3.2.3 Concrete mixture "GBFS + soluble silicate"

The results of determination of compressive and bending strengths of the concrete specimens made using the alkali-activated slag cement with high-modulus soluble silicate, sodium metasilicate, and sodium carbonate as alkaline activators as well as their autogenous deformations are given in Table 6. The characteristics are varied depending on composition and curing conditions.

The development of shrinkage/expansion deformations of the concrete containing "GBFS + soluble silicate" as cement and crushed basalt rock as aggregate suggested to conclude that at almost complete similarity of regularities, they differ from that made using the alkali-activated Portland cement only in absolute values of characteristics—those are in some cases a little bit higher. A value of maximal expansion of the concrete containing "GBFS + soluble silicate" as cement and crushed basalt rock as aggregate within the ranges of experiment was 0.45– 0.91 mm/m (Table 6) and those in the case of the alkali-activated Portland cement —0.46–0.81 mm/m (Table 5).

A character of strength gain of all compositions for all temperature regimes is stable and without any drops (Table 6).

## 4. Conclusions

and bending, of the specimens compared to those concretes of 28-day age at t = 65°С. The addition of the metakaolin additive allowed to reduce the expansion

6.1

8.0

6.2

8.8

10.7

12.0

12.1

10.8

5.9

6.9

6.0

7.2

1.7

2.5

2.0

2.1

"GBFS + high-modulus soluble silicate + glassy waste product of basalt fibers production"

bending, MPa, age, days

78.0 6.0

116.0 7.4

> 95.0 6.3

115.0 8.2

94.9 10.9

100.3 9.0

> 88.7 11.9

111.0 11.3

85.0 5.8

97.0 7.3

82.0 6.1

98.9 7.2

40.2 2.2

43.3 2.4

40.3 2.3

44.8 2.5

Strength characteristics and autogenous deformations of the concretes using cement system "GGBS + soluble

Shrinkage (expansion) deformations, mm/m, age, days2

1.21 1.01 0.78

+0.58 +0.88 +0.91

1.19 0.85 0.73

+0.44 +0.46 +0.47

0.83 0.86 0.82

+0.63 +0.86 +0.87

0.66 0.63 0.65

+0.41 +0.44 +0.45

— 1.17 1.20 —

— +0.12 +0.15 —

— 0.71 0.73 —

— 0.13 +0.09 —

— 1.33 1.40 —

— 0.75 0.67 —

— 0.87 0.89 —

— 0.37 0.34 —

28 90 180 28 90 180

108.0 7.2

120.1 7.0

103.7 6.6

119.8 9.0

95.0 11.1

97.2 8.9

99.8 12.0

115.2 11.2

values at an age of 180 days to the safer level—0.74 mm/m.

L/S1 Additive Temperature, °С Strength compressive/

"GBFS + high-modulus soluble silicate + crushed basalt stone"

65 103.3

65 100.3

65 102.0

65 108.0

65 94.8

65 95.2

65 42.4

65 42.1

"GBFS + high-modulus soluble silicate + expanded perlite"

"GBFS + high-modulus soluble silicate + crushed perlite rock"

0.36 — 20 61.7

Compressive Strength of Concrete

0.36 Metakaolin 20 81.3

0.45 — 20 92.0

0.45 Metakaolin 20 78.0

0.50 — 20 81.0

0.51 Metakaolin 20 79.8

0.35 — 20 37.0

0.36 Metakaolin 20 35.4

A minus sign (), shrinkage; plus sign (+), expansion.

glass" vs. curing conditions and concrete mixture design.

1

2

22

Table 6.

L/S, liquid-to-cement ratio.

The processes of structure formation in the ITZ "alkali-activated cementartificial aggregate" are studied. It is set that the interface between them practically disappears, which indicates about penetration of the elements and blurring the border between the cement stone and the aggregate.

It is established that the positive result of the processes of such interaction of the substances of cement elements and aggregate is the formation of alkaline and alkaline-alkali-earth alumina silicate hydrates—analogs of natural zeolites, transforming a destructive process of concrete corrosion into the constructive.

Comparative studies of the processes of the structure formation of the ITZ in the alkali-activated cement concretes with different alkali-susceptible aggregates confirmed that Al2O3 plays a determining role in these constructive processes.

