2.2.1. General Framework

The flexible load aggregator is an organic combination of multiple types of flexible loads. Through the energy management center, it participates in power grid operations and market transactions as a stakeholder. Flexible load aggregators determine the optimal bidding curve by maximizing their own interests. Figure 2 shows a schematic diagram of flexible load aggregators participating in the market composed of electric vehicles, temperature-controlled loads and distributed energy storage as typical flexible loads. The classification of flexible loads is conducive to the precise control of the power management department and to the flexible role of flexible loads. The framework of the market clearing and safety checking method in this paper is shown in Figure 3.

**Figure 2.** Diagram of flexible load aggregators participating in the market.

**Figure 3.** Market clearing and safety checking framework that considers the flexible load.


Preface

Flavonoids are the largest and most diverse group of secondary metabolites found in plants, including fruits, vegetables, grains, and herbs. They play a variety of significant roles in determining plant growth and development, including UV protection, pollinator attraction, and defense against environmental stresses, specifically pests and diseases. Recently, scientists have conducted a significant amount of research to develop an understanding of the biosynthesis and regulation mechanisms of flavonoids, as well as their potential future applications in crop breeding.

The discovery of novel enzymes and genes involved in flavonoid biosynthesis pathways is a recent and important advance in the understanding of flavonoid metabolism. This has enabled scientists to manipulate these pathways in plants, improving overall plant health, including stress tolerance and disease resistance, and producing flavonoids with desirable properties such as improved antioxidant activity or increased pigment content to enhance the nutritional value of the specific crop. For example, researchers have been able to increase the flavonoid content of crops such as tomatoes, grapes, rice, and soybeans by overexpressing specific flavonoid biosynthesis genes.

Another area of research that has focused on elaborating on the role of flavonoids is plant responses to abiotic and biotic stresses. Flavonoids are well known to play central roles in protecting plants against environmental stresses such as UV radiation, drought, and a variety of pathogens. Through understanding how flavonoids contribute to stress tolerance, researchers are seeking to develop new strategies to improve crop yields and resilience in the face of changing environmental conditions.

Recently, growing interest has also been observed in studying the potential health benefits of flavonoids for humans. Flavonoids have been shown to possess a range of beneficial effects on human health, including antioxidant and anti-inflammatory activities, and they may also exhibit anticancer and cardiovascular protective properties. By increasing the flavonoid content of crops, it may be possible to improve and enhance the nutritional quality of food to provide additional health benefits to consumers.

Overall, recent advances in flavonoid metabolism research have significant implications for crop breeding and food production, playing a critical role in the development of healthier and more sustainable food crops, as well as new applications in the pharmaceutical and cosmetics industries.

The book consists of seven chapters.

Chapter 1 'Chemistry and Role of Flavonoids in Agriculture: A Recent Update', explains the overall importance of flavonoids in plant systems. It describes the detailed biosynthesis and chemistry of these metabolites inside the plants and the pathways they adopt to combat biotic and abiotic stress. The importance of flavonoids in determining the future of plant breeding with respect to food quality is highlighted.

Chapter 2, 'Importance of Flavonoid as Secondary Metabolites', discusses the antiinflammatory, antioxidant, anticancer, anti-cholinesterase, antimicrobial, hepatoprotective, neuroprotective, cardioprotective, and antiallergic properties of flavonoids. Their scavenging activity enables superoxide, hydroxyl, and lipid radicals to play a crucial role against life-limiting diseases such as diabetes, cardiovascular disorder, and cancer.

Chapter 3, 'Flavonoids Biosynthesis in Plants as a Defense Mechanism: Role and Function Concerning Pharmacodynamics and Pharmacokinetic Properties', examines the biosynthesis pathway of flavonoids in plants and their role against abiotic and biotic stress factors. It also highlights the pharmacological functions of flavonoids and their impact on certain diseases, including dementia and Alzheimer's.

Chapter 4, 'Purple Corn Cob: Rich Source of Anthocyanins with Potential Application in the Food Industry', illustrates the value added by anthocyanins in the food coloring and beverage industry due to their antioxidant, anti-inflammatory and cardiovascular health benefits. Purple corn cob, a byproduct of corn, is cited as a specific example.

Chapter 5, 'Application of Liquid Chromatography in the Analysis of Flavonoid Metabolism in Plant', discusses the structural variability of different flavonoids and the use of methylation, glycosylation, acylation, and a further selection of different chromatographic techniques for analysis of specific compounds.

Chapter 6, 'Recent Advances in Flavonoid Metabolism: An Updated Review', describes the web of metabolic processes in which flavonoids are involved. It explains the influence of physical entities on flavonoid production and the regulatory mechanisms through which flavonoids function in plant cells. It also discusses minor entities and the interplay of various factors that are often ignored in flavonoid metabolism.

Chapter 7, 'Flavonoids: Recent Advances and Applications in Crop Breeding', describes the synchronized use of modern tools in breeding programs. The chapter explains the precise control exerted by flavonoids on plant reproduction and how it can be used to improve modern breeding techniques.

**Hafiz Muhammad Khalid Abbas**

Department of Plant Sciences, University of Tennessee, Knoxville, USA

**1**

**Chapter 1**

**Abstract**

**1. Introduction**

*Shyamal K. Jash*

Chemistry and Role of Flavonoids

Flavonoids are a remarkable group of plant secondary metabolites, and are of importance and interest to a wide variety of physical and biological scientists. Continuing works on their chemistry, occurrence, natural distribution and biological function have already resulted a lot and have created a stir in the field of chemical and biological sciences due to their immense biological and pharmacological/therapeutic potential. Also flavonoids play an important role in the biological activities of plant system. They can be responsible for the color of flowers and fruits and for the attraction of pollinators. The plant flavonoids are used naturally to improve their adaptation to environmental stress, to improve food quality, and to increase crop yield. The present book chapter deals with chemistry and significance role of reported novel

**Keywords:** naturally occurring flavonoids, biosynthesis, metabolism, chemistry of flavonoids, role of flavonoids in plants, agriculture, pest control, patent information

Nature is an extremely rich source of highly diverse and innovative chemical structures with a variety of structural arrangement and interesting biological activities, which have played a significant role in the process of drug discovery and design. Chemistry of Natural Products has lately undergone explosive growth; natural products are of much interest and of promise in the present day research directed particularly toward drug-design and drug-discovery. Much research works were already carried out and also intensive works are now going on world-wide in the perspective of academic as well as pharmacological/therapeutic scenario. Statistically, only less than ~10–15% of the plants have been investigated so far; a major portion of them is still being left. To gather more knowledge on the natural availability of chemical compounds, their structural variety, properties, and the isolated compounds for detailed studies in regards to biological and pharmacological potentials, more and more research is demanded for the exploration of chemical nature of plants, particularly those ones which have been used as traditional medicines all over the world. Hence, the present investigator has been motivated to undertake this work on some

Research into secondary metabolism has long centered on flavonoids. Scientists from a wide variety of fields are interested and intrigued by flavonoids, which are

natural flavonoids along with a variety of activities in agriculture.

plants traditionally used as medicine in India.

in Agriculture: A Recent Update

**Aqeel Ahmad** Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, China


**3. The psychedelic psychotherapy process**

Psychedelic medicines create a shift in access to knowledge and emotional experience both internally and externally. The tapestry of internal threads of experience ranging

from mental, emotional, somatic and nervous system realms is annexed and becomes available experientially, all while being woven into an expanded sense and concept of self. Correspondingly, the intersubjective space and all the elements in the surrounding sensory field of awareness—the so-called "*setting"—*becomes expansively resonant and apprehended through multiple sensory modes in a synesthetic melange, thereby enriching and refining the experience of the outer world.

Similar to the psychoanalytic method, where the removal of obstacles toward free association provides both the methodology and healing process, experiential attention to the self-sculpture allows for the acquisition of knowledge and correction simultaneously. Various self-components that have become exaggerated are softened, leading to the correction of imbalanced protective systems. Trauma blockages and projected interferences may come to be released, which in turn permit correction and repair. Access to the knowledge and wisdom of the mind and body naturally fosters enrichment, development and growth.


*2.1. Finite-Element Analysis of Finger Structure with the Fin Ray Effect*

The harvesting gripper's finger mechanism uses a triangular Fin-Ray soft finger component, which has a passive compliance quality and can implement an envelope while clamping spherical items. The general construction of the finger consists of the front and rear beams, cross beams, and base, as shown in Figure 1a. The front beam comes into contact with the fruits, and the front and rear beams are linked by cross beams. These cross-beam support rods are the foundation of Fin Ray fingers. Because of the presence of these crossbeam support rods, the Fin Ray structure can withstand greater loads than conventional flexible constructions.

