5.1.2. Laser Mode

The generation of spatter is influenced by the mode of the laser beam used in L-PBF. The main modes of lasers currently used in L-PBF are: the Gaussian beam, inverse Gaussian (annular) beams, flat-top beam, and Bessel beam. Several studies have shown that Bessel beams are significantly better than Gaussian beams in L-PBF. 5.1.2. Laser Mode The generation of spatter is influenced by the mode of the laser beam used in L-PBF. The main modes of lasers currently used in L-PBF are: the Gaussian beam, inverse Gaussian (annular) beams, flat-top beam, and Bessel beam. Several studies have shown that Bessel beams are significantly better than Gaussian beams in L-PBF.

[82]. The heat of the melt pool cannot be conducted quickly by the surrounding powder as the layer thickness rises, which leads to the instability of the melt pool, and the number of spatters increases accordingly. However, due to the limited area of laser irradiation, the increase in the spatter will slow down when the layer thickness reaches a certain thickness. Zhang et al. [38] found that spatter generation slows down when the layer thickness exceeds twice the size of the powder particles.

*Micromachines* **2022**, *13*, x FOR PEER REVIEW 28 of 42

**Figure 23.** (**a**) Side views of melt pool captured using Gaussian (top, gray border) and Bessel (bottom, dashed red border) lasers; (**b**) angle of melt pool steam relative to horizontal level as a function of time. (Reprinted with permission from Ref. [129]. Copyright 2021 AAAS). **Figure 23.** (**a**) Side views of melt pool captured using Gaussian (top, gray border) and Bessel (bottom, dashed red border) lasers; (**b**) angle of melt pool steam relative to horizontal level as a function of time. (Reprinted with permission from Ref. [129]. Copyright 2021 AAAS).

#### 5.1.3. Printing Strategy 5.1.3. Printing Strategy

The scanning strategy can be divided into two categories: scanning path and presintering method. The checkerboard scanning path can reduce the generation of spatter, and when the scanning direction is consistent with the gas flow direction, the spatter can be effectively removed. Pre-sintering with a low-energy density can also effectively suppress the generation of spatter. The scanning strategy can be divided into two categories: scanning path and presintering method. The checkerboard scanning path can reduce the generation of spatter, and when the scanning direction is consistent with the gas flow direction, the spatter can be effectively removed. Pre-sintering with a low-energy density can also effectively suppress the generation of spatter.

by the design of the equipment, and the optimizing of the laser scanning direction can be performed. Effective spatter removal can be achieved by changing the direction of the laser scanning so that the trajectory of the spatter is consistent with the direction of the protecting gas flow. Anwar et al. [84] found that spatters re-depositioned near the outlet of the build chamber were greatly decreased when the laser scans were against the direction of the protective gas flow, but large particle spatters were still difficult to be removed [85,120].

Pre-sintering can form necks between powder particles, which is often used in electron powder bed fusion (E-PBF) to prevent powder redistribution. Similarly, pre-sintering can be introduced into L-PBF to reduce the generation of spatters. Metal powder has a significantly higher thermal absorption rate than solid bulk metal, the amount of spatter generated during L-PBF can be reduced by using a scanning strategy of a low-energydensity laser pre-sintering [103]. Khairallah et al. [69] demonstrated that combining high laser power with pre-sintering can significantly suppress spatter generation, particularly oversized (~200 mm) back-ejected spatter (spatter in the backward direction) at the start of the scanning trajectory. Achee et al. [131] used pre-sintering to prevent spatter and denudation, and they found that the control of spatter and denudation was most effective when the pre-sintered VED was 1–4 J/mm3 . Moreover, Annovazzi et al. [132] indicated that pre-sintering powder could help prevent spattering. Constantin et al. [133] demonstrated that adding a re-coating step can increase the part quality compared to the conventional L-PBF process.

