**3.2 Adipose-derived mesenchymal stem cells (ADSC)**

The abundant availability of adipose tissue, its easy accessibility under local anesthesia, a less painful procedure for the patients, and no adverse effects on animal models treated make this source desirable for the extraction, process, and administration to patients [38, 39]. A study conducted by *Ohta Y. et al.* [40] revealed that the secretion of specific growth factors, cytokines, proteases, immunomodulatory factors, and cellular matrix molecules promotes ADSCs' ability to regenerate neural tissue. However, the lack of full functional recovery results and the gap of knowledge on the description of the pro-regenerative effects are some of the limitations described on the literature on the use of MSCs that needs to be addressed in order to improve outcomes on complete functional recovery in *in vivo* models of SCI [41–43].


*Article* **Barriers to Adopting Lean Construction in Small and Medium-Sized Enterprises—The Case of Peru**

**Cristian Huaman-Orosco 1, Andrews A. Erazo-Rondinel 2 and Rodrigo F. Herrera 3,\***

**Abstract:** The competitiveness in the construction industry is leading companies to implement the Lean philosophy to improve project management and prepare to begin the adoption of Construction 4.0. However, this implementation generates several barriers, depending on the type of company and the country where it is implemented. For this reason, the following research aims to identify the barriers generated in implementing the Lean philosophy in Peru and SMEs. The following study began with a literature review, followed by a questionnaire, which six Lean experts evaluated. Then, 127 Peruvian professionals answered the survey, and the data were analyzed with RII and Exploratory Factor Analysis. As a result, the barriers to Lean Construction were grouped into four groups to analyze their impact on the industry: collaboration, education and implementation, organizational vision and system; Lean theory and philosophy; and Lean tools, coordination, and information flow. Barriers were also analyzed by project type, stage, and organization size to conclude that implementation barriers are directly related to company size. Finally, the obtained barriers are discussed, and Construction 4.0 is proposed to reduce their impact on construction projects. These results can be helpful for implementers to plan strategies, improve knowledge about Lean Construction implementation, and adopt new techniques that could help improve the construction industry's productivity.

**Keywords:** Lean Construction; lean implementation; barriers; construction 4.0; Peru


As future research directions, the authors propose extrapolating the study to the European Union level but weighted by a series of variables that reflect the level of development of agricultural cooperatives in each state and its influence on investment options and directions.

**Author Contributions:** Conceptualization, M.L.Z., A.M.F. and V.M.A.; Data curation, A.M.F., F.B., M.S.D. and S.S.; Formal Analysis, M.L.Z., C.F. and V.M.A.; Investigation, A.M.F., F.B., M.S.D. and S.S.; Methodology, M.L.Z., A.M.F., C.F. and V.M.A.; Project Administration, M.S.D. and S.S.; Resources, A.M.F., S.S. and F.B.; Visualization, F.B., M.S.D. and S.S.; Supervision, M.S.D., C.F. and V.M.A.; Writing—original draft, M.L.Z., A.M.F., F.B., C.F. and V.M.A.; writing—review and editing, A.M.F., F.B. and M.S.D. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

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

#### **References**

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www.mdpi.com ISBN 978-3-0365-7612-1


*Article* **Planning Method and Principles of the Cloud Energy Storage Applied in the Power Grid Based on Charging and Discharging Load Model for Distributed Energy Storage Devices**

**Junfang Li 1,\*, Yue Xing 2 and Donghui Zhang 2**

**Abstract:** The cloud energy storage system (CES) is a shared distributed energy storage resource. The random disordered charging and discharging of large-scale distributed energy storage equipment has a great impact on the power grid. This paper solves two problems. On one hand, to present detailed plans for designing an orderly controlled CES system in a realistic power system. On the other hand, Monte Carlo simulation (MCS) is used for analyzing the load curves of five types of distributed energy storage systems to manage and operate the CES system. A method of its planning and the principles of CES for applied in a power grid, are presented by analyzing the impact based on five load curves including the electric vehicle (EV), the ice storage system, the demand response, the heat storage system, and the decentralized electrochemical energy storage system. The MCS simulates the random charging and discharging of the system over a five-year planned scaling of distributed energy storage from 2021 through 2025. The influence of distributed energy storage systems on power grid capacity, load characteristics, and safety margins is researched to summarize the applicable fields of CES in supporting large power grids. Finally, important conclusions are summarized and other research possibilities in this field are presented. This paper represents a significant reference for planners.

**Keywords:** cloud energy storage system; demand response; electric vehicles; ice storage system; load modelling; Monte Carlo simulation; power system planning; shared distributed energy storage system


2.3.3. Frozen Grated Peels (GP)

The peel separated from the fruit were grated and stored at −20 ◦C for three months. In order to investigate the effect of storage period on the fate of the residue, the amount of residue in the frozen grated peels were determined monthly.


2. Type 1 reaction

#### 2.1. Introduction

Type 1 reaction is a delayed hypersensitivity reaction. It mostly occurs in borderline patients as well as in patients with lepromatous leprosy (LL) and those with tuberculoid leprosy (TL) receiving therapy. Reaction can be the first sign of the disease and it often persists for a few weeks or months [5]. Classically, two subtypes of type 1 reactions have been described; first subtype is called reversal reactions, false exacerbation reaction or upgrading reactions and this type of reaction is reversible. Second subtype is called downgrading or downgrading reaction and it is associated with disease worsening. Upgrading (reversal) reactions occur in patients receiving therapy, and downgrading reactions occurs in patients who do not receive therapy. Due to decrease in bacterial load, borderline patients receiving therapy progress to tuberculoid phase of the disease spectrum. Bacterial load increases in patients who do not receive therapy and clinical appearance shifts to the lepromatous phase of the disease spectrum due to impaired cellular immunity [6].

commonly involved nerves. The patients may present with the symptoms of neural dysfunction such as loss of sensation, facial palsy, claw hand, and drop-foot. Hyperesthesia may occur in palmar and plantar areas, associated with widespread nerve damage [1]. The ability to close eyelids is lost due to damage in the facial nerves (lagophthalmos) [10]. Neural damage is important, as it is considered the main cause of deformities and sequelae in the course of reversal reactions. Neuritis episodes may be severe; however, it sometimes has an insidious and even painless course, which is called silent neuritis. Silent neuritis is defined as sensory or motor dysfunction in the absence of skin lesions observed in type 1 and type 2 reactions [11]. It may cause inflammatory eye diseases, including iritis and scleritis, and it may even result in blindness. Systemic symptoms such as weakness, fever, bone pain, lymphadenomegaly, joint pain, and generalized edema are rarely observed and these symptoms indicate the severity of clinical condition. Furthermore, systemic symptoms are minimal in patients close to the TL pole of the spectrum and more commonly observed in patients close to the LL pole. Fever is

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The risk of type 1 reaction may increase with vaccination, MDT, pregnancy, puerperality, infections, stress, trauma, and oral contraceptive use. The extensiveness of skin lesions has been described as an important risk factor both in patients with low and high bacilli load [1]. It has been shown that the risk of developing neural damage, along with the risk of developing reversal reaction, is 10-fold higher in patients in whom three or more body segments are affected [11]. Facial involvement is a risk factor for the development of reversal reaction, as it is for lagophthalmos [12]. Although factors which can induce type I reactions are not clearly known, recent studies have pointed to genetic factors [5]. Identification of the risk factors,

The type 1 reaction is characterized by edema in the upper dermis and disorganized granulomas. The foreign body giant cells, Langhans giant cells accompanied by epidermal erosion and spongiosis, and fibroplasia appear in the dermis. The necrosis, ulcer and inflammatory infiltration by neutrophils may be observed in severe reaction [13]. The cytology of preexisting granulomas is differentiated by the presence of large epitheloid cells and decreased number of bacilli. Inflammatory cells often infiltrate epidermis and increased neural destruction is observed. The edema inside and around the granulomas results in the damage of surrounding

The main goal of treatment in type 1 reaction is to suppress the cellular immunity. Prevention of nerve damage required early diagnosis and early institution of anti-inflammatory medications. MDT must be continued during the reactions. Corticosteroids are the most effective drugs used to treat reversal reaction. Their main effects are to inhibit activation of cellular immune response and suppress inflammatory response against M. leprae antigens in the skin

therefore, allows more meticulous follow-up of patients and early treatment [1].

usually absent and patients' general condition is good [6, 10].

2.4. Risk factors

2.5. Histopathology

tissues and nerves [1].

2.6. Treatment

#### 2.2. Pathogenesis

These reactions are associated with cellular immunity and particularly with the reaction of T helper 1 (Th1) cells to mycobacterial antigens. It has been demonstrated that cytokines derived from Th1 cells such as interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), interleukin-2 (IL-2), and interferon gamma-Ƴ (IFN-Ƴ) play a more prominent role. High levels of TNF-α, soluble IL-2 receptors, and adhesion molecules also reflect severity of local inflammation. Borderline leprosy patients with type 1 reaction show increased expression of TNF-α mRNA in peripheral nerves and skin. Type 1 reactions are mediated by Th1 lymphocytes and secreted proinflammatory cytokines IFN-Ƴ and IL-12, and free oxygen radicals [4, 5]. It was demonstrated that macrophages could initiate neural inflammatory process even in the absence of bacilli in the neural tissue [7].

#### 2.3. Clinical features

Reversal reaction episodes often occur within the first 6 months of multidrug therapy (MDT) [8]. After initiation of therapy, skin lesions with manifestations of regression or lesions appearing as hypochromic macules become erythematous and edematous, and these lesions, then, become scaled and rarely become ulcerated [9]. The existing lesions show signs of inflammation, but no new lesions occur. Previously unnoticed or invisible patches may become prominent. This may give the impression of the development of new lesions. The lesions are often painless, but tenderness may sometimes be found. The lesions are often accompanied by edema and neuritis in the extremities [6]. Edema in the hands and feet may be sometimes the main symptom of reversal reaction.  Isolated neuritis is commonly observed within the first 12 months of therapy. Nerve thickening and pain may occur and preexisting peripheral neuropathy may become prominent (sensory, motor, or autonomic). Ulnar, median, posterior tibial, fibular, radial, and facial nerves are the most commonly involved nerves. The patients may present with the symptoms of neural dysfunction such as loss of sensation, facial palsy, claw hand, and drop-foot. Hyperesthesia may occur in palmar and plantar areas, associated with widespread nerve damage [1]. The ability to close eyelids is lost due to damage in the facial nerves (lagophthalmos) [10]. Neural damage is important, as it is considered the main cause of deformities and sequelae in the course of reversal reactions. Neuritis episodes may be severe; however, it sometimes has an insidious and even painless course, which is called silent neuritis. Silent neuritis is defined as sensory or motor dysfunction in the absence of skin lesions observed in type 1 and type 2 reactions [11]. It may cause inflammatory eye diseases, including iritis and scleritis, and it may even result in blindness. Systemic symptoms such as weakness, fever, bone pain, lymphadenomegaly, joint pain, and generalized edema are rarely observed and these symptoms indicate the severity of clinical condition. Furthermore, systemic symptoms are minimal in patients close to the TL pole of the spectrum and more commonly observed in patients close to the LL pole. Fever is usually absent and patients' general condition is good [6, 10].

