*Article* **Anatomical, Physical, Chemical, and Biological Durability Properties of Two Rattan Species of Different Diameter Classes**

**Sheikh Ali Ahmed 1 , Reza Hosseinpourpia 1 , Christian Brischke 2 and Stergios Adamopoulos 3,\***

**Abstract:** Rattan cane is an important forest product with economic value. Its anatomical, physical, and biological properties vary with the cane height. This makes it difficult to select the appropriate cane diameter for harvesting. Understanding the material properties of rattan cane with different diameter sizes is important to enhance its utilization and performance for different end uses. Thus, the present study was performed on two rattan species, *Calamus zollingeri* and *Calamus ornatus,* at two different cane heights (bottom/mature and top/juvenile). *Calamus zollingeri* was studied at diameter classes of 20 mm and 30 mm, while *Calamus ornatus* was analyzed at a diameter class of 15 mm. The anatomical properties, basic density, volumetric swelling, dynamic moisture sorption, and biological durability of rattan samples were studied. The results showed that *C. zollingeri* with a 20 mm diameter exhibited the highest basic density, hydrophobicity, dimensional stability, and durability against mold and white-rot (*Trametes versicolor*) fungi. As confirmed by anatomical studies, this could be due to the higher vascular bundle frequency and longer thick-walled fibers that led to a denser structure than in the other categories. In addition, the lignin content might have a positive effect on the mass loss of different rattan canes caused by white-rot decay.

**Keywords:** *Calamus zollingeri*; *Calamus ornatus*; dynamic vapor sorption; basic density; volumetric swelling; white rot; mold

## **1. Introduction**

Rattan are spiny and climbing palms mainly distributed in Southeast Asia and in West and Central Africa [1]. With diverse uses, rattan have a high economic value and the most popular use is in furniture production. Depending on the stem diameter, rattan canes are generally classified into three categories: i.e., large (>18 mm), medium (10–18 mm), and small (<10 mm) diameter rattan. The medium and large diameter canes are used for furniture frames, walking sticks, sporting goods, and rural bridges, while small diameter canes are used either in round or split form, in basket making, chair seats, lampshades, and a variety of handicraft items [2]. Rattan canes are also widely used as excellent natural materials for ropes, decorative items, housing, craft products, umbrella handles, sporting goods, hats, cordage, birdcages, matting, baskets, hoops, and as implant materials [3,4]. In addition, other parts of the rattan, such as roots, fruits, and leaves, are used in folk medicines, while the shoots are edible because of the presence of high amounts of proteins, carbohydrates, vitamins, and other nutrients [5]. There are 12 different genera of rattan, which include more than 550 species [6], and only four of the genera are traded commercially, i.e., *Calamus*, *Daemonorops*, *Korthalsia*, and *Plectocomia* [7]. Among them, *Calamus* is the most species-rich genus of all palms with an estimated 374 species. *Calamus* grows over a large area and has

**Citation:** Ahmed, S.A.; Hosseinpourpia, R.; Brischke, C.; Adamopoulos, S. Anatomical, Physical, Chemical, and Biological Durability Properties of Two Rattan Species of Different Diameter Classes. *Forests* **2022**, *13*, 132. https:// doi.org/10.3390/f13010132

Academic Editors: Vicelina Sousa, Helena Pereira and Teresa Quilhó

Received: 16 November 2021 Accepted: 14 January 2022 Published: 17 January 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/).

excellent properties and extensive commercial uses. However, studies on this genus are still quite scarce. Commercially harvested rattan undergoes physico-chemical treatment and mechanical processing. Physico-chemical treatment involves seasoning or curing, which is boiling in oil, followed by drying, fumigation, bleaching, and deglazing. Deglazing or polishing is the mechanical removal of the highly silicified epidermis, enabling an easy bending of the cane to desired shapes [1]. Furthermore, scraping and polishing are used to smoothen the surfaces. Semi- or full polishing is done at various stages of the workflow and can be done after cutting, bending, molding, or assembling, and during the finishing process [8].

Rattan are monocotyledonous plants, and their stems are composed of vascular bundles embedded in the parenchymatous tissue. Rattan lacks the necessary lateral meristems to undergo secondary growth and thus only limited diameter growth is possible through ground parenchyma cell enlargement. Properties of the vascular bundle, such as the cell wall thickness of fibers, fiber ratio, and diameter of vessel elements in metaxylem, affect the moisture properties and volumetric shrinkage of rattan [9]. Vascular bundles in rattan canes provide the main reinforcing elements, together with their surrounding fiber sheaths. Remarkably, these reinforcing elements are densely distributed in the outer region and sparsely in the inner region [10]. Like other lignocellulosic materials, the physicomechanical properties of rattan are the most important factors for determination of cane processing and utilization. Those properties are influenced by the species, stem position, diameter, internode length, and density [5]. Different properties of rattan have previously been investigated, including moisture content (MC), density, bending modulus of elasticity, modulus of rupture, axial compression strength, and tensile strength [11]. Also, the factors influencing mechanical properties, such as species [12], microfibril angle [13], anatomical characteristics, temperature, MC, and test methods [14,15], have been discussed. However, it is hardly possible to make a comprehensive conclusion since the properties of rattan canes vary considerably with plant height [11,16]. Trees undergo secondary growth and age-related variability in wood properties is evident, but such variability is not apparent in rattan canes because of the absence of secondary growth [17].

Rattan canes have long been used in different applications; however, they exhibit the typical drawbacks of lignocellulosic materials, i.e., dimensional instability, low resistance against mold and rot fungi decay, and strength loss with increasing moisture content [18,19]. It is therefore required to complete our knowledge of those fundamental properties as they vary with cane diameter and vertical position. Thus, the aim of this study is to analyze the anatomical variations, basic density, volumetric swelling, chemical composition, vapor sorption, and resistance against mold and fungal decay of two rattan species, *Calamus zollingeri* and *Calamus ornatus*, in two different heights (bottom/mature and top/juvenile), and three diameter classes. The results of this study will provide the scientific basis for a wiser utilization of rattan canes, such as allocating the right parts and dimensions for specific final products.

#### **2. Materials and Methods**

#### *2.1. Source of Material*

Rattan canes of *Calamus zollingeri* Beccari and *Calamus ornatus* Blume grown in Sulawesi, Indonesia were collected from local suppliers for this study. Those canes were commercially polished using a custom-made sanding machine upon which sandpaper was used with a grit size of 220. The canes were 3000 mm long and belonged to three diameter classes, viz. 30, 20, and 15 mm. Both semi- and fully polished samples were used for *C. zollingeri* while only fully polished samples were used for *C. ornatus*. Samples of about 400 mm long were cut from the bottom and top ends of rattan canes to separate the mature and juvenile portions, respectively. Working samples for physical and anatomical studies were converted from these 400 mm internode samples (Figure 1). Only fully polished samples were used for testing anatomical characteristics and vapor sorption as no

differences were expected between semi- and fully polished samples, except from removal

of the epidermis and some part of the cortex tissues, as seen in Figure 1.

**Figure 1.** Schematic diagram of sample preparation and analyses. AVS: automated vapor sorption. Arrowheads in semi-polished sample show some cortex tissues. Cane length and diameter are not true to scale.

The number of samples used in this experiment per rattan species and diameter classes are shown in Table 1.

**Table 1.** Number of samples used per rattan species and diameter classes. Values in parentheses are standard deviations.

## *2.2. Frequency of Vascular Bundles and Fiber Length*

For analyzing the frequency of vascular bundles, 20 mm thick discs were cut from the cane and then blocks about 10 mm wide along the diameter were prepared. Sample blocks were then soaked in water for 8 h for softening. Cross-sections of 15–20 µm thick strips from periphery to periphery were prepared from the bottom and top samples of *C. zollingeri* and *C. ornatus* using a sledge microtome (WSL, Birmensdorf, Switzerland). One (1) sample per rattan species and portion (bottom and top) was used, i.e., a total of six randomly selected samples. The sections were stained with 1:1 solution of 1% Safranin O (Merck KGaA, Darmstadt, Germany) and Astra blue (Carl Roth GmbH, Karlsruhe, Germany) solution, washed with a series of alcohol solutions, and finally fixed on glass slides with EntellanTM mounting agent (Merck KGaA, Darmstadt, Germany). The glass slides were observed under a motorized Olympus BX63F light microscope (Tokyo, Japan) equipped with a DP73 color CCD cooled camera (max. 17.28 megapixel) and software program OLYMPUS cellSens Dimension, version 1.18 (Olympus, Tokyo, Japan). For every sample, the numbers of vascular bundles/mm2 area were counted from periphery to periphery. The vascular bundle consists of the conducting tissue, phloem, and xylem with fibers that provide structural support. Vascular bundles were counted in one mm2 rectangle area. Those vascular bundles were also counted as one when at least 50% of the area fell in one mm2 rectangle.

For analyzing the rattan fiber length, matchstick-sized samples were cut with a razor blade and put in glass vials containing 50:50 solutions by volume of hydrogen peroxide 20% and glacial acetic acid. The vials were placed in an oven at 60 ◦C for 2 days to macerate the material. After that period, the macerations were washed with de-ionized water and were stored in small glass containers with ethanol absolute. One droplet of the suspension containing rattan cells was placed on a slide and was observed under the microscope. Fifty intact fibers per sample (duplicate) were randomly selected to measure the length.

#### *2.3. Density and Volumetric Swelling*

Basic density values were measured for 80 rattan samples (400 mm long with dimeters of 15, 20, and 30 mm). Samples corresponded to the bottom (mature) and top (juvenile) parts of the canes.