It is shown that the addition of the metakaolin additive as an Al2O3-containing additive provides inhibition of alkaline corrosion processes, which is confirmed by long-term testing of strength characteristics and deformation (shrinkage/expansion) of concretes using different alkali-activated cements and alkali-susceptible natural aggregates.

Compressive Strength of Concrete


**5. Absorption coefficient of MQW structure**

Absorption coefficient is calculated as a function of operating wavelength for different well width, as shown in **Figure 8**. For lower well dimension, it is found that the absorption coefficient value is less compared to the higher well dimension. Again, when the energy difference between the bands increases, interband transition energy increases. This reduces the peak of absorbance amplitude, provided half-width at half-maximum is kept constant throughout the simulation.

**Figure 8.** Absorption coefficient for different well dimension with wavelength variation for parabolic, nonparabolic dispersion.

With increase of well dimension, redshift is observed for all the profiles corresponding to the transition energies; also peak value is shifted rightwards and the wavelength value increases. When the parabolic and nonparabolic dispersion relation is considered for same well dimension the peak value is greater for lower well dimension nonparabolic case. But with change in eigenenergy, for higher well dimension the parabolic relation gives a higher absorption peak value. Thus the nonparabolic dispersion relation takes the priority for simulation.

With parabolic and nonparabolic relations into consideration the material composition is varied in accordance with the wavelength. The absorption coefficient profiles are depicted in **Figure 9**. For parabolic dispersion, the transition energies are low, so the absorption peak values are less compared to that of nonparabolic case. Also for higher material composition the shift in absorption value is considerable. The peak absorption values are greater for higher material composition and also for nonparabolic dispersion.

**Figure 9.** Absorption coefficient for different material composition with wavelength variation for nonparabolic and parabolic dispersion.

## **6. Band structure of quantum cascade laser**

**5. Absorption coefficient of MQW structure**

the simulation.

38 Quantum Cascade Lasers

simulation.

dispersion.

Absorption coefficient is calculated as a function of operating wavelength for different well width, as shown in **Figure 8**. For lower well dimension, it is found that the absorption coefficient value is less compared to the higher well dimension. Again, when the energy difference between the bands increases, interband transition energy increases. This reduces the peak of absorbance amplitude, provided half-width at half-maximum is kept constant throughout

With increase of well dimension, redshift is observed for all the profiles corresponding to the transition energies; also peak value is shifted rightwards and the wavelength value increases. When the parabolic and nonparabolic dispersion relation is considered for same well dimension the peak value is greater for lower well dimension nonparabolic case. But with change in eigenenergy, for higher well dimension the parabolic relation gives a higher absorption peak value. Thus the nonparabolic dispersion relation takes the priority for

**Figure 8.** Absorption coefficient for different well dimension with wavelength variation for parabolic, nonparabolic

With parabolic and nonparabolic relations into consideration the material composition is varied in accordance with the wavelength. The absorption coefficient profiles are depicted in **Figure 9**. For parabolic dispersion, the transition energies are low, so the absorption peak values are less compared to that of nonparabolic case. Also for higher material composition the shift in absorption value is considerable. The peak absorption values are greater for higher

material composition and also for nonparabolic dispersion.

Electronic band structure of quantum cascade laser is analytically computed in presence of electric field applied along the direction of quantum confinement. At first, electronic and optoelectronic properties of the MQW structure is calculated. Next, miniband formation is observed for quantum cascade laser for a few precise magnitudes of electric fields. Separation of the miniband w.r.t. lowest energy band is calculated [68]. Al*x* Ga1−*x* As/GaAs composition is taken into account with the incorporation of Ben-Daniel Duke boundary conditions at heterointerfaces. Eigenstates are calculated in presence and absence of Kane-type first-order conduction band nonparabolicity. Its variation as a function of applied field is determined, and is compared with the findings of zero bias conditions.