#### 2.4. Risk factors

2. Type 1 reaction

82 Hansen's Disease - The Forgotten and Neglected Disease

impaired cellular immunity [6].

bacilli in the neural tissue [7].

2.3. Clinical features

2.2. Pathogenesis

Type 1 reaction is a delayed hypersensitivity reaction. It mostly occurs in borderline patients as well as in patients with lepromatous leprosy (LL) and those with tuberculoid leprosy (TL) receiving therapy. Reaction can be the first sign of the disease and it often persists for a few weeks or months [5]. Classically, two subtypes of type 1 reactions have been described; first subtype is called reversal reactions, false exacerbation reaction or upgrading reactions and this type of reaction is reversible. Second subtype is called downgrading or downgrading reaction and it is associated with disease worsening. Upgrading (reversal) reactions occur in patients receiving therapy, and downgrading reactions occurs in patients who do not receive therapy. Due to decrease in bacterial load, borderline patients receiving therapy progress to tuberculoid phase of the disease spectrum. Bacterial load increases in patients who do not receive therapy and clinical appearance shifts to the lepromatous phase of the disease spectrum due to

These reactions are associated with cellular immunity and particularly with the reaction of T helper 1 (Th1) cells to mycobacterial antigens. It has been demonstrated that cytokines derived from Th1 cells such as interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α), interleukin-2 (IL-2), and interferon gamma-Ƴ (IFN-Ƴ) play a more prominent role. High levels of TNF-α, soluble IL-2 receptors, and adhesion molecules also reflect severity of local inflammation. Borderline leprosy patients with type 1 reaction show increased expression of TNF-α mRNA in peripheral nerves and skin. Type 1 reactions are mediated by Th1 lymphocytes and secreted proinflammatory cytokines IFN-Ƴ and IL-12, and free oxygen radicals [4, 5]. It was demonstrated that macrophages could initiate neural inflammatory process even in the absence of

Reversal reaction episodes often occur within the first 6 months of multidrug therapy (MDT) [8]. After initiation of therapy, skin lesions with manifestations of regression or lesions appearing as hypochromic macules become erythematous and edematous, and these lesions, then, become scaled and rarely become ulcerated [9]. The existing lesions show signs of inflammation, but no new lesions occur. Previously unnoticed or invisible patches may become prominent. This may give the impression of the development of new lesions. The lesions are often painless, but tenderness may sometimes be found. The lesions are often accompanied by edema and neuritis in the extremities [6]. Edema in the hands and feet may be sometimes the main symptom of reversal reaction.  Isolated neuritis is commonly observed within the first 12 months of therapy. Nerve thickening and pain may occur and preexisting peripheral neuropathy may become prominent (sensory, motor, or autonomic). Ulnar, median, posterior tibial, fibular, radial, and facial nerves are the most

2.1. Introduction

The risk of type 1 reaction may increase with vaccination, MDT, pregnancy, puerperality, infections, stress, trauma, and oral contraceptive use. The extensiveness of skin lesions has been described as an important risk factor both in patients with low and high bacilli load [1]. It has been shown that the risk of developing neural damage, along with the risk of developing reversal reaction, is 10-fold higher in patients in whom three or more body segments are affected [11]. Facial involvement is a risk factor for the development of reversal reaction, as it is for lagophthalmos [12]. Although factors which can induce type I reactions are not clearly known, recent studies have pointed to genetic factors [5]. Identification of the risk factors, therefore, allows more meticulous follow-up of patients and early treatment [1].

#### 2.5. Histopathology

The type 1 reaction is characterized by edema in the upper dermis and disorganized granulomas. The foreign body giant cells, Langhans giant cells accompanied by epidermal erosion and spongiosis, and fibroplasia appear in the dermis. The necrosis, ulcer and inflammatory infiltration by neutrophils may be observed in severe reaction [13]. The cytology of preexisting granulomas is differentiated by the presence of large epitheloid cells and decreased number of bacilli. Inflammatory cells often infiltrate epidermis and increased neural destruction is observed. The edema inside and around the granulomas results in the damage of surrounding tissues and nerves [1].

#### 2.6. Treatment

The main goal of treatment in type 1 reaction is to suppress the cellular immunity. Prevention of nerve damage required early diagnosis and early institution of anti-inflammatory medications. MDT must be continued during the reactions. Corticosteroids are the most effective drugs used to treat reversal reaction. Their main effects are to inhibit activation of cellular immune response and suppress inflammatory response against M. leprae antigens in the skin and nerves. Corticosteroids increases vasodilation by inhibiting the release of mediators such as arachidonic acid (prostaglandins) metabolites and platelet activating factor (PAF), vasoactive amines, neuropeptides, interleukin-1 (IL-1), TNF-α, and nitric oxide (NO). They inhibit adhesion of neutrophils, eosinophils, and lymphocytes to the endothelial cells, their migration to the inflammation site, and decrease vascular permeability. They inhibit phagocytosis and production of oxygen-free radicals [1].

be more complicated than type 1 reaction due to systemic nature and recurrent episodes [4]. The differences between type 1 and type 2 reactions are summarized in Table 1 [1, 3, 4, 6, 10, 13]. Type 2 reaction course is 1–2 weeks, but may occur multiple recurrences over several months [5]. ENL is identified by Pocaterra et al. as single acute (one ENL episode lasting less than 6 months, recurrence is not), multiple acute (repeated discrete episodes) or chronic (an

Type III hypersensitivity reaction (immune complex

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New painful subcutaneous nodules in previously

Painful neuritis with or without loss of nerve function

formation and deposition)

Previous treatment or not

unaffected skin Necrotic areas

Rarely Common (Fever, weakness, lymphadenitis, iridocyclitis,

Lepromatous leprosy Vaccination Pregnancy Puerperality Puberty Infection Stress

and subcutaneous tissue

medium vessels

Clofazimine Thalidomide

Erythema nodosum leprosum Lucio's phenomenon

Erythema multiforme-like reaction

Borderline lepromatosis, lepromatosis

Polymorphous erythematous plaques

neuritis, arthritis, dactylitis, orchitis)

Neutrophilic infiltrate in the mid-deep dermis

Leukocytoclastic vasculitis of the small and

Acetylsalicylic acid, pentoxifylline Systemic corticosteroids

Pain or tenderness in one or more nerves Muscle weakness in the hands, feet, or face

episode lasting for more than 6 months, continuous episodes) [18].

Type 1 helper cells Type 2 helper cells

Parameter Type 1 reaction Type 2 reaction

Pathogenesis Type IV hypersensitivity reaction (delayed cell-mediated)

Tuberculoid, borderline tuberculoid,

Previous treatment (except in downgrading

Acute onset of erythema and swelling of

Painful neuritis with or without loss of

Pain or tenderness in one or more nerves Muscle weakness in the hands, feet, or face

Recurrence Less likely Most likely

Disorganized granuloma and necrosis or

Table 1. The differences between type 1 and type 2 reactions [1, 3, 4, 6, 10, 13].

Superficial dermal edema Dermal fibroplasia

ulceration in severe reactions

Treatment Nonsteroidal anti-inflammatory drug Systemic corticosteroids

Reversal reaction Downgrading reaction

borderline-borderline

reactions)

previous lesions No new lesions

nerve function

Risk factors Multidrug therapy Vaccination Pregnancy Puerperality Oral contraceptive Infection Stress Trauma

Histopathology Tuberculoid granuloma

Immunological response

Type of reaction

Clinical phenotype

Cutaneous features

Neurological features

Systemic manifestations

Clinically, corticosteroids change the course of reversal reactions in many ways. They decrease intraneural and cutaneous edema and promote rapid recovery of the symptoms [1]. Earlier initiation of corticosteroid treatment can eliminate the risk of permanent neural dysfunction [3]. Corticosteroids must be continued at immunosuppressive doses for prolonged period. A prednisolone dose of 40 mg has been suggested as the start dose to control many of the type I reactions. However, patients with neural involvement require a dose of 1 mg/kg (60 mg) or sometimes higher doses (2 mg/kg). [14] Prednisolone dose must be reduced only after observing clinical recovery and tapering the dose to 20 mg/day. Recovery is often occurs within 3 months but may sometimes exceed 6 months. Intravenous methylprednisolone pulse therapy has been used to control reactions. Pulse therapy is indicated in severe reversal reactions and in cases of acute or chronic neuritis who have previously received oral corticosteroid therapy for prolonged period. The therapy involves administration intravenous methylprednisolone at a dose of 1 gr/day for consecutive 3 days in the first week and this is followed by a dose of 1 gr/week for consecutive 4 weeks, and finally 1 gr/month for consecutive 4 months. Prednisone 0.5 mg/kg/day is administered between the cycles of pulse therapy [15]. The treatment should be modified with a return to the previous dose in case worsening of clinical condition. Correct start dose and dose tapering regimen for prednisone must be determined on a patient basis, and this decision must rely on the follow-up of the loss of sensory functions and motor examination findings. The recommended duration of treatment is often 4–9 months in patients with borderline tuberculoid (BT) leprosy, 6–9 months in patients with borderlineborderline (BB) leprosy, 6–18 months in patients with borderline lepromatous (BL) leprosy; however, the treatment may last 24 months or longer. Patients with recent neural lesions and particularly those with less than 6-month duration better respond to therapy compared with patients in whom therapy is initiated in late periods [1].

Immunosuppressive medications such as azathioprine and cyclosporine can be used alone or in combination with corticosteroids [16]. Thalidomide is an effective drug used as an alternative to corticosteroid therapy and it allows long-term disease control [17]. Nerve decompression surgery has a limited place and it is recommended for patients with permanent pain after corticosteroid therapy. Surgery can be performed in patients with TL and BT leprosy with neuralgia and nerve abscesses in whom therapy with immunosuppressive is not feasible [1].