Discs about 20 mm thick were cut from the middle of the original samples to obtain representative values of these cane portions (bottom and top). Samples were weighed on a balance with 0.001 g accuracy, put in an oven at 103 ± 2 ◦C until constant masses were attained and then the oven-dry masses were recorded. After that, all samples were submerged in a water bath for 14 days for complete saturation of the cell walls [20]. The samples' green volumes were recorded by the water-displacement method. Basic density (*R*) and volumetric swelling (*S*) determinations were performed using the following equations:

$$R\ (\text{g}/\text{cm}^3) = \frac{M\_\text{o}}{V\_2} \tag{1}$$

$$S\ \left(\%\right) = \frac{V\_2 - V\_1}{V\_1} \times 100\tag{2}$$

where *Mo* is the oven-dry mass of each sample in g, *V2* is the fully saturated (maximum), and *V1* is the oven-dried volume in cm3 .

#### *2.4. Chemical Composition Analysis*

Fully polished samples of 30 (length) × 10 (width) × 5 (thickness) mm3 each from the bottom and top of rattan canes were used. The chemical composition of the rattan samples was analyzed according to Ghavidel et al. 2021 [21] by grinding them in a Willey mill through a No. 40 mesh sieve (0.425 mm). Ground powder from the bottom and top samples were mixed homogenously and then analyzed for chemical compositions. The extractive content was determined on 2–3 g of oven-dried samples (at 103 ◦C for 24 h) using cyclohexane-ethanol (50:50 *v*/*v*) solution for 4 h. Then, the samples were oven-dried again and used for the assessment of holocellulose content by transferring to an Erlenmeyer flask, adding 80 mL of hot water (70 ◦C), 1 g of sodium chlorite, and 0.5 mL of acetic acid, keeping it for 6 h in a water bath at 70 ◦C. Ash content was determined according to the standard EN 15403 [22]. The lignin amount was assessed by subtracting the sum of all other components, i.e., holocellulose, ash, and extractive contents, from 100 wt%. Samples were measured in duplicate to calculate average values.

#### *2.5. Vapor Sorption Analysis*

The water vapor sorption behaviors of the bottom and top rattan samples were determined using an automated vapor sorption (AVS) apparatus (Q5000 SA, TA Instruments, New Castle, USA) following the procedure described in Hosseinpourpia et al. [23]. Approximately 8 mg of rattan powder (as made for chemical composition analysis) were used for each measurement. The samples were exposed to relative humidity (RH) that was increased from 0% to 90% in stepped sequences of 15% and of 5% from 90% to 95% RH, decreasing to 0% RH in a reverse order, at a constant temperature of 25 ◦C. The instrument maintained a constant target RH until the mass change in the sample (dm/dt) was less than 0.01% per min over a 10 min period. The equilibrium moisture content (EMC) of the

rattan samples was calculated based on their equilibrium weight at each given RH step throughout the sorption run measured by a micro balance.

#### *2.6. Durability Tests*

#### 2.6.1. Mold

Fully polished samples of 30 (length) × 10 (width) × 5 (thickness) mm3 were used for both mold and decay tests. All samples were conditioned at 20 ◦C and 65% RH in a climate chamber for three weeks before testing. An accelerated laboratory mold test was performed in a Memmert HCP 246 humidity chamber (Memmert GmbH, Germany), according to a previous study [24]. Five replications from each group giving a total of 30 samples were used for the accelerated mold test. Samples were suspended from the top of the chamber's support bars with the flat surface set vertical and parallel to the other sample surfaces with a 10 mm gap between in a randomly ordered fashion. The temperature and RH were then set to be 27 ◦C and 95%, respectively. Three Scots pine sapwood (*Pinus sylvestris* L.) samples infested mainly with *Aspergillus*, *Rhizopus*, and *Penicillium* genera were placed on the bottom of the climate chamber to be the sources of mold inocula. After 10 days of incubation, the experiment was stopped because of abundant mold growth on some of the sample surfaces. Both flat surfaces of the samples were evaluated visually and graded on a scale of 0 (no infestation) to 6 (extremely heavy infestation). More about the grading and method can be found in Sehlstedt-Persson et al. [25].

#### 2.6.2. Basidiomycete Decay Test

The resistance of the two rattan species against white-rot fungi decay was evaluated with a malt agar incubation test according to EN 113-2 [26]. Deviating from the standard, mini-block specimens of 30 (length) × 10 (width) × 5 (thickness) mm3 [27] were used and incubated for 8 weeks. Fifteen to 25 replicates per group were oven-dried at 103 ± 2 ◦C till constant mass and weighed to the nearest 0.001 g to determine the oven-dry mass.

After steam sterilization in an autoclave at 120 ◦C for 30 min, sets of two specimens of the same group were placed on fungal mycelium in Kolle flasks (100 ml malt extract agar, 4%). The white-rot fungus *Trametes versicolor* (L.) Lloyd. F strain was used for the tests. Furthermore, 10 replicates made from Scots pine sapwood and beech (*Fagus sylvatica* L.) were used as virulence controls. All specimens were incubated for 8 weeks at 22 ◦C and 70% RH.

After incubation, specimens were cleansed of adhering fungal mycelium, weighed to the nearest to 0.001 g, oven-dried at 103 ± 2 ◦C, and weighed again to the nearest 0.001 g to determine mass loss through wood-destroying basidiomycetes as follows:

$$ML\_F = \frac{M\_0 - M\_{0,\text{inc}}}{M\_0} \times 100\tag{3}$$

where *MLF* is the mass loss by fungal decay (%), *M0,inc* is the oven-dry mass after incubation (g), and *M0* is the oven-dry mass before incubation (g).

#### *2.7. Statistical Analysis*

To determine any statistically significant differences between the bottom and top samples, mean values were compared by a two-tailed group t-test at a 0.05 significance level (Excel 2016 program, Microsoft, Redmond, WA, USA). F-tests for mean fiber length, number of vascular bundles, basic density, volumetric swelling, and mold grades were performed using the IBM SPSS Statistics statistical software package, Version 24 (IBM Corporation, New York, USA). One-way analysis of variance (ANOVA) at a 0.05 significance level was applied to determine significant differences among rattan samples. When significant differences were found, Duncan's multiple-range test was performed.

#### **3. Results and Discussion 3. Results and Discussion**

#### *3.1. Anatomical and Physical Properties*

The anatomical characteristics of rattan samples were studied using light microscopy (Figure 2). The vascular bundles in rattan are scattered and embedded in the ground parenchymatous tissues. They are present just below the single layered epidermis and are small and incomplete, consisting of either clusters of fibers or a few phloem and vessel elements with fibers [28]. Vascular bundles present in the center are well developed. In both rattan species, vascular bundles consisted of two phloem fields and one metaxylem vessel and had horseshoe-shaped fibrous tissues. The ground tissue is parenchyma cells. According to Weiner and Liese [28], three forms of parenchyma cells are distinguished in cross sections, i.e., Type A: weakly branched with regular rounded intercellular spaces, Type B: small and rounded cells with irregular shaped intercellular spaces, and Type C: thinwalled, large, and round. The species showed the Type A parenchyma cell arrangement. During processing (polishing), the epidermis and some parts of the cortex were removed (Figure 1). *3.1. Anatomical and Physical Properties* The anatomical characteristics of rattan samples were studied using light microscopy (Figure 2). The vascular bundles in rattan are scattered and embedded in the ground parenchymatous tissues. They are present just below the single layered epidermis and are small and incomplete, consisting of either clusters of fibers or a few phloem and vessel elements with fibers [28]. Vascular bundles present in the center are well developed. In both rattan species, vascular bundles consisted of two phloem fields and one metaxylem vessel and had horseshoe-shaped fibrous tissues. The ground tissue is parenchyma cells. According to Weiner and Liese [28], three forms of parenchyma cells are distinguished in cross sections, i.e., Type A: weakly branched with regular rounded intercellular spaces, Type B: small and rounded cells with irregular shaped intercellular spaces, and Type C: thin-walled, large, and round. The species showed the Type A parenchyma cell arrangement. During processing (polishing), the epidermis and some parts of the cortex were removed (Figure 1).

**Figure 2.** Light microscopic images of cross-sections of *C. zollingeri* and *C. ornatus* with different diameter classes. Arrow heads show MX = metaxylem, PX = protoxylem, PH = phloem, FB = fiber bundle, and GP = ground parenchyma. Scale bars = 200 µm.

The mean values of fiber length ranged from 1008 µm to 1329 µm, which were in accordance with a previous study [18]. Fiber length and number of vascular bundles of the rattan samples clearly decreased from the bottom to the top (Table 2). A similar trend was also reported in previous findings [5,16,18,29]. When all values were considered from the bottom and top of the canes, mean fiber length and number of vascular bundles were found to be significantly higher in *C. zollingeri* than in *C. ornatus*. Except for the *C. zollingeri* that had a 30 mm diameter, fiber length and number of vascular bundles were significantly higher in the bottom than in the top samples. The number of vascular bundles increased significantly with a decrease in stem diameter (Table 2). Similar results were reported by Bhat et al. [16] with a less consistent longitudinal variation.

**Table 2.** Mean values of fiber length and number of vascular bundles of different fully polished rattan samples. Mean values (± standard deviations) of n = 100 per sample type for fiber length.

Mean values followed by different letters within a column indicate that there is a significant difference (*p* ≤ 0.05) as determined by ANOVA and Duncan's multiple range test. \* Significant differences at the 0.05 level.

