2. Nonlinear oscillation behavior in ionized gas plasma

An ionized gas plasma exhibits oscillatory motion with a small amplitude when the high-temperature front of a fiber fuse propagates toward the light source.

The density ρ of the plasma is assumed to be in the form ρ ¼ ρ0 þ ρ1, where ρ0 is the initial density of the stationary (unperturbed) part in the front region of the plasma and ρ1 is the perturbed density. The dynamical behavior of ρ1 resulting from fiber fuse propagation can be represented by the Van der Pol equation

$$\frac{d^2\rho\_1}{dt^2} - \varepsilon (\mathbf{1} - \beta \rho\_1 \mathbf{1}^2 + 2\eta \rho\_1) \frac{d\rho\_1}{dt} + a\rho\_0 \,^2\rho\_1 = \mathbf{0},\tag{1}$$

where ε is a parameter that characterizes the degree of nonlinearity and β characterizes the nonlinear saturation (see Appendix B). The nonlinearity parameter γ characterizes the oscillation pattern.

The angular frequency ω0 of the oscillation of the gas plasma is determined by the ion-sound velocity Cs and the free-running distance Lf of the ion-sound wave, and is given by

$$
\rho\_0 = 2\pi f = 2\pi \frac{C\_s}{L\_f}.\tag{2}
$$

where f is the frequency of the oscillation of the gas plasma. The ion-sound velocity Cs is given by [38]

$$\mathbf{C}\_{s} = \sqrt{\frac{RT\_{e}}{\mathbf{M}\_{i}}},\tag{3}$$

value (0.86) means that the increase in density of the core material reaches 86%, which is almost equal to the experimental value (87%) estimated by Dianov et al. [20]. On the other hand, it can be seen that for ε ¼ 0:1 the motion of the Van der Pol oscillator is very nearly harmonic, exhibiting alternate compression and rarefaction

Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 5, β ¼ 6:5, γ ¼ 0.

Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 0:1, β ¼ 6:5, γ ¼ 0.

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers

DOI: http://dx.doi.org/10.5772/intechopen.81154

Next, the oscillatory motion for ε ¼ 5, 9, and 14 with β ¼ 6:5 and γ ¼ 0 was examined. The calculated results are shown in Figures 4–6, respectively. It can be seen that for ε ¼ 5, 9, and 14, the oscillations consist of sudden transitions between compressed and rarefied regions. This type of motion is called a relaxation oscillation [56]. The Φ values of the motion corresponding to ε ¼ 5, 9, and 14 were estimated to be about 12.9, 21.6, and 36.1 μs, respectively. These Φ values are much

The oscillatory motion generated in the high-temperature front of the ionized gas plasma can be transmitted to the neighboring plasma at the rate of Vf when the fiber fuse propagates toward the light source. Figure 7 shows a schematic view of the dimensional relationship between the temperature and the perturbed density of

In Figure 7, Λ is the interval between the periodic compressed (or rarefied)

of the density with a relatively small period Φ of about 6:3μs.

larger than that (about 6.3 μs) for ε ¼ 0:1.

parts.

45

Figure 3.

Figure 4.

the ionized gas plasma during fiber fuse propagation.

where R is the gas constant, Te is the temperature of the electron, and Mi is the mass of the ion. The author estimated Cs ¼ 1300 m=s by using Te ¼ 5760 K, which was the average temperature of the radiation zone [57], and Mi ¼ 28 � 10�3 kg for a Siþ ion. The free-running distance Lf was assumed to be 1.3 mm, which was almost equal to the distance (about 1.5 mm [57]) of the radiation zone. Using Eq. (2) and the Cs (= 1300 m/s) and Lf (= 1.3 mm) values, the frequency f of the oscillation was estimated to be about 1 MHz. The relatively high f or ω0 values reported in the literature were 426–620 kHz [52, 53] and 14.5–40.9 MHz [35, 42, 45]. These relatively high frequencies are owing to the excitation of high-frequency electron oscillation together with ion oscillation in the ionized gas plasma. The f value (= 1 MHz) estimated above is comparable to these experimental values.