**Figure 1.** Characteristics of the Fin Ray finger: (**a**) basic components; (**b**) displacement of the fingertip; (**c**) structure of the Fin Ray finger.

#### 2.1.1. Pre-Preparation of the Simulation Experiment

The finger gripping force must be sufficient to improve the grasping stability. Furthermore, the pressure per unit area of the pericarp should be small enough to guarantee that the fruit pericarp remains intact. As a result, the finger gripping force and the bending degree are two critical criteria. The finger gripping force can ensure clamping stability, while the finger bending degree can assure clamping stability and safety by increasing the contact area between the fingers and the fruits. The stress of the Fin Ray finger during deformation is complicated by making the mathematical modeling difficult. As a result, using the simulated tests, this research investigates the effect of the front and rear beam thickness, the finger width, and the number of cross beams on the finger gripping force and bending degree, as shown in Figure 1a. In the simulation experiment, the contact stress between the finger and apple is used to characterize the gripping force, and the displacement of the fingertip is used to characterize the bending degree, as shown in Figure 1b.

 The cross beams are parallel to the base; the distance is equal, and the thickness of the cross beams is 1.40 mm. The little bulges are designed on the cross beams to increase the rigidity and strengthen the load capacity, as shown in Figure 1c.

The TPU 95A [49] was chosen as the finger material. The TPU soft material is a hyperelastic nonlinear material with isotropic properties throughout the stress process. Furthermore, because the bending deformation of the soft finger is a nonlinear large deformation, the Yeoh model can better represent its material properties [50]. The strain energy density function *W* can be written as follows:

$$\mathcal{W} = \sum\_{i=1}^{N} \mathbb{C}\_{i0} (I\_1 - 3)^i + \sum\_{k=1}^{N} \frac{1}{D\_k} (J - 1)^{2k} \,\mathrm{}\,\tag{1}$$

where *N* is the order of the model; *I*1 is the deformation tensor; *Ci*0 and *Dk* are the material constants; *J* is the volume ratio. When TPU is regarded as the incompressible material, *J* = 1.

The strain energy density function in the form of the binomial parameters is usually used [51], and the typical binomial parameter form of the Yeoh model is

$$\mathcal{W} = \mathbb{C}\_{10}(I\_1 - \mathfrak{Z}) + \mathbb{C}\_{20}(I\_1 - \mathfrak{Z})^2. \tag{2}$$

The fitting curve of the stress and strain of the TPU 95A was obtained through the uniaxial tensile test, as shown in Figure 2. The material parameters obtained after processing and analysis are shown in Table 1.

**Figure 2.** Strain–stress curve of the tensile test and fitting using the Yeoh model (TPU95A).

**Table 1.** Mechanical property parameters of materials.

Because the contact stress between the three fingers and the fruit is the same, the contact between a single finger and the fruit can be considered to reduce the quantity of simulation calculation, to simplify the analysis.

During the simulation, the center of the bottom plate of the gripper is kept aligned with the center of the fruit at a distance of 65 mm [49].

2.1.2. Influence of Geometric Parameters on Contact Stress and Fingertip Displacement

Each geometric parameter has a varied effect on the contact stress and fingertip displacement. All other parameters were held constant to compare their changes when the given parameters were altered, and the influence of the given single parameter on them was gradually optimized.

First, the influence of the thickness of the front and rear beams was analyzed. The stress increases dramatically as the thickness increases, while the fingertip displacement decreases, as shown in Figure 3a.

**Figure 3.** Changes in stress and displacement according to three factors: (**a**) thickness of front and rear beams; (**b**) width of fingers; (**c**) number of cross beams.

When the thickness of the front and rear beams is 2 mm, the stiffness of the finger after contact with the apple cannot be guaranteed, resulting in a small gripping force and easy fruit slip; when the thickness is 4.5 mm, the stress of the material itself will greatly limit its bending deformation and reduce the contact area between the fingers and fruit. At the same time, because excessive stress might cause fruit damage, the thickness of the front and back beams should not be too tiny or too large. When the thickness is 3.5 mm, the downward trend of the fingertip displacement becomes stronger as the thickness increases, while the upward trend of stress tends to be soft. As a result, selecting a thickness of 3.5 mm for the front and rear beams not only meets the requirement of the increasing gripping force but also allows fingers to make good contact with the fruits.

The effect of the finger width was then investigated. With the increase of the width, the fingertip displacement diminishes. However, the stress does not follow a constant pattern, as shown in Figure 3b. When the width is 10 mm, the stress and fingertip displacement is the greatest. This is because the finger width is excessively narrow, resulting in a limited contact area between the finger and the apple and high contact stress acting on the apple surface, which is easily damaged. Although the degree of the finger bend is greater when the finger is thin, it also results in insufficient grasping stiffness and fruit slide. When the width is 25 mm, the contact area between fingers and fruit increases, but its structure affects its bending, and it is not suitable for collecting fruits in the complex growing environment. When the width is 16 mm, as the width continues to increase, the fingertip displacement decreases dramatically and the stress tends to be flat. As a result, the best finger width is set to 16 mm in this study.

Finally, the number of beams was taken into account. Because the cross beams are the primary components that influence the stiffness of fingers, the number of cross beams has a substantial impact on the Young's modulus of the fingers [25]; hence, the distribution of the cross beams may have a major impact on the gripper performance. In distribution, there are several combinations of the cross beams. For the sake of simplicity, just the simplest equidistant parallel arrangement of the cross beams was considered in this study. Change the thickness of the front and rear beams to 3.5 mm, the width of the fingers to 16 mm, and change the number of cross beams. As the number of cross beams grows, so does the stress, and the fingertip displacement declines first and subsequently increases. When the number of beams is 9, the fingertip displacement reaches the maximum and then decreases again, as shown in Figure 3c. As a result, one selects nine as the optimal number of beams.

According to the results of the aforementioned analysis, the thickness of the front and rear beams has the greatest influence on the contact stress and fingertip displacement among the three geometric parameters. It is mostly because the finger surface is in direct contact with the fruit, and the thickness of the front and rear beams has a direct impact on the stiffness of the fingers. The structural parameters of the Fin Ray fingers are extremely complex, and this study just considers the most basic scenario. As a result, the best structural parameters are as follows: the thickness of the front and rear beams is 3.5 mm, the width of the fingers is 16 mm, and the number of beams is 9.

#### *2.2. Overall Design of the Soft Gripper*

The overall structure of the three-finger soft gripper for apple harvesting built with optimized Fin Ray fingers is shown in Figure 4a. It can be divided into three parts: the driving and sensing part, the transmission part, and the grasping part for clamping objects. The driving part is performed by a servo with torque and position feedback. To measure the relative distance between the gripper and the fruit, a distance sensor is mounted on the servo installation side of the gripper bottom plate. The transmission part is primarily accomplished by a slider, and the rocker mechanism was composed of a rocker, a connecting rod, a moving plate, and guide rods, as shown in Figure 4b. The servo rotates to drive the moving plate to move up and down. Because the fingers and their connectors are connected with the moving plate through the support rods, the fingers will move with the moving plate moving up and down, as shown in Figure 4c.

**Figure 4.** Overall design of the soft gripper: (**a**) overall structure; (**b**) details of transmission and the driving and sensing part; (**c**) the designed gripping mechanism; (**d**) details of the grasping part.

In the grasping part, three Fin-Ray finger units are evenly distributed around the bottom plate of the gripper disc, connected with the transmission mechanism by the finger connectors to drive the Fin Ray fingers. A silicone pad is attached to the surface of each finger to increase the contact friction between the finger and the fruit, which ensures the clamping stability, as shown in Figure 4d.

At the initial position, the finger connectors are inclined outward at a certain angle relative to the bottom plate. Because the bottom of the fingers is connected in parallel with the bottom of their connectors, and the finger has a triangular symmetrical structure, the clamping range of the gripper is expanded.

#### **3. Kinematic Mechanics Analysis of a Soft Gripper**

The driving force begins with the servo, travels through the slider and rocker mechanism, multi-link mechanism, and Fin Ray soft structure, and eventually acts on the gripped fruit. In conclusion, the static analysis of the rigid multi-link mechanism and the soft finger structure was performed to acquire the gripping force on the fruit surface. Simultaneously, the relationship between the gripper pulling force and the gripping force was investigated in connection with the pulling harvesting method. Because the three fingers are symmetrically arranged relative to the bottom plate of the gripper, and the structure is the same. Furthermore, the servo output torque operates on the center of the moving plate, and the movement process and stress situation are comparable. As a result, the stress analysis of

the direct contact between fingers and fruit begins with a single finger, making the analysis procedure simpler.


