*1.1. Research Background and Motivation*

Due to vigorous development of information technology, digital learning development and applied education are very common. Emotions are an important part of everyone and can affect behavior, thinking skills, decision-making, resilience, well-being, and the way human beings communicate with each other [1]. Based on the discussions, emotion not only is the driving factor that promotes learning but also is the primary factor that hinders the learning process as well. Hence, it is crucial to have reliable methods of emotion recognition in academic contexts [2]. The term "affective computing" was proposed by Professor Rosalind Picard in 1997 [3], and it has been guiding computers to identify and express emotions and respond intelligently to human emotions [4]. Owing to this, a trend has developed that applies emotional lenses to emerging academic research and positions emotion at the core of learning [5,6]. Kort and other scholars have proposed an emotion conceptualization module (2001) to combine affective computing with intelligent tutoring system for the purpose of identifying learners' emotions, responding to affections of current learners and promoting learning effectiveness [7]. Moreover, it can also identify the user's emotions and corresponding system responses as well as guide how to keep positive emotions via "mood proxy" and promote the achievement of learning objectives [8,9]. As Chen Huang Cheng mentioned in this book (2006), the best way to relieve negative emotions is to shift your thinking direction and appropriately reduce the expansion of negative emotions. Impacted with positive emotions, determination to solve problems will

**Citation:** Lin, H.-C.K.; Liao, Y.-C.; Wang, H.-T. Eye Movement Analysis and Usability Assessment on Affective Computing Combined with Intelligent Tutoring System. *Sustainability* **2022**, *14*, 16680. https://doi.org/10.3390/ su142416680

Academic Editor: Aras Bozkurt

Received: 11 October 2022 Accepted: 9 December 2022 Published: 13 December 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

be generated when encountering difficulties [10]. In many studies on the affective tutoring system, the experimental results mainly discuss the usability and interactivity of the system. In this study, we use Scan Path to understand the subject's eye movement trajectory and observe his/her eye movement fixation duration in each ROI block to understand if the subject is more willing to stay in the digital course after combining the tutoring system with the affective computing module.


**1. Introduction**

As well known, a pin-structured semiconductor photodetector (PD) is the most important active element of world-spread fiber-optics communication systems (FOCS) [1], where it performs the functions of an effective opticalelectric converter (OEC) in the receiver unit located at the far end of a telecom link. Additionally, in the last decade, this device has found wide application in the intensively developing radio electronic systems (RES) for civil and military purposes based on microwave photonics (MWP) technology [2, 3]. In these systems, the MWP circuitry also contains two more requisite units that carry out electrical-optic conversion (EOC) and processing of radio-frequency (RF) signals in the optical domain [4]. Therein, the EOC operation is realized either by direct

modulation of a semiconductor laser's injection current or by external modulation of an optical modulator pumped by a laser source power. After optical processing such as transmission, amplifying, filtering, time delay, etc., an OEC operation must be performed, for the implementation of which a pin-photodetector is used. Thus, unlike traditional FOCSs, both a laser and a photodetector must be present in a common MWP circuit, which paves the way for its simplifying and, therefore, reducing the cost of the device by combining EOC and OEC functions.

The study of the structures and constructions of modern photodiode and widespread edge emitting laser showed that the former cannot operate in the lasing mode, since there is no amplification layer and optical resonators that provide positive feedback. In addition, the latter is not suitable for operation in a photodetector mode, in principle, since it has a completely different design and even a very small reverse biasing leads to its failure. However, there is a semiconductor laser of a different design: a vertical cavity surface-emitting laser (VCSEL) with an epitaxial structure similar to a photodetector [5, 6], and its long-wavelength version (LW-VCSEL) has a great potential for the application in modern and prospective FOCSs [7] as well as in MWP circuits [8].

In general, a resonant cavity enhanced (RCE) PD based on a pin-photodiode or a Schottky-barrier photodiode is a long-time known optoelectronic device that overcomes the fundamental drawback of an inherent photodetector associated with a compromise between bandwidth and sensitivity [9, 10]. Its design with an active depletion region between two multilayer mirrors of a Fabry-Perot resonator is similar to a VCSEL. Modern development follows the path of researching and fabricating both individual RCE-PD chips in the short-wavelength or long-wavelength telecom spectral range [11, 12], as well as monolithically integrated chips containing on one substrate an optoelectronic pair based on a VCSEL and a RCE-PD [13]. So that, during a literature search, a publication was found [14] reporting the results of an experimental study of RCE photodiode based on a short-wavelength VCSEL with a quantum-well active region operating in the photovoltaic mode or in reverse bias mode. This technological study was carried out in order to determine the conditions for ensuring the maximum quantum efficiency of the OEC, which was regulated by sequentially etching the layers of the upper mirror, as well as the conditions for ensuring the maximum width of the frequency characteristic at the output. The latter was controlled by adjusting the diameter of the active layer.

The motivation for our recent investigation in this direction [15] was to measure the static and dynamic characteristics of the particular LW-VCSEL sample without any structural changes. For this goal, we simply reversed the DC bias polarity to assess the efficiency of its use as part of an optoelectronic coupler based on two identical LW-VCSEL chips, one of which worked as a laser source, and the other as a photodetector. An additional goal was to demonstrate the effective operation of a LW-VCSEL-based RCE photodetector (VCSEL-PD) in an economical photoreceiver for the currently widespread digital FOCS with dense wavelength division multiplexing (DWDM), due to the absence of a spectral demultiplexer needed for a standard DWDM FOCS. Leveraging this concept, two other applications combining LW-VCSEL in the laser and photodetector modes have recently been investigated including the uses in a high-speed optoelectronic switch device for integrated photonics-based optical beamforming network [16] and in cost-efficient optoelectronic frequency-converting transceiver for a base station of 5G cellular communication network [17].

To date, there is one more version of LW-VCSEL-based photodetector [18, 19], where a new concept using such an effective laser technique, especially for lowpower VCSEL, as optical injection locking (OIL) [20, 21], was proposed and preliminary investigated. From the operational point of view, an obvious advantage

**177**

**Figure 1.**

*Studying a LW-VCSEL-Based Resonant Cavity Enhanced Photodetector and Its Application…*

of this approach compared to our one is the possibility of full-duplex operation in a combined EOC/OEC without switching the polarity of the power supply. In the cited papers, an integrated consideration is used that addresses the effect of expanding the bandwidth of an OIL VCSEL-based photodetector (OIL-VCSEL-PD) and experimental study of the signal quality (bit error rate) in a FOCS, when digital signals at a speed of 12 Gbps are transmitted. However, the key parameters of the OIL-VCSEL-PD itself, such as responsivity, the level of introduced noise, etc., have

As a result, in present scientific publications there is no clear answer to the question of selecting the optimal photodetector for the application in microwave- photonics circuits. Eliminating it, this Chapter addresses a comparative experimental study reviewing the known, updated, and newer results to pursue advanced performances corresponding to the key OEC parameters of an inherent pin-photodetector as well as the two VCSEL-based photodetectors in free-running or OIL mode and their applications in the last generation of key MWP circuits for prospective photonics and radio-electronics systems. In particular, pursuing the goal to discovery optimal operation regimes for the VCSEL-based RCE photodetector, Section 2 reviews key features of the C-band (1530–1565 nm) free-running LW-VCSEL as the object for investigation. In addition, Section 3 presents the updated and newer results of measuring static and dynamic characteristics for the LW-VCSEL-based RCE photodetector under study in the above-mentioned operating modes. The results of design and comparative experimental research using a typical MWP circuit that includes OEC based on an inherent pin-photodetector or two versions of VCSEL-based RCE photodetectors under study are demonstrated in

For today, several technologies yielding LW-VCSEL with acceptable performances have been developed. Among them, wafer-fused LW-VCSELs under research (**Figure 1**) employing strained InP/InAlGaAs quantum well (QWs) active region, tunnel junction (TJ) for carrier and optical confinement, and distributed Bragg reflectors (DBR), have also reached the industrial production stage and proven reliability [8]. A particular preference of these LW-VCSELs is in covering the full ITU-T spectral range from O-band to U-band. Concerning MWP approach, an outstanding feature of LW-VCSELs is their compatibility with future large-scale silicon-based heterogeneous photonics integrated circuits [22], which should

*DOI: http://dx.doi.org/10.5772/intechopen.95560*

Section 4. Finally, Section 5 concludes the Chapter.

*Schematic of wafer-fused LW-VCSEL from beam express LLC, Switzerland.*

**2. The object for investigation**

not been studied at all.

#### *Studying a LW-VCSEL-Based Resonant Cavity Enhanced Photodetector and Its Application… DOI: http://dx.doi.org/10.5772/intechopen.95560*

of this approach compared to our one is the possibility of full-duplex operation in a combined EOC/OEC without switching the polarity of the power supply. In the cited papers, an integrated consideration is used that addresses the effect of expanding the bandwidth of an OIL VCSEL-based photodetector (OIL-VCSEL-PD) and experimental study of the signal quality (bit error rate) in a FOCS, when digital signals at a speed of 12 Gbps are transmitted. However, the key parameters of the OIL-VCSEL-PD itself, such as responsivity, the level of introduced noise, etc., have not been studied at all.

As a result, in present scientific publications there is no clear answer to the question of selecting the optimal photodetector for the application in microwave- photonics circuits. Eliminating it, this Chapter addresses a comparative experimental study reviewing the known, updated, and newer results to pursue advanced performances corresponding to the key OEC parameters of an inherent pin-photodetector as well as the two VCSEL-based photodetectors in free-running or OIL mode and their applications in the last generation of key MWP circuits for prospective photonics and radio-electronics systems. In particular, pursuing the goal to discovery optimal operation regimes for the VCSEL-based RCE photodetector, Section 2 reviews key features of the C-band (1530–1565 nm) free-running LW-VCSEL as the object for investigation. In addition, Section 3 presents the updated and newer results of measuring static and dynamic characteristics for the LW-VCSEL-based RCE photodetector under study in the above-mentioned operating modes. The results of design and comparative experimental research using a typical MWP circuit that includes OEC based on an inherent pin-photodetector or two versions of VCSEL-based RCE photodetectors under study are demonstrated in Section 4. Finally, Section 5 concludes the Chapter.