The oscillatory motion for ε ¼ 0:1, β ¼ 6:5, and γ ¼ 0 was calculated using Eq. (1). The calculated result is shown in Figure 3, where the perturbed density ρ1 is plotted as a function of time. When t≥80μs, the maximum and minimum values of ρ1 for the ionized gas plasma reach 0.86 and � 0.86, respectively. The maximum

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers DOI: http://dx.doi.org/10.5772/intechopen.81154

Figure 3. Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 0:1, β ¼ 6:5, γ ¼ 0.

Figure 4. Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 5, β ¼ 6:5, γ ¼ 0.

value (0.86) means that the increase in density of the core material reaches 86%, which is almost equal to the experimental value (87%) estimated by Dianov et al. [20].

On the other hand, it can be seen that for ε ¼ 0:1 the motion of the Van der Pol oscillator is very nearly harmonic, exhibiting alternate compression and rarefaction of the density with a relatively small period Φ of about 6:3μs.

Next, the oscillatory motion for ε ¼ 5, 9, and 14 with β ¼ 6:5 and γ ¼ 0 was examined. The calculated results are shown in Figures 4–6, respectively. It can be seen that for ε ¼ 5, 9, and 14, the oscillations consist of sudden transitions between compressed and rarefied regions. This type of motion is called a relaxation oscillation [56]. The Φ values of the motion corresponding to ε ¼ 5, 9, and 14 were estimated to be about 12.9, 21.6, and 36.1 μs, respectively. These Φ values are much larger than that (about 6.3 μs) for ε ¼ 0:1.

The oscillatory motion generated in the high-temperature front of the ionized gas plasma can be transmitted to the neighboring plasma at the rate of Vf when the fiber fuse propagates toward the light source. Figure 7 shows a schematic view of the dimensional relationship between the temperature and the perturbed density of the ionized gas plasma during fiber fuse propagation.

In Figure 7, Λ is the interval between the periodic compressed (or rarefied) parts.

plasma during fiber fuse propagation can be studied phenomenologically using the

parameters in the nonlinear oscillation model is reported.

Fiber Optics - From Fundamentals to Industrial Applications

dt2 � ε 1 � βρ1

d2 ρ1

ter γ characterizes the oscillation pattern.

and is given by

44

velocity Cs is given by [38]

2. Nonlinear oscillation behavior in ionized gas plasma

In this paper the author describes a novel nonlinear oscillation model using the Van der Pol equation and qualitatively explains both the silica-glass densification and cavity formation observed in fiber fuse propagation. Furthermore, an investigation of the relationship between several cavity patterns and the nonlinearity

An ionized gas plasma exhibits oscillatory motion with a small amplitude when

The density ρ of the plasma is assumed to be in the form ρ ¼ ρ0 þ ρ1, where ρ0 is the initial density of the stationary (unperturbed) part in the front region of the plasma and ρ1 is the perturbed density. The dynamical behavior of ρ1 resulting from

dt þ ω0

Lf

2

ρ1 ¼ 0 , (1)

: (2)

, (3)

the high-temperature front of a fiber fuse propagates toward the light source.

2 þ 2γρ1 � � dρ1

where ε is a parameter that characterizes the degree of nonlinearity and β characterizes the nonlinear saturation (see Appendix B). The nonlinearity parame-

The angular frequency ω0 of the oscillation of the gas plasma is determined by the ion-sound velocity Cs and the free-running distance Lf of the ion-sound wave,

ω0 ¼ 2πf ¼ 2π Cs

where f is the frequency of the oscillation of the gas plasma. The ion-sound

r

where R is the gas constant, Te is the temperature of the electron, and Mi is the mass of the ion. The author estimated Cs ¼ 1300 m=s by using Te ¼ 5760 K, which was the average temperature of the radiation zone [57], and Mi ¼ 28 � 10�3 kg for a Siþ ion. The free-running distance Lf was assumed to be 1.3 mm, which was almost equal to the distance (about 1.5 mm [57]) of the radiation zone. Using Eq. (2) and the Cs (= 1300 m/s) and Lf (= 1.3 mm) values, the frequency f of the oscillation was estimated to be about 1 MHz. The relatively high f or ω0 values reported in the literature were 426–620 kHz [52, 53] and 14.5–40.9 MHz [35, 42, 45]. These relatively high frequencies are owing to the excitation of high-frequency electron oscillation together with ion oscillation in the ionized gas plasma. The f value (= 1 MHz)

