4.1 Experimental Design 93
5.4.2 Participants 95
5.4.3 Results 95
5.4.4 Selecting the Elements of the Sensory Tactile Design Language 106
5.4.5 Summary 109
5.5 Summary and Discussion 109
5.5.1 Summary 109
5.5.2 Discussion 111
6. Quantification of Expected Properties with the Sensory Tactile Design Language 115
6.1 Multimodal Stimuli 116
6.1.1 Selection of the Scenes 116
6.1.2 Recording of the Scenes 117
6.1.3 Recorded Stimuli 119
6.2 Qualitative Communication in the Presence of Vibration 123
6.2.1 Experimental Design 123
6.2.2 Participants 124
6.2.3 Results 124
6.2.4 Summary 126
6.3 Quantitative Communication in the Presence of Vibration 126
6.3.1 Experimental Design 127
6.3.2 Participants 127
6.3.3 Results 127
6.3.4 Summary 129
6.4 Quantitative Communication in the Absence of Vibration 129
6.4.1 Experimental Design 130
6.4.2 Participants 132
6.4.3 Results 132
6.4.4 Summary 134
6.5 Summary and Discussion 135
7. Synthesis Models for the Translation of Sensory Tactile Properties into Vibration 137
7.1 Formalization of the Tactile Plausibility Illusion for Models 139
7.1.1 Formalization of Plausibility 139
7.1.2 Model Boundaries 143
7.2 Investigation of the Influence of Vibration Level on Attribute Ratings 144
7.2.1 Stimuli 145
7.2.2 Experimental Design 145
7.2.3 Participants 146
7.2.4 Results 146
7.2.5 Summary 148
7.3 Comparison of Modulated Vibration to Successive Impulse-like Vibration 148
7.3.1 Stimuli 149
7.3.2 Experimental Design 151
7.3.3 Participants 151
7.3.4 Results 151
7.3.5 Summary 153
7.4 Synthesis Based on the Discrete Estimates of a k-Nearest-Neighbor Classifier 153
7.4.1 Definition of the K-Nearest-Neighbor Classifier 154
7.4.2 Analysis Model 155
7.4.3 Synthesis Model 156
7.4.4 Interpolation of acceleration level for the vibration attribute profile pairs 158
7.4.5 Implementation of the Synthesis 159
7.4.6 Advantages and Disadvantages 164
7.5 Synthesis Based on the Quasi-Continuous Estimates of Regression Models 166
7.5.1 Overall Model Structure 168
7.5.2 Classification of the Excitation Pattern with a Support Vector Machine 171
7.5.3 General Approach to the Regression Models of each Excitation Pattern 178
7.5.4 Synthesis for the Impulse-like Excitation Pattern 181
7.5.5 Synthesis for the Bandlimited White Gaussian Noise Excitation Pattern 187
7.5.6 Synthesis for the Amplitude Modulated Sinusoidal Excitation Pattern 193
7.5.7 Synthesis for the Sinusoidal Excitation Pattern 199
7.5.8 Implementation of the Synthesis 205
7.5.9 Advantages and Disadvantages of the Approach 208
7.6 Validation of the Synthesis Models 210
7.6.1 Stimuli 212
7.6.2 Experimental Design 212
7.6.3 Participants 214
7.6.4 Results 214
7.6.5 Summary 219
7.7 Summary and Discussion 219
7.7.1 Summary 219
7.7.2 Discussion 222
8. General Discussion and Outlook 227
Acknowledgment 237
References 23
Global Cyber Attack Forecast using AI Techniques
The advancement of internet technology and growing involvement in the cyber world have made us prone to cyber-attacks inducing severe damage to individuals and organizations, including financial loss, identity theft, and reputational damage. The rapid emergence and evolution of new networks and new opportunities for businesses and technologies are increasing threats to security vulnerabilities. Hence cyber-crime analysis is one of the wide range applications of Data Mining that can be eventually used to predict and detect crime. However, there are several constraints while analyzing cyber-attacks, which are yet to be resolved for more accurate cyber security inspection.