#### 5.1.4. Pressure of Build Chamber

The environmental pressure within the build chamber affects spatter generation. As the environmental pressure increased, the total amount of spatter dropped gradually, but the hot spatter generated by argon gas flow entrainment increased [36], and the smoothness and continuity of the built layers was degraded [35], as illustrated in Figure 24**.** Kaserer et al. [122] investigated the effect of pressure variation on L-PBF. They discovered that the amount of spatter produced by the pure titanium and maraging steel 1.2709 used in the study did not change considerably when the process pressure was varied between 200 mbar and atmospheric pressure. *Micromachines* **2022**, *13*, x FOR PEER REVIEW 30 of 42

**Figure 24.** Schematic of powder spattering behavior as a function of time and environment pressure during L-PBF.(Reprinted with permission from Ref. [36]. Copyright 2018 Elsevier B.V.). **Figure 24.** Schematic of powder spattering behavior as a function of time and environment pressure during L-PBF.(Reprinted with permission from Ref. [36]. Copyright 2018 Elsevier B.V.).

powder-bed degradation throughout L-PBF.

The influence of inert gas on spatter is due to two factors: the primary component of the gas (Ar, He, N2, 50% Ar–50% He mixture) and the secondary component of the gas

of Argon). As a result of this high thermal conductivity, the temperature of the melt pool is lower and the back punch is smaller, resulting in less spatter generated. However, the rarity of Helium is the reason for its high price, in the range of about 3 to 6 times per cylinder compared to argon, so, taking this into account, there is more use of argon gas for production. Oxygen, being a tiny component of the inert gas, can cause spatter to increase and oxidize; therefore, lowering the oxygen level in the inert gas helps to suppress

• **Primary components of inert gases:** Pauzon et al. [125] studied the effect of protective gas on L-PBF of Ti-6Al-4V powder in three different conditions: pure argon, pure helium, and a helium and argon mix (oxygen content was controlled at 100 ppm). In comparison to the common use of argon, studies have indicated that using pure helium or a mixture of helium and argon can reduce hot spatter by at least 60% and ~30%, respectively, as shown in Figure 25. No influence of different protective gases on the number of cold spatters was detected. The study also found that adding helium to the gas can help cool spatter more quickly, which is important for limiting

• **Secondary component of the inert gas:** According to Wu et al. [124], the oxygen concentration in the protective environment increased considerably, resulting in the generation of spatter and an increase in the oxygen content of spatter during flight. By decreasing the oxygen level of the build chamber, the spatter generation can be re-

5.1.5. Protective Gas

spatter generation.

duced.

Based on research of the laser–powder bed interaction at sub-atmospheric pressures, Bidare et al. [121] demonstrated that while the ambient pressure decreased as gas entrainment rose, the expanding laser plume prevented the powder particles from reaching the melt pool. Li et al. [123] investigated the flow of gas, the gas–solid interaction, and the powder behavior in L-PBF at various ambient pressures. It was noted that as ambient pressure decreased, powder spatter particle and divergence angles increased, which is consistent with the Guo et al. [36] experiment results. They considered that as the ambient pressure decreased, the number of spatters grew monotonically. Spatter movement was suppressed by increasing the ambient pressure during L-PBF. Annovazzi et al. [132] demonstrated that vacuum conditions and a high laser velocity are detrimental to the stability of the powder layer, which induced more spatter.


4. Conclusions

Novel alkali lignin and poly (vinyl alcohol) (AL:PVA) nanofibrous membranes were tested for adsorption of pharmaceutical contaminants. Its efficiency to adsorb was first studied on a model contaminant, fluoxetine. An adsorption capacity of 78 mg/g was obtained which corresponds to the adsorption of 78% of fluoxetine present in the water. With further adsorption cycles, the membranes can adsorb up to 90% of contaminants. Compared to commercially available adsorbents (ionexchange resins, zeolites and silica), the results are similar to costly ion-exchange resins (75–80 mg/g). Using kinetic and isotherm models, it is possible to conclude that nanofibres follow a pseudo-first order kinetic model and Sips' isotherm model