5. Conclusions

Presented numerical results have demonstrated that:

For the approximate Rν-generalized solution obtained by the weighted finite-element method, an absolute error value is by one or two orders of magnitude less than the approximate generalized one obtained by the FEM or by the FEM with graded meshes; this holds for the overwhelming majority of nodes.


4.1.3. Containment

In the last decades, many containment interventions have been implemented in Europe with the objective of reducing land take. As a consequence, a number of sustainable strategies and green belts have been designed (e.g., the Grüner Ring in Leipzig, Corona Verde in Torino) to limit and control urban growth. Numerous interventions of this kind have proven successful in promoting sustainable development. For example, the Corona Verde strategy [40] envisages an ecological 'crown' around the metropolitan area of Torino (Italy), and brings together different intersectoral policies in order to reduce urban land consumption and to increase the quality of the rural–urban environment (e.g., through the mitigation and renaturation of infrastructural barriers, the conservation of the rural heritage).

Certain characteristics, such as the support of a strong political will and the adoption of long-term visions, seem to improve the implementation of these interventions. For example, the German government set the 30 hectares' target, with the ambitious goal of reducing annual land consumption to 30 hectares per day nationwide by 2020 (Umweltbundesamt— UBA, German Environment Agency: www.umweltbundesamt.de/en/ (accessed on 15 March 2021)). Cooperation that goes beyond municipal boundaries is another characteristic that often improves the successfulness of containment interventions. This is the case of Vision Rheintal (Austria) [41]. For the expert informant, its success is partly due to intramunicipal cooperation, as well as engagement with a heterogeneous group of experts (thus, promoting the transfer of expert knowledge) and the adoption of a holistic approach.

The adoption of legal binding instruments also seems to improve these interventions. For example, the 2014 Tuscany Regional Law on soil consumption (Italy) requires municipalities to delimit the borders of their more densely urbanized areas and to promote the urbanization of empty plots through simplified regulations and incentives. Non-residential transformations outside urbanized areas, which involve the consumption of new land, are only allowed if the co-planning conference provides a favorable opinion (Legge Regionale Toscana 65/2014). Similarly, the 2009 Law for the City of Sofia (Bulgaria), which works together with the city's General Urban Development Plan (GUDP), is considered to have produced positive outcomes, in particular by stating that "the designation of existing green plots or parts thereof in the urbanized territories, created according to the development plans cannot be changed" (art. 9). The GUDP, however, seems to have been less successful. In fact, inconsistencies seem to exist between the plan's overall goals and some of its measures and implementation tools [42]. Thus, certain interventions, if not implemented correctly, might lead to a discrepancy between the desired objectives and the actual outcomes. This might also be exacerbated by a lack of political will, technical capability and scarcity of economic resources.

Moreover, certain containment initiatives may turn out to be counterproductive for the promotion of sustainable land use. This seems to be the case of the Cork Area Strategic Plan (Ireland), which provides a long-term vision for the development of the Cork City-Region up to 2020. The expert reporting the intervention noted that, even though it aims to reduce urbanization in the countryside, an overexploitation of natural resources still occurs, and that the strategy is based on a pro-growth approach.


Organizational Learning Capability

Learning capability refers to those factors that facilitate organizational learning [29,30]. This is a concept related to the renewal of dynamic and continuous knowledge. Knowledge renewal is undoubtedly the greatest source of ability to learn and explore new knowledge while exploiting already known knowledge [31]. Organizational learning is a broad concept and occurs both within and outside of the organization itself [32].

Lichtenthaler [33] classified organizational learning into three processes: exploratory, exploitative and transformative. All three processes have positive effects on PRAC. Organizational learning requires organizations to plan, visualize and transact. According to Chiva et al. [34], OLC was born from experimentation, risk-taking, interaction with the external environment, dialogue and participatory decision-making.

Experimentation is the search for new ideas by firms, whereby they are curious to know or make changes in work processes. Risk-taking shows tolerance for ambiguity, uncertainty and mistakes that lead to organizational learning. Interaction with the environment shows the breadth of the firm's relationships with its environment. Dialogue is the collective search for assumptions, processes and certainties. Finally, decision making relates to the collaboration and participation that employees have in the process [35]


*Article* **Effect of Daily Light Integral on Cucumber Plug Seedlings in Artificial Light Plant Factory**

**Jiawei Cui 1,2, Shiwei Song 1, Jizhu Yu 2,\* and Houcheng Liu 1,\***

**\*** Correspondence<EMAIL_ADDRESS>(J.Y<EMAIL_ADDRESS>(H.L.)

**Abstract:** In a controlled environment, in an artificial light plant factory during early spring or midsummer, vegetable seedlings can be uniform, compact, and high quality. Appropriate light parameters can speed up the growth of seedlings and save on production costs. Two experiments were carried out in this study: (1) cucumber seedling growth under different daily light integrals (DLIs) (5.41–11.26 mol·m−2·d−1) and optimum DLI for seedling production were explored (experiment 1: Exp. 1); (2) under the same DLI selected by Exp. 1, the effects of different light intensities and photoperiods on cucumber seedlings were investigated (experiment 2: Exp. 2). The root biomass, root-to-shoot ratio, seedling index, and shoot dry matter rate increased as the DLI increased from 5.41 to 11.26 mol·m−2·d−1, while the shoot biomass and leaf area decreased in Exp. 1. The cucumber seedlings became more compact as DLI increased, but more flowers developed after transplanting when the DLI was 6.35 mol·m−2·d−1. Under the optimal DLI (6.35 mol·m−2·d−1), the optimal intensity was 110–125 μmol·m−2·s−1, and the optimal photoperiod was 14–16 h, in which plant biomass, shoot dry matter rate, seedling index, and photochemical efficiency were higher.

**Keywords:** daily light integral; cucumber seedling; seedling quality; flower development

#### **1. Introduction**

The daily light integral (DLI) is the total amount of photosynthetic light delivered to plants each day [1,2]. The DLI is an important environmental parameter for plants and displays stronger correlation with vegetative growth parameters than with photoperiod and light intensity [3,4]. Many studies have shown that a suitable DLI could promote the growth and development of plants, such as the germination rate of photoblastic seeds [5], shoot and root biomass [6–9], stem diameter [10,11], leaf area and leaf number [12], and the differentiation of flower buds [4,13,14].

The production of high-quality seedlings with characteristics of higher biomass, compactness and adequate leaf area in a short cultivation period is the target of producers. However, this constitutes a significant challenge under insufficient scrutiny [15,16]. Many operations use supplemental lighting to increase DLI under low irradiance to accelerate growth and improve the morphology of seedlings in typical greenhouses [17–19]. Cucumber seedlings became more compact and vigorous, with characteristics of a short hypocotyl length, large leaf area, and high biomass under a high DLI [19,20]. Increases in DLI during the seedling stage have been also reported to accelerate subsequent floral initiation and decrease the time to the first flowering after transplant [13,21,22]. The number of tomato floral buds and days to flowering increased corresponding to the decrease in the shading before anthesis [23].

However, higher DLI is correlated with more illuminating apparatus and electric energy consumption. Additionally, superfluous DLI with a high light intensity or long

**Citation:** Cui, J.; Song, S.; Yu, J.; Liu, H. Effect of Daily Light Integral on Cucumber Plug Seedlings in Artificial Light Plant Factory. *Horticulturae* **2021**, *7*, 139. https://doi.org/ 10.3390/horticulturae7060139

Academic Editor: Othmane Merah

Received: 16 April 2021 Accepted: 20 May 2021 Published: 7 June 2021

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

**Copyright:** © 2021 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/).

5

photoperiod may cause damage to the photosynthetic system and inhibits the production of photosynthates [24,25]. For example, high DLI results in a decrease in photosystem II (PSII) activity, thus leading to the low production of lettuce [26]. The total fresh mass and total dry mass of spinach were higher when DLI was 17.3 mol·m−2·d−1 compared with 20.2 mol·m−2·d−1 [27]. These reductions in biomass may result in a reduced source of flower bud formation, since it has been previously demonstrated that flower initiation requires a certain amount of photoassimilates [8]. Extra DLI did not further increase the flowering rate or floral bud number in some bedding plants [28–30]. Therefore, an optimal DLI which can only just meet the demand of seedling growth and facilitate late flower bud differentiation should be selected by the producer for energy-saving purposes.