The higher frequency of vascular bundles could result in higher basic density. Besides, compression strength and the apparent Young's modulus increases with an increase in the number of vascular bundles [30,31]. It is thus expected that the outer part of rattan cane with densely distributed vascular bundles would have better mechanical strength than the core part with sparse distribution [15]. Anatomical investigations on *C. zollingeri* and *C. ornatus* with different diameter classes demonstrate that the fiber length and the number of vascular bundles per unit area varied significantly. Those properties decreased consistently in cane height from bottom to top. As mentioned above, the increase of basic density is dependent on the increase of cell wall thickness. The increase of fiber wall thickness with age is more pronounced than in cortical and ground parenchyma tissues, and the thickening of the fiber wall with increasing stem density results from fibers forming polylamellate walls [32]. Basic density values were positively correlated with the frequency of vascular bundles; however, the correlation was poor (r = 0.39). This could be attributed to the differences of share and thickness of fiber cells in rattan samples [16].

The physical properties, i.e., basic density and volumetric swelling, of rattan samples from different diameter classes are shown in Table 3. The top samples of fully polished *C. zollingeri* with a 20 mm diameter exhibited the highest basic density. This density was about 32% higher than in the bottom and top samples of *C. ornatus* with 15 mm diameters. Those differences were found to be statistically significant. No significant differences were observed in semi- and fully polished *C. zollingeri* samples between diameter classes (20 and 30 mm) and cane height (bottom and top). The density of semi-polished samples was higher than fully polished ones, except for the top samples of *C. zollingeri* with 20 mm diameters. However, such differences were not evaluated from a statistical point of view. Those density differences could be explained by the fact that semi-polished samples had some remaining cortex. The cortex between epidermis (single cell layer) and the vascular system consists of parenchyma cells, fibers, and incomplete vascular bundles. Higher frequency of vascular bundles, thicker fiber cell walls, and smaller cell sizes in the cortex contribute to higher basic density than in the core [11,30]. The basic density tends to decrease with cane height from the basal to the top portion of the cane [5,29,33]. This could be attributed to the steady decrease of fiber cells from base to top [15]. However, diverged results of density with cane heights are also reported [5,11]. In this study, for both semi- and fully polished samples, no statistical differences of basic density were found between the bottom and top parts. Basic

density values are the result of various factors, such as the numerous fiber cells with thicker walls, higher vascular bundle frequency, narrower metaxylem vessel elements, and more lignified cells distributed in the cane. In particular, the higher percentage of fibers that constitute the total stem tissue considerably influences the density, and thus proportionally affects the strength properties of rattan cane [2,15].

**Table 3.** Mean basic density and volumetric swelling values of semi- and fully polished rattan samples in different diameter classes. Mean values (± standard deviations) of n = 8 per sample type.

Mean values followed by different letters within a column indicate that there is a significant difference (*p* ≤ 0.05) as determined by ANOVA and Duncan's multiple range test. \* Significant differences at the 0.05 level.

For fully polished samples, *C. ornatus* had the highest volumetric swelling, and differences were statistically significant from the other samples (Table 3). In bottom samples with 30 and 20 mm diameters, *C. ornatus* demonstrated about 46% and 42% higher volumetric swelling than *C. zollingeri*, respectively. These values were about 31% and 41% higher in the top samples of *C. ornatus* than in the top samples of *C. zollingeri*. No significant differences were observed in semi- and fully polished *C. zollingeri* samples between diameter classes (20 and 30 mm) and cane height (bottom and top). These results are in line with previous findings on other species of *Calamus* [34], although a significant increase of volumetric shrinkage from the bottom to the top of rattan cane is also reported [35]. The higher volumetric swelling values of *C. ornatus* could be caused by its lower basic density. Low basic density implies small cell wall thickness, and this in turn results in higher swelling [36].

Vascular bundles are scattered in the ground tissues (Figure 2). Just below the epidermis, vascular bundles are small and incomplete, consisting of either clusters of fibers or a few phloem and vessel elements with fibers. They are well-developed in the center of the stem cross-section. That implies a within-cane variation of density in the radial direction, i.e., a low-density core with large-diameter and low-frequency vascular bundles that is surrounded by a high-density outer zone with small-diameter and high-frequency vascular bundles [30].

Based on the anatomical and physical properties studied in rattan samples with different diameter classes, *C. zollingeri* with a 20 mm diameter showed longer fibers, higher basic density, and the lowest volumetric swelling in both the bottom and top of the canes. Therefore, we anticipate that *C. zollingeri* illustrates a more dimensional-stable character than the other rattan types.

#### *3.2. Chemical Composition Analysis*

The chemical composition of rattan samples in different diameter classes is shown in Table 4. The holocellulose content, which was about 78%, was identical in all rattan samples. This value agrees with previous studies [18,37]. The highest lignin content of 17.9% was obtained in *C. zollingeri* with a 30 mm diameter, while the *C. ornatus* exhibited the lowest lignin content of 9.1%. This might be related to the age of the rattan cane in that

the cambial cells produce more mature cells with progressing cane age [17]. The content of alcohol-benzene solubles in different rattan species shows a non-specific trend from the bottom to top samples [18,34]. *C. ornatus* was found to have higher extractive and ash contents compared with other rattan types. *C. zollingeri* with a 20 mm diameter had higher extractive content than that of *C. zollingeri* with a 30 mm diameter. The high ash content in material like rattan is generally attributed to the high silica content, which can affect its working properties for some specific applications [34]. lowest lignin content of 9.1%. This might be related to the age of the rattan cane in that the cambial cells produce more mature cells with progressing cane age [17]. The content of alcohol-benzene solubles in different rattan species shows a non-specific trend from the bottom to top samples [18,34]. *C. ornatus* was found to have higher extractive and ash contents compared with other rattan types. *C. zollingeri* with a 20 mm diameter had higher extractive content than that of *C. zollingeri* with a 30 mm diameter. The high ash content in material like rattan is generally attributed to the high silica content, which can affect its

The chemical composition of rattan samples in different diameter classes is shown in Table 4. The holocellulose content, which was about 78%, was identical in all rattan samples. This value agrees with previous studies [18,37]. The highest lignin content of 17.9% was obtained in *C. zollingeri* with a 30 mm diameter, while the *C. ornatus* exhibited the

**Table 4.** Chemical composition of rattan samples in different diameter classes (wt%).

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working properties for some specific applications [34].

*3.2. Chemical Composition Analysis*

#### *3.3. Vapor Sorption Analysis 3.3. Vapor Sorption Analysis*

The MC of rattan is a very important factor as it affects the mechanical properties. Water is a good plasticizer and acts as a softener. Uptake of water loosens the bonds between the structural polymers within the lignocellulosic materials, i.e., lignin, cellulose, and hemicelluloses [38,39]. During vapor sorption analysis, the rattan samples showed the typical sigmoidal character of cellulosic materials (Figure 3). Different moisture sorption behavior was observed in rattan samples at various relative humidities (RHs) during adsorption and desorption processes. The MC of rattan is a very important factor as it affects the mechanical properties. Water is a good plasticizer and acts as a softener. Uptake of water loosens the bonds between the structural polymers within the lignocellulosic materials, i.e., lignin, cellulose, and hemicelluloses [38,39]. During vapor sorption analysis, the rattan samples showed the typical sigmoidal character of cellulosic materials (Figure 3). Different moisture sorption behavior was observed in rattan samples at various relative humidities (RHs) during adsorption and desorption processes.

**Figure 3.** Equilibrium moisture content (EMC) of bottom/mature and top/juvenile rattan samples of different diameter classes (30, 20, and 15 mm) during the adsorption and desorption runs. **Figure 3.** Equilibrium moisture content (EMC) of bottom/mature and top/juvenile rattan samples of different diameter classes (30, 20, and 15 mm) during the adsorption and desorption runs.

The EMC of rattan samples increased with increasing RH from 0 to 95%. Identical EMC values were observed in the top and bottom samples within the same species. There The EMC of rattan samples increased with increasing RH from 0 to 95%. Identical EMC values were observed in the top and bottom samples within the same species. There were no differences in the EMC values of the samples at RHs below 60% during both adsorption and desorption runs. The moisture adsorption isotherms are similar to the one reported by Yang et al. [36]. The highest EMC value was obtained at 95% RH for sample *C. ornatus*, which was ca. 27%. The sharp upward bend above 70% RH is generally accepted to be related to the softening point of hemicelluloses [40]. Removal of the lignin increased the

moisture sorption capacity of holocellulose micro-veneers at RH above 75% [40]. Although the sorption mechanism of the rattan cell wall could be slightly different than wood, it is thus assumed that the higher EMC value of the *C. ornatus* samples could be mainly related to the lower lignin content as compared to other rattan samples, as indicated in chemical composition analysis (Table 4). As expected, at RHs above 75%, *C. zollingeri* with a 20 mm diameter demonstrated lower moisture sorption in comparison with *C. zollingeri* with a 30 mm diameter and *C. ornatus* in the top and bottom parts during both adsorption and desorption runs. The effect of high lignin content in rattan with a 30 mm diameter on moisture sorption might be offset by higher extractive and ash contents in *C. zollingeri* with a 20 mm diameter. The moisture sorption results are in accordance with the volumetric swelling values and confirmed a better hydrophobicity of *C. zollingeri* with a 20 mm diameter as compared with the other rattan samples. increased the moisture sorption capacity of holocellulose micro-veneers at RH above 75% [40]. Although the sorption mechanism of the rattan cell wall could be slightly different than wood, it is thus assumed that the higher EMC value of the *C. ornatus* samples could be mainly related to the lower lignin content as compared to other rattan samples, as indicated in chemical composition analysis (Table 4). As expected, at RHs above 75%, *C. zollingeri* with a 20 mm diameter demonstrated lower moisture sorption in comparison with *C. zollingeri* with a 30 mm diameter and *C. ornatus* in the top and bottom parts during both adsorption and desorption runs. The effect of high lignin content in rattan with a 30 mm diameter on moisture sorption might be offset by higher extractive and ash contents in *C. zollingeri* with a 20 mm diameter. The moisture sorption results are in accordance with the volumetric swelling values and confirmed a better hydrophobicity of *C. zollingeri* with a 20 mm diameter as compared with the other rattan samples.