which indicate that the adsorbent is of the physical type with adsorption of the contaminants on multiple sites at the same time in a multi- or monolayer pattern (depending on the concentration). Looking at thermodynamics, adsorption on AL: PVA nanofibres is a favourable, spontaneous and exothermic reaction. This information could be used for the design of a desorption method in which the fluoxetine can be retrieved safely, and the membrane reused for at least two more cycles. The adsorption of multiple pharmaceutical contaminants (fluoxetine, venlafaxine, carbamazepine and ibuprofen) showed that nanofibres have more affinity for alkaline compounds, which adsorb more given the right amount of possible intermolecular forces occurring. Hence, for remediation applications, it would become necessary to combine this adsorbent with another one for maximum retention efficiency.


**4. Discussion**

### *4.1. Main Findings*

Our extensive systematic review and meta-analysis did not provide support for an association between 25(OH)D related variants and T1D. Our review identified 10 studies for inclusion, which were all relatively high quality, presenting only minor systematic flaws in methodology. However, evidence from published studies was inconsistent, and for most polymorphisms, only a handful of studies were found. Many of the studies were small, limiting the statistical power of each meta-analysis, and preventing robust sensitivity analyses to evaluate associations by possible sources of heterogeneity, such as geographic location, and ancestry.

To the best of our knowledge, our study is the largest and most comprehensive systematic review and meta-analysis on the topic. The largest of the previous studies was a recently published MR study [45], which also provided a null finding, and from which raw data were included in this study. We conducted leave-one-out analyses, which suggested limited impact by any single study, alleviating concerns for bias caused by the inclusion of smaller or early studies. Furthermore, ethnicity is believed to have a major role in vitamin D synthesis (and possibly metabolism), however, subgroup analysis on Caucasian participants also provided no evidence for an association between the selected 25(OH)D related genetic variants and T1D.

From publications included in our review, those studies which found evidence for an association with T1D risk, tended to be comparatively small, while the association could not be confirmed in the large genetic databases. For example, Ramos-Lopez et al. [40] found an association of the *CYP2R1* common variant polymorphisms with T1D in 578 German participants, providing early support for the causal role of 25(OH)D in the pathogenesis of T1D. Hussein et al. [41] also found an association in an Egyptian sample (*n* cases = 120) between the *CYP2R1* common variant with risk of T1D. Smaller study over-estimates of effect can yield asymmetric funnel plots that can be explained by a restrictive study population [49]. However, the two smaller studies reporting an association included in this paper, had a matched case-control design, suggesting a possibility they were more carefully designed than the larger database based studies. For example, case ascertainment in the database studies typically had diagnoses confirmed by self-report or hospitalisation. Furthermore, despite including participants from diverse ethnic groups, Hussein and colleagues, had an ethnicity-matched control sample [41]. In contrast, recent larger studies in the European population including between 350 and 9358 cases [25,45,46], as well as our analyses including 3221 cases (387,397 controls) from the UK Biobank, did not find evidence for an association between any of the selected genetic variants and T1D. While we did not find evidence for publication bias, there was possible asymmetry in Begg's funnel plot for *GC* rs3755967 (Supplementary Figure S2). However, its interpretation should be taken as merely an evaluation of whether smaller studies gave different results to larger studies, as further formal testing for publication bias would have been largely underpowered due to the limited number of studies.