**Aflatoxin B1 and Sterigmatocystin Binding Potential of Non-***Lactobacillus* **LAB Strains**

### **Ildikó Bata-Vidács 1,\*, Judit Kosztik 1 , Mária Mörtl 2 , András Székács 2 and József Kukolya 1**

Received: 17 November 2020; Accepted: 11 December 2020; Published: 14 December 2020

**Abstract:** Research on the ability of lactic acid bacteria (LAB) to bind aflatoxin B1 (AFB1) has mostly been focusing on lactobacilli and bifidobacteria. In this study, the AFB1 binding capacities of 20 *Enterococcus* strains belonging to *E. casseliflavus*, *E. faecalis*, *E. faecium*, *E. hirae*, *E. lactis*, and *E. mundtii*, 24 *Pediococcus* strains belonging to species *P. acidilactici*, *P. lolii*, *P. pentosaceus*, and *P. stilesii*, one strain of *Lactococcus formosensis* and *L. garviae*, and 3 strains of *Weissella soli* were investigated in MRS broth at 37 ◦C at 0.2 µg/mL mycotoxin concentration. According to our results, among non-lactobacilli LAB, the genera with the best AFB1 binding abilities were genus *Pediococcus*, with a maximum binding percentage of 7.6% by *P. acidilactici* OR83, followed by genus *Lactococcus*. For AFB1 bio-detoxification purposes, beside lactobacilli, pediococci can also be chosen, but it is important to select a strain with better binding properties than the average value of its genus. Five *Pediococcus* strains have been selected to compare their sterigmatocystin (ST) binding abilities to AFB1 binding, and a 2–3-fold difference was obtained similar to previous findings for lactobacilli. The best strain was *P. acidilactici* OR83 with 18% ST binding capacity. This is the first report on ST binding capabilities of non-*Lactobacillus* LAB strains.

**Keywords:** aflatoxin B1; sterigmatocystin; lactic acid bacteria; mycotoxin binding; detoxification

**Key Contribution:** Forty-eight strains belonging to the genera *Enterococcus*, *Pediococcus*, *Weissella*, and *Lactococcus* were screened for aflatoxin B1 binding abilities, and also 5 *Pediococcus* strains have been tested for sterigmatocystin binding potential. It is the first time in the literature that sterigmatocystin binding of pediococci is presented. AFB1 and ST binding abilities of strains belonging to the same species vary highly.


**2. Indole and bioisosteric derivatives**

A guide of general principles has been applied throughout SARs for both melatonin receptors. The C5-OMe group of the indole ring is optimal, while the same substituent at positions 4, 6, or 7 leads to a drastic loss of affinity. However, congeners with a halogen at the 5-position do retain high affinity [13]. The relative position of the methoxy group and the *N*-acetylaminoethyl side chain seems to be the most important structural feature that increases the melatonin receptor binding affinity [14–16]. The syntheses of these derivatives are based on classic chemical procedures [17–19]. The indole ring could also be considered as a spacer [20, 21] with the pyrrole portion not involved in the receptor binding pocket, because it can be replaced

**5**

**Figure 2.**

*Highlighted synthetic routes of melatonin 1.*

*Synthetic Melatonin Receptor Agonists and Antagonists DOI: http://dx.doi.org/10.5772/intechopen.91424*

substitution exhibits very potent affinity [28].

and 6-methoxymelatonin by more than 100 times [32].

ligand recognition by melatonin receptors [16, 37, 38] (**Figure 3**).

linked to key amino acid residues of the melatonin receptor subtypes [39].

5-methoxyindole (**8**), as described in **Figure 2**.

by diverse aromatic scaffolds, such as naphthalene, benzofuran, benzothiophene, or benzocycloalkane rings [14, 22, 23]. Various congeners with substitutions in the positions 2 and 6 of melatonin have been synthesized. Substituents, like methyl, phenyl, or halogen at position 2 of melatonin, can increase receptor binding affinity by *ca* tenfold [24–27]. The presence of an optimal *N*-acyl group with a 2-halogen

Interestingly, substituents on the 2-position seem to direct the *N*-acetylaminoethyl

One of the synthetic routes for the production of 5-methoxyindole (**4**) is via the Leimgruber-Batcho reaction [33], modified by Repke and Ferguson [34] (**Figure 2**). A successful side chain functionalization was reported by Ates-Alagoz et al. [35] using the Vilsmeier-Haack formylation reaction of 5-methoxyindole (**4**). On the other hand, Righi et al. [36] applied the direct C3 reductive alkylation of *N*-benzyl-

In an attempt to map the receptor requirements, a series of phenylalkyl amides **9**–**11** were prepared and proven to exhibit the minimal structure required for the

Some C3-modified melatonin analogues have exhibited interesting melatoninergic activities. It has been shown that small modifications in the acyl chain are able to change the binding affinity for melatonin receptors. A typical modification to increase the activity is the replacement of the acetyl by an *N-*butanoyl chain. Depreux et al. reported a 100-fold higher affinity of 5-methoxy-*N*-butanoyltryptamine than melatonin [14]. Tsotinis et al. reported that upon the appropriate functionalization at the end of the C2 side chain, the azido compounds **16** were produced, which serve as photoactivity labels, while the respective isothiocyanate compounds **17** serve as electrophilic probes (**Figure 4**), in order to produce adducts covalently

Luzindole, N-acetyl-2-benzyltryptamine (**21**), is a selective melatonin receptor antagonist with approximately 11- to 25-fold higher affinity for the MT2 than the

side chain into the optimal conformation for interaction with the receptor and increase the ligand affinity [29, 30]. 6-Substituted analogues have been prepared [31] with the aim of retarding metabolism, because melatonin is degraded rapidly in vivo, mainly in the liver, by 6-hydroxylation followed by conjugation and excretion in the urine. A halogen substituent at the 6-position reduces binding affinity nonsignificantly, while the binding affinity of 6-hydroxymelatonin is decreased by 5 to 10 times

#### *Synthetic Melatonin Receptor Agonists and Antagonists DOI: http://dx.doi.org/10.5772/intechopen.91424*

*Melatonin - The Hormone of Darkness and Its Therapeutic Potential and Perspectives*

the main indole and bioisosteric aromatic nucleus derivatives: first, the conformationally restricted; the active chiral compounds second; and the derivatives with

A guide of general principles has been applied throughout SARs for both melatonin receptors. The C5-OMe group of the indole ring is optimal, while the same substituent at positions 4, 6, or 7 leads to a drastic loss of affinity. However, congeners with a halogen at the 5-position do retain high affinity [13]. The relative position of the methoxy group and the *N*-acetylaminoethyl side chain seems to be the most important structural feature that increases the melatonin receptor binding affinity [14–16]. The syntheses of these derivatives are based on classic chemical procedures [17–19]. The indole ring could also be considered as a spacer [20, 21] with the pyrrole portion not involved in the receptor binding pocket, because it can be replaced

**4**

**Figure 1.**

substituted 3-side chains third.

*Regulation of melatonin production.*

**2. Indole and bioisosteric derivatives**

by diverse aromatic scaffolds, such as naphthalene, benzofuran, benzothiophene, or benzocycloalkane rings [14, 22, 23]. Various congeners with substitutions in the positions 2 and 6 of melatonin have been synthesized. Substituents, like methyl, phenyl, or halogen at position 2 of melatonin, can increase receptor binding affinity by *ca* tenfold [24–27]. The presence of an optimal *N*-acyl group with a 2-halogen substitution exhibits very potent affinity [28].

Interestingly, substituents on the 2-position seem to direct the *N*-acetylaminoethyl side chain into the optimal conformation for interaction with the receptor and increase the ligand affinity [29, 30]. 6-Substituted analogues have been prepared [31] with the aim of retarding metabolism, because melatonin is degraded rapidly in vivo, mainly in the liver, by 6-hydroxylation followed by conjugation and excretion in the urine. A halogen substituent at the 6-position reduces binding affinity nonsignificantly, while the binding affinity of 6-hydroxymelatonin is decreased by 5 to 10 times and 6-methoxymelatonin by more than 100 times [32].

One of the synthetic routes for the production of 5-methoxyindole (**4**) is via the Leimgruber-Batcho reaction [33], modified by Repke and Ferguson [34] (**Figure 2**). A successful side chain functionalization was reported by Ates-Alagoz et al. [35] using the Vilsmeier-Haack formylation reaction of 5-methoxyindole (**4**). On the other hand, Righi et al. [36] applied the direct C3 reductive alkylation of *N*-benzyl-5-methoxyindole (**8**), as described in **Figure 2**.

In an attempt to map the receptor requirements, a series of phenylalkyl amides **9**–**11** were prepared and proven to exhibit the minimal structure required for the ligand recognition by melatonin receptors [16, 37, 38] (**Figure 3**).

Some C3-modified melatonin analogues have exhibited interesting melatoninergic activities. It has been shown that small modifications in the acyl chain are able to change the binding affinity for melatonin receptors. A typical modification to increase the activity is the replacement of the acetyl by an *N-*butanoyl chain. Depreux et al. reported a 100-fold higher affinity of 5-methoxy-*N*-butanoyltryptamine than melatonin [14]. Tsotinis et al. reported that upon the appropriate functionalization at the end of the C2 side chain, the azido compounds **16** were produced, which serve as photoactivity labels, while the respective isothiocyanate compounds **17** serve as electrophilic probes (**Figure 4**), in order to produce adducts covalently linked to key amino acid residues of the melatonin receptor subtypes [39].

Luzindole, N-acetyl-2-benzyltryptamine (**21**), is a selective melatonin receptor antagonist with approximately 11- to 25-fold higher affinity for the MT2 than the

**Figure 2.** *Highlighted synthetic routes of melatonin 1.*

**Figure 3.** *Phenylalkyl amides.*

**Figure 4.** *C2-functionalized melatonin analogues.*

MT1 receptor [4]. The synthesis of luzindole, achieved through a Pictet-Spengler reaction and formation of the intermediate β-carboline **19**, was first patented by Dubocovich et al. [40]. In 2008, Tsotinis et al. reported a new method of luzindole synthesis, through the C-3 indole nitroolefin **22**, leading to a much higher overall yield [41] (**Figure 5**).