**Figures 10**–**12** represent the electronic band structure of quantum cascade laser. For biasing, electric field is applied along the direction of quantum confinement, and eigenstates are computed. Results are also obtained when field is absent. While designing the structure, the most important aspect is that a distinguishable separation between injector and active region should be kept along with the miniband formation [68]. **Figure 10** shows the band diagram when external field is totally absent, and **Figure 11** demonstrated it for very high electric field (56.8 × 105 V/m). Here it may be noted that all the high magnitudes of electric field will not provide desirable QCL operation, as discrete miniband formation is necessary for that purpose. From the simulated observations, it may be indicated that the eigenenergy states are totally discrete in absence of external excitation, which are nothing but the eigenstates of a simple multiple quantum-well (MQW) structure.

**Figure 10.** Electronic band structure of QCL without external bias.

**Figure 11.** Electronic band structure of QCL with 56.8 × 105 V/m.

From **Figure 11**, it is observed that after application of very high electric field, miniband is formed over the ground state energy band. In this context, it may be noted down that after the injector region, active region starts, and the wavefunction starts to produce minibands. The energy gap between miniband and ground state energy band is distinguishable, which ensures the QCL operation. In this context, it may be pointed out that the magnitude of external field is chosen based on the structural dimensions and the material composition taken for the simulation. The structure is titled compared to **Figure 10**, along the direction of electric bias. Thus, the periodic growth of wavefunction in the miniband appears outside the confinement region, that is, in the quasi-continuous region. This band structure modulation is absent if the field is moderate (35.8 × 105 V/m).

Further reduction of electric field makes position of the miniband almost inside the confinement region, that is, miniband position is below the quasi-continuous region. This is shown in **Figure 12**. Eigenenergy variation with the applied bias for the laser is shown in **Figure 13**. Simulation result suggests that with increase of applied field, eigenenergy increases monotonically, and the rate reduces once filed crosses the value 35 × 105 V/m. Thus, stimulated emission between the miniband and the ground state energy band is effectively controlled by external bias.

**Figure 12.** Electronic band structure of QCL with 35.8 × 105 V/m.

**Figure 10.** Electronic band structure of QCL without external bias.

40 Quantum Cascade Lasers

**Figure 11.** Electronic band structure of QCL with 56.8 × 105 V/m.

**Figure 13.** Variation of eigenenergy with applied field.

## **7. Conclusion**

In this article, a detailed investigation on electrical and optoelectronic properties of multiple quantum well structure is carried out. Based on that structure, wavefunction in a quantum cascade laser at various biased conditions is analytically calculated and also for unbiased condition. It is proven and shown that miniband formation is only possible at some precise electric field. The method showed can also be applicable for the other structures. Key factor in this calculation is that position-dependent effective mass is considered for the simulation.

## **Author details**

## Arpan Deyasi

Address all correspondence to<EMAIL_ADDRESS>
Department of Electronics and Communication Engineering, RCC Institute of Information Technology, Kolkata, India


**Meet the editor**

Dr. Hussein Abdelhay Elsayed Kaoud is a full professor at Cairo University. He studied Veterinary Medical Sciences and received a master's degree in Medical Veterinary Sciences "Veterinary Medicine and Surgery" and a PhD in Epidemiology and Disease Prevention. He was the chairman of the Department of Animal Health and Preventive Medicine. He gave lectures in molecu-

lar epidemiology, biological control of pathogens, and biotechnology at different universities and has been a member for many of national and international publishing houses and a reviewer and editor for many indexed journals. His research interest is focused on advanced technology of basic life sciences after he had his DSc (2014). He has published more than 100 articles in international journals, 5 book chapters, more than 30 international books, and more than 40 national and regional books.


**7. Ablation**

#### **7.1. Radio-frequency ablation**

Radio-frequency ablation uses radio-frequency energy in the form of electrical current delivered from typically 4 to 8 mm catheter tip and collects it on an indifferent electrode patch which is commonly placed on the mid-spine in the lumbar region. The density of the current at the catheter tip causes an ablation lesion 4–6 mm deep in the cardiac tissue which interrupts electrical conduction. An 8 mm catheter tip is increasingly being used as the first choice in CTI ablation due to the length and depth of ablation line needed. Irrigated catheters with a shorter tip length of 3.5–4 mm are employed in redo cases where deeper ablation lesions are needed.