High heterogeneity was found in the meta-analysis *DHCR7/NADSYN1* rs12785878 polymorphism, (I2 = 64.8%), which was unanticipated given the studies included in the analyses of this variant were all of European ancestry, with adjustments for confounding factors. However, DHCR7 affects skin synthesis of vitamin D following exposure to UVB radiation from the sunlight and may be particularly sensitive to subtle variations in population structure. Variants affecting vitamin D metabolism have been shown to display population-specific patterns in frequency [50], and are believed to have contributed to adaptations during the evolutionary history which has allowed individuals to avoid severe vitamin D deficiency [51]. This has been seen in earlier vitamin D related genetic metaanalyses, which have allowed for the examination of population stratification. Notably, a large meta-analysis found the *Bsml* polymorphism in the vitamin D-receptor gene was only associated with T1D in those with Asian ancestry [52]. Differing environmental factors, such as geographical differences in diet and sun exposure, may also play a role to aggravate or compensate susceptibility conferred by variants in these genes [53].

### *4.2. Considerations of Alternative Explanation for Observed Results*

Vitamin D status is mainly determined by lifestyle factors, such as exposure to sunlight, dietary supplementation and intake, as well as personal characteristics including obesity and age. Indeed, common genetic variants typically have modest effects, and they only account for a small amount of the variation in 25(OH)D levels [54]. Therefore, even if variation in 25(OH)D concentrations is important for T1D, but only at the very extreme (such as clinical deficiency), this type of genetic instrument may not be able to pick up an association, especially if most of the population investigated has relatively normal concentrations. The influence of genetic variations may also be affected by interactions with other genes and by environmental factors.

Given the limited number of studies, we were unable to assess ethnic differences in the association between 25(OH)D variants and T1D. Given ethnicity may affect the function and expression of vitamin D related genes [50,52,53], it is possible that we may have missed associations that are only seen in a particular population group.

### *4.3. Strengths and Limitations*

Our study benefits from the systematic way in which results have been summarised, our comprehensive search strategy and the inclusion of grey literature. The design captures lifetime differences in 25(OH)D levels, rather than a single vitamin D measurement. Our study also has some limitations requiring consideration. Despite including information from the largest available databases to supplement all published data, available information remains limited. The relatively small number of included studies prevented us from undertaking analysis to examine the associations in diverse ethnic groups or to account for

other population characteristics. There was little to no information from populations that were vitamin D deficient. For example, the FinnGen study in Finland commenced in 2017, after the National Nutrition Council had launched the national food fortification of vitamin D (2002) [55]. Therefore, we are unable to exclude weak associations or associations that are only relevant in the context of very low 25(OH)D concentrations. We did not have access to individual level data for most of the studies, therefore, adjustments strategies could not be harmonised. Results could be limited by the absence of dietary information for all study participants, as studies have shown an association between vitamin D genes can vary due to diet, or even past sun exposure [56]. Furthermore, evidence participants of the UK Biobank are not representative of the UK population, having a healthy volunteer selection bias [57]. Thus, we are only able to investigate for a causal effect within the constraints of each study, which may have contributed to the null finding.

### *4.4. Guidelines for Future Research*

Investigating for smaller causal effects may be important for public health, due to a high prevalence of low 25(OH)D concentrations in many populations. Findings need to be elucidated by conducting larger scale epidemiological investigations, exploiting the potential for vitamin D related genetic variants as a risk factor for T1D, to confirm or refute the study findings. Furthermore, said studies will need to investigate the role of 25(OH)D related genetic variants in the context of clinical deficiency, where even subtle increases in concentrations may help, providing a more comprehensive understanding of the association between variants affecting serum 25(OH)D concentration and T1D.