The benzo[*b*]furan nucleus can replace the indole skeleton and retain its reactivity. 5-Methoxy-3-oxo-2,3-dihydrobenzo[*b*]furan (**25**) was prepared from 4-methoxyphenol (**23**) by acylation with chloracetonitrile followed by cyclization [42] (**Figure 6**).

**7**

**Figure 8.**

*Synthetic Melatonin Receptor Agonists and Antagonists DOI: http://dx.doi.org/10.5772/intechopen.91424*

4-vinyl-2, 3-dihydrobenzofuran (**26**).

**Figure 6.** *Tasimelteon.*

**Figure 7.** *Agomelatine.*

**3. Constrained polycyclic derivatives**

(**36**) [47] is illustrated in **Figure 8**.

*6,7,8,9-Tetrahydropyridino[1,2-a]indole.*

approved for medical use in Europe and Australia [46].

Tasimelteon, *N*-[[(1*R*,2*R*)-2-(2,3-dihydro-1-benzofuran-4-yl)cyclopropyl] methyl] propenamide (**27**), is a melatonin agonist, which bears the benzo[*b*]furan skeleton and was approved by the FDA, in January 2014, for the treatment of non-24 h

sleep–wake disorder [43]. The starting material for the synthesis of tasimelteon is the

The naphthalene scaffold can also be considered as a melatonin-acting biomolecule with high affinity and potency [44, 45]. The preparation of the key intermediate in this synthesis, 2-(7-methoxy-1-naphthyl)ethanol (**31**), is depicted in **Figure 7**. Agomelatine, *N*-[2-(7-methoxy-1-naphthyl)ethyl]acetamide (**32**), was recently

Tricyclic and even larger constrained derivatives have been investigated for their melatoninergic potency. The synthesis of 6,7,8,9-tetrahydropyridino[1,2-*a*]indole

**Figure 5.** *Luzindole.*

*Synthetic Melatonin Receptor Agonists and Antagonists DOI: http://dx.doi.org/10.5772/intechopen.91424*

**Figure 6.** *Tasimelteon.*

*Melatonin - The Hormone of Darkness and Its Therapeutic Potential and Perspectives*

MT1 receptor [4]. The synthesis of luzindole, achieved through a Pictet-Spengler reaction and formation of the intermediate β-carboline **19**, was first patented by Dubocovich et al. [40]. In 2008, Tsotinis et al. reported a new method of luzindole synthesis, through the C-3 indole nitroolefin **22**, leading to a much higher overall

The benzo[*b*]furan nucleus can replace the indole skeleton and retain its reactivity. 5-Methoxy-3-oxo-2,3-dihydrobenzo[*b*]furan (**25**) was prepared from 4-methoxyphenol (**23**) by acylation with chloracetonitrile followed by cyclization [42] (**Figure 6**).

**6**

**Figure 5.** *Luzindole.*

yield [41] (**Figure 5**).

*C2-functionalized melatonin analogues.*

**Figure 3.** *Phenylalkyl amides.*

**Figure 4.**

**Figure 7.** *Agomelatine.*

Tasimelteon, *N*-[[(1*R*,2*R*)-2-(2,3-dihydro-1-benzofuran-4-yl)cyclopropyl] methyl] propenamide (**27**), is a melatonin agonist, which bears the benzo[*b*]furan skeleton and was approved by the FDA, in January 2014, for the treatment of non-24 h sleep–wake disorder [43]. The starting material for the synthesis of tasimelteon is the 4-vinyl-2, 3-dihydrobenzofuran (**26**).

The naphthalene scaffold can also be considered as a melatonin-acting biomolecule with high affinity and potency [44, 45]. The preparation of the key intermediate in this synthesis, 2-(7-methoxy-1-naphthyl)ethanol (**31**), is depicted in **Figure 7**. Agomelatine, *N*-[2-(7-methoxy-1-naphthyl)ethyl]acetamide (**32**), was recently approved for medical use in Europe and Australia [46].


2.3.2. Herbivory and Food Webs

The accurate and repeatable identifications of species is imperative if we are to fully understand the ecology and evolution of interactions among partners in natural and humanaltered environments. This requirement is especially true for specialized interactions, including mutualisms and antagonisms. The application of DNA barcodes as species-level markers has revolutionized our ability to track species interactions and the community networks they form, in boreal, temperate, and tropical habitats.

Food web interactions have been greatly clarified with the application of DNA barcodes. Smith et al. [116] using the CO1 DNA barcode marker were able to verify the food web structure of the spruce budworm and its numerous parasitoids to understand the population dynamics of this major pest of trees in boreal forests. The utility of DNA barcodes to identify the diversity of host plants for herbivorous beetles have been demonstrated in both neotropical [62,117] and Asian tropical forests [118]. These early studies used a limited number of molecular markers and were only able to identity the hosts at the generic or familial level.

The most comprehensive analyses between herbivorous beetles and their host plants have been conducted by García-Robledo and colleagues [72,73,119]. The host-specific relationships between rolled-leaf beetles in the genera *Cephaloleia* and *Chelobasis* (Chrysomelidae) and plants in the order Zingiberales have been well-studied by ecologists [120], but the application of DNA barcodes to both the beetles and the hosts have provided a much more detailed and quantitative measure of these interactions [74]. One of the advantages of using an easily extracted DNA barcode is that the beetles can be identified at any of their life stages and not only as adults as in most previous investigations using morphological features [119]. Once the basic network of food web interactions is established using DNA barcodes, comparisons can be made across habitats, elevations, and temperature gradients. Most recently Palmer et al. [121] have extended this methodology to the interactions among katydids and their host plants in a wet forest habitat in Panama. They found that, in general, these insects consumed a broad range of flowering plants and were rarely specialists on only a few species. It has been shown in numerous cases (e.g., Hebert et al. [70]) that

DNA barcodes can detect the presence of cryptic species, especially in insects. This power of DNA barcoding has greatly improved the understanding of species boundaries in the rolled-leaf beetles, allowing for more precise mapping of the insect–host networks. The detection of these cryptic species clearly demonstrated that the elevational distributions and thermal tolerances of the beetles was much narrower than previously thought, which will have an impact on the food web networks as climate change differentially impacts both host and herbivore migrations [73].

DNA barcodes have also altered our view of why tropical biomes are so diverse. It has long been held that specialized ecological interactions, which are common in tropical forests, will lead to reproductive isolation and speciation, and hence greater biotic diversity in the tropics. One such specialization is that between tropical flowers and the nectar-robbing floral mites that are caried from plant to plant on the bills of hummingbird pollinators [122]. This specialization allows floral mites to easily find mates and reproduce, because many conspecifics accumulate in the flowers of only a few species of plants. This "mating rendezvous hypothesis" [123] accounted for the host specialization in these mites. However, using DNA barcode markers to identify the mites, rather than morphological identification, has now shown that most floral mites are generalists and not specialists [124]. The mating rendezvous hypothesis is no longer supported, at least for mite diversification.

This detailed understanding of herbivore–host interactions using DNA barcodes has also been applied to large mammalian herbivores. In a semiarid African savannah, Kartzinel et al. [125] determined the extent that sympatric mammalian browsers and grazers could partition their diets. After building a library of plant DNA barcodes for the local flora, they quantified the diet breadth, composition, and overlap for seven co-occurring mammal species, ranging in size from dik-diks to elephants using DNA metabarcoding. Earlier conclusions on competition and coexistence in these habitats based on low-resolution analyses were shown to be misleading, according to the more high-resolution taxonomic data provided by the metabarcoding results. This work in Africa has now been extended to demonstrate that the abundance and diversity of food plants is negatively associated with their mammalian herbivores, apparently to avoid consumption [126]. The same type of DNA barcoding protocol has also been adapted to tracking and identifying the vectors of bird-dispersed fruits and seeds in the field [127] in order to build a quantifiable network of frugivores and seed dispersal interactions.

### 2.3.3. Symbiotic Relationships and Plant-Pollinator Interactions

Symbioses, perhaps the most characteristic of "species interactions," entail very close relationships between two or more species living together, and DNA barcodes have facilitated researchers studying such close interactions [128]. In some groups (e.g., fungi, [129]), DNA barcoding has revolutionized the field, especially where symbiotic partners are very closely associated and interactions often exist at a cellular level (e.g., in lichens [130]). The use of DNA barcodes to understand symbioses is common in all major clades, including arthropods [131], vertebrates [132], green plants [133], and fungi [134]. An especially powerful tool for symbiosis-based research is metabarcoding [135], which allows for pooled sequencing from closely associated, symbiotic organisms that are otherwise difficult to isolate. The application of DNA barcodes to more closely track and untangle symbiotic relationships is still in its infancy (see below Section 3.1).

The interactions between plants and pollinators is a symbiotic mutualism that is critical for the survival of both partners. An understanding of the dynamics of these interactions is a priority for plant and insect ecologists to conserve biodiversity and to protect the agricultural crop supply chain. DNA barcodes have been explored for more than two decades as a means to identify plants from the insects that have visited them as pollinators [136]. Given the nature of pollination dynamics, samples removed either from plants or their pollinators can include a mixed community of pollen and, therefore, metabarcoding approaches provide a unique tool to identify the diversity contained in these mixed samples [137,138].

Clare et al. [139] were among the first to apply metabarcoding to study plant–pollinator interactions, extending the concepts earlier proposed by Valentini et al. [68] and Soininen et al. [140]. A key threshold for advancing these methods is a comprehensive DNA barcode sequence reference database. For example, the first national DNA barcode sequence reference database of Wales [141] has provided a benchmark for DNA metabarcoding studies of plant– pollinator interactions and this has recently grown into a comprehensive database for all of the United Kingdom [59]. Together, these databases have proven powerful for reconstructing bee foraging behavior [142–144]. These and other studies [145–147] have built a strong foundation for using DNA metabarcoding to study plant–pollinator interactions.