were no differences in the EMC values of the samples at RHs below 60% during both adsorption and desorption runs. The moisture adsorption isotherms are similar to the one reported by Yang et al. [36]. The highest EMC value was obtained at 95% RH for sample *C. ornatus*, which was ca. 27%. The sharp upward bend above 70% RH is generally accepted to be related to the softening point of hemicelluloses [40]. Removal of the lignin

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The EMC values vary a lot in rattan age and the length of cane [2]. The results from dynamic moisture sorption analysis imply that the cane type and diameter should be considered when using rattan products for applications in high humidity conditions. The rattan-water vapor interaction study also helps to understand the material properties of rattan canes before harvesting. For instance, a young rattan could have similar or higher strength properties than a mature one because the plant produces an over-built stem that could withstand future load requirements [41]. In all aspects of properties, consideration of diameter class before harvesting is very important because it can lead to the shortening of the plantation and harvesting processes. The EMC values vary a lot in rattan age and the length of cane [2]. The results from dynamic moisture sorption analysis imply that the cane type and diameter should be considered when using rattan products for applications in high humidity conditions. The rattan-water vapor interaction study also helps to understand the material properties of rattan canes before harvesting. For instance, a young rattan could have similar or higher strength properties than a mature one because the plant produces an over-built stem that could withstand future load requirements [41]. In all aspects of properties, consideration of diameter class before harvesting is very important because it can lead to the shortening of the plantation and harvesting processes.

#### *3.4. Mold and Decay Tests 3.4. Mold and Decay Tests*

After 10 days of incubation, mold growth was visually evaluated and graded on rattan samples of different diameter classes (Figure 4). The highest average mold rating was found on *C. ornatus* and the bottom sample of the 30 mm *C. zollingeri*. For *C. zollingeri*, statistically significant differences were neither observed between the bottom and top of the canes nor between the 30 mm and 20 mm diameter classes. Rattan hemicelluloses are partly composed of water-soluble polysaccharides, such as arabinogalactan, and partly of galactoglucomannan [18]. The sugar and acid units of hemicelluloses, such as arabinopyranose, arabinofuranose, galactose, methylglucuronic acid, and galacturonic acid are types of sugars and acids that are a source of fungal food. The chemical composition of the rattan samples illustrated a considerably lower lignin content in *C. ornatus*. This could be the reason for the higher mold infestation of this rattan type. However, differences in mold infestation between the bottom and top samples did not differ significantly. After 10 days of incubation, mold growth was visually evaluated and graded on rattan samples of different diameter classes (Figure 4). The highest average mold rating was found on *C. ornatus* and the bottom sample of the 30 mm *C. zollingeri*. For *C. zollingeri*, statistically significant differences were neither observed between the bottom and top of the canes nor between the 30 mm and 20 mm diameter classes. Rattan hemicelluloses are partly composed of water-soluble polysaccharides, such as arabinogalactan, and partly of galactoglucomannan [18]. The sugar and acid units of hemicelluloses, such as arabinopyranose, arabinofuranose, galactose, methylglucuronic acid, and galacturonic acid are types of sugars and acids that are a source of fungal food. The chemical composition of the rattan samples illustrated a considerably lower lignin content in *C. ornatus*. This could be the reason for the higher mold infestation of this rattan type. However, differences in mold infestation between the bottom and top samples did not differ significantly.

**Figure 4.** Mold grading of rattan samples for different diameter classes. Error bars show standard deviations. Bars with different letters indicate that there is a significant difference (*P* ≤ 0.05), as determined by ANOVA and Duncan's multiple range test. **Figure 4.** Mold grading of rattan samples for different diameter classes. Error bars show standard deviations. Bars with different letters indicate that there is a significant difference (*p* ≤ 0.05), as determined by ANOVA and Duncan's multiple range test.

The decay resistance of rattan samples against the white-rot fungus *Trametes versicolor* is shown in Figure 5. To validate the results, beech and pine sapwood samples were selected as controls. Among all rattan samples of different diameter classes, the *C. ornatus* illustrated the highest mass loss. These results are in accordance with the ones from mold test and dynamic vapor sorption analysis. The differences of mass loss between the top and bottom samples of each diameter class were statistically insignificant. Among the three diameter classes, *C. zollingeri* of 20 mm diameter showed the lowest mass loss for both the bottom and top samples (Figure 5). However, no obvious trend was observed for mass loss of both the top and bottom samples in all diameter classes. and bottom samples of each diameter class were statistically insignificant. Among the three diameter classes, *C. zollingeri* of 20 mm diameter showed the lowest mass loss for both the bottom and top samples (Figure 5). However, no obvious trend was observed for mass loss of both the top and bottom samples in all diameter classes.

The decay resistance of rattan samples against the white-rot fungus *Trametes versicolor* is shown in Figure 5. To validate the results, beech and pine sapwood samples were selected as controls. Among all rattan samples of different diameter classes, the *C. ornatus* illustrated the highest mass loss. These results are in accordance with the ones from mold test and dynamic vapor sorption analysis. The differences of mass loss between the top

*Forests* **2021**, *12*, x FOR PEER REVIEW 11 of 13

**Figure 5.** Mass loss of bottom/mature (B) and top/juvenile (T) rattan samples of different diameter classes (30, 20, and 15 mm) after decay test with the white-rot fungus *Trametes versicolor*. **Figure 5.** Mass loss of bottom/mature (B) and top/juvenile (T) rattan samples of different diameter classes (30, 20, and 15 mm) after decay test with the white-rot fungus *Trametes versicolor*.

As white-rot decay has a common feature of degrading lignin, cellulose, and hemicelluloses, the resistance of lignocellulosic material to this fungus highly depends on the relative proportion of their compositional polymers, i.e., it depends on the lignin content, carbohydrate ratio, and lignin monomer composition (mainly guiaicyl lignin) [42–44]. High mass loss of *C. ornatus* samples compared with the other rattan samples could be related to their considerably low lignin content, as demonstrated in chemical composition analysis (Table 4). As white-rot decay has a common feature of degrading lignin, cellulose, and hemicelluloses, the resistance of lignocellulosic material to this fungus highly depends on the relative proportion of their compositional polymers, i.e., it depends on the lignin content, carbohydrate ratio, and lignin monomer composition (mainly guiaicyl lignin) [42–44]. High mass loss of *C. ornatus* samples compared with the other rattan samples could be related to their considerably low lignin content, as demonstrated in chemical composition analysis (Table 4).

#### **4. Conclusions**

mechanical properties.

**4. Conclusions**  This study showed that *C. zollingeri* with a 20 mm diameter had the highest basic density in both bottom and top samples compared to *C. zollingeri* with a 30 mm diameter and *C. ornatus* with a 15 mm diameter. The reasoning for such higher density was supported by the anatomical features of higher vascular bundle frequency and longer thickwalled fibers. In addition, *C. zollingeri* with a 20 mm diameter exhibited the lowest volumetric swelling from an oven-dry condition to complete saturation. When water vapor sorption analysis was performed, this diameter class showed the lowest EMC at 95% RH, which verified its better dimensional stability even at high humidity levels. In addition, better resistance against mold and mass loss from white-rot fungal decay were also observed. Those properties followed a statistically similar pattern with sample height (bottom and top). From these findings, we conclude that *C. zollingeri* with a 20 mm diameter class exhibited better stability, moisture properties, and durability from older rattan with a 30 mm diameter class. On the contrary, *C. ornatus* with a 15 mm diameter showed inferior properties. Further research work needs to be extended to the evaluation of different This study showed that *C. zollingeri* with a 20 mm diameter had the highest basic density in both bottom and top samples compared to *C. zollingeri* with a 30 mm diameter and *C. ornatus* with a 15 mm diameter. The reasoning for such higher density was supported by the anatomical features of higher vascular bundle frequency and longer thick-walled fibers. In addition, *C. zollingeri* with a 20 mm diameter exhibited the lowest volumetric swelling from an oven-dry condition to complete saturation. When water vapor sorption analysis was performed, this diameter class showed the lowest EMC at 95% RH, which verified its better dimensional stability even at high humidity levels. In addition, better resistance against mold and mass loss from white-rot fungal decay were also observed. Those properties followed a statistically similar pattern with sample height (bottom and top). From these findings, we conclude that *C. zollingeri* with a 20 mm diameter class exhibited better stability, moisture properties, and durability from older rattan with a 30 mm diameter class. On the contrary, *C. ornatus* with a 15 mm diameter showed inferior properties. Further research work needs to be extended to the evaluation of different mechanical properties.