Under the same DLI, a longer photoperiod is more beneficial to the growth of plants. The plant height, shoot dry mass, root dry mass and chlorophyll content index of rudbeckia seedlings were larger with longer photoperiods [18]. A longer photoperiod with the same DLI increased the light interception, chlorophyll content index, quantum yield of photosystem II, and aboveground biomass of lettuce and mizuna [31,32].

Under artificial light conditions, DLI is completely supplied by lamps and varies via changing the light intensity or photoperiod. Due to the controllable illumination parameters, DLI parameters for plants are more reliable and can be used for plant cultivation and research with higher accuracy. Exploring the optimum DLI and illumination parameters is conducive to the scheduling and improvement of profitability.

Cucumber is cultivated worldwide, and its seedling stage is crucial for subsequent growth and development. Scarce research has been conducted on the effects of DLI from sole-source (SS) lighting on cucumber plug seedlings. Therefore, the objectives of our study were to determine the optimal DLI by investigating the morphology, biomass, chlorophyll fluorescence, and subsequent flower development of cucumber plug seedlings (Exp. 1); then the effects of different illumination intensities and times on the quality of cucumber seedlings were further investigated under the optimal DLI selected in Exp. 1, and the appropriate light parameters for cucumber plug seedlings were finally selected (Exp. 2).

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

#### *2.1. Plant Material*

In both Exp. 1 and 2, seeds of cucumber 'Yuexiu No.3 were place onto humid cotton in an incubator for 2 days. The temperature and relative humidity were set to 25 ◦C and 80%, respectively. The germinated seeds were sown into plug trays (50-cell size (28 mL)) in a substrate with peat, coconut coir and perlite (6: 3: 1, v: v: v) and placed into a walk-in growth chamber at the College of Horticulture of South China Agricultural University, Guangzhou. Each tray was a repeat. Each experiment conducted four treatments, in which three repeats were concluded. Before cotyledons were fully expanded after sowing, 800 ± 50 mL tap water was added to each tray every second day. Once cotyledons were fully expanded, 800 ± 50 mL 1/4 strength modified Hoagland and Arnon's nutrient solution was added to each tray every second day to provide (in mg·L−1) 53 nitrogen (N), 40 calcium (Ca), 59 potassium (K), 8 phosphorus (P), 25 magnesium (Mg), 33 sulphur (S), 0.56 iron (Fe), 0.5 boron (B), 0.5 manganese (Mn), 0.05 zinc (Zn), 0.01 molybdenum (Mo) and 0.005 copper (Cu) until the emergence of the second true leaf. Then, 800 ± 50 mL 1/2 strength modified Hoagland and Arnon's nutrient solution was added to each tray every second day until sampling.

#### *2.2. Growth Chamber Environment*

All the plug trays were placed on steel shelves in two vertical layers in a walk-in growth chamber, with an average daily temperature of 25 ◦C, relative humidity (RH) of 75%, and average carbon dioxide (CO2) concentration of 400 μmol·mol−1.

#### *2.3. Sole-Source Lighting Treatments*

Adjustable LED lamps of red (655–660 nm):blue (455–460 nm) = 1:1 (R1:B1) (Unihero technology Co. Ltd., Huizhou, China) were placed above the steel shelves providing sole-source lighting with different photosynthetic photon flux densities (PPFDs) and photoperiods. The spectra for PPFD at 200 μmol·m−2·s−1 are shown in Figure 1. Two experiment lighting treatments were conducted as follows. Exp. 1: the average total photon flux was delivered from sole-source light-emitting diodes (LEDs) with light ratios (%) of red/blue 50:50 to achieve target light intensities of 125 to 200 μmol·m−2·s−1 with 12–16 h photoperiods. Four gradients of DLIs in each run set from 7.47 to 11.26 mol·m−2·s−1 (run 1) and from 5.41 to 8.43 mol·m−2·s−1 (run 2), respectively (Table 1). Exp. 2: target light intensities were of the same light ratios as Exp. 1, of 110–175 μmol·m−2·s−1, with 10–16 h photoperiods, and four lighting treatments were conducted with the same DLI (6.35 mol·m−2·d−1) selected by Exp. 1 (Table 2).

**Figure 1.** Spectral quality of 200 μmol·m−2·s−1 from SS LEDs with light ratios (%) of red/blue 50:50.

**Table 1.** Illumination parameters of different treatments in Exp. 1.

\* The data represent the mean ± SE of 10 spots under lights in each treatment.

**Table 2.** Four combinations with different light intensities and photoperiods that achieve the same DLI in Exp. 2.

\* The data represent the mean ± SE of 10 spots under lights in each treatment.

#### *2.4. Morphology and Growth Measurement*

The morphology and growth of cucumber plug seedlings in both Exp. 1 and 2 were measured on the 26th day after sowing. Six seedlings of each repeat (i.e., 18 seedlings per DLI treatment) were randomly selected and measured to determine the hypocotyl length, stem diameter, total leaf area, shoot fresh mass, shoot dry mass, root fresh mass, and root dry mass. The fresh mass of seedlings was recorded by an electronic balance, and the dry mass was recorded after seedlings were heated to de-enzyme at 105 ◦C, then dried at 80 ◦C until steady.

Seedling index = (stem diameter/hypocotyl length + root dry mass/shoot dry mass) × total dry mass × 10 [33], root-to-shoot ratio = root dry mass/shoot dry mass, leaf area ratio = total leaf area/shoot dry mass, and shoot dry matter rate = shoot dry mass/shoot fresh mass were calculated [11,34].

#### *2.5. Physiological Characteristics and Photosynthesis Pigment Content*

The soluble sugar content was extracted and analyzed by anthrone colorimetry. A 0.5 g amount of leaf fresh sample was added to a test tube with 10 mL of distilled water, and then it was extracted in boiling water for 30 min. The extract was filtered into a 25 mL volumetric flask, the test tube and residue were rinsed repeatedly, and the volume was maintained to scale. An amount of 0.1 mL of the sample extract was absorbed into a 20 mL graduated test tube, followed by adding 1.9 mL of distilled water, 0.5 mL of ethyl anthrone acetate reagent and 5 mL of concentrated sulfuric acid. The solution was fully oscillated and cooled down to room temperature. The absorbance was measured at 630 nm by using a UV-spectrophotometer [35].

The soluble protein content was extracted and analyzed by Coomassie Brilliant Blue methods. Amount of 0.5 g of fresh leaf sample and 5 mL of distilled water were ground into a homogenate and centrifuged at 10,000× *g* for 10 min at 4 ◦C. After mixing 0.3 mL of supernatant and 0.7 mL of distilled water, 5 mL of Coomassie Brilliant Blue G-250 solution (0.1 g/L) was added to the mixture. After 2 min, the absorbance at 595 nm was determined by using a UV-spectrophotometer [35].

The content of photosynthesis pigment was determined by an acetone–ethanol blend method. An amount of 0.2 g of leaf with removed veins was placed into a test tube containing 20 mL of acetone and ethanol (1:1, *v:v*), and extracted under dark conditions. The absorbance at 663, 645 and 440 nm was determined by using a UV-spectrophotometer after the leaves turned white. Chlorophyll a (Chl a) content (mg·g−1) = (12.70 × A663 − 2.69 × A645) × 20 mL/(1000 × 0.2 g); chlorophyll b (Chl b) content (mg·g−1) = (22.90 × A645 − 4.86 × A663) × 20 mL/(1000 × 0.2 g); total chlorophyll (Total Chl) content (mg·g−1) = (8.02 × A663 + 20.20 × A645) × 20 mL/(1000 × 0.2 g); carotenoid content (mg·g−1) = (4.70 × A440 − 2.17 × A663 − 5.45 × A645) × 20 mL/(1000 × 0.2 g) [36].

#### *2.6. Chlorophyll Fluorescence*

Chlorophyll fluorescence was measured by MINI-PAM-II (WALZ company, Germany), and the actinic illumination was set at 286 μmol·m−2·s−1. Leaves were dark-acclimated for 20 min with the manufacturer's plastic and foam clips before measurements were recorded. Six seedlings of each repeat were randomly selected and measured, and the locus was the second true leaf of each seedling. The photochemical quenching indexes (qP and qL), the non-photochemical quenching indexes (qN and NPQ), photic injury nonphotochemical quenching quantum yield (Y(NO)), photoprotection non-photochemical quenching quantum yield (Y(NPQ)) and PSII conversion efficiency of light energy (ΦPSII), and maximal photochemical efficiency of PSII in the dark (Fv/Fm) were measured.