*Editorial* **Green Economy and Sustainable Development: The Outlook**

**Sergey Zhironkin 1,2,3,\* and Michal Cehlár 1,4**

Modern theories that make up the paradigm of sustainable development, and the best practices derived from them, are based on the consistency of individual and public needs, factors of economic growth and ecosystem conservation. The trend of green economy expansion is moving from a challenge facing modern society to the dominant area of scientific thinking, which is increasingly focused on solving the problems of reducing the anthropogenic impact on the environment, primarily on the climate. At the same time, the level of scientific and technological progress, and the quality of life that modern civilization has reached, require the preservation and increase in the specific consumption of various resources in the long term. Therefore, green economy technologies that ensure the transition to sustainable development are initially focused on the optimal and integrated use of non-renewable resources and the maximum involvement of renewable resources in the production of goods specific for a post-industrial era [1]. Based on this, the evolution of sustainable development methodology should be carried out in the system of innovative development of industrial technologies and their adaptation to the latest trends in energy and urbanism, ecology, finance and investment.

At the same time, sustainable development is associated with increasing the responsibility of business, governments and the entire society, around the world, for achieving a balance between current and future needs for subsoils, energy, traditional and new materials, and transport. Such responsibility equalizes environmental and social problems (poverty and malnutrition, inequalities in access to wealth and income distribution), which often have common roots. This, in turn, highlights the importance of interdisciplinary and multilateral research on sustainable development issues, the results of which can answer questions about green economy perspectives.

The green economy—the newest way to obtain and use resources—is a product of the Fourth Industrial Revolution and concentrates many of the achievements of Industry 4.0. The related structural shifts in the economy are caused by the emergence of new industries of waste recycling, zero-emission energy production, absorption of greenhouse gases emissions, green urbanism, and post-mining. These shifts should be matched by a parallel increase in productivity and labor safety, improved access to drinking water, food, energy, as well as in joining the efforts of national states and businesses in the fight against climate change, in replacing minerals with renewable resources.

However, a true transition to a green economy is possible only with the sustainable development of all industries and the saturation of both production and consumption with green technologies. Green production should be developed in basic industries (mining, energy, engineering, chemistry, transport), as well as in high-tech industries that set new horizons for environmentally oriented modernization. These processes, integral to sustainable development, are united in the "green growth" concept, the main trend of green

**Citation:** Zhironkin, S.; Cehlár, M. Green Economy and Sustainable Development: The Outlook. *Energies* **2022**, *15*, 1167. https://doi.org/ 10.3390/en15031167

Received: 31 January 2022 Accepted: 3 February 2022 Published: 4 February 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

economy development, which consists in increasing the production of so-called "sustainable goods and services", the main feature of which is recycling and zero emissions of toxic substances. At the same time, there is no consensus among academicians on the extent to which the growth trend of the green economy will coincide with traditionally driven growth (increase in the production of "high-carbon" energy, industries with large volumes of waste). Therefore, the creation of platforms for discussing the problems of sustainable development and the green economy is important for the publication of research papers on a wide range of related topics.

Thus, the discussions in the field of sustainable development, unfolding in the pages of scientific journals around the world, should provide the answers to a number of challenges facing the world economy.

The first challenge is to achieve the sustainable development goals set by the UN [2] (including ensuring universal access to affordable and clean energy sources, promoting decent work and economic growth, ensuring sustainable cities and communities, responsible consumption and production, et al.), without a simultaneous deterioration in the functioning of existing industries that concentrate investments, jobs, and tax payments. In other words, the balance between current and future production and consumption has not yet been found. The road is left wide open for unbalanced government policies towards a green economy, which could potentially cause a decline in investment activity and significantly slow down economic growth, especially in developing countries. Therefore, modern science faces the issue of ensuring the evolutionary development of green economy and regulating its expansion in such a way that the investments, jobs and consumer demand do not provoke national and global economic crises. It is important that the new "green" jobs are usually created in traditional industries and infrastructure, associated with the reduction in energy consumption, waste generation and emissions of toxic substances.

The second challenge is to ensure the investment attractiveness of the processes that form the green economy and the development of B2B, B2C, B2G, C2B, C2G, G2B, G2G relations in it, in which the development and implementation of standards for companies' environmental responsibility will not destroy the existing incentives for innovation. Setting eco-efficiency requirements for business can be an effective first step towards a green economy, sustainable energy production from alternative sources and sustainable urban development, without increasing pressure on the environment. The fact that these problems are reflected in a wide range of scientific publications inspires optimism for an increase in eco-efficient investments, the share of which reaches its maximum in the green economy.

The third challenge is the sustainable development of the energy sector and the expansion of its "green" segment producing zero emissions. The key trend in the development of modern industry is its ESG transformation, which combines the reduction of greenhouse gases emissions in energy production and transport (in the economy as a whole—a decrease in specific energy consumption), advances social responsibility and the efficiency of stakeholders' interactions, in solving sustainable development problems. As part of the ESG transformation, the development of green energy is aimed at the decarbonization of industry and cities, as a response to the growth of greenhouse gases emissions and the unfavorable climate changes caused by them. It implies increasing the share of carbon-free transport and cities during transition to the use of renewable energy sources (solar, wind, biomass, biogas, geothermal), as well as hydrogen fuel. It is important that the global research community does not demonstrate a technocratic approach to solving the problems of the green economy and energy, but fundamentally explores the possibilities of developing responsible ESG investment that takes into account environmental and social factors, when making decisions on the creation of new energy and industrial systems, as well as expanding urban agglomerations.

The fourth challenge to sustainable development is associated with the innovations in traditional industries that occupy an important place in the modern economy, in particular, mining. In the transition to a green economy, the most important step should be to ensure the main value of modern society—the labor safety and the protection of human lives. The

technological level of the extractive industries sets the pace for reducing the negative anthropogenic impact on the ecosystem and, at the same time, improving the quality of life of the population in industrial clusters, which is in line with the UN sustainable development goals. Therefore, research into the issues of modernization of mining equipment, in order to improve labor safety and prevent man-made disasters, should take an important place in the mainstream of sustainable development.

Considering the importance of these challenges for sustainable development, the purpose of this Special Issue is to disseminate the results of cutting-edge research and broadcast the opinions of scientists from around the world, providing technological breakthroughs in green energy and urbanism, recycling and modernization of basic industries, conducting fundamental research on the economic problems of the transition to sustainable development.

Acting as the Guest Editors of this Special Issue, we got a chance to see the comprehensive understanding of sustainable development and the green economy emerging in the international scientific community. The positive response of researchers from different countries, supported by the number and high quality of articles published in this Special Issue, contributed to the expansion of horizons in sustainable development research, by combining economic and technological approaches. These approaches are based on the accumulated results of theoretical analysis and practical experience in the balanced use of non-renewable and renewable resources, the transition towards a circular economy and zero emissions. A consistent and multi-stage progress of green economy allows for the protection the world community from crises of overproduction and underconsumption, increasing the equity of access to the modern blessings of civilization, and goes beyond the rigid framework of academic discussions. The stable expansion of the green economy should be accompanied by an increase in the social well-being of not only current, but also future generations, which increases the responsibility of researchers, investors and governments. This is the main idea that this Special Issue promotes.

Articles collected in the Special Issue and selected for publication cover a wide range of sustainability and green economy issues, including green urban development and recycling, strategic production planning and market integration, zero-emission alternative energy sources, and Industry 4.0 technologies to reduce energy consumption, innovative modernization of extractive industries to improve labor safety. A special place is occupied by studies of the post-industrial transformation of industrial clusters.

Articles published in this Special Issue, as a part of Energies, are grouped in accordance with their thematic area, which corresponds to the aforementioned challenges for green economy expansion and sustainable development.

With regard to the first challenge (fundamental research in achieving sustainable development goals and stabilizing the green transformation of the economy), four articles address the sustainability of cities, planned product aging, energy markets integration, regional operational programs financing. Their provisions are related to solving the fundamental problems of sustainable development.

The article by Margeta et al. [3] provides an overview of the problems of energy and water supply in modern cities. The authors note that the high concentration of the world population in urbanistic areas causes an overconcentration of energy and water consumption in them, which makes it relevant to find ways to reduce the dependence of modern cities on their external sources, taking into account climatic features and vulnerability to natural disasters. The relevance of the presented study lies in the fact that the Seawater Steam Engine (SSE) technology proposed by the authors, which is fully consistent with the philosophy of sustainable development and based on the original "loop" concept, makes it possible to ensure the energy security of the city and its provision with critical resources, using methods and means of accumulation of electric and thermal energy, based on geothermal sources.

Niklewicz-Pijaczy´nska et al. [4] presented a method for identifying the purchasing attitudes of durable goods' buyers, considering deliberate product aging. The authors analyze the negative externalities associated with the efforts of producers to program the replacement of goods by consumers, which generate significant private and social costs, and hinders sustainable development. The article presents a critique of the deliberate aging of products as inconsistent with the goals of sustainable development and contradictive to its model, and shows the results of an analysis of the factors of purchase of restitution goods, mainly, the income of buyers and the specifics of the goods. The main conclusion of the authors can be considered as the recognition of planned product aging as inappropriate for the tasks of preserving the environment by the majority of consumers, who positively assessed the transition to closed cycles of durable goods production.

In the article by Rybak et al. [5], the problem of achieving the Seventh Sustainable Development Goal (SDG7: affordable, reliable, sustainable and clean energy for all by 2030) is explored from the point of view of the integration of energy markets of European countries. The spatial information system proposed by the authors, based on the indicators used by Eurostat, was subjected to cluster and TSA analysis. As a result, it was found that in the course of the transformation of the energy systems of European countries, new unique clusters arise, and there is a need for additional indicators for assessing the production of affordable and clean energy. The author's findings, presented in the article, contribute to SDG7 achievement, in terms of realizing the potential of green energy to balance economic growth and increase health and well-being rates, as well as avoiding crises in energy production and consumption.

Mach et al. [6] reviewed the effectiveness of Regional Operational Programs, in the context of sustainable development of Polish provinces, by analyzing the correlation between public regulation and regional economic indicators that characterize sustainability (with an emphasis on employment and income indicators, housing construction). In the presented study, the authors used a method for determining the closeness of the relationship between public spending in the field of sustainable development and macroeconomic determinants, based on the temporal variability of the correlation and regression dependencies of the used determinants. Its use made it possible to determine the positive impact of Regional Operational Programs on regional entrepreneurial and socio-institutional capital. Its increase advances the regions on the path to sustainable development, which has a practical aspect for the effectiveness of EU funds disbursement.