**Author Contributions:** Conceptualization, S.A.A. and S.A.; methodology, S.A.A., R.H. and S.A.; software, S.A.A.; validation, S.A.A., R.H. and S.A.; formal analysis, S.A.A.; investigation, S.A.A.; R.H. and C.B.; visualization, S.A.A.; R.H. and C.B.; data curation, S.A.A. and S.A.; writing—original draft preparation, S.A.A; writing—review and editing, all authors. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors acknowledge funding provided by IKEA of Sweden.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

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

#### **References**


**1. Introduction**

174 Modern Metrology Concerns

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Many instruments can be used to measure radio frequency (RF) and microwave power. The most accurate one is a power sensor with a meter. The accuracy of RF and microwave power measurement depends on the accuracy of power sensor calibration. This chapter provides calibration methods of RF and microwave power sensor with system setup, modeling, equations, and analyses in different representations, traceability and measurement uncertainty evaluations. From the simple direct comparison transfer method, to the different improvements, and then the general analytical models, the methods provided in this chapter are useful for the guided-wave power sensor calibration in frequency range of a few MHz to several hundred GHz.


**1. Introduction**

Biocatalysis is the application of enzymes for chemical transformations of organic compounds. Enzymes as biocatalysts have many advantages [1–3]: (1) enzymes are very efficient catalysts. Typically the rates of enzyme-mediated processes are accelerated, compared to those of the corresponding nonenzymatic reaction, by a factor of 108 –1010. The acceleration may even exceed a value of 1012, which is far above the values that chemical catalysts are capable of achieving; (2) enzymes are environmentally acceptable. Unlike heavy metals, for instance, biocatalysts are completely degraded in the environment; (3) enzymes act under mild conditions. Enzymes act in a temperature range of 20–40°C, under neutral aqueous, and in the absence of substrate functional group protection. This minimizes problems of undesired side reactions such as decomposition, isomerization, racemization, and rearrangement, which often plague traditional methodology; (4) enzymes display high chemoselectivity, regioselectivity, and enantioselectivity. As a result, reactions that generally tend to be "cleaner" and laborious can largely be omitted; and (5) enzymes can catalyze a broad spectrum of reactions. There is an enzyme-catalyzed process equivalent to almost every type of organic reaction, such as oxidation, hydrolysis, addition, halogenation, alkylation, and isomerization. In addition, many enzymes accept unnatural substrates, and genetic engineering can further alter their stability, broaden their substrate specificity, and increase their specific activity. Thus, the application of enzymes in synthesis thus represents a remarkable opportunity for the development of industrial chemical and pharmaceutical processes [4–7].

organic solvents, not requiring cofactors, broad substrate tolerance, commercial availability, and high chemo-, regio-, and stereoselectivity. Hydrolases have demonstrated a great versatility in hydrolysis, transesterification, aminolysis reactions, etc. Some hydrolase-catalyzed promiscuous reactions have been done in the last decades (**Figure 1**). These research and other relevant reports encouraged us to believe that the catalytic activities for unconventional reactions rather than the well-known hydrolytic function may also have a natural role in hydrolase evolution. The aim of the present chapter is to give a brief overview of the hydrolasecatalyzed C▬C and C▬N reactions and present some of the most recent applications in different fields for recent decade. The main work in our group will be disclosed, highlighting the catalytic properties of hydrolases to catalyze not only single processes but also multicomponent and tandem reactions. Consequently, the promiscuous hydrolase-catalyzed reactions are outlined with focus on Michael

*Hydrolase-Catalyzed Promiscuous Reactions and Applications in Organic Synthesis*

*DOI: http://dx.doi.org/10.5772/intechopen.89918*

Michael addition is a 1,4-addition of a nucleophile to α,β-unsaturated compounds, and it is one of the most fundamental and important reactions for the formation of carbon-carbon bonds and carbon-heteroatom bonds in organic synthesis. Michael addition reactions are traditionally catalyzed under strong basic or acidic conditions, which can cause unwanted side reactions such as further condensation or polymerization of α,β-unsaturated compounds. Thus, biocatalysis can afford a green and facile method for organic synthesis. Among different biocatalysts, hydrolases such as protease and lipase have been widely used as a

Michael addition is the early promiscuous reaction catalyzed by hydrolase. In 1986, Kitazume et al. reported the hydrolytic enzyme-catalyzed stereospecific Michael addition reactions in buffer solution (pH = 8.0) at 40–41°C (**Figure 2**) [16]. This discovery overthrows the long erroneous concept of enzymology that "biocatalysis must be carried out in aqueous solution," making many organic reactions that cannot be carried out in water be completed in organic solvents and greatly expanding the application scope of enzymes as catalysts. Moreover, enzymes are frequently more stable in organic solvents than in water. Thus, some research groups began to focus on enzyme-catalyzed Michael addition reactions in organic

Lin and Gotor et al. firstly reported the hydrolase-catalyzed Michael addition of

imidazole with acrylates catalyzed by alkaline protease from *Bacillus subtilis* in organic solvent in 2004 [17, 18]. Subsequently, other hydrolase-catalyzed Michael addition reactions were reported. In 2010, Bhanage et al. developed an efficient protocol for the regioselective aza-Michael addition of amines with acrylates using

addition, aldol reaction, Mannich reaction, Biginelli reaction, etc.

green and efficient catalyst for Michael addition.

*The first hydrolase-catalyzed Michael addition in buffer.*

**2.1 Carbon-heteroatom bond formation Michael addition**

**2. Michael addition**

solvents.

**Figure 2.**

**35**

Although it is well known that a given enzyme is able to catalyze a specific reaction efficiently, some unexpected experimental results have indicated that many enzymes have catalytic promiscuity [8–12]. Enzyme promiscuity is classified into three categories: (a) condition promiscuity, which is an enzyme's ability to work under unexpected condition; (b) substrate promiscuity, which is an enzyme's ability to work with unexpected substrates; and (c) catalytic promiscuity, which is an enzyme's ability to catalyze unexpected reactions. Among them, catalytic promiscuity has gained much attention as it opens a wide scope for the industrial application of enzymes.

During the past decade, biocatalytic promiscuity, as a new frontier extending the use of enzymes in organic synthesis, has received considerable attention and expanded rapidly. A classic example of promiscuous enzymatic behavior is pyruvate decarboxylase, which not only decarboxylates pyruvate but also links acetaldehyde and benzaldehyde to form R-phenylacetylcarbinol. The use of pyruvate decarboxylase to form carbon–carbon bonds, which does not occur in the natural reaction, was first studied in 1921 and was applied in industry today [13]. As one of the most rapidly growing areas in enzymology, multifunctional biocatalytic reactions not only highlights the existing catalysts but may provide novel and practical synthetic pathways which are not currently available. Miao et al. reviewed enzyme promiscuity for carbon-carbon bond-forming reactions like aldol couplings, Michael(-type) additions, Mannich reactions, Henry reactions, and Knoevenagel condensations [14]. Gotor-Fernández et al. also highlighted the hydrolase-catalyzed reactions for nonconventional transformations in the same year [15].

Hydrolases (such as lipase, protease, acylase) have received extensive attention as biocatalysts for a long time due to their many attractive properties like stability in

**Figure 1.** *Hydrolase-catalyzed promiscuous reactions.*

### *Hydrolase-Catalyzed Promiscuous Reactions and Applications in Organic Synthesis DOI: http://dx.doi.org/10.5772/intechopen.89918*

organic solvents, not requiring cofactors, broad substrate tolerance, commercial availability, and high chemo-, regio-, and stereoselectivity. Hydrolases have demonstrated a great versatility in hydrolysis, transesterification, aminolysis reactions, etc. Some hydrolase-catalyzed promiscuous reactions have been done in the last decades (**Figure 1**). These research and other relevant reports encouraged us to believe that the catalytic activities for unconventional reactions rather than the well-known hydrolytic function may also have a natural role in hydrolase evolution.

The aim of the present chapter is to give a brief overview of the hydrolasecatalyzed C▬C and C▬N reactions and present some of the most recent applications in different fields for recent decade. The main work in our group will be disclosed, highlighting the catalytic properties of hydrolases to catalyze not only single processes but also multicomponent and tandem reactions. Consequently, the promiscuous hydrolase-catalyzed reactions are outlined with focus on Michael addition, aldol reaction, Mannich reaction, Biginelli reaction, etc.


*2.2. Sampling*

Sampling of soil at Smith's Lake and Charles Veryard Reserves was conducted on two occasions: in March 2017 (a grid of surface samples) and March 2018 (profile sampling at selected locations). In 2017, surface soil sampling locations were pre-selected prior to sampling using a randomised-within-grid sampling strategy (Figure 1) using a 52 × 52 m grid to maximise site coverage, and two samples per grid square, with the objective of sampling the grassed areas within the Reserves without statistical bias. In the field, preselected sample locations were located using handheld GPS. If randomised sample coordinates were too close to paved surfaces, water, structures, etc., the location was moved by approximately 5 m and the revised coordinates were recorded. For subsequent analysis, the sampling area was divided into zones based on exploratory data analyses (Figure 2).

**Figure 1.** Street map showing soil sampling locations, and the initial grid used for sampling design, at Smith's Lake and Charles Veryard Reserves. Contours are land elevations in metres; the pale red polygon shows moderate to high acid sulfate soil (ASS) risk.

**Figure 2.** Simplified map showing sampling zones at Smith's Lake and Charles Veryard Reserves. CVR is Charles Veryard Reserve; SLR is Smiths Lake Reserve.

Surface soil was sampled in cylindrical cores from 0–10 cm depth using a stainless steel corer. Triplicate cores at each location were bulked to achieve a sample mass of ca. 500 g, and stored in zip-lock plastic bags prior to transport back to the laboratory. Soil sample cavities were re-filled with clean soil supplied by the sampling team.

In 2018, a second sampling of soil profiles to up to 100 cm depth was conducted using Garret-style augers. Separate samples were collected for each of eight profiles (Figure 1) in 10 cm depth increments.