#### 3. Type 2 reaction

#### 3.1. Introduction

Type 2 reaction or erythema nodosum leprosum (ENL) occurs in patients with high bacilli load as in patients with multibacillar type leprosy (BL and LL) [5]. Type 2 reaction is considered to be more complicated than type 1 reaction due to systemic nature and recurrent episodes [4]. The differences between type 1 and type 2 reactions are summarized in Table 1 [1, 3, 4, 6, 10, 13]. Type 2 reaction course is 1–2 weeks, but may occur multiple recurrences over several months [5]. ENL is identified by Pocaterra et al. as single acute (one ENL episode lasting less than 6 months, recurrence is not), multiple acute (repeated discrete episodes) or chronic (an episode lasting for more than 6 months, continuous episodes) [18].

and nerves. Corticosteroids increases vasodilation by inhibiting the release of mediators such as arachidonic acid (prostaglandins) metabolites and platelet activating factor (PAF), vasoactive amines, neuropeptides, interleukin-1 (IL-1), TNF-α, and nitric oxide (NO). They inhibit adhesion of neutrophils, eosinophils, and lymphocytes to the endothelial cells, their migration to the inflammation site, and decrease vascular permeability. They inhibit phagocytosis and

Clinically, corticosteroids change the course of reversal reactions in many ways. They decrease intraneural and cutaneous edema and promote rapid recovery of the symptoms [1]. Earlier initiation of corticosteroid treatment can eliminate the risk of permanent neural dysfunction [3]. Corticosteroids must be continued at immunosuppressive doses for prolonged period. A prednisolone dose of 40 mg has been suggested as the start dose to control many of the type I reactions. However, patients with neural involvement require a dose of 1 mg/kg (60 mg) or sometimes higher doses (2 mg/kg). [14] Prednisolone dose must be reduced only after observing clinical recovery and tapering the dose to 20 mg/day. Recovery is often occurs within 3 months but may sometimes exceed 6 months. Intravenous methylprednisolone pulse therapy has been used to control reactions. Pulse therapy is indicated in severe reversal reactions and in cases of acute or chronic neuritis who have previously received oral corticosteroid therapy for prolonged period. The therapy involves administration intravenous methylprednisolone at a dose of 1 gr/day for consecutive 3 days in the first week and this is followed by a dose of 1 gr/week for consecutive 4 weeks, and finally 1 gr/month for consecutive 4 months. Prednisone 0.5 mg/kg/day is administered between the cycles of pulse therapy [15]. The treatment should be modified with a return to the previous dose in case worsening of clinical condition. Correct start dose and dose tapering regimen for prednisone must be determined on a patient basis, and this decision must rely on the follow-up of the loss of sensory functions and motor examination findings. The recommended duration of treatment is often 4–9 months in patients with borderline tuberculoid (BT) leprosy, 6–9 months in patients with borderlineborderline (BB) leprosy, 6–18 months in patients with borderline lepromatous (BL) leprosy; however, the treatment may last 24 months or longer. Patients with recent neural lesions and particularly those with less than 6-month duration better respond to therapy compared with

Immunosuppressive medications such as azathioprine and cyclosporine can be used alone or in combination with corticosteroids [16]. Thalidomide is an effective drug used as an alternative to corticosteroid therapy and it allows long-term disease control [17]. Nerve decompression surgery has a limited place and it is recommended for patients with permanent pain after corticosteroid therapy. Surgery can be performed in patients with TL and BT leprosy with neuralgia and nerve abscesses in whom therapy with immunosuppressive is not feasible [1].

Type 2 reaction or erythema nodosum leprosum (ENL) occurs in patients with high bacilli load as in patients with multibacillar type leprosy (BL and LL) [5]. Type 2 reaction is considered to

production of oxygen-free radicals [1].

84 Hansen's Disease - The Forgotten and Neglected Disease

patients in whom therapy is initiated in late periods [1].

3. Type 2 reaction

3.1. Introduction

Table 1. The differences between type 1 and type 2 reactions [1, 3, 4, 6, 10, 13].

#### 3.2. Pathogenesis

Type 2 reaction is associated with humoral immunity. This is a type 3 hypersensitivity reaction associated with the deposition of immunocomplexes produced by binding of antigens released by the destruction of bacilli with antibodies [6]. Immunocomplexes cannot be phagocytosed by the macrophages, cleared by the kidneys, and they are deposited on the vessel walls [19]. This reaction is also associated with increased levels of proinflammatory cytokines. Release of inflammatory cytokines and followed by neutrophilic infiltration contribute to the development of variable characteristic clinical findings depending on the involved organ. In type 2 reaction, vasculitis and/or concurrent panniculitis occurs with inflammatory infiltration by neutrophils [5].

3.5. Histopathology

3.6. Treatment

gangrenosum, and deep micotic infections [13, 23].

Two different histopathological variants have been described in ENL. First variant has been reported by Ridley as "the pink nodule type" or classical ENL (or mild ENL form). Typically, there are clusters of neutrophils accumulated around the foamy macrophages at the center of small granulomas. Eosinophils, plasma cells, and mast cells are present. Classical characteristics of vasculitis affecting small- or medium-sized vessels, necrotizing changes, and thrombosis formation have been reported in almost 25% of the patients. Indeed, vasculitic changes mostly occur in early lesions. Vasculitic changes involving neutrophilic infiltration, hemorrhage, and thrombus formation may be severe in necrotizing ENL. Necrosis in epidermis and dermis, collagen degeneration can be observed and this may result in dermal fibrosis [13]. Intact acid resistant bacilli (ARB) are found in the lesions of untreated patients, whereas granular and fragmented ARB are often found in patients receiving therapy. Lucio's phenomenon must be histopathologically differentiated from real erythema nodosum, Sweet syndrome, pyoderma

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Type 2 reaction often regresses with addition of clofazimine to the MDT. After the use of clofazimine-containing MDT, type 2 reaction prevalence has decreased in leprosy patients under therapy. Suppression of inflammation is the basis of therapy. Bed rest and drugs such as acetylsalicylic acid, corticosteroids, nonsteroidal anti-inflammatory drug (NSAID), chloroquine, antimony compounds, pentoxifylline, and thalidomide are used in the treatment [4, 24, 25].

Corticosteroids and thalidomide are still considered the mainstay of therapy in severe cases of type 2 reaction presenting with orchitis, iridocyclitis with glaucoma, and neuritis that cause neural dysfunction [14]. Administration of high doses of corticosteroids with pulse therapy and rapid dose tapering within 2–3 weeks have been deemed appropriate as type 2 reaction is an episodic disease. If maintenance therapy must be avoided particularly in patients with chronic recurrent ENL, as long term therapy with prednisolone causes dependence to corticosteroid therapy and side effects. Thalidomide seems to be the choice of drug in maintenance therapy. Action mechanism of thalidomide is not clear. It is thought to be effective in the inhibition of TNF-α. It has some side effects which do not necessitate discontinuation of therapy. Neuropathy has been reported in approximately 20–30% of patients. It is often masked by leprosy neuropathy [26]. It is well tolerated at a dose of 100–300 mg/day in cases with recurrent disease and it provides prolonged remission [4]. Clinical trials have shown that thalidomide rapidly controls ENL and it is superior to acetylsalicylic acid and pentoxifylline therapy. On the other hand, thalidomide is teratogenic when used in early periods of pregnancy [25]. Thalidomide analogs chemically resemble thalidomide, but side effects are not the

Clofazimine is recommended in the treatment of chronic recurrent reactions. Clofazimine is administered for 12 weeks together with corticosteroids at doses of 100 mg tid, 100 mg bid, or 100 mg/day. Clofazimine is less effective than corticosteroids and it often takes 4–6 weeks to be fully effective. Addition of clofazimine to the therapy is extremely beneficial in reducing corticosteroid doses or discontinuation of corticosteroid therapy in patients who have become

same. Revlimid and aktimid are promising drugs in this category [27].

#### 3.3. Clinical features

Type 2 reaction may occur in the early periods of therapy and even after completion of therapy, as it takes long time for the body to eliminate dead bacilli in the macrophages. It often occurs in the first three years after initiation of leprosy treatment. Sudden deterioration in clinical condition may be observed in patients with LL and rarely in patients with BL leprosy [6]. This reaction can involve multiple organs and systems. Immunocomplexes accumulate in the circulation and they are deposited in the skin, eyes, joints, lymph nodes, kidneys, liver, spleen, bone marrow, endothelium, and the testes. The lesions are multiple, bilateral, erythematous, firm, painful, subcutaneous nodules resembling erythema nodosum that are distributed symmetrically. Pustular, bullous ulcerated, and necrotic types have also been reported. Some nodules may persist as a chronic painful panniculitis and lead to scar. The target lesions of erythema multiforme may occur in any region [4, 6]. The lesions more often occur in external surfaces of the body [20]. General symptoms such as fever, weakness, edema, myalgia-arthralgia, dactylitis, bone tenderness, and lymphadenomegaly are observed prior to the occurrence of or concurrent with ENL lesions. Iridocyclitis, episcleritis, eye pain (photophobia), orchitis, liver, or kidney damage can be observed. Neuritis, painful enlarged nerves and nerve function impairment may occur [4, 5]. Necrosis can occur as a result of vascular thrombosis and ischemia. Vascular occlusion is probably associated with vasculitis caused by immunocomplex deposition on the vessel wall and leukocytoclasia. This should not be confused with Lucio's phenomenon observed with classical LL. In Lucio's phenomenon, the majority of the bacilli infect capillary endothelium, leading to endothelial proliferation, thrombosis, and vascular occlusion [21]. Laboratory tests show elevated levels of acute phase reactants such as C-reactive protein (CRP), α1-antitrypsin, α1-acit glycoprotein (AGP), and γ-globulins [22].

#### 3.4. Risk factors

Lepromatous leprosy forms with high bacilli load, vaccination, infection, puberty, pregnancy, puerperality, with significant hormonal changes occurring in women are risk factors for the development of type 2 reaction. Emotional and psychological stress and associated immunological and hormonal changes have been regarded to trigger these reactions; however, this has yet to be confirmed [4, 10].

#### 3.5. Histopathology

3.2. Pathogenesis

86 Hansen's Disease - The Forgotten and Neglected Disease

neutrophils [5].

3.4. Risk factors

yet to be confirmed [4, 10].