**Entropy Based Fatigue, Fracture, Failure Prediction and Structural Health Monitoring**

Cemal Basaran Edited by

Printed Edition of the Special Issue Published in *Entropy*

www.mdpi.com/journal/entropy


**2.4 Information communication technology (ICT) platforms**

Agricultural information is vast and covers many areas of expertise, depending on the specific agro-climatic zones and socio-economic contexts. To ensure its effective use, it is crucial to have a well-organized system for sharing this information. It is equally essential to disseminate the right information to the right people at the right time. Fortunately, with information and communication technology (ICT) advancements, we can leverage these tools to provide farmers with accurate, timely, and relevant information and services. This, in turn, helps them adopt new technologies more effectively and makes their agricultural endeavors more profitable [31]. Based on an analysis conducted by Ayim et al. [32], the primary ICT technologies used in Africa to improve agriculture productivity are text and voice-based services designed for mobile phones. The rise of smartphone technology, including apps, has also led to the development of innovations in the farming industry. Radio and television are also popular tools for sharing agricultural information with rural farmers. These can be as robust and interactive as virtual workshops and webinars where call-in segments or SMS/text interactions are included to address farmer queries in real-time during the broadcasting. Computers are a gadget primarily utilized by researchers. ICT has enabled the development of

#### *Agricultural Transformation in Maize Producing Areas of Africa DOI: http://dx.doi.org/10.5772/intechopen.112861*

dedicated websites, social media, mobile-based extension services, financial inclusion and mobile payments, and online communities to share information on agricultural technologies, including available technologies, coverage, best practices, pest and disease management, market prices, success stories, capacity-building events, and implementation guides, while also incorporating interactive features like search functions, discussion forums and chatbot for farmer engagement and query resolution by experts. Such channels include the TAAT website, https://taat-africa.org/, and the TAAT mobile app available on the App Store. Although there are many benefits to using ICT tools and systems in agriculture, most agricultural and farming communities in Africa need to adopt them to the extent necessary for significant agricultural development. Specific factors that hinder the widespread adoption and diffusion of these services include inadequate technological infrastructure, language barrier, affordability, unsuitable ICT policies, lack of awareness regarding the potential contribution of ICTs to the farm business, and a low level of user skills, particularly among farmers [33].

One such digital application relevant to maize-based systems is The Product Platform for Agricultural Solutions (ProPAS), which offers open access information about innovative technologies in English or French. Each profile covers various aspects relating to the problems addressed, functional principles, geographic suitability, composition, application, customer segmentation, capital/operational costs, expected benefits, and licensing (see **Figure 4**). The platform has two goals; to provide technology holders with a means to disseminate their proven and promising solutions and to encourage users to search through options that can assist their agricultural objectives (visit https://propas.iita.org/). The database allows filtering solutions based on multiple search fields such as relevant value chain, its form and type (i.e., genetics, input supply, management, equipment, and digital tools), location where available, and target beneficiaries. Fourteen of its solutions relate to maize, and another fourteen describe leguminous companion crops. In 2022, ProPAS received 27,207 visitors, of which 9.1% were profile views for maize technologies, and overall it attracted the most attention to equipment followed by genetics, management, and input supply.

#### **Figure 4.**

*Output from the ProPAS website describing "golden maize".*

### **2.5 Commercial licensing systems**

Limited investment by the commercial seed production sector impedes the availability of improved maize varieties to small-scale farmers across Sub-Saharan Africa. In response, The African Agricultural Technology Foundation (AATF) established a series of public-private ventures for the multiplication of high-yielding, droughttolerant TEGO® (conventional) and insect-protected TELA® (transgenic) maize hybrids. Seven African countries now produce seeds of these elite varieties, accompanied by a licensing model and agri-business training that now supplies millions of farmers through this mechanism [34]. Precautions are in place to ensure that this multiplication process ensures true-to-type seed with a high germination rate.

Hybrid maize varieties have a high market value and provide opportunities for businesses to generate investment returns from seed multiplication and developing new, improved lines. Significant increases in food and nutritional security and farm incomes are realized where TEGO® (**Figure 5**) [35] and TELA® seed systems are adopted because these varieties produce higher grain yield and quality than other cultivated lines under normal and lower rainfall. Royalty-free licensing results in new, improved maize varieties from public institutions becoming more rapidly available to farmers through commercial transfer rights to the private sector. This mechanism includes an agreement between the holder of intellectual properties for maize varieties and a legally eligible enterprise that intends to multiply and sell these seeds commercially.