Soil samples were air-dried in a laminar air-flow drying cabinet at 40 ◦C and sieved through a 2 mm aperture prior to analysis.


**1. Introduction**

186 Reverse Engineering – Recent Advances and Applications

Várady, T.; Benkö, P.; Kós, G.: Reverse Engineering Regular Objects: Simple Segmentation

Várady, T.; Martin, R.R.; Cox, J.: Reverse Engineering of Geometric Models - An

Venkataraman, S.; Sohoni, M.; Kulkarni, V.: A Graph-Based Framework for Feature

1998, 127–141. DOI:10.1142/S0218654398000106

194-205. DOI:10.1145/376957.376980

4485(96)00054-1

ZCorp, www.zcorp.com

and Surface Fitting Procedures, International Journal of Shape Modeling, 4(3-4),

Introduction, Computer-Aided Design, 29(4), 1997, 255–268. DOI:10.1016/S0010-

Recognition, Sixth ACM Symposium on Solid Modeling and Applications, 2001,

Due to increased market pressure, product specifications are required to be developed and updated on a rapid and continual basis. Companies know that to compete in the market they must learn to analyze and address the actual arithmetic increase, but to do so at an exponential pace.

Improving a product involves offering new features, new technology and attractive ways to enhance the quality for market launch. Companies are employing and reaping the benefits of market analysis techniques to assist in predicting what the market is postulating, now and in the future.

Customers anxiously await the release of new products, frequently and expeditiously. Many of these customers expect and anticipate that their favorite brand will launch a new product. In fact, frequency of product updates or the potential of model renewal and variety of versions has become another aspect in redefining the concept of a favorite brand.

The rapid pace of consumer demand compels companies to keep their products on the edge of technology and competitive in market place; therefore, their development process can be no less aggressive. To achieve optimum results, the products must be continuously improved, based on customer need.

Dufour (1996) is emphatic that many new products, even if unintended, are in most cases redesigns, based on an existing product. This activity, however, cannot be held solely in intuitive order, depending only on empiricism.

The redesign needs to be done through a systematic process that guides the work of the designer and the product development team from identification of the problem until the final design of the product, offering a greater chance of success.

Integrating Reverse Engineering and Design for Manufacturing

Fig. 2. Publications by keywords between 1980 and 2009

engineering.

and participatory way.

**2. Literature review**

**2.1 Product development process**

development (co-design) with customers.

of the research.

and Assembly in Products Redesigns: Results of Two Action Research Studies in Brazil 189

From this main objective on, it is established a secondary objective, to analyze the results from the application of the cited model to reduce production/assembling time, as well as the manufacturing/assembling costs on the redesign of products from the reverse

The employed research method was the action-research. According to Thiollent (2007) an action-research is a kind of an empirically social research, designed and carried out in close association with an action or with solving a collective problem, in which the researches and participants, representatives of the situation or the problem are involved in a cooperative

This chapter is structured as follows: section 2 presents initially a theoretical framework on the subject studied, followed by section 3 which describes the research method employed. Section 4 analyzes and discusses the results and, finally, section 5 presents the conclusions

According to Toledo *et al*. (2008), the product development process (PDP) is considered, increasingly, a critical process to the competitiveness of companies, with a view to a general need for frequent renewal of product lines, costs and development schedules, a more responsive product development to market needs and to companies participating in supplying chain of components and systems, training strategies to participate in joint

Silva (2001) considers that for small and medium companies to be regarded as pioneers in product development, it is not a critical success factor. So, additional scrutiny is applied to the study of manufacture and assembly, the structured assessments of conditions and the productive resources, internally and externally available, as a means of reducing costs and optimizing deadlines for product launching.

As a consequence, the redesign of products, supported by a Reverse Engineering (RE) approach, and integrated Design for Manufacturing and Assembly (DFMA) is a way these companies manage to launch new products with minimal investment and risk. A survey in the main scientific databases (Emerald, Science Direct and SciELO) revealed that this issue has generated 178 publications in journals during the period from 1980 to 2009, as shown in Figure 1.

Fig. 1. Publications by keywords in major databases

Figure 2 shows the distribution of these publications within this period, as they are contained in the article title, for the keywords: product redesign; Reverse Engineering; Design for Manufacturing and Assembly; design for manufacturing; design for assembly, and DFMA.

Of note in the analysis is that none of these publications dealt with the integration of RE with DFMA regarding the redesign of products, only with rapid prototyping; thus, this chapter aims to contribute to the knowledge base by filling the gap identified in the literature.

Therefore, the main objective of this study is to analyze the application of a model for the integrated use of the design for manufacturing and the rapid prototyping in a reverse engineering approach in the process of products redesign.

Fig. 2. Publications by keywords between 1980 and 2009

From this main objective on, it is established a secondary objective, to analyze the results from the application of the cited model to reduce production/assembling time, as well as the manufacturing/assembling costs on the redesign of products from the reverse engineering.

The employed research method was the action-research. According to Thiollent (2007) an action-research is a kind of an empirically social research, designed and carried out in close association with an action or with solving a collective problem, in which the researches and participants, representatives of the situation or the problem are involved in a cooperative and participatory way.

This chapter is structured as follows: section 2 presents initially a theoretical framework on the subject studied, followed by section 3 which describes the research method employed. Section 4 analyzes and discusses the results and, finally, section 5 presents the conclusions of the research.


*3.6. Relative Average Solvent Accessibility (RASA)*

The DOT residues buriedness is analysed by the NACCESS [47] program and the RASA of each residue is calculated by using Equation (4).

$$\text{RASA} = \frac{A\_{ilbd}}{\sum\_{i=1}^{n} (A\_{ilbd})} \tag{4}$$

where *Aibd*: RASA of *i*th residue binding with RNA in DOT region; *n*: number of DOT residues in a protein–RNA complex.

#### *3.7. Secondary Structure of Protein and RNA*

Secondary structure of both proteins and RNA molecules are analysed by DSSP and DSSR programs, respectively [48,49]. The DSSR program gives dot bracket notation of secondary structure of RNA as shown in Figure S1, in which "." represents unpaired nucleotide, "(" or ")" represent paired bases, and "{" or "}" or "[" or "]" or "<" or ">" represent pseudoknot bases.


**ICD in the Era of Telecardiology**

J. Taieb, J. Bouet, R. Morice, J. Hourdain, B. Jouve, Y. Rahal, T. Benchaa, H. Khachab, O. Rica and C. Barnay

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/53361


2.1.1. Benefits of ginger

compared to other medicines, the safety issue during pregnancy is a concern. Using herbal medicine in first 3 months and late in third trimester is dangerous for the foetus. Before using any herbal medicine, it is better to consult the doctor and the pharmacist to ensure that the herbs are appropriate and safe to use during pregnancy [12]. In pregnancy, mothers are concerned about all medications that may affect their health, the health of the foetus, and the pregnancy outcomes. Availing evidence-based information about benefits and untoward effects of herbal medicine use during pregnancy is important for safer pregnancy and healthy foetus. The aim of this chapter is to provide the best available information on benefits and untoward effects of herbal medicine use during pregnancy. This chapter identified the prevalence of herbal medicine use during pregnancy across regions and countries. The chapter also identified the commonly used herbs and described the character of women who used herbs during pregnancy. The benefits and untoward effects of commonly used herbal medicine during pregnancy are

2. Herbal medicine use during pregnancy: benefits and untoward effects

Herbal medicine use during pregnancy is common across regions and countries. The prevalence of herbal medicine use during pregnancy is varied across regions and countries. Multinational study conducted in different countries showed that 28.9% of pregnant women used herbal medicine during pregnancy [2, 4]. A literature review from the Middle East revealed that up to 82.2% of the women used herbal medicine at some point during pregnancy. The study also identified that many women used herbal medicine during the first trimester [5]. An observational cohort study done in South West England found that 26.7% of the women used a complementary or alternative medicine at least once during pregnancy. The use of herbs rose from 6% in the first trimester to 12.4% in the second trimester and to 26.3% in third trimester [13]. In Australia, 36% of the women took at least one herbal medicine during pregnancy [14]. Studies done in Africa showed the prevalence of herbal medicine use during pregnancy was

The most commonly consumed herbal medicines during pregnancy include; ginger [2, 4–11], cranberry [2, 4, 10–11], valerian [2, 4, 10], raspberry leaf [2, 4, 10–11, 13], chamomile [13–14], peppermint [5, 13], rosehip [13], thyme [5], fenugreek [5, 9], green tea, sage, and aniseed [5]. Eucalyptus, tenaadam (Ruta chalepensis), damakess (Ocimum lamiifolium), feto, omore are also other herbal medicines used during pregnancy [6–8]. Garlic [6–8, 15–18], palm kernel oil, bitter kola and dogonyaro (Azadirachta indica) are other herbs that are used during pregnancy [15–18]. Being students, having no education, having low income and having tertiary education level make women more likely to use herbal medicine during pregnancy [2, 4, 6–8, 15–18]. The other factors that make women more likely to consume herbal medicines are being primiparas [2, 4, 9],

Based on the available researches and literature reviews, the most commonly used herbal medicines during pregnancy are identified. The benefits and untoward effects of the herbs are

reviewed based on scientific findings.

104 Herbal Medicine

between 12 and 73.1% [3, 6–9, 15–19].

non-smoking [2, 9] and old age women [13–14].

also reviewed.

Ginger is used as anti-nauseant and anti-emetic for nausea and for hyperemesis gravidarum. The recommended daily dose of ginger is up to 1g dried powder [21]. A single blind clinical trial showed ginger as an effective herbal medicine for decreasing nausea and vomiting during pregnancy. This study also suggested a daily total of 100 mg ginger in a capsule [22].