3.3. Clinical features

Type 2 reaction is associated with humoral immunity. This is a type 3 hypersensitivity reaction associated with the deposition of immunocomplexes produced by binding of antigens released by the destruction of bacilli with antibodies [6]. Immunocomplexes cannot be phagocytosed by the macrophages, cleared by the kidneys, and they are deposited on the vessel walls [19]. This reaction is also associated with increased levels of proinflammatory cytokines. Release of inflammatory cytokines and followed by neutrophilic infiltration contribute to the development of variable characteristic clinical findings depending on the involved organ. In type 2 reaction, vasculitis and/or concurrent panniculitis occurs with inflammatory infiltration by

Type 2 reaction may occur in the early periods of therapy and even after completion of therapy, as it takes long time for the body to eliminate dead bacilli in the macrophages. It often occurs in the first three years after initiation of leprosy treatment. Sudden deterioration in clinical condition may be observed in patients with LL and rarely in patients with BL leprosy [6]. This reaction can involve multiple organs and systems. Immunocomplexes accumulate in the circulation and they are deposited in the skin, eyes, joints, lymph nodes, kidneys, liver, spleen, bone marrow, endothelium, and the testes. The lesions are multiple, bilateral, erythematous, firm, painful, subcutaneous nodules resembling erythema nodosum that are distributed symmetrically. Pustular, bullous ulcerated, and necrotic types have also been reported. Some nodules may persist as a chronic painful panniculitis and lead to scar. The target lesions of erythema multiforme may occur in any region [4, 6]. The lesions more often occur in external surfaces of the body [20]. General symptoms such as fever, weakness, edema, myalgia-arthralgia, dactylitis, bone tenderness, and lymphadenomegaly are observed prior to the occurrence of or concurrent with ENL lesions. Iridocyclitis, episcleritis, eye pain (photophobia), orchitis, liver, or kidney damage can be observed. Neuritis, painful enlarged nerves and nerve function impairment may occur [4, 5]. Necrosis can occur as a result of vascular thrombosis and ischemia. Vascular occlusion is probably associated with vasculitis caused by immunocomplex deposition on the vessel wall and leukocytoclasia. This should not be confused with Lucio's phenomenon observed with classical LL. In Lucio's phenomenon, the majority of the bacilli infect capillary endothelium, leading to endothelial proliferation, thrombosis, and vascular occlusion [21]. Laboratory tests show elevated levels of acute phase reactants such as C-reactive protein (CRP), α1-antitrypsin, α1-acit glycoprotein (AGP), and γ-globulins [22].

Lepromatous leprosy forms with high bacilli load, vaccination, infection, puberty, pregnancy, puerperality, with significant hormonal changes occurring in women are risk factors for the development of type 2 reaction. Emotional and psychological stress and associated immunological and hormonal changes have been regarded to trigger these reactions; however, this has Two different histopathological variants have been described in ENL. First variant has been reported by Ridley as "the pink nodule type" or classical ENL (or mild ENL form). Typically, there are clusters of neutrophils accumulated around the foamy macrophages at the center of small granulomas. Eosinophils, plasma cells, and mast cells are present. Classical characteristics of vasculitis affecting small- or medium-sized vessels, necrotizing changes, and thrombosis formation have been reported in almost 25% of the patients. Indeed, vasculitic changes mostly occur in early lesions. Vasculitic changes involving neutrophilic infiltration, hemorrhage, and thrombus formation may be severe in necrotizing ENL. Necrosis in epidermis and dermis, collagen degeneration can be observed and this may result in dermal fibrosis [13]. Intact acid resistant bacilli (ARB) are found in the lesions of untreated patients, whereas granular and fragmented ARB are often found in patients receiving therapy. Lucio's phenomenon must be histopathologically differentiated from real erythema nodosum, Sweet syndrome, pyoderma gangrenosum, and deep micotic infections [13, 23].

#### 3.6. Treatment

Type 2 reaction often regresses with addition of clofazimine to the MDT. After the use of clofazimine-containing MDT, type 2 reaction prevalence has decreased in leprosy patients under therapy. Suppression of inflammation is the basis of therapy. Bed rest and drugs such as acetylsalicylic acid, corticosteroids, nonsteroidal anti-inflammatory drug (NSAID), chloroquine, antimony compounds, pentoxifylline, and thalidomide are used in the treatment [4, 24, 25].

Corticosteroids and thalidomide are still considered the mainstay of therapy in severe cases of type 2 reaction presenting with orchitis, iridocyclitis with glaucoma, and neuritis that cause neural dysfunction [14]. Administration of high doses of corticosteroids with pulse therapy and rapid dose tapering within 2–3 weeks have been deemed appropriate as type 2 reaction is an episodic disease. If maintenance therapy must be avoided particularly in patients with chronic recurrent ENL, as long term therapy with prednisolone causes dependence to corticosteroid therapy and side effects. Thalidomide seems to be the choice of drug in maintenance therapy. Action mechanism of thalidomide is not clear. It is thought to be effective in the inhibition of TNF-α. It has some side effects which do not necessitate discontinuation of therapy. Neuropathy has been reported in approximately 20–30% of patients. It is often masked by leprosy neuropathy [26]. It is well tolerated at a dose of 100–300 mg/day in cases with recurrent disease and it provides prolonged remission [4]. Clinical trials have shown that thalidomide rapidly controls ENL and it is superior to acetylsalicylic acid and pentoxifylline therapy. On the other hand, thalidomide is teratogenic when used in early periods of pregnancy [25]. Thalidomide analogs chemically resemble thalidomide, but side effects are not the same. Revlimid and aktimid are promising drugs in this category [27].

Clofazimine is recommended in the treatment of chronic recurrent reactions. Clofazimine is administered for 12 weeks together with corticosteroids at doses of 100 mg tid, 100 mg bid, or 100 mg/day. Clofazimine is less effective than corticosteroids and it often takes 4–6 weeks to be fully effective. Addition of clofazimine to the therapy is extremely beneficial in reducing corticosteroid doses or discontinuation of corticosteroid therapy in patients who have become dependent on corticosteroids. The total duration of clofazimine therapy should not exceed 12 months [18].

Acknowledgements

Leyla Bilik, Betul Demir\* and Demet Cicek

\*Address all correspondence to<EMAIL_ADDRESS>
doi.org/10.1590/abd1806-4841.20132004

Author details

References

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[1] Nery JA, Bernardes Filho F, Quintanilha J, Machado AM, Oliveira Sde S, Sales AM Understanding the type 1 reactional state for early diagnosis and treatment: A way to avoid disability in leprosy. Anais Brasileiros de Dermatologia 2013;88:787–792. DOI: http://dx.

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[2] Scollard DM, Martelli CM, Stefani MM, Maroja Mde F, Villahermosa L, Pardillo F, et al. Risk factors for leprosy reactions in three endemic countries. The American Journal of

[3] Wu J, Boggild AK. Clinical pearls: Leprosy reactions. Journal of Cutaneous Medicine and

[4] Kahawita IP, Walker SL, Lockwood DNJ. Leprosy type 1 reactions and erythema nodosum leprosum. Anais Brasileiros de Dermatologia. 2008;83:75-82. DOI: 10.1590/S0365-05962

[5] Scollard D, Adams LB, Gillis TP, Krahenbuhl JL, Truman RW, Williams DL. The continuing challenges of leprosy. Clinical Microbiology Reviews. 2006;19:338-381. DOI: 10.1128/

[6] Lastoria JC, Abreu MA. Leprosy: Review of the epidemiological, clinical, and etiopathogenic aspects - part 1. Anais Brasileiros de Dermatologia 2014;89:205–218. DOI:

[7] Naafs B. Leprosy reactions. New knowledge. Tropical and Geographical Medicine. 1994;

[8] Graham A, Furlong S, Margoles LM, Owusu K. Clinical management of leprosy reac-

[9] Talhari S, Neves RG, de Oliveira MLW, de Andrade ARC, Ramos AMC, Penna GO, Talhari AC. Manifestações cutâneas e diagnóstico diferencial. In: Talhari S, Neves RG,

Tropical Medicine and Hygiene. 2015;92:108-114. DOI: 10.4269/ajtmh.13-0221

Corticosteroids and thalidomide are the mainstay of therapy in the control of type II reaction. Selective cytokine inhibitors and phosphodiesterase type-4 inhibitors with potential TNFalpha activity but without T-cell activating effect are new drugs [17].

#### 4. Differential diagnoses

In general, cutaneous drug reactions, local skin infections, relapses, diabetes, Bell's palsy, rheumatoid arthritis, rheumatic fever, and disc prolapse must be taken into consideration in differential diagnosis. It may manifest as various cutaneous drug reactions such as urticarial, lichenoid, exanthematous reactions, erythema nodosum, erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis. The patients usually suffer from itching and burning in some of these lesions, whereas these symptoms are not observed in patients with leprosy. Furthermore, new skin lesions do not resemble preexisting lesions. Localized skin infections developing in patients with leprosy are often confined to a particular body site. The lesions do not occur bilaterally and medical history is often remarkable for trauma or insect bites that could cause an infection. New lesions appear if relapse occurs, and this often has an insidious course rather than a severe clinical course. Reaction often occurs within the first 3 years after initiation of leprosy therapy and old lesions exhibit acute pain and tenderness. Diabetic patients are prone to infections and development of peripheral neuropathy. Furthermore, regulation of blood glucose is impaired upon administration of corticosteroids. All patients must be screened for diabetes and referred to an advanced facility if diabetes is diagnosed. Bell's palsy may mimic facial paralysis caused by leprosy reactions. These patients do not have nerve thickening, sensory loss along the nerve projection, and hypopigmented skin lesions. This condition is better evaluated by the ophthalmologists. In Bell's paralysis, widening of palpebral fissure is not associated with the drop of lower eyelid. It occurs in women at childbearing age with rheumatoid arthritis, joint pain, joint deformities, fever, skin rash, and multiple organ involvement. Rheumatoid factor is almost always found to be elevated. However, referral to an advanced facility may be sometimes required to differentiate rheumatoid arthritis from leprosy reaction. Patients with rheumatic fever are usually young patients with fever, joint pain, and skin rash for a short period. These patients have high antistreptolysin O titers and valvular involvement can be found that cause murmur on auscultation. Patients with disc prolapse may present with acute onset of neuropathy in the extremities. Patients often report weight lifting in the early periods or stretching in the back. These patients do not show skin lesions or nerve thickening [23, 28].

#### 5. Conclusion

The reactions can contribute to further deterioration of the quality of life in leprosy. Early diagnosis of reactions can prevent nerve damage and provide early intervention to systemic complications.