#### *2.7. Flowering in Cucumber Plant after Transplant*

As a supplementary experiment, only the run 2 in Exp. 1 was carried out for flowering statistics. After DLI treatments, nine cucumber seedlings from each DLI treatment were transplanted into a growth bag (15 cm diameter, 15 cm height) filled with substrate of peat, coconut coir and perlite (6:3:1, v:v:v). Plants were watered with 1/2 strength Hoagland and Arnon's nutrient solution before the first flower bloom, and then full strength nutrient solution. The days to first flower bloom from transplant, node of the first male flower, male flower number, node of first female flower, female flower number on main stem, number of lateral branches, and total female flower number under the 15th node were recorded at 60 days after the transplant.

#### *2.8. Statistical Analysis*

Data were analyzed by one-way ANOVA using PASW Statistics 18.0. Duncan's multiple range test at *p* < 0.05 was used to determine significant treatment differences. The plotting and fitting of monomial and binomial response functions were conducted using Origin 8.6.

#### **3. Results**

*3.1. Experiment 1*

3.1.1. Morphology and Growth of Cucumber Plug Seedlings

The morphology and growth of cucumber plug seedlings were affected by DLI. The hypocotyl length and leaf area of cucumber plug seedlings showed the same trend as DLI increased. Hypocotyl length decreased from 8.28 to 3.55 cm, while the leaf area decreased from 123.15 to 56.07 cm2, as DLI increased from 5.41 to 11.26 mol·m−2·d−1 (Figure 2a,c). The stem diameter of cucumber plug seedlings was not affected by DLI (Figure 2b). Shoot fresh mass and dry mass decreased as DLI increased from 5.41 to 11.26 mol·m−2·d−1. The root fresh mass and dry mass first increased and then decreased as the DLI increased, peaking at 8.43 mol·m−2·d−1 (Figure 3a). The root-to-ratio and seedling index first increased and then remained steady with the increase in DLI. At a lower DLI, the leaf area ratio decreased significantly with an increased DLI, but it remained at a low value under higher DLIs. The shoot dry mass rate increased from 0.073 to 0.095 as the DLI increased from 5.41 to 11.26 mol·m−2·d−1 (Figure 3b).

**Figure 2.** *Cont*.

**Figure 2.** Relationships between DLI and (**a**) hypocotyl length, (**b**) stem diameter and (**c**) leaf area of cucumber seedlings. Each symbol represents the mean of 18 plants in each treatment, and error bars represent SEs of means. Fitting formula shown in supplementary section.

3.1.2. Physiological Characteristics and Photosynthesis Pigment Content of Cucumber Plug Seedlings

The soluble sugar content of cucumber plug seedlings increased by 8.72 mg·g−1 linearly as the DLI increased from 5.41 to 11.26 mol·m−2·d−1 (Figure 4a). When the DLI was in the range of 6.35–8.52 mol·m−2·d−1, the soluble protein remained high but then fell dramatically beyond this range (Figure 4b). All the photosynthesis pigment contents were negatively correlated with DLI (Figure 5).

**Figure 3.**  Each symbol represents the mean of 18 plants in each treatment, and error bars represent SEs of means. Fitting formula shown in supplementary section.

**Figure 4.** Relationships between DLI and (**a**) soluble sugar content and (**b**) soluble protein content of cucumber seedlings. Each symbol represents the mean of three repeats in each treatment, and error bars represent SEs of means. Fitting formula shown in supplementary section.

**Figure 5.** Relationships between DLI and photosynthesis pigment content of cucumber seedlings. Each symbol represents the mean of three repeats in each treatment, and error bars represent SEs of means. Fitting formula shown in supplementary section.

#### 3.1.3. Flowering in Cucumber Plant after Transplant

The days to the first flower bloom from transplant, and the node of the first male and female flowers (data not shown) were unaffected by DLI. When DLI was about 6.35 mol·m−2·d−1, more male flowers, female flowers and lateral branches appeared (Table 3).

**Table 3.** The effect of DLI on cucumber plant flowering after transplant of cucumber plug seedlings in run 2 \*.

\* Presented values are means ± SEs (*n* = 9). a,b Different lowercase letters indicate statistically differences among treatments (*p* < 0.05).

*3.2. Experiment 2*

#### 3.2.1. Morphology and Growth of Cucumber Plug Seedlings

Under the same DLI, the hypocotyl length, stem diameter and shoot fresh mass were independent of changes in illumination strength and time (supplementary section and Figure 6a). The shoot dry mass, root fresh mass and root dry mass decreased by 50.24, 310.00 and 15.13 mg, respectively, as the light intensity increased from 111 to 177 μmol·m−2·s−1 and the photoperiod decreased from 16 to 10 h (Figure 6a). Two sets of low light intensities and long photoperiods (T1 and T2) had a higher root-to-shoot ratio, seedling index, shoot dry matter rate and lower leaf area ratio (Figure 6b).

**Figure 6.** The effects of different light intensities and photoperiods on (**a**) shoot fresh and dry mass, root fresh and dry mass (**b**) root-to-shoot ratio, seedling index, leaf area ratio, and shoot dry matter rate of cucumber seedlings. Different letters indicate statistically significant differences among treatments (*p* ≤ 0.05). Error bars show SEs (*n* = 18).

#### 3.2.2. Physiological Characteristics of Cucumber Plug Seedlings

The soluble sugar content was the highest in T1, and there were no significant differences in the other three treatments. The soluble sugar content in T1 was 25.66%, 27.95%, and 35.42% higher than in T2, T3, and T4, respectively (Figure 7a). There was no obvious pattern between the content of soluble protein with the variation of illumination parameters under the same DLI (Figure 7b).

**Figure 7.** The effects of different light intensities and photoperiods on (**a**) soluble sugar and (**b**) soluble protein content of cucumber seedlings. Different letters indicate statistically significant differences among treatments (*p* ≤ 0.05). Error bars show SEs (*n* = 9).

#### 3.2.3. Photosynthesis Pigment Content and Chlorophyll Fluorescence of Cucumber Plug Seedlings

When the light intensity increased and the photoperiod decreased, the contents of chlorophyll and carotenoid tended to increase (data shown in supplementary section). As the light intensity increased and the photoperiod decreased, the photochemical quenching indexes (qP and qL) and ΦPSII all showed a downwards trend, and the decreased range from T3 to T4 was sharp, and there were significant differences among the four treatments. The non-photochemical quenching indexes (qN and NPQ) and Y(NPQ) increased first then decreased later, which was the largest in T3. Y(NO) showed an increasing trend with the increase in light intensity and shortening of the photoperiod, and T4 was 146.84%, 144.89%, and 117.27% higher than T1, T2, and T3, respectively. The Fv/Fm of T4 was the smallest, and there was no difference among T1, T2, and T3 (Table 4).

**Table 4.** The effects of different light intensities and photoperiods on chlorophyll fluorescence of cucumber seedlings \*.

\* Presented values are means ± SEs (*n* = 18). a–d Different lowercase letters indicate statistically differences among treatments (*p* < 0.05).

#### **4. Discussion**

Under low irradiance conditions, plants extend stems and leaves to capture more light energy, and are prone to thin branches and leaves [34,37]. Increasing DLI along with low irradiance can effectively inhibit plants spindling growth (elongated hypocotyl, thin stem diameter) of cucumber seedling [17]. As the DLI increased, the hypocotyl length and leaf area decreased in this study, but the stem diameter remained at 3–3.3 cm.

With the increased DLI, cucumber seedling quality improved in some respects (Figure 3b). High-quality vegetable seedlings are usually compact and fully rooted transplants with a higher seedling index ratio and root-to-shoot ratio [15]. Hurt et al. [38] found that when DLI was increased to about 10 mol·m−2·d−1, the seedling quality index of five annual bedding plants was significantly improved. The root-to-shoot ratio of new guinea impatiens, geranium, and petunia cuttings were increased as DLI increased [11]. In this study, the root-to-shoot ratio and seedling index increased as DLI increasing from 5.4 to 8.5 mol·m−2·d−1, then, became

stable due to the decrease of root dry mass with DLI continuing to increase. A lower leaf area ratio and a higher shoot dry matter rate are also regarded as high quality, which represents a higher proportion of structural materials and carbohydrates per of unit fresh weight [34]. As the DLI increased, the leaf area ratio of eight kinds of bedding plants (i.e., ageratum, begonia, impatiens, marigold, petunia, salvia, vinca, and zinnia) decreased, while the shoot dry matter rate increased [34]. This phenomenon also occurred with the *Tecoma stans* [16], impatiens cuttings [37], *Heuchera americana* [39], lettuce [40], and *brassica* microgreens [41].