Although there are many strategies for intrusion detection, predicting upcoming cyber threats remains an open research challenge. Hence, this thesis seeks to utilize temporal correlations among attack frequencies within specific time periods to predict the future severity of cyber incidents. The research aims to address the current research limitations by introducing a real-time data collection framework that will provide up-to-date cyber-attack data. Furthermore, a platform for cyber-attack trend analysis has been developed using Power BI to provide insight into the current cyber-attack trend. A correlation was identified in the reported attack volume across consecutive time frames through collected attack data analysis. This thesis introduces a predictive model that forecasts the frequency of cyber-attacks within a specified time window, using solely a historical record of attack counts. The research includes various machine learning and deep learning methods to develop a prediction system based on multiple time frames with an over 15% improvement in accuracy compared to the conventional baseline model. Namely, our research demonstrates that cyber incidents are not entirely random, and by analyzing patterns and trends in past incidents, developed AI techniques can be used to improve cybersecurity measures and prevent future attacks
Geogenic carbon dioxide degassing from active tectonic areas of the Balkan Peninsula
Sin dagli anni ’70, la ricerca scientifica ha evidenziato una forte relazione tra il degassamento di carbonio profondo e le aree tettonicamente attive, sottolineando l’elevata importanza del contributo di queste emissioni nella quantificazione del carbonio globale.
La Penisola Balcanica presenta grandi aree caratterizzate da degassamento di carbonio di origine mantellica, da attività vulcaniche Quaternarie, da un’elevata sismicità e da strutture tettoniche a scala regionale. Purtroppo, la stima del degassamento di anidride carbonica profonda in quest’area è ancora poco studiata. La ricerca di questa tesi di dottorato si è focalizzata sulla (i) stima dell’output di carbonio profondo dalle grandi sorgenti carsiche della Grecia, e sulla (ii) caratterizzazione della composizione chimica e isotopica delle principali manifestazioni gassose della Macedonia del Nord. Inoltre, è stato condotto anche uno studio sull’impatto dei processi geogenici ed antropogenici sulla qualità delle acque dei grandi sistemi carsici della Grecia.
Negli acquiferi carsici delle Grecia sono state riconosciute tre principali composizioni chimiche dell’acqua: (i) bicarbonato-calcica per le sorgenti continentali; (ii) cloruro-sodica per le sorgenti in area di costa, (iii) solfato-calcica dovuta a processi di dissoluzione di gesso all’interno dell’acquifero. I risultati, in termini di specie maggiori ed elementi in traccia, sono stati comparati con i limiti sulle acque potabili imposte dalle Direttive della Comunità Europea, CE/98/83 e CE/2020/2184, i quali raramente vengono superati tranne per quei parametri che risentono della influenza dell’intrusione marina (Conduttività Elettrica, Na, Cl, B). In queste sorgenti, sono stati rivelati elevati valori di nitrato, sebbene sempre al di sotto del limite di potabilità .
Per quanto riguarda la composizione chimica dei gas disciolti e liberi, l’azoto risulta essere il gas dominante, con concentrazioni fino a 985,300 µmol mol-1. Il δ13CTDIC varia tra -16.6 ‰ e -0.10 ‰ (vs. V-PDB), mentre il δ13CCO2, misurato nel gas libero, varia da -29.9 ‰ a -7.41 ‰ (vs. V-PDB). La composizione isotopica dell’elio è stata misurata solo in pochi campioni (R/RA = 0.20 - 0.33), con valori che indicano una sorgente principalmente crostale. Applicando il bilancio di massa del carbonio, è stata fatta una stima del carbonio endogenico (1.43 × 109 mol a-1), la quale sorgente potrebbe essere associata a diverse sorgenti, tra cui termo-metamorfismo di carbonati indotto dall’intrusione di corpi magmatici di età Quaternaria e/o strutture tettoniche regionali.
La ricerca condotta in Macedonia del Nord rappresenta un primo catalogo delle principali manifestazioni gassose presenti nell’area, sebbene ancora incompleto. Le manifestazioni gassose campionate, comprendenti sia sistemi caldi sia sistemi freddi, sono stati suddivisi in tre gruppi: (i) dominati in N2; (ii) dominati in CO2; (iii) ricchi in H2S. Queste categorie sono ben separate geograficamente, associate, soprattutto, al regime tettonico estensionale e, spesso, associati alle aree di confine tra le principali unità geotettoniche. Il δ13CCO2 varia tra -15.7 ‰ e +1.0 ‰, mentre i valori di R/RA variano da 0.1 a 1.8, suggerendo un’origine perlopiù crostale con un contributo mantellico fino al 20%. La composizione isotopica del metano presenta valori di δ13CCH4 tra -57.8 ‰ e -7.2 ‰ e valori di δ2HCH4 tra -303 ‰ e -80 ‰.