**1.1 Objective of the chapter**

The objective of this chapter is to provide an in-depth understanding of DOE and its applications in quality control and assurance. We will explore various

**Figure 1.** *Design of Experiment (DOE).*

experimental designs, statistical techniques, and methodologies that are commonly used in DOE. Additionally, we will discuss its practical applications across various fields and the benefits and advantages that DOE offers in ensuring and improving quality standards.

#### **1.2 An overview and definitions of design of experiments (DOE)**

Definitions of Design of Experiments (DOE): DOE is a statistical methodology used to systematically plan, conduct, analyze, and interpret experiments to obtain valid and reliable results. It allows researchers to efficiently explore and identify the significant factors influencing a process or product's performance. DOE is an important statistical method used in controlling input factors or variables in order to ascertain the level of relationships with the output (responses) according to **Figure 1**, so as to ensure product or process quality. DOEs are usually carried out in five stages [7, 8] as shown in **Figure 2**. They are:

#### **1.3 History of DOE**

DOE has its roots in the work of Sir Ronald Fisher, who developed the basic principles of DOE in the early twentieth century. Fisher's work was initially applied to agricultural research, but it was soon adapted for use in other fields, including manufacturing, engineering, and medicine [9]. Since then, many scientists and statisticians have contributed to DOE development and its application in different fields [9–12].

#### **1.4 Types of DOE**

There are many different types of DOE, each with its own strengths and weaknesses [8, 13]. The best type of DOE to use will depend on the specific situation. Factors to consider include the number of factors, the number of levels for each factor, the desired level of confidence, and the time and budget constraints (**Figure 3**) [10, 14–16].

The most common types of DOE are:

#### *1.4.1 Full factorial designs*

These designs involve testing all possible combinations of factors. For example, if there are two factors with two levels each, there would be four possible combinations (2 × 2 = 4). Full factorial designs are the most comprehensive, but they can also be the most time-consuming and expensive.

**Figure 2.** *Five stages of DOE.*

#### *Quality Control and Quality Assurance – Techniques and Applications*


**1. Introduction**

To meet the sustainability agenda of urbanisation in the process of smart and sustainable urban development, there has been a certain consensus that, compared with new buildings, the protection and transformation of old buildings have been generally accepted, due to either social effects or environmental benefits [1]. In terms of the environment, renovating building materials of old buildings can reduce the pressure on energy consumption. By recycling existing materials, which can reduce carbon emissions, the impact on climate change can be reduced [1,2]. On the other hand, from a social perspective, old building protection projects can maintain social continuity and protect buildings that have been in disrepair for a long time [3].

However, given the insufficient awareness about the protection of historical buildings and facing a shortage of urban land, in numerous densely populated countries and regions, particularly in the fast-growing East Asia regions, historical buildings are demolished to meet various development needs. This practice is pervasive in many cities that are in the initial stage of economic development. For example, after the Second World War, Japan's large-scale urbanisation development resulted in the arbitrary destruction and demolition of many ancient buildings [4]. In the 1950s, the ancient walls of Beijing were demolished on a large scale [5]. Moreover, at the beginning of this century, Lee Tung Street in Hong Kong was demolished and rebuilt by the government as a pedestrian shopping street without any distinctive local style [6]. The continuous growth of modern cities is gradually compressing

**Citation:** Guo, N.; Chan, E.H.W.; Yung, E.H.K. Alternative Governance Model for Historical Building Conservation in China: From Property Rights Perspective. *Sustainability* **2021**, *13*, 203. https://doi.org/10.3390/su13010203

Received: 6 November 2020 Accepted: 24 December 2020 Published: 28 December 2020

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

**Copyright:** © 2020 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/).

the space of historical buildings. As such buildings are demolished, a city's features and its people's sense of identity in terms of culture are disappearing. Historical buildings are under many threats in many historic cities, including rapid urbanisation, an increasing housing demand, and socio-cultural and climate changes [7,8]. From the perspective of sustainable development, the adaptive reuse of historical buildings can play a decisive role not only in terms of heritage conservation, but also as an urban strategy capable of contributing to environmental protection and generating new economic, cultural, and social values [9,10].

In recent years, an increasing number of successful adaptive reuse projects have given the government confidence, and policy makers are also trying to apply this method more to protect historical buildings and blocks [11]. However, there are numerous cases of obstacles caused by unknown ownership and property rights, which seriously hinder the construction of smart and sustainable urban development. Specifically, unclear property rights can neither deter the destruction of important historical buildings nor effectively protect existing ones [12]. On the one hand, the government experiences difficulties paying high amounts of money for repairs. On the other hand, the excessive use of such historically valuable buildings with existing conditions may devastate numerous households. The government has encouraged the public to participate in adaptive reuse projects, which is an important measure for achieving sustainable urban development [13], but chaotic property rights, particularly as a legacy of transition from state-ownership property in China, seriously hinder the transformation of these buildings by developers. Incidents such as demolitions and violence against demolitions have occurred owing to mistrust among the government, residents, and developers [14,15]. Meanwhile, residents who do not cooperate in demolitions waste time and increase the cost of reconstruction projects [16,17]. Property rights issues hinder the renovation of old buildings, making sustainable urban development difficult to pursue. Such problems are particularly serious in developing countries such as China, which has transformed from a centrally planned to a market economy. Ancient buildings with rich historical and artistic value have become a sweet burden in the urbanisation of a city.

This study selected the most representative case, namely, the Pingjiang Historic Block in China, as the research test bed. An on-site field investigation was conducted in this district. A total of 63 historical buildings have been, are being, or are about to be transformed in this area. By examining these historical buildings, this study analyses the influence of the complex property rights structure on the protection and redevelopment of historical buildings. The problems in this test bed case are typical of numerous other historic cities in China and worldwide. Based on the Coase Theorem, the authors combined the reality and difficulties of historical building protection to establish an operational governance model founded on property rights. Therefore, the findings can provide a feasible operational model that can solve the primary problem in sustainable urban development and be applied to similar historical buildings in China and other countries during the smart and sustainable urban development process. The result may provide policy makers with measures to solve urbanisation challenges, such as the inadequacy of urban conservation management and sustainable development policies, dilemma in balancing public and private rights, the lack of resources amongst decision makers, and persistent conflict and competition between heritage conservation needs and developers' interests [7].


**Author details**

Natali Gomes Bordon1 \*, Niwton Leal Filho2 and Tony Vizcarra Bentos2

1 University of Campinas (UNICAMP), Campinas, Brazil

2 National Institute for Amazon Research (INPA), Manaus, Brazil

\*Address all correspondence to<EMAIL_ADDRESS>
© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


*3.4. Biological Assay*

The anti-inflammatory effects of the isolated compounds from *Penicillium citrinum* were evaluated by suppressing fMLP-induced O2 •– generation by human neutrophils. In addition, anti-cancer activity was evaluated by cytotoxicity assay and Western blot analysis.


Contents

Preface

This edited volume is a collection of reviewed and relevant research chapters concerning the developments within the "Aging - Life Span and Life Expectancy" field of study. The book includes scholarly contributions by various authors and has been edited by an expert in the field. Each contribution comes as a separate chapter

complete in itself but directly related to the book's topics and objectives.

The target audience comprises scholars and specialists in the field.

**InTechOpen**

Healthcare.

The book includes chapters dealing with the following topics: Psychotropic Medication Use and Mortality in Long-Term Care Residents; Evidence for the Effectiveness of Soy in Aging and Improving Quality of Life; Epidemiology and Management of Intracerebral Hemorrhage in Chile; Impact of Chronic Medical and Neuropsychiatric Illnesses on Quality of Life and Life Expectancy among Patients at the University of Port Harcourt Teaching Hospital (UPTH); Crude Birth Rate and Crude Mortality Rate in India: A Case of Application of Regression in


*2.5. pH Values*

Table 3 compared the pH values of packaged and unpackaged strawberries. The pH values of unpackaged strawberries increased significantly with the increase of storage time. The pH values of unpackaged strawberries reached to 3.99 ± 0.29 after six days. Han et al. demonstrated that the pH values of fruit are related to the fruit senescence [29]. A possible explanation for this might be the utilization of organic acids of fruit during respiration [30]. The pH difference between day 2 and day 4 was not statistically significant for all packaged groups. Martinez–Ferrer et al. considered that might be the low conversion rate of organic acids during respiration [30]. The pH values of strawberries packaged with PVA/CH-2, PVA/CH-2.5 and PVA/CH-3 were significantly different than the pH values of strawberries packaged with the PVA sample at day 6. The findings of the current study are consistent with those of Cong et al., who found that CH coating containing natamycin slowed the changes in pH values of Hami melons [31]. At six days, the pH values of fruits packaged with PVA/CH-2.5 was 3.65 ± 0.16, and the change was minimum (3.41 ± 0.08 for one day). A possible explanation for this might be that relatively small changes of O2 and CO2 levels resulted in slight changes of the pH values for strawberries [32].

**Table 3.** pH analysis of strawberries treated with different films during storage.

Notes: Values with the same letter are not statistically different, according to Duncan's Multiple Range Test at *p* < 0.05; a, b, means with the same letter in the same column are not significant different (*p* > 0.05).