With regard to the second challenge—the development of economic relations and processes that form a modern green economy—three articles have been published. They explore the problems of economic evaluation in waste disposal and recycling, increasing the efficiency in the use of material resources and optimizing their production, consumption and environmental regulation of the processes of the post-industrial economy. The scientific provisions outlined in these articles are of a practical nature and designed to help solve the short- and medium-term problems of the transition to the green economy.

The article by Stehlíková et al. [7] provides an approach to economic incentives for improving waste management (using the example of the Slovak Republic), taking into account the economic situation of households—the second waste producer after industry. In the course of the study, the authors used statistical methods, such as correlation analysis of economic indicators of household well-being and the quality of waste management, the results of which were verified using polynomial dependencies. The extension of this methodology to the regions of Slovakia, using cluster analysis, made it possible to determine the economic incentives for processing communal waste, to reduce their storage volumes and energy production.

Tausova et al. [8] analyzed the compliance of established practices and emerging trends in the use of material resources with the Environmental Policy Goals adopted in the European Union. The authors rightly note that the transition to a circular economy includes, in addition to new technologies for the design and consumption of materials, a reduction in the material and energy intensity of existing industrial production. The article provides a comparative analysis for the consumption of material resources in EU countries, using the cluster approach and statistical data processing by JMP software. The

authors have established that the relationship between tax regulation on the use of natural resources and energy production, and changes in the material consumption of industry, is close to linear. The results of the study made it possible to identify the heterogeneity of EU countries in the effectiveness of the economic policy of reducing the use of natural material resources and switching to their recycling, which helps to improve the process of setting energy and environmental goals.

Raszka et al. [9], in their article, give a comprehensive assessment of the potential for the post-industrial development of cities and municipalities, taking into account social, economic and environmental criteria. In their study, the authors set the task of identifying strategic goals, the achievement of which means sustainable development acceleration, using a multidimensional analysis method for this, considering the distances between individual diagnostic variables. The application of the research method to the Wałbrzych Region (Poland) made it possible to rank the municipalities in terms of the social, economic and environmental potential of post-industrial development, which outlines the ways to improve regional environmental and economic policy. The authors paid special attention to the changes in the living conditions of the population and the structure of jobs, development of cultural service and tourism.

Eight articles are devoted to the third challenge to sustainable development—overcoming the green energy limitations and decreasing greenhouse gases emissions. The authors consider the issues of optimizing the use of green energy, taking into account the achieved standards of living, the dependence of carbon dioxide emissions on changes in energy consumption, the development of alternative solar energy, greening of traditional thermal engineering, the impact of diffusion of Industry 4.0 technologies on energy consumption, achievement of near-zero carbon dioxide emission in urban areas. The main conclusions and proposals presented in these articles are mostly practical and can be used both in strategic and operational management of the green economy processes.

Malinowski [10] analyzes the relationship between the quality of life in the EU and the development of alternative energy, focusing on the key role of green modernization of energy production, in ensuring a high standard of living for future generations. The article presents the results of empirical studies on the relationship between the development of green energy and living standards, based on the TOPSIS method and multi-criteria selection of variables, which include publicly available data from the EUROSTAT database. The results of the statistical analysis performed showed a relatively high value of the Spearman rank correlation coefficient, between quality of life indicators and the development of green energy, which confirms the idea of the inevitability of the transition to alternative energy sources in the mainstream of sustainable development as a condition for increasing the well-being of future generations.

Fong et al. [11] studied the dependence of the dynamics of energy consumption and emissions of carbon dioxide (the main greenhouse gas) as the main obstacle to sustainable development. The originality of the author's approach is the use of economic indicators (labor, capital and energy resources) to analyze carbon dioxide emissions in relation to GDP production. The statistical data obtained in the Guangdong-Hong Kong-Macau Greater Bay Area were used as the factual basis of the study, and analyzed in three stages (SBM-DEA model, SFA analysis). The results of the study made it possible to propose a number of recommendations for the development of state incentives for energy efficient and low-carbon production, and the provision of modern environmental protection standards.

In the article by Rybár et al. [12], the concept of a non-metallic flat plate solar collector is reproduced and a technique for evaluating its efficiency is shown. In accordance with the principles of the transition to a green economy, the development of green energy should be accompanied by a reduction in the material intensity of energy production from alternative sources, in particular, a reduction in the content of metals in solar equipment. In accordance with this, the authors proposed, and experimentally confirmed, the prospect of replacing the metal parts of the solar collector with a block of foam glass. The article presents a two-stage evaluation of the flat plate solar collector, a quantitative evaluation

with a theoretical curve of the efficiency, followed by verification during experimental tests. As a result of experimental verification, the functionality of the concept of the flat plate solar collector was confirmed and problem areas were identified that require special attention when developing a prototype.

Bajno et al. [13], in their article, considered the possibilities of improving the traditional chimney system in reducing energy consumption, based on data obtained from the use of artificial neural networks in predicting temperature distributions in the building of chimney systems. The transition to the operation of energy-efficient buildings requires solving the problems of thermal energy losses, as soon as possible, in relation to a large number of existing buildings, as well as for facilities under construction. The authors conclude that improving the insulation of chimney systems is required to reduce energy consumption in older buildings, as well as avoiding the overheating of parts of rooms by regulating the amount of heat supplied to various parts of the building.

Beer et al. [14], in their article, presented the results of the development of the concept of a concentrated solar heater for segmented heat accumulators and an assessment of the prospects for its use in cooking, without burning fossil fuels. The traditional design of the earth oven, considered by the authors, is successfully supplemented with batteries that receive thermal energy from solar radiation in sufficient quantities. The original design proposed by the authors is quite simple and includes solar vacuum heat pipes, a solar radiation concentrator and heat accumulators. The design parameters were determined based on computational fluid dynamics and the transient simulation of selected operating situations and applied for three spatial points. As a result of the simulation, the possibility of safe and healthy cooking using heat accumulators was confirmed.

In the article by Khouri et al. [15], the prospects for innovative development of electricity production from solar energy, associated with the expansion of the range of materials used in the solar industry, are considered. The authors analyze the prospects for the use of the high purity polyvinyl butyral as a sealing material, based on the results of the molding process, homogenization, and analysis of physical and chemical characteristics during laboratory tests. The article pointed out that the applicability of polyvinyl butyral varies, depending on the location of the solar power plant, affecting UV radiation, atmospheric permeability, temperature ranges.

In an article by Wachnik et al. [16], the problem of the information gap in reducing the energy consumption in the industry, due to Industry 4.0 technologies diffusion, is considered. The authors advocate an absolute sense of the success of energy reduction industry-specific projects, associated with the development of IT, allowing for the optimization of decisions in the design of energy systems. Using the example of projects to minimize energy consumption at enterprises located in Poland, the authors presented the characteristics of information gaps in ICT projects in the industry, which are part of the methodology for reducing information risks in the energy sector and, ultimately, energy consumption.

Xu et al. [17] proposed the use of a three-stage planning method to achieve zero carbon dioxide emissions in the process of developing an integrated energy-planning scheme. The authors used a goal of the setting of regional integrated energy planning, which includes the definition of objects and the development of a strategy, as well as the formation of a methodology. The article proposes indicators for achieving planning goals, which are indices of the share of renewable energy in primary energy, the share of renewable energy in total consumption, and the reduction of carbon dioxide emissions, which are determined for each analyzed area for subsequent comparison. It is important that the results of the author's research can be translated, to improve integrated energy planning in various regions.

The fourth challenge facing sustainable development—the innovative modernization of traditional extractive industries to improve labor safety—is the subject of an article by Szurgacz et al. [18] The authors explore the safety issues of machines and workers in coal mines, associated with mechanical support in a longwall complex. In conditions of

increasing output capacity of longwall, it is important to ensure the introduction of new technologies to protect the working space from the impact of rock mass. In accordance with that, the authors develop the mean of automation in the hydraulic control of the roof support, suggesting the introduction of a two-valve unit into the hydraulic system that provides automatic expansion of the support sections. The article presents the results of tests of a real installation of automated control of mechanical support in a longwall, showing a reduction in working time of the support operator, which is important for improving labor safety and productivity.

The articles published in the Special Issue, "Green Economy and Sustainable Development", highlight topics of the future prospects for reducing the anthropogenic impact on the environment, while maintaining the trend towards improving the well-being of mankind. In the near future, the economies of countries—the main producers of raw materials and energy—should take a massive step forward, in terms of reducing greenhouse gases emissions (to zero in the future), expanding materials recycling and responsible waste management. The contribution of science to accelerating the transition to sustainable development and green economy is to form a systemic response to such challenges as reducing the anthropogenic impact on the environment, ensuring access to alternative energy with zero emissions for everyone, creating jobs and attracting investments in the green economy, increasing environmental and labor safety in traditional industries, including the mining of minerals.

To help in solving the problems of sustainable development, the current Special Issue brings together the work of researchers from the world's leading centers of Earth science, on the economic assessment of the prospects for the development of green energy and green urbanism, strategic planning in sustainable development, innovative modernization of mining and thermal power, material engineering.

Along with this, in the modern world, there are many gaps that hinder the transition to sustainable development and determine the further advancement of scientific ideas. These include post-mining and restoration of biodiversity in industrial clusters, the promotion of new materials and technologies for recycling and renewable energy, the development of unmanned equipment on the Industry 4.0 technology platform, etc. We are confident that this Special Issue of "Energies", dedicated to sustainable development, will contribute to the consolidation and popularization of the ideas of research teams from many countries around the world, including China, Australia, Slovakia, Poland, Russia and Germany.