The oscillatory motion for ε ¼ 0:1, β ¼ 6:5, and γ ¼ 0 was calculated using Eq. (1). The calculated result is shown in Figure 3, where the perturbed density ρ1 is plotted as a function of time. When t≥80μs, the maximum and minimum values of ρ1 for the ionized gas plasma reach 0.86 and � 0.86, respectively. The maximum

ffiffiffiffiffiffiffiffi RTe Mi

Cs ¼

estimated above is comparable to these experimental values.

fiber fuse propagation can be represented by the Van der Pol equation

Van der Pol equation [56].

The relationship between the period Φ and the interval Λ is

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers

μm observed in fiber fuse propagation [13, 23].

DOI: http://dx.doi.org/10.5772/intechopen.81154

enhanced with increasing pump power.

2.1 Power dependence of periodic cavity interval

Relationship between the period Φ and the nonlinearity parameter ε. β ¼ 6:5, γ ¼ 0.

Figure 8.

47

where Vf is the propagation velocity of the fiber fuse and Vf ¼ 1 m/s was assumed in the calculation. The Λ values of the motion corresponding to ε ¼ 5, 9, and 14 are thus estimated to be about 12.9, 21.6, and 36.1 μm, respectively, using Eq. (4) and Vf ¼ 1 m/s. If a large amount of molecular oxygen (O2) accumulates in the rarefied part, the periodic formation of bubbles (or cavities) will be observed. In such a case, Λ is equal to the periodic cavity interval. The estimated Λ values (12.9, 21.6, and 36.1 μm) are close to the experimental periodic cavity intervals of 13–22

Figure 8 shows the relationship between Φ and the nonlinearity parameter ε. As

Kashyap reported that the cavity shape was dependent on the nature of the input laser light (CW or pulses) [7, 15]. Todoroki classified the damage to the front part of a fiber fuse into three shapes (two spheroids and a long partially cylindrical cavity) depending on the pump power [23]. He also found that a rapid increase or decrease in the pump power results in an increase in the length of the cavity-free segment or the occurrence of an irregular cavity pattern, respectively [26]. These findings indicate that the cavity shape and the regularity of the cavity pattern may be determined by the degree of nonlinearity of the Van der Pol oscillator.

In what follows, the results of examining the relationship between the interval Λ

and the input laser power P0 observed in fiber fuse propagation are described.

It is well known that the fiber-fuse propagation velocity Vf increases with increasing input laser power P0 [7, 8, 22, 23, 25, 26, 58–60]. Furthermore, in

shown in Figure 8, Φ, which is proportional to the interval Λ, increases with increasing ε. That is, the increase in Φ and/or Λ occurs because of the enhanced nonlinearity. It was found that the experimental periodic cavity interval increases

with the laser pump power [13, 23]. It can therefore be presumed that the nonlinearity of the Van der Pol oscillator occurring in the ionized gas plasma is

Λ ¼ ΦVf , (4)

Figure 5. Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 9, β ¼ 6:5, γ ¼ 0.

Figure 6. Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 14, β ¼ 6:5, γ ¼ 0.

#### Figure 7.

Schematic view of the dimensional relationship between the temperature and the perturbed density of the ionized gas plasma during fiber fuse propagation.