Between 2013 and 2020, 7032 tons of Drought TEGO® and 161 tons of TELA® hybrid seeds were sold and planted on an estimated 287,720 hectares of cropland to produce over 1 million tons of grain. This maize is valued at US \$236 million, benefiting about 4.3 million people [34]. At the end of 2020, variety licenses were signed with 38 seed companies from seven countries to commercialize these elite TEGO® and TELA® maize hybrids and test new lines. In this way, the TEGO® and TELA® mechanism is intended to streamline the licensing process for elite, climate-smart maize and to link intellectual goods to commercial opportunities.

**Figure 5.** *TEGO® maize produced under commercial license.*

Stress-resilient crop varieties are often seen as inferior to regular hybrids, but this is a misconception. A multi-location evaluation study of stress-resilient maize hybrids by the International Maize and Wheat Improvement Center (CIMMYT) in Sub-Saharan Africa [36] found that stress-resilient maize hybrids produced yields that were on par with or even superior to regular hybrids under both favorable and unfavorable conditions. These hybrids are a good choice for farmers as they help to achieve more stable yields over time and build a more resilient food system.

#### **2.6 Contract mechanization services and applications**

An increasing amount and variety of mechanized agricultural services are offered to farmers across Sub-Saharan Africa. Unfortunately, this contracted and rented use of mechanization services remains limited because contracting businesses experience difficulties in informing and convincing lower-income farmers of their value. Ironically, these contracted services provide labor-reducing operations through equipment beyond small-scale farmers' purchasing power [37]. African countries must develop favorable arrangements to make agricultural mechanization accessible to small and medium-scale farmers. This could be done by incentivizing the private sector to scale up agricultural mechanization initiatives and targeting and engaging women farmers and youth by investing in supportive infrastructure and training [38]. ICT applications can help farmers access contract mechanization services by matching farmers with mechanization service providers, providing information about mechanization services, and tracking the progress of mechanization activities. For instance, data on the extent of land cultivated or harvested can be utilized to verify the fulfillment of mechanization services and ascertain whether farmers receive the expected benefits for their investments.

Nevertheless, there is a lot of debate about the role of mechanization and digitalization in African agricultural transformation. A study by Daum et al. [39] documented these concerns by national stakeholders in several African countries. Some argue that mechanization is essential for reducing drudgery, increasing productivity, and reducing poverty, while others say that it can lead to the displacement of rural labor and environmental degradation. Furthermore, there is a continued appeal for state-led mechanization in some countries, even though this approach has been criticized for being inefficient and corrupt. This has resulted in yet another debate about how governments should best promote mechanization in Africa. Some people believe that governments should provide subsidized tractors and run public hire centers, while others believe that the state should focus on creating an enabling environment for private actors.

On the other hand, digitalization is seen as a promising tool, but there are concerns about data sovereignty and the digital divide. Moreover, gender and age can influence how people view digitalization, with younger people and women being more likely to be optimistic about its potential. Therefore, policymakers and development institutions must consider local stakeholders' viewpoints to aid in selecting and designing the most promising policies/programs and ensure their effective implementation at the grassroots level.

Hello Tractor (**Figure 6**) is a success in this area, an award-winning equipmentsharing application that connects tractor operators to African smallholder farmers. This digital platform results in the collaborative use of mechanized field operations by creating a common marketplace between machine owners and farmers who request and pay for services via messaging. The smartphone application also supports credit scoring and provides market intelligence for risk management and loan repayment.

#### **Figure 6.**

*The hello tractor application accessible to farmers via a smart phone.*

This approach allows service providers to match seasonal demand for mechanization services and linked cash flows. Digital information and communication technology enable equipment owners to track the movement and use of their assets, expand their serviceable areas, and manage payment quickly and transparently. Reliable information and communication channels via smartphones allow clients equitable access to agricultural mechanization in ways that improve land productivity, reduce labor costs, and improve their incomes [40].