Inoltre, misure di flusso di CO2 al suolo sono state condotte a Duvalo Kosel, Petkoniva e Botun. Per quanto riguardo Duvalo Kosel, un’area studiata in dettaglio, si è stimato una emissione di CO2 di 66.9 t × d-1. A Petkoniva and Botun sono state condotte delle misure preliminari, limitate ad aree caratterizzate da forte alterazione del suolo e mancanza di vegetazione, rivelando un flusso di CO2 di 0.20 t × d-1 a Petkoniva e di 0.59 t × d-1 a Botun.Since the 1970s, scientific research evidenced the close relationship between deeply-derived carbon degassing and active tectonic zones, highlighting the utmost importance of tectonic degassing contribution within the global carbon cycle.
Large-scale degassing of mantle-derived carbon, Quaternary volcanic activity, seismic activity, and regional active fault systems are widespread in the Balkan Peninsula. However, the estimation of geogenic CO2 release from this area is currently still poorly quantified. This PhD research is focused on (i) the estimation of endogenous carbon release from the main karst hydro-systems of Greece and on (ii) the chemical and isotopic characterization of the main gas manifestation in North Macedonia. Moreover, a study about the geogenic and anthropogenic processes affecting the water quality of Hellenic karst aquifers was carried out.
Three main water types were recognized in the Hellenic karst aquifers: (i) calcium-bicarbonate for hinterland springs; (ii) sodium-chloride for coastal springs; (iii) calcium-sulfate derived from gypsum dissolution. Results in terms of major ions and trace elements were compared with the drinking water limits set by the Directive 98/83/EC and the Directive 2020/2184/EC, which are rarely exceeded except for parameters related to marine intrusion along the coastal areas (EC, Na, Cl, B). In these springs, the highest nitrate levels are also found, though always below the drinking water limit. Regarding the chemical composition of the dissolved and free gases collected in the above-mentioned springs, the nitrogen is the dominant gas (up to 985,300 µmol mol-1). The δ13CTDIC varies between -16.6 ‰ and -0.10 ‰ (vs. V-PDB), whereas the δ13CCO2 in free gases ranged from -29.9 ‰ to -7.41 ‰ (vs. V-PDB). The isotopic composition of helium was measured in few samples (R/RA = 0.20 - 0.33), with values indicating a mainly crustal source. An estimation of the endogenous carbon (1.43 × 109 mol a-1) released from these systems was carried out, applying the isotope-carbon mass balance. The geogenic source of carbon may be associated to multiple sources, such as thermo-metamorphism of buried carbonates associated to intrusions of Quaternary magmatic bodies and/or regional tectonic structures.
The research about the gas manifestations in North Macedonia represented a first catalogue, although still incomplete. The collected gas manifestations, comprising both thermal and cold systems, were subdivided in three groups: (i) N2-dominated group; (ii) CO2-dominated group; (iii) H2S-rich group. These categories are geographically well separated, mainly, related to the extensional tectonic regime of the area and, sometimes, associated with boundaries between the major geotectonic units. The δ13CCO2 varies between -15.7 ‰ and +1.0 ‰, whereas the R/RA values vary from 0.1 to 1.8, suggesting a prevailing crustal source with a mantle contribution up to 20%. On the other hand, the isotope composition of methane showed δ13CCH4 values ranging between -57.8 ‰ and -7.2 ‰ and δ2HCH4 varying from -303 ‰ to -80 ‰. Furthermore, soil CO2 flux measurements were carried out at Duvalo Kosel, Petkoniva and Botun. Regarding the former, a detailed investigation was carried out, estimanting a total CO2 output of 66.9 t × d-1. A preliminary investigation was done at Petkoniva and Botun, limited only to patches with heavy soil alteration and devoid of vegetation, revealing a CO2 output of 0.20 t × d-1 at Petkoniva and of 0.59 t × d-1 at Botun
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