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers DOI: http://dx.doi.org/10.5772/intechopen.81154

The relationship between the period Φ and the interval Λ is

$$
\Lambda = \Phi V\_f,\tag{4}
$$

where Vf is the propagation velocity of the fiber fuse and Vf ¼ 1 m/s was assumed in the calculation. The Λ values of the motion corresponding to ε ¼ 5, 9, and 14 are thus estimated to be about 12.9, 21.6, and 36.1 μm, respectively, using Eq. (4) and Vf ¼ 1 m/s. If a large amount of molecular oxygen (O2) accumulates in the rarefied part, the periodic formation of bubbles (or cavities) will be observed. In such a case, Λ is equal to the periodic cavity interval. The estimated Λ values (12.9, 21.6, and 36.1 μm) are close to the experimental periodic cavity intervals of 13–22 μm observed in fiber fuse propagation [13, 23].

Figure 8 shows the relationship between Φ and the nonlinearity parameter ε. As shown in Figure 8, Φ, which is proportional to the interval Λ, increases with increasing ε. That is, the increase in Φ and/or Λ occurs because of the enhanced nonlinearity. It was found that the experimental periodic cavity interval increases with the laser pump power [13, 23]. It can therefore be presumed that the nonlinearity of the Van der Pol oscillator occurring in the ionized gas plasma is enhanced with increasing pump power.

Kashyap reported that the cavity shape was dependent on the nature of the input laser light (CW or pulses) [7, 15]. Todoroki classified the damage to the front part of a fiber fuse into three shapes (two spheroids and a long partially cylindrical cavity) depending on the pump power [23]. He also found that a rapid increase or decrease in the pump power results in an increase in the length of the cavity-free segment or the occurrence of an irregular cavity pattern, respectively [26]. These findings indicate that the cavity shape and the regularity of the cavity pattern may be determined by the degree of nonlinearity of the Van der Pol oscillator.

In what follows, the results of examining the relationship between the interval Λ and the input laser power P0 observed in fiber fuse propagation are described.

### 2.1 Power dependence of periodic cavity interval

It is well known that the fiber-fuse propagation velocity Vf increases with increasing input laser power P0 [7, 8, 22, 23, 25, 26, 58–60]. Furthermore, in

Figure 8. Relationship between the period Φ and the nonlinearity parameter ε. β ¼ 6:5, γ ¼ 0.

Figure 6.

Figure 5.

Figure 7.

46

ionized gas plasma during fiber fuse propagation.

Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 14, β ¼ 6:5, γ ¼ 0.

Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 9, β ¼ 6:5, γ ¼ 0.

Fiber Optics - From Fundamentals to Industrial Applications

Schematic view of the dimensional relationship between the temperature and the perturbed density of the

addition to Vf , Todoroki reported the P0 dependence of Λ in an SMF-28e fiber at λ0 ¼ 1:48μm [13, 23].

In this study the author investigated the P0 dependence of Λ using the experimental Vf values [23, 26] and the calculated Φ values shown in Figure 8.

To explain the experimental Λ values in the P0 range from the threshold power (Pth ≃1:3W [61]) to 9 W, Λð Þ P0 can be represented by

$$
\Lambda(P\_0) = \Phi\_0 V\_f(P\_0) \left[ \mathbf{1} - \zeta \frac{\sqrt{\Phi\_n(\varepsilon) - \Phi\_n(\varepsilon = 0)}}{\Phi\_0} \right], \tag{5}
$$

where Φ0 and ζ are constants and Φn is the calculated Φ value shown in Figure 8. The second term �ζ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi Φnð Þ� ε Φnð Þ ε ¼ 0 p Vfð Þ P0 on the right of Eq. (5)

represents the contribution of the nonlinearity to the overall Λ value.

On the other hand, the relationship between the nonlinearity parameter ε and P0 can be expressed as

$$
\varepsilon = \chi (P\_0 - P\_{th})^{(m/2)},\tag{6}
$$

However, with increasing P0, the Λ values at P0>2:5 W are less than those calculated

This may be related to the modes of fiber fuse propagation reported by Todoroki [23, 26]. Todoroki classified the damage to the front part of a fiber fuse into three shapes (two spheroids and a long partially cylindrical cavity) depending on the pump power, and the appearance of the long partially cylindrical cavity was observed at P0>3:5 W [23] or P0>2:3 W [26]. As shown in Figure 9, the distinct contribution of the nonlinearity to the overall Λ value begins at P0 of 2.3–3.5 W, and the oscillatory motion of the gas plasma changes from a nearly harmonic oscillation (see Figure 3) to a relaxation oscillation (see Figure 4) with increasing P0. Therefore, the change from the spheroids of unstable and unimodal modes to the long partially cylindrical cavities of the cylindrical mode may be related to the contribu-