A randomized controlled clinical trial conducted on 120 women over 20 weeks of gestation with symptoms of morning sickness showed consumption of 1500 mg of dried ginger for 4 days improves nausea and vomiting. The study also revealed that newborns whose mothers consumed ginger during pregnancy had normal birth weights and normal APGAR score [23]. Consumption of ginger in amounts used in food preparation is likely to be safe. Taking 1–2 g dried ginger over the course of a day has been shown to relive symptoms of minor disorder of pregnancy [24–26]. Using higher doses of ginger is not safe for pregnant women. Thus, pregnant women should not use higher dose of ginger.


**1. Introduction**

Renewable energy, including photovoltaic power generation, has steadily increased globally through [1,2] continuous cost-cutting efforts based on eco-friendly elements and low maintenance costs [3,4], despite the high costs and relatively low economy in the early stages of its implementation [5]. Owing to economic security and increased supply of renewable energy [6,7], the achievement of grid parity has recently accelerated [8,9], with a certain percentage of fossil fuel usage steadily being replaced by renewable energy

**Citation:** Lee, K.; Cho, S.; Yi, J.; Chang, H. Prediction of Power Output from a Crystalline Silicon Photovoltaic Module with Repaired Cell-in-Hotspots. *Electronics* **2022**, *11*, 2307. https://doi.org/10.3390/ electronics11152307

Academic Editors: Luis Hernández-Callejo, Jesús Armando Aguilar Jiménez and Carlos Meza Benavides

Received: 23 June 2022 Accepted: 22 July 2022 Published: 24 July 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/).

usage, and hence, the total use of renewable energy has increased over the past decade [10]. Expanding the solar energy supply may reduce carbon dioxide emissions and achieve a healthy mix of energy sources to overcome the climate crisis [11,12]. However, the increasing demand for solar energy may cause shortages of the resources used in the advanced production of solar modules [13–15]. In particular, owing to the scarcity of resources such as silver, indium, and bismuth, target material consumptions of 2, 0.38, and 1.8 mg/Wp [16,17], respectively, have been proposed; thus, a significant reduction in material consumption is required to expand renewable energy supply [18].

The large-scale installation of photovoltaic modules results in the problems of economic use of resources during production and processing of waste modules after use [19,20]. By 2050, 80 million tons of accumulated photovoltaic modules are expected to reach their service life worldwide, with 10 million tons in the US alone [21]. With the rapid increase in the installation of photovoltaic modules in countries such as China, the collection and recycling of end-of-life photovoltaic modules is becoming an important task, and various methods of building efficient recycling systems are being investigated [22]. According to previous studies, the predicted accumulated waste that will be generated from 2020 to 2080 in existing solar power plants varies in proportion to solar installations, and is expected to peak at 130,000 tons in 2051 and 141,297 tons in 2054 [23]. Currently, the life of a photovoltaic module is approximately 20–30 years; therefore, the life of photovoltaic modules installed in the early 2000s will expire on a large scale, and the disposal of waste modules will increase rapidly. Photovoltaic modules consist of expensive materials, such as aluminum, silver, copper, tin, and silicon wafers. In addition, they can be used as highly attractive recycled materials in terms of the environmental charges imposed when filling landfills. In the recycling process of a general photovoltaic module, research has primarily focused on recycling by collecting silicon wafers and refabricating them into optimized silicon solar cells [24,25], pyrolyzing organic materials such as ethylene vinyl acetate (EVA) [26], and removing organic materials such as glass and ribbon metals [27,28]. As a research example on recovering the performance of photovoltaic modules, a technology for recovering the insulation resistance of aging modules by injecting coatings based on polyurethane, epoxy, silicone, and synthetic rubber of crystalline photovoltaic modules was introduced [29,30]. However, recycling or reuse technology generally involves removal of frames, junction boxes, or cables, etc., from crystalline photovoltaic modules, followed by thermal or chemical decomposition of the laminated module to collect glass, silicon, metal, and polymer [31,32].

This recycling technology is not currently widely used because it is expensive and the return on investment (ROI) is less than approximately −0.25 as of 2022 [33]. In addition, the recycling method, which involves collecting the raw materials separately, is not applicable to the recovery of damaged modules in an operating power plant because the failure of a part of the module results in the crushing of other usable parts. Accordingly, this paper proposes a technology to recover photovoltaic modules at the same or a higher level of the initial power value by replacing cells at a safety risk, such as power loss and hotspots, owing to damage to some cells of an aged silicon photovoltaic module. Most commercial solar power plants receive subsidies from the government. In this case, only certified modules of a particular model should be used during the generation period. If the module fails, it cannot be replaced by another model. Moreover, owing to the rapid improvement in cell efficiency every year [34,35], the module model continues to change. In commercial power plants, restoring the output of a module by cell replacement is very useful. Technological advancements in the restoration of the module result in a power deviation between the initial and new cell [36,37]. Therefore, when replacing a cell with a new cell having a higher power, the possibility of an electrical mismatch loss occurring should be considered, and the long-term power degradation of the initial cell should be confirmed. Hence, the purpose of the experiment was to determine the extent to which the output improvement of the new cell is reflected in the output of the module to be restored. Previous studies have shown that the prediction of power mainly includes power

degradation in modules with hotspots or how much power decreases as a result of EL in modules with potential-induced degradation (PID) [38,39]. However, the purpose of this study was to predict the improvement to power through replacement of damaged cells in a module, which has not been attempted before. The results of this study suggest that the energy and environmental costs of recycling modules can be significantly reduced by reusing waste modules in more diverse states.

#### **2. Experiments**

#### *2.1. Methods and Procedures*

The overall experiment was conducted in the following order: module power output and defect verification, calculation of grade of originally applied cells, grade verification of replacement cells, power prediction, module power recovery, comparison of predicted power output and experimental results, and application of correction values. First, the defects and power output of the module to be recovered were checked via electroluminescence (EL) measurement and a sun-simulator. EL measurements are used to identify internal defects that cannot be visually identified using EL in solar cells. Table 1 provides the nomenclature for the electrical characteristics of the module.

**Table 1.** Nomenclature for the electrical characteristics of the module.

The current corresponding to the cell *I*sc and the voltage at the same level as the module *V*oc were applied for the measurement. EL images of the module were captured in several parts of a darkroom, recollected, and displayed on a screen. The EL equipment manufactured by MC Science in Korea was used for the measurements. The simulator measures the module's *Isc*, *Voc*, *Pmax*, etc., under the standard test condition (STC) at 25 ◦C, 1 Sun (1000 W/m2), and air mass 1.5, and corrects the actual temperature to output the calculated value to the screen. The equipment used in this study was a Spire-Nissinbo Sun Simulator. The equipment was calibrated for proper use in the certification test of the photovoltaic module by receiving the AAA in three evaluation items: uniformity, stability, and spectrum. Measurements of power output from equipment are displayed in various ways, i.e., 1–4 digits after the decimal point; however, in this study, the third digit after the decimal point was rounded to two digits to maintain consistency. The CTM (cell to module) factor calculation method was applied to the power analysis of the cells used at the time of manufacturing the target samples and the review of the cells to be replaced [40]. The grade of the applied cell was inversely calculated based on the initial power output of the module disclosed on the Internet by the manufacturer. The module power after cell replacement was predicted after checking the grade of the cell to be replaced.

The CTM coefficient k-factor calculation method was used to analyze the power of the original cell of the target samples and review the replacement cell. Manufacturing modules from cells, models, and formulas for classifying the CTM coefficient k-factor, which affects efficiency or power, and analyzing loss or acquisition mechanisms have been presented in previous research [41,42]. If the dimension data and rated power of a module released by the module manufacturer are the initial power outputs of the module, the module efficiency is calculated to be 13.6%. Because the module power output is calculated from the sum of the CTM coefficient k factor and the initial solar cell power in the module power output calculation model, the power output of the module can be calculated using Equations (1) and (2) [41,43]. The factors *i* and *m* in Equations (1) and (2) are variables of the routinely used pie function, and refer to the extension of the CTM factor. The CTM k-factor consisted of 15 types: *k*1 (module margin), *k*2 (cell spacing), *k*3 (cover reflection), *k*4 (cover absorption), *k*5 (cover/encapsulant reflection), *k*6 (encapsulant absorption), *k*7 (interconnection shading), *k*8 (cell/encapsulant coupling), *k*9 (finger coupling), *k*10 (interconnector coupling), *k*11 (cover coupling), *k*12 (cell interconnection), *k*13 (string interconnection), *k*14 (electrical mismatch), and *k*15 (junction box and cabling). The meaning of *I* = 3−*m* in the ∏-function of Equation (1) means CTM k-factor from k3 to k15. Then, the sum of the cell power outputs from *j* = 1−*n* from the ∑-function is the number *n* of cells applied to the module.

$$P\_{module} = \prod\_{i=3}^{m} k\_i \cdot \sum\_{i=1}^{n} P\_{cell,i} \tag{1}$$

$$\text{CTM}\_{power} = \prod\_{i=3}^{m} k\_i \tag{2}$$

In terms of module efficiency, factors affecting the entire area of a gap module between modules are important; however, when a module is produced from a cell, a design margin (*k*1) to ensure an electrical insulation distance and a loss factor (*k*2) owing to the cell interval are not related to a power change. The module efficiency can be expressed by Equations (3) and (4) [41].