**Author Contributions:** The authors contributed equally to this work. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** This research was supported by TPU development program.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**


**2. CVD Setup for Growth of MoS2**

The basic concept of CVD is very simple, and it is schematically presented in Figure 1a: the precursors—either only S or both S and Mo compounds—are delivered in gaseous form to a substrate (placed on a susceptor of graphite or similar material) kept at high temperature, where the chemical reactions needed for the deposition of MoS2 occur. Most of the results reported in literature have been obtained using a standard horizontal reactor, such as that sketched in Figure 1. This configuration, although widely used, has the drawback of a nonuniform precursor gradient along the flow direction, resulting in a nonuniform deposition and in intrinsic difficulty in optimizing the growth parameter, since small changes in substrate position or in precursor supply may cause nonreproducible results. Development of vertical CVD reactors may help in solving these issues, since with this configuration, temperature and precursor supply may be more easily controlled and homogenized [29].

In the standard horizontal configuration, a quartz tube about 1 m long with a diameter of 2–5 cm is used. The heating is provided by a resistance placed around the tube. The reaction for MoS2 deposition requires a temperature in the 600–800 ◦C range, but in some cases, the supply of sulfur requires a second heating zone in the 100–200 ◦C range. In this case, to obtain better reproducibility and control, it is more convenient to separately and independently heat this additional zone (T2 in Figure 1a) in which the sulfur precursor is placed.

It is also possible to deposit the molybdenum precursors directly on the substrate, either in solid form (Figure 1b) or as a liquid solution (Figure 1c). Growth promoters, to obtain better control of the process, can be added either directly on the growth substrate or on a different substrate (Figure 1d). As a last method, the use of gaseous precursors (Figure 1e) avoids the need for placing the precursors inside the tube before the beginning of the process.

**Figure 1.** Schematic view of the CVD tube in different configurations for MoS2 flake growth: (**a**) with solid precursors separated by substrate; (**b**) with solid molybdenum deposited on growth substrate; (**c**) with liquid molybdenum precursors; (**d**) with solid precursors and drop-casted promoters (either on growth substrate or a different substrate); (**e**) with gaseous precursors.

> A standard routine to minimize the contamination from external air and O2 in the reaction tube is to purge the system with inert gas several times before starting the growth, eventually evacuating the tube with a rotary pump and then flushing with purified Ar or N2 up to ambient pressure, repeating this procedure several times.

> The actual CVD process depends on the chemical status of the used precursors (solid, liquid, gaseous), but it is nevertheless possible to divide it into the following steps:

> The precursors are brought into gaseous form and diluted in an inert carrier gas; e.g., powders are evaporated/sublimated, or a controlled amount of gas is measured by means of a mass flow controller.

> The reactive species are transported by the carrier gas to the substrate. Chemical reactions may also occur in this step, e.g., reducing reactions.

The precursors diffuse towards the substrate surface.

The precursors are adsorbed at the surface, where adatom adsorption and migration occurs. The MoS2 flakes synthesis occurs in this step. By-products re-evaporate or desorb into the gas streams and are carried away into the exhaust.

The heating ramp times are usually in the range of 10–30 min from room temperature to growth temperature. The heating of sulfur powders typically starts when the substrate is already at the target temperature; this permits avoiding injecting S into the system before a constant substrate temperature is reached, limiting prereactions. The MoS2 growth proceeds for about 10–20 min, and then the system naturally cool downs to ambient temperature. If powders are used as reagents, heating of the substrate and of the MoO3 powders occurs simultaneously, since they are usually placed very near the substrate. This means that Mo starts to evaporate before the substrate reaches the target temperature.

Flake synthesis is dependent on different parameters such as the growth temperature and the distance between the substrate and the powders. Flow rate, chamber pressure, precursor supply, powder dimension, and purity also affect the final outcome of the growth. Despite the simplicity of the process, if excellent control is not achieved, the results may not be completely reproducible, and large-scale deposition can be very hard to obtain.

While it has been shown that different carrier gases can strongly influence the growth of graphene [30], considerably less attention has been devoted to this topic for the growth of MoS2. Considering that S is a strong reducing agent, the use of a purified inert gas (N2 or Ar) is usually sufficient for the sulfurization reaction to occur, and the carrier gases can be considered as inert in the reactions at the basis of 2D nucleation and growth. The use of H2 is thus not common in the MoS2 CVD process. Nevertheless, it was argued that H2 can have beneficial effects, as it can inhibit the thermally induced etching effect and promote the desulfurization reaction [31]. By carefully adjusting the amount of hydrogen in a H–Ar mixed carrier gas, authors were able to obtain layers with high crystallinity and a nearly perfect S/Mo atomic ratio. It was also suggested that, in the case of MoS2 growth using Mo(CO)6 with (C2H5)2S as precursors, the presence of H2 is necessary for removing carbonaceous species generated during the MOCVD growth, permitting increasing the average grain size from hundreds of nanometres to more than 10 µm [32].

Carrier gas flow rate was reported to affect the morphology of flakes, as well as their size and density: lowering the gas carrier flow during the heating stage from 35 to 15 sccm permitted increasing the density and size of the flakes [33]. Moreover, the shape of MoS2 flakes changed from zigzag to triangular as the gas carrier flow was decreased, indicating higher material quality. This behaviour was directly related to the quantity of S in the gas phase. As the carrier flow increased, the S transport grew more efficient, and S reacted with MoO3 powders, suppressing their evaporation, lowering MoO3 partial pressure, and promoting zigzag edge termination.

In order to have better control over S and MoO3 reactions during the heating stage of the process, a procedure of "flow reversal" was proposed [34]. During the heating of the furnace, Ar was introduced from the side of the Mo powders towards the side of the S powders (Figure 2). In this way, S reached neither the substrate nor the Mo powders, and any unintentional reaction was prevented; growth and nucleation of MoS2 far from the steady growth regime was inhibited. Once the setpoint temperatures of both substrate and S powders were reached, the Ar flow direction was switched back to the standard direction, so that it entered from the S powder side and delivered S vapours to the Mo powders and the substrate. Using this two-stage growth, the mean side length of MoS2 flakes was increased up to 250–300 µm.

**Figure 2.** (**a**) Flow reversal method to improve MoS2 deposition; (**b**–**d**) typical optical images of MoS2 flakes obtained with the modified procedure. Adapted from [34].

Another custom setup to obtain better control of the precursor supply and to avoid cross-contamination of MoO3 and S powders consisted of placing S powders in a small tube nested inside another, larger tube so that S did not contaminate the MoO3 powders before entering the reaction zone [35].


Isolated Compounds Structure Determination Using NMR and MS

Fourteen compounds were isolated and identified using different spectroscopic techniques including (**1**) apigenin 6-*C*-(2-deoxy-*β*-D-galactopyranoside)-7-*O*-*β*-D-quinovopyranoside, (**2**) luteolin 6-*C*-α-L-rhamnopyranosyl-(1-2)-*β*-D-fucopyranoside, (**3**) apigenin 6-*C*-*β*-Dgalactopyranoside, (**4**) apigenin 6-*C*-*α*-L-rhamnopyranosyl-(1-2)-*β*-L-fucopyranoside, (**5**) carambolaside M, (**6**) carambolaside Ia, (**7**) carambolaside J, (**8**) phloretin 3 -*C*-(2-*O*-(*E*) cinnamoyl-3-*O*-*β*-D-fucopyranosyl-4-*O*-acetyl)-*β*-D-fucopyranosyl-6 -*O*-*β*-D fucopyranosyl- (1/2)-α-L arabinofuranoside, (**9**) carambolaside I, (**10a**) carambolaside P, (**10b**) carambolaside O, (**11a**) phloretin3 -*C*-(2-*O*-(*E*)-p-coumaroyl-3-*O*-*β-*D-fucosyl-4-*O*-acetyl)-*β*-D-fucosyl-6 -*O*-(2-*O*-*β*-D-fucosyl)-α-L-arabinofuranoside, (**11b**) phloretin3 -*C*-(2-*O*-(*E*)-p-coumaroyl-3- *O*-*β-*D-fucosyl-4-*O*-acetyl)-*β*-D-fucosyl-6 -*O*-(2-*O*-*β*-D-fucosyl)-α-L-arabinofuranoside, and (**12**) carambolaside Q.

New compounds for the first time to be identified *in nature*, including compounds **1**, **8**, **11a**, and **11b**, are discussed in detail in this section. All spectral data are provided in supplementary file. Compound **1** (Figure 2) was isolated as a yellowish amorphous powder soluble in 100% MeOH. The molecular formula of compound **1** was calculated as C27H30O13, based on a deprotonated ion peak calculated at *m*/*z* 561.16137, detected at *m*/*z* 561.1614 [M-H]− (calculated C27H29O13−, error −0.1 ppm) in the HR-ESI-MS spectrum (Figure S1). Compound 1 showed two UV maximums (λmax) (MeOH) at 270 nm (Band II) and 334 nm (Band I), characteristic for a flavone skeleton [27]. The IR spectrum of compound 1 illustrated a broad band at 3431.4 cm−1 and 1623 cm−1, consistent with the presence of hydroxy group and carbonyl functions [28].