The nonlinearity parameter γ characterizes the oscillation pattern. The oscilla-

The Λ and l values of the motion corresponding to ε ¼ 9, β ¼ 6:5, and γ ¼ 0 are estimated to be about 10.8 and 21.6 μm, respectively, using Eqs. (4) and (8) and

Next, the oscillatory motion for γ ¼ 2 and � 2 with ε ¼ 9 and β ¼ 6:5 was examined. The calculated results are shown in Figures 10 and 11, respectively. As shown in Figure 10, the retention time τr of the rarefied regions is larger than that of the compressed regions τc. As a result, the ratio l=Λ is larger than 0.5 in the case of

Time dependence of the perturbed density during fiber fuse propagation. ε ¼ 9, β ¼ 6:5, γ ¼ 2.

l ¼ τrVf : (8)

tory motion for ε ¼ 9, β ¼ 6:5, and γ ¼ 0 was shown in Figure 5, where the perturbed density ρ1 is plotted as a function of time. It can be seen in Figure 5 that the oscillations consist of sudden transitions between compressed and rarefied regions, and the retention time τr of the rarefied regions equals that of the compressed regions τc. The relationship between the period Φ (¼ τr þ τc) and the interval Λ is given by Eq. (4), and the relationship between τr and the length l of the

using Eq. (7) and approach the Λ values estimated using Eq. (5).

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers

DOI: http://dx.doi.org/10.5772/intechopen.81154

3. Effect of nonlinearity parameters on cavity patterns

Vf ¼ 1 m/s. That is, l=Λ ¼ 0:5 in the case of γ ¼ 0.

tion of the nonlinearity.

cavity is

Figure 10.

49

where χ is a constant and m is the order of the square root of the power difference P0 � Pth. ε and χ correspond to the induced polarization and nonlinear susceptibility in nonlinear optics, respectively [62]. In the calculation, the author adopted χ ¼ 1 and m ¼ 2.

Using Eq. (5), Φ0 ¼ 31:5μs, ζ ¼ 3:6, and the Φn values shown in Figure 8, the Λ values were calculated as a function of P0. The calculated results are shown in Figure 9. The blue solid line in Figure 9 is the curve calculated using

$$
\Lambda(P\_0) = \Phi\_0 V\_f(P\_0),
\tag{7}
$$

which is the first term on the right of Eq. (5).

As shown in Figure 9, Λ increases abruptly near the threshold power (Pth) and increases with increasing P0. The Λ values at P0 ¼ 2:0–2:5 W satisfy Eq. (7).

Figure 9.

Relationship between the interval Λ and the input power P0. The blue and black solid lines were calculated using Eqs. (7) and (5), respectively. The red open circles are the data reported by Todoroki [23, 26].

Cavity Generation Modeling of Fiber Fuse in Single-Mode Optical Fibers DOI: http://dx.doi.org/10.5772/intechopen.81154

However, with increasing P0, the Λ values at P0>2:5 W are less than those calculated using Eq. (7) and approach the Λ values estimated using Eq. (5).

This may be related to the modes of fiber fuse propagation reported by Todoroki [23, 26]. Todoroki classified the damage to the front part of a fiber fuse into three shapes (two spheroids and a long partially cylindrical cavity) depending on the pump power, and the appearance of the long partially cylindrical cavity was observed at P0>3:5 W [23] or P0>2:3 W [26]. As shown in Figure 9, the distinct contribution of the nonlinearity to the overall Λ value begins at P0 of 2.3–3.5 W, and the oscillatory motion of the gas plasma changes from a nearly harmonic oscillation (see Figure 3) to a relaxation oscillation (see Figure 4) with increasing P0. Therefore, the change from the spheroids of unstable and unimodal modes to the long partially cylindrical cavities of the cylindrical mode may be related to the contribution of the nonlinearity.