$$\eta\_{module} = \frac{P\_{module}}{E\_{STC} \cdot (A\_{module} + A\_{cell\ spacing} + A\_{cells})} \tag{3}$$

$$
\eta\_{modulc} = \overline{\eta\_c} \cdot (k\_1 + k\_2 - 1) \cdot \prod\_{i=3}^{m} k\_i \tag{4}
$$

Therefore, according to this model, the module efficiency is proportional to the average efficiency of the cell rather than being dominantly affected by the lowest efficiency. The average efficiency of the cell was calculated by considering the electrical mismatch loss (*k*14) of the cell to predict the power output of the module to be restored. For the loss caused by the electrical mismatch of cells, studies were published prior to research on the CTM factor, and the widely known definition of RPL is expressed as the difference between the maximum power (*Pmpc*) of *n* individual cells connected in series to form a cell string or module. RPL can be expressed as Equation (5) from the difference between the sum of the maximum power of all cells and the maximum power of the module.

$$RPL = \frac{\sum\_{i=1}^{n} \cdot P\_{mpii} - P\_{module}}{\sum\_{i=1}^{n} \cdot P\_{mpii}} \tag{5}$$

In theory, when individual cells operate completely independently, the maximum power output is denoted as *P max*, and when the average cell power output value in a group is *Pmax*, the calculation of RPLB (relative power loss of a module using Bucciarelli's equation) is as shown in Equation (6).

$$RPL\_B = \frac{P\_{\max}^{\prime} - P\_{module}}{n \cdot I\_{mp}^{-} V\_{mp}^{-}} \tag{6}$$

The power output after cell replacement and the state inside the module were also confirmed using the EL and Sun simulators. The cell replacement process is discussed in the next section. After cell replacement, the gain factor (power increment of the replacement cell), loss factor (long-term degradation, electrical mismatch), and unidentified tolerance parts of the module track the experimental results and apply the same to the two samples, correct the power predictions, and finally compare them with the results.


*3.1.2. SPECT-CT*

geometries, such as the conical geometry for example, accompanied sure with the development

16 Imaging and Radioanalytical Techniques in Interdisciplinary Research - Fundamentals and Cutting Edge Applications

Time-of-Flight technology has always held the promise of better PET imaging. Philips delivered on that promise with its innovative Astonish TF technology. Now with 4D TOF, Philips continues to push the envelope of PET imaging performance. See how 4D TOF

Design of Hybrid machines has been a very interesting research and technologic development axe in nuclear imaging during last fifteen years. Indeed, many hybrid PET-CT, SPECT-CT and PET-MRI machines were manufactured offering a variety of very interesting diagnostic applications by the combination of results of two imaging methods allowing the revelation of a very interesting pathologic information that cannot be revealed by a single technique alone. PET-CT is creating a new benchmark in imaging and analysis of cardiovascular disease. PET-CT enables the combination of PET myocardial perfusion and viability imaging with CT coronary angiography and calcium scoring in a single integrated environment. In oncology, it

SPECT-CT is a system designed entirely for nuclear medicine and has particular value in the cardiology cycle of care. This hybrid machine allows table to remain stationary in many cases, eliminating complexities inherent in table indexing, acquires the entire heart volume in just one rotation and permits patients to breathe normally during SPECT and CT acquisitions. In oncology, it plays an important role in diagnosis, treatment, and follow-up in the oncology cycle of care, including the use of low-dose localization and aids better visualization that is

Researchers continue to develop new ways of using PET. One recent development has been

provides more detailed images, which can aid in the more precise localization of cancerous growths. A hybrid PET-MRI scanner simultaneously delivers functional information plus anatomy and tissue characterization (soft tissue contrast and blood vessel physiology), from a state-of-the-art MRI scanner. At the same time, it provides metabolic imaging from PET technology. Fusing these images gives the best of both worlds, providing greatly superior

The first machine was created by University of Pittsburgh physicist David Townsend and engineer Ronald Nutt; the PET-CT machine was called the "Medical Science Invention of the Year" by *Time* magazine in 2000. After giving entire satisfactory at the research tests level and their importance in oncology and cardiology were well demonstrated, many international companies were interested in the fabrication of such kind of hybrid imaging machine. Actually, the market is shared mainly between General Electric (GE), Philips and Siemens (Figure 9).

into a single apparatus. Compared to CT, MRI generally

provides the integration of metabolic data from PET and anatomical data from CT.

of robust reconstruction algorithms.

Innovation is making an impact on PET imaging.

especially valuable during studies and in bone imaging.

information to what you'd get from either machine individually

Actually, the main hybrid machines routinely used in hospitals are the following:

the combination of PET and MRI2

*3.1.1. PET-CT*

2 MRI: MagneticResonance Imaging.

A variety of SPECT-CT scanners are nowadays available in many hospitals and oncology centres (Figure 10). GE proposes a robust SPECT-CT hybrid machine called "Infinia" which is a dual-head, large field for general applications. The Infinia has an open stand. It is available with SPECT thick crystals (5/8th) or thin (3/8th) depending on the intended application. It is available in solo or in combination with a scanner. The Infinia Hawkeye 4 SPECT/CT from GE Healthcare builds upon its performance with a wealth of innovations, from enabling low dosage and improved acquisition times to enhancing imaging results through scatter correc‐ tion modeling and reduction, motion detection and correction, and accurate attenuation correction. Hawkeye 4 should respond to all applications except exams angio CT or cardiology.

In 2010, Philips unveiled its own solution which involves a 3T MR and a high resolution PET scanner with an integrated rotating table that passes the patient from one machine immediately into the other. Philips Ingenuity TF PET/MR is a new modality so original and resourceful that it offers Astonish Time-of-Flight technology combined with the superior soft tissue imaging

Principles and Applications of Nuclear Medical Imaging: A Survey on Recent Developments

http://dx.doi.org/10.5772/54884

19

In 2011, Siemens Healthcare said that its hybrid PET-MRI scanner received USA Food and Drug Administration clearance. The device, the Biograph mMR, is the first integrated PET-MR device capable of doing simultaneous whole-body magnetic resonance imaging and positron emission tomography scans. It combines a 3-Tesla MR system with PET detectors, giving doctors the morphological and soft tissue information from MR with the cellular and metabolic

of Achieva 3.0T MRI in a whole-body footprint.

**Figure 11.** Actually available PET-MRI hybrid scanners.

subdivided again [32, 33]. The main are the following:

**3.2. Recent developments in nuclear medical image acquisition and analysis**

present the state-of-the-art and research topics regarding only these two axes.

In addition to conventional nuclear image processing methods described above, Registration and Validation are also a very important research axes in nuclear imaging. In this section, we

There is increasing interest in being able to automatically register medical images from either the same or different modalities. Registered images are proving useful in a range of applica‐ tions, not only providing more correlative information to aid in diagnosis, but also assisting with the planning and monitoring of therapy, both surgery and radiotherapy. The classifica‐ tion of registration methods is classically based on the criteria formulated by van den Elsen, Pol & and Viergever [31]. Many basic criteria can be used, which each can be developed and

**1.** Dimensionality: 2D or 3D only spatial dimensions or time series with spatial dimensions;

**2.** Nature of registration basis: Extrinsic, Intrinsic or Non-image based (calibrated coordinate

activity data from PET.

*3.2.1. Registration*

systems);

PHILIPS approaches the market hybrid machines by combining existing methods in its range. The hybrid machine called PRECEDENCE. Precedence SPECT/CT system offers the combi‐ nation of functional data from SPECT with high-resolution anatomical detail from a multi-slice diagnostic CT scanner to give clinicians a new standard of diagnostic confidence.

When SPECT functional data is fused with CT, the location and extent of disease may be better visualized and treated.

SEIMENS "Symbia" SPECT-CT hybrid machine is integrated SPECT and diagnostic multislice-CT bring a whole new dimension to nuclear medicine. With the ability to provide precise localization of tumors and other pathologies before disease reveals itself, Symbia has the potential to revolutionize treatment planning for cancer, heart disease, and neurological disorders. Symbia has enormous potential for cardiac imaging, revealing even the hard-todetect conditions that carry the highest risk for patients.

**Figure 10.** Examples of SPECT-CT hybrid scanners.


*2.1. First, Some Category Theory*

Category theory of Eilenberg and Mac Lane [19,54] constitutes the mathematical substance of institution theory. This situation is similar in other axiomatic approaches to model theory, such as in the above-mentioned Budapest school of abstract model theory. This means that the mathematical structures in institution theory are all categorical. On the other hand, the flow of ideas in institution theory is model theoretic. So, institution theory is a form of model theory that at the level of the mathematical structures is heavily based on categorical structures. This represents a sharp contrast to the widespread perception of category theory as a mere language that supports a clearer presentation and structuring of mathematical concepts that in fact do not have an inherent categorical nature. Institution theory without category theory is possible to the same extent as, for instance, group theory is possible without set theory!

Why such a reliance on category theory; is it indispensable for the axiomatic treatment of model theory? There are several reasons for this. One is that that set theoretical structures cannot support the required level of generality and abstraction. Another one is that category theory emphasises the relationships between objects rather than their internal structures. Moreover, category theory is conceptually a highly developed area of mathematics, so this brings in much conceptual and technical power.

However, the level of category theory involved in institution theory is rather elementary, as it hardly touches advanced concepts and techniques; the only slight exception being found in the area of stratified institutions. So, familiarity with concepts such as opposite (dual) of a category **C** (denoted **C**-), comma category, functor, (lax) natural transformation, (co)limit, and adjunction may be enough to be able to engage with the study of institutional model theory. In this survey, with a few exceptions, in general, we follow the terminology and the notations of [19]. As regards the notational conventions,