**5. Conclusion**

42 Bacterial Artificial Chromosomes

Molecular genetic studies have shown that hemizygosity of the elastin (*ELN*) gene accounts for the cardiovascular abnormalities observed in WBS patients. The other signs (facial dysmorphism, growth and mental retardation, etc.) observed in WBS are likely to be due to hemizygosity of other genes flanking the *ELN* locus. Although the unique combination of signs and anomalies is highly evocative, WBS patients usually present phenotypic variability, which could be explained by different deletion size and, therefore, by different

Several studies tried to define the WBS critical deletion region. Using sequence tagged site (STS) markers flanking the *ELN* gene, Perez-Jurado et al. (1996) and Wu et al. (1998) looked for the minimal deletion region responsible for the WBS phenotype in 123 patients. Markers from D7S489B (also named D7S489U) to D7S1870 were shown to be consistently removed, defining a 2 cM deletion in all informative patients (Perez Jurado et al., 1996;

Using BAC and PAC (P1-derived artificial chromosome) clones, Meng et al. (1998) constructed a physical map of the common deletion region. They localized the centromeric and telomeric deletion breakpoints to two genomic clones (containing D7S489B and

Based on the work by Valero et al. (2000) who found that 3 large region-specific segmental duplication or low copy repeat (LCR) elements flanked the common deletion region (Valero et al., 2000), Bayes et al. (2003) defined two common deletion regions in a set of 74 patients with WBS. Most of the patients (95%) had a 1.55 Mb deletion whereas the remaining 5%

Botta et al. (1999) reported a deletion of about 850 kb in two patients showing the full spectrum of the WBS phenotype (Botta et al., 1999). Furthermore, the analysis of the deletion size in WBS patients with "incomplete" phenotype revealed even more heterogeneity (Antonell et al., 2010). Using quantitative real-time PCR to scan 2.5 Mb of the WBS deletion region at a resolution of 100-300 kb among 65 patients with strong clinical indication of having WBS, Schubert and Laccone (2006) found that 21 patients had a deletion in the WBS region. Nineteen patients had a deletion ranging from 1.4 to 1.8 Mb in size whereas one had a 200 kb deletion and the remaining one a 2.5 Mb deletion

FISH using BAC clones has been extensively used to construct physical maps of the 7q region deleted in WBS and to define the commonly deleted region (Meng et al., 1998; Peoples et al., 2000; Perez Jurado et al., 1996; Wu et al., 1998). However, to our knowledge, no study has been conducted to determine the deletion size in WBS individuals using overlapping BACs. Indeed, the level of resolution is a limit to this technique. A BAC is considered as partially deleted by FISH analysis when the fluorescent signal of this clone is much stronger on one chromosome 7 than on the other. Furthermore, a BAC could be considered as present or absent (not partially deleted) if only a small part of the DNA sequence is removed or kept (usually less than 50 kb). Having resource to overlapping

BAC clones can increase the level of confidence but some uncertainty will remain.

D7S1870) flanking a 1.5 Mb deletion interval (Meng et al., 1998).

exhibited a larger deletion of approximately 1.84 Mb (Bayes et al., 2003).

**4. Discussion**

Wu et al., 1998).

(Schubert & Laccone, 2006).

sets of genes showing hemizygosity.

Thirteen patients had a deletion estimated at 1.17 Mb in size and the remaining patient a deletion size estimated at 1.41 Mb. All the patients had the "classical" WBS phenotype, but for the cognitive profile which was not evaluated. The margins of uncertainty of the centromeric and telomeric boundaries of the deletion were less than 100 kb in all 14 patients, a level obtained by microsatellite analysis or quantitative real-time PCR. Therefore, this approach is efficient to define the deletion size among WBS patients.


**1. Introduction**

During the last decade, the interest in low-frequency microwave remote sensing and technological advances in instrumentation and space technology have resulted in a series of new mission concepts to measure key components of the water cycle. Soil moisture is one of these key components, controlling the partition of energy at the surface and the interactions between the land surface and the atmosphere at varying temporal and spatial scales [1–4]. Theoretical and experimental

evidence supports the idea that L-band (1 to 2 GHz) microwave radiometry is the optimal technology for measuring global surface soil moisture (SM) on an operational basis. The emission of thermal microwave radiation from soils is strongly dependent on soil moisture content. L-band measurements are insensitive to cloud liquid water and, compared to higher microwave frequencies, they are more sensitive to deeper soil moisture layers (up to 5 cm) and penetrate through denser layers of vegetation canopy [5,6]. The latter is especially important for improvements in climate, numerical weather prediction, water and energy cycle science. As a result, the first two satellite missions specifically designed to measuring SM have an L-band radiometer on-board: ESA launched the Soil Moisture and Ocean Salinity (SMOS) mission in November 2009 [7] and NASA launched the Soil Moisture Active-Passive (SMAP) satellite in early 2015 [8]. SMOS unique payload is an L-band synthetic aperture radiometer with multi-angular and full-polarimetric capabilities that provides synoptic views of the Earth's global SM with a spatial resolution of ∼40 km and a 3-day revisit. SMAP has a real aperture L-band radiometer and an L-band radar to enhance the spatial resolution of the estimates from 36 km (radiometer only) to 9 km (radar-radiometer). However, operations of active-passive products ceased abruptly with the failure of the SMAP radar after about ten weeks of operations. Nonetheless, the radiometer is continuing to make measurements and four annual cycles of measurements are about to be completed.

Also during the last decade, satellite sensors with long technological heritage operating in the low-frequency microwave spectrum, that were initially devoted to atmospheric and/or oceanic sensing, have proved suitable for SM retrieval. As a result, several SM datasets from active and passive microwave sensors at C-band (6 GHz) and X-band (10 GHz) partially covering nearly the last 4 decades have been published and shared openly with the international community. Although these sensors are only sensitive to the top 1 cm of soil and have a larger attenuation in presence of vegetation, they can complement recent L-band missions and allow for a multi-decadal soil moisture observational data record. Spaceborne SM data sets from low-frequency microwaves have been widely validated under different biomes and climate conditions by comparison with ground-based observations (e.g., [9–16] and outputs of land surface models ([17–20]). Relevant for this work, Polcher et al. [20] showed that the rainfall driven structures of SM captured by the ORCHIDEE land surface model and SMOS are compatible, and comprehensive validations of SMOS retrievals have been undertaken showing good agreement with other sensors and consistent results over all surfaces, from very dry (Arizona, Sahel) to wet (tropical rain forests) [15].

Soil moisture was recognized by the Global Climate Observing System (GCOS) to be an Essential Climate Variable (ECV) in 2010. This underscores the potential of SM data sets to support the work of the United Nations Framework Convention on Climate Change (UNFCCC) and the Intergovernmental Panel on Climate Change (IPCC). In this context, the ESA's soil moisture Climate Change Initiative (CCI) is one of the first initiatives to merge the different microwave products available into a single soil moisture climate data record (http://www.esa-soilmoisture-cci.org/). One of the key steps in building a multi-decadal soil moisture data record is that, since different products display different ranges of soil moisture values, data have to be harmonized first using a common climatology. In its current version, the ESA CCI SM product uses the climatology provided by the Global Land Data Assimilation System (GLDAS-Noah) as a reference to scale the individual products. Despite some limitations, the ESA CCI SM product is nowadays the most complete and consistent long-term soil moisture data record available, covering (almost) the 40-year period from 1978 to June 2018 [21]. Recent research has been focused into incorporating SMOS to the climate data record [22]. However, the impact of using a model's climatology in absolute retrievals remains unclear, and the climate community has repeatedly argued for the need for a satellite-based SM record to serve as a reference for verifying land surface model performance and trends.

This study presents an SMOS-based L-band climatology that could potentially serve as a reference for the readily available microwave-based soil moisture data sets (from X-, C- and L-bands) into a long-term climate data record exclusively based on observational data sets. Ideally, an L-band climatology should be built from both SMOS and SMAP data. However, since a combined product is not yet available, and SMAP only covers a short observation period, this paper is focused on an L-band climatology solely based on SMOS observations. We show that this observation-driven climatology provides a close representation of the dominant features of temporal variability in the Earth's SM for the period 2010–2016, and allows identifying areas subjected to seasonal, subseasonal and long-term variability. Previous research showed that, despite being a short data set, SMOS provides coherent and reliable SM variability patterns at both seasonal and interannual scales [23,24]. In this work, the Seasonal Trend decomposition using Loess (STL) procedure [25] is implemented and tailored to the first six annual cycles of SMOS data to decompose the temporal variability of the signal. Our analysis quantifies how much SM variation is due to long-term influences, how much is due to seasonal cycle and how much is dominated by subseasonal short-term influences. This knowledge is critical for understanding how well climate data and land surface models compare with the remotely sensed variable. It also allows distinguishing between linear trends and interannual variability, which could be later related to main phenomena of global weather alterations over land (e.g., El Niño Southern Oscillation (ENSO)).

This paper is organized as follows. The SM dataset and the methodology followed to build the SM climatology and to provide a global assessment of SM variability are described in Section 2. Main results are shown in Section 3. The distribution of SM variance among temporal components is first analyzed at selected target sites representative of terrestrial biomes with distinct vegetation type and seasonality. The SMOS temporal series at these sites are compared to GLDAS-Noah and ERA5 modeled SM and to ground-based estimates available at one of the sites (REMEDHUS network, in Spain) to identify consistencies and potential shortcomings of building a climatology with observational data alone. Subsequently, the main features of SM temporal variability are analyzed at the global scale. Conclusions and perspectives from this work are given in Section 4.

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


**7. Independent control of layer nucleation and layer-growth**

The concentration difference between the two different nanowire species in the catalyst [89] implies that both these species could affect the growth in different ways. This was studied in detail, again using Au-catalyzed GaAs (and TMGa and AsH3 as precursors) [90]. Two sets of experiments were investigated – one was a TMGa series (where AsH3 and temperature were kept constant) and a second was AsH3 series (where TMGa and temperature were kept constant). The ledge-flow time was found to decrease drastically with increasing AsH3 flow (**Figure 3b)**; thus the ledge-flow process was understood to be limited by the As availability. This agrees well with the low As % present in the catalyst [89]. (The idea that ledge-flow is limited by As availability was proposed in an earlier study [84] but not elaborately investigated there.) On increasing TMGa flow in a separate experiment the incubation time decreased drastically while the ledge-flow time remained rather unchanged (**Figure 3c**). This indicated that nucleation of a new layer is triggered by excess Ga.

The experimental observations for the TMGa and AsH3 series matched stochastic Monte Carlo simulations done based on mass transport and nucleation theory [89]. An example of how As % and Ga % in the catalyst varies in an almost cyclic way during the simulated layer-growth cycle is shown in **Figure 3d**.

#### **Figure 3.**

*(a) TEM image showing ledge-flow growth of an atomic bilayer. (b,c) Ledge-flow time as a function of As-precursor flow (b) and Ga-precursor flow (c). (d) A representative example of simulation of Ga and As concentrations in the catalyst. (Plots (b), (c) and (d) are adapted from Maliakkal* et al. *[90] with permission. Further permissions should be directed to ACS.)*

**103**

properties.