*Article* **Contribution of Oxide Supports in Nickel-Based Catalytic Elimination of Greenhouse Gases and Generation of Syngas**

**Wasim Ullah Khan 1,\*, Mohammad Rizwan Khan 2, Rosa Busquets 3 and Naushad Ahmad 2**

**Abstract:** Carbon dioxide and/or dry methane reforming serves as an effective pathway to mitigate these greenhouse gases. This work evaluates different oxide supports including alumina, Y-zeolite and H-ZSM-5 zeolite for the catalysis of dry reforming methane with Nickel (Ni). The composite catalysts were prepared by impregnating the supports with Ni (5%) and followed by calcination. The zeolite supported catalysts exhibited more reducibility and basicity compared to the alumina supported catalysts, this was assessed with temperature programmed reduction using hydrogen and desorption using carbon dioxide. The catalytic activity, in terms of CH4 conversion, indicated that 5 wt% Ni supported on alumina exhibited higher CH4 conversion (80.5%) than when supported on Y-zeolite (71.8%) or H-ZSM-5 (78.5%). In contrast, the H-ZSM-5 catalyst led to higher CO2 conversion (87.3%) than Y-zeolite (68.4%) and alumina (83.9%) supported catalysts. The stability tests for 9 h time-on-stream showed that Ni supported with H-ZSM-5 had less deactivation (just 2%) due to carbon deposition. The characterization of spent catalysts using temperature programmed oxidation (O2-TPO), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) revealed that carbon deposition was a main cause of deactivation and that it occurred in the lowest degree on the Ni H-ZSM-5 catalyst.

**Keywords:** CO2; CH4; stability; H-ZSM-5; carbon deposition; greenhouse gas reduction


**2.1 Underrepresentation in STEM**

Severe underrepresentation of certain groups in science, technology, engineering, and mathematics (STEM) continues to be a serious problem in ensuring that the nation will have a well-trained and skillful workforce in tomorrow's high-tech sector [3]. Today, 30–40% of the workforce in critical areas such as aerospace engineering, next-generation computing, 2-D materials, therapeutics, and drug design is of international origin [4]. The University of Minnesota (UMN) has been successfully broadening participation in STEM for women, but so far not for Black, Indigenous and People of Color (BIPOC) students. Students enrolled in UMN are majority white female (35.5%). While the percentage of women undergraduate students in the College of Science and Engineering has risen from about 18 to 33% over the past decade, the percentage of African American students has remained around 1.6%. Demographic data on UMN enrollment show 4.04% Black or African American, 3.82% Hispanic or Latino, 3.3% two or more races, 0.309% American Indian or Alaska Native, and 0.0791% Native Hawaiian or Other Pacific Islanders. In 2020, however, BIPOC students comprised approximately 25% of the graduating classes in high schools in the Minneapolis/St. Paul area in Minnesota. The growing percentage

**Figure 1.** *STEM Cradle to Career Continuum [5].*

*Bridging the Digital Divide in Design and Mathematics through an Immersive Maker Program… DOI: http://dx.doi.org/10.5772/intechopen.111787*

of BIPOC students in the Twin Cities area, and in greater Minnesota, makes it an opportune time to develop programs that provide exposure to STEM, particularly in informal maker settings. MINNESOTA COMPASS, a STEM education advocacy group composed of educators and private-sector leaders from companies such as Boston Scientific and Ecolab, has championed what it refers to as the "STEM Cradle to Career Continuum." Their logic model (**Figure 1**) divides the continuum into early childhood, early to late elementary school, middle school, high school and postsecondary education, and early to mid-career. Disparities are recognized to be greatest in middle and high school, with wealthy communities having the means to provide many enriching after-school activities while under-resourced communities do not [6, 7].