The full assignment of 1H and 13C NMR data (Figures S2 and S3, Table 2) was adopted based on the analysis of the 1H-1H COSY, HSQC, and HMBC spectra (Figures S4–S6). The existence of a flavone unit could be easily assigned from the 1H NMR and 13C NMR spectra (Figures S2 and S3, Table 2) from key signals of 4 A2B2-type aromatic protons at δ 7.80 (2H, d, *J* = 8.8 Hz, H-2 /6 ) and at δ 6.77 (2H, d, *J* = 8.8 Hz, H-3 /5 ) for a *p*-disubstituted benzene ring, together with two aromatic singlets at δ 7.02 (H-8) and at δ 6.58 (H-3), referring to 6,7-disubstituted apigenin [29]. Moreover, 13C NMR (Figure S3) revealed 27 carbon resonances, which may be typical for di-glycosylated apigenin as follows: a carbon signal at δ 184.0 (C-4) assignable for a ketonic carbonyl, carbon resonances at δ 102.4 (C-3), δ 159.9 (C-5), δ 113.6 (C-6), δ 164.5 (C-7), and δ 96.4 (C-8) were similar to those reported for 6,7-disubstituted apigenin [29]. Excluding carbons of flavone unit, another 12 carbons were left assigned to two sugar moieties for deoxy-hexopyranosyl units. δ (Chemical shift) and *J* (coupling constant) values as well as the 1H-1H COSY spectrum (Figure S4) identified the first hexose moiety as 2-deoxy-β-D-galactose. The signals for an anomeric proton at δ 5.10 (dd, *J* = 12.1, 2.4 Hz, H-1), two protons at δ 2.83 (q, *J* = 12.1 Hz, H1-2) and at δ 1.59 (m, H2-2), two protons at δ 4.02 (dd, *J* = 12.1, 2.1 Hz, H1-6) and at δ 3.74 (dd, *J* = 12.1, 6.4 Hz, H2-6), six carbons at δ 70.5 (C-1), 32.3 (C-2), 71.6 (C-3), 78.7 (C-4), 76.1 (C-5), and δ 62.8 (C-6) are consistent with those of a 2-deoxy-β-D-galactose [30] attached at the C-6 position in apigenin via a C-glycosidic linkage, confirmed via HMBC correlations (Figure 3). The second sugar was assigned as β-quinovopyranose attached to carbon 7 via an oxygen bridge, based on its anomeric proton and carbon at δ 4.92 (1H, d, *J* = 7.7 Hz, H-1) and δ 103.8 (C-1). Further, methyl protons at δ 1.26 (3H, d, *J* = 6.5 Hz, H-6), four oxymethine carbons at δ 75.0 (C-2), 77.1 (C-3), 71.8 (C-4), and 72.1 (C-5), and a methyl carbon

at δ 17.9 (C-6) confirmed sugar constitution. This sugar unit was identified from large axial–axial coupling constants revealing the axial orientation of all the ring protons of this unit, in agreement with the literature [31]. Hence, compound **1** was identified as apigenin 6-*C*-(2-deoxy-β-D-galactopyranoside)-7-*O*-β-D-quinovopyranoside, a new compound first time to be isolated in planta.

**Figure 2.** Chemical structures of compounds **1**–**12** isolated from CLL extract.

**Figure 3.** Key HMBC correlations of compound **1**, **8**, and **11a**.

**Table 2.** 1H (600 MHz) and 13C NMR (150 MHz) data of compounds **1**–**4** in CD3OD.

Another novel dihydrochalcone reported for the first time is compound **8** (Figure 2), isolated as yellowish amorphous powder soluble in 100% MeOH, with an estimated molecular formula of C49H60O23, based on a deprotonated ion peak calculated at *m*/*z* 1015.34526 and detected at *m*/*z* 1015.3460 [M-H]− (calculated C49H59O23−, error −0.7 ppm) in the HR-ESI-MS spectrum. The IR spectrum of compound 8 showed absorption bands ascribable to hydroxyl (3432 cm−1) and carbonyl moeity (1616 cm−1) [28]. The 13C/DEPT spectrum (Figure S40) revealed the presence of 49 carbon atoms with 48 directly attached protons (3 × CH2, 11 × C, 31 × CH, 4 × CH3). Analysis of the 1H-1H COSY, HSQC, and HMBC spectra led to their assignment as the dihydrochalcone skeleton [28] (Figures S41–S43, Table 3). Typical signals for the dihydrochalcone of four A2B2-type aromatic protons were detected at δ 6.91 (1H, br.s, H-2), δ 7.09 (1H, d, *J* = 8.4 Hz, H-6), 6.62 (1H, br.s, H-3), and δ 6.70 (1H, d, *J* = 8.4 Hz, H-5), with an aromatic proton singlet at δ 6.00 (H-5 ) and four aliphatic methylene protons at δ 2.73 and δ 2.68 (H2-7) and δ 3.19 and δ 3.35 (H2-8) (Figure S38, Table 3). Further, 13C NMR (Figure S39, Table 3) revealed the signal at δ 205.1 (C-9) of a ketonic carbonyl and two aliphatic methylene carbons at δ 30.8

(C-7) and 49.1 (C-8), confirming the 3 -substituted phloretin structure. The presence of two trans-olefinic protons at δ 7.51 (1H, d, *J* = 16.0 Hz, H-7) and 6.26 (1H, d, *J* = 16.0 Hz, H-8), five aromatic protons at δ 7.51 (2H, d, *J* = 3.8 Hz, H-2/6) and 7.38 (3H, m, H-3/4/5), a carboxyl carbon at δ 168 (C-9), two olefinic carbons at δ 146 (C-7) and 119.3 (C-8), six aromatic carbons, typical for a cinnamoyl unit [32] and a resonance for a single acetate methyl singlet at δ 2.02, and two carbons of an acetyl moiety at δ 173.6 and 20.5 [33] that suggested a phloretin-acetylated cinnamate. However, the HMBC experiment (Figure S43) could not clarify the connection of the acetyl group, most probably due to the need for using the low-temperature NMR technique [34]. Excluding carbons of dihydrochalcone, acetyl moiety, and trans cinnamoyl units, 23 carbons remained in the 13C NMR spectrum, assigned for four sugar moieties including three hexoses and a pentose. Sugars δ (chemical shift) and J (coupling constant) values as well as 1H-1H-COSY cross peaks and three hexose moieties were determined to be β-fucopyranosyls. The signals for an anomeric proton at δ 5.09 (1H, d, *J* = 9.9 Hz, H-1), a methyl proton doublet at δ 1.31 (3H, d, *J* = 4.2 Hz, H3-6), five oxymethine carbons at δ 74.1 (C-1), 71.9 (C-2), 84.5 (C-3), 74.1 (C-4), and 76.3 (C-5), and a methyl carbon at δ 17.2 (C-6) are consistent with those of a β-fucosyl moiety attached to C-3 of the phloretin moiety via a *C*-glycosidic linkage [35]. The HMBC spectrum could not though confirm this linkage, as no correlation appeared between (H-1) and C-2 , C-3 , or C-4 , which is likely attributed to the phenomenon of coexistence of two conformationally variant rotamers, due to restricted rotation around the single bond between C-9 and C-1 resulting from the steric hindrance of the cinnamoyl moiety [34]. Further, the change pattern of δ values at C-1 (−1.7 ppm), C-2 (+1.9), and C-3 (−1.7), due to the esterification in comparison to the unesterified analog (carambolaside Ja), confirmed the connection of a cinnamoyl unit at C-2 [34]. The downfield shift in C-3 (Δδ + 1.6) and C-4 (Δδ +0.5), relative to those in compound 7 (Figure S32), located the acetyl moiety at C-4. A second hexose was assigned based on its anomeric signals at δ 4.36 (1H, d, *J* = 7.6 Hz, H-1) and δ 106 (C-1), a methyl proton doublet at δ 1.26 (3H, d, *J* = 6.4 Hz, H3-6), four oxymethine carbons at δ 72.3 (C-2), 74.7 (C-3), 73 (C-4), and 72 (C-5), and a methyl carbon at δ 16.8 (C-6), as β-fucopyranose connected via an oxygen linkage [35] between C-1 and C-3, confirmed by the HMBC correlations from H-1 to C-3 (Figure 3 and Figure S43). The third sugar signals were typical for a pentose from its anomeric proton at δ 5.71 (1H, s, H-A1), four oxymethine carbons at δ 106.6 (C-A1), 92.9 (C-A2), 76.3 (C-A3), and 84.1 (C-A4), and an oxymethylene carbon at δ 62 (C-A5) annotated as a α-arabinofuranosyl moiety [36]. Lastly, signals of a third β-fucopyranosyl moiety were assigned from its anomeric signal at δ 3.97 (1H, br.s, H-F1) and δ 105.6 (C-F1), methyl protons at δ 1.29 (1H, s, H1-F6) and δ 0.75 (2H, s, H2-F6), four oxymethine carbons at δ 72.9 (C-F2), 72.2 (C-F3), 75 (F4), and 71.9 (F5), and a methyl carbon at δ 16.9 (F6).

The HMBC experiment could not clarify the connection of the acetyl group, αarabinofuranosyl moiety, or the last *β*-fucopyranosyl moiety, which warranted using the low-temperature NMR technique [34]. Altogether, compound **8** was identified as phloretin 3 -*C*-(2-*O-(E)-*cinnamoyl-3-*O*-β-D-fucopyranosyl-4-*O*-acetyl)-β-D-fucopyranosyl-6 -*O*-β-D fucopyranosyl-(1/2)-α-L arabinofuranoside.

Compound **11** (Figure 2), another novel dihydrochalcone, was isolated as a yellowish amorphous powder soluble in 100% MeOH. The molecular formula of compound **11** was established as C49H60O24, based on a deprotonated mol. ion peak calculated at *m*/*z* 1031.34018 and detected at *m*/*z* 1031.3389 [M-H]− (calculated C49H59O24−, error +1.2 ppm) in its HR-ESI-MS spectrum (Figure S55). The IR spectrum of compound 11 revealed two major absorption bands at 3432 cm−h and 1616 cm−&, consistent to hydroxyl and carbonyl moieties, respectively [28].