*In Situ TEM Studies of III-V Nanowire Growth Mechanism*

During the incubation process the As concentration in the catalyst is in equilibrium with the ambient vapor. Once the layer nucleation happens the 'excess' As is consumed to form the GaAs nucleus and so As concentration quickly drops to a low level (where the As is in equilibrium with the solid GaAs nanowire). As soon as the layer is grown completely, the As % quickly rises and equilibrates again with the ambient vapor. Once this happens, the As contribution to the liquid supersaturation remains the same over the rest of the incubation period. However, the Ga building up in the catalyst keeps increasing the liquid chemical potential. Eventually, at some point after the liquid chemical potential is higher than the nucleation barrier, stochastically a nucleation event happens. Since the As % remains steady during the latter part of the incubation period, it is the Ga which is

The study demonstrated independent control of layer nucleation (by Ga) and layer completion (by As) in GaAs nanowires growth [90]. The underlying reason for the nucleation of layer and ledge-flow to be controllable independently is the very low solubility of As and the high solubility of Ga in the Au catalyst. Several other III-V and II-VI compound semiconductors also consist of a nonmetallic species (group V or VI, e.g., N, O, P, S), and a metallic species (group II or III, e.g., Ga, In, Zn, Mg) [101]. These nonmetallic species typically dissolve very little in catalyst (gold or other typical transition metal catalysts) while the metallic species readily forms alloys. In cases were the amount of nonmetallic species collected in the catalyst and available for growth is low, the layer growth process will be restricted by availability of this nonmetallic species. Thus, independent control of layer nucleation and growth would be possible in several other nanowire systems too [90]. The occasions where controlling the layer nucleation and growth are extremely relevant could include doping and growth of ternary compounds. In VLS growth, the nucleation stage determines the crystal stacking of the entire atomic layer [1]. However, dopant/impurity incorporation happening would strongly depend on ledge-flow. Since impurity incorporation could be happening due to step trapping, a slow ledge-flow would help limit the impurity incorporation. On the contrary, for

higher dopant incorporation, a fast ledge-flow could be advantageous [90].

Layer nucleation and growth for the different polytypes have been studied by in situ TEM. Before we discuss the key in situ results, let us discuss the concept of polytypism in nanowires and how the metastable structure could form. Nanowires enable the formation of metastable crystalline phases which do not form during its bulk growth. For example, most III-arsenides and III-phosphides form in the zincblende polytype when grown in bulk, because the bulk energy is lower for zincblende than wurtzite phase. But these materials can form in the wurtzite polytype in nanowires due to surface effects [2–4, 44, 110]. (Details of these crystal structures can be found elsewhere [4]). Controlled polytypism has great technological relevance because the electronic band structure depends on crystal structure. For example, GaP in the usual zincblende phase is an indirect bandgap material; while the wurtzite polytype has a pseudo-direct bandgap [111–113]. The valence and conduction bands of the two polytypes are often misaligned, so sections of one polytype in a matrix of the other polytype nanowire can confine electrons and/or holes. This enables crystal phase quantum dots with abrupt interfaces [114, 115]. Compositional quantum dots, on the other hand, often has a gradual variation of the composition (depending on the material combination chosen) deteriorating its

*DOI: http://dx.doi.org/10.5772/intechopen.95690*

triggering nucleation of a new layer [90].

**8. Polytypism in III-V nanowires**

#### *In Situ TEM Studies of III-V Nanowire Growth Mechanism DOI: http://dx.doi.org/10.5772/intechopen.95690*

*Nanowires - Recent Progress*

solubility in the Au-Ga alloy.

less than the amount of As required to form one complete bilayer. Indirect estimates based on ex situ growth, [95] phase diagrams, [109] and theoretical calculations related to Au-catalyzed GaAs nanowire growth [102, 103] also suggested low As

The concentration difference between the two different nanowire species in the catalyst [89] implies that both these species could affect the growth in different ways. This was studied in detail, again using Au-catalyzed GaAs (and TMGa and AsH3 as precursors) [90]. Two sets of experiments were investigated – one was a TMGa series (where AsH3 and temperature were kept constant) and a second was AsH3 series (where TMGa and temperature were kept constant). The ledge-flow time was found to decrease drastically with increasing AsH3 flow (**Figure 3b)**; thus the ledge-flow process was understood to be limited by the As availability. This agrees well with the low As % present in the catalyst [89]. (The idea that ledge-flow is limited by As availability was proposed in an earlier study [84] but not elaborately investigated there.) On increasing TMGa flow in a separate experiment the incubation time decreased drastically while the ledge-flow time remained rather unchanged (**Figure 3c**). This

**7. Independent control of layer nucleation and layer-growth**

indicated that nucleation of a new layer is triggered by excess Ga.

The experimental observations for the TMGa and AsH3 series matched stochastic Monte Carlo simulations done based on mass transport and nucleation theory [89]. An example of how As % and Ga % in the catalyst varies in an almost cyclic way during the simulated layer-growth cycle is shown in **Figure 3d**.

*(a) TEM image showing ledge-flow growth of an atomic bilayer. (b,c) Ledge-flow time as a function of As-precursor flow (b) and Ga-precursor flow (c). (d) A representative example of simulation of Ga and As concentrations in the catalyst. (Plots (b), (c) and (d) are adapted from Maliakkal* et al. *[90] with permission.*

**102**

**Figure 3.**

*Further permissions should be directed to ACS.)*

During the incubation process the As concentration in the catalyst is in equilibrium with the ambient vapor. Once the layer nucleation happens the 'excess' As is consumed to form the GaAs nucleus and so As concentration quickly drops to a low level (where the As is in equilibrium with the solid GaAs nanowire). As soon as the layer is grown completely, the As % quickly rises and equilibrates again with the ambient vapor. Once this happens, the As contribution to the liquid supersaturation remains the same over the rest of the incubation period. However, the Ga building up in the catalyst keeps increasing the liquid chemical potential. Eventually, at some point after the liquid chemical potential is higher than the nucleation barrier, stochastically a nucleation event happens. Since the As % remains steady during the latter part of the incubation period, it is the Ga which is triggering nucleation of a new layer [90].

The study demonstrated independent control of layer nucleation (by Ga) and layer completion (by As) in GaAs nanowires growth [90]. The underlying reason for the nucleation of layer and ledge-flow to be controllable independently is the very low solubility of As and the high solubility of Ga in the Au catalyst. Several other III-V and II-VI compound semiconductors also consist of a nonmetallic species (group V or VI, e.g., N, O, P, S), and a metallic species (group II or III, e.g., Ga, In, Zn, Mg) [101]. These nonmetallic species typically dissolve very little in catalyst (gold or other typical transition metal catalysts) while the metallic species readily forms alloys. In cases were the amount of nonmetallic species collected in the catalyst and available for growth is low, the layer growth process will be restricted by availability of this nonmetallic species. Thus, independent control of layer nucleation and growth would be possible in several other nanowire systems too [90].

The occasions where controlling the layer nucleation and growth are extremely relevant could include doping and growth of ternary compounds. In VLS growth, the nucleation stage determines the crystal stacking of the entire atomic layer [1]. However, dopant/impurity incorporation happening would strongly depend on ledge-flow. Since impurity incorporation could be happening due to step trapping, a slow ledge-flow would help limit the impurity incorporation. On the contrary, for higher dopant incorporation, a fast ledge-flow could be advantageous [90].

## **8. Polytypism in III-V nanowires**

Layer nucleation and growth for the different polytypes have been studied by in situ TEM. Before we discuss the key in situ results, let us discuss the concept of polytypism in nanowires and how the metastable structure could form. Nanowires enable the formation of metastable crystalline phases which do not form during its bulk growth. For example, most III-arsenides and III-phosphides form in the zincblende polytype when grown in bulk, because the bulk energy is lower for zincblende than wurtzite phase. But these materials can form in the wurtzite polytype in nanowires due to surface effects [2–4, 44, 110]. (Details of these crystal structures can be found elsewhere [4]). Controlled polytypism has great technological relevance because the electronic band structure depends on crystal structure. For example, GaP in the usual zincblende phase is an indirect bandgap material; while the wurtzite polytype has a pseudo-direct bandgap [111–113]. The valence and conduction bands of the two polytypes are often misaligned, so sections of one polytype in a matrix of the other polytype nanowire can confine electrons and/or holes. This enables crystal phase quantum dots with abrupt interfaces [114, 115]. Compositional quantum dots, on the other hand, often has a gradual variation of the composition (depending on the material combination chosen) deteriorating its properties.

Now let us first briefly discuss a simplified explanation for the occurrence of the metastable wurtzite structure in nanowires. During VLS growth, at appropriate catalyst contact angles, the nucleus of each layer is preferably formed at the triplephase-line because it eliminates the energy cost of a preexisting liquid segment [1]. For nucleation happening at the triple-phase-line the nanowire surface energy is a key factor [1]. The surface energy of possible wurtzite side facets could be lower than the zincblende counterparts [1]. In such cases, the wurtzite structure can be more favorable than zincblende for energy minimization, depending on the catalyst supersaturation and relevant interface energies [1]. Extensive models proposed by several groups to correlate the observed crystal structure at different conditions can be found elsewhere [1, 96, 103, 104, 116–118].

In GaAs nanowire growth studied ex situ for a very wide range of V/III ratios it was found that very low V/III ratios gives zincblende, a higher V/III results in wurtzite, and an even higher V/III give zincblende again [110]. A high V/III ratio (i.e. higher AsH3, which may also be interpreted as effectively lesser Ga) is associated with a smaller catalyst; while a low V/III results in bulged up catalyst with high contact angle [110]. There are also two intermediate transition regimes with mixed structures [110]. Theoretical models of Au-catalyzed GaAs growths could also simulate three different growth regimes [103, 104]. Often in typical experiment series a narrower range of V/III is studied, and thus it may happen that only a zincblende to wurtzite transition or only a wurtzite to zincblende transition is observed on increasing V/III ratio.

Jacobsson *et al.* observed two growth regimes in situ — at moderate V/III ratio wurtzite segments grew, and at low V/III the catalyst bulges and zincblende segments grew [84]. The wurtzite growth occurred while the nanowire-catalyst interface was one flat plane and the ledge-flow growth was gradual [84]. During zincblende growth the interface showed an oscillating truncated corner; the ledge-flow was "too rapid to observe" but was correlated to the cyclic dynamics of the truncation [84]. According to the study zincblende phase grows if any edge is truncated, whereas wurtzite grows only when the interface is flat [84]. They speculated that the truncation happening in the low V/III regime would make nucleation occur away from the triple-phase-line which in turn makes zincblende the preferred structure. (Note the authors had not claimed an if-and-only-if condition between interface geometry and crystal structure. However, in my personal experience, some readers misinterpreted that truncation was a necessity for low V/III zincblende growth.) The droplet contact angle was the key parameter in deciding the crystal structure [84]. Au:Ga ratio in the droplet was found to be not critical, hence a similar crystal structure–geometry correlation was speculated to be applicable to self-catalyzed wires too [84].