#### **2.2 Maker spaces and STEM**

Exposing students to STEM using maker spaces is of great interest among educational institutions across the United States because of demonstrated outcomes [8–11]. The maker space movement was originally developed outside of the school environment and mostly involved adults. Recently, however, there has been interest in integrating it into education, specifically to create opportunities that engage students in science, technology, engineering, and mathematics [12]. Investment by funding agencies, increased coverage in the popular press, and investment in maker spaces by museums are all signs of the growing interest in and validation of this type of engaged, informal, hands-on STEM learning. Tinkering Studio at the Exploratorium in San Francisco, Ingenuity Lab at the Lawrence Hall of Science in Berkeley, Maker Space at the New York Hall of Science, and MAKEShop at the Children's Museum of Pittsburgh [13, 14] are all high-profile examples of maker space exhibits. The US government has made substantial investment in maker spaces through funding agencies and other initiatives. The White House declared June 18, 2014, a "National Day of Making," and in 2015 expanded these activities to a Week of Making from June 12 to June 18 in Washington, DC. The initiative was an overall call to action for companies, colleges, and communities to promote invention, creativity, and resourcefulness and to celebrate the maker movement. While there are many types of "making," Bevan and Ryoo [15] identified three specific types of programs: those focused on entrepreneurship (i.e., making products for market), those focused on workforce development, and those focused on educational programs.

Researchers have discussed three types of educational making—assembly, creative construction, and open-ended inquiry [15–17]. In assembly, learners are given a step-by-step process of how to make an object that results in an identical object. Creative construction involves providing learners with a challenge to address, and the resulting design/object is personalized. Open-ended inquiry involves a learner developing an individual idea and figuring how to accomplish it. This method is often called "tinkering," since it emphasizes creativity [15]. "When Making is organized to leverage students' ideas and interests, it can create powerful conditions for learning to occur particularly for students who may not already affiliate as STEM learners" (p. 3). Maker spaces support a combination of creating, craft making, and experimentation. Evidence shows that these are attributes of top-performing scientist and that these skills are highly valued by STEM educators, professionals, and industry [18].

#### **2.3 Underrepresented students and maker spaces**

The Maker Movement is "traditionally viewed as grounded in gendered, white, middle-class cultural practices" [19, 20], and researchers have argued for making it more inclusive [21, 22]. Researchers at the November 2015 NSF Maker Summit in Washington, DC, funded by the National Science Foundation (NSF), discussed four key issues crucial to advancing the Maker Movement: (1) the relationship between informal and formal learning; (2) teaching, assessment, and evaluation; (3) diversity, accessibility, and inclusion; and (4) new technologies and innovation [12]. The summit participants highlighted the importance of diversity, accessibility, and inclusion in the maker movement to foster industry growth and economic and global workforce advancement. Summit participants also noted the need for the "emergence of strong leaders from underrepresented communities and advocates for diversity" [12]. Marsh et al. [22], in *Makerspaces in the Early Years: A Literature Review*, discuss the importance of inclusion because of limited literature on underrepresented groups and maker spaces. Kafai et al. [23] discuss "ethnocomputing" in their study, which links traditional indigenous sewing methods and the evolution of e-textiles in their culturally sensitive work to broaden participation in STEM among American Indian youth. Their making process highlights how combining traditional artifacts and recent technological developments can help participants acknowledge and learn about their cultural roots. Eglash [24] describes the synergetic connection in this making process as "design agency," a notion that not only does the maker influence the design but the design influences the maker.

Barton and Tan [21] note that makerspaces that explore communities and cultural traditions are an exception, and discuss community-centered making programs as a way to foster equity, learning, and making. Schwartz and Gutiérrez [25] contend that "[i]nventing, making, tinkering, designing, are indigenous practices, that is, practices that originate and occur naturally in particular ecologies" (p. 577). They argue for a "more culturally-responsive approach," where the making experience benefits both cultures and does not privilege the dominant perspective. Vossoughi et al. [20] also advocate for an equitably framed maker process rather than a situation where "workingclass communities of color are once again positioned as targets of intervention rather than sources of deep knowledge and skill, and dominant communities are reinscribed as being ahead, with something to teach or offer rather than something to learn" (p. 212).