High-quality seedlings exhibit luxuriant growth both before and post-transplant growth, which is mainly due to a higher shoot fresh and dry mass. Generally, increasing DLI can promote the accumulation of shoot biomass [41,42]. However, there was a negative correlation between DLI and biomass in this study. It is possible that higher DLIs exceeded the amount required for cucumber seedlings. As in Ji's [20] experiment, when DLI exceeded 14.4 mol·m−2·d−1, the correlation between the fresh mass and dry mass of the shoot in three cucumber seedlings and DLI changed from positive to negative. The promotion of DLI to flower development is usually accompanied by an increased shoot biomass [23,28,34,43]. Leaf area reached 500 cm2, and dry mass reached 3 g, which were prerequisite for the flowering of tomato seedlings, revealing that some level of photoassimilates is necessary for floral initiation [23]. In this study, the decreased shoot biomass and leaf area with a higher DLI might have slowed down the development of cucumber seedlings, which stunted flower development after transplant. Therefore, the optimal DLI for cucumber seedlings at the nursery stage was 6.35 mol·m−2·d−1, in which there is a higher shoot biomass and better floral initiation.

Under the optimal DLI (6.35 mol·m−2·d−1) screened by Exp. 1, a further exploration of appropriate lighting parameters combining different light intensities and photoperiods of cucumber seedlings was conducted. Under the same DLI, the variation of the light intensity and photoperiod mainly influences dry matter accumulation [44]. In this study, the shoot dry mass decreased with the increased light intensity and the reduction in the photoperiod, while there was no significant change in shoot fresh mass. Additionally, the combined treatment of a high light intensity and short photoperiod was not conducive to thicker leaves and stronger seedlings (Figure 6b).

In Exp. 2, the chlorophyll fluorescence parameters were consistent with the growth conditions, and also demonstrated that the combination of a low light intensity and long photoperiod was more favorable for the growth of cucumber seedlings. Under the same photoperiod, as PPFD increased, ΦPSII decreased in three species (*Ipomea batatas*, *Lactuca sativa*, and *Epipremnum aureum*) [45]. This phenomenon was also found in lettuce and mizuna under the same DLI, which meant that most PSII reaction centers were closed at high PPFDs [31,46]. In this study, ΦPSII decreased as PPFD increased, resulting in a decline in photosynthate. NPQ and Y(NPQ) increased first and then decreased, indicating that with the increase in light intensity and the shortening of the photoperiod, the photoprotection mechanism of cucumber seedlings was activated, but the excessive light intensity destroyed the PSII and reduced the photoprotection ability of cucumber seedlings [47]. Meanwhile, Y(NO) showed that the degree of light damage was severe in T4. Due to the low light intensity requirements, these combinations (low light intensities and long light durations) can also reduce capital expenses by reducing the cost of light fixtures [18,31].

With the increased DLI, the photosynthetic pigment showed a linear declining trend, which confirmed that leaves gained more light capture ability by increasing the chlorophyll content under lower DLIs [48,49]. The relative chlorophyll content of cucumber leaves of different ages decreased upon increasing the DLI, and the apparent quantum yield decreased according to the light response curve [50]. The chlorophyll content was positively correlated with shoot biomass in Exp. 1 and negatively correlated with shoot biomass in Exp. 2, which reveal that the chlorophyll content only represents the adaptability of plants to environmental changes and had no direct relationship with the amount of photosynthate produced by plants [49].

Plant leaves adapt to light conditions not only anatomically and morphologically, but also biochemically [48]. The increase of soluble sugar content increased the plant resistance to some extent [51]. Previous research has shown that increasing DLI promotes the accumulation of soluble sugar in lettuce [40]. Higher DLIs and longer photoperiods may be more beneficial to improve the resistance of cucumber seedlings. These might be future research perspectives.

#### **5. Conclusions**

In conclusion, within the range of 5.41–11.26 mol·m−2·d−1, the increment in DLI was conducive to a compact morphology but inhibited the shoot biomass of cucumber plug seedlings. The optimal DLI in an artificial light condition was 6.35 mol·m−2·d−1, for which the leaf area and shoot biomass were relatively high, and floral initiation was accelerated in the subsequent stage. Under the condition of optimal DLI (6.35 mol·m−2·d−1), the combinations of low light intensities and long photoperiods are more conducive to the accumulation of root growth and whole plant dry matter, with a relatively high seedling index and thicker leaves. Therefore, the optimal light intensity was 110–125 μmol·m−2·s−1, and the optimal photoperiod was 14–16 h for cucumber plug seedlings.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/horticulturae7060139/s1.

**Author Contributions:** Conceptualization, H.L.; data curation, J.C. and S.S.; formal analysis, S.S.; funding acquisition, H.L.; investigation, J.C.; methodology, J.Y. and H.L.; writing—original draft, J.C. and S.S.; writing—review and editing, J.Y. and H.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Key Research and Development Program of China (2017YFE0131000, 2019YFD1001900).

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Raw data is available on request.

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

#### **References**


*3.1. Surveying*

From the 1800s through the 1990s, the primary method that federal, state, and local governments have used to compile large education datasets is surveying. Historians estimate that early Sumerian societies around 3200 B.C. conducted censuses of their population to distribute resources and plan for levees and canals to ensure adequate water and food supply [22]. In modern societies, many countries have censuses written into their founding government documents, including the United States, Australia, several South American countries, and most of the European Union [22]. Other developing and developed countries, such as China and India, began mass collecting and publishing census data in the 1990s, and globally, nearly all forms of the census have included questions related to educational attainment level and the number of school-aged children in the household [22].

However, multiple issues arise when promoting equitable data collection for developing educational datasets through survey methods. First, organizations such as the OECD and the European Union now gather data online through Internet-based questionnaires and other methods using Internet technologies. By contrast, many developing nations do not have access to high-speed Internet—or any Internet—to facilitate effective and efficient data collection, especially in rural areas. Moreover, many developing nations have large swaths of people spread across rural, sparsely populated areas of the country, rendering robust and equitable data collection nearly impossible in countries within the Latin American and Caribbean region, Burundi, Uganda, and Nepal where rural populations comprise over 80% of the overall citizenry in each country [7].

Beyond geographic and technological limitations, many developing nations' governments do not have the human or financial resources to staff survey developers, census takers, or data architects to administer the work and disseminate its results. For instance, the United States begins its hiring process for its ten-year census two years before its administration, usually hiring over 200,000 temporary workers to complete the work [23]. Moreover, the U.S. Department of Education specifically created the National Center for Education Statistics to help liaise with schools to gather and disseminate educational data [15]. In these cases, many developing nations do not have the resources to create such offices and protocols to gather consistent, representative, reliable education data at any time interval, much less on a yearly basis as is the status quo in the United States and many other developed nations.

Finally, a wealth of education data is often tied to government funding or grant administration, requiring educational organizations to report data to their funding agency, usually a local-, state-, or federal-level entity. Although this method is not surveying in a typical sense, there are yearly reports that institutions of higher education must complete that often arrive in the form of a questionnaire. For instance, in the United States context, the process for distributing federal student aid to postsecondary students is mediated by the U.S. Department of Education through a program called Title IV, which authorizes U.S. institutions of higher education to administer financial aid programs through federal funds. As federal student aid is responsible for most of the student financing in the United States, there are over 6000 Title-IV-participating institutions of higher education in the United States. To participate, institutions must regularly report education data to the U.S. Department of Education related to the amount and type of aid that their students are receiving, as well as students' academic progress indicators [24]. Here, nationally representative educational datasets are being created in part by federal programming that requires institutional data reporting, yet many countries may not have these policy mechanisms in place through federal programs to gather such data.

#### *3.2. Technologically Mediated Data Sharing Agreements*

One of the largest international data-sharing platforms is the Statistical Data and Metadata eXchange (SDMX), sponsored by seven international organizations: the Bank for International Settlements (BIS), the European Central Bank (ECB), Eurostat (Statistical

Office of the European Union), the International Monetary Fund (IMF), the Organization for Economic Cooperation and Development (OECD), the United Nations Statistical Division (UNSD), and the World Bank. SDMX is a technology and data-sharing initiative that "aims at standardising and modernising the mechanisms and processes for the exchange of statistical data and metadata among international organisations and their member countries" [25] (para. 3). Extending the survey work performed by individual nations, the SDMX allows for larger, international organizations to integrate their data into an even larger repository, allowing for unique collaborations, such as the OECD working with the International Monetary Fund, to better understand how international monetary policies may affect low-GDP nations.