**Table 3.** 1H (600 MHz) and 13C NMR (150 MHz) data of compounds **5**–**9** in CD3OD isolated from CLL extract.

**Table 3.** *Cont.*

NMR spectral analysis confirmed that compound **11** existed in the form of a mixture of two diastereoisomers (**11a** and **11b**). 1H and 13C NMR data, in addition to the HSQC spectrum (Figures S56–S58), indicated a structure closely related to that of compound **8**, with an extra hydroxyl group characteristic for a p-coumaroyl moiety, instead of the cinnamoyl moiety in compound **8** existing in two diastereomers, i.e., (*E)* and (*Z*) isomers. Signals for *(E)*-isomer were assigned for the two olefinics at δ 7.45 (d, *J* = 14.3 Hz, H-7) and at 6.05 (d, *J* = 14.3 Hz, H-8), characteristic for an *(E)-p*-coumaroyl moiety in addition to four *p*-coupled aromatic protons at δ 7.36 (2H, d, *J* = 8.6 Hz, H-2/6) and 6.67 (2H, d, *J* = 8.5 Hz, H-3/5). Moreover, 13C NMR (Figure S57) exhibited a carboxyl carbon at δ 168.9 (C-9), two olefinic carbons at δ 145.2 (C-7) and 113.2 (C-8), and six aromatic carbons, typical for a *(E*)-coumaroyl unit [37]. In contrast, (*Z*)-*p*-coumaroyl moiety exhibited signals of four para-coupled aromatic protons at δ 7.19 and 7.4 (2H, s, H-2/6), unresolved peaks corresponding to H-3/5, and two olefinic protons at δ 6.69 (d, *J* = 11.2 Hz, H-7) and 5.60 (d, *J* = 11.6 Hz, H-8), coupled with a characteristic constant of *J* = 11.2 Hz. Then, 13C-NMR exhibited a carboxyl carbon at δ 168.9 (C-9), two olefinic carbons at δ 142.4 (C-7) and 114.8 (C-8), and six aromatic carbons typical for an (*Z*)*-*coumaroyl unit [37]. A resonance for a single acetate methyl singlet at δ 2.04 and two carbons of an acetyl moiety at (δ 172.0 and 19.1) were detected [33], as in compound **8**. The downfield-shifted C-3 (Δδ + 0.3) and C-4 (Δδ − 2), relative to those in compound **10** (Figure S51, Table 4), located the acetyl moiety at C-4. The HMBC experiment (Figure 3) could not confirm the connection of the acetyl group most probably due to the need for using low-temperature NMR technique, as in **8** [34]. Consequently, compound **11a** was established as phloretin 3 -*C*-(2-*O-(E)-*p-coumaroyl-3-*O*-β-D-fucosyl-4-*O*-acetyl)-β-D-fucosyl-6 -*O*-(2-*O*-β-D-fucosyl)-α-L-arabinofuranoside. Whereas **11b** was assigned as phloretin 3 -*C*-(2-*O*-*(Z)*-p-coumaroyl-3-*O*-β-D-fucosyl-4-*O*-acetyl)-β-D-fucosyl-6 -*O*-(2-*O*β-D-fucosyl)-α-L-arabinofuranoside. These compounds are reported for the first time in nature. Other identified compounds reported in the literature included carambolaside M (**5**) [11] (Figures S20–S24), carambolaside Ia (**6**) [11] (Figures S25–S29), carambolaside J (**7**) [11] (Figures S30–S36), carambolaside I (**9**) [34] (Figures S44–S48), carambolaside P and O (**10**) [11] (Figures S49–S54), carambolaside Q (**12**) [11] (Figures S61–S67), luteolin 6-C-α-L-rhamnopyranosyl-(1-2)-β-D-fucopyranoside (**2**) [38] (Figures S7–S11), apigenin 6-*C*-β-Dgalactopyranoside (**3**) [39] (Figures S12–S14) and apigenin 6-C-α-L-rhamnopyranosyl-(1-2) β-L-fucopyranoside (**4**) [38] (Figures S15–S19), by comparison of their spectroscopic data to those in previous references, but isolated for the first time from starfruit leaves.

**Table 4.** 1H (600 MHz) and 13C NMR (150 MHz) data of compounds **10**–**12** in CD3OD.

#### *2.3. Structure-Activity Relationship Assessment of Isolated Compounds as α-Glucosidase Inhibitors*

To further confirm potential efficacy of CLL compounds, isolated compounds were tested for their in vitro α-glucosidase inhibitory activity, to assess their efficacy. Considering the limitation of yield, in vivo assay was not possible to be performed. The efficacy of the isolated compounds was measured and discussed in relationship to the flavonoid structures, as discussed in the next subsections for each class separately, to identify the most crucial motifs within each for activity.


**Technology**

**What is your opinion on the following technologies that can help in fighting fires?**

Incentives for farmers/ranchers to avoid the use of fire Satellite images to support the preparation of vegetation Drone images to support the preparation of vegetation Camera systems for early fire detection Autonomous drones for early fire detection Artificial intelligence to predict the risk of fire Autonomous drones to monitor the evolution of fires Augmented reality to receive information during operations Mobile device to receive information during operations Voice assistant to receive information during operations

**Figure 2.** Results of the technology survey about forest fires in Spain.

As seen in Figures 1 and 2, the survey samples are very similar, only presenting small variations in the professions and tasks. The professionals could evaluate the utility of the different technologies with five ratings: "very high", "high", "average", "low", and "very low". However, we analyze the results considering three evaluations: positive (including "very high" and "high" answers), neutral (equivalent to "average" answer), and negative (including "low" and "very low" answers).

Three technological solutions for supporting prevention were evaluated: a system with incentives to avoid the use of fire in primary sector activities, satellite images to support the preparation of vegetation, and drone images for the same purpose. In this case, the professionals surveyed evaluate more positively the use of satellite and drone images (approximately, 60–70% positive, 20% neutral, and 10–20% negative).

Another three technological solutions were presented for surveillance and detection tasks: a system with cameras to monitor large and/or remote areas, autonomous drones to cover hard-to-reach areas, and the use of artificial intelligence to predict the risk of fire in every location. This last system received the best rating with 48% positive, 20% neutral, and 32% negative, whereas the other two received ratings of 35–44% positive, 16–24% neutral, and 40–41% negative.

A combination of two technologies was considered for extinguishing tasks: a first one for collecting real-time data from the fire, and a second one to display this data to the firefighter teams. For the first, we presented a fleet of autonomous drones that can monitor fire evolution in real-time. This solution is one of the best valued and the best that uses drones, having 66% positive, 12% neutral, and 22% negative evaluations. For the second, we posed three alternatives: augmented reality headset, mobile device, and voice assistant. The three alternatives are evaluated positively, but the mobile device receives the best score: 81% positive, 15% neutral, and 4% negative. Augmented reality receives 71% positive, 18% neutral, and 11% negative, whereas voice assistant achieves 60% positive, 23% neutral, and 17% negative. These results reveal that participants prefer visual over aural feedback and well-known over new devices, as well as they do not matter using their hands to manage these devices during operations.

A certain bias was detected in the evaluations of technologies by professionals, which positively affects those that are presented as a support for their current operations and negatively those that can change those operations or even threaten their jobs. This can be seen in detection, where they think that artificial intelligence can improve their effectiveness in surveillance, while they feel more threatened by autonomous systems with drones or cameras. Furthermore, the preference for well-known systems for receiving information (mobile devices) over more innovative ones (augmented reality) also reveals this conservative bias.


*3.2. Trend Analysis for Temperature, Precipitation and River Discharge*

Linear trends in the time series were analyzed using the Mann–Kendall test [32]. It was chosen, because it is a robust nonparametric test and it can handle missing data as well as it has higher power for non-normally distributed data, which are common in hydrological and meteorological data [33]. Each element is compared with its successors and ranked as larger, equal, or smaller. Based on this analysis, the statistical significance of rejecting the null hypothesis that there is no monotonic trend is tested (for all tests α = 0.05). The R package "Kendall" was used for the calculation [34].

The Theil–Sen approach was used in order to quantify the linear trend [35,36]. It computes the slope for all pairs of the ordinal time points of a time series and then used the median of these slopes as an estimate of the complete slope. This approach is commonly combined with the Mann–Kendall test and estimates the trend slope of a time series in its original unit. The R package "zyp" was used in order to calculate the Theil–Sen trend and includes a pre-whitening according to Ye et al. (2002) [37] if autocorrelation occurs [38].


**4. Conclusion**

An Eulerian/Lagragian approach has been presented to calculate evaporating sprays through a crossflow. A method developed to study isothermal turbulent two- and threedimensional dispersion was extended to the case of an array of evaporating biofuel droplets.

The droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the fuels used. Rapeseed Methyl Esters exhibit similar evaporating characteristics to DF-2, which indicates that it can be successfully used as an alternative fuel in many applications that utilize diffusion flames. The use of RME in homogeneous combustion systems may require a prohibitive level of pre-heating, and the use of Ethanol (obtained from sugar or starch crops) may be a better alternative.

### **5. Aknowledgements**

The present work has been performed in the scope of the activities of the AFTUR project. The financial support of the European Commission under Contract nº ENK5-CT-2002-00662 is gratefully acknowledged.

#### **6. References**

118 Fuel Injection in Automotive Engineering

diameter, d 230,3m 230,3m 230,3m 230,3m 230,3m

Rapeseed Methyl ester (RME)

10m/s 10m/s 10m/s 10m/s 10m/s

800ºK 800ºK 800ºK 800ºK 800ºK

800ºK 800ºK 800ºK 800ºK 800ºK

293ºK 293ºK 443ºK 293ºK 293ºK

1 bar 101 350Pa Diesel fuel

1 bar 101 350Pa

1 bar 101 350Pa

Kg/s

(DF-2) Ethanol

Rapeseed Methyl ester (RME)

> 1 bar 101 350Pa

quite similar to those obtained with more volatile fuels such as n-Heptane or Ethanol.

Mass loading 20x10-4 Kg/s 20x10-4 Kg/s 20x10-4 Kg/s 20x10-4 Kg/s 20x10-4

The evaporative characteristics of RME can be further analysed with the help of Fig.6 that shows a three-dimensional perspective of the mass fraction distribution with and without additional pre-heating. The results obtained with DF-2 and RME without additional preheating (Figs.6a and b) show that the mass fraction of fuel is always less than 0.04. For the DF-2 there is a larger evaporation near the injector, but further downstream the RME gives the higher values. When the additional pre-heating of 150K is used with RME, the domain shows a large region with a concentration of fuel vapour greater than 0.06, and the resulting pattern is

An Eulerian/Lagragian approach has been presented to calculate evaporating sprays through a crossflow. A method developed to study isothermal turbulent two- and threedimensional dispersion was extended to the case of an array of evaporating biofuel droplets. The droplet diameter, temperature and mass fraction distributions were found to be strongly dependent on the fuels used. Rapeseed Methyl Esters exhibit similar evaporating characteristics to DF-2, which indicates that it can be successfully used as an alternative fuel

Fuel n-Heptane

Droplets

Crossflow velocity, Wcrossflow

Crossflow temperature, Tcrossflow

Temperature of the walls, Twalls

Droplet injection velocity, Vp

Droplet injection temperature,

Ambient pressure

**4. Conclusion**

1 bar 101 350Pa

Table 5. Summary of test conditions.

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