In the management of especially typical atrial flutter, ablation has evolved as the first-line treatment, even after a single episode of documented symptomatic atrial flutter above antiarrhythmic pharmacotherapy [27]. In this multicentric prospective randomised study, amiodarone and radio-frequency ablation were compared in 104 patients (aged 78 +/-5 years; 20 women) with atrial flutter. The recurrence of atrial flutter was 3.8 % versus 29.5 %, P<0.0001. Ablation therapy for atrial flutter has a success rate depending on the studies of ~90–95 % [28]. The other forms of atrial flutter generally also respond best to ablation if the circuit can be mapped and a line of conduction is performed.

The conventional method of CTI ablation was to make a linear ablation line along CTI as guided by electrograms; however recently, the 'maximum voltage-guided' technique using radiofrequency application has been studied as an alternative method and has demonstrated to be equivocal in achieving bidirectional cavo-tricuspid isthmus block. Ablation for atrial flutter using the "Maximum Voltage Guided" technique results in significantly less ablation appli‐ cations than the traditional approach, potentially by concentrating ablation lesions on the muscle bundles responsible for Trans-isthmus conduction [29, 30].

### **7.2. Complications**

During ablation, signs that can indicate that the catheter is ablating in a possibly unsafe position can include ventricular ectopy or a sharp increase in measured catheter tip impedance. Ventricular ectopy could indicate that the ablation catheter is in close proximity to the tricuspid annulus or right ventricle and potentially result in valve damage. A sharp impedance rise could indicate that the catheter has been pulled back into the IVC or wedged into a pouch on the isthmus which can create a sharp temperate increase and a possibility of a steam pop.

In patients who have had persistent atrial flutter, ablation can result in post-reversion asystole. This is commonly due to underlying sinus node disease. So one should always be ready to pace in either the atria (assuming normal AV node conduction) or ventricle (assuming a ventricular catheter is in place). Rarely, cavo-tricuspid isthmus ablation can lead to atrioven‐ tricular block or myocardial infarction if the right coronary artery or the artery to the atrio‐ ventricular node is occluded by an ablation lesion.

Other complications which can potentially occur during atrial flutter ablation include venous access/puncture (one in 100) such as hematoma, bruising and deep vein thrombosis, with or without pulmonary embolism. A small risk of stroke (1 in 500), pericardial effusion or death (1 in 1,000) remains with radio-frequency ablation method.

#### **7.3. Emerging trends and novel technologies**

Recently, the focus of atrial flutter ablation has been on emerging technology. There has been some promising data about the use of contact force catheter and its effectiveness at predicting the lesion size using the lesion size index (LSI). It is based on an algorithm which integrates contact force, radio-frequency power and ablation duration to make a key parameter, forcetime integral [31]. Contact force catheters are used for pulmonary vein isolation. Contact force parameters however have not yet been employed for atrial flutter ablation. We are currently involved in a research study of a contact force catheter, and the initial results have shown that the guidance of CTI ablation using novel CF parameters can be performed successfully. It is independent of traditional parameters and demonstrates excellent short- to medium-term results.


**About the Editor**

#### **Quanxin Zhu**

Professor Quanxin Zhu received his Ph.D. degree from Sun Yatsen (Zhongshan) University, Guangzhou, China, in 2005. He is currently a Professor at Hunan Normal University, a distinguished professor of Hunan Province, Leading talent of scientific and technological innovation in Hunan Province, and deputy director of the Key Laboratory of computing and stochastic mathematics of the Ministry of education. He won the Alexander von Humboldt Foundation of Germany award and the Highly Cited Researcher Award from Clarivate Analytics in 2018 and 2022. He won the first prize of the Hunan Natural Science Award, and was ranked in the top two percent of the world's top scientists in 2020 to 2022. In addition, Professor Zhu is a senior member of the IEEE and the Lead Guest Editor of several international journals. Professor Zhu obtained the 2011 Annual Chinese "The One Hundred Most Influential International Academic Papers" Award and wasone of the most cited Chinese researchers from 2014–2021 (Elsevier). He is an associate editor of various international journals, including *IEEE Transactions on Automation Science and Engineering*, *Application Analysis*, etc., and a reviewer for more than 50 other journals. He is the author or co-author of more than 300 journal articles. His research interests include stochastic control, stochastic systems, stochastic stability, stochastic delayed systems, Markovian jump systems, and stochastic complex networks.