However, developing nations that cannot perform the national-level survey work to lay the foundation for international data sharing thus cannot reap the benefits of international platforms such as SDMX. In this case, educational datasets across nations may be further stratified by efforts such as the ones by SDMX, with developed nations already able to gather their own national-level data in addition to reaping the benefits of international data sharing, collaboration, and joint policy development. As a result, it is critical for developed nations to scaffold the efforts of developing nations to begin the national-level survey work to allow for developing nations to participate in international data-sharing agreements, such as SDMX.


**5.2.7 Inhibitor of apoptosis**

#### **<IP_ADDRESS> Caspase3 inhibitor**

Various chemotherapeutic agents induce apoptosis of hair follicle cells and cause CIA, although the underlying mechanisms are unclear. Caspase-3 is a key executor of apoptosis and its activation is normally used as an indicator of caspase-dependent apoptosis (Porter and Janicke, 1999). M50054, 2,2'-methylenebis, is an inhibitor of caspase-3 activation that was shown to inhibit etoposide-induced apoptosis in human monocytes. In neonatal rats, topical administration of M50054 reduces CIA induced by etoposide (Tsuda et al., 2001).

Chemotherapy-Induced Alopecia 65

p53-deficient mice show strongly down-regulated Fas in the hair follicle keratinocytes and highly up-regulated Bcl-2 in the dermal papilla as compared to wild-type mice. The role of Fas in the control of cyclophosphamide-induced apoptosis in keratinocytes was also investigated using Fas-deficient mice (Sharov et al., 2004). These mice show significantly reduced CIA and a parallel decrease in apoptotic keratinocytes and FADD and caspase-8 expression. Similarly, anti-Fas ligand neutralizing antibody inhibits cyclophosphamideinduced keratinocyte apoptosis. These studies indicate that Fas signaling is an important pathway in mediating the apoptosis induced by cyclophosphamide and suggest the crosstalk between p53 and Fas death signaling. However, the eventual hair loss observed in Fasdeficient mice points to the lower resistance of hair follicles to cyclophosphamide as compared to p53-deficient mice. Thus, it is likely that Fas signaling represents only a component of the p53-dependent apoptosis machinery in the hair follicles and that other p53 targets are also involved. Cyclophosphamide treatment also alters the expression of melanogenic proteins and causes apoptosis of hair follicle melanocytes (Sharov et al., 2003). In contrast to matrix keratinocytes, the melanocytes undergo apoptosis primarily through

The observation that antioxidants such as NAC protect against CIA in animals suggest the involvement of reactive oxygen species (ROS) in CIA. Various chemotherapeutic agents induce oxidative stress through multiple mechanisms, i.e., activation of NADPH oxidase system and mitochondrial respiration chain. Agents that induce a high level of ROS include anthracyclines (e.g., doxorubicin, epirubicin, and daunorubicin), alkylating agents (e.g., cyclophosphamide), platinum coordination complexes (e.g., cisplatin, carboplatin, and oxaliplatin), and epipodophyllotoxins (e.g., etoposide) (Conklin, 2004). Interestingly, anthracyclines, alkylating agents, platinum complexes, and epipodophyllotoxins also induce CIA more frequently and more severely than most other agents, suggesting a relationship between ROS generation and CIA. The exact mechanism of how ROS induces or promotes CIA is unclear, but likely involves apoptosis regulation since apoptosis of hair follicles is a hallmark of CIA and since ROS generation is generally required for the induction of

CIA is a major side effect that compromises patient quality of life, particularly for females and children. Overcoming CIA remains a major challenge in the management of cancer patients. Significant progresses in the pathobiology and molecular mechanisms of CIA have been made during the past decade, and several physical and pharmacological approaches to treat CIA have been attempted. However, effective treatment strategies have yet to be developed. A key to this success is a better understanding of the human CIA mechanisms which requires the development of more predictive experimental models. Animal models have been useful but have limitations and may not be predictive of human CIA. The newly developed organ culture system using human hair follicles is promising and could lead to the development of more effective treatment strategies for CIA. The recent success in combination chemotherapy also provides mechanistic insights to combating CIA through

Fas signaling but not p53 signaling.

apoptosis by chemotherapeutic agents (Simon et al., 2000).

the use of different combination strategies.

**6.3 Reactive oxygen species**

**7. Perspectives**

#### **<IP_ADDRESS> Anti-death FNK protein**

FNK protein constructed from rat Bcl-xL by site-directed mutagenesis (Y22F/Q26N/R165K) localizes to mitochondria and functions to maintain mitochondrial membrane potential (Aosh et al., 2000). Mitochondrial membrane potential regulates the release of cytochrome C, which once binds to caspase-activating proteins such as Apaf-1 initiates the intrinsic caspase cascade and apoptosis (Li et al., 1997). Recently, FNK protein has been fused to protein transduction domain (PTD) to improve its cellular entry. Subcutaneous injection of PTD-FNK protects against CIA induced by etoposide in the neonatal rat model. The fusion protein helps retain hair follicle structures, prevent hair follicle regression and maintain the anagen duration upon etoposide treatment (Nakashima-Kamimura et al., 2008). Indeed, its protective effect on CIA suggests that it could penetrate the epidermis and reach the dermal hair follicles. Localized administration of FNK fusion protein has been suggested as a potential protein therapy for CIA without affecting the chemotherapy efficacy.


**1. Introduction**

On 31 December 2019, a pneumonia of increasing incidence and unknown etiology in Wuhan, China was reported to the World Health Organization (WHO). Investigations led to the discovery of a novel coronavirus, later dubbed Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), which causes the pathology known as Coronavirus Disease 2019 (COVID-19) [1]. Despite initial containment measures recommended by the WHO in early January 2020, COVID-19 spread rapidly to other countries in the following weeks and was eventually classified as a global pandemic on 11 March

2020 [2,3]. Since then, it has posed major challenges to healthcare systems in affected countries around the world while crippling the global economy. At the time of our analysis, epidemiological data indicates that COVID-19 had since spread to 205 countries with over 3.1 million reported cases and over 227,000 deaths worldwide [4].

As effective antiviral therapies and vaccines remain unavailable, current efforts to halt the transmission of COVID-19 rely on social distancing, individual quarantine and isolation, and community containment measures [5]. Yet there has been great variation worldwide in the implementation of such measures. As demonstrated in China, the spread of the disease was slowed by effectively combining the largest quarantine ever implemented—over 200,000 people were either tracked via contact tracing or received medical observation as of 30 January 2020—with stringent community facemask use, limitations on social gatherings, isolation of affected workplace institutions, and lockdown of multiple public transportation outlets to isolate communities and towns with outbreaks [6,7]. However, this approach is resource-intensive and is less likely to be emulated by more liberal democracies [8]. Therefore, it may be useful to examine the differences in implementation of quarantine policies in different countries and their impact on disease mortality.

Numerous studies have examined the daily and cumulative number of confirmed cases by country and have analyzed variation in case-fatality rate (CFR), defined as number of deaths relative to number of confirmed cases. Estimates of CFR are placed at 2.3% in China, while estimates of infection-fatality ratio (IFR), which attempt to account for proportions of mild and asymptomatic disease, sits markedly lower at 0.1–0.94% [7,9–11]. However, because the exact proportions of mild and asymptomatic cases are variable and reliant on estimations in lieu of confirmatory testing, IFR-based metrics have yet to produce a reliable model [10,11]. Therefore, CFR remains a more concrete measure of describing and identifying predictive factors associated with disease mortality. CFR varies from country to country and, while multiple studies have found links to possible underlying factors driving changes in case mortality, a complete explanation of this variation remains unclear. Using country-specific data from global organizations, our study aims to identify factors that best explain differences in CFR among 39 highly impacted countries during the first five months of the COVID-19 pandemic. To the best of our knowledge, this is the first study to investigate multiple factors affecting CFR using country-specific data to drive our modeling.


**2. Early SNAP program**

474 Radioisotopes – Applications in Physical Sciences

1947, Gendler and Kock, 1949). Radioisotopes were also considered in early studies of

Fig. 1. Cutaway view of a radioisotope power source (RPS) (Image credit: DOE).

1954).