Polytypism in self-catalyzed GaAs nanowires was recently studied using in situ TEM-MBE by Panciera *et al* [99]. In this work the three regimes were observed as shown in **Figure 4e**, **g** and **h** (zincblende at low V/III ratio, wurtzite at higher V/III ratio, zincblende at even higher V/III ratio) [99]. In the high V/III zincblende regime, (which was not experimentally achievable in Jacobsson *et al.*), the nucleation was found to occur at the triple-phase-line, the ledge-flow was slow, and no truncation was observed. Their observations consistent with Jacobsson *et al.* include (i) control of crystal structure by contact angle, (ii) gradual ledge-flow and flat interface during wurtzite growth, and (iii) truncation and rapid ledge-flow observed in the low V/III zincblende growth [99].

However, it is not necessary that the low V/III zincblende growth can occur only with truncation. The growth of zincblende with a bulged particle (high contact angle) at low V/III ratio, but without truncation, has also been reported (**Figure 4f**) [89]. In this study the V/III ratio was decreased to observe bulging of the particle,

**105**

**Figure 4.**

*permission as per Creative Commons license.*

*In Situ TEM Studies of III-V Nanowire Growth Mechanism*

but a lower limit was set on the V/III ratio intentionally to avoid the truncation regime [89]. The V/III ratio was varied in small steps and maintained for some time to reach steady state [89] – this could be the reason why this intermediate zincblende regime with high contact angle and without truncation was observed in this study unlike the other two in situ studies discussed above [84, 99]. Thus, we can infer that the zincblende growth at low V/III does not necessarily require truncation. More detailed investigation is necessary to say if the nucleation happened at the triple-phase-line or the center in this case, and if the ledge-flow was gradual or instantaneous. Whether the presence of truncation makes the nucleation preferable

*(a)-(d) Schematic representation of crystal phases observed as a function of V/III ratio or catalyst contact angle. The catalyst-nanowire interface is either a single plane (b-d) or truncated (a). (e)-(h) shows TEM images with zincblende (ZB) or wurtzite (WZ) structures. Scalebars correspond to 5 nm. Inset of (e) shows a dynamic truncated corner during the zincblende growth at low V/III ratio. (e), (g) and (h) are adapted with permission from Panciera* et al. *[99] Copyright (2020) American Chemical Society. Image (f) showing low V/ III zincblende growth even without truncation is from another study – Maliakkal et al. [89]. Adapted with*

A heuristic explanation for the choice of crystal structure based on the currently available data [84, 89, 99] and theoretical calculations [1, 49] on GaAs VLS growth is as follows. The metastable wurtzite phase can grow only if the layer nucleates at the triple-phase-line [49]. If the nucleation is at triple-phase-line, either wurtzite or zincblende can form depending on the supersaturation and surface energies [1]. When nucleation occurs away from the triple-phase-line, it can form only zincblende structure [1, 49]. Now let us look at crystal structure as a function of the contact angle. Glas *et al.* predicted that nucleation is preferred at the triplephase-line for a range of contact angles [π − βc; βc], where the critical angle βc is a function of the relevant interface energies [1, 49]. Thus, at intermediate contact angles (i.e. intermediate V/III ratios), nucleation occurs at the triple-phase-line and wurtzite structure is formed as observed( **Figure 4c**,**g**) [99]. For the lower contact angle (**Figure 4d**,**h**), nucleation was reported to be zincblende and at the triplephase-line, [99] which demands that zincblende structure would have been the lower energy nucleus phase at those growth conditions [1]. For the higher contact angle regime, zincblende was found to grow, even without truncation [89]. It would have happened either (i) with nucleation away from the triple-phase-line giving

away from the triple phase line is also an open question.

*DOI: http://dx.doi.org/10.5772/intechopen.95690*

*In Situ TEM Studies of III-V Nanowire Growth Mechanism DOI: http://dx.doi.org/10.5772/intechopen.95690*

#### **Figure 4.**

*Nanowires - Recent Progress*

on increasing V/III ratio.

self-catalyzed wires too [84].

observed in the low V/III zincblende growth [99].

be found elsewhere [1, 96, 103, 104, 116–118].

Now let us first briefly discuss a simplified explanation for the occurrence of the metastable wurtzite structure in nanowires. During VLS growth, at appropriate catalyst contact angles, the nucleus of each layer is preferably formed at the triplephase-line because it eliminates the energy cost of a preexisting liquid segment [1]. For nucleation happening at the triple-phase-line the nanowire surface energy is a key factor [1]. The surface energy of possible wurtzite side facets could be lower than the zincblende counterparts [1]. In such cases, the wurtzite structure can be more favorable than zincblende for energy minimization, depending on the catalyst supersaturation and relevant interface energies [1]. Extensive models proposed by several groups to correlate the observed crystal structure at different conditions can

In GaAs nanowire growth studied ex situ for a very wide range of V/III ratios it was found that very low V/III ratios gives zincblende, a higher V/III results in wurtzite, and an even higher V/III give zincblende again [110]. A high V/III ratio (i.e. higher AsH3, which may also be interpreted as effectively lesser Ga) is associated with a smaller catalyst; while a low V/III results in bulged up catalyst with high contact angle [110]. There are also two intermediate transition regimes with mixed structures [110]. Theoretical models of Au-catalyzed GaAs growths could also simulate three different growth regimes [103, 104]. Often in typical experiment series a narrower range of V/III is studied, and thus it may happen that only a zincblende to wurtzite transition or only a wurtzite to zincblende transition is observed

Jacobsson *et al.* observed two growth regimes in situ — at moderate V/III ratio wurtzite segments grew, and at low V/III the catalyst bulges and zincblende segments grew [84]. The wurtzite growth occurred while the nanowire-catalyst interface was one flat plane and the ledge-flow growth was gradual [84]. During zincblende growth the interface showed an oscillating truncated corner; the ledge-flow was "too rapid to observe" but was correlated to the cyclic dynamics of the truncation [84]. According to the study zincblende phase grows if any edge is truncated, whereas wurtzite grows only when the interface is flat [84]. They speculated that the truncation happening in the low V/III regime would make nucleation occur away from the triple-phase-line which in turn makes zincblende the preferred structure. (Note the authors had not claimed an if-and-only-if condition between interface geometry and crystal structure. However, in my personal experience, some readers misinterpreted that truncation was a necessity for low V/III zincblende growth.) The droplet contact angle was the key parameter in deciding the crystal structure [84]. Au:Ga ratio in the droplet was found to be not critical, hence a similar crystal structure–geometry correlation was speculated to be applicable to

Polytypism in self-catalyzed GaAs nanowires was recently studied using in situ TEM-MBE by Panciera *et al* [99]. In this work the three regimes were observed as shown in **Figure 4e**, **g** and **h** (zincblende at low V/III ratio, wurtzite at higher V/III ratio, zincblende at even higher V/III ratio) [99]. In the high V/III zincblende regime, (which was not experimentally achievable in Jacobsson *et al.*), the nucleation was found to occur at the triple-phase-line, the ledge-flow was slow, and no truncation was observed. Their observations consistent with Jacobsson *et al.* include (i) control of crystal structure by contact angle, (ii) gradual ledge-flow and flat interface during wurtzite growth, and (iii) truncation and rapid ledge-flow

However, it is not necessary that the low V/III zincblende growth can occur only with truncation. The growth of zincblende with a bulged particle (high contact angle) at low V/III ratio, but without truncation, has also been reported (**Figure 4f**) [89]. In this study the V/III ratio was decreased to observe bulging of the particle,

**104**

*(a)-(d) Schematic representation of crystal phases observed as a function of V/III ratio or catalyst contact angle. The catalyst-nanowire interface is either a single plane (b-d) or truncated (a). (e)-(h) shows TEM images with zincblende (ZB) or wurtzite (WZ) structures. Scalebars correspond to 5 nm. Inset of (e) shows a dynamic truncated corner during the zincblende growth at low V/III ratio. (e), (g) and (h) are adapted with permission from Panciera* et al. *[99] Copyright (2020) American Chemical Society. Image (f) showing low V/ III zincblende growth even without truncation is from another study – Maliakkal et al. [89]. Adapted with permission as per Creative Commons license.*

but a lower limit was set on the V/III ratio intentionally to avoid the truncation regime [89]. The V/III ratio was varied in small steps and maintained for some time to reach steady state [89] – this could be the reason why this intermediate zincblende regime with high contact angle and without truncation was observed in this study unlike the other two in situ studies discussed above [84, 99]. Thus, we can infer that the zincblende growth at low V/III does not necessarily require truncation. More detailed investigation is necessary to say if the nucleation happened at the triple-phase-line or the center in this case, and if the ledge-flow was gradual or instantaneous. Whether the presence of truncation makes the nucleation preferable away from the triple phase line is also an open question.

A heuristic explanation for the choice of crystal structure based on the currently available data [84, 89, 99] and theoretical calculations [1, 49] on GaAs VLS growth is as follows. The metastable wurtzite phase can grow only if the layer nucleates at the triple-phase-line [49]. If the nucleation is at triple-phase-line, either wurtzite or zincblende can form depending on the supersaturation and surface energies [1]. When nucleation occurs away from the triple-phase-line, it can form only zincblende structure [1, 49]. Now let us look at crystal structure as a function of the contact angle. Glas *et al.* predicted that nucleation is preferred at the triplephase-line for a range of contact angles [π − βc; βc], where the critical angle βc is a function of the relevant interface energies [1, 49]. Thus, at intermediate contact angles (i.e. intermediate V/III ratios), nucleation occurs at the triple-phase-line and wurtzite structure is formed as observed( **Figure 4c**,**g**) [99]. For the lower contact angle (**Figure 4d**,**h**), nucleation was reported to be zincblende and at the triplephase-line, [99] which demands that zincblende structure would have been the lower energy nucleus phase at those growth conditions [1]. For the higher contact angle regime, zincblende was found to grow, even without truncation [89]. It would have happened either (i) with nucleation away from the triple-phase-line giving

zincblende structure or (ii) with nucleation at the triple-phase-line only, but with the zincblende structure having lower energy at those growth conditions. Note that in the above explanation or in references [1, 49] truncation was not explicitly needed to explain crystal phase switching. At extremely high contact angles and at extremely low contact angles, there could be either truncation or large tapering; [84, 99] but truncation is not a necessity for zincblende growth. The truncation might be responsible for the observed quasi-instantaneous ledge-flow though.