In 1951, the U.S. Atomic Energy Commission (AEC) signed several contracts to study a 1 kWe space power plant using reactors or radioisotopes. Several of these studies, which were completed in 1952, recommended the use of RPS (Corliss and Harvey, 1964). In 1954, the RAND Corporation issued the summary report of the Project Feedback military satellite study in which radioisotope power was considered (Lipp and Salter, 1954). Paralleling these studies, in 1954, K. C. Jordan and J. H. Birden of the AEC's Mound Laboratory conceived and built the first RTG using chromel-constantan thermocouples and a polonium-210 (210Po or Po-210) radioisotope heat source (see Figure 2). While the power produced (1.8 mWe) was low by today's standards, this first RTG showed the feasibility of RPS. A second "thermal battery" was built with more Po-210, producing 9.4 mWe. Jordan and Birden concluded that the Po-210 "thermal battery" would have about ten times the energy of ordinary dry cells of the same mass (Jordan and Birden,

nuclear-powered aircraft (Corliss and Harvey, 1964).

The AEC began the Systems for Nuclear Auxiliary Power (SNAP) program in 1955 with contracts let to the Martin Company (now Teledyne) to design SNAP-1 and to the Atomics International Division of North American Aviation, Inc. to design SNAP-2. (Under the AEC nomenclature system, the odd-numbered SNAPs had radioisotope heat sources and the even-numbered SNAPs had nuclear fission reactor heat sources.) SNAP-1 was to provide 500 We using the then readily available fission product radioisotope cerium-144 (144Ce) (Corliss and Harvey, 1964).

The Martin Company began with a 133-We RPS design using 144Ce as the radioisotope fuel and a Rankine thermal-to-electric conversion system. From this came the 500-We SNAP-1 RPS design based on 144Ce fuel and a Rankine conversion system (see Figure 3) (Corliss and Harvey, 1964). The use of a dynamic conversion system in the first RPS is a key historical fact in understanding the current focus on developing an Advanced Stirling Radioisotope

U.S. Space Radioisotope Power Systems and Applications: Past, Present and Future 477

As of 2010, as shown in Table 1, the U.S. has launched 45 RTGs, hundreds of RHUs and one space nuclear fission reactor. Of the RTGs flown, two different types of thermoelectric materials have been employed: telluride-alloy based or silicon-germanium-alloy based. The following sections will discuss these RTGS to be followed by sections discussing current

The initial and current thermoelectric material of choice is based on telluride technology alloyed with lead (Pb-Te) that, to a first approximation, can be used from room temperature to about 900 K before materials properties become an issue. Above 900 K, the U.S. has had great success with a silicon-germanium alloy (Si-Ge) that has operated exceedingly well at

For the upcoming Mars Science Laboratory (MSL) mission, the U.S. will use a telluridebased thermoelectric material because it meets the requirements of being able to operate both in space on the way to Mars and on the surface of Mars with its dusty, cold, carbon dioxide atmosphere (see Section 8). The successes of the earlier (1976 era) Viking Mars

The SNAP-3B RTG evolved out of the overall SNAP-3 program with the goal of providing 2.7 We to the U.S. Navy's Transit 4A and Transit 4 B navigational satellites. In particular, the SNAP-3B RTGs were to provide power to the crystal oscillator that was the heart of the electronic system used for Doppler-shift tracking, a precursor of today's global positioning system (Dick and Davis, 1962, JHU/APL, 1980). Both RTGs provided power to their respective spacecraft for over 10 years (Bennett, et al., 1983). Figure 5 shows models of the

Landers 1 and 2 using SNAP-19 telluride-based technology support this decision.

Fig. 4. Light-Weight Radioisotope Heater Unit (LWRU) (DOE)

efforts in radioisotope power sources.

**3. The early telluride-based RTGs**

SNAP-3B RTG and the successor SNAP-9A RTG.

temperatures of about 1300 K.

**3.1 SNAP-3B RTGs**

Generator (ASRG) (see Section 10). Depending on the design, dynamic conversion systems can provide double, triple and even quadruple the efficiency of state-of-practice thermoelectric conversion systems which means much less radioisotope fuel would be used to achieve the same electrical power (or, conversely, much more electrical power can be produced for the same quantity of radioisotope fuel used in an RTG).

Fig. 3. SNAP-1 turbomachinery package with the shaft assembly shown separately, ruler dimensions are in inches (TRW via Corliss and Harvey, 1964).

In parallel with the SNAP-1 program a series of radioisotope power sources were studied under the umbrella of the SNAP-3 program that was based largely on using thermoelectric elements in the converter. The early SNAP-3 generators were to use 210Po as the fuel but by the late 1950s it was clear that sufficient quantities of 238Pu would be available to provide the fuel for small RTGs. Plutonium-238 provided a number of features that made it more attractive than 144Ce or 210Po, including a longer half-life (87.7 years) and a more benign radiation emission (alpha particles, which can be stopped by material as thin as a sheet of paper) (Corliss and Harvey, 1964).

Safety is the principal design requirement in the use of RPS, so the heat source is designed to contain or immobilize the fuel throughout a range of postulated accidents such as explosions and atmospheric reentries. Over the years this safety design work has led to the development of the general-purpose heat source (GPHS) module, which is the basic building block of U.S. RPS (Bennett, 1995).

All of the U.S. RPS that have flown have been either RTGs or RHUs, (see Fig. 4).

Fig. 4. Light-Weight Radioisotope Heater Unit (LWRU) (DOE)

As of 2010, as shown in Table 1, the U.S. has launched 45 RTGs, hundreds of RHUs and one space nuclear fission reactor. Of the RTGs flown, two different types of thermoelectric materials have been employed: telluride-alloy based or silicon-germanium-alloy based. The following sections will discuss these RTGS to be followed by sections discussing current efforts in radioisotope power sources.


*Vicissitudes of the Oedipal Organization, and Their Impact on the Anticlerical Polemic DOI: http://dx.doi.org/10.5772/intechopen.107392*

Everywhere, enraged feminists confront allegedly male chauvinistic institutions and pro-family activists, while souverainistes oppose left-wing supported migratory policies and free speech advocates rail against contemporary cancel culture.

Within contemporary society, the orientation of social aggression seems to depend on the position in the Oedipal phantasy, which each group values the most. Specifically, social identity appears nowadays to coalesce around communityshared father's representations. For instance, Antifa activists smite statues of haughty, supercilious sadistic fathers of the nation, while conservatives reverently cherish the teachings of unlimitedly powerful but wise and fair community ancestors.

The heated confrontation between the LGBT community vs. conservative Catholic movements and institutions can offer a particularly straightforward example of a social conflict where such an Oedipal allegiance plays a major and thinly disguised role. The strife between Catholic clergy and LGBT community is an old one. While the Greek-Roman civilization showed a remarkable tolerance vis a vis the most diverse sexual practices, the Saint Apostles and the Church Fathers agreed that only those who resign to compulsory bodily gratifications, including homoerotic sexual pleasures, are able to reach genuine inner freedom. In the Middle Ages, Thomas Aquinas censored sodomy as the most serious of sexual misconducts ([7], IIa-IIae q. 154, a. 11 co.).

The confrontation between male Catholic clergy and advocates of free sexual life came to be even more heated in the following centuries, but the power balance piecemeal swung. Seventeenth-century libertines and freemasons led a particularly fierce campaign against Catholic institutions. We can date then the onset of modern anticlerical hate. During French *Terreur*, as well as in various revolutions the world over, Catholic priests were hanged, beheaded, or shot by the thousands.

In this social conflict, sexuality played a core role. Sexual misconduct was everywhere a favorite issue agitated by anticlerical polemicists. While from the pulpit Catholic priests used to rail against sexual freedom, sexual transgression of the clergy was the focus of an apparently inexhaustible public curiosity.

  According to the radicals' perspective, sexual misconduct by the clergy would be the unavoidable product of the impossible striving to maintain sexual abstinence, which is inherent in Christian ascetics [11]. A powerful media campaign is on its way the world over against the Church, which would have covertly promoted child sexual abuse and protected perpetrators. Political supporters of the rights of homosexual people are everywhere on the frontline in this confrontation.

While the judicial fallouts of such a campaign are in the public eye, most advanced western countries are piecemeal including within their legislation some acts punishing those beliefs which could possibly foster sexual-preference-based discrimination. A similar law proposal (commonly referred to as "Zan" law) is now pending at the Italian Parliament. Such laws have elicited enhanced concern and downright opposition in many, often Catholic, traditional-family movements, which obviously perceive them as targeted to suppress their activity.

So, at the dawn of the XXI century, the Catholic Church and homosexual organizations seem to be trapped more than ever in a complex network of reciprocal suspicion and hostility. Which social and emotional forces may lie under such

confrontation? Which conscious and unconscious dynamics may keep each opponent so close to and enraged at the other? Psychoanalysis can help us answer these questions.